Positive electrode active material, method for manufacturing the same, sodium-ion battery, and electric device

Abstract

The application relates to the field of positive electrode active materials for sodium ion batteries, and discloses a positive electrode active material, a preparation method thereof, a sodium ion battery and an electric device. The positive electrode active material has the 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 condition 2<=x<=4, 1<=y+n<=3, wherein y and n are not 0; z satisfies the condition 0<=z<=2, and w satisfies the condition 0

Description

TECHNICAL FIELD

[0001] The present application relates to the field of positive electrode active materials for sodium ion batteries, in particular to a positive electrode active material, a preparation method thereof, a sodium ion battery and an electric device. BACKGROUND

[0002] Sodium ion batteries are similar to the commonly used lithium ion batteries in many aspects, they are both reusable secondary batteries, including an anode (negative electrode), a cathode (positive electrode) and an electrolyte material, they can all store energy, and they are all charged and discharged via similar reaction mechanisms.

[0003] In the research of sodium ion battery cathode materials, people strive to find a cathode material with high energy density, good stability, environmentally friendly resources and energy saving. At present, the capacity of polyanion type cathode material is difficult to approach the theoretical capacity level, such as sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), the theoretical capacity is about 129 mAh / g, and the actual capacity is about 70 mAh / g, which is mainly due to low electronic conductivity and slow ion migration. It is particularly important to enhance this performance by doping. These modified polyanion type cathode materials have a certain promoting effect on the development of sodium ion battery cathode materials. SUMMARY

[0004] The purpose of the present application is to overcome the problems of low electronic conductivity and slow ion migration of polyanion type cathode materials in the prior art, and to provide a positive electrode active material, a preparation method thereof, a sodium ion battery and an electric device.

[0005] In order to achieve the above purpose, the first aspect of the present application provides a positive electrode active material, wherein the positive electrode active material has 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, Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, Ce; x satisfies the condition: 2≤x≤4, 1≤y+n≤3, wherein y and n are not 0; z satisfies the condition: 0≤z≤2, w satisfies the condition: 0<w≤0.35; u satisfies the condition: 0≤u≤0.2.

[0006] The second aspect of the present application provides a preparation method of a positive electrode active material, comprising:

[0007] (1) mixing a metal M source substance, a metal E source substance, an optional A source substance, a sodium source, a phosphorus source and a reducing agent to obtain a precursor solution;

[0008] (2) processing the precursor solution to obtain the positive electrode active material;

[0009] wherein A is selected from one or more of S, Si, B, As, Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, and E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, Ce.

[0010] The third aspect of the present application provides a sodium ion battery, wherein the sodium ion battery comprises the positive electrode active material or the positive electrode active material prepared by the preparation method.

[0011] The fourth aspect of the present application provides an electric device, wherein the electric device comprises the sodium ion battery.

[0012] Through the above technical solution, the present application dopes M and E into the polyanion type positive electrode material, the cell volume is increased, the Na ion migration speed is increased, the actual capacity is improved, and the rate performance is also improved due to the doping of element A at the P position. In addition, the conductivity is enhanced after the transition metal and rare earth metal are doped at the M position, and the electrochemical performance of the positive electrode active material is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 is the discharge voltage curve of Comparative Example 1 and Examples 1-7, a is the discharge voltage curve of Examples 1-3, and b is the discharge voltage curve of Examples 4-7;

[0014] Figure 2 is the discharge voltage curve of Comparative Example 2 and Examples 8-10;

[0015] Figure 3 is the discharge voltage curve of Comparative Example 3 and Examples 11-12;

[0016] Figure 4 is the rate performance result of Comparative Example 1 and Examples 1, 2, 6 and 7;

[0017] Figure 5 is the rate performance result of Comparative Example 2 and Examples 8-10;

[0018] Figure 6 is the rate performance result of Comparative Example 3 and Examples 11 and 12;

[0019] Figure 7are XRD test results of the positive electrode active materials of Example 1, Example 23 and Example 26, wherein Figure (a) is an XRD pattern of the positive electrode active material of Example 1, Figure (b) is an XRD pattern of the positive electrode active material of Example 23, and Figure (c) is an XRD pattern of the positive electrode active material of Example 26. DETAILED DESCRIPTION

[0020] The endpoints of the ranges and any values claimed herein are not to be understood as being limited to the exact values recited as implicitly included within the range. The ranges are understood to be shorthand for describing each and every value that falls within the range. Any value within the range, including the endpoints, can be combined with any other value or values, or other ranges, to achieve a new range. Unless otherwise stated, all ranges include any and all end points within the range.

[0021] The first aspect of the present application 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, Al, M is selected from one or more of Fe, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, E is selected from one or more of Zr, Tc, Ru, Rh, Ir, Nb, La, Ce; x satisfies the condition: 2≤x≤4, 1≤y+n≤3, wherein y and n are not 0; z satisfies the condition: 0≤z≤2, w satisfies the condition: 0<w≤0.35; u satisfies the condition: 0≤u≤0.2. The molecular formula of the positive electrode active material is confirmed by an elemental quantitative analysis-ICP method, using an ICP-OES-inductively coupled plasma atomic emission spectrometer, and finally combined with XRD to obtain the molecular formula of the positive electrode active material.

[0022] In the present application, the polyanion type positive electrode material is mainly focused on three types of intrinsic materials Na2FeP2O7, Na3Fe2(PO4)P2O7, Na4Fe3(PO4)2P2O7, which are doped, metal M and metal E are doped in Fe position, element A is doped in P position of phosphate, through the joint action of metal M and metal E and element A, a structure which keeps the original crystal point group structure unchanged is obtained, and the unit cell volume is increased, so that the ionic conductivity, rate, capacity and other electrochemical properties of the positive electrode active material of the present application are improved.

[0023] In some embodiments of the present application, the positive electrode active material of the present application belongs to a polyanion compound, which is usually formed by connecting MO6 octahedron and PO4 tetrahedron through co-point, co-edge, co-plane, etc. to form Na + Three-dimensional diffusion channels. The three-dimensional framework can make Na + In the process of embedding / detaching, the volume change is relatively small, and the corresponding cycle number is high. First, the metal E (transition metal Zr, Tc, Ru, Rh, Ir, Nb, rare earth metal La, Ce) is doped into the polyanion cell, and the cell volume is increased by 3.5%-8.7% compared with the volume of the undoped element. The increase in cell volume corresponds to the faster migration speed of Na ions, the actual capacity is improved, and the rate performance is also improved; in addition, after the transition metal and rare earth metal are doped into the M position, the electrical conductivity is enhanced.

[0024] In some embodiments of the present application, through first principles, it is simulated that the positive electrode active material has a bond length of A-O in the unit cell of The distance of M-O is The bond length in the above range is larger, the cell volume is larger, and the cell volume is increased by 3.5%-8.7% compared with the volume of the undoped element, which can reduce the Na ion diffusion energy barrier and improve the ionic conductivity of the positive electrode active material.

[0025] In some embodiments of the present application, preferably, wherein 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.

[0026] In some embodiments of the present application, 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; the positive electrode active material in the above range is, for example, a doped Na4Fe3(PO4)2P2O7.

[0027] In some embodiments of the present application, 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 uNa x M y E z (P 2 O 7 ) n (PO 4 ) u, 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 a doping of Na 2 FeP 2 O 7.

[0028] In some embodiments of the present application, preferably, 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 O 7 ) n (PO 4 ) u, wherein x = 3, 1.8≤y<2, 0<n≤0.2, z = 1, 0<w≤0.25; the positive electrode active material in the above range is for example a doping of Na 3 Fe 2 (PO 4 )P 2 O 7.

[0029] In some embodiments of the present application, 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 of 1C is 78%-94%, and the specific discharge capacity of the first cycle at 0.1C is 60-94 mAh / g.

[0030] The second aspect of the present application provides a preparation method of a positive electrode active material, wherein the method comprises:

[0031] (1) mixing a metal M source substance, a metal E source substance, an optional A source substance, a sodium source, a phosphorus source and a reducing agent to obtain a precursor solution;

[0032] (2) performing sintering treatment on the precursor solution to obtain the positive electrode active material;

[0033] 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.

[0034] In some embodiments of the present application, the metal M source substance, the metal E source substance, the optional A source substance, the sodium source, the phosphorus source and the reducing agent are mixed and dissolved in water to obtain the precursor solution.

[0035] In some embodiments of the present application, in step (2), the sintering treatment is specifically drying and sintering the precursor solution to obtain the positive electrode active material.

[0036] In some embodiments of the present application, the metal M source substance is selected from one or more of nitrate, oxalate and citrate of the metal M.

[0037] In some embodiments of the present application, the metal E source is selected from one or more of a sulfate, a chloride, a nitrate and an acetate of metal E.

[0038] In some embodiments of the present application, the A source is selected from one or more of a sulfate, a silicate, a borate, an arsenate, an aluminate.

[0039] In some embodiments of the present application, the sodium source is selected from one or more of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, sodium nitrate.

[0040] In some embodiments of the present application, the phosphorus source is selected from one or more of ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphonic acid.

[0041] In some embodiments of the present application, the reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid, tartaric acid. In addition to the reducing effect, the reducing agent also has the effect of carbon source and stabilizing Fe 3+ , and also has the effect of chelating agent and divalent iron ion binding to form chelate. In the final inert atmosphere calcination process, ascorbic acid forms in-situ carbon uniformly coated on the surface of the material, greatly improving the electrical conductivity of the material.

[0042] In some embodiments of the present application, the sintering temperature is 400-650℃, and the sintering time is 10-36h.

[0043] In some embodiments of the present application, pre-sintering is further performed before the sintering, the pre-sintering temperature is 260-330℃, and the pre-sintering time is 1-5h.

[0044] In some embodiments of the present application, the pre-sintering is performed in a hydrogen-argon mixed gas, wherein the volume percentage of hydrogen in the hydrogen-argon mixed gas can be 1-10%.

[0045] In some embodiments of the present application, the molar ratio of the metal M source, the metal E source, the A source, 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).

[0046] The third aspect of the present application provides a sodium ion battery, wherein the sodium ion battery comprises the positive electrode active material or the positive electrode active material prepared by the preparation method.

[0047] The fourth aspect of the present application provides an electric device, wherein the electric device comprises the sodium ion battery.

[0048] The application will be described in detail below through examples.

[0049] The positive electrode active material structure composition of the examples of the application is confirmed by elemental quantitative analysis-ICP method, an appropriate amount of powder is dissolved in strong acid, and finally ICP-OES-inductively coupled plasma atomic emission spectrometer is used to characterize the proportion of different elements, and finally the molecular formula of the positive electrode active material is obtained in combination with XRD.

[0050] The specific conditions not specified in the following examples and comparative examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used without specifying the manufacturer are conventional products that can be obtained by market purchase.

[0051] Example 1

[0052] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning, control the temperature at 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 S 0.05 O4)2P2O7, and perform XRD analysis on Example 1, and the analysis results are shown in Figure 7 (a).

[0053] Example 2

[0054] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning, control the temperature at 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0055] Example 3

[0056] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.033 mol of ammonium dihydrogen phosphate and 0.007 mol of sulfate, 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning, control the temperature at 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.65 S 0.35 O4)2P2O7.

[0057] Example 4

[0058] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning, control the temperature at 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0059] Example 5

[0060] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning, control the temperature at 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 La 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0061] Example 6

[0062] Dissolve 0.029 mol of iron 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 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Ru 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0063] Example 7

[0064] Dissolve 0.029 mol of iron 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 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Ru 0.1 (P 0.8 Si 0.2 O4)2P2O7.

[0065] Example 8

[0066] Dissolve 0.029 mol of nickel nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Ni 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0067] Example 9

[0068] Dissolve 0.029 mol of manganese nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Mn 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0069] Example 10

[0070] Dissolve 0.029 mol of titanium nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Ti 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0071] Example 11

[0072] Dissolve 0.029 mol of chromium nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and 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 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Cr 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0073] Example 12

[0074] Dissolve 0.029 mol of chromium nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and 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 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4CrZr(P 2.9 Zr 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0075] Example 13

[0076] Dissolve 0.029 mol of nickel nitrate and 0.001 mol of lanthanum nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and 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 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4NiLa(P 2.9 La 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0077] Example 14

[0078] Dissolve 0.029 mol of vanadium nitrate and 0.001 mol of iridium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and 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 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4V 2.9 Ir 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0079] Example 15

[0080] Dissolve 0.029 mol of cobalt nitrate and 0.001 mol of iridium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and 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 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4CoIr(P 2.9 Ir 0.1 (P 0.8 S 0.2 O4)2P2O7.

[0081] Example 16

[0082] Dissolve 0.029 mol of zinc nitrate and 0.001 mol of iridium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and 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 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4ZnIr(P 0.1 Ir 0.8 (P 0.2 S 2.9 O4)2P2O7.

[0083] Example 17

[0084] Dissolve 0.029 mol of iron nitrate and 0.001 mol of cerium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir magnetically, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 2 h at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4FeCe(P 0.1 Ce 0.95 (P 0.05 S 2.9 O4)2P2O7.

[0085] Example 18

[0086] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of technetium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Tc 0.1 (P 0.95 S 0.05 O4)2P2O7.

[0087] Example 19

[0088] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of niobium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of sulfate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Nb 0.1 (P 0.95 S 0.05 O4)2P2O7.

[0089] Example 20

[0090] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of borate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 B 0.05 O4)2P2O7

[0091] Example 21

[0092] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of arsenate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 As 0.05 O4)2P2O7.

[0093] Example 22

[0094] Dissolve 0.029 mol of ferric nitrate and 0.001 mol of zirconium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.039 mol of ammonium dihydrogen phosphate, 0.001 mol of arsenate, and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe 2.9 Zr 0.1 (P 0.95 Al 0.05 O4)2P2O7.

[0095] Example 23

[0096] Dissolve 0.038 mol of ferric nitrate and 0.002 mol of zirconium nitrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and 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 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 4 h of pre-burning at a temperature of 300°C, and then sinter at 600°C for 22 h to obtain carbon-coated Na2Fe 0.95 Zr 0.05 P 1.9 S 0.1 O7, and perform XRD analysis on Example 23, and the analysis results are shown in Figure 7 (b).

[0097] Example 24

[0098] Dissolve 0.038 mol of iron 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 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 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 4 h at a temperature of 300°C, and then sinter at 600°C for 22 h to obtain carbon-coated Na2Fe 0.95 Ru 0.05 P 1.9 S 0.1 O7.

[0099] Example 25

[0100] Dissolve 0.038 mol of iron nitrate and 0.002 mol of zirconium nitrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.076 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, and 0.08 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 4 h at a temperature of 300°C, and then sinter at 600°C for 22 h to obtain carbon-coated Na2Fe 0.95 Zr 0.05 P 1.9 Si 0.1 O7.

[0101] Example 26

[0102] Dissolve 0.038 mol of iron nitrate and 0.002 mol of zirconium nitrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.076 mol of ammonium dihydrogen phosphate, 0.004 mol of silicate, and 0.08 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution into a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for pre-burning for 4 h at a temperature of 300°C, and then sinter at 600°C for 22 h to obtain carbon-coated Na2Fe 1.9 Zr 0.1 (P 0.85 S 0.15 O4)P2O7, and perform XRD analysis on Example 26, and the analysis results are shown in Figure (c). Figure 7 (c) shown.

[0103] Example 27

[0104] Dissolve 0.038 mol of iron 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 slowly add 0.057 mol of ammonium dihydrogen phosphate and 0.003 mol of sulfate and 0.06 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 550°C for 20 h to obtain carbon-coated Na3Fe 1.9 Ru 0.1 (P 0.85 S 0.15 O4)P2O7.

[0105] Comparative Example 1

[0106] Dissolve 0.03 mol of iron nitrate nonahydrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.04 mol of ammonium dihydrogen phosphate and 0.04 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 500°C for 36 h to obtain carbon-coated Na4Fe3(PO4)2P2O7.

[0107] Comparative Example 2

[0108] Dissolve 0.04 mol of iron nitrate nonahydrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.08 mol of ammonium dihydrogen phosphate and 0.08 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 4 h of pre-burning at a temperature of 300°C, and then sinter at 600°C for 20 h to obtain carbon-coated Na2FeP2O7.

[0109] Comparative Example 3

[0110] Dissolve 0.04 mol of iron nitrate nonahydrate in 700 mL of deionized water, then add 0.12 mol of ascorbic acid, stir with a magnetic stirrer, and slowly add 0.06 mol of ammonium dihydrogen phosphate and 0.06 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation, place the sprayed powder in a hydrogen-argon mixed gas (5%) for 2 h of pre-burning at a temperature of 300°C, and then sinter at 550°C for 20 h to obtain carbon-coated Na3Fe2(PO4)P2O7.

[0111] Test Example 1: The positive electrode active material obtained in the examples and comparative examples is subjected to conductivity measurement, capacity retention after 1C cycle for 1200 cycles, and first cycle discharge specific capacity at 0.1C.

[0112] Electronic conductivity: The positive electrode active material is measured by direct current four-probe method;

[0113] 1200 cycle capacity retention: The positive electrode active material obtained in the examples and comparative examples is applied in a sodium ion battery, after constant volume charging and discharging at 0.2C, the discharge capacity is used as the rated capacity, the voltage range is 2-3.4V, 1C cycle is used, each step is rested for 10 minutes, the charging uses constant current and constant voltage mode, the cutoff current is 0.05C, and the charging uses constant current mode;

[0114] 0.1C first cycle discharge specific capacity: small soft packs are manually stacked, charged to 3.5V at 0.1C rate, aged for two days, and discharged to 2V at 0.1C for grading.

[0115] The test results are shown in Table 1.

[0116] Table 1

[0117]

[0118]

[0119] As can be seen from the results in Table 1, the positive electrode active material of the examples obtained by double doping according to the application has good conductivity, rate performance and high voltage, and has obviously better effects.

[0120] For doping of Na4Fe3(PO4)2P2O7 active material, by comparing Examples 1-22 and Comparative Example 1, by double doping M, E into polyanion type positive electrode material, the doping of element A at P position also improves the rate performance, 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.

[0121] For doping of Na2FeP2O7 active material, by comparing Examples 23-25 and Comparative Example 2, by double doping M, E into polyanion type positive electrode material, the doping of element A at P position also improves the rate performance, the effects of Examples 23-25 are all better than those of Comparative Example 2.

[0122] For doping of Na3Fe2(PO4)P2O7 active material, by comparing Examples 26-27 and Comparative Example 3, by double doping M, E into polyanion type positive electrode material, the doping of element A at P position also improves the rate performance, the effects of Examples 26-27 are all better than those of Comparative Example 3.

[0123] Test Example 2: Discharge voltage and rate performance test of examples and comparative examples.

[0124] Discharge voltage: positive electrode powder and conductive agent binder were made into slurry in a ratio of 100:4:2, coated on carbon-coated aluminum foil, and after baking, the electrode sheet was rolled, pressed at 1.9 g / cc, cut, weighed, vacuum baked at 120 degrees for one day, and a half-cell was made. The negative electrode was made of a hand rod sodium sheet, and the electrochemical performance of the positive electrode material was evaluated to obtain the discharge voltage curve of different positive electrode materials.

[0125] Rate performance: the charging rate was uniformly 0.2C, and the discharge rate was set to 0.1C, 0.2C, 0.5C, and 10C, each rate was cycled 5 times. Different discharge rates can reflect the ion diffusion capacity of the positive electrode material.

[0126] wherein, Figure 1 is the discharge voltage curve of Comparative Example 1 and Examples 1-7. It can be seen that the incorporation of Zr, La, Ru and anions S, Si makes the capacity of Na4Fe3(PO4)2P2O7 doped material play a greater role, and the voltage is also improved, which has a positive effect on increasing the energy density of the battery.

[0127] wherein, Figure 2 is the discharge voltage curve of Comparative 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.

[0128] wherein, Figure 3 is the discharge voltage curve of Comparative 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 Na3Fe2(PO4)P2O7 doped materials, greatly improving the electrochemical performance of such materials.

[0129] wherein, Figure 4 is the rate performance result of Comparative Example 1 and Examples 1, 2, 6, 7. Element doping can significantly improve the rate performance of Na4Fe3(PO4)2P2O7 doped materials.

[0130] wherein, Figure 5 is the rate performance result of Comparative Example 2 and Examples 23-25. Element doping can significantly improve the rate performance of Na2FeP2O7 doped materials.

[0131] wherein, Figure 6 is the rate performance result of Comparative Example 3 and Examples 26, 27. Element doping can significantly improve the rate performance of Na3Fe2(PO4)P2O7 doped materials.

[0132] wherein, Figure 7 The XRD patterns of the positive electrode active materials of Example 1, Example 23 and Example 26 are shown in Figure 1. The main peak positions and lattice parameters of the materials obtained from Examples 1, 23 and 26, combined with the elemental proportion analysis by ICP, can obtain the molecular formula of the corresponding examples, and the phase purity of the material after sintering is high.

[0133] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A positive electrode active material, characterized in that, The positive electrode active material has a composition represented by the following general formula: Na x M y E n (P 1-w A w O4) z (P 2-u A u O7), where 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, where neither y nor n is 0; z satisfies the condition: 0 ≤ z ≤ 2, w satisfies the condition: 0 < w ≤ 0.35; u satisfies the condition: 0 ≤ u ≤ 0.2; the positive electrode activity is used for a sodium ion battery; the method for preparing the positive electrode active material includes: (1) Mix the metal M source material, the metal E source material, the optional A source material, the sodium source, the phosphorus source and the reducing agent to obtain a precursor solution; (2) The precursor solution is sintered to obtain the positive electrode active material; 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.

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 the following general formula: Na x M y E n (P 1-w A w O4) z (P₂O₇), where x=4, 2.8≤y<3, 0 <n≤0.2,z=2,0<w≤0.25; Alternatively, the positive electrode active material has the composition shown in the following general formula: Na x M y E n (P 2-u A u O7), where x=2, 0.8≤y<1, 0 <n≤0.2,0<u≤0.2; Alternatively, the positive electrode active material has the composition shown in the following general formula: Na x M y E n (P 1-w A w O4) z (P₂O₇), where x=3, 1.8≤y<2, 0 <n≤0.2,z=1,0<w≤0.25。 4. The positive electrode active material according to claim 1 or 2, characterized in that, The positive electrode active material must meet at least one of the following conditions: electronic conductivity is 3×10⁻⁶. -9 -5×10 -7 S / cm, capacity retention rate after 1200 cycles at 1C is 78%-94%, and the first discharge specific capacity at 0.1C is 61-94mAh / g.

5. The positive electrode active material according to claim 3, characterized in that, The positive electrode active material must meet at least one of the following conditions: electronic conductivity is 3×10⁻⁶. -9 -5×10 -7 S / cm, capacity retention rate after 1200 cycles at 1C is 78%-94%, and the first discharge specific capacity at 0.1C is 61-94mAh / g.

6. A method for preparing the positive electrode active material according to any one of claims 1-5, characterized in that, include: (1) Mix the metal M source material, the metal E source material, the optional A source material, the sodium source, the phosphorus source and the reducing agent to obtain a precursor solution; (2) The precursor solution is sintered to obtain the positive electrode active material; 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.

7. The preparation method according to claim 6, characterized in that, In step (2), the sintering process specifically involves drying and sintering the precursor solution to obtain the positive electrode active material.

8. The preparation method according to claim 6 or 7, characterized in that, The metal M source material is selected from one or more of the nitrate, oxalate, and citrate of metal M; And / or, the metal E source material is selected from one or more of the sulfate, chloride, nitrate and acetate salts of metal E; And / or, the A source material is selected from one or more of sulfates, silicates, borates, arsenates, and aluminates; And / or, the sodium source is selected from one or more of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium nitrate; And / or, the phosphorus source is selected from ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphate; And / or, the reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid, and tartaric acid.

9. The preparation method according to claim 6 or 7, characterized in that, The sintering temperature is 400-650℃, and the sintering time is 10-36h.

10. The preparation method according to claim 6 or 7, characterized in that, Before sintering, a pre-sintering process is performed at a temperature of 260-330℃ for 1-5 hours.

11. The preparation method according to claim 8, characterized in that, Before sintering, a pre-sintering process is performed at a temperature of 260-330℃ for 1-5 hours.

12. The preparation method according to claim 9, characterized in that, Before sintering, a pre-sintering process is performed at a temperature of 260-330℃ for 1-5 hours.

13. The preparation method according to any one of claims 6, 7, 11, and 12, characterized in that, The molar ratio of the metal M source, metal E source, A source, 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).

14. The preparation method according to claim 8, characterized in that, The molar ratio of the metal M source, metal E source, A source, 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).

15. The preparation method according to claim 9, characterized in that, The molar ratio of the metal M source, metal E source, A source, 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).

16. The preparation method according to claim 10, characterized in that, The molar ratio of the metal M source, metal E source, A source, 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).

17. A sodium-ion battery, characterized in that, The sodium-ion battery comprises the positive electrode active material according to any one of claims 1-5 or the positive electrode active material obtained by the preparation method according to any one of claims 6-16.

18. An electrical appliance, characterized in that, Including the sodium-ion battery as described in claim 17.

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