LiNi0.8Co0.1Mn0.1O2(NCM811) cathode material has potential practical application for high energy density lithium-ion batteries. However, it suffers from serious capacity degradation because of structural instability and cationic mixing during charging/discharging cycles. In this work, micron-sized single crystals Li1-xKxNi0.8Co0.1Mn0.1O2(LKNCM) as composite cathode are successfully synthesized by molten salt-assisted growth method. LKNCM is regular plate-like polygon crystals (average grain size 1.31 mu m) with flat face. K(+)doping is helpful for the formation of Ni(3+)and Co(3+)in LKNCM crystals to some degree. Compared with pure NCM811, LKNCM possesses lower degree of Li+/Ni(2+)mixing and ordered layered structure. LKNCM delivers initial capacity of 192 mAh g(-1), and its capacity fading is less than 5% after 100 cycles at 0.1 C rate. Moreover, at 10 C rate it delivers initial capacity of 116 mAh g(-1)(the median voltage of 3.4 V) and remains 95.2% of initial capacity after 180 cycles. The ex situ surface analysis on the cycled positive and negative electrodes reveals that K(+)doping effectively suppresses side reaction and electrolyte decomposition during charging/discharging cycles.