Lithium ferrous silicate anode material coated with crystalline carbon and preparation method thereof

[0022] Example 1:

[0023] Using lithium acetate dihydrate, ferric nitrate, and ethyl orthosilicate as raw materials, weigh the corresponding substances according to the molar ratio of the substances to make the molar ratio of Li:Fe:Si 2:1:1, and measure 1.8ml of ethyl orthosilicate Ester was added to 15ml of ethanol with constant stirring, 0.32ml of acetic acid was added dropwise, 1.640g of lithium acetate was accurately weighed and added to the above mixed solution, after dissolution, 3.256g of ferric nitrate was added, 1.057g of ascorbic acid was mixed into a saturated aqueous solution and added dropwise to In the above-mentioned mixed solution, the mixed solution is transferred to a reaction kettle and reacted at 120°C for 20 hours to obtain a gel mixture, which is then dried in a drying box at 60°C to obtain a dry gel. The dry gel is crushed, pressed into tablets, in N 2 Under the protection of the atmosphere, calcined at 650°C for 10 hours to obtain carbon-coated lithium iron silicate powder. Li 2 FeSiO 4 The XRD pattern of /C is as figure 1 As shown, the characteristic peak of XRD and standard Li 2 FeSiO 4 The diffraction peaks of the powder XRD pattern correspond. Among them, the peak near 26.5° is the diffraction peak of graphite (PDF# 65-6212), indicating that the coated carbon is crystalline graphite. Synthetic powder Li 2 FeSiO 4 /C looks like figure 2 As shown, the particle size is between 50 and 120 nm, and the carbon content is 10.1 wt.%. Li 2 FeSiO 4 The cycle curve of /C composite material is as Figure 5 As shown, under the C/16 rate, the initial discharge capacity is 150.3mAhg -1 After 40 cycles, the specific capacity is 137.2mAhg -1.

[0024] Example 2:

[0025] Using lithium acetate, ferric nitrate, and ethyl orthosilicate as raw materials, weigh the corresponding substances according to the molar ratio of the substances so that the molar ratio of Li:Fe:Si is 2:1:1, measure 1.8ml of ethyl orthosilicate and add In 10ml of ethanol with constant stirring, add 0.32ml of acetic acid dropwise, accurately weigh 1.640g of lithium acetate and add to the above mixture, after dissolution, add 3.256g of ferric nitrate, and 0.700g of ascorbic acid into a saturated aqueous solution, and add dropwise to the above mixture In the solution, the mixed solution is transferred to the reaction kettle and reacted at 120°C for 5 hours to obtain a gel mixture, which is then dried in a drying box at 60°C to obtain a dry gel. The dry gel is crushed, pressed into tablets, in N 2 Under the protection of the atmosphere, it was calcined at 650°C for 7 hours to obtain carbon-coated lithium iron silicate powder. Synthetic powder Li 2 FeSiO 4 The microstructure of /C is as image 3 As shown, the carbon content is 5.3 wt.%, and the particle size is between 70 and 150 nm. The charge-discharge test was carried out under the same conditions as in Example 1, and the initial discharge capacity was 125.7mAhg under C/16 rate -1.

[0026] Example 3:

[0027] Using lithium acetate dihydrate, ferric nitrate, and ethyl orthosilicate as raw materials, weigh the corresponding substances according to the molar ratio of the substances to make the molar ratio of Li:Fe:Si 2:1:1, and measure 1.8ml of ethyl orthosilicate The ester was added to 18ml of ethanol and kept stirring, 0.32ml of acetic acid was added dropwise, 1.640g of lithium acetate was accurately weighed and added to the above mixture, after dissolution, 3.256g of ferric nitrate was added, and 1.929g of ascorbic acid was mixed into a saturated aqueous solution and added dropwise to In the above-mentioned mixed solution, the mixed solution is transferred to a reaction kettle and reacted at 180°C for 5 hours to obtain a gel mixture, which is then dried in a drying box at 60°C to obtain a dry gel. The dry gel is crushed, pressed into tablets, in N 2 Under the protection of the atmosphere, calcined at 750°C for 10 hours to obtain carbon-coated lithium iron silicate powder. Synthetic Li 2 FeSiO 4 /C powder is assembled into a battery, and its AC impedance spectrum is as Figure 4 As shown, when the test frequency range is 0.1 Hz to 100 kHz and the test temperature is 25°C, the charge transfer resistance Rct is 255Ω. In this composite material, the carbon content is 14.6% by weight, and the particle size is between 100 and 200 nm. The charge and discharge test is carried out under the same conditions as in Example 1. The initial discharge capacity is 135.9mAhg at C/16 rate. -1.