Carbon-coated current collector with high conductivity and high adhesive strength and application of carbon-coated current collector

Abstract

The invention discloses a carbon-coated current collector with high conductivity and high adhesive strength and application thereof, and relates to the technical field of lithium batteries. Wherein the carbon-coated current collector comprises an aluminum foil and carbon-coated slurry coated on the surface of the aluminum foil; the preparation method of the carbon-coated slurry comprises the following steps: mixing polyacrylic acid glue with deionized water to obtain a polyacrylic acid solution, adding polyurethane hybrid polyacrylate, dispersing at a low speed, adding half of carbon powder and half of graphite powder, dispersing at a high speed, adding the rest of carbon powder and graphite powder, dispersing uniformly, adding a noble metal conductive agent, continuously dispersing at a high speed, and drying to obtain the carbon-coated slurry. Adding deionized water to reduce the concentration of the mixed material, adding a pH regulator and a wetting agent, stirring, homogenizing, and discharging to obtain carbon coating slurry; and coating the carbon-coated slurry on the surface of an aluminum foil to obtain the carbon-coated current collector.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and specifically to a carbon-coated current collector with high conductivity and high adhesion force and its application. Background Art

[0002] Lithium-ion batteries (LIBs) have been widely accepted in many fields such as consumer electronics, transportation, power tools, and energy storage. The aluminum foil current collector refers to the process of combining aluminum foil with other materials (such as paper, plastic film, coatings, etc.) to form a composite material. This technology can endow the aluminum foil with new properties and functions to meet the needs of different industries. In the lithium battery industry, in order to improve the performance of lithium batteries, the strategy of using carbon-coated current collectors is adopted to improve the rate performance of lithium batteries and enhance the performance of lithium batteries. However, the film resistance of the carbon-coated aluminum foil current collector will directly affect the electrical performance of lithium batteries, and the adhesion force between the carbon-coated current collector and the positive active material will affect the cycle stability and cycle life of lithium batteries. In order for lithium battery samples to have excellent performance, it is necessary to develop a carbon-coated current collector material with both high conductivity and high adhesion force. Summary of the Invention

[0003] The purpose of the present invention is to provide a carbon-coated current collector with high conductivity and high adhesion force and its application to solve the problems raised in the prior art.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] A carbon-coated current collector with high conductivity and high adhesion force includes an aluminum foil and a carbon-coated slurry coated on the surface of the aluminum foil; the preparation steps of the carbon-coated slurry are as follows:

[0006] Mix polyacrylic acid glue and deionized water to obtain a polyacrylic acid solution, add polyurethane hybrid polyacrylate, disperse at low speed for 30 min, then add half of the carbon powder and half of the graphite powder, disperse at high speed for 30 - 40 min, then add the remaining carbon powder and graphite powder, continue to disperse at high speed for 60 - 65 min, add a noble metal conductive agent and disperse at high speed for 30 - 40 min, then add deionized water and continue to disperse at high speed for 30 - 40 min, add a pH regulator to adjust the pH of the system to 5 - 7, and finally add a wetting agent, stir at 10 - 15 rpm / min for 30 - 45 min, and homogenize 2 times at 300 bar to obtain the carbon-coated slurry.

[0007] Preferably, the content of polyacrylic acid in the polyacrylic acid solution is 10 - 15%.

[0008] The content of polyacrylic acid in the carbon-coated slurry is 7-10%; among them, the mass ratio of polyurethane hybrid polyacrylate, polyacrylic acid, carbon powder, graphite powder, noble metal conductive agent, pH regulator and wetting agent is (0.1-0.5):100:50:50:(1-10):5:20.

[0009] The noble metal conductive agent is titanium carbon nanotubes; the reason for choosing titanium carbon nanotubes is as follows:

[0010] ① High electrical conductivity: Titanium carbon nanotubes have excellent electrical conductivity, which can effectively improve the conductivity of electrode materials, thereby reducing the internal resistance of the battery and improving energy efficiency;

[0011] ② Mechanical strength: Titanium carbon nanotubes have good mechanical properties, including high strength and high elastic modulus. This enables the electrode material to withstand the volume changes during charging and discharging, thereby extending the service life of the battery;

[0012] ③ Chemical stability: The combination of titanium and carbon endows titanium carbon nanotubes with high chemical stability, which can remain stable within a wide pH range, reduce the reaction with the electrolyte, and extend the service life of the battery;

[0013] ④ Large specific surface area: The structure of titanium carbon nanotubes provides a large specific surface area, which helps to improve the lithium ion storage capacity and electrochemical activity of electrode materials.

[0014] The wetting agent is one of polyether siloxane, modified polyether siloxane and alcohol reagents; the alcohol reagent is one of ethanol and isopropanol.

[0015] The high-speed rotation speed is 2000-2600 rpm / min;

[0016] The low-speed rotation speed is 1000-1200 rpm / min;

[0017] The single-sided coating thickness of the carbon-coated slurry is 0.3-1 μm;

[0018] The preparation steps of polyurethane hybrid polyacrylate are as follows (by mass parts):

[0019] ① The first step: Take 5-7 parts of polyurethane and 2-5 parts of polyacrylate, add 0.01-0.05 parts of dibutyltin dilaurate at 25°C and react for 3-4 hours to generate a prepolymer with terminal isocyanate groups;

[0020] ② The second step: Take 20 parts of the prepolymer generated in the first step and react with 1 part of polyacrylate for 50-65 minutes, and combine through the reaction of terminal isocyanate and the hydroxyl group of polyacrylate to obtain a reaction mixture;

[0021] ③ Step 3: After heating the reaction mixture to 150 °C and reacting for 30 min to promote the formation of stronger bonding between the polyurethane and polyacrylate components, transfer it to a vacuum drying oven and dry and age it at 60 °C for 24 hours to obtain the finished product for use.

[0022] The mechanism of action of polyurethane hybrid polyacrylate in the electrode sheet made of coated current collector is as follows:

[0023] ① It contains double bonds with optimized functionality and can undergo thermal cross-linking during the drying process of the electrode sheet to form a stable and elastic three-dimensional network structure, which is beneficial to the structural stability of the electrode sheet layer;

[0024] ② Polyurethane hybrid polyacrylate contains abundant urethane bonds and can form hydrogen bonds with PVDF in the positive electrode active slurry, playing a bridging role in stabilizing the binder / active material interface. The formed elastic interface film helps to buffer the stress generated during the lithium deintercalation / insertion process of the positive electrode material and inhibits the generation of cracks and structural fragmentation of the positive electrode particles;

[0025] ③ The urethane groups in polyurethane hybrid polyacrylate can chelate with transition metal ions in the active material, thereby anchoring more transition metal ions on the positive electrode side to prevent their dissolution and reduction on the negative electrode side and staying in the intercalation layer of the negative electrode material, thus reducing the adverse effects on lithium deintercalation / insertion;

[0026] ④ The special structural design not only effectively enhances the connection between the coated carbon layer and the positive electrode layer, but also provides an electronic path between the two materials, effectively improving the conductivity of the electrode sheet.

[0027] Preferably, the polyurethane is prepared in the laboratory, and the preparation steps are as follows: Mix isophorone diisocyanate, polyethylene glycol, maleic anhydride and hydroxy silicone oil, heat up to 70 °C and react for 2 h, then cool down to 60 °C, add 2,2-dimethylolpropionic acid, dibutyltin dilaurate and acetone and continue to react for 2 h, cool down to 40 °C, add triethylamine and react for 8 - 10 min, and then carry out vacuum distillation to obtain polyurethane; in the reaction system, by mass, it includes 4 - 5 parts of isophorone diisocyanate, 12 - 15 parts of polyethylene glycol, 0.1 - 0.3 parts of maleic anhydride, 1 - 3 parts of hydroxy silicone oil, and 0.3 - 0.4 parts of dimethylolpropionic acid; the mass of dibutyltin dilaurate is 0.1 - 0.2% of the total mass of the reaction system; the mass of triethylamine is 3 - 4% of the total mass of the reaction system.

[0028] Preferably, the noble metal conductive agent is pretreated, and the specific steps are as follows: The noble metal conductive agent is placed in a toluene solution, ultrasonically dispersed for 10-20 min, 3-aminopropyltriethoxysilane is added, heated to 100 °C, kept warm and stirred for reaction for 4 h, centrifuged and washed, dried and then placed in a dimethyl sulfoxide solution, styrene-maleic anhydride copolymer is added, ultrasonically dispersed for 5-8 min, heated to 80 °C under a protective atmosphere, stirred for reaction for 24 h, cooled to room temperature, centrifuged and washed, and dried for standby; the mass ratio of the noble metal conductive agent to 3-aminopropyltriethoxysilane is 1:(2-3), and the addition amount of the styrene-maleic anhydride copolymer is 10-30% of the mass of 3-aminopropyltriethoxysilane.

[0029] An application of the above carbon-coated current collector in a positive electrode plate, wherein the surface density of the single-sided positive electrode active material in the positive electrode plate is 200 g / m 2 , and the tap density is 2.3-2.4 g / cc;

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] 1. In the solution, by adding polyurethane hybrid polyacrylate and noble metal conductive agent catalyst to the carbon-coated slurry, the cohesive strength, conductivity and adhesion of the carbon-coated layer are significantly improved. Specifically, polyurethane (PU) and polyacrylate (PA) are chemically hybridized to form a polymer material with excellent mechanical properties, chemical stability and adjustable properties; among them, polyurethane provides good toughness and elasticity, while polyacrylate enhances the hardness and wear resistance of the material; in addition, hydroxyl silicone oil and polyethylene glycol segments are introduced into the polyurethane, further improving the flexibility, adhesion and chemical stability of the carbon-coated layer; at the same time, the addition of the noble metal conductive agent effectively reduces the resistance of the carbon-coated layer, improves the conductivity, and reduces the internal resistance of the battery. These improvements work together to significantly improve the electrical performance and cycle life of the lithium battery;

[0032] 2. In the solution, by adding styrene-maleic anhydride copolymer to the surface of titanium carbon nanotubes, the dispersibility of titanium carbon nanotubes in the carbon-coated slurry is significantly improved, the agglomeration phenomenon of nanotubes is reduced, so that the conductive agent can be more evenly distributed in the carbon-coated layer, thereby improving the conductivity of the carbon-coated layer. The carboxyl and anhydride groups in the styrene-maleic anhydride copolymer can form hydrogen bonds or chemical bonds with the polyurethane hybrid polyacrylate in the carbon-coated layer, enhancing the interfacial bonding force between the titanium carbon nanotubes and the carbon-coated layer, reducing the shedding of the conductive agent, and further improving the conductive stability of the carbon-coated layer. In addition, the introduction of the styrene-maleic anhydride copolymer also enhances the mechanical strength and toughness of the carbon-coated layer, enabling it to better withstand volume changes during the charge and discharge process of the battery, reducing cracks and structural damage in the carbon-coated layer, and thus improving the cycle life of the battery. Specific embodiments

[0033] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0034] In the experiment, the precious metal conductive agent was titanium carbon nanotubes, purchased from Xi'an Qiyue Biotechnology Co., Ltd., model number Ti3C2-CNT, which is composed of titanium carbide-coated carbon nanotubes (carbon nanotube-modified titanium carbide Ti3C2 two-dimensional composite material). Product parameters include appearance as solid or powder, quality index of more than 95%, storage conditions of -20°C in the dark, and storage life of 1 year;

[0035] The wetting agent is modified polyether siloxane, model number IOTA 13190, purchased from Anhui Aiyota Silicone Oil;

[0036] The polyacrylic acid glue has a solid content of 20% and a viscosity of 800-3500 mPa.s; it was purchased from Sinopharm Group with a national medicine code of C278382500;

[0037] The average Mn of polyethylene glycol is 400, and the viscosity of hydroxy silicone oil is 350 mPa.s, both of which were purchased from Shanghai Aladdin Reagent;

[0038] Styrene-maleic anhydride copolymer model SMA-125 was purchased from Howin;

[0039] In the experiment, the preparation steps of polyurethane hybrid polyacrylate are as follows (in parts by mass):

[0040] ① Step 1: Take 7 parts of polyurethane and 3 parts of polyacrylate, add 0.02 parts of dibutyltin dilaurate and react at 25°C for 3.5 hours to generate a prepolymer with terminal isocyanate groups;

[0041] ② Step 2: Take 20 parts of the prepolymer produced in the first step and react with 1 part of polyacrylate for 60 minutes to obtain a reaction mixture through the reaction of isocyanate and hydroxyl groups;

[0042] ③ Step 3: Heat the reaction mixture to 150°C and react for 30 minutes to promote the formation of stronger bonds between the polyurethane and polyacrylate components. Transfer the mixture to a vacuum drying oven and dry and age it at 60°C for 24 hours to obtain the finished product for use.

[0043] Among them, the polyurethane in the polyurethane hybrid polyacrylate in Examples 1-6 was purchased from BASF, with the model being Elastollan; the polyacrylate model was BA122, purchased from Shanghai Kayin Chemical Co., Ltd.;

[0044] In Example 7, the polyurethane in the polyurethane hybrid polyacrylate was self-made in the laboratory; the polyacrylate model was BA122, purchased from Shanghai Kayin Chemical Co., Ltd.;

[0045] Example 1: This example provides a processing method for a carbon-coated current collector, and the specific steps are as follows:

[0046] Mix polyacrylic acid glue and deionized water. After obtaining a polyacrylic acid solution, load it into a 200L Shuangxing stirring tank, add polyurethane hybrid polyacrylate, and disperse it at a low speed of 1200 rpm / min for 30 min. Then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, add the remaining carbon powder and graphite powder, and disperse it at a high speed of 2400 rpm / min for 60 min. Add a noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min. Then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min. Add 0.05 mM sodium hydroxide and adjust the pH of the system to 6. Finally, add a modified polyether siloxane and stir it at a low speed of 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain a carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain a carbon-coated current collector;

[0047] The polyacrylic acid content in the above polyacrylic acid solution is 10%;

[0048] The solid content in the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.3:100:50:50:5:5:20.

[0049] Example 2: Referring to the processing method of Example 1, the difference is that: adjust the solid content in the carbon-coated slurry, polyurethane hybrid polyacrylate: polyacrylic acid = 0.1:100, and the specific steps are as follows:

[0050] Mix polyacrylic acid glue and deionized water. After obtaining the polyacrylic acid solution, load it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse it at a low speed of 1200 rpm / min for 30 min, then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, add the remaining carbon powder and graphite powder, disperse it at a high speed of 2400 rpm / min for 60 min, add the noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min, then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the pH of the system to 6, and finally add modified polyether siloxane, stir it at 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, with a single-sided carbon coating thickness of 0.5 μm, to obtain the carbon-coated current collector;

[0051] The content of polyacrylic acid in the above polyacrylic acid solution is 10%;

[0052] The solid content of the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.1:100:50:50:5:5:20.

[0053] Example 3: Refer to the processing method of Example 1. The difference is that: adjust the solid content in the carbon-coated slurry, polyurethane hybrid polyacrylate: polyacrylic acid = 0.2:100. The specific steps are as follows:

[0054] Mix polyacrylic acid glue and deionized water. After obtaining the polyacrylic acid solution, load it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse it at a low speed of 1200 rpm / min for 30 min, then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, add the remaining carbon powder and graphite powder, disperse it at a high speed of 2400 rpm / min for 60 min, add the noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min, then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the pH of the system to 6, and finally add modified polyether siloxane, stir it at 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, with a single-sided carbon coating thickness of 0.5 μm, to obtain the carbon-coated current collector;

[0055] The content of polyacrylic acid in the above polyacrylic acid solution is 10%;

[0056] The solid content of the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.2:100:50:50:5:5:20.

[0057] Example 4: Referring to the processing method of Example 1, the difference is that: the solid content in the carbon-coated slurry is adjusted, and polyurethane hybrid polyacrylate: polyacrylic acid = 0.4:100. The specific steps are as follows:

[0058] Mix polyacrylic acid glue and deionized water. After obtaining the polyacrylic acid solution, put it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse it at a low speed of 1200 rpm / min for 30 min, then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, then add the remaining carbon powder and graphite powder, disperse it at a high speed of 2400 rpm / min for 60 min, add the noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min, then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the pH of the system to 6, and finally add modified polyether siloxane, stir it at 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain the carbon-coated current collector;

[0059] The content of polyacrylic acid in the above polyacrylic acid solution is 10%;

[0060] The solid content of the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.4:100:50:50:5:5:20.

[0061] Example 5: Referring to the processing method of Example 1, the difference is that: the solid content in the carbon-coated slurry is adjusted, and polyurethane hybrid polyacrylate: polyacrylic acid = 0.5:100. The specific steps are as follows:

[0062] Mix polyacrylic acid glue and deionized water. After obtaining the polyacrylic acid solution, load it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse it at a low speed of 1200 rpm / min for 30 min, then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, then add the remaining carbon powder and graphite powder, disperse it at a high speed of 2400 rpm / min for 60 min, add the noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min, then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the system pH to 6, and finally add modified polyether siloxane, stir it at 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain the carbon-coated current collector;

[0063] The polyacrylic acid content in the above polyacrylic acid solution is 10%;

[0064] The solid content of the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.5:100:50:50:5:5:20.

[0065] Example 6: Refer to the processing method of Example 1, the difference is: adjust the carbon powder: graphite powder: noble metal conductive catalyst in the solid content of the carbon-coated slurry to 50:50:2; the specific steps are as follows:

[0066] Mix polyacrylic acid glue and deionized water. After obtaining the polyacrylic acid solution, load it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse it at a speed of 1200 rpm / min for 30 min, then add half of the carbon powder and half of the graphite powder, disperse it at a high speed of 2400 rpm / min for 30 min, then add the remaining carbon powder and graphite powder, disperse it at a high speed of 2400 rpm / min for 60 min, add the noble metal conductive agent and disperse it at a high speed of 2400 rpm / min for 20 min, then add deionized water and continue to disperse it at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the system pH to 6, and finally add modified polyether siloxane, stir it at a low speed of 15 rpm / min for 30 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain the carbon-coated current collector;

[0067] The polyacrylic acid content in the above polyacrylic acid solution is 10%;

[0068] The solid content in the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.3:100:50:50:2:5:20.

[0069] Example 7: Referring to the processing method of Example 2, the difference is that: the polyurethane is self-made in the laboratory and the noble metal catalyst is pretreated. The specific steps are as follows:

[0070] Mix polyacrylic acid glue and deionized water to obtain a polyacrylic acid solution, then put it into a 200L double-star stirring tank, add polyurethane hybrid polyacrylate, disperse at a speed of 1200 rpm for 30 min, add half of the carbon powder and half of the graphite powder, disperse at a high speed of 2400 rpm for 30 min, then add the remaining carbon powder and graphite powder, disperse at a high speed of 2400 rpm for 60 min, add the pretreated noble metal conductive agent and disperse at a high speed of 2400 rpm for 20 min, then add deionized water and continue to disperse at a high speed of 2400 rpm for 30 min, add 0.05 mM sodium hydroxide, adjust the pH of the system to 6, finally add modified polyether siloxane, stir at a low speed of 15 rpm for 30 min, and then homogenize at 300 bar twice to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain a carbon-coated current collector;

[0071] Among them, the preparation method of the polyurethane in the polyurethane hybrid polyacrylate is as follows:

[0072] Mix 5 g of isophorone diisocyanate, 15 g of polyethylene glycol, 0.2 g of maleic anhydride and 2 g of hydroxy silicone oil, heat up to 70 °C and react for 2 h, then cool down to 60 °C, add 0.4 g of 2,2-dimethylolpropionic acid, 0.03 g of dibutyltin dilaurate and 10 mL of acetone and continue to react for 2 h, cool down to 40 °C, add 0.8 g of triethylamine, react for 8 - 10 min, and then carry out vacuum distillation to obtain polyurethane;

[0073] The specific steps for pretreating the noble metal conductive agent are: put 1 g of the noble metal conductive agent into 30 mL of toluene solution, ultrasonically disperse for 20 min, add 3 g of 3-aminopropyltriethoxysilane, heat up to 100 °C, keep stirring and reacting for 4 h, centrifuge and wash, dry, then put it into 30 mL of dimethyl sulfoxide solution, add 0.6 g of styrene-maleic anhydride copolymer, ultrasonically disperse for 5 min, heat up to 80 °C under a protective atmosphere, stir and react for 24 h, then cool to room temperature, centrifuge and wash, and dry for standby;

[0074] The content of polyacrylic acid in the polyacrylic acid solution is 10%;

[0075] The solid content of the carbon-coated slurry is set to 10%; among them, polyurethane hybrid polyacrylate: polyacrylic acid: carbon powder: graphite powder: pretreated noble metal conductive agent: 0.05 mM sodium hydroxide: modified polyether siloxane = 0.1:100:50:50:5:5:20.

[0076] Comparative Example 1: As a control experiment for Example 1, polyurethane hybrid polyacrylate and noble metal conductive agent are not added. The specific steps are as follows:

[0077] Mix polyacrylic acid glue and deionized water to obtain a polyacrylic acid solution, then load it into a 200L double-star stirring tank, add half of the carbon powder and half of the graphite powder, disperse at a high speed of 2400 rpm / min for 30 min, then add the remaining carbon powder and graphite powder, disperse at a high speed of 2400 rpm / min for 60 min, then add deionized water and continue to disperse at a high speed of 2400 rpm / min for 30 min, add 0.05 mM sodium hydroxide, adjust the pH of the system to 6, and finally add modified polyether siloxane, stir at a low speed of 15 rpm / min for 30 min, and then homogenize twice at 300 bar to obtain the carbon-coated slurry; coat the carbon-coated slurry on the surface of the aluminum foil, and the single-sided carbon coating thickness is 0.5 μm to obtain the carbon-coated current collector;

[0078] The content of polyacrylic acid in the polyacrylic acid solution is 10%;

[0079] The solid content of the carbon-coated slurry is set to 10%; among them, polyacrylic acid: carbon powder: graphite powder: 0.05 mM sodium hydroxide: modified polyether siloxane = 100:50:50:5:20.

[0080] Detection test

[0081] 1. Penetration resistance and pole piece resistance: Take 2×2 cm specimens of the carbon-coated current collectors prepared in Examples 1-7 and the comparative examples, and test them on a membrane resistance tester. The data are recorded in Table 1;

[0082] 2. Pole piece peel strength: Take the carbon-coated current collectors prepared in Examples 1-7 and the comparative examples, and coat the positive electrode active material on the surface of the carbon-coated current collector. The positive electrode active material is composed of PVDF, carbon black, lithium iron phosphate, and solvent NMP; among them, the solid content of the slurry is 55%, and the component ratio of the solid is PVDF: lithium iron phosphate: carbon black = 2:97:1; the surface density of the single-sided positive electrode active material is 200 g / m 2 , the compaction density is 2.35 g / cc to obtain the positive electrode pole piece; stick it on the test board with 3M double-sided tape, separate the positive electrode active material from the carbon-coated current collector, stick the tape on the carbon-coated current collector, and test the 180° pole piece peel strength on a tensile machine and record it in Table 1.

[0083] Table 1

[0084] Project Through - resistance (mΩ) Pole - piece resistance (mΩ) Pole - piece peel force (N / m) Example 1 1.55 150 50.0 Example 2 2.88 215 24.3 Example 3 2.74 200 33.5 Example 4 2.21 183 32.4 Example 5 2.18 184 20.3 Example 6 4.11 200 15.5 Example 7 2.40 192 32.6 Comparative Example 1 5.52 288 10.2

[0085] Conclusion: From the above data, it can be seen that Example 1 has good high conductivity and high adhesion compared with Examples 2-6; in Example 7, the commercially available polyurethane was replaced with a product prepared in the laboratory on the basis of Example 1, and the noble metal conductive agent was pretreated, which improved the bonding effect to a certain extent and had good conductivity; in Comparative Example 1, the polyurethane hybrid polyacrylate and the noble metal conductive agent were not added, and the effect decreased significantly.

[0086] Through the synergistic effect of polyurethane hybrid polyacrylate, noble metal conductive agent catalyst and surface-modified titanium carbon nanotubes, the present invention provides a carbon-coated current collector with high conductivity and high adhesion, significantly improving the electrical performance and cycle life of lithium batteries, which meets the actual application.

[0087] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

Claims

1. A coated carbon current collector with high conductivity and high adhesion force, characterized in that, The carbon-coated current collector includes an aluminum foil and a carbon-coated slurry coated on the surface of the aluminum foil; the preparation steps of the carbon-coated slurry are as follows: Mix polyacrylic acid glue and deionized water to obtain a polyacrylic acid solution. Add polyurethane hybrid polyacrylate and disperse it at a low speed for 30 min. Then add half of the carbon powder and half of the graphite powder. After dispersing at a high speed for 30 - 40 min, add the remaining carbon powder and graphite powder, and continue to disperse at a high speed for 60 - 65 min. Then add a noble metal conductive agent and disperse at a high speed for 30 - 40 min. Add deionized water and continue to disperse at a high speed for 30 - 40 min. Add a pH regulator to adjust the pH of the system to 5 - 7. Finally, add a wetting agent and stir at 10 - 15 rpm / min for 30 - 45 min, and then homogenize it twice at 300 bar to obtain the carbon-coated slurry.

2. The carbon-coated current collector with high conductivity and high adhesion force according to claim 1, characterized in that The content of polyacrylic acid in the polyacrylic acid solution is 10 - 15%; the solid content of the carbon-coated slurry is 7 - 10%, and the mass ratio of polyurethane hybrid polyacrylate, polyacrylic acid, carbon powder, graphite powder, noble metal conductive agent, pH regulator and wetting agent is (0.1 - 0.5):100:50:50:(1 - 10):5:

20.

3. The carbon-coated current collector with high conductivity and high adhesion force according to claim 1, wherein The noble metal conductive agent is titanium carbon nanotubes; the wetting agent is one of polyether siloxane, modified polyether siloxane and alcohol reagents; the alcohol reagent is one of ethanol and isopropanol.

4. The carbon-coated current collector with high conductivity and high adhesion force according to claim 1, wherein The high-speed rotation speed is 2000 - 2600 rpm / min; the low-speed rotation speed is 1000 - 1200 rpm / min; the single-sided coating thickness of the carbon-coated slurry is 0.3 - 1 μm.

5. A carbon-coated current collector having high conductivity and high adhesion force according to claim 1, characterized in that, In terms of mass parts, the preparation steps of polyurethane hybrid polyacrylate are as follows: ① The first step: Take 5 - 7 parts of polyurethane and 2 - 5 parts of polyacrylate, add 0.01 - 0.05 parts of dibutyltin dilaurate at 25 °C and react for 3 - 4 h to generate a prepolymer with terminal isocyanate groups. ② The second step: Take 20 parts of the prepolymer generated in the first step and react with 1 part of polyacrylate for 50 - 65 min to obtain a reaction mixture. ③ The third step: Heat the reaction mixture to 150 °C and react for 30 min, then transfer it to a vacuum drying oven and dry and age it at 60 °C for 24 hours to obtain the finished product for use.

6. The carbon-coated current collector with high conductivity and high adhesion force according to claim 5, characterized in that The preparation steps of polyurethane are as follows: Mix isophorone diisocyanate, polyethylene glycol, maleic anhydride and hydroxy silicone oil, heat up to 70 °C and react for 2 h, then cool down to 60 °C, add 2,2 - dimethylolpropionic acid, dibutyltin dilaurate and acetone and continue to react for 2 h. Cool down to 40 °C and add triethylamine and react for 8 - 10 min, then carry out vacuum distillation to obtain polyurethane.

7. The carbon-coated current collector with high conductivity and high adhesion force according to claim 6, wherein The reaction system includes, in terms of mass parts, 4 - 5 parts of isophorone diisocyanate, 12 - 15 parts of polyethylene glycol, 0.1 - 0.3 parts of maleic anhydride, 1 - 3 parts of hydroxy silicone oil and 0.3 - 0.4 parts of dimethylolpropionic acid; the mass of dibutyltin dilaurate is 0.1 - 0.2% of the total mass of the reaction system; the mass of triethylamine is 3 - 4% of the total mass of the reaction system.

8. The carbon-coated current collector with high conductivity and high adhesion force according to claim 1, characterized in that The noble metal conductive agent is pretreated, and the specific steps are as follows: The noble metal conductive agent is placed in a toluene solution, ultrasonically dispersed for 10 - 20 min, 3-aminopropyltriethoxysilane is added, heated to 100 °C, kept warm and stirred for reaction for 4 h, centrifuged and washed, dried and then placed in a dimethyl sulfoxide solution, styrene-maleic anhydride copolymer is added, ultrasonically dispersed for 5 - 8 min, heated to 80 °C under a protective atmosphere, stirred for reaction for 24 h, cooled to room temperature, centrifuged and washed, and dried for standby.

9. The carbon-coated current collector with high conductivity and high adhesion force according to claim 8, characterized in that The mass ratio of the noble metal conductive agent to 3-aminopropyltriethoxysilane is 1:(2 - 3), and the addition amount of the styrene-maleic anhydride copolymer is 10 - 30% of the mass of 3-aminopropyltriethoxysilane.

10. Application of the carbon-coated current collector according to any one of claims 1-9 in a positive electrode sheet, characterized in that The areal density of the single-sided positive active material in the positive electrode sheet is 200 g / m 2 , and the tap density is 2.3 - 2.4 g / cc.