阅读说明：本技术 一种硅基负极材料及包含该硅基负极材料的锂离子电池 (Silicon-based negative electrode material and lithium ion battery containing same ) 是由 林少雄 陆大班 王辉 辛昱 刘盛华 于 2020-06-23 设计创作，主要内容包括：本发明公开了一种硅基负极材料,包含:硅基材料；碳层,所述碳层表面含羟基,并且所述碳层包覆在所述硅基材料表面；聚合物层,所述聚合物层包含可以与羟基键合的聚合物和/或聚合物单体,并且所述聚合物层包覆在所述碳层表面；以及碳纳米管,所述碳纳米管通过氢键和/或共价键连接在所述聚合物层表面。本发明还公开了含该硅基负极材料的锂离子电池。本发明的硅基负极材料的可以大幅度的减少硅负极的锂离子电池在循环前期因膨胀而导致失去接触的硅材料,从而改善循环前期的迅速衰减趋势。本方法的生产成本低、生产安全性高、操作方便且易于大规模量产使用。(The invention discloses a silicon-based negative electrode material, which comprises a silicon-based material; the surface of the carbon layer contains hydroxyl, and the carbon layer is coated on the surface of the silicon-based material; a polymer layer, wherein the polymer layer comprises polymers and/or polymer monomers which can be bonded with hydroxyl, and the polymer layer coats the surface of the carbon layer; and the carbon nano tube is connected to the surface of the polymer layer through a hydrogen bond and/or a covalent bond. The invention also discloses a lithium ion battery containing the silicon-based negative electrode material. The silicon-based negative electrode material can greatly reduce the silicon material of the lithium ion battery of the silicon negative electrode which loses contact due to expansion in the early period of circulation, thereby improving the rapid attenuation tendency in the early period of circulation. The method has the advantages of low production cost, high production safety, convenient operation and easy large-scale mass production and use.)

1. A silicon-based anode material, comprising:

a silicon-based material;

the surface of the carbon layer contains hydroxyl, and the carbon layer is coated on the surface of the silicon-based material;

a polymer layer, wherein the polymer layer comprises polymers and/or polymer monomers which can be bonded with hydroxyl, and the polymer layer coats the surface of the carbon layer;

and the carbon nano tube is connected to the surface of the polymer layer through a hydrogen bond and/or a covalent bond.

2. The silicon-based anode material according to claim 1, wherein the surface of the carbon nanotubes has active groups that can form hydrogen bonds and/or covalent bonds with components of the polymer layer; preferably, the active group is at least one of amino, carboxyl, hydroxyl, ester, unsaturated double bond and unsaturated triple bond.

3. The silicon-based anode material according to claim 1 or 2, wherein the carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof.

4. The silicon-based anode material according to any one of claims 1 to 3, wherein the polymer and/or polymer monomer comprises at least one of dimethylacrylamide, aniline, thiophene, pyrrole, polydimethylsiloxane, methyl methacrylate, ethyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylamide, maleic anhydride, sodium p-vinylbenzene sulfonate, sodium allyl sulfonate, vinyl acetate, isooctyl acrylate, and perfluoropolyether derivatives.

5. The silicon-based anode material according to any one of claims 1 to 4, wherein the silicon-based material is at least one of a pure silicon material, a silica material and a silicon alloy material.

6. Silicon-based anode material according to any of claims 1 to 5, characterized in that the silicon-based material has an average particle size D50 of 1 to 20 μm, preferably 5 to 7 μm.

7. The silicon-based anode material according to any one of claims 1 to 6, wherein the mass of the carbon layer accounts for 2.5 to 8.0 wt% of the total mass of the silicon-based anode material, the mass of the carbon nanotubes accounts for 0.5 to 2.0 wt% of the total mass of the silicon-based anode material, and the thickness of the polymer layer is 15 to 30 nm.

8. A method for preparing a silicon-based anode material according to any one of claims 1 to 7, comprising the steps of:

s1, coating a carbon layer on the surface of the silicon-based material to obtain a carbon-coated silicon-based material;

s2, uniformly dispersing a polymer or a polymer monomer in a nonpolar solvent to obtain a polymer modified solution;

s3, uniformly dispersing the carbon-coated silicon-based material in the polymer modification solution, and then filtering, cleaning and drying to obtain a secondary coated silicon-based material;

and S4, adding the secondary coated silicon-based material into the carbon nano tube dispersion liquid, uniformly stirring, and then filtering, cleaning and drying to obtain the carbon nano tube.

9. A lithium ion battery comprising the silicon-based negative electrode material according to any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material and a lithium ion battery containing the same.

Background

Silicon-based anode materials are considered as one of the alternative products of the existing commercial carbon anode materials, but cannot be commercialized due to the large volume effect in the charge and discharge processes, so that a great deal of modification research is performed by researchers. Based on two aspects of theoretical research and experimental research, the research progress of the silicon-based anode material is summarized, and the research on the novel alloy anode material is expected to be promoted.

In recent years, rapid development in the field of new energy power generation puts new requirements on matched energy storage systems. In the updating and upgrading of energy storage batteries, lithium ion batteries have become an important research field due to various advantages of the lithium ion batteries, and have been practically applied to a large number of energy storage projects to achieve certain results.

The capacity of the lithium ion battery is determined by active lithium ions of a positive electrode material and the lithium-inserting and extracting capacity of a negative electrode material, and the stability of the positive electrode and the negative electrode in various environments determines the performance of the battery and even seriously affects the safety of the battery, so that the performance of the electrode determines the comprehensive performance of the lithium ion battery to a certain extent.

However, the current commercial lithium ion battery cathode material is mainly graphite carbon cathode material, and the theoretical specific capacity is only 372mAh/g (LiC)₆) Further development of lithium ion batteries is severely limited. The silicon-based material is a research system with the highest theoretical specific capacity in the research of negative electrode materials, and the formed alloy is Li_xSi (x ═ 0-4.4), with a theoretical specific capacity of up to 4200mAh/g, is considered an alternative product to carbon negative electrode materials due to its low intercalation potential, low atomic mass, high energy density and high Li mole fraction in Li-Si alloys.

However, silicon anode materials have in the late place failed to achieve a wide range of commercial applications. While having many advantages, silicon anode materials also have several disadvantages. Firstly, the silicon negative electrode material undergoes volume change of more than 300% in the charging and discharging processes, such high volume expansion and shrinkage easily leads to the pulverization of the electrode material, the separation of the electrode material from the contact with the current collector and the electrode conductive network, and the volume change brings about the generation of new surfaces, so that a new solid-electrolyte interface (SEI) needs to be formed, thereby leading to the large consumption of the electrolyte and further leading to the substantial reduction of the cycle life. On the other hand, the electrical conductivity and lithium ion diffusion speed of silicon are lower than those of graphite, which limits the performance of silicon under high-current and high-power conditions.

The material mainly utilizes the gaps among graphite to embed nano silicon. Graphite, being a relatively "soft" graphite, can greatly buffer the expansion of silicon particles, and the first active lithium ions consumed are primarily required to generate SEI, so its coulombic efficiency is also in a marginally acceptable range. However, in order to buffer the expansion of nano-silicon and graphite, the compaction density of the material is relatively low, which results in the reduction of the volume energy density of the cell. More seriously, because the expansion of silicon is more than 300%, and the normal graphite expansion is about 10%, after the composite material undergoes expansion and contraction due to charging and discharging, the graphite is difficult to restore to the original state (namely the graphite and the silicon are converted from the initial surface contact into point contact), so that the nano silicon loses electric contact and is deactivated, which is one of the reasons that the cycle decay of the silicon-carbon material is fast.

At present, the mainstream commercial silicon oxide composite negative electrode material is generally coated with carbon, so that on one hand, the conductivity of the material is improved, and simultaneously, the silicon oxide material is prevented from directly contacting with electrolyte, and the cycle performance of the material is improved. The large-scale application of the silicon-based negative electrode material still faces a lot of tests, the cycle performance of the material is further improved, the production cost is reduced, and the majority of scientific researchers and manufacturers still pay great attention and great distance.

Disclosure of Invention

The invention aims to solve the problems of electronic contact caused by expansion of the conventional silicon-based negative electrode material in a lithium ion battery and SEI (solid electrolyte interphase) cracking in the expansion process, and provides a silicon-based negative electrode material suitable for the lithium ion battery and a corresponding lithium ion battery.

The invention provides a silicon-based negative electrode material, which comprises the following components:

a silicon-based material;

the surface of the carbon layer contains hydroxyl, and the carbon layer is coated on the surface of the silicon-based material;

a polymer layer, wherein the polymer layer comprises polymers and/or polymer monomers which can be bonded with hydroxyl, and the polymer layer coats the surface of the carbon layer;

and the carbon nano tube is connected to the surface of the polymer layer through a hydrogen bond and/or a covalent bond.

Preferably, the surface of the carbon nanotubes has reactive groups that can form hydrogen and/or covalent bonds with components of the polymer layer; preferably, the active group is at least one of amino, carboxyl, hydroxyl, ester, unsaturated double bond and unsaturated triple bond.

Preferably, the carbon nanotubes are single-walled carbon nanotubes, multi-walled carbon nanotubes, or a combination thereof.

Preferably, the polymer layer is composed of a polymer or a polymer monomer, the polymer or polymer monomer including at least one of dimethylacrylamide, aniline, thiophene, pyrrole, polydimethylsiloxane, methyl methacrylate, ethyl acrylate, butyl acrylate, hydroxyethyl acrylate, acrylamide, maleic anhydride, sodium p-vinylbenzene sulfonate, sodium allyl sulfonate, vinyl acetate, isooctyl acrylate, perfluoropolyether derivatives; preferably, the perfluoropolyether derivative is PFPE-OH, PFPE-COOH, or PFPE-Si.

Preferably, the silicon-based material is at least one of a pure silicon material, a silicon oxide material and a silicon alloy material.

Preferably, the silicon-based material has an average particle size D50 of 1 to 20 μm, preferably 5 to 7 μm.

Preferably, the mass of the carbon layer accounts for 2.5-8.0 wt% of the total mass of the silicon-based anode material, the mass of the carbon nano tube accounts for 0.5-2.0 wt% of the total mass of the silicon-based anode material, and the thickness of the polymer layer is 15-30 nm.

The preparation method of the silicon-based anode material comprises the following steps:

s1, coating a carbon layer on the surface of the silicon-based material to obtain a carbon-coated silicon-based material;

s2, uniformly dispersing the polymer and/or the polymer monomer in a nonpolar solvent to obtain a polymer modified solution;

s3, uniformly dispersing the carbon-coated silicon-based material in the polymer modification solution, and then filtering, cleaning and drying to obtain a secondary coated silicon-based material;

and S4, adding the secondary coated silicon-based material into the carbon nano tube dispersion liquid, uniformly stirring, and then filtering, cleaning and drying to obtain the carbon nano tube.

Preferably, the method for coating the carbon layer on the silicon-based surface comprises a solid phase method, a liquid phase method and a gas phase method.

Preferably, when the carbon layer is coated on the silicon-based surface by a liquid phase method, the carbon source is pitch, citric acid, monosaccharide, disaccharide, polysaccharide, saccharide derivative, polyimide, polyacrylonitrile, polystyrene, polydivinylbenzene, polyvinylpyridine, polypyrrole, polythiophene, polyaniline and a mixture or copolymer thereof.

Preferably, when the carbon layer is coated on the silicon-based surface by a vapor phase method, the carbon source is at least one of methane, ethane, propane, ethylene, propylene, acetylene, methanol and ethanol.

Preferably, the non-polar solvent is an alkane solvent, a hydrofluoroether solvent, or a combination thereof.

Preferably, the carbon nanotube dispersion is obtained by uniformly dispersing the carbon nanotubes in a solvent, wherein the solvent is water, an organic solvent or a combination thereof.

A lithium ion battery comprises the silicon-based negative electrode material.

The invention has the following beneficial effects:

the invention designs and manufactures a functionalized silicon-based negative electrode material and a lithium ion battery. The method is characterized in that a carbon layer is uniformly coated on the surface of a silicon-based material, wherein the surface of the carbon layer has defects and contains hydroxyl groups, then a polymer layer is coated on the surface of the carbon layer, and the components of the polymer layer comprise polymers and/or polymer monomers which can be bonded with the hydroxyl groups, so that the polymer layer has functional groups (such as carboxyl groups) which can be bonded with the hydroxyl groups, on one hand, acting force can be formed between the functional groups and the hydroxyl groups on the surface of the carbon layer so as to coat the surface of the carbon layer, and on the other hand, covalent bonds, hydrogen bonds and the like can be formed between the functional groups and carbon nanotubes with active groups on the. The carbon coating can ensure the rapid migration of electrons and ions in the process of lithium desorption and insertion; the polymer layer has elasticity, can buffer severe volume expansion of the silicon negative electrode material in the charging and discharging processes, and simultaneously isolates electrolyte to prevent the repeated generation of SEI; the carbon nano tube modified by covalent bonds, hydrogen bonds and the like can ensure the connection between material particles in a severe volume expansion process and maintain the stability of an electronic channel. And because of having good conductive action, can get rid of the use of conductive carbon in the processing procedure of electric core. The addition of the silicon-based negative electrode material can greatly reduce the silicon material which is lost in contact with the lithium ion battery of the silicon negative electrode due to expansion in the early period of circulation, thereby improving the rapid attenuation tendency (especially the silicon protoxide negative electrode) in the early period of circulation. The method has the advantages of low production cost, high production safety, convenient operation and easy large-scale mass production and use.

Drawings

Fig. 1 is a schematic diagram of one structure of a silicon-based anode material provided by the invention.

Fig. 2 is a comparison graph of battery cycle curves of a lithium ion battery assembled by the silicon-based negative electrode material of example 1 of the present invention and a lithium ion battery assembled by the commercial silicon negative electrode material of comparative example 1.

Fig. 3 is a surface topography of a commercially available silicon-based negative electrode material used in comparative example 1 after battery cycling.

Fig. 4 is a surface topography of the silicon-based negative electrode material prepared in embodiment 1 after battery cycling.

Detailed Description

The technical solution of the present invention will be described in detail below with reference to specific examples.