High Areal Capacity Bismuth Films for Li-Ion Batteries of High Energy Density and Rate

Bismuth films deposited by electron beam deposition were explored as a potential negative electrode material in Li-ion batteries of high power, high volumetric energy density, and areal capacity in excess of 3 mAh cm −2 . The effects of lithiation/delithiation rates on film cycle life are discussed along with nuances with respect to film thickness. The rate performance of the Bi films was evaluated, surpassing the critical combination of areal capacities and areal currents previously reported for Li alloy intermetallic films in literature. The observed areal current density, C rate capability, areal capacity, and volumetric capacity show promise, enabled by the superionic Li 3 Bi phase. Cycle life is further improved as a result of a kinetically stabilized Li 2 Bi phase first reported here in a pure Bi film. The mechanism behind the formation of the metastable phase was explored through the use of in situ X-ray diffraction and electrochemical impedance spectroscopy.