Sodium-ion battery layered oxide positive electrode material and preparation method

Abstract

The application discloses a sodium ion battery positive electrode material and a preparation method thereof. x Ni a Fe b Mn c Me d O2, x, a, b, c and d satisfy 0.6<=x<=1.5, 0

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery materials, and particularly relates to a sodium ion battery layered oxide positive electrode material, and further relates to a preparation method of the sodium ion battery layered oxide positive electrode material. BACKGROUND

[0002] In recent years, with the gradual exposure of problems such as scarcity, uneven distribution, and difficulty in development and utilization of lithium resources, the sodium ion battery with wide resource distribution has attracted attention again, and finding a low-cost alternative has become the focus of attention. At the same time, the development of the energy storage market with lower energy density has laid a foundation for the industrialization of sodium ion batteries. The research on sodium ion batteries has gradually matured in recent years. Due to the abundant reserves and low price of sodium, the cost of sodium ion batteries can be reduced by 30%-40% compared with lithium batteries, and the safety, high and low temperature, and fast charging performance of sodium batteries are more excellent, so sodium batteries have broad application prospects in the energy storage and two-wheeled vehicle markets. In recent years, the research on sodium ion batteries has experienced explosive growth, and global sodium ion battery companies have been established one after another, marking the arrival of the industrialization era of sodium ion batteries.

[0003] Currently, the sodium battery positive electrode materials that are widely concerned by researchers mainly include layered oxides, prussian blue compounds, and polyanion compounds. Among them, the layered oxide material has high specific capacity and comprehensive performance. The layered transition metal oxide (Na x MO2) structure is similar to that of lithium ion ternary materials, and the transition metal layer and alkali metal layer are arranged alternately. According to the coordination environment of sodium ions and the stacking mode of oxygen, it can be divided into O3 phase (octahedral type) and P2 phase (prismatic type). The O3 type structure has low capacity retention rate, but the Na + content is high, and the energy density is high. The P2 type structure is complementary to the O3 type structure, and has good cycle performance, but the specific capacity is limited.

[0004] As the most mature route, layered metal oxides have the highest specific capacity and significant advantages in compaction density, and have the potential to prepare high-energy-density sodium-ion batteries. Moreover, the preparation process is simple, easy to scale up, and easy to transfer from the technical end to the industrial end. At present, the preparation processes of layered metal oxides for industrialized sodium-ion batteries mainly include liquid phase method and solid phase method. Among them, except for raw materials and specific process parameters, the liquid phase method is highly consistent with the preparation process of lithium battery ternary positive electrode materials. The corresponding precursor is prepared by co-precipitation, and then sintered with a sodium source to obtain the positive electrode material. Compared with the liquid phase method, the solid phase method does not need a precursor preparation step, has a short process flow, and causes less environmental pollution. However, the precursor obtained by the existing liquid phase method is difficult to sinter into single crystal materials, and the process flow is long. The solid phase method needs to mix multiple raw materials, and it is difficult to ensure the uniform mixing of multiple raw materials during preparation, which can easily cause poor performance of the positive electrode material. The solid phase technology often has a high sintering temperature, a long reaction time, irregular material morphology, low compaction, and high material residual alkali, which seriously affects the processing performance of the battery, such as slurry coating, and the electrochemical performance is poor. SUMMARY

[0005] The purpose of the present application is to provide a sodium-ion battery layered oxide positive electrode material, which solves the problems of high difficulty in preparing layered oxide single crystal positive electrode materials, high sintering temperature, and poor processing performance, capacity and cycle performance caused by irregular morphology of the prepared single crystal materials, serious agglomeration and high total alkali in the prior art.

[0006] Another purpose of the present application is to provide a preparation method of a sodium-ion battery layered oxide positive electrode material.

[0007] The first technical solution adopted by the present application is a sodium-ion battery layered oxide positive electrode material, the chemical formula of which is: Na x Ni a Fe b Mn c Me d O2, wherein x, a, b, c, and d are the molar percentages of the corresponding elements.

[0008] The first technical solution of the present application is also characterized in that,

[0009] x, a, b, c, and d need to satisfy the following conditions simultaneously: 0.6≤x≤1.5, 0

[0010] Me is one of Ti, Al, Cu, Mg, Zr or Zn.

[0011] The second technical solution adopted by the present application is a preparation method of a sodium-ion battery layered oxide positive electrode material, which is specifically implemented according to the following steps:

[0012] Step 1, the nickel source, sodium source, manganese source, iron source, Me source and the auxiliary agent and the dopant are mixed uniformly according to a proportion to obtain a mixture, the mixture is sintered for the first time under an air or oxygen atmosphere, the temperature is raised for a period of time, the temperature is raised again, and then the sintering is continuously carried out, after the sintering is completed, the temperature is lowered to an out-of-furnace temperature, finally, the out-of-furnace temperature is reached and broken and sieved to obtain a first sintered product;

[0013] Step 2, the first sintered product obtained in the step 1 is mixed with a surface modifier, after being uniformly mixed, the temperature is raised to a reaction temperature under an air or oxygen atmosphere, and the second sintering is carried out, after the second sintering is completed, the temperature is lowered to an out-of-furnace temperature, the out-of-furnace temperature is reached and broken and sieved to obtain a second sintered product;

[0014] Step 3, the product of the step 2 is mixed with a coating agent, and then the third sintering is carried out under an air or oxygen atmosphere, and the third sintered product is sieved to obtain an O3 or P2 type layered oxide positive electrode material.

[0015] The second technical solution of the present application is also characterized in that,

[0016] In the step 1, the nickel source is nickel hydroxide or nickel oxide after further pre-sintering, and has a loose and porous morphology, and is a secondary spherical shape formed by accumulation of primary particles, wherein the primary particles are flaky or strip-shaped, the particle size of the secondary particles is 1-10 μm, the specific surface area is 5-150 m 2 / g; the sodium source is one or more of anhydrous sodium carbonate, sodium sulfate, sodium hydroxide, sodium nitrate or sodium acetate; the manganese source is one or more of manganese dioxide, dimanganese trioxide or trimanganese tetraoxide; the iron source is one or more of diiron trioxide or triiron tetraoxide; the Me source is one of TiO2, Al2O3, CuO, ZrO2, MgO and ZnO2; the auxiliary agent is one of NaNO3, NaF and NaOH, the molar ratio m of the auxiliary agent to the total amount of the sodium source is 0≤m≤1, and the metal element in the dopant is one or more of Mg, Zr, W, Ti, Y, Cu, Al, Sr, Mo and V, and the metal element in the dopant accounts for 10-10000 ppm of the total mass of the positive electrode material.

[0017] In the step 1, the mixing ratio of the nickel source, the sodium source, the manganese source, the iron source, the Me source, the auxiliary agent and the dopant satisfies the following conditions: Na x Ni a Fe b Mn c Me dO2, x, a, b, c, d are the mole percentage of corresponding elements respectively, x, a, b, c, d need to meet the following conditions simultaneously: 0.6<=x<=1.5, 0

[0018] The temperature of the first sintering in step 1 is 200-500 DEG C, the sintering time is 1-10h, the temperature of the continuous sintering after the second time of heating is 800-1100 DEG C, and the sintering time is 4-24h; the heating rate of the two times of heating is 0.5 DEG C-10 DEG C / min, and the cooling rate is 0.5 DEG C-10 DEG C / min.

[0019] In step 2, the surface modifier is one or more of (NH4)2HPO4, NH4H2PO4, H3PO4, HPO3, H3BO3, NH4HB4O7.3H2O, the temperature of the second sintering is 100-700 DEG C, the second sintering time is 2-20h, the cooling rate is 0.5 DEG C-10 DEG C / min, and the surface modifier accounts for 100-10000ppm of the total mass of the positive electrode material.

[0020] In step 3, the third sintering temperature is 100-700 DEG C, and the sintering time is 2-20h.

[0021] In step 3, the coating agent is one or more of Al2O3, TiO2, H3PO4, Li3PO4, H3BO3, C, B2O3, ZrO2, and the metal element in the coating agent accounts for 10-10000ppm of the total mass of the positive electrode material.

[0022] The beneficial effects of the present application are that, by using large specific surface spherical nickel hydroxide or further pre-sintered nickel oxide as the nickel source as the reaction site and template, the morphology and particle size of the product can be well controlled; and by adding an auxiliary agent during the one-step process, single-crystal sodium electric layered oxide positive electrode material can be obtained at a lower temperature and in a shorter reaction time, thereby effectively reducing energy consumption. As can be seen from the electron microscope and particle size results, the material obtained by the present application has a regular single-crystal morphology, good dispersibility, high tap density, and narrow particle size distribution; the single crystal is beneficial to improving the cycle stability of the material at high voltage, so the single-crystal layered oxide positive electrode material obtained by the present application has excellent capacity and electrochemical performance. The use of a surface modifier for secondary sintering effectively reduces the total alkalinity of the material, improves the surface performance of the material, and effectively improves the processing performance of the material in subsequent battery slurry coating and other processes, and the reduction of the total alkalinity is beneficial to the gas production control of the battery. The material is further coated with a coating agent, which effectively improves the structural stability and cycle stability of the material. The process of the present application is simple and suitable for large-scale, industrialized production. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is an SEM image of a layered oxide positive electrode material prepared in Example 1 of the present application;

[0024] Figure 2 is an XRD image of a layered oxide positive electrode material prepared in Example 1 of the present application;

[0025] Figure 3 is a first charge-discharge curve of a layered oxide positive electrode material prepared in Example 1 of the present application;

[0026] Figure 4 is an SEM image of a layered oxide positive electrode material prepared in Example 2 of the present application;

[0027] Figure 5 is an SEM image of a layered oxide positive electrode material prepared in Comparative Example 1 of the present application;

[0028] Figure 6 is an SEM image of a layered oxide positive electrode material prepared in Comparative Example 2 of the present application;

[0029] Figure 7 is an SEM image of a layered oxide positive electrode material prepared in Comparative Example 3 of the present application; DETAILED DESCRIPTION

[0030] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] The layered oxide positive electrode material of the sodium ion battery of the present application has a chemical formula of: Na x Ni a Fe b Mn c Me d O2, wherein x, a, b, c, and d are the molar percentages of the corresponding elements. The sodium ion battery positive electrode material has an O3 phase or a P2 phase crystal structure. x, a, b, c, and d simultaneously satisfy the following conditions: 0.6≤x≤1.5, 0

[0032] The application relates to a preparation method of a sodium ion battery layered oxide positive electrode material, and is specifically implemented according to the following steps:

[0033] Step 1, a nickel source, a sodium source, a manganese source, an iron source, an Me source and an auxiliary agent and a dopant are uniformly mixed in proportion to obtain a mixture, the mixture is subjected to first sintering in an air or oxygen atmosphere, then is subjected to temperature rising reaction for a period of time, is subjected to temperature rising again, and then is continuously sintered, after the sintering is completed, the temperature is lowered to an out-of-furnace temperature, and finally the out-of-furnace temperature is reached and crushing and screening are performed to obtain a first sintering product;

[0034] In step 1, the nickel source is nickel hydroxide or further pre-sintered nickel oxide, has a loose and porous morphology, is a secondary spherical or spherical-like shape formed by accumulation of primary particles, the primary particles are flaky or strip-shaped, the particle size of the secondary particles is 1-10 mu m, and the specific surface area is 5-150 m 2 / g; the sodium source is one or more of anhydrous sodium carbonate, sodium sulfate, sodium hydroxide, sodium nitrate or sodium acetate; the manganese source is one or more of manganese dioxide, dimanganese trioxide or trimanganese tetraoxide; the iron source is one or more of diiron trioxide or triiron tetraoxide; the Me source is one of TiO2, Al2O3, CuO, ZrO2, MgO and ZnO2; the auxiliary agent is one of NaNO3, NaF and NaOH, the molar ratio m of the auxiliary agent to the total amount of the sodium source is 0<=m<=1, and the metal element in the dopant is one or more of Mg, Zr, W, Ti, Y, Cu, Al, Sr, Mo and V, and the metal element in the dopant accounts for 10-10000 ppm of the total mass of the positive electrode material.

[0035] In step 1, the mixing ratio of the nickel source, the sodium source, the manganese source, the iron source, the Me source, the auxiliary agent and the dopant satisfies the following conditions: Na x Ni a Fe b Mn c Me d O2, x, a, b, c and d are respectively the molar percentage of the corresponding element, and x, a, b, c and d need to satisfy the following conditions simultaneously: 0.6<=x<=1.5, 0

[0036] In step 1, the temperature of the first sintering is 200-500 DEG C, and the sintering time is 1-10 h, after the temperature rising again, the temperature for continuously sintering is 800-1100 DEG C, and the sintering time is 4-24 h; the temperature rising rate of the two times of temperature rising is 0.5 DEG C-10 DEG C / min, and the temperature lowering rate is 0.5 DEG C-10 DEG C / min.

[0037] Step 2, the product of step 1 is mixed with a surface modifier, after mixing, the mixture is heated to a reaction temperature under air or oxygen atmosphere, and then is subjected to a second sintering, after the second sintering, the mixture is cooled to a discharge temperature, and then is discharged, crushed and sieved to obtain a second sintered product;

[0038] In step 2, the surface modifier is one or more of (NH4)2HPO4, NH4H2PO4, H3PO4, HPO3, H3BO3 and NH4HB4O7·3H2O, the second sintering temperature is 100-700℃, the second sintering time is 2-20h, the cooling rate is 0.5-10℃ / min, and the surface modifier accounts for 100-10000ppm of the total mass of the positive electrode material.

[0039] Step 3, the product of step 2 is mixed with a coating agent, and then is subjected to a third sintering under air or oxygen atmosphere, and then is sieved to obtain the O3 or P2 type layered oxide positive electrode material.

[0040] In step 3, the third sintering temperature is 100-700℃, and the sintering time is 2-20h.

[0041] In step 3, the coating agent is one or more of Al2O3, TiO2, H3PO4, Li3PO4, H3BO3, C, B2O3 and ZrO2, and the metal elements in the coating agent account for 10-10000ppm of the total mass of the positive electrode material.

[0042] Compared with the conventional method, in the present application, specific spherical nickel or nickel oxide after further pre-sintering is used as a nickel source, and then is subjected to a solid phase reaction with a solid phase iron source, a manganese source, a sodium source and an additive, etc., the low eutectic substance formed between the solid phase substances reduces the energy barrier of single crystal formation, so that the single crystal can be formed at a lower temperature and in a shorter reaction time, and the morphology and particle size of the product are well controlled.

[0043] In the first sintering process of the present application, an additive and a dopant are used simultaneously, the use of the additive reduces the sintering temperature, reduces the difficulty of realizing high temperature conditions and reduces energy consumption to a certain extent, and the use of the dopant improves the structural stability of the material, especially the air stability, which is beneficial to long-term storage and use of the material.

[0044] The present application modifies the surface of the material at a lower temperature through secondary sintering, consumes residual alkali on the surface of the material by chemical reaction between the surface modifier and the residual alkali, thereby greatly reducing the residual alkali value of the material, improving the processing performance of the material in the later stage, and also improving the comprehensive performance of the material, and greatly improving the production efficiency.

[0045] Example 1

[0046] The preparation method of the sodium-ion battery layered oxide positive electrode material of the present application comprises the following steps:

[0047] (1) 0.66 mol of nickel source Ni(OH)2, 1.02 mol of sodium source Na2CO3, 0.66 mol of iron source Fe2O3, 0.66 mol of manganese source MnO2, 0.02 mol of Me source TiO2, 20% of auxiliary agent NaF, and 1500 ppm of dopant ZrO2 are uniformly mixed, and then sintered in an air atmosphere, heated to a first sintering temperature of 500℃ at a rate of 2℃ / min, sintered for 7h, then heated to a second sintering temperature of 860℃ at a rate of 2℃ / min, sintered for 12h, and then cooled at a rate of 5℃ / min after sintering, and the product is discharged after sintering, crushed and sieved to obtain a layered oxide positive electrode material;

[0048] (2) The obtained layered oxide positive electrode material is uniformly mixed with 100 ppm of surface modifier H3PO4, and then secondary sintering is carried out in an air atmosphere, the sintering temperature is 650℃, the sintering time is 8h, and then the product is cooled in the furnace after sintering, and sieved after discharging to obtain a modified layered oxide positive electrode material;

[0049] (3) The modified layered oxide positive electrode material is mixed with 300 ppm of Al2O3, and then three times sintering is carried out in an air atmosphere, the sintering temperature is 300℃, the sintering time is 6h, and then the product is cooled in the furnace after sintering, and sieved after discharging to obtain the final product, the product electron microscope result is shown in Figure 1 , the XRD result is shown in Figure 2 , and the first charge-discharge curve of the button cell is shown in Figure 3 .

[0050] Example 2

[0051] The preparation method of the sodium-ion battery layered oxide positive electrode material of the present application comprises the following steps:

[0052] (1) mix 4.8 mol of a nickel source NiO with 2.5 mol of a sodium source Na2SO4, 1.8 mol of an iron source Fe2O3, 1 mol of a manganese source Mn3O4, and 0.6 mol of a Me source Al2O3, and then sinter in an air atmosphere, with the temperature being raised to a first sintering temperature of 200 DEG C at a rate of 3 DEG C / min, and the sintering time being 10 h, and then the temperature being raised to a second sintering temperature of 800 DEG C at a rate of 3 DEG C / min, and the sintering time being 4 h, and then the product being cooled at a rate of 5 DEG C / min in the furnace, and the product being crushed and sieved after being discharged from the furnace, to obtain a layered oxide positive electrode material;

[0053] (2) mix the obtained layered oxide positive electrode material with 3000 ppm of a surface modifier (NH4)2HPO4+H3BO3, and then perform secondary sintering in an air atmosphere, with the sintering temperature being 100 DEG C and the sintering time being 2 h, and then the product being cooled in the furnace after sintering, and the product being sieved after being discharged from the furnace, to obtain a modified layered oxide positive electrode material;

[0054] (3) mix the modified layered oxide positive electrode material with 2000 ppm of WO3, and then perform tertiary sintering in an air atmosphere, with the sintering temperature being 420 DEG C and the sintering time being 8 h, and then the product being cooled in the furnace after sintering, and the product being sieved after being discharged from the furnace, to obtain a final product, as shown in FIG. 1. Figure 4

[0055] Example 3

[0056] The preparation method of the sodium ion battery layered oxide positive electrode material of the present application comprises the following steps:

[0057] (1) mix 3.4 mol of a nickel source Ni(OH)2 with 7.6 mol of a sodium source Na2CO3, 3.4 mol of an iron source Fe2O3, 4.8 mol of a manganese source MnO2, and 3000 ppm of a dopant Y2O3, and then perform sintering in an air atmosphere, with the temperature being raised to a first sintering temperature of 500 DEG C at a rate of 5 DEG C / min, and the sintering time being 1 h, and then the temperature being raised to a second sintering temperature of 1100 DEG C at a rate of 5 DEG C / min, and the sintering time being 24 h, and then the product being cooled at a rate of 1 DEG C / min in the furnace after sintering, and the product being crushed and sieved after being discharged from the furnace, to obtain a layered oxide positive electrode material;

[0058] (2) mix the obtained layered oxide positive electrode material with 500 ppm of a surface modifier H3BO3, and then perform secondary sintering in an air atmosphere, with the sintering temperature being 700 DEG C and the sintering time being 20 h, and then the product being cooled in the furnace after sintering, and the product being sieved after being discharged from the furnace, to obtain a modified layered oxide positive electrode material;

[0059] ​(3) the modified layered oxide positive electrode material is mixed with 800 ppm of Li3PO4, and then sintered three times in an air atmosphere, the sintering temperature is 700 DEG C, the sintering time is 20 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, the product is sieved to obtain a final product.

[0060] Example 4

[0061] The preparation method of the sodium ion battery layered oxide positive electrode material of the application comprises the following steps:

[0062] (1) 2.6 mol of a nickel source Ni(OH)2, 8 mol of a sodium source Na2CO3, 1.8 mol of an iron source Fe2O3 and 2.7 mol of a manganese source MnO2 are uniformly mixed, and then sintered in an oxygen atmosphere, the temperature is raised to a first sintering temperature of 500 DEG C at a rate of 2 DEG C / min, the sintering time is 7 h, then the temperature is raised to a second sintering temperature of 860 DEG C at a rate of 2 DEG C / min, the sintering time is 12 h, after sintering, the product is cooled at a rate of 5 DEG C / min, and after the product is discharged from the furnace, the product is crushed and sieved to obtain a layered oxide positive electrode material;

[0063] (2) the obtained layered oxide positive electrode material is uniformly mixed with 500 ppm of a surface modifier HPO3, and then sintered twice in an air atmosphere, the sintering temperature is 650 DEG C, the sintering time is 8 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, the product is sieved to obtain a modified layered oxide positive electrode material;

[0064] (3) the modified layered oxide positive electrode material is mixed with 1200 ppm of Al2O3, and then sintered three times in an air atmosphere, the sintering temperature is 300 DEG C, the sintering time is 6 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, the product is sieved to obtain a final product.

[0065] Comparative Example 1

[0066] comprises the following steps:

[0067] (1) 0.66 mol of a nickel source amorphous NiO, 1.02 mol of a sodium source Na2CO3, 0.66 mol of an iron source Fe2O3, 0.66 mol of a manganese source MnO2, 0.02 mol of a Me source TiO2, 20% of an auxiliary agent NaF and 1500 ppm of a dopant ZrO2 are uniformly mixed, and then sintered in an air atmosphere, the temperature is raised to a first sintering temperature of 500 DEG C at a rate of 2 DEG C / min, the sintering time is 7 h, then the temperature is raised to a second sintering temperature of 860 DEG C at a rate of 2 DEG C / min, the sintering time is 12 h, after sintering, the product is cooled at a rate of 5 DEG C / min, and after the product is discharged from the furnace, the product is crushed and sieved to obtain a layered oxide positive electrode material;

[0068] (2) The obtained layered oxide positive electrode material is mixed with 400 ppm of surface modifier H3PO4, and secondary sintering is carried out in an air atmosphere, the sintering temperature is 650 DEG C, the sintering time is 8 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, sieving is carried out, and the modified layered oxide positive electrode material is obtained;

[0069] (3) The modified layered oxide positive electrode material is mixed with 300 ppm of Al2O3, and then three times of sintering is carried out in an air atmosphere, the sintering temperature is 300 DEG C, the sintering time is 6 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, sieving is carried out, and the final product is obtained, as shown in Figure 5

[0070] Comparative Example 2

[0071] The method comprises the following steps:

[0072] (1) 3 mol of nickel source Ni(OH)2 is uniformly mixed with 1.02 mol of sodium source Na2CO3, 1.5 mol of iron source Fe2O3, 3 mol of manganese source MnO2, 1 mol of Me source Al2O3, 13% of auxiliary agent NaF, and 5000 ppm of dopant Y2O3, and then sintering is carried out in an air atmosphere, the temperature is increased to a first sintering temperature of 500 DEG C at a rate of 2 DEG C / min, the sintering time is 7 h, then the temperature is increased to a second sintering temperature of 860 DEG C at a rate of 2 DEG C / min, the sintering time is 12 h, after sintering, the product is cooled at a rate of 5 DEG C / min, and after the product is discharged from the furnace, crushing and sieving are carried out, and the layered oxide positive electrode material is obtained;

[0073] (2) The obtained layered oxide positive electrode material is mixed with 6200 ppm of TiO2, and then three times of sintering is carried out in an air atmosphere, the sintering temperature is 300 DEG C, the sintering time is 6 h, after sintering, the product is cooled in the furnace, and after the product is discharged from the furnace, sieving is carried out, and the final product is obtained, as shown in Figure 6

[0074] Comparative Example 3

[0075] The method for preparing the layered oxide positive electrode material of the sodium ion battery comprises the following steps:

[0076] (1) 3 mol of nickel source Ni(OH)2 is uniformly mixed with 0.8 mol of sodium source Na2CO3, 4 mol of iron source Fe3O4, and 3 mol of manganese source Mn2O3, and then sintering is carried out in an air atmosphere, the temperature is increased to a first sintering temperature of 500 DEG C at a rate of 2 DEG C / min, the sintering time is 7 h, then the temperature is increased to a second sintering temperature of 860 DEG C at a rate of 2 DEG C / min, the sintering time is 12 h, after sintering, the product is cooled at a rate of 5 DEG C / min, and after the product is discharged from the furnace, crushing and sieving are carried out, and the layered oxide positive electrode material is obtained;

[0077] ​​(2) The obtained layered oxide positive electrode material is mixed with 1100 ppm surface modifier NH4H2PO4, and then secondarily sintered in an air atmosphere, the sintering temperature is 650°C, the sintering time is 8h, and the product is cooled in the furnace after sintering, and then sieved after being discharged from the furnace, to obtain the modified layered oxide positive electrode material;

[0078] (3) The modified layered oxide positive electrode material is mixed with 500 ppm Al2O3, and then thirdly sintered in an air atmosphere, the sintering temperature is 300°C, the sintering time is 6h, and the product is cooled in the furnace after sintering, and then sieved after being discharged from the furnace, to obtain the final product, as shown in Figure 7

[0079] Electrochemical performance test: The positive electrode materials obtained in Examples 1-4 and Comparative Examples 1-3 are used as active substances, and mixed according to the mass ratio of active substance: conductive agent (Super P): binder (PVDF) = 80:10:10, and then a proper amount of solvent NMP is added to adjust the solid content, and then stirred into a slurry by a pulp machine, and then coated on an aluminum foil, and then the coated sheet is dried in a 100°C oven for 4 hours. A sodium sheet is used as a negative electrode, glass fiber is used as a separator, and 1M NaClO4 (solvent EC:DEC = 1:1 Vol%) is used as an electrolyte, to assemble a button cell in a glove box. The battery is tested in a voltage range of 2.0-4.2V, after 0.2C activation for three weeks, rate test and cycle performance test are performed.

[0080] The performance test results of the products obtained in the examples and comparative examples are as follows:

[0081]

[0082] As can be seen from the above table, the positive electrode material prepared by the method of the present application has good pH value, first charge-discharge efficiency, discharge capacity and capacity retention rate, which is greatly improved compared with Comparative Examples 1-3.​

Claims

1. A method for preparing layered oxide cathode material for sodium-ion batteries, characterized in that, The specific steps are as follows: Step 1: Mix the nickel source, sodium source, manganese source, iron source, Me source, and additives and dopants in a certain proportion to obtain a mixture. Perform the first sintering of the mixture in an air or oxygen atmosphere. The temperature of the first sintering is 200-500℃ and the sintering time is 1-10h. Then, raise the temperature and react for a period of time. Raise the temperature again and continue sintering. After the second temperature is raised, continue sintering at a temperature of 800-1100℃ for 4-24h. After sintering, cool down to the furnace exit temperature. Finally, remove from the furnace, crush, and sieve to obtain the first sintered product. The nickel source is nickel hydroxide or nickel oxide after further pre-calcination. It has a loose and porous morphology, consisting of secondary spherical or near-spherical particles formed by the accumulation of primary particles. The primary particles are in the form of thin sheets or strips, while the secondary particles have a particle size of 1-10 μm and a specific surface area of ​​5-150 m². 2 / g; The auxiliary agent is one of NaNO3, NaF or NaOH. The metal element in the dopant is one or several of Mg, Zr, W, Ti, Y, Cu, Al, Sr, Mo, V. The Me source is one of TiO2, Al2O3, CuO, ZrO2, MgO, ZnO2. The mixing ratios of the nickel source, sodium source, manganese source, iron source, Me source, auxiliary agent and dopant in Step 1 satisfy the following conditions: Na x Ni a Fe b Mn c Me d In O2, x, a, b, c, d are the molar percentages of the corresponding elements respectively. x, a, b, c, d need to satisfy the following conditions simultaneously: 0.6 ≤ x ≤ 1.5, 0 < a ≤ 0.6, 0 ≤ b ≤ 0.5, 0 < c ≤ 0.5, 0 ≤ d ≤ 0.4, and a + b + c + d = 1. The metal element in the dopant accounts for 10 - 10000 ppm of the total mass of the cathode material; the molar ratio m of the auxiliary agent to the total sodium source is 0 ≤ m ≤ 1; Step 2: Mix the first sintered product obtained in Step 1 with the surface modifier. After mixing evenly, heat the mixture to the reaction temperature in an air or oxygen atmosphere and perform a second sintering. The temperature of the second sintering is 100-700℃ and the time of the second sintering is 2-20h. After the second sintering is completed, cool the mixture to the furnace exit temperature, remove it from the furnace, crush it, and sieve it to obtain the second sintered product. The surface modifier is one or more of (NH4)2HPO4, NH4H2PO4, H3PO4, HPO3, H3BO3, and NH4HB4O7·3H2O, and the surface modifier accounts for 100~10000ppm of the total mass of the cathode material. Step 3: Mix the product from Step 2 with the coating agent evenly, and then perform a third sintering in an air or oxygen atmosphere. The third sintering temperature is 100-700℃ and the sintering time is 2-20h. After sieving the third sintering product, O3 or P2 type layered oxide cathode material is obtained. The coating agent is one or more of Al2O3, TiO2, H3PO4, Li3PO4, H3BO3, C, B2O3, and ZrO2, and the metal element in the coating agent accounts for 10 to 10,000 ppm of the total mass of the cathode material.

2. The method for preparing the layered oxide cathode material for sodium-ion batteries according to claim 1, characterized in that, In step 1, the sodium source is one or more of anhydrous sodium carbonate, sodium sulfate, sodium hydroxide, sodium nitrate, or sodium acetate; the manganese source is one or more of manganese dioxide, manganese trioxide, or manganese tetroxide; and the iron source is one or more of ferric oxide or ferric oxide.

3. The method for preparing the layered oxide cathode material for sodium-ion batteries according to claim 2, characterized in that, In step 1, the heating rate for both heating cycles is 0.5℃~10℃ / min, and the cooling rate is 0.5℃~10℃ / min.

4. The method for preparing the layered oxide cathode material for sodium-ion batteries according to claim 3, characterized in that, In step 2, the cooling rate is 0.5℃~10℃ / min.

Images