Amorphous disordered precursor for positive electrode material of polyanion sodium-ion battery and its preparation method

Abstract

This invention discloses an amorphous disordered precursor for a polyanion-type sodium-ion battery cathode material and its preparation method. The precursor has the general chemical formula M. a (PO4) b (OH) c ·xH₂O, where M is one or more transition metal elements Fe, Co, or Mn, and the relationship between a, b, and c is 2a-3b-c=0 or 3a-3b-c=0; 1.0

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to an amorphous disordered precursor for a polyanionic sodium ion battery positive electrode material and a preparation method thereof. BACKGROUND

[0002] The polyanionic sodium ion battery positive electrode material has high structural stability, thermodynamic stability, excellent cycle stability and rate performance and is favored by the market. At present, the polyanionic material system researched more on the market includes sodium iron pyrophosphate phosphate, sodium pyrophosphate iron, sodium vanadium phosphate, sodium vanadium fluorophosphate and the like, which are formed into a three-dimensional framework structure by mutually crossing arrangement of alkali metal tetrahedron, transition metal tetrahedron / octahedron and anion tetrahedron / triangular pyramid in a common point / surface / line mode.

[0003] At present, the commercially available sodium iron pyrophosphate and the like are synthesized by a solid phase method, which uses high-crystallinity anhydrous FePO4, FeC2O4 and the like as a transition metal precursor source, combines a water-soluble sodium source, a phosphorus source and a carbon source, and realizes preparation of the material through processes such as grinding mixing, spray drying and sintering.

[0004] However, the high-crystallinity FePO4, FeC2O4 and the like are difficult to be completely dissolved in the solid grinding process, and they are often suspended in the solution in the form of solid particles of tens to hundreds of nanometers, the solid particles contain tens of thousands of atoms, and from the local point of view, the sodium, transition metal and phosphorus elements in the slurry are difficult to be mixed uniformly, and the sintering process is prone to cause phase separation, thereby affecting the performance of the material. Meanwhile, the high-crystallinity FePO4, FeC2O4 and the like have a long grinding time, high requirements for equipment parameters, high energy consumption and high process investment cost. Therefore, in order to obtain the polyanionic material with high phase purity and low manufacturing process cost, a suitable precursor needs to be developed for the polyanionic material, and the precursor needs to contain the elements required by the prepared material and exist in the form of amorphous bonding state. SUMMARY

[0005] The application aims to provide an amorphous disordered precursor for a polyanionic sodium ion battery positive electrode material and a preparation method thereof, which have the characteristics of adjustable structure, high phase purity, high compaction density, excellent electrochemical performance and low cost.

[0006] The application can be implemented by the following technical scheme:

[0007] The application discloses an amorphous disordered precursor for a polyanionic sodium ion battery positive electrode material, the precursor has a chemical general formula of M a (PO4) b (OH) c• xH2O, wherein M is one or more than two of transition metal elements Fe, Co or Mn, the relationship between a, b and c is 2a-3b-c=0 or 3a-3b-c=0; 1.0

[0008] Another aspect of the present application is to protect a preparation method of the above-mentioned poly-anionic sodium-ion battery cathode material amorphous disordered precursor, characterized in that comprising the following steps:

[0009] S1, preparation of precursor solution: mix transition metal M source, phosphorus source and water-soluble complexing agent with water, adjust the pH of the solution, promote the dissolution of transition metal, and avoid the generation of precipitation at the same time, to obtain the precursor solution;

[0010] S2, preparation of pre-oxidized precursor solution: add an acidic medium oxidant to the above-mentioned solution, oxidize the divalent metal ions in the solution to trivalent, to generate the pre-oxidized precursor solution;

[0011] S3, M a (PO4) b (OH) c • xH2O precipitation: add alkaline substances to the above-mentioned pre-oxidized precursor solution, adjust the pH of the solution, so that the transition metal ions in the solution generate M a (PO4) b (OH) c • xH2O precipitate;

[0012] S4, separation and treatment of precursor powder: after solid-liquid separation and drying of the above-mentioned precipitate, the poly-anionic cathode material M a (PO4) b (OH) c • xH2O precursor powder is obtained.

[0013] In the preparation method of the poly-anionic material precursor of the present application, the chemical general formula of the precursor is M a (PO4) b (OH) c • xH2O, which controls the pH reaction by using transition metal source and phosphorus source, and further controls the subsequent reaction rate by using water-soluble complexing agent to complex the transition metal ions in the solution. After the solution is oxidized, the pH of the solution is adjusted by adding alkaline, so that the transition metal ions in the solution generate M a (PO4) b (OH) c·xH2O precipitation, after the above precipitation solid-liquid separation, washing and drying, the final product is obtained. The precursor is a long-range disordered structure embedded by transition metal ions, phosphate and hydroxyl ions. The particle size is small, and there is no crystallinity. It is easy to grind and disperse, and when mixed with other components, it has good uniformity. After sintering, the prepared material has high crystallinity, high phase purity and excellent electrochemical performance.

[0014] Further, in step S1, the pH range is 0-1.5, which aims to ensure that the transition metal can be completely dissolved, and the transition metal ions in the solution do not react with components such as phosphate to generate precipitates.

[0015] Further, in step S3, the pH range is 1.5-6.0, which aims to make the transition metal ions in the solution co-precipitate with phosphate and hydroxyl ions to form M a (PO4) b (OH) c ·xH2O form, the precipitate has a long-range disordered nanocrystalline structure, which is beneficial to the uniform mixing of raw materials in the subsequent material preparation process; when the pH is lower than 1.5, the precipitate cannot be precipitated, and when the pH is higher than 6.0, M a (PO4) b (OH) c ·xH2O, the content of hydroxyl is too high, and the proportion of non-active ingredients is too large, which is not conducive to the preparation of subsequent materials.

[0016] Further, in step S4, the drying temperature is 50-200°C. When the temperature is lower than 50°C, M a (PO4) b (OH) c ·xH2O, the surface free water volatilizes too slowly and is not easy to remove completely, affecting the subsequent proportioning, and when the temperature is higher than 200°C, M a (PO4) b (OH) c ·xH2O, the elements will rearrange, melt and crystallize with each other, forming dense and hard blocky particles, affecting the synthesis of subsequent materials.

[0017] Further, in step S2, the acidic medium oxidizing agent is one or more of hydrogen peroxide, peroxyacetic acid, and ammonium persulfate; the purpose is to oxidize the divalent metal ions in the solution, so that they are more likely to produce precipitates with phosphate / hydroxyl ions at a higher pH in the subsequent process.

[0018] Further, in step S3, the alkaline substance is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonia, sodium citrate, and sodium acetate.

[0019] Further, in step S4, the solid-liquid separation method is one or more of centrifugation, filtration, filter pressing, and vacuum filtration, and the M a (PO4) b (OH) c ·xH2O surface free water is quickly removed.

[0020] Further, in step S1, the water-soluble complexing agent is one or more of an alcohol amine complexing agent, an aminocarboxylate complexing agent, a hydroxycarboxylate complexing agent, and a polyacrylic acid complexing agent, the alcohol amine complexing agent is one or more of monoethanolamine, diethanolamine, and triethanolamine, the aminocarboxylate complexing agent is one or more of sodium nitrilotriacetate, ethylenediaminetetraacetic acid and its sodium salt, and diethylenetriaminepentaacetic acid and its sodium salt, the hydroxycarboxylate complexing agent is one or more of tartaric acid, heptonic acid, sodium gluconate, sodium alginate, and citric acid, and the polyacrylic acid complexing agent is one or more of polymaleic anhydride, polyacrylic acid, polyhydroxyacrylic acid, maleic acid-acrylic acid copolymer, and polyacrylamide; the purpose is to complex the transition metal ions in the solution, reduce the free activity, slow down the precipitation rate with phosphate / hydroxyl, and facilitate the generation of nano-state particle precipitates.

[0021] Further, in step S1, the transition metal M source is one or more of a manganese source, a cobalt source, and an iron source, the manganese source is one or more of elemental manganese, manganese sulfate, manganese oxalate, manganese nitrate, manganese hydroxide, manganous anhydride, manganic anhydride, permanganic anhydride, manganese monoxide, manganese dioxide, dimanganese trioxide, and trimanganese tetraoxide, the cobalt source is one or more of elemental cobalt, cobalt nitrate, cobalt oxalate, cobalt sulfate, cobalt carbonate, cobalt oxide, cobalt hydroxide, cobaltic anhydride, and cobaltic oxide, and the iron source is one or more of elemental iron, iron oxalate, iron sulfate, iron citrate, iron nitrate, iron oxide, ferrous oxide, magnetite, ferrous hydroxide, and ferric hydroxide.

[0022] Further, in step S1, the phosphorus source is one or more of phosphoric acid, diphosphorus pentoxide, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, monobasic sodium / ammonium phosphate, dibasic sodium / ammonium phosphate, sodium / ammonium phosphate, sodium pyrophosphate, sodium pyrophosphate, sodium metaphosphate, and sodium polyphosphate.

[0023] Further, in step S1, the pH adjustment is added inorganic and / or organic acid. The inorganic acid is one or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and perchloric acid; the organic acid is one or more of citric acid, ascorbic acid, oxalic acid, formic acid, acetic acid, tartaric acid, malic acid, benzoic acid, salicylic acid, and succinic acid.

[0024] This invention discloses an amorphous disordered precursor for polyanionic sodium-ion battery cathode materials and its preparation method, which has the following beneficial effects:

[0025] First, the structure is adjustable: M a (PO4) b (OH) c The formulation characteristic of the xH2O precursor is 1.0.

[0026] Second, high phase purity: M a (PO4) b (OH) c The transition metal and phosphate ions in the xH2O precursor are relatively uniformly mixed. When using it as a precursor to prepare polyanionic materials, only the required sodium source and a small amount of phosphorus source need to be added. Since both sodium and phosphoric acid are water-soluble raw materials, they can be separated by M... a (PO4) b (OH) c • The pores in xH2O penetrate into the interior of the material, achieving uniform mixing between elements and thus preparing high-phase purity materials;

[0027] Third, high compaction density: M a (PO4) b (OH) c During the grinding process, the xH2O precursor, along with additional sodium and a small amount of phosphorus sources, interpenetrate to form a uniform distribution. During sintering, the elements bond with each other, crystal nuclei are formed in situ, and the epitaxial growth continues to spread, forming dense large-particle single crystals. Furthermore, the inter-crystal porosity is relatively small, the density is relatively large, and the compaction density is significantly improved.

[0028] Fourth, excellent electrochemical performance: due to M a (PO4) b (OH) c The xH2O precursor has high elemental uniformity, resulting in high crystallinity and phase purity of the prepared material. The elemental sites and sodium ion diffusion channels in the crystal exhibit a regular and orderly arrangement, increasing the redox transfer charge and improving the capacity. At the same time, the low ion transition energy barrier gives the material excellent rate performance.

[0029] ​Fifth, low process cost: The solid-state method for preparing polyanionic materials involves grinding, spray drying, sintering, and pulverization. Due to the excessively long grinding time and low solid content of precursors such as FePO4 or FeC2O4, the grinding and spraying stages of this method consume a lot of energy, resulting in high costs. M… a (PO4) b (OH) c The amorphous nature and elemental uniformity of the xH2O precursor allow for uniform mixing without prolonged grinding. Furthermore, the unique amorphous bonding state of the precursor reduces its hydrogen bonding with water, effectively increasing its solid content in the slurry, significantly reducing spray energy consumption, and saving manufacturing costs. Attached Figure Description

[0030] Figure 1 For the application of Fe in Example 1 2.91 (PO4) 2.0 (OH) 2.73 Preparation of 2H2O precursor and Na4Fe 2.91 SEM of (PO4)2P2O7 material;

[0031] Figure 2 Preparation of Na4Fe from anhydrous FePO4 and Mn2O3 precursors in Comparative Example 1 2.91 (PO4)2P2O7 material SEM. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the product of the present invention will be further described in detail below with reference to embodiments.

[0033] This invention can be achieved through the following technical solutions:

[0034] This invention discloses an amorphous disordered precursor for a polyanionic sodium-ion battery cathode material, the precursor having the general chemical formula M. a (PO4) b (OH) c ·xH₂O, where M is one or more transition metal elements Fe, Co, or Mn, and the relationship between a, b, and c is 2a - 3b - c = 0 or 3a - 3b - c = 0; 1.0

[0035] Another aspect of the present invention relates to a method for preparing an amorphous disordered precursor for the above-mentioned polyanionic sodium-ion battery cathode material, characterized by comprising the following steps:

[0036] ​S1, Preparation of precursor solution: mixing transition metal M source, phosphorus source and water-soluble complexing agent with water, adjusting solution pH to obtain precursor solution;

[0037] S2, Preparation of pre-oxidized precursor solution: adding acid medium oxidant to the above solution to generate pre-oxidized precursor solution;

[0038] S3, Precipitation of M a (PO4) b (OH) c ·xH2O: adding alkaline substance to the above pre-oxidized precursor solution, adjusting solution pH to make transition metal ions in the solution generate M a (PO4) b (OH) c ·xH2O precipitate;

[0039] S4, Separation and treatment of precursor powder: separating solid-liquid after the above precipitation, drying to obtain polyanionic positive electrode material precursor powder of M a (PO4) b (OH) c ·xH2O.

[0040] Further, in step S1, the pH range is 0-1.5.

[0041] Further, in step S3, the pH range is 1.5-6.0.

[0042] Further, in step S4, the drying temperature is 50-200°C.

[0043] Further, in step S2, the acid medium oxidant is one or more of hydrogen peroxide, peroxyacetic acid, and ammonium persulfate.

[0044] Further, in step S3, the alkaline substance is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonia, sodium citrate, and sodium acetate.

[0045] Further, in step S4, the solid-liquid separation method is one or more of centrifugation, filtration, pressure filtration, and vacuum filtration.

[0046] Further, in step S1, the water-soluble complexing agent is one or two or more of an alcohol amine complexing agent, an aminocarboxylic acid salt complexing agent, a hydroxycarboxylic acid salt complexing agent, and a polyacrylic acid complexing agent, the alcohol amine complexing agent is one or two or more of monoethanolamine, diethanolamine, and triethanolamine, the aminocarboxylic acid salt complexing agent is one or two or more of sodium nitrilotriacetate, ethylenediaminetetraacetic acid and its sodium salt, and diethylenetriaminepentaacetic acid and its sodium salt, the hydroxycarboxylic acid salt complexing agent is one or two or more of tartaric acid, heptonic acid, sodium gluconate, sodium alginate, and citric acid, and the polyacrylic acid complexing agent is one or two or more of polymaleic anhydride, polyacrylic acid, polyhydroxyacrylic acid, maleic acid-acrylic acid copolymer, and polyacrylamide.

[0047] Further, in step S1, the transition metal M source is one or two or more of a manganese source, a cobalt source, and an iron source, the manganese source is one or two or more of elemental manganese, manganese sulfate, manganese oxalate, manganese nitrate, manganese hydroxide, manganous acid anhydride, manganic acid anhydride, permanganic acid anhydride, manganese monoxide, manganese dioxide, and dimanganese trioxide, the cobalt source is one or two or more of elemental cobalt, cobalt nitrate, cobalt oxalate, cobalt sulfate, cobalt carbonate, cobalt oxide, cobalt hydroxide, cobaltic acid anhydride, and cobaltic oxide, and the iron source is one or two or more of elemental iron, iron oxalate, iron sulfate, iron citrate, iron nitrate, iron oxide, ferrous oxide, magnetite, ferrous hydroxide, and ferric hydroxide.

[0048] Further, in step S1, the phosphorus source is one or two or more of phosphoric acid, diphosphorus pentoxide, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, monosodium / ammonium phosphate monohydrate, disodium / ammonium phosphate dihydrate, sodium / ammonium phosphate, sodium pyrophosphate, sodium pyrophosphate, sodium metaphosphate, and sodium polyphosphate.

[0049] Further, in step S1, the pH adjustment is added inorganic and / or organic acid. The inorganic acid is one or two or more of hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, and perchloric acid; and the organic acid is one or two or more of citric acid, ascorbic acid, oxalic acid, formic acid, acetic acid, tartaric acid, malic acid, benzoic acid, salicylic acid, and succinic acid.

[0050] Example 1

[0051] The present embodiment is a kind of poly-anionic sodium ion battery positive electrode material amorphous disordered precursor, the precursor chemical general formula is M a (PO4) b (OH) c ·xH2O, wherein M is a transition metal element Fe, the relationship between a, b, c is 2a-3b-c=0; 1.0

[0052] The amorphous disordered precursor for the polyanionic sodium ion battery cathode material of the embodiment is prepared by the following method:

[0053] S1, preparation of the precursor solution: the transition metal M source, the phosphorus source and the water-soluble complexing agent are mixed with water, the solution pH is adjusted, and the precursor solution is obtained;

[0054] S2, preparation of the pre-oxidized precursor solution: an acidic medium oxidizing agent is added to the above solution to generate the pre-oxidized precursor solution;

[0055] S3, M a (PO4) b (OH) c ·xH2O precipitation: an alkaline substance is added to the above pre-oxidized precursor solution, the solution pH is adjusted, and the transition metal ions in the solution generate M a (PO4) b (OH) c ·xH2O precipitate;

[0056] S4, separation and treatment of the precursor powder: the above precipitate is separated from the liquid and dried to obtain the M a (PO4) b (OH) c ·xH2O precursor powder for the polyanionic cathode material.

[0057] In the specific process control, the pH range of step S1 is 1.5 and the pH range of step S3 is 4. In step S4 of the embodiment, the drying temperature is 50°C; and the solid-liquid separation mode of step S4 is centrifugation or filtration.

[0058] In the specific material addition, the acidic medium oxidizing agent is hydrogen peroxide or peroxyacetic acid; the alkaline substance is sodium carbonate, sodium bicarbonate or sodium hydroxide; the water-soluble complexing agent is an alcohol amine complexing agent or an amino carboxylate complexing agent, the alcohol amine complexing agent is monoethanolamine, diethanolamine or triethanolamine, the amino carboxylate complexing agent is sodium nitrilotriacetate, ethylenediaminetetraacetic acid or its sodium salt, or diethylenetriamine pentaacetic acid or its sodium salt; the pH adjustment additive is an inorganic acid or an organic acid, the inorganic acid is hydrochloric acid or nitric acid, and the organic acid is citric acid, ascorbic acid, oxalic acid, formic acid, acetic acid or tartaric acid.

[0059] In the main raw material, the transition metal M source in step S1 is an iron source, the iron source is elemental iron, iron oxalate or iron sulfate; and the phosphorus source is phosphoric acid, phosphorus pentoxide, pyrophosphoric acid or metaphosphoric acid.

[0060] Embodiment 2

[0061] The amorphous disordered precursor for the polyanionic sodium ion battery cathode material of the embodiment has a general chemical formula of M a (PO4)b (OH) c • xH2O, wherein M is a transition metal element Mn, the relationship between a, b, and c is 3a-3b-c=0; 1.0

[0062] The amorphous disordered precursor for the polyanionic sodium-ion battery cathode material of the embodiment is prepared by the following method:

[0063] S1, preparation of the precursor solution: the transition metal M source, the phosphorus source, and the water-soluble complexing agent are mixed with water, the solution pH is adjusted, and the precursor solution is obtained;

[0064] S2, preparation of the pre-oxidized precursor solution: an acidic medium oxidant is added to the above solution to generate the pre-oxidized precursor solution;

[0065] S3, M a (PO4) b (OH) c • xH2O precipitation: an alkaline substance is added to the above pre-oxidized precursor solution, the solution pH is adjusted, and the transition metal ions in the solution generate M a (PO4) b (OH) c • xH2O precipitate;

[0066] S4, separation and treatment of the precursor powder: the above precipitate is separated from the solid-liquid, dried, and the polyanionic cathode material M a (PO4) b (OH) c • xH2O precursor powder is obtained.

[0067] In the specific process control, the pH range of step S1 is 0.5.5 and the pH range of step S3 is 1.5. In step S4 of the embodiment, the drying temperature is 200°C; and the solid-liquid separation mode of step S4 is filtration.

[0068] In the specific material addition, the acidic medium oxidant is ammonium persulfate; the alkaline substance is sodium citrate and sodium acetate; the water-soluble complexing agent is a hydroxyl carboxylate complexing agent and a polyacrylic acid complexing agent, the hydroxyl carboxylate complexing agent is tartaric acid, heptonic acid salt, and sodium gluconate, the polyacrylic acid complexing agent is polymaleic anhydride, polyacrylic acid, polyhydroxyacrylic acid, and maleic acid acrylic acid copolymer; the inorganic acid for adjusting the pH is added, and the inorganic acid is hydrochloric acid, nitric acid, and sulfuric acid.

[0069] In the main raw material, the transition metal M source in step S1 is a manganese source, the manganese source is elemental manganese nitrate, manganese hydroxide, and manganous anhydride; the phosphorus source is phosphoric acid, diphosphorus pentoxide, monosodium / ammonium phosphate, disodium / ammonium phosphate, and sodium / ammonium phosphate.

[0070] Embodiment 3

[0071] The present embodiment is an amorphous disordered precursor for a polyanionic sodium-ion battery cathode material, which has a general chemical formula of M a (PO4) b (OH) c ·xH2O, wherein M is a transition metal element Co, the relationship between a, b and c is 2a-3b-c=0; 1.0

[0072] The amorphous disordered precursor for a polyanionic sodium-ion battery cathode material of the present embodiment is prepared by the following method:

[0073] S1, preparation of a precursor solution: mix a transition metal M source, a phosphorus source and a water-soluble complexing agent with water, adjust the pH of the solution, and obtain a precursor solution;

[0074] S2, preparation of a pre-oxidized precursor solution: add an acidic medium oxidant to the above solution to generate a pre-oxidized precursor solution;

[0075] S3, M a (PO4) b (OH) c ·xH2O precipitation: add a basic substance to the above pre-oxidized precursor solution, adjust the pH of the solution, and make the transition metal ions in the solution generate M a (PO4) b (OH) c ·xH2O precipitate;

[0076] S4, separation and treatment of the precursor powder: after the above precipitation is solid-liquid separated and dried, a polyanionic cathode material M a (PO4) b (OH) c ·xH2O precursor powder is obtained.

[0077] In the specific process control, the pH range of step S1 is 0, and the pH range of step S3 is 6.0. In step S4 of the present embodiment, the drying temperature is 120°C; and the solid-liquid separation method of step S4 is pressure filtration.

[0078] In the specific material addition, the acidic medium oxidant is hydrogen peroxide and ammonium persulfate; the basic substance is sodium carbonate, sodium bicarbonate and sodium acetate; the water-soluble complexing agent is an alcohol amine complexing agent and a polyacrylic acid complexing agent, the alcohol amine complexing agent is monoethanolamine, and the polyacrylic acid complexing agent is a maleic acid acrylic acid copolymer and polyacrylamide; the pH adjustment additive is an organic acid, and the organic acid is citric acid, ascorbic acid and oxalic acid.

[0079] In the main raw material, the transition metal M source in step S1 is a cobalt source, and the cobalt source is cobalt nitrate, cobalt oxalate, cobalt sulfate, cobalt carbonate, and cobalt oxide; the phosphorus source is phosphoric acid, phosphorus pentoxide, pyrophosphoric acid, sodium pyrophosphate, sodium metaphosphate, and sodium polyphosphate.

[0080] Example 4

[0081] The present embodiment is a kind of poly-anionic sodium ion battery positive electrode material amorphous disordered precursor, the chemical general formula of the precursor is M a (PO4) b (OH) c ·xH2O, wherein M is a transition metal element Fe, Co, the relationship between a, b and c is 3a-3b-c=0;1.0<a / b<2.0, the value range of x is x≥0.

[0082] The poly-anionic sodium ion battery positive electrode material amorphous disordered precursor of the present embodiment is prepared by the following method:

[0083] S1, preparation of precursor solution: mix the transition metal M source, phosphorus source and water-soluble complexing agent with water, adjust the pH of the solution, and obtain the precursor solution;

[0084] S2, preparation of pre-oxidized precursor solution: add an acidic medium oxidizing agent to the above solution to generate a pre-oxidized precursor solution;

[0085] S3, M a (PO4) b (OH) c ·xH2O precipitation: add a basic substance to the above pre-oxidized precursor solution, adjust the pH of the solution, and make the transition metal ions in the solution generate M a (PO4) b (OH) c ·xH2O precipitate;

[0086] S4, separation and treatment of precursor powder: after solid-liquid separation and drying of the above precipitation, the poly-anionic positive electrode material M a (PO4) b (OH) c ·xH2O precursor powder is obtained.

[0087] In the specific process control, the pH range of step S1 is 0.5, and the pH range of step S3 is 2.5. In step S4 of the present embodiment, the drying temperature is 100°C; the solid-liquid separation method of step S4 is vacuum filtration.

[0088] The acid medium oxidant is hydrogen peroxide, peroxyacetic acid and ammonium persulfate; the alkaline substance is sodium carbonate, ammonia and sodium citrate; the water-soluble complexing agent is an alcohol amine complexing agent, and the alcohol amine complexing agent is monoethanolamine, diethanolamine and triethanolamine; the inorganic and organic acid for adjusting pH is hydrochloric acid, nitric acid and sulfuric acid, and the organic acid is citric acid and ascorbic acid.

[0089] The transition metal M source in step S1 is a cobalt source and an iron source, the cobalt source is cobalt oxide, cobalt hydroxide, tricobalt tetraoxide and cobaltic oxide, the iron source is iron sulfate, iron citrate and iron nitrate; the phosphorus source is polyphosphoric acid, sodium / ammonium monohydrogen phosphate, sodium / ammonium dihydrogen phosphate, sodium / ammonium phosphate and sodium hydrogen pyrophosphate.

[0090] Example 5

[0091] The amorphous and disordered precursor for the polyanionic sodium ion battery cathode material has a chemical general formula of M a (PO4) b (OH) c ·xH2O, wherein M is a transition metal element Fe and Mn, the relationship between a, b and c is 2a-3b-c=0; 1.0

[0092] The amorphous and disordered precursor for the polyanionic sodium ion battery cathode material is prepared by the following method:

[0093] S1, preparation of the precursor solution: the transition metal M source, the phosphorus source and the water-soluble complexing agent are mixed with water, the solution pH is adjusted, and the precursor solution is obtained;

[0094] S2, preparation of the pre-oxidized precursor solution: the acid medium oxidant is added to the above solution to generate the pre-oxidized precursor solution;

[0095] S3, M a (PO4) b (OH) c ·xH2O precipitation: the alkaline substance is added to the above pre-oxidized precursor solution to adjust the solution pH, so that the transition metal ions in the solution generate M a (PO4) b (OH) c ·xH2O precipitate;

[0096] S4, separation and treatment of the precursor powder: the above precipitate is separated from the liquid and dried to obtain the M a (PO4) b (OH) c ·xH2O precursor powder for the polyanionic cathode material.

[0097] In the specific process control, the pH range of step S1 is 1.2, and the pH range of step S3 is 5. In step S4 of the embodiment, the drying temperature is 80°C; and the solid-liquid separation method of step S4 is centrifugation or vacuum filtration.

[0098] In the specific material addition, the acidic medium oxidant is peroxoacetic acid or ammonium persulfate; the basic substance is sodium carbonate, sodium citrate or sodium acetate; the water-soluble complexing agent is an aminocarboxylate complexing agent or a polyacrylic acid complexing agent, the aminocarboxylate complexing agent is ethylenediaminetetraacetic acid or its sodium salt, diethylenetriaminepentaacetic acid or its sodium salt, and the polyacrylic acid complexing agent is polymaleic anhydride, polyacrylic acid or polyhydroxyacrylic acid; the pH adjustment is added with an inorganic acid or an organic acid, the inorganic acid is hydrochloric acid, and the organic acid is citric acid, benzoic acid, salicylic acid or succinic acid.

[0099] In the main raw material, the transition metal M source in step S1 is a manganese source or an iron source, the manganese source is manganese hydroxide, manganous anhydride or manganic anhydride, and the iron source is iron citrate, ferric nitrate, iron oxide or ferrous oxide; the phosphorus source is phosphoric acid, diphosphorus pentoxide, sodium metaphosphate or sodium polyphosphate.

[0100] Embodiment 6

[0101] The amorphous disordered precursor for the polyanionic sodium ion battery cathode material of the embodiment has a chemical general formula of M a (PO4) b (OH) c ·xH2O, wherein M is a transition metal element Fe, Co or Mn, the relationship between a, b and c is 3a-3b-c=0; 1.0

[0102] The amorphous disordered precursor for the polyanionic sodium ion battery cathode material of the embodiment is prepared by the following method:

[0103] S1, preparation of the precursor solution: mix the transition metal M source, the phosphorus source and the water-soluble complexing agent with water, adjust the pH of the solution, and obtain the precursor solution;

[0104] S2, preparation of the pre-oxidized precursor solution: add the acidic medium oxidant to the above-mentioned solution to generate the pre-oxidized precursor solution;

[0105] S3, M a (PO4) b (OH) c ·xH2O precipitation: add the basic substance to the above-mentioned pre-oxidized precursor solution to adjust the pH of the solution, so that the transition metal ions in the solution generate M a (PO4) b (OH) c• xH2O precipitate;

[0106] S4, separation of the precursor powder: after the above precipitation, solid-liquid separation and drying, the polyanionic positive electrode material is obtained a (PO4) b (OH) c • xH2O precursor powder.

[0107] In the specific process control, the pH range of step S1 is 0.5 and the pH range of step S3 is 3. In step S4 of the embodiment, the drying temperature is 130°C; the solid-liquid separation mode of step S4 is centrifugation, filtration, filter pressing, vacuum filtration.

[0108] In the specific material addition, the acidic medium oxidant is hydrogen peroxide, peroxyacetic acid, ammonium persulfate; the basic substance is ammonia, sodium citrate, sodium acetate; the water-soluble complexing agent is an aminocarboxylate complexing agent, a hydroxycarboxylate complexing agent, the aminocarboxylate complexing agent is sodium nitrilotriacetic acid, ethylenediaminetetraacetic acid and its sodium salt, diethylenetriamine pentaacetic acid and its sodium salt, the hydroxycarboxylate complexing agent is tartaric acid, heptonic acid, sodium gluconate, sodium alginate; the inorganic and organic acids added for pH adjustment are hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, perchloric acid; the organic acid is citric acid.

[0109] In the main raw material, the transition metal M source in step S1 is a manganese source, a cobalt source, and an iron source, the manganese source is manganous anhydride, manganic anhydride, permanganic anhydride, manganese monoxide, manganese dioxide, the cobalt source is high cobalt oxide, the iron source is iron sulfate, iron citrate, iron nitrate, iron oxide; the phosphorus source is phosphoric acid, phosphorus pentoxide, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, monosodium / ammonium phosphate, disodium / ammonium phosphate.

[0110] Application Example 1 Fe 2.91 (PO4) 2.0 (OH) 2.73 • 2H2O precursor and synthesis of Na4Fe 2.91 (PO4)2P2O7 material and its electrochemical performance

[0111] Step 1: high-purity atomized iron powder, phosphoric acid, and citric acid are mixed with water in a molar ratio of 2.91:2:3, acetic acid is used to control the solution pH to 0.5, and the atomized iron powder is promoted to react to generate a transparent solution;

[0112] Step 2: hydrogen peroxide is added to the above solution to oxidize the divalent iron in the solution to trivalent iron to generate a pre-oxidation state precursor solution;

[0113] Step 3: sodium carbonate is slowly added to the above precursor solution to adjust the pH of the solution to 3.5, and the transition metal ions in the solution are converted to Fe 2.91 (PO4)2.0 (OH) 2.73 • 2H2O precipitation;

[0114] Step 4: After centrifugation, washing and drying of the above-mentioned precipitate, the poly-anionic positive electrode material is obtained. 2.91 (PO4) 2.0 (OH) 2.73 • 2H2O precursor powder.

[0115] The Fe 2.91 (PO4) 2.0 (OH) 2.73 • 2H2O precursor, sodium dihydrogen phosphate, sodium acetate are mixed with water in a molar ratio of 1:2:2 and citric acid (added amount is 0.5 times the molar amount of sodium acetate) and ground. Compared with the preparation of the anhydrous FePO4 precursor in Comparative Example 1, the grinding time is greatly reduced, the energy consumption is reduced, and the process cost is reduced. When the solid particle size Dmax in the slurry is ≤50 nm, the slurry is spray dried at an inlet temperature of 250°C and an outlet temperature of 80°C to remove the water, and a dry precursor powder is obtained. Finally, the above-mentioned precursor powder is calcined at 630°C for 8h in a nitrogen atmosphere, and after natural cooling, the Na4Fe 2.91 (PO4)2P2O7 material is obtained.

[0116] Figure 1 The SEM of the Na4Fe 2.91 (PO4)2P2O7 material is shown in Table 1. It presents a regular spherical morphology, and there is no obvious primary particle. The surface of the spherical particle has no obvious pores, cracks, etc. The material has a high degree of solidification and is relatively dense. In addition, the results in Table 1 show that the porosity and specific surface area of the material are 2.1% and 4.3 m 2 / g, respectively, which is significantly lower than that of Comparative Example 1. This proves that the material has a high degree of melting and growth between particles during sintering, effectively reducing the pore content and specific surface area, so that the compaction density is greatly improved to 2.35 g / cm 3 , which is much higher than that of Comparative Example 1. The XRD diffraction curve refinement calculation further proves that the phase purity of the material is as high as 98.9%, which is much higher than that of Comparative Example 1 (81.3%), indicating that the Fe 2.91 (PO4) 2.0 (OH) 2.73 • 2H2O precursor. The uniform distribution between transition metals and phosphorus elements effectively improves the mixing uniformity between ions during grinding, shortens the ion diffusion distance during sintering, and makes it easier to crystallize and nucleate, forming a material with more complete crystal form and higher phase purity.

[0117] Add Na4Fe2.91 (PO4)2P2O7 material , SurP, PVDF5130 in the ratio of 9.5:0.2:0.3 by mass ratio to NMP, mix the above materials uniformly with a high-speed homogenizer, form a black slurry with uniform color and high fluidity, Add , SurP, PVDF5130 in the ratio of 9.5:0.2:0.3 by mass ratio to NMP, mix the above materials uniformly with a high-speed homogenizer, form a black slurry with uniform color and high fluidity, The black slurry was coated on the aluminum foil by using a 150 um four-side coater, and the film was dried in a vacuum drying oven at 100 ℃ for 2 hours. The electrode film was punched into a circular sheet with a radius of 0.6 mm using a puncher, and a CR2016 type button cell was assembled in a glove box with a metal sodium as a counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) + 5% FEC as an electrolyte, and a PP / PE / PP three-layer separator.

[0118] The results of the electrochemical performance test in Table 1 show that the Na4Fe 2.91 The discharge gram capacity of the Na4Fe (PO4)2P2O7 electrode at a 0.1C (1C = 129 mAh / g) rate is 122.4 mAh / g, and the capacity is high, which is much higher than the discharge gram capacity of 82.3 mAh / g in Comparative Example 1, indicating that the high phase purity of the material reduces the adverse factors such as vacancies, defects, dislocations in the crystal structure that affect the performance of the material, thereby improving the effective gram capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at a 10C rate is as high as 98.9% compared with 0.1C, which is much higher than 82.4% in Comparative Example 1, and the reason is related to the high phase purity of the material. The higher the phase purity of the material, the higher the integrity of the primary grains, and the fewer the number of grain boundaries between the grains, so that the resistance to the migration of sodium ions is reduced, and the rate performance is greatly improved. Finally, the capacity retention rate of the electrode at a 1C rate after 1000 weeks of cycling is 98.9%, and there is almost no attenuation, which is related to the high integrity of the material. The interaction force generated during the sodium extraction process of each crystal is anisotropic, and the stress generated by the volume expansion can be uniformly released to the surrounding, so that the integrity between the crystals is effectively maintained. On the other hand, because the material has a low specific surface area and porosity, the degree of side reaction between the material and the electrolyte at a high voltage is reduced, and the interface stability is maintained, so that the cycle stability is high. In summary, the Na4Fe 2.91 (PO4) 2.0 (OH) 2.73 ·2H2O precursor has excellent electrochemical performance due to the high phase purity of the Na4Fe 2.91 (PO4)2P2O7 material.

[0119] Application Example 2 Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precursor and Na4Mn 2.037 Fe 0.873Synthesis of (PO4)2P2O7 material and its electrochemical performance

[0120] Step 1: high purity atomized iron powder, Mn2O3, phosphoric acid, citric acid were mixed with water according to the molar ratio of 0.873:1.0185:2:3, formic acid was used to control the solution PH to 0.5, promote the reaction of atomized iron powder and manganese sesquioxide, generate transparent brown yellow solution;

[0121] Step 2: add hydrogen peroxide to the above brown yellow solution, oxidize the divalent iron in the solution to trivalent iron, generate pre-oxidation state precursor solution;

[0122] Step 3: slowly add ammonia water to the above precursor solution, adjust the PH of the solution to 4.0, make the transition metal ions in the solution generate Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precipitate;

[0123] Step 4: after centrifugal separation, washing and drying of the above precipitate, the polyanion positive electrode material Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precursor powder is obtained.

[0124] The Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precursor, sodium dihydrogen phosphate, sodium hydroxide were mixed with water according to the molar ratio of 1:2:2 and citric acid (the addition amount is 0.5 times the molar amount of sodium hydroxide), and then grinded for about 0.5H. Compared with the preparation of the anhydrous FePO4 and manganese sesquioxide precursor in the comparative example 2, the grinding time is shortened, and the corresponding process energy consumption cost is reduced. When the solid particle size Dmax in the slurry is ≤30nm, the slurry is spray dried at an inlet temperature of 290°C and an outlet temperature of 100°C to remove water, and a dry precursor powder is obtained. Finally, the precursor powder is calcined at 650°C for 12h in a nitrogen atmosphere, and after natural cooling, Na4Mn 2.037 Fe 0.873 (PO4)2P2O7 material is obtained.

[0125] The results in Table 1 show that the porosity and specific surface area of the Na4Mn 2.037 Fe 0.873 (PO4)2P2O7 material are 1.8% and 5.6m 2 / g, which is much lower than the result of Comparative Example 2, which is related to the higher uniformity of the mixing of the material precursor. The more uniform the mixing of the ions, the higher the density of the particles formed by the local ion mutual melting bonding during the sintering process, and the more dense the particle growth, which greatly reduces the porosity between the particles, thereby reducing the specific surface area of the material and improving the compaction density (2.29 g / cm 3 ). The XRD diffraction curve refinement calculation further proves that the phase purity of the material is as high as 99.1%, which is much higher than that of Comparative Example 2 (65.2%), indicating that the Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precursor can effectively promote the growth of crystals during the sintering process, shorten the ion diffusion distance during the sintering process, and make it easier to crystallize and nucleate, thereby forming a material with high crystallinity and high phase purity.

[0126] Figure 2 Na4Mn 2.037 Fe 0.873 (PO4)2P2O7 material Add , SurP, PVDF5130 in the ratio of 9.5:0.2:0.3 by mass ratio to NMP, mix the above materials uniformly with a high-speed homogenizer, form a black slurry with uniform color and high fluidity, Add Then a 150-um four-side coater was used to coat the black slurry on an aluminum foil, and the film was dried in a vacuum drying oven at 100°C for 2 hours. A punching machine was used to punch the electrode film into a circular sheet with a radius of 0.6 mm, and a CR2016 type button cell was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%) + 5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0127] The electrochemical performance test results in Table 1 show that the electrode has a discharge capacity of 118.2 mAh / g at a rate of 0.1C (1C = 129 mAh / g), and the capacity is high, indicating that the number of redox charges involved in the structure is high, which is much higher than the result of Comparative Example 2, which is related to the high purity and crystallinity of the material. The higher the phase purity of the material, the fewer the defects in the crystal structure that hinder ion and electron transmission and diffusion, which is conducive to the high capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at a rate of 10C is as high as 97.1% compared with 0.1C, which is much higher than 46.6% in Comparative Example 2, indicating that the higher the phase purity of the material, the fewer the crystal defects, and the lower the diffusion energy barrier of sodium ions in the structure, without the problem of high diffusion energy barrier caused by defects. In addition, the higher phase purity avoids the blocking effect of grain boundaries caused by impurity phases, which affects the transmission of ions and is conducive to the improvement of the rate performance. Finally, the capacity retention rate of the electrode at a rate of 1C after 1000 cycles is 96.4%, and the cycle stability is excellent, indicating that the higher the phase purity of the material, the better the crystal completeness, and the more uniform the force generated by the volume expansion during the sodium extraction process of each crystal, which can reduce the probability of structure pulverization and improve the cycle stability. At the same time, the smaller specific surface area of the material will also reduce the catalysis of the electrolyte under high pressure, thereby reducing the side reactions at the material interface and improving the cycle stability. In summary, the Na4Mn 2.037 Fe 0.873 (PO4) 2.0 (OH) 2.079 ·2H2O precursor prepared by the above method has a higher phase purity and exhibits more excellent electrochemical performance. 2.037 Fe 0.873 (PO4)2P2O7 material prepared by the above method has a higher phase purity and exhibits more excellent electrochemical performance.

[0128] Comparative Example 1: Na4Fe 2.91 (PO4)2P2O7 material and its electrochemical performance

[0129] Anhydrous FePO4, phosphoric acid, and sodium acetate were mixed with citric acid (added in an amount of 0.5 times the molar amount of sodium acetate) in a molar ratio of 2.91:1.0:4.0, and water was added and ground for about 13H. The grinding time is longer than that of Application Example 1, the energy consumption is higher, the efficiency is lower, and the process cost is high. When the solid particle size Dmax in the slurry is ≤50 nm, the slurry is spray dried at an inlet temperature of 250°C and an outlet temperature of 80°C to remove water, and a dry precursor powder is obtained. Finally, the precursor powder is calcined at 630°C for 8h in a nitrogen atmosphere, and after natural cooling, Na4Fe 2.91 (PO4)2P2O7 material is obtained.

[0130] , SurP, PVDF5130 in the ratio of 9.5:0.2:0.3 by mass ratio to NMP, mix the above materials uniformly with a high-speed homogenizer, form a black slurry with uniform color and high fluidity, Na4Fe 2.91 The SEM of the Na4Fe (PO4)2P2O7 material presents irregular blocky particles, and the particles are about 50-100 nm primary particles accumulated, and there are a large number of pores between the particles. The results in Table 1 show that the porosity and specific surface area of the material are 22.3% and 15.4 m2 / g, respectively. 2 / g, which is greatly increased compared with application example 1, which is related to the anhydrous FePO4 precursor, which is a high-temperature sintering phase, and the particle hardness is large, and there are many edges and corners after grinding. These particles are stacked with each other during the spraying process, forming a porous spherical arrangement, and the pores are not removed after sintering, causing the porosity and specific surface area to increase, and the compaction density to decrease (1.76 g / cm 3 ). The XRD diffraction curve refinement calculation further proves that the phase purity of the material is only 81.3%, which is much lower than that of application example 1, indicating that the FePO4 precursor is not conducive to the uniform mixing of ions during the grinding process, causing phase separation during the sintering process, affecting the crystal structure of the material and its phase purity.

[0131] Add Na4Fe 2.91 (PO4)2P2O7 material , SurP, PVDF5130 in the ratio of 9.5:0.2:0.3 by mass ratio to NMP, mix the above materials uniformly with a high-speed homogenizer, form a black slurry with uniform color and high fluidity, ​ ​ Then the black slurry was coated on the aluminum foil using a 150 um four-side coater, and the film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a round sheet with a radius of 0.6 mm using a sheet puncher, and a metal sodium was used as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%)+5% FEC was used as the electrolyte, and a PP / PE / PP three-layer separator was used as the separator, and a CR2016 type button cell was assembled in a glove box.

[0132] The results in Table 1 show that the discharge gram capacity of the material is only 82.3 mAh / g at 0.1C (1C = 129 mAh / g), which is much lower than the discharge gram capacity of the material in Application Example 1, which is consistent with the lower purity of the material, indicating that the material prepared by using anhydrous FePO4 as the precursor may contain non-active sodium iron phosphate or low-capacity sodium pyrophosphate impurities, which reduces the effective active ingredients, transition metal redox number and sodium ion extraction number per unit mass, and reduces the gram capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at 10C is only 82.4% compared with 0.1C, and the lower rate performance is related to the existence of impurities in the material. There are more crystal boundaries between the impurities and the main phase, and the transmission rate of sodium ions at the crystal boundary is low, which causes a certain hysteresis, resulting in the decline of the rate performance of the material. Finally, the capacity retention rate of the electrode at 1C after 1000 cycles is only 91.5%, which has a certain decay, and the reason is that during the sodium extraction process, the Na4Fe 2.91 (PO4)2P2O7 crystal expands and shrinks, causing micro-cracks between the crystal faces and the impurities, and the penetration of electrolyte into the surface will accelerate the dissolution of interface elements, leading to the destruction of the interface structure and the decline of the cycle stability. In addition, the high specific surface area of the material will catalyze the reaction between the material and the electrolyte at high voltage, leading to the dissolution of the interface and other problems, affecting the cycle stability of the material. In summary, the Na4Fe 2.91 (PO4)2P2O7 material prepared by using anhydrous FePO4 precursor has lower phase purity, which causes the non-uniformity of the material reaction, accelerating the deterioration of the electrochemical performance of the material.

[0133] Na4Mn 2.037 Fe 0.873 (PO4)2P2O7 material and its electrochemical performance

[0134] Anhydrous FePO4, Mn2O3, phosphoric acid, sodium hydroxide, and citric acid (added amount is 0.5 times the molar amount of sodium hydroxide) are mixed with water in a molar ratio of 0.873:1.0185:3.127:4.0 and ground for about 20H. The grinding time is longer than that of Application Example 2, mainly because Mn2O3 has high crystallinity and high crystal hardness, which is difficult to grind, resulting in high process energy consumption, low efficiency, and high cost investment. When the solid particle size Dmax in the slurry is ≤30 nm, the slurry is spray dried at an inlet temperature of 290°C and an outlet temperature of 100°C to remove water, and a dry precursor powder is obtained. Finally, the precursor powder is calcined at 650°C for 12h in a nitrogen atmosphere, and the Na4Mn 2.037 Fe 0.873 (PO4)2P2O7 material is obtained after natural cooling.

[0135] The material porosity and specific surface area are 20.7% and 18.7m 2 / g, much higher than that of application example 2, which is related to the anhydrous FePO4, Mn2O3 precursor. The type of precursor is a high-temperature sintering phase, which has a large particle hardness. After grinding, there are many edges and corners. After spray drying, it is easy to form a porous structure. After sintering, these pores cannot be removed, resulting in an increase in porosity and specific surface area and a decrease in compacted density (1.65 g / cm 3 ). The XRD diffraction curve refinement calculation further proves that the phase purity of the material is only 65.2%, much lower than that of application example 2, indicating that the anhydrous FePO4, Mn2O3 precursor is not conducive to the uniform mixing of ions during the grinding process, resulting in phase separation during the sintering process, affecting the crystal structure and phase purity of the material.

[0136] ​ Na4Mn 2.037 Fe 0.873 (PO4)2P2O7material ​ ​ ​ Then the black slurry was coated on the aluminum foil using a 150-um four-side coater. The film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a round sheet with a radius of 0.6 mm using a sheet puncher. A CR2016 type button cell was assembled in a glove box using metallic sodium as the counter electrode, 1 mol / L NaClO4 EC+DEC (1:1 vol%)+5% FEC as the electrolyte, and a PP / PE / PP three-layer separator.

[0137] The results in Table 1 show that the discharge specific capacity of the material is only 57.4 mAh / g at a rate of 0.1C (1C=129 mAh / g), much lower than that of application example 2, which is related to the low phase purity of the material described above. This indicates that the use of anhydrous FePO4, Mn2O3 as a precursor may produce impurity phases such as inactive sodium iron phosphate, sodium manganese phosphate, or low-capacity sodium iron pyrophosphate, sodium manganese pyrophosphate, etc. in the material, reducing the active ingredients in the material per unit mass, leading to a decrease in the specific capacity of the material. In addition, as shown in Table 1, the capacity retention rate of the electrode at a rate of 10C is only 46.6% compared to 0.1C. The low rate performance is related to the presence of impurity phases described above. The existence of a large number of grain boundaries between the impurity phases and the main phase will lead to a decrease in the transmission rate of sodium ions or blockage, resulting in a decrease in the rate performance of the material. Ultimately, the capacity retention rate of the electrode at a rate of 1C after 1000 weeks of cycling is only 82.1%, with a serious decay, which indirectly reflects the instability of the material structure. The reason is that during the sodium extraction process, Na4Mn 2.037 Fe0.873 The volume expansion rate of (PO4)2P2O7 crystal is different from that of impurity phase, which leads to micro-cracks at the interface of the crystal. The penetration of electrolyte into the material surface along the cracks will accelerate the dissolution of interface elements, leading to the destruction of the interface structure and the decline of cycle stability. In addition, the high specific surface area of the material will catalyze the reaction of the material and electrolyte at high voltage, leading to problems such as dissolution and structure rockification of the interface, affecting the cycle stability of the material. In summary, the Na4Mn 2.037 Fe 0.873 The non-uniformity of the material reaction caused by the low phase purity of the (PO4)2P2O7 material will accelerate the deterioration of the electrochemical performance of the material.

[0138] Table 1 Performance test results

[0139]

[0140] The above examples are only specific embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. It should be noted that for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these obvious alternative forms all belong to the protection scope of the present application.

Claims

1. A method for preparing an amorphous disordered precursor for a polyanionic sodium-ion battery cathode material, characterized in that The method comprises the following steps: S1, preparation of a precursor solution: a transition metal M source, a phosphorus source and a water-soluble complexing agent are mixed with water, the pH of the solution is adjusted to 0-1.5, and a precursor solution is obtained; the water-soluble complexing agent is one or more than two of an alcohol amine complexing agent, an amino carboxylate complexing agent, a hydroxyl carboxylate complexing agent, and a polyacrylic acid complexing agent; the alcohol amine complexing agent is one or more than two of monoethanolamine, diethanolamine and triethanolamine; the amino carboxylate complexing agent is one or more than two of sodium nitrilotriacetate, ethylenediaminetetraacetic acid and its sodium salt, diethylenetriamine pentaacetic acid and its sodium salt; the hydroxyl carboxylate complexing agent is one or more than two of tartaric acid, heptonic acid, sodium gluconate, sodium alginate and citric acid; and the polyacrylic acid complexing agent is one or more than two of polymaleic anhydride, polyacrylic acid, polyhydroxyacrylic acid, maleic acid acrylic acid copolymer and polyacrylamide; S2, preparation of a pre-oxidized precursor solution: an acidic medium oxidizing agent is added to the above solution to generate a pre-oxidized precursor solution; the acidic medium oxidizing agent is one or more than two of hydrogen peroxide, peroxyacetic acid and ammonium persulfate; S3, M a (PO4) b (OH) c • xH2O precipitate: add a basic substance to the above pre-oxidized precursor solution, adjust the pH of the solution, and make the transition metal ions in the solution generate M a (PO4) b (OH) c • xH2O precipitate; S4, separation treatment of the precursor powder: after the above precipitation solid-liquid separation and drying, the polyanion positive electrode material is obtained a (PO4) b (OH) c xH2O precursor powder; wherein M is one or two or more of transition metal elements Fe, Co or Mn, the relationship between a, b and c is 2a-3b-c=0 or 3a-3b-c=0; 1.0 2. The method of claim 1, wherein the method is characterized by: In step S3, the pH range is 1.5-6.

0.

3. The method of claim 1, wherein the method further comprises: adding a sodium source to the mixture of the metal oxide and the polymer. In step S4, the drying temperature is 50-200℃.

4. The method of claim 1, wherein the method is characterized by: In step S3, the alkaline substance is one or more than two of sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonia, sodium citrate and sodium acetate.

5. The method of claim 1, wherein the method is characterized by: In step S4, the solid-liquid separation method is one or more than two of centrifugation, filtration, pressure filtration and vacuum filtration.

6. The method for preparing the amorphous and disordered precursor for the positive electrode material of a polyanionic sodium ion battery according to claim 1, characterized in that: In step S1, the transition metal M source is one or more than two of a manganese source, a cobalt source and an iron source; the manganese source is one or more than two of elemental manganese, manganese sulfate, manganese oxalate, manganese nitrate, manganese hydroxide, manganous anhydride, manganic anhydride, permanganic anhydride, manganese monoxide, manganese dioxide and dimanganese trioxide; the cobalt source is one or more than two of elemental cobalt, cobalt nitrate, cobalt oxalate, cobalt sulfate, cobalt carbonate, cobalt oxide, cobalt hydroxide, trimanganese tetroxide and cobaltic oxide; and the iron source is one or more than two of elemental iron, iron oxalate, iron sulfate, iron citrate, iron nitrate, iron oxide, ferrous oxide, trimiron tetroxide, ferrous hydroxide and ferric hydroxide; In step S1, the phosphorus source is one or more than two of phosphoric acid, diphosphorus pentoxide, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, monosodium / ammonium phosphate, disodium / ammonium phosphate, sodium / ammonium phosphate, sodium pyrophosphate, sodium pyrophosphate, sodium metaphosphate and sodium polyphosphate; In step S1, the pH is adjusted by adding an inorganic acid and / or an organic acid; the inorganic acid is one or more than two of hydrochloric acid, nitric acid, sulfuric acid and hydrofluoric acid; and the organic acid is one or more than two of citric acid, ascorbic acid, oxalic acid, formic acid, acetic acid, tartaric acid, malic acid, benzoic acid and salicylic acid.

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