Revealing the Degradation Mechanism of LiMn FePO by the Single-Particle Electrochemistry Method.

The commercial application of LiMn FePO materials has always been a great challenge because of their unsatisfactory structure stability during cycling and the safety issue. Herein, single-particle (SP) electrodes, where aggregated LiMn FePO is dispersed into SPs so they can distribute homogeneously in the carbon-nanotube networks, have been prepared and characterized to probe the degradation mechanism of LiMn FePO for the first time. Compared with a conventionally prepared cathode, the SP LiMn FePO cathode shows prominent capacity-fading with cycle numbers, which can be attributed to the formation of the MnF nanocrystals on the surface of LiMn FePO because of the reaction between F and dissolved Mn at the interface between the electrolyte and LiMn FePO. The different electrochemical behaviors can be ascribed to LiMn FePO SPs surface reconstruction with MnF nucleation and growth by the interfacial reactions. In addition, by applying a thin protecting layer of AlO on the surface of LiMn FePO, the interfacial side reactions can be suppressed. This work demonstrates that the SP method is a powerful tool to extract the information of interfacial reactions, which sometimes appear to be negligible compared with bulk reactions.