Preparation method of sodium ion all-solid-state battery positive electrode

Abstract

The invention belongs to the technical field of sodium ion batteries. The invention provides a sodium ion all-solid-state battery positive electrode preparation method, which comprises: S1, coating the surface of chromium-doped sodium nickel manganese oxide with a Na3Al2 (PO4) 3 and sodium dodecyl phosphate composite layer to obtain a modified chromium-doped sodium nickel manganese oxide material; s2, the modified chromium-doped sodium nickel manganese oxide material obtained in the S1, graphite, polyvinylidene fluoride and N-methyl pyrrolidone are mixed according to the mass ratio of 8: (1.4-1.6): (0.75-0.85): (3.8-4.2), and slurry is obtained; and S3, coating an aluminum foil with the slurry obtained in the step S2 to prepare a positive electrode plate, then drying the positive electrode plate, and punching the positive electrode plate into a circle to obtain the sodium ion all-solid-state battery positive electrode with the surface loading capacity of 5.4-6.2 mg / cm < 2 >. According to the invention, the capacity retention ratio of the sodium ion solid-state battery can be effectively improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion battery technology, specifically relating to a method for preparing a positive electrode for a sodium-ion all-solid-state battery. Background Technology

[0002] Faced with the shortage of traditional fossil fuels and greenhouse gas emissions, new rechargeable batteries, represented by lithium-ion batteries, have shown unique advantages. For example, lithium-ion batteries have high energy density, high operating voltage, low self-discharge rate, and good cycle performance. Their applications have expanded from small portable electronic products to electric vehicles and energy storage. However, the abundance of metallic lithium on Earth is only 0.006%, making the search for alternatives an urgent priority. Sodium, as the second lightest metallic element after lithium, has an abundance of 2.3% to 2.8%. Therefore, applying sodium to the battery field can reduce raw material costs and ensure sustainable use.

[0003] In existing technologies, when layered sodium nickel manganese oxide is used as the positive electrode of sodium-ion solid-state batteries, the initial discharge specific capacity is relatively high at a cutoff voltage of 4.2V. However, the capacity decays rapidly, with a capacity retention rate of approximately 90.5% after the 10th cycle and approximately 76% after the 30th cycle. This is because when charged to 4.2V, the layered sodium nickel manganese oxide undergoes an irreversible P2→O2 phase transition, causing the Na+ coordination environment to change from a triangular prism to an octahedron. The larger radius of Na+ ions causes a significant volume change during the phase transition, leading to the structural collapse of the layered positive electrode material and consequently a significant decrease in the capacity retention rate of the sodium-ion solid-state battery. Summary of the Invention

[0004] To address the problems existing in the background technology, the present invention provides a method for preparing a cathode of a sodium-ion all-solid-state battery, which can effectively improve the capacity retention rate of sodium-ion solid-state batteries.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a cathode for a sodium-ion all-solid-state battery includes the following steps:

[0007] S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of chromium-doped sodium nickel manganate to obtain a modified chromium-doped sodium nickel manganate material.

[0008] S2. The modified chromium-doped sodium nickel manganate material obtained in S1, graphite, polyvinylidene fluoride and N-methylpyrrolidone are mixed in a mass ratio of 8: (1.4-1.6): (0.75-0.85): (3.8-4.2) to obtain a slurry;

[0009] S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate, then dried and punched into a circle to obtain the positive electrode of the sodium-ion all-solid-state battery, with an areal loading of 5.4-6.2 mg / cm³. 2 .

[0010] Furthermore, the preparation method of the chromium-doped sodium nickel manganate is as follows:

[0011] A1. Dissolve 1 mol of nickel sulfate, 1 mol of manganese sulfate and 1 mol of chromium sulfate in 1500-1800 mL of deionized water to obtain the first solution;

[0012] A2. Add the first solution obtained in A1 to the reaction vessel, then add 2.1-2.25L of sodium hydroxide solution with a concentration of 2mol / L and 2.1-2.2L of ammonia water with a concentration of 0.6mol / L. After stirring the reaction, age it under nitrogen protection, then filter and wash with ethanol until no sulfate ions are detected in the filtrate. Dry under vacuum to obtain the precursor powder.

[0013] A3. After mixing the precursor powder obtained in A2 with the sodium source by ball milling for 2-4 hours, place it in a corundum crucible and calcine it in an air atmosphere. After natural cooling, a black blocky product is obtained. Grind and sieve to obtain chromium-doped nickel manganate sodium.

[0014] Furthermore, in A2, the stirring speed is 400-600 rpm, the reaction temperature is 50-60℃, and the reaction time is 10-12 h.

[0015] Furthermore, in A2, the aging time is 1-2 hours.

[0016] Furthermore, in A3, the molar amount of sodium in the sodium source is 2-2.2 mol.

[0017] Furthermore, in A3, calcination is carried out in stages, with a pre-calcination time of 4-6 hours at a temperature of 350-400℃ and a sintering time of 12-15 hours at a temperature of 800-880℃.

[0018] Furthermore, the specific operating steps of S1 are as follows:

[0019] S11. Dissolve 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate in 480-520mL of ethanol aqueous solution, add 100g of chromium-doped sodium nickel manganate, disperse by ultrasonication, evaporate at 80±2℃ for 1-1.2h, and heat treat at 550±10℃ for 2.8-3.2h to obtain chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer;

[0020] S12. Dissolve 1.2g of sodium dodecyl phosphate in 700-800mL of isopropanol to obtain a mixture; add the chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer obtained in S11 to the mixture, stir and dry at 80±2℃, and then anneal at 120℃ for 1-1.2h to obtain the modified chromium-doped sodium nickel manganate material.

[0021] Further, in S11, the volume ratio of ethanol to water in the ethanol aqueous solvent is 1:(0.8-1.2).

[0022] Furthermore, in S11, the ultrasonic power is 160-180W, and the ultrasonic dispersion time is 15-20min.

[0023] Furthermore, in S3, the specific drying operation is as follows: place the positive electrode plate in a drying oven, dry it at 80±2℃ for 25-35 minutes, and then dry it at 95-100℃ for 80-90 minutes.

[0024] This application has the following beneficial effects:

[0025] 1. This invention involves coating the surface of chromium-doped sodium nickel manganate with a composite layer of Na3Al2(PO4)3 and sodium dodecyl phosphate. Na3Al2(PO4)3 can be considered as Na… + With Al2(PO4)3 3- The combination of Al2(PO4)3 3- Some parts are similar to the AI-PO4 units in the NASICON-type framework. On the one hand, the AI-PO4 units are similar to the surface Cr... 3 AlPO4 forms Al-O-Cr bonds, blocking the pathway of Cr³⁺ catalyzing electrolyte oxidation. At the same time, Al-O-Cr bonds passivate the surface activity of Cr³⁺, thereby reducing the thickness of the CEI (solid electrolyte interphase) film and the interfacial impedance, and improving cycle stability. The rigid AlPO4 framework can also anchor the lattice transition metal layer through Al-O-Cr bonds, effectively suppressing structural slip and volume strain during deep sodium removal, reducing the irreversibility of phase transition at high voltage of 4.2V, and improving the capacity retention rate of the battery at 4.2V high voltage.

[0026] On the other hand, the P=O bonds of PO4³⁻ in the AI-PO4 unit form P-OM bonds with the surface transition metal, filling oxygen vacancies, suppressing lattice oxygen loss and structural collapse, and improving the capacity retention rate of the battery under 4.2V high voltage.

[0027] 2. The flexible layer formed by sodium dodecyl phosphate buffers local stress through its amorphous structure, reduces particle crack density, and prevents active material peeling and electrical contact failure. At the same time, the open framework of sodium dodecyl phosphate increases the interfacial Na⁺ diffusion coefficient by several times, alleviates interfacial ion accumulation at the end of charge and discharge, improves rate performance, and increases the capacity retention rate of the battery under 4.2V high voltage. Attached Figure Description

[0028] Figure 1 The capacity retention rate comparison trend of the positive electrodes prepared in Examples 1-4 and Comparative Examples 1-3 of the present invention for sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles). Detailed Implementation

[0029] The present application will be further described in detail below with reference to the embodiments.

[0030] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0031] Example 1

[0032] (a) Preparation of chromium-doped sodium nickel manganate, the preparation method is as follows:

[0033] A1. Dissolve 1 mol of nickel sulfate (NiSO4), 1 mol of manganese sulfate (MnSO4), and 1 mol of chromium sulfate (Cr2(SO4)3) in 1600 mL of deionized water. Heat to approximately 40°C during dissolution to accelerate the process, and purge with nitrogen gas to prevent the formation of MnSO4. 2+ Oxidation yields the first solution.

[0034] A2. Add the first solution obtained in A1 to the reactor, and then add 2.2L of a 2mol / L sodium hydroxide solution (to provide OH-). - Precipitated metal ions, total OH- - 4.4 mol (slightly in excess of the total metal ions to ensure complete precipitation) and 2.1 L of 0.6 mol / L ammonia solution (ammonia acts as a complexing agent, providing NH3, which preferentially reacts with Ni). 2+ Cr 3+ Formation of [Ni(NH3)6] 2+ [Cr(NH3)6] 3+ Complexes can slow down the precipitation rate and improve particle uniformity.

[0035] The mixture was stirred at 500 rpm and reacted at 55°C for 11 hours, followed by aging under nitrogen protection for 1.5 hours. This process promoted the dissolution and redeposition of small particles onto the surface of larger particles (Ostwald aging), thereby increasing crystallinity. Nitrogen protection prevented the growth of Mn. 2+Oxidation leads to structural defects. Then it is filtered and washed with ethanol until no sulfate is detected in the filtrate, and the determination of SO4 2- Using a BaCl2 solution, if there is no white precipitate, it is qualified. Then it is dried in vacuum at 60 °C for 12 h to avoid decomposition or oxidation of the precursor at high temperature, and the precursor powder is obtained.

[0036] A3. The precursor powder obtained in A2 is ball-milled and mixed with a sodium source for 3 h. The sodium source is sodium acetate, and the molar amount of sodium element in the sodium source is 2.1 mol. Wet ball-milling (ethanol medium) for 3 h, with a rotation speed of 250 rpm and a ball-to-material ratio of 5:1, to ensure uniform mixing of the sodium source and the precursor. Then it is placed in a corundum crucible and subjected to segmented calcination in an air atmosphere. The pre-burning time is 5 h at a temperature of 380 °C, and the sintering time is 14 h at a temperature of 850 °C. Then it is naturally cooled (reducing thermal stress cracks with the furnace) to obtain a black块状 product, which is ground and sieved (400 mesh) to obtain sodium nickel manganese chromium oxide.

[0037] (II) A method for preparing a positive electrode of a sodium-ion all-solid-state battery, comprising the following steps:

[0038] S1. Coat a composite layer of Na3Al2(PO4)3 and sodium dodecyl phosphate on the surface of sodium nickel manganese chromium oxide to obtain a modified sodium nickel manganese chromium oxide material.

[0039] The specific operation steps are as follows: S11. Dissolve 11.44 g of aluminum nitrate and 4.76 g of sodium dihydrogen phosphate in 500 mL of an ethanol-water solvent (the volume ratio of ethanol to water is 1:1). Add 100 g of sodium nickel manganese chromium oxide, and disperse it by ultrasonic wave. The ultrasonic power is 170 W, and the ultrasonic dispersion time is 18 min. Then it is evaporated at 80 °C for 1.1 h and heat-treated at 550 °C for 3 h to obtain sodium nickel manganese chromium oxide with a Na3Al2(PO4)3 nanolayer. S12. Dissolve 1.2 g of sodium dodecyl phosphate in 750 mL of isopropanol to obtain a mixed solution; add the sodium nickel manganese chromium oxide with a Na3Al2(PO4)3 nanolayer obtained in S11 to the mixed solution. After stirring and drying at 80 °C, it is annealed at 120 °C for 1.1 h to remove the residual solvent, and the modified sodium nickel manganese chromium oxide material is obtained.

[0040] S2. Mix the modified sodium nickel manganese chromium oxide material obtained in S1, graphite, polyvinylidene fluoride, and N-methylpyrrolidone according to a mass ratio of 8:1.5:0.8:4 to obtain a slurry.

[0041] S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 30 minutes to slowly evaporate N-methylpyrrolidone and prevent rapid shrinkage leading to cracking. It is then dried at 98°C for 85 minutes to completely remove residual solvent, and the polyvinylidene fluoride crystallizes to enhance bonding strength. The plate is then punched into a circle to obtain the positive electrode for a sodium-ion all-solid-state battery with an areal loading of 5.6 mg / cm³. 2 .

[0042] (III) Preparation of sodium-ion all-solid-state batteries, which is an existing technology, is carried out in a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm, temperature 25 ± 2℃). The stacking assembly steps include: ① placing a stainless steel shell (concave side up) on the base of a tablet press; ② placing the positive electrode prepared in this invention in the center; ③ covering with a solid electrolyte layer (Na3Zr2Si2PO4). 12 ), 80μm thick, first cold pressing: pressure 4MPa, hold for 10s; ④ Place sodium metal anode (rolled to 50μm foil), second cold pressing: pressure 3MPa, hold for 5s, pressure 6MPa, hold for 15s; ⑤ Sequentially stack elastic auxiliary film (buffer pressure) and stainless steel gasket, seal by laser welding (power 50W, speed 10mm / s).

[0043] Example 2

[0044] The difference between this embodiment and Embodiment 1 is that: a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0045] S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of chromium-doped sodium nickel manganate to obtain a modified chromium-doped sodium nickel manganate material. The specific operation steps are as follows: S11. 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate are dissolved in 480mL of ethanol-water solvent (ethanol and water volume ratio is 1:1), 100g of chromium-doped sodium nickel manganate is added, ultrasonically dispersed at an ultrasonic power of 160W for 20min, then evaporated at 80℃ for 1h, and heat-treated at 550℃ for 2.8h to obtain chromium-doped sodium nickel manganate with a Na3Al2(PO4)3 nanolayer. S12. Dissolve 1.2g of sodium dodecyl phosphate in 700mL of isopropanol to obtain a mixture; add the chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer obtained in S11 to the mixture, stir and dry at 80℃, and then anneal at 120℃ for 1h to obtain the modified chromium-doped sodium nickel manganate material.

[0046] S2. The modified chromium-doped sodium nickel manganate material obtained in S1, graphite, polyvinylidene fluoride and N-methylpyrrolidone are mixed in a mass ratio of 8:1.4:0.75:3.8 to obtain a slurry.

[0047] S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 25 minutes, followed by drying at 95°C for 90 minutes. It is then punched into a circle to obtain the positive electrode of a sodium-ion all-solid-state battery with an areal loading of 6.2 mg / cm³. 2 .

[0048] Example 3

[0049] The difference between this embodiment and Embodiment 1 is that: a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0050] S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of chromium-doped sodium nickel manganate to obtain a modified chromium-doped sodium nickel manganate material. The specific operation steps are as follows: S11. 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate are dissolved in 520mL of ethanol-water solvent (ethanol and water volume ratio is 1:1), 100g of chromium-doped sodium nickel manganate is added, ultrasonically dispersed at an ultrasonic power of 180W for 15min, then evaporated at 80℃ for 1.2h, and heat-treated at 550℃ for 3.2h to obtain chromium-doped sodium nickel manganate with a Na3Al2(PO4)3 nanolayer. S12. Dissolve 1.2g of sodium dodecyl phosphate in 800mL of isopropanol to obtain a mixture; add the chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer obtained in S11 to the mixture, stir and dry at 80℃, and then anneal at 120℃ for 1.2h to obtain the modified chromium-doped sodium nickel manganate material.

[0051] S2. The modified chromium-doped sodium nickel manganate material obtained in S1, graphite, polyvinylidene fluoride and N-methylpyrrolidone are mixed in a mass ratio of 8:1.6:0.85:4.2 to obtain a slurry.

[0052] S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 35 minutes, followed by drying at 95°C for 90 minutes. It is then punched into a circle to obtain the positive electrode of a sodium-ion all-solid-state battery with an areal loading of 5.4 mg / cm³. 2 .

[0053] Example 4

[0054] The difference between this embodiment and Embodiment 1 is that: a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0055] S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of chromium-doped sodium nickel manganate to obtain a modified chromium-doped sodium nickel manganate material. The specific operation steps are as follows: S11. 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate are dissolved in 500mL of ethanol-water solvent (ethanol and water volume ratio is 1:1), 100g of chromium-doped sodium nickel manganate is added, ultrasonically dispersed at an ultrasonic power of 180W for 20min, then evaporated at 80℃ for 1.2h, and heat-treated at 550℃ for 2.8h to obtain chromium-doped sodium nickel manganate with a Na3Al2(PO4)3 nanolayer. S12. Dissolve 1.2g of sodium dodecyl phosphate in 750mL of isopropanol to obtain a mixture; add the chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer obtained in S11 to the mixture, stir and dry at 80℃, and then anneal at 120℃ for 1h to obtain the modified chromium-doped sodium nickel manganate material.

[0056] S2. The modified chromium-doped sodium nickel manganate material obtained in S1, graphite, polyvinylidene fluoride and N-methylpyrrolidone are mixed in a mass ratio of 8:1.5:0.75:4.2 to obtain a slurry.

[0057] S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 30 minutes, followed by drying at 100°C for 90 minutes. It is then punched into a circle to obtain the positive electrode of a sodium-ion all-solid-state battery with an areal loading of 6.0 mg / cm³. 2 .

[0058] Comparative Example 1

[0059] The difference between this comparative example and Example 1 is that the modified chromium-doped sodium nickel manganate material is replaced with sodium nickel manganate. That is, sodium nickel manganate is not doped with chromium; and its surface is not coated with a Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer.

[0060] Specifically, a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0061] Sodium nickel manganate, graphite, polyvinylidene fluoride, and N-methylpyrrolidone were mixed in a mass ratio of 8:1.5:0.8:4 to obtain a slurry.

[0062] The slurry is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 30 minutes, then at 98°C for 85 minutes. It is then punched into a circle to obtain the positive electrode of a sodium-ion all-solid-state battery.

[0063] Comparative Example 2

[0064] The difference between this comparative example and Example 1 is that the modified chromium-doped sodium nickel manganate material is replaced with chromium-doped sodium nickel manganate. That is, the surface is not coated with a Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer.

[0065] Specifically, a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0066] A slurry was prepared by mixing chromium-doped sodium nickel manganate, graphite, polyvinylidene fluoride, and N-methylpyrrolidone in a mass ratio of 8:1.5:0.8:4.

[0067] The slurry is coated onto aluminum foil to form a positive electrode plate. The positive electrode plate is then placed in a drying oven and dried at 80°C for 30 minutes, then at 98°C for 85 minutes. It is then punched into a circle to obtain the positive electrode of a sodium-ion all-solid-state battery.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that the modified chromium-doped sodium nickel manganate material is replaced with modified sodium nickel manganate. That is, the sodium nickel manganate is not doped with chromium.

[0070] Specifically, a method for preparing a sodium-ion all-solid-state battery cathode includes the following steps:

[0071] S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of sodium nickel manganate to obtain modified sodium nickel manganate. The specific operation steps are as follows: S11. 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate are dissolved in 500mL of ethanol-water solvent (ethanol and water volume ratio is 1:1), 100g of sodium nickel manganate is added, ultrasonically dispersed at a power of 170W for 18min, then evaporated at 80℃ for 1.1h, and heat-treated at 550℃ for 3h to obtain sodium nickel manganate with a Na3Al2(PO4)3 nanolayer. S12. 1.2g of sodium dodecyl phosphate is dissolved in 750mL of isopropanol to obtain a mixture; the sodium nickel manganate with a Na3Al2(PO4)3 nanolayer obtained in S11 is added to the mixture, stirred and dried at 80℃, and then annealed at 120℃ for 1.1h to obtain modified sodium nickel manganate.

[0072] S2. The modified sodium nickel manganate, graphite, polyvinylidene fluoride and N-methylpyrrolidone obtained in S1 are mixed in a mass ratio of 8:1.5:0.8:4 to obtain a slurry.

[0073] S3. Coat the slurry obtained in S2 onto aluminum foil to form a positive electrode plate. Then place the positive electrode plate in a drying oven and dry it at 80°C for 30 minutes, then at 98°C for 85 minutes. Punch it into a circle to obtain the positive electrode of the sodium-ion all-solid-state battery.

[0074] Experimental Example: Experimental Subjects: Sodium-ion all-solid-state battery cathodes prepared in Examples 1-4 and Comparative Examples 1-3. Experimental Item: Capacity retention rate of sodium-ion all-solid-state batteries. Experimental Method: Under constant temperature environment (25℃±2℃), charge at 0.5C constant current and constant voltage to 4.2V (cutoff current 0.02C), discharge at 0.2C to 2.0V, and record the initial capacity C0; after 30 cycles of the above charge-discharge scheme, record the capacity C. 30 Capacity retention rate = C 30 / C0×100%. Experimental results: see Table 1.

[0075] Table 1. Experimental Data

[0076] Cut-off voltage / V Loop count / time Capacity retention rate / % Example 1 4.2 30 91.5 Example 2 4.2 30 91.3 Example 3 4.2 30 92.0 Example 4 4.2 30 91.9 Comparative Example 1 4.2 30 75.7 Comparative Example 2 4.2 30 71.8 Comparative Example 3 4.2 30 87.2

[0077] Results Analysis: Analysis of Examples 1-4, combined with data from Table 1 and... Figure 1 It can be seen that the positive electrode prepared by the present invention (Examples 1-4) using sodium nickel manganate as the base material for sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles) has a capacity retention rate of over 91.3%.

[0078] Analyze Example 1 and Comparative Examples 1-3 and combine the data in Table 1 and Figure 1 Specifically, comparing Comparative Example 1 and Comparative Example 2, it can be seen that compared to Comparative Example 1 using sodium nickel manganate, Comparative Example 2 using chromium-doped sodium nickel manganate resulted in a decrease in the capacity retention of the cathode used in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles). This indicates that chromium doping of sodium nickel manganate alone leads to a decrease in the capacity retention of the cathode used in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles). This is mainly because Cr... 3+ When doped with sodium nickel manganate, Cr 3+ Replace Ni 2+ This triggers strong Jahn-Teller distortion, leading to Cr under 4.2V high voltage. 3+ The P2→O2 phase transition is accelerated in sodium nickel manganate doping, resulting in a sudden change in lattice volume and a significant increase in the internal crack rate of the particles; Cr 3+ Doping can also lead to the generation of oxygen vacancies through charge compensation, and the loss of lattice oxygen during deep sodium removal; which in turn leads to a decrease in the capacity retention rate of the battery at a high voltage of 4.2V.

[0079] Comparing Comparative Examples 1 and 3, it can be seen that, compared to Comparative Example 1 which uses sodium nickel manganate, Comparative Example 3, with its sodium nickel manganate surface coated with a Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer, resulted in a significantly improved capacity retention rate for the positive electrode used in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles). This indicates that coating the sodium nickel manganate surface with a Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer can improve the capacity retention rate of the positive electrode used in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles).

[0080] Comparing with Example 1, it can be seen that chromium-doped sodium nickel manganate, with a surface coating of Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer, resulted in a cathode with a further improved capacity retention rate in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles) compared to Comparative Example 3. This indicates that the two (chromium doping of sodium nickel manganate and surface coating of Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer) can produce a synergistic effect, jointly improving the capacity retention rate of the cathode in sodium-ion all-solid-state batteries (cutoff voltage 4.2V, 30 cycles).

[0081] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0082] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a positive electrode for a sodium-ion all-solid-state battery, characterized in that, Includes the following steps: S1. A Na3Al2(PO4)3 and sodium dodecyl phosphate composite layer is coated on the surface of chromium-doped sodium nickel manganate to obtain a modified chromium-doped sodium nickel manganate material. S2. The modified chromium-doped sodium nickel manganate material obtained in S1, graphite, polyvinylidene fluoride and N-methylpyrrolidone are mixed in a mass ratio of 8: (1.4-1.6): (0.75-0.85): (3.8-4.2) to obtain a slurry; S3. The slurry obtained in S2 is coated onto aluminum foil to form a positive electrode plate, then dried and punched into a circle to obtain the positive electrode of the sodium-ion all-solid-state battery, with an areal loading of 5.4-6.2 mg / cm³. 2 .

2. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 1, characterized in that, The preparation method of the chromium-doped sodium nickel manganate is as follows: A1. Dissolve 1 mol of nickel sulfate, 1 mol of manganese sulfate and 1 mol of chromium sulfate in 1500-1800 mL of deionized water to obtain the first solution; A2. Add the first solution obtained in A1 to the reaction vessel, then add 2.1-2.25L of sodium hydroxide solution with a concentration of 2mol / L and 2.1-2.2L of ammonia water with a concentration of 0.6mol / L. After stirring the reaction, age it under nitrogen protection, then filter and wash with ethanol until no sulfate ions are detected in the filtrate. Dry under vacuum to obtain the precursor powder. A3. After mixing the precursor powder obtained in A2 with the sodium source by ball milling for 2-4 hours, calcination is carried out in an air atmosphere, followed by natural cooling, grinding and sieving to obtain chromium-doped nickel manganate sodium.

3. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 2, characterized in that, In A2, the stirring speed is 400-600 rpm, the reaction temperature is 50-60℃, and the reaction time is 10-12 h.

4. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 2, characterized in that, In A2, the aging time is 1-2 hours.

5. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 2, characterized in that, In A3, the molar amount of sodium in the sodium source is 2-2.2 mol.

6. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 2, characterized in that, In A3, calcination is carried out in stages, with a pre-calcination time of 4-6 hours at a temperature of 350-400℃ and a sintering time of 12-15 hours at a temperature of 800-880℃.

7. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 1, characterized in that, The specific operating steps for S1 are as follows: S11. Dissolve 11.44g of aluminum nitrate and 4.76g of sodium dihydrogen phosphate in 480-520mL of ethanol aqueous solution, add 100g of chromium-doped sodium nickel manganate, disperse by ultrasonication, evaporate at 80±2℃ for 1-1.2h, and heat treat at 550±10℃ for 2.8-3.2h to obtain chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer; S12. Dissolve 1.2g of sodium dodecyl phosphate in 700-800mL of isopropanol to obtain a mixture; add the chromium-doped sodium nickel manganate with Na3Al2(PO4)3 nanolayer obtained in S11 to the mixture, stir and dry at 80±2℃, and then anneal at 120℃ for 1-1.2h to obtain the modified chromium-doped sodium nickel manganate material.

8. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 7, characterized in that, In S11, the volume ratio of ethanol to water in the ethanol aqueous solvent is 1:(0.8-1.2).

9. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 7, characterized in that, In S11, the ultrasonic power is 160-180W and the ultrasonic dispersion time is 15-20min.

10. The method for preparing the positive electrode of a sodium-ion all-solid-state battery according to claim 1, characterized in that, In S3, the specific drying operation is as follows: place the positive electrode plate in the drying oven, dry it at 80±2℃ for 25-35 minutes, and then dry it at 95-100℃ for 80-90 minutes.

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