Influence of Ti doping on microstructure and electrochemical performance of LiNi0.5Mn1.5O4 cathode material for lithium-ion batteries

LiNi0.5Mn1.5O4 cathode material has been synthesized by a combined coprecipitation-hydrothermal method followed by high-temperature calcination. Ti doping was achieved via acetic acid glacial assisted sol-gel method by using titanium(IV) butoxide as Ti source. The effects of different Ti doping contents on the structure, morphology and electrochemical properties of LiNi0.5Mn1.5O4 materials were systematically investigated. The as-synthesized samples were characterized by XRD, FT-IR, SEM, TEM, XPS, EIS and constant-current charge/discharge test. It is found that although Ti doping can effectively inhibit the formation of LixNi1-xO impurity phase, excessive Ti doping results in the appearance of Li2TiO3 secondary phase. SEM observation shows that Ti doping can improve the crystallinity of particles, and particle size shows a gradual increasing trend with Ti doping content. LiNi0.5Mn1.5O4 material doped with 3% Ti shows high phase purity and crystallinity, appropriate Mn3+ content and particle size with uniform distribution, thereby leading to its optimal electrochemical performance. Its discharge capacity at 10 C rate can reach 127.3 mA h g−1, and capacity retention rate can reach 91.7 % after 200 cycles at 1C and 25 °C. Post-mortem analysis shows that appropriate Ti doping can efficiently ameliorate electrolyte decomposition and other side reactions, thus leading to the formation of thinner SEI/CEI layer on electrode surface, and then better cycling performance achieved.