Mapping the Distribution and the Microstructural Dimensions of Metallic Lithium Deposits in an Anode-Free Battery by in Situ EPR Imaging

Understanding the global process of Li plating and stripping on the electrode surface is of great importance for developing next-generation Li-ion batteries with high safety. The noninvasive electron paramagnetic resonance imaging (EPRI) technique can monitor the variation in Li deposits inside a battery during charge and discharge while preserving the pristine state of the electrode. In this study, using an anode-free battery as a model system, we obtained the semiquantitative distribution of Li deposits via in situ spatial-spatial EPRI and estimated the sizes of the Li microstructures via in situ spectral-spatial EPRI. Operando EPR spectra were recorded during the period between imaging experiments as a byproduct. The images showed that some local excessive deposits are formed during plating, which could lead to dead Li during stripping. In addition, it is found that the sizes of the Li microstructures are reduced and their homogeneity becomes poorer after cycling. These results shed light on the plating and stripping processes of metallic Li from the perspectives of both macroscale and microscale.