Low-temperature-resistant lithium iron phosphate positive electrode material and preparation method thereof

Abstract

The application discloses a low-temperature-resistant lithium iron phosphate positive electrode material and a preparation method thereof. The low-temperature-resistant lithium iron phosphate positive electrode material comprises the following raw material components in parts by weight: lithium iron phosphate active material 90-120 parts, conductive agent 10-15 parts, binder 8-12 parts, additive 5-8 parts and solvent 60-70 parts. The lithium iron phosphate active material is lithium iron phosphate coated with a carbon layer, and at least one metal element selected from aluminum, magnesium, chromium, vanadium and cobalt is doped in the lithium iron phosphate active material. The additive comprises nitrogen-doped carbon fiber compounded with titanium dioxide and titanium dioxide fiber coated with a polypyrrole layer. The titanium dioxide fiber coated with the polypyrrole layer is obtained by loading first pyrrole monomers on porous titanium dioxide fiber and then polymerizing the first pyrrole monomers with second pyrrole monomers. The low-temperature-resistant lithium iron phosphate positive electrode material has excellent low-temperature resistance and conductivity, and can improve the electrochemical performance of a battery at low temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a low-temperature resistant lithium iron phosphate positive electrode material and a preparation method thereof. Background Art

[0002] With rapid economic development, humanity's demand for and consumption of energy is increasing. At the same time, worsening environmental pollution and energy shortages pose a significant threat to human survival and development. Lithium-ion batteries, due to their high voltage, high specific energy, and long cycle life, are increasingly being used in new energy vehicles, consumer electronics, power tools, electric bicycles, and other market sectors.

[0003] Lithium-ion batteries primarily consist of four components: a positive electrode, a negative electrode, a separator, and an electrolyte. At lower temperatures, the rate of lithium ion transmission slows, leading to rapid capacity decay and poor rate performance. Therefore, there is an urgent need to develop lithium-ion batteries that can still function properly under low-temperature conditions.

[0004] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the Invention

[0005] The object of the present invention is to provide a low-temperature resistant lithium iron phosphate cathode material and a preparation method thereof, wherein the low-temperature resistant lithium iron phosphate cathode material still has excellent electrochemical properties at low temperatures.

[0006] In order to achieve the above object, a specific embodiment of the present invention provides the following technical solutions:

[0007] A low-temperature resistant lithium iron phosphate positive electrode material, comprising the following raw material components in parts by weight: 90-120 parts of lithium iron phosphate active material, 10-15 parts of conductive agent, 8-12 parts of binder, 5-8 parts of additive and 60-70 parts of solvent;

[0008] The lithium iron phosphate active material is lithium iron phosphate with a carbon layer coated on the surface, and the lithium iron phosphate active material is doped with at least one metal element selected from aluminum, magnesium, chromium, vanadium, and cobalt;

[0009] The additives include nitrogen-doped carbon fibers compounded with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer;

[0010] The titanium dioxide fiber coated with the polypyrrole layer is obtained by first loading a first pyrrole monomer on the porous titanium dioxide fiber and then polymerizing the first pyrrole monomer with the second pyrrole monomer.

[0011] In one or more embodiments of the present invention, the mass ratio of the nitrogen-doped carbon fiber composited with titanium dioxide to the titanium dioxide fiber coated with a polypyrrole layer is (1-3):1.

[0012] In one or more embodiments of the present invention, the nitrogen-doped carbon fiber composited with titanium dioxide is prepared as follows:

[0013] Polyacrylonitrile and titanium dioxide are dispersed in a solvent, subjected to electrostatic spinning and drying to obtain polyacrylonitrile fibers;

[0014] In a nitrogen atmosphere, the polyacrylonitrile fiber was calcined at 800° C.-820° C. for 2 h-3 h.

[0015] In one or more embodiments of the present invention, the mass ratio of polyacrylonitrile to titanium dioxide is (10-15):1.

[0016] In one or more embodiments of the present invention, the titanium dioxide fiber coated with the polypyrrole layer is prepared as follows:

[0017] The porous titanium dioxide fiber and the first pyrrole monomer are mixed at a mass ratio of 1:(3-5), ultrasonically dispersed for 30 min-60 min, and the titanium dioxide fiber is taken out;

[0018] The titanium dioxide fiber is dispersed in water, and the second pyrrole monomer and the initiator are added, and the mixture is stirred and reacted for 8 hours to 10 hours. The mixture is then filtered, washed, and dried to obtain the titanium dioxide fiber coated with the polypyrrole layer.

[0019] In one or more embodiments of the present invention, the porous titanium dioxide fiber is prepared as follows:

[0020] Tetrabutyl titanate, polyvinyl pyrrolidone and solvent are mixed at a mass ratio of 10:(1-2):(18-25) to prepare a spinning solution, and the precursor fiber is prepared by electrospinning.

[0021] The precursor fiber is calcined and cooled to obtain porous titanium dioxide fiber.

[0022] In one or more embodiments of the present invention, the calcination temperature is 500° C.-600° C. and the time is 2-3 hours.

[0023] In one or more embodiments of the present invention, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

[0024] In one or more embodiments of the present invention, the binder is polyvinylidene fluoride; and / or the solvent is N-methylpyrrolidone.

[0025] Another specific embodiment of the present invention provides a technical solution as follows:

[0026] A method for preparing a low-temperature resistant lithium iron phosphate positive electrode material comprises taking various raw material components according to a proportion, mixing them evenly, and obtaining the low-temperature resistant lithium iron phosphate positive electrode material.

[0027] Compared with the existing technology, the present invention improves the low-temperature resistance of the positive electrode material by combining nitrogen-doped carbon fibers composited with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer. It maintains high electrochemical performance at lower temperatures such as -20°C and -30°C, allowing the battery to be used normally at low temperatures. DETAILED DESCRIPTION

[0028] To help those skilled in the art better understand the technical solutions of the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0029] The present invention provides a low-temperature resistant lithium iron phosphate positive electrode material in a specific embodiment, comprising the following raw material components by weight: 90-120 parts of lithium iron phosphate active material, 10-15 parts of conductive agent, 8-12 parts of binder, 5-8 parts of additive and 60-70 parts of solvent; the lithium iron phosphate active material is lithium iron phosphate with a carbon layer coated on the surface, and the lithium iron phosphate active material is doped with at least one metal element selected from aluminum, magnesium, chromium, vanadium and cobalt; the additives include nitrogen-doped carbon fibers composited with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer; wherein the titanium dioxide fibers coated with the polypyrrole layer are obtained by first loading a first pyrrole monomer on a porous titanium dioxide fiber and then polymerizing it with a second pyrrole monomer.

[0030] Specifically, carbon coating of lithium iron phosphate helps improve the conductivity of the cathode material and improves cycling performance. It also enhances the ion transport efficiency of the cathode material, thereby improving its electrochemical performance at low temperatures. Furthermore, doping with aluminum, magnesium, chromium, vanadium, or cobalt can further enhance lithium ion transport efficiency, further improving the cathode material's low-temperature resistance.

[0031] The additive used in the present invention, titanium dioxide is added to carbon fiber, it is possible to improve the structural stability of carbon fiber in a low temperature environment, thereby maintaining the structural stability of the positive electrode material at low temperatures, nitrogen doping can improve the electronic conductivity of carbon fiber, and contribute to improving the low temperature resistance of carbon fiber. The pores possessed by porous titanium dioxide fiber can provide a transmission path for lithium ions, and the low temperature resistance of porous titanium dioxide fiber is excellent, and the structural stability is high. By first loading the first pyrrole monomer in porous titanium dioxide fiber, then forming polypyrrole through polymerization, so that the pores of porous titanium dioxide fiber and the surface load have a polypyrrole layer, thereby strengthening the conductive properties of porous titanium dioxide fiber.

[0032] Nitrogen-doped carbon fibers composited with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer are used in combination. The two are overlapped to form a network structure in the positive electrode material, which effectively improves the low-temperature resistance of the positive electrode material and improves the conductivity, thereby improving the electrochemical performance of the battery in a low-temperature environment.

[0033] Furthermore, the mass ratio of the nitrogen-doped carbon fiber composited with titanium dioxide to the titanium dioxide fiber coated with the polypyrrole layer is (1-3):1.

[0034] Specifically, by controlling the dosage, the nitrogen-doped carbon fibers composited with titanium dioxide and the titanium dioxide fibers coated with a polypyrrole layer can better improve the electrochemical performance of the battery in a low-temperature environment.

[0035] Furthermore, nitrogen-doped carbon fibers composited with titanium dioxide were prepared as follows:

[0036] Polyacrylonitrile and titanium dioxide are dispersed in a solvent at a mass ratio of (10-15):1, and then subjected to electrostatic spinning and drying to obtain polyacrylonitrile fibers;

[0037] In a nitrogen atmosphere, the polyacrylonitrile fiber was calcined at 800° C.-820° C. for 2 h-3 h.

[0038] Specifically, the above method can be used to prepare carbon fibers with a porous structure, which helps to improve the transmission efficiency of lithium ions, thereby improving the electrochemical performance of the battery.

[0039] Furthermore, titanium dioxide fibers coated with a polypyrrole layer were prepared as follows:

[0040] The porous titanium dioxide fiber and the first pyrrole monomer are mixed at a mass ratio of 1:(3-5), ultrasonically dispersed for 30 min-60 min, and the titanium dioxide fiber is taken out;

[0041] The titanium dioxide fiber is dispersed in water, and the second pyrrole monomer and the initiator are added, and the mixture is stirred and reacted for 8 hours to 10 hours. The mixture is then filtered, washed, and dried to obtain the titanium dioxide fiber coated with the polypyrrole layer.

[0042] Specifically, by adopting the above method, the polypyrrole layer can be loaded on the pores and surface of the porous titanium dioxide fiber, so that the conductivity of the porous titanium dioxide fiber is effectively improved, and the stability of the polypyrrole layer loaded on the porous titanium dioxide fiber is ensured, so that the porous titanium dioxide fiber can continue to exhibit low temperature resistance and high conductivity.

[0043] Furthermore, the porous titanium dioxide fiber is prepared as follows:

[0044] Tetrabutyl titanate, polyvinyl pyrrolidone and solvent are mixed at a mass ratio of 10:(1-2):(18-25) to prepare a spinning solution, and the precursor fiber is prepared by electrospinning.

[0045] The precursor fiber is calcined at 500° C.-600° C. for 2-3 hours and cooled to obtain porous titanium dioxide fiber.

[0046] Furthermore, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fibers. Using the above conductive agents can ensure that the positive electrode material has beneficial conductive properties.

[0047] Furthermore, the binder is polyvinylidene fluoride and the solvent is N-methylpyrrolidone.

[0048] Another specific embodiment of the present invention provides a method for preparing a low-temperature resistant lithium iron phosphate positive electrode material, wherein the raw material components are taken according to a ratio and mixed evenly to obtain the low-temperature resistant lithium iron phosphate positive electrode material.

[0049] The present invention is further described in detail below with reference to specific embodiments.

[0050] Preparation Example 1

[0051] Polyacrylonitrile and titanium dioxide with a mass ratio of 10:1 and a titanium dioxide particle size of 15-20 nm were dispersed in DMF (N,N-dimethylformamide) using 15 mL of DMF per 1 g of polyacrylonitrile. The mixture was magnetically stirred at 500 rpm for 15 hours to obtain a dispersion. The dispersion was spun using an electrospinning apparatus with a spinning voltage of 16.2 kV, a syringe pump flow rate of 0.9 mL / h, and a receiving distance of 15 cm. The resulting fiber membrane was cut into 3*3 cm pieces and calcined at 810°C for 2 hours under a nitrogen atmosphere to obtain nitrogen-doped carbon fibers composited with titanium dioxide with a diameter of 300-400 nm.

[0052] Preparation Example 2

[0053] Polyacrylonitrile and titanium dioxide (15-20 nm in particle size) were dispersed in DMF (N,N-dimethylformamide) at a mass ratio of 15:1. The mixture was stirred magnetically at 500 rpm for 15 hours to obtain a dispersion. The dispersion was then electrospun using an electrospinning apparatus with a spinning voltage of 16.2 kV, a syringe pump flow rate of 0.9 mL / h, and a receiving distance of 15 cm. The resulting fiber membrane was cut into 3 x 3 cm pieces and calcined at 800°C for 2 hours under a nitrogen atmosphere to obtain nitrogen-doped carbon fibers composited with titanium dioxide, with a diameter of 300-400 nm.

[0054] Preparation Example 3

[0055] Tetrabutyl titanate, polyvinyl pyrrolidone, and acetone were mixed in a mass ratio of 10:1:18 and magnetically stirred at 500 rpm for 10 hours to obtain a dispersion. The dispersion was then spun at a spinning voltage of 16.2 kV, a syringe pump flow rate of 0.5 mL / h, and a fixed receiving distance of 24 cm. The resulting fibers were then calcined at 550°C for 3 hours and cooled to produce porous titanium dioxide fibers with a diameter of 300-350 nm.

[0056] Porous titanium dioxide fibers and pyrrole monomers were mixed in a mass ratio of 1:3, ultrasonically dispersed for 40 minutes, and the fibers were removed to obtain a titanium dioxide fiber precursor. The titanium dioxide fiber precursor was dispersed in water using 100 mL of water per 1 gram of titanium dioxide fiber precursor. Pyrrole monomer was then added to the water at a mass ratio of 1:5. A 0.2 mol / L FeCl2·6H2O aqueous solution was then added dropwise, with a mass ratio of 1:2 between the titanium dioxide fiber precursor and FeCl2·6H2O. The mixture was stirred at 300 rpm for 12 hours, then centrifuged for washing and dried at 50°C for 10 hours to obtain titanium dioxide fibers coated with a polypyrrole layer.

[0057] Preparation Example 4

[0058] Tetrabutyl titanate, polyvinyl pyrrolidone, and acetone were mixed in a mass ratio of 10:2:25 and magnetically stirred at 500 rpm for 10 hours to obtain a dispersion. The dispersion was then spun at a spinning voltage of 16.2 kV, a syringe pump flow rate of 0.5 mL / h, and a fixed receiving distance of 24 cm. The resulting fibers were then calcined at 550°C for 3 hours and cooled to produce porous titanium dioxide fibers with a diameter of 300-350 nm.

[0059] Porous titanium dioxide fibers and pyrrole monomers were mixed in a mass ratio of 1:5, ultrasonically dispersed for 60 minutes, and the fibers were removed to obtain a titanium dioxide fiber precursor. The titanium dioxide fiber precursor was dispersed in water using 100 mL of water per 1 g of titanium dioxide fiber precursor. Pyrrole monomer was then added to the water at a mass ratio of 1:5. A 0.2 mol / L FeCl2·6H2O aqueous solution was then added dropwise, with a mass ratio of 1:2 between the titanium dioxide fiber precursor and FeCl2·6H2O. The mixture was stirred at 300 rpm for 12 hours, then centrifuged for washing and dried at 50°C for 10 hours to obtain titanium dioxide fibers coated with a polypyrrole layer.

[0060] Preparation Example 5

[0061] Lithium carbonate, ferric nitrate and ammonium dihydrogen phosphate in a molar ratio of 1:1:1 were added to a nitric acid solution, and citric acid in a molar ratio of 1:1 to ferric nitrate was added to adjust the pH of the solution to 3 to obtain solution A.

[0062] Ammonium metavanadate and cobalt nitrate (0.5% of the total molar amount of lithium carbonate, ferric nitrate, and ammonium dihydrogen phosphate, with a molar ratio of ammonium metavanadate to cobalt nitrate of 2:1) were added to water. Glucose was then added at a mass of 30% of the total mass of lithium carbonate, ferric nitrate, and ammonium dihydrogen phosphate, and mixed to obtain solution B. The volume ratio of solution B to solution A was 1:3.

[0063] Solution A was heated to 75°C, solution B was added to solution A and heating was stopped. Solution A and solution B reacted and released heat to evaporate the mixed solution to dryness to obtain a precursor. The precursor was vacuum dried at 150°C for 12 hours and ball-milled for later use.

[0064] Under a nitrogen atmosphere, the precursor was sintered at 500°C for 4 hours, then heated to 700°C, and an ethanol aqueous solution with a mass concentration of 80% was introduced at the same time. The amount of ethanol aqueous solution was calculated as 200 mL for 1 kg of precursor. The precursor was sintered for 8 hours and cooled to obtain lithium iron phosphate active material.

[0065] Example 1

[0066] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3 in a mass ratio of 1:1.

[0067] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0068] Example 2

[0069] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 110 parts of lithium iron phosphate active material, 15 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, 6 parts of additives and 65 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3 in a mass ratio of 1:1.

[0070] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0071] Example 3

[0072] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 120 parts of lithium iron phosphate active material, 10 parts of conductive carbon black, 12 parts of polyvinylidene fluoride, 8 parts of additives and 70 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3 in a mass ratio of 1:1.

[0073] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0074] Example 4

[0075] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3 in a mass ratio of 2:1.

[0076] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0077] Example 5

[0078] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3 in a mass ratio of 3:1.

[0079] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0080] Example 6

[0081] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additives include the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 2 and the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 4 in a mass ratio of 1:1.

[0082] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0083] Comparative Example 1

[0084] A low-temperature resistant lithium iron phosphate positive electrode material comprises, by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride and 60 parts of N-methylpyrrolidone.

[0085] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0086] Comparative Example 2

[0087] A low-temperature resistant lithium iron phosphate positive electrode material comprises, by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additive is the nitrogen-doped carbon fiber composited with titanium dioxide in Preparation Example 1.

[0088] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0089] Comparative Example 3

[0090] A low-temperature resistant lithium iron phosphate positive electrode material comprises, by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additive is the titanium dioxide fiber coated with a polypyrrole layer in Preparation Example 3.

[0091] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0092] Comparative Example 4

[0093] Tetrabutyl titanate, polyvinyl pyrrolidone, and acetone were mixed in a mass ratio of 10:2:25 and magnetically stirred at 500 rpm for 10 hours to obtain a dispersion. The dispersion was then spun at a spinning voltage of 16.2 kV, a syringe pump flow rate of 0.5 mL / h, and a fixed receiving distance of 24 cm. The resulting fibers were then calcined at 550°C for 3 hours and cooled to produce porous titanium dioxide fibers with a diameter of 300-350 nm.

[0094] Based on 100 mL of water per 1 g of porous titanium dioxide fiber, the porous titanium dioxide fiber was dispersed in water, and then pyrrole monomer was added to the water at a mass ratio of 1:5. Then, a 0.2 mol / L FeCl2·6H2O aqueous solution was added dropwise, and the mass ratio of porous titanium dioxide fiber to FeCl2·6H2O was 1:2. The mixture was stirred at 300 rpm for 12 h, then centrifuged and washed, and dried at 50°C for 10 h to obtain titanium dioxide fiber coated with a polypyrrole layer.

[0095] A low-temperature resistant lithium iron phosphate positive electrode material comprises, in parts by weight, 90 parts of lithium iron phosphate active material, 12 parts of conductive carbon black, 8 parts of polyvinylidene fluoride, 5 parts of additives and 60 parts of N-methylpyrrolidone, wherein the additives comprise nitrogen-doped carbon fibers composited with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer in Preparation Example 1 in a mass ratio of 1:1.

[0096] The above raw materials are mixed evenly to obtain a low-temperature resistant lithium iron phosphate positive electrode material.

[0097] Performance Testing

[0098] The low-temperature-resistant lithium iron phosphate cathode material was coated on aluminum foil and dried in an 80°C oven to produce a positive electrode sheet. The positive electrode sheet was assembled into a button battery with an electrolyte of 1 mol / L LiPF6 (EC:DMC=1:1) and a lithium sheet as the negative electrode.

[0099] The battery was charged with a current of 0.5C at room temperature. After 5 minutes, it was discharged to 2.5V with 0.2C, and the capacity was recorded and recorded as capacity 1. After the battery was charged with 0.5C again, the battery was placed at -20℃ and -30℃ respectively, and discharged with a current of 0.2C. The capacity at -20℃ was recorded as capacity 2, and the capacity at -30℃ was recorded as capacity 3. The capacity retention rate of the battery at -20℃ was capacity 2 / capacity 1×100%, and the capacity retention rate of the battery at -30℃ was capacity 3 / capacity 1×100%.

[0100] Table 1 Electrochemical test results

[0101] Group -20℃ / 0.2C low temperature discharge capacity retention rate / % -30℃ / 0.2C low temperature discharge capacity retention rate / % Example 1 88.2 83.4 Example 2 88.7 83.6 Example 3 89.0 84.2 Example 4 88.3 83.5 Example 5 88.5 83.7 Example 6 88.1 83.2 Comparative Example 1 71.4 65.3 Comparative Example 2 73.8 67.9 Comparative Example 3 73.5 67.7 Comparative Example 4 74.2 68.2

[0102] As can be seen from Table 1, compared with Comparative Examples 1-3, the present invention combines nitrogen-doped carbon fibers composited with titanium dioxide with titanium dioxide fibers coated with a polypyrrole layer to significantly improve the electrochemical performance of the battery at low temperatures. Combined with Comparative Example 4, it can be seen that first loading pyrrole monomers onto porous titanium dioxide fibers and then forming a polypyrrole layer through polymerization can further improve the low-temperature resistance and electrochemical performance of the battery.

[0103] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0104] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A low-temperature resistant lithium iron phosphate positive electrode material, characterized in that: The invention comprises the following raw material components in parts by weight: 90-120 parts of lithium iron phosphate active material, 10-15 parts of conductive agent, 8-12 parts of binder, 5-8 parts of additive and 60-70 parts of solvent; The lithium iron phosphate active material is lithium iron phosphate with a carbon layer coated on the surface, and the lithium iron phosphate active material is doped with at least one metal element selected from aluminum, magnesium, chromium, vanadium, and cobalt; The additives include nitrogen-doped carbon fibers compounded with titanium dioxide and titanium dioxide fibers coated with a polypyrrole layer; The titanium dioxide fiber coated with the polypyrrole layer is obtained by first loading a first pyrrole monomer on the porous titanium dioxide fiber and then polymerizing the first pyrrole monomer with the second pyrrole monomer.

2. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 1, characterized in that The mass ratio of the nitrogen-doped carbon fiber composited with titanium dioxide to the titanium dioxide fiber coated with a polypyrrole layer is (1-3):

1.

3. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 1, characterized in that The nitrogen-doped carbon fiber composited with titanium dioxide is prepared as follows: Polyacrylonitrile and titanium dioxide are dispersed in a solvent, subjected to electrostatic spinning and drying to obtain polyacrylonitrile fibers; In a nitrogen atmosphere, the polyacrylonitrile fiber was calcined at 800° C.-820° C. for 2 h-3 h.

4. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 3, characterized in that The mass ratio of the polyacrylonitrile to titanium dioxide is (10-15):

1.

5. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 1, characterized in that The titanium dioxide fiber coated with the polypyrrole layer is prepared as follows: The porous titanium dioxide fiber and the first pyrrole monomer are mixed at a mass ratio of 1:(3-5), ultrasonically dispersed for 30 min-60 min, and the titanium dioxide fiber is taken out; The titanium dioxide fiber is dispersed in water, and the second pyrrole monomer and the initiator are added, and the mixture is stirred and reacted for 8 hours to 10 hours. The mixture is then filtered, washed, and dried to obtain the titanium dioxide fiber coated with the polypyrrole layer.

6. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 5, characterized in that The porous titanium dioxide fiber is prepared as follows: Tetrabutyl titanate, polyvinyl pyrrolidone and solvent are mixed at a mass ratio of 10:(1-2):(18-25) to prepare a spinning solution, and the precursor fiber is prepared by electrospinning. The precursor fiber is calcined and cooled to obtain porous titanium dioxide fiber.

7. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 6, characterized in that The calcination temperature is 500-600° C. and the time is 2-3 hours.

8. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 1, characterized in that The conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon fibers.

9. The low-temperature resistant lithium iron phosphate positive electrode material according to claim 1, characterized in that The binder is polyvinylidene fluoride; and / or the solvent is N-methylpyrrolidone.

10. The method for preparing the low-temperature resistant lithium iron phosphate positive electrode material according to any one of claims 1 to 9, characterized in that: The raw material components are taken according to the proportion and mixed evenly to obtain the low-temperature resistant lithium iron phosphate positive electrode material.