Composite current collector, and preparation method therefor and use thereof

Abstract

The present application discloses a composite current collector, and a preparation method therefor and a use thereof. The composite current collector comprises a carbon-coated current collector; the carbon-coated current collector comprises a current collector substrate and a carbon coating layer located on the surface of the current collector substrate; rod-like structures are grown in situ on the carbon coating layer; each rod-like structure comprises a rod-like body and carbon particles embedded on the rod-like body; the material of the rod-like body comprises Ni and Mo. In the present application, the rod-like structures having a specific composition are grown in situ on the carbon coating layer of the carbon-coated current collector, thereby effectively increasing the adhesion and peeling strength between the current collector and a positive electrode active material. In addition, the carbon particles are embedded on the rod-like body, thereby ensuring that the composite current collector has good electrical conductivity, which is beneficial to improving the electrochemical performance of electrodes prepared using the composite current collector.

Description

A composite current collector, its preparation method and application Technical Field

[0001] This application relates to the field of battery technology, such as a composite current collector, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries (LIBs) have been widely adopted in various fields such as consumer electronics, transportation, power tools, and energy storage. The current collector, as one of the key components in a lithium-ion battery, plays a crucial role. Its main functions are: to carry the electrode active material, to collect and output the current generated by the active material, and to input the electrode current to the active material.

[0003] Aluminum foil current collectors are composite materials formed by combining aluminum foil with other materials (such as paper, plastic film, coatings, etc.). These composite materials can endow aluminum foil with new properties and functions to meet the needs of different industries. In the lithium battery industry, the strategy of using carbon-coated current collectors can improve the rate of lithium batteries and overall performance. However, the relatively low adhesion of carbon-coated aluminum foil current collectors affects the subsequent coating of the positive electrode active material. Therefore, it is necessary to develop and manufacture a carbon-coated current collector with higher adhesion to ensure the connection between the positive electrode active material and the carbon coating layer. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0005] This application proposes a composite current collector, its preparation method, and its application.

[0006] In a first aspect, this application provides a composite current collector, the composite current collector including a carbon-coated current collector, the carbon-coated current collector including a current collector substrate and a carbon coating layer located on the surface of the current collector substrate, a rod-shaped structure growing in situ on the carbon coating layer, the rod-shaped structure including a rod-shaped body and carbon particles embedded in the rod-shaped body, the material of the rod-shaped body including Ni and Mo.

[0007] This application does not specifically limit the type of current collector substrate; for example, it can be aluminum foil.

[0008] This application increases the surface complexity and roughness of a current collector by in-situ growing a rod-shaped structure of a specific composition on the carbon coating layer. Roughness refers to the degree of non-uniformity and roughness of the carbon coating surface, which significantly affects the adhesion and performance of the current collector. Higher surface roughness provides more mechanical locking points, resulting in stronger adhesion. Therefore, the composite current collector of this application increases the contact area and embedding degree with the positive electrode active material during rolling, allowing for better bonding between the positive electrode active material and the carbon coating layer, effectively improving the adhesion and peel strength between the current collector and the positive electrode active material. Simultaneously, the presence of carbon particles embedded in the rod-shaped body ensures good conductivity of the composite current collector, which is beneficial for improving the electrochemical performance of electrodes prepared using it.

[0009] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. The technical objectives and beneficial effects of this application can be better achieved through the following optional technical solutions.

[0010] In one embodiment, the material of the rod-shaped body is doped or undoped NiMoO4, wherein the doping element is at least one of P, S, C or Se.

[0011] In one embodiment, the rod-shaped structures on the carbon coating layer appear as straw-like structures. The straw-like shape is defined as follows: multiple rod-shaped structures are clustered together and radiating outwards, with the angle θ between the rod-shaped structures and the plane of the carbon coating layer primarily within the range of 30°-90°. Exemplarily, θ can be 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, 85°, or 90°, etc.

[0012] In one embodiment, the rod-like structure is a prismatic microrod with a rectangular cross-section. The length of the rectangle is in the range of 0.03 μm to 0.07 μm, for example, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, or 0.07 μm; the width of the rectangle is in the range of 0.02 μm to 0.06 μm, for example, 0.02 μm, 0.03 μm, 0.04 μm, or 0.07 μm. μm, 0.05μm, or 0.06μm, etc.; the length of the rod-shaped structure is in the range of 0.5μm-1.2μm, for example, it can be 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1μm, 1.05μm, 1.1μm, 1.15μm, or 1.2μm, etc.

[0013] In one embodiment, the included angle θ is in the range of 45°-90°, and can be selected to be in the range of 60°-90°.

[0014] Secondly, this application provides a method for preparing a composite current collector as described in the first aspect, the method comprising the following steps:

[0015] (1) Prepare a mixed salt solution using nickel salt, molybdenum salt and solvent;

[0016] (2) The mixed salt solution and the carbon-coated current collector are placed in a reaction vessel, the reaction vessel is sealed and heated, and the reaction is carried out under a certain temperature and pressure to obtain the composite current collector.

[0017] The method of this application can utilize a carbon-coated current collector to grow a rod-shaped structure in situ. The rod-shaped body of the structure includes Ni and Mo. Since the carbon-coated current collector contains carbon, carbon particles can be introduced onto the rod-shaped body after the reaction in a sealed reaction vessel.

[0018] The composite current collector prepared by the method of this application effectively improves the adhesion and peel strength between the current collector and the positive electrode active material, and has good conductivity, which can enhance the electrochemical performance of the electrode of the battery prepared using it.

[0019] The method described in this application is simple, greatly reducing experimental operations and steps, and lowering the amount of machinery and equipment used and the difficulty of operation, thereby reducing production costs and equipment maintenance costs, which is conducive to its widespread use.

[0020] In the method of this application, since the carbon-coated current collector is lightweight and thin, when it is placed in the reaction vessel together with the mixed salt solution, it is easy for the carbon-coated current collector to be drawn to the bottom of the reaction vessel under the action of water pressure. In this case, it is necessary to peel the carbon-coated current collector off from the bottom of the reaction vessel so that the pressure on both sides of the carbon-coated current collector is equal, so that the carbon-coated current collector is suspended in the solution, thereby growing microstructures on both sides.

[0021] In one embodiment, the reaction vessel is a reaction kettle.

[0022] In one embodiment, the nickel salt in step (1) includes NiSO4·6H2O.

[0023] In one embodiment, the molybdenum salt in step (1) includes Na2MoO4·2H2O and / or ammonium molybdate.

[0024] In one embodiment, in step (1), the molar ratio of nickel in the nickel salt to molybdenum in the molybdenum salt is greater than or equal to 1.5:1, for example, it can be 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 3.8:1, 4:1, 4.3:1, 4.5:1, 4.7:1, 4.8:1, 5:1, 5.3:1, 5.5:1, 5.7:1, or 6:1, etc. Within this range, the optimal interfacial microenvironment can be obtained, thereby improving the coating peel strength. The technical principle is as follows: Nickel can promote the number and density of rod-like structures. To grow abundant straw-like microrods, sufficient Ni2+ and an appropriate amount of molybdenum ions are required. However, the number of microrod structures is not necessarily better the more there are. Exceeding a certain number will reduce the toughness of the composite current collector. Therefore, the molar ratio of nickel to molybdenum can be selected in the range of (1.5-6):1.

[0025] In one embodiment, the mixed salt solution is prepared as follows: a nickel salt (e.g., NiSO4·6H2O) and a solvent are mixed and stirred until the solution is clear and transparent to obtain a first solution; a molybdenum salt (Na2MoO4·2H2O) and a solvent are mixed and stirred until the solution is clear and transparent to obtain a second solution; the first solution and the second solution are mixed and stirred evenly to obtain the mixed salt solution.

[0026] In one embodiment, the pH of the mixed salt solution in step (1) is 6.5-7.5, for example, it can be 6.5, 6.6, 6.8, 7, 7.1, 7.2, 7.3, 7.4 or 7.5.

[0027] For some salts (e.g., NiSO4·6H2O and Na2MoO4·2H2O), the solution obtained after adding the solvent is neutral. Therefore, a mixed salt solution that meets the pH requirement can be obtained directly without adjusting the pH of the solution. However, for some salts (e.g., ammonium molybdate), the pH of the solution obtained after adding the solvent is less than 6.5. Therefore, a pH adjuster needs to be added to adjust the pH to the required pH.

[0028] In one embodiment, when the solvent used in the preparation of the carbon-coated current collector is water, the solvent in step (1) includes at least one of dimethylformamide, N-methylpyrrolidone (NMP), and methyl ethyl ketone (MEK). Under this condition, the reaction in step (2) is a solvothermal reaction. Since the solvent used in the preparation of the carbon-coated current collector is water, there will be no problem of damaging the integrity of the coating of the carbon-coated current collector during the reaction in step (2).

[0029] In one embodiment, when the solvent used in the preparation of the carbon-coated current collector is an oil-based solvent, the solvent in step (1) is water. In one embodiment, the oil-based solvent is N-methylpyrrolidone. Under these conditions, the reaction in step (2) is a hydrothermal reaction. Since the solvent used in the preparation of the carbon-coated current collector is an oil-based solvent, there will be no problem of damaging the integrity of the carbon-coated current collector coating during the reaction in step (2).

[0030] In one embodiment, the oil-based solvent includes N-methylpyrrolidone.

[0031] In one embodiment, when the carbon-coated current collector is a sodium-electric current collector, and the carbon coating slurry used in the preparation of the sodium-electric current collector contains a crosslinking agent, the solvent in step (1) is water. Under this condition, the reaction in step (2) is a hydrothermal reaction. Since the carbon coating slurry used in the preparation of the sodium-electric current collector contains a crosslinking agent, it has good water resistance, and the integrity of the coating of the carbon-coated current collector will not be damaged during the reaction in step (2).

[0032] In one embodiment, the crosslinking agent includes at least one of methacrylic acid, methyl vinyl acid, and isopropylacrylic acid.

[0033] In one embodiment, step (2) involves heating to 120°C-240°C, for example, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, or 240°C.

[0034] In one embodiment, during the reaction process described in step (2), the pressure inside the reaction vessel is 2-3 atmospheres, for example, it can be 2 atmospheres, 2.2 atmospheres, 2.5 atmospheres, 2.7 atmospheres or 3 atmospheres, etc.

[0035] In one embodiment, the reaction time in step (2) is 8h-18h, for example, it can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h or 18h.

[0036] Optionally, the drying method is oven drying, and the oven drying temperature is 50℃-60℃, for example, 50℃, 52℃, 53℃, 55℃, 58℃ or 60℃, etc.

[0037] This application does not limit the drying time; those skilled in the art can select the time according to actual needs.

[0038] As an optional technical solution of the preparation method described in this application, the preparation method of the carbon-coated current collector in step (2) includes the following steps:

[0039] (A) Disperse the raw materials for the carbon coating layer in a solvent to obtain a carbon coating slurry;

[0040] (B) The carbon coating slurry is coated onto the surface of the current collector substrate, and after drying, a carbon coating layer is formed on the surface of the current collector substrate to obtain the carbon-coated current collector.

[0041] In one embodiment, the raw materials for the carbon coating layer in step (A) include a conductive agent and a binder.

[0042] In one embodiment, the conductive agent comprises carbon powder, and optionally also includes graphite powder.

[0043] In one embodiment, the mass percentages of the carbon powder and the graphite powder in the conductive agent are 70%-100% and 0%-30%, respectively. The mass percentage of carbon powder in the conductive agent is "70%-100%", for example, it can be 70%, 72%, 75%, 78%, 80%, 85%, 90%, 95%, or 100%, etc.; the mass percentage of graphite powder in the conductive agent is "0%-30%", for example, it can be 0%, 1%, 2%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, 20%, 22%, 24%, 25%, 28%, or 30%, etc. When the mass percentage of carbon powder is 100%, it indicates that the conductive agent is composed of carbon powder; when the mass percentage of graphite powder is 0%, it indicates that the conductive agent does not contain graphite powder.

[0044] In one embodiment, the adhesive comprises at least one of acrylate, polyacrylic acid, modified polyacrylic acid, or waterborne polyurethane, optionally modified polyacrylic acid.

[0045] In one embodiment, the adhesive is a modified polyacrylic acid liquid with a solid content of 15%-30%, for example, it can be 15%, 16%, 17%, 18%, 20%, 22%, 24%, 25%, 26%, 28%, or 30%, etc.; the viscosity of the modified polyacrylic acid liquid is 200 mPa·s-1500 mPa·s, for example, it can be 200 mPa·s, 300 mPa·s, 400 mPa·s, 500 mPa·s, etc. a·s, 550mPa·s, 600mPa·s, 650mPa·s, 700mPa·s, 750mPa·s, 800mPa·s, 850mPa·s, 900mPa·s, 95 0mPa·s, 1000mPa·s, 1050mPa·s, 1100mPa·s, 1200mPa·s, 1300mPa·s, 1400mPa·s or 1500mPa·s, etc.

[0046] In one embodiment, the raw material for the carbon coating layer in step (A) further includes a wetting agent.

[0047] In one embodiment, the wetting agent includes at least one of polyether siloxane, modified polyether siloxane, and alcohol, with modified polyether siloxane being optional.

[0048] Modified polyether siloxanes are a special type of siloxane material that modifies the properties of siloxanes by introducing polyether segments, thereby improving their flexibility, chemical resistance, and low-temperature performance.

[0049] The structure of modified polyether siloxanes consists of a siloxane backbone and polyether segments, which are linked together through copolymerization or grafting reactions. This structure endows modified polyether siloxanes with good mechanical properties, thermal stability, and chemical stability.

[0050] This application does not specifically limit the source of the modified polyether siloxane. For example, it can be a commercially available product. An exemplary source is: purchased from Dow Corning Incorporated, USA, model: DC-595.

[0051] In one embodiment, the amount of the wetting agent is 3%-20% of the total mass of the reaction system, for example, it can be 3%, 4%, 5%, 6%, 7%, 8%, 10%, 12%, 13%, 14%, 15%, 17%, 18%, or 20%. Here, the total mass of the reaction system refers to the mass of all liquids after the addition of the wetting agent.

[0052] As an optional technical solution of the preparation method described in this application, step (A) includes:

[0053] S1 adds a conductive agent to the adhesive solution and disperses it to obtain the first material;

[0054] S2 adds a wetting agent to the first material, stirs and then homogenizes it to obtain a carbon coating slurry.

[0055] In this application, adhesive liquid refers to an adhesive that is in the form of a liquid.

[0056] In one embodiment, step S1 includes: first adding a portion of conductive agent to the adhesive solution, performing a first high-speed stirring, and then adding the remaining conductive agent to the resulting material, and performing a second high-speed stirring.

[0057] In one embodiment, the portion of the conductive agent accounts for 40%-60% of the total conductive agent, for example, it can be 40%, 42%, 44%, 45%, 48%, 50%, 53%, 55%, 57% or 60%, etc.

[0058] In one embodiment, the rotation speed of the first high-speed stirring is 2000rpm-2600rpm, for example, it can be 2000rpm, 2100rpm, 2150rpm, 2200rpm, 2250rpm, 2300rpm, 2350rpm, 2400rpm, 2500rpm, 2550rpm or 2600rpm, etc.

[0059] In one embodiment, the time for the first high-speed stirring is 30-60 minutes, for example, it can be 30 minutes, 35 minutes, 38 minutes, 40 minutes, 43 minutes, 46 minutes, 48 ​​minutes, 50 minutes, 53 minutes, 56 minutes or 60 minutes.

[0060] In one embodiment, the rotation speed of the second high-speed stirring is 2000rpm-2600rpm, for example, it can be 2000rpm, 2100rpm, 2150rpm, 2200rpm, 2250rpm, 2300rpm, 2350rpm, 2400rpm, 2500rpm, 2550rpm or 2600rpm, etc.

[0061] In one embodiment, the second high-speed stirring time is 60-90 minutes, for example, it can be 60 minutes, 65 minutes, 70 minutes, 75 minutes, 80 minutes, 85 minutes or 90 minutes.

[0062] In one embodiment, the stirring speed in step S2 is 10 rpm to 15 rpm, for example, it can be 10 rpm, 11 rpm, 12 rpm, 13 rpm or 15 rpm.

[0063] In one embodiment, the stirring time in step S2 is 30 min to 45 min, for example, it can be 30 min, 35 min, 38 min, 40 min, 43 min or 45 min, etc.

[0064] This application does not specify the number of homogenization processes, but generally more than 2 times is sufficient, such as 2, 3 or 4 times. The number of homogenization processes can be determined by the art based on actual needs.

[0065] In one embodiment, the homogenization pressure in step S2 is 300 bar to 600 bar, for example, it can be 300 bar, 325 bar, 350 bar, 370 bar, 400 bar, 450 bar, 475 bar, 500 bar, 520 bar, 550 bar, 580 bar or 600 bar, etc.

[0066] In one embodiment, the preparation method further includes:

[0067] After step S1 and before step S2, the following steps are performed:

[0068] (a) Add solvent to the first material to reduce the concentration of the slurry, and disperse at high speed for 30 min to 45 min (e.g., 2000 rpm, 2100 rpm, 2150 rpm, 2200 rpm, 2250 rpm, 2300 rpm, 2350 rpm, 2400 rpm, 2500 rpm, 2550 rpm or 2600 rpm, etc.) at a speed of 2000 rpm to 2600 rpm (e.g., 2000 rpm, 2100 rpm, 2150 rpm, 2200 rpm, 2250 rpm, 2300 rpm, 2350 rpm, 2400 rpm, 2500 rpm, 2550 rpm or 2600 rpm, etc.).

[0069] (b) Adjust the pH of the slurry obtained in step (a) to 5-7 using a pH adjuster (e.g., it can be 5, 5.5, 5.8, 6, 6.5 or 7, etc.).

[0070] In one embodiment, the amount of pH adjuster added is 5wt%-10wt% of the adhesive solution, for example, it can be 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, or 10wt%.

[0071] Thirdly, this application provides an electrode sheet, the electrode sheet comprising a current collector and an active layer disposed on the surface of the current collector, wherein the current collector is the composite current collector described in the first aspect or the composite current collector prepared by the method described in the second aspect.

[0072] The electrode in this application can be either a positive electrode or a negative electrode. For a positive electrode, the current collector is a positive current collector and the active layer is a positive active layer; for a negative electrode, the current collector is a negative current collector and the active layer is a negative active layer.

[0073] In one embodiment, the positive current collector is the composite current collector described in the first aspect, wherein the current collector substrate is aluminum foil.

[0074] In one embodiment, the positive electrode material layer includes a positive electrode active material, a binder, and an optional conductive agent.

[0075] In one embodiment, the negative electrode current collector is the composite current collector described in the first aspect, wherein the current collector substrate is copper foil.

[0076] In one embodiment, the negative electrode material layer includes a negative electrode active material, a binder, and an optional conductive agent.

[0077] Fourthly, this application provides a battery including a positive electrode, a negative electrode, and a separator, wherein the positive electrode and / or the negative electrode are selected from the electrode types described in the third aspect.

[0078] The numerical range described in this application includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this application will not exhaustively list the specific point values ​​included in the range.

[0079] Compared with related technologies, this application has the following advantages:

[0080] (1) This application increases the complexity and roughness of the surface by growing a rod-shaped structure of a specific composition in situ on the carbon coating layer of the carbon-coated current collector. This increases the contact area and embedding degree with the positive electrode active material during rolling, allowing the positive electrode active material to bond better with the carbon coating layer. This effectively improves the adhesion and peel strength between the current collector and the positive electrode active material. At the same time, since carbon particles are embedded in the rod-shaped body, the composite current collector has good conductivity, which is beneficial to improving the electrochemical performance of the electrode prepared using it.

[0081] (2) The method of this application is simple, the experimental operation and experimental steps are greatly reduced, the amount of machinery and equipment used and the difficulty of operation are reduced, thereby reducing the production cost and equipment maintenance cost, which is conducive to promotion and use.

[0082] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0083] The accompanying drawings are used to provide a further understanding of the technical solutions in this paper and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions in this paper and do not constitute a limitation on the technical solutions in this paper.

[0084] Figures 1 and 2 are scans of the carbon coating layer in the composite current collector prepared in Example 1 at different magnifications. Detailed Implementation

[0085] The technical solution of this application will be further described below with reference to the accompanying drawings and specific embodiments.

[0086] The embodiments of this application are described in detail below so that the advantages and features of the application can be more easily understood by those skilled in the art, thereby making a clearer and more explicit definition of the scope of protection of this application.

[0087] In this embodiment, the sources of the raw materials are as follows:

[0088] The modified polyacrylic acid adhesive was purchased from Sinopharm Chemical Reagent Co., Ltd., with an average molecular weight of MW~5000, a solid content of 20%, and a viscosity of 1000 mPa·s.

[0089] The modified polyether siloxane is available from Sinopharm Group, 99% pure, and produced by Beijing Wokai Biotechnology Co., Ltd.

[0090] Example 1

[0091] This embodiment provides a composite current collector, including a carbon-coated current collector. The carbon-coated current collector includes a current collector substrate and a carbon coating layer located on the surface of the current collector substrate. A rod-shaped structure is grown in situ on the carbon coating layer. The rod-shaped structure includes a rod-shaped body and carbon particles embedded in the rod-shaped body.

[0092] The current collector substrate is aluminum foil, and the rod-shaped body is made of NiMoO4.

[0093] The rod-shaped structure appears as straw on the carbon coating layer. The straw-like shape is characterized by multiple rod-shaped structures clustered together and radiating outwards. The angle θ between the rod-shaped structure and the plane of the carbon coating layer is mainly in the range of 30°-90°.

[0094] As can be seen from Figures 1 and 2, the rod-shaped structure is a prism-shaped microrod with a rectangular cross-section. The length of the rectangle is in the range of 0.03μm-0.07μm, the width of the rectangle is in the range of 0.02μm-0.06μm, and the length of the rod-shaped structure is in the range of 0.5μm-1.2μm.

[0095] This embodiment also provides a method for preparing the above-mentioned composite current collector, including the following steps:

[0096] (1) Preparation of carbon-coated current collector:

[0097] S1 mixes the modified polyacrylic acid adhesive with water and stirs it slowly at 600 rpm for 30 minutes to obtain the diluted polyacrylic acid adhesive (viscosity 800 mPa·s).

[0098] S2 First dispersion: Mix carbon powder and graphite powder at a mass ratio of 70:30 to obtain a conductive agent. Add 50% of the conductive agent to the colloid obtained in step S1 and disperse at a high speed of 2000 rpm for 30 minutes.

[0099] S3 Second Dispersion: Continue to add 50% conductive agent and disperse at high speed of 2600 rpm for 30 minutes.

[0100] S4 Third dispersion: Add water to reduce the viscosity of the slurry and prevent the slurry from being too sticky to disperse evenly. Disperse at a high speed of 2000 rpm for 30 minutes.

[0101] S5 tests the pH of the slurry. The pH of the slurry is adjusted to 5 with water and sodium bicarbonate because a pH greater than 7 will cause the viscosity to rise sharply.

[0102] S6 is used to thoroughly stir and disperse the slurry at a high speed of 2250 rpm for 60 minutes.

[0103] Add a wetting agent (modified polyether siloxane) to S7, with the amount of wetting agent accounting for 10% of the total mass of the reaction system. After addition, stir slowly at 10 rpm for 45 min. Remove air bubbles by vacuuming and homogenize at a pressure of 300 bar to obtain the carbon coating slurry.

[0104] S8 Coats the carbonized slurry obtained in step S7 onto the surface of the aluminum foil, and after drying, forms a carbonized layer on the surface of the aluminum foil to obtain a carbonized current collector.

[0105] (2) Mix NiSO4·6H2O, Na2MoO4·2H2O and NMP to obtain a mixed salt solution, wherein the molar ratio of nickel to molybdenum is 4:1.

[0106] (3) Place the mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) into a Teflon high-pressure reactor. Gently peel the carbon-coated current collector from the bottom of the reactor to suspend it in the solution. Seal the reactor and react at 180°C for 12 hours. The pressure inside the reactor is 2.2 atmospheres. After cooling to room temperature, take out the sample and place it in an oven to dry at 60°C for 12 hours to obtain the composite current collector.

[0107] Example 2

[0108] This embodiment provides a composite current collector, including a carbon-coated current collector. The carbon-coated current collector includes a current collector substrate and a carbon coating layer located on the surface of the current collector substrate. A rod-shaped structure is grown in situ on the carbon coating layer. The rod-shaped structure includes a rod-shaped body and carbon particles embedded in the rod-shaped body.

[0109] The current collector substrate is aluminum foil, and the rod-shaped body is made of NiMoO4.

[0110] The rod-shaped structure appears as straw on the carbon coating layer. The straw-like shape is characterized by multiple rod-shaped structures clustered together and radiating outwards. The angle θ between the rod-shaped structure and the plane of the carbon coating layer is mainly in the range of 30°-90°.

[0111] The rod-shaped structure is a prism-shaped microrod with a rectangular cross-section. The length of the rectangle is in the range of 0.03μm-0.07μm, the width of the rectangle is in the range of 0.02μm-0.06μm, and the length of the rod-shaped structure is in the range of 0.5μm-1.2μm.

[0112] This embodiment also provides a method for preparing the above-mentioned composite current collector, including the following steps:

[0113] (1) Preparation of carbon-coated current collector:

[0114] S1 mixes the modified polyacrylic acid adhesive with water and stirs it slowly at 600 rpm for 30 minutes to obtain the diluted polyacrylic acid adhesive (viscosity 800 mPa·s).

[0115] S2 First dispersion: Mix carbon powder and graphite powder at a mass ratio of 80:20 to obtain a conductive agent. Add 40% of the conductive agent to the colloid obtained in step S1 and disperse at a high speed of 2600 rpm for 40 min.

[0116] S3 Second Dispersion: Continue to add 60% conductive agent and disperse at high speed of 2000 rpm for 90 minutes.

[0117] S4 Third dispersion: Add water to reduce the viscosity of the slurry and prevent the slurry from being too sticky to disperse evenly. Disperse at high speed of 2400 rpm for 30 minutes.

[0118] S5 tests the pH of the slurry. The pH of the slurry is adjusted to 6 with water and sodium bicarbonate because a pH greater than 7 will cause the viscosity to rise sharply.

[0119] S6 is used to thoroughly stir and disperse the slurry at a high speed of 2300 rpm for 55 minutes.

[0120] Add a wetting agent (modified polyether siloxane) to S7, with the amount of wetting agent accounting for 10% of the total mass of the reaction system. After addition, stir slowly at 15 rpm for 30 min. Remove air bubbles by vacuuming and homogenize at a pressure of 600 bar to obtain the carbon coating slurry.

[0121] S8 Coats the carbonized slurry obtained in step S7 onto the surface of the aluminum foil, and after drying, forms a carbonized layer on the surface of the aluminum foil to obtain a carbonized current collector.

[0122] (2) Mix NiSO4·6H2O, Na2MoO4·2H2O and NMP to obtain a mixed salt solution, wherein the molar ratio of nickel to molybdenum is 6:1.

[0123] (3) Place the mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) into a Teflon high-pressure reactor. Gently peel the carbon-coated current collector from the bottom of the reactor so that it is suspended in the solution. Seal the reactor and react at 220°C for 9 hours. The pressure inside the reactor is 2.8 atmospheres. After cooling to room temperature, take out the sample and put it in an oven. Dry it at 55°C for 11 hours to obtain a composite current collector.

[0124] Example 3

[0125] This embodiment provides a composite current collector, including a carbon-coated current collector. The carbon-coated current collector includes a current collector substrate and a carbon coating layer located on the surface of the current collector substrate. A rod-shaped structure is grown in situ on the carbon coating layer. The rod-shaped structure includes a rod-shaped body and carbon particles embedded in the rod-shaped body.

[0126] The current collector substrate is aluminum foil, and the rod-shaped body is made of NiMoO4.

[0127] The rod-shaped structure appears as straw on the carbon coating layer. The straw-like shape is characterized by multiple rod-shaped structures clustered together and radiating outwards. The angle θ between the rod-shaped structure and the plane of the carbon coating layer is mainly in the range of 30°-90°.

[0128] The rod-shaped structure is a prism-shaped microrod with a rectangular cross-section. The length of the rectangle is in the range of 0.03μm-0.07μm, the width of the rectangle is in the range of 0.02μm-0.06μm, and the length of the rod-shaped structure is in the range of 0.5μm-1.2μm.

[0129] This embodiment also provides a method for preparing the above-mentioned composite current collector, including the following steps:

[0130] (1) Preparation of carbon-coated current collector:

[0131] S1 mixes the modified polyacrylic acid adhesive with water and stirs it slowly at 600 rpm for 30 minutes to obtain the diluted polyacrylic acid adhesive (viscosity 800 mPa·s).

[0132] S2 First dispersion: Using carbon powder as a conductive agent, 50% of the conductive agent is added to the adhesive obtained in step S1, and the mixture is dispersed at a high speed of 2300 rpm for 60 min.

[0133] S3 Second Dispersion: Continue to add 50% conductive agent and disperse at high speed of 2250 rpm for 70 min.

[0134] S4 Third Dispersion: Add water to reduce the viscosity of the slurry and prevent the slurry from being too viscous to disperse evenly. Disperse at high speed of 2600 rpm for 30 minutes.

[0135] S5 tests the pH of the slurry. The pH of the slurry is adjusted to 7 with water and sodium bicarbonate because a pH greater than 7 will cause the viscosity to rise sharply.

[0136] S6 is used to thoroughly stir and disperse the slurry at a high speed of 2250 rpm for 60 minutes.

[0137] Add a wetting agent (modified polyether siloxane) to S7, with the amount of wetting agent accounting for 10% of the total mass of the reaction system. After addition, stir slowly at 15 rpm for 40 min. Remove air bubbles by vacuuming and homogenize at a pressure of 450 bar to obtain the carbon coating slurry.

[0138] S8 Coats the carbonized slurry obtained in step S7 onto the surface of the aluminum foil, and after drying, forms a carbonized layer on the surface of the aluminum foil to obtain a carbonized current collector.

[0139] (2) Mix NiSO4·6H2O, Na2MoO4·2H2O and NMP to obtain a mixed salt solution, wherein the molar ratio of nickel to molybdenum is 3.5:1.

[0140] (3) Place the mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) into a Teflon high-pressure reactor. Gently peel the carbon-coated current collector from the bottom of the reactor to suspend it in the solution. Seal the reactor and react at 160°C for 15 hours. The pressure inside the reactor is 2 atmospheres. After cooling to room temperature, take out the sample and place it in an oven to dry at 60°C for 12 hours to obtain the composite current collector.

[0141] Example 4

[0142] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 1:1, and the rest is the same as in Example 1.

[0143] Example 5

[0144] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 1.5:1, and the rest is the same as in Example 1.

[0145] Example 6

[0146] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 2:1, and the rest is the same as in Example 1.

[0147] Example 7

[0148] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 3:1, and the rest is the same as in Example 1.

[0149] Example 8

[0150] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 5:1, and the rest is the same as in Example 1.

[0151] Example 9

[0152] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 7:1, and the rest is the same as in Example 1.

[0153] Example 10

[0154] This embodiment provides a composite current collector and its preparation method. The difference between the preparation method and that in Embodiment 1 is that the water in step S1 is replaced with NMP, and the NMP in step (2) is replaced with water.

[0155] Example 11

[0156] This embodiment provides a composite current collector and its preparation method. The difference between the preparation method and that in Example 1 is that Na2MoO4·2H2O in step (2) is replaced with ammonium molybdate, resulting in a pH of 6 for the prepared mixed salt solution.

[0157] Comparative Example 1

[0158] This embodiment provides a composite current collector and its preparation method. The difference between the preparation method and that in embodiment 1 is that in step (3), 180°C is replaced with 100°C.

[0159] The comparative example failed to grow a straw-like structure due to the reaction temperature being too low.

[0160] Comparative Example 2

[0161] This embodiment provides a composite current collector and its preparation method. The molar ratio of NiSO4·6H2O to Na2MoO4·2H2O is 1:0, and the rest is the same as in Example 1.

[0162] test:

[0163] (1) Preparation of positive electrode:

[0164] 1. PVDF, lithium iron phosphate and carbon black were dispersed in NMP solvent according to the mass ratio of PVDF: lithium iron phosphate: carbon black = 2:97:1 to prepare a positive electrode slurry with a solid content of 50%.

[0165] 2. Coat the positive electrode slurry onto carbon-coated aluminum foil and bake at 120°C for 20 minutes;

[0166] 3. Apply the electrode sheet at a concentration of 2.35 g / cm³. 2 The positive electrode active material is pressed together with the carbon-coated aluminum foil by compaction density roller pressing to obtain the positive electrode sheet;

[0167] 4. Cut the positive electrode sheet into 12cm×2cm pieces and place them in a vacuum drying oven for later use.

[0168] (2) Positive electrode peeling force test:

[0169] The prepared positive electrode sheet was attached to the test plate with 2cm of 3M double-sided tape to separate the active material on the positive electrode sheet from the carbon coating layer. The active material was then attached to the carbon-coated aluminum foil with tape and the 180° positive electrode peel force was tested on a tensile testing machine.

[0170] (3) Peel strength test method for carbon coating:

[0171] Cut the carbon-coated aluminum foil into 12cm×5cm pieces, attach the sample to the test plate with 3M double-sided tape, then attach the adhesive tape to the surface of the carbon-coated sample, squeeze out the air bubbles in the adhesive tape, and perform a peel force test on the carbon coating layer on a tensile testing machine.

[0172] The test results are shown in Table 1.

[0173] Table 1

[0174] As shown in Table 1, this application increases the surface complexity and roughness by in-situ growing a rod-shaped structure of a specific composition on the carbon coating layer of the carbon-coated current collector. This increases the contact area and embedding degree with the positive electrode active material during rolling, allowing for better bonding between the positive electrode active material and the carbon coating layer. This effectively improves the adhesion and peel strength between the current collector and the positive electrode active material. Simultaneously, because carbon particles are embedded in the rod-shaped body, the composite current collector exhibits good conductivity, which is beneficial for improving the electrochemical performance of the electrode prepared using it.

[0175] Meanwhile, a comparison between Example 1 and Examples 4-9 shows that the molar ratio of nickel to molybdenum affects the microstructure of the carbon coating layer on the surface of the current collector, the peeling force between the carbon coating layer and the positive electrode, and the battery impedance, thereby affecting the battery performance. If the nickel content is too low, it will reduce the number and density of the rod-like structures; if the nickel content is too high, it will lead to an excessive number of microrods, reducing the toughness of the current collector and the peeling force between the carbon coating layer and the positive electrode.

[0176] A comparison of Examples 1 and 11 shows that if sodium molybdate is replaced with ammonium molybdate, the pH of the solution obtained by dissolving ammonium molybdate in the solvent is 6, which is too acidic and not conducive to morphology control, thus leading to a decrease in the peeling force of the carbon coating layer and the positive electrode.

[0177] The comparison between Example 1 and Comparative Example 1 shows that if the reaction temperature is too low, a straw-like structure cannot be grown, which in turn affects the peeling force of the carbon coating layer and the positive electrode, as well as the battery impedance.

[0178] The comparison between Example 1 and Comparative Example 2 shows that if molybdenum salt is not used in the preparation process, the peeling force of the carbon coating layer and the positive electrode will be greatly reduced.

[0179] The applicant declares that this application illustrates the detailed method of this application through the above embodiments, but this application is not limited to the above detailed method, that is, it does not mean that this application must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to this application, equivalent substitutions of the raw materials of this application's product, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of this application.

Claims

1. A composite current collector, comprising a carbon-coated current collector, the carbon-coated current collector comprising a current collector substrate and a carbon coating layer located on the surface of the current collector substrate, wherein a rod-shaped structure is grown in situ on the carbon coating layer, the rod-shaped structure comprising a rod-shaped body and carbon particles embedded in the rod-shaped body, the material of the rod-shaped body comprising Ni and Mo.

2. The composite current collector according to claim 1, wherein, The rod-shaped body is made of doped or undoped NiMoO4, wherein the doping element is at least one of P, S, C or Se.

3. The composite current collector according to claim 1 or 2, wherein, The rod-shaped structure appears as straw on the carbon coating layer. The straw-like shape is characterized by multiple rod-shaped structures clustered together and radiating outwards. The angle θ between the rod-shaped structure and the plane of the carbon coating layer is mainly in the range of 30°-90°.

4. The composite current collector according to any one of claims 1-3, wherein, The rod-shaped structure is a prism-shaped microrod with a rectangular cross-section. The length of the rectangle is in the range of 0.03μm-0.07μm, the width of the rectangle is in the range of 0.02μm-0.06μm, and the length of the rod-shaped structure is in the range of 0.5μm-1.2μm.

5. The composite current collector according to claim 3, wherein, The included angle θ is in the range of 45°-90°, and can be selected in the range of 60°-90°.

6. A method for preparing a composite current collector as described in any one of claims 1-5, comprising the following steps: (1) Prepare a mixed salt solution using nickel salt, molybdenum salt and solvent; (2) The mixed salt solution and the carbon-coated current collector are placed in a reaction vessel, the reaction vessel is sealed and heated, and the reaction is carried out under a certain temperature and pressure to obtain the composite current collector.

7. The preparation method according to claim 6, wherein, The nickel salt in step (1) includes NiSO4·6H2O.

8. The preparation method according to claim 6 or 7, wherein, The molybdenum salt in step (1) includes Na2MoO4·2H2O and / or ammonium molybdate.

9. The preparation method according to any one of claims 6-8, wherein, In step (1), the molar ratio of nickel in the nickel salt to molybdenum in the molybdenum salt is greater than or equal to 1.5:1, and can be selected as (1.5-6):1; Optionally, the pH of the mixed salt solution in step (1) is 6.5-7.5; Optionally, when the solvent used in the preparation of the carbon-coated current collector is water, the solvent in step (1) includes at least one of dimethylformamide, N-methylpyrrolidone, and methyl ethyl ketone; Optionally, when the solvent used in the preparation of the carbon-coated current collector is an oil-based solvent, the solvent in step (1) is water; Optionally, the oil-based solvent includes N-methylpyrrolidone; Optionally, when the carbon-coated current collector is a sodium-electric current collector and the carbon-coated slurry used in the preparation of the sodium-electric current collector contains a crosslinking agent, the solvent in step (1) is water; Optionally, the crosslinking agent includes at least one of methacrylic acid, methyl vinyl acid, and isopropylacrylic acid.

10. The preparation method according to any one of claims 6-9, wherein, In step (2), heat to 120℃-240℃; Optionally, during the reaction described in step (2), the pressure inside the reaction vessel is 2-3 atmospheres; Optionally, the reaction time in step (2) is 8h-18h; Optionally, after the reaction described in step (2), a sampling and drying step is also performed.

11. The preparation method according to any one of claims 6-10, wherein, The preparation method of the carbon-coated current collector in step (2) includes the following steps: (A) Disperse the raw materials for the carbon coating layer in a solvent to obtain a carbon coating slurry; (B) The carbon coating slurry is coated onto the surface of the current collector substrate, and after drying, a carbon coating layer is formed on the surface of the current collector substrate to obtain the carbon-coated current collector.

12. The preparation method according to claim 11, wherein, The raw materials for the carbon coating layer in step (A) include conductive agents and binders; Optionally, the conductive agent includes carbon powder, and optionally also includes graphite powder; Optionally, the carbon powder and the graphite powder account for 70%-100% and 0%-30% of the mass of the conductive agent, respectively; Optionally, the adhesive includes at least one of acrylate, polyacrylic acid, modified polyacrylic acid, or waterborne polyurethane, and may be modified polyacrylic acid; Optionally, the adhesive is a modified polyacrylic acid liquid with a solid content of 15%-30% and a viscosity of 200 mPa·s-1500 mPa·s. Optionally, the raw material for the carbon coating layer in step (A) further includes a wetting agent; Optionally, the wetting agent includes at least one of polyether siloxane, modified polyether siloxane, and alcohol, with modified polyether siloxane being optional. Optionally, the amount of the wetting agent is 3%-20% of the total mass of the reaction system.

13. The preparation method according to claim 11 or 12, wherein, Step (A) includes: S1 adds a conductive agent to the adhesive solution and disperses it to obtain the first material; S2 adds a wetting agent to the first material, stirs and then homogenizes it to obtain a carbon coating slurry; Optionally, step S1 includes: first adding a portion of conductive agent to the adhesive solution, performing a first high-speed stirring, and then adding the remaining conductive agent to the obtained material, performing a second high-speed stirring. Optionally, the conductive agent accounts for 40%-60% of the total conductive agent; Optionally, the rotation speed of the first high-speed stirring is 2000 rpm to 2600 rpm; Optionally, the first high-speed stirring time is 30-60 minutes; Optionally, the rotation speed of the second high-speed stirring is 2000 rpm to 2600 rpm; Optionally, the second high-speed stirring time is 60-90 minutes; Optionally, the stirring speed in step S2 is 10 rpm to 15 rpm; Optionally, the stirring time in step S2 is 30 min to 45 min; Optionally, the pressure of the homogenization process in step S2 is 300 bar to 600 bar; Optionally, the preparation method further includes: After step S1 and before step S2, the following steps are performed: (a) Add solvent to the first material to reduce the concentration of the slurry, and disperse at a high speed of 2000rpm-2600rpm for 30min-45min. (b) Adjust the pH of the slurry obtained in step (a) to 5-7 using a pH adjuster; Optionally, the amount of pH adjuster added is 5wt%-10wt% of the adhesive solution.

14. An electrode sheet, wherein, The electrode includes a current collector and an active layer disposed on the surface of the current collector, wherein the current collector is a composite current collector as described in any one of claims 1-5 or a composite current collector prepared by the method described in any one of claims 6-13.

15. A battery comprising a positive electrode, a negative electrode, and a separator, wherein, The positive electrode and / or the negative electrode are selected from the electrodes described in claim 14.

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