CN114937765B - A modified polyimide-coated silicon/lithium silicate negative electrode material and preparation method thereof, and a lithium-ion battery - Google Patents

Abstract

The present invention provides a silicon composite material, including a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the silicon/lithium silicate composite material; the modified polyimide is a lithium ion doped polyimide. The modified polyimide coated silicon/lithium silicate negative electrode material with a specific structure, the silicon/lithium silicate composite material has a structure in which nano silicon particles are uniformly dispersed in the lithium silicate phase. The lithium silicate phase in the present invention can improve the lithium ion conductivity, while buffering the volume expansion of silicon during the charging and discharging process. The polyimide coating layer has excellent mechanical properties and after being modified with lithium ions, it ensures that the material has a high first effect, high reversible capacity, and excellent cycle performance. The preparation method provided by the present invention prepares the silicon/lithium silicate composite material by simple mechanical ball milling, has low energy consumption, saves cost, is green and environmentally friendly, has a simple preparation process, can be industrialized, has a high degree of practicality, and has broad application prospects in lithium ion battery negative electrodes.

Description

A modified polyimide-coated silicon/lithium silicate negative electrode material and preparation method thereof, lithium ion battery

Technical Field

The present invention belongs to the technical field of silicon composite materials, and relates to a silicon composite material and a preparation method thereof, and a lithium ion battery, and in particular to a modified polyimide-coated silicon/lithium silicate negative electrode material and a preparation method thereof, and a lithium ion battery.

Background technique

Lithium-ion batteries have extremely important applications in electronic products, electric vehicles, energy storage and other fields due to their advantages such as high energy density, high output voltage, long cycle life and low environmental pollution. The current commercial lithium-ion battery negative electrode material is mainly graphite negative electrode material, with a theoretical capacity of only 372mAh/g and an actual capacity between 340 and 360mAh/g, which cannot meet the design requirements of high specific energy batteries. Therefore, the development of the next generation of new negative electrode materials with high specific capacity, good cycle stability and rate performance to achieve widespread use in electronic products and electric vehicles has become a key research topic in the battery field.

Silicon-based materials are abundant in sources and have a high specific capacity (4200mAh/g). At the same time, their lithium insertion potential (0.4V) is close to that of graphite (0.1V), making them ideal negative electrode materials for high specific energy batteries. However, due to the poor conductivity of silicon materials themselves and the severe volume effect produced during electrochemical lithium insertion and extraction, the material structure is destroyed and mechanically pulverized, resulting in separation between electrode materials and between electrode materials and current collectors, and then loss of electrical contact, resulting in a sharp decline in the cycle performance of the electrode. The current method to solve this problem is to use materials with lower expansion coefficients as the matrix, embed or encapsulate active silicon in these matrix materials to alleviate the volume changes caused by the insertion and extraction of lithium ions. The matrix material plays a role in buffering mechanical stress. The more common matrix materials are carbon materials and polymer materials. However, compared with silicon, although carbon materials have better mechanical properties and lower volume expansion rate (only 9%, far lower than 400% of silicon), the absolute volume expansion still exists. Therefore, the construction method of this type of composite material can alleviate the volume effect of silicon to a certain extent, but the long-term electrochemical cycle stability of silicon materials has not been significantly improved. Moreover, in the subsequent cycles, as the cycle reaction continues, the interface bonding between the matrix material and the silicon active center will also be severely damaged due to the mismatch of volume expansion, resulting in the attenuation of electrochemical cycle performance. For example, the patent application with publication number CN108321368A applies for a polymer-coated silicon/lithium metasilicate negative electrode material and a preparation method thereof, wherein a silicon/lithium silicate composite material is prepared by ball milling active lithium powder and silicon oxide in an inert atmosphere, and polymerizing polyaniline, polypyrrole, polydopamine and other polymers in situ on the surface of the composite material. First, lithium powder is relatively active, has strict environmental requirements, and is not suitable for industrial production. At the same time, the polar heteroatoms in the polymer will consume lithium ions in the electrolyte and reduce the first cycle efficiency. The first efficiency of the electrode material prepared by it is only 70%, which does not meet the requirements of commercial products of negative electrode materials.

Therefore, how to find a more appropriate way to solve the above-mentioned problems existing in the existing silicon negative electrode and to produce a commercial silicon-carbon negative electrode product with high reversible capacity, excellent cycle performance, and suitable for industrial promotion and application has become one of the urgent problems to be solved by many front-line researchers and scientific research enterprises.

Summary of the invention

In view of this, the technical problem to be solved by the present invention is to provide a silicon composite material and a preparation method thereof, a lithium ion battery, and in particular a lithium ion battery modified polyimide coated silicon/lithium silicate negative electrode material. The silicon composite material provided by the present invention has the characteristics of high reversible capacity, excellent cycle performance, etc., and the process is simple and easy to operate, convenient for large-scale production, high degree of practicality, and has broad application prospects in the negative electrode of lithium ion batteries.

The present invention provides a silicon composite material, comprising a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the silicon/lithium silicate composite material;

The modified polyimide is lithium ion doped polyimide.

Preferably, in the silicon/lithium silicate composite material, nano silicon particles are dispersed in the lithium silicate material;

The particle size of the nano silicon particles is greater than or equal to 10 nm;

The lithium ion doped polyimide includes lithium ion modified polyimide.

Preferably, in the silicon composite material, the mass content of the silicon/lithium silicate composite material is 93% to 99%;

The D50 particle size of the silicon composite material is 1 to 10 μm;

The silicon composite material is a negative electrode material for lithium-ion batteries.

Preferably, the silicon composite material further comprises a conductive carbon material;

The conductive carbon material includes one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene and carbon fibers;

The conductive carbon material includes one or more of a conductive carbon material composited on the silicon/lithium silicate composite material, a conductive carbon material coated on the silicon/lithium silicate composite material, a conductive carbon material doped in the modified polyimide coating layer, and a conductive carbon material composited on the modified polyimide coating layer.

The present invention provides a method for preparing a silicon composite material, comprising the following steps:

1) Under a protective atmosphere, ball-milling silicon dioxide, lithium hydroxide and a mixed solution to obtain a silicon/lithium silicate composite material;

2) The silicon/lithium silicate composite material obtained in the above steps, the polymer monomer and the solvent containing lithium salt are mixed, and then subjected to polymerization reaction, and then spray-dried and heated for curing to obtain a silicon composite material.

Preferably, the particle size of the silicon oxide is 3 to 10 μm;

The atomic ratio of Si to O in the silicon oxide is n, 0.8≤n＜1.6;

The molar ratio of silicon oxide to lithium hydroxide is (6-9):1;

The mixed solution includes a mixed solution of water and alcohol;

The ball milling time is 6 to 10 hours.

Preferably, the polymer monomers include dianhydride monomers and diamine monomers;

The dianhydride monomer includes one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride and 1,2,4,5-pyromellitic dianhydride;

The diamine monomer includes one or more of p-phenylenediamine, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfone, 2,2-bis[4-(2,4-diaminophenoxy)phenyl]propane and 1,4-diaminocyclohexane;

The molar ratio of the dianhydride monomer to the diamine monomer is (1-1.05):1;

The step 2) also includes a conductive carbon material.

Preferably, the conductive carbon material includes one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene and carbon fiber;

The lithium salt includes one or more of LiBOB, LiPF ₆ and LiFSI;

The molar ratio of the lithium salt to the dianhydride monomer is (1-15):100;

The solvent includes one or more of acetone, dimethyl sulfoxide and N,N-dimethylformamide;

The step 2) is specifically as follows:

The conductive carbon material, lithium salt, dianhydride monomer and solvent are first mixed, and then the diamine monomer is added for polymerization reaction, and then the silicon/lithium silicate composite material obtained in the above steps is added, and finally the silicon composite material is obtained after spray drying and heating curing.

Preferably, the polymerization reaction temperature is 40 to 70°C;

The polymerization reaction time is 1 to 4 hours;

The spray drying temperature is 150-200°C;

The temperature of the heating and curing is 300-450°C;

The heating and curing time is 2 to 6 hours.

The present invention also provides a lithium ion battery, comprising a positive electrode and a negative electrode;

The negative electrode comprises a silicon composite negative electrode material;

The silicon composite negative electrode material includes the silicon composite material described in any one of the above technical solutions or the silicon composite material prepared by the preparation method described in any one of the above technical solutions.

The present invention provides a silicon composite material, including a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the silicon/lithium silicate composite material; the modified polyimide is a lithium ion doped polyimide. Compared with the prior art, the present invention aims at modifying the existing silicon-carbon negative electrode material mainly by carbon coating and then undergoing a pre-lithiation process to improve the battery performance, which is not only costly, but also prone to mismatch between the carbon coating layer and the active material during the cycle process, affecting the electrochemical performance; and the polymer-coated silicon-carbon negative electrode material currently used, the polar heteroatoms in the polymer will consume lithium ions in the electrolyte, affecting the battery's first cycle efficiency and other issues. Based on research, the present invention believes that the heteroatoms contained in the polymer coating will consume lithium ions in the electrolyte, thereby causing an increase in the first irreversible capacity.

Based on this, the present invention creatively designs a silicon composite material with a specific structure. This modified polyimide-coated silicon/lithium silicate negative electrode material includes a silicon/lithium silicate composite material and a modified polyimide coating layer coated outside the composite material. The silicon/lithium silicate composite material has a structure in which nano silicon particles (<10nm) are uniformly dispersed in the lithium silicate phase, and the modified polyimide coating layer is obtained by polymerizing dianhydride monomers and diamine monomers in a solvent containing lithium ions. The lithium silicate phase in the present invention can improve the lithium ion conductivity and buffer the volume expansion of silicon during the charge and discharge process. The polyimide coating layer has excellent mechanical properties and after being modified with lithium ions, it ensures that the material has a high first effect, high reversible capacity, and excellent cycle performance.

The present invention also provides a method for preparing a modified polyimide-coated silicon/lithium silicate negative electrode material. The silicon/lithium silicate composite material is prepared by simple mechanical ball milling, which abandons the high-temperature calcination in the traditional preparation method, greatly reduces energy consumption, saves costs, is green and environmentally friendly, has the characteristics of simple preparation process, low environmental requirements, industrial production, high degree of practicality, etc., and has broad application prospects in lithium-ion battery negative electrodes.

Experimental results show that the composite of lithium silicate in the modified polyimide-coated silicon/lithium silicate negative electrode material prepared by the present invention can significantly improve the ionic conductivity of the material, and at the same time can buffer the volume effect (volume expansion) of silicon during the charging and discharging process, which is beneficial to improving the lithium ion conductivity; the polyimide coating layer has excellent mechanical properties and after lithium ion modification, it ensures that the material has a higher first effect, reversible capacity and better cycle performance.

Detailed ways

In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the invention.

All raw materials of the present invention are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses analytically pure materials or materials of conventional purity used in the field of lithium ion negative electrode preparation.

The present invention provides a silicon composite material, comprising a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the silicon/lithium silicate composite material;

The modified polyimide is lithium ion doped polyimide.

In the present invention, the lithium ion doped polyimide preferably includes lithium ion modified polyimide.

In the present invention, in the silicon/lithium silicate composite material, the nano silicon particles are preferably dispersed in the lithium silicate material.

In the present invention, the particle size of the nano-silicon particles is preferably greater than or equal to 10 nm, more preferably greater than or equal to 12 nm, and more preferably greater than or equal to 14 nm.

In the present invention, in the silicon composite material, the mass content of the silicon/lithium silicate composite material is preferably 93% to 99%, more preferably 94% to 98%, and more preferably 95% to 97%.

In the present invention, the D50 particle size of the silicon composite material is preferably 1 to 10 μm, more preferably 3 to 8 μm, and even more preferably 5 to 6 μm.

In the present invention, the silicon composite material is preferably a negative electrode material for a lithium ion battery.

In the present invention, the silicon composite material preferably includes a conductive carbon material.

In the present invention, the conductive carbon material preferably includes one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene and carbon fibers, and more preferably conductive carbon black, acetylene black, carbon nanotubes, graphene or carbon fibers.

In the present invention, the conductive carbon material preferably includes one or more of a conductive carbon material composited on the silicon/lithium silicate composite material, a conductive carbon material coated on the silicon/lithium silicate composite material, a conductive carbon material doped in the modified polyimide coating layer, and a conductive carbon material composited on the modified polyimide coating layer, and more preferably includes a conductive carbon material composited on the silicon/lithium silicate composite material, a conductive carbon material coated on the silicon/lithium silicate composite material, a conductive carbon material doped in the modified polyimide coating layer, and a conductive carbon material composited on the modified polyimide coating layer.

The present invention is to complete and refine the overall technical solution, better ensure the specific structure and morphology of the composite material, better inhibit the volume expansion of silicon, and thus improve the first effect, reversible capacity and cycle performance of the battery. The modified polyimide-coated silicon/lithium silicate negative electrode material can be specifically:

It is composed of a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the outside of the composite material. The silicon/lithium silicate composite material has a structure in which nano silicon particles (<10nm) are uniformly dispersed in a lithium silicate phase, and the modified polyimide coating layer is obtained by polymerizing a dianhydride monomer and a diamine monomer in a solvent containing lithium ions.

Specifically, the weight content of the silicon/lithium silicate composite material in the negative electrode material is 93% to 99%, and the weight content of the modified polyimide coating layer in the negative electrode material is 0.5% to 7%.

Specifically, the modified polyimide-coated silicon/lithium silicate negative electrode material has a particle size D50 of 1 to 10 μm, preferably 3 to 7 μm.

The present invention provides a method for preparing a silicon composite material, comprising the following steps:

1) Under a protective atmosphere, ball-milling silicon dioxide, lithium hydroxide and a mixed solution to obtain a silicon/lithium silicate composite material;

2) The silicon/lithium silicate composite material obtained in the above steps, the polymer monomer and the solvent containing lithium salt are mixed, and then subjected to polymerization reaction, and then spray-dried and heated for curing to obtain a silicon composite material.

The method of the present invention is to ball-mill silicon dioxide, lithium hydroxide and a mixed solution under a protective atmosphere to obtain a silicon/lithium silicate composite material.

In the present invention, the particle size of silicon 2 oxide is preferably 3 to 10 μm, more preferably 5 to 9 μm, and more preferably 6 to 8 μm.

In the present invention, the atomic ratio of Si to O in the silicon monoxide is n, preferably 0.8≤n＜1.6, more preferably 0.9≤n≤1.5, more preferably 1.0≤n≤1.4, more preferably 1.1≤n≤1.3.

In the present invention, the molar ratio of silicon monoxide to lithium hydroxide is preferably (6-9):1, more preferably (6.5-8.5):1, and more preferably (7-8):1.

In the present invention, the mixed solution preferably includes a mixed solution of water and alcohol.

In the present invention, the ball milling time is preferably 6 to 10 h, more preferably 6.5 to 9.5 h, more preferably 7 to 9 h, and more preferably 7.5 to 8.5 h.

The present invention further mixes the silicon/lithium silicate composite material obtained in the above steps, polymer monomers and a solvent containing lithium salt, performs polymerization reaction, and then spray-dries and heat-cures to obtain a silicon composite material.

In the present invention, the polymer monomers preferably include dianhydride monomers and diamine monomers.

In the present invention, the dianhydride monomer preferably includes one or more of pyromellitic dianhydride, dibenzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride and 1,2,4,5-pyromellitic dianhydride, and more preferably pyromellitic dianhydride, dibenzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride or 1,2,4,5-pyromellitic dianhydride.

In the present invention, the diamine monomer preferably includes one or more of p-phenylenediamine, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfone, 2,2-bis[4-(2,4-diaminophenoxy)phenyl]propane and 1,4-diaminocyclohexane, and more preferably p-phenylenediamine, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfone, 2,2-bis[4-(2,4-diaminophenoxy)phenyl]propane or 1,4-diaminocyclohexane.

In the present invention, the molar ratio of the dianhydride monomer to the diamine monomer is preferably (1-1.05):1, more preferably (1.01-1.04):1, and more preferably (1.02-1.03):1.

In the present invention, the step 2) preferably includes a conductive carbon material.

In the present invention, the conductive carbon material preferably includes one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene and carbon fibers, and more preferably conductive carbon black, acetylene black, carbon nanotubes, graphene or carbon fibers.

In the present invention, the lithium salt preferably includes one or more of LiBOB, LiPF6 and LiFSI, and more preferably LiBOB, LiPF6 or LiFSI.

In the present invention, the molar ratio of the lithium salt to the dianhydride monomer is preferably (1-15):100, more preferably (4-12):100, and even more preferably (7-9):100.

In the present invention, the solvent preferably includes one or more of acetone, dimethyl sulfoxide and N,N-dimethylformamide, more preferably acetone, dimethyl sulfoxide or N,N-dimethylformamide.

In the present invention, the step 2) is preferably:

The conductive carbon material, lithium salt, dianhydride monomer and solvent are first mixed, and then the diamine monomer is added for polymerization reaction, and then the silicon/lithium silicate composite material obtained in the above steps is added, and finally the silicon composite material is obtained after spray drying and heating curing.

In the present invention, the polymerization reaction temperature is preferably 40 to 70°C, more preferably 45 to 65°C, and more preferably 50 to 60°C.

In the present invention, the polymerization reaction time is preferably 1 to 4 hours, more preferably 1.5 to 3.5 hours, and more preferably 2 to 3 hours.

In the present invention, the spray drying temperature is preferably 150 to 200°C, more preferably 160 to 190°C, and even more preferably 170 to 180°C.

In the present invention, the temperature of the heating and curing is preferably 300 to 450°C, more preferably 330 to 420°C, and even more preferably 360 to 390°C.

In the present invention, the heating and curing time is preferably 2 to 6 hours, more preferably 2.5 to 5.5 hours, more preferably 3 to 5 hours, and more preferably 3.5 to 4.5 hours.

The present invention is to complete and refine the overall preparation process, better ensure the specific structure and morphology of the composite material, better inhibit the volume expansion of silicon, and thus improve the first effect, reversible capacity and cycle performance of the battery. The preparation method of the modified polyimide-coated silicon/lithium silicate negative electrode material can be specifically:

The preparation method of modified polyimide coated silicon/lithium silicate negative electrode material comprises the following steps:

S1. Preparation of silicon/lithium silicate composite material: taking silicon oxide, lithium hydroxide, and a water/ethanol mixed solution (2:3), ball milling under a nitrogen atmosphere to obtain a silicon/lithium silicate composite material;

S2. Preparation of modified polyimide coating layer: uniformly dispersing the silicon/lithium metasilicate composite material, conductive carbon material and polymer monomer in S1 in a lithium salt-containing solvent, performing polymerization reaction, spray drying and heating to obtain the modified polyimide-coated silicon/lithium metasilicate negative electrode material.

Specifically, in the S1, the particle size of the silicon monoxide is 3 to 10 μm; the concentration of the lithium hydroxide is 1 mol/L, and the purity of the nitrogen is 99.99%; the atomic ratio of Si to O in the silicon monoxide is n, 0.8≤n＜1.6.

Specifically, in S1, the molar ratio of silicon dioxide to lithium hydroxide is 9:1 to 6:1. The ball milling time is 6 to 10 hours, and the ball milling is mechanical ball milling.

Specifically, in S2, the conductive carbon material is one or a mixture of conductive carbon black, acetylene black, carbon nanotubes, graphene, and carbon fibers; the lithium salt is one of LiBOB, LiPF ₆ , and LiFSI, and the added amount is 1% to 15% of the dianhydride monomer.

Specifically, in S2, the polymer monomers are dianhydride monomers and diamine monomers, and the ratio of dianhydride to diamine is 1-1.05:1-1. The required solvent is at least one of acetone, dimethyl sulfoxide, and N,N-dimethylformamide.

Specifically, the dianhydride monomer includes at least one of pyromellitic acid dianhydride, benzophenone dianhydride, biphenyl dianhydride, diphenyl ether dianhydride, and 1,2,4,5-pyromellitic acid dianhydride. The diamine monomer is at least one of p-phenylenediamine, 4,4'-diamino-3,3'-dimethylbiphenyl, 4,4'-diaminodiphenyl sulfone, 2,2-bis[4-(2,4-diaminophenoxy)phenyl]propane, and 1,4-diaminocyclohexane.

Specifically, in S2, the spray drying temperature is 150-200° C., the heating curing condition is 300-450° C., and the heating time is 2-6 hours.

The present invention provides a lithium ion battery, comprising a positive electrode and a negative electrode;

In the present invention, the negative electrode preferably comprises a silicon composite negative electrode material

In the present invention, the silicon composite negative electrode material preferably includes the silicon composite material described in any one of the above technical solutions or the silicon composite material prepared by the preparation method described in any one of the above technical solutions.

The above steps of the present invention provide a modified polyimide-coated silicon/lithium silicate negative electrode material and a preparation method thereof, and a lithium ion battery. This is a modified polyimide-coated silicon/lithium silicate negative electrode material with a specific structure, including a silicon/lithium silicate composite material and a modified polyimide coating layer coated outside the composite material. The silicon/lithium silicate composite material has a structure in which nano silicon particles (<10nm) are uniformly dispersed in the lithium silicate phase, and the modified polyimide coating layer is obtained by polymerization of dianhydride monomers and diamine monomers in a solvent containing lithium ions. The lithium silicate phase in the present invention can improve the lithium ion conductivity and buffer the volume expansion of silicon during the charging and discharging process. The polyimide coating has excellent mechanical properties and after being modified with lithium ions, it ensures that the material has a high first effect, high reversible capacity, and excellent cycle performance.

The present invention also provides a method for preparing a modified polyimide-coated silicon/lithium silicate negative electrode material. The silicon/lithium silicate composite material is prepared by simple mechanical ball milling, which abandons the high-temperature calcination in the traditional preparation method, greatly reduces energy consumption, saves costs, is green and environmentally friendly, has the characteristics of simple preparation process, low environmental requirements, industrial production, high degree of practicality, etc., and has broad application prospects in lithium-ion battery negative electrodes.

Experimental results show that the composite of lithium silicate in the modified polyimide-coated silicon/lithium silicate negative electrode material prepared by the present invention can significantly improve the ionic conductivity of the material, and at the same time can buffer the volume effect (volume expansion) of silicon during the charging and discharging process, which is beneficial to improving the lithium ion conductivity; the polyimide coating layer has excellent mechanical properties and after lithium ion modification, it ensures that the material has a higher first effect, reversible capacity and better cycle performance.

In order to further illustrate the present invention, a silicon composite material and a preparation method thereof, and a lithium-ion battery provided by the present invention are described in detail in combination with the following examples. However, it should be understood that these examples are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given only to further illustrate the features and advantages of the present invention, rather than to limit the claims of the present invention, and the protection scope of the present invention is not limited to the following examples.

Example 1

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere, and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) Disperse 0.2 g of carbon nanotubes in 100 mL of NMP solution, disperse by ultrasonication, add 0.02 mmol of LiPF ₆ to dissolve, then add 1 mmol of 1,2,4,5-pyromellitic dianhydride, and stir at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.02:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Example 2

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere, and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) Disperse 0.2 g of carbon nanotubes in 100 mL of NMP solution, disperse by ultrasonication, add 0.02 mmol of LiFSI to dissolve, then add 1 mmol of 1,2,4,5-pyromellitic dianhydride, and stir at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.02:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Example 3

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere, and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) 0.2 g of carbon nanotubes were dispersed in 100 mL of NMP solution, ultrasonically dispersed, 0.04 mmol of LiFSI was added to dissolve, and then 1 mmol of 1,2,4,5-pyromellitic dianhydride was added and stirred at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.02:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Example 4

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere, and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) 0.2 g of carbon nanotubes were dispersed in 100 mL of NMP solution, ultrasonically dispersed, 0.04 mmol of LiFSI was added to dissolve, and then 1 mmol of 1,2,4,5-pyromellitic dianhydride was added and stirred at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.04:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Example 5

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) 0.4 g of carbon nanotubes were dispersed in 100 mL of NMP solution, ultrasonically dispersed, 0.04 mmol of LiFSI was added to dissolve, and then 1 mmol of 1,2,4,5-pyromellitic dianhydride was added and stirred at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.04:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Comparative Example 1

Ball-milled raw silicon is selected as the negative electrode material.

Comparative Example 2

15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere and vacuum-dried to obtain a silicon/lithium silicate composite material;

Comparative Example 3

(1) 15.0 g of silicon dioxide, 5.4 g of lithium hydroxide, and 15 g of a water/ethanol mixed solution (2:3) were mechanically ball-milled for 8 h under a nitrogen atmosphere, and vacuum-dried to obtain a silicon/lithium silicate composite material;

(2) Dispersing 0.2 g of carbon nanotubes in 100 mL of NMP solution, ultrasonically dispersing, adding 1 mmol of 1,2,4,5-pyromellitic dianhydride, and stirring at room temperature for 2 h;

(3) heating the above solution to 50° C., adding 4,4′-diaminodiphenyl ether dropwise to the NMP solution containing lithium ions at a molar ratio of diamine monomer to dianhydride monomer of 1:1.01, and reacting for 2 h;

(4) adding the silicon/lithium silicate composite material prepared in step (1) to the obtained mixed system, wherein the weight ratio of the sum of the weight of the polyimide monomer dianhydride and the monomer diamine to the silicon/lithium silicate composite material is 0.02:1, and stirring for 1 hour;

(5) The solid material obtained by spray drying the above dispersion was sieved and treated at 400° C. for 2 h under a nitrogen atmosphere to finally obtain a lithium ion-doped polyimide-coated silicon/lithium silicate negative electrode material.

Example 6

The silicon negative electrode materials prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were tested for electrical properties, and the main steps included:

The active material: conductive agent: binder are mixed in a mass ratio of 8:1:1 (solid content is 40-45%); the slurry is coated on copper foil, and vacuum dried, rolled, and cut into pieces to prepare pole pieces; a lithium sheet is used as a counter electrode, a polyethylene-polypropylene composite diaphragm is used as a diaphragm, and 1.0 mol/L LiPF ₆ (EC/DMC/EMC=1:1:1) containing 5% FEC is used as an electrolyte to assemble a button battery. The charge and discharge current is 0.1C, and the voltage range is 0.002-2.0V.

See Table 1, which shows the electrical performance test data of silicon negative electrode materials prepared in the examples and comparative examples of the present invention.

Table 1

From the test results in Table 1, it can be seen that the modified polyimide-coated silicon/lithium silicate negative electrode material in the present invention improves the ionic conductivity of the negative electrode material through the composite of lithium silicate, and the polyimide coating layer has excellent mechanical properties and reduces the release of irreversible capacity after lithium ion modification. Through the synergistic effect between each other, the initial efficiency and cycle performance of the material are improved.

The above is a detailed introduction to a modified polyimide-coated silicon/lithium silicate negative electrode material and its preparation method and lithium-ion battery provided by the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method and its core ideas of the present invention, including the best mode, and also enables any technician in the field to practice the present invention, including the manufacture and use of any device or system, and the implementation of any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, the present invention can also be improved and modified in several ways, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements that are not different from the text of the claims, or if they include equivalent structural elements that are not substantially different from the text of the claims, then these other embodiments should also be included in the scope of the claims.

Claims (10)

1. The silicon composite material is characterized by comprising a silicon/lithium silicate composite material and a modified polyimide coating layer coated on the silicon/lithium silicate composite material;

the modified polyimide is lithium ion doped polyimide;

In the silicon/lithium silicate composite material, nano silicon particles are dispersed in a lithium silicate material;

the grain diameter of the nano silicon particles is more than or equal to 10nm;

The lithium ion doped polyimide comprises lithium ion modified polyimide;

the silicon composite material further comprises a conductive carbon material;

the conductive carbon material comprises one or more of a conductive carbon material compounded on the silicon/lithium silicate composite material, a conductive carbon material coated on the silicon/lithium silicate composite material, a conductive carbon material doped in the modified polyimide coating layer and a conductive carbon material compounded on the modified polyimide coating layer;

The preparation method of the silicon composite material is characterized by comprising the following steps:

1) Ball milling is carried out on the silicon oxide, the lithium hydroxide and the mixed solution in a protective atmosphere to obtain a silicon/lithium silicate composite material;

2) The conductive carbon material, the lithium salt, the dianhydride monomer and the solvent are mixed firstly, then diamine monomer is added for polymerization reaction, then the silicon/lithium silicate composite material obtained by the steps is added, and finally the silicon composite material is obtained after spray drying and heating curing.

2. The silicon composite material according to claim 1, wherein the mass content of the silicon/lithium silicate composite material in the silicon composite material is 93% -99%;

the D50 particle size of the silicon composite material is 1-10 mu m.

3. The silicon composite of claim 1, wherein the silicon composite is a lithium ion battery anode material.

4. The silicon composite of claim 1, wherein the conductive carbon material comprises one or more of conductive carbon black, acetylene black, carbon nanotubes, graphene, and carbon fibers.

5. The silicon composite material according to claim 1, wherein the particle size of the silica is 3 to 10 μm;

the atomic ratio of Si to O in the silicon oxide is n, n is more than or equal to 0.8 and less than 1.6;

The molar ratio of the silicon oxide to the lithium hydroxide is (6-9): 1.

6. The silicon composite of claim 1, wherein the mixed solution comprises a mixed solution of water and alcohol;

the ball milling time is 6-10 hours.

7. The silicon composite of claim 1, wherein the dianhydride monomer comprises one or more of pyromellitic dianhydride, benzophenone dianhydride, biphenyl dianhydride, and diphenyl ether dianhydride;

The diamine monomer comprises one or more of p-phenylenediamine, 4' -diamino-3, 3' -dimethylbiphenyl, 4' -diamino diphenyl sulfone, 2-bis [4- (2, 4-diamino phenoxy) phenyl ] propane and 1, 4-diamino cyclohexane;

The molar ratio of the dianhydride monomer to the diamine monomer is (1-1.05): 1.

8. The silicon composite of claim 1, wherein the lithium salt comprises one or more of LiBOB, liPF ₆, and LiFSI;

The molar ratio of the lithium salt to the dianhydride monomer is (1-15): 100;

the solvent comprises one or more of acetone, dimethyl sulfoxide and N, N-dimethylformamide.

9. The silicon composite material according to claim 1, wherein the polymerization reaction temperature is 40-70 ℃;

the polymerization reaction time is 1-4 hours;

the temperature of the spray drying is 150-200 ℃;

the temperature of the heating and curing is 300-450 ℃;

and the heating and curing time is 2-6 hours.

10. A lithium ion battery is characterized by comprising a positive electrode and a negative electrode;

the negative electrode comprises a silicon composite negative electrode material;

The silicon composite anode material comprises the silicon composite material according to any one of claims 1 to 9.