High entropy doped O3 phase layered oxide and preparation method thereof, sodium ion battery positive electrode material and battery

Abstract

The invention discloses a high entropy doped O3 phase layered oxide and a preparation method thereof, a sodium ion battery positive electrode material and a battery, wherein the chemical formula of the high entropy doped O3 phase layered oxide is Na x A y M z O2, wherein Na represents sodium, A is selected from iron, nickel and manganese; M represents a doping element, and M is selected from five or more metal elements different from sodium and A in the third to fifth periods of the periodic table, 0.9≤x≤1, 0.8≤y<1, 0<z≤0.2, y+z=1; by doping five or more metal elements at low contents in the iron-nickel-manganese-based layered oxide lattice (high entropy doping), the obtained high entropy doped O3 phase layered oxide exhibits excellent environmental stability and water resistance, and when it is used as a positive electrode material for sodium ion batteries, it exhibits optimization of cycle capacity and rate performance.

Description

Technical Field

[0001] The invention belongs to the field of new materials and sodium ion batteries, and in particular relates to a high entropy doped O3 phase layered oxide and a preparation method thereof, a sodium ion battery positive electrode material and a battery. Background Art

[0002] Sodium-ion batteries (SIBs) are considered to be the most promising large-scale energy storage systems to replace lithium-ion batteries (LIBs). Their main advantages are the abundant natural resources of sodium, excellent safety performance, and similar chemical properties to commercial lithium-ion batteries (LIBs).

[0003] In the long-term research on sodium-ion batteries, a large number of electrode materials have been proposed and used as positive electrode materials (such as transition metal oxides, Prussian blue and polyanion materials, etc.), which show excellent electrochemical performance when paired with metallic sodium. However, for practical applications, the unsatisfactory initial Coulomb efficiency of sodium batteries, the insufficient recyclable sodium content and the poor industrial preparation feasibility of positive electrode materials still hinder the commercial application of sodium-ion batteries. Among various types of positive electrode materials, layered transition metal oxides Na x TMO2 (TM is transition metal) has high reversible capacity and energy density up to 500Wh kg -1 and good cycle stability have attracted widespread attention. O3 phase manganese-based layered structure oxide has Ni 2+ / 3+ / 4+ The high working potential and high capacity of Mn are inherent advantages. More importantly, compared with the sodium-deficient P2-type compounds, this type of compound has a higher sodium content, which can provide more cyclable sodium and high initial Coulombic efficiency, which plays a pivotal role in practical sodium-ion full battery systems. First, Mn 3+ The Jahn-Teller effect and multiple phase transitions during sodium removal / intercalation, such as from O3 to O′3, P3, P′3, and P3″ phases, have an adverse effect on the cycling performance. To eliminate these obstacles, element doping / substitution has been demonstrated to be an effective method to alleviate such adverse effects and ultimately improve the electrochemical performance. For example, the O3-Na[Li 0.05 (Ni 0.25 Fe 0.25 Mn 0.5 ) 0.95]O2 is synthesized by a co-precipitation method, and the O3 phase has a high reversible capacity and good cycle life. At the same time, previous studies have shown that Ni and Co are common elements in sodium-rich positive electrode materials, which can provide considerable capacity and are conducive to the formation of layered oxides; Li, Fe, Co, Cu, Ti, Zn, Zr, Sb and Mg are common doping elements in positive electrode materials. Among them, the synergistic effect of Ti and Cu can significantly improve the environmental and structural stability of the positive electrode; Fe can improve the cycle stability of the positive electrode material. Secondly, the poor stability of the O3 phase in the air also increases the difficulty of synthesis, and even makes the material impossible to achieve practical application. In order to solve the problem of air stability, the Obrova team reported P2-Na 2 / 3 Ni 1 / 6 Cu 1 / 6 Mn 2 / 3 The O2 cathode is doped with Cu to improve the air stability of the cathode. Therefore, the O3 phase cathode material needs to achieve a reasonable balance between stability and electrochemical performance.

[0004] Single element doping can indeed improve the electrochemical or physical properties of O3 phase sodium ion battery cathode materials, but this improvement is limited to a single aspect and cannot achieve simultaneous improvement of electrochemical performance and air / environmental stability. This requires an entropy stabilization strategy that utilizes the synergistic effect of multiple elements to enhance the electrochemical and physical properties of cathode materials. In addition, the synthesis process using the coprecipitation synthesis method is relatively complicated, and the cost of synthesizing cathode materials is high, so it is necessary to explore simple and efficient synthesis methods. Summary of the invention

[0005] The present invention aims at the technical problem that the air / environmental stability of the O3 phase layered oxide positive electrode material of the sodium ion battery is poor, and provides a technical solution by doping five or more metal elements (high entropy doping) in a low content in the iron-nickel-manganese-based layered oxide lattice.

[0006] The first aspect of the present invention provides a high entropy doped O3 phase layered oxide, the chemical formula of the high entropy doped O3 phase layered oxide is Na x A y M z O2, wherein Na represents sodium element, A is selected from three elements: iron (Fe), nickel (Ni), and manganese (Mn); M represents a doping element, and M is selected from at least five metal elements different from A in the third to fifth periods in the periodic table, 0.9≤x≤1, 0.8≤y<1, 0<z≤0.2, y+z=1.

[0007] In some embodiments, the doping element M is selected from five or more elements of cobalt (Co), copper (Cu), titanium (Ti), magnesium (Mg), zinc (Zn), calcium (Ca), vanadium (Ti), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tin (Sn), antimony (Sb), and aluminum (Al).

[0008] In some embodiments, the doping elements M include: at least 1 to 3 metal elements selected from the fifth period, and at least 2 to 4 metal elements selected from the third period and / or the fourth period.

[0009] In some embodiments, the metal elements of the fifth period are selected from zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tin (Sn), and antimony (Sb); the metal elements of the third period are selected from magnesium (Mg) and aluminum (Al); the metal elements of the fourth period are selected from calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), cobalt (Co), copper (Cu), and zinc (Zn).

[0010] In some embodiments, the index value of each doping element in the chemical formula of the high entropy doped O3 phase layered oxide is ≤0.05.

[0011] In some embodiments, the chemical formula of the high entropy doped O3 phase layered oxide is represented by Na x (Mn α Fe β Niγ)(M 1a M 2b M 3c M 4d M 5e M 6f )O2, y=α+β+γ, z=a+b+c+d+e+f, wherein M1, M2, M3, M4, M5, M6 represent different metal elements respectively; 0.1≤α≤0.5, 0.1≤β≤0.4, 0.1≤γ≤0.3, 0<a≤0.05, 0<b≤0.05, 0<c≤0.05, 0<d≤0.05, 0<e≤0.05, 0≤f≤0.05; preferably, 0<a≤0.04, 0<b≤ 0.04, 0<c≤0.04, 0<d≤0.04, 0<e≤0.04, 0≤f≤0.04; more preferably, 0<a≤0.03, 0<b≤0.03, 0<c≤0.03, 0<d≤0.03, 0<e≤0.03, 0≤f≤0.03; even more preferably, 0<a≤0.02, 0<b≤0.02, 0<c≤0.02, 0<d≤0.02, 0<e≤0.02, 0≤f≤0.02.

[0012] In some embodiments, the doping element M includes: at least two of titanium (Ti), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), and magnesium (Mg); and / or, at least one element of tin (Sn), antimony (Sb), niobium (Nb), molybdenum (Mo), and zirconium (Zr).

[0013] In some embodiments, the XRD diffraction pattern of the high entropy doped O3 phase layered oxide includes strong diffraction peaks (003) and (104), and weak diffraction peaks (006), (101), and (012) relative to the strong diffraction peaks.

[0014] The second aspect of the present invention provides a method for preparing the above-mentioned high entropy doped O3 phase layered oxide, the steps comprising:

[0015] According to the chemical formula of the high-entropy doped O3 phase layered oxide, sodium salt and oxide of A in corresponding molar ratios, as well as oxide powder of the doping element M are weighed and mixed to obtain a mixed powder; the mixed powder is pressed to obtain a pressed block; and the block is sintered.

[0016] In some implementations, the sintering process includes: a heating and heat preservation section, wherein the heating temperature of the heating and heat preservation section is between 500 and 600° C., and the heat preservation time is between 1 and 12 hours.

[0017] In some embodiments, the sintering process includes at least two heating and insulation sections, wherein the heating temperature of the first heating and insulation section is between 500 and 600°C, and the insulation time is between 1 and 12 hours, and the heating temperature of the second heating and insulation section is between 700°C and 1100°C.

[0018] In some embodiments, the sodium salt is selected from one or more of sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), sodium acetate (CH3COONa), sodium oxalate (Na2C2O4), sodium citrate (C6H5Na3O7), sodium nitrate (NaNO3), and sodium hydroxide (NaOH).

[0019] In some implementations, the above-mentioned mixing process includes ball milling mixing, in which the mass ratio of balls to materials in the ball milling mixing is (5-20):1, the dispersant is one or more of ethanol, acetone, N-methylpyrrolidone (NMP), isopropyl alcohol (IPA) or water, the ball milling speed is 300 to 600 r / min, and the ball milling time is 3 to 24 h.

[0020] In some implementations, in the above-mentioned pressing process, the steps more specifically include: loading the mixed powder into a mold and pressing it under pressure to form it; preferably, the pressing pressure is 5 to 30 MPa.

[0021] In some implementations, in the sintering process, the sintering temperature is between 500 and 1100° C., the heating rate is between 3 and 20° C. / min, and the sintering time is between 1 and 36 hours.

[0022] The third aspect of the present invention provides a sodium ion battery positive electrode material, which includes: the high entropy doped O3 phase layered oxide as described above; or the high entropy doped O3 phase layered oxide obtained by the above preparation method.

[0023] A fourth aspect of the present invention provides a sodium ion battery, characterized in that it comprises the above-mentioned sodium ion battery positive electrode material.

[0024] The fifth aspect of the present invention is an electrical device, characterized in that it comprises the above-mentioned sodium ion battery. The electrical device includes automobiles, electric vehicles, energy storage power stations, electronic appliances, etc.

[0025] Compared with the prior art, the present invention provides a novel high-entropy doped O3 phase layered oxide and a preparation method thereof. Compared with the traditional co-precipitation method, the preparation method (high-temperature solid-phase sintering method) has a simple process, is easy to industrialize and scale up production, and reduces the cost of the product. The prepared high-entropy doped O3 phase layered oxide exhibits excellent environmental stability and water resistance. When it is used as a positive electrode material for a sodium ion battery, it exhibits optimized cycle capacity and rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 1 is the XRD spectrum of the high entropy doped O3 phase layered oxide and the comparative sample in Example 2 of the present invention.

[0027] Figure 2 1 and 2 are SEM images and element distribution diagrams of the high entropy doped O3 phase layered oxide in Example 2 of the present invention.

[0028] Figure 3 These are the electrochemical performance test results of the high entropy doped O3 phase layered oxide and the control sample in Example 2 of the present invention as the positive electrode material of a sodium ion battery; wherein (a) is the cycle performance test at a 0.1C rate, (b) is the performance test at a 0.1 to 10C rate, (c) is the cycle performance test at a 1C rate, and (d) is the cycle performance test at a 5C rate.

[0029] Figure 4 The structural characterization and electrochemical performance test results of the high entropy doped O3 phase layered oxide and the control sample as the positive electrode material of the sodium ion battery after immersion in water in Example 2 of the present invention; wherein (a) is the XRD diffraction result of the HE-doping O3 phase after immersion in water for 12 hours and in air for 7 days, and (b) is the electrochemical performance of the doped O3 phase after immersion in water for 12 hours.

[0030] Figure 5 The high entropy doped O3 phase layered oxide Na1Mn in Example 3 of the present invention 0.4 Fe 0.3 Ni 0.2 Ti 0.02 Cu 0.02 Sn 0.02 Sb 0.02 Zn 0.02 O2 and comparison samples with different doping element contents Na1Mn 0.4 Fe 0.3 Ni 0.1 Ti 0.04 Cu 0.04 Sn 0.04 Sb 0.04 Zn 0.04 O2, as a positive electrode material for sodium ion batteries, structural characterization and electrochemical performance test results; (a) is the XRD diffraction result of HE-doping O3 phase with different doping contents; the electrochemical performance tests of HE-doping O3 with different doping contents mainly include (b) 0.1C small rate test, (c) 5C long cycle test and (d) 0.1C-10C rate performance test.

[0031] Figure 6 The structural characterization and electrochemical performance test results of the high entropy doped O3 phase layered oxide with different Mn contents in Example 4 of the present invention; wherein (a) is the XRD diffraction result of HE-doping O3 phase with different Mn contents, and (b) is the electrochemical performance test result of HE-doping O3 phase with different Mn contents.

[0032] Figure 7 The structural characterization and electrochemical performance test results of the high-entropy doped O3 phase layered oxides of six elements in Example 5 of the present invention and their comparative samples; (a) is the XRD diffraction result, and (b) is the electrochemical performance test result.

[0033] Figure 8 The structural characterization and electrochemical performance test results of the high entropy doped O3 phase layered oxide sintered at 500°C and the comparative sample in Example 6 of the present invention; (a) is the XRD diffraction result, and (b) is the electrochemical performance test result. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described below by specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combination step, or other methods and steps can be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and does not limit the order of arrangement of each method or limit the scope of implementation of the present invention. The change or adjustment of the relative relationship thereof can also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0035] The sources of the raw materials and instruments used in the examples are not particularly limited and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0036] The preparation method of the sodium ion battery positive electrode sheet recorded in the present invention comprises the following steps: 1) mixing the sodium ion battery positive electrode material (in the present invention, a high entropy doped O3 phase layered oxide) with a conductive agent (Super P) and a binder (PVDF) in a mass ratio of 7:2:1 and grinding for 10 minutes, then adding an appropriate amount of N-methylpyrrolidone (NMP) and grinding for another 20 minutes to prepare a mixed slurry; 2) coating the obtained mixed slurry on an aluminum foil disc with a diameter of 12 mm, with a loading amount of 1.4 mg / cm 2 , then pre-dry the coated electrode sheet at 40°C for 0.5h to 5h, and then dry it in a vacuum oven at 80°C for 24h.

[0037] The same method is used to replace the high entropy doped O3 phase layered oxide with other layered oxides (see the specific examples for specific types) to obtain a comparative positive electrode sheet.

[0038] The assembly method of the sodium ion battery recorded in the present invention comprises the following steps: using a metallic sodium sheet as a negative electrode and the positive electrode sheet prepared as above as a positive electrode, making a CR2032 button battery in an argon glove box, wherein a glass fiber diaphragm is used as a diaphragm, an electrolyte is used as a 1M NaClO4 solution, and the solvent is ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1, and contains 2% by volume of fluoroethylene carbonate (FEC).

[0039] The charge and discharge performance test of the sodium ion battery in the present invention is carried out on a Land BT2000 battery test system, the test temperature is room temperature, the test voltage range is 2.0 to 4.2V, and the rate range is 0.1 to 10C.

[0040] Example 1

[0041] This embodiment provides a high entropy doped O3 phase layered oxide Na xA y M z O2, A is selected from A is selected from three elements of iron (Fe), nickel (Ni), and manganese (Mn), M represents a doping element, and the M is selected from five or more metal elements in the third to fifth periods of the periodic table that are different from sodium (Na), iron (Fe), nickel (Ni), and manganese (Mn); in this embodiment, the M element is selected from five or more elements of cobalt (Co), copper (Cu), titanium (Ti), magnesium (Mg), zinc (Zn), calcium (Ca), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tin (Sn), antimony (Sb), and aluminum (Al), 0.9≤x≤1, 0.8≤y<1, 0<z≤0.2, y+z=1.

[0042] In one embodiment, the M element in the high entropy doped O3 phase layered oxide is selected from five or six metal elements, and its chemical formula is Na x (Mn α Fe β Niγ)(M 1a M 2b M 3c M 4d M 5e M 6f )O2, wherein M1, M2, M3, M4, M5, and M6 represent different doping elements, 0.1≤α≤0.5, 0.1≤β≤0.4, 0.1≤γ≤0.3, 0<a≤0.04, 0<b≤0.04, 0<c≤0.04, 0<d≤0.04, 0<e≤0.04, and 0≤f≤0.04.

[0043] In one embodiment, the doping elements M include at least 1 to 3 metal elements selected from the fifth period and at least 2 to 4 metal elements selected from the third period and / or the fourth period; by staggered matching between the sizes of metal atoms in different periods, an entropy-stable high-entropy doped O3 phase layered oxide is obtained, that is, by staggered matching between metal atoms in different periods, the structural stability of the high-entropy doped O3 phase layered compound can be increased; in a preferred embodiment, the metal elements of the fifth period are selected from zirconium (Zr), niobium (Nb), molybdenum (Mo), ruthenium (Ru), tin (Sn), and antimony (Sb); the metal elements of the third period are selected from magnesium (Mg) and aluminum (Al); the metal elements of the fourth period are selected from calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), cobalt (Co), copper (Cu), and zinc (Zn);

[0044] In a specific embodiment, the doping element M includes: at least two of titanium (Ti), vanadium (V), chromium (Cr), copper (Cu), zinc (Zn), and magnesium (Mg); and / or, at least one of tin (Sn), antimony (Sb), niobium (Nb), molybdenum (Mo), and zirconium (Zr).

[0045] The preparation steps of the high entropy doped O3 phase layered oxide include:

[0046] S01: weighing raw materials of corresponding molar ratios according to the chemical formula of the high entropy doped O3 phase layered oxide to obtain a mixed powder, and then mixing the mixed powder, wherein the raw materials include: sodium salt and oxide of A, and oxide powder of doping element M;

[0047] S02: pressing the mixed powder after ball milling to obtain a pressed block;

[0048] S03: sintering the block.

[0049] In a specific implementation, the purpose of the above-mentioned mixing treatment is to fully and evenly mix the raw materials. Any method that can achieve the purpose of uniform mixing using different mechanical equipment can be used, such as mechanical stirring and dispersion. In a specific embodiment, the mixing treatment uses ball milling for mixing. More specifically, wet ball milling is preferred. The solvents that can be added when wet ball milling include but are not limited to ethanol, water, N-methylpyrrolidone (NMP), isopropyl alcohol (IPA) and other liquids. The liquid only needs to cover the ball milling balls, and it can also be changed according to different situations. The time for wet ball milling can be selected from 3 to 24 hours, and the ball milling speed is 300 to 600r / min; more preferably, the ball milling time is 5 to 20 hours, and the rotation speed is about 300 to 400r / min.

[0050] In a specific implementation, in the above-mentioned pressing treatment, cold pressing treatment is preferably adopted, and the pressing pressure is 5 to 30 MPa, preferably, the pressure is 5 to 10 MPa.

[0051] In a specific implementation, in the above sintering process, the sintering temperature is between 500 and 1100° C., the heating rate is between 3 and 20° C. / min, and the sintering time is between 1 and 24 hours.

[0052] More preferably, the sintering treatment includes at least two heating and holding intervals, so that the doping elements diffuse more evenly into the lattice of the layered oxide, forming a high entropy doped O3 phase layered oxide, and reaching an entropy stable state. The first heating and holding interval is preferably 500 to 600°C, and the holding time is between 1 and 12 hours; this heating and holding interval solves or alleviates the problem that sodium carbonate is easy to sink during the sintering process, resulting in the difficulty of mixing Na and other metal atoms such as Mn, Fe, Ni in the layered oxide structure; the second heating and holding interval is preferably 700 to 1100°C, and the holding time is between 1 and 24 hours, so that the doping atoms can be fully diffused.

[0053] During the sintering process, the sodium salt in the raw material is heated and reacts with the metal oxide under high temperature conditions to undergo a solid phase sintering reaction. In one embodiment, the sodium salt is sodium carbonate (Na2CO3). In other embodiments, the sodium carbonate in the raw material can also be replaced by other sodium salts, such as sodium bicarbonate (NaHCO3), sodium acetate (CH3COONa), sodium oxalate (Na2C2O4), sodium citrate (C6H5Na3O7), sodium nitrate (NaNO3), sodium hydroxide (NaOH), etc. The nickel oxide in the raw material includes NiO and Ni2O3; the manganese oxide includes: MnO, MnO2, Mn2O3, Mn3O4, Mn2O5, etc.; the manganese oxide in the raw material includes: MnO, MnO2, Mn2O3, Mn3O4, Mn2O5, etc.

[0054] It should be noted that in step S01, the meaning of "corresponding molar ratio" in the present invention includes not only the stoichiometric molar ratio of each element in the chemical formula of the high entropy doped O3 phase layered oxide, but also the molar ratio of Na1Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.02 Cu 0.0 2Sn 0.02 Sb 0.02 Zn 0.02 O2 as an example, the stoichiometric molar ratio refers to the preparation of unit mole of Na1Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.0 2Cu 0.02 Sn 0.02 Sb 0.02 Zn 0.02O2, wherein the molar ratio of each element is Na: Mn: Fe: Ni: Ti: Cu: Sn: Sb: Zn = 1: 0.4: 0.3: 0.2: 0.02: 0.02: 0.02: 0.02: 0.02; that is, based on the ratio of the numerical values ​​of the subscripts of the elements in the chemical formula; it also includes the stoichiometric molar ratio of one or more raw material components being appropriately increased or decreased, and the actual feed amount of the raw material component corresponding to the calculated feed molar ratio; more specifically, the feed molar ratio after the appropriate increase or decrease adjustment is 90% to 110% of the stoichiometric molar ratio; in the specific implementation, the use of the feed molar ratio and the stoichiometric molar ratio both belong to the meaning of the "corresponding molar ratio" of the present invention. In a specific embodiment, the actual feed molar ratio of Na2CO3 is 102% to 105% of the stoichiometric molar ratio, and the remaining oxides of A and M are calculated according to the stoichiometric molar ratio, and the feed amount is calculated according to the feed molar ratio and the stoichiometric molar ratio respectively.

[0055] Example 2

[0056] This embodiment provides a specific high entropy doped O3 phase layered oxide Na1Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.02 Cu 0.02 Sn 0.02 Sb 0.02 Zn 0.02 O2 and a preparation method thereof, wherein the preparation method comprises the following steps:

[0057] S11: According to the chemical formula of high entropy doped O3 phase layered oxide, raw materials with corresponding molar ratios are weighed to obtain a mixed powder, and then the mixed powder is ball-milled; specifically, Na2CO3, MnO2, Fe2O3, NiO, TiO2, CuO, SnO2, Sb2O5 and ZnO powders are weighed according to a molar ratio of 0.525:0.4:0.15:0.2:0.02:0.02:0.02:0.01:0.02, respectively, and placed in a ball mill, ball milling balls are added according to a ball-to-material mass ratio of 10:1, and then an appropriate amount of ethanol is added as a dispersant, and finally the ball mill is placed on a ball mill for ball milling for 4 hours. After the ball milling is completed, the ball mill is placed in an 80°C blast oven and dried for 10 hours to obtain a ball-milled mixed powder;

[0058] S12: cold pressing the ball-milled mixed powder at a pressure of 10 MPa; specifically, placing the dried mixed powder in a circular groove mold with a diameter of 14 mm, and pressing the mixed powder at a pressure of 10 MPa to obtain a circular block with a diameter of 14 mm;

[0059] S13: Sintering the block. Specifically, the pressed round block is placed in an alumina crucible, and then the crucible is placed in a muffle furnace. The sintering procedure is to heat up from room temperature to 500°C, then keep it warm for 5 hours, then heat up to 900°C, and then keep it warm for 12 hours. The heating rate is 5°C / min. After naturally cooling to room temperature, take it out to obtain the target product.

[0060] Preparation of comparative samples: A similar preparation method as above is adopted, except that the type and amount of metal oxides in the raw materials are changed to prepare comparative samples of non-high entropy doped O3 phase layered oxides, including: mono-doping (hereinafter referred to as mono-doping) Na1Mn 0.4 Fe 0.3 Ni 0.2 Cu 0.1 O2, binary doping (hereinafter referred to as binary-doping) Na1Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.05 Cu 0.05 O2, ternary doping (hereinafter referred to as ternary-doping) Na1Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.033 Cu 0.033 Sb 0.033 O2.

[0061] The obtained target product and the comparative sample were tested by X-ray diffraction (XRD). Figure 1 As shown, it can be seen that the prepared high entropy doping (hereinafter referred to as HE-doping), binary-doping and ternary-doping samples all have diffraction peaks at 17.0°, 33.7°, 35.3°, 36.6° and 42.2°. These diffraction peaks are characteristic peaks of the O3 phase, corresponding to the crystal planes (003), (006), (101), (102) and (104), respectively. Among them, (003) and (104) are strong diffraction peaks, and (006), (101) and (102) are relatively weak diffraction peaks. Compared with the diffraction peak of 17.0° of the (003) plane of the mono-dopingO3 phase, the diffraction peaks of the (003) plane of the binary-doping and HE-doing O3 phases are 16.5° and 16.4°, respectively. This indicates that the interplanar spacing of binary-doping and HE-doping increases, that is, the introduction of elements with high ionic radius will increase the lattice spacing. Figure 2 This is the SEM photograph and element distribution diagram of the high-entropy doped O3 phase layered oxide. It can be seen that the elements Na, Mn, Fe, Ni, Ti, Cu, Sn, Sb, and Zn are evenly distributed, indicating that a homogeneous layered oxide is obtained.

[0062] This embodiment also provides a use of the HE-doping O3 phase layered oxide obtained above as a positive electrode material for a sodium ion battery, that is, a positive electrode material for a sodium ion battery and a sodium ion battery. The compaction density of the HE-doping O3 phase positive electrode material tested is 3.38 g / cm 3 .

[0063] The HE-doping O3 phase layered oxide and the control sample obtained above were made into positive electrode sheets and assembled to obtain a sodium ion battery. Figure 3 The electrochemical performance test results of the HE-doping O3 phase layered oxide of the present invention and the comparative sample as the positive electrode material of the sodium ion battery are given. Figure 3 a is the cycle performance test at a rate of 0.1C. It can be seen that the HE-dopingO3 phase has an initial discharge capacity of 158 mAh / g, which is higher than other single-element or multi-element doped O3 phases; Figure 3 b is the rate performance test, and the results show that the HE-doping O3 phase has significantly excellent rate performance; Figure 3 c and d are the cycle performance tests at 1C and 5C rates, respectively. The results show that the discharge specific capacity of HE-doping O3 phase at 1C and 5C rates are 113 mAh / g and 83 mAh / g, respectively, and it has good cycle stability, which is significantly better than the mono- and di-doped O3 phases.

[0064] In order to verify the stability of the O3 phase of the HE-doping of the present invention, the O3 phase of the HE-doping of the present invention was immersed in water for 12 hours and exposed to air for 7 days, and then the sample was dried (vacuum 80°C, 12 hours) and then subjected to XRD test. The test results are shown in Figure 4 As shown in a, it can be seen that there is no difference in the XRD spectrum of the sample after immersion in water and exposure to air compared with the initial sample, indicating that its structure has not changed. The HE-doping O3 phase is relatively stable in both air and water-containing environments, and has environmental stability and water resistance. In order to further verify the electrochemical performance of the HE-doping O3 phase immersed in water, the HE-doping O3 phase immersed in water was assembled into a battery and the cycling performance at a rate of 0.1C was tested. Figure 4 The results of b show that although immersed in water for 12 h, the HE-doping O3 phase can still maintain a high capacity of 153 mAh / g (mono-doping 130 mAh / g, binary-doping 128 mAh / g), and the capacity retention rate after 100 cycles is 75.2%, which is much better than that of mono-doping (49.6%) and binary-doping (44.8%) O3 phases.

[0065] In other embodiments, the content of the raw material Na2CO3 is reduced to obtain a high entropy doped O3 phase layered oxide with a low sodium content; in a specific embodiment, Na2CO3, MnO2, Fe2O3, NiO, TiO2, CuO, SnO2, Sb2O5 and ZnO powders are weighed respectively according to a molar ratio of 0.45:0.4:0.15:0.2:0.02:0.02:0.02:0.01:0.02, and the other conditions remain unchanged to obtain a high entropy doped O3 phase layered oxide Na 0.9 Mn 0.4 Fe 0.3 Ni 0.2 Ti 0.02 Cu 0.02 Sn 0.02 Sb 0.02 Zn 0.02 O2.

[0066] Example 3

[0067] In this embodiment, another high entropy doped O3 phase layered oxide Na1Mn with different doping element contents was prepared by changing the ratio of metal oxides in the raw materials through a preparation method similar to that of embodiment 2. 0.4 Fe 0.3 Ni 0.1 Ti 0.04 Cu 0.04 Sn 0.04 Sb 0.04 Zn 0.04 O2, and used it as the positive electrode material of sodium ion battery, assembled the battery and tested the electrochemical performance. The test results are as follows Figure 5 shown.

[0068] The electrochemical performance test results of the two high entropy doped O3 phase layered oxides with different doping element contents in Examples 2 and 3 as positive electrode materials for sodium ion batteries are compared. The results are shown in Figure 5 .like Figure 5 The XRD diffraction pattern of a, high-doped O3 pure phase Na1Mn can also be obtained by high-temperature solid phase sintering method. 0.4 Fe 0.3 Ni 0.1 Ti 0.04 Cu 0.04 Sn 0.04 Sb 0.0 4Zn 0.04 O2. From Figure 5 bd It can be seen that the high entropy doped O3 phase layered oxide Na1Mn in Example 2 0.4 Fe 0.3 Ni 0.2 Ti0.0 2Cu 0.02 Sn 0.02 Sb 0.02 Zn 0.02 Although the doping element content of O2 is lower than that of Na1Mn in Example 3, 0.4 Fe 0.3 Ni 0.1 Ti 0.04 Cu 0.04 Sn 0.04 Sb 0.04 Zn 0.04 O2, but from the perspective of specific capacity, cycle performance and rate performance, the high entropy doped O3 phase layered oxide in Example 2 is better than that in Example 3. It can be seen that the content of doping elements is also one of the factors affecting its performance as a positive electrode material for sodium ion batteries, and the higher the doping content, the better. On the contrary, a lower doping amount is beneficial to the electrochemical performance improvement of high entropy doped O3 phase layered oxide as a positive electrode material for sodium ion batteries. Therefore, the high entropy doped O3 phase layered oxide is represented by the chemical formula, Na x (Mn αF e β Ni γ )(M 1a M 2b M 3c M 4d M 5e M 6f )O2, wherein 0.1≤α≤0.5, 0.1≤β≤0.4, 0.1≤γ≤0.3, preferably, 0<a≤0.03, 0<b≤0.03, 0<c≤0.03, 0<d≤0.03, 0<e≤0.03, 0≤f≤0.03. More preferably, 0<a≤0.02, 0<b≤0.02, 0<c≤0.02, 0<d≤0.02, 0<e≤0.02, 0≤f≤0.02.

[0069] Example 4

[0070] In this embodiment, another high entropy doped O3 phase layered oxide Na1Mn with different Mn element contents was prepared by changing the ratio of metal oxides in the raw materials through a preparation method similar to that of Example 2. 0.5 Fe 0.3 Ni 0.1 Cu 0.02 Ti 0.02 Sn 0.02 Sb 0.0 2Zn 0.02 O2, and used it as the positive electrode material for sodium ion batteries. The specific results are as follows Figure 6 shown.

[0071] like Figure 6As shown in a, the appearance of (003) and (104) crystal planes in the XRD diffraction pattern proves that Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.0 2Ti 0.02 Sn 0.02 Sb 0.02 Zn 0.02 O2 is in the O3 phase. In addition, Figure 6 The electrochemical data of b show that at 1C rate, the high manganese positive electrode Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.02 Ti 0.02 Sn 0.02 Sb 0.02 Zn 0.02 O2 has a discharge specific capacity of 112 mAh / g, and its capacity retention rate is 77.7%, which has a certain cycle stability.

[0072] Comparing the electrochemical performance test results of the O3 phase high entropy doped layered oxide prepared in this embodiment with those prepared in Example 2, it can be seen that when the doping elements are the same, the capacity is reduced by increasing the manganese content. x (Mn α Fe β Niγ)(M 1a M 2b M 3c M 4d M 5e M 6f )O2, more preferably, 0.1≤α≤0.4, 0.1≤β≤0.3, 0.1≤γ≤0.2, 0<a≤0.02, 0<b≤0.02, 0<c≤0.02, 0<d≤0.02, 0<e≤0.02, 0≤f≤0.02.

[0073] Example 5

[0074] In this embodiment, a preparation method similar to that of embodiment 2 is used to change the ratio of metal oxides in the raw materials and add ZrO2 to prepare another high entropy doped O3 phase layered oxide Na1Mn with six doping elements. 0.5 Fe 0.3 Ni 0.1 Cu 0.02 Ti 0.02 Mg 0.02 Zn 0.02 Sb 0.01 Zr 0.01 O2. Its comparison sample is a single Cu-doped Na1Mn0.5 Fe 0.3 Ni 0.1 Cu 0.1 O2 and binary Cu and Mg doped Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.05 Mg 0.05 O2. The specific implementation results are as follows Figure 7 shown.

[0075] like Figure 7 As shown in a, the appearance of (003) and (104) crystal planes in the XRD diffraction pattern proves that Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.0 2Ti 0.02 Mg 0.02 Zn 0.02 Sb 0.01 Zr 0.01 O2、Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.1 O2 and Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.05 Mg 0.05 O2 is in the O3 phase. In addition, Figure 6 The electrochemical data of b show that at 1C rate, the hexavalent doped cathode material Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.02 Ti 0.02 Mg 0.02 Zn 0.02 Sb 0.01 Zr 0.01 O2 has a discharge capacity of 121 mAh / g, which is much higher than that of Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.1 O2(112mAh / g) and Na1Mn 0.5 Fe 0.3 Ni 0.1 Cu 0.05 Mg 0.05 O2 (108 mAh / g), and it has a relatively high capacity retention rate of 70%, indicating that hexavalent high entropy doping is also beneficial to the improvement of electrochemical performance.

[0076] Example 6

[0077] In this embodiment, the high entropy doped layered oxide Na1Mn was prepared by a preparation method similar to that of embodiment 2, by changing the holding time during the sintering process, that is, removing the holding time of 500-600°C for 6-12h, and comparing it with the holding time and method in embodiment 2. 0.4 Fe 0.3 Ni 0.2 Cu 0.02 Ti 0.02 Sn 0.02 Zn 0.02 Sb 0.02 O2. The specific implementation results are as follows Figure 8 shown.

[0078] like Figure 8 As shown in a, the HE-doping sample sintered at 500℃ is O3 phase, while the HE-doping sample not sintered at 500℃ is P2 / O3 composite phase, which shows that the insulation time is favorable for the sintering to form pure O3 phase, mainly because sodium carbonate is easy to sink during the sintering process. Increasing or decreasing the insulation sintering from 500 to 600℃ can alleviate this phenomenon, which is conducive to solving or alleviating the problem of mixed arrangement of Na and other metal atoms such as Mn, Fe, Ni in the layered oxide structure. The HE-doping O3 phase sintered at 500℃ has an initial discharge capacity of 122mAh / g, while the initial capacity of the HE-doping P2 / O3 phase not sintered is 58mAh / g. Although the HE-doping P2 / O3 phase not sintered has good cycle stability, the discharge capacity of the HE-doping O3 phase is about twice that of the HE-doping P2 / O3 phase not sintered.

[0079] Therefore, in the sintering process of the high entropy doped O3 phase layered oxide of the present invention, it is preferred to include a heating and heat preservation section, the heating temperature of the heating and heat preservation section is between 500°C and 600°C, and the heat preservation time is between 1h and 12 hours. In a specific embodiment, at least two heating and heat preservation sections are included, wherein the heating temperature of the first heating and heat preservation section is between 500°C and 600°C, the heat preservation time is between 1 and 12 hours, and the heating temperature of the second heating and heat preservation section is between 700°C and 1100°C, and the heat preservation time is preferably between 1 and 24 hours. In another specific embodiment, more than three heating and heat preservation sections, as well as the adjustment of the temperature and time of the heating and heat preservation sections, can be included to shorten the heating and heat preservation time under the premise of ensuring that multiple doping elements are fully diffused, so as to reduce the energy consumption of preparation. The adjustment of the specific process in these sintering treatments can be achieved through a limited number of process optimization tests, which are all within the technical concept of the present invention.

[0080] It should be noted that the XRD diffraction pattern of the above-mentioned high entropy doped O3 phase layered oxide includes strong diffraction peaks (003) and (104) relative to weak diffraction peaks (006), (101), and (012). Compared with the strong diffraction peaks (003) and (104), in some embodiments, the diffraction intensity (104) is stronger than (003), and in other embodiments, the diffraction intensity (003) is stronger than (104); similarly, the intensity of each weak diffraction peak (006), (101), and (012) is relative to the strong diffraction peaks (003) and (104). In different embodiments, the diffraction intensity of each (006), (101), and (012) may be different.

[0081] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A high entropy doped O3 phase layered oxide with environmental stability, characterized in that: The chemical formula of the high entropy doped O3 phase layered oxide is Na x A y M z O2, where Na represents sodium, A is selected from iron, nickel and manganese; M represents a doping element, 0.9≤ x ≤1,0.8≤ y <1,0< z ≤0.2, y + z =1; The M is selected from five or more elements of copper, titanium, magnesium, zinc, zirconium, tin and antimony; The chemical formula of the high entropy doped O3 phase layered oxide is Na x (Mn α Fe β Ni γ ) (M 1a M 2b M 3c M 4d M 5e M 6f ) O2, y = α + β+γ , z = a + b + c + d + e + f ,0< a ≤0.05,0< b ≤0.05,0< c ≤0.05,0< d ≤0.05,0< e ≤0.05,0≤ f ≤0.

05.

2. The high entropy doped O3 phase layered oxide according to claim 1, characterized in that: The M includes: at least 1 to 3 metal elements selected from the fifth period, and at least 2 to 4 metal elements selected from the third period and the fourth period; The metal elements of the fifth period are selected from zirconium, tin and antimony; the metal elements of the third period are selected from magnesium; and the metal elements of the fourth period are selected from titanium, copper and zinc.

3. The high entropy doped O3 phase layered oxide according to claim 1, characterized in that: In the chemical formula of the high entropy doped O3 phase layered oxide, 0 < a ≤0.04,0< b ≤0.04,0< c ≤0.04,0< d ≤0.04,0< e ≤0.04,0≤ f ≤0.

04.

4. The high entropy doped O3 phase layered oxide according to claim 3, characterized in that: 0＜ a ≤0.03，0＜ b ≤0.03，0＜ c ≤0.03，0＜ d ≤0.03，0＜ e ≤0.03，0≤ f ≤0.03。 5. The high entropy doped O3 phase layered oxide according to claim 3, characterized in that: 0＜ a ≤0.02，0＜ b ≤0.02，0＜ c ≤0.02，0＜ d ≤0.02，0＜ e ≤0.02，0≤ f ≤0.02。 6. The high entropy doped O3 phase layered oxide according to any one of claims 1 to 5, characterized in that: The M includes: at least two of titanium, copper, zinc and magnesium; and / or at least one element selected from the group consisting of tin, antimony and zirconium.

7. The high entropy doped O3 phase layered oxide according to any one of claims 1 to 5, characterized in that: The XRD diffraction spectrum of the high entropy doped O3 phase layered oxide includes strong diffraction peaks (003) and (104), and weak diffraction peaks (006), (101), and (012) relative to the strong diffraction peaks.

8. A method for preparing a high entropy doped O3 phase layered oxide according to any one of claims 1 to 7, characterized in that the steps include: According to the chemical formula of the high entropy doped O3 phase layered oxide, sodium salt, oxide of A and oxide of M in corresponding molar ratios are weighed and mixed to obtain a mixed powder; The mixed powder is pressed to obtain a pressed block; sintering the block; The sintering process includes at least two heating and heat preservation sections, wherein the heating temperature of the first heating and heat preservation section is between 500°C and 600°C, and the heat preservation time is between 1 and 12 hours, and the heating temperature of the second heating and heat preservation section is between 700°C and 1100°C.

9. The preparation method according to claim 8, characterized in that: The sodium salt is selected from at least one of sodium carbonate, sodium bicarbonate, sodium acetate, sodium oxalate, sodium citrate and sodium nitrate; And / or, the mixing treatment includes ball milling, wherein the ball-to-material mass ratio in the ball milling is (5-20):1, the dispersant is one or more of ethanol, acetone, N-methylpyrrolidone, isopropanol or water, the ball milling speed is 300 to 600 r / min, and the ball milling time is 3 to 24 h; And / or, in the pressing process, the steps more specifically include: loading the mixed powder into a mold and pressing and molding it under pressure; And / or, during the sintering process, the heating rate is 3 to 20° C. / min and the sintering time is 1 to 36 hours.

10. The preparation method according to claim 9, characterized in that: The pressurized pressure is 5 to 30 MPa.

11. A sodium ion battery positive electrode material, characterized in that: The sodium ion battery positive electrode material comprises: a high entropy doped O3 phase layered oxide according to any one of claims 1 to 7; or a high entropy doped O3 phase layered oxide obtained by the preparation method according to any one of claims 8 to 10.

12. A sodium ion battery, characterized in that: Comprising the sodium ion battery positive electrode material as claimed in claim 11.

13. An electrical device, characterized in that: Comprising the sodium ion battery as claimed in claim 12.

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