Unravelling the Mechanism of Pulse Current Charging for Enhancing the Stability of Commercial LiNi_0.5Mn_0.3Co_0.2O₂/Graphite Lithium-Ion Batteries

The key to advancing lithium-ion battery (LIB) technology, particularly with respect to the optimization of cycling protocols, is to obtain comprehensive and in-depth understanding of the dynamic electrochemical processes during battery operation. This work shows that pulse current (PC) charging substantially enhances the cycle stability of commercial LiNi_0.5Mn_0.3Co_0.2O₂ (NMC532)/graphite LIBs. Electrochemical diagnosis unveils that pulsed current effectively mitigates the rise of battery impedance and minimizes the loss of electrode materials. Operando and ex situ Raman and X-ray absorption spectroscopy reveal the chemical and structural changes of the negative and positive electrode materials during PC and constant current (CC) charging. Specifically, Li-ions are more uniformly intercalated into graphite and the Ni element of NMC532 achieves a higher energy state with less Ni─O bond length variation under PC charging. Besides, PC charging suppresses the electrolyte decomposition and continuous thickening of the solid-electrolyte-interphase (SEI) layer on graphite anode. These findings offer mechanistic insights into Li-ion storage in graphite and NMC532 and, more importantly, the role of PC charging in enhancing the battery cycling stability, which will be beneficial for advancing the cycling protocols for future LIBs and beyond.