Enhancing phase stability and kinetics of lithium-rich layered oxide for an ultra-high performing cathode in Li-ion batteries

Abstract

To achieve a higher capacity and rate capability, the electrochemical performance of doped Li-rich layered oxide (LLO), in which Co and O ions are substituted with various dopants (Ti, Zr, Ce, Mo, W, and F), is investigated using first-principles calculations. W and Mo are candidate dopants to enhance the phase stability but are excluded due to the decreased average cell voltage of 2.5–5.4 %, lowering the energy density of a battery. Instead, F is selected as a promising dopant because F-doped LLO can achieve high structural stability without a reduction in the average cell voltage compared with un-doped LLO. The Li slab distance in F-doped LLO expands approximately 3–8% depending on the Li concentration, and the activation energy for Li hopping is reduced about 30%, suggesting faster Li ion diffusion. The enthalpy of formation of F-doped LLO is reduced to 5.3–12.4 kJ mol−1 during de-lithiation, implying an increase in phase stability. Based on the DFT prediction, we experimentally demonstrate F-doped LLO (Li1.17Ni0.17Co0.17Mn0.50O1.96F0.04) exhibits a high capacity of 252.2 mAh g−1 at 0.33C rate in the cut-off voltage range of 3.0–4.6 V. The rate capability is enhanced, and the capacity is retained up to 83% at 3C compared with the 0.33C rate.