Metal composite lithium iron phosphate solid-phase deposition coated lithium manganese iron phosphate positive electrode material and preparation method thereof

Abstract

The invention discloses a metal composite lithium iron phosphate solid-phase deposition coated lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the technical field of lithium ion battery positive electrode materials. The preparation method of the metal composite lithium iron phosphate solid-phase deposition coated lithium iron manganese phosphate positive electrode material comprises the following steps: S1, preparing a lithium iron manganese phosphate material and sintering; s2, grinding lithium iron phosphate into nano particles, and mixing the nano particles with a sugar source to form lithium iron phosphate nano slurry; s3, transferring into a CVD (Chemical Vapor Deposition) fluidized bed in the lithium manganese iron phosphate cooling and sintering stage, spraying lithium iron phosphate nano slurry, gasifying and drying the lithium iron phosphate material, and coating the surface of the lithium manganese iron phosphate with the lithium iron phosphate material through solid-phase deposition; and S4, carrying out composite coating of carbon and metal oxide on the lithium manganese iron phosphate coated with the lithium iron phosphate to obtain the lithium manganese iron phosphate coated with the lithium iron phosphate. According to the invention, the problem of poor uniformity of lithium iron phosphate coated lithium iron manganese phosphate is solved, the electrical property of lithium iron manganese phosphate is improved, the ferromanganese dissolution is improved, and the cycle performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery positive electrode materials, and in particular to a lithium manganese iron phosphate positive electrode material coated with a metal composite lithium iron phosphate solid phase deposition and a preparation method thereof. Background Art

[0002] The current mainstream olivine structure LiFePO4 cathode material has good cycle stability, high safety, and high discharge capacity (170mAh·g -1 ) and low cost, however, its further development is limited by its low discharge platform (3.4V vs Li / Li+) and low energy density. LiFeMnPO4 combines the advantages of LiFePO4 and LiMnPO4, offering the same safety and high energy density as LiFePO4, thus possessing competitive advantages and promising market prospects. However, LiFeMnPO4 still suffers from issues such as small primary particles, poor conductivity, large specific surface area, poor processability, and poor cycling performance. Summary of the Invention

[0003] Based on the problems existing in the background technology, the present invention provides a metal composite lithium iron phosphate solid-phase deposition-coated lithium manganese iron phosphate positive electrode material and a preparation method thereof, which solves the problem of poor uniformity of lithium iron phosphate-coated lithium manganese iron phosphate, improves the electrical properties of lithium manganese iron phosphate (improves conductivity and capacity), improves manganese iron dissolution, and improves cycle performance.

[0004] The present invention is implemented through the following technical solutions:

[0005] A method for preparing a lithium manganese iron phosphate positive electrode material coated with a metal composite lithium iron phosphate solid phase deposition comprises the following steps:

[0006] S1. A Li source compound, a Mn source compound, an Fe source compound, a P source compound, a doping source, a carbon source and deionized water are added to a ball mill, a reaction accelerator is added, and the mixture is chemically reacted to form a lithium manganese iron phosphate phase. The lithium manganese iron phosphate phase is ground to obtain a grinding slurry, a grinding slurry is sprayed, and the obtained spray material is sintered;

[0007] S2. Grinding the lithium iron phosphate into nanoparticles and mixing with a sugar source to form a lithium iron phosphate nanoslurry;

[0008] S3. After the sintering of the lithium iron phosphate is completed, the cooling stage is transferred to the CVD fluidized bed, and the lithium iron phosphate nano-slurry is sprayed to achieve gasification and drying of the lithium iron phosphate material and solid phase deposition coating on the surface of the lithium iron phosphate;

[0009] S4. The lithium manganese iron phosphate coated with lithium iron phosphate is composite-coated with carbon and metal oxide to obtain a lithium manganese iron phosphate positive electrode material solid-phase coated with metal composite lithium iron phosphate.

[0010] Furthermore, in step S1, the lithium manganese iron phosphate precursor or the lithium manganese iron phosphate material is directly used for sintering.

[0011] Furthermore, the stoichiometric ratio of the lithium manganese iron phosphate raw material in step S1 is: Li / P=1.01-1.07, (Mn+Fe) / P=0.93-0.99;

[0012] The amount of doping source added is 0.2-10% of the theoretical mass of lithium manganese iron phosphate;

[0013] The amount of carbon source added is 2-20% of the mass of the theoretically generated lithium manganese iron phosphate.

[0014] Furthermore, in step S1, the Li source compound is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, and lithium phosphate;

[0015] The Mn source compound is one or more of manganese carbonate, manganese trioxide, manganese trioxide, manganese oxalate, manganese phosphate, ferromanganese tetraoxide, ferromanganese trioxide, ferromanganese carbonate, ferromanganese phosphate, and ferromanganese oxalate;

[0016] The Fe source compound is one or more of ferric phosphate, ferrous oxide, ferrous oxalate, ferromanganese tetroxide, ferromanganese sesquioxide, ferromanganese carbonate, ferromanganese phosphate, and ferromanganese oxalate;

[0017] The doping source compound is one or more of magnesium acetate, magnesium oxide, titanium dioxide, ammonium niobium oxalate, niobium pentoxide, vanadium or a vanadium compound;

[0018] The P source compound is one or more of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, manganese phosphate, and iron phosphate;

[0019] The carbon source is one or more of glucose, lactose, sucrose, polyvinyl alcohol, phenolic resin, epoxy resin, and ascorbic acid;

[0020] The reaction accelerator is a substance with redox properties such as oxalic acid, hydrogen peroxide, vitamin C, sulfur dioxide, hydrazine hydrate, and lithium borohydride.

[0021] Furthermore, the sintering temperature in step S1 is 500-700°C.

[0022] Furthermore, in step S2, the amount of lithium iron phosphate used is 0.5-30% of the mass of lithium iron manganese phosphate; the particle size D50 of the lithium iron phosphate slurry is less than 1 μm;

[0023] The sugar source is one or more of glucose, PEG, lactose, and sucrose, and the amount used accounts for 3%-20% of the mass of the lithium iron phosphate.

[0024] Furthermore, in step S3, the temperature is lowered to 400-700°C.

[0025] Furthermore, in step S4, the amount of carbon source added is 0.1-4% of the weight of lithium manganese iron phosphate, and the thickness of the carbon layer coating is 0.2-20 nm.

[0026] Furthermore, in step S4, the metal oxide particle size D50 is less than 1 μm, and the metal oxide is one or more of iron oxide, magnesium oxide, titanium oxide, nickel oxide, cobalt oxide, niobium oxide, vanadium oxide, and zirconium oxide.

[0027] Furthermore, in step S4, the amount of metal oxide used is 0.5-5% of the lithium manganese iron phosphate, and the thickness of the coating layer is 1-10 nm.

[0028] The invention also discloses a lithium manganese iron phosphate positive electrode material coated with a metal composite lithium iron phosphate solid phase deposition prepared by the preparation method.

[0029] Beneficial effects of the present invention:

[0030] The present invention uses CVD fluidized bed technology to achieve uniform solid-phase deposition and coating of lithium iron phosphate nanoparticles on the surface of lithium iron manganese phosphate materials, and then combines the composite coating of carbon layers and metal oxide layers to form a composite protection system with a three-layer core-shell structure. The present invention solves the problem of poor uniformity of lithium iron phosphate coating on lithium iron manganese phosphate in traditional wet mixing processes. The CVD fluidized bed solid-phase deposition technology can achieve comprehensive and uniform coating of lithium iron manganese phosphate particles; three layers of protective shells, LFP, carbon layer and metal oxide, are deposited in sequence to form a multiple protective barrier. The synergistic effect of each layer not only improves the conductivity of the material, but also effectively blocks the corrosion of the active material by the electrolyte, thereby improving the overall stability of the material. Compared with traditional processes, the method of the present invention is more efficient, reduces intermediate links and energy consumption, and at the same time, due to the improved recycling performance of the material, the battery life is extended and the cost of use is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to further explain the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0032] Figure 1 Schematic diagram of the process for preparing lithium manganese iron phosphate material by traditional wet coating;

[0033] Figure 2 This is a schematic diagram of the CVD fluidized bed solid phase deposition coating process of the present invention;

[0034] Figure 3 This is the principle diagram of CVD fluidized bed solid phase deposition coating;

[0035] Figure 4 The XRD results of the metal composite lithium iron phosphate solid-phase coated lithium manganese iron phosphate positive electrode material prepared in Example 1 are as follows:

[0036] Figure 5 This is an electron microscope photo of the lithium manganese iron phosphate positive electrode material coated with metal composite lithium iron phosphate solid phase deposition prepared in Example 1;

[0037] Figure 6 The distribution of manganese, iron and phosphorus elements in the lithium manganese iron phosphate positive electrode material coated with metal composite lithium iron phosphate solid phase deposition prepared in Example 1. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described in detail below with reference to specific embodiments, but the protection scope of the present invention is not limited to the following embodiments.

[0039] Example 1

[0040] A method for preparing a lithium manganese iron phosphate positive electrode material coated with a metal composite lithium iron phosphate solid phase deposition comprises the following steps:

[0041] S1. According to the stoichiometric ratio of Li / P=1.05, (Mn+Fe) / P=0.95, Mn / Fe=1.53, niobium pentoxide (dopant source) was added in an amount of 4% of the theoretical mass of lithium manganese iron phosphate; glucose (carbon source) was added in an amount of 10% of the theoretical mass of lithium manganese iron phosphate; the raw materials were weighed, and a Li source compound, a Mn source compound, an Fe source compound, a P source compound, a doping source, a carbon source and deionized water were added to a ball mill, and oxalic acid as a reaction promoter was added. The ball mill was milled at 220 rpm for 24 hours to generate a lithium manganese iron phosphate phase. The lithium manganese iron phosphate phase was ground for 2 hours to obtain a mill slurry, the mill slurry was sprayed, and the sprayed material was sintered at a temperature of 650 ° C for 4 hours;

[0042] S2. The lithium iron phosphate is ground to nanoparticles of D50 = 0.8μm and mixed with glucose to form a lithium iron phosphate nano-slurry, the amount of lithium iron phosphate is 15% of the mass of lithium iron manganese phosphate, the amount of glucose accounts for 10% of the amount of lithium iron phosphate;

[0043] S3. When the lithium iron phosphate is cooled to 500 ℃, it is transferred to the CVD fluidized bed and the lithium iron phosphate nano-slurry is sprayed and reacted for 2 hours to achieve gasification and drying of the lithium iron phosphate material and solid phase deposition coating on the surface of the lithium iron phosphate;

[0044] S4. The lithium iron manganese phosphate particles coated with lithium iron phosphate were maintained in a CVD fluidized bed and sprayed with an aqueous solution containing 2% sucrose, the amount of sucrose being 2% by weight of the lithium iron manganese phosphate. The reaction temperature was controlled at 500 ° C for 2 hours to achieve gasification of the carbon source and solid deposition on the particle surface to form a carbon coating layer having a thickness of about 10 nm.

[0045] S5. After the carbon coating is completed, the material is kept in the CVD fluidized bed and sprayed with a dispersion containing 2% nano-scale titanium dioxide (D50 = 0.5 μm), where the amount of nano-scale titanium dioxide is 2% of the mass of the lithium manganese iron phosphate. The temperature is controlled at 500°C for 3 hours to achieve metal oxide vapor deposition, forming an outer metal oxide coating layer with a thickness of about 5 nm, and finally obtaining a composite material with a three-layer core-shell structure, thereby obtaining a lithium manganese iron phosphate positive electrode material solid-phase coated with a metal composite lithium iron phosphate.

[0046] Figure 4 The XRD result of the metal composite lithium iron phosphate solid phase coated lithium manganese phosphate positive electrode material prepared in Example 1. The core of the present invention is to form lithium iron phosphate (LFP) coated lithium manganese phosphate through chemical reaction, and the physical phase is as follows Figure 4 As shown: LFP can be seen, but the amount is relatively small, indicating that new lithium iron phosphate has been partially formed, and a small part has retained the original lithium iron phosphate.

[0047] And through the electron microscope photos, it can be seen that there is more iron coating on the surface. The EDS scan of the LMFP particles found that the iron content at the edge of the ball is higher than that inside, indicating that LFP has been coated on the surface of the material ( Figure 5 and Figure 6 ).

[0048] Example 2

[0049] In this embodiment, lithium manganese iron phosphate is directly sintered at 650° C. for 4 hours; the remaining steps are the same as in Example 1.

[0050] Comparative Example 1

[0051] This comparative example uses a traditional wet-coated lithium manganese iron phosphate material.

[0052] Lithium manganese iron phosphate and lithium iron phosphate are mixed in a ratio of 9:1, and a traditional wet mixing coating process is used: after mixing the two powders, water and dispersant are added, stirred evenly and dried, heat treated at 600°C for 4 hours, and then carbon coated and metal oxide coated.

[0053] Comparative Example 2

[0054] This comparative example is a lithium iron phosphate material coated only with carbon.

[0055] Lithium manganese iron phosphate was prepared according to step S1 of Example 1, but lithium iron phosphate coating was not performed, and only carbon and metal oxide coating was performed.

[0056] Comparative Example 3

[0057] This comparative example is a lithium iron phosphate material.

[0058] Test Example 1

[0059] The lithium nickel iron phosphate positive electrode materials prepared in the examples and comparative examples were tested by ICP to determine the ratio of manganese and iron elements in the materials; the specific surface area of the materials was tested by nitrogen adsorption-desorption method; the carbon content in the materials was determined by a carbon-sulfur analyzer; and the electrical conductivity of the materials was measured by a four-probe resistance test system. The samples were pressed into discs with a diameter of 10 mm and a thickness of about 2 mm for testing.

[0060] The lithium nickel iron phosphate cathode materials prepared in the examples and comparative examples were assembled into button-type half-cells and charged using constant current and constant voltage. The physical and chemical properties and electrochemical performance results are shown in Table 1.

[0061] Table 1

[0062]

[0063] Compared with Comparative Example 2, it was found that the capacity and rate performance of the material were improved due to the coating of lithium iron phosphate, and the energy density was also improved by nearly 5%.

[0064] Test Example 2

[0065] Metal ion dissolution test

[0066] 0.5 g of sample powder from the examples and comparative examples was weighed and placed in 15 mL of electrolyte (1 M LiPF6 in EC / DMC / EMC solution). The electrolyte was then immersed at 60°C for 7 days. The immersion solution was then removed and the amount of manganese and iron ions dissolved in the electrolyte was measured by ICP-OES.

[0067] Table 2

[0068] Group Manganese dissolution (ppm) Iron dissolution (ppm) Example 1 22 18 Example 2 25 20 Comparative Example 1 55 45 Comparative Example 2 39 27 Comparative Example 3 / 51

[0069] The results in Table 2 show that the dissolution of manganese iron has been significantly improved, which will greatly benefit the recycling process. Because of the CVD coating method, the dissolution of iron is also improved compared to the lithium iron phosphate on the market.

[0070] Finally, it should be noted that the above-described embodiments merely represent several implementation methods of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made by a person skilled in the art without departing from the spirit of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention should be based on the appended claims.

Claims

1. A method for preparing a lithium manganese iron phosphate positive electrode material coated with a metal composite lithium iron phosphate solid phase deposition, characterized in that: The following steps are involved: S1. A Li source compound, a Mn source compound, an Fe source compound, a P source compound, a doping source, a carbon source and deionized water are added to a ball mill, a reaction accelerator is added, and the mixture is chemically reacted to form a lithium manganese iron phosphate phase. The lithium manganese iron phosphate phase is ground to obtain a grinding slurry, a grinding slurry is sprayed, and the obtained spray material is sintered; S2. Grinding the lithium iron phosphate into nanoparticles and mixing with a sugar source to form a lithium iron phosphate nanoslurry; S3. In the lithium manganese iron phosphate cooling stage, the lithium iron phosphate nano-slurry is sprayed to achieve gasification and drying of the lithium iron phosphate material and solid phase deposition coating on the surface of the lithium manganese iron phosphate; S4. The lithium manganese iron phosphate coated with lithium iron phosphate is composite-coated with carbon and metal oxide to obtain a lithium manganese iron phosphate positive electrode material solid-phase coated with metal composite lithium iron phosphate.

2. The preparation method according to claim 1, characterized in that In step S1, the lithium manganese iron phosphate precursor or the lithium manganese iron phosphate material is directly used for sintering.

3. The preparation method according to claim 1, characterized in that The stoichiometric ratio of the lithium manganese iron phosphate raw material in step S1 is: Li / P=1.01-1.07, (Mn+Fe) / P=0.93-0.99; The amount of doping source added is 0.2-10% of the theoretical mass of lithium manganese iron phosphate; The amount of carbon source added is 2-20% of 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 Li source compound is one or more of lithium hydroxide, lithium carbonate, lithium dihydrogen phosphate, and lithium phosphate; The Mn source compound is one or more of manganese carbonate, manganese trioxide, manganese trioxide, manganese oxalate, manganese phosphate, ferromanganese tetraoxide, ferromanganese trioxide, ferromanganese carbonate, ferromanganese phosphate, and ferromanganese oxalate; The Fe source compound is one or more of ferric phosphate, ferrous oxide, ferrous oxalate, ferromanganese tetroxide, ferromanganese sesquioxide, ferromanganese carbonate, ferromanganese phosphate, and ferromanganese oxalate; The doping source compound is one or more of magnesium acetate, magnesium oxide, titanium dioxide, ammonium niobium oxalate, niobium pentoxide, vanadium or a vanadium compound; The P source compound is one or more of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, manganese phosphate, and iron phosphate; The carbon source is one or more of glucose, lactose, sucrose, polyvinyl alcohol, phenolic resin, epoxy resin, and ascorbic acid; The reaction accelerator is one or more of oxalic acid, hydrogen peroxide, vitamin C, sulfur dioxide, hydrazine hydrate, and lithium borohydride.

5. The preparation method according to claim 1, characterized in that The sintering temperature in step S1 is 500-700°C.

6. The preparation method according to claim 1, characterized in that In step S2, the amount of lithium iron phosphate used is 0.5-30% of the mass of lithium manganese iron phosphate; the particle size D50 of the lithium iron phosphate slurry is less than 1 μm; The sugar source is one or more of glucose, PEG, lactose, and sucrose, and the amount used accounts for 3%-20% of the mass of the lithium iron phosphate.

7. The preparation method according to claim 1, characterized in that In step S3, the temperature is lowered to 400-700°C.

8. The preparation method according to claim 1, characterized in that In step S4, the amount of carbon source added is 0.1-4% of the weight of lithium manganese iron phosphate, and the thickness of the carbon layer coating is 0.2-20 nm.

9. The preparation method according to claim 1, characterized in that In step S4, the metal oxide is one or more of iron oxide, magnesium oxide, titanium oxide, nickel oxide, cobalt oxide, niobium oxide, vanadium oxide, and zirconium oxide; The metal oxide particle size D50 is less than 1 μm, the amount of the metal oxide is 0.5-5% of the mass of the lithium manganese iron phosphate, and the coating layer thickness is 1-10 nm.

10. A lithium manganese iron phosphate positive electrode material coated with metal composite lithium iron phosphate solid phase deposition prepared by the preparation method according to any one of claims 1 to 9.

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