Armored vehicle low-temperature sodium ion battery positive electrode material and preparation method thereof

Abstract

The application discloses an armored vehicle low-temperature sodium ion battery positive electrode material and a preparation method thereof, and particularly relates to the technical field of electrochemistry, and relates to an armored vehicle low-temperature sodium ion battery positive electrode material and a preparation method thereof; the armored vehicle low-temperature sodium ion battery positive electrode material is prepared from ferric chloride hexahydrate, manganese chloride tetrahydrate, sodium ferrocyanide and carboxylated multi-walled carbon nanotubes through co-precipitation synthesis and dehydration, phosphating hydrothermal reaction, carbon nanotube winding and thermal reduction, and surface polymer coating; the manganese iron-based prussian white with an open three-dimensional ion channel is used as an active framework, the intrinsic electronic structure is optimized by using manganese doping, and the content of crystallization water hindering ion migration is effectively controlled by using an accurate low-temperature dehydration process in the synthesis, so that the sodium ion diffusion capacity and charge transfer efficiency of the material in a low-temperature environment are improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical technology, and more specifically, to a low-temperature sodium-ion battery cathode material for armored vehicles and its preparation method. Background Technology

[0002] With the development of modern military technology, armored vehicles have extremely high requirements for energy storage power sources, which must meet the characteristics of low-temperature start-up, high-power fast charging and discharging, high safety, and long cycle life. An ideal vehicle power source must work reliably in extreme environments and be able to withstand high-power pulse discharge and fast charging. Sodium-ion batteries are considered a promising alternative for military special power sources due to their abundant resources, low cost, intrinsic safety, and wide temperature range potential. Therefore, developing a sodium-ion battery cathode material is of great significance for improving armored vehicles.

[0003] Battery cathode materials in related technologies include layered transition metal oxides, polyanionic compounds, and Prussian blue analogues. Among them, layered transition metal oxides have a transition metal as their core component, forming a charge-compensating redox center that directly contributes to capacity. Their layered structure provides a two-dimensional channel for reversible insertion and extraction of sodium ions, determining the material's theoretical specific capacity and voltage plateau. The framework of polyanionic compounds consists of transition metals and polyanionic groups. The polyanionic groups can improve the working voltage and stabilize the crystal framework through a strong inductive effect, while the transition metal provides redox activity. Together, they achieve high voltage stability and thermal safety of the material. The basic building block of Prussian blue analogues is an open three-dimensional framework formed by transition metals and cyanide ligands, providing spacious ion migration channels, which is beneficial for rapid charge and discharge.

[0004] However, in practical applications, it still has some drawbacks, such as low low-temperature conductivity. Traditional layered oxides shrink between layers at low temperatures, significantly increasing the sodium ion diffusion barrier and leading to a substantial decrease in capacity and power. Although polyanionic compounds have stable structures, their electronic conductivity is generally low, making it difficult to meet high power requirements. The cycle life is short. Prussian blue materials prepared by traditional methods are difficult to precisely control vacancy defects and water of crystallization content, which damages structural integrity, hinders ion transport, and triggers side reactions, resulting in short cycle life and low coulombic efficiency. The electron transport efficiency is low. Traditional methods cannot build a stable and continuous conductive network on the surface of active particles, limiting the improvement in electron transport efficiency. Summary of the Invention

[0005] To improve the above-mentioned problems and reduce the issues of low low-temperature conductivity, short cycle life, and low electron transport efficiency of battery cathode materials in related technologies, this invention provides a low-temperature sodium-ion battery cathode material for armored vehicles and its preparation method, in order to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A low-temperature sodium-ion battery cathode material for armored vehicles and its preparation method thereof, comprising the following steps: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at a temperature of 50-70℃ and a pH of 3±0.2 for 8-24 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. Disperse the precursor powder obtained in S1 in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. Then transfer the suspension to a hydrothermal reactor and react at 100-140℃ for 4-12 hours. After the reaction is completed, cool naturally, collect the solid product by centrifugation, wash it three times with deionized water, and then dry it under vacuum at 80℃ for 12 hours to obtain the core-shell structure powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated to dryness by stirring in a water bath at 60℃. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 300-500℃ at a heating rate of 2-10℃ / min under a mixed atmosphere of argon and hydrogen, and held for 1-4 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 250-400℃ at a heating rate of 2-8℃ / min under the protection of flowing argon gas. It is then kept at a constant temperature for 2-6 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0007] Preferably, the cathode material for the low-temperature sodium-ion battery of the armored vehicle is prepared by co-precipitation synthesis and dehydration of ferric chloride hexahydrate, manganese chloride tetrahydrate, sodium ferrocyanide, and carboxylated multi-walled carbon nanotubes, followed by hydrothermal phosphating, carbon nanotube winding and thermal reduction, and surface polymer coating. The raw materials for preparation include: 33.3-41.1 parts of ferric chloride hexahydrate, 10.2-17.9 parts of manganese chloride tetrahydrate, 78.8 parts of sodium ferrocyanide, and 3-10 parts of carboxylated multi-walled carbon nanotubes.

[0008] Preferably, the total metal ion concentration of phase A is 0.1 mol / L.

[0009] Preferably, the concentration of phase B is 0.1 mol / L.

[0010] Preferably, the deionized aqueous solution is an aqueous solution containing 1 wt% sodium citrate and 0.5 wt% polyvinylpyrrolidone complexing agent.

[0011] Preferably, the concentration of the ammonium dihydrogen phosphate aqueous solution is 0.1 mol / L.

[0012] Preferably, the solid content of the suspension is 5 wt%.

[0013] Preferably, the composite solution is an aqueous solution containing 1 wt% graphene oxide quantum dots.

[0014] Preferably, the polymer solution is a 3wt% polyvinylidene fluoride-hexafluoropropylene copolymer solution, and the solvent is a mixture of N-methylpyrrolidone and acetone in a volume ratio of 1:1.

[0015] 1. This invention uses manganese-iron-based Prussian white with open three-dimensional ion channels as the active framework and optimizes its intrinsic electronic structure by manganese doping. At the same time, a precise low-temperature dehydration process is used in the synthesis to effectively control the content of crystal water that hinders ion migration, thereby improving the sodium ion diffusion ability and charge transfer efficiency of the material in a low-temperature environment. 2. This invention constructs a dense interface passivation layer in situ on the surface of active particles through hydrothermal phosphating, and then coats it with a flexible polymer corrosion inhibitor layer using spray drying technology. At the same time, it uses a three-dimensional carbon network to buffer the volume strain during the cycling process, thereby suppressing the side reactions of the electrolyte and the gradual damage to the material structure during long-term cycling, and improving the cycle life. 3. This invention constructs a three-dimensional interconnected conductive network on the surface of a material by chemically bonding carboxylated carbon nanotubes and graphene quantum dots. Through solvothermal and thermal reduction processes, the intrinsic insulating properties of the particles are transformed into excellent electronic conductors of the overall composite material, thereby improving its electron transport efficiency. Detailed Implementation

[0016] The present invention will be further described in detail below with reference to the embodiments of the present invention. Unless otherwise specified below, the raw materials used in the various examples and embodiments of the present invention are all commercially available common materials. Preparation Examples 1-5 A low-temperature sodium-ion battery cathode material for armored vehicles, the composition and corresponding proportions of which are shown in the table below, is prepared using the following method: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. The total metal ion concentration in phase A is 0.1 mol / L; The concentration of phase B is 0.1 mol / L; The deionized water solution is an aqueous solution containing 1 wt% sodium citrate and 0.5 wt% polyvinylpyrrolidone complexing agent; S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. The concentration of the ammonium dihydrogen phosphate aqueous solution was 0.1 mol / L; The solid content of the suspension is 5 wt%; S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. The composite solution is an aqueous solution containing 1 wt% graphene oxide quantum dots; S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. The polymer solution is a 3 wt% polyvinylidene fluoride-hexafluoropropylene copolymer solution, and its solvent is a mixture of N-methylpyrrolidone and acetone in a volume ratio of 1:1. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0017] Table: Components and their mass ratios (g) of the raw materials used in Preparation Examples 1-5 Preparation Example 6 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 50℃ and pH 3±0.2 for 8 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0018] Preparation Example 7 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 70℃ and pH 3±0.2 for 24 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0019] Preparation Example 8 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 100°C for 4 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0020] Preparation Example 9 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 140°C for 12 hours. After the reaction is completed, the mixture is naturally cooled, the solid product is collected by centrifugation, and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0021] Preparation Example 10 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 300℃ at a heating rate of 2℃ / min under a mixed atmosphere of argon and hydrogen, and held for 1 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0022] Preparation Example 11 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 400℃ at a heating rate of 6℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 350°C at a heating rate of 3°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 3 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0023] Preparation Example 12 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 250°C at a heating rate of 2°C / min under the protection of flowing argon gas. It is then kept at the same temperature for 2 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0024] Preparation Example 13 A low-temperature sodium-ion battery cathode material for armored vehicles differs from Preparation Example 1 in that its preparation method is as follows: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at 55℃ and pH 3±0.2 for 12 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. The precursor powder obtained in S1 is dispersed in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. The suspension is then transferred to a hydrothermal reactor and reacted at 120°C for 6 hours. After the reaction is completed, the mixture is naturally cooled, and the solid product is collected by centrifugation and washed three times with deionized water. Then, it is dried under vacuum at 80°C for 12 hours to obtain a core-shell structured powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated by stirring in a water bath at 60℃ until dry. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 500℃ at a heating rate of 5℃ / min under a mixed atmosphere of argon and hydrogen, and held for 2 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 400°C at a heating rate of 8°C / min under the protection of flowing argon gas. It is then kept at a constant temperature for 6 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

[0025] Performance testing The low-temperature sodium-ion battery cathode materials for armored vehicles prepared in each embodiment were selected for testing. The test subjects were 130 samples of the low-temperature sodium-ion battery cathode materials for armored vehicles, with 10 samples in each group. Their low-temperature conductivity, cycle life, and electron transport efficiency were tested. The specific testing steps are as follows: Low-temperature conductivity: First, samples were taken from the low-temperature sodium-ion battery cathode material for armored vehicles prepared in the examples. The apparent diffusion coefficient of sodium ions in the battery at -40℃ was measured using constant current intermittent titration technology to characterize the low-temperature conductivity of the cathode material for armored vehicles. The test results and evaluation criteria are as follows: Sodium ion apparent diffusion coefficient > (Considered as having high conductivity at low temperatures); Sodium ion apparent diffusion coefficient < (Considered as low conductivity at low temperatures).

[0026] Cycle life: First, samples of the low-temperature sodium-ion battery cathode material for armored vehicles prepared in the examples were taken. At a constant temperature of 25°C, 1000 constant-current charge-discharge cycles were performed on coin cells at a relatively high rate of 2C. The capacity retention rate was then calculated to characterize the cycle life of the low-temperature sodium-ion battery cathode material for armored vehicles. The test results and evaluation criteria are as follows: Capacity retention > 85.0% (considered strong cycle life); Capacity retention rate <85.0% (considered as poor cycle life).

[0027] Electron transport efficiency: First, samples of the low-temperature sodium-ion battery cathode material for armored vehicles prepared in the examples were taken. The cathode material powder was pressed into a dense thin sheet under high pressure using the four-probe method, and its room temperature electronic conductivity was measured. This was used to characterize the electron transport efficiency of the low-temperature sodium-ion battery cathode material for armored vehicles. The test results and evaluation criteria are as follows: Electron conductivity > (Considered as having high electron transmission efficiency); Electron conductivity < (This is considered to be due to weak electron transmission efficiency).

[0028] It should be specifically noted that the above-mentioned low-temperature sodium-ion battery positive electrode material for armored vehicles is produced in accordance with normal production methods. Any defective low-temperature sodium-ion battery positive electrode material produced is discarded.

[0029] Examples 1-5 The corresponding relationship of the preparation methods of a low-temperature sodium-ion battery cathode material for armored vehicles is shown in the table below.

[0030] Table: Comparison of Cathode Materials Used in Low-Temperature Sodium-Ion Batteries for Armored Vehicles in Examples 1-5 The cathode materials of the low-temperature sodium-ion battery for armored vehicles in Examples 1-5 above were extracted, and their apparent diffusion coefficient of sodium ions, capacity retention rate and electronic conductivity were tested according to the above measurement steps and measurement standards. The average value of the test results was recorded in the table below.

[0031] Table: Performance test results of apparent diffusion coefficient, capacity retention and electronic conductivity of sodium ions in Examples 1-5 As can be seen from the table above, the preparation processes of the low-temperature sodium-ion battery cathode materials for armored vehicles in Examples 1-5 all effectively improve the production efficiency of the cathode materials. Ferric chloride hexahydrate and manganese chloride tetrahydrate, acting as transition metal sources, coordinate with the ferrocyanide groups provided by sodium ferrocyanide through a co-precipitation reaction, constructing a manganese-iron-based Prussian white crystal framework with open three-dimensional channels. This framework is the basis for sodium storage activity, providing a foundation for the rapid insertion and extraction of sodium ions, especially for diffusion at low temperatures. Sodium citrate and... Polyvinylpyrrolidone (PVP) was used as a bifunctional complexing agent and morphology modifier. Sodium citrate controlled nucleation and growth rates by chelating metal ions, while PVP adsorbed onto the crystal nucleus surface to inhibit excessive growth and aggregation. The synergistic effect of both resulted in precursor particles with uniform size and good dispersibility, laying the morphological foundation for subsequent uniform interface modification and coating. An ammonium dihydrogen phosphate aqueous solution was used to generate an amorphous phosphate interface layer on the surface of Prussian white particles through a hydrothermal reaction. This effectively isolated the active material from direct contact with the electrolyte, significantly inhibiting... This study aims to mitigate the dissolution of transition metals, interfacial side reactions, and gradual destruction of crystal structures during cycling. Carboxylated multi-walled carbon nanotubes (MWCNTs) and graphene oxide quantum dots (BODs) jointly construct a hierarchical three-dimensional conductive network. MWCNTs, with their high aspect ratio and one-dimensional conductivity, establish high-speed pathways for long-range electron transport between particles. BODs, with their small size, high specific surface area, and abundant functional groups, not only form strong chemical bonds with carbon nanotubes and particle surfaces after thermal reduction, enhancing network robustness, but their excellent conductivity also strengthens network nodes like welding points. A solution of vinylidene fluoride hexafluoropropylene copolymer, dissolved in a mixed solvent of N-methylpyrrolidone and acetone, is spray-dried to form a continuous, flexible, and electrochemically stable polymer film on the outermost layer of the material. This further consolidates interfacial stability and buffers volume changes during charge and discharge. Working synergistically with the inner phosphate interface and the three-dimensional conductive network, it ensures the structural integrity of the material under extreme low temperatures and long-term cycling conditions. This achieves the goal of improving the production efficiency of low-temperature sodium-ion battery cathode materials for armored vehicles. Its apparent diffusion coefficient of sodium ions is It is considered to have high low-temperature conductivity; its capacity retention is 88.2-95.4%, which is considered to indicate high cycle life; and its electronic conductivity is... This is considered to be due to high electron transmission efficiency; It is evident that, given a fixed amount of raw materials, the production efficiency of the cathode material for low-temperature sodium-ion batteries used in armored vehicles can be increased by adjusting the proportions of these materials. Based on the data in the table above, it is clear that the cathode material prepared using 35.9 parts of ferric chloride hexahydrate, 15.3 parts of manganese chloride tetrahydrate, 78.8 parts of sodium ferrocyanide, and 8 parts of carboxylated multi-walled carbon nanotubes exhibits the strongest low-temperature conductivity. This is attributed to the higher manganese doping ratio, which effectively enhances the bonding strength and charge delocalization between the metal and cyanide groups within the Prussian white crystal framework, thereby improving the material's semiconductor properties and providing a superior intrinsic basis for charge transfer at low temperatures. Simultaneously, the significantly increased content of carboxylated multi-walled carbon nanotubes in this ratio constructs a denser and more interconnected three-dimensional continuous high-speed electron pathway within the material, greatly compensating for the interfacial electron conduction attenuation caused by low temperatures. This ensures that electrons can be efficiently transported to the active interface during electrochemical reactions, as shown in Examples 1-5.

[0032] It is evident that, given a fixed amount of raw materials, the production efficiency of the cathode material for low-temperature sodium-ion batteries used in armored vehicles can be increased by adjusting the proportions of these materials. Based on the data in the table above, it is clear that the cathode material prepared using 33.3 parts of ferric chloride hexahydrate, 17.9 parts of manganese chloride tetrahydrate, 78.8 parts of sodium ferrocyanide, and 10 parts of carboxylated multi-walled carbon nanotubes exhibits the strongest cycle life and electron transport efficiency. This is attributed to the higher manganese doping ratio, which enhances the covalent nature of the metal-nitrogen bonds within the crystal framework, significantly improving the material's structural stability. The material exhibits qualitative and phase transition resistance, effectively suppressing capacity decay during long-cycle cycling. Simultaneously, the highest proportion of carboxylated multi-walled carbon nanotubes forms an extremely dense and interconnected three-dimensional conductive framework in the composite material. This not only provides high-speed and redundant electron transport channels, significantly improving overall electronic conductivity, but also effectively buffers volume changes in the active material during repeated sodium ion insertion / extraction processes, maintaining the mechanical integrity of the electrode structure. This dual guarantee of internal stability and external conductivity enables the material to maintain extremely high capacity retention and interface stability during long-term cycling, thus exhibiting the strongest cycle life and electron transport efficiency, as obtained in Examples 1-5.

[0033] Examples 6-13 The corresponding relationship of the preparation methods of a low-temperature sodium-ion battery cathode material for armored vehicles is shown in the table below.

[0034] Table: Comparison of Cathode Materials Used in Low-Temperature Sodium-Ion Batteries for Armored Vehicles in Examples 6-13 The cathode materials of the low-temperature sodium-ion battery for armored vehicles in Examples 6-13 above were extracted, and their apparent diffusion coefficient of sodium ions, capacity retention rate and electronic conductivity were tested according to the above measurement steps and measurement standards. The average value of the test results was recorded in the table below.

[0035] Table: Performance test results of apparent diffusion coefficient, capacity retention and electronic conductivity of sodium ions in Examples 1 and 6-13 As can be seen from the table above, the preparation processes of the low-temperature sodium-ion battery cathode materials for armored vehicles in Examples 1-5 all effectively improve the production efficiency of the cathode materials. Ferric chloride hexahydrate and manganese chloride tetrahydrate, acting as transition metal sources, coordinate with the ferrocyanide groups provided by sodium ferrocyanide through a co-precipitation reaction, constructing a manganese-iron-based Prussian white crystal framework with open three-dimensional channels. This framework is the basis for sodium storage activity, providing a foundation for the rapid insertion and extraction of sodium ions, especially for diffusion at low temperatures. Sodium citrate and... Polyvinylpyrrolidone (PVP) was used as a bifunctional complexing agent and morphology modifier. Sodium citrate controlled nucleation and growth rates by chelating metal ions, while PVP adsorbed onto the crystal nucleus surface to inhibit excessive growth and aggregation. The synergistic effect of both resulted in precursor particles with uniform size and good dispersibility, laying the morphological foundation for subsequent uniform interface modification and coating. An ammonium dihydrogen phosphate aqueous solution was used to generate an amorphous phosphate interface layer on the surface of Prussian white particles through a hydrothermal reaction. This effectively isolated the active material from direct contact with the electrolyte, significantly inhibiting... This study aims to mitigate the dissolution of transition metals, interfacial side reactions, and gradual destruction of crystal structures during cycling. Carboxylated multi-walled carbon nanotubes (MWCNTs) and graphene oxide quantum dots (BODs) jointly construct a hierarchical three-dimensional conductive network. MWCNTs, with their high aspect ratio and one-dimensional conductivity, establish high-speed pathways for long-range electron transport between particles. BODs, with their small size, high specific surface area, and abundant functional groups, not only form strong chemical bonds with carbon nanotubes and particle surfaces after thermal reduction, enhancing network robustness, but their excellent conductivity also strengthens network nodes like welding points. A solution of vinylidene fluoride hexafluoropropylene copolymer, dissolved in a mixed solvent of N-methylpyrrolidone and acetone, is spray-dried to form a continuous, flexible, and electrochemically stable polymer film on the outermost layer of the material. This further consolidates interfacial stability and buffers volume changes during charge and discharge. Working synergistically with the inner phosphate interface and the three-dimensional conductive network, it ensures the structural integrity of the material under extreme low temperatures and long-term cycling conditions. This achieves the goal of improving the production efficiency of low-temperature sodium-ion battery cathode materials for armored vehicles. Its apparent diffusion coefficient of sodium ions is It is considered to have high low-temperature conductivity; its capacity retention is 90.9-91.7%, which is considered to indicate high cycle life; and its electronic conductivity is... This is considered to be due to high electron transmission efficiency; It is evident that, given a fixed amount of raw materials, the production efficiency of low-temperature sodium-ion battery cathode materials for armored vehicles can be increased by adjusting the preparation conditions. Based on the data in the table above, it is clear that when preparing low-temperature sodium-ion battery cathode materials for armored vehicles, increasing the temperature and duration of the co-precipitation reaction, the temperature and duration of the hydrothermal reaction, the heating rate and holding time of the thermal reduction process, and the heating rate, heat treatment temperature, and holding time of the final heat treatment process all contribute to an initial increase followed by a decrease in the low-temperature conductivity, cycle life, and electron transport efficiency of the prepared low-temperature sodium-ion battery cathode material. Specifically, when the co-precipitation reaction is carried out at 55℃ for 12 hours, the hydrothermal reaction is carried out at 120℃ for 6 hours, the thermal reduction process involves heating at a rate of 5℃ / min followed by holding for 2 hours, and the final heat treatment process involves heating at a rate of 3℃ / min to 350℃ and holding for 3 hours, the low-temperature conductivity of the prepared low-temperature sodium-ion battery cathode material for armored vehicles is significantly improved. The highest efficiency, cycle life, and electron transport efficiency were achieved. This was attributed to the fact that appropriately increasing the co-precipitation temperature and duration promoted the uniform growth and full crystallization of precursor nuclei, effectively controlling the concentration of crystal water and defects while obtaining suitable particle morphology, thus providing a structural basis for subsequent modification. Optimization of the temperature and time in the hydrothermal process ensured that the phosphate interface layer could be densely formed in situ without excessive thickening, achieving a balance between a stable core and ensuring ion permeability. The moderate heating rate and holding time in the thermal reduction process allowed the graphene oxide quantum dots to be fully reduced and form a stable chemical bond with the carbon nanotubes and particle surfaces, constructing a strong and highly conductive three-dimensional network, while avoiding damage to the carbon material structure caused by prolonged high-temperature treatment. The final heat treatment used a matched combination of heating rate and temperature duration, ensuring that the surface polymer layer was fully cured and cross-linked to exert its optimal buffering and protective effect, while avoiding excessive temperature leading to decomposition of the active framework or damage to the conductive network, as obtained in Examples 1 and 6-13.

[0036] It is evident that, given a fixed amount of raw materials, the production efficiency of low-temperature sodium-ion battery cathode materials for armored vehicles can be increased by adjusting the preparation conditions. Based on the data in the table above, it is clear that increasing the thermal reduction temperature enhances the low-temperature conductivity, cycle life, and electron transport efficiency of the prepared cathode material. Thermal reduction at 500℃ yields the most efficient cathode material in terms of low-temperature conductivity, cycle life, and electron transport efficiency. This is because at this temperature, the oxygen-containing functional groups on the surface of graphene oxide quantum dots are fully and completely removed, restoring their intrinsic conductivity to near that of pristine graphene. The high temperature promotes chemical bonding between carboxylated carbon nanotubes and reduced graphene quantum dots, as well as between them and the phosphating interface layer, forming a strong and highly interconnected three-dimensional conductive network. This network not only provides an extremely efficient electron transport highway, significantly improving electronic conductivity, but its mechanical stability also better buffers the volumetric strain during the cycling of active materials, directly contributing to the long cycle life. In addition, appropriate high-temperature treatment helps to eliminate residual internal stress in the composite material, promotes close contact between the core-shell interface and the carbon network, and reduces the interfacial charge transfer impedance. This allows sodium ions to be inserted and extracted more smoothly at various temperatures, including low temperatures, thereby simultaneously improving the low-temperature conductivity of the material, as obtained in Examples 1 and 6-13.

[0037] This specific embodiment is merely an explanation of the present invention and not a limitation thereof. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but as long as they are within the scope of the claims of the present invention, they are protected by patent law.

Claims

1. A low-temperature sodium-ion battery cathode material for armored vehicles, characterized in that, By weight, the cathode material for the low-temperature sodium-ion battery of the armored vehicle is prepared by co-precipitation synthesis and dehydration of ferric chloride hexahydrate, manganese chloride tetrahydrate, sodium ferrocyanide, and carboxylated multi-walled carbon nanotubes, followed by hydrothermal phosphating, carbon nanotube winding and thermal reduction, and surface polymer coating. The raw materials for its preparation include: Ferric chloride hexahydrate 33.3-41.1 parts, manganese chloride tetrahydrate 10.2-17.9 parts, sodium ferrocyanide 78.8 parts, and carboxylated multi-walled carbon nanotubes 3-10 parts.

2. The method for preparing the low-temperature sodium-ion battery cathode material for armored vehicles according to claim 1, characterized in that, The preparation process of the cathode material for the low-temperature sodium-ion battery used in armored vehicles includes the following steps: S1. Ferric chloride hexahydrate and manganese chloride tetrahydrate were dissolved together in deionized water to prepare phase A; then sodium ferrocyanide was dissolved in deionized water to prepare phase B; under nitrogen protection and stirring speed of 100 r / min, phase A and phase B were simultaneously and dripped into 100 ml of deionized water bottom solution through a dual-channel metering pump at a rate of 50 mL / h. The reaction was maintained at a temperature of 50-70℃ and a pH of 3±0.2 for 8-24 h, and then allowed to stand for 6 h. The resulting precipitate was then separated by centrifugation and washed three times each with deionized water and anhydrous ethanol. The washed wet filter cake was then transferred to a vacuum freeze dryer, pre-frozen at -50℃ for 4 h, and then dried under a vacuum of less than 10 Pa for 48 h to obtain precursor powder. S2. Disperse the precursor powder obtained in S1 in an aqueous solution of ammonium dihydrogen phosphate to form a suspension. Then transfer the suspension to a hydrothermal reactor and react at 100-140℃ for 4-12 hours. After the reaction is completed, cool naturally, collect the solid product by centrifugation, wash it three times with deionized water, and then dry it under vacuum at 80℃ for 12 hours to obtain the core-shell structure powder. S3. The core-shell structure powder obtained in S2 and carboxylated multi-walled carbon nanotubes were added to 3 times the volume of anhydrous ethanol. After ultrasonic dispersion for 30 min, the solvent was evaporated to dryness by stirring in a water bath at 60℃. The resulting composite material was then immersed in the composite solution and stirred for 2 h for adsorption. After centrifugation, the composite material was placed in a tube furnace and heated to 300-500℃ at a heating rate of 2-10℃ / min under a mixed atmosphere of argon and hydrogen, and held for 1-4 h to obtain the intermediate powder. S4. The intermediate powder obtained in S3 is slowly added to the polymer solution and stirred at 500 r / min to form a uniform slurry. The slurry is then granulated by spray drying, with the inlet temperature controlled at 120℃ and the outlet temperature at 70℃. The resulting microspheres are further dried under vacuum at 80℃ for 6 hours to obtain the composite material. S5. The composite material obtained in S4 is placed in an atmosphere furnace and heated to 250-400℃ at a heating rate of 2-8℃ / min under the protection of flowing argon gas. It is then kept at a constant temperature for 2-6 hours. After that, it is gently depolymerized by an air jet mill and finally sieved through a 400-mesh sieve to obtain the low-temperature sodium-ion battery cathode material for armored vehicles.

3. The method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The total metal ion concentration of phase A is 0.1 mol / L.

4. The method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The concentration of phase B is 0.1 mol / L.

5. The method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The deionized aqueous solution is an aqueous solution containing 1 wt% sodium citrate and 0.5 wt% polyvinylpyrrolidone complexing agent.

6. The low-temperature sodium-ion battery cathode material for armored vehicles according to claim 4, characterized in that: The concentration of the ammonium dihydrogen phosphate aqueous solution is 0.1 mol / L.

7. The method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The solid content of the suspension is 5 wt%.

8. The method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The composite solution is an aqueous solution containing 1 wt% graphene oxide quantum dots.

9. A method for preparing a low-temperature sodium-ion battery cathode material for armored vehicles according to claim 2, characterized in that: The polymer solution is a 3wt% polyvinylidene fluoride-hexafluoropropylene copolymer solution, and its solvent is a mixture of N-methylpyrrolidone and acetone in a volume ratio of 1:1.

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