Facile Formation of a LiF-Carbon Layer as an Artificial Cathodic Electrolyte Interphase through Encapsulation of a Cathode with Carbon Monofluoride

Lithium batteries that utilize a lithium anode and a high voltage cathode are highly required to meet the growing demand for electrification of transportation. High voltage lithium cobalt oxide (LiCoO2, LCO) can be a promising choice for lithium batteries with high energy and power. However, intrinsic structural instability at high voltages (>4.2 V) leads to significant capacity loss during the repeated cycles of charge–discharge. Herein, a simple and effective method has been proposed to prepare an artificial protective layer of LCO, enabling the LCO to achieve long-term cycle stability at 4.5 V. It is found that carbon monofluoride reacts with LCO via defluorination at 400 °C to form a LiF-C layer on LCO, which suppresses side reactions at the electrolyte/electrode interface. Moreover, the LiF-C layer plays a key role in not only facilitating charge transport but also restricting Co dissolution from the cathode. The Li//LiF-C coated LCO cells deliver an initial discharge capacity of 186 mAh g–1 at 0.1C and exhibit excellent cycling and rate performance: 161 mAh g–1 after 180 cycles (90% of the initial value at 0.5C) and 115 mAh g–1 at 10C (63.2% of the 0.1C capacity).