Lithium manganese iron phosphate material and preparation method therefor, and lithium battery

Abstract

The present invention relates to a lithium manganese iron phosphate material and a preparation method therefor, and a lithium battery. The lithium manganese iron phosphate material comprises an inner core and a coating layer coating the outer surface of the inner core, wherein the material of the inner core comprises Li, M and PO4 in a non-stoichiometric composition, wherein M is FeyMnxDz, and D is a metal element; and the material of the coating layer comprises a carbon material. The lithium manganese iron phosphate material has both good structural stability, a good actual gram volume and a long cycle life.

Description

Lithium iron manganese phosphate material, preparation method of lithium iron manganese phosphate material and lithium battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on November 21, 2023, with application number 202311569508.9. 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, a preparation method of the lithium iron manganese phosphate material, and a lithium battery. Background Art

[0003] With the continuous development of portable electronic devices, electric vehicles and large-scale energy storage markets, the demand for lithium batteries continues to grow. The positive electrode sheet is one of the key components of lithium batteries, and the positive electrode material has an important impact on the performance of lithium batteries. Olivine-type positive electrode materials have the advantages of high safety performance and low cost. Among them, lithium iron manganese phosphate and lithium iron phosphate are both olivine-type positive electrode materials. Lithium iron phosphate has high safety and cycle life, but its voltage platform is low, which makes it difficult to meet the demand for higher energy density. Compared with lithium iron phosphate, the high voltage characteristics of manganese give lithium iron manganese phosphate a higher voltage platform, thus having a higher energy density. In addition, lithium iron phosphate takes into account the high safety, high cycle life, low cost, and environmental friendliness of lithium iron phosphate. Lithium iron manganese phosphate is currently one of the research hotspots of lithium battery positive electrode materials.

[0004] In related technologies, although lithium manganese iron phosphate materials prepared by high-temperature solid-phase synthesis can be used as electrode materials for lithium batteries, with the widespread application of lithium batteries, the market has put forward higher requirements on the performance of lithium batteries, such as rate charge and discharge performance. Therefore, how to improve the actual gram capacity and cycle life of lithium manganese iron phosphate is of great significance. Technical issues

[0005] The present application provides a lithium iron manganese phosphate material, a preparation method of the lithium iron manganese phosphate material, and a lithium battery to solve the above technical problems. Technical Solutions

[0006] The present application provides a lithium iron manganese phosphate material, a preparation method of the lithium iron manganese phosphate material, and a lithium battery to improve the actual gram capacity and cycle life of the lithium iron manganese phosphate.

[0007] In a first aspect, an embodiment of the present application provides a lithium iron manganese phosphate material, wherein the lithium iron manganese phosphate material includes a core and a coating layer coated on an outer surface of the core;

[0008] The core material includes Li, M and PO4 with non-stoichiometric composition, M is Fey Mn x D z , wherein D is a metal element, and the metal element does not include Fe or Mn, x, y and z represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material respectively, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material;

[0009] In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01-1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95-1.10, and the ratio of the molar amount of A to the molar amount of PO4 is 0.90-1.15.

[0010] In some embodiments of the present application, in the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.03-1.07, and / or the ratio of the molar amount of Li to the molar amount of PO4 is 1.00-1.05, and / or the ratio of the molar amount of A to the molar amount of PO4 is 0.95-1.10.

[0011] In a second aspect, an embodiment of the present application provides a method for preparing a lithium manganese iron phosphate material, comprising the following steps:

[0012] Providing a first slurry including a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source, and a D source;

[0013] Grinding the first slurry to obtain a second slurry;

[0014] spray drying the second slurry to obtain a pre-burned material; and

[0015] sintering the pre-burned material under a protective gas atmosphere to obtain a lithium manganese iron phosphate material having a coating layer, wherein the coating layer is made of a carbon material;

[0016] The prepared lithium manganese iron phosphate material includes a core and a coating layer coated on the outer surface of the core; the material of the core includes Li, M and PO4 with a non-stoichiometric composition, M is Fe y Mn x D z , wherein D is a metal element, and the metal element does not include Fe or Mn, x, y and z respectively represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material; in the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01 to 1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95 to 1.10, and the ratio of the molar amount of A to the molar amount of PO4 is 0.90 to 1.15.

[0017] In a third aspect, an embodiment of the present application provides a lithium battery, comprising one or more battery cells, wherein the battery cells comprise a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector, wherein the material of the positive electrode active material layer comprises lithium manganese iron phosphate material;

[0018] The lithium manganese iron phosphate material includes a core and a coating layer coated on the outer surface of the core; the core material includes Li, M and PO4 with a non-stoichiometric composition, where M is Fe y Mn x D z , wherein D is a metal element, and the metal element does not include Fe or Mn, x, y and z represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material respectively, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material;

[0019] In the lithium manganese iron phosphate material, the molar ratio of Li to A is 1.01-1.10, the molar ratio of Li to PO4 is 0.95-1.10, and the molar ratio of A to PO4 is 0.90-1.15. Beneficial effects

[0020] The beneficial effects of the present application are as follows: in the lithium iron manganese phosphate material, there is a specific molar ratio between Li, M and PO4 in the core, so that the lithium iron manganese phosphate material has good structural stability, actual gram capacity and cycle life. If the ratio of the molar amount of Li to A is lower than 1.01 (i.e., the Li content is low), the actual gram capacity will be reduced. If the ratio of the molar amount of Li to A is greater than 1.10 (i.e., the Li content is high), then when the lithium iron manganese phosphate material is wetted by water, the residual alkali content on the surface of the lithium iron manganese phosphate material will increase. If the residual alkali content is too high, the lithium battery will have the problem of "flatulence", resulting in a decrease in the cycle performance of the lithium battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a schematic structural diagram of a lithium battery provided in an embodiment of the present application.

[0022] FIG2 is a schematic diagram of the structure of a battery cell unit in a lithium battery provided in an embodiment of the present application.

[0023] FIG3 is a schematic structural diagram of a positive electrode sheet provided in an embodiment of the present application.

[0024] FIG4 is an X-ray diffraction pattern of the material obtained through the iron removal treatment process in step S1.5 of Example 1 of the present application.

[0025] FIG5 is an electron microscope image of the lithium manganese iron phosphate material in Example 1 of the present application.

[0026] FIG6 is a Raman spectrum of the lithium manganese iron phosphate material in Example 1 of the present application. Modes for Carrying Out the Invention

[0027] 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.

[0028] It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Each embodiment 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.

[0029] In the description of this application, the term "including" means "including but not limited to".

[0030] 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.

[0031] 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").

[0032] The term "solid content" refers to the ratio of the mass of solid matter in the slurry to the total mass of the slurry.

[0033] The present invention provides a lithium manganese iron phosphate material, which includes a core and a coating layer coated on the outer surface of the core, wherein the core material includes Li, M and PO4 with a non-stoichiometric composition, M is Fe y Mn x D z , where D is a metal element, excluding Fe or Mn; x, y, and z represent the molar amounts of Fe, Mn, and the metal element in the lithium manganese iron phosphate material, respectively; the sum of the molar amounts of Fe, Mn, and the metal element is A; and the coating layer material includes a carbon material. In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01 to 1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95 to 1.10, and the ratio of A to the molar amount of PO4 is 0.90 to 1.15.

[0034] In the lithium iron phosphate material of the embodiment of the present application, there is a specific molar ratio between Li, M and PO4 in the core, so that the lithium iron phosphate material has good structural stability, actual gram capacity and cycle life. If the ratio of the molar amount of Li to A is lower than 1.01 (that is, the Li content is low), the actual gram capacity will be reduced. If the ratio of the molar amount of Li to A is greater than 1.10 (that is, the Li content is high), when the lithium iron phosphate material is wetted by water, the residual alkali content on the surface of the lithium iron phosphate material will increase. If the residual alkali content is too high, the lithium battery will have the problem of "flatulence", resulting in a decrease in the cycle performance of the lithium battery.

[0035] In addition, the lithium manganese iron phosphate material includes a coating layer, and the material of the coating layer includes a carbon material, which has technical effects: first, effective carbon coating can construct a conductive network to provide a medium for electron transmission, thereby improving the electron transmission efficiency; second, it can inhibit the growth of lithium manganese iron phosphate particles and inhibit the "agglomeration" phenomenon of lithium manganese iron phosphate particles, thereby reducing Li + transmission distance and improve ionic conductivity; thirdly, the coating layer has a protective effect on the core, which can improve or avoid the problem of Fe and Mn dissolution caused by the infiltration of water (such as electrolyte) into the core.

[0036] In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of PO4 is, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.10, or a value between any two of the foregoing values. The ratio of the molar amount of Li to A is, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, or a value between any two of the foregoing values. The ratio of the molar amount of A to the molar amount of PO4 is, for example, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.10, 1.11, 1.12, 1.13, 1.14, 1.15, or a value between any two of the foregoing values.

[0037] In order to further improve the gram capacity and cycle life of the lithium manganese iron phosphate material, in some embodiments of the present application, in the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.03 to 1.07, and / or the ratio of the molar amount of Li to the molar amount of PO4 is 1.00 to 1.05, and / or the ratio of the molar amount of A to the molar amount of PO4 is 0.95 to 1.10.

[0038] In order to improve the compactibility of the lithium manganese iron phosphate material, in some embodiments of the present application, the D50 particle size of the core is less than 10 μm, for example, less than 9 μm, less than 8 μm, less than 7 μm, less than 6 μm, less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm or less than 1 μm.

[0039] In order to improve the coating uniformity of the coating layer and improve or avoid the "agglomeration" problem of free carbon, in some embodiments of the present application, the mass of the carbon material accounts for 0.5% to 3% of the total mass of the lithium manganese iron phosphate material, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a value between any two of the foregoing values.

[0040] In some embodiments of the present application, the thickness of the coating layer is 3 nm to 5 nm, for example, it can be 3 nm, 4 nm, 5 nm, or a value between any two of the aforementioned values.

[0041] It should be noted that the lithium manganese iron phosphate material of the embodiment of the present application has a -1 There is a strong absorption peak at the D band of carbon (sp 3 hybrid carbon), and lithium manganese iron phosphate material at 1590 cm -1 There is also a strong absorption peak at the G band of carbon (sp 2 Hybridized carbon), the ratio of D band to G band is ID / IG, which can characterize the conductivity of residual carbon. The smaller the value of ID / IG, the higher the sp2 The higher the content of hybrid carbon, the higher the conductivity of carbon. Conversely, the larger the value of ID / IG, the higher the sp 3 The higher the content of hybridized carbon, the lower the conductivity of the carbon.

[0042] In order to further improve the electron transmission efficiency of the lithium manganese iron phosphate material, in some embodiments of the present application, 0.50<ID / IG<0.95, and ID / IG can be, for example, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.92, 0.94 or a value between any two of the foregoing values.

[0043] In order to further improve the gram capacity and cycle life of the lithium manganese iron phosphate material, in some embodiments of the present application, in M, D is selected from one or more of Mg, Ti, V, Ni, Co, Al, Nb, Nd, Y, Mo, Sr, La, Zr, B and Ca; and / or, in M, 0.1<x<0.9, 0.1<y<0.5, 0<Z<0.5.

[0044] The present application also provides a method for preparing a lithium iron manganese phosphate material, which can be used to prepare any of the lithium iron manganese phosphate materials described above, comprising the following steps:

[0045] S1. Providing a first slurry including a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source, and a D source;

[0046] S2, grinding the first slurry to obtain a second slurry;

[0047] S3, spray drying the second slurry to obtain a pre-burned material;

[0048] S4. Under a protective gas atmosphere, the pre-burned material is sintered to obtain a lithium manganese iron phosphate material having a coating layer, wherein the coating layer is made of a carbon material.

[0049] Specifically, in step S1, the D source includes a metal element and does not include Fe or Mn. The molar ratio of Li in the lithium source to P in the phosphorus source is 0.95 to 1.10, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.10, or a value between any two of the foregoing values.

[0050] In step S1, each raw material can be selected according to conventional methods in the art. The lithium source can be one or more of lithium oxide, lithium hydroxide, and lithium salts. The lithium oxide includes, but is not limited to, Li2O. The anions generated by the ionization of the lithium salt include, but are not limited to, one or more of oxalate ions, carbonate ions, sulfate ions, nitrate ions, acetate ions, halide ions, phosphate ions, and dihydrogen phosphate ions. Examples of lithium salts include one or more of lithium carbonate, lithium sulfate, lithium nitrate, lithium acetate, lithium dihydrogen phosphate, lithium phosphate, and lithium oxalate.

[0051] The manganese source can be one or more of manganese oxide, manganese hydroxide and manganese salt. Manganese oxide includes but is not limited to one or more of manganese monoxide, manganese dioxide and manganese tetraoxide. The anions generated by the ionization of manganese salt include but are not limited to one or more of oxalate ion, carbonate ion, sulfate ion, nitrate ion, acetate ion, halide ion and phosphate ion. Examples of manganese sources are one or more of manganese carbonate, manganese phosphate, manganese oxalate, manganese nitrate, manganese acetate, manganese sulfate and manganese chloride.

[0052] The iron source is one or more of iron oxide, iron hydroxide and iron salt. The iron oxide includes but is not limited to one or more of ferroferric oxide, ferrous oxide and ferrous oxide. The anions generated by the ionization of the iron salt include but are not limited to one or more of oxalate ion, carbonate ion, sulfate ion, nitrate ion, acetate ion, halide ion and phosphate ion. Examples of iron salts are one or more of ferrous sulfate, ferric chloride, ferrous phosphate, ferric phosphate, ferrous pyrophosphate, ferric pyrophosphate, ferric nitrate, ferric acetate, ferric citrate, ferrous oxalate and ferrous chloride.

[0053] The phosphorus source includes but is not limited to one or more of phosphoric acid and phosphorus-containing metal salts, wherein the phosphorus-containing metal salt includes but is not limited to one or more of ammonium phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate and iron phosphate.

[0054] The carbon source can be one or more of an inorganic carbon source and an organic carbon source, wherein the inorganic carbon source includes but is not limited to one or more of graphene, carbon nanotubes and graphite, and the organic carbon source includes but is not limited to one or more of glucose, sucrose, lactose, starch, organic acid, vitamins and phenolic resin. The amount of the carbon source is such that the mass of the carbon material in the prepared lithium manganese iron phosphate material accounts for 0.5% to 3% of the total mass of the lithium manganese iron phosphate material, and / or the thickness of the coating layer is 3nm to 5nm. The carbon source can act as a reducing agent, effectively improving or avoiding the reduction of Mn in the sintering process. 2+ and Fe 2+ The problem of oxidation.

[0055] The D source is, for example, a compound containing one or more of Mg, Ti, V, Ni, Co, Al, Nb, Nd, Y, Mo, Sr, La, Zr, B and Ca, and the compound may be an oxide, hydroxide or metal salt compound. Taking the D source as a titanium source as an example, the titanium source may be one or more of titanium oxide, metatitanic acid, tetrabutyl titanate, titanium hydroxide and titanium salts, titanium oxides include but are not limited to TiO2, anions generated by the ionization of titanium salts include but are not limited to one or more of oxalate ions, carbonate ions, sulfate ions, nitrate ions, acetate ions, halogen ions and phosphate ions, and examples of titanium salts include one or more of titanium sulfate, titanium nitrate and titanium chloride; taking the D source as a cobalt source as an example, the cobalt source includes but is not limited to one or more of cobalt trioxide, cobalt nitrate, cobaltous oxide, cobalt acetate and cobalt phosphate; taking the D source as a nickel source as an example, nickel sources include but are not limited to The invention is limited to one or more of nickelous oxide, nickel oxide, nickel nitrate, nickel acetate and nickel phosphate; taking the D source as a magnesium source as an example, the magnesium source includes but is not limited to one or more of magnesium oxide, magnesium chloride, magnesium sulfate, magnesium nitrate and magnesium acetate; taking the D source as a zinc source as an example, the zinc source includes but is not limited to one or more of zinc oxide, zinc nitrate, zinc sulfate, zinc chloride and zinc acetate; taking the D source as a vanadium source as an example, the vanadium source includes but is not limited to one or more of vanadium oxide, vanadium pentoxide, vanadium trioxide, vanadium nitrate and vanadium acetate; taking the D source as a niobium source as an example, the niobium source includes but is not limited to one or more of niobium pentoxide, niobium hydroxide, niobium oxalate, niobium acetate and niobium nitrate.

[0056] In step S1, the solvent for the first slurry can be, for example, water and / or an organic solvent. Water is preferably deionized water. Optional organic solvents include, but are not limited to, alcohols with 1 to 10 carbon atoms, such as one or more of methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-methyl-2-propanol, n-pentanol, 2-methyl-1-butanol, and 2,2-dimethyl-1-propanol. The solvent for the first slurry is preferably water because, compared to organic solvents, water is less expensive and offers advantages such as environmental friendliness, low equipment requirements, and high safety.

[0057] In some embodiments of the present application, the solid content of the first slurry is 10% to 40%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a value between any two of the foregoing values, so that the first slurry has a suitable viscosity for subsequent grinding processing.

[0058] In step S2, the purpose of the grinding process is to refine the raw materials, improve the uniformity of the subsequent spray drying process and sintering process, and help control the particle size of crystal growth during the sintering process. The grinding method includes but is not limited to one or more of sand milling, ball milling, mechanical stirring milling and air flow milling. The process conditions of the grinding process can refer to the conventional conditions adopted in the art, for example: grinding is carried out by sand milling, and sand milling is carried out at a speed of 200r / min to 1000r / min for 1h to 6h.

[0059] In step S3, the process conditions for the spray drying treatment may refer to conventional conditions used in the art.

[0060] In step S4, the purpose of the sintering process is to cause all raw materials to undergo a solid-phase reaction to produce lithium manganese iron phosphate. In some embodiments of the present application, the protective gas is selected from one or more of nitrogen, argon, helium, argon, neon, krypton, and xenon. The sintering process can be performed in a muffle furnace, tubular furnace, rotary kiln, roller hearth kiln, or pusher kiln.

[0061] The process conditions of the sintering treatment are one of the key influencing factors of ID / IG. In order to further improve the electron transmission efficiency of the lithium manganese iron phosphate material, in some embodiments of the present application, 0.50<ID / IG<0.95, and the process conditions of the sintering treatment can be determined according to the range of ID / IG, for example: the sintering treatment temperature is 600℃~800℃, and the sintering treatment time is 4h~8h.

[0062] In order to obtain a lithium iron manganese phosphate material with a specific particle size, in some embodiments of the present application, after the sintering step and before the step of obtaining the lithium iron manganese phosphate material, the preparation method of the lithium iron manganese phosphate material further includes the steps of: crushing the sintered material obtained after the sintering treatment, and then passing the crushed material through a 150-200 mesh sieve for screening, and the material passing through the sieve is the lithium iron manganese phosphate material.

[0063] An embodiment of the present application further provides an electrode sheet, which includes the lithium iron manganese phosphate material as described in any one of the foregoing descriptions, or the lithium iron manganese phosphate material prepared by any one of the preparation methods described in the foregoing descriptions.

[0064] An embodiment of the present application also provides a lithium battery, which includes but is not limited to a button battery, a soft-pack battery, a square lithium battery and a cylindrical lithium battery. The lithium battery includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode sheet collector and a positive electrode active material layer arranged on the surface of the positive electrode collector. The material of the positive electrode active material layer includes the lithium manganese iron phosphate material as described in any one of the foregoing, or the lithium manganese iron phosphate material prepared by any one of the preparation methods described in the foregoing.

[0065] Taking a square lithium battery as an example, as shown in Figures 1 and 2, the lithium battery 1 includes one or more battery cell units 11, and the battery cell unit 11 includes a positive electrode sheet 111, a separator 112 and a negative electrode sheet 113 stacked in sequence; as shown in Figure 3, the positive electrode sheet 111 includes a positive electrode current collector 1111 and a positive electrode active material layer 1112 arranged on the surface of the positive electrode current collector 1111, and the material of the positive electrode active material layer 1112 includes the lithium iron manganese phosphate material as described in any one of the above, or the lithium iron manganese phosphate material prepared by any one of the preparation methods described in the above.

[0066] The materials of the positive electrode active material layer also include a positive electrode binder and a positive electrode conductor. The materials of the positive electrode current collector, the positive electrode binder, and the positive electrode conductor can be conventional materials in the art. For example, the positive electrode current collector material includes, but is not limited to, aluminum foil or composite aluminum foil; the positive electrode binder includes, but is not limited to, one or more of vinylidene fluoride / hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, and polytetrafluoroethylene; and the positive electrode conductor includes, but is not limited to, one or more of carbon black, graphite, and graphene.

[0067] The method for preparing a positive electrode sheet, for example, includes the steps of: mixing a lithium manganese iron phosphate material, a positive electrode conductive agent, a positive electrode binder, and a first solvent to obtain a first mixture; then, coating the first mixture on a positive electrode current collector, followed by a drying process and a roll-pressing process to obtain a positive electrode sheet. It should be noted that the first mixture can also be cast onto a separate carrier to form a film layer, which is then separated from the carrier and laminated onto the surface of the positive electrode current collector. The first solvent includes, but is not limited to, N-methylpyrrolidone, dimethylformamide, or ethylene glycol dimethyl ether.

[0068] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on the surface of the negative electrode current collector. The material of the negative electrode active material layer includes a negative electrode active substance, a negative electrode binder, and a negative electrode conductive agent. The materials of the negative electrode current collector, the negative electrode active substance, the negative electrode binder, and the negative electrode conductive agent can be conventional materials in the art. For example, the material of the negative electrode current collector includes but is not limited to copper foil, composite copper foil, or copper mesh; the negative electrode active substance includes but is not limited to one or more of lithium单质, a metal that can be alloyed with lithium, a semi-metal, a transition metal oxide, a non-transition metal oxide, and a carbon material. The metal or semi-metal that can be alloyed with lithium includes but is not limited to Si, Sn, Al, Ge, Pb, Bi, Sb, Si-Y1 alloy (Y1 is an alkali metal, alkaline earth metal, group 13-16 element, transition metal, rare earth element, or a combination thereof, excluding Si), and Sn-Y2 alloy (Y2 is an alkali metal, alkaline earth metal, group 13-16 element, transition metal, rare earth element, or a combination thereof, excluding Sn). The transition metal oxide includes but is not limited to one or more of lithium titanium oxide, vanadium oxide, lithium vanadium oxide, and titanium niobium oxide. The non-transition metal oxide includes but is not limited to SnO2 and SiO x (0 < x < 2), and the carbon material includes but is not limited to one or more of crystalline carbon (such as graphite) and amorphous carbon. The negative electrode binder is deionized water or can be the same as the positive electrode binder, and the negative electrode conductive agent can be the same as the positive electrode conductive agent. The preparation method of the negative electrode sheet can be carried out by referring to the preparation method of the positive electrode sheet.

[0069] The material of the separator includes but is not limited to one or more of glass fiber, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene.

[0070] It should be noted that the lithium battery of the embodiment of the present application may further include other conventional structural components. For example, the lithium battery of the embodiment of the present application further includes an electrolyte. The electrolyte infiltrates the battery cell. The electrolyte includes a lithium salt and an organic solvent. Among them, the organic solvent includes but is not limited to a combination of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene sulfite, ethyl acetate, diethyl sulfite, 1,3-propane sultone; the lithium salt includes but is not limited to LiPF6, LiClO4, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiODFB, LiTFSI, LiFSI, LiCl, LiI, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2), wherein x and y are integers of 1 to 20, and the ratio of the mass of the lithium salt to the total mass of the electrolyte is 10% to 15%. For another example, referring to FIG1 , the lithium battery 1 further includes a housing 12, a positive electrode column 13, and a negative electrode column 14. The material of the housing 12 is, for example, aluminum. The battery cell 11 is disposed within the housing 12. The positive electrode tab 114 of the battery cell 11 is welded to the positive electrode column 13 via a connecting piece 15 to form the positive electrode of the lithium battery 10. The negative electrode tab 115 of the battery cell 11 is welded to the negative electrode column 14 via a connecting piece 15 to form the negative electrode of the lithium battery 10.

[0071] The technical solutions and technical effects of the present application are described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of the present application and do not specifically limit the present application.

[0072] Example 1

[0073] This embodiment provides a lithium manganese iron phosphate material and a preparation method thereof, wherein the lithium manganese iron phosphate material comprises a core and a coating layer coated on the outer surface of the core, wherein the material of the core is Li 0.96 Fe 0.3 Mn 0.6 V 0.04 PO4, the material of the coating layer includes carbon material, the mass of the carbon material accounts for 1.5% of the total mass of the lithium manganese iron phosphate material, the thickness of the coating layer is 3nm, and the ratio of the D band to the G band of the carbon material ID / IG is 0.8.

[0074] The preparation method of lithium manganese iron phosphate material includes the following steps:

[0075] S1.1. Add 45.76 kg of manganese tetraoxide, 45.25 kg of ferric phosphate, 35.46 kg of lithium carbonate, 3 kg of vanadium trioxide, 80.68 kg of 85% by mass phosphoric acid aqueous solution, and 2.72 kg of glucose into a mixer to mix the raw materials for 2 hours to obtain a mixture, and then transfer the mixture to a sand mill. Deionized water is added to the mixture at a mass ratio of the mixture to deionized water of 1:1.5 to obtain a first slurry;

[0076] S1.2. Sand mill the first slurry at a speed of 500 rpm and a time of 1.5 h to obtain a second slurry.

[0077] S1.3. The second slurry is subjected to a spray drying process, and the slurry is kept in a stirring state during the entire spray drying process to obtain a pre-burned material. The particle size distribution of the pre-burned material is in the range of 2 μm to 5 μm;

[0078] S1.4. Place the pre-fired material in a kiln and introduce protective N2 gas at a flow rate of 80 mL / min. Then, heat the furnace from room temperature to 750°C at a heating rate of 5°C / min, sinter at 750°C for 6 h, and cool to room temperature to obtain the fired material.

[0079] S1.5. The burned material is sequentially subjected to air flow crushing treatment and 150-mesh sieve screening treatment, and the material passing through the 150-mesh sieve is subjected to an iron removal treatment process. The material obtained by the iron removal treatment process is subjected to X-ray diffraction analysis. The X-ray diffraction analysis spectrum is shown in Figure 4, which proves that the material obtained by the iron removal treatment process is lithium manganese iron phosphate material.

[0080] The prepared lithium manganese iron phosphate material was observed using a scanning electron microscope (SEM). As shown in Figure 5, the lithium manganese iron phosphate material has a good morphology. Figure 6 is a Raman spectrum of the prepared lithium manganese iron phosphate material, which proves that the lithium manganese iron phosphate material has a Raman spectrum at 1330 cm -1 There is a strong absorption peak at the D band of carbon (sp 3 hybrid carbon), and lithium manganese iron phosphate material at 1590 cm -1 There is also a strong absorption peak at the G band of carbon (sp 2 hybrid carbon).

[0081] Example 2

[0082] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 0.97 Fe 0.3 Mn 0.6 V 0.04 PO4.

[0083] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "35.46 kg of lithium carbonate" in step S1.1 is replaced by "35.83 kg of lithium carbonate".

[0084] Example 3

[0085] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 0.99 Fe 0.3 Mn 0.6 V 0.04 PO4.

[0086] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "35.46 kg of lithium carbonate" in step S1.1 is replaced by "36.57 kg of lithium carbonate".

[0087] Example 4

[0088] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.01 Fe 0.3 Mn 0.6 V 0.04 PO4.

[0089] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "35.46 kg of lithium carbonate" in step S1.1 is replaced by "37.31 kg of lithium carbonate".

[0090] Example 5

[0091] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.03 Fe 0.3 Mn 0.6 V 0.04 PO4.

[0092] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "35.46 kg of lithium carbonate" in step S1.1 is replaced by "38.05 kg of lithium carbonate".

[0093] Example 6

[0094] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 0.95 Fe 0.3 Mn 0.6 V 0.04 PO4.

[0095] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "35.46 kg of lithium carbonate" in step S1.1 is replaced by "35.09 kg of lithium carbonate".

[0096] Example 7

[0097] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is LiFe 0.35 Mn 0.6 V 0.02 PO4.

[0098] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 45.76 kg of manganese tetraoxide, 52.79 kg of iron phosphate, 36.94 kg of lithium carbonate, 1.50 kg of vanadium trioxide, 74.92 kg of 85% mass percentage phosphoric acid aqueous solution and 2.72 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0099] Example 8

[0100] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.03 Fe 0.35 Mn 0.6 V 0.05 PO4.

[0101] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 45.76 kg of manganese tetraoxide, 52.79 kg of iron phosphate, 38.05 kg of lithium carbonate, 3.74 kg of vanadium trioxide, 74.92 kg of 85% mass percentage phosphoric acid aqueous solution and 2.72 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0102] Example 9

[0103] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.04 Fe 0.35 Mn 0.64V 0.02 PO4.

[0104] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 52.79 kg of iron phosphate, 38.42 kg of lithium carbonate, 1.50 kg of vanadium trioxide, 74.92 kg of 85% mass percentage phosphoric acid aqueous solution and 2.72 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixed material to the deionized water to obtain a first slurry."

[0105] Example 10

[0106] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the lithium iron manganese phosphate material in this embodiment is different in that the mass of the carbon material accounts for 0.5% of the total mass of the lithium iron manganese phosphate material.

[0107] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "2.72 kg of glucose" in step S1.1 is replaced by "0.91 kg of glucose".

[0108] Example 11

[0109] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the lithium iron manganese phosphate material in this embodiment is different in that the mass of the carbon material accounts for 2% of the total mass of the lithium iron manganese phosphate material.

[0110] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "2.72 kg of glucose" in step S1.1 is replaced by "3.63 kg of glucose".

[0111] Example 12

[0112] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the lithium iron manganese phosphate material in this embodiment is different in that the mass of the carbon material accounts for 3% of the total mass of the lithium iron manganese phosphate material.

[0113] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the preparation method of the lithium iron manganese phosphate material in this embodiment is different in that: "2.72 kg of glucose" in step S1.1 is replaced by "5.44 kg of glucose".

[0114] Example 13

[0115] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference of the lithium iron manganese phosphate material in this embodiment is that the ratio ID / IG of the D band to the G band of the carbon material is 0.7.

[0116] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.4 is replaced by "placing the pre-burned material in a kiln, introducing protective gas N2, the flow rate of N2 is 80mL / min, and then heating from room temperature to 750℃ at a heating rate of 5℃ / min, and sintering at 750℃ for 8h, cooling to room temperature, and obtaining burnt material".

[0117] Example 14

[0118] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference of the lithium iron manganese phosphate material in this embodiment is that the ratio ID / IG of the D band to the G band of the carbon material is 0.95.

[0119] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.4 is replaced by "placing the pre-burned material in a kiln, introducing protective gas N2, the flow rate of N2 is 80mL / min, and then heating from room temperature to 750℃ at a heating rate of 5℃ / min, and sintering at 750℃ for 5h, cooling to room temperature, and obtaining burnt material".

[0120] Example 15

[0121] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.04 Fe 0.32 Mn 0.64 Ti 0.04 PO4.

[0122] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 38.42 kg of lithium carbonate, 3.19 kg of titanium dioxide, 78.38 kg of 85% mass percent phosphoric acid aqueous solution and 2.77 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0123] Example 16

[0124] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.03 Fe 0.32 Mn 0.62 Nb 0.04 PO4.

[0125] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 47.29 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 38.05 kg of lithium carbonate, 5.32 kg of niobium pentoxide, 78.38 kg of 85% mass percentage phosphoric acid aqueous solution and 2.78 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixed material to the deionized water to obtain a first slurry."

[0126] Example 17

[0127] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.01 Fe 0.32 Mn 0.6 Y 0.04 PO4.

[0128] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 45.76 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 37.31 kg of lithium carbonate, 4.52 kg of yttrium oxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.77 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0129] Example 18

[0130] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this embodiment is that the core material is Li 1.02 Fe 0.32 Mn 0.62 Zr 0.04 PO4.

[0131] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this embodiment is that: step S1.1 is replaced by "take 47.29 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 37.68 kg of lithium carbonate, 4.93 kg of zirconium dioxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.78 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0132] Comparative Example 1

[0133] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this comparative example is that the core material is LiFe 0.32 Mn 0.64 V 0.04 PO4.

[0134] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 36.94 kg of lithium carbonate, 3 kg of vanadium trioxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.77 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixed material to the deionized water to obtain a first slurry."

[0135] Comparative Example 2

[0136] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this comparative example is that the core material is LiFe 0.32 Mn 0.64 Ti 0.04 PO4.

[0137] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 36.94 kg of lithium carbonate, 3.19 kg of titanium dioxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.76 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0138] Comparative Example 3

[0139] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this comparative example is that the core material is LiFe 0.32 Mn 0.64 Nb 0.04 PO4.

[0140] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 36.94 kg of lithium carbonate, 5.32 kg of niobium pentoxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.80 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixed material to the deionized water to obtain a first slurry".

[0141] Comparative Example 4

[0142] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this comparative example is that the core material is LiFe 0.32 Mn 0.64 Y 0.04 PO4.

[0143] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 36.94 kg of lithium carbonate, 4.52 kg of yttrium oxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.80 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0144] Comparative Example 5

[0145] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the lithium iron manganese phosphate material in Example 1, the difference between the lithium iron manganese phosphate material in this comparative example is that the core material is LiFe 0.32 Mn 0.64 Zr 0.04 PO4.

[0146] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the difference of the preparation method of lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 48.81 kg of manganese tetraoxide, 48.26 kg of iron phosphate, 36.94 kg of lithium carbonate, 4.93 kg of zirconium dioxide, 78.38 kg of 85% mass percentage of phosphoric acid aqueous solution and 2.80 kg of glucose and add them to a mixer to mix the raw materials for 2 hours to obtain a mixed material, and then transfer the mixed material to a sand mill, and add deionized water to the mixed material at a mass ratio of 1:1.5 of the mass of the mixture to deionized water to obtain a first slurry."

[0147] Experimental example

[0148] The lithium manganese iron phosphate materials in Examples 1 to 18 and Comparative Examples 1 to 5 were assembled into button-type batteries to test their electrochemical properties. The specific operation process includes the following steps:

[0149] S100, mixing lithium manganese iron phosphate material: Super P (conductive carbon black): polyvinylidene fluoride (binder) in a mass ratio of 90:5:5 to obtain a mixture;

[0150] S200, adding an appropriate amount of N-methylpyrrolidone to the mixture obtained in step S100, and then placing the mixture in a vacuum ball mill at a speed of 600 r / min for 2 h to obtain a slurry;

[0151] S300, using a coating machine to coat the slurry prepared in step S200 on the surface of an aluminum foil current collector with a thickness of 0.020 mm, and then vacuum drying it at 110° C. for 12 hours to obtain an electrode sheet;

[0152] S400, using the electrode sheet prepared in step S300 as the positive electrode sheet, the metal lithium sheet as the counter electrode, Celgard 2400 porous polypropylene membrane PP as the separator, and the electrolyte being a LiPF6 solution with a concentration of 1 mol / L (the solvent being a solution prepared by polycarbonate EC and dimethyl carbonate DMC in a volume ratio of 1:1), to assemble into a CR2032 button cell in a glove box;

[0153] S500: At room temperature (25°C), test the initial discharge capacity in grams of a CR2032 button cell at a charge of 0.2C; and at a high temperature (45°C), test the capacity retention rate of a CR2032 button cell after 100 charge-discharge cycles at a charge of 1C.

[0154] The test results are shown in Table 1 below:

[0155] Table 1 Summary of power-off test results

[0156] As shown in Table 1, the electrochemical performance of the lithium iron manganese phosphate materials in Examples 1 to 12 is significantly better than that of the lithium iron manganese phosphate material in Comparative Example 1, the electrochemical performance of the lithium iron manganese phosphate material in Example 15 is significantly better than that of the lithium iron manganese phosphate material in Comparative Example 2, the electrochemical performance of the lithium iron manganese phosphate material in Example 16 is significantly better than that of the lithium iron manganese phosphate material in Comparative Example 3, the electrochemical performance of the lithium iron manganese phosphate material in Example 17 is significantly better than that of the lithium iron manganese phosphate material in Comparative Example 4, and the electrochemical performance of the lithium iron manganese phosphate material in Example 18 is significantly better than that of the lithium iron manganese phosphate material in Comparative Example 5, which shows that there is a special relationship between Li, M and PO4 in the core. A certain molar ratio makes the lithium manganese iron phosphate material have good gram capacity and cycle life. If the ratio of the molar amount of Li to A is lower than 1.01 (that is, the Li content is low), the gram capacity will be reduced; if the ratio of the molar amount of Li to A is greater than 1.10 (that is, the Li content is high), then when the lithium manganese iron phosphate material is wetted by water, the residual alkali amount on the surface of the lithium manganese iron phosphate material will increase, so that during the slurrying process, the alkaline groups will attack the surface groups of polyvinylidene fluoride, prompting the polyvinylidene fluoride to undergo a bimolecular elimination reaction, thereby increasing the number of conjugated bonds and increasing the viscosity of the slurry. When the residual alkali amount is too high, the side reactions between the positive electrode and the electrolyte increase, and the problem of "flatulence" of the lithium battery is likely to occur, resulting in a decrease in the cycle performance of the lithium battery.

[0157] After the button test, the inductively coupled plasma (ICP) method was used to detect the dissolution amount of Mn and Fe in the electrolyte of the button battery including the lithium manganese iron phosphate material in Example 1, the button battery including the lithium manganese iron phosphate material in Example 10, the button battery including the lithium manganese iron phosphate material in Example 11, and the button battery including the lithium manganese iron phosphate material in Example 12. The test results are shown in Table 2 below:

[0158] Table 2 Dissolution of Mn and Fe in the electrolyte of button batteries

[0159] As can be seen from Table 2, after the button test, the amount of Mn and Fe dissolved in the electrolyte of the button battery including the lithium manganese iron phosphate material in Example 1 is the lowest. The reason may be that: the carbon material content of the lithium manganese iron phosphate material in Example 10 is low, so the coating uniformity of the coating layer on the core is not good, part of the surface of the core may be exposed, and the exposed material surface is in direct contact with the electrolyte, resulting in a high amount of Mn and Fe dissolved; in addition, the coating layer cannot fully cover the core, resulting in an incomplete conductive network constructed, thereby reducing the electrochemical performance of the lithium manganese iron phosphate material; the carbon material content of the lithium manganese iron phosphate material in Examples 11 and 12 is high, which increases the specific surface area of ​​the lithium manganese iron phosphate material, resulting in the lithium manganese iron phosphate material being prone to "agglomeration" problems, the solution processing performance of the lithium manganese iron phosphate material is deteriorated, and homogenous gel or uneven coating is very likely to occur, and the content of free carbon is increased, and the free carbon is very easy to agglomerate, resulting in poor coating effect of the coating layer on the core, resulting in a high amount of Mn and Fe dissolved.

Claims

1. A lithium iron manganese phosphate material, comprising a core and a coating layer coated on the outer surface of the core; in, The core material includes Li, M and PO4 with non-stoichiometric composition, M is Fe y Mn x D z , wherein D is a metal element, and the metal element does not include Fe or Mn, x, y and z represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material respectively, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material; In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01-1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95-1.10, and the ratio of the molar amount of A to the molar amount of PO4 is 0.90-1.

15.

2. The lithium iron manganese phosphate material according to claim 1, wherein: In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.03-1.07, and / or the ratio of the molar amount of Li to the molar amount of PO4 is 1.00-1.05, and / or the ratio of the molar amount of A to the molar amount of PO4 is 0.95-1.

10.

3. The lithium iron manganese phosphate material according to claim 1 or 2, wherein: The D50 particle size of the inner core is less than 10 μm.

4. The lithium iron manganese phosphate material according to any one of claims 1 to 3, wherein: The mass of the carbon material accounts for 0.5% to 3% of the total mass of the lithium iron manganese phosphate material; and / or The coating layer has a thickness of 3 nm to 5 nm.

5. The lithium iron manganese phosphate material according to claim 4, wherein: The ratio of the D band to the G band of the carbon material is ID / IG, and 0.50<ID / IG<0.

95.

6. The lithium iron manganese phosphate material according to any one of claims 1 to 5, wherein: In M, D is selected from one or more of Mg, Ti, V, Ni, Co, Al, Nb, Nd, Y, Mo, Sr, La, Zr, B and Ca; and / or In M, 0.1<x<0.9, 0.1<y<0.5, 0<Z<0.

5.

7. A method for preparing lithium manganese iron phosphate material, comprising the following steps: Providing a first slurry including a lithium source, a manganese source, an iron source, a phosphorus source, a carbon source, and a D source; Grinding the first slurry to obtain a second slurry; spray drying the second slurry to obtain a pre-burned material; as well as Under an atmosphere of protective gas, the pre-burned material is sintered to obtain a lithium manganese iron phosphate material having a coating layer, wherein the material of the coating layer is a carbon material; The prepared lithium manganese iron phosphate material comprises a core and a coating layer coated on the outer surface of the core; the core The material includes Li, M and PO4 with a non-stoichiometric composition, where M is Fe y Mn x D z , wherein D is a metal element, and the metal element does not include Fe or Mn, x, y and z respectively represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material; in the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01 to 1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95 to 1.10, and the ratio of the molar amount of A to the molar amount of PO4 is 0.90 to 1.

15.

8. The preparation method according to claim 7, wherein: The sintering temperature is 600° C. to 800° C., and the sintering time is 4 h to 8 h; and / or After the sintering step and before the step of obtaining the lithium iron manganese phosphate material, the method for preparing the lithium iron manganese phosphate material further includes the steps of: crushing the sintered material obtained after the sintering step, and then passing the crushed material through a 150-200 mesh sieve for screening, and the material passing through the sieve is the lithium iron manganese phosphate material; and / or The protective gas is selected from one or more of nitrogen, argon, helium, argon, neon, krypton and xenon.

9. The preparation method according to claim 7 or 8, wherein: In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.03-1.07, and / or the ratio of the molar amount of Li to the molar amount of PO4 is 1.00-1.05, and / or the ratio of the molar amount of A to the molar amount of PO4 is 0.95-1.

10.

10. The preparation method according to any one of claims 7 to 9, wherein The D50 particle size of the inner core is less than 10 μm.

11. The preparation method according to any one of claims 7 to 10, wherein The mass of the carbon material accounts for 0.5% to 3% of the total mass of the lithium iron manganese phosphate material; and / or The coating layer has a thickness of 3 nm to 5 nm.

12. The preparation method according to any one of claims 7 to 11, wherein The ratio of the D band to the G band of the carbon material is ID / IG, 0.50<ID / IG<0.95; and / or In M, D is selected from one or more of Mg, Ti, V, Ni, Co, Al, Nb, Nd, Y, Mo, Sr, La, Zr, B and Ca; and / or In M, 0.1<x<0.9, 0.1<y<0.5, 0<Z<0.

5.

13. A lithium battery, comprising one or more battery cells, wherein the battery cells comprise a positive electrode sheet, a separator and a negative electrode sheet stacked in sequence, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, wherein the material of the positive electrode active material layer comprises lithium iron manganese phosphate material; The lithium iron manganese phosphate material comprises a core and a coating layer coated on the outer surface of the core; the material of the core Comprising Li, M and PO4 with non-stoichiometric composition, M being Fe y Mn x D z ,in, D is a metal element, and the metal element does not include Fe or Mn, x, y and z represent the molar amounts of Fe, Mn and the metal element in the lithium manganese iron phosphate material respectively, and the sum of the molar amounts of Fe, Mn and the metal element is A; the material of the coating layer includes a carbon material; In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.01-1.10, the ratio of the molar amount of Li to the molar amount of PO4 is 0.95-1.10, and the ratio of the molar amount of A to the molar amount of PO4 is 0.90-1.

15.

14. The lithium battery according to claim 13, wherein: In the lithium manganese iron phosphate material, the ratio of the molar amount of Li to the molar amount of A is 1.03-1.07, and / or the ratio of the molar amount of Li to the molar amount of PO4 is 1.00-1.05, and / or the ratio of the molar amount of A to the molar amount of PO4 is 0.95-1.

10.

15. The lithium battery according to claim 13 or 14, wherein: The D50 particle size of the core is less than 10 μm; and / or The mass of the carbon material accounts for 0.5% to 3% of the total mass of the lithium iron manganese phosphate material; and / or The coating layer has a thickness of 3 nm to 5 nm; and / or The ratio of the D band to the G band of the carbon material is ID / IG, 0.50<ID / IG<0.95; and / or In M, D is selected from one or more of Mg, Ti, V, Ni, Co, Al, Nb, Nd, Y, Mo, Sr, La, Zr, B and Ca; and / or In M, 0.1<x<0.9, 0.1<y<0.5, 0<Z<0.5.

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