In situ synchrotron wide-angle X-ray scattering study on rapid lithiation of graphite anode via direct contact method for Li-ion capacitors

•Phase transformation of graphite was characterized by in situ X-ray scattering.•Direct contact between graphite and lithium metal leads fast lithiation.•The direct contact method is a robust pre-doping process without any safety issues.•The study provides an alternative pre-doping method for Li-ion capacitors.

Lithium pre-doping of graphite anode is a key process to achieve high energy density lithium-ion capacitor. In this study, in situ synchrotron wide-angle X-ray scattering examinations directly revealed that the direct contact (DC) method, simply achieved through direct physical contact between graphite electrode and sacrificial lithium metal in electrolyte, provides much faster phase transformation from stage 1ʹ to stage 1 than conventional electronic charger (EC) and external short circuit (ESC) methods at the same doping time level. The observations indicate that DC method achieves faster pre-lithiation rate of graphite electrode than EC and ESC processes.