Achieving high energy density and long cycle life of high-voltage cathode LiNi0.5Mn1.5O4 for lithium metal batteries: Suppressing the phase transition from cubic phase to tetragonal phase via Ta doping

LiNi0.5Mn1.5O4 has been disregarded in the electric vehicle battery market due to its low capacity. Extending the voltage range to 2 V–5 V enables excess Li+ insertion into the 16c octahedral sites of the spinel lattice, leading to a substantial improvement in specific capacity and energy density. The surplus of Li+ can be appropriately supplied by the metallic lithium at the anode of lithium metal batteries (LMBs). Nevertheless, severe capacity decay is still a problem. To solve this problem, Ta-doped LiNi0.5Mn1.5O4 materials with excellent performance were achieved in this study. The resulting LiNi0.5Mn1.485Ta0.015O4 sample exhibits the best electrochemical performance with an initial capacity of 233 mAh g−1 at 0.1 C, an energy density of 825 Wh kg−1, and a capacity retention of 81.6 % after 100 cycles at 1C. Such promoted electrochemical performance is primarily attributed to the strong Ta–O bond energy (805 kJ mol−1), which inhibits the phase transition from cubic to tetragonal phase at the 2.7 V plateau, minimizes the volume changes and stabilizes the crystal structure. Furthermore, Ta doping stabilizes the three-dimensional channel for diffusion of Li+ ions, which leads to enhanced rate capability (from 123 mAh g−1 to 161.5 mAh g−1 at 2 C).