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

Abstract

The application 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 manganese iron phosphate positive electrode material comprises the following steps: S1, preparing a lithium manganese iron phosphate material and performing sintering; S2, grinding lithium iron phosphate into nanoparticles, mixing the nanoparticles with a sugar source to form lithium iron phosphate nano slurry; S3, in the lithium manganese iron phosphate cooling sintering stage, spraying the lithium iron phosphate nano slurry into a CVD fluidized bed, realizing gasification drying of the lithium iron phosphate material and solid-phase deposition coating of the lithium iron phosphate material on the surface of the lithium manganese iron phosphate; and S4, performing composite coating of carbon and metal oxides on the lithium manganese iron phosphate coated with the lithium iron phosphate, and the metal composite lithium iron phosphate solid-phase deposition coated lithium manganese iron phosphate positive electrode material is obtained. The application solves the problem of poor uniformity of lithium iron phosphate coated lithium manganese iron phosphate, improves the electrical performance of the lithium manganese iron phosphate, improves manganese iron dissolution, and improves the cycle performance.

Description

TECHNICAL FIELD

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

[0002] At present, mainstream olivine structure LiFePO4 positive electrode materials have the advantages of good cycle stability, high safety, high discharge capacity (170 mAh.g -1 ), low cost and the like, however, the low discharge platform (3.4 V vs. Li / Li+) and low energy density of the materials limit the further development of the materials. LiFeMnPO4 materials combine the advantages of LiFePO4 and LiMnPO4 materials, have the same good safety as LiFePO4 and the same high energy density as LiMnPO4, and have competitive advantages and market prospects. However, the LiFeMnPO4 material still has the problems of small primary particles, poor electrical conductivity, large specific surface area, poor processing performance, poor cycle performance and the like. SUMMARY

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

[0004] The application is implemented through the following technical scheme:

[0005] A preparation method of a metal composite lithium iron phosphate solid phase deposition coated lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0006] S1. Li source compounds, Mn source compounds, Fe source compounds, P source compounds, doping sources, carbon sources and deionized water are added in a ball mill tank, a reaction promoter is added, chemical reaction is carried out, lithium manganese iron phosphate phases are generated, the lithium manganese iron phosphate phases are ground to obtain a first grinding pulp, the first grinding pulp is sprayed, and the sprayed material is sintered;

[0007] S2. The lithium iron phosphate is ground into nanoparticles, and a sugar source is mixed to form a lithium iron phosphate nano slurry;

[0008] S3. In the cooling stage after the sintering of the lithium manganese iron phosphate is completed, the lithium iron phosphate nano slurry is sprayed into a CVD fluidized bed, so that the lithium iron phosphate material is gasified and dried and solid phase deposition coated on the surface of the lithium manganese iron phosphate;

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

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

[0011] Further, 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 the doping source added is 0.2-10% of the theoretical mass of the lithium manganese iron phosphate generated;

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

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

[0015] The manganese source compound is one or more of manganese carbonate, trimanganese tetroxide, dimanganese trioxide, manganese oxalate, manganese phosphate, trimanganese tetroxide iron, dimanganese trioxide iron, manganese carbonate iron, manganese phosphate iron, and manganese oxalate iron;

[0016] The iron source compound is one or more of iron phosphate, diiron trioxide, ferrous oxalate, trimanganese tetroxide iron, dimanganese trioxide iron, manganese carbonate iron, manganese phosphate iron, and manganese oxalate iron;

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

[0018] The phosphorus 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 promoter is a substance with redox properties such as oxalic acid, hydrogen peroxide, vitamin C, sulfur dioxide, hydrazine hydrate, and lithium borohydride.

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

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

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

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

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

[0026] Further, the particle size D50 of the metal oxide in step S4 is less than 1 um, 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] Further, the amount of the metal oxide in step S4 is 0.5-5% of the lithium manganese iron phosphate, and the thickness of the coating layer is 1-10 nm.

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

[0029] The application has the following beneficial effects:

[0030] The application realizes uniform solid-phase deposition coating of lithium iron phosphate nanoparticles on the surface of lithium manganese iron phosphate material by CVD fluidized bed technology, and further realizes composite coating of carbon layer and metal oxide layer, thereby forming a composite protection system with a three-layer core-shell structure. The application solves the problem of poor uniformity of lithium iron phosphate coated lithium manganese iron phosphate in traditional wet mixing process, and realizes comprehensive and uniform coating of lithium manganese iron phosphate particles by CVD fluidized bed solid-phase deposition technology. The three-layer protection shell of LFP, carbon layer and metal oxide is deposited in sequence, thereby forming a multiple protection barrier, and the layers synergize to improve the conductivity of the material and effectively block the corrosion of the electrolyte on the active material, thereby improving the overall stability of the material. Compared with the traditional process, the method of the application is more efficient, reduces intermediate links and energy consumption, prolongs the service life of the battery due to the improved material cycle performance, and reduces the use cost. BRIEF DESCRIPTION OF DRAWINGS

[0031] The accompanying drawings are used to provide further explanation of the application, and constitute a part of the specification, and are used to explain the application together with embodiments of the application, and do not constitute a limitation on the application. In the drawings:

[0032] Figure 1 It is a process schematic diagram for preparing lithium manganese iron phosphate material by traditional wet coating;

[0033] Figure 2 It is a CVD fluidized bed solid-phase deposition coating process schematic diagram of the application;

[0034] Figure 3 CVD fluidized bed solid phase deposition coating principle for lithium iron phosphate;

[0035] Figure 4 XRD result diagram of metal composite lithium iron phosphate solid phase coated lithium manganese iron phosphate positive electrode material prepared for example 1

[0036] Figure 5 Metal composite lithium iron phosphate solid phase deposition coated lithium manganese iron phosphate positive electrode material electron microscope photo prepared for example 1

[0037] Figure 6 Manganese iron phosphorus element distribution of metal composite lithium iron phosphate solid phase deposition coated lithium manganese iron phosphate positive electrode material prepared for example 1 DETAILED DESCRIPTION

[0038] The technical solutions of the present application will be further described in combination with specific examples, but the protection scope of the present application is not limited to the following examples.

[0039] Example 1

[0040] A preparation method of a metal composite lithium iron phosphate solid phase deposition coated lithium manganese iron phosphate positive electrode material, comprising the following steps:

[0041] S1. According to the stoichiometric ratio of Li / P=1.05, (Mn+Fe) / P=0.95, Mn / Fe=1.53, the addition amount of niobium pentoxide (doping source) is 4% of the theoretical mass of generated lithium manganese iron phosphate; the addition amount of glucose (carbon source) is 10% of the theoretical mass of generated lithium manganese iron phosphate; the raw materials are weighed, Li source compound, Mn source compound, Fe source compound, P source compound, doping source, carbon source and deionized water are added in a ball mill tank, reaction promoter oxalic acid is added, ball milling is carried out at a speed of 220 rpm for 24 hours, lithium manganese iron phosphate phase is generated, the lithium manganese iron phosphate phase is ground for 2 hours to obtain a first grinding slurry, the first grinding slurry is sprayed, and the sprayed material is sintered at a temperature of 650 DEG C for 4 hours;

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

[0043] S3. When the lithium manganese iron phosphate is cooled to 500 DEG C, it is transferred into a CVD fluidized bed, the lithium iron phosphate nano slurry is sprayed, and the reaction is carried out for 2 hours to realize gasification drying of the lithium iron phosphate material and solid phase deposition coating on the surface of the lithium manganese iron phosphate;

[0044] S4. The lithium manganese iron phosphate particles coated with lithium iron phosphate are maintained in the CVD fluidized bed, and a 2% sucrose aqueous solution is sprayed, the amount of sucrose being 2% of the weight of the lithium manganese iron phosphate, and the temperature is controlled at 500 DEG C for 2 hours to realize carbon source gasification and solid phase deposition on the particle surface to form a carbon coating layer with a thickness of about 10 nm;

[0045] S5. After the carbon coating is completed, the material is continuously maintained in the CVD fluidized bed, and a 2% nano-sized titanium dioxide (D50 = 0.5 μm) dispersion liquid is sprayed, the amount of nano-sized titanium dioxide being 2% of the mass of the lithium manganese iron phosphate, and the temperature is controlled at 500 DEG C for 3 hours to realize metal oxide gas phase deposition to form an outer metal oxide coating layer with a thickness of about 5 nm, and finally a composite material with a three-layer core-shell structure is obtained, and a metal composite lithium iron phosphate solid phase coated lithium manganese iron phosphate positive electrode material is obtained.

[0046] Figure 4 The XRD result graph of the metal composite lithium iron phosphate solid phase coated lithium manganese iron phosphate positive electrode material prepared in this embodiment 1 is shown. The core of the application is that lithium iron phosphate (LFP) coated lithium manganese iron phosphate is formed by chemical reaction, and the phase is as shown in Figure 4 : it can be seen that LFP exists, the amount is relatively small, and it is indicated that part of the lithium manganese iron phosphate is formed, and a small part of the original lithium iron phosphate is retained.

[0047] And it can be seen from the electron microscope photograph that iron is coated on the surface, and the edge part of the ball is found to have a higher iron content than the inside by performing an eds scan on the LMFP particles, which indicates that LFP has been coated on the surface of the material Figure 5 and Figure 6 ).

[0048] Embodiment 2

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

[0050] Comparative Example 1

[0051] The lithium manganese iron phosphate material in this comparative example is coated by a traditional wet method.

[0052] The lithium manganese iron phosphate and the lithium iron phosphate are mixed in a ratio of 9:1, and a traditional wet mixing and coating process is used: after the two powders are mixed, water and a dispersant are added, and after stirring uniformly, drying is performed, heat treatment is performed at 600 DEG C for 4 hours, and then carbon coating and metal oxide coating are performed.

[0053] Comparative Example 2

[0054] The lithium iron phosphate material in this comparative example is only carbon coated.

[0055] The lithium manganese iron phosphate was prepared according to the procedure of Step S1 of Example 1, without coating of lithium iron phosphate, only coating of carbon and metal oxides.

[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 measured for the content ratio of manganese and iron elements in the material by ICP; the specific surface area of the material was tested by nitrogen adsorption-desorption method; the carbon content in the material was measured by carbon-sulfur analyzer; and the electrical conductivity of the material was measured by four-probe resistance test system, after the sample was pressed into a round sheet with a diameter of 10 mm and a thickness of about 2 mm.

[0060] The lithium nickel iron phosphate positive electrode materials prepared in the examples and comparative examples were assembled into button half-batteries, and charged by constant current and constant voltage, and the results of physical and chemical properties and electrochemical properties are shown in Table 1.

[0061] Table 1

[0062]

[0063] It is found from Comparative Example 2 that because of the coating of lithium iron phosphate, the capacity and rate performance of the material are improved, and the energy density is also improved by nearly 5%.

[0064] Test Example 2

[0065] Metal ion leaching test

[0066] 0.5 g of sample powder of the examples and comparative examples was weighed and placed in 15 mL of electrolyte (1 M LiPF6 solution in EC / DMC / EMC), and soaked at 60°C for 7 days. Then the soaking solution was taken out, and the leaching amount of manganese and iron ions in the electrolyte was tested by ICP-OES.

[0067] Table 2

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

[0069] As can be seen from the results in Table 2, the manganese and iron leaching is significantly improved: this will be very helpful for cycling. Because the coating method of CVD is used, the leaching of iron is also improved compared with the market lithium iron phosphate.

[0070] Finally, it should be noted that the above-described embodiments only express several embodiments of the present application, and are not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the concept of the present application shall be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A method for preparing a metal composite lithium iron phosphate solid phase deposition coated lithium manganese iron phosphate cathode material, characterized in that, Comprising the following steps: S1. Adding Li source compound, Mn source compound, Fe source compound, P source compound, doping source, carbon source and deionized water in a ball mill tank, adding a reaction promoter, mixing to carry out chemical reaction, generating a lithium manganese iron phosphate phase, grinding the lithium manganese iron phosphate phase to obtain a first grinding pulp, spraying the first grinding pulp, and sintering the obtained spray material; S2. Grinding the lithium iron phosphate to nanoparticles, mixing with a sugar source to form a lithium iron phosphate nano slurry; S3. In the cooling stage of the lithium manganese iron phosphate, a CVD fluidized bed is used to spray the lithium iron phosphate nano slurry, realizing gasification drying and solid phase deposition of the lithium iron phosphate nano slurry and coating on the surface of the lithium manganese iron phosphate; S4. The lithium manganese iron phosphate coated with lithium iron phosphate is subjected to composite coating of carbon and metal oxides to obtain a metal composite lithium iron phosphate solid phase coated lithium manganese iron phosphate positive electrode material; The reaction promoter in step S1 is one or more of oxalic acid, hydrogen peroxide, vitamin C, sulfur dioxide, hydrazine hydrate, and lithium borohydride; In step S3, the temperature is reduced to 400-700℃; The metal oxide in step S4 is one or more of iron oxide, magnesium oxide, titanium oxide, nickel oxide, cobalt oxide, niobium oxide, vanadium oxide, and zirconium oxide.

2. The production method according to claim 1, characterized by, In step S1, the lithium manganese iron phosphate material is directly sintered.

3. The production method according to claim 1, characterized by, In step S1, the stoichiometric ratio of the lithium manganese iron phosphate raw material 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 the generated lithium manganese iron phosphate; The amount of carbon source added is 2-20% of the theoretical mass of the generated lithium manganese iron phosphate.

4. The method of claim 1, wherein, The Li source compound in step S1 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, trimanganese tetroxide, dimanganese trioxide, manganese oxalate, manganese phosphate, trimanganese tetroxide iron, dimanganese trioxide iron, manganese carbonate iron, manganese iron phosphate, and manganese iron oxalate; The Fe source compound is one or more of iron phosphate, diiron trioxide, ferrous oxalate, trimanganese tetroxide iron, dimanganese trioxide iron, manganese carbonate iron, manganese iron phosphate, and manganese iron oxalate; The doping source is one or more of magnesium acetate, magnesium oxide, titanium dioxide, ammonium niobium oxalate, di-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.

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

6. The method of claim 1, wherein, In step S2, the amount of lithium iron phosphate 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 1um; The sugar source is one or more of glucose, lactose, and sucrose, and the amount is 3%-20% of the mass of lithium iron phosphate.

7. 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 is 0.2-20nm.

8. The method of claim 1, wherein, The metal oxide particle size D50 in step S4 is less than 1 um, the amount of metal oxide is 0.5-5% of the mass of the lithium iron manganese phosphate, and the thickness of the coating layer is 1-10 nm.

9. A metal composite lithium iron phosphate solid-phase deposition coated lithium manganese iron phosphate positive electrode material prepared by the preparation method in any one of claims 1-8.

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