In Operando Detection of the Onset and Mapping of Lithium Plating Regimes during Fast Charging of Lithium-ion Batteries.

Existing in operando methods for detection of plated lithium can only detect the presence of plating after the charge is complete and irreversible damage has already occurred. In this work, the characteristic potential minimum on the graphite electrode during high rate lithiation is proposed and assessed as an in operando technique for detecting the onset of lithium plating. While other studies have shown that rapid self-heating of a cell can cause this type of "voltage overshoot," we confirm through temperature-controlled coin cell experiments that such a voltage profile can also be caused by the occurrence of severe lithium plating. In cells which demonstrated voltage overshoot, macroscopically observable lithium plating films were present on the graphite electrodes upon disassembly, resulting in very poor single-cycle Coulombic efficiency. The significance of this voltage characteristic is confirmed through direct observation of the onset of lithium plating in an in-situ optical microscopy cell. We observe that the growth of large metallic lithium deposits within the porous electrode structure can cause swelling and cracking of the graphite electrode, suggesting loss of active material due to mechanical electrode degradation as an important consequence of severe lithium plating.