Composite cathode sheet, method for preparing the same, and use thereof

Abstract

The application provides a composite positive electrode sheet, a preparation method and application thereof. The composite positive electrode sheet comprises a positive electrode current collector, a carbon coating layer and an active material layer which are sequentially stacked, wherein the carbon coating layer comprises dopamine modified nano-conductive carbon material, and the active material layer comprises a silane coupling agent coated positive electrode active material. The composite positive electrode sheet can improve the adhesion between the active material and the carbon coating layer, and the adhesion between the carbon coating layer and the current collector, thereby comprehensively improving the adhesion between the active material and the current collector, reducing the probability of active material falling off during the cycle process of the battery, thereby reducing the problem of unstable capacity during the use of the battery, and improving the compaction density and energy density of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a composite positive electrode sheet, a preparation method and application thereof. BACKGROUND

[0002] After the slurry of the lithium ion battery positive electrode active material is prepared, it needs to be coated on the surface of the current collector such as aluminum foil to obtain a positive electrode sheet. However, when the active slurry is directly coated on the surface of the aluminum foil, the contact resistance between the active material and the foil is high, the peeling strength is low, and the cohesion between the active material particles is also low.

[0003] During the electrical performance test and the cycle performance test of the prepared battery, and in the actual use process of the battery, the active material and the foil substrate will be separated or the active material will be powdery, which will cause the capacity of the battery to be unstable during use.

[0004] By coating a carbon coating layer on the surface of the current collector, the electrical conduction between the current collector and the active material can be improved, and the contact resistance between the active material and the current collector can be reduced. However, after further coating of the active material, the adhesion between the carbon coating layer on the surface of the current collector and the current collector is reduced, and the carbon coating layer will also be separated. SUMMARY

[0005] The main purpose of the present application is to provide a composite positive electrode sheet, a preparation method and application thereof, so as to solve the problem of low adhesion between the positive electrode active material and the current collector and easy separation in the prior art.

[0006] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a composite positive electrode sheet is provided, which comprises a positive electrode current collector, a carbon coating layer and an active material layer which are stacked in sequence, wherein the carbon coating layer comprises dopamine-modified nano-conductive carbon material, and the active material layer comprises positive electrode active material coated with silane coupling agent. The composite positive electrode sheet of the present application can improve the adhesion between the active material and the carbon coating layer, and the adhesion between the carbon coating layer and the current collector, thereby comprehensively improving the adhesion between the active material and the current collector, reducing the probability of active material separation during the cycle process of the battery, thereby reducing the problem of unstable capacity during the use of the battery, and improving the compaction density and energy density of the battery.

[0007] Further, in the carbon coating layer, the nano-conductive carbon material comprises nano-conductive graphite and / or nano-conductive carbon black; and / or the weight ratio of dopamine to nano-conductive material is (20-40):100, preferably (25-35):100. Under the above conditions, the self-polymerization effect of dopamine can be better improved.

[0008] Furthermore, in the active material layer, the positive electrode active material includes one or more of lithium iron phosphate, lithium iron manganese, and nickel cobalt manganese; and / or the weight ratio of silane coupling agent to positive electrode active material is 100:(30-50), preferably 100:(35-45). Under the above conditions, the electrical conductivity of the positive electrode active particles can be further improved.

[0009] Furthermore, the weight ratio of the nano-conductive material to the positive electrode active material is 100:(30-50). Under these conditions, the adhesion strength between the positive electrode active material and the carbon coating layer can be better improved.

[0010] Furthermore, the silane coupling agent includes one or more of KH550, KH560, and KH570; and / or the positive electrode current collector includes aluminum foil and / or copper foil. This can further reduce costs.

[0011] According to another aspect of the present invention, a method for preparing the above-mentioned composite positive electrode sheet is provided, comprising the following steps: Step S1, dissolving dopamine in a buffer solution, adding and dispersing nano-conductive carbon material, and coating it onto the surface of the positive current collector to obtain a carbon coating layer; Step S2, mixing the positive active material with a silane coupling agent and coating it onto the surface of the carbon coating layer to obtain the composite positive electrode sheet. The above preparation method is simple and easy to operate. The composite positive electrode sheet obtained has high adhesion between the positive active material and the current collector and is not easily detached. Furthermore, the preparation process does not use harmful components, resulting in minimal harm to the human body and minimal environmental pollution during production and use, making it an environmentally friendly and safe positive electrode sheet.

[0012] Furthermore, the solid-liquid ratio of dopamine to buffer solution is (20–40):1000. Under these conditions, the solubility is even better.

[0013] Furthermore, the mass concentration of the buffer solution is 0.5%–2%. Under these conditions, the solubility and dissolution rate of dopamine can be further improved.

[0014] Furthermore, the dispersion is ultrasonic dispersion for 30–50 minutes; and / or a stirring step is included after dispersion for 22–26 hours; and / or the coating is applied by brushing or spraying. These conditions facilitate practical operation.

[0015] According to another aspect of the present invention, a battery is provided, comprising the composite positive electrode sheet described above. Due to the use of the composite positive electrode sheet of the present invention, the probability of active material shedding during cycling is lower, resulting in better battery performance.

[0016] The technical solution of this invention includes three aspects: First, it uses dopamine-modified nano-conductive carbon material. Dopamine uses the layered structure of the nano-conductive carbon material as a template to self-polymerize on the surface of the layers to form polydopamine, thereby improving the adhesion between the carbon coating layer and the current collector substrate. Second, it uses a positive electrode active material coated with a silane coupling agent. The silane coupling agent coating layer can provide a fast electron transport channel for the positive electrode active material, making electrons easier to transport during charging and discharging, resulting in better rate performance. Third, dopamine can chemically cross-link with the silane coupling agent, thereby enhancing the cohesive force between the positive electrode active material and the carbon coating layer. The composite positive electrode sheet of this invention can improve the adhesion between the active material and the carbon coating layer, and between the carbon coating layer and the current collector, thereby comprehensively improving the adhesion performance between the active material and the current collector, reducing the probability of active material detachment during battery cycling, and thus reducing the problem of unstable capacity performance during battery use, while also improving the compaction density and energy density of the battery. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] As described in the background section of this invention, existing technologies suffer from low adhesion between the positive electrode active material and the current collector, leading to easy detachment. To address these issues, in a typical embodiment of this invention, a composite positive electrode sheet is provided, comprising a positive electrode current collector, a carbon coating layer, and an active material layer stacked sequentially. The carbon coating layer comprises dopamine-modified nano-conductive carbon material, and the active material layer comprises a positive electrode active material coated with a silane coupling agent. The composite positive electrode sheet may also include conventional additives such as binders, which can be added as needed by those skilled in the art.

[0019] In the composite positive electrode of this invention, dopamine (DA)-modified nano-conductive carbon material is used. The layered structure of the nano-conductive carbon material provides a template for the self-polymerization of dopamine. Dopamine contains many amine and catechol functional groups, which undergo a self-polymerization reaction on the surface of the nano-conductive carbon material layer to form polydopamine (PDA) with strong adhesion properties. PDA can adhere to various matrices by oxidizing the catechol groups into quinones. Dopamine modification can improve the adhesion of the nano-conductive material layers. When a carbon coating layer containing nano-conductive carbon material is uniformly coated on the surface of the current collector, the adhesion between the carbon coating layer and the current collector can be greatly improved. When using conventional binders, dopamine can also undergo chemical cross-linking with the conventional binders, further improving the cohesive force of the carbon coating layer while reducing the amount of binder used. Furthermore, it can increase the adhesion between the active material and the current collector, thereby improving the battery's compaction density, energy density, etc., and preventing the active material from detaching due to the peeling of the carbon coating layer from the current collector.

[0020] In the composite positive electrode sheet of this invention, a silane coupling agent is used to coat the positive electrode active material. Introducing small molecules of the coupling agent onto the surface of the positive electrode active material forms a coating layer, providing a fast electron transport channel for the positive electrode active material. This facilitates electron transport during charging and discharging, improving the battery's rate performance. The silane coupling agent coating not only improves the electrical conductivity of the positive electrode active particles but also enhances the dispersibility of the positive electrode active material particles, thereby improving the processing performance of the positive electrode sheet.

[0021] In the composite positive electrode sheet of this invention, when the positive electrode active material coated with a silane coupling agent is applied to the surface of the carbon coating layer, the silane coupling agent can chemically crosslink with polydopamine, further enhancing the adhesion between the active material and the carbon coating layer. This, in turn, improves the adhesion between the active material and the current collector, and also enhances the cohesive force between the active material particles, thereby increasing the peel strength between the active material and the current collector. Furthermore, it improves the electrical conductivity between the active material and the carbon coating layer, reducing contact resistance.

[0022] The composite positive electrode sheet of the present invention can improve the electrical conductivity between the current collector and the active material, and improve the adhesion between the active material and the carbon coating layer, and between the carbon coating layer and the current collector, thereby comprehensively improving the adhesion performance between the active material and the current collector, reducing the probability of active material falling off during battery cycling, and thus reducing the problem of unstable capacity performance of the battery during use. At the same time, it improves the compaction density and energy density of the battery, and is also an environmentally friendly and safe positive electrode sheet.

[0023] In order to better improve the self-polymerization effect of dopamine and thus improve the adhesion between the carbon coating layer and the current collector, in a preferred embodiment, the nano-conductive carbon material in the carbon coating layer includes nano-conductive graphite and / or nano-conductive carbon black; and / or the weight ratio of dopamine to nano-conductive carbon material is (20-40):100, and for similar reasons, it is further preferred to be (25-35):100.

[0024] In a preferred embodiment, the positive electrode active material in the active material layer includes one or more of lithium iron phosphate, lithium iron manganese, and nickel cobalt manganese; and / or the weight ratio of silane coupling agent to positive electrode active material is 100:(30-50), preferably 100:(35-45), thereby further improving the electrical conductivity of positive electrode active particles, improving the dispersibility of positive electrode active material particles, and improving rate performance.

[0025] To further enhance the overall cohesiveness of the electrode active material and improve the adhesion strength between the positive electrode active material and the carbon coating layer, in a preferred embodiment, the weight ratio of the nano-conductive material to the positive electrode active material is 100:(30-50). This can better improve the adhesion performance between the active material and the current collector, reduce the probability of active material detachment, and improve the battery's compaction density, energy density, and cycle capacity stability.

[0026] In order to enable the silane coupling agent to better modify the surface of the positive electrode material after mixing with the positive electrode active material, thereby further improving the bonding strength between the material and the foil, in a preferred embodiment, the silane coupling agent includes one or more of KH550, KH560 and KH570; and / or the positive electrode current collector includes aluminum foil and / or copper foil, which can further reduce costs.

[0027] In another typical embodiment of the present invention, a method for preparing the above-mentioned composite positive electrode sheet is also provided, comprising the following steps: Step S1, dissolving dopamine in a buffer solution, adding nano-conductive carbon material for dispersion, and coating it on the surface of the positive current collector to obtain a carbon coating layer; Step S2, mixing the positive active material with a silane coupling agent and coating it on the surface of the carbon coating layer to obtain the composite positive electrode sheet.

[0028] This invention first dissolves dopamine in a buffer solution, then adds nano-conductive carbon material for dispersion. During this process, dopamine acts like a surfactant, helping conductive graphite to disperse better in the solvent. The dispersed material is then coated onto the surface of the positive electrode current collector to obtain a carbon coating layer. Next, the positive electrode active material is mixed with a silane coupling agent. During this process, the silane coupling agent modifies the surface of the positive electrode active material to improve the adhesion strength between the material and the foil. Coated onto the surface of the carbon coating layer, the silane coupling agent can chemically crosslink with polydopamine, further enhancing the adhesion between the active material and the carbon coating layer. This, in turn, improves the adhesion between the active material and the current collector, as well as the cohesive force between the active material particles and the electrical conductivity between the active material and the carbon coating layer, resulting in a composite positive electrode sheet.

[0029] To better suit practical operation, it is preferable to mix lithium iron phosphate, conductive paste, carbon black, PVDF, and NMP solvent after mixing the positive electrode active material with the silane coupling agent to form a slurry, thereby obtaining a positive electrode slurry with a solid content of 60-70%, which is beneficial for actual coating and improvement of electrode electrical performance.

[0030] The above preparation method is simple and easy to operate. The composite positive electrode sheet obtained has high adhesion between the positive active material and the current collector and is not easily detached. At the same time, the preparation process does not use harmful ingredients, and it causes little harm to the human body and minimal environmental pollution during production and use, making it an environmentally friendly and safe positive electrode sheet.

[0031] In a preferred embodiment, the solid-liquid ratio of dopamine to buffer solution is (20-40):1000, which provides better dissolution. The solid-liquid ratio refers to the ratio of the mass (g) of dopamine to the volume (ml) of buffer solution.

[0032] To further improve the solubility and dissolution rate of dopamine, in a preferred embodiment, the mass concentration of the buffer solution is 0.5-2%, and the buffer solution can be Tris buffer (tris(hydroxymethyl)aminomethane) buffer. The above buffer solution can be commercially available or prepared using conventional methods in the art. For example, 12.1 g of Tris (tris(hydroxymethyl)aminomethane) can be mixed with 17.5 g of NaCl, 1500 ml of distilled water can be added, and concentrated HCl can be added dropwise under magnetic stirring until the pH reaches 7.4. Then, distilled water can be added to a final volume of 2000 ml to obtain the buffer solution.

[0033] In a preferred embodiment, dispersion is performed by ultrasonic dispersion for 30–50 min; and / or a stirring step is included after dispersion for 22–26 h; and / or coating is performed by brushing or spraying. Under the above conditions, the dispersion of dopamine and nano-conductive carbon materials is more uniform, which is more conducive to the self-polymerization of dopamine on the surface of the nano-conductive carbon material as a template to form polydopamine, further improving the adhesion between the carbon coating layer and the current collector substrate.

[0034] In another typical embodiment of the present invention, a battery is also provided, including the composite positive electrode sheet described above. Due to the use of the composite positive electrode sheet of the present invention, the electrical conductivity between the positive current collector and the active material is better, the adhesion between the active material and the current collector is better, the probability of active material shedding during battery cycling is lower, the cycle capacity is stable, and the electrochemical performance is significantly improved.

[0035] Typically, but not limitingly, the weight ratio of dopamine to the nano-conductive material in the carbon coating layer is 20:100, 25:100, 30:100, 35:100, 40:100, or any two of these values.

[0036] Typically, but not limitingly, the weight ratio of the silane coupling agent to the positive electrode active material in the active material layer is 100:30, 100:35, 100:40, 100:45, 100:50, or any two of these values.

[0037] Typical, but not limiting, weight ratios of nanoconductive materials to positive electrode active materials are 100:30, 100:35, 100:40, 100:45, 100:50, or any two of these values.

[0038] Typical, but not limiting, buffer concentrations are 0.5%, 1%, 1.5%, 2%, or any two of these values.

[0039] Typical, but not limiting, solid-liquid ratios of dopamine to buffer solution are 20:1000, 25:1000, 30:1000, 35:1000, 40:1000, or any two of these values.

[0040] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0041] Example 1

[0042] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 20 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0043] (2) Mix 50 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0044] Example 2

[0045] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 40 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0046] (2) Mix 50 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0047] Example 3

[0048] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 20 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0049] (2) Mix 30 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0050] Example 4

[0051] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 20 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0052] (2) Mix 50 parts of lithium iron phosphate with 120 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0053] Example 5

[0054] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 38 parts of dopamine to the buffer, and then add 100 parts of nano-conductive graphite to the buffer. Use an ultrasonic disperser to ultrasonically disperse for 40 min and stir for 24 h to prepare dopamine-modified nano-conductive graphite. Spray it onto the surface of aluminum foil to prepare a carbon coating layer.

[0055] (2) Mix 36 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0056] Example 6

[0057] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 25 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0058] (2) Mix 35 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0059] Example 7

[0060] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 35 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0061] (2) Mix 45 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0062] Example 8

[0063] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 0.5%, add 38 parts of dopamine to the buffer, and then add 100 parts of nano-conductive carbon black to the buffer. Use an ultrasonic disperser to ultrasonically disperse for 30 min and stir for 22 h to prepare dopamine-modified nano-conductive carbon black. Spray it onto the surface of copper foil to prepare a carbon coating layer.

[0064] (2) Mix 36 parts of lithium iron manganese with 100 parts of silane coupling agent KH550 evenly to obtain lithium iron manganese coated with silane coupling agent. Then, mix the lithium iron manganese: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0065] Example 9

[0066] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 2%, add 38 parts of dopamine to the buffer, then add 100 parts of nano-conductive carbon black to the buffer, use an ultrasonic disperser to ultrasonically disperse for 50 min, stir for 26 h to prepare dopamine-modified nano-conductive carbon black, and spray it on the surface of copper foil to prepare a carbon coating layer.

[0067] (2) Mix 36 parts of nickel cobalt manganese with 100 parts of silane coupling agent KH570 evenly to obtain nickel cobalt manganese coated with silane coupling agent. Then, mix the nickel cobalt manganese: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0068] Comparative Example 1 (without dopamine)

[0069] (1) Prepare a carbon coating layer by spraying nano-conductive graphite onto the surface of aluminum foil.

[0070] (2) Mix 50 parts of lithium iron phosphate with 100 parts of silane coupling agent KH560 evenly to obtain lithium iron phosphate coated with silane coupling agent. Then, mix the slurry according to the ratio of lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content, and coat it on the carbon coating layer to obtain the positive electrode sheet.

[0071] Comparative Example 2: Silane-free Coupling Agent

[0072] (1) Prepare 1000 mL of Tris buffer with a mass concentration of 1%, add 20 parts of dopamine to the buffer, then add 100 parts of nano-conductive graphite to the buffer, use an ultrasonic disperser to ultrasonically disperse for 40 min, stir for 24 h to prepare dopamine-modified nano-conductive graphite, and spray it on the surface of aluminum foil to prepare a carbon coating layer.

[0073] (2) Take 50 parts of lithium iron phosphate and mix them according to the following ratio: lithium iron phosphate: conductive paste: carbon black: PVDF = 96:1.2:0.8:2.0, with NMP as the solvent and 65% solid content. Coat the mixture onto the carbon coating layer to obtain the positive electrode sheet.

[0074] The positive electrode sheets of the above embodiments and comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0075] Performance tests:

[0076] Electrode peel strength, electrode cohesion: GB / T 2792-1998;

[0077] Electrode resistors, film resistors: resistivity tester.

[0078] Table 1

[0079]

[0080] As can be seen from the above, compared with the carbon coating layer of Comparative Example 1 without dopamine coating, the carbon coating layer of Example 1 with added dopamine shows a significantly improved adhesion to the current collector. Compared with the comparative example, the embodiments of the present invention use dopamine-modified nano-conductive carbon materials. Dopamine uses the layered structure of the nano-conductive carbon material as a template to self-polymerize on the surface of the layers to form polydopamine, thereby improving the adhesion between the carbon coating layer and the current collector substrate. The positive electrode active material coated with a silane coupling agent provides a fast electron transport channel for the positive electrode active material, making electron transport easier during charging and discharging, resulting in better rate performance. Dopamine can chemically crosslink with the silane coupling agent, thereby enhancing the cohesive force between the positive electrode active material and the carbon coating layer.

[0081] It is evident that the composite positive electrode sheet of the present invention can improve the adhesion between the active material and the carbon coating layer, and between the carbon coating layer and the current collector, thereby comprehensively improving the adhesion performance between the active material and the current collector, reducing the probability of active material detachment during battery cycling, and thus reducing the problem of unstable capacity performance during battery use, while improving the compaction density and energy density of the battery. Furthermore, it can be seen that the bonding characteristics of the positive electrode sheet are even better when all process parameters are within the preferred range of the present invention.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite cathode electrode sheet, characterized by, The positive electrode current collector, the carbon coating layer and the active material layer are sequentially stacked, wherein the carbon coating layer comprises dopamine-modified nano-conductive carbon material, the dopamine is used as a template for the lamellar structure of the nano-conductive carbon material, and the dopamine is self-polymerized on the lamellar surface to form polydopamine; and the active material layer comprises a silane coupling agent-coated positive electrode active material.

2. The composite cathode electrode sheet according to claim 1, characterized by In the carbon coating layer, The nano-conductive carbon material comprises nano-conductive graphite and / or nano-conductive carbon black; and / or The weight ratio of the dopamine to the nano-conductive carbon material is (20-40):

100.

3. The composite cathode electrode sheet according to claim 1, characterized by, In the carbon coating layer, The weight ratio of the dopamine to the nano-conductive carbon material is (25-35):

100.

4. The composite cathode electrode tab according to claim 1 or 2, characterized in that, In the active material layer, The positive electrode active material comprises one or more of lithium iron phosphate, lithium iron manganese and nickel cobalt manganese; and / or The weight ratio of the silane coupling agent to the positive electrode active material is 100:(30-50).

5. The composite cathode electrode tab of claim 1 or 2, wherein, In the active material layer, The weight ratio of the silane coupling agent to the positive electrode active material is 100:(35-45).

6. The composite positive electrode plate according to claim 1 or 2, wherein The weight ratio of the nano-conductive carbon material to the positive electrode active material is 100:(30-50).

7. The composite positive electrode plate according to claim 1 or 2, wherein The silane coupling agent comprises one or more of KH550, KH560 and KH570; and / or The positive electrode current collector comprises an aluminum foil and / or a copper foil.

8. The method of producing the composite cathode electrode sheet according to any one of claims 1 to 7, characterized by, The method comprises the following steps: S1. Dissolving dopamine in a buffer solution, adding nano-conductive carbon material for dispersion, and coating on the surface of a positive electrode current collector to obtain a carbon coating layer; S2. Mixing a positive electrode active material with a silane coupling agent, and coating on the surface of the carbon coating layer to obtain the composite positive electrode plate.

9. The production method according to claim 8, characterized by, The solid-liquid ratio of the dopamine to the buffer solution is (20-40):1000.

10. The method of claim 8, wherein, The mass concentration of the buffer solution is 0.5-2%.

11. The preparation method according to claim 8, characterized in that, The dispersion is ultrasonic dispersion, and the ultrasonic dispersion time is 30-50 min; and / or The dispersion is further followed by a stirring step, and the stirring time is 22-26 h; and / or The coating is brushing or spraying.

12. A battery, characterized by The method comprises the composite positive electrode plate according to any one of claims 1-7.

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