Modified layered oxide material, preparation method thereof, positive electrode sheet and sodium battery

Abstract

The present invention relates to a modified layered oxide material comprising a C@fluoride@sodium ion layered oxide, wherein the fluoride is a multinary metal fluoride containing an alkali metal. The C in the C@fluoride@sodium ion layered oxide is formed by high-temperature sintering of a cubic phenolic resin. The present invention also discloses a method for preparing the modified layered oxide material, a positive electrode sheet, and a sodium ion battery prepared therefrom. The modified layered oxide material of the present invention can improve the specific capacity, cycle stability, and rate performance of sodium ion batteries.

Description

Technical Field

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

[0002] Sodium-ion batteries (SIBs), due to their abundant sodium resources, low cost, and similar physical and chemical properties to lithium-ion batteries, hold promise for addressing future energy storage needs. However, due to the higher molecular weight of sodium and the larger radius of sodium ions compared to lithium ions, their energy density is lower than that of lithium-ion batteries, significantly hindering their commercialization. Developing high-performance electrode materials is a key challenge for the application of SIBs.

[0003] Among various cathode materials for sodium-ion batteries, O3-phase layered oxides have attracted widespread attention due to their advantages of providing sufficient sodium in the full cell, high electrochemical activity, high theoretical specific capacity, and ease of synthesis. However, problems such as poor capacity utilization and cycling performance limit the practical application of O3-phase layered oxides. Doping with heterogeneous elements has been a frequently used method, but it does not completely solve these problems. Therefore, improving the specific capacity and cycling stability of O3-type layered cathode materials for sodium-ion batteries has become a key issue in sodium-ion battery-related technologies. Summary of the Invention

[0004] To this end, the technical problem to be solved by the present invention is to provide a modified layered oxide material, which is applied to sodium ion batteries to improve the specific capacity, cycle stability and rate performance of sodium ion batteries.

[0005] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0006] A first aspect of the present invention provides a method for preparing a modified layered oxide material, comprising the following steps:

[0007] providing one or more fluorides, wherein the fluorides are multinary metal fluorides containing an alkali metal;

[0008] Dispersing 10-260 parts by mass of the fluoride in a solvent, then adding 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenol compound, and 10-250 parts by mass of an aldehyde compound to the solvent, and mixing them uniformly to obtain a first mixed solution;

[0009] placing the first mixed solution in a boiling water bath for polymerization reaction to form a second mixed solution of the phenolic resin containing the fluoride;

[0010] wet-milling the second mixed solution at a rotation speed of 100 to 3000 rpm for 2 to 15 hours to allow the fluoride to completely adhere to the phenolic resin, and then drying the mixture at a temperature of 40 to 120° C. to obtain a phenolic resin powder coated with fluoride;

[0011] adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder, and ball-milling and mixing to obtain a mixture;

[0012] The mixture is placed in an inert environment and solid-state sintered at a temperature of 500-900° C. for 10-48 hours to obtain C@the fluoride@the sodium ion layered oxide, i.e., a modified layered oxide material; wherein @ indicates being coated.

[0013] In one embodiment of the present invention, the step of providing one or more fluorides includes: dissolving one or more metal salts in a solvent, adding an aqueous solution of alkali metal fluoride to the resulting solution, stirring the reaction for 0.2-6 hours and then filtering, and then drying at a temperature of 40-120°C for 2-16 hours to obtain the alkali metal-containing multinary metal fluoride.

[0014] Furthermore, in one embodiment of the present invention, the molar ratio of the metal salt to the alkali metal fluoride is 0.01-2:0.01-2.

[0015] Furthermore, in one embodiment of the present invention, in the step of dissolving one or more metal salts in a solvent, the solvent is one or more of ethanol, water, acetone, methanol, toluene, pentane, ethyl acetate and diethyl ether.

[0016] Preferably, the solvent is an ethanol-water solution, and the volume ratio of ethanol to water is 0.01-50:0.01-50.

[0017] Furthermore, in one embodiment of the present invention, in the step of dissolving one or more metal salts in a solvent, the metal salt is selected from one of manganese acetate, manganese titanate, magnesium acetate, magnesium carbonate, magnesium nitrate, zinc acetate, zinc chloride, zinc carbonate, calcium acetate, calcium carbonate, calcium nitrate, ferrous acetate, ferric nitrate, ferrous oxalate, copper acetate, copper chloride, copper sulfate, copper nitrate, chromium acetate, chromium nitrate, chromium chloride, chromium carbonate, zirconium acetate, zirconium oxide, molybdenum acetate, molybdenum oxide, and molybdenum carbonate.

[0018] Furthermore, in one embodiment of the present invention, the alkali metal fluoride is selected from one of lithium fluoride, sodium fluoride and potassium fluoride.

[0019] In one embodiment of the present invention, in the step of dispersing 10-260 parts by mass of the fluoride in a solvent, then adding 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenol compound, and 10-250 parts by mass of an aldehyde compound to the solvent and mixing them uniformly to obtain a first mixed solution, the solvent is one or more of ethanol, water, acetone, methanol, toluene, pentane, ethyl acetate, and diethyl ether.

[0020] Preferably, the solvent is an ethanol-water solution, and the volume ratio of ethanol to water is 5-140:5-120.

[0021] Furthermore, in one embodiment of the present invention, in the step of dispersing 10-260 parts by mass of the fluoride in a solvent, then adding 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenolic compound and 10-250 parts by mass of an aldehyde compound to the solvent and mixing them uniformly to obtain a first mixed solution, the phenolic compound is selected from one or more of resorcinol, hydroquinone, phenol, pyrogallol and pyrogallol, preferably phenol.

[0022] Furthermore, in one embodiment of the present invention, 10-260 parts by mass of the fluoride is dispersed in a solvent, and then 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenolic compound and 10-250 parts by mass of an aldehyde compound are added to the solvent and mixed uniformly to obtain a first mixed solution. In the step, the aldehyde compound is selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, ivinal, isocyclic citral, citronellal, methylcitronellal, benzaldehyde, phenylacetaldehyde, phenylpropionaldehyde, cinnamaldehyde, lily's aldehyde, citral, citronellal, hydroxycitronellal and perillaldehyde, and is preferably formaldehyde.

[0023] In one embodiment of the present invention, in the step of adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder and mixing them uniformly by ball milling to obtain a mixture, the sodium ion layered oxide powder is a primary particle with a particle size D50 of 20-300 nm.

[0024] In one embodiment of the present invention, in the step of adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder and mixing them uniformly by ball milling to obtain a mixture, the mass ratio of the fluoride-coated phenolic resin powder to the sodium ion layered oxide powder is 1:9.5-12.5.

[0025] The second aspect of the present invention provides a modified layered oxide material, which includes C@fluoride@sodium ion layered oxide, wherein the fluoride is a multinary metal fluoride containing an alkali metal, and the sodium ion layered oxide is an O3 phase layered oxide.

[0026] In one embodiment of the present invention, the molecular formula of the multinary metal fluoride containing alkali metal is A x M y M' z F3, wherein 0<x, y, z≤1, M and M' are each selected from one of Mg, Zn, Mn, Ca, Fe, Cu, Ti, Cr, Zr or Mo; and A is an alkali metal element.

[0027] In one embodiment of the present invention, the molecular formula of the sodium ion layered oxide is NaNi a Fe b Mn c O2, where 0<a, b, c≤1, and a+b+c=1.

[0028] In one embodiment of the present invention, the C@fluoride@sodium ion layered oxide has a cubic structure.

[0029] In one embodiment of the present invention, the particle size D50 of C@fluoride in the C@fluoride@sodium ion layered oxide is 300-500 nm.

[0030] A third aspect of the present invention provides a positive electrode sheet, comprising the modified layered oxide material obtained by the above-mentioned preparation method or the above-mentioned modified layered oxide material.

[0031] A fourth aspect of the present invention provides a sodium ion battery comprising the above-mentioned positive electrode sheet.

[0032] The above technical solution of the present invention has the following advantages over the prior art:

[0033] The present invention provides a modified layered oxide material that can improve the specific capacity, cycle stability and rate performance of sodium ion batteries.

[0034] The present invention proposes a modified layered oxide material, C@fluoride@sodium ion layered oxide, with a C@fluoride core and a sodium ion layered oxide coating. The fluoride is soluble in ether electrolytes. During battery cycling, the core C@fluoride slowly releases alkali metal ions to replenish those removed by the positive electrode material, increasing capacity. Simultaneously, trace amounts of fluoride ions are released, moving with the electrolyte to the negative electrode surface to form a stable SEI membrane structure, enhancing the system's cyclic stability. Furthermore, the C in this modified layered oxide material is formed by calcining and carbonizing a cubic phenolic resin, which significantly increases the material's conductivity, thereby improving the battery's rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings, wherein

[0036] Figure 1 A of the present invention x M y M' z The structural formula of F3;

[0037] Figure 2 LiMg is the material of Example 1 0.4 Zn 0.1 Element distribution map of F3;

[0038] Figure 3 LiMg is the material of Example 1 0.4 Zn 0.1 X-ray diffraction pattern of F3;

[0039] Figure 4 For example 1 phenolic resin composite LiMg 0.4 Zn 0.1 Simplified diagram of the formation mechanism of F3 material;

[0040] Figure 5 For example 1 phenolic resin composite LiMg 0.4 Zn 0.1 Scanning electron microscope image of F3 material;

[0041] Figure 6 Example 1 material C@LiMg 0.4 Zn 0.1 Scanning electron microscope image of F3@NNFM;

[0042] Figure 7 Example 1 Material C@LiMg 0.4 Zn 0.1 X-ray diffraction pattern of F3@NNFM material. DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0044] It is contemplated that the claimed inventive compositions, mixtures, systems, methods, and processes include variations and adaptations developed using the information obtained from the embodiments described herein. Adaptations and / or variations of the compositions, mixtures, systems, methods, and processes described herein can be made by one of ordinary skill in the relevant art.

[0045] It should be understood that the order of steps or the order in which specific actions are performed is immaterial, as long as the present invention remains operable. Furthermore, two or more step actions may be performed simultaneously.

[0046] The present invention provides a method for preparing a modified layered oxide material, comprising the following steps:

[0047] providing one or more fluorides, wherein the fluorides are multinary metal fluorides containing an alkali metal;

[0048] Dissolving one or more metal salts in a solvent (ethanol-water solution with a volume ratio of ethanol to water of 0.01-50:0.01-50) at a molar ratio of the metal salt to the alkali metal fluoride of 0.01-2:0.01-2, adding the alkali metal fluoride aqueous solution to the resulting solution, stirring for 0.2-6 hours, filtering, and then drying at a temperature of 40-120° C. for 2-16 hours to obtain the alkali metal-containing multinary metal fluoride;

[0049] Dispersing 10-260 parts by mass of the fluoride in a solvent (an ethanol-water solution having a volume ratio of 5-140 ethanol to water: 5-120), then adding 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenol compound, and 10-250 parts by mass of an aldehyde compound to the solvent, and mixing them uniformly to obtain a first mixed solution;

[0050] placing the first mixed solution in a boiling water bath for polymerization reaction to form a second mixed solution of the phenolic resin containing the fluoride;

[0051] wet-milling the second mixed solution at a rotation speed of 100 to 3000 rpm for 2 to 15 hours to allow the fluoride to completely adhere to the phenolic resin, and then drying the mixture at a temperature of 40 to 120° C. to obtain a phenolic resin powder coated with fluoride;

[0052] adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder, and ball-milling and mixing to obtain a mixture;

[0053] The mixture is placed in an inert environment and solid-state sintered at a temperature of 500-900° C. for 10-48 hours to obtain C@the fluoride@the sodium ion layered oxide, i.e., a modified layered oxide material; wherein @ indicates being coated.

[0054] The preparation method of the modified layered oxide material of the present invention comprises the following steps: in an alkaline solution, phenolic compounds and aldehyde compounds are polymerized by heating in a boiling water bath to form a cubic phenolic resin; fluoride is added and mixed so that the fluoride adheres to the cubic phenolic resin to form fluoride-coated phenolic resin powder; finally, layered oxide powder is added, ball milled to form a coating layer on the surface of the fluoride-coated phenolic resin powder, and solid-state sintering is performed to carbonize the phenolic resin to form a cubic carbon structure, thereby forming a C@fluoride@sodium ion layered oxide material, i.e., a modified layered oxide material.

[0055] The metal salt is selected from one of manganese acetate, manganese titanate, magnesium acetate, magnesium carbonate, magnesium nitrate, zinc acetate, zinc chloride, zinc carbonate, calcium acetate, calcium carbonate, calcium nitrate, ferrous acetate, ferric nitrate, ferrous oxalate, copper acetate, copper chloride, copper sulfate, copper nitrate, chromium acetate, chromium nitrate, chromium chloride, chromium carbonate, zirconium acetate, zirconium oxide, molybdenum acetate, molybdenum oxide, and molybdenum carbonate;

[0056] The alkali metal fluoride is selected from one of lithium fluoride, sodium fluoride and potassium fluoride.

[0057] The phenol compound is selected from one or more of resorcinol, hydroquinone, phenol, pyrogallol, and pyrogallol, preferably phenol.

[0058] The aldehyde compound is selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, ivinal, isocyclic citral, citronellal, methylcitronellal, benzaldehyde, phenylacetaldehyde, phenylpropionaldehyde, cinnamaldehyde, lilyral, citral, citronellal, hydroxycitronellal, and perillaldehyde, preferably formaldehyde.

[0059] The mass concentration of the aldehyde compound is 10-37 wt %.

[0060] The dispersion can be carried out by powder dispersion means commonly used in the art, preferably ultrasonic dispersion.

[0061] After the wet ball milling, the method further includes washing with deionized water and ethanol.

[0062] The mass ratio of the fluoride-coated phenolic resin powder to the sodium ion layered oxide powder is 1:9.5-12.5.

[0063] The sodium ion layered oxide powder is a primary particle with a particle size D50 of 20-300 nm.

[0064] Further, the sodium ion layered oxide is an O3-phase layered oxide. The molecular formula of the O3-phase layered oxide is Na x TMO2, where 0.8 < x ≤ 1, and TM is selected from one or more elements such as Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Li, etc. Different doping elements may cause slight differences in the performance of the O3-phase layered oxide, but the cycle performance and capacity improvement are still the primary problems to be solved.

[0065] Further, the molecular formula of the sodium ion layered oxide is NaNi a Fe b Mn c O2, where 0 ≤ a, b, c ≤ 1, and a + b + c = 1. Preferably, the NaNi a Fe b Mn c O2 includes NaNiO2, NaFeO2, NaMnO2, NaNi 0.1 Fe 0.2 Mn 0.7 O2, NaNi 0.5 Fe 0.5 O2, NaNi 0.34 Fe 0.33 Mn 0.33 O2, NaNi 0.2 Fe 0.3 Mn 0.5 O2, or one or more of them.

[0066] The operation of ball milling and mixing uniformly can be obtained by conventional preparation means in the art, including one of dry ball milling or wet ball milling.

[0067] After the ball milling and mixing are uniform, it further includes washing with deionized water and ethanol.

[0068] The sodium ion layered oxide powder can be obtained by conventional preparation means in the art. Preferably, it can be prepared according to the following method:

[0069] Mix the precursor and sodium salt and perform solid-state sintering to obtain the O3-phase layered oxide cathode material;

[0070] [[ID=�5]]Where the precursor is selected from one or more of nickel oxide, nickel iron oxide, nickel iron manganese oxide, manganese oxide, iron oxide, manganese iron oxide, nickel manganese oxide, nickel hydroxide, iron hydroxide, manganese hydroxide, nickel iron hydroxide, nickel iron manganese hydroxide, and nickel manganese hydroxide;

[0071] The sodium salt is selected from sodium carbonate, sodium hydroxide, sodium oxide, sodium peroxide, sodium phosphate, sodium sulfate, sodium dihydrogen phosphate, sodium bisulfate, and sodium phenoxide;

[0072] The molar ratio of the precursor to the sodium salt is 0.01-1:0.01-1.25.

[0073] The solid-state sintering temperature is 700-1200°C, preferably 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, or any value between 700-1200°C; the heating rate is 0.01-10°C / min, preferably 0.01°C / min, 0.05°C / min, 0.1°C / min, 0.5°C / min, 1°C / min, 3°C / min, 5°C / min, 7°C / min, 10°C / min, or any value between 0.01-10°C / min; the holding time is 10-48h, preferably 10, 15, 20, 25, 30, 35, 45, or any value between 10-48h.

[0074] The present invention also provides a modified layered oxide material, which comprises C@fluoride@sodium ion layered oxide, wherein the fluoride is a multinary metal fluoride containing an alkali metal.

[0075] The modified layered oxide material C@fluoride@sodium ion layered oxide is a core-shell structure, with C@fluoride as the core and sodium ion layered oxide as the coating layer. The particle size D50 of the core C@fluoride is 300-500nm. The particle size of the core is too large (greater than 300nm), and the layered oxide content of the coating layer is relatively small, which affects the initial capacity and energy density of the battery. The particle size of the core is too small (less than 500nm). During the cycle, the alkali metal ions released by the dissolution of fluoride are relatively small, and the capacity improvement during the cycle is limited; and the content of the released fluoride ions is low, and a stable SEI film cannot be formed on the surface of the negative electrode, which does not improve the cycle stability of the system.

[0076] The modified layered oxide material C@fluoride@sodium ion layered oxide has a cubic structure, which can provide a larger contact area, thereby improving the conductivity of the material and thus improving the battery rate performance.

[0077] The present invention also provides a positive electrode plate comprising the modified layered oxide material, which can increase battery capacity and cycle stability, thereby significantly improving the electrochemical performance of sodium ion batteries.

[0078] In detail, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer provided on at least one side of the current collector. The positive electrode active material layer is obtained by coating the positive electrode slurry on the current collector, drying it, and cold pressing it. The positive electrode slurry includes a positive electrode material (modified layered oxide material), a conductive agent, a binder, and a solvent. Among them, the current collector can be selected as aluminum foil, the conductive agent and the binder each account for less than or equal to 5%, the conductive agent can be selected from carbon black, carbon nanotubes, graphene, etc., the binder can be selected from polyvinylidene chloride (PVDF), and the solvent can be selected from N-methylpyrrolidone (NMP).

[0079] Specifically, when preparing the positive electrode sheet, the raw materials to be prepared can be weighed first, and the positive electrode material (modified layered oxide material): conductive carbon: PVDF are mixed in a mass ratio of 90:5:5, and then dissolved in a certain amount of NMP. After stirring evenly, it is coated on the current collector, and then dried and cut into pieces to obtain the positive electrode sheet.

[0080] The positive electrode sheets provided in the embodiments of the present invention were prepared using the above-described method. To ensure control of a single variable for comparison and to avoid the influence of interfering factors on the experimental results, the scope of protection of the present invention is not limited by the above ratio ranges. The ratios of the positive electrode material, conductive agent, and binder can also be adjusted according to specific circumstances without affecting the performance of the modified layered oxide material provided by the present invention.

[0081] An embodiment of the present invention further provides a sodium ion battery comprising the aforementioned positive electrode sheet. Therefore, the sodium ion battery also has the advantage of excellent electrochemical performance. The present invention further provides a sodium ion battery comprising the aforementioned positive electrode sheet, or a positive electrode sheet prepared by the aforementioned preparation method.

[0082] The present invention has no particular limitation on the preparation method of the sodium ion battery, and any battery preparation method known to those skilled in the art can be used.

[0083] In detail, the sodium ion battery specifically includes a shell, a positive electrode sheet, a diaphragm, a negative electrode sheet and an electrolyte. Among them, the positive electrode sheet, the diaphragm and the negative electrode sheet are stacked and arranged, and a bare cell is formed by lamination or winding. The bare cell is placed in the shell and injected with electrolyte to obtain a battery. For example, a winding process can be used to prepare a bare cell. The diaphragm is first wound 5 / 6 turns, and then the positive electrode sheet and the negative electrode sheet are wound in turn, for a total of 8 turns. Finally, the positive electrode sheet is wound to ensure that the negative electrode sheet is completely wrapped in the positive electrode sheet. The finished winding core is welded with the pole ears and glued, and then it is sealed with aluminum-plastic film, baked in a vacuum oven for 40-120 hours, taken out, and the water content is tested (H2O<200ppm is required). Then, according to a certain injection coefficient and ratio, the liquid is injected, sealed, aged, formed and capacity tested to obtain a sodium ion battery.

[0084] The negative electrode sheet may include a current collector and a negative electrode active material layer. The current collector may be copper foil. The negative electrode active material layer is obtained by applying a negative electrode active slurry to the current collector, drying it, and cold pressing it. The negative electrode active slurry includes a negative electrode material, a conductive agent, a binder, a dispersant, and a solvent. The amount of the conductive agent and the binder is less than or equal to 10%. The negative electrode material may be soft carbon, hard carbon, or composite carbon. The conductive agent may be conductive carbon black, conductive graphite, vapor-grown carbon fiber, carbon nanotubes, etc. The binder may be styrene-butadiene rubber, the dispersant may be CMC, and the solvent may be N-methylpyrrolidone (NMP). For example, the mass ratio of negative electrode hard carbon material: conductive carbon: CMC / SBR may be 95:2.5:2.5. In addition, the electrolyte is obtained by dissolving 1M sodium hexafluorophosphate in a solvent with a volume ratio of EC:DEC = 1:1 + 5% FEC.

[0085] Specifically, when preparing the negative electrode sheet, the raw materials to be prepared can be weighed first, and the negative electrode hard carbon material: conductive carbon: CMC / SBR mass ratio is 95:2.5:2.5. Then, they are dissolved in a certain amount of NMP, stirred evenly, and coated on the current collector. After drying and cutting, the negative electrode sheet can be obtained.

[0086] In order to further understand the present invention, the modified layered oxide material provided by the present invention, its preparation method and application are described and introduced in detail in combination with specific examples and comparative examples. The protection scope of the present invention is not limited by the following examples.

[0087] Example 1

[0088] S1: Add a certain amount (molar ratio of 1:0.535) of precursor salt (nickel iron manganese hydroxide) and sodium carbonate into the reaction vessel, and mix them evenly with ball mill (speed: 600 rpm; time: 2.4 h); perform solid-state sintering on the mixture at a temperature of 980 ° C; a heating rate of 4.5 ° C / min; and a holding time of 10.5 h. 0.34 Fe 0.33 Mn 0.33 O2(NNFM) powder.

[0089] S2: Dissolve 6.4mmol of magnesium acetate and 1.6mmol of zinc acetate in a mixed solution containing 10ml of water and 10ml of ethanol. Then, add 40ml of an aqueous solution containing 16mmol of lithium fluoride dropwise and continue stirring. Stir for 1.5h and keep at room temperature for 24h. 0.4 Zn 0.1 F3 was collected by centrifugation, washed with water and ethanol to remove impurities, and finally dried at 60 ° C for 6 h to obtain LiMg 0.4 Zn 0.1F3 nanoparticles.

[0090] S3: 100mgLiMg 0.4 Zn 0.1 F3 nanoparticles were dispersed in a mixture of 20 ml of deionized water and 40 ml of ethanol by ultrasonication and stirring. Then, 600 mg of ammonia solution (28 wt%), 100 mg of resorcinol, and 100 mg of formaldehyde (37 wt%) were added to the solution in sequence. The mixture was ball-milled at room temperature for 12 hours and dried at 80°C to obtain composite LiMg. 0.4 Zn 0.1 F3 material.

[0091] S4: Take 100mg of composite LiMg 0.4 Zn 0.1 1 g of NNFM powder was added to the F3 material and ball milled at 500 rpm for 3.5 h to obtain NNFM-coated composite LiMg 0.4 Zn 0.1 F3 material was centrifuged and washed with deionized water and ethanol for several times. In an Ar atmosphere, the heating rate was 5℃ / min and sintered at 800℃ for 6h to obtain cubic structure C@LiMg 0.4 Zn 0.1 F3@NNFM materials.

[0092] When the current density is 0.1C, the above materials are used as positive electrode (90% active material LiMg 0.4 Zn 0.1 F3@NNFM, 5% conductive carbon superP, 5% binder PVDF), hard carbon material as the negative electrode (85% active material hard carbon, 10% conductive carbon superP, 5% binder with CMC), and a standard electrolyte of 1M sodium hexafluorophosphate dissolved in EC and THF (volume ratio 1:1) + 5% DENE solution were used to conduct experiments on soft-pack batteries.

[0093] Figure 3 Material LiMg 0.4 Zn 0.1 The XRD (X-ray diffraction) pattern of F3 shows that the material is composed of two phases, LiMgF3 and LiZnF3; Figure 4 For example 1 phenolic resin composite LiMg 0.4 Zn 0.1 A simplified diagram of the formation mechanism of F3 material, briefly describing the formation process of the composite material; Figure 5 For example 1 phenolic resin composite LiMg 0.4 Zn 0.1 Scanning electron microscopy (SEM) image of F3 material, the surface of the material is rough and angular; Figure 6 Example 1 material C@LiMg0.4 Zn 0.1 The SEM image of F3@NNFM shows that the surface of the material is smooth, indicating that the NNFM material coating effect is very good; Figure 7 Example 1 material C@LiMg 0.4 Zn 0.1 The X-ray diffraction (XRD) pattern of F3@NNFM material shows that its main peaks are consistent with the O3 phase standard card. The appearance of individual peaks and peak shifts are mainly due to LiMg 0.4 Zn 0.1 The presence of a small amount of F3 leads to

[0094] An initial specific capacity of 140.5 mAh / g was achieved in the voltage range of 2-4 V. After 50, 100, 500, and 1000 cycles, the discharge specific capacity of the material was 139.4, 130.2, 128.5, and 120.7 mAh / g, respectively. After 1000 cycles, the capacity retention rate was 85.9%, and the battery capacity and cycle performance were excellent.

[0095] Example 2

[0096] S1: Add a certain amount (molar ratio of 1:0.535) of precursor salt (nickel iron manganese hydroxide) and sodium carbonate into the reaction vessel, and mix them evenly with ball mill (speed: 600 rpm; time: 2.4 h); perform solid-state sintering on the mixture at a temperature of 980 ° C; a heating rate of 4.5 ° C / min; and a holding time of 10.5 h. 0.34 Fe 0.33 Mn 0.33 O2(NNFM) powder.

[0097] S2: Dissolve 6.4mmol of magnesium acetate and 1.6mmol of zinc acetate in a mixed solution containing 10ml of water and 10ml of ethanol. Then, add 40ml of an aqueous solution containing 16mmol of lithium fluoride dropwise and continue stirring. Stir for 1.5h and keep at room temperature for 24h. 0.4 Zn 0.1 F3 was collected by centrifugation, washed with water and ethanol to remove impurities, and finally dried at 60 ° C for 6 h to obtain LiMg 0.4 Zn 0.1 F3 nanoparticles.

[0098] S3: Take 100mgLiMg 0.4 Zn 0.1 F3 nanoparticles were added with 1 g of NNFM powder and ball milled at 500 rpm for 3.5 h to obtain NNFM-coated LiMg 0.4 Zn 0.1F3 nanoparticles were centrifuged and washed with deionized water and ethanol for several times. Under Ar atmosphere, the heating rate was 5℃ / min and sintered at 800℃ for 6h to obtain LiMg 0.4 Zn 0.1 F3@NNFM materials.

[0099] When the current density is 0.1C, the above materials are used as positive electrode (90% active material LiMg 0.4 Zn 0.1 F3@NNFM, 5% conductive carbon superP, 5% binder PVDF), hard carbon material as the negative electrode (85% active material hard carbon, 10% conductive carbon superP, 5% binder with CMC), and a standard electrolyte of 1M sodium hexafluorophosphate dissolved in EC and THF (volume ratio 1:1) + 5% DENE solution were used to conduct experiments on soft-pack batteries.

[0100] An initial specific capacity of 130.2 mAh / g was achieved in the voltage range of 2-4 V. After cycling for 50, 100, 500, and 1000 cycles, the discharge specific capacity of the material was found to be 128.4, 119.2, 112.8, and 109.4 mAh / g, respectively. The capacity retention rate after 1000 cycles was 84.02%.

[0101] Example 3

[0102] Compared with Example 1, the difference is that 6.4 mmol of calcium carbonate is used to replace magnesium acetate in step S2 to prepare LiCa 0.4 Zn 0.1 F3 nanoparticles, and finally C@LiCa 0.4 Zn 0.1 F3@NNFM materials.

[0103] Example 4

[0104] Compared with Example 1, the difference is that 1.6 mmol of ferrous acetate is used to replace zinc acetate in step S2 to prepare LiMg 0.4 Fe 0.1 F3 nanoparticles, and finally C@LiMg 0.4 Fe 0.1 F3@NNFM materials.

[0105] Example 5

[0106] Compared with Example 1, the difference is that in step S2, 1.6 mmol of chromium chloride is used to replace zinc acetate to prepare LiMg 0.4 Cr 0.1 F3 nanoparticles, and finally C@LiMg 0.4 Cr 0.1 F3@NNFM materials.

[0107] Example 6

[0108] Compared with Example 1, the difference is that 1.6 mmol of zirconium acetate is used to replace zinc acetate in step S2 to prepare LiMg 0.4 Zr 0.1 F3 nanoparticles, and finally C@LiMg 0.4 Zr 0.1 F3@NNFM materials.

[0109] Example 7

[0110] Compared with Example 1, the difference is that in step S2, 1.6 mmol manganese titanate is used to replace zinc acetate to prepare LiMg 0.4 Mn 0.1 F3 nanoparticles, and finally C@LiMg 0.4 Mn 0.1 F3@NNFM materials.

[0111] Example 8

[0112] Compared with Example 1, the difference is that 1.6 mmol of molybdenum oxide is used to replace zinc acetate in step S2 to prepare LiMg 0.4 Mo 0.1 F3 nanoparticles, and finally C@LiMg 0.4 Mo 0.1 F3@NNFM materials.

[0113] Comparative Example 1

[0114] Compared with Example 1, the difference is that there is no step S2-S4, and NaNi is directly obtained. 0.34 Fe 0.33 Mn 0.33 O2(NNFM) powder.

[0115] Comparative Example 2

[0116] Compared with Example 1, the difference is that only 6.4 mmol of magnesium acetate is used in step S2 to prepare LiMg 0.4 F3 nanoparticles, and finally C@LiMg 0.4 F3@NNFM materials.

[0117] Comparative Example 3

[0118] Compared with Example 1, the difference is that only 1.6 mmol zinc acetate is used in step S2 to prepare LiZn 0.1 F3 nanoparticles, and finally C@LiMg 0.4 F3@NNFM materials.

[0119] Performance testing method:

[0120] (1) Capacity, rate performance, and cycle performance tests: The battery was tested using a constant current charge and discharge mode with a discharge cutoff voltage of 2.0 V and a charge cutoff voltage of 4.0 V. The battery was tested at rates of 0.1C, 2C, and 10C, and the capacity was recorded. After 500 and 1000 cycles of charge and discharge at a rate of 1C, the capacity was recorded.

[0121] (2) First coulombic efficiency test method: Use constant current charge and discharge mode, with a discharge cut-off voltage of 2.0 V and a charge cut-off voltage of 4.0 V. Charge and discharge at a rate of 0.1C, and record the first charge and discharge capacity. First coulombic efficiency = first discharge capacity / first charge capacity * 100%.

[0122] (3) SEM test method: First stick a layer of conductive glue on the sample holder, sprinkle the evenly ground powder on the conductive glue, then use an ear suction ball to blow away the powder that is not adhered to the surface, and place it under a scanning electron microscope for observation.

[0123] (4) XRD test method: The prepared powder material was ground and then transferred to a glass slide stage, and then transferred to an X-ray diffractometer for scanning test. The scanning range was 10-80° and the scanning speed was 5° / min.

[0124] The obtained battery was subjected to the above electrochemical performance test, and the results are shown in Table 1.

[0125] Table 1 Main parameters and sodium ion battery performance of the embodiments and comparative examples

[0126]

[0127] As can be seen from the above table, the introduction of dual-phase alkali metal fluoride by the preparation method provided by the present invention can greatly improve the specific capacity, rate performance and cycle stability of the full battery. 0.4 Zn 0.1 F3@NNFM material, Example 1 uses a phenolic compound and an aldehyde compound to form a cubic polymer, which is used as a template to attach a dual-phase alkali metal fluoride LiMg 0.4 Zn 0.1 F3, forming C@LiMg with a cubic structure 0.4 Zn 0.1The presence of carbon in F3@NNFM material can improve the conductivity of the material, so the battery prepared by the modified layered oxide material of Example 1 shows better rate performance. From the comparison of Example 1, Example 2 and Comparative Example 1, it can be seen that compared with the unmodified NNFM material, the modified layered oxide material has improved capacity, rate performance and cycle stability. 0.4 F3 material modified layered oxide, two-phase composition A x M y M z The layered oxide modified by F3 material has better performance.

[0128] In summary, the modified layered oxide material prepared by the method provided by the present invention has excellent capacity utilization, rate performance and cycle stability.

[0129] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing a modified layered oxide material, characterized in that: The following steps are involved: providing one or more fluorides, wherein the fluorides are multinary metal fluorides containing an alkali metal; Dispersing 10-260 parts by mass of the fluoride in a solvent, then adding 20-800 parts by mass of an ammonia solution, 10-250 parts by mass of a phenol compound, and 10-250 parts by mass of an aldehyde compound to the solvent, and mixing them uniformly to obtain a first mixed solution; placing the first mixed solution in a boiling water bath for polymerization reaction to form a second mixed solution of the phenolic resin containing the fluoride; wet-milling the second mixed solution at a rotation speed of 100 to 3000 rpm for 2 to 15 hours to allow the fluoride to completely adhere to the phenolic resin, and then drying the mixture at a temperature of 40 to 120° C. to obtain a phenolic resin powder coated with fluoride; adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder, and ball-milling and mixing to obtain a mixture; The mixture is placed in an inert environment and solid-state sintered at a temperature of 500-900° C. for 10-48 hours to obtain C@the fluoride@the sodium ion layered oxide, i.e., a modified layered oxide material; wherein @ indicates being coated.

2. The method for preparing a modified layered oxide material according to claim 1, characterized in that: The step of providing multiple fluorides includes: first dissolving multiple metal salts in a solvent according to a molar ratio of metal salt to alkali metal fluoride of 0.01-2:0.01-2, then adding an alkali metal fluoride aqueous solution to the resulting solution, stirring the reaction for 0.2-6 hours and then filtering, and then drying at a temperature of 40-120° C. for 2-16 hours to obtain the alkali metal-containing multi-metal fluoride.

3. The method for preparing a modified layered oxide material according to claim 2, wherein: The metal salt is selected from one of manganese acetate, magnesium acetate, magnesium carbonate, magnesium nitrate, zinc acetate, zinc chloride, zinc carbonate, calcium acetate, calcium nitrate, ferrous acetate, ferric nitrate, ferrous oxalate, copper acetate, copper chloride, copper sulfate, copper nitrate, chromium acetate, chromium nitrate, chromium chloride, zirconium acetate, and molybdenum acetate; The alkali metal fluoride is selected from one of lithium fluoride, sodium fluoride and potassium fluoride.

4. The method for preparing a modified layered oxide material according to claim 1, wherein: In the step of dispersing 10-260 parts by mass of the fluoride in a solvent, the solvent is an ethanol aqueous solution, and the volume ratio of ethanol to water is 5-140:5-120; The phenolic compound is selected from one or more of resorcinol, hydroquinone, phenol, pyrogallol, and pyrogallol; The aldehyde compound is selected from one or more of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, ivinal, isocyclic citral, citronellal, methylcitronellal, benzaldehyde, phenylacetaldehyde, phenylpropionaldehyde, cinnamaldehyde, lilyral, citral, citronellal, hydroxycitronellal, and perillaldehyde.

5. The method for preparing a modified layered oxide material according to claim 1, wherein: In the step of adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder, the sodium ion layered oxide is a primary particle with a particle size D50 of 20-300 nm.

6. The method for preparing a modified layered oxide material according to claim 1, wherein: In the step of adding sodium ion layered oxide powder to the fluoride-coated phenolic resin powder, the mass ratio of the fluoride-coated phenolic resin powder to the sodium ion layered oxide powder is 1:9.5-12.

5.

7. A modified layered oxide material prepared by the method according to any one of claims 1 to 6, characterized in that: The modified layered oxide material includes C@fluoride@sodium ion layered oxide, wherein the fluoride is a multinary metal fluoride containing an alkali metal, and the sodium ion layered oxide is an O3 phase layered oxide; the modified layered oxide material C@fluoride@sodium ion layered oxide is a core-shell structure, with C@fluoride as the core and the sodium ion layered oxide as the coating layer.

8. The modified layered oxide material according to claim 7, characterized in that: The C@fluoride@sodium ion layered oxide has a cubic structure.

9. The modified layered oxide material according to claim 7, characterized in that: The molecular formula of the multinary metal fluoride containing alkali metal is A x M y M' z F3, Among them, 0<x, y, z≤1, M and M' are each selected from one of the elements Mg, Zn, Mn, Ca, Fe, Cu, Ti, Cr, Zr or Mo; A is an alkali metal element.

10. The modified layered oxide material according to claim 7, characterized in that: The molecular formula of the sodium ion layered oxide is NaNi a Fe b Mn c O2, where 0<a, b, c≤1, and a+b+c=1.

11. The modified layered oxide material according to claim 7, characterized in that: The particle size D50 of C@fluoride in the C@fluoride@sodium ion layered oxide is 300-500 nm.

12. A positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the current collector, wherein the positive electrode active material layer comprises a positive electrode material, a binder, and a conductive agent, characterized in that: The positive electrode material comprises the modified layered oxide material according to any one of claims 7 to 11.

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