Composite lithium manganese iron phosphate material, and preparation method therefor and use thereof

Abstract

A composite lithium manganese iron phosphate material, and a preparation method therefor and the use thereof, which are used in the technical field of lithium-ion battery positive electrode materials. The composite lithium manganese iron phosphate material comprises a lithium manganese iron phosphate active material and a solid additive, the solid additive comprising a porous solid electrolyte and a lithium manganese iron phosphate deposit, wherein the lithium manganese iron phosphate deposit is deposited on pores and the surface of the porous solid electrolyte, and the solid additive is dispersed inside and on the surface of the lithium manganese iron phosphate active material in a particle form. A solid electrolyte transport channel is added to the lithium manganese iron phosphate active material, thereby increasing the contact between a positive electrode and a solid electrolyte sheet, and significantly improving both the transport efficiency and ionic conductivity of interface lithium ions and the cycling stability and chargeable and dischargeable capacity of a battery.

Description

A composite lithium manganese iron phosphate material and its preparation method and application Technical Field

[0001] The present disclosure relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a composite lithium iron manganese phosphate material and a preparation method and application thereof. Background Art

[0002] Currently, commercial lithium-ion batteries use liquid organic electrolytes. The electrolyte and electrode materials are prone to side reactions during the charging and discharging process, resulting in irreversible attenuation of battery capacity. At the same time, the liquid organic electrolytes may volatilize, dry up, and leak during battery service, affecting the service life of the lithium-ion battery.

[0003] Compared with traditional electrolyte lithium-ion batteries, all-solid-state lithium batteries have the following advantages: (1) They completely eliminate the safety hazards of electrolyte corrosion and leakage and have higher thermal stability. (2) They do not need to be encapsulated in liquid and support serial stacking and bipolar structures, which improves production efficiency. (3) Due to the solid-state properties of solid electrolytes, multiple electrodes can be stacked. (4) They have a wide electrochemical stability window (up to 5V or more) and can match high-voltage electrode materials. (5) Solid electrolytes are generally single-ion conductors, with almost no side reactions and longer service life.

[0004] However, solid-state batteries still face some problems that hinder their industrialization. Among them, one of the most important problems at present is that there have always been serious problems at the electrode / electrolyte solid-solid interface in all-solid-state batteries, including large interface impedance, poor interface stability, interface stress changes, etc., which directly affect the performance of the battery. For example, the high interface resistance between the solid electrolyte and the electrode leads to slow charge transfer. The continuous development of the interface resistance layer between the positive electrode and the solid electrolyte leads to a decrease in the cycle performance of the solid-state battery. Therefore, the interface contact problem between the electrode and the solid electrolyte is one of the main shortcomings that need to be overcome for the successful commercialization of secondary lithium batteries.

[0005] In view of this, the present disclosure is proposed.

[0006] Summary of the Invention

[0007] The present invention aims to provide a composite lithium manganese iron phosphate material having excellent interfacial lithium ion transmission efficiency, ionic conductivity, battery cycle stability, and charge and discharge capacity.

[0008] The purpose of the present disclosure includes providing a method for preparing a composite manganese iron phosphate lithium material, which is simple to operate and easy to implement. The prepared composite manganese iron phosphate lithium material has excellent interfacial lithium ion transmission efficiency, ionic conductivity, battery cycle stability and charge and discharge capacity.

[0009] The purpose of the present disclosure includes providing an application of a composite lithium iron manganese phosphate material in preparing a positive electrode material in a solid-state lithium-ion battery.

[0010] An object of the present disclosure includes providing a solid-state lithium-ion battery.

[0011] In order to achieve at least one of the above-mentioned objectives of the present disclosure, the following technical solutions may be adopted:

[0012] In a first aspect, the present disclosure provides a composite lithium iron manganese phosphate material, which includes a lithium iron manganese phosphate active material and a solid additive. The solid additive includes a porous solid electrolyte and a lithium iron manganese phosphate deposit. The lithium iron manganese phosphate deposit is deposited in the pores and surface of the porous solid electrolyte, and the solid additive is dispersed in the interior and surface of the lithium iron manganese phosphate active material in the form of particles.

[0013] In some embodiments of the present disclosure, the mass ratio of the lithium manganese iron phosphate active material to the solid additive is (15-30):1.

[0014] In some embodiments of the present disclosure, the mass ratio of the lithium manganese iron phosphate deposit to the porous solid electrolyte is 1:(10-15).

[0015] In some embodiments of the present disclosure, the particle size of the composite lithium manganese iron phosphate material is 1.2 μm-3 μm.

[0016] In some embodiments of the present disclosure, the particle size of the porous solid electrolyte is 200 nm-400 nm.

[0017] In some embodiments of the present disclosure, the thickness of the lithium manganese iron phosphate deposit on the surface of the porous solid electrolyte is 30 nm to 70 nm.

[0018] In some embodiments of the present disclosure, the porosity of the porous solid electrolyte is lithium lanthanum zirconium oxide with a porosity of 15% to 30%.

[0019] In a second aspect, the present disclosure provides a method for preparing the composite lithium iron manganese phosphate material as described in any one of the above embodiments, comprising:

[0020] An iron source, a manganese source, a phosphorus source, and a porous inorganic solid electrolyte are mixed in a reaction base solution to perform a first hydrothermal reaction, and the mixture is filtered and dried to obtain a solid electrolyte with deposited manganese iron phosphate; the solid electrolyte with deposited manganese iron phosphate is mixed with a lithium source solution to perform a second hydrothermal reaction, and the reactants are washed and dried to obtain a porous solid electrolyte with lithium manganese iron phosphate deposited in the pores and on the surface, which serves as the solid additive;

[0021] The solid additive is mixed with the lithium iron manganese phosphate active material and then calcined to obtain the composite lithium iron manganese phosphate material.

[0022] In some embodiments of the present disclosure, before the iron source, the manganese source and the phosphorus source are mixed with the porous inorganic solid electrolyte, the iron source, the manganese source and the phosphorus source are first mixed with water in a molar ratio of (0.3-0.5): (0.5-0.7): (1-1.2) to form a mixed solution, and the pH of the mixed solution is less than 1.5.

[0023] In some embodiments of the present disclosure, the ratio of the mixed solution, the porous inorganic solid electrolyte and the reaction base solution is (50-100) mL: 1 g: (70-150) mL.

[0024] In some embodiments of the present disclosure, NaOH solution is further added to the mixed solution, the porous inorganic solid electrolyte and the reaction base solution to adjust the pH of the reaction system to 4-6, and the concentration of the NaOH solution is 1.5 mol / L-2.5 mol / L.

[0025] In some embodiments of the present disclosure, the reaction base liquid comprises water and concentrated ammonia water in a volume ratio of 4-6:1, and the mass concentration of the concentrated ammonia water is 25%-28%.

[0026] In some embodiments of the present disclosure, the first hydrothermal reaction comprises stirring the reaction under a nitrogen atmosphere at a temperature of 40-80° C. for 12 h to 24 h, with a stirring rate of 400-800 rpm.

[0027] In some embodiments of the present disclosure, the second hydrothermal reaction comprises a hydrothermal reaction at 150-200° C. for 48-72 hours.

[0028] In some embodiments of the present disclosure, the mass volume ratio of the deposited manganese iron phosphate solid electrolyte to the lithium source solution is (8-10) g:70 mL.

[0029] In some embodiments of the present disclosure, the lithium source solution includes a lithium hydroxide solution or a lithium acetate solution, and the concentration of the lithium source is 2 mol / L-5 mol / L.

[0030] In some embodiments of the present disclosure, the particle size of the lithium manganese iron phosphate active material is 800 nm-1000 nm.

[0031] In some embodiments of the present disclosure, the solid additive is mixed with the lithium iron manganese phosphate active material by ball milling, the ball milling speed is 600 r / min-1000 r / min, and the ball milling time is 4 h-8 h.

[0032] In some embodiments of the present disclosure, the calcination temperature is 650° C.-950° C., and the calcination time is 4 h-10 h.

[0033] In some embodiments of the present disclosure, the method for preparing the composite lithium manganese iron phosphate material also includes preparing a porous inorganic solid electrolyte: mixing and calcining a solid lithium source, a zirconium source and a lanthanum source to obtain an inorganic solid electrolyte, mixing the inorganic solid electrolyte with a polymer aqueous solution to prepare a slurry, and then drying and removing the polymer to obtain a porous inorganic solid electrolyte.

[0034] In some embodiments of the present disclosure, the solid-liquid mass ratio of the inorganic solid electrolyte to the high molecular polymer aqueous solution is 1:(1.5-3).

[0035] In some embodiments of the present disclosure, the mass fraction of the high molecular weight polymer in the high molecular weight polymer aqueous solution is 0.05%-3%.

[0036] In some embodiments of the present disclosure, the high molecular weight polymer includes at least one of polyvinyl pyrrolidone and carboxymethyl cellulose.

[0037] In some embodiments of the present disclosure, the step of mixing and calcining the solid-state lithium source, the zirconium source, and the lanthanum source includes: wet ball milling the solid-state lithium source, the zirconium source, and the lanthanum source at a speed of 300 r / min-500 r / min for 2 h-3 h, drying at 70°C-90°C for 4 h-6 h, and then calcining at 800°C-900°C for 10 h-14 h.

[0038] In some embodiments of the present disclosure, the mass sum of the zirconium source and the lanthanum source and the molar ratio of the solid lithium source is 5:7.8.

[0039] In some embodiments of the present disclosure, the ball milling aid in the wet ball milling is isopropyl alcohol, the amount of the ball milling aid added is 8 mL-12 mL above the solid liquid level, and the ball milling balls are zirconia balls with a diameter of 4 mm-6 mm.

[0040] In some embodiments of the present disclosure, the iron source includes at least one of ferrous hydroxide, ferrous phosphate, ferrous acetate, ferrous acetate, ferrous carbonate, ferrous oxide, ferrous oxide, ferric oxalate and ferrous oxalate.

[0041] In some embodiments of the present disclosure, the manganese source includes at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese dioxide, dimanganese trioxide, and trimanganese tetraoxide.

[0042] In some embodiments of the present disclosure, the phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate.

[0043] In a third aspect, the present disclosure provides the application of the composite manganese iron phosphate material according to any one of the above embodiments or the composite manganese iron phosphate material prepared by the preparation method of the composite manganese iron phosphate material according to any one of the above embodiments in the preparation of positive electrode materials in solid-state lithium-ion batteries.

[0044] In a fourth aspect, the present disclosure provides a solid-state lithium-ion battery comprising a positive electrode, a negative electrode, and a solid electrolyte sheet located between the positive and negative electrodes, wherein the positive electrode comprises the composite lithium iron manganese phosphate material described in any one of the above embodiments or the composite lithium iron manganese phosphate material prepared by the preparation method of the composite lithium iron manganese phosphate material described in any one of the above embodiments.

[0045] Compared with the prior art, the advantages of the present invention include:

[0046] The composite lithium iron manganese phosphate material provided by the present disclosure is prepared by depositing lithium iron manganese phosphate deposits in the pores and on the surface of a porous solid electrolyte, wherein the lithium iron manganese phosphate deposits form a relatively thin layered structure on the surface of the porous solid electrolyte. The lithium iron manganese phosphate deposits are used as solid additives, and then the solid additives are composited with the lithium iron manganese phosphate active material. This adds solid electrolyte transmission channels to the lithium iron manganese phosphate active material, thereby improving the transmission efficiency of lithium ions at the interface between the material and the electrolyte. In addition, the presence of solid electrolyte particles in the lithium iron manganese phosphate active material increases the contact between the positive electrode and the solid electrolyte sheet, improves the problem of large interface resistance in solid-state batteries, improves the cycle stability of the battery, increases the interface ion conductivity between the lithium iron manganese phosphate positive electrode material and the solid electrolyte, and avoids the problem of poor interface compatibility caused by direct sintering of the solid electrolyte and the positive electrode material. This ensures close contact between the positive electrode and the solid electrolyte during the solid-state battery cycle, establishes more efficient ion transmission efficiency, and is conducive to improving the ionic conductivity at the interface between the positive electrode and the solid electrolyte, thereby increasing the lithium ion transmission rate and obtaining a higher charge and discharge capacity.

[0047] The method for preparing the composite lithium iron manganese phosphate material provided by the present disclosure is simple and easy to implement. It can deposit lithium iron manganese phosphate within the pores of a porous solid electrolyte, while forming a relatively thin lithium iron manganese phosphate deposit on the surface. It can also combine solid additives with the lithium iron manganese phosphate active material. The prepared composite lithium iron manganese phosphate material has excellent interfacial lithium ion transmission efficiency, ionic conductivity, battery cycle stability, and charge and discharge capacity. It can be widely used to prepare positive electrode materials for solid-state lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0049] FIG1 is an electron microscope scanning image of the composite lithium manganese iron phosphate material provided in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0050] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0051] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0052] The present disclosure provides a composite lithium iron manganese phosphate material, which includes a lithium iron manganese phosphate active material and a solid additive. The solid additive includes a porous solid electrolyte and lithium iron manganese phosphate deposits deposited in the pores and surface of the porous solid electrolyte. The solid additive is dispersed in the interior and surface of the lithium iron manganese phosphate active material.

[0053] In the present disclosure, the porous solid electrolyte comprises a porous lithium lanthanum zirconium oxide (LZO) with a porosity of 15% to 30%. The mass ratio of the LMPP active material to the solid additive is (15-30):1. The mass ratio of the LMPP deposit to the porous solid electrolyte is (10-15):1. The particle size of the LMPP active material is 800nm ​​to 1000nm. The particle size of the porous solid electrolyte is 200nm to 400nm. The thickness of the LMPP deposit on the surface of the porous solid electrolyte is 30nm to 70nm.

[0054] In the present disclosure, by controlling the particle size and mass ratio of the lithium iron manganese phosphate active material and the porous solid electrolyte, the solid additive can be dispersed in the interior and surface of the lithium iron manganese phosphate active material instead of forming a core-shell structure. In the present disclosure, the lithium iron manganese phosphate active material is mainly used, and the solid additive is added to the lithium iron manganese phosphate active material, thereby increasing the solid electrolyte transmission channel and improving the transmission efficiency of lithium ions at the interface between the material and the electrolyte. In addition, the presence of solid electrolyte particles in the lithium iron manganese phosphate active material increases the contact between the positive electrode and the solid electrolyte sheet, improves the problem of large interface resistance in solid-state batteries, improves the cycle stability of the battery, and increases the interface ion conductivity between the lithium iron manganese phosphate active material and the solid electrolyte.

[0055] Furthermore, the present disclosure provides a method for preparing the composite lithium manganese iron phosphate material, which comprises the following steps:

[0056] S1. Preparation of porous inorganic solid electrolyte.

[0057] (1) A solid lithium source, a zirconium source, and a lanthanum source are mixed and calcined to obtain an inorganic solid electrolyte.

[0058] A solid lithium source, a zirconium source, and a lanthanum source are mixed at a molar ratio of 5:7.8, based on the mass of the zirconium source and lanthanum source to the solid lithium source. The mixture is then wet-milled at a speed of 300-500 rpm for 2-3 hours. Isopropyl alcohol is used as a milling aid in an amount exceeding the liquid level of the solid material by 8-12 mL. Zirconia balls with a diameter of 4-6 mm are used for the milling. After milling, the mixture is dried at 70-90°C for 4-6 hours and then calcined at 800-900°C for 10-14 hours.

[0059] The iron source includes, but is not limited to, at least one of ferrous hydroxide, ferrous phosphate, ferric acetate, ferrous acetate, ferrous carbonate, ferric oxide, ferric tetroxide, ferric oxalate, and ferrous oxalate. The manganese source includes, but is not limited to, at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese dioxide, manganese trioxide, and manganese tetraoxide. The phosphorus source includes, but is not limited to, at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate, and lithium phosphate.

[0060] (2) The inorganic solid electrolyte and the polymer aqueous solution are mixed to form a slurry, and then dried and calcined to remove the polymer to obtain a porous inorganic solid electrolyte.

[0061] The solid-liquid mass ratio of the inorganic solid electrolyte to the polymer aqueous solution is 1:(1.5-3), and the mass fraction of the polymer in the polymer aqueous solution is 0.05%-3%. In the present disclosure, the slurry is spray-dried with an inlet temperature of 350°C and an outlet temperature of 120°C, and then calcined at 700°C-900°C for 3h-5h to remove the polymer.

[0062] In the present disclosure, the high molecular polymer includes but is not limited to at least one of polyvinyl pyrrolidone and carboxymethyl cellulose.

[0063] S2. Preparation of solid additives.

[0064] (1) An iron source, a manganese source, and a phosphorus source are mixed with water in a molar ratio of (0.3-0.5):(0.5-0.7):(1-1.2) to form a mixed solution, wherein the pH of the mixed solution is less than 1.5. Water and concentrated ammonia water are mixed in a volume ratio of (4-6):1 to form a reaction base solution, wherein the mass concentration of the concentrated ammonia water is 25%-28%.

[0065] In some embodiments, the molar ratio of the iron source, the manganese source, and the phosphorus source can be, for example, any one of 0.3:0.5:1, 0.4:0.6:1.1, 0.5:0.7:1.2, 0.3:0.7:1, 0.4:0.6:1.2, 0.5:0.5:1, or a range between any two thereof. In some embodiments, the volume ratio of water to concentrated aqueous ammonia in the reaction base liquid is any one of 4:1, 4.5:1, 5:1, 5.5:1, 6:1, or a range between any two thereof. In some embodiments, the mass concentration of concentrated aqueous ammonia is any one of 25%, 26%, 27%, 28%, or a range between any two thereof.

[0066] (2) A mixed solution containing an iron source, a manganese source, and a phosphorus source and a porous inorganic solid electrolyte are mixed in a reaction base liquid, wherein the ratio of the mixed solution, the porous inorganic solid electrolyte, and the reaction base liquid is 50 mL-100 mL: 1 g: 70-150 mL. NaOH solution is also added to the mixed solution, the porous inorganic solid electrolyte, and the reaction base liquid to adjust the pH of the reaction system to 4-6, and the concentration of the NaOH solution is 1.5 mol / L-2.5 mol / L. Subsequently, a first hydrothermal reaction is performed, wherein the first hydrothermal reaction comprises stirring the reaction under a nitrogen atmosphere at a temperature of 40°C-80°C for 12 h-24 h at a stirring rate of 400 rpm-800 rpm. After the first hydrothermal reaction is completed, the solid electrolyte of deposited manganese iron phosphate is obtained by filtration and drying.

[0067] In some embodiments, the temperature of the first hydrothermal reaction can be, for example, any one of 40°C, 50°C, 60°C, 70°C, 80°C, or a range between any two of them; the reaction time can be, for example, any one of 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, 24h, or a range between any two of them; the stirring speed can be, for example, any one of 400r / mim, 500r / mim, 600r / mim, 700r / mim, 800r / mim, or a range between any two of them.

[0068] (3) The solid electrolyte with deposited manganese iron phosphate is mixed with a lithium source solution (concentration of 2-5 mol / L) at a mass volume ratio of (8 g-10 g):70 mL, and a second hydrothermal reaction is carried out at 150-200° C. for 48-72 hours. The reactant is washed and dried to obtain a porous solid electrolyte with lithium manganese iron phosphate deposited in the pores and on the surface as a solid additive. The lithium source solution includes a lithium hydroxide solution or a lithium acetate solution.

[0069] In some embodiments, the mass volume ratio of the deposited solid electrolyte of manganese iron phosphate to the lithium source solution is 8g:70mL, 9g:70mL, 10g:70mL, or a range between any two of them; the temperature of the second hydrothermal reaction can be, for example, 150°C, 160°C, 170°C, 180°C, 190°C, or 200°C, or a range between any two of them; the reaction time can be, for example, 48h, 50h, 52h, 54h, 56h, 58h, 60h, 62h, 64h, 66h, 68h, 70h, or 72h, or a range between any two of them.

[0070] S3. Preparation of composite lithium manganese iron phosphate material.

[0071] The solid additive is mixed with the lithium iron manganese phosphate active material and then calcined to obtain a composite lithium iron manganese phosphate material.

[0072] In the present disclosure, the particle size of the lithium iron manganese phosphate active material is 800 nm to 1000 nm, the mass ratio of the lithium iron manganese phosphate active material to the solid additive is (15-30):1, and the solid additive and the lithium iron manganese phosphate active material are ball-milled at a speed of 600-1000 r / min for 4-8 hours. The calcination temperature is 650°C to 950°C for 4-10 hours.

[0073] In some embodiments, the particle size of the lithium manganese iron phosphate active material can be, for example, any one of 800 nm, 850 nm, 900 nm, 950 nm, and 1000 nm, or a range between any two thereof; the mass ratio of the lithium manganese iron phosphate active material to the solid additive can be, for example, any one of 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, and 30:1, or a range between any two thereof; the ball milling speed can be, for example, any one of 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 21:1, 22:1, 23:1, 24:1, 25:1, 26:1, 27:1, 28:1, 29:1, and 30:1, or a range between any two thereof; For example, it can be any one of 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, or a range value between any two of them; the ball milling time can be, for example, any one of 4h, 5h, 6h, 7h, 8h, or a range value between any two of them; the calcination temperature can be, for example, any one of 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, or a range value between any two of them; the calcination time can be, for example, 4h, 5h, 6h, 7h, 8h, 9h, 10h.

[0074] The lithium ion transmission efficiency, battery cycle stability, and interfacial ion conductivity between the lithium manganese iron phosphate positive electrode material and the solid electrolyte of the composite lithium manganese iron phosphate material obtained by the above preparation method have been significantly improved. It can be widely used in the preparation of positive electrode materials in solid-state lithium-ion batteries.

[0075] Specifically, the present disclosure also provides a solid-state lithium-ion battery, which includes a positive electrode, a negative electrode, and a solid electrolyte sheet located between the positive and negative electrodes, wherein the positive electrode includes the above-mentioned composite manganese iron phosphate lithium material.

[0076] The technical solution of the present disclosure is further described below in conjunction with specific implementation methods.

[0077] Example 1

[0078] This embodiment provides a composite lithium manganese iron phosphate material, the preparation method of which includes the following steps:

[0079] S1. Preparation of porous inorganic solid electrolyte.

[0080] Lanthanum oxide, zirconium oxide and lithium hydroxide were mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide was 1.2:1, the particle size of lanthanum oxide and zirconium oxide was 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide was 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol were added to the mixture. After the isopropyl alcohol was added, the liquid level exceeded 10mL of solid matter, and the mixture was ball milled at a speed of 400r / min for 2.5h, then dried at 80℃ for 5h, and then calcined at 850℃ for 12h to obtain an inorganic solid electrolyte. Subsequently, the mixture was mixed with a 2% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:2. The mixture was then spray-dried at an inlet temperature of 350℃ and an outlet temperature of 120℃. The mixture was then calcined at 800℃ for 4h to remove the carboxymethyl cellulose, thereby forming pores to obtain a porous inorganic solid electrolyte with a particle size of 300nm (porosity of 20%).

[0081] S2. Preparation of solid additives.

[0082] (1) 0.04 M FeSO4·7H2O, 0.06 M MnSO4·H2O, and 0.11 M H3PO4 were dissolved in water to obtain a mixed solution, and deionized water with a volume ratio of 5:1 and concentrated ammonia with a mass concentration of 26% were mixed to obtain a reaction base solution.

[0083] (2) The mixed solution, the porous inorganic solid electrolyte prepared in step S1, and a 2 mol / L NaOH solution were added to the reaction base solution to adjust the pH of the reaction system to 5. The reaction was stirred at 60°C under a nitrogen atmosphere for 18 h at a stirring rate of 600 rpm. The reaction product was filtered, washed with deionized water, and dried under vacuum at 100°C for 12 h. The solid-to-liquid ratio of the porous inorganic solid electrolyte to the mixed solution was 1 g:75 mL.

[0084] (3) The solid electrolyte of deposited manganese iron phosphate prepared in step (2) is added to a 3.5 mol / L LiOH solution (the solid-liquid ratio of the solid electrolyte of deposited manganese iron phosphate to the LiOH solution is 9 g:70 mL) and subjected to hydrothermal reaction at 175° C. for 60 h. The reaction product is washed and dried to obtain a porous solid electrolyte with lithium manganese iron phosphate deposited in the pores and on the surface as a solid additive, wherein the thickness of the lithium manganese iron phosphate deposit on the surface of the porous solid electrolyte is 50 nm.

[0085] S3. Preparation of composite lithium manganese iron phosphate material.

[0086] The solid additive obtained in step S2 was mixed with a lithium iron manganese phosphate active material having a particle size of 900 nm in a mass ratio of 1:20, ball-milled at 800 rpm for 6 h to achieve uniform mixing, heated to 800° C. at a rate of 10° C. / min, and calcined for 7 h. After pulverization, a composite lithium iron manganese phosphate material having a particle size of 1.5 μm was obtained. Referring to FIG. 1 , it can be seen that the solid additive is loaded both inside and on the surface of the lithium iron manganese phosphate active material. The presence of the solid electrolyte particles in the lithium iron manganese phosphate active material increases the solid electrolyte transport channel, which is beneficial for increasing the contact between the positive electrode and the solid electrolyte sheet, improving the problem of high interfacial resistance in solid-state batteries, improving the cycle stability of the battery, and increasing the interfacial ionic conductivity between the lithium iron manganese phosphate positive electrode material and the solid electrolyte.

[0087] Example 2

[0088] This embodiment provides a composite lithium manganese iron phosphate material, the preparation method of which includes the following steps:

[0089] S1. Preparation of porous inorganic solid electrolyte.

[0090] Lanthanum oxide, zirconium oxide and lithium hydroxide were mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide was 1.2:1, the particle size of lanthanum oxide and zirconium oxide was 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide was 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol were added to the mixture. After the isopropyl alcohol was added, the liquid level exceeded 10mL of solid matter, and the mixture was ball milled at a speed of 400r / min for 2.5h, then dried at 80℃ for 5h, and then calcined at 850℃ for 12h to obtain an inorganic solid electrolyte. Subsequently, the mixture was mixed with a 2% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:2. The mixture was then spray-dried at an inlet temperature of 350℃ and an outlet temperature of 120℃. The mixture was then calcined at 800℃ for 4h to remove the carboxymethyl cellulose, thereby forming pores to obtain a porous inorganic solid electrolyte with a particle size of 300nm (porosity of 20%).

[0091] S2. Preparation of solid additives.

[0092] (1) 0.03M FeSO4·7H2O, 0.07M MnSO4·H2O, and 0.1M H3PO4 were dissolved in water to obtain a mixed solution, and deionized water with a volume ratio of 4:1 and concentrated ammonia with a mass concentration of 25% were mixed to obtain a reaction base solution.

[0093] (2) The mixed solution, the porous inorganic solid electrolyte prepared in step S1, and a 1.5 mol / L NaOH solution were added to the reaction base solution to adjust the pH of the reaction system to 4. The reaction was stirred at 40°C under a nitrogen atmosphere for 24 h at a stirring rate of 800 rpm. The reaction product was filtered, washed with deionized water, and dried under vacuum at 100°C for 12 h. The solid-to-liquid ratio of the porous inorganic solid electrolyte to the mixed solution was 1 g:50 mL.

[0094] (3) The solid electrolyte of deposited manganese iron phosphate prepared in step (2) was added to a 2 mol / L LiOH solution (the solid-liquid ratio of the solid electrolyte of deposited manganese iron phosphate to the LiOH solution was 8 g:70 mL), and the reaction was hydrothermally reacted at 150° C. for 72 h. The reaction product was washed and dried to obtain a porous solid electrolyte with lithium manganese iron phosphate deposited in the pores and on the surface as a solid additive, wherein the thickness of the lithium manganese iron phosphate deposit on the surface of the porous solid electrolyte was 70 nm.

[0095] S3. Preparation of composite lithium manganese iron phosphate material.

[0096] The solid additive obtained in step S2 was mixed with the lithium manganese iron phosphate active material with a particle size of 800 nm in a mass ratio of 1:15, ball milled at 600 r / min for 4 h to mix evenly, heated to 650°C at a rate of 10°C / min and calcined for 10 h. After crushing, a composite lithium manganese iron phosphate material with a particle size of 1.2 μm was obtained.

[0097] Example 3

[0098] This embodiment provides a composite lithium manganese iron phosphate material, the preparation method of which includes the following steps:

[0099] S1. Preparation of porous inorganic solid electrolyte.

[0100] Lanthanum oxide, zirconium oxide and lithium hydroxide were mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide was 1.2:1, the particle size of lanthanum oxide and zirconium oxide was 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide was 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol were added to the mixture. After the isopropyl alcohol was added, the liquid level exceeded 10mL of solid matter, and the mixture was ball milled at a speed of 400r / min for 2.5h, then dried at 80℃ for 5h, and then calcined at 850℃ for 12h to obtain an inorganic solid electrolyte. Subsequently, the mixture was mixed with a 2% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:2. The mixture was then spray-dried at an inlet temperature of 350℃ and an outlet temperature of 120℃. The mixture was then calcined at 800℃ for 4h to remove the carboxymethyl cellulose, thereby forming pores to obtain a porous inorganic solid electrolyte with a particle size of 300nm (porosity of 20%).

[0101] S2. Preparation of solid additives.

[0102] (1) 0.05 M FeSO4·7H2O, 0.05 M MnSO4·H2O, and 0.12 M H3PO4 were dissolved in water to obtain a mixed solution, and deionized water with a volume ratio of 6:1 and concentrated ammonia with a mass concentration of 28% were mixed to obtain a reaction base solution.

[0103] (2) The mixed solution, the porous inorganic solid electrolyte prepared in step S1, and a 2.5 mol / L NaOH solution were added to the reaction base solution to adjust the pH of the reaction system to 6. The reaction was stirred at 80°C under a nitrogen atmosphere for 12 h at a stirring rate of 400 rpm. The reaction product was filtered, washed with deionized water, and dried under vacuum at 100°C for 12 h. The solid-to-liquid ratio of the porous inorganic solid electrolyte to the mixed solution was 1 g:100 mL.

[0104] (3) The solid electrolyte of deposited manganese iron phosphate prepared in step (2) was added to a 5 mol / L LiOH solution (the solid-liquid ratio of the solid electrolyte of deposited manganese iron phosphate to the LiOH solution was 10 g:70 mL), and the reaction was hydrothermally reacted at 200° C. for 48 h. The reaction product was washed and dried to obtain a porous solid electrolyte with lithium manganese iron phosphate deposited in the pores and on the surface as a solid additive, wherein the thickness of the lithium manganese iron phosphate deposit on the surface of the porous solid electrolyte was 30 nm.

[0105] S3. Preparation of composite lithium manganese iron phosphate material.

[0106] The solid additive obtained in step S2 was mixed with the lithium manganese iron phosphate active material with a particle size of 1000 nm in a mass ratio of 1:30, ball milled at 1000 r / min for 8 h to mix evenly, heated to 950°C at a rate of 10°C / min and calcined for 4 h. After crushing, a composite lithium manganese iron phosphate material with a particle size of 1.8 μm was obtained.

[0107] Example 4

[0108] This embodiment is basically the same as the embodiment 1, and the only difference is that the parameters in step S1 are different.

[0109] S1. Preparation of porous inorganic solid electrolyte.

[0110] Lanthanum oxide, zirconium oxide, and lithium hydroxide were mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide was 1.2:1, the particle size of lanthanum oxide and zirconium oxide was 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide was 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol were added to the mixture. After the isopropyl alcohol was added, the liquid level exceeded 8mL of solid matter, and the mixture was ball milled at a speed of 300r / min for 3h, then dried at 70℃ for 6h, and then calcined at 800℃ for 14h to obtain an inorganic solid electrolyte. Subsequently, the mixture was mixed with a 1% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:1.5. The mixture was then spray-dried at an inlet temperature of 350℃ and an outlet temperature of 120℃. The mixture was then calcined at 700℃ for 3h to remove the carboxymethyl cellulose, thereby forming pores to obtain a porous inorganic solid electrolyte with a particle size of 200nm (porosity of 15%).

[0111] Example 5

[0112] This embodiment is basically the same as the embodiment 1, and the only difference is that the parameters in step S1 are different.

[0113] S1. Preparation of porous inorganic solid electrolyte.

[0114] Lanthanum oxide, zirconium oxide and lithium hydroxide were mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide was 1.2:1, the particle size of lanthanum oxide and zirconium oxide was 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide was 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol were added to the mixture. After the isopropyl alcohol was added, the liquid level exceeded 12mL of solid matter, and the mixture was ball milled at a speed of 500r / min for 2h, then dried at 90℃ for 4h, and then calcined at 900℃ for 10h to obtain an inorganic solid electrolyte. Subsequently, it was mixed with a 4% by mass aqueous solution of carboxymethyl cellulose and slurried at a solid-liquid mass ratio of 1:3. It was then spray-dried at an inlet temperature of 350℃ and an outlet temperature of 120℃. It was then calcined at 900℃ for 5h to remove the carboxymethyl cellulose, thereby forming pores to obtain a porous inorganic solid electrolyte with a particle size of 400nm (porosity of 30%).

[0115] Comparative Example 1

[0116] This comparative example provides a composite lithium manganese iron phosphate material. The difference between this comparative example and Example 1 is that the solid electrolyte used in this comparative example is not pore-formed.

[0117] In step (1), lanthanum oxide, zirconium oxide and lithium hydroxide are mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide is 1.2:1, the particle size of lanthanum oxide and zirconium oxide is 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide is 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropanol are added to the mixture, after the isopropanol is added, the liquid level must exceed 10mL of the solid matter, ball milling is carried out at a speed of 400r / min for 2.5h, and then drying is carried out at 80°C for 5h, and then calcining is carried out at 850°C for 12h to obtain an inorganic solid electrolyte.

[0118] Comparative Example 2

[0119] This comparative example provides a composite lithium iron manganese phosphate material. This comparative example differs from Example 1 in that, in this comparative example, the porous inorganic solid electrolyte is directly composited with the lithium iron manganese phosphate active material, without depositing lithium iron manganese phosphate in the gaps and on the surface of the porous inorganic solid electrolyte. Specifically, the steps include:

[0120] (1) Lanthanum oxide, zirconium oxide and lithium hydroxide are mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide is 1.2:1, the particle size of lanthanum oxide and zirconium oxide is 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide is 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol are added to the mixture, after the addition of isopropyl alcohol, the liquid level exceeds 10mL of solid matter, and the mixture is ball milled at a speed of 400r / min for 2.5h, then dried at 80℃ for 5h, and then calcined at 850℃ for 12h to obtain an inorganic solid electrolyte. Subsequently, the mixture is mixed with a 2% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:2, and then spray dried at an inlet temperature of 350℃ and an outlet temperature of 120℃, and then calcined at 800℃ for 4h to remove the carboxymethyl cellulose to form pores to obtain a porous inorganic solid electrolyte with a particle size of 300nm.

[0121] (2) The product of step (1) was mixed with lithium manganese iron phosphate active material with a particle size of 900 nm in a mass ratio of 1:20, ball milled at 800 r / min for 6 h to mix evenly, and heated to 800 ° C at a rate of 10 ° C / min and calcined for 7 h to obtain an inorganic solid electrolyte composite lithium manganese iron phosphate positive electrode material.

[0122] Comparative Example 3

[0123] This comparative example provides a composite lithium iron manganese phosphate material. The difference between this comparative example and Example 1 is that in this comparative example, a porous inorganic solid electrolyte and lithium iron manganese phosphate are directly hydrothermally formed into a precursor, which is then mixed with a lithium source and calcined to form a core-shell structure. Specifically, the steps include:

[0124] (1) Lanthanum oxide, zirconium oxide and lithium hydroxide are mixed, wherein the molar ratio of lanthanum oxide to zirconium oxide is 1.2:1, the particle size of lanthanum oxide and zirconium oxide is 10nm-30nm, and the molar ratio of (lanthanum oxide + zirconium oxide) to lithium hydroxide is 5:7.8; zirconium oxide balls with a diameter of 5mm and isopropyl alcohol are added to the mixture, after the addition of isopropyl alcohol, the liquid level exceeds 10mL of solid matter, and the mixture is ball milled at a speed of 400r / min for 2.5h, then dried at 80℃ for 5h, and then calcined at 850℃ for 12h to obtain an inorganic solid electrolyte. Subsequently, the mixture is mixed with a 2% by mass carboxymethyl cellulose aqueous solution and slurried at a solid-liquid mass ratio of 1:2, and then spray dried at an inlet temperature of 350℃ and an outlet temperature of 120℃, and then calcined at 800℃ for 4h to remove the carboxymethyl cellulose to form pores to obtain a porous inorganic solid electrolyte with a particle size of 300nm.

[0125] (2) 0.04M FeSO4·7H2O, 0.06M MnSO4·H2O and 0.11M H3PO4 were dissolved in water to obtain a mixed solution, and deionized water with a volume ratio of 5:1 and concentrated ammonia with a mass concentration of 26% were mixed to obtain a reaction base solution.

[0126] (3) The mixed solution, the porous inorganic solid electrolyte prepared in step (1), and a 2 mol / L NaOH solution were added to the reaction base solution to adjust the pH of the reaction system to 5. The reaction was stirred at 60°C under a nitrogen atmosphere for 18 h at a stirring rate of 600 rpm. The reaction product was filtered, washed with deionized water, and dried under vacuum at 100°C for 12 h. The solid-to-liquid ratio of the porous inorganic solid electrolyte to the mixed solution was 1 g:75 mL.

[0127] (4) The solid electrolyte of deposited manganese iron phosphate prepared in step (3) was mixed with LiOH in a mass ratio of 1:20, ball-milled at 800 r / min for 6 h to mix evenly, and then heated to 800 ° C at a rate of 10 ° C / min and calcined for 7 h to obtain a composite manganese iron phosphate lithium material.

[0128] Comparative Example 4

[0129] This comparative example is substantially the same as Example 1, except that, in step S3, the mass ratio of the lithium manganese iron phosphate active material to the solid additive in this comparative example 1 is 7:3.

[0130] Comparative Example 5

[0131] This comparative example is substantially the same as Example 1, except that, in step S3, the mass ratio of the lithium manganese iron phosphate active material to the solid additive in this comparative example 1 is 40:1.

[0132] Comparative Example 6

[0133] This comparative example is substantially the same as Example 1, except that the particle size of the lithium manganese iron phosphate active material is 2000 nm, and the particle size of the porous solid electrolyte is 100 nm.

[0134] Performance testing

[0135] The lithium manganese iron phosphate materials obtained in the above examples and comparative examples were made into positive electrode sheets, and all-solid-state lithium-ion batteries were made for performance comparison. The battery includes a positive electrode, a negative electrode, and a solid electrolyte sheet located between the positive and negative electrodes. The mass ratio of the active material (the composite lithium manganese iron phosphate material disclosed herein), the battery solid electrolyte, the conductive carbon, and the binder in the positive electrode is 8:1:1:1. The lithium sheet is the negative electrode, and the solid electrolyte layer is Li7La3Zr2O 12 The battery was subjected to charge and discharge tests (test voltage range: 2.75-4.2V) as well as electrochemical impedance spectroscopy and cyclic voltammetry tests at 25°C. The performance test results are shown in Table 1.

[0136] Table 1. Statistics of performance test results for different examples

[0137] As can be seen from the above table, the performance obtained by the embodiments of the present disclosure is significantly better than that of the comparative examples. Among them, the solid electrolyte of comparative example 1 is not pore-forming, resulting in that when preparing the solid additive, lithium iron manganese phosphate can only be deposited on the surface of the solid electrolyte, which will cause the contact area between the solid electrolyte and the lithium iron manganese phosphate active material to be reduced, thereby causing the first charge and discharge capacity at different voltages to be lower than that of Example 1. In comparative example 2, the porous inorganic solid electrolyte is directly compounded with the lithium iron manganese phosphate active material, and the interface impedance between the porous inorganic solid electrolyte and the lithium iron manganese phosphate active material is large and the interface stability is poor, thereby causing the first charge and discharge capacity at different voltages to be lower than that of Example 1. In comparative example 3, a core-shell structure is formed, and the coating layer formed by lithium iron manganese phosphate on the surface of the solid electrolyte is relatively thick, and the interface resistance between the lithium iron manganese phosphate active material and the solid electrolyte is relatively large. In Comparative Examples 4 and 5, the mass ratio of the lithium iron manganese phosphate active material and the solid additive was varied. When the mass ratio was too low, the active material content of the positive electrode material was too low, resulting in a reduction in the battery's charge and discharge capacity. When the mass ratio was too high, the content of the solid electrolyte and its contact area with the lithium iron manganese phosphate decreased, resulting in a decrease in the conductivity of the positive electrode material and the lithium ion transmission efficiency at the solid electrolyte interface. In Comparative Example 6, the particle size of the lithium iron manganese phosphate active material was too large, while the particle size of the porous solid electrolyte was too small. This also resulted in a decrease in the contact area of ​​the lithium iron manganese phosphate within the pores of the solid electrolyte, resulting in a decrease in the conductivity of the positive electrode material and the lithium ion transmission efficiency at the solid electrolyte interface.

[0138] In summary, the composite lithium iron manganese phosphate material provided by the present disclosure is prepared by depositing lithium iron manganese phosphate deposits in the pores and surface of a porous solid electrolyte, wherein the lithium iron manganese phosphate deposits form a thin layered structure on the surface of the porous solid electrolyte, and using it as a solid additive. The solid additive is then composited with the lithium iron manganese phosphate active material, thereby increasing the solid electrolyte transmission channel in the lithium iron manganese phosphate active material, improving the transmission efficiency of lithium ions at the interface between the material and the electrolyte, and the presence of solid electrolyte particles in the lithium iron manganese phosphate active material increases the contact between the positive electrode and the solid electrolyte sheet, improving the problem of large interface resistance in solid-state batteries, improving the cycle stability of the battery, and increasing the interface ion conductivity between the lithium iron manganese phosphate positive electrode material and the solid electrolyte. It also avoids the problem of poor interface compatibility caused by direct use of solid electrolyte and positive electrode material sintering, ensuring close contact between the positive electrode and the solid electrolyte during the solid-state battery cycle, establishing a more efficient ion transmission efficiency, and facilitating the improvement of the ionic conductivity at the interface between the positive electrode and the solid electrolyte, thereby increasing the lithium ion transmission rate and obtaining a higher charge and discharge capacity.

[0139] The method for preparing the composite lithium iron manganese phosphate material provided by the present disclosure is simple and easy to implement. It can deposit lithium iron manganese phosphate within the pores of a porous solid electrolyte, while forming a relatively thin lithium iron manganese phosphate deposit on the surface. It can also combine solid additives with the lithium iron manganese phosphate active material. The prepared composite lithium iron manganese phosphate material has excellent interfacial lithium ion transmission efficiency, ionic conductivity, battery cycle stability, and charge and discharge capacity. It can be widely used to prepare positive electrode materials for solid-state lithium-ion batteries.

[0140] The above describes in detail the optional embodiments of the present disclosure, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure can be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present disclosure and fall within the scope of protection of the present disclosure. Industrial Applicability

[0141] The composite lithium iron manganese phosphate material provided by the present disclosure is prepared by depositing lithium iron manganese phosphate deposits in the pores and on the surface of a porous solid electrolyte, wherein the lithium iron manganese phosphate deposits form a relatively thin layered structure on the surface of the porous solid electrolyte. The lithium iron manganese phosphate deposits are used as solid additives, and then the solid additives are composited with the lithium iron manganese phosphate active material. This adds solid electrolyte transmission channels to the lithium iron manganese phosphate active material, thereby improving the transmission efficiency of lithium ions at the interface between the material and the electrolyte. In addition, the presence of solid electrolyte particles in the lithium iron manganese phosphate active material increases the contact between the positive electrode and the solid electrolyte sheet, improves the problem of large interface resistance in solid-state batteries, improves the cycle stability of the battery, increases the interface ion conductivity between the lithium iron manganese phosphate positive electrode material and the solid electrolyte, and avoids the problem of poor interface compatibility caused by direct sintering of the solid electrolyte and the positive electrode material. This ensures close contact between the positive electrode and the solid electrolyte during the solid-state battery cycle, establishes more efficient ion transmission efficiency, and is conducive to improving the ionic conductivity at the interface between the positive electrode and the solid electrolyte, thereby increasing the lithium ion transmission rate and obtaining a higher charge and discharge capacity.

[0142] The method for preparing the composite lithium iron manganese phosphate material provided by the present disclosure is simple and easy to implement. It can deposit lithium iron manganese phosphate within the pores of a porous solid electrolyte, while forming a relatively thin lithium iron manganese phosphate deposit on the surface. It can also combine solid additives with the lithium iron manganese phosphate active material. The prepared composite lithium iron manganese phosphate material has excellent interfacial lithium ion transmission efficiency, ionic conductivity, battery cycle stability, and charge and discharge capacity. It can be widely used to prepare positive electrode materials for solid-state lithium-ion batteries.

Claims

1. A composite lithium manganese iron phosphate material, characterized in that: It includes a lithium iron manganese phosphate active material and a solid additive. The solid additive includes a porous solid electrolyte and a lithium iron manganese phosphate deposit. The lithium iron manganese phosphate deposit is deposited in the pores and surface of the porous solid electrolyte. The solid additive is dispersed in the interior and surface of the lithium iron manganese phosphate active material in the form of particles.

2. The composite lithium iron manganese phosphate material according to claim 1, characterized in that: The mass ratio of the lithium manganese iron phosphate active material to the solid additive is (15-30):

1.

3. The composite lithium iron manganese phosphate material according to any one of claims 1-2, characterized in that: The mass ratio of the lithium manganese iron phosphate deposit to the porous solid electrolyte is 1:(10-15).

4. The composite lithium iron manganese phosphate material according to any one of claims 1 to 3, characterized in that: The particle size of the composite lithium manganese iron phosphate material is 1.2 μm-3 μm.

5. The composite lithium iron manganese phosphate material according to any one of claims 1 to 4, characterized in that: The particle size of the porous solid electrolyte is 200nm-400nm.

6. The composite lithium iron manganese phosphate material according to any one of claims 1 to 5, characterized in that: The thickness of the lithium manganese iron phosphate deposit on the surface of the porous solid electrolyte is 30nm-70nm.

7. The composite lithium iron manganese phosphate material according to any one of claims 1 to 6, characterized in that: The porosity of the porous solid electrolyte is lithium lanthanum zirconium oxide with a porosity of 15%-30%.

8. A method for preparing the composite lithium iron manganese phosphate material according to any one of claims 1 to 7, characterized in that: It includes: An iron source, a manganese source, a phosphorus source and a porous inorganic solid electrolyte are mixed in a reaction bottom liquid to carry out a first hydrothermal reaction, and then filtered and dried to obtain a solid electrolyte of deposited manganese iron phosphate; The solid electrolyte with deposited manganese iron phosphate is mixed with a lithium source solution to carry out a second hydrothermal reaction, and the reactants are washed and dried to obtain a porous solid electrolyte with manganese iron phosphate lithium deposits deposited in the pores and on the surface as the solid additive; The solid additive and the lithium iron manganese phosphate active material are mixed and then calcined to obtain the composite lithium iron manganese phosphate material.

9. The method for preparing the composite lithium iron manganese phosphate material according to claim 8, characterized in that: Before being mixed with the porous inorganic solid electrolyte, the iron source, the manganese source and the phosphorus source are first mixed with water in a molar ratio of (0.3-0.5):(0.5-0.7):(1-1.2) to form a mixed solution, and the pH of the mixed solution is less than 1.

5.

10. The method for preparing the composite lithium iron manganese phosphate material according to claim 9, characterized in that: The ratio of the mixed solution, the porous inorganic solid electrolyte and the reaction base solution is (50-100) mL: 1 g: (70-150) mL.

11. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 9 to 10, characterized in that: NaOH solution is further added to the mixed solution, the porous inorganic solid electrolyte and the reaction base solution to adjust the pH of the reaction system to 4-6, and the concentration of the NaOH solution is 1.5 mol / L-2.5 mol / L.

12. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 11, characterized in that: The reaction base liquid comprises water and concentrated ammonia water in a volume ratio of (4-6):1, and the mass concentration of the concentrated ammonia water is 25%-28%.

13. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 12, characterized in that: The first hydrothermal reaction includes stirring the reaction for 12h-24h in a nitrogen atmosphere at a temperature of 40°C-80°C, and a stirring rate of 400r / mim-800r / mim.

14. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 13, characterized in that: The second hydrothermal reaction includes a hydrothermal reaction at 150° C.-200° C. for 48 h-72 h.

15. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 14, characterized in that: The mass volume ratio of the deposited manganese iron phosphate solid electrolyte to the lithium source solution is (8-10) g:70 mL.

16. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 15, characterized in that: The lithium source solution includes a lithium hydroxide solution or a lithium acetate solution, and the concentration of the lithium source is 2 mol / L-5 mol / L.

17. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 16, characterized in that: The particle size of the lithium manganese iron phosphate active material is 800nm-1000nm.

18. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 17, characterized in that: The solid additive is mixed with the lithium iron manganese phosphate active material by ball milling, the ball milling speed is 600r / min-1000r / min, and the ball milling time is 4h-8h.

19. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 18, characterized in that: The calcination temperature is 650° C.-950° C., and the calcination time is 4 h-10 h.

20. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 19, characterized in that: The method for preparing the composite lithium manganese iron phosphate material also includes preparing a porous inorganic solid electrolyte: A solid lithium source, a zirconium source and a lanthanum source are mixed and calcined to obtain an inorganic solid electrolyte, the inorganic solid electrolyte is mixed with a high molecular polymer aqueous solution to prepare a slurry, and then the high molecular polymer is dried and removed to obtain a porous inorganic solid electrolyte.

21. The method for preparing the composite lithium iron manganese phosphate material according to claim 20, characterized in that: The solid-liquid mass ratio of the inorganic solid electrolyte to the high molecular polymer aqueous solution is 1:(1.5-3).

22. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 20-21, characterized in that: The mass fraction of the high molecular weight polymer in the high molecular weight polymer aqueous solution is 0.05%-3%.

23. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 20 to 22, characterized in that: The high molecular polymer includes at least one of polyvinyl pyrrolidone and carboxymethyl cellulose.

24. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 20 to 23, characterized in that: The step of mixing and calcining the solid lithium source, the zirconium source and the lanthanum source comprises: wet ball milling the solid lithium source, the zirconium source and the lanthanum source at a speed of 300r / min-500r / min for 2h-3h, drying at 70℃-90℃ for 4h-6h, and then calcining at 800℃-900℃ for 10h-14h.

25. The method for preparing the composite lithium iron manganese phosphate material according to claim 24, characterized in that: The mass and molar ratio of the zirconium source and the lanthanum source to the solid lithium source is 5:7.

8.

26. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 24-25, characterized in that: The ball milling aid in the wet ball milling is isopropanol, the amount of the ball milling aid added is 8mL-12mL above the liquid level of the solid matter, and the ball milling balls are zirconia balls with a diameter of 4mm-6mm.

27. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 26, characterized in that: The iron source includes at least one of ferrous hydroxide, ferrous phosphate, ferrous acetate, ferrous acetate, ferrous carbonate, ferrous oxide, ferrous tetroxide, ferric oxalate and ferrous oxalate.

28. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 27, characterized in that: The manganese source includes at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese dioxide, manganese trioxide and manganese tetraoxide.

29. The method for preparing the composite lithium iron manganese phosphate material according to any one of claims 8 to 28, characterized in that: The phosphorus source includes at least one of lithium dihydrogen phosphate, ammonium phosphate, ammonium dihydrogen phosphate and lithium phosphate.

30. Use of the composite lithium iron manganese phosphate material according to any one of claims 1 to 7 or the composite lithium iron manganese phosphate material prepared by the preparation method of the composite lithium iron manganese phosphate material according to any one of claims 8 to 29 in preparing positive electrode materials for solid-state lithium-ion batteries.

31. A solid-state lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, and a solid electrolyte sheet located between the positive and negative electrodes, wherein the positive electrode includes the composite lithium iron manganese phosphate material as described in any one of claims 1 to 7 or the composite lithium iron manganese phosphate material prepared by the preparation method of the composite lithium iron manganese phosphate material as described in any one of claims 8 to 29.

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