Sodium-ion battery cathode material, preparation method thereof, sodium-ion battery cathode plate, and sodium-ion battery

Abstract

The present invention provides a cathode material for a sodium-ion battery, a method for preparing the same, a cathode electrode for a sodium-ion battery, and a sodium-ion battery. The cathode material for a sodium-ion battery includes a core and a shell covering the surface of the core, wherein the core contains a layered oxide treated with a residual alkali solvent, and the shell is a composite coating layer, and the residual alkali solvent contains an organic solvent. The cathode material of the present invention has an extremely low content of residual alkali in the layered oxide, and has improved gas generation performance and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a cathode material for a sodium-ion battery, a preparation method thereof, a cathode electrode sheet for a sodium-ion battery, and a sodium-ion battery. Background Art

[0002] Sodium-ion batteries have broad application prospects in the energy storage field due to their cost advantages. Their working principle is similar to that of lithium-ion batteries, and they utilize the reversible insertion and extraction of sodium ions between the positive and negative electrodes to achieve energy storage and release.

[0003] A widely concerned cathode material for sodium-ion batteries is a transition metal layered oxide cathode material with high specific capacity. However, the layered oxide cathode material has poor water resistance because the layer spacing is large, which is easy to undergo an ion exchange reaction with hydrogen ions in water molecules in the air, and alkaline substances are generated on the material surface.

[0004] At the same time, during the sintering process of the layered oxide cathode material by the high-temperature solid-state method, after the sodium salt and metal oxide form a layered structure through the breaking and recombination of chemical bonds, part of the sodium salt does not enter the bulk phase structure of the material but remains on the material surface to form alkaline substances.

[0005] This will change the crystal structure of the material and reduce the crystallinity of the material. Moreover, the strong alkaline environment formed on the material surface will cause the binder to defluorinate and fail, and the alkali will corrode the current collector with amphoteric metal properties (such as aluminum foil).

[0006] The decomposition of alkaline substances at high voltages is one of the reasons for battery swelling, thus bringing potential safety hazards; the surface alkaline compounds will also cause irreversible capacity loss and deteriorate the cycle performance at the same time.

[0007] Therefore, there is still a need for an improved cathode material for sodium-ion batteries that can at least solve one of the above problems. Summary of the Invention

[0008] In order to solve the above technical problems, it is necessary to control the content of residual alkalis such as sodium carbonate and sodium hydroxide in the cathode material of the sodium-ion battery, and improve the processing performance and electrical performance of the sodium-ion battery. Therefore, the present invention provides a new cathode material for a sodium-ion battery, a preparation method thereof, a cathode prepared from the cathode material, and a sodium-ion battery including the cathode.

[0009] Specifically, the present invention provides:

[0010] 1. A cathode material for a sodium-ion battery, comprising a core treated with a residual alkali dissolving agent and a shell coating the surface of the core, wherein the core contains a layered oxide, the shell is a composite coating layer, and the residual alkali dissolving agent contains an organic solvent.

[0011] Through the above technical solution, the residual alkali on the surface of the core containing the layered oxide can be completely removed, and compared with pickling and water washing, this technical solution will not cause the sodium in the bulk phase of the layered oxide to dissolve out.

[0012] In addition, by coating the surface of the core with a composite coating layer, the direct contact between the layered oxide and air and electrolyte is blocked, greatly improving the air stability and interfacial stability of the layered oxide cathode material.

[0013] Among them, the residual alkali contains at least one of sodium carbonate and sodium hydroxide, the residual alkali solvent is an organic solvent, and the organic solvent contains one or more of alcohol solvents, ketone solvents, and ether solvents.

[0014] Preferably, calculated as free sodium, the residual alkali accounts for 0.10 - 0.30% of the total weight of the core.

[0015] Preferably, the organic solvent contains glycerol, or a mixed solvent of glycerol and other alcohol solvents, ketone solvents or ether solvents, and in the mixture solvent, the weight ratio of glycerol is 70% - 100%.

[0016] Among them, the composite coating layer contains fluorosulfate compound nanoparticles, a first conductive agent, and a first binder after carbonization.

[0017] Preferably, in the cathode material, the fluorosulfate compound nanoparticles and the first conductive agent are fixed by the first binder after carbonization and are dispersed on the surface of the core in a completely coated manner.

[0018] Among them, the fluorosulfate compound is represented by Na a Fe b N c (SO4) d Fe, where a≥1.5, b≥0, c≥0, d≥0, e≥0;

[0019] Among them, N is one or more selected from Ti, Zr, Sr, Al, and Mn, and the values of a, b, c, d, and e satisfy the charge balance of the chemical formula.

[0020] Among them, the D50 of the fluorosulfate compound nanoparticles is 1 - 1000 nm.

[0021] Among them, the layered oxide is composed of Na x Ni y Fe z Mn i M 1-y-z-iO2 represents, where 0.5 < x < 1.5, 0 < y ≤ 0.8, 0 < z ≤ 0.33, 0 < i ≤ 0.5, and the values of x, y, z, and i satisfy the charge balance of the chemical formula;

[0022] where M is selected from one or more elements of Li, B, Mg, Cu, Zn, Co, Ca, Ba, Sr, Al, B, Cr, Zr, Y, Sr, Ti, Sn, V, Mo, W, Ru, Nb, Sb, and Nb.

[0023] Through the above further technical solutions, the present invention can also improve the rate performance and working voltage of the cathode material, has good cycle performance at 2 - 4.5V, and remains stable within the conventional working voltage (1.5 - 4.0V) of the layered oxide cathode material for a long time, thereby protecting the interfacial stability of the layered oxide cathode material throughout its life cycle.

[0024] 2. A method for preparing a sodium-ion battery cathode material, the method comprising the following steps:

[0025] Treating a core containing a layered oxide with a residual alkali solvent containing an organic solvent,

[0026] Coating the treated core with a composite coating layer to obtain a coated product, and

[0027] Sintering the coated product to obtain the sodium-ion battery cathode material.

[0028] Among them, the step of treating a core containing a layered oxide with a residual alkali solvent containing an organic solvent includes dispersing the layered oxide particles in an organic solvent to dissolve and remove the residual alkali on the surface of the layered oxide particles; and filtering the obtained solid-liquid mixture to obtain a treated core with a solvent content not greater than 1% by weight.

[0029] Among them, the step of coating the treated core with a composite coating layer includes:

[0030] Dispersing fluorosulfate compound nanoparticles, a conductive agent, and a binder in an organic solvent to obtain a composite coating layer slurry, and then mixing the treated core with the composite coating layer slurry to obtain a coated product composed of a core and a composite coating layer precursor coated on the surface of the core;

[0031] Preferably, the step of sintering the coated product includes sintering the coated product at a pressure of 10 - 10 3 Pa and a sintering temperature of 300 - 450°C for 1 - 12h to obtain a sodium-ion battery cathode material with low residual alkali, where the residual alkali accounts for 0.10 - 0.30% by weight of the total weight of the core in terms of free sodium. Among them, the D50 of the layered oxide particles is 3 - 12μm;

[0032] Preferably, the first binder is asphalt;

[0033] Preferably, the first conductive agent is one or more of carbon nanotubes, vapor-grown carbon fibers, graphene, and carbon black;

[0034] Preferably, in the sodium ion battery material, by weight, the content of the layered oxide is 85% to 99.9%, the content of the fluorinated sulfate compound is 0.1% to 5%, the content of the conductive agent is 0.1% to 5%, and the content of the binder is 0.1% to 5%.

[0035] 3. A positive electrode tab for a sodium ion battery, comprising:

[0036] A positive electrode current collector,

[0037] A positive electrode film disposed on at least one surface of the positive electrode current collector, the positive electrode film comprising a positive electrode active material, a second binder, and a second conductive agent, and the positive electrode active material being the above-mentioned positive electrode material for a sodium ion battery.

[0038] 4. A sodium ion battery, comprising a positive electrode tab, a negative electrode tab, a separator, and an electrolyte, wherein the positive electrode tab is the above-mentioned positive electrode tab for a sodium ion battery.

[0039] The present invention has at least one of the following advantages:

[0040] 1. Before the core (such as Na x Ni y Fe z Mn i M 1-y-z-i O2) is coated with the composite coating layer, the residual alkali on its surface (such as sodium carbonate and sodium hydroxide) is dissolved by using a residual alkali dissolving agent (such as glycerol or a mixture of glycerol and ether solvents, ketone solvents, etc.), and the residual alkali can be removed very thoroughly; compared with pickling and water washing, this method will not cause the dissolution of sodium in the bulk phase of the layered oxide;

[0041] 2. The composite coating layer completely coats the surface of the layered oxide, blocking the direct contact between the layered oxide and air and the electrolyte, and greatly improving the air stability and interface stability of the layered oxide positive electrode material;

[0042] 3. In the composite coating layer, a fluorinated sulfate compound, such as Na a Fe b N c (SO4) d F eIt has a unique struvite structure, good rate performance, and a high working voltage. It has good cycling performance in the range of 2 - 4.5V and can remain stable within the conventional working voltage (1.5 - 4.0V) of the layered oxide cathode material, thereby protecting the interfacial stability of the layered oxide cathode material throughout its entire life cycle.

[0043] 4. In the composite coating layer, the carbonized pitch can be used to fix the coating layer, ensuring the stability of the coating layer during the expansion and contraction process of the layered oxide cathode material. At the same time, the carbonized pitch also has a certain electrical conductivity, which compensates to a certain extent for the disadvantage of insufficient electronic conductivity of the fluorosulfate compound.

[0044] 5. To further compensate for the disadvantage of insufficient electronic conductivity of the compound, a conductive agent can be added to the composite coating layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The scanning electron microscope photographs of the cathode material before being coated with the composite coating layer and the photographs of the cathode material after being coated in Example 1 are shown.

[0046] Figure 2 The scanning electron microscope photographs of the cathode material after being coated with the composite coating layer in Example 1 are shown.

[0047] Figure 3 The change of the capacity retention rate of the sodium-ion soft-pack battery prepared with the cathode materials in Example 3 and Comparative Example 3 with the number of cycles is shown.

[0048] Figure 4 The schematic diagram of the core-shell structure of the sodium-ion battery cathode material of an embodiment of the present invention is shown. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0049] Before a more detailed description of the present disclosure, it should be understood that the content of the present disclosure is not limited to the specific embodiments described, and thus, the embodiments of the present disclosure can of course vary. It should also be understood that since the content of the present disclosure is only defined by the appended claims, the terms used herein are only for describing specific embodiments and are not intended to be limiting.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art.

[0051] All publications and patents referred to in this specification are incorporated herein by reference as if each individual publication or patent was specifically and separately indicated to be incorporated herein by reference, and are incorporated herein by reference for the purpose of disclosing and describing the methods and / or structures related to the publications cited.

[0052] After reading the disclosure of the present application, it will be apparent to those skilled in the art that each embodiment described and illustrated herein has discrete components and features, which can be easily separated from each other or combined with the features of any one of several other embodiments without departing from the scope and spirit of the present invention. Any method recited can be implemented in the order of the recited events or in any other order that is logically feasible.

[0053] It must be noted that in this specification and the appended claims, unless the context clearly dictates otherwise, the singular forms "a", "an", "the", and the indefinite form of a manner without specifying a quantity cover situations having a plurality of referents.

[0054] Unless otherwise indicated, all numbers expressing quantities and physical characteristics used in the disclosure of the present invention should be understood to be modified in all instances by the term "about". Thus, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations, and those skilled in the art can appropriately change these approximations in light of the teachings disclosed herein to obtain the desired characteristics. It is not intended to limit the application of the doctrine of equivalents of the scope of the claims, and each numerical parameter should at least be regarded as obtained according to the reported significant digits and by conventional rounding methods. Additionally, a numerical range represented by end values includes those end values, as well as all sub-ranges and numerical values within that range (e.g., 30 - 40 includes 30, 31, 31.5, 32.3, 35 - 40, etc.). A numerical value in the form of X ± Y herein represents a numerical range from X - Y to X + Y, which also includes the end values X - Y, X + Y, as well as all sub-ranges and numerical values within that range (e.g., 30 ± 5 includes 25, 26, 27, 28, 29.5, 30.8, 31 - 33, 31 - 35, 35, etc.).

[0055] In this context, D50 refers to the particle size value corresponding to a cumulative volume distribution percentage of 50% in the volume particle size distribution curve of the particles. D50 is also known as the median diameter or mid-value diameter.

[0056] The present disclosure provides a novel cathode material for a sodium-ion battery, a method for preparing the same, a cathode prepared from the cathode material, and a sodium-ion battery including the cathode.

[0057] According to the related art, there are various methods for controlling the residual alkali content of the cathode material and improving the performance such as the stability of the sodium-ion battery, including:

[0058] 1. A method for preparing a cathode material for a sodium-ion battery with sodium fast ion conductor inlay coating, which includes using the sodium residue on the surface of the cathode material for a sodium-ion battery as a raw material, and in-situ synthesizing the cathode material with sodium fast ion conductor inlay coating through a solvothermal (hydrothermal)-heat treatment process. This can reduce the residual alkali content on the surface of the cathode material for a sodium-ion battery, and at the same time, the formed sodium fast ion conductor can enhance the air stability of the cathode material, thereby enhancing the storage performance, interfacial stability, and sodium ion diffusion ability of the Na x MO2 material.

[0059] However, sodium fast ion conductors are usually Na y M2(X)3, such as Na3V2(PO4)3. Although they have excellent ionic conductivity characteristics, their electronic conductivity is very low. In this method, no carbon or other conductive materials are used for modification, which will lead to poor rate performance of the cathode material for a sodium-ion battery in this method;

[0060] In addition, the Na x MO2 cathode material in this method is a typical layered structure, with rich phase changes and a volume change of about 10% during charge and discharge. In this method, the Na y M2(X)3 sodium fast ion conductor is directly inlaid on the surface of the Na x MO2 cathode material. This bonding method is not firm. During the expansion and contraction process of the NaxMO2 cathode material, the Na y M2(X)3 sodium fast ion conductor is likely to fall off, and the Na x MO2 cathode material is re-exposed to the electrolyte, greatly reducing the cycle and storage stability;

[0061] In addition, in this technology, due to the residual alkali of the Na x MO2 cathode material being wrapped on its surface, only the part directly in contact with the Na y M2(X)3 precursor can be consumed through high-temperature reaction, and other residual alkali still remains on the surface of the NaxMO2 cathode material. Especially in the Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide, the residual alkali content (calculated by the weight of sodium carbonate and sodium hydroxide) is as high as tens of thousands of ppm or more. If the technology in this method is used, a high residual alkali content will still remain on the surface of the Na x MO2 cathode material, resulting in serious gas generation during high-temperature cycling and storage, and the improvement effect on this type of material is not good.

[0062] 2. A method for preparing a modified cathode material for a sodium-ion battery, which includes a M2 b V c (PO4)d F e nanoparticles or Na a M2 b V c (PO4) d F e The composite is coated on the surface of the O3-phase cathode material Na x Cu y Fe z Mn i M1 1-y-z-i O2 by ball milling, thereby reducing the contact area between the electrolyte and the O3-phase cathode material and reducing the side reactions between the electrode materials; and the selected coating material itself can provide capacity and has a stable structure, which can maintain the structural stability of the cathode material, thereby improving the cycle stability of the battery.

[0063] However, the technology in this method is not applicable to Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide because in Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide, the residual alkali content (calculated by the weight of sodium carbonate and sodium hydroxide) is as high as tens of thousands of ppm or more. If the technology in this method is used, the residual alkali content will not decrease, resulting in serious gas generation during high-temperature cycling and storage, and the improvement effect on this type of material is not good. The technology in this method is not applicable to Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide, which has rich phase changes during charge and discharge and a volume change of about 10%. In this invention, Na a M2 b V c (PO4) d F e If directly coated on the surface of the Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide cathode material, this bonding method is not firm. During the expansion and contraction process of the Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide cathode material, Na a M2 bV c (PO4) d F e The coating layer is prone to peeling off, and Na x Ni y Fe z Mn i M 1-y-z-i When the O2-layered oxide cathode material is re-exposed to the electrolyte, the cycling and storage stability are greatly reduced;

[0064] In addition, Na a M2 b V c (PO4) d F e V in it is toxic and expensive, and it is not applicable in the field of sodium-ion batteries pursuing low cost.

[0065] 3. The method using an acidic solution utilizes the full reaction of the acidic solution with the residual alkali on the surface of the original cathode material, thereby reducing the concentration of the surface residual alkali and forming a sodium salt with high ionic conductivity, preventing the further generation of residual alkali, and improving the rate performance and cycling performance of the cathode material.

[0066] However, the technology in this method is not applicable to Na x Ni y Fe z Mn i M 1-y-z-i O2-layered oxide because Na x Ni y Fe z Mn i M 1-y-z-i In the acidic solution, the O2-layered oxide will not only consume the residual alkali on its surface through reaction, but also induce the dissolution of sodium in its bulk phase, resulting in a reduction in its specific capacity.

[0067] 4. The method for coating and modifying the cathode material of a sodium-ion battery uses a solvothermal method to dissolve a manganese source in ethanol. The sodium source provided by the surface residual alkali of the layered transition metal oxide can in-situ generate a substance of Na j MnO2 on the material surface, forming a dense manganese-rich shell layer structure protection layer on the material surface, reducing the contact area of the interior exposed to the electrolyte, thereby reducing the occurrence of interfacial side reactions, improving the cycling stability of the material, and at the same time playing a role in reducing the surface residual alkali of the material, improving the processing performance of the material, and reducing the requirements for the storage and use environment.

[0068] However, in this method, since the residual alkali of the layered oxide cathode material is wrapped on its surface, only the part directly in contact with the manganese source can be consumed by high-temperature reaction, and other residual alkalis still remain in Na xThe surface of the MO2 cathode material. Especially in Na x Ni y Fe z Mn i M 1-y-z-i In the O2 layered oxide, the residual alkali content (calculated by the weight of sodium carbonate and sodium hydroxide) is as high as tens of thousands of ppm or more. If the technology in this method is used, there will still be a high residual alkali content remaining on the surface of the Na x MO2 cathode material, resulting in serious gas generation during high-temperature cycling and storage, and the improvement effect on this type of material is not good.

[0069] In addition, the Na j MnO2 rich manganese shell in this method, although having good air stability, is unstable at high voltages, prone to the Jahn-Teller effect, resulting in the dissolution of metallic manganese and migration to the negative electrode, causing the SEI to rupture and the battery to easily generate gas. More seriously, due to the rich manganese shell being on the surface of the layered oxide, the rich manganese shell is prone to excessive sodium deintercalation during high-rate charging, further exacerbating the above phenomenon.

[0070] The present invention provides an improved sodium-ion battery cathode material, comprising air-stable and low-residual-alkali Na x Ni y Fe z Mn i M 1-y-z-i O2 layered oxide with a coating layer. This cathode material is insensitive to moisture and carbon dioxide in the air, is easy to process, and has excellent cycling and storage stability.

[0071] In one aspect, the present invention provides a sodium-ion battery cathode material, including a core treated with a residual alkali dissolving agent and a shell coating the surface of the core, wherein the core comprises a layered oxide, and the shell is a composite coating layer, and the residual alkali dissolving agent comprises an organic solvent. Figure 4 Shows a schematic diagram of the core-shell structure of the sodium-ion battery cathode material of an embodiment of the present invention, where 1 represents the composite coating layer and 2 represents the core.

[0072] Preferably, the composite coating layer comprises fluorosulfate compound nanoparticles, a first conductive agent, and a carbonized first binder.

[0073] Preferably, in the cathode material, the fluorosulfate compound nanoparticles and the first conductive agent are fixed by the carbonized first binder and dispersed on the surface of the core in a fully coated manner.

[0074] Preferably, in the sodium ion battery material, by weight, the content of the layered oxide is 85% to 99.9%, the content of the fluorinated sulfate compound is 0.1% to 5%, the content of the first conductive agent is 0.1% to 5%, and the weight ratio of the first binder is 0.1% to 5%.

[0075] Preferably, the layered oxide is represented by Na x Ni y Fe z Mn i M 1-y-z-i O2, where 0.5 < x < 1.5, 0 < y ≤ 0.8, 0 < z ≤ 0.33, 0 < i ≤ 0.5, and the values of x, y, z, and i satisfy the charge balance of the chemical formula;

[0076] where M is selected from one or more elements of Li, B, Mg, Cu, Zn, Co, Ca, Ba, Sr, Al, B, Cr, Zr, Y, Sr, Ti, Sn, V, Mo, W, Ru, Nb, Sb, and Nb.

[0077] Preferably, the residual alkali contains at least one of sodium carbonate and sodium hydroxide, and in terms of free sodium, the residual alkali accounts for 0.10 - 0.30% by weight of the total weight of the core.

[0078] Preferably, the residual alkali dissolving agent is an organic solvent, and the organic solvent contains one or more of alcohol solvents, ketone solvents, and ether solvents.

[0079] Preferably, the organic solvent contains glycerol, or a mixed solvent of glycerol and other alcohol solvents, ketone solvents, or ether solvents, where in the mixed solvent, the weight ratio of glycerol is 70% - 100%.

[0080] The other alcohol solvents can be at least one of ethanol, butanol, butanediol, and pentanol.

[0081] The ketone solvents can be at least one of acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and isophorone.

[0082] The ether solvents can be at least one of diethyl ether, tetrahydrofuran, and 1,4 - dioxane.

[0083] The fluorinated sulfate compound can be represented by Na a Fe b N c (SO4) d F e where a ≥ 1.5, b ≥ 0, c ≥ 0, d ≥ 0, e ≥ 0;

[0084] Wherein N is one or more selected from Ti, Zr, Sr, Al, and Mn, and the values of a, b, c, d, and e satisfy the charge balance of the chemical formula.

[0085] Preferably, the D50 of the fluorosulfate compound nanoparticles is 1 - 1000 nm.

[0086] In a second aspect, a method for preparing a sodium-ion cathode material is provided, including the following steps:

[0087] Treating a core containing a layered oxide with a residual alkali dissolving agent containing an organic solvent,

[0088] Coating the treated core with a composite coating layer to obtain a coated product and

[0089] Sintering the coated product to obtain the sodium-ion battery cathode material.

[0090] In one embodiment, the method for preparing a sodium-ion cathode material may include the following steps: (1) providing layered oxide particles; (2) treating the layered oxide particles with a residual alkali dissolving agent to provide low-residual-alkali layered oxide, wherein the residual alkali dissolving agent contains an organic solvent; and (3) coating the low-residual-alkali layered oxide with a composite coating layer slurry to form a product including a core and a shell; and (4) sintering the product obtained in step (3), and the binder is carbonized during the high-temperature sintering process to obtain the sodium-ion cathode material.

[0091] Preferably, the step of treating a core containing a layered oxide with a residual alkali dissolving agent containing an organic solvent includes dispersing the layered oxide particles in an organic solvent to dissolve and remove the residual alkali on the surface of the layered oxide particles; and filtering the obtained solid-liquid mixture to obtain a treated core wet powder with a solvent content of not more than 1% by weight.

[0092] For example, the layered oxide particles can be added to an organic solvent as a residual alkali dissolving agent to dissolve and remove the residual alkali on the surface of the layered oxide to obtain a solid-liquid mixture; and then the solid-liquid mixture obtained in step (11) is filtered to obtain a core wet powder with a solvent content of less than or equal to 1%.

[0093] Preferably, the step of coating the treated core with a composite coating layer includes:

[0094] Dispersing fluorosulfate compound nanoparticles, a conductive agent, and a binder in an organic solvent to obtain a composite coating layer slurry, and then mixing the treated core with the composite coating layer slurry to obtain a coated product composed of a core and a composite coating layer precursor coated on the surface of the core.

[0095] Preferably, the step of sintering the coated product includes sintering the coated product at a pressure of 10 to 10 3 Pa and a sintering temperature of 300 to 450 °C for 1 to 12 h, thereby obtaining a cathode material for a sodium-ion battery with low residual alkali.

[0096] For example, Na a Fe b M c (SO4) d F e nanoparticles, a first conductive agent, and a first binder are dispersed in an organic solvent to obtain a slurry. Then, the wet powder is placed in the slurry, and after sufficient stirring, a product composed of a core and a composite coating precursor layer coated on the surface of the core is obtained; then sintering is carried out under a vacuum condition (10 to 10 3 Pa), the sintering temperature is 300 to 450 °C, and the sintering time is 1 to 12 h, thereby obtaining a cathode material for a sodium-ion battery with ultra-low residual alkali and air stability.

[0097] The D50 of the layered oxide particles can be 3 to 12 μm;

[0098] Specifically, the preparation method of the low-residual-alkali layered oxide is as follows:

[0099] (1) The layered oxide (for example, Na x NiyFe z Mn i M 1-y-z-i O2) is added to glycerol or a mixed solvent thereof with other alcohols, ketones, or ethers (by weight, the proportion of glycerol is 70% to 100%) according to a weight ratio of 1:2 to 1:10 and stirred for 15 to 90 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0100] (2) The solid-liquid mixture is filtered under pressure to obtain a wet powder with a solvent content less than or equal to 1%. In this method, it is not necessary to dry and remove the solvent, and it can be directly used for the preparation of the composite coating precursor, simplifying the process and having a low cost.

[0101] The organic solvent is glycerol or a mixed solvent thereof with other alcohols, ketones, or ethers (by weight, the proportion of glycerol is 70% to 100%).

[0102] In a third aspect, a cathode plate for a sodium-ion battery is provided, including: a cathode current collector and a cathode membrane. The cathode membrane is disposed on at least one surface of the cathode current collector. The cathode membrane may include a cathode active material, a second binder, and a second conductive agent, and the cathode active material uses the above-mentioned cathode material for a sodium-ion battery.

[0103] The first binder and the second binder may be the same or different and may be one or more of asphalt, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylates, polyacrylonitrile, sodium carboxymethyl cellulose and styrene-butadiene rubber. The first binder or the second binder accounts for less than or equal to 10% by weight of the positive electrode of the sodium ion battery.

[0104] Preferably, the first binder is asphalt.

[0105] The first conductive agent and the second conductive agent may be the same or different and may be one or more of carbon black, carbon nanotubes, multi-walled carbon nanotubes, single-walled carbon nanotubes, vapor-generated carbon fibers, Ketjen black, and graphene. The second conductive agent accounts for less than or equal to 20% by weight of the positive electrode of the sodium ion battery.

[0106] In a fourth aspect, a sodium ion battery is provided, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet adopts the above-mentioned positive electrode sheet of the sodium ion battery. The separator can be located between the positive electrode sheet and the negative electrode sheet.

[0107] Hereinafter, the present invention will be described by way of specific examples, but the present invention is by no means limited to these examples.

[0108] Example 1

[0109] Prepare the very low residual alkali core as follows:

[0110] (1) The layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added to glycerol at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0111] (2) The solid-liquid mixture is heated and filtered to obtain a core wet powder having a solvent content of 0.5%.

[0112] The composite layered oxide cathode material was prepared as follows:

[0113] (1) Na3Fe with a D50 of 50 nm 1.95 Mn 0.05 (SO4)3F particles, carbon nanotubes and asphalt are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned core wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 1 / 3Fe 1 / 3 Mn 1 / 3 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 1 / 3 Fe 1 / 3 Mn1 / 3O2、Na3Fe 1.95 Mn 0.05 The weight ratios of (SO4)3F, carbon nanotubes, and pitch are 95%, 2%, 1%, and 2%, respectively;

[0114] (2) In 10 2 Sintering under vacuum conditions, sintering temperature 400℃, sintering time 3h;

[0115] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0116] Example 2

[0117] Prepare the very low residual alkali core as follows:

[0118] (1) The layered oxide NaNi with a D50 of 3 μm 0.30 Fe 0.33 Mn 0.25 Cu 0.12 O2 was added to glycerol and ethanol (90% and 10% by weight, respectively) in a weight ratio of 1:5 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0119] (2) The solid-liquid mixture is filtered to obtain a core wet powder having a solvent content of 1%.

[0120] The composite layered oxide cathode material was prepared as follows:

[0121] (1) Na3Fe with a D50 of 100 nm 1.95 Mn 0.05 (SO4)3F particles, carbon black and carbonized asphalt are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned kernel wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 0.30 Fe 0.33 Mn 0.25 Cu 0.12 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 0.30 Fe 0.33 Mn 0.25 Cu 0.12 O2、Na3Fe 1.95 Mn 0.05 The weight ratios of (SO4)3F, carbon black, and pitch are 90%, 5%, 2%, and 3%, respectively;

[0122] (2) In 10 3 Sintering under vacuum conditions of Pa, sintering temperature of 450℃, sintering time of 6h;

[0123] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0124] Example 3

[0125] Prepare the core of the extremely low residual alkali layer as follows:

[0126] (1) The layered oxide NaNi with a D50 of 8 μm 0.50 Fe 0.2 Mn 0.2 Cu 0.1 O2 was added to glycerol and ethanol (90% and 10% by weight, respectively) in a weight ratio of 1:8 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0127] (2) The solid-liquid mixture is filtered to obtain a core wet powder having a solvent content of 1%.

[0128] The composite layered oxide cathode material was prepared as follows:

[0129] (1) Na3Fe with a D50 of 30 nm 1.95 Mn 0.05 (SO4)3F particles, gas-phase generated carbon fibers and asphalt are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned kernel wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 0.50 Fe 0.2 Mn 0.2 Cu 0.1 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 0.50 Fe 0.2 Mn 0.2 Cu 0.1 O2、Na3Fe 1.95 Mn 0.05 The weight ratios of (SO4)3F, gas-phase generated carbon fiber, and pitch were 96%, 2%, 1%, and 1%, respectively;

[0130] (2) Sintering under 10Pa vacuum conditions, sintering temperature 350℃, sintering time 12h;

[0131] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0132] Example 4

[0133] Prepare the very low residual alkali core as follows:

[0134] (1) The layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3Mn 1 / 3 O2 was added to glycerol at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0135] (2) The solid-liquid mixture is filtered to obtain a wet powder of the inner core having a solvent content of 0.5%.

[0136] The composite layered oxide cathode material was prepared as follows:

[0137] (1) Na3Fe with a D50 of 50 nm 1.95 Mn 0.05 (SO4)3F particles, carbon nanotubes and polyvinylidene fluoride are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned core wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2、Na3Fe 1.95 Mn 0.05 The weight ratios of (SO4)3F, carbon nanotubes, and polyvinylidene fluoride are 95%, 2%, 1%, and 2%, respectively;

[0138] (2) In 10 2 Drying under vacuum conditions of Pa, drying temperature 150℃, drying time 4h;

[0139] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0140] Example 5

[0141] Prepare the very low residual alkali core as follows:

[0142] (1) The layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added to glycerol at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0143] (2) The solid-liquid mixture is filtered to obtain a wet powder of the inner core having a solvent content of 0.5%.

[0144] The composite layered oxide cathode material was prepared as follows:

[0145] (1) Na3Fe with a D50 of 50 nm 1.95 Mn0.05 (SO4)3F particles and asphalt are dispersed in glycerol to obtain a slurry. Then, the above-mentioned core wet powder is placed in the slurry, and after sufficient stirring, a product composed of a core of extremely low residual alkali NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 and a precursor of a composite coating layer covering the surface of the core is obtained. The weight ratios of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na3Fe 1.95 Mn 0.05 (SO4)3F and asphalt are 9%, 3% and 2% respectively;

[0146] (2) Sintering is carried out under a vacuum condition of 10 2 Pa, the sintering temperature is 400 °C, and the sintering time is 3 h;

[0147] (3) An ultra-low residual alkali and air-stable cathode material for sodium-ion batteries is obtained.

[0148] Example 6

[0149] The extremely low residual alkali core is prepared by the following method:

[0150] (1) Layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is added to glycerol at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0151] (2) The solid-liquid mixture is filtered to obtain a core wet powder with a solvent content of 0.5%.

[0152] The composite layered oxide cathode material is prepared by the following method:

[0153] (1) NaNi with a D50 of 50 nm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 particles, carbon nanotubes and asphalt are dispersed in glycerol to obtain a slurry. Then, the above-mentioned core wet powder is placed in the slurry, and after sufficient stirring, a product composed of a core of extremely low residual alkali NaNi 1 / 3 Fe 1 / 3Mn 1 / 3 O2 and a precursor of a composite coating layer covering the surface of the core is obtained. The weight ratios of NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3Mn 1 / 3 O2, carbon nanotubes and asphalt are 97%, 1% and 2% respectively;

[0154] (2) In 10 2 Sintering under vacuum conditions, sintering temperature 400℃, sintering time 3h;

[0155] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0156] Example 7

[0157] (1) The layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was added into a mixture of glycerol and acetone (90% and 10% by weight, respectively) at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0158] (2) The solid-liquid mixture is heated and filtered to obtain a core wet powder having a solvent content of 0.5%.

[0159] The composite layered oxide cathode material was prepared as follows:

[0160] (1) Na3Fe with a D50 of 50 nm 1.92 Mn 0.08 (SO4)3F particles, carbon nanotubes and asphalt are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned core wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 1 / 3Fe 1 / 3 Mn 1 / 3 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2、Na3Fe 1.92 Mn 0.08 The weight ratios of (SO4)3F, carbon nanotubes, and pitch are 95%, 2%, 1%, and 2%, respectively;

[0161] (2) In 10 2 Sintering under vacuum conditions, sintering temperature 400℃, sintering time 3h;

[0162] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0163] Example 8

[0164] (1) The layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was added into a mixture of glycerol and ether (90% and 10% by weight, respectively) at a weight ratio of 1:10 and stirred for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0165] (2) The solid-liquid mixture is heated and filtered to obtain a core wet powder having a solvent content of 0.5%.

[0166] The composite layered oxide cathode material was prepared as follows:

[0167] (1) Na3Fe with a D50 of 50 nm 1.95 Mn 0.05 (SO4)3F particles, carbon nanotubes and asphalt are dispersed in propylene glycol to obtain a slurry, and then the above-mentioned core wet powder is placed in the slurry and stirred thoroughly to obtain a NaNi 1 / 3Fe 1 / 3 Mn 1 / 3 O2 is the product of the core and the composite coating layer precursor coated on the core surface, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2、Na3Fe 1.95 Mn 0.05 The weight ratios of (SO4)3F, carbon nanotubes, and pitch are 95%, 2%, 1%, and 2%, respectively;

[0168] (2) In 10 2 Sintering under vacuum conditions, sintering temperature 400℃, sintering time 3h;

[0169] (3) Obtaining ultra-low residual alkali and air-stable sodium-ion battery positive electrode materials.

[0170] Comparative Example 1

[0171] The positive electrode material was prepared according to the method of Example 1, except that the layered oxide NaNi with a D50 of 6 μm was used without the above-mentioned special solvent treatment. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2.

[0172] Comparative Example 2

[0173] The positive electrode material was prepared according to the method of Example 1, except that a layered oxide NaNi with a D50 of 3 μm was used without any special solvent treatment. 0.30 Fe 0.33 Mn 0.25 Cu 0.12 O2.

[0174] Comparative Example 3

[0175] Prepare the positive electrode material according to the method of Example 1, except that the layered oxide NaNi with a D50 of 8 μm without special solvent treatment is used. 0.50 Fe 0.2 Mn 0.2 Cu 0.1 O2.

[0176] Comparative Example 4

[0177] Prepare an extremely low residual alkali positive electrode material by the following method:

[0178] (1) Add the layered oxide NaNi with a D50 of 6 μm 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 to glycerol at a weight ratio of 1:10 and stir for 60 min to dissolve and remove the residual alkali (sodium carbonate and sodium hydroxide) on the surface of the layered oxide;

[0179] (2) Filter the solid-liquid mixture to obtain a wet powder with a solvent content of 0.5%;

[0180] (3) Sinter the wet powder under a vacuum condition of 10 2 Pa, the sintering temperature is 400 °C, and the sintering time is 3 h; and

[0181] (4) Obtain a sodium-ion battery positive electrode material with extremely low residual alkali.

[0182] Test Example 1

[0183] Use a scanning electron microscope (JSM-IT500 of JEOL, Japan) to test the photos of the positive electrode material before being coated with the composite coating and the positive electrode material after being coated in Example 1, respectively. Then, use a transmission electron microscope TEM for further observation, and it can be seen that the core-shell structure of the prepared positive electrode material is as Figure 4 shown.

[0184] Test Example 2

[0185] According to the principle of acid-base titration, test the free sodium content of the positive electrode materials in Examples 1-7 and Comparative Examples 1-4 above by the following methods respectively:

[0186] 1. Take 10 g of each sodium-ion battery layered oxide positive electrode material and place it in a 250 ml beaker. Add 90 g of glycerol or its aqueous solution, place a polytetrafluoroethylene magnetic stirrer of model A820, and stir in an environment of 25 °C to 100 °C for 10 min at a rotation speed of 550 r / min to fully dissolve the residual alkali on the surface of the layered oxide positive electrode material in the solvent;

[0187] 2. Pour all of the above solution into a 200 ml centrifuge tube, centrifuge at a high speed of 10000 r / min for 5 min, take the supernatant, and filter it through a filter paper to obtain the test solution 1;

[0188] 3. In a vacuum environment of less than or equal to -95 kPa, heat the test solution 1 to 80 °C - 300 °C to bake off the solvent. During the vacuum baking process, repeatedly evacuate the air. The vacuum baking time is 0.5 - 4 h to obtain residual alkali solids such as sodium carbonate and sodium hydroxide;

[0189] 4. Dissolve the above residual alkali solids such as sodium carbonate and sodium hydroxide in a 250 ml conical flask, add pure water to make up the volume to 100 ml, place a polytetrafluoroethylene magnetic stirrer of model A820, stir at room temperature for 10 min at a speed of 550 r / min to fully dissolve the residual alkali such as sodium carbonate and sodium hydroxide in pure water to obtain the test solution 2;

[0190] 5. Use a pipette to transfer 10 ml of the test solution 2, and perform a test on an automatic potentiometric titrator. The solvent for acid-base neutralization titration is hydrochloric acid with a concentration of 0.05 mol / L to obtain the contents of sodium hydroxide and sodium carbonate.

[0191] The results are listed in Tables 1 and 2 below.

[0192] Test Example 3

[0193] Respectively use the materials obtained in the above Examples 1 - 3 and Comparative Examples 1 - 3 as the positive electrode materials. Respectively dissolve the positive electrode materials, conductive agents (carbon black) and binders (polyvinylidene fluoride) in Examples 1 - 3 and Comparative Examples 1 - 3 in a solvent according to a mass percentage of 85:10:5, control the solid content at 60%, coat it on an aluminum foil current collector, dry it in vacuum, and roll and punch to obtain positive electrode sheets.

[0194] Use hard carbon as the negative electrode material. Dissolve the negative electrode material, conductive agent (graphene) and binder (polyvinylidene fluoride) in a solvent according to a mass percentage of 85:10:5, control the solid content of the obtained negative electrode slurry to be above 50%, coat it on an aluminum foil current collector, dry it in vacuum, and roll and punch to obtain negative electrode sheets.

[0195] Stack the above positive and negative electrode sheets and the separator, encapsulate them in an aluminum plastic film, and then inject an electrolyte of sodium hexafluorophosphate NaPF6 (0.8 mol / L) / ethylene carbonate EC + dimethyl carbonate DMC + ethyl methyl carbonate EMC (v / v = 1:1:1) to obtain a 2 Ah soft-pack battery after formation and grading.

[0196] Perform a cycle test on the above sodium-ion soft-pack battery at an ambient temperature of 45 °C, with a voltage range of 1.5 - 4.0 V, and 1C charge / 1C discharge. After 50 cycles, obtain the capacity retention rate. The results are listed in Table 1 below.Figure 3 The capacity retention rate of the sodium-ion soft-pack batteries prepared from the positive electrode materials in Example 3 and the comparative examples is also shown as varying with the number of cycles.

[0197] The above-mentioned sodium-ion soft-pack batteries were stored at 100% SOC for 7 days at an ambient temperature of 55°C, and the volume change of the batteries before and after storage was tested by the water displacement method to obtain the gas generation rate of different batteries during high-temperature storage.

[0198] Test Example 4

[0199] The capacity ratio η (i.e., rate performance) of the soft-pack batteries prepared by the method of Test Example 3 using the positive electrode materials of Examples 1-7 and Comparative Examples 1-4 respectively was tested according to the following method:

[0200] 1. At an ambient temperature of 25°C, constant current charging was carried out at a current of 0.33C until 4.0V, and then constant voltage charging was carried out until the charging current was 0.05C. At this time, the soft-pack battery reached a fully charged state;

[0201] 2. Then, constant current discharge was carried out at 0.33C until 1.5V to obtain the 0.33C discharge capacity C1;

[0202] 3. The battery was charged to full charge according to the charging method in step 1;

[0203] 4. Then, constant current discharge was carried out at 1C until 1.5V to obtain the 1C discharge capacity C2;

[0204] 5. The 3C / 0.33C capacity ratio η of the soft-pack battery was calculated. The capacity ratio η is the manifestation of the rate performance, and the calculation method of η is as follows:

[0205] η = C2 / C1 test

[0206] The results are listed in Table 2 below.

[0207] Table 1

[0208] Item Free sodium content / % Capacity retention rate / % after 50 cycles of 1C / 1C at 45°C Gas generation rate / % after storing for 7 days at 55°C with 100% SOC Example 1 0.11% 99.5% 0.01% Example 2 0.12% 99.6% 0.03% Example 3 0.23% 98.8% 0.23% Comparative Example 1 3.02% 93.3% 7.86% Comparative Example 2 1.57% 93.8% 6.18% Comparative Example 3 4.28% 92.0% 8.43%

[0209] As can be seen from the examples and comparative examples in Table 1 above, the method of the present invention can significantly reduce the residual alkali content in the layered oxide positive electrode material, which is very beneficial to the processing of the positive electrode material and no gel phenomenon will occur. At the same time, with the reduction of the residual alkali content, the gas generation caused by the decomposition of sodium carbonate at high voltage is greatly reduced, and the cycle stability is also greatly improved.

[0210] Table 2

[0211]

[0212] As can be seen from Examples 4, 5, 6, 7 and Comparative Example 4 in Table 2 above, the composite coating layer can well inhibit the side reactions between the surface of the cathode material and the electrolyte, greatly improving the cycle performance and gas generation characteristics of the battery; the composite coating layer also plays a role in quickly conducting ions and electrons, improving the rate performance of the battery.

[0213] If the carbonized pitch with good ion and electron conduction in the composite coating layer is replaced with the insulating substance polyvinylidene fluoride (PVDF), the rate performance of the battery will decrease.

[0214] If the conductive agent in the composite coating layer is directly removed, it will also lead to a decrease in the rate performance of the battery.

[0215] If Na3Fe2(SO4)3F in the composite coating layer is replaced with a layered oxide having the same components as the core, due to the lower stability of the layered oxide than Na3Fe2(SO4)3F, the cycle performance and gas generation characteristics of the battery will decrease.

[0216] As can be seen from Examples 1-8 and Comparative Examples 1-4 in Tables 1 and 2 above, although the composite coating layer can effectively improve the cycle performance and gas generation characteristics of the battery, if the residual alkali in the layered oxide core is fully removed (i.e., not a core with low residual alkali), the residual alkali on the surface of the layered oxide cathode material will decompose and generate gas during cycling or high-temperature storage, resulting in poor cycle performance and gas generation characteristics.

[0217] Therefore, the low-residual-alkali layered oxide cathode material core and the composite coating layer shell in this application are both indispensable. The lack of any one of them will result in poor performance of the obtained composite cathode material. The composite coating layer on the surface of the layered oxide cathode material can well inhibit the direct contact between the surface of the layered oxide cathode material and the electrolyte, reduce side reactions, greatly reduce gas generation during storage, and improve cycle stability.

[0218] Especially in sodium-ion batteries with layered oxides having a relatively high nickel content, the effect is more significant.

[0219] The composite coating layers in this application are all simple and easy to obtain, without precious metals, and have low costs. The obtained cathode materials have great cost advantages.

[0220] It can be understood that the above embodiments are only exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A cathode material for a sodium-ion battery, characterized in that It includes a core treated with a residual alkali dissolving agent and a shell coating the surface of the core, wherein the core contains a layered oxide, the shell is a composite coating layer, and the residual alkali dissolving agent contains an organic solvent; The composite coating layer contains nanometer particles of a fluorinated sulfate compound, a first conductive agent, and a first binder after carbonization; The fluorinated sulfate compound is represented by Na a Fe b N c (SO4) d F e where a≥1.5, b≥0, c≥0, d≥0, e≥0; Wherein N is at least one selected from Ti, Zr, Sr, Al, and Mn, and the values of a, b, c, d, and e satisfy the charge balance of the chemical formula.

2. The cathode material for a sodium-ion battery according to claim 1, characterized in that, The residual alkali contains at least one of sodium carbonate and sodium hydroxide, the residual alkali dissolving agent is an organic solvent, and the organic solvent contains one or more of an alcohol solvent, a ketone solvent, and an ether solvent.

3. The cathode material for a sodium-ion battery according to claim 1, characterized in that, Calculated as free sodium, the residual alkali accounts for 0.10 - 0.30% of the total weight of the core.

4. The cathode material for a sodium-ion battery according to claim 2, characterized in that, The organic solvent contains glycerol, or a mixed solvent of glycerol and other alcohol solvents, ketone solvents, or ether solvents, wherein in the mixed solvent, the weight ratio of glycerol is 70% - 100%.

5. The cathode material for a sodium-ion battery according to claim 1, characterized in that, In the positive electrode material, the nanometer particles of the fluorinated sulfate compound and the first conductive agent are fixed by the first binder after carbonization and are dispersed on the surface of the core in a completely coating manner.

6. The cathode material for a sodium-ion battery according to claim 5, wherein The D50 of the nanometer particles of the fluorinated sulfate compound is 1 - 1000 nm.

7. The cathode material for a sodium-ion battery according to any one of claims 1-6, characterized in that The layered oxide is represented by Na x Ni y Fe z Mn i M 1-y-z-i O2, where 0.5 < x < 1.5, 0 < y ≤ 0.8, 0 < z ≤ 0.33, 0 < i ≤ 0.5, and the values of x, y, z, and i satisfy the charge balance of the chemical formula; Wherein M is selected from one or more elements of Li, B, Mg, Cu, Zn, Co, Ca, Ba, Sr, Al, B, Cr, Zr, Y, Sr, Ti, Sn, V, Mo, W, Ru, Nb, Sb, and Nb.

8. The cathode material for a sodium-ion battery according to any one of claims 1-6, characterized in that, The D50 of the nanometer particles of the fluorinated sulfate compound is 1 - 1000 nm; The first binder is one or more of asphalt, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose, and styrene-butadiene rubber; The first conductive agent is at least one of carbon nanotubes, vapor-grown carbon fibers, graphene, and carbon black; In the positive electrode material of the sodium-ion battery, by weight, the content of the layered oxide is 85% - 99.9%, the content of the fluorinated sulfate compound is 0.1% - 5%, the content of the first conductive agent is 0.1% - 5%, and the content of the first binder is 0.1% - 5%.

9. The cathode material for a sodium-ion battery according to any one of claims 1-6, characterized in that, The D50 of the layered oxide particles is 3 - 12 μm; the first binder is asphalt.

10. A method for preparing a cathode material for a sodium-ion battery, characterized in that The method includes the following steps: Treating a core containing a layered oxide with a residual alkali dissolving agent containing an organic solvent, Coating the treated core with a composite coating layer to obtain a coated product, and Sintering the coated product to obtain the positive electrode material of the sodium-ion battery.

11. The method for preparing a cathode material for a sodium-ion battery according to claim 10, wherein The step of treating a core containing a layered oxide with a residual alkali dissolving agent containing an organic solvent includes dispersing the layered oxide particles in an organic solvent to dissolve and remove the residual alkali on the surface of the layered oxide particles; and filtering the obtained solid-liquid mixture to obtain a treated core with a solvent content not greater than 1% by weight.

12. The method according to claim 11, wherein The step of coating the treated core with a composite coating layer includes: Disperse the fluorosulfate compound nanoparticles, the first conductive agent, and the first binder in an organic solvent to obtain a composite coating slurry, and then mix the treated core with the composite coating slurry to obtain a coated product composed of the core and a composite coating precursor coated on the surface of the core.

13. The method according to claim 11, characterized in that, The step of coating the treated core with the composite coating includes: The step of sintering the coated product includes sintering the coated product at a pressure of 10 to 10 3 Pa and a sintering temperature of 300 to 450 °C for 1 to 12 h, thereby obtaining a cathode material for a sodium-ion battery with low residual alkali. Based on free sodium, the residual alkali accounts for 0.10 - 0.30 wt% of the total weight of the core.

14. The method according to claim 12, characterized in that, The D50 of the fluorosulfate compound nanoparticles is 1 - 1000 nm; The first binder is one or more of asphalt, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyacrylonitrile, sodium carboxymethyl cellulose, and styrene-butadiene rubber; The first conductive agent is at least one of carbon nanotubes, vapor-grown carbon fibers, graphene, and carbon black; In the positive electrode material of the sodium-ion battery, by weight, the content of the layered oxide is 85% - 99.9%, the content of the fluorosulfate compound is 0.1% - 5%, the content of the first conductive agent is 0.1% - 5%, and the content of the first binder is 0.1% - 5%.

15. The method according to claim 12, wherein The D50 of the layered oxide particles is 3 - 12 μm; the first binder is asphalt.

16. A positive electrode sheet of a sodium-ion battery, characterized in that Comprising: A positive electrode current collector, A positive electrode film disposed on at least one surface of the positive electrode current collector, the positive electrode film including a positive electrode active material, a second binder, and a second conductive agent, and the positive electrode active material being the positive electrode material of the sodium-ion battery according to any one of claims 1 to 6.

17. A sodium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, characterized in that The positive electrode sheet is the positive electrode sheet of the sodium-ion battery according to claim 16.

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