A surface modification method of a sodium-ion battery cathode material and a sodium-ion battery cathode material

Abstract

The application provides a surface modification method of a sodium ion battery positive electrode material and the sodium ion battery positive electrode material. After sintering preparation of the positive electrode material, surface modification is performed on the sodium ion battery positive electrode material by using chlorosulfonic acid and liquid nitrogen, residual alkali on the surface of the material is eliminated, moderate surface defects are introduced, active sites are increased, and the electrochemical characteristics of the electrode material are improved. The modified sodium ion battery positive electrode material obtained by the application has more excellent charge-discharge efficiency and cycle stability, the method has the advantages of simple process and low cost, and can meet the demand of large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of sodium ion batteries, in particular to a surface modification method of a sodium ion battery cathode material and a sodium ion battery cathode material. BACKGROUND

[0002] Sodium ion batteries have attracted extensive attention due to their low cost and abundant resources, and have become a potential alternative for large-scale energy storage, especially in the context of growing demand for clean energy and sustainable development. However, sodium ion batteries still lag behind commercialized lithium ion batteries in terms of energy density and cycle life. During charging and discharging, the cathode material undergoes volume changes due to the insertion and extraction of sodium ions, which easily leads to structural damage and performance degradation, and further causes sodium ion loss, thereby affecting energy density and cycle stability. Therefore, reducing Na + loss is crucial for practical applications.

[0003] Introducing sodium compensation additives to the cathode is a direct and effective method to supplement Na + . The ideal additive should meet the requirements of high capacity utilization, appropriate decomposition voltage, and controllable gas release. Although a variety of sodium compensation additives such as Na2C4O4, Na2CO3, NaN3, etc. have been developed recently, many still face the bottlenecks of continuous gas generation, severe residue after decomposition, and inappropriate oxidation potential, which hinder the improvement of energy density and pose safety hazards. Therefore, developing effective sodium compensation measures is of great significance for the further industrialization of sodium ion batteries.

[0004] Using layered oxides as sodium compensation agents for sodium ion batteries can effectively improve performance, but poor air stability is a major problem. When exposed to air, residual alkali is easily formed on the surface of layered oxides, which reduces the electrochemical activity. Therefore, effective surface treatment measures need to be taken to enhance its stability and improve the electrochemical performance. Through surface modification, such as coating a protective layer or chemical treatment, surface impurities can be removed and the interface characteristics of the material can be improved, thereby optimizing the performance of layered oxides in batteries and ensuring their reliability and durability in practical applications. SUMMARY

[0005] To solve the above problems, the present application provides a surface modification method of a sodium ion battery cathode material and a sodium ion battery cathode material, which uses chlorosulfonic acid and liquid nitrogen to modify the surface of the sodium ion battery cathode material, solving the technical problems of residual alkali formation on the surface of layered oxides and improving battery performance.

[0006] To achieve the above purpose, the present application proposes the following technical solution: a surface modification method of a sodium ion battery cathode material, comprising the following steps,

[0007] S1. The nickel-iron-manganese hydroxide precursor is mixed with a sodium source by ball milling, and then sintered in an oxidizing atmosphere to obtain a mixture powder, and the mixture powder is heat-treated in a tube furnace to obtain the positive electrode material;

[0008] S2. The obtained positive electrode material is placed in a polytetrafluoroethylene container, and chlorosulfonic acid is added in an amount of 1-5% of the mass of the positive electrode material, and the surface is etched by reacting for 10-30 min, and then liquid nitrogen is immediately added in a ratio of 1:1-1:1.5 to the amount of chlorosulfonic acid added.

[0009] S3. After the liquid nitrogen is volatilized, the reaction mixture is taken out and washed, and then dried to obtain the surface-modified sodium-ion battery positive electrode material.

[0010] Preferably, in step S1, the sodium source is selected from one or more of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate, and sodium acetate; the chemical formula of the nickel-iron-manganese hydroxide precursor is Ni a Fe b Mn c (OH)2, wherein 0

[0011] Preferably, in step S1, the ball milling is performed at a speed of 300-600 rpm for 8-10 h.

[0012] Preferably, in step S1, the heat treatment is performed by placing the mixture powder in an oven at 400-500℃ for 3-6 h, then heating to 750-950℃, and holding for 10-20 h, and the sintering process is performed in an oxygen atmosphere at a heating rate of 3-5℃ / min.

[0013] Preferably, the nickel-iron-manganese hydroxide precursor is prepared by a co-precipitation method.

[0014] Preferably, the preparation method of the nickel-iron-manganese hydroxide precursor comprises the following steps:

[0015] (1) A mixed metal salt solution of nickel, iron, and manganese, an alkali solution, and an ammonia solution are passed into a reaction kettle in parallel flow, heated and stirred to perform a co-precipitation reaction, and a reaction slurry is obtained;

[0016] (2) The reaction slurry is aged, solid-liquid separated, washed, and dried to obtain a precursor material.

[0017] Preferably, in step (1), the temperature of the co-precipitation reaction system is controlled at 60-80℃, the pH is 8-13, the stirring speed is 400-1000 r / min, and the ammonia concentration is 10-20 g / L.

[0018] The application provides the sodium ion battery positive electrode material obtained by the method.

[0019] The application also provides a sodium ion battery comprising the sodium ion battery positive electrode material obtained by the method.

[0020] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0021] In the sintering process of NaNi a Fe b Mn c O2, after the sintering is completed, the positive electrode material is cooled to a specified temperature in the furnace, then reacts with chlorosulfonic acid to eliminate residual alkali on the surface of the material, and then the degree of reaction with liquid nitrogen is controlled. The treatment of chlorosulfonic acid introduces moderate surface defects, increases active sites, and improves the electrochemical properties of the electrode material. The addition amount of chlorosulfonic acid is 1% to 5% of the mass of the layered oxide material. When the concentration is low, the chlorosulfonic acid mainly optimizes the surface properties of the material by removing surface impurities and introducing moderate defects. When the concentration is high, the reaction intensity is significantly enhanced, which may lead to excessive corrosion. Therefore, combined with liquid nitrogen cooling, the reaction process can be accurately controlled to adjust the intensity and depth of the reaction, precisely control the formation of surface defects, and avoid excessive damage to the material.

[0022] The modified sodium ion battery positive electrode material obtained by the application has more excellent charge-discharge efficiency and cycle stability, the method has the advantages of simple process and low cost, and can meet the demand of large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 X-ray diffraction pattern of the sample prepared in Example 1;

[0024] Figure 2 Surface SEM image of the sample prepared in Example 1;

[0025] Figure 3 Cross-sectional SEM image of the sample prepared in Example 1;

[0026] Figure 4 XPS image of Ni 2p of Example 1;

[0027] Figure 5 SEM image of the cross section of the sample prepared in Comparative Example 1;

[0028] Figure 6 Cycle curve of the battery assembled by the positive electrode material of Example 1 and Comparative Example 1 at a current density of 130 mA / g;

[0029] Figure 7Surface SEM image of the sample prepared for Comparative Example 2;

[0030] Figure 8 X-ray diffraction pattern of the positive electrode material prepared for Comparative Example 2;

[0031] Figure 9 Cycle curve graph of the battery assembled with the positive electrode material prepared for Comparative Example 2 at a current density of 130 mA / g;

[0032] Figure 10 Cycle curve graph of the battery assembled with the positive electrode material prepared for Example 2 at a current density of 130 mA / g;

[0033] Figure 11 Cycle curve graph of the battery assembled with the positive electrode material prepared for Example 3 at a current density of 130 mA / g;

[0034] Figure 12 XPS pattern of the sample Ni treated with sulfuric acid for Comparative Example 3;

[0035] Figure 13 XPS pattern of the sample Ni treated with hydrochloric acid for Comparative Example 3;

[0036] Figure 14 Cycle curve graph of the battery assembled with the positive electrode material prepared for Comparative Example 3 treated with sulfuric acid at a current density of 130 mA / g;

[0037] Figure 15 Cycle curve graph of the battery assembled with the positive electrode material prepared for Comparative Example 3 treated with hydrochloric acid at a current density of 130 mA / g;

[0038] Figure 16 Cross-sectional SEM image of the sample prepared for Comparative Example 2;

[0039] Figure 17 XPS pattern of the sample Ni treated with chlorosulfonic acid for Example 3. DETAILED DESCRIPTION

[0040] For the purpose of better illustrating the object, technical scheme and advantages of the present application, the present application will be further described below in conjunction with specific examples.

[0041] Example 1

[0042] (1) A soluble mixed metal sulfate solution of nickel, iron and manganese was prepared according to the molar ratio of Ni:Fe:Mn = 1:1:1, wherein the total metal ion molar concentration of nickel, iron and manganese was 2.5 mol / L;

[0043] (2) prepare a 5 mol / L sodium hydroxide solution and a 6 mol / L ammonia solution;

[0044] (3) the mixed metal salt solution, the sodium hydroxide solution and the ammonia water are added into the reaction kettle in parallel flow, the flow rates are 1 L / h, 2 L / h and 0.5 L / h respectively, the pH value is controlled to be 10, the reaction temperature is 60℃, the stirring speed is 500 r / min, the ammonia concentration is 15 g / L, after the addition of the mixed metal salt solution is completed, the addition of the sodium hydroxide solution and the ammonia water is stopped, and the stirring is continued, the reaction stirring and aging is carried out for 10 h, and then the reaction is stopped;

[0045] (4) the slurry obtained by the reaction is filtered, washed with pure water for multiple times, and dried in a 120℃ oven to obtain a precursor material;

[0046] (5) the obtained precursor material is mixed with sodium carbonate at a molar ratio of 1:1.15. The ball milling speed is 400 rpm, and the ball milling time is 8 h.

[0047] (6) after the ball milling is completed, the mixture powder is placed in a tube furnace and heated at 400℃ for 4 h, and then heated to 800℃ and kept for 12 h. The heating rate during the sintering process is 5℃ / min, and the heat treatment is carried out in an oxygen atmosphere. The material obtained after sintering is a layered oxide material.

[0048] (7) the sintered material is placed in a polytetrafluoroethylene container, and then chlorosulfonic acid is added. The addition amount of chlorosulfonic acid is 1% of the mass of the layered oxide material, and the reaction is carried out for 25 min.

[0049] (8) after the reaction is completed, liquid nitrogen is added. The ratio of the addition amount of liquid nitrogen to the addition volume of chlorosulfonic acid is 1:1.

[0050] (9) after the liquid nitrogen is volatilized, the obtained powder is the sample.

[0051] Figure 1 The X-ray diffraction pattern of the sample prepared in Example 1 shows that the material has an O3 type structure. Figure 2 The SEM image of the sample prepared in Example 1 shows that the positive electrode composite material is spherical, has strip-shaped cracks on the surface, and the diameter is about 3-5 μm. The sample is etched by argon ion beam cross-section grinding technology at an etching rate of 700 μm / h, and the cross-section of the sample is obtained. The cross-section SEM image of the sample is obtained by SEM testing Figure 3 The cross-section SEM image shows that there is no crack in the material. Figure 3 Figure 4 The XPS diagram of Ni 2p of Example 1 shows that the proportion of Ni is 33.29%. 3+

[0052] Comparative Example 1​​

[0053] (1) A soluble mixed metal sulfate solution of nickel, iron, and manganese is prepared according to a molar ratio of Ni:Fe:Mn = 1:1:1, wherein the total molar concentration of metal ions of nickel, iron, and manganese is 2.0 mol / L;

[0054] (2) A 6 mol / L sodium hydroxide solution and an 8 mol / L ammonia solution are prepared;

[0055] (3) The mixed metal salt solution, the sodium hydroxide solution, and the ammonia water are added into a reaction kettle in parallel flow at flow rates of 1 L / h, 2 L / h, and 0.5 L / h, respectively, the pH value is controlled at 11, the reaction temperature is 60°C, the stirring speed is 550 r / min, the ammonia concentration is 15 g / L, after the addition of the mixed metal salt solution is completed, the addition of the sodium hydroxide solution and the ammonia water is stopped, and the stirring is continued, the reaction is aged for 12 h, and the reaction is stopped;

[0056] (4) The slurry obtained by the reaction is filtered, washed with pure water multiple times, and dried in an oven at 120°C to obtain a precursor material;

[0057] (5) The precursor material obtained is mixed with sodium carbonate at a molar ratio of 1:1.05. The ball milling speed is 500 rpm, and the ball milling time is 10 h.

[0058] (6) After the ball milling is completed, the mixture powder is placed in a tube furnace and heated at 450°C for 5 h, and then heated to 850°C and kept for 15 h. The heating rate during the sintering process is 4°C / min, and the heat treatment is performed in an oxygen atmosphere.

[0059] (7) The sintered material is placed in a polytetrafluoroethylene container, and chlorosulfonic acid is immediately added. The amount of chlorosulfonic acid added is 3% of the mass of the layered oxide material, and the reaction is performed for 15 min. The powder obtained after the reaction is completed is the sample. The material obtained after sintering is the desired layered oxide material.

[0060] Figure 5 The SEM image of the cross section of the sample prepared for Comparative Example 1 is shown in the figure. It can be seen from the figure that the positive electrode composite material is spherical, has cracks inside, and the diameter is about 3-5 μm. Compared with Example 1, it shows that liquid nitrogen treatment is beneficial to inhibit the further reaction of chlorosulfonic acid to avoid damaging the material structure.

[0061] The positive electrode materials prepared in Example 1 and Comparative Example 1 are respectively prepared into positive electrode sheets, metal sodium is used as the negative electrode, and a button cell is assembled. The button cell is subjected to charge and discharge test at 25°C in a voltage range of 2V-4V.

[0062] Figure 6The cycle curve of the battery assembled by the positive electrode material of Example 1 and the positive electrode material of Comparative Example 1 at a current density of 130 mA / g is shown in the figure. Figure 6 It can be seen that the cycle performance of the battery assembled by the positive electrode material prepared in Example 1 is better than that of the battery assembled by the positive electrode material prepared in Comparative Example 1. After 100 cycles, the specific capacity of the battery assembled by the positive electrode material of Example 1 is 99.7 mAh / g, and the capacity retention rate is 91.1%; while the specific capacity of the battery assembled by the positive electrode material of Comparative Example 1 is 82.3 mAh / g, and the capacity retention rate is only 73.6%. The above results show that the performance of the modified positive electrode material is obviously improved.

[0063] Comparative Example 2

[0064] (1) A soluble mixed metal sulfate solution of nickel, iron and manganese was prepared according to the molar ratio of Ni:Fe:Mn = 1:1:1, wherein the total metal ion molar concentration of nickel, iron and manganese was 3.0 mol / L;

[0065] (2) A 5 mol / L sodium hydroxide solution and an 8 mol / L ammonia solution were prepared;

[0066] (3) The mixed metal salt solution, the sodium hydroxide solution and the ammonia were added into the reaction kettle in parallel flow, the pH value was controlled at 11, the reaction temperature was 65℃, the stirring speed was 500 r / min, the ammonia concentration was 12 g / L, and after the addition of the mixed metal salt solution was completed, the addition of the sodium hydroxide solution and the ammonia was stopped, and the stirring was continued, the reaction was aged for 12 h, and the reaction was stopped;

[0067] (4) The slurry obtained by the reaction was filtered, washed with pure water for several times, and dried in an oven at 120℃ to obtain a precursor material;

[0068] (5) The precursor material obtained was mixed with sodium carbonate at a molar ratio of 1:1.20. The ball milling speed was 550 rpm, and the ball milling time was 10 h.

[0069] (6) After the ball milling was completed, the mixture powder was placed in a tube furnace and heated at 500℃ for 6 h, and then heated to 950℃ and kept for 18 h. The heating rate during sintering was 3℃ / min, and the heat treatment was carried out in an oxygen atmosphere. After the sintering was completed, the sample was immediately cooled to room temperature.

[0070] Figure 7 The surface SEM image of the sample prepared in Comparative Example 2 is shown in the figure, Figure 16 The cross-sectional SEM image of the sample prepared in Comparative Example 2 is shown in the figure, from which it can be seen that the positive electrode composite material is spherical, and there are no cracks on the surface and inside, and there are residual alkali spots on the surface, with a diameter of about 3-5 μm. Figure 8The X-ray diffraction pattern of the sample prepared for Comparative Example 2 shows that the obtained sample has an O3 structure and Na2CO3. Compared with Comparative Example 1, it shows that chlorosulfonic acid can treat the surface residual alkali.

[0071] The positive electrode material prepared in Comparative Example 2 was prepared into a positive electrode sheet, and a metal sodium was used as a negative electrode to assemble a button cell. The button cell was subjected to charge-discharge test at 25℃ in a voltage range of 2V-4V. Figure 9 The cycle curve of the battery assembled by the positive electrode material prepared in Comparative Example 2 at a current density of 130mA / g is shown in Figure 6. It can be seen that the specific capacity of the battery is 89.3mAh / g after 100 cycles in a voltage range of 2V-4V, and the capacity retention rate is 86.4%. Figure 9 The cycle performance of the battery assembled by the positive electrode material prepared in Comparative Example 1 and Comparative Example 2 can be seen that the material without chlorosulfonic acid and liquid nitrogen treatment has poor performance. The performance comparison of Comparative Example 1 and Comparative Example 2 shows that the surface residual alkali without electrochemical activity can be treated after chlorosulfonic acid treatment. However, Comparative Example 1 does not have liquid nitrogen treatment, and chlorosulfonic acid further penetrates into the material, forming cracks and destroying the material structure stability, thereby reducing the electrochemical performance of the material.

[0072] Example 2

[0073] (1) A soluble mixed metal sulfate solution of nickel, iron and manganese was prepared according to the molar ratio of Ni:Fe:Mn=4:4:2, wherein the total metal ion molar concentration of nickel, iron and manganese was 3.0mol / L;

[0074] (2) A 5mol / L sodium hydroxide solution and an 8mol / L ammonia solution were prepared;

[0075] (3) The mixed metal salt solution, the sodium hydroxide solution and the ammonia were added into the reaction kettle in parallel flow, and the flow rates were 1L / h, 2L / h and 0.5L / h respectively. The pH value was controlled at 10, the reaction temperature was 70℃, the stirring speed was 600r / min, and the ammonia concentration was 18g / L. After the addition of the mixed metal salt solution was completed, the addition of the sodium hydroxide solution and the ammonia was stopped, and the stirring was continued. The reaction was aged for 10h, and then the reaction was stopped;

[0076] (4) The obtained slurry was filtered, washed with pure water for several times, and dried in a 120℃ oven to obtain a precursor material;

[0077] (5) The obtained precursor material was mixed with sodium carbonate at a molar ratio of 1:1.05. The ball milling speed was 600rpm, and the ball milling time was 10h.

[0078] (6) After the ball milling is completed, the mixture powder is placed in a tube furnace and kept at 450℃ for 5h, and then heated to 900℃ and kept for 18h, the heating rate is 3℃ / min during the sintering process, and the heat treatment is performed in an oxygen atmosphere. The material obtained after sintering is the desired layered oxide material.

[0079] (7) The sintered material is placed in a polytetrafluoroethylene container, and chlorosulfonic acid is then added, the amount of chlorosulfonic acid added is 3% of the mass of the layered oxide material, and the reaction is performed for 15min.

[0080] (8) After the reaction is completed, liquid nitrogen is added, and the ratio of the amount of liquid nitrogen added to the volume of chlorosulfonic acid added is 1:1.3.

[0081] (9) After the liquid nitrogen is volatilized, the obtained powder is the sample.

[0082] The positive electrode material prepared in Example 2 is prepared into a positive electrode sheet, a metal sodium is used as a negative electrode, and a button cell is assembled, respectively. The button cell is subjected to charge-discharge test at 25℃ in a voltage range of 2V-4V.

[0083] Figure 10 The cycle curve of the battery assembled by the positive electrode material prepared in Example 2 is shown in the figure. It can be seen that, in the voltage range of 2V-4V, after 100 cycles, the specific capacity is 103.6mAh / g, and the capacity retention rate is 95.3%. Figure 10

[0084] Example 3

[0085] (1) A soluble mixed metal sulfate solution of nickel, iron and manganese is prepared according to the molar ratio of Ni:Fe:Mn=4:4:2, wherein the total molar concentration of metal ions of nickel, iron and manganese is 3.0mol / L;

[0086] (2) A 5mol / L sodium hydroxide solution and an 8mol / L ammonia solution are prepared;

[0087] (3) The mixed metal salt solution, the sodium hydroxide solution and the ammonia water are added into the reaction kettle in parallel flow, the flow rates are 1L / h, 2L / h and 0.5L / h respectively, the pH value is controlled to be 12, the reaction temperature is 75℃, the stirring speed is 700r / min, and the ammonia concentration is 18g / L. After the addition of the mixed metal salt solution is completed, the addition of the sodium hydroxide solution and the ammonia water is stopped, and the stirring is continued. The reaction is aged for 10h, and then the reaction is stopped;

[0088] (4) The slurry obtained by the reaction is filtered, washed with pure water for multiple times, and dried in a 120℃ oven to obtain a precursor material;

[0089] ​(5) The obtained precursor material is mixed with sodium carbonate with a molar ratio of precursor to sodium of 1:1.20. The ball milling speed is 700 rpm, and the ball milling time is 10 h.

[0090] (6) After ball milling, the mixture powder is placed in a tube furnace and heated at 450℃ for 4 h, then heated to 950℃ for 20 h, and the heating rate during sintering is 5℃ / min. The heat treatment is carried out in an oxygen atmosphere. The material obtained after sintering is the desired layered oxide material.

[0091] (7) The sintered material is placed in a polytetrafluoroethylene container, and then chlorosulfonic acid is added, with an addition amount of 5% of the mass of the layered oxide material, and reacted for 15 min.

[0092] (8) After the reaction is completed, liquid nitrogen is added, and the ratio of the amount of liquid nitrogen added to the amount of chlorosulfonic acid added is 1:1.5.

[0093] (9) After the liquid nitrogen is volatilized, the obtained powder is the sample.

[0094] The positive electrode material prepared in Example 3 is prepared into a positive electrode sheet, and a metal sodium is used as a negative electrode to assemble a button cell. The button cell is subjected to charge and discharge test at a voltage range of 2V-4V at 25℃.

[0095] Figure 11 The cycle curve of the battery assembled with the positive electrode material prepared in Example 3 at a current density of 130mA / g is shown in FIG. 2. It can be seen that, in the voltage range of 2V-4V, after 100 cycles, the specific capacity is 98.1mAh / g, and the capacity retention rate is 91.2%. Figure 11 Figure 17 The XPS diagram of the sample Ni of Example 3 is shown in FIG. 3. It can be seen that, the content of Ni2p is 31.36%. Comparing Example 1, Example 2 and Example 3, it can be seen that the optimal addition amount of chlorosulfonic acid is 3%. 3+

[0096] Comparative Example 3

[0097] (1) A soluble mixed metal sulfate solution of nickel, iron and manganese is prepared according to the molar ratio of Ni:Fe:Mn=4:4:2, wherein the total metal ion molar concentration of nickel, iron and manganese is 3.0mol / L;

[0098] (2) A 5mol / L sodium hydroxide solution and an 8mol / L ammonia solution are prepared;

[0099] ​​(3) The mixed metal salt solution, sodium hydroxide solution and ammonia water are added into the reaction kettle in parallel flow, the pH value is controlled at 12, the reaction temperature is 75°C, the stirring speed is 700 r / min, the ammonia concentration is 18 g / L, and after the addition of the mixed metal salt solution is completed, the addition of the sodium hydroxide solution and the ammonia water is stopped, and the stirring is continued, and the reaction stirring aging is 10 h, and the reaction is stopped;

[0100] (4) The slurry obtained by the reaction is filtered, washed with pure water for multiple times, and dried in a 120°C oven to obtain a precursor material;

[0101] (5) The obtained precursor material is mixed with sodium carbonate with a molar ratio of precursor to sodium of 1:1.20. The ball milling speed is 700 rpm, and the ball milling time is 10 h.

[0102] (6) After the ball milling is completed, the mixture powder is placed in a tube furnace and heated at 450°C for 4 h, and then heated to 950°C and kept for 20 h. The heating rate during the sintering process is 5°C / min, and the heat treatment is carried out in an oxygen atmosphere.

[0103] (7) The sintered material is placed in a polytetrafluoroethylene container, and then sulfuric acid or hydrochloric acid is added, and the amount of sulfuric acid or hydrochloric acid added is 3% of the mass of the layered oxide material, and the reaction is carried out for 15 min.

[0104] (8) After the reaction is completed, liquid nitrogen is added, and the ratio of the amount of liquid nitrogen added to the amount of sulfuric acid or hydrochloric acid added is 1:1.5.

[0105] (9) After the liquid nitrogen is volatilized, the obtained powder is the sample.

[0106] Figure 12 The XPS diagram of the sample Ni treated with sulfuric acid in Comparative Example 3 shows that the Ni 3+ content is 22.49%. Figure 13 The XPS diagram of the sample Ni treated with hydrochloric acid in Comparative Example 3 shows that the Ni 3+ content is 23.96%. Compared with Example 1, the content of Ni 3+ in Example 1 is increased, indicating that the sample treated with chlorosulfonic acid has more defects and more active sites.

[0107] Figure 14 The cycle curve diagram of the battery assembled by the positive electrode material prepared by treating Comparative Example 3 with sulfuric acid at a current density of 130 mA / g. It can be seen from Figure 14 that in the voltage range of 2V-4V, after 100 cycles, the material treated with sulfuric acid has a specific capacity of 96.7 mAh / g, and the capacity retention rate is 89.1%; Figure 15The cycle curve of the battery assembled by the positive electrode material prepared by the sulfuric acid treatment of Comparative Example 3 at a current density of 130 mA / g, the positive electrode material prepared by the hydrochloric acid treatment has a specific capacity of 95.6 mAh / g and a capacity retention rate of 90.6% after 100 cycles in the voltage range of 2V-4V. By comparing Example 2 and Comparative Example 3, it can be seen that chlorosulfonic acid has the best effect on electrochemical improvement.

[0108] The present application relates to a surface modification method for sodium-ion battery cathode additives, specifically, surface treatment of layered oxide cathode materials by chlorosulfonic acid, and the use of liquid nitrogen to control the extent of the reaction. This method effectively adjusts the surface structure and chemical properties of the material by etching with chlorosulfonic acid in a low-temperature environment, thereby improving the electrochemical performance of the battery. The strong corrosive nature of chlorosulfonic acid not only removes impurities from the surface of the material, but also increases the active sites. By introducing moderate surface defects, the treatment of chlorosulfonic acid can improve the electrochemical properties of the electrode material, thereby improving its charge-discharge efficiency and cycle stability in sodium-ion batteries. This selective treatment ensures that the material maintains structural integrity while optimizing the electrochemical reaction process, fully exploiting its potential, while liquid nitrogen cooling can precisely control the reaction process, avoiding excessive damage to the material. The treated layered oxide material as a sodium-ion battery cathode additive exhibits higher charge-discharge efficiency and cycle stability, and is an effective means to improve the performance of electrode materials in the field of sodium-ion batteries.

[0109] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A method for surface modification of a sodium-ion battery cathode material, characterized by: The method comprises the following steps: S1. After mixing the nickel-iron-manganese hydroxide precursor and the sodium source by ball milling, sintering is performed in an oxidizing atmosphere to obtain a mixture powder, and the mixture powder is subjected to heat treatment in a tube furnace, and the obtained powder is the positive electrode material; S2. The obtained positive electrode material is placed in a polytetrafluoroethylene container, chlorosulfonic acid is added, the addition amount of the chlorosulfonic acid is 1%-5% of the mass of the positive electrode material, surface etching is performed after reaction for 10-30 min, and then liquid nitrogen is immediately added, and the ratio of the addition amount of the liquid nitrogen to the addition amount of the chlorosulfonic acid is 1:1-1:1.5; S3. After the liquid nitrogen is volatilized, the reaction mixture is taken out and washed, and then dried to obtain the surface-modified sodium ion battery positive electrode material; In step S1, the chemical formula of the nickel-iron-manganese hydroxide precursor is Ni a Fe b Mn c (OH)2, wherein 0 < a ≤ 1, 0 < b ≤ 1, 0 < c ≤ 1, and the molar ratio of the nickel-iron-manganese hydroxide precursor to the sodium source is 1:1.05-1:1.25; The heat treatment is that the mixture powder is placed at 400-500℃ for 3-6h, and then heated to 750-950℃, and kept for 10-20h, the heating rate during the sintering process is 3-5℃ / min, and the sintering process is performed in an oxygen atmosphere.

2. The method of claim 1, wherein: In step S1, the sodium source is selected from one or more of sodium carbonate, sodium bicarbonate, sodium citrate, sodium oxalate and sodium acetate.

3. The method of claim 1, wherein: In step S1, the ball milling is performed at a rotation speed of 300-600rpm for 8-10h.

4. The method according to any one of claims 1 to 3, characterized in that: The nickel-iron-manganese hydroxide precursor is prepared by a co-precipitation method.

5. The method of claim 4, wherein: The preparation method of the nickel-iron-manganese hydroxide precursor comprises the following steps: (1) A mixed metal salt solution of nickel, iron and manganese, a lye and an ammonia solution are passed into a reaction kettle in parallel flow, heated and stirred to perform a co-precipitation reaction to obtain a reaction slurry; (2) After aging, solid-liquid separation, washing and drying of the reaction slurry, the precursor material is obtained.

6. The method of claim 5, wherein: In step (1), the temperature of the co-precipitation reaction system is controlled to be 60-80℃, the pH is 8-13, the stirring speed is 400-1000r / min, and the ammonia concentration is 10-20g / L.

7. The sodium ion battery positive electrode material obtained by the method of any one of claims 1-6.

8. A sodium-ion battery, characterized in that: The sodium ion battery positive electrode material obtained by the method of any one of claims 1-6.

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