A nano-polyanion sodium ion battery positive electrode material and preparation method thereof

Abstract

The present invention discloses a nano-polyanion sodium ion battery cathode material and a preparation method thereof. The preparation method comprises the following steps: S1, preparation of a homogeneous slurry; S2, preparation of a precursor powder; S3, preparation of a pre-crystallized precursor powder; S4, preparation of a pre-mixed precursor: mixing the pre-crystallized powder with a pore-forming agent, and dry ball milling the mixture to achieve uniform mixing of the two to form a pre-mixed precursor; S5, high-temperature calcination: calcining the pre-mixed precursor at a high temperature under a protective atmosphere, and naturally cooling the mixture to obtain the nano-polyanion sodium ion battery cathode material. The nano-polyanion sodium ion battery cathode material and the preparation method thereof of the present invention have the characteristics of complete nanoparticles, high compaction density, excellent rate performance, and effectively improved capacity.

Description

Technical Field

[0001] The present 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 (NABs) have gained market favor due to their high structural stability, low cost, and excellent cycle stability. Currently, the most widely studied polyanion material system is composite sodium iron phosphate (Na4Fe3(PO4)2P2O7), which consists of alkali metal groups, transition metal groups, and two anionic groups arranged in a cross-point / surface / line pattern to form a three-dimensional framework. However, nanofabrication of this composite structure is 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 the transition metal particles, causing the particles to stick together. During the subsequent sintering process, the particles melt and diffuse at the sticking points, crystallizing and nucleating to form interwoven secondary particle agglomerates. These agglomerates contain numerous pores, resulting in a low compacted density, making processing difficult and limiting their application and promotion. Summary of the Invention

[0005] The purpose of the present invention is to provide a nano-state 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 achieved through the following technical solutions:

[0007] The present invention discloses a method for preparing a nano-polyanion sodium ion battery positive electrode material, comprising the following steps:

[0008] S1. Preparation of a homogeneous slurry: mixing an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source, and wet-grinding the mixture to form a homogeneous slurry;

[0009] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder;

[0010] S3. Preparation of pre-crystallized precursor powder: pre-sintering the precursor powder at a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder;

[0011] S4. Preparation of premixed precursor: mixing the pre-crystallized powder with the pore-forming agent, and performing dry ball milling to achieve uniform mixing of the two to form a premixed precursor;

[0012] 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.

[0013] The present invention discloses a process for preparing a nano-polyanion-type positive electrode material for a talent battery. This process replaces the traditional monomolecular phosphorus source with a chain-type phosphorus-containing compound. The weak interaction between the lone pairs of electrons on the oxygen atoms connected to the phosphorus in the chain-type phosphorus-containing compound and the transition metal particle interface prevents adhesion between particles during the drying process. Simultaneously, a pore-forming agent is mixed with the pre-calcined black precursor powder. The gases released during the high-temperature decomposition of the pore-forming agent hinder the fusion growth between particles, thereby disrupting the formation of secondary particle agglomerates. Ultimately, primary nanoparticles with uniform particle size and high particle integrity are obtained, thereby improving the material's compaction density, processing performance, and electrochemical properties.

[0014] 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 conducive to the mutual bonding and growth between the elements during the sintering process, and to generate a structure with high purity and complete crystal form.

[0015] 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.

[0016] 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 gasification 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.

[0017] 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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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 edetate.

[0022] 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, manganic anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is one or more of cobalt oxide, cobalt oxide, cobalt tetroxide, cobalt oxalate, etc.

[0023] Preferably, the chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine 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.

[0024] 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.

[0025] 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 temperatures, 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 larger than nanometer level.

[0026] Another aspect of the present invention is to protect a nano-polyanion sodium ion battery positive electrode material, which is prepared using the above-mentioned preparation method.

[0027] 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.

[0028] 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.

[0029] The present invention provides a nano-polyanion sodium ion battery cathode material and a preparation method thereof, which has the following beneficial effects:

[0030] First, the nanoparticles are complete. The chain-type 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 attached to the phosphorus atoms, which easily generate weak interactions with transition metal elements. It disperses between transition metal particles in the slurry, acting as a bridge. During the drying process, it prevents the adhesion and agglomeration of transition metal particles caused by water evaporation, which is a key step in the construction of nanomaterial precursors. After the precursor powder is pre-calcined at low temperature, the chain-type phosphorus-containing compound decomposes by chain scission, resulting in localized contact between primary crystal nuclei. This step requires the addition of a pore-forming agent to disrupt this contact. The pore-forming agent utilizes gases such as carbon dioxide and nitrogen dioxide released during its high-temperature pyrolysis to block further contact between the primary crystal nuclei, thereby forming a single nanomaterial particle.

[0031] 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 solid single crystal primary particles. During the powder rolling process, different primary particles fill each other, which can achieve lower porosity and higher compaction density (2.15-2.25g / cm 3 ).

[0032] Third, the rate performance is excellent. The present invention improves the transmission dynamics of electrons and ions in the material through 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-sizing, the specific surface area increases, the wetting area of ​​the electrolyte at the material interface increases, and the number of ions diffused at the interface between the electrolyte and the material will increase significantly; fourth, after the material is nano-sizing, the distribution area and uniformity of the conductive carbon layer at the material interface increase, effectively expanding the electron transmission path; for the above reasons, after the material is nano-sizing, the electronic conductivity and ionic conductivity will be significantly improved, and the material will obtain high-rate properties.

[0033] Fourth, capacity is significantly increased. In addition to the material's inherent structure, the capacity is also influenced by pseudocapacitance at the interface. Nanosizing the material increases its specific surface area, and during charge and discharge, the amount of charge that can be stored increases year-on-year, accompanied by an increase in pseudocapacitance adsorbed on the material interface. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 For application example 1, nanometer Na4Fe 2.91 (PO4)2P2O7 material morphology;

[0035] Figure 2 Comparative Example 1 Agglomerated Na4Fe 2.91 (PO4)2P2O7 material morphology. DETAILED DESCRIPTION

[0036] 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 with reference to embodiments.

[0037] The present invention discloses a method for preparing a nano-polyanion sodium ion battery positive electrode material, comprising the following steps:

[0038] S1. Preparation of a homogeneous slurry: mixing an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source, and wet-grinding the mixture to form a homogeneous slurry;

[0039] S2. Preparation of precursor powder: drying the homogeneous slurry to complete solid-liquid separation to obtain dry precursor powder;

[0040] S3. Preparation of pre-crystallized precursor powder: pre-sintering the precursor powder at a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder;

[0041] S4. Preparation of premixed precursor: mixing the pre-crystallized powder with the pore-forming agent, and performing dry ball milling to achieve uniform mixing of the two to form a premixed precursor;

[0042] 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.

[0043] 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 conducive to the mutual bonding and growth between the elements during the sintering process, and to generate a structure with high purity and complete crystal form.

[0044] 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.

[0045] 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 gasification 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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 edetate.

[0051] 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, manganic anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is one or more of cobalt oxide, cobalt oxide, cobalt tetroxide, cobalt oxalate, etc.

[0052] Preferably, the chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine 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.

[0053] 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.

[0054] 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 temperatures, 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 larger than nanometer level.

[0055] Another aspect of the present invention is to protect a nano-polyanion sodium ion battery positive electrode material, which is prepared using the above-mentioned preparation method.

[0056] 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.

[0057] 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.

[0058] Example 1

[0059] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0060] S1. Preparation of a homogeneous slurry: 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 to achieve homogeneous dispersion.

[0061] 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.

[0062] S3. Preparation of pre-crystallized precursor powder: Pre-sintering the precursor powder at a 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 h, and a protective atmosphere of nitrogen.

[0063] S4. Preparation of premixed precursor: pre-crystallized powder and pore-forming agent are mixed and dry ball milled to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is planetary ball milling.

[0064] S5. High-temperature calcination: The premixed precursor is calcined at high temperature under a protective atmosphere, and then cooled naturally to obtain a nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 800°C and a holding time of 0.5 hours in an argon protective atmosphere.

[0065] 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.

[0066] Example 2

[0067] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0068] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm; the wet-ground method is ball milling dispersion.

[0069] 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.

[0070] S3. Preparation of pre-crystallized precursor powder: Pre-sintering the precursor powder at a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are: a sintering temperature of 300° C., a holding time of 0.5 h, and a protective atmosphere of nitrogen or argon.

[0071] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and use dry ball milling to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is high-energy grinding.

[0072] S5. High-temperature calcination: The premixed precursor is calcined at high temperature under a protective atmosphere, and then cooled naturally to obtain a nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 600°C and a holding time of 0.2 hours in a protective atmosphere of hydrogen and carbon monoxide.

[0073] 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 pyrodiethylenetriamine penta (methylene phosphonic acid), 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, and polyamino polyether methylene phosphonic 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.

[0074] Example 3

[0075] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0076] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm; the wet-ground method is sand milling dispersion.

[0077] 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 or high-temperature evaporation.

[0078] S3. Preparation of pre-crystallized precursor powder: Pre-sinter the precursor powder at a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are a sintering temperature of 200°C and a holding time of 2 hours in a protective atmosphere of carbon monoxide and helium.

[0079] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and use dry ball milling to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method is high-speed mixing.

[0080] S5. High-temperature calcination: Calcine the premixed precursor at high temperature under a protective atmosphere and allow the mixture to cool naturally to obtain the nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 400°C and a holding time of 1 hour in a protective atmosphere of nitrogen or helium.

[0081] 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, or sodium hydroxide; the water-insoluble transition metal source is a manganese source, and the manganese source is manganese monoxide, manganese dioxide, or manganese trioxide; the chain phosphorus-containing compound is polyaminopolyether 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, or ethanol; and the pore-forming agent is oxalic acid or ammonium oxalate.

[0082] Example 4

[0083] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0084] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm. The wet-ground method includes homogeneous dispersion or ball milling.

[0085] 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 pyrolysis.

[0086] S3. Preparation of pre-crystallized precursor powder: Pre-sintering the precursor powder at a 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; the protective atmosphere is nitrogen, carbon monoxide.

[0087] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and perform dry ball milling to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method includes planetary ball milling and high-energy grinding.

[0088] S5. High-temperature calcination: The premixed precursor is calcined at high temperature under a protective atmosphere, and then cooled naturally to obtain a nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 600°C and a holding time of 1 hour in a protective atmosphere of nitrogen, carbon monoxide, and helium.

[0089] 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.

[0090] Example 5

[0091] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0092] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm. The wet-ground method is ball milling or sand milling.

[0093] S2. Preparation of precursor powder: drying the homogeneous slurry, completing solid-liquid separation, and obtaining dry precursor powder. Specifically, the drying method is spray drying, high temperature evaporation,

[0094] S3. Preparation of pre-crystallized precursor powder: Pre-sintering the precursor powder at a 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 hours; the protective atmosphere is nitrogen, argon, or helium.

[0095] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and perform dry ball milling to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method includes planetary ball milling and high-energy grinding.

[0096] S5. High-temperature calcination: Calcine the premixed precursor at high temperature under a protective atmosphere and allow the mixture to cool naturally to obtain the nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 500°C and a holding time of 2 hours in a protective atmosphere of nitrogen or argon.

[0097] In this embodiment, the alkali metal source is a sodium source, and the sodium source is sodium acetate, sodium sulfate, or sodium nitrate; the water-insoluble transition metal source is a cobalt source, and the cobalt source is cobalt oxide or high cobalt oxide; the chain phosphorus-containing compound is sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylidene diphosphonic acid, aminotrimethylenephosphonic acid, and ethylenediaminetetramethylenephosphonic 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, or ammonium chloride.

[0098] Example 6

[0099] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0100] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm. The wet-ground method includes homogeneous dispersion or sand milling.

[0101] 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.

[0102] S3. Preparation of pre-crystallized precursor powder: Pre-sintering the precursor powder at a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder. Specifically, the low-temperature pre-sintering conditions are a sintering temperature of 300°C and a holding time of 2 hours in a protective atmosphere of nitrogen, carbon monoxide, and helium.

[0103] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and use dry ball milling to achieve uniform mixing of the two to form a premixed precursor. Specifically, the dry ball milling method includes planetary ball milling, high-speed mixing.

[0104] S5. High-temperature calcination: The premixed precursor is calcined at high temperature under a protective atmosphere, and then cooled naturally to obtain a nano-polyanion sodium-ion battery cathode material. Specifically, the high-temperature calcination conditions are a sintering temperature of 700°C and a holding time of 0.7 hours in a protective atmosphere of carbon monoxide and helium.

[0105] 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 bis-1,6-hexamethylenetriamine penta-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.

[0106] Example 7

[0107] This embodiment relates to a nano-polyanion sodium ion battery positive electrode material, the preparation method of which includes the following steps:

[0108] S1. Preparation of a homogeneous slurry: An alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source are mixed and wet-ground to form a homogeneous slurry. Specifically, the maximum particle size Dmax of the solid particles in the homogeneous slurry is ≤ 100 nm. The wet-ground method includes homogeneous dispersion, ball milling, or sand milling.

[0109] 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.

[0110] S3. Preparation of pre-crystallized precursor powder: Pre-sinter the precursor powder at a 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 for 3 hours in a protective atmosphere of nitrogen, argon, hydrogen, carbon monoxide, or helium.

[0111] S4. Preparation of premixed precursor: Mix the pre-crystallized powder with the pore-forming agent and perform dry ball milling 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.

[0112] S5. High temperature calcination: calcining the premixed precursor at high temperature under a protective atmosphere, and then cooling naturally to obtain the nano-state polyanion type sodium ion battery positive electrode material. Specifically, the high temperature calcination conditions are sintering temperature 400-800℃, holding time>0.1H; the protective atmosphere is nitrogen, argon, hydrogen, carbon monoxide, helium

[0113] 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 phenolate, sodium tert-butoxide, sodium phenolate, 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, ferric tetroxide, ferrous oxalate, ferric phosphate, and ferrous phosphate; the manganese source is one or more of manganese monoxide, manganese dioxide, manganese trioxide, manganic 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, hydroxyethylene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine penta methylene phosphonic acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, polyol phosphate, 2-hydroxyphosphonoacetic acid, polyamino polyether methylene phosphonic acid, bis-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, ammonium chloride.

[0114] Application Example 1 Nano-state Na4Fe 2.91 Synthesis and electrochemical properties of (PO4)2P2O7 materials

[0115] Nano-state Na4Fe in this embodiment 2.91 The preparation method of (PO4)2P2O7 material comprises the following steps:

[0116] Step 1: Sodium citrate, ferric hydroxide, sodium pyrophosphate, and hydroxyethylidene diphosphonic acid are mixed with glucose (added in an amount of 5% by weight of ferric hydroxide) in a molar ratio of 1:2.91:0.125:1.938, and water is added. The mixture is ground using a sand mill with a solid content controlled at 35% until the particle size Dmax of the ferric hydroxide particles in the slurry is ≤100, forming a uniform homogeneous emulsion.

[0117] 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;

[0118] Step 3: In a nitrogen atmosphere, the dried precursor powder was 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 natural cooling to obtain black pre-crystallized precursor powder;

[0119] Step 4: Mix the black pre-crystallized precursor powder with oxalic acid (5.3% of the precursor weight) and grind them in a dry planetary ball mill with a ball milling ratio of 20:1 for ≥10 h to ensure uniform mixing between the two to form a premixed precursor.

[0120] 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 cooling naturally, the nano-Na4Fe 2.91 (PO4)2P2O7 material.

[0121] Figure 1 Nano-state Na4Fe 2.91 The morphology of the (PO4)2P2O7 material shows that it is nano-particles of about 100nm. 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 nano-state.

[0122] Will Nano-state 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, indicating that the material has low adsorption of solvents and binders during the homogenization process. As can be seen from Table 1, the porosity of the nanomaterial is only 0.2%, and the powder compaction density 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 battery cell preparation process to a certain extent and ensure the smooth progress of slurrying, coating and other processes. OfThe black slurry was then coated onto aluminum foil using a 150 μm four-sided film preparation device and dried in a vacuum drying oven at 100°C for 2 hours. A sheet puncher was used to punch the electrode film into discs with a radius of 0.6 mm. CR2016 button cells were assembled in a glove box using sodium metal 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.

[0123] 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. This shows 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.

[0124] Application Example 2 Synthesis and Electrochemical Performance of Nano-Na3V2(PO4)3 Materials

[0125] The preparation method of the nano-state Na3V2(PO4)3 material of this embodiment includes the following steps:

[0126] Step 1: Vanadium pentoxide, polyaminopolyether methylenephosphonic acid, sodium acetate and sucrose (added in an amount of 6% of the weight of the vanadium pentoxide) are mixed in a molar ratio of 1:3:3 with water, and ground using a sand mill with a solid content controlled at 47% until the particle size of the vanadium pentoxide in the slurry is Dmax ≤ 100, forming a uniform homogeneous emulsion;

[0127] Step 2: spray drying the homogeneous solution at 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;

[0128] Step 3: In a nitrogen atmosphere, the dried precursor powder is kept at 260°C for 5 hours to promote the decomposition of polyaminopolyether methylene phosphonic acid, sucrose, etc., to complete the formation of primary crystal nuclei of nano-state Na3V2(PO4)3 material, and then naturally cooled to obtain black pre-crystallized precursor powder;

[0129] Step 4: Mix the black pre-crystallized precursor powder with ammonium oxalate (4.1% of the precursor weight) and grind them in a dry planetary ball mill with a ball milling ratio of 20:1 for ≥10 h to ensure uniform mixing between the two to form a premixed precursor.

[0130] Step 5: In an argon atmosphere, the premixed precursor is calcined at 720°C for 8 hours. 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.

[0131] Will Nano-state Na3V2(PO4)3 material , SurP, PVDF5130 are mixed in a mass ratio of 9.6:0.2:0.2 Homogenate, solid content controlled at 58%, The viscosity of the slurry is 4000~5000mPa·s, and the fluidity is good, indicating that the nanomaterial is not easy to absorb solvents and binders during the homogenization process, maintaining good dispersion and fluidity. As can be seen from Table 1, the porosity of the nanomaterial is only 0.1%, and the powder compaction density is as high as 2.25g / cm 3 This is consistent with the lower viscosity and better fluidity of the above-mentioned slurry, 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. To a certain extent, it can improve the stability of the slurry in the process of battery cell preparation and ensure the smooth progress of the slurry, coating and other processes. Of The black slurry was then coated onto aluminum foil using a 150 μm four-sided film preparation device and dried in a vacuum drying oven at 100°C for 2 hours. A sheet puncher was used to punch the electrode film into discs with a radius of 0.6 mm. CR2016 button cells were assembled in a glove box using sodium metal 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.

[0132] 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. This shows that after the material is nano-sized, the exposed interface of the material increases in contact with the electrolyte, the sodium ion reaction sites increase, the reaction of sodium ions in the material phase structure is more sufficient, and the deintercalation capacity is improved. 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. This shows that after the material is nano-sized, the sodium ion reaction kinetics are improved, the reaction sites at the material interface increase, 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.

[0133] Comparative Example 1 Agglomerated Na4Fe 2.91 Synthesis and electrochemical properties of (PO4)2P2O7 materials

[0134] Agglomerated Na4Fe in this example 2.91 The preparation method of (PO4)2P2O7 material comprises the following steps:

[0135] Step 1: Mix ferric hydroxide and sodium dihydrogen phosphate in a molar ratio of 2.91:4 with glucose (added in an amount of 7% by weight of the ferric hydroxide) and add water, grind using a sand mill, control the solid content at 35%, and grind until the particle size of the ferric hydroxide particles in the slurry is Dmax ≤ 100, forming a uniform homogeneous emulsion;

[0136] 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;

[0137] 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.

[0138] Figure 2 Agglomerated Na4Fe 2.91 The morphology of the (PO4)2P2O7 material shows that it 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 the agglomeration phenomenon.

[0139] Agglomerated stateNa4Fe 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 discharged slurry is 8000~10000mPa·s, which is too high and has poor fluidity. This indicates that the interface and internal pores of the material have serious liquid and glue absorption during the slurry processing. As can be seen from Table 1, 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-state material in Application Example 1, the higher porosity results in a fluffy material structure, a significant decrease in density, 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 slurry and coating processes. Of The black slurry was then coated onto aluminum foil using a 150 μm four-sided film preparation device and dried in a vacuum drying oven at 100°C for 2 hours. A sheet puncher was used to punch the electrode film into discs with a radius of 0.6 mm. CR2016 button cells were assembled in a glove box using sodium metal 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.

[0140] 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 inside them. The formation of this interface will reduce the effective area for sodium ions to be deintercalated and deintercalated 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 is 86.3% relative to that at a rate of 0.1C, 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.

[0141] Comparative Example 2 Synthesis and Electrochemical Performance of Agglomerated Na3V2(PO4)3 Materials

[0142] The preparation method of the agglomerated Na3V2(PO4)3 material of this embodiment comprises the following steps:

[0143] Step 1: Vanadium pentoxide, sodium dihydrogen phosphate, and sucrose (added in an amount of 6% by weight of the vanadium pentoxide) are mixed with water in a molar ratio of 1:3, and ground using a sand mill with a solid content controlled at 47% until the particle size of the vanadium pentoxide in the slurry is Dmax ≤ 100, forming a uniform homogeneous emulsion;

[0144] Step 2: spray drying the homogeneous solution at 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;

[0145] 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.

[0146] Will reunite Na3V2(PO4)3 material , SurP, PVDF5130 are mixed in a mass ratio of 9.6:0.2:0.2 Homogenate, solid content controlled at 58%, The viscosity of the discharged slurry is 11,000-13,000 mPa·s, indicating poor fluidity and high viscosity. This indicates that during the homogenization process, the slurry and binder are adsorbed on the surface or in the pore structure of the agglomerate, resulting in a reduction in the free solvent or binder, which in turn leads to increased slurry viscosity and decreased fluidity. As can be seen from Table 1, the porosity of the agglomerated material is as high as 2.5%, and the powder compaction density is only 1.88 g / cm 3 This high-porosity, low-compaction powder material easily absorbs 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 processes such as homogenization and coating. Of The black slurry was then coated onto aluminum foil using a 150 μm four-sided film preparation device and dried in a vacuum drying oven at 100°C for 2 hours. A sheet puncher was used to punch the electrode film into discs with a radius of 0.6 mm. CR2016 button cells were assembled in a glove box using sodium metal 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.

[0147] 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. This indicates that some sodium storage sites in the agglomerated material are inactivated. The reason is that the deintercalation and deintercalation paths of sodium ions at the agglomerated interface of the material are destroyed, resulting in blocked deintercalation and failure of capacity utilization. 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-material in Application Example 2. This indicates that after the material agglomerates, 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, the diffusion time is prolonged, and the grain boundaries formed by agglomeration also hinder the diffusion of sodium ions, which ultimately affects the diffusion rate of sodium ions and leads to a decline in the rate performance of the material.

[0148] The performance test results of Application Example 1-2 and Comparative Example 1-2 are shown in Table 1:

[0149] Table 1 Performance test results

[0150]

[0151] The above embodiments are merely specific embodiments of the present invention, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the scope of the present invention, and such obvious alternatives are all within the scope of protection of the present invention.

Claims

1. A method for preparing a nano-polyanion sodium ion battery cathode material, characterized in that The following steps are involved: S1. Preparation of a homogeneous slurry: mixing an alkali metal source, a water-insoluble transition metal source, a chain phosphorus-containing compound, and an organic carbon source, and wet-grinding the mixture 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 a low temperature under a protective atmosphere to obtain pre-crystallized precursor powder; S4. Preparation of premixed precursor: mixing the pre-crystallized powder with the pore-forming agent, and performing dry ball milling to achieve uniform mixing of the two to form a premixed precursor; S5. High-temperature calcination: calcining the premixed precursor at high temperature under a protective atmosphere, and then cooling naturally to obtain a nano-polyanion sodium ion battery cathode material; The chain phosphorus-containing compound is one or more of sodium pyrophosphate, sodium metaphosphate, sodium polyphosphate, hydroxyethylidene diphosphonic acid, hydroxyethylene diphosphonic acid, amino trimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid, diethylenetriamine 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.

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

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

5. The method for preparing the nano-polyanion sodium ion battery positive electrode material according to claim 1, wherein: 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 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 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 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 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 edetate; 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, ferric 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, cobalt oxide, cobalt oxide, cobalt oxalate, etc.; 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 cathode material, characterized by: Prepared by the preparation method of any one of claims 1-9; the polyanion sodium ion battery positive electrode material 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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