Positive electrode active material and preparation method therefor, positive electrode sheet, battery, and electric device

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device. The positive electrode active material is an iron-based sulfate sodium ion battery positive electrode material, and the X-ray diffraction pattern of the positive electrode active material has a first characteristic peak within the range of 34.9° to 35.3° and has a second characteristic peak within the range of 35.3° to 35.5°. The peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.1≤I1 / I2≤1.5. When the peak intensity ratio of the first characteristic peak and the second characteristic peak in the X-ray diffraction pattern of the positive electrode active material satisfies the condition, it is indicated that the form of existence of Fe in the positive electrode active material is mainly Fe2+, and the mass percentage of Fe3+ in the material is less than 1.5%, and the form of existence of Fe3+ is mainly Fe3O4 impurity phase, so that the reaction activity of the positive electrode material is reduced.

Description

Cathode active material, preparation method thereof, cathode sheet, battery and electric device

[0001] Priority information

[0002] The present disclosure claims priority to and the benefit of Chinese Patent Application No. 202410544773.X, filed April 30, 2024, and incorporates it by reference in its entirety. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of sodium ion batteries, and in particular, the present disclosure relates to a cathode active material, a preparation method thereof, a cathode sheet, a battery and an electric device. BACKGROUND

[0004] Lithium ion batteries are currently widely used in electric vehicles and electronic products such as notebook computers and mobile phones, and are increasingly closely related to human production and life. However, with the fluctuation of lithium resources prices, low-cost sodium ion batteries similar in working principle have gradually attracted widespread attention and are expected to partially replace lithium ion batteries in the field of low-speed electric vehicles and energy storage, making an important contribution to the further expansion of the battery market size.

[0005] Among them, similar to the lithium iron phosphate cathode material in lithium ion batteries, polyanion-type materials exhibit lower cost and the best cycle performance among several cathode materials for sodium ion batteries. In particular, sodium ferrous sulfate carbon composite (Na 2+2x Fe 2-x (SO4)3@C) has low raw material cost, low sintering energy consumption and high discharge voltage platform, and has good application prospects.

[0006] However, such materials have poor thermal stability, and even after a low-temperature sintering process with inert gas protection, Fe3O4or Fe2O3impurities containing Fe 3+ are still prone to occur. As in the literature published by Li et al. (J. Mater. Chem. A, 2019, 7, 14656-14669, DOI: 10.1039 / c9ta03089a), Na6Fe5(SO4)8@CNTs materials with high initial discharge specific capacity and discharge voltage were prepared using a solid-phase mixing and low-temperature sintering process, but more than 20% of Fe 2+ was oxidized to Fe 3+ , seriously affecting the cycle performance of the material.

[0007] In order to protect Fe 2+ from oxidation, metal powder elements (such as Fe) are added during the ball milling mixing process in the prior art to protect Fe 2+reduction protection, but this also increases the risk of magnetic foreign matter and impurities in the product. In addition, there is prior art in which an organic antioxidant (such as ascorbic acid) is added to a Na2SO4 and FeSO4 nH2O solution before preparing the precursor to protect Fe 2+ . However, organic materials are prone to decomposition when heated, and it is difficult to maintain the antioxidant effect during subsequent sintering, and low-temperature sintering is not conducive to effective carbonization of the material, which adversely affects the performance of the material as an impurity. Therefore, there is an urgent need to provide a new preparation method that can solve the oxidation problem of Fe 2+ in sodium ferrous sulfate carbon composite materials while reducing the introduction of impurities.

[0008] SUMMARY

[0009] The present disclosure aims to at least partially solve one of the technical problems in the related art. To this end, one object of the present disclosure is to provide a positive electrode active material and a preparation method thereof, which aims to solve the oxidation problem of Fe 2+ in sodium ferrous sulfate carbon composite materials while reducing the introduction of impurities and improving the specific capacity and cycle stability of the material.

[0010] To this end, the first aspect of the present disclosure provides a positive electrode active material. According to an embodiment of the present disclosure, the positive electrode active material is an iron-based sodium sulfate battery positive electrode material, and the X-ray diffraction pattern of the positive electrode active material has a first characteristic peak in the range of 34.9° to 35.3° and a second characteristic peak in the range of 35.3° to 35.5°;

[0011] wherein the peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy 1.1≤I1 / I2≤1.5.

[0012] The first characteristic peak belongs to the (-132) crystal plane of the positive electrode active material, and the second characteristic peak is a composite characteristic peak resulting from the overlap of the characteristic peak of the (112) crystal plane and the strongest characteristic peak of the (311) crystal plane of Fe3O4 at 35.4°, which is generated by a side reaction of the decomposition of FeSO4. Therefore, the higher the relative peak intensity of the second characteristic peak, the stronger the side reaction that occurs during the preparation process of the positive electrode active material, the more impurities, and the less available Fe 2+ / Fe 3+ pairs, resulting in a decrease in the specific capacity and cycle performance of the positive electrode active material. When the peak intensity ratio of the first characteristic peak and the second characteristic peak in the X-ray diffraction pattern (XRD pattern) of the positive electrode active material satisfies the above condition, it indicates that the form of Fe in the positive electrode active material is mainly Fe 2+ , and Fe 3+The mass percentage of Fe in the material is less than 1.5%, which greatly reduces the amount of Fe present in the positive electrode active material, which is mainly in the form of Fe3O4 impurity phase. 3+ The content of [specific element] increases the reactivity of the positive electrode active material.

[0013] According to embodiments of this disclosure, the peak intensity I of the first characteristic peak of the positive electrode active material after being left to stand in an open environment at 25°C and 30% relative humidity for 24 hours is... 1’ The peak intensity I of the second characteristic peak 2’ satisfy:

[0014] 1.05≤I 1’ / I 2’ ≤1.4;

[0015] This indicates that the positive electrode active material can also ensure Fe during storage. 2+ Not oxidized, Fe 3+ The content remains basically unchanged, and the structure of the positive electrode active material has good stability.

[0016] According to embodiments of this disclosure, the peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy the condition: 1.2 ≤ I1 / I2 ≤ 1.4. This indicates that the Fe in the positive electrode active material mainly exists as Fe. 2+ Fe 3+ Its mass percentage in the material is even lower.

[0017] According to embodiments of this disclosure, 1.1≤I 1’ / I 2’ ≤1.25;

[0018] When the positive electrode active material meets the above conditions, it is easier to store and has good structural stability.

[0019] According to embodiments of this disclosure, the positive electrode active material satisfies at least one of the following conditions:

[0020] The positive electrode active material D 50 4-10μm;

[0021] The positive electrode active material D 100 Satisfy: 6μm < D 100 <20μm;

[0022] The specific surface area of ​​the positive electrode active material is 5-25m². 2 / g.

[0023] According to embodiments of this disclosure, the positive electrode active material has the chemical formula shown in formula (1):

[0024] Na 2x Fe 2-y M y (SO4) (2+x-z) (SO3) z @C (1)

[0025] wherein, 1≤x≤2.04, preferably 1≤x≤1.4; 0≤y≤0.2; 0

[0026] M is selected from at least one of Mn, Co, Ni, Mg, Cu, Zn.

[0027] Thus, the crystal structure of the positive electrode active material is improved by element doping, the thermal stability of the material is improved, and the side reaction of Fe3O4 or Fe2O3 impurities generated by decomposition of the positive electrode active material itself is inhibited. At the same time, the material structure formula contains SO3 2- , which can also ensure the protection of Fe 2+ in the material during storage, and improve the air stability of the material structure. The doping of transition metal elements and the presence of SO3 2- make the Fe 3+ content in the positive electrode active material very low, and exhibit high specific capacity and good cycle stability and storage performance.

[0028] The second aspect of the present disclosure provides a preparation method of a positive electrode active material, the preparation method comprising:

[0029] (1) preparing a reducing agent solution, mixing an inorganic conductive carbon material with the reducing agent solution to obtain a mixed solution 1;

[0030] (2) mixing Na2SO4, FeSO4·7H2O, and an optional sulfate with the mixed solution 1 to obtain a mixed solution 2;

[0031] (3) spray drying the mixed solution 2 to obtain a positive electrode active material precursor;

[0032] (4) sintering the positive electrode active material precursor to obtain the positive electrode active material;

[0033] wherein, the reducing agent in the reducing agent solution is NaHSO3 and / or Na2S2O5;

[0034] The sulfate is used to provide M elements, and the M elements are selected from at least one of Mn, Co, Ni, Mg, Cu, and Zn.

[0035] The present disclosure provides a method of element doping and inorganic reducing agent synergistic effect to improve the thermal stability of the positive electrode active material, and Fe 2+effective protection. Among them, the element doping improves the problem that the crystal structure of sodium ferrous sulfate material is easy to decompose under heat, effectively reducing impurities. The introduction of inorganic reducing agent from synthesis to storage process for a long time to Fe 2+ effective protection, improve the specific capacity and stability of the material. The synergistic effect of the two methods is of great significance for producing high-quality polyanion sodium electrode active material.

[0036] According to an embodiment of the present disclosure, the mass of the solvent in the reducing agent solution in step (1) is 2-3 times the mass of FeSO4·7H2O added in step (2).

[0037] According to an embodiment of the present disclosure, in step (1), the inorganic conductive carbon material includes at least one selected from graphene, reduced graphene oxide, conductive graphite, acetylene black, ketjen black, mesoporous carbon, and carbon nanotubes.

[0038] According to an embodiment of the present disclosure, in step (2), the molar ratio of Na2SO4, FeSO4·7H2O and sulfate is δ:2-y:y.

[0039] Wherein, 0.96≤δ≤2; 0≤y≤0.2.

[0040] According to an embodiment of the present disclosure, the molar ratio of sodium element in the reducing agent to Na2SO4 is 2n:δ.

[0041] Wherein, 0<n≤0.04.

[0042] According to an embodiment of the present disclosure, in step (2), the mass ratio of the completely dehydrated Na2SO4, FeSO4·7H2O and sulfate to the mass of the inorganic conductive carbon material is 100:(0.5-10).

[0043] According to an embodiment of the present disclosure, in step (3), the spray drying conditions include:

[0044] The inlet air temperature is 130-160℃; the outlet air temperature is not less than 80℃.

[0045] According to an embodiment of the present disclosure, in step (3), the D 50 of the positive electrode active material precursor is 4-10μm;

[0046] The D 100 of the positive electrode active material precursor satisfies: 6μm<D 100 <20μm.

[0047] According to an embodiment of the present disclosure, in step (4), the sintering conditions include sintering at 300-380℃ for 8-20h.

[0048] The third aspect of the present disclosure provides a positive electrode sheet, which comprises the positive electrode active material of the first aspect or the positive electrode active material prepared by the preparation method of the second aspect.

[0049] The fourth aspect of the present disclosure provides a battery, which comprises the positive electrode sheet of the third aspect.

[0050] The fifth aspect of the present disclosure provides an electric device, which comprises the battery of the fourth aspect.

[0051] Additional aspects and advantages of the present disclosure will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0052] The above and / or additional aspects and advantages of the present disclosure will become apparent and be readily appreciated from the following description, including the appended drawings.

[0053] FIG. 1 shows the SEM image of the spray precursor obtained in Example 1 of the present disclosure;

[0054] FIG. 2 shows the SEM image of the positive electrode active material obtained in Example 1 of the present disclosure;

[0055] FIG. 3 shows the comparison between the XRD pattern of the positive electrode active material obtained in Example 1 of the present disclosure and the standard spectrum of the crystal structure of sodium ferrous sulfate analog material (wherein the standard spectrum is derived from the literature DOI: 10.1039 / C9TA00116F (J. Mater. Chem. A, 2019, 7, 8226-8233));

[0056] FIG. 4 shows the comparison between the XRD pattern of the positive electrode active material obtained in Example 1 of the present disclosure and the standard spectrum of the crystal structure of sodium ferrous sulfate analog material (wherein the standard spectrum is derived from the literature DOI: 10.1039 / C9TA00116F (J. Mater. Chem. A, 2019, 7, 8226-8233)) after the material is placed in an open system for 24 hours;

[0057] FIG. 5 shows the constant current charge-discharge curve of the sodium ion battery prepared based on the positive electrode active material of Example 1 of the present disclosure at 0.1C;

[0058] FIG. 6 shows the cycle curve of the sodium ion battery prepared based on the positive electrode active material of Example 1 of the present disclosure at 1C;

[0059] FIG. 7 shows the SEM image of the positive electrode active material obtained in Example 7 of the present disclosure;

[0060] FIG. 8 shows the gel phenomenon occurring in the preparation of the positive electrode slurry in Example 7 of the present disclosure;

[0061] Figure 9 shows the XRD pattern of the positive electrode active material obtained in Comparative Example 2 of the present disclosure;

[0062] Figure 10 shows the XRD pattern of the positive electrode active material obtained in Comparative Example 2 of the present disclosure after the material was left in an open system for 24 h;

[0063] Figure 11 shows the XRD pattern of the positive electrode active material obtained in Comparative Example 4 of the present disclosure.

[0064] DETAILED DESCRIPTION

[0065] Embodiments of the present disclosure are described in detail below. The embodiments described below are examples for explaining the present disclosure and should not be understood as limiting the present disclosure.

[0066] Further, the terms "first", "second", etc. are used herein for descriptive purposes only and should not be construed as indicating or implying relative importance or an indicated number of technical features. Thus, features defined with "first", "second" etc. can explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "plurality" is at least two, for example two, three, etc., unless otherwise explicitly specified.

[0067] The ranges disclosed by the present disclosure are defined in the form of lower and upper limits, a given range is defined by selecting a lower limit and an upper limit, the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this way can include or not include the end values, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range. For example, if the ranges 60-120 and 80-110 are listed for a particular parameter, it is understood that the ranges 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present disclosure, unless otherwise stated, the numerical range "a-b" represents a shorthand notation for any real combination of integers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein, "0-5" is just a shorthand notation for these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0068] If not specifically stated, all embodiments of the present disclosure and optional embodiments can be combined with each other to form new technical solutions.

[0069] If not specifically stated, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0070] If not specifically stated, all steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed in sequence, or steps (b) and (a) performed in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0071] The first aspect of the present disclosure provides a positive electrode active material, which is an iron-based sulfate sodium-ion battery positive electrode material, and the X-ray diffraction pattern of the positive electrode active material has a first characteristic peak in the range of 34.9° to 35.3° and a second characteristic peak in the range of 35.3° to 35.5°.

[0072] Wherein, the peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.1≤I1 / I2≤1.5.

[0073] In the prior art, the positive electrode active material has poor thermal stability and is prone to contain Fe 3+ or Fe2O3 impurities. In order to solve this problem, metal powder elements (such as Fe) are added during preparation to protect the reduction of Fe 2+ , but this also increases the risk of containing magnetic foreign matter and impurities in the product. In addition, organic antioxidants can also be added during preparation, but they are prone to decomposition, and it is difficult to maintain the antioxidant effect during subsequent calcination. At the same time, low-temperature sintering is not conducive to effective carbonization, which has an adverse effect on the performance of the material as an impurity. The present disclosure found that when the peak intensity ratio of the first characteristic peak and the second characteristic peak in the X-ray diffraction pattern (XRD pattern) of the positive electrode active material satisfies the above condition, it indicates that the form of Fe in the positive electrode active material is mainly Fe 2+ , and the mass percentage of Fe 3+ in the material is less than 1.5%, which greatly reduces the content of Fe 3+ in the positive electrode active material, which mainly exists in the form of Fe3O4 impurities, and increases the reactivity of the positive electrode active material. This is because the first characteristic peak belongs to the (-132) crystal plane of the positive electrode active material, and the second characteristic peak belongs to the (112) crystal plane. The characteristic peak of FeSO4 occurs decomposition side reaction to produce Fe 3+of Fe3O4 at 35.4° of (311) crystal face overlaps to generate a composite characteristic peak. Therefore, the higher the relative peak intensity of the second characteristic peak is, the stronger the side reaction in the preparation process of the positive electrode active material is, the more impurities increase, and the less available Fe 2+ / Fe 3+ electronic pairs decrease, resulting in the decrease of specific capacity and cycle performance of the positive electrode active material.

[0074] According to a specific embodiment of the present disclosure, the positive electrode active material satisfies the following condition: 1’ and the peak intensity I 2’ satisfies:

[0075] 1.05≤I 1’ / I 2’ ≤1.4.

[0076] When the positive electrode active material satisfies the above condition, it indicates that the material can also be protected by the reducing agent during storage, the content of Fe3+ is basically unchanged, and the material has good structural stability.

[0077] According to a specific embodiment of the present disclosure, the peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.2≤I1 / I2≤1.4. This indicates that the existing form of Fe in the positive electrode active material is mainly Fe 2+ , the mass ratio of Fe 3+ in the material is lower,

[0078] According to a specific embodiment of the present disclosure, 1.1≤I 1’ / I 2’ ≤1.25.

[0079] When the positive electrode active material satisfies the above condition, it is more beneficial for storage, and the positive electrode active material has good structural stability.

[0080] The relative humidity is defined as the percentage of the actual water vapor density (denoted as d1) in a unit volume of air and the saturated water vapor density (denoted as d2) at the same temperature, i.e. RH(%) = d1 / d2 x 100%; another calculation method is: the percentage of the actual air water vapor pressure (denoted as p1) and the saturated water vapor pressure (denoted as p2) at the same temperature, i.e. RH(%) = p1 / p2 x 100%.

[0081] According to a specific embodiment of the present disclosure, the positive electrode active material satisfies at least one of the following conditions:

[0082] The D50 4-10μm;

[0083] The positive electrode active material D 100 Satisfy: 6μm < D 100 <20μm;

[0084] The specific surface area of ​​the positive electrode active material is 5-25 m². 2 / g.

[0085] The morphology of the positive electrode active material is not particularly limited, but is preferably composed of regular spherical particles. The particle size range of the positive electrode active material is preferably small, and the D-value of the positive electrode active material is preferably [missing information]. 50 The range is 4-10 μm, as some specific examples, such as D. 50 The particle sizes are 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm, etc. Regularly shaped particles are produced. Because the particle size of the precursor extends to the cathode material, it affects electrochemical performance. Therefore, it is necessary to control the D of the cathode active material. 50 A particle size of 4-10 μm is required to achieve good electrical performance, which can be achieved by adjusting the spray drying parameters during the preparation process. The preferred positive electrode active material has a D... 100 Satisfy: 6μm < D 100 <20μm, as some specific examples, such as D 100 The sizes are 19μm, 18μm, 17μm, 16μm, etc.

[0086] Preferably, the specific surface area of ​​the positive electrode active material is 5-25 m². 2 / g, as some specific examples, such as a specific surface area of ​​5m² 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g、25m 2, etc. When the specific surface area of the positive active material is in the range of 5-25 m 2 / g, the material is not prone to the adverse phenomenon of gelation during the preparation of the positive electrode slurry due to the water absorption property of sodium ferrous sulfate-based materials.

[0087] According to a specific embodiment of the present disclosure, the positive active material has a chemical formula shown in formula (1):

[0088] Na 2x Fe 2-y M y (SO4) (2+x-z) (SO3) z @C (1)

[0089] wherein 1≤x≤2.04, 0≤y≤0.2; 0

[0090] M is selected from at least one of Mn, Co, Ni, Mg, Cu, Zn.

[0091] wherein the chemical composition of the positive active material includes the doping element M and SO3 2- The doping element can improve the crystal structure of the material, improve the thermal stability of the material, and inhibit the side reaction of the decomposition of sodium ferrous sulfate-based materials to produce Fe3O4 or Fe2O3 impurities. SO3 2- derived from the inorganic reducing agent added during preparation, and in the presence of oxygen in the system during preparation or material storage, Fe 2+ reacts preferentially to convert to SO4 2- Therefore, the transition metal element doping and SO3 2- protective synergy, the synthesized sodium ferrous sulfate-based carbon composite sodium ion battery positive electrode material Fe 3+ has a very low content and exhibits high specific capacity, good cycle stability, and storage performance.

[0092] wherein the closer x in the chemical formula is to 1, the higher the proportion of Na + participates in the electrochemical reaction process of intercalation / deintercalation, and the theoretical specific capacity of the material is also higher. Specifically, 1≤x≤2.04, and as some specific examples, x can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.04, etc.; preferably 1≤x≤1.4.

[0093] y corresponds to the doping amount of the doping element in the chemical formula, the doping element can improve the structural stability of the material, but has no significant effect on the capacity improvement, so a lower doping amount is preferred. 0≤y≤0.2, as some specific examples, y can be 0, 0.1, 0.2, etc. The doping element M includes but is not limited to Mn, Co, Ni, Mg, Cu, Zn.

[0094] z in the chemical formula corresponds to the residual amount of the reducing agent in the prepared positive electrode active material, which is only added in a small amount during preparation. Therefore, 0 less than Na2SO3 as a stronger reducing agent is more resistant to Fe 2+ than NaHSO3 in the presence of trace amounts of oxygen, and is preferentially reacted to convert into the raw material Na2SO4, which continues to participate in the solid-phase reaction with FeSO4 in the subsequent sintering process without other effects. If the oxygen content in the sintering atmosphere is extremely low, Na2SO3 is not oxidized during the sintering process, and can also protect Fe 2+ in the material storage process for a long time, improving the air stability of the material structure. Therefore, to some extent, the chemical formula of the positive electrode active material will change with the time of placement, that is, z tends to decrease until it is zero.

[0095] At the same time, it can be known from the chemical formula that the positive electrode active material is coated with a carbon material, wherein the carbon material includes but is not limited to graphene, reduced graphene oxide, conductive graphite, acetylene black, Ketjen black, mesoporous carbon, and carbon nanotubes. The mass fraction of the carbon material in the positive electrode active material is 0.5-10%, as some specific examples, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, etc. The type of conductive carbon selected for addition will have a significant impact on the specific surface area of the material, but the upper limit can be controlled by adjusting the parameter settings during preparation to prepare a spray feed precursor with regular morphology.

[0096] The second aspect of the present disclosure provides a preparation method of a positive electrode active material, the preparation method comprising:

[0097] (1) preparing a reducing agent solution, mixing an inorganic conductive carbon material with the reducing agent solution to obtain a mixed solution 1.

[0098] According to specific embodiments of the present disclosure, the reducing agent in the reducing agent solution is preferably NaHSO3 and / or Na2S2O5, and meanwhile the reducing agent solution is preferably an acidic solution, i.e. the reducing agent is in an acidic condition during the preparation of the solution, which can effectively inhibit Fe 2+ from being oxidized or hydrolyzed, so as to maintain the stability of Fe 2+ in the subsequent preparation and spraying process.

[0099] According to specific embodiments of the present disclosure, the specific type of the inorganic conductive carbon material is not particularly limited, and can be selected by those skilled in the art according to actual conditions. For example, the inorganic conductive carbon material can include at least one of graphene, reduced graphene oxide, conductive graphite, acetylene black, ketjen black, mesoporous carbon, and carbon nanotubes.

[0100] Specifically, step (1) can be: weighing a small amount of inorganic reducing agent into a proper amount of deionized water, and stirring rapidly until the inorganic reducing agent is completely dissolved to obtain a uniform acidic aqueous solution protected by the reducing agent.

[0101] Weighing a certain amount of one or more inorganic conductive carbon materials into the above-mentioned acidic aqueous solution with reducing agent, and continuously stirring and ultrasonic dispersing to obtain a mixed solution 1 with uniform distribution of carbon particles.

[0102] (2) mixing Na2SO4, FeSO4·7H2O and optional sulfate with the mixed solution 1 to obtain a mixed solution 2.

[0103] According to specific embodiments of the present disclosure, the sulfate is used to provide M elements selected from at least one of Mn, Co, Ni, Mg, Cu, and Zn. That is, the sulfate includes but is not limited to MnSO4, CoSO4, NiSO4, MgSO4, CuSO4, ZnSO4, and their crystal hydrates.

[0104] According to specific embodiments of the present disclosure, the mass of the solvent in the reducing agent solution in step (1) is 2-3 times the mass of FeSO4·7H2O added in step (2). The solvent includes but is not limited to deionized water. The solubility of FeSO4·7H2O in water at room temperature is greater than 50 g. Although adding too much water is beneficial to the dispersion of the solute and the improvement of the dissolution rate, it will cause the reduction of the spray drying efficiency and the increase of the production cost caused by the consumption of water resources.

[0105] According to specific embodiments of the present disclosure, in step (2), the molar ratio of Na2SO4, FeSO4·7H2O and the sulfate is δ:2-y:y.

[0106] wherein 0.96≤δ≤2; as some specific examples, δ is 0.96, 1, 1.5, 2, etc.; 0≤y≤0.2, as some specific examples, y is 0, 0.1, 0.2, etc.

[0107] According to a specific embodiment of the present disclosure, the molar ratio of sodium element to Na2SO4 in the reducing agent is 2n:δ.

[0108] wherein 0

[0109] According to a specific embodiment of the present disclosure, the mass ratio of the mass of the completely dehydrated Na2SO4, FeSO4·7H2O and sulfate salt to the mass of the inorganic conductive carbon material is 100:(0.5-10), as some specific examples, 100:0.5, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, 100:4.5, 100:5, 100:5.5, 100:6, 100:6.5, 100:7, 100:7.5, 100:8, 100:8.5, 100:9, 100:9.5, 100:10, etc. Since the intrinsic electronic conductivity of sodium ferrous sulfate material is lower than that of other types of sodium ion battery cathode materials, and the inhibition of FeSO4 side reaction also consumes a small amount of carbon, more conductive carbon needs to be added when preparing the solution.

[0110] Specifically, step (2) can be: weighing an appropriate amount of anhydrous Na2SO4, FeSO4·7H2O and at least one M sulfate salt, and adding them into the above-mentioned mixed solution 1, and performing long-time rapid stirring until the several raw materials in the solution are completely dissolved, to obtain a mixed solution 2 to be sprayed.

[0111] (3) performing spray drying on the mixed solution 2 to obtain a cathode active material precursor.

[0112] According to a specific embodiment of the present disclosure, the conditions of the spray drying include:

[0113] The inlet air temperature is 130-160°C, as some specific examples, 130°C, 140°C, 150°C, 160°C, etc., and the inlet air temperature less than 160°C can inhibit the rapid dehydration of FeSO4 into Fe(OH)SO4 in air under heating; the outlet air temperature is not less than 80°C, as some specific examples, 80°C, 90°C, 100°C, 105°C, etc., which is conducive to removing moisture to achieve a certain degree of dryness.

[0114] According to a specific embodiment of the present disclosure, the cathode active material precursor has a regular spherical particle morphology, and the average particle size D50 The range is 4-10 μm, as some specific examples, such as D. 50 The particle sizes are 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc. The largest particle size D... 100 Satisfy: 6μm < D 100 <20μm, as some specific examples, such as D 100 The particle sizes are 19μm, 18μm, 17μm, 16μm, 15μm, 14μm, 13μm, 12μm, 11μm, 10μm, 9μm, 8μm, and 7μm. The particle size of the precursor and the positive electrode active material obtained after sintering are basically the same.

[0115] Specifically, step (3) can be: spray drying the above mixed solution under set parameters while continuously stirring, and collect the spray material precursor directly after spraying is completed.

[0116] (4) The positive electrode active material precursor is sintered to obtain the positive electrode active material.

[0117] During sintering, both NaHSO3 and Na2S2O5 are first converted to Na2SO3 upon heating, during which some SO2 is generated. Because... Less than Na₂SO₃, as a stronger reducing agent, is more effective than Fe in the presence of trace amounts of oxygen. 2+ The reaction occurs preferentially, transforming into the raw material Na2SO4, which continues to participate in the solid-state reaction with FeSO4 during subsequent sintering without producing other effects. If the oxygen content in the sintering atmosphere is extremely low, Na2SO3 will not be oxidized during sintering and can also protect Fe for a long time during material storage. 2+ This improves the air stability of the material structure.

[0118] According to specific embodiments of this disclosure, the sintering process is the process by which the precursor completely loses its water of crystallization and undergoes a solid-state reaction. The sintering conditions affect the residual water content, crystal strength, and impurity content of the material. The sintering conditions can be: 300-380℃, with specific examples including 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, and 380℃, etc., for 8-20 hours, with specific examples including 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, and 20h. The heating rate is not particularly limited, and those skilled in the art can make reasonable selections based on actual conditions. Preferably, it is 1-3℃ / min, with specific examples including 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, and 3℃ / min.

[0119] Specifically, step (4) can be: placing the above-mentioned spray material precursor in a continuously-inflating inert atmosphere furnace to perform a low-temperature sintering process, and finally obtaining a sodium ferrite sulfite carbon composite sodium-ion battery positive electrode material.

[0120] The third aspect of the present disclosure provides a positive electrode tab, which comprises the positive electrode active material of the first aspect of the present disclosure or the positive electrode active material prepared by the method of the second aspect of the present disclosure.

[0121] The positive electrode tab generally comprises a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer comprises the positive electrode active material.

[0122] The positive electrode current collector can adopt a conventional metal foil or a composite current collector (a metal material can be disposed on a polymer substrate to form a composite current collector). As an example, the positive electrode current collector can comprise at least one of a copper foil, an aluminum foil, a nickel foil, a stainless steel foil, a stainless steel mesh, and a carbon-coated aluminum foil.

[0123] The positive electrode active material comprises the positive electrode active material of the first aspect of the present disclosure or the positive electrode active material prepared by the method of the second aspect of the present disclosure.

[0124] The positive electrode active material layer can further optionally comprise a conductive agent and a binder. The conductive agent is used to improve the conductivity of the positive electrode active material layer, and the binder is used to firmly bond the positive electrode active material and the binder to the positive electrode current collector. The present disclosure does not make specific limitations on the types of conductive agents and binders, which can be selected according to actual needs.

[0125] As an example, the conductive agent can comprise at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; and the binder can comprise at least one of polyvinylidene fluoride (PVDF), a polyvinylidene fluoride copolymer, or a modified (e.g., carboxylic acid, acrylic acid, acrylonitrile, etc.) derivative thereof.

[0126] These materials can all be obtained through commercial channels.

[0127] The fourth aspect of the present disclosure provides a battery comprising the positive electrode tab of the third aspect of the present disclosure. Thus, the battery has excellent cycle life.

[0128] The battery refers to a battery that can be activated by charging after discharging to continue to use.

[0129] It can be understood that the battery proposed by the present disclosure is a lithium-ion battery.

[0130] Generally, a battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet and functions to separate them. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet.

[0131] [The negative electrode sheet]

[0132] In the battery, the negative electrode sheet generally includes a negative current collector and a negative active material layer disposed on the negative current collector, the negative active material layer including a negative active material.

[0133] The negative current collector is generally a structure or a part that collects current, and can be any of various materials known in the art to be suitable for use as a negative current collector in a lithium secondary battery. For example, the negative current collector can be a conventional metal foil or a composite current collector (e.g., a composite current collector can be formed by disposing a metal material on a polymer substrate). As an example, the negative current collector can be a copper foil or a lithium sheet.

[0134] The negative active material is not limited in particular and can be any of various active materials known in the art to be suitable for use in a battery negative electrode. The negative active material can be selected by a person skilled in the art as desired. As an example, the negative active material can be a combination of one or more of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate, or other metal capable of forming an alloy with lithium. The graphite can be selected from a combination of one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from a combination of one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon alloy; and the tin-based material can be selected from a combination of one or more of elemental tin, tin oxide compound, tin alloy. These materials can be obtained commercially.

[0135] In some embodiments, the negative active material can include a silicon-based material in order to further increase the energy density of the battery.

[0136] The negative active material layer can also optionally include a binder, a conductive agent, and other optional additives.

[0137] As an example, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0138] As an example, the binder can include one or more of styrene butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0139] As an example, the other optional additive can include a thickening and dispersing agent (e.g., sodium carboxymethyl cellulose CMC-Na), a PTC thermistor material.

[0140] [Electrolyte]

[0141] The electrolyte can include an electrolyte salt and a solvent.

[0142] As an example, the electrolyte salt can include one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), lithium perchlorate (NaClO4), sodium bisfluorosulfonylimide (NaFSI), sodium trifluoromethylsulfonate (NaTFS).

[0143] As an example, the solvent can include at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0144] In some embodiments, an additive is further included in the electrolyte. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving certain performance of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature performance of the battery, and an additive for improving low-temperature performance of the battery.

[0145] [Separator]

[0146] As the above-described separator, the present disclosure is not particularly limited, and any publicly known porous structure separator having electrochemical stability and mechanical stability can be used according to actual needs, and for example, can include a combination of at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fiber.

[0147] The fifth aspect of the present disclosure provides a power consuming device comprising the battery of the fourth aspect. Specifically, the battery can serve as a power source of the power consuming device, or as an energy storage unit of the power consuming device. The power consuming device can include, but is not limited to, a mobile device (e.g., a mobile phone, a laptop), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, an energy storage system.

[0148] The solutions of the present disclosure will be explained below in conjunction with examples. Those skilled in the art will understand that the examples below are only for illustration of the present disclosure and should not be considered as limiting the scope of the present disclosure. If no specific technology or condition is specified in the examples, the technology or condition described in the literature in the art or according to the product manual is used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be obtained commercially.

[0149] Example 1

[0150]

【Na 2.04 Fe 1.9 Mg 0.1 (SO4) 3.02-z (SO3) z @C Preparation

[0151] The added inorganic reducing agent is NaHSO3, and the selected conductive carbon is graphene nanosheet. The detailed preparation process is as follows:

[0152] Step one: weigh 0.04 mol of NaHSO3 reducing agent and add it to 1200 mL of deionized water. After rapid stirring, the dispersant is completely dissolved to form an acidic solution with reducing properties;

[0153] Step two: weigh 20 g of graphene nanosheet and add it to the above dispersant solution. After continuous stirring and ultrasonic dispersion, a uniformly suspended graphene suspension is obtained;

[0154] Step three: weigh 1 mol of anhydrous Na2SO4, 1.9 mol of FeSO4·7H2O and 0.1 mol of MgSO4·7H2O, and add them to the above suspension in sequence. Continue stirring until the above sulfate raw materials are completely dissolved to obtain a green graphene suspension;

[0155] Step four: spray dry the above suspension under continuous high-speed stirring. Set the inlet temperature in the equipment drying chamber to 150°C, and maintain the outlet temperature at 100°C. The solution is added at a rate of 400 mL / h. After spraying, the spray precursor for sintering is directly collected.

[0156] Step five: the spray feed precursor is placed in a tube furnace with continuous dry inert gas, and the temperature is raised to 380°C at a rate of 1.5°C / min, and kept at 380°C for 12h, to obtain the sodium ferrous sulfate carbon composite material of the above chemical type.

[0157]

Preparation of the battery

[0158] The prepared sodium ferrous sulfate carbon composite material, polyvinylidene fluoride (PVDF) and conductive carbon (mass ratio of 8:1:1) are mixed into a film, which is used as the positive electrode, the metal sodium is used as the negative electrode, the glass fiber membrane is used as the separator, and the 1 mol / L NaPF6 solution in ethylene carbonate / propylene carbonate (molar ratio of 1:1) is used as the electrolyte, which is assembled in the R2032 type button cell shell to form a sodium ion battery.

[0159] The sodium ion batteries containing the positive electrode active materials of examples 2-10 and comparative examples 1-4 are the same as example 1 except for different parameters (see table 1 for details), and the chemical formula of the obtained positive electrode active material is shown in table 2.

[0160] Table 1

[0161] Table 1 (continued)

[0162] Table 1 (continued)

[0163] In table 1, " / " means no addition.

[0164] Table 2

[0165] Test and analysis:

[0166] 1. Physicochemical analysis is performed on the positive electrode active materials of examples 1-10 and comparative examples 1-4, respectively, and the test results are shown in table 3.

[0167] (1) The morphology of the prepared sample is observed by scanning electron microscope to determine the physical and chemical indexes of the positive electrode active material;

[0168] (2) The carbon content of the sample is characterized by thermogravimetric analysis;

[0169] (3) The average particle size D 50 and the maximum particle size D 100 of the sample are tested by laser particle size analyzer and dry test process;

[0170] (4) XRD spectra of the material were obtained using an X-ray diffractometer to analyze the crystal structure and characteristic peak intensity of the sample;

[0171] (5) The specific surface area of the sample was tested using a specific surface area tester, and the content of Fe in the sample was determined using a potassium dichromate (K2Cr2O7) titration method 3+ according to GB / T33828-2017).

[0172] 2. The electrochemical performance of lithium ion batteries containing the positive electrode active materials of Examples 1-10 and Comparative Examples 1-4 was tested, and constant current charge and discharge tests were performed at a voltage range of 2.0-4.5 V and a current density of 0.1 C and 1 C (1 C = 100 mAh / g), respectively, to obtain the specific capacity and cycle performance of the material. The test results are shown in Table 3.

[0173] Table 3

[0174] Result analysis:

[0175] The positive electrode active material in Example 1 was prepared by the method provided in the present disclosure. The SEM image of the spray feed precursor obtained in this example is shown in FIG. 1, the SEM image of the positive electrode active material is shown in FIG. 2, and the corresponding XRD spectrum is shown in FIG. 3. The XRD spectrum of the material after being placed in an open system for 24 h is shown in FIG. 4, and in combination with the data (I1 / I2, I 1’ / I 2’ , ΔI1 / I2) in Table 3, it can be seen that the form of Fe in the positive electrode active material is mainly Fe 2+ , and it can remain stable without being oxidized for a long storage time. The electrochemical performance of the battery containing it is shown in Table 3 and FIGS. 5-6, which shows that the specific capacity and cycle stability of the battery can be improved. Similarly, Examples 2-10 also have the above advantages.

[0176] In addition, compared with Example 1, the inlet air temperature of Example 7 is increased, and the specific surface area reaches 22.2 m 2 / g, as shown in FIG. 7. Compared with Example 1, the particle surface pores of the prepared positive electrode active material are obviously, which may be caused by the rapid dehydration. The D 50 of the material is 7.8 μm, and the particle size D 100 of the largest particle is 23.1 μm, which is also larger than that of Example 1. Due to the large particle size, high specific surface area and irregular morphology, the material has a more significant gel phenomenon in the process of making electrode slurry due to its water absorption properties, which affects the electrochemical performance of the material to some extent. The state of the gel is shown in FIG. 8.

[0177] Comparative Example 1, the sintering temperature in step five is increased, and the results show that the content of Fe in the positive electrode active material is relatively high.3+ , i.e. the occurrence of the side reaction of ferrous phosphate cannot be inhibited;

[0178] Comparative Example 2, compared with Example 1, no reducing agent was added, and its XRD pattern (Figure 9) showed that I1 / I2=0.85, indicating that there were more Fe3O4 impurities in the material composition. 3+ This is because under the condition of higher sintering at 380°C, without the addition of reducing agent, the decomposition side reaction of Fe2SO4 is serious, and more Fe3O4 impurities are produced. The specific discharge capacity of the material at 0.1C is only 80.3 mAh / g, and the capacity retention rate at 1C is 93.5%. Without the protection of reducing agent, the electrochemical performance is significantly affected. As shown in the XRD pattern (Figure 10) after standing, other impurities also appeared in the material after standing, indicating its poor storage performance;

[0179] Comparative Example 3 also did not add reducing agent, but reduced the sintering temperature, which reduced the oxidation of Fe 2+ to a certain extent, but the solid solution reaction of the material sintered at low temperature was not complete, and a small amount of crystal water was left. The specific discharge capacity of the battery containing it was only 78.3 mAh / g, and the capacity retention rate was only 92.3% after 80 cycles of 1C charge and discharge, and ΔI1 / I 2达 to 8.5% after standing under the same conditions, indicating the poor properties of the material lacking reducing agent in storage performance;

[0180] Comparative Example 4, compared with Example 1, increased the amount of reducing agent used. Because too much reducing agent was added, the consumption of reducing agent under N2 sintering conditions was less, resulting in the appearance of more obvious Na2SO3 impurities in the XRD pattern (Figure 11). The electrochemical performance of the sample was adversely affected, and the specific discharge capacity at 0.1C was only 81.3 mAh / g.

[0181] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present disclosure. In the present specification, the illustrative description of the above terms is not necessarily directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0182] Although the embodiments of the present disclosure have been shown and described above, it is understood that the above-described embodiments are exemplary, and it is not construed that the present disclosure is limited to the above-described embodiments, and a person of ordinary skill in the art can make changes, modifications, replacements, and variations to the above-described embodiments within the scope of the present disclosure.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material is an iron-based sulfate sodium-ion battery positive electrode material, and the positive electrode active material has a first characteristic peak in the range of 34.9° to 35.3° and a second characteristic peak in the range of 35.3° to 35.5° in an X-ray diffraction pattern. The peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.1≤I1 / I2≤1.

5.

2. The positive electrode active material according to claim 1, characterized by the peak intensity I of the first characteristic peak after the positive electrode active material is left in an open environment at a temperature of 25°C and a relative humidity of 30% for 24 hours 1’ to the peak intensity I of the second characteristic peak 2’ satisfies: 1.05≤I 1’ / I 2’ ≤1.4; 3. The positive electrode active material according to claim 2, characterized by The peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.2≤I1 / I2≤1.

4.

4. The positive electrode active material according to claim 2, characterized by The peak intensity I1 of the first characteristic peak and the peak intensity I2 of the second characteristic peak satisfy: 1.1≤I1 / I2≤1.

25. 1’ / I 2’ ≤1.

25.

5. The positive electrode active material according to claim 1, characterized by The positive electrode active material satisfies at least one of the following conditions: D of the positive electrode active material is 4-10 μm. 50 4-10 μm; D of the positive electrode active material is 6 μm or more and less than 20 μm. 100 satisfies: 6 μm < D < 20 μm. 100 20 μm; The specific surface area of the positive electrode active material is 5-25 m 2 / g.

6. The positive electrode active material according to any one of claims 1 to 5, characterized by The positive electrode active material has a chemical formula represented by Formula (1): Na 2x Fe 2-y M y (SO4) (2+x-z) (SO3) z @C (1) wherein 1≤x≤2.04, preferably 1≤x≤1.4; 0≤y≤0.2; 0 M is selected from at least one of Mn, Co, Ni, Mg, Cu, Zn.

7. A method for producing a positive electrode active material, characterized by, The preparation method comprises: (1) preparing a reducing agent solution, mixing an inorganic conductive carbon material with the reducing agent solution to obtain a mixed solution 1; (2) mixing Na2SO4, FeSO4·7H2O, and an optional sulfate with the mixed solution 1 to obtain a mixed solution 2; (3) performing spray drying on the mixed solution 2 to obtain a positive electrode active material precursor; (4) sintering the positive electrode active material precursor to obtain the positive electrode active material; The reducing agent in the reducing agent solution is NaHSO3 and / or Na2S2O5. The sulfate is used to provide M elements selected from at least one of Mn, Co, Ni, Mg, Cu, and Zn.

8. The preparation method according to claim 7, characterized in that, In step (1), the mass of the solvent in the reducing agent solution is 2-3 times the mass of FeSO4·7H2O added in step (2).

9. The preparation method according to claim 7, characterized in that, In step (1), the inorganic conductive carbon material comprises at least one selected from graphene, reduced graphene oxide, conductive graphite, acetylene black, ketjen black, mesoporous carbon, and carbon nanotubes.

10. The method of claim 7, wherein, In step (2), the molar ratio of Na2SO4, FeSO4·7H2O, and the sulfate is δ:2-y:y; wherein 0.96≤δ≤2; 0≤y≤0.

2.

11. The method of claim 10, wherein, The molar ratio of sodium elements in the reducing agent to Na2SO4 is 2n:δ; wherein 0 12. The method of claim 7, wherein, In step (2), the mass ratio of the mass of the completely dehydrated Na2SO4, FeSO4·7H2O, and the sulfate to the mass of the inorganic conductive carbon material is 100:(0.5-10).

13. The preparation method according to claim 7, characterized in that, In step (3), the conditions of the spray drying comprise: The inlet air temperature is 130-160℃; and the outlet air temperature is not less than 80℃.

14. The preparation method according to claim 7, characterized in that, In step (3), the D50 of the positive electrode active material precursor is 4-10 pm. 50 4-10 pm; D of the positive electrode active material precursor is 6 μm or more and less than 20 μm. 100 satisfies: 6 μm < D < 20 μm. 100 satisfies: 6 μm < D < 20 μm.

15. The method of claim 7, wherein the method further comprises, In step (4), the conditions of the sintering comprise sintering at 300-380℃ for 8-20h.

16. A positive electrode sheet characterized by comprising: The positive electrode active material is prepared by the preparation method of any one of claims 7-15.

17. A battery, characterized by The battery comprises the positive electrode tab of claim 16.

18. An electrical device, characterized by The battery comprises the battery of claim 17.

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