Composite current collector, method for preparing the same, battery electrode and sodium ion battery

Abstract

The application provides a composite current collector and a preparation method thereof, a battery electrode and a sodium ion battery, and relates to the field of sodium ion batteries. The preparation method of the composite current collector comprises the following steps: pretreating a base material; mixing a first emulsion, a first crosslinking agent and a conductive material to obtain a first slurry; coating the first slurry on at least one side surface of the base material and performing a first heat curing treatment to form a bottom layer on at least one side of the base material; mixing a second emulsion, a second crosslinking agent and an inorganic filler to obtain a second slurry; coating the second slurry on at least one side surface of the bottom layer and performing a second heat curing treatment to form a surface layer on at least one side of the bottom layer; and performing a curing treatment on the base material with the bottom layer and the surface layer to obtain the composite current collector. The composite current collector prepared by the application has high water resistance, and the problem of poor water resistance of traditional water-based carbon-coated current collectors is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a composite current collector, a preparation method thereof, a battery electrode and a sodium ion battery. BACKGROUND

[0002] With the gradual application of lithium ion batteries to the energy storage field, the supply and demand problem of lithium resources has become increasingly prominent, while sodium resources are abundant, widely distributed and low in cost, so sodium ion batteries have attracted much attention in recent years. However, the large-scale application of sodium ion batteries faces many challenges, among which the current collector technology bottleneck is particularly prominent. As a component that carries active materials and conducts current in the battery, the performance of the current collector directly affects the energy density, cycle life and safety of the battery.

[0003] Currently, the negative electrode current collector of sodium ion batteries generally uses water-based carbon-coated aluminum foil (an aluminum substrate coated with a conductive carbon layer). However, water-based carbon-coated aluminum foil has poor water resistance. Specifically, the primer layer of water-based carbon-coated aluminum foil and the negative electrode water-based slurry both use water as a solvent, and water-water mutual solubility occurs during negative electrode coating, resulting in damage to the primer layer and ultimately forming film surface defects on the surface of the electrode. This not only increases the instability of the process, but also deteriorates the rate performance, cycle life and safety of the battery, restricting the further improvement of the comprehensive performance of sodium ion batteries.

[0004] Therefore, it is crucial to develop a current collector with high water resistance for promoting the development and industrial application of sodium ion batteries. SUMMARY

[0005] The present application aims to provide a composite current collector, a preparation method thereof, a battery electrode and a sodium ion battery to solve the above problems.

[0006] To achieve the above purpose, the following technical solutions are adopted in the present application:

[0007] A preparation method of a composite current collector, comprising:

[0008] pretreating a substrate;

[0009] mixing a first emulsion, a first crosslinking agent and a conductive material to obtain a first slurry;

[0010] coating the first slurry on at least one side surface of the substrate and performing a first heat curing treatment to form a primer layer on at least one side of the substrate;

[0011] mixing a second emulsion, a second crosslinking agent and an inorganic filler to obtain a second slurry;

[0012] coating the second slurry on at least one side surface of the primer layer and performing a second heat curing treatment to form a surface layer on at least one side of the primer layer;

[0013] The substrate with the bottom layer and the surface layer is subjected to a maturation treatment to obtain a composite current collector.

[0014] According to an embodiment of the present application, the substrate comprises any one of an aluminum foil, an aluminum mesh, a PET composite aluminum foil, and a copper foil.

[0015] The pre-treatment mode comprises any one of corona, pickling, electroplating, and etching.

[0016] The surface tension of the substrate subjected to the pre-treatment is ≥ 32 dyn / cm.

[0017] According to an embodiment of the present application, the first emulsion is a carboxyl acrylic emulsion.

[0018] The first cross-linking agent is a trifunctional aziridine, which is pentaerythritol tris(3-aziridinyl) propionate.

[0019] The conductive material comprises conductive carbon black and carbon nanotubes, and the mass ratio of the conductive carbon black to the carbon nanotubes is 1:9 to 9:1.

[0020] In terms of mass percentage, the proportion of the first emulsion in the first slurry is 88-94%, the proportion of the first cross-linking agent in the first slurry is 3-8%, and the proportion of the conductive material in the first slurry is 1-6%.

[0021] According to an embodiment of the present application, the temperature of the first thermal curing treatment is 140-160°C.

[0022] The time of the first thermal curing treatment is 1-5 min.

[0023] The first thermal curing treatment is performed in an atmosphere with an oxygen content of less than 1000 ppm.

[0024] The thickness of the bottom layer is 0.5-1.5 μm.

[0025] According to an embodiment of the present application, the second emulsion is a hydroxyl acrylic-polyurethane emulsion.

[0026] The second cross-linking agent is a blocked HDI isocyanate.

[0027] The inorganic filler is nanometer boehmite.

[0028] In terms of mass percentage, the proportion of the second emulsion in the second slurry is 88-94.5%, the proportion of the second cross-linking agent in the second slurry is 3-8%, and the proportion of the inorganic filler in the second slurry is 0.5-4.2%.

[0029] According to an embodiment of the present application, the second heat curing treatment is performed under infrared radiation, and the wavelength of the infrared radiation is 2.5-3.5 μm;

[0030] The surface temperature of the cured material is 110-130℃;

[0031] The time of the infrared radiation is 1.5-5.5 min;

[0032] The power density of the infrared radiation is 12-20 kW / m 2 ;

[0033] The thickness of the surface layer is 0.4-0.8 μm.

[0034] According to an embodiment of the present application, the temperature of the maturation treatment is 70-90℃;

[0035] The time of the maturation treatment is 25-35 min.

[0036] The present application also provides a composite current collector prepared by the method for preparing a composite current collector described above.

[0037] The present application also provides a battery electrode comprising the composite current collector described above.

[0038] The battery electrode further comprises an active layer on at least one side surface of the composite current collector.

[0039] The battery electrode comprises at least one of a positive electrode and a negative electrode.

[0040] The active layer comprises a positive electrode active material or a negative electrode active material.

[0041] The present application also provides a sodium ion battery comprising the composite current collector described above or comprising the battery electrode described above.

[0042] Compared with the prior art, the present application has the following beneficial effects:

[0043] The composite current collector prepared by the present application has high water resistance, which improves the poor water resistance of traditional water-based carbon-coated current collectors. In addition, the current collector of the present application also has high flexibility, which can withstand mechanical stress in subsequent electrode processing processes such as rolling, slitting and winding without cracking or falling off, greatly improving the process yield and battery consistency. BRIEF DESCRIPTION OF DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as limiting the scope of the present application.

[0045] Figure 1 Flow chart for the preparation method of the composite current collector of the present application;

[0046] Figure 2 Structure diagram of the composite current collector of the present application;

[0047] Figure 3 Physical diagram of the composite current collector prepared in Example 1;

[0048] Figure 4 Physical diagram of the negative electrode sheet prepared in Example 1;

[0049] Figure 5 Physical diagram of the positive electrode sheet prepared in Example 1. DETAILED DESCRIPTION

[0050] As used herein:

[0051] “Prepared from” is synonymous with “comprising”. The terms “comprising”, “including”, “having” or “with” or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0052] The conjunction “consisting of’ excludes any element, step, or ingredient not specified. If used in a claim, this phrase shall not be construed to mean that the claimed composition, step, or process excludes additional unrecited materials from being present in the composition, step, or process, but rather that the claimed composition, step, or process does not include any element, step, or ingredient not specified in the claim. When the phrase “consisting of’ follows the introductory clauses of a claim, it shall be interpreted to exclude any element not specified in the claim.

[0053] When expressing amounts, concentrations, or other values or parameters of a range, preferably a range, or a series of upper preferred values and lower preferred values, it is to be understood that the disclosure specifically envisions all ranges formed from any of the upper values or preferred values with any of the lower values or preferred values, even if that range is not expressly disclosed. For example, where a range "1-5" is disclosed, then "1-4", "1-3", "1-2", "1-2 and 4-5", "1-3 and 5", and the like, are all expressly stated to be contemplated. Where a range of values is expressed in the text as including both endpoints, it is intended to include the endpoints in the range. When numerical ranges are presented in the text, unless otherwise indicated, the range is intended to include both the upper and lower values and all integers and fractions within that range.

[0054] In these embodiments, the parts and percentages described are by mass, unless otherwise indicated.

[0055] "Parts by mass" refers to a basic unit of measurement that represents the proportional relationship of the mass of multiple components, 1 part can represent any unit mass, such as 1 g, 2.689 g, etc. If we say that the mass of component A is a parts, and the mass of component B is b parts, it means that the ratio of the mass of component A to the mass of component B is a:b. Alternatively, it means that the mass of component A is aK, and the mass of component B is bK (K is an arbitrary number, representing a multiple factor). It must not be misunderstood that, unlike parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0056] "and / or" is used to indicate that one or both of the described situations can occur, for example, A and / or B includes (A and B) and (A or B).

[0057] A method for preparing a composite current collector, with reference to Figure 1 and Figure 2 , comprising:

[0058] pretreating the substrate;

[0059] mixing the first emulsion, the first crosslinking agent, and the conductive material to obtain a first slurry;

[0060] coating the first slurry on at least one side surface of the substrate, performing a first heat curing treatment, and forming a bottom layer on at least one side of the substrate;

[0061] mixing the second emulsion, the second crosslinking agent, and the inorganic filler to obtain a second slurry;

[0062] coating the second slurry on at least one side surface of the bottom layer, performing a second heat curing treatment, and forming a top layer on at least one side of the bottom layer;

[0063] subjecting the substrate with the bottom layer and the top layer to a curing treatment to obtain a composite current collector.

[0064] The cross-linking degree of the bottom layer prepared by the application is greater than or equal to 85%, and the bottom layer with high cross-linking degree can play a role of anti-permeation, which can effectively improve the water resistance of the composite current collector. The cross-linking degree of the surface layer prepared by the application is greater than or equal to 60%, and the surface layer with low cross-linking degree has good flexibility.

[0065] According to the embodiments of the application, the substrate includes any one of aluminum foil, aluminum mesh, PET composite aluminum foil, and copper foil.

[0066] The pre-treatment method includes any one of corona, pickling, electroplating, and etching.

[0067] The surface tension of the substrate after the pre-treatment is greater than or equal to 32 dyn / cm.

[0068] In some embodiments, when the pre-treatment method is corona, the power of the corona is 4-6 KW, preferably 5 KW; and the processing speed of the corona is 10-20 m / min, preferably 10 m / min.

[0069] According to the embodiments of the application, the first emulsion is a carboxyl acrylic emulsion.

[0070] The first cross-linking agent is a trifunctional aziridine.

[0071] In some embodiments, the trifunctional aziridine is pentaerythritol tris(3-aziridinyl) propionate.

[0072] The conductive material includes conductive carbon black and carbon nanotubes, and the mass ratio of the conductive carbon black to the carbon nanotubes is 1:9-9:1.

[0073] In some embodiments, the mass ratio of the conductive carbon black to the carbon nanotubes is 1:9, 8:2, 7:3, 9:1, or any value between 1:9 and 9:1.

[0074] The proportion of the first emulsion in the first slurry is 88-94% by mass percentage, the proportion of the first cross-linking agent in the first slurry is 3-8% by mass percentage, and the proportion of the conductive material in the first slurry is 1-6% by mass percentage.

[0075] For example, the proportion of the first emulsion in the first slurry is 88%, 89%, 90%, 91%, 92%, 93%, 94%, or any value between 88% and 94%, the proportion of the first cross-linking agent in the first slurry is 3%, 4%, 5%, 6%, 7%, 8%, or any value between 3% and 8%, and the proportion of the conductive material in the first slurry is 1%, 2%, 3%, 4%, 5%, 6%, or any value between 1% and 6%.

[0076] In some embodiments, in the step of applying the first slurry on at least one side surface of the substrate, the application mode comprises any one of spraying, roller coating, and gravure coating, and the application speed is 8-15 m / min.

[0077] According to embodiments of the present application, the temperature of the first heat curing treatment is 140-160℃; for example, the temperature of the first heat curing treatment is 140℃, 150℃, 160℃, or any value between 140-160℃.

[0078] The time of the first heat curing treatment is 1-5 min; for example, the time of the first heat curing treatment is 1 min, 2 min, 3 min, 4 min, 5 min, or any value between 1-5 min.

[0079] The first heat curing treatment is performed in an atmosphere with an oxygen content lower than 1000 ppm;

[0080] In some embodiments, the first heat curing treatment is performed in a hot air circulating curing oven, and the air speed of the first heat curing treatment is 7.5-8.5 m / s.

[0081] The thickness of the bottom layer is 0.5-1.5 μm. For example, the thickness of the bottom layer is 0.5 μm, 1 μm, 1.5 μm, or any value between 0.5-1.5 μm.

[0082] After the first heat curing treatment is completed, the crosslinking degree of the bottom layer is tested, and the crosslinking degree of the bottom layer is ≥85%, and the surface carboxyl content of the bottom layer is 1.0-1.2 mmol / g.

[0083] According to embodiments of the present application, the second emulsion is a hydroxyl acrylate-polyurethane emulsion;

[0084] The second crosslinking agent is a blocked HDI isocyanate.

[0085] The inorganic filler is nanometer boehmite. The inorganic filler can improve the mechanical strength and wear resistance of the coating; at the same time, it can significantly prolong the penetration path of the corrosion medium, thereby enhancing the corrosion resistance of the current collector.

[0086] The second emulsion accounts for 88-94.5% in the second slurry by mass percentage, the second crosslinking agent accounts for 3-8% in the second slurry, and the inorganic filler accounts for 0.5-4.2% in the second slurry.

[0087] For example, the second emulsion accounts for 88%, 89%, 90%, 91%, 92%, 93%, 94%, 94.5% or any value between 88-94.5% in the second slurry, the second cross-linking agent accounts for 3%, 4%, 5%, 6%, 7%, 8% or any value between 3-8% in the second slurry, and the inorganic filler accounts for 0.5%, 1%, 2%, 3%, 4%, 4.2% or any value between 0.5-4.2% in the second slurry.

[0088] In the second slurry of the present application, the blocked HDI isocyanate can chemically react with the hydroxyl group in the second emulsion (cross-linking) to form urethane bonds. This process connects linear polymer chains into a three-dimensional network structure, significantly improving the final resistance of the film coating; the interface between the surface layer and the bottom layer chemically reacts (-COOH reacts with -NCO) to firmly bond and has high adhesion.

[0089] In some embodiments, in the step of applying the second slurry on at least one side surface of the bottom layer, the application method includes any one of spraying, rolling, and gravure coating, and the application speed is 8-15 m / min.

[0090] According to the embodiments of the present application, the second thermal curing process is carried out under infrared radiation, and the wavelength of the infrared radiation is 2.5-3.5 μm; for example, the wavelength of the infrared radiation is 2.5 μm, 3 μm, 3.5 μm or any value between 2.5-3.5 μm.

[0091] The surface temperature of the cured material is 110-130°C; for example, the surface temperature of the cured material is 110°C, 120°C, 130°C or any value between 110-130°C.

[0092] The time of the infrared radiation is 1.5-5.5 min; for example, the time of the infrared radiation is 1.5 min, 2.5 min, 3.5 min, 4.5 min, 5.5 min or any value between 1.5-5.5 min.

[0093] The power density of the infrared radiation is 12-20 kW / m 2 ; for example, the power density of the infrared radiation is 12 kW / m 2 , 15 kW / m 2 , 18 kW / m 2 , 20 kW / m 2 or any value between 12-20 kW / m 2 .

[0094] The thickness of the surface layer is 0.4-0.8 μm. For example, the thickness of the surface layer is 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or any value between 0.4-0.8 μm.

[0095] After the second heat curing treatment is completed, the cross-linking degree of the surface layer is tested, and the cross-linking degree of the surface layer is ≥60%, and the residual isocyanate is <0.1%.

[0096] According to the embodiments of the present application, the temperature of the maturation treatment is 70-90°C; for example, the temperature of the maturation treatment is 70°C, 80°C, 90°C, or any value between 70-90°C;

[0097] The time of the maturation treatment is 25-35 min. For example, the time of the maturation treatment is 25 min, 30 min, 35 min, or any value between 25-35 min.

[0098] In some embodiments, the maturation treatment is carried out in a tunnel type hot air maturation furnace, and the wind speed of the maturation treatment is 3 m / s, and the tension is 14-16 N.

[0099] After the maturation treatment is completed, the internal stress of the coating is tested by X-ray diffraction method <0.5 MPa, and the interface bonding energy is tested by nano-scratch method >25 J / m 2 , the roughness Ra is between 0.8-1.2 μm, the C=C conversion rate gradient is measured by micro-infrared mapping, the cross-linking density ratio of the bottom layer to the surface layer is between 1.1-2, and the cross-linking density change gradient of the interface region is ≥1.8% / μm.

[0100] The step-by-step curing process adopted in the present application can trigger the reaction of the first slurry and the second slurry in stages, avoid excessive cross-linking, and the roughness Ra of the surface layer of the present application is between 0.8-1.2 μm, which increases the bite force of the surface coating and the active layer, and increases the peeling strength of the pole piece. The present application effectively improves the water resistance, pole piece peeling force, and flexibility of the bottom layer.

[0101] The present application also provides a composite current collector prepared by the preparation method of the composite current collector described above.

[0102] The present application also provides a battery electrode comprising the composite current collector described above.

[0103] The battery electrode further comprises an active layer located on at least one side surface of the composite current collector.

[0104] The battery electrode comprises at least one of a positive electrode and a negative electrode.

[0105] The active layer comprises a positive electrode active material or a negative electrode active material.

[0106] In some embodiments, the negative active material comprises hard carbon, the hard carbon comprising at least one of biohard carbon, resin hard carbon, coal-based hard carbon, pitch-based hard carbon.

[0107] In some embodiments, the positive active material comprises a polyanion compound, the polyanion compound having a chemical formula of Na3(VO x PO4)2F 3-2x wherein 0≤x≤1; the positive active material having a particle size Dv50≤8 μm.

[0108] In some embodiments, the negative active material has a particle size of 3-7 μm.

[0109] When the battery electrode is a negative electrode, the active layer further comprises a negative conductive agent, a negative binder, a dispersant aid, a negative binder;

[0110] The negative conductive agent comprises at least one of SP, acetylene black, ketjen black, carbon nanotube, graphene, conductive graphite;

[0111] The dispersant aid comprises CMC;

[0112] The negative binder comprises at least one of SBR, PAA.

[0113] In some embodiments, the negative conductive agent comprises SP and carbon nanotube, the proportion of SP in the active layer being 1.5-3%, and the proportion of carbon nanotube in the active layer being 0.2-0.8%.

[0114] In some embodiments, in terms of mass percentage, the proportion of the negative active material in the active layer is 90%-94.8%, the proportion of the negative conductive agent in the active layer is 1.7-3.8%, the proportion of the dispersant aid in the active layer is 1.5-2.5%, and the proportion of the negative binder in the active layer is 2-4%.

[0115] In some embodiments, when the battery electrode is a positive electrode, the active layer further comprises a positive conductive agent, a positive binder, a dispersant aid, a positive binder.

[0116] The present application also provides a sodium-ion battery comprising the composite current collector described above or comprising the battery electrode described above.

[0117] The embodiments of the present application will be described in detail below with specific examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application. The specific conditions are not specified in the examples, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0118] The raw material information used in the following examples and comparative examples is as follows:

[0119] The carboxyl acrylic emulsion is Acronal PRO 8977 product of BASF Company.

[0120] The tri-functional aziridine is pentaerythritol tris(3-aziridinyl) propionate, and its molecular formula is C 20 H 33 N3O7, which is TB11636 product of Hubei Taibang Chemical Industry Co., Ltd.

[0121] The hydroxyl acrylic-polyurethane emulsion is WL-153 product of Xiamen Kangdilong.

[0122] The blocked HDI isocyanate is YSM-121 product of Shenzhen Huanna Eastman Technology Co., Ltd.

[0123] Example 1

[0124] a. Select 12 μm aluminum foil for pretreatment: use corona treatment method, control the power of the corona machine at 5 KW; the treatment speed is controlled at 10 m / min; the surface tension of the aluminum foil after corona treatment is 32 dyn / cm, and the treated aluminum foil is ready for use;

[0125] b. Preparation of primer slurry: add and mix the carboxyl acrylic emulsion, tri-functional aziridine, conductive carbon black and carbon nanotube in the star stirrer according to the proportion, and prepare the primer slurry; wherein, the carboxyl acrylic emulsion accounts for 92% in the primer slurry, the tri-functional aziridine accounts for 5% in the primer slurry, the total content of the conductive carbon black and the carbon nanotube accounts for 3% in the primer slurry, and the mass ratio of the conductive carbon black to the carbon nanotube is 8:2; mix the above materials to prepare the primer slurry;

[0126] c. Primer coating: use the precise micro-gravure coater to uniformly coat the primer slurry prepared in step b on both surfaces of the aluminum foil after the pretreatment in step a, and control the coating speed at 10 m / min;

[0127] d. First heat curing treatment: the double-layer coated aluminum foil is subjected to the first heat curing treatment, using the hot air circulation curing oven, the temperature is set at 150±2℃, the time is set at 3 min, the air speed is 8±0.5 m / s, and the oxygen content is controlled below 1000 ppm, after curing, the crosslinking degree of the primer is 85.3%, and the carboxyl content of the primer surface is 1.08 mmol / g; the thickness of the single-layer primer is controlled at 1.0±0.3 μm.

[0128] e. Face coating slurry preparation: the hydroxy acrylate-polyurethane emulsion, blocked HDI isocyanate, and nanometer boehmite are added in a star stirrer in a proportion and uniformly mixed to prepare a face coating slurry; wherein, the hydroxy acrylate-polyurethane emulsion accounts for 94% in the face coating slurry by mass percentage; the blocked HDI isocyanate accounts for 5% in the face coating slurry; and the nanometer boehmite accounts for 1% in the face coating slurry; the above materials are mixed to prepare the face coating slurry;

[0129] f. Face coating: the face coating slurry is uniformly coated on both sides of the aluminum foil with the bottom layer processed in step d by using a precision micro-gravure coater, and the coating speed is controlled at 8 m / min;

[0130] g. Second heat curing treatment: the aluminum foil obtained in step f is subjected to a second heat curing treatment, an infrared radiation curing system is used, the radiation wavelength is 3 μm, the surface temperature of the cured material is 120±3.0℃, the infrared radiation time is controlled at 2.0±0.05 min, and the power density of the infrared radiation is 15 kW / m 2 .

[0131] After the second heat curing treatment, the crosslinking degree of the face layer is tested, and the crosslinking degree of the face layer is measured to be 60%, and the residual isocyanate is 0.06%; the thickness of the single face layer is controlled to be 0.6±0.2 μm.

[0132] h. Aging: the composite aluminum foil obtained in step g is subjected to aging, a tunnel type hot air aging furnace is used, the temperature is set to be 80±2℃, the time is 30±1.0 min, the wind speed is 3 m / s, and the tension is controlled to be 15±1 N, to obtain a composite current collector. The actual picture of the composite current collector prepared in Example 1 is shown in Figure 3 .

[0133] After the end, the internal stress of the coating is tested by X-ray diffraction method to be 0.41 MPa, the interface bonding energy is tested by nano-scratch method to be 36 J / m 2 , the roughness Ra is 1.1 μm, the C=C conversion rate gradient is measured by micro-infrared mapping, the crosslinking density ratio of the primer layer to the face coating layer is 1.42, and the crosslinking density change gradient in the interface area is 1.8% / μm.

[0134] i. The negative electrode slurry is uniformly coated on both sides of the composite current collector obtained in step h by using a slot extrusion coater, and a negative electrode sheet is prepared through rolling, slitting, and sheeting. The actual picture of the negative electrode sheet prepared in Example 1 is shown in Figure 4The negative electrode slurry is prepared by putting 92 parts by weight of biological hard carbon, 2.5 parts by weight of SP, 0.5 parts by weight of CNT, 2 parts by weight of CMC, and 3 parts by weight of SBR into a planetary mixer, and adding deionized water to control the viscosity of the slurry to 2000 mPa.s and the solid content to 36%; wherein the D50 of the hard carbon is 5 μm.

[0135] j. The positive electrode slurry is uniformly coated on both sides of the composite current collector obtained in step h by using a slot extrusion coater, and the positive electrode sheet is prepared by rolling, slitting, and sheeting, etc. The actual picture of the positive electrode sheet prepared in Example 1 is shown in FIG. 1. Figure 5 The positive electrode slurry is prepared by putting 94 parts by weight of Na3(VO4)2F, 2 parts by weight of SP, and 4 parts by weight of PVDF into a planetary mixer, and adding NMP to control the viscosity of the slurry to 3000 mPa.s and the solid content to 52%; wherein the D50 of Na3(VO4)2F is 6.5 μm. 0.7 1.6 0.7 1.6

[0136] k. The prepared positive electrode sheet and negative electrode sheet are assembled into a sodium ion battery together with a separator, an electrolyte, and a shell.

[0137] Example 2

[0138] The difference between Example 2 and Example 1 is that the mass ratio of the conductive carbon black to the carbon nanotube in step b is changed from 8:2 to 7:3. The other steps are the same as those in Example 1.

[0139] Example 3

[0140] The difference between Example 3 and Example 1 is that the mass ratio of the conductive carbon black to the carbon nanotube in step b is changed from 8:2 to 9:1. The other steps are the same as those in Example 1.

[0141] Example 4

[0142] The difference between Example 4 and Example 1 is that the total content of the conductive carbon black and the carbon nanotube in the primer slurry in step b is changed from 3% to 2.5%, and the content of the carboxyl acrylic emulsion in the primer slurry is changed from 92% to 92.5%. The other steps are the same as those in Example 1.

[0143] Example 5

[0144] The difference between Example 5 and Example 1 is that the total content of the conductive carbon black and the carbon nanotube in the primer slurry in step b is changed from 3% to 3.5%, and the content of the carboxyl acrylic emulsion in the primer slurry is changed from 92% to 91.5%. The other steps are the same as those in Example 1.

[0145] Example 6 ​​​​

[0146] Example 6 differs from Example 1 in that the ratio of nanobohmite in the topcoat slurry in step e is changed from 1% to 0.5%, and the ratio of hydroxyl acrylate-polyurethane emulsion in the topcoat slurry is changed from 94% to 94.5%. The rest is the same as Example 1.

[0147] Example 7

[0148] Example 7 differs from Example 1 in that the ratio of nanobohmite in the topcoat slurry in step e is changed from 1% to 1.5%, and the ratio of hydroxyl acrylate-polyurethane emulsion in the topcoat slurry is changed from 94% to 93.5%. The rest is the same as Example 1.

[0149] Example 8

[0150] Example 8 differs from Example 1 in that the temperature of the first heat curing treatment in step d is changed from 150°C to 140°C. The rest is the same as Example 1.

[0151] Example 9

[0152] Example 9 differs from Example 1 in that the temperature of the first heat curing treatment in step d is changed from 150°C to 160°C. The rest is the same as Example 1.

[0153] Example 10

[0154] Example 10 differs from Example 1 in that the temperature of the second heat curing treatment in step g is changed from 120°C to 110°C. The rest is the same as Example 1.

[0155] Example 11

[0156] Example 11 differs from Example 1 in that the temperature of the second heat curing treatment in step g is changed from 120°C to 130°C. The rest is the same as Example 1.

[0157] Example 12

[0158] Example 12 differs from Example 1 in that the temperature of the aging in step h is changed from 80°C to 70°C. The rest is the same as Example 1.

[0159] Example 13

[0160] Example 13 differs from Example 1 in that the temperature of the aging in step h is changed from 80°C to 90°C. The rest is the same as Example 1.

[0161] Example 14

[0162] Example 14 differs from Example 1 in that the aluminum foil in step a is replaced by a copper foil with a surface roughness Ra = 0.65 μm and a thickness of 12 μm. Steps b-h are the same as in Example 1. The composite current collector prepared in Example 14 using a copper foil as the substrate is used to prepare a negative electrode sheet. The specific method and parameters for preparing the negative electrode sheet are the same as steps i of Example 1.

[0163] Example 14 differs from Example 1 in that the aluminum foil in step a is replaced by a copper foil with a surface roughness Ra = 0.65 μm and a thickness of 12 μm. Steps b-h are the same as in Example 1. The composite current collector prepared in Example 14 using a copper foil as the substrate is used to prepare a negative electrode sheet. The specific method and parameters for preparing the negative electrode sheet are the same as steps i of Example 1.

[0164] Comparative Example 1

[0165] Comparative Example 1 differs from Example 1 in that the time for the first heat curing treatment in step d is changed from 3 min to 0.5 min. The other steps are the same as in Example 1.

[0166] Comparative Example 2

[0167] Comparative Example 2 differs from Example 1 in that steps e-h are omitted and the product prepared in step d is used as the composite current collector. The other steps are the same as in Example 1.

[0168] Comparative Example 3

[0169] Comparative Example 3 differs from Example 1 in that 3% of conductive carbon black is added in step b instead of carbon nanotubes. The other steps are the same as in Example 1.

[0170] Comparative Example 4

[0171] Comparative Example 4 differs from Example 1 in that 3% of carbon nanotubes is added in step b instead of conductive carbon black. The other steps are the same as in Example 1.

[0172] Comparative Example 5

[0173] Comparative Example 5 differs from Example 1 in that no nanobohmite is added in step e and the proportion of hydroxyl acrylate-polyurethane emulsion in the topcoat slurry is adjusted from 94% to 95%. The other steps are the same as in Example 1.

[0174] Comparative Example 6

[0175] The aluminum foil treated in step a of Example 1 is used as the negative electrode current collector and is used to coat the negative electrode slurry to prepare a negative electrode sheet. The specific method and parameters for preparing the negative electrode sheet are the same as steps i of Example 1.

[0176] The composite current collector prepared in Example 1 is used as the positive electrode current collector and is used to coat the positive electrode slurry in the same way as in Example 1 to prepare a positive electrode. The positive electrode is assembled into a sodium ion battery.

[0177] Comparative Example 7

[0178] The negative electrode slurry was coated using a copper foil with a surface roughness Ra = 0.65 pm and a thickness of 12 pm as the negative electrode current collector to prepare a negative electrode sheet. The specific method and parameters for preparing the negative electrode sheet were the same as step i of Example 1.

[0179] The composite current collector prepared in Example 1 was used as the positive electrode current collector, and the positive electrode slurry was coated according to the same method as Example 1 to prepare a positive electrode. A sodium ion battery was assembled.

[0180] The composite current collectors of Examples 1-14 and Comparative Examples 1-7 were tested, and the specific test method was as follows:

[0181] Interlayer adhesion (crosshatch method): 1. A multi-blade cutting tool (knife spacing 1 mm or 2 mm) was used to draw 10 x 10 squares on the surface of the coating, and the cutting was performed to the substrate; 2. The debris was removed with a soft brush; 3. A special adhesive tape (such as 3M 610) was firmly pressed on the square area; 4. After 60-120 seconds, the tape was quickly torn off at an angle of 180°; 5. The coating peeling in the square area was observed under a microscope;

[0182] Sheet resistance (four-probe method): 1. Four equally spaced probes were brought into contact with the surface of the sample; 2. A constant direct current (I) was applied to the outer two probes; 3. The voltage drop (V) between the inner two probes was measured; 4. The sheet resistance was calculated according to the formula: Rs = (pi / ln2) x (V / I) = 4.532 x (V / I) (Ω / □); 5. At least 5 measurements were taken at different positions and the average value was reported, and the standard deviation (uniformity) was reported;

[0183] Water resistance: 1. The sample was completely immersed in deionized water at 40°C ± 2°C; 2. After 72 hours of immersion, the surface water was absorbed with filter paper; 3. The surface was immediately observed for phenomena such as blistering, discoloration, peeling, etc. and recorded;

[0184] Flexibility: Refer to GB / T 6742 - Paint film bending test (cylindrical shaft).

[0185] Electrolyte resistance: 1. In an argon-filled glove box (H2O, O2 < 0.1 ppm), the sample was immersed in 1M LiPF6 (volume ratio of EC to DEC, EMC is 1:1:1) electrolyte and sealed; 2. The sealed bottle was placed in an oven at 60°C for 72 hours; 3. After taking out, it was gently rinsed with EC / DEC solvent and dried; 4. The resistance change rate AR% was tested.

[0186] The test results of Examples 1-14 and Comparative Examples 1-7 are shown in Table 1 below.

[0187] Table 1 Test results comparison table of composite current collectors of examples 1-14 and comparative examples 1-7

[0188]

[0189] As can be seen from Table 1, the comprehensive performance of the composite current collectors of examples 1-14 is significantly better than that of comparative examples 1-7.

[0190] The sodium ion batteries of examples 1-14 and comparative examples 1-7 were tested under the same conditions, and the specific test methods were as follows:

[0191] 3C rate discharge retention rate: at 25℃, the battery was rested for 5 min, 0.2C constant current constant voltage charging to 4.2V, the cutoff current was 0.05C, rested for 5 min, 0.2C constant current discharging to 2V, rested for 5 min; 0.2C constant current constant voltage charging to 4.2V, the cutoff current was 0.05C, rested for 5 min, 3C constant current discharging to 2V, rested for 5 min, and the 3C discharge capacity / 0.2C discharge capacity was calculated, that is, the 3C capacity retention rate (1C=3000mAh);

[0192] 500th cycle capacity retention rate: at 25℃, 1C constant current discharging to 2V, rested for 5 min; 1C constant current constant voltage charging to 4.2V, the cutoff current was 0.1C, rested for 5 min, and the above steps were cycled for 500 times, and the 500th discharge capacity / first discharge capacity was the 500th cycle capacity retention rate (1C=3000mAh);

[0193] Table 2 Test results comparison table of sodium ion batteries of examples 1-14 and comparative examples 1-7

[0194]

[0195] As can be seen from Table 2, the comprehensive electrochemical performance of examples 1-14 is significantly better than that of comparative examples 1-7.

[0196] Compared with example 1, the interlayer adhesion of comparative example 1 is poor, the internal resistance is large, the water resistance and electrolyte resistance are poor, and the electrochemical performance of the battery of comparative example 1 is also worse than that of example 1, which may be caused by the too short time of the first thermal curing in comparative example 1.

[0197] Compared with example 1, the water resistance and electrolyte resistance of comparative example 2 are significantly worse than those of example 1, and the electrochemical performance of the battery of comparative example 2 is also worse than that of example 1. This may be caused by the fact that the current collector of comparative example 2 only has a bottom layer, losing the protection of the surface layer.

[0198] Compared with Example 1, the sheet resistance of Comparative Example 3 and Comparative Example 4 increases, and the conductive effect becomes poor; the electrochemical performance of Comparative Example 3 and Comparative Example 4 is inferior to that of Example 1, indicating that the effect of using the conductive carbon black and the carbon nanotube in combination is superior to that of using the conductive carbon black or the carbon nanotube alone.

[0199] Compared with Example 1, the water resistance and electrolyte resistance of the composite current collector of Comparative Example 5 are obviously poor, and the electrochemical performance of the battery of Comparative Example 5 is also inferior to that of Example 1, which may be due to the fact that no nanobeamite is added in Comparative Example 5.

[0200] Example 14 has excellent performance comparable to that of Examples 1-13, indicating that when the substrate is a copper foil, the prepared composite current collector can achieve performance comparable to that of the composite current collector prepared from an aluminum foil, indicating that the preparation method of the composite current collector of the application is suitable for a copper foil substrate and an aluminum foil substrate.

[0201] Compared with Example 1, the performance of the current collector of Comparative Example 6 and the electrochemical performance of the battery are inferior to those of Example 1, which may be due to the fact that no coating is made on the negative electrode current collector of Comparative Example 6.

[0202] Compared with Example 14, the performance of the current collector of Comparative Example 7 and the electrochemical performance of the battery are inferior to those of Example 14, which may be due to the fact that no coating is made on the negative electrode current collector of Comparative Example 7.

[0203] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and such modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the examples of the application.

[0204] In addition, those skilled in the art can understand that although some of the embodiments herein include certain features included in other embodiments rather than other features, the combination of the features of different embodiments means to be within the scope of the application and form different embodiments. For example, in the above claims, any one of the claimed embodiments can be used in any combination. The information disclosed in the BACKGROUND section is only intended to deepen the understanding of the overall background of the application and should not be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A method for preparing a composite current collector, characterized in that, include: Pre-treat the substrate; The first emulsion, the first crosslinking agent, and the conductive material are mixed to obtain the first slurry; The first slurry is coated on at least one side surface of the substrate and subjected to a first thermosetting treatment to form an underlayer on at least one side of the substrate; The second emulsion, the second crosslinking agent, and the inorganic filler are mixed to obtain the second slurry; The second slurry is coated onto at least one surface of the substrate, and a second thermosetting treatment is performed to form a top layer on at least one side of the substrate. A composite current collector is obtained by aging a substrate with a bottom layer and a top layer. The first emulsion is a carboxylated acrylic emulsion, the conductive material includes conductive carbon black and carbon nanotubes, the first thermosetting treatment time is 1-5 min, the second emulsion is a hydroxyl acrylic-polyurethane emulsion, and the second crosslinking agent is a blocked HDI isocyanate.

2. The method for preparing the composite current collector according to claim 1, characterized in that, The substrate includes any one of aluminum foil, aluminum mesh, PET composite aluminum foil, and copper foil; The pretreatment method includes any one of corona treatment, pickling, electroplating, and etching; And / or, the surface tension of the substrate after the pretreatment is ≥32 dyn / cm.

3. The method for preparing the composite current collector according to claim 1, characterized in that, The first crosslinking agent is a trifunctional aziridine, wherein the trifunctional aziridine is pentaerythritol tris(3-aziridine)propionate; The mass ratio of the conductive carbon black to the carbon nanotubes is 1:9 to 9:

1. By mass percentage, the first emulsion accounts for 88-94% of the first slurry, the first crosslinking agent accounts for 3-8% of the first slurry, and the conductive material accounts for 1-6% of the first slurry.

4. The method for preparing the composite current collector according to claim 3, characterized in that, The temperature of the first thermosetting treatment is 140-160℃; The first thermosetting process is carried out in an atmosphere with an oxygen content of less than 1000 ppm; The thickness of the bottom layer is 0.5-1.5 μm.

5. The method for preparing the composite current collector according to claim 1, characterized in that, The inorganic filler is nano-boehmite; By mass percentage, the second emulsion accounts for 88-94.5% of the second slurry, the second crosslinking agent accounts for 3-8% of the second slurry, and the inorganic filler accounts for 0.5-4.2% of the second slurry.

6. The method for preparing the composite current collector according to claim 5, characterized in that, The second thermosetting treatment is carried out under infrared radiation, wherein the wavelength of the infrared radiation is 2.5-3.5 μm; The surface temperature of the material being cured is 110-130℃; The duration of the infrared radiation is 1.5-5.5 minutes; The power density of the infrared radiation is 12-20 kW / m². 2 ; The thickness of the surface layer is 0.4-0.8 μm.

7. The method for preparing the composite current collector according to any one of claims 1-6, characterized in that, The aging process is performed at a temperature of 70-90℃. The ripening process takes 25-35 minutes.

8. A composite current collector, characterized in that, The composite current collector is prepared by the method for preparing the composite current collector according to any one of claims 1-7.

9. A battery electrode, characterized in that, The battery electrode includes the composite current collector as described in claim 8; The battery electrode further includes an active layer, which is located on at least one side surface of the composite current collector; The battery electrodes include at least one positive electrode and a negative electrode; The active layer includes a positive electrode active material or a negative electrode active material.

10. A sodium-ion battery, characterized in that, It includes the composite current collector as described in claim 8 or the battery electrode as described in claim 9.

Images