Simple water treatment strategy to optimize the Li₂MnO₃ activation of lithium-rich cathode materials

Li-rich layered oxides, despite their superhigh capacity, still suffer from oxygen release and structural transformation during the first charge process, causing low Coulomb efficiency and continuous capacity fading. Preactivation has been widely recognized as a promising strategy to improve electrochemical performance of Li-rich material, though still plagued by the complexity of adopted methods and vulnerability of material structure. Here, we present a novel and gentle water treatment strategy to realize preactivation. Composition and structure analysis reveal that the Li-rich oxides can react with water by the extraction of lithium ion. In situ X-ray diffraction indicates that water treatment optimizes the activation process of Li-rich cathode material by decreasing transition metal ion diffusion. After treatment, the target material displays improved Coulombic efficiency of 86% and high discharge capacity of 279 mAh g^-1 and shows prominent cycling stability of 114% after 200 cycles. By studying gradient activation in the initial charge, we find that separate activation of the platform region (4.4-4.6 V) has significant effect on the improvement of material capacity, which may be mainly responsible for the improvement of discharge capacity and Coulombic efficiency of Li-rich materials from preactivation.