Hydrophobic Ni-Rich Layered Oxides as Cathode Materials for Lithium-Ion Batteries

Ni-rich layered oxide materials have been considered as promising cathode materials for high energy density Li-ion batteries because of their high reversible capacity. One of their catastrophic failure modes is the formation of residual lithium compounds on the oxide surface when it is exposed to air. In this paper, it is demonstrated that water is essential for the formation of residual lithium at room temperature. Furthermore, hydrophobic LiNi0.8Co0.1Mn0.1O2 is introduced to suppress the formation of residual lithium because the hydrophobic surface inhibits contact between water and LiNi0.8Co0.1Mn0.1O2. Hydrophobic LiNi0.8Co0.1Mn0.1O2 is obtained through surface engineering using hydrophobic organic molecules, such as polydimethylsiloxane. Hydrophobic polydimethylsiloxane-grafted LiNi0.8Co0.1Mn0.1O2 suppresses the formation of residual lithium even in humid air, leading to the negligible surface degradation of LiNi0.8Co0.1Mn0.1O2. As a result, hydrophobic LiNi0.8Co0.1Mn0.1O2 shows excellent electrochemical performance even after storage in humid air for 2 weeks.