A ternary nickel-iron-manganese sodium acid positive electrode material in nanosheet form, a preparation method and application thereof

Abstract

This invention provides a nanosheet-like ternary sodium nickel iron manganese oxide cathode material, its preparation method, and its applications. The ternary sodium nickel iron manganese oxide cathode material has a nanosheet structure, and the spacing between the transition metal oxide layer and the sodium layer, as well as the valence state of Mn, are controlled by varying the contents of Fe and Ni. The molecular formula is Na. x Ni 1 / 3‑y Fe y Mn 2 / 3 O2 where 0.44≤x≤0.67, 0≤y≤1 / 3; also provides a preparation method for this material: mix and dissolve transition metal salts of nickel, iron and manganese, then add sodium salt to dissolve to obtain a mixed metal ion salt solution, add citric acid dropwise, heat and stir, dry, and sinter to obtain a ternary nickel-iron-manganese sodium cathode material.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to a nanosheet-shaped ternary nickel-iron-manganese cathode material with good cycle performance, its preparation method, and its application. Background Technology

[0002] P2-phase nickel-manganese-based cathode materials, as a classic class of sodium-ion battery cathode materials, have been favored by energy storage researchers due to their high specific capacity, high operating voltage, and stability in air. However, the inherent drawbacks of P2-phase nickel-manganese-based cathode materials, such as the ordered arrangement of sodium ions and vacancies, structural collapse during charge and discharge, and limited energy density, have limited their further development. To improve the electrochemical performance of P2-phase nickel-manganese-based sodium-ion battery cathode materials, current research mainly employs methods such as doping substitution, controlling microstructure, oxide coating, and creating mixed phases to improve material performance from different perspectives. Studies have shown that a well-designed structure can facilitate rapid insertion and extraction of sodium ions while alleviating structural stress during charge and discharge, thereby improving the material's electrochemical performance.

[0003] Patent document CN108987711B discloses a spherical sodium-ion battery cathode quaternary material and its preparation method, which prepares a spherical Na... 0.5 Mn 0.6 Ni 0.2 Cu x Mg y O2 cathode material (x = 0.1, y = 0.1; or x = 0.05, y = 0.15; or x = 0.12, y = 0.08) improves the cycle stability of the material. However, this material still suffers from a serious problem of ordered arrangement of sodium ions and vacancies, and Cu... 2+ / Cu 3+ The redox potential is low, and Mg 2+ Lacking electrochemical activity, the material has a low discharge capacity and its rate performance cannot be guaranteed. Existing sodium-ion battery oxide cathode materials mostly have a spherical structure, resulting in a long sodium-ion diffusion path. Furthermore, the ordered arrangement of sodium ions and vacancies within the material increases the sodium-ion diffusion barrier, leading to poor cycle and rate performance. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the background art above, and to provide a ternary nickel-iron-manganese cathode material with high discharge specific capacity and sheet-like structure, as well as its preparation method and application.

[0005] To solve the above-mentioned technical problems, the technical solution proposed by this invention is as follows:

[0006] A nanosheet-like ternary nickel-iron-manganese sodium cathode material, wherein the ternary nickel-iron-manganese sodium cathode material has a nanosheet structure, and the spacing between the transition metal oxide layer and the sodium layer, as well as the valence state of Mn, are controlled by different contents of Fe and Ni. The molecular formula is Na. x Ni 1 / 3-y Fe y Mn 2 / 3 O2 where 0.44≤x≤0.67, 0≤y≤1 / 3.

[0007] Preferably, the ternary nickel-iron-manganese cathode material has a sheet thickness of 50 nm to 1 μm and a sheet width of 1 to 10 μm.

[0008] Based on the overall inventive concept, this invention also provides a method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material, comprising the following steps:

[0009] (1) Mix and dissolve the transition metal salts of nickel, iron and manganese to obtain a nickel-iron-manganese transition metal salt solution, and then add sodium salt to dissolve to obtain a mixed metal ion salt solution.

[0010] (2) Add the mixed metal ion salt solution obtained in step (1) to the citric acid solution, heat and stir to form a viscous gel;

[0011] (3) The viscous gel obtained in step (2) is dried and calcined to obtain sodium nickel iron manganate precursor;

[0012] (4) The sodium nickel iron manganese precursor obtained in step (3) is sintered to obtain ternary sodium nickel iron manganese cathode material.

[0013] Preferably, the transition metal salt in step (1) is one or more of soluble nitrates, acetates, sulfates, and oxalates; the sodium salt is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; and the molar ratio of each element in the transition metal salts of nickel, iron, and manganese is Mn∶(Ni+Fe)=2~3∶1.

[0014] Preferably, the concentration of the nickel-iron-manganese transition metal salt solution in step (1) is 0.01 to 0.1 mol / L; the molar ratio of sodium ions to nickel-iron-manganese metal ions in the mixed metal ion salt solution is 0.44 to 0.67:1.

[0015] Preferably, the molar concentration ratio of the citric acid solution to the molar concentration of the metal ions in the mixed metal ion salt solution in step (2) is 1 to 2:1; the mixed metal ion salt solution is added to the citric acid solution by a peristaltic pump at a pumping speed of 50 to 500 mL. Controlling the flow rate of the metal salt solution ensures sufficient complexation between the metal ions and citric acid, preventing excessively rapid entry of metal ions that would lead to insufficient complexation with citric acid and thus preventing segregation during the water bath process.

[0016] Preferably, the heating and stirring in step (2) is water bath heating, the temperature of the water bath process is 60-90℃, and the stirring speed is 50-500r / min.

[0017] Too low a stirring speed will cause uneven composition during the evaporation of the solution, resulting in segregation of the raw materials and making it impossible to obtain a gel with uniform composition. Too high a stirring speed will cause the solution to stick to the container wall, and sample loss will cause changes in the proportion of different metal ions, ultimately leading to a deviation between the prepared gel composition and the expected composition.

[0018] Preferably, the drying conditions in step (3) are: under vacuum conditions, the temperature is 60-90°C, the drying time is 8-16h, the calcination temperature is 400-700°C, and the calcination time is 4-10h.

[0019] Preferably, the temperature of the sintering process in step (4) is 800-950°C and the sintering time is 8-20h.

[0020] This invention ensures the feeding rate of the nickel-iron-manganese metal solution, the proportion of citric acid, and the water bath time during the material preparation process, thereby ensuring the uniformity of the raw materials and ultimately obtaining a material with good morphology, which is a regular hexagonal prism-shaped sheet.

[0021] Based on the overall inventive concept, this invention also provides the application of nanosheet-like ternary nickel-iron-manganese sodium cathode material in batteries.

[0022] This invention utilizes Fe 3+ Replace part of Ni 2+ Eliminating the ordered ionic arrangement in P2 type sodium nickel manganate materials and reducing Na + The insertion / extraction energy barrier is broken, thereby enhancing the material's high-rate discharge capability. Furthermore, Fe... 3+ A larger ionic radius can increase the interlayer spacing of the transition metal oxide layers and decrease the interlayer spacing of the sodium layers, thereby improving the cycling stability of the material. Simultaneously, by replacing low-valence metal ions with high-valence metal ions, the valence equilibrium of Mn in the bulk phase of the material is maintained. 3+ The increased content achieves the goal of improving the discharge specific capacity of the material.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The ternary nickel-iron-manganese sodium cathode material designed in this invention has a nanosheet structure. In this invention, different contents of Fe and Ni can significantly control the spacing between the transition metal oxide layer and the sodium layer, as well as the valence state of Mn. Utilizing Fe... 3+ Ionic radius and Similar to each other, but with different Fermi levels, the nanosheet structure disrupts the charge order in the transition metal layer, transforming the two-phase reaction into a homogeneous solid-phase reaction. Specifically, this manifests as the disappearance of the charge-discharge plateau during material cycling, resulting in a smoother charge-discharge curve and ultimately improved cycling and rate performance. Furthermore, the nanosheet structure exposes more electrochemically active crystal planes, shortening the Na... + diffusion pathway, Fe 3+ with Ni 2+ Different valence states will cause some Mn in the system to... 4+ Reduced to Mn 3+ This improves the discharge specific capacity of the material. The nanosheet-structured sodium nickel iron manganese oxide cathode material exhibits excellent electrochemical performance, maintaining a capacity of 112 mAh g / L at a current rate of 2C. -1 The specific discharge capacity.

[0025] 2. The preparation process of this invention is simple, the process is short, and the raw materials are readily available. No toxic or harmful substances are generated during the preparation process, making it easy to achieve large-scale production. Compared with the traditional sol-gel method, which requires pH adjustment, the experimental conditions of this invention are simpler. It does not require the use of ammonia to adjust the pH. Even under low acidity conditions, it can ensure good complexation between citric acid and metal ions. The prepared material has a good hexagonal prism morphology, is a pure phase material, and exhibits excellent electrochemical performance. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 The XRD patterns of the nanosheet sodium nickel iron manganate cathode material prepared in Example 1 and sodium nickel manganate in Comparative Example 1 are shown.

[0028] Figure 2 The image shows the refined XRD pattern and crystal structure diagram of the nanosheet sodium nickel iron manganese oxide cathode material prepared in Example 1.

[0029] Figure 3The image shows a SEM image of the nanosheet sodium nickel iron manganese oxide cathode material prepared in Example 1.

[0030] Figure 4 The image shows the elemental surface scan of the nanosheet sodium nickel iron manganese oxide cathode material prepared in Example 1.

[0031] Figure 5 The first charge-discharge curve of a coin cell assembled from the nanosheet-structured sodium nickel iron manganese oxide material prepared in Example 1 at a discharge rate of 1C.

[0032] Figure 6 The XRD pattern and crystal structure diagram of the nanosheet sodium nickel manganate cathode material prepared for Comparative Example 1 are shown.

[0033] Figure 7 The first charge-discharge curve of a coin cell assembled from the nanosheet-structured sodium nickel manganate material prepared for Comparative Example 1 at a discharge rate of 1C.

[0034] Figure 8 The graph shows the cycle performance of a coin cell assembled with the nanosheet sodium nickel iron manganese oxide cathode material prepared in Example 1 and the sodium nickel manganese oxide material in Comparative Example 1 at a discharge rate of 1C.

[0035] Figure 9 The rate performance diagram shows the coin cell assembled with the nanosheet sodium nickel iron manganese oxide cathode material prepared in Example 1 and the sodium nickel manganese oxide material in Comparative Example 1. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0039] Example 1:

[0040] A nanosheet-like ternary sodium nickel iron manganese oxide cathode material, exhibiting a nanosheet structure, utilizes varying Fe and Ni contents to control the spacing between the transition metal oxide layer and the sodium layer, as well as the valence state of Mn. Its molecular formula is Na. 2 / 3 Ni 7 / 24 Fe 1 / 24 Mn2 / 3 O2.

[0041] A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material includes the following steps:

[0042] (1) Dissolve manganese acetate, nickel acetate, ferric nitrate and sodium acetate in deionized water in a molar ratio of 2 / 3:7 / 24:1 / 24:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution in 1.2 times the molar amount of the transition metal.

[0043] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution using a peristaltic pump at a rate of 100 mL / h;

[0044] (3) Place the mixed solution from step (2) in a water bath and stir it at 80°C and 200 r / min to form a viscous gel.

[0045] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel iron manganate precursor.

[0046] (5) The sodium iron manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0047] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0048] like Figure 1 As shown in the XRD pattern of the nanosheet sodium nickel iron manganese oxide cathode material prepared in this embodiment, the sample peaks are sharp and there are no impurity peaks, indicating that the introduction of iron did not change the crystal structure of the material.

[0049] like Figure 2 As shown, the sodium layer spacing of the nanosheet-like sodium nickel iron manganese oxide cathode material prepared in this embodiment is [value missing]. The interlayer spacing of the transition metal oxide layer is A lower sodium interlayer spacing ensures that the material maintains good cycling stability during cycling.

[0050] like Figure 3 As shown, the nanosheet-structured sodium nickel iron manganese oxide cathode material prepared in this embodiment has a smooth surface without impurities, a particle size of about 5 μm, and a sheet thickness of about 500 nm. The material has a nanosheet structure.

[0051] like Figure 4 As shown in the EDS image of the nanosheet-structured sodium nickel iron manganese oxide cathode material prepared in this embodiment, the Fe element is uniformly distributed, indicating that Fe has successfully entered the material, thus indicating the successful preparation of the sodium nickel iron manganese oxide cathode material.

[0052] like Figure 5 As shown, the coin cell assembled in this embodiment can achieve an initial discharge specific capacity of 142.3 mAh g at a 1C discharge rate within a voltage range of 1.5-4.15V. -1 The charge-discharge curve of the material is relatively smooth, and there is no obvious charge-discharge voltage plateau.

[0053] like Figure 8 As shown, the battery assembled in this embodiment retains 71.4% of its capacity after 100 cycles at a current rate of 1C within a voltage range of 1.5-4.15V.

[0054] like Figure 9 As shown, the battery assembled in this embodiment has discharge specific capacities of 145.4, 136.2, 124.6, and 104.4 mAh g at current rates of 0.2, 0.5, 1, and 2C within a voltage range of 1.5-4.15V. -1 .

[0055] Example 2:

[0056] A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material includes the following steps:

[0057] (1) Dissolve manganese acetate, nickel acetate, ferric nitrate and sodium acetate in deionized water at a molar ratio of 2 / 3:15 / 48:1 / 48:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution at 1.2 times the molar amount of the transition metal.

[0058] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution by pumping it into the solution at a rate of 100 mL / h using a peristaltic pump;

[0059] (3) Place the mixed solution from step (2) in a water bath and stir it at 80°C and 200 r / min to form a viscous gel.

[0060] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel iron manganate precursor.

[0061] (5) The sodium iron manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0062] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0063] After the materials in this embodiment were assembled into a half-cell, their electrochemical performance was tested in the range of 1.5-4.15V. The initial discharge specific capacity at a 1C current rate reached 142.3 mAh / g, and the capacity retention rate after 100 cycles at a 1C current rate was 70.3%. The rate performance of the prepared cathode material was tested, and its discharge specific capacities at 0.2, 0.5, 1, and 2C were 142.6, 130.4, 119.4, and 97.4 mAh / g, respectively.

[0064] Example 3:

[0065] A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material includes the following steps:

[0066] (1) Dissolve manganese acetate, nickel acetate, ferric nitrate and sodium acetate in deionized water in a molar ratio of 2 / 3:7 / 24:1 / 24:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution in 2.4 times the molar amount of the transition metal.

[0067] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution by pumping it into the solution at a rate of 100 mL / h using a peristaltic pump;

[0068] (3) Place the mixed solution from step (2) in a water bath and stir it at 80°C and 200 r / min to form a viscous gel.

[0069] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel iron manganate precursor.

[0070] (5) The sodium iron manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0071] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0072] After the materials in this embodiment were assembled into a half-cell, their electrochemical performance was tested in the range of 1.5-4.15V. The initial discharge specific capacity at a 1C current rate reached 143.6 mAh / g, and the capacity retention rate after 100 cycles at a 1C current rate was 70.1%. The rate performance of the prepared cathode material was tested, and its discharge specific capacities at 0.2, 0.5, 1, and 2C were 142.2, 131.7, 120.5, and 100.5 mAh / g, respectively.

[0073] Example 4:

[0074] A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material includes the following steps:

[0075] (1) Dissolve manganese acetate, nickel acetate, ferric nitrate and sodium acetate in deionized water in a molar ratio of 2 / 3:7 / 24:1 / 24:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution in 1.2 times the molar amount of the transition metal.

[0076] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution by pumping it into the solution at a rate of 100 mL / h using a peristaltic pump;

[0077] (3) Place the mixed solution from step (2) in a water bath and stir it at 60°C and 200 r / min to form a viscous gel.

[0078] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel iron manganate precursor.

[0079] (5) The sodium iron manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0080] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0081] After the materials in this embodiment were assembled into a half-cell, their electrochemical performance was tested in the range of 1.5-4.15V. The initial discharge specific capacity at a 1C current rate reached 140.3 mAh / g, and the capacity retention rate after 100 cycles at a 1C current rate was 70.3%. The prepared cathode material was tested for rate performance, and its discharge specific capacities at 0.2, 0.5, 1, and 2C were 140.9, 128.7, 115.4, and 90.1 mAh / g, respectively.

[0082] Example 5:

[0083] A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material includes the following steps:

[0084] (1) Dissolve manganese acetate, nickel acetate, ferric nitrate and sodium acetate in deionized water in a molar ratio of 2 / 3:7 / 24:1 / 24:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution in 1.2 times the molar amount of the transition metal.

[0085] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution by pumping it into the solution at a rate of 100 mL / h using a peristaltic pump;

[0086] (3) Place the mixed solution from step (2) in a water bath and stir it at 80°C and 200 r / min to form a viscous gel.

[0087] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel iron manganate precursor.

[0088] (5) The sodium iron manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0089] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0090] After the materials in this embodiment were assembled into a half-cell, electrochemical performance tests were conducted in the range of 1.5-4.15V. The initial discharge specific capacity at a 1C current rate reached 139.1 mAh / g, and the capacity retention rate after 100 cycles at a 1C current rate was 69.5%. Rate performance tests were conducted on the prepared cathode material, and its discharge specific capacities at 0.2, 0.5, 1, and 2C were 139.9, 123.7, 108.4, and 89.1 mAh / g, respectively.

[0091] Comparative Example 1:

[0092] A method for preparing a nanosheet-like binary sodium nickel manganate cathode material includes the following steps:

[0093] (1) Dissolve manganese acetate, nickel acetate and sodium acetate in deionized water in a molar ratio of 2 / 3:1 / 3:2 / 3 to prepare 100 mL of a 0.05 mol / L transition metal ion solution, and prepare 100 mL of a 0.06 mol / L citric acid solution in 1.2 times the molar amount of the transition metal.

[0094] (2) Dissolve 100 mL of 0.05 mol / L transition metal from step (1) in 100 mL of citric acid solution by pumping it into the solution at a rate of 100 mL / h using a peristaltic pump;

[0095] (3) Place the mixed solution from step (2) in a water bath and stir it at 80°C and 200 r / min to form a viscous gel.

[0096] (4) After drying the gel in step (3) at 80°C for 10 hours in a vacuum drying oven, it is sintered at 450°C for 4 hours in an air atmosphere in a muffle furnace to obtain sodium nickel manganate precursor.

[0097] (5) The sodium nickel manganate precursor in step (4) is sintered in a muffle furnace at 900°C for 12 h in an air atmosphere to obtain sodium iron manganate cathode material.

[0098] Battery assembly: Weigh 0.2000g of the sodium nickel iron manganese oxide positive electrode material obtained in this example, add 0.0250g of conductive carbon black as a conductive agent and 0.0250g of PVDF (polyvinylidene fluoride) as a binder, mix evenly and coat it on aluminum foil to form a positive electrode sheet. In a vacuum glove box, use a metallic sodium sheet as the negative electrode, a Whatman GF / D glass fiber separator, and a 1mol / L NaClO4 electrolyte (EC:DMC = 1:1 (volume ratio) + 5% FEC) to assemble a CR2025 coin cell.

[0099] like Figure 1 As shown, the XRD pattern of the sodium nickel manganate cathode material prepared in this comparative example has sharp peaks and no impurity peaks.

[0100] like Figure 6 As shown, the sodium layer spacing of the nanosheet-like sodium nickel iron manganese oxide cathode material prepared in this embodiment is [value missing]. The interlayer spacing of the transition metal oxide layer is

[0101] like Figure 7 As shown, the coin cell assembled in this comparative example achieves an initial discharge specific capacity of 136.2 mAh g at a 1C discharge rate within a voltage range of 1.5-4.15V. -1 The material's charge-discharge curves show multiple distinct charge-discharge voltage plateaus, corresponding to the orderly arrangement of sodium ions and vacancies.

[0102] like Figure 8 As shown, the battery assembled in this comparative example retains 60.1% of its capacity after 100 cycles at a current rate of 1C within a voltage range of 1.5-4.15V.

[0103] like Figure 9 As shown, the battery assembled in this embodiment has discharge specific capacities of 154.3, 123.6, 103.6, and 81.3 mAh g at current rates of 0.2, 0.5, 1, and 2C within a voltage range of 1.5-4.15V. -1 .

Claims

1. A method for preparing a nanosheet-like ternary nickel-iron-manganese sodium cathode material, characterized in that, The ternary nickel-iron-manganese oxide cathode material has a hexagonal prism-shaped nanosheet structure. The spacing between the transition metal oxide layer and the sodium layer, as well as the valence state of Mn, are controlled by varying the contents of Fe and Ni. Its molecular formula is Na. x Ni 1 / 3-y Fe y Mn 2 / 3 O2, where 0.44≤x≤0.67, 0<y≤1 / 3, is prepared by the following steps: (1) Mix and dissolve the transition metal salts of nickel, iron and manganese to obtain a nickel-iron-manganese transition metal salt solution, and then add sodium salt to dissolve to obtain a mixed metal ion salt solution; (2) The mixed metal ion salt solution obtained in step (1) is added to the citric acid solution and heated and stirred to form a viscous gel; wherein, the molar concentration of the citric acid solution is 1~2:1 to the molar concentration of the metal ions in the mixed metal ion salt solution; the mixed metal ion salt solution is added to the citric acid solution by a peristaltic pump, the pumping speed of the peristaltic pump is 50~500 mL; the heating and stirring is carried out by water bath heating, the temperature of the water bath process is 60~90℃, and the stirring speed is 50~500 r / min; (3) The viscous gel obtained in step (2) is dried and calcined to obtain sodium nickel iron manganate precursor; (4) The sodium nickel iron manganese precursor obtained in step (3) is sintered to obtain ternary sodium nickel iron manganese cathode material.

2. The preparation method according to claim 1, characterized in that, The transition metal salt mentioned in step (1) is one or more of soluble nitrates, acetates, sulfates, and oxalates; the sodium salt is one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, and sodium acetate; the molar ratio of each element in the transition metal salts of nickel, iron, and manganese is: Mn∶(Ni+Fe)=2~3∶1.

3. The preparation method according to claim 1, characterized in that, The concentration of the nickel-iron-manganese transition metal salt solution in step (1) is 0.01~0.1 mol / L; the molar ratio of sodium ions to nickel-iron-manganese metal ions in the mixed metal ion salt solution is 0.44~0.67∶1.

4. The preparation method according to claim 1, characterized in that, The drying conditions in step (3) are: under vacuum conditions, the temperature is 60~90 ℃, and the drying time is 8~16h; the calcination temperature is 400~700℃, and the calcination time is 4~10h.

5. The preparation method according to claim 1, characterized in that, The sintering process described in step (4) is carried out at a temperature of 800~950 ℃ and for a sintering time of 8~20 h.

6. The preparation method according to claim 1, characterized in that, The ternary nickel-iron-manganese cathode material has a sheet thickness of 50 nm to 1 μm and a sheet width of 1 to 10 μm.

7. The application of the nanosheet-like ternary nickel-iron-manganese cathode material prepared by the preparation method as described in claim 1 in a battery.

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