Positive electrode material and preparation method therefor and use thereof

Abstract

Provided are a positive electrode material and a preparation method therefor and a use thereof. The positive electrode material comprises a matrix, and a first carbon layer and a superionic conductor layer which are sequentially coated on the surface of the matrix. The matrix is made of Na4Fe2.9-yM y(PO4)2(P2O7), wherein 0<y≤0.2, and M is selected from at least one of Ag, Cu or Nb. The superionic conductor layer is made of Na4MnV(PO4)3. The positive electrode material has a molecular formula of (1-x)Na4Fe2.9-yMy(PO4) 2(P2O7)@C1@xNa4MnV(PO4)3, wherein 0<y≤0.2, and C1 represents the first carbon layer. The positive electrode material has high structural stability, and also has the characteristics of high average working voltage, high energy density, high discharge specific capacity, high cycle performance and high rate performance. In addition, the preparation method is simple and involves low costs.

Description

Cathode material, preparation method and application thereof

[0001] The present application claims priority to the Chinese patent application No. 202410645192.5, filed on May 23, 2024, and entitled "Cathode material, preparation method and application thereof", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of secondary batteries, in particular to a cathode material, a preparation method and application thereof. BACKGROUND

[0003] Currently, iron-based polyanion compound Na4Fe3(PO4)2(P2O7) (simplified as NFPP) material is attracting much attention due to its low cost, green environmental protection, and high theoretical capacity (129 mAhg -1 ). However, the actual average working voltage of the NFPP material is relatively low (~2.85 V vs. Na + / Na), which greatly affects the energy density, thereby limiting the application of the NFPP material in commerce. In order to solve the above problems, the traditional method commonly uses the method of crystal defect regulation to improve the average working voltage of the NFPP material. However, this method sacrifices part of the capacity of the NFPP material, and therefore the effect of improving the energy density is poor.

[0004] Meanwhile, the NFPP material has the problem of low intrinsic electronic and ionic conductivity. In order to solve this problem, the traditional method mostly adopts modification of the NFPP material, such as particle nanocrystallization, off-body phase doping, and compounding with commercial carbon nanotubes or graphene with excellent conductivity. However, when the NFPP material is compounded with carbon nanotubes or graphene or Ketjenblack with high conductivity, not only the preparation process is complex and the cost is high, but also the industrial production of the NFPP material is not conducive.

[0005] Therefore, there is an urgent need to develop a sodium-ion battery cathode material with high average working voltage, high energy density, high discharge specific capacity, high cycle performance, and high rate performance, and a simple preparation method and low cost. SUMMARY

[0006] Therefore, it is necessary to provide a cathode material, a preparation method and application thereof in view of the above problems. The cathode material not only has high structural stability, but also has the characteristics of high average working voltage, high energy density, high discharge specific capacity, high cycle performance, and high rate performance, and has a simple preparation method and low cost.

[0007] A cathode material, comprising:

[0008] a substrate, a material of the substrate is Na4Fe 2.9-y M y (PO4)2(P2O7), wherein, 0

[0009] a first carbon layer, the first carbon layer is coated on an outer surface of the substrate; and

[0010] a super ionic conductor layer, the super ionic conductor layer is coated on an outer surface of the first carbon layer, a material of the super ionic conductor layer is Na4MnV(PO4)3;

[0011] wherein, a molecular formula of the positive electrode material is (1-x)Na4Fe 2.9-y M y (PO4)2(P2O7)@C1@xNa4MnV(PO4)3, wherein, 0

[0012] The positive electrode material provided by the application has a molecular formula of Na4Fe 2.9-y M y (PO4)2(P2O7) as a substrate, the material has iron vacancies, and is doped with metal cations M to replace part of the iron sites, so that the first carbon layer can synergize with the doped metal cations M to improve the electronic conductivity and reversible discharge specific capacity of the positive electrode material; at the same time, under the driving of thermodynamic action, part of Mn 2+ , V 3+ in Na4MnV(PO4)3 also enters the iron vacancies of the material and cooperates with the doped metal cations M, so that the energy density of the positive electrode material can be improved while the stability and discharge specific capacity of the positive electrode material are improved.

[0013] Therefore, the positive electrode material has high structural stability, and has the characteristics of high average working voltage, high energy density, high discharge specific capacity, high cycle performance and high rate performance.

[0014] A preparation method of the positive electrode material, comprising:

[0015] mixing a sodium source, an iron source, an M source, a phosphorus source, a first carbon source and water to prepare a mixture, performing spray drying treatment on the mixture, and then sintering to obtain Na4Fe 2.9-y M ya M source selected from a compound containing at least one of Ag, Cu or Nb;

[0016] The super ionic conductor layer precursor material and the Na4Fe 2.9-y M y The super ionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder or Na4MnV(PO4)@C2 precursor powder, and C2 represents a second carbon layer.

[0017] The preparation method of the positive electrode material can further improve the compaction density and electrochemical performance of the positive electrode material, is simple to operate, has a short process flow, is conducive to reducing cost and improving production efficiency, and is easy to mass industrialize.

[0018] A positive electrode sheet prepared from the positive electrode material.

[0019] A sodium ion battery prepared from the positive electrode sheet. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0021] Fig. 1 is an X-ray diffraction (XRD) comparison diagram of the positive electrode material prepared in Example 1 and Comparative Example 3;

[0022] Fig. 2 is a grain transmission electron microscope (TEM) diagram of the positive electrode material prepared in Example 1, wherein (a) represents the TEM diagram of the grain interior, (b) represents the TEM enlarged diagram of part of the outer structure of the grain, and NFNPP in the diagram represents Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7), NFNPP represents Na4Fe

[0023] Fig. 3 is a grain transmission electron microscope (TEM) diagram of the positive electrode material prepared in Comparative Example 3, wherein NFNPP in the diagram represents Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7), C1 represents a first carbon layer;

[0024] Figure 4 is a graph of the first three cycle charge-discharge curves of a battery using the positive electrode material prepared in Example 1, at a current density of 5C, in a voltage range of 2V to 4.2V;

[0025] Figure 5 is a graph of the rate performance comparison of batteries using the positive electrode materials prepared in Example 1 and Comparative Example 3, at different current densities (1C = 129mAh / g), in a voltage range of 2V to 4.2V;

[0026] Figure 6 is a graph of the cycle performance comparison of batteries using the positive electrode materials prepared in Example 1 and Comparative Example 3, at a current density of 10C, in a voltage range of 2V to 4.2V. DETAILED DESCRIPTION

[0027] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0028] The positive electrode material provided by the present application comprises:

[0029] a substrate, the material of the substrate being Na4Fe 2.9-y M y (PO4)2(P2O7), wherein 0 < y ≤ 0.2, and M is selected from at least one of Ag, Cu or Nb;

[0030] a first carbon layer, the first carbon layer being coated on the outer surface of the substrate; and

[0031] a superionic conductor layer, the superionic conductor layer being coated on the outer surface of the first carbon layer, and the material of the superionic conductor layer being Na4MnV(PO4)3.

[0032] wherein the molecular formula of the positive electrode material is (1-x)Na4Fe 2.9-y M y (PO4)2(P2O7)@C1@xNa4MnV(PO4)3, wherein 0 < x ≤ 0.2, and C1 represents the first carbon layer.

[0033] In the present application, the molecular formula of the positive electrode material is Na4Fe 2.9-y M yThe material of (PO4)2(P2O7) as a matrix can reduce the generation of non-active NaFePO4 phase, reduce the loss of material capacity, and reduce the generation of other impurities such as Na2FeP2O7, improve the phase purity, and is beneficial to improve the reversible capacity of the positive electrode material. At the same time, by introducing a cation M to replace part of Fe sites, wherein M is selected from at least one of Ag, Cu or Nb, and controlling the doping amount parameter y of the cation M, the electronic conductivity of the positive electrode material can be improved, and the intercalation pseudo-capacitance contribution in the charging and discharging process of the positive electrode material does not affect the structure and phase purity of the material, thereby improving the reversible specific capacity and cycle stability of the positive electrode material.

[0034] At the same time, a first carbon layer is coated on the outer surface of the matrix, which can cooperate with the doped metal cation M in the material to improve the electronic conductivity and reversible discharge specific capacity of the positive electrode material.

[0035] Further, a superionic conductor layer is coated on the outer surface of the first carbon layer, and the material of the superionic conductor layer is Na4MnV(PO4)3. Under the driving of thermodynamics, part of Mn 2+ , V 3+ in Na4MnV(PO4)3 will enter the bulk phase of the matrix, that is, the iron vacancy, and cooperate with the doped metal cation M, which can improve the energy density of the positive electrode material while improving the stability of the positive electrode material.

[0036] In addition, the Na4MnV(PO4)3 has a sodium superionic conductor (NASICON) structure, so that the Na4MnV(PO4)3 material not only has a stable crystal structure, but also has high average working voltage and excellent rate performance, thereby effectively improving the energy density, discharge specific capacity and rate performance of the positive electrode material.

[0037] Therefore, the positive electrode material of the present application not only has high structural stability, but also has high average working voltage, high energy density, high discharge specific capacity, high cycle performance and high rate performance.

[0038] Optionally, the mass fraction of the first carbon layer in the positive electrode material is 1.2%-1.6%, and the thickness of the first carbon layer is 0.8nm-1.5nm. By controlling the content and thickness of the first carbon layer, the electronic conductivity of the positive electrode material can be better improved, the transmission path of sodium ions can be effectively avoided, and the compaction density of the positive electrode material can be further improved.

[0039] Optionally, the first carbon layer has reactive groups, which are connected to the superionic conductor layer by hydrogen bonds. This configuration allows the first carbon layer and the superionic conductor layer to be connected by hydrogen bonds, thereby increasing the bonding force between them. This ensures that the superionic conductor layer tightly coats the outer surface of the first carbon layer, resulting in a spherical shell-like structure for the cathode material. This effectively prevents the structure of the cathode material from being damaged during charging and discharging, thus avoiding rapid capacity decay.

[0040] Furthermore, the reactive groups are selected from hydroxyl and / or amino groups. This configuration not only allows for better hydrogen bonding with the phosphate groups in the Na4MnV(PO4)3 material, resulting in a better connection between the reactive groups and the superionic conductor layer, thus achieving hydrogen bonding between the first carbon layer and the superionic conductor layer and improving the bonding force between them, but also enables the reactive groups to form hydrogen bonds with the phosphate groups in the matrix material, achieving a tight connection between the first carbon layer and the matrix. This improves the interlayer bonding force, ensuring that the first carbon layer tightly coats the outer surface of the matrix, and the superionic conductor layer tightly coats the outer surface of the first carbon layer. Consequently, this enhances the structural stability of the cathode material and improves its discharge specific capacity and energy density.

[0041] Optionally, the thickness of the superionic conductor layer is 2nm-3nm. This setting, by controlling the thickness of the superionic conductor layer, can better avoid increasing the transport path of sodium ions and better avoid the formation of an unstable and unevenly thick cathode electrolyte interface layer between the Na4MnV(PO4)3 material and the electrolyte, thereby better improving the rate performance and energy density of the cathode material.

[0042] Optionally, the cathode material further includes a second carbon layer, which coats the outer surface of the superionic conductor layer. This configuration creates a barrier between the superionic conductor layer and the electrolyte, preventing manganese ions dissolved from the Na4MnV(PO4)3 structure from reacting with the electrolyte and simultaneously increasing the interfacial electronic conductivity of Na4MnV(PO4)3, thereby further improving the electronic conductivity of the cathode material.

[0043] Furthermore, the thickness of the second carbon layer is 0.1 nm to 0.2 nm. This configuration allows for more efficient sodium ion transport and provides better interfacial electron transport capabilities.

[0044] Optionally, the compaction density of the cathode material is 1.60 g / cm³. 3 -2.15g / cm 3 .

[0045] This application also provides a method for preparing a cathode material, comprising:

[0046] S1, mixing a sodium source, an iron source, an M source, a first carbon source, and water to prepare a mixture, spray-drying the mixture, and sintering to obtain a Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder, and the M source is selected from a compound containing at least one of Ag, Cu, or Nb;

[0047] S2, mixing the super-ionic conductor layer precursor material and the Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder, and then drying and sintering to obtain the positive electrode material, wherein the super-ionic conductor layer precursor material is selected from a Na4MnV(PO4)3 precursor powder or a Na4MnV(PO4)@C2 precursor powder, and C2 represents a second carbon layer.

[0048] In step S1, the mass fraction of the first carbon source in the mixture is 2.5%-3.5%. In this way, the first carbon coating layer can be better formed, the electronic conductivity of the positive electrode material is improved, and the compaction density of the positive electrode material is further improved.

[0049] Optionally, the first carbon source is at least one of a high-molecular polymer or a carbon material with a surface modified with a reactive group. The high-molecular polymer is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, or polyacrylonitrile.

[0050] The carbon material with the surface modified with the reactive group is obtained through surface treatment with a small-molecule organic compound, such as a chemical oxidation method, an acid treatment method, etc. The small-molecule organic compound is selected from at least one of glucose, sucrose, fructose, maltose, citric acid, tartaric acid, or ascorbic acid, and the reactive group is selected from a hydroxyl group and / or an amino group.

[0051] It should be noted that although the above small-molecule organic compounds themselves have a hydroxyl group and / or an amino group, the hydroxyl group and / or the amino group will be removed after sintering, so that the first carbon layer formed basically does not contain the hydroxyl group and / or the amino group.

[0052] When the first carbon layer C1 has the reactive group, the structural stability of the positive electrode material can be improved. Therefore, to make the first carbon layer C1 have the reactive group, the surface treatment method, such as a plasma treatment method, a chemical oxidation method, an acid treatment method, etc., can be used to treat the Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder.

[0053] In order to simplify the preparation steps, small-molecule organic substances such as glucose, sucrose, fructose, maltose, citric acid, tartaric acid or ascorbic acid can be surface treated in the present application. For example, tartaric acid and ethylenediaminetetraacetic acid are heat treated in anhydrous ethanol to obtain carbon materials surface modified with hydroxyl and / or amino groups. Thus, the carbon material surface modified with reactive groups as the first carbon source can make the prepared first carbon layer directly have reactive groups.

[0054] In view of the coating effect of the first carbon layer, the first carbon source in the present application is more preferably a combination of a high molecular polymer and a carbon material surface modified with reactive groups, and the mass ratio of the high molecular polymer and the carbon material surface modified with reactive groups is preferably 1:1-1:3, and further preferably 1:2. In this way, the high molecular polymer can form a continuous carbon coating layer at high temperature, and the carbon material surface modified with reactive groups can fill the places not completely coated, so that under the synergistic cooperation of the two, a more uniform and continuous and complete first carbon layer can be formed on the outer surface of the substrate particles, and the first carbon layer has reactive groups.

[0055] Optionally, the M source is selected from at least one of niobium pentoxide, silver nitrate, copper nitrate, tetrabutyl titanate, chromium nitrate nonahydrate, manganese acetate tetrahydrate, ammonium metavanadate, tantalum oxide, aluminum nitrate nonahydrate, and zinc nitrate hexahydrate.

[0056] Optionally, the sodium source is selected from at least one of tetrasodium pyrophosphate decahydrate, anhydrous sodium acetate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium citrate dihydrogen, sodium carbonate, sodium bicarbonate, sodium tartrate, sodium tert-butoxide, sodium sulfate, and sodium ethoxide.

[0057] Optionally, the iron source is selected from at least one of iron nitrate nonahydrate, iron powder, iron acetate, ferrocene, iron phosphate, iron citrate, iron acetylacetone, iron oxalate, and iron oleate.

[0058] Optionally, the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, hypophosphorous acid, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0059] Optionally, the process parameters of the spray drying treatment include: an inlet temperature of 160-240°C, an outlet temperature of 88-105°C, and a peristaltic pump flow rate of 20-65 mL / min. The Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder.

[0060] Optionally, the sintering comprises: sintering at 150-230℃ for 1-5h under a protective atmosphere, then increasing the temperature at a rate of 1-5℃ / min to 400-460℃ and sintering for 5-14h. In this way, the crystallinity of the Na4Fe 2.9-y M y The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5. 2.9-y M y The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0061] In an embodiment, the sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5. 2.9-y M y The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0062] The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0063] The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5. 2.9-y M y The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0064] The sintering protective atmosphere can be an inert gas atmosphere or a mixture of inert gas and hydrogen, preferably a mixture of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, preferably 95:5.

[0065] In the present application, the superionic conductor layer precursor material can be prepared by a sol-gel method or a spray drying method, and the spray drying method is preferred.

[0066] Optionally, when the superionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder, the specific steps for preparing the Na4MnV(PO4)3 precursor powder by using the spray drying method are as follows:

[0067] S21, mixing and preparing a mixture by mixing a sodium source, a manganese source, a vanadium source, a phosphorus source, and water;

[0068] S22, performing spray drying treatment on the mixture, and then performing sintering under a protective atmosphere to obtain the Na4MnV(PO4)3 precursor powder.

[0069] In step S21, the sodium source is selected from at least one of sodium acetate, disodium hydrogen phosphate, sodium dihydrogen phosphate, sodium dihydrogen citrate, sodium carbonate, sodium bicarbonate, sodium tartrate, sodium tert-butoxide, sodium sulfate, and sodium ethoxide; the manganese source is selected from at least one of manganese acetate tetrahydrate, manganese carbonate, manganese acetylacetonate, manganese oxalate dihydrate, manganese citrate, and manganese stearate; the vanadium source is selected from at least one of ammonium metavanadate, vanadium pentoxide, vanadium oxide, vanadium acetylacetonate, sodium metavanadate, and vanadyl acetylacetonate; and the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, hypophosphorous acid, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0070] In step S22, the process parameters of the spray drying treatment include: an inlet temperature of 170-210°C, an outlet temperature of 90-100°C, and a peristaltic pump flow rate of 20-40 mL / min. The mixture can be further formed to have a uniform particle size and a single phase, and the Na4MnV(PO4)3 precursor powder with a hollow sphere structure can be formed.

[0071] Optionally, the sintering includes: sintering at 150-230°C for 1-5 h, then increasing the temperature at a rate of 1-5°C / min to 400-460°C, and sintering for 5-14 h. In this way, the crystallization rate of the Na4MnV(PO4)3 can be controlled, the Na4MnV(PO4)3 crystals can be prevented from being formed, and the organic gas in the raw material can also be discharged.

[0072] In an embodiment, in step S22, the protective atmosphere can be selected from an inert gas atmosphere, or can be selected from a mixed atmosphere of inert gas and hydrogen, and is further preferably a mixed atmosphere of argon and hydrogen, wherein the volume ratio of argon to hydrogen is 90:10-98:2, and is preferably 95:5.

[0073] It should be noted that in the present application, when the super ionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder, the outer surface of the super ionic conductor layer in the prepared positive electrode material is not coated with a second carbon layer. In order to form a second carbon layer on the outer surface of the super ionic conductor layer, the positive electrode material obtained in step S2, i.e. (1-x)Na4Fe 2.9-y M y (PO4)2(P2O7)@C1@xNa4MnV(PO4)3 is subjected to carbonization treatment to obtain (1-x)Na4Fe 2.9-y M y (PO4)2(P2O7)@C1@xNa4MnV(PO4)3@C2.

[0074] In view of simplifying the steps and improving the coating effect of the second carbon layer on the super ionic conductor layer, it is preferred in the present application that the super ionic conductor layer precursor material is selected from Na4MnV(PO4)3@C2 precursor powder.

[0075] Alternatively, when the super ionic conductor layer precursor material is selected from Na4MnV(PO4)3@C2 precursor powder, the preparation method can refer to the preparation method of Na4MnV(PO4)3 precursor powder, wherein the mixture further comprises a second carbon source, and the mass fraction of the second carbon source in the mixture is 0.1%-1.0%. In this way, the second carbon layer can be better formed, and Na4MnV(PO4)3@C2 precursor powder is obtained, so as to further improve the electronic conductivity of the positive electrode material and improve the cycle stability and rate performance of the positive electrode material.

[0076] Alternatively, the second carbon source is selected from at least one of glucose, sucrose, citric acid, fructose, maltose, tartaric acid or ascorbic acid.

[0077] As can be seen, in the preparation method of the positive electrode material of the present application, the spray drying method is used to respectively prepare the super ionic conductor layer precursor material and Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder, and then the two are mixed and subjected to wet ball milling, and then sintering, so that the particle size of the positive electrode material is reduced, and then the specific surface area of the reaction is increased, which is not only beneficial to the infiltration of the electrolyte, but also can improve the reaction activity and charge transport of the positive electrode material, so as to further improve the compaction density and electrochemical performance of the positive electrode material, and at the same time, the operation is simple, the process flow is short, which is beneficial to reducing the cost and improving the production efficiency, and is easy to be large-scale industrialized.

[0078] In addition, the present application also provides a positive electrode sheet prepared by using the positive electrode material as described above.

[0079] In addition, the application also provides a sodium ion battery prepared by using the above positive electrode sheet.

[0080] Hereinafter, the positive electrode material, the preparation method and the application thereof will be further illustrated by the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the application, and should not be regarded as limiting the scope of the application. The specific conditions not specified in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained by market purchase.

[0081] Meanwhile, it should be pointed out that in the present application, the phase of the positive electrode material is analyzed and tested by X-ray diffraction, the micro-morphology of the positive electrode material is characterized by transmission electron microscopy, and the compaction density of the positive electrode material is tested by a compaction density tester under a pressure of 300 Mpa.

[0082] Example 1

[0083] Tartaric acid, anhydrous ethanol and ethylenediaminetetraacetic acid were magnetically stirred at room temperature for 10 min, and then placed in a magnetic stirrer at a temperature of 140℃ for 40 min to obtain a carbon material powder with rich hydroxyl and amino groups on the surface, i.e. a carbon material with reactive groups on the surface.

[0084] The Na4Fe 2.85 Nb 0.05 The mass fraction of the carbon material powder with rich hydroxyl and amino groups in the mixture was 1.0%, and the mass fraction of polyvinylpyrrolidone in the mixture was 2.0%. Then, the mixture was subjected to spray drying treatment, and the process parameters of the spray drying treatment included: an inlet temperature of 170℃, an outlet temperature of 94℃, and a peristaltic pump flow rate of 30 mL / min. Subsequently, sintering was carried out in an argon / hydrogen (volume ratio 95:5) filled tube furnace, wherein the first stage sintering temperature was 200℃, the sintering time was 3h, and then the temperature was increased to 450℃ at a rate of 2℃ / min and sintered for 6h, to obtain a Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder.

[0085] A mixture was prepared by mixing manganese acetate tetrahydrate, ammonium metavanadate, sodium acetate, ammonium dihydrogen phosphate, citric acid and deionized water in a mass ratio of Na4MnV(PO4)3, wherein the mass fraction of citric acid in the mixture was 0.5%, and then the mixture was subjected to spray drying treatment, wherein the process parameters of the spray drying treatment included an inlet temperature of 185°C, an outlet temperature of 96°C, and a peristaltic pump flow rate of 25 mL / min, followed by sintering treatment in an argon / hydrogen gas (volume ratio 95:5)-filled tube furnace, wherein the first-stage sintering temperature was 200°C, the sintering time was 3 h, and then the temperature was increased to 450°C at a rate of 2°C / min and sintered for 6 h, to obtain Na4MnV(PO4)3@C2 precursor powder with removed organic groups and a second carbon layer on the surface.

[0086] The above-obtained Na4Fe 2.85 Nb 0.05 The Na4MnV(PO4)3@C2 precursor powder and the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material was 1.38%.

[0087] As can be seen from FIG. 1, the positive electrode material simultaneously has the crystal structures of Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7) and Na4MnV(PO4)3, and the diffraction peak type is sharp, indicating that the positive electrode material has good crystallinity.

[0088] As can be seen from FIG. 2(a) and FIG. 2(b), the positive electrode material of the present embodiment has a core-shell structure, and the inside is Na4Fe 2.85 Nb 0.05The crystal structure is (PO4)2(P2O7), and the outer surface is uniformly coated with a first carbon layer, a superionic conductor layer Na4MnV(PO4)3 and a second carbon layer in sequence. The thickness of the first carbon layer C1 is about 1.10 nm, the thickness of the superionic conductor layer Na4MnV(PO4)3 is 2.30 nm, and the thickness of the second carbon layer C2 is about 0.12 nm.

[0089] As can be seen from Figures 4 to 6, the cathode material of this embodiment has high discharge specific capacity, high rate performance, and high cycle performance.

[0090] Meanwhile, the compaction density of the cathode material in this embodiment is 2.15 g / cm³. 3 .

[0091] In addition, upon testing, the Na4Fe in the cathode material of Example 1 was found to be... 2.85 Nb 0.05 The bulk phase of (PO4)2(P2O7) contains small amounts of Mn and V, indicating that under thermal driving force, some Mn and V in the Na4MnV(PO4)3 structure can enter Na4Fe. 2.85 Nb 0.05 In the bulk phase of (PO4)2(P2O7), it works synergistically with doped Nb to improve the average operating voltage, electronic conductivity and structural stability of the cathode material.

[0092] Example 2

[0093] The only difference between Example 2 and Example 1 is that ascorbic acid and concentrated nitric acid are reacted at 80°C for 2 hours, and ammonia gas is introduced during the reaction to obtain carbon material powder with abundant hydroxyl and amino groups on the surface, that is, carbon material with reactive groups modified on the surface.

[0094] With Na4Fe 2.8 Cu 0.1 Based on the stoichiometric ratio of (PO4)2(P2O7), ferric nitrate nonahydrate, copper nitrate, ammonium dihydrogen phosphate, tetrasodium pyrophosphate decahydrate, carbon material powder with abundant hydroxyl and amino groups on its surface, polyvinyl alcohol, and deionized water were mixed evenly to obtain a mixture. The mass fraction of the carbon material powder with abundant hydroxyl and amino groups in the mixture was 1%, and the mass fraction of polyvinyl alcohol in the mixture was 2%. All other conditions were kept the same, resulting in Na4Fe2O3 with organic groups removed and a first carbon layer coated on its surface. 2.8 Cu 0.1 (PO4)2(P2O7)@C1 precursor powder.

[0095] Na4MnV(PO4)3@C2 precursor powder was prepared using the method described in Example 1, and then Na4Fe 2.8 Cu0.1 The Na4Fe 2.8 Cu 0.1 The Na4Fe

[0096] The compacted density of the positive electrode material obtained in this example is 1.98 g / cm 3 The thickness of the first carbon layer C1 is about 1.21 nm, the thickness of the super ionic conductor layer Na4MnV(P04)3 is 2.89 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0097] Example 3

[0098] Example 3 is compared with Example 1, and the only difference is that the Na4Fe 2.7 Ag 0.2 The Na4Fe 2.7 Ag 0.2 The Na4Fe

[0099] The Na4MnV(P04)3@C2 precursor powder is prepared by the method of Example 1, and then the Na4Fe 2.7 Ag 0.2 The Na4Fe 2.7 Ag 0.2 The Na4Fe

[0100] The compacted density of the positive electrode material obtained in this example is 2.01 g / cm 3, the thickness of the first carbon layer C1 is about 1.02 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.32 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0101] Example 4

[0102] Example 4 differs from Example 1 only in that, based on the stoichiometric ratio of Na4MnV(PO4)3, manganese acetate tetrahydrate, ammonium metavanadate, sodium acetate, ammonium dihydrogen phosphate and deionized water are uniformly mixed to obtain a mixture, and then the mixture is subjected to spray drying treatment, and the rest of the conditions are the same, to obtain a Na4MnV(PO4)3 precursor powder from which organic groups are removed.

[0103] Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder is prepared by the method of Example 1, and then Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder and the Na4MnV(PO4)3 precursor powder are mixed in a mass ratio of 9:1, and the rest of the conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.32%.

[0104] The positive electrode material obtained in this example has a tap density of 2.14 g / cm 3 , the thickness of the first carbon layer C1 is about 1.15 nm, and the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.25 nm.

[0105] Example 5

[0106] Example 5 differs from Example 2 only in that, based on the stoichiometric ratio of Na4MnV(PO4)3, manganese acetate tetrahydrate, ammonium metavanadate, sodium acetate, ammonium dihydrogen phosphate and deionized water are uniformly mixed to obtain a mixture, and then the mixture is subjected to spray drying treatment, and the rest of the conditions are the same, to obtain a Na4MnV(PO4)3 precursor powder from which organic groups are removed.

[0107] Na4Fe 2.8 Cu 0.1 (PO4)2(P2O7)@C1 precursor powder is prepared by the method of Example 2, and then Na4Fe 2.8 Cu 0.1The Na4Fe (PO4) 2 (P2O7) @C1 precursor powder and the Na4MnV (PO4) 3 precursor powder are mixed in a mass ratio of 4:1, and the rest of the conditions are the same, to obtain the positive electrode material, that is, 0.8Na4Fe 2.8 Cu 0.1 The Na4Fe (PO4) 2 (P2O7) @C1@0.2Na4MnV (PO4) 3 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.36%.

[0108] The compaction density of the positive electrode material obtained in this example is 1.95g / cm 3 The thickness of the first carbon layer C1 is about 1.25nm, and the thickness of the super ionic conductor layer Na4MnV (PO4) 3 is 2.87nm.

[0109] Example 6

[0110] Example 6 is compared with Example 4, and the difference is only that the Na4Fe 2.85 Nb 0.05 The Na4Fe (PO4) 2 (P2O7) @C1 precursor powder and the Na4MnV (PO4) 3 precursor powder are mixed in a mass ratio of 4:1, and the rest of the conditions are the same, to obtain the positive electrode material, that is, 0.8Na4Fe 2.85 Nb 0.05 The Na4Fe (PO4) 2 (P2O7) @C1 precursor powder and the Na4MnV (PO4) 3 precursor powder are mixed in a mass ratio of 4:1, and the rest of the conditions are the same, to obtain the positive electrode material, that is, 0.8Na4Fe

[0111] The Na4MnV (PO4) 3 precursor powder is prepared by the method of Example 4, and then the Na4Fe 2.85 Nb 0.05 The Na4Fe (PO4) 2 (P2O7) @C1 precursor powder and the Na4MnV (PO4) 3 precursor powder are mixed in a mass ratio of 4:1, and the rest of the conditions are the same, to obtain the positive electrode material, that is, 0.8Na4Fe 2.85 Nb 0.05 The Na4Fe (PO4) 2 (P2O7) @C1@0.1Na4MnV (PO4) 3 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.25%.

[0112] The compaction density of the positive electrode material obtained in this example is 1.95g / cm 3 The thickness of the first carbon layer C1 is about 1.25nm, and the thickness of the super ionic conductor layer Na4MnV (PO4) 3 is 2.87nm.

[0113] Example 7

[0114] Example 7 differs from Example 1 only in that the carbon material powder with rich hydroxyl and amino groups on the surface is replaced by tartaric acid in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, and the rest of the conditions are the same, to obtain the positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.13%.

[0115] The tap density of the positive electrode material obtained in this example is 2.13 g / cm 3 The thickness of the first carbon layer C1 is about 1.00 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.28 nm, and the thickness of the second carbon layer C2 is about 0.13 nm.

[0116] Example 8

[0117] Example 8 differs from Example 1 only in that the carbon material powder with rich hydroxyl and amino groups on the surface is replaced by tartaric acid in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, and the rest of the conditions are the same, to obtain the positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.34%.

[0118] The tap density of the positive electrode material obtained in this example is 2.13 g / cm 3 The thickness of the first carbon layer C1 is about 1.00 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.28 nm, and the thickness of the second carbon layer C2 is about 0.13 nm.

[0119] Example 9

[0120] Example 9 differs from Example 1 only in that the carbon material powder with rich hydroxyl and amino groups on the surface is replaced by tartaric acid in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, and the rest of the conditions are the same, to obtain the positive electrode material, i.e., 0.9Na4Fe2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the first carbon layer is at a mass fraction of 2.05% in the positive electrode material.

[0121] The compacted density of the positive electrode material obtained in this example is 1.78 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.48 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.30 nm, and the thickness of the second carbon layer C2 is about 0.13 nm.

[0122] Example 10

[0123] Example 10 differs from Example 1 only in that, in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, the mass fraction of the carbon material powder with rich hydroxyl and amino groups in the mixture is 0.60%, the mass fraction of polyvinylpyrrolidone in the mixture is 1.20%, and the remaining conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the first carbon layer is at a mass fraction of 0.90% in the positive electrode material.

[0124] The compacted density of the positive electrode material obtained in this example is 2.08 g / cm3. 3 The thickness of the first carbon layer C1 is about 0.82 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.29 nm, and the thickness of the second carbon layer C2 is about 0.14 nm.

[0125] Example 11

[0126] Example 11 differs from Example 1 only in that, in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, the mass fraction of the carbon material powder with rich hydroxyl and amino groups in the mixture is 4%, the mass fraction of polyvinylpyrrolidone in the mixture is 1%, and the remaining conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the first carbon layer is at a mass fraction of 1.95% in the positive electrode material.

[0127] The tap density of the positive electrode material obtained in this example is 1.67 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.39 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.28 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0128] Example 12

[0129] Example 12 differs from Example 1 only in that in the step of preparing the Na4MnV(PO4)3@C2 precursor powder, the mass fraction of citric acid in the mixture is 2.00%, and the other conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.37%.

[0130] The tap density of the positive electrode material obtained in this example is 1.97 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.13 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.35 nm, and the thickness of the second carbon layer C2 is about 0.81 nm.

[0131] Example 13

[0132] Example 13 differs from Example 1 only in that in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, the process parameters of the spray drying treatment include: the inlet temperature is 165°C, the outlet temperature is 90°C, the peristaltic pump flow rate is 30 mL / min, and then sintering is carried out in an argon / hydrogen gas (volume ratio 95:5) filled tube furnace, wherein the first stage sintering temperature is 210°C, the sintering time is 2h, and then the temperature is increased to 450°C at a rate of 2°C / min and sintered for 8h, and the other conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.28%.

[0133] The tap density of the positive electrode material obtained in this example is 2.12 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.03 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.36 nm, and the thickness of the second carbon layer C2 is about 0.13 nm.

[0134] Example 14

[0135] Example 14 differs from Example 1 only in that in the step of preparing the Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder, followed by sintering in a tube furnace filled with argon / hydrogen gas (volume ratio 95:5) at a sintering temperature of 550 °C for 10 h, with all other conditions being the same, an anode material, namely, 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material was obtained, wherein the first carbon layer accounts for 1.40% of the mass fraction of the anode material.

[0136] The tap density of the anode material obtained in this example was 1.78 g / cm 3 The thickness of the first carbon layer C1 was about 1.21 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 was 2.32 nm, and the thickness of the second carbon layer C2 was about 0.12 nm.

[0137] Example 15

[0138] Example 15 differs from Example 1 only in that in the step of preparing the Na4MnV(PO4)3@C2 precursor powder, the process parameters of the spray drying treatment included an inlet temperature of 190 °C, an outlet temperature of 95 °C, and a peristaltic pump flow rate of 40 mL / min, followed by sintering in a tube furnace filled with argon / hydrogen gas (volume ratio 95:5) at a first-stage sintering temperature of 180 °C for 4 h, followed by a temperature increase at a rate of 2 °C / min to 470 °C and sintering at this temperature for 6 h, with all other conditions being the same, an anode material, namely, 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material was obtained, wherein the first carbon layer accounts for 1.32% of the mass fraction of the anode material.

[0139] The tap density of the anode material obtained in this example was 2.08 g / cm 3 The thickness of the first carbon layer C1 was about 1.15 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 was 2.37 nm, and the thickness of the second carbon layer C2 was about 0.16 nm.

[0140] Example 16

[0141] Example 16 is the same as Example 1 except that in the step of preparing the Na4MnV(PO4)3@C2 precursor powder, the sintering is then carried out in a tube furnace filled with argon / hydrogen gas (volume ratio 95:5), wherein the sintering temperature is 550°C and the sintering time is 10 h, and the rest of the conditions are the same, to obtain the positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.37%.

[0142] The tap density of the positive electrode material obtained in this example is 1.89 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.13 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.28 nm, and the thickness of the second carbon layer C2 is about 0.10 nm.

[0143] Example 17

[0144] Example 17 is the same as Example 1 except that the ball milling speed is 400 r / min and the ball milling time is 5 h to achieve the effect of secondary ball crushing and uniform mixing of the materials; then the mixture is placed in a forced air drying machine at 100°C for 10 h to obtain a dried mixed powder, and finally the sintering is carried out in a tube furnace filled with argon / hydrogen gas (volume ratio 95:5), wherein the sintering temperature is 600°C and the sintering time is 8 h, to obtain the positive electrode material, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.41%.

[0145] The tap density of the positive electrode material obtained in this example is 2.01 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.23 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.27 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0146] Comparative Example 1

[0147] Comparative Example 1 is the same as Example 1 except that the mixture of Na4Fe 2.95 Nb 0.05 (PO4)2(P2O7) is used as the reference, and the nine hydrated ferric nitrate, the niobium pentoxide, the ammonium dihydrogen phosphate, the tetrasodium pyrophosphate decahydrate, the carbon material powder with rich hydroxyl and amino groups on the surface, the polyvinylpyrrolidone, and the deionized water are uniformly mixed to obtain a mixture, and the rest of the conditions are the same, to obtain the positive electrode material, i.e., 0.9Na4Fe2.95 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the first carbon layer is 1.35% by mass fraction of the positive electrode material.

[0148] The positive electrode material obtained in this comparative example has a tap density of 2.11 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.06 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.29 nm, and the thickness of the second carbon layer C2 is about 0.12 nm.

[0149] Comparative Example 2

[0150] Comparative Example 2 is the same as Example 1 except that Na3V2(PO4)3 is used instead of Na4MnV(PO4)3 precursor powder, and the positive electrode material obtained is 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na3V2(PO4)3@C2 material, wherein the first carbon layer is 1.36% by mass fraction of the positive electrode material.

[0151] The positive electrode material obtained in this comparative example has a tap density of 2.09 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.07 nm, the thickness of the super ionic conductor layer Na3V2(PO4)3 is 2.26 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0152] Comparative Example 3

[0153] Comparative Example 3 is the same as Example 1 except that it does not contain Na4MnV(PO4)3@C2 precursor powder. That is, Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder is sintered in a tube furnace filled with argon / hydrogen gas (volume ratio 95:5) at a sintering temperature of 550°C for 10 hours to obtain a positive electrode material, namely, Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 material. Wherein the first carbon layer is 1.41% by mass fraction of the positive electrode material.

[0154] The positive electrode material obtained in this comparative example has a tap density of 1.92 g / cm3. 3 The thickness of the first carbon layer C1 is about 1.22 nm.

[0155] As can be seen from Figure 1, the positive electrode material obtained in this comparative example is only Na4Fe 2.85 Nb0.05 (PO4)2(P2O7) structure. As can be seen from Figure 3, Na4Fe 2.85 Nb 0.05 The outer surface of (PO4)2(P2O7) is only covered with a first carbon layer C1. As can be seen from Figures 5 and 6, compared with Example 1, the absence of a superionic conductor layer and a second carbon layer results in poorer cycle performance, rate performance, and lower energy density of the cathode material.

[0156] Comparative Example 4

[0157] Comparative Example 4 differs from Example 1 only in that it uses Na4Fe 2.9 Based on the stoichiometric ratio of (PO4)2(P2O7), ferric nitrate nonahydrate, ammonium dihydrogen phosphate, tetrasodium pyrophosphate decahydrate, carbon material powder with abundant hydroxyl and amino groups on its surface, polyvinylpyrrolidone, and deionized water were mixed evenly to obtain a mixture. All other conditions remained the same to obtain the positive electrode material, namely, 0.9Na4Fe. 2.9 The material is (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2, wherein the first carbon layer has a mass fraction of 1.33% in the cathode material.

[0158] The compaction density of the cathode material obtained in this comparative example is 2.12 g / cm³. 3 The thickness of the first carbon layer C1 is approximately 1.08 nm, the thickness of the superionic conductor layer Na4MnV(PO4)3 is 2.34 nm, and the thickness of the second carbon layer C2 is approximately 0.11 nm.

[0159] Comparative Example 5

[0160] Comparative Example 5 differs from Example 1 only in that it uses Na4Fe 2.85 Al 0.05 Based on the stoichiometric ratio of (PO4)2(P2O7), ferric nitrate nonahydrate, aluminum nitrate nonahydrate, ammonium dihydrogen phosphate, tetrasodium pyrophosphate decahydrate, carbon material powder with abundant hydroxyl and amino groups on its surface, polyvinylpyrrolidone, and deionized water were mixed evenly to obtain a mixture. All other conditions remained the same to obtain the positive electrode material, namely, 0.9Na4Fe. 2.85 Al 0.05 The material is (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2, wherein the first carbon layer has a mass fraction of 1.38% in the cathode material.

[0161] The compaction density of the cathode material obtained in this comparative example is 2.13 g / cm³. 3, the thickness of the first carbon layer C1 is about 1.12 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.25 nm, and the thickness of the second carbon layer C2 is about 0.10 nm.

[0162] Comparative Example 6

[0163] Comparative Example 6 differs from Example 1 only in that Na4Fe 1.9 Nb(PO4)2(P2O7) is used as the reference, nine hydrated ferric nitrate, niobium pentoxide, ammonium dihydrogen phosphate, ten hydrated tetrasodium pyrophosphate, carbon material powder with rich hydroxyl and amino groups on the surface, polyvinylpyrrolidone and deionized water are uniformly mixed to obtain a mixture, and the remaining conditions are the same, to obtain a positive electrode material, i.e., 0.9Na4Fe 1.9 Nb1(PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.36%.

[0164] The compaction density of the positive electrode material obtained in this comparative example is 2.01 g / cm 3 , the thickness of the first carbon layer C1 is about 1.08 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 2.34 nm, and the thickness of the second carbon layer C2 is about 0.12 nm.

[0165] Comparative Example 7

[0166] Comparative Example 7 differs from Example 1 only in that Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1 precursor powder and Na4MnV(PO4)3@C2 precursor powder are mixed in a mass ratio of 5:5 and placed in a ball mill pot, and the remaining conditions are the same, to obtain a positive electrode material, i.e., 0.5Na4Fe 2.6 Nb 0.3 (PO4)2(P2O7)@C1@0.5Na4MnV(PO4)3@C2 material, wherein the mass fraction of the first carbon layer in the positive electrode material is 1.40%.

[0167] The compaction density of the positive electrode material obtained in this comparative example is 1.71 g / cm 3 , the thickness of the first carbon layer C1 is about 1.21 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 is 5.34 nm, and the thickness of the second carbon layer C2 is about 0.11 nm.

[0168] Comparative Example 8

[0169] Comparative Example 8 differs from Example 1 only in that Na4Fe 2.85 Nb0.05 The Na4MnV(PO4)3@C2 precursor powder was mixed with the (PO4)2(P2O7)@C1 precursor powder in a mass ratio of 9:1, and then placed in a beaker, followed by adding anhydrous ethanol for ultrasonic treatment for 8 h. Then, the mixture was placed in a blast drying machine at 120 °C for 8 h to obtain a dry mixed powder. The rest of the conditions were the same, and the positive electrode material was obtained, i.e., 0.9Na4Fe 2.85 Nb 0.05 (PO4)2(P2O7)@C1@0.1Na4MnV(PO4)3@C2 material, wherein the first carbon layer accounts for 1.37% of the mass fraction of the positive electrode material.

[0170] The compaction density of the positive electrode material obtained in the comparative example was 1.72 g / cm 3 The thickness of the first carbon layer C1 was about 1.12 nm, the thickness of the super ionic conductor layer Na4MnV(PO4)3 was 2.33 nm, and the thickness of the second carbon layer C2 was about 0.12 nm.

[0171] Comparative Example 9

[0172] 3 mmol of citric acid, 6.1 mmol of sodium acetate, 2 mmol of manganese acetate, 1.9 mmol of iron nitrate nonahydrate, 0.1 mmol of ammonium metavanadate, and 6 mmol of ammonium dihydrogen phosphate were dissolved in 50 mL of deionized water, and stirred and mixed uniformly to form a mixed solution A. 0.192 g of graphene was dissolved in 50 mL of a deionized water solution, and after ultrasonic dispersion treatment at a power of 700 kW for 48 h, the mixture was uniformly mixed, and then slowly added to the mixed solution A, and further mixed uniformly to obtain a mixed solution B. The graphene was multi-layer graphene with a single-layer thickness of 0.5 nm-6 nm. The mixed solution B was stirred at 90 °C until the solution was evaporated to form a gel, and then placed in a blast drying oven at 120 °C for 12 h to obtain a precursor. The precursor was first ground into a powder, and then placed in a tube furnace filled with a protective atmosphere, and pre-sintered at a temperature increasing rate of 2 °C / min to 400 °C, and after holding for 6 h, the furnace was cooled to obtain a pre-sintered solid. The protective atmosphere was a mixed gas of argon and hydrogen, i.e., a mixed gas of argon and hydrogen, wherein the volume ratio of argon to hydrogen was 9:1. The pre-sintered solid was ground into a powder, and then placed in a tube furnace filled with a protective atmosphere, and sintered at a temperature increasing rate of 2 °C / min to 650 °C, and after holding for 12 h, the furnace was cooled, wherein the protective atmosphere was a mixed gas of argon and hydrogen, i.e., a mixed gas of argon and hydrogen, wherein the volume ratio of argon to hydrogen was 9:1, to obtain a positive electrode material, i.e., (Na3FeMn(PO4)P2O7) 0.95 / (Na4MnV(PO4)3) 0.05 @C.

[0173] The positive electrode materials prepared by using Examples 1 to 17 and Comparative Examples 1 to 9 are assembled into CR2032 type batteries as positive electrode sheets.

[0174] The method for assembling the CR2032 type battery is as follows: the positive electrode material is placed in a beater with acetylene black and polyvinylidene fluoride in a mass ratio of 80:10:10, then a nitrogen methyl pyrrolidone solvent is added and mixed uniformly to obtain a slurry, the slurry is uniformly coated on the surface of a carbon-coated aluminum foil and placed in a vacuum drying oven at 100°C for 10h. At the same time, sodium metal and glass fiber are used as the counter electrode and the separator respectively, and a propylene carbonate (PC) and fluoroethylene carbonate (FEC) (volume ratio 95:5) solution of 1molL -1 of NaClO4 is used as the electrolyte to assemble the CR2032 type battery.

[0175] Subsequently, the constant current charge-discharge test of the battery at 25°C is carried out on a new Wei multi-channel test system, the voltage window is 2.0V to 4.2V, different rate tests are carried out on each CR2032 type battery respectively, and the test results are shown in Tables 1 and 2.

[0176] Table 1

[0177] Table 2

[0178] The technical features of the above-described embodiments can be combined arbitrarily, and for the sake of brevity, all possible combinations of the technical features in the above-described embodiments are not described, however, as long as the combinations of the technical features do not contradict, they should be considered as the scope of the description.

[0179] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A positive electrode material, wherein, The positive electrode material comprises: a matrix of material Na4Fe 2.9-y M y (PO4)2(P2O7), wherein 0 < y < 0.2, M is selected from at least one of Ag, Cu or Nb; a first carbon layer, which is coated on the outer surface of the substrate; and a super ionic conductor layer, which is coated on the outer surface of the first carbon layer, and the material of the super ionic conductor layer is Na4MnV(PO4)3. The molecular formula of the positive electrode material is (1-x)Na4Fe 2.9-y M y PO4)2(P2O7)@C1@xNa4MnV(PO4)3, wherein 0 2. The positive electrode material of claim 1, wherein, The mass fraction of the first carbon layer in the positive electrode material is 1.2%-1.6%, and the thickness of the first carbon layer is 0.8 nm-1.5 nm.

3. The positive electrode material according to claim 1 or 2, wherein The first carbon layer has a reactive group, and a hydrogen bond is formed between the reactive group and the super ionic conductor layer.

4. The cathode material of claim 3, wherein, The reactive group is selected from hydroxyl and / or amino.

5. The cathode material according to any one of claims 1 to 4, wherein, The thickness of the super ionic conductor layer is 2 nm-3 nm.

6. The cathode material of any one of claims 1-5, wherein, The positive electrode material further comprises a second carbon layer, which is coated on the outer surface of the super ionic conductor layer, and the thickness of the second carbon layer is 0.1 nm-0.2 nm.

7. The cathode material of any one of claims 1-6, wherein, The compacted density of the positive electrode material is 1.60 g / cm 3 - 2.15 g / cm 3 .

8. A method of producing the positive electrode material as claimed in any one of claims 1 to 7, wherein, The preparation method comprises: A mixture is prepared by mixing a sodium source, an iron source, an M source, a phosphorus source, a first carbon source, and water, the mixture is subjected to a spray drying process, and then sintered to obtain a Na4Fe 2.9-y M y (PO4)2(P2O7)@C1 precursor powder, the M source is selected from a compound containing at least one of Ag, Cu, or Nb; The super ionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder or Na4MnV(PO4)@C2 precursor powder, and C2 represents a second carbon layer. 2.9-y M y The super ionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder or Na4MnV(PO4)@C2 precursor powder, and C2 represents a second carbon layer.

9. The method of producing a cathode material according to claim 8, wherein, In preparing Na4Fe 2.9-y M y In the step of preparing the (PO4)2(P2O7)@C1 precursor powder, at least one of the following conditions is met: (1) the mass fraction of the first carbon source in the mixture is 2.5%-3.5%; (2) the first carbon source comprises a high molecular polymer and a carbon material modified with a reactive group, and the mass ratio of the high molecular polymer to the carbon material modified with a reactive group is 1:1-1:3, the high molecular polymer is selected from at least one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene glycol, or polyacrylonitrile, and the reactive group in the carbon material modified with a reactive group is selected from hydroxyl and / or amino; (3) the M source is selected from at least one of niobium pentoxide, silver nitrate, copper nitrate, tetrabutyl titanate, chromium nitrate nonahydrate, manganese acetate tetrahydrate, ammonium metavanadate, tantalum oxide, aluminum nitrate nonahydrate, and zinc nitrate hexahydrate; (4) the process parameters of the spray drying treatment include: an inlet temperature of 160°C-240°C, an outlet temperature of 88°C-105°C, and a peristaltic pump flow rate of 20 mL / min-65 mL / min; (5) the sintering comprises: sintering at 150°C-230°C for 1 h-5 h under a protective atmosphere, then increasing the temperature at a rate of 1°C / min-5°C / min to 400°C-460°C, and sintering for 5 h-14 h.

10. The method of producing a positive electrode material according to claim 8 or 9, wherein In the step of preparing the positive electrode material, at least one of the following conditions is met: (1) the process parameters of the wet ball milling include: the ball milling medium is anhydrous ethanol, the ball milling rotation speed is 350 r / min-500 r / min, and the ball milling time is 5 h-20 h; (2) the drying temperature is 80°C-150°C, and the drying time is 3 h-12 h; (3) the sintering comprises: sintering at 500°C-600°C for 6 h-14 h under a protective atmosphere.

11. The method of producing a cathode material according to any one of claims 8 to 10, wherein, When the super ionic conductor layer precursor material is selected from Na4MnV(PO4)3 precursor powder, the preparation method of the super ionic conductor layer precursor material comprises: mixing a sodium source, a manganese source, a vanadium source, a phosphorus source, and water to prepare a mixture, performing spray drying treatment on the mixture, and then performing sintering under a protective atmosphere to obtain the super ionic conductor layer precursor material.

12. The method of producing a cathode material according to any one of claims 8 to 10, wherein, When the super ionic conductor layer precursor material is selected from Na4MnV(PO4)@C2 precursor powder, the preparation method of the super ionic conductor layer precursor material comprises the following steps: mixing a sodium source, a manganese source, a vanadium source, a phosphorus source, a second carbon source, and water to prepare a mixture, wherein the mass fraction of the second carbon source in the mixture is 0.1%-1.0%, and the second carbon source is at least one selected from glucose, sucrose, citric acid, fructose, maltose, tartaric acid, or ascorbic acid.

13. A positive electrode sheet prepared by using the positive electrode material according to any one of claims 1 to 7.

14. A sodium ion battery prepared by using the positive electrode sheet according to claim 13.

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