Nano-state polyanionic sodium ion battery positive electrode material and preparation method thereof

Abstract

The invention discloses a nano-state polyanionic sodium ion battery positive electrode material and a preparation method thereof. The preparation method comprises the following steps: S1, preparing homogeneous slurry; s2, preparing precursor powder; s3, preparing precursor powder in a pre-crystalline state; s4, preparation of a premixed precursor: mixing the pre-crystalline powder with a pore-forming agent, and performing dry ball milling to realize uniform mixing of the pre-crystalline powder and the pore-forming agent so as to form the premixed precursor; and S5, high-temperature calcination: carrying out high-temperature calcination on the premixed precursor in a protective atmosphere, and naturally cooling to obtain the nano-state polyanionic sodium-ion battery positive electrode material. The nano-state polyanionic sodium ion battery positive electrode material and the preparation method thereof have the characteristics of complete nanoparticles, high compaction density, excellent rate capability and effective capacity improvement.

Description

Technical Field

[0001] The invention relates to the technical field of secondary batteries, and in particular to a nano-polyanion sodium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] Polyanion sodium ion batteries have gained market favor for their high structural stability, low cost, and excellent cycle stability. At present, the most studied polyanion material system on the market is composite sodium iron phosphate (Na4Fe3(PO4)2P2O7), which is composed of alkali metal groups, transition metal groups, and two anion groups arranged in a common point / surface / line manner to form a three-dimensional framework structure. The nano-scale preparation of this composite structure is relatively difficult, resulting in low material compaction density, difficult processing, and poor electrochemical performance.

[0003] At present, the production of composite sodium iron phosphate is often synthesized by the solid phase method, which uses a water-soluble sodium source, a water-insoluble transition metal source and a water-soluble single-molecule phosphorus source as raw materials, and the material is prepared through processes such as grinding and mixing, spray drying, and sintering.

[0004] However, during the spray drying stage, as the water evaporates, single-molecule phosphorus source crystals precipitate and adhere to the surface of transition metal particles, causing particle adhesion. During the subsequent sintering process, the adhesion of the particles melts and diffuses, crystallizes and nucleates, and forms intertwined secondary particle agglomerates. There are a large number of pores in this agglomerate, resulting in a low compaction density of the material, making processing difficult and limiting its application and promotion. Summary of the invention

[0005] The purpose of the present invention is to provide a nano-polyanion type sodium ion battery positive electrode material and a preparation method thereof, which has the characteristics of complete nanoparticles, high compaction density, excellent rate performance and effectively improved capacity.

[0006] The present invention can be implemented by the following technical solutions: The present invention discloses a method for preparing a nano-polyanion type sodium ion battery positive electrode material, comprising the following steps: S1. Preparation of homogeneous slurry: mixing and wet-grinding an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source to form a homogeneous slurry; S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder; S3, preparation of pre-crystallized precursor powder: pre-sintering the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder; S4, preparation of premixed precursor: mixing pre-crystallized powder with pore-forming agent, and using dry ball milling to achieve uniform mixing of the two to form a premixed precursor; S5. High-temperature calcination: Under a protective atmosphere, the premixed precursor is calcined at a high temperature, and the temperature is naturally reduced to obtain a nano-polyanion sodium ion battery positive electrode material.

[0007] The present invention discloses a process for preparing a positive electrode material for a nano-state polyanion-type talent battery, which replaces the traditional single-molecule phosphorus source with a chain phosphorus-containing compound, and utilizes the weak interaction force generated by the lone pair of electrons on the oxygen atom connected to phosphorus in the chain phosphorus-containing compound structure and the interface of the transition metal particles to hinder the adhesion between particles during the drying process. At the same time, a pore-forming agent is mixed with the pre-calcined black precursor powder, and the gas released during the high-temperature pyrolysis of the pore-forming agent is utilized to hinder the melting growth between particles, thereby destroying the formation of secondary particle agglomerates, and finally obtaining primary nanoparticles with uniform particle size and high particle integrity, thereby improving the compaction density, processing performance and electrochemical performance of the material.

[0008] Furthermore, in step S1, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100nm; the purpose is to ensure that the alkali metal ions, transition metal particles, chain phosphorus-containing compound molecules and organic carbon source molecules in the slurry can fully contact to form a near-ionic mixture, which is beneficial to the mutual bonding and growth between the elements during the sintering process to generate a structure with high purity and complete crystal form.

[0009] Furthermore, in step S3, the low-temperature pre-sintering conditions are a sintering temperature of 200-400°C and a holding time of >0.1H; the purpose is to ensure the generation of primary crystal nuclei of the material and provide a template for the subsequent formation of nano-state materials; when the temperature is <200°C, the easily decomposable components in the precursor powder are not completely volatilized, and primary crystal nuclei are difficult to form; when the temperature is >400°C, the precursor powder transitions to melt growth, and large millimeter-sized particles are easily formed, which affects the electrochemical properties of the material.

[0010] Furthermore, in step S5, the high-temperature calcination conditions are a sintering temperature of 400-800°C and a holding time of >0.1H; one purpose is to promote atomic rearrangement of the primary crystal nucleus under high temperature conditions to form a more complete crystal structure; the second purpose is to promote the decomposition and gas production of the pore-forming agent at high temperature, thereby blocking the bonding between the primary crystal nucleus particles and retaining the guaranteed nano-state primary particles.

[0011] Furthermore, in step S1, the wet grinding method is one or more of homogeneous dispersion, ball milling dispersion, and sand milling dispersion; its purpose is to utilize the mechanical force or shear force existing in the wet grinding process to achieve the crushing of solid particles in the slurry and the uniform mixing of the raw materials.

[0012] Furthermore, in step S2, the drying method is one or more of flash drying, spray drying, high temperature cracking, and high temperature evaporation; its purpose is to use high temperature to achieve rapid separation between solid and liquid in the homogeneous slurry, prevent ion segregation caused by too long evaporation time, and affect the uniformity between elements in the precursor powder.

[0013] Furthermore, in steps S3 and S5, the protective atmosphere is one or more of nitrogen, argon, hydrogen, carbon monoxide, and helium; its purpose is to prevent the oxidation of transition metals during the low-temperature / high-temperature sintering process of the material, thereby inhibiting the separation of material phases caused by the oxidation of transition metals.

[0014] Furthermore, in step S4, the dry ball milling method is one or more of planetary ball milling, high-energy grinding, and high-speed mixing, the purpose of which is to evenly disperse the pore-forming agent into the gaps of the pre-crystallized precursor powder to ensure that the mutual melting growth between the particles is blocked during the subsequent sintering process.

[0015] Preferably, the alkali metal source is a sodium source, and the sodium source is one or more of sodium acetate, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium formate, sodium citrate, sodium gluconate, sodium methoxide, sodium phenolate, sodium tert-butoxide, sodium phenolate, sodium butyrate, sodium tartrate, sodium oleate, and sodium ethylenediaminetetraacetate.

[0016] Preferably, the water-insoluble transition metal source is one or more of an iron source, a manganese source, and a cobalt source; the iron source is one or more of ferric hydroxide, ferrous hydroxide, ferric oxide, ferrous oxide, ferric oxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the manganese source is one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganous anhydride, manganic anhydride, and permanganic anhydride; and the cobalt source is one or more of cobalt oxide, cobalt oxide, cobalt tetroxide, cobalt oxalate, etc.

[0017] Preferably, the chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, polyaminopolyethermethylenephosphonic acid, and bis-1,6-hexamethylenetriaminepentamethylenephosphonic acid. ; Preferably, the organic carbon source is one or more of citric acid, starch, maltose, sucrose, ascorbic acid, glucose, asphalt, phenolic resin, cellulose, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol.

[0018] Preferably, the pore-forming agent is one or more of oxalic acid, ammonium oxalate, ammonium nitrate, ammonium sulfate, and ammonium chloride; its characteristic is that at high temperature, the molecules can be completely decomposed into gas; its function is to act as a gaseous blocker to hinder the mutual melting during the growth of primary crystal nuclei and prevent the formation of large particles above the nanometer level.

[0019] Another aspect of the present invention is to protect a nano-polyanion sodium ion battery positive electrode material, which is prepared by the above preparation method.

[0020] Furthermore, the secondary battery is a sodium ion battery, the polyanion sodium ion battery positive electrode material is a polyanion sodium ion battery positive electrode material, and the polyanion sodium ion battery positive electrode material is an iron-based, manganese-based or cobalt-based polyanion sodium ion battery positive electrode material and its derivatives.

[0021] Furthermore, the positive electrode material of the polyanion sodium ion battery is sodium iron phosphate, sodium manganese iron phosphate, sodium cobalt phosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, and sodium cobalt pyrophosphate.

[0022] The present invention discloses a nano-polyanion sodium ion battery positive electrode material and a preparation method thereof, which has the following beneficial effects: First, the nanoparticles are complete. The chain phosphorus-containing compound is formed by the deoxygenation condensation of polyphosphates. It is characterized by the presence of lone pairs of electrons on the oxygen atoms connected to the phosphorus atoms. It is easy to produce weak interaction forces with transition metal elements and disperse between transition metal particles in the slurry, playing a bridging role. During the drying process, it can avoid the adhesion and agglomeration of transition metal particles caused by water evaporation, which is the core link in the construction of nanomaterial precursors. When the precursor powder is pre-burned at low temperature, the chain phosphorus-containing compound breaks and decomposes, which will lead to mutual contact of local primary crystal nuclei. After this link, additional pore-forming agents need to be added to destroy this contact. It uses the carbon dioxide, nitrogen dioxide and other gases released during the high-temperature pyrolysis of the pore-forming agent to block the further contact of the primary crystal nuclei, thereby forming a single nanomaterial particle.

[0023] Second, the compaction density is high. The sodium polyanion materials on the market are all secondary particle agglomerates. This is caused by the adhesion of particles after the inorganic single-molecule phosphorus source melts at the interface of different transition metal particles during the sintering process. This secondary particle agglomerate contains a large number of pore structures. During the powder rolling process, the agglomerate cannot be crushed and the internal pore structure cannot be broken, resulting in a low powder compaction density (1.8-1.9g / cm 3 ), the processing becomes worse. After the material is nano-sized, it is closer to a solid single crystal primary particle. During the powder rolling process, different primary particles fill each other, which can achieve a lower porosity and a higher compaction density (2.15-2.25g / cm3 ).

[0024] Third, the rate performance is excellent. The present invention improves the transmission dynamics of electrons and ions in the material through the nano-sizing of the material. First, the nano-sizing of the material effectively shortens the diffusion distance of sodium ions from the interface to the bulk phase, and reduces the diffusion time of ions in the bulk phase of the material; second, the nano-sized materials are mostly single-crystalline primary particles, and there are no grain boundaries in the particles, and the resistance disappears during the ion diffusion process; third, after the material is nano-sized, the specific surface area increases, the wetting area of ​​the electrolyte at the material interface increases, and the diffusion number of ions at the interface between the electrolyte and the material will increase significantly; fourth, after the material is nano-sized, the distribution area and uniformity of the conductive carbon layer at the material interface increase, which effectively expands the path of electron transmission; for the above reasons, after the material is nano-sized, the electronic conductivity and ionic conductivity will be significantly improved, and the material will obtain high-rate properties.

[0025] Fourth, the capacity is effectively improved. In addition to the material's own structure, the pseudocapacitance of the interface also contributes to the capacity. After the material is nano-sized, the specific surface area increases. During the charging and discharging process, the amount of charge that can be stored increases year-on-year with the increase of the pseudocapacitance adsorbed on the material interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 For application example 1, nano-Na4Fe 2.91 (PO4)2P2O7 material morphology; Figure 2 Comparative Example 1 Agglomerated Na4Fe 2.91 (PO4)2P2O7 material morphology. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention is further described in detail below in conjunction with embodiments.

[0028] The present invention discloses a method for preparing a nano-polyanion type sodium ion battery positive electrode material, comprising the following steps: S1. Preparation of homogeneous slurry: mixing and wet-grinding an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source to form a homogeneous slurry; S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder; S3, preparation of pre-crystallized precursor powder: pre-sintering the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder; S4, preparation of premixed precursor: mixing pre-crystallized powder with pore-forming agent, and using dry ball milling to achieve uniform mixing of the two to form a premixed precursor; S5. High-temperature calcination: Under a protective atmosphere, the premixed precursor is calcined at a high temperature, and the temperature is naturally reduced to obtain a nano-polyanion sodium ion battery positive electrode material.

[0029] Furthermore, in step S1, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100nm; the purpose is to ensure that the alkali metal ions, transition metal particles, chain phosphorus-containing compound molecules and organic carbon source molecules in the slurry can fully contact to form a near-ionic mixture, which is beneficial to the mutual bonding and growth between the elements during the sintering process to generate a structure with high purity and complete crystal form.

[0030] Furthermore, in step S3, the low-temperature pre-sintering conditions are a sintering temperature of 200-400°C and a holding time of >0.1H; the purpose is to ensure the generation of primary crystal nuclei of the material and provide a template for the subsequent formation of nano-state materials; when the temperature is <200°C, the easily decomposable components in the precursor powder are not completely volatilized, and primary crystal nuclei are difficult to form; when the temperature is >400°C, the precursor powder transitions to melt growth, and large millimeter-sized particles are easily formed, which affects the electrochemical properties of the material.

[0031] Furthermore, in step S5, the high-temperature calcination conditions are a sintering temperature of 400-800°C and a holding time of >0.1H; one purpose is to promote atomic rearrangement of the primary crystal nucleus under high temperature conditions to form a more complete crystal structure; the second purpose is to promote the decomposition and gas production of the pore-forming agent at high temperature, thereby blocking the bonding between the primary crystal nucleus particles and retaining the guaranteed nano-state primary particles.

[0032] Furthermore, in step S1, the wet grinding method is one or more of homogeneous dispersion, ball milling dispersion, and sand milling dispersion; its purpose is to utilize the mechanical force or shear force existing in the wet grinding process to achieve the crushing of solid particles in the slurry and the uniform mixing of the raw materials.

[0033] Furthermore, in step S2, the drying method is one or more of flash drying, spray drying, high temperature cracking, and high temperature evaporation; its purpose is to use high temperature to achieve rapid separation between solid and liquid in the homogeneous slurry, prevent ion segregation caused by too long evaporation time, and affect the uniformity between elements in the precursor powder.

[0034] Furthermore, in steps S3 and S5, the protective atmosphere is one or more of nitrogen, argon, hydrogen, carbon monoxide, and helium; its purpose is to prevent the oxidation of transition metals during the low-temperature / high-temperature sintering process of the material, thereby inhibiting the separation of material phases caused by the oxidation of transition metals.

[0035] Furthermore, in step S4, the dry ball milling method is one or more of planetary ball milling, high-energy grinding, and high-speed mixing, the purpose of which is to evenly disperse the pore-forming agent into the gaps of the pre-crystallized precursor powder to ensure that the mutual melting growth between the particles is blocked during the subsequent sintering process.

[0036] Preferably, the alkali metal source is a sodium source, and the sodium source is one or more of sodium acetate, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium formate, sodium citrate, sodium gluconate, sodium methoxide, sodium phenolate, sodium tert-butoxide, sodium phenolate, sodium butyrate, sodium tartrate, sodium oleate, and sodium ethylenediaminetetraacetate.

[0037] Preferably, the water-insoluble transition metal source is one or more of an iron source, a manganese source, and a cobalt source; the iron source is one or more of ferric hydroxide, ferrous hydroxide, ferric oxide, ferrous oxide, ferric oxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the manganese source is one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganous anhydride, manganic anhydride, and permanganic anhydride; and the cobalt source is one or more of cobalt oxide, cobalt oxide, cobalt tetroxide, cobalt oxalate, etc.

[0038] Preferably, the chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, diethylenetriaminepentamethylenephosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, polyaminopolyethermethylenephosphonic acid, and bis-1,6-hexamethylenetriaminepentamethylenephosphonic acid. ; Preferably, the organic carbon source is one or more of citric acid, starch, maltose, sucrose, ascorbic acid, glucose, asphalt, phenolic resin, cellulose, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol.

[0039] Preferably, the pore-forming agent is one or more of oxalic acid, ammonium oxalate, ammonium nitrate, ammonium sulfate, and ammonium chloride; its characteristic is that at high temperature, the molecules can be completely decomposed into gas; its function is to act as a gaseous blocker to hinder the mutual melting during the growth of primary crystal nuclei and prevent the formation of large particles above the nanometer level.

[0040] Another aspect of the present invention is to protect a nano-polyanion sodium ion battery positive electrode material, which is prepared by the above preparation method.

[0041] Furthermore, the secondary battery is a sodium ion battery, the polyanion sodium ion battery positive electrode material is a polyanion sodium ion battery positive electrode material, and the polyanion sodium ion battery positive electrode material is an iron-based, manganese-based or cobalt-based polyanion sodium ion battery positive electrode material and its derivatives.

[0042] Furthermore, the positive electrode material of the polyanion sodium ion battery is sodium iron phosphate, sodium manganese iron phosphate, sodium cobalt phosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, and sodium cobalt pyrophosphate.

[0043] Example 1 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet-grinding method is homogeneous dispersion.

[0044] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is flash drying or spray drying.

[0045] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are a sintering temperature of 400° C., a holding time of 0.4 hours, and a protective atmosphere of nitrogen.

[0046] S4, preparation of premixed precursor: pre-crystallized powder and pore former are mixed, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is planetary ball milling.

[0047] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 800°C, a heat preservation time of 0.5H, and an argon protective atmosphere.

[0048] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate; the water-insoluble transition metal source is an iron source, and the iron source is ferric hydroxide and ferrous hydroxide; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, and hydroxyethylidene diphosphonic acid; the organic carbon source is citric acid, starch, maltose, sucrose, ascorbic acid, and glucose; and the pore-forming agent is oxalic acid, ammonium oxalate, and ammonium nitrate.

[0049] Example 2 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is ball milling dispersion.

[0050] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is spray drying.

[0051] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are sintering temperature of 300° C., holding time of 0.5 h, and the protective atmosphere is nitrogen or argon.

[0052] S4, preparation of premixed precursor: pre-crystallized powder and pore-forming agent are mixed, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is high-energy grinding.

[0053] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 600°C and a holding time of 0.2H; the protective atmosphere is hydrogen and carbon monoxide.

[0054] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium citrate, sodium gluconate, sodium methoxide, sodium phenol, sodium tert-butoxide, sodium phenol, and sodium butyrate; the water-insoluble transition metal source is an iron source, and the iron source is ferric oxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the chain phosphorus-containing compound is pyrodiethylenetriaminepenta(methylenephosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, and polyaminopolyether methylenephosphonic acid; the organic carbon source is sucrose, ascorbic acid, glucose, and asphalt; and the pore-forming agent is ammonium nitrate, ammonium sulfate, and ammonium chloride.

[0055] Example 3 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is sand grinding dispersion.

[0056] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is high temperature cracking and high temperature evaporation.

[0057] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are sintering temperature of 200°C and holding time of 2 hours; the protective atmosphere is carbon monoxide and helium.

[0058] S4, preparation of premixed precursor: pre-crystallized powder and pore-forming agent are mixed, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is high-speed mixing.

[0059] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 400°C and a heat preservation time of 1H; the protective atmosphere is nitrogen or helium.

[0060] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, and sodium hydroxide; the water-insoluble transition metal source is a manganese source, and the manganese source is manganese monoxide, manganese dioxide, and manganese trioxide; the chain phosphorus-containing compound is polyamino polyether methylene phosphonic acid and bis(1,6-hexamethylenetriaminepenta(methylenephosphonic acid); the organic carbon source is citric acid, starch, maltose, sucrose, ascorbic acid, glucose, asphalt, phenolic resin, cellulose, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol; and the pore-forming agent is oxalic acid and ammonium oxalate.

[0061] Example 4 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is homogeneous dispersion and ball milling dispersion.

[0062] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is spray drying or high temperature cracking.

[0063] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are sintering temperature of 300° C., holding time of 1 hour, and the protective atmosphere is nitrogen, carbon monoxide.

[0064] S4. Preparation of premixed precursor: pre-crystallized powder is mixed with pore-forming agent, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is planetary ball milling and high-energy grinding.

[0065] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 600°C and a heat preservation time of 1H; the protective atmosphere is nitrogen, carbon monoxide, and helium.

[0066] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium gluconate, sodium methoxide, sodium phenol, and sodium tert-butoxide; the water-insoluble transition metal source is a manganese source, and the manganese source is manganese anhydride and permanganate anhydride; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate, and sodium polyphosphate; the organic carbon source is citric acid, starch, maltose, sucrose, ascorbic acid, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol; and the pore-forming agent is oxalic acid, ammonium sulfate, and ammonium chloride.

[0067] Example 5 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is ball milling dispersion or sand milling dispersion.

[0068] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is spray drying, high temperature evaporation, S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are a sintering temperature of 350° C. and a holding time of 0.5 h; the protective atmosphere is nitrogen, argon, or helium.

[0069] S4. Preparation of premixed precursor: pre-crystallized powder is mixed with pore-forming agent, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is planetary ball milling and high-energy grinding.

[0070] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 500°C and a heat preservation time of 2 hours; the protective atmosphere is nitrogen or argon.

[0071] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate, sodium sulfate, and sodium nitrate; the water-insoluble transition metal source is a cobalt source, and the cobalt source is cobalt oxide and high cobalt oxide; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, aminotri (methylene phosphonic acid), and ethylenediaminetetra (methylene phosphonic acid); the organic carbon source is citric acid, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol; and the pore-forming agent is oxalic acid, ammonium oxalate, and ammonium chloride.

[0072] Example 6 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is homogeneous dispersion and sand grinding dispersion.

[0073] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is flash drying or spray drying.

[0074] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are sintering temperature of 300° C., holding time of 2 hours, and the protective atmosphere is nitrogen, carbon monoxide, and helium.

[0075] S4. Preparation of premixed precursor: pre-crystallized powder and pore-forming agent are mixed, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is planetary ball milling, high-speed mixing.

[0076] S5, high temperature calcination: calcine the premixed precursor at high temperature under a protective atmosphere, and cool it naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are a sintering temperature of 700°C and a holding time of 0.7H; the protective atmosphere is carbon monoxide and helium.

[0077] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate, sodium tert-butoxide, sodium phenol, sodium butyrate, sodium tartrate, sodium oleate, and sodium ethylenediaminetetraacetate; the water-insoluble transition metal source is a cobalt source, and the cobalt source is cobalt oxide, cobalt oxalate, etc.; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate 2-hydroxyphosphonoacetic acid, polyaminopolyether methylenephosphonic acid, and di-1,6-hexamethylenetriaminepenta(methylenephosphonic acid); the organic carbon source is citric acid, starch, maltose, lactic acid, cyclodextrin, and ethanol; and the pore-forming agent is oxalic acid, ammonium sulfate, and ammonium chloride.

[0078] Example 7 This embodiment relates to a nano-polyanion type sodium ion battery positive electrode material, and the preparation method thereof comprises the following steps: S1. Preparation of homogeneous slurry: Mix and wet-grind the alkali metal source, the water-insoluble transition metal source, the chain phosphorus-containing compound, and the organic carbon source to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm; the wet grinding method is homogeneous dispersion, ball milling dispersion, and sand milling dispersion.

[0079] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder. Specifically, the drying method is flash drying, spray drying, high temperature cracking, and high temperature evaporation.

[0080] S3. Preparation of pre-crystallized precursor powder: pre-sinter the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are a sintering temperature of 250° C. and a holding time of 3 hours; the protective atmosphere is nitrogen, argon, hydrogen, carbon monoxide, or helium.

[0081] S4. Preparation of premixed precursor: pre-crystallized powder and pore-forming agent are mixed, and dry ball milling is used to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method includes planetary ball milling, high-energy grinding, and high-speed mixing.

[0082] S5, high temperature calcination: in a protective atmosphere, the premixed precursor is calcined at high temperature, and the temperature is naturally reduced to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the conditions for high temperature calcination are sintering temperature 400-800℃, insulation time> 0.1H; the protective atmosphere is nitrogen, argon, hydrogen, carbon monoxide, helium In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium formate, sodium citrate, sodium gluconate, sodium methoxide, sodium phenol, sodium tert-butoxide, sodium phenol, sodium butyrate, sodium tartrate, sodium oleate, and sodium ethylenediaminetetraacetate; the water-insoluble transition metal source is an iron source, a manganese source, and a cobalt source, and the iron source is one or more of ferric hydroxide, ferrous hydroxide, ferric oxide, ferrous oxide, ferric oxide, ferrous tetroxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the manganese source is one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganous anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is cobalt oxide, high cobalt oxide, cobalt tetroxide, One or more of cobalt oxalate, etc.; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylene triamine penta methylene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, polyamino polyether methylene phosphonic acid, di-1,6-hexamethylene triamine penta methylene phosphonic acid; the organic carbon source is citric acid, starch, maltose, sucrose, ascorbic acid, glucose, asphalt, phenolic resin, cellulose, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, ethanol; the pore-forming agent is oxalic acid, ammonium oxalate, ammonium nitrate, ammonium sulfate, and ammonium chloride.

[0083] Application Example 1 Nano-state Na4Fe 2.91 Synthesis and electrochemical properties of (PO4)2P2O7 materials The nanostructured Na4Fe 2.91 The preparation method of (PO4)2P2O7 material comprises the following steps: Step 1: Sodium citrate, ferric hydroxide, sodium pyrophosphate, hydroxyethylidene diphosphonic acid are mixed with glucose (the addition amount is 5% of the weight of ferric hydroxide) in a molar ratio of 1:2.91:0.125:1.938, and water is added, and the mixture is ground with a sand mill, and the solid content is controlled at 35%, and the particle size of the ferric hydroxide particles in the slurry is Dmax≤100, so as to form a uniform homogeneous emulsion; Step 2: spray drying the homogeneous solution at an air inlet temperature of 280°C and an air outlet temperature of 100°C to achieve solid-liquid separation and obtain a dry precursor powder; Step 3: In a nitrogen atmosphere, the dried precursor powder is kept at 300°C for 2 hours to promote the decomposition of hydroxyethylidene diphosphonic acid, sodium citrate, phenolic resin, etc., and complete the nano-state Na4Fe 2.91 The formation of primary crystal nuclei of (PO4)2P2O7 material, and the black pre-crystallized precursor powder is obtained by natural cooling; Step 4: Mix the black pre-crystallized precursor powder with oxalic acid (the addition amount is 5.3% of the precursor weight), and grind it with a dry planetary ball mill. The ball milling ratio is controlled at 20:1, and the time is ≥10h to ensure uniform mixing between the two to form a premixed precursor; Step 5: In an argon atmosphere, the premixed precursor is calcined at 650°C for 10 hours. The gas released by the decomposition of oxalic acid during the high-temperature sintering process is used to block the melting between the particles. After natural cooling, the nano-Na4Fe 2.91 (PO4)2P2O7 material.

[0084] Figure 1 Nano-state Na4Fe 2.91 The morphology of the (PO4)2P2O7 material shows that it is nanoparticles of about 100 nm in size. The particles are regular and evenly distributed, with no obvious pores on the surface and high density. This shows that the secondary sintering process using chain phosphorus-containing compounds and pore-forming agents can effectively avoid the melt agglomeration growth of the material during high-temperature sintering and keep it in the form of nanoparticles.

[0085] Will Nano-Na4Fe 2.91 (PO4)2P2O7 Materials , SurP, PVDF5130 in a mass ratio of 9.5:0.2:0.3 For example, the solid content of the mixed slurry is controlled at 62%. The viscosity of the slurry is 3000~4000mPa·s, and the fluidity is good, which means that the material has low adsorption of solvent and binder during the homogenization process. It can be further seen from Table 1 that the porosity of the nanomaterial is only 0.2%, and the compacted density of the powder is as high as 2.20g / cm 3 Compared with the agglomerated material in Comparative Example 1, it has lower porosity, denser structural arrangement, and higher compaction density, which can improve the slurry stability during the preparation of the battery cell to a certain extent and ensure the smooth progress of the slurrying, coating and other processes. Of The black slurry was then coated on aluminum foil using a 150um four-sided preparation device, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator, and assembled into a CR2016 button cell in a glove box.

[0086] The electrochemical performance test results in Table 1 show that the material has a discharge capacity of 122.3 mAh / g at a rate of 0.1C (1C = 129 mAh / g), which is much higher than the discharge capacity of 110.4 mAh / g in Comparative Example 1. The difference in electrochemical performance is related to the particle size distribution of the material. After the material is nano-sized, the contact area between its interface and the electrolyte increases, the sodium ion deintercalation sites at the interface increase, the material reaction is more complete, and the capacity is higher. In addition, at a rate of 10C, the capacity retention rate of the material relative to that at a rate of 0.1C is 95.7%, which shows excellent rate performance compared to the 86.3% capacity retention rate of the agglomerate material in Comparative Example 1, indicating that after the material is nano-sized, the diffusion path of sodium ions from the material interface to its bulk structure becomes shorter, the diffusion time is reduced, and the diffusion capacity is greatly improved, which is very suitable for the high-power characteristics of batteries in high-power scenarios.

[0087] Application Example 2 Synthesis and Electrochemical Performance of Nano-Na3V2(PO4)3 Materials The preparation method of the nano Na3V2(PO4)3 material of this embodiment comprises the following steps: Step 1: Mix vanadium pentoxide, polyamino polyether methylene phosphonic acid, sodium acetate and sucrose (added in an amount of 6% of the weight of vanadium pentoxide) in a molar ratio of 1:3:3 with water, grind with a sand mill, control the solid content at 47%, grind until the particle size of vanadium pentoxide in the slurry is Dmax≤100, and form a uniform homogeneous emulsion; Step 2: spray drying the homogeneous solution, with an air inlet temperature of 240°C and an air outlet temperature of 800°C, to achieve solid-liquid separation and obtain a dry precursor powder; Step 3: In a nitrogen atmosphere, the dried precursor powder is kept at 260°C for 5 hours to promote the decomposition of polyaminopolyether methylenephosphonic acid, sucrose, etc., to complete the formation of primary crystal nuclei of nano-Na3V2(PO4)3 material, and then naturally cooled to obtain a black pre-crystallized precursor powder; Step 4: Mix the black pre-crystallized precursor powder with ammonium oxalate (the addition amount is 4.1% of the precursor weight), and grind it with a dry planetary ball mill. The ball milling ratio is controlled at 20:1, and the time is ≥10h to ensure uniform mixing between the two to form a premixed precursor; Step 5: In an argon atmosphere, the premixed precursor is calcined at 720°C for 8 hours, and the gas released by the decomposition of ammonium oxalate during the high-temperature sintering process is used to block the melting between the particles. After natural cooling, the nano-Na3V2(PO4)3 material is obtained.

[0088] Will Nano-state Na3V2(PO4)3 material , SurP, PVDF5130 are mixed in a mass ratio of 9.6:0.2:0.2 Homogenize, solid content controlled at 58%,The viscosity of the slurry is 4000~5000mPa·s, and the fluidity is good, which means that the nano-state material is not easy to absorb solvents and binders during the homogenization process, and maintains good dispersibility and fluidity. It can be further seen from Table 1 that the porosity of the nano-state material is only 0.1%, and the compacted density of the powder is as high as 2.25g / cm 3 This is consistent with the fact that the above-mentioned slurry has lower viscosity and better fluidity, indicating that after the material is nano-sized, the particles do not have a large number of pore structures caused by agglomeration, and the surface structure of the nanoparticles themselves is densely arranged with low porosity, which can improve the stability of the slurry in the process of battery cell preparation to a certain extent and ensure the smooth progress of the slurrying, coating and other processes. Of The black slurry was then coated on aluminum foil using a 150um four-sided preparation device, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator, and assembled into a CR2016 button cell in a glove box.

[0089] The electrochemical performance test results in Table 1 show that the material has a discharge capacity of 115.7 mAh / g at a rate of 0.1C (1C = 120 mAh / g), which is much higher than the discharge capacity of 102.3 mAh / g in Comparative Example 2, indicating that after the material is nano-sized, the exposed interface of the material has an increased contact area with the electrolyte, the sodium ion reaction sites have increased, the sodium ion reaction in the material phase structure is more sufficient, and the deintercalation capacity has increased. In addition, at a rate of 10C, the capacity retention rate of the material relative to that at a rate of 0.1C is 96.2%, which shows excellent rate performance compared to the 80.9% capacity retention rate of the agglomerate material in Comparative Example 2, indicating that after the material is nano-sized, the sodium ion reaction kinetics are improved, the reaction sites at the material interface are increased, and the diffusion distance from the material interface to the bulk structure is shortened, the diffusion time is greatly reduced, and the rate performance is significantly improved.

[0090] Comparative Example 1 Agglomerated Na4Fe 2.91 Synthesis and electrochemical properties of (PO4)2P2O7 materials Agglomerated Na4Fe in this example 2.91 The preparation method of (PO4)2P2O7 material comprises the following steps: Step 1: Mix ferric hydroxide and sodium dihydrogen phosphate with glucose (the addition amount is 7% of the weight of ferric hydroxide) in a molar ratio of 2.91:4 with water, grind with a sand mill, control the solid content at 35%, grind until the particle size of ferric hydroxide particles in the slurry is Dmax≤100, and form a uniform homogeneous emulsion; Step 2: spray drying the homogeneous solution at an air inlet temperature of 280°C and an air outlet temperature of 100°C to achieve solid-liquid separation and obtain a dry precursor powder; Step 3: In an argon atmosphere, the precursor powder was calcined at 650 °C for 10 h to promote the decomposition of glucose and the melting, crystallization, and nucleation growth of the material. After natural cooling, the agglomerated Na4Fe 2.91 (PO4)2P2O7 material.

[0091] Figure 2 Agglomerated Na4Fe 2.91 The morphology of the (PO4)2P2O7 material is a secondary particle formed by the agglomeration of primary particles of about 100 nm. There are a large number of pores on the particles, and there is an obvious melting growth phenomenon between the primary particles. This is mainly due to the melting and nucleation growth of the single-molecule phosphorus source during the spray drying and subsequent high-temperature sintering process, which eventually leads to adhesion between the particles and then agglomeration.

[0092] Aggregate Na4Fe 2.91 (PO4)2P2O7 Materials , SurP, PVDF5130 in a mass ratio of 9.5:0.2:0.3 For example, the solid content of the mixed slurry is controlled at 62%. The viscosity of the slurry is 8000~10000mPa·s, which is too high and has poor fluidity, indicating that the interface and a large number of pores inside the material have serious liquid and glue absorption during the slurry processing. It can be further seen from Table 1 that the porosity of the nanomaterial is as high as 3.6%, and the powder compaction density is only 1.82g / cm 3 Compared with the nano-material in Application Example 1, the higher porosity results in a fluffy material structure, a significant decrease in compactness, and a low compaction density, which to a certain extent leads to a decrease in the stability of the slurry during the preparation of the battery cell, which is not conducive to the slurrying and coating processes. Of The black slurry was then coated on aluminum foil using a 150um four-sided preparation device, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator, and assembled into a CR2016 button cell in a glove box.

[0093] The electrochemical performance test results in Table 1 show that the discharge capacity of the material at a rate of 0.1C (1C=129mAh / g) is only 110.4mAh / g, which is much lower than the discharge capacity of 122.3mAh / g of the nanomaterial in Application Example 1. The difference in electrochemical capacity is related to the agglomeration of the particles. When the particles are agglomerates, there are a large number of connection interfaces caused by melting. The formation of the interface reduces the effective area for sodium ion deintercalation at the material interface, resulting in inactivation of some sites and a decrease in capacity. In addition, at a rate of 10C, the capacity retention rate of the material relative to that at a rate of 0.1C is 86.3%, which is much lower than the capacity retention rate of 95.7% in Application Example 1, showing poor rate performance. This indicates that after the material agglomerates, the contact surface between the material and the electrolyte is reduced, that is, the sodium ion migration channel is reduced. Larger particles will also increase the diffusion distance of sodium ions from the interface to the bulk phase, and the diffusion time will increase. At the same time, the grain boundaries formed by the molten interface between the particles also hinder the transmission of sodium ions. The above reasons together lead to a decrease in the rate performance of the agglomerate.

[0094] Comparative Example 2 Synthesis and electrochemical performance of agglomerated Na3V2(PO4)3 materials The preparation method of the agglomerated Na3V2(PO4)3 material of this embodiment comprises the following steps: Step 1: Mix vanadium pentoxide, sodium dihydrogen phosphate and sucrose (the added amount is 6% of the weight of vanadium pentoxide) with water in a molar ratio of 1:3, grind with a sand mill, control the solid content at 47%, grind until the particle size of vanadium pentoxide in the slurry is Dmax≤100, and form a uniform homogeneous emulsion; Step 2: spray drying the homogeneous solution, with an air inlet temperature of 240°C and an air outlet temperature of 800°C, to achieve solid-liquid separation and obtain a dry precursor powder; Step 3: In an argon atmosphere, the premixed precursor is calcined at 720°C for 8 hours to promote the decomposition of sucrose and the melting, crystallization, and nucleation growth of the material. After natural cooling, the agglomerated Na3V2(PO4)3 material is obtained.

[0095] Will reunite Na3V2(PO4)3 material , SurP, PVDF5130 are mixed in a mass ratio of 9.6:0.2:0.2 Homogenize, solid content controlled at 58%, The viscosity of the discharged slurry is 11000~13000mPa·s, with poor fluidity and high viscosity, indicating that the slurry and binder are adsorbed on the surface or pore structure of the agglomerate during the homogenization process, resulting in a reduction in the free solvent or binder, which in turn leads to increased slurry viscosity and decreased fluidity. It can be further seen from Table 1 that the porosity of the agglomerated material is as high as 2.5%, and the powder compaction density is only 1.88g / cm 3This high-porosity and low-compaction powder material can easily absorb the molten liquid components in the slurry, resulting in a decrease in the stability of the slurry. This is consistent with the high viscosity and poor fluidity of the slurry mentioned above, indicating that the agglomerated material will produce a large number of pore structures due to its non-compactness during agglomeration, which will to a certain extent reduce the stability of the slurry during the preparation of the battery cell, and is not conducive to the smooth progress of the slurrying, coating and other processes. Of The black slurry was then coated on aluminum foil using a 150um four-sided preparation device, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine, with metallic sodium as the counter electrode, 1 mol / L NaClO4EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator, and assembled into a CR2016 button cell in a glove box.

[0096] The electrochemical performance test results in Table 1 show that the material has a discharge capacity of 102.3 mAh / g at a rate of 0.1C (1C = 120 mAh / g), which is much lower than the discharge capacity of 115.7 mAh / g in Application Example 2, indicating that some sodium storage sites in the agglomerated material are inactivated, and the reason is that the deintercalation and deintercalation paths of sodium ions are destroyed at the agglomerated interface of the material, resulting in the obstruction of deintercalation and the failure of capacity. In addition, at a rate of 10C, the capacity retention rate of the material relative to that at a rate of 0.1C is only 80.9%, which is poor compared with the capacity retention rate of 96.2% of the nano-state material in Application Example 2. This shows that after the material is agglomerated, the contact interface with the electrolyte is reduced, the sodium ion deintercalation sites are reduced, the diffusion distance of sodium ions from the interface to the bulk phase is increased, and the diffusion time is prolonged. At the same time, the grain boundaries formed by agglomeration will also cause the diffusion of sodium ions to be obstructed, which ultimately affects the diffusion rate of sodium ions and leads to a decrease in the rate performance of the material.

[0097] The performance test results of application examples 1-2 and comparative examples 1-2 are shown in Table 1: Table 1 Performance test results The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A method for preparing a nano-polyanion type sodium ion battery positive electrode material, characterized in that The following steps are involved: S1. Preparation of homogeneous slurry: mixing and wet-grinding an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source to form a homogeneous slurry; S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder; S3, preparation of pre-crystallized precursor powder: pre-sintering the precursor powder at low temperature under a protective atmosphere to obtain pre-crystallized precursor powder; S4, preparation of premixed precursor: mixing pre-crystallized powder with pore-forming agent, and using dry ball milling to achieve uniform mixing of the two to form a premixed precursor; S5. High-temperature calcination: Under a protective atmosphere, the premixed precursor is calcined at a high temperature, and the temperature is naturally reduced to obtain a nano-polyanion sodium ion battery positive electrode material.

2. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S1, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤100 nm.

3. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S3, the low-temperature pre-sintering conditions are a sintering temperature of 200-400°C and a holding time of >0.1H.

4. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S5, the high temperature calcination conditions are a sintering temperature of 400-800°C and a holding time of >0.1H.

5. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S1 , the wet grinding method is one or more of homogeneous dispersion, ball milling dispersion, and sand milling dispersion.

6. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S2, the drying method is one or more of flash drying, spray drying, high temperature cracking, and high temperature evaporation.

7. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In steps S3 and S5, the protective atmosphere is one or more of nitrogen, argon, hydrogen, carbon monoxide, and helium.

8. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 1, characterized in that: In step S4, the dry ball milling method is one or more of planetary ball milling, high energy grinding, and high speed mixing.

9. The method for preparing the nano-polyanion type sodium ion battery positive electrode material according to claim 8, characterized in that: The alkali metal source is a sodium source, and the sodium source is one or more of sodium acetate, sodium sulfate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium formate, sodium citrate, sodium gluconate, sodium methoxide, sodium phenolate, sodium tert-butoxide, sodium phenolate, sodium butyrate, sodium tartrate, sodium oleate, and sodium ethylenediaminetetraacetate; The water-insoluble transition metal source is one or more of an iron source, a manganese source, and a cobalt source; the iron source is one or more of ferric hydroxide, ferrous hydroxide, ferric oxide, ferrous oxide, ferric tetroxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the manganese source is one or more of manganese monoxide, manganese dioxide, dimanganese trioxide, trimanganese tetraoxide, manganous anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is one or more of cobalt oxide, high cobalt oxide, tricobalt tetroxide, cobalt oxalate, etc.; The chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylene triamine penta methylene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, polyamino polyether methylene phosphonic acid, and bis-1,6-hexamethylene triamine penta methylene phosphonic acid; The organic carbon source is one or more of citric acid, starch, maltose, sucrose, ascorbic acid, glucose, asphalt, phenolic resin, cellulose, polyvinyl alcohol, polypropylene alcohol, polyacrylic acid, succinic acid, lactic acid, cyclodextrin, and ethanol; The pore-forming agent is one or more of oxalic acid, ammonium oxalate, ammonium nitrate, ammonium sulfate and ammonium chloride.

10. A nano-polyanion sodium ion battery positive electrode material, characterized in that: The polyanion sodium ion battery positive electrode material is prepared by the preparation method of any one of claims 1 to 9; the positive electrode material of the polyanion sodium ion battery is sodium iron phosphate, sodium manganese iron phosphate, sodium cobalt phosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron pyrophosphate or sodium manganese pyrophosphate, sodium cobalt pyrophosphate.

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