Efficient Preparation of Li2FeSiO4/C with High Purity and Excellent Electrochemical Performance in Li-Ion Batteries.

One method to enhance the electrochemical performance of carbon-coated Li2FeSiO4 cathode material in lithium-ion batteries is to produce an ideal Li2FeSiO4 precursor with minimal impurities. A novel precursor for Li2FeSiO4 (Li2O·FeCO3·CH3OSiO2H) was synthesized through a methanol solvothermal reaction under stringent conditions (180 °C and 2.7 MPa), achieving a purity level of 93.2%. During synthesis, the new Li2FeSiO4 precursor exhibits unique self-purification properties and maintains a fine morphology after annealing. The resulting carbon-coated Li2FeSiO4 composites demonstrate a Brunauer-Emmett-Teller specific surface area of 102.4 m2/g and approximately 81% mesoporous volume, with 90% of the pore sizes measuring less than 39 nm. As a cathode material for lithium-ion batteries, this carbon-coated Li2FeSiO4 exhibits initial specific capacities of 172.3 mAh/g (charge) and 159.3 mAh/g (discharge). Remarkably, nearly 50% of the theoretical specific capacity remains after 1300 cycles at a rate of 0.1 C. The excellent electrochemical performance of the carbon-coated Li2FeSiO4 materials is demonstrated by their high lithium-ion diffusivity (DLi+) value of 1.26 × 10-11 cm2/s. Additionally, the enormous capacities-controlled diffusion contribution, which accounts for 70% of the total diffusion at a rate of 1C, is noteworthy. This performance can be attributed to the high purity of the carbon-free Li2FeSiO4 composite, which contains 91% Li2FeSiO4, as well as its favorable morphology.