Next-generation Li-ion battery achieved by the low temperature plasma processes

The automobile industry is currently shifting towards hybrid and electric vehicles powered by electrochemical energy storage systems, or batteries. However, these batteries are less fuel efficient than conventional gasoline systems, and it is therefore important to develop high-performance batteries that have a high energy density, high electromotive force, and a long charge/discharge cycle life. Recently, because of the limited capacity of carbon (graphite) anodes in Li-ion batteries, the development of alternative anode materials that are reactive with Li has been actively promoted. Among these, Si, Ge, and Sn are the most interesting materials because they have high theoretical capacities of 4,200, 1,600, and 993 mAh/g, respectively, which are much higher than the value of 372 mAh/g for conventional carbon active material. In this study, we show an method to fabricate Ge and GeSn nanostructures films for Li-ion-battery anodes with low-temperature plasma. The advantage of our process is that it allows direct fabrication of nanoparticle films on a current collector without pretreatment and temperature control by employing a simple single-step procedure [1,2]. Nanostructured Ge and GeSn films were fabricated by using He radio-frequency magnetron plasma sputtering deposition. Amorphous Ge and GeSn nanoparticles were arranged without aggregation by off-axis sputtering deposition in the high He-gas-pressure range of 0.1 Torr. The Ge film porosity was over 30%. We tested the charge/discharge cycle performance of Li-ion batteries with nanostructured Ge and GeSn anodes.The GeSn anode (3at% Sn) achieved a higher capacity of 1,128 mAh/g after 60 cycles with 92% capacity retention. Precise control of the nano-morphology and electrical characteristics by a single step procedure using low temperature plasma is effective for stable cycling of high-capacity Ge anodes.

[1] G. Uchida et al., Sci. Rep. 12, 1701 (2022). [2] J. Hayashi et al., Jpn. J. Appl. Phys. 61, SA1002 (2021).