CN110690433B - Silicon-based negative electrode material for lithium ion battery and preparation method thereof - Google Patents
Silicon-based negative electrode material for lithium ion battery and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a silicon-based negative electrode material for a lithium ion battery and a preparation method thereof, belonging to the technical field of lithium ion batteries. The silicon-based negative electrode material for the lithium ion battery sequentially comprises from inside to outside: a silicon-based composite material, a carbon nanomaterial coating layer and a polymer coating layer; the mass ratio of the polymer coating layer to the silicon-based composite material is 0.05-0.4: 1, and the mass ratio of the carbon nano material coating layer to the silicon-based composite material is 0.001-0.1: 1. The silicon-based composite material is prepared from raw materials such as a silicon-based composite material, a polymer, a carbon nano material and the like by a one-step coating method or a multi-step coating method. The silicon-based negative electrode material can effectively release stress generated by volume expansion under extremely high pole piece compaction density, has excellent processing performance, and can effectively improve the cycle performance and energy density of a battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a silicon-based negative electrode material for a lithium ion battery and a preparation method thereof.
Background
The lithium ion battery has the characteristics of high energy density, long service life, no pollution, excellent storage performance and the like, and thus becomes a preferred battery system for 3C products, electric automobiles and large-scale energy storage equipment. At present, graphite carbon-based negative electrode materials widely used by lithium ion batteries have low capacity and cannot meet the requirements of high-performance lithium ion battery negative electrodes. The theoretical capacity of the silicon material is up to 4200mAh/g, and the silicon material has the advantages of low potential, stable and long platform discharge, high safety performance, environmental friendliness, no pollution and the like, and is considered to be one of the most commercialized high-energy-density negative electrode materials in the market. However, silicon serving as a lithium ion battery cathode material has large volume expansion and contraction in the charging and discharging processes, so that silicon particles are easily crushed to destroy the structure, a conductive network is influenced to reduce the conductivity, and an exposed fresh silicon interface continuously consumes electrolyte to form a new SEI film, so that the performance of the battery is rapidly reduced.
Chinese patent inventions CN103474667A, CN102394287A, CN103474667A, CN103367727A and the like compound nano silicon-based materials and buffer base materials such as carbon materials and the like in different modes, and then coat the surface with a carbon layer. The methods inhibit the volume expansion of silicon in the process of lithium intercalation and deintercalation to a certain extent and improve the performance of the silicon. However, the above improvement means only considers the performance improvement of the material, and the influence on the performance of the electrode made of the material is not considered. The contact between the silicon-based materials after the pole piece is rolled is very tight, but due to the intrinsic volume expansion of the silicon-based materials, stress can be generated in the charging and discharging process to cause irreversible separation among the particles, so that the pole piece wrinkles and the binding agent fails to cause the falling of active substances and the damage of a conductive network, and the cycle performance of the pole piece and the battery cell is seriously influenced.
The Chinese patent CN109830673A forms a certain cavity between the silicon particles and the carbon coating layer, so that a space is reserved for silicon expansion in the electrochemical process, and the service life and the safety of the material are improved. But due to the existence of the cavity structure, the processing performance and the compaction density of the pole piece of the material are greatly limited, so that the capacity and the energy density of the pole piece and the battery cell are seriously influenced.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention aims to provide a silicon-based negative electrode material for a lithium ion battery and a preparation method thereof.
In order to solve the problems, the technical scheme adopted by the invention is as follows:
a silicon-based negative electrode material for a lithium ion battery sequentially comprises the following components from inside to outside: a silicon-based composite material, a carbon nanomaterial coating layer and a polymer coating layer; the mass ratio of the polymer coating layer to the silicon-based composite material is 0.05-0.4: 1, and the mass ratio of the carbon nano material coating layer to the silicon-based composite material is 0.001-0.1: 1.
As a preferred embodiment of the invention, the silicon-based composite material is silicon-based particles coated with carbon, and the silicon-based particles are silicon or SiOXOr a mixture of the two; wherein x is more than 0 and less than or equal to 1.
In a preferred embodiment of the present invention, the carbon nanomaterial coating layer is one or a mixture of two or more of carbon nanotubes, graphene, and carbon nanofibers.
In a preferred embodiment of the present invention, the polymer coating layer is one or a mixture of two or more of solid olefinic acid ester compounds, solid carbonic acid ester compounds, solid acetic acid ester compounds, solid carboxylic acid ester compounds and solid oxalic acid ester compounds which are soluble in the electrolyte of the lithium ion battery.
Further preferably, the polymer coating includes, but is not limited to: polymethyl methacrylate and derivatives thereof, cyclic glycerol carbonate derivatives, cyclic glycerol sulfite derivatives, triphosgene and derivatives thereof.
The silicon-based negative electrode material also comprises a binder, wherein the mass ratio of the binder to the silicon-based composite material is 0.001-0.01: 1; the binder is one or a mixture of more than two of polytetrafluoroethylene, styrene butadiene rubber, sodium carboxymethylcellulose and polyvinylidene fluoride.
The invention also provides a preparation method of the silicon-based negative electrode material for the lithium ion battery, which comprises the following steps:
1) dispersing a carbon nano material and a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution; wherein the mass percentage of the polymer and the solvent is 5-20%;
2) putting the silicon-based composite material into a fluidized bed, pumping the mixed solution prepared in the step 1) into the fluidized bed for reaction at a speed of 0.1g/min-100g/min, and obtaining the silicon-based negative electrode material after the reaction is finished.
Preferably, the mass percentage of the carbon nanomaterial in the solvent in the step 1) is 1%, and the mass percentage of the polymer in the solvent is 10%.
The invention also provides another preparation method of the silicon-based negative electrode material for the lithium ion battery, which comprises the following steps:
1) coating a carbon nano material coating layer on the surface of the silicon-based composite material;
2) dissolving a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution, wherein the mass percent of the polymer is 5-20%;
3) placing the silicon-based composite material prepared in the step 1) into a fluidized bed, pumping the mixed solution prepared in the step 2) into the fluidized bed for reaction at a speed of 0.1g/min-100g/min, and obtaining the silicon-based negative electrode material after the reaction is finished.
As a preferred embodiment of the present invention, the carbon nanomaterial coating layer in step 1) is formed by coating a carbon nanomaterial on the surface of the silicon-based composite material by a ball milling method, a fluidized bed coating method, or a chemical vapor deposition method.
Further, when the carbon nanomaterial coating layer is coated by a ball milling method or a fluidized bed coating method, the carbon nanomaterial, the binder and N-methylpyrrolidone or deionized water are mixed and then coated on the surface of the silicon-based composite material.
Compared with the prior art, the invention has the beneficial effects that:
the silicon-based negative electrode material for the lithium ion battery is prepared by coating a carbon nano material on the surface of a silicon-based composite material and then coating a polymer which can be dissolved in an electrolyte solvent, wherein the polymer coating layer occupies a certain volume space in a pole piece made of the silicon-based negative electrode material; after the battery core is assembled and is filled with electrolyte, the polymer coating is dissolved by the electrolyte, and the occupied area of the polymer coating can provide space required by expansion for the silicon-based material in the charging and discharging processes, so that the stress generated by volume expansion can be effectively released, and the contact stress with surrounding particles is relieved; meanwhile, the carbon nano material coated on the surface can still keep physical contact with peripheral particles after the polymer coating is ablated, so that the integrity of the conductive network and the adhesive network is maintained, and the electrochemical performance of the battery cell is improved.
The preparation method of the invention innovatively applies the in-situ self-ablation technology to the field of lithium ion battery cathode materials, provides an expansion space for the silicon-based materials in the battery cell and maintains the integrity of the adhesive network and the conductive network, and has good application prospect in the production aspect of the silicon-based materials.
Detailed Description
The present invention will be described in further detail with reference to specific embodiments.
A silicon-based negative electrode material for a lithium ion battery sequentially comprises the following components from inside to outside: a silicon-based composite material, a carbon nanomaterial coating layer and a polymer coating layer; wherein the mass ratio of the polymer coating layer to the silicon-based composite material is 0.05-0.4: 1, and the mass ratio of the carbon nano material coating layer to the silicon-based composite material is 0.001-0.1: 1.
In the formula, the silicon-based composite material is silicon-based particles coated with carbon, and the silicon-based particles are silicon or SiOX(x is more than 0 and less than or equal to 1) or a mixture of the two. The carbon nano material coating layer is one or a mixture of more than two of carbon nano tubes, graphene and carbon nano fibers. The polymer coating layer is one or a mixture of more than two of solid olefine acid ester compounds, solid carbonate compounds, solid acetate compounds, solid carboxylate compounds and solid oxalate compounds which can be dissolved in the lithium ion battery electrolyte. Further preferably, the polymer coating includes, but is not limited to: polymethyl methacrylate and derivatives thereof, cyclic glycerol carbonate derivatives, cyclic glycerol sulfite derivatives, triphosgene and derivatives thereof.
Further, the silicon-based negative electrode material also comprises a binder, wherein the mass ratio of the binder to the silicon-based composite material is 0.001-0.01: 1; the binder is one or a mixture of more than two of polytetrafluoroethylene, styrene butadiene rubber, sodium carboxymethylcellulose, polyvinylidene fluoride and sodium alginate.
The preparation method of the silicon-based negative electrode material for the lithium ion battery can adopt the following two methods for preparation:
one-step coating method
1) Dispersing a carbon nano material and a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution; wherein the mass percentage of the polymer and the solvent is 5-20%; preferably, the mass percentage of the carbon nano material in the solvent is 1%, and the mass percentage of the polymer in the solvent is 10%;
2) putting the silicon-based composite material into a fluidized bed, pumping the mixed solution prepared in the step 1) into the fluidized bed for reaction at a speed of 0.1g/min-100g/min, and obtaining the silicon-based negative electrode material after the reaction is finished.
Two-step and multi-step coating method
1) Coating a carbon nano material coating layer on the surface of the silicon-based composite material, and specifically adopting the following three methods for coating:
A. ball milling method:
mixing the silicon-based composite material, the carbon nano material, the binder polyvinylidene fluoride and the N-methyl pyrrolidone, then carrying out ball milling, taking out, drying, grinding and crushing. Wherein the mass ratio of the silicon-based composite material to the N-methyl pyrrolidone is 1: 0.5 to 3.
Or mixing the silicon-based composite material, the carbon nano material, the binder and the deionized water, then carrying out ball milling, taking out, drying, grinding and crushing. Wherein the mass ratio of the silicon-based composite material to the deionized water is 1: 0.5 to 3.
B. Fluidized bed coating method:
and (2) placing the silicon-based composite material in a fluidized bed, pumping the carbon nano material and the N-methyl pyrrolidone solution of the polyvinylidene fluoride binder into the fluidized bed for reaction, taking out the silicon-based composite material after the reaction is finished, drying the silicon-based composite material, and grinding and crushing the silicon-based composite material. Wherein the mass ratio of the silicon-based composite material to the N-methyl pyrrolidone is 1: 0.5 to 3.
Or the silicon-based composite material is placed in a fluidized bed, the deionized water solution of the carbon nano material and the binder is pumped into the fluidized bed for reaction, and the mixture is taken out after the reaction is finished and dried, and then is ground and crushed. Wherein the mass ratio of the silicon-based composite material to the deionized water is 1: 0.5 to 3.
C. Chemical vapor deposition method: and (3) placing the silicon-based composite material in a chemical vapor deposition furnace for growing the carbon nano material, taking out, grinding and crushing.
2) Dissolving a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution, wherein the mass percent of the polymer is 5-20%; preferably, the mass percentage of the polymer is 10%;
3) placing the silicon-based composite material prepared in the step 1) into a fluidized bed, pumping the mixed solution prepared in the step 2) into the fluidized bed for reaction at the speed of 0.1-100 g/min, wherein the air inlet temperature is 60-200 ℃, and obtaining the silicon-based negative electrode material after the reaction is finished.
Example 1
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material, 0.5g of polyvinylidene fluoride and 0.5g of carbon nano tube into a ball milling tank containing 250g of N-methylpyrrolidone, uniformly stirring, taking out, drying, and grinding and crushing to obtain the silicon-based composite material with the carbon nano tube coating layer on the surface;
B. b, adding the silicon-based composite material prepared in the step A into a cavity of a fluidized bed;
C. adding 125g of polymethyl methacrylate into 1250g of dimethyl carbonate, and stirring until the solid is completely dissolved;
D. and D, pumping the polymethyl methacrylate solution prepared in the step C into a fluidized bed at the speed of 80g/min, and obtaining the silicon-based negative electrode material with the surface coated with the polymethyl methacrylate after the reaction is finished.
Example 2
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material into a cavity of a fluidized bed;
B. adding 5g of sodium carboxymethylcellulose, 50g of carbon nanotube and graphene mixture into 1500g of deionized water, uniformly stirring, pumping into a fluidized bed at the speed of 50g/min, controlling the air inlet temperature at 200 ℃, taking out a sample after the reaction is finished, and crushing to obtain a silicon-based composite material with the surface coated with the carbon nanotube and graphene mixture;
C. b, adding the silicon-based composite material obtained in the step B into a cavity of a fluidized bed;
D. adding 200g of bis (2, 3-cyclic carbonate glycerol) carbonate into 4000g of ethylene carbonate, and stirring until the solid is completely dissolved;
E. and D, pumping the bis (2, 3-cyclic carbonate glyceride) carbonate solution prepared in the step D into a fluidized bed at the speed of 100g/min, and obtaining the silicon-based negative electrode material with the surface coated with the bis (2, 3-cyclic carbonate glyceride) carbonate after the reaction is finished.
Example 3
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of the silicon-based composite material into an ethanol solution of nickel nitrate, uniformly mixing, drying and grinding; then placing the carbon nano fiber in a chemical vapor deposition furnace for growing the carbon nano fiber; cooling to room temperature after the reaction is finished, taking out and grinding to obtain the silicon-based composite material with the carbon nano material coating layer on the surface;
B. b, adding the silicon-based composite material prepared in the step A into a cavity of a fluidized bed;
C. adding 25g of tetra (1, 2-cyclosulfidic acid glyceride) pyromellitic acid ester into 125g of mixed solution of ethylene carbonate and dimethyl carbonate, and stirring until the solid is completely dissolved;
D. and D, pumping the tetra (1, 2-cyclosulfidic glyceride) pyromellitic acid ester solution prepared in the step C into a fluidized bed at the speed of 60g/min, and obtaining the silicon-based negative electrode material with the surface coated with the tetra (1, 2-cyclosulfidic glyceride) pyromellitic acid ester after the reaction is finished.
Example 4
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material into a cavity of a fluidized bed;
B. adding 40g of a mixture of the carbon nano tube and the graphene and 150g of bis (2, 3-cyclic glycerol carbonate) oxalate into 2000g of ethylene carbonate, and fully mixing;
C. and D, pumping the mixed solution prepared in the step B into a fluidized bed at the speed of 90g/min, and obtaining the silicon-based negative electrode material with the surface coated with the carbon nano tube, the graphene and the bis (2, 3-cyclic carbon glyceride) oxalate after the reaction is finished.
Example 5
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material, 0.5g of butadiene styrene rubber and 0.5g of carbon nanotubes into a ball milling tank containing 1500g of deionized water, uniformly stirring, taking out, drying, and grinding and crushing to obtain the silicon-based composite material with the carbon nanotube coating on the surface;
B. b, adding the silicon-based composite material prepared in the step A into a cavity of a fluidized bed;
C. adding 125g of polymethyl methacrylate into 1250g of dimethyl carbonate, and stirring until the solid is completely dissolved;
D. and D, pumping the polymethyl methacrylate solution prepared in the step C into a fluidized bed at the speed of 80g/min, and obtaining the silicon-based negative electrode material with the surface coated with the polymethyl methacrylate after the reaction is finished.
Example 6
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material into a cavity of a fluidized bed;
B. adding 5g of polyvinylidene fluoride and 10g of graphene into 250g N-methyl pyrrolidone, uniformly stirring, pumping into a fluidized bed at the speed of 50g/min, controlling the air inlet temperature at 100 ℃, taking out a sample after the reaction is finished, and crushing to obtain a silicon-based composite material with the surface coated with the graphene mixture;
C. b, adding the silicon-based composite material obtained in the step B into a cavity of a fluidized bed;
D. adding 200g of bis (2, 3-cyclic carbonate glycerol) carbonate into 4000g of ethylene carbonate, and stirring until the solid is completely dissolved;
E. and D, pumping the bis (2, 3-cyclic carbonate glyceride) carbonate solution prepared in the step D into a fluidized bed at the speed of 100g/min, and obtaining the silicon-based negative electrode material with the surface coated with the bis (2, 3-cyclic carbonate glyceride) carbonate after the reaction is finished.
Example 7
A preparation method of a silicon-based negative electrode material for a lithium ion battery comprises the following steps:
A. adding 500g of silicon-based composite material, 0.5g of sodium alginate and 0.5g of carbon nano tube into a ball milling tank containing 1500g of deionized water, uniformly stirring, taking out, drying, and grinding and crushing to obtain the silicon-based composite material with the carbon nano tube coating on the surface;
B. b, adding the silicon-based composite material prepared in the step A into a cavity of a fluidized bed;
C. adding 125g of polymethyl methacrylate into 1250g of dimethyl carbonate, and stirring until the solid is completely dissolved;
D. and D, pumping the polymethyl methacrylate solution prepared in the step C into a fluidized bed at the speed of 80g/min, and obtaining the silicon-based negative electrode material with the surface coated with the polymethyl methacrylate after the reaction is finished.
Comparative example 1
The silicon-based composite body used in example 1 was used as comparative example 1, which was a sample before improvement.
And (3) performance verification:
the silicon-based negative electrode materials of the lithium ion battery prepared in the seven embodiments and the silicon-based composite material of the comparative example 1 are respectively manufactured into pole pieces and used as working electrodes, and LiPF is used6The button cell is assembled by using/DMC + EC + DEC (1: 1: 1) as electrolyte, the charging and discharging cut-off voltage is 0.01-1.5V, the charging and discharging are carried out by using 100mA/g constant current, the first charging specific capacity, the first coulombic efficiency and the 50-cycle retention rate are measured, and the results are shown in table 1.
TABLE 1 comparison of initial specific charge capacity, initial coulombic efficiency, 50 cycle retention
| Specific capacity for first charge (mAh/g) | First coulombic efficiency (%) | 50-week cycle maintenance (%) | |
| Example 1 | 1350 | 61 | 70 |
| Example 2 | 1676 | 74 | 77 |
| Example 3 | 1349 | 62 | 71 |
| Example 4 | 1674 | 73 | 74 |
| Example 5 | 1346 | 62 | 71 |
| Example 6 | 1673 | 75 | 76 |
| Example 7 | 1350 | 61 | 69 |
| Comparative example 1 | 1345 | 61 | 18 |
As can be seen from table 1, compared with the silicon-based composite material which is not coated with the in-situ self-ablation coating layer in comparative example 1, the cycle retention rate of the silicon-based negative electrode material prepared in the four embodiments of the present invention is greatly improved, which indicates that the polymer coating layer of the present invention is dissolved by the electrolyte after being assembled into a battery cell and injected with the electrolyte, and the occupied area of the polymer coating layer can provide a space required for expansion of the silicon-based composite material during the charging and discharging processes, effectively release the stress generated by volume expansion, and alleviate the contact stress with surrounding particles.
The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.
Claims (9)
1. A silicon-based negative electrode material for a lithium ion battery is characterized in that: comprises the following components in sequence from inside to outside: a silicon-based composite material, a carbon nanomaterial coating layer and a polymer coating layer; wherein the mass ratio of the polymer coating layer to the silicon-based composite material is 0.05-0.4: 1, and the mass ratio of the carbon nano material coating layer to the silicon-based composite material is 0.001-0.1: 1; the silicon-based composite material is silicon-based particles coated with carbon, and the silicon-based particles are silicon or SiOXOr a mixture of the two, wherein x is more than 0 and less than or equal to 1; the polymer coating layer is a polymer which can be dissolved in the electrolyte of the lithium ion battery.
2. The silicon-based negative electrode material for the lithium ion battery as claimed in claim 1, wherein: the carbon nano material coating layer is one or a mixture of more than two of carbon nano tubes, graphene and carbon nano fibers.
3. The silicon-based negative electrode material for the lithium ion battery as claimed in claim 1, wherein: the polymer coating layer is one or a mixture of more than two of solid olefine acid ester compounds, solid carbonate compounds, solid acetate compounds, solid carboxylate compounds and solid oxalate compounds which can be dissolved in the lithium ion battery electrolyte.
4. The silicon-based negative electrode material for the lithium ion battery as claimed in claim 3, wherein: the polymer coating includes, but is not limited to: polymethyl methacrylate and derivatives thereof, cyclic glycerol carbonate derivatives, cyclic glycerol sulfite derivatives, triphosgene and derivatives thereof.
5. The silicon-based negative electrode material for the lithium ion battery according to any one of claims 1 to 4, wherein: the adhesive is also included, and the mass ratio of the adhesive to the silicon-based composite material is 0.001-0.01: 1; the binder is one or a mixture of more than two of polytetrafluoroethylene, styrene butadiene rubber, sodium carboxymethylcellulose and polyvinylidene fluoride.
6. A preparation method of the silicon-based negative electrode material for the lithium ion battery as claimed in any one of claims 1 to 5, characterized by comprising the following steps: the method comprises the following steps:
1) dispersing a carbon nano material and a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution; wherein the mass percentage of the polymer and the solvent is 5-20%;
2) putting the silicon-based composite material into a fluidized bed, pumping the mixed solution prepared in the step 1) into the fluidized bed for reaction at a speed of 0.1g/min-100g/min, and obtaining the silicon-based negative electrode material after the reaction is finished.
7. A preparation method of the silicon-based negative electrode material for the lithium ion battery as claimed in any one of claims 1 to 5, characterized by comprising the following steps: the method comprises the following steps:
1) coating a carbon nano material coating layer on the surface of the silicon-based composite material;
2) dissolving a polymer in a solvent of a lithium ion battery electrolyte to prepare a mixed solution, wherein the mass percent of the polymer is 5-20%;
3) placing the silicon-based composite material prepared in the step 1) into a fluidized bed, pumping the mixed solution prepared in the step 2) into the fluidized bed for reaction at a speed of 0.1g/min-100g/min, and obtaining the silicon-based negative electrode material after the reaction is finished.
8. The method for preparing the silicon-based negative electrode material for the lithium ion battery according to claim 7, wherein the method comprises the following steps: the carbon nano material coating layer in the step 1) is formed by coating the carbon nano material on the surface of the silicon-based composite material by a ball milling method, a fluidized bed coating method or a chemical vapor deposition method.
9. The method for preparing a silicon-based negative electrode material for a lithium ion battery according to claim 8, wherein the method comprises the following steps: when the carbon nano material coating layer is coated by adopting a ball milling method or a fluidized bed coating method, the carbon nano material, the adhesive and the N-methyl pyrrolidone or the deionized water are mixed and then coated on the surface of the silicon-based composite material.
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