Suppressing surface and bulk degradation of single-crystal LiNiO2 through additive-driven interfacial stabilization

초록

Single crystal-Ni-rich layered oxides are emerging as next generation cathodes for lithium-ion batteries (LIBs) due to their superior mechanical and electrochemical stability. However, they still suffer from degradation during cycling, which arises from different origins compared with polycrystalline cathodes. In this study, we demonstrate that the degradation of single-crystal cathodes can be effectively suppressed through interfacial stabilization. When both LiPO2F2 and fluoroethylene carbonate (FEC) are introduced as electrolyte additives, a LiF-rich passivation layer forms even before cycling begins, which reducing polarization at the early stage. Upon cycling, in additive-free electrolytes, the cathode-electrolyte interface fails to stabilize, leading to the formation of thick and fractured cathode-electrolyte interphase (CEI) layers at both the particle and electrode levels, which induce inhomogeneous electrochemical reactions. As a result, more damaged particles are observed, including planar gliding cracks and thick rock-salt phase transformation, which in turn accelerate capacity fading. These findings highlight that stabilizing the cathode-electrolyte interface is a critical strategy to fully realize the advantages of single-crystal cathodes by mitigating severe degradation.

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