阅读说明：本技术 一种硅碳负极材料、锂离子电池负极及锂离子电池 (Silicon-carbon negative electrode material, lithium ion battery negative electrode and lithium ion battery ) 是由 薛旭金 罗传军 孙永明 王永勤 薛峰峰 刘海霞 郭贤慧 李洁 王菲菲 许胜霞 于 2018-08-02 设计创作，主要内容包括：本发明涉及一种硅碳负极材料、锂离子电池负极及锂离子电池。该硅碳负极材料的制备包括：1)将纳米硅和碳源物质球磨混合,经煅烧后制备硅基复合材料；2)将硅基复合材料于可溶性碳源溶液中分散均匀,干燥除去溶剂后,得到包覆复合材料；3)将包覆复合材料煅烧,得到碳包覆多级复合材料；4)将碳包覆多级复合材料和碳材料于糖类水溶液中分散均匀,干燥除去溶剂。本发明通过多次硅碳复合过程制备多级硅碳复合材料,进而提高硅碳负极的结构稳定性和导电性。因多级硅碳复合结构的存在,该硅碳负极材料具有高比表面积,有利于电解液和负极材料的充分接触和锂离子的快速交换,可以为锂离子电池电化学性能的发挥提供优良条件。(The invention relates to a silicon-carbon negative electrode material, a lithium ion battery negative electrode and a lithium ion battery. The preparation method of the silicon-carbon negative electrode material comprises the following steps: 1) ball-milling and mixing nano silicon and carbon source substances, and calcining to prepare the silicon-based composite material; 2) uniformly dispersing the silicon-based composite material in a soluble carbon source solution, and drying to remove the solvent to obtain a coated composite material; 3) calcining the coated composite material to obtain a carbon-coated multistage composite material; 4) the carbon-coated multistage composite material and the carbon material are uniformly dispersed in a carbohydrate water solution, and the solvent is removed by drying. According to the invention, the multilevel silicon-carbon composite material is prepared through multiple silicon-carbon composite processes, so that the structural stability and the conductivity of the silicon-carbon cathode are improved. Due to the existence of the multi-stage silicon-carbon composite structure, the silicon-carbon negative electrode material has high specific surface area, is beneficial to full contact between electrolyte and the negative electrode material and quick exchange of lithium ions, and can provide excellent conditions for the exertion of the electrochemical performance of the lithium ion battery.)

1. The silicon-carbon negative electrode material is characterized by being prepared by the following steps:

1) ball-milling and mixing nano silicon and carbon source substances, and calcining to prepare the silicon-based composite material;

2) uniformly dispersing the silicon-based composite material in a soluble carbon source solution, and drying to remove the solvent to obtain a coated composite material;

3) calcining the coated composite material in a protective atmosphere to obtain a carbon-coated multistage composite material;

4) and (3) uniformly dispersing the carbon-coated multistage composite material and the carbon material in a carbohydrate water solution, and drying to remove the solvent to obtain the carbon-coated multistage composite material.

2. The silicon-carbon anode material of claim 1, wherein in the step 1), the nano-silicon is at least one of hollow silicon nanospheres, silicon nanowires, silicon nanotubes, silicon nanofilms and porous silicon.

3. The silicon-carbon anode material according to claim 1, wherein the carbon source substance in step 1) comprises a carbon material and/or a pyrolytic carbon material.

4. The silicon-carbon anode material of claim 1, wherein in step 2), the soluble carbon source solution is an aqueous solution of a saccharide.

5. The silicon-carbon anode material as claimed in claim 1, wherein in the step 2), a nitrogen source substance is further added during the dispersion process.

6. The silicon-carbon anode material as claimed in claim 1 or 5, wherein in the step 2), a surfactant is further added during the dispersion process.

7. The silicon-carbon negative electrode material of claim 6, wherein the surfactant is at least one of sodium dodecylbenzene sulfonate, sodium cocoyl oxyethyl sulfonate, sodium diisooctyl succinate sulfonate, sodium p-methoxyfatty amido benzene sulfonate, cetyltrimethylammonium bromide, sodium alkyl benzene sulfonate, ammonium alkyl benzene sulfonate, sodium lignin sulfonate, ammonium lignin sulfonate, and dicetyl calcium phosphate.

8. The silicon-carbon anode material as claimed in claim 1, wherein in the step 4), the saccharide used in the aqueous saccharide solution is at least one of fructose, sucrose and glucose.

9. A lithium ion battery negative electrode using the silicon-carbon negative electrode material according to claim 1.

10. A lithium ion battery using the lithium ion battery negative electrode according to claim 9.

Technical Field

The invention belongs to the field of lithium ion battery cathode materials, and particularly relates to a silicon-carbon cathode material, a lithium ion battery cathode and a lithium ion battery.

Background

Lithium ion batteries have been widely used in the fields of small portable electronic devices such as mobile phones, notebook computers, digital cameras, and the like, due to their advantages of high capacity, no memory effect, rapid reversible charge and discharge, and the like. At present, a commercial lithium ion battery mainly adopts a graphite negative electrode material, but the theoretical specific capacity of the lithium ion battery is 372mAh/g, and the specific capacity of the conventional graphite negative electrode material is close to the theoretical value of the graphite negative electrode material, so that the development potential of the graphite negative electrode material is limited, and the wide requirements of the current society on the lithium ion battery with high specific energy and high power density are difficult to meet.

Due to the high lithium storage capacity (the theoretical specific capacity is 4200mAh/g) and abundant resources, the silicon material is considered to be one of ideal candidate materials for developing a new generation of high specific energy and high power density lithium ion battery negative electrode material. However, the silicon material has a rapid capacity decay during use, so that its practical application is limited. Analysis shows that the silicon material has larger lithium-intercalated volume expansion and contraction (more than 300 percent) and causes material damage and pulverization, which is the main reason for low conductivity and faster capacity decay of the material. Therefore, the volume expansion of the silicon material is inhibited, and the structural stability of the material is improved, so that the significance of improving the conductivity and the cycle stability of the silicon material is great. At present, the volume expansion of a silicon material is mainly improved through the nanocrystallization of silicon, the alloying of silicon and metal, and the compounding of silicon and an active or inactive material, wherein the compounding of silicon and an active substance carbon has a larger application prospect.

The patent application with publication number CN103367727A discloses a silicon-carbon cathode material of a lithium ion battery, which is characterized in that nano-silicon, a dispersant, a binder and granular graphite are mixed in an organic solvent, a composite nano-silicon/graphite polymer is obtained by drying, the composite nano-silicon/graphite polymer is added into a dispersion liquid of a carbon source precursor, the mixture and the drying are carried out, and then the temperature is increased to 600-1150 ℃ for heat treatment, thus obtaining the silicon-carbon cathode material of the lithium ion battery. In the practical application process, the silicon-carbon cathode material has poor structural stability, and the problems of material pulverization, poor electrochemical performance and the like caused by volume expansion of the silicon-carbon cathode material cannot be effectively relieved.

Disclosure of Invention

The invention aims to provide a silicon-carbon negative electrode material, so that the problem of poor structural stability of the conventional silicon-carbon negative electrode material is solved.

The invention also provides a lithium ion battery cathode and a lithium ion battery based on the silicon-carbon cathode material.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a silicon-carbon negative electrode material is prepared by the following steps:

1) ball-milling and mixing nano silicon and carbon source substances, and calcining to prepare the silicon-based composite material;

2) uniformly dispersing the silicon-based composite material in a soluble carbon source solution, and drying to remove the solvent to obtain a coated composite material;

3) calcining the coated composite material in a protective atmosphere to obtain a carbon-coated multistage composite material;

4) and (3) uniformly dispersing the carbon-coated multistage composite material and the carbon material in a carbohydrate water solution, and drying to remove the solvent to obtain the carbon-coated multistage composite material.

According to the silicon-carbon negative electrode material provided by the invention, the multilevel silicon-carbon composite material is prepared through multiple silicon-carbon composite processes, so that the structural stability and the electrical conductivity of the silicon-carbon negative electrode are improved, the carbohydrate has a polyhydroxy structure, on one hand, a large ball can be formed to coat the surface of the composite material, the nano silicon is expanded from zero dimension to three dimension to construct a three-dimensional conductive network, so that the good electrical conductivity of carbon is fully exerted, and the charge transmission is rapidly carried out; on the other hand, the polymer can be crosslinked with the binder in the subsequent electrode preparation process, so that the binding force between the binder and the electrode material is improved, and the stable structure of the electrode is further kept.

The silicon-carbon negative electrode material provided by the invention has a high specific surface area due to the existence of a multi-stage silicon-carbon composite structure, is beneficial to full contact between electrolyte and the negative electrode material and rapid exchange of lithium ions, and can provide good conditions for the exertion of the electrochemical performance of a battery.

In the step 1), the nano-silicon is a silicon nano-material existing in the prior art, and preferably is at least one of hollow silicon nanospheres, silicon nanowires, silicon nanotubes, silicon nano-films and porous silicon in order to optimize the electrode reaction process of silicon.

The carbon source material includes a carbon material and/or a pyrolytic carbon material. The carbon material includes at least one of graphite, carbon nanotube, amorphous carbon, and graphene. The pyrolytic carbon material includes inorganic pyrolytic carbon and/or organic pyrolytic carbon. The inorganic pyrolytic carbon comprises at least one of glucose, sucrose, citric acid, salicylic acid, starch, gluconic acid, sodium gluconate, calcium gluconate, zinc gluconate, sodium acetate, sodium oleate, sodium tartrate, calcium stearate, sodium benzoate, potassium sorbate, sodium citrate, calcium citrate, zinc citrate, lithium citrate, copper citrate and ammonium citrate. The organic pyrolytic carbon comprises at least one of phenolic resin, asphalt, polyaniline and polydopamine. When the carbon material is used as the carbon source substance, the flexible graphite and other materials have obvious buffer effect on the volume expansion of silicon, and a series of problems caused by the volume expansion of the silicon material can be avoided. When the pyrolytic carbon material is used as a carbon source substance, the pyrolytic carbon material is characterized in that the pyrolytic carbon material becomes amorphous carbon in the thermal cracking carbonization process, so that effective carbon coating on silicon particles can be realized, and further the volume expansion of the silicon material is relieved.

In order to improve the multistage composite effect of the silicon-carbon cathode, the mass ratio of the nano silicon to the carbon source substance is preferably (10-30): 1. the ball milling mixing is preferably wet milling mixing, and an organic solvent is added as a milling medium during the wet milling, wherein the organic solvent can be at least one of ethanol, ethyl acetate, N-methylpyrrolidone, chloroform, acetone and diethyl ether. In order to improve the wet grinding effect and optimize the composite quality of silicon and carbon, the rotation speed during ball milling is preferably 300-500r/min, and the time is 3-8 h. Wet grinding, heating and drying to volatilize the organic solvent completely, and calcining the heated and dried solid matter to prepare the silicon-based composite material. The heating drying is drying for 4-6h under the conditions of negative pressure and 60-100 ℃.

The calcining temperature is 600-800 ℃, and the time is 2-6 h. The organic solvent generated by heating and drying can be recycled after being recovered and purified.

When selecting ammonium citrate and the like as carbon source substances, waste gas is generated in the calcining process in the step 1), and the tail gas can be discharged up to the standard or comprehensively utilized by corresponding tail gas treatment means. When the carbon source substance is ammonium citrate, waste gas generated in the calcining process is absorbed by hydrofluoric acid to prepare an ammonium fluoride solution for producing other fluorides.

In step 2), in order to form a more uniform and stable carbon coating layer and improve the coating quality, preferably, the soluble carbon source solution is a saccharide aqueous solution, the saccharide is oligosaccharide and/or polysaccharide, and further preferably, the saccharide is at least one of fructose, sucrose and glucose. The carbohydrate aqueous solution has low cost and certain viscosity, and can form a carbon coating layer with better structural stability. The concentration of the saccharide aqueous solution is 5-15g/L by integrating factors such as cost, silicon-carbon composite quality and the like.

In order to optimize the silicon and carbon composite effect, preferably, the addition amount of each liter of soluble carbon source solution corresponding to the silicon-based composite material is 5-20 g.

In order to further optimize the conductivity of the silicon-carbon cathode and perfect the conductive network of the silicon-carbon cathode, in the step 2), a nitrogen source substance is also added in the dispersing process. Preferably, the nitrogen source substance is at least one of polypyrrole, polyvinylpyrrolidone and polyacryl pyrrole.

In order to further improve the dispersion effect of the silicon-based composite material and the nitrogen source substance and further improve the coating effect of carbon, preferably, a surfactant is also added in the dispersion process. The surfactant is an anionic surfactant, and the anionic surfactant is at least one of sodium dodecyl benzene sulfonate, sodium cocoyl oxyethyl sulfonate, sodium diisooctyl succinate sulfonate, sodium p-methoxy fatty amido benzene sulfonate, cetyl trimethyl ammonium bromide, sodium alkyl benzene sulfonate, ammonium alkyl benzene sulfonate, sodium lignin sulfonate, ammonium lignin sulfonate and dicetyl calcium phosphate.

In the step 2), dispersed slurry is formed after uniform dispersion, and in the dispersed slurry, the mass content of the nitrogen source substance is 3-10%, and the mass content of the surfactant is 0.05-0.2%. The dispersion mode can adopt mixing modes such as manual stirring and mixing, magnetic stirring and mixing, mechanical stirring and mixing, ultrasonic mixing and the like. The drying is carried out for 5-10h under the conditions of negative pressure and 300 ℃ of 100-. Preferably, the drying temperature is 120 ℃, the pressure is-0.1 MPa, and the drying time is 8 h.

In the step 3), the protective atmosphere is one of nitrogen, argon, helium and neon. The calcining temperature is 800-1000 ℃, and the time is 5-10 h. The rate of raising the temperature to 800-1000 ℃ is 1-10 ℃/h, preferably 5 ℃/h.

In the step 4), the saccharide is at least one of fructose, sucrose and glucose. The concentration of the saccharide aqueous solution is 5-15 g/L. In order to further improve the silicon-carbon composite effect, preferably, the addition amount of the carbon-coated multi-stage composite material is 5-30g per liter of the saccharide aqueous solution. The mass ratio of the carbon-coated multistage composite material to the carbon material is (10-20) to (80-90). The carbon material includes at least one of graphite, carbon nanotube, amorphous carbon, graphene.

The uniform dispersion is realized by ultrasonic mixing with the power of 50-100Hz and the time of 1-5 h. The drying is carried out for 10-12h under the conditions of negative pressure and 120 ℃ of 100-.

In order to further form more layers of silicon-carbon composite structures, preferably, step 2) and step 3) are repeated before step 4) is performed. More preferably, the number of repetitions is 1 to 3. The performances of the multi-level silicon-carbon composite structure such as specific surface area, structural stability, conductivity and the like are further optimized, but the corresponding manufacturing cost is increased, and the performance can be flexibly selected according to practical conditions of application scenes, performance requirements and the like of the battery.

A lithium ion battery cathode adopting the silicon-carbon cathode material.

The lithium ion battery cathode comprises a silicon-carbon cathode material, a Super-P carbon black conductive agent and a sodium carboxymethylcellulose binder, wherein the mass ratio of the silicon-carbon cathode material to the Super-P carbon black conductive agent to the sodium carboxymethylcellulose is (7-9): (0.5-1.5): (0.5-1.5). Uniformly dispersing the silicon-carbon negative electrode material, the conductive agent and the binder in a solvent to prepare negative electrode material slurry, coating the negative electrode material slurry on a current collector, and drying to obtain the corresponding lithium ion battery negative electrode.

The lithium ion battery cathode has high liquid absorption rate and good structural stability, has higher specific capacity compared with the conventional lithium ion battery cathode, and can be used for constructing a high-energy-density lithium ion battery.

A lithium ion battery adopting the lithium ion battery cathode.

On the basis of the lithium ion battery cathode, the conventional anode, electrolyte and diaphragm can be selected, and then the lithium ion battery is assembled according to the prior art. The lithium ion battery has high specific capacity, good cycle performance and rate capability and excellent electrochemical performance.

Drawings

Fig. 1 is a process flow diagram of a silicon carbon anode material of example 2 of the present invention;

FIG. 2 is a process flow diagram of a silicon carbon anode material according to example 3 of the present invention;

FIG. 3 is an X-ray diffraction pattern of a silicon carbon negative electrode material of example 1 of the present invention;

fig. 4 is an SEM image of the silicon carbon negative electrode material of example 1 of the present invention.

Detailed Description

The following examples are provided to further illustrate the practice of the invention.