Composite current collector, method for preparing the same and use thereof

Abstract

The application discloses a composite current collector and a preparation method and application thereof. The composite current collector comprises a carbon-coated current collector, the carbon-coated current collector comprises a current collector substrate and a carbon-coated layer on the surface of the current collector substrate, and a rod-shaped structure is in-situ grown on the carbon-coated layer, the rod-shaped structure comprises a rod-shaped body and carbon particles embedded on the rod-shaped body, and the material of the rod-shaped body comprises Ni and Mo. The application effectively improves the adhesion and peeling strength of the current collector and a positive active material by in-situ growing the rod-shaped structure with a specific composition on the carbon-coated layer of the carbon-coated current collector. Meanwhile, since the carbon particles are embedded on the rod-shaped body, the composite current collector has good electrical conductivity, and the electrochemical performance of an electrode prepared by using the composite current collector is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a composite current collector and a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries (LIB) have been widely accepted in many fields such as consumer electronics, transportation, electric tools and energy storage. The current collector in the lithium ion battery, as one of the key components, plays a relatively important role. Its main functions are: carrying electrode active material, collecting and outputting the current generated by the active material, and inputting the electrode current to the active material.

[0003] The aluminum foil current collector refers to a composite material formed by combining an aluminum foil with other materials (such as paper, plastic film, coating, etc.). This composite material 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 can improve the rate of lithium batteries and improve the performance of lithium batteries. However, the low adhesion of carbon-coated aluminum foil current collectors affects the subsequent coating of positive active materials, and therefore, it is necessary to develop and manufacture a carbon-coated current collector with high adhesion to ensure the connection between the positive active material and the carbon-coated layer. SUMMARY

[0004] In view of the above problems existing in the prior art, the purpose of the present application is to provide a composite current collector and a preparation method and application thereof.

[0005] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0006] In a first aspect, the present application provides a composite current collector, which comprises a carbon-coated current collector, the carbon-coated current collector comprising a current collector substrate and a carbon-coated layer located on the surface of the current collector substrate, a rod-like structure being grown in situ on the carbon-coated layer, the rod-like structure comprising a rod-like body and carbon particles embedded on the rod-like body, and the material of the rod-like body comprising Ni and Mo.

[0007] The present application does not make specific limitations on the type of current collector substrate, which can be, for example, an aluminum foil.

[0008] The present application increases the complexity and roughness of the surface by growing rod-like structures of specific composition in situ on the carbon coating layer of the carbon-coated current collector, wherein the roughness refers to the unevenness and roughness of the surface of the carbon coating layer, which has an important influence on the adhesion and performance of the carbon-coated current collector, the higher the roughness of the surface of the carbon coating layer, the more mechanical locking points it provides, thereby making the adhesion stronger. Therefore, the composite current collector of the present application increases the contact area and embedding degree with the positive active material during rolling, and the positive active material and the carbon coating layer can be better combined, effectively improving the adhesion and peel strength of the current collector and the positive active material. At the same time, since the carbon particles are embedded in the rod-like body, the composite current collector has good electrical conductivity, which is conducive to improving the electrochemical performance of the electrode prepared therefrom.

[0009] The following is a preferred technical solution of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

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

[0011] Preferably, the rod-like structure appears as a straw on the carbon coating layer, and the straw is that a plurality of rod-like structures are gathered into clusters and are divergent, and the included angle θ between the rod-like structure and the plane of the carbon coating layer is mainly in 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] Preferably, the rod-like structure is a prismatic microrod, the cross section of which is a rectangle, the length of the rectangle is in the range of 0.03 μm-0.07 μm, for example, it can be 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm or 0.07 μm, etc.; the width of the rectangle is in the range of 0.02 μm-0.06 μm, for example, it can be 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm or 0.06 μm, etc.; the rod length of the rod-like structure is in the range of 0.5 μm-1.2 μm, for example, it can be 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.05 μm, 1.1 μm, 1.15 μm or 1.2 μm, etc.

[0013] Preferably, the included angle θ is in the range of 45°-90°, more preferably in the range of 60°-90°.

[0014] In a second aspect, the present application provides a preparation method of the composite current collector according to the first aspect, and the preparation method comprises the following steps:

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

[0016] (2) placing the mixed salt solution and a carbon-coated current collector in a reaction container, sealing the reaction container and heating, and reacting under a certain temperature and pressure to obtain the composite current collector.

[0017] The method of the present application can grow rod-like structures in situ by using a carbon-coated current collector, and the rod-like structures comprise Ni and Mo in the rod-like main body, and, since the carbon-coated current collector contains carbon elements, carbon particles can be introduced on the rod-like main body after the reaction in the sealed reaction container.

[0018] The composite current collector prepared by the method of the present application effectively improves the adhesion and peeling strength of the current collector and the positive active material, and has good electrical conductivity, which can improve the electrochemical performance of the electrode of the battery prepared by using the same.

[0019] The method of the present application is simple, and the experimental operation and experimental steps are greatly reduced, the use amount of machine equipment and the operation difficulty are reduced, thereby reducing the production cost and the maintenance cost of the equipment, and facilitating popularization and use.

[0020] In the method of the present application, since the carbon-coated current collector is light in weight and small in thickness, it is easy to be absorbed to the bottom of the reaction container under the action of water pressure when the carbon-coated current collector is placed in the reaction container together with the mixed salt solution, in this case, the carbon-coated current collector needs to be lifted from the bottom of the reaction container, so that the pressure of the two surfaces of the carbon-coated current collector is equal, and the carbon-coated current collector is suspended in the solution, so as to grow microstructures on the two surfaces.

[0021] In an embodiment, the reaction container is a reaction kettle.

[0022] Preferably, the nickel salt in step (1) comprises NiSO4·6H2O.

[0023] Preferably, the molybdenum salt in step (1) comprises Na2MoO4·2H2O and / or ammonium molybdate.

[0024] Preferably, in step (1), the molar ratio of the nickel element in the nickel salt to the molybdenum element 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 preferred range, the optimal interfacial micro-environment can be obtained, thereby improving the peeling force of the coating. The technical principle is as follows: the nickel element can promote the number and compactness of the rod-like structures, and sufficient Ni2+and an appropriate amount of molybdenum ions are required for the growth of abundant rice straw-like micro-rods. However, the number of micro-rod structures is not the more the better, and exceeding a certain number will reduce the toughness of the composite current collector. Therefore, the molar ratio of the nickel element to the molybdenum element is more preferably in the range of (1.5-6):1.

[0025] In one embodiment, the mixed salt solution is prepared in the following manner: 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 uniformly to obtain the mixed salt solution.

[0026] Preferably, 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, etc.

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

[0028] Preferably, when the solvent used in the preparation of the coated carbon current collector is water, the solvent in step (1) comprises 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, and since the solvent used in the preparation of the coated carbon current collector is water, there is no problem of damaging the integrity of the coating of the coated carbon current collector during the reaction in step (2).

[0029] Preferably, 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-methyl pyrrolidone. Under this condition, the reaction in step (2) is a hydrothermal reaction, and since the solvent used in the preparation of the carbon-coated current collector is an oil-based solvent, there is no problem of damaging the integrity of the coating of the carbon-coated current collector during the reaction in step (2).

[0030] Preferably, the oil-based solvent comprises N-methyl pyrrolidone.

[0031] Preferably, when the carbon-coated current collector is a sodium battery coating current collector, and the carbon-coated slurry used in the preparation of the sodium battery coating current collector comprises a cross-linking agent, the solvent in step (1) is water. Under this condition, the reaction in step (2) is a hydrothermal reaction, and since the carbon-coated slurry used in the preparation of the sodium battery coating current collector comprises a cross-linking agent, it has good water resistance, and there is no problem of damaging the integrity of the coating of the carbon-coated current collector during the reaction in step (2).

[0032] Preferably, the cross-linking agent comprises at least one of methacrylic acid, methyl vinyl acid, and isopropyl acrylic acid.

[0033] Preferably, the heating in step (2) is to 120-240°C, for example, it can be 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, etc.

[0034] Preferably, during the reaction in step (2), the pressure in 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] Preferably, the reaction time in step (2) is 8-18 hours, for example, it can be 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, or 18 hours, etc.

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

[0037] The present application does not limit the drying time, and the skilled person in the art can select the time according to the actual needs.

[0038] As a preferred technical solution of the preparation method of the present application, the preparation method of the carbon-coated current collector in step (2) comprises the following steps:

[0039] (A) dispersing the raw material of the carbon coating layer in a solvent to obtain a carbon coating slurry;

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

[0041] Preferably, the raw material of the carbon coating layer in step (A) comprises a conductive agent and a binder.

[0042] Preferably, the conductive agent comprises carbon powder, and preferably further comprises graphite powder.

[0043] Preferably, the mass ratio of the carbon powder and the graphite powder in the conductive agent is 70%-100% and 0%-30% respectively. The mass ratio of the 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 ratio of the 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 ratio of the carbon powder is 100%, it means that the conductive agent is composed of carbon powder. When the mass ratio of the graphite powder is 0%, it means that the conductive agent does not contain graphite powder.

[0044] Preferably, the binder comprises at least one of acrylate, polyacrylic acid, modified polyacrylic acid or water-based polyurethane, and preferably is modified polyacrylic acid.

[0045] Preferably, the binder is modified polyacrylic acid glue, and the solid content is 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 glue is 200mPa.s-1500mPa.s, for example, it can be 200mPa·s, 300mPa·s, 400mPa·s, 500mPa·s, 550mPa·s, 600mPa·s, 650mPa·s, 700mPa·s, 750mPa·s, 800mPa·s, 850mPa·s, 900mPa·s, 950mPa·s, 1000mPa·s, 1050mPa·s, 1100mPa·s, 1200mPa·s, 1300mPa·s, 1400mPa·s or 1500mPa·s, etc.

[0046] Preferably, the raw material of the carbon coating layer in step (A) further comprises a wetting agent.

[0047] Preferably, the wetting agent comprises at least one of polyether siloxane, modified polyether siloxane and alcohol, preferably modified polyether siloxane.

[0048] Modified polyether siloxane is a special type of siloxane material, which modifies the performance of siloxane by introducing polyether segments, improving its flexibility, chemical corrosion resistance and low temperature performance.

[0049] The structure of modified polyether siloxane is composed of siloxane skeleton and polyether segment, which are connected by copolymerization or grafting reaction. This structure makes modified polyether siloxane have good mechanical properties, thermal stability and chemical stability.

[0050] The source of modified polyether siloxane is not specifically limited in the present application, which can be a commercially available product, for example, DC-595 purchased from Dow Corning Company, USA.

[0051] Preferably, 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%, etc. Here, the total mass of the reaction system refers to the mass of all liquids after adding the wetting agent.

[0052] As a preferred technical solution of the preparation method of the present application, step (A) comprises:

[0053] S1 adds conductive agent to the binder glue solution, disperses to obtain a first material;

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

[0055] In the present application, the binder glue solution refers to the abbreviation of the binder in the form of glue solution.

[0056] Preferably, step S1 comprises: first adding a part of the conductive agent to the binder glue solution, performing first high-speed stirring, then adding the remaining conductive agent to the obtained material, and performing second high-speed stirring.

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

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

[0059] Preferably, the time of the first high-speed stirring is 30 min-60 min, for example, it can be 30 min, 35 min, 38 min, 40 min, 43 min, 46 min, 48 min, 50 min, 53 min, 56 min or 60 min, etc.

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

[0061] Preferably, the time of the second high-speed stirring is 60 min-90 min, for example, it can be 60 min, 65 min, 70 min, 75 min, 80 min, 85 min or 90 min, etc.

[0062] Preferably, the rotating speed of the stirring in step S2 is 10 rpm-15 rpm, for example, it can be 10 rpm, 11 rpm, 12 rpm, 13 rpm or 15 rpm, etc.

[0063] Preferably, the time of the stirring in step S2 is 30 min-45 min, for example, it can be 30 min, 35 min, 38 min, 40 min, 43 min or 45 min, etc.

[0064] The number of homogenization treatments is not specifically limited in the present application, and it is generally greater than 2, for example, 2, 3 or 4, etc., and the number of homogenization treatments can be determined according to actual needs in the art.

[0065] Preferably, the pressure of the homogenization treatment in step S2 is 300 bar-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] Preferably, the preparation method further comprises:

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

[0068] (a) adding a solvent to the first material to reduce the concentration of the slurry, and high-speed dispersing at a rotation speed of 2000 rpm-2600 rpm (for example, it can be 2000 rpm, 2100 rpm, 2150 rpm, 2200 rpm, 2250 rpm, 2300 rpm, 2350 rpm, 2400 rpm, 2500 rpm, 2550 rpm, or 2600 rpm, etc.) for 30 min-45 min (for example, it can be 30 min, 35 min, 38 min, 40 min, 43 min, or 45 min, etc.).

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

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

[0071] In a third aspect, the present application provides a pole piece, 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 of the first aspect or the composite current collector prepared by the method of the second aspect.

[0072] The pole piece in the present application can be a positive pole piece or a negative pole piece. For the positive pole piece, the current collector therein is a positive current collector, and the active layer is a positive active layer; for the negative pole piece, the current collector therein is a negative current collector, and the active layer is a negative active layer.

[0073] In an embodiment, the positive current collector is the composite current collector of the first aspect, wherein the current collector substrate is an aluminum foil.

[0074] In an embodiment, the positive material layer comprises a positive active material, a binder, and optionally a conductive agent.

[0075] In an embodiment, the negative current collector is the composite current collector of the first aspect, wherein the current collector substrate is a copper foil.

[0076] In an embodiment, the negative material layer comprises a negative active material, a binder, and optionally a conductive agent.

[0077] In a fourth aspect, the present application provides a battery comprising a positive pole piece, a negative pole piece, and a separator, wherein the positive pole piece and / or the negative pole piece is selected from the pole piece of the third aspect.

[0078] The numerical ranges recited herein include all values from and including the lower and upper values. This is true even if the values included in the lower or upper range are outside of the recited range. The ranges are presented essentially to reflect the broadest intended support in the field, and to provide the support in the known art. The exact numerical ranges include every number between the recited lower value and the recited upper value. That is, all indicated numerical values can contain any combinations and sub-combinations thereof as well as any number or range of values that are in between the recited values. Although specific numerical ranges have been recited, it is contemplated that the numerical values recited can be outside of the range.

[0079] Compared with the prior art, the present application has the following beneficial effects:

[0080] (1) The present application increases the complexity and roughness of the surface by growing rod-shaped structures of specific composition in situ on the carbon-coated layer of the carbon-coated current collector, increases the contact area and embedding degree with the positive active material during rolling, and the positive active material and the carbon-coated layer can be better combined, effectively improving the adhesion and peeling strength of the current collector and the positive active material. At the same time, since the carbon particles are embedded on the rod-shaped body, the composite current collector has good electrical conductivity, which is beneficial to improve the electrochemical performance of the electrode prepared therefrom.

[0081] (2) The method of the present application is simple, and the experimental operation and experimental steps are greatly reduced, the use amount and operation difficulty of the machine equipment are reduced, thereby reducing the production cost and equipment maintenance cost, and facilitating popularization and use. BRIEF DESCRIPTION OF DRAWINGS

[0082] Figure 1 and Figure 2 are scanning images of the carbon-coated layer in the composite current collector prepared in Example 1 at different magnifications. DETAILED DESCRIPTION

[0083] The technical solutions of the present application will be further illustrated by specific embodiments in combination with the accompanying drawings.

[0084] The embodiments of the present application will be described in detail below, so that the advantages and features of the present application can be more easily understood by those skilled in the art, and the protection scope of the present application can be more clearly defined.

[0085] In the embodiments of the present application, the purchase sources of the raw materials are as follows:

[0086] The modified polyacrylic acid glue solution is purchased from the National Pharmaceutical Group Chemical Reagent Co., Ltd., with an average molecular weight M.W of 5000, a solid content of 20%, and a viscosity of 1000 mPa·s.

[0087] The modified polyether siloxane can be purchased from the National Pharmaceutical Group, with a purity of 99%, produced by Beijing Woke Biological Technology Co., Ltd.

[0088] Example 1

[0089] The embodiment provides a composite current collector, including a carbon-coated current collector, the carbon-coated current collector including a current collector substrate and a carbon-coated layer on the surface of the current collector substrate, and rod-shaped structures in situ grown on the carbon-coated layer, the rod-shaped structures including a rod-shaped body and carbon particles embedded on the rod-shaped body.

[0090] The current collector substrate is an aluminum foil, and the material of the rod-shaped body is NiMoO4.

[0091] The rod-shaped structures present a straw-like shape on the carbon-coated layer, the straw-like shape being that a plurality of the rod-shaped structures gather into clusters and present a divergent shape, and the included angle θ between the rod-shaped structures and the plane of the carbon-coated layer is mainly in the range of 30°-90°.

[0092] In combination Figure 1 And Figure 2 It can be known that the rod-shaped structures are prismatic microrods, the cross section of the prismatic microrods is a rectangle, the length of the rectangle is in the range of 0.03 μm-0.07 μm, the width of the rectangle is in the range of 0.02 μm-0.06 μm, and the rod length of the rod-shaped structures is in the range of 0.5 μm-1.2 μm.

[0093] The embodiment further provides a preparation method of the composite current collector.

[0094] (1) preparing a carbon-coated current collector:

[0095] S1 mixing a modified polyacrylic acid glue solution with water, slowly stirring at a speed of 600 rpm for 30 min to obtain a diluted polyacrylic acid glue solution (the viscosity is 800 mPa·s).

[0096] S2 first dispersion: mixing carbon powder and graphite powder according to a mass ratio of 70:30 to obtain a conductive agent, and adding 50% of the conductive agent into the glue solution obtained in step S1 and high-speed dispersing at a speed of 2000 rpm for 30 min.

[0097] S3 second dispersion: continuously adding 50% of the conductive agent and high-speed dispersing at a speed of 2600 rpm for 30 min.

[0098] S4 third dispersion: adding water to reduce the viscosity of the slurry, preventing the slurry from being too viscous to be uniformly dispersed, and high-speed dispersing at a speed of 2000 rpm for 30 min.

[0099] S5 testing the pH of the slurry, and adjusting the pH of the slurry to 5 by using water and sodium bicarbonate, because the viscosity of the slurry will sharply increase when the pH of the slurry is greater than 7.

[0100] S6 fully stirring and dispersing, and high-speed dispersing the slurry at a speed of 2250 rpm for 60 min.

[0101] S7 Add wetting agent (modified polyether siloxane), the amount of wetting agent is 10% of the total mass of the reaction system. After adding, slowly stir at 10 rpm for 45 min. Vacuum degassing to remove bubbles, homogenization treatment at a pressure of 300 bar to obtain a carbon-coated slurry.

[0102] S8 The carbon-coated slurry obtained in step S7 is coated on the surface of the aluminum foil, and after drying, a carbon-coated layer is formed on the surface of the aluminum foil to obtain a carbon-coated current collector.

[0103] (2) Mix NiSO4·6H2O, Na2MoO4·2H2O and NMP to obtain a mixed salt solution, wherein the molar ratio of nickel element to molybdenum element is 4:1.

[0104] (3) Put the mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) into a Teflon high-pressure reaction kettle, gently lift the carbon-coated current collector from the bottom of the reaction kettle, and make it suspended in the solution. Seal, react at 180℃ for 12h, the pressure in the reaction kettle is 2.2atm, cool to room temperature, take out the sample, put it into an oven, and dry at 60℃ for 12h to obtain a composite current collector.

[0105] Example 2

[0106] The present embodiment provides a composite current collector, which comprises a carbon-coated current collector, the carbon-coated current collector comprises a current collector substrate and a carbon-coated layer on the surface of the current collector substrate, and a rod-like structure is grown in situ on the carbon-coated layer, the rod-like structure comprises a rod-like body and carbon particles embedded on the rod-like body.

[0107] The current collector substrate is an aluminum foil, and the material of the rod-like body is NiMoO4.

[0108] The rod-like structure on the carbon-coated layer presents a straw-like shape, that is, a plurality of rod-like structures are gathered into clusters and present a divergent shape, and the included angle θ between the rod-like structure and the plane of the carbon-coated layer is mainly in the range of 30°-90°.

[0109] The rod-like structure is a prismatic microrod, the cross section is a rectangle, 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 rod length of the rod-like structure is in the range of 0.5μm-1.2μm.

[0110] The present embodiment also provides a preparation method of the above-mentioned composite current collector, comprising the following steps:

[0111] (1) Preparation of carbon-coated current collector:

[0112] S1: The modified polyacrylic acid glue solution is mixed with water and stirred slowly at a speed of 600 rpm for 30 min to obtain a diluted polyacrylic acid glue solution (with a viscosity of 800 mPa·s).

[0113] S2: First dispersion: carbon powder and graphite powder are mixed at a mass ratio of 80:20 to obtain a conductive agent, and 40% of the conductive agent is added to the glue solution obtained in step S1 and dispersed at a high speed of 2600 rpm for 40 min.

[0114] S3: Second dispersion: 60% of the conductive agent is continuously added and dispersed at a high speed of 2000 rpm for 90 min.

[0115] S4: Third dispersion: water is added to reduce the viscosity of the slurry to prevent the slurry from being too viscous to disperse uniformly, and the slurry is dispersed at a high speed of 2400 rpm for 30 min.

[0116] S5: The pH of the slurry is tested, and 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.

[0117] S6: The slurry is dispersed at a high speed of 2300 rpm for 55 min.

[0118] S7: A wetting agent (modified polyether siloxane) is added, and the amount of the wetting agent accounts for 10% of the total mass of the reaction system. After adding, it is slowly stirred at 15 rpm for 30 min. Vacuum is applied to remove bubbles, and homogenization is performed at a pressure of 600 bar to obtain a carbon-coated slurry.

[0119] S8: The carbon-coated slurry obtained in step S7 is coated on the surface of an aluminum foil, and after drying, a carbon-coated layer is formed on the surface of the aluminum foil to obtain a carbon-coated current collector.

[0120] (2) NiSO4·6H2O, Na2MoO4·2H2O and NMP are mixed to obtain a mixed salt solution, wherein the molar ratio of nickel element to molybdenum element is 6:1.

[0121] (3) The mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) are placed in a Teflon high-pressure reaction kettle, the carbon-coated current collector is gently lifted from the bottom of the reaction kettle and suspended in the solution, sealed, and reacted at 220°C for 9 h, the pressure in the reaction kettle is 2.8 atm, and the sample is taken out after cooling to room temperature and placed in an oven and dried at 55°C for 11 h to obtain a composite current collector.

[0122] Example 3

[0123] The embodiment provides a composite current collector, including a carbon-coated current collector, the carbon-coated current collector including a current collector substrate and a carbon-coated layer on the surface of the current collector substrate, and a rod-shaped structure in-situ grown on the carbon-coated layer, the rod-shaped structure including a rod-shaped body and carbon particles embedded on the rod-shaped body.

[0124] The current collector substrate is an aluminum foil, and the material of the rod-shaped body is NiMoO4.

[0125] The rod-shaped structure is in a straw shape on the carbon-coated layer, and the straw shape is that a plurality of the rod-shaped structures are gathered into clusters and are divergent, and the included angle θ between the rod-shaped structure and the plane of the carbon-coated layer is mainly in the range of 30°-90°.

[0126] The rod-shaped structure is a prismatic microrod, the cross section of the rod-shaped structure is a rectangle, the length of the rectangle is in the range of 0.03 μm-0.07 μm, the width of the rectangle is in the range of 0.02 μm-0.06 μm, and the rod length of the rod-shaped structure is in the range of 0.5 μm-1.2 μm.

[0127] The embodiment also provides a preparation method of the composite current collector.

[0128] (1) preparing the carbon-coated current collector:

[0129] S1 mixing the modified polyacrylic acid glue solution with water, slowly stirring at a speed of 600 rpm for 30 min to obtain a diluted polyacrylic acid glue solution (the viscosity is 800 mPa·s).

[0130] S2 first dispersion: adding 50% of the conductive agent to the glue solution obtained in step S1, and high-speed dispersing at a speed of 2300 rpm for 60 min.

[0131] S3 second dispersion: continuously adding 50% of the conductive agent, and high-speed dispersing at a speed of 2250 rpm for 70 min.

[0132] S4 third dispersion: adding water to reduce the viscosity of the slurry, preventing the slurry from being too viscous to be uniformly dispersed, and high-speed dispersing at a speed of 2600 rpm for 30 min.

[0133] S5 testing the pH of the slurry, and adjusting the pH of the slurry to 7 by using water and sodium bicarbonate, because the pH of the slurry greater than 7 will cause the viscosity to sharply increase.

[0134] S6 sufficiently stirring and dispersing, and high-speed dispersing the slurry at a speed of 2250 rpm for 60 min.

[0135] S7 Add wetting agent (modified polyether siloxane), the amount of wetting agent is 10% of the total mass of the reaction system. After adding, slowly stir at 15 rpm for 40 min. Vacuum degassing to remove bubbles, homogenization treatment at a pressure of 450 bar to obtain a carbon-coated slurry.

[0136] S8 The carbon-coated slurry obtained in step S7 is coated on the surface of the aluminum foil, and after drying, a carbon-coated layer is formed on the surface of the aluminum foil to obtain a carbon-coated current collector.

[0137] (2) Mix NiSO4·6H2O, Na2MoO4·2H2O and NMP to obtain a mixed salt solution, wherein the molar ratio of nickel element to molybdenum element is 3.5:1.

[0138] (3) Put the mixed salt solution obtained in step (2) and the carbon-coated current collector obtained in step (1) into a Teflon high-pressure reaction kettle, gently lift the carbon-coated current collector from the bottom of the reaction kettle, and make it suspended in the solution, seal, react at 160℃ for 15h, the pressure in the reaction kettle is 2atm, after cooling to room temperature, take out the sample, put it into an oven, and dry at 60℃ for 12h to obtain a composite current collector.

[0139] Example 4

[0140] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 1:1, and the others are the same as in Example 1.

[0141] Example 5

[0142] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 1.5:1, and the others are the same as in Example 1.

[0143] Example 6

[0144] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 2:1, and the others are the same as in Example 1.

[0145] Example 7

[0146] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 3:1, and the others are the same as in Example 1.

[0147] Example 8

[0148] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 5:1, and the others are the same as in Example 1.

[0149] Example 9

[0150] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 7:1, and the other conditions are the same as in Example 1.

[0151] Example 10

[0152] This example provides a composite current collector and a preparation method thereof, the difference between the preparation method and Example 1 is that the water in step S1 is replaced by NMP, and the NMP in step (2) is replaced by water.

[0153] Example 11

[0154] This example provides a composite current collector and a preparation method thereof, the difference between the preparation method and Example 1 is that Na2MoO4·2H2O in step (2) is replaced by ammonium molybdate, resulting in a mixed salt solution with a pH of 6.

[0155] Comparative Example 1

[0156] This example provides a composite current collector and a preparation method thereof, the difference between the preparation method and Example 1 is that 180°C is replaced by 100°C in step (3).

[0157] This comparative example cannot grow a straw-like structure due to the excessively low reaction temperature.

[0158] Comparative Example 2

[0159] This example provides a composite current collector and a preparation method thereof, the molar ratio of NiSO4·6H2O:Na2MoO4·2H2O = 1:0, and the other conditions are the same as in Example 1.

[0160] Test:

[0161] (1) Preparation of positive electrode sheet:

[0162] 1. According to the mass ratio PVDF: lithium iron phosphate: carbon black = 2:97:1, disperse PVDF, lithium iron phosphate and carbon black in solvent NMP to prepare a positive electrode slurry with a solid content of 50%;

[0163] 2. The positive electrode slurry is coated on a carbon-coated aluminum foil and baked at 120°C for 20 minutes;

[0164] 3. The electrode sheet is rolled at a compaction density of 2.35 g / cm 2 , and the positive electrode active material and the carbon-coated aluminum foil are pressed together to obtain a positive electrode sheet;

[0165] 4. The positive electrode sheet is cut into 12 cm x 2 cm and placed in a vacuum drying oven for standby.

[0166] (2) Positive electrode peeling force test:

[0167] The prepared positive electrode sheet is attached to the test plate with 2 cm of 3M double-sided tape, the active material on the positive electrode sheet is separated from the carbon coating layer, the tape paper is attached to the carbon-coated aluminum foil, and the 180° positive electrode peeling force is tested on the tensile testing machine.

[0168] (3) Carbon coating layer peeling force test method:

[0169] The carbon-coated aluminum foil is cut into 12 cm x 5 cm, the sample is attached to the test plate with 3M double-sided tape, the tape paper is attached to the surface of the carbon-coated sample, the air bubbles in the tape paper are squeezed out, and the carbon coating layer peeling force is tested on the tensile testing machine.

[0170] The test results are shown in Table 1.

[0171] Table 1

[0172]

[0173]

[0174] As can be seen from Table 1, by growing a rod-shaped structure of a specific composition in situ on the carbon coating layer of the carbon-coated current collector, the complexity and roughness of the surface are increased, the contact area and embedding degree with the positive electrode active material during rolling are increased, the positive electrode active material and the carbon coating layer can be better combined, and the adhesion and peeling strength of the current collector and the positive electrode active material are effectively improved. At the same time, since the carbon particles are embedded in the rod-shaped body, the composite current collector has good electrical conductivity, which is beneficial to improve the electrochemical performance of the electrode prepared therefrom.

[0175] At the same time, by comparing Example 1 with Examples 4-9, it can be seen that the molar ratio of nickel and molybdenum affects the micro-morphology of the carbon coating layer on the surface of the current collector, affects the peeling force of the carbon coating layer and the positive electrode, and affects the performance of the battery, if the content of nickel is too low, the number and density of the rod-shaped structures will be reduced; if the content of nickel is too high, the number of micro-rods will be too high, reducing the toughness of the current collector and the peeling force of the carbon coating layer and the positive electrode.

[0176] By comparing Example 1 with Example 11, it can be seen that if sodium molybdate is replaced by ammonium molybdate, since the solution obtained by dissolving ammonium molybdate in a solvent has a pH of 6, which is too acidic, it is not conducive to the control of the morphology, and thus the peeling force of the carbon coating layer and the positive electrode is reduced.

[0177] As can be seen from the comparison between Example 1 and Comparative Example 1, if the reaction temperature is too low, the rice straw-like structure cannot be grown, and thus the peeling force of the carbon coating layer and the positive electrode and the battery impedance are affected.

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

[0179] The applicant declares that the detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A composite current collector, characterized by, The composite current collector comprises a carbon-coated current collector, the carbon-coated current collector comprises a current collector substrate and a carbon-coated layer on the surface of the current collector substrate, and a rod-shaped structure is in-situ grown on the carbon-coated layer, the rod-shaped structure comprises a rod-shaped body and carbon particles embedded on the rod-shaped body, and the material of the rod-shaped body comprises Ni and Mo; 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; The rod-shaped structure presents a straw-like shape on the carbon-coated layer, the straw-like shape is that a plurality of rod-shaped structures are gathered into clusters and present a divergent shape, and the included angle θ between the rod-shaped structure and the plane of the carbon-coated layer is in the range of 30°-90°.

2. The composite current collector of claim 1, wherein The rod-shaped structure is a prismatic microrod, the cross section of the rod-shaped structure is a rectangle, the length of the rectangle is in the range of 0.03 μm-0.07 μm, the width of the rectangle is in the range of 0.02 μm-0.06 μm, and the length of the rod-shaped structure is in the range of 0.5 μm-1.2 μm.

3. The composite current collector of claim 1, wherein The included angle θ is in the range of 45°-90°.

4. The composite current collector of claim 3, wherein, The included angle θ is in the range of 60°-90°.

5. A method of making a composite current collector as claimed in any one of claims 1 to 4, characterised in that, The preparation method comprises the following steps: (1) a mixed salt solution is prepared by using a nickel salt, a molybdenum salt and a solvent; (2) the mixed salt solution and the carbon-coated current collector are placed in a reaction container, the reaction container is sealed and heated, and the reaction is carried out under a certain temperature and pressure to obtain the composite current collector; In step (1), the molar ratio of the nickel element in the nickel salt to the molybdenum element in the molybdenum salt is (1.5-7):

1.

6. The production method according to claim 5, wherein In step (1), the nickel salt comprises NiSO4·6H2O.

7. The preparation method according to claim 5, characterized in that, In step (1), the molybdenum salt comprises Na2MoO4·2H2O and / or ammonium molybdate.

8. The preparation method according to claim 5, characterized in that, In step (1), the molar ratio of the nickel element in the nickel salt to the molybdenum element in the molybdenum salt is (1.5-6):

1.

9. The preparation method according to claim 5, characterized in that, In step (1), the pH of the mixed salt solution is 6.5-7.

5.

10. The method of claim 5, wherein, When the solvent used in the preparation process of the carbon-coated current collector is water, the solvent in step (1) comprises at least one of dimethylformamide, N-methylpyrrolidone and methyl ethyl ketone.

11. The method of claim 5, wherein, When the solvent used in the preparation process of the carbon-coated current collector is an oil-based solvent, the solvent in step (1) is water.

12. The method of claim 11, wherein, The oil-based solvent comprises N-methylpyrrolidone.

13. The preparation method according to claim 5, characterized in that, When the carbon-coated current collector is a sodium battery carbon-coated current collector, and a crosslinking agent is contained in the carbon-coated slurry used in the preparation process of the sodium battery carbon-coated current collector, the solvent in step (1) is water.

14. The method of claim 13, wherein, The crosslinking agent comprises at least one of methacrylic acid, methacrylic acid and isopropyl acrylic acid.

15. The preparation method according to claim 5, characterized in that, In step (2), the heating is to 120°C-240°C.

16. The method of claim 5, wherein, In step (2), the pressure in the reaction container during the reaction is 2-3 atmospheres.

17. The preparation method according to claim 5, characterized in that, In step (2), the reaction time is 8h-18h.

18. The method of claim 5, wherein, After the reaction in step (2), the steps of sampling and drying are further carried out.

19. The method of claim 5, wherein, In step (2), the preparation method of the carbon-coated current collector comprises the following steps: (A) dispersing raw materials of the carbon-coated layer in a solvent to obtain a carbon-coated slurry; (B) applying the carbon-coated slurry to the surface of the current collector substrate, and forming a carbon-coated layer on the surface of the current collector substrate after drying to obtain the carbon-coated current collector.

20. The method of claim 19, wherein, The carbon-coated layer of step (A) comprises a conductive agent and a binder.

21. The method of claim 20, wherein, The conductive agent comprises carbon powder.

22. The method of claim 21, wherein, The conductive agent further comprises graphite powder.

23. The preparation method according to claim 22, characterized in that, The mass ratio of the carbon powder and the graphite powder in the conductive agent is 70%-100% and 0%-30%, respectively.

24. The method of claim 20, wherein, The binder comprises at least one of acrylate, polyacrylic acid, modified polyacrylic acid, or water-based polyurethane.

25. The method of claim 24, wherein, The binder is modified polyacrylic acid.

26. The method of claim 24, wherein, The binder is modified polyacrylic acid glue with a solid content of 15%-30%, and the viscosity of the modified polyacrylic acid glue is 200 mPa.s-1500 mPa.s.

27. The preparation method according to claim 19, characterized in that, The carbon-coated layer of step (A) further comprises a wetting agent.

28. The method of claim 27, wherein, The wetting agent comprises at least one of polyether siloxane, modified polyether siloxane, and alcohol.

29. The method of claim 28, wherein, The wetting agent is modified polyether siloxane.

30. The preparation method according to claim 27, characterized in that, The amount of the wetting agent is 3%-20% of the total mass of the reaction system.

31. The preparation method according to claim 19, characterized in that, Step (A) comprises: S1 adding the conductive agent to the binder glue, dispersing to obtain a first material; S2 adding the wetting agent to the first material, stirring, and then homogenizing to obtain a carbon-coated slurry.

32. The method of claim 31, wherein, Step S1 comprises: first adding a part of the conductive agent to the binder glue, performing first high-speed stirring, then adding the remaining conductive agent to the obtained material, and performing second high-speed stirring.

33. The method of claim 32, wherein the method further comprises, The part of the conductive agent accounts for 40%-60% of the total amount of the conductive agent.

34. The method of claim 32, wherein the step of forming the first and second layers is performed by a method selected from the group consisting of: 5 extrusion, injection molding, and compression molding. The speed of the first high-speed stirring is 2000 rpm-2600 rpm.

35. The preparation method according to claim 32, characterized in that, The time of the first high-speed stirring is 30 min-60 min.

36. The preparation method according to claim 32, characterized in that, The speed of the second high-speed stirring is 2000 rpm-2600 rpm.

37. The method of claim 32, wherein the method is carried out at a temperature of about 20°C to about 30°C. The time of the second high-speed stirring is 60 min-90 min.

38. The method of claim 31, wherein the method is performed in a single step. The speed of the stirring of step S2 is 10 rpm-15 rpm.

39. The method of claim 31, wherein, The time of the stirring of step S2 is 30 min-45 min.

40. The method of claim 31, wherein, The pressure of the homogenization of step S2 is 300 bar-600 bar.

41. The method of claim 31, wherein, The preparation method further comprises: After step S1 and before step S2, the following steps are performed: (a) adding a solvent to the first material to reduce the concentration of the slurry, and dispersing at a speed of 2000 rpm-2600 rpm for 30 min-45 min; (b) adjusting the pH of the slurry obtained in step (a) to 5-7 using a pH adjuster.

42. The method of claim 41, wherein, The addition amount of the pH adjuster is 5wt%-10wt% of the binder glue.

43. A pole piece characterized by, The pole piece comprises a current collector and an active layer arranged on the surface of the current collector, and the current collector is the composite current collector of any one of claims 1-4 or the composite current collector prepared by the method of any one of claims 5-42.

44. A battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, characterized by The positive pole piece and / or the negative pole piece are selected from the pole piece of claim 43.

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