Polymer monomer for in-situ coating of cathode material, preparation method and application thereof

Abstract

The application provides a kind of in situ coated positive electrode material polymer monomer, its preparation method and application, with compound A shown structure: compound A, R1 It is C1~C3 alkyl, n is polymerization degree, n=6000~10000.The application realizes dense coating layer by in situ coated sodium electric layer oxygen positive electrode material through polymerization, avoids the loss of active sodium caused by the corrosion of active material by air, and improves the air stability.By using the conductive properties of the monomer pyrrole structure after polymerization and the active sodium ions contained in sodium sulfonate, the dual function of ion and electron conduction is realized, which ensures that the composite sodium ion positive electrode material obtained after coating has high ion conductivity and good electron conductivity, and meets the ion transmission and electron exchange of layer oxygen positive electrode material in the charging and discharging process.At the same time, the active sodium ions in sodium sulfonate can also supplement the active sodium ions of the positive electrode in the cycle process.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a polymer monomer for in-situ coating of a positive electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] Due to the depletion of fossil fuels, the proportion of renewable energy generation is increasing. However, renewable energy power is generally unstable, requiring the use of energy storage batteries to balance peaks and valleys. Although lithium-ion batteries have been widely used in various fields, especially for large-scale energy storage, the low abundance of lithium in the Earth's crust makes them unable to meet the growing demand in the future. As a new energy storage technology, sodium-ion batteries offer advantages such as safety, efficiency, environmental friendliness, and low cost. They are considered a supplement or alternative to lithium-ion batteries and are expected to be widely used in large-scale energy storage and other fields.

[0003] In order to accelerate the development of sodium-ion batteries, exploring cathode materials with excellent performance has always been a research hotspot in this field. In recent years, more and more cathode materials for sodium-ion batteries have been developed. The most studied cathode materials mainly include Prussian blue, polyanions and layered oxides. Among them, layered oxide cathode materials have shown great commercial potential due to their high theoretical specific capacity, good conductivity, fast diffusion kinetics, high operating voltage, and easy large-scale production and preparation, and have received widespread attention. However, there are still a series of problems in the widespread application of layered oxide cathode materials, such as poor air stability, easy embedding of H2O and CO2 molecules in the air into the layered structure, and spontaneous Na + / H + This exchange results in the loss of active sodium and the formation of surface residual alkalis such as NaOH and Na2CO3. These electrochemically inactive residual sodium compounds can further cause slurry gelation and current collector corrosion, which is very detrimental to subsequent electrode manufacturing and battery performance. In addition, when layered oxides circulate in the electrolyte, they produce a series of interfacial side reactions, leading to irreversible transition metal dissolution and gas release.

[0004] In response to the above-mentioned problems of sodium-ion layered oxide positive electrode materials, the most commonly used method is to coat them with a carbon layer, an inorganic solid electrolyte layer and an organic polymer layer to prepare a composite positive electrode material. However, in order to ensure the transmission of sodium ions, the carbon material coating layer is usually a porous layer, which cannot completely isolate the air and achieve the air stability of the active material. In addition, the carbon material coating layer is usually used to improve the conductivity of the active material, relying on the exposed positive electrode area of ​​the pores of the coating layer to ensure ion transmission. Compared with the uncoated method, this method limits the ion transmission of the active material to a certain extent. The coating of the inorganic solid electrolyte layer is usually to enhance the active ion transmission, while maintaining the structural stability when the active ion is deintercalated and the volume changes. Whether it is a simple carbon material coating or an inorganic solid electrolyte coating, in order to ensure the normal electron and ion conductivity of the active material after coating, the coating layer is a porous layer, which cannot achieve dense coating and realize the air stability of the active material. Summary of the Invention

[0005] The purpose of the present invention is to provide a polymer monomer for in-situ coating anode materials, a preparation method and application thereof. The sodium ion layered oxide cathode material of the present invention has good stability, thereby improving the cycle stability and life of the battery.

[0006] The present invention provides a polymer monomer for in-situ coating of a positive electrode material, having the structure shown in compound A:

[0007] ;

[0008] In compound A, R1 is a C1~C3 alkyl group, n is the degree of polymerization, and n=6000~10000.

[0009] Preferably, R1 is -CH3, -CH2CH3, -CH2F, -CH2OCH3, -CH2CH2F or -CH(CH3)2.

[0010] The present invention provides a method for preparing a polymer monomer for in-situ coating anode material as described above, comprising the following steps:

[0011] A) Compound B and di-tert-butyl dicarbonate are mixed in an alcohol solvent and stirred to react to obtain Compound C;

[0012] B) dispersing compound C and zinc chloride in an aprotic solvent, adding hydrochloric acid dropwise, heating and reacting under stirring to obtain compound D;

[0013] C) Compound D is dispersed in a sodium sulfite aqueous solution and heated in a first reaction vessel to react to obtain a mixture containing Compound E. The mixture containing Compound E is then transferred to a second reaction vessel, and trifluoroacetic acid is added dropwise to the mixture. The mixture is stirred continuously to react to obtain Compound A.

[0014] ; ; ; ; .

[0015] Preferably, the alcohol solvent in step A) is methanol;

[0016] The reaction temperature in step A) is 40-50° C., and the reaction time in step A) is 1-3 hours.

[0017] Preferably, the aprotic solvent in step B) is one or more of diethyl ether, carbon tetrachloride, dimethyl sulfoxide and acetone;

[0018] The reaction temperature in step B) is 30-50° C., and the reaction time in step B) is 2-6 hours.

[0019] Preferably, in step C), the temperature for reacting compound D with sodium sulfite is 180-220° C., and the reaction time is 2-5 hours;

[0020] In step C), the reaction temperature of the mixture containing compound E and trifluoroacetic acid is 180-220° C., and the reaction time is 1-3 hours.

[0021] The present invention provides an in-situ coated sodium ion positive electrode material, comprising a sodium ion layered oxide positive electrode material and a coating layer coated on the surface of the sodium ion layered oxide;

[0022] The coating layer includes a compound shown in formula I:

[0023] Formula I;

[0024] In Formula I, R1 is a C1-C3 alkyl group, R2 is a substituted or unsubstituted C1-C5 alkyl group, and n is the degree of polymerization, which is 6000-10000.

[0025] The present invention provides a method for preparing the above-mentioned in-situ coated sodium ion positive electrode material, comprising the following steps:

[0026] a) mixing a sodium ion layered oxide dispersion and a compound A dispersion to perform an in-situ polymerization reaction to obtain an intermediate;

[0027] The sodium ion layered oxide dispersion comprises a sodium ion layered oxide positive electrode material and an inert organic solvent;

[0028] The compound A dispersion comprises compound A, an initiator and an inert organic solvent;

[0029] ;

[0030] b) mixing the intermediate, R2-NH2 and a strong acid resin, and modifying the mixture to obtain an in-situ coated sodium ion positive electrode material.

[0031] Preferably, the molar ratio of the sodium ion layered oxide positive electrode material to compound A is 1:(2-6);

[0032] The temperature of the in-situ polymerization in step A) is 0-25° C., and the time of the in-situ polymerization in step A) is 3-8 hours;

[0033] The modification temperature in step B) is 75-90° C., and the modification time in step B) is 12-24 hours.

[0034] The present invention provides a positive electrode, comprising a current collector and a positive electrode active material layer composited on the surface of the current collector, wherein the positive electrode active material layer comprises the in-situ coated sodium ion positive electrode material described above or the in-situ coated sodium ion positive electrode material prepared by the preparation method described above.

[0035] The present invention provides a sodium ion battery comprising the positive electrode described above.

[0036] The present invention provides a polymerizable monomer for in-situ coating of a positive electrode material, having the structure shown in Compound A: In Compound A, R1 is a C1-C3 alkyl group, and n represents the degree of polymerization, with n=6000-10000. The present invention synthesizes a novel monomeric 1-alkylketone-2-sodium methanesulfonate-pyrrole compound (Compound A), which is then polymerized to in-situ coat the sodium-electrolyte layer oxygen positive electrode material, creating a dense coating layer. This prevents air erosion of the active material, which can cause loss of active sodium, and improves air stability. By utilizing the electronically conductive properties of the polymerized pyrrole structure and the active sodium ions contained in the sodium sulfonate, the dual functions of ion conduction and electron conduction are achieved, ensuring that the resulting composite sodium ion positive electrode material exhibits both high ion conductivity and good electronic conductivity, satisfying the requirements for ion transport and electron exchange in the layer oxygen positive electrode material during charge and discharge. Furthermore, the active sodium ions in the sodium sulfonate can replenish the active sodium ions in the positive electrode during cycling.

[0037] In addition, in view of the fact that it is difficult to avoid the transition metal ions in the structure from being released during the ion deintercalation process and being transferred to the electrolyte through ion transport, thereby triggering side reactions and leading to rapid consumption of the electrolyte, the present invention further modifies the coating layer on the basis of in-situ coating, and uses alkyl ketones and amino compounds to generate Schiff base structures to anchor the released transition metal ions, inhibit side reactions, and reduce cyclic gas production. This modified polymer coating not only maintains the stability of the electrode material, but also helps to improve the cycle stability and life of the battery. The improved methods of the present invention from multiple angles provide strong technical support for the industrialization and commercial application of sodium ion batteries. DETAILED DESCRIPTION

[0038] The present invention provides a polymer monomer for in-situ coating of a positive electrode material, having the structure shown in compound A:

[0039] ;

[0040] In compound A, R1 is a C1~C3 alkyl group, preferably, R1 is -CH3, -CH2CH3, -CH2F, -CH2OCH3, -CH2CH2F or -CH(CH3)2; n is the degree of polymerization, n=6000~10000, preferably, n is 7000~9000.

[0041] In the present invention, the compound A is one or more of compound A1 to compound A6:

[0042] .

[0043] The present invention preferably provides a method for preparing the polymer monomer for in-situ coating of the positive electrode material as described above, comprising the following steps:

[0044] A) Compound B and di-tert-butyl dicarbonate are mixed in an alcohol solvent and stirred to react to obtain Compound C;

[0045] B) dispersing compound C and zinc chloride in an aprotic solvent, adding hydrochloric acid dropwise, heating and reacting under stirring to obtain compound D;

[0046] C) dispersing compound D in a sodium sulfite aqueous solution, heating to react, to obtain a mixture containing compound E, and then dropwise adding trifluoroacetic acid to the mixture while continuously stirring to react, to obtain compound A;

[0047] ; ; ; ; .

[0048] Specifically, the preparation process of compound A can refer to the reaction formulas shown in Formula II to Formula III:

[0049] Formula II;

[0050] Formula III.

[0051] The present invention preferably disperses compound B in methanol, and after uniform dispersion, adds a certain amount of di-tert-butyl dicarbonate (Boc2O) to protect the pyrrole amino group, stirs at 40-50°C for 1-3 hours, cools, and passes through a chromatography column to obtain compound C with a purity of 99%;

[0052] In the present invention, the compound B is preferably a compound represented by any one of Formulas B1 to B6:

[0053]

[0054] In the present invention, the molar ratio of compound B to Boc2O is preferably (0.8~1):1, more preferably (0.9~1):1; the reaction temperature is preferably 40~50°C, more preferably 42~48°C, such as 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, preferably a range value with any of the above values ​​as the upper or lower limit; the reaction time is preferably 1~3 hours, more preferably 1~2 hours.

[0055] After obtaining compound C, the present invention preferably dissolves compound C in an aprotic solvent, adds zinc chloride for dispersion, adds hydrochloric acid dropwise, heats to 30-50° C., and stirs for 2-6 hours to obtain a mixture containing compound D. The mixture is purified by chromatography to obtain compound D with a purity of 99%.

[0056] In the present invention, the aprotic solvent is preferably one or more of diethyl ether, carbon tetrachloride, dimethyl sulfoxide and acetone; the molar ratio of zinc chloride to compound C is preferably (1-2):1, more preferably (1.2-1.8):1; the molar ratio of hydrochloric acid to compound C is preferably (1-1.2):1, and the concentration of hydrochloric acid is preferably 0.1-1 mol / L, more preferably 0.5 mol / L; the reaction temperature is preferably 30-50°C, more preferably 35-45°C, such as 30°C, 31°C, 32°C, 33°C, 34°C, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, preferably a range with any of the above values ​​as the upper or lower limit; the reaction temperature is preferably 2-6 hours, more preferably 3-5 hours.

[0057] After obtaining compound D, the present invention preferably takes a certain amount of compound D and disperses it in a sodium sulfite aqueous solution. After uniform dispersion, the mixed reactant is transferred to a first reaction vessel, heated to 180~220°C, and reacted for 2~5 hours to obtain a mixture containing compound E, which is transferred to a second reaction vessel. Then, trifluoroacetic acid (TFA) is added dropwise to the mixture, and continuously stirred. The reaction is carried out for 1~3 hours to obtain a mixture containing compound A, which is purified by chromatography to obtain compound A with a purity of 99%.

[0058] In the present invention, the molar ratio of the compound D to sodium sulfite is 1: (1.2-1.8), more preferably 1: (1.3-1.7), and most preferably 1: (1.5-1.6), and the concentration of the sodium sulfite is preferably 0.1-1 mol / L, more preferably 0.5 mol / L; the molar ratio of the compound D to TFA is preferably 1: (1.2-1.5), more preferably 1: (1.3-1.4); the temperature for the reaction of the compound D with sodium sulfite is preferably 180-220°C, more preferably 190-210°C, such as 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, preferably with any of the above values ​​as the upper or lower limit of the range; the concentration of the compound D and sodium sulfite is preferably 0.1-1 mol / L, more preferably 0.5 mol / L; the molar ratio of the compound D to TFA is preferably 1: (1.2-1.5), more preferably 1: (1.3-1.4); the temperature for the reaction of the compound D with sodium sulfite is preferably 180-220°C, more preferably 190-210°C, such as 180°C, 185°C, 190°C, 195°C, 200°C, 205°C, 210°C, 215°C, 220°C, preferably with any of the above values ​​as the upper or lower limit of the range; The reaction time of sodium acetic acid is preferably 2 to 5 hours, more preferably 3 to 4 hours; the reaction temperature of the mixture containing compound E and trifluoroacetic acid is preferably 180 to 220 ° C, more preferably 190 to 210 ° C, such as 180 ° C, 185 ° C, 190 ° C, 195 ° C, 200 ° C, 205 ° C, 210 ° C, 215 ° C, 220 ° C, preferably a range value with any of the above values ​​as the upper or lower limit; the reaction time of the mixture containing compound E and trifluoroacetic acid is preferably 1 to 3 hours, more preferably 1 to 2 hours. The first reaction vessel is preferably a high-temperature and high-pressure reactor, which can form a closed reaction environment to prevent the reactant solvent with a lower boiling point from evaporating in an open container and taking away the reactant. The second reaction vessel is preferably a normal pressure reactor.

[0059] The present invention provides an in-situ coated sodium ion positive electrode material, comprising a sodium ion layered oxide positive electrode material and a coating layer coated on the surface of the sodium ion layered oxide positive electrode material;

[0060] The coating layer includes a compound shown in formula I,

[0061] Formula I;

[0062] In Formula I, R1 is a C1-C3 alkyl group, R2 is a substituted or unsubstituted C1-C5 alkyl group, and n is the degree of polymerization, which is 6000-10000.

[0063] In the present invention, the sodium ion layered oxide may have a structural formula of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0064] In the present invention, the coating layer includes the compound represented by formula I, which is obtained by in-situ polymerization of compound A and then modification with an amino compound (R2-NH2).

[0065] In Formula I, R1 is a C1-C3 alkyl group, such as a methyl, ethyl, propyl, or isopropyl group. Preferably, R1 is -CH3, -CH2CH3, -CH2F, -CH2OCH3, -CH2CH2F, or -CH(CH3)2. R2 is a substituted or unsubstituted C1-C5 alkyl group, preferably an unsubstituted C1-C5 alkyl group, a halogen-substituted C1-C5 alkyl group, or an alkoxy-substituted C1-C5 alkyl group. More preferably, R2 is -CH2CH3, -CH2CH2CH3, -CH2OCH3, -CH2CH2CHCH3F, -CH2CH2OCH3, or -CH2OCH(CH3)2. n is the degree of polymerization, n = 6000-10000, preferably, n is 7000-9000.

[0066] In the present invention, the coating layer is a polymer coating layer obtained by in-situ polymerization of monomer compound A on the surface of the sodium ion layered oxide and then modification with an amino compound. The thickness of the coating layer is preferably 0.01-0.2 μm, more preferably 0.05-0.15 μm.

[0067] The present invention also provides a method for preparing the above-mentioned in-situ coated sodium ion positive electrode material, comprising the following steps:

[0068] a) mixing a sodium ion layered oxide dispersion and a compound A dispersion to perform an in-situ polymerization reaction to obtain an intermediate;

[0069] The sodium ion layered oxide dispersion comprises sodium ion layered oxide and an inert organic solvent;

[0070] The compound A dispersion comprises compound A, an initiator, a catalyst and an inert organic solvent;

[0071] Formula II;

[0072] b) mixing the intermediate, R2-NH2 and a strong acid resin, and modifying the mixture to obtain a sodium ion layered oxide positive electrode material.

[0073] In the present invention, the structure and preparation method of compound A are consistent with the structure and preparation method of compound A described above, and the present invention will not repeat them here.

[0074] After obtaining compound A, the present invention mixes the compound A with an inert organic solvent and stirs for 1 to 3 hours to fully dissolve the compound A. Then, an initiator and a catalyst are added and stirred continuously to obtain a dispersion of compound A after the mixture is fully dissolved.

[0075] In the present invention, the inert organic solvent is preferably an anhydrous or low water-active organic solvent, more preferably dichloromethane and / or chloroform; the initiator is preferably ferric chloride (FeCl3), and the catalyst is preferably boron trifluoride etherate (BF3·OEt2) and / or p-toluenesulfonic acid (TsOH); the molar ratio of the initiator to compound A is preferably (0.01-0.1):1, more preferably (0.03-0.08):1, such as 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0. 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, preferably a range value with any of the above values ​​as the upper or lower limit; the molar ratio of the catalyst to compound A is preferably (0.001~0.01):1, more preferably (0.003~0.008):1, such as 0.001:1, 0.003:1, 0.005:1, 0.007:1, 0.008:1, 0.01:1, preferably a range value with any of the above values ​​as the upper or lower limit.

[0076] The invention mixes sodium ion layered oxide with an inert organic solvent, stirs and uniformly disperses the mixture in the organic solvent, and obtains a sodium ion layered oxide dispersion.

[0077] In the present invention, the inert organic solvent is preferably an anhydrous or low water-active organic solvent, more preferably dichloromethane and / or chloroform; the inert organic solvent used in the sodium ion layered oxide dispersion and the inert organic solvent used in the compound A dispersion may be of the same or different types, preferably the same type of inert organic solvent is used.

[0078] In the present invention, the molar ratio of the sodium ion layered oxide to compound A is preferably 1:(2-6), more preferably 1:(3-5), such as 1:2, 1:3, 1:4, 1:5, 1:6, and preferably a range value with any of the above values ​​as the upper or lower limit.

[0079] After obtaining the sodium ion layered oxide dispersion and the compound A dispersion, the present invention mixes the two and performs an in-situ polymerization reaction as shown in Formula IV. After the reaction is completed, the reactants are filtered, washed and dried to obtain a sodium ion layered oxide coated with polymer A.

[0080] Formula IV.

[0081] In the present invention, the temperature of the in situ polymerization reaction is preferably 0-25°C, more preferably 5-20°C, such as 0°C, 5°C, 10°C, 15°C, 20°C, 25°C, preferably a range value with any of the above values ​​as the upper or lower limit; the time of the in situ polymerization reaction is preferably 3-8 hours, more preferably 4-6 hours.

[0082] In the present invention, the drying temperature is preferably 40-45°C, such as 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, preferably a range value with any of the above values ​​as the upper or lower limit; the drying time is preferably 2-6 h, more preferably 3-5 h.

[0083] In order to further suppress the dissolution of transition metal ions during the cycle, the present invention mixes the obtained polymer A-coated sodium ion layered oxide, a strong acid resin and R2-NH2, and performs a modification reaction as shown in Formula V to obtain a sodium ion layered oxide positive electrode material.

[0084] Formula V.

[0085] In the present invention, the strong acid resin is preferably a strong acid gel resin; the R2-NH2 preferably has a structure shown in any one of Formula VI to Formula XI,

[0086] .

[0087] In the present invention, the molar ratio of the polymer A to R2-NH2 is preferably 1:(1.1-2), more preferably 1:(1.2-1.8), such as 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, preferably a range value with any of the above values ​​as the upper or lower limit; the molar ratio of the polymer A to the strong acid resin is preferably 1:(0.01-0.05), more preferably 1:(0.02-0.04), such as 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, preferably a range value with any of the above values ​​as the upper or lower limit.

[0088] In the present invention, the temperature of the modification reaction is preferably 75-90° C., more preferably 80-85° C., and the time of the modification reaction is preferably 12-24 hours, more preferably 16-18 hours.

[0089] The present invention also provides another in-situ coated sodium ion positive electrode material, comprising a sodium ion layered oxide positive electrode material and a coating layer (unmodified) coated on the surface of the sodium ion layered oxide positive electrode material;

[0090] The coating (unmodified) comprises polymer A,

[0091]

[0092] In the present invention, the type of the sodium ion layered oxide and the values ​​of n and R1 in polymer A are consistent with the type of the sodium ion layered oxide and the values ​​of n and R1 in polymer A described above, and the present invention will not be repeated here.

[0093] The coating layer (unmodified) includes polymer A, which is formed by in-situ polymerization of compound A on the surface of sodium ion layered oxide.

[0094] In the present invention, the preparation method of the in-situ coated sodium ion positive electrode material having an unmodified coating layer is consistent with the method of preparing the sodium ion layered oxide coated with polymer A in step a) of the preparation method of the in-situ coated sodium ion positive electrode material described above, and the present invention will not be repeated here.

[0095] The present invention also provides a positive electrode, comprising a current collector and a positive electrode active material layer composited on the surface of the current collector, wherein the positive electrode active material layer comprises any one or two of the two in-situ coated sodium ion positive electrode materials described above.

[0096] In the present invention, the positive electrode active material layer also includes a conductive agent and a binder. The present invention has no special restrictions on the types of the conductive agent and the binder. The conductive agent and the binder commonly used in the positive electrode of sodium ion batteries in the field can be used. For example, the conductive agent can be conductive carbon black SP, and the binder can be PVDF.

[0097] The present invention mixes the above-mentioned in-situ coated sodium ion positive electrode material, conductive agent, binder and solvent, controls the solid content to be 65-75%, preferably 70%, and fully stirs to obtain a positive electrode slurry, which is then coated on the surface of a current collector such as aluminum foil and dried to obtain a positive electrode.

[0098] The present invention also provides a sodium ion battery comprising the positive electrode, negative electrode, separator and electrolyte described above.

[0099] In the present invention, the separator is preferably a polypropylene (PP) or polyethylene (PE) separator; the negative electrode material is selected from a hard carbon negative electrode; and the electrolyte includes a sodium salt, a non-aqueous organic solvent, and an additive.

[0100] In the present invention, the sodium salt is preferably any one or more of sodium hexafluorophosphate (NaPF6), perchloric acid (NaClO4), sodium tetrafluoroborate (NaBF4), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonylimide (NaFSI) and sodium difluorooxalatoborate (NaODFB), preferably NaPF6 and / or NaFSI; the mass fraction of the sodium salt in the electrolyte raw material is preferably 12-16%, more preferably 13-15%.

[0101] In the present invention, the non-aqueous organic solvent is preferably one or more of organic esters, C1-10 alkyl ethers, cyclic ethers, sulfones and dinitriles; the organic esters are preferably at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate (MPC), methyl formate (MF), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), butyl propionate (BP) and ethyl butyrate (EB); the C1-10 alkyl ethers are at least one of dimethyl ether, diethyl ether and methyl ethyl ether; the dinitriles are at least one of adiponitrile, succinonitrile and glutaronitrile; the sulfones are at least one of dimethyl sulfoxide and sulfolane; the mass fraction of the non-aqueous organic solvent in the electrolyte raw material is preferably 77-85%, more preferably 80-82%.

[0102] In the present invention, the additive includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), diethylene sulfate (DTD), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), 1,4-butane sultone (BS), tris(trimethylsilyl) phosphate (TMSP), tris(trimethylsilyl) borate (TMSB) and succinic anhydride (SA); the mass fraction of the additive in the electrolyte raw material is preferably 1-6%, more preferably 2-5%.

[0103] Compared with the prior art, the present invention has the following advantages:

[0104] (1) Through in-situ polymerization coating, the sodium layered oxide active material is densely coated to avoid air erosion and achieve air stability of the sodium layered oxide active material. At the same time, the side reaction of the electrolyte on the surface of the active material during the electrochemical process is suppressed, which inhibits gas production. In addition, the polymer coating can well adapt to the volume change caused by the active ion deintercalation process, inhibit the structural collapse caused by phase change, and maintain the structural stability during the cycle process.

[0105] (2) The sodium-ion layered oxide positive electrode material is coated with a polymer having both electrical and ion conductivity as shown in Formula I, thereby ensuring that the coated composite positive electrode active material has both high electrical and ion conductivity, thereby achieving better electrochemical performance, inhibiting the charge and discharge process of the sodium-ion layered oxide positive electrode, and thereby improving the cycle performance.

[0106] (3) The sodium sulfonate on the ion-conducting side chain of the compound represented by formula I in the coating layer is an active sodium ion, which can achieve the high ion-conducting performance of the coating layer while realizing the role of sodium replenishment in the positive electrode, thereby further improving the cycle life.

[0107] (4) The Schiff base structure in the compound represented by formula I in the coating layer can coordinate well with the transition metal ions, thereby anchoring the transition metal ions and preventing the transition metal ions from transferring to the negative electrode to catalyze the decomposition of the electrolyte. The side reactions caused by the transition metal ions are suppressed by the double confinement effect of the coating layer and the coating surface layer.

[0108] In order to further illustrate the present invention, the following detailed description of a polymer monomer for in-situ coating of a positive electrode material provided by the present invention, its preparation method and application is provided in conjunction with the examples, but it should not be understood as limiting the scope of protection of the present invention.

[0109] Example 1

[0110] Preparation of Compound I

[0111] Reaction 1

[0112]

[0113] Reaction 2

[0114]

[0115] 1. Disperse 15 mmol of compound B1 in 200 ml of methanol. After uniform dispersion, add 15 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 40°C for 3 h, cool, and pass through a chromatography column to obtain compound C with a purity of 99% and a yield of 60.2%. GC-MS (m / z): calcd. for C 12 H 17 O4N, 239.27, found 239.56.

[0116] 2. Dissolve 10 mmol of compound C in 150 ml of ether, add 10 mmol of zinc chloride for dispersion, add 20 ml of hydrochloric acid dropwise, heat to 30°C, and stir for 6 h to obtain a mixture containing compound D. Purify the mixture by chromatography to obtain compound D with a purity of 99% and a yield of 63.4%. GC-MS (m / z): calcd. for C 12 H 16 O3ClN, 257.71, found257.92;

[0117] 3. 10 mmol of compound D was dispersed in 24 ml of aqueous sodium sulfite solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 200°C. The reaction was carried out for 4 h to obtain a mixture containing compound E. 12 mmol of TFA was then added dropwise to the mixture with continuous stirring. The reaction was carried out for 2 h to obtain a mixture containing compound A. The mixture was purified by chromatography to obtain compound I with a purity of 99% and a yield of 62.7%. GC-MS (m / z): calcd. for NaC7H8O4NS, 225.19, found 225.63.

[0118] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0119] Reaction 1

[0120]

[0121] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in dichloromethane and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0122] 2. Then, 6 mol of compound I was dissolved in dichloromethane and stirred for 1.5 h to fully dissolve compound I. After compound I was dissolved, 0.12 mol of initiator ferric chloride (FeCl3) and 0.006 mol of catalyst boron trifluoride etherate (BF3•OEt2) were added and stirred continuously to fully dissolve.

[0123] 3. Mix the positive electrode material dispersion and the compound I solution, stir evenly, control the temperature at 10°C, react for 6 hours, filter, wash, and dry the reaction mixture to obtain a sodium ion layered oxide positive electrode material 1 coated with polymer I.

[0124] 4. The sodium ion layered oxide positive electrode material 1 coated with polymer I prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0125] Preparation of electrolyte 1 sample

[0126] In an argon glove box with a water and oxygen content of ≤0.1 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were uniformly mixed to obtain an organic solvent. Subsequently, sodium hexafluorophosphate (NaPF6) and sodium trifluoromethanesulfonimide (NaFSI) were slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added and stirred evenly to obtain electrolyte 1, wherein the amounts of NaPF6, NaFSI, EC, DEC, EMC, FEC, and VC used were 13%, 1%, 20%, 13%, 50%, 2%, and 1% of the total mass of the electrolyte, respectively.

[0127] Preparation of experimental battery 1 sample

[0128] 1. The hard carbon negative electrode, conductive agent carbon black (SuperP), thickener sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.3:1.2:1:1.5. After mixing, N-methyl pyrrolidone was added to control the theoretical solid content to 50%. The negative electrode slurry was obtained by homogenization using a vacuum defoamer, and the negative electrode slurry was evenly coated on a 17 μm thick aluminum foil. After drying, rolling, and cutting, a 58 mm × 76 mm negative electrode sheet was obtained.

[0129] 2. Prepare soft-pack laminated batteries at an ambient dew point of ≤-45°C. Stack the coated modified positive electrode sheet, PE separator, and negative electrode sheet in sequence, with the positive and negative electrode tabs on the same side. Place the separator between the positive and negative electrode sheets to isolate them, and obtain a bare cell.

[0130] 3. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 h, cool to below 40°C, and inject the prepared electrolyte 1 sample to obtain an experimental battery 1 sample. Subsequently, carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0131] Example 2

[0132] Preparation of Compound II

[0133] Compound B2 was prepared according to Reaction Scheme 1 (referenced from the literature "One-Step Synthesis of 3-Aryl- and 3,4-Diaryl-(1H)-Pyrroles Using Tosylmethyl Isocyanide (TOSMIC)"), where Ar1 is -CH2OH and Ar2 is -COCH2CH3.

[0134] Reaction 1

[0135]

[0136] Reaction 2

[0137]

[0138] Reaction 3

[0139]

[0140] 1. Disperse 20 mmol of compound B2 in 250 ml of methanol. After uniform dispersion, add 25 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 45°C for 2 h, cool and pass through a chromatography column to obtain compound C2 with a purity of 99% and a yield of 62.7%. GC-MS (m / z): calcd. for C 13 H 19 O4N, 253.3, found 253.46.

[0141] 2. Dissolve 10 mmol of compound C2 in 150 ml of carbon tetrachloride, add 12 mmol of zinc chloride for dispersion, add 22 ml of hydrochloric acid dropwise, heat to 35°C, and stir for 5 h to obtain a mixture containing compound D2. The mixture was purified by column chromatography to obtain compound D2 with a purity of 99% and a yield of 63.4%. GC-MS (m / z): calcd. for C 13 H 18 O3ClN, 271.74, found 272.05;

[0142] 3. 10 mmol of compound D2 was dispersed in 28 ml of sodium sulfite aqueous solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 180°C for 5 h to obtain a mixture containing compound E2. 13 mmol of TFA was then added dropwise to the mixture with continuous stirring. The mixture was reacted for 3 h to obtain a mixture containing compound II. The mixture was purified by column chromatography to obtain compound II with a purity of 99% and a yield of 61.3%. GC-MS (m / z): calcd. for NaC8H 10 O4NS, 239.22, found239.41.

[0143] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0144] Reaction 1

[0145]

[0146] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn1 / 3 O2) is dispersed in dichloromethane and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0147] 2. Then, 4 mol of compound II was dissolved in dichloromethane and stirred for 1 hour to fully dissolve compound II. After compound II was dissolved, 0.04 mol of initiator ferric chloride (FeCl3) and 0.012 mol of catalyst p-toluenesulfonic acid (TsOH) were added and stirred continuously to fully dissolve.

[0148] 3. Mix the positive electrode material dispersion and compound II solution, stir evenly, control the temperature at 20°C, react for 3 hours, filter, wash and dry the reaction mixture to obtain sodium ion layered oxide positive electrode material 2 coated with polymer II.

[0149] 4. The sodium ion layered oxide positive electrode material 2 coated with polymer II prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0150] Preparation of electrolyte 2 sample

[0151] In an argon glove box with a water and oxygen content of ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were uniformly mixed to obtain an organic solvent. Then, sodium hexafluorophosphate (NaPF6) and sodium trifluoromethanesulfonimide (NaFSI) were slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added and stirred evenly to obtain electrolyte 1, wherein the usage amounts of NaPF6, NaFSI, PC, DEC, EMC, FEC, and VC were 13%, 1%, 20%, 13%, 50%, 2%, and 1% of the total mass of the electrolyte, respectively.

[0152] Preparation of experimental battery 2 samples

[0153] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1.

[0154] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake it at 90°C for 12 hours, cool it to below 40°C, and then inject the prepared polymer precursor electrolyte 2 to obtain the experimental battery 2 sample. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0155] Example 3

[0156] Preparation of Compound III

[0157] Compound B3 was prepared according to Reaction Scheme 1 (from the literature "One-Step Synthesis of 3-Aryl- and 3,4-Diaryl-(1H)-Pyrroles Using Tosylmethyl Isocyanide (TOSMIC)"), Ar 1 -CH2OH, Ar 2 It is -COCH2F.

[0158] Reaction 1

[0159]

[0160] Reaction 2

[0161]

[0162] Reaction 3

[0163]

[0164] 1. Disperse 18 mmol of compound B3 in 250 ml of methanol. After uniform dispersion, add 20 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 50°C for 1 hour, cool, and pass through a chromatography column to obtain compound C3 with a purity of 99% and a yield of 60.2%. GC-MS (m / z): calcd. for C 12 H 16 O4FN, 257.26, found 257.8.

[0165] 2. Dissolve 10 mmol of compound C2 in 150 ml of dimethyl sulfoxide, add 15 mmol of zinc chloride for dispersion, add 24 ml of hydrochloric acid dropwise, heat to 45°C, and stir for 3 h to obtain a mixture containing compound D3. The mixture was purified by column chromatography to obtain compound D3 with a purity of 99% and a yield of 61.5%. GC-MS (m / z): calcd. for C 12 H 15 O3ClFN, 275.7, found 276.05;

[0166] 3. 10 mmol of compound D3 was dispersed in 30 ml of aqueous sodium sulfite solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 220°C for 2 h to obtain a mixture containing compound E3. 15 mmol of TFA was then added dropwise to the mixture with continuous stirring. The reaction was continued for 1 h to obtain a mixture containing compound III. The mixture was purified by chromatography to obtain compound III with a purity of 99% and a yield of 62.8%. GC-MS (m / z): calcd. for NaC7H7O4FNS, 243.18, found 243.69.

[0167] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0168] Reaction 1

[0169]

[0170] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in chloroform and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0171] 2. Then, 10 mol of compound II was dissolved in chloroform and stirred for 3 h to fully dissolve compound II. After compound III was dissolved, 1 mol of initiator ferric chloride (FeCl3) and 0.05 mol of catalyst boron trifluoride etherate (BF3•OEt2) were added and stirred continuously to fully dissolve.

[0172] 3. Mix the positive electrode material dispersion with the compound III solution, stir evenly, control the temperature at 15°C, react for 4.5 hours, filter, wash, and dry the reaction mixture to obtain a sodium ion layered oxide positive electrode material coated with polymer III.

[0173] 4. The sodium ion layered oxide positive electrode material 3 coated with polymer III prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0174] Prepare the electrolyte 3 sample as follows:

[0175] In an argon glove box with a water and oxygen content of ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were uniformly mixed to obtain an organic solvent. Then, sodium hexafluorophosphate (NaPF6) and sodium trifluoromethanesulfonimide (NaFSI) were slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added and stirred evenly to obtain electrolyte 3. Among them, the usage amounts of NaPF6, NaFSI, EC, PC, DEC, DMC, FEC and VC were 13.5%, 1.5%, 25%, 8%, 16%, 30%, 5% and 1% of the total mass of the electrolyte, respectively.

[0176] Preparation of experimental battery 3 samples

[0177] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1.

[0178] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 hours, cool to below 40°C, and inject the prepared polymer precursor electrolyte 3 to obtain experimental battery 3 sample. Subsequently, carry out packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0179] Example 4

[0180] Preparation of Compound IV

[0181] Compound B4 was prepared according to Reaction Scheme 1 (from the literature "One-Step Synthesis of 3-Aryl- and 3,4-Diaryl-(1H)-Pyrroles Using Tosylmethyl Isocyanide (TOSMIC)"), Ar 1 -CH2OH, Ar 2 It is -COCH2OCH3.

[0182] Reaction 1

[0183]

[0184] Reaction 2

[0185]

[0186] Reaction 3

[0187]

[0188] 1. Disperse 17 mmol of compound B4 in 250 ml of methanol. After uniform dispersion, add 20 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 42°C for 2.5 h, cool, and pass through a chromatography column to obtain compound C4 with a purity of 99% and a yield of 63.4%. GC-MS (m / z): calcd. for C 13 H 19 O5N, 269.3, found 269.48.

[0189] 2. Dissolve 10 mmol of compound C4 in 150 ml of acetone, add 20 mmol of zinc chloride for dispersion, add 24 ml of hydrochloric acid dropwise, heat to 50°C, and stir for 2.5 h to obtain a mixture containing compound D4. The mixture was purified by column chromatography to obtain compound D4 with a purity of 99% and a yield of 60.5%. GC-MS (m / z): calcd. for C 13 H 18 O4ClN, 287.74, found 288.15;

[0190] 3. 10 mmol of compound D4 was dispersed in 36 ml of sodium sulfite aqueous solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 210°C for 3 h to obtain a mixture containing compound E4. 14 mmol of TFA was then added dropwise to the mixture with continuous stirring. The reaction was continued for 1.8 h to obtain a mixture containing compound IV. The mixture was purified by column chromatography to obtain compound IV with a purity of 99% and a yield of 62.8%. GC-MS (m / z): calcd. for NaC8H 10 O5NS, 255.22, found255.41.

[0191] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0192] Reaction 1

[0193]

[0194] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in chloroform and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0195] 2. Then, 12 mol of compound IV was dissolved in chloroform and stirred for 2.5 h to fully dissolve compound II. After compound IV was dissolved, 0.96 mol of initiator ferric chloride (FeCl3) and 0.12 mol of catalyst boron trifluoride etherate (BF3•OEt2) were added and stirred continuously to fully dissolve.

[0196] 3. Mix the positive electrode material dispersion and compound IV solution, stir evenly, control the temperature at 5°C, react for 7 hours, filter, wash and dry the reaction mixture to obtain sodium ion layered oxide positive electrode material 4 coated with polymer IV.

[0197] 4. The sodium ion layered oxide positive electrode material 4 coated with polymer IV prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0198] Preparation of electrolyte 4 samples

[0199] In an argon glove box with a water and oxygen content of ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were uniformly mixed to obtain an organic solvent. Then, sodium hexafluorophosphate (NaPF6) and sodium trifluoromethanesulfonimide (NaFSI) were slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added and stirred evenly to obtain electrolyte 3. The amounts of NaPF6, NaFSI, EC, PC, DEC, DMC, FEC, and VC used were 14.5%, 1.5%, 25%, 5%, 20%, 30%, 3%, and 1% of the total mass of the electrolyte, respectively.

[0200] Preparation of experimental battery 4 samples

[0201] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1.

[0202] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake it at 90°C for 12 hours, cool it to below 40°C, and then inject the prepared polymer precursor electrolyte 4 to obtain the experimental battery 4 sample. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0203] Example 5

[0204] Preparation of Compound V

[0205] Compound B5 was prepared according to Reaction Scheme 1 (from the literature "One-Step Synthesis of 3-Aryl- and 3,4-Diaryl-(1H)-Pyrroles Using Tosylmethyl Isocyanide (TOSMIC)"), Ar 1 -CH2OH, Ar 2 It is -COCH2CH2F.

[0206] Reaction 1

[0207]

[0208] Reaction 2

[0209]

[0210] Reaction 3

[0211]

[0212] 1. Disperse 12 mmol of compound B5 in 250 ml of methanol. After uniform dispersion, add 15 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 46°C for 1.8 h, cool, and pass through a chromatography column to obtain compound C5 with a purity of 99% and a yield of 61.3%. GC-MS (m / z): calcd. for C 13 H 18 O4FN, 271.29, found 271.46.

[0213] 2. Dissolve 10 mmol of compound C5 in 150 ml of ether, add 16 mmol of zinc chloride for dispersion, add 22 ml of hydrochloric acid dropwise, heat to 40°C, and stir for 3.5 h to obtain a mixture containing compound D5. The mixture was purified by column chromatography to obtain compound D5 with a purity of 99% and a yield of 61.3%. GC-MS (m / z): calcd. for C 13 H 17 O3ClFN, 289.73, found 289.95;

[0214] 3. 10 mmol of compound D5 was dispersed in 32 ml of aqueous sodium sulfite solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 190°C for 3.5 h to obtain a mixture containing compound E5. 13 mmol of TFA was then added dropwise to the mixture with continuous stirring. The reaction was continued for 2.4 h to obtain a mixture containing compound V. The mixture was purified by chromatography to obtain compound V with a purity of 99% and a yield of 64.1%. GC-MS (m / z): calcd. for NaC8H9O4FNS, 257.21, found 257.61.

[0215] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0216] Reaction 1

[0217]

[0218] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in dichloromethane and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0219] 2. Then, 8 mol of compound V was dissolved in dichloromethane and stirred for 1 hour to fully dissolve compound V. After compound V was dissolved, 0.48 mol of initiator ferric chloride (FeCl3) and 0.056 mol of catalyst p-toluenesulfonic acid (TsOH) were added and stirred continuously to fully dissolve.

[0220] 3. Mix the positive electrode material dispersion and the compound V solution, stir evenly, control the temperature at 0°C, react for 8 hours, filter, wash, and dry the reaction mixture to obtain a sodium ion layered oxide positive electrode material 5 coated with polymer V.

[0221] 4. The sodium ion layered oxide positive electrode material 5 coated with polymer V prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0222] Preparation of electrolyte 5 samples

[0223] In an argon glove box with a water and oxygen content of ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and diethyl carbonate (EMC) were uniformly mixed to obtain an organic solvent. Then, sodium hexafluorophosphate (NaPF6) was slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) and vinylene carbonate (VC) were added and stirred evenly to obtain electrolyte 5. Among them, the usage amounts of NaPF6, EC, PC, DEC, EMC, FEC and VC were 12%, 15%, 5%, 20%, 44%, 2.5% and 1.5% of the total mass of the electrolyte, respectively.

[0224] Preparation of experimental battery 5 samples

[0225] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1.

[0226] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 hours, cool to below 40°C, and inject the prepared polymer precursor electrolyte 5 to obtain an experimental battery 5 sample. Subsequently, the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes are carried out.

[0227] Example 6

[0228] Preparation of Compound VI

[0229] Compound B6 was prepared according to Reaction Scheme 1 (from the literature "One-Step Synthesis of 3-Aryl- and 3,4-Diaryl-(1H)-Pyrroles Using Tosylmethyl Isocyanide (TOSMIC)"), Ar 1 -CH2OH, Ar 2 It is -CO(CH3)2.

[0230] Reaction 1

[0231]

[0232] Reaction 2

[0233]

[0234] Reaction 3

[0235]

[0236] 1. Disperse 12 mmol of compound B6 in 250 ml of methanol. After uniform dispersion, add 12 mmol of di-tert-butyl dicarbonate (Boc2O). Stir at 48°C for 1.2 h, cool, and pass through a chromatography column to obtain compound C6 with a purity of 99% and a yield of 60.2%. GC-MS (m / z): calcd. for C 14 H 21 O4N, 267.32, found 267.46.

[0237] 2. Dissolve 10 mmol of compound C6 in 150 ml of ether, add 18 mmol of zinc chloride for dispersion, add 20 ml of hydrochloric acid dropwise, heat to 50°C, and stir for 2.5 h to obtain a mixture containing compound D6. The mixture was purified by column chromatography to obtain compound D6 with a purity of 99% and a yield of 63.2%. GC-MS (m / z): calcd. for C 14 H 20 O3ClN, 285.77, found 285.95;

[0238] 3. 10 mmol of compound D6 was dispersed in 24 ml of aqueous sodium sulfite solution. After uniform dispersion, the mixture was transferred to a reactor and heated to 205°C for 3.5 h to obtain a mixture containing compound E6. 12 mmol of TFA was then added dropwise to the mixture with continuous stirring. The reaction was continued for 1.4 h to obtain a mixture containing compound V. The mixture was purified by column chromatography to obtain compound VI with a purity of 99% and a yield of 62.1%. GC-MS (m / z): calcd. for NaC9H 12 O4NS, 253.52, found253.8.

[0239] Preparation of in-situ coated sodium ion layered oxide positive electrode materials and sodium ion layered oxide positive electrode sheets

[0240] Reaction 1

[0241]

[0242] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in chloroform and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0243] 2. Then, 4 mol of compound VI was dissolved in chloroform and stirred for 2.2 h to fully dissolve compound VI. After compound VI was dissolved, 0.16 mol of initiator ferric chloride (FeCl3) and 0.04 mol of catalyst p-toluenesulfonic acid (TsOH) were added and stirred continuously to fully dissolve.

[0244] 3. Mix the positive electrode material dispersion and the compound VI solution, stir evenly, control the temperature at 15°C, react for 4 hours, filter, wash, and dry the reaction mixture to obtain a sodium ion layered oxide positive electrode material 6 coated with polymer VI.

[0245] 4. The sodium ion layered oxide positive electrode material 6 coated with polymer V prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0246] Preparation of electrolyte 6 samples

[0247] In an argon glove box with water and oxygen contents ≤0.1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and diethyl carbonate (EMC) were uniformly mixed to obtain an organic solvent. Then, sodium hexafluorophosphate (NaPF6) and sodium trifluoromethanesulfonimide (NaFSI) were slowly added to the organic solvent. After complete dissolution, fluoroethylene carbonate (FEC) was added and stirred evenly to obtain electrolyte 3. The amounts of NaPF6, NaFSI, EC, PC, DEC, EMC, and VC used were 13%, 1%, 15%, 5%, 20%, 45%, and 1% of the total mass of the electrolyte, respectively.

[0248] Preparation of experimental battery 6 samples

[0249] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1.

[0250] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake it at 90°C for 12 hours, cool it to below 40°C, and then inject the prepared polymer precursor electrolyte 6 to obtain the experimental battery 6 sample. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0251] Example 7

[0252] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0253] Reaction 1

[0254]

[0255] 1. The sodium ion layered oxide positive electrode material 1 coated with polymer I obtained in Example 1 was dispersed in compound VII containing a strong acid resin, and heated and stirred at 80° C. for 15 h to obtain a further modified composite positive electrode material 1;

[0256] 2. The composite positive electrode material 1 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0257] Preparation of electrolyte 7 samples

[0258] Preparation method and electrolyte formula are the same as those of Example 1 Electrolyte 1 sample

[0259] Preparation of experimental battery 7 samples

[0260] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0261] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 h, cool to below 40°C, inject the prepared electrolyte 7 samples, and obtain 7 experimental battery samples. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0262] Example 8

[0263] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0264] Reaction 1

[0265]

[0266] 1. The sodium ion layered oxide positive electrode material 2 coated with polymer II obtained in Example 2 was dispersed in compound VIII containing a strong acid resin, and heated and stirred at 80° C. for 12 h to obtain a further modified composite positive electrode material 2;

[0267] 2. The composite positive electrode material 2 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0268] Preparation of electrolyte 8 sample

[0269] The preparation method and electrolyte formula are the same as those of Example 2 Electrolyte 2 Sample

[0270] Preparation of experimental battery 8 samples

[0271] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0272] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 h, cool to below 40°C, and inject 8 samples of the prepared electrolyte to obtain 8 experimental battery samples. Subsequently, carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0273] Example 9

[0274] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0275] Reaction 1

[0276]

[0277] 1. The sodium ion layered oxide positive electrode material 3 coated with polymer III obtained in Example 3 was dispersed in compound IX containing a strong acid resin, and heated and stirred at 80° C. for 24 h to obtain a further modified composite positive electrode material 3;

[0278] 2. The composite positive electrode material 3 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0279] Preparation of electrolyte 9 sample

[0280] The preparation method and electrolyte formula are the same as those of Example 3 Electrolyte 3 Sample

[0281] Preparation of experimental battery 9 samples

[0282] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0283] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 hours, cool to below 40°C, and inject 9 samples of the prepared electrolyte to obtain 9 samples of experimental batteries. Subsequently, carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0284] Example 10

[0285] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0286] Reaction 1

[0287]

[0288] 1. The sodium ion layered oxide positive electrode material 4 coated with polymer IV obtained in Example 4 was dispersed in compound X containing a strong acid resin, and heated and stirred at 80° C. for 24 h to obtain a further modified composite positive electrode material 4;

[0289] 2. The composite positive electrode material 4 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By fully stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0290] Preparation of 10 samples of electrolyte

[0291] The preparation method and electrolyte formula are the same as those of Example 4 Electrolyte 4 Sample

[0292] Preparation of 10 experimental battery samples

[0293] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0294] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 h, cool to below 40°C, inject 10 samples of the prepared electrolyte, and obtain 10 samples of the experimental battery. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0295] Example 11

[0296] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0297] Reaction 1

[0298]

[0299] 1. The sodium ion layered oxide positive electrode material 5 coated with polymer V obtained in Example 5 was dispersed in compound XI containing a strong acid resin, and heated and stirred at 80° C. for 18 h to obtain a further modified composite positive electrode material 5;

[0300] 2. The composite positive electrode material 5 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0301] Preparation of electrolyte 11 samples

[0302] Preparation method and electrolyte formula are the same as Example 5 Electrolyte 5 Sample

[0303] Preparation of experimental battery 11 samples

[0304] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0305] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake it at 90°C for 12 hours, cool it to below 40°C, and inject the prepared electrolyte 11 sample to obtain the experimental battery 11 sample. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0306] Example 12

[0307] Preparation of modified in-situ coated sodium ion layered oxide cathode materials

[0308] Reaction 1

[0309]

[0310] 1. The sodium ion layered oxide positive electrode material 6 coated with polymer VI obtained in Example 6 was dispersed in compound XII containing a strong acid resin, and heated and stirred at 80° C. for 16 h to obtain a further modified composite positive electrode material 6;

[0311] 2. The composite positive electrode material 6 prepared above was mixed with the conductive agent SP, the binder PVDF and the solvent NMP, and the theoretical solid content was controlled to 70%. By sufficient stirring, a uniformly dispersed positive electrode slurry was prepared, and the slurry was coated on aluminum foil. After drying, rolling and die-cutting, a positive electrode sheet was obtained.

[0312] Preparation of electrolyte 12 samples

[0313] Preparation method and electrolyte formula are the same as Example 6 Electrolyte 6 Sample

[0314] Preparation of 12 experimental battery samples

[0315] 1. The preparation of negative electrode sheets and the assembly of bare cells are the same as in Example 1;

[0316] 2. Place the bare battery cell in an aluminum-plastic film outer package, vacuum bake at 90°C for 12 hours, cool to below 40°C, and inject the prepared electrolyte 12 samples to obtain 12 experimental battery samples. Then carry out the packaging, infiltration, formation, aging, secondary vacuum packaging, and capacity division processes.

[0317] Comparative Example 1

[0318] 1. 2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in chloroform and stirred continuously to make the positive electrode material evenly dispersed in the solvent;

[0319] 2、Subsequently, 6 mol of pyrrole monomer is dispersed in dichloromethane, and stirred for 1.5 h to allow the pyrrole monomer to be fully dispersed. After being well dispersed, 0.3 mol of initiator boron trifluoride diethyl ether (BF3•OEt2) is added and continuously stirred to allow it to be fully dissolved;

[0320] 3、The positive electrode material dispersion liquid is mixed with the pyrrole monomer dispersion liquid, and stirred uniformly, with the temperature controlled at 10°C, and reacted for 6 h. The mixture after reaction is filtered, washed, and dried to obtain a sodium ion layered oxide positive electrode material coated with polypyrrole comparative sample 1.

[0321] 5、The above prepared composite positive electrode material comparative sample 1 is mixed with conductive agent SP, binder PVDF, and solvent NMP, with the theoretical solid content controlled at 70%, and uniformly dispersed positive electrode slurry is prepared through sufficient stirring. The positive electrode slurry is coated on an aluminum foil, and after drying, rolling, and die cutting, a comparative sample positive electrode sheet 1 is obtained.

[0322] The negative electrode material and comparative sample battery 1 are prepared as in Example 1

[0323] Comparative Sample 2

[0324] 1、2 mol of sodium ion layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is dispersed in chloroform, and continuously stirred to allow the positive electrode material to be uniformly dispersed in the solvent;

[0325] 2、Subsequently, 6 mol of methyl methacrylate monomer is dispersed in chloroform, and stirred for 1.5 h to allow the methyl methacrylate monomer to be fully dispersed. After being well dispersed, 0.3 mol of initiator azobisisobutyronitrile is added and continuously stirred to allow it to be fully dissolved;

[0326] 3、The positive electrode material dispersion liquid is mixed with the methyl methacrylate monomer dispersion liquid, and stirred uniformly, with the temperature controlled at 55°C, and reacted for 3 h. The mixture after reaction is filtered, washed, and dried to obtain a sodium ion layered oxide positive electrode material coated with polypyrrole comparative sample 2.

[0327] 5、The above prepared composite positive electrode material comparative sample 2 is mixed with conductive agent SP, binder PVDF, and solvent NMP, with the theoretical solid content controlled at 70%, and uniformly dispersed positive electrode slurry is prepared through sufficient stirring. The positive electrode slurry is coated on an aluminum foil, and after drying, rolling, and die cutting, a comparative sample positive electrode sheet 2 is obtained.

[0328] The negative electrode material and comparative sample battery 2 are prepared as in Example 2

[0329] Comparative Sample 3

[0330] Using uncoated sodium layered oxide positive electrode active material (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) was mixed with a conductive agent SP, a binder PVDF, and a solvent NMP, and the theoretical solid content was controlled to 70%. The mixture was fully stirred to prepare a uniformly dispersed positive electrode slurry, which was then coated on aluminum foil. After drying, roller pressing, and die-cutting, a comparative positive electrode sheet 3 was obtained.

[0331] The preparation of negative electrode material and comparative sample battery 3 is the same as that of Example 3

[0332] In order to verify the air stability of the sodium-electrolyte layered oxide positive electrode material in situ coated with the newly synthesized monomer in the present invention, the composite positive electrode materials prepared in Examples 1 to 6 and the positive electrode material of Comparative Example 3 were exposed to an air environment (temperature 25°C, dew point -3.89°C) for 12 hours and then homogenized as positive electrode active materials (considering the water absorption of the binder and solvent, the homogenization was carried out in a dry room environment, temperature: 20°C, dew point -46.5°C), and the slurry state was observed. The homogenization ratio was the same as in Example 1.

[0333] Table 1 State of the homogenized slurry of positive electrode materials in Examples 1 to 6 and Comparative Example 3

[0334]

[0335] To verify the electrochemical performance of the composite cathode material prepared by the present invention, the first efficiency and differential capacity of Examples 1 to 12 and Comparative Examples 1 to 3 were compared (the battery cell design capacity is 1.12 Ah), and the room temperature cycling performance and rate performance were further tested in a constant temperature room.

[0336] 1. Room temperature cycle performance test conditions

[0337] Test temperature: 25℃;

[0338] Voltage range: 2-4.0V

[0339] Charge / discharge rate: 1C

[0340] 2. Rate performance test conditions

[0341] Test temperature: 25℃;

[0342] Voltage range: 2-4.0V

[0343] Test rate: 0.2C / 0.5C / 1C / 2C / 3C / 5C

[0344] Table 2 First effect and fractional capacity of Examples 1 to 12 and Comparative Examples 1 to 3

[0345]

[0346] According to the initial efficiency and the discharging capacity of the samples, the coated cathodes of Examples 1-12 and Comparative Examples 1-2 have higher initial efficiency and discharging capacity than the uncoated cathode material of Comparative Example 3, indicating that the coating of the polymer can effectively inhibit the side reaction of the cathode and the electrolyte in the electrochemical process and reduce the loss of active sodium. The cathodes of Examples 1-12 prepared by the new synthesized double functional coating layer of the application have higher initial efficiency and discharging capacity than the composite cathodes of Comparative Examples 1-2 coated by a single conductive or ion conductive polymer layer. On the one hand, it indicates that the composite cathode prepared by the application has better stability, and on the other hand, it indicates that the composite cathode prepared by the application has better electron transmission and ion transmission capacity, which can avoid the capacity loss caused by polarization. In addition, compared with Examples 1-6, Examples 7-12 have certain beneficial effects on the initial efficiency and capacity of the battery by further modifying the surface double functional coating layer.

[0347] Table 3 Room temperature cycle capacity and retention rate of Examples 1-12 and Comparative Examples 1-3

[0348]

[0349] According to the room temperature cycle capacity and retention rate of the batteries of Examples 1-12 and Comparative Examples 1-3, the coated cathode can effectively inhibit the side reaction and structure collapse of the cathode during the cycle process. However, compared with the composite cathode coated by a single conductive polymer or ion conductive polymer layer of Comparative Examples 1-2, the application uses an ion and electron conductive polymer layer to coat, which maintains the high ion and electron transmission capacity of the composite cathode, reduces polarization, and provides a certain amount of active sodium ions through the sodium sulfonate of the coating layer, thereby achieving a certain sodium supplement effect, so that the sample battery has higher capacity retention. At the same time, according to Examples 7-12, by further modifying the surface coating layer of the coated cathode material prepared by the application, the polymer coating and surface anchoring realize the double confinement of transition metal ions, which strengthens the inhibition of the side reaction of transition metal ion dissolution and the collapse of the cathode structure during the cycle process, and further improves the cycle life of the battery.

[0350] Table 4 Rate test data of sample batteries in Examples 1-12 and Comparative Examples 1-3

[0351]

[0352] According to the rate discharge and rate charge capacity retention rates of Examples 1-12 and Comparative Examples 1-3, the use of a conductive polymer or ion-conducting polymer layer coating in Comparative Examples 1-2 can improve the rate performance of the battery to a certain extent compared to Comparative Example 3. However, compared to Examples 1-12 of the present invention, the battery prepared using a composite positive electrode coated with an ionic and electronic dual-conducting layer has better rate performance. According to the rate performance of Examples 1-6 and Examples 7-12, further modification of the coating layer surface also slightly improves the rate performance.

[0353] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A polymer monomer for in-situ coating of a positive electrode material, having the structure shown in Compound A: ； In compound A, R1 is -CH3, -CH2CH3, -CH2F, -CH2OCH3, -CH2CH2F or -CH(CH3)2.

2. The method for preparing the polymer monomer for in-situ coating of the positive electrode material according to claim 1, comprising the following steps: A) Compound B and di-tert-butyl dicarbonate are mixed in an alcohol solvent and stirred to react to obtain Compound C; B) dispersing compound C and zinc chloride in an aprotic solvent, adding hydrochloric acid dropwise, heating and reacting under stirring to obtain compound D; C) Compound D is dispersed in a sodium sulfite aqueous solution and heated in a first reaction vessel to react to obtain a mixture containing Compound E. The mixture containing Compound E is then transferred to a second reaction vessel, and trifluoroacetic acid is added dropwise to the mixture. The mixture is stirred continuously to react to obtain Compound A. ； ； ； ； 。 3. The preparation method according to claim 2, characterized in that The alcohol solvent in step A) is methanol; The reaction temperature in step A) is 40-50° C., and the reaction time in step A) is 1-3 hours.

4. The preparation method according to claim 2, characterized in that The aprotic solvent in step B) is one or more of diethyl ether, carbon tetrachloride, dimethyl sulfoxide and acetone; The reaction temperature in step B) is 30-50° C., and the reaction time in step B) is 2-6 hours.

5. The preparation method according to claim 2, characterized in that In step C), the reaction temperature of compound D and sodium sulfite is 180-220° C., and the reaction time is 2-5 hours; In step C), the reaction temperature of the mixture containing compound E and trifluoroacetic acid is 180-220° C., and the reaction time is 1-3 hours.

6. An in-situ coated sodium ion positive electrode material, comprising a sodium ion layered oxide positive electrode material and a coating layer coated on the surface of the sodium ion layered oxide; The coating layer includes a compound shown in formula I: Formula I; In formula I, R1 is -CH3, -CH2CH3, -CH2F, -CH2OCH3, -CH2CH2F or -CH(CH3)2, R2 is an unsubstituted C1-C5 alkyl group, a halogen-substituted C1-C5 alkyl group or an alkoxy-substituted C1-C5 alkyl group, and n is the degree of polymerization, n=6000-10000; The method for preparing the in-situ coated sodium ion positive electrode material comprises the following steps: a) mixing a sodium ion layered oxide dispersion and a compound A dispersion to perform an in-situ polymerization reaction to obtain an intermediate; The sodium ion layered oxide dispersion comprises a sodium ion layered oxide positive electrode material and an inert organic solvent; The compound A dispersion comprises compound A, an initiator, a catalyst and an inert organic solvent; The initiator is ferric chloride, and the catalyst is boron trifluoride etherate and / or p-toluenesulfonic acid. ； b) mixing the intermediate, R2-NH2 and a strong acid resin, and modifying the mixture to obtain an in-situ coated sodium ion positive electrode material.

7. A method for preparing the in-situ coated sodium ion positive electrode material according to claim 6, comprising the following steps: a) mixing a sodium ion layered oxide dispersion and a compound A dispersion to perform an in-situ polymerization reaction to obtain an intermediate; The sodium ion layered oxide dispersion comprises a sodium ion layered oxide positive electrode material and an inert organic solvent; The compound A dispersion comprises compound A, an initiator, a catalyst and an inert organic solvent; The initiator is ferric chloride, and the catalyst is boron trifluoride etherate and / or p-toluenesulfonic acid. ； b) mixing the intermediate, R2-NH2 and a strong acid resin, and modifying the mixture to obtain an in-situ coated sodium ion positive electrode material.

8. The preparation method according to claim 7, characterized in that The molar ratio of the sodium ion layered oxide positive electrode material to compound A is 1:(2-6); The temperature of the in-situ polymerization in step A) is 0-25° C., and the time of the in-situ polymerization in step A) is 3-8 hours; The modification temperature in step B) is 75-90° C., and the modification time in step B) is 12-24 hours.

9. A positive electrode comprising a current collector and a positive electrode active material layer composited on the surface of the current collector, wherein the positive electrode active material layer comprises the in-situ coated sodium ion positive electrode material according to claim 6 or the in-situ coated sodium ion positive electrode material prepared by the preparation method according to any one of claims 7 to 8.

10. A sodium ion battery comprising the positive electrode according to claim 9.

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