Effect of SnCl2 addition on the structure and lithium storage performance of SiOC anodes

Sn/SiOC composites with varying Sn content were prepared by the sol–gel method with phenyltriethoxysilane (PhTES) and Tin(II) chloride dihydrate (SnCl 2 ·2H 2 O) as precursors. The effect of SnCl 2 addition on the microstructure, morphology and lithium storage performance of SiOC anodes was investigated. Incorporation of SnCl 2 not only reduces carbon-contained units of SiOC ceramics, but also increases the oxygen-containing functional groups on the surface of carbon during the pyrolysis conversion. The formation of Sn involves carbothermal reduction reaction of SnO 2 with the free carbon, and the degree of carbothermal reduction increases with the increase of Sn/Si ratio, which results in the reduction of carbon content and destruction of SiOC matrix. The size of Sn nanograins increases from 20 nm to 450 nm with the increasing Sn/Si ratio. The rate capability of Sn/SiOC composites increases first and then decreases with the increase of Sn content. The SiOC and Sn-PhTES-0.15 derived Sn/SiOC composite exhibit better electrochemical performance, which delivers a stable reversible capacity of 485 mAh g −1 and 411 mAh g −1 , respectively at 186 mA g −1 after 250 cycles. The uniform dispersed Sn nanograins (below 20 nm), Si O C structure units and the free carbon phase both contribute to better electrochemical properties. However, the free carbon provides a higher reversible capacity than that of Sn and Si O C units, which results in the inferior lithium storage capacity of Sn/SiOC composites.