Investigation on the effect of Na doping on structure and Li-ion kinetics of layered LiNi0.6Co0.2Mn0.2O2 cathode material

Introducing the Na ion into the Ni-rich LiNi0.6Co0.2Mn0.2O2, Li1-xNaxNi0.6Co0.2Mn0.2O2 (x = 0, 0.01, 0.03) has been synthesized by high-temperature solid method. The effect of Na dopants on the structure, morphology, electrochemical properties, Li ion diffusion coefficient and the activation barriers has been extensively studied. Rietveld refinement results reveal that Na doping suppress cation mixing degree effectively and enlarge Li slab space. Electrochemical testing shows that Na-doped electrodes exhibit higher initial coulombic efficiency, good capacity retention and superior rate capability. Using experiments combined with first-principles calculations, we confirmed that the Na doping has enlarged Li slab space and then made the activation barrier of Li migration be reduced resulting higher Li+ diffusion coefficients.