Carbon covering to improve the storage performance of LiMn2O4 electrode at 60 °C

To improve the storage performance of LiMn2O4 cathode at elevated temperature (60 °C), a carbon layer is introduced to directly cover the surface of commercial LiMn2O4-based electrode via room-temperature DC magnetron sputtering. The as-modified cathode (LMO-C) displays enhanced capacity retention after storage at the charge state (4.35 V) under 60 °C as compared to the bare LiMn2O4 cathode (LMO-N). Specially, after 7, 14 days storage at 60 °C, the capacity retention of LMO-N is 89%, 17%, while the capacity retention of LMO-C is 92%, 85%, respectively, with respect to its own capacity before storage. Moreover, the charge–diachage curves and electrochemical impedance spectroscopy results demonstrate that LMO-C has much less increased electrode polarization and electrochemical impedance than LMO-N during the elevated-temperature storage process. SEM and TEM images of both sampes after storage show that LMO-C remains the intial morphology while LMO-N suffers morphological and sturctural degradations.