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LiNi x Co y Mn 1−x−y O 2 (NCM) undergoes severe lattice distortion and capacity decay during charging and discharging at high voltages, affecting its cycle life. Here, dual-site doping of Cu 2+ singlecrystal LiNi 0.5 Co 0.2 Mn 0.3 O 2 (SC-NCM523) was prepared by a moltensalt-assisted method. Cu 2+ is doped into the manganese (Mn) and lithium (Li) sites, which inhibits the occurrence of cation mixing while acting as a pillar to broaden and stabilize the channels for Li + transport, and it enables high voltage stability and rate performance of the material simultaneously. The sample has a discharge capacity of 190.6 mAh g −1 in the first cycle at 0.1 C (1 C = 200 mA g −1 ) at a high cutoff voltage of 4.5 V and a capacity retention rate of 82.2% after 200 cycles at 1 C. Meanwhile, the capacity retention rate is up to 77.0% after 250 cycles at a current density of 5 C. This work is a guideline for the subsequent study of stabilizing the ontological structure of single-crystal cathode materials.