Large scale green production of ultra-high capacity anode consisting of graphene encapsulated silicon nanoparticles

Abstract

Graphite, which is commercially used as anode material in Li-ion batteries, has a low theoretical capacity of 372 mA h g⁻¹, and therefore should be replaced by an alternative with high capacity and cyclability for the automotive and other applications. The new material should also be capable of being fabricated by energy efficient non-polluting methods at a reasonable cost. This paper reports on the fabrication of a graphene–silicon nanocomposite which meets all these characteristics. High quality graphene was scalably produced by exfoliation of graphite in molten lithium chloride. Graphene nanosheets produced were found to be capable of wrapping silicon nanoparticles injected into the molten salt, leading to the fabrication of graphene encapsulated silicon nanoparticles with a controllable chemical composition. The electrochemical performance of graphene encapsulated silicon nanoparticles was evaluated and compared with that of Si nanoparticles and mechanically blended Si/graphene. The graphene encapsulated silicon nanoparticles exhibited an excellent stable electrochemical lithiation/delithiation performance with the capacity value of about 2000 mA h per gram of silicon at a high current density of 0.5 A g⁻¹. The nanocomposite sample containing 50 wt% Si showed a reversible capacity of 981 mA h g⁻¹ after 260 cycles. By increasing the amount of Si content of the nanocomposite to 91 wt%, the reversible stable capacity increased to 2217 mA h g⁻¹, demonstrating the capability of the molten salt method to correlate the cost and electrochemical performance of the graphene–silicon nanocomposite product.