CN112186188B - Silicon-based negative electrode material, preparation method and application thereof - Google Patents

Abstract

The invention discloses a silicon-based negative electrode material and a preparation method and application thereof, wherein the silicon-based negative electrode material comprises the following components: the core comprises a silicon-based material; the lithium silicate coating layer comprises Li₂Si₂O₅The lithium silicate coating layer is arranged at the periphery of the inner core, pores are formed on the lithium silicate coating layer, and a distance exists between the lithium silicate coating layer and the inner core; the carbon coating layer is coated on the lithium silicate coating layer. Therefore, the silicon-based negative electrode material has high first-effect and cycling stability, and the first-effect and cycling performance of the lithium battery can be improved by loading the negative electrode prepared from the silicon-based negative electrode material in the lithium battery.

Description

Silicon-based negative electrode material, preparation method and application thereof

technical field

The invention belongs to the field of batteries, and in particular relates to a silicon-based negative electrode material and a preparation method and application thereof.

Background technique

Silicon-based anode materials mainly include elemental nano-silicon and silicon oxide. Their advantages are rich in resources and high specific capacity. The disadvantage is that the volume expansion is huge during the charging and discharging process. The elemental silicon reaches 300%, and the silicon oxide is slightly lower. 150%, resulting in extremely poor cycle performance of silicon-based anode materials, which is not conducive to commercial applications.

At present, the mainstream carbon coating methods can effectively improve the cycle performance of silicon-based anode materials, but no matter what carbon coating method (gas phase coating, liquid phase coating, solid phase coating) is adopted, the carbon source is The physical pyrolysis of organic carbon sources belongs to the category of physical modification, and due to the limited strength of the carbon layer, there is still a high risk of damage during long-term cycling, resulting in a relatively general cycle performance of silicon-based anode materials.

Therefore, a special coating method is urgently needed to enhance the cycle performance of silicon-based anode materials.

SUMMARY OF THE INVENTION

The present invention aims to solve one of the technical problems in the related art at least to a certain extent. To this end, an object of the present invention is to propose a silicon-based negative electrode material and a preparation method and application thereof. The silicon-based negative electrode material has high initial efficiency and cycle stability, and the silicon-based negative electrode material is loaded and used in a lithium battery. The prepared negative electrode can improve the first efficiency and cycle performance of the lithium battery.

In one aspect of the present invention, the present invention provides a silicon-based negative electrode material. According to an embodiment of the present invention, the silicon-based negative electrode material includes:

an inner core comprising a silicon-based material;

Lithium silicate coating layer, the lithium silicate coating layer includes Li ₂ Si ₂ O ₅ , the lithium silicate coating layer is arranged on the periphery of the inner core, and the lithium silicate coating layer has pores , and there is a distance between the lithium silicate coating layer and the inner core;

A carbon coating layer, the carbon coating layer is coated on the lithium silicate coating layer.

According to the silicon-based negative electrode material of the embodiment of the present invention, by forming a lithium silicate coating layer including Li ₂ Si ₂ O ₅ on the periphery of the inner core, there is a distance between the lithium silicate coating layer and the inner core, that is, the lithium silicate coating layer is the inner core. The expansion reserves expansion space, when the silicon-based anode material is charged and discharged, the expansion stress is relatively low, and the strength of the lithium silicate coating layer is greater than that of the physical pyrolysis carbon layer, thereby improving the cycle stability of the material, and The lithium silicate coating layer of the present application only contains Li ₂ Si ₂ O ₅ . Because the crystalline Li ₂ Si ₂ O ₅ does not react with water, there are no negative problems such as dissolution in the subsequent homogenization process. There are many pores on the lithium silicate coating layer, which facilitates the conduction of lithium ions and reduces the polarization of the material. In addition, a carbon coating layer is coated on the surface of the lithium silicate coating layer, which can effectively avoid the negative electrode silicon. The direct contact between the base material and the electrolyte reduces the occurrence of side reactions and improves the first effect, and the carbon coating itself also has the effect of limiting the expansion of the silicon-based core, thereby further improving the cycle performance of the material. Therefore, the silicon-based negative electrode material of the structure of the present application has high first effect and cycle stability, and the first effect and cycle performance of the lithium battery can be improved by loading the negative electrode prepared by using the silicon-based negative electrode material in a lithium battery.

In addition, the silicon-based negative electrode material according to the above embodiments of the present invention may also have the following additional technical features:

In some embodiments of the present invention, the silicon-based material includes at least one of elemental nano-silicon and silicon oxide.

In some embodiments of the present invention, the particle size D50 of the elemental nano-silicon is 5-100 nm, and preferred ranges include 5-20 nm, 20-30 nm, 30-50 nm, 50-80 nm, 80-100 nm, 30- 80nm, 30-100nm, 50-100nm, etc.

In some embodiments of the present invention, the chemical formula of the silicon oxide is SiO _x , and x is 0.5˜1.5.

In some embodiments of the present invention, the particle size D50 of the silicon oxide is 100 nm to 15 μm, and preferred ranges include 100 nm to 1 μm, 1 to 15 μm, and the like.

In some embodiments of the present invention, the thickness of the lithium silicate coating layer is 10-100 nm. Thus, the cycle performance of the silicon-based negative electrode material can be improved. For example, 10-50 nm, 50-100 nm, etc. are mentioned.

In some embodiments of the present invention, based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate coating layer is 5-30%. Thus, the cycle performance of the silicon-based negative electrode material can be improved. For example, 5-10%, 10-15%, 15-30%, etc. are mentioned.

In some embodiments of the present invention, the thickness of the carbon coating layer is 1-50 nm. Thus, the first effect and cycle performance of the silicon-based negative electrode material can be improved. For example, 5-18 nm, 18-35 nm, 35-50 nm, etc. are mentioned.

In some embodiments of the present invention, the mass proportion of the carbon coating layer is 1-20% based on the total mass of the silicon-based negative electrode material. Thus, the first effect and cycle performance of the silicon-based negative electrode material can be improved. For example, 5-10%, 10-15%, 15-20%, etc. are mentioned.

In yet another aspect of the present invention, the present invention provides a method for preparing the above-mentioned silicon-based negative electrode material. According to an embodiment of the present invention, the method includes:

(1) coating silicon dioxide on the surface of the silicon-based material to obtain a first precursor;

(2) coating the water-soluble lithium source on the first precursor to obtain a second precursor;

(3) sintering the second precursor under an inert atmosphere, so that a part of the silicon dioxide reacts with the water-soluble lithium source, so as to form a surface of the silicon-based material containing Li ₂ Si ₂ O ₅ lithium silicate coating layer to obtain the third precursor;

(4) etching the third precursor to remove another part of the silicon dioxide and lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer, so as to obtain the a fourth precursor having pores and a hollow core-shell structure on the lithium silicate coating layer;

(5) Coating a carbon coating layer on the surface of the fourth precursor, so as to obtain a silicon-based negative electrode material.

According to the method for preparing the above-mentioned silicon-based negative electrode material according to the embodiment of the present invention, the surface of the silicon-based material is coated with silicon dioxide, and then the water-soluble lithium source is coated on the silicon-based material with silicon dioxide under an inert atmosphere. After roasting, a part of the silica reacts with the water-soluble lithium source to generate different kinds of lithium silicate (the water-soluble lithium source is lithium carbonate as an example SiO ₂ +1/2Li ₂ CO ₃ →1/2Li ₂ Si ₂ O ₅ + 1/2CO ₂ , SiO ₂ +Li ₂ CO ₃ →Li ₂ SiO ₃ +CO ₂ , SiO ₂ +2Li ₂ CO ₃ →Li ₄ SiO ₄ +2CO ₂ ), that is, forming on the surface of the silicon-based material core contains another part of the Lithium silicate coating layer of silicon oxide, Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ and Li ₄ SiO ₄ , and then the obtained precursor is etched to remove another part of the silicon dioxide in the precursor And lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer, that is, a lithium silicate coating layer including Li ₂ Si ₂ O ₅ is formed on the periphery of the silicon-based material, and due to another part of silicon dioxide There will be a distance between the formed lithium silicate coating layer and the inner core, which reserves an expansion space for the expansion of the inner core. When the silicon-based anode material is charged and discharged, the expansion stress is relatively low, and the lithium silicate coating The strength of the coating layer is greater than that of the physical pyrolysis carbon layer, thereby improving the cycle stability of the material, and the lithium silicate coating layer of the present application only contains Li ₂ Si ₂ O ₅ , because the crystalline Li ₂ Si ₂ O _5. It does not react with water, and there are no negative problems such as dissolution in the subsequent homogenization process. At the same time, along with the etching of other types of lithium silicate and remaining silicon dioxide, there are many pores on the lithium silicate coating layer. It facilitates the conduction of lithium ions, reduces the polarization of the material, and finally coats a carbon coating on the surface of the lithium silicate coating. The reaction occurs to improve the first effect, and the carbon coating itself also has the effect of limiting the expansion of the silicon-based core, thereby further improving the cycle performance of the material. Therefore, the above-mentioned silicon-based negative electrode material with high first effect and cycle stability can be obtained by using this method, and the negative electrode prepared by using the silicon-based negative electrode material can be loaded in a lithium battery, so that the first effect and cycle performance of the lithium battery can be improved. .

In addition, the method for preparing the above-mentioned silicon-based negative electrode material according to the above-mentioned embodiment of the present invention may also have the following additional technical features:

In some embodiments of the present invention, in step (1), the silicon dioxide is amorphous silicon dioxide, and the thickness of the amorphous silicon dioxide coating layer formed on the surface of the silicon-based material is 30-150 nm . For example, 30-80 nm, 80-100 nm, 100-150 nm, etc. are mentioned.

In some embodiments of the present invention, in step (1), based on the total mass of the first precursor, the mass ratio of the amorphous silica coating layer is 5-20%. For example, 5-10%, 10-20%, etc. are mentioned.

In some embodiments of the present invention, in step (2), the water-soluble lithium source is coated on the first precursor by spray drying.

In some embodiments of the present invention, in step (2), the water-soluble lithium source includes at least one of lithium carbonate, lithium oxalate, lithium nitrate and lithium acetate.

In some embodiments of the present invention, in step (2), the molar ratio of lithium in the water-soluble lithium source to oxygen in the silica is 0.08-0.2.

In some embodiments of the present invention, in step (3), the sintering temperature is 700-900°C, the heating rate is 0.5°C/min-10°C/min, and the sintering time is 1-36h.

In some embodiments of the present invention, in step (4), the precursor obtained in step (3) is etched with hydrofluoric acid.

In some embodiments of the present invention, in step (4), the concentration of the hydrofluoric acid is 0.5-1.0 mol/L, and the etching time is 1-120 min.

In a third aspect of the present invention, the present invention provides a negative electrode. According to an embodiment of the present invention, the negative electrode is prepared by using the above-mentioned silicon-based negative electrode material or the silicon-based negative electrode material obtained by the above-mentioned method. Therefore, the negative electrode is made by using the above-mentioned silicon-based negative electrode material with high first effect and excellent cycle stability, so that the negative electrode has high first effect and cycle performance.

In a fourth aspect of the present invention, the present invention provides a lithium battery. According to an embodiment of the present invention, the lithium battery includes the above-mentioned negative electrode. Therefore, by loading the negative electrode with high first effect and cycle performance prepared by using the silicon-based negative electrode material, the lithium battery has high first effect and cycle performance.

Additional aspects and advantages of the present invention will be set forth, in part, from the following description, and in part will be apparent from the following description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of embodiments taken in conjunction with the accompanying drawings, wherein:

1 is a schematic cross-sectional structure diagram of a silicon-based negative electrode material according to an embodiment of the present invention;

2 is a schematic flowchart of a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

3 is a schematic structural diagram of a silicon-based material in a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

4 is a schematic cross-sectional structural diagram of a silicon-based material surface coating to form an amorphous silicon dioxide layer in a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

5 is a schematic cross-sectional structure diagram of coating an aqueous lithium source precursor in a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

6 is a schematic cross-sectional structural diagram of a precursor coated with a lithium silicate coating layer in a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

7 is a schematic cross-sectional structure diagram of a precursor of a hollow core-shell structure in a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention;

8 is a schematic cross-sectional structure diagram of a silicon-based negative electrode material obtained by a method for preparing a silicon-based negative electrode material according to an embodiment of the present invention.

Detailed ways

The following describes in detail the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the present invention and should not be construed as limiting the present invention.

In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", " Back, Left, Right, Vertical, Horizontal, Top, Bottom, Inner, Outer, Clockwise, Counterclockwise, Axial , "radial", "circumferential" and other indicated orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying the indicated device or Elements must have a particular orientation, be constructed and operate in a particular orientation and are therefore not to be construed as limitations of the invention.

In addition, the terms "first" and "second" are only used for descriptive purposes, and should not be construed as indicating or implying relative importance or implying the number of indicated technical features. Thus, a feature delimited with "first", "second" may expressly or implicitly include at least one of that feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

In one aspect of the present invention, the present invention provides a silicon-based negative electrode material. According to an embodiment of the present invention, referring to FIG. 1 , the silicon-based negative electrode material includes an inner core 100 , a lithium silicate coating layer 200 and a carbon coating layer 300 .

According to an embodiment of the present invention, referring to FIG. 1 , the inner core 100 includes a silicon-based material, preferably, the silicon-based material includes at least one of elemental nano-silicon and silicon oxide; wherein, the particle size D50 of elemental nano-silicon is 5˜5 100 nm; the chemical formula of the silicon oxide is SiO _x , x is 0.5-1.5, and the particle size D50 of the silicon oxide is 100 nm-15 μm.

According to an embodiment of the present invention, referring to FIG. 1 , the lithium silicate coating layer 200 includes Li ₂ Si ₂ O ₅ , the lithium silicate coating layer 200 is disposed on the periphery of the core 100 , and the lithium silicate coating layer 200 has pores on it , and there is a distance between the lithium silicate cladding layer 200 and the inner core 100 . The inventors found that by forming the lithium silicate coating layer 200 including Li ₂ Si ₂ O ₅ on the periphery of the inner core 100 , there is a distance between the lithium silicate coating layer 200 and the inner core 100 , which is a pre-expansion of the inner core 100 . The expansion space is left, when the silicon-based negative electrode material is charged and discharged, the expansion stress is relatively low, and the strength of the lithium silicate coating layer is greater than that of the physical pyrolysis carbon layer, thereby improving the cycle stability of the material, and the present application The lithium silicate coating layer 200 only contains Li ₂ Si ₂ O ₅ . Because the crystalline Li ₂ Si ₂ O ₅ does not react with water, there are no negative problems such as dissolution in the subsequent homogenization process. The lithium oxide coating 200 has many pores, which facilitates the conduction of lithium ions and reduces the polarization of the material. Further, the thickness of the lithium silicate coating layer 200 is 10-100 nm. The inventors found that when the thickness of the lithium silicate coating layer 200 is less than 10 nm, the expansion restriction effect of the lithium silicate coating layer on the core of the silicon-based material is relatively limited, and when the thickness of the lithium silicate coating layer 200 is high At 100 nm, since lithium silicate is an inactive substance, the specific capacity of the material may drop significantly. Meanwhile, based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate coating layer 200 is 5-30%. Thus, the cycle stability of the silicon-based negative electrode material can be improved.

According to an embodiment of the present invention, referring to FIG. 1 , the carbon coating layer 300 is coated on the lithium silicate coating layer 200 . The inventor found that by coating the carbon coating layer on the surface of the lithium silicate coating layer, the carbon coating layer can effectively avoid the direct contact between the negative electrode silicon-based material and the electrolyte, reduce the occurrence of side reactions, improve the first effect, and the The carbon cladding itself also has the effect of limiting expansion, thereby further improving the cycling performance of the material. Further, the thickness of the carbon coating layer 300 is 1˜50 nm. The inventor found that when the thickness of the carbon coating layer 300 is less than 1 nm, the effect of the carbon coating layer on isolating the electrolyte is not obvious, and when the thickness of the carbon coating layer 300 is higher than 50 nm, the lithium ion is deintercalated. The path becomes longer, which is not conducive to the exertion of the magnification performance. Meanwhile, based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer 300 is 1-20%. The inventors found that when the mass ratio of the carbon coating layer 300 is less than 1%, the effect of the carbon coating layer on isolating the electrolyte is not obvious due to its low thickness, and when the mass ratio of the carbon coating layer 300 is high At 20%, due to the low intrinsic specific capacity of the carbon coating layer, the specific capacity of the material will be greatly reduced. Conducive to multiplying performance.

According to the silicon-based negative electrode material of the embodiment of the present invention, by forming a lithium silicate coating layer including Li ₂ Si ₂ O ₅ on the periphery of the inner core, there is a distance between the lithium silicate coating layer and the inner core, that is, the lithium silicate coating layer is the inner core. The expansion reserves expansion space, when the silicon-based anode material is charged and discharged, the expansion stress is relatively low, and the strength of the lithium silicate coating layer is greater than that of the physical pyrolysis carbon layer, thereby improving the cycle stability of the material, and The lithium silicate coating layer of the present application only contains Li ₂ Si ₂ O ₅ . Because the crystalline Li ₂ Si ₂ O ₅ does not react with water, there are no negative problems such as dissolution in the subsequent homogenization process. There are many pores on the lithium silicate coating, which facilitates the conduction of lithium ions and reduces the polarization of the material. In addition, a carbon coating layer is coated on the surface of the lithium silicate coating layer, which can effectively avoid the negative electrode silicon base. The direct contact between the material and the electrolyte reduces the occurrence of side reactions and improves the first effect, and the carbon coating itself also has the effect of limiting expansion, thereby further improving the cycle performance of the material. Therefore, the silicon-based negative electrode material of the structure of the present application has high first effect and cycle stability, and the first effect and cycle performance of the lithium battery can be improved by loading the negative electrode prepared by using the silicon-based negative electrode material in a lithium battery.

In yet another aspect of the present invention, the present invention provides a method for preparing the above-mentioned silicon-based negative electrode material. According to an embodiment of the present invention, with reference to Figures 2-8, the method includes:

S100: Coating silicon dioxide on the surface of silicon-based materials

In this step, silicon dioxide is coated on the surface of the silicon-based material to obtain a first precursor, and the silicon-based material is coated with silicon dioxide by mixing ethyl orthosilicate and/or sodium silicate on the silicon-based material. surface hydrolysis polymerization. Specifically, the silicon dioxide coated on the surface of the silicon-based material is amorphous silicon dioxide, and the thickness of the amorphous silicon dioxide coating layer formed on the surface of the silicon-based material is 30-150 nm; and based on the total amount of the first precursor The mass ratio of the amorphous silica coating layer is 5-20%, so as to ensure that sufficient lithium silicate phase is generated in the subsequent sintering process. At the same time, ethyl orthosilicate and/or sodium silicate are hydrolyzed by mixing ethyl orthosilicate and/or sodium silicate with the silicon-based material, then placing it in a solvent including water and ethanol and controlling the pH Polymerization to form an amorphous silicon dioxide layer (refer to FIG. 4 ) on the surface of the silicon-based material (refer to FIG. 3 ). It should be noted that the process of coating silicon dioxide on the surface of the silicon-based material by the hydrolysis polymerization of ethyl orthosilicate and/or sodium silicate is an existing conventional technology, and the process conditions are not repeated here.

S200: Coating the water-soluble lithium source on the first precursor

In this step, referring to FIG. 5 , the water-soluble lithium source is coated on the first precursor obtained in step S100 by spray drying, preferably the water-soluble lithium source is at least one of lithium carbonate, lithium oxalate, lithium nitrate and lithium acetate One, and the spray drying inlet temperature is 160-230°C, and the outlet temperature is 100-120°C, and the spray drying equipment can be pressure type, two-fluid, four-fluid or centrifugal spray drying. Compared with the use of metallic elemental lithium, lithium hydride and strongly alkaline lithium hydroxide, metallic elemental lithium will react violently with moisture in the air, and will also be rapidly oxidized in the air; while lithium hydride reacts violently with water to form corrosive Lithium hydroxide and flammable and explosive gas hydrogen; strong alkaline lithium hydroxide will react with the material itself, etc. The above lithium sources have special requirements for the actual use environment, such as air humidity, inert atmosphere, etc., which limit this type of lithium hydroxide. The large-scale use of lithium sources, and the application of water-soluble lithium sources, has no special requirements for the use environment, and is friendly and harmless to operators.

Further, the molar ratio of lithium in the water-soluble lithium source coated on the first precursor obtained in step S100 to oxygen in the amorphous silicon dioxide layer on the first precursor obtained in step S100 is 0.08-0.2 . The inventors found that if the molar ratio of lithium to oxygen is too low, the formation of lithium silicate itself will be limited, resulting in poor coating effect of the lithium silicate coating layer. It is related to the molar ratio of lithium to oxygen, taking lithium carbonate as an example, specifically SiO ₂ +1/2Li ₂ CO ₃ →1/2Li ₂ Si ₂ O ₅ +1/2CO ₂ , SiO ₂ +Li ₂ CO ₃ → Li ₂ SiO ₃ +CO ₂ , SiO ₂ +2Li ₂ CO ₃ →Li ₄ SiO ₄ +2CO ₂ , in order to make the obtained lithium silicate mainly Li ₂ Si ₂ O ₅ , the equilibrium lithium to oxygen molar ratio is 0.5, and because excess silica needs to be introduced in the structural design of the present invention, so that a hollow core-shell structure is obtained by etching the excess silica with hydrofluoric acid, so the molar ratio of lithium to oxygen is not higher than 0.2.

S300: sintering the second precursor in an inert atmosphere

In this step, in an inert atmosphere, the second precursor obtained in step S200 is sintered, so that a part of the silicon dioxide in the amorphous silicon dioxide layer in the second precursor reacts with the water-soluble lithium source to generate different kinds of silicon Lithium oxide (water-soluble lithium source takes lithium carbonate as an example: SiO ₂ +1/2Li ₂ CO ₃ →1/2Li ₂ Si ₂ O ₅ +1/2CO ₂ , SiO ₂ +Li ₂ CO ₃ →Li ₂ SiO ₃ +CO ₂ , SiO ₂ +2Li ₂ CO ₃ →Li ₄ SiO ₄ +2CO ₂ ), on the surface of the core of the silicon-based material to form another part of silicon dioxide, Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ and Li ₄ SiO ₄ The lithium silicate coating layer (refer to FIG. 6 ) is the third precursor.

Further, the sintering temperature in the above-mentioned sintering process is 700-900°C, the heating rate is 0.5°C/min-10°C/min, and the sintering time is 1-36h.

S400: Etch the third precursor

In this step, hydrofluoric acid (the concentration of hydrofluoric acid is 0.5-1.0 mol/L) is used to etch the third precursor obtained in step S300 (etching time is 1-120 min), and the above-mentioned third precursor is removed Another part of the silicon dioxide in the medium amorphous silicon dioxide layer and lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer to obtain the lithium silicate coating layer with pores and a hollow core-shell structure The fourth precursor is to form a lithium silicate coating layer including Li ₂ Si ₂ O ₅ on the periphery of the silicon-based material, and due to the removal of another part of silicon dioxide, the formed lithium silicate coating layer and the inner core are formed between There will be a distance (refer to Figure 7), which reserves an expansion space for the expansion of the inner core. When the silicon-based anode material is charged and discharged, the expansion stress is relatively low, and the strength of the lithium silicate coating layer is greater than that of the physical pyrolysis carbon layer. strength, thereby improving the cycle stability of the material, and the lithium silicate coating layer of the present application only contains Li ₂ Si ₂ O ₅ , because the crystalline Li ₂ Si ₂ O ₅ does not react with water, in the subsequent There are no negative problems such as dissolution during the homogenization process. At the same time, along with the etching of other types of lithium silicate and remaining silicon dioxide, the lithium silicate coating has many pores, which facilitates the conduction of lithium ions and reduces the polarity of the material. to obtain the precursor of the hollow core-shell structure.

S500: coating the surface of the fourth precursor with a carbon coating layer

In this step, the surface of the lithium silicate coating layer of the fourth precursor of the hollow core-shell structure obtained in step S400 is coated with a carbon coating layer (refer to FIG. 8 ) to obtain a silicon-based negative electrode material, and the carbon coating layer can It can effectively avoid the direct contact between the negative electrode silicon-based material and the electrolyte, reduce the occurrence of side reactions, and improve the first effect, and the carbon coating itself also has the effect of limiting expansion, thereby further improving the cycle performance of the material. Specifically, the surface-coated carbon coating layer of the fourth precursor of the hollow core-shell structure obtained in step S400 may adopt gas-phase coating, liquid-phase coating or solid-phase coating, for example, the gas-phase coating uses organic compounds such as methane and acetylene Carbon-containing gas is used for coating; liquid-phase coating is performed with glucose, sucrose, phenolic resin solution, etc., and solid-phase coating is performed with asphalt powder or the like.

According to the method for preparing the above-mentioned silicon-based negative electrode material according to the embodiment of the present invention, the surface of the silicon-based material is coated with silicon dioxide, and then the water-soluble lithium source is coated on the silicon-based material with silicon dioxide under an inert atmosphere. After roasting, a part of the silica reacts with the water-soluble lithium source to generate different kinds of lithium silicate (the water-soluble lithium source is lithium carbonate as an example SiO ₂ +1/2Li ₂ CO ₃ →1/2Li ₂ Si ₂ O ₅ + 1/2CO ₂ , SiO ₂ +Li ₂ CO ₃ →Li ₂ SiO ₃ +CO ₂ , SiO ₂ +2Li ₂ CO ₃ →Li ₄ SiO ₄ +2CO ₂ ), that is, forming on the surface of the silicon-based material core contains another part of the Lithium silicate coating layer of silicon oxide, Li ₂ Si ₂ O ₅ , Li ₂ SiO ₃ and Li ₄ SiO ₄ , and then the obtained precursor is etched to remove another part of the silicon dioxide in the precursor And lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer, that is, a lithium silicate coating layer including Li ₂ Si ₂ O ₅ is formed on the periphery of the silicon-based material, and due to another part of silicon dioxide There will be a distance between the formed lithium silicate coating layer and the inner core, which reserves an expansion space for the expansion of the inner core. When the silicon-based anode material is charged and discharged, the expansion stress is relatively low, and the lithium silicate coating The strength of the coating layer is greater than that of the physical pyrolysis carbon layer, thereby improving the cycle stability of the material, and the lithium silicate coating layer of the present application only contains Li ₂ Si ₂ O ₅ , because the crystalline Li ₂ Si ₂ O _5. It does not react with water, and there are no negative problems such as dissolution in the subsequent homogenization process. At the same time, along with the etching of other types of lithium silicate and remaining silicon dioxide, the lithium silicate coating has many pores, which is convenient for The conduction of lithium ions reduces the polarization of the material. Finally, a carbon coating is coated on the surface of the lithium silicate coating. The carbon coating can effectively avoid the direct contact between the negative electrode silicon-based material and the electrolyte and reduce side reactions. occur, improve the first effect, and the carbon coating itself also has the effect of limiting expansion, thereby further improving the cycle performance of the material. Therefore, the above-mentioned silicon-based negative electrode material with high first effect and cycle stability can be obtained by using this method, and the negative electrode prepared by using the silicon-based negative electrode material can be loaded in a lithium battery, so that the first effect and cycle performance of the lithium battery can be improved. .

It should be noted that the features and advantages described above for the silicon-based negative electrode material are also applicable to the method for preparing the silicon-based negative electrode material, which will not be repeated here.

In a third aspect of the present invention, the present invention provides a negative electrode. According to an embodiment of the present invention, the negative electrode is prepared by using the above-mentioned silicon-based negative electrode material or the silicon-based negative electrode material obtained by the above-mentioned method. Therefore, the negative electrode is made by using the above-mentioned silicon-based negative electrode material with high first effect and excellent cycle stability, so that the negative electrode has high first effect and cycle performance. It should be noted that the features and advantages described above for the silicon-based negative electrode material and the preparation method thereof are also applicable to the negative electrode, which will not be repeated here.

In a fourth aspect of the present invention, the present invention provides a lithium battery. According to an embodiment of the present invention, the lithium battery includes the above-mentioned negative electrode. Therefore, by loading the above-mentioned negative electrode with high initial effect and cycle performance prepared by using the silicon-based negative electrode material, the lithium battery has high initial effect and cycle performance. It should be noted that the features and advantages described above for the negative electrode are also applicable to the lithium battery, and are not repeated here.

The embodiments of the present invention will be described in detail below. It should be noted that the embodiments described below are exemplary and are only used to explain the present invention, but should not be construed as limiting the present invention. In addition, if not clearly stated, all the reagents used in the following examples are commercially available, or can be synthesized according to the methods herein or known, and the reaction conditions not listed are also readily available to those skilled in the art.

Example 1

(1) Using ethyl orthosilicate as a raw material, the surface of 50 nm elemental silicon is coated to form amorphous SiO ₂ to obtain a first precursor, wherein the thickness of the amorphous SiO ₂ layer is 30 nm, based on the first precursor The total mass of the amorphous _SiO2 layer is 5%;

(2) using lithium carbonate as a raw material, using two-fluid spray drying to coat the surface of the first precursor with lithium carbonate to obtain a second precursor, wherein Li and no lithium in the lithium carbonate coated on the first precursor are The molar ratio of O in the shaped silicon dioxide layer is 0.12;

(3) sintering the second precursor in a tube furnace, the protective atmosphere is nitrogen, heating up to 830°C at a rate of 3°C/min, holding for 6 hours, and naturally cooling to room temperature to obtain the third precursor;

(4) The third precursor is acid-washed for 60 min with hydrofluoric acid with a concentration of 0.5 mol/L, dried, and sieved with 400 meshes to obtain the fourth precursor (wherein, lithium silicate (Li ₂ Si ₂ O ₅ ) The thickness of the coating layer is 10 nm, and based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate (Li ₂ Si ₂ O ₅ ) coating layer is 15%);

(5) Using sucrose as a raw material, the fourth precursor is subjected to liquid-phase carbon coating treatment (based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer is 10%), and finally a hollow core-shell structure is obtained. Silicon-based anode material (carbon coating thickness of 35nm).

Example 2

(1) Using ethyl orthosilicate as a raw material, the surface of 50 nm elemental silicon is coated to form amorphous SiO ₂ to obtain a first precursor, wherein the thickness of the amorphous SiO ₂ layer is 35 nm, based on the first precursor The total mass of the amorphous SiO ₂ layer is 5.5%;

(2) using lithium carbonate as a raw material, using two-fluid spray drying to coat the surface of the first precursor with lithium carbonate to obtain a second precursor, wherein Li and no lithium in the lithium carbonate coated on the first precursor are The molar ratio of O in the shaped silicon dioxide layer is 0.12;

(3) sintering the second precursor in a tube furnace, the protective atmosphere is nitrogen, heating up to 830°C at a rate of 3°C/min, holding for 6 hours, and naturally cooling to room temperature to obtain the third precursor;

(4) The third precursor is acid-washed for 60 min with hydrofluoric acid with a concentration of 0.5 mol/L, dried, and sieved with 400 meshes to obtain the fourth precursor (wherein, lithium silicate (Li ₂ Si ₂ O ₅ ) The thickness of the coating layer is 10 nm, and based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate (Li ₂ Si ₂ O ₅ ) coating layer is 15%);

(5) Using pitch as a raw material, the fourth precursor is subjected to solid-phase carbon coating treatment (based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer is 10%), and finally a hollow core-shell structure is obtained. Silicon-based anode material (carbon coating thickness of 30 nm).

Example 3

(1) Using sodium silicate as a raw material, the surface of 3 μm SiO is coated to form amorphous SiO ₂ to obtain a first precursor, wherein the thickness of the amorphous SiO ₂ layer is 50 nm, based on the total mass of the first precursor , the mass ratio of the amorphous SiO ₂ layer is 7%;

(2) using lithium oxalate as a raw material, using two-fluid spray drying to coat the surface of the first precursor with lithium carbonate, to obtain a second precursor, wherein Li and no lithium in the lithium carbonate coated on the first precursor are The molar ratio of O in the shaped silicon dioxide layer is 0.1;

(3) the second precursor is sintered in a tube furnace, the protective atmosphere is nitrogen, the temperature is raised to 820°C at a rate of 3°C/min, the temperature is kept for 6 hours, and the third precursor is naturally cooled to room temperature;

(4) The third precursor is acid-washed for 60 min with hydrofluoric acid with a concentration of 1 mol/L, dried, and sieved with 400 meshes to obtain the fourth precursor (wherein, lithium silicate (Li ₂ Si ₂ O ₅ ) package The thickness of the coating layer is 20 nm, and based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate (Li ₂ Si ₂ O ₅ ) coating layer is 10%);

(5) Using acetylene as a raw material, the fourth precursor is subjected to gas-phase carbon coating treatment (based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer is 5%), and finally a hollow core-shell structure of silicon is obtained Base anode material (carbon coating thickness of 18 nm).

Example 4

(1) Using sodium silicate as a raw material, the surface of 5 μm SiO is coated to form amorphous SiO ₂ to obtain a first precursor, wherein the thickness of the amorphous SiO ₂ layer is 80 nm, based on the total mass of the first precursor , the mass ratio of the amorphous SiO ₂ layer is 10%;

(2) using lithium oxalate as a raw material, using two-fluid spray drying to coat the surface of the first precursor with lithium carbonate, to obtain a second precursor, wherein Li and no lithium in the lithium carbonate coated on the first precursor are The molar ratio of O in the shaped silicon dioxide layer is 0.1;

(3) sintering the second precursor in a tube furnace, the protective atmosphere is nitrogen, the temperature is raised to 840°C at a rate of 3°C/min, the temperature is maintained for 6 hours, and the third precursor is naturally cooled to room temperature;

(4) The third precursor is acid-washed for 60 min with hydrofluoric acid with a concentration of 1 mol/L, dried, and sieved with 400 meshes to obtain the fourth precursor (wherein, lithium silicate (Li ₂ Si ₂ O ₅ ) package The thickness of the coating layer is 50 nm, and based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate (Li ₂ Si ₂ O ₅ ) coating layer is 10%);

(5) Using acetylene as a raw material, the fourth precursor is subjected to gas-phase carbon coating treatment (based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer is 7%), and finally a hollow core-shell structure of silicon is obtained Base anode material (carbon coating thickness of 24 nm).

Comparative Example 1

Using acetylene as a raw material, the surface of 50 nm elemental silicon is coated with amorphous carbon (based on the total mass of the silicon-based negative electrode material, the mass proportion of amorphous carbon is 10%).

Comparative Example 2

Using high-temperature pitch as a raw material, the surface of 5 μm SiO was coated with amorphous carbon (based on the total mass of the silicon-based negative electrode material, the mass proportion of amorphous carbon was 7%).

The silicon-based negative electrode materials obtained in Examples 1-4 and Comparative Examples 1-2 were respectively prepared according to the mass ratio of active material, acetylene black, and adhesive (the mass ratio of CMC and SBR was 1:1) as 80:5:15. Slurry, apply the slurry on copper foil to make a negative pole piece, the load is 3mg/cm ² , the metal lithium piece is used as the counter electrode, the polypropylene microporous film (celgard2400) is used as the separator, 1mol/L LiPF ₆ The solution (DC, DEC, EMC volume ratio of 1:1:1) was used as the electrolyte, and a 2016 button battery was assembled in the glove box. The electrical performance test results are shown in Table 1. The charging and discharging system: the charging and discharging range is 0.005～ 1.5V, 0.1C charge and discharge for the first cycle, 0.2C charge and discharge for the second to 200th cycle.

The electrical performance results of the corresponding batteries of Examples 1-4 and Comparative Examples 1-2

The silicon-based materials of Examples 1-2 and Comparative Example 1 are all nano-silicon. Nano-silicon is characterized by high specific capacity but poor cycle performance. The silicon-based negative electrode material in Comparative Example 1 only has a carbon coating layer and no silicic acid. Lithium coating layer, and because lithium silicate is an inactive material, does not contribute to the specific capacity, so the specific capacity of Comparative Example 1 is higher than that of Example 1-2, while the first effect and cycle performance of the corresponding battery of Example 1-2 are both better than the corresponding battery of Comparative Example 1.

The silicon-based materials of Examples 3-4 and Comparative Example 2 are all made of silicon oxide. The characteristics of silicon oxide are that the specific capacity is lower than that of nano-silicon, and the cycle performance is better than that of nano-silicon. Therefore, Examples 3-4 and Comparative Examples The specific capacity of the corresponding battery of Example 2 is lower than that of the corresponding battery of Example 1-2, but the cycle performance of the corresponding battery of Example 3-4 and Comparative Example 2 is better than that of the corresponding battery of Example 1-2.

In the description of this specification, description with reference to the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples", etc., mean specific features described in connection with the embodiment or example , structure, material or feature is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may combine and combine the different embodiments or examples described in this specification, as well as the features of the different embodiments or examples, without conflicting each other.

Although the embodiments of the present invention have been shown and described above, it should be understood that the above-mentioned embodiments are exemplary and should not be construed as limiting the present invention. Embodiments are subject to variations, modifications, substitutions and variations.

Claims (19)

1. a silicon-based negative electrode material, is characterized in that, comprises: an inner core comprising a silicon-based material; Lithium silicate coating layer, the lithium silicate coating layer only contains Li ₂ Si ₂ O ₅ , the lithium silicate coating layer is arranged on the periphery of the inner core, and the lithium silicate coating layer has pores, and there is a distance between the lithium silicate coating layer and the inner core; a carbon coating layer, the carbon coating layer is coated on the lithium silicate coating layer, Wherein, the thickness of the lithium silicate coating layer is 10-100 nm, The method for preparing the silicon-based negative electrode material includes: (1) Coating silicon dioxide on the surface of a silicon-based material to obtain a first precursor; (2) coating the water-soluble lithium source on the first precursor to obtain a second precursor; (3) sintering the second precursor under an inert atmosphere, so that a part of the silicon dioxide reacts with the water-soluble lithium source, so as to form a surface of the silicon-based material containing Li ₂ Si ₂ O ₅ lithium silicate coating layer to obtain the third precursor; (4) etching the third precursor to remove another part of the silicon dioxide and lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer, so as to obtain the a fourth precursor having pores and a hollow core-shell structure on the lithium silicate coating layer; (5) Coating a carbon coating layer on the surface of the fourth precursor, so as to obtain the silicon-based negative electrode material. 2 . The silicon-based negative electrode material according to claim 1 , wherein the silicon-based material comprises at least one of elemental nano-silicon and silicon oxide. 3 . 3 . The silicon-based negative electrode material according to claim 2 , wherein the particle size D50 of the elemental nano-silicon is 5-100 nm. 4 . 4 . The silicon-based negative electrode material according to claim 2 , wherein the chemical formula of the silicon oxide is SiO _x , and x is 0.5˜1.5. 5 . 5 . The silicon-based negative electrode material according to claim 2 , wherein the particle size D50 of the silicon oxide is 100 nm˜15 μm. 6 . 6 . The silicon-based negative electrode material according to claim 1 , wherein, based on the total mass of the silicon-based negative electrode material, the mass ratio of the lithium silicate coating layer is 5-30%. 7 . 7 . The silicon-based negative electrode material according to claim 1 , wherein the carbon coating layer has a thickness of 1 to 50 nm. 8 . 8 . The silicon-based negative electrode material according to claim 1 , wherein, based on the total mass of the silicon-based negative electrode material, the mass ratio of the carbon coating layer is 1-20%. 9 . 9. A method for preparing the silicon-based negative electrode material according to any one of claims 1-8, characterized in that, comprising: (1) Coating silicon dioxide on the surface of a silicon-based material to obtain a first precursor; (2) coating the water-soluble lithium source on the first precursor to obtain a second precursor; (3) sintering the second precursor under an inert atmosphere, so that a part of the silicon dioxide reacts with the water-soluble lithium source, so as to form a surface of the silicon-based material containing Li ₂ Si ₂ O ₅ lithium silicate coating layer to obtain the third precursor; (4) etching the third precursor to remove another part of the silicon dioxide and lithium silicate other than Li ₂ Si ₂ O ₅ in the lithium silicate coating layer, so as to obtain the a fourth precursor having pores and a hollow core-shell structure on the lithium silicate coating layer; (5) Coating a carbon coating layer on the surface of the fourth precursor, so as to obtain a silicon-based negative electrode material. The method according to claim 9, characterized in that, in step (1), the silicon dioxide is amorphous silicon dioxide, and the amorphous silicon dioxide coating formed on the surface of the silicon-based material The layer thickness is 30 to 150 nm. 11 . The method according to claim 10 , wherein in step (1), based on the total mass of the first precursor, the mass ratio of the amorphous silica coating layer is 5～11 . 20%. 12 . The method according to claim 9 , wherein in step (2), the water-soluble lithium source is coated on the first precursor by spray drying. 13 . The method according to claim 9, wherein in step (2), the water-soluble lithium source comprises at least one of lithium carbonate, lithium oxalate, lithium nitrate and lithium acetate. The method according to claim 9, characterized in that, in step (2), the molar ratio of lithium in the water-soluble lithium source to oxygen in the silica is 0.08-0.2. 15 . The method according to claim 9 , wherein, in step (3), the sintering temperature is 700-900° C., the heating rate is 0.5° C./min-10° C./min, and the sintering time is 1-15° C. 15 . 36h. 16 . The method according to claim 9 , wherein, in step (4), the third precursor is etched with hydrofluoric acid. 17 . 17 . The method according to claim 16 , wherein in step (4), the concentration of the hydrofluoric acid is 0.5-1.0 mol/L, and the etching time is 1-120 min. 18 . 18. A negative electrode, characterized in that the negative electrode adopts the silicon-based negative electrode material according to any one of claims 1-8 or the silicon-based negative electrode obtained by the method according to any one of claims 9-17 materials are prepared. 19 . A lithium battery, characterized in that, the lithium battery comprises the negative electrode of claim 18 .

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