Supercritical CO2-enhanced surface modification on LiFePO4 cathodes through ex-situ carbon coating for lithium-ion batteries

Abstract

This work reports an efficient and effective ex-situ carbon-coating strategy for lithium iron phosphate (LFP) using supercritical CO2 (SCCO2) to improve its electrochemical performance. The SCCO2 possesses unique features including gas-like diffusivity and zero surface tension, which facilitate the penetration of carbon precursors among active materials and enable the formation of high-quality carbon-coated LFP (s-LFP/C). Compared to the conventional ball-milling process, the carbon coating layer assisted by SCCO2 comprises a higher fraction of graphitic carbon and fewer oxygen-derived functional groups, both are advantageous for electron transport. Additionally, the optimal s-LFP/C-containing half-cells reveal an outstanding specific discharge capacity (ca. 99 mAh g−1 at 10 C) and cycle life (ca. 95% for 150 cycles at 0.5 C) contributed from reduced charge-transfer impedance and comparable ionic diffusivity. Taken together, the SCCO2-coating technique highlighted herein offers a promising opportunity to build a homogeneous and highly conductive carbon layer for boosting the electrochemical characteristics of LFP cathode in lithium-ion batteries.