Tin-based materials have been arousing extensive interest for using as anode electrodes in the field of lithium ion batteries (LIBs) due to the fact that Sn could alloy with Li to form Li_4.4Sn and deliver extremely high capacity of 994 mAh g^-1. However, the significant volume change of Sn particles during charge-discharge cycles hinders the practical use of Sn-based materials. One possible solution to this volume-change issue is to switch bulk material to thin-film material, which could effectively reduce stress caused by the large volume change upon cycling.

In this work, SnS-SnSe composite thin films are synthesized by plused laser deposition method. The initial discharge capacity of SnS-SnSe composite film is 1225.8 mAh g^-1. The reaction mechanism of the composite with Li has been investigated. It is revealed that SnS-SnSe composite thin film firstly reacted with Li during discharge to form Li₂S、Li₂Se and Sn, then Sn reacted with Li to form Li_xSn alloy. During charge process, Li_xSn firstly decomposed to form elementary Sn, then Sn catalyzed Li₂S and Li₂Se to decompose to reform SnS-SnSe composite thin film. Li₂S and Li₂Se produced during discharge process act as buffer material which might release stress caused by volume change, thus enhancing cycling performance of the component film. Additionally, SnS-SnSe composite thin film possesses more grain boundaries than single SnS or SnSe thin film, which could effectively enhance electrochemical activity and contribute to the capacity increment.