Medium entropy stabilized disordered LiNi0.5Mn1.5O4 cathode with enhanced electrochemical performance

High entropy electrode materials have attracted extensive attention due to their excellent structure stability during cycling, leading to super long cycle life. However, the traditional equimolar strategy is not suitable for electrode materials if high-capacity is considered. Here, we successfully prepared LiNi0.5Mn1.5O4 cathode with high stability and long cycle life by using a multiple-element doping strategy (medium entropy). Combining with differential scanning calorimetry (DSC), Raman spectra and X-ray photoelectron spectroscopy, it is found that Co, Cr, Al co-doped LiNi0.5Mn1.5O4 (medium entropy sample) exhibits disordered structure (Fd3̅m) with limited Mn3+ and enriched Al3+ on the surface, which can inhibit the dissolution of Mn2+ ions and surface side reaction. With disordered structure and medium entropy, the Li+ ion diffusivity in co-doped LiNi0.5Mn1.5O4 is improved, leading to better rate performance. In-situ X-ray diffraction indicates mostly solid solution process in co-doped LiNi0.5Mn1.5O4 and less volume change (5.4 % vs. 5.8 % in undoped sample) during charge-discharge. Owing to the better structure and interface stability, co-doped LiNi0.5Mn1.5O4 shows excellent cycle stability, with 92 % capacity retention after 500 cycles at 1 C rate. Meanwhile, the specific capacity of the medium entropy sample is even increased from 132 mAh/g to 138 mAh/g, proving the advantage of medium entropy strategy in electrode materials.