High-capacity, low-residual sodium sodium-ion battery layered positive electrode material, preparation method therefor, and sodium-ion battery

Abstract

A high-capacity, low-residual sodium sodium-ion battery layered positive electrode material, the chemical formula of the sodium-ion battery layered positive electrode material being NaaM1bNiwFexMnyCuzM21-w-x-y-zO2. M1 comprises one or more of Ca, Li, or K, and M2 comprises one or more of Mg, Zn, Al, Zr, Ti, Nb, Mo, Y, Ta, W, Sr, Ba, B, or P, where 0.85≤a<0.98, 0<b≤0.05, 0.90≤a+b≤0.98, w≥0.1, x≥0.1, y≥0.1, z≥0, and 0.9≤w+x+y+z≤1.0.

Description

A high-capacity, low-residual-sodium sodium-ion battery layered positive electrode material, a preparation method thereof, and a sodium-ion battery

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202311803899.6, filed on December 25, 2023, entitled “A high-capacity, low-residual sodium layered positive electrode material for sodium ion batteries, a preparation method thereof, and a sodium ion battery,” the entire text of which is hereby incorporated by reference. Technical Field

[0003] The present application belongs to the technical field of sodium ion batteries, and in particular relates to a high-capacity, low-residual-sodium sodium ion battery layered positive electrode material, a preparation method thereof, and a sodium ion battery. Background Art

[0004] With the continuous expansion of the lithium-ion battery market in recent years, the demand for lithium resources has also continued to rise. However, due to the uneven geographical distribution of lithium resources, the price of lithium-ion batteries fluctuates greatly, making their application in some low-cost scenarios difficult. Therefore, developing a new energy storage system with abundant resources and low prices to replace lithium-ion batteries is a top priority in current battery development.

[0005] Sodium ions have an electrochemical deintercalation mechanism similar to that of lithium ions. Although sodium-ion batteries lack the energy density of lithium-ion batteries, their application in the small power market and future large-scale energy storage still holds great potential. The cathode, as the most critical component of the battery system, determines the electrochemical performance of sodium-ion batteries. Transition metal layered oxide cathodes offer the advantages of high energy density, high reversible capacity, and high operating potential. Their simple synthesis process allows for compatibility with high-nickel ternary material production lines in related technologies, making them considered the most promising sodium-ion cathode material for mass production.

[0006] However, the current layered positive electrode materials for sodium-ion batteries have problems such as high oxide impurity content or high residual sodium, which is not conducive to improving the capacity of sodium-ion batteries. In addition, high residual sodium will cause sodium-ion batteries to produce gas at high voltage, posing certain safety risks. Summary of the Invention

[0007] The present application provides a high-capacity, low-residual-sodium layered positive electrode material for a sodium ion battery, a preparation method thereof, and a sodium ion battery.

[0008] In the first aspect, a high-capacity, low-residual-sodium sodium-ion battery layered positive electrode material is provided, wherein the chemical formula of the sodium-ion battery layered positive electrode material is Na a M1 b Ni w Fe x Mny Cu z M2 1-w-x-y-z O2, wherein M1 is a first doping element including one or more of Ca, Li or K, M2 is a second doping element including one or more of Mg, Zn, Al, Zr, Ti, Nb, Mo, Y, Ta, W, Sr, Ba, B or P, 0.85≤a<0.98, 0<b≤0.05, and 0.90≤a+b≤0.98, w≥0.1, x≥0.1, y≥0.1, z≥0, 0.9≤w+x+y+z≤1.0.

[0009] Optionally, the sodium ion battery layered positive electrode material contains an oxide heterophase, the oxide heterophase includes one or more of NiO, CuO or ZnO, and the total mass of the oxide heterophase in the sodium ion battery layered positive electrode material does not exceed 2wt%.

[0010] Optionally, the mass percentage of the oxide impurity phase is obtained by XRD ray diffraction testing and refinement using jade software, wherein the scanning range of the XRD test is 10°≤2θ≤80°, and the scanning rate is about 5° / min.

[0011] Optionally, the residual sodium Na2CO3 on the surface of the sodium ion battery layered positive electrode material is not higher than 0.15wt%, and the residual NaOH is not higher than 0.10wt%.

[0012] Optionally, the test method for residual sodium on the surface includes: using deionized water and an organic solvent as residual alkali test solvents, adding an acid solution for acid-base neutralization, using a potentiometric titration method to test the residual Na2CO3 of the sample in deionized water, and testing the NaOH content in an organic solvent.

[0013] Optionally, the organic solvent includes one or more of methanol, ethanol, isopropanol, ethylene glycol, benzyl alcohol or glycerol; the acid used in the acid-base neutralization includes one or more of sulfuric acid, nitric acid, hydrochloric acid, acetic acid or oxalic acid.

[0014] In a second aspect, a method for preparing a high-capacity, low-residual-sodium sodium-ion battery layered positive electrode material is provided, comprising the following steps:

[0015] (1) mixing a salt solution containing Ni, Fe, and Mn or a salt solution containing Ni, Fe, Mn, and Cu in proportion to perform a coprecipitation reaction to prepare a nickel-iron-manganese ternary or nickel-iron-manganese-copper quaternary precursor material;

[0016] (2) The precursor material obtained in step (1) is mixed with a sodium source, a compound containing an M1 element, and a compound containing an M2 element, and the mixture is sintered. The mixture is cooled to room temperature and then crushed and sieved to obtain a layered positive electrode material for a sodium ion battery.

[0017] Optionally, the sodium source in step (2) includes one or more of Na2CO3, NaHCO3 or NaOH; the compound containing the M1 element includes but is not limited to one or more of Li2CO3, K2CO3, CaCO3 or CaO; the compound containing the M2 element includes one or more of MgCO3, MgO, ZnO, Al2O3, ZrO2, TiO2, Nb2O5, MoO3, Y2O3, Ta2O5, WO3, BaO, BaCO3, SrCO3, SrO, H3BO3, B2O3, H3PO4, Na3PO4 or NaH2PO4.

[0018] Optionally, the sintering in step (2) is a two-stage sintering, wherein the first stage sintering is carried out at about 450°C to 850°C, and the temperature is kept at about 3h to 8h, and then the temperature is raised to about 860°C to 1000°C for the second stage sintering, and the temperature is kept at about 10h to 15h; the heating rate during the sintering process is about 1°C / min to 10°C / min.

[0019] Optionally, the heating rate is about 3°C / min.

[0020] Optionally, the sintering in step (2) is carried out in a compressed air atmosphere, and the dew point of the compressed air is about -50°C to -25°C.

[0021] In a third aspect, a sodium ion battery is provided, wherein the positive electrode material in the sodium ion battery is the sodium ion battery layered positive electrode material or the sodium ion battery layered positive electrode material obtained by the preparation method.

[0022] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] FIG1 is a SEM image of the layered cathode material for a sodium ion battery corresponding to Example 1;

[0025] FIG2 is a SEM image of the layered cathode material for a sodium ion battery corresponding to Comparative Example 1;

[0026] FIG3 is an XRD pattern of the layered cathode material for a sodium ion battery corresponding to Comparative Example 1;

[0027] FIG4 is an XRD pattern of the layered cathode material for a sodium ion battery corresponding to Comparative Example 3;

[0028] FIG5 is an XRD pattern of the layered cathode material for sodium ion batteries corresponding to Example 1;

[0029] FIG6 is a comparison diagram of the first-cycle electrochemical curves of the button cells corresponding to Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0030] To facilitate understanding of the present application, the present application will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments of the specification, but the scope of protection of the present application is not limited to the following specific embodiments.

[0031] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this application.

[0032] Regarding the layered positive electrode materials for sodium-ion batteries in the related art, due to the low solubility of transition metal ions in sodium-based materials, when the sodium source is insufficient, the generated sodium-based positive electrode material will be accompanied by oxide impurities, and electrochemically active elements such as Ni and Cu will precipitate, which will affect the number of charge transfers during the charge and discharge process of the positive electrode material and reduce the reversible capacity of the material. At the same time, the oxides attached to the surface of the material will affect the conduction of ions / electrons in the material and affect the electrochemical performance. When the sodium source in the material is sufficient, although the transition metal ions can be fully retained in the bulk structure and the formation of oxide impurities can be suppressed, excess sodium will remain on the surface of the material to form residual alkaline substances such as sodium carbonate / sodium hydroxide, which are ionic compounds. The cations and anions are densely arranged in the lattice through ionic bonds and have no conductive ability. This will increase the interfacial resistance, affect the conduction of ions / electrons, and thus reduce the capacity, which is not conducive to the performance of the positive electrode material. The presence of residual alkali in the electrode can also cause defluorination of the PVDF (polyvinylidene fluoride) binder, leading to agglomeration of composite particles, which affects the adhesion of the coating and causes the slurry to gel. This makes the electrode susceptible to powdering and flaking after drying. Alkaline slurries can also corrode the aluminum current collector, affecting electron transmission and even causing gas generation at high voltages, posing a safety hazard.

[0033] Therefore, how to avoid the formation of oxide impurities and at the same time control the residual alkali content of the material at a low level is a difficult problem that needs to be solved in the industrialization process of high-performance sodium battery positive electrodes.

[0034] Based on the above technical problems, in the first aspect, some embodiments of the present application provide a sodium ion battery layered positive electrode material with high capacity and low residual sodium. The chemical formula of the sodium ion battery layered positive electrode material is Na a M1 b Ni w Fe x Mn y Cu z M2 1-w-x-y- z O2, wherein M1 is a first doping element including one or more of Ca, Li or K, M2 is a second doping element including one or more of Mg, Zn, Al, Zr, Ti, Nb, Mo, Y, Ta, W, Sr, Ba, B or P, 0.85≤a<0.98, 0<b≤0.05, and 0.90≤a+b≤0.98, w≥0.1, x≥0.1, y≥0.1, z≥0, 0.9≤w+x+y+z≤1.0.

[0035] In the sodium ion battery layered positive electrode material provided in the embodiment of the present application, by doping the sodium ion battery layered positive electrode material with an M1 element having a radius or chemical properties similar to that of a sodium ion, the M1 element occupies the sodium position during high-temperature sintering, and at the same time, the stoichiometry of the sodium element and the M1 doping element is regulated to satisfy 0.90≤a+b≤0.98. While improving the residual alkali content of the sodium ion battery layered positive electrode material, the material has a suitable sodium content. When doping with the M1 element having a radius or chemical properties similar to that of a sodium ion, there is no obvious oxide impurity phase, and the obtained sodium ion battery layered positive electrode material has the characteristics of low residual alkali and high capacity.

[0036] In some embodiments, the sodium ion battery layered positive electrode material contains an oxide heterophase, which includes one or more of NiO, CuO or ZnO, and the total mass of the oxide heterophase in the sodium ion battery layered positive electrode material does not exceed 2 wt%.

[0037] In some embodiments, the mass percentage of the oxide impurity phase is measured by XRD diffraction and refined using jade software, wherein the scanning range of the XRD test is 10°≤2θ≤80°, and the scanning rate is about 5° / min.

[0038] In some embodiments, the surface residual sodium Na2CO3 of the sodium ion battery layered positive electrode material is not higher than 0.15 wt%, and the NaOH is not higher than 0.10 wt%.

[0039] In some embodiments, the method for testing residual sodium on the surface includes: using deionized water and an organic solvent as residual alkali test solvents, adding an acid solution for acid-base neutralization, using a potentiometric titration method to test the residual Na2CO3 of the sample in deionized water, and testing the NaOH content in an organic solvent.

[0040] In some embodiments, the organic solvent includes one or more of methanol, ethanol, isopropanol, ethylene glycol, benzyl alcohol, or glycerol; the acid used in the acid-base neutralization includes one or more of sulfuric acid, nitric acid, hydrochloric acid, acetic acid, or oxalic acid.

[0041] In a second aspect, some embodiments of the present application further provide a method for preparing a high-capacity, low-residual-sodium layered positive electrode material for a sodium ion battery, comprising the following steps:

[0042] (1) mixing a salt solution containing Ni, Fe, and Mn or a salt solution containing Ni, Fe, Mn, and Cu in proportion to perform a coprecipitation reaction to prepare a nickel-iron-manganese ternary or nickel-iron-manganese-copper quaternary precursor material;

[0043] (2) The precursor material obtained in step (1) is mixed with a sodium source, a compound containing an M1 element, and a compound containing an M2 element, and the mixture is sintered. The mixture is cooled to room temperature and then crushed and sieved to obtain a layered positive electrode material for a sodium ion battery.

[0044] In some embodiments, the sodium source in step (2) includes one or more of Na2CO3, NaHCO3 or NaOH; the compound containing the M1 element includes but is not limited to one or more of Li2CO3, K2CO3, CaCO3 or CaO; the compound containing the M2 element includes one or more of MgCO3, MgO, ZnO, Al2O3, ZrO2, TiO2, Nb2O5, MoO3, Y2O3, Ta2O5, WO3, BaO, BaCO3, SrCO3, SrO, H3BO3, B2O3, H3PO4, Na3PO4 or NaH2PO4.

[0045] In some embodiments, the sintering in step (2) is a two-stage sintering, wherein the first stage sintering is performed at about 450°C to 850°C and kept warm for about 3h to 8h, and then the temperature is raised to about 860°C to 1000°C for the second stage sintering, and kept warm for about 10h to 15h; the heating rate during the sintering process is about 1°C / min to 10°C / min.

[0046] In some optional embodiments, the heating rate is about 3°C / min.

[0047] In some embodiments, the sintering in step (2) is carried out in a compressed air atmosphere, and the dew point of the compressed air is -50° C. to -25° C. Controlling the dew point can further prevent sodium ions from precipitating from the interlayers during the cooling process.

[0048] In a third aspect, some embodiments of the present application further provide a sodium ion battery, wherein the positive electrode material in the sodium ion battery is the sodium ion battery layered positive electrode material described in the first aspect or the sodium ion battery layered positive electrode material obtained by the preparation method described in the second aspect.

[0049] Compared with the related art, the beneficial effects of this application are:

[0050] (1) The present application simultaneously regulates the stoichiometry of sodium element and M1 doping element to satisfy 0.90≤a+b≤0.98. While improving the residual alkali of the sodium ion battery layered positive electrode material, the M1 element with a radius or chemical properties similar to that of the sodium ion is used for doping. After high-temperature calcination, the M1 element occupies the sodium layer, inhibiting the formation of inactive oxide impurities when the sodium source is insufficient. The obtained sodium ion battery layered positive electrode material does not have obvious oxide impurities and has the characteristics of low residual alkali and high capacity.

[0051] (2) The present application controls the feeding amount of raw materials and additives, and at the same time constrains the molar amount of sodium and doping element M1, so that the proportion of oxide impurities in the structure does not exceed 2wt%, the residual alkali Na2CO3 on the surface of the material is not higher than 0.15wt%, and NaOH is not higher than 0.10wt%, thereby obtaining a high-capacity, low-residual-sodium layered positive electrode material for sodium ion batteries;

[0052] (3) The present application adopts a two-step sintering process method. In the first stage of sintering, the precursor is fully pre-oxidized to remove moisture from the precursor and eliminate internal defects. The precursor after defect repair is sintered at a higher temperature in the second stage, and the grains are continuously fused to form an internally ordered phase structure, thereby avoiding the precipitation of oxides caused by local instability of the material. At the same time, the environmental dew point is controlled within a specific range throughout the material preparation process to prevent sodium carbonate and M1 element raw materials from absorbing environmental moisture and affecting the uniformity of the mixture to cause element segregation, and can effectively protect the positive electrode material to avoid the precipitation of interlayer sodium ions from the interlayer during the cooling process, resulting in an increase in the residual alkali of the material.

[0053] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0054] In the following examples, the oxide impurity ratio of the layered cathode material for sodium-ion batteries was determined by XRD diffraction analysis and refined using Jade software. The XRD scan range was 10° ≤ 2θ ≤ 80°, with a scan rate of approximately 5° / min. The unit cell parameter c was refined using TOPAS software, and the error values ​​Rp and Rwp of the fitted curves were both less than 5%.

[0055] In the following examples, the test method for residual sodium on the surface is as follows: the material is dissolved in deionized water and 99% ethanol solution, titrated with HCl solution, and the residual Na2CO3 of the sample is tested in deionized water, and the content of NaOH is tested in ethanol.

[0056] In the following embodiments, the assembly method and test conditions of the sodium ion battery are as follows: the positive electrode material, acetylene black and PVDF are mixed in a ratio of about 90:5:5, NMP is added for slurrying, and the sodium positive electrode sheet is made after vacuum drying at 80°C, which is assembled into a sodium button cell with a sodium sheet, a diaphragm and an electrolyte. The capacity test is carried out on a blue battery test system with a test voltage range of 2.0V to 4.2V and a test current density of 20mA / g.

[0057] Example 1

[0058] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.01wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.11wt%, and NaOH is about 0.09wt%.

[0059] The method for preparing the layered positive electrode material for sodium ion batteries of this embodiment comprises the following steps:

[0060] (1) Preparation of nickel-manganese-iron precursor: NiSO4, MnSO4, and FeSO4 are prepared into a mixed metal salt solution of about 1.0 mol / L according to a metal molar ratio of about 1:1:1, and then the prepared mixed metal salt solution, a precipitant NaOH solution, and a complexing agent NH3·H2O solution are added to a reactor in parallel, and the system pH is controlled between 8.5 and 9.5. The system is heated and stirred to perform a co-precipitation reaction. After the reaction is completed, the slurry is subjected to solid-liquid separation. After separation, the solid is washed with deionized water and dried in an oven to obtain a nickel-iron-manganese precursor;

[0061] (2) The nickel-iron-manganese precursor prepared in step (1), Na2CO3, and CaCO3 are dry-mixed in an element molar ratio of about 1.00:0.96:0.01. After mixing evenly, the mixture is heated to about 450°C in a compressed air atmosphere (the dew point of the compressed air is controlled at -45°C to -40°C) at a heating rate of about 5°C / min, sintered for about 6 hours, and then heated to about 900°C at a constant heating rate of about 3°C / min, sintered for about 12 hours, naturally cooled to room temperature, and passed through a 400-mesh sieve to obtain a sodium ion battery layered positive electrode material with a chemical formula of Na 0.96 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, its XRD pattern is shown in Figure 5, the material structure is a single O3 phase, and there is no oxide impurity phase as shown in the SEM picture in Figure 1.

[0062] Example 2

[0063] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.92 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.45wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.05wt%, and NaOH is about 0.04wt%.

[0064] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0065] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, and CaCO3 are dry mixed at an element molar ratio of about 1.00:0.92:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.92 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0066] Example 3

[0067] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.88 Ca 0.02 Ni 0.33 Fe 0.33 Mn 0.33O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.78wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.03wt%, and NaOH is about 0.02wt%.

[0068] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0069] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, and CaCO3 are dry mixed at an element molar ratio of about 1.00:0.88:0.02. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.88 Ca 0.02 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0070] Example 4

[0071] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 Li 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.11wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.14wt%, and NaOH is about 0.08wt%.

[0072] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0073] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, and Li2CO3 are dry mixed at an element molar ratio of about 1.00:0.96:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 Li 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0074] Example 5

[0075] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 K 0.01 Ni 0.33 Fe 0.33 Mn 0.33O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.09wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.13wt%, and NaOH is about 0.06wt%.

[0076] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0077] The preparation method of the precursor is consistent with that of Example 1. Nickel iron manganese precursor, Na2CO3, and K2CO3 are dry mixed at an element molar ratio of about 1.00:0.96:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 K 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0078] Example 6

[0079] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 Li 0.01 K 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 0.92wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.13wt%, and NaOH is about 0.06wt%.

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

[0081] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, Li2CO3, and K2CO3 are dry mixed at an element molar ratio of about 1.00:0.96:0.01:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 Li 0.01 K 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0082] Example 7

[0083] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 Ca 0.01 Ni 0.40 Fe 0.20 Mn 0.40O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.89wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.14wt%, and NaOH is about 0.09wt%.

[0084] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0085] (1) Preparation of nickel-manganese iron precursor: NiSO4, MnSO4, and FeSO4 are prepared into a mixed metal salt solution of about 1.0 mol / L according to a metal molar ratio of about 4:2:4. The prepared mixed metal salt solution, a precipitant NaOH solution, and a complexing agent NH3·H2O solution are then added to a reactor in parallel. The pH of the system is controlled between 8.5 and 9.5. The mixture is heated and stirred to perform a co-precipitation reaction. After the reaction is completed, the slurry is subjected to solid-liquid separation. After separation, the solid is washed with deionized water and dried in an oven to obtain a nickel-iron-manganese precursor.

[0086] (2) The nickel iron manganese precursor prepared in step (1), Na2CO 33 , CaCO3 according to the element molar ratio of about 1.00:0.96:0.01 were dry mixed, and after dry mixing, in a compressed air atmosphere (dew point controlled at -30 ℃ ~ -25 ℃), at a heating rate of about 5 ℃ / min, heated to about 450 ℃, sintered for about 6 hours, and then heated to about 900 ℃ at a heating rate of about 3 ℃ / min, sintered for about 12 hours, cooled naturally to room temperature, and passed through a 400 mesh sieve to obtain a sodium ion battery layered positive electrode material with the chemical formula of Na 0.96 Ca 0.01 Ni 0.40 Fe 0.20 Mn 0.40 O2.

[0087] Example 8

[0088] The sodium ion battery layered cathode material of this embodiment has the chemical formula Na 0.96 Ca 0.01 Ni 0.25 Fe 0.30 Mn 0.25 Cu 0.20 O2, the oxide impurities are NiO and CuO, and the impurities account for about 1.56wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.07wt%, and NaOH is about 0.05wt%.

[0089] The preparation method of the positive electrode material of this embodiment includes the following steps:

[0090] NiSO4, MnSO4, FeSO4, and CuSO4 were prepared into a solution of about 1.0 mol / L at a metal molar ratio of about 5:6:5:4. The remaining steps were consistent with the preparation method of the precursor in Example 1. Nickel-iron-manganese-copper precursor, Na2CO3, and CaCO3 were dry-mixed at an element molar ratio of about 1.00:0.96:0.01. The preparation method of the positive electrode material was consistent with that in Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material was Na 0.96 Ca 0.01 Ni 0.25 Fe 0.30 Mn 0.25 Cu 0.20 O2.

[0091] Comparative Example 1

[0092] The sodium ion battery layered cathode material of this comparative example has the chemical formula Na 0.96 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, accounting for approximately 3.07wt% of the sodium-ion battery layered cathode material. The residual sodium Na2CO3 was approximately 0.10wt%, and NaOH was approximately 0.07wt%. The XRD pattern of the sodium-ion battery layered cathode material in this comparative example is shown in Figure 3. In addition to the structural diffraction peak of O3, the material structure is also accompanied by a distinct NiO impurity phase peak. The SEM image is shown in Figure 2.

[0093] The preparation method of the positive electrode material of this comparative example comprises the following steps:

[0094] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor and Na2CO3 are dry mixed at an element molar ratio of about 1.00:0.96. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0095] Comparative Example 2

[0096] The sodium ion battery layered cathode material of this comparative example has the chemical formula Na 0.96 Ni 0.25 Fe 0.30 Mn 0.25 Cu 0.20 O2, the oxide impurities are NiO and CuO, and the impurities account for about 3.99wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.13wt%, and NaOH is about 0.09wt%.

[0097] The preparation method of the positive electrode material of this comparative example comprises the following steps:

[0098] The preparation method of the precursor is consistent with that of Example 8. The nickel iron manganese copper precursor and Na2CO3 are dry mixed at an element molar ratio of about 1.00:0.96. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 Ni 0.25 Fe 0.30 Mn 0.25 Cu 0.20 O2.

[0099] Comparative Example 3

[0100] The sodium ion battery layered cathode material of this comparative example has the chemical formula Na 0.96 Ni 0.31 Fe 0.31 Mn 0.31 Zn 0.07 O2, the oxide impurities are NiO and ZnO, accounting for approximately 3.98wt% of the layered cathode material for sodium-ion batteries. The residual sodium Na2CO3 content is approximately 0.14wt%, and the NaOH content is approximately 0.12wt%. The XRD pattern of the layered cathode material for sodium-ion batteries in this comparative example is shown in Figure 4. In addition to the structural diffraction peaks for O3, the material structure also exhibits distinct ZnO impurity peaks.

[0101] The preparation method of the positive electrode material of this comparative example comprises the following steps:

[0102] A sulfate or nitrate solution containing Ni, Mn, Fe, and Zn is prepared in a corresponding molar ratio of about 1.0 mol / L. The remaining steps are consistent with the preparation method of the precursor in Example 1. The nickel iron manganese zinc precursor and Na2CO3 are dry-mixed at an element molar ratio of about 1.00:0.96. The preparation method of the positive electrode material is consistent with Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.96 Ni 0.31 Fe 0.31 Mn 0.31 Zn 0.07 O2.

[0103] Comparative Example 4

[0104] The sodium ion battery layered cathode material of this comparative example has the chemical formula Na 0.88 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 3.95wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.04wt%, and NaOH is about 0.03wt%.

[0105] The preparation method of the positive electrode material of this comparative example comprises the following steps:

[0106] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, and CaCO3 are dry mixed at an element molar ratio of about 1.00:0.88:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 0.88 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0107] Comparative Example 5

[0108] The sodium ion battery layered cathode material of this comparative example has the chemical formula Na 1.00 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2, the oxide impurity phase is NiO, and the impurity phase accounts for about 1.43wt% in the layered positive electrode material of sodium ion batteries. The tested residual sodium Na2CO3 is about 0.19wt%, and NaOH is about 0.12wt%.

[0109] The preparation method of the positive electrode material of this comparative example comprises the following steps:

[0110] The preparation method of the precursor is consistent with that of Example 1. The nickel iron manganese precursor, Na2CO3, and CaCO3 are dry mixed at an element molar ratio of about 1.00:1.00:0.01. The preparation method of the positive electrode material is consistent with that of Example 1. The chemical formula of the obtained sodium ion battery layered positive electrode material is Na 1.00 Ca 0.01 Ni 0.33 Fe 0.33 Mn 0.33 O2.

[0111] Table 1 Performance test data of sodium ion battery layered positive electrode materials of Examples 1 to 8 and Comparative Examples 1 to 5

[0112] As can be seen from the table above, after sintering of Comparative Example 1, the proportion of NiO in the material is about 3.07%, and the discharge specific capacity at 2.0V to 4.2V is about 168.5mAh / g. After doping with about 0.01mol of Ca (Example 1), the proportion of NiO in the material is reduced to about 1.01%, and the discharge specific capacity is increased to about 176.8mAh / g. This is because in the O3 phase structure of the sodium-deficient phase, elements with similar chemical properties or similar ionic radii can be doped into the octahedral sites occupied by sodium ions to ensure the stability of the structure, and the transition metal is constrained in the layered structure to provide the oxidation / reduction charge required in the charge and discharge process, thereby obtaining a high-capacity and low-residual-alkali sodium ion battery layered positive electrode material. The decrease in the unit cell parameter c indicates that the Ca element is successfully incorporated into the Na layer, reducing the electrostatic repulsion of the adjacent oxygen layer. Comparative Examples 2 and 3 show that even if Cu and Zn in the transition metal are selected as doping elements for replacement, the material still cannot achieve a high specific capacity. As can be seen from Examples 2 to 8, in different sodium combinations and different ratios of metal elements Ca, Li and K, controlling 0.90≤a+b≤0.98, the doped samples significantly reduced the proportion of oxide impurities in the material, and obtained high-capacity sodium ion battery layered positive electrode materials. As can be seen from Comparative Example 4, when the chemical formula Na a M1 b Ni w Fe x Mn y Cu z M2 1-w-x-y-z In O2, a+b is less than 0.9, the number of ions occupied by the sodium layer is too small, and the structural stability cannot be maintained, resulting in the dissolution of transition metals, and the proportion of inactive oxides is high, which affects the capacity. In Comparative Example 5, when Ca is doped in a material that is not lacking in sodium, that is, a+b>0.98, Ca cannot be incorporated into the sodium layer or the Na layer is occupied, causing Na ions to escape to the surface to form Na2CO3 / NaOH, and the residual alkali of the material is too high, thereby affecting the specific capacity. In summary, under the corresponding process conditions, sodium-doping is performed on the sodium-deficient O3 phase material, satisfying 0.90≤a+b≤0.98, the oxide impurity phase of the material accounts for ≤2wt%, and Na2CO3≤0.15wt%, NaOH≤0.10wt%, the material can exhibit a high discharge specific capacity.

[0113] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0114] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A layered cathode material for a sodium-ion battery with high capacity and low residual sodium. The chemical formula of the layered cathode material for the sodium-ion battery is Na a M1 b Ni w Fe x Mn y Cu z M2 1-w-x-y-z O2, where M1 is the first doping element, including one or more of Ca, Li or K; M2 is the second doping element, including one or more of Mg, Zn, Al, Zr, Ti, Nb, Mo, Y, Ta, W, Sr, Ba, B or P; 0.85 ≤ a < 0.98, 0 < b ≤ 0.05, and 0.90 ≤ a + b ≤ 0.98, w ≥ 0.1, x ≥ 0.1, y ≥ 0.1, z ≥ 0, 0.9 ≤ w + x + y + z ≤ 1.

0.

2. The layered cathode material for sodium ion battery according to claim 1, wherein, The sodium-ion battery layered cathode material contains an oxide impurity phase, which includes one or more of NiO, CuO or ZnO, and the total mass percentage of the oxide impurity phase in the sodium-ion battery layered cathode material does not exceed 2 wt%.

3. The layered cathode material for sodium ion battery according to claim 2, wherein, The mass percentage of the oxide impurity phase is obtained by testing through XRD (X-ray diffraction) method and refined using jade software. Among them, the scanning range of the XRD method test is 10° ≤ 2θ ≤ 80°, and the scanning rate is about 5° / min.

4. The layered cathode material for a sodium-ion battery according to any one of claims 1 to 3, wherein, The residual sodium Na2CO3 on the surface of the sodium-ion battery layered cathode material is not higher than 0.15 wt%, and NaOH is not higher than 0.10 wt%.

5. A preparation method of the sodium-ion battery layered cathode material according to any one of claims 1 to 4, comprising the following steps: (1) Mix salt solutions containing Ni, Fe, Mn or salt solutions containing Ni, Fe, Mn, Cu in proportion for coprecipitation reaction to prepare a nickel-iron-manganese ternary or nickel-iron-manganese-copper quaternary precursor material; (2) Mix the precursor material obtained in step (1) with a sodium source, a compound containing element M1, and a compound containing element M2 and perform sintering to obtain the sodium-ion battery layered cathode material.

6. The method according to claim 5, wherein, In step (2), the sodium source includes one or more of Na2CO3, NaHCO3 or NaOH; the compound containing element M1 includes one or more of Li2CO3, K2CO3, CaCO3 or CaO; the compound containing element M2 includes one or more of MgCO3, MgO, ZnO, Al2O3, ZrO2, TiO2, Nb2O5, MoO3, Y2O3, Ta2O5, WO3, BaO, BaCO3, SrCO3, SrO, H3BO3, B2O3, H3PO4, Na3PO4 or NaH2PO4.

7. The method according to claim 5 or 6, wherein In step (2), the sintering is two-stage sintering. First, perform the first-stage sintering at 450°C to 850°C for about 3h to 8h, then raise the temperature to about 860°C to 1000°C for the second-stage sintering and keep it warm for about 10h to 15h; the heating rate during the sintering process is about 1°C / min to 10°C / min.

8. The method according to any one of claims 5 to 7, wherein In step (2), the sintering is carried out in compressed air, and the dew point of the compressed air is about -50°C to -25°C.

9. A sodium-ion battery, wherein the positive electrode material in the sodium-ion battery is the sodium-ion battery layered positive electrode material described in any one of claims 1 to 4 or the sodium-ion battery layered positive electrode material obtained by the preparation method described in any one of claims 5 to 8.

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