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

Abstract

A lithium manganese iron phosphate material, a preparation method for the lithium manganese iron phosphate material, and a lithium battery. The lithium manganese iron phosphate material comprises a core and a coating layer coating the outer surface of the core, wherein the material of the core comprises Li, Fe, Mn, Nb, and PO4 with a non-stoichiometric composition, and the material of the coating layer comprises LiNbO3 and / or Li3NbO4. The lithium manganese iron phosphate material has excellent rate performance, cycle performance and safety performance.

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 202311566671.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, 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] Although lithium manganese iron phosphate materials prepared by traditional high-temperature solid-phase synthesis methods 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 further improving the initial capacity of lithium batteries. Therefore, how to improve the electrochemical performance 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 electrochemical performance of lithium iron manganese phosphate.

[0007] The technical solution of this application is as follows:

[0008] In the first aspect, the present application 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 material of the core includes Li, Fe, Mn, Nb and PO4 with a non-stoichiometric composition, and the material of the coating layer includes LiNbO3 and / or Li3NbO4.

[0009] In a second aspect, the present application provides a method for preparing a lithium manganese iron phosphate material, comprising the following steps:

[0010] dispersing a lithium source, a manganese source, an iron source, a phosphorus source, and a niobium source in a dispersion medium to form a first mixed system, and mixing the first mixed system with a complexing agent to form a gel; and

[0011] The gel is sintered in an atmosphere of a first protective gas to obtain a lithium manganese iron phosphate material.

[0012] In a third aspect, an embodiment of the present application provides a lithium battery, wherein the battery cell comprises 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;

[0013] The lithium manganese iron phosphate material comprises a core and a coating layer coated on the outer surface of the core; the core material comprises Li, Fe, Mn, Nb and PO4 with a non-stoichiometric composition, and the coating layer material comprises LiNbO3 and / or Li3NbO4; and / or the preparation method of the lithium manganese iron phosphate material comprises the following steps:

[0014] dispersing a lithium source, a manganese source, an iron source, a phosphorus source, and a niobium source in a dispersion medium to form a first mixed system, and mixing the first mixed system with a complexing agent to form a gel; and

[0015] The gel is sintered in an atmosphere of a first protective gas to obtain a lithium manganese iron phosphate material. Beneficial effects

[0016] The beneficial effects of the present application are as follows: in the lithium manganese iron phosphate material, on the one hand, the material of the core includes lithium manganese iron phosphate doped with Nb, and Nb doping helps to stabilize the lattice of the lithium manganese iron phosphate and promote the order of the cation arrangement, thereby improving the stability of the lithium manganese iron phosphate material, which is beneficial to improving the capacity retention rate of the lithium manganese iron phosphate material in long cycles; on the other hand, the material of the coating layer includes LiNbO3 and / or Li3NbO4, which has a protective effect on the core, and can improve or avoid the problem of Fe and Mn dissolution caused by the infiltration of the core by the electrolyte, and because the coating layer contains Li, based on the high conductivity of lithium ions, it effectively isolates the electrolyte while ensuring that the lithium manganese iron phosphate material has good conductivity, and through the synergistic effect of core doping with Nb and surface coating with LiNbO3 and / or Li3NbO4, the rate, cycle and safety performance of the lithium manganese iron phosphate material are effectively improved.

[0017] Compared with a positive electrode sheet comprising a conventional lithium iron manganese phosphate material, an electrode sheet comprising the lithium iron manganese phosphate material has a higher compaction density.

[0018] Compared with a lithium battery whose positive electrode active material layer includes a conventional lithium manganese iron phosphate material, a lithium battery whose positive electrode active material layer includes the lithium manganese iron phosphate material has a higher initial capacity and a higher long-cycle capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a schematic flow chart of a method for preparing a lithium manganese iron phosphate material provided in an embodiment of the present application.

[0020] FIG2 is a schematic structural diagram of a lithium battery provided in an embodiment of the present application.

[0021] FIG3 is a schematic diagram of the structure of a battery cell unit in a lithium battery provided in an embodiment of the present application.

[0022] FIG4 is a schematic structural diagram of a positive electrode sheet provided in an embodiment of the present application.

[0023] FIG5 is an X-ray diffraction analysis spectrum of the lithium iron manganese phosphate material in Example 1 of the present application and the lithium iron manganese phosphate material in Comparative Example 3.

[0024] FIG6 is an enlarged view of a part of FIG5 .

[0025] FIG7 is a scanning electron microscope image of the lithium manganese iron phosphate material in Example 1 of the present application.

[0026] FIG8 is a cycle curve diagram of the first to sixteenth soft-pack lithium batteries in a 45° C., 1C / 1C cycle test. 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. 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.

[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] An embodiment of the present application provides a lithium iron manganese phosphate material, which includes a core and a coating layer covering the outer surface of the core. Among them, the material of the core includes Li, Fe, Mn, Nb and PO4 with a non-stoichiometric composition, and the material of the coating layer includes LiNbO3 and / or Li3NbO4.

[0034] In the lithium iron manganese phosphate material of the embodiment of the present application, on the one hand, the material of the core includes lithium iron manganese phosphate doped with Nb. Nb doping helps to stabilize the lattice of lithium iron manganese phosphate, promotes the orderliness of cation arrangement, thereby improving the stability of the lithium iron manganese phosphate material and being beneficial to enhancing the capacity retention rate of the lithium iron manganese phosphate material during long cycles; on the other hand, the material of the coating layer includes LiNbO3 and / or Li3NbO4, which has a protective effect on the core, can improve or avoid the problem of Fe and Mn dissolution caused by the core being infiltrated by the electrolyte, and since the coating layer contains Li, based on the high conductivity of lithium ions, while effectively isolating the electrolyte, it ensures that the lithium iron manganese phosphate material has good conductivity. Through the synergistic effect of doping Nb in the core and coating LiNbO3 and / or Li3NbO4 on the surface, the rate performance, cycle performance and safety performance of the lithium iron manganese phosphate material can be effectively improved.

[0035] In order to further improve the electrochemical performance of the lithium iron manganese phosphate material, in some embodiments of the present application, the material of the core is Li a Fe x Mn y Nb z (PO4) b , where a, x, y, z and b respectively represent the molar amounts of Li, Fe, Mn, Nb and PO4 in the core; where, 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or, 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.1.

[0036] In order to further improve the compaction and rate performance of the lithium manganese iron phosphate material, in some embodiments of the present application, the lithium manganese iron phosphate material is a secondary spherical structure, and the D50 particle size of the lithium manganese iron phosphate material is 5μm to 9μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm or a value between any two of the aforementioned values; and / or, the difference between the D90 particle size of the lithium manganese iron phosphate material and the D10 particle size of the lithium manganese iron phosphate material is X, and the ratio of X to the D50 particle size X / D50 is 0.2 to 1.8, and X / D50 can be, for example, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8 or a value between any two of the aforementioned values. It should be noted that the relevant conventional lithium manganese iron phosphate material is generally a single crystal morphology, with a relatively small particle size, a D50 particle size of 2μm to 3μm, and a relatively low compaction. The compaction density of the positive electrode sheet is generally 1.9g / cm 3 ~2.1g / cm 3 In the embodiment of the present application, the compaction density of the positive electrode sheet made of lithium manganese iron phosphate material can reach 2.35g / cm 3 Compared with the conventional single crystal morphology of lithium manganese iron phosphate material, the primary particle size of the lithium manganese iron phosphate material in the embodiment of the present application is about 300 nm, the lithium ion escape path is relatively short, and thus the rate performance is better.

[0037] In order to improve the coating uniformity of the coating layer and ensure that the lithium manganese iron phosphate material has good rate, cycle and safety performance, in some embodiments of the present application, the thickness of the coating layer is 10nm to 30nm, for example, 10nm, 15nm, 20nm, 25nm, 30nm or a value between any two of the foregoing values.

[0038] It should be noted that the relevant technology mainly adopts high-temperature solid-phase synthesis method to prepare lithium manganese iron phosphate material. This method mainly adopts mechanical means to mix and refine the raw materials, which can easily lead to uneven microscopic distribution of raw materials and greater diffusion difficulty, and impurities are easily introduced during the mechanical refinement process. In addition, this method also has the disadvantages of long sintering time, many reaction steps, high energy consumption, and large lithium loss, making it difficult to control the stoichiometric ratio of the product and easy to form impurities. There are large differences in composition, structure, particle size distribution, etc. between different batches of products, and the production repeatability and consistency are poor. Therefore, the lithium manganese iron phosphate material prepared by high-temperature solid-phase synthesis has the problem of unstable electrochemical performance.

[0039] Based on this, an embodiment of the present application 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, as shown in FIG1 , comprising the following steps:

[0040] S1. dispersing a lithium source, a manganese source, an iron source, a phosphorus source, and a niobium source in a dispersion medium to form a first mixed system, and mixing the first mixed system with a complexing agent to form a gel;

[0041] S2. Sintering the gel in an atmosphere of a first protective gas to obtain a lithium manganese iron phosphate material.

[0042] In the preparation method of the lithium iron manganese phosphate material in the embodiment of the present application, the sol-gel method is first used to mix all the raw materials to form a sol, and the sol is aged and the colloid particles are slowly polymerized to form a gel with a three-dimensional spatial network structure. The gel is then sintered to obtain the lithium iron manganese phosphate material. Among them, the sol-gel technology has the advantages of low equipment requirements and easy control of reaction process conditions. Compared with the traditional high-temperature solid-phase synthesis method for preparing lithium iron manganese phosphate material, the preparation method of the lithium iron manganese phosphate material in the embodiment of the present application has a lower sintering temperature, and the uniformity and chemical purity of the prepared lithium iron manganese phosphate material are higher, thereby improving the electrochemical properties and performance stability of the lithium iron manganese phosphate material.

[0043] Specifically, in step S1, the dispersion medium includes water, preferably deionized water. It is understood that the dispersion medium may also include one or more additives to promote dispersion of the raw materials, such as acids, bases, or surfactants. The raw materials can be selected according to conventional methods in the art, and each raw material can be water-soluble.

[0044] The lithium source may be one or more of lithium oxide, lithium hydroxide and lithium salt, lithium oxide includes but is not limited to Li2O, anions generated by ionization of lithium salt include but are not limited to one or more of oxalate ion, carbonate ion, sulfate ion, nitrate ion, acetate ion, halide ion, phosphate ion and dihydrogen phosphate ion, examples of lithium salt are one or more of lithium carbonate, lithium sulfate, lithium nitrate, lithium acetate, lithium dihydrogen phosphate, lithium phosphate and lithium oxalate.

[0045] The manganese source can be a divalent manganese compound, for example, it can be one or more of manganese oxide, manganese hydroxide and manganese salt. The manganese oxide includes but is not limited to one or more of manganese monoxide and manganese tetraoxide. The anions generated by the ionization of the 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.

[0046] The iron source can be a divalent iron compound, for example, it can be one or more of iron oxides, ferrous hydroxide, and iron salts. The iron oxides include, but are not limited to, one or more of magnetite and ferrous oxide. The anions generated by the ionization of iron salts include, but are not limited to, one or more of oxalate ions, carbonate ions, sulfate ions, nitrate ions, acetate ions, halide ions, and phosphate ions. Examples of iron salts are one or more of ferrous sulfate, ferrous chloride, ferrous phosphate, ferrous pyrophosphate, ferrous nitrate, ferrous acetate, ferrous oxalate, and ferrous chloride.

[0047] The phosphorus source can be one or more of phosphoric acid and phosphorus-containing metal salts. Among them, the phosphorus-containing metal salts include, but are not limited to, one or more of ammonium phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate, and iron phosphate.

[0048] The niobium source can be niobium oxides (Nb x O y ), including, but not limited to, one or more of NbO, NbO 2、 Nb2O3, and Nb2O5.

[0049] In some embodiments of the present application, the complexing agent is selected from one or more of polyacrylic acid, citric acid, polyacrylamide, hydrolyzed polymaleic anhydride, polyhydroxyacrylic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium gluconate, and sodium alginate.

[0050] In order to further improve the electrochemical performance of the lithium iron manganese phosphate material, in some embodiments of the present application, in the first mixed system, Li:Mn:Fe:P:Nb is a:x:y:z:b, where 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or,

[0052] 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.1.

[0051] In some embodiments of the present application, in the step of mixing the first mixed system with the complexing agent to form a gel, the molar ratio of metal cations in the first mixed system to the complexing agent is 1:(3 - 5). For example, it can be 1:3, 1:4, 1:5, or a value between any two of the foregoing ratios. If the addition amount of the complexing agent is less, for example, the molar ratio of metal cations in the first mixed system to the complexing agent is greater than 1: Three, the quality of the formed gel is poor; if the addition amount of the complexing agent is more, for example, the molar ratio of metal cations in the first mixed system to the complexing agent is less than 1: Five, not only will the complexing agent be wasted and the manufacturing cost be increased, but the excess complexing agent may have an adverse effect on the electrochemical performance of the lithium iron manganese phosphate material.

[0052] In order to further improve the chemical purity of the prepared lithium manganese iron phosphate material, in some embodiments of the present application, the step of mixing the first mixed system with the complexing agent to form a gel includes: mixing the first mixed system with the complexing agent to obtain a second mixed system, and then stirring the second mixed system at 60°C to 90°C under an atmosphere of a second protective gas to form a gel, wherein the second protective gas is selected from one or more of nitrogen, argon, helium, argon, neon, krypton and xenon.

[0053] In step S2, the purpose of the sintering process is to cause the raw materials to undergo a solid-phase reaction to produce the lithium manganese iron phosphate material. To further improve the chemical purity of the resulting lithium manganese iron phosphate material, in some embodiments of the present application, the first 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.

[0054] In some embodiments of the present application, the sintering treatment temperature is 600℃~800℃, for example, it can be 600℃, 650℃, 700℃, 750℃, 800℃ or a value between any two of the foregoing values, and the sintering treatment time is 8h~12h, for example, it can be 8h, 9h, 10h, 11h, 12h or a value between any two of the foregoing values.

[0055] In order to improve the coating integrity and uniformity of the coating layer on the core, and to improve the uniformity of Nb doping in the core, thereby further improving the electrochemical properties of the prepared lithium manganese iron phosphate material, in some embodiments of the present application, the sintering treatment of the gel includes the steps of: performing a first sintering sub-treatment on the gel at a first temperature, the first temperature is 300°C to 500°C, and the time of the first sintering sub-treatment is 3h to 5h, to obtain a pre-fired material; and, performing a second sintering sub-treatment on the pre-fired material at a second temperature, the second temperature is 600°C to 800°C, and the time of the second sintering sub-treatment is 8h to 12h. Since Nb compounds that do not contain Li easily react with Li-containing compounds (such as lithium carbonate) to form LiNbO3 at 300℃~500℃, the gel is first pre-fired at a low temperature (first sintering sub-treatment) during the sintering process of the gel to provide a mild environment for the grains to grow slowly and evenly, so that a uniform and dense coating layer is formed on the outer surface of the inner core before the second sintering sub-treatment. The main component of the coating layer is LiNbO3, which effectively improves the problems of incomplete coating, low coating uniformity and poor coating stability of the coating layer formed by a single high-temperature sintering; in the subsequent second sintering sub-treatment, due to the high temperature of the second sintering sub-treatment, at least part of the LiNbO3 is converted into LiNbO4, and based on the Nb ion radius Since the radius of Nb ions is smaller than that of Mn and Fe ions, a part of Nb ions will diffuse into the bulk phase of the core material to replace the metal ions to form bulk Nb doping, which is beneficial to stabilizing the lattice, thereby improving the stability of the obtained lithium manganese iron phosphate material and effectively improving the problem of poor Nb doping uniformity in the first high-temperature sintering.

[0056] In order to further improve the uniformity of Nb doping in the core and the coating layer, in some embodiments of the present application, the pre-sintered material is crushed and then subjected to a second sintering process.

[0057] 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.

[0058] The present application also provides an electrode sheet comprising any of the aforementioned lithium iron manganese phosphate materials, or a lithium iron manganese phosphate material produced by any of the aforementioned methods for producing a lithium iron manganese phosphate material. Compared to positive electrode sheets comprising conventional lithium iron manganese phosphate materials, the electrode sheet of the present application has a higher compaction density.

[0059] The present application also provides a lithium battery, including but not limited to button cells, soft-pack cells, prismatic lithium batteries, and cylindrical lithium batteries. The lithium battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode sheet current collector, and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The material of the positive electrode active material layer includes the lithium iron manganese phosphate material described in any one of the above descriptions, or the lithium iron manganese phosphate material prepared by any one of the preparation methods described in the above descriptions. Compared to lithium batteries whose positive electrode active material layer includes conventional lithium iron manganese phosphate material, the lithium battery of the present application has a higher initial capacity and a higher long-cycle capacity retention rate.

[0060] Taking a square lithium battery as an example, as shown in Figures 2 and 3, 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 4, 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 obtained by any one of the preparation methods described in the above.

[0061] Among them, the materials of the positive electrode active material layer further include a positive electrode binder and a positive electrode conductive agent. The materials of the positive electrode current collector, the positive electrode binder, and the positive electrode conductive agent can be conventional materials in the art. For example, the materials of the positive electrode current collector include, but are 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; the positive electrode conductive agent includes, but is not limited to, one or more of carbon black, graphite, and graphene.

[0062] The preparation method of the positive electrode sheet includes, for example, the steps of: mixing a lithium iron manganese 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 the positive electrode current collector, and then successively performing a drying treatment process and a rolling process to obtain the positive electrode sheet. It should be noted that the first mixture can also be cast on a separate carrier to form a film layer, then the film layer is separated from the carrier, and then the film layer is laminated on the surface of the positive electrode current collector. Among them, the first solvent includes, but is not limited to, N-methylpyrrolidone, dimethylformamide, or ethylene glycol dimethyl ether.

[0063] 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 materials of the negative electrode active material layer include 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 materials of the negative electrode current collector include, but are 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, an alkaline earth metal, a group 13-16 element, a transition metal, a rare earth element, or a combination thereof, excluding Si), and Sn-Y2 alloy (Y2 is an alkali metal, an alkaline earth metal, a group 13-16 element, a transition metal, a 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 one or more of them. The carbon material includes, but is not limited to, 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.

[0064] The material of the diaphragm includes, but is not limited to, one or more of glass fiber, polyester, Teflon, polyethylene, polypropylene, and polytetrafluoroethylene.

[0065] It should be noted that the lithium battery of the embodiment of the present application may also include other conventional structural components. For example: the lithium battery of the embodiment of the present application also includes an electrolyte, the electrolyte soaks the battery cell, the electrolyte includes a lithium salt and an organic solvent, wherein 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, and 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+1 SO2), 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.

[0066] The technical solutions and technical effects of the present application are described in detail below through specific embodiments. The following embodiments are only some embodiments of the present application and do not specifically limit the present application.

[0067] Example 1

[0068] This embodiment provides a lithium manganese iron phosphate material and a preparation method thereof. The lithium manganese iron phosphate material includes a core and a coating layer coated on the outer surface of the core, wherein the material of the core is LiFe 0.40 Mn 0.55 Nb 0.05 PO4, the coating layer includes LiNbO3 and Li3NbO4, and the coating layer has a thickness of 15 nm. The D50 particle size of the lithium manganese iron phosphate material is 8 μm, the difference between the D90 particle size of the lithium manganese iron phosphate material and the D10 particle size of the lithium manganese iron phosphate material is X, and the ratio of X to D50 particle size (X / D50) is 1.15.

[0069] The preparation method of lithium manganese iron phosphate material includes the following steps:

[0070] S1.1. Add 47.58 kg of manganese acetate, 28.77 kg of ferrous oxalate, 18.47 kg of lithium carbonate, 57.52 kg of ammonium dihydrogen phosphate, and 2.93 kg of Nb2O3 to a mixer to obtain a mixture; then add deionized water to the mixture at a mass ratio of 1:1.5, and stir at 600 r / min until the mixture is uniformly mixed to obtain a first mixed system;

[0071] S1.2. Adding a complexing agent, citric acid and polyacrylic acid (in a mass ratio of citric acid to polyacrylic acid of 1:1), to the first mixed system at room temperature in a molar ratio of metal cation to complexing agent of 1:3; then, stirring the second mixed system continuously at 85°C under a nitrogen atmosphere until a gel is formed;

[0072] S1.3. Transfer the gel obtained in step S1.3 into a kiln, introduce protective gas N2 at a flow rate of 80 mL / min, then heat from room temperature to 400°C at a heating rate of 5°C / min, and sinter at 400°C for 4 h to obtain a pre-sintered material;

[0073] S1.4. Mechanically crush the pre-burned material, transfer the crushed material into a kiln, introduce protective N2 gas at a flow rate of 80 mL / min, then heat to 750°C at a heating rate of 5°C / min, and sinter at 750°C for 10 h to obtain a burnt material;

[0074] S1.5. The calcined 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. Then, the material obtained by the iron removal treatment process is subjected to X-ray diffraction (XRD) analysis. The XRD analysis patterns are shown in Figures 5 and 6, which prove that the material that has completed the iron removal treatment is lithium manganese iron phosphate material.

[0075] The lithium manganese iron phosphate material prepared in step S1.5 was observed using a scanning electron microscope (SEM). As shown in FIG7 , the lithium manganese iron phosphate material has a good secondary spherical structure.

[0076] Example 2

[0077] 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 LiFe0.40 Mn 0.55 Nb 0.05 (PO4) 0.92 .

[0078] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the difference in the preparation method of the lithium iron manganese phosphate material in this embodiment is that "57.52 kg of ammonium dihydrogen phosphate" in step S1.1 is replaced by "52.91 kg of ammonium dihydrogen phosphate".

[0079] Example 3

[0080] 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 0.40 Mn 0.55 Nb 0.05 (PO4) 1.02 .

[0081] 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: "57.52 kg of ammonium dihydrogen phosphate" in step S1.1 is replaced by "58.67 kg of ammonium dihydrogen phosphate".

[0082] Example 4

[0083] 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 0.40 Mn 0.55 Nb 0.05 (PO4) 1.1 .

[0084] Compared with the preparation method of lithium iron manganese phosphate material in Example 1, the preparation method of lithium iron manganese phosphate material in this embodiment is different in that: "57.52 kg of ammonium dihydrogen phosphate" in step S1.1 is replaced by "63.27 kg of ammonium dihydrogen phosphate".

[0085] Example 5

[0086] 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 0.40 Mn 0.55 Nb 0.05 (PO4) 0.95 .

[0087] Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the difference in the preparation method of the lithium iron manganese phosphate material in this embodiment is that "57.52 kg of ammonium dihydrogen phosphate" in step S1.1 is replaced by "54.64 kg of ammonium dihydrogen phosphate".

[0088] Example 6

[0089] 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 0.91 Fe 0.40 Mn 0.55 Nb 0.05 PO4.

[0090] 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: "18.47 kg of lithium carbonate" in step S1.1 is replaced by "16.81 kg of lithium carbonate".

[0091] Example 7

[0092] 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 0.40 Mn 0.55 Nb 0.05 PO4.

[0093] 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: "18.47 kg of lithium carbonate" in step S1.1 is replaced by "17.55 kg of lithium carbonate".

[0094] Example 8

[0095] 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 1.05 Fe 0.40 Mn 0.55 Nb 0.05 PO4.

[0096] 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: "18.47 kg of lithium carbonate" in step S1.1 is replaced by "19.39 kg of lithium carbonate".

[0097] Example 9

[0098] 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 1.09 Fe 0.40 Mn 0.55 Nb 0.05 PO4.

[0099] 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: "18.47 kg of lithium carbonate" in step S1.1 is replaced by "20.13 kg of lithium carbonate".

[0100] Example 10

[0101] 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 0.40 Mn 0.55 Nb 0.001 PO4.

[0102] 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: "2.93 kg of Nb2O3" in step S1.1 is replaced by "0.58 kg of Nb2O3".

[0103] Example 11

[0104] 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 0.40 Mn 0.55 Nb 0.15 PO4.

[0105] 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: "2.93 kg of Nb2O3" in step S1.1 is replaced by "8.77 kg of Nb2O3".

[0106] Example 12

[0107] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the difference in the preparation method of the lithium iron manganese phosphate material in this embodiment is that: step S1.4 is replaced by "transferring the gel prepared in step S1.3 into a kiln, introducing protective gas N2 with a flow rate of 80 mL / min, and then heating from room temperature to 750°C at a heating rate of 5°C / min, and sintering at 750°C for 10 hours to obtain a sintered material", and step S1.5 is omitted.

[0108] Example 13

[0109] This embodiment provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the difference in the preparation method of the lithium iron manganese phosphate material in this embodiment is that: in step S1.3, "the complexing agent is citric acid and polyacrylic acid (the mass ratio of citric acid to polyacrylic acid is 1:1)" is replaced by "the complexing agent is citric acid".

[0110] Comparative Example 1

[0111] This comparative example provides a lithium manganese iron phosphate material and a preparation method thereof. The lithium manganese iron phosphate material is a LiFe 0.4 Mn 0.6 PO4, D50 particle size is 2μm.

[0112] The preparation method of the lithium manganese iron phosphate material in this comparative example comprises the following steps:

[0113] S10.1. 51.91 kg of manganese acetate, 28.77 kg of ferrous oxalate, 18.47 kg of lithium carbonate, and 57.52 kg of ammonium dihydrogen phosphate were added to a mixer, and deionized water was added to the mixture at a mass ratio of 1:1.5, and mixed to obtain a first slurry.

[0114] S10.2. Sand mill the first slurry at a speed of 400 rpm and a time of 2 h to obtain a second slurry.

[0115] S10.3. Spray-dry the second slurry, ensuring that the slurry is stirred throughout the spray-drying process, to obtain a precursor material having a particle size distribution D50 in the range of 1 μm to 5 μm;

[0116] S10.4. Place the precursor 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 rate of 5°C / min, sinter at 750°C for 10 h, and cool to room temperature to obtain a sintered material.

[0117] S10.5. The burned material is sequentially subjected to air flow pulverization treatment and 150-mesh sieve screening treatment, and the material passing through the 150-mesh sieve is subjected to a treatment to remove elemental iron to obtain lithium manganese iron phosphate material.

[0118] Comparative Example 2

[0119] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the preparation method of the lithium iron manganese phosphate material in comparative example 1, the difference of the preparation method of the lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 51.91 kg of manganese acetate, 28.77 kg of ferrous oxalate, 18.47 kg of lithium carbonate, 57.52 kg of ammonium dihydrogen phosphate and 2.93 kg of Nb2O3 and add them to a mixer to obtain a mixed material, and then add deionized water to the mixed material at a mass ratio of the mixed material to deionized water of 1:1.5 to obtain a first slurry."

[0120] Comparative Example 3

[0121] This comparative example provides a lithium iron manganese phosphate material and a preparation method thereof. Compared with the preparation method of the lithium iron manganese phosphate material in Example 1, the difference of the preparation method of the lithium iron manganese phosphate material in this comparative example is that: step S1.1 is replaced by "take 51.91 kg of manganese acetate, 28.77 kg of ferrous oxalate, 18.47 kg of lithium carbonate and 57.52 kg of ammonium dihydrogen phosphate and add them to a mixer to obtain a mixed material, and then add deionized water to the mixed material at a mass ratio of 1:1.5 to the deionized water, and stir at a speed of 600 r / min until the mixed material is completely dissolved to obtain a first mixed system."

[0122] The material after the iron removal treatment was subjected to X-ray diffraction (XRD) analysis, and the XRD analysis patterns are shown in Figures 3 and 4. It should be noted that, as shown in Figures 5 and 6, compared with the lithium manganese iron phosphate material in this comparative example, the peak position of the lithium manganese iron phosphate material in Example 1 shifts to a larger angle, indicating that some Nb ions are incorporated into the bulk structure of the lithium manganese iron phosphate. The reason is that: the radius of the Nb ion is Compared with the smaller ionic radius of Mn and Fe, according to the Bragg equation 2dsinθ=nλ, the smaller the ionic radius, the smaller the corresponding d will be, and the larger the θ angle, the more the peak position will shift to a larger angle.

[0123] Experimental example

[0124] Soft-pack lithium batteries were prepared using the lithium iron manganese phosphate materials of Examples 1 to 13 and Comparative Examples 1 to 3 to obtain first to sixteenth soft-pack lithium batteries. The positive electrode sheets of the soft-pack lithium batteries included a positive electrode current collector and a positive electrode active layer disposed on the surface of the positive electrode current collector. The material of the positive electrode active layer included the lithium iron manganese phosphate material prepared in each Example or Comparative Example. The material of the positive electrode current collector was carbon-coated aluminum foil. The negative electrode sheets of the soft-pack lithium batteries included a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector was copper foil. The material of the negative electrode active layer included graphite. The only difference between the first to sixteenth soft-pack lithium batteries is that the lithium iron phosphate material in the positive electrode sheet of each soft-pack lithium battery is different. The lithium iron phosphate material of the first soft-pack lithium battery is the lithium iron phosphate material in Example 1, the lithium iron phosphate material of the second soft-pack lithium battery is the lithium iron phosphate material in Example 2, the lithium iron phosphate material of the third soft-pack lithium battery is the lithium iron phosphate material in Example 3, and so on. The lithium iron phosphate material of the sixteenth soft-pack lithium battery is the lithium iron phosphate material in Comparative Example 3.

[0125] The method for preparing the positive electrode sheet includes the following steps:

[0126] The four raw materials were weighed according to a mass ratio of 97:0.4:0.5:2.1 of lithium manganese iron phosphate material: carbon black conductive (Super PLL): carbon nanotubes: polyvinylidene fluoride, and the four raw materials were evenly mixed with N-methylpyrrolidone to obtain a positive electrode slurry with a solid content of 65%. Then, the positive electrode slurry was coated on a carbon-coated aluminum foil with a thickness of 12 μm (coated on both sides) by a coating machine, and then baked and cured at 120°C to form a positive electrode active material layer, and then cold pressed to the corresponding thickness by a roller press to obtain a positive electrode sheet with a thickness of 160 μm.

[0127] The preparation method of the negative electrode sheet includes the following steps: weighing the above four raw materials according to the mass ratio of graphite: conductive carbon black (Super PLL): carboxymethyl cellulose: styrene-butadiene rubber of 97:0.7:1.25:1.05, and evenly mixing the above four raw materials with N-methylpyrrolidone to obtain a negative electrode slurry, wherein the solid content of the negative electrode slurry is 55%; then, the negative electrode slurry is coated on a carbon-coated aluminum foil with a thickness of 8 μm (coated on both sides) by a coating machine, and then placed at 80°C for baking and curing to form a negative electrode active material layer, and then cold pressed to the corresponding thickness by a roller press to obtain a negative electrode sheet with a thickness of 120 μm.

[0128] The preparation method of the electrolyte includes the steps of: mixing the above three elements of ethylene carbonate (EC): diethyl carbonate (DEC): ethyl methyl carbonate (EMC) in a volume ratio of 4:3:3 to obtain a solvent, then adding LiPF6 and additives to the solvent, and mixing them evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the electrolyte is 1.0 mol / L, the mass of the additive accounts for 10% of the total mass of the electrolyte, and the additive is composed of vinylene carbonate, 1,3-propane sultone, fluoroethylene carbonate and cyclohexylbenzene, and the mass ratio of vinylene carbonate: 1,3-propane sultone: fluoroethylene carbonate: cyclohexylbenzene is 3:2:1:1.

[0129] The positive electrode sheet, the negative electrode sheet and the 12μm PP separator are stacked to obtain a bare cell, which is then placed on an outer packaging aluminum-plastic film to be assembled into a 2Ah soft-pack cell. The electrolyte is injected, and the soft-pack lithium battery is obtained through aging, formation, shaping, packaging and other processes.

[0130] First, the compaction density of the positive electrode sheets made of lithium manganese iron phosphate materials in Examples 1 to 13 and Comparative Examples 1 to 3 was tested respectively. Three parallel samples were set for each positive electrode sheet, and the compaction density value of each positive electrode sheet was taken as the average value of the three parallel samples.

[0131] The compaction density detection method includes the following steps: taking the positive electrode sheet obtained after roller pressing, cutting it to obtain a disc test sample, and the circular area of ​​the disc test sample is 2500mm 2 , obtain the thickness (L1) and weight (W1) of the wafer test sample; then, use acetone-ethanol solution to clean and remove the positive electrode active material layer of the positive electrode sheet, and obtain the thickness (L2) and weight (W2) of the carbon-coated aluminum foil; finally, the difference between W1 and W2 is set to dW, the difference between L1 and L2 is set to dL, the area of ​​the wafer test sample is S, the quotient obtained by dividing dW by S is the surface density, and the quotient obtained by dividing the surface density by dL is the compacted density.

[0132] The test results are shown in Table 1 below:

[0133] Table 1 Compacted density of positive electrode sheets made using lithium manganese iron phosphate materials in Examples 1 to 13 and Comparative Examples 1 to 3

[0134] It can be seen from Table 1 that compared with the positive electrode sheets made of lithium iron manganese phosphate materials in Comparative Examples 1 to 3, the positive electrode sheets made of lithium iron manganese phosphate materials in Examples 1 to 13 have higher compaction density. For example, the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Example 2 is 12% higher than the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Comparative Example 1, the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Example 2 is 13% higher than the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Comparative Example 2, and the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Example 3 is 2.1% higher than the compaction density of the positive electrode sheet made of lithium iron manganese phosphate material in Comparative Example 2.

[0135] This shows that the lithium manganese iron phosphate material of the embodiment of the present application has a secondary spherical structure, and the particle size is larger than that of the lithium manganese iron phosphate material with a conventional single crystal morphology, which is beneficial to improving the compaction density of the positive electrode sheet. The reason is that for the same substance, the powder has a single particle size and a similar geometric shape. The larger the particle size, the smaller the contact area between the particles, the smaller the interaction force between the particles (such as mechanical entanglement force and friction force), and the better the fluidity, and it is easier to form a tightly packed state, so that the filling density is greater and the porosity is smaller. Under the action of the same pressure, the volume occupied by the particle gaps is smaller, and it is easier to obtain a relatively large compaction density.

[0136] Then, the electrical performance test of the first soft-pack lithium battery to the sixteenth soft-pack lithium battery was performed respectively, and the test method included the steps of: charging each soft-pack lithium battery at 25°C at a constant current and constant voltage rate of 0.2C to 4.2V, wherein the constant voltage charging cut-off current was 0.02C, and then discharging at 0.2C constant current until the voltage reached 2.5V, obtaining the first discharge capacity and the first charge capacity at 25°C and 0.2C rate, and calculating the first charge and discharge efficiency of each soft-pack lithium battery at 25°C and 0.2C rate (the ratio of the first discharge capacity to the first charge capacity × 100%). The test results are shown in Table 2 below. In addition, the performance of the first soft-pack lithium battery to the sixteenth soft-pack lithium battery at 45°C and 1C / 1C cycle was tested respectively, wherein the cycle curves of the first soft-pack lithium battery and the sixteenth soft-pack lithium battery are shown in Figure 8.

[0137] Table 2 Summary of electrical performance test results of the first to sixteenth soft-pack lithium batteries

[0138] It can be seen from Table 2 that compared with the fourteenth to sixteenth soft-pack lithium batteries, the electrical performance of the first to thirteenth soft-pack lithium batteries is superior, specifically, compared with the fourteenth to sixteenth soft-pack lithium batteries, the first to thirteenth soft-pack lithium batteries have higher initial capacity and higher long cycle capacity retention rate. Taking the first soft-pack lithium battery and the fourteenth soft-pack lithium battery as examples, the first charge capacity of the first soft-pack lithium battery at 25°C and 0.2C rate is 6% higher than that of the fourteenth soft-pack lithium battery, the first discharge capacity of the first soft-pack lithium battery at 25°C and 0.2C rate is 10.4% higher than that of the fourteenth soft-pack lithium battery, and the first charge and discharge efficiency of the first soft-pack lithium battery at 25°C and 0.2C rate is 3.6% higher than that of the fourteenth soft-pack lithium battery; in addition, as shown in Figure 5, the performance of the first soft-pack lithium battery at 45°C and 1C / 1C cycle is significantly better than that of the sixteenth soft-pack lithium battery, indicating that the capacity retention rate of the first soft-pack lithium battery during the cycle is better than that of the sixteenth soft-pack lithium battery.

[0139] In summary, for the lithium iron phosphate material of the embodiment of the present application, on the one hand, the material of the core includes lithium iron phosphate doped with Nb, and Nb doping helps to stabilize the lattice of lithium iron phosphate and promote the order of cation arrangement, thereby improving the stability of the lithium iron phosphate material, which is beneficial to improving the capacity retention rate of the lithium iron phosphate material in long cycles; on the other hand, the material of the coating layer includes LiNbO3 and / or Li3NbO4, which has a protective effect on the core and can improve or avoid the problem of Fe and Mn dissolution caused by the infiltration of the core by the electrolyte, and because the coating layer contains Li, based on the high conductivity of lithium ions, it effectively isolates the electrolyte while ensuring that the lithium iron phosphate material has good conductivity. The synergistic effect of core doping with Nb and surface coating with LiNbO3 and / or Li3NbO4 can effectively improve the rate, cycle and safety performance of the lithium iron phosphate material.

Claims

1. A lithium iron manganese phosphate material, comprising a core and a coating layer coated on the outer surface of the core; wherein: The material of the core includes Li, Fe, Mn, Nb and PO4 with a non-stoichiometric composition, and the material of the coating layer includes LiNbO3 and / or Li3NbO4.

2. The lithium iron manganese phosphate material according to claim 1, wherein: The material of the core is Li a Fe x Mn y Nb z (PO4) b , wherein a, x, y, z and b represent the molar amounts of Li, Fe, Mn, Nb and PO4 in the core, respectively; Wherein, 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or, 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.

1.

3. The lithium iron manganese phosphate material according to claim 1 or 2, wherein: The lithium iron manganese phosphate material has a secondary spherical structure, and the D50 particle size of the lithium iron manganese phosphate material is 5 μm to 9 μm; and / or, the difference between the D90 particle size and the D10 particle size of the lithium iron manganese phosphate material is X, and the ratio X / D50 of X to the D50 particle size is 0.2 to 1.

8.

4. The lithium iron manganese phosphate material according to any one of claims 1 to 3, wherein: The thickness of the coating layer is 10 nm to 30 nm.

5. A preparation method of a lithium iron manganese phosphate material, comprising the following steps: Disperse a lithium source, a manganese source, an iron source, a phosphorus source and a niobium source in a dispersion medium to form a first mixed system, and mix the first mixed system with a complexing agent to form a gel; and Under the atmosphere of a first protective gas, perform a sintering treatment on the gel to obtain a lithium iron manganese phosphate material.

6. The method for preparing lithium iron manganese phosphate material according to claim 5, wherein: The complexing agent is selected from one or more of polyacrylic acid, citric acid, polyacrylamide, hydrolyzed polymaleic anhydride, polyhydroxyacrylic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium gluconate and sodium alginate.

7. The method for preparing the lithium iron manganese phosphate material according to claim 5 or 6, wherein: In the step of mixing the first mixed system with the complexing agent to form a gel, the molar ratio of metal cations in the first mixed system to the complexing agent is 1:(3 - 5).

8. The method for preparing the lithium iron manganese phosphate material according to any one of claims 5 to 7, wherein: In the first mixed system, Li:Mn:Fe:P:Nb is a:x:y:z:b, wherein, 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or, 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.

1.

9. The method for preparing the lithium iron manganese phosphate material according to any one of claims 5 to 8, wherein: The temperature of the sintering treatment is 600 °C to 800 °C, and the time of the sintering treatment is 8 h to 12 h; Alternatively, the sintering treatment of the gel includes the steps: performing a first sintering sub-treatment on the gel at a first temperature, the first temperature being 300 °C to 500 °C, and the time of the first sintering sub-treatment being 3 h to 5 h to obtain a pre-sintered material; and, performing a second sintering sub-treatment on the pre-sintered material at a second temperature, the second temperature being 600 °C to 800 °C, and the time of the second sintering sub-treatment being 8 h to 12 h.

10. The method for preparing the lithium iron manganese phosphate material according to any one of claims 5 to 9, wherein: The first protective gas is selected from one or more of nitrogen, argon, helium, argon, neon, krypton and xenon; and / or The step of mixing the first mixed system with the complexing agent to form a gel includes: mixing the first mixed system with the complexing agent to obtain a second mixed system, and then, under the atmosphere of a second protective gas, stirring the second mixed system at 60 °C to 90 °C to form a gel, wherein the second protective gas is selected from one or more of nitrogen, argon, helium, argon, neon, krypton and xenon; 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 also includes the steps of: crushing the 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.

11. The method for preparing the lithium iron manganese phosphate material according to any one of claims 5 to 10, wherein: The lithium source is selected from one or more of lithium oxide, lithium hydroxide, lithium carbonate, lithium sulfate, lithium nitrate, lithium acetate, lithium dihydrogen phosphate, lithium phosphate and lithium oxalate; and / or The manganese source is selected from one or more of manganese monoxide, manganese tetraoxide, manganese hydroxide, manganese carbonate, manganese phosphate, manganese oxalate, manganese nitrate, manganese acetate, manganese sulfate and manganese chloride; and / or The titanium source is selected from one or more of ferrous oxide, ferrous oxide, ferrous hydroxide, ferrous sulfate, ferrous chloride, ferrous phosphate, ferrous phosphate, ferrous pyrophosphate, ferrous nitrate, ferrous acetate, ferrous oxalate and ferrous chloride; and / or The phosphorus source is selected from one or more of phosphoric acid, ammonium phosphate, ammonium dihydrogen phosphate, potassium dihydrogen phosphate, sodium dihydrogen phosphate and ferric phosphate; and / or The niobium source is selected from NbO, NbO 2、 One or more of Nb2O3 and Nb2O5.

12. 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; in, The lithium iron manganese phosphate material comprises a core and a coating layer coated on the outer surface of the core; wherein the material of the core comprises Li, Fe, Mn, Nb and PO4 with a non-stoichiometric composition, and the material of the coating layer comprises LiNbO3 and / or Li3NbO4; and / or, the preparation method of the lithium iron manganese phosphate material comprises the following steps: dispersing a lithium source, a manganese source, an iron source, a phosphorus source, and a niobium source in a dispersion medium to form a first mixed system, and mixing the first mixed system with a complexing agent to form a gel; and The gel is sintered in an atmosphere of a first protective gas to obtain a lithium manganese iron phosphate material.

13. The lithium battery according to claim 12, wherein: The material of the core is Li a Fe x Mn y Nb z (PO4) b , where a, x, y, z, and b respectively represent the molar amounts of Li, Fe, Mn, Nb, and PO4 in the core; wherein, 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or, 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.1; and / or The lithium iron manganese phosphate material has a secondary spherical structure, and the D50 particle size of the lithium iron manganese phosphate material is 5 μm to 9 μm; and / or, the difference between the D90 particle size of the lithium iron manganese phosphate material and the D10 particle size of the lithium iron manganese phosphate material is X, and the ratio of X to the D50 particle size X / D50 is 0.2 to 1.8; and / or The coating layer has a thickness of 10 nm to 30 nm.

14. The lithium battery according to claim 12 or 13, wherein: The complexing agent is selected from one or more of polyacrylic acid, citric acid, polyacrylamide, hydrolyzed polymaleic anhydride, polyhydroxyacrylic acid, ethylenediaminetetraacetic acid, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, sodium gluconate and sodium alginate; and / or In the step of mixing the first mixed system with a complexing agent to form a gel, the molar ratio of the metal cation in the first mixed system to the complexing agent is 1:(3-5); and / or In the first mixed system, Li:Mn:Fe:P:Nb is a:x:y:z:b, where 0.2 < y ≤ 0.9, 0 < z < 0.2, 0.9 < a / b < 1.1; and / or, 0.9 < (x + y + z) / b < 1.2, 0.9 < a / (x + y + z) < 1.1.

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