Modifying the Surface of a High-Voltage Lithium-Ion Cathode

Ni-rich lithium nickel manganese cobalt oxides (LiNi_xMn_yCo_1-x-yO₂, NMCs) suffer from poor cycling stability at potentials above 4.2 V vs Li/Li⁺. This degraded cyclability at high potentials has been largely ascribed to the parasitic reactions between the delithiated cathode and the nonaqueous electrolyte. In this study, we mitigated the performance degradation of high-voltage NMC 622 by designing a functional interfacial layer that consists of a surface doping by Ti⁴⁺ and a TiO₂ coating at the same time. The doping of Ti⁴⁺ near the surface of NMC can suppress the irreversible phase transformation, while the TiO₂ coating can kinetically reduce the rate of the electron-transfer reaction between the delithiated cathode and the solvent. It is revealed that this interfacial engineering approach significantly enhanced both the cycling stability and the rate performance of NMC 622.