Investigation of Ordering on Oxygen-Deficient LiNi0.5Mn1.5O4-delta Thin Films for Boosting Electrochemical Performance in All-Solid-State Thin-Film Batteries

All-solid-state thin-film batteries (ASSTFBs) are promising next-generation battery systems, but critical challenges such as low-energy-density remain. The low-energy-density might persist with low-voltage cathode material; hence, high-voltage cathode material development is required. While LiNi0.5Mn1.5O4 (LNM) has been considered a promising high-voltage cathode material. This study investigates the electrochemical properties of LNM thin films based on the correlation between the ordering of cations (Ni and Mn) and oxygen vacancies (V-O). The authors find that the cations' order changes from a disordered structure to an ordered structure with an increased oxygen flow rate during deposition. The optimized LNM fabricated using a 60:40 ratio of Ar to O-2 exhibits the highest rate capability (321.4 mAh cm(-3) @ 20 C) and most prolonged cycle performance for 500 cycles. The role of V-O within the LNM structure and the lower activation energy of ordered LNM compared to disordered LNM through first-principles density functional theory calculations is elucidated. The superior electrochemical performance (276.9 mAh cm(-3) @ 0.5 C) and high cyclic performance (at 93.9%, 500 cycles) are corroborated by demonstrating flexible ASSTFB cells using LiPON solid-state electrolyte and thin-film Li anode. This work paves the way for future research on the fabrication of high-performance flexible ASSTFBs.

Automated summary

This study investigates the electrochemical properties of LNM thin films and reveals that the ordering of cations can be controlled through adjusting the oxygen flow rate. The optimized LNM material exhibits the highest rate capability and cyclic performance. The low activation energy and superior electrochemical performance of ordered LNM are explained through first-principles calculations.