SiO_x coated graphite with inorganic aqueous binders as high-performance anode for lithium-ion batteries

Inorganic aqueous binders (IAB) are an emerging class of aqueous binders. They offer exceptional physicochemical properties like intrinsic ionic conductivity, high thermal stability (>1000 degrees C), and environmental benignity making them attractive. In a previous study, we found that graphite anode shows improved electrochemical performance with these binders as compared to conventional PVDF binder for lithium-ion batteries (LIB). However, the cyclic performance of graphite-IAB at a higher rate (e.g., 1C) showed a declining trend. We attributed it to the poor binding strength between graphite and IAB due to insufficient functional groups in graphite. Therefore, in this report SiOx-based surface coatings of graphite are employed to improve its rate capability with silicate-based IAB by providing functional silicon oxide polymorphs on the coated graphite as an intermediate layer. The nature and structural arrangement of these coatings are investigated by tip-enhanced Raman spectroscopy (TERS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Optimized SiOx-coated graphite (GS) with sodium metasilicate binder leads to excellent cyclic stability with a capacity retention of >90 % at 20C for >4000 cycles. A high specific capacity of >315 mAhg(-1) at 2C, stable for over 1000 cycles, is achieved for GS with IAB. The improved performance of the coated graphite is attributed to ameliorated binding with IAB as well as stable solid electrolyte interphase. We propose inorganic aqueous binders in combination with SiOx-coated graphite as an approach to realize a stable anode for LIB.