Elucidating ‘Transfer‐Lithiation’ from Graphite to Si within Composite Anodes during Pre‐Lithiation and Regular Charging

AbstractSi‐based anodes can increase specific energy and energy density of Li ion batteries. However, the volume‐induced material stress and capacity loss necessitates only a partial Si utilization within composite anodes, typically with state‐of‐the‐art graphite, so called Si/Gr composites. In this work, various Si nanowires (SiNWs), a promising Si architecture for these composites, are investigated and modified via pre‐lithiation. Though, charged pre‐lithiated anodes show potentials below 0 V vs. Li|Li+ in the initial cycles, they do not show indications for metallic Li, which is likely a hint for a triggered surface Li depletion in course of a continuous “transfer‐lithiation” from lithiated Gr to Si, which is indicated by decreasing LiC6 and increasing LixSiy signals via nuclear magnetic resonance (NMR), X‐ray diffraction (XRD) as well as shifts in capacities of respective voltage plateaus during discharge after storage. A relevant contribution of self‐discharge is unlikely as shown by a stable open‐circuit‐voltage during storage in charged state and similar subsequent discharge capacities, being consequently a hint for an intra‐electrode capacity shift. The process of transfer lithiation is finally validated via solid‐state 7Li NMR for varied Si morphology, i. e., amorphous and crystalline, as well as during pre‐lithiation with passivated lithium metal powder (PLMP).