Grain boundary optimization in Li–Mg alloy anodes via controlled cooling rates and cold rolling

Abstract

The commercialization of Li-metal batteries is primarily hindered by the poor stability and safety risks associated with the use of Li-metal anodes. As an alternative, research is being conducted to improve the stability of anodes using Li–Mg alloys. However, after Li stripping, Li-poor Li–Mg alloys lower the usability of Li; moreover, the mechanism by which the cycling characteristics improve when the grain boundary density increases remains obscure. In this study, we controlled the grain size of Li–Mg alloys by adjusting the cold rolling and solidification rates, and investigated the effect of grain boundaries on the deposition and stripping characteristics of Li⁺ ions. Thus, an Li-rich Li–Mg phase was formed at the grain boundaries when casting Li–Mg alloys. As the grain boundary density increased, more sites with preferential Li⁺ deposition and stripping were observed, leading to a reduction in the overpotential and improved cycling characteristics. An optimized grain size was discovered through symmetric cell tests of the Li–Mg alloys with various grain sizes ranging from 7 to 298 μm, and a superior cycling performance of up to 1500 h (375 cycles) was achieved at the optimal grain size. These results are expected to provide an important foundation for the development of stable and safe Li-metal anodes using Li–Mg alloys.