Unveiling voltage evolution during Li plating-relaxation-Li stripping cycling of lithium-ion batteries

The unwanted Li plating on graphite anode surface in lithium-ion batteries causes poor cycling performance along with raised safety risk once Li dendrites penetrate separator. Voltage characteristics during relaxation and discharging have been recognized as the most direct and convenient indictor for Li plating detection, where unveiling voltage evolution during plating-relaxation-stripping cycling needs to be emphasized to facilitate Li plating detection. This study fabricates Li|graphite cells to implement Li plating-relaxation-stripping protocols through over-lithiation before internal short circuit, and the Li nucleation-growth process is linked to voltage evolution assisting with the post-mortem approaches. The Li plating voltage initially displays continuous decline indicated as Li nucleation, until the formation of Li plating plateau indicated as Li growth. The plating-relaxation-stripping voltage patterns show highly correlation that the occurrence of Li plating plateau exactly corresponds to the appearance of a mixed relaxation plateau attributed to the equilibrium of Li stripping and Li re-intercalation into graphite, while the disappearance of the mixed relaxation plateau just corresponds to the advent of Li stripping plateau. Three stages are finally divided associated with characteristic Li plating -relaxation-stripping voltage patterns, where Stage I indicates the occurrence of Li plating plateau behaving as predominant LixC6; Stage II is characterized as the occurrence of mixed relaxation plateau manifested as Li coexisting with LixC6; Stage III is distinguished by the appearance of Li stripping plateau indicated as predominant Li and dead Li. This work proposes underlying evolution mechanism of Li plating-relaxation-stripping cycling, which contributes to sufficient evidence for reliable Li plating detection.