Storage-Induced Surface/Interfacial Degradation of Ni-Rich Layered Cathodes

Ni-rich layered cathodes are regarded as the most promising candidates for next-generation power batteries due to their large capacity. However, Ni-rich cathodes are highly sensitive to moisture in air and are prone to triggering surface chemical reactions to generate residual lithium compounds during production and storage, which poses a significant obstacle to their practical application. This paper systematically investigated the critical factors (humidity, temperature, and time) that affect the growth of residual lithium compounds and variations on the surface/interfacial structure, aiming to elucidate the surface/interfacial degradation of Ni-rich cathodes during storage. It was discovered that a surface chemical reaction with moist air induces the active lattice Li + ions in the subsurface region to gradually segregate into the surface and participate in the formation and continuous growth of amorphous Li 2 CO 3 layers on cathode particles. Synchronously, induced by consumption of lattice Li + ions, a structural degeneration from the layered to rock-salt phase was found in the near-surface region of Ni-rich cathodes. Consequently, the substantially increased electrode interfacial impedance contributed by the inactive surface/interface phase results in the deterioration of electrochemical performance. This work provides insights into the failure mechanism of Ni-rich cathodes during storage.