Effects of Fluorine and Chromium Doping on the Performance of Lithium-Rich Li1+xMO2(M = Ni, Mn, Co) Positive Electrodes

Abstract

Lithium-rich metal oxides Li1+zMO2 (M = Ni, Co Mn, etc.) are promising positive electrode materials for high-energy lithium-ion batteries, with capacities of 250–300 mAh·g–1 that closely approach theoretical intercalation limits. Unfortunately, these materials suffer severe capacity fade on cycling, among other performance issues. While ion substitution can improve the performance of many of these materials, the underlying mechanisms of property modification are not completely understood. In this work we show enhanced performance of the Li1+zMO2 electrode, consisting of Li2MnO3 (with C2/m space group) and LiMO2 (with R3m space group) phases, and establish the effects of cationic and anionic substitution on the phase and structure evolution underpinning performance changes. While the undoped material has a high capacity of ∼270 mAh·g–1, only 79% of this remains after 200 cycles. Including ∼2% Cr in the material, likely at the R3m metal (3a) site, improved cycle performance by ∼13%, and including ∼5% F in...