A magnetic heat coupling assisted lithium iron phosphate battery and a preparation method thereof

Abstract

The application relates to the technical field of lithium ion batteries, and discloses a magnetic-thermal coupling assisted lithium iron phosphate battery and a preparation method thereof. The preparation method comprises the following steps: preparing a lithium iron phosphate composite positive electrode material with a magnetic-thermal effect, wherein the composite positive electrode material is a lithium iron phosphate material coated with ferroferric oxide; preparing a positive electrode sheet by taking the lithium iron phosphate composite positive electrode material as a positive electrode active material; and assembling a lithium ion battery by taking the positive electrode sheet, a metal lithium negative electrode, a diaphragm and an electrolyte. In the application, nano ferroferric oxide material is loaded on the surface of a lithium iron phosphate positive electrode material, and an external magnetic field is introduced during the use of the battery, so that the ferroferric oxide material generates a magnetic-thermal effect under the action of the magnetic field, thereby forming a local thermal field in the battery. The strategy effectively improves the reaction environment of the battery under a low-temperature condition without changing the original structure of the lithium iron phosphate positive electrode material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a magnetothermal-coupled assisted lithium iron phosphate battery and its preparation method. Background Technology

[0002] Lithium-ion batteries have attracted widespread research attention due to their advantages such as high power and high energy density, and have been successfully applied in fields such as pure electric vehicles, hybrid electric vehicles, and energy storage power stations. As a key component of lithium-ion batteries, cathode materials need to simultaneously meet requirements such as high capacity, strong stability, and low toxicity.

[0003] Compared to other cathode materials (such as LiCoO2, LiNiO2, and LiMn2O4), lithium iron phosphate (LiFePO4) cathode materials have advantages such as higher theoretical specific capacity (approximately 170 mAh / g), stable operating voltage (3~5 V), structural stability, good cycle performance, low raw material cost, and environmental friendliness. Therefore, they are considered one of the important cathode materials for power lithium-ion batteries. However, in winter and in high-latitude, high-altitude regions, the lower ambient temperature exacerbates the inherent low electron migration rate and low ionic conductivity of LiFePO4 materials, leading to a significant decrease in battery capacity and power under low-temperature conditions, and in severe cases, even battery performance failure.

[0004] To address the issue of insufficient low-temperature performance in lithium iron phosphate (LiFePO4) batteries, ion doping and surface coating are two commonly used modification techniques aimed at improving the material's electrical conductivity and the battery's electrochemical performance under low-temperature conditions. Ion doping typically involves introducing specific elements (such as yttrium, zirconium, and aluminum) to improve the bulk conductivity and electrochemical performance of LiFePO4. For example, a small amount of yttrium-doped LiFePO4 can significantly improve the material's electronic conductivity and electrochemical performance, but excessive doping may lead to crystal structure destruction and blockage of lithium-ion transport channels; Zr 4+ Doped LiFePO4 can reduce charge transfer impedance and improve rate discharge performance, but it is expensive and the doping concentration needs to be precisely controlled. Surface-rich aluminum LiFePO4 materials exhibit good electrochemical performance at low temperatures, but the introduction of aluminum may change the electronic structure of the material, thereby increasing the complexity of the preparation process.

[0005] While ion doping has shown some effectiveness in improving the conductivity of LiFePO4, problems remain, including excessive doping leading to crystal structure deformation, the high cost of some dopant elements, and complex fabrication processes. Surface coating technology, on the other hand, improves the low-temperature performance of batteries by forming a conductive layer (such as carbon nanotubes, polyethylene, or polyols) on the surface of LiFePO4 particles, thereby enhancing the ion and electron transport rates at the interface. For example, carbon coatings can enhance material conductivity and control particle size, helping to maintain battery stability at low temperatures; aluminum-rich LiFePO4 materials improve rate performance and low-temperature performance by forming a uniform amorphous coating layer. However, surface coating technology also suffers from challenges such as difficulty in precisely controlling coating thickness, complex fabrication processes, and variations in material compatibility.

[0006] Overall, ion doping and surface coating are effective means to improve the performance of LiFePO4 batteries, but they still have certain limitations in terms of cost, process complexity, and large-scale application. These issues limit the promotion of related technologies in large-scale applications. Therefore, there is an urgent need to develop a low-cost, high-performance, and simple process method to improve the cathode reaction kinetics and fundamentally improve the performance and cycle stability of LiFePO4 batteries at low temperatures. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of existing technologies by proposing a magnetothermal-coupled assisted lithium iron phosphate battery and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a magnetothermal-assisted lithium iron phosphate battery includes the following steps:

[0010] Step 1: Prepare a lithium iron phosphate composite cathode material with magnetocaloric effect, wherein the composite cathode material is lithium iron phosphate material coated with iron oxide;

[0011] Step 2: Use the lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode sheet;

[0012] Step 3: Assemble the lithium-ion battery using the positive electrode, lithium metal negative electrode, separator, and electrolyte.

[0013] Preferably, the preparation of the lithium iron phosphate composite cathode material includes the following steps:

[0014] Hydroxylated lithium iron phosphate powder is obtained by hydroxylating lithium iron phosphate powder.

[0015] Iron source, sodium acetate and polyvinylpyrrolidone are added to a solvent and mixed. Then the hydroxylated lithium iron phosphate powder is added. After ultrasonic dispersion, a homogeneous reaction is carried out to coat the surface of lithium iron phosphate with iron oxide, so as to obtain lithium iron phosphate powder coated with iron oxide.

[0016] The obtained lithium iron phosphate powder coated with iron tetroxide was subjected to magnetic separation, washing and drying, and then calcined under an inert atmosphere to obtain the lithium iron phosphate composite cathode material.

[0017] Preferably, the preparation of the lithium iron phosphate composite cathode material includes the following steps: hydroxylating lithium iron phosphate powder to obtain hydroxylated lithium iron phosphate powder; mixing the hydroxylated lithium iron phosphate powder with an iron source in a solvent, heating and reacting to obtain a mixed powder; calcining the mixed powder directly under an inert atmosphere to thermally decompose the iron source into iron(III) oxide and coat it onto the surface of the lithium iron phosphate, thereby obtaining the lithium iron phosphate composite cathode material.

[0018] Preferably, the method for hydroxylating lithium iron phosphate powder is as follows: dispersing lithium iron phosphate powder in an aqueous hydrogen peroxide solution, reacting under heating and stirring conditions, and then centrifuging, washing and drying.

[0019] Preferably, the method for hydroxylating lithium iron phosphate powder is as follows: lithium iron phosphate powder is treated with oxygen plasma.

[0020] Preferably, step 2, which involves using lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode electrode sheet, includes: mixing and grinding the lithium iron phosphate composite cathode material, conductive carbon black, and polyvinylidene fluoride in a mass ratio of 8:1:1, and adding N-methylpyrrolidone for mixing to obtain a cathode slurry; coating the cathode slurry onto a carbon-coated aluminum foil current collector with a coating thickness of 100~250 μm, and then vacuum drying it; and cutting the dried electrode sheet into electrode sheets suitable for battery assembly, such as a circular sheet with a diameter of 12 mm, to obtain the cathode electrode sheet.

[0021] Preferably, the iron source is ferric chloride hexahydrate or ferric acetylacetonate (III).

[0022] A magnetothermal coupling assisted lithium iron phosphate composite cathode material, wherein the composite cathode material is lithium iron phosphate material coated with iron oxide, the iron oxide is loaded on the surface of lithium iron phosphate particles, and has magnetothermal response capability under the action of an alternating magnetic field.

[0023] A magnetothermal-coupled assisted lithium iron phosphate battery is prepared using the preparation method described above.

[0024] Preferably, during use, an alternating magnetic field is applied to the lithium battery to cause the iron(III) oxide in the lithium iron phosphate composite cathode material to generate a magnetocaloric effect under the action of the magnetic field, thereby improving the battery performance under low-temperature conditions.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention utilizes a simple process to prepare a lithium iron phosphate composite cathode material with a magnetocaloric effect. By loading nano-sized iron oxide (Fe3O4) material onto the surface of the lithium iron phosphate cathode material and introducing an external magnetic field during battery use, the iron oxide material generates a magnetocaloric effect under the magnetic field, thereby forming a localized thermal field inside the battery. This strategy effectively improves the battery's reaction environment at low temperatures without altering the original structure of the lithium iron phosphate cathode material.

[0027] Under the influence of an external magnetic field, the nano-iron oxide material loaded on the surface of lithium iron phosphate can generate heat. This heat can increase the overall temperature of the battery system, thereby improving the electron migration rate and ionic conductivity of the lithium iron phosphate cathode material, enhancing electron transport capabilities, and accelerating the cathode reaction process. Simultaneously, the heat generated by the magnetocaloric effect can also improve the mass transfer process of the battery system, promoting lithium-ion diffusion and contributing to improved cycle stability.

[0028] Furthermore, the magnetocaloric effect can further reduce the activation energy of the electrode reaction and accelerate the reaction rate, enabling the battery to maintain high efficiency even under high charge-discharge rates, thereby enhancing the battery's overall performance at low temperatures. Through the magnetocaloric coupling-assisted strategy, the lithium iron phosphate battery of this invention can achieve stable charge-discharge cycles in low-temperature environments.

[0029] The magnetothermal coupled assisted lithium iron phosphate battery provided by this invention is in the form of a button cell and exhibits good cycle stability under low temperature conditions. Its discharge specific capacity remains at about 100 mAh / g, and its capacity retention rate is 70.4% after 600 cycles. It has the potential to improve the performance of lithium-ion batteries in low temperature environments.

[0030] On the other hand, the synthesis process of this invention is simple and controllable, the material system used is well-defined, the preparation process is low-cost, and the performance is stable, avoiding the problems of complex processes and high costs in existing lithium iron phosphate cathode material modification technologies. This invention enhances the low-temperature performance of lithium iron phosphate batteries through external field assistance, providing new ideas and practical basis for the design of stable battery systems under extreme environmental conditions, and has good engineering application prospects. Attached Figure Description

[0031] Figure 1 Morphology of commercial lithium iron phosphate powder;

[0032] Figure 2 Morphology of Fe3O4-coated lithium iron phosphate powder;

[0033] Figure 3 Cyclic performance diagrams for commercial lithium iron phosphate powder and Fe3O4-coated lithium iron phosphate. Detailed Implementation

[0034] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention is described in detail below, but this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the methods used in this invention are conventional methods in this technical field. In this invention, materials, reagents, or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] In one embodiment, the present invention provides a method for preparing a magnetothermal-assisted lithium iron phosphate battery, comprising the following steps:

[0036] Step 1: Prepare a lithium iron phosphate composite cathode material with magnetocaloric effect, wherein the composite cathode material is lithium iron phosphate material coated with iron oxide;

[0037] Step 2: Use the lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode sheet;

[0038] Step 3: Assemble the lithium-ion battery using the positive electrode, lithium metal negative electrode, separator, and electrolyte.

[0039] During battery use, an alternating magnetic field is applied to the lithium-ion battery, causing the iron(III) oxide in the lithium iron phosphate composite cathode material to generate a magnetocaloric effect under the action of the magnetic field, thereby improving the battery performance under low-temperature conditions.

[0040] As a preferred embodiment of the present invention, the preparation of the lithium iron phosphate composite cathode material includes the following steps: hydroxylating lithium iron phosphate powder to obtain hydroxylated lithium iron phosphate powder; mixing iron source, sodium acetate and polyvinylpyrrolidone in a solvent, then adding the hydroxylated lithium iron phosphate powder, dispersing by ultrasound, and performing a homogeneous reaction to coat the surface of lithium iron phosphate with iron oxide to obtain iron oxide-coated lithium iron phosphate powder; subjecting the obtained iron oxide-coated lithium iron phosphate powder to magnetic separation, washing and drying, and then calcining it under an inert atmosphere to obtain the lithium iron phosphate composite cathode material.

[0041] In this embodiment, the concentration of the hydrogen peroxide aqueous solution was 0.1 mol / L, the stirring temperature was 60 ℃, and the stirring time was 15~30 min; the centrifugation speed was 8000 rpm, and the centrifugation time was 3~5 min; the drying treatment was carried out under vacuum at 80 ℃, and the drying time was 6~12 h.

[0042] The homogeneous reaction was carried out at 150–200 °C with a heating rate of 1–5 °C / min and a reaction time of 6–12 h.

[0043] Preferably, the homogeneous reaction is carried out at 200 °C, with a heating rate of 5 °C / min and a reaction time of 8 h.

[0044] Calcination was carried out under an argon atmosphere, with a heating rate of 5-10 °C / min, a calcination temperature of 400-600 °C, and a calcination time of 2-5 h.

[0045] Preferably, the calcination is carried out under an argon atmosphere, with a heating rate of 5 °C / min, a calcination temperature of 500 °C, and a calcination time of 3 h.

[0046] By adjusting the amount of iron source, the mass ratio of iron tetroxide in the prepared iron tetroxide-coated lithium iron phosphate composite cathode material is 2% to 10%.

[0047] By adjusting the amount of iron source, the mass ratio of iron tetroxide in the prepared iron tetroxide-coated lithium iron phosphate composite cathode material is 5%.

[0048] In a preferred embodiment of the present invention, the preparation of the lithium iron phosphate composite cathode material includes the following steps:

[0049] Hydroxylated lithium iron phosphate powder is obtained by hydroxylating lithium iron phosphate powder.

[0050] Hydroxylated lithium iron phosphate powder is mixed with an iron source in a solvent and heated to obtain a mixed powder. The mixed powder is then calcined directly under an inert atmosphere to thermally decompose the iron source into iron(III) oxide, which coats the surface of the lithium iron phosphate, thus obtaining the lithium iron phosphate composite cathode material.

[0051] In this embodiment, calcination is carried out under an argon atmosphere, with a heating rate of 5 °C / min, a calcination temperature of 350 °C, and a calcination time of 4 h.

[0052] As a preferred embodiment of the present invention, the method for hydroxylating lithium iron phosphate powder is as follows: dispersing lithium iron phosphate powder in an aqueous hydrogen peroxide solution, reacting under heating and stirring conditions, and then centrifuging, washing and drying.

[0053] In this embodiment, the solution stirring time for the hydroxylation process is 30 min; the centrifugation time for the hydroxylation process is 3-5 min, preferably 5 min; and the drying time for the hydroxylation process under vacuum conditions is 6-12 h, preferably 12 h.

[0054] As a preferred embodiment of the present invention, the method for hydroxylating lithium iron phosphate powder is as follows: the lithium iron phosphate powder is treated with oxygen plasma for 5 to 10 minutes, preferably 8 minutes.

[0055] In a preferred embodiment of the present invention, step 2, which involves using lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode sheet, includes:

[0056] The lithium iron phosphate composite cathode material, conductive carbon black and polyvinylidene fluoride are mixed and ground in a mass ratio of 8:1:1, and N-methylpyrrolidone is added and mixed for 10-30 min, preferably 15 min, to obtain cathode slurry.

[0057] The positive electrode slurry is coated onto a carbon-coated aluminum foil current collector with a coating thickness of 100~250 μm, preferably 200 μm, and then vacuum dried for 8~12 h, preferably 12 h.

[0058] The dried electrode sheet is cut into round pieces with a diameter of 12 mm to obtain the positive electrode sheet.

[0059] In a preferred embodiment of the present invention, the iron source is ferric chloride hexahydrate or ferric acetylacetone (III).

[0060] In a preferred embodiment of the present invention, the assembly of the coin cells is carried out in a glove box under an argon protective atmosphere, with H2O content less than 0.1 ppm and O2 content less than 0.1 ppm. A lithium metal sheet with a diameter of 12 mm is used as the counter electrode; a PE / PP / PE three-layer composite membrane with a diameter of 16 mm (Celgard 2325) is used as the separator; the electrolyte is prepared by dissolving 1 mol / L lithium hexafluorophosphate in an organic solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1. During battery assembly, the positive electrode casing, positive electrode plate, separator, lithium sheet, and negative electrode casing are assembled sequentially, with 30 μL of the electrolyte added to both the positive and negative electrode sides. After assembly, the coin cells are sealed using a sealing machine, and the sealed coin cells are removed from the glove box and left to stand for 6 hours to allow the electrolyte to fully wet the electrode materials.

[0061] In one embodiment, the present invention also proposes a magnetothermal coupling assisted lithium iron phosphate composite cathode material, wherein the composite cathode material is lithium iron phosphate material coated with iron tetroxide, the iron tetroxide is loaded on the surface of lithium iron phosphate particles, and has magnetothermal response capability under the action of an alternating magnetic field.

[0062] In one embodiment, the present invention also proposes a magnetothermal-coupled assisted lithium iron phosphate battery, which is prepared by the preparation method described above.

[0063] In a preferred embodiment of the present invention, during the use of the lithium battery, an alternating magnetic field is applied to the lithium battery, causing the iron(III) oxide in the lithium iron phosphate composite cathode material to generate a magnetocaloric effect under the action of the magnetic field, so as to improve the performance of the battery under low temperature conditions.

[0064] In this embodiment, the frequency of the AC electromagnet is 50 Hz, and the magnetic field strength of the AC electromagnet is 50~500 mT, preferably 200 mT.

[0065] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0066] Example 1: Magnetothermal coupled lithium iron phosphate battery was prepared according to the following method.

[0067] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0068] Step 1: Disperse a certain amount of lithium iron phosphate powder in 30 mL of 0.1 mol / L hydrogen peroxide aqueous solution and stir at 60 °C for 30 min;

[0069] Step 2: Transfer the above solution to a 50 mL centrifuge tube and centrifuge at 8000 rpm for 5 min. Wash the product obtained by centrifugation thoroughly with deionized water and anhydrous ethanol. Repeat three times until the product is neutral (pH=7).

[0070] Step 3: Dry the powder obtained above under vacuum at 80 °C for 12 h to obtain hydroxylated lithium iron phosphate powder;

[0071] Step 4: Add 0.26 g of ferric chloride hexahydrate, 0.4 g of anhydrous sodium acetate and 0.2 g of polyvinylpyrrolidone to 30 mL of ethylene glycol and stir for 30 min to mix them thoroughly. After obtaining a transparent orange-yellow solution, add 1 g of the hydroxylated lithium iron phosphate powder and ultrasonically disperse for 30 min.

[0072] Step 5: Transfer the obtained mixed solution to a 50 mL hydrothermal reactor, set the homogeneous reactor temperature to 200 ℃, the heating rate to 5 ℃ / min, and maintain the hydrothermal reaction for 8 h;

[0073] Step 6: After the reaction is completed, the mixture is cooled to room temperature and separated by magnetic separation to obtain lithium iron phosphate powder coated with iron oxide. The powder is then washed and centrifuged three times with deionized water and anhydrous ethanol, and dried under vacuum at 80 °C for 12 h.

[0074] Step 7: Place the obtained iron oxide-coated lithium iron phosphate powder in a tube furnace, heat it to 500 ℃ at a heating rate of 5 ℃ / min under an argon atmosphere, and calcine it for 3 h;

[0075] Step 8: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron tetroxide.

[0076] (2) The assembly method of lithium iron phosphate battery is as follows:

[0077] Step 1: Grind and mix the lithium iron phosphate composite cathode material, conductive carbon black and polyvinylidene fluoride in a mass ratio of 8:1:1, then add a certain amount of N-methylpyrrolidone and mix for 10~30 min to obtain cathode slurry.

[0078] Step 2: Coat the positive electrode slurry onto the carbon-coated aluminum foil current collector with a coating thickness of 200 μm, and dry the coated electrode under vacuum conditions for 12 h;

[0079] Step 3: Cut the dried electrode into round pieces with a diameter of 12 mm to serve as the positive electrode, and weigh them to calculate the mass of the active material.

[0080] Step 4: The button cell assembly is carried out in a glove box with an argon protective atmosphere containing less than 0.1 ppm H2O and less than 0.1 ppm O2. A 12 mm diameter lithium metal sheet is used as the counter electrode, and a PE / PP / PE three-layer composite membrane is used as the separator. The separator is Celgard 2325 with a diameter of 16 mm. The electrolyte is 1 mol / L lithium hexafluorophosphate dissolved in an organic solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1. During assembly, the positive electrode casing, positive electrode sheet, separator, lithium sheet, and negative electrode casing are assembled sequentially, and 30 μL of the electrolyte is added to both the positive and negative electrode sides.

[0081] Step 5: After assembly, use a sealing machine to seal the button cell. Remove the sealed button cell from the glove box and let it stand for 6 hours to allow the electrolyte to fully wet the electrode material.

[0082] The coin cell assembled according to the above method was subjected to low-temperature testing. Under the conditions of 0 ℃ and an alternating magnetic field with a magnetic field strength of 200 mT and a frequency of 50 Hz, the battery showed good cycle stability, with its discharge specific capacity remaining at 100 mAh / g and a capacity retention rate of 70.4% after 600 cycles.

[0083] Example 2: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0084] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0085] Step 1: Place 1 g of lithium iron phosphate powder in the plasma treatment chamber, introduce oxygen, and adjust the plasma treatment power to 100 W. Treat with oxygen plasma for 8 min to introduce oxygen-containing polar groups on the surface of lithium iron phosphate powder.

[0086] Step 2: Following step 4 in Example 1, the hydroxylated lithium iron phosphate powder is mixed with an iron source, sodium acetate, and polyvinylpyrrolidone in a solvent and then ultrasonically dispersed.

[0087] Step 3: Perform a homogeneous reaction on the above mixed solution according to step 5 in Example 1;

[0088] Step 4: Perform magnetic separation, washing, and drying of the reaction product according to step 6 in Example 1;

[0089] Step 5: Calcine the obtained product under an inert atmosphere, following step 7 in Example 1.

[0090] Step 6: Following step 8 in Example 1, the calcined product is ground to obtain a lithium iron phosphate composite cathode material coated with iron tetroxide.

[0091] (2) Assembly and testing of lithium iron phosphate batteries:

[0092] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0093] Example 3: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0094] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0095] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0096] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0097] Step 3: Following step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0098] Step 4: Add 0.345 g of acetylacetone iron (III) and 1 g of the hydroxylated lithium iron phosphate powder to 50 mL of ethanol solution, heat and stir to obtain a mixed powder;

[0099] Step 5: Place the above mixed powder in a tube furnace, heat it to 350 °C at a heating rate of 5 °C / min under an argon atmosphere, and calcine it for 4 h;

[0100] Step 6: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron oxide.

[0101] (2) Assembly and testing of lithium iron phosphate batteries:

[0102] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0103] Example 4: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0104] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0105] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0106] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0107] Step 3: Following step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0108] Step 4: Add 0.1 g of ferric chloride hexahydrate, 0.2 g of anhydrous sodium acetate and 0.1 g of polyvinylpyrrolidone to 30 mL of ethylene glycol and stir for 30 min to mix them thoroughly. After obtaining a transparent orange-yellow solution, add 1 g of the hydroxylated lithium iron phosphate powder and ultrasonically disperse for 30 min.

[0109] Step 5: Perform a homogeneous reaction on the above mixed solution according to Step 5 in Example 1;

[0110] Step 6: Following step 6 in Example 1, the reaction product is subjected to magnetic separation, washing, and drying.

[0111] Step 7: Following step 7 in Example 1, calcine the obtained product under an inert atmosphere;

[0112] Step 8: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron tetroxide.

[0113] (2) Assembly and testing of lithium iron phosphate batteries:

[0114] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0115] Example 5: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0116] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0117] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0118] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0119] Step 3: Following Step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0120] Step 4: Add 0.138 g of acetylacetone iron (III) and 1 g of the hydroxylated lithium iron phosphate powder to 50 mL of ethanol solution, heat and stir to obtain a mixed powder;

[0121] Step 5: Place the above mixed powder in a tube furnace, heat it to 350 °C at a heating rate of 5 °C / min under an argon atmosphere, and calcine it for 4 h;

[0122] Step 6: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron oxide.

[0123] (2) Assembly and testing of lithium iron phosphate batteries:

[0124] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0125] Example 6: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0126] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0127] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0128] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0129] Step 3: Following Step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0130] Step 4: Add 0.52 g of ferric chloride hexahydrate, 0.8 g of anhydrous sodium acetate and 0.4 g of polyvinylpyrrolidone to 30 mL of ethylene glycol and stir for 30 min to mix them thoroughly. After obtaining a transparent orange-yellow solution, add 1 g of the hydroxylated lithium iron phosphate powder and ultrasonically disperse for 30 min.

[0131] Step 5: Perform a homogeneous reaction on the above mixed solution according to Step 5 in Example 1;

[0132] Step 6: Following step 6 in Example 1, the reaction product is subjected to magnetic separation, washing, and drying.

[0133] Step 7: Following step 7 in Example 1, calcine the obtained product under an inert atmosphere;

[0134] Step 8: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron tetroxide.

[0135] (2) Assembly and testing of lithium iron phosphate batteries:

[0136] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0137] Example 7: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0138] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0139] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0140] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0141] Step 3: Following Step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0142] Step 4: Add 0.69 g of acetylacetone iron (III) and 1 g of the hydroxylated lithium iron phosphate powder to 50 mL of ethanol solution, heat and stir to obtain a mixed powder;

[0143] Step 5: Place the above mixed powder in a tube furnace, heat it to 350 °C at a heating rate of 5 °C / min under an argon atmosphere, and calcine it for 4 h;

[0144] Step 6: After calcination, the obtained powder is poured into a mortar and ground for 15 minutes to obtain lithium iron phosphate composite cathode material coated with iron oxide.

[0145] (2) Assembly and testing of lithium iron phosphate batteries:

[0146] The lithium iron phosphate composite cathode material was prepared into a cathode sheet using the same method as in Example 1, and the coin cell assembly and testing were completed according to the steps in Example 1.

[0147] Example 8: The preparation method of magnetothermal coupling assisted lithium iron phosphate battery is as follows.

[0148] (1) The preparation method of lithium iron phosphate composite cathode material is as follows:

[0149] Step 1: Following Step 1 in Example 1, the lithium iron phosphate powder is subjected to hydroxylation treatment;

[0150] Step 2: Following Step 2 in Example 1, the hydroxylated product is centrifuged and washed;

[0151] Step 3: Following Step 3 in Example 1, the cleaned product is dried to obtain hydroxylated lithium iron phosphate powder.

[0152] Step 4: Perform a pretreatment on the hydroxylated lithium iron phosphate powder according to step 4 in Example 1;

[0153] Step 5: Perform a homogeneous reaction on the mixed solution according to Step 5 in Example 1;

[0154] Step 6: Following step 6 in Example 1, the reaction product is subjected to magnetic separation, washing, and drying.

[0155] Step 7: Following step 7 in Example 1, calcine the obtained product under an inert atmosphere;

[0156] Step 8: Following step 8 in Example 1, the calcined product is ground to obtain a lithium iron phosphate composite cathode material coated with iron tetroxide.

[0157] (2) Assembly and testing of lithium iron phosphate batteries:

[0158] Assemble the button cell according to the method described in Example 1 and conduct low-temperature testing. Under the conditions of 0 °C and an alternating magnetic field with a magnetic field strength of 300 mT and a frequency of 50 Hz, the discharge specific capacity of the battery remains at 80 mAh / g.

[0159] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a magnetothermal-coupled assisted lithium iron phosphate battery, characterized in that, Includes the following steps: Step 1: Prepare a lithium iron phosphate composite cathode material with magnetocaloric effect. The composite cathode material is lithium iron phosphate material coated with iron(III) oxide (Fe3O4). The lithium iron phosphate composite cathode material is prepared by either method one or method two: Method 1: Hydroxylated lithium iron phosphate powder is obtained by hydroxylating lithium iron phosphate powder; iron source, sodium acetate and polyvinylpyrrolidone are added to a solvent and mixed, and then the hydroxylated lithium iron phosphate powder is added. After ultrasonic dispersion, a homogeneous reaction is carried out. In the homogeneous reaction, the temperature of the homogeneous reactor is set at 200 ℃, the heating rate is 5 ℃ / min, and the hydrothermal reaction is maintained for 8 h, so that iron(III) oxide is coated on the surface of lithium iron phosphate, and iron(III) oxide coated lithium iron phosphate powder is obtained; the obtained iron(III) oxide coated lithium iron phosphate powder is subjected to magnetic separation, washing and drying, and then calcined under an inert atmosphere to obtain the lithium iron phosphate composite cathode material. Method 2: Hydroxylated lithium iron phosphate powder is obtained by hydroxylating lithium iron phosphate powder; the hydroxylated lithium iron phosphate powder is mixed with an iron source in a solvent and heated to obtain a mixed powder; the mixed powder is directly calcined under an inert atmosphere to thermally decompose the iron source to form iron(III) oxide and coat the surface of lithium iron phosphate, thereby obtaining the lithium iron phosphate composite cathode material. Step 2: Use the lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode sheet; Step 3: Assemble the lithium-ion battery using the positive electrode, lithium metal negative electrode, separator, and electrolyte.

2. The method for preparing a magnetothermal-coupled assisted lithium iron phosphate battery according to claim 1, characterized in that, The specific method for hydroxylating lithium iron phosphate powder is as follows: dispersing lithium iron phosphate powder in an aqueous hydrogen peroxide solution, reacting under heating and stirring conditions, followed by centrifugation, washing and drying.

3. The method for preparing a magnetothermal-coupled assisted lithium iron phosphate battery according to claim 1, characterized in that, The specific method for hydroxylation treatment of lithium iron phosphate powder is as follows: lithium iron phosphate powder is treated with oxygen plasma.

4. The method for preparing a magnetothermal-coupled assisted lithium iron phosphate battery according to claim 1, characterized in that, Step 2, which involves using lithium iron phosphate composite cathode material as the cathode active material to prepare the cathode sheet, includes: The lithium iron phosphate composite cathode material, conductive carbon black and polyvinylidene fluoride were mixed and ground in a mass ratio of 8:1:1, and N-methylpyrrolidone was added for mixing to obtain cathode slurry. The positive electrode slurry is coated onto a carbon-coated aluminum foil current collector with a coating thickness of 100~250 μm and then vacuum dried. The dried electrode sheets are cut into sizes suitable for battery assembly to obtain the positive electrode sheets.

5. The method for preparing a magnetothermal-coupled assisted lithium iron phosphate battery according to claim 1, characterized in that, The iron source is ferric chloride hexahydrate or ferric acetylacetone (III).

6. A magnetothermal-coupled assisted lithium iron phosphate composite cathode material, characterized in that, The lithium iron phosphate composite cathode material is prepared by any one of the preparation methods described in claims 1-5, and the lithium iron phosphate composite cathode material is lithium iron phosphate material coated with iron tetroxide.

7. A magnetothermal-coupled assisted lithium iron phosphate battery, characterized in that, It is prepared using the preparation method described in any one of claims 1-5.

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