Novel Composition of Co-Free LiNiMnAlO₂ Cathode Materials.

Ni-rich LiNiMnO₂ 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 LiNiMnO₂ 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) and Mn (402 kJ mol). In this study, Al-doped LiNiMnAlO₂ (= 0, 0.05, 0.1) was synthesized using the coprecipitation method. Al had a higher bond strength (512 kJ mol) between oxygen and metal ions compared to that of Ni and Mn ions. Additionally, Al is usually stabilized in the form of Al. 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 LiNiMnAlO₂ exhibited the high capacity retention of 97.1% after 30 cycles at 1 C at 55 °C.