Effects of the Nb₂O₅-Modulated Surface on the Electrochemical Properties of Spinel LiMn₂O₄Cathodes

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 °C). In this case, a significantly improved electrochemical performance was obtained, even during cycling at 55 °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.