Electrochemical Preparation of Si Based Anode Material in Molten CaCl2

Abstract

Graphite, which is commercially used as anode material in lithium-ion battery (LIB), has a low theoretical capacity of 372 mAh/g, and therefore should be replaced by alternative material with high capacity for the toward vehicles and other applications. Not only that, the cost and environmental issues should be considered in the production of alternative materials. In this regard, silicon materials have received the extensive research interest due to their high specific capacity of 3579 mAh/g, a low lithiation reaction voltage plateau (vs. Li/Li+) and abundant sources. Unfortunately, Si electrode typically suffers from irreversible capacity fading during cycling from their volume expansion and low intrinsic electronic conductivity. Recently, development of nanostructural design with various morphologies, Si nanowires, Si nanoparticles, and porous structures has received attention as a promising way to solve these problems. Nanostructural design largely improve cycle life by providing a sufficient free volume to accommodate silicon electrode expansion. However, commercially utilization of Si electrode is still insurmountable owing to some critical issues such as high costs, poor scalability and hazardous precursors. Furthermore, nanostructure Si includes severe side reactions due to a large surface area, low tap density. Here, we simply use the SiO2+Graphite mixture as the starting material and synthesize Si@SiC@Graphite composite material through electro-deoxidation method applied with the FFC Cambridge process, a simple approach for the high-purity extraction of metals from solid oxides via molten salt electrolysis that is known to be energy-saving and environmentally friendly. The electro-deoxidation was carried out in a molten CaCl2 at 1123 K in cell voltage of 2.6 V and 2.9 V. As an anode material, the prepared Si@SiC@graphite composite resolves all of the aforementioned critical issues and shows 900 mAh/g after 300 cycles without capacity fading. Furthermore, we fabricated high tap-density Si@SiC@graphite powder (~ 0.76 g/ml) using a mechanical pressing method, resulting in a high capacity (> 3.0 mAh/cm2) at the large loading of cathode, verifying the successful design of stable electron transfer and high dense structure.