Online Digital Holographic Method for Interface Reaction Monitoring in Lithium-Ion Batteries

Understanding the reaction mechanisms at the interface of electrode and electrolyte is both of fundamental interest and essential to improve lithium-ion battery (LIB) performance. Herein, we report an online digital holographic method to in situ observe the entire interface change between electrode and electrolyte in lithium-ions batteries. The accuracy of this technology is well verified in LiFePO4/graphite full-cell systems, graphite/Li half-cell systems in EC-based and PC-based electrolyte, respectively, and supported by the characterized results of conventional instruments, including scanning electron microscopy and X-ray photoelectron spectroscopy. In particular, the time resolution of the digital holographic method is 0.04 s and fast enough to distinguish detail reduction process of ethylene carbonate (EC), for which EC will be first reduced to generate lithium alkyl carbonates, and then the reduction product is Li2CO3 to form a stable SEI films. To our best of knowledge, this is the first report on the reduction order of the EC solvent and can act as an effective complement to understanding the formation mechanisms of SEI films.