CN115881961B - Composite lithium silicon alloy lithium supplementing agent with core-shell structure and preparation method and application thereof - Google Patents

Abstract

The present invention provides a composite lithium-silicon alloy lithium replenisher with a core-shell structure, and a preparation method and application thereof. The composite lithium-silicon alloy lithium replenisher comprises a lithium-silicon alloy core and a first coating layer and a second coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside; the first coating layer comprises an oxide coating layer; the second coating layer comprises a lithium compound coating layer. The composite lithium-silicon alloy lithium replenisher provided by the present invention has a high gram capacity, thereby improving the lithium replenishment efficiency and cycle performance of the negative electrode, and can be directly added to the negative electrode slurry during homogenization, and has high compatibility with the current lithium battery process.

Description

A composite lithium-silicon alloy lithium supplement with a core-shell structure and its preparation method and application

Technical Field

The present invention belongs to the technical field of lithium supplement material, and in particular relates to a composite lithium-silicon alloy lithium supplement with a core-shell structure, and a preparation method and application thereof.

Background Art

With the rapid development and continuous expansion of new energy vehicles, the market demand for power batteries with both high energy and high power is gradually increasing. In order to improve the energy density of power batteries, the development and application of high-capacity positive and negative electrodes have developed rapidly. For example, high-capacity silicon negative electrodes, silicon-carbon negative electrodes, and tin-based negative electrodes have gradually been widely used and industrialized in high-performance lithium batteries. However, compared with conventional graphite negative electrodes, high-capacity negative electrode materials have huge volume changes during charging, discharging and cycling, which makes the SEI film formed on its surface easy to break, causing the side reactions to continue to intensify, causing the battery capacity to decay rapidly during the cycle.

In order to further improve the cycle performance of materials such as silicon negative electrodes, the existing technology can significantly reduce the volume expansion of materials during cycling through methods such as nano-processing and surface coating, thereby improving the cycle performance of batteries. In addition, the existing technology also discloses pre-physical and chemical treatment of materials, and the use of lithium replenishers to replenish lithium in positive and negative electrodes, thereby compensating for the irreversible capacity loss of the battery during the first cycle of charging and discharging and the cycle process, and can also effectively improve the cycle life and storage performance of lithium batteries.

CN105489846A discloses the use of lithium belt composite to replenish negative electrode lithium, and metal lithium is directly compounded on the surface of the negative electrode sheet, thereby improving the cycle performance of the battery. CN108520978A discloses the use of lithium-naphthalene organic solvent to replenish negative electrode lithium, and the negative electrode sheet is directly immersed in the lithium-naphthalene solvent to achieve chemical pre-embedded lithium, thereby reducing irreversible capacity loss. Literature (XinSua, Chikai Lin, XiaopingWang et.al, A new strategy to mitigate the initial capacity loss of lithium ion batteries, Journal of Power Sources324 (2016), 150-157) uses lithium-rich lithium iron acid as a positive electrode lithium replenisher, thereby significantly improving the cycle performance of the cobalt acid lithium battery system. However, the above-mentioned lithium replenishment method has extremely high requirements for environmental temperature and humidity, and highly active lithium metal or lithium replenishment solvents are very easy to react with moisture in the air and carbon dioxide, etc., resulting in the battery having potential safety hazards and lithium replenishment agent failure. In addition, the above-mentioned lithium replenishment method has poor compatibility with the conventional winding battery preparation process, low production efficiency, and slow industrialization progress. Moreover, the above-mentioned lithium replenisher produces a large amount of gas during the formation and circulation process, and the interface state of the electrode is poor, resulting in no obvious improvement in the battery's cycle performance.

As the electric market continues to increase its demand for high-capacity and long-cycle-life lithium batteries, the development of lithium batteries with high specific capacity and long cycle life has become an important trend in the industry. Using lithium replenishers to pre-treat lithium batteries can significantly reduce the irreversible capacity loss during the battery cycle, so it is of great significance to design and develop lithium replenishers with good compatibility, high lithium replenishment efficiency and no side effects.

Summary of the invention

In view of the deficiencies of the prior art, the purpose of the present invention is to provide a composite lithium silicon alloy lithium supplement agent with a core-shell structure, and a preparation method and application thereof. The composite lithium silicon alloy lithium supplement agent provided by the present invention has a high gram capacity, thereby improving the lithium supplement efficiency and cycle performance of the negative electrode, and can be directly added to the negative electrode slurry during homogenization, and has high compatibility with the current lithium battery process. At the same time, the composite lithium silicon alloy lithium supplement agent has good environmental compatibility, is in full contact with the electrolyte, has a high utilization rate, and has no obvious gas production, thereby significantly improving the electrical performance of the lithium battery.

In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

In a first aspect, the present invention provides a composite lithium-silicon alloy lithium supplement agent having a core-shell structure, wherein the composite lithium-silicon alloy lithium supplement agent comprises a lithium-silicon alloy core and a first coating layer and a second coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside;

The first coating layer is an oxide coating layer;

The second coating layer includes a lithium compound coating layer.

The lithium-silicon alloy core used in the present invention has sufficient gaps, which can effectively suppress the stress generated by the lithium-silicon alloy, significantly improve the battery cycle stability, and by coating the surface of the lithium-silicon alloy with a first coating layer, it can effectively suppress the reaction of the lithium-silicon alloy with moisture in the environment, improve the environmental compatibility of the lithium supplement, and can be directly added to the negative electrode slurry during homogenization, and has high compatibility with the current lithium battery process. In addition, the present invention also coats the surface of the first coating layer with a second coating layer, which can prevent it from directly contacting the electrolyte and reduce some residual lithium on the surface of the lithium-silicon alloy.

Therefore, the composite lithium-silicon alloy lithium supplementer with a core-shell structure provided by the present invention has a first coating layer that can effectively improve the conductivity of the lithium-silicon alloy powder, and a second coating layer that can effectively improve the ionic conductivity of the material, so the gram capacity of the lithium supplementer can be significantly improved, thereby improving the lithium supplement efficiency and cycle performance of the negative electrode.

Preferably, the first coating layer comprises any one of aluminum oxide, silicon oxide or titanium oxide, or a combination of at least two thereof.

Preferably, the second coating layer includes any one of lithium carbonate, lithium phosphate or lithium aluminate, or a combination of at least two of them.

In the present invention, the use of the above-mentioned specific type of coating layer has the advantage of significantly improving the environmental stability of the lithium supplement agent, and can be directly added to the negative electrode slurry as an additive; in addition, the double-layer coating structure and the porous structure significantly improve the electronic conductivity and ion conductivity of the lithium supplement agent, significantly improve its lithium supplement effect, thereby significantly improving the kinetic performance and cycle life of the lithium battery.

Preferably, the elemental mass percentage of lithium and silicon in the lithium-silicon alloy core is (20-40):(60-80), preferably (25-35):(65-75), for example, it can be 20:80, 22:78, 25:75, 28:72, 30:70, 32:68, 35:65, 38:62, 40:60.

In the present invention, by adjusting the mass percentage of lithium and silicon in the lithium-silicon alloy core, the lithium-silicon lithium supplement agent has a suitable lithium supplement potential and lithium supplement gram capacity. If the mass percentage is too low, the lithium supplement agent potential will be too high, the lithium supplement gram capacity will be low, and the lithium supplement efficiency will be insufficient. On the contrary, the hollow lithium supplement agent will form a huge volume strain when lithium is inserted and deintercalated, resulting in particle breakage, increased side reactions, and battery cycle life attenuation.

Preferably, the thickness of the first coating layer is 5 to 50 nm, preferably 10 to 30 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm.

In the present invention, by adjusting the thickness of the first coating layer, a protective layer is formed on the surface of the highly active hollow lithium silicon lithium supplement agent to improve its environmental stability. If the thickness is too small, it will lead to uneven coating, and the lithium supplement agent will react with water and oxygen in the external environment, and the stability will be reduced. On the contrary, if the coating layer is too thick, it will affect the electron and ion transmission during the deintercalation process of the lithium supplement agent, and the lithium supplement capacity will be significantly reduced.

Preferably, the thickness of the second coating layer is 5 to 50 nm, preferably 15 to 35 nm, for example, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm.

In the present invention, by adjusting the thickness of the second coating layer, the residual alkali on the surface of the lithium supplement is significantly reduced. At the same time, the coating of the surface lithium salt can significantly improve its ion conductivity and improve the electrode kinetics. If the thickness is too small, it will not be possible to form a uniform coating. Otherwise, it will lead to an increase in the lithium ion transmission path and hinder the electrochemical reaction.

Preferably, the average particle size of the composite lithium-silicon alloy lithium supplement agent is 10-20 μm, for example, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm.

In the present invention, by adjusting the average particle size of the composite lithium-silicon alloy lithium replenisher, the stability of the prepared negative electrode slurry is good, the lithium replenisher in the prepared negative electrode sheet is fully in contact with the active particles and the electrolyte, and the lithium replenishment is uniform and fast. If the particle size is too small, the lithium replenisher will agglomerate, the slurry stability will be poor, and the lithium replenishment will be uneven. Otherwise, the lithium replenisher deintercalation path will be large and the lithium replenishment rate will be significantly reduced.

In a second aspect, the present invention provides a method for preparing a composite lithium-silicon alloy lithium supplement having a core-shell structure according to the first aspect, the method comprising the following steps:

(1) mixing a silicon-containing alloy and a pure metal, melting and solidifying and atomizing to obtain a precursor powder, chemically etching the precursor powder to obtain silicon particles, and then evaporating the silicon particles and lithium metal to obtain a lithium-silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) and the first coating layer precursor material, and heating to obtain a lithium silicon alloy material coated by the first coating layer;

(3) The lithium-silicon alloy material coated by the first coating layer obtained in step (2) is mixed with the second coating layer precursor and subjected to heat treatment to obtain the composite lithium-silicon alloy lithium supplement agent with a core-shell structure.

In the present invention, the preparation method of step (1) above can be used to prepare a lithium-silicon alloy core with a hollow structure, which has the advantages of promoting lithium ion transmission and buffering the volume strain occurring during electrochemical deintercalation.

Preferably, the silicon-containing alloy in step (1) comprises any one of an aluminum-silicon alloy and a magnesium-silicon alloy.

Preferably, the pure metal in step (1) includes pure aluminum or pure magnesium.

Preferably, the mass percentage of silicon in the smelted silicon-containing alloy in step (1) is 10% to 20%, for example, 10%, 12%, 15%, 18%, or 20%.

In the present invention, the mass percentage of silicon in the smelted silicon-containing alloy is controlled so that the lithium supplement has a high specific capacity.

Preferably, the smelting temperature in step (1) is 700-800°C, for example, 700°C, 720°C, 750°C, 780°C, 800°C; the smelting time is 4-6h, for example, 4h, 4.5h, 5h, 5.5h, 6h.

In the present invention, the smelting in step (1) is carried out under vacuum conditions.

Preferably, the coagulation atomization gas flow rate in step (1) is 30-40 m ³ /h, for example, 30 m ³ /h, 32 m ³ /h, 35 m ³ /h, 38 m ³ /h, 40 m ³ /h; the inner diameter of the ceramic tube is 8 mm, and the nozzle gap is 0.6 mm.

In the present invention, the solidification atomization method has the advantage of forming silicon-containing alloy particles with small particle size and uniform distribution.

Preferably, the chemical etching process in step (1) also includes crushing and screening processes before the chemical etching process.

In the present invention, the particle size of the product after sieving is 10 to 20 μm, for example, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm.

Preferably, the chemical etching treatment in step (1) is performed using a mixed solution of phosphoric acid, nitric acid and acetic acid.

Preferably, the volume ratio of phosphoric acid, nitric acid and acetic acid in the mixed solution of phosphoric acid, nitric acid and acetic acid is (70-80):(5-10):(10-25), for example, it can be 70:5:25, 72:8:20, 75:5:20, 78:5:17, 80:10:10.

Preferably, the chemical etching treatment in step (1) further includes washing and drying treatment.

Preferably, the washing is performed with deionized water.

In the present invention, the temperature of the drying treatment is 100 to 120°C.

Preferably, the evaporation in step (1) is performed in an inert atmosphere.

In the present invention, the inert atmosphere includes but is not limited to argon or nitrogen.

Preferably, the evaporation temperature in step (1) is 100-200°C, for example, 100°C, 120°C, 150°C, 180°C, 200°C; and the pressure is 10 ^-4 -10 ^-2 Pa.

In the present invention, the evaporation time in step (1) is 5 to 30 min, for example, it can be 5 min, 8 min, 10 min, 12 min, 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, or 30 min.

In the present invention, the content of lithium metal deposited on the silicon particles is adjusted by regulating the temperature and time of the evaporation in step (1).

Preferably, the heating temperature in step (2) is 400-600°C, for example, 400°C, 420°C, 450°C, 480°C, 500°C, 520°C, 550°C, 580°C, or 600°C.

Preferably, the heating temperature in step (3) is 150-250°C, for example, 150°C, 180°C, 200°C, 220°C, or 250°C.

In a third aspect, the present invention provides a negative electrode sheet, comprising a negative electrode active material layer and a current collector, wherein the negative electrode active material layer comprises the composite lithium-silicon alloy lithium supplement having a core-shell structure according to the first aspect.

In a fourth aspect, the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, wherein the negative electrode sheet comprises the negative electrode sheet according to the third aspect.

The lithium ion battery prepared by the negative electrode sheet provided by the present invention has the advantages of improving the lithium replenishment efficiency and cycle performance of the negative electrode.

Compared with the prior art, the present invention has the following beneficial effects:

The present invention provides a composite lithium-silicon alloy lithium supplement, wherein the lithium-silicon alloy core used in the present invention has sufficient gaps, can effectively suppress the stress generated by the lithium-silicon alloy, significantly improve the battery cycle stability, and by coating the surface of the lithium-silicon alloy with a first coating layer, it can effectively suppress the reaction of the lithium-silicon alloy with moisture in the environment, improve the environmental compatibility of the lithium supplement, and can be directly added to the negative electrode slurry during homogenization, and has high compatibility with the current lithium battery process. In addition, the present invention also coats the surface of the first coating layer with a second coating layer, which can prevent it from directly contacting the electrolyte and reduce some residual lithium on the surface of the lithium-silicon alloy.

Therefore, the composite lithium-silicon alloy lithium supplementer with a core-shell structure provided by the present invention has a first coating layer that can effectively improve the conductivity of the lithium-silicon alloy powder, and a second coating layer that can effectively improve the ionic conductivity of the material, so the gram capacity of the lithium supplementer can be significantly improved, thereby improving the lithium supplement efficiency and cycle performance of the negative electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a flow chart of the preparation of a composite lithium-silicon alloy lithium supplement provided in Example 1;

2 is a schematic diagram of the structure of the composite lithium-silicon alloy lithium supplement provided in Example 1, wherein 11 is a lithium-silicon alloy core, 12 is a pore structure, 13 is an alumina coating layer, and 14 is a lithium carbonate coating layer.

DETAILED DESCRIPTION

The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

Example 1

The present embodiment provides a composite lithium-silicon alloy lithium supplement agent with a core-shell structure and an average particle size of 15 μm, the composite lithium-silicon alloy lithium supplement agent comprising a lithium-silicon alloy core and an aluminum oxide coating layer and a lithium carbonate coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside. The elemental mass percentage of lithium to silicon in the lithium-silicon alloy core is 30:70, and the thickness of the aluminum oxide coating layer and the thickness of the lithium carbonate coating layer are both 25 nm.

This embodiment also provides a method for preparing a composite lithium-silicon alloy lithium supplement, as shown in FIG1 , which comprises the following steps:

(1) Mixing Al-Si 30 alloy and pure aluminum, and obtaining precursor powder through vacuum melting and rapid solidification atomization, wherein the vacuum melting temperature is 750°C and the time is 5h, and obtaining Al-Si master alloy with a silicon content of 15%; the gas flow rate of rapid solidification atomization is 35m ³ /h, the inner diameter of the ceramic tube is 8mm, and the nozzle gap is 0.6mm. The precursor powder is crushed and sieved through a 300-mesh sieve to obtain Al-Si powder with a particle size of 15μm, and chemically etched with a mixed solution of phosphoric acid, nitric acid and acetic acid (the volume ratio of phosphoric acid, nitric acid and acetic acid is 75:5:20), washed with deionized water and dried at 110°C to obtain silicon particles, and then the silicon particles and lithium metal are evaporated at 150°C in an argon atmosphere (pressure of 10 ^-3 Pa) to obtain a lithium silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) with aluminum oxide, and heating at 500° C. to obtain a lithium silicon alloy material coated with aluminum oxide;

(3) The lithium-silicon alloy material coated with aluminum oxide obtained in step (2) is heated at 200° C. in a carbon dioxide atmosphere to obtain the composite lithium-silicon alloy lithium supplement having a core-shell structure.

FIG. 2 shows that the lithium-silicon alloy core of the composite lithium-silicon alloy lithium supplement has a hollow structure.

Example 2

The present embodiment provides a composite lithium-silicon alloy lithium supplement agent with a core-shell structure having an average particle size of 12 μm, the composite lithium-silicon alloy lithium supplement agent comprising a lithium-silicon alloy core and an aluminum oxide coating layer and a lithium carbonate coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside. The elemental mass percentage of lithium to silicon in the lithium-silicon alloy core is 25:75, and the thickness of the aluminum oxide coating layer and the thickness of the lithium carbonate coating layer are both 15 nm.

This embodiment also provides a method for preparing a composite lithium-silicon alloy lithium supplement, which comprises the following steps:

(1) Al-Si 30 alloy and pure aluminum are mixed, and a precursor powder is obtained by vacuum melting and rapid solidification atomization, wherein the vacuum melting temperature is 720°C and the time is 5.5h, and an Al-Si intermediate alloy with a silicon content of 12% is obtained; the gas flow rate of the rapid solidification atomization is 32m ³ /h, the inner diameter of the ceramic tube is 8mm, and the nozzle gap is 0.6mm. The precursor powder is crushed and sieved through a 300-mesh sieve to obtain an Al-Si powder with a particle size of 15μm, and chemically etched with a mixed solution of phosphoric acid, nitric acid and acetic acid (the volume ratio of phosphoric acid, nitric acid and acetic acid is 72:10:18), washed with deionized water and dried at 110°C to obtain silicon particles, and then the silicon particles and lithium metal are evaporated at 120°C in an argon atmosphere (pressure of 10 ^-3 Pa) to obtain a lithium silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) with aluminum oxide, and heating at 450° C. to obtain a lithium silicon alloy material coated with aluminum oxide;

(3) The lithium-silicon alloy material coated with aluminum oxide obtained in step (2) is heated at 180° C. in a carbon dioxide atmosphere to obtain the composite lithium-silicon alloy lithium supplement having a core-shell structure.

Example 3

The present embodiment provides a composite lithium-silicon alloy lithium supplement agent with a core-shell structure and an average particle size of 18 μm, the composite lithium-silicon alloy lithium supplement agent comprising a lithium-silicon alloy core and an aluminum oxide coating layer and a lithium carbonate coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside. The elemental mass percentage of lithium to silicon in the lithium-silicon alloy core is 35:65, and the thickness of the aluminum oxide coating layer and the thickness of the lithium carbonate coating layer are both 35 nm.

This embodiment also provides a method for preparing a composite lithium-silicon alloy lithium supplement, which comprises the following steps:

(1) Al-Si 30 alloy and pure aluminum are mixed, and a precursor powder is obtained by vacuum melting and rapid solidification atomization, wherein the vacuum melting temperature is 780°C and the time is 4.5h, and an Al-Si intermediate alloy with a silicon content of 18% is obtained; the gas flow rate of the rapid solidification atomization is 38m ³ /h, the inner diameter of the ceramic tube is 8mm, and the nozzle gap is 0.6mm. The precursor powder is crushed and sieved through a 300-mesh sieve to obtain an Al-Si powder with a particle size of 15μm, and chemically etched with a mixed solution of phosphoric acid, nitric acid and acetic acid (the volume ratio of phosphoric acid, nitric acid and acetic acid is 78:7:15), washed with deionized water and dried at 110°C to obtain silicon particles, and then the silicon particles and lithium metal are evaporated at 180°C in an argon atmosphere (pressure of 10 ^-3 Pa) to obtain a lithium silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) with aluminum oxide, and heating at 550° C. to obtain a lithium silicon alloy material coated with aluminum oxide;

(3) The lithium-silicon alloy material coated with aluminum oxide obtained in step (2) is heated at 220° C. in a carbon dioxide atmosphere to obtain the composite lithium-silicon alloy lithium supplement having a core-shell structure.

Example 4

The present embodiment provides a composite lithium-silicon alloy lithium supplement agent with a core-shell structure and an average particle size of 10 μm, the composite lithium-silicon alloy lithium supplement agent comprising a lithium-silicon alloy core and a titanium oxide coating layer and a lithium phosphate coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside. The elemental mass percentage of lithium to silicon in the lithium-silicon alloy core is 20:80, and the thickness of the titanium oxide coating layer and the thickness of the lithium phosphate coating layer are both 5 nm.

This embodiment also provides a method for preparing a composite lithium-silicon alloy lithium supplement, which comprises the following steps:

(1) Mixing Al-Si 30 alloy and pure aluminum, and obtaining precursor powder through vacuum melting and rapid solidification atomization, wherein the vacuum melting temperature is 700°C and the time is 6 hours, and obtaining Al-Si intermediate alloy with a silicon content of 10%; the gas flow rate of rapid solidification atomization is 30m ³ /h, the inner diameter of the ceramic tube is 8mm, and the nozzle gap is 0.6mm. The precursor powder is crushed and sieved through a 300-mesh sieve to obtain Al-Si powder with a particle size of 15μm, and chemically etched with a mixed solution of phosphoric acid, nitric acid and acetic acid (the volume ratio of phosphoric acid, nitric acid and acetic acid is 70:5:25), washed with deionized water and dried at 110°C to obtain silicon particles, and then the silicon particles and lithium metal are evaporated at 100°C in an argon atmosphere (pressure of 10 ^-4 Pa) to obtain a lithium silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) with titanium oxide, and heating at 400° C. to obtain a lithium silicon alloy material coated with titanium oxide;

(3) The lithium-silicon alloy material coated with titanium oxide obtained in step (2) is mixed with nickel phosphate and calcined at 200° C. to obtain the composite lithium-silicon alloy lithium supplement having a core-shell structure.

Example 5

The present embodiment provides a composite lithium-silicon alloy lithium supplement agent with a core-shell structure and an average particle size of 20 μm, the composite lithium-silicon alloy lithium supplement agent comprising a lithium-silicon alloy core and a titanium oxide coating layer and a lithium phosphate coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside. The elemental mass percentage of lithium to silicon in the lithium-silicon alloy core is 40:60, and the thickness of the titanium oxide coating layer and the thickness of the lithium phosphate coating layer are both 50 nm.

This embodiment also provides a method for preparing a composite lithium-silicon alloy lithium supplement, which comprises the following steps:

(1) Al-Si 30 alloy and pure aluminum are mixed, and a precursor powder is obtained by vacuum melting and rapid solidification atomization, wherein the vacuum melting temperature is 800°C and the time is 4 hours, and an Al-Si intermediate alloy with a silicon content of 20% is obtained; the gas flow rate of the rapid solidification atomization is 40m ³ /h, the inner diameter of the ceramic tube is 8mm, and the nozzle gap is 0.6mm. The precursor powder is crushed and sieved through a 300-mesh sieve to obtain an Al-Si powder with a particle size of 15μm, and then chemically etched with a mixed solution of phosphoric acid, nitric acid and acetic acid (the volume ratio of phosphoric acid, nitric acid and acetic acid is 80:10:10), washed with deionized water and dried at 110°C to obtain silicon particles, and then the silicon particles and lithium metal are evaporated at 200°C in an argon atmosphere (pressure of 10 ^-2 Pa) to obtain a lithium silicon alloy;

(2) mixing the lithium silicon alloy obtained in step (1) with titanium oxide, and heating at 600° C. to obtain a lithium silicon alloy material coated with titanium oxide;

(3) The lithium-silicon alloy material coated with titanium oxide obtained in step (2) is mixed with nickel phosphate and calcined at 250° C. to obtain the composite lithium-silicon alloy lithium supplement having a core-shell structure.

Example 6

The difference between this embodiment and embodiment 1 is that the element mass percentage of lithium and silicon in the lithium-silicon alloy core is 50:50, and the rest is the same as embodiment 1.

Example 7

The difference between this embodiment and embodiment 1 is that the element mass percentage of lithium and silicon in the lithium-silicon alloy core is 10:90, and the rest is the same as embodiment 1.

Example 8

The difference between this embodiment and embodiment 1 is that the thickness of the aluminum oxide coating layer and the lithium carbonate coating layer are both 1 nm, and the rest are the same as embodiment 1.

Example 9

The difference between this embodiment and embodiment 1 is that the thickness of the aluminum oxide coating layer and the lithium carbonate coating layer are both 55 nm, and the rest are the same as embodiment 1.

Example 10

The difference between this embodiment and embodiment 1 is that the evaporation temperature in step (1) is 50° C. and the time is 30 min. The rest is the same as embodiment 1.

Embodiment 11

The difference between this embodiment and embodiment 1 is that the evaporation temperature in step (1) is 250° C. and the time is 30 min. The rest is the same as embodiment 1.

Example 12

The difference between this embodiment and embodiment 1 is that in step (1), an aluminum-silicon intermediate alloy with a silicon content of 5% is obtained, and the rest is the same as embodiment 1.

Example 13

The difference between this embodiment and embodiment 1 is that in step (1), an aluminum-silicon intermediate alloy with a silicon content of 40% is obtained, and the rest is the same as embodiment 1.

Embodiment 14

The difference between this embodiment and embodiment 1 is that in step (1), aluminum silicon powder with a particle size of 40 μm is obtained by sieving through a 300-mesh sieve, and the rest is the same as embodiment 1.

Comparative Example 1

The difference between this comparative example and Example 1 is that the lithium silicon alloy is replaced by pure silicon, and the rest is the same as Example 1.

Comparative Example 2

The difference between this comparative example and Example 1 is that the aluminum oxide coating layer is not coated, and the lithium carbonate coating layer is directly coated on the surface of the lithium silicon alloy core. The rest is the same as Example 1.

Comparative Example 3

The difference between this comparative example and Example 1 is that the lithium carbonate coating layer is not coated, and the aluminum oxide coating layer is directly coated on the surface of the lithium silicon alloy core. The other aspects are the same as Example 1.

Application Examples 1 to 14 and Comparative Application Examples 1 to 3

The composite lithium-silicon alloy lithium supplement with a core-shell structure provided in Examples 1 to 14 and Comparative Examples 1 to 3 is used to prepare a lithium-ion battery, and the preparation method is as follows:

Preparation of positive electrode sheet: After fully stirring the positive electrode active material lithium iron phosphate, conductive carbon black and polyvinylidene fluoride in a mass ratio of 97:1:2, a positive electrode slurry is obtained, and the prepared slurry is coated on aluminum foil, and a positive electrode sheet is obtained after drying and rolling;

Preparation of negative electrode sheet: graphite, the above lithium supplement, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are fully stirred in a mass ratio of 95.5:1:0.5:1.2:1.8 to obtain negative electrode slurry, the prepared slurry is coated on copper foil, and the negative electrode sheet is obtained after drying and rolling;

The electrolyte has a conventional formula: the lithium salt is 1 mol/L LiPF ₆ , and the volume ratio of the solvent is EC:DMC:DEC=5:3:2.

Preparation of lithium-ion batteries: The positive electrode, negative electrode, separator and electrolyte are combined to form a button battery of model 2032.

Test conditions

The lithium-ion batteries prepared in Application Examples 1 to 14 and Comparative Application Examples 1 to 3 were subjected to performance tests respectively, and the test methods are as follows:

The charge and discharge capacity in grams during the first three weeks was tested at a current density of 0.33C, with the charge and discharge voltage range being 2.5 to 3.65V.

The test results are shown in Table 1:

Table 1

It can be seen from the data in Table 1 that the lithium-ion batteries obtained in Application Examples 1-5 provided by the present invention have higher specific capacity and higher first coulombic efficiency. This is because the lithium-silicon alloy core in the lithium replenisher used therein has a hollow structure and sufficient gaps, which can effectively suppress the stress generated by the lithium-silicon alloy. The first coating layer can effectively improve the conductivity of the lithium-silicon alloy powder, and the second coating layer can effectively improve the ionic conductivity of the material, so the gram capacity of the lithium replenisher can be significantly improved, thereby improving the lithium replenishment efficiency and cycle performance of the negative electrode.

Application Examples 6-7 are cases where the elemental mass percentages of lithium and silicon are out of range, indicating that by adjusting the elemental mass percentages of lithium and silicon in the lithium-silicon alloy core, the lithium-silicon lithium supplement has a suitable lithium supplement potential and lithium supplement gram capacity; Application Examples 8-9 are cases where the coating thickness is out of range, which enables uniform coating and promotes ion and electron transport; Application Examples 10-11 are cases where the evaporation parameters are out of range, which regulate the lithium deposition amount to obtain a higher specific capacity; Application Examples 12-13 also regulate the mass percentage of silicon to make the lithium supplement have a high specific capacity; Application Example 14 shows that if the particle size is too large, the prepared lithium supplement is not easy to disperse in the slurry.

Comparative Application Example 1 replaces the pure silicon core, which has a large volume change and unstable structure, reducing the cycle stability of the battery; Comparative Application Examples 2-3 show that a single-layer coating cannot achieve the ideal technical effect of the present invention.

The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims (25)

1. A composite lithium-silicon alloy lithium supplement agent with a core-shell structure, characterized in that the composite lithium-silicon alloy lithium supplement agent comprises a lithium-silicon alloy core and a first coating layer and a second coating layer sequentially coated on the surface of the lithium-silicon alloy core from the inside to the outside; The first coating layer comprises any one of aluminum oxide, magnesium oxide or titanium oxide, or a combination of at least two thereof; The second coating layer comprises any one of lithium carbonate, lithium phosphate or lithium aluminate or a combination of at least two thereof; The lithium silicon alloy is obtained by the following preparation method: The silicon-containing alloy and pure metal are mixed, and a precursor powder is obtained through melting and solidification atomization. The precursor powder is chemically etched to obtain silicon particles, and then the silicon particles and lithium metal are evaporated to obtain a lithium-silicon alloy. 2. The composite lithium-silicon alloy lithium supplement according to claim 1, characterized in that the element mass percentage of lithium and silicon in the lithium-silicon alloy core is (20-40):(60-80). 3. The composite lithium-silicon alloy lithium supplement according to claim 2, characterized in that the element mass percentage of lithium and silicon in the lithium-silicon alloy core is (25-35):(65-75). 4 . The composite lithium-silicon alloy lithium supplement according to claim 1 , wherein the thickness of the first coating layer is 5 to 50 nm. 5 . The composite lithium-silicon alloy lithium supplement according to claim 4 , wherein the thickness of the first coating layer is 10 to 30 nm. 6 . The composite lithium-silicon alloy lithium supplement according to claim 1 , wherein the thickness of the second coating layer is 5 to 50 nm. 7 . The composite lithium-silicon alloy lithium supplement according to claim 6 , wherein the thickness of the second coating layer is 15 to 35 nm. 8 . The composite lithium-silicon alloy lithium supplement according to claim 1 , wherein the average particle size of the composite lithium-silicon alloy lithium supplement is 10 to 20 μm. 9. A method for preparing a composite lithium-silicon alloy lithium supplement agent with a core-shell structure according to any one of claims 1 to 8, characterized in that the method comprises the following steps: (1) mixing a silicon-containing alloy and a pure metal, melting and solidifying and atomizing to obtain a precursor powder, chemically etching the precursor powder to obtain silicon particles, and then evaporating the silicon particles and lithium metal to obtain a lithium-silicon alloy; (2) mixing the lithium silicon alloy obtained in step (1) and the first coating layer precursor material, and heating to obtain a lithium silicon alloy material coated by the first coating layer; (3) The lithium-silicon alloy material coated by the first coating layer obtained in step (2) is mixed with the second coating layer precursor and subjected to heat treatment to obtain the composite lithium-silicon alloy lithium supplement agent with a core-shell structure. 10. The method according to claim 9, characterized in that the silicon-containing alloy in step (1) comprises one of an aluminum-silicon alloy and a magnesium-silicon alloy. 11. The method according to claim 9, characterized in that the pure metal in step (1) comprises pure aluminum or pure magnesium. 12. The method according to claim 9, characterized in that the mass percentage of silicon in the smelted silicon-containing alloy in step (1) is 10% to 20%. 13. The method according to claim 9, characterized in that the smelting temperature in step (1) is 700-800°C and the time is 4-6 hours. 14. The method according to claim 9, characterized in that the gas flow rate of the coagulation atomization in step (1) is 30-40 ^m3 /h, the inner diameter of the ceramic tube is 8 mm, and the nozzle gap is 0.6 mm. 15. The method according to claim 9, characterized in that the chemical etching treatment in step (1) also includes crushing and screening treatment. 16. The method according to claim 9, characterized in that the chemical etching treatment in step (1) is performed using a mixed solution of phosphoric acid, nitric acid and acetic acid. 17. The method according to claim 16, characterized in that the volume ratio of phosphoric acid, nitric acid and acetic acid in the mixed solution of phosphoric acid, nitric acid and acetic acid is (70-80):(5-10):(10-25). 18. The method according to claim 9, characterized in that the chemical etching treatment in step (1) further includes washing and drying treatment. 19. The method according to claim 18, characterized in that the washing is performed with deionized water. 20. The method according to claim 9, characterized in that the evaporation in step (1) is performed in an inert atmosphere. 21. The method according to claim 9, characterized in that the evaporation temperature in step (1) is ^100-200 °C and the pressure is ^10-4-10-2Pa . 22. The method according to claim 9, characterized in that the heating temperature in step (2) is 400-600°C. 23. The method according to claim 9, characterized in that the heating temperature in step (3) is 150-250°C. 24 . A negative electrode sheet, characterized in that the negative electrode sheet comprises a negative electrode active material layer and a current collector, wherein the negative electrode active material layer comprises the composite lithium-silicon alloy lithium supplement having a core-shell structure according to any one of claims 1 to 8. 25 . A lithium ion battery, characterized in that the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and the negative electrode sheet comprises the negative electrode sheet according to claim 24 .