Sodium battery precursor and preparation method thereof, sodium battery positive electrode material and sodium battery

Abstract

The invention provides a sodium electric precursor and a preparation method thereof, a sodium electric positive electrode material and a sodium battery. The sodium electric precursor comprises a seed crystal, a middle layer and a shell, the component of the seed crystal comprises oleic acid modified nano FeCO3, the components of the middle layer and the shell comprise ferromanganese hydroxide, the concentration ratio of Fe < 2 + > to Fe < 3 + > in the middle layer is larger than that of the shell, and the concentration ratio of Mn < 4 + > to Mn < 3 + > in the middle layer is smaller than that of the shell. The sodium electric precursor provided by the invention does not contain nickel, so that the preparation cost is reduced; the seed crystal comprises nano FeCO3 modified by oleic acid, so that the structural defects are reduced, and the sodium battery positive electrode material has relatively high capacity; the seed crystal, the middle layer and the shell form a core-shell structure, so that the volume change and stress accumulation of sodium ions in the embedding / de-embedding process are inhibited, and the cycling stability is improved; fe is enriched in the middle layer, so that the capacity of the sodium battery positive electrode material can be improved; mn < 4 + > is enriched in the shell, so that the cycling stability of the sodium battery positive electrode material is improved.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and relates to a sodium battery precursor, and more particularly to a sodium battery precursor and its preparation method, a sodium battery cathode material and a sodium battery. Background Technology

[0002] Sodium-ion batteries have shown great application potential in large-scale energy storage due to their advantages such as widely available raw materials, low cost, and good environmental compatibility. The overall performance of sodium-ion batteries largely depends on their cathode materials, and the key performance indicators of cathode materials, such as capacity, voltage, and cycle stability, are directly determined by the chemical composition, microstructure, and phase composition of the sodium battery precursor. Therefore, the development of high-performance sodium battery precursors is an important means to improve the overall performance of sodium-ion batteries.

[0003] However, the sodium-ion battery precursors upon which current mainstream sodium-ion battery layered oxide cathode materials rely all have certain drawbacks. Nickel-manganese based precursors, in particular, still result in high raw material costs due to the use of expensive nickel. Meanwhile, nickel-free manganese-iron based precursors lack the redox couple of nickel, leading to lower reversible capacity, poor structural stability, and unsatisfactory cycle performance in the final sodium-ion battery cathode material. Therefore, these defects in existing sodium-ion battery precursors severely restrict the improvement of energy density and cycle performance of sodium-ion batteries at a lower cost.

[0004] To improve the performance of sodium-ion battery precursors, existing technologies often employ optimization strategies such as elemental doping and phase structure modulation. However, these existing improvement schemes have significant limitations. They not only easily lead to the dissolution of transition metal ions, causing the cycle stability of sodium-ion battery cathode materials to fail to meet the requirements of practical applications, but also suffer from complex processes, high energy consumption, and are not conducive to large-scale production. Furthermore, they fail to fundamentally resolve the contradiction between cost and capacity in sodium-ion battery cathode materials. Therefore, developing a novel sodium-ion battery precursor that enables sodium-ion battery cathode materials prepared from sodium-ion battery precursors to possess the advantages of high capacity, high stability, and low cost is a crucial challenge currently facing us.

[0005] For example, CN118630198A discloses a multi-element doped iron-manganese sodium-ion battery cathode material, its preparation method, and a sodium-ion battery. The general formula of the sodium transition metal oxide in the cathode material is: Na x Fe a Mn b M c N d L eO2; where 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, a+b+c+d+e=1, M is one of Li and K, and N and L are two different elements among Mg, Al, B, La, Zn, Ti, Ca, Zr, and Cu.

[0006] For example, CN119764436A discloses an iron-rich phase iron-manganese P3 type sodium-ion battery cathode material, preparation method, and battery. The general formula of the sodium transition metal oxide of the cathode material is: NaFeMn iron P3 phase as the main phase. Compared with the traditional O3 phase nickel-iron-manganese 111 cathode material (sodium = 1.0), it increases the structural stability and air stability of the material. In a higher voltage range (2~4.3V), it ensures the charge-discharge capacity and long cycle capacity of the material. Compared with the traditional P2 phase iron-manganese cathode material, it improves the capacity and charge-discharge capacity of the cathode material.

[0007] In summary, existing sodium battery precursors all have certain drawbacks, including the difficulty in simultaneously achieving high capacity, high stability, and low cost in sodium battery cathode materials prepared from sodium battery precursors. Therefore, developing and designing a novel sodium battery precursor and its preparation method, as well as sodium battery cathode materials and sodium batteries, is of paramount importance. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a sodium battery precursor, its preparation method, a sodium battery cathode material, and a sodium battery. The sodium battery precursor provided by this invention does not contain nickel, reducing the preparation cost of both the precursor and the cathode material. The seed crystals of the sodium battery precursor include oleic acid-modified nano-FeCO3, reducing structural defects and resulting in a high capacity for the sodium battery cathode material. The seed crystals, intermediate layer, and outer shell of the sodium battery precursor together constitute a stable core-shell structure, effectively suppressing volume changes and stress accumulation during sodium ion insertion / extraction, reducing the risk of phase transitions and cracking during cycling. Therefore, the sodium battery cathode material prepared from the sodium battery precursor exhibits high cycle stability. The intermediate layer is enriched with Fe²⁺, which is beneficial for improving the capacity of the sodium battery cathode material. The outer shell is enriched with Mn. 4+ This improves the cycle stability of sodium-ion battery cathode materials.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a sodium-electric precursor, the sodium-electric precursor comprising a seed crystal, an intermediate layer and a shell;

[0011] The seed crystal comprises oleic acid-modified nano-FeCO3, and both the intermediate layer and the outer shell comprise manganese iron hydroxide, with Fe in the intermediate layer... 2+ with Fe 3+ The concentration ratio is greater than that of Fe in the shell. 2+ with Fe 3+ The concentration ratio of Mn in the intermediate layer 4+ With Mn 3+ The concentration ratio is less than that of Mn in the shell. 4+ With Mn 3+ The ratio of their concentrations.

[0012] The sodium-ion battery precursor provided by this invention is a manganese-iron based sodium-ion battery precursor. Firstly, the sodium-ion battery precursor does not contain nickel, thus reducing raw material costs and consequently lowering the preparation costs of the sodium-ion battery precursor and the sodium-ion battery cathode material. Secondly, the seed crystals of the sodium-ion battery precursor include oleic acid-modified nano-FeCO3, which provides nucleation sites, improves the crystallinity of the sodium-ion battery precursor, and reduces structural defects. Therefore, the sodium-ion battery cathode material prepared from the sodium-ion battery precursor has a high capacity. Thirdly, the seed crystals, intermediate layer, and outer shell of the sodium-ion battery precursor together constitute a stable core-shell structure, which can effectively suppress volume changes and stress accumulation of sodium ions during insertion / extraction, reducing the risk of phase transitions and cracks during cycling. Therefore, the sodium-ion battery cathode material prepared from the sodium-ion battery precursor has high cycling stability. Fourthly, the intermediate layer is enriched with a high concentration of Fe²⁺, providing high capacity and contributing to improved capacity of the sodium-ion battery cathode material; the outer shell is enriched with a high concentration of Mn. 4+ As the outermost layer, it effectively suppresses the side reactions between the sodium electrode material and the electrolyte, thereby improving the cycle stability of the sodium electrode material.

[0013] Preferably, the mass fraction of iron in the seed crystal of the sodium-electric precursor is 2wt% to 3wt%, based on the total mass of metal elements in the sodium-electric precursor. For example, it can be 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, or 3.0wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0014] Preferably, the thickness of the intermediate layer is 1μm to 3μm, for example, it can be 1.0μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2.0μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm or 3.0μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0015] Preferably, the outer shell comprises a first shell layer, a second shell layer, and a third shell layer sequentially covering the crystal from the seed crystal to the outer shell; the first shell layer, the second shell layer, and the third shell layer contain Fe. 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ The concentration ratios of the components increase sequentially.

[0016] In this invention, Fe in the first shell, second shell, and third shell 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ The concentration ratios of Fe²⁺ and Fe³⁺ increase sequentially. The first shell is enriched with a high concentration of Fe²⁺. Since the redox reaction of Fe²⁺ / Fe³⁺ is an important source of capacity in sodium-ion batteries, the first shell provides high capacity, which is beneficial to improving the capacity of sodium-ion cathode materials. The second shell, as a gradient transition region between composition and structure, acts as a buffer zone and can effectively buffer the rich Fe²⁺ content during charging and discharging. 2+ The first shell and Mn-rich 4+ The internal stress caused by lattice variations in the third shell reduces the risk of cracking in sodium-ion cathode materials and enhances their structural stability; the third shell is enriched with a high concentration of Mn. 4+ Because of Mn 4+ It can form an extremely stable and chemically inert surface structure. Therefore, the third shell, as the outermost layer, effectively suppresses the side reactions between the sodium electrode material and the electrolyte, thereby improving the cycle stability of the sodium electrode material.

[0017] Preferably, the thickness of the first shell layer is 0.5μm to 1.0μm, for example, it can be 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm or 1.0μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0018] Preferably, the thickness of the second shell layer is 1.0 μm to 1.5 μm, for example, it can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0019] Preferably, the thickness of the third shell layer is 1.5μm to 2.0μm, for example, it can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm or 2.0μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, in the intermediate layer and the outer shell, the molar ratio of manganese to iron is independently (0.8~1.2):1, for example, it can be 0.8:1, 0.9:1, 1.0:1, 1.1:1 or 1.2:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0021] In a second aspect, the present invention provides a method for preparing the sodium-ion precursor described in the first aspect, the method comprising:

[0022] (1) In a protective atmosphere, oleic acid-modified nano-FeCO3 is initially mixed with the reaction substrate to obtain an initial mixture; the obtained initial mixture is then mixed with manganese-iron mixed salt solution, precipitant solution and complexing agent solution to carry out a co-precipitation reaction to obtain a solution containing a half-step precursor.

[0023] (2) In an oxygen-containing atmosphere, the solution containing the semi-step precursor, the manganese-iron mixed salt solution, the precipitant solution and the complexing agent solution obtained in step (1) are mixed and co-precipitated to obtain the manganese-iron precursor.

[0024] Preferably, the method for preparing the oleic acid-modified nano FeCO3 includes: modifying nano FeCO3 with oleic acid to obtain oleic acid-modified nano FeCO3.

[0025] Preferably, the mass ratio of oleic acid to nano-FeCO3 used in the modification is (0.05~0.2):100, for example, it can be 0.05:100, 0.06:100, 0.07:100, 0.08:100, 0.09:100, 0.10:100, 0.11:100, 0.12:100, 0.13:100, 0.14:100, 0.15:100, 0.16:100, 0.17:100, 0.18:100, 0.19:100 or 0.20:100, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the D50 particle size of the nano FeCO3 is 80nm~120nm, for example, it can be 80nm, 82nm, 84nm, 86nm, 88nm, 90nm, 92nm, 94nm, 96nm, 98nm, 100nm, 102nm, 104nm, 106nm, 108nm, 110nm, 112nm, 114nm, 116nm, 118nm or 120nm, but is not limited to the listed values, other unlisted values ​​within this range are also applicable.

[0027] Preferably, the modification method includes:

[0028] First, nano-FeCO3 is dispersed in a solvent to form a suspension. Then, oleic acid is added dropwise to the resulting suspension under continuous stirring to form a mixture. The mixture is then stirred further to anchor the carboxyl groups of the oleic acid molecules to the surface of the nano-FeCO3 through coordination. Finally, solid-liquid separation is performed to obtain oleic acid-modified nano-FeCO3.

[0029] Preferably, the solvent includes any one or a combination of at least two of water, ethanol, or n-hexane. Typical but non-limiting combinations include combinations of water and ethanol, ethanol and n-hexane, water and n-hexane, or water, ethanol, and n-hexane.

[0030] Preferably, during the coprecipitation reaction in step (1), the pH of the reaction solution is controlled to be 9.0~9.5, the temperature to be 45℃~50℃, the concentration of the complexing agent to be 0.1mol / L~0.5mol / L, and the total concentration of metal ions to be 0.5mol / L~1.5mol / L.

[0031] In this invention, during the coprecipitation reaction in step (1), the pH of the reaction solution is controlled to be 9.0~9.5, for example, it can be 9.0, 9.05, 9.1, 9.15, 9.2, 9.25, 9.3, 9.35, 9.4, 9.45 or 9.5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] In this invention, during the coprecipitation reaction in step (1), the temperature of the reaction solution is controlled at 45℃~50℃, for example, it can be 45.0℃, 45.5℃, 46.0℃, 46.5℃, 47.0℃, 47.5℃, 48.0℃, 48.5℃, 49.0℃, 49.5℃ or 50.0℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] In this invention, during the coprecipitation reaction in step (1), the concentration of the complexing agent in the reaction solution is controlled to be 0.1 mol / L to 0.5 mol / L. For example, it can be 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, or 0.5 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] In this invention, during the coprecipitation reaction in step (1), the total concentration of metal ions in the reaction solution is controlled to be 0.5 mol / L to 1.5 mol / L. For example, it can be 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the coprecipitation reaction in step (2) includes a first coprecipitation stage, a second coprecipitation stage and a third coprecipitation stage performed sequentially; in the first coprecipitation stage, the second coprecipitation stage and the third coprecipitation stage, the concentration of oxygen in the oxygen-containing atmosphere increases sequentially.

[0036] Preferably, during the first co-precipitation stage, the volume ratio of protective gas to oxygen in the oxygen-containing atmosphere is (7.5~9.5):1, and the reaction time is no more than 1 hour.

[0037] In this invention, during the first co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (7.5~9.5):1, for example, it can be 7.5:1, 7.8:1, 8.0:1, 8.2:1, 8.4:1, 8.6:1, 8.8:1, 9.0:1, 9.2:1, 9.4:1 or 9.5:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] In this invention, during the first coprecipitation stage, the reaction time is no more than 1 hour, for example, it can be 0.2 hours, 0.4 hours, 0.6 hours, 0.8 hours or 1 hour, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0039] Preferably, during the second co-precipitation stage, the volume ratio of protective gas to oxygen in the oxygen-containing atmosphere is (3~5):1, and the reaction time is 1h~2h.

[0040] In this invention, during the second co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (3~5):1, for example, it can be 3:1, 3.2:1, 3.4:1, 3.6:1, 3.8:1, 4:1, 4.2:1, 4.4:1, 4.6:1, 4.8:1 or 5:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In this invention, during the second coprecipitation stage, the reaction time is 1h to 2h, for example, it can be 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, during the third co-precipitation stage, the volume ratio of protective gas to oxygen in the oxygen-containing atmosphere is (0.5~1.5):1, and the reaction time is 1.5h~2h.

[0043] In this invention, during the third co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (0.5~1.5):1, for example, it can be 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1 or 1.5:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0044] In this invention, during the third coprecipitation stage, the reaction time is 1.5h to 2h, for example, it can be 1.5h, 1.55h, 1.6h, 1.65h, 1.7h, 1.75h, 1.8h, 1.85h, 1.9h, 1.95h or 2h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] Preferably, during the coprecipitation reaction in step (2), the pH is controlled at 8.5~9.0, the temperature at 60℃~65℃, the concentration of the complexing agent is 0.2mol / L~0.6mol / L, and the total concentration of metal ions is 0.8mol / L~1.8mol / L.

[0046] In this invention, during the coprecipitation reaction described in step (2), the pH is controlled to be 8.5~9.0, for example, it can be 8.5, 8.55, 8.6, 8.65, 8.7, 8.75, 8.8, 8.85, 8.9, 8.95 or 9.0, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] In this invention, during the coprecipitation reaction in step (2), the temperature is controlled at 60℃~65℃, for example, it can be 60.0℃, 60.5℃, 61.0℃, 61.5℃, 62.0℃, 62.5℃, 63.0℃, 63.5℃, 64.0℃, 64.5℃ or 65.0℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0048] In this invention, during the coprecipitation reaction in step (2), the concentration of the complexing agent is controlled to be 0.2 mol / L to 0.6 mol / L. For example, it can be 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, 0.55 mol / L, or 0.6 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] In this invention, during the coprecipitation reaction described in step (2), the total concentration of metal ions is controlled to be 0.8 mol / L to 1.8 mol / L. For example, it can be 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, or 1.8 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, in the manganese-iron mixed salt solution described in steps (1) and (2), the molar ratio of manganese ions to iron ions is independently (0.8~1.2):1, for example, it can be 0.8:1, 0.9:1, 1.0:1, 1.1:1 or 1.2:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, in the manganese-iron mixed salt solution described in steps (1) and (2), the total concentration of metal ions is independently 1.0 mol / L to 2.0 mol / L, for example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0052] Preferably, the precipitant solutions in steps (1) and (2) each independently include any one or at least two of sodium carbonate solution, sodium bicarbonate solution, or sodium hydroxide solution. Typical but non-limiting combinations include combinations of sodium carbonate solution and sodium bicarbonate solution, combinations of sodium bicarbonate solution and sodium hydroxide solution, combinations of sodium carbonate solution and sodium hydroxide solution, or combinations of sodium carbonate solution, sodium bicarbonate solution, and sodium hydroxide solution.

[0053] Preferably, in the precipitant solutions described in steps (1) and (2), the concentration of the precipitant is independently 2.0 mol / L to 4.0 mol / L, for example, it can be 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3.0 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L or 4.0 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the complexing agent solutions in steps (1) and (2) each independently comprise any one or a combination of at least two of ammonia, ethylenediaminetetraacetic acid solution, citric acid solution, tartaric acid solution, or ethylenediamine solution. Typical but non-limiting combinations include a combination of ammonia and ethylenediaminetetraacetic acid solution, a combination of citric acid solution and tartaric acid solution, a combination of ethylenediaminetetraacetic acid solution and ethylenediamine solution, or a combination of ammonia, citric acid solution, and tartaric acid solution.

[0055] Preferably, in the complexing agent solutions described in steps (1) and (2), the concentration of the complexing agent is independently 5.0 mol / L to 10.0 mol / L, for example, it can be 5.0 mol / L, 5.5 mol / L, 6.0 mol / L, 6.5 mol / L, 7.0 mol / L, 7.5 mol / L, 8.0 mol / L, 8.5 mol / L, 9.0 mol / L, 9.5 mol / L or 10.0 mol / L, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0056] As a preferred embodiment of the preparation method of the present invention, the preparation method includes:

[0057] (I) First, disperse nano-FeCO3 with a D50 particle size of 80nm~120nm in water, ethanol or n-hexane to form a suspension; under continuous stirring, add oleic acid dropwise to the resulting suspension to form a mixture, and ensure that the mass ratio of oleic acid to nano-FeCO3 is (0.05~0.2):100; then continue to stir the resulting mixture so that the carboxyl groups of oleic acid molecules are anchored to the surface of nano-FeCO3 through coordination, and then perform solid-liquid separation to obtain oleic acid modified nano-FeCO3;

[0058] (II) In a protective atmosphere, the oleic acid-modified nano-FeCO3 obtained in step (I) is initially mixed with the reaction substrate to obtain a preliminary mixture; the obtained preliminary mixture is then further mixed with a manganese-iron mixed salt solution, a precipitant solution, and a complexing agent solution to obtain a reaction solution. The pH of the reaction solution is controlled at 9.0~9.5, the temperature at 45℃~50℃, the concentration of the complexing agent at 0.1mol / L~0.5mol / L, and the total concentration of metal ions at 0.5mol / L~1.5mol / L to carry out a co-precipitation reaction to obtain a solution containing a semi-step precursor.

[0059] (III) In an oxygen-containing atmosphere, the solution containing the semi-step precursor, the manganese-iron mixed salt solution, the precipitant solution and the complexing agent solution obtained in step (II) are mixed to obtain a reaction solution. The pH of the reaction solution is controlled at 8.5~9.0, the temperature at 60℃~65℃, the concentration of the complexing agent at 0.2mol / L~0.6mol / L, and the total concentration of metal ions at 0.8mol / L~1.8mol / L. A co-precipitation reaction is carried out to obtain the manganese-iron precursor.

[0060] The coprecipitation reaction in step (III) includes a first coprecipitation stage, a second coprecipitation stage, and a third coprecipitation stage performed sequentially. In the first coprecipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (7.5~9.5):1, and the reaction time is no more than 1 hour. In the second coprecipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (3~5):1, and the reaction time is 1 hour to 2 hours. In the third coprecipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (0.5~1.5):1, and the reaction time is 1.5 hours to 2 hours.

[0061] Thirdly, the present invention provides a sodium-ion battery cathode material, which is prepared from the sodium-ion battery precursor described in the first aspect.

[0062] Fourthly, the present invention provides a sodium battery, the sodium battery comprising the sodium cathode material described in the third aspect.

[0063] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] The sodium-ion battery precursor provided by this invention is a manganese-iron based sodium-ion battery precursor. Firstly, the sodium-ion battery precursor does not contain nickel, thus reducing raw material costs and consequently lowering the preparation costs of the sodium-ion battery precursor and the sodium-ion battery cathode material. Secondly, the seed crystals of the sodium-ion battery precursor include oleic acid-modified nano-FeCO3, which provides nucleation sites, improves the crystallinity of the sodium-ion battery precursor, and reduces structural defects. Therefore, the sodium-ion battery cathode material prepared from the sodium-ion battery precursor has a high capacity. Thirdly, the seed crystals, intermediate layer, and outer shell of the sodium-ion battery precursor together constitute a stable core-shell structure, which can effectively suppress volume changes and stress accumulation of sodium ions during insertion / extraction, reducing the risk of phase transitions and cracks during cycling. Therefore, the sodium-ion battery cathode material prepared from the sodium-ion battery precursor has high cycling stability. Fourthly, the intermediate layer is enriched with a high concentration of Fe²⁺, providing high capacity and contributing to improved capacity of the sodium-ion battery cathode material; the outer shell is enriched with a high concentration of Mn. 4+ As the outermost layer, it effectively suppresses the side reactions between the sodium electrode material and the electrolyte, thereby improving the cycle stability of the sodium electrode material. Detailed Implementation

[0066] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0067] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0068] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0069] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0070] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0071] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0072] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0073] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0074] Example 1

[0075] This embodiment provides a sodium-electric precursor, which includes a seed crystal, an intermediate layer with a thickness of 2 μm, and a shell.

[0076] The seed crystals consist of oleic acid-modified nano-FeCO3, and based on the total mass percentage of metal elements in the sodium-electric precursor, the mass fraction of iron in the seed crystals of the sodium-electric precursor is 2.5 wt%.

[0077] Both the intermediate layer and the outer shell consist of manganese-iron hydroxide, and the molar ratio of manganese to iron in both the intermediate layer and the outer shell is 1:1; and the intermediate layer contains Fe 2+ with Fe 3+ The concentration ratio is greater than that of Fe in the shell. 2+ with Fe 3+ The concentration ratio of Mn in the intermediate layer 4+ With Mn 3+ The concentration ratio is less than that of Mn in the shell. 4+ With Mn 3+ The ratio of their concentrations;

[0078] The outer shell comprises, from the seed crystal to the outer shell, a first shell layer with a thickness of 0.8 μm, a second shell layer with a thickness of 1.2 μm, and a third shell layer with a thickness of 1.8 μm, sequentially covering the crystal; and the Fe in the first shell layer, the second shell layer, and the third shell layer... 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ The concentration ratios of the components increase sequentially.

[0079] The method for preparing the sodium-ion precursor is as follows:

[0080] (I) First, disperse nano-FeCO3 with a D50 particle size of 100 nm in water to form a suspension; under continuous stirring, add oleic acid dropwise to the resulting suspension to form a mixture, and ensure that the mass ratio of oleic acid to nano-FeCO3 is 0.1:100; then continue to stir the resulting mixture so that the carboxyl groups of oleic acid molecules are anchored to the surface of nano-FeCO3 through coordination, and then perform solid-liquid separation to obtain oleic acid modified nano-FeCO3;

[0081] (II) In a nitrogen atmosphere, the oleic acid-modified nano-FeCO3 obtained in step (I) is initially mixed with the reaction substrate to obtain a preliminary mixture; then the obtained preliminary mixture is further mixed with a manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, and the molar ratio of manganese ions to iron ions is 1:1 independently), a precipitant solution (sodium carbonate solution) and a complexing agent solution (ammonia water) to obtain a reaction solution. The pH of the reaction solution is controlled at 9.2, the temperature at 48℃, the concentration of the complexing agent at 0.3 mol / L, and the total concentration of metal ions at 1.0 mol / L to carry out a co-precipitation reaction to obtain a solution containing a semi-step precursor;

[0082] (III) In an oxygen-containing atmosphere (composed of nitrogen and oxygen), the solution containing the semi-step precursor obtained in step (II), the manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, and the molar ratio of manganese ions to iron ions is 1:1 independently), the precipitant solution (sodium carbonate solution) and the complexing agent solution (ammonia water) are mixed to obtain a reaction solution. The pH of the reaction solution is controlled at 8.8, the temperature at 62℃, the concentration of the complexing agent is 0.4 mol / L, and the total concentration of metal ions is 1.3 mol / L. A co-precipitation reaction is carried out to obtain the manganese-iron precursor.

[0083] The coprecipitation reaction in step (III) includes a first coprecipitation stage, a second coprecipitation stage, and a third coprecipitation stage performed sequentially. In the first coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 8.5:1. In the second coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 4:1. In the third coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 1:1.

[0084] Example 2

[0085] This embodiment provides a sodium-electric precursor, which includes a seed crystal, an intermediate layer with a thickness of 1 μm, and a shell.

[0086] The seed crystal comprises oleic acid-modified nano-FeCO3, with the total mass of metal elements in the sodium-electric precursor as 100%, and the mass fraction of iron in the seed crystal of the sodium-electric precursor as 2 wt%.

[0087] Both the intermediate layer and the outer shell consist of manganese-iron hydroxide, and the molar ratio of manganese to iron in both the intermediate layer and the outer shell is 1:1; and the intermediate layer contains Fe 2+ with Fe 3+ The concentration ratio is greater than that of Fe in the shell. 2+ with Fe 3+ The concentration ratio of Mn in the intermediate layer 4+ With Mn 3+ The concentration ratio is less than that of Mn in the shell. 4+ With Mn 3+ The ratio of their concentrations;

[0088] The outer shell comprises, from the seed crystal to the outer shell, a first shell layer with a thickness of 0.5 μm, a second shell layer with a thickness of 1.5 μm, and a third shell layer with a thickness of 2.0 μm, sequentially covering the seed crystal; and Fe in the first shell layer, the second shell layer, and the third shell layer... 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ The concentration ratios of the components increase sequentially.

[0089] The method for preparing the sodium-ion precursor is as follows:

[0090] (I) First, disperse nano-FeCO3 with a D50 particle size of 80 nm in water, ethanol or n-hexane to form a suspension; under continuous stirring, add oleic acid dropwise to the resulting suspension to form a mixture, and ensure that the mass ratio of oleic acid to nano-FeCO3 is 0.05:100; then continue to stir the resulting mixture so that the carboxyl groups of oleic acid molecules are anchored to the surface of nano-FeCO3 through coordination, and then perform solid-liquid separation to obtain oleic acid modified nano-FeCO3;

[0091] (II) In an argon atmosphere, the oleic acid-modified nano-FeCO3 obtained in step (I) is initially mixed with the reaction substrate to obtain an initial mixture; the initial mixture is then further mixed with a manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, with the molar ratio of manganese ions to iron ions being 1:1 independently), a precipitant solution (sodium bicarbonate solution) and a complexing agent solution (ammonia water) to obtain a reaction solution. The pH of the reaction solution is controlled at 9.0, the temperature at 50℃, the concentration of the complexing agent at 0.1 mol / L, and the total concentration of metal ions at 0.5 mol / L to carry out a co-precipitation reaction to obtain a solution containing a semi-step precursor.

[0092] (III) In an oxygen-containing atmosphere (composed of argon and oxygen), the solution containing the semi-step precursor obtained in step (II), the manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, and the molar ratio of manganese ions to iron ions is 1:1 independently), the precipitant solution (sodium bicarbonate solution) and the complexing agent solution (ammonia water) are mixed to obtain a reaction solution. The pH of the reaction solution is controlled at 8.5, the temperature at 65℃, the concentration of the complexing agent is 0.2 mol / L, and the total concentration of metal ions is 0.8 mol / L. A co-precipitation reaction is carried out to obtain the manganese-iron precursor.

[0093] The coprecipitation reaction in step (III) includes a first coprecipitation stage, a second coprecipitation stage, and a third coprecipitation stage performed sequentially. In the first coprecipitation stage, the volume ratio of argon to oxygen in the oxygen-containing atmosphere is 9.5:1. In the second coprecipitation stage, the volume ratio of argon to oxygen in the oxygen-containing atmosphere is 5:1. In the third coprecipitation stage, the volume ratio of argon to oxygen in the oxygen-containing atmosphere is 1.5:1.

[0094] Example 3

[0095] This embodiment provides a sodium-electric precursor, which includes a seed crystal, an intermediate layer with a thickness of 3 μm, and a shell.

[0096] The seed crystal comprises oleic acid-modified nano-FeCO3, and the total mass percentage of metal elements in the sodium-electric precursor is 100%, with the iron element in the seed crystal of the sodium-electric precursor being 3 wt%.

[0097] Both the intermediate layer and the outer shell consist of manganese-iron hydroxide, and the molar ratio of manganese to iron in both the intermediate layer and the outer shell is 1:1; and the intermediate layer contains Fe 2+ with Fe 3+ The concentration ratio is greater than that of Fe in the shell. 2+ with Fe 3+ The concentration ratio of Mn in the intermediate layer 4+ With Mn 3+ The concentration ratio is less than that of Mn in the shell. 4+ With Mn 3+ The ratio of their concentrations;

[0098] The outer shell comprises, from the seed crystal to the outer shell, a first shell layer with a thickness of 1.0 μm, a second shell layer with a thickness of 1.0 μm, and a third shell layer with a thickness of 1.5 μm, sequentially covering the seed crystal; and the Fe in the first shell layer, the second shell layer, and the third shell layer... 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ The concentration ratios of the components increase sequentially.

[0099] The method for preparing the sodium-ion precursor is as follows:

[0100] (I) First, disperse nano-FeCO3 with a D50 particle size of 120 nm in water, ethanol or n-hexane to form a suspension; under continuous stirring, add oleic acid dropwise to the resulting suspension to form a mixture, and ensure that the mass ratio of oleic acid to nano-FeCO3 is 0.2:100; then continue to stir the resulting mixture so that the carboxyl groups of oleic acid molecules are anchored to the surface of nano-FeCO3 through coordination, and then perform solid-liquid separation to obtain oleic acid modified nano-FeCO3;

[0101] (II) In a nitrogen atmosphere, the oleic acid-modified nano FeCO3 obtained in step (I) is initially mixed with the reaction substrate to obtain an initial mixture; the initial mixture is then further mixed with a manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, with the molar ratio of manganese ions to iron ions being 1:1 independently), a precipitant solution (sodium carbonate solution) and a complexing agent solution (ammonia water) to obtain a reaction solution. The pH of the reaction solution is controlled at 9.5, the temperature at 45℃, the concentration of the complexing agent at 0.5 mol / L, and the total concentration of metal ions at 1.5 mol / L to carry out a coprecipitation reaction to obtain a solution containing a semi-step precursor.

[0102] (III) In an oxygen-containing atmosphere (composed of nitrogen and oxygen), the solution containing the semi-step precursor obtained in step (II), the manganese-iron mixed salt solution (composed of manganese sulfate, ferric sulfate and water solvent, and the molar ratio of manganese ions to iron ions is 1:1 independently), the precipitant solution (sodium carbonate solution) and the complexing agent solution (ammonia water) are mixed to obtain a reaction solution. The pH of the reaction solution is controlled at 9.0, the temperature at 60℃, the complexing agent concentration at 0.6 mol / L, and the total concentration of metal ions at 1.8 mol / L. A co-precipitation reaction is carried out to obtain the manganese-iron precursor.

[0103] The coprecipitation reaction in step (III) includes a first coprecipitation stage, a second coprecipitation stage, and a third coprecipitation stage performed sequentially. In the first coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 7.5:1. In the second coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 3:1. In the third coprecipitation stage, the volume ratio of nitrogen to oxygen in the oxygen-containing atmosphere is 0.5:1.

[0104] Example 4

[0105] This embodiment provides a sodium-electric precursor, wherein the total mass of metal elements in the sodium-electric precursor is taken as 100%, and the mass fraction of iron in the seed crystal of the sodium-electric precursor is 1 wt%; and the thickness ratio of the intermediate layer, the first shell layer, the second shell layer and the third shell layer remains unchanged.

[0106] That is, by controlling the amount of manganese-iron mixed salt solution mixed in steps (II) and (III) of the preparation method of sodium-electric precursor, the mass of iron element in the seed crystal of sodium-electric precursor / (mass of iron element in the seed crystal of sodium-electric precursor + total mass of manganese and iron elements in all manganese-iron mixed salt solutions mixed in steps (II) and (III)) is equal to 1wt%, and the rest is the same as in Example 1.

[0107] Example 5

[0108] This embodiment provides a sodium-electric precursor, wherein the mass fraction of iron in the seed crystal of the sodium-electric precursor is 5 wt%, and the thickness ratio of the intermediate layer, the first shell layer, the second shell layer and the third shell layer remains unchanged;

[0109] That is, by controlling the amount of manganese-iron mixed salt solution mixed in steps (II) and (III) of the preparation method of the sodium-electric precursor, the mass of iron element in the seed crystal of the sodium-electric precursor / (mass of iron element in the seed crystal of the sodium-electric precursor + total mass of manganese and iron elements in all manganese-iron mixed salt solutions mixed in steps (II) and (III)) is equal to 5wt%, and the rest is the same as in Example 1.

[0110] Example 6

[0111] This embodiment provides a sodium-electric precursor, except that the first shell layer with a thickness of 0.8 μm in the outer shell is omitted;

[0112] That is, the first coprecipitation stage in step (III) of the preparation method of the sodium-ion precursor is omitted, and the time of the second coprecipitation stage is extended so that the thickness of the second shell is the same as the sum of the thickness of the first shell and the second shell in Example 1, and all other aspects are the same as in Example 1.

[0113] Example 7

[0114] This embodiment provides a sodium-electric precursor, except that the second shell layer with a thickness of 1.2 μm in the outer shell is omitted;

[0115] That is, the second coprecipitation stage in step (III) of the preparation method of the sodium-ion precursor is omitted, and the time of the first coprecipitation stage is extended so that the thickness of the first shell is the same as the sum of the thicknesses of the first shell and the second shell in Example 1, and all other aspects are the same as in Example 1.

[0116] Example 8

[0117] This embodiment provides a sodium-electric precursor, except that the second shell layer with a thickness of 1.2 μm in the outer shell is omitted;

[0118] That is, the second coprecipitation stage in step (III) of the preparation method of the sodium-ion precursor is omitted, and the time of the third coprecipitation stage is extended so that the thickness of the third shell is the same as the sum of the thickness of the second shell and the third shell in Example 1, and all other aspects are the same as in Example 1.

[0119] Example 9

[0120] This embodiment provides a sodium-electric precursor, except that the third shell layer with a thickness of 1.8 μm in the outer shell is omitted;

[0121] That is, the third coprecipitation stage in step (III) of the preparation method of the sodium-ion precursor is omitted, and the time of the second coprecipitation stage is extended so that the thickness of the second shell is the same as the sum of the thickness of the second shell and the third shell in Example 1, and all other aspects are the same as in Example 1.

[0122] Example 10

[0123] This embodiment provides a sodium-ionized precursor. Except for step (I) of the preparation method of the sodium-ionized precursor, in which the mass ratio of oleic acid to nano-FeCO3 is guaranteed to be 0.01:100, all other steps are the same as in Example 1.

[0124] Example 11

[0125] This embodiment provides a sodium-ion battery precursor. Except for step (I) of the preparation method of the sodium-ion battery precursor, in which the mass ratio of oleic acid to nano FeCO3 is 0.4:100, all other steps are the same as in Example 1.

[0126] Comparative Example 1

[0127] This comparative example provides a sodium-electric precursor, except that the components of the seed crystal are replaced with unmodified nano-FeCO3;

[0128] That is, step (I) of the preparation method of the sodium-ion precursor is omitted, and except that the oleic acid modified nano FeCO3 in step (II) is replaced with nano FeCO3, the rest is the same as in Example 1.

[0129] Comparative Example 2

[0130] This comparative example provides a sodium-electric precursor, except that the intermediate layer of the sodium-electric precursor is omitted;

[0131] That is, step (II) of the preparation method of the sodium-ion precursor is omitted; and except that the solution containing the half-step precursor in step (III) is replaced with the initial mixture in step (II), everything else is the same as in Example 1.

[0132] Comparative Example 3

[0133] This comparative example provides a sodium-electric precursor, except that the outer shell of the sodium-electric precursor is omitted and the thickness of the intermediate layer is the same as the total thickness of the intermediate layer and the outer shell in Example 1.

[0134] Except for omitting step (III) in the preparation method of the sodium-ion precursor and extending the co-precipitation reaction time in step (II), the rest is the same as in Example 1.

[0135] Sodium-ion cathode material was prepared using the sodium-ion precursors provided in the above embodiments and comparative examples. The method for preparing the sodium-ion cathode material is as follows: the sodium-ion precursor and Na2CO3 were mixed at a stoichiometric ratio of 1:1.05 by ball milling at a speed of 300 rpm for 2 hours to obtain a mixture; the obtained mixture was then heated to 850°C in air at a heating rate of 3°C / min and sintered for 15 hours, and then cooled in the furnace. The product obtained after cooling was ground and passed through a 400-mesh sieve to obtain the sodium-ion cathode material.

[0136] Sodium batteries were prepared using the obtained sodium-ion positive electrode material. The method for preparing sodium batteries was as follows: the obtained sodium-ion positive electrode material was dissolved in N-methylpyrrolidone solvent with acetylene black conductive agent and polyvinylidene fluoride binder at a mass ratio of 8:1:1, and stirred for 6 hours to obtain a slurry; the obtained slurry was coated on aluminum foil current collector, vacuum dried at 120°C for 12 hours, pressed into positive electrode sheets by a roller mill, and then cut into positive electrode sheets in an argon-filled glove box, using metallic sodium sheet as negative electrode, glass fiber membrane as separator, and 1 mol / L NaClO4 solution (solvent including EC and PC in a volume ratio of 1:1) as electrolyte to obtain CR2032 type button battery.

[0137] The capacity of the obtained sodium batteries was tested using a Blue Battery Testing System at 25°C within a voltage range of 2.0–4.0V (vs. Na / Na). + Within 0.1C, a constant current charge-discharge test was performed, and the specific capacity of the first discharge was recorded. The capacity of the sodium battery is shown in Table 1.

[0138] The obtained sodium battery was subjected to cycle stability testing. The cycle stability testing method was as follows: using a blue battery testing system, at 25°C, within a voltage range of 2.0~4.0V (vs. Na / Na). + Within 100 cycles, the sodium battery was subjected to constant current charge-discharge cycles at a current density of 0.5C. The capacity retention rate of the sodium battery after 100 cycles is shown in Table 1.

[0139] Table 1

[0140]

[0141] From Table 1, we can obtain:

[0142] (1) The sodium batteries prepared using the sodium battery precursors provided in Examples 1 to 3 of the present invention exhibit high capacity and excellent cycle stability;

[0143] (2) By comparing Example 1 with Examples 4 and 5, it can be seen that in this invention, when the total mass of metal elements in the sodium battery precursor is 100% and the mass fraction of iron in the seed crystal of the sodium battery precursor is 2wt%~3wt%, the sodium battery exhibits better electrochemical performance. This is because the seed crystal in this content range can provide a suitable amount and uniform nucleation sites for the growth of the intermediate layer, which is conducive to inducing the formation of a highly crystalline and low-defect intermediate layer, thereby improving the cycle stability of the sodium battery prepared with the sodium battery precursor.

[0144] (3) By comparing Example 1 with Examples 6-9, it can be seen that in this invention, the outer shell includes a first shell layer, a second shell layer, and a third shell layer sequentially covering the crystal from the seed crystal to the outer shell; Fe in the first shell layer, the second shell layer, and the third shell layer2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ When the concentration ratio of Fe in the first, second, and third shells increases sequentially, the sodium battery exhibits superior electrochemical performance. This is because: Fe in the first, second, and third shells... 2+ with Fe 3+ The concentration ratios of Mn and Mn decrease sequentially. 4+ With Mn 3+ When the concentration ratio of Fe²⁺ to Fe³⁺ increases sequentially, the first shell is enriched with a high concentration of Fe²⁺. Since the redox reaction of Fe²⁺ / Fe³⁺ is an important source of capacity in sodium-ion batteries, the first shell provides high capacity, which is beneficial to improving the capacity of sodium-ion cathode materials. The second shell, as a gradient transition region of composition and structure, acts as a buffer zone and can effectively buffer the rich Fe²⁺ content during charging and discharging. 2+ The first shell and Mn-rich 4+ The internal stress caused by lattice variations in the third shell reduces the risk of cracking in sodium-ion cathode materials and enhances their structural stability; the third shell is enriched with a high concentration of Mn. 4+ Because of Mn 4+ It can form an extremely stable and chemically inert surface structure. Therefore, the third shell, as the outermost layer, effectively suppresses the side reactions between the sodium electrode material and the electrolyte, thereby improving the cycle stability of the sodium electrode material.

[0145] (4) By comparing Example 1 with Examples 10 and 11, it can be seen that when the mass ratio of oleic acid to nano FeCO3 used in the modification is (0.05~0.2):100, the sodium battery exhibits better electrochemical performance. This is because at this mass ratio, oleic acid can form a suitable monomolecular coating layer on the surface of nano FeCO3, which can effectively prevent the agglomeration of nanoparticles, ensure the uniformity and dispersion of its role as seed crystals, and optimize its effect of inducing crystallization during precursor synthesis, thereby making the final cathode material have a more complete crystal structure and a more stable interface.

[0146] (5) By comparing Example 1 with Comparative Examples 1-3, it can be seen that the sodium battery precursor provided by the present invention is a manganese-iron based sodium battery precursor. Firstly, the sodium battery precursor does not contain nickel, so the raw material cost is low, thereby reducing the preparation cost of the sodium battery precursor and the sodium battery cathode material. Secondly, the seed crystal of the sodium battery precursor includes oleic acid-modified nano-FeCO3, which provides nucleation sites, improves the crystallinity of the sodium battery precursor, and reduces the structural defects of the sodium battery precursor. Therefore, the sodium battery prepared from the sodium battery precursor is more efficient. The cathode material exhibits high capacity. Thirdly, the seed crystals, intermediate layer, and outer shell of the sodium-ion precursor together constitute a stable core-shell structure, effectively suppressing volume changes and stress accumulation during sodium ion insertion / extraction, reducing the risk of phase transitions and cracking during cycling. Therefore, the sodium-ion cathode material prepared using the sodium-ion precursor has high cycling stability. Fourthly, the intermediate layer is enriched with a high concentration of Fe²⁺, providing high capacity and contributing to improved capacity of the sodium-ion cathode material; the outer shell is enriched with a high concentration of Mn. 4+ As the outermost layer, it effectively suppresses the side reactions between the sodium electrode material and the electrolyte, thereby improving the cycle stability of the sodium electrode material.

[0147] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A sodium precursor, characterized in that, The sodium battery precursor comprises a seed, an intermediate layer and an outer shell. The components of the seed crystal include oleic acid-modified nano FeCO3, the components of the intermediate layer and the shell both include manganese iron hydroxide, and the concentration ratio of Fe 2+ to Fe 3+ in the intermediate layer is greater than the concentration ratio of Fe 2+ to Fe 3+ in the shell, the concentration ratio of Mn 4+ to Mn 3+ in the intermediate layer is less than the concentration ratio of Mn 4+ to Mn 3+ in the shell.

2. The sodium electro-precurser of claim 1, wherein, The mass fraction of iron in the seed of the sodium battery precursor is 2wt%-3wt% based on the total mass of metal elements in the sodium battery precursor.

3. The sodium electro-precurser of claim 1, wherein, The thickness of the intermediate layer is 1μm-3μm. Preferably, the shell comprises, in the direction from the seed crystal to the shell, a first shell layer, a second shell layer and a third shell layer in turn; the concentration ratio of Fe 2+ to Fe 3+ of the first shell layer, the second shell layer and the third shell layer is in turn smaller, and the concentration ratio of Mn 4+ to Mn 3+ is in turn larger. Preferably, the thickness of the first shell layer is 0.5μm-1.0μm. Preferably, the thickness of the second shell layer is 1.0μm-1.5μm. Preferably, the thickness of the third shell layer is 1.5μm-2.0μm. Preferably, the molar ratio of manganese to iron in the intermediate layer and the outer shell is (0.8-1.2):1, respectively.

4. A method for preparing the sodium precursor according to any one of claims 1 to 3, characterized in that, The preparation method comprises: (1) mixing the oleic acid modified nano FeCO3 with a reaction bottom solution in a protective atmosphere to obtain a preliminary mixed solution; then mixing the obtained preliminary mixed solution with a manganese-iron mixed salt solution, a precipitant solution and a complexing agent solution to perform a co-precipitation reaction to obtain a solution containing a semi-step precursor; (2) mixing the solution containing the semi-step precursor obtained in step (1), the manganese-iron mixed salt solution, the precipitant solution and the complexing agent solution in an oxygen-containing atmosphere to perform a co-precipitation reaction to obtain a manganese-iron precursor.

5. The preparation method according to claim 4, characterized in that, The method for preparing the oleic acid modified nano FeCO3 comprises modifying the nano FeCO3 with oleic acid to obtain the oleic acid modified nano FeCO3. Preferably, the mass ratio of the oleic acid to the nano FeCO3 used in the modification is (0.05-0.2):

100. Preferably, the D50 particle size of the nano FeCO3 is 80nm-120nm. Preferably, the modification method comprises: first dispersing the nano FeCO3 in a solvent to form a suspension; under continuous stirring, adding the oleic acid dropwise to the obtained suspension to form a mixed solution; continuing to stir the obtained mixed solution to anchor the carboxyl groups of the oleic acid molecules on the surface of the nano FeCO3 through coordination, and then performing solid-liquid separation to obtain the oleic acid modified nano FeCO3.

6. The preparation method according to claim 4, characterized in that, In the co-precipitation reaction of step (1), the pH of the reaction solution is controlled to be 9.0-9.5, the temperature is controlled to be 45°C-50°C, the concentration of the complexing agent is controlled to be 0.1mol / L-0.5mol / L, and the total concentration of metal ions is controlled to be 0.5mol / L-1.5mol / L.

7. The preparation method according to claim 4, characterized in that, The co-precipitation reaction of step (2) comprises a first co-precipitation stage, a second co-precipitation stage and a third co-precipitation stage performed in sequence; in the first co-precipitation stage, the second co-precipitation stage and the third co-precipitation stage, the concentration of oxygen in the oxygen-containing atmosphere increases in sequence. Preferably, in the first co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (7.5-9.5):1, and the reaction time is not higher than 1h. Preferably, in the second co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (3-5):1, and the reaction time is 1h-2h. Preferably, in the third co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (0.5-1.5):1, and the reaction time is 1.5h-2h. Preferably, the co-precipitation reaction in step (2) is controlled at a pH of 8.5-9.0, a temperature of 60-65℃, a complexing agent concentration of 0.2-0.6 mol / L, and a total metal ion concentration of 0.8-1.8 mol / L.

8. The preparation method according to claim 4, characterized in that, The preparation method comprises: (I) first dispersing nano FeCO3 with a D50 particle size of 80-120 nm in water, ethanol or n-hexane to form a suspension; under continuous stirring, adding oleic acid dropwise to the obtained suspension to form a mixture, and ensuring that the mass ratio of the oleic acid to the nano FeCO3 is (0.05-0.2):100; continuing to stir the obtained mixture to anchor the carboxyl groups of the oleic acid molecules on the surface of the nano FeCO3 by coordination, and then performing solid-liquid separation to obtain oleic acid-modified nano FeCO3; (II) in a protective atmosphere, mixing the oleic acid-modified nano FeCO3 obtained in step (I) with a reaction bottom solution to obtain a preliminary mixture; then mixing the obtained preliminary mixture with a manganese-iron mixed salt solution, a precipitant solution and a complexing agent solution to obtain a reaction solution, and controlling the pH of the reaction solution to be 9.0-9.5, the temperature to be 45-50℃, the concentration of the complexing agent to be 0.1-0.5 mol / L, and the total concentration of metal ions to be 0.5-1.5 mol / L, to perform a co-precipitation reaction to obtain a solution containing a semi-step precursor; (III) in an oxygen-containing atmosphere, mixing the solution containing the semi-step precursor obtained in step (II), a manganese-iron mixed salt solution, a precipitant solution and a complexing agent solution to obtain a reaction solution, and controlling the pH of the reaction solution to be 8.5-9.0, the temperature to be 60-65℃, the concentration of the complexing agent to be 0.2-0.6 mol / L, and the total concentration of metal ions to be 0.8-1.8 mol / L, to perform a co-precipitation reaction to obtain a manganese-iron precursor. The co-precipitation reaction in step (III) comprises a first co-precipitation stage, a second co-precipitation stage and a third co-precipitation stage performed in sequence; in the first co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (7.5-9.5):1, and the reaction time is not higher than 1 h; in the second co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (3-5):1, and the reaction time is 1-2 h; in the third co-precipitation stage, the volume ratio of the protective gas to oxygen in the oxygen-containing atmosphere is (0.5-1.5):1, and the reaction time is 1.5-2 h.

9. A sodium electro-positive cathode material, characterized in that, The sodium battery comprises the sodium battery positive electrode material of claim 9.

10. A sodium battery, characterized by, The sodium battery comprises the sodium battery positive electrode material of claim 9.

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