Lithium manganese iron phosphate material and preparation method therefor, positive electrode material and secondary battery

Abstract

The present disclosure relates to the technical field of battery materials, and particularly to a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode material and a secondary battery The preparation method for the lithium manganese iron phosphate material includes steps of: (a) mixing a first solution including a lithium source and a second solution including a phosphorus source, and adjusting pH to range from 6 to 9, so as to render a mixed solution, where the lithium source includes at least one of lithium carbonate and lithium dihydrogen phosphate; (b) adding a third solution including a divalent manganese source and a divalent iron source into the mixed solution, and performing a thermal-insulation reaction at 90 °C to 100 °C; and (c) performing solid-liquid separation on a material having undergone the reaction in step (b), and collecting and drying a solid, so as to render the lithium manganese iron phosphate material. The present disclosure can realize synthesis of the lithium manganese iron phosphate material with high crystallinity and without carbon coating, under a condition of normal pressure and low temperature, by adopting suitable reaction raw materials, without using high-pressure equipment, thus having low energy consumption and high yield, and being more suitable for industrial production.

Description

LITHIUM MANGANESE IRON PHOSPHATE MATERIAL AND PREPARATION METHOD THEREFOR, POSITIVE ELECTRODE MATERIAL AND SECONDARY BATTERY

[0001] The present disclosure claims the priority to the Singaporean patent application with the filing No. 10202500212P filed on January 23, 2025 with the Singaporean Patent Office, and entitled “LITHIUM MANGANESE IRON PHOSPHATE MATERIAL AND PREPARATION METHOD THEREFOR, POSITIVE ELECTRODE MATERIAL AND SECONDARY BATTERY”, the contents of which are incorporated herein by reference in entirety.TECHNICAL FIELD

[0002] The present disclosure relates to the technical field of battery materials, and particularly to a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode material and a secondary battery.BACKGROUND ART

[0003] Secondary batteries are widely applied in various electronic devices due to characteristics such as high capacity and long service lifetime. With the application and promotion of the secondary batteries, demands for performance of the secondary batteries are also gradually increasing Lithium manganese iron phosphate positive electrode material, due to good cycle performance, high energy density and good low-temperature performance, has become one of the most concerned positive electrode active materials

[0004] The existing preparation processes of lithium manganese iron phosphate mainly include a solid phase method, a hydrothermal (solvothermal) method, a sol-gel method, and so on. However, the lithium manganese iron phosphate material prepared by the solid phase method is difficult to control in morphology and dimension, and has poor uniformity and serious agglomeration, thus affecting exertion of electrochemical performance thereof The hydrothermal (solvothermal) method needs to be implemented under a high-temperature high-pressure condition, and the sol-gel method has a long production cycle, both of which are not conducive to large-scale efficient production.SUMMARY

[0005] Tn the first aspect, the present disclosure provides a preparation method for a lithium manganese iron phosphate material, including steps of:

[0006] (a) mixing a first solution including a lithium source and a second solution including a phosphorus source, and adjusting pH to range from 6 to 9, so as to render a mixed solution, where the lithium source includes at least one of lithium carbonate and lithium dihydrogen phosphate;

[0007] (b) adding a third solution including a divalent manganese source and a divalent iron source into the mixed solution, and performing a thermal-insulation reaction at 90 °C to 100 °C; and

[0008] (c) performing solid-liquid separation on a material having undergone the reaction in step (b), and collecting and drying a solid, so as to render the lithium manganese iron phosphate material.

[0009] In some embodiments, the phosphorus source includes at least one of phosphoric acid and lithium dihydrogen phosphate.

[0010] Tn some embodiments, the th erm al -insulation reaction is performed at normal pressure.

[0011] In some embodiments, duration of the thermal-insulation reaction ranges from 3 h to 8 h. Further, the thermal-insulation reaction is accompanied by stirring; and a speed of the stirring ranges from 50 rpm to 400 rpm.

[0012] In some embodiments, the first solution, the second solution and the third solution use water as a solvent.

[0013] In some embodiments, in step (b), the third solution is added into the mixed solution dropwise; and duration of the dropwise addition ranges from 0.5 h to 3 h.

[0014] In some embodiments, a molar ratio of a total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the lithium source in terms of Li+is 1: (3-3.3); and a molar ratio of the total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the phosphorus source in terms of POfi' is 1: (0.9- 1.2).

[0015] In some embodiments, a molar ratio of the divalent manganese source in terms of Mn2+to the divalent iron source in terms of Fe2+ranges from 1: 9 to 9: 1

[0016] In some embodiments, in the first solution, a molar concentration of the lithium source ranges from 1 mol / L to 3 mol / L; and in the third solution, a total molar concentration of the divalent manganese source and the divalent iron source ranges from 1 mol / L to 3 mol / L.

[0017] Tn some embodiments, the divalent manganese source includes at least one of manganous sulfate, manganous chloride, manganese acetate and manganese nitrate, and the divalent iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous acetate and ferrous nitrate.

[0018] In the second aspect, the present disclosure provides a lithium manganese iron phosphate material prepared by the preparation method of the first aspect.

[0019] In some embodiments, BET specific surface area of the lithium manganese iron phosphate material ranges from 4.1 m2 / g to 18.7 m2 / g, and a tap density ranges from 0.92 g / cm3to 1.21 g / cm3.

[0020] In the third aspect, the present disclosure provides a positive electrode material made from the lithium manganese iron phosphate material prepared by the preparation method of the first aspect.

[0021] In the fourth aspect, the present disclosure provides a secondary battery, including a positive electrode plate, where the positive electrode plate includes the positive electrode material according to any embodiments of the third aspect of the present disclosureBRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate technical solutions in embodiments of the present disclosure or the prior art, drawings which need to be used in the description of the embodiments or the prior art will be briefly introduced below. Apparently, the drawings in the following description show some embodiments of the present disclosure, and those ordinarily skilled in the art still could obtain other drawings in light of these drawings, without using any inventive efforts.|0023| FIG. 1 shows scanning electron microscope (SEM) images of lithium manganese iron phosphate materials prepared in different examples of the present disclosure; and

[0024] FIG. 2 is an X-ray diffraction (XRD) spectrogram of the lithium manganese iron phosphate materials prepared in different examples of the present disclosureDETAILED DESCRIPTION OF EMBODIMENTS

[0025] Technical solutions of the present disclosure will be described clearly and completely below in conjunction with the drawings and embodiments, while those skilled in the art would understand that the embodiments described below are some but not all embodiments of the present disclosure, and they are merely used for illustrating the present disclosure, but should notbe considered as limiting the scope of the present disclosure All of other embodiments obtained by those ordinarily skilled in the art based on the embodiments in the present disclosure without using any inventive efforts shall fall within the scope of protection of the present disclosure. Embodiments, for which no concrete conditions are specified, are performed according to conventional conditions or conditions recommended by manufactures. Where manufacturers of reagents or instruments used are not specified, they are conventional products commercially available.

[0026] Tn the description of the present disclosure, it should be noted that terms such as “first”, “second”, and “third” are merely used for descriptive purpose, but should not be construed as indicating or implying importance in the relativity.

[0027] In the existing preparation processes of lithium manganese iron phosphate, although the solid phase method has a simple process and a low preparation cost, the prepared lithium manganese iron phosphate material has poor uniformity, thus affecting electrochemical performance thereof. The hydrothermal (solvothermal) method is to synthesize the lithium manganese iron phosphate material by hydrothermal or solvothermal reaction under high temperature and high pressure, which is more beneficial to regulating and controlling a particle size and uniformity of a product than the solid phase method. However, in the existing hydrothermal (solvothermal) method, when a pure water phase system is used, a reaction temperature of 150 °C or higher is usually required, which inevitably requires use of a high-pressure reaction kettle and corresponding supporting equipment, thus increasing the production cost. When an organic solvent such as ethylene glycol is added, the reaction temperature can be reduced to about 120 °C to 130 °C, but the introduction of the organic solvent adds a step of solvent separation on the one hand, and on the other hand, it has also brought about an environmental protection problem.

[0028] In view of this, the inventors of the present disclosure have made in-depth study on the synthesis process of the lithium manganese iron phosphate material, and by regulating, controlling and optimizing reaction raw materials and reaction steps, preparation of the lithium manganese iron phosphate material can be realized under a milder and more controllable condition, and uniformity of the lithium manganese iron phosphate material can be ensured.

[0029] The present disclosure provides a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode material and a secondary battery. The lithium manganese iron phosphate material having both high crystallinity and good electrochemicalperformance can be obtained, thus enabling the secondary battery to have both good cycle stability and discharge capacity.

[0030] The present disclosure will be described in detail below.

[0031] In the first aspect, the present disclosure provides a preparation method for a lithium manganese iron phosphate material, including steps as follows:

[0032] (a) mixing a first solution including a lithium source and a second solution including a phosphorus source, and adjusting pH to range from 6 to 9, so as to render a mixed solution, where the lithium source includes at least one of lithium carbonate and lithium dihydrogen phosphate;

[0033] (b) adding a third solution including a divalent manganese source and a divalent iron source into the mixed solution, and performing a thermal-insulation reaction at 90 °C to 100 °C; and

[0034] (c) performing solid-liquid separation on a material having undergone the reaction in step (b), and collecting and drying a solid, so as to render the lithium manganese iron phosphate material.

[0035] The preparation process of the lithium manganese iron phosphate material provided in the present disclosure is simple, and through the thermal-insulation reaction under a condition of 100 °C or a lower temperature, various raw material components are enabled to fully chemically react in a short period of time. In the hydrothermal method, materials in a solution need to be converted into an ionic state to react. Taking lithium phosphate as the lithium source and phosphorus source as an example for description, lithium phosphate has very low solubility in water, so that there are extremely few lithium ions and phosphorus ions in an aqueous solution, and they are difficult to combine with divalent manganese ions and divalent iron ions. Therefore, conditions such as high temperature and high pressure are required to promote a progress of reaction. The inventors of the present disclosure innovatively find in researches that lithium carbonate, when being used as the lithium source, reacts first with the phosphorus source in system, to form lithium dihydrogen phosphate, which has remarkably higher solubility in water than the lithium source such as lithium phosphate, so that there are a large amount of lithium ions and phosphorus ions in the aqueous solution, and they are easier to combine with the divalent manganese ions and divalent iron ions, so that the reaction can be completed at normal pressure and a lower reaction temperature (<100 °C). Moreover, the preparation method of the present disclosure does not need nitrogen protection, thus further simplifying reaction steps and reducing the production cost. When lithium dihydrogen phosphate is used as the lithium source,in combination with the lithium source such as lithium carbonate, the preparation of lithium manganese iron phosphate can be realized at normal pressure and a lower reaction temperature (<100 °C). However, since a ratio of lithium to phosphorus in the lithium dihydrogen phosphate is 1:1, the lithium source such as lithium carbonate is further needed to supplement an amount of lithium required for preparing the lithium manganese iron phosphate, thus increasing types of raw materials, and causing complexity in operation.

[0036] The preparation method for a lithium manganese iron phosphate provided in the present disclosure meets requirements for industrial mass production, and is easy to amplify the reaction Besides, compared with the existing hydrothermal method, the preparation method for a lithium manganese iron phosphate provided in the present disclosure has a higher yield. Moreover, in the present disclosure, various additives such as a complexing agent and a precipitating agent do not need to be added during the reaction, thus avoiding generation of a large amount of liquid wastes, and also enabling post-treatment process to be simpler, green and environmentally friendly and energy-saving.

[0037] The lithium manganese iron phosphate material obtained by the preparation method for a lithium manganese iron phosphate in the present disclosure has advantages such as controllable morphology, adjustable particle size, good uniformity, and high batch stability and consistency, and the lithium manganese iron phosphate obtained has higher crystallinity without impurity phase.

[0038] In some embodiments, in the adjusting pH to range from 6 to 9, pH specifically can be adjusted to be 6, 6.5, 7, 7.5, 8, and 9 or within a range formed by any above values. In a reaction system of the present disclosure, by adjusting the pH, a lithium manganese iron phosphate crystal is changed in growth rate and direction, so as to change morphology and dimension thereof. For example, in the present disclosure, by adjusting the pH to be within the range of 6-9, the lithium manganese iron phosphate material with the morphology such as rhombus flaky shape, nano small cubic shape, octahedron shape, micron-grade blocky shape, or dense spherical shape and uniform particle size distribution can be obtained, so as to meet different application requirements.

[0039] In some embodiments, the reaction is performed in an air atmosphere.

[0040] In some embodiments, a reagent used for adjusting pH can be selected from a conventional acid and a conventional alkali, where the acid may include at least one of sulfuric acid, hydrochloric acid and nitric acid; and the alkali may include at least one of sodium hydroxide and ammonia water. Sulfuric acid, hydrochloric acid, nitric acid, and ammonia watercan be used at an industrial-grade concentration, or can be appropriately diluted with water; and sodium hydroxide can be added in a solid form, but is not limited thereto, for example, it can also be added in the form of aqueous solution.

[0041] In some embodiments, the phosphorus source includes at least one of phosphoric acid and lithium dihydrogen phosphate. The use of phosphoric acid as the phosphorus source is more conducive to reaction with lithium carbonate to form lithium dihydrogen phosphate. Optionally, the second solution is an aqueous phosphoric acid solution with a mass fraction ranging from 70% to 90%, for example, industrial-grade phosphoric acid with a mass fraction of 85 %, thus facilitating industrial production.

[0042] In some embodiments, a temperature of the thermal-insulation reaction can be 90 °C, 92 °C, 95 °C, 98 °C, and 100 °C or within a range formed by any above values. In some embodiments, the thermal-insulation reaction is performed at normal pressure. When the temperature of the thermal-insulation reaction is less than 90°C, the lithium manganese iron phosphate material cannot be obtained. The temperature of the thermal-insulation reaction in the present disclosure is controlled at 100 °C or below, so that while ensuring smooth synthesis of the lithium manganese iron phosphate material, special equipment such as a high-pressure reaction kettle is avoided, the reaction can be performed in a conventional reaction kettle, and the reaction kettle may not be airtight, as long as the reaction temperature is ensured to meet the above condition. Thus, not only the reaction can be easy to control, but also energy consumption can be reduced, and production can be easy to amplify. In the above, the normal pressure can be 0.1013 mPa±0.05 mPa. The normal pressure usually refers to standard atmospheric pressure, but it can be understood that due to influence of operation, equipment or environment, pressure with certain fluctuation is still within the scope of protection of the present disclosure.|0043| In some embodiments, in step (a), the first solution and the second solution can be mixed in a common reaction kettle at room temperature. Specifically, the first solution can be added into the second solution for mixing. It should be understood that a mixing process may be accompanied by stirring.

[0044] In some embodiments, duration of the thermal-insulation reaction ranges from 3 h to 8 h, and may be, for example, 3 h, 4 h, 5 h, 6 h, 7 h, and 8 h or within a range formed by any above values. Thus, it is conducive to promoting full reaction of raw materials of lithium manganese iron phosphate. Further, the duration of the thermal-insulation reaction ranges from 3 h to 4 h, thus being capable of further improving production efficiency, enabling an entirepreparation process to be completed within about 8 h, and remarkably improving the production efficiency.

[0045] In some embodiments, the thermal-insulation reaction is accompanied by stirring, where a speed of the stirring ranges from 50 rpm to 400 rpm, and may be, for example, 50 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm, 350 rpm, and 400 rpm or within a range formed by any above values, so as to facilitate uniformity of mixing and reaction of various components in the system.

[0046] In some embodiments, in step (b), the third solution is added into the mixed solution dropwise; and duration of the dropwise addition ranges from 0.5 h to 3 h, and may be, for example, 0.5 h, 1 h, 2 h, and 3 h or within a range formed by any above values. The dropwise addition of the third solution is conducive to improving both uniformity of the reaction and production efficiency, avoiding too severe local reaction and deteriorated product uniformity possibly caused by too fast addition, and also avoiding reduced production efficiency caused by too slow addition.

[0047] In some embodiments, a molar ratio of a total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the lithium source in terms of Li+is 1: (3-3.3) (from 1: 3 to 1: 3.3), and may be, for example, 1: 3, 1: 3.1, 1: 3.2, and 1: 3.3 or within a range formed by any above values; and a molar ratio of the total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the phosphorus source in terms ofPOf" is 1: (0.9-1.2) (from 1: 0.9 to 1: 1.2), and may be, for example, 1: 0.9, 1: 1, 1: 1.05, 1: 1.1, 1: 1.15, and 1: 1.2 or within a range formed by any above values.

[0048] In some embodiments, a molar ratio of the divalent manganese source in terms of Mn2+to the divalent iron source in terms of Fe2+ranges from 1: 9 to 9: 1, and may be, for example, 1: 9, 2: 8, 3: 7, 4: 6, 5: 5, 6: 4, 7: 3, 8: 2, and 9: 1 or within a range formed by any above values. Specific amounts of the divalent manganese source and divalent iron source added can be calculated according to a stoichiometric ratio of target lithium manganese iron phosphate.

[0049] In some embodiments, in the first solution, a molar concentration of the lithium source ranges from 1 mol / L to 3 mol / L, and may be, for example, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, and 3 mol / L or within a range formed by any above values, optionally, from 2.5 mol / L to 3 mol / L; and in the third solution, a total molar concentration of the divalent manganese source and the divalent iron source ranges from 1 mol / L to 3 mol / L, and may be, for example, 1mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, and 3 mol / L or within a range formed by any above values, optionally from 2.5 mol / L to 3 mol / L.

[0050] In the reaction system of the present disclosure, as the reaction proceeds, the lithium source will be gradually present in the form of lithium dihydrogen phosphate with high solubility, accordingly, in the preparation method of the present disclosure, the first solution including the lithium source at a high molar concentration, the second solution including the phosphorus source and the third solution including the divalent manganese source and the divalent iron source can be used, which not only can ensure stable synthesis of the lithium manganese iron phosphate material, but also can remarkably improve a solid content of the reaction system, that is, in the reaction system of the same volume, the preparation method of the present disclosure has remarkably improved yield of the lithium manganese iron phosphate material, breaks through yield limit of the lithium manganese iron phosphate material synthesized by a conventional liquid phase method, and is more beneficial to the industrial production.

[0051] In some embodiments, the divalent manganese source includes at least one of manganous sulfate, manganous chloride, manganese acetate and manganese nitrate; and the divalent iron source includes at least one of ferrous sulfate, ferrous chloride, ferrous acetate and ferrous nitrate. In the preparation method of the present disclosure, unless specifically indicated, various raw materials can be directly commercially available, and various raw materials can include crystal water or not.

[0052] In some embodiments, the first solution, the second solution and the third solution use water as a solvent. It can be understood that, the solutions in the present disclosure do not limit a dissolution state of a solute therein. Taking the first solution as an example, the lithium source therein can be dispersed in water, and can also be partially dissolved or partially dispersed in water, and present in the form of suspension. When the lithium source is dispersed in water in a suspending form, a molar concentration of the first solution refers to a ratio of an amount of substance in all lithium sources in the suspension to a volume of the suspension.

[0053] In some embodiments, the solid-liquid separation includes any one of pressure filtration, suction filtration and centrifugation; and the drying includes any one of spray drying, flash evaporation, microwave drying and stoving Optionally, before the drying, a washing treatment is performed on the solid. Taking the stoving as an example for description, the stoving specifically can be performed under a condition of 80 °C-90 °C for 5 h or more, but is not limited thereto, as long as a water content of the lithium manganese iron phosphate material canmeet requirement of the positive electrode material for the lithium manganese iron phosphate raw materials.

[0054] In some embodiments, the materials of the reaction system are reduced to a temperature of 70 °C or below, and then subjected to the solid-liquid separation.

[0055] In the second aspect, the present disclosure provides a lithium manganese iron phosphate material prepared by the preparation method of the first aspect. The lithium manganese iron phosphate material in the present disclosure has a chemical formula of LiMnxFei-xPO4, where 0.1<x<0.9.

[0056] The lithium manganese iron phosphate provided in the present disclosure has characteristics of regular morphology, uniform particle dimension, narrow particle size distribution, uniform element distribution, high crystallinity and high batch stability and consistency.

[0057] In some embodiments, the morphology of the lithium manganese iron phosphate material includes at least one of rhombus flaky shape, nano cubic shape, octahedron shape, micron blocky shape and spherical shape. Optionally, a primary particle size of the lithium manganese iron phosphate material ranges from 0.1 pm to 10 pm, and may be, for example, 0.1 pm, 0.2 pm, 0.3 pm, 0.5 pm, 0.8 pm, 1 pm, 3 pm, 5 pm, 7 pm, and 10 pm or within a range formed by any above values.

[0058] In some embodiments, BET specific surface area of the lithium manganese iron phosphate material ranges from 4.1 m2 / g to 18.7 m2 / g, and may be, for example, 4.1 m2 / g, 5 m2 / g, 7 m2 / g, 9 m2 / g, 12 m2 / g, 14 m2 / g, 16 m2 / g, and 18.7 m2 / g or within a range formed by any above values; a tap density ranges from 0.92 g / cm3to 1.21 g / cm3, and may be, for example, 0.92 g / cm3, 0.95 g / cm1, I g / cm3, 1.05 g / cm1, 1.1 g / cm3, 1.15 g / cm3, l.2l g / cm3or within a range formed by any above values. The lithium manganese iron phosphate material with certain morphology, with suitable specific surface area and tap density, is more conducive to improving dispersibility and compaction density of the positive electrode material, and thus is more conducive to full exertion of the electrochemical performance thereof.

[0059] In the third aspect, the present disclosure provides a positive electrode material prepared from the lithium manganese iron phosphate material prepared by the preparation method of the first aspect.

[0060] In some embodiments, D50 particle size of the positive electrode material ranges from 0.89 pm to I.l3 pm, and may be, for example, 0.89 pm, 0.95 pm, I pm, 1.05 pm, 1.1 pm, and 1.13 pm or within a range formed by any above values.

[0061] In some embodiments, BET specific surface area of the positive electrode material ranges from 12.8 m2 / g to 17.3 m2 / g, and may be, for example, 12.8 m2 / g, 13.5 m2 / g, 14 m2 / g, 15 m2 / g, 16 m2 / g, 17 m2 / g, 17.3 m2 / g or within a range formed by any above values.

[0062] In some embodiments, raw materials of the positive electrode material include the lithium manganese iron phosphate material, a lithium source, a phosphorus source, a carbon source and a doping metal source in a molar ratio of 1: (0.02-0.04): (0.03-0.05): (0.04-0.08): (0.01-0.03).

[0063] In some embodiments, a preparation method for the positive electrode material may include: uniformly mixing the lithium manganese iron phosphate material prepared by the method of the first aspect of the present disclosure with a lithium source, a phosphorus source, a carbon source and an optional doping metal source, so as to render mixed raw materials; and performing a sintering treatment on the mixed raw materials, so as to render the positive electrode material, where a corresponding doping metal in the doping metal source includes, but is not limited to, at least one of Co, Mg, Zn, Ca, Ti, V, Ni and Cr.

[0064] In some embodiments, the sintering treatment includes: calcining at 700 °C-750 °C for 8 h-12 h in a protective atmosphere. In the above, the protective atmosphere can be provided by nitrogen and / or an inert gas.

[0065] In some embodiments, the doping metal source may include at least one of oxide, carbonate, acetate, hydrochloride and nitrate of doping metal. Taking the doping metal source being magnesium salt as an example for description, the magnesium source may include at least one of magnesium oxide, magnesium carbonate and magnesium acetate.

[0066] In some embodiments, the carbon source includes, but is not limited to, at least one of glucose, sucrose, starch, fructose and polyvinylalcohol.

[0067] In some embodiments, a solvent, such as water, may also be added into the mixed raw materials. Further, when the mixed raw materials include water, the mixed raw materials are dried in advance, and then the sintering treatment is performed. A specific drying method is not limited, for example, spray drying can be used, so as to be more helpful to ensure dimension uniformity of the positive electrode material, and so on.

[0068] In the fourth aspect, the present disclosure provides a secondary battery, including a positive electrode plate, where the positive electrode plate includes the positive electrode material according to any embodiment of the third aspect of the present disclosure.

[0069] In some embodiments, the positive electrode plate of the present disclosure includes a positive electrode current collector and a positive electrode film layer provided on at least onesurface of the positive electrode current collector, where the positive electrode film layer includes the positive electrode material according to any embodiment of the third aspect of the present disclosure; the positive electrode current collector has two surfaces opposite in a thickness direction thereof; and the positive electrode film layer is provided on either or both of the two opposite surfaces of the positive electrode current collector.

[0070] In some embodiments, based on a total weight of the positive electrode film layer, a content of the positive electrode active material in the positive electrode film layer is greater than or equal to 50 wt%, optionally from 85 wt% to 99 wt%, for example, from 90 wt% to 99 wt%.

[0071] In some embodiments, the positive electrode film layer further optionally includes a conductive agent and / or a binder. For example, the conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer and a tetrafluoroethylene-hexafluoropropylene copolymer.

[0072] The present disclosure can realize synthesis of the lithium manganese iron phosphate material with high crystallinity and without carbon coating, under a condition of normal pressure and low temperature, by adopting suitable reaction raw materials, without using high-pressure equipment, thus having low energy consumption and high yield, and being more suitable for industrial production.

[0073] The preparation method of the present disclosure can be performed in a pure water phase system, and omits a step of solvent separation, thus not only complying with the concept of green chemistry, but also simplifying the steps.

[0074] The present disclosure can regulate and control the morphology and particle size of the lithium manganese iron phosphate material, so as to render a positive electrode material finish product with different morphologies, dimensions and performances, thus meeting different application requirements

[0075] Example 1

[0076] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0077] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reactionkettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding industrial-grade ammonia water (25 wt%) to adjust pH value to 8.5;

[0078] (2) into 16.9 kg of manganese sulfate monohydrate and 250.2 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 1 h into the reaction kettle in step (1), with a stirring speed being 100 rpm; and after ending the dropwise addition, heating the mixture to 95 °C, and performing thermal-insulation reaction for 4 h, and

[0079] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (a) in FIG. 1. The obtained lithium manganese iron phosphate material was rhombus flaky particles, with a dimension about 300 nm-500 nm.

[0080] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid, glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials, and adding phosphoric acid in the form of industrial-grade 85 wt% phosphoric acid; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.1Fe0.9)0.98Mg0.02PO4.[00811 Example 2

[0082] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0083] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding industrial-grade ammonia water (25 wt%) to adjust pH value to 7.5;

[0084] (2) into 50.7 kg of manganese sulfate monohydrate and 194.6 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 1.5 h into the reaction kettle in step (1), with a stirring speed being 100 rpm; and after ending the dropwise addition, heating mixture to 95 °C, and performing thermalinsulation reaction for 3 h; and

[0085] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (b) in FIG. 1. The obtained lithium manganese iron phosphate material was rhombus elongated flaky particles, with a dimension about 700 nm-900 nm.

[0086] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.3Fe0.7)0.98Mg0.02PO4.

[0087] Example 3

[0088] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0089] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding industrial-grade ammonia water (25 wt%) to adjust pH value to 9;

[0090] (2) into 84.5 kg of manganese sulfate monohydrate and 139 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 0.5 h into the reaction kettle in step (1), with a stirring speed being 50rpm; and after ending the dropwise addition, heating mixture to 90 °C, and performing thermalinsulation reaction for 3 h; and[0091J (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (c) in FIG 1. The obtained lithium manganese iron phosphate material was secondary spherical particles formed by agglomeration of flaky particles, with a dimension about 40 pm

[0092] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material, and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.5Fe0.5)0.98Mg0.02PO4.

[0093] Example 4

[0094] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0095] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding industrial-grade ammonia water (25 wt%) to adjust pH value to 8;

[0096] (2) into 92.95 kg of manganese sulfate monohydrate and 125.1 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution, then adding the metal solution dropwise within 1 h into the reaction kettle in step (1), with a stirring speed being 100 rpm; and after ending the dropwise addition, heating mixture to 90 °C, and performing thermalinsulation reaction for 4 h; and

[0097] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving theproduct at 80 °C for 10 h using a blast oven An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (d) in FIG. 1. The obtained lithium manganese iron phosphate material was micron-grade flaky particles, with a dimension about 1 pm -2 pm.

[0098] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.55Fe0.45)0.98Mg0.02PO4.

[0099] Example 5

[0100] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0101] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding industrial-grade ammonia water (25 wt%) to adjust pH value to 7.6;

[0102] (2) into 101.4 kg of manganese sulfate monohydrate and 111.2 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 1.5 h into the reaction kettle in step (1), with a stirring speed being 150 rpm; and after ending the dropwise addition, heating mixture to 95 °C, and performing thermalinsulation reaction for 5 h; and

[0103] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (e) in FIG. 1. The obtained lithium manganese iron phosphate material was nanoscale blocky particles, with a dimension about 100 nm-200 nm.

[0104] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.6Fe0.4)0.98Mg0.02PO4.

[0105] Example 6

[0106] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0107] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2, and adding sulfuric acid (mass fraction being 98 wt%) to adjust pH value to 7;

[0108] (2) into 109.85 kg of manganese sulfate monohydrate and 97.3 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 2 h into the reaction kettle in step (1), with a stirring speed being 200 rpm; and after ending the dropwise addition, heating mixture to 95 °C, and performing thermalinsulation reaction for 6 h; and

[0109] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (f) in FIG 1. The obtained lithium manganese iron phosphate material was nanoscale flaky particles, with a dimension about 200 nm-300 nm.

[0110] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice amass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material, and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.65Fe0.35)0.98Mg0.02PO4.

[0111] Example 7

[0112] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0113] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%), adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding sulfuric acid (mass fraction being 98 wt%) to adjust pH value to 6.5;

[0114] (2) into 118.3 kg of manganese sulfate monohydrate and 83.4 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution, then adding the metal solution dropwise within 2.5 h into the reaction kettle in step (1), with a stirring speed being 250 rpm; and after ending the dropwise addition, heating mixture to 100 °C, and performing thermalinsulation reaction for 7 h; and

[0115] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (g) in FIG. 1. The obtained lithium manganese iron phosphate material was octahedron particles, with a dimension about 700 nm-900 nm.

[0116] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.7Fe0.3)0.98Mg0.02PO4.

[0117] Example 8

[0118] A preparation method for a lithium manganese iron phosphate material was provided, including steps as follows:

[0119] (1) into a 1500 L reaction kettle, adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%); adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension into the reaction kettle under a room-temperature condition, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding sulfuric acid (mass fraction being 98 wt%) to adjust pH value to 6,

[0120] (2) into 126.75 kg of manganese sulfate monohydrate and 69.5 kg of ferrous sulfate heptahydrate, adding 350 L of water to make manganese sulfate monohydrate and ferrous sulfate heptahydrate to be completely dissolved, so as to render a metal solution; then adding the metal solution dropwise within 3 h into the reaction kettle in step (1), with a stirring speed being 300 rpm; and after ending the dropwise addition, heating mixture to 100 °C, and performing thermalinsulation reaction for 8 h; and

[0121] (3) after ending the reaction, cooling the reaction kettle to a temperature of 70 °C or below, performing pressure filtration and washing, and then collecting a product, and stoving the product at 80 °C for 10 h using a blast oven. An SEM image of the lithium manganese iron phosphate material prepared in the present example is as shown in (h) in FIG. 1. The obtained lithium manganese iron phosphate material was elongated rod-shaped particles, with a dimension about 10 pm.

[0122] A preparation method for a positive electrode material included steps as follows: mixing the above lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.75Fe0.25)0.98Mg0.02PO4.

[0123] Example 9

[0124] The present example followed the preparation methods for the lithium manganese iron phosphate material and the positive electrode material in Example 5, and was different merely in that in step (1), 99.16 kg of lithium dihydrogen phosphate was used to replace 110 kg ofindustrial -grade concentrated phosphoric acid (85 wt%) in Example 5, and the amount of lithium carbonate was adjusted from 120 kg to 80 kg, while remaining steps were unchanged.[0125J Comparative Example 1

[0126] A preparation method for a positive electrode material included steps as follows: mixing a lithium manganese iron phosphate material, lithium carbonate, phosphoric acid (industrial-grade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 1: 0.03: 0.04: 0.06: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material, and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.8Fe0.2)0.98Mg0.02PO4.

[0127] In the above, the lithium manganese iron phosphate material was prepared with reference to Example 1 in the Chinese patent application with publication No. CN115180607A.

[0128] Comparative Example 2

[0129] A preparation method for a positive electrode material included steps as follows: mixing trimanganese tetraoxide, iron phosphate, lithium carbonate, phosphoric acid (industrialgrade 85 wt% phosphoric acid), glucose, and magnesium oxide weighed in a molar ratio of 0.2: 0.4: 0.502: 1.03: 0.08: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 2 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li1.04(Mn0.6Fe0.4)0.98Mg0.02PO4.

[0130] Comparative Example 3

[0131] A preparation method for a positive electrode material included steps as follows: mixing ferromanganese oxalate (molar ratio of manganese to iron being 6: 4), lithium carbonate, phosphoric acid, glucose, and magnesium oxide weighed in a molar ratio of 1: 0.502: 1.03: 0.065: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Lii.o4(Mno.6Feo.4)o.98Mgo.o2P04.

[0132] Comparative Example 4

[0133] A preparation method for a positive electrode material included steps as follows: mixing ferromanganese carbonate (molar ratio of manganese to iron being 6: 4), lithiumcarbonate, glucose, and magnesium oxide weighed in a molar ratio of 1: 0502: 0.08: 0.02 with pure water, an amount of the pure water used being twice a mass of solid materials; then performing sand milling at a rotational speed of 2000 rpm for 1 h, and performing spray drying, so as to render a dry material; and calcining the dry material at 720 °C for 10 h in a nitrogen atmosphere, so as to render a positive electrode material Li₁.₀₄(Mn₀.₆Fe₀.₄)₀.₉₈Mg₀.₀₂PO₄

[0134] Comparative Example 5

[0135] Comparative Example 5 followed the preparation method for a lithium manganese iron phosphate material in Example 1, and was different in step (1).

[0136] Step (1) of Comparative Example 5 included: adding 122 kg of lithium phosphate into 600 L of pure water, so as to render a lithium phosphate suspension; adding the lithium phosphate suspension into a 1500 L reaction kettle under a room-temperature condition, then adding 10 kg of industrial-grade concentrated phosphoric acid (85 wt%), so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 6.2; and adding industrial-grade ammonia water (25 wt%), to adjust pH value to 8.5.

[0137] Remaining steps were consistent. This comparative example cannot render the substance lithium manganese iron phosphate, and an obtained product included crystal phases such as lithium phosphate, hydrated ferrous phosphate, and ferric pyrophosphate, and was a mixture including elements of lithium, iron, manganese, and phosphorus.

[0138] Comparative Example 6

[0139] Comparative Example 6 followed the preparation method for a lithium manganese iron phosphate material in Example 1, and was different in step (1).

[0140] Step (1) of Comparative Example 6 included: adding 110 kg of industrial-grade concentrated phosphoric acid (85 wt%) into a 1500 L reaction kettle; adding 120 kg of lithium carbonate into 600 L of pure water, so as to render a lithium carbonate suspension; adding the lithium carbonate suspension under a room-temperature condition into the reaction kettle, so as to render a mixed solution of lithium salt and phosphorus salt, with pH of the mixed solution being 7.2; and adding sulfuric acid (mass fraction being 98 wt%), to adjust pH value to 4.

[0141] The rest of the steps were consistent, this Comparative Example cannot obtain the lithium manganese iron phosphate. The obtained product contains lithium phosphate, hydrated ferrous phosphate and other crystalline phases, and is a mixture containing lithium, iron, manganese, and phosphorus elements.

[0142] Experimental Example

[0143] The lithium manganese iron phosphate materials prepared in different examples were tested for BET specific surface area and tap density, and test results are shown in TABLE 1. The positive electrode materials prepared in different examples and comparative examples were tested for carbon content, D50 particle size, BET specific surface area and compaction density, and test results are shown in TABLE 2. Batteries were prepared with the positive electrode materials prepared in different examples and comparative examples, and tested for electrochemical performance, with test results shown in TABLE 3.

[0144] Specifically, a preparation method for the batteries for tests and test methods were as follows.

[0145] Preparation of positive electrode plate includes adding the positive electrode materials prepared in the above examples and comparative examples, a conductive agent carbon nanotube, and a binder PVDF into N-methylpyrrolidone (NMP) in a mass ratio of 90: 5: 5 for mixing, homogenizing, coating mixture on an aluminum foil, rolling, and slicing, so as to render the positive electrode plate.

[0146] Battery assembly includes taking a metallic lithium plate as a negative electrode, and a polyethylene porous membrane with a thickness of 25 μm as a separator, selecting a solution of 1 mol / L LiPF₆ in ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1: 1 as an electrolytic solution, and assembling the positive electrode plate, the separator, the negative electrode plate and the electrolytic solution into a 2032 type button battery in an argon glove box with a water content and an oxygen content both being less than 1 ppm.

[0147] Electrochemical performance tests includes performing charge and discharge tests on the batteries using LAND CT 2001A charge and discharge instrument from Wuhan LANHE Electronics Co., Ltd., with a charge and discharge voltage ranging from 2.0 V to 4.35 V; performing a specific capacity test on the assembled lithium-ion batteries at 0.1 C and 1 C rates respectively; and performing a cycle performance test at 1 C rate.

[0148] TABLE 1 Test Results of Lithium Manganese Iron Phosphate Materials in Different ExamplesNo. Mn / Fe molar ratio BET (m2 / g) Tap density (g / cm3) Example 1 1: 9 14.9 1.10Example 2 3: 7 12.1 1.07Example 3 5: 5 6.3 1.13Example 4 55: 45 9.8 0.92Example 5 6: 4 13.2 0.96Example 6 65: 35 18.7 1.14Example 7 7: 3 6.9 1.17Example 8 75: 25 4.1 1.21Example 9 6: 4 12.8 0.98

[0149] FIG. 2 shows an XRD spectrogram of the lithium manganese iron phosphate materials prepared in Example 1, Example 5 and Example 8, and it can be seen from FIG. 2 that the lithium manganese iron phosphate materials prepared by the preparation method of the present disclosure had high purity, without impure phases.|0150| TABLE 2 Test Results of Positive Electrode materials in Different Examples and Comparative ExamplesCarbon Compaction D50 BETNo. Positive electrode material content density (pm) (m2 / g)(wt%) (g / cm3) Example 1 Li i.o4(Mno.1F eo.9)o.9sMgo.o2P04 1.39 0.89 12.8 2.49 Example 2 Li i.o4(Mno.jF eo.7)o.9sMgo.o2P04 1.45 0.96 13.9 2.43 Example 3 Li i.o4(Mno.5F eo 5)o9sMgoo2P04 1.70 1.11 15.7 2.39 Example 4 Li l. O4(Mno.55F e0.45)0.98Mg0.02PO4 1.71 1.13 16.5 2.31 Example 5 Li i.o4(Mno.& F eo.4)o.98Mgo.o2P04 1.70 1.09 17.3 2.25 Example 6 Lii.o4(Mno.65Feo.35)o.9sMgo.o2P04 1.69 1.10 16.1 2.35 Example 7 Lii.o4(Mno.7Feo.3)o.98Mgo.o2P04 1.73 1.07 15.2 2.37 Example 8 Li i. O4(Mno.75F eo.25)o.98Mg0.02P04 1.72 1.08 15.5 2.38 Example 9 Li i.o4(Mno.6F eo4)o9sMgoo2P04 1.69 1.09 17.4 2.26 ComparativeLi i o4(Mno sF eo 2)o98Mgoo2P04 2.21 0.97 23.1 2.15 Example 1ComparativeLi i.o4(Mno.6F eo4)o9sMgoo2P04 1.73 1.10 16.6 2.31 Example 2ComparativeLi i.o4(Mno.6F eo.4)o.98Mgo.o2P04 1.72 1.11 17.4 2.19 Example 3ComparativeLi i.o4(Mno.6F eo.4)o.98Mgo.o2P04 1.70 1.12 17.1 2.25 Example 4

[0151] TABLE 3 Test Results of Batteries Made from Positive Electrode Materials in Different Examples and Comparative Examples0.1 C discharge specific 1 C discharge specific Capacity retention after 100 No.capacity (mAh / g) capacity (mAh / g) cycles at 1 C (%) Example 1 162.6 151.1 99.9 Example 2 159.7 150.3 99.6 Example 3 153.5 140.3 98.8 Example 4 151.6 139.1 99.7 Example 5 154.8 145.5 99.6 Example 6 155.2 147.8 99.5 Example 7 154.9 142.5 98.6 Example 8 150.3 138.2 98.7 Example 9 155.1 145.6 99.6 Comparative145.6 135.8 92.5 Example 1Comparative143.9 125.9 93.2 Example 2Comparative144.1 130.3 94.1 Example 3Comparative146.7 132.6 95.3 Example 4

[0152] It can be seen from the above test results that the positive electrode material further prepared from the lithium manganese iron phosphate material prepared by the preparation method of the present disclosure, when being used in the lithium-ion battery, can remarkably improve the discharge capacity and cycle stability of the lithium-ion battery. Therefore, the preparation method for the lithium manganese iron phosphate material in the present disclosure is more suitable for industrial production, and can improve the electrochemical performance of the lithium-ion battery.

[0153] Finally, it should be noted that various embodiments above are merely used for describing the technical solutions of the present disclosure, rather than limiting the present disclosure; while the detailed description is made to the present disclosure with reference tovarious preceding embodiments, those ordinarily skilled in the art should understand that they still could modify the technical solutions described in the various preceding embodiments, or make equivalent substitutions to some or all of the technical features therein; and these modifications or substitutions do not make the essence of corresponding technical solutions depart from the scope of the technical solutions of the various embodiments of the present disclosure.INDUSTRIAL APPLICABILITY

[0154] The present disclosure can realize synthesis of the lithium manganese iron phosphate material with high crystallinity and without carbon coating under a condition of normal pressure and low temperature, without using high-pressure equipment, thus having low energy consumption and high yield, and being more suitable for industrial production. Moreover, the preparation method of the present disclosure can be performed in a pure water phase system, and omits a step of solvent separation, thus not only complying with the concept of green chemistry, but also simplifying the steps.

Claims

CLAIMS1. A preparation method for a lithium manganese iron phosphate material, comprising steps of:(a) mixing a first solution comprising a lithium source and a second solution comprising a phosphorus source, and adjusting pH to range from 6 to 9, so as to render a mixed solution, wherein the lithium source comprises at least one of lithium carbonate and lithium dihydrogen phosphate;(b) adding a third solution comprising a divalent manganese source and a divalent iron source into the mixed solution, and performing a thermal-insulation reaction at 90 °C to 100 °C; and(c) performing solid-liquid separation on a material having undergone the reaction in step (b), and collecting and drying a solid, so as to render the lithium manganese iron phosphate material.

2. The preparation method according to claim 1, wherein the phosphorus source comprises at least one of phosphoric acid and lithium dihydrogen phosphate.

3. The preparation method according to claim 1 or 2, wherein a duration of the thermalinsulation reaction ranges from 3 h to 8 h.4 The preparation method according to any one of claims 1-3, wherein the thermalinsulation reaction is performed at a normal pressure.

5. The preparation method according to any one of claims 1-4, wherein the thermalinsulation reaction is accompanied by stirring; and a speed of the stirring ranges from 50 rpm to 400 rpm.6 The preparation method according to any one of claims 1-5, wherein the first solution, the second solution and the third solution use water as a solvent.7 The preparation method according to any one of claims 1-6, wherein in step (b), the third solution is added into the mixed solution dropwise; and a duration of the dropwise addition ranges from 0.5 h to 3 h.

8. The preparation method according to any one of claims 1-7, wherein a molar ratio of a total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the lithium source in terms of Li+is 1: (3-3.3); anda molar ratio of the total amount of the divalent manganese source in terms of Mn2+and the divalent iron source in terms of Fe2+to an amount of the phosphorus source in terms of PO43-is 1: (0.9-1.2).

9. The preparation method according to any one of claims 1-8, wherein a molar ratio of the divalent manganese source in terms of Mn2+to the divalent iron source in terms of Fe2+ranges from 1: 9 to 9: 1.

10. The preparation method according to any one of claims 1-9, wherein in the first solution, a molar concentration of the lithium source ranges from 1 mol / L to 3 mol / L; andin the third solution, a total molar concentration of the divalent manganese source and the divalent iron source ranges from 1 mol / L to 3 mol / L.

11. The preparation method according to any one of claims 1-10, wherein the divalent manganese source comprises at least one of manganous sulfate, manganous chloride, manganese acetate and manganese nitrate; and the divalent iron source comprises at least one of ferrous sulfate, ferrous chloride, ferrous acetate and ferrous nitrate.

12. A lithium manganese iron phosphate material prepared by the preparation method according to any one of claims 1-11.13 The lithium manganese iron phosphate material according to claim 12, wherein BET specific surface area of the lithium manganese iron phosphate material ranges from 4.1 m2 / g to 18.7 m2 / g, and a tap density ranges from 0.92 g / cm3to 1.21 g / cm3.14 A positive electrode material, comprising the lithium manganese iron phosphate material prepared by the preparation method according to any one of claims 1-11.

15. A secondary battery, comprising a positive electrode plate, wherein the positive electrode plate comprises the positive electrode material according to claim 14.

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