In our work, a series of Li1-xMxCoO2 (M = Na, x = 0–0.05) samples are synthesized by the solid-state calcination route. Electrochemical measurements show that high-rate capacities and high-voltage performances receive obvious improvements with an appropriate content of Na-doping. Specially, the capacity retentions of Li0.97Na0.03CoO2 and LiCoO2 are 65.6% and 62.7% after the 100th cycle at 3.0–4.5 V, respectively. The discharge capacity of Li0.97Na0.03CoO2 compared with the pristine electrode LiCoO2 is greatly enhanced from 125 to 135 mAh·g−1 at the rate of 5 C and 98 to 120 mAh·g−1 at the rate of 10 C (1C = 140 mA g−1) respectively. With the larger radius of Na+ substituted for the smaller radius of Li+, it is found that the bond length of LiO is reduced from 2.0801 Å to 2.0781 Å, which is helpful for stabilizing the structure of LiCoO2 and improving the cycle capability at high voltages. At the same time, the inter-planar distance of Li slabs is expanded from 2.5904 Å to 2.59511 Å which can accelerate the diffusion of Li+ and improve the rate capacity. Therefore, Na-doped LiCoO2 shows outstanding high-voltage and high-rate performances, and the strategy can also be popularized and applied to other layered cathodes.