Lithium manganese iron phosphate precursor, lithium manganese iron phosphate material as well as preparation method and application of lithium manganese iron phosphate precursor and lithium manganese iron phosphate material

Abstract

The invention discloses a lithium manganese iron phosphate precursor, a lithium manganese iron phosphate material and a preparation method and application thereof, the lithium manganese iron phosphate precursor comprises an inner core, an inner core layer and a shell layer coating the outer surface of the inner core, and the inner core is an ionic conductive agent; the inner core layer is a manganese-rich layer, the shell layer is an iron-rich layer, and the mass of the inner core, the mass of the inner core layer and the mass of the shell layer respectively account for 0.50-8.00%, 52.00-69.00% and 23.00-47.50% of the mass of the lithium manganese iron phosphate precursor. The lithium manganese iron phosphate precursor has a specific structure which comprises the inner core, the inner core layer and the shell layer, the specific structure can effectively inhibit Mn dissolution and promote lithium ion diffusion, and a stable environment is provided for lithium ion diffusion; therefore, the conductivity and the structural stability of the lithium manganese iron phosphate material prepared from the lithium manganese iron phosphate precursor can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode materials, and more specifically, to a lithium iron manganese phosphate precursor, a lithium iron manganese phosphate material, and a preparation method and application thereof. Background Art

[0002] Olivine lithium iron phosphate (LiFePO 4 ) compounds are currently one of the most promising cathode materials, especially in the field of electric vehicles or energy storage batteries, due to their low price, high thermal stability, excellent safety performance and outstanding cycle life. 4 The material has inherently poor electrical and ionic conductivity, which affects its electrochemical performance. Partial substitution of Fe with Mn to form lithium manganese iron phosphate (LiMn x Fe 1-x PO 4 ) solid solution, which can enhance electronic conductivity and have a higher voltage platform and energy density. In terms of significantly improved electrochemical performance, long cycle life, and simple synthesis process, lithium manganese iron phosphate material is considered to be one of the most promising high energy and power density positive electrode materials for the next generation of lithium-ion batteries.

[0003] With the development of technology in the field of electric vehicles and energy storage batteries, and the increasing requirements for the performance of positive electrode materials, higher requirements are placed on the conductivity of lithium iron manganese phosphate materials. Therefore, the development of a lithium iron manganese phosphate precursor that can improve the conductivity of lithium iron manganese phosphate materials has important economic value. Summary of the invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a lithium iron manganese phosphate precursor, a lithium iron manganese phosphate material and a preparation method and application thereof.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] In a first aspect, the present invention provides a lithium iron manganese phosphate precursor, wherein the lithium iron manganese phosphate precursor comprises, from the inside to the outside, an inner core, an inner core layer and an outer shell layer;

[0007] The inner core is an ion conductive agent, and the mass of the inner core accounts for 0.50-8.00% of the mass of the lithium iron manganese phosphate precursor;

[0008] The inner core layer contains Mn, Fe, M1 and P, wherein the M1 is a doping metal element; the molar ratio of the Mn, Fe and M1 is Mn:Fe:M1=x:(1-xy):y, 0.5≤x<1, 0<y≤0.05; the ratio of the sum of the amounts of the Mn, Fe and M1 elements to the amount of the P element is (Mn+Fe+M1):P=1:(0.6-1.05); the mass of the inner core layer accounts for 52.00-69.00% of the mass of the lithium manganese iron phosphate precursor;

[0009] The outer shell layer contains Mn element, Fe element, M2 element and P element, wherein the M2 element is a doped metal element; the molar ratio of the Mn element, Fe element and M2 element is Mn:Fe:M2=a:(1-ab):b, 0<a<0.5, 0<b≤0.05; the ratio of the sum of the moles of the Mn element, Fe element and M2 element to the mole of the P element is (Mn+Fe+M2):P=1:(0.6-1.05); the mass of the outer shell layer accounts for 23.00-47.50% of the mass of lithium manganese iron phosphate.

[0010] The lithium iron manganese phosphate precursor of the present invention has a specific structure, including an inner core, an inner core layer and an outer shell layer. The specific structure can effectively inhibit the dissolution of Mn while promoting the diffusion of lithium ions, and provide a stable environment for the diffusion of lithium ions, thereby facilitating the improvement of the conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0011] In addition, when the mass of the core core accounts for too large a percentage of the mass of the lithium iron manganese phosphate precursor, the amount of active substances in the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor will be reduced, affecting the energy density of the lithium-ion battery, and will also hinder the diffusion of lithium ions, which is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the mass of the core core accounts for too small a percentage of the mass of the lithium iron manganese phosphate precursor, the specific structure of the lithium iron manganese phosphate precursor cannot effectively promote the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0012] In addition, in the present invention, the inner core layer and the outer shell layer of the lithium iron manganese phosphate precursor can respectively adjust the internal crystal structure of the inner core layer and the outer shell layer by adding appropriate amounts of doping metal elements M1 and M2, which is helpful to improve the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby protecting and promoting the diffusion of lithium ions, and further facilitating the improvement of the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer is too much, the doping metal elements M1 and M2 will destroy the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to maintaining the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby not conducive to improving the conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor; at the same time, the doping metal elements M1 and M2 will gather at the grain boundaries, which may have an adverse effect on the performance of the lithium iron manganese phosphate material. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer respectively is too small, the doping metal elements M1 and M2 cannot well regulate the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to constructing a stable specific structure of the lithium manganese iron phosphate precursor, cannot promote the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium manganese iron phosphate material prepared using the lithium manganese iron phosphate precursor.

[0013] Preferably, the inner core layer further contains O element; and in the inner core layer, the molar ratio of the P element to the O element is P:O=1:4.

[0014] Preferably, the outer shell layer further contains O element; and in the outer shell layer, the molar ratio of the P element to the O element is P:O=1:4.

[0015] Preferably, the mass of the inner core layer accounts for 57.00-62.00% of the mass of the lithium manganese iron phosphate precursor.

[0016] More preferably, the mass of the inner core layer accounts for 57.26-61.93% of the mass of the lithium manganese iron phosphate precursor.

[0017] Preferably, the mass of the outer shell layer accounts for 34.00-38.00% of the mass of the lithium iron manganese phosphate.

[0018] More preferably, the mass of the outer shell layer accounts for 34.50-37.80% of the mass of the lithium iron manganese phosphate, and specifically 34.74-37.57%.

[0019] Preferably, in the inner core layer, the molar ratio of the Mn element, the Fe element and the M1 element is Mn:Fe:M1=(0.500-0.948):(0.050-0.498):(0.002-0.050).

[0020] More preferably, in the core layer, the molar ratio of the Mn element, the Fe element, and the M1 element is Mn:Fe:M1 = 0.900:(0.050 - 0.098):(0.002 - 0.050).

[0021] Preferably, in the shell layer, the molar ratio of the Mn element, the Fe element, and the M2 element is Mn:Fe:M2 = (0.100 - 0.400):(0.550 - 0.898):(0.002 - 0.050).

[0022] More preferably, in the shell layer, the molar ratio of the Mn element, the Fe element, and the M2 element is Mn:Fe:M2 = 0.100:(0.850 - 0.898):(0.002 - 0.050).

[0023] Preferably, the M1 element and the M2 element are each independently selected from at least one of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si.

[0024] Preferably, the ionic conductive agent is at least one of LATP (lithium aluminum titanium phosphate), LAGP (lithium aluminum germanium phosphate), and LLTO (lithium lanthanum titanate).

[0025] More preferably, the chemical composition general formula of the LATP (lithium aluminum titanium phosphate) is Li 1+c Al c Ti 2-c (PO 4 ) 3 , 0 < c ≤ 0.5.

[0026] More preferably, the chemical composition general formula of the LAGP (lithium aluminum germanium phosphate) is Li 1+d Al d Ge 2-d (PO 4 ) 3 , 0 < d ≤ 0.5.

[0027] More preferably, the chemical composition general formula of the LLTO (lithium lanthanum titanate) is Li 3e La 2 / 3-e Ti f T 1-f O 3 , 0 < e < 2 / 3, 0 < f ≤ 1, where the T is independently selected from at least one of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

[0028] In the present invention, the LATP (lithium aluminum titanium phosphate), LAGP (lithium aluminum germanium phosphate) and LLTO (lithium lanthanum titanate) can be obtained from the market or prepared by conventional preparation methods in the art. The present invention provides a preparation method for each of LATP, LAGP and LLTO, specifically:

[0029] The preparation method of the LATP (lithium aluminum titanium phosphate) is:

[0030] Li source, Al source, Ti source and P source are weighed according to the molecular stoichiometric ratio, mixed, and heat treated at 800-950°C for 6-20h to obtain LATP; wherein the Li source may be selected from but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, etc., the Al source may be selected from but not limited to aluminum oxide, aluminum nitrate, aluminum phosphate, aluminum isopropoxide, etc., the Ti source may be selected from but not limited to titanium oxide, tetrabutyl titanate, titanium carbide, titanium pyrophosphate, etc., and the P source may be selected from but not limited to ammonium dihydrogen phosphate, phosphorus pentoxide, titanium pyrophosphate, etc.

[0031] The preparation method of the LAGP (lithium aluminum germanium phosphate) is:

[0032] Li source, Al source, Ge source and P source are weighed according to the molecular stoichiometric ratio, mixed, and heat treated at 700-900° C. for 6-20 h to obtain LAGP; wherein the Li source may be selected from but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, etc., the Al source may be selected from but not limited to aluminum oxide, aluminum nitrate, aluminum phosphate, aluminum isopropoxide, etc., the Ge source may be selected from but not limited to germanium dioxide, germanium monoxide, titanium carbide, titanium pyrophosphate, etc., and the P source may be selected from but not limited to ammonium dihydrogen phosphate, phosphorus pentoxide, titanium pyrophosphate, etc.

[0033] The preparation method of the LLTO (lithium lanthanum titanate) is:

[0034] Li source, La source, Ti source and T source are weighed according to the molecular stoichiometric ratio, mixed, and heat treated at 1000-1200°C for 6-20h to obtain LLTO; wherein the Li source may be selected from but not limited to lithium hydroxide monohydrate, lithium carbonate, lithium nitrate, lithium acetate, etc., the La source may be selected from but not limited to lanthanum oxide, lanthanum fluoride, lanthanum acetate, etc., the Ti source may be selected from but not limited to titanium oxide, tetrabutyl titanate, titanium carbide, titanium pyrophosphate, etc., and the T source is at least one of the oxides and carbonates of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

[0035] In the present invention, "weighing by molecular weight ratio" means weighing by the ratio of the amount of each element in the chemical composition formula (i.e., molar ratio). For example, the chemical composition formula of LATP (lithium aluminum titanium phosphate) is Li 1+c Al c Ti 2-c (PO4 ) 3 In the preparation method of LATP, "weighing according to molecular stoichiometric ratio" specifically refers to weighing the Li source, Al source, Ti source, and P source respectively according to the ratio of the amount of substances of the elements Li, Al, Ti, and P (i.e., molar ratio) (1+c):c:(2-c):3.

[0036] In the present invention, the D50 particle size of the ion conductive agent is nanometer size, preferably 20-200nm, which can be achieved by grinding and / or ball milling and / or sand milling LATP (lithium aluminum titanium phosphate), LLTO (lithium lanthanum titanate), LAGP (lithium aluminum germanium phosphate) until the D50 particle size is nanometer size. When ball milling is used to achieve the D50 particle size of the ion conductive agent to be 20-200nm, the ball milling speed is 100-700rpm, and the ball milling time is 2-24h.

[0037] In a second aspect, the present invention provides a method for preparing a lithium iron manganese phosphate precursor, the preparation method comprising the following steps:

[0038] S1. Mix the ion conductive agent and the manganese source, iron source, M1 source, and phosphorus source required for the inner core layer, react under the condition of pH = 2-12, and age to obtain a precursor containing an ion conductive agent;

[0039] S2. Mix the precursor containing the ion conductive agent obtained in step S1 with the manganese source, iron source, M2 source and phosphorus source required for the outer shell layer, react under the condition of pH = 2-12, and age to obtain a lithium manganese iron phosphate precursor.

[0040] Preferably, in step S1, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source is Mn:Fe:M1=x:(1-xy):y, 0.5≤x<1, 0<y≤0.05; the ratio of the sum of the molar amounts of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source to the molar amount of the P element of the phosphorus source is (Mn+Fe+M1):P=1:(0.6-1.05).

[0041] More preferably, in step S1, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source is Mn:Fe:M1=(0.500-0.948):(0.050-0.498):(0.002-0.050).

[0042] More preferably, in step S1, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source is Mn:Fe:M1=0.900:(0.050-0.098):(0.002-0.050).

[0043] Preferably, in step S2, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source is Mn:Fe:M2=a:(1-ab):b, 0<a<0.5, 0<b≤0.05; the ratio of the sum of the molar amounts of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source to the molar amount of the P element of the phosphorus source is (Mn+Fe+M2):P=1:(0.6-1.05).

[0044] More preferably, in step S2, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source is Mn:Fe:M2=(0.100-0.400):(0.550-0.898):(0.002-0.050).

[0045] More preferably, in step S2, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source is Mn:Fe:M2=0.100:(0.850-0.898):(0.002-0.050).

[0046] Preferably, in step S1, the ion conductive agent is an ion conductive agent suspension; the mass fraction of the ion conductive agent in the ion conductive agent suspension is 0.1-30%, specifically 0.8-13.5% or 0.81-13.07%; the solvent of the ion conductive agent suspension is at least one of water, anhydrous ethanol, methanol and acetone.

[0047] Preferably, in step S1 and / or S2, the pH regulator is at least one of ammonia water, sodium hydroxide, potassium hydroxide, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid and citric acid.

[0048] More preferably, the concentration of the ammonia water is 0.1-15 mol / L, specifically 2-5 mol / L.

[0049] Preferably, in step S1 and / or S2, the pH range is 4-7.

[0050] Preferably, at least one of the following (1)-(5) is included:

[0051] (1) In step S1 and / or S2, the manganese source is at least one of manganese sulfate, manganese oxalate, manganese phosphate, and manganese nitrate;

[0052] (2) In step S1 and / or S2, the iron source is at least one of ferrous sulfate, ferrous oxalate, ferrous nitrate, and ferrous chloride;

[0053] (3) In step S1, the M1 source is at least one of the oxalates, chlorides, nitrates, sulfates, phosphates, and hydroxides of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si;

[0054] (4) In step S2, the M2 source is at least one of the oxalates, chlorides, nitrates, sulfates, phosphates, and hydroxides of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si;

[0055] (5) In step S1 and / or S2, the phosphorus source is at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0056] Preferably, in step S1 and / or S2, the reaction temperature is 20-80°C.

[0057] Preferably, in step S1 and / or S2, the reaction is carried out at a rotation speed of 100-800 rpm.

[0058] Preferably, in step S1 and / or S2, the aging temperature is 20-80° C. and the time is 2-12 h.

[0059] Preferably, in step S2, after the aging, filtering, washing and drying are also included.

[0060] Preferably, in step S1 and / or S2, the reaction and / or the aging are carried out under the protection of an inert gas.

[0061] More preferably, the inert gas is at least one of nitrogen, helium, neon and argon.

[0062] In a third aspect, the present invention provides application of the above-mentioned lithium iron manganese phosphate precursor in lithium iron manganese phosphate materials.

[0063] In a fourth aspect, the present invention provides a method for preparing a lithium iron manganese phosphate material, the preparation method comprising the following steps:

[0064] The lithium iron manganese phosphate material is obtained by mixing a lithium iron manganese phosphate precursor, a lithium source, a carbon source and a phosphorus source and sintering.

[0065] In the preparation method of the lithium iron manganese phosphate material of the present invention, the lithium source will penetrate into the inner core layer and the outer shell layer of the lithium iron manganese phosphate precursor during sintering, and finally obtain the lithium iron manganese phosphate material having an inner core containing an ion conductive agent, an inner core layer containing manganese-rich and iron-poor lithium iron manganese phosphate, an outer shell layer containing manganese-poor and iron-rich lithium iron manganese phosphate, and carbon coated on the surface of the outer shell layer.

[0066] The existence of the lithium iron manganese phosphate precursor lays the structural foundation of the lithium iron manganese phosphate material. The specific structure of the lithium iron manganese phosphate precursor can effectively inhibit the dissolution of Mn while promoting the diffusion of lithium ions and providing a stable environment for the diffusion of lithium ions, which is beneficial to improve the conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0067] Preferably, the sintering is performed under a protective atmosphere.

[0068] More preferably, the protective atmosphere is at least one of nitrogen, argon, hydrogen, helium and neon.

[0069] Preferably, at least one of the following (1)-(6) is included:

[0070] (1) The ratio of the total amount of metal elements in the lithium iron phosphate precursor, the amount of Li element in the lithium source, and the total amount of P element in the mixture is metal element: Li: P = 1: (1.00-1.10): (1.00-1.10), wherein the total amount of metal elements in the lithium iron phosphate precursor refers to the total amount of Mn element, Fe element, M1 element, and M2 element in the lithium iron phosphate precursor, and the total amount of P element in the mixture refers to the total amount of P element in the lithium iron phosphate precursor, P element in the lithium source, and P element in the phosphorus source;

[0071] (2) The mass of the carbon source accounts for 1.5-6.0% of the total mass of the lithium iron manganese phosphate precursor, the lithium source, the phosphorus source and the carbon source;

[0072] (3) The sintering temperature is 500-900° C. and the sintering time is 6-20 hours;

[0073] (4) The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate;

[0074] (5) The carbon source is at least one of sucrose, glucose, citric acid, fructose, starch, maltose, lactose, ascorbic acid, polypropylene, polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), carbon nanotubes (CNT), and graphene;

[0075] (6) The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

[0076] Sucrose, glucose, citric acid, fructose, starch, maltose, lactose, ascorbic acid, polypropylene, polyvinyl pyrrolidone (PVP), polyethylene glycol (PEG), carbon nanotubes (CNT), and graphene commonly used in the art can be used in the present invention.

[0077] More preferably, the carbon source is glucose and carbon nanotubes in a mass ratio of (0.1-10):1.

[0078] More preferably, the carbon source is glucose and PEG in a mass ratio of (0.1-10):1.

[0079] In a fifth aspect, the present invention provides a lithium manganese iron phosphate material prepared by the preparation method described in the fourth aspect.

[0080] In a sixth aspect, the present invention provides an electrode material, wherein the electrode material contains the lithium manganese iron phosphate material as described in the fifth aspect, a conductive agent and a binder.

[0081] In the present invention, the conductive agent and the binder are conventional conductive agents and binders in the art.

[0082] A seventh aspect is a method for preparing an electrode material, comprising the following steps:

[0083] The lithium manganese iron phosphate material, the conductive agent and the binder as described in the fifth aspect are mixed to obtain the electrode material.

[0084] In an eighth aspect, the present invention provides an electrode, comprising a current collector, wherein the electrode material as described in the seventh aspect is disposed on the surface of the current collector.

[0085] In the present invention, conventional current collectors in the art can be used in the present invention.

[0086] In a ninth aspect, the present invention provides a method for preparing an electrode, comprising the following steps:

[0087] The electrode material as described in the seventh aspect is coated on the current collector to obtain an electrode.

[0088] In the tenth aspect, the present invention provides a lithium-ion battery, comprising an electrode group and an electrolyte, wherein the electrode group and the electrolyte are sealed in a battery shell; the electrode group comprises a positive electrode, a separator and a negative electrode, and the separator is arranged between the positive electrode and the negative electrode; the positive electrode is the electrode described in the eighth aspect.

[0089] In the present invention, the separator, electrolyte and negative electrode are all conventional separators, electrolytes and negative electrodes in the art.

[0090] Compared with the prior art, the present invention has the following beneficial effects:

[0091] The lithium iron manganese phosphate precursor of the present invention has a specific structure, including an inner core, an inner core layer and an outer shell layer. The specific structure can effectively inhibit the dissolution of Mn while promoting the diffusion of lithium ions, and provide a stable environment for the diffusion of lithium ions, thereby facilitating the improvement of the conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0092] In addition, when the mass of the core core accounts for too large a percentage of the mass of the lithium iron manganese phosphate precursor, the amount of active substances in the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor will be reduced, affecting the energy density of the lithium-ion battery, and will also hinder the diffusion of lithium ions, which is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the mass of the core core accounts for too small a percentage of the mass of the lithium iron manganese phosphate precursor, the specific structure of the lithium iron manganese phosphate precursor cannot effectively promote the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0093] In addition, in the present invention, the inner core layer and the outer shell layer of the lithium iron manganese phosphate precursor can respectively adjust the internal crystal structure of the inner core layer and the outer shell layer by adding appropriate amounts of doping metal elements M1 and M2, which is helpful to improve the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby protecting and promoting the diffusion of lithium ions, and further facilitating the improvement of the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer is too much, the doping metal elements M1 and M2 will destroy the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to maintaining the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby not conducive to improving the conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor; at the same time, the doping metal elements M1 and M2 will gather at the grain boundaries, which may have an adverse effect on the performance of the lithium iron manganese phosphate material. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer respectively is too small, the doping metal elements M1 and M2 cannot well regulate the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to constructing a stable specific structure of the lithium manganese iron phosphate precursor, cannot promote the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium manganese iron phosphate material prepared using the lithium manganese iron phosphate precursor. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Figure 1 This is a schematic diagram of the structure of the lithium manganese iron phosphate precursor of Example 1.

[0095] Figure 2 Figures A and B are SEM images of the lithium iron manganese phosphate precursor in Example 1, and Figures C and E are EDS images of the manganese, iron, and phosphorus elements in the lithium iron manganese phosphate precursor, respectively.

[0096] Figure 3 This is the SEM image of the lithium manganese iron phosphate material of Application Example 1.

[0097] Figure 4 This is the charge and discharge curve of lithium manganese iron phosphate material in Application Example 1. DETAILED DESCRIPTION

[0098] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0099] The experimental methods in the following examples without specifying specific conditions are generally carried out according to conventional conditions in the art or according to conditions recommended by the manufacturer; the raw materials, reagents, etc. used, unless otherwise specified, are all raw materials and reagents that can be obtained from commercial channels such as conventional markets.

[0100] In each embodiment, comparative example, application example and comparative application example of the present invention, the use of reagents is as follows:

[0101] The chemical formula of LATP (lithium aluminum titanium phosphate) is Li 1.4 Al 0.4 Ti 1.6 (PO 4 ) 3 The preparation method is as follows: lithium carbonate, aluminum oxide, titanium oxide, and ammonium dihydrogen phosphate are weighed according to a molecular weight ratio (i.e., the molar ratio of lithium carbonate, aluminum oxide, titanium oxide, and ammonium dihydrogen phosphate is 0.7:0.2:1.6:3), mixed, and heat-treated at 800°C for 15 hours to obtain LATP; 1000g LATP is added to 1500mL pure water, ball-milled at 600rpm for 12 hours, dried, and ground to obtain LATP with a D50 particle size of 100nm;

[0102] The chemical formula of LAGP (lithium aluminum germanium phosphate) is Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 The preparation method is as follows: lithium carbonate, aluminum oxide, germanium dioxide, and ammonium dihydrogen phosphate are weighed according to a molecular weight ratio (i.e., the molar ratio of lithium carbonate, aluminum oxide, germanium dioxide, and ammonium dihydrogen phosphate is 0.7:0.2:1.6:3), mixed, and heat-treated at 900°C for 8 hours to obtain LAGP; 1000g LAGP is added to 1500mL pure water, ball-milled at 600rpm for 12 hours, dried, and ground to obtain LAGP with a D50 particle size of 100nm;

[0103] The chemical formula of LLTO (lithium lanthanum titanate) is Li 0.3 La 0.567 TiO 3The preparation method is as follows: lithium carbonate, lanthanum oxide, and titanium oxide are weighed according to a molecular weight ratio (i.e., the molar ratio of lithium carbonate, lanthanum oxide, and titanium oxide is 0.15:0.28:1), mixed, and heat-treated at 1100° C. for 12 hours to obtain LLTO; 1000 g of LLTO is added to 1500 mL of pure water, ball-milled at a speed of 600 rpm for 12 hours, dried, and ground to obtain LLTO with a D50 particle size of 100 nm;

[0104] Glucose, D769078 (model or product number), McLean (manufacturer);

[0105] Carbon nanotubes (CNT), G991390 (model or product number), McLean (manufacturer);

[0106] Polyethylene glycol (PEG), PEG-800 (model or product number), Wanhua Chemical (manufacturer);

[0107] Sucrose, S818045 (model or product number), McLean (manufacturer);

[0108] In the present invention, the D50 particle size is measured by Malvern Panalytical Laser D50 Particle Sizer Mastersizer 3000.

[0109] Example 1

[0110] This embodiment provides a lithium manganese iron phosphate precursor, and its structural schematic diagram is as follows Figure 1 As shown, the lithium manganese iron phosphate precursor is composed of an inner core, an inner core layer and an outer shell layer from the inside to the outside;

[0111] The inner core is an ion conductive agent LATP, and the mass of the inner core accounts for 3.00% of the mass of the lithium manganese iron phosphate precursor;

[0112] The inner core layer contains Mn, Fe, Mg, P and O elements, and the molar ratio of the Mn, Fe and Mg elements is Mn:Fe:Mg=0.900:0.095:0.005; the ratio of the sum of the amounts of the Mn, Fe and Mg elements to the amount of the P element is (Mn+Fe+Mg):P=1:1, and the molar ratio of the P element to the O element is P:O=1:4; the mass of the inner core layer accounts for 60.37% of the mass of the lithium manganese iron phosphate precursor;

[0113] The outer shell layer contains Mn, Fe, Ti, P and O elements, and the molar ratio of the Mn, Fe and Ti elements is Mn:Fe:Ti=0.100:0.895:0.005; the ratio of the sum of the amounts of the Mn, Fe and Ti elements to the amount of the P element is (Mn+Fe+Ti):P=1:1, and the molar ratio of the P element to the O element is P:O=1:4; the mass of the outer shell layer accounts for 36.63% of the mass of the lithium manganese iron phosphate precursor;

[0114] The preparation method of the lithium manganese iron phosphate precursor comprises the following steps:

[0115] S1. Add 11.340 mol manganese sulfate (MnSO 4 ), 1.200 mol ferrous sulfate (FeSO 4 )、0.063 mol magnesium sulfate (MgSO 4 , M1 source) to prepare A1 solution; add 12.603 mol of diammonium phosphate (NH 4 H 2 PO 4 ) prepare B1 solution;

[0116] Add 2102mL of 5.00% LATP suspension (ionic conductive agent suspension, solvent is pure water) and 20L of pure water into the reactor, adjust the pH to 6.0 with 2mol / L ammonia water, introduce nitrogen, exhaust the air in the reactor, continue to introduce nitrogen, add solution A1 and solution B1 into the reactor, and add 2mol / L ammonia water, while controlling the feed rate of ammonia water to maintain the system pH = 6.0, react at 50°C and 450rpm until the D50 particle size of the particles in the system is 2.0-2.5μm, stop stirring, and age at 50°C for 2h to obtain a precursor containing an ionic conductive agent;

[0117] S2. Add 0.760 mol manganese sulfate (MnSO 4 ), 6.802 mol ferrous sulfate (FeSO 4 )、0.038 mol titanium sulfate (Ti(SO 4 ) 2 , M2 source) to prepare A2 solution, add 7.600 mol of diammonium phosphate (NH 4 H 2 PO 4 ) prepare B2 solution;

[0118] Continuously introduce nitrogen, add solution A2 and solution B2 to the precursor containing the ion conductive agent obtained in step S1, and add 2 mol / L ammonia water, while controlling the feeding rate of ammonia water to maintain the system pH = 6.0, react at 50 ° C and 450 rpm until the D50 particle size of the particles in the system is 6.0-8.0 μm, stop stirring, age at 50 ° C for 4 hours, filter, wash repeatedly with pure water 4-6 times, filter, and dry in a vacuum drying oven at 100 ° C overnight to obtain a lithium manganese iron phosphate precursor. The SEM and EDS images of the lithium manganese iron phosphate precursor are as follows Figure 2 As shown;

[0119] Wherein, in step S1, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the Mg element of the Mg source is Mn:Fe:Mg=0.900:0.095:0.005; the ratio of the sum of the amount of the Mn element of the manganese source, the Fe element of the iron source, and the Mg element of the Mg source to the amount of the P element of the phosphorus source is (Mn+Fe+Mg):P=1:1;

[0120] In step S2, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the Ti element of the Ti source is Mn:Fe:Ti=0.100:0.895:0.005; the ratio of the sum of the moles of the Mn element of the manganese source, the Fe element of the iron source, and the Ti element of the Ti source to the mole of the P element of the phosphorus source is (Mn+Fe+Ti):P=1:1.

[0121] Examples 2-3 and Comparative Examples 1-2

[0122] Example 2-3 and Comparative Example 1-2 provide different lithium iron manganese phosphate precursors, which differ from Example 1 in that the mass fraction of the ion conductive agent LATP suspension, the amount of LATP, and the mass percentages of the inner core, inner core layer and outer shell layer in the lithium iron manganese phosphate precursor are different, and the rest are consistent with Example 1, as shown in the following table:

[0123] Table 1 Amount of ionic conductive agent LATP used in Examples 1-3 and Comparative Examples 1-2

[0124]

[0125] Embodiment 4-5

[0126] Embodiment 4-5 provides different lithium iron manganese phosphate precursors, which differ from Embodiment 1 in that the type of ion conductive agent is different, and the rest is consistent with Embodiment 1, as shown in the following table:

[0127] Table 2 Types of ion conductive agents in Examples 1, 4-5

[0128]

[0129] Examples 6-7 and Comparative Examples 3-4

[0130] Examples 6-7 and Comparative Examples 3-4 provide different lithium manganese iron phosphate precursors, which differ from Example 1 in that the molar ratios of Mn, Fe, and Mg in the inner core layer (Mn:Fe:Mg) and the amounts of the relevant raw materials in step S1 are different, and the rest are consistent with Example 1, as shown in the following table:

[0131] Table 3 Experimental parameters of Examples 1, 6-7 and Comparative Examples 3-4

[0132]

[0133] Embodiment 8-9

[0134] Embodiments 8-9 provide different lithium iron manganese phosphate precursors, which differ from Embodiment 1 in that the type of M1 source in step S1 and the amount of each related raw material in step S1 are different, and the rest are consistent with Embodiment 1, as shown in the following table:

[0135] Table 4 Experimental parameters of Examples 1, 8-9

[0136]

[0137]

[0138] Examples 10-11 and Comparative Examples 5-6

[0139] Examples 10-11 and Comparative Examples 5-6 provide different lithium manganese iron phosphate precursors, which differ from Example 1 in that the molar ratios of Mn, Fe, and Ti in the outer shell layer (Mn:Fe:Ti) and the amounts of the relevant raw materials in step S2 are different, and the rest are consistent with Example 1, as shown in the following table:

[0140] Table 5 Experimental parameters of Examples 1, 10-11 and Comparative Examples 5-6

[0141]

[0142] Examples 12-13

[0143] Embodiments 12-13 provide different lithium manganese iron phosphate precursors, which differ from Embodiment 1 in that the type of M2 source in step S2 and the amount of each related raw material in step S2 are different, and the rest are consistent with Embodiment 1, as shown in the following table:

[0144] Table 6 Experimental parameters of Examples 1, 12-13

[0145]

[0146] Application examples and comparative application examples

[0147] Application Example 1

[0148] This application example provides a lithium manganese iron phosphate material, and its SEM image is as follows Figure 3 As shown, the preparation method thereof comprises the following steps:

[0149] The lithium iron manganese phosphate precursor (1500 g) and the lithium source lithium carbonate (Li 2 CO 3 ), the carbon source and the phosphorus source ammonium dihydrogen phosphate are uniformly mixed, put into a quartz sagger and placed in a box furnace, heated to 620°C at a rate of 10°C / min under nitrogen protection, sintered for 10h, and cooled to room temperature to obtain lithium manganese iron phosphate material;

[0150] The ratio of the sum of the amounts of metal elements in the lithium iron manganese phosphate precursor, the amount of Li element in the lithium source (lithium carbonate), and the sum of the amounts of P element in the mixture is metal element: Li: P = 1: 1.05: 1.05, wherein the sum of the amounts of metal elements in the lithium iron manganese phosphate precursor refers to the sum of the amounts of Mn element, Fe element, M1 element, and M2 element in the lithium iron manganese phosphate precursor, and the sum of the amounts of P element in the mixture refers to the sum of the amounts of P element in the lithium iron manganese phosphate precursor, the P element in the lithium source, and the P element in the phosphorus source (ammonium dihydrogen phosphate);

[0151] The mass of the carbon source accounts for 5% of the total mass of the lithium manganese iron phosphate precursor, the lithium source, the phosphorus source and the carbon source, and the carbon source is glucose and carbon nanotubes (CNT) in a mass ratio of 10:1.

[0152] Application Example 2-13

[0153] Application Example 2-13 provides different lithium iron manganese phosphate materials. The difference between Application Example 2-13 and Application Example 1 is that Application Example 2-13 uses the lithium iron manganese phosphate precursor of Example 2-13 to replace the lithium iron manganese phosphate precursor of Example 1, and the rest is consistent with Application Example 1.

[0154] Application Examples 14-16

[0155] Application Examples 14-16 provide different lithium manganese iron phosphate materials. The difference between them and Application Example 1 is that the types of carbon sources in Application Examples 14-16 are different, and the rest are consistent with Application Example 1, as shown in the following table:

[0156] Table 7 Types of carbon sources in Application Examples 1, 14-16

[0157] Type of carbon source Application Example 1 Glucose and carbon nanotubes at a mass ratio of 10:1 Application Example 14 Glucose and PEG in a mass ratio of 10:1 Application Example 15 All glucose Application Example 16 All sucrose

[0158] Comparative Application Examples 1-6

[0159] Comparative Application Examples 1-6 provide different lithium iron manganese phosphate materials. The difference between them and Application Example 1 is that Comparative Application Examples 1-6 use the lithium iron manganese phosphate precursors of Comparative Examples 1-6 to replace the lithium iron manganese phosphate precursor of Example 1, and the rest is consistent with Application Example 1.

[0160] Performance Testing

[0161] The performance tests of lithium manganese iron phosphate materials of each application example and comparative application example are as follows:

[0162] (1) Preparation of button-type lithium-ion batteries

[0163] A1. The lithium iron manganese phosphate material and the conductive agent (carbon black) of each application example or comparative application example are placed in an oven, baked at 120°C for 4 hours, and then cooled in a drying container; then, the lithium iron manganese phosphate material, the binder (polyvinylidene fluoride, PVDF), and the conductive agent (carbon black) are weighed in a corresponding proportion of 80:10:10 in a small beaker of 50 mL, and then N-methylpyrrolidone solution is added, and the mixture is stirred with a stirrer to form a paste to obtain an electrode material;

[0164] A2. The electrode material is evenly coated on the aluminum foil (current collector) to obtain a single-sided surface density of 60g / m 2 The positive electrode sheet (electrode) is then placed in a blast drying oven and dried at 120°C for 2 hours, and then pressed into a circular positive electrode sheet with a diameter of 12 mm;

[0165] A3. In an argon atmosphere glove box, a circular cathode sheet was used as the positive electrode, a lithium sheet was used as the negative electrode, an aluminum foil was used as the current collector, and a 1 mol / L LiPF 6 Ethylene carbonate solution, dimethyl carbonate (DMC) and diethyl carbonate (DEC) are used as electrolytes, polypropylene microporous membrane Celgard 2300 is used as a separator, the separator is arranged between the positive electrode and the negative electrode, the positive electrode, the separator and the negative electrode are used as an electrode group, and the electrode group and the electrolyte are sealed with a battery shell to obtain a lithium ion battery (CR2032 button-type lithium ion battery).

[0166] (2) Test of various performance parameters

[0167] At 25℃±2℃, the assembled button-type lithium-ion battery was placed on a battery test system (Blue Electric Series Battery Test System) for charge-discharge cycle test; the test conditions were as follows: the charge and discharge rates were 0.1C, 1C, and 8C, the voltage range was 2.5V-4.3V, and one charge and one discharge was considered one cycle; the conductivity, charge specific capacity, discharge specific capacity, first charge and discharge efficiency (i.e., first cycle coulomb efficiency), and capacity retention rate after 200 cycles were recorded; where:

[0168] Discharge specific capacity (mAh / g) = discharge capacity (unit: mAh) / mass of lithium manganese iron phosphate material (unit: g);

[0169] Charging capacity (mAh / g) = charging capacity (unit: mAh) / mass of lithium manganese iron phosphate material (unit: g);

[0170] First charge and discharge efficiency (%) = first discharge specific capacity / first charge specific capacity;

[0171] Capacity retention rate after 200 cycles (%) = discharge capacity at the 200th cycle / discharge capacity at the first cycle;

[0172] The experimental results are as follows:

[0173] Table 8 Performance test results of lithium manganese iron phosphate materials for various application examples and comparative applications

[0174]

[0175]

[0176] Figure 4 This is the charge and discharge curve of lithium manganese iron phosphate material in Application Example 1.

[0177] From Table 8 and Figure 4 It can be seen that the lithium iron manganese phosphate precursor of the present invention has a specific structure, including an inner core, an inner core layer and an outer shell layer. The specific structure can effectively inhibit the dissolution of Mn while promoting the diffusion of lithium ions, and provide a stable environment for the diffusion of lithium ions, thereby facilitating the improvement of the electrical conductivity and structural stability of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0178] Specifically, by comparing Examples 1-3 and Comparative Examples 1-2, it can be seen that when the mass of the core core accounts for too large a percentage of the mass of the lithium iron manganese phosphate precursor, the amount of active substances in the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor will be reduced, affecting the energy density of the lithium-ion battery, and will also hinder the diffusion of lithium ions, which is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the mass of the core core accounts for too small a percentage of the mass of the lithium iron manganese phosphate precursor, the specific structure of the lithium iron manganese phosphate precursor cannot play a good role in promoting the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor.

[0179] By comparing Examples 1, 6-11 and Comparative Examples 3-6, it can be known that in the present invention, the inner core layer and the outer shell layer of the lithium iron manganese phosphate precursor can respectively adjust the internal crystal structure of the inner core layer and the outer shell layer by adding appropriate amounts of doping metal elements M1 and M2, which is helpful to improve the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby protecting and promoting the diffusion of lithium ions, and further facilitating the improvement of the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer is too much, the doping metal elements M1 and M2 will destroy the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to maintaining the stability of the specific structure of the lithium iron manganese phosphate precursor, thereby not conducive to improving the conductivity of the lithium iron manganese phosphate material prepared using the lithium iron manganese phosphate precursor; at the same time, the doping metal elements M1 and M2 will gather at the grain boundaries, which may have an adverse effect on the performance of the lithium iron manganese phosphate material. When the amount of doping metal elements M1 and M2 added to the inner core layer and the outer shell layer respectively is too small, the doping metal elements M1 and M2 cannot well regulate the internal crystal structure of the inner core layer and the outer shell layer, which is not conducive to constructing a stable specific structure of the lithium manganese iron phosphate precursor, cannot promote the diffusion of lithium ions, and is not conducive to improving the conductivity of the lithium manganese iron phosphate material prepared using the lithium manganese iron phosphate precursor.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A lithium manganese iron phosphate precursor, characterized in that: The lithium iron manganese phosphate precursor is composed of an inner core, an inner core layer and an outer shell layer from the inside to the outside; The inner core is an ion conductive agent, and the mass of the inner core accounts for 0.50-8.00% of the mass of the lithium iron manganese phosphate precursor; The inner core layer contains Mn, Fe, M1 and P, wherein the M1 is a doping metal element; the molar ratio of the Mn, Fe and M1 is Mn:Fe:M1=x:(1-xy):y, 0.5≤x<1, 0<y≤0.05; the ratio of the sum of the amounts of the Mn, Fe and M1 elements to the amount of the P element is (Mn+Fe+M1):P=1:(0.6-1.05); the mass of the inner core layer accounts for 52.00-69.00% of the mass of the lithium manganese iron phosphate precursor; The outer shell layer contains Mn element, Fe element, M2 element and P element, wherein the M2 element is a doped metal element; the molar ratio of the Mn element, Fe element and M2 element is Mn:Fe:M2=a:(1-ab):b, 0<a<0.5, 0<b≤0.05; the ratio of the sum of the moles of the Mn element, Fe element and M2 element to the mole of the P element is (Mn+Fe+M2):P=1:(0.6-1.05); the mass of the outer shell layer accounts for 23.00-47.50% of the mass of lithium manganese iron phosphate.

2. The lithium iron manganese phosphate precursor according to claim 1, characterized in that: Including at least one of the following (1)-(8): (1) The mass of the inner core layer accounts for 57.00-62.00% of the mass of the lithium manganese iron phosphate precursor; (2) The mass of the outer shell layer accounts for 34.00-38.00% of the mass of the lithium iron manganese phosphate; (3) The inner core layer further contains an O element; and in the inner core layer, the molar ratio of the P element to the O element is P:O=1:4; (4) The outer shell layer further contains an O element; and in the outer shell layer, the molar ratio of the P element to the O element is P:O=1:4; (5) In the inner core layer, the molar ratio of the Mn element, the Fe element, and the M1 element is Mn:Fe:M1=(0.500-0.948):(0.050-0.498):(0.002-0.050); (6) In the outer shell layer, the molar ratio of the Mn element, the Fe element, and the M2 element is Mn:Fe:M2=(0.100-0.400):(0.550-0.898):(0.002-0.050); (7) The M1 element and the M2 element are independently selected from at least one of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si; (8) The ion conductive agent is at least one of LATP, LAGP and LLTO.

3. The lithium iron manganese phosphate precursor according to claim 2, characterized in that: Including at least one of the following (1)-(7): (1) The mass of the inner core layer accounts for 57.26-61.93% of the mass of the lithium manganese iron phosphate precursor; (2) The mass of the outer shell layer accounts for 34.50-37.80% of the mass of the lithium iron manganese phosphate, and specifically may be 34.74-37.57%; (3) In the inner core layer, the molar ratio of the Mn element, the Fe element, and the M1 element is Mn:Fe:M1=0.900:(0.050-0.098):(0.002-0.050); (4) In the outer shell layer, the molar ratio of the Mn element, the Fe element, and the M2 element is Mn:Fe:M2=0.100:(0.850-0.898):(0.002-0.050); (5) The chemical composition formula of the LATP is Li 1+c Al c Ti 2-c (PO4)3,0<c≤0.5; (6) The chemical composition formula of the LAGP is Li 1+d Al d Ge 2-d (PO4)3,0<d≤0.5; (7) The general chemical formula of the LLTO is Li 3e La 2 / 3-e Ti f T 1-f O3, where 0 < e < 2 / 3 and 0 < f ≤ 1, and wherein T is independently selected from at least one of Nb, W, Hf, Ru, Mo, Nd, Ba, Ga, In, Ge, Sn, Sb, and Se.

4. The method for preparing the lithium iron manganese phosphate precursor according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: S1. Mix the ion conductive agent and the manganese source, iron source, M1 source, and phosphorus source required for the inner core layer, react under the condition of pH = 2-12, and age to obtain a precursor containing an ion conductive agent; S2. Mix the precursor containing the ion conductive agent obtained in step S1 with the manganese source, iron source, M2 source and phosphorus source required for the outer shell layer, react under the condition of pH = 2-12, and age to obtain a lithium manganese iron phosphate precursor.

5. The method for preparing a lithium iron manganese phosphate precursor according to claim 4, characterized in that: Including at least one of the following (1)-(4): (1) In step S1 and / or S2, the pH range is 4-7; (2) In step S1 and / or S2, the reaction temperature is 20-80°C; (3) In step S1, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source is Mn:Fe:M1=x:(1-xy):y, 0.5≤x<1, 0<y≤0.05; the molar ratio of the sum of the moles of the Mn element of the manganese source, the Fe element of the iron source, and the M1 element of the M1 source to the mole of the P element of the phosphorus source is (Mn+Fe+M1):P=1:(0.6-1.05); (4) In step S2, the molar ratio of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source is Mn:Fe:M2=a:(1-ab):b, 0<a<0.5, 0<b≤0.05; the ratio of the sum of the molar amounts of the Mn element of the manganese source, the Fe element of the iron source, and the M2 element of the M2 source to the molar amount of the P element of the phosphorus source is (Mn+Fe+M2):P=1:(0.6-1.05).

6. The method for preparing a lithium iron manganese phosphate precursor according to claim 4, characterized in that: Including at least one of the following (1)-(5): (1) In step S1 and / or S2, the manganese source is at least one of manganese sulfate, manganese oxalate, manganese phosphate, and manganese nitrate; (2) In step S1 and / or S2, the iron source is at least one of ferrous sulfate, ferrous oxalate, ferrous nitrate, and ferrous chloride; (3) In step S1, the M1 source is at least one of the oxalates, chlorides, nitrates, sulfates, phosphates, and hydroxides of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si; (4) In step S2, the M2 source is at least one of the oxalates, chlorides, nitrates, sulfates, phosphates, and hydroxides of Ti, Mg, Al, Ni, Nb, Co, Cu, and Si; (5) In step S1 and / or S2, the phosphorus source is at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

7. Use of the lithium iron manganese phosphate precursor according to any one of claims 1 to 3 in lithium iron manganese phosphate materials.

8. A method for preparing lithium manganese iron phosphate material, characterized in that: The preparation method comprises the following steps: The lithium iron manganese phosphate precursor according to any one of claims 1 to 3, a lithium source, a carbon source and a phosphorus source are mixed and sintered to obtain the lithium iron manganese phosphate material.

9. The method for preparing lithium iron manganese phosphate material according to claim 8, characterized in that: Including at least one of the following (1)-(6): (1) The ratio of the total amount of metal elements in the lithium iron phosphate precursor, the amount of Li element in the lithium source, and the total amount of P element in the mixture is metal element: Li: P = 1: (1.00-1.10): (1.00-1.10), wherein the total amount of metal elements in the lithium iron phosphate precursor refers to the total amount of Mn element, Fe element, M1 element, and M2 element in the lithium iron phosphate precursor, and the total amount of P element in the mixture refers to the total amount of P element in the lithium iron phosphate precursor, P element in the lithium source, and P element in the phosphorus source; (2) The mass of the carbon source accounts for 1.5-6.0% of the total mass of the lithium iron manganese phosphate precursor, the lithium source, the phosphorus source and the carbon source; (3) The sintering temperature is 500-900° C. and the sintering time is 6-20 hours; (4) The lithium source is at least one of lithium carbonate, lithium hydroxide, lithium phosphate, and lithium dihydrogen phosphate; (5) The carbon source is at least one of sucrose, glucose, citric acid, fructose, starch, maltose, lactose, ascorbic acid, polypropylene, polyvinyl pyrrolidone, polyethylene glycol, carbon nanotubes, and graphene; (6) The phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate.

10. A lithium manganese iron phosphate material, characterized in that: The method is prepared by any one of claims 8 to 9.

11. An electrode material, characterized in that: The electrode material contains the lithium manganese iron phosphate material as claimed in claim 10, a conductive agent and a binder.

12. A method for preparing an electrode material, characterized in that: The steps include: The lithium manganese iron phosphate material, the conductive agent and the binder as described in claim 10 are mixed to obtain the electrode material.

13. An electrode, characterized in that: It comprises a current collector, on the surface of which the electrode material as claimed in claim 11 is arranged.

14. A method for preparing an electrode, characterized in that: The steps include: The electrode material as claimed in claim 11 is coated on the current collector to obtain an electrode.

15. A lithium ion battery, characterized in that: It includes an electrode group and an electrolyte, and the electrode group and the electrolyte are sealed in a battery shell; the electrode group includes a positive electrode, a separator and a negative electrode, and the separator is arranged between the positive electrode and the negative electrode; the positive electrode is the electrode as claimed in claim 13.

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