Positive electrode active material and preparation method therefor, sodium ion battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a sodium ion battery, and an electric device. The positive electrode active material has compositions as shown in the following general formula: NaxMyEn(P1-wAwO4)z(P2-uAuO7), wherein A is selected from one or more of S, Si, B, As and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La and Ce; x satisfies the condition: 2≤x≤4, 1≤y+n≤3, wherein y and n are both not 0; z satisfies the condition: 0≤z≤2, and w satisfies the condition: 0<w≤0.35; and u satisfies the condition: 0≤u≤0.2.

Description

Positive electrode active material and preparation method thereof, sodium ion battery and electrical equipment

[0001] Priority information and cross-references

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on November 30, 2023, with application number 202311636031.1 and invention name “Positive electrode active material and preparation method thereof, sodium ion battery and electrical equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the field of positive electrode active materials for sodium ion batteries, and in particular to a positive electrode active material and a preparation method thereof, a sodium ion battery and electrical equipment. Background Art

[0004] Sodium-ion batteries are similar in many ways to the lithium-ion batteries commonly used today. They are both reusable secondary batteries, including an anode (negative electrode), a cathode (positive electrode), and an electrolyte material. They are both able to store energy, and they are both charged and discharged through similar reaction mechanisms.

[0005] In the research of sodium-ion battery cathode materials, researchers are committed to finding a cathode material with high energy density, good stability, environmental friendliness, and resource conservation. Currently, it is difficult for polyanion cathode materials to achieve a capacity close to their theoretical capacity. For example, the theoretical capacity of sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) is 129mAh / g, but the actual capacity is around 70mAh / g. This is mainly due to low electronic conductivity and slow ion migration. Enhancing this performance through doping is particularly important. These modified polyanion cathode materials have a certain promoting effect on the development of sodium-ion battery cathode materials.

[0006] Summary of the Invention

[0007] The first aspect of the present invention provides a positive electrode active material, wherein the positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P 2-u A uO7), wherein A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce; x satisfies the following conditions: 2≤x≤4, 1≤y+n≤3, wherein both y and n are not 0; z satisfies the following conditions: 0≤z≤2, w satisfies the following conditions: 0<w≤0.35; and u satisfies the following conditions: 0≤u≤0.2.

[0008] A second aspect of the present invention provides a method for preparing a positive electrode active material, comprising:

[0009] (1) mixing a metal M source material, a metal E source material, an optional A source material, a sodium source, a phosphorus source, and a reducing agent to obtain a precursor solution;

[0010] (2) treating the precursor solution to obtain the positive electrode active material;

[0011] Among them, A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce.

[0012] A third aspect of the present invention provides a sodium ion battery, wherein the sodium ion battery comprises the positive electrode active material or the positive electrode active material obtained by the preparation method.

[0013] A fourth aspect of the present invention provides an electrical device, which includes the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figures 1a-1b are discharge voltage curves for Comparative Example 1 and Examples 1-7, Figure 1a is a discharge voltage curve for Examples 1-3, and Figure 1b is a discharge voltage curve for Examples 4-7;

[0015] FIG2 is a discharge voltage curve for Comparative Example 2 and Examples 8-10;

[0016] FIG3 is a discharge voltage curve for Comparative Example 3 and Examples 11-12;

[0017] FIG4 is a comparative example 1 and examples 1, 2, 6, 7 rate performance results;

[0018] Figure 5 is the rate performance results for Comparative Example 2 and Examples 8-10;

[0019] FIG6 is a comparative example 3 and examples 11 and 12 rate performance results;

[0020] 7a is an XRD graph of the positive electrode active material of Example 1, FIG. 7b is an XRD graph of the positive electrode active material of Example 23, and FIG. 7c is an XRD graph of the positive electrode active material of Example 26. DETAILED DESCRIPTION

[0021] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0022] The first aspect of the present invention provides a positive electrode active material, wherein the positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P 2-u A u O7), wherein A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce; x satisfies the following conditions: 2≤x≤4, 1≤y+n≤3, wherein both y and n are not 0; z satisfies the following conditions: 0≤z≤2, w satisfies the following conditions: 0<w≤0.35; and u satisfies the following conditions: 0≤u≤0.2. The molecular formula of the positive electrode active material is confirmed by elemental quantitative analysis-ICP method, using ICP-OES-inductively coupled plasma atomic emission spectrometry, and finally combining XRD to obtain the molecular formula of the positive electrode active material.

[0023] In the present invention, the polyanion positive electrode materials are mainly doped with three major intrinsic materials: Na2FeP2O7, Na3Fe2(PO4)P2O7, and Na4Fe3(PO4)2P2O7. Metal M and metal E are doped at the Fe position, and element A is doped at the P position in the phosphate group. Through the joint action of metal M, metal E and element A, a structure that maintains the original crystal point group structure unchanged is obtained, and the unit cell volume is increased, so that the electrochemical properties of the positive electrode active material of the present invention, such as ionic conductivity, rate, and capacity, are improved.

[0024] In some specific embodiments of the present invention, the positive electrode active material of the present invention is a polyanionic compound, which is generally formed by MO6 octahedron and PO4 tetrahedron connected by common points, common edges, common faces, etc. to form Na+ Three-dimensional diffusion channel. The three-dimensional framework can make Na + During the embedding / de-embedding process, a relatively small volume change occurs, and the corresponding number of cycles will be very high. First, the metal E (transition metals Zr, Tc, Ru, Rh, Ir, Nb, rare earth metals La, Ce) is doped into the polyanion unit cell, and the unit cell volume is increased. The unit cell volume increases by 3.5%-8.7% compared to the volume of the undoped elements. The increase in unit cell volume corresponds to a faster migration speed of Na ions, which increases the actual capacity and the rate performance. In addition, after the transition metal and rare earth metal are doped at the M position, the conductivity is enhanced.

[0025] In some specific embodiments of the present invention, the first principle simulation results show that the bond length of AO in the unit cell of the positive electrode active material is The distance of MO is The bond length in the above range becomes larger, the unit cell volume becomes larger, and the ratio of the unit cell volume to the undoped element increases by 3.5%-8.7%, which can reduce the Na ion diffusion energy barrier and improve the ionic conductivity of the positive electrode active material.

[0026] In some specific embodiments of the present invention, preferably, M is selected from one or more of Fe, Mn, V, Ni or Co, E is selected from one or more of Zr, La or Ru, and A is selected from S and / or Si.

[0027] In some specific embodiments of the present invention, the positive electrode active material has the following general formula: Na x M y E n (P 1-w A w O4) z (P2O7), wherein x=4, 2.8≤y<3, 0<n≤0.2, z=2, 0<w≤0.25; the positive electrode active material in the above range is, for example, doped Na4Fe3(PO4)2P2O7.

[0028] In some specific embodiments of the present invention, preferably, the positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 2-u A u O7), wherein x=2, 0.8≤y<1, 0<n≤0.2, 0<u≤0.25; the positive electrode active material in the above range is, for example, doped Na2FeP2O7.

[0029] In some specific embodiments of the present invention, preferably, the positive electrode active material has a composition shown in the following general formula: Nax M y E n (P 1-w A w O4) z (P2O7), wherein x=3, 1.8≤y<2, 0<n≤0.2, z=1, 0<w≤0.25, and the positive electrode active material in the above range is, for example, doped Na3Fe2(PO4)P2O7.

[0030] In some specific embodiments of the present invention, the electronic conductivity of the positive electrode active material is 1×10 -9 -5×10 -7 S / cm, the capacity retention rate after 1200 cycles at 1C is 78%-94%, and the first cycle discharge specific capacity at 0.1C is 60-94mAh / g.

[0031] A second aspect of the present invention provides a method for preparing a positive electrode active material, comprising:

[0032] (1) mixing a metal M source material, a metal E source material, an optional A source material, a sodium source, a phosphorus source, and a reducing agent to obtain a precursor solution;

[0033] (2) sintering the precursor solution to obtain the positive electrode active material;

[0034] Among them, A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce.

[0035] In some specific embodiments of the present invention, a metal M source, a metal E source, an optional A source, a sodium source, a phosphorus source, and a reducing agent are mixed and dissolved in water to obtain a precursor solution.

[0036] In some specific embodiments of the present invention, in step (2), the sintering treatment specifically includes: drying and sintering the precursor solution to obtain the positive electrode active material.

[0037] In some specific embodiments of the present invention, the metal M source material is selected from one or more of metal M nitrates, oxalates, and citrates.

[0038] In some specific embodiments of the present invention, the metal E source material is selected from one or more of metal E sulfates, chlorides, nitrates and acetates.

[0039] In some specific embodiments of the present invention, the A source material is selected from one or more of sulfate, silicate, borate, arsenate, and aluminate.

[0040] In some specific embodiments of the present invention, the sodium source is selected from one or more of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium nitrate.

[0041] In some embodiments of the present invention, the phosphorus source is selected from ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphonic acid.

[0042] In some specific embodiments of the present invention, the reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid, and tartaric acid. In addition to the reducing effect, the reducing agent also has the function of carbon source and stabilizing Fe 3+ It plays the role of a chelating agent and combines with divalent iron ions to form a chelate. During the final calcination process under an inert atmosphere, ascorbic acid will form in-situ carbon uniformly coated on the surface of the material, greatly improving the conductive properties of the material.

[0043] In some specific embodiments of the present invention, the sintering temperature is 400-650° C., and the sintering time is 10-36 hours.

[0044] In some specific embodiments of the present invention, pre-sintering is performed before the sintering, the pre-sintering temperature is 260-330° C., and the pre-sintering time is 1-5 hours.

[0045] In some specific embodiments of the present invention, the pre-calcination is carried out in a hydrogen-argon mixed gas, wherein the volume percentage of hydrogen in the hydrogen-argon mixed gas may be 1-10%.

[0046] In some specific embodiments of the present invention, the molar ratio of the metal M source material, metal E source material, A source material, sodium source, phosphorus source and reducing agent is (0.001-0.999): (0.001-0.999): (0.0001-0.2): (0.001-1.35): (0.001-1.99): (0.001-3.2).

[0047] A third aspect of the present invention provides a sodium ion battery, wherein the sodium ion battery comprises the positive electrode active material or the positive electrode active material obtained by the preparation method.

[0048] A fourth aspect of the present invention provides an electrical device, which includes the sodium ion battery.

[0049] The present invention will be described in detail below through examples.

[0050] The structural composition of the positive electrode active material of the embodiment of the present invention is confirmed by elemental quantitative analysis-ICP method. An appropriate amount of powder is taken and dissolved in a strong acid. Finally, ICP-OES-inductively coupled plasma atomic emission spectrometer is used to characterize the proportion of different elements. Finally, the molecular formula of the positive electrode active material is obtained by combining XRD.

[0051] In the following examples and comparative examples, if no specific conditions are specified, the experiments were carried out under conventional conditions or those recommended by the manufacturer. All reagents and instruments used, if no manufacturer is specified, are commercially available conventional products.

[0052] Example 1

[0053] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 S 0.05 O4)2P2O7, XRD analysis was performed on Example 1, and the analysis results are shown in Figure 7a.

[0054] Example 2

[0055] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0056] Example 3

[0057] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.033 mol of ammonium dihydrogen phosphate, 0.007 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.65 S 0.35 O4)2P2O7.

[0058] Example 4

[0059] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0060] Example 5

[0061] 0.029 mol of ferric nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 La 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0062] Example 6

[0063] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of Ru(NO)(NO3)3 in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the powder after spraying in a hydrogen-argon mixture (5%) for 2 hours at a temperature of 300°C, and then sinter at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Ru 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0064] Example 7

[0065] 0.029 mol of ferric nitrate and 0.001 mol of Ru(NO)(NO3)3 were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Ru 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0066] Example 8

[0067] 0.029 mol of nickel nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Ni 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0068] Example 9

[0069] 0.029 mol of manganese nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-encapsulated Na4Mn 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0070] Example 10

[0071] 0.029 mol of titanium nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred with a magnetic force, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Ti 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0072] Example 11

[0073] 0.029 mol of chromium nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred with a magnetic force, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Cr 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0074] Example 12

[0075] 0.029 mol of chromium nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Cr 2.9 Zr 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0076] Example 13

[0077] 0.029 mol of nickel nitrate and 0.001 mol of lanthanum nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Ni 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0078] Example 14

[0079] 0.029 mol of vanadium nitrate and 0.001 mol of iridium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4V 2.9 Ir 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0080] Example 15

[0081] 0.029 mol of cobalt nitrate and 0.001 mol of iridium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Co 2.9 Ir 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0082] Example 16

[0083] 0.029 mol of zinc nitrate and 0.001 mol of iridium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-encapsulated Na4Zn 2.9 Ir 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0084] Example 17

[0085] 0.029 mol of ferric nitrate and 0.001 mol of cerium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred with a magnetic force, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Ce 0.1 (P 0.95 S 0.05 O4)2P2O7.

[0086] Example 18

[0087] 0.029 mol of ferric nitrate and 0.001 mol of technetium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Te 0.1 (P 0.95 S 0.05 O4)2P2O7.

[0088] Example 19

[0089] 0.029 mol of ferric nitrate and 0.001 mol of niobium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Nb 0.1 (P 0.95 S 0.05 O4)2P2O7.

[0090] Example 20

[0091] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of borate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 B 0.05 O4)2P2O7

[0092] Example 21

[0093] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of arsenate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 As 0.05 O4)2P2O7.

[0094] Example 22

[0095] 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate were dissolved in 600 mL of deionized water, and then 0.10 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of aluminate, and 0.04 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 500°C for 36 hours to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 Al 0.05 O4)2P2O7.

[0096] Example 23

[0097] 0.038 mol of ferric nitrate and 0.002 mol of zirconium nitrate were dissolved in 700 mL of deionized water, and then 0.12 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.076 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate, and 0.08 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined in a hydrogen-argon mixture (5%) for 4 hours at a temperature of 300°C, and then sintered at 600°C for 22 hours to obtain carbon-coated Na2Fe 0.95 Zr 0.05 P 1.9 S 0.1 O7. Example 23 was subjected to XRD analysis, and the analysis results are shown in Figure 7b.

[0098] Example 24

[0099] Dissolve 0.038 mol of ferric nitrate and 0.002 mol of Ru(NO)(NO3)3 in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.076 mol of ammonium dihydrogen phosphate, 0.004 mol of sulfate and 0.08 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the powder after spraying in a hydrogen-argon mixture (5%) for 4 hours at a temperature of 300°C, and then sinter at 600°C for 22 hours to obtain carbon-coated Na2Fe 0.95 Ru 0.05 P 1.9 S 0.1 O7.

[0100] Example 25

[0101] 0.038 mol of ferric nitrate and 0.002 mol of zirconium nitrate were dissolved in 700 mL of deionized water, and then 0.12 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.076 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate and 0.08 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined in a hydrogen-argon mixture (5%) for 4 hours at a temperature of 300°C, and then sintered at 600°C for 22 hours to obtain carbon-coated Na2Fe 0.95 Zr 0.05 P 1.9 Si 0.1 O7.

[0102] Example 26

[0103] 0.038 mol of ferric nitrate nonahydrate and 0.002 mol of zirconium nitrate were dissolved in 700 mL of deionized water, and then 0.12 mol of ascorbic acid was added. The mixture was stirred magnetically, and then 0.057 mol of ammonium dihydrogen phosphate, 0.003 mol of sulfate, and 0.06 mol of sodium acetate were slowly added. After stirring for 1 hour, the reaction solution was transferred to a spray dryer for spray granulation. The sprayed powder was pre-calcined for 2 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 550°C for 20 hours to obtain carbon-coated Na3Fe 1.9 Zr 0.1 (P 0.85 S 0.15 O4) P2O7, Example 26 was subjected to XRD analysis, and the analysis results are shown in Figure 7c.

[0104] Example 27

[0105] Dissolve 0.038 mol of ferric nitrate nonahydrate and 0.002 mol of Ru(NO)(NO3)3 in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.057 mol of ammonium dihydrogen phosphate, 0.003 mol of sulfate and 0.06 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the powder after spraying in a hydrogen-argon mixture (5%) for 2 hours at a temperature of 300°C, and then sinter at 550°C for 20 hours to obtain carbon-coated Na3Fe 1.9 Ru 0.1 (P 0.85 S 0.15 O4)P2O7.

[0106] Comparative Example 1

[0107] Dissolve 0.03 mol of ferric nitrate nonahydrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic force, and then slowly add 0.04 mol of ammonium dihydrogen phosphate and 0.04 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the sprayed powder in a hydrogen-argon mixture (5%) for 2 hours at a temperature of 300°C, and then sinter at 500°C for 36 hours to obtain carbon-encapsulated Na4Fe3(PO4)2P2O7.

[0108] Comparative Example 2

[0109] Dissolve 0.04 mol of ferric nitrate nonahydrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.08 mol of ammonium dihydrogen phosphate and 0.08 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the sprayed powder in a hydrogen-argon mixture (5%) for 4 hours at a temperature of 300°C, and then sinter at 600°C for 20 hours to obtain carbon-encapsulated Na2FeP2O7.

[0110] Comparative Example 3

[0111] Dissolve 0.04 mol of ferric nitrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir magnetically, and slowly add 0.06 mol of ammonium dihydrogen phosphate and 0.06 mol of sodium acetate; after stirring for 1 hour, transfer the reaction solution to a spray dryer for spray granulation, and pre-calculate the sprayed powder in a hydrogen-argon mixture (5%) for 2 hours at a temperature of 300°C, and then sinter at 550°C for 20 hours to obtain carbon-encapsulated Na3Fe2(PO4)P2O7.

[0112] Test Example 1: The positive electrode active materials obtained in the examples and comparative examples were subjected to the following tests: conductivity, capacity retention after 1200 cycles at 1C, and first-cycle discharge capacity at 0.1C.

[0113] Electronic conductivity: The positive electrode active material is measured using a DC four-probe method;

[0114] 1200-cycle capacity retention rate: The positive electrode active materials obtained in the examples and comparative examples were applied to sodium ion batteries. After constant capacity was determined by 0.2C charge and discharge, the discharge capacity was used as the rated capacity. The voltage range was 2-3.4V, and a 1C cycle was adopted. Each step was left for 10 minutes. The charging was carried out in constant current and constant voltage mode with a cut-off current of 0.05C and the charging was carried out in constant current mode.

[0115] First cycle discharge capacity at 0.1C: A small soft pack was made by hand, charged to 3.5V at a rate of 0.1C, aged for two days, and discharged to 2V at a rate of 0.1C.

[0116] The test results are shown in Table 1.

[0117] Table 1

[0118] It can be seen from the results in Table 1 that the embodiment of the positive electrode active material obtained by dual doping of the present invention has good conductivity, rate capability and high voltage, and has significantly better effects.

[0119] Regarding the doping of Na4Fe3(PO4)2P2O7 active materials, by comparing Examples 1-22 and Comparative Example 1, by doping M and E into the polyanion positive electrode material, the element A is doped at the P position, so that the rate performance is also improved. M is preferably selected from one or more of Fe, Mn, V, Ni or Co, E is preferably selected from one or more of Zr, La or Ru, and A is preferably selected from S and / or Si.

[0120] As for the doping of Na2FeP2O7 active materials, by comparing Examples 23-25 ​​and Comparative Example 2, by doping M and E into the polyanion positive electrode material, element A is doped at the P position, so that the rate performance is also improved. The effects of Examples 23-25 ​​are better than those of Comparative Example 2.

[0121] Regarding the doping of Na3Fe2(PO4)P2O7 active materials, by comparing Examples 26-27 and Comparative Example 3, by doping M and E into the polyanion positive electrode material, the element A is doped at the P position, so that the rate performance is also improved. The effects of Examples 26-27 are better than those of Comparative Example 3.

[0122] Test Example 2: Discharge voltage and rate performance test of the embodiments and comparative examples.

[0123] Discharge voltage: The positive electrode powder and conductive agent binder are prepared into a slurry in a ratio of 100:4:2, coated on carbon-coated aluminum foil, and rolled into electrodes after baking. The electrodes are compacted to 1.9g / cc. The electrodes are cut, weighed, and baked at 120 degrees in a vacuum for one day to make a button half-cell. The negative electrode is a sodium sheet made by hand. The electrochemical properties of the positive electrode material are evaluated, and the discharge voltage curves of different positive electrode materials are obtained.

[0124] Rate performance: The charging rate is uniformly 0.2C, and the discharge rate is set to 0.1C\0.2C\0.5C\10C. Each rate is cycled 5 times. Discharge at different rates can reflect the ability of the positive electrode material to diffuse ions.

[0125] Among them, Figure 1a-Figure 1b are the discharge voltage curves of Example 1 and Examples 1-7. It can be seen that the incorporation of Zr\La\Ru and anions S\Si enables the capacity of the Na4Fe3(PO4)2P2O7 doped material to be further utilized and the voltage is also improved, which has a positive effect of increasing the energy density of the battery.

[0126] Among them, Figure 2 is the discharge voltage curve of Example 2 and Examples 23-25. It can be seen that the incorporation of Zr\Ru and anions S\Si also increases the capacity and voltage of Na2FeP2O7-doped materials, greatly improving the electrochemical performance of such materials.

[0127] Among them, Figure 3 is the discharge voltage curve of Example 3 and Examples 26-27. It can be seen that the incorporation of Zr\Ru and anion S also increases the capacity and voltage of the Na3Fe2(PO4)P2O7 doped material, greatly improving the electrochemical performance of this type of material.

[0128] 4 is the rate performance results of Example 1 and Examples 1, 2, 6, and 7. Element doping can significantly improve the rate performance of Na4Fe3(PO4)2P2O7-doped materials.

[0129] 5 is the rate performance results of Comparative Example 2 and Examples 23-25. Element doping can significantly improve the rate performance of Na2FeP2O7 doped materials.

[0130] 6 is the rate performance results of Example 3 and Examples 26 and 27. Element doping can significantly improve the rate performance of Na3Fe2(PO4)P2O7 doped materials.

[0131] Among them, Figures 7a, 7b, and 7c are the XRD patterns of the positive electrode active materials of Examples 1, 23, and 26 of the present invention, respectively. From the main peak positions and lattice parameters of the materials obtained in Examples 1, 23, and 26, combined with the element ratio analysis of ICP, the molecular formula of the corresponding examples can be obtained, and the phase purity of the materials after sintering is high.

[0132] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A positive electrode active material, characterized in that: The positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P 2-u A u O7), wherein A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce; x satisfies the following conditions: 2≤x≤4, 1≤y+n≤3, wherein both y and n are not 0; z satisfies the following conditions: 0≤z≤2, w satisfies the following conditions: 0<w≤0.35; and u satisfies the following conditions: 0≤u≤0.

2.

2. The positive electrode active material according to claim 1, characterized in that M is selected from one or more of Fe, Mn, V, Ni or Co, E is selected from one or more of Zr, La or Ru, and A is selected from S and / or Si.

3. The positive electrode active material according to claim 1 or 2, characterized in that: The positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P2O7), wherein x=4, 2.8≤y<3, 0<n≤0.2, z=2, 0<w≤0.25; Or, the positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 2-u A u O7), wherein x=2, 0.8≤y<1, 0<n≤0.2, 0<u≤0.2; Or, the positive electrode active material has a composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P2O7), wherein x=3, 1.8≤y<2, 0<n≤0.2, z=1, 0<w≤0.

25.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The performance of the positive electrode active material at least meets one of the following conditions: the electronic conductivity is 3×10 -9 -5×10 -7 S / cm, the capacity retention rate after 1200 cycles at 1C is 78%-94%, and the first cycle discharge specific capacity at 0.1C is 61-94mAh / g.

5. A method for preparing a positive electrode active material, characterized in that: include: (1) mixing a metal M source material, a metal E source material, an optional A source material, a sodium source, a phosphorus source and a reducing agent to obtain a precursor solution; (2) sintering the precursor solution to obtain the positive electrode active material; Among them, A is selected from one or more of S, Si, B, As, and Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, and Ce.

6. The preparation method according to claim 5, characterized in that: In step (2), the sintering treatment specifically comprises: drying and sintering the precursor solution to obtain the positive electrode active material; Preferably, the metal M source material is selected from one or more of nitrates, oxalates and citrates of metal M; Preferably, the metal E source material is selected from one or more of the metal E sulfate, chloride, nitrate and acetate; Preferably, the A source material is selected from one or more of sulfate, silicate, borate, arsenate, and aluminate; Preferably, the sodium source is selected from one or more of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium nitrate; Preferably, the phosphorus source is selected from ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphonic acid; Preferably, the reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid and tartaric acid.

7. The preparation method according to claim 5 or 6, characterized in that: The sintering temperature is 400-650° C., and the sintering time is 10-36 hours.

8. The preparation method according to any one of claims 5 to 7, characterized in that: Before the sintering, pre-sintering is performed, the pre-sintering temperature is 260-330° C., and the pre-sintering time is 1-5 hours.

9. The preparation method according to any one of claims 5 to 8, characterized in that: The molar ratio of the metal M source material, the metal E source material, the A source material, the sodium source, the phosphorus source and the reducing agent is (0.001-0.999): (0.001-0.999): (0.0001-0.2): (0.001-1.35): (0.001-1.99): (0.001-3.2).

10. A sodium ion battery, characterized in that: The sodium ion battery comprises the positive electrode active material according to any one of claims 1 to 4 or the positive electrode active material obtained by the preparation method according to any one of claims 5 to 9.

11. An electrical device, characterized in that: Including the sodium ion battery according to claim 10.

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