High-entropy high-sodium ferro-manganese series sodium ion battery positive electrode material, preparation method and battery

Abstract

The invention discloses a sodium ion battery positive electrode material, a preparation method and a battery. The general formula of a sodium transition metal oxide of the positive electrode material is Na < x > Fe Mn M < c > Nd < LeP < f > O < 2 >, 0.7 < = x < = 0.9, 0.4 > = a > = 0.1, 0.8 > = b > = 0.4, 0.1 > = c > 0, 0.1 > = d > 0, 0.1 > = e > 0, 0.1 > = f > 0, a + b + c + d + e + f = 1, M, N, L and P are four different elements in Li, K, Mg, Ni, Zn, Ca, Cu, Al, B, La, Zr and Ti, and the four selected elements are + 1 valence, + 2 valence, + 3 valence and + 4 valence respectively. In this way, high charging capacity can be provided, and structure expansion and contraction can be suppressed; more active sites are achieved, and ultrahigh discharge capacity and ultrahigh cycling stability are achieved; the structure stability is extremely high, and the sodium ion battery has relatively high specific capacity and relatively long circulation.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material, a preparation method and a sodium ion battery. Background Art

[0002] Sodium-ion battery cathode materials use sodium as raw materials. Compared with lithium-ion battery materials, they have low cost, wide sources of raw materials, and high capacity, and have extremely high research and application value. As one of the core materials of sodium-ion battery cathode materials, sodium-ion battery layered transition metal oxides have been widely studied.

[0003] According to the environment of Na+, layered materials can be divided into two categories: P-phase materials and O-phase materials (specifically, they can be divided into P2, P3 and O3). Among them, the research on P-phase materials is mainly based on nickel-manganese system; the research on O-phase materials is mainly based on nickel-iron-manganese or copper-iron-manganese system. However, for the current sodium-ion battery layered oxides, whether it is the P-phase nickel-manganese system or the O-phase nickel-iron-manganese or copper-iron-manganese system, at the moment when the price of lithium batteries is falling, the price and cost advantages of this type of sodium-ion battery layered oxides have not been highlighted. In addition, due to the low average voltage of sodium-ion batteries (generally around 3V), it cannot meet the voltage range matching the lithium battery system; and the pursuit of high voltage characteristics, whether for the P-phase nickel-manganese system or the O-phase nickel-iron-manganese or copper-iron-manganese system, there are insurmountable obstacles: specifically, for the P-phase nickel-manganese system, the contribution of oxygen anions will cause the expansion and contraction of the structure and the change of the interlayer distance, resulting in poor material circulation; and for the O-phase nickel-iron-manganese or copper-iron-manganese system, high voltage causes iron or copper to escape from the structure, producing gas and affecting the circulation.

[0004] In actual scenarios, the matching of electrolytes is also a challenge. For example, in one related technology, it needs to be prepared through a complex sol-gel method, and it needs to be operated at an ultra-high voltage (4.5V) to ensure its high capacity, which limits its practical application. In another related technology, a ball milling calcination method is used to prepare high-entropy sodium-ion battery positive electrode materials, but the process requires secondary sintering, which increases cost and energy consumption, and the prepared materials are mainly O3 phases, with poor air stability, which also limits its practical application. In order to achieve electrode materials with high specific capacity and high stability, how to design iron-manganese positive electrode materials with high capacity, long cycle and ultra-high stability at ultra-high voltage to further reduce the overall cost of sodium-ion batteries and improve the overall performance of existing sodium-ion batteries is of great significance. Summary of the invention

[0005] The present application provides a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material, a preparation method and a sodium ion battery. The positive electrode material is a high-entropy high-sodium iron-manganese multiphase blended transition metal oxide layered structure, the main phase is the P2 phase, and may contain a small amount of mixed phase (the mixed phase is at least one of the O3 phase or the P3 phase). Compared with traditional P2 phase positive electrode materials (Na≤0.67), this material has a higher sodium content (Na≥0.7), which solves the problem of insufficient sodium content and low capacity of general P-phase layered oxides; at the same time, this material aims at the oxygen anion phase transition of nickel-manganese materials under high voltage and the instability of iron-manganese (or nickel-iron-copper-manganese) materials under high voltage. This material adopts a multi-doping strategy, introduces four doping elements (+1 valence, +2 valence, +3 valence, +4 valence), and further activates the disordered distribution of cations in the material according to the high-low matching principle (generally speaking, the higher the valence, the less the molar number of matching), so that low-valence elements (such as Li, K, etc.) further form a rivet effect, thereby increasing the structural stability of the material; and at high voltage, provides more redox active sites for elements such as iron, copper, nickel, and manganese, while inhibiting the oxygen anion phase transition of the material. This seven-element high-entropy high-sodium positive electrode material not only provides high charging capacity, but also suppresses the structural expansion and contraction caused by the contribution of oxygen anions in the general nickel-iron-copper-manganese system under high voltage. At the same time, the seven-element high-entropy doped structure enables the material to have more redox active sites, realizing the ultra-high discharge capacity of the material. In addition, it also solves the problem of iron / copper element escape and cycle attenuation in the general nickel-iron-copper-manganese material under high voltage. It achieves super strong cycle stability under ultra-high voltage, and the sodium-ion battery manufactured has a higher specific capacity and a longer cycle.

[0006] In the first aspect, the present application provides a seven-element high entropy high sodium iron-manganese system sodium ion battery positive electrode material, the general formula of the sodium transition metal oxide of the positive electrode material is Na x Fe a Mn b M c N d L e P f O2; wherein, 0.7≤x≤0.9, 0.4≥a≥0.1, 0.8≥b≥0.4, 0.1≥c>0, 0.1≥d>0, 0.1≥e>0, 0.1≥f>0, a+b+c+d+e+f=1, M, N, L, P are four different elements among Li, K, Mg, Ni, Zn, Ca, Cu, Al, B, La, Zr, Ti, and the four selected elements are +1, +2, +3, and +4, respectively.

[0007] In a second aspect, the present application provides a method for preparing a seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material, comprising the following steps:

[0008] According to the stoichiometric ratio, an iron salt and a manganese salt are mixed and dissolved in water to obtain a corresponding first transition metal salt aqueous solution, and the obtained first transition metal salt aqueous solution is precipitated by a coprecipitation method, the pH value is controlled, and a first transition metal hydroxide precipitation precursor is obtained after spray drying;

[0009] According to the stoichiometric ratio, the sodium-containing compound, the first transition metal hydroxide precipitation precursor, and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound are mixed, ball-milled, pressed, and sintered to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0010] In a third aspect, the present application provides another method for preparing a seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material, comprising the following steps:

[0011] According to the stoichiometric ratio, the sodium-containing compound, the iron-containing compound, the manganese-containing compound, the M-containing compound, the N-containing compound, the L-containing compound and the P-containing compound are mixed, ball-milled, refined, tableted and sintered to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0012] In a fourth aspect, the present application provides a sodium ion battery, comprising a positive electrode material, wherein the positive electrode material comprises the seven-element high-entropy high sodium iron-manganese sodium ion battery positive electrode material as described in the first aspect above, or comprises the seven-element high-entropy high sodium iron-manganese sodium ion battery positive electrode material prepared by the preparation method of the seven-element high-entropy high sodium iron-manganese sodium ion battery positive electrode material as described in the second aspect or the third aspect above.

[0013] The technical effects of this application are:

[0014] Compared with the prior art, the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material provided in the embodiment of the present application is designed from the traditional P2 phase iron-manganese or nickel-manganese transition metal oxide layered structure. Traditional P2 phase iron-manganese or nickel-manganese materials (Na≤0.67) have the problems of insufficient first charge and low gram capacity. This material design has the characteristics of high sodium, which effectively solves this problem. At the same time, based on the structural design and the principle of rivet effect, this material adopts a multi-element doping strategy to further stabilize the interlayer structure of the material, increase the structural stability of the material, and effectively inhibit the oxygen anion phase transition of the material under high voltage, preventing the collapse of the interlayer structure and the capacity decay of the material, and achieving super strong cycle stability under ultra-high voltage.

[0015] The seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material in this application is mainly composed of P2 phase material and contains a mixed phase. While having a higher gram capacity, the material stability is enhanced; the gram capacity and cycle stability of the prepared sodium ion battery are greatly improved.

[0016] Firstly, compared with the traditional P2 phase positive electrode material (Na≤0.67), this material has a higher sodium content (Na≥0.7), which solves the problem of insufficient sodium content and low capacity of general P-phase layered oxides; without activating the contribution of oxygen anions, for P-phase materials with Na≤0.67, the general first-charge gram capacity is only 90mAh / g, while the design of this material increases the sodium content to Na≥0.7 or even Na≥0.75 at the beginning of the structural design. This design effectively improves the first-charge gram capacity of the material (≥110mAh / g).

[0017] On the second aspect, compared with traditional nickel-manganese materials, the problem of oxygen anion contribution under high voltage has not been properly solved. The contribution of oxygen anions is a double-edged sword in material performance. Although this contribution can greatly improve the first charge gram capacity of the material (increase the capacity by about 20 mAh / g), excessive Na ion escape will cause about 20% of the structural irreversible phase change and quickly decay the cycle performance of the material. In solving this type of problem, this application optimizes and improves the formulation process, adopts a multi-element doping strategy, introduces four doping elements (+1 valence, +2 valence, +3 valence, +4 valence), and follows the high-low matching principle (generally speaking, the higher the valence, the less the molar number), further activating the disordered distribution of cations in the material, so that low-valence elements (such as Li, K, etc.) further form a rivet effect, which increases the structural stability of the material and effectively inhibits the occurrence of oxygen anion phase change in the material under high voltage.

[0018] On the third aspect, for general iron-manganese materials, under high voltage, the iron or copper elements in the material will be irreversibly removed as the charge and discharge proceed, causing the decay of the cycle and capacity. The material in this application further optimizes the formula, uses a specific stoichiometric ratio design principle, and improves the use of inert elements such as stable elements (such as Al, B, La, Zr, Ti) under the premise of the above-mentioned rivet effect, adopts the multi-element doping principle of active / inert elements combined, and reasonably designs the stacking effect between the interlayer structure, while providing more redox active sites for elements such as iron, copper, nickel, and manganese, effectively suppressing the removal of elements such as iron in the material, and increasing the long cycle capacity of the material.

[0019] Fourthly, the high-entropy high-sodium iron-manganese-based sodium ion battery cathode material in this application adopts a multi-element high-entropy doping strategy, and the doped material will form a valence stacking effect (for example, Mg 2+ 、Al 3+ etc. occupying the Fe 3+ , Mn 4+ Nearby, additional Na + The vacancies occupied by the Fe and Mn electrodes further activate the redox active sites of the main materials, greatly improving the discharge capacity of the material.

[0020] The high sodium design principle adopts the rivet effect, valence stacking effect, high entropy multi-element stacking, etc. to increase the structural stability of the material. While providing more redox active sites for elements such as iron, copper, nickel, and manganese at high voltage, it inhibits the oxygen anion phase change of the material and the release of iron elements. The seven-element high entropy high sodium material in this application not only provides high charging capacity, but also inhibits the structural expansion and contraction caused by the contribution of oxygen anions of the general nickel-iron-copper-manganese system at high voltage; at the same time, the seven-element high entropy doped structure enables the material to have more redox active sites, achieving the ultra-high discharge capacity of the material; in addition, it also solves the problem of iron / copper release and cycle attenuation of general nickel-iron-copper-manganese materials at high voltage; and achieves ultra-strong cycle stability at ultra-high voltage.

[0021] At the same time, the preparation method of the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material provided in the embodiment of the present application can be obtained by co-precipitation combined with calcination, or by mixing, ball milling, refinement, tableting, and sintering. It has the characteristics of cheap and easy available raw materials and simple preparation process. The obtained seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material has a complete crystal form and high purity.

[0022] The sodium ion battery provided in the embodiment of the present application utilizes a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material as the positive electrode material. The positive electrode material has extremely high material structure stability, high gram capacity and first efficiency. The prepared sodium ion battery has a high specific capacity and a long cycle.

[0023] In order to more clearly demonstrate the technical means of the present application and ensure the smooth implementation of the contents of the specification, some typical embodiments of the present application are listed below together with drawings and detailed descriptions. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 XRD patterns of the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode materials prepared in Examples 1 to 8 of the present application and the materials prepared in Comparative Examples 1 to 3;

[0025] Figure 2 This is a SEM image of the seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material prepared in Example 1 of the present application;

[0026] Figure 3 A schematic diagram of the first cycle charge and discharge curve of a sodium ion half-cell assembled with the materials of Example 1 of the present application at 2.0-4.3V and 0.1C;

[0027] Figure 4 A schematic diagram of the first cycle charge and discharge curve of a sodium ion half-cell assembled with the material of Comparative Example 1 at 2.0-4.3V and 0.1C;

[0028] Figure 5 Schematic diagram of long cycle of a sodium ion half-cell assembled with materials from Example 1 and Comparative Example 1 of the present application at 2.0-4.3V and 0.5C. DETAILED DESCRIPTION

[0029] In order to make the invention purpose and technical solution of the present application clearer and easier to understand, the content of the present application is further described in detail below in conjunction with the accompanying drawings and examples. However, it should be clear that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. Without departing from the spirit and substance of the present application, modifications and replacements made to the method, preparation steps or conditions of the present application are within the scope of the present application.

[0030] The present application provides a seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material. The sodium transition metal oxide of the positive electrode material has the following general formula:

[0031] Na x Fe a Mn b M c N d L e P f O2;

[0032] Among them, 0.7≤x≤0.9, 0.4≥a≥0.1, 0.8≥b≥0.4, 0.1≥c>0, 0.1≥d>0, 0.1≥e>0, 0.1≥f>0, a+b+c+d+e+f=1, M, N, L, P are four different elements among Li, K, Mg, Ni, Zn, Ca, Cu, Al, B, La, Zr, and Ti, and the four selected elements are +1, +2, +3, and +4, respectively.

[0033] For example: x is 0.7, 0.75, 0.8, 0.85, 0.9, etc.; a is 0.1, 0.2, 0.25, 0.3, 0.4, etc.; b is 0.4, 0.5, 0.55, 0.6, 0.7, 0.8, etc.; c is 0.025, 0.05, 0.075, 0.1, etc.; d is 0.025, 0.05, 0.075, 0.1, etc.; e is 0.025, 0.05, 0.075, 0.1, etc.; f is 0.025, 0.05, 0.075, 0.1, etc.

[0034] In some embodiments, 0.7≤x≤0.8, 0.3≥a≥0.2, 0.6≥b≥0.5. For example, x is 0.7, 0.75, 0.8, etc.; a is 0.2, 0.25, 0.3, etc.; b is 0.5, 0.55, 0.6, etc.

[0035] In some embodiments, the sodium transition metal oxide may be

[0036] Na 0.8 Fe 0.2 Mn 0.5 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 Li 0.1 Mg 0.05 B 0.025 Ti 0.025 O2、Na 0.7 Fe 0.2 Mn 0.6 Li 0.1 Zn 0.05 La 0.025 Zr 0.025 O2、Na 0.8 Fe 0.2 Mn 0.5 K 0.1 Cu 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 K 0.1 Ca 0.05 B 0.025 Zr 0.025 O2、Na 0.7 Fe 0.2 Mn 0.55 K 0.1 Mg 0.05 Al 0.025 Ti 0.075 O2、Na 0.7 Fe 0.25 Mn 0.55 Li 0.05 Ni 0.05 Al 0.05 Ti 0.05 O2、Na 0.7 Fe 0.25 Mn 0.55 K 0.05 Ni 0.05 B 0.05 Zr 0.05 O2, at least one of.

[0037] like Figure 1 As shown, Figure 1 So

[0038] Na0.8 Fe 0.2 Mn 0.5 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 Li 0.1 Mg 0.05 B 0.025 Ti 0.025 O2、Na 0.7 Fe 0.2 Mn 0.6 Li 0.1 Zn 0.05 La 0.025 Zr 0.025 O2、Na 0.8 Fe 0.2 Mn 0.5 K 0.1 Cu 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 K 0.1 Ca 0.05 B 0.025 Zr 0.025 O2、Na 0.7 Fe 0.2 Mn 0.55 K 0.1 Mg 0.05 Al 0.025 Ti 0.075 O2、Na 0.7 Fe 0.25 Mn 0.55 Li 0.05 Ni 0.05 Al 0.05 Ti 0.05 O2、Na 0.7 Fe 0.25 Mn 0.55 K 0.05 Ni 0.05 B 0.05 Zr 0.05 Taking O2 as an example, the XRD (X-ray diffraction) spectrum, the horizontal axis is twice the incident angle of the X-ray (θ) (2θ, the unit is degree), and the vertical axis is the intensity after diffraction (intensity, au in the figure is the abbreviation of absorbance unit); according to Figure 1It can be seen that the crystal structure of this type of sodium transition metal oxide shows that the main phase is a P2 phase sodium transition metal oxide layered structure, and some samples contain a small amount of mixed phase (P3 and / or O3 phase, shown in the diffraction peak 2θ=42°, marked with asterisks), and have a higher sodium content. While maintaining a higher capacity, it also maintains excellent structural stability.

[0039] The present application embodiment provides a method for preparing the above-mentioned seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material, which comprises the following steps:

[0040] According to the stoichiometric ratio, an iron salt and a manganese salt are mixed and dissolved in water to obtain a corresponding first transition metal salt aqueous solution, and the obtained first transition metal salt aqueous solution is precipitated by a coprecipitation method, the pH value is controlled, and a first transition metal hydroxide precipitation precursor is obtained after spray drying;

[0041] According to the stoichiometric ratio, the sodium-containing compound, the first transition metal hydroxide precipitation precursor, and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound are mixed, ball-milled, pressed, and sintered to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0042] The embodiment of the present application provides another method for preparing the above-mentioned seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material, which comprises the following steps: mixing, ball-milling, refining, tableting, and sintering sodium-containing compounds, iron-containing compounds, manganese-containing compounds, M-containing compounds, N-containing compounds, L-containing compounds, and P-containing compounds according to a stoichiometric ratio to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0043] The preparation method is explained in detail below.

[0044] According to the stoichiometric ratio, an iron salt and a manganese salt are mixed and dissolved in water to obtain a corresponding first transition metal salt aqueous solution, the first transition metal salt aqueous solution is precipitated by a coprecipitation method, the pH value is controlled, and the first transition metal hydroxide precipitation precursor is obtained after spray drying; according to the stoichiometric ratio, a sodium-containing compound, the first transition metal hydroxide precipitation precursor and an M-containing compound, an N-containing compound, an L-containing compound, and a P-containing compound are mixed, ball-milled, tableted, and sintered, and the sintering conditions are first sintered at a constant temperature of 400-550° C. for 1-5 hours, then heated to 900-1100° C. and sintered at a constant temperature for 10-24 hours, and the sintering atmosphere is oxygen or air or a mixed gas of oxygen and air to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0045] In some embodiments, the feeding ratio of the iron salt and the manganese salt for the co-precipitation reaction is (0.2-0.6):1.

[0046] In some embodiments, in terms of molar ratio, the sodium in the sodium-containing compound: the iron and manganese in the first transition metal hydroxide precipitation precursor: the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound are as follows: (0.7 to 0.9): (0.7 to 1.0): (0 to 0.4), and the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound in (0 to 0.4) is greater than zero. That is, according to the molar ratio, the range of sodium in the sodium-containing compound is greater than or equal to 0.7 and less than or equal to 0.9, for example, 0.7, 0.8, 0.9, etc.; the range of iron and manganese in the first transition metal hydroxide precipitation precursor is greater than or equal to 0.7 and less than or equal to 1.0, for example, 0.7, 0.8, 0.9, 1.0, etc.; the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound is greater than zero and less than or equal to 0.4, for example: 0.05, 0.1, 0.2, 0.3, 0.4, etc.

[0047] In some embodiments, the sodium-containing compound is at least one of sodium carbonate, sodium acetate, and sodium hydroxide. The iron salt is at least one of ferric nitrate, ferric chloride, and ferric acetate; the manganese salt is at least one of manganese nitrate, manganese chloride, and manganese acetate; before the coprecipitation reaction, it is necessary to prepare the iron salt and the manganese salt into corresponding aqueous solutions to improve the reaction efficiency of the coprecipitation reaction.

[0048] In some embodiments, when performing a coprecipitation reaction, a precipitant needs to be added to the solution to adjust the pH value of the reaction system. The precipitant used can be a mixed solution of sodium hydroxide and ammonia water.

[0049] In some embodiments, the M-containing compound is at least one of an M-containing metal oxide, an M-containing oxide, an M-containing carbonate, and an M-containing hydroxide; the N-containing compound is at least one of an N-containing metal oxide, an N-containing oxide, an N-containing carbonate, and an N-containing hydroxide; the L-containing compound is at least one of an L-containing metal oxide, an L-containing oxide, an L-containing carbonate, and an L-containing hydroxide; the P-containing compound is at least one of a P-containing metal oxide, an P-containing oxide, a P-containing carbonate, and a P-containing hydroxide.

[0050] Alternatively, in some embodiments, sodium-containing compounds, iron-containing compounds, manganese-containing compounds, and M-containing compounds, N-containing compounds, L-containing compounds, and P-containing compounds are mixed, ball-milled, refined, tableted, and sintered according to a stoichiometric ratio. The sintering conditions are first constant-temperature sintering at 400-550°C for 1-5 hours, then heating to 900-1100°C and constant-temperature sintering for 10-24 hours. The sintering atmosphere is oxygen or air or a mixture of oxygen and air to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0051] In some embodiments, according to the molar ratio, the feeding ratio of sodium in the sodium-containing compound: iron in the iron-containing compound: manganese in the manganese-containing compound: M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound is (0.7-0.9):(0.1-0.4):(0.4-0.8):(0-0.4), and the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound in (0-0.4) is greater than zero. That is, according to the molar ratio, the range of sodium in the sodium-containing compound is greater than or equal to 0.7 and less than or equal to 0.9, for example, 0.7, 0.8, 0.9, etc.; the range of iron in the iron-containing compound is greater than or equal to 0.1 and less than or equal to 0.4, for example, 0.1, 0.2, 0.3, 0.4, etc.; the range of manganese in the manganese-containing compound is greater than or equal to 0.4 and less than or equal to 0.8, for example, 0.4, 0.5, 0.6, 0.7, 0.8, etc.; the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound is greater than 0 and less than or equal to 0.4, for example, 0.05, 0.1, 0.2, 0.3, 0.4, etc.

[0052] In some embodiments, the iron-containing compound is at least one of ferrous oxide, ferric oxide, ferric hydroxide, ferric carbonate, and ferrous oxalate; the manganese-containing compound is at least one of manganous oxide, manganese tetraoxide, manganese hydroxide, manganese carbonate, and manganese oxalate; the sodium-containing compound is at least one of sodium carbonate, sodium acetate, and sodium hydroxide.

[0053] The M-containing compound is at least one of an M-containing metal oxide, an M-containing oxide, an M-containing carbonate, and an M-containing hydroxide; the N-containing compound is at least one of an N-containing metal oxide, an N-containing oxide, an N-containing carbonate, and an N-containing hydroxide; the L-containing compound is at least one of an L-containing metal oxide, an L-containing oxide, an L-containing carbonate, and an L-containing hydroxide; the P-containing compound is at least one of a P-containing metal oxide, a P-containing oxide, a P-containing carbonate, and a P-containing hydroxide.

[0054] In some embodiments, when the sodium-containing compound is mixed with the first transition metal hydroxide precipitation precursor and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound, or when the sodium-containing compound, the iron-containing compound, the manganese-containing compound, and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound are mixed, mechanical grinding can be adopted, or they can be made into a solution, mixed and ultrasonically shaken to form a slurry, and then dried, ball milled, etc. The purpose of mixing is to make the sodium-containing compound and the first transition metal hydroxide precipitation precursor and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound mixed evenly, or to make the sodium-containing compound, the iron-containing compound, the manganese-containing compound, and the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound mixed evenly, so as to facilitate sintering into a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

[0055] In some embodiments, the sintering conditions are first sintering at a constant temperature of 400-550° C. for 1-5 hours, then heating to 900-1100° C. and sintering at a constant temperature for 10-24 hours, and the sintering atmosphere is oxygen or air or a mixture of oxygen and air.

[0056] The preparation method of the seven-element high-entropy high-sodium iron-manganese series sodium ion battery positive electrode material provided in the embodiment of the present application can be obtained by co-precipitation combined with calcination, or by mixing, ball milling, refining, tableting, and sintering. It has the characteristics of cheap and readily available raw materials and a simple preparation process. The obtained seven-element high-entropy high-sodium iron-manganese series sodium ion battery positive electrode material has a complete crystal form and high purity.

[0057] The sodium ion battery provided in the embodiment of the present application provides a higher gram capacity and extremely strong structural stability for the sodium ion battery of the present application due to the use of a seven-element high entropy high sodium iron-manganese sodium ion battery positive electrode material as a positive electrode material; relative to the traditional iron-manganese or nickel-manganese P2 phase transition metal oxides, the positive electrode material adopts a high sodium design principle, while introducing a rivet effect, a valence stacking effect, and a high entropy multi-element stacking to increase the structural stability of the material, while providing more redox active sites for elements such as iron, copper, nickel, and manganese at high voltage, inhibiting the material from undergoing oxygen anion phase transition and the release of iron, etc., achieving super strong cycle stability of the material at ultra-high voltage, and the prepared sodium ion battery has a higher specific capacity and a longer cycle. Therefore, the embodiment of the present application also provides a positive electrode sheet and a sodium ion battery using the above-mentioned seven-element high entropy high sodium iron-manganese sodium ion battery positive electrode material.

[0058] Among them, the positive electrode sheet contains a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material as the positive electrode active material, and also contains a conductive agent and a binder.

[0059] Specifically, the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material is mixed with a conductive agent, a binder and a solvent to form a positive electrode slurry, which is coated on the surface of the positive electrode current collector, and then dried, rolled and cut into pieces to form a positive electrode sheet. The mass ratio of the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material, the conductive agent and the binder in the positive electrode sheet is 8:1:1. When preparing the positive electrode slurry, the solvent can be N-methylpyrrolidone (NMP).

[0060] The sodium ion battery includes the above-mentioned positive electrode sheet, or the positive electrode material contains the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material of the embodiment of the present application.

[0061] In some embodiments, the positive electrode material of the sodium ion battery of the embodiment of the present application may contain at least one of a positive electrode material with a P3 phase structure and an O3 phase positive electrode material in addition to the positive electrode material with a P2 main phase structure in the present application.

[0062] In some embodiments, the sodium ion battery provided in the embodiments of the present application uses metallic sodium as the negative electrode material, and the electrolyte is any one of 1M NaPF6 / (EC:DMC=1:1) electrolyte, 1M NaPF6 / PC electrolyte, and 1M NaClO4 / (EC:PC=1:1) electrolyte, wherein EC represents ethylene carbonate, DMC represents dimethyl carbonate, PC represents propylene carbonate, EC:DMC=1:1 represents a solvent formed by ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, and EC:PC represents a solvent formed by ethylene carbonate and propylene carbonate in a volume ratio of 1:1.

[0063] In some embodiments, the sodium ion battery provided in the embodiments of the present application uses a diaphragm that is a polyolefin microporous membrane such as polyethylene, polypropylene, etc., such as a Celgard diaphragm.

[0064] Example 1

[0065] A method for preparing a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material comprises the following steps:

[0066] (a) iron sulfate and manganese sulfate are mixed and dissolved in water at a molar ratio of 2:5 to prepare a 1.0 mol / L mixed transition metal salt solution, a mixed aqueous solution of 1.0 mol / L sodium hydroxide and 0.10 mol / L ammonia water is used as a precipitant, the pH value is controlled to be about 8-10, and an iron-manganese hydroxide precursor is prepared by coprecipitation, and the obtained precursor is spray-dried to obtain a powder.

[0067] (b) Sodium carbonate, the hydroxide precursor powder obtained in step (a), lithium carbonate, nickel hydroxide, aluminum oxide and titanium dioxide are mixed in a molar ratio of 0.4:0.7:0.05:0.1:0.025:0.05 and added into a ball mill together with grinding beads of the same weight, and ball milled at a speed of 200 r / min for 2 h. The mixed powder is taken out and mixed evenly in a mortar.

[0068] (c) The powder mixed in step (b) was pressed into a disc with a diameter of 20 mm on a cold press at a pressure of 100 MPa for 5 min.

[0069] (d) The pressed flake mixture in step (c) was placed in a tubular furnace, heated to 500°C in a mixed atmosphere of oxygen and air (mixing ratio 2:8) and sintered at a constant temperature for 2 h, then heated to 950°C and sintered at a constant temperature for 20 h, and naturally cooled to room temperature to obtain sample 1, whose molecular formula is Na 0.8 Fe 0.2 Mn 0.5 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2.

[0070] The obtained sample 1 was subjected to XRD and SEM (Scanning Electron Microscope) tests. The specific test results are shown in Figure 1 and Figure 3 , the cycle performance is shown in Table 1.

[0071] Example 2

[0072] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 3:5 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and lithium carbonate, magnesium carbonate, boron trioxide, and titanium dioxide were mixed in a molar ratio of 0.375:0.8:0.05:0.05:0.0125:0.025, and then the treatment method (b)-(d) in Example 1 was used to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.75 Fe 0.3 Mn 0.5 Li 0.1 Mg 0.05 B 0.025 Ti 0.025 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0073] Example 3

[0074] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 2:6 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and lithium carbonate, zinc oxide, lanthanum oxide, and zirconium oxide were mixed in a molar ratio of 0.35:0.8:0.05:0.05:0.0125:0.025, and then the treatment method (b)-(d) in Example 1 was used to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.7 Fe 0.2 Mn 0.6 Li 0.1 Zn 0.05 La 0.025 Zr 0.025 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0075] Example 4

[0076] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 2:5 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and potassium carbonate, copper hydroxide, aluminum oxide, and titanium dioxide were mixed in a molar ratio of 0.4:0.7:0.05:0.1:0.025:0.05, and then the treatment method (b)-(d) in Example 1 was followed to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.8 Fe 0.2 Mn 0.5 K 0.1 Cu 0.1 Al 0.05 Ti 0.05 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0077] Example 5

[0078] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 3:5 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and potassium carbonate, calcium hydroxide, boron trioxide, and zirconium oxide were mixed in a molar ratio of 0.375:0.8:0.05:0.05:0.0125:0.025, and then the treatment method (b)-(d) in Example 1 was used to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.75 Fe 0.3 Mn 0.5 K 0.1 Ca 0.05 B 0.025 Zr 0.025 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0079] Example 6

[0080] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 2:5.5 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and potassium carbonate, magnesium carbonate, aluminum oxide, and titanium dioxide were mixed in a molar ratio of 0.35:0.75:0.05:0.05:0.0125:0.075, and then the treatment method (b)-(d) in Example 1 was used to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.7 Fe 0.2 Mn 0.55 K 0.1 Mg 0.05 Al 0.025 Ti 0.075 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0081] Example 7

[0082] Referring to Example 1, ferrous sulfate and manganese sulfate were prepared in a molar ratio of 2.5:5.5 to prepare a hydroxide precursor, sodium carbonate, the prepared hydroxide precursor and lithium carbonate, nickel hydroxide, aluminum oxide, and titanium dioxide were mixed in a molar ratio of 0.35:0.8:0.025:0.05:0.025:0.05, and then the treatment method (b)-(d) in Example 1 was used to obtain a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material Na 0.7 Fe 0.25 Mn 0.55 Li 0.05 Ni 0.05 Al 0.05 Ti 0.0 5O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0083] Example 8

[0084] According to the molar ratio, sodium carbonate, ferrous oxalate, manganese dioxide, potassium carbonate, nickel hydroxide, boron trioxide and zirconium oxide are mixed in a molar ratio of 0.35:0.125:0.55:0.025:0.05:0.025:0.05, and added to a ball mill together with grinding beads of the same weight, and part of ethanol is added at the same time. The high-energy ball mill is carried out at a speed of 300r / min for 8h, and the mixed powder is taken out and dried, mixed evenly in a mortar, and then referred to the treatment method (c)-(d) in Example 1, after tableting and sintering, a seven-element high-entropy high-sodium iron-manganese system sodium ion battery positive electrode material Na is obtained. 0.7 Fe0.25 Mn 0.55 K 0.05 Ni 0.05 B 0.05 Zr 0.05 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0085] Comparative Example 1

[0086] A P2-type nickel-iron-copper-manganese layered sodium transition metal oxide positive electrode material without high sodium multi-element doping:

[0087] (a) nickel sulfate, iron sulfate, copper sulfate and manganese sulfate are mixed and dissolved in water at a molar ratio of 1:1:1:7 to prepare a 1.0 mol / L mixed transition metal salt solution of nickel sulfate, copper sulfate, iron sulfate and manganese sulfate, and a mixed aqueous solution of 1.0 mol / L sodium carbonate and 0.10 mol / L ammonia water is used as a precipitant, and the pH value is controlled to be about 8.0, and a nickel-iron-copper-manganese hydroxide precursor is prepared by coprecipitation.

[0088] (b) Sodium carbonate and the hydroxide precursor obtained in step (a) were mixed at a molar ratio of 0.335:1 and added into a ball mill and ball milling balls, and ball milled at a speed of 200 r / min for 2 h. The mixed powders were taken out and mixed evenly in a mortar.

[0089] (c) The uniformly mixed precursor powders were pressed into discs with a diameter of 20 mm on a cold press at a pressure of 100 MPa for 5 min.

[0090] (d) The sheet precursor pressed in step (c) was placed in a tube furnace, heated to 500° C. and sintered at a constant temperature for 2 h in a mixed atmosphere of oxygen and air (mixing ratio 2:8), then heated to 900° C. and sintered at a constant temperature for 20 h, and naturally cooled to room temperature to obtain a comparative example sample Na 0.67 Ni 0.1 Fe 0.1 Cu 0.1 Mn 0.7 O2,

[0091] Its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0092] Comparative Example 2

[0093] A seven-element high-entropy high-sodium P2-type iron-manganese-nickel-copper-magnesium-zinc layered sodium transition metal oxide positive electrode material without +1, +2, +3, +4 valence doping:

[0094] (a) nickel sulfate, iron sulfate, copper sulfate, manganese sulfate, magnesium sulfate and zinc sulfate are mixed and dissolved in water at a molar ratio of 1:1:1:6:0.05:0.05 to prepare a 1.0 mol / L mixed transition metal salt solution of nickel sulfate, copper sulfate, iron sulfate, manganese sulfate, magnesium sulfate and zinc sulfate, and a mixed aqueous solution of 1.0 mol / L sodium carbonate and 0.10 mol / L ammonia water is used as a precipitant, and the pH value is controlled to be about 8.0, and iron, manganese, nickel, copper, magnesium and zinc hydroxide precursors are prepared by coprecipitation.

[0095] (b) Sodium carbonate and the hydroxide precursor obtained in step (a) were mixed at a molar ratio of 0.335:1 and added into a ball mill and ball milling balls, and ball milled at a speed of 200 r / min for 2 h. The mixed powders were taken out and mixed evenly in a mortar.

[0096] (c) The uniformly mixed precursor powders were pressed into discs with a diameter of 20 mm on a cold press at a pressure of 100 MPa for 5 min.

[0097] (d) The sheet precursor pressed in step (c) was placed in a tube furnace, heated to 500° C. and sintered at a constant temperature for 2 h in a mixed atmosphere of oxygen and air (mixing ratio 2:8), then heated to 900° C. and sintered at a constant temperature for 20 h, and naturally cooled to room temperature to obtain a comparative example sample Na 0.67 Fe 0.1 Mn 0.6 Ni 0.1 Cu 0.1 Mg 0.05 Zn 0.05 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0098] Comparative Example 3

[0099] A seven-element high entropy high sodium, but using +1, +2, +3, +4 valence doped O3 type iron-manganese lithium-nickel-aluminum-titanium layered sodium transition metal oxide positive electrode material:

[0100] (a) Iron sulfate, manganese sulfate and nickel sulfate are mixed and dissolved in water at a molar ratio of 1:6:1 to prepare a 1.0 mol / L mixed transition metal salt solution of iron sulfate, manganese sulfate and nickel sulfate, and a mixed aqueous solution of 1.0 mol / L sodium carbonate and 0.10 mol / L ammonia water is used as a precipitant, and the pH value is controlled to be about 8.0 to co-precipitate and prepare a nickel-iron-copper-manganese-magnesium-zinc hydroxide precursor.

[0101] (b) Sodium carbonate is mixed with the hydroxide precursor obtained in step (a), lithium carbonate, aluminum oxide and titanium dioxide in a molar ratio of 0.5:0.8:0.05:0.025:0.05, and added into a ball mill and ball mills, and ball milled at a speed of 200 r / min for 2 h. The mixed powder is taken out and mixed evenly in a mortar.

[0102] (c) The uniformly mixed precursor powders were pressed into discs with a diameter of 20 mm on a cold press at a pressure of 100 MPa for 5 min.

[0103] (d) The sheet precursor pressed in step (c) was placed in a tube furnace, heated to 500° C. and sintered at a constant temperature for 2 h in a mixed atmosphere of oxygen and air (mixing ratio 2:8), then heated to 900° C. and sintered at a constant temperature for 20 h, and naturally cooled to room temperature to obtain a comparative example sample Na 1.0 Fe 0.1 Mn 0.6 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2, its XRD spectrum is as follows Figure 1 The cycle performance is shown in Table 1.

[0104] Application Example 1

[0105] A sodium ion battery, the preparation method of which comprises the following steps:

[0106] (1) The sample obtained in Example 1 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0107] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0108] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0109] Application Example 2

[0110] A sodium ion battery, the preparation method of which comprises the following steps:

[0111] (1) The sample obtained in Example 2 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0112] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0113] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0114] Application Example 3

[0115] A sodium ion battery, the preparation method of which comprises the following steps:

[0116] (1) The sample obtained in Example 3 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0117] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0118] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0119] Application Example 4

[0120] A sodium ion battery, the preparation method of which comprises the following steps:

[0121] (1) The sample obtained in Example 4 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0122] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0123] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0124] Application Example 5

[0125] A sodium ion battery, the preparation method of which comprises the following steps:

[0126] (1) The sample obtained in Example 5 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0127] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0128] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0129] Application Example 6

[0130] A sodium ion battery, the preparation method of which comprises the following steps:

[0131] (1) The sample obtained in Example 6 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0132] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0133] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0134] Application Example 7

[0135] A sodium ion battery, the preparation method of which comprises the following steps:

[0136] (1) The sample obtained in Example 7 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0137] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0138] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0139] Application Example 8

[0140] A sodium ion battery, the preparation method of which comprises the following steps:

[0141] (1) The sample obtained in Example 8 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0142] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0143] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0144] Application Example 9

[0145] A sodium ion battery, the preparation method of which comprises the following steps:

[0146] (1) The sample obtained in Comparative Example 1 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0147] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0148] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0149] Application Example 10

[0150] A sodium ion battery, the preparation method of which comprises the following steps:

[0151] (1) The sample obtained in Comparative Example 1 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0152] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0153] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0154] Application Example 11

[0155] A sodium ion battery, the preparation method of which comprises the following steps:

[0156] (1) The sample obtained in Comparative Example 1 was used as a positive electrode active material, mixed with conductive carbon black and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, dissolved in N-methylpyrrolidone (NMP) solvent to prepare a positive electrode slurry, and coated on an aluminum foil, dried, and cut to obtain a positive electrode sheet.

[0157] (2) The positive electrode obtained in step (1) was assembled with metal sodium and Celgard separator into a sodium ion battery, wherein the electrolyte of the sodium ion battery was a mixture of 1M NaPF6 / (EC:DMC=1:1) (according to the volume ratio of EC:DMC=1:1). After assembly, the battery was allowed to stand for 24 hours, and then subjected to charge and discharge activation test.

[0158] Specifically, the test method is: charge and discharge three times at a current density of 0.1C (1C = 100 mA / g) within a voltage range of 2.0-4.3V; and then perform a cycle performance test at 0.5C (1C = 100 mA / g). The results are shown in Table 1.

[0159] Figure 1The main diffraction peaks of all samples from Example 1 to Example 8 show a P2 type structure, some samples contain a small amount of mixed phase (P3 or / and O3 phase, shown at the diffraction peak 2θ=42°, asterisk mark: Example 1, Example 2, Example 4, Example 5), and the sodium content is Na=0.7-0.8, and the crystal form is complete, proving that the obtained material is a seven-element high-entropy high-sodium iron-manganese system sodium ion battery positive electrode material with a main phase of P2 type (some samples contain a small amount of P3 / O3 mixed phase):

[0160] Na 0.8 Fe 0.2 Mn 0.5 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 Li 0.1 Mg 0.05 B 0.025 Ti 0.025 O2、Na 0.7 Fe 0.2 Mn 0.6 Li 0.1 Zn 0.05 La 0.025 Zr 0.025 O2、Na 0.8 Fe 0.2 Mn 0.5 K 0.1 Cu 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 K 0.1 Ca 0.05 B 0.025 Zr 0.025 O2、Na 0.7 Fe 0.2 Mn 0.55 K 0.1 Mg 0.05 Al 0.025 Ti 0.075 O2、Na 0.7 Fe 0.25 Mn 0.55 Li 0.05 Ni 0.05 Al 0.05 Ti 0.05 O2、Na 0.7 Fe 0.25 Mn 0.55 K 0.05 Ni0.05 B 0.05 Zr 0.05 O2.

[0161] from Figure 2 It can be seen from the SEM that sample 1 of Example 1 has a lamellar structure, and the lamellar structure is clear and complete. Please note that Figure 2 The dimension in the lower right corner is 10 μm.

[0162] Figure 1 The main diffraction peaks of the samples of Comparative Example 1 and Comparative Example 2 are shown to be P2 type structures. Figure 1 The main diffraction peak of the sample of Comparative Example 3 shown shows an O3 type structure.

[0163] The seven-element high entropy high sodium iron-manganese sodium ion battery positive electrode material Na obtained in Example 1 0.8 Fe 0.2 Mn 0.5 Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2 and the positive electrode material Na obtained in Comparative Example 1 0.67 Ni 0.1 Fe 0.1 Cu 0.1 Mn 0.7 O2 was used as the positive electrode material to assemble sodium ion batteries with sodium metal negative electrode and the electrochemical performance was tested. The results are as follows: Figure 3 and Figure 4 As shown. Figure 3 In the sodium ion battery assembled by the sample of Example 1, the first-cycle charge capacity is about 115 mAh / g when cycled at a current density of 0.1 C (10 mA / g) in the voltage range of 2.0 to 4.3 V, and the contribution of oxygen anions is not activated; while the discharge capacity is as high as about 130 mAh / g, indicating that the multi-element high entropy doping structure and the valence stacking effect design fully activate the redox active sites in the material, so that the material does not activate the contribution of oxygen anions during the charging process, but can more effectively receive more sodium ions during the discharge process.

[0164] exist Figure 4In the figure, the first cycle charging capacity of the sodium ion battery assembled by the sample of Comparative Example 1 is between 2 and 4.3 V, which also reaches about 110 mAh / g, and after 4.2 V, there is an obvious oxygen anion contribution (in the dotted frame, it is displayed as a charging curve similar to a horizontal line, and the capacity contribution is about 20 mAh / g); according to the data ratio, if the oxygen anion contribution is not activated, the capacity is only about 90 mAh / g; and the data in Example 1 show that the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material in this application does not activate the oxygen anion contribution. Due to the multi-element high-entropy doping effect and the valence stacking effect design, the material has more redox active sites, and the material exhibits a charging capacity of about 115 mAh / g, while the discharge capacity is as high as about 130 mAh / g.

[0165] At the same time, in the subsequent long cycle test (2-4.3V, 0.5C), if Figure 5 As shown, when cycled at 0.5C (50mA / g), the material of Example 1 further exhibited a reversible initial capacity of about 117mAh / g, and after 100 long cycles, the capacity was still about 113mAh / g, and the retention rate was still about 96%. However, when cycled at 0.5C (50mA / g), the material of Comparative Example 1 initially only showed a reversible initial capacity of 94mAh / g, and after 100 cycles, it had a reversible capacity of only 78mAh / g, and the capacity attenuation problem due to the activation of oxygen anions was more obvious.

[0166] The reason is that: Example 1 in this application adopts the high sodium high entropy design principle, and the introduced cationic disordered elements (Li, K, etc.) form a rivet effect between structures. At the same time, the valence stacking effect and high entropy multi-element stacking increase the structural stability of the material. At high voltage, elements such as iron, copper, nickel, and manganese provide more redox active sites, while inhibiting the material from undergoing oxygen anion phase transition and the removal of iron elements, etc. When Na ions enter and exit the structure, under the premise of not activating the contribution of oxygen anions, Na ions can still rely on the rich redox active sites for deintercalation, combined with the rivet effect between structures, multi-element stacking effect, etc., greatly enhancing the expansion and contraction ability and cycle stability of the material structure.

[0167] In addition, Table 1 shows the charge-discharge capacity test and long cycle test results at 0.5C for the materials of Examples 1-8 and Comparative Examples 1-3. The results show that Examples 1-8 all exhibit high specific charge capacity (≈100-120mAh / g), and the capacity retention rate after 100 cycles is close to or exceeds 90%, showing excellent cycle performance. In comparison, although the material of Comparative Example 1 shows a higher initial charge capacity (≈110mAh / g, 0.1C, Figure 4), but once the oxygen anion contribution is activated and the cycle begins at a higher rate (0.5C), the cycle stability and capacity performance are poor (Table 1). The cycle stability and capacity performance of the materials of Comparative Examples 2 and 3 are also poor. Therefore, the seven-element high-entropy high-sodium material of the embodiment of the present application, while providing a high charging capacity, suppresses the structural expansion and contraction caused by the oxygen anion contribution of the general nickel-iron-copper-manganese system under high voltage; at the same time, the seven-element high-entropy doped structure enables the material to have more redox active sites, thereby achieving the ultra-high discharge capacity of the material; in addition, it also solves the problem of iron / copper element escape and cycle attenuation of general nickel-iron-copper-manganese materials under high voltage; and achieves super strong cycle stability under ultra-high voltage. And the positive electrode material of the present application has extremely high material structure stability, and the prepared sodium ion battery has a high specific capacity and a long cycle.

[0168] Table 1

[0169]

[0170]

[0171] It should be understood that the terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0172] It should also be understood that the term “and / or” used in the specification and appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0173] The above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material, characterized in that: The positive electrode material includes a sodium transition metal oxide whose main phase is a P2 phase, and the sodium transition metal oxide of the positive electrode material has the general formula shown below: And x Fe a Mn b I c N d L e P f O2; Among them, 0.7≤x≤0.9, 0.4≥a≥0.1, 0.8≥b≥0.4, 0.1≥c>0, 0.1≥d>0, 0.1≥e>0, 0.1≥f>0, a+b+c+d+e+f=1, M, N, L, P are four different elements among Li, K, Mg, Ni, Zn, Ca, Cu, Al, B, La, Zr, and Ti, and the four selected elements are +1, +2, +3, and +4, respectively.

2. The positive electrode material according to claim 1, characterized in that 0.7≤x≤0.8, 0.3≥a≥0.2, 0.6≥b≥0.

5.

3. The positive electrode material according to claim 2, characterized in that The sodium transition metal oxide is Na 0.8 Fe 0.2 Mn 0. 5Li 0.1 Ni 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 Li 0.1 Mg 0.05 B 0.025 Ti 0.025 O2、Na 0.7 Fe 0.2 Mn 0.6 Li 0.1 Zn 0.05 La 0.025 Zr 0.025 O2、Na 0.8 Fe 0.2 Mn 0.5 K 0.1 Cu 0.1 Al 0.05 Ti 0.05 O2、Na 0.75 Fe 0.3 Mn 0.5 K 0.1 Ca 0.05 B 0.025 Zr 0.025 O2、Na 0.7 Fe 0.2 Mn 0.55 K 0.1 Mg 0.05 Al 0.025 Ti 0.075 O2、Na 0.7 Fe 0.25 Mn 0.55 Li 0.05 Ni 0.05 Al 0.05 Ti 0.05 O2、Na 0.7 Fe 0.2 5Mn 0.55 K 0.05 Ni 0.05 B 0.05 Zr 0.05 O2, at least one of.

4. A method for preparing a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises: According to the stoichiometric ratio, an iron salt and a manganese salt are mixed and dissolved in water to obtain a corresponding first transition metal salt aqueous solution, the first transition metal salt aqueous solution is precipitated by a coprecipitation method, the pH value is controlled, and a first transition metal hydroxide precipitation precursor is obtained after spray drying; according to the stoichiometric ratio, a sodium-containing compound, the first transition metal hydroxide precipitation precursor, and an M-containing compound, an N-containing compound, an L-containing compound, and a P-containing compound are mixed, ball-milled, tableted, and sintered to obtain the seven-element high-entropy high-sodium iron-manganese-based sodium ion battery positive electrode material.

5. The preparation method according to claim 4, wherein the feeding ratio of the iron salt and the manganese salt for the coprecipitation reaction is (0.2-0.6):1; Sodium in the sodium-containing compound: iron and manganese in the first transition metal hydroxide precipitation precursor: M, N, L, P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound = (0.7-0.9): (0.7-1.0): (0-0.4), and the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound in (0-0.4) is greater than zero; The sintering conditions are: first sinter at a constant temperature of 400-550°C for 1-5 hours, then heat up to 900-1100°C and sinter at a constant temperature for 10-24 hours. The sintering atmosphere is oxygen or air or a mixture of oxygen and air.

6. The preparation method according to claim 4, characterized in that: The sodium-containing compound is at least one of sodium carbonate, sodium acetate and sodium hydroxide; The iron salt is at least one of ferric nitrate, ferric chloride and ferric acetate; The manganese salt is at least one of manganese nitrate, manganese chloride and manganese acetate; The M-containing compound is at least one of an M-containing metal oxide, an M-containing oxide, an M-containing carbonate, and an M-containing hydroxide; The N-containing compound is at least one of a N-containing metal oxide, a N-containing oxide, a N-containing carbonate, and a N-containing hydroxide; The L-containing compound is at least one of an L-containing metal oxide, an L-containing oxide, an L-containing carbonate, and an L-containing hydroxide. The P-containing compound is at least one of a P-containing metal oxide, a P-containing oxide, a P-containing carbonate, and a P-containing hydroxide.

7. A method for preparing a seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material as claimed in any one of claims 1 to 3, characterized in that: The preparation method comprises: According to the stoichiometric ratio, the sodium-containing compound, the iron-containing compound, the manganese-containing compound, the M-containing compound, the N-containing compound, the L-containing compound and the P-containing compound are mixed, ball-milled, refined, tableted and sintered to obtain the seven-element high-entropy high-sodium iron-manganese sodium ion battery positive electrode material.

8. The preparation method according to claim 7, characterized in that: According to the molar ratio, the sodium in the sodium-containing compound: the iron in the iron-containing compound: the manganese in the manganese-containing compound: the M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound are fed in a ratio of (0.7 to 0.9): (0.1 to 0.4): (0.4 to 0.8): (0 to 0.4), and the sum of the ranges of M, N, L, and P in the M-containing compound, the N-containing compound, the L-containing compound, and the P-containing compound in (0 to 0.4) is greater than zero; The sintering conditions are: first sintering at a constant temperature of 400-550°C for 1-5 hours, then heating to 900-1100°C and sintering at a constant temperature for 10-24 hours, and the sintering atmosphere is oxygen or air or a mixture of oxygen and air; The iron-containing compound is at least one of ferrous oxide, ferric oxide, ferric hydroxide, ferric carbonate, and ferrous oxalate; The manganese-containing compound is at least one of manganous oxide, manganese tetraoxide, manganese hydroxide, manganese carbonate, and manganese oxalate; The sodium-containing compound is at least one of sodium carbonate, sodium acetate and sodium hydroxide; The M-containing compound is at least one of an M-containing metal oxide, an M-containing oxide, an M-containing carbonate, and an M-containing hydroxide; The N-containing compound is at least one of a N-containing metal oxide, a N-containing oxide, a N-containing carbonate, and a N-containing hydroxide; The L-containing compound is at least one of an L-containing metal oxide, an L-containing oxide, an L-containing carbonate, and an L-containing hydroxide. The P-containing compound is at least one of a P-containing metal oxide, a P-containing oxide, a P-containing carbonate, and a P-containing hydroxide.

9. A sodium ion battery comprising a positive electrode material, characterized in that: The positive electrode material comprises the seven-element high entropy high sodium iron-manganese sodium ion battery positive electrode material as described in any one of claims 1 to 3, or comprises the seven-element high entropy high sodium iron-manganese sodium ion battery positive electrode material prepared by the preparation method as described in any one of claims 4 to 8.

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