Non-stoichiometric sodium ion battery polyanionic positive electrode material precursor and preparation method thereof

Abstract

The invention discloses a non-stoichiometric sodium ion battery polyanionic positive electrode material precursor and a preparation method thereof. The chemical formula of the precursor is shown in the specification. Ax (My) m + (XaOb) n-(OH-) z.mH2O; wherein A is one or more than two of cations H < + >, Na < + > or NH4 < + >, M is one or more than two of ferrited metal elements Fe, Co and Mn, and X is one or more than two of anion elements P, S and Si; wherein the relationship among x, y and z is x + my-n-z = 0, 0lt; xlt; 1, 0.5 lt; y < = 2, 0lt; zlt, zlt; 1; a is 1 or 2; b is 4 or 7; m is larger than or equal to 0. The non-stoichiometric sodium ion battery polyanionic positive electrode material precursor and the preparation method thereof have the characteristics of high phase purity, high compaction density, low cost and excellent electrochemical performance.

Description

Technical Field

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

[0002] Polyanion-type sodium ion battery cathode materials have gradually become a research hotspot in the field of energy storage due to their high structural stability, thermodynamic stability, excellent cycle stability and rate performance, and have been widely favored by the market. This type of material can not only maintain stable electrochemical performance under high voltage, but also has a long cycle life and good safety. Therefore, it has broad application prospects in electric vehicles, large-scale energy storage systems and other fields. At present, the polyanion-type material systems that are widely studied on the market mainly include sodium iron pyrophosphate (Na 2 FeP 2 O 7 ), sodium iron pyrophosphate (NaFePO 4 )、Sodium vanadium phosphate(Na 3 V 2 (PO 4 ) 3 ), sodium vanadium fluorophosphate (Na 3 V 2 (PO 4 ) 2 F 3 ) etc. The structural characteristics of these materials are that alkali metal tetrahedrons, transition metal tetrahedrons or octahedrons, anion tetrahedrons or trihedrons are arranged in a co-point, co-planar or co-linear manner to form a stable three-dimensional framework structure. This structure can not only effectively accommodate the insertion and extraction of sodium ions, but also maintain the structural integrity of the material during the charge and discharge process, thereby improving the overall performance of the battery.

[0003] At present, commercially available materials such as sodium iron pyrophosphate are mainly synthesized by solid phase method. 4 、FeC 2 O 4 etc. as transition metal precursor sources, combined with water-soluble sodium sources (such as Na 2 CO 3 or NaOH), phosphorus source (such as NH 4 H 2 PO 4 ) and a carbon source (such as glucose or citric acid), and the material is prepared through grinding, mixing, spray drying, high-temperature sintering and other processes. However, this synthesis method has some obvious limitations. First, the highly crystalline FePO 4 、FeC 2 O 4Solids such as those are difficult to completely dissolve during the grinding process and usually suspend in the solution as solid particles ranging from dozens to hundreds of nanometers in size. These solid particles contain tens of thousands of atoms, making it difficult for sodium, transition metals, and phosphorus elements in the slurry to be uniformly mixed within a local range. This non-uniformity is prone to cause phase separation during the subsequent sintering process, thereby affecting the electrochemical properties of the material, such as capacity decay and decline in rate performance. Secondly, high-crystalline FePO 4 、FeC 2 O 4 and other solids take a long time during the grinding process, have high requirements for equipment parameters, consume a large amount of energy, resulting in a relatively high process input cost, and limit the feasibility of their large-scale industrial production. Summary of the Invention

[0004] The purpose of the present invention is to provide a non-stoichiometric polyanionic cathode material precursor for sodium-ion batteries and its preparation method, which have the characteristics of high phase purity, high tap density, low cost, and excellent electrochemical performance.

[0005] The present invention can be achieved through the following technical solutions:

[0006] The present invention discloses a non-stoichiometric polyanionic cathode material precursor for sodium-ion batteries, and the chemical formula of this precursor is.A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O;

[0007] Among them, A is one or more of the cations H + , Na + or NH 4 + ; M is one or more of the transition metal elements Fe, Co, and Mn; X is one or more of the anion elements P, S, and Si;

[0008] Among them, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0.

[0009] The present invention aims at the above-mentioned problems. In order to obtain polyanionic materials with high phase purity and low preparation process cost, the development of an adapted precursor becomes the key. An ideal precursor should contain all the elements required for the prepared material (such as sodium, transition metals, phosphorus, etc.) and exist in an amorphous or low crystalline form. Such an amorphous precursor can effectively avoid the problem of uneven distribution of solid particles and ensure uniform mixing of elements at the atomic level, thereby forming a single phase material during the sintering process. In addition, amorphous precursors usually have high reactivity and can complete sintering at a lower temperature, thereby reducing energy consumption and production costs.

[0010] Specifically for the present invention, the chemical formula of the precursor is A x (M y ) m (X a O b ) n- (OH - ) z ·mH 2 O, which is obtained by mutual reaction of alkali metal source, transition metal source and phosphorus source, precipitation, solid-liquid separation, washing and drying. The precursor has a long-range disordered structure formed by the mutual interlocking of alkali metal ions, transition metal ions and anion groups. It has a small particle size and no crystallinity, and is easy to grind and disperse. When mixed with other components, it shows excellent uniformity. After sintering, the obtained material has high crystallinity, high phase purity, and exhibits excellent electrochemical properties.

[0011] Another object of the present invention is to protect the preparation method of the above-mentioned non-stoichiometric sodium ion battery polyanion type positive electrode material precursor, comprising the following steps:

[0012] S1. Preparation of precursor solution: dissolving the transition metal element M source with acid and adjusting the pH to obtain a clear precursor solution;

[0013] S2, pre-oxidation treatment: adding an oxidant to the above-mentioned precursor solution to oxidize the transition metal ions to generate a pre-oxidation precursor solution;

[0014] S3, aging precipitation: under temperature control, anion element X source and cation A source are added to the above pre-oxidation precursor solution, dissolved and the solution pH is adjusted for aging to form A. x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitation;

[0015] S4, high temperature calcination: x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor.

[0016] Furthermore, in step S1, the pH range is 0-4.5. Within this range, the transition metal compound can be completely dissolved and evenly diffused into the solution in the form of ions, which is convenient for the subsequent precipitation reaction.

[0017] Further, in step S3, the pH range is 4.0-7.0, the purpose of which is to cause the alkali metal ions, transition metal ions and anionic groups in the solution to produce a coprecipitation reaction, with A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O forms, and the precipitate presents a long-range disordered nanocrystalline structure; when the pH is lower than 4.0, some ions in the solution cannot be effectively precipitated, while when the pH is higher than 7.0, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The hydroxide content in O is too high and the proportion of inactive ingredients is too large, which is not conducive to the preparation of subsequent materials.

[0018] Furthermore, in step S2, the amount of the oxidant added is 0.5 to 2 times the molar ratio of the transition metal element in the solution. Within this range, the transition metal element can be completely oxidized, which is convenient for subsequent precipitation.

[0019] Furthermore, in step S3, the temperature of the temperature-controlled reaction is 25-120°C, the purpose of which is to make the ions in the solution bond with each other and precipitate out in the form of precipitation; when the temperature is lower than 25°C, the diffusion rate between ions in the solution is low, the precipitation reaction is slow, and the precipitation is incomplete; and when the temperature is higher than 120°C, the solution is prone to violent boiling at high temperature, affecting the stable progress of the precipitation reaction.

[0020] Furthermore, in step S3, the aging time is ≥ 0.01H, the purpose of which is to promote the diffusion and rearrangement of ions in the solution, induce crystallite growth and improve particle morphology, which is beneficial to the subsequent material processing and performance improvement.

[0021] Furthermore, in step S4, the conditions for high temperature calcination are: calcination temperature 100-300°C, calcination time ≥ 0.01H, the purpose of which is to further remove A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitates free water on the surface and bound water inside; when the temperature is below 100℃, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The free water on the surface of O evaporates too slowly, and the internal bound water is not easy to remove, which affects the subsequent ratio. When the temperature is higher than 300℃, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The elements in O further melt and crystallize to form dense and hard block particles, which affect the synthesis of subsequent materials.

[0022] Further, in step S4, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2After solid-liquid separation of the precipitate, high-temperature calcination is performed. The solid-liquid separation method is one or more of centrifugation, filtration, filter pressing, and vacuum filtration. A is achieved by centrifugal force or gravity extrusion. x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O The free water on the surface is removed quickly.

[0023] Further, the transition metal M source is one or more of a manganese source, a cobalt source, and an iron source; the manganese source is manganese nitrate, manganese sulfate, manganese acetate, manganese chloride, elemental manganese, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganese oxalate, manganese hydroxide, manganous anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is cobalt sulfate, cobalt nitrate, cobalt chloride, methylcobalamin, hydroxycobalamin, adenosylcobalamin, elemental cobalt, cobalt tetraoxide, cobalt oxide, cobalt oxalate, cobalt carbonate, cobalt oxide, and cobalt hydroxide; the iron source is ferric acetate, ferric sulfate / ferrous sulfate, ferric nitrate, ferric chloride / ferrous chloride, ferric citrate, ferrous ammonium sulfate, elemental iron, ferric oxalate, ferric oxide, ferrous oxide, ferric oxide, ferrous hydroxide, and ferric hydroxide;

[0024] Furthermore, the acid dissolution adopts one or more of sulfuric acid compounds, phosphoric acid compounds, silica compounds, nitric acid, nitrous acid, hydrochloric acid, formic acid, acetic acid, citric acid, benzoic acid, oxalic acid, salicylic acid, and lactic acid; the sulfuric acid compound is one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfonic acid, and aminosulfonic acid; the phosphoric acid compound is one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid; the silica compound is one or more of orthosilicic acid, polysilicic acid, and metasilicic acid; the oxidant is one or more of oxygen, chlorine, iodine, hydrogen peroxide, nitric acid and other compounds.

[0025] Further, the anion X source is one or more of a sulfur source, a phosphorus source, and a silicon source; the sulfur source is one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfuric acid, sulfonic acid, sulfamic acid, sodium sulfate, ammonium sulfate, ammonium hydrogen sulfate, ferrous sulfate, and ammonium ferrous sulfate; the phosphorus source is one or more of phosphoric acid, sodium / ammonium phosphate, sodium monohydrogen phosphate / ammonium, sodium / ammonium dihydrogen phosphate, phosphorous acid, sodium phosphite, hypophosphorous acid, sodium hypophosphite, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate, metaphosphoric acid, sodium metaphosphate, polyphosphoric acid, and sodium polyphosphate; the silicon source is one or more of orthosilicic acid, polysilicic acid, metasilicic acid, and sodium silicate.

[0026] Further, in step S3, the cation A source is one or more of an acid source, a sodium source, and an ammonium source. The acid source here is selected from the solvent used for the acid dissolution in the aforementioned step S1. The acid source used can be added simultaneously with the pH adjustment. The sodium source is one or more of sodium carbonate, sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate. The ammonium source is one or more of ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate, ammonium oxalate, ammonium perchlorate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0027] The present invention discloses a non-stoichiometric sodium ion battery polyanion type positive electrode material precursor and a preparation method thereof, which has the following beneficial effects:

[0028] First, the phase purity is high, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The alkali metal elements, transition metals and anion groups in the O precursor are in a highly uniform mixed state. When using it as a precursor to prepare polyanionic materials, only an appropriate amount of water-soluble sodium source and a small amount of phosphorus source need to be added to meet the chemical ratio requirements. Since both the sodium source and the phosphorus source have excellent water solubility, they can penetrate into the material through the pore structure in the precursor to achieve uniform distribution of elements, thereby preparing a target material with high phase purity;

[0029] Second, high compaction density, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The O precursor and the additional sodium source and a small amount of phosphorus source interpenetrate each other during the grinding process to form a uniform distribution. During the sintering process, the elements bond with each other, forming a crystal nucleus in situ, and continue to grow epitaxially and diffusely, eventually forming a dense large-grained single crystal. In addition, there are fewer pores between the crystals and the density is high, which greatly improves the compaction density;

[0030] Third, low cost, when using FePO 4 or FeC 2 O 4 When using precursors such as A to prepare polyanionic materials, the grinding and spraying stages consume a lot of energy and are very expensive due to the long grinding time and low solid content of the precursors.x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor has unique amorphous properties and highly uniform element distribution. This microstructure allows the mixing process to quickly achieve uniform mixing of ingredients without long grinding. In addition, its special amorphous bonding state changes the interaction mode with water molecules, greatly reducing the hydrogen bonding force with water, and can achieve a higher solid content in slurry preparation. In the spray drying stage, due to the significant increase in solid content, the amount of water to be evaporated is greatly reduced, thereby greatly reducing the energy consumption of spraying;

[0031] Fourth, excellent electrochemical performance, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 The element mixing uniformity of the O precursor is extremely high, and the prepared material has high crystallinity and phase purity. The element occupancy in the crystal and the sodium ion diffusion channel show a regular and orderly arrangement, which increases the number of redox transfer charges and improves the capacity. At the same time, the low ion transition energy barrier makes the material have excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 For the Na in Application Example 1 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 O precursor prepared from Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Material SEM;

[0033] Figure 2 The anhydrous FePO in Comparative Example 1 4 Na 4 Fe 2.91 (PO 4 ) 2 P 2 O7 SEM of the material Specific implementation manners

[0034] In order to enable those skilled in the art of the present technology to better understand the technical solution of the present invention, the products of the present invention will be further described in detail below in conjunction with embodiments and the accompanying drawings.

[0035] The present invention discloses a non-stoichiometric sodium ion battery polyanionic cathode material precursor, and the chemical formula of the precursor is A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O;

[0036] Among them, A is one or more of the cations H + , Na + or NH 4 + , M is one or more of the transition metal elements Fe, Co, Mn, and X is one or more of the anion elements P, S, Si;

[0037] Among them, the relationship among x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0.

[0038] Another object of the present invention is to protect a method for preparing the non-stoichiometric sodium ion battery polyanionic cathode material precursor, including the following steps:

[0039] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0040] S2. Pre-oxidation treatment: Add an oxidizing agent to the above precursor solution to oxidize the transition metal ions to generate a pre-oxidized precursor solution;

[0041] S3. Aging precipitation: Under temperature control conditions, add the anion element X source and the cation A source to the above pre-oxidized precursor solution, dissolve and adjust the pH of the solution for aging, and then form A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate;

[0042] S4, high temperature calcination: x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor.

[0043] Further, in step S1, the pH range is 0-4.5.

[0044] Further, in step S3, the pH range is 4.0-7.0.

[0045] Furthermore, in step S2, the amount of the oxidant added is 0.5 to 2 times the molar ratio of the transition metal element in the solution.

[0046] Furthermore, in step S3, the temperature of the temperature-controlled reaction is 25-120°C.

[0047] Further, in step S3, the aging time is ≥ 0.01H.

[0048] Furthermore, in step S4, the conditions for high temperature calcination are: calcination temperature 100-300° C., calcination time ≥ 0.01H.

[0049] Further, in step S4, A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 After solid-liquid separation of the precipitate, high-temperature calcination is performed. The solid-liquid separation method is one or more of centrifugation, filtration, filter pressing, and vacuum filtration.

[0050] Further, the transition metal M source is one or more of a manganese source, a cobalt source, and an iron source; the manganese source is manganese nitrate, manganese sulfate, manganese acetate, manganese chloride, elemental manganese, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganese oxalate, manganese hydroxide, manganous anhydride, manganic anhydride, and permanganic anhydride; the cobalt source is cobalt sulfate, cobalt nitrate, cobalt chloride, methylcobalamin, hydroxycobalamin, adenosylcobalamin, elemental cobalt, cobalt tetraoxide, cobalt oxide, cobalt oxalate, cobalt carbonate, cobalt oxide, and cobalt hydroxide; the iron source is ferric acetate, ferric sulfate / ferrous sulfate, ferric nitrate, ferric chloride / ferrous chloride, ferric citrate, ferrous ammonium sulfate, elemental iron, ferric oxalate, ferric oxide, ferrous oxide, ferric oxide, ferrous hydroxide, and ferric hydroxide;

[0051] Furthermore, the acid dissolution adopts one or more of sulfuric acid compounds, phosphoric acid compounds, silica compounds, nitric acid, nitrous acid, hydrochloric acid, formic acid, acetic acid, citric acid, benzoic acid, oxalic acid, salicylic acid, and lactic acid; the sulfuric acid compound is one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfonic acid, and aminosulfonic acid; the phosphoric acid compound is one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid; the silica compound is one or more of orthosilicic acid, polysilicic acid, and metasilicic acid; the oxidant is one or more of oxygen, chlorine, iodine, hydrogen peroxide, nitric acid and other compounds.

[0052] Further, the anion X source is one or more of a sulfur source, a phosphorus source, and a silicon source; the sulfur source is one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfuric acid, sulfonic acid, sulfamic acid, sodium sulfate, ammonium sulfate, ammonium hydrogen sulfate, ferrous sulfate, and ammonium ferrous sulfate; the phosphorus source is one or more of phosphoric acid, sodium / ammonium phosphate, sodium monohydrogen phosphate / ammonium, sodium / ammonium dihydrogen phosphate, phosphorous acid, sodium phosphite, hypophosphorous acid, sodium hypophosphite, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate, metaphosphoric acid, sodium metaphosphate, polyphosphoric acid, and sodium polyphosphate; the silicon source is one or more of orthosilicic acid, polysilicic acid, metasilicic acid, and sodium silicate.

[0053] Further, in step S3, the cation A source is one or more of an acid source, a sodium source, and an ammonium source. The acid source here is selected from the solvent used for the acid dissolution in the aforementioned step S1. The acid source used can be added simultaneously with the pH adjustment. The sodium source is one or more of sodium carbonate, sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, sodium nitrate, sodium silicate, sodium acetate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate. The ammonium source is one or more of ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate, ammonium oxalate, ammonium perchlorate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, and ammonium phosphate.

[0054] Example 1

[0055] This embodiment discloses a non-stoichiometric sodium ion battery polyanionic cathode material precursor and a preparation method thereof. The chemical general formula of the precursor is A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O, where A is one or more of the cations H + , Na + or NH 4 + ; M is one or more of the transition metal elements Fe, Co, Mn; X is one or more of the anion elements P, S, Si; among them, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0..

[0056] The non-stoichiometric sodium ion battery polyanionic cathode material precursor of this embodiment is prepared by the following method:

[0057] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0058] S2. Pre-oxidation treatment: Add an oxidant to the above precursor solution to oxidize transition metal ions to generate a pre-oxidized precursor solution;

[0059] S3. Aging precipitation: Under temperature control conditions, add the anion element X source and the cation A source to the above pre-oxidized precursor solution, dissolve and adjust the solution pH for aging, and then form an A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate;

[0060] S4. High-temperature calcination: Heat the A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2O precipitate is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor.

[0061] In terms of specific process control, the pH range of step S1 is 0.5, and the pH range of step S3 is 4.5. The amount of oxidant added in step S2 is 0.5 times the molar ratio of the transition metal element in the solution. The temperature in step S3 is controlled to be 25°C. In step S4 of this embodiment, the temperature of high-temperature calcination is 150°C; the solid-liquid separation method in step S4 is filter press.

[0062] In terms of specific material addition, the acid in step S1 is a sulfuric acid compound, specifically including sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, and hydrogen sulfide. The oxidant in step S2 is oxygen, chlorine, or hydrogen peroxide.

[0063] In terms of the main raw materials, in step S1, the transition metal M source is a manganese source, and the manganese source is manganese nitrate, manganese sulfate, manganese acetate, manganese chloride, elemental manganese, manganese monoxide, manganese dioxide, manganese trioxide, and manganese tetraoxide. In step S3, the anion element X is a sulfur source, and the sulfur source is sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfuric acid, and aminosulfonic acid. In step S3, the cation A source is a sodium source, and the sodium source is sodium carbonate, sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, and sodium nitrate.

[0064] Example 2

[0065] This embodiment discloses a non-stoichiometric sodium ion battery polyanion type positive electrode material precursor and a preparation method thereof. The precursor has a chemical formula of A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O, where A is a cation H + 、Na + or NH 4 +One or more of the following, M is one or more of the transition metal elements Fe, Co, Mn, and X is one or more of the anion elements P, S, Si; wherein, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0..

[0066] The non-stoichiometric sodium-ion battery polyanionic cathode material precursor of this example is prepared by the following method:

[0067] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0068] S2. Pre-oxidation treatment: Add an oxidant to the above precursor solution to oxidize the transition metal ions to form a pre-oxidized precursor solution;

[0069] S3. Aging precipitation: Under temperature control conditions, add the anion element X source and the cation A source to the above pre-oxidized precursor solution, dissolve and adjust the pH of the solution for aging, and then form A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate;

[0070] S4. High-temperature calcination: High-temperature calcine the A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate, and after cooling, the non-stoichiometric A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor is obtained.

[0071] In specific process control, the pH range in step S1 is 1.0, and the pH range in step S3 is 5.0. The addition amount of the oxidizing agent in step S2 is 1.0 times the molar ratio of the transition metal element in the solution. The temperature in step S3 is controlled at 50 °C. In step S4 of this embodiment, the temperature for high-temperature calcination is 180 °C; the solid-liquid separation method in step S4 is centrifugation.

[0072] In terms of specific material addition, the acid in step S1 is a phosphorus-containing acidic compound, specifically including phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid. The oxidizing agent in step S2 is oxygen.

[0073] In terms of the main raw materials, the transition metal M source in step S1 is a cobalt source, and the cobalt source is cobalt sulfate, cobalt nitrate, cobalt chloride, methylcobalamin, hydroxocobalamin, adenosylcobalamin, elemental cobalt, cobalt tetroxide, and cobalt(III) oxide. In step S3, the anion element X is a phosphorus source, and the phosphorus source is phosphoric acid, sodium / ammonium phosphate, sodium / ammonium monohydrogen phosphate, sodium / ammonium dihydrogen phosphate, and phosphorous acid. In step S3, the cation A source is a sodium source, and the sodium source is sodium carbonate, sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, and sodium nitrate.

[0074] Example 3

[0075] This example discloses a non-stoichiometric sodium-ion battery polyanionic cathode material precursor and its preparation method. The chemical general formula of the precursor is A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O, where A is one or more of the cations H + , Na + or NH 4 + ; M is one or more of the transition metal elements Fe, Co, Mn; X is one or more of the anion elements P, S, Si; among them, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0..

[0076] The non-stoichiometric sodium-ion battery polyanionic cathode material precursor of this example is prepared by the following method:

[0077] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0078] S2, pre-oxidation treatment: adding an oxidant to the above-mentioned precursor solution to oxidize the transition metal ions to generate a pre-oxidation precursor solution;

[0079] S3, aging precipitation: under temperature control, anion element X source and cation A source are added to the above pre-oxidation precursor solution, dissolved and the solution pH is adjusted for aging to form A. x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitation;

[0080] S4, high temperature calcination: x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor.

[0081] In terms of specific process control, the pH range of step S1 is 1.5, and the pH range of step S3 is 5.5. The amount of oxidant added in step S2 is 1.2 times the molar ratio of the transition metal element in the solution. The temperature in step S3 is controlled to 75°C. In step S4 of this embodiment, the temperature of high-temperature calcination is 180°C; the solid-liquid separation method in step S4 is filter press.

[0082] In terms of specific material addition, the acid in step S1 is a silicon-containing acid compound, specifically including orthosilicic acid, polysilicic acid, and metasilicic acid. The oxidant in step S2 is hydrogen peroxide.

[0083] In terms of main raw materials, in step S1, the source of transition metal M is an iron source, which is ferric acetate, ferric sulfate / ferrous iron, ferric nitrate, ferric chloride / ferrous iron. In step S3, the anion element X is a silicon source, which is orthosilicic acid, polysilicic acid, metasilicic acid, and sodium silicate. In step S3, the source of cation A is an ammonium source, which is ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate, and ammonium oxalate.

[0084] Example 4

[0085] This embodiment discloses a non-stoichiometric sodium-ion battery polyanionic cathode material precursor and a preparation method thereof. The chemical general formula of the precursor is A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O, where A is one or more of the cations H + , Na + or NH 4 + ; M is one or more of the transition metal elements Fe, Co, Mn; X is one or more of the anion elements P, S, Si; among them, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0..

[0086] The non-stoichiometric sodium-ion battery polyanionic cathode material precursor of this embodiment is prepared by the following method:

[0087] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0088] S2. Pre-oxidation treatment: Add an oxidant to the above precursor solution to oxidize the transition metal ions to generate a pre-oxidized precursor solution;

[0089] S3. Aging precipitation: Under temperature control conditions, add the anion element X source and the cation A source to the above pre-oxidized precursor solution, dissolve and adjust the pH of the solution for aging, and then form an A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate;

[0090] S4. High-temperature calcination: Heat A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2O precipitate is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor.

[0091] In terms of specific process control, the pH range of step S1 is 2.0, and the pH range of step S3 is 6.0. The amount of oxidant added in step S2 is 1.8 times the molar ratio of the transition metal element in the solution. The temperature in step S3 is controlled to 90°C. In step S4 of this embodiment, the temperature of high-temperature calcination is 200°C; the solid-liquid separation method in step S4 is centrifugation.

[0092] In terms of specific material addition, the acid in step S1 is a sulfuric acid compound, specifically including sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, and hydrogen sulfide. The oxidant in step S2 is oxygen, chlorine, or hydrogen peroxide.

[0093] In terms of the main raw materials, in step S1, the transition metal M source is a manganese source, and the manganese source is manganese nitrate, manganese sulfate, manganese acetate, manganese chloride, elemental manganese, manganese monoxide, manganese dioxide, manganese trioxide, and manganese tetraoxide. In step S3, the anion element X is a phosphorus source, and the phosphorus source is phosphoric acid, sodium phosphate / ammonium, sodium monohydrogen phosphate / ammonium, sodium dihydrogen phosphate / ammonium, and phosphorous acid. In step S3, the cation A source is a sodium source, and the sodium source is sodium carbonate, sodium carbonate, sodium hydroxide, sodium chloride, sodium sulfate, and sodium nitrate.

[0094] Example 5

[0095] This embodiment discloses a non-stoichiometric sodium ion battery polyanion type positive electrode material precursor and a preparation method thereof. The precursor has a chemical formula of A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O, where A is a cation H + 、Na + or NH 4 +One or more of them, M is one or more of transition metal elements Fe, Co, and Mn, and X is one or more of anion elements P, S, and Si; wherein, the relationship between x, y, and z is x + my - n - z = 0, 0 < x < 1, 0.5 < y ≤ 2, 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0..

[0096] The non-stoichiometric sodium-ion battery polyanionic cathode material precursor of this example is prepared by the following method:

[0097] S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution;

[0098] S2. Pre-oxidation treatment: Add an oxidant to the above precursor solution to oxidize the transition metal ions to generate a pre-oxidized precursor solution;

[0099] S3. Aging and precipitation: Under temperature control conditions, add the anion element X source and the cation A source to the above pre-oxidized precursor solution, dissolve and adjust the solution pH for aging, and then form A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate;

[0100] S4. High-temperature calcination: High-temperature calcine the A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precipitate, and after cooling, the non-stoichiometric A x (M y ) m+ (X a O b ) n- (OH - ) z ·mH 2 O precursor is obtained.

[0101] In terms of specific process control, the pH range of step S1 is 3.0, and the pH range of step S3 is 6.5. The amount of oxidant added in step S2 is 2.0 times the molar ratio of the transition metal element in the solution. The temperature in step S3 is controlled to be 110°C. In step S4 of this embodiment, the temperature of high-temperature calcination is 250°C; the solid-liquid separation method in step S4 is filter press.

[0102] In terms of specific material addition, the acid in step S1 is a silicon-containing acidic compound, specifically including orthosilicic acid, polysilicic acid, and metasilicic acid. The oxidant in step S2 is oxygen, chlorine, or hydrogen peroxide.

[0103] In terms of main raw materials, in step S1, the source of transition metal M is an iron source, which is ferric acetate, ferric sulfate / ferrous iron, ferric nitrate, ferric chloride / ferrous iron. In step S3, the anion element X is a silicon source, which is orthosilicic acid, polysilicic acid, metasilicic acid, and sodium silicate. In step S3, the source of cation A is an ammonium source, which is ammonium sulfate, ammonium nitrate, ammonium carbonate, ammonium acetate, and ammonium oxalate.

[0104] Application Example 1 Non-stoichiometric Na 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 Preparation of O precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Synthesis and electrochemical properties of materials

[0105] This embodiment involves a non-stoichiometric ratio Na 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 O precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, its preparation and synthesis steps are:

[0106] S1. Preparation of precursor solution: dissolve ferrous sulfate and pyrophosphoric acid in water at a molar ratio of 1.455:1, and add formic acid to adjust the pH of the solution to 2.0 to form a light green transparent solution;

[0107] S2, pre-oxidation treatment: adding hydrogen peroxide to the above solution to oxidize the divalent iron in the solution into trivalent iron to generate a pre-oxidized precursor solution;

[0108] S3, aging precipitation: under the condition of heating at 80°C, slowly add sodium carbonate to the above precursor solution, adjust the pH of the solution to 5.6, so that the transition metal ions in the solution generate Na 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 ·mH 2 O precipitation;

[0109] S4, high temperature calcination: the above precipitate is centrifuged, washed and calcined at 200°C for 2 hours, and the polyanion positive electrode material is obtained after natural cooling. 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 O precursor powder.

[0110] Will Na 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 The FePO4 precursor is mixed with sodium acetate in a molar ratio of 1:3.74, and sucrose is added (the amount of sucrose is 0.2 times the molar amount of sodium acetate), and then ground after adding water, and the grinding time is about 0.2H. Compared with the preparation method using anhydrous FePO4 precursor in Comparative Example 1, this process significantly shortens the grinding time, reduces energy consumption and process costs. When the maximum particle size (Dmax) of the solid particles in the slurry is ≤50nm, the slurry is spray dried, and the inlet temperature is set to 250°C and the outlet temperature is set to 80°C to remove moisture and obtain a dry precursor powder. Finally, in a nitrogen atmosphere, the precursor powder is calcined at 630°C for 8 hours, and Na is obtained after natural cooling. 4 Fe2.91 (PO 4 ) 2 P 2 O 7 Material.

[0111] Figure 1 Shows Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The SEM image of the material shows a regular spherical morphology, with no obvious primary particles, and no obvious pores or cracks on the surface of the spherical particles, indicating that the material has a high degree of solidification and density. The data in Table 1 further show that the porosity and specific surface area of ​​the material are 3.2% and 5.6m² / g, respectively, which are significantly lower than those in Comparative Example 1. This proves that the material has undergone a higher degree of melting during the sintering process, and the growth between particles is denser, thereby effectively reducing the pore content and specific surface area. Therefore, its compacted density is greatly increased to 2.37g / cm³, which is much higher than that in Comparative Example 1. In addition, the refined calculation results of the XRD diffraction curve show that the phase purity of the material is as high as 99.3%, which is much higher than 82.6% in Comparative Example 1. This shows that Na 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 The uniform distribution of transition metals and phosphorus in the O precursor significantly improves the mixing uniformity of ions during the grinding process, shortens the diffusion distance of ions during sintering, and makes it easier to crystallize and nucleate, thus forming a material with more complete crystal form and higher phase purity.

[0112] Will Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, SurP, and PVDF5130 were mixed with NMP in a mass ratio of 9.5:0.2:0.3. The above materials were mixed evenly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity. Then, the black slurry was coated on aluminum foil using a 150um four-sided preparation device. The film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Metal sodium was used as the counter electrode and 1 mol / L NaClO 4EC+DEC (1:1 vol%) + 5% FEC was used as the electrolyte and the separator was a PP / PE / PP three-layer separator, which was assembled into a CR2016 button cell in a glove box.

[0113] The electrochemical performance test results in Table 1 show that Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The discharge capacity of the electrode at a rate of 0.1C (1C=129mAh / g) reaches 124.6mAh / g, which is significantly higher than 86.5mAh / g of Comparative Example 1. This excellent capacity performance is attributed to the high phase purity of the material, which effectively reduces unfavorable factors such as vacancies, defects and dislocations in the crystal structure, thereby improving its capacity per gram. In addition, the capacity retention rate of the electrode at a rate of 10C is as high as 97.5%, which is much better than 84.3% of Comparative Example 1. This is mainly due to the high phase purity of the material, which makes the primary grains more complete and the number of grain boundaries is reduced, thereby reducing the resistance during the migration of sodium ions and significantly improving the rate performance. At a rate of 1C, after 1000 cycles, the capacity retention rate of the electrode is still as high as 98.9%, with almost no attenuation. This excellent cycle stability is due to the high integrity of the material's crystal structure, which allows the stress generated during the sodium ion extraction process to be evenly released, effectively maintaining the stability of the crystal structure; on the other hand, the material's low specific surface area and porosity reduce the side reactions with the electrolyte at high voltage, thereby maintaining the interface stability. 0.135 (Fe 1.455 ) 3+ (P 2 O 7 ) 4- (OH - ) 0.5 0.01H 2 NaO was prepared as a precursor 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, due to its high phase purity, exhibits significantly improved electrochemical performance, including higher gram capacity, excellent rate capability and outstanding cycling stability.

[0114] Application Example 2 Non-stoichiometric ratio (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - )0.3175 0.01H 2 Preparation of O precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Synthesis and electrochemical properties of materials

[0115] This embodiment involves a non-stoichiometric ratio (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - ) 0.3175 0.01H 2 O precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, its preparation and synthesis steps are:

[0116] S1. Preparation of precursor solution: ferrous sulfate and phosphoric acid were mixed with water at a molar ratio of 0.7275:1.0, and the pH of the solution was adjusted to 0.25 with citric acid to generate a transparent light green solution;

[0117] S2, pre-oxidation treatment: adding hydrogen peroxide to the above light green solution to oxidize the divalent iron in the solution into trivalent iron to generate a pre-oxidized precursor solution;

[0118] S3, aging precipitation: under the condition of heating at 90°C, slowly add ammonia water to the above precursor solution, adjust the pH of the solution to 5.9, so that the transition metal ions in the solution generate (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - ) 0.3175 ·mH 2 O precipitation;

[0119] S4, high temperature calcination: the above precipitate is centrifuged, washed and calcined at 250 ° C for 2 hours, and the polyanion positive electrode material is obtained by natural cooling with non-stoichiometric ratio (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH -) 0.3175 0.01H 2 O precursor powder.

[0120] (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - ) 0.3175 0.01H 2 O precursor, sodium hydroxide and citric acid (the amount added is 0.5 times the molar amount of sodium hydroxide) are mixed with water in a molar ratio of 1:5.50 and ground for about 0.5 hours. 2 O 4 The grinding time of the precursor 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 with an inlet air temperature of 290℃ and an outlet air temperature of 100℃ to remove moisture and obtain a dry precursor powder. Finally, the precursor powder is calcined at 600℃ for 12h in a nitrogen atmosphere, and Na is obtained after natural cooling. 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Material.

[0121] The data in Table 1 show that Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The porosity and specific surface area of ​​the material are 4.6% and 6.3m² / g, respectively, which are significantly lower than the results of Comparative Example 2. This phenomenon is closely related to the high mixing uniformity of the material precursor. The uniformity of ion distribution promotes the molten bonding of local ions during sintering, forming a more compact particle structure, thereby greatly reducing the porosity between particles, reducing the specific surface area, and increasing its compaction density to 2.30g / cm³. In addition, the XRD diffraction curve refinement calculation results show that the phase purity of the material is as high as 98.9%, much higher than 87.4% of Comparative Example 2. This further confirms that (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - ) 0.3175 0.01H 2The uniform distribution of elements in the O precursor effectively promotes the growth of crystals during sintering. By shortening the ion diffusion distance, the material is easier to crystallize and nucleate, ultimately forming a NaO with high crystallinity and excellent phase purity. 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Material.

[0122] Will Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, SurP, and PVDF5130 were mixed with NMP in a mass ratio of 9.5:0.2:0.3. The above materials were mixed evenly using a high-speed homogenizer to form a black slurry with uniform color and high fluidity. Then, the black slurry was coated on aluminum foil using a 150um four-sided preparation device. The film was dried in a vacuum drying oven at 100°C for 2 hours. The electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Metal sodium was used as the counter electrode and 1 mol / L NaClO 4 EC+DEC (1:1 vol%) + 5% FEC was used as the electrolyte and the separator was a PP / PE / PP three-layer separator, which was assembled into a CR2016 button cell in a glove box.

[0123] According to the electrochemical performance test data in Table 1, the electrode exhibits a discharge capacity of 120.2 mAh / g at a rate of 0.1C (1C = 129 mAh / g), and the capacity is highly utilized. This means that in the material structure, there are more charges involved in the redox reaction, which is significantly superior to Comparative Example 2. The reason is closely related to the high phase purity and crystallinity of the above-mentioned materials. The higher the phase purity of the material, the fewer defects in the crystal structure that hinder the transmission and diffusion of ions and electrons, thereby creating favorable conditions for the material to exert its high capacity characteristics. In addition, it can be seen from the data in Table 1 that the capacity retention rate of the electrode at a rate of 10C is as high as 98.2% compared to that at 0.1C, far exceeding 88.2% of Comparative Example 2. This clearly shows that the higher the phase purity of the material, the fewer crystal defects, the lower the energy barrier for the diffusion of sodium ions in the structure, and the problem of high diffusion energy barrier will not be caused by defects. At the same time, the higher phase purity effectively avoids the grain boundary blocking effect caused by the presence of impurity phases, greatly promotes the transmission of ions, and plays a positive role in improving the rate performance of the material. In the end, the electrode retained 97.6% of its capacity after 1000 cycles of testing at a rate of 1C, showing extremely excellent cycle stability. This fully demonstrates that the higher the phase purity of the material, the better the integrity of the crystal form. During the process of sodium extraction and insertion of each crystal, the force generated by volume expansion is more uniform, which can effectively reduce the possibility of structural pulverization, thereby significantly improving the cycle stability. In addition, the smaller specific surface area of ​​the material reduces the catalytic effect on the electrolyte under high pressure to a certain extent, reduces the side reactions at the material interface, and further enhances its cycle stability. In summary, with (NH 4 ) 0.5 (Fe 0.7275 ) 3+ (PO 4 ) 3- (OH - ) 0.3175 0.01H 2 NaO precursor 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, with its higher phase purity, exhibits more outstanding electrochemical performance.

[0124] Comparative Example 1 Anhydrous FePO 4 Precursor preparation Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Materials and their electrochemical properties

[0125] This embodiment involves anhydrous FePO 4 Precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, its preparation and synthesis steps are:

[0126] Weigh anhydrous FePO 4 , phosphoric acid, and sodium acetate are mixed in a molar ratio of 2.91:1.0:4.0, and glucose is added at the same time, and its addition amount is 0.1 times the molar amount of sodium acetate. The above raw materials are ground after adding water, and the grinding time is about 13 hours. Compared with Application Example 1, this process takes longer to grind, significantly increases energy consumption, reduces efficiency, and greatly increases process costs. When the particle size Dmax of the solid particles in the slurry is ≤50nm, the slurry is spray dried. During spray drying, the inlet temperature is set to 250°C and the outlet temperature is set to 80°C to fully remove moisture and obtain a dry precursor powder. Subsequently, the precursor powder is placed in a nitrogen atmosphere and calcined at a high temperature of 630°C for 8 hours. After natural cooling, Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Material.

[0127] from Figure 2 The Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The SEM image of the material shows that the material is in the form of irregular block particles, which are composed of primary particles of about 50-100nm, and there are a lot of pores between the particles. According to the data in Table 1, the porosity of the material is 20.4%, and the specific surface area is 14.3m² / g, which is significantly increased compared with the application example 1. This is consistent with the anhydrous FePO 4 The precursor is closely related, because it is a high-temperature sintered phase, the particles are hard, and there are many edges and corners after grinding. During the spraying process, these particles stack on each other to form a porous spherical arrangement, and the pores remain after sintering, resulting in an increase in porosity and specific surface area, and a decrease in compaction density to 1.82g / cm³. It is further confirmed by XRD diffraction curve refinement calculation that the phase purity of the material is only 82.6%, which is much lower than that of Application Example 1. This shows that FePO 4 The grinding process of the precursor is not conducive to uniform mixing of ions, resulting in phase separation during sintering, which seriously affects the crystal structure and phase purity of the material.

[0128] Will Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Materials, SurP, PVDF5130 were added with NMP in a mass ratio of 9.5:0.2:0.3, and a high-speed homogenizer was used to fully mix to form a black slurry with uniform color and good fluidity. Next, the black slurry was coated on aluminum foil using a 150um four-sided preparation device, and then the coated film was placed in a 100°C vacuum drying oven and dried for 2 hours. After that, the electrode film was punched into a disc with a radius of 0.6 mm using a punching machine. Metal sodium was used as the counter electrode, and 1 mol / L NaClO 4 EC+DEC (1:1 vol%)+5%FEC was used as the electrolyte and PP / PE / PP three-layer membrane was used as the separator, which were assembled into CR2016 type button cells in a glove box.

[0129] The results in Table 1 show that the discharge capacity of the material at a rate of 0.1C (1C = 129 mAh / g) is only 86.5 mAh / g, which is much lower than the discharge capacity of the material in Application Example 1. This is consistent with the low purity of the material, indicating that the anhydrous FePO 4 The materials prepared as precursors may contain impurities such as inactive sodium iron phosphate or low-capacity sodium iron pyrophosphate, which reduces the effective active ingredients in the unit mass of the material, reduces the number of transition metal redox and the number of sodium ion deintercalation, resulting in a decrease in the material's gram capacity. In addition, the data in Table 1 show that at a rate of 10C, the capacity retention rate of the electrode is only 84.3% compared to 0.1C. The lower rate performance is related to the presence of impurities in the material. There are many grain boundaries between the impurities and the main phase. The transmission rate of sodium ions at the grain boundaries is slow, and there is a hysteresis phenomenon, which leads to a decrease in the rate performance of the material. In the end, after 1000 weeks of long-term cycling at a rate of 1C, the capacity retention rate of the electrode was only 90.2%, showing a certain degree of attenuation. The reason is that during the deintercalation of sodium, Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The expansion and contraction of the crystals cause microcracks between them and the impurity phase crystal planes. The electrolyte penetrates into the surface, accelerating the dissolution of interface elements, destroying the interface structure and reducing the cycle stability. At the same time, the high specific surface area of ​​the material will catalyze its reaction with the electrolyte under high voltage, leading to problems such as interface dissolution, further affecting the cycle stability of the material. In summary, the anhydrous FePO 4 Na 4 Fe 2.91 (PO 4 ) 2P 2 O 7 The low phase purity of the material causes uneven material reaction, which accelerates the degradation of the electrochemical performance of the material.

[0130] Comparative Example 2 FeC 2 O 4 Precursor preparation Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Materials and their electrochemical properties

[0131] This embodiment involves FeC 2 O 4 Precursor and Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The material, its preparation and synthesis steps are:

[0132] According to the molar ratio of 2.91:4.0:4.0, accurately weigh FeC 2 O 4 , phosphoric acid, sodium hydroxide, and citric acid, the amount of which is 0.5 times the molar amount of sodium hydroxide. These raw materials are mixed and ground after adding water, and the grinding time is about 18 hours. Compared with application example 2, the grinding time of this process is significantly longer. This is mainly due to the fact that FeC 2 O 4 It has a high degree of crystallinity and a large crystal hardness, which greatly increases the difficulty of grinding, resulting in increased process energy consumption, reduced efficiency, and significantly increased cost investment. When the particle size Dmax of the solid particles in the slurry is ≤30nm, the slurry is spray dried. During the spray drying process, the inlet air temperature is set to 290°C and the outlet air temperature is set to 100°C to fully remove moisture and obtain a dry precursor powder. Subsequently, the precursor powder is placed in a nitrogen atmosphere and calcined at a high temperature of 600°C for 12 hours. After natural cooling, Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Material.

[0133] According to the physical and chemical test data in Table 1, the porosity of the material is 18.2% and the specific surface area is 13.9 m² / g, which is significantly higher than that of Application Example 2. 2 O 4The precursor is closely related. This type of precursor belongs to the high-temperature sintering phase, the particles are hard, and there are many edges and corners after grinding. During the spray drying process, these particles stack on each other and easily form a porous structure. After sintering, these pores are still retained, resulting in an increase in the porosity and specific surface area of ​​the material, and a decrease in the compaction density to 1.93g / cm³. It is further confirmed by XRD diffraction curve refinement calculation that the phase purity of the material is only 87.4%, which is much lower than that of Application Example 2. This shows that anhydrous FeC 2 O 4 The grinding process of the precursor is not conducive to the uniform mixing of ions, which causes phase separation during the sintering process, seriously affecting the crystal structure of the material and its phase purity.

[0134] Will Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 Add NMP to the material, SurP, and PVDF5130 in a mass ratio of 9.5:0.2:0.3, and use a high-speed homogenizer to fully stir and mix to form a black slurry with uniform color and good fluidity. Then, use a 150um four-sided preparation device to evenly coat the black slurry on aluminum foil, and then place the coated film in a 100°C vacuum drying oven to dry for 2 hours. After that, use a punching machine to punch the electrode film into a disc with a radius of 0.6mm. Using metallic sodium as the counter electrode, 1mol / LNaClO 4 EC+DEC (1:1 vol%)+5%FEC was used as the electrolyte and PP / PE / PP three-layer membrane was used as the separator, which were assembled into CR2016 type button cells in a glove box.

[0135] The results in Table 1 show that the discharge capacity of the material at a rate of 0.1C (1C = 129 mAh / g) is only 90.5 mAh / g, which is much lower than the value of Application Example 2. This is consistent with the low purity of the material, indicating that the anhydrous FeC 2 O 4In the materials prepared as precursors, due to the uneven mixing between elements, inactive sodium iron phosphate, sodium manganese phosphate or low-capacity sodium iron pyrophosphate, sodium manganese pyrophosphate and other impurities may be produced, which reduces the active ingredients in the unit mass of the material, resulting in a decrease in the gram capacity of the material. In addition, the data in Table 1 show that the capacity retention rate of the electrode at a rate of 10C is only 88.2% compared to 0.1C. The low rate performance is related to the presence of the above-mentioned impurity phases. A large number of grain boundaries will be generated between the impurity phase and the main phase, which hinders the transmission of sodium ions and leads to a decrease in the rate performance of the material. In the end, after a long cycle of 1000 weeks at a rate of 1C, the capacity retention rate of the electrode was only 92.1%, which was severely attenuated, which indirectly reflects the instability of the material structure. The reason is that during the sodium insertion and deinsertion process, Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The difference in volume expansion rate between the crystal and the impurity phase makes it easy to generate microcracks at the crystal interface. The electrolyte penetrates into the material surface along the cracks, accelerating the dissolution of interface elements, destroying the interface structure, and reducing the cycle stability. At the same time, the high specific surface area of ​​the material will catalyze its reaction with the electrolyte under high voltage, causing problems such as interface dissolution and structural lithification, further affecting the cycle stability of the material. In summary, the anhydrous FeC 2 O 4 Na 4 Fe 2.91 (PO 4 ) 2 P 2 O 7 The low phase purity of the material causes uneven material reaction, which accelerates the degradation of the electrochemical performance of the material.

[0136] Table 1 Performance test results

[0137] Application Example 1 Comparative Example 1 Application Example 2 Comparative Example 2 Phase purity (%) 99.3 82.6 98.9 87.4 Porosity (%) 3.2 20.4 4.6 18.2 <![CDATA[Specific surface area (m 2 / g)]]> 5.6 14.3 6.3 13.9 <![CDATA[Compaction density (g / cm 3 )]]> 2.37 1.82 2.30 1.93 0.1C discharge specific capacity (mAh / g) 124.6 86.5 120.2 90.5 Capacity retention rate at 10C rate (10C / 0.1C%) 97.5 84.3 98.2 88.2 1000-cycle cycle retention rate at 1C rate (%) 98.9 90.2 97.6 92.1

[0138] The above embodiments are only specific embodiments of the present invention, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A non-stoichiometric sodium ion battery polyanion positive electrode material precursor, characterized in that: The chemical formula of the precursor is: x (M y ) m+ (X a O b ) n- (OH - ) z mH2O; Where A is a cation H + 、Na + or NH4 + One or more of, M is one or more of the transition metal elements Fe, Co, Mn, and X is one or more of the anion elements P, S, Si; Among them, the relationship between x, y, and z is x + my - n - z = 0, where 0 < x < 1, 0.5 < y ≤ 2, and 0 < z < 1; a takes the value of 1 or 2; b takes the value of 4 or 7; the value range of m is m ≥ 0.

2. A method for preparing the non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 1, characterized in that It includes the following steps: S1. Preparation of the precursor solution: Acid-dissolve the transition metal element M source and adjust the pH to obtain a clear precursor solution; S2. Pre-oxidation treatment: Add an oxidant to the above precursor solution to oxidize the transition metal ions to generate a pre-oxidized precursor solution; S3, aging precipitation: under temperature control, anion element X source and cation A source are added to the above pre-oxidation precursor solution, dissolved and the solution pH is adjusted for aging to form A. x (M y ) m+ (X a O b ) n- (OH - ) z mH2O precipitation; S4, high temperature calcination: x (M y ) m+ (X a O b ) n- (OH - ) z mH2O precipitation is calcined at high temperature, and then cooled to obtain non-stoichiometric ratio A x (M y ) m+ (X a O b ) n- (OH - ) z mH2O precursor.

3. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S1, the pH range is 0 - 4.

5.

4. The method for preparing the non-stoichiometric sodium ion battery polyanion positive electrode material precursor d according to claim 2, characterized in that: In step S3, the pH range is 4.0 - 7.

0.

5. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S2, the addition amount of the oxidant is 0.5 - 2 times the molar ratio of the transition metal element in the solution.

6. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S3, the temperature of the temperature-controlled reaction is 25 - 120 °C.

7. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S3, the aging time ≥ 0.01H.

8. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S4, the conditions for high-temperature calcination are: the calcination temperature is 100 - 300 °C, and the calcination time ≥ 0.01H.

9. The method for preparing a non-stoichiometric sodium ion battery polyanion positive electrode material precursor according to claim 2, characterized in that: In step S4, A x (M y ) m+ (X a O b ) n- (OH - ) z The mH2O precipitate is calcined at high temperature after solid-liquid separation. The solid-liquid separation method is one or more of centrifugation, filtration, filter pressing, and vacuum filtration.

10. The preparation method of the non-stoichiometric sodium-ion battery polyanionic cathode material precursor according to claim 2, characterized in that: 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 manganese nitrate, manganese sulfate, manganese acetate, manganese chloride, elemental manganese, manganese monoxide, manganese dioxide, manganese sesquioxide, manganese tetroxide, manganese oxalate, manganese hydroxide, manganous anhydride, manganic anhydride, permanganic anhydride, etc. The cobalt source is one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, methylcobalamin, hydroxocobalamin, adenosylcobalamin, elemental cobalt, cobalt tetroxide, cobalt(III) oxide, cobalt oxalate, cobalt carbonate, cobalt oxide, cobalt hydroxide, etc. The iron source is one or more of iron acetate, iron sulfate / ferrous sulfate, iron nitrate, iron chloride / ferrous chloride, iron citrate, ammonium ferrous sulfate, elemental iron, iron oxalate, iron oxide, ferrous oxide, iron tetroxide, ferrous hydroxide, ferric hydroxide, etc.; The acid dissolution uses one or more of sulfuric acid-containing compounds, phosphoric acid-containing compounds, silicic acid-containing compounds, nitric acid, nitrous acid, hydrochloric acid, formic acid, acetic acid, citric acid, benzoic acid, oxalic acid, salicylic acid, lactic acid, etc. The sulfuric acid-containing compounds are one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrosulfuric acid, sulfurous acid, sulfamic acid, etc. The phosphoric acid-containing compounds are one or more of phosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, etc. The silicic acid-containing compounds are one or more of orthosilicic acid, polysilicic acid, metasilicic acid, etc.; The oxidant is one or more of compounds such as oxygen, chlorine, iodine, hydrogen peroxide, nitric acid, etc.; The anion X source is one or more of a sulfur source, a phosphorus source, and a silicon source; the sulfur source is one or more of sulfuric acid, sulfurous acid, thiosulfuric acid, persulfuric acid, hydrogen sulfide, sulfuric acid, sulfamic acid, sodium sulfate, ammonium sulfate, ammonium hydrogen sulfate, ferrous sulfate, and ammonium ferrous sulfate; the phosphorus source is one or more of phosphoric acid, sodium / ammonium phosphate, sodium / ammonium hydrogen phosphate, sodium / ammonium dihydrogen phosphate, phosphorous acid, sodium phosphite, hypophosphorous acid, sodium hypophosphite, pyrophosphoric acid, sodium pyrophosphate, sodium hydrogen pyrophosphate, metaphosphoric acid, sodium metaphosphate, polyphosphoric acid, and sodium polyphosphate; the silicon source is one or more of orthosilicic acid, polysilicic acid, metasilicic acid, and sodium silicate.

Images