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

Abstract

A positive electrode active material, a preparation method therefor, a sodium ion battery and an electrical device. The positive electrode active material has the following general formula: NaxMy(P1-wAwO4)z(P2-uAuO7), wherein M is one or more selected from Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb; A is one or more selected from Ga, Sb, Se, Te, Bi and In; x satisfies the condition 2≤x≤4; and y satisfies the condition 1≤y≤4; z satisfies the condition 0≤z≤2; w satisfies the condition 0＜w≤0.25; u satisfies the condition 0≤u＜0.2; and u and z cannot be 0 at the same time.

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 202311638513.0 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, consisting of an anode (negative electrode), a cathode (positive electrode), and an electrolyte material. They are both capable of storing energy, and they are both charged and discharged via similar reaction mechanisms.

[0005] In contrast, sodium-ion battery technology is still in its relatively early stages, but is considered beneficial. Compared with lithium, sodium reserves are much more abundant, but the potential of the positive active material of the existing sodium battery is low. Among them, polyanion positive electrode materials are difficult to perform at a level close to the theoretical capacity. For example, the theoretical capacity of sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) is 129mAh / g, but the actual performance is around 70. This is mainly due to low electronic conductivity and slow ion migration. Therefore, it is more important to regulate the capacity, voltage and rate of modified polyanion positive electrode 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 (P 1-w A w O4) z (P 2-u A uO7), wherein M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi and In; x satisfies the condition: 2≤x≤4; y satisfies the condition: 1≤y≤4; z satisfies the condition: 0≤z≤2; w satisfies the condition: 0<w≤0.25; u satisfies the condition: 0≤u≤0.2, wherein u and z cannot be 0 at the same time.

[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 A source material, a sodium source, a phosphorus source, and a reducing agent to obtain a precursor solution;

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

[0011] Wherein, M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi and In.

[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 8-11;

[0016] FIG3 is a discharge voltage curve for Comparative Example 3 and Examples 12-13;

[0017] Figure 4 is the rate performance results of Comparative Example 1 and Examples 2, 4, 6, and 7;

[0018] Figure 5 is the rate performance results of Comparative Example 2 and Examples 8, 9, 10, and 11;

[0019] FIG6 is a comparative example 3 and examples 12 and 13 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 24, and FIG. 7c is an XRD graph of the positive electrode active material of Example 28. 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 (P 1-w A w O4) z (P 2-u A u O7), wherein M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn, and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi, and In; x satisfies the condition: 2≤x≤4; y satisfies the condition: 1≤y≤4; z satisfies the condition: 0≤z≤2; w satisfies the condition: 0<w≤0.25; u satisfies the condition: 0≤u≤0.2, wherein u and z cannot be 0 at the same time. 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 combined with XRD to obtain the molecular formula of the positive electrode active material.

[0023] In the present invention, the distance of AO in the unit cell of the positive electrode active material is obtained by first principle simulation. The distance of MO is By co-doping the transition metal at the M position and the A metal at the P position to regulate the performance, the unit cell volume becomes larger and the bond length becomes longer. This change can reduce the Na ion diffusion energy barrier and improve the ionic conductivity.

[0024] In the present invention, the performance is mainly controlled by co-doping the transition metal at the M position and the A metal at the P position, which can fully utilize the advantages of different elements and enhance the performance of the polyanion positive electrode material. For example, the size of one or more of Ga, Ge, Sb, Se, Te, Bi, and In in metal A is larger than that of P. After one or more of Ga, Ge, Sb, Se, Te, Bi, and In in metal A is doped into the unit cell, the volume and the distance between the AO bonds change, and the distance between the AO bonds in the unit cell is The researchers found that the larger unit cell volume and bond length increased. This change can reduce the Na ion diffusion barrier and improve ionic conductivity. This preliminary evidence suggests that the incorporation of large anions has the potential to improve the electrochemical properties of polyanionic materials.

[0025] 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 + The volume change during the insertion / deinsertion process is relatively small, and the corresponding number of cycles will be very high. First, metal A (Ga, Ge, Sb, Se, Te, Bi, In) is doped into the polyanion unit cell, and the distance between AO is The PO distance before incorporation is The volume of the unit cell expands, the migration speed of Na ions becomes faster, the actual capacity is improved, and the rate performance is also improved; in addition, after Mn is doped at the M position, the voltage increases, and after Ti is doped, the electronic conductivity is improved.

[0026] In some specific embodiments of the present invention, M is selected from one or more of Ti, Mn, Fe, Mg, and Ca, and A is selected from one or more of Ga, Bi, and Se. When M is selected from Mn, the metallic Mn improves voltage performance; when M is selected from Ti, the metallic Ti improves electronic conductivity; and when M is selected from Mg and Ca, the cycling performance and processing performance can be improved.

[0027] In some specific embodiments of the present invention, M contains at least Fe and Mg, or at least Fe and Ca, and A is selected from Ga and / or Se; preferably, the molar ratio of Fe to Mg in M ​​is 2.9-3:0.001-0.02, or the molar ratio of Fe to Ca is 2.9-3:0.001-0.02.

[0028] In some specific embodiments of the present invention, the molar ratio of Fe to Mg in M ​​is 2.9-3:0.001-0.02, or the molar ratio of Fe to Ca is 2.9-3:0.001-0.02.

[0029] In some specific embodiments of the present invention, the positive electrode active material has the following general formula: Na x M y (P 1-w A w O4) z (P2O7), wherein x=4, y=3, z=2, 0<w≤0.25; the positive electrode active material in the above range is, for example, doped Na4Fe3(PO4)2P2O7.

[0030] In some specific embodiments of the present invention, preferably, the positive electrode active material has a composition shown in the following general formula: NaxM y (P 2-u A u O7), wherein x=2, y=1, 0≤u≤0.25; the positive electrode active material in the above range is, for example, doped Na2FeP2O7.

[0031] 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 (P 1-w A w O4)z(P2O7), wherein x=3, y=2, z=1, 0<w≤0.25, and the positive electrode active material in the above range is, for example, doped Na3Fe2(PO4)P2O7.

[0032] In some specific embodiments of the present invention, the performance of the positive electrode active material satisfies at least one of the following conditions: the electronic conductivity is 1×10 -8 -6×10 -7 S / cm, the capacity retention rate after 1200 cycles at 1C is 82%-97%, and the first cycle discharge specific capacity at 0.1C is 82-93mAh / g.

[0033] A second aspect of the present invention provides a method for preparing a positive electrode active material, comprising:

[0034] (1) mixing a metal M source material, a metal A source material, a sodium source, a phosphorus source, and a reducing agent to obtain a precursor solution;

[0035] (2) sintering the precursor solution to obtain the positive electrode active material;

[0036] Wherein, M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi and In.

[0037] In some specific embodiments of the present invention, a metal M source material, a metal A source material, a sodium source, a phosphorus source, and a reducing agent are mixed and dissolved in water to obtain a precursor solution.

[0038] In some specific embodiments of the present invention, the sintering is specifically: granulating and sintering the precursor solution to obtain the positive electrode active material, wherein the granulation can be spray granulation.

[0039] In some specific embodiments of the present invention, the metal M source is selected from one or more of metal nitrates, metal oxalates, and metal citrates;

[0040] In some specific embodiments of the present invention, the metal A source is selected from one or more of metal nitrates, metal oxalates, and metal citrates;

[0041] 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;

[0042] In some specific embodiments of the present invention, the phosphorus source is selected from ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphonic acid;

[0043] 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 its reducing effect, the reducing agent also acts as a carbon source and stabilizes metal ions, and acts as a chelating agent to combine with divalent iron ions to form a chelate, thereby stabilizing the metal M ions. During the final calcination process under an inert atmosphere, ascorbic acid forms in-situ carbon that is evenly coated on the material surface, greatly improving the conductive properties of the material.

[0044] In some specific embodiments of the present invention, the sintering temperature is 400-650° C., and the sintering time is 10-36 hours.

[0045] In some specific embodiments of the present invention, pre-sintering is performed before the sintering, wherein the pre-sintering temperature is 260-330° C. and the pre-sintering time is 1-5 hours.

[0046] 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%.

[0047] In some specific embodiments of the present invention, the molar ratio of the metal M source material, metal A source material, sodium source, phosphorus source and reducing agent is (0.01-0.1): (0.0001-0.1): (0.01-0.1): (0.01-0.1): (0.01-0.1).

[0048] In the present invention, the composition and structure of the positive electrode active material can be determined by nuclear magnetic resonance, infrared, XRD, elemental analysis, etc., or by preparing and feeding.

[0049] 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.

[0050] A fourth aspect of the present invention provides an electrical device, which includes the sodium ion battery.

[0051] The present invention will be described in detail below through examples.

[0052] 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.

[0053] 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.

[0054] Example 1

[0055] 0.02978 mol of ferric nitrate, 0.0002 mol of zirconium nitrate and 0.00002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 2.978 Zr 0.02 Mg 0.002 (P 0.995 Ga 0.005 O4)2P2O7, XRD analysis was performed on Example 1, and the analysis results are shown in Figure 7a.

[0056] Example 2

[0057] 0.02978 mol of ferric nitrate, 0.0002 mol of cadmium nitrate and 0.00002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 2.978 Cd 0.02 Mg 0.002 (P 0.995 Ga 0.005 O4)2P2O7.

[0058] Example 3

[0059] 0.02978 mol of ferric nitrate, 0.0002 mol of zirconium nitrate and 0.00002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 2.978 Cr 0.02 Mg 0.002 (P 0.995 Ga 0.005 04)2P2O7.

[0060] Example 4

[0061] 0.0296 mol of ferric nitrate, 0.0002 mol of nickel nitrate and 0.0002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 2.960 Ni 0.02 Mg 0.02 (P 0.995 Ga 0.005 O4)2P2O7.

[0062] Example 5

[0063] 0.0296 mol of ferric nitrate, 0.0002 mol of zirconium nitrate and 0.0002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 2.960 Zr 0.02 Mg 0.02 (P 0.995 Ga 0.005 04)2P2O7.

[0064] Example 6

[0065] 0.0296 mol of ferric nitrate, 0.0002 mol of manganese nitrate and 0.0002 mol of magnesium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Mn 0.02 Mg 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0066] Example 7

[0067] 0.0296 mol of ferric nitrate, 0.0002 mol of cadmium nitrate and 0.0002 mol of calcium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Cd 0.02 Ca0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0068] Example 8

[0069] 0.0296 mol of ferric nitrate, 0.0002 mol of manganese nitrate and 0.0002 mol of calcium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Mn 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0070] Example 9

[0071] 0.0296 mol of ferric nitrate, 0.0002 mol of copper nitrate and 0.0002 mol of calcium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Cu 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0072] Example 10

[0073] 0.0296 mol of ferric nitrate, 0.0002 mol of nickel nitrate and 0.0002 mol of calcium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Ni 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0074] Example 11

[0075] 0.0296 mol of ferric nitrate, 0.0002 mol of zinc nitrate and 0.0002 mol of calcium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 2.960 Zn 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0076] Example 12

[0077] 0.02998 mol of ferric nitrate and 0.00002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 2.998 Mg 0.002 (P 0.995 Ga 0.005 04)2P2O7.

[0078] Example 13

[0079] 0.02995 mol of ferric nitrate and 0.00005 mol of calcium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 2.995 Ca 0.005 (P 0.995 Ga 0.005 O4)2P2O7.

[0080] Example 14

[0081] 0.02998 mol of ferric nitrate and 0.00002 mol of magnesium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of germanate, 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 2.998 Mg 0.002 (P 0.995 Ge 0.005 04)2P2O7.

[0082] Example 15

[0083] 0.0298 mol of ferric nitrate and 0.0002 mol of cadmium 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 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 2.98 Cd 0.02 (P 0.995 Ga 0.005 O4)2P2O7.

[0084] Example 16

[0085] 0.0298 mol of ferric nitrate and 0.0002 mol of cadmium 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 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 2.98 Cd 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0086] Example 17

[0087] 0.015 mol of ferric nitrate and 0.015 mol of manganese 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 selenate, 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 1.5 Mn 1.5 (P 0.8 Se 0.2 O4)2P2O7.

[0088] Example 18

[0089] 0.015 mol of ferric nitrate and 0.015 mol of manganese 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 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 1.5 Mn 1.5 (P 0.9 Se 0.1 O4)2P2O7.

[0090] Example 19

[0091] 0.02 mol of ferric nitrate and 0.01 mol of manganese 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 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 Na4Fe2Mn1(P 0.9 Se 0.1 O4)2P2O7.

[0092] Example 20

[0093] 0.015 mol of ferric nitrate and 0.015 mol of manganese 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 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of bismuthate, 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 1.5 Mn 1.5 (P 0.9 Bi 0.1 O4)2P2O7.

[0094] Example 21

[0095] 0.015 mol of ferric nitrate and 0.015 mol of manganese 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 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of gallate, 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 1.5 Mn 1.5 (P 0.9 Ga 0.1 O4)2P2O7.

[0096] Example 22

[0097] 0.015 mol of ferric nitrate and 0.015 mol of titanium 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 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 1.5 Ti 1.5 (P 0.9 Se 0.1 O4)2P2O7.

[0098] Example 23

[0099] 0.015 mol of ferric nitrate and 0.015 mol of titanium 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 bismuthate, 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 1.5 Ti 1.5 (P 0.8 Bi 0.2 O4)2P2O7.

[0100] Example 24

[0101] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of manganese 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 hydroxyethylidene diphosphate, 0.004 mol of selenate, and 0.08 mol of sodium nitrate 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 4 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 600°C for 20 hours to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Se 0.1 O7. Example 24 was subjected to XRD analysis, and the analysis results are shown in Figure 7b.

[0102] Example 25

[0103] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of manganese 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 hydroxyethylidene diphosphate, 0.004 mol of bismuthate and 0.08 mol of sodium nitrate 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 20 hours to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Bi 0.1 O7.

[0104] Example 26

[0105] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of titanium 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 hydroxyethylidene diphosphate, 0.004 mol of selenate, and 0.08 mol of sodium nitrate 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 4 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 600°C for 20 hours to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Se 0.1 O7.

[0106] Example 27

[0107] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of manganese 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 hydroxyethylidene diphosphonic acid, 0.004 mol of antimonate, and 0.08 mol of sodium nitrate 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 4 hours under a hydrogen-argon mixture (5%) at a temperature of 300°C, and then sintered at 600°C for 20 hours to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Sb 0.1 O7.

[0108] Example 28

[0109] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of manganese 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 0.058 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, and 0.06 mol of sodium carbonate 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-encapsulated Na3FeMn(P 0.9 Se 0.1 O4) P2O7, Example 28 was subjected to XRD analysis, and the analysis results are shown in Figure 7c.

[0110] Example 29

[0111] 0.02 mol of ferric nitrate nonahydrate and 0.02 mol of titanium 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 0.058 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, and 0.06 mol of sodium carbonate 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 Na3FeTi(P 0.9 Se 0.1 O4)P2O7.

[0112] Comparative Example 1

[0113] 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.

[0114] Comparative Example 2

[0115] 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.

[0116] Comparative Example 3

[0117] 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 force, and then slowly add 0.08 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.

[0118] Test Example 1: The electronic conductivity, 1200-cycle capacity retention rate, and first-cycle discharge specific capacity at 0.1C of the positive electrode active materials obtained in the examples and comparative examples were measured;

[0119] Electronic conductivity: The positive electrode active material is measured using a DC four-probe method;

[0120] 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.

[0121] 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.

[0122] The test results are shown in Table 1.

[0123] Table 1

[0124] It can be seen from the results in Table 1 that for the doping of Na4Fe3(PO4)2P2O7 active materials, by comparing Examples 1-23 and Comparative Example 1, the performance is regulated by co-doping of metal M and metal A, and dual anion and cation doping has a great effect on improving the cycle, and the effects of Examples 1-23 are better than those of Comparative Example 1; for the doping element M, Mg and Ca are better than other elements, and the electronic conductivity is significantly improved; among them, as shown in the results of Examples 1-11 and Examples 12-23, specifically, by comparing Example 2 with Example 15, it can be seen that dual cation doping of Mg and other elements has better electronic conductivity, 1200 cycle capacity retention rate and first cycle discharge specific capacity at 0.1C; by comparing Example 7 with Example 16, it can be seen that dual cation doping of Ca and other elements has better electronic conductivity, 1200 cycle capacity retention rate and first cycle discharge specific capacity at 0.1C.

[0125] As for the doping of Na2FeP2O7 active material, by comparing Examples 24-27 and Comparative Example 2, the performance is regulated by co-doping of metal M and metal A. The effects of Examples 24-27 are all better than those of Comparative Example 2.

[0126] Regarding the doping of Na3Fe2(PO4)P2O7 active materials, by comparing Examples 28-29 and Comparative Example 3, the performance is regulated by co-doping of metal M and metal A. The effects of Examples 28-29 are better than those of Comparative Example 3.

[0127] Test Example 2: Discharge voltage and rate performance test of the embodiments and comparative examples.

[0128] 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.

[0129] 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.

[0130] Figures 1a-1b show the discharge voltage curves for Example 1 and Examples 17-23. The positive electrode active materials obtained by dual-doping with Mn, Ti, and Se, Bi, and Ga exhibit enhanced performance, such as improved cycling performance, voltage, and capacity. (Mn reduces electronic conductivity, while Ti increases it; this applies to the following two materials).

[0131] 2 is a discharge voltage curve of Comparative Example 2 and Examples 24-27. Dual doping of Mn, Ti, and Bi\Se\Sb improves the discharge voltage, capacity, and cycle performance of the positive electrode active material.

[0132] 3 is a discharge voltage curve of Comparative Example 3 and Examples 28-29. Dual doping with Mn, Ti, and Se improves the discharge voltage, capacity, and cycle performance of the positive electrode active material.

[0133] Among them, Figure 4 shows the rate performance results of Example 1 and Examples 17, 18, 19, and 20. At 0.1C\0.2C\0.5C\10C, dual doping greatly improves the rate performance of the positive electrode active material. This is because the large size of Mn\Ti\Se\Ga expands the ion channel and reduces the sodium ion diffusion energy barrier.

[0134] 5 shows the rate performance results of comparative example 2 and embodiments 24, 25, 26, and 27. At 0.1C, 0.2C, 0.5C, and 10C, dual doping greatly improves the rate performance of the positive electrode active material.

[0135] 6 shows the rate performance results of Comparative Example 3 and Examples 28 and 29. At 0.1C, 0.2C, 0.5C, and 10C, dual doping greatly improves the rate performance of the positive electrode active material.

[0136] Among them, Figures 7a, 7b, and 7c are the XRD patterns of the positive electrode active materials of Examples 1, 24, and 28 of the present invention, respectively. From the main peak positions and lattice parameters of the materials obtained in Examples 1, 24, and 28, 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.

[0137] 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 (P 1-w A w O4) z (P 2-u A u O7), wherein M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi and In; x satisfies the condition: 2≤x≤4; y satisfies the condition: 1≤y≤4; z satisfies the condition: 0≤z≤2; w satisfies the condition: 0<w≤0.25; u satisfies the condition: 0≤u≤0.2, wherein u and z cannot be 0 at the same time.

2. The positive electrode active material according to claim 1, characterized in that in, M is selected from one or more of Ti, Mn, Fe, Mg, and Ca, and A is selected from one or more of Ga, Bi, and Se.

3. The positive electrode active material according to claim 1 or 2, characterized in that: in, M contains at least Fe and Mg, or at least Fe and Ca, and A is selected from Ga and / or Se; Preferably, the molar ratio of Fe to Mg in M ​​is 2.9-3:0.001-0.02, or the molar ratio of Fe to Ca is 2.9-3:0.001-0.

02.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that: The positive electrode active material has a composition shown in the following general formula: Na x M y (P 1-w A w O4) z (P2O7), where x=4, y=3, 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 (P 2-u A u O7), where x=2, y=1, 0<u≤0.2; Or, the positive electrode active material has a composition shown in the following general formula: Na x M y (P 1-w A w O4) z (P2O7), wherein x=3, y=2, z=1, 0<w≤0.

25.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that: The performance of the positive electrode active material at least meets one of the following conditions: the electronic conductivity is 1×10 -8 -6×10 - 7 S / cm, the capacity retention rate after 1200 cycles at 1C is 82%-97%, and the first cycle discharge specific capacity at 0.1C is 82-93mAh / g.

6. A method for preparing a positive electrode active material, characterized in that: include: (1) mixing a metal M source material, a metal 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, M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn and Nb, and A is selected from one or more of Ga, Sb, Se, Te, Bi and In.

7. The preparation method according to claim 6, characterized in that: The sintering specifically comprises: granulating 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 metal nitrates, metal oxalates, and metal citrates; Preferably, the metal A source material is selected from one or more of metal nitrates, metal oxalates, and metal citrates; 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.

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

9. The preparation method according to any one of claims 6 to 8, characterized in that: Before the sintering, pre-sintering is performed, wherein the pre-sintering temperature is 260-330° C. and the pre-sintering time is 1-5 hours.

10. The preparation method according to any one of claims 6 to 9, characterized in that: The molar ratio of the metal M source material, the metal A source material, the sodium source, the phosphorus source and the reducing agent is (0.01-0.1): (0.0001-0.1): (0.01-0.1): (0.01-0.1): (0.01-0.1).

11. 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 5 or the positive electrode active material obtained by the preparation method according to any one of claims 6 to 10.

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

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