Reduced energy barrier for Li+ diffusion in LiCoO2 via dual doping of Ba and Ga

Abstract LiCoO2 is the dominantly used cathode material in lithium-ion batteries. However, its high-rate capacity and cyclability are limited, especially under high charging voltages, mainly due to the high Li+ diffusion barrier. To solve it, we purpose a doping scheme based on two foreign elements: one is with tremendously large ionic radius and weak electronegativity, and the other one has an ionic radius slightly larger than Co, an electronegativity a little weaker than Co, and a high binding energy with O. Ba and Ga are chosen according to this criterion, and their doping effects are compared with that of La and Al. Briefly, Ba is superior to La in weakening the attraction of O2- to Li+ because of its weaker electronegativity and larger ionic radius. Meanwhile, Ga is more capable of enhancing the structural stability at high voltages than Al mainly due to its higher binding energy with O. LiCo0.998Ba0.001Ga0.001O2 increases Li+ diffusivity from 0.77 × 10-14 to 1.06 × 10–13 cm2∙s-1, resulting in a significantly enhanced rate capacity of 114.3 mAh g-1 at 10 C, much better than pristine counterpart (1.6 mAh∙g-1). Additionally, it exhibits a particularly high capacity of 199.3 mAh g-1, and 85% capacity retention over 100 cycles at 0.5 C in 3.0–4.5 V.