Lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a lithium manganese iron phosphate positive electrode material and a preparation method thereof, and the lithium manganese iron phosphate positive electrode material is of a composite coating doped structure and is composed of a matrix and a composite coating layer; the matrix is doped lithium manganese iron phosphate, and the composite coating layer is composed of a metal oxide, a lithium-containing metal oxide and carbon. The preparation method comprises the following steps: weighing a lithium source, a phosphorus source, an iron source, a manganese source, a doped metal source and a carbon source, uniformly mixing, ball-milling, sanding and calcining to obtain a precursor; pre-sintering the precursor to obtain an intermediate; uniformly mixing the intermediate with a doped metal source and a carbon source, and calcining; and cooling, grinding and sieving the sintered product of the composite coated doped lithium manganese iron phosphate positive electrode material to obtain the composite coated doped lithium manganese iron phosphate positive electrode material. According to the invention, the dissolution of manganese in the positive electrode material is effectively prevented, the structure of the positive electrode material is stabilized, the conductivity of the positive electrode material is improved, and the prepared material is high in conductivity, good in stability, simple in preparation process, short in period and suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery electrode materials, and more particularly to a lithium manganese iron phosphate cathode material and its preparation method. Background Technology

[0002] With the promotion of new energy sources, lithium-ion batteries are widely used in consumer electronics, new energy vehicles, smart grids, and other fields. In 1997, Goodenough et al. first reported lithium iron phosphate (LFP) with olivine phosphate, which possesses advantages such as good thermal stability, good conductivity, safety and non-toxicity, low price, and ease of production, leading to its large-scale application as a cathode material for lithium-ion batteries. Lithium iron phosphate has a working voltage of approximately 3.4 V, which is relatively low compared to ternary layered oxides, resulting in lower energy density in lithium-ion batteries made with it as the cathode material. Lithium manganese phosphate has a similar crystal structure to lithium iron phosphate, with a working voltage of 4.1 V. Lithium-ion batteries made with lithium manganese phosphate as the cathode material have higher energy density.

[0003] Therefore, by utilizing the high conductivity of lithium iron phosphate and the high operating voltage of lithium manganese phosphate, lithium manganese iron phosphate is considered to be a promising candidate to replace lithium iron phosphate as the main cathode material for next-generation lithium-ion batteries.

[0004] However, the development of lithium manganese iron phosphate is hindered by problems such as low ion conductivity, low electronic conductivity, lattice mismatch affecting grain boundary migration rate and manganese dissolution in electrochemical reactions.

[0005] To address these issues, researchers have proposed numerous modification schemes. For instance, Chinese patent CN118919700A discloses a lithium manganese iron phosphate cathode material and its preparation method. The cathode material comprises a lithium manganese iron phosphate core and a nitride coating layer. By using nitrides for surface modification, not only are side reactions with water isolated and the dissolution of manganese ions suppressed, but also the high-temperature resistance of nitrides effectively suppresses the gas expansion problem of lithium manganese iron phosphate cells and improves cycle stability.

[0006] Chinese patent CN114655943B discloses a lithium manganese iron phosphate composite material and its preparation method. By coating the core with an outer shell and doping the core with strontium, and doping the outer shell with zirconium, the low-temperature and rate performance of lithium manganese iron phosphate is improved, the leaching of manganese is reduced, and the structural stability of the material is enhanced.

[0007] However, lithium manganese iron phosphate materials still have problems such as low ionic conductivity and electronic conductivity, and the cathode material is prone to side reactions in the electrolyte.

[0008] Therefore, in order to solve the technical problems of low discharge capacity, poor cycle retention, low rate performance, low ionic conductivity, and low electronic conductivity of lithium manganese iron phosphate cathode materials, it is an urgent problem for those skilled in the art to provide a method that can effectively improve the ionic conductivity, electronic conductivity, and electrochemical performance of lithium manganese iron phosphate cathode materials. Summary of the Invention

[0009] In view of this, the present invention provides a lithium manganese iron phosphate cathode material and its preparation method.

[0010] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0011] A lithium manganese iron phosphate cathode material, wherein the material is a composite coated doped structure, consisting of a substrate and a composite coating layer; wherein the substrate is doped lithium manganese iron phosphate, and the composite coating layer is composed of metal oxide, lithium-containing metal oxide, and carbon.

[0012] Preferably, the matrix chemical composition is Li x Mn y Fe z M a PO4, wherein 0.9≤x≤1.10, 0≤y≤1, 0≤z≤1, 0≤a≤0.2, and M is one or more of the elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu;

[0013] Preferably, the mass of the matrix material is M, the total mass of the coating layer is m, and the coating layer content is 0 based on the total mass. <m / (M+m)≤20%。

[0014] Preferably, the metal oxide is a metal oxide containing one or more of the metal elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu;

[0015] The lithium-containing metal oxide is a lithium-containing metal oxide containing one or more of the metal elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu.

[0016] The carbon is one or a mixture of several of the following: amorphous carbon, carbon nanotubes, graphene, graphite, and pseudographite.

[0017] Preferably, the thickness of the composite coating layer is n, 0 <n≤20nm。

[0018] The mass of carbon in the composite coating is m1, and its mass percentage is 0. <m1 / (M+m)≤0.05。

[0019] The mass of the metal oxide in the composite coating layer is m2, and its mass percentage is 0. <m2 / (M+m2)≤0.1。

[0020] The composite coating layer contains lithium metal oxide with a mass of m3 and a mass percentage of 0. <m3 / (M+m3)≤0.1。

[0021] A method for preparing lithium manganese iron phosphate cathode material includes the following steps:

[0022] Step 1: Weigh the lithium source, phosphorus source, iron source, manganese source, doped metal source, and carbon source, mix them evenly, and then ball-mill, sand-mill, dry, and calcine to obtain the precursor;

[0023] Step 2: Place the precursor in a vacuum or protective atmosphere for pre-calcination to obtain the intermediate;

[0024] The third step is to take the precursor from the first step and calcine it in a vacuum or protective atmosphere, or to take the intermediate from the second step, mix it evenly with the doped metal source and carbon source, dry it, and then calcine it in a vacuum or protective atmosphere.

[0025] Step 4: The composite coated and doped lithium manganese iron phosphate cathode material obtained by sintering is cooled, ground, and sieved to obtain the composite coated and doped lithium manganese iron phosphate cathode material.

[0026] Preferably, in steps two and three, the protective atmosphere is one or a combination of argon, nitrogen, helium, or neon.

[0027] Preferably, in the first step, the calcination temperature is 300-600℃ and the holding time is 1-10 hours;

[0028] Preferably, in the third step, the calcination temperature is 500-900℃ and the holding time is 2-15 hours.

[0029] Application of a lithium manganese iron phosphate cathode material in lithium-ion batteries.

[0030] The present invention achieves the following technical effects compared to the prior art:

[0031] (1) The present invention coats an appropriate amount of metal oxide, lithium-containing metal oxide and carbon in situ onto the substrate surface to prepare a composite coated doped lithium manganese iron phosphate cathode material, which can reduce the direct contact between the cathode material and the electrolyte, reduce the side reactions at the interface, and inhibit the dissolution of transition metal manganese.

[0032] Moreover, some coating elements were incorporated into the crystal of the cathode material, which stabilized the crystal structure of the cathode material and improved its conductivity and crystallinity.

[0033] (2) The composite-coated doped lithium manganese iron phosphate cathode material of the present invention has better conductivity and lower charge transfer impedance. +It has a larger diffusion coefficient and improved electronic conductivity; when used as a cathode material for lithium-ion batteries, the battery has better rate performance and better cycle life. Moreover, the preparation process is simple, the cycle is short, and the output is large, making it suitable for industrial production. Attached Figure Description

[0034] Figure 1 This is a SEM image of the lithium manganese iron phosphate cathode material in Example 4 of this invention;

[0035] Figure 2 These are electrochemical test graphs of the button batteries made of lithium manganese iron phosphate cathode material in Example 4 of the present invention and the comparative example at 25°C. Figure a shows the rate performance graph, and Figure b shows the 1C cycle performance graph. It can be seen that the rate and cycle performance of Example 4 are better.

[0036] Figure 3 These are the XRD patterns of Embodiment 4 and the comparative example of the present invention. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1:

[0039] 4.86 g of lithium carbonate, 9.108 g of ferrous oxalate, 18.6969 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.61 g of glucose and 0.0792 g of zirconium dioxide were dissolved in 88 g of anhydrous ethanol solution and 260 g of ball milling was added. After ball milling for 4 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 200 ml of anhydrous ethanol, sand milled for 1.5 hours (1500 rpm), and then placed in a forced-air drying oven to dry and obtain precursor 2.

[0040] Precursor 2 was sintered in a vacuum box furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, precursor 1 was mixed with 1.09g of glucose, 40ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm) and then dried to obtain intermediate 2.

[0041] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 6 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0042] Transmission electron microscopy revealed that the total thickness of the metal oxide, lithium-containing metal oxide, and carbon coating layer was 4 nm.

[0043] Example 2:

[0044] 4.86g of lithium carbonate, 9.062g of ferrous oxalate, 18.6025g of manganese acetate, 14.693g of ammonium dihydrogen phosphate, 1.61g of glucose, and 0.1187g of zirconium dioxide were dissolved in 88g of anhydrous ethanol solution and 260g of ball milling was added. After ball milling for 4 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 200ml of anhydrous ethanol, sand milled for 1.5 hours (1600 rpm), and then placed in a forced-air drying oven to dry, thus obtaining precursor 2.

[0045] Precursor 2 was sintered in a vacuum box furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, precursor 1 was mixed with 1.09g of glucose, 40ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm). After drying, intermediate 2 was obtained.

[0046] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 6 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0047] Example 3:

[0048] 4.86 g of lithium carbonate, 9.016 g of ferrous oxalate, 18.50808 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.61 g of glucose and 0.1583 g of zirconium dioxide were dissolved in 88 g of anhydrous ethanol solution and 260 g of ball milling was added. After ball milling for 4 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 200 ml of anhydrous ethanol, sand milled for 1.5 hours (1700 rpm), and then placed in a forced-air drying oven to dry and obtain precursor 2.

[0049] Precursor 2 was sintered in a vacuum box furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, precursor 1 was mixed with 1.09g of glucose, 40ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm) and then dried to obtain intermediate 2.

[0050] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 6 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0051] Example 4:

[0052] 4.86g of lithium carbonate, 8.74g of ferrous oxalate, 17.9415g of manganese acetate, 14.693g of ammonium dihydrogen phosphate, 1.61g of glucose, and 0.3958g of zirconium dioxide were dissolved in 88g of anhydrous ethanol solution and 260g of ball milling was added. After ball milling for 4 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 200ml of anhydrous ethanol, sand milled for 1.5 hours (1800 rpm), and then placed in a forced-air drying oven to dry, thus obtaining precursor 2.

[0053] Precursor 2 was sintered in a vacuum box furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, precursor 1 was mixed with 1.09g of glucose, 40ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm). After drying, intermediate 2 was obtained.

[0054] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 6 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0055] Among them, such as Figure 1-3 The figures shown are, respectively, SEM images of the lithium manganese iron phosphate cathode material of Example 4 of the present invention, XRD patterns of the lithium manganese iron phosphate cathode materials of Example 4 of the present invention and the comparative example, and electrochemical data diagrams of Example 4 of the present invention and the comparative example.

[0056] Example 5:

[0057] 9.72g of lithium carbonate, 16.04g of ferrous oxalate, 39g of manganese acetate, 29.386g of ammonium dihydrogen phosphate, 3.22g of glucose, and 0.7915g of zirconium dioxide were dissolved in 176g of anhydrous ethanol solution and 520g of ball milling was added. After ball milling for 5 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 400ml of anhydrous ethanol, sand milled for 2 hours (1800 rpm), and then placed in a forced-air drying oven to dry, thus obtaining precursor 2.

[0058] Precursor 2 was sintered in a vacuum box furnace at 400℃ and held for 5 hours to obtain intermediate 1. The heating rate was 5℃ / min. Then, precursor 1 was mixed with 2.18g of glucose, 80ml of anhydrous ethanol and 260g of ball milling were added, and the mixture was ball milled for 2 hours (400 rpm). After drying, intermediate 2 was obtained.

[0059] Intermediate 2 was sintered in a box-type atmosphere furnace at 650°C and held for 5 hours. The heating rate was 5°C / min. After cooling, grinding and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0060] Example 6:

[0061] 24.3g of lithium carbonate, 42.32g of ferrous oxalate, 86.8745g of manganese acetate, 73.465g of ammonium dihydrogen phosphate, 8.05g of glucose, and 3.168g of zirconium dioxide were dissolved in 440g of anhydrous ethanol solution and 1300g of ball milling was added. After ball milling for 6 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 1000ml of anhydrous ethanol, sand milled for 3 hours (2000 rpm), and then placed in a forced-air drying oven to dry, thus obtaining precursor 2.

[0062] Precursor 2 was sintered in a vacuum box furnace at 500℃ and held for 6 hours to obtain intermediate 1. The heating rate was 6℃ / min. Then, precursor 1 was mixed with 5.45g of glucose, 200ml of anhydrous ethanol and 650g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm) and then dried to obtain intermediate 2.

[0063] Intermediate 2 was sintered in a box-type atmosphere furnace at 750°C and held for 8 hours. The heating rate was 7°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0064] Example 7:

[0065] 9.72g of lithium carbonate, 12.56g of ferrous oxalate, 33.9944g of manganese acetate, 29.386g of ammonium dihydrogen phosphate, 3.22g of glucose, and 1.583g of zirconium dioxide were dissolved in 176g of anhydrous ethanol solution and 520g of ball milling was added. After ball milling for 6 hours (300 rpm), precursor 1 was obtained. Precursor 1 was mixed with 400ml of anhydrous ethanol, sand milled for 2 hours (1900 rpm), and then placed in a forced-air drying oven to dry and obtain precursor 2.

[0066] Precursor 2 was sintered in a vacuum box furnace at 400℃ and held for 5 hours to obtain intermediate 1. The heating rate was 3℃ / min. Then, precursor 1 was mixed with 2.18g of glucose, 80ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 2 hours (400 rpm). After drying, intermediate 2 was obtained.

[0067] Intermediate 2 was sintered in a box-type atmosphere furnace at 800°C and held for 6 hours. The heating rate was 6°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0068] Example 8:

[0069] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, 0.1 g of niobium oxide, and 0.17 g of calcium acetate were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling machine was added; after ball milling for 6 hours (400 rpm), precursor 1 was obtained.

[0070] Precursor 1 was sintered in a box furnace at 550°C and held for 6 hours to obtain intermediate 1. The heating rate was 2°C / min. Then, intermediate 1 was mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was ball-milled for 3 hours (400 rpm), then removed and dried in a forced-air drying oven to obtain intermediate 2.

[0071] Intermediate 2 was sintered in a box-type atmosphere furnace at 750°C and held for 7 hours. The heating rate was 8°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0072] Example 9:

[0073] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, 0.1 g of niobium oxide, and 0.038 g of titanium oxide were dissolved in 88 g of anhydrous ethanol solution and 260 g of ball milling was added; after ball milling for 4 hours (400 rpm), precursor 1 was obtained.

[0074] Precursor 1 was sintered in a box-type atmosphere furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, intermediate 1 was mixed with 1.09g glucose and 100ml anhydrous ethanol, milled for 2 hours (1600 rpm), and then dried in a forced-air drying oven to obtain intermediate 2.

[0075] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 8 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0076] Example 10:

[0077] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, 0.065 g of alumina, and 0.038 g of titanium dioxide were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling was added; after ball milling for 6 hours (300 rpm), precursor 1 was obtained.

[0078] Precursor 1 was sintered in a box furnace at 300°C and held for 3 hours to obtain intermediate 1. The heating rate was 5°C / min. Then, intermediate 1 was mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was then milled for 2 hours (1500 rpm) and then placed in a forced-air drying oven to obtain intermediate 2.

[0079] Intermediate 2 was sintered in a box-type atmosphere furnace at 900°C and held for 10 hours. The heating rate was 10°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0080] Example 11:

[0081] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, and 0.413 g of magnesium acetate were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling was added; after ball milling for 5 hours (400 rpm), precursor 1 was obtained.

[0082] Precursor 1 was sintered in a box furnace at 500°C and held for 4 hours to obtain intermediate 1. The heating rate was 5°C / min. Then, intermediate 1 was mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was then milled for 1 hour (1200 rpm) and then placed in a forced-air drying oven to obtain intermediate 2.

[0083] Intermediate 2 was sintered in a box-type atmosphere furnace at 750°C and held for 6 hours. The heating rate was 6°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0084] Example 12:

[0085] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose and 0.34 g of calcium acetate were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling was added; after ball milling for 3 hours (400 rpm), precursor 1 was obtained.

[0086] Precursor 1 was sintered in a box-type atmosphere furnace at 450°C and held for 5 hours to obtain intermediate 1. The heating rate of the above heating step was 6°C / min.

[0087] Intermediate 1 was then mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was then milled for 3 hours (1400 rpm) and removed, and dried in a forced-air drying oven to obtain intermediate 2. Intermediate 2 was sintered in a box-type atmosphere furnace at 800℃ and held for 8 hours. The heating rate was 7℃ / min. After cooling, grinding, and sieving, the intermediate composite-coated doped lithium manganese iron phosphate cathode material was obtained.

[0088] Example 13:

[0089] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, and 0.13 g of alumina were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling was added; after ball milling for 5 hours (300 rpm), precursor 1 was obtained.

[0090] Precursor 1 was sintered in a box furnace at 600℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, intermediate 1 was mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was milled for 1.5 hours (1200 rpm) and then placed in a forced-air drying oven to obtain intermediate 2.

[0091] Intermediate 2 was sintered in a box-type atmosphere furnace at 850°C and held for 10 hours. The heating rate was 6°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0092] Example 14:

[0093] 4.86 g of lithium carbonate, 11.31 g of ferrous oxalate, 15.49 g of manganese acetate, 14.693 g of ammonium dihydrogen phosphate, 1.09 g of glucose, and 0.076 g of titanium dioxide were dissolved in 88 g of anhydrous ethanol and 260 g of ball milling was added; after ball milling for 6 hours (400 rpm), precursor 1 was obtained.

[0094] Precursor 1 was sintered in a box furnace at 500°C and held for 6 hours to obtain intermediate 1. The heating rate was 4°C / min. Then, intermediate 1 was mixed with 1.09g of glucose, and 200ml of anhydrous ethanol was added. The mixture was then milled for 2 hours (2000 rpm) and then dried in a forced-air drying oven to obtain intermediate 2.

[0095] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 8 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0096] Comparative example:

[0097] 4.86g of lithium carbonate, 9.2g of ferrous oxalate, 18.8858g of manganese acetate, 14.693g of ammonium dihydrogen phosphate, and 1.61g of glucose were dissolved in 88g of anhydrous ethanol solution and 260g of ball milling was added. After ball milling for 4 hours (400 rpm), precursor 1 was obtained. Precursor 1 was mixed with 200ml of anhydrous ethanol, sand milled (1600 rpm), and then placed in a forced-air drying oven to dry for 12 hours to obtain precursor 2.

[0098] Precursor 2 was sintered in a box furnace at 450℃ and held for 4 hours to obtain intermediate 1. The heating rate was 4℃ / min. Then, precursor 1 was mixed with 1.09g of glucose, 40ml of anhydrous ethanol and 130g of ball milling were added, and the mixture was ball milled for 1 hour (400 rpm) and then dried to obtain intermediate 2.

[0099] Intermediate 2 was sintered in a box-type atmosphere furnace at 700°C and held for 6 hours. The heating rate was 5°C / min. After cooling, grinding, and sieving, the intermediate composite coated doped lithium manganese iron phosphate cathode material was obtained.

[0100] Table 1 shows the AC impedance, lithium-ion diffusion coefficient, and electronic conductivity data of some embodiments and comparative examples of the present invention.

[0101] Table 1:

[0102] Serial Number First charge specific capacity (mAh / g) First discharge specific capacity (mAh / g) First charge / discharge efficiency (%) Capacity retention rate (%) after 100 cycles Example 1 156.04 149.56 95.85 98.71 Example 3 159.18 151.01 94.39 98.84 Example 4 161.6 157.97 97.75 98.06 Example 9 154.15 146.76 95.21 98.88 Example 11 160.61 151.6 94.39 97.91 Example 12 157.96 148.02 93.71 98.08 Example 13 155.91 148.44 95.2 96.67 Example 14 158.18 150.36 95.06 98.86 Comparative Example 157.51 144.8 91.93 92.72

[0103] Table 2 shows the electrochemical data of some embodiments and comparative examples of the present invention.

[0104] Table 2:

[0105] Serial Number <![CDATA[Impedance R ct (Ω)]]> <![CDATA[Lithium ion diffusion coefficient D Li (cm 2 s -1 )]]> Electron conductivity σ (s / cm) Example 1 211.7 <![CDATA[2.9328×10 -14 ]]> <![CDATA[7.28×10 -3 ]]> Example 3 189.2 <![CDATA[4.5426×10 -14 ]]> <![CDATA[7.5×10 -3 ]]> Example 4 142 <![CDATA[9.9213×10 -14 ]]> <![CDATA[8.48×10 -3 ]]> Comparative Example 328.59 <![CDATA[9.8631×10 -14 ]]> <![CDATA[1.43×10 -3 ]]>

[0106] .

[0107] The above description is merely a preferred embodiment of the present invention and does not constitute any limitation on the technical scope of the present invention. Therefore, any minor modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A lithium manganese iron phosphate cathode material, characterized in that, The material is a composite coated doped structure, consisting of a matrix and a composite coating layer; wherein the matrix is ​​doped lithium manganese iron phosphate, and the composite coating layer is composed of metal oxides, lithium-containing metal oxides, and carbon.

2. The lithium iron phosphate cathode material according to claim 1, characterized in that, The matrix has a chemical composition of Li. x Mn y Fe z M a PO4, wherein 0.9≤x≤1.10, 0≤y≤1, 0≤z≤1, 0≤a≤0.2, and M is one or more combinations of elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu.

3. The lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The mass of the matrix material is M, and the total mass of the coating layer is m. Based on the total mass, the coating layer content is 0. <m / (M+m)≤20%。 4. The lithium manganese iron phosphate cathode material according to claim 1, characterized in that, The metal oxide is a metal oxide containing one or more of the metal elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu. The lithium-containing metal oxide is a lithium-containing metal oxide containing one or more of the metal elements Zr, Mg, Ti, Nb, Al, Zn, V, and Cu. The carbon is one or a mixture of several of the following: amorphous carbon, carbon nanotubes, graphene, graphite, and pseudographite.

5. The lithium iron phosphate cathode material according to claim 1, characterized in that, The thickness of the composite coating layer is n, 0 <n≤20nm。 The mass of carbon in the composite coating is m1, and its mass percentage is 0. <m1 / (M+m)≤0.05。 The mass of the metal oxide in the composite coating layer is m2, and its mass percentage is 0. <m2 / (M+m2)≤0.1。 The composite coating layer contains lithium metal oxide with a mass of m3 and a mass percentage of 0. <m3 / (M+m3)≤0.1。 6. A method for preparing a lithium manganese iron phosphate cathode material, characterized in that, Includes the following steps: Step 1: Weigh the lithium source, phosphorus source, iron source, manganese source, doped metal source, and carbon source, mix them evenly, and then ball-mill, sand-mill, dry, and calcine to obtain the precursor; Step 2: Place the precursor in a vacuum or protective atmosphere for pre-calcination to obtain the intermediate; The third step is to take the precursor from the first step and calcine it in a vacuum or protective atmosphere, or to take the intermediate from the second step, mix it evenly with the doped metal source and carbon source, dry it, and then calcine it in a vacuum or protective atmosphere. Step 4: The composite coated and doped lithium manganese iron phosphate cathode material obtained by sintering is cooled, ground, and sieved to obtain the composite coated and doped lithium manganese iron phosphate cathode material.

7. The method for preparing a lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In steps two and three, the protective atmosphere is one or a combination of argon, nitrogen, helium, or neon.

8. The method for preparing a lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In the first step, the calcination temperature is 300-600℃ and the holding time is 1-10 hours.

9. The method for preparing a lithium manganese iron phosphate cathode material according to claim 6, characterized in that, In the third step, the calcination temperature is 500-900℃, and the holding time is 2-15 hours.

10. The application of a lithium iron phosphate cathode material according to claims 1-5 in lithium-ion batteries.

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