Preparation method of positive electrode material for improving cycle performance of sodium battery

Abstract

The invention relates to the technical field of batteries, in particular to a preparation method of a positive electrode material for improving the cycle performance of a sodium battery. According to the invention, sodium ferric phosphate, manganese carbonate and lithium hydroxide are added, blended and sintered to obtain modified sodium ferric phosphate. And mixing the modified sodium ferric phosphate, a carbon nanotube acetone solution and glucose, and carrying out ball milling and high-temperature sintering to obtain the positive electrode active material. And uniformly stirring and mixing the positive active material, the binder and the modified carbon nanotube conductive material, then coating an aluminum foil with the mixture, and drying to obtain the positive pole piece.

Description

Technical Field

[0001] The invention relates to the technical field of batteries, and in particular to a method for preparing a positive electrode material for improving the cycle performance of a sodium battery. Background Art

[0002] Sodium-ion batteries are considered to be a promising energy storage solution due to the abundance and low cost of sodium resources in the earth's crust. Among them, sodium iron phosphate materials, as a potential positive electrode material for sodium-ion batteries, have attracted widespread attention due to their high theoretical capacity, good thermal stability and environmental friendliness. However, they still face some challenges in practical applications, especially those related to cycle performance. The crystal structure of sodium iron phosphate materials is similar to that of lithium iron phosphate in lithium-ion batteries, which belongs to the olivine structure. In this structure, sodium ions occupy specific lattice positions for reversible deintercalation during the charge and discharge process. However, compared with lithium iron phosphate materials, sodium iron phosphate materials exhibit larger volume changes during the charge and discharge process, which may lead to structural degradation of the material and attenuation of electrochemical performance. In addition, the Fe / Na anti-site defects present in the positive electrode materials of sodium iron phosphate materials are the key factors affecting their long-term cycle performance. These defects disrupt the order of the crystal structure, resulting in obstruction of the sodium ion transmission path, thereby reducing the ionic conductivity of the material. At the same time, anti-site defects may also cause changes in the electron conduction path, further affecting the overall electrochemical performance.

[0003] In order to overcome the defects of the prior art, the present invention provides a method for preparing a positive electrode material for improving the cycle performance of a sodium battery. Summary of the invention

[0004] The object of the present invention is to provide a method for preparing a positive electrode material for improving the cycle performance of a sodium battery, so as to solve the problems in the prior art.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A method for preparing a positive electrode material for improving the cycle performance of a sodium battery comprises the following steps: mechanically mixing sodium iron phosphate, manganese carbonate and lithium hydroxide uniformly, and then sintering at 730-750° C. for 10-12 hours in a nitrogen environment to obtain modified sodium iron phosphate.

[0007] More optimally, when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (50-55):1, and the mass ratio of sodium iron phosphate to lithium hydroxide is (10-12):1.

[0008] More optimally, the sintering parameters are: heating rate of 15-20°C / min, and annealing rate of 25-30°C / min.

[0009] More optimally, the modified sodium iron phosphate, carbon nanotube acetone solution and glucose are mixed and fully ball-milled for 8-10 hours to obtain a mixture; the mixture is vacuum dried, ground and sintered at high temperature to obtain a positive electrode active material; the positive electrode active material, binder polyvinylidene fluoride and modified carbon nanotube conductive material are stirred and mixed, coated on 15um aluminum foil, and dried at 110-120°C for 20-24 hours to obtain a positive electrode sheet.

[0010] More optimally, the proportion of carbon nanotubes in the mixture is 5-7wt% and the proportion of glucose in the mixture is 15-18wt%; high-temperature sintering parameters: pre-sintering at 300-400℃ for 1-2h, then sintering at 650-750℃ for 8-10h; the mixing mass ratio of positive electrode active material, binder polyvinylidene fluoride, and modified carbon nanotube conductive material is 8:1:(1-2).

[0011] More optimally, the preparation steps of the modified carbon nanotube conductive material are:

[0012] Step 1: Evenly mix polyvinyl pyrrolidone and methanol, then add carboxylated carbon nanotubes, fully stir and disperse for 1-2 hours to obtain a carbon nanotube suspension; evenly mix cobalt nitrate hexahydrate and methanol, then add the carbon nanotube suspension, fully stir and disperse for 2-3 hours, then add 2-methylimidazole solution and fully stir for 2-3 hours, after the stirring is completed, stand, centrifuge, wash, dry, and calcine to obtain a carbon nanotube hybrid MOF material;

[0013] Step 2: Under vacuum conditions, mix aniline monomer and carbon nanotube hybrid MOF material, add hydrochloric acid solution, stir and react at 0-4°C for 3-4 hours, then slowly add ammonium persulfate solution dropwise under nitrogen environment, continue stirring and react for 30-35 hours, and after the reaction is completed, wash, dry and grind to obtain modified carbon nanotube conductive material.

[0014] More optimally, in step one, when preparing carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate, and 2-methylimidazole is 1:(0.5-0.7):2:2; calcination parameters: heating rate of 10-15°C / min, sintering at 750-800°C for 4.5-5.5h.

[0015] More optimally, in step 2, when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material used is 20-25wt%.

[0016] Beneficial effects of the present invention:

[0017] The invention is characterized in that modified sodium iron phosphate is obtained by adding sodium iron phosphate, manganese carbonate and lithium hydroxide, and then mixing and sintering. +and high-valence metal cations Mn 2+ are ion-doped to finally obtain modified sodium iron phosphate. Li + doping causes the two stable intermediate phases of conventional NaFePO 4 to become three stable intermediate phases. The formation of multiple intermediate phases not only increases the theoretical capacity and average voltage of NaFePO 4 , but also reduces the volume change during charging. Therefore, Li ion doping at the Fe 2+ site can stabilize the lattice of NaFePO 4 and reduce the adverse effects of Fe / Na antisite defects in the NaFePO 4 framework. Mn element doping results in the formation of a stable intermediate solid solution phase of Na y Mn x Fe (1-x) PO 4 (x < y) during charge and discharge. This phase transition mechanism effectively reduces the electrode volume change and lattice mismatch, and reduces the stress caused by sodium transfer during charge and discharge, thereby improving the cycle stability.

[0018] The feature of the present invention is that modified sodium iron phosphate, a carbon nanotube acetone solution, and glucose are mixed, and the positive electrode active material is obtained after ball milling and high-temperature sintering. In this step, the carbon nanotubes and glucose are uniformly dispersed in the modified sodium iron phosphate by ball milling. During the high-temperature sintering process, these carbon sources will carbonize and form a continuous conductive network on the material surface, which helps the transmission of electrons in the electrode, thereby improving the overall conductivity; in addition, the carbon layer can promote the diffusion of lithium ions, enabling lithium ions to be embedded in and extracted from the material more quickly, thereby improving the kinetic performance of the electrode; the carbon layer can also act as a buffer layer to reduce the volume change of the material during charge and discharge, thereby improving the structural stability of the material.

[0019] The feature of the present invention is that the positive electrode active material, the binder, and the modified carbon nanotube conductive material are stirred and mixed, and then coated on the aluminum foil, and dried to obtain the positive electrode plate. The preparation process of the modified carbon nanotube conductive material is as follows: by adding polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate, and 2-methylimidazole, a carbon nanotube hybrid MOF material is prepared; and then aniline monomer, carbon nanotube hybrid MOF material, hydrochloric acid solution and ammonium persulfate solution are mixed to obtain a modified carbon nanotube conductive material. In step one, the carboxylated carbon nanotubes are used as the skeleton, and the MOF material is connected and inserted into the structure of the carboxylated carbon nanotubes, and finally a carbon nanotube hybrid MOF material is obtained, which combines the conductivity of carbon nanotubes and the porous structure of MOF, providing a higher surface area and adsorption capacity. Furthermore, in step 2, aniline monomer, hydrochloric acid solution and ammonium persulfate solution are added to the carbon nanotube hybrid MOF material, thereby further inserting the conductive polymer polyaniline into the porous conductive network structure of the carbon nanotube hybrid MOF material. By continuously dispersing and growing polyaniline into the conductive network, the pore structure inside the material can be further increased, so that the composite material with a multi-level structure has a higher specific surface area, which can provide a fast channel for the embedding and extraction of electrolyte ions and electrons.

[0020] In summary, the carbon nanotubes and carbonized glucose network in the positive electrode active material and the carbon nanotubes and polyaniline network in the modified carbon nanotube conductive material can form a continuous conductive network. This linkage effect enables electrons to be efficiently transmitted throughout the positive electrode sheet, reducing the charge transfer resistance. In addition, the carbon coating layer of the positive electrode active material can provide structural support for the modified carbon nanotube conductive material, and the high conductivity of the modified carbon nanotube conductive material can further enhance the conductive properties of the positive electrode active material. DETAILED DESCRIPTION

[0021] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Source of raw materials:

[0023] Polyvinylidene fluoride is Solvay 5130; SuperP is Swiss Termega; carbon nanotubes are provided by Jiangsu Xianfeng Nanomaterials Technology Co., Ltd. with a specification of 95%; glucose is provided by Sigma-Aldrich with a specification of AR; carboxylated carbon nanotubes are provided by Nanjing Xianfeng Nanotechnology Co., Ltd. with a specification of 95%; polyvinyl pyrrolidone is provided by Shanghai Aladdin Biochemical Technology Co., Ltd. with a molecular weight of 24,000.

[0024] Example 1: S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing the modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0025] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent SuperP are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent SuperP is 8:1:1.

[0026] Example 2: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (40-45): 1

[0027] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 42:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0028] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0029] Example 3: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (45-50): 1

[0030] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 47:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0031] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0032] Example 4: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (55-60): 1

[0033] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 57:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0034] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0035] Example 5: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (60-65): 1

[0036] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 62:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0037] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0038] Example 6: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to lithium hydroxide is (6-8): 1

[0039] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 7:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0040] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0041] Example 7: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to lithium hydroxide is (8-10): 1

[0042] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 9:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0043] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0044] Example 8: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to lithium hydroxide is (12-14): 1

[0045] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 13:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0046] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0047] Example 9: is basically the same as Example 1, except that when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to lithium hydroxide is (14-16): 1

[0048] S1: Sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1, and the mass ratio of sodium iron phosphate to lithium hydroxide is 15:1; sintering parameters: heating rate is 20°C / min, and annealing rate is 30°C / min;

[0049] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0050] Example 10: S1: The sodium iron phosphate material, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain a modified sodium iron phosphate material; when preparing the modified sodium iron phosphate material, the mass ratio of the sodium iron phosphate material to the manganese carbonate is 52:1, and the mass ratio of the sodium iron phosphate material to the lithium hydroxide is 11:1; sintering parameters: heating rate of 20°C / min, annealing rate of 30°C / min;

[0051] S2: Step 1: Mix the modified sodium iron phosphate, carbon nanotube acetone solution and glucose, and fully ball-mill for 10 hours to obtain a mixture; vacuum dry, grind and sinter the mixture at high temperature to obtain a positive electrode active material; the carbon nanotube accounts for 7wt% and the glucose accounts for 18wt% in the mixture; high temperature sintering parameters: pre-sinter at 400℃ for 1.5h, and then sinter at 750℃ for 10h;

[0052] Step 2: Mix polyvinyl pyrrolidone and methanol evenly, then add carboxylated carbon nanotubes, stir and disperse for 2 hours to obtain a carbon nanotube suspension; mix cobalt nitrate hexahydrate and methanol evenly, then add carbon nanotube suspension, stir and disperse for 3 hours, then add 2-methylimidazole solution and stir for 3 hours, after stirring, stand, centrifuge, wash, dry and calcine to obtain a carbon nanotube hybrid MOF material; when preparing the carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate and 2-methylimidazole is 1:0.7:2:2; calcination parameters: heating rate of 10°C / min, sintering at 750°C for 5.5 hours;

[0053] Step 3: Under vacuum conditions, aniline monomer and carbon nanotube hybrid MOF material are mixed, hydrochloric acid solution is added, stirred and reacted at 0°C for 4 hours, and then ammonium persulfate solution is slowly added dropwise under a nitrogen environment, and the stirring reaction is continued for 35 hours. After the reaction is completed, the modified carbon nanotube conductive material is obtained by washing, drying and grinding; when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material is 25wt%;

[0054] Step 4: After mixing the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material, apply them to 15um aluminum foil, and dry them at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:1.5.

[0055] Example 11: The same as Example 10, except that the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:(0.5-1)

[0056] S1: The sodium iron phosphate material, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours in a nitrogen environment to obtain a modified sodium iron phosphate material; when preparing the modified sodium iron phosphate material, the mass ratio of the sodium iron phosphate material to manganese carbonate is 52:1, and the mass ratio of the sodium iron phosphate material to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, annealing rate is 30°C / min;

[0057] S2: Step 1: Mix the modified sodium iron phosphate, carbon nanotube acetone solution and glucose, and fully ball-mill for 10 hours to obtain a mixture; vacuum dry, grind and sinter the mixture at high temperature to obtain a positive electrode active material; the carbon nanotube accounts for 7wt% and the glucose accounts for 18wt% in the mixture; high temperature sintering parameters: pre-sinter at 400℃ for 1.5h, and then sinter at 750℃ for 10h;

[0058] Step 2: Mix polyvinyl pyrrolidone and methanol evenly, then add carboxylated carbon nanotubes, stir and disperse for 2 hours to obtain a carbon nanotube suspension; mix cobalt nitrate hexahydrate and methanol evenly, then add carbon nanotube suspension, stir and disperse for 3 hours, then add 2-methylimidazole solution and stir for 3 hours, after stirring, stand, centrifuge, wash, dry and calcine to obtain a carbon nanotube hybrid MOF material; when preparing the carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate and 2-methylimidazole is 1:0.7:2:2; calcination parameters: heating rate of 10°C / min, sintering at 750°C for 5.5 hours;

[0059] Step 3: Under vacuum conditions, aniline monomer and carbon nanotube hybrid MOF material are mixed, hydrochloric acid solution is added, stirred and reacted at 0°C for 4 hours, and then ammonium persulfate solution is slowly added dropwise under a nitrogen environment, and the stirring reaction is continued for 35 hours. After the reaction is completed, the modified carbon nanotube conductive material is obtained by washing, drying and grinding; when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material is 25wt%;

[0060] Step 4: After mixing the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material, apply them to a 15um aluminum foil, and dry them at 120°C for 24 hours to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:0.7.

[0061] Example 12: The same as Example 10, except that the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:(2-3)

[0062] S1: The sodium iron phosphate material, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours in a nitrogen environment to obtain a modified sodium iron phosphate material; when preparing the modified sodium iron phosphate material, the mass ratio of the sodium iron phosphate material to manganese carbonate is 52:1, and the mass ratio of the sodium iron phosphate material to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, annealing rate is 30°C / min;

[0063] S2: Step 1: Mix the modified sodium iron phosphate, carbon nanotube acetone solution and glucose, and fully ball-mill for 10 hours to obtain a mixture; vacuum dry, grind and sinter the mixture at high temperature to obtain a positive electrode active material; the carbon nanotube accounts for 7wt% and the glucose accounts for 18wt% in the mixture; high temperature sintering parameters: pre-sinter at 400℃ for 1.5h, and then sinter at 750℃ for 10h;

[0064] Step 2: Mix polyvinyl pyrrolidone and methanol evenly, then add carboxylated carbon nanotubes, stir and disperse for 2 hours to obtain a carbon nanotube suspension; mix cobalt nitrate hexahydrate and methanol evenly, then add carbon nanotube suspension, stir and disperse for 3 hours, then add 2-methylimidazole solution and stir for 3 hours, after stirring, stand, centrifuge, wash, dry and calcine to obtain a carbon nanotube hybrid MOF material; when preparing the carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate and 2-methylimidazole is 1:0.7:2:2; calcination parameters: heating rate of 10°C / min, sintering at 750°C for 5.5 hours;

[0065] Step 3: Under vacuum conditions, aniline monomer and carbon nanotube hybrid MOF material are mixed, hydrochloric acid solution is added, stirred and reacted at 0°C for 4 hours, and then ammonium persulfate solution is slowly added dropwise under a nitrogen environment, and the stirring reaction is continued for 35 hours. After the reaction is completed, the modified carbon nanotube conductive material is obtained by washing, drying and grinding; when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material is 25wt%;

[0066] Step 4: After mixing the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material, apply them to 15um aluminum foil, and dry them at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:2.5.

[0067] Comparative Example 1: No manganese carbonate is introduced in step S1, and the rest is the same as Example 1, and the specific steps are as follows: S1: sodium iron phosphate and lithium hydroxide are mechanically mixed evenly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing the modified sodium iron phosphate, the mass ratio of sodium iron phosphate to lithium hydroxide is 11:1; sintering parameters: heating rate of 20°C / min, annealing rate of 30°C / min;

[0068] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0069] Comparative Example 2: No lithium hydroxide is introduced in step S1, and the rest is the same as Example 1, and the specific steps are as follows: S1: Sodium iron phosphate and manganese carbonate are mechanically mixed evenly, and then sintered at 750°C for 12 hours under a nitrogen environment to obtain modified sodium iron phosphate; when preparing the modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is 52:1; sintering parameters: heating rate of 20°C / min, annealing rate of 30°C / min;

[0070] S2: The prepared modified sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P are stirred and mixed, and then coated on a 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the conductive agent Super P is 8:1:1.

[0071] Comparative Example 3: In step S1, manganese carbonate and lithium hydroxide are introduced, and sodium iron phosphate is used as the positive electrode active material. The rest is the same as Example 1, and the specific steps are as follows: S1: Sodium iron phosphate is used as the positive electrode active material; the positive electrode active material, binder polyvinylidene fluoride, and conductive agent Super P are stirred and mixed, and then coated on 15um aluminum foil, and dried at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, binder polyvinylidene fluoride, and conductive agent Super P is 8:1:1.

[0072] Comparative Example 4: The prepared modified sodium iron phosphate is used as the positive electrode active material, and the rest is the same as Example 10, and the specific steps are as follows:

[0073] S1: The sodium iron phosphate material, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours in a nitrogen environment to obtain a modified sodium iron phosphate material; when preparing the modified sodium iron phosphate material, the mass ratio of the sodium iron phosphate material to manganese carbonate is 52:1, and the mass ratio of the sodium iron phosphate material to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, annealing rate is 30°C / min;

[0074] S2: Step 1: Using the prepared modified sodium iron phosphate as a positive electrode active material;

[0075] Step 2: Mix polyvinyl pyrrolidone and methanol evenly, then add carboxylated carbon nanotubes, stir and disperse for 2 hours to obtain a carbon nanotube suspension; mix cobalt nitrate hexahydrate and methanol evenly, then add carbon nanotube suspension, stir and disperse for 3 hours, then add 2-methylimidazole solution and stir for 3 hours, after stirring, stand, centrifuge, wash, dry and calcine to obtain a carbon nanotube hybrid MOF material; when preparing the carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate and 2-methylimidazole is 1:0.7:2:2; calcination parameters: heating rate of 10°C / min, sintering at 750°C for 5.5 hours;

[0076] Step 3: Under vacuum conditions, aniline monomer and carbon nanotube hybrid MOF material are mixed, hydrochloric acid solution is added, stirred and reacted at 0°C for 4 hours, and then ammonium persulfate solution is slowly added dropwise under a nitrogen environment, and the stirring reaction is continued for 35 hours. After the reaction is completed, the modified carbon nanotube conductive material is obtained by washing, drying and grinding; when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material is 25wt%;

[0077] Step 4: After mixing the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material, apply them to 15um aluminum foil, and dry them at 120°C for 24h to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:1.5.

[0078] Comparative Example 5: The modified carbon nanotube conductive material is replaced with the conductive agent Super P, and the rest is the same as Example 10, and the specific steps are as follows:

[0079] S1: The sodium iron phosphate material, manganese carbonate and lithium hydroxide are mechanically mixed uniformly, and then sintered at 750°C for 12 hours in a nitrogen environment to obtain a modified sodium iron phosphate material; when preparing the modified sodium iron phosphate material, the mass ratio of the sodium iron phosphate material to manganese carbonate is 52:1, and the mass ratio of the sodium iron phosphate material to lithium hydroxide is 11:1; sintering parameters: heating rate is 20°C / min, annealing rate is 30°C / min;

[0080] S2: Step 1: Mix the modified sodium iron phosphate, carbon nanotube acetone solution and glucose, and fully ball-mill for 10 hours to obtain a mixture; vacuum dry, grind and sinter the mixture at high temperature to obtain a positive electrode active material; the carbon nanotube accounts for 7wt% and the glucose accounts for 18wt% in the mixture; high temperature sintering parameters: pre-sinter at 400℃ for 1.5h, and then sinter at 750℃ for 10h;

[0081] Step 2: After the positive electrode active material, the binder polyvinylidene fluoride and the conductive agent Super P are stirred and mixed, they are coated on a 15um aluminum foil and dried at 120°C for 24 hours to obtain a positive electrode sheet; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride and the conductive agent Super P is 8:1:1.5.

[0082] Detection test:

[0083] Battery assembly: The button battery shell is selected from the CR2032 model, the diaphragm is selected from the 20um diaphragm, and the electrode is selected from the positive electrode prepared by the present invention. In a glove box filled with argon, the button battery is assembled in the following assembly order: battery shell - placing the positive electrode - dripping the electrolyte - placing the diaphragm - dripping the electrolyte - placing the sodium sheet - placing the gasket spring - battery shell.

[0084] Cycle performance test: A button battery charge and discharge tester (Wuhan Blue Electric, CT3002A) was used to perform 30, 50, and 100 cycles of 0.2C charge and discharge tests on the button battery, with a voltage range of 3.0-3.8V.

[0085] Positive electrode sheet resistivity test: The positive electrode sheet prepared by the present invention was selected, and the positive electrode sheet was fixed and tested using a ST-2258A four-probe tester, and the test was performed 5 times to obtain the average value. The test results are shown in the following table.

[0086] 30-cycle performance 50-cycle performance 100-cycle performance <![CDATA[Resistivity test ( mΩ ·cm)]]> Example 1 95.4％ 93.1％ 89.8％ 546 Example 2 90.1％ 88.2％ 82.1％ 584 Example 3 90.6％ 88.9％ 83.1％ 577 Example 4 90.9％ 89.1％ 82.9％ 573 Example 5 90.3％ 88.6％ 82.3％ 582 Example 6 91.6％ 88.8％ 81.8％ 562 Example 7 91.8％ 89.6％ 82.5％ 561 Example 8 91.9％ 89.3％ 82.6％ 560 Example 9 91.0％ 87.8％ 81.3％ 571 Example 10 98.7％ 96.3％ 91.4％ 435 Embodiment 11 96.7％ 94.8％ 88.1％ 456 Example 12 97.2％ 95.1％ 89.6％ 448 Comparative Example 1 87.6％ 81.9％ 75.2％ 633 Comparative Example 2 87.5％ 81.1％ 74.7％ 636 Comparative Example 3 80.1％ 71.2％ 62.7％ 737 Comparative Example 4 95.2％ 91.9％ 88.5％ 474 Comparative Example 5 94.3％ 91.5％ 87.2％ 503

[0087] Conclusion: This application adopts the calcination method to prepare the modified NaFePO 4 Materials, basic metal ions Li+ and high-valent metal cations Mn 2+ Ion doping was performed to obtain modified NaFePO 4 Li+ doping makes conventional NaFePO 4 The two stable intermediate phases are transformed into three stable intermediate phases, and the formation of multiple intermediate phases not only improves the NaFePO 4 Theoretical capacity and average voltage, but also reduce the volume change during charging, so Fe 2+ Li ion doping at the site can stabilize NaFePO 4 lattice, and relieve NaFePO 4 The adverse effect of Fe / Na anti-site defects in the framework. Mn doping causes the formation of Na y Mn x Fe (1-x) PO 4A stable intermediate solid solution phase of (x < y). This phase transition mechanism effectively reduces the volume change of the electrode and lattice mismatch, and reduces the stress caused by the transfer of sodium during charge and discharge, thereby improving the cycle stability. Therefore, the cycle performance of Example 1 is superior to that of Examples 2 - 9 and Comparative Examples 1 - 3, and the electrical conductivity is also relatively strong.

[0088] Based on Examples 1 - 9, the present invention prepared a cathode active material and a modified carbon nanotube conductive material. After stirring and mixing the cathode active material, binder, and modified carbon nanotube conductive material, they were coated on an aluminum foil and dried to obtain a cathode electrode sheet (see Examples 10 - 12). A variety of continuous porous conductive networks were introduced into the cathode electrode sheet prepared according to the preparation method of the present invention, which can significantly improve the electrical conductivity of the cathode electrode sheet. Therefore, the cathode electrode sheet prepared by the present invention has a low resistivity (435 mΩ·cm, 456 mΩ·cm, 448 mΩ·cm).

[0089] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device.

[0090] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material for improving the cycle performance of a sodium battery, characterized in that: The following steps are involved: The sodium iron phosphate, manganese carbonate and lithium hydroxide are mechanically mixed evenly, and then sintered at 730-750° C. for 10-12 hours in a nitrogen environment to obtain modified sodium iron phosphate.

2. The method for preparing a positive electrode material for improving the cycle performance of a sodium battery according to claim 1, characterized in that: When preparing modified sodium iron phosphate, the mass ratio of sodium iron phosphate to manganese carbonate is (50-55):1, and the mass ratio of sodium iron phosphate to lithium hydroxide is (10-12):

1.

3. The method for preparing a positive electrode material for improving the cycle performance of a sodium battery according to claim 1, characterized in that: Sintering parameters: heating rate is 15-20℃ / min, annealing rate is 25-30℃ / min.

4. A positive electrode material for improving the cycle performance of a sodium battery, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 3.

5. A positive electrode sheet prepared based on the positive electrode material according to claim 4, characterized in that: The modified sodium iron phosphate, carbon nanotube acetone solution and glucose are mixed and fully ball-milled for 8-10 hours to obtain a mixture; the mixture is vacuum dried, ground and sintered at high temperature to obtain a positive electrode active material; the positive electrode active material, binder polyvinylidene fluoride and modified carbon nanotube conductive material are stirred and mixed, coated on 15um aluminum foil, and dried at 110-120°C for 20-24 hours to obtain a positive electrode sheet.

6. The positive electrode sheet prepared from the positive electrode material according to claim 5, characterized in that: The proportion of carbon nanotubes in the mixture is 5-7wt% and the proportion of glucose in the mixture is 15-18wt%; High temperature sintering parameters: pre-sintering at 300-400°C for 1-2h, then sintering at 650-750°C for 8-10h; the mixing mass ratio of the positive electrode active material, the binder polyvinylidene fluoride, and the modified carbon nanotube conductive material is 8:1:(1-2).

7. The positive electrode sheet prepared from the positive electrode material according to claim 5, characterized in that: The preparation steps of the modified carbon nanotube conductive material are as follows: Step 1: Evenly mix polyvinyl pyrrolidone and methanol, then add carboxylated carbon nanotubes, fully stir and disperse for 1-2 hours to obtain a carbon nanotube suspension; evenly mix cobalt nitrate hexahydrate and methanol, then add the carbon nanotube suspension, fully stir and disperse for 2-3 hours, then add 2-methylimidazole solution and fully stir for 2-3 hours, after the stirring is completed, stand, centrifuge, wash, dry, and calcine to obtain a carbon nanotube hybrid MOF material; Step 2: Under vacuum conditions, mix aniline monomer and carbon nanotube hybrid MOF material, add hydrochloric acid solution, stir and react at 0-4°C for 3-4 hours, then slowly add ammonium persulfate solution dropwise under nitrogen environment, continue stirring and react for 30-35 hours, and after the reaction is completed, wash, dry and grind to obtain modified carbon nanotube conductive material.

8. The positive electrode sheet prepared from the positive electrode material according to claim 7, characterized in that: In step 1, when preparing carbon nanotube hybrid MOF material, the reaction mass ratio of polyvinyl pyrrolidone, carboxylated carbon nanotubes, cobalt nitrate hexahydrate, and 2-methylimidazole is 1: (0.5-0.7): 2: 2; calcination parameters: heating rate of 10-15°C / min, sintering at 750-800°C for 4.5-5.5h.

9. The positive electrode sheet prepared from the positive electrode material according to claim 7, characterized in that: In step 2, when preparing the modified carbon nanotube conductive material, the amount of carbon nanotube hybrid MOF material used is 20-25wt%.

10. Use of the positive electrode sheet according to claim 5 in a button battery.