Revealing the onset condition of Li plating on graphite electrodes under fast-charging

Abstract

Li plating on graphite-based electrodes is the primary issue hindering the fast charging of electric vehicle batteries. Although wide attention has been paid to this topic, the fundamental understanding of Li plating onset is still under debate (concentration control or potential control?) due to overpotential coupling and highly localized deposition in porous electrodes. Here, the Li plating reaction overpotential and surface equilibrium potential of graphite are first measured separately from the overall voltage by the decoupling measurement technique developed in our previous work. It is found that a Li plating reaction overpotential of <0 V triggers Li plating on graphite electrodes under fast charging, rather than the commonly believed voltage (graphite vs. Li/Li⁺) of <0 V or surface concentration saturation. Based on the overpotential criterion, electrochemical modeling well predicts Li plating/stripping behavior on porous graphite electrodes and reveals different limiting processes leading to Li plating which can be reconciled by this overpotential-control mechanism. Experimental demonstration is given by the cases of regulating interface Li⁺ intercalation and liquid-phase ion transport. This work clarifies the onset condition of Li plating and indicates the optimization directions of fast-charging graphite electrodes.