Preparation method of sodium self-supplementing P2 type positive electrode material

Abstract

The invention belongs to the technical field of battery energy storage, and particularly relates to a preparation method of a self-sodium-supplementing P2-type positive electrode material, which comprises the following steps: (S1) under inert atmosphere and stirring conditions, dipping P2-type positive electrode material powder in a solution A containing sodium alkoxide, a buffering agent and a dispersing agent, and carrying out first-stage sodium supplementing to obtain a positive electrode material 1; (S2) dipping the positive electrode material after the first sodium supplementation in a solution B containing aryl sodium, a buffering agent and a dispersing agent, and carrying out second-stage sodium supplementation to obtain a positive electrode material 2; and (S3) sequentially neutralizing, washing and drying the positive electrode material 2 to obtain the self-sodium-supplementing P2 type positive electrode material. The electrochemical performance of the material is remarkably improved by accurately controlling the sodium modification degree and residual alkali through gradient sodium modification at two ends. And the energy density and the stability of the whole battery are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery energy storage, and particularly relates to a preparation method of a self-complementary sodium P2-type cathode material. Background Art

[0002] With the continuous growth of global energy demand and the emphasis on environmental protection, the development of high-energy-density, low-cost, and environmentally friendly energy storage technologies has become a focus in the scientific community today. Among them, sodium-ion batteries have become ideal alternatives due to their rich resources, low cost, and relatively low potential. In this field, sodium-free anode all-solid-state batteries (RSBs) have received extensive attention due to their significant advantages in energy density, material cost, and resource sustainability. Compared with the traditional graphite||NCM811 system, sodium-free anode all-solid-state batteries exhibit higher energy density and lower material cost. During the charging process of sodium-free anode all-solid-state batteries, Na metal is directly deposited on the anode current collector, accompanied by the formation of a solid electrolyte interface (SEI) and irreversible Na + loss. The sodium loss in this process will lead to battery capacity decay. Therefore, achieving effective sodium supplementation is crucial for battery performance.

[0003] Traditional sodium supplementation methods mainly include sodium supplementation through the separator and sodium supplementation at the cathode. Sodium supplementation through the separator technology compensates for the initial Na loss by adding a sodium supplement agent to the separator of the battery. In addition, sodium oxalate (Na2C2O4) and sodium squarate (Na2C4O4) have been widely studied as sodium supplement agents. The sodium supplementation technology of sodium oxalate relies on the decomposition of sodium oxalate to generate sodium ions, but the by-products during the decomposition process will have a negative impact on battery performance. Similarly, although sodium squarate can effectively compensate for sodium ions, its decomposition by-products also limit the sodium supplementation efficiency. To overcome these limitations, researchers have explored the method of pre-intercalating sodium in the anode and cathode for sodium storage, which not only improves the sodium supplementation efficiency but also helps to achieve high energy density of the battery.

[0004] However, there are serious problems in directly applying the pre-lithiation strategy of lithium-ion batteries to the sodiation of P2-type sodium-ion battery cathode materials in the prior art. P2-type materials have unique structural characteristics: an ABBA oxygen ion stacking sequence, sodium ions occupy the trigonal prism positions, and there is a relatively large space in the interlayer structure. When using a strongly reducing sodiating reagent, sodium ions will not only be embedded in the lattice positions but also form extremely active sodium alkaline compounds on the surface of the material. These "residual alkalis" will react violently with the electrolyte solvent molecules after contacting the electrolyte, consuming the electrolyte solvent molecules and causing the surface structure to be damaged. In addition, the two-dimensional planar Na+ migration channels of P2-type materials are more susceptible to being blocked by surface residual alkalis, seriously reducing battery performance.

[0005] In a sodium-free anode full battery, the energy density of the battery can be maximized by pre-embedding sodium in the positive electrode. This method not only reduces the impact of initial Na loss on battery performance, but also helps to extend the battery life and has less impact on the environment. Overall, the advantages of sodium-free anode full batteries in terms of energy density, cost-effectiveness and sustainability make it an important development direction in the field of battery research. By continuously optimizing the sodium replenishment technology, especially developing a mild gradient sodiumization process suitable for the characteristics of P2-type materials and a precise regulation mechanism of residual alkali, the performance of the battery system can be further improved, providing a new development path for future energy storage technologies. With the deepening of research and the continuous advancement of technology, sodium-free anode full batteries are expected to play a more important role in the future energy market. This battery technology not only provides a feasible solution to the resource limitations and cost issues faced by traditional lithium-ion batteries, but also demonstrates its potential in achieving higher energy density and longer service life.

[0006] There are serious problems in directly copying the pre-lithiation strategy in lithium-ion batteries and applying it to the sodiumization of P2-type sodium-ion battery positive electrode materials. This is mainly due to the unique structural characteristics of P2-type materials: it has an ABBA oxygen ion stacking sequence, sodium ions occupy triangular prism positions, and there is a large space in the interlayer structure. When treated with a strong reducing sodium reagent (such as sodium biphenyl, sodium naphthalene, etc.), the sodium ions will not only embed into the predetermined lattice position, but also form highly active alkaline compounds such as Na2O, Na2CO3 and NaOH on the surface of the material (collectively referred to as "residual alkali"). These residual alkali compounds will react violently when they subsequently come into contact with the electrolyte. On the one hand, they consume the solvent molecules in the electrolyte, resulting in an increase in the internal resistance of the battery; on the other hand, local corrosion reactions will occur between the residual alkali and the transition metal oxides on the surface of the material, destroying the surface structural integrity of the material and causing the dissolution of transition metals (especially Mn and Ni). In addition, due to the Na + The ion migration channel is two-dimensional and is more susceptible to blockage by surface residual alkali than the three-dimensional channel of O3-type materials.

[0007] CN118039844A discloses a sodium battery positive electrode composite material, wherein the sodium battery positive electrode sodium supplement additive comprises a cyclic organic compound; the chemical structural formula of the cyclic organic compound is NaxCyOz, 5≤x≤z, y≥6, z≥6. CN114790013A discloses a self-supplementing sodium ion battery positive electrode active material, wherein the material is a sodium-rich manganese-based cyclic oxide material, and the chemical general formula is: Na x Ni a Cu b Fe c Mn d M e 0 2±δHowever, none of these patents have solved the problem of poor sodiation efficiency of P2-type cathode materials. Summary of the Invention

[0008] The present invention provides a method for developing a self-complementary sodium cathode material and its application in a rechargeable sodium battery with high energy density. The core of the invention lies in providing a preparation method of a cathode material that can effectively compensate for sodium loss in situ during the formation of the initial solid electrolyte interface (SEI), solving the problem of initial sodium loss in traditional sodium-ion batteries. Through innovative cathode material design and optimized battery structure, the energy density and cycle stability of sodium batteries are significantly improved. To achieve the above object, the present invention adopts the following technical solutions:

[0009] A method for preparing a self-complementary sodium P2-type cathode material, comprising the following steps:

[0010] (S1) Under an inert atmosphere and stirring conditions, the P2-type cathode material powder is impregnated in solution A containing sodium alkoxide, buffer, and dispersant for the first-stage sodium compensation to obtain cathode material 1;

[0011] (S2) The cathode material after the first-stage sodium compensation is impregnated in solution B containing aryl sodium, buffer, and dispersant for the second-stage sodium compensation to obtain cathode material 2;

[0012] (S3) Cathode material 2 is sequentially subjected to neutralization treatment, washing, and drying to obtain a self-complementary sodium P2-type cathode material.

[0013] Further, in step (S1), the P2-type sodium-ion battery cathode material is selected from sodium nickel manganese oxide (Na x Ni y Mn z O2) and sodium nickel manganese titanium oxide (Na x Ni y Mn z Ti m O2).

[0014] Further, in step (S1), the sodium alkoxide is selected from at least one of sodium tert-butoxide, sodium ethoxide, and sodium propoxide, and the buffer is selected from at least one of sodium acetate, sodium propionate, sodium butyrate, sodium citrate, and sodium benzoate.

[0015] Sodium carboxymethyl cellulose (CMC) is used as a dispersion stabilizer, and its long-chain structure effectively prevents the aggregation of P2 material particles, ensuring that the sodiating agent uniformly contacts the surfaces of all particles, while the sodium acetate buffer system maintains a suitable pH environment to prevent local over-alkalization.

[0016] Further, in step (S1), in solution A, the concentration of sodium alkoxide is 0.1 - 0.2 M, the concentration of the buffer is 0.1 - 0.3 M, and the concentration of the dispersant is 0.5 - 2 wt%.

[0017] Further, in step (S1), the first-stage sodium supplementation reacts at 40 - 50 °C for 1 - 5 min. After the sodium supplementation ends, the cathode material is taken out and dried, and then the second-stage sodium supplementation of step (S2) can be carried out.

[0018] Further, in step (S2), the aryl sodium is selected from at least one of naphthyl sodium, anthracenyl sodium, biphenyl sodium, tetracenyl sodium, phenyl sodium, and phenanthryl sodium; the dispersant is selected from at least one of sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyethylene glycol, polyvinyl alcohol (PVA), sodium alginate, etc., and the buffer is selected from at least one of sodium acetate, sodium propionate, sodium butyrate, sodium citrate, and sodium benzoate.

[0019] Further, in step (S2), in solution B, the concentration of aryl sodium is 0.3 - 0.5 M, the concentration of the buffer is 0.1 - 0.3 M, and the concentration of the dispersant is 0.5 - 2 wt%.

[0020] Further, in step (S2), the second-stage sodium supplementation reacts at 15 - 30 °C for 1 - 5 min.

[0021] Further, steps (S1) and (S2) are carried out under an inert atmosphere and stirring conditions. The inert atmosphere is nitrogen and / or argon; the stirring rate is 300 - 600 rpm; during impregnation, the solid-liquid ratio is 1 g: 8 - 15 mL. The solvents of solution A and solution B are selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, THF, acetonitrile, N-methylpyrrolidone (NMP), etc.

[0022] Further, in step (S3), the neutralization treatment is to immerse the sodium-supplemented material in a solution containing a neutralizing agent. The dosage of the neutralizing agent accounts for 0.1 - 0.5 vol%, and it is stirred at 25 - 30 °C for 5 - 10 minutes to ensure sufficient neutralization of the residual alkali on the surface. The neutralizing agent is selected from at least one of ethyl acetate, acetic acid, triethyl phosphate, and trimethyl phosphate; the solvent of the neutralizing agent solution is selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), tetrahydrofuran (THF), or dioxolane (DOL), etc. The role of the neutralizing agent is to neutralize the residual sodium species. The neutralizing agent is preferably ethyl acetate. Ethyl acetate undergoes a transesterification reaction with the residual basic sodium compounds on the surface (such as Na2O, Na2CO3, and NaOH, etc.) to form a more stable and less active sodium acetate compound, achieving effective neutralization of the residual sodium species. The neutralization treatment is the key to ensuring the electrochemical performance of the self-sodium-supplemented material, which not only ensures sufficient sodium storage for subsequent compensation but also avoids the adverse effects of excessive residual alkali on the battery performance.

[0023] Further, in step (S3), the solvent for washing is selected from dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC), ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethoxyethane (DME), tetrahydrofuran (THF), or dioxolane (DOL), etc. There is no special limitation on drying, such as vacuum drying at 50 - 80 °C.

[0024] The present invention adopts a two-stage sodiumation process. In the first sodiumation stage, sodium alkoxide with a lower concentration (0.1 - 0.2 M) is used at a higher temperature, which can increase the kinetic energy of sodium ions, enabling them to preferentially enter the crystal surface and shallow channels. At the same time, the low-concentration reagent avoids excessive accumulation of surface sodium species. The second-stage sodiumation is a consolidation stage, which is carried out at a lower temperature with a higher concentration of aryl sodium. The first stage has "activated" the lattice channels, and the high-concentration aryl sodiumating agent in the second stage can provide a sufficient concentration gradient to promote the migration of sodium ions into the lattice interior. The reduced temperature slows down the surface reaction rate, which helps the sodium ions to migrate orderly to the deep positions of the lattice, avoiding the formation of excessive basic sodium compounds on the surface.

[0025] In view of the characteristics of P2-type materials, the present invention designs a mild gradient sodiumation process and introduces a precise residual alkali regulation mechanism. Specifically, by controlling the gradient changes of the types, concentrations, and reaction temperatures of the sodiumating reagents, sodium ions are preferentially embedded in the material lattice rather than accumulating on the surface; at the same time, a specific weak acidic buffer is introduced to achieve in-situ neutralization of the residual alkali. Without destroying the main structure of the material, the surface Na / O ratio is controlled within an appropriate range of the theoretical value, effectively solving the problem of residual alkali during the sodiumation process.

[0026] The second object of the present invention is to provide a sodium battery, the positive electrode of which comprises the above-mentioned self-complementary sodium positive electrode material.

[0027] Further, in order to enhance the performance of the sodium battery, the self-complementary sodium positive electrode material is coupled with other types of positive electrode materials, such as O3-type layered oxide positive electrodes, sodium vanadium phosphate (NVP), sodium fluorovanadium phosphate (NVPF), sodium iron sulfate (Na2FeSO4), Prussian blue-based materials, etc. The coupling process involves precise calculation of the proportions of each component and ensuring uniform mixing of the materials. By coupling different types of positive electrode materials, high reversible capacity and excellent electrochemical performance can be achieved, which is crucial for improving the overall energy density of the battery.

[0028] In a preferred technical solution of the present invention, the positive electrode of the sodium battery is prepared from raw materials comprising the following parts by mass: 100 parts by mass of a precursor, 5-15 parts by mass of a chelating agent, and 10-20 parts by mass of a polymerizing agent; the precursor comprises raw materials in the following parts by mass: 20-30 parts by mass of the self-complementary sodium positive electrode material, 40-60 parts by mass of NASICON-structured Na3V2(PO4)2F3 as a high-capacity framework phase, and 25-35 parts by mass of Na 0.44 MnO2 as a tunnel structure. The above three positive electrode materials serve as the precursor, and together with the chelating agent and the polymerizing agent, they jointly form a ternary composite positive electrode material. The ternary composite positive electrode material can be prepared by the sol-gel method. The chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid (EDTA), and pyruvic acid; the polymerizing agent is selected from at least one of ethylene glycol, glycerol, and polyvinyl alcohol (PVA).

[0029] Specifically, the ternary composite positive electrode material is prepared by a preparation method comprising the following steps: The self-complementary sodium positive electrode material, Na3V2(PO4)2F3, and Na 0.44 MnO2 are mixed evenly in proportion to form a precursor solution, a chelating agent and a polymerizing agent are added, and the mixture is stirred at 60-90 °C for 5-10 h to form a gel. After the gel is dried, it is calcined at 500-800 °C for 4-8 h in an inert atmosphere to obtain the ternary composite positive electrode material.

[0030] The P2-type material is prone to phase transformation in the highly sodiated state. By introducing the structurally stable tunnel-type Na 0.44 MnO2 as the "framework phase", the volume change of the overall electrode is inhibited. At the same time, the rigid polyhedral structure of NVPF provides additional mechanical support, and the relatively high electronic conductivity of NVPF compensates for the low conductivity of the P2 material, improving the kinetic performance of the overall electrode. The three positive electrode materials form a composite structure through the sol-gel method, and a conductive agent (such as acetylene black) forms a three-dimensional conductive network therein.

[0031] The composite material formed by coupling the above self-complementary sodium cathode material and the ternary composite cathode material has the following microscopic structural characteristics: (1) P2-type particles serve as the main framework; (2) Na 0.44 MnO2 nanorods (about 100 nm in length and 20 - 30 nm in diameter) are distributed in the particle gaps to form an ion rapid transport channel; (3) NVPF nanoparticles (30 - 50 nm) are attached to the surface of the P2-type particles to form an electron rapid transport network.

[0032] Compared with the prior art, the self-complementary sodium cathode provided by the present invention can release extra sodium ions from its structure during the initial charging stage of the battery to compensate for the initial sodium loss during the SEI formation process. This self-complementary sodium mechanism significantly improves the initial cycle efficiency of the battery and has significant advantages in improving the energy density and cycle stability of sodium-ion batteries, providing a new research direction and application potential for the further development of sodium-ion battery technology. Detailed implementation manners

[0033] Through the gradient sodiation process of the present invention, the sodiation process of the P2-type material can be divided into two stages. First, the sodium agent of low-concentration sodium alkoxide preferentially opens the surface ion channels at high temperature; second is the bulk sodium ion intercalation and surface passivation stabilization. The high-concentration aryl sodium agent provides a sufficient concentration gradient, and sodium ions migrate inward along the activated channels. Meanwhile, the ethyl acetate neutralization treatment converts the residual active sodium species into stable compounds. This staged sodiation process ensures that the finally formed self-complementary sodium cathode material has a moderate surface sodium content and a sufficient bulk sodium content, can provide extra sodium ions during the first cycle of the battery, effectively compensate for the irreversible sodium loss during the SEI formation process, and thus significantly improve the first efficiency and cycle stability of the battery.

[0034] Example 1

[0035] (S1) Under a nitrogen atmosphere, the P2-type sodium nickel manganese titanium oxide Na 0.67 Ni 0.33 Mn 0.33 Ti 0.33 O2 powder is impregnated in solution A. The solvent of solution A is THF, the concentration of sodium tert-butoxide is 0.1 M, the concentration of CMC-Na is 0.8 wt%, and 0.2 M of sodium acetate is introduced as a pH buffer. The solid-liquid ratio of the P2-type sodium nickel manganese titanium oxide to solution A is 1 g:10 mL, and the reaction is carried out at 400 rpm and 50 °C for 3 min for the first sodium supplementation. After the sodium supplementation is completed, the material is taken out and dried for the next stage of sodium supplementation;

[0036] (S2) The dried material from step (S1) is immersed in solution B. The solvent of solution B is DMSO, the concentration of sodium biphenyl is 0.5 M, the concentration of CMC-Na is 0.8 wt%, and 0.2 M of sodium acetate is introduced as a pH buffer. The solid-liquid ratio of the dried material to solution B is 1 g:10 mL. The reaction is carried out at 400 rpm and 25 °C for 5 min to perform the second sodium supplementation and complete the sodium supplementation in the consolidation stage.

[0037] (S3) The sodium-supplemented cathode material is washed multiple times with dimethyl carbonate and finally surface-modified with dimethyl carbonate containing 0.1 vol% of ethyl acetate to neutralize the residual sodium species, followed by vacuum drying to obtain the self-sodium-supplemented P2-type cathode material.

[0038] 4) Assemble a button battery: Assemble the cathode shell, cathode electrode sheet, Whatman separator, anode hard carbon electrode sheet, and anode shell in sequence, inject an electrolyte with 1 M concentration of NaPF6 as the solute and DEGDME as the solvent, and seal it completely for electrochemical performance testing.

[0039] Example 2

[0040] Prepare a self-sodium-supplemented cathode full cell by the same method as in Example 1, except that in step (S1), P2-type sodium nickel manganese titanium oxide (Na 0.67 Ni 0.33 Mn 0.33 Ti 0.33 O2) is replaced with (Na 0.67 Ni 0.33 Mn 0.67 O2), the concentration of sodium tert-butoxide is 0.2 M, and the process conditions for the first sodium supplementation are reaction at 40 °C for 5 min.

[0041] Example 3

[0042] Prepare a self-sodium-supplemented cathode full cell by the same method as in Example 1, except that in step (S1), the concentration of sodium tert-butoxide is 0.3 M.

[0043] Example 4

[0044] Prepare a self-sodium-supplemented cathode full cell by the same method as in Example 1, except that in step (S1), sodium tert-butoxide is replaced with sodium ethoxide at an equimolar concentration.

[0045] Example 5

[0046] Prepare a self-sodium-supplemented cathode full cell by the same method as in Example 1, except that in step (S1), the process conditions for the first sodium supplementation are reaction at 25 °C for 5 min.

[0047] Example 6

[0048] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S2), the concentration of sodium biphenyl is 0.3 M.

[0049] Example 7

[0050] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S2), the concentration of sodium biphenyl is 0.2 M.

[0051] Example 8

[0052] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S2), sodium biphenyl is replaced with sodium naphthyl of the same molar concentration.

[0053] Comparative Example 1

[0054] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S1), sodium tert-butoxide is replaced with sodium biphenyl of the same molar concentration.

[0055] Comparative Example 2

[0056] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S2), sodium biphenyl is replaced with sodium tert-butoxide of the same molar concentration.

[0057] Comparative Example 3

[0058] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S1), sodium tert-butoxide is replaced with sodium biphenyl of the same molar concentration; in step (S2), sodium biphenyl is replaced with sodium tert-butoxide of the same molar concentration.

[0059] Comparative Example 4

[0060] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, with the difference that: in step (S3), the surface modification treatment with ethyl acetate is not carried out.

[0061] Example 9

[0062] Prepare the self-complementary sodium cathode full cell according to the same method as in Example 1, except that the cathode uses a coupled material:

[0063] 1) Design a multifunctional composite cathode: First, prepare the self-complementary sodium P2-type Na 0.67+ x Ni 0.33 Mn 0.33 Ti 0.33 O2 material. Then select NASICON structure Na3V2(PO4)2F3 (55 wt%) as the high-capacity framework phase, and combine it with the tunnel structure Na0.44 MnO2 (25 wt%) and self-complementary sodium Na 0.67+x Ni 0.33 Mn 0.33 Ti 0.33 O2 (20 wt%) are mixed to form a ternary composite system as the precursor.

[0064] 2) Material composite is carried out by sol-gel method: Prepare the precursor solution of the ternary composite system. The solvent is a mixed solution of water and ethanol (volume ratio of water:ethanol is 9:1), and the solid content is controlled at 20 wt%. Add 5 wt% of citric acid as a chelating agent and 10 wt% of ethylene glycol as a polymerization agent of the precursor to the precursor solution, and stir at 80 °C for 6 hours to form a homogeneous gel. After drying the gel at 120 °C, calcine it at 600 °C for 4 hours in an argon atmosphere to form a nano-composite structure as the ternary composite material. The sol-gel method is used to make various materials form close interfacial contact.

[0065] 3) Preparation of composite electrode: Mix the prepared ternary composite material with a conductive agent (such as carbon black) and a binder (such as polyvinylidene fluoride) according to a mass ratio of 8:1:1, and add an appropriate amount of NMP to form a homogeneous slurry. Coat the slurry evenly on the aluminum foil and dry it in vacuum at 80 °C for 12 hours to obtain the composite positive electrode sheet.

[0066] 4) Assembly of button battery: Assemble the positive electrode shell, positive electrode sheet, Whatman separator, negative hard carbon electrode sheet, and negative electrode shell in sequence, inject an electrolyte with 1 M concentration of NaPF6 as the solute and DEGDME as the solvent, and seal it completely for electrochemical performance testing.

[0067] Application example Testing of Electrochemical Performance

[0068] Electrochemical performance testing: Test the batteries assembled in the examples and comparative examples. Charge and discharge cycles are carried out at a current density of 1C in the voltage range of 2.5 - 4.15V. The electrochemical performance of the rechargeable self-complementary sodium positive electrode full batteries of the examples and comparative examples of the present invention was tested, and the results are shown in Table 1.

[0069] Table 1 Electrochemical performance data

[0070]

[0071] The data in Table 1 clearly demonstrate the significant advantages of the gradient sodiation and residual alkali control technology of the present invention. After the P2 type is subjected to gradient sodiation, the capacity retention rate remains above 90% after 100 cycles, and the preferred embodiments reach above 95%, which is far higher than the traditional method. From the test results of the batteries in Table 1, it can be seen that for the full battery with the self-complementary sodium cathode adapted to the modified anode current collector, it makes up for the sodium loss in the process of forming the initial SEI in the first cycle of the sodium-free anode and prevents subsequent rapid capacity decay, relatively improving the cycle retention rate. In summary, the present invention proposes an efficient self-complementary sodium cathode material and its application in high-energy-density sodium batteries, effectively solving the problem of sodium loss in sodium-free anode batteries, and overcoming the challenges brought by the special structure of P2-type materials through an innovative gradient sodiation process and a precise residual alkali regulation mechanism. Through the carefully designed chemical sodiation treatment, the present invention not only improves the energy density and cycle stability of the battery, but also reduces the manufacturing cost, providing a new research direction and application potential for the development of rechargeable sodium battery technology.

Claims

1. A method for preparing a self-supplementing sodium P2 type positive electrode material, characterized in that: The following steps are involved: (S1) Under an inert atmosphere and stirring conditions, the P2 type positive electrode material powder is immersed in a solution A containing sodium alcoholate, a buffer and a dispersant to perform a first stage of sodium supplementation to obtain a positive electrode material 1; (S2) the positive electrode material after the first sodium supplementation is immersed in a solution B containing aryl sodium, a buffer and a dispersant, and a second stage of sodium supplementation is performed to obtain a positive electrode material 2; (S3) The positive electrode material 2 is sequentially neutralized, washed, and dried to obtain a self-supplementing sodium P2 type positive electrode material.

2. The preparation method according to claim 1, characterized in that: In step (S1), the positive electrode material of the P2 type sodium ion battery is selected from sodium nickel manganese oxide and sodium nickel manganese titanium oxide.

3. The preparation method according to claim 1, characterized in that: In step (S1), the sodium alkoxide is selected from at least one of sodium tert-butoxide, sodium ethoxide and sodium propoxide; and / or In step (S2), the aryl sodium is selected from at least one of naphthyl sodium, anthryl sodium, biphenyl sodium, tetracene sodium, phenyl sodium, and phenanthryl sodium.

4. The preparation method according to claim 1, characterized in that: The buffer is selected from at least one of sodium acetate, sodium propionate, sodium butyrate, sodium citrate and sodium benzoate; the dispersant is selected from at least one of sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyethylene glycol, polyvinyl alcohol (PVA), sodium alginate and the like.

5. The preparation method according to claim 1, characterized in that: In step (S1), in solution A, the concentration of sodium alkoxide is 0.1-0.2M, the concentration of buffer is 0.1-0.3M, and the concentration of dispersant is 0.5-2wt%; the first stage of sodium supplementation is to react at 40-50°C for 1-5min; and / or In step (S2), in solution B, the concentration of aryl sodium is 0.3-0.5M, the concentration of buffer is 0.1-0.3M, and the concentration of dispersant is 0.5-2wt%; the second stage of sodium supplementation is to react at 15-30°C for 1-5min.

6. The preparation method according to claim 1, characterized in that: Steps (S1) and (S2) are carried out under an inert atmosphere and stirring conditions, wherein the inert atmosphere is nitrogen and / or argon; the stirring rate is 300-600 rpm; during impregnation, the solid-liquid ratio is 1 g:8-15 mL; and the solvents of solution A and solution B are selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, THF, acetonitrile, N-methylpyrrolidone (NMP), etc.

7. The preparation method according to claim 1, characterized in that: In step (S3), the neutralizing agent is selected from at least one of ethyl acetate, acetic acid, triethyl phosphate, and trimethyl phosphate; the material after sodium supplementation is immersed in a solution containing the neutralizing agent and stirred at 25-30° C. for 5-10 minutes; in the solution containing the neutralizing agent, the neutralizing agent accounts for 0.1-0.5 vol%; the solvent is selected from dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, ethyl methyl carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, and dioxolane.

8. A sodium battery, wherein the positive electrode thereof comprises the self-supplementing sodium P2 type positive electrode material prepared by the preparation method according to any one of claims 1 to 7.

9. The sodium battery according to claim 8, characterized in that: The positive electrode includes a ternary composite positive electrode material, which is prepared from the following raw materials in parts by weight: 100 parts by weight of a precursor, 5-15 parts by weight of a chelating agent, and 10-20 parts by weight of a polymerizing agent; the precursor includes the following raw materials in parts by weight: 20-30 parts by weight of a self-supplementing sodium positive electrode material, 40-60 parts by weight of a NASICON structure Na3V2(PO4)2F3, 25-35 parts by weight of Na 0.44 MnO2; the chelating agent is selected from at least one of citric acid, ethylenediaminetetraacetic acid, and pyruvic acid; the polymerizing agent is selected from at least one of ethylene glycol, glycerol, and polyvinyl alcohol (PVA).

10. The sodium battery according to claim 9, characterized in that: The positive electrode is prepared by a preparation method comprising the following steps: a self-supplementing sodium P2 type positive electrode material prepared by the preparation method according to any one of claims 1 to 7, Na3V2(PO4)2F3, Na 0.44 MnO2 is mixed evenly in proportion and prepared into a precursor solution with a solvent. A chelating agent and a polymerizing agent are added and stirred at 60-90°C for 5-10 hours to form a gel. After the gel is dried, it is calcined at 500-800°C for 4-8 hours in an inert atmosphere to obtain a ternary composite positive electrode material.

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