Prime-coated copper foil for improving stripping and cycle performance of negative pole piece and preparation method of prime-coated copper foil

Abstract

The invention discloses a prime coat copper foil for improving stripping and cycle performance of a negative pole piece and a preparation method of the prime coat copper foil, and relates to the technical field of current collectors. The preparation method comprises the following steps: adding magnesium lithium silicate and ammonium carbonate into prime coating slurry, and then coating a copper foil with the prime coating slurry to obtain a prime-coated copper foil; after surface carboxyl of magnesium lithium silicate and oxygen-containing groups of polyacrylic acid are compounded, a large number of high-strength hydrogen bonds are formed, and when a negative electrode generates huge expansion stress in the circulation process, a hydrogen bond network between magnesium lithium silicate nanosheets and a polymer is broken, absorbs energy and buffers the structural change of an active material, so that the circulation performance of a battery end is improved; ammonium carbonate is heated and decomposed into NH3 and CO2, gas escapes and leaves nanoscale pores in the coating, on one hand, the gas can generate a stronger anchoring effect with a negative electrode active material to improve the stripping force of a pole piece, and on the other hand, the pores can serve as buffer pores to inhibit volume expansion of silicon particles during lithium intercalation and improve the cycle performance.

Description

Undercoated copper foil and its preparation method for improving the stripping and cycle performance of negative electrode sheets Technical Field

[0001] This invention relates to the field of current collector technology, specifically to a base-coated copper foil and its preparation method for improving the peeling and cycle performance of the negative electrode sheet. Background Technology

[0002] Today, the new energy field is constantly developing towards high capacity and high energy density. The traditional lithium battery anode material graphite can no longer fully meet the requirements of various fields, and the solution of doping graphite with silicon is gradually being applied by many battery manufacturers.

[0003] With the doping of silicon-based anodes, defects at the anode end gradually become apparent: poor separation between the active material and the current collector leads to powder shedding and rapid capacity decay after long cycles. Therefore, improving the cycle decay of silicon-doped anodes has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a base-coated copper foil and its preparation method that improves the peeling and cycle performance of the negative electrode sheet, so as to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a base-coated copper foil that improves the peeling and cycle performance of the negative electrode sheet, comprising the following steps: Step 1: mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coated slurry; Step 2: taking copper foil, uniformly coating the base-coated slurry on the upper and lower surfaces of the copper foil, drying to obtain a base-coated copper foil.

[0006] Further, in step 1, the active material is a mixture of conductive agent, lithium magnesium silicate and ammonium carbonate; the conductive agent is acetylene black; in step 1, the mass ratio of polyacrylic acid to active material is 2:(2~3); the mass ratio of pure water, isopropanol and active material is (70~80):(8~10):6.

[0007] Furthermore, the lithium magnesium silicate accounts for 0.7-1.5% of the total mass of polyacrylic acid and active materials; the ammonium carbonate accounts for 2.2-3.0% of the total mass of polyacrylic acid and active materials; and the conductive agent accounts for 55.9-56.7% of the total mass of polyacrylic acid and active materials.

[0008] Furthermore, in step 1, the solid content of the primer slurry is 8-10%.

[0009] Furthermore, in step 2, the thickness of the copper foil is 6~8μm.

[0010] Furthermore, in step 2, the coating speed is 40~50 m / min; in step 2, the drying process conditions are: temperature 110~120℃, total oven length 30m; in step 2, the surface density of the primer slurry is 2.0~3.0 g / m³. 2 .

[0011] Furthermore, the polyacrylic acid is modified using the following specific process: Step A: Acrylic acid and trimethylolpropane are mixed and stirred evenly, then concentrated sulfuric acid is added, the mixture is heated to react, and dehydrated under reduced pressure to obtain a branched product; Step B: Under a nitrogen atmosphere, hydrogen-containing silicone oil, allyl alcohol polyether, and catalyst are mixed and heated to react to obtain hydroxyl-terminated silicone oil; Step C: Emulsifier and deionized water are mixed, and 1 / 2 mass of ammonium persulfate is added. The mixture is heated to 70-75°C, and methyl α-methacrylate, butyl acrylate, methacrylic acid, the branched product, hydroxyl-terminated silicone oil, and the remaining ammonium persulfate are added. The mixture is heated to react and kept at this temperature for 2-3 hours. The pH is adjusted to 7.0-7.5, and the mixture is stirred evenly to obtain modified polyacrylic acid.

[0012] Furthermore, in step A, the molar ratio of acrylic acid to trimethylolpropane is (5~7):1; in step A, the amount of concentrated sulfuric acid added is 0.1~0.3% of the mass of acrylic acid; and the mass fraction of the concentrated sulfuric acid is 98%.

[0013] Furthermore, in step A, the process conditions for the heating reaction are: temperature 85~95℃, time 3.5~4.5h; in step A, the process conditions for dehydration under reduced pressure are: temperature 90~105℃, vacuum degree 2~8kPa, time 1~2h.

[0014] Furthermore, in step B, the molar ratio of hydrogen-containing silicone oil to allyl alcohol polyether is (2.0~2.8):1; the catalyst is chloroplatinic acid, and the amount of chloroplatinic acid added is 3~12 ppm of the total mass of hydrogen-containing silicone oil and allyl alcohol polyether.

[0015] Furthermore, in step B, the process conditions for the heating reaction are: temperature 120~140℃, time 1.5~2.5h.

[0016] Further, in step C, the mass ratio of ammonium persulfate, emulsifier, deionized water, methyl α-methacrylate, butyl acrylate, methacrylic acid, branched product, and hydroxyl-terminated silicone oil is (0.4~0.8):(3~7):(120~160):(30~40):(10~20):(5~10):(20~30):(10~20); the emulsifier is OP-10.

[0017] Furthermore, in step C, the process conditions for the heating reaction are: temperature 80~90℃, time 2.5~3.5h.

[0018] In the above technical solution, in step A, the carboxyl group of acrylic acid and the hydroxyl group of trimethylolpropane undergo an esterification reaction under the action of concentrated sulfuric acid to form a product with a branched structure containing multiple acrylate bonds. In step B, hydrosilylation occurs between the silicon-hydrogen bonds of the hydrogen-containing silicone oil and the carbon-carbon double bonds of the allyl alcohol polyether under the catalysis of chloroplatinic acid, introducing polyether segments to obtain hydroxyl-terminated silicone oil. In step C, methyl α-methacrylate, butyl acrylate, methacrylic acid, the branched product and the hydroxyl-terminated silicone oil undergo free radical copolymerization under the action of ammonium persulfate, introducing organosilicon segments to obtain modified polyacrylic acid.

[0019] This invention also provides the application of a bottom-coated copper foil to improve the peeling and cycle performance of the negative electrode sheet, specifically including the following process: S1: Mix the active material, Super P, styrene-butadiene rubber, and carboxymethyl cellulose, stir evenly to obtain a negative electrode slurry, then coat it on the upper and lower surfaces of the bottom-coated copper foil, and dry it to obtain a negative electrode sheet; S2: Mix LFP (lithium iron phosphate), PVDF (polyvinylidene fluoride), and Super P, stir evenly to obtain a positive electrode slurry, then coat it on the upper and lower surfaces of an aluminum foil, and dry it to obtain a positive electrode sheet; S3: Roll, slit, and die-cut the negative electrode sheet and the positive electrode sheet, then stack and assemble them with the separator in the order of "negative electrode sheet-separator-positive electrode sheet-separator", then inject the electrolyte and form a capacity test to obtain a soft-pack battery.

[0020] Furthermore, in S1, the active material is graphite and silicon carbon in a mass ratio of (14~16):1; in S1, the mass ratio of the active material, Super P, styrene-butadiene rubber, and carboxymethyl cellulose is (93~95):(1.5~2.5):(1.2~1.7):(0.3~0.8).

[0021] Furthermore, in S1, the coating thickness of the negative electrode slurry is 60~80μm.

[0022] Furthermore, in S1, the drying process conditions are: temperature 80~90℃, time 0.8~1.0h.

[0023] Furthermore, in S2, the mass ratio of LFP, PVDF, and Super P is (90~96):(2~5):(2~5).

[0024] Furthermore, in S2, the coating thickness of the positive electrode slurry is 80~100μm.

[0025] Furthermore, in S2, the drying process conditions are: temperature 120~140℃, time 30~50min.

[0026] Furthermore, in S3, the diaphragm is a polyethylene diaphragm with a thickness of 12~16μm.

[0027] Furthermore, in S3, the electrolyte is obtained by mixing LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate), DMC (dimethyl carbonate), EMC (ethyl methyl carbonate), VC (ethylene carbonate), and FEC (fluoroethylene carbonate) in a mass ratio of 11:30:30:27:1:0.5.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The lithium magnesium silicate added to the primer slurry in this application can significantly improve the mechanical strength and toughness of the coating. After the carboxyl groups on its surface are combined with the oxygen-containing groups of modified polyacrylic acid, a large number of high-strength hydrogen bonds are formed. When the negative electrode generates huge expansion stress during cycling, the hydrogen bond network between the lithium magnesium silicate nanosheets and the polymer will break preferentially, absorb energy, buffer the structural changes of the active material, and thus improve the cycle performance of the battery.

[0029] 2. In addition, ammonium carbonate is added to the primer slurry. During the drying process of the primer slurry, the ammonium carbonate is decomposed into NH3 and CO2 by heat. The gas escapes and leaves nanoscale pores in the coating. On the one hand, it can generate a stronger anchoring effect with the negative electrode active material and improve the electrode peeling force. On the other hand, the pores themselves can act as buffer pores to suppress the volume expansion of silicon particles during lithium intercalation and improve cycle performance.

[0030] 3. The modified polyacrylic acid prepared in this application forms a cross-linked network through branching sites, which can encapsulate the active material in the network, inhibiting the shedding caused by the expansion of the active material and improving the peel strength of the negative electrode. The modified polyacrylic acid also contains flexible organosilicon segments and polyether segments, which can effectively absorb stress, inhibit electrode cracking, and improve the service life of the soft-pack battery. In addition, the polyether segments have good affinity for the electrolyte, which helps to enhance the wettability of the electrolyte, improve ionic conductivity, and further enhance the cycle performance of the soft-pack battery. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] In the following specific embodiments: copper foil, 8μm thick; hydrogen-containing silicone oil, model SI-H202, sourced from Laiyang Shengbang Organosilicon Technology Co., Ltd.; propylene alcohol polyether, model JFB-23, sourced from Jiangsu Haian Petrochemical Plant; catalyst: chloroplatinic acid; emulsifier: OP-10; acetylene black, model N550, sourced from Tianjin Yiborui Chemical Co., Ltd.; lithium magnesium silicate, dispersion viscosity 2000-4500cps, sourced from Shijiazhuang Yitian Mineral Products Co., Ltd.; graphite, model FSN-1; silicon carbide, model KQ100-3F, sourced from Guangdong Kaijin New Energy Technology Co., Ltd.; Super P, brand Temi Gao, particle size 40nm, specific surface area 62m². 2 / g; PVDF, grade Suwei 5130; carboxymethyl cellulose, product number XWS001, sourced from Dacheng County Yibo Chemical Co., Ltd.; styrene-butadiene rubber, product number BM430B, sourced from Dongguan Caihua Plastics Technology Co., Ltd.

[0033] The concentrated sulfuric acid has a mass fraction of 98%; the drying oven used during drying is 30m long.

[0034] Example 1: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the conductive agent is 80:10:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0035] Example 2: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the conductive agent is 80:10:6; lithium magnesium silicate accounts for 0.7% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0036] Example 3: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the conductive agent is 80:10:6; lithium magnesium silicate accounts for 0.9% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0037] Example 4: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the polyacrylic acid is 80:10:6; lithium magnesium silicate accounts for 1.3% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0038] Example 5: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the conductive agent is 80:10:6; lithium magnesium silicate accounts for 1.5% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0039] Example 6: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the polyacrylic acid is 80:10:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.2% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0040] Example 7: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the polyacrylic acid is 80:10:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.4% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0041] Example 8: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the conductive agent is 80:10:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.8% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0042] Example 9: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; pure water, isopropanol The mass ratio of the active material to the polyacrylic acid is 80:10:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 3.0% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0043] Example 10: A method for preparing a base-coated copper foil to improve the peeling and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:3; Pure water, isopropanol, and isopropanol are mixed with the active material and stirred evenly to obtain a base-coated copper foil; The mass ratio of propanol to active material is 65:9:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.3% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 9%; in step 2, the coating speed is 45 m / min; in step 2, the drying process conditions are: temperature 115℃; in step 2, the coating surface density of the primer slurry is 2.5 g / m². 2 .

[0044] Example 11: A method for preparing a base-coated copper foil to improve the stripping and cycle performance of the negative electrode, comprising the following steps: Step 1: Mixing pure water, polyacrylic acid, isopropanol and active materials, stirring evenly to obtain a base-coating slurry; Step 2: Taking copper foil, uniformly coating the base-coating slurry on the upper and lower surfaces of the copper foil, and drying to obtain a base-coated copper foil; In Step 1, the active material is a mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; In Step 1, the mass ratio of polyacrylic acid to active material is 2:2; Pure water, isopropanol, and active materials are mixed and stirred evenly to obtain a base-coated copper foil; The mass ratio of propanol to active material is 70:8:6; lithium magnesium silicate accounts for 1.1% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 55.9% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 8%; in step 2, the coating speed is 40 m / min; in step 2, the drying process conditions are: temperature 110℃; in step 2, the coating surface density of the primer slurry is 2.0 g / m². 2 .

[0045] Example 12: A method for preparing a base-coated copper foil that improves the stripping and cycle performance of the negative electrode, comprising the following steps: (1) Preparation of modified polyacrylic acid: Step A: Mix acrylic acid and trimethylolpropane, stir evenly, then add concentrated sulfuric acid, heat to react, remove water under reduced pressure, and obtain branched product; Step B: Under nitrogen atmosphere protection, mix hydrogen-containing silicone oil, allyl alcohol polyether, and catalyst, heat to react, and obtain hydroxyl-terminated silicone oil; Step C: Mix emulsifier and deionized water, add 1 / 2 mass of ammonium persulfate, heat to 75°C, and add α-methyl methacrylate, butyl acrylate, methacrylic acid, branched product, and hydroxyl-terminated silicone oil. Modified polyacrylic acid was obtained by heating and reacting basic silicone oil and residual ammonium persulfate, maintaining the temperature for 3 hours, adjusting the pH to 7.5, and stirring until homogeneous. In step A, the molar ratio of acrylic acid to trimethylolpropane was 7:1; the amount of concentrated sulfuric acid added in step A was 0.3% of the mass of acrylic acid; the heating reaction conditions in step A were: temperature 95℃, time 4.5 hours; the dehydration conditions in step A were: temperature 105℃, vacuum degree 8 kPa, time 2 hours. In step B, the molar ratio of hydrogen-containing silicone oil to allyl alcohol polyether was 2.8:1; the heating reaction conditions in step B were: temperature 140℃, time 2 hours. 5h; In step C, the mass ratio of ammonium persulfate, emulsifier, deionized water, methyl α-methacrylate, butyl acrylate, methacrylic acid, branched products, and terminal hydroxyl silicone oil is 0.8:7:160:40:20:10:30:20; In step C, the process conditions for heating reaction are: temperature 90℃, time 3.5h; (2) Preparation of base-coated copper foil: Step 1: Mix pure water, polyacrylic acid, isopropanol and active materials, stir evenly to obtain base-coated slurry; Step 2: Take copper foil, coat the base-coated slurry evenly on the upper and lower surfaces of the copper foil, dry to obtain base-coated copper foil; In step 1, the active material is ethyl acetate. A mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; in step 1, the mass ratio of polyacrylic acid to active material is 2:3; the mass ratio of pure water, isopropanol, and active material is 80:10:6; lithium magnesium silicate accounts for 1.3% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.7% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0046] Example 13: A method for preparing a base-coated copper foil that improves the stripping and cycle performance of the negative electrode, comprising the following steps: (1) Preparation of modified polyacrylic acid: Step A: Mix acrylic acid and trimethylolpropane, stir evenly, then add concentrated sulfuric acid, heat to react, remove water under reduced pressure, and obtain branched product; Step B: Under nitrogen atmosphere protection, mix hydrogen-containing silicone oil, allyl alcohol polyether, and catalyst, heat to react, and obtain hydroxyl-terminated silicone oil; Step C: Mix emulsifier and deionized water, add 1 / 2 mass of ammonium persulfate, heat to 73°C, and add α-methyl methacrylate, butyl acrylate, methacrylic acid, branched product, and hydroxyl-terminated silicone oil. Modified polyacrylic acid was obtained by heating and reacting basic silicone oil and residual ammonium persulfate, maintaining the temperature for 2.5 hours, adjusting the pH to 7.3, and stirring until homogeneous. In step A, the molar ratio of acrylic acid to trimethylolpropane was 6:1; the amount of concentrated sulfuric acid added in step A was 0.2% of the mass of acrylic acid; the heating reaction conditions in step A were: temperature 90℃, time 4.0 hours; the dehydration conditions in step A were: temperature 95℃, vacuum degree 6 kPa, time 1.5 hours. In step B, the molar ratio of hydrogen-containing silicone oil to allyl alcohol polyether was 2.4:1; the heating reaction conditions in step B were: temperature 130℃, time... 2.0h; In step C, the mass ratio of ammonium persulfate, emulsifier, deionized water, methyl α-methacrylate, butyl acrylate, methacrylic acid, branched products, and terminal hydroxyl silicone oil is 0.6:5:140:35:15:7:25:15; In step C, the process conditions for heating reaction are: temperature 85℃, time 3.0h; (2) Preparation of base-coated copper foil: Step 1: Mix pure water, polyacrylic acid, isopropanol and active materials, stir evenly to obtain base-coated slurry; Step 2: Take copper foil, evenly coat the base-coated slurry on the upper and lower surfaces of the copper foil, dry to obtain base-coated copper foil; In step 1, the active material is A mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; in step 1, the mass ratio of polyacrylic acid to active material is 2:3; the mass ratio of pure water, isopropanol, and active material is 75:9:6; lithium magnesium silicate accounts for 1.3% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 56.3% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0047] Example 14: A method for preparing a base-coated copper foil that improves the stripping and cycle performance of the negative electrode, comprising the following steps: (1) Preparation of modified polyacrylic acid: Step A: Mix acrylic acid and trimethylolpropane, stir evenly, then add concentrated sulfuric acid, heat to react, remove water under reduced pressure, and obtain branched product; Step B: Under nitrogen atmosphere protection, mix hydrogen-containing silicone oil, allyl alcohol polyether, and catalyst, heat to react, and obtain terminal hydroxyl silicone oil; Step C: Mix emulsifier and deionized water, add 1 / 2 mass of ammonium persulfate, heat to 70°C, and add α-methyl methacrylate, butyl acrylate, methacrylic acid, branched product, and terminal hydroxyl silicone oil. Hydroxysilicone oil and residual ammonium persulfate were heated and reacted, and kept at this temperature for 2 hours. The pH was adjusted to 7.0, and the mixture was stirred until homogeneous to obtain modified polyacrylic acid. In step A, the molar ratio of acrylic acid to trimethylolpropane was 5:1. In step A, the amount of concentrated sulfuric acid added was 0.1% of the mass of acrylic acid. In step A, the heating reaction conditions were: temperature 85℃, time 3.5 hours. In step A, the dehydration conditions under reduced pressure were: temperature 90℃, vacuum degree 2 kPa, time 1 hour. In step B, the molar ratio of hydrogen-containing silicone oil to allyl alcohol polyether was 2.0:1. In step B, the heating reaction conditions were: temperature 120℃, time 1 hour. 0.5h; In step C, the mass ratio of ammonium persulfate, emulsifier, deionized water, methyl α-methacrylate, butyl acrylate, methacrylic acid, branched products, and terminal hydroxyl silicone oil is 0.4:3:120:30:10:5:20:10; In step C, the process conditions for heating reaction are: temperature 80℃, time 2.5h; (2) Preparation of base-coated copper foil: Step 1: Mix pure water, polyacrylic acid, isopropanol and active materials, stir evenly to obtain base-coated slurry; Step 2: Take copper foil, coat the base-coated slurry evenly on the upper and lower surfaces of the copper foil, dry to obtain base-coated copper foil; In step 1, the active material is ethyl acetate. A mixture of acetylene black, lithium magnesium silicate, and ammonium carbonate; in step 1, the mass ratio of polyacrylic acid to active material is 2:3; the mass ratio of pure water, isopropanol, and active material is 70:8:6; lithium magnesium silicate accounts for 1.3% of the total mass of polyacrylic acid and active material; ammonium carbonate accounts for 2.6% of the total mass of polyacrylic acid and active material; the conductive agent accounts for 55.9% of the total mass of polyacrylic acid and active material; in step 1, the solid content of the primer slurry is 10%; in step 2, the coating speed is 50 m / min; in step 2, the drying process conditions are: temperature 120℃; in step 2, the coating surface density of the primer slurry is 3.0 g / m². 2 .

[0048] Comparative Example 1: Compared with Example 1, lithium magnesium silicate was not added to the primer slurry, and all other conditions remained the same as in Example 1.

[0049] Comparative Example 2: Compared with Example 1, ammonium carbonate was not added to the primer slurry, and all other conditions remained the same as in Example 1.

[0050] Comparative Example 3: No primer was applied to the copper foil surface; the copper foil was used directly.

[0051] Experiment: The copper foil with bottom coating obtained in the examples and comparative examples was used to make a soft-pack battery, and the performance of the soft-pack battery was tested. The preparation process of the soft-pack battery is as follows: S1: The active material, Super P, styrene-butadiene rubber, and carboxymethyl cellulose were mixed and stirred evenly to obtain a negative electrode slurry. This slurry was then coated onto the upper and lower surfaces of the copper foil with bottom coating and dried to obtain a negative electrode sheet. S2: LFP, PVDF, and Super P were mixed and stirred evenly to obtain a positive electrode slurry. This slurry was then coated onto the upper and lower surfaces of an aluminum foil and dried to obtain a positive electrode sheet. S3: The negative and positive electrode sheets were rolled, slit, and die-cut. They were then stacked and assembled with the separator in the order of "negative electrode sheet-separator-positive electrode sheet-separator". Electrolyte was then injected and the battery was tested for capacity to obtain a soft-pack battery. In S1, the active material was a graphite and silicon-carbon composite material at a mass ratio of 16:1. In S1, the active material, Super P, Super P, and Super P were mixed and stirred evenly to obtain a negative electrode slurry. This slurry was then coated onto the upper and lower surfaces of the aluminum foil and dried to obtain a positive electrode sheet. The mass ratio of P, styrene-butadiene rubber, and carboxymethyl cellulose is 95:2.5:1.7:0.8; in S1, the coating thickness of the negative electrode slurry is 80 μm; in S1, the drying process conditions are: temperature 90℃, time 1.0 h; in S2, the mass ratio of LFP, PVDF, and Super P is 96:5:5; in S2, the coating thickness of the positive electrode slurry is 100 μm; in S2, the drying process conditions are: temperature 140℃, time 50 min; in S3, the separator is a polyethylene separator with a thickness of 16 μm; in S3, the electrolyte is obtained by mixing LiPF6, EC, DMC, EMC, VC, and FEC in a mass ratio of 11:30:30:27:1:0.5.

[0052] Cyclic performance test: The soft-pack battery was charged and discharged using a charge-discharge tester. The voltage range was 2.8~3.75V and the discharge current was 1C. The capacity retention rate was tested after 100 and 300 cycles. Peel force test: The copper foil with bottom coating obtained in the examples and comparative examples was used to make negative electrode sheets. The negative electrode sheets were cut into 10×4cm samples and fixed on a steel plate. The steel plate and the sample were fixed in the sample test area of ​​the peel force tester for testing. The speed was set to 100mm / min and the test distance was 100mm.

[0053] Based on the data in the table above, the following conclusions can be drawn: Compared with Example 1, the negative electrode sheets prepared by the copper foil undercoating in Examples 12-14 have higher peel strength and better cycle performance of the soft-pack battery. This is because the cross-linked network formed by the modified polyacrylic acid can encapsulate the active material in the network, inhibiting the shedding caused by the expansion of the active material and improving the peel strength of the negative electrode sheet. The polyether segments have good affinity for the electrolyte, which helps to enhance the wettability of the electrolyte, improve the ionic conductivity, and further enhance the cycle performance of the soft-pack battery. Compared with Example 1, the peel strength of the negative electrode sheet and the cycle performance of the soft-pack battery in Comparative Examples 1 and 2 both decreased to varying degrees. This is because lithium magnesium silicate can significantly improve the mechanical strength and toughness of the coating, and its surface carboxyl groups and polyacrylic acid... After the oxygen-containing groups are combined, a large number of high-strength hydrogen bonds are formed. When huge expansion stress is generated during cycling, the hydrogen bond network will break preferentially, absorb energy, buffer the structural changes of the active material, and thus improve the cycle performance of the battery. When ammonium carbonate is heated, it decomposes into NH3 and CO2. The gas escapes and leaves nanoscale pores in the coating, which can generate a stronger anchoring effect with the negative electrode active material, improve the electrode peeling force, and the pores themselves can act as buffer pores to suppress the volume expansion of silicon particles during lithium intercalation and improve cycle performance. Compared with Example 1, Comparative Example 3 has the worst peel strength and cycle performance. It can be seen that the setting of modified polyacrylic acid, lithium magnesium silicate and ammonium carbonate in this application can promote the comprehensive improvement of the peeling performance of the prepared negative electrode and the cycle performance of the prepared soft pack battery.

[0054] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for preparing a base-coated copper foil that improves the peeling and cycle performance of the negative electrode, characterized in that: The process includes the following steps: Step 1: Mix pure water, polyacrylic acid, isopropanol and active material, stir evenly to obtain a base coating slurry; Step 2: Take copper foil, evenly coat the base coating slurry on the upper and lower surfaces of the copper foil, and dry to obtain a base-coated copper foil; In Step 1, the active material is a mixture of conductive agent, lithium magnesium silicate and ammonium carbonate; the conductive agent is acetylene black; In Step 1, the mass ratio of polyacrylic acid to active material is 2:(2~3).

2. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 1, characterized in that: The lithium magnesium silicate accounts for 0.7 to 1.5% of the total mass of polyacrylic acid and active materials.

3. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 2, characterized in that: The ammonium carbonate accounts for 2.2 to 3.0% of the total mass of polyacrylic acid and active materials.

4. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 3, characterized in that: In step 1, the solid content of the primer slurry is 8-10%.

5. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 4, characterized in that: In step 2, the thickness of the copper foil is 6~8μm.

6. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 5, characterized in that: In step 2, the coating speed is 40~50m / min.

7. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 6, characterized in that: In step 2, the drying process conditions are: temperature 110~120℃.

8. The method for preparing the undercoated copper foil for improving the peeling and cycle performance of the negative electrode sheet according to claim 7, characterized in that: In step 2, the surface density of the primer slurry is 2.0~3.0 g / m². 2 .

9. The method for preparing the undercoated copper foil for improving the stripping and cycle performance of the negative electrode sheet according to claim 1, characterized in that: The modified polyacrylic acid is processed as follows: Step A: Acrylic acid and trimethylolpropane are mixed and stirred evenly, then concentrated sulfuric acid is added, the mixture is heated to react, and dehydrated under reduced pressure to obtain a branched product; Step B: Under a nitrogen atmosphere, hydrogen-containing silicone oil, allyl alcohol polyether, and catalyst are mixed and heated to react to obtain hydroxyl-terminated silicone oil; Step C: Emulsifier and deionized water are mixed, 1 / 2 mass of ammonium persulfate is added, the temperature is raised to 70~75℃, methyl α-methacrylate, butyl acrylate, methacrylic acid, branched product, hydroxyl-terminated silicone oil, and the remaining ammonium persulfate are added, the mixture is heated to react, and kept at this temperature for 2~3 hours. The pH is adjusted to 7.0~7.5, and the mixture is stirred evenly to obtain modified polyacrylic acid.

10. The copper foil with a base coating for improving the peeling and cycle performance of the negative electrode sheet according to any one of claims 1 to 9, characterized in that: It is used to manufacture pouch cells.

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