WO2025002078A1 - Composite negative electrode material and preparation method therefor, and battery - Google Patents

Abstract

A composite negative electrode material and a preparation method therefor, and a battery. The composite negative electrode material comprises a carbon material and a silicon-based material; pores are formed in the composite negative electrode material; for three pores which are not on a same straight line, the pore sizes of the three pores are respectively D₁, D₂, and D₃, and pore distances are respectively L₁, L₂, and L₃; A₁ is defined as the minimum value among L₁ ²-(L₂/2)², L₁ ²-(L₃/2)², L₂ ²-(L₁/2)², L₂ ²-(L₃/2)², L₃ ²-(L₁/2)², and L₃ ²-(L₂/2)²; B₁ is D₁+D₂+D₃; and 0.4<A₁/B₁<50. In the composite negative electrode material, A₁/B₁ satisfies the range of 0.4-50, which means pores in the material are distributed in a reasonable range. This indicates that, on the one hand, most pores of the original carbon material are effectively filled with a silicon-based material, i.e., the interior of the sample is relatively compact, which means the proportion of silicon and carbon in the sample is controlled to be within a reasonable range, and the specific capacity and initial efficiency of the composite negative electrode material are relatively high. On the other hand, the interior of the sample is not of a completely compact structure, thereby reducing the problem of excessive local stress in the material due to no pores or few pores being present, guaranteeing the integrity of the structure of the composite negative electrode material, and improving the cycle performance.

Description

Composite negative electrode material and preparation method thereof, and battery

This application claims the priority of the Chinese patent application filed with the State Intellectual Property Office on June 29, 2023, with application number 202310784881X and application name “Composite negative electrode material, preparation method thereof, and battery”, all contents of which are incorporated by reference in this application.

Technical Field

The present application relates to the technical field of negative electrode materials, and in particular to composite negative electrode materials, preparation methods thereof, and batteries.

Background Art

Lithium-ion batteries have the advantages of high energy density, high cycle life, low environmental pollution and no memory effect, so they are widely used in electric vehicles and consumer electronic products. The low theoretical specific capacity (372mAh/g) of traditional negative electrode carbon materials limits their widespread use. In order to improve the energy density of lithium-ion batteries, people began to look for high-capacity negative electrode materials. Silicon-based negative electrode materials have gradually become a research hotspot because of their theoretical specific capacity of up to 4200mAh/g. However, the volume expansion of silicon-based negative electrode materials is relatively serious during the alloying process with lithium, and as the cycle progresses, silicon-based negative electrode materials will undergo attenuation mechanisms such as pulverization, contact loss with conductive agents and current collectors, and the formation of unstable solid electrolyte interfaces (SEI), which leads to the degradation of the electrochemical performance of negative electrode materials.

Carbon materials have rich pore structures. When they are prepared as composite negative electrode materials with silicon-based materials, carbon materials can provide a large amount of embedding space for silicon-based materials, reduce the expansion effect of silicon-based materials, and improve their pulverization or formation of unstable solid electrolyte interfaces. In the process of filling silicon-based materials, the filling amount of silicon-based materials will affect the pore distribution of the composite negative electrode material, and then affect the electrochemical performance of the composite negative electrode material. It is understandable that if the filling amount of silicon-based materials is too small, the pore distribution of the composite negative electrode material is sparse, and the silicon-based material has enough expansion space, but it cannot fully utilize the high capacity advantage of silicon; if the filling amount of silicon-based materials is too much, the high capacity advantage of silicon-based materials can be utilized, but the composite negative electrode material will have no pores or less pores. The composite negative electrode material will cause stress concentration due to the expansion effect of silicon-based materials, affecting the structural stability.

Therefore, controlling the pore distribution of the composite negative electrode material after filling with silicon-based materials is crucial to improving the electrochemical performance of batteries prepared with the composite negative electrode material.

Application Contents

The purpose of the present application is to provide a composite negative electrode material and a preparation method thereof, and a battery. After the silicon-based material is filled in the carbon material to form a composite negative electrode material, the pore distribution of the composite negative electrode material is within a reasonable range, thereby obtaining a composite negative electrode material with excellent initial effect and cycle performance.

In a first aspect, the present application provides a composite negative electrode material, the composite negative electrode material comprising a carbon material and a silicon-based material, the carbon material having pores, and at least a portion of the silicon-based material being distributed in the pores of the carbon material;

The composite negative electrode material has pores. For any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are _D1 , _D2 , and _D3 , respectively, and the pore distances are _L1 ^, _L2 , and _L3 , respectively. _A1 is defined as _the ^minimum value of _L12- ⁽ _{L2 /} 2) ² , _L12- ( _L3 /2) ₂ , _L22- ⁽ L1/2) ^{2 , L22-} _{( L3} /2) ² , ^L32- ( _L1 /2) ² , or _L32- ( ^L2 /2) ² , _B1 is _D1 + _D2 + _D3 , and 0.4＜ _A1 / _B1 ＜50.

In a second aspect, the present application provides a method for preparing a composite negative electrode material, comprising the following steps:

Providing a carbon material with pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material comprises a carbon material and a silicon-based material, and the composite negative electrode material has pores;

In the composite negative electrode material, for the three holes that are not on the same straight line, the pore sizes of the three holes are D ₁ , D ₂ , D ₃ , the hole spacings are L ₁ , L ₂ , and L ₃ respectively, A ₁ is defined as the _minimum value among L ₁ ² -(L ₂ /2) ² , L ₁ ² -(L ₃ /2) ² , L ₂ ² -(L ₁ /2) ² , L 2 ² -(L ₃ /2) ² , L ₃ ² -(L ₁ /2) ² or L ₃ ² -(L ₂ /2) ² , B ₁ is D ₁ +D ₂ +D ₃ , and 0.4＜A ₁ /B ₁ ＜50;

In the carbon material, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are d' ₁ , d' ₂ , and d' ₃ , respectively, and the pore distances are l' ₁ , l' ₂ , and l' ₃ , respectively. _A'2 is defined as the minimum ^value among l' _22- ⁽ l' ₁ /2) ² , l' _22- ⁽ l' ₃ / ₂ ^{) 2 ,} l' _32- (l' ₁ /2) ² , l' ^{32- (} _{l' 2} / ₂ ) ² , l'12-(l' ₂ /2)2, or l'12-(l' ₃ /2) ² , _B'2 is d' ₁ +d' ₂ +d' ₃ , and _C'1 is l' _22- (l' ₁ / ^{2)2, l'22- (} _{l' 3} /2) ^{2 .} , the ^maximum value _among l' ₃ ² -(l' ₁ /2) ² , l' 3 2 -(l' ₂ /2) ² , l' ₁ ² -(l' ₂ /2) ² or l' ₁ ² -(l' ₃ /2) ² , B' ₂ /C' ₁ >1, and B' ₂ /A' ₂ ≤4.

In a third aspect, the present application provides a battery, comprising the composite negative electrode material described in any one of the first aspect or the composite negative electrode material prepared by the preparation method described in any one of the second aspect.

Compared with the prior art, this application has at least the following beneficial effects:

The composite negative electrode material of the present application includes a carbon material and a silicon-based material, at least part of the silicon-based material is located in the pores of the carbon material to form a composite negative electrode material with a reasonable pore distribution. At this time, for any three adjacent pores of the composite negative electrode material that are not on the _same straight line, the pore sizes of the three pores are _D1 , _D2 , and _D3 , respectively, and _the pore distances are ^L1 _, ^L2 _, and L3, respectively ^. _A1 is defined as the ^minimum value ^of _L12- ( _L2 /2) ² , _L12- ( _{L3 /} 2) ² , _L22- ( _L1 /2) ² , _L22- ⁽ _L3 /2)2, ^L32- (L1/2) ² , or _L32- ( _L2 /2) ² , _B1 is _D1 + _D2 + _D3 , and the relationship between _A1 and _B1 satisfies 0.4＜ _A1 / _B1 ＜50. It can be understood that _A1 represents the compactness of three adjacent pores, and _B1 represents the pore size of the three pores. When _A1 / _B1 is within the above range, it means that the compactness and pore size of the three pores that are not on the same straight line in the composite negative electrode material obtained after the silicon-based material is filled with the carbon material are moderate, that is, the pore distribution is moderate and not too sparse or dense. On the one hand, it means that most of the pores of the carbon material are effectively filled with the silicon-based material, that is, the interior of the composite negative electrode material is relatively dense, and the silicon-based material with high stability can provide abundant lithium storage sites, thereby improving the specific capacity and initial efficiency of the composite negative electrode material; on the other hand, the applicant found that if the filling amount of the silicon-based material is too large, the silicon-based materials are stacked more tightly, and the distance between the three pores that are not on the same straight line in the pores of the composite negative electrode material formed after filling is too far, and the pore size is too small, so that _A1 /B1 is ₁ is too small, which will result in the composite negative electrode material having no pores or fewer pores. The above situation will make it difficult to effectively relieve the stress of the silicon-based material during the charge and discharge process, and there will be a problem of excessive local stress inside the composite negative electrode material, resulting in damage or collapse of the structure inside the composite negative electrode material. At this time, if the electrolyte continues to infiltrate, the SEI film thickens, and the cycle performance of the battery prepared by the composite negative electrode material deteriorates. In the present application, when _A1 / _B1 of the composite negative electrode material is within the above range, the composite negative electrode material is not a completely dense structure, the pore distribution is appropriate, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, thereby improving the cycle performance of the battery prepared by the composite negative electrode material.

The preparation method of the negative electrode material provided in the present application utilizes a vapor deposition process to deposit a silicon-based material onto a carbon material with a reasonable pore distribution, thereby preparing a composite negative electrode material of the present application having excellent specific capacity, first efficiency and cycle performance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic diagram showing the relationship between the pore diameters and pore distances of three pores that are not on the same straight line in a composite negative electrode material provided in an embodiment of the present application;

FIG2 is a schematic diagram showing the relationship between the pore diameters and pore distances of three pores that are not on the same straight line in the carbon material of the composite negative electrode material provided in an embodiment of the present application;

FIG3 is a schematic diagram of a process for preparing a composite negative electrode material according to an embodiment of the present application;

FIG4 is a comparison diagram of adsorption curves of the carbon material raw material provided in Example 1 of the present application and the composite negative electrode material after deposition of the silicon-based material.

DETAILED DESCRIPTION

In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings.

It should be understood that the term "and/or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character "/" in this article generally indicates that the associated objects before and after are in an "or" relationship.

An embodiment of the present application provides a composite negative electrode material, which includes a carbon material and a silicon-based material, the carbon material having pores, and at least part of the silicon-based material is distributed in the pores of the carbon material; as shown in FIG1 , the composite negative electrode material has pores, and for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are D ₁ , D ₂ , and D ₃ , respectively _, and the pore distances are L ₁ , L ₂ , and L ₃ , respectively, and A ₁ is defined as the _{minimum value of L 1 2 -(L 2} ^{/2) 2 ,} _L ¹ ₂ ^- ₍ ^L ₃ /2) ² , L ₂ ² -(L ₁ /2) ² , L ₂ ² -(L ₃ /2) 2 , L 3 2 -(L 1 /2) ² or L ₃ ² -(L ₂ /2) ² , B ₁ is D ₁ +D ₂ +D ₃ , and 0.4＜A ₁ /B ₁ ＜50.

In the particle structure of the composite negative electrode material provided in this embodiment, _A1 represents the compactness of three adjacent pores, _{and B1} represents the pore size of the three pores. It can be understood that when _A1 / _B1 is within the above range, it means that the compactness and pore size of the three pores that are not on the same straight line in the composite negative electrode material obtained after the silicon-based material is filled with the carbon material are moderate, that is, the pore distribution is not too sparse or dense. On the one hand, it means that most of the pores of the carbon material are effectively filled with the silicon-based material, that is, the interior of the composite negative electrode material is relatively dense, and the silicon-based material with high stability can provide abundant lithium storage sites, thereby improving the specific capacity and initial efficiency of the composite negative electrode material; on the other hand, the applicant found that if the filling amount of the silicon-based material is too large, the silicon-based materials are stacked more tightly, and the distance between the three pores that are not on the same straight line in the pores of the composite negative electrode material formed after filling is too far, and the pore size is too small, so that _A1 /B1 is ₁ is too small, then the composite negative electrode material has no pores or fewer pores, the above situation will make it difficult to effectively relieve the stress of the silicon-based material during the charge and discharge process, and there will be a problem of excessive local stress inside the composite negative electrode material, resulting in damage or collapse of the structure inside the composite negative electrode material. At this time, if the electrolyte continues to infiltrate, the SEI film thickens, and the cycle performance of the battery prepared by the composite negative electrode material deteriorates. In the present application, when _A1 / _B1 of the composite negative electrode material is within the above range, the inside of the composite negative electrode material is not a completely dense structure, the pore distribution is appropriate, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, and thus can improve the cycle performance of the battery prepared by the composite negative electrode material.

In some embodiments, the specific surface area of the carbon material after removing the silicon-based material from the composite negative electrode material is 300 m ² /g to 2500 m ² /g. Specifically, the specific surface area can be 300 m ² /g, 500 m ² /g, 1000 m ² /g, 1500 ^{m 2 /} g, 2000 m 2 /g, 2100 m ² /g, 2200 m ² /g, 2300 m ² /g, 2400 m ² /g and 2500 m ² /g, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the carbon material after the silicon-based material is removed from the composite negative electrode material has pores, and at least part of the silicon-based material is filled in the pores. It can be understood that the carbon material can play a role in supporting the skeleton and also has good electrical conductivity, which can ensure the powder conductivity of the prepared composite negative electrode material. At this time, when the silicon-based material is filled in the pores of the carbon material, on the one hand, the specific capacity of the composite negative electrode material can be increased, and on the other hand, the pores after the carbon material is filled with the silicon-based material are reduced, which can increase the density of the composite negative electrode material and improve the structural stability of the composite negative electrode material particles.

In some embodiments, the pore volume of all pores in the carbon material after removing the silicon-based material from the composite negative electrode material is Specifically, the pore volume can be 0.4 ^{cm 3} /g, 0.5 cm ³ /g ^, 0.6 cm ³ /g ^, 0.7 cm ³ /g ^, 0.8 cm 3 /g, 0.9 cm 3 /g, 1.0 cm 3 /g, ^{1.1 cm 3} /g, 1.2 cm ³ /g, 1.3 cm 3 /g ^, 1.4 cm 3 /g ^, 1.5 cm ³ /g, 1.6 cm ³ /g, 1.7 cm ³ /g, 1.8 cm ³ /g, 1.9 cm 3 /g and 2 cm ³ /g, and of course, it can also be other values between 0.4 cm ³ /g and 2 cm ³ /g, which is not limited here.

In some embodiments, in the carbon material after the silicon-based material is removed from the composite negative electrode material, the pore size of at least part of the pores gradually decreases from the surface of the carbon material to the inside, wherein the average pore size change of each 1 μm extended from the surface of the carbon material to the inside is ≥0.1 nm, and optionally, the average pore size change of each 1 μm extended can be specifically 0.1 nm, 0.15 nm, 0.2 nm, 0.25 nm, 0.3 nm, 0.35 nm, 0.4 nm, 0.45 nm and 0.5 nm, etc., of course, it can also be other values within the above range, which is not limited here. It can be understood that the average pore size change of each 1 μm extended is within the above range, which is conducive to the diffusion of gas into the carbon material, and can make the silicon-based material uniformly and effectively filled in the pores of the carbon material, thereby ensuring that the opening porosity of the pores in the composite negative electrode material is within a suitable range.

In some embodiments, in the carbon material after the silicon-based material is removed from the composite negative electrode material, the cross-section of the hole is funnel-shaped or inverted cone-shaped. It can be understood that the funnel-shaped or inverted cone-shaped hole has a large air inlet, and the reaction gas containing the silicon source gas and hydrogen can be deeply introduced into the pores of the carbon material, which is conducive to the deposition of the silicon-based material in the pores of the carbon material, and can also reduce the reaction gas from decomposing too fast on the surface of the carbon material and depositing on the surface of the carbon material, resulting in the pores being closed, thereby causing too little deposition of the silicon-based material in the pores of the carbon material, thereby affecting the structural stability of the composite negative electrode material.

In some embodiments, the density of the carbon material after removing the silicon-based material from the composite negative electrode material is ≤1.50 g/cm ³ , and can be specifically 0.1 g/cm ³ , 0.2 g/cm ³ , 0.3 g/cm ³ , 0.4 g/cm ³ , 0.5 g/cm ³ , 0.6 g/cm ³ , 0.7 g/cm ^{3 , 0.8 g/cm 3 ,} 0.9 g/cm ³ , 1.0 g/cm ³ , 1.10 g/cm ³ , 1.20 g/cm ³ , 1.30 g/cm ³ , 1.40 g/cm ³ and 1.50 g/cm ³ , etc., and of course, it can also be other values within the above range, which is not limited here. It can be understood that the carbon material has a large number of pores, the presence of which reduces the density of the carbon material, and sufficient pores are conducive to the deposition of the silicon-based material.

In some embodiments, the distribution density of pores in the carbon material after the silicon-based material is removed from the composite negative electrode material is 1/μm ² to 1000/μm ^2. Specifically, the distribution density of pores in the carbon material can be 1/μm ² , 5/μm ² , 10/μm ² , 20/μm ² , 50/μm ² , 100/μm ² , 150/μm ² , 200/μm ² , 300/μm ² , 500/μm ² , 600/μm ² , 700/μm ² , 800/μm ² , 900/μm ² and 1000/μm ^2, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the average pore size of the carbon material after removing the silicon-based material from the composite negative electrode material is 0.1nm to 50nm, specifically 0.1nm, 0.5nm, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm and 50nm, etc., of course, it can also be other values within the above range, which is not limited here. It is understandable that the pore size distribution of carbon materials will directly affect the deposition of silicon-based materials. When the pore size of the carbon material is too small, it is difficult to introduce the reaction gas containing silicon source gas and hydrogen deeply into the pores of the carbon material. The silicon-based material is more likely to be deposited on the surface of the carbon material rather than in the pores, which can easily lead to the pores on the surface of the composite negative electrode material being closed prematurely, and the content of silicon-based material filled in the composite negative electrode material is too small, resulting in the degradation of the electrochemical performance of the material; and when the pore size of the carbon material is too large, its mechanical strength will deteriorate, and at the same time, the segregation problem of silicon-based materials will occur, and when the pore size exceeds a certain value, there will be no real improvement in the entry of the reaction gas containing silicon source gas and hydrogen, which will also lead to poor electrochemical performance of the material.

In some embodiments, the porosity of the carbon material after the silicon-based material is removed from the composite negative electrode material is 45% to 75%. Specifically, the porosity of the carbon material can be 45%, 48%, 50%, 55%, 57%, 60%, 65%, 68%, 70%, 71%, 72%, 73%, 74% and 75%, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, in the carbon material after removing the silicon-based material from the composite negative electrode material, as shown in FIG. For any three adjacent holes on the same straight line, the apertures of the three holes are d ₁ , d ₂ , and d ₃ , and the hole spacings are l ₁ , l ₂ , and l ₃ , respectively. A ₂ is defined as the minimum value among l ₂ ² -(l ₁ /2) ^{2 ,} l ₂ ² _- (l ₃ /2) ² , l ₃ ² - ⁽ l ₁ /2) ² , l ₃ ² -(l ₂ /2) 2 , l 1 2 -(l ₂ /2) ² , or l ₁ ² -(l ₃ /2) ² , B ₂ is d ₁ +d ₂ +d ₃ , and C ₁ is l ₂ ² -(l ₁ /2) ² , l ₂ ² -(l ₃ /2) ² , l ₃ ² -(l ₁ /2) ² , l ₃ ² -(l ₂ /2) ² , the maximum value among l ₁ ² -(l ₂ /2) ² or l ₁ ² -(l ₃ /2) ² , B ₂ /C ₁ >1, and B ₂ /A ₂ ≤4.

It can be understood that when B ₂ /C ₁ >1 and B ₂ /A ₂ ≤4 in the carbon material after the silicon-based material is removed from the composite negative electrode material, it means that the pore distribution in the carbon material does not have the situation that the pore distribution is too concentrated or the pore distribution is too sparse, which is conducive to the deposition of the silicon-based material in the pores of the carbon material. Controlling B ₂ /C ₁ >1 and B ₂ /A ₂ ≤4 in the carbon material can, on the one hand, ensure that the silicon-based material is fully deposited in the pores of the carbon material, which is conducive to the improvement of the specific capacity of the composite negative electrode material; on the other hand, it can reduce the excessive deposition of the silicon-based material in the pores of the carbon material, reserve a certain buffer space for the volume expansion of the silicon-based material, and alleviate the stress release of the composite negative electrode material, which is conducive to the improvement of the cycle performance of the composite negative electrode material.

In some embodiments, the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include micropores, mesopores and macropores, wherein the volume proportion of micropores in all pores is 30% to 99%, the volume proportion of mesopores in all pores is 5% to 70%, and the volume proportion of macropores in all pores is 0 to 5%.

Specifically, the volume proportion of micropores in all pores can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 99%, etc., and of course it can also be other values between 30% and 99%, which are not limited here.

The volume proportion of mesopores in all pores can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% and 70%, etc., and of course it can also be other values within the above range, which is not limited here.

Specifically, the volume proportion of macropores in all pores may be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 5%, etc., and of course, it may also be other values within the above range, which are not limited here.

In some embodiments, the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include mesopores, wherein the volume proportion of pores with a pore size of 2nm to 20nm in the mesopores is >90%, specifically 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99%, etc., and of course it can also be other values within the above range, which is not limited here.

In some embodiments, the pores in the carbon material after the silicon-based material is removed from the composite negative electrode material include mesopores, wherein the volume proportion of pores with a pore size of 5nm to 20nm in the mesopores is 10% to 50% of all mesopores, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, 47%, 48%, 49% and 50%, etc., of course, it can also be other values between 10% and 50%, which are not limited here.

It can be understood that the pore size distribution of the carbon material after the silicon-based material is removed from the composite negative electrode material is appropriate, which helps to form gas phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, and reduce the density gradient of the carbon material, thereby improving the density of the composite negative electrode material.

In some embodiments, the filling rate of the pores of the composite negative electrode material is ≥ 70%. Specifically, the filling rate of the pores can be 70%, 71%, 72%, 73%, 74%, 75%, 80%, 83%, 85%, 87%, 90%, 91%, 93%, 95%, 96%, 97% and 99%, etc., and of course, it can also be other values within the above range, which are not limited here. Preferably, the filling rate of the pores is 80% to 90%. It can be understood that the filling rate of the pores within the above range is beneficial to improve the specific capacity of the composite negative electrode material on the one hand, and on the other hand, it is beneficial to improve the structural stability of the composite negative electrode material, thereby reducing the structural collapse of the composite negative electrode material during the cycle.

In some embodiments, the mass proportion of silicon-based materials in the composite negative electrode material is 15% to 60%, which can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% and 60%, etc., of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the average particle size of the silicon-based material is less than 50 nm. Specifically, the average particle size of the silicon-based material can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 46 nm, 47 nm, 48 nm, 49 nm, and 50 nm, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the silicon-based material includes at least one of amorphous silicon, crystalline silicon, silicon oxide, silicon alloy, and a composite of crystalline silicon and amorphous silicon; specifically, the silicon alloy can be a silicon-lithium alloy, a silicon-magnesium alloy, etc. Of course, it should be noted that in some cases, the silicon alloy includes elemental particles and alloys.

In some embodiments, the silicon-based material includes amorphous silicon. It is understood that the silicon-based material in the composite negative electrode material includes amorphous silicon, which expands isotropically during lithium insertion, which can reduce the collapse of the pore structure, inhibit the rapid attenuation of specific capacity, and improve the lithium insertion cycle performance.

In some embodiments, the specific surface area of the composite negative electrode material is 1 m ² /g to 500 m ² /g. Specifically, the specific surface area of the composite negative electrode material can be 1 m ² /g, 5 m ² /g, 10 m ² /g, 50 m ² /g, 100 m ² /g, 150 m ² /g, ²⁰⁰ m 2 /g, 250 m ² /g, 300 m ² /g, 350 m ² /g, 400 m ² /g, 450 m ² /g and 500 m ² /g, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the pore volume of the pores in the composite negative electrode material is 0.001 ^{cm 3 /g to 0.6 cm 3 /g, specifically 0.001 cm 3 /} g, 0.005 cm ^{3 /g, 0.01 cm 3 /g, 0.05 cm 3 /g, 0.1 cm 3 /g, 0.15 cm 3 /g, 0.2 cm 3 / g, 0.25 cm 3 /g, 0.3 cm 3 /g, 0.35 cm 3 / g , 0.4 cm 3 / g} , 0.45 cm ³ /g, 0.5 cm 3 /g, 0.55 cm ³ /g and 0.6 cm ³ /g, etc. Of course, it can also be other values within the above range, which is not limited here. Compared with the pore volume of carbon materials, the pore volume of the composite negative electrode material after composite silicon-based materials is significantly reduced, the density of the composite negative electrode material is increased, and the composite negative electrode material also reserves a proper amount of pores to alleviate the volume expansion caused by the silicon-based material during lithium insertion and extraction, which is beneficial to improve the cycle performance of the material. Preferably, the pore volume of the pores in the composite negative electrode material is 0.05 ^cm3 /g to ^{0.5 cm3} /g.

In some embodiments, the volume proportion of the pores in the composite negative electrode material is ≤20%. Specifically, the volume proportion of the pores in the composite negative electrode material can be 1%, 3%, 5%, 7%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% and 20%, etc., and of course, it can also be other values within the above range, which are not limited here. Preferably, the volume proportion of the pores in the composite negative electrode material is 5% to 15%.

In some embodiments, the density of the composite negative electrode material is 1.9 g/cm ³ to 2.3 g/cm ³ , specifically 1.9 g/cm ³ , 1.95 g/cm ³ , 2.0 g/cm ³ , 2.1 g/cm ³ , 2.15 g/cm ³ , 2.2 g/cm ³ , 2.25 g/cm ³ and 2.3 g/cm ³ , etc. Of course, it can also be other values within the above range, which are not limited here. It can be seen that since the silicon-based material is filled in the pores of the carbon material, the density of the carbon material is increased, so that the overall density of the composite negative electrode material is increased by 80% to 120% compared with the initial carbon material.

In some embodiments, the porosity of the composite negative electrode material is 5% to 20%. Specifically, the porosity of the composite negative electrode material can be 5%, 6%, 7%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc. Of course, it can also be other values between 5% and 20%, which are not limited here. It is understandable that due to factors such as diffusion limitations, it is impossible for silicon-based materials to be deposited in the pores of carbon materials and to achieve 100% pore filling. When the porosity is lower than 5%, the composite negative electrode material does not have enough pores to withstand the volume expansion during charging and discharging; when the porosity is higher than 20%, on the one hand, the composite negative electrode material has a low specific capacity due to too little Si filling; on the other hand, due to the large number of pores in the composite negative electrode material, its overall stability is poor. During the preparation of the electrode sheet, the pressure generated by the rolling process is extremely high, and the material structure capacity is Prone to collapse.

In some embodiments, the open pores of the pores in the composite negative electrode material account for 2% to 20% of the total pores, which can be 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc., and of course, it can also be other values within the above range, which are not limited here. It should be noted that the open porosity of the pores in the composite negative electrode material refers to the volume ratio of the open pore volume to the pore volume of all pores in the composite negative electrode material, where all pores include open pores and closed pores. When the open porosity is too large, it means that most of the pores in the carbon material are not effectively filled, and the deposition efficiency of the silicon-based material is insufficient. When the open porosity is too small, it means that the filling rate of the pores in the carbon material is high, and there is not enough pore space in the composite negative electrode material to buffer the volume expansion of the silicon-based material during the lithium insertion and extraction process. In this way, when inserting and extracting lithium, the volume expansion of the silicon-based material causes the expansion pressure in the material structure to be too large, resulting in the structural instability of the composite negative electrode material and the degradation of the electrochemical performance. Therefore, controlling the open porosity of the pores in the composite negative electrode material within the above range is beneficial to improving the specific capacity of the composite negative electrode material on the one hand, and on the other hand, the pores after the carbon material is filled with the silicon-based material are reduced, which can increase the density of the composite negative electrode material and improve the structural stability of the particles. The open porosity within the appropriate range can also provide expansion space for the silicon-based material, reduce the collapse of the material structure caused by volume expansion during the lithium insertion and extraction process, effectively reduce the occurrence of side reactions, and thus improve the material's cycle performance. And find a balance between volume energy density, rolled particle strength, and particle stability during the cycle, and comprehensively improve the various aspects of the negative electrode material performance.

In some embodiments, the pore size of the pores in the composite negative electrode material is Dnm, and the value range of D is 0.1 to 100. Specifically, the pore size of the pores in the composite negative electrode material can be 0.1mm, 0.5nm, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm and 100nm, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, in the composite negative electrode material, the average pore distance between any two adjacent pores is Lnm, and the value range of L is 1 to 300. Specifically, the average pore distance between any two adjacent pores in the composite negative electrode material can be 1nm, 5nm, 10nm, 50nm, 70nm, 100nm, 110nm, 150nm, 180nm, 200nm, 230nm, 250nm, 280nm, 290nm and 300nm, etc., and of course, it can also be other values between 1nm and 300nm, which are not limited here.

In some embodiments, the pore size of the composite negative electrode material is Dnm, the average pore distance between any two adjacent pores is Lnm, and L≥4×D. Specifically, L can be 4×D, 5×D, 6×D, 7×D, 8×D, 10×D, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, as a preferred technical solution of the present application, in the composite negative electrode material, for any three adjacent holes that are not on the same straight line, the pore sizes of the three ^holes are _D1 , _D2 , and _D3 , respectively, and the pore distances are _L1 , _L2 , and _L3 ^{, respectively, and A1 is defined as the minimum value of L12-(L2/2)2} _, ^L12- _{( L3} ^/ ₂ ^{) 2} _, ^L22- _{( L1} /2) _{2 , L22-} ⁽ _L3 /2) ² , L32-( _L1 /2) ² , or _L32- ( ^L2 /2) ² , _B1 is _D1 + _D2 + _D3 , and 3＜ _A1 / _B1 ＜50. More preferably, 10＜ _A1 / _B1 ＜30. It can be understood that when _A1 / _B1 is within the above range, on the one hand, the silicon-based material can be fully deposited in the pores of the carbon material, which is beneficial to the improvement of the specific capacity of the composite negative electrode material; on the other hand, after the silicon-based material is deposited, the composite negative electrode material will leave an appropriate amount of pores inside the material that can be used to buffer the volume expansion of silicon, thereby facilitating the improvement of the material's cycle performance.

In some embodiments, the carbon material after removing the silicon-based material from the composite negative electrode material is tested by the _N2 adsorption-desorption method, and has a peak _Q1 in the range of 2nm to 50nm; the composite negative electrode material is tested by the _N2 adsorption-desorption method, and the composite negative electrode material has a peak _Q2 in the range of 2nm to 50nm, and satisfies the following relationship _Q2 / _Q1≤0.6 . It can be understood that _Q2 / _Q1 can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55 and 0.6, etc.

It should be noted that the _N2 adsorption-desorption method tests the amount of silicon-based material in the composite negative electrode material before and after _deposition , that is, the composite negative electrode material here is the carbon material after the silicon-based material is deposited. When the peak values of the carbon material before deposition and the carbon material after deposition of the silicon-based material in the range of 2nm to 50nm satisfy the above relationship, the silicon-based material can be evenly filled in the pores of the carbon material. At this time, a large number of pores in the composite negative electrode material are filled. On the one hand, the structural stability of the material during the charging and discharging process can be guaranteed. On the other hand, the pores in the composite negative electrode material that are not completely filled can effectively provide expansion space for the silicon-based material distributed around it.

In some embodiments, the differential capacity curve (dQ/dV) of the composite negative electrode material does not have a characteristic peak representing the formation of a crystalline Li ₁₅ Si ₄ alloy phase at about 0.44 V, indicating that Si in the alloy remains amorphous when lithiated to lithiated silicon, and crystalline Li ₁₅ Si ₄ is substantially not generated.

In some embodiments, the mass proportion of oxygen in the composite negative electrode material is ≤10wt%. Specifically, the mass proportion of oxygen in the composite negative electrode material can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% and 10wt%, which are not limited here. It can be understood that if the mass proportion of oxygen is too high, the silicon-based material in the composite negative electrode material will be partially oxidized, and the pores will be at least partially destroyed, thereby affecting the cycle stability of the material. Controlling the mass proportion of oxygen in the composite negative electrode material within the above range can ensure that a large amount of inactive SiO ₂ will not be generated in the material, thereby reducing the cycle performance of the composite negative electrode material.

In a second aspect, the present application also provides a method for preparing a composite negative electrode material, as shown in FIG3 , comprising the following steps:

Providing a carbon material with pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material includes a carbon material and a silicon-based material, and the composite negative electrode material has pores;

In the composite negative electrode material, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are D ₁ , D ₂ , and D ₃ , respectively, and the pore distances are L ₁ , L ₂ , and _{L 3} , respectively ^, A ₁ is defined as the ^minimum value of L ₁ ² -(L ₂ / ₂ ) ² , L ₁ ² -(L ₃ /2) ² , L ₂ ² -(L ₁ /2) ² , L 2 ² -(L 3 /2) ² , L ₃ 2 -(L ₁ /2) 2 or L ₃ ² -(L ₂ /2) ² , B ₁ is D ₁ +D ₂ +D ₃ , and 0.4＜A ₁ /B ₁ ＜50;

In carbon materials, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are d' ₁ , d' ₂ , and d' ₃ , respectively, and the ^pore spacings are l' ₁ , l' ₂ , and l' ₃ , respectively ^. _A'2 is defined as the minimum value ^among l' _22- (l' ₁ / ² ) ² , l' _22- ( _{l'3 /} 2) ² , l' _32- (l' ₁ / ₂ ) ² , l' ^{32- (} _{l' 2} / ² ) ₂ , l' ^12- (l'2/2)2, or l'12-(l' ₃ /2) ² , _B'2 is d' ₁ +d' ₂ +d' ₃ , and _C'1 is l' _22- (l' ₁ / ² ) ² , _l' ^22- (l' ₃ /2) ^2. , the ^maximum value _among l' ₃ ² -(l' ₁ /2) ² , l' 3 2 -(l' ₂ /2) ² , l' ₁ ² -(l' ₂ /2) ² or l' ₁ ² -(l' ₃ /2) ² , B' ₂ /C' ₁ >1, and B' ₂ /A' ₂ ≤4.

In the above scheme, the preparation method of the negative electrode material provided in the present application utilizes a vapor deposition process to fully fill the silicon-based material into the pores of the carbon material, so as to prepare the composite negative electrode material of the present application having excellent specific capacity, first efficiency and cycle performance.

The above technical solution is explained below in conjunction with specific embodiments:

Step S101, providing a carbon material having pores.

In some embodiments, the above-mentioned carbon material having pores can be obtained commercially, or obtained by the following preparation method, which comprises:

Step S1011, dissolving phenolic small molecules in a deionized water solution containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to the phenolic small molecules is 4:1;

Step S1012, adding zinc acetate to the mixed solution, stirring at room temperature for 24 hours to obtain a precipitate, washing with deionized water and drying to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to phenolic small molecules is 4:1.

Step S1013, finally placing the metal coordination compound powder in a quartz tube, purging with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heating to 1000° C. at a rate of 5° C./min, and keeping the temperature for 3 hours, and cooling to obtain a porous carbon material.

The main reason why the carbon materials derived from the above metal coordination compounds have a porous structure is the template effect and carbon thermal activation of nano ZnO. Specifically, the coordinated Zn ²⁺ thermally evolves into ZnO particles, and the ZnO nanoparticles formed in situ in the carbonaceous structure act as a template to produce a placeholder effect, which is conducive to the formation of micropores and mesopores; at the same time, ZnO undergoes a carbon thermal reduction reaction with carbon atoms, and the carbonaceous matrix is etched to form pores. The generated gas and the evaporation of elemental Zn can further expand the pore size or generate additional micro/mesopores. In addition, the subsequent high-temperature carbon thermal reduction plays an important role in the generation of pores. The high zinc content produces more significant nanoparticle template effect and thermal activation effect during pyrolysis, and the obtained carbon material has the characteristics of high specific surface area.

As an optional solution of the present application, the phenolic small molecule in step S1011 can be catechol, which is a phenolic molecule with the simplest structural composition and a single chelating site (synthetic phenol group). The catechol is mixed with zinc salts such as zinc acetate in step S1012 in an alkaline aqueous solution to obtain a metal coordination compound at room temperature. During the mixing process, NaOH is added to the deionized aqueous solution, which can promote the rapid deprotonation of the phenolic hydroxyl group in the catechol through an acid-base reaction, and then react with Zn2 ⁺ to form an insoluble metal complex precipitate, and finally the dried metal coordination compound is subjected to a high temperature treatment of 1000°C in an inert nitrogen atmosphere to obtain a carbon material.

As another optional scheme of the present application, the phenolic small molecule in step S1011 can also be methyl gallate. The aromatic ring of methyl gallate contains at least one single chelating group. The single chelating group is the key to forming a thermally stable metal coordination compound. Only when the coordination compound has sufficiently high thermal stability can it be converted into a carbon material through subsequent heat treatment.

In addition to the above special instructions, other types of phenolic small molecules can also be used, such as 4-methylcatechol, 2,3-dihydroxynaphthalene, 3,4-dihydroxybenzonitrile, 3-hydroxyaminobenzoic acid, pyrogallol and baicalin, etc., which can be selected according to actual needs and are not limited here.

In some embodiments, the specific surface area of the carbon material is 300 m ² /g to 2500 m ² /g. Specifically, the specific surface area of the carbon material can be 300 m ² /g, 500 m ² /g, 1000 m ² /g, 1500 m ² /g, 2000 m ² /g, 2100 m ² /g, 2200 m ² /g, 2300 m 2 /g, 2400 ^{m 2 /} g and 2500 m ² /g, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the pore volume of all pores in the carbon material is 0.4 ^{cm 3} /g to 2 cm ³ / ^g . Specifically, the pore volume of all pores in the carbon material can be 0.4 cm 3 /g, 0.5 cm ³ /g, 0.6 cm ³ /g, 0.7 cm ³ /g ^, 0.8 cm ³ /g ^, 0.9 cm ³ /g, 1.0 cm 3 /g, 1.1 cm 3 /g, 1.2 cm 3 /g, 1.3 cm 3 / ^g , 1.4 cm ³ /g, 1.5 cm ³ /g ^, 1.6 cm 3 /g, 1.7 cm ³ /g, 1.8 ^{cm 3 /g, 1.9 cm 3} /g and 2 cm ³ /g, etc., and of course, it can also be other values between 0.4 cm ³ /g and 1.8 ^{cm 3} /g, which is not limited here.

In some embodiments, the pore size of at least part of the pores gradually decreases from the surface to the interior of the carbon material. It can be understood that the pore structure with the above-mentioned pore size change is conducive to the diffusion of gas into the interior of the carbon material, and can make the silicon-based material evenly and effectively filled in the pores of the carbon material, thereby ensuring that the opening porosity of the pores in the composite negative electrode material is within an appropriate range.

In some embodiments, the density of the carbon material is ≤1.50 g/cm ³ , and can be specifically 0.1 g/cm ³ , 0.2 g/cm ³ , 0.3 g/cm ³ , 0.4 g/cm ³ , 0.5 g/cm ³ , 0.6 g/cm ³ , 0.7 g/cm ³ , 0.8 g/cm ³ , 0.9 g/cm ³ , 1.0 g/cm ³ , 1.10 g/cm ³ , 1.20 g/cm ³ , 1.30 g/cm ³ , 1.40 g/cm ³ and 1.50 g/cm ³ , etc., and can also be other values within the above range, which are not limited here. It can be understood that the carbon material has a large number of pores, the presence of which reduces the density of the carbon material, and sufficient pores are conducive to the deposition of silicon-based materials. When the density of the carbon material is too large, the pores become smaller, Si deposition is prone to being insufficient, and the specific capacity of the composite negative electrode material cannot be effectively improved.

In some embodiments, the distribution density of the pores in the carbon material is 1/μm ² to 1000/μm ^2. Specifically, the distribution density of the pores in the carbon material can be 1/μm ² , 5/μm ² , 10/μm ² , 20/μm ² , 50/μm ² , 100/μm ^{2, 150/μm 2 ,} 200/μm ² , 300/μm ² , 500/μm ² , 600/μm ² , 700/μm ² , 800/μm ² , 900/μm ² , 1000/μm ^2, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the average pore size of the carbon material is 0.1nm to 50nm, specifically 0.1nm, 0.5nm, 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm and 50nm, etc. Of course, it can also be other values of 0.1nm to 50nm, which are not limited here. It is understandable that the pore size distribution of carbon materials will directly affect the deposition of silicon-based materials. When the pore size of the carbon material is too small, it is difficult to introduce the reaction gas containing silicon source gas deeply into the pores of the carbon material. The silicon-based material is more likely to be deposited on the surface of the carbon material rather than in the pores, which can easily lead to the pores on the surface of the composite negative electrode material being closed prematurely, and the content of silicon-based material filled in the composite negative electrode material is too small, thereby causing the electrochemical performance of the material to deteriorate. If the pore size of the carbon material is too large, its mechanical strength will deteriorate, and the problem of silicon-based material segregation will occur. When the pore size exceeds a certain value, the pressure difference effect decreases, which is not conducive to the reaction gas containing silicon source gas and hydrogen entering the pores of the carbon material, resulting in no obvious improvement in the electrochemical performance of the material.

In some embodiments, the porosity of the carbon material is 45% to 75%. Specifically, the porosity of the carbon material can be 45%, 48%, 50%, 55%, 57%, 60%, 65%, 68%, 70%, 71%, 72%, 73%, 74% and 75%, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the filling rate of the pores of the composite negative electrode material is ≥ 70%. Specifically, the filling rate of the pores can be 70%, 71%, 72%, 73%, 74%, 75%, 80%, 83%, 85%, 87%, 90%, 91%, 93%, 95%, 96%, 97% and 99%, etc., and of course, it can also be other values within the above range, which are not limited here. Preferably, the filling rate of the pores is 80% to 90%. It can be understood that the filling rate of the pores within the above range is beneficial to improve the specific capacity of the composite negative electrode material on the one hand, and on the other hand, it is beneficial to improve the structural stability of the composite negative electrode material, thereby reducing the structural collapse of the composite negative electrode material during the cycle.

In some embodiments, in the carbon material, as shown in FIG2 , for any three adjacent pores that are not on the ^same straight line, the pore sizes of the three pores are d' ₁ , d' ₂ , and d' ₃ , respectively, and the pore distances are l' ₁ , _{l' 2} ^, and l' ₃ , respectively. _A'2 is defined as the ^{minimum value among l'22-(l'1/2)2, l'22-(l'3/2)2, l'32-} _{( l'} ^{1 /} ₂ ⁾ _{2 ,} ^{l' 32-} ( _{l' 2} /2) ² , l' _12- ⁽ l' ₂ /2)2, or l' ^12- (l' ₃ /2) ² ; _B'2 is d' ₁ +d' ₂ +d'₃;_C'1 is l'22- ₍ l'1/2) ² , l' _22- (l' ₃ /2) ² , or l' _12- (l'3/ ² )2. The maximum value among l _{' 3} /2) ^{2 ,} l' ₃ ² -(l' ₁ /2) ² , l' ₃ ² - ⁽ l' ₂ /2) 2 , l' ₁ 2 -(l' ₂ /2) ² or l' ₁ ² -(l' ₃ /2) ² , B' ₂ /C' ₁ ＞1, and B' ₂ /A' ₂ ≤4.

It can be understood that when B' ₂ /C' ₁ >1 and B' ₂ /A' ₂ ≤4 in the carbon material, it means that the pore distribution in the carbon material is uniform, and there is no situation where the pore distribution is too concentrated or too sparse, which is conducive to the deposition of silicon-based materials in the pores of the carbon material. Controlling B' ₂ /C' ₁ >1 and B' ₂ /A' ₂ ≤4 in the carbon material can, on the one hand, ensure that the silicon-based material is fully deposited in the pores of the carbon material, which is conducive to the improvement of the specific capacity of the composite negative electrode material; on the other hand, it can reduce the excessive deposition of silicon-based materials in the pores of the carbon material, reserve a certain buffer space for the volume expansion of the silicon-based material, and alleviate the stress release of the composite negative electrode material, which is conducive to the improvement of the cycle performance of the composite negative electrode material.

In some embodiments, the pores in the carbon material include micropores, mesopores and macropores, wherein the volume of micropores accounts for 30% to 99% of all pores, the volume of mesopores accounts for 5% to 70% of all pores, and the volume of macropores accounts for 0 to 5% of all pores.

Specifically, the volume proportion of micropores in all pores can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% and 99%, etc., and of course it can also be other values between 30% and 99%, which are not limited here.

The volume proportion of mesopores in all pores can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% and 70%, etc., and of course it can also be other values within the above range, which is not limited here.

Specifically, the volume proportion of macropores in all pores can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the pores in the carbon material include mesopores, wherein the volume proportion of pores with a pore size of 2 nm to 20 nm in all mesopores is >90%, specifically 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% and 99%, etc., and of course, it can also be other values within the above range, which are not limited here.

In some embodiments, the pores in the carbon material include mesopores, wherein the volume proportion of pores with a pore size of 5 nm to 20 nm in all mesopores is 10% to 50%, specifically 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 46%, 47%, 48%, 49% and 50%, etc., and of course it can also be other values between 10% and 50%, which are not limited here.

It can be understood that the appropriate pore size distribution of the carbon material helps to form gas-phase mass transfer channels inside the carbon material during the deposition process, improve the internal diffusion environment of the carbon material, reduce the density gradient of the carbon material, and thus improve the density of the composite negative electrode material.

In some embodiments, the cross section of the hole is funnel-shaped or inverted cone-shaped. It is understandable that the funnel-shaped or inverted cone-shaped hole has a large gas inlet, which can deeply introduce the reaction gas containing the silicon source gas into the pores of the carbon material, which is conducive to the deposition of the silicon-based material in the pores of the carbon material, and can also reduce the reaction gas from decomposing too fast on the surface of the carbon material and depositing on the surface of the carbon material, resulting in the pores being closed, thereby causing too little deposition of the silicon-based material in the pores of the carbon material, thereby affecting the structural stability of the composite negative electrode material.

In some embodiments, the carbon material includes a catalyst, and the catalyst is located in the pores. It can be understood that the catalyst located in the pores provides a site for the reaction gas containing the silicon source gas to deposit and decompose the silicon-based material to prepare the silicon-carbon composite, and the presence of the catalyst in the carbon material is conducive to the deposition of the silicon-based material in the pores, and can promote the silicon-based material to be deposited in the pores of the carbon material instead of being deposited on the surface of the carbon material.

In some embodiments, the catalyst and the carbon material may be doped in liquid phase or solid phase. For example, carbon particles may be suspended in a doping solution containing a catalyst, and then solid-liquid separation and drying may be performed to obtain a carbon material containing a catalyst. Alternatively, a catalyst may be mixed with a solution containing a polymer monomer, and then a polymerization reaction may be performed to obtain a polymer containing a catalyst, which may then be further carbonized to obtain a carbon material containing a catalyst. In the actual preparation process, the carbon material may also be prepared in other ways, which are not limited here.

In some embodiments, the carbon material includes a catalyst, and the catalyst includes at least one of Ni, Cu, Fe, Mn, Au, Al, Sn, Pd, Pt, Ru, and Ir. It can be understood that the metal catalyst in the carbon material undergoes a eutectic reaction with the silicon source gas, and the silicon source gas reacts with the metal catalyst to form a liquid alloy. At a certain deposition temperature, the liquid alloy crystallizes and precipitates silicon-based materials and metal catalysts; the presence of the metal catalyst can accelerate the rate of the hydrosilation reaction, making the reaction of the Si-H bond with the unsaturated organic matter easier to proceed. The hydrosilation reaction refers to the addition reaction of the Si-H group with the unsaturated carbon-carbon bond when the hydride is added to the unsaturated organic compound. Here, the main reason is the presence of the metal catalyst, which greatly reduces the activation energy of the reaction and makes the hydrogenation reaction easier to proceed.

In some embodiments, the mass proportion of the catalyst in the carbon material is 0.1% to 20%, specifically 0.1%, 0.5%, 1%, 3%, 5%, 7%, 10%, 11%, 15%, 16%, 17%, 18%, 19% and 20%, etc., and of course, other values between 0.1% and 20% are also possible, which are not limited here. An appropriate amount of catalyst can serve as an active site for silicon deposition, which is conducive to the deposition of silicon-based materials in the pores of the carbon material.

In some embodiments, the carbon material may further include a catalyst precursor, the catalyst precursor including a metal salt and/or a metal oxide, and the metal includes at least one of Ni, Cu, Fe, Mn, Au, Al, Sn, Pd, Pt, Ru and Ir.

In some embodiments, the metal salt comprises at least one of a halide, a nitrate, a carbonate, a carboxylate, and a sulfate. A sort of.

In some embodiments, the mass proportion of the catalyst precursor in the carbon material is 0.1% to 10%. Specifically, the mass proportion of the catalyst precursor can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% and 10%, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, before introducing the reaction gas containing silicon source gas under negative pressure, the method further includes the following steps: evacuating the chamber and stopping evacuating the chamber when the deposition pressure of the vapor deposition reaches 0.1 kPa to 50 kPa; and then introducing a protective atmosphere to control the oxygen content in the vapor deposition reaction chamber to be less than 5%.

It is understandable that before the reaction gas containing silicon source gas is introduced, a vacuuming step is first performed, so that a certain pressure difference exists between the inner and outer surfaces of the carbon material particles when the reaction gas containing silicon source gas is introduced, thereby facilitating the reaction gas containing silicon source gas to penetrate into the interior of the carbon material particles; a protective atmosphere is introduced to control the oxygen content in the vapor deposition reaction chamber to be less than 5%, specifically 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% and 4.7%, etc., so as to reduce the oxidation of silicon-based materials in the material to generate _SiO2 , and the synergistic effect of the protective atmosphere and hydrogen can better control the gas reaction rate in the deposition process, thereby controlling the deposition speed of the silicon-based material, so that the silicon-based material can be uniformly filled in the pores of the carbon material instead of being deposited on the surface of the carbon material.

In some embodiments, the steps of evacuating the chamber and passing the protective atmosphere may be repeated multiple times to make the pressure in the reaction chamber reach 0.1 kPa to 50 kPa, and the oxygen content is less than 5%.

S102, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material.

In some embodiments, the deposition temperature of the vapor deposition is 400° C. to 650° C. Specifically, the deposition temperature may be 400° C., 420° C., 450° C., 470° C., 490° C., 500° C., 530° C., 550° C., 580° C., 600° C., 610° C., 620° C., 630° C., 640° C., and 640° C., etc. Of course, it may also be other values between 400° C. and 650° C., which are not limited here.

In some embodiments, the heating rate of vapor deposition is 2°C/min to 20°C/min, specifically 2°C/min, 5°C/min, 6°C/min, 7°C/min, 8°C/min, 9°C/min, 10°C/min, 13°C/min, 15°C/min, 16°C/min, 17°C/min, 18°C/min, 19°C/min and 20°C/min, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the deposition pressure of the vapor deposition is 0.1 kPa to 50 kPa. Specifically, the deposition pressure can be 0.1 kPa, 0.5 kPa, 1 kPa, 5 kPa, 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa and 50 kPa, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the deposition time of vapor deposition is 2 hours to 1000 hours. Specifically, the deposition time can be 2 hours, 5 hours, 10 hours, 50 hours, 100 hours, 150 hours, 200 hours, 250 hours, 300 hours, 350 hours, 400 hours, 500 hours, 600 hours, 650 hours, 700 hours, 800 hours, 900 hours, and 1000 hours, etc. Of course, it can also be other values between 2 hours and 1000 hours, which are not limited here.

It can be understood that the process conditions of vapor deposition (such as deposition temperature, deposition pressure and deposition time) will affect the deposition of silicon-based materials in the pores of carbon materials. By controlling the temperature, pressure and time of vapor deposition within the above range, it can be ensured that the reaction gas containing the silicon source gas does not decompose and deposit before entering the pores of the carbon material, but quickly decomposes and deposits after entering the pores.

In some embodiments, vapor deposition is performed under a protective atmosphere.

In some embodiments, the protective atmosphere includes at least one of nitrogen, argon, helium, neon, krypton, and xenon.

In some embodiments, the volume ratio of the protective atmosphere to the reaction gas is 1:10 to 10:1. The volume ratio of atmosphere to reaction gas can be 1:1, 1:2, 1:5, 1:7, 1:8, 1:10, 10:1, 9:1, 6:1, 5:1, 4:1 and 2:1, etc. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the raw material of the silicon source gas includes at least one of monosilane, disilane, monochlorosilane, dichlorosilane, trichlorosilane and tetrachlorosilane. It should be noted that when the raw material of the silicon source gas is monosilane, disilane, monochlorosilane or dichlorosilane, it is gaseous at room temperature; when the raw material of the silicon source gas is trichlorosilane or tetrachlorosilane, it is liquid at room temperature, and during the vapor deposition process, the liquid silicon source will be vaporized to become a gaseous silicon source.

In some embodiments, the volume proportion of hydrogen in the reaction gas containing silicon source gas and hydrogen is 50% to 98%, specifically 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97% and 98%, and of course, it can also be other values within the above range, which are not limited here. If the mass proportion of hydrogen is too low, the cracking rate of the gaseous silicon source is too fast, and it is easy to quickly decompose and deposit on the surface of the carbon material, thereby causing the problem of sealing; when the volume proportion of hydrogen is too high, although the reaction process can be well controlled, the decomposition rate of the gaseous silicon source is too slow, thereby affecting the deposition efficiency. Therefore, by controlling the volume proportion of hydrogen to 50% to 98%, under the synergistic effect of the protective atmosphere and hydrogen, the decomposition rate of the gaseous silicon source can be controlled, thereby controlling the deposition rate of the silicon-based material, so that the silicon-based material can be evenly and effectively filled in the pores of the carbon material, reducing the problem of the gaseous silicon source decomposing too quickly and depositing on the surface of the carbon material, thereby causing the pores in the carbon material to be closed.

In some embodiments, the method further comprises: cooling, washing and drying the vapor-deposited reaction product to obtain a composite negative electrode material.

In some embodiments, the washing method comprises ultrasonic cleaning.

In some embodiments, the washing solvent comprises anhydrous ethanol.

In some embodiments, the washing time is 30 min to 60 min, specifically 30 min, 35 min, 40 min, 45 min, 50 min, 51 min, 53 min, 55 min 56 min, 57 min, 58 min, 59 min and 60 min. Of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the drying time is 20 min to 100 min. Specifically, the drying time can be 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min, 85 min, 90 min, 95 min and 100 min, etc., and of course, it can also be other values within the above range, which is not limited here.

In some embodiments, the drying temperature is 70°C to 90°C, specifically 70°C, 75°C, 80°C, 81°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C and 90°C. Of course, it can also be other values between 70°C and 90°C, which are not limited here.

The open pores in the composite negative electrode material prepared in this embodiment account for 2% to 20% of the total pores, which can be 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 17%, 18%, 19% and 20%, etc., and of course, it can also be other values within the above range, which are not limited here. If the open porosity is too large, it means that the amount of silicon-based material filled in the carbon material is too small, resulting in a low specific capacity of the composite negative electrode material, and too many pores in the composite negative electrode material are likely to affect the overall structural stability of the material; if the open porosity is too small, it means that the silicon-based material is filled in the carbon material too much, resulting in too little pore space for buffering volume expansion, and there is not enough pore space in the composite negative electrode material to withstand the volume expansion during charging and discharging. In fact, due to factors such as diffusion limitation, it is impossible for the open pores of the carbon material to be 100% filled with Si. Therefore, the open porosity of the pores in the composite negative electrode material is controlled to be between 2% and 20% of the total pores. On the one hand, the silicon-based material can be fully filled in the pores of the carbon material, thereby increasing the specific capacity of the material; on the other hand, a certain amount of pore space is reserved for buffering volume expansion without significantly reducing the structural stability of the material, thereby making the overall material The performance is better.

In some embodiments, the method further comprises: performing a surface coating treatment on the composite negative electrode material obtained above to form a coating layer on the surface of the composite negative electrode material to obtain a composite negative electrode material having a coating layer on the surface.

It can be understood that during the above-mentioned surface coating treatment, the coating material is coated on the surface of the composite negative electrode material so that part of the open pores on the surface of the composite negative electrode material are covered by the coating material, and the remaining pores can alleviate the volume expansion of silicon; and in the process of vapor deposition, it is difficult to ensure that all silicon-based materials are deposited inside the composite negative electrode material. Therefore, the coating layer can also cover and protect a small amount of Si particles exposed on the surface of the composite negative electrode material, while reducing the direct contact between the Si particles and the electrolyte without affecting the transmission of lithium ions, which is beneficial to the formation of a thinner SEI film when the material contacts the electrolyte, so that it consumes less electrolyte, has a better cycle retention rate and lower volume expansion, and can also improve the specific capacity of the material.

In some embodiments, the coating material includes at least one of a carbon material, a metal oxide material, a polymer material, and a nitride material.

In some embodiments, the carbon material includes at least one of soft carbon, hard carbon, crystalline carbon, and amorphous carbon.

In some embodiments, the metal oxide material includes at least one of oxides of Sn, Ge, Fe, Si, Cu, Ti, Na, Mg, Al, Ca, and Zn.

In some embodiments, the nitride material includes at least one of silicon nitride, aluminum nitride, titanium nitride, and tantalum nitride.

In some embodiments, the polymer material includes at least one of polyaniline, polyacrylic acid, polyurethane, polydopamine, polyacrylamide, sodium carboxymethyl cellulose, polyimide, and polyvinyl alcohol.

In some embodiments, the composite negative electrode material having a carbon coating layer on the surface is tested by the _N2 adsorption-desorption method, and the composite negative electrode material having a carbon coating layer on the surface has a peak _Q3 in the range of 2nm to 50nm, and satisfies the following relationship _Q3 / _Q2≤0.3 . Specifically, _Q3 / _Q2 can be 0.1, 0.15, _0.2 , ^0.21 , 0.22, 0.23, 0.25, 0.26, 0.26, 0.28, 0.29 and 0.3, etc., and of course, it can also be other values within the above range, which is not limited here.

It should be noted that when the peak values of the carbon material after depositing the silicon-based material and the negative electrode material after being coated with the carbon coating layer tested by the _N2 adsorption-desorption method in the range of 2nm to 50nm satisfy the above relationship, part of the silicon-based material exposed on the surface of the carbon material after depositing the silicon-based material can be coated by the carbon coating layer, which can reduce the direct contact between the part of the exposed silicon-based material and the electrolyte, reduce the occurrence of side reactions of the negative electrode material, and the negative electrode material coated with the carbon coating layer can improve the structural stability during the charge and discharge process.

The present application also provides a battery, which includes the above-mentioned composite negative electrode material.

The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Example 1

(1) Dissolving catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 2:1; adding zinc acetate to the mixed solution, stirring at room temperature for 24 hours to obtain a precipitate, washing with deionized water and drying to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, placing the metal coordination compound powder in a quartz tube, purging with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heating to 1000°C at a rate of 5°C/min, maintaining the temperature for 3 hours, and cooling to obtain a porous carbon material.

The porous carbon material is loaded into the CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the deposition pressure reaches 2 kPa, the evacuation is stopped; the CVD furnace is powered on, and argon gas is introduced at a rate of 10 L/min to purify the CVD Furnace, at this time, the oxygen content in the furnace is ≤5%.

(2) The furnace temperature is raised to 400°C at a heating rate of 10°C/min, and the vacuum system is reopened to evacuate to 2 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then, the reaction gas is introduced at a rate of 3 L/min for chemical vapor deposition for 50 hours to obtain a reaction product; wherein the reaction gas is a mixed gas of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas is 55%.

(3) Argon gas was introduced at a rate of 10 L/min, the partial pressure of argon gas was controlled at 0.1 kPa, and the vacuum pump speed was adjusted to control the deposition pressure in the CVD furnace at 2 kPa.

(4) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure in the CVD furnace reaches normal pressure, then open the vent valve. After the temperature in the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

FIG4 is a comparison diagram of adsorption curves of the composite negative electrode material and the carbon material provided in Example 1 of the present application. As shown in FIG4 , the carbon material after removing the silicon-based material from the composite negative electrode material is tested by the N ₂ adsorption-desorption method, and has a peak value Q ₁ in the range of 2nm to 50nm, Q ₁ =0.82; the composite negative electrode material is tested by the N ₂ adsorption-desorption method, and has a peak value Q ₂ in the range of 2nm to 50nm, Q ₂ =0.46, Q ₂ /Q ₁ =0.56.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Embodiment 2:

(1) Dissolve catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 6:1; add zinc acetate to the mixed solution, stir at room temperature for 24 hours to obtain a precipitate, wash with deionized water and dry to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, place the metal coordination compound powder in a quartz tube, purge with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heat to 1000°C at a rate of 5°C/min, keep warm for 3 hours, and cool to obtain a porous carbon material.

The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 6 kPa, the evacuation is stopped. The CVD furnace is powered on and nitrogen is introduced at a rate of 2 L/min. At this time, the oxygen content in the furnace is ≤5%.

(2) The furnace temperature is raised to 500°C at a heating rate of 5°C/min, and the vacuum system is reopened to evacuate to 6 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then, the reaction gas is introduced at a rate of 50 L/min for chemical vapor deposition for 20 hours to obtain a reaction product; wherein the reaction gas is monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas is 75%.

(3) Nitrogen was introduced at a rate of 2 L/min, the nitrogen partial pressure was controlled at 0.2 kPa, the vacuum pump speed was adjusted, and the deposition pressure in the CVD furnace was controlled at 8 kPa.

(4) Turn off the power and close the vacuum system, introduce nitrogen into the CVD furnace until the pressure in the CVD furnace reaches normal pressure, then open the vent valve, stop introducing nitrogen after the temperature in the CVD furnace cools to room temperature, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 40 minutes, and then dry it in an oven at 80°C for 90 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.28; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.05, Q ₂ /Q ₁ =0.18.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 3

(1) Dissolving catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 4:1; adding zinc acetate to the mixed solution, stirring at room temperature for 24 hours to obtain a precipitate, washing with deionized water and drying to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, placing the metal coordination compound powder in a quartz tube, purging with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heating to 1000°C at a rate of 5°C/min, maintaining the temperature for 3 hours, and cooling to obtain a porous carbon material.

The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 10 kPa, the evacuation is stopped. The CVD furnace is powered on and argon gas is introduced at a rate of 16 L/min. At this time, the oxygen content in the furnace is ≤5%.

(2) The furnace temperature was raised to 450°C at a heating rate of 15°C/min, and the vacuum system was reopened to evacuate to 10 kPa. At this time, the oxygen content in the furnace was ≤0.5%; then, the reaction gas was introduced at a rate of 5 L/min for chemical vapor deposition for 6 hours to obtain a reaction product, wherein the reaction gas was methane silicon and hydrogen, and the volume proportion of hydrogen in the reaction gas was 95%.

(3) Argon gas was introduced at a rate of 16 L/min, the partial pressure of argon gas was controlled at 0.15 kPa, the vacuum pump speed was adjusted, and the deposition pressure in the CVD furnace was controlled at 2 kPa.

(4) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure in the CVD furnace reaches normal pressure, then open the vent valve. After the temperature in the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 30 minutes, and then dry it in an oven at 80°C for 30 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.59; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.35, Q ₂ /Q ₁ =0.59.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 4

(1) Dissolving catechol in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 8:1; adding zinc acetate to the mixed solution, stirring at room temperature for 24 hours to obtain a precipitate, washing with deionized water and drying to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to catechol is 4:1; finally, placing the metal coordination compound powder in a quartz tube, purging with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, heating to 1000°C at a rate of 5°C/min, maintaining the temperature for 3 hours, and cooling to obtain a porous carbon material.

The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the pressure in the CVD furnace reaches 5 kPa, the evacuation is stopped. The CVD furnace is powered on, and nitrogen is introduced at a rate of 15 L/min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

(2) The furnace temperature is raised to 650°C at a heating rate of 10°C/min, and the vacuum system is reopened to evacuate to 5 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then, the reaction gas is introduced at a rate of 20 L/min for chemical vapor deposition for 5 hours to obtain a reaction product, wherein the reaction gas is methane silicon and hydrogen, and the volume proportion of hydrogen in the reaction gas is 60%.

(3) Nitrogen was introduced at a rate of 12 L/min, the partial pressure of nitrogen was controlled to be 0.08 kPa, and the vacuum pump speed was adjusted to CVD The deposition pressure in the furnace was controlled at 1 kPa.

(4) Turn off the power and close the vacuum system, introduce nitrogen into the CVD furnace until the pressure in the CVD furnace reaches normal pressure, then open the vent valve, stop introducing nitrogen after the temperature in the CVD furnace cools to room temperature, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 35 minutes, and then dry it in an oven at 90°C for 80 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.62; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.23, Q ₂ /Q ₁ =0.37.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 5

The difference from Example 3 is that:

4-methylcatechol is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to catechol is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 4-methylcatechol is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

A carbon material with pores is selected, and specific parameters of the pore structure of the carbon material are shown in Table 1.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.78; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.34, Q ₂ /Q ₁ =0.43.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 6

The difference from Example 3 is that:

2,3-dihydroxynaphthalene is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 2,3-dihydroxynaphthalene is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 2,3-dihydroxynaphthalene is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

A carbon material with pores is selected, and specific parameters of the pore structure of the carbon material are shown in Table 1.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm-50nm, Q ₁ =0.50; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm-50nm, Q ₂ =0.2, Q ₂ /Q ₁ =0.40.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 7

The difference from Example 3 is that:

3,4-dihydroxybenzonitrile is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 3,4-dihydroxybenzonitrile is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 3,4-dihydroxybenzonitrile is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

A carbon material with pores is selected, and specific parameters of the pore structure of the carbon material are shown in Table 1.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm-50nm, Q ₁ =0.67; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm-50nm, Q ₂ =0.17, Q ₂ /Q ₁ =0.25.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 8

The difference from Example 3 is that:

3-hydroxyamine benzoate is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to 3-hydroxyamine benzoate is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to 3-hydroxyamine benzoate is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

A carbon material with pores is selected, and specific parameters of the pore structure of the carbon material are shown in Table 1.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.75; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.33, Q ₂ /Q ₁ =0.44.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 9

The difference from Example 3 is that:

The mixed solution is prepared by dissolving pyrogallol in deionized water containing NaOH, wherein the molar ratio of NaOH to pyrogallol is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to pyrogallol is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

A carbon material with pores is selected, and specific parameters of the pore structure of the carbon material are shown in Table 1.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.80; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.25, Q ₂ /Q ₁ =0.31.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 10

The difference from Example 1 is:

(3) Argon gas was introduced at a rate of 50 L/min, the partial pressure of argon gas was controlled at 10 kPa, and the vacuum pump speed was adjusted to control the deposition pressure in the CVD furnace at 50 kPa.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.83; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.17, Q ₂ /Q ₁ =0.20.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Embodiment 11

The difference from Example 1 is:

After step (4), the prepared composite negative electrode material is subjected to surface coating treatment to obtain a composite negative electrode material having a coating layer on the surface.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm-50nm, Q ₁ =0.86; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm-50nm, Q ₂ =0.5, Q ₂ /Q ₁ =0.58.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 12

The difference from Example 1 is:

(2) The furnace temperature is raised to 700°C at a heating rate of 10°C/min, and the vacuum system is reopened to evacuate to 2 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then, the reaction gas is introduced at a rate of 3 L/min for chemical vapor deposition for 50 hours to obtain a reaction product; wherein the reaction gas is a mixed gas of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas is 55%.

In the composite negative electrode material prepared in this embodiment, the carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material; the composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and the peak value Q ₁ was within the range of 2nm to 50nm, Q 1 = 0.43; the carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and the peak value Q 1 was within the range of 2nm to 50nm, Q ₁ = 0.43. Q ₂ , Q ₂ =0.14, Q ₂ /Q ₁ =0.33.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Example 13

The difference from Example 3 is that:

Baicalein is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to Baicalein is 4:1; zinc acetate is added to the mixed solution, and the precipitate is obtained after stirring at room temperature for 24 hours, and the metal coordination compound powder is obtained after washing with deionized water and drying, wherein the molar ratio of zinc acetate to Baicalein is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after purging with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is kept for 3 hours, and the temperature is lowered to obtain a porous carbon material.

The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the deposition pressure reaches 2 kPa, the evacuation is stopped. The CVD furnace is powered on, and argon gas is introduced at a rate of 10 L/min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

(2) The CVD furnace is connected in series with an evaporation furnace. SiO _1.5 particles are placed in the evaporation furnace and the furnace temperature is raised to 1400°C at a heating rate of 10°C/min, so that the SiO _1.5 particles evaporate into gas.

(3) At the same time, the CVD furnace temperature was raised to 650°C at a heating rate of 10°C/min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

(4) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure in the CVD furnace reaches normal pressure, then open the vent valve. After the temperature in the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm-50nm, Q ₁ =0.45; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm-50nm, Q ₂ =0.22, Q ₂ /Q ₁ =0.50.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Embodiment 14

(1) The difference from Example 3 is that:

Methyl gallate is dissolved in deionized water containing NaOH to obtain a mixed solution, wherein the molar ratio of NaOH to methyl gallate is 4:1; zinc acetate is added to the mixed solution, and the mixture is stirred at room temperature for 24 hours to obtain a precipitate, which is washed with deionized water and dried to obtain a metal coordination compound powder, wherein the molar ratio of zinc acetate to methyl gallate is 4:1; finally, the metal coordination compound powder is placed in a quartz tube, and after being purged with high-purity nitrogen for 10 minutes to remove the air inside the quartz tube, the temperature is increased to 1000°C at a rate of 5°C/min, and the temperature is maintained for 3 hours, and the temperature is lowered to obtain a porous carbon material.

In the above preparation process, the presence of at least one single chelating group in the aromatic ring is the key to forming a thermally stable metal coordination compound. Only when the coordination compound has sufficiently high thermal stability can it be converted into a carbon material by heat treatment.

The porous carbon material is loaded into a CVD furnace, and the CVD furnace is evacuated to exhaust the air in the CVD furnace. When the deposition pressure reaches 2 kPa, the evacuation is stopped. The CVD furnace is powered on, and argon gas is introduced at a rate of 10 L/min to purify the CVD furnace. At this time, the oxygen content in the furnace is ≤5%.

(2) The CVD furnace is connected in series with an evaporation furnace. Al particles are first placed in the evaporation furnace, and the furnace temperature is raised to 1200°C at a heating rate of 10°C/min, so that the Al particles evaporate into gas.

(3) At the same time, the CVD furnace temperature was raised to 500°C at a heating rate of 10°C/min, and the vacuum system was reopened to evacuate the vacuum to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

(4) The CVD furnace is connected in series with an evaporation furnace, and the Si particles are placed in the evaporation furnace. The furnace temperature is raised to 2700°C at a heating rate of 10°C/min, so that the Si particles evaporate into gas.

(5) At the same time, the CVD furnace temperature was raised to 500°C at a heating rate of 10°C/min, and the vacuum system was reopened to evacuate the vacuum to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%.

(6) The CVD furnace temperature was further increased to 700°C at a heating rate of 10°C/min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace was ≤0.5%, so that Si and Al reacted to form Al-Si alloy.

(7) Turn off the power and close the vacuum system, and introduce argon into the CVD furnace until the pressure inside the CVD furnace reaches normal pressure, then open the vent valve. After the temperature inside the CVD furnace cools to room temperature, stop introducing argon, take out the reaction product, ultrasonically clean it with anhydrous ethanol for 20 minutes, and then dry it in an oven at 70°C for 60 minutes to obtain a composite negative electrode material.

The composite negative electrode material prepared in this embodiment includes a carbon material and a silicon-based material. The carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material. The composite negative electrode material has pores, and has three pores that are not on the same straight line.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.45; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.18, Q ₂ /Q ₁ =0.40.

The parameters of the composite negative electrode material in this embodiment are detailed in Table 2.

Comparative Example 1

The difference from Example 1 is:

The reaction gas introduced in step (2) contains only monosilane and no hydrogen.

The composite negative electrode material obtained in this comparative example comprises a carbon material, a silicon-based material and a carbon coating layer, and the carbon material has pores.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.82; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.54, Q ₂ /Q ₁ =0.66.

Comparative Example 2

The difference from Example 1 is:

No vacuum is performed in step (1).

The composite negative electrode material obtained in this comparative example comprises a carbon material, a silicon-based material and a carbon coating layer, and the carbon material has pores.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.82; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.59, Q ₂ /Q ₁ =0.72.

Comparative Example 3

The difference from Example 1 is:

In step (2), the furnace temperature was raised to 400°C at a heating rate of 10°C/min, and the vacuum system was reopened and evacuated to 2 kPa. At this time, the oxygen content in the furnace is ≤0.5%; then the reaction gas is introduced at a rate of 5L/min for chemical vapor deposition for 100 hours to obtain a reaction product; wherein the reaction gas is a mixed gas of monosilane and hydrogen, and the volume proportion of hydrogen in the reaction gas is 55%.

The carbon material after removing the silicon-based material from the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₁ in the range of 2nm to 50nm, Q ₁ =0.82; the composite negative electrode material was tested by the N ₂ adsorption-desorption method, and had a peak Q ₂ in the range of 2nm to 50nm, Q ₂ =0.62, Q ₂ /Q ₁ =0.76.

Performance Testing

(1) Test method for specific surface area of composite negative electrode materials or carbon materials:

The specific surface area was measured using the American Micromeritics TriStar 3000 specific surface area and pore size analyzer.

(2) Test method for density of composite negative electrode material or carbon material:

The powder is placed in an environment filled with _N2 , and the nitrogen gas replacement amount is measured to calculate the density.

(3) Testing method for pore volume of composite negative electrode materials or carbon materials:

The test was conducted using the ASAP2460 equipment from Micromeritics, USA. The pore volume V was calculated using the BJHDesorption cumulative volume of pores model. Calculated within the aperture range.

Micromeretics ASAP 2460 was used for micropore and mesopore analysis. At liquid nitrogen temperature, the equilibrium adsorption of nitrogen on the surface of an object is related to its pore size and other characteristics. Combined with the law of the change of adsorption amount with relative pressure during adsorption, multiple models can be fitted to calculate the pore size. The report generated by the software uses density functional theory (abbreviated as DFT) method to calculate the pore size distribution, total pore volume and pore volume within a certain range.

The true density P of the negative electrode material is tested, and the porosity of the negative electrode material is calculated to be V/(V+1/P).

(4) Pore diameter of composite negative electrode materials or carbon materials and pore diameter testing method:

Take an appropriate amount of sample particles, measure the pore diameter and the pore diameter change from the surface to the center of the particle under a transmission electron microscope (TEM) (SEM can also be used), select three holes in the sample that are not on the same straight line, the pore diameters of the three holes are _D1 ^, _D2 , and _D3 , and the pore distances are _L1 , _L2 ^, and _L3 , respectively. Define _A1 as the ^minimum value ^of _L12- ( _L2 /2) ² , _L12- ( _{L3 /} 2) ² , _L22- ( _L1 /2 ^{) 2} , _L22- ( _L3 /2) ² , ^L32- ( _L1 /2)2, ^or _L32- ( _L2 /2) ² , _B1 is _D1 + _D2 + _D3 , and calculate the value of _A1 / _B1 .

(5) Test method for the distribution density of pores in carbon materials:

After taking an appropriate amount of sample particles and cutting them, the number of pores per unit area on the cut surface of the carbon material is measured to obtain the distribution density of pores in the carbon material.

(6) Test method for mass content of silicon-based materials in composite negative electrode materials:

The mass of the composite negative electrode material is weighed as M1, the mass of the material tested after etching the silicon-based material is m ² , and (M1-m ² )/M1 is the mass content of the silicon-based material in the composite negative electrode material.

(7) Testing method for filling rate of carbon material pores:

The volume of the pores in the composite negative electrode material before etching the active substance is V1, and the volume of the pores after etching the silicon-based material is V2. (V2-V1)/V2 is the filling rate of the silicon-based material in the pores of the carbon material.

(8) Electrochemical performance test

1) The test method for the first discharge specific capacity and the first coulombic efficiency (ICE) is as follows: a negative electrode slurry is prepared according to the mass ratio of the composite negative electrode material, conductive carbon black and polyacrylic acid (PPA) of 75:15:10, coated on copper foil, and dried to make a negative electrode. Electrode. A metal lithium sheet was used as the counter electrode and assembled into a button cell in a glove box filled with argon. The button cell was charged and discharged at a current density of 0.1C in the charge and discharge range of 0.01V-5V to obtain the first discharge specific capacity and first coulombic efficiency (ICE) of the button cell.

2) The test method for the capacity retention rate and the electrode thickness expansion rate after 50 cycles is as follows: the composite negative electrode material, conductive carbon black (Super-P), conductive graphite (KS-6), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are prepared into a negative electrode slurry according to a mass ratio of 92:2:2:2:2, coated on copper foil, and dried to form a negative electrode electrode. The proportion of Si-C and graphite in the mixture of the composite negative electrode material with a carbon coating layer and graphite is determined by the first reversible specific capacity of the two and the capacity required to be matched between the two. A metal lithium sheet is used as the counter electrode and assembled into a button cell in an argon-filled glove box. At a current density of 1C, the button cell is charged and discharged 50 times in the charge and discharge range of 0.01V-5V to obtain the capacity retention rate and the electrode thickness expansion rate after the battery is cycled 50 times.

(9) Test method for porosity of composite negative electrode materials or carbon materials:

a. First use an electronic balance to measure the mass M ₁ (g) of the sample in air;

b. Place the sample in molten paraffin under vacuum, so that the molten paraffin fully fills the pores of the sample. After soaking for 1 hour until fully saturated, take out the sample and carefully wipe off the paraffin on the surface of the sample. Then use an electronic balance to measure the mass of the sample in air _M2 (g);

c. Place the paraffin-filled sample on a sling and immerse it in water and weigh it, mass M ₃ (g);

d. Immerse the hanger without sample in water and weigh it, mass M ₄ (g).

The porosity of the sample was calculated according to the following formula:

At the same time, the open porosity of the sample can be calculated according to the following formula:

Wherein, ρ _s is the density of the dense solid corresponding to the carbon material (g/cm ³ ), ρ _L is the density of water (g/cm ³ ), and ρ _ME is the density of paraffin (g/cm ³ ).

(10) Removing the silicon-based material from the composite negative electrode material by etching:

Add a 1M nitric acid solution to the composite negative electrode material and soak it for 4 hours. Then, add a 20% mass fraction HF acid solution drop by drop into the composite negative electrode material, which will produce yellow smoke. Repeat the dripping several times until no yellow smoke is produced in the solution. Finally, use a 1M nitric acid solution to digest the residue, then wash and dry to obtain the composite negative electrode material after removing the silicon-based material.

(10) Test on the change of average pore size of carbon material after removing silicon-based material from composite negative electrode material:

Use magnetron sputtering technology or focused ion beam (FIB) technology to gradually remove the surface layer of the carbon material, and combine imaging technology to observe and record the changes in the internal pore size of the carbon material with depth, and then obtain the internal pore size change trend. Or use FIB technology to cut particles, use FIB technology to cut carbon material particles, and then image the cut surface to obtain pore size information, and perform probability statistical analysis on these data to statistically analyze the pore size changes of carbon materials.

Table 1 Parameters of carbon materials

Table 2 Parameters of composite negative electrode materials

Table 3 Performance test results of embodiments and comparative examples

According to the results shown in Tables 1 to 3, the composite negative electrode material prepared in the embodiments of the present application has a high first discharge specific capacity, a first coulombic efficiency and a capacity retention rate after 50 cycles, and the electrode thickness expansion rate after 50 cycles is low. This is because in the particle structure of the composite negative electrode material prepared in this embodiment, any three adjacent pores that are not on the same straight line are taken, the pore sizes of the three pores are D ₁ , D ₂ , and D ₃ , and the pore distances are L ₁ , L ₂ , and L ₃ , respectively. A ₁ is defined as the minimum value of L ₁ ² -(L ₂ /2) ² , L ₁ ² -(L ₃ /2) ² , L ₂ ² -(L ₁ /2) ² , L ₂ ² -(L ₃ /2) ² , L ₃ ² -(L ₁ /2) ² or L ₃ ² -(L ₂ /2) ² , B ₁ is D ₁ +D ₂ +D ₃ , and the relationship between A ₁ and B ₁ satisfies 0.4＜A ₁ /B ₁ ＜50. At this time, A ₁ /B 1 is less than 0.5. ₁ Within the above range, the pore distribution inside the composite negative electrode material is within a reasonable range, that is, the pore distribution is moderate and not too sparse or dense. On the one hand, it shows that most of the pores of the composite material are effectively filled with silicon-based materials, that is, the inside of the composite negative electrode material is relatively dense, and the highly stable silicon-based material can provide abundant lithium storage sites, thereby improving the specific capacity and first efficiency of the composite negative electrode material; on the other hand, the inside of the composite negative electrode material is not a completely dense structure, and the silicon-based material has a certain expansion space, which can ensure the structural stability of the composite negative electrode material during the cycle, alleviate the expansion of the pole piece, and improve the cycle performance of the battery prepared with the composite negative electrode material.

It can be seen from the table that compared with Example 1, although the capacity retention rate of the composite negative electrode material of Example 10 is higher after 50 cycles, the initial discharge specific capacity is lower. This is because the air flow of argon introduced during the preparation process is too large, resulting in an excessive argon partial pressure, which causes the deposition rate of the silicon-based material to be too slow. At the same deposition time, the deposition rate of the silicon-based material in the carbon material is too slow, resulting in a low filling rate of the pores in the carbon material, and too little deposition of the silicon-based material in the pores. The high capacity advantage of silicon cannot be fully utilized, making it difficult to improve the specific capacity of the composite negative electrode material, resulting in a low initial discharge specific capacity of the composite negative electrode material.

Compared with Example 1, although the composite negative electrode material in Example 14 has higher initial coulombic efficiency and capacity retention rate after 50 cycles, and lower electrode thickness expansion rate after 50 cycles, the initial discharge specific capacity is poor. This is because the silicon-based material deposited in Example 14 is a silicon alloy, and the mass percentage of silicon in the silicon alloy is lower than that of pure crystalline silicon, which leads to too little deposited silicon content in the pores, and the high capacity advantage of silicon cannot be fully utilized, resulting in the composite negative electrode material. The specific capacity is difficult to improve, resulting in a low first discharge specific capacity of the composite negative electrode material.

Compared with Example 1, in the composite negative electrode material of Comparative Example 1, only monosilane among the reaction gases introduced during the preparation process does not contain hydrogen. Therefore, the decomposition rate of monosilane is too fast and deposited on the surface of the carbon material, resulting in the pores on the surface of the carbon material being closed. The open porosity is only 0.5%, and it is difficult for the silicon-based material to deposit and fill in the pores of the carbon material. The filling rate of the pores in the carbon material is too low, and the deposition amount of the silicon-based material in the pores is too small, which cannot fully utilize the high capacity advantage of silicon, making it difficult to improve the specific capacity of the composite negative electrode material, thereby resulting in a low first discharge specific capacity of the material.

Compared with Example 1, the composite negative electrode material of Comparative Example 2 does not perform a vacuum step during the preparation process, which is not conducive to the deposition of silicon-based materials in the carbon material. The open porosity is only 0.8%. The silicon-based material is deposited on the surface of the carbon material, resulting in the pores on the surface of the carbon material being closed, and it is difficult to deposit into the pores of the carbon material. The filling rate of the pores in the carbon material is low, and the deposition amount of the silicon-based material in the pores is too small, which cannot fully utilize the high capacity advantage of silicon, making it difficult to improve the specific capacity of the composite negative electrode material, resulting in a low first discharge specific capacity of the material.

Compared with Example 1, the content of monosilane in the reaction gas introduced in Comparative Example 3 increases, the amount of silicon-based material deposited in the pores is too much, and there are no pores or fewer pores inside the composite negative electrode material. Although the first discharge specific capacity and the first coulomb efficiency of the composite negative electrode material are increased, the excessive silicon-based material makes it difficult to effectively relieve the stress of the silicon-based material during the cycle, and the composite negative electrode material will have the problem of excessive local stress. The thickness expansion rate of the electrode sheet increases after 50 cycles, and the composite negative electrode material undergoes pulverization and contact loss with the conductive agent and the current collector, resulting in a decrease in the capacity retention rate after 50 cycles.

Claims (15)

A composite negative electrode material, characterized in that the composite negative electrode material comprises a carbon material and a silicon-based material, the carbon material has pores, and at least part of the silicon-based material is distributed in the pores of the carbon material; The composite negative electrode material has pores. For any three adjacent pores that are not on the same straight line, the pore diameters of the three pores are _D1 , _D2 , and _D3 , respectively, and the pore distances are _L1 ^, _L2 , and _L3 , respectively. _A1 is defined as _the ^minimum value of _L12- ⁽ _{L2 /} 2) ² , _L12- ( _L3 /2) ₂ , _L22- ⁽ L1/2) ^{2 , L22-} _{( L3} /2) ² , ^L32- ( _L1 /2) ² , or _L32- ( ^L2 /2) ² , _B1 is _D1 + _D2 + _D3 , and 0.4＜ _A1 / _B1 ＜50. The composite negative electrode material according to claim 1, characterized in that, in the carbon material after the silicon-based material is removed from the composite negative electrode material, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are _d1 , _d2 , and _d3 , respectively, and the ^pore distances are _l1 , _{l2 ,} and _l3 , respectively _{, A2} is defined as the minimum value of _{l22- ( l1} /2) ² , ^{l22- (} _l3 /2) ² , _l32- ( _l1 /2) ² , _l32- (l2/2) ^{2 , l12-} (l2/2) ² _, or _l12- ( _l3 /2) ² , _B2 is _d1 + _d2 + _d3 , and _C1 is _l22- ( _l1 / ₂ ) ² , _l22- ( ^l3 /2) ² , ^l32- ( _l1 /2) ² , or _l12- (l3/2) ^2. -(l ₁ /2) ² , l ₃ ² -(l ₂ /2) ² , l ₁ ² -(l ₂ /2) ² or l ₁ ² -(l ₃ /2) ² , and B ₂ /C ₁ >1, B ₂ /A ₂ ≤4. The composite negative electrode material according to claim 1 is characterized in that the average pore size of the pores in the composite negative electrode material is Dnm, and the value range of D is 0.1 to 100. The composite negative electrode material according to claim 1 is characterized in that, in the composite negative electrode material, the average pore distance between any two adjacent pores is Lnm, and the value range of L is 1 to 300. The composite negative electrode material according to claim 1 is characterized in that the average pore size of the pores in the composite negative electrode material is Dnm, the average pore distance between any two adjacent pores is Lnm, and L≥4×D. The composite negative electrode material according to claim 1, characterized in that the pore volume of the pores in the composite negative electrode material is 0.001 ^{cm 3} /g to 0.6 ^{cm 3} /g. The composite negative electrode material according to claim 1 is characterized in that the open pores in the composite negative electrode material account for 2% to 20% of the total pores. The composite negative electrode material according to claim 1 is characterized in that the pores in the carbon material after removing the silicon-based material from the composite negative electrode material include micropores, mesopores and macropores; wherein the volume proportion of the micropores in all pores is 30% to 99%, the volume proportion of the mesopores in all pores is 5% to 70%, and the volume proportion of the macropores in all pores is 0 to 5%. The composite negative electrode material according to claim 8 is characterized in that the pores in the carbon material after removing the silicon-based material from the composite negative electrode material include mesopores, wherein the volume proportion of pores with a pore diameter of 2nm to 20nm in the mesopores is >90%; the volume proportion of pores with a pore diameter of 5nm to 20nm in the mesopores is 10% to 50%. The composite negative electrode material according to claim 1 is characterized in that, in the carbon material after the silicon-based material is removed from the composite negative electrode material, the pore size of at least part of the pores gradually decreases from the surface to the inside of the carbon material, wherein the average pore size change from the surface to the inside of the carbon material is ≥0.1nm per 1μm extension. The composite negative electrode material according to claim 1 is characterized in that the mass proportion of the silicon-based material in the composite negative electrode material is 15% to 60%. The composite negative electrode material according to claim 1 is characterized in that, when the carbon material after removing the silicon-based material from the composite negative electrode material is tested by _N2 adsorption-desorption method, it has a peak value _Q1 in the range of 2nm to 50nm; when the composite negative electrode material is tested by _N2 adsorption-desorption method, it has a peak value _Q2 in the range of 2nm to 50nm, and satisfies the following relationship _Q2 / _Q1≤0.6 . The composite negative electrode material according to claim 1, characterized in that the oxygen element in the composite negative electrode material The mass proportion is ≤10wt%. A method for preparing a composite negative electrode material, characterized in that it comprises the following steps: Providing a carbon material with pores, introducing a reaction gas containing a silicon source gas and hydrogen under a negative pressure environment, and performing vapor deposition on the carbon material to obtain a composite negative electrode material; wherein the composite negative electrode material comprises a carbon material and a silicon-based material, and the composite negative electrode material has pores; In the composite negative electrode material, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are D ₁ , D ₂ , and D ₃ , respectively, and the pore distances are L ₁ , L ₂ , and L ₃ , respectively, A ₁ is defined as the minimum value of L ₁ ² -(L ₂ / ² ) ² , L ₁ ^{2 -} (L ₃ /2) ² , L _{2 2} -(L ₁ /2) ² , L 2 ² -(L ₃ /2) ² , L ₃ 2 -(L ₁ /2) ² or L ₃ ² -(L ₂ /2) ² , B ₁ is D ₁ +D ₂ +D ₃ , and 0.4＜A ₁ /B ₁ ＜50; In the carbon material, for any three adjacent pores that are not on the same straight line, the pore sizes of the three pores are d' ₁ , d' ₂ , and d' ₃ , respectively, and the pore distances are l' ₁ , l' ₂ , and l' ₃ , respectively. _A'2 is defined as the minimum ^value among l' _22- ⁽ l' ₁ /2) ² , l' _22- ⁽ l' ₃ / ₂ ^{) 2 ,} l' _32- (l' ₁ /2) ² , l' ^{32- (} _{l' 2} / ₂ ) ² , l'12-(l' ₂ /2)2, or l'12-(l' ₃ /2) ² , _B'2 is d' ₁ +d' ₂ +d' ₃ , and _C'1 is l' _22- (l' ₁ / ^{2)2, l'22- (} _{l' 3} /2) ^{2 .} , the ^maximum value _among l' ₃ ² -(l' ₁ /2) ² , l' 3 2 -(l' ₂ /2) ² , l' ₁ ² -(l' ₂ /2) ² or l' ₁ ² -(l' ₃ /2) ² , B' ₂ /C' ₁ >1, and B' ₂ /A' ₂ ≤4. A battery, characterized in that the battery comprises the composite negative electrode material according to any one of claims 1 to 13 or the composite negative electrode material prepared by the preparation method of the composite negative electrode material according to claim 14.