Preparation of Sioc Li-Ion Capacitor By TEOS Based Sol-Gel Method with Different Silicones Precursors

Abstract

Since the development of Li ion battery, carbonous materials e.g. graphite had been widely used in commercial lithium-ion batteries. However, the practical capacity of graphite reached an almost theoretical limit. Therefore, promising anode materials, such as Sn, Si etc. have been considered to replace the graphite though they are not stable during charge-discharge cycles. It was recently reported that amorphous SiOC anode performs high capacity and superior cycling durability. SiOC material has high chemical stability and mechanical strength. In this study, we used a TEOS based sol-gel method with different silicones precursorsto synthesize SiOC directly on the Cu foil as a simple and cheap way. The silicones used in this study were PDMS(dimethylpolysiloxane), silanol- terminated PDMS, Cyclotetrasiloxane, polyether-modified silicone, alkyl-modified silicone and phenol-modified silicone. They were mixed respectively with TEOS (Tetraethyl orthosilicate), which was considered to perform a sol-gel reaction, and water in ethanol. The mole ratio of the TEOS/ silicone / H2O was 1:1:4, and the volume ratio of the mixture and ethanol was 1:1. 10 μl of HCl(37wt%) was added as catalyst before stirring. The sol solution was spin-coated onto the Cu foil. We evaluated these kinds of anode by battery charge-discharge test. Pore distribution and composition was measured by small angle X-ray scattering (SAXS) and X-ray photoelectron spectrometry, respectively. Amorphous SiOC thin films with all precursors showed a high cycling durability. The SiOC film from PDMS sol solution which was heated to 50ºC for 30 minutes during stirring achieved a best specific discharge capacity of about 1050 mAh/g even after 100 cycles, others are distributed from 150-400mAh/g. The SAXS of this sample shows a stronger peak of micropores(pore size <6 nm)than other samples. As a contest, we repeated the experiment without TEOS, and it became pyrolysis of silicones. The anodes made during the contest experiment showed low cycling durability but higher average specific capacity.