Prussian blue composite positive electrode material for sodium ion battery

Abstract

The invention relates to the field of sodium ion battery positive electrode materials, and discloses a Prussian blue composite positive electrode material for a sodium ion battery. According to the sodium ion battery positive electrode material prepared by the invention, a Co-doped NaNi0. 4Fe0. 2Mn0. 4O2 material is taken as a core, a niobium-modified iron-based Prussian blue material is taken as a first shell layer, and polyaniline is taken as a second shell layer; compared with the traditional single layered transition metal oxide, Prussian blue analogue or other materials as the positive electrode material, the positive electrode material provided by the invention is of a composite structure, and has better cycling stability, rate capability and longer service life compared with the single positive electrode material.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery positive electrode materials, and particularly relates to a prussian blue composite positive electrode material for a sodium ion battery. BACKGROUND

[0002] With the increasing demand for renewable energy storage and large-scale energy storage systems worldwide, it is urgent to develop low-cost, high-safety and resource-abundant electrochemical energy storage technologies. Although lithium ion batteries have dominated the market of portable electronic devices and electric vehicles, the cost problem caused by the increasing scarcity and uneven geographical distribution of lithium resources has seriously restricted their further application in the field of large-scale energy storage. Under this background, sodium ion batteries are considered as a strong competitor for the next generation of large-scale energy storage technology due to their abundant sodium resources, wide distribution, low cost and similar working principle to lithium ion batteries.

[0003] The positive electrode material is a key component that determines the energy density, cycle life, rate performance and cost of a sodium ion battery. Compared with lithium ion batteries, sodium ions have larger ionic radius and mass, which leads to slow embedding / extraction dynamics in the host material and easy causes large volume change and phase change of the host material. At present, the mainstream positive electrode materials of sodium ion batteries mainly include layered transition metal oxides, polyanion compounds and prussian blue analogues. Although these materials have their own advantages, they all have inherent technical bottlenecks, which limit their commercial application. Therefore, developing high-performance and structurally stable positive electrode materials is a core challenge for the development of sodium ion battery technology. SUMMARY

[0004] In order to solve the above technical problems, the application provides a prussian blue composite positive electrode material for a sodium ion battery.

[0005] The object of the application can be achieved by the following technical solutions. A prussian blue composite positive electrode material for a sodium ion battery, which is a core-shell structure composed of a core layer Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material (Co-doped NaNi 0.4 Fe 0.2 Mn 0.4 O2 material), a first shell layer coated outside the core layer and a second shell layer coated outside the first shell layer; the first shell layer is a niobium-modified iron-based prussian blue material, and the second shell layer is polyaniline. Further, the prussian blue composite positive electrode material for a sodium ion battery is prepared by the following steps. Step S1: preparing Co-NaNi 0.4 Fe0.2 Mn 0.4 O2 material; Step S2: uniformly mixing Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material, niobium-modified iron-based Prussian blue material and anhydrous ethanol in a mass ratio of 100:1-5:10 to form a mixture, and then placing the mixture in a ball mill for ball milling at a ball milling ratio of 1:5 for 12 h, and then placing the mixture in an argon atmosphere and heat treating at 400°C for 1 h, so that the Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is uniformly coated with the niobium-modified iron-based Prussian blue material to form a first shell layer, thereby preparing a positive electrode material precursor; Step S3: ultrasonically treating 2 g of the positive electrode material precursor in 200 mL of deionized water for 30 min, stirring for 1 h, adjusting the pH of the system to 2.5 by using a 1 mol / L hydrochloric acid solution, adding 5-10 mL of aniline and stirring for 30 min, slowly adding 50 mL of an ammonium persulfate solution dropwise in an ice water bath, and reacting for 3 h after the dropwise addition is completed, and then filtering, washing and drying, thereby obtaining a Prussian blue composite positive electrode material for sodium ion batteries; Further, the positive electrode material precursor is coated with polyaniline having a conductive property, and a continuous, high-conductive thin film can be formed on the surface of the positive electrode material precursor, the isolated particles are "bridged" to form an electron superconducting network penetrating through the electrode, the charge transfer impedance of the entire electrode is significantly reduced, and the rate and capacity of the positive electrode material are improved.

[0006] Further, the Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is prepared by the following steps: Step A1: preparing a Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor; Step A2: preparing a Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material; Further, the specific preparation process of the Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor is as follows: Step A11: weighing nickel sulfate hexahydrate, manganese sulfate monohydrate and ferrous sulfate heptahydrate, and dissolving them in deionized water, which is denoted as a metal salt solution; Step A12: 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia solution are mixed uniformly, denoted as mixed solution; Step A13: Deionized water and 13.5 mol / L ammonia solution are sequentially added into the reactor, and the temperature is raised to 55℃, nitrogen is introduced for 15 min, then the metal salt solution is added and stirred, at the same time, the mixed solution is added to control the pH of the system at about 10.7, the temperature is maintained and stirred for 10 h, then washed and dried to obtain Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor; Further, in the metal salt solution of step A11, the molar ratio of Ni:Fe:Mn is 4:2:4, and the concentration of the metal salt solution is 2 mol / L; Further, in the mixed solution of step A12, the volume ratio of sodium hydroxide solution to ammonia solution is 8:2; Further, in step A13, the amount ratio of deionized water, ammonia and metal salt solution is 2L:100mL:500mL; Further, in step A2, the molar ratio of Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is as follows: The Co-NaNi 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor, cobalt oxalate dihydrate and alcohol are added into a mortar for wet grinding and mixing, then sodium carbonate is added for wet grinding to make them uniformly mixed, then high temperature sintering is carried out, and then cooled to room temperature, and sieved through a 200 mesh sieve to obtain Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material; Further, in step A2, (Ni+Fe+Mn):Co=1-x:x, wherein x=0.005, 0.01, 0.015, and the molar ratio of total metal to sodium carbonate is 1:0.525; Further, in step A2, the high temperature sintering condition is as follows: in oxygen atmosphere, the temperature is kept at 450℃ for 5h, then the temperature is raised to 880℃ for 15h, and the heating rate is 5℃ / min; Further, in the Co-doped NaNi .4 Fe 0.2 Mn 0.4 O2 material, Co doping into the crystal lattice can play the role of "pillar", anchoring the transition metal layer and the sodium layer, effectively inhibiting the sliding and structural rearrangement of the oxygen layer during the cycle process, thereby significantly improving the structural stability of the material and inhibiting harmful phase transformation; and due to the similar ionic radius of Co and Ni 2+Mn 4+ Different, the doping can cause slight adjustment of the lattice parameters, usually, the doping can slightly expand the spacing of the sodium layer, and the wider sodium ion transmission channel reduces the energy barrier of sodium ion diffusion, thereby improving the intrinsic ion conductivity of the material to a certain extent, which is beneficial to the rate performance.

[0007] Further, the niobium-modified iron-based Prussian blue material in step S2 is prepared by the following steps: Step S21: mix ferrous sulfate heptahydrate, manganese sulfate anhydrous, nickel sulfate hexahydrate, niobium chloride and sodium citrate dihydrate in deionized water and stir uniformly, denoted as solution A; dissolve sodium ferrocyanide decahydrate and ascorbic acid in deionized water, denoted as solution B; dissolve polyvinylpyrrolidone and sodium chloride in deionized water, denoted as solution C; Step S22: under the condition of nitrogen, solution C is placed in an oil bath, and the temperature is raised to 50℃, solution A and solution B are added to solution C under stirring, after reaction for 12h and aging for 12h, centrifugation, washing and drying, the niobium-modified iron-based Prussian blue material is obtained; Further, the traditional PBA material is prone to a large number of [Fe(CN)6] 4- Vacancies and coordinated water molecules exist in the synthesis process, these defects can occupy sodium sites, hinder ion transmission, and cause structural instability, and Nb 5+ Due to its high charge and strong coordination ability, it can more effectively occupy these vacancies, or form a more stable coordination structure with cyanide, thereby reducing lattice defects and coordinated water, which makes the crystal structure of the PBA shell more complete and stable, and is not easy to collapse after long-term cycling, thereby continuously protecting the inside; Further, the amount ratio of ferrous sulfate heptahydrate, manganese sulfate anhydrous, nickel sulfate hexahydrate, niobium chloride, sodium citrate dihydrate and deionized water in solution A in step S21 is 3mmol:0.5-1.5mmol:0.5-1.0mmol:0.1-0.5mmol:25mmol:50mL; Further, the amount ratio of sodium ferrocyanide decahydrate, ascorbic acid and deionized water in solution B in step S21 is 5mmol:0.9-1.2g:50mL; Further, the amount ratio of polyvinylpyrrolidone, sodium chloride and deionized water in solution C in step S21 is 0.8-1.2g:2.7-3.2g:100mL; Further, the ammonium persulfate solution in step S3 is prepared by mixing and stirring ammonium persulfate and deionized water in an amount ratio of 1.5-2.5g:50mL, and adjusting the pH to 2.5 by using 1mol / L hydrochloric acid solution.

[0008] The beneficial effects of the present application are: The prepared sodium ion battery positive electrode material is Co-doped NaNi 0.4 Fe 0.2 Mn 0.4 O2 (NFM) material is a core, a first shell layer of a niobium modified iron-based prussian blue material, and a second shell layer of polyaniline; compared with a traditional single layered transition metal oxide, a prussian blue analogue or other materials as a positive electrode material, the positive electrode material in the application is a composite structure, and has better cycle stability, rate performance and longer service life than the above single positive electrode material.

[0009] The Co-doped NaNi0 .4 Fe 0.2 Mn 0.4 O2 material in the core layer, the crystal structure of the NFM is stabilized by Co doping, and the phase transition is inhibited, and the PBA (prussian blue material) shell layer and the PANI (polyaniline) coating layer serve as a physical barrier, reducing the direct contact of the core layer material with the electrolyte, reducing the dissolution of transition metals and side reactions, the double shell layer effectively isolates the electrolyte from the erosion of the core layer material, especially the oxidative decomposition under high voltage, thereby forming a more stable solid-state electrolyte interface film, reducing the irreversible consumption of active sodium and materials, and improving the cycle stability. And in the process of battery charging and discharging, the embedding and extraction of sodium ions will cause the volume change of the material, and the flexible PANI layer and the open structure PBA layer can buffer this volume strain, prevent the particles from cracking and pulverization, maintain the integrity of the electrode structure, and further improve the service life of the positive electrode material. In addition, the PBA material has an open three-dimensional channel, which is beneficial to the rapid migration of sodium ions, and provides a “highway” for the sodium ions to enter and exit the internal core layer material, and the outermost conductive polymer PANI forms a continuous electron conductive network outside the particles, greatly improving the electron transport efficiency between particles and particles, and further improving the rate performance of the positive electrode material by utilizing the synergistic effect of the two. DETAILED DESCRIPTION

[0010] The technical solutions in the embodiments of the application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the protection scope of the application.

[0011] Embodiment 1: A prussian blue composite positive electrode material for a sodium ion battery, which is prepared by the following steps: Step S1: preparing Co-doped NaNi 0.4 Fe 0.2 Mn 0.4 O2 material; Further, the Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is prepared by the following steps: Further, step A1: preparing Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor: Further, step A11: weighing nickel sulfate hexahydrate, manganese sulfate monohydrate and ferrous sulfate heptahydrate, dissolving them in deionized water, and recording as a metal salt solution, the molar ratio of Ni:Fe:Mn in the metal salt solution is 4:2:4, and the concentration of the metal salt solution is 2 mol / L; Further, step A12: uniformly mix 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia solution, and record as a mixed solution, the volume ratio of sodium hydroxide solution to ammonia solution is 8:2; Further, step A13: deionized water and 13.5 mol / L ammonia water are sequentially added to the reactor, and the temperature is raised to 55°C, nitrogen is introduced for 15 min, then the metal salt solution is added and stirred, and the mixed solution is added to control the pH of the system at about 10.7, the temperature is maintained and stirred for 10 h, then washed and dried to obtain the Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor, the amount ratio of deionized water, ammonia water and metal salt solution is 2L:100mL:500mL; Further, step A2: preparing Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material: the Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor, cobalt oxalate dihydrate and alcohol are added to a mortar for wet grinding, mixed thoroughly, then sodium carbonate is added for wet grinding to make it uniformly mixed, then high-temperature sintering is performed, then cooled to room temperature, and sieved through a 200 mesh sieve to obtain the Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material; Further, in step A2, (Ni+Fe+Mn):Co=1-x:x, wherein x=0.005, and the molar ratio of total metal to sodium carbonate is 1:0.525; Further, in step A2, the high-temperature sintering conditions are: maintaining at 450°C for 5h in an oxygen atmosphere, then raising the temperature to 880°C for 15h, and the temperature raising rate is 5°C / min.

[0012] Step S2: preparing Co-NaNi0.4 Fe 0.2 Mn 0.4 O2 material, niobium-modified iron-based Prussian blue material and anhydrous ethanol are mixed uniformly at a mass ratio of 100:1:10 to form a mixture, and then the mixture is placed in a ball mill for ball milling at a ball milling ratio of 1:5 for 12 h. Then, the mixture is placed in an argon atmosphere and heat treated at 400°C for 1 h to obtain a Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is uniformly coated with the niobium-modified iron-based Prussian blue material to form a first shell layer, thereby obtaining a positive electrode material precursor. Further, the niobium-modified iron-based Prussian blue material in step S2 is prepared by the following steps: Further, in step S21, 3 mmol of ferrous sulfate heptahydrate, 1.0 mmol of manganese sulfate anhydrous, 0.5 mmol of nickel sulfate hexahydrate, 0.5 mmol of niobium chloride and 25 mmol of sodium citrate dihydrate are mixed and stirred uniformly in 50 mL of deionized water, denoted as solution A; 5 mmol of sodium ferrocyanide decahydrate and 0.9 g of ascorbic acid are dissolved in 50 mL of deionized water, denoted as solution B; 0.8 g of polyvinylpyrrolidone and 2.7 g of sodium chloride are dissolved in 100 mL of deionized water, denoted as solution C. Further, in step S22, under a nitrogen atmosphere, solution C is placed in an oil bath and heated to 50°C. Solution A and solution B are added to solution C under stirring. After reaction for 12 h and aging for 12 h, centrifugation, washing and drying are performed to obtain the niobium-modified iron-based Prussian blue material.

[0013] In step S3, 2 g of the positive electrode material precursor is ultrasonically treated in 200 mL of deionized water for 30 min and stirred for 1 h. Then, the pH of the system is adjusted to 2.5 using a 1 mol / L hydrochloric acid solution. Then, 5 mL of aniline is added and stirred for 30 min. Then, 50 mL of an ammonium persulfate solution is slowly added dropwise under an ice water bath. After the addition is completed, the reaction is performed for 3 h. Then, filtration, washing and drying are performed to obtain the Prussian blue composite positive electrode material for sodium ion batteries. Further, the ammonium persulfate solution in step S3 is prepared by mixing and stirring ammonium persulfate and deionized water at a use ratio of 1.5 g:50 mL, and the pH is adjusted to 2.5 using a 1 mol / L hydrochloric acid solution.

[0014] In example 2, a Prussian blue composite positive electrode material for sodium ion batteries is prepared by the following steps: In step S1, a Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is prepared. Further, the Co-NaNi 0.4 Fe0.2 Mn 0.4 O2 material, prepared by the following steps: Further, step A1: preparing Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor: Further, step A11: weighing nickel sulfate hexahydrate, manganese sulfate monohydrate and ferrous sulfate heptahydrate, dissolving them in deionized water, denoted as a metal salt solution, the molar ratio of Ni:Fe:Mn in the metal salt solution is 4:2:4, and the concentration of the metal salt solution is 2 mol / L; Further, step A12: uniformly mixing 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia solution, denoted as a mixed solution, the volume ratio of sodium hydroxide solution to ammonia solution is 8:2; Further, step A13: adding deionized water and 13.5 mol / L ammonia water into the reactor in turn, and heating to 55°C, then adding the metal salt solution after purging with nitrogen for 15 min and stirring, while adding the mixed solution to control the pH of the system at about 10.7, maintaining the temperature and stirring for 10 h, washing and drying to obtain Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor, the amount ratio of deionized water, ammonia water and metal salt solution is 2L:100mL:500mL; Further, step A2: preparing Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material: adding the Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor, cobalt oxalate dihydrate and alcohol into a mortar for wet grinding, mixing thoroughly, then adding sodium carbonate for wet grinding to mix uniformly, then high-temperature sintering, and then cooling to room temperature, passing through a 200-mesh sieve to obtain Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material; Further, in step A2, (Ni+Fe+Mn):Co=1-x:x, wherein x=0.01, and the molar ratio of total metal to sodium carbonate is 1:0.525; Further, in step A2, the high-temperature sintering condition is: holding at 450°C for 5h in an oxygen atmosphere, then heating to 880°C for 15h, and the heating rate is 5°C / min.

[0015] Step S2: preparing Co-NaNi 0.4 Fe 0.2 Mn 0.4O2 material, niobium-modified iron-based Prussian blue material, and anhydrous ethanol were mixed uniformly at a mass ratio of 100:2.5:10 to form a mixture. The mixture was then ball-milled at a ratio of 1:5 for 12 hours, followed by heat treatment at 400℃ under argon atmosphere for 1 hour, thus forming the Co-NaNi alloy. 0.4 Fe 0.2 Mn 0.4 The O2 material is uniformly coated with niobium-modified iron-based Prussian blue material to form the first shell layer, thus obtaining the cathode material precursor; Furthermore, the niobium-modified iron-based Prussian blue material described in step S2 is specifically prepared by the following steps: Further, in step S21: 3 mmol ferrous sulfate heptahydrate, 1.5 mmol anhydrous manganese sulfate, 0.2 mmol nickel sulfate hexahydrate, 0.3 mmol niobium chloride, and 25 mmol sodium citrate dihydrate are mixed and stirred evenly in 50 mL of deionized water, and this is recorded as solution A; 5 mmol sodium ferrocyanide decahydrate and 1.0 g ascorbic acid are dissolved in 50 mL of deionized water, and this is recorded as solution B; 1.0 g polyvinylpyrrolidone and 3 g sodium chloride are dissolved in 100 mL of deionized water, and this is recorded as solution C; Further, in step S22: under nitrogen conditions, solution C is placed in an oil bath and heated to 50°C. Under stirring conditions, solutions A and B are added to solution C. After reacting for 12 hours and aging for 12 hours, the solution is centrifuged, washed, and dried to obtain niobium-modified iron-based Prussian blue material.

[0016] Step S3: 2g of the cathode material precursor was ultrasonically treated in 200mL of deionized water for 30min and stirred for 1h. The pH of the system was adjusted to 2.5 using 1mol / L hydrochloric acid solution. Then, 7.5mL of aniline was added and stirred for 30min. Then, 50mL of ammonium persulfate solution was slowly added dropwise under an ice-water bath. After the addition was completed, the reaction was carried out for 3h. The mixture was then filtered, washed, and dried to obtain the Prussian blue composite cathode material for sodium-ion batteries. Furthermore, the ammonium persulfate solution in step S3 is prepared by mixing and stirring ammonium persulfate and deionized water at a ratio of 2g:50mL, and adjusting the pH to 2.5 using 1mol / L hydrochloric acid solution.

[0017] Example 3: A Prussian blue composite cathode material for sodium-ion batteries, specifically prepared by the following steps: Step S1: Preparation of Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 materials; Further, the Co-NaNi described in step S1 0.4 Fe 0.2 Mn 0.4 O2 material is prepared by the following steps: Further, step A1: preparing Ni 0.4 Fe 0.2 Mn 0.4 (OH)2precursor: Further, step A11: weighing nickel sulfate hexahydrate, manganese sulfate monohydrate and ferrous sulfate heptahydrate, dissolving them in deionized water, denoted as a metal salt solution, the molar ratio of Ni:Fe:Mn in the metal salt solution is 4:2:4, and the concentration of the metal salt solution is 2 mol / L; Further, step A12: uniformly mixing 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia solution, denoted as a mixed solution, the volume ratio of sodium hydroxide solution to ammonia solution is 8:2; Further, step A13: adding deionized water and 13.5 mol / L ammonia water into the reactor in turn, and heating to 55°C, then adding the metal salt solution after purging with nitrogen for 15 min and stirring, while adding the mixed solution to control the pH of the system at about 10.7, maintaining the temperature and stirring for 10 h, washing and drying to obtain Ni 0.4 Fe 0.2 Mn 0.4 (OH)2precursor, the amount ratio of deionized water, ammonia water and metal salt solution is 2L:100mL:500mL; Further, step A2: preparing Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2material: adding Ni 0.4 Fe 0.2 Mn 0.4 (OH)2precursor, cobalt oxalate dihydrate and alcohol into a mortar for wet grinding, mixing thoroughly, then adding sodium carbonate for wet grinding to mix uniformly, then high-temperature sintering, and then cooling to room temperature, passing through a 200-mesh sieve to obtain Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2material; Further, in step A2, (Ni+Fe+Mn):Co=1-x:x, wherein x=0.015, and the molar ratio of total metal to sodium carbonate is 1:0.525; Further, in step A2, the high-temperature sintering condition is: keeping at 450°C for 5h in an oxygen atmosphere, then heating to 880°C for 15h, and the heating rate is 5°C / min.

[0018] Step S2: preparing Co-NaNi 0.4 Fe 0.2 Mn 0.4O2 material, niobium-modified iron-based Prussian blue material and anhydrous ethanol are mixed uniformly in a mass ratio of 100:5:10 to form a mixture, and then the mixture is placed in a ball mill for ball milling at a ball milling ratio of 1:5 for 12 h. Then, the mixture is placed in an argon atmosphere and heat treated at 400°C for 1 h to form a first shell layer on the surface of the O2 material, thereby obtaining a positive electrode material precursor. 0.4 Fe 0.2 Mn 0.4 O2 material, niobium-modified iron-based Prussian blue material and anhydrous ethanol are mixed uniformly in a mass ratio of 100:5:10 to form a mixture, and then the mixture is placed in a ball mill for ball milling at a ball milling ratio of 1:5 for 12 h. Then, the mixture is placed in an argon atmosphere and heat treated at 400°C for 1 h to form a first shell layer on the surface of the O2 material, thereby obtaining a positive electrode material precursor. Further, the niobium-modified iron-based Prussian blue material in step S2 is prepared by the following steps: Further, step S21: 3 mmol of ferrous sulfate heptahydrate, 0.5 mmol of manganese sulfate anhydrous, 0.9 mmol of nickel sulfate hexahydrate, 0.1 mmol of niobium chloride and 25 mmol of sodium citrate dihydrate are mixed and stirred uniformly in 50 mL of deionized water, denoted as solution A; 5 mmol of sodium ferrocyanide decahydrate and 1.2 g of ascorbic acid are dissolved in 50 mL of deionized water, denoted as solution B; 1.2 g of polyvinylpyrrolidone and 3.2 g of sodium chloride are dissolved in 100 mL of deionized water, denoted as solution C. Further, step S22: under nitrogen conditions, solution C is placed in an oil bath and heated to 50°C, and solution A and solution B are added to solution C under stirring conditions. After reaction for 12 h and aging for 12 h, centrifugation, washing and drying are performed to obtain the niobium-modified iron-based Prussian blue material.

[0019] Step S3: 2 g of the positive electrode material precursor is ultrasonically treated in 200 mL of deionized water for 30 min and stirred for 1 h, and then the pH of the system is adjusted to 2.5 using a 1 mol / L hydrochloric acid solution. Then, 10 mL of aniline is added and stirred for 30 min, and then 50 mL of ammonium persulfate solution is slowly added dropwise under an ice water bath. After the addition is completed, the reaction is carried out for 3 h, and then filtration, washing and drying are performed to obtain the Prussian blue composite positive electrode material for sodium ion batteries. Further, the ammonium persulfate solution in step S3 is prepared by mixing ammonium persulfate and deionized water in a use amount ratio of 2.5 g:50 mL and stirring, and the pH is adjusted to 2.5 using a 1 mol / L hydrochloric acid solution.

[0020] Comparative Example 1: This comparative example is a sodium ion battery positive electrode material, specifically a NaNi 0.4 Fe 0.2 Mn 0.4 O2 material.

[0021] Comparative Example 2: This comparative example is a sodium ion battery positive electrode material, specifically a Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material.

[0022] Comparative Example 3: This comparative example is a sodium ion battery cathode material, specifically a cathode material precursor prepared in Example 2.

[0023] The sodium ion battery cathode materials prepared in Examples 1-3 and Comparative Examples 1-3 were mixed in a mass ratio of the cathode material prepared in the examples and comparative examples: binder (PVDF): cathode conductive agent = 8:1:1 to obtain a cathode slurry. The cathode slurry was coated on the surface of an aluminum foil, vacuum dried, and cut and pressed into a sheet. A sodium sheet was used as the negative electrode, and an electrolyte of 0.5M NaPF6 (a mixture of PC and FEC in a volume ratio of 95:5) was used. A sodium ion battery was assembled, allowed to stand for 24h, and then measured for voltage stability. After voltage stability was measured, the battery was subjected to charge-discharge tests at a rate of 0.1C in a voltage range of 2.0V-4.5V at 25°C. The test results are shown in Table 1. Table 1: Performance test results

[0024] As can be seen from Table 1, the sodium ion battery cathode material prepared in the present application has excellent cycle stability, rate performance, and service life after electrochemical performance testing.

[0025] The above content is merely an example and explanation of the concept of the present application. Those skilled in the art of the present technology can make various modifications or supplements to the described specific examples or use similar ways to replace them, as long as they do not deviate from the scope defined by the concept of the present application, and all of them should belong to the protection scope of the present application.

Claims

1. A Prussian blue composite cathode material for sodium-ion batteries, characterized in that, The Prussian blue composite cathode material used in the sodium-ion battery has a core-shell structure, consisting of a core layer of Co-NaNi. 0.4 Fe 0.2 Mn 0.4 It consists of O2 material, a first shell layer covering the core layer, and a second shell layer covering the first shell layer; the first shell layer is niobium-modified iron-based Prussian blue material, and the second shell layer is polyaniline; The Prussian blue composite cathode material for sodium-ion batteries is prepared by the following steps: Step S1: Preparation of Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 materials; Step S2: Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material, niobium-modified iron-based Prussian blue material, and anhydrous ethanol were mixed uniformly at a mass ratio of 100:1-5:10 to form a mixture. The mixture was then ball-milled at a ratio of 1:5 for 12 hours, followed by heat treatment at 400℃ under argon atmosphere for 1 hour, thus forming the Co-NaNi alloy. 0.4 Fe 0.2 Mn 0.4 The O2 material is uniformly coated with niobium-modified iron-based Prussian blue material to form the first shell layer, thus obtaining the cathode material precursor; Step S3: 2g of the cathode material precursor was ultrasonically treated in 200mL of deionized water for 30min and stirred for 1h. The pH of the system was adjusted to 2.5 using 1mol / L hydrochloric acid solution. Then, 5-10mL of aniline was added and stirred for 30min. Then, 50mL of ammonium persulfate solution was slowly added dropwise under an ice-water bath. After the addition was completed, the reaction was carried out for 3h. The mixture was then filtered, washed, and dried to obtain the Prussian blue composite cathode material for sodium-ion batteries. The Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material is prepared by the following steps: Step A1: Preparation of Ni 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor; Step A2: Preparation of Co-NaNi 0.4 Fe 0.2 Mn 0.4 O2 material.

2. The Prussian blue composite cathode material for sodium-ion batteries according to claim 1, characterized in that, The Ni mentioned in step A1 0.4 Fe 0.2 Mn 0.4 The specific preparation process of the (OH)2 precursor is as follows: Step A11: Weigh out nickel sulfate hexahydrate, manganese sulfate monohydrate and ferrous sulfate heptahydrate and dissolve them in deionized water, and record this as a metal salt solution; Step A12: Mix 10 mol / L sodium hydroxide solution and 13.5 mol / L ammonia solution thoroughly, and record the mixture as the mixed solution; Step A13: Deionized water and 13.5 mol / L ammonia solution were added sequentially to the reactor, and the temperature was raised to 55°C. Nitrogen gas was introduced for 15 minutes, and then the metal salt solution was added and stirred. At the same time, the mixture was added to maintain the pH of the system at around 10.

7. The temperature was maintained and the mixture was stirred for 10 hours. After washing and drying, Ni was obtained. 0.4 Fe 0.2 Mn 0.4 (OH)2 precursor.

3. The Prussian blue composite cathode material for sodium-ion batteries according to claim 2, characterized in that, In step A11, the molar ratio of Ni:Fe:Mn in the metal salt solution is 4:2:4, and the concentration of the metal salt solution is 2 mol / L. In step A12, the volume ratio of sodium hydroxide solution to ammonia solution is 8:

2. In step A13, the volume ratio of deionized water, ammonia solution and metal salt solution is 2L:100mL:500mL.

4. The Prussian blue composite cathode material for sodium-ion batteries according to claim 1, characterized in that, In step A2, Co-NaNi 0.4 Fe 0.2 Mn 0.4 The specific preparation process of O2 materials is as follows: Ni 0.4 Fe 0.2 Mn 0.4 (OH)₂ precursor, cobalt oxalate dihydrate, and alcohol are added to a mortar and wet-milled until thoroughly mixed. Sodium carbonate is then added and wet-milled until homogeneous. The mixture is then sintered at high temperature, cooled to room temperature, and passed through a 200-mesh sieve to obtain Co-NaNi. 0.4 Fe 0.2 Mn 0.4 O2 material.

5. The Prussian blue composite cathode material for sodium-ion batteries according to claim 4, characterized in that, In step A2, (Ni+Fe+Mn):Co=1-x:x, where x=0.005, 0.01, 0.015, and the total metal molar ratio and the molar ratio of sodium carbonate are 1:0.

525. The high-temperature sintering conditions are: holding at 450℃ for 5 hours in an oxygen atmosphere, then raising the temperature to 880℃ and holding for 15 hours, with a heating rate of 5℃ / min.

6. The Prussian blue composite cathode material for sodium-ion batteries according to claim 1, characterized in that, The niobium-modified iron-based Prussian blue material described in step S2 is prepared by the following steps: Step S21: Mix ferrous sulfate heptahydrate, anhydrous manganese sulfate, nickel sulfate hexahydrate, niobium chloride, and sodium citrate dihydrate in deionized water and stir until homogeneous. This mixture is labeled as solution A. Dissolve sodium ferrocyanide decahydrate and ascorbic acid in deionized water. This mixture is labeled as solution B. Dissolve polyvinylpyrrolidone and sodium chloride in deionized water. This mixture is labeled as solution C. Step S22: Under nitrogen conditions, solution C is placed in an oil bath and heated to 50°C. Under stirring, solutions A and B are added to solution C. After reacting for 12 hours and aging for 12 hours, the solution is centrifuged, washed, and dried to obtain niobium-modified iron-based Prussian blue material.

7. The Prussian blue composite cathode material for sodium-ion batteries according to claim 6, characterized in that, In step S21, the ratio of ferrous sulfate heptahydrate, anhydrous manganese sulfate, nickel sulfate hexahydrate, niobium chloride, sodium citrate dihydrate, and deionized water in solution A is 3 mmol: 0.5-1.5 mmol: 0.5-1.0 mmol: 0.1-0.5 mmol: 25 mmol: 50 mL. In solution B, the ratio of sodium ferrocyanide decahydrate, ascorbic acid, and deionized water is 5 mmol: 0.9-1.2 g: 50 mL. In solution C, the ratio of polyvinylpyrrolidone, sodium chloride, and deionized water is 0.8-1.2 g: 2.7-3.2 g: 100 mL.

8. The Prussian blue composite cathode material for sodium-ion batteries according to claim 1, characterized in that, The ammonium persulfate solution described in step S3 is prepared by mixing and stirring ammonium persulfate and deionized water at a ratio of 1.5-2.5g:50mL, and adjusting the pH to 2.5 using 1mol / L hydrochloric acid solution.

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