Novel Li/Li_xSn_y thin film designed as an anode for lithium-ion microbatteries

Miniaturization of lithium-ion batteries has become an extremely hot topic with the rapid development of microelectronic devices. Li metal being the most desirable anode has disadvantages in terms of dendrite formation, huge volumetric change of Li and its stripping and loss during cycling, etc., which restricts its application. The formation of well-matching interfaces is a key requirement to construct safe all-solid-state microbatteries. Herein, we show that a small addition of Sn to Li film anode is a promising solution, because this lithium-tin (Li_xSn_y) alloy can overcome some critical obstacles of lithium anode. The Li/Li_xSn_y thin film anode was deposited by a combination of magnetron sputtering and thermal evaporation on a copper foil substrate, electrochemically tested in comparison with pure Sn and Li anodes. These studies revealed that this anode with the preformed Li₂Sn₅ alloy demonstrated remarkably improved characteristics its counterparts. The Li/Li_xSn_y electrode showed a higher initial capacity and better cyclability during 100 charge-discharge cycles than monolithic Sn, and a lower overpotential, than monolithic Li. Among two Li/Li_xSn_y thin film electrodes with the thicknesses of 500 nm and 1000 nm of deposited Sn and Li layers, the latter one demonstrates a better stability against degradation, providing sufficient reservoirs of Li ions (Li regions) and easy pathways for them via Li_xSn_y alloy.