Thermal Synergy Effect between LiNi0.5Co0.2Mn0.3O2 and LiMn2O4 Enhances the Safety of Blended Cathode for Lithium Ion Batteries.

The layer-structured LiNi0.5Co0.2Mn0.3O2 (L523) with high specific capacity and the spinel LiMn2O4 (LMO) with excellent thermostability complement each other in a blended cathode for better heat stability and electrochemical performance. The delithiated LMO starts to react with electrolyte at 160-200 °C to cause structural instability, and the delithiated L523 generates massive heat when its temperature is raised above 275 °C with the electrolyte present, but we found that the blended cathode shows a remarkable improvement in thermal stability since the reaction at 160-200 °C between LMO and the electrolyte disappears, and the total heat generated from the reaction between L523 and the electrolyte is drastically reduced. The reaction between LMO and the electrolyte at 160-200 °C causes structural instability of LMO as a self-accelerating attack from HF. With L523 present, this reaction is eliminated because the H(+) from HF and Li(+) in L523 undergo exchange reaction to prevent further generation of HF. The presence of LMO, however, reduces the total heat generated by L523 reacting with the electrolyte at high temperature. This thermal synergy between LMO and L523 not only improves the thermal safety of the blended cathode but also preserves their structures for better electrochemical performance.