Composite lithium manganese iron phosphate material and its preparation method and application

Abstract

The present application discloses a composite lithium iron manganese phosphate material, its preparation method and application. The composite lithium iron manganese phosphate material of the present application includes lithium iron manganese phosphate and metal olefins bonded to the surface of the lithium iron manganese phosphate. The composite lithium iron manganese phosphate material of the present application is bonded to the surface of the lithium iron manganese phosphate, and the metal olefins form a conductive network structure between the lithium iron manganese phosphate particles. Moreover, the metal olefins have a large specific surface area. When compounded with the lithium iron manganese phosphate, the electronic conductivity and lithium ion diffusion rate of the lithium iron manganese phosphate are significantly improved, and ultimately the rate performance and cycle performance of the composite lithium iron manganese phosphate material of the present application are significantly improved. The preparation method thereof can ensure that the structure and electrochemical properties of the prepared composite lithium iron manganese phosphate material are stable, the efficiency is high, and the production cost is saved.

Description

Technical Field

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

[0002] Lithium-ion batteries are widely used in many fields such as 3C electronic products, power vehicles and energy storage power stations due to their high energy density, low self-discharge, no memory effect and long cycle life. They are currently a research hotspot in new energy storage and conversion systems.

[0003] Lithium-ion batteries consist of anode materials, cathode materials, separators, electrolytes, and battery casings. The cathode material is a crucial component, determining various performance indicators and accounting for approximately half of the battery's cost. Therefore, developing high-performance cathode materials is crucial for furthering the commercial development of lithium-ion batteries. Currently, the most commercially available cathode materials include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and nickel-cobalt-manganese ternary materials. Among them, lithium iron phosphate, with its olivine structure, offers numerous advantages, including high theoretical capacity, excellent capacity retention, low cost, and environmental friendliness. However, due to its inherent drawbacks of slow lithium ion diffusion and poor electronic conductivity, electrochemical polarization often occurs during charge and discharge, resulting in poor performance at high charge and discharge rates. Furthermore, its low discharge plateau results in low energy density. These drawbacks severely restrict its practical application. Therefore, modifying lithium iron phosphate by element doping is a commonly used regulatory strategy in industry. Studies have shown that doping with manganese elements can effectively improve some of the charge and discharge platforms of lithium iron phosphate, significantly improve the energy density of the material, and at the same time improve the material's electrical conductivity and lithium ion diffusion rate to a certain extent. However, the electronic conductivity and lithium ion diffusion rate of lithium manganese iron phosphate materials need to be further improved, and the rate performance and cycle stability are poor. Summary of the Invention

[0004] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and to provide a composite lithium manganese iron phosphate material and a preparation method thereof, so as to solve the technical problems of the existing lithium manganese iron phosphate having unsatisfactory performance such as electronic conductivity and lithium ion diffusion rate.

[0005] Another object of the present application is to provide a positive electrode and a secondary battery containing the positive electrode to solve the technical problem of low rate performance of existing lithium manganese iron phosphate secondary batteries.

[0006] To achieve the above application objectives, the first aspect of the present application provides a composite lithium iron manganese phosphate material. The composite lithium iron manganese phosphate material of the present application comprises lithium iron manganese phosphate and a metal olefin bonded to the surface of the lithium iron manganese phosphate.

[0007] In a second aspect of the present application, a method for preparing a composite lithium iron manganese phosphate material is provided. The method for preparing a composite lithium iron manganese phosphate material of the present application comprises the following steps:

[0008] Mixing lithium manganese iron phosphate, a metalloene precursor, an organic solvent, and a surfactant to obtain a mixed solution;

[0009] The mixed solution is subjected to a hydrothermal reaction to grow metalloene on the surface of lithium manganese iron phosphate.

[0010] The third aspect of the present application provides a positive electrode, which includes a current collector and a positive electrode active layer bonded to the current collector, wherein the positive electrode active material contained in the positive electrode active layer includes the composite manganese iron lithium phosphate material of the present application.

[0011] In a fourth aspect, the present application provides a secondary battery, which includes a positive electrode, and the positive electrode is the positive electrode of the present application.

[0012] Compared with the existing technology, this application has the following technical effects:

[0013] The composite lithium iron manganese phosphate material of the present application combines metalloene on the surface of the lithium iron manganese phosphate. When the lithium iron manganese phosphate particles contact each other or agglomerate to form secondary particles, the metalloene forms a conductive network structure between the lithium iron manganese phosphate particles. Moreover, the metalloene has a large specific surface area. When it is compounded with the lithium iron manganese phosphate, the electronic conductivity and lithium ion diffusion rate of the lithium iron manganese phosphate are significantly improved, and ultimately the rate performance and cycle performance of the composite lithium iron manganese phosphate material of the present application are significantly improved.

[0014] The preparation method of the composite lithium iron manganese phosphate material of the present application enables a metalloene precursor to grow in two dimensions on the surface of the lithium iron manganese phosphate in the presence of a surfactant and form a metalloene, thereby enabling the metalloene to be in situ bonded to the surface of the lithium iron manganese phosphate, and imparting to the prepared composite lithium iron manganese phosphate material the electronic conductivity and lithium ion diffusion rate possessed by the composite lithium iron manganese phosphate material of the present application as described above. In addition, the preparation method of the present application can ensure that the structure and electrochemical properties of the prepared composite lithium iron manganese phosphate material are stable, efficient, and save production costs.

[0015] Since the positive electrode of the present application contains the composite manganese iron lithium phosphate material of the present application, the positive electrode of the present application has high ion diffusion efficiency and can improve rate performance and cycle performance when used in a battery.

[0016] Since the secondary battery of the present application contains the positive electrode of the present application, the secondary battery of the present application has high rate performance and charge-discharge performance, and good cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation methods of the present application or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the specific implementation methods or the description of the prior art. Obviously, the drawings described below are some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] Figure 1 This is a schematic flow chart of a method for preparing a composite lithium iron manganese phosphate material according to an embodiment of the present application;

[0019] Figure 2 This is a scanning electron microscope (SEM) image of the composite lithium manganese iron phosphate material in Example A1 of the present application;

[0020] Figure 3 This is a transmission electron microscope (TEM) image of the composite lithium iron manganese phosphate material in Example A1 of the present application;

[0021] Figure 4 2 are X-ray diffraction (XRD) patterns of the products in Example A1 and Comparative Example A1 of the present application. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0023] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0024] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0025] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0026] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0027] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0028] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0029] In the first aspect, the embodiments of the present application provide a composite lithium iron manganese phosphate material. The composite lithium iron manganese phosphate material of the embodiments of the present application includes lithium iron manganese phosphate and metalloene bonded to the surface of the lithium iron manganese phosphate. In this way, the composite lithium iron manganese phosphate material of the embodiments of the present application is bonded with metalloene on the surface of the lithium iron manganese phosphate. When the lithium iron manganese phosphate particles contact each other or agglomerate to form secondary particles, the metalloene forms a conductive network structure between the lithium iron manganese phosphate particles; when the lithium iron manganese phosphate itself is a secondary particle, the metalloene can be bonded in the pores between the surface of the lithium iron manganese phosphate and the adjacent lithium iron manganese phosphate. At this time, the metalloene forms a conductive network structure in the lithium iron manganese phosphate secondary particles. Since the metalloene contained in the composite lithium iron manganese phosphate material can form a conductive network structure between adjacent lithium iron manganese phosphates, and the metalloene has a large specific surface area, it is compounded with the lithium iron manganese phosphate, thereby significantly improving the electronic conductivity and lithium ion diffusion rate of the lithium iron manganese phosphate, and ultimately significantly improving the rate performance and cycle performance of the composite lithium iron manganese phosphate material of the embodiments of the present application.

[0030] In addition, although a higher content of metalloalkene in the composite lithium iron manganese phosphate material can effectively improve the electronic conductivity and lithium ion diffusion rate of the composite lithium iron manganese phosphate material, it will also lead to a relatively low content of lithium iron manganese phosphate, thereby affecting the capacity of the composite lithium iron manganese phosphate material. Therefore, in the embodiment, the mass percentage of metalloalkene in the composite lithium iron manganese phosphate material is 0.5-50%. Metalloalkene in this mass content range can not only effectively form a rich conductive network in the composite lithium iron manganese phosphate material, but also ensure the content of lithium iron manganese phosphate, thereby improving the capacity of the composite lithium iron manganese phosphate material.

[0031] In the embodiment, the metalloalkene may be bonded to the surface of the lithium manganese iron phosphate by in-situ growth bonding, although other bonding methods are certainly not excluded.

[0032] The inventors further characterized the composite lithium iron manganese phosphate material of the embodiment of the present application and found that the metalloene contained in the composite lithium iron manganese phosphate material of the embodiment of the present application has at least one of the following characteristics:

[0033] Electron microscopic analysis of the metalloene, such as transmission electron microscopy (TEM), shows that the metalloene is a two-dimensional sheet structure with an average length and / or width of 100 to 500 nm. The metalloene is relatively evenly distributed on the surface of the lithium manganese iron phosphate.

[0034] Electron microscopy analysis also shows that the thickness of a single metallograph is 0.2 to 0.45 nm, and the number of atomic layers is generally distributed between 1 and 10 layers. Therefore, the total thickness of a single metallograph can be 0.2 to 5 nm.

[0035] Further electron microscopic analysis, such as TEM analysis, reveals that the metalloene exhibits a two-dimensional olefinic structure while also exhibiting a curved surface morphology. This curved morphology can induce lattice stress, which can regulate the electronic structure of surface atoms and optimize their adsorption energy, thereby enhancing their binding force with lithium manganese iron phosphate and promoting electrochemical synergy.

[0036] In an embodiment, the metal of the metalloene includes Pd or a Pd-based alloy, and the elements contained in the Pd-based alloy include at least one element of Pt, Rh, Ru, Ir, W, Mo, V, Fe, Co, Ni, Au, Ag, Cu, Cr, Ta, Mn, Zn, Nb, Y, Ce, and Bi in addition to Pd.

[0037] These metals or alloys can effectively form metalloene structures, improve the lithium ion diffusion rate characteristics of metalloene, and have good conductivity. They can also improve the structural stability of lithium manganese iron phosphate, ultimately significantly improving the rate performance and cycle performance of the composite lithium manganese iron phosphate material of the embodiment of the present application.

[0038] In a further embodiment, the molar ratio of Pd to any other element in the Pd-based alloy is 1:(0.1-9.9). By adjusting and optimizing the types and contents of the metal elements contained in the alloy, the lithium ion diffusion rate characteristics of the metalloene can be further improved, and the metalloene has good electrical conductivity and the bonding strength between the metalloene and the lithium iron manganese phosphate can be enhanced.

[0039] In addition, testing has shown that the particle size distribution of the composite manganese iron phosphate lithium material is between 0.1 and 10 μm.

[0040] In the second aspect, the present invention also provides a method for preparing the composite manganese iron lithium phosphate material. The process flow of the composite manganese iron lithium phosphate material of the present invention is as follows: Figure 1 As shown, the following steps are included:

[0041] S01: mixing lithium manganese iron phosphate, a metalloene precursor, an organic solvent, and a surfactant to obtain a mixed solution;

[0042] S02: subjecting the mixed solution to a hydrothermal reaction treatment to grow metalloene on the surface of the lithium manganese iron phosphate.

[0043] The preparation method of the composite lithium iron manganese phosphate material in the embodiment of the present application enables a metalloene precursor to grow in two dimensions on the surface of the lithium iron manganese phosphate in the presence of a surfactant and form a metalloene, thereby enabling the metalloene to be in situ bonded to the surface of the lithium iron manganese phosphate, and imparting to the prepared composite lithium iron manganese phosphate material the electronic conductivity and lithium ion diffusion rate possessed by the composite lithium iron manganese phosphate material in the embodiment of the present application described above. In addition, the preparation method in the embodiment of the present application can ensure that the structure and electrochemical properties of the prepared composite lithium iron manganese phosphate material are stable, efficient, and save production costs.

[0044] Step S01:

[0045] The metalloene precursor in step S01 is the metalloene precursor contained in the composite lithium manganese iron phosphate material of the embodiment of the present application.

[0046] In some embodiments, the metal olefin precursor may be a mixture including a Pd source or a Pd source and at least one of a Pt source, a Rh source, a Ru source, an Ir source, a W source, a Mo source, a V source, a Fe source, a Co source, a Ni source, an Au source, an Ag source, a Cu source, a Cr source, a Ta source, a Mn source, a Zn source, a Nb source, a Y source, a Ce source, and a Bi source. In the embodiment, in the metal olefin precursor, the molar ratio of Pd source to any one of Pt source, Rh source, Ru source, Ir source, W source, Mo source, V source, Fe source, Co source, Ni source, Au source, Ag source, Cu source, Cr source, Ta source, Mn source, Zn source, Nb source, Y source, Ce source, and Bi source is 1:(0.1-9.9), and the metal contained in the formed metal olefin can be a molar ratio of Pd to at least one element of Pt, Rh, Ru, Ir, W, Mo, V, Fe, Co, Ni, Au, Ag, Cu, Cr, Ta, Mn, Zn, Nb, Y, Ce, and Bi of 1:(0.1-9.9).

[0047] In the embodiments, the metalloene precursor includes a Pd source and at least one of a Rh source, a Mo source, an Fe source, a Co source, and a Ni source. These metal sources are compounded to enhance the lithium ion diffusion rate and conductivity of the resulting metalloene, further improving the rate capability and cycling performance of the composite lithium iron manganese phosphate material of the embodiments of the present application.

[0048] Among them, at least one source compound among the above Pd source, Pt source, Rh source, Ru source, Ir source, W source, Mo source, V source, Fe source, Co source, Ni source, Au source, Ag source, Cu source, Cr source, Ta source, Mn source, Zn source, Nb source, Y source, Ce source, and Bi source includes a soluble inorganic salt or / and organic salt containing the corresponding metal element.

[0049] Specifically, in the embodiment, the Pd source can be at least one of a soluble inorganic palladium salt and an organic palladium salt. In an exemplary embodiment, the palladium source can be at least one of palladium acetate, palladium chloride, palladium nitrate, palladium sulfate, palladium iodide, palladium dibromide, palladium hydroxide, potassium chloropalladate, sodium chloropalladate, ammonium chloropalladate, dichlorodiamminepalladium, dichlorotetraamminepalladium, sodium tetrachloropalladate, ammonium tetrachloropalladate, potassium tetrabromopalladate, potassium chloropalladate, tetraamminepalladium sulfate, tetraamminepalladium nitrate, palladium trifluoroacetate, lithium tetrachloropalladate, triphenylphosphine palladium acetate, ethylenediaminepalladium chloride, sodium hexachloropalladate, bis(tricyclohexylphosphine)palladium, tetrakis(triphenylphosphine)palladium, palladium(II) acetate (trimer), bis(acetylacetonate)palladium, bis(acetonitrile)palladium chloride, butylene palladium chloride dimer, hexafluoroacetylacetonate palladium, bis(cyanobenzene)palladium dichloride, bis(dibenzylideneacetone)palladium, bis(ethylenediamine)palladium chloride, tetraaminopalladium tetrachloride, and palladium acetylacetonate.

[0050] In an embodiment, the Pt source may be at least one of a soluble inorganic platinum salt and an organic platinum salt. In an exemplary embodiment, the Pt source may be at least one of platinum dichloride, sodium chloroplatinite, tetraammine platinum nitrate, potassium tetranitroplatinate, platinum nitrate, dinitrosodiammineplatinum, bis(cyanophenyl)dichloroplatinum, ammonium chloroplatinite, bis(tri-tert-butylphosphine)platinum, platinum tetrachloride, chloroplatinic acid, potassium chloroplatinate, potassium chloroplatinite, trans-diammoniumdichloroplatinum, potassium trichloroammoniumplatinate, cis-dichlorobis(pyridyl)platinum, sodium hexachloroplatinate, platinum acetylacetonate, tetrakis(triphenylphosphine)platinum, ammonium chloroplatinate, ethylenediamineplatinum chloride, cis-dichlorobis(diethylsulfide)platinum, and cis-diaminediiodideplatinum.

[0051] In an embodiment, the Rh source may be at least one of a soluble inorganic rhodium salt and an organic rhodium salt. In an exemplary embodiment, the Rh source may be at least one of rhodium iodide, rhodium nitrate, rhodium sulfate, potassium hexachlororhodium, rhodium octanoate dimer, di-μ-chloro-tetracarbonyldirhodium, rhodium acetate dimer, tetrakis(triphenylphosphine) rhodium hydride, rhodium trichloride, bis(triphenylphosphine)carbonyl rhodium chloride, rhodium acetylacetonate, bis(ethylene) acetylacetonatoyl rhodium, dicyclooctene rhodium chloride dimer, rhodium trifluoroacetate dimer, chlorodi(vinyl) rhodium dimer, ammonium chlororhodium, triphenylphosphine rhodium chloride, tris(triphenylphosphine)carbonyl rhodium hydride, bis(1,5-cyclooctadiene)-trifluoromethanesulfonic acid rhodium, (1,5-cyclooctadiene) 2,4-pentanedione rhodium, dicarbonyl acetylacetonato rhodium, and chloronorbornadiene rhodium dimer.

[0052] In an embodiment, the Ru source may be at least one of a soluble inorganic ruthenium salt and an organic ruthenium salt. In an exemplary embodiment, the Ru source may be at least one of ruthenium acetate, ruthenium acetate, ruthenium bromide, ruthenium iodide, ammonium hexafluororuthenate, potassium perruthenate, ruthenium hexacarbonyl chloride, triruthenium dodecacarbonyl, ruthenium trichloride, hexaammineruthenium chloride, ruthenium acetylacetonate, ruthenium nitrosyl acetate, and potassium pentachlororuthenate.

[0053] In an embodiment, the Ir source may be at least one of a soluble inorganic iridium salt and an organic iridium salt. In an exemplary embodiment, the Ir source may be at least one of iridium acetate, iridium chloride, iridium tetrachloride, iridium iodide, tetrairidium dodecacarbonyl, potassium hexafluoroiridate, iridium dicarbonyl acetylacetonate, iridium tris(acetylacetonate), bis(ethylene)iridium acetylacetonate, ammonium hexachloroiridate, and sodium hexachloroiridate.

[0054] In an embodiment, the W source may be at least one of a soluble inorganic tungsten salt and an organic tungsten salt. In an exemplary embodiment, the W source may be at least one of tungsten hexacarbonyl, tungsten ethoxide, sodium tungstate, ammonium tungstate, bismuth tungstate, phosphotungstic acid, silver tungstate, zinc tungstate, lithium tungstate, magnesium tungstate, ammonium tetrathiotungstate, sodium metatungstate monohydrate, ammonium paratungstate, ammonium metatungstate, and sodium phosphotungstate.

[0055] In an embodiment, the Mo source can be at least one of a soluble inorganic molybdenum salt and an organic molybdenum salt. In an exemplary embodiment, the Mo source can be at least one of nickel chloride, nickel bromide, nickel selenide, nickel iodide hydrate, nickel fluoride tetrahydrate, nickel chromite, nickel hydroxide, nickel sulfide, nickel thiocyanate, nickel ammonium sulfate, nickel sulfide, nickel sulfate, nickel phthalocyanine, basic nickel carbonate, nickel trifluoroacetate, nickel acetylacetonate, nano nickel ferrite, nickel fluoride, nickel stearate, potassium hexafluoronickelate, nickel citrate, nickel nitrate, nickel stannate dihydrate, nickel acetate, nickel hexaammine chloride, nickel oxalate, nickel hypophosphite hexahydrate, nickel ammonium sulfate, nickel formate dihydrate, nickel perchlorate hexahydrate, nickel tetrafluoroborate hexahydrate, and potassium tetracyanonickel (II) hydrate.

[0056] In an embodiment, the V source may be at least one of a soluble inorganic vanadium salt and an organic vanadium salt. In an exemplary embodiment, the V source may be at least one of vanadyl acetylacetonate, vanadium dichloride, vanadium acetylacetonate, bismuth vanadate, magnesium vanadate, sodium metavanadate, ammonium metavanadate, potassium metavanadate, silver metavanadate, and sodium orthovanadate.

[0057] In an embodiment, the Fe source may be at least one of a soluble inorganic iron salt and an organic iron salt. In an exemplary embodiment, the Fe source may be at least one of iron phthalocyanine, ferric pyrophosphate, potassium ferric cyanide, ferric perchlorate, ferrous ammonium sulfate, ferric phosphate, ferric chloride, ferric dichloride, tert-butylferrocene, triferric dodecacarbonyl, ferric acetate, ferric p-toluenesulfonate, ferric ammonium citrate, acetylferrocene, ferric citrate, ferric trifluoromethanesulfonate, ferric oxalate, ferric nitrate, ferric acetylacetonate, ferrous sulfate, sodium ferrocyanide, sodium nitrosoferricyanide, and ferrous acetylacetonate.

[0058] In an embodiment, the Co source may be at least one of a soluble inorganic cobalt salt and an organic cobalt salt. In an exemplary embodiment, the Co source may be at least one of cobalt acetate, methylcobalamin, cobalt sulfate, cobalt nitrate, cobalt iodide, cobalt phosphate, hydroxocobalamin, cobalt oxalate, cobalt chloride, cobalt titanate, lithium cobaltate, cobalt aluminate, cobalt isooctanoate, cobalt citrate, cobalt hydroxide, cobalt naphthenate, adenosylcobaltamine, potassium cobalt cyanide, cobalt bromide, cobalt selenide, cobalt sulfide, cobalt carbonate, cobalt phthalocyanine, sodium cobalt nitrite, potassium cobalt nitrite, dicobalt octacarbonyl, tetracobalt dodecacarbonyl, cobalt sulfamate, hydroxocobalamin hydrochloride, hexaamminecobalt chloride, cobaltous fluoride tetrahydrate, cobalt acetylacetonate, sodium hexanitrocobaltate, cobalt perchlorate hexahydrate, pentaamminechlorocobalt chloride, and vitamin B12.

[0059] In an embodiment, the Ni source may be at least one of a soluble inorganic nickel salt and an organic nickel salt. In an exemplary embodiment, the Ni source may be at least one of molybdenum acetate, molybdenum fluoride, molybdenum pentachloride, molybdenum boride, molybdenum phosphide, potassium molybdate, copper molybdate, ammonium molybdate, zinc molybdate, hexacarbonyl molybdenum, molybdenum acetylacetonate, ammonium octamolybdate, ammonium tetrathiomolybdate, sodium molybdate, phosphomolybdic acid hydrate, 2-ethylhexanoic acid molybdenum salt, ammonium phosphomolybdate hydrate, ammonium tetramolybdate hydrate, cyclopentadienyl molybdenum tetrachloride, tricarbonyl cycloheptatrienyl molybdenum, and bis(cyclopentadienyl) molybdenum dichloride.

[0060] In an embodiment, the Au source may be at least one of a soluble inorganic gold salt and an organic gold salt. In an exemplary embodiment, the Au source may be at least one of gold acetate, gold chloride, gold(II) chloride, sodium tetrabromoaurate, potassium gold chloride, chloroauric acid, and sodium tetrachloroaurate.

[0061] In an embodiment, the Ag source may be at least one of a soluble inorganic silver salt and an organic silver salt. In an exemplary embodiment, the Ag source may be at least one of silver chloride, silver nitrate, silver bromide, silver iodide, silver fluoride, silver selenide, silver telluride, silver acetylacetonate, and tetra(acetonitrile)silver tetrafluoroborate.

[0062] In an embodiment, the Cu source may be at least one of a soluble inorganic copper salt and an organic copper salt. In an exemplary embodiment, the Cu source may be at least one of copper chloride, cuprous chloride, copper chromite, copper phthalocyanine, copper sulfate, copper acetylacetonate, perfluorocopper phthalocyanine, copper nitrate, copper ethyl acetoacetate, copper oxalate, copper molybdate, copper citrate, copper fluoroborate, copper pyrophosphate, and copper stearate.

[0063] In an embodiment, the Cr source may be at least one of a soluble inorganic chromium salt and an organic chromium salt. In an exemplary embodiment, the Cr source may be at least one of chromium acetate, chromium fluoride, chromium nitride, chromium nicotinate, chromium selenide, chromium sulfate, chromium boride, chromium phosphate, copper chromite, chromium chloride, chromium acetylacetonate, chromium sulfide, benzene tricarbonyl chromium, sodium chromate, chromium nitrate, and potassium chromium sulfate.

[0064] In an embodiment, the Ta source may be at least one of a soluble inorganic tantalum salt and an organic tantalum salt. In an exemplary embodiment, the Ta source may be at least one of tantalum methoxide, tantalum phosphide, potassium fluorotantalate, tantalum chloride, tantalum sulfide, tantalum pentabromide, tantalum isopropoxide, and tantalum diboride.

[0065] In an embodiment, the Mn source may be at least one of a soluble inorganic manganese salt and an organic manganese salt. In an exemplary embodiment, the Mn source may be at least one of manganese carbonate, manganese fluoride, manganese nitride, manganese fluoride, manganese bromide, manganese chloride, manganese carbide, manganese phosphide, potassium permanganate, potassium manganate, manganese acetate, manganese nitrate, manganese phosphate, manganese dihydrogen phosphate, manganese oxalate, manganese pentacarbonyl, manganese decacarbonyl, manganese sulfate, manganese acetate, manganese acetylacetonate, and manganese pyrophosphate.

[0066] In an embodiment, the Zn source may be at least one of a soluble inorganic zinc salt and an organic zinc salt. In an exemplary embodiment, the Zn source may be at least one of zinc chloride, zinc iodide, zinc lactate, zinc phytate, zinc fluoride, zinc bromide, zinc formate, zinc selenide, zinc sulfide, zinc sulfate, zinc borate, zinc phthalocyanine, zinc tungstate, zinc molybdate, zinc stannate, zinc selenite, zinc citrate, zinc borohydride, zinc trifluoroacetate, and zinc acetylacetonate.

[0067] In an embodiment, the Nb source may be at least one of a soluble inorganic niobium salt and an organic niobium salt. In an exemplary embodiment, the Nb source may be at least one of niobium oxalate, sodium niobate, potassium niobate, lithium niobate, magnesium niobate, and ammonium hexafluoroniobate.

[0068] In an embodiment, the Y source may be at least one of a soluble inorganic yttrium salt and an organic yttrium salt. In an exemplary embodiment, the Y source may be at least one of yttrium acetate, yttrium metaphosphate, yttrium fluoride, yttrium isopropoxide, yttrium bromide, yttrium sulfide, yttrium iodide, yttrium phosphate, yttrium acetylacetonate, yttrium carbonate, yttrium trifluoroacetate, yttrium acetate, yttrium nitrate, yttrium hexafluoro-acetylacetonate, and yttrium sulfate.

[0069] In an embodiment, the Ce source may be at least one of a soluble inorganic cerium salt and an organic cerium salt. In an exemplary embodiment, the Ce source may be at least one of cerium fluoride, ammonium cerium nitrate, cerium sulfate, cerium bromide, cerium sulfide, cerium chloride, cerium isopropoxide, cerium acetylacetonate, and cerous sulfate.

[0070] In the embodiment, the Bi source can be at least one of a soluble inorganic bismuth salt and an organic bismuth salt. In an exemplary embodiment, the Bi source can be at least one of bismuth subnitrate, bismuth subcarbonate, bismuth nitrate, bismuth sulfate, bismuth phosphate, bismuth vanadate, bismuth tungstate, bismuth germanate, bismuth citrate, bismuth acetate, and bismuth subsalicylate.

[0071] In an embodiment, the metalloalkene precursor can be added in a molar ratio of lithium iron manganese phosphate to the metalloalkene precursor of 1: (0.1 to 6.8) and mixed with components including lithium iron manganese phosphate, a surfactant, etc. By adjusting the content of the metalloalkene precursor, the dispersion uniformity of each component, such as the metalloalkene precursor, in the mixed solution is improved, and the amount and uniformity of the metalloalkene precursor grown on the surface of the lithium iron manganese phosphate is increased, thereby adjusting the content of the metalloalkene contained in the prepared composite lithium iron manganese phosphate material, thereby improving the capacity of the composite lithium iron manganese phosphate material while improving the electronic conductivity and lithium ion diffusion rate of the composite lithium iron manganese phosphate material.

[0072] The presence of surfactants can effectively make the metal precursor dispersed uniformly in the organic solvent, and shows that the surfactant also acts as a capping agent in this system. It can adsorb on specific atomic crystal planes and thus hinder the growth of these crystal planes, while the crystal planes that are not adsorbed with surfactants can continue to grow, thereby achieving anisotropic growth, and ultimately enabling the metal precursor to combine with two-dimensional structured metalene on the surface of lithium manganese iron phosphate.

[0073] In an embodiment, the surfactant can be added to the mixture with components including the lithium manganese iron phosphate and the metalloene precursor at a molar ratio of 1:(0.1-9.6) of lithium manganese iron phosphate to surfactant. By adjusting the content of the surfactant, the uniformity of the dispersion of the components, including the metalloene precursor, in the mixed solution is improved, and the uniformity of the growth of the metalloene precursor on the surface of the lithium manganese iron phosphate and the stability of its chemical properties are improved.

[0074] In an exemplary embodiment, the surfactant may include hexadecyltrimethylammonium bromide, hexadecyldimethylethylammonium bromide, hexadecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium chloride, dihexadecyldimethylammonium bromide, 1-naphthylmethylammonium bromide, benzyltrimethylammonium bromide, tetra-n-octylammonium bromide, tetrahexylammonium bromide, tetramethylammonium bromide, dodecyldimethylbenzylammonium bromide, benzyltributylammonium bromide, triethylmethylammonium bromide, methyltrioctylammonium bromide, tetradecyltrimethylammonium bromide, didecyldimethylammonium bromide, At least one of dodecyldimethylethylammonium bromide, 3-bromopropyltrimethylammonium bromide, phenyltrimethylammonium tribromide, n-octyltrimethylammonium bromide, decanyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, benzyltriethylammonium bromide, tetradecylammonium bromide, tetrapentylammonium bromide, phenyltrimethylammonium bromide, tetrabutylammonium bromide, tetrapropylammonium bromide, 2-bromoethyltrimethylammonium bromide, tetrabutylammonium tribromide, ammonium bromide, potassium bromide, sodium iodide, potassium iodide, ascorbic acid, and polyvinylpyrrolidone.

[0075] Lithium manganese iron phosphate, as the electrode material component of the composite lithium manganese iron phosphate material in the above-mentioned application embodiment, can be directly made of lithium manganese iron phosphate material, or improved lithium manganese iron phosphate based on existing lithium manganese iron phosphate, such as doped lithium manganese iron phosphate. It can be directly purchased or prepared according to the following methods:

[0076] S011: mixing a lithium source, an iron source, a manganese source, a phosphorus source, and a carbon source to obtain a lithium iron manganese phosphate precursor;

[0077] S012: calcining the lithium manganese iron phosphate precursor in step S011.

[0078] The lithium source, iron source, manganese source, phosphorus source, and carbon source in step S011 constitute a lithium iron manganese phosphate precursor. In some embodiments, the molar ratio of lithium source: iron source: manganese source: phosphorus source: carbon source can be 1:(0.1-0.9):(0.1-0.9):(0.5-3.1):(0.01-0.9), that is, the lithium source, iron source, manganese source, phosphorus source, and carbon source contained in the lithium iron manganese phosphate precursor are mixed in a ratio of 1:(0.1-0.9):(0.1-0.9):(0.5-3.1):(0.01-0.9).

[0079] In an exemplary embodiment, the lithium source may include at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium formate, lithium silicate, lithium sulfate, lithium phosphate, lithium oxalate, lithium octanoate, lithium citrate, lithium salicylate, lithium orthosilicate, lithium permanganate, lithium trifluoroacetate, lithium acetoacetate, lithium difluorophosphate, lithium hexafluorophosphate, lithium benzoate, lithium metaphosphate, lithium pyruvate, lithium acetate, lithium fluoride, lithium bromide, lithium methoxide, lithium ethoxide, lithium oxide, lithium nitride, and lithium sulfide.

[0080] In an exemplary embodiment, the iron source may include at least one of ferrous oxalate, ferrous nitrate, ferrous sulfide, ferrous sulfate, ferrous phosphate, ferrous iodide, ferrous fluoride, ferrous bromide, ferrous acetylacetonate, ferrous gluconate, ferrous chloride, and ferrous acetate.

[0081] In an exemplary embodiment, the manganese source may include at least one of manganese carbonate, manganese fluoride, manganese nitride, manganese fluoride, manganese bromide, manganese chloride, manganese carbide, manganese phosphide, potassium permanganate, potassium manganate, manganese acetate, manganese nitrate, manganese phosphate, manganese dihydrogen phosphate, manganese oxalate, manganese pentacarbonyl, manganese decacarbonyl, manganese sulfate, manganese acetate, manganese acetylacetonate, and manganese pyrophosphate.

[0082] In an exemplary embodiment, the phosphorus source may include at least one of sodium pyrophosphate, sodium phosphite, sodium metaphosphate, sodium tripolyphosphate, sodium hexafluorophosphate, ammonium hypophosphite, ammonium polyphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hexafluorophosphate, ammonium phosphate, potassium hypophosphite, potassium pyrophosphate, tripotassium phosphate, potassium phosphite, potassium metaphosphate, and potassium hexafluorophosphate.

[0083] In an exemplary embodiment, the carbon source may include at least one of glucose, sucrose, citric acid, ascorbic acid, starch, phenolic resin, acetylene black, graphene, and carbon nanotubes.

[0084] In addition, the mixing process in step S011 can be a method of directly mixing the components contained in the lithium iron manganese phosphate precursor, or ball milling the components together with a solvent. When the components contained in the lithium iron manganese phosphate precursor are ball milled together with a solvent, they are dried and ground after ball milling. In an exemplary embodiment, the solvent ball milled together with the lithium iron manganese phosphate precursor can include at least one of methanol, ethanol, glycerol, isopropyl alcohol, oleylamine, oleic acid, toluene, aniline, octadecylamine, chloroform, carbon tetrachloride, dimethyl sulfoxide, dimethylformamide, acetone, ethylenediamine, acetaldehyde, formic acid, and acetic acid.

[0085] In an exemplary embodiment, the ball milling speed may be 300 to 500 r / min, and the ball milling time may be 2 to 12 h.

[0086] The calcination process in step S012 converts the lithium iron manganese phosphate precursor into lithium iron manganese phosphate. In an embodiment, the calcination process may be performed at a temperature of 650-850°C.

[0087] In an exemplary embodiment, the calcination process may be a secondary sintering process as follows:

[0088] The first calcination temperature is 300-450°C and the calcination time is 5-18h;

[0089] The second calcination temperature is 650-850°C, and the calcination time is 10-48h.

[0090] In addition, the calcination treatment is carried out in an inert gas atmosphere to improve the electrochemical performance of lithium manganese iron phosphate.

[0091] In some embodiments, as in the above-mentioned step S01, the molar ratio of lithium manganese iron phosphate, metal olefin precursor, and surfactant is 1: (0.1 to 6.8): (0.1 to 9.6). In other embodiments, the amount of lithium manganese iron phosphate, metal olefin precursor, and surfactant dissolved or dispersed in the organic solvent in step S01 can be controlled to control the concentration of the mixed solution, thereby adjusting the binding morphology and uniform dispersion of the metal olefin on the lithium manganese iron phosphate in step S02. For example, in the embodiment, by controlling the dispersion amount of lithium manganese iron phosphate, metal olefin precursor, and surfactant in the organic solvent, such as taking the metal olefin precursor as a reference concentration, the total molar concentration of the metal olefin precursor in the mixed solution is 0.05 to 11.6 mol / L.

[0092] The organic solvent in step S01 constitutes the solvent carrier of the mixed solution. Therefore, the organic solvent should be able to effectively dissolve or disperse the metal alkene precursor and the surfactant, and of course should ensure the stability of the lithium iron manganese phosphate and effectively disperse the lithium iron manganese phosphate, so as to achieve the dispersion of the components, improve the metal alkene in situ with relative uniformity on the surface of the lithium iron manganese phosphate during the hydrothermal reaction treatment, and improve the generation efficiency of the metal alkene, improve the interaction between the metal alkene and the lithium iron manganese phosphate, thereby improving the role of the metal alkene in the prepared composite lithium iron manganese phosphate material, the electronic conductivity and the lithium ion diffusion rate of the composite lithium iron manganese phosphate material.

[0093] In an exemplary embodiment, the organic solvent may include at least one of methanol, ethanol, glycerol, isopropanol, oleylamine, oleic acid, toluene, aniline, octadecylamine, chloroform, carbon tetrachloride, dimethyl sulfoxide, dimethylformamide, acetone, ethylenediamine, acetaldehyde, formic acid, and acetic acid. These organic solvents can effectively dissolve the components and surfactants contained in the metalloalkene precursor and improve the stability and dispersibility of the lithium iron manganese phosphate, while forming a solvent system for the hydrothermal reaction in step S02. On the other hand, the organic solvent can provide reducing properties for the system, smoothly reducing the metal ions in the solvent, which is conducive to the formation of the target metalloalkene, showing the metalloalkene morphological characteristics and microstructure contained in the composite lithium iron manganese phosphate material as described above, thereby improving the role of the metalloalkene in the prepared composite lithium iron manganese phosphate material, and improving the electronic conductivity and lithium ion diffusion rate of the composite lithium iron manganese phosphate material.

[0094] Step S02:

[0095] In step S02, the mixed solution is subjected to a hydrothermal reaction treatment, that is, the mixed solution in step S01 is subjected to a heat treatment, so that the metalloene precursor generates metalloene, specifically growing metalloene on the surface of lithium manganese iron phosphate, specifically such as the metalloene contained in the composite lithium manganese iron phosphate material above. In the embodiment, the temperature of the hydrothermal reaction treatment is 50 to 200°C, and the holding time is 2 to 24 hours. The conditions of the hydrothermal reaction are conducive to the generation of the target metalloene, and can improve its reaction efficiency, and can enable the generated metalloene to have the morphological characteristics and structure of the metalloene contained in the composite lithium manganese iron phosphate material above. In a specific embodiment, the hydrothermal reaction can be carried out in a sealed container, such as a sealed hydrothermal reactor or a pressure-resistant tube.

[0096] After the hydrothermal reaction is completed, the mixed solution after the reaction, that is, the reaction solution containing the composite manganese iron lithium phosphate material, can be cooled, such as to room temperature. The cooling process can be performed by natural cooling or other cooling methods to cool the mixture to room temperature.

[0097] After the hydrothermal reaction, the generated composite lithium manganese iron phosphate material is dispersed in the organic solvent. Therefore, in a further embodiment, after the hydrothermal reaction step, the following steps are further included:

[0098] The reaction solution containing the composite manganese iron lithium phosphate material is subjected to solid-liquid separation treatment, drying treatment and grinding treatment.

[0099] Among them, solid-liquid separation can be, but not limited to, filtration. Other methods of separating precipitates can also be used to collect filter residues. In order to improve the purity of the composite lithium manganese iron phosphate material, the filter residue can be washed to remove impurities such as unreacted source compounds. For example, the filter residue can be washed with anhydrous ethanol. Drying treatment is to remove residual organic solvents or washing solvents in the filter residue. For example, the filter residue, such as the washed filter residue, can be vacuum dried, such as drying in a vacuum drying oven at 80°C for 8 hours.

[0100] The grinding process is performed to control the particle size of the filter residue, thereby controlling the particle size of the composite manganese iron lithium phosphate material. For example, the particle size of the obtained composite manganese iron lithium phosphate material is controlled to be within the particle size range of 0.1 to 10 μm of the composite manganese iron lithium phosphate material mentioned above.

[0101] In a third aspect, the present invention further provides a positive electrode, which includes a positive electrode current collector and a positive electrode active layer bonded to the positive electrode current collector.

[0102] The positive electrode current collector of the positive electrode can be, but is not limited to, any one of copper foil and aluminum foil.

[0103] The positive electrode active layer of the positive electrode includes components such as a positive electrode active material, a binder and a conductive agent.

[0104] The positive electrode active material in the positive electrode active layer is the composite lithium iron manganese phosphate material described in the embodiments of the present application. Therefore, the positive electrode of the present embodiment has high rate performance and fast charging characteristics, and the active layer has a high compaction density and high energy density. In the embodiment, the composite lithium iron manganese phosphate material of the present embodiment can be controlled to account for 85% to 97% by weight of the positive electrode active layer.

[0105] In an embodiment, the binder in the positive electrode active layer may account for 1% to 3% by weight of the positive electrode active layer. In a specific embodiment, the binder includes one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0106] In an embodiment, the conductive agent in the positive electrode active layer may account for 1% to 2% by weight of the positive electrode active layer. In a specific embodiment, the conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes.

[0107] In the embodiment, the positive electrode preparation process can be: mixing the positive electrode active material, the conductive agent and the binder to obtain an electrode slurry, coating the electrode slurry on the current collector, and preparing the positive electrode through steps such as drying, rolling, and die cutting.

[0108] Fourthly, the embodiment of the present application also provides a secondary battery. The secondary battery of the embodiment of the present application includes necessary components such as a positive electrode, a negative electrode, a separator and an electrolyte, and of course also includes other necessary or auxiliary components. Among them, the positive electrode is the positive electrode of the embodiment of the present application mentioned above, that is, the positive electrode active layer contained in the positive electrode contains the composite manganese iron lithium phosphate material of the embodiment of the present application above. Since the secondary battery of the embodiment of the present application contains the composite manganese iron lithium phosphate material of the embodiment of the present application above, the secondary battery of the embodiment of the present application has high energy density, rate performance and fast charging characteristics.

[0109] The following describes the composite lithium manganese iron phosphate material and its preparation method according to the embodiment of the present application through a number of specific embodiments.

[0110] 1. Composite lithium manganese iron phosphate material and preparation method thereof:

[0111] Example A1

[0112] This embodiment provides a composite lithium iron manganese phosphate material and a preparation method thereof. The composite lithium iron manganese phosphate material includes lithium iron manganese phosphate and a metal alkene bonded to the surface of the lithium iron manganese phosphate. The preparation method of the composite lithium iron manganese phosphate material of this embodiment includes the following steps:

[0113] S1. Preparation of lithium manganese iron phosphate:

[0114] S11. Weigh 4 g of lithium carbonate, 3.2 g of ferrous sulfate, 3.5 g of manganese carbonate, 6.9 g of ammonium dihydrogen phosphate, and 0.75 g of glucose using a balance, then weigh 50 mL of anhydrous ethanol using a graduated cylinder, add them to an agate ball mill, and mill at 400 rpm for 5 h.

[0115] S12. After the solution in S11 is thoroughly ball-milled and uniformly mixed, it is placed in a vacuum drying oven at a drying temperature of 60°C for 8 hours;

[0116] S13. After grinding the dried product obtained in S12, sieve it with a 200-mesh sieve; place the sieved powder in a tube furnace, purge it with nitrogen, and calcine it at 350°C for 8 hours; grind the sample after the first calcination, and then place it in a tube furnace again, purge it with nitrogen, and calcine it at 700°C for 12 hours. The resulting powder is LiMn 0.6 Fe 0.4 PO4 / C lithium manganese iron phosphate material;

[0117] S2. Hydrothermal preparation of lithium manganese iron phosphate / metalloene:

[0118] S21. Use a pipette to measure 10 mL of oleylamine and pour it into a 30 mL pressure-resistant glass tube for magnetic stirring. Use a balance to measure 20 mg of lithium manganese iron phosphate powder, 5 mg of palladium chloride powder, 10 mg of tungsten hexacarbonyl powder, and 10 mg of ascorbic acid powder in S1. Add them one by one (the order of adding the components is not strictly required) to the pressure-resistant glass tube and stir until the solution is evenly mixed.

[0119] S22. The pressure-resistant glass tube in S21 was sealed and then subjected to a hydrothermal reaction at a temperature of 90°C for 5 hours and then cooled naturally to obtain a hydrothermal product.

[0120] S23. The hydrothermal product obtained in S22 is centrifuged and washed three times with anhydrous ethanol. The washed product is placed in a vacuum drying oven, maintained at 80°C, and dried for 8 hours. The dried material is ground with a mortar (such as an agate mortar) to obtain a dry powder, which is a lithium manganese iron phosphate / palladium metalloalkene composite lithium manganese iron phosphate material, marked as LM 0.6 F 0.4 P / Pd-M.

[0121] Example A2

[0122] This embodiment provides a composite lithium iron manganese phosphate material and a preparation method thereof. The composite lithium iron manganese phosphate material includes lithium iron manganese phosphate and a metal olefin bonded on the surface of the lithium iron manganese phosphate.

[0123] The preparation method of the composite lithium iron manganese phosphate material of this embodiment includes the following steps:

[0124] S1. Preparation of lithium manganese iron phosphate:

[0125] S11. Weigh 1.2 g of lithium hydroxide, 2.9 g of ferrous oxalate, 4.9 g of potassium permanganate, 4.4 g of sodium hypophosphite, and 1.5 g of sucrose using a balance, then weigh 40 mL of anhydrous ethanol using a graduated cylinder. Add these to an agate ball mill and mill at 360 rpm for 6 h.

[0126] S12. After the solution in S11 is thoroughly ball-milled and uniformly mixed, it is placed in a vacuum drying oven at a drying temperature of 70°C for 7 hours;

[0127] S13. After grinding the dried product obtained in S12, sieve it with a 200-mesh sieve; place the sieved powder in a tube furnace, purge it with nitrogen, and calcine it at 400°C for 6 hours; grind the sample after the first calcination, and then place it in a tube furnace again, purge it with nitrogen, and calcine it at 650°C for 13 hours. The resulting powder is LiMn 0.6 Fe 0.4 PO4 / C lithium manganese iron phosphate material;

[0128] S2. Hydrothermal preparation of lithium manganese iron phosphate / metalloene:

[0129] S21. Use a pipette to measure 10 mL of oleylamine and pour it into a 30 mL pressure-resistant glass tube for magnetic stirring; use a balance to measure 20 mg of lithium manganese iron phosphate powder in S1, 5 mg of palladium acetylacetonate powder, 10 mg of molybdenum acetylacetonate powder, 20 mg of iron pentacarbonyl powder, and 10 mg of potassium bromide powder. Add them one by one (the order of adding the components is not strictly required) to the pressure-resistant glass tube and stir until the solution is evenly mixed;

[0130] S22. The pressure-resistant glass tube in S21 was sealed and then subjected to a hydrothermal reaction at a temperature of 100 ° C. for 6 h and then cooled naturally to obtain a hydrothermal product.

[0131] S23. The hydrothermal product obtained in S22 is centrifuged and washed three times with anhydrous ethanol. The washed product is placed in a vacuum drying oven, maintained at 60°C, and dried for 6 hours. The dried material is ground with a mortar (such as an agate mortar) to obtain a dry powder, which is a composite lithium manganese iron phosphate material of lithium iron manganese phosphate / palladium molybdenum iron ternary metal olefin, marked as LM 0.6 F 0.4 P / PdMoFe-M.

[0132] Example A3

[0133] This embodiment provides a composite lithium iron manganese phosphate material and a preparation method thereof. The composite lithium iron manganese phosphate material includes lithium iron manganese phosphate and a metal olefin bonded on the surface of the lithium iron manganese phosphate.

[0134] The preparation method of the composite lithium iron manganese phosphate material of this embodiment includes the following steps:

[0135] S1. Preparation of lithium manganese iron phosphate:

[0136] S11. Weigh 2.1 g of lithium chloride, 2.8 g of ferrous chloride, 5.6 g of manganese sulfate, 4.1 g of ammonium hypophosphite, and 1.1 g of ascorbic acid using a balance, then weigh 50 mL of anhydrous ethanol using a graduated cylinder, add them together to an agate ball mill, and mill at 450 rpm for 4 h.

[0137] S12. After the solution in S11 is thoroughly ball-milled and uniformly mixed, it is placed in a vacuum drying oven at a drying temperature of 80°C for 5 hours;

[0138] S13. After grinding the dried product obtained in S12, sieve it with a 200-mesh sieve; place the sieved powder in a tube furnace, purge it with nitrogen, and calcine it at 400°C for 5 hours; grind the sample after the first calcination, and then place it in the tube furnace again, purge it with nitrogen, and calcine it at 700°C for 12 hours. The resulting powder is LiMn 0.6 Fe 0.4 PO4 / C lithium manganese iron phosphate material;

[0139] S2. Hydrothermal preparation of lithium manganese iron phosphate / metalloene:

[0140] S21. Use a pipette to measure 10 mL of oleic acid and pour it into a 30 mL pressure-resistant glass tube for magnetic stirring; use a balance to measure 20 mg of lithium manganese iron phosphate powder in S1, 10 mg of ammonium chloropalladate powder, 10 mg of molybdenum chloride powder, 20 mg of pentacarbonyl iron powder, 10 mg of dodecyltrimethylammonium bromide powder, and add them one by one (the order of adding the components is not strictly required) to the pressure-resistant glass tube and stir until the solution is evenly mixed;

[0141] S22. The pressure-resistant glass tube in S21 was sealed and then subjected to a hydrothermal reaction at a temperature of 120°C for 3 hours and then cooled naturally to obtain a hydrothermal product.

[0142] S23. The hydrothermal product obtained in S22 is centrifuged and washed three times with anhydrous ethanol. The washed product is placed in a vacuum drying oven, maintained at 80°C, and dried for 8 hours. The dried material is ground with a mortar (such as an agate mortar) to obtain a dry powder, which is a composite lithium manganese iron phosphate material of lithium iron manganese phosphate / palladium iron metalloene, marked as LM 0.6 F 0.4 P / PdFe-M.

[0143] Example A4

[0144] This embodiment provides a composite lithium iron manganese phosphate material and a preparation method thereof. The composite lithium iron manganese phosphate material includes lithium iron manganese phosphate and a metal olefin bonded on the surface of the lithium iron manganese phosphate.

[0145] The preparation method of the composite lithium iron manganese phosphate material of this embodiment includes the following steps:

[0146] S1. Preparation of lithium manganese iron phosphate:

[0147] S11. Use a balance to weigh 5.5g lithium sulfate, 3.5g ferrous acetate, 6.1g potassium permanganate, 5.8g potassium hypophosphite, and 0.8g citric acid, then use a graduated cylinder to weigh 50mL of anhydrous ethanol, add them together to an agate ball mill, and ball mill at a speed of 380r / min for 5 hours;

[0148] S12. After the solution in S11 is thoroughly ball-milled and uniformly mixed, it is placed in a vacuum drying oven at 80°C for 12 h.

[0149] S13. After grinding the dried product obtained in S12, sieve it with a 200-mesh sieve; place the sieved powder in a tube furnace, purge it with nitrogen, and calcine it at 360°C for 7 hours; grind the sample after the first calcination, and then place it in a tube furnace again, purge it with nitrogen, and calcine it at 720°C for 10 hours. The resulting powder is LiMn 0.6 Fe 0.4 PO4 / C lithium manganese iron phosphate material;

[0150] S2. Hydrothermal preparation of lithium manganese iron phosphate / metalloene:

[0151] S21. Use a pipette to measure 10 mL of ethylenediamine and pour it into a 30 mL pressure-resistant glass tube and stir magnetically; use a balance to measure 20 mg of lithium manganese iron phosphate powder in S1, 10 mg of palladium acetate powder, 10 mg of molybdenum acetylacetonate powder, 10 mg of cobalt acetylacetonate powder, 15 mg of potassium iodide powder, and add them one by one (the order of adding the components is not strictly required) to the pressure-resistant glass tube and stir until the solution is evenly mixed;

[0152] S22. The pressure-resistant glass tube in S21 was sealed and then subjected to a hydrothermal reaction at a temperature of 150°C for 4 hours and then cooled naturally to obtain a hydrothermal product.

[0153] S23. The hydrothermal product obtained in S22 is centrifuged and washed three times with anhydrous ethanol. The washed product is placed in a vacuum drying oven, maintained at 80°C, and dried for 10 hours. The dried material is ground with a mortar (e.g., an agate mortar) to obtain a dry powder, which is a lithium manganese iron phosphate / palladium molybdenum iron ternary metal olefin composite positive electrode material, labeled LM 0.6 F 0.4 P / PdMoCo-M.

[0154] Comparative Example A1

[0155] This comparative example provides a lithium iron manganese phosphate material. The lithium iron manganese phosphate material in this comparative example is the lithium iron manganese phosphate material prepared in step S1 of Example A1, and is marked as LM 0.6 F 0.4 P / C.

[0156] 2. Lithium-ion battery example:

[0157] Examples B1 to B4 and Comparative Example B1 each provide a lithium-ion battery. Each lithium-ion battery is assembled into a lithium-ion battery according to the following method:

[0158] 2.1 Positive electrode:

[0159] The composite lithium manganese iron phosphate materials provided in Examples A1 to A4 and Comparative Example A1 were used as the positive electrode active materials of lithium-ion battery Examples B1 to B4 and Comparative Example B1, respectively. The positive electrode sheets were prepared by the following method:

[0160] (1) Preparation of slurry: 23.75 g of positive electrode active material, 0.5 g of superconducting carbon black (SP), and 0.75 g of binder polyvinylidene fluoride (PVDF) were added simultaneously into a 500 mL agate ball mill jar, and then 16 g of solvent N-methylpyrrolidone (NMP) was added. The slurry was prepared by ball milling at a speed of 360 r / min for 4 h.

[0161] (2) Slurry coating: Adjust the scale of the scraper of the coating machine and evenly apply the milled slurry on the aluminum foil. Place the coated electrode in a vacuum drying oven at 130°C for 3 hours.

[0162] (3) Rolling and punching: Place the aluminum foil coated with slurry flatly in the middle of the roller and roll the electrode; place the front of the rolled electrode close to the punched area and punch the electrode in sequence; the compaction density of the electrode is controlled at 2.0-2.4g / cm 3 , with a diameter of 14 mm and a thickness of 0.05 to 0.10 mm; place the punched electrode in a vacuum drying oven at 130°C and bake for 3 hours;

[0163] 2.2 Assemble button cells. In a glove box, assemble them in the order of negative electrode shell, shrapnel, steel sheet, lithium sheet, diaphragm, positive electrode sheet and positive electrode shell. In the process, inject 10μL of electrolyte, and then use a sealing machine to seal the button cells. The electrochemical performance of these four groups of button cells was tested.

[0164] 3. Characterization of composite lithium manganese iron phosphate and electrochemical performance of lithium-ion batteries:

[0165] 3.1 Characterization of composite lithium manganese iron phosphate

[0166] The composite manganese iron lithium phosphate provided in Examples A1 to A4 were subjected to SEM analysis respectively, wherein the SEM image of the composite manganese iron lithium phosphate provided in Example A1 is as follows: Figure 2 As shown. Figure 2 It can be seen that the surface of the lithium manganese iron phosphate particles is coated with flaky metalloene, and the metalloene effectively fills the gaps between the lithium manganese iron phosphate particles, forming a mutually cross-linked conductive network. This structure can greatly improve the material conductivity and lithium ion diffusion rate. We further characterized the transmission electron microscopy spectrum of the composite material provided in Example A1, and the results are as follows: Figure 3 As shown in the figure, it can be clearly seen that the two-dimensional metalloene is tightly coated on the surface of the lithium iron manganese phosphate particles. The metalloene has a highly curved structural characteristic. Their size is between 100 and 500 nm, the number of atomic layers of the metalloene is 1 to 10 layers, and the thickness of the metalloene is 0.2 to 0.45 nm. The distribution is relatively uniform, which is consistent with the characterization results of SEM.

[0167] 3.2 X-ray diffraction (XRD) analysis of composite lithium manganese iron phosphate:

[0168] The products of Example A1 and Comparative Example A1 were subjected to XRD analysis respectively. Figure 4 As shown, the product of Comparative Example A1 is a typical lithium iron manganese phosphate material. In the XRD pattern of Example A1, the diffraction peak appearing near 40.6 degrees corresponds to the (111) crystal plane of Pd metalloene, indicating that we have successfully prepared a composite material of lithium iron manganese phosphate and Pd metalloene. The XRD patterns of the composite lithium iron manganese phosphate provided in Examples A2 to A4 are similar to those in Example A1. Figure 4 Basically the same.

[0169] 3.2 Characterization of Lithium-ion Batteries

[0170] The electrochemical performance of the lithium secondary batteries in Examples B1 to B4 and Comparative Example B1 was tested according to the relevant performance tests listed in Table 1 below. The test conditions were determined according to industry standard test methods. The battery discharge test conditions were as follows:

[0171] The relevant electrochemical performance test results of the lithium secondary battery are shown in Table 1 below.

[0172] Table 1

[0173]

[0174] As can be seen from Table 1, the present invention significantly improves the conductivity and lithium ion migration rate of the lithium manganese iron phosphate material through the composite of metal ene, and improves the rate performance and cycle stability of lithium manganese iron phosphate when used as a positive electrode material. Among them, when Pd metal ene is composited with lithium manganese iron phosphate (Example B1), the resistivity of the material is the lowest (5.6Ω·cm) and the lithium ion migration rate is the highest (8.1×10 -13 cm 2 / S), the discharge specific capacity at 0.1C can reach 159.6mAh / g, the discharge specific capacity at 1C can reach 137.9mAh / g, the charge specific capacity at 5C is 122.1mAh / g, and the charge and discharge specific capacity after 200 cycles reaches 99.1%. The above parameters are all superior to those of pure lithium manganese iron phosphate materials, fully demonstrating the beneficial effects of the present invention.

[0175] The above embodiments merely illustrate several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A composite lithium manganese iron phosphate material, characterized in that: The composite material comprises lithium manganese iron phosphate and a metalloalkene bonded to the surface of the lithium manganese iron phosphate; the mass percentage of the metalloalkene in the composite lithium manganese iron phosphate material is 0.5% to 50%; The metal of the metalloene includes Pd or a Pd-based alloy; The metalloene is in a flake shape, and has an average length and / or width of 100 to 500 nm; The total thickness of the metalloene monolith is 0.2 to 5 nm; The number of atomic layers of the metalloalkene is 1 to 10; The thickness of the metalloalkene monolayer is 0.2 to 0.45 nm; The surface of the metalloene has a curved morphology.

2. The composite lithium manganese iron phosphate material according to claim 1, wherein: The particle size of the composite lithium manganese iron phosphate material is 0.1 to 10 μm.

3. The composite lithium manganese iron phosphate material according to claim 1 or 2, characterized in that: In addition to Pd, the elements contained in the Pd-based alloy also include at least one of Pt, Rh, Ru, Ir, W, Mo, V, Fe, Co, Ni, Au, Ag, Cu, Cr, Ta, Mn, Zn, Nb, Y, Ce, and Bi.

4. The composite lithium iron manganese phosphate material according to claim 1, wherein: In the Pd-based alloy, the molar ratio of Pd to all other elements is 1:(0.1-9.9).

5. A method for preparing the composite lithium iron manganese phosphate material according to any one of claims 1 to 4, characterized in that: The steps include: Mixing lithium manganese iron phosphate, a metalloene precursor, an organic solvent, and a surfactant to obtain a mixed solution; The mixed solution is subjected to a hydrothermal reaction treatment to grow metalloene on the surface of the lithium manganese iron phosphate.

6. The preparation method according to claim 5, wherein: The metal olefin precursor includes a Pd source or a Pd source and at least one of a Pt source, a Rh source, a Ru source, an Ir source, a W source, a Mo source, a V source, a Fe source, a Co source, a Ni source, an Au source, an Ag source, a Cu source, a Cr source, a Ta source, a Mn source, a Zn source, a Nb source, a Y source, a Ce source, and a Bi source; and / or The organic solvent comprises at least one of methanol, ethanol, glycerol, isopropanol, oleylamine, oleic acid, toluene, aniline, octadecylamine, chloroform, carbon tetrachloride, dimethyl sulfoxide, dimethylformamide, acetone, ethylenediamine, acetaldehyde, formic acid, and acetic acid; and / or The surfactants include hexadecyltrimethylammonium bromide, hexadecyldimethylethylammonium bromide, hexadecyldimethylbenzylammonium chloride, hexadecyltrimethylammonium chloride, dihexadecyldimethylammonium bromide, 1-naphthylmethylammonium bromide, benzyltrimethylammonium bromide, tetra-n-octylammonium bromide, tetrahexylammonium bromide, tetramethylammonium bromide, dodecyldimethylbenzylammonium bromide, benzyltributylammonium bromide, triethylmethylammonium bromide, methyltrioctylammonium bromide, tetradecyltrimethylammonium bromide, didecyldimethylammonium bromide, dodecyldimethylammonium bromide, At least one of methylethylammonium bromide, 3-bromopropyltrimethylammonium bromide, phenyltrimethylammonium tribromide, n-octyltrimethylammonium bromide, decanyltrimethylammonium bromide, octadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, benzyltriethylammonium bromide, tetradecylammonium bromide, tetrapentylammonium bromide, phenyltrimethylammonium bromide, tetrabutylammonium bromide, tetrapropylammonium bromide, 2-bromoethyltrimethylammonium bromide, tetrabutylammonium tribromide, ammonium bromide, potassium bromide, sodium iodide, potassium iodide, ascorbic acid, and polyvinylpyrrolidone; and / or The molar ratio of the lithium manganese iron phosphate, the metalloalkene precursor, and the surfactant is 1: (0.1-6.8): (0.1-9.6); and / or In the mixed solution, the total molar concentration of the metalloalkene precursor is 0.05 to 11.6 mol / L.

7. The preparation method according to claim 5 or 6, characterized in that: The metal olefin precursor includes a Pd source and at least one of a Rh source, a Mo source, a Fe source, a Co source, and a Ni source.

8. The preparation method according to claim 6, wherein: At least one source compound among the Pd source, Pt source, Rh source, Ru source, Ir source, W source, Mo source, V source, Fe source, Co source, Ni source, Au source, Ag source, Cu source, Cr source, Ta source, Mn source, Zn source, Nb source, Y source, Ce source, and Bi source includes a soluble inorganic salt or / and a soluble organic salt containing the corresponding metal element.

9. The preparation method according to claim 5 or 6, characterized in that: The temperature of the hydrothermal reaction treatment is 50-200°C and the holding time is 2-24 hours; and / or After the hydrothermal reaction treatment step, the method further comprises the following steps: The reaction solution containing the composite manganese iron lithium phosphate material is subjected to solid-liquid separation treatment, drying treatment and grinding treatment.

10. A positive electrode, characterized in that: The invention comprises a current collector and a positive electrode active layer bonded to the current collector, wherein the positive electrode active material contained in the positive electrode active layer comprises the composite lithium iron manganese phosphate material according to any one of claims 1 to 4 or the composite lithium iron manganese phosphate material prepared by the preparation method according to any one of claims 5 to 9.

11. A secondary battery comprising a positive electrode, characterized in that: The positive electrode is the positive electrode according to claim 10.

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