Step-by-step layered entropy-increasing O3 type sodium ion battery high-entropy layered positive electrode material and preparation method thereof

Abstract

The invention discloses an O3-type sodium-ion battery high-entropy layered positive electrode material capable of increasing configuration entropy through step-by-step layering and a preparation method of the O3-type sodium-ion battery high-entropy layered positive electrode material. In the structure of the high-entropy layered positive electrode, an alkali metal layer has at least three components and a proper amount of vacancies, meanwhile, a transition metal layer has at least five components, the chemical general formula is (NaxMy) (FebCocNidMneNf) O2, and M and N are located in the alkali metal layer and the transition metal layer respectively. The preparation method comprises the following steps: firstly, enabling a transition metal layer of a layered positive electrode (AM) (TM) O2 to comprise at least five different components by using high-temperature solid-phase sintering to obtain a high-entropy precursor Naa (FebCocNidMneNf) O2, and then enabling an alkali metal layer to comprise at least three different components by using ion exchange to prepare the high-entropy layered positive electrode. Wherein a is more than 0.65 and less than or equal to 0.80; 0 < b, c, d and f < = 0.2; 0.2 < e < = 0.3; 0.65 < = x < 0.80; 0 < y < = 0.05; 0.65 < x + y < 0.80, and b + c + d + e + f < = 1 are satisfied. The battery assembled by the high-entropy layered positive electrode material provided by the invention is excellent in performance, still has the reversible specific capacity of 107mAh / g under 2000mA / g, and has a wide application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical new energy technology, and specifically relates to an O3 type high entropy layered cathode material that increases configurational entropy by step-by-step layering and a preparation method thereof. Background Art

[0002] Due to the abundant and uniform distribution of resources and the compatibility of equipment with lithium-ion batteries, sodium-ion batteries have good application potential in large-scale energy storage systems. Layered transition metal oxides, as one of the representative cathode materials of sodium-ion batteries, have the advantages of convenient synthesis and high energy density. However, the key properties of this type of material (such as specific capacity, rate performance and cycle stability) still do not meet the requirements of practical applications. The complex phase evolution during the charge and discharge process, accompanied by large volume changes and stress accumulation, threatens the structural integrity of the layered cathode and the cycle stability of the battery, which has stimulated the research on the modification of layered cathode materials.

[0003] The "entropy tuning" strategy, based on the thermodynamic concept of "entropy" and using elemental doping, is an effective method for improving the long-term cycling stability of layered cathodes. According to the relationship between entropy and enthalpy (ΔG = ΔH - T·ΔS), when the configurational entropy of a system balances or exceeds its enthalpy, the system will tend toward entropy stability. Higher entropy values ​​lead to more stable crystal structures.

[0004] However, due to the limitations of traditional methods such as one-step solid-phase and sol-gel methods, it is difficult to simultaneously finely control the composition of both the transition metal and alkali metal layers of a layered cathode. Current research generally relies on introducing multiple components into the transition metal layer to increase the overall configurational entropy of the material. However, achieving entropy increase solely by adding components to a single layer increases the difficulty of selecting different elements for subsequent material design, especially considering the physicochemical properties of the selected elements, such as size, bonding state, electronegativity, and electrochemical activity / inactivity. Furthermore, simply combining multiple components in the transition metal layer does not result in a pure phase of high entropy. Such materials typically require long, high-temperature sintering at 800°C-1100°C to ensure uniform distribution of the elements and the formation of a pure phase. Improper control of component ratios or insufficient sintering temperature or time can easily lead to elemental segregation or residual impurities. Further increasing the entropy of the transition metal layer further increases the difficulty and cost of controlling the pure phase. Furthermore, the need to precisely control the concentrations of each component increases the difficulty and cost of a one-step synthesis. Furthermore, as the number and concentration of components within a single layer increase, the material's entropy increase tends to saturate. Therefore, it is necessary to develop new material design strategies to increase the upper limit of entropy and further improve the overall performance of the material. Summary of the Invention

[0005] In view of the above-mentioned problem that the entropy increase of the positive electrode material reduces the phase purity and restricts the further improvement of the key characteristics of the sodium ion battery, the purpose of the present invention is to provide an O3 single-phase sodium ion battery high-entropy layered positive electrode material with step-by-step layered entropy increase and a preparation method thereof.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] The present invention provides a high entropy layered cathode material for sodium ion batteries with step-by-step entropy increase. The material has an O3 crystal structure and a superlattice structure at a low sodium content, and the chemical formula is (Na x M y )(Fe b Co c Ni d Mn e N f )O2. The first step is to obtain a high entropy precursor Na by high temperature solid phase sintering to make the transition metal layer contain at least five different components and the alkali metal layer contain a large number of vacancies. a (Fe b Co c Ni d Mn e N f )O2; in the second step, the alkali metal layer contains at least two different trace components in addition to Na through ion exchange reaction, and retains at least 0.20 vacancies, thereby obtaining a high entropy layered positive electrode material in which the alkali metal layer and the transition metal layer contain at least three and at least five different components.

[0008] The high entropy layered cathode material has a superlattice structure, and the superlattice structure is manifested in that superlattice diffraction peaks are present at 18-23° and 40-45° in the XRD spectrum of the cathode material.

[0009] The a, b, c, d, e, f, x, and y are the corresponding element molar ratios or the corresponding total molar ratios of multiple elements, respectively, and satisfy the following relationship: 0.65<x+y<0.80, b+c+d+e+f≤1, and 0.65<a≤0.80; 0<b, c, d, f≤0.2; 0.2<e≤0.3; 0.65≤x<0.80; 0<y<0.05.

[0010] The purpose of the high-temperature solid-phase sintering is to control the composition and proportion of the transition metal layer to achieve a partial increase in the configurational entropy, obtain a single-layer high-entropy material of the transition metal layer with an entropy value greater than 1.50R and serve as a precursor; the second step of the ion exchange reaction only introduces a small amount of elements (0<y<0.05) into the alkali metal layer, and cooperates with vacancy control to achieve a significant increase in the material configurational entropy, and the entropy value increases to at least 2.0R.

[0011] Furthermore, the elements included in the nitrogen in the high-entropy layered positive electrode are all located in the transition metal layer, with at least one element present, each element being present in an amount of at least 0.1 mol and an electronegativity of no more than 2.05. The difference in ionic radius between the elements in the transition metal layer, including nitrogen, is no more than 30%. The nitrogen is preferably an electrochemically inactive element, specifically including but not limited to Mg, Al, Ti, V, Cr, Cu, Nb, Sn, and Sb. More preferably, the nitrogen includes Ti.

[0012] Furthermore, the elements M in the high-entropy layered cathode are all located in the alkali metal layer, of at least two types, with a total element content of no more than 0.05 mol and an ionic valence of no more than +3. The difference in ionic radius between each element in the alkali metal layer M and Na is no more than 45%, and the alkali metal layer has at least 0.20 vacancies. The M specifically includes, but is not limited to, Sr, Ba, and La.

[0013] The present invention also provides a method for preparing a high-entropy layered positive electrode material for sodium ion batteries with step-by-step entropy increase, which comprises high-temperature solid-phase sintering combined with ion exchange reaction.

[0014] The first step is to increase the configuration entropy of the transition metal layer by high temperature solid phase sintering, which includes the following steps:

[0015] According to the high entropy precursor Na a (Fe b Co c Ni d Mn e N f )O2 is mixed with the metal salts or gold oxides corresponding to sodium, iron, cobalt, nickel, manganese and N in the required stoichiometric ratio and ground for 20-30 minutes to obtain powder A, wherein the sodium source is in excess of 5%. The powder A is pressed into a disc A under a pressure of 10-15 MPa, placed in a crucible and placed in a tube furnace. It is sintered at a high temperature of 900-1000°C for 12-15 hours in an oxygen-containing atmosphere. When the furnace temperature drops to 100-200°C, it is taken out and quickly ground for 2-3 minutes to obtain a high entropy precursor. Preferably, the pressure is 10 MPa. Preferably, the oxygen-containing atmosphere is pure oxygen. Preferably, the high-temperature sintering conditions are sintering at 950°C for 12 hours, and the heating and cooling rates are both 5°C / min. Preferably, the sampling temperature is 150°C.

[0016] The second step is to increase the configurational entropy of the alkali metal layer through ion exchange reaction, which can be any of the following:

[0017] (1) Low-temperature molten salt ion exchange: In a glove box, a high-entropy precursor is mixed with a low-melting-point salt or oxide corresponding to the element contained in M ​​and ground for 5-8 minutes to obtain powder B; the powder B is pressed into a disc B under a pressure of 10-15 MPa, placed in a crucible and placed in a tube furnace and sintered at a low temperature of 150-400°C for 4-8 hours in an oxygen-containing atmosphere; after the furnace temperature drops to 100-200°C, the sample is taken out and quickly ground for another 2-3 minutes, washed twice with ethanol aqueous solution, and then vacuum filtered and vacuum dried at 80-100°C for 10-12 hours to obtain a high-entropy layered positive electrode material.

[0018] Preferably, the tableting pressure is 10 MPa. Preferably, the low-temperature sintering conditions are sintering at 350°C for 8 hours, with a heating and cooling rate of 5°C / min, and the oxygen-containing atmosphere is pure oxygen. Preferably, the sampling temperature is 150°C. Preferably, the vacuum drying temperature is 80°C, and the drying time is 12 hours.

[0019] (2) Liquid phase ion exchange: The salt or chloride corresponding to the element contained in M ​​is dissolved in an ethanol-water solution and mixed evenly to obtain a solution precursor; the solution precursor is adjusted to a pH value and then mixed with a high entropy precursor, heated and stirred at 60-100°C, washed twice with an ethanol-water solution, vacuum filtered and dried in a forced air drying oven to obtain powder C; the powder C is placed in a tubular furnace and heat treated at 800°C-1000°C in an oxygen-containing atmosphere for 12-15 hours, and the furnace temperature is lowered to between 100-200°C to remove the powder to obtain a high entropy layered positive electrode material.

[0020] Preferably, the pH value is controlled within the range of 0.5-3.0. Preferably, the heating and stirring temperature is 90°C. Preferably, the heat treatment conditions are 800°C for 12 hours, with a heating and cooling rate of 5°C / min, and the oxygen-containing atmosphere is pure oxygen. Preferably, the sampling temperature is 150°C.

[0021] The present invention also provides a sodium-ion battery positive electrode plate, comprising the above-mentioned high-entropy layered positive electrode material, a conductive additive, and a binder. Optionally, the mass ratio of the high-entropy layered positive electrode, the conductive additive, and the binder is 75:15:10, 80:10:10, or 90:5:5. Preferably, the mass ratio is 75:15:10.

[0022] The present invention also provides a sodium ion battery, which includes a positive electrode, and the positive electrode includes the above-mentioned positive electrode plate.

[0023] The present invention also provides a use of the high-entropy layered positive electrode material in a sodium ion battery to improve rate performance.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention uses a step-by-step synthesis process to perform layered entropy control on the O3-type (AM) (TM) O2 layered oxide positive electrode to obtain a high-entropy layered positive electrode material with at least three and at least five different components in the alkali metal layer and the transition metal layer, respectively. Unlike the traditional means of introducing too many components in equal molar ratios or near molar ratios into the transition metal layer, the present invention relies on the addition of trace components in the alkali metal layer and the retention of a large number of vacancies to further significantly increase the overall configurational entropy of the material. At the same time, it avoids the introduction of too many components into the transition metal layer to form element enrichment and destroy the phase purity, and still maintains the O3-type layered structure at low sodium content, effectively reducing the difficulty and cost of synthesis. The moderate disordering of the transition metal layer enhances the structural strength and achieves long-cycle stability of the battery. The multiple trace components and a large number of vacancies in the alkali metal layer reduce the energy barrier of the alkali metal ions, enhance the transmission kinetics, and enable the material to exhibit excellent rate performance. The step-by-step layered entropy increase method provided by the present invention comprehensively improves multiple key characteristics of the layered positive electrode of sodium ion batteries, including rate and cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 XRD patterns of the high-entropy layered cathode materials prepared in Example 1 and Example 2.

[0027] Figure 2 This is the XRD pattern of the high entropy layered positive electrode material prepared in Comparative Examples 1-9.

[0028] Figure 3 The cycle performance of the sodium ion battery prepared in Example 1 is shown. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to specific embodiments. However, the description of the embodiments is for a better and more comprehensive understanding of the technical solutions of the present invention, and is not intended to limit the scope of protection of the present invention.

[0030] Unless otherwise specified, the materials, reagents, and instruments involved in the following examples can be prepared by existing methods or obtained from commercial channels. The professional terms used have the same meanings as those generally understood by professionals in the field.

[0031] The conductive additive used in the present invention can be at least one of Super P, acetylene black, and Ketjen black; the binder used is PVDF; the sodium ion battery electrolyte used is: 1 mol / L NaClO4 dissolved in 100% PC, and 5 vol% FEC additive is added.

[0032] Example 1

[0033] This embodiment provides a high entropy layered cathode material for sodium ion batteries with a step-by-step entropy increase layered structure, wherein the alkali metal layer contains three components and 0.25 mole vacancies and the transition metal layer contains six components. The chemical formula is (Na0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2, with an entropy value of 2.17R, is prepared by high-temperature solid-phase sintering combined with low-temperature molten salt ion exchange. The specific steps are as follows:

[0034] (1) Preparation of Na 0.80 (Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy precursor

[0035] 0.85 mol of sodium carbonate, 0.18 mol of ferric oxide, 0.18 mol of cobalt oxide, 0.18 mol of nickel oxide, 0.26 mol of manganese oxide, 0.10 mol of titanium dioxide, and 0.10 mol of copper oxide were mixed, ground in a mortar for 20 minutes, pressed into 10 mm discs under a pressure of 10 MPa, and placed in a tube furnace for calcination at 950 ° C for 12 hours under a flowing oxygen atmosphere with a heating and cooling rate of 5 ° C / min. After cooling to 150 ° C, the sample was taken out and quickly ground for another 2 minutes to obtain a high entropy precursor.

[0036] (2) Preparation (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered cathode material

[0037] The high-entropy precursor obtained in step (1) was mixed with 0.025 mol of lanthanum hydroxide and 0.025 mol of strontium hydroxide, ground in a mortar for 5 minutes, and pressed into a 10 mm disc under a pressure of 10 MPa; the disc was placed in a tubular furnace and sintered at 300°C for 4 hours under a flowing oxygen atmosphere, with a heating and cooling rate of 5°C / min; when the furnace temperature dropped to 150°C, the sample was taken out and quickly ground into a powder for 2 minutes, then washed twice with ethanol aqueous solution, vacuum filtered, and vacuum dried at 80°C for 12 hours to obtain a high-entropy layered positive electrode material.

[0038] (3) Preparation (Na 0.70 La 0.025 Sr 0.025)(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered positive electrode

[0039] The high entropy layered positive electrode material obtained in step (2) was mixed evenly with Super P and PVDF in a mass ratio of 75:15:10, an appropriate amount of N-methylpyrrolidone solvent was added and mixed quickly and evenly, and then coated on an aluminum foil current collector, and placed in a vacuum drying oven at 80°C for 12 hours to obtain a high entropy layered positive electrode sheet.

[0040] (4) Assembly and testing of sodium ion batteries

[0041] The battery was assembled in an argon atmosphere glove box. The high-entropy layered positive electrode obtained in step (3) was cut into 10 mm pieces and then assembled with a metal sodium negative electrode, a separator, and an electrolyte to form a button cell. Charge and discharge tests were conducted under the conditions of a charge cutoff voltage of 4.1 V and a discharge cutoff voltage of 1.9 V.

[0042] Example 2

[0043] This embodiment provides a high-entropy layered positive electrode as described in Example 1, which is prepared by high-temperature solid-phase sintering combined with liquid-phase ion exchange reaction. The specific steps are as follows:

[0044] (1) Preparation of Na 0.80 (Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy precursor, the implementation steps are the same as Example 1.

[0045] (2) Preparation (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered cathode material

[0046] Lanthanum hydroxide and strontium hydroxide are dissolved in an ethanol aqueous solution in a stoichiometric ratio, and the pH value of the solution is controlled within the range of 0.5-3 with an acidic regulator to obtain a solution precursor; high-entropy precursor powder is added to the solution precursor, and the mixture is heated and stirred at 90°C for 8 hours. Excess salt is washed with an ethanol aqueous solution and then vacuum filtered. After drying, the mixture is placed in a crucible and placed in a tubular furnace for heat treatment at 800°C in pure oxygen for 12 hours. When the furnace temperature drops to 150°C, the sample is taken out to obtain a high-entropy layered positive electrode material, and the heating and cooling rates are both 5°C / min.

[0047] (3) Preparation (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered positive electrode

[0048] The high entropy layered positive electrode material obtained in step (2) was mixed evenly with Super P and PVDF in a mass ratio of 75:15:10, an appropriate amount of N-methylpyrrolidone solvent was added and mixed quickly and evenly, and then coated on an aluminum foil current collector, and placed in a vacuum drying oven at 80°C for 12 hours to obtain a high entropy layered positive electrode sheet.

[0049] (4) The assembly and testing of the sodium ion battery are the same as in Example 1.

[0050] Comparative Example 1

[0051] This comparative example provides a sodium ion battery high entropy layered cathode material with no vacancies in the alkali metal layer and only containing Na, and a transition metal layer containing five components, the chemical formula of which is NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti 0.2 O2, with an entropy of 1.61R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0052] (1) Preparation of NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti 0.2 O2 high entropy layered cathode materials

[0053] 1.05 mol of sodium carbonate, 0.20 mol of ferric oxide, 0.20 mol of cobalt oxide, 0.20 mol of nickel oxide, 0.20 mol of manganese oxide, and 0.20 mol of titanium dioxide were mixed, ground in a mortar for 20 minutes, pressed into 10 mm discs under a pressure of 10 MPa, and placed in a tubular furnace and calcined at 950 ° C for 12 hours under a flowing oxygen atmosphere with a heating and cooling rate of 5 ° C / min. After cooling to 150 ° C, the sample was taken out and quickly ground for 2 minutes to obtain a high-entropy layered positive electrode material.

[0054] (2) Preparation of NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti 0.2 O2 high entropy layered positive electrode

[0055] The high entropy layered positive electrode material obtained in step (2) was mixed evenly with Super P and PVDF in a mass ratio of 75:15:10, an appropriate amount of N-methylpyrrolidone solvent was added and mixed quickly and evenly, and then coated on an aluminum foil current collector, and placed in a vacuum drying oven at 80°C for 12 hours to obtain a high entropy layered positive electrode sheet.

[0056] (3) Assembly and testing of sodium ion batteries

[0057] The battery was assembled in an argon atmosphere glove box. The high-entropy layered positive electrode obtained in step (2) was cut into 10 mm pieces and then assembled into a button cell with a metal sodium negative electrode and electrolyte. Charge and discharge tests were conducted under the conditions of a charge cutoff voltage of 4.1 V and a discharge cutoff voltage of 1.9 V.

[0058] Comparative Example 2

[0059] This comparative example provides a sodium ion battery high entropy layered cathode material with no vacancies in the alkali metal layer and only containing Na, and a transition metal layer containing seven components, the chemical formula of which is NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Sn 0.1 Al 0.05 Mg 0.05 O2, with an entropy of 1.82R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0060] (1) Preparation of NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Sn 0.1 Al 0.05 Mg 0.05 O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0061] (2) Preparation of NaFe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Sn 0.1 Al 0.05 Mg 0.05 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Comparative Example 1.

[0062] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0063] Comparative Example 3

[0064] This comparative example provides a sodium ion battery high entropy layered cathode material with no vacancies in the alkali metal layer and only containing Na, and a transition metal layer containing seven components, the chemical formula of which is NaFe 1 / 6 Co 1 / 6 Ni 2 / 9 Mn 1 / 6 Ti 1 / 6 Mg 1 / 18 Cu 1 / 18 O2, with an entropy of 1.85R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0065] (1) Preparation of NaFe 1 / 6 Co 1 / 6 Ni 2 / 9 Mn 1 / 6 Ti 1 / 6 Mg 1 / 18 Cu 1 / 18 O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0066] (2) Preparation of NaFe 1 / 6 Co 1 / 6 Ni 2 / 9 Mn 1 / 6 Ti 1 / 6 Mg 1 / 18 Cu 1 / 18 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Comparative Example 1.

[0067] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0068] Comparative Example 4

[0069] This comparative example provides a sodium ion battery high entropy layered cathode material containing Na and 0.20 mole vacancies in the alkali metal layer and five components in the transition metal layer. The chemical formula is Na 0.80 Fe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti0.2 O2, with an entropy of 1.79R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0070] (1) Preparation of Na 0.80 Fe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti 0.2 O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0071] (2) Preparation of Na 0.80 Fe 0.2 Co 0.2 Ni 0.2 Mn 0.2 Ti 0.2 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Comparative Example 1.

[0072] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0073] Comparative Example 5

[0074] This comparative example provides a sodium ion battery high entropy layered cathode material containing three components and 0.25 mole vacancies in the alkali metal layer and six components in the transition metal layer, with the chemical formula being (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.1 8Mn 0.26 Ti 0.1 Cu 0.1 )O2, with an entropy value of 2.17R, was prepared by a one-step solid phase method. The specific steps are as follows:

[0075] (1) Preparation (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0076] (2) Preparation (Na 0.70 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1Cu 0.1 )O2 high entropy layered positive electrode plate, the implementation steps are the same as those of comparative example 1.

[0077] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0078] Comparative Example 6

[0079] This comparative example provides a sodium ion battery high entropy layered cathode material containing Na and 0.30 mole vacancies in the alkali metal layer and six components in the transition metal layer, with the chemical formula being Na 0.70 Fe 1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 3 Ti 1 / 12 Cu 1 / 12 O2, with an entropy of 1.93R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0080] (1) Preparation of Na 0.70 Fe 1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 3 Ti 1 / 12 Cu 1 / 12 O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0081] (2) Preparation of Na 0.70 Fe 1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 3 Ti 1 / 12 Cu 1 / 12 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Comparative Example 1.

[0082] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0083] Comparative Example 7

[0084] This comparative example provides a sodium ion battery high entropy layered cathode material containing Na and 0.30 mole vacancies in the alkali metal layer and seven components in the transition metal layer, with the chemical formula being Na 0.70 Fe 1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 6 Ti 1 / 12 Cu 1 / 6 Mg 1 / 12 O2, with an entropy of 2.16R, was prepared using a one-step solid phase method. The specific steps are as follows:

[0085] (1) Preparation of Na 0.70 Fe1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 6 Ti 1 / 12 Cu 1 / 6 Mg 1 / 12 O2 high entropy layered positive electrode material, the implementation steps are the same as those of Comparative Example 1.

[0086] (2) Preparation of Na 0.70 Fe 1 / 6 Co 1 / 6 Ni 1 / 6 Mn 1 / 6 Ti 1 / 12 Cu 1 / 6 Mg 1 / 12 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Comparative Example 1.

[0087] (3) The assembly and testing of the sodium ion battery are the same as those in Comparative Example 1.

[0088] Comparative Example 8

[0089] This comparative example provides a sodium ion battery high entropy layered cathode material containing Na and 0.3 mole vacancies in the alkali metal layer and six components in the transition metal layer, with the chemical formula being Na 0.70 Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 O2, with an entropy of 1.99R, is prepared by high-temperature solid-phase sintering combined with low-temperature molten salt ion exchange. The specific steps are as follows:

[0090] (1) Preparation of Na 0.75 Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 O2 high entropy precursor, the implementation steps are the same as Example 1.

[0091] (2) Preparation of Na 0.70 Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 The implementation steps of the O2 high entropy layered positive electrode material are the same as those of Example 1, but no other metal source is added, that is, no other components are introduced into the alkali metal layer.

[0092] (3) Preparation of Na 0.70 Fe 0.18 Co0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 The O2 high entropy layered positive electrode plate is implemented in the same steps as in Example 1.

[0093] (4) The assembly and testing of the sodium ion battery are the same as in Example 1.

[0094] Comparative Example 9

[0095] This comparative example provides a sodium ion battery high entropy layered cathode material containing three components and 0.05 mole vacancies in the alkali metal layer and six components in the transition metal layer, with the chemical formula being (Na 0.90 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2, with an entropy value of 2.02R, is prepared by high-temperature solid-phase sintering combined with low-temperature molten salt ion exchange. The specific steps are as follows:

[0096] (1) Preparation of NaFe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 O2 high entropy precursor, the implementation steps are the same as Example 1.

[0097] (2) Preparation (Na 0.90 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered positive electrode material, the implementation steps are the same as Example 1.

[0098] (3) Preparation (Na 0.90 La 0.025 Sr 0.025 )(Fe 0.18 Co 0.18 Ni 0.18 Mn 0.26 Ti 0.1 Cu 0.1 )O2 high entropy layered positive electrode plate, the implementation steps are the same as Example 1.

[0099] (4) The assembly and testing of the sodium ion battery are the same as in Example 1.

[0100] Table 1 shows the crystal structure and configurational entropy calculation results of the high entropy layered cathode materials prepared in different embodiments and comparative examples.

[0101] Table 2 shows the rate performance test results (1C=200mAh / g) of the high entropy layered cathode materials prepared in different embodiments and comparative examples within the voltage range of 1.9-4.1V.

[0102] Table 1: Comparison of crystal structures and configurational entropies of different examples and comparative examples

[0103] Crystal structure type Whether there is impurity phase Configuration entropy Example 1 O3 none 2.17R Example 2 O3 none 2.17R Comparative Example 1 O3 none 1.62R Comparative Example 2 O3 NiO 1.82R Comparative Example 3 O3 NiO 1.85R Comparative Example 4 O3+P2 NiO 1.79R Comparative Example 5 O3+P2 NiO 2.17R Comparative Example 6 O3+P2 NiO 1.93R Comparative Example 7 O3 NiO 2.16R Comparative Example 8 O3 NiO 1.99R Comparative Example 9 O3 <![CDATA[Na3MnO4]]> 2.02R

[0104] Table 2: Comparison of rate performance of different examples and comparative examples

[0105]

[0106]

[0107] Combining Table 1 and Table 2, we can see that:

[0108] Comparing Comparative Examples 1-3, it is difficult to control the phase purity of the synthesized material by relying on the one-step solid-phase method to adjust only the components and proportions of the transition metal layer to achieve entropy increase, and it is at the expense of some reversible capacity. When the transition metal components are increased from five to seven, the configurational entropy of Comparative Example 2 increases from 1.61R to 1.82R. However, at the same time, due to competition for transition metal sites, a NiO impurity phase appears in Comparative Example 2. After adjusting the components and proportions of the transition metal layer, the entropy value of Comparative Example 3 further increases slightly to 1.85R, but the NiO impurity phase still exists.

[0109] Comparing Comparative Examples 1 and 4, increasing entropy by solely manipulating alkali metal layer vacancies using a one-step solid-phase method also compromises the material's phase purity. When the alkali metal layer vacancy concentration increases to 0.20 mol, the material's configurational entropy increases from 1.61R to 1.79R, but the crystal structure transforms from an O3 single phase to an O3P2 dual phase, with the simultaneous formation of a NiO impurity phase. This is because the reduced sodium content in layered transition metal oxides favors the more thermodynamically stable P2 structure.

[0110] Comparing Example 1 with Comparative Example 5, which relies on a one-step solid-phase method to increase the components of the alkali metal and transition metal layers while retaining a large number of vacancies in the alkali metal layer, it is also difficult to obtain pure O3 phase material. In Comparative Example 5, synthesized via a one-step solid-phase method, the alkali metal layer contains three components and 0.25 mol of vacancies, and the transition metal layer contains six components, but the crystal structure is an O3P2 dual phase, and NiO impurities are also produced.

[0111] Comparing Comparative Examples 1, 6, and 7, it is difficult to synthesize pure phase materials by simultaneously increasing the transition metal layer composition and the alkali metal layer vacancy concentration using a one-step solid-phase method. After significantly increasing the alkali metal layer vacancy concentration and transition metal layer composition to achieve a significant entropy increase, both Comparative Examples 6 and 7 exhibited a large amount of NiO impurity phase, negatively impacting rate performance. Furthermore, since the vacancy concentration had reached 0.3 mol at this point, Comparative Example 6 had already transitioned to a predominantly P2 phase.

[0112] Comparing Example 1, Comparative Example 8, and Comparative Example 9, even with the layered, stepwise entropy increase method, phase purity cannot be guaranteed when the alkali metal layer contains a large number of vacancies but only Na, or when the alkali metal layer contains at least three components but only a small number of vacancies. In particular, when there are too few vacancies, the increase in the alkali metal layer components leads to the formation of Na3MnO4 impurities.

[0113] By increasing entropy step by step and layer by layer, while adjusting the transition metal layer components and the vacancy concentration of the alkali metal layer, different types of components are introduced into the alkali metal layer to synthesize pure phase materials. The alkali metal layer of Example 1 contains six components, the alkali metal layer contains Na and two trace components, and retains a vacancy concentration of 0.25 moles, so the configuration entropy is significantly increased to 2.17R, and the pure O3 crystal structure is still maintained at a low sodium content. Avoid sacrificing capacity by adding too many inactive components to the transition metal layer, but introduce only 0.05 moles of elements into the alkali metal layer to ensure a capacity output of 141mAh / g of the material, the capacity retention at 10C reaches 75.9%, and there is still a reversible specific capacity of 91mAh / g at 20C, with long cycle stability.

[0114] In summary, the method for preparing high-entropy layered positive electrode materials for sodium-ion batteries by step-by-step layered entropy increase provided by the present invention can effectively ensure the phase purity of the positive electrode material, improve the structural stability, and exhibit excellent rate performance at high rates without sacrificing capacity and cycle stability, thereby improving the overall performance of the material.

Claims

1. A high-entropy layered cathode material for sodium ion batteries with step-by-step entropy increase, characterized in that: The general chemical formula of the high entropy layered cathode material is: (Na x M y )(Fe b Co c Ni d Mn e N f )O2; wherein b, c, d, e, f, x, y are corresponding element molar ratios or corresponding total molar ratios of multiple elements, 0<b, c, d, f≤0.2; 0.2<e≤0.3; 0.65≤x<0.80; 0<y<0.05; and satisfy the relationship 0.65<x+y<0.80, b+c+d+e+f≤1; the alkali metal layer of the high entropy layered positive electrode material retains at least 0.20 moles of vacancies; The high entropy layered cathode material still maintains an O3-type crystal structure and a space group R3m at a low sodium content, and has a superlattice structure. The superlattice is manifested as superlattice diffraction peaks at 18-23° and 40-45° in the XRD spectrum of the cathode material.

2. The high entropy layered cathode material according to claim 1, characterized in that The N is located in the transition metal layer and contains at least one element, wherein the molar ratio of each element is at least 0.1; the electronegativity of each element contained in the N does not exceed 2.05; the difference in atomic radius between the elements including N in the transition metal layer does not exceed 30%; N specifically includes but is not limited to at least one of Mg, Al, Ti, V, Cr, Cu, Nb, Sn, and Sb.

3. The high entropy layered cathode material according to claim 1, characterized in that The M is located in the alkali metal layer and contains at least two different types of elements in addition to Na, wherein the total content of each element does not exceed 0.05 molar ratio; the ionic valence state of each element contained in the M is not more than +3, and the difference in atomic radius from Na is not more than 45%; M specifically includes but is not limited to at least two of Sr, Ba, and La.

4. A method for preparing the high entropy layered cathode material according to claims 1-3, characterized in that: The preparation method is a combination of high temperature solid phase sintering and ion exchange reaction: the first step is to use high temperature solid phase sintering to prepare a transition metal layer containing a high entropy precursor Na a (Fe b Co c Ni d Mn e N f )O2, wherein 0.65<a≤0.80; the second step is to introduce at least two different types of trace elements other than Na into the sodium layer by ion exchange reaction and retain at least 0.2 moles of vacancies.

5. The preparation method according to claim 4, characterized in that The high temperature solid phase sintering comprises the following steps: (1) Grinding the metal salts or metal oxides corresponding to each element in a mortar for 20-30 minutes according to the stoichiometric ratio of the high entropy precursor, and pressing them into a disc A under a pressure of 10-15 MPa; (2) placing the wafer A in a crucible and sintering it at high temperature in a tube furnace; the high temperature sintering temperature is 900-1000°C, the sintering time is 12-15 hours, the sintering atmosphere is an oxygen-containing atmosphere, and the heating and cooling rates are 3-8°C / min; (3) After the furnace temperature drops to 100-200°C, the wafer A is taken out and quickly ground for 2-3 minutes to obtain a high entropy precursor.

6. The preparation method according to claim 4, characterized in that The ion exchange reaction includes any one of low-temperature molten salt ion exchange or liquid phase ion exchange; The low-temperature molten salt ion exchange comprises: (1) mixing the high entropy precursor with the low melting point salt or oxide corresponding to the element contained in M ​​and grinding them in a mortar for 5-8 minutes, and pressing them into a disc B under a pressure of 10-15 MPa; (2) placing the disc B in a crucible and sintering it at a low temperature in a tube furnace; the low temperature sintering temperature is 150-400°C, the sintering time is 4-8 hours, the sintering atmosphere is an oxygen-containing atmosphere, and the heating and cooling rates are 3-8°C / min; (3) After the furnace temperature drops to 100-200°C, the disc is taken out and rapidly ground for 2-3 minutes to obtain powder B; (4) washing powder B twice with an ethanol-water solution, vacuum filtering, and vacuum drying to obtain a high-entropy layered cathode material; the vacuum drying temperature is 80-100° C., and the drying time is 10-12 h; The liquid phase ion exchange comprises: (1) dissolving the salt or chloride corresponding to the element contained in M ​​in an ethanol aqueous solution and mixing them uniformly to obtain a solution precursor, wherein the pH value of the solution precursor is controlled in the range of 0.5-3.0; (2) adding the high entropy precursor to the solution precursor, heating and stirring, washing twice with an ethanol-water solution, vacuum filtering, and drying to obtain powder C; the heating temperature is 60-100° C., and the stirring time is 6-8 h; (3) Powder C is placed in a crucible and placed in a tubular furnace for heat treatment to obtain a high-entropy layered positive electrode material; the heat treatment temperature is 800-1000°C, the heat treatment time is 12-15h, the heat treatment atmosphere is an oxygen-containing atmosphere, and the heating and cooling rates are both 3-8°C / min.

7. The preparation method according to claim 4, characterized in that After high-temperature sintering, the configurational entropy of the high-entropy precursor increases to at least 1.50R; after ion exchange, the configurational entropy of the high-entropy layered cathode material increases to at least 2.00R; wherein R is the universal gas constant.

8. A sodium ion battery positive electrode sheet comprising the high entropy layered positive electrode material according to claims 1-3, characterized in that: The positive electrode sheet comprises the high entropy layered positive electrode material, a conductive additive and a binder.

9. A sodium ion battery, characterized in that: The sodium ion battery includes a positive electrode, which contains a high-entropy layered positive electrode material as described in any one of claims 1 to 3 or prepared by the preparation method according to any one of claims 4 to 8.

10. Use of the high entropy layered cathode material for sodium ion batteries according to claims 1-3 to improve rate performance in sodium ion batteries.

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