Novel Composition of Co-Free LiNi_0.875-Mn_0.125AlO₂ Cathode Materials

Ni-rich LiNi_1-MnO₂ cathode materials have attracted widespread interest as promising alternative cathode materials owing to their higher capacity, lower cost, and lower toxicity compared to those of LiCoO₂. Therefore, we designed herein a LiNi_0.875Mn_0.125O₂ positive electrode material. However, as the Ni content increases, the materials suffer from an extensive phase transition during the de-lithiation process owing to the low-bond strength of Ni (391.6 kJ mol^-1) and Mn (402 kJ mol^-1). In this study, Al-doped LiNi_0.875-Mn_0.125AlO₂ (x= 0, 0.05, 0.1) was synthesized using the coprecipitation method. Al had a higher bond strength (512 kJ mol^-1) between oxygen and metal ions compared to that of Ni and Mn ions. Additionally, Al is usually stabilized in the form of Al³⁺. Therefore, the increased bond strength decreased the electrostatic repulsion with oxygen during the de-lithiation process and prevented cation mixing by stabilizing the Ni ion's valence, thereby resulting in increased structural stability. X-ray diffraction (XRD) was used to characterize their structures and calculate the cation mixing value. The electrochemical properties showed that LiNi_0.775Mn_0.125Al_0.1O₂ exhibited the high capacity retention of 97.1% after 30 cycles at 1 C at 55 °C.