Improving the electrochemical properties of a SiO@C/graphite composite anode for high-energy lithium-ion batteries by adding lithium fluoride

Silicon monoxide has attracted wide interest as a negative material for lithium-ion batteries because of its high theoretical capacity. Moreover, in this paper, lithium fluoride serves as an additive, which can improve the initial coulombic efficiency of silicon monoxide-based electrodes. This work develops a simple two-step method to prepare a lithium fluoride-modified SiO@C/graphite composite as an anode for lithium-ion batteries. First, SiO@C is prepared via a chemical vapor deposition method; then, SiO@C/graphite-LiF is obtained by mixing SiO@C, graphite and LiF in a stirrer. The phase composition, particle appearance and electrochemical properties of the SiO@C/graphite-LiF composites are characterized via X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge and discharge analyses. The SiO@C/graphite-7.5% LiF composite shows a high capacity retention rate of over 91% after 100 cycles. The capacity of SiO@C/graphite-LiF is close to 200 mAh g(-1) at 3.2 A g(-1), which is much higher than that of SiO@C/graphite (only 21 mAh g(-1)). This result is mainly because Li ion transport is improved during the lithiation/delithiation process and stabilizes the solid electrolyte interface layer due to lithium fluoride addition. The encouraging results suggest that adding lithium fluoride to SiO-based materials is an effective strategy to improve the electrochemical properties and can be applied to high-energy storage systems.