A gallium atom iron site doped lithium manganese iron phosphate cathode material and a preparation method thereof

Abstract

The application provides a gallium atom iron site doped lithium manganese iron phosphate positive electrode material and a preparation method thereof, and belongs to the field of electrochemical energy storage. The specific process is as follows: gallium nitrate is added into a mixed solution of ethanol and glycerol, and then transferred into a hydrothermal reaction kettle for hydrothermal treatment to obtain a gallium atom ligand as a gallium source. Lithium carbonate is added into an 85% aqueous phosphoric acid solution for reaction, and then a manganese source, a carbon source, iron phosphate and the gallium source are added into the reaction solution one by one to form a mixed slurry. The mixed slurry is subjected to sand milling treatment, and then spray drying. The dried powder is subjected to fluidized sintering under the protection of an inert atmosphere, and finally a gallium atom iron site doped lithium manganese iron phosphate material is obtained. The gallium atom ligand as the gallium source makes the surface morphology of the obtained gallium doped lithium manganese iron phosphate material smoother, and the specific surface area is significantly reduced. The gallium doped lithium manganese iron phosphate material applied to a lithium ion battery positive electrode material exhibits excellent electrochemical performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, specifically relating to a gallium atom iron site doped lithium manganese iron phosphate cathode material and its preparation method. Background Technology

[0002] Lithium iron phosphate (LiFePO4) with an olivine structure is widely used as a cathode material in lithium-ion batteries (LIBs) due to its low cost, excellent cycle stability, and safety. However, compared with other commercially available cathode materials, LiFePO4 has lower energy density and redox potential (~3.4V vs. Li). + The low conductivity of both Li and Li severely limits their development in electric vehicles. Lithium manganese phosphate (LiMnPO4), also with an olivine structure, has gradually attracted attention due to its high redox potential of ~4.1V. However, the intrinsic conductivity of LiMnPO4 is five orders of magnitude lower than that of LiFePO4, and it also contains Mn... 3+ The Jahn-Teller effect easily causes structural collapse of electrode materials during cycling, resulting in poor rate capability and long-cycle performance of LiMnPO4, which greatly limits its development and application. However, lithium manganese iron phosphate (LiMnPO4) is obtained by partially replacing Mn with Fe. x Fe 1−x PO4 is considered an effective strategy to improve the electrochemical performance of LiMn. x Fe 1−x PO4 not only possesses the high safety and long cycling performance of LiFePO4, but also has a higher energy density. However, it suffers from poor cycling performance due to manganese ion dissolution, and the synthesis process easily leads to uneven solid solution formation, resulting in poor electrochemical performance. Doping with high-valence metal ions is a very effective strategy for modifying the electrochemical performance of materials.

[0003] CN117199348A discloses a vanadium-doped lithium manganese iron phosphate material with phosphorus sites. Vanadium doping improves the intrinsic conductivity of the material and greatly enhances its electrochemical performance.

[0004] CN117658094A discloses a titanium-doped lithium manganese iron phosphate material. Titanium doping reduces the resistance to electron transport at the electrode / solution interface and plays a role in stabilizing the crystal lattice, thereby improving the cycling and rate performance of the material.

[0005] CN116477594A discloses a zinc-doped lithium manganese iron phosphate material. Zinc doping can improve the conductivity of the material, accelerate the lithium ion diffusion rate, and enhance the electrochemical performance of the lithium manganese iron phosphate composite material. Summary of the Invention

[0006] The purpose of this invention is to improve the problems of excessive specific surface area and poor electrical performance of existing lithium manganese iron phosphate cathode materials, and to provide a gallium atom iron site doped lithium manganese iron phosphate cathode material prepared using gallium atom ligands as gallium sources and its preparation method.

[0007] The raw materials used in this invention patent are phosphoric acid, lithium carbonate, manganese tetroxide, iron phosphate, gallium nitrate, gallium chloride, gallium trioxide, glycerol, ethanol, and glucose.

[0008] Gallium nitrate was added to a mixture of glycerol and ethanol, and then transferred to a hydrothermal reactor and reacted at 100-250°C for 5-15 hours to obtain gallium atom ligands as gallium sources.

[0009] The amount of gallium nitrate added is 0.1-0.5 mol / L; the volume ratio of glycerol to ethanol is 1:5-5:1.

[0010] Using gallium atom ligands as gallium sources to dope lithium manganese iron phosphate can make it easier for gallium atoms to be doped into the crystal lattice and bind more tightly to metal ions.

[0011] Lithium carbonate is then slowly added to the dilute phosphoric acid aqueous solution, and mixture A is obtained after the reaction is complete. The dilute phosphoric acid aqueous solution is prepared by adding 85% phosphoric acid to 100-300 mL of deionized water and stirring until homogeneous. The mass concentration of the dilute phosphoric acid aqueous solution is 30-70%.

[0012] Lithium carbonate is first reacted in dilute phosphoric acid. This is because the reaction between lithium carbonate and phosphoric acid produces a large amount of carbon dioxide gas, and the reaction is quite vigorous. The gas is eliminated first, and lithium dihydrogen phosphate is generated.

[0013] Manganese tetroxide, ferric phosphate, carbon source, and gallium source were added to the mixture and stirred until homogeneous. The mixture was then poured into a sand mill for grinding, and the particle size D of the milled slurry was controlled. 99 ≤0.6μm, to obtain mixed slurry B. Mixed slurry B is then spray-dried at an inlet temperature of 150-300°C. o C, outlet temperature is 50-100 o C, air flow rate set to 5-10m 3 / h. The dried powder is then fluidized and sintered under an inert atmosphere at a temperature of 400-750°C. o C, sintering time is 5-12h.

[0014] The molar ratio of the raw materials used, lithium carbonate, manganese oxide, iron phosphate, and phosphoric acid, is (0.7-1.3):(0.4-0.8):(0.2-0.5):(1.0-1.3), wherein the molar amounts of lithium carbonate, manganese oxide, iron phosphate, and phosphoric acid are calculated as lithium, manganese, iron, and phosphorus, respectively.

[0015] The manganese oxide is at least one of manganese monoxide, manganese dioxide, manganese trioxide, and manganese tetroxide.

[0016] The carbon source is at least one of sucrose, glucose, polyethylene glycol, polyvinylpyrrolidone, and dopamine hydrochloride, and the carbon content of the finished product is controlled to be 0.5-1.5 wt%.

[0017] Controlling the particle size of the milled slurry output during the sand milling process (B) 99 ≤0.6μm.

[0018] The inert protective gas used in the fluidized bed sintering process is at least one of nitrogen or argon, and the sintering temperature is 400-750°C. o C, sintering time is 5-12h.

[0019] Another technical solution of the present invention is to provide a gallium atom iron site doped lithium manganese iron phosphate cathode material prepared by the above preparation method, wherein the content of gallium atom iron site doping in the finished product is controlled at 1000-10000ppm.

[0020] The gallium atom iron-site doped lithium manganese iron phosphate cathode material and its preparation method invented in this patent have the following characteristics:

[0021] (1) Low raw material cost, abundant manganese and iron sources.

[0022] (2) It is prepared by sand milling and high temperature sintering. The preparation process is simple and can synthesize lithium manganese iron phosphate in large quantities. The experimental scale-up effect is excellent and it is convenient for industrial production.

[0023] (3) The surface morphology of gallium atom iron site doped lithium manganese iron phosphate material prepared by using gallium atom organic ligands as gallium source becomes smoother and flatter, forming a dense sphere, significantly reducing the specific surface area and improving the electrochemical performance. Attached Figure Description

[0024] Figure 1 This is a comparison diagram of the XRD pattern of the sample prepared in Example 1 and the standard card.

[0025] Figure 2 The charge-discharge curves of the sample prepared in Example 1 at 0.1, 0.33, and 0.5C are shown.

[0026] Figure 3 This is an SEM image of the sample prepared in Example 1.

[0027] Figure 4 SEM image of the sample prepared in Comparative Example 1. Detailed Implementation

[0028] Example 1

[0029] 434.12 g of gallium nitrate was added to a mixture of 360 mL of glycerol and ethanol (volume ratio 1:5), and then transferred to a hydrothermal reactor and reacted at 200 °C for 10 h to obtain gallium atom ligands, which were used as gallium sources and denoted as Ga-N.

[0030] 122g of 85% phosphoric acid was added to 300mL of deionized water and stirred until homogeneous to form a phosphoric acid aqueous solution. Then, 37.74g of battery-grade lithium carbonate was added to the dilute phosphoric acid aqueous solution, and after the reaction was complete, mixture A was obtained. 45.76g of manganese tetroxide, 74.74g of ferric phosphate, 27.74g of glucose, and 0.469g of Ga-N were weighed and added to the mixture, and stirred until homogeneous. The diluted slurry was then poured into a sand mill for sand milling to obtain mixed slurry B. Mixed slurry B was then spray-dried with an inlet temperature of 200℃, an outlet temperature of 90℃, and a gas flow rate of 6m³ / h. 3 / h. The dried powder is transferred to a tube furnace and heated under an inert atmosphere at 5... o Heating to 700℃ at a heating rate of C / min and holding for 8 hours yielded gallium-doped lithium manganese iron phosphate material with a gallium doping content of 5000ppm. Figure 1 The image shows a comparison of the XRD pattern of the prepared sample with that of the LiMnPO4 standard card (PDF#74-0375). The image shows that the characteristic peaks are high and sharp, and no impurity peaks were observed, indicating that the doping of gallium atoms does not change the crystal structure of the material. Figure 2 The charge-discharge curves of the prepared lithium manganese iron phosphate at rates of 0.1, 0.33, and 0.5C are shown. At the three different rates, it can contribute a discharge specific capacity of 153.2, 151.1, and 149.8 mAh / g, respectively, demonstrating excellent rate performance. Figure 3 The SEM images show that the prepared sample is a sphere with a diameter of about 8-10 μm, and the surface of the sphere is smooth and dense.

[0031] Example 2

[0032] The operation steps are basically the same as in Example 1, except that the amount of Ga-N added is changed to 0.188g to obtain gallium atom iron site doped lithium manganese iron phosphate material with a gallium doping amount of 1500ppm.

[0033] Example 3

[0034] The operation steps are basically the same as in Example 1, except that the amount of Ga-N added is changed to 0.797g to obtain gallium atom iron site doped lithium manganese iron phosphate material with a gallium doping amount of 8500ppm.

[0035] Example 4

[0036] The operation steps are basically the same as in Example 1, except that Ga-N is no longer used as the gallium source, but gallium trioxide is used as the gallium source for doping. The amount of gallium trioxide added is 1.279g, and gallium atom iron site doped lithium manganese iron phosphate material is obtained with a gallium doping amount of 5000ppm.

[0037] Example 5

[0038] The operation steps are basically the same as in Example 1, except that Ga-N is no longer used as the gallium source, but gallium chloride is used as the gallium source for doping. The amount of gallium chloride added is 0.880g, and gallium atom iron site doped lithium manganese iron phosphate material is obtained with a gallium doping amount of 5000ppm.

[0039] Comparative Example 1

[0040] The operation steps are basically the same as in Example 1, except that no gallium source is added during the feeding process to obtain pure phase lithium manganese iron phosphate material. Figure 4 The SEM images show that the surface of the prepared sample spheres has a large number of pores and is not dense enough, resulting in a large specific surface area of ​​the sample.

[0041] Table 1. Summary of electrical performance and specific surface area results for each embodiment and comparative example.

[0042]

Claims

1. A method for preparing gallium-doped lithium manganese iron phosphate cathode material, characterized in that: Includes the following steps: (1) Add gallium nitrate to a mixture of glycerol and ethanol, and then transfer it to a hydrothermal reactor and react at 100-250℃ for 5-15h to obtain gallium atom ligands as gallium source; (2) Lithium carbonate is slowly added to a dilute phosphoric acid aqueous solution to carry out the reaction. After the reaction is complete, mixture A is obtained. (3) Add manganese oxide, iron phosphate, carbon source and gallium source to mixture A and stir evenly. After grinding and spray drying, fluidize and sinter under inert atmosphere protection to obtain gallium atom iron site doped lithium manganese iron phosphate cathode material. The content of gallium atom iron site doping in the finished product is controlled at 1000-10000ppm. The molar ratio of the raw materials used, lithium carbonate, manganese oxide, iron phosphate, and phosphoric acid, is (0.7-1.3):(0.4-0.8):(0.2-0.5):(1.0-1.3), wherein the molar amounts of lithium carbonate, manganese oxide, iron phosphate, and phosphoric acid are calculated as lithium, manganese, iron, and phosphorus, respectively.

2. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The amount of gallium nitrate added is 0.1-0.5 mol / L; the volume ratio of glycerol to ethanol is 1:5-5:

1.

3. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The mass concentration of dilute phosphoric acid aqueous solution is 30-70%.

4. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The manganese oxide is at least one of manganese monoxide, manganese dioxide, manganese trioxide, and manganese tetroxide.

5. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The carbon source is at least one of sucrose, glucose, polyethylene glycol, polyvinylpyrrolidone, and dopamine hydrochloride, and the carbon content of the finished product is controlled to be 0.5-1.5 wt%.

6. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: Controlling the particle size D of the milled slurry output during the milling process of mixture A 99 ≤0.6μm.

7. The method for preparing a gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The mixture A is atomized and dried under an inert atmosphere, wherein the inert atmosphere is at least one of nitrogen or argon; the inlet temperature for atomization and drying is 150-300°C. o C, outlet temperature is 50-100 o C, air flow rate set to 5-10m 3 / h.

8. The method for preparing gallium atom iron-site doped lithium manganese iron phosphate cathode material as described in claim 1, characterized in that: The inert protective gas used in the fluidized bed sintering process is at least one of nitrogen or argon, and the sintering temperature is 400-750°C. o C, sintering time is 5-12h.

9. The gallium-doped lithium iron phosphate cathode material prepared by the preparation method according to any one of claims 1-8, characterized in that: The content of gallium atom iron site doping in the finished product is controlled at 1000-10000ppm.

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