Preparation, characterization and electrochemical performance of LiNi xCoyCuzMn2-x-y-zO4 as positive electrodes in lithium rechargeable batteries
A series of spinel compounds including LiCu0.25Co0.25Ni0.25Mn1.25O4 and LiMn2O4 were prepared by the sol–gel method using glycine, ethanol, and ammonia solutions. The structural and magnetic properties were examined by X-ray diffraction, Scanning Electron Microscopy, and electron spin resonance. The prepared powders have spinel-phase cubic structure with space group Fd3m. It is found that the Curie constant “Cp” and the effective magnetic moment “μeff” values decrease with the more metal doping. The electrochemical properties were characterized and found to be superior for the LiCu0.25Co0.25Ni0.25Mn1.25O4. It was observed that the Warburg impedance coefficient (?w) was 122 Ω.s-0.5 for LiCu0.25Co0.25Ni0.25Mn1.25O4 (sample B), which was lower than the value for LiMn2O4 (sample A), 819Ω.s-0.5. Also, the diffusion coefficient (D) values of the lithium ions diffusing into the bulk electrode materials were calculated. Sample B had a higher “D” value than sample A. The prepared multi-doped lithium manganate spinel material delivered a higher specific discharge capacity of ~150 mAhg-1 compared to 115 mAhg-1 for LiMn2O4 after 150 cycles.