Propelling performance of silicon thin film lithium ion battery by appropriate dopants

Although pristine silicon (Si) has been employed as a high-capacity anode material, high performance of Si-based lithium-ion battery (LIB) still remains challenging constrained mainly by low intrinsic electrical conductivity of the semiconductor. This drawback can be addressed by doping Si with group III and V elements; nevertheless, a systematic study on the doping species is rarely reported. Herein, the effects of dopants (boron and arsenic) in Si thin film anodes, prepared by electron beam evaporation from different target materials (including pristine, p-type, and n-type Si), on the performance of LIB are investigated. In a coin cell configuration, the doped Si films are inferior to the pristine counterparts in terms of irreversible capacity loss at the first circle, possibly due to incorporation of more lithium ions with a higher conductivity in the former. Intriguingly, boron and arsenic ions are demonstrated as regulating dopants that can deteriorate (for the former) or enhance (for the latter) the capacity retention and rate capabilities of the pristine Si-based LIBs. Electrochemical impedance spectroscopy and microstructure characterizations reveal that the high electrical conductivity and chemical reactivity of boron ions with electrolytes aggravate the formation and propagation of cracks into the depth during cycling and thicken the thickness of solid electrode interphase, consequently increasing charge transfer impedance. This study clarifies the working mechanisms of different doping species in the Si thin film anodes in response to electrochemical cycling and shed light on the improved performance of thin film based LIBs with appropriate dopants.