Spontaneous Strain Buffer Enables Superior Cycling Stability in Single-Crystal Nickel-Rich NCM Cathode

Abstract

The capacity degredation in layered Ni-rich LiNi_<i>x</i>Co_<i>y</i>Mn_<i>z</i>O₂ (<i>x</i> ≥ 0.8) cathode largely originated from drastic surface reactions and intergranular cracks in polycrystalline particles. Herein, we report a highly stable single-crystal LiNi_0.83Co_0.12Mn_0.05O₂ cathode material, which can deliver a high specific capacity (∼209 mAh g^-1 at 0.1 C, 2.8-4.3 V) and meanwhile display excellent cycling stability (>96% retention for 100 cycles and >93% for 200 cycles). By a combination of <i>in situ</i> X-ray diffraction and <i>in situ</i> pair distribution function analysis, an intermediate monoclinic distortion and irregular H3 stack are revealed in the single crystals upon charging-discharging processes. These structural changes might be driven by unique Li-intercalation kinetics in single crystals, which enables an additional strain buffer to reduce the cracks and thereby ensure the high cycling stability.