X-ray and thermal analysis of high-capacity iron- and nickel-containing lithium-rich layered-oxide cathode treated by carbothermal reduction

A high-capacity iron- and nickel-substituted ${\text{Li}}_2{\text{MnO}}_3$ cathode [i.e., ${\text{Li}}_{1.26}{\text{Fe}}_{0.11}$ ${\text{Ni}}_{0.11}{\text{Mn}}_{0.52}{\text{O}}_2$ (LFNM)] treated by carbothermal reduction was analyzed, and the results clarified that it has both high capacity and high safety levels. X-ray analysis of a reduced LFNM (R-LFNM) cathode clarified the following. Migration of transition metals in the lattice as a result of the carbothermal reduction stabilizes the layered lattice structure, which prevents lattice shrinkage during charging and enhances charge compensation. As a result, more lithium ions can return to the cathode during discharging; namely, the irreversible capacity of the cathode decreases. Thermal stability of the R-LFNM cathode was evaluated by differential scanning calorimetry (DSC), and the results show that the total heat evolved from the R-LFNM cathode remains at a lower level compared with that of other cobalt- and nickel-containing ${\text{Li}}_2{\text{MnO}}_3$ cathodes. An analysis of the lattice structure reveals that low exothermic heat from the charged R-LFNM cathode results from the distinctive property of its crystal lattice changing from layered to thermally stable spinel during charging.