Nickel-rich high-voltage sodium-ion positive electrode material for battery, preparation method therefor, and application thereof

Abstract

The present invention relates to the technical field of sodium-ion batteries, and disclosed are a nickel-rich high-voltage sodium-ion positive electrode material, a preparation method therefor, and an

Description

FIELD

[0001] The present disclosure belongs to the technical field of sodium-ion batteries, and specifically relates to a positive electrode material for a nickel-rich high-voltage sodium-ion battery and a preparation method and application thereof. BACKGROUND

[0002] Lithium-ion batteries have satisfactory properties, such as high energy density and excellent cycle life, and are successfully applied in mobile electronic devices, transportation power, and energy storage power. At present, thanks to the vigorous development of new energy sources, there is more demand for lithium battery energy storage equipment in fields such as hybrid electric vehicles (HEV), electric vehicles (EV), and smart grids. The current conundrum is that the sharp rise in the cost of lithium and the materials associated with the manufacture of lithium-ion batteries has led to an increase in the price of lithium-ion batteries. The lack of resource prospects and uneven distribution of lithium, therefore, has prompted research into more sustainable and lower-cost, more efficient options.

[0003] Sodium-ion batteries would be a suitable alternative. Sodium is more abundant in the earth’s crust; the standard redox potential of sodium is only 0.326V higher than that of lithium metal, and its electronegativity is only 0.05 V lower than that of lithium. However, the theoretical mass specific capacity (3860 mAh-g’1) and the theoretical volume specific capacity (2060 mAh-cm’3) of lithium is much higher than the theoretical mass specific capacity (1160 mAh-g1) and the theoretical volume specific capacity (1130 mAh-cm’3) of sodium. It can be seen that the performance of sodium-ion battery is inferior to that of lithium-ion battery. Therefore, since 2001, researchers have carried out a lot of research on improving the electrochemical performance of sodium, such as developing high-performance electrode materials, providing superior operating voltage, ascertaining the decomposition reaction of the electrode in the electrolyte and the formation of products, and enhancing the electrochemical cycle stability, which will be beneficial to solve the problems of energy density and lifespan of sodium-ion batteries.

[0004] In recent years, with the continuous increase in the price of lithium-ion batteries, especially the consumption of lithium resources and not abundant lithium reserves in the world, we will have to face the dilemma of lithium shortage in the future. The study indicates that sodium, which has similar chemical properties to lithium, is very promising to become the next-generation secondary battery after lithium-ion batteries. Nevertheless, because the larger radius of the sodium ions, the heavier the atomic weight, and the higher standard potential of sodium usually leads to poor reversibility and lower energy density, in general the performance of sodium-ion batteries is not as good as that of lithium-ion batteries. For example, the electrochemical performance of sodium iron phosphate positive electrode materials in terms of capacity, voltage, and cycle ability is lower than that of lithium iron phosphate positive electrode materials.

[0005] Currently, Na4MP2O7 (M=Fe, Co, Mn, Cu, PO4, SO4, CO3) polyanionic positive electrode material, capable of operating at high voltages >3.5 V (vs Na+ / Na) and exhibiting excellent cycling stability, is a promising positive electrode material. For example, Na4Co3(PO4)2P2O7 provides a capacity of 95 mAh-g1 at 0.2C rate in the 3.0-4.4 V (vs Na+ / Na) voltage window and a capacity retention of >95% over 100 cycles; Na4Fe3(PO4)2(P2O?), as a positive electrode material for sodium-ion batteries, releases a reversible capacity of 129 mAh-g4, and the average operating voltage exceeds 3.2 V (vs Na+ / Na) electrodes. Nevertheless, for Na4MPO4-type sodium-ion batteries, low energy density and poor cycle performance are still the biggest shortcomings, and the energy density of batteries depends on the specific capacity and operating voltage of the material. Therefore, it is urgent to develop a positive electrode material with high specific capacity and high initial operating voltage. SUMMARY

[0006] The present disclosure aims to solve at least one of the above-mentioned technical problems existing in the prior art. To this end, the present disclosure proposes a nickel-rich high-voltage sodium-ion positive electrode material and a preparation method and application 15 1024 thereof, and the sodium-ion positive electrode material has excellent cycle performance, high specific capacity and an initial operating voltage of up to 3.8V

[0007] To achieve the above object, the present disclosure adopts the following technical solutions: 5

[0008] A preparation method of a sodium-ion positive electrode material having a general formula of NasNit(PO4)(SO4) / F@M-C, wherein M is oxide of at least one of zinc, nickel, aluminum, manganese, chromium, molybdenum, manganese, copper and calcium, and 2<s<4, 0.5<t<1.5, wherein the method comprises steps of:

[0009] mixing a nickel source solution, sulfuric acid source, phosphoric acid source and fluorine 10 source for a microwave hydrothermal reaction, and performing heating to obtain a triacid salt precursor, wherein the nickel source solution is obtained by dissolving nickel source in an organic acid; the organic acid is at least one of tartaric acid, oxalic acid, citric acid, formic acid, and acetic acid; and the nickel source is at least one of nickel sulfate, nickel hydroxide, nickel nitrate, nickel chloride and nickel carbonate; 15

[0010] mixing the triacid salt precursor with sodium source and a stabilizer, and heating for reaction to obtain NasNit(PO4)(SO4) / F; and

[0011] adding a sodium washing agent to the NasNit(PO4)(SO4) / F for soaking, and sintering to obtain the sodium-ion positive electrode material, wherein the sodium washing agent is at least one of zinc sulfate, nickel sulfate, aluminum sulfate, manganese sulfate, chromium sulfate, 20 molybdenum sulfate, copper sulfate and calcium sulfate.

[0012] In an embodiment, a value range of s is 2.5<s<3.5, and a value range of t is 0.5<t<1.2.

[0013] In an embodiment, the sulfuric acid source is at least one of sulfuric acid, sodium sulfate, ammonium sulfate, ammonium hydrogen sulfate, sodium hydrogen sulfate and nickel sulfate.

[0014] In an embodiment, the phosphoric acid source is at least one of phosphoric acid, sodium 25 phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate and nickel phosphate.

[0015] In an embodiment, the fluorine source is at least one of ammonium fluoride, potassium 15 1024 fluoride, sodium fluoride and hydrogen fluoride; the sodium source is at least one of sodium hydroxide, sodium citrate, sodium oxalate, sodium acetate, sodium phosphate, sodium sulfate, sodium carbonate and sodium chloride; the stabilizer is at least one of 1,4-benzenedicarboxylic acid 2,5-dipropoxy- 1,4-dihydrazide, N,N,N’ ,N’ -tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-5 diamine, and 4,4’,4-trimethyl-2,2’:6’,2-terpyridine.

[0016] In an embodiment, a temperature of the microwave hydrothermal reaction is 100-300°C, and a duration of the microwave hydrothermal reaction is 1-60 min; and a solid-liquid ratio of the NasNit(PO4)(SO4) / F to the sodium washing agent is (0.1-3): (1-5) g / ml.

[0017] With respect to the prior art, the present disclosure has the following beneficial effects: 10

[0018] 1. In the sodium-ion positive electrode material of the present disclosure, by adding a stabilizer, the structural stability of the positive electrode material is strengthened and the cyclic discharge performance of the material is improved; the coating layer (after the sodium washing agent treatment, the metal ions are hydrolyzed and deposited on the surface of the positive electrode material, and are dehydrated to become metal ions, and the metal ions tightly combine with the 15 positive electrode material to form the coating layer) in the sodium-ion positive electrode material can improve the ion and electron transport kinetic properties of the material, improve the cycling performance of the positive electrode material, prevent the nickel-rich high-voltage sodium-ion positive electrode material from continuing to agglomerate and grow, and control the particle size.

[0019] 2. In the preparation method of the present disclosure, the internal particle distribution of 20 the triacid salt precursor synthesized by the microwave method is more uniform, and the electron transfer rate and heat transfer efficiency inside the obtained nickel-rich high-voltage

[0031] Preferably, the sodium washing agent is at least one of zinc sulfate, nickel sulfate, aluminum sulfate, manganese sulfate, chromium sulfate, molybdenum sulfate, copper sulfate and calcium sulfate.

[0032] On the one hand, the sodium washing agent can wash away the residual sodium hydroxide on the surface of the positive electrode material, reduce the residual sodium in the positive electrode material, and reduce the side reactions on the surface of the positive electrode material. On the other hand, the sodium ions in the sodium hydroxide on the surface of the positive electrode material are exchanged with acid salts. Some metal ions are added to be hydrolyzed and deposited on the surface of the positive electrode material, dehydrated after drying, and become metal oxides and deposit on the surface of the positive electrode material.

[0033] Preferably, a temperature of the sintering is 400-800°C., and an atmosphere of the sintering is an inert gas.

[0034] A battery, comprising the sodium-ion positive electrode material.

[0035] Preferably, a battery prepared by the sodium-ion positive electrode material has an operating platform voltage of greater than 3.8V during the first discharge.

[0036] With respect to the prior art, the present disclosure has the following beneficial effects:

[0037] 1. In the sodium-ion positive electrode material of the present disclosure, by adding a stabilizer, the structural stability of the positive electrode material is strengthened and the cyclic discharge performance of the material is improved; the coating layer (after the sodium washing agent treatment, the metal ions are hydrolyzed and deposited on the surface of the positive electrode material, and are dehydrated to become metal ions, and the metal ions tightly combine with the positive electrode material to form the coating layer) in the sodium-ion positive electrode material can improve the ion and electron transport kinetic properties of the material, improve the cycling performance of the positive electrode material, prevent the nickel-rich high-voltage sodium-ion positive electrode material from continuing to agglomerate and grow, and control the particle size.

[0038] 2. In the preparation method of the present disclosure, the internal particle distribution of the triacid salt precursor synthesized by the microwave method is more uniform, and the electron transfer rate and heat transfer efficiency inside the obtained nickel-rich high-voltage positive electrode material are of high consistency, which is conducive to the stability of the internal structure of the material. In addition, as a stabilizer is conductive to the stabilized structure and good heat dissipation characteristics, a stabilizer is added to the positive electrode material, so that the stability of the structure of the positive electrode material is strengthened and the cycle discharge performance of the material is improved.

[0039] 3. In the present disclosure, during the preparation of a precursor of the nickel-rich high-voltage sodium-ion positive electrode material, the triacid salt precursor is synthesized using micro wave, in which the temperature rises rapidly, and the reaction is generally completed within 3-20 minutes. Therefore, the reaction process is very fast and the reaction time is shortened by more than 90%. In addition, the synthesis temperature is controlled at 100-300°C, which is much lower than the conventional high-temperature treatment of 400-800°C, so the reaction temperature of microwave synthesis of triacid salt precursors is lower. In a controlled electromagnetic environment, the crystal nucleation and growth of the triacid salt precursor are accelerated, the grain morphology is controllable, and the uniformity of the triacid salt precursor is good, which is conducive to the synthesis of a material with high crystallinity and uniform and complete particles. BRIEF DESCRIPTION OF DRAWINGS

[0040] FIG. 1 is a process flow diagram of preparing a sodium-ion positive electrode material in Example 1 of the present disclosure;

[0041] FIG. 2 is a schematic diagram of the sodium-ion positive electrode material prepared in Example 1 of the present disclosure;

[0042] FIG. 3 is an SEM image of the sodium-ion positive electrode material prepared in Example 1 of the present disclosure;

[0043] FIG. 4 is a TEM image of the sodium-ion positive electrode material prepared in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0044] The concept of the present disclosure and the technical effects produced thereby will be clearly and completely described below in conjunction with the examples, so as to fully understand the purpose, characteristics and effects of the present disclosure. Obviously, the described examples are only a part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments of the present disclosure, other embodiments obtained by those skilled in the art without creative efforts are all within the scope of protection of the present disclosure. Example 1

[0045] The sodium-ion positive electrode material of this example has a formula of Na2.6Nii.2(PO4)(SO4) / F@Al2O3-C.

[0046] The process flow diagram of the sodium-ion positive electrode material prepared in this example is shown in FIG. 1. In FIG. 1, nickel hydroxide and citric acid were mixed to obtain solution A; ammonium sulfate, phosphoric acid, and ammonium fluoride were mixed to obtain solution B; under stirring, solution B was added to solution A to obtain solution C; and solution C was placed in a ceramic crucible, sent to a microwave reactor, heated and cooled to obtain a triacid salt precursor. After ball-milling the tri acid salt precursor, it was mixed with sodium hydroxide, N,N,N’,N’-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine slurry evenly, and the mixture was heated to obtain Na2.6Nii.2(PO4)(SO4) / F. Aluminum sulfate and Na2.6Nii.2(PO4)(SO4) / F were soaked, heated and cooled to obtain Na2.6Nii.2(PO4)(SO4) / F@Al2O3-C.

[0047] The specific steps for the preparation of the sodium-ion positive electrode material in this example are as follows:

[0048] (1) Microwave hydrothermal synthesis of tri acid salt precursor: 1.12 g of nickel hydroxide was mixed with 150 mL of 5.5w% citric acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 14.9 mL of 0.67 mol / L phosphoric acid, and 9 mL of 0.17 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 20 mL of solution C was taken and placed in a ceramic crucible, which was sent to a microwave reactor filled with argon gas at 350W. The microwave reactor was set as follows: the first stage was heating at 110C and stable evaporation for 6 min, the second stage was heating at 275°C and stable evaporation for 25 min, the heating time between the two stages was 180 s, and the temperature was lowered. A triacid salt precursor was obtained.

[0049] (2) Synthesis of Na2.6Nii.2(PO4)(SO4) / F: After ball-milling the triacid salt precursor for 7.5 h, it was mixed with 17.5 mL of 1.5 mol / L sodium hydroxide and 18 mL of 1.66 wt% N,N,N’,N’-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine slurry evenly under stirring. The mixture was heated in a heating furnace at 300°C for 8h under the argon atmosphere to obtain a sodium-ion positive electrode material Na2.6Nii.2(PO4)(SO4) / F.

[0050] (3) Sodium washing treatment: 4.5 mL of 0.019 mol / L aluminum sulfate was divided into three equal parts, mixed with 1.5 g of sodium-ion positive electrode material Na2.6Nii.2(PO4)(SO4) / F. The mixture was soaked for three times, and dried in an oven at 110°C for 10 h overnight. It was sintered in the heating furnace at 470°C for 8 h under the argon atmosphere, and cooled to obtain a sodium-ion positive electrode material—Na2.6Nii.2(PO4)(SO4) / F@Al2O3-C. Example 2

[0051] The sodium-ion positive electrode material of this example has a formula of Na3.4Nio.s(P04)(S04) / F@CuO-C.

[0052] The specific steps for the preparation of the sodium-ion positive electrode material in this example are as follows:

[0053] (1) Microwave hydrothermal synthesis of triacid salt precursor: 1.24 g of nickel sulfate was dissolved in 150 mL of 7.1 w% oxalic acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 1.33 g of diammonium hydrogen phosphate, and 12 mL of 0.18 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 20 mL of solution C was taken and placed in a ceramic crucible, which was sent to a microwave reactor filled with argon gas at 500W. The micro wave reactor was set as follows: the first stage was heating at 115°C and stabilization for 3 min, the second stage was heating at 240°C and stabilization for 20 min, the heating time between the two stages was 180 s, and the temperature was lowered. A triacid salt precursor was obtained.

[0054] (2) Synthesis of Na3.4Nio.s(P04)(S04) / F: After ball-milling the triacid salt precursor to a particle size of <50 pm, it was mixed with 22.7 mL of 1.5 mol / L sodium hydroxide and 18 mL of 1.5 wt% 1.4-benzenedicarboxylic acid 2,5-dipropoxy-1,4-dihydrazide slurry evenly under stirring. The mixture was heated in a heating furnace at 540°C for 6.5h under the argon atmosphere to obtain a sodium-ion positive electrode material Na3.4Nio.s(P04)(S04) / F.

[0055] (3) Sodium washing treatment: 4.5 mL of 0.032 mol / L copper sulfate was divided into three equal parts, mixed with 1.5 g of sodium-ion positive electrode material Na3.4Nio.s(P04)(S04) / F. The mixture was soaked for three times, and dried in an oven at 150'C for 4 h. It was sintered in the heating furnace at 590°C for 6.5 h under the argon atmosphere, and cooled to obtain a sodium-ion positive electrode material—Na3.4Nio.8(P04)(S04) / F@CuO-C. Example 3

[0056] The sodium-ion positive electrode material of this example has a formula of Na3Ni(PO4)(SO4) / F@ZnO-C.

[0057] The specific steps for the preparation of the sodium-ion positive electrode material in this example are as follows:

[0058] (1) Microwave hydrothermal synthesis of triacid salt precursor: 1.3 g of nickel chloride was dissolved in 500 mL of 0.317mol / Lw% citric acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 1.33 g of di ammonium hydrogen phosphate, and 17 mL of 0.18 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 200 mL of solution C was taken and placed in a ceramic crucible, which was sent to a microwave reactor filled with argon gas at 350W. The microwave reactor was set as follows: the first stage was heating at 115°C and stable evaporation for 3 min, the second stage was heating at 275°C and stable evaporation for 20 min, the heating time between the two stages was 180 s, and the temperature was lowered. A triacid salt precursor was obtained.

[0059] (2) Synthesis of Na3Ni(PO4)(SO4) / F: After ball-milling the triacid salt precursor to a particle size of <50 pm, it was mixed with 20 mL of 1.5 mol / L sodium hydroxide and 22 mL of 1.5 wt% 4,4’,4-trimethyl-2,2’:6’,2-terpyridine slurry evenly under stirring. The mixture was heated in a heating furnace at 620°C for 8h under the argon atmosphere to obtain a sodium-ion positive electrode material Na3Ni(PO4)(SO4) / F.

[0060] (3) Sodium washing treatment: 6 mL of 0.063 mol / L zinc sulfate was divided into three equal parts, mixed with 2.0 g of sodium-ion positive electrode material Na3Ni(PO4)(SO4) / F. The mixture was soaked for three times, and dried in an oven at 125°C for 3 h. It was sintered in the heating furnace at 470°C for 6.5 h under the argon atmosphere, and cooled to obtain a sodium-ion positive electrode material—Na3Ni(PO4)(SO4) / F@ZnO-C. Comparative Example 1

[0061] The sodium-ion positive electrode material of this comparative example has a formula of Na3.4Nio.8(P04)(S04) / F@ AI2O3.

[0062] The specific steps for the preparation of the sodium-ion positive electrode material in this comparative example are as follows:

[0063] (1) Microwave hydrothermal synthesis of triacid salt precursor: 1.24 g of nickel sulfate was dissolved in 50 mL of 5.5w% citric acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 16 mL of 0.67 mol / L phosphoric acid, and 12 mL of 0.18 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 200 mL of solution C was taken and placed in a ceramic crucible, which was heated at 540°C for 8 h under argon atmosphere and cooled to obtain a triacid salt precursor.

[0064] (2) Synthesis of Na3.4Nio.s(P04)(S04) / F: After ball-milling the triacid salt precursor to a particle size of <50 pm, it was mixed with 22.7 mL of 1.5 mol / L sodium hydroxide and 18 mL of 1.5 wt% 4,4’,4-trimethyl-2,2’:6’,2-terpyridine slurry evenly under stirring. The mixture was heated in a heating furnace at 540°C for 6.5h under the argon atmosphere to obtain a sodium-ion positive electrode material—Na3.4Nio.8(P04)(S04) / F-C. Comparative Example 2

[0065] The sodium-ion positive electrode material of this comparative example has a formula of Na3.4Nio.8(P04)(S04) / F@ AI2O3.

[0066] The specific steps for the preparation of the sodium-ion positive electrode material in this comparative example are as follows:

[0067] (1) Microwave hydrothermal synthesis of triacid salt precursor: 1.24 g of nickel sulfate was dissolved in 50 mL of 5.5w% citric acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 1.42 g of di ammonium hydrogen phosphate, and 12 mL of 0.18 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 200 mL of solution C was taken and placed in a ceramic crucible, which was heated at 540°C for 8 h under argon atmosphere and cooled to obtain a triacid salt precursor.

[0068] (2) Synthesis of Na3.4Nio.8(P04)(S04) / F: After ball-milling the triacid salt precursor to a particle size of <50 pm, it was mixed with 22.7 mL of 1.5 mol / L sodium hydroxide evenly under stirring. The mixture was heated in a heating furnace at 540°C for 6.5h under the argon atmosphere to obtain a sodium-ion positive electrode material Na3.4Nio.s(P04)(S04) / F.

[0069] (3) Sodium washing treatment: 6 mL of 0.022 mol / L aluminum sulfate was divided into three equal parts, mixed with 2.0 g of sodium-ion positive electrode material Na3.4Nio.s(P04)(S04) / F. The mixture was soaked for three times, and dried in an oven at 95°C to constant weight. It was sintered in the heating furnace at 540°C for 6.5 h under the argon atmosphere, and cooled to obtain a sodium-ion positive electrode material—Na3 4Nio.8(P04)(S04) / F@A1203. Comparative Example 3

[0070] The sodium-ion positive electrode material of this comparative example has a formula of Na3Ni(PO4)(SO4) / F.

[0071] The specific steps for the preparation of the sodium-ion positive electrode material in this comparative example are as follows:

[0072] (1) Microwave hydrothermal synthesis of triacid salt precursor: 1.55 g of nickel sulfate was dissolved in 50 mL of 5.5w% citric acid to obtain solution A. 19 mL of 0.53 mol / L ammonium sulfate, 1.53 g of diammonium hydrogen phosphate, and 12 mL of 0.18 mol / L ammonium fluoride were mixed to obtain solution B. Under stirring, solution B was gradually added dropwise to solution A to obtain solution C. 200 mL of solution C was taken and placed in a ceramic crucible, which was sent to a microwave reactor filled with argon gas at 350W. The microwave reactor was set as follows: the first stage was heating at 90°C and stable evaporation for 6 min, the second stage was heating at 275°C and stable evaporation for 25 min, the heating time between the two stages was 180 s, and the temperature was lowered. A triacid salt precursor was obtained.

[0073] (2) Synthesis of Na3Ni(PO4)(SO4) / F: The triacid salt precursor was ball-milled to a 5 particle size of <50 pm, mixed with 20 mL of 1.5 mol / L sodium hydroxide, and dried in an oven at 125°C for 3h. The mixture was heated in a heating furnace at 540°C for 8h under the argon atmosphere to obtain a sodium-ion positive electrode material—Na3Ni(PO4)(SO4) / F. Analysis of Examples 1-3 and Comparative Examples 1-3: 10 CO 15

[0074] The sodium-ion positive electrode material prepared in Examples 1-3 and Comparative Examples 1-3, carbon black conductive agent, and polytetrafluoroethylene were mixed and dissolved in deionized water in a mass ratio of 80:10:10 to prepare a slurry, which was then coated on aluminum foil to form electrode sheet. The electrode sheet was placed in a drying box to dry at 80°C for 12 h, and stamped into a disc in a mold. The disc was cut into a counter electrode sheet with a diameter of 10 mm. 1.0 mol / L NaC104 as electrolyte was added to carbonate. Celgard(RTM)2400 was used as separator. The battery was assembled in a vacuum glove box under argon atmosphere. The AC impedance and cyclic voltammetry of the button battery were tested by electrochemical workstation, and the charge and discharge of the button battery was tested by the LAND battery test system. The current density of the test was 30 mA g'1. Table 1 Test data of battery obtained from the positive electrode materials prepared in Examples 20 1-3 and Comparative Examples 1-3 Sample Discharge Capacity (mAhg'1) Discharge Efficiency (%) Operating Platform Voltage at First Discharge (V) 1st 10th 100th 1st 10th 100th Example 1 132.6 121.3 108.7 98.2 89.9 80.5 3.8 Example 2 131.4 122.9 108.2 97.3 91.3 80.1 3.8 Example 3 128.3 119.8 107.5 95.1 88.7 79.6 3.8 Comparative Example 1 117.7 110.8 91.3 92.7 87.2 71.9 3.7 Comparative Example 2 117.5 109.1 93.2 92.5 86.3 70.8 3.6 Comparative Example 3 115.6 107.6 89.8 91.0 88.0 73.5 3.7 15 1024

[0075] In Table 1, the first discharge capacity of Examples 1-3 was 128.3-132.6 mAh-g4 and the platform voltage at the first discharge was 3.8V, whereas the first discharge capacity of Comparative Examples 1-3 was 115.6-117.7 mAhg4 and the platform voltage at the first discharge 5 was 3.6-3.7V. In addition, at the 100th discharge; the discharge capacity of Examples 1-3 was still 107.5-108.7 mAh g'1, and the first discharge capacity of Comparative Examples 1-3 was 89.8-93.2 mAh g'1. The discharge efficiency of the battery obtained from the positive electrode material prepared in Examples 1-3 was also higher than that of the battery obtained from the positive electrode material prepared in Comparative Examples 1-3 in the first, 10th, and 100th discharge, 10 respectively. It shows that the electrochemical performance of nickel-rich high-voltage sodium-ion positive electrode material has been improved after microwave hydrothermal treatment, addition of stabilizer, and soaking with sodium washing agent.

[0076] From FIG. 2 and FIG. 4, the surface of the sodium-ion positive electrode material prepared in Example 1 was coated with a layer of aluminium oxide, which was closely combined 15 with the sodium-ion positive electrode material. In FIG. 3, the surface of the nickel-rich high- voltage sodium-ion positive electrode material was relatively rough, and the particle size was about 12 pm.

[0077]

Claims

26 06 241. A preparation method of a sodium-ion positive electrode material having a general formula 5 of NasNit(PO4)(SO4) / F@M-C, wherein M is oxide of at least one of zinc, nickel, aluminum, manganese, chromium, molybdenum, manganese, copper and calcium, and 2<s<4, 0.5<t<1.5, wherein the method comprises steps ofmixing a nickel source solution, sulfuric acid source, phosphoric acid source and fluorine source for a microwave hydrothermal reaction, and performing heating to obtain a triacid salt 10 precursor, wherein the nickel source solution is obtained by dissolving nickel source in an organic acid; the organic acid is at least one of tartaric acid, oxalic acid, citric acid, formic acid, and acetic acid; and the nickel source is at least one of nickel sulfate, nickel hydroxide, nickel nitrate, nickel chloride and nickel carbonate;mixing the triacid salt precursor with sodium source and a stabilizer, and heating for reaction 15 to obtain NasNit(PO4)(SO4) / F; andadding a sodium washing agent to the Na,Nit(PO4)(SO4) / F for soaking, and sintering to obtain the sodium-ion positive electrode material, wherein the sodium washing agent is at least one of zinc sulfate, nickel sulfate, aluminum sulfate, manganese sulfate, chromium sulfate, molybdenum sulfate, copper sulfate and calcium sulfate.

202. The preparation method according to claim 1, wherein a value range of s is 2.5<s<3.5, and a value range of t is 0.5<t<l .2.

3. The preparation method according to claim 1 or 2, wherein the sulfuric acid source is at 25 least one of sulfuric acid, sodium sulfate, ammonium sulfate, ammonium hydrogen sulfate, sodium hydrogen sulfate and nickel sulfate.

4. The preparation method according to claim 1 or 2, wherein the phosphoric acid source is at least one of phosphoric acid, sodium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate and nickel phosphate.5 5. The preparation method according to claim 1 or 2, wherein the fluorine source is at leastone of ammonium fluoride, potassium fluoride, sodium fluoride and hydrogen fluoride; the sodium source is at least one of sodium hydroxide, sodium citrate, sodium oxalate, sodium acetate, sodium phosphate, sodium sulfate, sodium carbonate and sodium chloride; the stabilizer is at least one of 1,4-benzenedicarboxylic acid 2,5-dipropoxy-l,4-dihydrazide, N,N,N’,N’-tetrakis(4-10 methoxyphenyl)-9H-carbazole-3,6-diamine, and 4,4’,4-trimethyl-2,2’:6’,2-terpyridine.

6. The preparation method according to claim 1 or 2, wherein a temperature of the microwave hydrothermal reaction is 100-300°C, and a duration of the microwave hydrothermal reaction is 1-60 mm; and a solid-liquid ratio of the NasNit(PO4)(SO4) / F to the sodium washing agent is (0.1-3):15 (1-5) g / ml.26 06 24

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