Designing high-voltage and high-rate Li1-xNaxCoO2 by enlarging Li layer spacing

The Na-doped LiCoO2 exhibits excellent electrochemical properties such as high-rate performances (5C and 10C) and high-voltage performances between 4.3 and 4.5 V. 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.193