A positive electrode material and preparation method thereof, a positive electrode sheet and a sodium ion battery

Abstract

The present invention relates to the field of batteries, and more specifically, to a positive electrode material, a preparation method thereof, a positive electrode sheet, and a sodium-ion battery. The positive electrode material has a core-shell structure, wherein the core of the core-shell structure is a Prussian blue material, and the shell of the core-shell structure comprises at least one of aluminum oxide, titanium dioxide, and silicon dioxide. The shell structure of the positive electrode material effectively prevents the Prussian blue material from absorbing moisture from the air, thereby reducing the hygroscopicity of the Prussian blue material.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery. Background Art

[0002] After the water of crystallization of Prussian blue is completely removed, the crystal structure transforms into a rhombohedral system. This rhombohedral structure readily absorbs water when exposed to air, easily transforming back into a monoclinic structure containing water of crystallization. Therefore, reducing the water of crystallization content of Prussian blue and improving its hygroscopic properties have become unresolved challenges for battery cathode materials.

[0003] Prior art uses neutral ligands (L) to coordinate the transition metal (M), partially or completely replacing the coordinated water, thereby reducing the water absorption capacity of Prussian blue-based cathode materials. However, the neutral ligands in this method cannot exchange with interstitial water (water of crystallization), and the water content in interstitial sites is generally much greater than that in defect sites. Therefore, this method cannot completely solve the problem of water and moisture absorption in cathode materials. Moreover, the exchanged ligands (H3CN, NH3, CO, and C5H5N) are prone to electrochemical oxidative decomposition at high potentials, which may damage the material structure and cause performance degradation.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One aspect of the present invention relates to a positive electrode material, wherein the positive electrode material is a core-shell structure, the core of the core-shell structure is a Prussian blue material, and the shell of the core-shell structure includes at least one of aluminum oxide, titanium dioxide and silicon dioxide.

[0006] The positive electrode material has a shell structure, which is coated on the surface of the Prussian blue material and can prevent the Prussian blue material from absorbing moisture, thereby reducing the hygroscopicity of the Prussian blue material.

[0007] According to another aspect of the present invention, the present invention also relates to a method for preparing a positive electrode material, comprising the following steps:

[0008] Under heating conditions, the Prussian blue raw material and the alcohol solution of the coating agent are mixed in a non-aqueous liquid medium.

[0009] The method for preparing the positive electrode material is simple to operate, and the positive electrode material prepared by the method is of excellent quality and has low water content and hygroscopicity.

[0010] According to another aspect of the present invention, the present invention also relates to a positive electrode plate, comprising the positive electrode material.

[0011] The positive electrode plate is made of a specific positive electrode material and has low water content and moisture absorption performance.

[0012] According to another aspect of the present invention, the present invention also relates to a sodium ion battery, comprising the above-mentioned positive electrode plate.

[0013] The sodium ion battery has a higher cycle retention rate and lower gas production.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] (1) The positive electrode material provided by the present invention includes a Prussian blue material and a specific shell structure wrapped on the surface. Compared with the prior art, the ability to isolate moisture from the air is significantly improved, and the hygroscopic performance is significantly reduced.

[0016] (2) The method for preparing the positive electrode material provided by the present invention comprises mixing and heating the Prussian blue raw material, the non-aqueous liquid phase medium and the alcohol solution of the coating agent. The operation is simple, the process is easy to implement, and the quality of the prepared positive electrode material is excellent.

[0017] (3) Compared with the prior art, the positive electrode provided by the present invention has improved water isolation ability and reduced moisture absorption performance, and can be used to prepare sodium ion batteries.

[0018] (4) The sodium ion battery provided by the present invention, including the positive electrode sheet, has a high cycle retention rate, and its volume does not change significantly during the standard number of cycles. It has excellent quality and meets industry standards. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0020] According to one aspect of the present invention, the present invention relates to a positive electrode material, wherein the positive electrode material is a core-shell structure, the core of the core-shell structure is a Prussian blue material, and the shell of the core-shell structure includes at least one of aluminum oxide, titanium dioxide and silicon dioxide.

[0021] Compared with the prior art, the positive electrode material provided by the present invention is not easily affected by moisture in the air because of its shell structure on the surface.

[0022] Preferably, the mass ratio of the shell structure to the positive electrode material is 1:(100-1000) (eg, 1:100, 1:300, 1:500, 1:700, 1:900 or 1:1000).

[0023] Preferably, the particle size of the positive electrode material is 0.1 to 5 μm (eg, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm).

[0024] Preferably, the shell has a thickness of 5 to 50 nm (eg, 5 nm, 10 nm, 15 nm, 25 nm, 30 nm, 35 nm, 45 nm, or 50 nm).

[0025] Preferably, the Prussian blue material comprises A x M y M' 1-y [Fe(CN)6] 1-z nH2O, wherein A includes Na and / or K; M includes at least one of Fe, Co, Mn, Ni and Cu; M' includes at least one of Fe, Co, Mn, Ni and Cu; 0≤x≤2,0 <y≤1,0≤z<1,0<n<3.5。

[0026] According to another aspect of the present invention, the present invention also relates to a method for preparing a positive electrode material, comprising the following steps:

[0027] Under heating conditions, the Prussian blue raw material and the alcohol solution of the coating agent are mixed in a non-aqueous liquid medium.

[0028] The method for preparing the positive electrode material provided by the present invention can obtain the positive electrode material through simple operation steps, and the prepared positive electrode material has excellent quality and low hygroscopicity.

[0029] Fe(CN)6 and (M y M' 1-y )N6 octahedra are connected by C≡N to form a three-dimensional framework structure. The alkali metal ions A and water molecules in the interstitial positions are located in the three-dimensional channels of the framework structure. The ion content of A, the defect concentration of Fe(CN)6, and the presence of water molecules in the interstitial and defect positions (collectively referred to as crystal water) in the structure will affect the crystal symmetry of the Prussian blue raw material. The structure is usually cubic, monoclinic or rhombohedral.

[0030] The Prussian blue raw material prepared using the aqueous solution co-precipitation method contains approximately 2 moles of interstitial water (n=2) per mole, as well as a small amount of coordinated water at defect sites (the higher the concentration of A, the higher the specific capacity of the material and the smaller the defect z). Approximately 10% of the crystalline water can be removed during high-temperature drying (>100°C), resulting in a monoclinic crystal structure. The crystalline water of the monoclinic Prussian blue raw material must be completely removed before filling the battery cell. Any remaining crystalline water will enter the electrolyte during charging along with the release of alkali metal ions, causing capacity decay and increased gas production.

[0031] The coating agent of the present invention undergoes a hydrolysis reaction with the crystal water released from the Prussian blue raw material in a non-aqueous liquid medium, forming a dense oxide shell structure on the surface of the Prussian blue raw material. The oxide shell structure effectively prevents the Prussian blue material from absorbing water vapor from the air, thereby reducing the hygroscopicity of the Prussian blue material.

[0032] The non-aqueous liquid phase medium in the present invention serves as a heating medium, isolating moisture from the air and heating the Prussian blue raw material dispersed therein to a temperature at which water of crystallization is released. The released water of crystallization reacts with the added coating agent on the surface of the Prussian blue material to form a corresponding oxide shell structure. Excess unreacted water of crystallization is converted into steam and evaporates. The oxide shell structure on the surface of the rhombohedral Prussian blue material, from which water of crystallization has been removed, effectively prevents the absorption of water vapor from the air, thereby reducing the hygroscopicity of the Prussian blue material.

[0033] Preferably, the Lushi blue raw material comprises A x M y M' 1-y [Fe(CN)6] 1-z nH2O, wherein A includes Na and / or K; M includes at least one of Fe, Co, Mn, Ni and Cu; M' includes at least one of Fe, Co, Mn, Ni and Cu; 0≤x≤2,0 <y≤1,0≤z<1,0<n≤3.5。

[0034] Preferably, the method for preparing the Prussian blue raw material comprises the following steps:

[0035] The Prussian blue complex and the transition metal salt are mixed and reacted to obtain the Prussian blue material.

[0036] Preferably, the Prussian blue complex comprises at least one of potassium ferrocyanide and sodium ferrocyanide.

[0037] Preferably, the Prussian blue complex is a Prussian blue complex solution.

[0038] Preferably, the concentration of the Prussian blue complex solution is 0.1-0.6 M (eg, 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M or 0.6 M).

[0039] Preferably, the transition metal salt includes at least one of Fe, Co, Mn, Ni and Cu.

[0040] Preferably, the transition metal salt includes at least one of chloride, sulfate, nitrate and acetate.

[0041] Preferably, the temperature of the mixing reaction is 30 to 100° C., and the mixing reaction time is 4 to 72 hours. The mixing reaction temperature may be, but is not limited to, 30° C., 40° C., 45° C., 50° C., 60° C., 70° C., 80° C., 85° C., 90° C., or 100° C.; and the mixing reaction time may be, but is not limited to, 4 hours, 12 hours, 20 hours, 28 hours, 36 hours, 44 hours, 52 hours, 60 hours, 68 hours, or 72 hours.

[0042] Preferably, the method for preparing the Prussian blue raw material further comprises a first solid-liquid separation, water washing, a first drying and pulverizing.

[0043] Preferably, the coating agent includes at least one of aluminum isopropoxide, titanium isopropoxide, titanium tetrachloride, tetra-n-butyl titanate and tetraethoxysilane.

[0044] Aluminum isopropoxide (Al{OCH(CH3)2}3), a white crystal, block, or powder, is highly hygroscopic and decomposes in water to form aluminum hydroxide, a tetramer at room temperature. It is produced by the reaction of metallic aluminum with isopropanol, or aluminum trichloride with sodium isopropoxide, in the presence of a catalyst. It can be used as a reducing agent, a strong dehydrating agent, and is used in reducing compounds and organic synthesis. The shell structure obtained by hydrolysis is aluminum oxide.

[0045] Titanium isopropoxide (Ti{OCH(CH3)2}4) does not polymerize in non-polar solvents and is a tetrahedral diamagnetic molecule. It can be prepared by reacting titanium tetrachloride with isopropanol. The shell structure obtained by hydrolysis is titanium dioxide.

[0046] Titanium tetrachloride (TiCl4) has a tetrahedral structure, each Ti 4+ With four ligands Cl - Ti and the noble gas argon have the same number of electrons, resulting in a closed-shell structure. Therefore, the titanium tetrachloride molecule is a regular tetrahedron with a high degree of symmetry. The shell structure obtained by hydrolysis is titanium dioxide.

[0047] Tetrabutyl titanate (C 16 H 36 O4Ti), condensation catalyst, cross-linking agent. The shell structure obtained by hydrolysis is titanium dioxide.

[0048] Tetraethoxysilane (Si(OC2H5)4) is a colorless liquid that is slightly soluble in water. It hydrolyzes slowly in pure water, but hydrolysis is accelerated in the presence of acids or bases. Furthermore, it reacts with boiling water to produce an electrolyte-free silica sol. The resulting shell structure upon hydrolysis is silicon dioxide.

[0049] Preferably, the non-aqueous liquid medium includes at least one of polyethylene glycol, mineral oil, silicone oil and high-temperature heat-conducting oil.

[0050] Preferably, the alcohol solution comprises at least one of ethanol and isopropanol.

[0051] Preferably, the mass ratio of the Prussian blue raw material to the coating agent is 100:(0.4-4) (eg, 100:0.4, 100:1, 100:2, 100:3 or 100:4).

[0052] Preferably, the mixing specifically includes: dispersing the Prussian blue raw material in the non-aqueous liquid medium to obtain a first dispersion system, and then dropwise adding the alcohol solution of the coating agent into the first dispersion system.

[0053] Preferably, the concentration of the alcohol solution of the coating agent is 0.1 to 0.7 mol / L (eg, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L or 0.7 mol / L).

[0054] Preferably, the heating temperature is 100-150°C (e.g., 100°C, 110°C, 120°C, 130°C, 140°C or 150°C), and the heating time is 2-12h (e.g., 2°C, 4°C, 6°C, 8°C, 10°C or 12°C).

[0055] The heating temperature can ensure that the crystal water in the Prussian blue material is well released. The released crystal water reacts with the added coating agent on the surface of the Prussian blue material to generate a shell structure. The shell structure layer on the surface of the Prussian blue material with the crystal water removed and in a rhombohedral crystal system can prevent the absorption of water vapor in the air, thereby reducing the hygroscopic performance of the Prussian blue material.

[0056] Preferably, the mixing is performed under protective gas conditions.

[0057] In one embodiment, the protective gas comprises nitrogen.

[0058] Preferably, the method for preparing the positive electrode material further comprises: performing solid-liquid separation on the mixture obtained after mixing, and drying the solid matter after the solid-liquid separation;

[0059] Preferably, the drying treatment temperature is 100-150°C (for example, 100°C, 110°C, 120°C, 130°C, 140°C or 150°C), and the drying treatment time is 12-48h (for example, 12h, 16h, 20h, 24h, 28h, 32h, 36h, 40h or 48h).

[0060] According to another aspect of the present invention, the present invention also relates to a positive electrode plate, comprising the positive electrode material.

[0061] Preferably, the positive electrode plate is mainly made of slurry and aluminum foil through a second drying process.

[0062] Preferably, the slurry mainly includes the following raw materials:

[0063] 85-95 parts of positive electrode material, 1-5 parts of conductive agent, and 2-6 parts of binder.

[0064] The positive electrode plate provided by the present invention is mainly made of slurry and aluminum foil. The slurry contains the positive electrode material. Compared with the existing technology, it has better moisture isolation ability and reduced moisture absorption performance, which meets the requirements of sodium ion batteries for positive electrode plates.

[0065] Among them, by weight, the positive electrode material can be, for example, but not limited to 85 parts, 87 parts, 89 parts, 91 parts, 93 parts or 95 parts; the conductive agent can be, for example, but not limited to 1 part, 2 parts, 3 parts, 4 parts or 5 parts; the binder can be, for example, but not limited to 2 parts, 3 parts, 4 parts, 5 parts or 6 parts.

[0066] Preferably, the viscosity of the slurry is 1500-10000 Pa·s (for example, 1500 Pa·s, 2500 Pa·s, 3500 Pa·s, 4500 Pa·s, 5500 Pa·s, 6500 Pa·s, 7500 Pa·s, 8500 Pa·s, 9500 Pa·s or 10000 Pa·s).

[0067] Preferably, the thickness of the aluminum foil is 10 to 45 μm (eg, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm).

[0068] Preferably, the thickness of the positive electrode sheet is 50 to 200 μm (for example, 50 μm, 70 μm, 90 μm, 110 μm, 130 μm, 150 μm, 170 μm, 190 μm or 200 μm).

[0069] Preferably, the density of the aluminum foil surface coated with the slurry is 10 to 50 mg / cm 2 (e.g. 10 mg / cm 2 , 20mg / cm2 , 25mg / cm 2 、30mg / cm 2 , 40mg / cm 2 , 45mg / cm 2 or 50 mg / cm 2 ).

[0070] Preferably, the vacuum degree of the second drying is less than or equal to 133 Pa (eg, 133 MPa, 130 MPa, 127 MPa or 120 MPa).

[0071] Preferably, the second drying temperature is 120-150°C (e.g., 120°C, 125°C, 130°C, 140°C, 145°C or 150°C), and the second drying time is 10-72h (e.g., 10h, 20h, 30h, 40h, 50h, 60h, 70h or 72h).

[0072] According to another aspect of the present invention, the present invention also relates to a sodium ion battery, comprising the above-mentioned positive electrode plate.

[0073] The sodium ion battery provided by the present invention has a high cycle retention rate and low gas production.

[0074] Preferably, the sodium ion battery further includes a negative electrode plate.

[0075] Preferably, the negative electrode plate is mainly made of a slurry made of hard carbon, conductive carbon and a binder, which is coated on the surface of an aluminum foil and then dried for a third time.

[0076] Preferably, the mass ratio of the hard carbon, the conductive carbon and the binder is (90-95):(5-8):(5-8).

[0077] Preferably, the third drying has a vacuum degree of ≤-0.095 MPa, a temperature of 80-120° C., and a time of 10-72 h.

[0078] The present invention will be further explained below with reference to specific embodiments and comparative examples.

[0079] Example 1

[0080] The method for preparing the positive electrode material of this embodiment includes the following steps:

[0081] 1. Disperse 100 parts of Prussian blue raw material (Na2Fe[Fe(CN)6]·H2O) in 100 parts of polyethylene glycol and heat to 130°C;

[0082] 2. Add 0.4 parts of aluminum isopropoxide dropwise under nitrogen protection, stir and age for 10 hours;

[0083] 3. Then filter, dry and vacuum pack to obtain the positive electrode material.

[0084] Example 2

[0085] The method for preparing the positive electrode material of this embodiment includes the following steps:

[0086] 1. Disperse 100 parts of Prussian blue raw material (KCu[Fe(CN)6]·2H2O) in 100 parts of mineral oil and heat to 120°C;

[0087] 2. Add 2 parts of titanium isopropoxide dropwise under nitrogen protection and stir and age for 8 hours;

[0088] 3. Then filter, dry and vacuum pack to obtain the positive electrode material.

[0089] Example 3

[0090] The method for preparing the positive electrode material of this embodiment includes the following steps:

[0091] 1. Disperse 100 parts of Prussian blue raw material (NaMn[Fe(CN)6]·3H2O) in 100 parts of silicone oil and heat to 100°C;

[0092] 2. Add 3 parts of titanium tetrachloride dropwise under nitrogen protection, stir and age for 12 hours;

[0093] 3. Then filter, dry and vacuum pack to obtain the positive electrode material.

[0094] Example 4

[0095] The method for preparing the positive electrode material of this embodiment includes the following steps:

[0096] 1. Disperse 100 parts of Prussian blue raw material (Ni[Fe(CN)6]·H2O) in 100 parts of high-temperature heat transfer oil at a heating temperature of 150°C;

[0097] 2. Add 4 parts of tetraethoxysilane dropwise under nitrogen protection, stir and age for 2 hours;

[0098] 3. Then filter, dry and vacuum pack to obtain the positive electrode material.

[0099] Example 5

[0100] The method for preparing the positive electrode sheet of this embodiment includes the following steps:

[0101] 1. Mix 90 parts of the positive electrode material of Example 1, 3 parts of conductive carbon, and 5 parts of a binder to form a slurry, stir for 25 hours, and apply the slurry on the surface of a 30 μm thick aluminum foil;

[0102] 2. Dry the plate in a vacuum oven for 55 hours at a vacuum degree of 133 MPa and a temperature of 130°C.

[0103] 3. Rolling the sheet on a roller press to obtain the positive electrode sheet.

[0104] Example 6

[0105] The method for preparing the positive electrode sheet of this embodiment includes the following steps:

[0106] 1. Mix 98 parts of the positive electrode material of Example 1, 2 parts of conductive carbon, and 4 parts of a binder to form a slurry, stir for 15 hours, and apply the slurry on the surface of a 25 μm thick aluminum foil;

[0107] 2. Dry the plate in a vacuum oven for 48 hours at a vacuum degree of 130 MPa and a temperature of 125°C.

[0108] 3. Rolling the sheet on a roller press to obtain the positive electrode sheet.

[0109] Example 7

[0110] The method for preparing the positive electrode sheet of this embodiment includes the following steps:

[0111] 1. Mix 85 parts of the positive electrode material of Example 1, 1 part of conductive carbon, and 6 parts of a binder to form a slurry, stir for 20 hours, and apply the slurry on the surface of a 45 μm thick aluminum foil;

[0112] 2. Dry the plate in a vacuum oven for 72 hours at a vacuum degree of 125 MPa and a temperature of 150°C;

[0113] 3. Rolling the sheet on a roller press to obtain the positive electrode sheet.

[0114] Example 8

[0115] The method for preparing the positive electrode sheet of this embodiment includes the following steps:

[0116] 1. Mix 95 parts of the positive electrode material of Example 1, 5 parts of conductive carbon, and 2 parts of a binder to form a slurry, stir for 5 hours, and apply the slurry on the surface of a 10 μm thick aluminum foil;

[0117] 2. Dry the plate in a vacuum oven for 10 hours at a vacuum degree of 120 MPa and a temperature of 120°C.

[0118] 3. Rolling the sheet on a roller press to obtain the positive electrode sheet.

[0119] Example 9

[0120] The method for preparing the sodium ion battery of this embodiment comprises the following steps:

[0121] 1. Prepare a slurry of 90 parts hard carbon, 5 parts conductive carbon C45, 3 parts carboxymethyl cellulose (CMC), and 2 parts styrene-butadiene rubber (SBR). Apply the resulting slurry to a 30 μm thick aluminum foil.

[0122] 2. Dry in a vacuum oven at -0.095 MPa for 72 hours at 80°C to obtain the negative electrode sheet;

[0123] 3. The positive electrode sheet, negative electrode sheet and polyethylene separator of Example 5 are stacked in a dry environment (dew point ≤ -40°C) to form a soft-pack battery, and then liquid is injected, formed, and capacity is divided.

[0124] Example 10

[0125] The method for preparing the sodium ion battery of this embodiment comprises the following steps:

[0126] 1. Prepare a slurry of 95 parts hard carbon, 8 parts conductive carbon C45, 4 parts carboxymethyl cellulose (CMC), and 4 parts styrene-butadiene rubber (SBR). Apply the resulting slurry to a 30 μm thick aluminum foil.

[0127] 2. Dry in a vacuum oven at -0.095 MPa for 10 h at 120°C to obtain the negative electrode sheet;

[0128] 3. The positive electrode sheet, negative electrode sheet and polypropylene separator of Example 5 were stacked in a dry environment (dew point ≤ -40°C) to form a soft pack battery, and then liquid was injected, formed and capacity was divided.

[0129] Comparative Example 1

[0130] The only difference between this comparative example and Example 1 is that no coating agent is used.

[0131] Comparative Example 2

[0132] The sodium ion battery of this comparative example adopts the positive electrode material of Example 1. The difference between the preparation method of the positive electrode material and that of the example is that the heating temperature is different, and the heating temperature is 80°C; the positive electrode sheet is prepared according to the method of Example 5; and the sodium ion battery is prepared according to the method of Example 9.

[0133] Experimental example

[0134] Two groups of positive electrode materials prepared from Examples 1-4 and Comparative Examples 1-2 were collected. The first group was removed from the sample in a dry environment and tested for moisture content. The second group was exposed to air (temperature 20°C, humidity 40%) for 1 hour, tested for moisture content, and then dried and sampled again in a dry environment. Moisture content was measured using a Karl-Fischer titrator with a cutoff temperature of 200°C. The results of the moisture content tests are shown in Table 1.

[0135] The positive electrode materials from Examples 1-4 and Comparative Examples 1-2 were fabricated into positive electrode sheets according to Example 5. The resulting positive electrode sheets were then fabricated into sodium-ion batteries according to Example 9, and the sodium-ion battery from Comparative Example 2 was tested. The electrolyte consisted of 1.0 M NaPF₆ dissolved in ethylene carbonate (EC) and diethyl carbonate (DEC), with a mass ratio of EC to DEC of 1:3. The battery cycling performance test results are shown in Table 1.

[0136] Table 1 Water content of positive electrode and battery cycle performance test

[0137]

[0138]

[0139] It can be seen from the test results of the experimental examples of the present invention that the water content of the positive electrode sheet provided by the present invention is significantly reduced, indicating that the shell structure on the surface of the positive electrode material reduces the moisture absorption capacity of the Prussian blue material after drying. The positive electrode material prepared by the present invention is used to prepare sodium ion batteries, which can make the battery have better cycle stability and significantly reduce gas production.

[0140] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode material, characterized in that The positive electrode material is a core-shell structure, the core of the core-shell structure is a Prussian blue material with a rhombohedral crystal system, and the shell of the core-shell structure includes at least one of aluminum oxide and titanium dioxide; The method for preparing the positive electrode material comprises the following steps: Under heating conditions, a Prussian blue raw material and an alcohol solution of a coating agent are mixed in a non-aqueous liquid medium; performing solid-liquid separation on the mixture obtained after mixing, and drying the solid matter after the solid-liquid separation; The coating agent includes at least one of aluminum isopropoxide, titanium isopropoxide, titanium tetrachloride, and tetra-n-butyl titanate; The non-aqueous liquid phase medium includes at least one of polyethylene glycol, mineral oil, silicone oil and high-temperature heat transfer oil; The mass ratio of the Prussian blue raw material to the coating agent is 100: (0.4~4); The heating temperature is 100-140° C., and the heating time is 2-12 hours; The mixing is carried out under protective gas conditions; The Prussian blue raw material includes A x M y M' 1-y [Fe(CN)6] 1-z nH2O, wherein A includes Na and / or K; M includes at least one of Fe, Co, Mn, Ni and Cu; M' includes at least one of Fe, Co, Mn, Ni and Cu; 0≤x≤2,0 <y≤1,0≤z<1,0<n≤3.5; The shell of the core-shell structure is a dense oxide shell structure.

2. The positive electrode material according to claim 1, characterized in that The mass ratio of the shell structure to the positive electrode material is 1:(100-1000); The particle size of the positive electrode material is 0.1~5μm; The shell has a thickness of 5 to 50 nm.

3. The positive electrode material according to claim 1, characterized in that The alcohol solution includes at least one of ethanol and isopropanol.

4. The positive electrode material according to claim 1, characterized in that The mixing specifically includes: dispersing the Prussian blue raw material in the non-aqueous liquid medium to obtain a first dispersion system, and then dropwise adding the alcohol solution of the coating agent into the first dispersion system.

5. The positive electrode material according to claim 1, characterized in that The concentration of the alcohol solution of the coating agent is 0.1-0.7 mol / L.

6. The positive electrode material according to claim 1, characterized in that The drying temperature is 100-150° C., and the drying time is 12-48 hours.

7. A positive electrode plate, characterized in that: The positive electrode material comprises the positive electrode material according to any one of claims 1 to 6.

8. A sodium ion battery, characterized in that: Including the positive electrode sheet according to claim 7.

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