Effects of the Nb2O5-Modulated Surface on the Electrochemical Properties of Spinel LiMn2O4 Cathodes

Nb2O5 has attracted substantial attention because of its effectiveness in improving the capacity retention and rate capability of cathode materials. However, modulating the interactions between Nb2O5- and Mn-contained cathode materials is the key to the success of the cycling performance. In this paper, we investigated the general and atomic-level structural interactions between the LiMn2O4 spinel cathode material and 0.5-3 wt % Nb2O5. The results showed that Nb2O5 was predominately bond on the surface of the LiMn2O4 spinel cathode by carefully controlled coating concentration and temperature (e.g., 0.5 wt % at 500 degrees C). In this case, a significantly improved electrochemical performance was obtained, even during cycling at 55 degrees C or between 3 and 5.1 V. In contrast, Nb5+ ions diffused into the cathode structure at a high coating concentration, and the temperature was charge compensated by the generation of more Mn3+ ions. This caused severe Jahn-Teller distortion during cycling and consequently decreased the cycling performance.