Fluoride cathode composite material for sodium-ion batteries and method of making the same

Abstract

The application discloses a fluoride positive electrode composite material for a sodium ion battery and a preparation method thereof. x M y F7, wherein, 0<=x<=2, y=2-x; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; the fluoride positive electrode material has a spinel structure, and comprises one or more of 2O phase, 2M phase, 3T phase and 4M phase crystal structures; N ions and M ions in the fluoride positive electrode material form octahedral configurations NF6 and MF6 with six F ions respectively, the NF6 and the MF6 are connected through a single fluorine ion, and a three-dimensional framework structure is formed.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery materials, in particular to a fluoride positive electrode composite material for a sodium ion battery and a preparation method thereof. BACKGROUND

[0002] The development of electrochemical energy storage technology and the modernization process of human society are closely related. Among all electrochemical energy storage technologies, secondary batteries have attracted great attention since their inception due to their high voltage, long service life, green environmental protection, and high energy density. As an outstanding representative of secondary battery technology, lithium ion batteries currently occupy almost all commercial markets. However, due to the shortage of lithium resources and the soaring price of lithium, the development of lithium ion batteries has encountered a bottleneck, and in the face of future large-scale energy storage application scenarios, lithium ion batteries will be powerless. Therefore, it is urgent to develop new energy storage technologies beyond lithium ion batteries.

[0003] Sodium, as an element in the same group as lithium, has similar chemical properties, ion intercalation and deintercalation mechanisms, and electrochemical potentials. Therefore, sodium ion batteries, as a supplement to lithium ion battery technology, have attracted increasing attention. Sodium is one of the most abundant elements on Earth, and its distribution is wide and easy to exploit, making sodium ion batteries promising in the future energy storage technology map. As the sodium storage end in secondary batteries, the positive electrode material directly determines the key properties of the battery such as voltage, capacity, and energy density. Therefore, finding excellent positive electrode material systems has always been the main goal of the development of secondary batteries. Currently, sodium ion battery positive electrode materials are mainly divided into three categories: transition metal layered oxides, polyanion oxides, and Prussian blue analogues. However, these three types of positive electrode material systems also face their own problems in practical work.

[0004] For commercial lithium ion batteries, layered oxides are the best positive electrode material. However, compared with lithium ions, sodium ions have higher oxidation-reduction potentials and larger radii, which makes sodium ion layered oxides exhibit lower average voltage and steeper voltage curve in the battery environment, resulting in insufficient battery energy density and limiting their widespread application in sodium ion battery systems. For polyanion oxides, due to the presence of polyanion groups, the voltage of the material will be improved according to the induction effect, but the larger molar mass will inevitably limit the improvement of battery energy density. Prussian blue analogues are prepared by low-temperature wet chemical methods, which often exist in the form of hydrates, causing irreversible reduction of the electrochemical properties of the battery during the cycling process.

[0005] Among the existing methods for improving the above-mentioned positive electrode materials, academic literature 1 "Highly Stable Fe 2+ / Ti 3+Na2TiFeF7, published in the academic literature 2, Polymorphism in Weberite Na2Fe2F7 and its Effects on Electrochemical Properties as a Na-Ion Cathode, published on April 25, 2023, discloses Na2Fe2F7; the materials of the two literatures, although improved in performance relative to layered oxide materials, are still not ideal in terms of average operating voltage and specific energy, and cannot better meet the application requirements of sodium-ion batteries.

[0006] Therefore, it is necessary to find new sodium-ion cathode materials with higher energy density and higher operating voltage beyond the existing material system. SUMMARY

[0007] The embodiments of the present application aim to provide a fluoride cathode composite material for sodium-ion batteries and a preparation method thereof. The fluoride cathode material in the fluoride cathode composite material of the present application has a magnesioice structure and includes one or more of 2O phase, 2M phase, 3T phase, and 4M phase crystal structures. Compared with existing layered oxide cathode materials, the anions in the fluoride cathode material system are fluoride ions, and according to the induction effect, the voltage is much higher than that of oxides. Compared with layered oxide cathode materials, the sodium ions in the fluoride cathode composite material of the present application interact weakly with each other, and the voltage curve is relatively flat. The fluoride cathode composite material of the present application can output higher specific energy relative to layered oxide materials. Therefore, the application of the fluoride cathode composite material of the present application in sodium-ion batteries can improve the electrochemical performance of sodium-ion batteries.

[0008] To this end, in a first aspect, the embodiments of the present application provide a fluoride cathode composite material for sodium-ion batteries, which includes a fluoride cathode material and a carbon coating layer coated on the outer surface of the fluoride cathode material.

[0009] The chemical general formula of the fluoride cathode material is Na2N x M yF7, wherein, 0≤x≤2, y=2-x; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi;

[0010] The structure of the fluoride positive electrode material is a magnesia spinel structure, including one or more of 2O phase, 2M phase, 3T phase, 4M phase crystal structure;

[0011] The N ion and the M ion in the fluoride positive electrode material form an octahedral configuration NF6 and MF6 with six F ions respectively, and the NF6 and the MF6 are connected through a single fluorine ion to form a three-dimensional framework structure;

[0012] The mass percentage of the carbon coating layer in the fluoride positive electrode composite material is 0-10%.

[0013] Preferably, when the crystal structure of the fluoride positive electrode material is 2O phase, the space group is Imma;

[0014] When the crystal structure of the fluoride positive electrode material is 2M phase, the space group is C2 / c;

[0015] When the crystal structure of the fluoride positive electrode material is 3T phase, the space group is P3121;

[0016] When the crystal structure of the fluoride positive electrode material is 4M phase, the space group is C2 / c;

[0017] The mass percentage of the carbon coating layer in the fluoride positive electrode composite material is 0.5%-10%.

[0018] In a second aspect, the present application provides a preparation method of the fluoride positive electrode composite material for sodium ion batteries in the first aspect, and the method is a solid phase method, including:

[0019] The required stoichiometric sodium fluoride, N fluoride and M fluoride are placed in a ball mill, and after being uniformly mixed by ball milling under an argon atmosphere, a precursor powder is obtained;

[0020] The obtained precursor powder is placed in a crucible and placed in a high-temperature furnace for heat treatment under an argon atmosphere, and after cooling to room temperature, discharging and grinding, a fluoride positive electrode material is obtained;

[0021] The fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for sodium ion batteries;

[0022] N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi;

[0023] The rotation speed of the ball mill is 300 rpm-600 rpm, and the ball milling time is 10 hours-24 hours.

[0024] The heat treatment is specifically: heat treatment at 500℃-1000℃ for 30min-1 hour.

[0025] The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

[0026] In a third aspect, the application provides a preparation method of the fluoride positive electrode composite material for sodium ion batteries in the first aspect, which is a sol-gel method, comprising:

[0027] The required stoichiometric sodium fluoride, fluoride of N and fluoride of M are respectively dissolved in a solvent, and citric acid is added to form a precursor gel;

[0028] The precursor gel is placed in a crucible and placed in a high-temperature furnace for low-temperature pretreatment under an argon atmosphere to obtain a pretreated powder;

[0029] The pretreated powder is subjected to high-temperature heat treatment under an argon atmosphere, cooled to room temperature, discharged, ground, and then a fluoride positive electrode material is obtained;

[0030] The fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for sodium ion batteries;

[0031] N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi;

[0032] The solvent includes anhydrous ethanol or deionized water;

[0033] The low-temperature pretreatment is specifically: pre-burning at 250℃-500℃ for 2 hours-6 hours;

[0034] The high-temperature heat treatment is specifically: heat treatment at 800℃-1000℃ for 2 hours-24 hours;

[0035] The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

[0036] In a fourth aspect, the embodiments of the present application provide a preparation method of the fluoride positive electrode composite material for sodium ion batteries in the first aspect, the method is a spray drying method, and the method comprises the following steps:

[0037] uniformly mixing sodium fluoride, fluoride of N, and fluoride of M in a required stoichiometric amount to obtain a precursor;

[0038] adding the precursor into a solvent in a certain proportion and uniformly stirring to form a slurry;

[0039] placing the slurry in a spray dryer to perform spray drying, and obtaining a precursor powder;

[0040] placing the precursor powder into a crucible, placing the crucible in a high-temperature furnace, performing heat treatment under an argon atmosphere, cooling to room temperature, discharging, and grinding to obtain a fluoride positive electrode material;

[0041] performing carbon coating treatment on the fluoride positive electrode material to obtain the fluoride positive electrode composite material for sodium ion batteries;

[0042] wherein N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb and Bi; and M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb and Bi;

[0043] the uniform mixing method is grinding mixing or ball milling mixing;

[0044] the solvent comprises anhydrous ethanol or deionized water;

[0045] the heat treatment method specifically comprises heat treatment at 800-1000 DEG C for 2-24 hours;

[0046] the inlet temperature of the spray dryer is 150-190 DEG C, the outlet temperature is 70-100 DEG C, and the feeding speed is 200-600 mL / h;

[0047] the carbon coating treatment comprises any one of gas phase coating, liquid phase coating or solid phase coating.

[0048] In a fifth aspect, the embodiments of the present application provide a preparation method of the fluoride positive electrode composite material for sodium ion batteries in the first aspect, the preparation method is a co-precipitation method, and the method comprises the following steps:

[0049] dissolving fluoride of N and fluoride of M in a required stoichiometric amount in deionized water, and uniformly stirring to form a mixed solution;

[0050] The mixed solution of complexing agent ammonia and sodium hydroxide is used as a precipitant, and is brought into the reaction kettle by a peristaltic pump under a nitrogen atmosphere to react with the precipitant to generate a precipitate;

[0051] The precipitate is washed with deionized water at least three times, and is uniformly mixed with sodium fluoride according to a stoichiometric ratio after drying to obtain a precursor mixture;

[0052] The precursor mixture is placed in a crucible and is put into a high-temperature furnace for heat treatment under an argon atmosphere, and is discharged after cooling to room temperature and grinding to obtain a fluoride positive electrode material;

[0053] The fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for a sodium ion battery;

[0054] N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi; and M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi.

[0055] Preferably, the temperature of the circulating water bath of the reaction kettle is 50-80℃, and the rotation speed is 500-800rpm;

[0056] The pH value in the reaction kettle is controlled to be 9.0-11.5;

[0057] The feeding speed of the peristaltic pump is 100-300ml / h.

[0058] The molar ratio of ammonia to sodium hydroxide in the precipitant is [7:3]-[9:1];

[0059] The temperature of the heat treatment is 600-1000℃, and the heat treatment time is 12-24 hours;

[0060] The carbon coating treatment includes any one of gas-phase coating, liquid-phase coating, or solid-phase coating.

[0061] In a sixth aspect, the embodiments of the present application provide a positive electrode sheet of a sodium ion secondary battery, wherein the positive electrode sheet comprises the fluoride positive electrode composite material for a sodium ion battery according to the first aspect.

[0062] In a seventh aspect, the embodiments of the present application provide a sodium ion battery, wherein the sodium ion battery comprises the positive electrode sheet according to the sixth aspect.

[0063] In an eighth aspect, the embodiments of the present application provide a use of the sodium-ion battery of the seventh aspect, the sodium-ion battery being used for large-scale energy storage equipment of solar power generation, wind power generation, smart grid peak shaving, distributed power station or communication base station, or energy supply equipment of electric vehicles.

[0064] The fluoride positive electrode composite material provided by the embodiments of the present application contains a fluoride positive electrode material Na2N x M y F7 has a magnesium spinel structure, including one or more of 2O phase, 2M phase, 3T phase, 4M phase crystal structures, the N ions and the M ions in the fluoride positive electrode material form an octahedral configuration NF6 and MF6 with six F ions respectively, the NF6 and the MF6 are connected through a single fluorine ion, and a three-dimensional metal skeleton structure is formed, so that the material exhibits excellent structural stability, and the structure of the material does not change during the battery cycle process; in addition, compared with the existing layered oxide positive electrode material, the anion in the fluoride positive electrode material system is fluorine ion, and according to the induction effect, the voltage is much higher than that of the oxide, and compared with the layered oxide positive electrode material, the sodium ions in the fluoride positive electrode composite material of the present application interact weakly, and the voltage curve is relatively flat, the fluoride positive electrode composite material of the present application can output higher specific energy compared with the layered oxide material, therefore, the fluoride positive electrode composite material of the present application can improve the energy density and cycle stability of the sodium-ion battery when applied to the sodium-ion battery. BRIEF DESCRIPTION OF DRAWINGS

[0065] The technical solutions of the embodiments of the present application are described in detail below with reference to the drawings and examples.

[0066] Figure 1 is a flowchart of a solid-phase method for preparing the fluoride positive electrode composite material provided by the embodiments of the present application.

[0067] Figure 2 is a flowchart of a sol-gel method for preparing the fluoride positive electrode composite material provided by the embodiments of the present application.

[0068] Figure 3 is a flowchart of a spray drying method for preparing the fluoride positive electrode composite material provided by the embodiments of the present application.

[0069] Figure 4 is a flowchart of a co-precipitation method for preparing the fluoride positive electrode composite material provided by the embodiments of the present application.

[0070] Figure 5 is a schematic diagram of the crystal structure of the fluoride positive electrode composite material provided by the first embodiment.

[0071] Figure 6is the X-ray diffraction (XRD) pattern of the fluoride positive electrode composite provided in Example 1.

[0072] Figure 7 is the voltage-capacity curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 1.

[0073] Figure 8 is the sodium-ion migration energy barrier curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 1.

[0074] Figure 9 is the voltage-capacity curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 2.

[0075] Figure 10 is the sodium-ion migration energy curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 2.

[0076] Figure 11 is the voltage-capacity curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 3.

[0077] Figure 12 is the sodium-ion migration energy curve of the sodium-ion battery of the fluoride-containing positive electrode composite provided in Example 3. DETAILED DESCRIPTION

[0078] The application will be further described in the following with the aid of the accompanying drawings and specific embodiments, but it should be understood that these embodiments are only used for more detailed description and should not be understood as limiting the application in any form, i.e. not intended to limit the protection scope of the application.

[0079] The fluoride positive electrode composite for the sodium-ion battery provided by the embodiment of the application comprises: a fluoride positive electrode material, and a carbon coating layer coated on the outer surface of the fluoride positive electrode material; wherein the mass percentage of the carbon coating layer in the fluoride positive electrode composite is 0-10%, preferably 0.5%-10%.

[0080] The chemical general formula of the fluoride positive electrode material is Na2N x M y F7, wherein 0≤x≤2, y=2-x; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements;

[0081] The structure of the fluoride positive electrode material is a magnesium cryolite structure, including one or more of 2O phase, 2M phase, 3T phase and 4M phase crystal structures; specifically, when the crystal structure of the fluoride positive electrode material is the 2O phase, the space group is Imma; when the crystal structure is the 2M phase, the space group is C2 / c; when the crystal structure is the 3T phase, the space group is P3121; and when the crystal structure is the 4M phase, the space group is C2 / c.

[0082] The N ion and the M ion in the fluoride positive electrode material form an octahedral configuration NF6 and MF6 with six F ions, respectively, and the NF6 and the MF6 are connected by a single fluorine ion to form a three-dimensional framework structure. The present application provides four preparation methods for preparing the above-mentioned fluoride positive electrode composite material, including a solid phase method, a sol-gel method, a spray drying method or a co-precipitation method, and the processes of the four preparation methods for the fluoride positive electrode composite material will be described in detail below.

[0083] The first preparation method is a solid phase method, as shown in Figure 1 The specific steps include the following steps:

[0084] In step 110, the required stoichiometric amounts of sodium fluoride, fluoride of N and fluoride of M are placed in a ball mill, and after being uniformly mixed by ball milling under an argon atmosphere, a precursor powder is obtained.

[0085] Wherein, N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb and Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb and Bi elements.

[0086] The rotation speed of the ball mill is 300 rpm-600 rpm, and the ball milling time is 10 hours-24 hours.

[0087] In step 120, the obtained precursor powder is placed in a crucible and placed in a high-temperature furnace for heat treatment under an argon atmosphere, and after cooling to room temperature, the fluoride positive electrode material is obtained after discharging and grinding.

[0088] Wherein, the heat treatment is specifically: heat treatment at a temperature of 500-1000℃ for 30 minutes-1 hour.

[0089] In step 130, the fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for a sodium ion battery.

[0090] Wherein, the carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

[0091] The second preparation method is a sol-gel method, and a crystal material with high purity can be obtained by the sol-gel method, as shown in Figure 2As shown, specifically comprising the following steps:

[0092] Step 210, the required stoichiometric amount of sodium fluoride, fluoride of N, fluoride of M, respectively, is dissolved in a solvent, and citric acid is added to form a precursor gel;

[0093] Wherein, N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements;

[0094] The solvent includes anhydrous ethanol or deionized water.

[0095] Step 220, the precursor gel is placed in a crucible and placed in a high-temperature furnace for low-temperature pretreatment under an argon atmosphere to obtain a pretreated powder;

[0096] Wherein, the low-temperature pretreatment is specifically: pre-burning at 250-500℃ for 2-6 hours. Step 230, the pretreated powder is subjected to high-temperature heat treatment under an argon atmosphere, cooled to room temperature, discharged and ground to obtain a fluoride positive electrode material;

[0097] Wherein, the high-temperature heat treatment is specifically: heat treatment at 800-1000℃ for 2-24 hours.

[0098] Step 240, the fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for sodium ion batteries;

[0099] Wherein, the carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

[0100] The third preparation method is a spray drying method, as shown in Figure 3 As shown, specifically comprising the following steps:

[0101] Step 310, the required stoichiometric amount of sodium fluoride, fluoride of N, fluoride of M is mixed uniformly to obtain a precursor;

[0102] Wherein, N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements;

[0103] The method for mixing uniformly is grinding mixing or ball milling mixing.

[0104] Step 320, the precursor is added to a certain proportion of solvent and stirred uniformly to form a slurry;

[0105] The solvent includes anhydrous ethanol or deionized water.

[0106] In step 330, the slurry is placed in a spray dryer to perform spray drying, and a precursor powder is obtained.

[0107] Specifically, the inlet temperature of the spray dryer is 150-190°C, the outlet temperature is 70-100°C, and the feeding speed is 200-600 mL / h.

[0108] In step 340, the precursor powder is placed in a crucible and placed in a high-temperature furnace for heat treatment under an argon atmosphere. After cooling to room temperature, the fluorine anode material is obtained after grinding and discharging.

[0109] The heat treatment method is specifically as follows: heat treatment at 800-1000°C for 2-24 hours.

[0110] In step 350, the fluorine anode material is subjected to carbon coating treatment to obtain a fluorine anode composite material for a sodium ion battery.

[0111] The carbon coating treatment includes any one of gas phase coating, liquid phase coating, or solid phase coating.

[0112] The fourth preparation method is a co-precipitation method. The co-precipitation method can obtain a crystal material with uniform element distribution and no voids, such as Figure 4 as shown, specifically including the following steps:

[0113] In step 410, the required stoichiometric amount of fluoride of N and fluoride of M is dissolved in deionized water, and stirred uniformly to form a mixed solution.

[0114] N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi; and M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi.

[0115] In step 420, the mixed solution of the complexing agent ammonia and sodium hydroxide is used as a precipitant and placed in a reaction kettle. The mixed solution is brought into the reaction kettle by a peristaltic pump under a nitrogen atmosphere to react with the precipitant to generate a precipitate.

[0116] The temperature of the circulating water bath of the reaction kettle is 50-80°C, and the rotation speed is 500-800 rpm.

[0117] The pH value in the reaction kettle is controlled to be between 9.0 and 11.5.

[0118] The feeding speed of the peristaltic pump is 100-300 ml / h.

[0119] The molar ratio of ammonia water to sodium hydroxide in the precipitant is [7:3]-[9:1].

[0120] In step 430, the precipitate is washed with deionized water at least three times, and after drying, is uniformly mixed with sodium fluoride in a stoichiometric ratio to obtain a precursor mixture.

[0121] In step 440, the precursor mixture is placed in a crucible and put into a high-temperature furnace for heat treatment under an argon atmosphere, and after cooling to room temperature, is discharged and ground to obtain a fluoride positive electrode material.

[0122] The temperature of the heat treatment is between 600 DEG C and 1000 DEG C, and the heat treatment time is 12 hours-24 hours.

[0123] In step 450, the fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for a sodium ion battery.

[0124] The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

[0125] The three methods of gas phase coating, liquid phase coating or solid phase coating for carbon coating treatment of the fluoride positive electrode material in the above four preparation methods are conventional methods, and the purpose is to improve the conductivity of the material and reduce the side reaction of the material with the electrolyte during the charge and discharge cycle.

[0126] The above fluoride positive electrode composite material provided by the embodiments of the present application can be used as a positive active material or a sodium supplement additive of other positive active materials, is mixed with a conductive agent and a binder to prepare a slurry, and is coated on a positive current collector to prepare a positive electrode sheet, wherein the positive current collector includes but is not limited to an aluminum foil.

[0127] The above positive electrode sheet containing the fluoride positive electrode composite material for a sodium ion battery provided by the embodiments of the present application can be assembled into a sodium ion battery together with a separator, an electrolyte or a solid electrolyte, and a negative electrode sheet; the sodium ion battery is used for large-scale energy storage equipment of solar power generation, wind power generation, smart grid peak shaving, distributed power station or communication base station, or for energy supply equipment of electric vehicles.

[0128] The fluoride positive electrode composite material Na2N x M y F7 is applied to a sodium ion battery, and the fluoride positive electrode composite material Na2N x M y F7 can cycle two electrons, and after full charging, the chemical formula changes to N x M y F7 can cycle two electrons, and after full charging, the chemical formula changes to N xM y F7, assuming that the valence state of N is raised by a, and the valence state of M is raised by b, as long as the electrical neutrality of the compound is ensured, that is, x*a+y*b=2, for example, Na2V 2+ V 3+ F7→V 3+ V 4+ F7。

[0129] The fluoride positive electrode composite material Na2MnMoF7 provided by the embodiment of the application has the advantages of high capacity, high stability, and high safety. x M y F7 is applied to a sodium ion battery, because fluorine has the strongest electronegativity, the N-F and M-F bonds formed by the redox active metals N and M and fluorine ions have large bond energies, which specifically means that the compound skeleton is "inert" and the structure is more stable; in addition, sodium salts containing fluorine (for example, NaPF6) are often used in the electrolyte of a sodium battery, and the anion component of the fluoride material of the application is the same, so it can be predicted that, compared with oxide cathode materials, the fluoride material can largely avoid corrosion.

[0130] In order to better understand the technical solutions provided by the application, the following describes the preparation process and characteristics of the fluoride positive electrode composite material for a sodium ion battery provided by the application with multiple specific examples.

[0131] Embodiment 1

[0132] The embodiment provides a process for preparing a fluoride positive electrode composite material for a sodium ion battery by a solid phase method and performance testing, and the specific process is as follows:

[0133] (1) Place the required stoichiometric amounts of sodium fluoride (analytical pure), manganese fluoride (analytical pure), and molybdenum fluoride (analytical pure) in a ball mill, set the rotation speed of the ball mill to 600 rpm, and ball mill the mixture for 10 hours under an argon atmosphere. After uniform mixing, 200 g of a precursor powder is obtained.

[0134] (2) Put the obtained precursor powder into a crucible and place it in a high-temperature furnace for heat treatment. Under an argon atmosphere, heat to 800℃ and keep for 1 hour. After cooling to room temperature, discharge and grind to obtain a fluoride positive electrode material with a chemical formula of Na2MnMoF7.

[0135] (3) Perform carbon coating treatment on the obtained fluoride positive electrode material by gas phase coating. Specifically, place 200 g of the fluoride positive electrode material in a rotary furnace and heat to 800℃ under an argon atmosphere. Introduce argon and acetylene gas in a volume ratio of 2:1 for gas phase coating. After keeping for 90 min, turn off the gas source and cool to room temperature. After discharging and grading, a fluoride positive electrode composite material with a carbon coating layer is obtained.

[0136] The fluoride positive electrode material prepared in this embodiment contains 2O, 2M, 3T, and 4M crystal structures, and a schematic diagram of the crystal structure is shown in Figure 5 .

[0137] The XRD pattern of the fluoride positive electrode material prepared in this embodiment is shown in Figure 6 .

[0138] The fluoride positive electrode composite material prepared in this embodiment was used to prepare a positive electrode sheet, and a sodium ion battery was assembled and tested, the process being as follows:

[0139] Preparation of the positive electrode sheet: the fluoride positive electrode composite material of Example 1 was mixed with acetylene black and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 80:10:10, an appropriate amount of N-methyl pyrrolidone (NMP) solution was added, and the mixture was ground to form a slurry in a dry environment at room temperature. Then the slurry was uniformly coated on an aluminum current collector, and after drying by infrared lamp, it was cut into (8x8) mm 2 pieces, i.e. a positive electrode sheet. The positive electrode sheet was dried at 110°C for 10 hours under vacuum conditions, and then transferred to a glove box for standby.

[0140] Assembly of the sodium ion battery: the assembly of the full battery was carried out in an argon glove box. The above positive electrode sheet was used, hard carbon was used as the counter electrode, and a 1M NaClO4 / ethylene carbonate, dimethyl carbonate, propylene carbonate (EC:DMC:PC volume ratio of 1:1:1) + 2% fluoroethylene carbonate (FEC) solution was used as the electrolyte, and two CR2032 button full batteries were assembled.

[0141] Battery test: the specific method was as follows: using constant current charge and discharge mode, the charge and discharge test was carried out at a current density of C / 20 (1C=168mA / g), the discharge cut-off voltage was 1.5V, and the charge cut-off voltage was 4.5V. The voltage-capacity curve obtained by testing is shown in Figure 7 . It can be seen that the battery capacity is 168mAh / g, the average voltage reaches 3.53V, and the specific energy is 595Wh / kg. The summary is shown in Table 1.

[0142] Based on the density functional theory, the migration energy of Na + in Na2MnMoF7 was calculated, and the results are shown in Figure 8 . It can be seen that the migration energy barrier of Na + in Na2MnMoF7 is 320meV, which proves that Na + can migrate rapidly in the structure system of Na2MnMoF7, indicating that Na2MnMoF7 also has excellent rapid charge and discharge performance.

[0143] Example 2

[0144] The embodiment provides a process for preparing a fluoride positive electrode composite material for a sodium ion battery by using a sol-gel method and performance testing, and the specific process is as follows:

[0145] (1) The required stoichiometric sodium fluoride (analytical pure) and vanadium fluoride (analytical pure) are respectively dissolved in deionized water, and citric acid is added to form a precursor gel.

[0146] (2) The precursor gel is placed in a crucible and placed in a high-temperature furnace for low-temperature pretreatment. Under an argon atmosphere, the temperature is raised to 300°C for 4 hours of pre-burning, and 200g of pretreated powder is obtained.

[0147] (3) The pretreated powder is heated to 900°C in a high-temperature furnace under an argon atmosphere for 6 hours of high-temperature heat treatment, and after cooling to room temperature, the material is discharged and ground to obtain a fluoride positive electrode material with a chemical formula of Na2V2F7.

[0148] (4) The fluoride positive electrode material is subjected to carbon coating treatment, and liquid phase coating is adopted. Specifically, 200g of fluoride positive electrode material is mixed with a pitch emulsion in a mass ratio of 15:1, stirred for 8 hours to form a homogeneous slurry, and the slurry is dried and placed in a rotary furnace. Under an argon atmosphere, the temperature is raised to 900°C for 100min of insulation, and after cooling and discharging, the fluoride positive electrode composite material with a carbon coating layer is obtained.

[0149] The fluoride positive electrode material prepared in this embodiment contains 2O, 2M and 4M three crystal structures.

[0150] The fluoride positive electrode composite material prepared in this embodiment is used to prepare a positive electrode sheet, and a sodium ion battery is assembled for testing. The battery preparation and testing process are the same as in Example 1.

[0151] The voltage-capacity curve of the test is shown in Figure 9 , and it can be seen that the battery capacity is 204mAh / g, the average voltage reaches 3.16V, and the specific energy is 647Wh / kg. The summary is shown in Table 1.

[0152] Based on the density functional theory, the migration energy of Na + in Na2V2F7 is calculated, as shown in Figure 10 , it can be seen that the migration energy barrier of Na + in Na2V2F7 is 500meV, which proves that Na + can quickly migrate in the Na2V2F7 structure system, indicating that Na2V2F7 also has excellent fast charging and discharging performance.

[0153] Example 3

[0154] This embodiment provides a process for preparing a fluoride cathode composite material for sodium ion batteries using a spray drying method and a performance test. The specific process is as follows:

[0155] (1) Grind and mix the required stoichiometric amounts of sodium fluoride (analytical grade), chromium fluoride (analytical grade), and vanadium fluoride (analytical grade) to obtain 200 g of precursor.

[0156] (2) Add 200 g of the precursor to a certain proportion of deionized water and stir evenly to form a slurry.

[0157] (3) The slurry is placed in a spray dryer for spray drying to obtain a precursor powder; wherein the inlet temperature of the spray dryer is 150°C, the outlet temperature is 100°C, and the feed rate is 200 mL / h.

[0158] (4) The precursor powder is placed in a crucible and placed in a high-temperature furnace for heat treatment. The temperature is raised to 900°C and heat treated for 5 hours under an argon atmosphere. After cooling to room temperature and grinding, a fluoride positive electrode material with the chemical formula of Na2CrVF7 is obtained.

[0159] (5) The fluoride positive electrode material is subjected to carbon coating treatment by gas phase coating, specifically: 200 g of fluoride positive electrode material is placed in a rotary kiln, heated to 800 °C under an argon atmosphere, and argon and acetylene gas are introduced at a volume ratio of 2:1 for gas phase coating. After keeping the temperature for 90 minutes, the gas source is turned off, and the material is discharged and classified after cooling to room temperature to obtain a fluoride positive electrode composite material containing a carbon coating layer.

[0160] The fluoride positive electrode material prepared in this embodiment includes four crystal structures: 2O, 2M, 3T, and 4M.

[0161] The fluoride positive electrode composite material prepared in this example was used to prepare a positive electrode sheet, and a sodium ion battery was assembled for testing. The battery preparation and testing process were the same as in Example 1.

[0162] The voltage-capacity curve of the test is as follows: Figure 11 As shown, the battery capacity is 202mAh / g, the average voltage reaches 3.19V, and the specific energy is 645Wh / kg, as summarized in Table 1.

[0163] Calculation of Na in Na2CrVF7 based on density functional theory + The migration energy, such as Figure 12 As shown, it can be seen that Na in Na2CrVF7 + The migration energy barrier is 510 meV, which proves that Na + It can migrate rapidly within the Na2CrVF7 structure system, indicating that Na2CrVF7 also has excellent fast charge and discharge performance.

[0164] Example 4

[0165] The present embodiment provides a process for preparing a fluoride positive electrode composite material for sodium ion batteries by co-precipitation and performance testing, the specific process is as follows:

[0166] (1) Dissolve the required stoichiometric amount of sodium fluoride (analytical pure), nickel fluoride (analytical pure) and molybdenum fluoride (analytical pure) in deionized water, stir uniformly to form a mixed solution.

[0167] (2) The mixed solution of complexing agent ammonia and sodium hydroxide is used as a precipitant and placed in a reaction kettle. Under a nitrogen atmosphere, the mixed solution is introduced into the reaction kettle by a peristaltic pump to react with the precipitant to form a precipitate.

[0168] The temperature of the circulating water bath of the reaction kettle is 80℃, the rotation speed is 600rpm, and the pH value in the reaction kettle is controlled at 10; the feeding speed of the peristaltic pump is 200ml / h; the molar ratio of ammonia to sodium hydroxide in the precipitant is 7:3.

[0169] (3) The precipitate is washed with deionized water at least three times, dried and uniformly mixed with sodium fluoride according to the stoichiometric ratio to obtain a precursor mixture.

[0170] (4) The precursor mixture is placed in a crucible and put into a high-temperature furnace for heat treatment under an argon atmosphere. After cooling to room temperature, the material is discharged and ground to obtain a fluoride positive electrode material with the chemical formula Na2NiMoF7.

[0171] The heat treatment temperature is between 600℃-1000℃, and the heat treatment time is 12-24 hours.

[0172] (5) The fluoride positive electrode material is subjected to carbon coating treatment, and the solid phase coating is adopted. Specifically, the fluoride positive electrode material and conductive carbon black with a mass ratio of 100:2 are placed in a ball mill, the rotation speed of the ball mill is set to 600rpm, and the mixture is ball milled for 3 hours under an argon atmosphere. Sintering at 500℃ for 2 hours to obtain a fluoride positive electrode composite material with a carbon coating layer.

[0173] The fluoride positive electrode material prepared in the present embodiment contains 2O, 2M, 3T and 4M four crystal structures.

[0174] The fluoride positive electrode composite material prepared in the present embodiment is used to prepare a positive electrode sheet, and a sodium ion battery is assembled for testing. The battery preparation and testing process are the same as in Example 1.

[0175] The tested battery has a capacity of 167mAh / g, an average voltage of 3.69V, and a specific energy of 615Wh / kg. The results are shown in Table 1.

[0176] Based on the density functional theory calculation of Na2NiMoF7 in Na + migration energy barrier is 428meV, which proves that Na + can migrate rapidly within the Na2NiMoF7 structure system, indicating that Na2NiMoF7 also has excellent rapid charge and discharge performance.

[0177] Example 5

[0178] The present embodiment provides a process for preparing a fluoride positive electrode composite material for a sodium ion battery using a sol-gel method and performance testing, and the specific process is as follows:

[0179] (1) The required stoichiometric sodium fluoride (analytical pure), nickel fluoride (analytical pure) and manganese fluoride (analytical pure) are dissolved in deionized water respectively, and citric acid is added to form a precursor gel.

[0180] (2) Put the precursor gel into a crucible and place it in a high-temperature furnace for low-temperature pretreatment. Under argon atmosphere, heat to 500℃ for 5 hours, and get 200g of pretreated powder.

[0181] (3) Heat the pretreated powder to 1000℃ in a high-temperature furnace, and heat treat under argon atmosphere for 10 hours. After cooling to room temperature, discharge and grind to obtain a fluoride positive electrode material with the chemical formula Na2NiMnF7.

[0182] (4) Carbon-coated treatment of the fluoride positive electrode material is carried out by gas phase coating. Specifically, 200g of fluoride positive electrode material is placed in a rotary furnace and heated to 800℃ under argon atmosphere. Argon and acetylene gas are introduced at a volume ratio of 2:1 for gas phase coating. After 110min of heat preservation, the gas source is closed, and the material is discharged and graded after cooling to room temperature, to obtain a fluoride positive electrode composite material with a carbon-coated layer.

[0183] The fluoride positive electrode material prepared in the present embodiment contains 2O, 2M, 3T and 4M four crystal structures.

[0184] The fluoride positive electrode composite material prepared in the present embodiment is used to prepare a positive electrode sheet, and a sodium ion battery is assembled for testing. The battery preparation and testing process are the same as in Example 1.

[0185] The test battery has a capacity of 178mAh / g, an average voltage of 3.41V, and a specific energy of 609Wh / kg. The results are shown in Table 1.

[0186] Based on the density functional theory calculation of Na2NiMnF7 in Na + migration energy barrier is 428meV, which proves that Na +Na2NiMnF7 also has excellent rapid charge and discharge performance.

[0187] Example 6

[0188] The embodiment provides a process for preparing a fluoride positive electrode composite material for a sodium ion battery by a solid phase method and performance test, and the specific process is as follows:

[0189] (1) Put the required stoichiometric sodium fluoride (analytical pure), cobalt fluoride (analytical pure) and molybdenum fluoride (analytical pure) into a ball mill, set the rotation speed of the ball mill to 600 rpm, and mill for 10 hours under an argon atmosphere. After uniform mixing, 200g of precursor powder is obtained.

[0190] (2) Put the obtained precursor powder into a crucible and place it in a high-temperature furnace for heat treatment. Under an argon atmosphere, heat to 800℃ and keep for 1 hour. After cooling to room temperature, discharge and grind to obtain a fluoride positive electrode material with the chemical formula Na2CoMoF7.

[0191] (3) The obtained fluoride positive electrode material is subjected to carbon coating treatment. Liquid phase coating is adopted, specifically: 200g of fluoride positive electrode material and graphene are dissolved in ethanol according to a ratio of 20:1, stirred for 1 hour to form a uniform slurry, then the slurry is directly dried and placed in a rotary furnace, heated to 850℃ under a protective atmosphere for 1.5 hours, and then discharged and classified to obtain a fluoride positive electrode composite material containing a carbon coating layer.

[0192] The fluoride positive electrode material prepared in the embodiment contains two crystal structures of 2O and 2M.

[0193] The fluoride positive electrode composite material prepared in the embodiment is used to prepare a positive electrode sheet, and a sodium ion battery is assembled for testing. The battery preparation and testing process are the same as those of Example 1.

[0194] The capacity of the tested battery is 168mAh / g, the average voltage reaches 3.63V, and the specific energy is 609Wh / kg. The summary is shown in Table 1.

[0195] Based on the density functional theory, the migration energy barrier of Na + in Na2CoMoF7 is 344meV, which proves that Na + can quickly migrate within the Na2CoMoF7 structure system, indicating that Na2CoMoF7 also has excellent rapid charge and discharge performance.

[0196] To better illustrate the effect of the embodiment of the application, Comparative Examples 1-4 are compared with the above embodiment.

[0197] Comparative Example 1

[0198] This comparative example adopts the traditional method to prepare the layered oxide positive electrode material P2 type Na 2 / 3 CoO2, and using the obtained P2-Na 2 / 3 The positive electrode was prepared from CoO2 and a sodium ion battery was assembled for testing. The battery preparation and testing process were the same as in Example 1. The test capacity, average voltage and specific energy data are summarized in Table 1.

[0199] Calculation of P2-Na based on density functional theory 2 / 3 Na in CoO2 + The migration energy barrier is 200 meV.

[0200] Comparative Example 2

[0201] In this comparative example, the traditional method was used to prepare the polyanion oxide positive electrode material Na2Fe2(SO4)3, and the obtained Na2Fe2(SO4)3 was used to prepare the positive electrode plate, and the sodium ion battery was assembled for testing. The battery preparation and testing process were the same as in Example 1. The test capacity, average voltage and specific energy data are summarized in Table 1.

[0202] Calculation of Na in Na2Fe2(SO4)3 based on density functional theory + The migration energy barrier is 550 meV.

[0203] Comparative Example 3

[0204] The material Na2TiFeF7 obtained from the document 1 described in the background art is used as comparative example 3.

[0205] The Na2TiFeF7 prepared in this comparative example was used to prepare a positive electrode sheet, and a sodium ion battery was assembled for testing. The battery preparation and testing process were the same as in Example 1. The test capacity, average voltage and specific energy data are summarized in Table 1.

[0206] Calculation of Na in Na2TiFeF7 based on density functional theory + The migration energy barrier is 344 meV.

[0207] Comparative Example 4

[0208] The material Na2Fe2F7 obtained from the document 2 described in the background technology is used as comparative example 4.

[0209] The Na2Fe2F7 prepared in this comparative example was used to prepare a positive electrode sheet, and a sodium ion battery was assembled for testing. The battery preparation and testing process were the same as in Example 1. The test capacity, average voltage and specific energy data are summarized in Table 1.

[0210] Calculation of Na in Na2Fe2F7 based on density functional theory+ The migration energy barrier is 269 meV.

[0211] Table 1 summarizes the capacity, average voltage and specific energy data of the sodium ion batteries prepared in Examples 1-6 and Comparative Examples 1-4:

[0212]

[0213] Comparing the data in Table 1, we can see that the batteries in Examples 1-6 achieved higher capacities than those in Comparative Examples 1 and 2. This is because the fluoride cathode composite materials prepared in these examples possess a three-dimensional framework, making them relatively stable during electrical cycling. They can insert or remove two electrons per chemical formula, thus providing a higher capacity. Furthermore, the voltages of the batteries in Examples 1-6 were higher than those in Comparative Example 1. This is because the replacement of oxygen anions with fluoride ions significantly increases the voltage of the materials due to the inductive effect.

[0214] The average operating voltage of the batteries in Examples 1-6 is higher than that in Comparative Examples 3 and 4. This is because different redox-active metals are used in the fluoride positive electrode composite materials prepared in the embodiments of the present invention. Combined with the inductive effect of fluoride ions and the higher stability of the material crystal structure, the synergistic effect of multiple aspects can bring higher operating voltage to the material, so that the battery has better electrochemical performance.

[0215] Therefore, compared with Comparative Examples 1-4, Examples 1-6 have an advantage in at least one of the two indicators, voltage and capacitance, so that the specific energy of Examples 1-6 is significantly greater than that of Comparative Examples 1-4.

[0216] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A fluoride cathode composite material for a sodium-ion battery, characterized in that, The fluoride positive electrode composite material comprises: a fluoride positive electrode material, and a carbon coating layer coated on the outer surface of the fluoride positive electrode material; The chemical general formula of the fluoride positive electrode material is Na2N x M y F7, wherein 0≤x≤2, y=2-x; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements. The structure of the fluoride positive electrode material is a magnesium cryolite structure, and comprises one or more of 2O phase, 2M phase, 3T phase, and 4M phase crystal structures; and the structure of the fluoride positive electrode material at least comprises 4M phase crystal structure; The N ions and M ions in the fluoride positive electrode material form octahedral configurations NF6 and MF6 with six F ions respectively, and the NF6 and MF6 are connected through a single fluorine ion to form a three-dimensional framework structure; The mass percentage of the carbon coating layer in the fluoride positive electrode composite material is 0-10%.

2. The fluoride cathode composite material for sodium-ion batteries according to claim 1, characterized in that, When the crystal structure of the fluoride positive electrode material is 2O phase, the space group is Imma; When the crystal structure of the fluoride positive electrode material is 2M phase, the space group is C2 / c; When the crystal structure of the fluoride positive electrode material is 3T phase, the space group is P3121; When the crystal structure of the fluoride positive electrode material is 4M phase, the space group is C2 / c; The mass percentage of the carbon coating layer in the fluoride positive electrode composite material is 0.5%-10%.

3. A method of preparing the fluoride cathode composite material for sodium-ion batteries according to any of the preceding claims 1-2, characterized in that, The method is a solid phase method, comprising: Placing sodium fluoride, fluoride of N, and fluoride of M in a ball mill in a required stoichiometric amount, uniformly mixing under an argon atmosphere, to obtain a precursor powder; Placing the obtained precursor powder into a crucible, and placing the crucible into a high-temperature furnace to perform heat treatment under an argon atmosphere, and then cooling to room temperature, discharging, and grinding to obtain a fluoride positive electrode material; Performing carbon coating treatment on the fluoride positive electrode material to obtain a fluoride positive electrode composite material for a sodium ion battery; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi; and M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, and Bi; The rotation speed of the ball mill is 300 rpm-600 rpm, and the ball milling time is 10 hours-24 hours; The heat treatment is specifically: heat treatment at a temperature of 500-1000°C for 30 minutes-1 hour; The carbon coating treatment comprises any one of gas phase coating, liquid phase coating, or solid phase coating.

4. A method of preparing the fluoride cathode composite material for sodium-ion batteries according to any one of claims 1-2, characterized in that, The method is a sol-gel method, comprising: Dissolving sodium fluoride, fluoride of N, and fluoride of M in solvents in a required stoichiometric amount, respectively, and adding citric acid to form a precursor gel; Placing the precursor gel into a crucible, and placing the crucible into a high-temperature furnace to perform low-temperature pretreatment under an argon atmosphere, to obtain a pretreated powder; Performing high-temperature heat treatment on the pretreated powder under an argon atmosphere, and then cooling to room temperature, discharging, and grinding to obtain a fluoride positive electrode material; Performing carbon coating treatment on the fluoride positive electrode material to obtain a fluoride positive electrode composite material for a sodium ion battery; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; The solvent includes anhydrous ethanol or deionized water; The low-temperature pretreatment is specifically 2-6 hours of pre-sintering at 250-500 DEG C; The high-temperature heat treatment is specifically 2-24 hours of heat treatment at 800-1000 DEG C; The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

5. A method of preparing the fluoride cathode composite material for sodium-ion batteries according to any one of claims 1-2, characterized in that, The method is a spray drying method, comprising: Mixing the required stoichiometric amount of sodium fluoride, fluoride of N and fluoride of M uniformly to obtain a precursor; After adding the precursor into a certain proportion of solvent, stirring uniformly to form a slurry; After the slurry is placed in a spray dryer for spray drying, a precursor powder is obtained; The precursor powder is placed in a crucible, placed in a high-temperature furnace, heat treated under argon atmosphere, cooled to room temperature, discharged, ground to obtain a fluoride positive electrode material; The fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for sodium ion battery; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; The method for mixing uniformly is grinding mixing or ball milling mixing; The solvent includes anhydrous ethanol or deionized water; The method for heat treatment is specifically 2-24 hours of heat treatment at 800-1000 DEG C; The inlet temperature of the spray dryer is 150-190 DEG C, the outlet temperature is 70-100 DEG C, and the feeding speed is 200-600 mL / h; The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

6. A method of preparing a fluoride cathode composite material for sodium-ion batteries according to any of the preceding claims 1-2, characterized in that, The preparation method is a co-precipitation method, comprising: Dissolve the required stoichiometric amount of fluoride of N and fluoride of M in deionized water, and stir uniformly to form a mixed solution; The mixed solution of the complexing agent ammonia and sodium hydroxide is used as a precipitant, placed in a reaction kettle, and under a nitrogen atmosphere, the mixed solution is brought into the reaction kettle by a peristaltic pump to react with the precipitant to generate a precipitate; The precipitate is washed with deionized water at least three times, dried, and uniformly mixed with sodium fluoride according to the stoichiometric ratio to obtain a precursor mixture; The precursor mixture is placed in a crucible, put into a high-temperature furnace, heat treated under argon atmosphere, cooled to room temperature, discharged, ground to obtain a fluoride positive electrode material; The fluoride positive electrode material is subjected to carbon coating treatment to obtain a fluoride positive electrode composite material for sodium ion battery; N is any one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements; M is any one of Ti, Cr, Mn, Co, Ni, Cu, Nb, Mo, Sn, Sb, Bi elements.

7. The production method according to claim 6, wherein The temperature of the circulating water bath of the reaction kettle is 50-80 DEG C, and the rotating speed is 500-800 rpm; The pH value in the reaction kettle is controlled between 9.0-11.5; The feeding speed of the peristaltic pump is 100-300 ml / h; The molar ratio of ammonia to sodium hydroxide in the precipitant is [7:3]-[9:1]; The temperature of the heat treatment is between 600-1000 DEG C, and the heat treatment time is 12-24 hours; The carbon coating treatment includes any one of gas phase coating, liquid phase coating or solid phase coating.

8. A positive electrode plate for a sodium ion secondary battery, characterized in that: The positive electrode sheet comprises the fluoride positive electrode composite material of any one of claims 1-2.

9. A sodium-ion battery, characterized in that, The sodium ion battery comprises the positive electrode sheet of claim 8.

10. Use of the sodium-ion battery of claim 9, characterized in that The sodium ion battery is used for large-scale energy storage equipment of solar power generation, wind power generation, smart grid peak shaving, distributed power station or communication base station, or for energy supply equipment of electric vehicles.

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