Lithium manganese iron phosphate material and preparation method therefor, positive electrode sheet, and lithium ion battery

Abstract

Provided are a lithium manganese iron phosphate material and a preparation method therefor, a positive electrode sheet, and a lithium ion battery. The lithium manganese iron phosphate material comprises a core and a coating layer that coats the surface of the core. The chemical formula of the material of the core is LiaMnbFecMdPO4, wherein M comprises at least one element among magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum. The coating layer is formed by sintering a carbon source, and the carbon coating layer comprises graphitized carbon.

Description

Lithium manganese iron phosphate material and preparation method thereof, positive electrode sheet and lithium ion battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 15, 2023, with application number 202311520716.X. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of electrode materials, and in particular to a lithium iron manganese phosphate material and a preparation method thereof, a positive electrode sheet and a lithium ion battery. Background Art

[0003] The positive electrode material of lithium-ion secondary batteries is mainly lithium iron phosphate (LiFePO4). Lithium iron manganese phosphate (LiMnFePO4) is a positive electrode material obtained by adding manganese to LiFePO4. The addition of manganese can make lithium iron manganese phosphate have a higher voltage platform. The redox voltage of lithium iron manganese phosphate is approximately 4.1V, and the redox voltage of lithium iron phosphate is approximately 3.4V. In related technologies, lithium iron manganese phosphate as a positive electrode material for batteries is still in the early stages of industrialization. The main reason is that the cycle performance and specific energy of lithium iron manganese phosphate are low, which seriously affects its commercial application. Technical issues

[0004] The present application provides a lithium iron manganese phosphate material, a preparation method of the lithium iron manganese phosphate material, and a lithium-ion battery, which can improve the technical problems of low specific energy and poor cycle performance of lithium iron manganese phosphate. Technical Solutions

[0005] In a first aspect, the present invention provides a lithium iron manganese phosphate material, wherein the lithium iron manganese phosphate material comprises a core and a coating layer coated on the surface of the core, wherein the material of the core comprises a chemical formula of Li a Mn b Fe c M d PO4, wherein M includes at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, the coating layer is configured to be formed by sintering a carbon source, and the carbon coating layer includes graphitized carbon.

[0006] In a second aspect, an embodiment of the present application provides a method for preparing a lithium manganese iron phosphate material, the preparation method comprising:

[0007] Mixing a lithium source, a manganese source, an iron source, a phosphorus source, a doping metal source, and a carbon source to obtain a precursor 1;

[0008] Under the protection of an inert atmosphere, the precursor 1 is sintered to obtain a lithium manganese iron phosphate material;

[0009] The doping metal source includes one or more of magnesium source, calcium source, strontium source, cobalt source, titanium source, zirconium source, molybdenum source, vanadium source, niobium source, nickel source, scandium source, chromium source, copper source, zinc source, beryllium source, lanthanum source and aluminum source.

[0010] In a third aspect, an embodiment of the present application provides a method for preparing a lithium manganese iron phosphate material, the preparation method comprising the following steps:

[0011] Mixing a manganese source, an iron source, a phosphorus source, a doping metal M source, hydrogen peroxide and a complexing agent to obtain a mixed solution 1;

[0012] The mixed solution 1 is heated, filtered and dried to obtain the precursor 2;

[0013] The precursor 2, a carbon source, a lithium source, and a surfactant are mixed to obtain a precursor 3;

[0014] The precursor 3 is sintered to obtain lithium manganese iron phosphate material;

[0015] The doping metal source includes one or more of magnesium source, calcium source, strontium source, cobalt source, titanium source, zirconium source, molybdenum source, vanadium source, niobium source, nickel source, scandium source, chromium source, copper source, zinc source, beryllium source, lanthanum source and aluminum source.

[0016] In a fourth aspect, the present application provides a positive electrode plate, comprising a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is located on the surface of the positive electrode current collector, and the material of the positive electrode active material layer comprises the above-mentioned lithium manganese iron phosphate material or the lithium manganese iron phosphate material obtained by the above-mentioned preparation method.

[0017] In a fifth aspect, the present application provides a lithium-ion battery, which includes the above-mentioned lithium iron manganese phosphate material.

[0018] Beneficial effects of this application

[0019] The beneficial effects of this application are:

[0020] (1) The present application dopes a metal element M into the core material of lithium manganese iron phosphate to improve the cycle performance of the lithium manganese iron phosphate material, and coats the outer surface of the core material of the lithium manganese iron phosphate with a carbon coating layer containing graphitized carbon, thereby improving the specific energy of the lithium manganese iron phosphate material through the graphitized carbon;

[0021] (2) The specific energy of the battery can be improved by using graphitized carbon materials in the carbon coating. When the graphitized carbon contained in the carbon coating is higher, the lithium ion interface diffusion is related, and thus the rate performance of the battery is better, the specific capacity is higher, and thus the specific energy is higher; however, the faster the lithium ion interface diffusion, the worse the capacity retention rate of the battery will be, which may lead to the worse cycle retention rate of the battery. Therefore, the cycle performance of the battery can be improved by doping the metal element M in the core material of the lithium manganese iron phosphate, thereby synergistically improving the technical problems of low specific energy and poor cycle performance of lithium manganese iron phosphate by doping with metal elements and using a carbon coating containing graphitized carbon. Modes for Carrying Out the Invention

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art, and the materials and reagents used in the Examples and Comparative Examples of this application are commercially available. In addition, any methods and materials similar or equivalent to those described herein can be applied to this application. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0023] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. The various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0024] In the description of this application, the term "including" means "including but not limited to".

[0025] The terms "multiple", "multiple times" or similar expressions refer to two (times) or more than two (times), for example, it can be two (times), three (times), four (times), five (times), six (times), etc.

[0026] The selection scope of the term "and / or" includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, and the said any and all combinations include any two related listed items, any more related listed items, or the combination of all related listed items. For example, "A and / or B" includes three parallel solutions of A, B and A+B. For another example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, the technical solution connected by "logical OR"), and also includes any and all combinations of A, B, C, and D, that is, the combination of any two or any three of A, B, C, and D, and also includes the four-item combination of A, B, C, and D (that is, the technical solution connected by "logical AND").

[0027] In the first aspect, the present application provides a lithium iron manganese phosphate material, which includes a doped lithium iron manganese phosphate core and a carbon coating layer formed on the surface of the doped lithium iron manganese phosphate core. The chemical formula of the doped lithium iron manganese phosphate is Li a Mn b Fe c M d PO4, wherein the doping metal M includes one, two or more elements selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum.

[0028] The carbon source used to form the carbon coating layer includes an organic carbon source. Suitable organic carbon sources include at least one of glucose, xylitol, PEG (polyethylene glycol), sucrose, lactose, and citric acid polyacrylamide.

[0029] The above-mentioned carbon coating layer includes a certain amount of graphitized carbon. The graphitization of the carbon source refers to the non-graphite carbon being heated to a temperature above its graphitization temperature in a high temperature environment, a protective medium or isolated from air. Due to physical changes, the hexagonal carbon atom plane network layer stacking structure is improved and developed, and transformed into graphite carbon with a three-dimensional regular and ordered structure of graphite. The graphitization of the carbon source can improve the volume density, electrical conductivity, thermal conductivity, corrosion resistance and mechanical processing performance of the material. In this application, the organic carbon source will form a certain degree of graphitization order after high-temperature calcination and carbonization. It is understandable that due to the organic carbon The graphitization temperature of the source is usually relatively high. Therefore, the organic carbon source in the present application can also form a certain degree of graphitization order after high-temperature sintering in a protective medium in a high-temperature environment lower than its graphitization temperature. The degree of graphitization of the organic carbon source is related to the properties of the organic carbon source itself, as well as the provided roasting temperature and roasting time. The closer the graphitization temperature of the organic carbon source is to the provided sintering temperature and the longer the roasting time is, the higher the graphitization degree of the organic carbon source is. The graphitized carbon contained in the above-mentioned carbon coating layer of the present application is not completely graphitized carbon, but carbon that forms a certain graphitized three-dimensional regular structure.

[0030] Furthermore, when the carbon source is calcined at different calcination temperatures, the graphitized carbon formed by the carbon source will have different graphitization degrees. Different calcination temperatures and holding times are controlled according to different carbon sources, thereby controlling the mass percentage content of the graphitized carbon.

[0031] Preferably, in some embodiments of the present application, the content of graphitized carbon accounts for 0.48% to 1.02% by mass of the lithium manganese iron phosphate active material, wherein the calculation formula for the content of graphitized carbon is:

[0032] Graphitized carbon content = (graphitization degree * weight of carbon source) / weight of lithium manganese iron phosphate active material

[0033] It is understandable that the content of graphitized carbon in the doped lithium manganese iron phosphate material can be any value between 0.48% and 1.02%, such as 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or the content of graphitized carbon in the lithium manganese iron phosphate material can be any range between 0.48% and 1.02%, such as 0.48% to 0.8%, 0.48% to 0.9%, 0.6% to 0.9%, 0.6% to 1.0%.

[0034] By adding a certain amount of graphitized carbon to the carbon coating layer of the lithium manganese iron phosphate material, it is beneficial to increase the charge and discharge specific energy of the positive electrode material. Since the interior of the carbon coating layer contains a certain amount of graphitized carbon, the graphitized carbon has a regularly ordered three-dimensional structure. Because it is beneficial for lithium ions to diffuse inside it, the higher the content of graphitized carbon in the carbon coating layer, the faster the diffusion rate of lithium ions, and thus the better the rate performance of the lithium manganese iron phosphate active material, the higher the gram capacity, and thus the higher the specific energy; however, if the diffusion rate of lithium ions in the lithium manganese iron phosphate active material is too fast, the capacity retention rate of the lithium manganese iron phosphate active material will be reduced, and the cycle performance of the lithium manganese iron phosphate active material will deteriorate.

[0035] Preferably, in some embodiments of the present application, in the lithium manganese iron phosphate material, the mass percentage of the carbon coating layer is in the range of 0.5%-3%, wherein the mass percentage of the carbon coating layer can be any value between 0.5%-3%, for example, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, 2.8%, or the content of the carbon coating layer can be any range between 0.5% and 3%, for example, 0.5% to 1.5%, 0.5% to 2%, 1% to 3%, 2% to 3%.

[0036] The lithium manganese iron phosphate material is configured as a multi-metal doped lithium manganese iron phosphate material. The lithium manganese iron phosphate has the same olivine structure as lithium iron phosphate, wherein PO4 has a stable tetrahedral structure. In the process of fully charging the battery, the tetrahedral structure of PO4 is used as a structural support, so that the lithium manganese iron phosphate material has excellent thermodynamic and kinetic stability. Adding manganese material to lithium iron phosphate can increase the voltage platform of the positive electrode material, wherein the voltage platform of the lithium manganese iron phosphate material is 4.1V, and the voltage platform of the lithium iron phosphate positive electrode material is 3.4V, thereby effectively improving the energy density of the battery. However, with the increase of manganese element, the conductivity and electrochemical activity of the lithium manganese iron phosphate material decrease. The lithium manganese iron phosphate material provided in this application includes at least one doping metal element M, wherein the doping element shown in M ​​is introduced to replace the Fe metal site in the LiMnFePO4 crystal, thereby improving the lithium ion diffusion channel and thus improving the conductivity of the positive electrode material, or doping the metal element M and oxygen to form a more stable lattice framework, thereby enhancing the stability of the structure, improving the rate performance and cycle stability of the material, and at the same time improving the energy density.

[0037] Preferably, in some embodiments of the present application, M includes at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum. It is understood that M may include one metal element, two metal elements, or three metal elements, and in a preferred embodiment, among the metal elements included in M, the phosphates of some of the metal elements have an olivine structure. For example, when M is nickel or cobalt, or when M is nickel and cobalt, the phosphate of M element and manganese phosphate or iron phosphate are all configured to have an olivine structure, thereby forming a multi-element olivine-based positive electrode material. The charge-discharge curve and cycle performance curve of the multi-element olivine-based positive electrode material can be regarded as the linear superposition of the charge-discharge curve and cycle performance curve of the olivine structure formed by the phosphate of each metal element, thereby effectively improving the cycle performance of the positive electrode material.

[0038] In the doped lithium manganese iron phosphate material, oxygen atoms form a hexagonal close-packed lattice, the tetrahedral voids in the lattice are occupied by phosphoric acid and anions, and the octahedral holes in the lattice are occupied by lithium ions, iron, manganese and M elements, and the voids occupied by lithium ions form continuous channels in the entire lattice. Therefore, the ratio of the lithium content to the doping metal element M, and the ratio of the doping element M to the phosphorus content are all related to the number of holes in the lattice structure formed by the positive electrode material. The higher the ratio of the lithium content to the doping metal element content, the higher the gram capacity of the positive electrode material, but the alkalinity of the material is enhanced and the side reactions increase. The higher the ratio of the doping metal element M to the phosphorus content, the lower the gram capacity of the positive electrode material and the lower the specific energy, but it is beneficial to improve the cycle performance of the positive electrode material.

[0039] In a preferred embodiment, considering the effects of various elements in the doped lithium manganese iron phosphate material, the inventors found that Li a Mn b Fe c M d When the molar ratio range of each element in PO4 meets the following conditions, it is beneficial to balance the specific energy and cycle performance of lithium manganese iron phosphate materials, among which 0.98≤a≤1.10, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.01≤d≤0.12, and 0.98≤a / (b+c+d)≤1.03.

[0040] In alternative embodiments, Li a Mn b Fe c M dThe molar ratio range of each element in PO4 can also be 0.98≤a≤1.05, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.005≤d≤0.12, and 0.98≤a / (b+c+d)≤1.03.

[0041] Furthermore, the molar ratio range of the lithium element can be any range from 0.98 to 1.10, the molar ratio range of the manganese element can be any range from 0.10 to 0.68, the molar ratio range of the iron element can be any range from 0.20 to 0.70, and the molar ratio range of the doping metal M can be any range from 0.005 to 0.12, which are not listed one by one in the embodiments of the present application.

[0042] The ratio of a / (b+c+d) can be any value between 0.98 and 1.03, such as 0.99, 1.0, 1.01, and 1.02, or the ratio of a / (b+c+d) can be any range between 0.98 and 1.03, such as 0.98 to 1.02, or 0.99 to 1.01.

[0043] In a further preferred embodiment, in Li a Mn b Fe c M d In PO4, the molar content of iron element is less than the molar content of manganese element, wherein appropriately increasing the molar content of manganese element relative to the molar content of iron element is beneficial to increasing the energy density of lithium manganese iron phosphate material.

[0044] In a second aspect, the present application provides a preparation method for the above-mentioned lithium manganese iron phosphate material, wherein the preparation method is a solid phase synthesis method, and the specific preparation method includes:

[0045] (1) Prepare sufficient amounts of lithium source, manganese source, iron source, doping metal source, phosphorus source and carbon source, and mix the lithium source, manganese source, iron source, M source, phosphorus source and carbon source to obtain precursor 1; wherein the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, the M element in the doping metal source and the phosphorus element in the phosphorus source are in the order of Li a Mn b Fe c M d The stoichiometric ratio in PO4 is as follows: 0.98≤a≤1.10, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.01≤d≤0.12, and 0.98≤a / (b+c+d)≤1.03, and the mass percentage of the carbon source in the formed lithium manganese iron phosphate active material is in the range of 0.5%-3%;

[0046] (2) calcining the precursor 1 under an inert atmosphere and cooling it to room temperature to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. Suitable process control parameters of the sintering process include: heating to 600-950°C at a heating rate of 2 min-10 min°C and keeping the temperature for 5-24 h.

[0047] In a third aspect, the present application further provides a preparation method for the above-mentioned lithium manganese iron phosphate material. The second preparation method includes a hybrid process of liquid phase synthesis and solid phase synthesis. The specific preparation method includes:

[0048] (1) mixing a manganese source, an iron source, a phosphorus source, a doping metal M source, hydrogen peroxide, and a complexing agent to obtain a mixed solution 1;

[0049] (2) heating the mixed solution 1, filtering and drying the mixed solution to obtain the precursor 2; wherein the heating temperature is 60° C. to 95° C.;

[0050] (3) mixing the precursor 2, a carbon source, a lithium source, and a surfactant to obtain a precursor 3;

[0051] (4) Sintering the precursor 3 to obtain a lithium manganese iron phosphate material; suitable process control parameters of the sintering process include: heating to 600-950°C at a heating rate of 2 min-10 min°C, and keeping the temperature for 5-24 hours.

[0052] In step 1 to step 3 of the above preparation method 2, the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, the M element in the doping metal source, and the phosphorus element in the phosphorus source are in the order of Li a Mn b Fe c M d The stoichiometric ratio in PO4 is as follows: 0.98≤a≤1.05, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.005≤d≤0.12, and 0.98≤a / (b+c+d)≤1.03. The mass percentage of the carbon source in the formed lithium manganese iron phosphate active material is in the range of 0.5%-3%.

[0053] The complexing agent used in the above-mentioned preparation method 2 includes one or more of HEDP (hydroxyethyl diphosphonic acid), ATMP (aminotrimethylphosphonic acid), or DTPA (tetramethylenediamine diacetate).

[0054] The surfactant used in the above preparation method 2 includes PEG (polyethylene glycol) or ATMP (aminotrimethylphosphonic acid).

[0055] Among them, in the above two synthesis methods, the doping metal source includes one or more of magnesium source, calcium source, strontium source, cobalt source, titanium source, zirconium source, molybdenum source, vanadium source, niobium source, nickel source, scandium source, chromium source, copper source, zinc source, beryllium source, lanthanum source and aluminum source.

[0056] When glucose is included in the carbon source, the carbonization temperature of glucose is 300°C, and the graphitization temperature of glucose is not lower than 800°C. Therefore, under a long-term roasting temperature of 600-950°C and the protection of an inert atmosphere, glucose will form a three-dimensional structure with a certain graphitization regular arrangement. The higher the roasting temperature and the longer the roasting holding time, the higher the graphitization degree of glucose.

[0057] Preferably, in some implementations of the present application, the lithium source in the above two synthesis methods includes at least one of lithium carbonate and lithium dihydrogen phosphate.

[0058] Preferably, in some implementations of the present application, the iron source in the above two synthesis methods includes at least one of ferric phosphate, ferric hydrogen phosphate, ferric dihydrogen phosphate, ferric acetate, and iron powder.

[0059] Preferably, in some implementations of the present application, the manganese source in the above two synthesis methods includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate, manganese oxalate, manganese phosphate, and manganese hydrogen phosphate.

[0060] Preferably, in some implementations of the present application, the phosphorus source in the above two synthesis methods includes at least one of phosphoric acid and ammonium dihydrogen phosphate.

[0061] Preferably, in some embodiments of the present application, the M source in the above two synthesis methods includes at least one of phosphates, hydrogen phosphates, dihydrogen phosphates, carbonates, formates, acetates, glycolates, lactates, tartrates, oxalates, oxides, hydroxides, fluorides, chlorides, nitrates, sulfates, and bromides of at least one element selected from the group consisting of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum.

[0062] Furthermore, in some preferred implementations, the M source includes a phosphate of at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum, and the M source includes a phosphate of at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum configured to form an olivine structure. For example, when M is nickel or cobalt, or when M is nickel and cobalt, the phosphate of M and manganese phosphate or iron phosphate are all configured to form an olivine structure, thereby forming a multi-element olivine-based positive electrode material. The charge-discharge curve and cycle performance curve of the multi-element olivine-based positive electrode material can be regarded as a linear superposition of the charge-discharge curve and cycle performance curve of the olivine structure formed by the phosphate of each metal element, thereby effectively improving the cycle performance of the positive electrode material.

[0063] It should be noted that in the second preparation method, the precursor of manganese ferrophosphate is synthesized by the liquid phase method, which can achieve the mixing of Mn and Fe at the atomic level, form a uniform manganese ferrophosphate precursor, and reduce the segregation and dissolution of Mn; at the same time, the solid phase method is used to synthesize Li a Mn b Fe c M d PO4 can reduce the damage to the ferromanganese phosphate precursor and is easy to implement industrially.

[0064] In a fourth aspect, the present application provides a positive electrode plate, which includes a positive electrode collector and a positive electrode active material layer. The positive electrode active material layer is located on the surface of the positive electrode collector, and the material of the positive electrode active material layer includes the above-mentioned lithium manganese iron phosphate material or the lithium manganese iron phosphate material obtained by the above-mentioned preparation method.

[0065] In a fifth aspect, the present application provides a lithium-ion battery, which includes the above-mentioned lithium iron manganese phosphate material or the lithium iron manganese phosphate material obtained by the above-mentioned preparation method, wherein the lithium-ion battery can be an aluminum shell lithium-ion battery or a soft-pack lithium-ion battery.

[0066] The technical solutions and technical effects are described in detail below by providing specific embodiments and comparative examples. It should be noted that the embodiments provided below are only some embodiments of the present application and do not specifically limit the present application.

[0067] Performance Test 1:

[0068] By comparing and analyzing the specific energy performance and cycle performance parameters of the three lithium iron manganese phosphate materials provided in Example 1, Example 2, and Example 3 and the two lithium iron manganese phosphate materials provided in Comparative Example 1 and Comparative Example 2, it is verified that the specific energy performance and cycle performance of the lithium iron manganese phosphate material provided in the present application are significantly improved over the specific energy performance and cycle performance of the lithium iron manganese phosphate material in the related art.

[0069] Example 1:

[0070] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 PO4, the carbon source forming the coating layer of the lithium manganese iron phosphate material includes glucose and PEG, and the lithium manganese iron phosphate material is prepared by the following preparation method:

[0071] (1) Prepare sufficient amounts of lithium carbonate, manganese carbonate, iron phosphate, magnesium oxide, phosphoric acid, glucose and PEG, and mix and grind the lithium carbonate, manganese carbonate, iron phosphate, magnesium oxide, phosphoric acid, glucose and PEG to obtain precursor 1; wherein the lithium element in lithium carbonate, the manganese element in manganese carbonate, the iron element in iron phosphate, the magnesium element in magnesium oxide, and the phosphorus element in phosphoric acid are in the chemical formula Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Mg:P=1.03:0.65:0.35:0.1:1;

[0072] (2) The precursor 1 is sintered under an inert atmosphere and cooled to room temperature under an inert atmosphere to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. The process control parameters of the suitable sintering process include: heating to 800°C at a heating rate of 6 min°C and keeping warm for 18 hours; wherein glucose and PEG are in the presence of Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at a high temperature to form graphitized carbon. The mass percentage content of the graphitized carbon in the lithium manganese iron phosphate material is 1.0%.

[0073] Example 2:

[0074] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1 PO4, the carbon source for forming the carbon coating layer of the lithium manganese iron phosphate material includes glucose and PEG, and the lithium manganese iron phosphate material is prepared by the following preparation method:

[0075] (1) Prepare sufficient amounts of lithium carbonate, manganese carbonate, iron phosphate, Nb2O5, phosphoric acid, glucose and PEG, and mix and grind the lithium carbonate, manganese carbonate, iron phosphate, Nb2O5, phosphoric acid, glucose and PEG to obtain precursor 1; wherein the lithium element in lithium carbonate, the manganese element in manganese carbonate, the iron element in iron phosphate, the Nb element in Nb2O5 and the phosphorus element in phosphoric acid are in the chemical formula Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Nb:P=1.02:0.58:0.35:0.1:1;

[0076] (2) calcining the precursor 1 under an inert atmosphere and cooling it to room temperature to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. Suitable process control parameters of the calcination process include: heating to 800°C at a heating rate of 6 min°C and keeping the temperature for 18 h; wherein glucose and PEG are in the presence of Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1 A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at high temperature to form graphitized carbon. The content of graphitized carbon in the lithium manganese iron phosphate material is 0.8%.

[0077] Example 3:

[0078] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02 PO4, the carbon source for forming the carbon coating layer of the lithium manganese iron phosphate material includes glucose and PEG, and the lithium manganese iron phosphate material is prepared by the following preparation method:

[0079] (1) Prepare sufficient amounts of lithium carbonate, manganese carbonate, iron phosphate, Nb2O5, TiO2, phosphoric acid, glucose and PEG, and grind and mix the lithium carbonate, manganese carbonate, iron phosphate, Nb2O5, TiO2, phosphoric acid, glucose and PEG to obtain a precursor 1; wherein the lithium element in the lithium carbonate, the manganese element in the manganese carbonate, the iron element in the iron phosphate, the niobium element in the Nb2O5, the titanium element in the TiO2, and the phosphorus element in the phosphoric acid are in accordance with the chemical formula Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02The stoichiometric ratio in PO4 is proportioned, that is, the molar ratio of Li:Mn:Fe:Nb:Ti:P=1.01:0.58:0.35:0.08:0.02:1;

[0080] (2) calcining the precursor 1 under an inert atmosphere and cooling it to room temperature to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. Suitable process control parameters of the calcination process include: heating to 800°C at a heating rate of 6 min°C and keeping the temperature for 18 h; wherein glucose and PEG are in the presence of Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02 A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at a high temperature to form graphitized carbon. The content of graphitized carbon in the lithium manganese iron phosphate material is 0.5%.

[0081] Comparative Example 1:

[0082] This comparative example 1 provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.04 Mn 0.55 Fe 0.35 Mg 0.1 PO4, the carbon source for forming the carbon coating layer of the lithium manganese iron phosphate material is graphite, and the lithium manganese iron phosphate material is prepared by the following preparation method:

[0083] (1) Prepare sufficient amounts of lithium carbonate, manganese carbonate, iron phosphate, magnesium oxide, phosphoric acid, and graphite, and mix the lithium carbonate, manganese carbonate, iron phosphate, magnesium oxide, phosphoric acid, and graphite to obtain a precursor 1; wherein the lithium element in the lithium carbonate, the manganese element in the manganese carbonate, the iron element in the iron phosphate, the magnesium element in the magnesium oxide, and the phosphorus element in the phosphoric acid are in the chemical formula Li 1.04 Mn 0.55 Fe 0.35 Mg 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Mg:P=1.04:0.55:0.35:0.1:1;

[0084] (2) calcining the precursor 1 under an inert atmosphere and cooling it to room temperature to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. Suitable process control parameters of the calcination process include: heating to 800°C at a heating rate of 6 min°C and keeping the temperature for 18 hours; wherein the graphite is in the presence of Li 1.04 Mn 0.55 Fe 0.35 Mg0.1 A carbon coating layer is formed on the outer surface of PO4, and the mass percentage of graphite in the lithium manganese iron phosphate material is 1.2%.

[0085] Comparative Example 2:

[0086] This comparative example 1 provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.04 Mn 0.55 Fe 0.35 Co 0.1 PO4, the carbon source for forming the carbon coating layer of the lithium manganese iron phosphate material is carbon black, and the lithium manganese iron phosphate material is prepared by the following preparation method:

[0087] (1) Prepare sufficient amounts of lithium carbonate, manganese carbonate, iron phosphate, cobalt oxide, phosphoric acid, and carbon black, and mix the lithium carbonate, manganese carbonate, iron phosphate, cobalt oxide, phosphoric acid, and carbon black to obtain a precursor 1; wherein the lithium element in the lithium carbonate, the manganese element in the manganese carbonate, the iron element in the iron phosphate, the cobalt element in the cobalt oxide, and the phosphorus element in the phosphoric acid are in accordance with the chemical formula Li 1.04 Mn 0.55 Fe 0.35 Co 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Co:P=1.04:0.55:0.35:0.1:1;

[0088] (2) calcining the precursor 1 under an inert atmosphere and cooling it to room temperature to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. Suitable process control parameters of the calcination process include: heating to 800°C at a heating rate of 6 min°C and keeping the temperature for 18 hours; wherein the carbon black is in the presence of Li 1.04 Mn 0.55 Fe 0.35 Mg 0.1 A carbon coating layer is formed on the outer surface of PO4, and carbon black is calcined at a high temperature to form a certain amount of graphitized carbon. The mass percentage of graphitized carbon in the lithium manganese iron phosphate material is 1.05%.

[0089] The preparation methods of the lithium ion batteries of the embodiments and comparative examples are as follows:

[0090] (1) Preparation of negative electrode sheet

[0091] The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber and the thickener sodium carboxymethyl cellulose are mixed in a weight ratio of graphite: acetylene black: styrene butadiene rubber: sodium carboxymethyl cellulose = 95:2:2:1, and an appropriate amount of deionized water is added and stirred thoroughly to form a uniform negative electrode slurry; the slurry is coated on the negative electrode current collector copper foil, dried and cold pressed to obtain a negative electrode sheet.

[0092] (2) Preparation of positive electrode sheet

[0093] The corresponding positive electrode active material, conductive agent acetylene black and binder polyvinylidene fluoride are mixed in a weight ratio of 96:2:2, and N-methylpyrrolidone is used as a solvent. After thorough grinding and stirring, a uniform positive electrode slurry is formed. The slurry is coated on the positive electrode current collector aluminum foil, dried and cold pressed to obtain a positive electrode sheet.

[0094] (3) Preparation of batteries

[0095] The positive electrode sheet, separator (PE / PP porous polymer film), and negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to play an isolating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging foil, and a lithium ion electrolyte composed of organic solvents such as EC (ethylene carbonate) / EMC (ethyl methyl carbonate) and LiPF6 is injected into the dried battery, and then after vacuum packaging, standing, formation, shaping and other processes, a lithium ion battery is obtained.

[0096] Performance testing method:

[0097] Use a constant temperature box battery test cabinet to cycle charge and discharge for three weeks at a specified temperature and a current of 0.1C to obtain the actual capacity Q of the lithium-ion battery;

[0098] The batteries made of lithium manganese iron phosphate materials prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were respectively subjected to 1C discharge specific energy (mAh / g) test;

[0099] The batteries made of lithium manganese iron phosphate materials prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were respectively subjected to 1C charging specific energy (mAh / g) test;

[0100] In a constant temperature environment of 25°C, a battery cycle charge and discharge life test was carried out under 1C-1C charge and discharge conditions to test the battery capacity of the lithium manganese iron phosphate materials prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 to drop to 20% of the rated capacity. The number of cycles that the battery can achieve;

[0101] In a constant temperature environment of 45°C, a battery cycle charge and discharge life test was carried out under 1C-1C charge and discharge conditions to test the number of cycles that the battery can achieve when the battery capacity of the lithium manganese iron phosphate materials prepared in Examples 1, 2, 3, Comparative Example 1 and 2 drops to 20% of the rated capacity;

[0102] After testing, the battery adopts the lithium manganese iron phosphate positive electrode material prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2, and the obtained battery 1C charge specific energy (mAh / g), 1C discharge specific energy (mAh / g), battery cycle charge and discharge life test (number) under 1C-1C charge and discharge conditions in a constant temperature environment of 25°C, and battery cycle charge and discharge life test (number) under 1C-1C charge and discharge conditions in a constant temperature environment of 45°C are shown in the following Table 2:

[0103] Table 1. Composition of lithium manganese iron phosphate cathode materials in Examples and Comparative Examples

[0104] Table 2. Specific energy test data and cycle performance test data of the embodiments and comparative examples

[0105] The battery 1C charge specific energy of the lithium manganese iron phosphate material provided by Example 1 can reach 556 mAh / g, and the battery 1C discharge specific energy can reach 518 mAh / g, which is significantly improved compared with Comparative Examples 1 and 2;

[0106] The battery of the lithium manganese iron phosphate material provided by Example 3 can be tested for 5000 charge and discharge cycles at 1C-1C in a constant temperature environment at 25°C; and 3000 charge and discharge cycles at 1C-1C in a constant temperature environment at 45°C, which is significantly improved compared to Comparative Examples 1 and 2.

[0107] By comparing the battery 1C charge specific energy and 1C discharge specific energy test data of the lithium manganese iron phosphate material provided in Example 1, Example 2, and Example 3, when the content of graphitized carbon in the lithium manganese iron phosphate material is between 0.48% and 1.02%, as the content of graphitized carbon increases, the charge and discharge specific energy of the positive electrode material increases, and in a constant temperature environment of 25°C, under the condition of 1C-1C charge and discharge, the number of charge and discharge cycle tests of the battery decreases. At the same time, in a constant temperature environment of 45°C, under the condition of 1C-1C charge and discharge, the number of charge and discharge cycle tests of the battery also decreases.

[0108] By comparing the battery 1C charge specific energy and 1C discharge specific energy test data of the lithium manganese iron phosphate material provided in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2, when the content of graphitized carbon in the lithium manganese iron phosphate material is greater than 1.02%, the charge and discharge specific energy of the positive electrode material is significantly reduced;

[0109] By comparing the lithium manganese iron phosphate battery provided in Example 1, Example 2 and Example 3, the battery is subjected to charge and discharge cycle test times at 1C-1C charge and discharge conditions in a constant temperature environment of 25°C. a Mn b Fe c M d The ratio of a / (b+c+d) in PO4 is between 0.98 and 1.03. As the ratio of a / (b+c+d) increases, the cycle life of the battery increases. By comparing the battery of lithium manganese iron phosphate provided by Examples 1, 2 and 3 in a constant temperature environment of 45°C and under 1C-1C charge and discharge conditions, the number of charge and discharge cycle tests of the battery is as follows: a Mn b Fe c M d The ratio of a / (b+c+d) in PO4 is between 0.98 and 1.03. As the ratio of a / (b+c+d) increases, the cycle life of the battery increases;

[0110] By comparing the lithium manganese iron phosphate battery provided by Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2, the battery is subjected to charge and discharge cycle tests at 1C-1C under a constant temperature environment of 25°C. a Mn b Fe c M d When the ratio of a / (b+c+d) in PO4 is greater than 1.03, the cycle life of the battery is significantly reduced. By comparing the lithium manganese iron phosphate battery provided by Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2, the battery is subjected to charge and discharge cycle tests at a constant temperature of 45°C and a charge and discharge condition of 1C-1C. When the positive electrode material Li a Mn b Fe c M d When the ratio of a / (b+c+d) in PO4 is greater than 1.03, the cycle life of the battery is significantly reduced.

[0111] Lithium-ion batteries prepared using the above-mentioned lithium manganese iron phosphate material will have the problem of manganese precipitation during use, that is, manganese ions in the positive electrode material are precipitated from the positive electrode material and deposited on the negative electrode or other components. Manganese precipitation will lead to a decrease in battery capacity, a shortened battery life and a decrease in safety performance.

[0112] By adopting the second preparation method provided in the embodiment of the present application, that is, synthesizing the precursor 2 of manganese iron phosphate by a liquid phase method and synthesizing the lithium manganese iron phosphate material by a solid phase method, by synthesizing the precursor 2 of manganese iron phosphate by a liquid phase method, the mixing of Mn and Fe at the atomic level can be achieved to form a uniform precursor of manganese iron phosphate, thereby reducing the precipitation of manganese.

[0113] Performance Test 2:

[0114] The three lithium manganese iron phosphate materials provided in Examples 4, 5, and 6 were synthesized by the second preparation method provided in the above embodiments, and the two lithium manganese iron phosphate materials provided in Comparative Examples 1 and 2 were synthesized by a pure solid-phase method, and the manganese precipitation weight of the lithium battery materials prepared in Examples 4, 5, 6, Comparative Examples 1, and 2 were analyzed and tested.

[0115] Example 4:

[0116] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 PO4, lithium manganese iron phosphate material is prepared by the following preparation method:

[0117] (1) preparing sufficient amounts of manganese sulfate, ferric phosphate, magnesium oxide, and phosphoric acid, mixing them, slowly adding hydrogen peroxide and HEDP to obtain a mixture 1, heating the mixture 1 to 90° C., filtering, and drying to obtain a precursor 2;

[0118] (2) Precursor 2, glucose, PEG and lithium carbonate are mixed and ground to obtain precursor 3; wherein the lithium element in lithium carbonate, the manganese element in manganese sulfate, the iron element in iron phosphate, the magnesium element in magnesium oxide, and the phosphorus element in phosphoric acid are mixed according to the chemical formula Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Mg:P=1.03:0.65:0.35:0.1:1;

[0119] (3) The precursor 3 is sintered under an inert atmosphere and cooled to room temperature under an inert atmosphere to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. The process control parameters of the suitable sintering process include: heating to 800°C at a heating rate of 6 min°C and keeping warm for 18 hours; wherein glucose and PEG are in the presence of Li 1.03 Mn 0.65 Fe 0.35 Mg 0.1 A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at a high temperature to form graphitized carbon. The mass percentage content of the graphitized carbon in the lithium manganese iron phosphate material is 1.0%.

[0120] Example 5:

[0121] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1 PO4, lithium manganese iron phosphate material is prepared by the following preparation method:

[0122] (1) preparing sufficient amounts of manganese sulfate, iron phosphate, Nb2O5, and phosphoric acid, mixing them, slowly adding hydrogen peroxide and HEDP to obtain a mixture 1, heating the mixture 1 to 90°C, filtering, and drying to obtain a precursor 2;

[0123] (2) Precursor 2, glucose, PEG and lithium carbonate are mixed and ground to obtain precursor 3; wherein the lithium element in lithium carbonate, the manganese element in manganese sulfate, the iron element in iron phosphate, the niobium element in niobium oxide, and the phosphorus element in phosphoric acid are mixed according to the chemical formula Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Nb:P=1.02:0.58:0.35:0.1:1;

[0124] (3) The precursor 3 is sintered under an inert atmosphere and cooled to room temperature under an inert atmosphere to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. The process control parameters of the suitable sintering process include: heating to 800°C at a heating rate of 6 min°C and keeping warm for 18 hours; wherein glucose and PEG are in the presence of Li 1.02 Mn 0.58 Fe 0.35 Nb 0.1A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at high temperature to form graphitized carbon. The content of graphitized carbon in the lithium manganese iron phosphate material is 0.8%.

[0125] Example 6:

[0126] This embodiment provides a lithium manganese iron phosphate material, wherein the chemical formula of the core material of the lithium manganese iron phosphate material is Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02 PO4, lithium manganese iron phosphate material is prepared by the following preparation method:

[0127] (1) preparing sufficient amounts of manganese sulfate, iron phosphate, Nb2O5, TiO2, and phosphoric acid, mixing them, slowly adding hydrogen peroxide and HEDP to obtain a mixture 1, heating the mixture 1 to 90°C, filtering and drying, and obtaining a precursor 2;

[0128] (2) Precursor 2, glucose, PEG and lithium carbonate are mixed and ground to obtain precursor 3; wherein the lithium element in lithium carbonate, the manganese element in manganese sulfate, the iron element in iron phosphate, the niobium element in niobium oxide, the titanium element in titanium oxide, and the phosphorus element in phosphoric acid are mixed according to the chemical formula Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02 The stoichiometric ratio in PO4 is proportioned, that is, according to the molar ratio of Li:Mn:Fe:Nb:Ti:P=1.01:0.58:0.35: 0.08:0.02:1;

[0129] (3) The precursor 3 is sintered under an inert atmosphere and cooled to room temperature under an inert atmosphere to obtain a powder, wherein the inert atmosphere includes nitrogen or argon or a mixture of nitrogen and argon. The process control parameters of the suitable sintering process include: heating to 800°C at a heating rate of 6 min°C and keeping warm for 18 hours; wherein glucose and PEG are in the presence of Li 1.01 Mn 0.58 Fe 0.35 Nb 0.08 Ti 0.02 A carbon coating layer is formed on the outer surface of PO4, and glucose and PEG are calcined at a high temperature to form graphitized carbon. The content of graphitized carbon in the lithium manganese iron phosphate material is 0.5%.

[0130] Comparative Example 1 and Comparative Example 2 are the same as those provided in the Performance Test 1 section.

[0131] The preparation methods of the lithium ion batteries of Examples 4-6 and Comparative Examples 1-2 are the same as above.

[0132] Manganese ion precipitation weight test method:

[0133] (1) Using the lithium-ion battery samples of Examples 4-6 and Comparative Examples 1-2, each lithium-ion battery sample was charged to a standard voltage to ensure that the battery was in normal working condition for 24 hours;

[0134] (2) taking out the lithium ion battery samples of Examples 4-6 and Comparative Examples 1-2, and decomposing the lithium ion battery samples of Examples 4-6 and Comparative Examples 1-2, by subjecting the batteries to solvent extraction and dissolving the manganese ions in the batteries using an appropriate solvent;

[0135] (3) The weight of manganese ions in the lithium ion battery samples of Examples 4-6 and Comparative Examples 1-2 was determined respectively. In the weight measurement method, manganese ions were precipitated from the solution using a solvent. After drying and weighing, the weight of the precipitated manganese ions was calculated.

[0136] The manganese precipitation weight of the lithium ion batteries prepared in Examples 4-6 and Comparative Examples 1-2 was tested and the results are as follows:

[0137] Table 3. Manganese precipitation analysis data of Examples 4-6 and Comparative Examples 1-2

[0138] By comparing and analyzing the manganese precipitation weight of Examples 4-6 with that of Comparative Examples 1-2, it can be concluded that the second preparation method provided in the embodiments of the present application, that is, synthesizing the precursor by a liquid phase method and synthesizing the lithium manganese iron phosphate material by a solid phase method, can significantly reduce the manganese precipitation in the lithium ion battery and prepare a lithium ion battery with better performance.

Claims

1. A lithium iron manganese phosphate material, comprising a core and a coating layer coated on the surface of the core, wherein the material of the core comprises a chemical formula of Li a Mn b Fe c M d PO 4 , wherein M includes at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum and aluminum, and the carbon coating layer includes graphitized carbon.

2. The lithium iron manganese phosphate material according to claim 1, in, The mass percentage of the graphitized carbon in the lithium manganese iron phosphate material is 0.48% to 1.02%.

3. The lithium iron manganese phosphate material according to claim 1, in, The coating layer is configured to be formed by sintering a carbon source, and the carbon source forming the coating layer includes at least one of glucose, xylitol, polyethylene glycol, sucrose, lactose, and citric acid polyacrylamide.

4. The lithium iron manganese phosphate material according to any one of claims 1 to 3, in, The mass percentage of the carbon coating layer in the lithium manganese iron phosphate material is 0.5%-3%.

5. The lithium iron manganese phosphate material according to any one of claims 1 to 3, in, In the Li a Mn b Fe c M d PO 4 0.98≤a≤1.10, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.01≤d≤0.12, 0.98≤a / (b+c+d)≤1.03; or, in the Li a Mn b Fe c M d PO 4 Among them, 0.98≤a≤1.05, 0.10≤b≤0.68, 0.20≤c≤0.70, 0.005≤d≤0.12, 0.98≤a / (b+c+d)≤1.

03.

6. The lithium iron manganese phosphate material according to claim 5, in, In the Li a Mn b Fe c M d PO 4 In the experiment, the molar content of manganese is greater than that of iron.

7. A method for preparing lithium manganese iron phosphate material, the preparation method The following steps are involved: The lithium source, manganese source, iron source, phosphorus source, doped metal M source and carbon source are mixed to obtain Precursor 1; Under the protection of an inert atmosphere, the precursor 1 is sintered to obtain a lithium manganese iron phosphate material; Among them, the doped metal M source includes one or more of a magnesium source, a calcium source, a strontium source, a cobalt source, a titanium source, a zirconium source, a molybdenum source, a vanadium source, a niobium source, a nickel source, a scandium source, a chromium source, a copper source, a zinc source, a beryllium source, a lanthanum source and an aluminum source.

8. The method for preparing the lithium iron manganese phosphate material according to claim 7, in, In the step of mixing a lithium source, a manganese source, an iron source, a phosphorus source, a doped metal M source, and a carbon source to obtain a precursor 1, the molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, and the doped metal element in the doped metal source is (0.98-1.10): (0.10-0.68): (0.20-0.70): (0.01-0.12).

9. The method for preparing the lithium iron manganese phosphate material according to claim 7, in, The sintering treatment of the precursor 1 includes heating the precursor 1 to a first temperature at a first heating rate and keeping the temperature for a first time; wherein: The first heating rate is 2°C / min-10°C / min; and / or The first temperature is 600°C-950°C; and / or The first time is 5-24h.

10. A method for preparing lithium manganese iron phosphate material, the preparation method The following steps are involved: Mixing a manganese source, an iron source, a phosphorus source, a doped metal M source, hydrogen peroxide and a complexing agent to obtain a mixed solution 1; The mixed solution 1 is heated, filtered and dried to obtain a precursor 2; The precursor 2, a carbon source, a lithium source, and a surfactant are mixed to obtain a precursor 3; The precursor 3 is sintered to obtain a lithium manganese iron phosphate material; The doping metal source includes magnesium source, calcium source, strontium source, cobalt source, titanium source, zirconium source, molybdenum source, vanadium source, niobium source, nickel source, scandium source, chromium source, copper source, zinc source, beryllium source, lanthanum source and and one or more of an aluminum source.

11. The method for preparing the lithium iron manganese phosphate material according to claim 10, in, In the step of mixing a lithium source, a manganese source, an iron source, a phosphorus source, a doped metal M source, and a carbon source to obtain a precursor 1, the molar ratio of the lithium element in the lithium source, the manganese element in the manganese source, the iron element in the iron source, and the doped metal element in the doped metal source is (0.98-1.05): (0.10-0.68): (0.20-0.70): (0.005-0.12).

12. The method for preparing the lithium iron manganese phosphate material according to claim 10, in, Heating the mixed solution 1 includes heating the mixed solution 1 to a second temperature, wherein the second temperature is 60° C.-95° C.

13. The method for preparing the lithium iron manganese phosphate material according to claim 10, in, The sintering treatment of the precursor 3 includes heating the precursor 3 to a first temperature at a first heating rate and keeping the temperature for a first time; wherein: The first heating rate is 2°C / min-10°C / min; and / or The first temperature is 600°C-950°C; and / or The first time is 5-24h.

14. The method for preparing the lithium iron manganese phosphate material according to claim 7 or 10, in, The lithium source includes at least one of lithium carbonate and lithium dihydrogen phosphate.

15. The method for preparing the lithium iron manganese phosphate material according to claim 7 or 10, in, The iron source includes at least one of ferrous sulfate, ferric phosphate, ferric hydrogen phosphate, ferric dihydrogen phosphate, ferric acetate, and iron powder.

16. The method for preparing the lithium iron manganese phosphate material according to claim 7 or 10, in, The manganese source includes at least one of manganese sulfate, manganese carbonate, manganese nitrate, manganese acetate, manganese oxalate, manganese phosphate, and manganese hydrogen phosphate.

17. The method for preparing the lithium iron manganese phosphate material according to claim 7 or 10, in, The phosphorus source includes at least one of phosphoric acid and diammonium phosphate.

18. The method for preparing the lithium iron manganese phosphate material according to claim 7 or 10, It is characterized in that The doping metal M source includes at least one of phosphates, hydrogen phosphates, dihydrogen phosphates, carbonates, formates, acetates, glycolates, lactates, tartrates, oxalates, oxides, hydroxides, fluorides, chlorides, nitrates, sulfates, and bromides of at least one element selected from magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum.

19. The method for preparing the lithium iron manganese phosphate material according to claim 18, in, The doping metal source includes a phosphate of at least one element selected from the group consisting of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum, and the doping metal source includes a phosphate of at least one element selected from the group consisting of magnesium, calcium, strontium, cobalt, titanium, zirconium, molybdenum, vanadium, niobium, nickel, scandium, chromium, copper, zinc, beryllium, lanthanum, and aluminum configured as an olivine structure.

20. The method for preparing the lithium iron manganese phosphate material according to claim 10, in, The complexing agent includes at least one of HEDP, ATMP and DTPA.

21. The method for preparing the lithium iron manganese phosphate material according to claim 10, in, The surfactant includes at least one of PEG and ATMP.

22. A positive electrode plate, comprising a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer is located on the surface of the positive electrode current collector, and the material of the positive electrode active material layer comprises the lithium manganese iron phosphate material according to any one of claims 1 to 6 or the lithium manganese iron phosphate material obtained by the preparation method according to any one of claims 7 to 21.

23. A lithium ion battery, comprising the lithium iron manganese phosphate material according to any one of claims 1 to 6.

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