Surface engineering of single-crystal NCM811 with graphene for enhanced mechanical integrity

Abstract

The severity of cracking and planar gliding along (003) facets due to the irreversible phase transition and anisotropic volume change in single-crystalline Ni-rich layered oxides leads to sluggish redox kinetics and poor cycling performance. In this work, we coated the single-crystal LiNi0.8Co0.1Mn0.1O2 with exfoliated graphene nanoplates by using an amphiphilic surfactant oleic acid as an adhesive. The robust structure of graphene is uniformly coated on the surface, providing chemo-mechanical strength to the particle surface. The coating layer suppresses the irreversible phase transition and anisotropic volume change that effectively inhibits the mechanical stress and planar gliding during the long-term cycling. Additionally, the coating serves as a passivation layer that prevents the parasitic side reactions and mitigates the electrolytic infiltration into the particles, facilitating fast Li+ diffusion kinetics. Therefore, the modified cathode demonstrates a capacity retention of 92.2 % at 1C and 94.5 % at 5C between 2.7 and 4.3 V vs. Li+/Li compared to the pristine (70 % at 1C and 66.5 % at 5C). Hence, this coating strategy is beneficial to provide a shield against mechanical degradation and sluggish kinetics for single-crystal Ni-rich layered oxide cathodes.