Energy storage has become a key issue because of the increasing demand for electronic devices, electric vehicles and large-capacity energy storage system. Among the various energy storage systems, lithium-ion batteries have dominated the power sources for portable electronics over the past decades and are now powering electric vehicles. In order to further improve the energy density of lithium-ion batteries, silicon-based anode materials have been actively studied. Silicon has a high theoretical capacity, a low reduction potential, is environmentally benign and is low cost, making it attractive candidate for next-generation lithium-ion batteries. However, the silicon-based materials undergo large volume changes during the alloying/de-alloying reaction, resulting in pulverization of the electrode. In addition, the large volume change results in the continuous breakdown and formation of solid-electrolyte interphase (SEI) layer during the repeated cycling which results in a serious capacity decline during the repeated cycling. To solve these problems, many studies have been carried out by different approaches such as controlling the particle size and morphology, alloying with inert metals, embedding silicon in a conductive material, and applying several functional binders.
In this work, we synthesized Si-based alloy materials composed of Si, Al, Fe and Ti, which could deliver a high specific capacity of 1200 mAhg-1. They were double-layer coated by porous reduced graphene oxide (porous r-GO) and poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG) to suppress volume change of Si alloy and irreversible reaction of the electrolyte solution with Si alloy. Double-layer coating of Si alloy materials with porous r-GO and PEDOT-co-PEG was confirmed by FE-SEM, HR-TEM, XRD and EDS. The protective double layer formed on the surface of Si alloy materials effectively maintained the electrode structure without severe volume change and significantly improved the cycling stability as compared to pristine Si alloy material. Detailed characterization and electrochemical performance of the pristine, single-layer and double-layer coated silicon alloy materials will be presented.