High-compaction high-capacity positive electrode slurry based on polyanion positive electrode material, pole piece, sodium ion battery and preparation method of sodium ion battery

Abstract

The invention discloses high-compaction high-capacity positive electrode slurry based on a polyanion positive electrode material, a pole piece, a sodium ion battery and a preparation method of the sodium ion battery, and the positive electrode slurry of composite powder is prepared by simply dry-mixing polyanion positive electrode material powder and layered oxide positive electrode material powder of the sodium ion battery. Or in the slurry preparation process, sodium ion battery polyanion type positive electrode material powder and layered oxide positive electrode material powder are respectively added for slurry stirring and mixing, so that composite positive electrode slurry is obtained, the obtained slurry is coated, and the sodium ion battery is prepared. The compaction density and gram volume of the composite positive plate are regulated and controlled by controlling the adding proportion of the two positive electrode materials of the slurry and the types of the positive electrode materials.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a high-density high-capacity positive electrode slurry, a pole piece and a sodium ion battery based on a polyanion positive electrode material and a preparation method thereof. Background Art

[0002] Polyanion sodium ion batteries are suitable for large-scale energy storage, two-wheeled vehicles and low-speed electric vehicles due to their abundant resources, low cost, high stability and good safety. However, the gram capacity and compaction density of polyanion positive electrode materials for sodium ion batteries (such as sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron phosphate pyrophosphate, sodium iron sulfate, etc.) are relatively low, with a gram capacity of about 90-120 mAh / g and a compaction density of about 1.3-2.0 g / cm 3 The gram capacity of lithium iron phosphate cathode material is 150-165 mAh / g, and the compaction density is about 2.3-2.6 g / cm 3 Therefore, although the unit cost of polyanion cathode materials for sodium-ion batteries is cheaper than that of lithium iron phosphate cathodes, the energy density of lithium iron phosphate batteries is significantly higher than that of polyanion sodium-ion batteries. The amount of positive and negative electrode materials required for sodium-ion batteries per watt-hour of electricity is higher, and the cost of lithium iron phosphate batteries has decreased, making the cost of lithium iron phosphate batteries per watt-hour lower than that of polyanion sodium-ion batteries. This poses a huge challenge to the cost of sodium-ion batteries and seriously hinders the commercialization of sodium-ion batteries.

[0003] In addition, most of the capacity of polyanion sodium-ion batteries is concentrated on the voltage platform, and there is almost no capacity contribution in the low-voltage and high-voltage areas. Therefore, the battery capacity cannot be deduced based on the voltage value, which brings difficulties to battery management, battery pack capacity balancing, and power estimation. Layered oxides (such as sodium nickel iron manganese oxide, sodium copper iron manganese oxide, sodium nickel manganese oxide, etc.) have capacity contributions in both low-voltage and high-voltage areas, and have higher gram capacity and compaction density, but they still have problems such as low cycle stability, sensitivity to moisture, and poor thermal stability.

[0004] In order to improve the comprehensive performance of polyanion sodium ion batteries such as specific energy, cycle stability, and safety, reduce their manufacturing cost per watt-hour, and enhance the cost advantage and application potential of sodium ion batteries, the present invention combines the advantages of sodium ion battery polyanion positive electrode materials and layered oxides, prepares polyanion positive electrode materials and layered oxide composite positive electrode slurry and positive electrode sheets to improve the compaction density and capacity of the polyanion positive electrode materials, and assembles the prepared composite electrode sheets into soft-pack batteries. Summary of the invention

[0005] The present invention aims to provide a high-density high-capacity positive electrode slurry, a pole piece and a sodium ion battery based on a polyanion positive electrode material and a preparation method thereof. In view of the problems of low specific energy, high cost per watt-hour of electricity, and difficult battery management of polyanion sodium ion batteries, a high-density high-capacity pole piece based on a polyanion positive electrode material and a preparation method of a sodium ion battery are proposed.

[0006] The composite powder positive electrode slurry is prepared by simply dry mixing the sodium ion battery polyanion positive electrode material powder and the layered oxide positive electrode material powder. Alternatively, in the slurry preparation process, the sodium ion battery polyanion positive electrode material powder and the layered oxide positive electrode material powder are added separately for slurry stirring and mixing to obtain a composite positive electrode slurry, and the obtained slurry is coated to make a sodium ion battery. The compaction density and gram capacity of the composite positive electrode sheet are regulated by controlling the addition ratio of the two positive electrode materials in the slurry and the type of positive electrode material.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material, comprising:

[0009] S1: Add a certain amount of polyvinylidene fluoride binder to N-methylpyrrolidone solvent, stir at a low speed to mix evenly, and then stir at a medium speed in a vacuum to obtain melt A; S2: Add a certain amount of conductive agent slurry to solution A, stir at a medium speed in a vacuum to obtain suspension A. If no conductive agent slurry is added, jump to the next S3; S3: Add a certain amount of conductive agent powder to suspension A, stir at a low speed until the conductive powder is dispersed, and then stir at a medium speed in a vacuum to obtain suspension B; S4: Add polyanionic positive electrode material or layered oxide positive electrode material or half of the composite positive electrode material to suspension B, stir at a low speed to disperse, and then stir at a high speed in a vacuum to obtain suspension Liquid C; S5: add layered oxide positive electrode material or polyanion positive electrode material or the other half of the composite positive electrode material to the suspension C, stir at a low speed until the active powder is dispersed, and then stir at a high speed in a vacuum to obtain a suspension D; S6: add a certain amount of slurry additive to the suspension D, and stir at a high speed in a vacuum to obtain a suspension E. If no slurry additive is added, jump to the next step; S7: add a certain amount of N-methylpyrrolidone solvent to the suspension E, and stir at a high speed in a vacuum to obtain a suspension F; S8: The suspension F is stirred and defoamed under a vacuum state to obtain the final positive electrode slurry.

[0010] In some embodiments, in S1 to S8, the addition amounts of the respective materials are weighed according to the slurry ratio, and the slurry ratio is: positive electrode material or composite positive electrode material: conductive agent slurry ∶ conductive agent powder ∶ polyvinylidene fluoride binder ∶ slurry additive = 90 to 98 ∶ 0 to 0.3 ∶ 1 to 5 ∶ 1 to 5 ∶ 0 to 0.5.

[0011] In some embodiments, the low-speed stirring parameters are 500 to 1500 rpm for the stirring paddle and 500 to 1500 rpm for the dispersing paddle; the medium-speed stirring parameters are 1500 to 2000 rpm for the stirring paddle and 1500 to 2000 rpm for the dispersing paddle; the high-speed stirring parameters are 2000 to 4500 rpm for the stirring paddle and 2000 to 4500 rpm for the dispersing paddle, and the vacuum degree is -80 to 95 kPa.

[0012] In some embodiments, the low-speed stirring time is 10 to 30 minutes, and the medium- and high-speed stirring times are 30 to 180 minutes.

[0013] In some embodiments, the polyvinylidene fluoride binder includes one or more of different types of binders prepared by emulsion polymerization and suspension polymerization processes, and the PVDF dissolution concentration is 3% to 10%.

[0014] In some embodiments, the conductive agent slurry includes one or more of a single-walled carbon nanotube nitrogen dispersion, a graphene dispersion, and a reduced graphene oxide dispersion using N-methylpyrrolidone as a solvent.

[0015] In some embodiments, the conductive agent powder includes, but is not limited to, one or more of conductive carbon black, acetylene black, Ketjen black, multi-walled carbon nanotubes, carbon nanofibers (such as VGCF), conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, etc.), graphene, and reduced graphene oxide.

[0016] In some embodiments, in S4 and S5: the layered oxide positive electrode material includes P 2 phase and O 3phase of sodium manganate, sodium iron manganate, sodium nickel manganate, sodium nickel iron manganate, and sodium copper iron manganate; the polyanion positive electrode material includes sodium vanadium phosphate, sodium vanadium iron phosphate, sodium vanadium manganese phosphate, sodium vanadium fluorophosphate, sodium vanadium iron phosphate, sodium vanadium manganese fluorophosphate, sodium vanadium manganese, sodium iron phosphate pyrophosphate, sodium iron phosphate, sodium iron fluoride phosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron manganese pyrophosphate, sodium iron manganese phosphate, and sodium iron sulfate. One or more; the composite positive electrode material includes various polyanion positive electrode materials (such as sodium vanadium phosphate, sodium vanadium iron phosphate, sodium vanadium manganese phosphate, sodium vanadium fluorophosphate, sodium vanadium iron phosphate, sodium vanadium manganese fluorophosphate, sodium iron pyrophosphate, sodium iron phosphate, sodium iron fluoride phosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron manganese phosphate, sodium iron manganese pyrophosphate, sodium iron manganese phosphate, sodium iron sulfate) and one or more with layered oxide positive electrode (P 2 Phase and O 3 A composite positive electrode material obtained by uniformly mixing one or more of sodium manganate, sodium ferromanganate, sodium nickel manganate, sodium nickel ferromanganate, and sodium copper ferromanganate by mechanical method or chemical method.

[0017] In some embodiments, the layered oxide positive electrode material or the polyanionic positive electrode material or the composite positive electrode material is consistent with S4. If S4 adds a polyanionic positive electrode material, then S5 adds a layered oxide positive electrode material. If S4 adds a layered oxide positive electrode material, then S5 adds a polyanionic positive electrode material. If S4 adds half of the composite positive electrode material, then S5 adds the other half of the composite positive electrode material.

[0018] In some embodiments, the layered oxide cathode material or polyanion cathode material or composite cathode material in S4 and S5 may also be added all at once or multiple times.

[0019] In some embodiments, the mixing or composite ratio of the layered oxide positive electrode material and the polyanion positive electrode material in the composite positive electrode material in S4 and S5 is 1-10:1-10.

[0020] In some embodiments, the slurry adjuvant includes one or more of anhydrous oxalic acid, anhydrous sodium phytate, acetic acid, ascorbic acid, anhydrous citric acid, malonic acid, malic acid, caffeic acid, polyvinyl pyrrolidone, propylene polyoxyethylene polyoxypropylene ether-n-vinyl pyrrolidone copolymer, silicone defoamer, and polyether defoamer.

[0021] In some embodiments, in S7, the amount of N-methylpyrrolidone solvent added is controlled according to the solid content of the slurry in the range of 30% to 60%, and the viscosity of the slurry is controlled to be 3000 to 10000 Pa·s.

[0022] In some embodiments, the defoaming vacuum degree in S8 is -95 to -80 kPa, and the stirring blade speed is 500 to 3000 rpm.

[0023] In some embodiments, the positive electrode slurry is applied to the surface of the aluminum current collector by extrusion coating or doctor blade coating, and then vacuum dried, rolled, cut and dried to obtain a positive electrode sheet.

[0024] In some embodiments, the positive electrode sheets are assembled into a sodium ion battery by winding and stacking.

[0025] In some embodiments, the aluminum current collector includes one of a pure aluminum foil current collector, a novel composite aluminum current collector, and a carbon-coated current collector, and the thickness of the current collector is 3 to 15 μm.

[0026] In some embodiments, the coating thickness is 90 to 500 μm.

[0027] In some embodiments, the vacuum drying temperature is 60-150° C., the vacuum pressure is 20-1000 Pa, and the drying time is 12-48 hours.

[0028] In some embodiments, the cutting includes one or more of knife die cutting, knife slitting, and laser die cutting.

[0029] In some embodiments, the sodium ion battery includes a soft pack battery, a cylindrical battery, or a square aluminum shell battery.

[0030] In some embodiments, the tabs of the sodium ion battery include a single tab or a multi-tab structure.

[0031] Working principle and beneficial effects of the present invention:

[0032] The composite pole piece based on the polyanion and layered oxide positive electrode of the present invention not only has higher compaction density and gram capacity, but also has excellent cycle performance. The compaction density and gram capacity of the composite pole piece can be regulated by adjusting the blending ratio and type of blending materials of the polyanion and layered oxide positive electrode materials. The method is compatible with existing processes and equipment and does not require adjustment. In addition, the sodium ion battery prepared using the composite positive electrode has higher specific energy, excellent cycle performance, and capacity contribution in both high voltage and low voltage regions, which is beneficial to battery management, battery pack charge balance and charge estimation, and has the potential for large-scale application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The first week charge and discharge curves of the positive electrode sheet-sodium sheet button half-cell prepared in Example 1, Example 2 and Comparative Example 1 at a rate of 0.1C;

[0034] Figure 2 The charge and discharge curves of the positive electrode sheets prepared in Example 1, Example 2, Example 3 and Comparative Example 1 for hard carbon soft-pack full batteries at a rate of 0.1C;

[0035] Figure 3 1C cycle stability of the positive electrode sheets prepared in Example 1, Example 2, Example 3 and Comparative Example 1 for hard carbon soft-pack full batteries. DETAILED DESCRIPTION

[0036] The following is further described in detail through specific implementation methods:

[0037] Example 1

[0038] Sodium vanadium phosphate:O 3 The ratio of sodium nickel iron manganate: carbon black conductive agent: graphite conductive agent: binder is 55.8:37.2:1.5:1.5:4. 1.6 g of polyvinylidene fluoride powder and 40 g of N-methylpyrrolidone solvent are weighed and poured into a stirring tank. The polyvinylidene fluoride powder is dispersed in deionized water by stirring at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm). The polyvinylidene fluoride powder is stirred at a medium speed (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) under vacuum (-88 kPa) for more than 30 minutes until the polyvinylidene fluoride is dissolved to obtain solution A.

[0039] ② Weigh 0.6 g of carbon black conductive agent SP and 0.6 g of graphite conductive agent KS-6 powder respectively and pour them into solution A. Stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the conductive agent powders. Then stir at medium speed (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) in vacuum for 60 minutes to obtain suspension A.

[0040] ③ Weigh 22.32 g of sodium vanadium phosphate cathode material and pour it into suspension A, stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension B;

[0041] ④ Weigh the remaining 14.88g O 3 The sodium nickel iron manganate positive electrode material was poured into the suspension B and stirred at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to make O 3 The sodium nickel iron manganate cathode material powder was dispersed and stirred at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension C;

[0042] ⑤ Observe whether the slurry has an appropriate viscosity. If it is too viscous, add an appropriate amount of N-methylpyrrolidone solvent, and then stir at a high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes.

[0043] ⑥ Turn off the dispersing paddle, adjust the stirring paddle to medium speed (stirring paddle 1500 rpm, dispersing paddle 1500 rpm), and stir for 30 minutes under vacuum to defoam to obtain the final positive electrode slurry.

[0044] ⑦ The coating is carried out by doctor blade coating, the current collector is pure aluminum current collector, the current collector thickness is 12μm, the coating thickness is 120μm, and then it is dried by air blast.

[0045] ⑧ Dry the electrode at a vacuum of 100Pa and 110℃ for 12 hours, and roll the electrode to a compaction density of 2.5g / cm 3 , use a tool to cut into long strips of pole pieces.

[0046] ⑨ Assemble button-type half-cells to test the performance of the electrode pieces. The button-type battery assembly method is as follows: stack the negative electrode shell, gasket, sodium sheet, and diaphragm in the center in sequence, add 70 μL of electrolyte, then stack the positive electrode sheet, gasket, and positive electrode shell in the center respectively, and finally package them at a pressure of 90 MPa.

[0047] ⑩ The winding process is adopted to manufacture soft-pack batteries. The battery cells are prepared according to the processes of electrode preparation, winding, shell sealing, liquid injection, formation, and secondary sealing. The battery cells have a single-pole ear structure.

[0048] Example 2

[0049] ①According to sodium vanadium phosphate:O 3 1.6 g of polyvinylidene fluoride powder and 40 g of N-methylpyrrolidone solvent were weighed and poured into a stirring tank. The polyvinylidene fluoride powder was dispersed in deionized water by stirring at a low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm). The polyvinylidene fluoride powder was stirred at a medium speed (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) under vacuum (-88 kPa) for more than 30 minutes until the polyvinylidene fluoride was dissolved to obtain solution A.

[0050] ② Weigh 0.6 g of carbon black conductive agent SP and 0.6 g of graphite conductive agent KS-6 powder respectively and pour them into solution A. Stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the conductive agent powders. Then stir at medium speed (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) in vacuum for 60 minutes to obtain suspension A.

[0051] ③ Weigh 22.32g of sodium vanadium phosphate positive electrode material and 14.88g of O 3 The two positive electrode materials were mixed evenly by ball milling to obtain sodium vanadium phosphate and O 3 Composite positive electrode material of sodium nickel iron manganese oxide;

[0052] ④ Weigh 18.6 g of the composite cathode material obtained in step ③ and pour it into suspension A, stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the composite cathode material powder, and stir at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension B;

[0053] ⑤ Weigh the remaining 18.6 g of the composite cathode material obtained in step ③ and pour it into the suspension B, stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the composite cathode material powder, and stir at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension C;

[0054] ⑥ Observe whether the slurry has an appropriate viscosity. If it is too viscous, add an appropriate amount of N-methylpyrrolidone solvent, and then stir at a high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes.

[0055] ⑦ Turn off the dispersing paddle, adjust the stirring paddle to medium speed (stirring paddle 1500 rpm, dispersing paddle 1500 rpm), and stir for 30 minutes under vacuum to defoam to obtain the final positive electrode slurry.

[0056] ⑧ The coating was carried out by blade coating, the current collector was pure aluminum, the current collector thickness was 12 μm, the coating thickness was 120 μm, and then air-dried.

[0057] ⑨ Dry the electrode at a vacuum of 100Pa and 110℃ for 12 hours, and roll the electrode to a compaction density of 2.5g / cm 3 , use a tool to cut into long strips of pole pieces.

[0058] ⑩ Assemble button-type half-cells to test the performance of the pole pieces and use the winding process to make soft-pack batteries.

[0059] Example 3

[0060] Sodium vanadium phosphate of Example 3 / O 3 The preparation method of the phase sodium nickel iron manganate composite positive electrode slurry and positive electrode sheet is consistent with that in Example 1, and the slurry ratio is changed to sodium vanadium phosphate: O3 phase sodium nickel iron manganate: carbon black conductive agent: graphite conductive agent: binder = 18.6:74.4:1.5:1.5:4.

[0061] Comparative Example 1

[0062] Comparative Example 1 is a method for preparing a sodium vanadium phosphate positive electrode slurry and a positive electrode sheet, and the specific steps are:

[0063] ① According to the ratio of sodium vanadium phosphate: carbon black conductive agent: graphite conductive agent: binder = 93:1.5:1.5:4, weigh 1.6g polyvinylidene fluoride powder and 40g N-methylpyrrolidone solvent into a stirring tank, stir at low speed (stirring paddle 1000rpm, dispersing paddle 1000rpm) to disperse the polyvinylidene fluoride powder in deionized water, and stir at medium speed (stirring paddle 1500rpm, dispersing paddle 2000rpm) under vacuum (-88kPa) for more than 30 minutes until the polyvinylidene fluoride is dissolved to obtain solution A;

[0064] ② Weigh 0.6 g of carbon black conductive agent SP and 0.6 g of graphite conductive agent KS-6 powder respectively and pour them into solution A. Stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the conductive agent powders. Then stir at medium speed (stirring paddle 1500 rpm, dispersing paddle 2000 rpm) in vacuum for 60 minutes to obtain suspension A.

[0065] ③ Weigh 18.6 g of sodium vanadium phosphate cathode material and pour it into suspension A, stir at low speed (stirring paddle 1000 rpm, dispersing paddle 1000 rpm) for 15 minutes to disperse the sodium vanadium phosphate cathode material powder, and stir at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension B;

[0066] ④ Weigh the remaining 18.6g sodium vanadium phosphate positive electrode material and pour it into suspension B. Stir at low speed (stirring paddle 1000rpm, dispersing paddle 1000rpm) for 15 minutes to make O 3 The sodium nickel iron manganate cathode material powder was dispersed and stirred at high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes to obtain suspension C;

[0067] ⑤ Observe whether the slurry has an appropriate viscosity. If it is too viscous, add an appropriate amount of N-methylpyrrolidone solvent, and then stir at a high speed (stirring paddle 2000 rpm, dispersing paddle 3000 rpm) in vacuum for 60 minutes.

[0068] ⑥ Turn off the dispersing paddle, adjust the stirring paddle to medium speed (stirring paddle 1500 rpm, dispersing paddle 1500 rpm), and stir for 30 minutes under vacuum to defoam to obtain the final positive electrode slurry.

[0069] ⑦ The coating is carried out by blade coating, the current collector is pure aluminum current collector, the current collector thickness is 12μm, the coating thickness is 120μm, and then air drying is performed.

[0070] ⑧ Dry the electrode at 100Pa vacuum and 110℃ for 12 hours. Since the sodium vanadium phosphate electrode is compacted to a compaction density of 1.6g / cm 3Above this point, the pole piece curling and material falling begin to appear. Therefore, the sodium vanadium phosphate pole piece can only be compacted to 1.50g / cm 3 , use a tool to cut into long strips of pole pieces.

[0071] ⑨ Assemble button-type half-cells to test the performance of the pole pieces, and use the winding process to make soft-pack batteries.

[0072] Table 1 is a statistical data of the electrical performance of the positive electrode sheets prepared in Example 1, Example 2 and Comparative Example 1 for the first three weeks of charge and discharge at a rate of 0.1C for sodium sheet button half-cells. It can be concluded that the discharge capacity in grams of the high-capacity composite electrode sheets prepared in Example 1 and Example 2 is about 14.88 mAh / g higher than that of the pure sodium vanadium phosphate electrode sheet prepared in Comparative Example 1.

[0073] Table 1

[0074]

[0075] Table 2 Statistics of the positive electrode sheet parameters prepared in Example 1, Example 2, Example 3 and Comparative Example 1 and their electrical performance data in the first 3 weeks of soft-pack full battery formation. It can be concluded that the compaction density and specific energy of the high-capacity and high-compacted composite electrode sheets prepared in Example 1, Example 2 and Example 3 are significantly higher than those in Comparative Example 1.

[0076]

[0077] As can be seen from Table 1,

[0078] The present invention successfully prepares a high-density high-capacity positive electrode sheet based on a polyanion positive electrode material. Compared with the traditional polyanion positive electrode sheet prepared in Comparative Example 1, the high-density high-capacity positive electrode sheet (Examples 1 to 3) of the present invention can significantly improve the discharge capacity in grams, the compaction density and the specific energy of the sodium ion battery.

Claims

1. A method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material, characterized in that: include: S1: adding a certain amount of polyvinylidene fluoride binder into N-methylpyrrolidone solvent, stirring at a low speed to mix evenly, and then stirring at a medium speed in a vacuum to obtain melt A; S2: Add a certain amount of conductive agent slurry to solution A, and stir at medium speed in vacuum to obtain suspension A. If no conductive agent slurry is added, jump to the next S3; S3: Add a certain amount of conductive agent powder to suspension A, stir at a low speed until the conductive powder is dispersed, and then stir at a medium speed in a vacuum to obtain suspension B; S4: adding a polyanionic positive electrode material or a layered oxide positive electrode material or half the amount of a composite positive electrode material to the suspension B, stirring and dispersing at a low speed, and then stirring at a high speed in a vacuum to obtain a suspension C; S5: adding layered oxide positive electrode material or polyanion positive electrode material or the other half of the composite positive electrode material to the suspension C, stirring at a low speed until the active powder is dispersed, and then stirring at a high speed in a vacuum to be uniform, and then adding a certain amount of nitrogen methyl pyrrolidone solvent thereto, and stirring at a high speed in a vacuum to be uniform to obtain a suspension D; S6: Add a certain amount of slurry additive to the suspension D, and stir at high speed under vacuum to obtain suspension E. If no slurry additive is added, skip to the next step; S7: adding a certain amount of N-methylpyrrolidone solvent to the suspension E, and stirring at high speed in vacuum to obtain a suspension F; S8: The suspension F is stirred and defoamed under vacuum to obtain the final positive electrode slurry.

2. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 1, characterized in that: In S1 to S8, the added amount of each material is weighed according to the slurry ratio, and the slurry ratio is: positive electrode material or composite positive electrode material: conductive agent slurry: conductive agent powder: polyvinylidene fluoride binder: slurry additive = 90-98: 0-0.3: 1-5: 1-5: 0-0.

5.

3. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 2, characterized in that: The conductive agent slurry includes one or more of a single-walled carbon nanotube nitrogen dispersion, a graphene dispersion, and a reduced graphene oxide dispersion using N-methylpyrrolidone as a solvent.

4. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 3, characterized in that: Conductive agent powder includes but is not limited to one or more of conductive carbon black, acetylene black, Ketjen black, multi-walled carbon nanotubes, carbon nanofibers (such as VGCF), conductive graphite (such as KS-6, KS-15, SFG-6, SFG-15, etc.), graphene, and reduced graphene oxide.

5. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 4, characterized in that: In S4 and S5: the layered oxide positive electrode material includes one or more of sodium manganate, sodium iron manganate, sodium nickel manganate, sodium nickel iron manganate, and sodium copper iron manganate in P2 phase and O3 phase; the polyanion positive electrode material includes one or more of sodium vanadium phosphate, sodium iron vanadium phosphate, sodium vanadium manganese phosphate, sodium vanadium fluorophosphate, sodium iron vanadium fluorophosphate, sodium manganese vanadium fluorophosphate, sodium iron pyrophosphate, sodium iron phosphate, sodium iron fluorophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron manganese phosphate, sodium iron pyrophosphate, sodium iron manganese phosphate, and sodium iron sulfate; the composite positive electrode material includes various polyanions A composite positive electrode material obtained by uniformly mixing one or more of ionic positive electrode materials (such as sodium vanadium phosphate, sodium vanadium iron phosphate, sodium vanadium manganese phosphate, sodium vanadium fluorophosphate, sodium vanadium iron fluorophosphate, sodium vanadium manganese fluorophosphate, sodium iron phosphate pyrophosphate, sodium iron phosphate, sodium iron fluorophosphate, sodium iron pyrophosphate, sodium manganese pyrophosphate, sodium iron manganese phosphate, sodium iron manganese pyrophosphate, sodium iron manganese phosphate, and sodium iron sulfate) with one or more of layered oxide positive electrodes (sodium manganate, sodium iron manganate, sodium nickel manganate, sodium nickel iron manganate, and sodium copper iron manganate of P2 phase and O3 phase) through mechanical mixing or chemical compounding.

6. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 5, characterized in that: The mixing or composite ratio of the layered oxide positive electrode material and the polyanion positive electrode material in the composite positive electrode material in S4 and S5 is 1-10:1-10.

7. The method for preparing a high-density high-capacity positive electrode slurry based on a polyanion positive electrode material according to claim 6, characterized in that: The slurry additive includes one or more of anhydrous oxalic acid, anhydrous sodium phytate, acetic acid, ascorbic acid, anhydrous citric acid, malonic acid, malic acid, caffeic acid, polyvinyl pyrrolidone, propylene polyoxyethylene polyoxypropylene ether-n-vinyl pyrrolidone copolymer, silicone defoamer, and polyether defoamer.

8. A positive electrode sheet, comprising applying the positive electrode slurry according to any one of claims 1 to 7 onto the surface of an aluminum current collector by extrusion coating or doctor blade coating, vacuum drying, roller pressing, cutting and drying to obtain a positive electrode sheet.

9. A sodium ion battery, wherein the positive electrode sheet according to claim 8 is assembled into a sodium ion battery by winding and laminating.

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