Low-expansion silicon-carbon negative lithium ion battery and preparation method thereof

Abstract

This invention relates to a low-expansion silicon-carbon anode lithium-ion battery and its preparation method, comprising the following steps: S1, preparing a first slurry using graphite, a first conductive agent, a first binder, and a solvent as raw materials. S2, preparing a second slurry using silicon-carbon, a second conductive agent, a second binder, and a solvent. S3, coating the surface of the negative electrode current collector in the order of first slurry / second slurry / first slurry, and obtaining a negative electrode sheet after drying, rolling, and slicing. S4, preparing a pre-formed positive electrode sheet using NCM ternary material, a positive electrode conductive agent, a positive electrode binder, and a solvent as raw materials. S5, coating the surface of the pre-formed positive electrode sheet with PVDF adhesive. S6, assembling the battery cell, inserting it into a casing, injecting electrolyte, sealing, and allowing it to stand. S7, performing charging formation under high temperature and high pressure to obtain a lithium-ion battery. Compared with ordinary silicon-carbon anode lithium-ion batteries, the low-expansion silicon-carbon anode lithium-ion battery of this invention increases the room temperature cycle life from about 200 cycles to over 1000 cycles, and the high temperature cycle life from less than 100 cycles to over 500 cycles.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a low-expansion silicon-carbon anode lithium-ion battery and its preparation method. Background Technology

[0002] As the energy density requirements of lithium-ion batteries increase, the theoretical capacity of traditional graphite anodes, which is only 372 mAh / g, can no longer meet the demand. Silicon-carbon anodes, on the other hand, have a capacity of 3579 mAh / g (nearly 10 times that of graphite anodes). Driven by the market, silicon-carbon anodes are being used more and more widely.

[0003] Because pure silicon-carbon materials expand extremely much, silicon-carbon anodes are currently mainly made by physically mixing graphite materials and a certain proportion of silicon-carbon materials with binders and conductive agents during the slurry mixing process. The mixed slurry is then coated onto a current collector and dried to obtain silicon-carbon anode sheets. These are then combined with high-nickel cathodes to form semi-solid-state batteries, with a rate cycle performance of several hundred cycles.

[0004] Although silicon-carbon anodes have high capacity, they undergo an alloying reaction during lithium intercalation, resulting in a dramatic volume expansion of over 300% (compared to about 20% for graphite). Even silicon-carbon / graphite composite anodes expand significantly, leading to electrode structure pulverization, breakage of the conductive network, and continuous rupture and regeneration of the solid electrolyte interphase (SEI) membrane. This consumes active lithium and drastically shortens the cycle life of the electrolyte. Therefore, developing low-expansion silicon-carbon anode sheets can reduce the damage to the battery caused by anode expansion and improve battery cycle life. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned technical problems existing in the prior art and to provide a low-expansion silicon-carbon anode lithium-ion battery and its preparation method.

[0006] To address the shortcomings of the aforementioned technical problems, the present invention provides a method for preparing a low-expansion silicon-carbon anode lithium-ion battery, comprising the following steps: S1. Graphite, first conductive agent, first binder and solvent are stirred and mixed evenly, and then sieved to obtain the first slurry; S2. The silicon carbide, the second conductive agent, the second binder and the solvent are stirred and mixed evenly, and then sieved to obtain the second slurry; S3. The slurry is applied to the surface of the negative electrode current collector in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet. S4. Mix NCM ternary material, positive electrode conductive agent, positive electrode binder and solvent evenly, and obtain positive electrode slurry after sieving. Then, coat the positive electrode slurry onto the surface of the positive electrode current collector and dry it to obtain a pre-made positive electrode sheet. S5. Coat the surface of the pre-made positive electrode sheet with PVDF adhesive, and then dry, roll and slice it to obtain the positive electrode sheet. S6. Stack the positive electrode, separator and negative electrode to form a cell, put it into the housing, inject the assembled battery into electrolyte, seal and let it stand. S7. The battery is activated by charging at a temperature of 45~85℃ and a pressure of 0.6~3MPa to obtain a low-expansion silicon-carbon negative electrode lithium-ion battery.

[0007] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the first conductive agent and the second conductive agent are both at least one of conductive carbon black, carbon fiber, and carbon nanotubes.

[0008] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the mass ratio of graphite, first conductive agent and first binder is 90~96:1~3:3~7, and the mass ratio of silicon-carbon, second conductive agent and second binder is 90~96:1~3:3~7.

[0009] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the first binder and the second binder are both composite binders with a mass ratio of LA133 and SBR of 2~4:1~3.

[0010] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the positive electrode binder is PVDF.

[0011] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the mass ratio of graphite in the first slurry is 50~99%, and the mass ratio of silicon-carbon in the second slurry is 1~50%.

[0012] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the coating thickness of the PVDF adhesive in step S5 is 2~4μm.

[0013] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention: the ternary material is of type 333, type 523 or type 622.

[0014] As a further optimization of the preparation method of the low-expansion silicon-carbon negative electrode lithium-ion battery of the present invention, the standing time is 24 to 36 hours.

[0015] This invention also provides a low-expansion silicon-carbon anode lithium-ion battery, prepared by the above method. Compared with ordinary silicon-carbon anode lithium-ion batteries, the room temperature cycle life is increased from about 200 cycles to more than 1000 cycles, and the high temperature cycle life is increased from less than 100 cycles to more than 500 cycles.

[0016] The present invention has the following beneficial effects: The silicon-carbon anode lithium-ion battery of the present invention has a "sandwich" structure anode active layer, wherein the inner graphite anode active material is tightly bonded to the current collector. During charging, lithium ions pass sequentially through the outer graphite layer, the middle silicon-carbon layer, and the inner graphite layer. When passing through the outer graphite layer, the graphite slightly expands, giving the middle silicon-carbon layer a certain pre-pressure. When the lithium ions reach the middle silicon-carbon layer, the silicon-carbon layer expands. At this time, the inner graphite layer can provide a certain space for the expansion of the silicon layer. After the graphite anodes on both sides expand, they can constrain the expansion of the middle silicon-carbon layer. The outer graphite layer does not cause lithium plating due to the loosening of expanded particles. At the same time, the high temperature and high pressure formation method can soften the binder on the positive electrode surface into a viscous flow state, which not only bonds the separator, but also bonds the anode through the separator, tightly bonding the positive and negative electrodes of the cell and the separator together, further constraining the expansion of the anode, and improving the cycle life of the silicon-carbon anode semi-solid battery as a whole. Attached Figure Description

[0017] Figure 1 The graphs show the 1C / 3C cycle curves of lithium-ion batteries from Example 1 and Comparative Example 1 at 25°C. Figure 2 The graphs show the 1C / 3C cycle curves of lithium-ion batteries in Example 1 and Comparative Example 1 at 45°C. Detailed Implementation

[0018] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0019] A method for preparing a low-expansion silicon-carbon anode lithium-ion battery includes the following steps: S1. Graphite, first conductive agent, first binder and solvent are stirred and mixed evenly, and then sieved to obtain the first slurry; Both the first and second conductive agents are at least one of conductive carbon black, carbon fiber, and carbon nanotubes. Both the first and second adhesives are composite adhesives with a mass ratio of LA133 to SBR of 2~4:1~3; The mass ratio of graphite, the first conductive agent, and the first binder is 90~96:1~3:3~7; The mass ratio of graphite in the first slurry is 50-99%.

[0020] S2. The silicon carbide, the second conductive agent, the second binder and the solvent are stirred and mixed evenly, and then sieved to obtain the second slurry; The mass ratio of silicon carbide, the second conductive agent, and the second binder is 90~96:1~3:3~7; Both the first and second adhesives are composite adhesives with a mass ratio of LA133 to SBR of 2~4:1~3; The mass ratio of silicon and carbon in the second slurry is 1-50%.

[0021] S3. The slurry is applied to the surface of the negative electrode current collector in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet. S4. Mix NCM ternary material, positive electrode conductive agent, positive electrode binder and solvent evenly, and obtain positive electrode slurry after sieving. Then, coat the positive electrode slurry onto the surface of the positive electrode current collector and dry it to obtain a pre-made positive electrode sheet. The ternary materials are of type 333, 523, or 622; The positive electrode binder is PVDF.

[0022] S5. Coat the surface of the pre-made positive electrode sheet with PVDF adhesive, and then dry, roll and slice it to obtain the positive electrode sheet. The coating thickness of the PVDF adhesive is 2~4μm.

[0023] S6. Stack the positive electrode, separator and negative electrode to form a cell and put it into the casing. Inject the assembled battery with electrolyte, seal it and let it stand for 24 to 36 hours.

[0024] S7. The battery is activated by charging at a temperature of 45~85℃ and a pressure of 0.6~3MPa to obtain a low-expansion silicon-carbon negative electrode lithium-ion battery.

[0025] <Example 1> Graphite, conductive carbon black, and negative electrode composite binder are weighed according to a mass ratio of 92:2:6. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of graphite in the first slurry is 65%.

[0026] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0027] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the first slurry.

[0028] Weigh silicon carbide, conductive carbon black, and negative electrode composite binder according to a mass ratio of 93:3:3. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of silicon carbide in the second slurry is 30%.

[0029] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0030] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the second slurry.

[0031] The slurry is applied to the surface of the negative electrode current collector (copper foil) in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0032] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode sheet is ≤300ppm.

[0033] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0034] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 96:2:2. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 45%.

[0035] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0036] The vacuum-stirred cathode slurry was sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-type extrusion coating process was then used to coat both sides of the cathode slurry onto a 15μm thick pure aluminum foil (cathode current collector), followed by drying to obtain the pre-fabricated cathode sheet.

[0037] A PVDF adhesive was coated onto the surface of the pre-fabricated positive electrode sheet, with a coating thickness of 3 μm. The coated aluminum foil was then transferred to a vacuum drying oven and dried at -0.1 MPa and 100 °C for 16 h. After drying, the moisture content of the electrode sheet was ≤300 ppm.

[0038] The dried positive electrode sheet is placed in a roller press for cold rolling and then cut into the same size as the negative electrode sheet using a laser slicer. A 1mm blank is left on one side of the positive electrode sheet. After slicing, the burrs are removed to obtain the positive electrode sheet.

[0039] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0040] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0041] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0042] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0043] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0044] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 65°C and 2MPa pressure.

[0045] <Example 2> Graphite, conductive carbon black, and negative electrode composite binder are weighed according to a mass ratio of 90:3:7. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 2:3. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of graphite in the first slurry is 50%.

[0046] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0047] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the first slurry.

[0048] Weigh silicon carbide, conductive carbon black, and negative electrode composite binder according to a mass ratio of 90:3:7. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 2:3. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of silicon carbide in the second slurry is 35%.

[0049] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0050] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the second slurry.

[0051] The slurry is applied to the surface of the negative electrode current collector (copper foil) in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0052] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode sheet is ≤300ppm.

[0053] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0054] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 94:3:3. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 40-50%.

[0055] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0056] The vacuum-stirred cathode slurry was sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-type extrusion coating process was then used to coat both sides of the cathode slurry onto a 15μm thick pure aluminum foil (cathode current collector), followed by drying to obtain the pre-fabricated cathode sheet.

[0057] A PVDF adhesive was coated onto the surface of the pre-fabricated positive electrode, with a coating thickness of 2 μm. The coated aluminum foil was then transferred to a vacuum drying oven and dried at -0.1 MPa and 100 °C for 16 h. After drying, the moisture content of the electrode was ≤300 ppm.

[0058] The dried positive electrode sheet is placed in a roller press for cold rolling and then cut into the same size as the negative electrode sheet using a laser slicer. A 1mm blank is left on one side of the positive electrode sheet. After slicing, the burrs are removed to obtain the positive electrode sheet.

[0059] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0060] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0061] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0062] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0063] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0064] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 45℃ and 0.6MPa pressure.

[0065] <Example 3> Graphite, conductive carbon black, and negative electrode composite binder are weighed at a mass ratio of 96:1:3. The negative electrode composite binder is a mixture of LA133 and SBR at a mass ratio of 4:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of graphite in the first slurry is 50%.

[0066] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0067] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the first slurry.

[0068] Weigh silicon carbide, conductive carbon black, and negative electrode composite binder at a mass ratio of 96:1:3. The negative electrode composite binder is a mixture of LA133 and SBR at a mass ratio of 4:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of silicon carbide in the second slurry is 50%.

[0069] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0070] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the second slurry.

[0071] The slurry is applied to the surface of the negative electrode current collector (copper foil) in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0072] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode is ≤500ppm.

[0073] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0074] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 98:1:1. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 50%.

[0075] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0076] The vacuum-stirred cathode slurry was sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-type extrusion coating process was then used to coat both sides of the cathode slurry onto a 15μm thick pure aluminum foil (cathode current collector), followed by drying to obtain the pre-fabricated cathode sheet.

[0077] A PVDF adhesive was coated onto the surface of the pre-fabricated positive electrode, with a coating thickness of 4 μm. The coated aluminum foil was then transferred to a vacuum drying oven and dried at -0.1 MPa and 100 °C for 16 h. After drying, the moisture content of the electrode was ≤300 ppm.

[0078] The dried positive electrode sheet is placed in a roller press for cold rolling and then cut into the same size as the negative electrode sheet using a laser slicer. A 1mm blank is left on one side of the positive electrode sheet. After slicing, the burrs are removed to obtain the positive electrode sheet.

[0079] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0080] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0081] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0082] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0083] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0084] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 85℃ and 3MPa pressure.

[0085] <Comparative Example 1> The preparation method of this comparative lithium-ion battery is as follows: Weigh the negative electrode active material, conductive carbon black, and negative electrode composite binder according to a mass ratio of 92:2:6. The negative electrode active material consists of 50% silicon carbon and 50% graphite. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is based on controlling the mass ratio of graphite in the slurry to be 65%.

[0086] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0087] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the negative electrode slurry.

[0088] The negative electrode slurry is coated onto the surface of the negative electrode current collector (copper foil), and then dried, rolled, and sliced ​​to obtain the negative electrode sheet.

[0089] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode sheet is ≤300ppm.

[0090] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0091] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 96:2:2. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 45%.

[0092] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0093] The vacuum-stirred positive electrode slurry is sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-fitting extrusion coating process is used to coat both sides of a 15μm thick pure aluminum foil (positive electrode current collector) and dry it. The dried positive electrode sheet is then cold-rolled in a roller press and cut to the size matching the negative electrode sheet using a laser slicing machine. A 1mm blank is left on one side of the positive electrode sheet. After slicing, burrs are removed to obtain the positive electrode sheet.

[0094] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0095] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0096] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0097] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0098] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0099] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 65°C and 2MPa pressure.

[0100] <Comparative Example 2> Graphite, conductive carbon black, and negative electrode composite binder are weighed according to a mass ratio of 92:2:6. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of graphite in the first slurry is 65%.

[0101] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0102] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the first slurry.

[0103] Weigh silicon carbide, conductive carbon black, and negative electrode composite binder according to a mass ratio of 93:3:3. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of silicon carbide in the second slurry is 50%.

[0104] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0105] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the second slurry.

[0106] The slurry is applied to the surface of the negative electrode current collector (copper foil) in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet.

[0107] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode sheet is ≤300ppm.

[0108] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0109] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 96:2:2. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 45%.

[0110] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0111] The vacuum-stirred positive electrode slurry is sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-fitting extrusion coating process is used to coat both sides of a 15μm thick pure aluminum foil (positive electrode current collector) and dry it. The dried positive electrode sheet is then cold-rolled in a roller press and cut to the size matching the negative electrode sheet using a laser slicing machine. A 1mm blank is left on one side of the positive electrode sheet. After slicing, burrs are removed to obtain the positive electrode sheet.

[0112] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0113] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0114] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0115] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0116] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0117] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 65°C and 2MPa pressure.

[0118] <Comparative Example 3> The preparation method of this comparative lithium-ion battery is as follows: Weigh the negative electrode active material, conductive carbon black, and negative electrode composite binder according to a mass ratio of 92:2:6. The negative electrode active material consists of 50% silicon carbon and 50% graphite. The negative electrode composite binder is a mixture of LA133 and SBR in a mass ratio of 1:1. The aqueous solvent is deionized water, and the amount of solvent added is controlled to ensure that the mass ratio of graphite in the first slurry is 65%.

[0119] First, add deionized water and composite binder to a mixing tank and pre-stir at room temperature and 800 rpm for 30 minutes until the binder is completely dissolved. Then add the negative electrode active material and conductive agent, and stir at 1200 rpm for 120 minutes.

[0120] The stirred slurry was sieved through a 300-mesh metal sieve to remove undispersed material agglomerates. After sieving, the slurry was placed in a vacuum environment for degassing for 30 minutes until no obvious bubbles were visible, thus obtaining the negative electrode slurry.

[0121] The negative electrode slurry is coated onto the surface of the negative electrode current collector (copper foil), and then dried, rolled, and sliced ​​to obtain the negative electrode sheet.

[0122] After coating, the copper foil is first pre-baked at 60℃ for 2 hours to remove surface free moisture. Then it is transferred to an 80℃ forced-air drying oven for 24 hours, or a segmented drying tunnel is used. After drying, the moisture content of the electrode sheet is ≤300ppm.

[0123] The dried negative electrode sheet is placed in a roller press for cold rolling. The rolled electrode sheet is then cut into a preset size using a laser slicer. After slicing, the burrs on the edge of the electrode sheet are removed to obtain the negative electrode sheet.

[0124] Weigh out NCM ternary material, conductive carbon black, and PVDF in a mass ratio of 96:2:2. Use N-methylpyrrolidone (NMP) as a solvent, and add solvent to control the solid content of the positive electrode slurry to 45%.

[0125] First, add NMP and PVDF to a sealed stirring tank and pre-stir at room temperature and 900 r / min for 60 min until PVDF is completely dissolved. Then add the positive electrode composite active material and conductive agent, and stir at high speed of 1500 r / min for 180 min. During the stirring process, the tank is filled with nitrogen for protection. Finally, stir under vacuum for 60 min.

[0126] The vacuum-stirred cathode slurry was sieved through a 200-mesh metal screen to remove hard agglomerates and ensure uniform particle size. A slot-type extrusion coating process was then used to coat both sides of the cathode slurry onto a 15μm thick pure aluminum foil (cathode current collector), followed by drying to obtain the pre-fabricated cathode sheet.

[0127] A PVDF adhesive was coated onto the surface of the pre-fabricated positive electrode sheet, with a coating thickness of 3 μm. The coated aluminum foil was then transferred to a vacuum drying oven and dried at -0.1 MPa and 100 °C for 16 h. After drying, the moisture content of the electrode sheet was ≤300 ppm.

[0128] The dried positive electrode sheet is placed in a roller press for cold rolling and then cut into the same size as the negative electrode sheet using a laser slicer. A 1mm blank is left on one side of the positive electrode sheet. After slicing, the burrs are removed to obtain the positive electrode sheet.

[0129] Assembly was carried out in a dry room with humidity ≤1%RH and temperature 25±5℃. Bare cells were prepared by alternating layers of positive electrode / separator / negative electrode, with one more negative electrode than positive electrode.

[0130] The separator is a three-layer composite polyolefin membrane made of PP / PE / PP. During the lamination process, the positive and negative electrode tabs are aligned, and the electrode sheets are free from misalignment and wrinkles. The laminated bare cells are then installed into a battery casing of a pre-designed size (0.15mm thick aluminum-plastic film); after casing, the electrode tabs are welded.

[0131] Electrolyte injection was carried out in a drying room with humidity ≤0.5%RH and temperature 25±5℃. Vacuum injection was used, with injection pressure at -0.1MPa, to improve electrolyte wetting efficiency.

[0132] Immediately after liquid injection, the shell is sealed. The soft-pack aluminum-plastic film is heat-sealed with a heat-sealing temperature of 180℃, a heat-sealing pressure of 0.3MPa, and a heat-sealing time of 3~5s.

[0133] After sealing, the battery is placed in a constant temperature chamber at 25±5℃ and normal pressure for 36 hours to promote the electrolyte to fully wet the pores of the positive electrode, negative electrode and separator, and ensure that the electrolyte is evenly distributed inside the cell.

[0134] A low-expansion silicon-carbon anode lithium-ion battery was prepared by charging and forming the battery at 65°C and 2MPa pressure.

[0135] <1C / 3C Cycling Performance at 25℃> The batteries from Example 1 and Comparative Examples 1-3 were subjected to 1C / 3C cycle performance tests at 25°C.

[0136] Test equipment: Lithium-ion battery comprehensive performance tester (supports constant current charge / discharge and low-temperature testing; can acquire voltage, current, and capacity data in real time). High and low temperature test chamber (temperature control range -40℃~85℃, temperature accuracy ±1℃, can achieve constant temperature environment control, built-in battery test fixtures). Data acquisition software (linked with the tester, can record and export voltage and capacity retention data during discharge in real time).

[0137] First, the 1C rated discharge capacity of the two batteries was tested at room temperature, which served as the benchmark for the subsequent low-temperature 30C discharge capacity retention rate. All battery samples were placed in an environment of 25±5℃ for 2 hours to allow the internal temperature of the batteries to match the ambient temperature. The batteries were then fully charged using a constant current-constant voltage (CC-CV) method: a charging rate of 0.5C was applied, constant current charging was performed until the battery's nominal upper limit voltage was reached, then constant voltage charging was switched until the charging current dropped to 0.05C, at which point charging was stopped. After full charging, the batteries were allowed to stand for 30 minutes, and then discharged at a constant current of 1C until the battery's nominal lower limit voltage was reached. The actual 1C discharge capacity of each battery was recorded.

[0138] Following the 0.5C CC-CV charging process described above, the battery samples were fully charged again. After charging, they were left to stand at 25±5℃ for 30 minutes to ensure uniform charge distribution. The battery voltage was checked after full charge to confirm that all batteries reached the nominal upper limit voltage, with no overcharging or undercharging.

[0139] Place the fully charged battery sample into a high and low temperature test chamber preheated to 25°C. Secure the battery to the test fixture inside the chamber, ensuring that the battery tabs are in tight contact with the tester electrodes without any looseness, to avoid excessive contact resistance that could lead to data deviation. Close the test chamber door and allow it to stand in a constant temperature environment of 25±1°C for 2~4 hours to ensure that the battery core temperature fully reaches 25°C.

[0140] In a constant temperature environment of 25±1℃, continuous cycle testing was conducted according to the standard charge and discharge regime until the test termination conditions were met. The test chamber was kept at a constant temperature throughout the entire cycle without interruption. Charge and discharge regime: Charging: Charge at a constant current of 1C to 4.20V, then switch to constant voltage charging until the current drops to 0.05C, then stop charging and let it stand for 5 minutes after charging is complete; Discharge: Discharge at a constant current of 3C to 2.5V, then stop discharging and let stand for 5 minutes after discharge is complete; Definition of a single cycle: One complete cycle is defined as the completion of one "charge-rest-discharge-rest" cycle, corresponding to one cycle count unit on the horizontal axis.

[0141] Data Acquisition: After each cycle, the battery tester and data acquisition software automatically record the actual discharge capacity of that cycle and simultaneously calculate the capacity retention rate after that cycle.

[0142] Test termination condition (industry-standard lithium battery cycle life test): When the capacity retention rate of a battery drops below 80% for the first time, the cycle test of that battery shall be stopped.

[0143] The final test results are as follows Figure 1 As shown, by Figure 1 It can be seen that the room temperature cycling performance of the embodiments is much better than that of the comparative examples, with comparative example 2 being better than comparative example 3, and comparative example 3 being better than comparative example 1. Both the negative electrode and the coated positive electrode of the present invention can improve battery performance, and the combined effect of the two is far better than that of a single application.

[0144] <1C / 3C Cycling Performance at 45℃> The batteries from Example 1 and Comparative Examples 1-3 were subjected to 1C / 3C cycle performance tests at 45°C.

[0145] Test equipment: Lithium-ion battery comprehensive performance tester (supports constant current charge / discharge and low-temperature testing; can acquire voltage, current, and capacity data in real time). High and low temperature test chamber (temperature control range -40℃~85℃, temperature accuracy ±1℃, can achieve constant temperature environment control, built-in battery test fixtures). Data acquisition software (linked with the tester, can record and export voltage and capacity retention data during discharge in real time).

[0146] First, the 1C rated discharge capacity of the two batteries was tested at room temperature, which served as the benchmark for the subsequent low-temperature 30C discharge capacity retention rate. All battery samples were placed in an environment of 25±5℃ for 2 hours to allow the internal temperature of the batteries to match the ambient temperature. The batteries were then fully charged using a constant current-constant voltage (CC-CV) method: a charging rate of 0.5C was applied, constant current charging was performed until the battery's nominal upper limit voltage was reached, then constant voltage charging was switched until the charging current dropped to 0.05C, at which point charging was stopped. After full charging, the batteries were allowed to stand for 30 minutes, and then discharged at a constant current of 1C until the battery's nominal lower limit voltage was reached. The actual 1C discharge capacity of each battery was recorded.

[0147] Following the 0.5CCC-CV charging process described above, the battery samples were fully charged again. After charging, they were left to stand at 25±5℃ for 30 minutes to ensure uniform charge distribution. The battery voltage after full charge was checked, confirming that all batteries reached the nominal upper limit voltage, with no overcharging or undercharging.

[0148] Place the fully charged battery sample into a high and low temperature test chamber preheated to 45℃. Secure the battery to the test fixture inside the chamber, ensuring that the battery tabs are in tight contact with the tester electrodes without any looseness, to avoid excessive contact resistance that could lead to data deviation. Close the test chamber door and allow it to stand in a constant temperature environment of 45±1℃ for 2~4 hours to ensure that the battery core temperature fully reaches 45℃.

[0149] In a constant temperature environment of 45±1℃, continuous cycle testing was conducted according to the standard charge and discharge regime until the test termination conditions were met. The test chamber was kept at a constant temperature throughout the entire cycle without interruption. Charge and discharge regime: Charging: Charge at a constant current of 1C to 4.20V, then switch to constant voltage charging until the current drops to 0.05C, then stop charging and let it stand for 5 minutes after charging is complete; Discharge: Discharge at a constant current of 3C to 2.5V, then stop discharging and let stand for 5 minutes after discharge is complete; Definition of a single cycle: One complete cycle is defined as the completion of one "charge-rest-discharge-rest" cycle, corresponding to one cycle count unit on the horizontal axis.

[0150] Data Acquisition: After each cycle, the battery tester and data acquisition software automatically record the actual discharge capacity of that cycle and simultaneously calculate the capacity retention rate after that cycle.

[0151] Test termination condition (industry-standard lithium battery cycle life test): When the capacity retention rate of a battery drops below 80% for the first time, the cycle test of that battery shall be stopped.

[0152] The final test results are as follows Figure 2 As shown, by Figure 2 It can be seen that the high-temperature cycling of the examples is much better than that of the comparative examples, with comparative example 2 being better than comparative example 3, and comparative example 3 being better than comparative example 1. The verification results are consistent with the results of the room temperature cycling.

[0153] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a low-expansion silicon-carbon anode lithium-ion battery, characterized in that, Includes the following steps: S1. Graphite, first conductive agent, first binder and solvent are stirred and mixed evenly, and then sieved to obtain the first slurry; S2. The silicon carbide, the second conductive agent, the second binder and the solvent are stirred and mixed evenly, and then sieved to obtain the second slurry; S3. The slurry is applied to the surface of the negative electrode current collector in the order of first slurry / second slurry / first slurry, and then dried, rolled and sliced ​​to obtain the negative electrode sheet. S4. Mix NCM ternary material, positive electrode conductive agent, positive electrode binder and solvent evenly, and obtain positive electrode slurry after sieving. Then, coat the positive electrode slurry onto the surface of the positive electrode current collector and dry it to obtain a pre-made positive electrode sheet. S5. Coat the surface of the pre-made positive electrode sheet with PVDF adhesive, and then dry, roll and slice it to obtain the positive electrode sheet. S6. Stack the positive electrode, separator and negative electrode to form a cell, put it into the housing, inject the assembled battery into electrolyte, seal and let it stand. S7. The battery is activated by charging at a temperature of 45~85℃ and a pressure of 0.6~3MPa to obtain a low-expansion silicon-carbon negative electrode lithium-ion battery.

2. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 1, characterized in that, The first conductive agent and the second conductive agent are both at least one of conductive carbon black, carbon fiber and carbon nanotube.

3. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 1, characterized in that, The mass ratio of graphite, the first conductive agent, and the first binder is 90~96:1~3:3~7, and the mass ratio of silicon carbide, the second conductive agent, and the second binder is 90~96:1~3:3~7.

4. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 3, characterized in that, Both the first adhesive and the second adhesive are composite adhesives with a mass ratio of LA133 to SBR of 2~4:1~3.

5. The method for preparing a low-expansion silicon-carbon anode lithium-ion battery as described in claim 1, characterized in that, The positive electrode binder is PVDF.

6. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 2, characterized in that, The first slurry contains 50-99% graphite by mass, and the second slurry contains 1-50% silicon and carbon by mass.

7. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 1, characterized in that, In step S5, the coating thickness of the PVDF adhesive is 2~4μm.

8. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 1, characterized in that: The ternary material is of type 333, type 523, or type 622.

9. The method for preparing a low-expansion silicon-carbon negative electrode lithium-ion battery as described in claim 1, characterized in that: The settling time is 24 to 36 hours.

10. A low-expansion silicon-carbon negative electrode lithium-ion battery, prepared by the method described in any one of claims 1-9.

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