Positive electrode sheet, method for manufacturing the same, and battery

Abstract

The present invention provides a positive electrode sheet, a method for manufacturing the same, and a battery that can improve the conductivity and stability of a battery, further enhance the adhesive strength between the current collector and the active material layer, improve the peel strength of the positive electrode sheet, and improve the long-term cycle stability of the battery. [Solution] The positive electrode sheet of the present invention comprises a current collector, an active material layer, and a conductive layer provided between the current collector and the active material layer, wherein the conductive layer contains MXene material. The addition of MXene material increases the adhesive strength between the current collector and the active material layer, thereby ensuring a certain peel strength for the electrode sheet while reducing the adhesive content in the active material layer and increasing the proportion of active material mass in the active material layer. In this way, the battery capacity is increased and the stability of long-term battery use is guaranteed under the same coating surface density conditions.

Description

[Technical Field]

[0001] The present invention relates to the technical field of batteries, and more particularly to positive electrode sheets, methods for manufacturing the same, and batteries. [Background technology]

[0002] Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive and negative electrodes can be further subdivided into raw materials such as current collectors, active materials, and auxiliary materials. The current collector is a crucial component of the electrode sheet and affects the processability, electrical performance, and safety performance of the battery, playing a very important role in the industrial production and application of batteries.

[0003] The positive electrode current collector is mainly aluminum foil, while most negative electrode current collectors use copper foil. To further enhance the current-carrying ability of the positive electrode current collector and obtain more desirable electrode performance, the aluminum current collector is usually coated with a layer to improve its conductivity. By coating the aluminum current collector with carbon, the conductivity of the aluminum foil is improved, and at the same time, the adhesive strength between the current collector and the active material layer can be further improved, and the processability of the metal flake material of the current collector can also be improved. However, with existing carbon coating formulations, while the conductivity of the aluminum current collector can be improved, the adhesive strength between the current collector and the active material cannot be improved. [Overview of the project] [Problems that the invention aims to solve]

[0004] In view of the above, the object of the present invention is to provide a positive electrode sheet, a method for manufacturing the same, and a battery. [Means for solving the problem]

[0005] Based on the above objective, a first aspect of the present invention provides a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer, and a conductive layer provided between the current collector and the active material layer. The conductive layer includes an MXene material.

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

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

[0008] Optionally, the MXene material contains transition metal carbides and / or transition metal nitrides. The transition metal carbide is 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 including one or more of the above. The transition metal nitride is Ti2NT x 、V2NT x 、W2NT x 、Ti4N3T x including one or more of the above.

[0009] Optionally, the active material layer contains an active material, a conductive agent, and an adhesive, and the mass ratio of the active material, the conductive agent, and the adhesive is (97 to 99):(0.5 to 1):(0.4 to 2).

[0010] Optionally, the conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, carbon nanofibers, and graphene.

[0011] Optionally, the adhesive is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polystyrene-butadiene copolymer, and sodium carboxymethylcellulose.

[0012] A second aspect of the present invention provides a method for manufacturing a positive electrode sheet, which includes the following: The method involves preparing a conductive layer slurry, wherein the conductive layer slurry contains MXene material. The method involves applying the conductive layer slurry onto a current collector to produce an intermediate electrode sheet, wherein the intermediate electrode sheet includes a current collector and a conductive layer applied onto the current collector. A slurry of the active material layer is prepared, and the slurry of the active material layer is applied onto a conductive layer to produce a positive electrode sheet.

[0013] Optionally, the conductive layer slurry includes an MXene material, a conductive agent, an adhesive, a dispersant, and a solvent. The mass ratio of the MXene material, conductive agent, adhesive, and dispersant is 0.5-3:32-37:58-66:0.2-1. The active material layer slurry comprises an active material, a conductive agent, an adhesive, a dispersant, and a solvent, and the mass ratio of the active material, conductive agent, adhesive, and dispersant is 97-99:0.5-1:0.4-2:0.05-0.1.

[0014] A third aspect of the present invention provides a battery. The battery includes a positive electrode sheet manufactured by any one of the first aspects described above or by the manufacturing method described above, a separator, and a negative electrode sheet. [Effects of the Invention]

[0015] From the above, it can be seen that in the positive electrode sheet, method for manufacturing the same, and battery provided by the present invention, the positive electrode sheet includes a current collector, an active material layer, and a conductive layer provided between the current collector and the active material layer, and the conductive layer includes MXene material. Adding MXene material to the conductive layer can improve the conductivity and stability of the battery, further strengthen the adhesive strength between the current collector and the active material layer, improve the peel strength of the positive electrode sheet, and improve the long-term cycle stability of the battery. [Modes for carrying out the invention]

[0016] To further clarify the object, technical solution, and advantages of the present invention, the present invention will be described in more detail below, along with specific embodiments.

[0017] It should be noted that, unless otherwise defined, the technical terms used in the following embodiments have the same implications as those generally understood by those skilled in the art. The test reagents used in the following embodiments are all conventional biochemical reagents unless otherwise specified. The test methods are all conventional methods unless otherwise specified.

[0018] Lithium-ion batteries are a type of chemical battery that achieves discharge by the movement of lithium ions between the positive and negative electrodes. Due to their advantages such as high energy density, high operating voltage, long cycle life, and high charge / discharge rate, lithium-ion batteries are widely used in the fields of new energy vehicles and storage batteries.

[0019] Lithium-ion batteries mainly consist of a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. The positive and negative electrode sheets can be further subdivided into raw materials such as current collectors, active materials, and auxiliary materials. The current collector is a crucial component of the electrode sheet and affects the processability, electrical performance, and safety performance of the battery, playing a very important role in the industrial production and application of batteries.

[0020] The positive electrode current collector is mainly aluminum foil, while most negative electrode current collectors use copper foil. To further enhance the conductivity of the positive electrode current collector and obtain more desirable electrode performance, aluminum current collectors are usually coated with a layer to improve conductivity. By coating the aluminum current collector with carbon, the conductivity of the aluminum foil is improved, and at the same time, the adhesive strength between the current collector and the active material layer can be further increased, and the processability of the metal flake material of the current collector is also improved.

[0021] Existing carbon coating formulations can improve the conductivity of aluminum current collectors, but they cannot improve the adhesive strength between the current collector and the active material.

[0022] The inventors discovered that because the contact area between the rigid positive electrode current collector and the positive electrode active material layer is limited, the adhesive strength between the positive electrode current collector and the positive electrode active material layer is limited, and the bonding force between them is also limited. In this case, during long charge-discharge cycles, the volume of the electrodes continues to change, leading to loosening of the material particles. This gradually reduces the bonding force between the positive electrode current collector and the positive electrode active material layer, causing powder to fall out and rapidly degrading the battery capacity and cycle life.

[0023] Therefore, the most pressing issue to be resolved is how to increase the adhesive strength between the positive electrode current collector and the positive electrode active material layer without affecting the conductive performance.

[0024] Based on this, a first aspect of the present invention provides a positive electrode sheet. The positive electrode sheet includes a current collector, an active material layer, and a conductive layer provided between the current collector and the active material layer. The conductive layer includes MXene material.

[0025] Specifically, MXene materials are novel two-dimensional materials composed of metal carbides or metal nitrides. Typical MXene materials have the chemical formula M n+1 X n T mIt is represented as follows: "M" represents a metallic element, mainly transition metals (e.g., elements such as chromium, molybdenum, manganese, iron, cobalt, copper, aluminum, silver, nickel, palladium, platinum, and ruthenium). "X" represents the elements carbon and nitrogen. "T" represents a functional group on the material surface, such as a hydroxyl group (-OH) or halogen groups (-F, -Cl).

[0026] MXene material possesses excellent flexibility, good electronic conductivity, electrical conductivity, and superior mechanical properties.

[0027] In this invention, MXene material is added to the conductive layer. One aspect of this invention is that, since MXene material has excellent conductive properties, the addition of MXene material acts as a conductive agent, improving the DC internal resistance of the lithium-ion battery, reducing heat generation in the actual application of the battery, and thereby improving the conductive performance and stability of the battery. Another aspect is that MXene material is rich in functional groups such as hydroxyl groups, halogen groups, and transition metals. These functional groups can bond with various ions in the active material layer (e.g., fluoride ions, acid radical ions, hydroxyl groups, carboxyl groups, etc.) through hydrogen bonding, acting as connecting bridges. This enhances the adhesive strength between the current collector and the active material layer, thereby increasing the peel strength of the positive electrode sheet and improving the long-term cycle stability of the battery.

[0028] Furthermore, the addition of MXene material increases the adhesive strength between the current collector and the active material layer, thereby ensuring a certain level of peel strength in the electrode sheet while reducing the adhesive content in the active material layer and increasing the proportion of active material mass in the active material layer. In this way, under the same coating surface density conditions, the battery capacity is increased and the stability of long-term battery use is guaranteed.

[0029] Therefore, adding MXene material to the conductive layer can simultaneously improve the conductivity and peel strength of the positive electrode sheet, and can also increase the battery capacity.

[0030] In some embodiments, the ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40~120).

[0031] Specifically, when the ratio of the thickness of the conductive layer to the thickness of the active material layer is 1:(40~120), both the thickness of the conductive layer and the active material layer are considered appropriate. The installation of a conductive layer can enhance the adhesive strength between the current collector and the active material layer without excessively increasing the overall thickness of the positive electrode sheet, and at the same time, it does not affect the energy density of the battery.

[0032] If the ratio of the thickness of the conductive layer to the thickness of the active material layer is less than 1:120, the conductive layer becomes too thin. When the addition ratio of MXene material is constant, an excessively thin conductive layer requires a very small amount of MXene material to be added, and the adhesive strength between the current collector and the active material layer cannot be significantly increased.

[0033] If the ratio of the thickness of the conductive layer to the thickness of the active material layer is greater than 1:40, the conductive layer becomes too thick. While this can significantly increase the adhesive strength between the current collector and the active material layer, it affects the battery's dynamic parameters, degrading performance and making it unsuitable for battery use.

[0034] Furthermore, a ratio of the thickness of the conductive layer to the thickness of the active material layer is preferably 1:(60~100). This significantly enhances the adhesive strength between the current collector and the active material layer, while preventing an excessive increase in the overall thickness of the positive electrode sheet and simultaneously not affecting the energy density of the battery.

[0035] 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.

[0036] As an example, the thickness of the conductive layer is 1 to 5 μm, and preferably 1 to 1.5 μm.

[0037] As an example, the thickness of the active material layer is 40 to 120 μm, and preferably 60 to 100 μm.

[0038] In some embodiments, the conductive layer further comprises a conductive agent and an adhesive, and the mass ratio of the MXene material to the conductive agent and the adhesive is (0.5~3):(32~37):(58~66).

[0039] Specifically, conductive agents are used to further enhance the conductive performance between the conductive layer and the current collector. Adhesives are used not only to improve the adhesive strength between the various components of the conductive layer, but also to improve the adhesive strength between the conductive layer and the active material layer.

[0040] When the mass ratio of MXene material, conductive agent, and adhesive is (0.5~3):(32~37):(58~66), the mass content of each component in the conductive layer is appropriate, which not only enhances the adhesive strength between the current collector and the active material layer but also improves the conductive performance of the current collector without adversely affecting other electrical performance of the battery.

[0041] If the proportion of MXene material in the conductive layer is too small, the MXene material cannot effectively enhance the adhesive strength between the current collector and the active material layer. If the proportion of MXene material in the conductive layer is too large, the MXene material can effectively enhance the adhesive strength between the current collector and the active material layer. However, experiments have shown that excessive amounts of MXene material significantly worsen the DC internal resistance of the battery, resulting in undesirable effects on the battery.

[0042] If the proportion of adhesive in the conductive layer is too small, it cannot effectively increase the adhesive strength between the various components in the conductive layer. If the proportion of adhesive is too large, experiments have shown that excessive amounts of adhesive cannot continuously improve the adhesive strength between the various components in the conductive layer, instead wasting adhesive and reducing the mass percentage content of MXene material, thus affecting the conductive performance of the battery.

[0043] Furthermore, when the mass ratio of MXene material, conductive agent, and adhesive is (2-3):(32-37):(58-66), the mass content of each component in the conductive layer is preferable, which not only significantly enhances the adhesive strength between the current collector and the active material layer, but also significantly improves the conductive performance of the current collector.

[0044] Examples of mass ratios of MXene material, conductive agent, and adhesive include 0.5:32:58, 0.5:37:66, 1:33:60, 1.5:35:62, 2:37:64, 2.5:35:66, and 3:34:59.

[0045] In some embodiments, the MXene material comprises transition metal carbides and / or transition metal nitrides. Transition metal carbides are 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 Includes one or more of the following. Transition metal nitrides are Ti2NTs. x V2NT x , W2NT x Ti4N3T x Includes one or more of the following.

[0046] Specifically, the MXene material may contain only transition metal carbides, only transition metal nitrides, or both transition metal carbides and transition metal nitrides. Among these, the transition metal carbide may consist of only one carbide, or it may be a mixture of two or more carbides. For example, the transition metal carbide may consist of only Ti3C2, a mixture of Ti3AlC2 and Ti2C, or a mixture of Ti2AlC, Nb2C, Nb2AlC and Nb4C3, and is not specifically limited here. The transition metal nitride may be Ti2AlN alone, Ti4AlN3 alone, or a mixture of Ti2AlN and Ti4AlN3.

[0047] In some embodiments, the active material layer comprises an active material layer, a conductive agent, and an adhesive, and the mass ratio of the active material, conductive agent, and adhesive is (97-99):(0.5-1):(0.4-2).

[0048] Specifically, compared to conventional active material layers, the proportion of active material in the active material layer of the present invention is increased, while the proportion of adhesive is decreased. This is because the addition of MXene material increases the adhesive strength between the fluid collector and the active material layer, allowing for a certain level of peel strength in the electrode sheet while reducing the adhesive content in the active material layer and increasing the active material content. As a result, under the same coating surface density conditions, the battery capacity is increased and the stability of long-term battery use is guaranteed.

[0049] However, experiments have verified that if the proportion of adhesive mass is too low, the peel strength of the positive electrode sheet decreases significantly.

[0050] As examples, the mass ratios of the active material, conductive agent, and adhesive are 99:0.5:0.4, 97:0.9:2, 98:0.7:1, 98.5:0.7:1.5, and 97.5:0.5:2.

[0051] In some embodiments, the conductive agent is at least one of conductive carbon black, conductive graphite, carbon nanotubes, nanocarbon fibers, and graphene.

[0052] Specifically, the conductive agent may be at least one of conductive carbon black, conductive graphite, carbon nanotubes, nanocarbon fibers, and graphene, or a mixture of two or more of these.

[0053] The conductive agent in the conductive layer and the conductive agent in the active material layer may be the same or different; this limitation is not limited here.

[0054] In some embodiments, the adhesive is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, and sodium carboxymethylcellulose.

[0055] Specifically, various ions in the adhesive, such as the acid ions of polyacrylic acid, the fluoride ions of polyvinylidene fluoride, the hydroxyl groups of polyvinyl alcohol, and the carboxyl groups of sodium carboxymethylcellulose, bond to the functional groups (hydroxyl groups, halogen groups, etc.) on the surface of the MXene material through hydrogen bonding. By acting as a connecting bridge, this increases the adhesive strength between the conductive layer and the positive electrode active material layer, improves the peel strength of the positive electrode sheet, and enhances the long-term cycle stability of the battery.

[0056] The present invention further provides a method for producing a positive electrode sheet, including the following: Step S100 involves preparing a conductive layer slurry, the conductive layer slurry comprising MXene material. Step S200 involves applying a conductive layer slurry onto a current collector to obtain an intermediate electrode sheet, the intermediate electrode sheet comprising a current collector and a conductive layer applied onto the current collector. In step S300, an active material layer slurry is prepared, and the active material layer slurry is applied onto the conductive layer to obtain a positive electrode sheet.

[0057] Specifically, the conductive layer slurry contains MXene material, a conductive agent, an adhesive, a dispersant, and a solvent. The mass ratio of the MXene material, conductive agent, adhesive, and dispersant is 0.5-3:32-37:58-66:0.2-1.

[0058] The active material layer slurry contains an active material, a conductive agent, an adhesive, a dispersant, and a solvent. The mass ratio of the active material, conductive agent, adhesive, and dispersant is 97-99:0.5-1:0.4-2:0.05-0.1.

[0059] The dispersant is at least one of the following: polyvinylpyrrolidone, polyethylene glycol, styrene-maleic anhydride copolymer, or acrylic acid oligomer. The dispersant is used to improve the dispersibility of each component of the conductive layer and to ensure uniform mixing of the components.

[0060] The dispersant in the conductive layer slurry may be deionized water, and the solvent in the active material layer slurry may be N-methylpyrrolidone.

[0061] When preparing the positive electrode sheet, first, MXene material, conductive agent, adhesive, and dispersant are uniformly mixed with deionized water according to a predetermined mass ratio to obtain a conductive layer slurry.

[0062] Next, a conductive layer slurry is applied to the current collector, and an intermediate electrode sheet is fabricated through processes such as firing, electrophoresis, and winding. The current collector may be made of aluminum, titanium, or other metal alloy material. The thickness of the current collector may be 10 to 25 μm.

[0063] Then, the active material, conductive agent, adhesive, and dispersant are uniformly mixed according to a predetermined mass ratio to prepare a positive electrode active slurry. Subsequently, the positive electrode active slurry is applied onto a conductive layer, and after processes such as firing and roll pressing, a positive electrode sheet is finally obtained.

[0064] The active material may be one or more of lithium iron phosphate, ternary lithium, or manganese-iron lithium.

[0065] The solid content of the positive electrode slurry is 63% ± 5%, and may be adjusted based on the differences in the selected active material.

[0066] By adding MXene material to the conductive layer in the positive electrode sheet obtained by this manufacturing method, the conductivity and stability of the battery can be improved. Furthermore, the adhesive strength between the current collector and the active material layer can be enhanced, increasing the peel strength of the positive electrode sheet and improving the long-term cycle stability of the battery.

[0067] The present invention further provides a battery comprising a positive electrode sheet made of any one of the first embodiments described above or a positive electrode sheet made by the manufacturing method of the second embodiment described above, a separator, and a negative electrode sheet.

[0068] Specifically, the positive electrode sheet, separator, and negative electrode sheet may be assembled by winding or lamination.

[0069] The separator may be a polypropylene separator, a polyethylene separator, or a modified composite separator thereof.

[0070] The battery further contains an electrolyte. The electrolyte contains one or more of the following: propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0071] The battery will achieve the technical effects of any of the embodiments described above, which will not be repeated here.

[0072] The present invention will be further explained below with reference to specific examples and comparative examples.

[0073] Example 1: A positive electrode sheet comprising a current collector, an active material layer, and a conductive layer provided between the current collector and the active material layer. The conductive layer is Ti3C2T with a mass ratio of 0.5:35.5:64. x It contains conductive carbon black and polyacrylic acid. The current collector is aluminum foil. The active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 97.6:0.8:1.6.

[0074] The method for manufacturing the positive electrode sheet includes the following: Ti3C2T with a mass ratio of 0.5:35:64:0.5 x A conductive layer slurry is prepared by mixing, dispersing, and grinding conductive carbon black, polyacrylic acid, and deionized water. The slurry has a solid content of 45% ± 3% and a viscosity of ≥ 150 mPa.s. The conductive layer slurry is transferred to a slurry tank and gravure coating is performed. It is coated onto an aluminum foil with a thickness of 13 μm to obtain an intermediate electrode sheet (hereinafter referred to as carbon-coated aluminum foil). Of this, the thickness of the conductive layer slurry coating is 1 μm. Lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride are dry-mixed in a mass ratio of 97.5:0.8:1.6 for 20-30 minutes to ensure uniform dispersion. Then, N-methylpyrrolidone (NMP) is added and the mixture is stirred for 30-60 minutes. Subsequently, a dispersant is added and the mixture is stirred for a further 150-240 minutes until the slurry is uniformly dispersed. The amount of NMP is adjusted to control the viscosity of the slurry, maintaining the final viscosity of the resulting active material layer slurry at 5000-10000 mPa.s. The solid content of the slurry is 65% ± 5%. The obtained active material layer slurry is applied onto the conductive layer of the intermediate electrode sheet described above. The coating surface density is 302.4 mg / 1540.25 mm². 2 The design capacity is 100 Ah. Subsequently, the positive electrode sheet is manufactured through processes such as firing and roll pressing. The thickness of the positive electrode active material layer after roll pressing is 80 μm.

[0075] How to assemble a lithium-ion battery: The positive electrode sheet described above is assembled into a lithium-ion battery. Graphite is used for the negative electrode, a polypropylene separator is used, a carbonate electrolyte is used, and the lithium salt is LiPF6. The lithium-ion battery is manufactured by winding, heat pressing, assembling, and performing chemical conversion processes using the aforementioned raw materials. A performance test will be conducted on a lithium-ion battery with a rated capacity of 100Ah.

[0076] Example 2 The difference from Example 1 is that the conductive layer is Ti3C2T with a mass ratio of 1:35.5:64.x It contains conductive carbon black and polyacrylic acid.

[0077] Example 3 The difference from Example 1 is that the conductive layer is Ti3C2T with a mass ratio of 2:35.5:64. x It contains conductive carbon black and polyacrylic acid.

[0078] Example 4 The difference from Example 1 is that the conductive layer is Ti3C2T with a mass ratio of 3:35.5:64. x It contains conductive carbon black and polyacrylic acid.

[0079] Example 5 The difference from Example 1 is that the thickness of the conductive layer coating is 2 μm.

[0080] Example 6 The difference from Example 1 is that the thickness of the conductive layer coating is 0.67 μm.

[0081] Example 7 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:1.2.

[0082] Example 8 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:1.0.

[0083] Example 9 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.8.

[0084] Example 10 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:2.0.

[0085] Example 11 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.4.

[0086] Example 12 The difference from Example 1 is that the MXene material is Ti2NT x The point is that...

[0087] Example 13 The difference from Example 1 is that the MXene material is Ti3C3T x and Ta4C3T x The key point is that it is a mixture of [something].

[0088] Comparative Example 1 The difference from Example 1 is that the conductive layer is Ti3C2T with a mass ratio of 0.3:35.5:64. x It contains conductive carbon black and polyacrylic acid.

[0089] Comparative Example 2 The difference from Example 1 is that the conductive layer is Ti3C2T with a mass ratio of 4:35.5:64. x It contains conductive carbon black and polyacrylic acid.

[0090] Comparative Example 3 The difference from Example 1 is that the conductive layer is Ti3C2T x The key point is that it does not include this.

[0091] Comparative Example 4 The difference from Example 1 is that the positive electrode sheet does not contain a conductive layer.

[0092] Comparative Example 5 The difference from Example 1 is that the thickness of the conductive layer coating is 0.6 μm.

[0093] Comparative Example 6 The difference from Example 1 is that the thickness of the conductive layer coating is 2.3 μm.

[0094] Comparative Example 7 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:0.3.

[0095] Comparative Example 8 The difference from Example 1 is that the active material layer contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 97.6:0.8:2.1.

[0096] Comparative Example 9 The difference from Example 1 is that the positive electrode sheet does not contain a conductive layer, but the active material layer is Ti3C2T with a mass ratio of 0.5:97.1:0.8:1.6. x It contains lithium iron phosphate, conductive carbon black, and polyvinylidene fluoride.

[0097] The following performance tests were performed on the positive electrode sheets or batteries prepared in each example and comparative example. (1) To verify whether the performance characteristics of the carbon-coated aluminum foil with the conductive layer applied met the requirements, an adhesion strength test was performed on the carbon-coated aluminum. Adhesion strength test: A sample strip measuring 20 mm in width and 120 mm in length was cut, baked at 100°C for 10 minutes, then 3M adhesive tape was applied to the sample strip, pressed 5 times with a roller, and the tape was peeled off. If no carbon coating layer adhered to the tape, it was judged as a pass; otherwise, it was judged as a fail. (2) To verify the effect of carbon-coated aluminum foil on improving adhesive strength, a peel strength test was performed on the positive electrode sheet. One side of a double-sided tape approximately 12 cm long was attached to a stainless steel plate along the marked line. The prepared sample was attached to the other side of the double-sided tape in the order indicated. A roller was pressed once along the electrode sheet, the sample to be tested was placed on the measuring stand, secured with screws, and the test was started. The average value showing relatively stable data was selected. Peel strength = selected average value (mN) / sample width (mm). The test was performed 10 times, and the average value was obtained. (3) To evaluate the effect of the conductivity of carbon-coated aluminum foil on electrode sheets, a sheet resistance test was conducted. The electrode sheet was molded using a pellet molding machine to a size of 1540.25 mm. 2 The sheet resistance of the electrode sheet was tested by cutting it into circular pieces and placing them in the middle of a sheet resistance meter, and the measurement results were read. The test was performed 10 times, and the average value was obtained. (4) To verify the effect of MXene-added carbon-coated aluminum foil on improving battery performance, the capacity and DC resistance (DCR) of batteries from different groups were tested. Capacity Test: I. Discharged to 2.0V with a constant current of 0.5C (50A). II. Charged to 3.65V with a constant current of 0.5C (50A) and a constant voltage of 0.05C (5A). III. Discharged to 2.0V with a constant current of 0.5C (50A), and the discharge capacity for this test was recorded. 25 cells were tested for each group, and the average value was calculated.

[0098] DCR Test Flow: The battery was left in a constant temperature chamber at 25°C for 1 hour, then charged with a constant current at a 1C rate to 3.65V, and then charged with a constant voltage until the current was less than 0.05C. At this time, the state of charge (SOC) of the battery was 100%. After standing for 30 minutes, the battery was discharged again at a constant current at a 1C rate for 30 minutes to adjust the state of charge (SOC) of the battery to 50%. Battery A with a 50% SOC was then left standing for 30 minutes, discharged at a constant current at a 0.2C rate for 30 seconds, and then discharged at a constant current at a 1C rate for 5 seconds. The voltage U1 at the last second of the constant current discharge at the 0.2C rate, the voltage U2 at the last second of the constant current discharge at the 1C rate, and the current I1 and I2 after the constant current discharge at the 0.2C rate and 1C rate respectively were recorded. The DCR (Discharge Coverage) was calculated for a battery at 25°C, SOC (State of Charge) of 50%, and a constant current discharge of 1C for 30 seconds, using the formula: DCR = (U2-U1) / (I2-I1).

[0099] The test results are shown in Table 2.

[0100] Table 1: List of experimental parameters

[0101] [Table 1]

[0102] Table 2: List of Test Results

[0103] [Table 2]

[0104] Referring to Tables 1 and 2, compared to Comparative Example 3, the addition of MXene material to the conductive layer in Examples 1 to 13 significantly enhances the adhesive strength between the current collector and the active material layer, resulting in a significantly higher peel strength of the positive electrode sheet. At the same time, the addition of MXene material does not degrade the adhesion of the carbon-coated aluminum foil, the electrode sheet, or the performance of the lithium-ion battery.

[0105] As can be seen from the data for Examples 1 to 4, under the condition that other conditions are constant, the greater the amount of MXene added, the more pronounced the improvement in the peel strength of the electrode sheet.

[0106] As can be seen by comparing the data for Examples 1, 5, and 6, with the same active material layer thickness and the same ratio of conductive layer thickness, the thicker the conductive layer coating, the more pronounced the improvement in the peel strength of the electrode sheet.

[0107] As can be seen by comparing the data for Example 1 and Examples 7 to 11, under the condition that other conditions are constant, the greater the amount of polyvinylidene fluoride added to the active material layer, the more pronounced the improvement in the peel strength of the electrode sheet. However, under the condition that the total mass is constant, if the amount of polyvinylidene fluoride added is high, the proportion of the active material's mass ratio decreases, which may affect the battery capacity.

[0108] In Comparative Example 1, the amount of MXene material added to the conductive layer was too small, which prevented an effective improvement in the peel strength of the electrode sheet, resulting in a relatively low peel strength of the electrode sheet.

[0109] In Comparative Example 2, the amount of MXene material added to the conductive layer was too high, which, although it significantly improved the peel strength of the electrode sheet, greatly worsened the DCR and had an undesirable effect on the lithium-ion battery.

[0110] In Comparative Example 3, the conductive layer is Ti3C2T x Because it does not contain [specific ingredient], the peel strength of the electrode sheet cannot be improved by the MXene material, and the peel strength of the electrode sheet is relatively low.

[0111] In Comparative Example 4, since the positive electrode sheet does not contain a conductive layer, the electrical performance of the positive electrode sheet cannot be improved by a conductive layer, resulting in a high DCR and low battery capacity. Furthermore, the adhesive strength of the carbon-coated aluminum foil is unacceptable, and the peel strength of the electrode sheet is low.

[0112] In Comparative Example 5, the coating thickness of the conductive layer was too thin, which prevented improvement in the peel strength of the electrode sheet, resulting in a relatively low peel strength of the electrode sheet.

[0113] In Comparative Example 6, although the excessive thickness of the conductive layer coating can effectively enhance the adhesive strength between the current collector and the active material layer, thereby improving the peel strength of the electrode sheet, the excessively thick coating film has an undesirable effect on the electrical performance of the battery, resulting in a decrease in battery capacity.

[0114] In Comparative Example 7, the amount of polyvinylidene fluoride added was too small, which reduced the peel strength of the electrode sheet and made it unsuitable for actual use.

[0115] In Comparative Example 8, although the amount of polyvinylidene fluoride added significantly improved the peel strength of the electrode sheet, when the total mass is constant, adding too much polyvinylidene fluoride results in a proportion of the active material's mass being too small, which significantly reduces the battery's capacity.

[0116] In Comparative Example 9, the positive electrode sheet does not contain a conductive layer, but the active material layer contains Ti3C2Tx The material is added. Experimental data shows that adding MXene material to the active material does not improve the peel strength of the electrode sheet. Furthermore, because no conductive layer is provided, the electrical performance of the positive electrode sheet cannot be improved by a conductive layer, resulting in a high DCR, high sheet resistance, and a relatively low battery capacity.

[0117] In summary, in this invention, MXene material is added to the conductive layer. Since MXene material has excellent conductive properties, the addition of MXene material acts as a conductive agent, improving the DC internal resistance of the lithium-ion battery, reducing heat generation in the actual application of the battery, and thereby improving the conductive performance and stability of the battery.

[0118] Another aspect is that MXene material is rich in functional groups such as hydroxyl groups, halogen groups, and transition metals. These functional groups can bond with various ions in the active material layer (e.g., fluoride ions, acid radical ions, hydroxyl groups, carboxyl groups, etc.) through hydrogen bonding, acting as connecting bridges. This enhances the adhesive strength between the current collector and the active material layer, thereby improving the peel strength of the positive electrode sheet and enhancing the long-term cycle stability of the battery.

[0119] Furthermore, the addition of MXene material increases the adhesive strength between the current collector and the active material layer, thereby ensuring a certain level of peel strength in the electrode sheet while reducing the adhesive content in the active material layer and increasing the proportion of active material mass in the active material layer. In this way, under the same coating surface density conditions, the battery capacity is increased and the stability of long-term battery use is guaranteed.

[0120] Those skilled in the art will understand that the above descriptions of embodiments are merely illustrative and do not mean that the scope of the present invention (including the claims) is limited to these examples. Technical features of the above embodiments or different embodiments may be combined in accordance with the concept of the present invention, and the steps may be performed in any order. Furthermore, many variations of the above embodiments of the present invention exist, but are not described in detail for the sake of brevity.

[0121] The embodiments of the present invention are intended to encompass all such substitutions, modifications, and variations within the 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 invention are all covered within the scope of the present invention. [Industrial applicability]

[0122] The present invention relates to the technical field of batteries, and more particularly to positive electrode sheets, methods for manufacturing the same, and batteries.

Claims

1. Current collector and, The active material layer, A conductive layer provided between the current collector and the active material layer Includes, The conductive layer contains MXene material. Characterized by, Positive electrode sheet.

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

3. The conductive layer further comprises 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). Characterized by, The positive electrode sheet according to claim 1.

4. The MXene material comprises a transition metal carbide and / or a transition metal nitride. The transition metal carbide is Ti ３ C ２ T ｘ Ti ２ CT ｘ Nb ２ CT ｘ Nb ４ C ３ T ｘ Ta ４ C ３ T ｘ V ４ C ３ T ｘ V ２ CT ｘ Mo ２ CT ｘ TiVCT ｘ TiNbCT ｘ TiTaCT ｘ VNbCT ｘ Ti ２ VC ２ T ｘ Ti ２ TaC ２ T ｘ Mo ２ TiC ２ T ｘ Ti ３ CNT ｘ Mo ２ Ti ２ C ３ T ｘ includes one or more of these The transition metal nitride is Ti ２ NT ｘ , V ２ NT ｘ , W ２ NT ｘ Ti ４ N ３ T ｘ Characterized by including one or more of the following: The positive electrode sheet according to claim 1.

5. The active material layer comprises an active material, a conductive agent, and an adhesive, and the mass ratio of the active material, the conductive agent, and the adhesive is (97-99):(0.5-1):(0.4-2). Characterized by, The positive electrode sheet according to claim 1.

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

7. The adhesive is at least one of polyacrylic acid, polyvinylidene fluoride, polyvinyl alcohol, polystyrene-butadiene copolymer, and sodium carboxymethylcellulose. Characterized by, A positive electrode sheet according to any one of claims 1 to 5.

8. The preparation of a conductive layer slurry, wherein the conductive layer slurry contains MXene material, The process involves applying the conductive layer slurry onto a current collector to produce an intermediate electrode sheet, wherein the intermediate electrode sheet includes a current collector and a conductive layer applied onto the current collector. The process involves preparing an active material layer slurry and applying the active material layer slurry onto the conductive layer to produce a positive electrode sheet. including Characterized by, Method for manufacturing a positive electrode sheet.

9. The conductive layer slurry comprises an 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 to 3: 32 to 37: 58 to 66: 0.2 to 1. The active material layer slurry comprises an active material, a conductive agent, an adhesive, a dispersant, and a solvent, and the mass ratio of the active material, the conductive agent, the adhesive, and the dispersant is 97-99:0.5-1:0.4-2:0.05-0.

1. Characterized by, A method for producing a positive electrode sheet according to claim 8.

10. A positive electrode sheet according to any one of claims 1 to 7 or a positive electrode sheet manufactured by the manufacturing method according to claim 8 or 9, a separator, and a negative electrode sheet are included. Characterized by, battery.

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