Solid–Liquid Interfacial Reaction Trigged Propagation of Phase Transition from Surface into Bulk Lattice of Ni-Rich Layered Cathode

Solid–liquid interfacial reaction plays a crucial role for rechargeable batteries, and the reaction products are normally termed as solid liquid interface (SEI) layers. However, it remains far from clear as to how the solid–liquid interfacial reaction affects the bulk lattice. Here we demonstrate that the solid–liquid interfacial reaction extends beyond the SEI layer and essentially controls the bulk lattice behavior of the electrode. We discover that, for the Ni rich cathode (LiNi 0.76 Co 0.10 Mn 0.14 O 2 ), adjusting the electrolyte chemistry triggers the anisotropic propagation of layered to rock salt phase transition into the bulk lattice, and consequently causes the progressive voltage and capacity decay. The ab initio computation suggests that, at the rock salt/layered interface, the interlayer migration of Ni ions is promoted, whereas the intralayer diffusion along the {003} channels is retarded. It is further suggested that the oxygen vacancies as a consequence of interfacial reactions preferentially diffuse along {104} planes, subsequently facilitating the rock salt bulk growth. The present observation provides a general view of how the solid–liquid interfacial reaction traverses beyond a geometrical interface and critically controls the underlying bulk lattice behavior and is of general importance for tailoring interfacial structure and chemistry for optimization of battery performance.