MXene / mesoporous alumina composite material, lithium iron phosphate positive pole piece, preparation method of lithium iron phosphate positive pole piece and battery

Abstract

The invention discloses an MXene / mesoporous alumina composite material, a lithium iron phosphate positive pole piece, a preparation method of the lithium iron phosphate positive pole piece and a battery, the MXene / mesoporous alumina composite material is composed of a mesoporous alumina ball and MXene attached to the surface of the mesoporous alumina ball and / or the inner wall of a pore channel; mXene is attached to the surface of the mesoporous alumina ball and / or the inner wall of a pore channel in a vacuum-assisted impregnation and self-assembly manner to form a three-dimensional conductive network skeleton. The MXene / mesoporous alumina composite material is applied to a lithium iron phosphate positive pole piece, so that the mechanical strength of the lithium iron phosphate positive pole piece is effectively improved, and material pulverization and contact failure in the cycle process are reduced, thereby reducing the internal resistance increase in the cycle process, prolonging the service life of a battery and enhancing the structural stability of an electrode.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to an MXene / mesoporous alumina composite material, a lithium iron phosphate cathode sheet, a method for preparing the same, and a battery. Background Technology

[0002] Lithium iron phosphate (LFP) batteries dominate the power battery and energy storage fields due to their high safety, long cycle life, and low cost. However, their inherent low electronic conductivity and slow lithium-ion diffusion severely limit their rate performance and low-temperature performance, becoming a key bottleneck, especially in applications requiring fast charging. Existing improvement technologies mainly suffer from the following shortcomings: (1) Particle nano-sizing and carbon coating: This is the industry standard practice, but if the carbon coating layer is too thick, it will hinder ion transport, and if it is too thin, the conductivity will be poor. There is limited room for further optimization, and the preparation process consumes a lot of energy.

[0003] (2) Adding conductive agents: Introducing materials such as carbon black, carbon nanotubes, and graphene into the electrode, but traditional conductive agents mainly participate in the construction of electron conduction networks and contribute very little to ion transport. In high-pressure electrodes, ion transport impedance becomes the main problem, making it difficult to significantly improve the overall rate performance.

[0004] (3) Introducing functional additives: Recent studies have attempted to use porous alumina or graphyne to improve interfaces or ion transport. However, these materials either have insufficient conductivity or are expensive and have complex processes. For example, the conductivity of alumina is insufficient to support an effective electronic pathway; the preparation conditions of graphyne are harsh and the cost is high, so it is not yet feasible for large-scale application and it is difficult to achieve the best balance between improving electronic conductivity and ion transport.

[0005] In summary, current performance optimization methods for lithium iron phosphate cathode materials mostly focus on improving electronic conductivity or enhancing ion diffusion channels, making it difficult to achieve synergistic improvement in both electron and ion channels. This is particularly challenging in constructing cathode materials that combine high energy density, high rate capability, and low-temperature performance. Therefore, there is an urgent need to develop a novel composite material system with a rational structure, controllable process, and moderate cost that can significantly improve the synergistic electron and ion transport capabilities in lithium iron phosphate electrodes. This will help overcome existing performance bottlenecks and meet the comprehensive performance requirements of next-generation power batteries and energy storage systems for cathode materials. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide an MXene / mesoporous alumina composite material, a lithium iron phosphate cathode sheet, a method for preparing the same, and a battery.

[0007] To achieve the above objectives, a first aspect of the present invention provides an MXene / mesoporous alumina composite material, comprising mesoporous alumina spheres and MXene attached to the surface and / or inner wall of the pores of the mesoporous alumina spheres; wherein the MXene is attached to the surface and / or inner wall of the pores of the mesoporous alumina spheres by vacuum-assisted impregnation and self-assembly to form a three-dimensional conductive network skeleton.

[0008] Furthermore, the MXene is Ti3C2T x T x It is one of -O, -OH and -F; the length of the MXene is less than 5nm and the thickness is less than 2nm.

[0009] Furthermore, the mesoporous alumina spheres have a pore size of 5-20 nm and a specific surface area of ​​300-600 m². 2 / g; the mass ratio of MXene to mesoporous alumina is 1:(5-20). The mesoporous alumina spheres provide ordered ion channels and high specific surface area, which can accelerate electrolyte penetration and lithium ion diffusion. At the same time, by adjusting the composite ratio of MXene, conductivity and mechanical stability can be balanced, and the overall performance of the material can be optimized.

[0010] Preferably, the mesoporous alumina spheres have a pore size of 8-12 nm and a specific surface area of ​​400-500 m². 2 / g. This preferred pore size range, while ensuring sufficient ion channel size, can effectively prevent structural collapse and excessive electrolyte adsorption, thereby improving the structural stability and reuse life of the composite material.

[0011] A second aspect of the present invention provides a lithium iron phosphate positive electrode sheet, comprising an aluminum current collector and a positive electrode active material layer coated on the aluminum current collector, wherein the positive electrode active material layer comprises lithium iron phosphate active material, a conductive agent and a binder, and the aforementioned MXene / mesoporous alumina composite material. The mass fraction of the MXene / mesoporous alumina composite material is 0.5%-3% of the mass of the lithium iron phosphate active material. While ensuring high energy density, only an appropriate amount of composite material is added to form an effective conduction network, improving the rate performance and low-temperature performance of the electrode without significantly affecting the compaction density.

[0012] Preferably, the mass fraction of the MXene / mesoporous alumina composite material is 1%-2% of the mass of the lithium iron phosphate active material.

[0013] Furthermore, in the positive electrode active material layer, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder is (95-96.5):(0.5-3):(1-1.5):(1-1.5).

[0014] Preferably, in the positive electrode active material layer, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent, and binder is 96.5:1.5:1:1. This ratio has been experimentally verified as the optimal ratio, exhibiting excellent charge-discharge performance and cycle stability under both high-rate and low-temperature environments.

[0015] Furthermore, the conductive agent is selected from conductive carbon black, carbon nanotubes, or graphene, and the binder is selected from polyvinylidene fluoride, polyacrylic acid, or polyethylene oxide.

[0016] Preferably, the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride (PVDF). The conductive carbon black and MXene synergistically form a complementary conductive network, and PVDF has good film-forming properties and electrolyte stability, which helps to enhance the structural integrity and long-term cycling stability of the electrode.

[0017] A third aspect of the present invention provides a method for preparing the above-mentioned lithium iron phosphate positive electrode sheet, comprising the following steps: MXene dispersion was mixed with mesoporous alumina powder, and then subjected to ultrasonic treatment, vacuum-assisted impregnation and drying to obtain MXene / mesoporous alumina composite material; The lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder are mixed in a solvent according to the specified ratio to form a uniform slurry; The slurry is coated onto an aluminum current collector, dried, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0018] The preparation method of the lithium iron phosphate cathode sheet of the present invention is simple and controllable, without the need for high-temperature sintering or complex chemical reactions, which helps to maintain the layered structure and surface activity of MXene, while ensuring that MXene can fully penetrate into the mesoporous alumina channels to achieve stable composite.

[0019] Furthermore, the MXene dispersion is prepared by etching Ti3AlC2 ceramic with hydrofluoric acid followed by ultrasonic exfoliation, with a concentration of 1-5 mg / mL; the ultrasonic treatment time is 5-10 hours, and the ultrasonic frequency is 20-40 kHz; the vacuum-assisted impregnation is performed at a vacuum level of -0.08 to -0.1 MPa for 3-5 hours; the drying temperature after vacuum-assisted impregnation is 60-100℃, and the drying time is 8-16 hours. These optimized process parameters ensure that MXene is uniformly loaded onto the alumina framework, forming a continuous and stable conductive network, while avoiding damage to the MXene structure caused by high temperatures, thus improving product quality consistency and process adaptability.

[0020] Preferably, the concentration of the MXene dispersion is 2 mg / mL, the ultrasonic treatment time is 8 hours, the vacuum degree is -0.095 MPa, the holding time is 4 hours, the vacuum-assisted impregnation drying temperature is 80°C, and the drying time is 12 hours.

[0021] Furthermore, the solvent is N-methylpyrrolidone. N-methylpyrrolidone has excellent polarity and solubility, which can stably disperse MXene and binders, resulting in higher slurry uniformity and improved electrode film quality and coating consistency.

[0022] Furthermore, the slurry is dried at 80-120°C after being coated onto the aluminum current collector. Within this temperature range, the solvent can be effectively evaporated without damaging the composite structure, which helps to form a dense and flat electrode sheet, improving its mechanical properties and adhesion.

[0023] A fourth aspect of the present invention provides a battery comprising the aforementioned lithium iron phosphate cathode. By introducing an MXene / mesoporous alumina composite cathode structure, the overall battery performance, low-temperature adaptability, and cycle life are significantly enhanced.

[0024] Furthermore, the battery retains more than 96% of its capacity at 25°C and 3C discharge rate, and more than 70% of its capacity at -20°C, further demonstrating the excellent performance of the battery of the present invention in high-rate and extreme low-temperature environments, making it suitable for fast charging of electric vehicles and use in frigid regions.

[0025] Furthermore, the battery also includes a negative electrode, a separator, and an electrolyte.

[0026] Furthermore, the battery retains over 94% of its capacity after 1000 cycles at 25°C using a 1C rate, and its DC internal resistance increases by less than 20% after 1000 cycles. This further demonstrates that the battery of the present invention possesses excellent long-term cycle stability and extremely low degradation characteristics, which is beneficial for meeting the stringent requirements of energy storage systems and electric vehicles for ultra-long lifespan and improving its performance throughout its entire life cycle.

[0027] Compared with the prior art, the present invention has the following advantages: Firstly, the MXene / mesoporous alumina composite material of this invention synergistically constructs a "dual-continuous" transport network, innovatively combining MXene, which has metallic conductivity, with mesoporous alumina, which has regular ion channels. MXene is responsible for constructing ultrafast electron pathways, while the pores of the mesoporous alumina and the functional groups on the surface of MXene are jointly responsible for efficient lithium-ion transport. By constructing a three-dimensional cross-linked electron-ion dual-continuous network structure, the electronic conductivity and ion migration efficiency of the composite material are significantly improved, effectively solving the core problem of electron-ion transport mismatch in high-pressure lithium iron phosphate cathodes.

[0028] Secondly, the lithium iron phosphate cathode sheet of this invention can significantly improve the rate performance and low-temperature performance of the battery. Thanks to the unique dual-continuous network, the transmission impedance of lithium ions and electrons in the cathode is greatly reduced. Experiments show that the battery using the lithium iron phosphate cathode sheet of this invention can achieve a capacity retention rate of over 96% under 3C high-rate discharge; and at a low temperature of -20°C, the capacity retention rate exceeds 70%, far exceeding conventional technologies.

[0029] Third, the three-dimensional framework formed by MXene and mesoporous alumina in this invention effectively improves the mechanical strength of the electrode, reduces material pulverization and contact failure during cycling, thereby reducing the increase in internal resistance during cycling, extending the battery's lifespan, and enhancing the stability of the electrode structure.

[0030] Fourth, the preparation process of the lithium iron phosphate positive electrode sheet of the present invention is simple and easy to industrialize. The preparation process of this composite electrode is compatible with the existing electrode slurry processing technology, does not require complex or expensive equipment, and has the potential for large-scale production. Attached Figure Description

[0031] Figure 1 This is a schematic diagram illustrating the synthesis of the MXene / mesoporous alumina composite material of the present invention. Detailed Implementation

[0032] The following details the MXene / mesoporous alumina composite material, lithium iron phosphate cathode sheet, preparation method thereof, and battery embodiments of the present invention. This description is provided to enable those skilled in the art to fully understand the invention and is not intended to limit the subject matter described in the claims.

[0033] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0034] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined to form new technical solutions. All technical features and optional technical features of the present invention can be combined to form new technical solutions. All steps of the present invention can be performed sequentially or randomly.

[0035] The present invention discloses an MXene / mesoporous alumina composite material, which is composed of mesoporous alumina spheres and MXene attached to the surface and / or the inner wall of the pores of the mesoporous alumina spheres; the MXene is attached to the surface and / or the inner wall of the pores of the mesoporous alumina spheres by vacuum-assisted impregnation and self-assembly to form a three-dimensional conductive network skeleton.

[0036] In some implementations, the MXene is Ti3C2T. x T x It is a surface functional group. In some preferred embodiments, T x It is one of -O, -OH and -F; the length of the MXene is less than 5nm and the thickness is less than 2nm.

[0037] In some embodiments, the mesoporous alumina spheres have a pore size of 5-20 nm and a specific surface area of ​​300-600 m². 2 / g, for example, the pore size of mesoporous alumina spheres can be 5nm, 10nm, or 20nm, or other unlisted values ​​within the range of 5-20nm; the specific surface area can be 300m². 2 / g、450m 2 / g or 600m 2 / g, or 300-600m 2 Other values ​​not listed within the / g range. The pore size of the mesoporous alumina spheres is 5-20 nm, which is sufficient to ensure rapid electrolyte wetting and smooth lithium ion transport.

[0038] In some embodiments, mesoporous alumina spheres can be prepared by a sol-gel in-situ template method with the addition of an organic template agent. For example, an aluminum alkoxide precursor is first prepared, then a template agent is added and hydrolyzed to form porous alumina spheres. After calcination to remove the template agent, mesoporous alumina spheres that meet the above requirements for pore size and specific surface area can be obtained.

[0039] In some embodiments, the mass ratio of MXene to mesoporous alumina is 1:(5-20). For example, the mass ratio of MXene to mesoporous alumina can be 1:5, 1:10, or 1:20, or other unlisted values ​​within the range of 1:(5-20).

[0040] In some preferred embodiments, the mesoporous alumina spheres have a pore size of 8-12 nm and a specific surface area of ​​400-500 m². 2 / g.

[0041] The present invention provides a lithium iron phosphate positive electrode sheet, comprising an aluminum current collector and a positive electrode active material layer coated on the aluminum current collector, wherein the positive electrode active material layer comprises lithium iron phosphate active material, a conductive agent and a binder, and the aforementioned MXene / mesoporous alumina composite material.

[0042] In some embodiments, the mass fraction of the MXene / mesoporous alumina composite material is 0.5%-3% of the mass of the lithium iron phosphate active material. For example, the mass fraction of the MXene / mesoporous alumina composite material can be 0.5%, 1.5%, or 3% of the mass of the lithium iron phosphate active material, or other unlisted values ​​within the range of 0.5%-3%.

[0043] In some preferred embodiments, the mass fraction of the MXene / mesoporous alumina composite material is 1%-2% of the mass of the lithium iron phosphate active material.

[0044] In some embodiments, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent, and binder in the positive electrode active material layer is (95-96.5):(0.5-3):(1-1.5):(1-1.5). For example, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent, and binder can be 96.5:1.5:1:1, 95:3:1:1, or other unlisted values ​​within the range of (95-96.5):(0.5-3):(1-1.5):(1-1.5).

[0045] In some preferred embodiments, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder in the positive electrode active material layer is 96.5:1.5:1:1.

[0046] In some embodiments, the conductive agent is selected from conductive carbon black, carbon nanotubes, or graphene, and the binder is selected from polyvinylidene fluoride, polyacrylic acid, or polyethylene oxide.

[0047] In some preferred embodiments, the conductive agent is conductive carbon black, and the binder is polyvinylidene fluoride.

[0048] The method for preparing the lithium iron phosphate positive electrode sheet of the present invention includes the following steps: S1: Mix MXene dispersion with mesoporous alumina powder, and then perform ultrasonic treatment, vacuum-assisted impregnation and drying to obtain MXene / mesoporous alumina composite material; S2: Mix lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder in solvent according to the specified ratio to form a uniform slurry; S3: The slurry is coated onto an aluminum current collector, dried, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0049] In some embodiments, in step S1: the MXene dispersion is prepared by etching Ti3AlC2 ceramic with hydrofluoric acid and then ultrasonically exfoliating, with a concentration of 1-5 mg / mL. For example, the concentration of the MXene dispersion can be 1 mg / mL, 2 mg / mL, or 5 mg / mL, or other unlisted values ​​within the range of 1-5 mg / mL; the ultrasonic treatment time is 5-10 hours, and the ultrasonic frequency is 20-40 kHz. For example, the ultrasonic treatment time can be 5 hours, 8 hours, or 10 hours, or other unlisted values ​​within the range of 5-10 hours. The ultrasonic frequency can be 20 kHz, 30 kHz, or 40 kHz, or other unlisted values ​​within the range of 20-40 kHz.

[0050] In some embodiments, the vacuum degree of the vacuum-assisted impregnation is -0.08 to -0.1 MPa, and the holding time is 3 to 5 hours. For example, the vacuum degree can be -0.08 MPa, -0.095 MPa, or -0.1 MPa, or other unlisted values ​​in the range of -0.08 to -0.1 MPa; the holding time can be 3 hours, 4 hours, or 5 hours, or other unlisted values ​​in the range of 3 to 5 hours.

[0051] In some embodiments, the drying temperature after vacuum-assisted impregnation is 60-100°C, and the drying time is 8-16 hours. For example, the drying temperature can be 60°C, 80°C, or 100°C, or other unlisted values ​​within the range of 60-100°C, and the drying time can be 8 hours, 12 hours, or 16 hours, or other unlisted values ​​within the range of 8-16 hours.

[0052] In some preferred embodiments, the concentration of the MXene dispersion is 2 mg / mL, the ultrasonic treatment time is 8 hours, the vacuum degree is -0.095 MPa, the holding time is 4 hours, the drying temperature is 80°C, and the drying time is 12 hours.

[0053] In some embodiments, in step S2, the solvent is N-methylpyrrolidone.

[0054] In some implementations, the drying temperature in step S3 is 80-120°C, for example, 80°C, 90°C, or 120°C, or other unlisted values ​​within the range of 80-120°C.

[0055] A battery according to the present invention includes the above-mentioned lithium iron phosphate positive electrode.

[0056] In some embodiments, the battery further includes a negative electrode, a separator, and an electrolyte.

[0057] Specifically, the battery retains over 96% of its capacity at 25°C and 3C discharge rate, and over 70% of its capacity at -20°C. After 1000 cycles at 25°C and 1C rate, the battery retains over 94% of its capacity, and the DC internal resistance growth rate after 1000 cycles is less than 20%.

[0058] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0059] Example 1: The preparation method of the MXene / mesoporous alumina composite material of the present invention includes the following steps: 1) Mesoporous alumina spheres (pore size 10 nm, specific surface area 450 m²) were synthesized by in-situ template method. 2 / g).

[0060] 2) Ti3AlC2 ceramics were etched with hydrofluoric acid and then ultrasonically exfoliated to prepare single-layer or few-layer Ti3C2T. x MXene dispersion (concentration 2 mg / mL), Ti3C2T x It possesses -O, -OH and -F functional groups.

[0061] 3) Add 10g of mesoporous alumina balls to 500mL of MXene dispersion, sonicate for 8 hours at a frequency of 20kHz, and then maintain at a vacuum of -0.095MPa for 4 hours to ensure that MXene fully penetrates into the pores.

[0062] 4) The mixture was filtered and vacuum dried at 80°C for 12 hours. After grinding, the MXene / mesoporous alumina composite material was obtained.

[0063] Example 2 The preparation method of the MXene / mesoporous alumina composite material of the present invention includes the following steps: 1) Mesoporous alumina spheres (pore size 5 nm, specific surface area 300 m²) were synthesized by in-situ template method. 2 / g).

[0064] 2) Ti3AlC2 ceramics were etched with hydrofluoric acid and then ultrasonically exfoliated to prepare single-layer or few-layer Ti3C2T. x MXene dispersion (concentration 0.5 mg / mL), Ti3C2T xIt possesses -O, -OH and -F functional groups.

[0065] 3) Add 10g of mesoporous alumina balls to 1000mL of MXene dispersion, sonicate for 5 hours at a frequency of 30kHz, and then maintain at a vacuum of -0.08MPa for 3 hours to ensure that MXene fully penetrates into the pores.

[0066] 4) The mixture was filtered and vacuum dried at 60°C for 16 hours. After grinding, the MXene / mesoporous alumina composite material was obtained.

[0067] Example 3 The preparation method of the MXene / mesoporous alumina composite material of the present invention includes the following steps: 1) Mesoporous alumina spheres (pore size 20 nm, specific surface area 600 m²) were synthesized by in-situ template method. 2 / g).

[0068] 2) Ti3AlC2 ceramics were etched with hydrofluoric acid and then ultrasonically exfoliated to prepare single-layer or few-layer Ti3C2T. x MXene dispersion (concentration 5 mg / mL), Ti3C2T x It possesses -O, -OH and -F functional groups.

[0069] 3) Add 10g of mesoporous alumina balls to 400mL of MXene dispersion, sonicate for 10 hours at a frequency of 40kHz, and then maintain at a vacuum of -0.1MPa for 5 hours to ensure that MXene fully penetrates into the pores.

[0070] 4) The mixture was filtered and vacuum dried at 100°C for 8 hours. After grinding, the MXene / mesoporous alumina composite material was obtained.

[0071] like Figure 1 As shown, the MXene / mesoporous alumina composite materials prepared in Examples 1-3 of this invention consist of mesoporous alumina spheres and MXene attached to the surface and / or inner walls of the pores of the mesoporous alumina spheres. The MXene is attached to the surface and / or inner walls of the pores of the mesoporous alumina spheres through vacuum-assisted impregnation and self-assembly, forming a three-dimensional conductive network framework. MXene not only provides excellent electronic conductivity, but its surface lithiophilic functional groups can also strongly adsorb lithium ions, producing a synergistic effect with the ion transport channels of mesoporous alumina, jointly constructing a low-torsion electron-ion dual continuous fast transport network.

[0072] Example 4 The method for preparing the lithium iron phosphate positive electrode sheet of the present invention includes the following steps: 1) Mix lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder in solvent at a mass ratio of 96.5:1.5:1:1 to form a uniform slurry; 2) The slurry is coated onto an aluminum current collector, dried at 90°C, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0073] Example 5 The method for preparing the lithium iron phosphate positive electrode sheet of the present invention includes the following steps: 1) Mix lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder in solvent at a mass ratio of 95:3:1:1 to form a uniform slurry; 2) The slurry is coated onto an aluminum current collector, dried at 80°C, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0074] Example 6 The method for preparing the lithium iron phosphate positive electrode sheet of the present invention includes the following steps: 1) Mix lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder in solvent at a mass ratio of 96.5:0.5:1.5:1.5 to form a uniform slurry; 2) The slurry is coated onto an aluminum current collector, dried at 120°C, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0075] Example 7 A battery is assembled into a pouch cell using the lithium iron phosphate positive electrode sheet prepared in Example 4, the artificial graphite negative electrode, and the lithium salt electrolyte.

[0076] Example 8 A battery is assembled into a pouch cell using the lithium iron phosphate positive electrode sheet prepared in Example 5, the artificial graphite negative electrode, and the lithium salt electrolyte.

[0077] Example 9 A battery is assembled into a pouch cell using the lithium iron phosphate positive electrode sheet prepared in Example 6, the artificial graphite negative electrode, and the lithium salt electrolyte.

[0078] Comparative Example 1 The preparation method of the lithium iron phosphate positive electrode sheet in this comparative example includes the following steps: 1) Lithium iron phosphate active material, mesoporous alumina powder, conductive agent and binder are mixed in a solvent at a mass ratio of 96.5:1.5:1:1 to form a uniform slurry; wherein, the mesoporous alumina powder is synthesized into mesoporous alumina balls according to the method of step 1) of Example 1, without adding MXene dispersion, and directly undergoes the same washing and drying process (vacuum drying at 80°C for 12 hours), and then ground to obtain mesoporous alumina powder.

[0079] 2) The slurry is coated onto an aluminum current collector, dried at 90°C, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0080] Comparative Example 2: The preparation method of the lithium iron phosphate positive electrode sheet in this comparative example includes the following steps: 1) Lithium iron phosphate active material, MXene powder, conductive agent and binder are mixed in solvent at a mass ratio of 96.5:1.5:1:1 to form a uniform slurry; wherein, MXene powder is prepared into MXene dispersion according to the method of step 2) of Example 1, without adding mesoporous alumina, and is directly vacuum dried at 80°C for 12 hours, and then ground to obtain MXene powder.

[0081] 2) The slurry is coated onto an aluminum current collector, dried at 90°C, and rolled to obtain a lithium iron phosphate positive electrode sheet.

[0082] Comparative Example 3: The method for preparing the battery in this comparative example includes the following steps: 1) Mix lithium iron phosphate active material, conductive agent and binder in solvent at a mass ratio of 98:1:1 to form a uniform slurry; 2) The slurry is coated onto the aluminum current collector, dried at 90°C, and rolled to obtain the positive electrode sheet; 3) Assemble the positive electrode, artificial graphite negative electrode, and lithium salt electrolyte into a soft-pack battery.

[0083] Comparative Example 4: The method for preparing the battery in this comparative example includes the following steps: 1) The lithium iron phosphate active material, the mesoporous alumina powder prepared in Comparative Example 1, the conductive agent and the binder were mixed in a solvent at a mass ratio of 96.5:1.5:1:1 to form a uniform slurry; wherein, the mesoporous alumina powder was synthesized into mesoporous alumina balls according to the method of step 1) of Example 1, without adding MXene dispersion, and directly subjected to the same washing and drying process (vacuum drying at 80°C for 12 hours), and ground to obtain mesoporous alumina powder.

[0084] 2) The slurry is coated onto the aluminum current collector, dried at 90°C, and rolled to obtain the positive electrode sheet; 3) Assemble the positive electrode, artificial graphite negative electrode, and lithium salt electrolyte into a soft-pack battery.

[0085] Comparative Example 5: The method for preparing the battery in this comparative example includes the following steps: 1) The lithium iron phosphate active material, the MXene powder prepared in Comparative Example 2, the conductive agent and the binder were mixed in a solvent at a mass ratio of 96.5:1.5:1:1 to form a uniform slurry; wherein, the MXene powder was prepared into an MXene dispersion according to the method of step 2) of Example 1, without adding mesoporous alumina, and was directly vacuum dried at 80°C for 12 hours, and then ground to obtain pure MXene powder.

[0086] 2) The slurry is coated onto the aluminum current collector, dried at 90°C, and rolled to obtain the positive electrode sheet; 3) Assemble the positive electrode, artificial graphite negative electrode, and lithium salt electrolyte into a soft-pack battery.

[0087] Performance testing: To compare the improvement effect of the MXene / mesoporous alumina composite material prepared in this invention on the electrode structure, the positive electrode sheets prepared in Examples 4, 5, and 6 were compared with the positive electrode sheets prepared in Comparative Examples 1 and 2.

[0088] The testing methods include: Electrode peel strength test (mechanical properties): A 180° peel test was conducted using a tensile testing machine (Instron 3300). The electrode was cut into strips 20 mm wide, and 3M tape was used to adhere the electrode surface. The electrode was stretched at a speed of 50 mm / min, and the average force value when the electrode coating separated from the current collector was recorded and converted into peel strength (N / m).

[0089] Electrode resistivity test (electronic conductivity): The surface resistance of the electrode was measured using a four-probe resistance meter (ST2263), and the unit is mΩ. The lower the value, the more complete the electronic conductivity network of the electrode.

[0090] Electrolyte absorbance test (ion wettability): Weigh the cut electrode sheet and record the weight as W0. Immerse it in standard electrolyte for 2 hours. After removal, use filter paper to absorb the surface liquid and weigh it immediately, recording the weight as W1. Calculation formula: Absorption rate = (W1 - W0) / W1 × 100%.

[0091] The test results are shown in Table 1 below: Table 1 Based on the test results in Table 1, the following analytical conclusions can be drawn: (1) Significant improvement in mechanical strength In Comparative Example 1, although the pure mesoporous alumina particles have high hardness, they lack connection with the active material and aluminum current collector, resulting in the lowest peel strength (12.4 N / m), and the electrode is prone to brittle cracking and powdering. In Comparative Example 2, although pure MXene is prone to agglomeration and difficult to disperse, the improvement in adhesion is limited (22.8 N / m).

[0092] Examples 4 and 5 of the present invention show that, with the increase of the amount of composite material added, the peel strength is significantly improved to over 40 N / m (up to 48.9 N / m). This is because MXene forms a flexible coating layer on the surface of mesoporous alumina, the alumina particles are embedded in the electrode as rigid anchors, and the MXene functional groups interact strongly with the binder and current collector to form a reinforced structure.

[0093] (2) Cooperative optimization of electron / ion transport networks Electronic conductivity: Comparative Example 1 exhibits a high resistance of 98.4 mΩ due to the insulating properties of alumina, severely hindering electron transport. In contrast, Example 4 (1.5% added) shows a resistance reduced to 55.6 mΩ, significantly better than Comparative Example 2 (78.2 mΩ) containing pure MXene. This demonstrates that mesoporous alumina effectively disperses MXene, preventing its aggregation and maximizing its conductivity.

[0094] (3) Ion wettability: In Comparative Example 2, MXene was difficult to disperse and easily agglomerated, resulting in the lowest liquid absorption rate (11.5%). However, Example 4 maintained a high liquid absorption rate (20.5%), comparable to pure mesoporous alumina (Comparative Example 1). This proves that the composite material of the present invention retains the rich mesoporous structure of alumina, providing sufficient electrolyte channels for lithium ion transport.

[0095] The electrochemical performance of the batteries prepared in Examples 7-9 and Comparative Examples 3-5 was tested, and the test results are shown in Table 2 below: Table 2 Based on the test results in Table 2, the following analytical conclusions can be drawn: (1) Rate performance analysis (3C / 1C capacity retention) Simply adding mesoporous alumina (Comparative Example 4) has limited effect on rate capability improvement because alumina is insulating and hinders electron transport. While simply adding MXene (Comparative Example 5) improves conductivity (91.3%), the small size and large specific surface area of ​​MXene make it prone to aggregation and uneven dispersion, limiting ion transport channels and resulting in a lower improvement compared to the composite material. Examples 7-9 of this invention improve retention to over 96%, demonstrating that the composite material constructs an "electron-ion dual continuous rapid transport network." MXene provides an ultrafast electron pathway, while its dispersion on mesoporous alumina provides high-speed ion channels, reducing polarization and thus releasing more capacity at high rates.

[0096] (2) Low temperature performance analysis (capacity retention rate at -20°C) Compared to Comparative Example 3 (53%), this invention improves the low-temperature capacity by nearly 20 percentage points. This is mainly due to the rich pore structure of mesoporous alumina, which has the ability to adsorb and retain electrolyte (wetting), and the high conductivity of MXene. The two work together to reduce the electrochemical impedance at low temperatures, solving the problem of slow diffusion of lithium iron phosphate at low temperatures.

[0097] (3) Long-cycle stability analysis (1C cycle 1000 cycles) The battery of this invention exhibits minimal capacity decay after long-term cycling. Further verification demonstrates that the three-dimensional framework enhances the mechanical strength of the electrodes, and the composite material, acting as a supplement to the binder and conductive agent, firmly locks in the active material, reducing material shedding and pulverization during cycling.

[0098] (4) Internal resistance (DCR) growth rate analysis (after 1000 cycles) A significant increase in the internal resistance of a comparative battery usually indicates contact failure between the active particles and the current collector or conductive network. The battery of this invention shows extremely low internal resistance growth, directly proving that the "rigid alumina + flexible MXene" framework structure maintains a stable conductive network connection during long-term expansion and contraction, effectively suppressing the generation of "contact failure" and "dead active material".

[0099] In summary, as can be seen from the table, the battery using the lithium iron phosphate cathode sheet of this invention has better discharge capacity, rate performance, low-temperature capacity retention, cycle performance, and DC internal resistance (DCR) growth after cycling than the comparative example. By constructing an MXene / mesoporous alumina three-dimensional network, the battery achieves a balance of high rate, long life and excellent low-temperature performance.

[0100] The above are merely specific embodiments of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention. All other details not described in detail belong to the prior art.

Claims

1. An MXene / mesoporous alumina composite material, characterized in that, It consists of mesoporous alumina spheres and MXenes attached to the surface and / or inner walls of the pores of the mesoporous alumina spheres; the MXenes are attached to the surface and / or inner walls of the pores of the mesoporous alumina spheres by vacuum-assisted impregnation and self-assembly to form a three-dimensional conductive network skeleton.

2. The MXene / mesoporous alumina composite material according to claim 1, characterized in that, The MXene is Ti3C2T x T x It is one of -O, -OH and -F; the length of the MXene is less than 5nm and the thickness is less than 2nm.

3. The MXene / mesoporous alumina composite material according to claim 1, characterized in that, The mesoporous alumina spheres have a pore size of 5-20 nm and a specific surface area of ​​300-600 m². 2 / g; the mass ratio of MXene to mesoporous alumina is 1:(5-20).

4. A lithium iron phosphate positive electrode sheet, characterized in that, It includes an aluminum current collector and a positive electrode active material layer coated on the aluminum current collector, wherein the positive electrode active material layer includes lithium iron phosphate active material, conductive agent and binder, and the MXene / mesoporous alumina composite material as described in any one of claims 1-3.

5. The lithium iron phosphate positive electrode sheet according to claim 4, characterized in that, The mass fraction of the MXene / mesoporous alumina composite material is 0.5%-3% of the mass of the lithium iron phosphate active material.

6. The lithium iron phosphate positive electrode sheet according to claim 4, characterized in that, In the positive electrode active material layer, the mass ratio of lithium iron phosphate active material, MXene / mesoporous alumina composite material, conductive agent and binder is (95-96.5):(0.5-3):(1-1.5):(1-1.5).

7. The lithium iron phosphate positive electrode sheet according to claim 4, characterized in that, The conductive agent is selected from conductive carbon black, carbon nanotubes or graphene, and the binder is selected from polyvinylidene fluoride, polyacrylic acid or polyethylene oxide.

8. A method for preparing a lithium iron phosphate positive electrode sheet according to any one of claims 4-7, characterized in that, Includes the following steps: MXene dispersion was mixed with mesoporous alumina powder, and then subjected to ultrasonic treatment, vacuum-assisted impregnation and drying to obtain MXene / mesoporous alumina composite material; The active material of lithium iron phosphate, MXene / mesoporous alumina composite material, conductive agent and binder are mixed in a solvent to form a homogeneous slurry; The slurry is coated onto an aluminum current collector, and after drying and rolling, a lithium iron phosphate positive electrode sheet is obtained.

9. The preparation method according to claim 8, characterized in that, The MXene dispersion was prepared by etching Ti3AlC2 ceramic with hydrofluoric acid and then ultrasonically exfoliating, with a concentration of 1-5 mg / mL. The ultrasonic treatment lasts for 5-10 hours, and the ultrasonic frequency is 20-40 kHz; the vacuum degree of the vacuum-assisted impregnation is -0.08 to -0.1 MPa, and the holding time is 3-5 hours. The temperature for drying after vacuum-assisted impregnation is 60-100℃, and the drying time is 8-16 hours; The solvent is N-methylpyrrolidone; The slurry is dried at 80-120℃ after being coated onto the aluminum current collector.

10. A battery, characterized in that, It includes the lithium iron phosphate positive electrode sheet according to any one of claims 4 to 7.

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