In-situ construction of a thermodynamically stabilized interface on the surface of single crystalline Ni-rich cathode materials via a one-step molten-salt route

Nickel rich LiNi_xCo_yMn_1−x−yO₂ cathode materials have been studied extensively to increase the energy density of lithium-ion batteries (LIBs) due to their advantages of high capacity and low cost. However, the anisotropic crystal expansion and contraction inside the secondary particles would cause detrimental micro-cracks and severe parasitic reactions at the electrode/electrolyte interface during cycling, which severely decreases the stability of crystalline structure and cathode-electrolyte interphase and ultimately affects the calendar life of batteries. Herein, a thermodynamically stabilized interface is constructed on the surface of single-crystalline Ni-rich cathode materials (SC811@RS) via a facile molten-salt route to suppress the generation of microcracks and interfacial parasitic side reactions simultaneously. Density functional theory calculations show that the formation energy of interface layer (−1.958 eV) is more negative than that of bulk layered structure (−1.421 eV). Such a thermodynamically stable protective layer can not only prevent the direct contact between highly reactive LiNi_xCo_yMn_1−x−yO₂ and electrolyte, but also mitigate deformation of structure caused by stress thus strengthening the mechanical properties. Raman spectra further confirm the excellent structural reversibility and reaction homogeneity of SC811@RS at particle, electrode, and time scales. Consequently, SC811@RS cathode material delivers significantly improved cycling stability (high capacity retention of 92% after 200 cycles at 0.5 C) compared with polycrystalline LiNi_0.8Co_0.1Mn_0.1O₂ (82%).