Improvement of interfacial stability of LiMn2O4 cathode material by Al2O3 coating

Among rechargeable battery systems, Li-ion batteries technology is the most suitable for automotive applications (e.g. HEVs and PHEVs) thanks to its high power and high energy values. In this regard, spinel LiMn2O4 has drawn much attention with respect yo the other cathode materials since it has a low price, is environmental friendly and exhibits an excellent safety. However, LiMn2O4 shows several drawbacks such as severe Mn dissolution at high temperature, capacity fading, low electronic conductivity and poor high-rate capability. The former two disadvantages are mainly due to the following factors: 1. Dissolution of trivalent Mn3+ ions in according with the disproportional reaction (2Mn3+ --> Mn2+ + Mn4+) which leads to both active material loss and capacity fade; 2. Jahn-Teller distortion that consists in transition phase from cubic to tetragonal one in which there is less symmetry and more disorder. In addition at high temperature, LiMn2O4 delivers poor electrochemical performances due to severe Mn dissolution by HF generated from F-containing inorganic electrolyte salt. In order to solve partially or completely these problems, coating the surface of LiMn2O4 with appropriate coating materials, which avoid the Mn dissolution and suppress the electrolyte degradation, is a promising strategy. In this context, Al2O3 coating layer has been chosen in order to improve the cyclability and the interfacial stability of pristine LiMn2O4 material. The comparison of electrochemical performance and the study of interfacial properties between CMC-based LiMn2O4 and Al2O3-coated LiMn2O4 electrodes, at 25 °C and 50 °C, have been carried out by charge/discharge cycles at different C rate and ac-impedance analysis. from the obtained results, it is possible to assume that an enhancement of room temperature and high temperature cycling performance for LiMn2O4 by Al2O3 coating has been achieved. In addition, the preliminary EIS analysis confirmed the better interfacial and structural stability of Al2O3-coated LiMn2O4 with respect to the pristine material.