Abstract
Using pulse electrolysis, Ni-Sn alloy films of three compositions (NiSn9, Ni2Sn8, and Ni3Sn7) were prepared for a negative electrode. FESEM observations indicated that the crystal grain size of the film decreased, and that the film was densified with increased Ni contents. Tape tests indicated that adhesion between the film and a current collector increased concomitantly with increased Ni content. The galvanostatic charge-discharge tests indicated that the capacity retention rate at the 30th cycle rose with increased Ni content. Ex-situ FE-SEM observations indicated that cracks in the film were generated in the Ni2Sn8 and Ni3Sn7 alloy films after the first discharge. Ex-situ XRD measurements showed that the charge-discharge reaction of the Ni3Sn7 alloy film was attributable to alloying/dealloying a Ni3Sn4 phase with lithium. No β-Sn phase was extricated after the first discharging. In addition to the decrease in the crystal grain size and the increase in the adhesion between the film and the current collector along with increase in the Ni content, results showed that cycle performance can be improved if extrication of the β-Sn phase can be repressed, even if a crack is generated in the film during charging and discharging.
