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

Abstract

The present invention relates to the field of positive electrode active materials for sodium ion batteries, and discloses a positive electrode active material and a preparation method thereof, a sodium ion battery and an electrical device. 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, 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

Description

Technical Field

[0001] The present invention relates to the field of cathode active materials for sodium ion batteries, and particularly to a cathode active material, a preparation method thereof, a sodium ion battery, and an electrical device using the same. Background Art

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

[0003] In contrast, sodium ion battery technology is still in its relatively initial stage, but it is considered beneficial. Sodium reserves are much richer than lithium. However, the potential of the cathode active material of existing sodium batteries is relatively low. Among them, it is difficult for polyanion-based cathode materials to reach a level close to the theoretical capacity. For example, the theoretical capacity of sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7) is 129 mAh / g, and the actual capacity is only about 70 mAh / g. This is mainly due to low electronic conductivity and slow ion migration. Therefore, it is important to regulate and modify the capacity, voltage, and rate performance of polyanion-based cathode materials. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of low electronic conductivity and slow ion migration of polyanion-based cathode materials in the prior art, and to provide a cathode active material, a preparation method thereof, a sodium ion battery, and an electrical device using the same.

[0005] To achieve the above purpose, in the first aspect of the present invention, a cathode active material is provided, wherein the cathode active material has a composition represented by the following general formula: Na x M y (P 1-w A w O4) z (P 2-u A u O7), where M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn, and Nb; 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, where u and z cannot be 0 at the same time.

[0006] In the second aspect of the present invention, a preparation method of a cathode active material is provided, which includes:

[0007] (1) Mix 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;

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

[0009] 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.

[0010] The third aspect of the present invention provides a sodium ion battery, wherein the sodium ion battery includes the positive electrode active material described above or the positive electrode active material obtained by the preparation method described above.

[0011] The fourth aspect of the present invention provides an electrical device, which includes the sodium ion battery described above.

[0012] Through the above technical solutions, the positive electrode active material provided by the present invention can regulate its performance through the co-doping of metal M and metal A, making full use of the advantages of different elements, enhancing the performance of the polyanion positive electrode material. The co-doping of multiple metals makes the bond length larger, thereby expanding the unit cell volume, reducing the Na ion diffusion barrier, increasing the Na ion migration speed, improving the actual capacity, and at the same time improving the voltage and rate performance, and enhancing the electronic conductivity. Description of the Drawings

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

[0014] Figure 2 are the discharge voltage curves of Comparative Example 2 and Examples 8-11;

[0015] Figure 3 are the discharge voltage curves of Comparative Example 3 and Examples 12-13;

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

[0017] Figure 5 are the rate performance results of Comparative Example 2 and Examples 8, 9, 10, 11;

[0018] Figure 6 are the rate performance results of Comparative Example 3 and Examples 12, 13;

[0019] Figure 7XRD patterns of the positive electrode active materials of Embodiment 1, Embodiment 24, and Embodiment 28 of the present invention. Among them, Figure (a) is the XRD pattern of the positive electrode active material of Embodiment 1, Figure (b) is the XRD pattern of the positive electrode active material of Embodiment 24, and Figure (c) is the XRD pattern of the positive electrode active material of Embodiment 28. Detailed implementation manners

[0020] In the ranges disclosed herein, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0021] The first aspect of the present invention provides a positive electrode active material, wherein the positive electrode active material has a composition represented by the following general formula: Na x M y (P 1-w A w O4) z (P 2-u A u O7), where M is selected from one or more of Fe, Ti, V, Cr, Mn, Mg, Ca, Zr, Cd, Co, Ni, Cu, Zn, and Nb; 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, where 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. An ICP - OES - inductively coupled plasma atomic emission spectrometer is used, and finally the molecular formula of the positive electrode active material is obtained by combining with XRD.

[0022] In the present invention, through first - principles, it is simulated that the distance between A - O in the unit cell of the positive electrode active material is The distance between M - O is By jointly 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 larger. This change can reduce the Na - ion diffusion energy barrier and improve the ionic conductivity.

[0023] In the present invention, the performance is mainly regulated by the co-doping of transition metals at the M position and A metals at the P position, which can make full use of the advantages of different elements and enhance the performance of the polyanion cathode material. For example, the sizes of one or more of Ga, Ge, Sb, Se, Te, Bi, and In in metal A are larger than P. After one or more of Ga, Ge, Sb, Se, Te, Bi, and In in metal A are incorporated into the unit cell, the volume and the distance of the A-O bond change, and the distance of the unit cell A-O is Finally, it is found that the unit cell volume increases and the bond length increases. This change can reduce the Na ion diffusion barrier and improve the ionic conductivity. It is preliminarily proved that the incorporation of large-size anions has the potential to improve the electrochemical performance of polyanion-based materials.

[0024] In some specific embodiments of the present invention, the positive electrode active material of the present invention belongs to a polyanion-type compound, and the polyanion-type compound is usually formed by connecting MO6 octahedrons and PO4 tetrahedrons through ways such as sharing points, edges, and faces to form a Na + three-dimensional diffusion channel. The three-dimensional framework can make Na + generate a relatively small volume change during the process of insertion / extraction, corresponding to a very high number of cycles. First, metal A (Ga, Ge, Sb, Se, Te, Bi, In) is incorporated into the polyanion unit cell, and the distance of A-O is The distance of P-O before incorporation is The volume of the unit cell expands, the migration speed of Na ions becomes faster, the actual capacity is increased, and at the same time, the rate performance is also improved; in addition, after Mn is incorporated at the M position, the voltage increases, and after Ti is incorporated, the electronic conductivity is improved.

[0025] 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 as Mn, the metal Mn improves the voltage performance. When M is selected as Ti, the metal Ti improves the electronic conductivity. When M is selected as Mg and Ca, the cycle performance and processing performance can be improved.

[0026] 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 and Mg in M is 2.9-3:0.001-0.02, or the molar ratio of Fe and Ca in M is 2.9-3:0.001-0.02.

[0027] In some specific embodiments of the present invention, the molar ratio of Fe and Mg in M is 2.9-3:0.001-0.02, or the molar ratio of Fe and Ca in M is 2.9-3:0.001-0.02.

[0028] In some specific embodiments of the present invention, the positive electrode active material has a composition represented by 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; the positive electrode active material within the above range is, for example, a doping of Na4Fe3(PO4)2P2O7.

[0029] In some specific embodiments of the present invention, preferably, the positive electrode active material has a composition represented by the following general formula: Na x M y (P 2-u A u O7), where x = 2, y = 1, 0 ≤ u ≤ 0.25; the positive electrode active material within the above range is, for example, a doping of Na2FeP2O7.

[0030] In some specific embodiments of the present invention, preferably, the positive electrode active material has a composition represented by the following general formula: Na x M y (P 1-w A w O4) z (P2O7), where x = 3, y = 2, z = 1, 0 < w ≤ 0.25, and the positive electrode active material within the above range is, for example, a doping of Na3Fe2(PO4)P2O7.

[0031] In some specific embodiments of the present invention, the performance of the positive electrode active substance 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 initial discharge specific capacity at 0.1C is 82 - 93 mAh / g.

[0032] The second aspect of the present invention provides a method for preparing a positive electrode active material, which includes:

[0033] (1) Mixing a metal M source substance, a metal A source substance, a sodium source, a phosphorus source, and a reducing agent to obtain a precursor solution;

[0034] (2) Sintering the precursor solution to obtain the positive electrode active material;

[0035] 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.

[0036] 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.

[0037] In some specific embodiments of the present invention, the sintering is specifically as follows: granulating and sintering the precursor solution to obtain the positive electrode active material, wherein the granulation can be spray granulation.

[0038] In some specific embodiments of the present invention, the metal M source material is selected from one or more of metal nitrates, metal oxalates, and metal citrates;

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

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

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

[0042] In some specific embodiments of the present invention, the reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid, and tartaric acid. In addition to its reducing effect, the reducing agent also acts as a carbon source and a stabilizer for metal ions, and acts as a chelating agent to form a chelate with divalent iron ions, playing a role in stabilizing metal M ions. During the final calcination process in an inert atmosphere, ascorbic acid will form in-situ carbon to uniformly coat the surface of the material, greatly improving the electrical conductivity of the material.

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

[0044] In some specific embodiments of the present invention, pre-sintering is also carried out before the sintering. Among them, the pre-sintering temperature is 260 - 330 °C, and the pre-sintering time is 1 - 5 h.

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

[0046] In some specific embodiments of the present invention, 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).

[0047] 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 determined by the preparation feedstock.

[0048] In the third aspect of the present invention, a sodium-ion battery is provided, wherein the sodium-ion battery includes the positive electrode active material described above or the positive electrode active material obtained by the preparation method described above.

[0049] In the fourth aspect of the present invention, an electrical device is provided, which includes the sodium-ion battery described above.

[0050] The present invention will be described in detail below through examples.

[0051] The structural composition of the positive electrode active material in the examples of the present invention was confirmed by elemental quantitative analysis - ICP method. An appropriate amount of powder was taken and dissolved in strong acid, and finally the proportion of different elements was characterized by ICP-OES - inductively coupled plasma atomic emission spectrometer. Finally, the molecular formula of the positive electrode active material was obtained by combining XRD.

[0052] For those not specifying specific conditions in the following examples and comparative examples, they were carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specifying the manufacturer, they were all conventional products that could be obtained through commercial channels.

[0053] Example 1

[0054] Dissolve 0.02978 mol of iron nitrate, 0.0002 mol of zirconium nitrate, and 0.00002 mol of magnesium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.978 Zr 0.02 Mg 0.002 (P 0.995 Ga 0.005 O4)2P2O7. Perform XRD analysis on Example 1, and its analysis results are as Figure 7 (a) shown.

[0055] Example 2

[0056] Dissolve 0.02978 mol of iron nitrate, 0.0002 mol of cadmium nitrate, and 0.00002 mol of magnesium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Next, slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.978 Cd 0.02 Mg 0.002 (P 0.995 Ga 0.005 (PO4)2P2O7.

[0057] Example 3

[0058] Dissolve 0.02978 mol of iron nitrate, 0.0002 mol of zirconium nitrate, and 0.00002 mol of magnesium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Next, slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.978 Cr 0.02 Mg 0.002 (P 0.995 Ga 0.005 (PO4)2P2O7.

[0059] Example 4

[0060] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of nickel nitrate, and 0.0002 mol of magnesium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Next, slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Ni 0.02 Mg 0.02 (P 0.995 Ga 0.005 (PO4)2P2O7.

[0061] Example 5

[0062] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of zirconium nitrate and 0.0002 mol of magnesium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Zr 0.02 Mg 0.02 (P 0.995 Ga 0.005 (PO4)2P2O7

[0063] Example 6

[0064] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of manganese nitrate and 0.0002 mol of magnesium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Mn 0.02 Mg 0.02 (P 0.99 Ga 0.01 (PO4)2P2O7

[0065] Example 7

[0066] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of cadmium nitrate and 0.0002 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir with a magnetic stirrer. Then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Cd 0.02 Ca0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0067] Example 8

[0068] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of manganese nitrate and 0.0002 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Mn 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0069] Example 9

[0070] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of copper nitrate and 0.0002 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Cu 0.02 Ca 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0071] Example 10

[0072] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of nickel nitrate and 0.0002 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Ni 0.02 Ca 0.02 (P 0.99 Ga 0.01 (PO4)2P2O7.

[0073] Example 11

[0074] Dissolve 0.0296 mol of iron nitrate, 0.0002 mol of zinc nitrate and 0.0002 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.960 Zn 0.02 Ca 0.02 (P 0.99 Ga 0.01 (PO4)2P2O7.

[0075] Example 12

[0076] Dissolve 0.02998 mol of iron nitrate and 0.00002 mol of magnesium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h, control the temperature at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.998 Mg 0.002 (P 0.995 Ga 0.005 (PO4)2P2O7.

[0077] Example 13

[0078] Dissolve 0.02995 mol of iron nitrate and 0.00005 mol of calcium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.995 Ca 0.005 (P 0.995 Ga 0.005 (PO4)2P2O7

[0079] Example 14

[0080] Dissolve 0.02998 mol of iron nitrate and 0.00002 mol of magnesium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of germanate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.998 Mg 0.002 (P 0.995 Ge 0.005 (PO4)2P2O7

[0081] Example 15

[0082] Dissolve 0.0298 mol of iron nitrate and 0.0002 mol of cadmium nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid, stir with a magnetic stirrer, and then slowly add 0.0399 mol of ammonium dihydrogen phosphate, 0.0001 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.98 Cd 0.02 (P 0.995 Ga 0.005 (PO4)2P2O7

[0083] Example 16

[0084] Dissolve 0.0298 mol of iron nitrate and 0.0002 mol of cadmium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.0398 mol of ammonium dihydrogen phosphate, 0.0002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe 2.98 Cd 0.02 (P 0.99 Ga 0.01 O4)2P2O7.

[0085] Example 17

[0086] Dissolve 0.015 mol of iron nitrate and 0.015 mol of manganese nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of selenate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Mn 1.5 (P 0.8 Se 0.2 O4)2P2O7.

[0087] Example 18

[0088] Dissolve 0.015 mol of iron nitrate and 0.015 mol of manganese nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Mn 1.5 (P 0.9 Se 0.1 O4)2P2O7.

[0089] Example 19

[0090] Dissolve 0.02 mol of iron nitrate and 0.01 mol of manganese nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe2Mn1(P 0.9 Se 0.1 O4)2P2O7.

[0091] Example 20

[0092] Dissolve 0.015 mol of iron nitrate and 0.015 mol of manganese nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of bismuthate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Mn 1.5 (P 0.9 Bi 0.1 (P

[0093] Example 21

[0094] Dissolve 0.015 mol of iron nitrate and 0.015 mol of manganese nitrate in 600 mL of deionized water, then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of gallate, 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 under a hydrogen-argon mixture (5%) and pre-burn it for 2 h at a temperature controlled at 300 °C, and then sinter it at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Mn 1.5 (P 0.9 Ga 0.1 O4)2P2O7.

[0095] Example 22

[0096] Dissolve 0.015 mol of iron nitrate and 0.015 mol of titanium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.038 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Ti 1.5 (P 0.9 Se 0.1 O4)2P2O7.

[0097] Example 23

[0098] Dissolve 0.015 mol of iron nitrate and 0.015 mol of titanium nitrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, slowly add 0.036 mol of ammonium dihydrogen phosphate, 0.004 mol of bismuthate, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe 1.5 Ti 1.5 (P 0.8 Bi 0.2 O4)2P2O7.

[0099] Example 24

[0100] Dissolve 0.02 mol of iron nitrate nonahydrate and 0.02 mol of manganese nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.076 mol of hydroxyethylidene diphosphonic acid, 0.004 mol of selenate, and 0.08 mol of sodium nitrate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn for 4 h at a temperature controlled at 300 °C, and then sinter at 600 °C for 20 h to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Se 0.1 O7. Perform XRD analysis on Example 24, and the analysis results are as shown in Figure 7 (b).

[0101] Example 25

[0102] Dissolve 0.02 mol of iron(III) nitrate nonahydrate and 0.02 mol of manganese nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.076 mol of hydroxyethylidene diphosphonic acid, 0.004 mol of bismuthate, and 0.08 mol of sodium nitrate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn it at 300 °C for 4 h, then sinter it at 600 °C for 20 h to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Bi 0.1 O7.

[0103] Example 26

[0104] Dissolve 0.02 mol of iron(III) nitrate nonahydrate and 0.02 mol of titanium nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.076 mol of hydroxyethylidene diphosphonic acid, 0.004 mol of selenate, and 0.08 mol of sodium nitrate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn it at 300 °C for 4 h, then sinter it at 600 °C for 20 h to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Se 0.1 O7.

[0105] Example 27

[0106] Dissolve 0.02 mol of iron(III) nitrate nonahydrate and 0.02 mol of manganese nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.076 mol of hydroxyethylidene diphosphonic acid, 0.004 mol of antimonate, and 0.08 mol of sodium nitrate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn it at 300 °C for 4 h, then sinter it at 600 °C for 20 h to obtain carbon-coated Na2Fe 0.5 Mn 0.5 P 1.9 Sb 0.1 O7.

[0107] Example 28

[0108] Dissolve 0.02 mol of iron(III) nitrate nonahydrate and 0.02 mol of manganese(II) nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.058 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, and 0.06 mol of sodium carbonate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 550 °C for 20 h to obtain carbon-coated Na3FeMn(P 0.9 Se 0.1 O4)P2O7. Perform XRD analysis on Example 28, and the analysis results are as Figure 7 (c) shows.

[0109] Example 29

[0110] Dissolve 0.02 mol of iron(III) nitrate nonahydrate and 0.02 mol of titanium(IV) nitrate in 700 mL of deionized water. Then add 0.12 mol of ascorbic acid and stir magnetically. Next, slowly add 0.058 mol of ammonium dihydrogen phosphate, 0.002 mol of selenate, and 0.06 mol of sodium carbonate. After stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 550 °C for 20 h to obtain carbon-coated Na3FeTi(P 0.9 Se 0.1 O4)P2O7.

[0111] Comparative Example 1

[0112] Dissolve 0.03 mol of iron(III) nitrate nonahydrate in 600 mL of deionized water. Then add 0.10 mol of ascorbic acid and stir magnetically. Next, 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 under a hydrogen-argon mixture (5%) and pre-burn for 2 h at a temperature controlled at 300 °C, and then sinter at 500 °C for 36 h to obtain carbon-coated Na4Fe3(PO4)2P2O7.

[0113] Comparative Example 2

[0114] Dissolve 0.04 mol of iron(III) 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 under a hydrogen-argon mixture (5%) for pre-sintering for 4 h at a temperature controlled at 300 °C, and then sinter at 600 °C for 20 h to obtain carbon-coated Na2FeP2O7.

[0115] Comparative Example 3

[0116] Dissolve 0.04 mol of iron(III) 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 0.06 mol of sodium acetate; after stirring for 1 h, transfer the reaction solution to a spray dryer for spray granulation. Place the sprayed powder under a hydrogen-argon mixture (5%) for pre-sintering for 2 h at a temperature controlled at 300 °C, and then sinter at 550 °C for 20 h to obtain carbon-coated Na3Fe2(PO4)P2O7.

[0117] Test Example 1: Measure the electronic conductivity, 1200-cycle capacity retention rate, and first-cycle discharge specific capacity at 0.1C for the positive electrode active materials obtained in the examples and comparative examples;

[0118] Electronic conductivity: Measure the positive electrode active material using the direct current four-probe method;

[0119] 1200-cycle capacity retention rate: Apply the positive electrode active materials obtained in the examples and comparative examples in sodium-ion batteries. After constant current and constant voltage charging at 0.2C to a fixed volume, use the discharge capacity as the rated capacity, with a voltage range of 2 - 3.4V, cycle at 1C, hold for 10 minutes at each step, charge using the constant current and constant voltage mode with a cut-off current of 0.05C, and discharge using the constant current mode;

[0120] First-cycle discharge specific capacity at 0.1C: Manually stack and make small soft packs, charge at a rate of 0.1C to 3.5V for formation, after aging for two days, discharge at 0.1C to 2V for grading.

[0121] The test results are shown in Table 1.

[0122] Table 1

[0123]

[0124]

[0125]

[0126] It can be seen from the results in Table 1 that for the doping of the Na4Fe3(PO4)2P2O7 active material, by comparing Examples 1-23 with Comparative Example 1, the performance is regulated by the co-doping of metal M and metal A. The double doping of cations and anions plays a great role in improving the cycle performance, and the effects of Examples 1-23 are better than those of Comparative Example 1; for the doping element M, Mg and Ca are superior to other elements, significantly improving the electronic conductivity; among them, as shown by the results of Examples 1-11 and Examples 12-23, specifically, by comparing Example 2 and Example 15, it can be seen that the cation double 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 and Example 16, it can be seen that the cation double doping of Ca and other elements has better electronic conductivity, 1200-cycle capacity retention rate, and first-cycle discharge specific capacity at 0.1C.

[0127] For the doping of the Na2FeP2O7 active material, by comparing Examples 24-27 with Comparative Example 2, the performance is regulated by the co-doping of metal M and metal A, and the effects of Examples 24-27 are better than those of Comparative Example 2.

[0128] For the doping of the Na3Fe2(PO4)P2O7 active material, by comparing Examples 28-29 with Comparative Example 3, the performance is regulated by the co-doping of metal M and metal A, and the effects of Examples 28-29 are better than those of Comparative Example 3.

[0129] Test Example 2: Test the discharge voltage and rate performance of the examples and comparative examples.

[0130] Discharge voltage: The positive electrode powder, conductive agent, and binder are made into a slurry in a ratio of 100:4:2, coated on carbon-coated aluminum foil, baked and then roll-pressed into a pole piece. The pole piece is compacted at 1.9 g / cc, the pole piece is cut, weighed, baked in a vacuum at 120 °C for one day, and a coin-type half-cell is made. The negative electrode uses a sodium foil on a hand rod to evaluate the electrochemical performance of the positive electrode material, and the discharge voltage curves of different positive electrode materials are obtained.

[0131] Rate performance: The charging is uniformly carried out at 0.2C, and the discharge rates are set at 0.1C, 0.2C, 0.5C, and 10C. Each rate is cycled 5 times. The discharge at different rates can reflect the ion diffusion ability of the positive electrode material.

[0132] Among them, Figure 1 shows the discharge voltage curves of Comparative Example 1 and Examples 17-23. Some properties of the positive electrode active materials obtained by double doping with Mn, Ti and Se, Bi, Ga are enhanced, such as improving the cycle performance, voltage, and capacity. (Mn reduces the electronic conductivity, and Ti increases the electronic conductivity, which is the same for the following two types of materials).

[0133] Among them, Figure 2It is the discharge voltage curves of Comparative Example 2 and Examples 24-27. The double doping of Mn, Ti and Bi\Se\Sb improves the discharge voltage, capacity and cycling performance of the cathode active material.

[0134] Among them, Figure 3 It is the discharge voltage curves of Comparative Example 3 and Examples 28-29. The double doping of Mn, Ti and Se improves the discharge voltage, capacity and cycling performance of the cathode active material.

[0135] Among them, Figure 4 It is the rate performance results of Comparative Example 1 and Examples 17, 18, 19, 20. At 0.1C\0.2C\0.5C\10C, the double doping greatly improves the rate performance of the cathode active material. This is because the large-sized Mn\Ti\Se\Ga expands the ion channels and reduces the sodium ion diffusion energy barrier.

[0136] Among them, Figure 5 It is the rate performance results of Comparative Example 2 and Examples 24, 25, 26, 27. At 0.1C\0.2C\0.5C\10C, the double doping greatly improves the rate performance of the cathode active material.

[0137] Among them, Figure 6 It is the rate performance results of Comparative Example 3 and Examples 28, 29. At 0.1C\0.2C\0.5C\10C, the double doping greatly improves the rate performance of the cathode active material.

[0138] Among them, Figure 7 It is the XRD pattern of the cathode active material of Example 1, Example 24 and Example 28 of the present invention. From the main peak positions and lattice parameters of the materials obtained in Examples 1, 24, 28, combined with the elemental ratio analysis of ICP, the molecular formula of the corresponding example can be obtained, and the phase purity of the material after sintering is high.

[0139] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

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 (P 1-w A w O4) z (P 2-u A u O7), where M is selected from one or more of Fe, Ti, Cr, Mn, Mg, Ca, Zr, Cd, Ni, Cu, Zn; A is selected from one or more of Ga, Sb, Se, Bi; 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, where u and z cannot be 0 at the same time.

2. The positive electrode active material according to claim 1, characterized in that, Among them, 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, Among them, M contains at least Fe and Mg, or at least Fe and Ca, and A is selected from Ga and / or Se.

4. The positive electrode active material according to claim 3, characterized in that, Among them, 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 in M is 2.9 - 3:0.001 - 0.

02.

5. The positive electrode active material according to claim 1, characterized in that, The positive electrode active material has a composition represented by 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 represented by 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 represented by the following general formula: Na x M y (P 1-w A w O4) z (P2O7), where x = 3, y = 2, z = 1, 0 < w ≤ 0.

25.

6. The positive electrode active material according to any one of claims 1 or 5, characterized in that, 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 is 82%-97% after 1200 cycles at 1C, and the initial discharge specific capacity is 82-93 mAh / g at 0.1C.

7. A method for preparing a positive electrode active material according to any one of claims 1 - 6, characterized in that, It includes: (1) Mix 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) Sinter the precursor solution to obtain the positive electrode active material; Among them, M is selected from one or more of Fe, Ti, Cr, Mn, Mg, Ca, Zr, Cd, Ni, Cu, and Zn, and A is selected from one or more of Ga, Sb, Se, and Bi.

8. The preparation method according to claim 7, characterized in that, The sintering specifically is: granulate and sinter the precursor solution to obtain the positive electrode active material.

9. The preparation method according to claim 7, characterized in that, The metal M source material is selected from one or more of metal nitrates, metal oxalates, and metal citrates.

10. The preparation method according to claim 7, characterized in that, The metal A source material is selected from one or more of metal nitrates, metal oxalates, and metal citrates.

11. The preparation method according to claim 7, characterized in that, The sodium source is selected from one or more of sodium carbonate, sodium dihydrogen phosphate, sodium acetate, and sodium nitrate.

12. The preparation method according to claim 7, characterized in that, The phosphorus source is selected from ammonium dihydrogen phosphate and / or hydroxyethylidene diphosphonic acid.

13. The preparation method according to claim 7, characterized in that, The reducing agent is selected from one or more of oxalic acid, citric acid, ascorbic acid, and tartaric acid.

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

15. The preparation method according to claim 7, characterized in that, Pre-sintering is also carried out before the sintering, where the pre-sintering temperature is 260 - 330 °C, and the pre-sintering time is 1 - 5 h.

16. The preparation method according to claim 7, 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).

17. A sodium-ion battery, characterized in that, The sodium ion battery includes the positive electrode active material described in any one of claims 1 - 6 or the positive electrode active material obtained by the preparation method described in any one of claims 7 - 16.

18. An electrical device, characterized in that, It includes the sodium ion battery described in claim 17.

Images