Rapidly-Formed Interphase Facilitating Fast-Charging Lithium-Ion Batteries

Sluggish lithium-ion (Li + ) transport through the electrode–electrolyte interface hinders fast charging of lithium-ion batteries. Contrary to the conventionally slow-formed solid electrolyte interphase (SEI), fast-formed SEI is proposed and evidenced to be beneficial in enhancing the interfacial Li + transport and thus the fast-charging of the graphite anode. Various characterization techniques including cryogenic transmission electron microscopy, in situ Raman spectroscopy, and gas chromatography are applied to uncover the nanostructure, formation pathways, and stability of SEI layers formed at varied current densities during the formation process. The results show that the rapidly formed SEI layer has more crystalline inorganic components with reduced size (4.4 nm at 5C vs. 8.0 nm at 0.2C), elevated stacking density (33% vs. 12%), thinner (∼7 nm vs. 18 nm), and faster Li + diffusion. With such a preformed SEI layer, the capacity retention of the LiFePO 4 ||graphite cell is dramatically improved from 65% to 98% at 1C after 400 cycles.