Preparation method of high-energy-density sodium battery positive electrode material

Abstract

The invention relates to the technical field of sodium battery positive electrode materials, in particular to a preparation method of a high-energy-density sodium battery positive electrode material, which comprises the following steps: S1, mixing and sintering a sodium source, a precursor, a boron source and a bismuth source to obtain an intermediate, the metal elements in the precursor comprising nickel, iron, manganese and copper; and S2, mixing the intermediate and a coating agent, and sintering to obtain the sodium battery positive electrode material. The copper element is added in the precursor, on one hand, growth of grain size can be promoted, on the other hand, lattice mismatch of the sodium layer and the transition metal layer can be reduced, mixed arrangement can be inhibited, further, through doping of the boron element and the bismuth element, the grain boundary can be optimized, meanwhile, the grain size can be further increased, and the performance of the device is improved. The compaction density of the positive electrode material is improved, and the high-energy-density sodium battery positive electrode material is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of sodium battery positive electrode materials, and in particular to a method for preparing a sodium battery positive electrode material with high energy density. Background Art

[0002] With the rapid development of the new energy industry, the global demand for lithium resources has grown rapidly. However, due to the limited lithium resources in the earth's crust, it is impossible to meet the increasingly mature battery industry chain in the long term. Therefore, we have to speed up the search for a new battery material as a substitute for lithium batteries. The principle of sodium ion batteries is similar to that of lithium ion batteries. Both are "rocking chair batteries", but the earth has extremely abundant energy storage, low price and high safety. It has received widespread attention and has been widely used in household energy storage, large-scale energy storage, and power fields.

[0003] Layered structure is one of the common positive electrode materials in sodium batteries and has a high specific capacity. However, polycrystalline layered transition metal oxides show poor cycling performance during long-term cycling due to grain boundary cracking and side reactions in contact with the electrolyte. Single crystal materials can reduce contact with the electrolyte due to their smaller specific surface area, thereby inhibiting the occurrence of some side reactions. In addition, fewer grain boundaries in single crystal materials can reduce the generation of cracks during the cycle, further improving the material's cycling performance.

[0004] In the prior art, single crystal materials often have a larger electrode compaction density, which can further improve the volume energy density of the battery. However, the synthesized sodium-electrolyte layered oxide single crystal material is small in size and has a low compaction density, resulting in insufficient volume energy density. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of the sodium battery layered oxide single crystal material in the prior art, such as small size, low compaction density and insufficient volume energy density, thereby providing a method for preparing a high energy density sodium battery positive electrode material.

[0006] To this end, the present invention provides a method for preparing a high energy density sodium positive electrode material, comprising the following steps: S1, mixing a sodium source, a precursor, a boron source and a bismuth source, and sintering to obtain an intermediate, wherein the metal elements in the precursor include nickel, iron, manganese and copper; S2, mixing the intermediate and a coating agent, and sintering to obtain the sodium positive electrode material.

[0007] In some embodiments, the sodium source in step S1 includes at least one of sodium carbonate, sodium hydroxide, and sodium chloride.

[0008] In some embodiments, the boron source includes at least one of boron oxide and boric acid.

[0009] In some embodiments, the bismuth source includes at least one of bismuth oxide, bismuth chloride, bismuth nitrate, and bismuth sulfate.

[0010] In some embodiments, the molar ratio of the sodium source to the precursor is 0.95-1.05:1.

[0011] In some embodiments, based on the precursor, the molar amount of the boron source is 0.25-2% of the molar amount of the precursor.

[0012] In some of the embodiments, based on the precursor, the molar amount of the bismuth source is 0.2-1% of the molar amount of the precursor.

[0013] In some of the embodiments, the sintering step in step S1 specifically includes, in an air atmosphere, first keeping the temperature at 500-850° C. for 2-6 hours, and then keeping the temperature at 900-1200° C. for 5-15 hours.

[0014] In some embodiments, the coating agent includes at least one of nickel oxide, manganese oxide, or titanium oxide.

[0015] In some of the embodiments, based on the mass of the intermediate, the mass fraction of the coating agent is 0.5-2%.

[0016] In some of the embodiments, the specific step of sintering in step S2 includes keeping the temperature at 750-950° C. for 3-8 hours in an air atmosphere.

[0017] In some embodiments, the chemical formula of the precursor is Ni a Fe b Mn c Cu d (OH)2, wherein 0.2≤a≤0.4, 0.2≤b≤0.4, 0.2≤c≤0.4, 0.02≤d≤0.05.

[0018] In some embodiments, the preparation method of the precursor includes, in an inert atmosphere, forming a metal salt solution from a nickel source, an iron source, a manganese source, and a copper source, and reacting the metal salt solution, a precipitant, and a complexing agent to form a precursor. Preferably, the nickel source includes at least one of nickel sulfate, nickel nitrate, and nickel chloride; preferably, the iron source includes at least one of ferric sulfate, ferric nitrate, and ferric chloride; preferably, the manganese source includes at least one of manganese sulfate, manganese nitrate, and manganese chloride; preferably, the copper source includes at least one of copper sulfate, copper nitrate, and copper chloride; preferably, the precipitant includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, sodium carbonate, and ammonium carbonate; preferably, the complexing agent includes at least one of ammonia water and citric acid.

[0019] In some of the embodiments, in the preparation method of the precursor, the pH value of the reaction system is 12-12.3, the reaction temperature is 63-67°C, and the reaction time is 15h; preferably, during the reaction, the flow rate of the metal salt solution into the reaction system is 5-7L / h, the flow rate of the complexing agent into the reaction system is 6-10g / L, and the flow rate of the inert gas into the reaction system is 5-8L / min.

[0020] In some embodiments, the total concentration of metal ions in the metal salt solution is 2-4 mol / L.

[0021] In some embodiments, the complexing agent is ammonia water, and the concentration of ammonia water is 15-30wt%.

[0022] In some embodiments, the precipitant is an aqueous sodium hydroxide solution, and the concentration of the aqueous sodium hydroxide solution is 20-40 wt %.

[0023] On the other hand, the present invention provides a sodium battery, comprising a sodium positive electrode material, wherein the sodium positive electrode material is prepared by the above-mentioned method for preparing a high energy density sodium positive electrode material.

[0024] The technical solution of the present invention has the following advantages:

[0025] The present invention provides a method for preparing a high energy density sodium positive electrode material, comprising the following steps: S1, mixing a sodium source, a precursor, a boron source and a bismuth source, sintering to obtain an intermediate, wherein the metal elements in the precursor include nickel, iron, manganese and copper; S2, mixing the intermediate and a coating agent, sintering to obtain a sodium positive electrode material. The present invention can promote the growth of grain size by adding copper elements to the precursor, and on the other hand, the copper element can reduce the lattice mismatch between the sodium layer and the transition metal layer and inhibit the mixing. Furthermore, the present invention can optimize the grain boundary by doping boron elements and bismuth elements, and at the same time can further increase the size of the grains, thereby significantly improving the compaction density of the positive electrode material, and obtaining a high energy density sodium positive electrode material; at the same time, the present invention also provides a coating agent to coat the sodium positive electrode material for two sintering, which is not only conducive to reducing the residual alkali content of the sodium positive electrode material and improving the material cycle stability, but also can avoid particle agglomeration, resulting in a problem of reduced compaction density. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is a microscopic morphology of the sodium positive electrode material prepared in Example 1 of the present invention, Figure 1 The scale bar in the figure is 20 μm;

[0028] Figure 2 This is the XRD diagram of the sodium positive electrode material prepared in Example 1 of the present invention;

[0029] Figure 3 This is a microscopic morphology of the sodium positive electrode material obtained in Comparative Example 1 of the present invention. Figure 3 The scale bar in the figure is 20 μm. DETAILED DESCRIPTION

[0030] The following examples are provided for a better understanding of the present invention. The present invention is not limited to the best implementation mode described, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts is within the protection scope of the present invention.

[0031] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0032] Example 1

[0033] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0034] (1) According to the molar ratio of NiSO4, FeSO4, MnSO4 and CuSO4 being 0.3:0.33:0.33:0.04, NiSO4, FeSO4, MnSO4 and CuSO4 were weighed, and a metal salt solution with a metal salt concentration of 3 mol / L was prepared with water as a solvent (the metal salt concentration was 3 mol / L, indicating that the total amount of NiSO4, FeSO4, MnSO4 and CuSO4 in each liter of solution was 3 mol), and 20 wt% ammonia water and 30 wt% NaOH solution were prepared;

[0035] Protective gas (nitrogen) was introduced into the reaction system at a gas flow rate of 6 L / min. The metal salt solution and ammonia water were mixed at a flow rate of 6 L / h for the metal salt solution and 8 g / L for the ammonia water. The pH value of the system was controlled to 12 using NaOH solution. The reaction temperature was controlled to 65°C and the reaction was carried out for 15 hours. The precursor was obtained by filtration, washing and drying.

[0036] (2) Sodium carbonate and the precursor obtained in step (1) are weighed and mixed in a molar ratio of sodium carbonate to the precursor of 1:1, and H3BO3 and Bi2O3 are added thereto, wherein the amount of H3BO3 added is 1% of the molar amount of the precursor, and the amount of Bi2O3 added is 0.25% of the molar amount of the precursor. The above materials are placed in an Eirish high speed mixer at a speed of 3000 rpm and mixed for 10 minutes. After mixing evenly, the mixture is calcined at 800°C for 4 hours in an air atmosphere, and then heated to 1050°C and calcined for 10 hours at a heating rate of 2°C / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0037] (3) Weigh a sintered product and TiO2, wherein the mass of TiO2 is 1% of the sintered product, mix the two at 3000 rpm for 10 min, raise the temperature to 900°C at a heating rate of 2°C / min in an air atmosphere, keep the temperature for 6 h, cool to room temperature, sieve and remove iron to obtain a sodium positive electrode material.

[0038] The morphology of the sodium positive electrode material formed in this embodiment was photographed by electron microscope, see Figure 1 It can be seen that in this embodiment, after adding Cu as the main element and B and Bi as the dopant, the size of the single crystal of the sodium positive electrode material obtained is significantly increased, and the dispersibility is greatly improved, which helps to improve the compaction density of the material.

[0039] And draw an X-ray diffraction diagram of the sodium positive electrode material formed in this embodiment, see Figure 2 It can be seen that the sodium positive electrode material prepared in this embodiment is a standard O3 phase, and no other impurities are introduced.

[0040] Example 2

[0041] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0042] (1) NiSO4, FeSO4, MnSO4 and CuSO4 were weighed according to a molar ratio of NiSO4, FeSO4, MnSO4 and CuSO4 of 0.25:0.4:0.3:0.05, and water was used as a solvent to prepare a metal salt solution with a metal salt concentration of 3 mol / L, and 20 wt% ammonia water and 30 wt% NaOH solution were prepared;

[0043] Protective gas (nitrogen) was introduced into the reaction system at a gas flow rate of 6 L / min. The metal salt solution and ammonia water were mixed at a metal salt solution flow rate of 6 L / h and an ammonia water flow rate of 8 g / L. The pH value of the system was controlled to 12.3 using NaOH solution. The reaction temperature was controlled to 65°C and the reaction was carried out for 15 hours. The precursor was obtained by filtration, washing and drying.

[0044] (2) Sodium carbonate and Ni were weighed and mixed in a molar ratio of sodium carbonate to precursor of 0.95:1. 0.3 Fe 0.33 Mn 0.33 Cu 0.04 (OH)2 precursor, and add H3BO3 and Bi2O3 thereto, wherein the added amount of H3BO3 is 2% of the molar amount of the precursor, and the added amount of Bi2O3 is 0.5% of the molar amount of the precursor. The above materials are placed in an Eirich high speed mixer at a rotation speed of 3000rpm and mixed for 10min to obtain a mixture. In an air atmosphere, the mixture is calcined at 600℃ for 4h, and then heated to 1000℃ and calcined for 10h, with a heating rate of 2℃ / min. After natural cooling, it is crushed and sieved to obtain a sintered product.

[0045] (3) Weigh a sintered product and NiO, wherein the mass of NiO is 2% of the sintered product, mix the two at 3000 rpm for 10 min, raise the temperature to 800° C. at a heating rate of 2° C. / min in an air atmosphere, keep the temperature for 6 h, cool to room temperature, sieve and remove iron to obtain a sodium positive electrode material.

[0046] Example 3

[0047] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0048] (1) NiSO4, FeSO4, MnSO4 and CuSO4 were weighed according to a molar ratio of NiSO4, FeSO4, MnSO4 and CuSO4 of 0.38:0.2:0.4:0.02, and water was used as a solvent to prepare a metal salt solution with a metal salt concentration of 3 mol / L, and 20 wt% ammonia water and 30 wt% NaOH solution were prepared;

[0049] Protective gas (nitrogen) was introduced into the reaction system at a gas flow rate of 6 L / min. The metal salt solution and ammonia water were mixed at a metal salt solution flow rate of 6 L / h and an ammonia water flow rate of 8 g / L. The pH value of the system was controlled to 12.3 using NaOH solution. The reaction temperature was controlled to 65°C and the reaction was carried out for 15 hours. The precursor was obtained by filtration, washing and drying.

[0050] (2) Sodium carbonate and Ni were weighed and mixed in a molar ratio of sodium carbonate to precursor of 0.95:1. 0.3 Fe 0.33 Mn 0.33 Cu 0.04(OH)2 precursor, and add H3BO3 and Bi2O3 thereto, wherein the added amount of H3BO3 is 0.5% of the molar amount of the precursor, and the added amount of Bi2O3 is 0.25% of the molar amount of the precursor. The above materials are mixed at a rotation speed of 3000 rpm for 10 minutes to obtain a mixture. In an air atmosphere, the mixture is calcined at 800°C for 4 hours, and then heated to 1100°C and calcined for 10 hours, with a heating rate of 5°C / min. After natural cooling, it is crushed and sieved to obtain a sintered product.

[0051] (3) Weigh a sintered product, MnO2 and TiO2, wherein the mass of MnO2 is 1% of the sintered product and the mass of TiO2 is 1% of the sintered product, mix the three at 3000 rpm for 10 min, increase the temperature to 950°C at a heating rate of 5°C / min in an air atmosphere, keep the temperature for 5 h, cool to room temperature, sieve and remove iron to obtain a sodium positive electrode material.

[0052] Example 4

[0053] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0054] (1) nickel chloride, ferric nitrate, manganese nitrate and cupric chloride are weighed according to a molar ratio of nickel chloride, ferric nitrate, manganese nitrate and cupric chloride of 0.2:0.4:0.2:0.02, and a metal salt solution with a metal salt concentration of 2 mol / L is prepared using water as a solvent, and a 20 wt % citric acid and 30 wt % KOH solution is prepared;

[0055] Protective gas (argon) was introduced into the reaction system at a gas flow rate of 5 L / min. The metal salt solution and ammonia water were mixed at a metal salt solution flow rate of 5 L / h and a citric acid flow rate of 10 g / L. The pH value of the system was controlled to 12.3 using KOH solution. The reaction temperature was controlled to 63°C and the reaction was carried out for 18 hours. The precursor was obtained by filtration, washing and drying.

[0056] (2) Sodium chloride and the precursor obtained in step (1) are weighed and mixed according to a molar ratio of sodium chloride to precursor of 0.95:1, and boron oxide and bismuth chloride are added thereto, wherein the amount of boron oxide added is 0.25% of the molar amount of the precursor, and the amount of bismuth chloride added is 1% of the molar amount of the precursor. After the above materials are mixed evenly, the mixture is calcined at 500° C. for 6 h in an air atmosphere, and then the temperature is increased to 1200° C. and calcined for 5 h at a heating rate of 2° C. / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0057] (3) Weigh a sintered product and manganese oxide, wherein the mass of manganese oxide is 0.5% of the sintered product, mix the two evenly, raise the temperature to 750°C at a heating rate of 2°C / min in an air atmosphere, keep the temperature for 8 hours, cool to room temperature, sieve and remove iron, and obtain a sodium positive electrode material.

[0058] Example 5

[0059] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0060] (1) nickel nitrate, ferric chloride, manganese chloride and copper nitrate were weighed according to a molar ratio of 0.4:0.2:0.:4:0.05, and a metal salt solution with a metal salt concentration of 4 mol / L was prepared using water as a solvent, and 15 wt % ammonia water and 40 wt % NaOH solution were prepared;

[0061] Protective gas (nitrogen) was introduced into the reaction system at a gas flow rate of 8 L / min. The metal salt solution and ammonia water were mixed at a flow rate of 7 L / h for the metal salt solution and 6 g / L for the ammonia water. The pH value of the system was controlled to 12.3 using NaOH solution. The reaction temperature was controlled to 67°C and the reaction was carried out for 12 h. The precursor was obtained by filtration, washing and drying.

[0062] (2) According to the molar ratio of sodium hydroxide to precursor being 1.05:1, sodium hydroxide and the precursor obtained in step (1) are weighed and mixed, and boric acid and bismuth nitrate are added thereto, wherein the amount of boric acid added is 2% of the molar amount of the precursor, and the amount of bismuth nitrate added is 0.2% of the molar amount of the precursor. After the above materials are mixed evenly, the mixture is calcined at 850° C. for 2 h in an air atmosphere, and then the temperature is increased to 900° C. and calcined for 15 h at a heating rate of 2° C. / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0063] (3) Weigh a sintered product and nickel oxide, wherein the mass of nickel oxide is 2% of the sintered product, mix the two evenly, raise the temperature to 950°C at a heating rate of 2°C / min in an air atmosphere, keep the temperature for 3 hours, cool to room temperature, sieve and remove iron, and obtain a sodium positive electrode material.

[0064] Example 6

[0065] This embodiment provides a method for preparing a sodium positive electrode material, and the specific steps and parameters are as follows:

[0066] (1) According to the molar ratio of NiSO4, FeSO4, MnSO4 and CuSO4 being 0.3:0.33:0.33:0.04, NiSO4, FeSO4, MnSO4 and CuSO4 were weighed, and a metal salt solution with a metal salt concentration of 3 mol / L was prepared with water as a solvent (the metal salt concentration was 3 mol / L, indicating that the total amount of NiSO4, FeSO4, MnSO4 and CuSO4 in each liter of solution was 3 mol), and 30 wt% ammonia water and 20 wt% NaOH solution were prepared;

[0067] Protective gas (nitrogen) was introduced into the reaction system at a gas flow rate of 6 L / min. The metal salt solution and ammonia water were mixed at a flow rate of 6 L / h for the metal salt solution and 8 g / L for the ammonia water. The pH value of the system was controlled to 12 using NaOH solution. The reaction temperature was controlled to 65°C and the reaction was carried out for 15 hours. The precursor was obtained by filtration, washing and drying.

[0068] (2) Sodium carbonate and the precursor obtained in step (1) are weighed and mixed in a molar ratio of sodium carbonate to the precursor of 1:1, and H3BO3 and bismuth sulfate are added thereto, wherein the amount of H3BO3 added is 1% of the molar amount of the precursor, and the amount of bismuth sulfate added is 0.25% of the molar amount of the precursor. After the above materials are mixed evenly, the mixture is calcined at 800°C for 4h in an air atmosphere, and then heated to 1050°C for 10h at a heating rate of 2°C / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0069] (3) Weigh a sintered product and TiO2, wherein the mass of TiO2 is 1% of the sintered product, mix the two evenly, raise the temperature to 900°C at a heating rate of 2°C / min in an air atmosphere, keep the temperature for 6 hours, cool to room temperature, sieve and remove iron, and obtain a sodium positive electrode material.

[0070] Comparative Example 1

[0071] This comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those in Example 1, except that step (1) does not contain CuSO4, that is, the obtained precursor is a NiFeMn ternary precursor, and at the same time, the mixed material in step (2) does not contain H3BO3 and Bi2O3. The specific steps are as follows:

[0072] (1) NiSO4, FeSO4 and MnSO4 were weighed according to a molar ratio of NiSO4, FeSO4 and MnSO4 of 0.34:0.33:0.33, and water was used as a solvent to prepare a metal salt solution with a metal salt concentration of 3 mol / L, and 20 wt% ammonia water and 30 wt% NaOH solution were prepared;

[0073] Protective gas was introduced into the reaction system at a gas flow rate of 6 L / min. The metal salt solution and ammonia water were mixed at a metal salt solution flow rate of 6 L / h and an ammonia water flow rate of 8 g / L. The pH value of the system was adjusted to 12 using NaOH solution. The reaction temperature was controlled at 65°C and the reaction was carried out for 15 hours. The precursor was obtained by filtration, washing and drying.

[0074] (2) Sodium carbonate and the precursor obtained in step (1) are weighed and mixed in a molar ratio of sodium carbonate to the precursor of 1:1, and the above materials are mixed at a rotation speed of 3000 rpm for 10 min to obtain a mixture. The mixture is calcined at 800°C for 4 h in an air atmosphere, and then heated to 1050°C for 10 h at a heating rate of 2°C / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0075] (3) Weigh a sintered product and TiO2, wherein the mass of TiO2 is 1% of the sintered product, mix the two at 3000 rpm for 10 min, raise the temperature to 900°C at a heating rate of 2°C / min in an air atmosphere, keep the temperature for 6 h, cool to room temperature, sieve and remove iron to obtain a sodium positive electrode material.

[0076] The microscopic morphology of the sodium cathode material was taken by electron microscope, see Figure 3 It can be seen that the sodium positive electrode material formed in Comparative Example 1 is a single crystal or a single crystal stacked in a quasi-single crystal morphology, but there are problems such as small single crystal size and serious adhesion between particles, resulting in low compaction density of the material and poor cycle performance.

[0077] Comparative Example 2

[0078] The present comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those of Example 1, except that the mixture in step (2) does not contain H3BO3 and Bi2O3, that is, sodium carbonate with a molar ratio of 1:1 and the precursor obtained in step (1) are mixed at a rotation speed of 3000 rpm for 10 min to obtain a mixture, and the mixture is calcined at 800°C for 4 h in an air atmosphere, and then heated to 1050°C and calcined for 10 h at a heating rate of 2°C / min. After natural cooling, the mixture is crushed and sieved to obtain a calcined product.

[0079] The remaining steps are the same as those in Example 1.

[0080] Comparative Example 3

[0081] This comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those in Example 1, except that step (1) does not contain CuSO4, that is, the obtained precursor is a NiFeMn ternary precursor.

[0082] Comparative Example 4

[0083] This comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those in Example 1, except that in step (2), the mixture does not contain Bi2O3 but only contains H3BO3, and the added amount of H3BO3 is 1% of the molar amount of the precursor.

[0084] Comparative Example 5

[0085] This comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those in Example 1, except that in step (2), the mixture does not contain H3BO3 but only contains Bi2O3, and the added amount of Bi2O3 is 0.25% of the molar amount of the precursor.

[0086] Comparative Example 6

[0087] This comparative example provides a method for preparing a sodium positive electrode material. The specific steps and parameters are the same as those in Example 1, except that step (3) does not contain TiO2, that is, a sintered product is placed in an air atmosphere, the temperature is increased to 900°C at a heating rate of 2°C / min, the temperature is kept for 6 hours, and the product is cooled to room temperature. After screening and iron removal, a sodium positive electrode material is obtained.

[0088] Experimental example

[0089] The particle size (D50) and compaction density of the sodium positive electrode materials obtained in Examples 1-6 and Comparative Examples 1-6 were measured. The results are shown in Table 1.

[0090] Wherein, the particle size (D50) of the sodium positive electrode material is measured by a laser particle size tester;

[0091] The compaction density is measured by a powder compaction density instrument with a pressure of 13KN.

[0092] According to the mass ratio of active material, polyvinylidene fluoride and carbon black being 95:2.5:2.5, the sodium positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-6 were evenly mixed with polyvinylidene fluoride and carbon black, an appropriate amount of 1-methyl-2-pyrrolidone was added, mixed evenly to form a slurry, evenly coated on an aluminum sheet, dried, and pressed into a positive electrode sheet, a 1 mol / L NaClO4 propylene carbonate (PC) solution was used as an electrolyte, and a metal sodium sheet was used as a negative electrode to assemble a 2032 button-type sodium ion battery.

[0093] The button-type sodium ion battery formed was measured at a voltage range of 2.0V-4.0V, the capacity of 0.1C charge / 0.1C discharge, the cut-off current ratio was 0.05C, and the button discharge energy density was measured as the energy density. The results are shown in Table 1.

[0094] Table 1 Performance determination of sodium positive electrode materials

[0095]

[0096]

[0097] According to the data in Table 1, the precursor of Comparative Example 3 lacks copper and is not doped with Bi and B elements, which not only limits the grain growth but also has poor grain boundary optimization effect. Comparative Example 2 lacks Bi and B elements, which makes it impossible to catalyze grain growth and grain boundary optimization. Due to the lack of copper metal in the precursor of Comparative Example 3, the grain size growth is limited. Comparative Examples 1-3 result in small sodium positive electrode materials and low compaction density, and the final sodium battery has poor charging, discharging and energy density performance; resulting in low grain size and compaction density, and the formed sodium battery has poor charging, discharging and energy density performance; Comparative Examples 4 and 5 are doped with B or Bi elements to increase the single crystal size, but the compaction density is still poor, and Comparative Example 6 is not coated. Due to the high residual alkali in the sample of Comparative Example 6, the particle agglomeration problem occurs, the compaction density decreases, and the charging, discharging and energy density are affected; the grain size of the sodium positive electrode material formed by the method provided in the embodiment of the present invention is increased, the compaction density is greatly improved, and the charging, discharging and energy density of the formed sodium battery are good.

[0098] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

Claims

1. A method for preparing a high energy density sodium positive electrode material, characterized in that: The following steps are included: S1, mixing a sodium source, a precursor, a boron source and a bismuth source, and sintering to obtain an intermediate, wherein the metal elements in the precursor include nickel, iron, manganese and copper; S2, mixing the intermediate and the coating agent, and sintering to obtain a sodium positive electrode material.

2. The method for preparing a high energy density sodium positive electrode material according to claim 1, characterized in that: In step S1, the sodium source includes at least one of sodium carbonate, sodium hydroxide and sodium chloride; and / or, The boron source comprises at least one of boron oxide and boric acid; and / or, The bismuth source includes at least one of bismuth oxide, bismuth chloride, bismuth nitrate, and bismuth sulfate.

3. The method for preparing a high energy density sodium positive electrode material according to claim 2, characterized in that: The molar ratio of the sodium source to the precursor is 0.95-1.05:1; and / or, Based on the precursor, the molar amount of the boron source is 0.25-2% of the molar amount of the precursor; and / or, Based on the precursor, the molar amount of the bismuth source is 0.2-1% of the molar amount of the precursor; and / or, The sintering step in step S1 specifically includes, in an air atmosphere, firstly keeping the temperature at 500-850° C. for 2-6 hours, and then keeping the temperature at 900-1200° C. for 5-15 hours.

4. The method for preparing a high energy density sodium positive electrode material according to claim 1, characterized in that: The coating agent comprises at least one of nickel oxide, manganese oxide or titanium oxide; and / or, Based on the mass of the intermediate, the mass fraction of the coating agent is 0.5-2%; and / or, The specific steps of sintering in step S2 include keeping the temperature at 750-950° C. for 3-8 hours in an air atmosphere.

5. The method for preparing a high energy density sodium positive electrode material according to claim 1, characterized in that: The chemical formula of the precursor is Ni a Fe b Mn c Cu d (OH)2, wherein 0.2≤a≤0.4, 0.2≤b≤0.4, 0.2≤c≤0.4, 0.02≤d≤0.

05.

6. The method for preparing a high energy density sodium positive electrode material according to claim 5, characterized in that: The preparation method of the precursor comprises: in an inert atmosphere, forming a metal salt solution from a nickel source, an iron source, a manganese source and a copper source, and reacting the metal salt solution, a precipitant and a complexing agent to form a precursor.

7. The method for preparing a high energy density sodium positive electrode material according to claim 6, characterized in that: In the method for preparing the precursor, the pH value of the reaction system is 12-12.3, the reaction temperature is 63-67° C., and the reaction time is 12-18 h; and / or, In the precursor preparation method, the flow rate of the metal salt solution into the reaction system is 5-7 L / h, the flow rate of the complexing agent into the reaction system is 6-10 g / L, and the flow rate of the inert gas into the reaction system is 5-8 L / min.

8. The method for preparing a high energy density sodium positive electrode material according to claim 1, characterized in that: The nickel source includes at least one of nickel sulfate, nickel nitrate and nickel chloride; and / or, The iron source includes at least one of ferric sulfate, ferric nitrate and ferric chloride; The manganese source includes at least one of manganese sulfate, manganese nitrate and manganese chloride; and / or, The copper source includes at least one of copper sulfate, copper nitrate and copper chloride; and / or, The precipitant includes at least one of sodium hydroxide, potassium hydroxide, ammonia water, sodium carbonate and ammonium carbonate; and / or, The complexing agent includes at least one of ammonia water and citric acid.

9. The method for preparing a high energy density sodium positive electrode material according to claim 8, characterized in that: The total concentration of metal ions in the metal salt solution is 2-4 mol / L; and / or, The complexing agent is ammonia water, and the concentration of ammonia water is 15-30wt%; and / or, The precipitant is a sodium hydroxide aqueous solution, and the concentration of the sodium hydroxide aqueous solution is 20-40wt%.

10. A sodium battery, characterized in that: It comprises a sodium positive electrode material, and the sodium positive electrode material is prepared by the preparation method of the high energy density sodium positive electrode material according to any one of claims 1 to 9.

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