Spherical and core-shell-structured LiMn1.5Ni0.5O4 lithium-ion battery cathode with enhanced cyclability

Spherical LiMn1.5Ni0.5O4(LMN) spinel materials with Co or Al doping were synthesized using coprecipitation technique and the dopants' impacts on cathode performance were explored. While both dopants were conducive to the capacity retention of LMN spinel, aluminum was more effective. Cobalt doping also helped increase the discharge capacity of control spinel, unlike aluminum. Core-shell-structured materials with Co-doped core and Al-doped shell segments were synthesized with the aim to create synergy between two dopants. Indeed, the best cathode performance in terms of lithium capacity and cyclability was reached with core-shell material. The best cathode material denoted as CS 3-1 had a first cycle lithium capacity of 133.1 mAh g(-1) and exhibited capacity fade rate of 0.08% per cycle. X-ray diffraction and FTIR studies revealed that all cathode materials were single phase and spinel type with Fd3m space group. Focused-ion beam (FIB) and Scanning Electron Microscope photos showed that spinel materials were made of distinct spherical particles 3-4 mu m in diameter. The core-shell structure was also substantiated with the photos. Energy dispersive analysis confirmed that constituent elements Mn, Ni, Co and Al had a homogeneous distribution within spherical particles. Electrochemical impedance spectroscopy results showed that Al doping on the surface was beneficial to reducing impedance growth, thereby explaining the better cyclability and rate performance of these cathodes.