Revealing the Overlithiation Effect on Cycling and Calendar Aging of the Silicon/Graphite Electrode for High-Energy Lithium-Ion Batteries

Abstract

Lithium (Li) plating, triggered by fast charging and low temperature, will cause performance degradation and safety concern for lithium-ion batteries (LIBs). However, the strategically limited and controlled Li deposition might be advantageous for enhancing energy density. The detailed mechanism and regulation for performance improvement remain yet to be fully unexplored. This study meticulously modulates the overlithiation capacity to regulate the Li plating and probes its effects on the stability of high-capacity silicon/graphite (Si/Gr) electrodes through consecutive cycling and over the calendar aging period. In the Si/Gr electrode (20 wt% Si) with a 20% overlithiation degree exhibits enhanced reversible capacity in comparison to the pristine Si/Gr electrode. This improvement is attributed to precision-controlled Li deposition, the increased electrochemical utilization of Si and Gr above 0 V, and the additional intercalation/alloying reactions below 0 V, which decelerate the progression of capacity degradation and significantly boost the electrochemical performance of Si/Gr electrodes. Moreover, this tailored Si/Gr electrode with a 20% overlithiation degree attenuates the deterioration associated with calendar aging. This research not only elucidates the intricate interplay and mechanisms of Li plating on Si/Gr electrodes during overlithiation but also presents new understanding and approach to advance the LIBs' performance and extend their service lifespan.