New insight into the mechanism of LiPO2F2 on the interface of high-voltage cathode LiNi0.5Mn1.5O4 with truncated octahedral structure

The development of high energy density material is of great importance and urgency for new generation of energy storage system. However, electrolyte formula for high voltage system remains a challenge. The use of various functional additives gives rise to the complexity of electrolyte system and hinders completely understanding of the action mechanism of additives. Herein, we report the adaptability and mechanism of a single additive LiPO2F2 added in the conventional LiPF6-based electrolyte system. The resulting conclusion displays a notable improvement in the cycling stability for 5 V-class cathode LiNi0.5Mn1.5O4, the capacity retention increase from 85.76% to 95.92%. It is comforting that the rate performance is not reduced due to the increase in cycle stability, and it also shows good advantages in terms of high rate and reversibility. Meanwhile, detailed analysis about interface mechanism for LiPO2F2 by the surface testing (SEM, TEM and XPS) give the direct characterizations. Common ion effect of the decomposition product Li3PO4 from additive is probed from the above characterization and combined with DFT calculations and some clever experiments to prove the positive effect of additives. The findings obtained from this work may provide a useful guidance for the research on electrolyte formulation for high voltage system.