Enhanced Structural and Electrochemical Performance of LiNi0.5Mn1.5O4 Cathode Material by PO43−/Fe3+ Co-Doping

Series of PO43−/Fe3+ co-doped samples of LiNi0.5Mn1.5-5/3xFexP2/3xO4 (x = 0.01, 0.02, 0.03, 0.04, 0.05) have been synthesized by the coprecipitation–hydrothermal method, along with high-temperature calcination using FeSO4 and NaH2PO4 as Fe3+ and PO43− sources, respectively. The effects of the PO43−/Fe3+ co-doping amount on the crystal structure, particle morphology and electrochemical performance of LiNi0.5Mn1.5O4 are intensively studied. The results show that the PO43−/Fe3+ co-doping amount exerts a significant influence on the crystal structure and particle morphology, including increased crystallinity, lowered Mn3+ content, smaller primary particle size with decreased agglomeration and the exposure of high-energy (110) and (311) crystal surfaces in primary particles. The synergy of the above factors contributes to the obviously ameliorated electrochemical performance of the co-doped samples. The LiNi0.5Mn1.45Fe0.03P0.02O4 sample exhibits the best cycling stability, and the LiNi0.5Mn1.4333Fe0.04P0.0267O4 sample displays the best rate performance. The electrochemical properties of LiNi0.5Mn1.5-5/3xFexP2/3xO4 can be regulated by adjusting the PO43−/Fe3+ co-doping amount.