CN114242972B - Nickel-rich high-voltage sodium-ion battery positive electrode material and preparation method and application thereof - Google Patents

Abstract

The present invention belongs to the technical field of sodium ion batteries, and discloses a nickel-rich high-voltage sodium ion positive electrode material, a preparation method thereof, and an application thereof. The general formula of the sodium ion positive electrode material is Na _s Ni _t (PO ₄ )(SO ₄ )/F@M‑C, 2≤s≤4, 0.5≤t≤1.5; M is an oxide of at least one of zinc, nickel, aluminum, manganese, chromium, molybdenum, manganese, copper, and calcium. In the sodium ion positive electrode material of the present invention, a stabilizer is added to strengthen the structural stability of the positive electrode material and improve the cyclic discharge performance of the material; the coating layer in the sodium ion positive electrode material (formed by the tight combination of the metal oxide and the positive electrode material) can stabilize the ion and electron transport kinetics of the material, improve the cyclic performance of the positive electrode material, hinder the material from continuing to agglomerate, and control the particle size.

Description

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

Technical Field

The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a nickel-rich high-voltage sodium ion battery positive electrode material and a preparation method and application thereof.

Background Art

Lithium-ion batteries have satisfactory performance, such as high energy density and excellent cycle life, and are successfully used in mobile electronic devices, transportation electric and energy storage electricity. Currently, thanks to the vigorous development of new energy, there is a greater demand for lithium-ion energy storage devices in the fields of hybrid electric vehicles (HEV), electric vehicles (EV), smart grids, etc. The current problem is that the cost of lithium and materials related to lithium battery manufacturing has risen sharply, leading to an increase in the price of lithium-ion batteries. Therefore, the insufficient resource prospects and uneven distribution of lithium have prompted the research of more sustainable and cost-effective options.

Sodium-ion batteries will 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 0.05V lower than that of lithium. However, the theoretical mass capacity (3860mAh·g ^-1 ) and theoretical volume capacity (2060mAh·cm ^-3 ) of lithium are much higher than those of sodium (1160mAh·g ^-1 ) and theoretical volume capacity (1130mAh·cm ^-3 ). It can be seen that the performance of sodium-ion batteries is inferior to that of lithium-ion batteries. Therefore, since 2001, researchers have conducted a lot of research on improving the electrochemical performance of sodium, such as developing high-performance electrode materials, providing superior working voltage, exploring the decomposition reaction of electrodes in electrolytes and the formation of products, and enhancing electrochemical cycle stability, which will help solve the energy density and life problems of sodium-ion batteries.

In recent years, with the continuous increase in the price of lithium-ion batteries, especially the consumption of lithium resources and the limited global lithium reserves, we will have to face the dilemma of lithium shortage in the future. Studies have found that sodium, which has similar chemical properties to lithium, is very likely to become the next generation of secondary batteries after lithium-ion batteries. However, due to the larger radius of sodium ions and the heavier atomic weight, coupled with the higher standard potential of sodium, it usually leads to poor reversibility and lower energy density. Therefore, sodium-ion batteries usually do not perform as well as lithium-ion batteries. For example, the electrochemical properties of sodium iron phosphate positive electrode materials in terms of capacity, voltage, and cycle capacity are all lower than those of lithium iron phosphate positive electrode materials.

At present, Na ₄ MP ₂ O ₇ (M＝Fe, Co, Mn, Cu, PO4, SO ₄ , CO ₃ ) polyanion cathode material can operate at a high voltage of >3.5V (vsNa ⁺ /Na) and exhibit excellent cycle stability, and is a very promising cathode material. For example, Na ₄ Co ₃ (PO ₄ ) ₂ P ₂ O ₇ provides a capacity of 95 mAh·g ^-1 at a rate of 0.2C in the voltage window of 3.0-4.4 V (vs Na ⁺ /Na), and the capacity retention rate is >95% in 100 cycles; Na ₄ Fe ₃ (PO ₄ ) ₂ (P ₂ O ₇ ) as a positive electrode material for sodium ion batteries releases a reversible capacity of 129 mAh·g ^-1 , and the average operating voltage exceeds 3.2 V (vs Na ⁺ /Na) electrode, but for Na ₄ MPO _4- type sodium ion batteries, low energy density and poor cycle performance are still its biggest shortcomings. The energy density of the battery 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 first operating voltage.

Summary of the invention

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

To achieve the above object, the present invention adopts the following technical solutions:

A sodium ion positive electrode material has a general formula of _NasNit ( _{PO4 )} ( _SO4 )/F@MC, 2≤s≤4, 0.5≤t≤1.5; M is an oxide of at least one of zinc, nickel, aluminum, manganese, chromium, molybdenum, manganese, copper and calcium.

Preferably, the value range of s is 2.5≤s≤3.5, and the value range of t is 0.5≤t≤1.2.

Preferably, the sodium ion positive electrode material has a formula of at least one of Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ -C, Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@CuO-C, and Na ₃ Ni(PO ₄ )(SO ₄ )/F@ZnO-C.

A method for preparing a sodium ion positive electrode material comprises the following steps:

A nickel source solution, a sulfuric acid source, a phosphoric acid source and a fluorine source are mixed, subjected to microwave hydrothermal reaction, and concentrated to obtain a triacid salt precursor;

The triacid precursor is mixed with a sodium source and a stabilizer, and heated to react to obtain Na _s Ni _t (PO ₄ )(SO ₄ )/F;

A sodium washing agent is added to _{the NasNit} ( _PO4 )( _SO4 )/F for impregnation and sintering to obtain the sodium ion positive electrode material.

Preferably, the nickel source solution is obtained by mixing a nickel source with an organic acid.

More preferably, the organic acid is at least one of tartaric acid, oxalic acid, citric acid, formic acid or acetic acid.

Further preferably, the concentration of the organic acid is 0.01-12 wt %.

Further preferably, the nickel source is at least one of nickel sulfate, nickel hydroxide, nickel nitrate, nickel chloride or nickel carbonate.

Preferably, the sulfuric acid source is at least one of sulfuric acid, sodium sulfate, ammonium sulfate, ammonium bisulfate, sodium bisulfate or nickel sulfate.

Preferably, the phosphoric acid source is at least one of phosphoric acid, sodium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate or nickel phosphate.

Preferably, the fluorine source is at least one of ammonium fluoride, potassium fluoride, sodium fluoride or hydrogen fluoride.

Preferably, the temperature of the microwave hydrothermal reaction is 100-300° C., and the time of the microwave hydrothermal reaction is 1-60 min; preferably, the temperature is 120-240° C., and the time is preferably 5-300 min.

Preferably, the concentration further includes infiltrating and drying the triacid precursor.

Preferably, the triacid precursor is ball-milled for 0.5-12 hours before the mixing, and the particle size after ball-milling is less than 50 μm.

Preferably, the sodium source is at least one of sodium hydroxide, sodium citrate, sodium oxalate, sodium acetate, sodium phosphate, sodium sulfate, sodium carbonate or sodium chloride.

Preferably, the stabilizer is at least one of 1,4-phthalic acid, 2,5-dipropoxy-1,4-diacylhydrazide, N,N,N',N'-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine, and 4,4',4-trimethyl-2,2':6',2-terpyridine.

Preferably, the stabilizer is 0.01-5 wt % of the total mass of the triacid salt precursor and the sodium source.

Preferably, the infiltration further includes drying, and the drying temperature is 60-150°C.

Preferably, the heating reaction temperature is 300-800° C., and the heating reaction time is 0.5-24 h.

Preferably, the solid-liquid ratio of _{the NasNit} ( _PO4 )( _SO4 )/F to the sodium washing agent is (0.1-3):(1-5) g/ml.

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

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 by acid salts, and some metal ions are added to hydrolyze and deposit on the surface of the positive electrode material, and then dried and dehydrated to become metal oxides deposited on the surface of the positive electrode material.

Preferably, the sintering temperature is 400-800° C., and the sintering atmosphere is an inert gas.

A battery comprises the sodium ion positive electrode material.

Preferably, the working platform voltage of the battery prepared with the sodium ion positive electrode material during the first discharge is greater than 3.8V.

Compared with the prior art, the beneficial effects of the present invention are as follows:

1. By adding a stabilizer to the sodium ion positive electrode material of the present invention, the structural stability of the positive electrode material is enhanced and the cyclic discharge performance of the material is improved; the coating layer in the sodium ion positive electrode material (after being treated with a sodium washing agent, the metal ions are hydrolyzed and deposited on the surface of the positive electrode material, and after dehydration, they become metal oxides, and the metal oxides are tightly combined with the positive electrode material) can improve the ion and electron transport kinetics of the material, improve the cyclic performance of the positive electrode material, hinder the nickel-rich high-pressure sodium ion positive electrode material from continuing to agglomerate and grow, and control the particle size.

2. In the preparation method of the present invention, the internal particle distribution of the triacid precursor synthesized by the microwave method is more uniform, and the consistency of the electron transfer rate and heat transfer efficiency at various locations in the obtained nickel-rich high-voltage positive electrode material is very high, which is beneficial to the internal structural stability of the material; and then the stabilizer is added to the positive electrode material by utilizing the stable structure and good heat dissipation characteristics of the stabilizer, so as to enhance the structural stability of the positive electrode material and improve the cyclic discharge performance of the material.

3. The present invention utilizes microwaves to synthesize triacid precursors to rapidly heat up during the preparation of nickel-rich high-pressure sodium ion cathode material precursors. Generally, the reaction is complete within 3-20 minutes, so the reaction process is very fast, shortening the reaction time by more than 90%. Furthermore, the synthesis temperature is controlled at 100-300°C, which is much lower than the conventional high-temperature treatment of 400-800°C. Therefore, the microwave synthesis of triacid precursors has a lower reaction temperature. Under a controllable electromagnetic environment, the nucleation and growth of the triacid precursors are accelerated, and the grain morphology is controllable. At the same time, the triacid precursors have better uniformity, which is conducive to the synthesis of materials with high crystallinity and uniform and complete particles.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a process flow chart of preparing a sodium ion positive electrode material according to Example 1 of the present invention;

FIG2 is a schematic diagram of a sodium ion positive electrode material prepared in Example 1 of the present invention;

FIG3 is a SEM image of the sodium ion positive electrode material prepared in Example 1 of the present invention;

FIG. 4 is a TEM image of the sodium ion positive electrode material prepared in Example 1 of the present invention.

DETAILED DESCRIPTION

The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

Example 1

The sodium ion positive electrode material of this embodiment has a formula of Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ -C.

The process flow chart of the sodium ion positive electrode material prepared in this embodiment is shown in Figure 1. In Figure 1, nickel hydroxide is mixed with citric acid to obtain solution A, ammonium sulfate, phosphoric acid, and ammonium fluoride are mixed to obtain solution B, stirred, solution B is added to solution A to obtain solution C, solution C is placed in a ceramic crucible, sent to a microwave reactor, heated and cooled to obtain a triacid precursor. After ball milling, the triacid precursor is evenly mixed with sodium hydroxide and N, N, N', N'-tetrakis (4-methoxyphenyl) -9H-carbazole-3, 6-diamine slurry, and heated to obtain Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ ) / F. Aluminum sulfate is infiltrated with Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ ) / F, heated, and cooled to obtain Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ ) / F @ Al ₂ O ₃ -C.

The specific steps for preparing the sodium ion positive electrode material of this embodiment are as follows:

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

(2) Synthesis of Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled for 7.5 h, and then stirred and mixed evenly 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. The mixture was heated at 300° C. for 8 h in an argon furnace to obtain the sodium ion positive electrode material Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F.

(3) Sodium washing treatment: 4.5 mL of 0.019 mol/L aluminum sulfate was divided into three parts, mixed with 1.5 g of sodium ion positive electrode material Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F, impregnated three times, dried in an oven at 110°C for 10 h overnight, sintered at 470°C for 8 h in an argon environment in a heating furnace, and cooled to obtain the sodium ion positive electrode material - Na _2.6 Ni _1.2 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ -C.

Example 2

The sodium ion positive electrode material of this embodiment has a formula of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@CuO-C.

The preparation method of the sodium ion positive electrode material of this embodiment has the following specific steps:

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

(2) Synthesis of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled to a particle size of <50 μm, and stirred and mixed evenly 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-diacylhydrazine slurry. The mixture was heated at 540°C for 6.5 h in an argon environment in a heating furnace to obtain a sodium ion positive electrode material - Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F.

(3) Sodium washing treatment: 4.5 mL of 0.032 mol/L copper sulfate was divided into three parts, mixed with 1.5 g of sodium ion positive electrode material Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F, impregnated three times, dried in an oven at 150°C for 4 h, sintered at 590°C in an argon environment in a heating furnace for 6.5 h, and cooled to obtain the sodium ion positive electrode material - Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@CuO-C.

Example 3

The sodium ion positive electrode material of this embodiment has the formula of Na ₃ Ni(PO ₄ )(SO ₄ )/F@ZnO-C.

The preparation method of the sodium ion positive electrode material of this embodiment has the following specific steps:

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

(2) Synthesis of Na ₃ Ni(PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled to a particle size of <50 μm, and stirred and mixed evenly 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, and heated at 620° C. for 8 h in an argon furnace to obtain the sodium ion positive electrode material Na ₃ Ni(PO ₄ )(SO ₄ )/F.

(3) Sodium washing treatment: 6 mL of 0.063 mol/L zinc sulfate was divided into three parts, mixed with 2.0 g of sodium ion positive electrode material Na ₃ Ni(PO ₄ )(SO ₄ )/F, impregnated three times, dried in an oven at 125°C for 3 h, sintered at 470°C in an argon environment in a heating furnace for 6.5 h, and cooled to obtain the sodium ion positive electrode material - Na ₃ Ni(PO ₄ )(SO ₄ )/F@ZnO-C.

Comparative Example 1

The sodium ion positive electrode material of this comparative example has a formula of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ .

The preparation method of the sodium ion positive electrode material of this comparative example comprises the following specific steps:

(1) Microwave hydrothermal synthesis of triacid precursor: 1.24 g nickel sulfate was dissolved in 50 mL 5.5 w% citric acid to obtain solution A, 19 mL 0.53 mol/L ammonium sulfate, 16 mL 0.67 mol/L phosphoric acid, and 12 mL 0.18 mol/L ammonium fluoride were mixed to obtain solution B, and 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, heated at 540 °C in an argon environment for 8 h, and then cooled to obtain a triacid precursor.

(2) Synthesis of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled to a particle size of <50 μm, and stirred and mixed evenly 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. The mixture was heated at 540°C for 6.5 h in an argon environment in a heating furnace to obtain a sodium ion positive electrode material - Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/FC.

Comparative Example 2

The sodium ion positive electrode material of this comparative example has a formula of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ .

The preparation method of the sodium ion positive electrode material of this comparative example comprises the following specific steps:

(1) Microwave hydrothermal synthesis of triacid precursor: 1.24 g nickel sulfate was dissolved in 50 mL 5.5 w% citric acid to obtain solution A, 19 mL 0.53 mol/L ammonium sulfate, 1.42 g diammonium hydrogen phosphate, and 12 mL 0.18 mol/L ammonium fluoride were mixed to obtain solution B, and 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, heated at 540 °C in an argon environment for 8 h, and then cooled to obtain a triacid precursor.

(2) Synthesis of Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled to a particle size of <50 μm, mixed evenly with 22.7 mL of 1.5 mol/L sodium hydroxide, and heated at 540°C for 6.5 h in an argon furnace to obtain the sodium ion positive electrode material Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F.

(3) Sodium washing treatment: 6 mL of 0.022 mol/L aluminum sulfate was divided into three parts, mixed and impregnated with 2.0 g of sodium ion positive electrode material Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F for three times, dried in an oven at 95°C to constant weight, sintered at 540°C in an argon environment in a heating furnace for 6.5 h, and then cooled to obtain the sodium ion positive electrode material - Na _3.4 Ni _0.8 (PO ₄ )(SO ₄ )/F@Al ₂ O ₃ .

Comparative Example 3

The sodium ion positive electrode material of this comparative example has a formula of Na ₃ Ni(PO ₄ )(SO ₄ )/F.

The preparation method of the sodium ion positive electrode material of this comparative example comprises the following specific steps:

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

(2) Synthesis of Na ₃ Ni(PO ₄ )(SO ₄ )/F: The triacid precursor was ball-milled to a particle size of <50 μm, mixed evenly with 20 mL of 1.5 mol/L sodium hydroxide, dried in an oven at 125°C for 3 h, and heated at 540°C for 8 h in an argon furnace to obtain the sodium ion positive electrode material - Na ₃ Ni(PO ₄ )(SO ₄ )/F.

Analysis of Examples 1-3 and Comparative Examples 1-3:

The sodium ion positive electrode material, carbon black conductive agent, and polytetrafluoroethylene prepared in Example 1-3 and Comparative Example 1-3 were mixed and dissolved in deionized water at a mass ratio of 80:10:10 to form a slurry, and then coated on aluminum foil to form a pole piece, which was placed in a drying oven and dried at 80°C for 12 hours, and then stamped into a disc by a mold; the disc was cut into a counter electrode pole piece with a diameter of 10 mm; 1.0 mol/L NaClO ₄ was added to the carbonate as an electrolyte, Celgard2400 was used as a diaphragm, and the battery was assembled in a vacuum glove box under an argon atmosphere. The button cell was subjected to AC impedance and cyclic voltammetry tests using an electrochemical workstation, and the button cell was subjected to charge and discharge tests using a LAND battery test system, and the current density of the test was 30 mA·g ^-1 .

Table 1 Battery test data obtained from positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-3

In Table 1, the first discharge capacity of Example 1-3 is 128.3-132.6mAh·g ^-1 , and the platform voltage is 3.8V during the first discharge. The first discharge capacity of Comparative Example 1-3 is 115.6-117.7mAh·g ^-1 , and the platform voltage is 3.6-3.7V during the first discharge. When the 100th discharge, the discharge capacity of Example 1-3 is still 107.5-108.7mAh·g ^-1 , and the first discharge capacity of Comparative Example 1-3 is 89.8-93.2mAh·g ^-1 ; the battery obtained by the positive electrode material prepared in Example 1-3 has higher discharge efficiency in the first, 10th, and 100th times than the battery obtained by the positive electrode material prepared in Comparative Example 1-3. This indicates that the electrochemical performance of the nickel-rich high-pressure sodium ion positive electrode material is improved after microwave hydrothermal treatment, addition of stabilizer, and sodium washing agent infiltration treatment.

From Figures 2 and 4, a layer of aluminum oxide is attached to the surface of the sodium ion positive electrode material prepared in Example 1, which is tightly combined with the sodium ion positive electrode material. The surface of the nickel-rich high-pressure sodium ion positive electrode material in Figure 3 is relatively rough, and the particle size is about 12 μm.

The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims (7)

1. A method for preparing a sodium ion positive electrode material, characterized in that it comprises the following steps: A nickel source solution, a sulfuric acid source, a phosphoric acid source and a fluorine source are mixed, subjected to microwave hydrothermal reaction, and concentrated to obtain a triacid salt precursor; The triacid salt precursor is mixed with a sodium source and a stabilizer, and heated to react to obtain Na _s Ni _t (PO ₄ )(SO ₄ )/F; Adding a sodium washing agent to the Na _s Ni _t (PO ₄ )(SO ₄ )/F for impregnation and sintering to obtain a sodium ion positive electrode material; The general formula of the sodium ion positive electrode material is Na _s Ni _t (PO ₄ ) (SO ₄ )/F@MC; M is at least one oxide of zinc, nickel, aluminum, manganese, chromium, molybdenum, copper, and calcium, wherein 2≤s≤4, 0.5≤t≤1.5; The stabilizer is at least one of 1,4-phthalic acid, 2,5-dipropoxy-1,4-diacylhydrazide, N,N,N',N'-tetrakis(4-methoxyphenyl)-9H-carbazole-3,6-diamine, and 4,4',4-trimethyl-2,2':6',2-terpyridine; The sodium washing agent is at least one of zinc sulfate, nickel sulfate, aluminum sulfate, manganese sulfate, chromium sulfate, molybdenum sulfate, copper sulfate or calcium sulfate; The nickel source solution is obtained by dissolving a 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; the nickel source is at least one of nickel sulfate, nickel hydroxide, nickel nitrate, nickel chloride, or nickel carbonate; The fluorine source is at least one of ammonium fluoride, potassium fluoride, sodium fluoride or hydrogen fluoride. 2. The preparation method according to claim 1 is characterized in that the value range of s is 2.5≤s≤3.5, and the value range of t is 0.5≤t≤1.2. 3. The preparation method according to claim 1, characterized in that the sulfuric acid source is at least one of sulfuric acid, sodium sulfate, ammonium sulfate, ammonium bisulfate, sodium bisulfate or nickel sulfate. 4. The preparation method according to claim 1, characterized in that the phosphate source is at least one of phosphoric acid, sodium phosphate, ammonium phosphate, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, sodium hydrogen phosphate or nickel phosphate. 5. The preparation method according to claim 1, wherein the sodium source is at least one of sodium hydroxide, sodium citrate, sodium oxalate, sodium acetate, sodium phosphate, sodium sulfate, sodium carbonate or sodium chloride. 6. The preparation method according to claim 1, characterized in that the temperature of the microwave hydrothermal reaction is 100-300°C, and the time of the microwave hydrothermal reaction is 1-60 min. 7. A battery, characterized in that it comprises a sodium ion positive electrode material prepared by the preparation method according to claim 1.