Ferric phosphate coated ferrous manganese oxalate hybrid phase material, preparation method thereof, positive electrode material and battery

Abstract

The invention belongs to the technical field of new energy batteries, and particularly relates to an iron phosphate coated manganous oxalate hybrid phase material and a preparation method thereof, a positive electrode material and a battery, the iron phosphate coated manganous oxalate hybrid phase material comprises manganous oxalate and iron phosphate coated with manganous oxalate, the chemical general formula of the iron phosphate coated manganous oxalate hybrid phase material is FexMn1-xC2O4 / FePO4, x is greater than or equal to 0.1 and less than or equal to 0.9, the content of FePO4 is less than or equal to 10.3 wt%, and x is greater than or equal to 0.1 and less than or equal to 0.9. The iron phosphate-coated ferrous manganese oxalate hybrid phase material is composed of hexahedron-shaped particles, the length of the hexahedron is 0.12 [mu] m-2. 4 [mu] m, the width of the hexahedron is 0.08 [mu] m-0. 86 [mu] m, the height of the hexahedron is 0.04 [mu] m-0. 65 [mu] m, and the hexahedron-shaped iron phosphate-coated ferrous manganese oxalate hybrid phase material is large in specific surface area, uniform in particle shape and good in stability. The contact area between the positive electrode material prepared from the hybrid phase material and an electrolyte is increased, so that the ion mobility in the positive electrode material is improved; and the composition gradient design is realized, the high specific energy density of the positive electrode material is improved, the dissolution of the manganese element is relieved, the influence of the dissolution of the manganese element is reduced, and the stability of the cycle performance of the battery prepared from the positive electrode material is improved.

Description

Technical Field

[0001] This application belongs to the field of new energy battery technology, and in particular relates to iron phosphate coated ferrous manganese oxalate hybrid phase material and its preparation method, cathode material and battery. Background Technology

[0002] Lithium iron phosphate (LFP) has a low lithium insertion / extraction potential of approximately 3.4V, resulting in a relatively low theoretical specific capacity (approximately 170 mAh / g) and electronic conductivity. In contrast, lithium manganese phosphate (LMP) with an olivine-type structure has a higher lithium insertion / extraction potential of approximately 4.1V and offers a 35% increase in energy density. However, the low ionic and electronic conductivity of LMP hinders its further development.

[0003] Currently, lithium iron manganese phosphate (LFP) has been prepared based on lithium iron phosphate and lithium manganese phosphate, which improves the low energy density problem of lithium iron phosphate and the low conductivity problem of lithium manganese phosphate. However, the conductivity of LFP is 10. -13 S / cm, with a conductivity of 10 for layered ternary materials. -3 Compared to existing technologies, lithium iron phosphate (LFP) exhibits lower conductivity (S / cm), resulting in poorer electrochemical performance in lithium-ion batteries. Furthermore, manganese in LFP readily dissolves during charge and discharge, and trivalent manganese ions are prone to the John-Teller effect, leading to decreased cycle stability. Existing technologies using precursors obtained through mechanical mixing or co-precipitation cannot achieve atomically uniform composite composition between the two phases, resulting in defects such as component segregation or high interfacial impedance, further reducing the electrochemical performance of lithium-ion batteries made from LFP.

[0004] In addition, sodium batteries prepared using iron phosphate and manganese phosphate as precursors, and sodium iron phosphate pyrophosphate manganese iron phosphate, also suffer from the problem of manganese leaching reducing the electrochemical performance of sodium batteries.

[0005] The existing technology for preparing lithium manganese iron phosphate / sodium manganese iron pyrophosphate cathode materials has the problem that manganese is easily dissolved, which reduces the electrochemical performance of the battery. Summary of the Invention

[0006] This application provides iron phosphate-coated ferrous manganese oxalate hybrid phase material and its preparation method, cathode material and battery, aiming to solve to some extent the problem that manganese element is easily dissolved in the cathode material prepared from precursors of lithium iron manganese phosphate / sodium iron manganese pyrophosphate, which reduces the electrochemical performance of the battery.

[0007] In a first aspect, this application provides an iron phosphate-coated ferrous manganese oxalate hybrid phase material, which includes ferrous manganese oxalate and iron phosphate coated with ferrous manganese oxalate, with the general chemical formula Fe. xMn 1-x The C2O4 / FePO4 material, wherein 0.1≤x≤0.9 and the FePO4 content≤10.3 wt%, is composed of hexagonal particles with a length of 0.12μm~2.4μm, a width of 0.08μm~0.86μm, and a height of 0.04μm~0.65μm.

[0008] Secondly, this application provides a method for preparing an iron phosphate-coated ferrous manganese oxalate hybrid phase material as described in the first aspect, comprising the following steps: S1, ferrous salt, manganese salt and antioxidant are added to deionized water, stirred and dissolved to obtain the first solution, wherein the molar ratio of iron to manganese in the first solution is 1:0.33~3; S2, under inert atmosphere and constant temperature conditions, add oxalate-containing solution to the first solution, and simultaneously add acid and first alkali solution to form oxalate-containing mixed solution. Adjust the pH of the oxalate-containing mixed solution to 2-7, stir to carry out precipitation reaction for 0.5-8 hours, let stand for aging for 0.5-6 hours, and then filter, wash and dry to obtain ferrous manganese oxalate precursor; S3, add ferric salt to deionized water, stir to dissolve, and obtain the second solution; S4, add the phosphate-containing reagent to deionized water, stir to dissolve, and obtain the third solution; S5, the ferrous manganese oxalate precursor obtained in step S2 is added to the second solution, stirred, and then the third solution is added, along with acid and the second alkali solution to form a precursor solution. The pH of the precursor solution is adjusted to 2.0~3.0. After stirring and reacting, the intermediate product is obtained by spray drying. S6. The intermediate product obtained in step S5 is placed in a box sintering furnace and dried at 120℃~250℃. After cooling, a hexagonal morphology iron phosphate coated ferrous manganese oxalate hybrid phase material is obtained.

[0009] In one embodiment, the molar ratio of iron to manganese in the first solution is 1:0.33~3, the concentration of both iron and manganese in the first solution is 0.1mol / L~4mol / L, and the mass-volume concentration of the antioxidant in the first solution is 0.05g / L~10g / L. The oxalate concentration of the oxalate-containing solution is 0.2 mol / L to 1.2 mol / L, the concentration of the acid solution is 0.5 mol / L to 3.5 mol / L, and the concentration of the first alkaline solution is 0.3 mol / L to 2 mol / L. The precipitation reaction temperature is 45℃~65℃, and the rate of adding oxalate-containing solution is 20mL / min~50mL / min; The concentration of ferric ions in the second solution is 0.2 mol / L to 1.5 mol / L, and the concentration of phosphate ions in the third solution is 0.5 mol / L to 3.5 mol / L. The concentration of the second alkali solution is 0.1~1 mol / L, the reaction time of the stirring reaction in step S5 is 0.5h~4h, and the spray drying device is a centrifugal spray dryer.

[0010] In one embodiment, the three-stage solid-state sintering process in step S6 is as follows: the temperature is raised to 300℃~350℃ at a heating rate of 10℃ / min and held for 2h~4h; then the temperature is raised to 450℃~550℃ at a heating rate of 5℃ / min and held for 3h~5h; then the temperature is raised to 600℃~700℃ at a heating rate of 2℃ / min and held for 1h~3h.

[0011] In one embodiment, the ferrous salt is one or more of ferrous sulfate, ferrous chloride, ferrous fluoroborate, and ferrous acetate. Manganese salts are one or more of manganese sulfate, manganese chloride, manganese acetate, and manganese formate. The antioxidant is one or more of the following: sodium bisulfite, sodium thiosulfate, disodium ethylenediaminetetraacetate, sodium metabisulfite, and ascorbic acid. The inert atmosphere is one or a mixture of argon or nitrogen; The oxalate-containing solution is an aqueous solution containing at least one of sodium oxalate, sodium hydrogen oxalate, potassium oxalate, and potassium hydrogen oxalate. The acid solution is one or more of dilute sulfuric acid, dilute hydrochloric acid, and acetic acid; The first alkaline solution is any one of ammonia water, sodium hydroxide solution, or potassium hydroxide solution; The second alkaline solution is either ammonia water or urea water solution; The ferric salt is an aqueous solution containing at least one of ferric citrate, ferric lactate, ferric formate, and ferric acetate; The phosphate-containing reagent is a combination of one or more of phosphoric acid, monoammonium hydrogen phosphate, and diammonium hydrogen phosphate.

[0012] Thirdly, this application provides a cathode material, which is either lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material or sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material. Both lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material and sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material use iron phosphate coated ferrous manganese oxalate hybrid phase material as described in the first aspect as a precursor, or both use iron phosphate coated ferrous manganese oxalate hybrid phase material prepared by the preparation method of iron phosphate coated ferrous manganese oxalate hybrid phase material as described in any one of the second aspects as a precursor.

[0013] In one embodiment, the general chemical formula of the lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material is LiFe. x Mn 1-x PO4 / C, where 0.1≤x≤0.91, lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material includes lithium manganese iron phosphate, lithium iron phosphate coated on the surface of lithium manganese iron phosphate, and a carbon layer coated on the surface of lithium iron phosphate, with a carbon layer thickness of 1nm~8nm.

[0014] In one embodiment, a method for preparing lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material includes: The iron phosphate-coated ferrous manganese oxalate hybrid phase material was used as a precursor and mixed with lithium salt and ammonium dihydrogen phosphate to obtain a first precursor mixture. Then, 2wt%~4wt% of carbon source was added to the first precursor mixture. The mixture was ball-milled with anhydrous ethanol as the ball milling medium, and then dried and ground. The ground material was sintered in an inert gas atmosphere, and then cooled, ground and sieved to obtain lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material. The sintering process is as follows: heat up to 300℃~350℃ at a heating rate of 10℃ / min and hold for 2h~4h; then heat up to 450℃~550℃ at a heating rate of 5℃ / min and hold for 3h~5h; then heat up to 600℃~700℃ at a heating rate of 2℃ / min and hold for 1h~3h.

[0015] In one embodiment, the general chemical formula of the sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material is Na₄(Fe₂O₃)₂O₃@sodium manganese ...@sodium iron pyrophosphate / carbon cathode material is Na₄(Fe₂O₃)� x Mn 1-x )3(PO4)2P2O7 / C, where 0.82≤x≤0.91, sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material includes sodium manganese pyrophosphate, sodium iron pyrophosphate coated on the surface of sodium manganese pyrophosphate, and a carbon layer coated on the surface of sodium iron pyrophosphate, with a carbon layer thickness of 1nm~8nm.

[0016] In one embodiment, a method for preparing sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material includes: Ferric phosphate-coated ferrous manganese oxalate hybrid phase material was used as a precursor and mixed with sodium salt and ammonium dihydrogen phosphate to obtain a second precursor mixture. Then, 2wt%~4wt% of carbon source was added to the second precursor mixture. The mixture was ball-milled with anhydrous ethanol as the ball milling medium, and then dried and ground. The ground material was sintered in an inert gas atmosphere, then cooled, ground and sieved to obtain sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material. The sintering process is as follows: heat to 350℃~400℃ at a heating rate of 10℃ / min and hold for 2h~4h; then heat to 450℃~550℃ at a heating rate of 5℃ / min and hold for 3h~5h; then heat to 600℃~700℃ at a heating rate of 2℃ / min and hold for 3h~6h.

[0017] Fourthly, this application provides a battery including a positive electrode prepared using the positive electrode material as described in any one of the third aspects.

[0018] It is understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant descriptions in the first aspect above, and will not be repeated here.

[0019] The advantages of this application compared to the prior art are: The iron phosphate-coated ferrous manganese oxalate hybrid phase material of this application includes ferrous manganese oxalate and iron phosphate coated with ferrous manganese oxalate, with the general chemical formula Fe. x Mn 1-x The C2O4 / FePO4 mixture, wherein 0.1 ≤ x ≤ 0.9, and the FePO4 content ≤ 10.3 wt%, consists of iron phosphate-coated ferromanganese oxalate hybrid phase materials composed of hexagonal particles with lengths ranging from 0.12 μm to 2.4 μm, widths ranging from 0.08 μm to 0.86 μm, and heights ranging from 0.04 μm to 0.65 μm. The hexagonal iron phosphate-coated ferrous manganese oxalate hybrid phase material has a large specific surface area and uniform hexagonal particle morphology, which increases the contact area between the cathode material and the electrolyte, thereby improving the ionic conductivity of the cathode material. Furthermore, the iron phosphate-coated ferrous manganese oxalate hybrid phase material uses ferrous manganese oxalate as the matrix, with iron phosphate coating the surface of the ferrous manganese oxalate matrix, achieving a compositional gradient design. This retains the high specific energy density of the cathode material while mitigating the problem of manganese leaching from the material surface, reducing the impact of manganese leaching, and improving the stability of the cathode material's cycle performance. In addition, the preparation method of the iron phosphate-coated ferrous manganese oxalate hybrid phase material in this application simplifies the process by controlling the amount of manganese salt added and adjusting the pH of the oxalate-containing mixed solution and the precursor solution to a suitable range, thus obtaining the iron phosphate-coated ferrous manganese oxalate hybrid phase material composed of hexagonal particles. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of an iron phosphate-coated ferrous manganese oxalate hybrid phase material provided in an embodiment of this application; Figure 2 This is a scanning electron microscope image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of Example 2 of this application; Figure 3 This is a scanning electron microscope image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of Example 3 of this application; Figure 4 This is a scanning electron microscope image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of Example 4 of this application; Figure 5 This is a scanning electron microscope image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of Example 5 of this application; Figure 6 This is a schematic diagram of the electrochemical cycle life test data of the lithium-ion battery prepared by lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material in Example 6 of this application at a current density of 0.2C; Detailed Implementation To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0022] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, a~b (i.e., a and b), a~c, b~c, or a~b~c, where a, b, and c can be single or multiple.

[0024] The terms "first" and "second" are used only to describe the purpose and to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the provisions of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0025] The terminology used in the embodiments of this application is for the purpose of describing particular implementations only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the implementations of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0026] It should be understood that in the various embodiments of this application, the sequence number of each process does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the implementation regulations of this application.

[0027] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0028] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application are available on the market or can be prepared by existing methods.

[0030] Currently, lithium iron manganese phosphate (LFP) has been prepared based on lithium iron phosphate and lithium manganese phosphate, which improves the low energy density problem of lithium iron phosphate and the low conductivity problem of lithium manganese phosphate. However, the conductivity of LFP is 10. -13 S / cm, with a conductivity of 10 for layered ternary materials. -3Compared to existing technologies, lithium iron phosphate (LFP) exhibits lower conductivity (S / cm), resulting in poorer electrochemical performance in lithium-ion batteries. Furthermore, manganese in LFP readily dissolves during charge and discharge, and trivalent manganese ions are prone to the John-Teller effect, leading to decreased cycle stability. Existing technologies using mechanical mixing or co-precipitation methods to prepare LFP precursors cannot achieve atomically uniform composite composition between the two phases, resulting in defects such as component segregation or high interfacial impedance. Moreover, severe particle agglomeration occurs, with the synthesized precursor particles being irregular nanoparticles, further exacerbating the John-Teller effect and reducing the electrochemical performance of lithium-ion batteries made from LFP.

[0031] In addition, sodium batteries prepared using iron phosphate and manganese phosphate as precursors, and sodium iron phosphate pyrophosphate manganese iron phosphate, also suffer from the problem of manganese leaching reducing the electrochemical performance of sodium batteries.

[0032] To address the aforementioned problems to some extent, such as Figure 1 As shown, the first aspect of this application provides an iron phosphate-coated ferrous manganese oxalate hybrid phase material (hereinafter referred to as: ferrous manganese oxalate / iron phosphate hybrid phase material), which includes ferrous manganese oxalate and iron phosphate coated with ferrous manganese oxalate, with the general chemical formula Fe. x Mn 1-xThe C2O4 / FePO4 mixture, wherein 0.1≤x≤0.9 and the FePO4 content≤10.3 wt%, is composed of hexagonal particles with a length of 0.12μm~2.4μm, a width of 0.08μm~0.86μm, and a height of 0.04μm~0.65μm. The hexagonal ferromanganese oxalate / ferric phosphate hybrid phase material has a large specific surface area, and the hexagonal particles have a uniform morphology, which increases the contact area between the cathode material prepared using the ferromanganese oxalate / ferric phosphate hybrid phase material and the electrolyte, thereby improving the lithium-ion or sodium-ion conductivity of the cathode material. Furthermore, the ferromanganese oxalate / ferric phosphate hybrid phase material uses ferromanganese oxalate as the matrix, with ferric phosphate coating the surface of the ferromanganese oxalate matrix, achieving a composition gradient design. Even if some manganese dissolves from the ferromanganese oxalate, the ferric phosphate entering the coating layer forms ferromanganese phosphate, thus retaining the high specific energy density advantage of the cathode material while mitigating the dissolution of manganese on the surface of the hybrid phase material. The problem of manganese dissolution was addressed, reducing the impact of manganese leaching and improving the stability of the cathode material's cycle performance. Furthermore, the length of the micro / nano-scale dimensions shortens the ion diffusion path, improving the material's rate performance; it increases the specific surface area, enhancing reactivity; it also reduces surface side reactions (such as electrolyte decomposition), thereby improving the cathode material's cycle stability; it further reduces the risk of particle agglomeration, improving the material's processing performance; the nanoscale width enhances anisotropy, promoting ion diffusion along specific crystal planes and improving the material's kinetic performance; and the nanoscale height significantly reduces ion diffusion resistance in the axial direction, mitigating the performance degradation caused by structural anisotropy.

[0033] Secondly, this application provides a method for preparing a ferrous manganese oxalate / ferric phosphate hybrid phase material, as described in the first aspect, comprising the following steps: S1, ferrous salt, manganese salt and antioxidant are added to deionized water, stirred and dissolved to obtain the first solution, wherein the molar ratio of iron to manganese in the first solution is 1:0.33~3; S2, under inert atmosphere and constant temperature conditions, add oxalate-containing solution to the first solution, and simultaneously add acid and first alkali solution to form oxalate-containing mixed solution. Adjust the pH of the oxalate-containing mixed solution to 2-7, stir to carry out precipitation reaction for 0.5-8 hours, let stand for aging for 0.5-6 hours, and then filter, wash and dry to obtain ferrous manganese oxalate precursor; S3, add ferric salt to deionized water, stir to dissolve, and obtain the second solution; S4, add the phosphate-containing reagent to deionized water, stir to dissolve, and obtain the third solution; S5, the ferrous manganese oxalate precursor obtained in step S2 is added to the second solution, stirred, and then the third solution is added, along with acid and the second alkali solution to form a precursor solution. The pH of the precursor solution is adjusted to 2.0~3.0. After stirring and reacting, the intermediate product is obtained by spray drying. S6. The intermediate product obtained in step S5 is placed in a box sintering furnace and dried at 120℃~250℃. After cooling, a hexagonal morphology of ferrous manganese oxalate / ferric phosphate hybrid phase material is obtained.

[0034] In this embodiment, the preparation method of the ferrous manganese oxalate / ferric phosphate hybrid phase material involves controlling the amount of manganese salt added via a liquid-phase method, adjusting the iron-manganese ratio to a preset ratio, and achieving atomic-level uniform mixing of manganese and iron elements and uniform coating of ferric phosphate on the surface of ferrous manganese oxalate through a continuous precipitation method. The pH values ​​of the oxalate-containing mixed solution and the precursor solution are adjusted to a preset range. Under the preset pH range and inert atmosphere, the oxidation of Fe is prevented. 2+ Oxidation to Fe 3+ Under supersaturation-driven conditions, Fe 2+ With C2O4 2- Rapidly combining to form micro-nuclei, these nuclei grow into hexagonal morphologies through Ostwald ripening. Low supersaturation promotes the anisotropic growth of ferrous manganese oxalate nuclei, forming regular hexagons. The growth rate of the top and bottom faces of the hexagons is slow, while the lateral growth rate is fast, resulting in a length dimension greater than the width and height. A small amount of ferric phosphate coats the surface of the hexagonal ferrous manganese oxalate, maintaining the hexagonal morphology without disrupting its structure. This yields a ferrous manganese oxalate / ferric phosphate hybrid phase material composed of hexagonal particles, simplifying the preparation process. The inert atmosphere in step S2 prevents ferrous Fe from escaping during stirring. 2+ The ions are oxidized to Fe by oxygen in the air. 3+ .

[0035] In one embodiment, the concentrations of iron and manganese in the first solution are both 0.1 mol / L to 4 mol / L, and the mass-volume concentration of the antioxidant in the first solution is 0.05 g / L to 10 g / L; the oxalate concentration in the oxalate-containing solution is 0.2 mol / L to 1.2 mol / L, the acid concentration is 0.5 mol / L to 3.5 mol / L, and the concentration of the first alkali solution is 0.3 mol / L to 2 mol / L; the precipitation reaction temperature is 45℃ to 65℃, and the rate of addition of the oxalate-containing solution is 20 mL / min to 50 mL / min; the concentration of ferric ions in the second solution is 0.2 mol / L to 1.5 mol / L, the concentration of phosphate ions in the third solution is 0.5 mol / L to 3.5 mol / L, and the concentration of the second alkali solution is 0.1 mol / L to 1 g / L. The reaction time for stirring in step S5 is 0.5 h to 4 h, and the spray drying device is a centrifugal spray dryer. Parameters that are too small or too large outside the range set in this embodiment will cause irregular hexagonal morphology of the ferrous manganese oxalate / ferric phosphate hybrid phase material.

[0036] In one embodiment, steps S2 and S5 are both carried out in a continuous coprecipitation reactor, which includes a first pipe, a second pipe, and a third pipe. In step S2, the first pipe is used to add an oxalate-containing solution to the first solution, the second pipe is used to add a first alkali solution to the first solution, and the third pipe is used to add an acid solution to the first solution. In step S5, since the addition rate and concentration of the oxalate-containing solution, acid solution, first alkali solution, third solution, and second alkali solution can be controlled individually through each pipe, the addition amount of the oxalate-containing solution, acid solution, first alkali solution, third solution, and second alkali solution can be precisely controlled. This allows for precise control of the pH value of the oxalate-containing mixed solution and the precursor solution, thereby controlling the morphology of the intermediate product of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material to form a more regular and hexagonal morphology of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material.

[0037] In one embodiment, the drying process in step S6 is as follows: the temperature is increased to 120°C to 250°C at a heating rate of 2°C / min to 10°C / min, and then kept at that temperature for 6h to 12h.

[0038] In one embodiment, the ferrous salt is a combination of one or more of ferrous sulfate, ferrous chloride, ferrous fluoroborate, and ferrous acetate; the manganese salt is a combination of one or more of manganese sulfate, manganese chloride, manganese acetate, and manganese formate; the antioxidant is a combination of one or more of sodium bisulfite, sodium thiosulfate, disodium ethylenediaminetetraacetate, sodium metabisulfite, and ascorbic acid; the inert atmosphere is a mixture of one or more of argon or nitrogen; the oxalate-containing solution is an aqueous solution including at least one of sodium oxalate, sodium hydrogen oxalate, potassium oxalate, and potassium hydrogen oxalate; the acid is a combination of one or more of dilute sulfuric acid, dilute hydrochloric acid, and acetic acid; the first alkaline solution is any one of ammonia, sodium hydroxide solution, and potassium hydroxide solution; the second alkaline solution is any one of ammonia and urea aqueous solution; the ferric salt is an aqueous solution including at least one of ferric citrate, ferric lactate, ferric formate, and ferric acetate; and the phosphate-containing reagent is a combination of one or more of phosphoric acid, ammonium monohydrogen phosphate, and ammonium dihydrogen phosphate.

[0039] Thirdly, this application provides a cathode material, which is either lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material or sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material. Both lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material and sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material use ferrous manganese oxalate / iron phosphate hybrid phase material as described in the first aspect as a precursor, or both use ferrous manganese oxalate / iron phosphate hybrid phase material obtained by the preparation method of iron phosphate / ferrous manganese oxalate hybrid phase material as described in any one of the second aspects as a precursor.

[0040] In one embodiment, the general chemical formula of the lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material is LiFe. x Mn 1-x PO4 / C, where 0.1≤x≤0.91, lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material includes lithium manganese iron phosphate, lithium iron phosphate coated on the surface of manganese iron phosphate, and a carbon layer coated on the surface of lithium iron phosphate, with a carbon layer thickness of 1nm~8nm.

[0041] In one embodiment, a method for preparing lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material includes: mixing a ferrous manganese oxalate / iron phosphate hybrid phase material as a precursor with lithium salt and ammonium dihydrogen phosphate to obtain a first precursor mixture; adding 2wt%~4wt% of carbon source by weight of the first precursor mixture; ball milling with anhydrous ethanol as the ball milling medium; drying and grinding the mixture; sintering the ground material in an inert gas atmosphere; and then cooling, grinding, and sieving to obtain lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material; the sintering process is as follows: heating to 300℃~350℃ at a heating rate of 10℃ / min and holding for 2h~4h; then heating to 450℃~550℃ at a heating rate of 5℃ / min and holding for 3h~5h; and then heating to 600℃~700℃ at a heating rate of 2℃ / min and holding for 1h~3h.

[0042] It should be noted that during the sintering process of preparing lithium iron phosphate@lithium manganese iron phosphate / carbon cathode materials, high-temperature sintering is carried out under the protection of inert gases (such as N2, Ar), during which the material undergoes phase transformation and chemical reactions, and ferrous manganese oxalate (Fe) is produced. x Mn 1- x C2O4) undergoes thermal decomposition first at high temperatures: oxalate is unstable upon heating, releasing gaseous products (mainly CO, CO2, and H2O (if water of crystallization is present)). Ferrous manganese oxalate decomposes into ferromanganese oxide ((Fe, Mn)O) and escapes as gas. Simultaneously, other components also react: ammonium dihydrogen phosphate (NH4H2PO4) decomposes, releasing NH3 and H2O, ultimately providing PO4. 3- Source. Lithium salts (such as Li₂CO₃) decompose to provide Li. + The carbon source undergoes pyrolysis to form amorphous carbon or carbon with a low degree of graphitization, which coats the particle surface and / or fills the spaces between particles. Iron phosphate (FePO4) reacts with lithium salts to form lithium iron phosphate (LiFePO4). The ferrous manganese oxide ((Fe, Mn)O) produced during decomposition reacts with the surrounding lithium source (Li). + ) and phosphate source (PO4) 3- A solid-state reaction occurs, producing lithium manganese iron phosphate (LiMn). x Fe 1-x PO4). The coating structure also evolved accordingly, with the precursor core (ferrous manganese oxalate) decomposing and reacting to generate LiMn. x Fe 1-x PO4. The precursor shell (iron phosphate) reacts with lithium salt to form LiFePO4. Since the precursor structure is "iron phosphate coated with ferrous manganese oxalate," after sintering, LiMn is formed under the proposed preparation method. x Fe 1-xThe structure of a PO4 core (high manganese content, high operating voltage) coated with a LiFePO4 shell (high iron content, high stability / conductivity) is known as "lithium manganese iron phosphate@lithium iron phosphate". Carbon formed by the pyrolysis of the carbon source uniformly coats the entire surface of the composite material particles and / or fills the spaces between the particles, forming a conductive network, thus obtaining the lithium iron phosphate@lithium manganese iron phosphate / carbon cathode material.

[0043] In existing technologies, sodium-ion batteries utilize a cathode material made of sodium iron pyrophosphate (NFPP). NFPP is a composite polyanionic cathode material for sodium-ion batteries, possessing high reversible specific capacity and long cycle life. However, NFPP has low intrinsic electronic conductivity (approximately 10⁻⁶). -10 The conductivity of NFPP cathode materials (S / cm) results in poor rate performance of sodium-ion batteries. Existing technologies improve the conductivity of NFPP cathode materials through carbon coating, utilizing Mn... 2+ Partial Fe replacement 2+ Adjusting lattice parameters to enhance Na + The diffusion rate of NFPP cathode materials can be improved, thereby enhancing the rate performance of sodium-ion batteries. However, using iron phosphate and manganese phosphate as precursors, traditional solid-state methods struggle to achieve highly homogenized and directional doping of iron and manganese, and it is difficult to control the particle size and morphology of the product. Sol-gel or hydrothermal methods can improve material uniformity, but process control is challenging and yields are low. Co-precipitation methods can achieve uniform distribution of manganese and iron in NFPP, but the dissolution of Mn leads to capacity decay and reduced cycle performance.

[0044] In one embodiment, the general chemical formula of the sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material is Na₄(Fe₂O₃)₂. x Mn 1-x The cathode material is 3(PO4)2P2O7 / C, where 0.82≤x≤0.91. The sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material includes sodium manganese pyrophosphate, sodium iron pyrophosphate coated on the surface of the sodium manganese pyrophosphate, and a carbon layer coated on the surface of the sodium iron pyrophosphate, with a carbon layer thickness of 1nm~8nm. Using the sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material of this embodiment can reduce the dissolution of manganese and improve the electrochemical performance of sodium-ion batteries.

[0045] In one embodiment, a method for preparing sodium manganese ferric pyrophosphate@sodium iron pyrophosphate / carbon cathode material includes: mixing a ferrous manganese oxalate / ferric phosphate hybrid phase material as a precursor with sodium salt and ammonium dihydrogen phosphate to obtain a second precursor mixture; adding 2wt%~4wt% of carbon source by weight of the second precursor mixture; ball milling with anhydrous ethanol as the ball milling medium; drying and grinding the mixture; sintering the ground material under an inert gas atmosphere; and then cooling, grinding, and sieving to obtain sodium manganese ferric pyrophosphate@sodium iron pyrophosphate / carbon cathode material; the sintering process is as follows: using... The temperature was increased to 350℃~400℃ at a heating rate of 10℃ / min and held for 2h~4h; then increased to 450℃~550℃ at a heating rate of 5℃ / min and held for 3h~5h; then increased to 600℃~700℃ at a heating rate of 2℃ / min and held for 3h~6h. The sodium iron manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material prepared in this embodiment reduced the dissolution of manganese and improved the electrochemical performance of sodium-ion batteries. The specific sintering formation principle is similar to that of lithium iron phosphate@lithium iron manganese phosphate / carbon cathode material and will not be described in detail here.

[0046] The technical solution of this application will be illustrated below through specific embodiments and comparative examples.

[0047] Example 1; A ferrous manganese oxalate / ferric phosphate hybrid material, comprising ferrous manganese oxalate and ferric phosphate coated with ferrous manganese oxalate, has the general chemical formula (Fe). 0.5 Mn 0.5 )PO4 / FePO4, where, x The FePO4 content is ≤10.3 wt%. The ferrous manganese oxalate / ferric phosphate hybrid phase material is composed of hexagonal particles with a length of 0.12μm~2.4μm, a width of 0.08μm~0.86μm, and a height of 0.04μm~0.65μm.

[0048] Example 2; A method for preparing a ferrous manganese oxalate / ferric phosphate hybrid phase material includes the following steps: S1, dissolve 2 mol of ferrous salt FeSO4•7H2O and 2 mol of manganese salt MnSO4•H2O in 1 L of deionized water, then add 5 g of ascorbic acid (antioxidant), stir and dissolve to obtain the first solution, wherein the molar ratio of iron to manganese in the first solution is 1:1.

[0049] S2, the first solution is added to a continuous co-precipitation reactor. Stirring continues under an argon atmosphere and a constant temperature of 50°C. A 1 mol / L (NH4)C2O4•H2O solution (containing oxalate) is added to the first solution through the first pipe. Simultaneously, 0.5 mol / L ammonia water (NH3•H2O) (the first alkaline solution) and 1 mol / L dilute sulfuric acid (acid solution) are added through the second and third pipes respectively to form a mixed solution containing oxalate. The pH of the mixed solution containing oxalate is adjusted to 5.0 (with a deviation of 0.05, i.e., pH 4.95~5.05). Stirring is continued at 500 rpm until the (NH4)C2O4•H2O solution addition is complete, followed by a 2-hour precipitation reaction. The mixture is then allowed to stand for 1 hour, and after pressure filtration, washing, and drying, a pale yellow powdery ferrous manganese oxalate precursor is obtained. The chemical formula of the ferrous manganese oxalate precursor is Fe. 0.5 Mn 0.5 C2O4•2H2O, wherein drying involves transferring the washed ferrous manganese oxalate precursor to a vacuum drying oven at 80°C and drying for 12 hours.

[0050] S3. Add 0.5 mol / L of ferric citrate (a ferric salt) to deionized water, stir to dissolve, and obtain the second solution.

[0051] S4. Add 2 mol / L ammonium dihydrogen phosphate, a phosphate-containing reagent, to deionized water, stir to dissolve, and obtain the third solution.

[0052] S5, the ferrous manganese oxalate precursor obtained in step S2 is added to the second solution, stirred, and then the third solution is added, along with the second alkali solution to form a precursor solution. The pH of the precursor solution is adjusted to 2.0. After stirring and reacting, the intermediate product is obtained by spray drying. The molar ratio of manganese to iron in the second solution is 4:6.

[0053] S6. The intermediate product obtained in step S5 is placed in a box sintering furnace for drying and cooling to obtain a hexagonal morphology iron phosphate-coated ferrous manganese oxalate hybrid phase material (i.e., ferrous manganese oxalate / iron phosphate hybrid phase material), with the general chemical formula Fe. 0.5 Mn 0.5 C2O4 / FePO4; The drying process in step S6 is as follows: the temperature is increased to 120℃~250℃ at a heating rate of 2℃ / min~10℃ / min, and then kept at that temperature for 6h~12h.

[0054] Figure 2 Here is a scanning electron microscope (SEM) image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of this embodiment, as shown below. Figure 2As shown, the morphology of the iron phosphate-coated ferrous manganese oxalate hybrid phase material is a regular hexagonal cube (i.e., hexagonal). The aggregation phenomenon of iron phosphate-coated ferrous manganese oxalate is suppressed, and the distribution is relatively regular. This morphological distribution increases the specific surface area of ​​the iron phosphate-coated ferrous manganese oxalate hybrid phase material, provides more diffusion paths and channels for lithium ion transport, and reduces the influence of manganese dissolution, thereby improving the electrochemical performance of the cathode material prepared using the iron phosphate-coated ferrous manganese oxalate hybrid phase material as a precursor.

[0055] Example 3: The difference from Example 2 is that in step S2, the pH of the mixed solution containing oxalate is adjusted to 6.0 (with a deviation of 0.05, i.e., pH value of 5.95~6.05). The chemical formula of the ferrous manganese oxalate precursor is Fe. 0.4 Mn 0.6 C2O4•2H2O, the molar ratio of iron to manganese in the first solution is 4:6, and the molar ratio of manganese to iron in the second solution in step S5 is 5:5. The remaining steps are the same as in Example 2.

[0056] Figure 3 Here is a scanning electron microscope (SEM) image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of this embodiment, as shown below. Figure 3 As shown, the morphology of the iron phosphate-coated ferrous manganese oxalate hybrid phase material is a regular hexagonal cube shape. The aggregation phenomenon of iron phosphate-coated ferrous manganese oxalate is suppressed, and the distribution is relatively regular. This morphological distribution increases the specific surface area of ​​the iron phosphate-coated ferrous manganese oxalate hybrid phase material, provides more diffusion paths and channels for lithium ion transport, and reduces the influence of manganese dissolution, thereby improving the electrochemical performance of the cathode material prepared using the iron phosphate-coated ferrous manganese oxalate hybrid phase material as a precursor.

[0057] Example 4: The difference from Example 2 is that in step S2, the pH of the oxalate-containing mixed solution is adjusted to 7.0 (with a deviation of 0.05, i.e., pH 6.95~7.05). The chemical formula of the ferrous manganese oxalate precursor is Fe. 0.3 Mn 0.7 C2O4•2H2O, the molar ratio of iron to manganese in the first solution is 3:7, the molar ratio of manganese to iron in the second solution in step S5 is 6:4, and the remaining steps are the same as in Example 2.

[0058] Figure 4 Here is a scanning electron microscope (SEM) image of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material of this embodiment, as shown below. Figure 4 As shown, the cubic morphology of the iron phosphate-coated ferrous manganese oxalate hybrid phase material begins to break down, with small fragments appearing. The crystallization of the iron phosphate-coated ferrous manganese oxalate hybrid phase material is incomplete and has poor crystallinity.

[0059] Example 5: The difference from Example 2 is that there are only steps S1 and S2. In step S2, the pH value of the mixed solution containing oxalate is adjusted to 4.0 (with a deviation of 0.05, i.e., the pH value is 3.95~4.05). The rest of the steps S1 and S2 are the same as in Example 2, and there are no subsequent steps S3, S4, S5 and S6.

[0060] Figure 5 Here is a scanning electron microscope image of the ferrous manganese oxalate precursor in this embodiment, as shown below. Figure 5 As shown, the morphology of the ferrous manganese oxalate hybrid phase material is a hexagonal cubic shape, but the particle size uniformity of ferrous manganese oxalate is inconsistent, and some ferrous manganese oxalate exhibits agglomeration.

[0061] Example 6; Methods for preparing lithium manganese iron phosphate@lithium iron phosphate / carbon cathode materials include: The ferrous manganese oxalate / iron phosphate hybrid phase material obtained in Example 2 was used as a precursor and mixed with lithium salt Li2CO3 and ammonium dihydrogen phosphate (NH4H2PO4) in a molar ratio of 2:1:2 to obtain a first precursor mixture. Then, 3 wt% of glucose (carbon source) was added to the first precursor mixture, and the mixture was ball-milled with anhydrous ethanol as the ball milling medium at a speed of 300 rpm for 4 hours. After drying and grinding, the washed ferrous manganese oxalate precursor was transferred to a vacuum drying oven at 80°C and dried for 12 hours. The ground material was sintered in a tube furnace under an argon atmosphere, then cooled, ground, and sieved to obtain lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material with the chemical formula LiFe. 0.6 Mn 0.4 PO4 / C; The sintering process is as follows: the temperature is increased to 300℃ at a heating rate of 10℃ / min and held for 3 hours; then the temperature is increased to 500℃ at a heating rate of 5℃ / min and held for 4 hours; then the temperature is increased to 700℃ at a heating rate of 2℃ / min and held for sintering for 6 hours.

[0062] Using the lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material obtained in Example 6 as the active material, super carbon as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder, the active material, conductive agent, and binder were mixed and uniformly coated on aluminum foil. After drying, a cathode sheet was formed. The mass ratio of lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material, super carbon, and polyvinylidene fluoride was 90:5:5. The cathode sheet, a negative electrode sheet, a separator (Celgard2400), and an electrolyte were used to prepare a lithium-ion battery. The electrolyte was a 1 mol / L solution of LiPF6 / ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1.

[0063] Figure 6A schematic diagram illustrating the electrochemical cycle life test data of a lithium-ion battery prepared using lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material at a 1C current density, as shown below. Figure 6 As shown, the lithium-ion battery prepared using lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material achieved an initial discharge capacity of 144.2 mAh / g at a current density of 0.2C, and a discharge capacity of 133 mAh / g after 100 cycles, with a cycle retention rate of 92.23%. This indicates that the cathode material prepared using the hexagonal morphology of the ferrous manganese oxalate / iron phosphate hybrid phase material as a precursor in this embodiment exhibits a high discharge capacity at a current density of 0.2C. Simultaneously, the cathode material prepared using the hexagonal morphology of the ferrous manganese oxalate / iron phosphate hybrid phase material as a precursor demonstrates excellent cycle performance, achieving a retention rate of 92.23% after 100 cycles. Due to the modification of the precursor morphology and the control of the hybrid phase process, the energy density and cycle stability of the lithium battery were improved.

[0064] Example 7; Methods for preparing sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode materials include: S1, dissolve 0.85 mol of ferrous salt FeSO4•7H2O and 0.15 mol of manganese salt MnSO4•H2O in 1 L of deionized water, then add 5 g of ascorbic acid (antioxidant), stir to dissolve, and obtain the first solution, wherein the molar ratio of iron to manganese in the first solution is 0.85:0.15.

[0065] S2, the first solution is added to a continuous co-precipitation reactor. Stirring continues under an argon atmosphere and a constant temperature of 50°C. A 1 mol / L (NH4)C2O4•H2O solution (containing oxalate) is added to the first solution through the first pipe. Simultaneously, 0.5 mol / L ammonia water (NH3•H2O) (the first alkaline solution) and 1 mol / L dilute sulfuric acid (acid solution) are added through the second and third pipes respectively to form a mixed solution containing oxalate. The pH of the mixed solution containing oxalate is adjusted to 6.0 (with a deviation of 0.05, i.e., pH 5.95~6.05). Stirring is continued at 500 rpm until the (NH4)C2O4•H2O solution addition is complete, followed by a 2-hour precipitation reaction. The mixture is then allowed to stand for 1 hour, and after pressure filtration, washing, and drying, a pale yellow powdery ferrous manganese oxalate precursor is obtained. The chemical formula of the ferrous manganese oxalate precursor is Fe. 0.85 Mn 0.15 C2O4•2H2O, wherein drying involves transferring the washed ferrous manganese oxalate precursor to a vacuum drying oven at 80°C and drying for 12 hours.

[0066] S3. Add 0.5 mol / L of ferric citrate (a ferric salt) to deionized water, stir to dissolve, and obtain the second solution.

[0067] S4. Add 2 mol / L ammonium dihydrogen phosphate, a phosphate-containing reagent, to deionized water, stir to dissolve, and obtain the third solution.

[0068] S5, the ferrous manganese oxalate precursor obtained in step S2 is added to the second solution, stirred, and then the third solution is added, along with the second alkali solution to form a precursor solution. The pH of the precursor solution is adjusted to 2.0. After stirring and reacting, the intermediate product is obtained by spray drying. The molar ratio of manganese to iron in the second solution is 1:9.

[0069] S6. The intermediate product obtained in step S5 is placed in a box sintering furnace for drying and cooling to obtain a hexagonal morphology of iron phosphate coated with ferrous manganese oxalate hybrid phase material. The drying process in step S6 is as follows: the temperature is increased to 120℃~250℃ at a heating rate of 2℃ / min~10℃ / min, and then kept at that temperature for 6h~12h.

[0070] The iron phosphate-coated ferrous manganese oxalate hybrid precursor obtained in this embodiment was mixed with sodium salt Na2CO3 and ammonium dihydrogen phosphate (NH4H2PO4) in a molar ratio of 3:2:4 to obtain a second precursor mixture. Then, 3 wt% of glucose (carbon source) was added to the second precursor mixture, and the mixture was ball-milled using anhydrous ethanol as the ball milling medium at a speed of 300 rpm for 4 hours. The mixture was then dried and ground. Drying involved transferring the washed ferrous manganese oxalate precursor to a vacuum drying oven at 80°C for 12 hours. The ground material was sintered in a tube furnace under an argon atmosphere, then cooled, ground, and sieved to obtain sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material with the chemical formula Na4(Fe2O3)2. 0.9 Mn 0.1 )3(PO4)2P2O7 / C; The sintering process is as follows: the temperature is increased to 300℃ at a heating rate of 10℃ / min and held for 2 hours; then the temperature is increased to 500℃ at a heating rate of 5℃ / min and held for 4 hours; then the temperature is increased to 650℃ at a heating rate of 2℃ / min and held for 4 hours.

[0071] Using the sodium manganese ferric pyrophosphate@sodium iron pyrophosphate / carbon cathode material obtained in Example 7 as the active material, super carbon as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder, the active material, conductive agent, and binder were mixed and uniformly coated on aluminum foil. After drying, a cathode sheet was formed. The mass ratio of sodium manganese ferric pyrophosphate@sodium iron pyrophosphate / carbon cathode material, super carbon, and polyvinylidene fluoride was 90:5:5. The cathode sheet, negative electrode sheet, separator (Celgard2400), and electrolyte were used to prepare a sodium-ion battery. The electrolyte was a 1 mol / L solution of NaPF6 / ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of EC to DMC of 1:1.

[0072] The sodium-ion battery prepared with sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material achieved an initial discharge capacity of 112 mAh / g at a current density of 0.1C, and a discharge capacity of 107.52 mAh / g after 100 cycles, with a cycle retention rate of 96%.

[0073] Comparative Example 1 Ferrous oxalate, manganese acetate, Li₂CO₃, and NH₄H₂PO₄ were added to a ball mill jar in a molar ratio of 0.6:0.4:0.5:1, with the iron-manganese molar ratio being 6:4. 3 wt% glucose was added as a carbon source to the mixture of ferrous oxalate, manganese acetate, Li₂CO₃, and NH₄H₂PO₄. Anhydrous ethanol was used as the milling medium. The milling speed was 300 rpm for 4 h. The milled mixture was then placed in an 80℃ vacuum drying oven and vacuum dried for 12 h. Finally, the dried material was ground and placed in a tube furnace under Ar atmosphere protection. It was held at 300℃ for 3 h, then heated to 500℃ and held for 4 h, followed by sintering at 700℃ for 6 h. After cooling in the furnace, the material was ground and sieved to obtain LiFe. 0.6 Mn 0.4 PO4 / C cathode material.

[0074] A lithium-ion battery was prepared using the lithium manganese iron phosphate / carbon cathode material obtained by the solid-state method, and the method for preparing the lithium-ion battery was the same as in Example 6. The lithium-ion battery prepared using the lithium manganese iron phosphate / carbon cathode material obtained by the solid-state method in this comparative example was subjected to electrochemical cycle life testing at a current density of 0.2C. The test results were as follows: the initial discharge capacity was 127 mAh / g, and after 100 cycles, the discharge capacity was 115.1 mAh / g, with a cycle retention rate of 90.63%. The lithium manganese iron phosphate material prepared by the solid-state method had a lower discharge capacity at a current density of 0.2C than the material in Example 6, and its cycle retention rate was also lower than that of Example 6.

[0075] Comparative Example 2 Ferrous oxalate, manganese acetate, Na₂CO₃, and NH₄H₂PO₄ were added to a ball mill jar in a molar ratio of 2.7:0.3:2:4, with an iron-manganese molar ratio of 9:1. 3wt% glucose was added as the carbon source to the mixture of ferrous oxalate, manganese acetate, Na₂CO₃, and NH₄H₂PO₄, and anhydrous ethanol was used as the ball milling medium. The ball milling speed was 300 rpm for 4 h. The milled mixture was then placed in an 80℃ vacuum drying oven and vacuum dried for 12 h. Finally, the dried material was ground and placed in a tube furnace under an Ar atmosphere. It was held at 300℃ for 2 h, then heated to 500℃ and held for 4 h, then heated to 650℃ and held for 4 h. After cooling in the furnace, the material was ground, sieved, and Na₄(Fe)₂O₃ was obtained. 0.9 Mn 0.1 )3(PO4)2P2O7 / C cathode material.

[0076] Sodium-manganese iron sodium pyrophosphate / carbon cathode material prepared by solid-state method was used to prepare a sodium-ion battery, and the preparation method was the same as in Example 7. Sodium-manganese iron sodium pyrophosphate / carbon cathode material prepared by solid-state method in this comparative example was also used to prepare a sodium-ion battery, and the preparation method was the same as in Example 7. The lithium-ion battery prepared from the sodium-manganese iron sodium pyrophosphate / carbon cathode material obtained by solid-state method in this comparative example underwent electrochemical cycle life testing at a current density of 0.1C. The test results were: initial discharge capacity of 105 mAh / g, discharge capacity of 96.6 mAh / g after 100 cycles, and cycle retention rate of 92%. The discharge capacity of the sodium-manganese iron sodium pyrophosphate / carbon material prepared by solid-state method at a current density of 0.1C is lower than that of the material in Example 7, and the cycle retention rate is also lower than that of Example 7.

[0077] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0078] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0079] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be included within the protection scope of this application.

Claims

1. A ferric phosphate-coated ferrous manganese oxalate hybrid phase material, characterized in that, Ferric phosphate-coated ferrous manganese oxalate hybrid materials include ferrous manganese oxalate and ferric phosphate coated with ferrous manganese oxalate, with the general chemical formula Fe. x Mn 1-x The C2O4 / FePO4 material, wherein 0.1≤x≤0.9 and the FePO4 content≤10.3 wt%, is composed of hexagonal particles with a length of 0.12μm~2.4μm, a width of 0.08μm~0.86μm, and a height of 0.04μm~0.65μm.

2. A method for preparing ferric phosphate-coated ferrous manganese oxalate hybrid phase material, characterized in that, The preparation of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material as described in claim 1 includes the following steps: S1, ferrous salt, manganese salt and antioxidant are added to deionized water, stirred and dissolved to obtain the first solution, wherein the molar ratio of iron to manganese in the first solution is 1:0.33~3; S2, under inert atmosphere and constant temperature conditions, add oxalate-containing solution to the first solution, and simultaneously add acid and first alkali solution to form oxalate-containing mixed solution. Adjust the pH of the oxalate-containing mixed solution to 2-7, stir to carry out precipitation reaction for 0.5-8 hours, let stand for aging for 0.5-6 hours, and then filter, wash and dry to obtain ferrous manganese oxalate precursor; S3, add ferric salt to deionized water, stir to dissolve, and obtain the second solution; S4, add the phosphate-containing reagent to deionized water, stir to dissolve, and obtain the third solution; S5, the ferrous manganese oxalate precursor obtained in step S2 is added to the second solution, stirred, and then the third solution is added, along with acid and the second alkali solution to form a precursor solution. The pH of the precursor solution is adjusted to 2.0~3.

0. After stirring and reacting, the intermediate product is obtained by spray drying. S6. The intermediate product obtained in step S5 is placed in a box sintering furnace and dried at 120℃~250℃. After cooling, a hexagonal morphology iron phosphate coated ferrous manganese oxalate hybrid phase material is obtained.

3. The preparation method of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material as described in claim 2, characterized in that, The concentrations of iron and manganese in the first solution are both 0.1 mol / L to 4 mol / L, and the mass-volume concentration of the antioxidant in the first solution is 0.05 g / L to 10 g / L. The oxalate concentration of the oxalate-containing solution is 0.2 mol / L to 1.2 mol / L, the concentration of the acid solution is 0.5 mol / L to 3.5 mol / L, and the concentration of the first alkaline solution is 0.3 mol / L to 2 mol / L. The precipitation reaction temperature is 45℃~65℃, and the rate of adding oxalate-containing solution is 20mL / min~50mL / min; The concentration of ferric ions in the second solution is 0.2 mol / L to 1.5 mol / L, and the concentration of phosphate ions in the third solution is 0.5 mol / L to 3.5 mol / L. The concentration of the second alkali solution is 0.1~1 mol / L, the reaction time of the stirring reaction in step S5 is 0.5h~4h, and the spray drying device is a centrifugal spray dryer.

4. The preparation method of the ferric phosphate-coated ferrous manganese oxalate hybrid phase material as described in claim 2, characterized in that, Ferrous salts are one or more of ferrous sulfate, ferrous chloride, ferrous fluoroborate, and ferrous acetate. Manganese salts are one or more of manganese sulfate, manganese chloride, manganese acetate, and manganese formate. The antioxidant is one or more of the following: sodium bisulfite, sodium thiosulfate, disodium ethylenediaminetetraacetate, sodium metabisulfite, and ascorbic acid. The inert atmosphere is one or a mixture of argon or nitrogen; The oxalate-containing solution is an aqueous solution containing at least one of sodium oxalate, sodium hydrogen oxalate, potassium oxalate, and potassium hydrogen oxalate. The acid solution is one or more of dilute sulfuric acid, dilute hydrochloric acid, and acetic acid; The first alkaline solution is any one of ammonia water, sodium hydroxide solution, or potassium hydroxide solution; The second alkaline solution is either ammonia water or urea water solution; The ferric salt is an aqueous solution containing at least one of ferric citrate, ferric lactate, ferric formate, and ferric acetate; The phosphate-containing reagent is a combination of one or more of phosphoric acid, monoammonium hydrogen phosphate, and diammonium hydrogen phosphate.

5. A positive electrode material, characterized in that, The cathode material is lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material or sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material. Both lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material and sodium manganese iron pyrophosphate@sodium iron pyrophosphate / carbon cathode material use iron phosphate coated ferrous manganese oxalate hybrid phase material as described in claim 1 as a precursor, or both use iron phosphate coated ferrous manganese oxalate hybrid phase material prepared by the preparation method of iron phosphate coated ferrous manganese oxalate hybrid phase material as described in any one of claims 2 to 4 as a precursor.

6. The cathode material as described in claim 5, characterized in that, The general chemical formula for lithium manganese iron phosphate @ lithium iron phosphate / carbon cathode material is LiFe x Mn 1-x PO4 / C, where 0.1≤x≤0.91, lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material includes lithium manganese iron phosphate, lithium iron phosphate coated on the surface of lithium manganese iron phosphate, and a carbon layer coated on the surface of lithium iron phosphate, with a carbon layer thickness of 1nm~8nm.

7. The cathode material as described in claim 6, characterized in that, Methods for preparing lithium manganese iron phosphate@lithium iron phosphate / carbon cathode materials include: The iron phosphate-coated ferrous manganese oxalate hybrid phase material was used as a precursor and mixed with lithium salt and ammonium dihydrogen phosphate to obtain a first precursor mixture. Then, 2wt%~4wt% of carbon source was added to the first precursor mixture. The mixture was ball-milled with anhydrous ethanol as the ball milling medium, and then dried and ground. The ground material was sintered in an inert gas atmosphere, and then cooled, ground and sieved to obtain lithium manganese iron phosphate@lithium iron phosphate / carbon cathode material. The sintering process is as follows: heat up to 300℃~350℃ at a heating rate of 10℃ / min and hold for 2h~4h; then heat up to 450℃~550℃ at a heating rate of 5℃ / min and hold for 3h~5h; then heat up to 600℃~700℃ at a heating rate of 2℃ / min and hold for 1h~3h.

8. The cathode material as described in claim 5, characterized in that, Sodium manganese pyrophosphate @ sodium iron pyrophosphate / carbon cathode material has the general chemical formula Na₄(Fe) x Mn 1-x )3(PO4)2P2O7 / C, where 0.82≤x≤0.91, sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material includes sodium manganese pyrophosphate, sodium iron pyrophosphate coated on the surface of sodium manganese pyrophosphate, and a carbon layer coated on the surface of sodium iron pyrophosphate, with a carbon layer thickness of 1nm~8nm.

9. The cathode material as described in claim 8, characterized in that, Methods for preparing sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode materials include: Ferric phosphate-coated ferrous manganese oxalate hybrid phase material was used as a precursor and mixed with sodium salt and ammonium dihydrogen phosphate to obtain a second precursor mixture. Then, 2wt%~4wt% of carbon source was added to the second precursor mixture. The mixture was ball-milled with anhydrous ethanol as the ball milling medium, and then dried and ground. The ground material was sintered in an inert gas atmosphere, then cooled, ground and sieved to obtain sodium manganese pyrophosphate@sodium iron pyrophosphate / carbon cathode material. The sintering process is as follows: heat to 350℃~400℃ at a heating rate of 10℃ / min and hold for 2h~4h; then heat to 450℃~550℃ at a heating rate of 5℃ / min and hold for 3h~5h; then heat to 600℃~700℃ at a heating rate of 2℃ / min and hold for 3h~6h.

10. A battery, characterized in that, This includes using the cathode material as described in any one of claims 5 to 9.

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