Bi-metal-loaded bi-nonmetal-coordinated carbon-coated lithium manganese iron phosphate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of new energy materials, in particular to bimetal-loaded binonmetal-coordinated carbon-coated lithium manganese iron phosphate as well as a preparation method and application thereof. According to the invention, phthalocyanine complex derived nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate is treated by plasma, defect sites are constructed on the surface of a carbon coating layer, and conditions are created for coordination of metal and nonmetal oxygen in acetylacetone transition metal salt and the carbon coating layer. And then, through a sintering process, preparing the carbon-coated lithium manganese iron phosphate with double metal loaded and double non-metal coordination. According to the material, electron orbital filling of bimetal is optimized, the synergistic effect of all the components is fully exerted, the coordination mode of bimetal and binonmetal is regulated and controlled, the conductivity and cycling stability of the material are remarkably improved, and manganese dissolution is effectively reduced. A lithium ion battery constructed based on the material shows excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy materials, in particular to a carbon-coated lithium manganese iron phosphate with double non-metallic coordination supported by double metals, and a preparation method and application thereof. BACKGROUND

[0002] The positive electrode material of a lithium ion battery is a decisive factor of the energy density of the battery. Developing a high-energy-density positive electrode material has become the key to the technological innovation of current power lithium batteries and energy storage lithium batteries. Limited by the high cost and low safety of ternary positive electrode materials, and the limited theoretical specific capacity and low voltage platform of lithium iron phosphate (LFP), the commercial mainstream ternary positive electrode material and lithium iron phosphate positive electrode material cannot meet the development needs of current lithium ion batteries. As an upgraded version of lithium iron phosphate, lithium manganese iron phosphate (LMFP) has a higher working voltage platform, is green and environmentally friendly, has low cost and high safety, and has excellent thermal stability, chemical stability and green economy of lithium iron phosphate, as well as the high energy density characteristics of ternary positive electrode materials, and is expected to become a new generation of mainstream positive electrode material.

[0003] However, due to the doping of manganese elements with poor electrical conductivity in lithium iron phosphate, the electronic conductivity and ionic conductivity of lithium manganese iron phosphate are poor, which leads to slow lithium ion diffusion dynamics, thereby affecting the rate performance of the material. At the same time, the Jahn-Teller effect induced by Mn 3+ causes the material to continuously dissolve manganese during the lithium intercalation / delithiation process, thereby destroying the material structure and reducing the cycle stability. Although the carbon coating strategy is widely used to improve the electrical conductivity of lithium manganese iron phosphate and inhibit the interface side reaction between the electrolyte and the material to improve the cycle stability of the material, the traditional carbon coating method often has problems such as uneven coating, high content of amorphous carbon, and poor improvement effect, and has limited modification effect on the inherent defects of the above lithium manganese iron phosphate.

[0004] In view of the shortcomings of the traditional carbon coating, the prior art proposes to use different transition metal phthalocyanines as carbon sources to coat lithium iron phosphate, and a LiFeO4 / C composite material is prepared. The first discharge specific capacity of the material with the best performance prepared by this method is as high as 150.7 mAh / g, and after 50 cycles, it still maintains a high discharge specific capacity of 127.6 mAh / g. Although the electrical conductivity and interface compatibility of the material are improved to some extent, there are still significant defects: during the charging and discharging process, internal stress is generated in the material particles due to repeated expansion and compression, causing cracks in the interior of the material particles, and the solvent in the electrolyte can penetrate into the interior of the positive electrode material, interfering with the Li +Meanwhile, the carbon coating layer fails to completely inhibit the decomposition of the electrolyte, and the decomposition products of the electrolyte will precipitate on the positive and negative electrodes and the separator to form surface impedance as the cycle number increases, resulting in serious capacity attenuation. In addition, the specific capacity stability of the prepared series of LiFeO4 / C composite materials is poor and the improvement space is limited, the first charge specific capacity is 93-153.6 mAh / g, and the first discharge specific capacity is 94.1-150.7 mAh / g. Such a large fluctuation makes it difficult to accurately control the performance of the material in practical application, and seriously restricts the application prospect of the material in the field of large-scale energy storage and power lithium batteries. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the defects and shortcomings in the prior art that the manganese iron phosphate material has low ion and electron conductivity, poor rate performance, Mn 3+ poor cycle stability caused by elution, and rapid cycle performance decay, large specific capacity fluctuation and limited improvement caused by interface impedance accumulation existing in transition metal phthalocyanine coating.

[0006] Another object of the present application is to provide a carbon-coated manganese iron phosphate material loaded with double metals and coordinated with double non-metals.

[0007] Another object of the present application is to provide a lithium ion battery positive electrode.

[0008] Still another object of the present application is to provide a lithium ion battery.

[0009] The above objects of the present application are achieved by the following technical solutions. The present application protects a preparation method of carbon-coated manganese iron phosphate material loaded with double metals and coordinated with double non-metals, comprising the following steps: S1. In a protective gas atmosphere, mix lithium salt, manganese source, phosphoric acid source, iron source, phthalocyanine coordination compound and doped metal source uniformly in a solvent to obtain a slurry, grind, dry, calcine and post-treat the slurry to obtain a carbon-coated manganese iron phosphate material doped with nitrogen coordination and metal doped by phthalocyanine coordination compound; S2. In a protective gas atmosphere, perform plasma treatment on the carbon-coated manganese iron phosphate material doped with nitrogen coordination and metal doped by phthalocyanine coordination compound obtained in step S1, add acetylacetone transition metal salt, mix uniformly in an organic solvent, post-treat to obtain an intermediate, and sinter the intermediate to obtain the carbon-coated manganese iron phosphate material loaded with double metals and coordinated with double non-metals; In step S1, the metal in the doped metal source is selected from at least one of Mg, Ti, V, Co, Ni, Cr, Zn, Cu, Zr, Nb, Mo, Al, Ta, W and Ca.

[0010] This invention uses plasma treatment on nitrogen-coordinated, metal-doped carbon-coated lithium manganese iron phosphate (LiMnFePO4) derived from a phthalocyanine ligand to create defect sites on the surface of the carbon coating. Specifically, these sites are etched around the metal site (i.e., the first coordinated metal) of the phthalocyanine ligand, creating coordination sites. This creates conditions for the coordination of the metal (i.e., the second coordinated metal) and non-metallic oxygen from the acetylacetonate transition metal salt with the carbon coating. Subsequently, through a sintering process, a carbon-coated LiMnFePO4 material with a bimetallic-loaded, bi-nonmetallic coordination (the bi-nonmetallic is nitrogen and oxygen, with the nitrogen derived from the phthalocyanine ligand and the oxygen derived from the acetylacetonate transition metal salt) is successfully produced. This bimetallic-loaded, bi-nonmetallic coordinated carbon layer structure significantly improves the material's performance. Specifically, by optimizing the electron filling of the bimetallic electron orbitals, the material leverages the synergistic effect between the components and modulates the coordination patterns of the metal and non-metal. This not only activates the activity of the bimetallic sites but also optimizes the atomic distribution pattern on the carbon coating surface and the material's internal electronic structure. As a result, the electronic coupling effect of the material is enhanced, and the adsorption and migration kinetics of electrons and ions by the carbon coating are also improved. In addition, the metal cations in the doped metal source can improve the rate performance and cycle life of lithium manganese iron phosphate by regulating the electronic / ionic conductivity, lattice stability and electrochemical activity of lithium manganese iron phosphate. The above improvements significantly enhance the conductivity and surface activity of lithium manganese iron phosphate materials, promote the diffusion of lithium ions, increase the lithium ion migration rate during charging and discharging, alleviate the volume expansion effect of the material during the lithium insertion / delithiation process, thereby improving the cycle stability of the material and effectively reducing manganese dissolution.

[0011] Furthermore, in steps S1 to S2, the protective gas includes one or more of argon, nitrogen, helium, and hydrogen.

[0012] Furthermore, in step S1, the lithium salt includes one or more of lithium carbonate, lithium dihydrogen phosphate, lithium phosphate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0013] Furthermore, in step S1, the manganese source includes one or more of manganese tetraoxide, manganese oxide, manganese dioxide, manganous chloride, manganous sulfate, manganese nitrate, manganese carbonate, manganese acetate, and manganese oxalate.

[0014] Furthermore, in step S1, the phosphoric acid source includes one or more of lithium dihydrogen phosphate, lithium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid, ammonium hypophosphite, and ammonium polyphosphate.

[0015] Furthermore, in step S1, the iron source includes one or more of ferric phosphate, ferric oxide, ferrous oxide, ferrous oxide, ferrous chloride, ferric chloride, ferrous sulfate, ferrous nitrate, ferric citrate, ferric acetate, ammonium ferric sulfate, and ferrous oxalate.

[0016] Further, in step S1, the phthalocyanine complex includes one or more of transition metal phthalocyanine, alkaline earth metal phthalocyanine, alkali metal phthalocyanine.

[0017] Further, in step S1, the transition metal phthalocyanine includes one or more of phthalocyanine chromium, phthalocyanine cobalt, phthalocyanine iron, phthalocyanine nickel, phthalocyanine copper, phthalocyanine zinc, phthalocyanine manganese.

[0018] Further, in step S1, the alkaline earth metal phthalocyanine is phthalocyanine calcium and / or phthalocyanine magnesium.

[0019] Further, in step S1, the alkali metal phthalocyanine is phthalocyanine sodium.

[0020] Preferably, in step S1, the molar ratio of the lithium salt, the manganese source, the iron source and the phosphoric acid source is 1: (0.02-0.98): (0.02-0.98): (0.9-1.1); the sum of the coefficients of the manganese source and the iron source is 1 (i.e. the coefficient of the manganese source + the coefficient of the iron source = 1).

[0021] Preferably, in step S1, the amount of the phthalocyanine complex added is 1.5-5 wt% based on the mass of the theoretical generated lithium manganese iron phosphate.

[0022] More preferably, in step S1, the amount of the phthalocyanine complex added is 2-3.5 wt% based on the mass of the theoretical generated lithium manganese iron phosphate.

[0023] Further, in step S1, the doping metal source is selected from a doping metal oxide or a doping metal salt.

[0024] Further, in step S1, the Mg is selected from a magnesium oxide or a magnesium salt.

[0025] Further, in step S1, the Mg is selected from a magnesium oxide or a magnesium salt.

[0026] Further, in step S1, the Mg is selected from a magnesium oxide or a magnesium salt.

[0027] Further, in step S1, the Ti is selected from a titanium oxide or a titanium salt.

[0028] Further, in step S1, the Ti is selected from a titanium oxide or a titanium salt.

[0029] Further, in step S1, the Ti is selected from a titanium oxide or a titanium salt.

[0030] Further, in step S1, the V is selected from a vanadium oxide or a vanadium salt.

[0031] Furthermore, the vanadium oxide is selected from vanadium monoxide, vanadium trioxide, vanadium dioxide or vanadium pentoxide.

[0032] Furthermore, the vanadium salt is selected from vanadyl sulfate, vanadyl dichloride, vanadium oxalate, vanadyl oxalate or a hydrate of any of the above vanadium salts.

[0033] Furthermore, in step S1, the Co is selected from cobalt oxide or cobalt salt.

[0034] Furthermore, the cobalt oxide is selected from cobaltous oxide, cobalt oxide or cobalt trioxide.

[0035] Furthermore, the cobalt salt is selected from cobalt sulfate, cobalt chloride, cobalt acetate, cobalt nitrate or a hydrate of any of the above cobalt salts.

[0036] Furthermore, in step S1, the Ni is selected from nickel oxide or nickel salt.

[0037] Furthermore, the nickel oxide is selected from nickel oxide or nickel trioxide.

[0038] Furthermore, the nickel salt is selected from nickel sulfate, nickel chloride, nickel acetate, nickel nitrate or a hydrate of any of the above nickel salts.

[0039] Furthermore, in step S1, the Cr is selected from chromium oxide or chromium salt.

[0040] Furthermore, the chromium oxide is selected from chromium oxide, chromium trioxide or chromium trioxide.

[0041] Furthermore, the chromium salt is selected from chromium sulfate, chromium chloride, chromium acetate, chromium oxalate, chromium nitrate or a hydrate of any of the above chromium salts.

[0042] Furthermore, in step S1, the Zn is selected from zinc oxide or zinc salt.

[0043] Furthermore, the zinc oxide is zinc oxide.

[0044] Furthermore, the zinc salt is selected from zinc sulfate, zinc chloride, zinc acetate, zinc oxalate, zinc nitrate or a hydrate of any of the above zinc salts.

[0045] Furthermore, in step S1, the Cu is selected from copper oxide or copper salt.

[0046] Furthermore, the copper oxide is selected from cupric oxide or cuprous oxide.

[0047] Furthermore, the copper salt is selected from copper sulfate, copper chloride, copper acetate, copper nitrate or a hydrate of any of the above copper salts.

[0048] Furthermore, in step S1, the Zr is selected from zirconium oxide or zirconium salt.

[0049] Further, the zirconium oxide is zirconium dioxide.

[0050] Further, the zirconium salt is selected from zirconium sulfate, zirconium tetrachloride, zirconium acetate, zirconium oxychloride, zirconium nitrate or a hydrate of any of the above zirconium salts.

[0051] Further, in step S1, the Nb is selected from a niobium oxide or a niobium salt.

[0052] Further, the niobium oxide is selected from niobium monoxide, niobium dioxide, di-niobium trioxide or di-niobium pentoxide.

[0053] Further, the niobium salt is selected from ammonium niobium oxalate, niobium oxalate or a hydrate of any of the above niobium salts.

[0054] Further, in step S1, the Mo is selected from a molybdenum oxide or a molybdenum salt.

[0055] Further, the molybdenum oxide is selected from molybdenum dioxide or molybdenum trioxide.

[0056] Further, the molybdenum salt is selected from molybdenum sulfate, molybdenum chloride, molybdenum acetate, ammonium molybdate, molybdenum nitrate or a hydrate of any of the above molybdenum salts.

[0057] Further, in step S1, the Al is selected from an aluminum oxide or an aluminum salt.

[0058] Further, the aluminum oxide is aluminum oxide.

[0059] Further, the aluminum salt is selected from aluminum sulfate, aluminum chloride, aluminum nitrate or a hydrate of any of the above aluminum salts.

[0060] Further, in step S1, the Ta is selected from a tantalum oxide or a tantalum salt.

[0061] Further, the tantalum oxide is di-tantalum pentoxide.

[0062] Further, the tantalum salt is selected from tantalum sulfate, tantalum pentachloride, tantalum ethoxide, tantalum butoxide, tantalum isopropoxide or a hydrate of any of the above tantalum salts.

[0063] Further, in step S1, the W is selected from a tungsten oxide or a tungsten salt.

[0064] Further, the tungsten oxide is selected from tungsten dioxide, tungsten trioxide, blue tungsten or purple tungsten.

[0065] Further, the tungsten salt is selected from tungsten nitrate, tungsten chloride, tungsten phosphate or a hydrate of any of the above tungsten salts.

[0066] Further, in step S1, the Ca is selected from a calcium oxide or a calcium salt.

[0067] Further, the calcium oxide is selected from calcium oxide or calcium peroxide.

[0068] Further, the calcium salt is selected from calcium bicarbonate, calcium dihydrogen phosphate, calcium chloride, calcium acetate, calcium nitrate or a hydrate of any of the above calcium salts.

[0069] Preferably, in step S1, the doping amount of metal cations in the doping metal source is 100-10000 ppm; doping the above amount of metal cations inside the lithium iron manganese phosphate is more conducive to the full play of its capacity characteristics and cycle stability.

[0070] Further, in step S1, the solvent includes one or more of water, methanol, and ethanol.

[0071] Preferably, in step S1, the mixing time is 0.5-4 h.

[0072] Further, in step S1, the particle size of the grinded slurry is 0.30 μm≤D 50 ≤0.35 μm.

[0073] Further, in step S1, the drying is spray drying.

[0074] Further, in step S1, the calcination equipment is a box furnace, a roller kiln, or a tube furnace.

[0075] Preferably, in step S1, the calcination equipment is a box furnace.

[0076] Further, in step S1, the calcination temperature is 600-850 ℃.

[0077] Preferably, in step S1, the calcination temperature is 700-800 ℃.

[0078] Further, in step S1, the heating rate of calcination is 1-10 ℃ / min.

[0079] Preferably, in step S1, the calcination time is 5-18 h.

[0080] Further, in step S1, the post-processing includes cooling, crushing, and sieving.

[0081] Further, the cooling is cooling the calcined product to room temperature.

[0082] Further, the crushing is using air flow crushing.

[0083] Further, the mesh size of the sieve is 200-400 mesh.

[0084] Specifically, in step S1, the post-treatment comprises cooling the calcined product to room temperature, then using airflow to crush the cooled product, and then sieving the crushed product using a sieve with a mesh size of 200-400.

[0085] Further, in step S2, the plasma treatment is performed for 5-100 s.

[0086] Further, in step S2, the transition metal in the acetylacetone transition metal salt is selected from Ti, V, Cr, Co, Fe, Ni, Cu, Zn, Mo, W or Mn.

[0087] Still further, in step S2, the acetylacetone transition metal salt comprises one or more of titanium acetylacetonate, vanadium acetylacetonate, chromium acetylacetonate, cobalt acetylacetonate, iron acetylacetonate, nickel acetylacetonate, copper acetylacetonate, zinc acetylacetonate, molybdenum acetylacetonate, tungsten acetylacetonate, and manganese acetylacetonate.

[0088] Further, in step S2, the mass ratio of the phthalocyanine ligand derivative nitrogen-ligand-metal-doped carbon-coated lithium iron manganese phosphate and the acetylacetone transition metal salt is 1: (0.5-2.5).

[0089] Further, in step S2, the organic solvent comprises one or more of dichloromethane, isopropyl alcohol, methanol, ethanol, and oleylamine.

[0090] Preferably, in step S2, the mixing is performed by stirring.

[0091] Preferably, in step S2, the mixing is performed for 0.5-4 h.

[0092] Further, in step S2, the post-treatment comprises centrifugation and drying.

[0093] Still further, the centrifugation is performed at 6000-10000 rpm for 5-15 min.

[0094] Still further, the drying is performed at 50-100 ℃ for 6-18 h.

[0095] Specifically, in step S2, the post-treatment comprises centrifuging the mixed reaction liquid at 6000-10000 rpm for 5-15 min, and drying the precipitate obtained after centrifugation at 50-100 ℃ for 6-18 h.

[0096] Further, in step S2, the sintering is performed at a temperature of 300-400 ℃.

[0097] Preferably, in step S2, the sintering is performed for 1-8 h.

[0098] Further, in step S2, the mesh size of the screening sieve is 200-400 mesh.

[0099] The application protects the double-metal-loaded double-non-metal-coordinated carbon-coated lithium iron manganese phosphate prepared by the above preparation method.

[0100] The application protects a lithium ion battery positive electrode, which comprises a current collector and a positive electrode active material loaded on the current collector, wherein the positive electrode active material comprises the aforementioned double-metal-loaded double-non-metal-coordinated carbon-coated lithium iron manganese phosphate.

[0101] Preferably, the current collector is an aluminum foil or a carbon-coated aluminum foil.

[0102] Further, as a preferred method, the preparation method of the lithium ion battery positive electrode comprises the following steps: dispersing the double-metal-loaded double-non-metal-coordinated carbon-coated lithium iron manganese phosphate, conductive agent carbon black and binder polyvinylidene fluoride in an N-methylpyrrolidone dispersant to obtain a positive electrode slurry, and then coating the positive electrode slurry on an aluminum foil, and after vacuum drying at 80-140 ℃ for 12-24 h, the positive electrode is obtained.

[0103] Further, the mass ratio of the double-metal-loaded double-non-metal-coordinated carbon-coated lithium iron manganese phosphate and the conductive agent carbon black is (70-95):(3-20).

[0104] Further, the mass ratio of the double-metal-loaded double-non-metal-coordinated carbon-coated lithium iron manganese phosphate and the binder polyvinylidene fluoride is (70-95):(2-20).

[0105] The application protects a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode is the aforementioned lithium ion battery positive electrode.

[0106] The lithium ion battery prepared by the application exhibits excellent charge and discharge capacity, capacity retention rate, rate performance and cycle stability.

[0107] Further, as a preferred method, the positive electrode of the lithium ion battery is the aforementioned lithium ion battery positive electrode, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0108] Compared with the prior art, the application has the following beneficial effects: The present application constructs defect sites on the surface of the carbon coating layer of the phthalocyanine ligand derivative nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate by plasma treatment, and creates conditions for the coordination of metal, non-metallic oxygen and the carbon coating layer in the acetylacetone transition metal salt. Subsequently, a carbon coated lithium manganese iron phosphate material with double metal loaded double non-metal coordination is prepared by a sintering process. The material optimizes the electron orbital filling of the double metal, fully plays the synergistic effect between the components, regulates the coordination mode of the double metal and the double non-metal, significantly improves the conductivity, cycle stability of the material, and effectively reduces the manganese dissolution. The lithium ion battery based on the material exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0109] Figure 1 SEM images of the carbon coated lithium manganese iron phosphate with double metal loaded double non-metal coordination in Example 1 under different magnifications (A~B). DETAILED DESCRIPTION

[0110] The present application will be further described below in conjunction with the drawings and specific examples in the specification, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0111] Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0112] Figure 1 A is Figure 1 A in the A graph, Figure 1 B is Figure 1 B in the B graph.

[0113] Example 1 A phthalocyanine ligand derivative nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a carbon coated lithium manganese iron phosphate with double metal loaded double non-metal coordination, a lithium ion battery and a preparation method thereof 1. Preparation of a phthalocyanine ligand derivative nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate Lithium carbonate, trimanganese tetroxide, anhydrous iron phosphate and lithium dihydrogen phosphate were weighed in a stoichiometric ratio of lithium:manganese:iron:phosphoric acid of 1.03:0.6:0.4:1.03 and dispersed in pure water; 2.2wt% of iron phthalocyanine was added as a carbon source, titanium dioxide dopant with a Ti doping amount of 2000 ppm and magnesium oxide dopant with a Mg doping amount of 2000 ppm, based on the mass of the theoretically generated lithium manganese iron phosphate. After being fully dispersed and uniform, the slurry was transferred into a horizontal sand mill system for coarse grinding and fine grinding until the slurry D 50The slurry is then transferred to a spray granulation dryer for granulation drying to obtain a spray powder. The spray powder is placed in a nitrogen atmosphere box furnace for high-temperature sintering, and is heated to 750 °C at a heating rate of 3 °C / min and is kept for 9 h. After natural cooling to room temperature, the sintered product is sieved through a 200-mesh sieve to obtain the phthalocyanine iron derivative nitrogen coordination-titanium and magnesium co-doped carbon-coated lithium manganese iron phosphate, i.e., the phthalocyanine coordination derivative nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate.

[0114] 2. Preparation of double-metal-loaded double-non-metal coordination carbon-coated lithium manganese iron phosphate The phthalocyanine coordination derivative nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate obtained in step 1 is subjected to Ar plasma treatment for 20 s using a plasma generator to etch the surface layer of metal-doped nitrogen-coordinated carbon-coated layer. Then, it is dispersed in dichloromethane solvent to form a solution. Based on the dosage of the phthalocyanine iron added in step 1, cobalt acetylacetonate is added to the solution at a molar ratio of 1:1 of phthalocyanine iron to cobalt acetylacetonate, and after stirring at room temperature for 1 h, centrifugation is performed at 7000 rpm for 5 min, and drying is performed at 80 °C for 12 h to obtain an intermediate powder. The intermediate powder is placed in a nitrogen atmosphere box furnace for low-temperature sintering treatment, and is heated to 300 °C at a heating rate of 3 °C / min and is kept for 3 h. After natural cooling to room temperature, the sintered product is sieved through a 200-mesh sieve to obtain spherical double-metal (iron and cobalt) loaded double-non-metal (nitrogen and oxygen) coordination carbon-coated lithium manganese iron phosphate.

[0115] 3. Preparation of lithium ion battery The double-metal-loaded double-non-metal coordination carbon-coated lithium manganese iron phosphate obtained above is dissolved in N-methyl pyrrolidone dispersant together with conductive agent carbon black and binder polyvinylidene fluoride at a mass ratio of 94:4:2 to obtain a positive electrode slurry, which is then coated on an aluminum foil. After vacuum drying at 120 °C for 12 h, a lithium ion battery positive electrode material sheet is obtained.

[0116] A CR2032 type button lithium ion battery is assembled in a Milan glove box under an atmosphere of O2≤0.01 ppm and H2O≤0.01 ppm, the positive electrode is the lithium ion battery positive electrode described above, the negative electrode is a metal lithium sheet, the separator is a polyethylene film, and the electrolyte is prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethylene carbonate (EC) at a volume ratio of 1:1:1.

[0117] Example 2: A phthalocyanine coordination derivative nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate, a double-metal-loaded double-non-metal coordination carbon-coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, the stoichiometric ratio of lithium: manganese: iron: phosphoric acid is changed from 1.03: 0.6: 0.4: 1.03 to 1.03: 0.8: 0.2: 1.03, the addition amount of phthalocyanine iron is changed from 2.2 wt% to 2.8 wt%, the Ti doping amount is changed from 2000 ppm to 3000 ppm, and the slurry particle size D 50 changed from 0.32 μm to 0.33 μm.

[0118] The other steps and conditions are consistent with Example 1.

[0119] Example 3 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, the stoichiometric ratio of lithium: manganese: iron: phosphoric acid is changed from 1.03: 0.6: 0.4: 1.03 to 1.03: 0.7: 0.3: 1.03, the addition amount of phthalocyanine iron is changed from 2.2 wt% to 2.8 wt%, the Ti doping amount is changed from 2000 ppm to 3000 ppm, and the slurry particle size D 50 changed from 0.32 μm to 0.31 μm; in the preparation of the double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, the sintering temperature is changed from 300 ℃ to 350 ℃.

[0120] The other steps and conditions are consistent with Example 1.

[0121] Example 4 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, the carbon source is changed from phthalocyanine iron to phthalocyanine magnesium, obtaining a phthalocyanine magnesium derived nitrogen coordination-titanium magnesium co-doped carbon coated lithium manganese iron phosphate; in the preparation of the double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, a spherical double metal (magnesium and cobalt) loaded double non-metal (nitrogen and oxygen) coordination carbon coated lithium manganese iron phosphate is obtained.

[0122] The other steps and conditions are consistent with Example 1.

[0123] Example 5 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, the carbon source is changed from phthalocyanine iron to phthalocyanine copper to obtain phthalocyanine copper derived nitrogen coordination-titanium magnesium co-doped carbon coated lithium manganese iron phosphate; and in the preparation of the double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, spherical double metal (copper and cobalt) loaded double non-metal (nitrogen and oxygen) coordination carbon coated lithium manganese iron phosphate is obtained.

[0124] The other steps and conditions are consistent with those of Example 1.

[0125] Example 6 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, the carbon source is changed from phthalocyanine iron to phthalocyanine nickel to obtain phthalocyanine nickel derived nitrogen coordination-titanium magnesium co-doped carbon coated lithium manganese iron phosphate; and in the preparation of the double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, spherical double metal (nickel and cobalt) loaded double non-metal (nitrogen and oxygen) coordination carbon coated lithium manganese iron phosphate is obtained.

[0126] The other steps and conditions are consistent with those of Example 1.

[0127] Comparative Example 1 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate, a single metal loaded nitrogen coordination carbon coated lithium manganese iron phosphate, a lithium ion battery and a preparation method thereof The difference from Example 1 is that in the preparation of the double metal loaded double non-metal coordination carbon coated lithium manganese iron phosphate, no plasma treatment is performed.

[0128] 1. A phthalocyanine ligand derived nitrogen coordination-metal doped carbon coated lithium manganese iron phosphate Lithium carbonate, trimanganese tetroxide, anhydrous iron phosphate and lithium dihydrogen phosphate are weighed according to the stoichiometric ratio of lithium: manganese: iron: phosphoric acid as 1.03: 0.6: 0.4: 1.03 and dispersed in pure water; 2.2wt% of phthalocyanine iron is added as a carbon source, and titanium dioxide with a Ti doping amount of 2000 ppm and magnesium oxide with an Mg doping amount of 2000 ppm are added as doping agents, accounting for 2.2wt% of the theoretical mass of the generated lithium manganese iron phosphate. After being fully dispersed and uniform, the slurry is transferred into a horizontal sand mill system for coarse grinding and fine grinding until the slurry D 50The slurry was then transferred to a spray granulation dryer for granulation drying to obtain a spray powder. The spray powder was placed in a nitrogen atmosphere box furnace for high-temperature sintering. The temperature was raised to 750 °C at a rate of 3 °C / min and maintained for 9 h, and after natural cooling to room temperature, the carbon-coated lithium manganese iron phosphate was obtained after screening treatment.

[0129] 2. Preparation of single-metal nitrogen-coordinated carbon-coated lithium manganese iron phosphate The carbon-coated lithium manganese iron phosphate was dispersed in dichloromethane to form a solution. Cobalt acetylacetonate was added to the solution in a molar ratio of 1:1 of iron phthalocyanine to cobalt acetylacetonate based on the amount of iron phthalocyanine added in step 1. After stirring at room temperature for 1 h, the intermediate powder was obtained by centrifugation and drying. The intermediate powder was placed in a nitrogen atmosphere box furnace for low-temperature sintering treatment. The temperature was raised to 300 °C at a rate of 3 °C / min and maintained for 3 h, and after natural cooling to room temperature, the spherical single-metal (iron) nitrogen-coordinated carbon-coated lithium manganese iron phosphate was obtained after screening treatment.

[0130] 3. Preparation of lithium ion battery The spherical single-metal (iron) nitrogen-coordinated carbon-coated lithium manganese iron phosphate obtained above was dissolved in N-methylpyrrolidone dispersant in a mass ratio of 94:4:2 with conductive agent carbon black and binder polyvinylidene fluoride to obtain a positive electrode slurry, which was then coated on an aluminum foil. After vacuum drying at 120 °C for 12 h, the lithium ion battery positive electrode material sheet was obtained.

[0131] The CR2032 type button lithium ion battery was assembled in a Milan glove box under an atmosphere of O2≤0.01 ppm and H2O≤0.01 ppm. The positive electrode was the lithium ion battery positive electrode described above, the negative electrode was a metal lithium sheet, the separator was a polyethylene film, and the electrolyte was prepared by dissolving 1 mol / L of LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1.

[0132] Comparative Example 2 - A phthalocyanine complex-derived nitrogen-coordinated metal-doped carbon-coated lithium manganese iron phosphate, a double-metal nitrogen-coordinated carbon-coated lithium manganese iron phosphate, a lithium ion battery, and a method for preparing the same The difference from Example 1 is that in the preparation of the double-metal nitrogen-coordinated carbon-coated lithium manganese iron phosphate, cobalt acetylacetonate was replaced by cobalt chloride to obtain a double-metal (iron and cobalt) nitrogen-coordinated carbon-coated lithium manganese iron phosphate.

[0133] The other steps and conditions are the same as in Example 1.

[0134] Comparative Example 3 A phthalocyanine ligand derived nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate, single metal loaded nitrogen coordination carbon-coated lithium manganese iron phosphate, lithium ion battery and preparation method thereof The difference from Example 1 is that in the preparation of the double metal loaded double non-metal coordination carbon-coated lithium manganese iron phosphate, cobalt acetylacetone is not added, and a single metal (iron) loaded nitrogen coordination carbon-coated lithium manganese iron phosphate is prepared.

[0135] The other steps and conditions are consistent with Example 1.

[0136] Comparative Example 4 A glucose derived metal doped carbon-coated lithium manganese iron phosphate precursor, single metal loaded oxygen coordination carbon-coated lithium manganese iron phosphate, lithium ion battery and preparation method thereof The difference from Example 1 is that in the preparation of the phthalocyanine ligand derived nitrogen coordination-metal doped carbon-coated lithium manganese iron phosphate, the phthalocyanine ligand is replaced with an equal amount of glucose as a carbon source to prepare a glucose-titanium-magnesium co-doped carbon-coated lithium manganese iron phosphate, which is then subjected to high-temperature sintering, plasma treatment, and cobalt acetylacetone treatment to prepare a single metal (cobalt) loaded oxygen coordination carbon-coated lithium manganese iron phosphate.

[0137] The other steps and conditions are consistent with Example 1.

[0138] Experimental Example 1 Material composition and microstructure characterization (1) SEM measurement The double metal loaded double non-metal coordination carbon-coated lithium manganese iron phosphate prepared in Example 1 was characterized by a scanning electron microscope, and the results are shown in FIG. 1. Figure 1 The double metal loaded double non-metal coordination carbon-coated lithium manganese iron phosphate prepared in Example 1 has a spherical structure composed of uniform nanoparticles forming a dense micron structure, which can effectively improve the energy density of the material.

[0139] The morphology of the double metal loaded double non-metal coordination carbon-coated lithium manganese iron phosphate in Examples 2-6 is basically the same as that in Example 1, and will not be described here.

[0140] (2) Metal / non-metal element content detection in the double metal loaded double non-metal coordination carbon-coated layer An appropriate amount of metal loaded non-metal coordination carbon-coated lithium manganese iron phosphate obtained in Examples 1-6 and Comparative Examples 1-4 was taken into a centrifuge tube, an appropriate amount of hydrochloric acid was added and heated for 2 h, then cooled and diluted. The inductively coupled plasma emission spectrometer was used to measure.

[0141] The detection data are shown in Table 1.

[0142] Table 1 Content of doped elements in metal loaded non-metal coordination carbon-coated lithium manganese iron phosphate

[0143] Note: Since both acetylacetone and manganese iron lithium phosphate contain oxygen atoms, ICP detection cannot distinguish the specific source of the detected oxygen atoms, so the actual content of oxygen atoms in the target substance cannot be accurately obtained by ICP detection; the actual doping amount of some metal cations is slightly higher or slightly lower than the theoretical value, which is within the normal error range.

[0144] From the data in Table 1, the molar ratio of the two coordination metals in the carbon coating layer of Examples 1-6 is close to 1:1, indicating that after using phthalocyanine coordination as the carbon source, high-temperature calcination, plasma treatment and transition metal salt loading of acetylacetone, the two metals are successfully coordinated and doped into the carbon skeleton. In Comparative Example 1, since the nitrogen coordination-metal doped carbon-coated manganese iron lithium phosphate derived from phthalocyanine coordination was not subjected to plasma treatment, the carbon coating layer did not form defect sites, resulting in the inability of the metal cobalt and non-metallic oxygen in the cobalt acetylacetone to coordinate with the carbon coating layer, so the second coordination metal was not detected. In Comparative Example 2, cobalt chloride was used instead of cobalt acetylacetone, and the chlorine in cobalt chloride cannot form a coordination bond with the carbon coating layer, so only a double-metal-loaded single-non-metal (nitrogen) coordination carbon-coated manganese iron lithium phosphate can be obtained. In Comparative Example 3, cobalt acetylacetone was not introduced during the preparation of the material, and only iron phthalocyanine was used as the carbon source to prepare a single-metal (iron) loaded nitrogen-doped carbon-coated manganese iron lithium phosphate. In Comparative Example 4, glucose was used as the carbon source to prepare a carbon-coated manganese iron lithium phosphate precursor, which was subjected to plasma treatment, and then cobalt acetylacetone was added to load cobalt into the carbon structure through oxygen coordination, finally generating a single-metal (cobalt) loaded oxygen-coordinated carbon-coated manganese iron lithium phosphate.

[0145] Experimental Example 2 Physical properties of metal-loaded non-metal coordination carbon-coated manganese iron lithium phosphate cathode material and physicochemical performance test of lithium ion battery based on the material (1) Electrochemical test The metal-loaded non-metal-coordinated carbon-coated lithium iron manganese phosphate obtained in Examples 1-6 and Comparative Examples 1-4 was used as a positive active material. The active material, conductive agent carbon black, and binder polyvinylidene fluoride were weighed in a mass ratio of 94:4:2, dispersed in an N-methylpyrrolidone dispersant to form a uniformly dispersed positive electrode slurry, and then coated on an aluminum foil. After vacuum drying at 120°C for 12 h, the sheet was punched and weighed to obtain a round electrode sheet. A lithium metal sheet was used as the negative electrode, the prepared electrode sheet was used as the positive electrode, a polyethylene film was used as the separator, and an electrolyte was prepared by dissolving 1 mol / L LiPF6 in a mixed solvent of dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethylene carbonate (EC) in a volume ratio of 1:1:1. A 2032 type lithium ion button cell was assembled in a Milan glove box (O2≤0.01 ppm, H2O≤0.01 ppm) and left to stand for 12 h before being subjected to electrochemical performance testing at room temperature. The test voltage range was set to 2-4.5 V, and the charge and discharge tests were performed at a rate of 0.1 C / 1 C current. The calculation formula is as follows: First cycle discharge efficiency = first cycle discharge specific capacity / first cycle charge specific capacity x 100%; Capacity retention rate = 100th cycle specific capacity / first cycle discharge specific capacity x 100%.

[0146] (2) Powder resistance test method An automatic powder resistivity tester was used to apply a specific excitation current to the metal-loaded non-metal-coordinated carbon-coated lithium iron manganese phosphate positive electrode material powder prepared in Examples 1-6 and Comparative Examples 1-4, accurately measure the corresponding voltage value, and obtain the surface resistivity and resistance data of the material.

[0147] (3) Manganese dissolution amount test The metal-loaded non-metal-coordinated carbon-coated lithium iron manganese phosphate positive electrode material obtained in Examples 1-6 and Comparative Examples 1-4 was dissolved in pure water for pretreatment, and then an inductively coupled plasma test was used to detect the Mn dissolution amount in the supernatant.

[0148] Table 2 Physical properties of the metal-loaded non-metal-coordinated carbon-coated lithium iron manganese phosphate positive electrode material and physicochemical performance tests of lithium ion batteries constructed based on the material

[0149] From the data in Table 2, it can be seen that the double-metal loaded double-nonmetal coordinated carbon-coated lithium manganese iron phosphate material prepared in Examples 1-6 exhibits excellent conductivity (powder resistance ≤22 Ω·cm), electrochemical performance (0.1 C initial charge or discharge specific capacity >158 mAh / g), effective suppression of the Jahn-Teller effect caused by manganese dissolution (Mn dissolution ≤150 ppm), and improved cycle stability of the material at a 1 C rate (100 cycle capacity retention rate ≥98.9%). The above excellent performance can be attributed to the double-metal loaded double-nonmetal coordinated carbon coating layer, which optimizes the electron filling of the central double-metal electron orbit. This optimization effectively exerts a synergistic effect between the components, regulates the coordination mode of the metal loading site and the coordinated nonmetal, activates the activity of the double-metal site, and optimizes the atomic distribution mode on the surface of the carbon coating layer and the internal electronic structure of the material. These improvements collectively enhance the electronic coupling effect of the overall material and improve the adsorption and migration dynamics of electrons and ions by the carbon coating layer.

[0150] As can be seen by comparing Example 1 and Comparative Example 1, in Comparative Example 1, although phthalocyanine coordination was used as the carbon source, the metal and nonmetal (oxygen) provided by the acetylacetone transition metal salt cannot be coordinated and modified with the carbon coating layer due to the lack of plasma treatment, resulting in an increase in the powder resistance of the material, a decrease in the discharge specific capacity, a decrease in the cycle stability, and an increase in the manganese dissolution.

[0151] As can be seen by comparing Example 1 and Comparative Example 2, in Comparative Example 2, the use of cobalt chloride instead of cobalt acetylacetonate results in the prepared material being a double-metal loaded single-nonmetal (nitrogen) coordinated carbon-coated lithium manganese iron phosphate material. This structural change has a series of adverse effects: the conductivity of the material is affected due to the lack of an optimized atomic distribution mode and internal electronic structure within the material, specifically, the powder resistance increases, the discharge specific capacity decreases, the cycle stability decreases, and the manganese dissolution increases.

[0152] As can be seen by comparing Example 1 and Comparative Example 3, in Comparative Example 3, although the spherical single-metal (iron) loaded nitrogen coordinated carbon material is subjected to plasma treatment, no acetylacetone transition metal salt is added, which results in unsatisfactory performance of the obtained material. This is because the plasma treatment introduces a large number of defect sites on the surface of the carbon coating layer, and the lack of filling and modification of the defects by metal ions causes some active lithium ions to tend to be embedded in these defect sites during the intercalation and deintercalation of lithium ions, thereby reducing the number of effective active sites of the material and leading to the loss of active lithium. This reduction in active sites and loss of active lithium ultimately results in an increase in the powder resistance of the material, a decrease in the discharge specific capacity, a decrease in the cycle stability, and an increase in the manganese dissolution.

[0153] By comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, an equal amount of glucose is used to replace phthalocyanine iron as a carbon source to prepare a single-metal (cobalt) supported oxygen-coordinated carbon-coated lithium manganese iron phosphate. This substitution results in the material obtained having poorer electronic conductivity, lithium ion migration rate, and charge-discharge capacity than when phthalocyanine iron is used as a carbon source in Example 1. Specifically, the introduction of phthalocyanine iron provides a more optimal electron conduction path and lithium ion diffusion channel for the lithium manganese iron phosphate material, thereby improving the electrochemical performance of the material. In addition, the specific structure of phthalocyanine iron helps to stabilize the crystal structure of the material, reducing the volume change during the charge-discharge process, thereby improving the cycle stability and rate performance. In contrast, the single-metal (cobalt) supported oxygen-coordinated carbon-coated lithium manganese iron phosphate, although a certain number of defect sites are introduced through plasma treatment, these defect sites may capture part of the active lithium during the lithium intercalation / deintercalation process, reducing the number of effective active sites of the material, resulting in the loss of active lithium, ultimately increasing the resistance of the powder, reducing the specific discharge capacity, weakening the cycle stability, and exacerbating manganese dissolution.

[0154] The above examples are preferred embodiments of the present application, but the embodiments of the present application are not limited to the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application should be equivalent replacement methods, and are included within the scope of protection of the present application.

Claims

1. A method for preparing bimetallic-loaded bimetallic coordinated carbon-coated lithium manganese iron phosphate, characterized in that: The following steps are involved: S1. Under a protective gas atmosphere, a lithium salt, a manganese source, a phosphate source, an iron source, a phthalocyanine ligand, and a doping metal source are uniformly mixed in a solvent to obtain a slurry. The resulting slurry is ground, dried, calcined, and post-treated to obtain a phthalocyanine ligand-derived nitrogen-coated-metal-doped carbon-coated lithium manganese iron phosphate; S2. Under a protective gas atmosphere, plasma-treating the phthalocyanine ligand-derived nitrogen-coordinated-metal-doped carbon-coated lithium manganese iron phosphate obtained in step S1, adding a transition metal salt of acetylacetonate, mixing in an organic solvent, and post-treating to obtain an intermediate, sintering the obtained intermediate, and sieving to obtain the bimetallic-loaded bimetallic-coordinated carbon-coated lithium manganese iron phosphate; Wherein, in step S1, the metal of the doping metal source is selected from at least one of Mg, Ti, V, Co, Ni, Cr, Zn, Cu, Zr, Nb, Mo, Al, Ta, W, and Ca.

2. The preparation method according to claim 1, characterized in that In step S1, the molar ratio of the lithium salt, the manganese source, the iron source, and the phosphoric acid source is 1: (0.02-0.98): (0.02-0.98): (0.9-1.1).

3. The preparation method according to claim 1, characterized in that: In step S1, the amount of the phthalocyanine ligand added is 1.5-5 wt % based on the mass of the theoretically generated lithium manganese iron phosphate.

4. The preparation method according to claim 1, characterized in that In step S1, the phthalocyanine ligand includes one or more of transition metal phthalocyanine, alkaline earth metal phthalocyanine, and alkali metal phthalocyanine.

5. The preparation method according to claim 1, characterized in that: In step S2, the transition metal in the acetylacetonate transition metal salt is selected from Ti, V, Cr, Co, Fe, Ni, Cu, Zn, Mo, W or Mn.

6. The preparation method according to claim 1, characterized in that: In step S1, the doping amount of the metal cation in the doping metal source is 100-10000 ppm.

7. The preparation method according to claim 1, characterized in that: In step S2, the mass ratio of the phthalocyanine ligand-derived nitrogen coordination-metal-doped carbon-coated lithium manganese iron phosphate and the acetylacetonate transition metal salt is 1:(0.5-2.5).

8. The bimetallic-loaded bimetallic-coordinated carbon-coated lithium manganese iron phosphate prepared by the preparation method according to any one of claims 1 to 7.

9. A lithium ion battery positive electrode, characterized in that: The invention comprises a current collector and a positive electrode active material loaded on the current collector, wherein the positive electrode active material comprises the carbon-coated lithium manganese iron phosphate with bimetallic loading and bi-nonmetallic coordination as claimed in claim 8.

10. A lithium ion battery, characterized in that: The invention comprises an electrolyte, a separator, a positive electrode and a negative electrode, wherein the positive electrode comprises the positive electrode of the lithium-ion battery according to claim 9.

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