Influence of Sn content on microstructure and electrochemical properties of Sn–NiTi film anodes in lithium ion batteries

Sn–NiTi composite thin films consisting of different amounts of Sn, prepared by directly co-sputtering pure Sn and NiTi alloy, have been characterized as anodes for lithium ion batteries. The composite films with relative low Sn content (20.2, 25.2 wt%) had a microstructure of microsized Sn particles uniformly dispersed in the porous a-NiTi matrix. In contrast, in the film with a higher Sn content (39.0 wt%), a part of the Sn reacted with NiTi to formed Ni3Sn4 intermetallic surrounding the Sn. The inactive NiTi covered and protected most of the surface of Sn in these composite films and resulted in quite low initial irreversible capacity losses and greatly enhanced cycle performances. The results showed that the Sn–NiTi film with 39.0 wt% Sn delivered higher reversible capacity and superior capacity retention, which was attributed to the interfacial reaction between Sn and NiTi phases, as well as the good electrochemical reversibility of nanocrystalline Ni3Sn4 formed in NiTi matrix.

► Sn–NiTi films with different Sn contents were deposited on Cu by co-sputtering.
► The NiTi–20.2%Sn film had microsized Sn dispersed in porous amorphous NiTi matrix.
► Nanocrystalline Ni3Sn4 formed and surrounded outside the Sn in NiTi–39%Sn film.
► The NiTi–39%Sn film yielded better performance due to the existence of Ni3Sn4.