A high entropy strategy sodium ion battery layered positive electrode material, preparation method and use

Abstract

The present invention relates to a sodium ion battery layered positive electrode material of a high entropy strategy, a preparation method and a use thereof, and belongs to the technical field of sodium ion battery materials. In the present invention, a six-element high entropy positive electrode material is prepared by designing six elements in the crystal structure of a transition metal layer, which significantly improves the crystal structure stability of the positive electrode material, and obtains a high-performance sodium ion battery layered oxide positive electrode material with significantly improved cycle performance and rate performance.

Description

Technical Field

[0001] The invention relates to a sodium ion battery layered positive electrode material of a high entropy strategy, a preparation method and application thereof, and belongs to the technical field of sodium ion battery materials. Background Art

[0002] As the requirements for new large-scale energy storage systems continue to increase, sodium-ion batteries have attracted widespread attention due to their abundant resources, easy availability, and obvious cost advantages. Among the many components of sodium-ion batteries, the performance of the positive electrode material system plays a key role in the single cell device. The layered transition metal oxide positive electrode system has the advantages of diversified synthesis methods and easy control of component structure. However, the layered oxide positive electrode material system has problems such as irreversible phase change, crystal structure collapse failure, and irreversible transition metal ion migration, which means that its electrochemical performance still has a lot of room for improvement.

[0003] At present, many studies have achieved certain results through special crystal structure design, element doping, surface coating and other means, but further optimization and improvement are still needed. At the same time, there is still room for improvement in experimental design, operational convenience and cost issues. 0.5 Mn 0.5 As a classic O3 phase structure material, O2 material has problems such as poor rate performance, poor cycle stability, multiple phase transitions during charge and discharge, and poor air stability. Through this high entropy modification strategy, the advantages of multiple elements are combined to significantly improve the rate performance, cycle stability, and air stability of the material system. Summary of the invention

[0004] The technical problem to be solved by the present invention is that NaNi 0.5 Mn 0.5 When O2 materials are used in sodium ion batteries, there are problems with poor rate performance and cycle performance. The present invention provides a sodium ion battery layered positive electrode material, a preparation method and use of a high entropy strategy. In the field of sodium ion battery layered positive electrode oxide materials, a transition metal layer has 5 or more transition metals, which can be considered as a high entropy oxide material; in the present invention, a six-element high entropy positive electrode material is prepared by designing six elements in the crystal structure of the transition metal layer, which significantly improves the crystal structure stability of the positive electrode material, and obtains a high-performance sodium ion battery layered oxide positive electrode material with significantly improved cycle performance and rate performance.

[0005] A high entropy strategy sodium ion battery layered cathode material having a chemical formula of:

[0006] Na a A b Ni cM d N e Mn f R g O2

[0007] a+2b+2c+3d+3e+4f+4g=2;

[0008] And 0.25<(b+g) / a<0.35, 0.3<(d+e) / a<0.45, 0.15 <c / a<0.25,0.15<f / a<0.22;

[0009] in,

[0010] Element A is selected from Cu, Mg or Zn;

[0011] The M element is selected from Fe or a mixture of Fe and X element. In the mixture of Fe and X, the molar percentage of X is 1-20%; the X element is selected from one of Al, Ga, Cr or V.

[0012] The N element is selected from Co or a mixture of Co and X element. In the mixture of Co and X, the molar percentage of X is 1-20%; the X element is selected from one of Al, Ga, Cr or V.

[0013] The R element is selected from Ti, Sn, Zr, Mo, Ru or Nb.

[0014] In one embodiment, the cathode material is NaCu 1 / 6 Ni 1 / 6 Fe 1 / 6 Co 1 / 6 Mn 1 / 6 Ti 1 / 6 O2, NaCu 0.1 Ni 0.2 Fe 0.25 Co 0.15 Mn 0.2 Ti 0.1 O2, NaCu 0.1 Ni 0.2 Fe 0.35 Co 0.05 Mn 0.2 Ti 0.1 O2 or NaMg 1 / 6 Ni 1 / 6 Fe 1 / 6 Co 1 / 6Mn1 / 6Ti 1 / 6 O2, NaCu 0.1 Ni 0.2 Fe 0.2 Co 0.17 Al 0.03 Mn0.2 Ti 0.1 O2.

[0015] The method for preparing the layered positive electrode material for sodium ion batteries using the high entropy strategy is to prepare the material by a sol-gel method or a solid phase method.

[0016] The sol-gel method comprises: dissolving a sodium source, a manganese source and an inorganic salt containing elements A, M, N and R in water, adding a complexing agent, reacting to form a gel, and obtaining a positive electrode material after drying and calcining.

[0017] The sodium source is selected from sodium nitrate, and the manganese source is selected from manganese nitrate; the inorganic salt containing the A element is selected from copper nitrate, magnesium nitrate or zinc nitrate; the inorganic salt containing the M element is selected from iron nitrate or a mixture of iron nitrate and the nitrate of the X element; the inorganic salt containing the N element is selected from cobalt nitrate or a mixture of cobalt nitrate and the inorganic salt of the X element, and the inorganic salt of the X element is selected from aluminum nitrate, gallium nitrate, chromium nitrate or vanadyl sulfate; the inorganic salt containing the R element is selected from titanate, stannous oxalate, zirconium oxychloride, molybdenum nitrate, ruthenium oxide or niobium hydroxide.

[0018] The complexing agent is citric acid, ascorbic acid, maleic acid, oxalic acid, ammonium oxalate, ethanolamine, diethanolamine or triethanolamine.

[0019] The calcination process is calcining at 850-1050° C. for 2-20 hours.

[0020] The solid phase method comprises: mixing precursors of sodium, manganese, A, M, N and R elements, ball milling and calcining to obtain the positive electrode material.

[0021] The precursors are oxides, carbonates or hydroxides.

[0022] The calcination process is carried out at 850-1050° C. for 2-20 hours.

[0023] The application of the above-mentioned positive electrode material in the manufacture of sodium ion batteries.

[0024] The layered cathode material of the sodium ion battery of the high entropy strategy has the chemical formula:

[0025] Na a A b Ni c M d Mn e N f O2

[0026] a+2b+2c+3d+4e+4f=2; the ratio of b, c, d, e to a is greater than 0.10 and less than 0.20;

[0027] in,

[0028] Element A is selected from Cu, Mg or Zn;

[0029] The M element is selected from Fe or a mixture of Fe and X element, wherein the molar percentage of X in the mixture of Fe and X is 1-20%; the X element is selected from one of Al, Ga, Cr or V;

[0030] The N element is selected from Ti, Sn, Zr, Mo, Ru or Nb.

[0031] The positive electrode material has a chemical formula of NaCu 0.15 Ni 0.25 Fe 0.15 Mn 0.3 Ti 0.15 O2.

[0032] The preparation method of the layered positive electrode material of the sodium ion battery using the high entropy strategy is prepared by a sol-gel method or a solid phase method.

[0033] The sol-gel method comprises: dissolving a sodium source, a manganese source and an inorganic salt containing elements A, M and N in water, adding a complexing agent, reacting to form a gel, and obtaining a positive electrode material after drying and calcining.

[0034] The sodium source is selected from sodium nitrate, the manganese source is selected from manganese nitrate or manganese acetate; the inorganic salt containing element A is selected from copper nitrate, magnesium nitrate or zinc nitrate; the inorganic salt containing element M is selected from iron nitrate or a mixture of iron nitrate and nitrate of element X, and the inorganic salt of element X is selected from aluminum nitrate, gallium nitrate, chromium nitrate or vanadyl sulfate; the inorganic salt containing element N is selected from titanate, stannous oxalate, zirconium oxychloride, molybdenum nitrate, ruthenium chloride or niobium hydroxide.

[0035] The complexing agent is citric acid, ascorbic acid, maleic acid, oxalic acid, ammonium oxalate, ethanolamine, diethanolamine or triethanolamine.

[0036] The calcination process is calcining at 850-1050° C. for 2-20 hours.

[0037] The solid phase method comprises: mixing precursors containing sodium, manganese, A, M, and N elements, ball milling, and calcining to obtain a positive electrode material.

[0038] The precursor is an oxide, a carbonate or a hydroxide.

[0039] Beneficial Effects

[0040] This patent is aimed at NaNi 0.5 Mn0.5 The problems existing in O2 positive electrode materials are improved by using materials of the six-element high entropy material system. The high entropy strategy adopted for the sodium ion battery layered positive electrode material Na a A b Ni c M d N e Mn f R g In O2, as A element (Cu or Mg or Zn) and M / N element (mainly Fe 3+ ,Co 3+ ), can compensate for the charge and enhance the stability of the layered structure, R elements (Ti or Sn / Zr / Mo / Ru / Nb) are beneficial to the stability of the crystal structure and improve the working voltage of the material; the appropriate dose of Fe 3+ It can support the crystal structure through partial ion migration; Co 3+ It is beneficial to improve the electronic conductivity of the material and stabilize the crystal structure of the transition metal layer; in addition, a small amount of Al / Ga / Cr / V can be further added to the M and N elements to contribute to the capacity or stabilize the crystal structure in a wide voltage operating range. In summary, through this high entropy strategy, the synergistic effect of multiple elements significantly improves the cycle stability and rate performance of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 :X-ray powder diffraction spectrum of the material

[0042] Figure 2 :Scanning electron microscope image of the material

[0043] Figure 3 : Element distribution map of materials

[0044] Figure 4 :Charge and discharge curves of the material in the first three cycles at a current density of 10mA / g

[0045] Figure 5 :Charge and discharge curves of materials at different current densities

[0046] Figure 6 :Cycling performance of materials at different current densities

[0047] Figure 7 :Long cycle performance curve of the material at a current density of 0.2A / g

[0048] Figure 8 :X-ray diffraction patterns of materials synthesized by sol-gel method

[0049] Fig. 9 :Scanning electron microscope image of sol-gel synthesized materials

[0050] Fig.10 :Element distribution map of sol-gel synthesized materials

[0051] Fig.11 :The charge-discharge curves of the first three cycles of sol-gel synthesis at a current density of 10 mA / g

[0052] Fig.12 :X-ray powder diffraction spectrum of the material

[0053] Fig.13 :Scanning electron microscope image of the material

[0054] Fig.14 : Element distribution map of materials

[0055] Fig.15 :Charge and discharge curves of the material in the first three cycles at a current density of 10mA / g

[0056] Fig.16 :Long cycle performance curve of the material at a current density of 0.2A / g

[0057] Fig.17 :X-ray powder diffraction spectrum of the material

[0058] Fig.18 :Scanning electron microscope image of the material

[0059] Fig.19 : Element distribution map of materials

[0060] Fig. 20 :Charge and discharge curves of the material in the first three cycles at a current density of 10mA / g

[0061] Fig.21 :Long cycle performance curve of the material at a current density of 0.2A / g

[0062] Fig. 22 :X-ray powder diffraction spectrum of the material

[0063] Fig.23 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0064] Fig.24 :Long cycle performance curve of the material at a current density of 0.2A / g

[0065] Fig.25 :X-ray powder diffraction spectrum of the material

[0066] Fig.26 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0067] Fig. 27:X-ray powder diffraction spectrum of the material

[0068] Fig.28 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0069] Fig.29 :Long cycle performance curve of the material at a current density of 0.2A / g

[0070] Fig.30 :X-ray powder diffraction spectrum of the material

[0071] Fig.31 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0072] Fig.32 :Long cycle performance curve of the material at a current density of 0.2A / g

[0073] Fig.33 :X-ray powder diffraction spectrum of the material

[0074] Fig.34 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0075] Fig.35 :X-ray powder diffraction spectrum of the material

[0076] Fig.36 :Typical charge and discharge curve of the material at a current density of 10mA / g

[0077] Fig.37 :Long cycle performance curve of the material at a current density of 0.2A / g DETAILED DESCRIPTION

[0078] In the battery performance test used in the following examples, the following method was first used to assemble the electrode materials into a battery. The positive electrode material was used: conductive agent (acetylene black): binder (polyvinylidene fluoride PVDF) = 7:2:1 and N-methylpyrrolidone NMP was used as a solvent to mix evenly, coated on aluminum foil, and cut into a 12mm diameter disc as a positive electrode after vacuum drying at 120°C. Metallic sodium was used as the negative electrode, glass fiber membrane as the diaphragm, 1.0M NaClO4 PC+5% FEC as the electrolyte, and button cells were assembled in an argon protection glove box. The electrochemical performance test was carried out at room temperature 25°C.

[0079] Example 1

[0080] The material prepared by high temperature solid phase method, the raw materials are Na2CO3, NiO, CuO, CoO, Fe2O3, TiO2, and Mn2O3, according to the corresponding molar ratio, 300rpm ball milling for 5h, wet grinding aid is anhydrous ethanol, and dried at 80℃ to obtain the precursor powder. The precursor powder is placed in a muffle furnace for calcination, the temperature is increased by 5℃ / min, calcined at 900℃ for 12h, and cooled naturally to obtain the high entropy positive electrode material NaCu 1 / 6 Ni 1 / 6 Fe 1 / 6 Co 1 / 6 Mn 1 / 6 Ti 1 / 6 O2. The X-ray powder diffraction test results of the material are as follows Figure 1 , space group is R3m, and there are trace amounts of CuO impurities. The SEM images of the materials synthesized by high temperature solid phase method are shown in Figure 2 The morphology is irregular layered particles with a particle size of 2-5 microns. The energy spectrometer test results are as follows Figure 3 As shown in the figure, they are the distribution diagrams of Na, O, Ni, Fe, Mn, Cu, Co, and Ti elements in the material particles. Each element is evenly distributed in the material particles. The relevant electrochemical performance tests of the materials are carried out, such as Figure 4 The charge and discharge curve of the material at a current density of 10mA / g has a voltage window of 2-4V and a reversible specific capacity of 114.2mAh / g. Figure 5 As shown, under the test conditions of current density of 0.01, 0.02, 0.05, 0.1, 0.2, 0.5 and 1A / g, the discharge specific capacity is 120.9, 116.5, 113.8, 111.1, 107.8, 103.3 and 98.7 mAh g, respectively. -1 , with excellent rate performance. Figure 6 As shown, the material was cycled 5 times at different current densities. After 35 cycles, the capacity reached 115.9 mAh / g at a current of 0.02 A / g. Compared with the previous discharge capacity retention rate of 0.02 A / g (116.5 mAh / g), it was as high as 99.5%. Figure 7 This is the long cycle performance curve of the material at a current density of 0.2A / g. After 200 cycles, the capacity retention rate is 91%, which has excellent cycle stability.

[0081] Example 2

[0082] The material prepared by the sol-gel method is sodium nitrate, nickel nitrate, iron nitrate, manganese nitrate, cobalt nitrate, copper nitrate and tetrabutyl titanate, which are dissolved in 15 ml of pure water in corresponding molar ratios to form solution A, and a certain molar ratio of monohydrated citric acid and ascorbic acid are dissolved in 15 ml of pure water to form solution B. After stirring for 15 minutes, B is slowly added to A, dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours. The product is placed in a muffle furnace for calcination, heated at 5°C / min, pre-fired at 400°C for 2 hours, then heated to 900°C for 12 hours, and cooled naturally to obtain a high entropy positive electrode material NaCu 1 / 6 Ni 1 / 6 Fe 1 / 6Co 1 / 6 Mn 1 / 6 Ti 1 / 6 O2. The X-ray powder diffraction test results of the material are as follows Figure 1 , space group is R3m, and there are trace amounts of CuO impurities. The SEM images of the materials synthesized by the sol-gel method are shown in Fig. 9 , the primary particles with a particle size of 1-3 microns agglomerate to form irregular secondary particles. The energy spectrometer test results are as follows Fig.10 As shown in the figure, they are the distribution diagrams of Na, O, Ni, Fe, Mn, Cu, Co, and Ti elements in the material particles. Each element is evenly distributed in the material particles. The relevant electrochemical performance tests of the materials are carried out, such as Fig.11 The material was synthesized by sol-gel method at 10 mA g -1 The charge and discharge curve under current density has a voltage window of 2-4V and a reversible specific capacity of 123.6mAh / g.

[0083] Example 3

[0084] The material prepared by high temperature solid phase method, the raw materials are Na2CO3, NiO, CuO, CoO, Fe2O3, TiO2, and Mn2O3, according to the corresponding molar ratio, 300rpm ball milling for 5h, wet grinding aid is anhydrous ethanol, and dried at 80℃ to obtain the precursor powder. The precursor powder is placed in a muffle furnace for calcination, the temperature is increased by 5℃ / min, calcined at 900℃ for 12h, and cooled naturally to obtain the high entropy positive electrode material NaCu 0.1 Ni 0.2 Fe 0.25 Co 0.15 Mn 0.2 Ti 0.1 O2. The X-ray powder diffraction test results of the material are as follows Fig.12 , space group is R3m. The SEM image of the material synthesized by high temperature solid phase method is shown in Fig.13 The morphology is irregular layered particles with a particle size of 2-5 microns. The energy spectrometer test results are as follows Fig.14As shown in the figure, they are the distribution diagrams of Na, O, Ni, Fe, Mn, Cu, Co, and Ti elements in the material particles. Each element is evenly distributed in the material particles. The relevant electrochemical performance tests of the materials are carried out, such as Fig.15 The charge and discharge curve of the material at a current density of 10mA / g has a voltage window of 2-4V and a reversible specific capacity of 122.7mAh / g. Fig.16 For positive electrode materials at 0.2A·g -1 The long cycle performance under current density is 82.6% after 100 cycles, which shows excellent cycle stability.

[0085] Example 4

[0086] The material prepared by high temperature solid phase method, the raw materials are Na2CO3, NiO, CuO, CoO, Fe2O3, TiO2, and Mn2O3, according to the corresponding molar ratio, 300rpm ball milling for 5h, wet grinding aid is anhydrous ethanol, and dried at 80℃ to obtain the precursor powder. The precursor powder is placed in a muffle furnace for calcination, the temperature is increased by 5℃ / min, calcined at 900℃ for 12h, and cooled naturally to obtain the high entropy positive electrode material NaCu 0.1 Ni 0.2 Fe 0.35 Co 0.05 Mn 0.2 Ti 0.1 O2. The X-ray powder diffraction test results of the material are as follows Fig.17 , space group is R3m. The SEM image of the material synthesized by high temperature solid phase method is shown in Fig.18 The morphology is irregular layered particles with a particle size of 2-5 microns. The energy spectrometer test results are as follows Fig.19 As shown in the figure, they are the distribution diagrams of Na, O, Ni, Fe, Mn, Cu, Co, and Ti elements in the material particles. Each element is evenly distributed in the material particles. The relevant electrochemical performance tests of the materials are carried out, such as Fig. 20 The charge and discharge curve of the material at a current density of 10mA / g has a voltage window of 2-4V and a reversible specific capacity of 125.4mAh / g. Fig.19 For positive electrode materials at 0.2A·g -1 The long cycle performance under current density is 80.7% after 100 cycles, which shows excellent cycle stability.

[0087] Example 5

[0088] The material was prepared by high temperature solid phase method. The raw materials were Na2CO3, NiO, MgO, CoO, Fe2O3, TiO2, and Mn2O3. According to the corresponding molar ratio, the ball milling was carried out at 300rpm for 5h. The wet grinding aid was anhydrous ethanol. The precursor powder was dried at 80℃. The precursor powder was placed in a muffle furnace for calcination, the temperature was increased by 5℃ / min, calcined at 900℃ for 12h, and cooled naturally to obtain the high entropy positive electrode material NaMg 1 / 6 Ni 1 / 6 Fe 1 / 6 Co 1 / 6 Mn1 / 6Ti 1 / 6 O2. The X-ray powder diffraction test results of the material are shown in the figure, and the space group is R3m. The relevant electrochemical performance tests of the material are carried out, such as Figure 22-Figure 24 As shown in the figure, the charge and discharge curve of the material at a current density of 10mA / g, the voltage window is 2-4V, and the reversible specific capacity is 121.8mAh / g. -1 Long cycle performance under current density, the capacity retention rate is 75% after 200 cycles, and it has excellent cycle stability.

[0089] Example 6

[0090] The material prepared by the sol-gel method is sodium nitrate, nickel nitrate, iron nitrate, aluminum nitrate, manganese nitrate, cobalt nitrate, copper nitrate and tetrabutyl titanate, which are dissolved in 15 ml of pure water according to the corresponding molar ratio to form solution A, and a certain molar ratio of monohydrated citric acid and ascorbic acid is dissolved in 15 ml of pure water to form solution B. After stirring for 15 minutes, B is slowly added to A, dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours. The product is placed in a muffle furnace for calcination, heated at 5°C / min, pre-fired at 400°C for 2 hours, then heated to 900°C for 12 hours, and cooled naturally to obtain a high entropy positive electrode material NaCu 0.1 Ni 0.2 Fe 0.2 Co 0.17 Al 0.03 Mn 0.2 Ti 0.1 O2. The X-ray powder diffraction test results of the material are as follows Figure 1 , the space group is R3m. The relevant electrochemical performance tests of the materials are carried out, such as Figure 26-Figure 27 The charge and discharge curve of the material synthesized by the sol-gel method at a current density of 10mA / g has a voltage window of 2-4.2V and a reversible specific capacity of 123.2mAh / g.

[0091] In the comparative test, the NaNi 0.5 Mn 0.5 O2,NaNi 0.35 Fe0.15 Co 0.15 Mn 0.3 O2,NaNi 0.35 Cu 0.15 Ti 0.15 Mn 0.3 O2, three comparative experiments, the transition metal elements in the components are 2, 4, and 4, which means that they are not considered to belong to the range of high entropy materials.

[0092] Comparative Example 1

[0093] This example is compared with Example 1, and the valence state is kept consistent to prepare the material NaNi without Cu and Ti. 0.35 Fe 0.15 Co 0.15 Mn 0.35 O2.

[0094] The material prepared by the sol-gel method is sodium nitrate, nickel nitrate, iron nitrate, manganese nitrate, and cobalt nitrate. The raw materials are dissolved in 15 ml of pure water according to the corresponding molar ratio to form solution A. A certain molar ratio of monohydrated citric acid and ascorbic acid is dissolved in 15 ml of pure water to form solution B. After stirring for 15 minutes, B is slowly added to A, dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours. The product is placed in a muffle furnace for calcination, heated at 5°C / min, pre-fired at 400°C for 2 hours, then heated to 900°C for 12 hours, and cooled naturally to obtain the comparative sample material NaNi 0.35 Fe 0.15 Co 0.15 Mn 0.35 O2. The X-ray powder diffraction test results of the material are as follows Fig. 27 , the space group is R3m. The relevant electrochemical performance tests of the materials are carried out, such as Fig.28 The charge and discharge curve of the material at a current density of 10mA / g has a voltage window of 2-4V and a reversible specific capacity of 126.9mAh / g. Fig.29 The long cycle performance of the positive electrode material at a current density of 0.2A g-1, the capacity retention rate after 200 cycles is 65%. It can be seen that due to the Cu 2+ Charge compensation can be performed, Ti 4+ It is beneficial to stabilize the crystal structure. Compared with comparative example 1, the performance of the embodiment is significantly improved.

[0095] Comparative Example 2

[0096] This example is compared with Example 1, and the valence state is kept consistent to prepare the material NaNi without Co and Fe. 0.35 Cu 0.15 Ti 0.15 Mn 0.35O2.

[0097] The material prepared by the sol-gel method is sodium nitrate, nickel nitrate, manganese nitrate, copper nitrate and tetrabutyl titanate, which are dissolved in 15 ml of pure water according to the corresponding molar ratio to form solution A, and a certain molar ratio of monohydrated citric acid and ascorbic acid are dissolved in 15 ml of pure water to form solution B. After stirring for 15 minutes, B is slowly added to A, dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours. The product is placed in a muffle furnace for calcination, heated at 5°C / min, pre-fired at 400°C for 2 hours, then heated to 900°C for 12 hours, and cooled naturally to obtain the comparative sample material NaNi 0.35 Cu 0.15 Ti 0.15 Mn 0.35 O2. The X-ray powder diffraction test results of the material are as follows Fig.30 , the space group is R3m. The relevant electrochemical performance tests of the materials are carried out, such as Fig.31 The charge and discharge curve of the material at a current density of 10mA / g has a voltage window of 2-4V and a reversible specific capacity of 120.8mAh / g. Fig.32 For positive electrode materials at 0.2Ag -1 The long cycle performance under current density shows that the capacity retention rate is 82% after 44 cycles. It can be seen that a certain proportion of Fe 3+ It is beneficial to the stability of the crystal structure, Co 3+ It is beneficial to improve the electronic conductivity and stabilize the transition metal layer framework. Compared with comparative example 2, the performance of the embodiment is significantly improved.

[0098] Comparative Example 3

[0099] The material prepared by the sol-gel method is sodium nitrate, nickel nitrate, and manganese nitrate. The raw materials are dissolved in 15 ml of pure water according to the corresponding molar ratio to form solution A. A certain molar ratio of monohydrated citric acid and ascorbic acid is dissolved in 15 ml of pure water to form solution B. After stirring for 15 minutes, B is slowly added to A, dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours. The product is placed in a muffle furnace for calcination, the temperature is increased at 5°C / min, pre-calcined at 400°C for 2 hours, then heated to 900°C for 12 hours, cooled naturally, and calcined twice to obtain the comparative sample material NaNi 0.5 Mn 0.5 O2. The X-ray powder diffraction test results of the material are as follows Fig.33 , the space group is R3m. The relevant electrochemical performance tests of the materials are carried out, such as Fig.34The charge and discharge curve of the material at a current density of 10mA / g, the voltage window is 2-4V, and the reversible specific capacity is 97mAh / g. It can be seen that the six-element quotient entropy positive electrode material provided by this patent is superior to the NaNi in the prior art. 0.5 Mn 0.5 For O2, the performance has been significantly improved.

[0100] Comparative Example 4

[0101] Compared with the embodiment, this comparative example prepared some five-element quotient entropy materials. Its main preparation process and performance parameters are as follows: the material prepared by high temperature solid phase method, the raw materials are Na2CO3, NiO, CuO, Fe2O3, TiO2, and Mn2O3, according to the corresponding molar ratio, 300rpm ball milling for 5h, wet grinding aid is anhydrous ethanol, and dried at 80℃ to obtain the precursor powder. The precursor powder is placed in a muffle furnace for calcination, the temperature is increased by 5℃ / min, calcined at 900℃ for 12h, and naturally cooled to obtain the high entropy positive electrode material NaCu 0.15 Ni 0.25 Fe 0.15 Mn 0.3 Ti 0.15 O2. The X-ray powder diffraction test results of the material are as follows Fig.35 , the space group is R3m. The relevant electrochemical performance tests of the materials are carried out, such as Fig.36 As shown in the figure, the charge and discharge curve of the material at a current density of 10 mA / g has a voltage window of 2-4 V and a reversible specific capacity of 127.6 mAh / g. Fig.37 For positive electrode materials at 0.2A·g -1 Long cycle performance under current density, the capacity retention rate is 80% after 200 cycles, and it has excellent cycle stability.

Claims

1. Application of a sodium ion battery layered cathode material of a high entropy strategy in the preparation of a sodium ion battery with a reversible specific capacity of 123.2 mAh / g, characterized in that: The positive electrode material has the chemical formula NaCu 0.1 Ni 0.2 Fe 0.2 Co 0.17 Al 0.03 Mn 0.2 Ti 0. 1O2; The preparation method of the positive electrode material is to prepare it by using a sol-gel method, wherein the raw materials are sodium nitrate, nickel nitrate, iron nitrate, aluminum nitrate, manganese nitrate, cobalt nitrate, copper nitrate and tetrabutyl titanate, which are dissolved in 15 ml of pure water according to corresponding molar ratios to form solution A, and a certain molar ratio of monohydrated citric acid and ascorbic acid are dissolved in 15 ml of pure water to form solution B, and solution B is slowly added to solution A after stirring for 15 minutes, and dried at 90°C to form a sol, and dried in a 120°C forced air drying oven for 3 hours, and the product is placed in a muffle furnace for calcination, the temperature is increased at 5°C / min, pre-calcined at 400°C for 2 hours, and then heated to 900°C for 12 hours, and cooled naturally to obtain the positive electrode material; The testing method of the reversible specific capacity is as follows: The electrode materials are assembled into a battery, using positive electrode material: conductive agent: binder = 7:2:1 and using N-methylpyrrolidone NMP as a solvent to mix evenly, coated on aluminum foil, and vacuum dried at 120°C and cut into discs with a diameter of 12 mm as positive electrode sheets; the conductive agent is acetylene black, the binder is PVDF, metallic sodium is used as the negative electrode, the glass fiber membrane is used as the diaphragm, 1.0M NaClO4PC+5%FEC is used as the electrolyte, and button cells are assembled in an argon protection glove box, and the electrochemical performance test is carried out at room temperature 25°C.

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