The effect of mild activation on the electrochemical performance of pitch-coated graphite for the lithium-ion battery anode material

Abstract

In order to improve the rate performance of a graphite anode for lithium-ion batteries (LIBs), mild activation was applied after a coating process to deposit unique coating layer with additional sites where lithium ions are able to be inserted on the graphite anode. In this study, we coated the pitch onto spherical natural graphite (SG) by using toluene and drying, before mild activation to control the coating layer structure, which contributes to preserving the intact structural integrity of graphite anodes during the repeated charging and discharging process. The crystal structure and surface of pitch-coated graphite with mild activation was observed using XRD, Raman spectra, TEM, SEM analyses to verify the formation of the coating layer. The pitch-coated graphite with mild activation can provide improved cycle stability (86.3% after 30 cycles at 0.5 C-rate) and high rate capability (91.0% at 1 C-rate/0.1 C-rate). Notably, complicated voltage profiles of as-prepared samples demonstrate that mild activation can be utilized to establish the lithium-ion insertion sites, such as partially charge transferring surface sites (Type 1), edges of carbon hexagon clusters (Type 3), and micro-void structures by hexagonal planes (Type 4).