CN114824177A - Preparation method of silicon negative electrode composite pole piece - Google Patents

Abstract

The invention discloses a preparation method of a silicon negative electrode composite pole piece, which relates to the technical field of lithium ion batteries. The resin dispersion is coated on the current collector, and dried to obtain a composite current collector; the silicon negative electrode active material, the superconducting carbon black conductive agent, the single-walled carbon nanotube, and the binder are mixed to obtain a negative electrode slurry, which is coated On the composite current collector, dry to obtain a silicon negative electrode sheet; dissolve the elastic resin in an organic solvent, add the graphene dispersion to it, stir and mix, and then coat it on the silicon negative electrode sheet, dry, and hot-rolled , that is, the silicon anode composite pole piece is obtained. In the present invention, a conductive buffer layer is designed on the current collector in advance, and a graphene-elastic resin layer is designed on the negative pole piece, and the volume change of silicon is suppressed by changing the electrode composition and structure, and its cycle performance is improved.

Description

A kind of preparation method of silicon negative electrode composite pole piece

technical field

The invention relates to the technical field of lithium ion batteries, in particular to a preparation method of a silicon negative electrode composite pole piece.

Background technique

High-capacity anode materials have become one of the goals of lithium-ion battery development, and silicon materials have become one of the research hotspots because of their theoretical specific capacity as high as 4200 mAh·g ^-1 . However, the silicon anode material has a large volume change (>300%) during the electrochemical cycle. This volume change generates large internal stress inside the material and damages the material structure. During the charge-discharge process, this structural expansion/contraction change destroys the electrode structural stability, leading to the collapse of the electrode structure and the rapid decay of the electrochemical performance, resulting in a rapid deterioration of the cycle performance. Therefore, effectively suppressing the structural damage caused by the volume change of silicon and improving its electrochemical cycle performance are urgent problems to be solved in the art. To solve this problem, researchers have done a lot of work, including: introducing other metals or non-metals into silicon materials to form composite materials, preparing nano-structured silicon materials, choosing different binders, and using amorphous silicon materials. etc., have played a positive role in improving the cycle of silicon materials. However, from the current research trend, most of the research work is to improve the performance of silicon materials by changing the structure or composition of the material itself, while the research work on improving the electrochemical performance of silicon by changing the composition and structure of electrodes is relatively small. In fact, whether the electrode composition and structure are reasonable has a very significant effect on the electrochemical performance of the material, and is an important research work in the production of lithium ion batteries.

SUMMARY OF THE INVENTION

Based on the technical problems existing in the background technology, the present invention proposes a preparation method of a silicon negative electrode composite pole piece. By designing a conductive buffer layer on the current collector in advance, and then designing a graphene-elastic resin layer on the negative electrode pole piece, by changing the electrode composition and structure to suppress the volume change of silicon and improve its cycling performance.

The preparation method of a silicon negative electrode composite pole piece proposed by the present invention comprises the following steps:

S1. Dissolve the elastic resin in an organic solvent, add a conductive filler to it, stir and mix to obtain a conductive elastic resin dispersion;

S2, coating the conductive elastic resin dispersion on the current collector, drying to remove the solvent, to obtain a composite current collector;

S3, mixing the silicon negative electrode active material, the superconducting carbon black conductive agent, the single-walled carbon nanotubes, and the binder to obtain a negative electrode slurry, coating the negative electrode slurry on the composite current collector, and drying to obtain a silicon negative electrode pole piece;

S4, dissolve the elastic resin in an organic solvent, add graphene dispersion to it, stir and mix to obtain a graphene elastic resin dispersion; then coat it on the silicon negative electrode sheet, dry, and hot-roll to obtain silicon Negative composite pole piece.

Preferably, the elastic resin is a thermoplastic polyurethane elastomer.

Preferably, in S1, the conductive filler includes any one of carbon black and metal particles; the addition amount of the conductive filler is 3-20 wt % of the mass of the elastic resin.

Preferably, in S2, the current collector includes any one of conductive metal foil, porous current collector, and foam current collector.

Preferably, in S2, the drying temperature is 120-150°C.

Preferably, in S3, the silicon anode material includes any one of elemental silicon, silicon oxide, and silicon-based composite materials.

In the present invention, the mass ratio of the silicon negative electrode active material, the superconducting carbon black conductive agent, the single-walled carbon nanotube, and the binder in the negative electrode slurry is 60-90:5-25:2-6:3-9.

In the present invention, the silicon-based composite material includes silicon carbon material and the like.

Preferably, in S4, the concentration of the elastic resin dissolved in the solvent is 5-25wt%; the concentration of the graphene dispersion is 0.1-0.5mg/mL; the amount of graphene added is 1-10wt% of the mass of the elastic resin .

Preferably, the temperature of the hot rolling is 60-90°C.

The present invention also proposes a silicon negative electrode composite pole piece prepared by the above method.

Compared with the prior art, the beneficial effects of the present invention are embodied in the following aspects:

1. In the present invention, a layer of conductive buffer material composed of elastic resin and conductive filler is coated on the current collector, and the solvent is removed by drying to form micropores in the elastic resin, thereby obtaining a conductive buffer layer on the surface of the current collector. The design of the conductive buffer layer increases the bonding force between the silicon anode active material and the current collector. At the same time, the hot rolling process is used to further strengthen the bonding force, improve the peel strength, and effectively relieve the huge stress caused by the large volume deformation of silicon. The material is not easy to fall off from the current collector, and good electrical contact is maintained; and the current collector includes porous and foamed foil materials, which has a better effect on suppressing the volume expansion of silicon.

2. Coating a layer of graphene-elastic resin material on the silicon negative pole piece, the ultra-high elasticity and self-healing can effectively bind the expansion of silicon, and tightly cover the silicon material in an elastic net; at the same time, graphite The addition of graphene improves the electrical conductivity, thermal conductivity and tensile strength of the TPU material, and the unique two-dimensional large π-conjugated structure of graphene is synergistically enhanced with the polymer elastic resin, which effectively inhibits the volume expansion of silicon.

3. The preparation method of the present invention is simple and easy to implement, and is beneficial to industrialized production.

By changing the composition and structure of the electrode, the invention uses the structure of the electrode itself to suppress the volume change of silicon and improve its cycle performance.

Detailed ways

Hereinafter, the technical solutions of the present invention will be described in detail through specific embodiments.

Example 1

A preparation method of a silicon negative electrode composite pole piece, the steps are as follows:

S1. Dissolve the thermoplastic polyurethane elastomer in N-methylpyrrolidone (NMP) solvent, dissolve at 50° C. for 2 hours, and control the polymer concentration to be 5 wt%; then add aluminum metal conductive filler accounting for 3% of the mass of the thermoplastic polyurethane elastomer, Stir at room temperature for 15 min, and let stand for about 1 h after stirring to eliminate bubbles in the polymer solution; coat the polymer solution on a 9 μm copper foil current collector, the coating thickness is controlled at 2 μm, and dry at 120 °C to remove the solvent. , micropores are formed in the elastic resin, and a composite current collector with a conductive buffer layer is obtained for use.

S2. Mix slurry according to the ratio of silicon: SP: SWCNT: PAA = 60: 25: 6: 9 to obtain a negative electrode slurry, which is then coated on the above composite current collector and dried to obtain the desired silicon negative electrode pole piece ;

S3, adding 0.5mg/mL graphene dispersion to the above-mentioned 5wt% polyurethane solution, the amount of graphene added is 10wt% of the quality of the elastic resin, mixed evenly and coated on the silicon negative pole piece obtained in S2, dried , the desired silicon anode composite pole piece is obtained by hot rolling.

The peel strength test was carried out on the prepared silicon negative electrode composite pole piece. The test results showed that the peeling force was increased from 38N/m of the conventional silicon negative electrode pole piece to 64N/m.

The above-mentioned silicon negative electrode composite electrode sheet, lithium iron phosphate positive electrode sheet, separator, electrolyte and the like are assembled together to form a full battery. To test the cycle life of the full battery, the test step adopts the 1C/1C-100% SOC cycle system, and the final measured battery cycle life is 1000 weeks.

The above-mentioned conventional silicon negative pole piece, that is, the silicon negative pole piece obtained by drying only the synthetic slurry in step S2 is coated on the copper foil current collector; For a full battery of the same size assembled together, the cycle life test is only 400 to 500 weeks. It can be seen that the silicon electrode prepared by the present invention has a better effect on cycle improvement, and the cycle life is prolonged by one time.

Example 2

A preparation method of a silicon negative electrode composite pole piece, the steps are as follows:

S1. Dissolve the thermoplastic polyurethane elastomer in N,N-dimethylformamide (DMF) solvent, dissolve at 60°C for 3 hours, and control the polymer concentration to 25%; then add silver that accounts for 20% of the thermoplastic polyurethane elastomer mass The metal conductive filler was stirred at room temperature for 15 minutes, and then stood for about 1 hour after stirring to eliminate the bubbles in the polymer solution; the polymer solution was coated on a 6 μm copper foil current collector, and the coating thickness was controlled at 4 μm, and baked at 120 °C. After dry removal of the solvent, micropores are formed in the elastic resin to obtain a composite current collector with a conductive buffer layer for use.

S2. Mix slurry according to the ratio of silicon: SP: SWCNT: PAA = 90: 5: 2: 3 to obtain a negative electrode slurry, which is then coated on the above-mentioned composite current collector and dried to obtain the desired silicon negative electrode pole piece .

S3. Add 0.1 mg/mL graphene slurry to the above-mentioned 15 wt % polyurethane solution. The amount of graphene added is 1 wt % of the mass of the elastic resin. After mixing evenly, it is coated on the silicon negative electrode sheet obtained in S2, and dried. The desired silicon anode composite pole piece is obtained by hot rolling.

The peeling strength test of the prepared silicon anode composite pole piece was carried out. The test results showed that the peeling force was increased from 23N/m of the conventional silicon anode pole piece to 38N/m.

The above-mentioned silicon negative electrode composite pole piece, ternary 532 single crystal positive pole piece, separator, electrolyte, etc. are assembled together to form a full battery. To test the cycle life of the full battery, the test step adopts the 1C/1C-100% SOC cycle system, and the final measured battery cycle life is 800 weeks.

The above-mentioned conventional silicon negative pole piece, that is, the silicon negative pole piece obtained by drying only the synthetic slurry in step S2 is coated on the copper foil current collector; For a full battery of the same size assembled with electrolytes and other components, the cycle life test is only 320 weeks. It can be seen that the silicon electrode prepared by the present invention has a better effect on cycle improvement, and the cycle life is prolonged by 1.5 times.

Example 3

S1. Dissolve the thermoplastic polyurethane elastomer in dimethyl sulfoxide (DMSO) solvent, dissolve at 50°C for 4 hours, and control the polymer concentration to 10%; then add acetylene black conductive filler accounting for 12% of the mass of the thermoplastic polyurethane elastomer, Stir for 15 min at room temperature, and let stand for about 1 h after stirring to eliminate the bubbles in the polymer solution; coat the polymer solution on the 8 μm copper foil current collector, the coating thickness is controlled at 3 μm, and dry at 120 °C to remove the solvent. , micropores are formed in the elastic resin, and a composite current collector with a conductive buffer layer is obtained for use.

S2. Mix slurry according to the ratio of silicon: SP: SWCNT: PAA = 75: 15: 4: 6 to obtain a negative electrode slurry, which is then coated on the above-mentioned composite current collector and dried to obtain the desired silicon negative electrode pole piece .

S3, adding 0.3 mg/mL graphene slurry to the above-mentioned 10 wt % polyurethane solution, the amount of graphene added is 5 wt % of the mass of the elastic resin, and after mixing evenly, it is coated on the silicon negative electrode sheet obtained in S2, dried, The desired silicon anode composite pole piece is obtained by hot rolling.

The peeling strength test of the prepared silicon negative electrode composite pole piece was carried out. The test results showed that the peeling force was increased from 30N/m of the conventional silicon negative electrode pole piece to 56N/m.

The above-mentioned silicon negative electrode composite pole piece, ternary high nickel 811 positive pole piece, separator, electrolyte and the like are assembled together to form a full battery. To test the cycle life of the full battery, the test step adopts the 0.5C/0.5C-100% SOC cycle system, and the final measured battery cycle life is 900 weeks.

The above-mentioned conventional silicon negative pole piece, that is, the silicon negative pole piece obtained by drying only the synthetic slurry in step S2 is coated on the copper foil current collector; For a full battery of the same size assembled with electrolytes and other components, the cycle life test is only 600 weeks. It can be seen that the silicon electrode prepared by the present invention has a better effect on cycle improvement, and the cycle life is prolonged by 0.5 times.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. The equivalent replacement or change of the inventive concept thereof shall be included within the protection scope of the present invention.

Claims (9)

1. a preparation method of silicon negative electrode composite pole piece, is characterized in that, comprises the following steps: S1. Dissolve the elastic resin in an organic solvent, add a conductive filler to it, stir and mix to obtain a conductive elastic resin dispersion; S2, coating the conductive elastic resin dispersion on the current collector, drying to remove the solvent, to obtain a composite current collector; S3, mixing the silicon negative electrode active material, the superconducting carbon black conductive agent, the single-walled carbon nanotubes, and the binder to obtain a negative electrode slurry, coating the negative electrode slurry on the composite current collector, and drying to obtain a silicon negative electrode pole piece; S4, dissolve the elastic resin in an organic solvent, add graphene dispersion to it, stir and mix to obtain a graphene elastic resin dispersion; then coat it on the silicon negative electrode sheet, dry, and hot-roll to obtain silicon Negative composite pole piece. 2 . The method for preparing a silicon negative electrode composite pole piece according to claim 1 , wherein the elastic resin is a thermoplastic polyurethane elastomer. 3 . 3. The method for preparing a silicon negative electrode composite pole piece according to claim 1, wherein in S1, the conductive filler comprises any one of carbon black and metal particles; the amount of the conductive filler added is the quality of the elastic resin 3-20wt%. 4 . The method for preparing a silicon negative electrode composite pole piece according to claim 1 , wherein in S2 , the current collector comprises any one of conductive metal foil, porous current collector, and foam current collector. 5 . 5 . The method for preparing a silicon negative electrode composite pole piece according to claim 1 , wherein, in S2 , the drying temperature is 120-150° C. 6 . 6 . The method for preparing a silicon negative electrode composite pole piece according to claim 1 , wherein, in S3 , the silicon negative electrode material comprises any one of elemental silicon, silicon oxide, silicon carbon material, and silicon-based composite material. 7 . 7. the preparation method of silicon negative electrode composite pole piece according to claim 1, is characterized in that, in S4, the concentration that the elastic resin is dissolved in solvent and is prepared is 5-25wt%; The concentration of graphene dispersion liquid is 0.1- 0.5mg/mL; the amount of graphene added is 1-10wt% of the mass of the elastic resin. 8 . The method for preparing a silicon negative electrode composite pole piece according to claim 1 , wherein, in S4 , the temperature of the hot rolling is 60-90° C. 9 . 9. The silicon negative electrode composite pole piece prepared by the method of any one of claims 1-8.