Pre-Lithiation of Silicon Anodes by Thermal Evaporation of Lithium for Boosting the Energy Density of Lithium Ion Cells

Silicon (Si) is one of the most promising anode candidates to further push the energy density of lithium ion batteries. However, its practical usage is still hindered by parasitic side reactions including electrolyte decomposition and continuous breakage and (re-)formation of the solid electrolyte interphase (SEI), leading to consumption of active lithium. Pre-lithiation is considered a highly appealing technique to compensate for active lithium losses. A critical parameter for a successful pre-lithiation strategy by means of Li metal is to achieve lithiation of the active material/composite anode at the most uniform lateral and in-depth distribution possible. Despite extensive exploration of various pre-lithiation techniques, controlling the lithium amount precisely while keeping a homogeneous lithium distribution remains challenging. Here, the thermal evaporation of Li metal as a novel pre-lithiation technique for pure Si anodes that allows both, that is, precise control of the degree of pre-lithiation and a homogeneous Li deposition at the surface is reported. Li nucleation, mechanical cracking, and the ongoing phase changes are thoroughly evaluated. The terms dry-state and wet-state pre-lithiation (without/with electrolyte) are revisited. Finally, a series of electrochemical methods are performed to allow a direct correlation of pre-SEI formation with the electrochemical performance of pre-lithiated Si.