Positive pole piece, preparation method thereof and battery

Abstract

The invention provides a positive pole piece and a preparation method thereof and a battery, the positive pole piece comprises a current collector, an active material layer and a conductive layer arranged between the current collector and the active material layer, the conductive layer comprises an MXene material, and the MXene material is added in the conductive layer, so that the conductive electrical property and stability of the battery can be improved, and the service life of the battery is prolonged. And the bonding force between the current collector and the active material layer can be enhanced, the stripping force of the positive pole piece is improved, and the long-term cycling stability of the battery is improved. Besides, due to the addition of the MXene material, the adhesive force between the current collector and the active material layer is improved, so that the content of an adhesive in the active material layer can be reduced and the content of an active material in the active material layer can be increased under the condition of ensuring certain peel strength of the pole piece, and the capacity of the battery is improved under the condition of the same coating surface density; and the long-term use stability of the battery is ensured.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a positive electrode plate, a preparation method thereof, and a battery. Background Art

[0002] Lithium-ion batteries primarily consist of a positive electrode, negative electrode, electrolyte, and separator. The positive and negative electrodes can be further subdivided into raw materials such as current collectors, active materials, and auxiliary materials. As a crucial component of the electrode sheet, the current collector influences the battery's processing, electrical, and safety performance, playing a crucial role in the industrial production and application of batteries.

[0003] The current collector for the positive electrode is primarily aluminum foil, while the current collector for the negative electrode is mostly copper foil. To further enhance the conductivity of the positive electrode current collector and achieve better electrode performance, the aluminum current collector is typically plated to improve its conductivity. Carbon coating on the aluminum current collector improves the conductivity of the aluminum foil and also enhances the adhesion between the current collector and the active material layer, improving the processing properties of the current collector foil. However, existing carbon coating formulations only improve the conductivity of the aluminum current collector and do not enhance the adhesion between the current collector and the active material layer. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a positive electrode plate, a preparation method thereof, and a battery.

[0005] Based on the above objectives, the first aspect of the present application provides a positive electrode sheet, including a current collector, an active material layer, and a conductive layer arranged between the current collector and the active material layer, wherein the conductive layer includes a MXene material.

[0006] Optionally, the ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40-120).

[0007] Optionally, the conductive layer further includes a conductive agent and an adhesive, and the mass ratio of the MXene material, the conductive agent and the adhesive is (0.5-3): (32-37): (58-66).

[0008] Optionally, the MXene material includes transition metal carbides and / or transition metal nitrides;

[0009] The transition metal carbide includes: Ti3C2T x 、Ti2CT x 、Nb2CT x 、Nb4C3T x 、Ta4C3T x 、V4C3T x 、V2CT x 、Mo2CT x、TiVCT x 、TiNbCT x 、TiTaCT x 、VNbCT x 、Ti2VC2T x 、Ti2TaC2T x 、Mo2TiC2T x 、Ti3CNT x 、Mo2Ti2C3T x One or more of;

[0010] The transition metal nitride includes: Ti2NT x 、V2NT x 、W2NT x 、Ti4N3T x One or more of .

[0011] Optionally, the active material layer includes an active material, a conductive agent and a binder, and the mass ratio of the active material, the conductive agent and the binder is (97-99): (0.5-1): (0.4-2).

[0012] Optionally, the conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, nanocarbon fibers and graphene.

[0013] Optionally, the adhesive is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polystyrene butadiene copolymer and sodium carboxymethyl cellulose.

[0014] A second aspect of the present application provides a method for preparing a positive electrode sheet, comprising:

[0015] Preparing a conductive layer slurry, wherein the conductive layer slurry includes a MXene material;

[0016] Applying the conductive layer slurry on a current collector to prepare an intermediate electrode, wherein the intermediate electrode comprises a current collector and a conductive layer applied on the current collector;

[0017] An active material layer slurry is prepared, and the active material layer slurry is coated on the conductive layer to prepare a positive electrode sheet.

[0018] Optionally, the conductive layer slurry comprises a MXene material, a conductive agent, an adhesive, a dispersant and a solvent, and the mass ratio of the MXene material, the conductive agent, the adhesive and the dispersant is 0.5-3:32-37:58-66:0.2-1;

[0019] The active material layer slurry includes active material, conductive agent, binder, dispersant and solvent, and the mass ratio of the active material, conductive agent, binder and dispersant is 97-99:0.5-1:0.4-2:0.05-0.1.

[0020] A third aspect of the present application provides a battery, comprising the positive electrode sheet described in any one of the first aspects above or the positive electrode sheet prepared by the preparation method described in any one of the second aspects above, a separator, and a negative electrode sheet.

[0021] As can be seen from the above description, the positive electrode sheet, preparation method thereof, and battery provided in the present application, the positive electrode sheet includes a current collector, an active material layer, and a conductive layer arranged between the current collector and the active material layer, the conductive layer includes MXene material, and adding MXene material to the conductive layer can improve the conductive electrical performance and stability of the battery, and can also enhance the adhesion between the current collector and the active material layer, improve the peeling force of the positive electrode sheet, and improve the long-term cycle stability of the battery. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below with reference to specific embodiments.

[0023] It should be noted that, unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods described, unless otherwise specified, are all conventional methods.

[0024] Lithium-ion batteries are a type of chemical battery that relies on the shuttle of lithium ions between a positive and negative electrode to discharge. Due to their high energy density, high operating voltage, long cycle life, and high charge and discharge rates, they are widely used in new energy vehicles and energy storage batteries.

[0025] Lithium-ion batteries primarily consist of positive and negative electrodes, electrolytes, and separators. These electrodes can be further subdivided into raw materials such as current collectors, active material layers, and auxiliary materials. As a crucial component of the electrode sheets, current collectors influence the battery's processing, electrical, and safety performance, playing a crucial role in the industrial production and application of batteries.

[0026] The current collector for the positive electrode is primarily aluminum foil, while the current collector for the negative electrode is mostly copper foil. To further enhance the conductivity of the positive electrode current collector and achieve better electrode performance, the aluminum current collector is typically plated to improve its conductivity. Carbon coating on the aluminum current collector improves the conductivity of the foil and also enhances the adhesion between the current collector and the active material layer, improving the processing properties of the current collector foil.

[0027] However, the existing carbon coating formula can only improve the conductive properties of the aluminum current collector, but cannot improve the adhesion between the current collector and the active material layer.

[0028] The inventors discovered that the limited contact area between the rigid positive current collector and the positive active material layer results in limited bonding strength and a limited binding force between the two. Consequently, over long charge and discharge cycles, the constant changes in electrode volume cause the material particles to loosen, further reducing the bonding force between the positive current collector and the positive active material layer. This leads to powder shedding and a rapid decline in battery capacity and cycle life.

[0029] Therefore, how to enhance the adhesion between the positive electrode current collector and the positive electrode active material layer without affecting the conductive performance is an urgent problem to be solved.

[0030] Based on this, the first aspect of the present application provides a positive electrode sheet, including a current collector, an active material layer, and a conductive layer arranged between the current collector and the active material layer, wherein the conductive layer includes a MXene material.

[0031] Specifically, MXene materials are a new type of two-dimensional material composed of metal carbides or nitrides. Generally, MXene materials can be represented by the chemical formula M n+1 X n T m Indicates, "M" represents metal elements, mainly transition metals (such as chromium, molybdenum, manganese, iron, cobalt, copper, aluminum, silver, nickel, palladium, platinum, ruthenium, etc.); "X" represents carbon and nitrogen elements; "T" represents functional groups on the surface of the material, such as hydroxyl (-OH), halogen groups (-F, -Cl), etc.

[0032] MXene materials have excellent flexibility, good electronic conductivity, electrical conductivity and excellent mechanical properties.

[0033] In this application, MXene material is added to the conductive layer. On the one hand, due to the excellent conductive properties of MXene material, the addition of MXene material can act as a conductive agent, improve the DC internal resistance of the lithium-ion battery, reduce the heat generation of the battery in practical applications, and thus improve the conductive performance and stability of the battery;

[0034] On the other hand, since MXene materials contain abundant functional groups such as hydroxyl groups, halogen groups, and transition metals, the functional groups can combine with various ions in the active material layer (such as fluoride ions, acid radical ions, hydroxyl groups, carboxyl groups, etc.) in the form of hydrogen bonds, acting as a connecting bridge, thereby enhancing the adhesion between the current collector and the active material layer, thereby improving the peeling force of the positive electrode sheet and improving the long-term cycle stability of the battery.

[0035] In addition, since the addition of MXene material improves the adhesion between the current collector and the active material layer, the content of the adhesive in the active material layer can be reduced while ensuring a certain peel strength of the electrode, and the mass proportion of the active material in the active material layer can be increased. In this way, under the same coating surface density, the capacity of the battery is increased and the stability of the battery during long-term use is guaranteed.

[0036] Therefore, adding MXene materials to the conductive layer can simultaneously improve the conductivity and peeling force of the positive electrode sheet, and also increase the capacity of the battery.

[0037] In some embodiments, the ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40-120).

[0038] Specifically, when the ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40~120), the thickness of the conductive layer and the thickness of the active material layer are moderate, so that the provision of the conductive layer can not only enhance the adhesion between the current collector and the active material layer, but also will not excessively increase the thickness of the entire positive electrode sheet, and at the same time will not affect the energy density of the battery.

[0039] When the thickness ratio of the conductive layer to the active material layer is less than 1:120, the conductive layer is too thin. When the addition ratio of MXene material is constant, the too thin conductive layer results in too little MXene material being added, which cannot significantly enhance the adhesion between the current collector and the active material layer.

[0040] When the thickness ratio of the conductive layer to the active material layer is greater than 1:40, the conductive layer is too thick. Although it can significantly enhance the adhesion between the current collector and the active material layer, it affects the kinetic parameters of the battery, reduces performance, and is not conducive to the use of the battery.

[0041] Furthermore, the thickness ratio of the conductive layer to the active material layer is preferably 1:(60-100), which can significantly enhance the adhesion between the current collector and the active material layer without excessively increasing the thickness of the entire positive electrode sheet and at the same time not affecting the energy density of the battery.

[0042] For example, the ratio of the thickness of the conductive layer to the thickness of the active material layer may be 1:20, 1:25, 1:30, 1:35, 1:40, etc.

[0043] Illustratively, the thickness of the conductive layer is 1 to 5 μm, preferably 1 to 1.5 μm.

[0044] Illustratively, the thickness of the active material layer is 40 to 120 μm, preferably 60 to 100 μm.

[0045] In some embodiments, the conductive layer further includes a conductive agent and an adhesive, and the mass ratio of the MXene material, the conductive agent, and the adhesive is (0.5-3): (32-37): (58-66).

[0046] Specifically, the conductive agent is used to further improve the conductive properties of the conductive layer and the current collector. The adhesive is used to improve the adhesion between the various components of the conductive layer and the adhesive between the conductive layer and the active material layer.

[0047] The mass ratio of MXene material, conductive agent and adhesive is (0.5~3):(32~37):(58~66). In this way, the mass content of each component in the conductive layer is moderate, which can not only enhance the adhesion between the current collector and the active material layer, but also improve the conductive properties of the current collector without adversely affecting other electrical properties of the battery.

[0048] When the mass proportion of MXene material in the conductive layer is too small, the MXene material cannot effectively enhance the adhesion between the current collector and the active material layer; when the mass proportion of MXene material in the conductive layer is too large, although the MXene material can effectively enhance the adhesion between the current collector and the active material layer, experiments have shown that excessive MXene material will significantly deteriorate the DC internal resistance of the battery, thereby having adverse effects on the battery.

[0049] When the mass proportion of the adhesive in the conductive layer is too small, the adhesion between the various components of the conductive layer cannot be effectively improved; when the mass proportion of the adhesive is too large, experiments have verified that too much adhesive cannot continue to improve the adhesion between the various components of the conductive layer, but instead causes a waste of adhesive and reduces the mass percentage of MXene material, thereby affecting the conductive performance of the battery.

[0050] Furthermore, the mass ratio of MXene material, conductive agent and adhesive is (2-3): (32-37): (58-66). In this way, the mass content of each component in the conductive layer is better, which can not only significantly enhance the adhesion between the current collector and the active material layer, but also significantly improve the conductive performance of the current collector.

[0051] For example, the mass ratio of MXene material, conductive agent and adhesive can be 0.5:32:58, 0.5:37:66, 1:33:60, 1.5:35:62, 2:37:64, 2.5:35:66, 3:34:59, etc.

[0052] In some embodiments, the MXene material includes: a transition metal carbide and / or a transition metal nitride;

[0053] Transition metal carbides include: Ti3C2T x 、Ti2CT x 、Nb2CT x 、Nb4C3T x 、Ta4C3T x 、V4C3T x 、V2CT x 、Mo2CT x 、TiVCT x 、TiNbCT x 、TiTaCT x 、VNbCT x 、Ti2VC2T x 、Ti2TaC2T x 、Mo2TiC2T x 、Ti3CNT x 、Mo2Ti2C3T x One or more of;

[0054] Transition metal nitrides include: Ti2NT x 、V2NT x 、W2NT x 、Ti4N3T x One or more of .

[0055] Specifically, the MXene material may include only transition metal carbides, only transition metal nitrides, or both transition metal carbides and transition metal nitrides.

[0056] The transition metal carbide may include only one type of carbide or a mixture of two or more types of carbides. For example, the transition metal carbide may be only Ti3C2, or a mixture of Ti3AlC2 and Ti2C, or a mixture of Ti2AlC, Nb2C, Nb2AlC, and Nb4C3, without specific limitation herein.

[0057] The transition metal nitride may be Ti2AlN only, Ti4AlN3 only, or a mixture of Ti2AlN and Ti4AlN3.

[0058] In some embodiments, the active material layer includes an active material, a conductive agent, and a binder, and the mass ratio of the active material, the conductive agent, and the binder is (97-99): (0.5-1): (0.4-2).

[0059] Specifically, compared to existing active material layers, the active material content of the active material layer of this application is increased, while the binder content is reduced. This is because the addition of MXene material improves the adhesion between the current collector and the active material layer. Therefore, while ensuring a certain peel strength of the electrode, the binder content in the active material layer can be reduced and the active material content in the active material layer can be increased. In this way, at the same coating surface density, the battery capacity is increased and the long-term stability of the battery is guaranteed.

[0060] However, experiments have shown that if the mass proportion of the adhesive is too small, the peeling force of the positive electrode sheet will be significantly reduced.

[0061] Illustratively, the mass ratio of the active material, the conductive agent, and the binder may be 99:0.5:0.4, 97:0.9:2, 98:0.7:1, 98.5:0.7:1.5, or 97.5:0.5:2.

[0062] In some embodiments, the conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers, and graphene.

[0063] Specifically, the conductive agent may be one of conductive carbon black, conductive graphite, carbon nanotubes, nanocarbon fibers and graphene, or a mixture of two or more thereof.

[0064] The conductive agent in the conductive layer and the conductive agent in the active material layer may be the same or different, and is not limited here.

[0065] In some embodiments, the binder is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, and sodium carboxymethyl cellulose.

[0066] Specifically, various ions in the adhesive, such as acid ions in polyacrylic acid, fluoride ions in polyvinylidene fluoride, hydroxyl groups in polyvinyl alcohol, and carboxyl groups in sodium carboxymethyl cellulose, will combine with the functional groups on the surface of the MXene material (such as hydroxyl groups, halogen groups, etc.) in the form of hydrogen bonds, thereby acting as a connecting bridge, thereby enhancing the adhesion between the conductive layer and the positive electrode active material layer, improving the peeling force of the positive electrode sheet, and improving the long-term cycle stability of the battery.

[0067] The present application also provides a method for preparing a positive electrode sheet, comprising:

[0068] Step S100: preparing a conductive layer slurry, wherein the conductive layer slurry includes a MXene material;

[0069] Step S200: coating a conductive layer slurry on a current collector to prepare an intermediate electrode, wherein the intermediate electrode comprises a current collector and a conductive layer coated on the current collector;

[0070] Step S300: prepare active material layer slurry, and apply the active material layer slurry on the conductive layer to prepare a positive electrode sheet.

[0071] Specifically, the conductive layer slurry includes a MXene material, a conductive agent, an adhesive, a dispersant and a solvent, and the mass ratio of the MXene material, the conductive agent, the adhesive and the dispersant is 0.5-3:32-37:58-66:0.2-1.

[0072] The active material layer slurry includes an active material, a conductive agent, a binder, a dispersant and a solvent, wherein the mass ratio of the active material, the conductive agent, the binder and the dispersant is 97-99: 0.5-1: 0.4-2: 0.05-0.1.

[0073] The dispersant is at least one of polyvinyl pyrrolidone, polyethylene glycol, styrene maleic anhydride copolymer, and acrylic acid oligomer. The dispersant is used to improve the dispersion performance between the various components of the conductive layer so that the various components can be evenly mixed.

[0074] The dispersant in the conductive layer slurry may be deionized water, and the solvent in the active material layer slurry may be N-methylpyrrolidone.

[0075] When preparing the positive electrode sheet, first, the MXene material, conductive agent, adhesive and dispersant deionized water are mixed evenly according to a predetermined mass ratio to obtain a conductive layer slurry.

[0076] Next, the conductive layer slurry is coated on the current collector, and the intermediate electrode is prepared through processes such as baking, electrophoresis, and winding. The current collector can be made of aluminum, titanium, or other metal alloy materials, and the thickness of the current collector can be 10 to 25 μm.

[0077] Then, the active material, conductive agent, adhesive and dispersant are mixed evenly in a predetermined mass ratio to prepare a positive electrode active slurry, and then the positive electrode active slurry is coated on the conductive layer, and then the positive electrode sheet is finally prepared through processes such as baking and rolling.

[0078] The active material may be one or more of lithium iron phosphate, ternary lithium, and manganese iron lithium.

[0079] The solid content of the positive electrode slurry can be selected to be 63%±5%, which is adjusted according to the difference in the active material selected.

[0080] In the positive electrode sheet prepared by this preparation method, the addition of MXene material in the conductive layer can improve the conductive performance and stability of the battery, and can also enhance the adhesion between the current collector and the active material layer, improve the peeling force of the positive electrode sheet, and improve the long-term cycle stability of the battery.

[0081] The present application also provides a battery, comprising the positive electrode sheet of any one of the first aspect or the positive electrode sheet prepared by the preparation method of the second aspect, a separator and a negative electrode sheet.

[0082] Specifically, the positive electrode sheet, the separator and the negative electrode sheet can be assembled in the form of winding or lamination.

[0083] The diaphragm can be a polypropylene diaphragm, a polyethylene diaphragm and modified composite diaphragms thereof.

[0084] The battery further includes an electrolyte, which includes one or more of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0085] The battery has the technical effects of any of the above embodiments and will not be described in detail here.

[0086] The present application is further discussed below through specific examples and comparative examples.

[0087] Example 1:

[0088] A positive electrode sheet includes a current collector, an active material layer, and a conductive layer disposed between the current collector and the active material layer, wherein the conductive layer includes Ti3C2T with a mass ratio of 0.5:35.5:64. x , conductive carbon black, and polyacrylic acid. The current collector is aluminum foil. The active material layer comprises lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 97.6:0.8:1.6.

[0089] A method for preparing a positive electrode sheet, comprising:

[0090] Ti3C2T with a mass ratio of 0.5:35:64:0.5 x Conductive carbon black, polyacrylic acid and deionized water are prepared into a conductive layer slurry through a process of stirring, dispersing and grinding. The slurry has a solid content of 45%±3% and a viscosity of ≥150mPa.s.

[0091] The conductive layer slurry was transferred to a slurry tank for gravure coating and coated onto an aluminum foil with a thickness of 13 μm to obtain an intermediate electrode (hereinafter referred to as carbon-coated aluminum foil), wherein the coating thickness of the conductive layer slurry was 1 μm.

[0092] Lithium iron phosphate, conductive carbon black and polyvinylidene fluoride in a mass ratio of 97.5:0.8:1.6 were dry-mixed for 20-30 minutes to disperse them evenly, and then N-methylpyrrolidone (NMP) was added and stirred for 30-60 minutes. After that, a dispersant was added and stirred for 150-240 minutes to ensure that the slurry was evenly dispersed. The amount of NMP was adjusted to control the slurry viscosity so that the final viscosity of the active material layer slurry was maintained at 5000-10000 mPa.s and the slurry solid content was 65%±5%.

[0093] The obtained active material layer slurry was coated on the conductive layer of the intermediate electrode layer, with a coating density of 302.4 mg / 1540.25 mm 2 The designed capacity is 100Ah, and then it is prepared into a positive electrode sheet through baking, rolling and other methods. The thickness of the positive electrode active material layer after rolling is 80μm.

[0094] A method for assembling a lithium-ion battery:

[0095] The above-mentioned positive electrode sheets are assembled into a lithium-ion battery. The negative electrode is equipped with graphite, the separator is a polypropylene separator, the electrolyte is a carbonate electrolyte, and the lithium salt is LiPF6. The above raw materials are then wound, hot-pressed, assembled, and chemically formed into a lithium-ion battery.

[0096] Rated capacity 100Ah, performance test for lithium ion.

[0097] Example 2

[0098] The difference from Example 1 is that the conductive layer includes Ti3C2T3 in a mass ratio of 1:35.5:64. x , conductive carbon black and polyacrylic acid.

[0099] Example 3

[0100] The difference from Example 1 is that the conductive layer includes Ti3C2T3 in a mass ratio of 2:35.5:64. x , conductive carbon black and polyacrylic acid.

[0101] Example 4

[0102] The difference from Example 1 is that the conductive layer includes Ti3C2T3 in a mass ratio of 3:35.5:64. x , conductive carbon black and polyacrylic acid.

[0103] Example 5

[0104] The difference from Example 1 is that the coating thickness of the conductive layer is 2 μm.

[0105] Example 6

[0106] The difference from Example 1 is that the coating thickness of the conductive layer is 0.67 μm.

[0107] Example 7

[0108] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:1.2.

[0109] Example 8

[0110] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:1.0.

[0111] Example 9

[0112] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.8.

[0113] Example 10

[0114] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:2.0.

[0115] Example 11

[0116] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.4.

[0117] Example 12

[0118] The difference from Example 1 is that the MXene material is Ti2NT x .

[0119] Example 13

[0120] The difference from Example 1 is that the MXene material is Ti3C3T x and Ta4C3T x mixture.

[0121] Comparative Example 1

[0122] The difference from Example 1 is that the conductive layer includes Ti3C2T3 in a mass ratio of 0.3:35.5:64. x , conductive carbon black and polyacrylic acid.

[0123] Comparative Example 2

[0124] The difference from Example 1 is that the conductive layer includes Ti3C2T3 in a mass ratio of 4:35.5:64. x, conductive carbon black and polyacrylic acid.

[0125] Comparative Example 3

[0126] The difference from Example 1 is that the conductive layer does not include Ti3C2T x .

[0127] Comparative Example 4

[0128] The difference from Example 1 is that the positive electrode plate does not include a conductive layer.

[0129] Comparative Example 5

[0130] The difference from Example 1 is that the coating thickness of the conductive layer is 0.6 μm.

[0131] Comparative Example 6

[0132] The difference from Example 1 is that the coating thickness of the conductive layer is 2.3 μm.

[0133] Comparative Example 7

[0134] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.3.

[0135] Comparative Example 8

[0136] The difference from Example 1 is that the active material layer includes lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:2.1.

[0137] Comparative Example 9

[0138] The difference from Example 1 is that the positive electrode sheet does not include a conductive layer, but the active material layer includes Ti3C2T3 in a mass ratio of 0.5:97.1:0.8:1.6. x , lithium iron phosphate, conductive carbon black and polyvinylidene fluoride.

[0139] The following performance tests were performed on the positive electrode sheets or batteries prepared in the examples and comparative examples.

[0140] (1) In order to verify whether the various properties of the carbon-coated aluminum foil coated with a conductive layer meet the requirements, the adhesion test of the carbon-coated aluminum foil is carried out.

[0141] Adhesion test: Cut a sample with a width of 20mm and a length of 120mm, bake the sample at 100℃ for 10 minutes, stick it on the sample with 3M tape, roll it with a roller five times, and then peel off the tape. If there is no carbon coating layer on the tape, it is qualified, otherwise it is unqualified.

[0142] (2) In order to verify the improvement effect of carbon-coated aluminum foil on adhesion, the peeling force of the positive electrode sheet was tested.

[0143] Take one side of a double-sided tape about 12 cm long and stick it on the stainless steel plate along the marked line. Stick the prepared sample on the other side of the double-sided tape in the marked order. Roll the roller once along the direction of the electrode. Place the sample to be tested on the measuring platform, fix it with screws, and start the test. Intercept relatively stable data to display the average value. Peel strength = selected average value (mN) / sampling width (mm). Test 10 times and take the average value.

[0144] (3) In order to evaluate the effect of carbon-coated aluminum foil on the conductivity of the electrode sheet, a membrane resistance test was performed.

[0145] Cut the electrode sheet into 1540.25mm pieces using a sheet press. 2 Place the disc in the middle of the diaphragm resistance tester to test the diaphragm resistance of the electrode plate, read the test results, and take the average value after 10 tests.

[0146] (4) In order to verify the improvement effect of carbon-coated aluminum foil with MXene added on battery performance, the capacity and direct current internal resistance (DCR) of batteries in different groups were tested.

[0147] Capacity test: I. 0.5C (50A) constant current discharge to 2.0V; II. 0.5C (50A) constant current charge to 3.65V, and constant voltage to 0.05C (5A); III. 0.5C (50A) constant current discharge to 2.0V, record the discharge capacity, and calculate the average value of 25 battery cells in each group.

[0148] DCR test process: In a 25°C constant temperature chamber, place the battery for 1 hour, charge it at a constant current rate of 1C to 3.65V, and then charge it at a constant voltage until the current is less than or equal to 0.05C. At this point, the battery's state of charge (SOC) is 100%. Let it rest for 30 minutes, then discharge it at a constant current rate of 1C for 30 minutes to adjust the battery's state of charge (SOC) to 50%. Battery A with a 50% SOC is allowed to rest for another 30 minutes, then discharge it at a constant current rate of 0.2C for 30 seconds, followed by a constant current discharge at a rate of 1C for 5 seconds. Record the voltage U1 at the last second of the 0.2C constant current discharge, the voltage U2 at the last second of the 1C constant current discharge, as well as the current I1 of the 0.2C constant current discharge and the current I2 of the 1C constant current discharge. Calculate the DCR of the battery at 25°C, 50% SOC, and 1C constant current discharge for 30 seconds = (U2-U1) / (I2-I1).

[0149] The test results are shown in Table 2.

[0150] Table 1 Experimental parameters

[0151]

[0152]

[0153] Table 2 Test results list

[0154]

[0155]

[0156] As shown in Tables 1 and 2, compared to Comparative Example 3, the addition of MXene to the conductive layer in Examples 1 through 13 significantly enhances the adhesion between the current collector and the active material layer, thereby significantly improving the peel strength of the positive electrode sheet. Furthermore, the addition of MXene does not degrade the performance of the carbon-coated aluminum foil, electrode sheet, or lithium-ion battery.

[0157] Comparing the relevant data of Examples 1 to 4, it can be seen that, under the condition that other conditions remain constant, the more MXene is added, the more obvious the improvement effect on the electrode peeling force is.

[0158] Comparing the relevant data of Example 1, Example 5 and Example 6, it can be seen that under the premise of the same active material layer thickness and the same conductive layer ratio, the thicker the coating thickness of the conductive layer, the more obvious the improvement effect on the electrode peeling force.

[0159] Comparing the data from Examples 1 and 7-11 shows that, under constant other conditions, the greater the amount of PVDF added to the active material layer, the more pronounced the improvement in electrode peel strength. However, under constant total mass, a higher amount of PVDF reduces the active material mass, which in turn affects battery capacity.

[0160] In Comparative Example 1, since the amount of MXene material added to the conductive layer is too small, it cannot effectively improve the electrode peeling force, resulting in a low electrode peeling force.

[0161] In Comparative Example 2, since the amount of MXene material added to the conductive layer is too much, although it can significantly improve the electrode peeling force, it will greatly deteriorate the DCR and have an adverse effect on the lithium-ion battery.

[0162] In Comparative Example 3, since the conductive layer does not include Ti3C2T x , so that it is impossible to improve the electrode peeling force by MXene materials, resulting in a low electrode peeling force.

[0163] In Comparative Example 4, the positive electrode sheet lacks a conductive layer, preventing the conductive layer from improving its electrical performance. This results in a high DCR and low battery capacity. Furthermore, the carbon-coated aluminum foil exhibits substandard adhesion, resulting in very low peel strength.

[0164] In Comparative Example 5, since the coating thickness of the conductive layer is too thin, it cannot effectively improve the electrode peeling force, resulting in a low electrode peeling force.

[0165] In Comparative Example 6, since the coating thickness of the conductive layer is too thick, although it can effectively enhance the adhesion between the current collector and the active material layer and improve the electrode peeling force, too thick a coating thickness will have an adverse effect on the electrical performance of the battery, resulting in a reduction in the battery capacity.

[0166] In Comparative Example 7, since the amount of polyvinylidene fluoride added is too small, the peeling force of the electrode is significantly reduced, which is not conducive to practical use.

[0167] In Comparative Example 8, since the amount of polyvinylidene fluoride added is too much, although the peeling force of the electrode can be significantly improved, under the condition of a certain total mass, the excessive amount of polyvinylidene fluoride added will result in the mass proportion of the active material being too small, thereby significantly reducing the capacity of the battery.

[0168] In Comparative Example 9, the positive electrode sheet does not include a conductive layer, but Ti3C2T is added to the active material layer. x Experimental data shows that adding MXene to the active material does not improve the peeling force of the electrode. Furthermore, the absence of a conductive layer prevents the positive electrode from improving its electrical performance, resulting in a high DCR, high sheet resistance, and low battery capacity.

[0169] In summary, in this application, MXene material is added to the conductive layer. On the one hand, due to the excellent conductive properties of MXene material, the addition of MXene material can act as a conductive agent, improve the DC internal resistance of the lithium-ion battery, reduce the heat generation of the battery in practical applications, and thus improve the conductive performance and stability of the battery;

[0170] On the other hand, since MXene materials contain abundant functional groups such as hydroxyl groups, halogen groups, and transition metals, the functional groups can combine with various ions in the active material layer (such as fluoride ions, acid radical ions, hydroxyl groups, carboxyl groups, etc.) in the form of hydrogen bonds, acting as a connecting bridge, thereby enhancing the adhesion between the current collector and the active material layer, thereby improving the peeling force of the positive electrode sheet and improving the long-term cycle stability of the battery.

[0171] In addition, since the addition of MXene material improves the adhesion between the current collector and the active material layer, the content of the adhesive in the active material layer can be reduced while ensuring a certain peel strength of the electrode, and the mass proportion of the active material in the active material layer can be increased. In this way, under the same coating surface density, the capacity of the battery is increased and the stability of the battery during long-term use is guaranteed.

[0172] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Within the scope of the present disclosure, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the above embodiments of the present disclosure, which are not provided in detail for the sake of simplicity.

[0173] The embodiments of the present disclosure are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a current collector, an active material layer and a conductive layer arranged between the current collector and the active material layer, wherein the conductive layer comprises MXene material.

2. The positive electrode sheet according to claim 1, characterized in that: The ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40-120).

3. The positive electrode sheet according to claim 1, characterized in that: The conductive layer further includes a conductive agent and an adhesive, and the mass ratio of the MXene material, the conductive agent and the adhesive is (0.5-3): (32-37): (58-66).

4. The positive electrode sheet according to claim 1, characterized in that: The MXene material includes transition metal carbides and / or transition metal nitrides; The transition metal carbide includes: Ti3C2T x 、Ti2CT x 、Nb2CT x 、Nb4C3T x 、Ta4C3T x 、V4C3T x 、V2CT x 、Mo2CT x 、TiVCT x 、TiNbCT x 、TiTaCT x 、VNbCT x 、Ti2VC2T x 、Ti2TaC2T x 、Mo2TiC2T x 、Ti3CNT x 、Mo2Ti2C3T x One or more of; The transition metal nitride includes: Ti2NT x 、V2NT x 、W2NT x 、Ti4N3T x One or more of .

5. The positive electrode sheet according to claim 1, characterized in that: The active material layer includes an active material, a conductive agent and a binder, and the mass ratio of the active material, the conductive agent and the binder is (97-99): (0.5-1): (0.4-2).

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, nanocarbon fibers and graphene.

7. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The adhesive is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polystyrene butadiene copolymer and sodium carboxymethyl cellulose.

8. A method for preparing a positive electrode sheet, characterized in that: include: Preparing a conductive layer slurry, wherein the conductive layer slurry includes a MXene material; Applying the conductive layer slurry on a current collector to prepare an intermediate electrode, wherein the intermediate electrode comprises a current collector and a conductive layer applied on the current collector; An active material layer slurry is prepared, and the active material layer slurry is coated on the conductive layer to prepare a positive electrode sheet.

9. The preparation method according to claim 8, characterized in that The conductive layer slurry includes a MXene material, a conductive agent, an adhesive, a dispersant, and a solvent, wherein the mass ratio of the MXene material, the conductive agent, the adhesive, and the dispersant is 0.5-3:32-37:58-66:0.2-1; The active material layer slurry includes active material, conductive agent, binder, dispersant and solvent, and the mass ratio of the active material, conductive agent, binder and dispersant is 97-99:0.5-1:0.4-2:0.05-0.

1.

10. A battery, characterized in that: The invention comprises the positive electrode sheet according to any one of claims 1 to 7 or the positive electrode sheet prepared by the preparation method according to any one of claims 8 to 9, a separator and a negative electrode sheet.

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