The electrochemical properties of $SnO_2$ and $SnN_x$ thin films prepared by reactive RF magnetron sputtering method were investigated by cycling experiment with giving cut-off voltage and current density in 1M $LiClO_4$ PC(propylene carbonate).
The deposited tin oxide thin films decompose into metallic tin and $Li_2O$ during lithium insertion and $Li_2O$ makes irreversible capacity loss. After first cycle, reversible cycling occurs by Li-Sn alloying/dealloying. As the deposition temperature increases, the crystallinity becomes better and discharge capacity increases until 300℃. After second cycle, the discharge capacity increases gradually and this is due to the increase of the particle size(aggregation) of metallic tin.
The tin nitride thin films show similar electrochemical properties with the tin oxide thin films. The irreversible capacity loss occurs at the first cycle and then reversible cycle is proceeded. Ex-situ XRD study shows that the tin nitride decomposes and only metallic tin takes part in cycling after the first cycle. So the tin nitride have the same properties with the tin oxide, and proposed charge/discharge mechanism is $SnN_x$ + Li → Li-N compound + Li-Sn alloy ↔ Li-N compound + Li + Sn.
As the working pressure increases from 10mtorr to 40mtorr, the crystallinity becomes better and capacity retention is improved. The discharge capacity increases until 30mtorr.
The working pressure is fixed to 30mtorr and as the deposition temperature increases from room temperature to 300℃, the crystallinity becomes better and good capacity retention property was observed at room temperature, 100℃, and 200℃. And this makes the tin nitride thin film a promising negative electrode for lithium microbattery.
