A facile and low-cost Al2O3 coating as an artificial solid electrolyte interphase layer on graphite/silicon composites for lithium-ion batteries

Graphite/silicon (G/Si) composites are considered as possible alternative anode materials to commercial graphite anodes. However, the unstable solid electrolyte interphase (SEI) on G/Si particles results in rapid capacity decay, impeding practical applications. Herein, a facile and low-cost Al2O3 coating was developed to fabricate stable artificial SEI layers on G/Si composites. The amorphous Al2O3 coating with a thickness of 10-15 nm was synthesized by a simple sol-gel method followed by high-temperature annealing. The Al2O3 coated G/Si anode delivers an initial discharge capacity of 540 mAh g-1 at 25 °C and has improved Coulombic efficiency and cycling stability. After 100 cycles, the capacity retention is 76.4%, much higher than the 56.4% of the uncoated anode. Furthermore, the Al2O3 coating was found to be more effective at improving the stability of G/Si at a higher temperature (55 °C). This was explained by the Al2O3 coating suppressing the growth of SEI on Si/G and thus reducing the charge transfer resistance at the G/Si-electrolyte interface. It is expected that the Al2O3 coating prepared by the sol-gel process can be applied to other Si-based anodes in the manufacture of practical high-performance lithium-ion batteries.