Rapid fabrication of a novel Sn–Ge alloy: structure–property relationship and its enhanced lithium storage properties

A rapid solidification and high throughput melt spinning process is developed for the fabrication of new Sn-Ge alloys as anodes for high capacity lithium-ion batteries. Compared to pure micron-sized Sn and Ge, the alloy possesses enhanced lithium storage properties. High, reversible and stable capacities of over 1000 mA h g super(-1) are maintained over 60 cycles at 0.1 C. A good rate capability of 500 mA h g super(-1) at 5 C is also achieved, making it very attractive for very fast charge/discharge applications. More remarkably, it has a tap density of 2.05 g cm super(-3) and thus high volumetric capacities of 2050 mA h cm super(-3) at 0.1 C and 1025 mA h cm super(-3) at 5 C. The electrode was investigated via ex situXRD, EXAFS and TEM at various cut-off voltages during the first cycle and after the first cycle to establish the structure-property relationship. The Sn-Ge alloy is observed to undergo a transformation from the crystalline Sn-Ge alloy into phase separated nanocrystalline Sn in an amorphous Ge matrix. The excellent lithium storage properties exhibited by Sn-Ge are attributed to the synergistic effect between the phases and the phase transformation occurred.