Synthesis of Alkali Transition Metal Oxides Derived from Prussian Blue Analogues Toward Low Cationic Disorder for Li-Ion Battery Cathodes

Abstract

LiNixCoyMnzO2 (NCM) cathode materials are technologically important for high energy density Li-ion batteries. However, critical issues on Li+/Ni2+ cation disorder and poor Li-ion kinetics remain challenging, hampering the commercialization. Here, we report a new synthetic method of LiNixCoyMnzO2 derived from (Na0.25K0.15)Ni2.6-xMnx[Co(CN)6]2 (PBA) and appealing physicochemical aspects for advanced Li-ion batteries. A chemical lithiation process is developed for an efficient phase transition of the PBA to the layered structure NCM at a relatively low calcination temperature. As-prepared NCM possesses a LiO2 slab space of 2.637 Å close to an ideal value of 2.64 Å due to ∼1 atom % of an extremely suppressed Li+/Ni2+ disorder, leading to enhanced reversibility of a and c lattice constant changes upon cycling. Besides, a chemical densification process is invented to obtain a well-defined cubic structure at a high calcination temperature over 700 °C. Resultant NCM microcubes show superior cyclability and rate capability in a wide potential window of 2.7–4.5 V versus Li/Li+. Our results demonstrate the importance of suppressing the Li–Ni cation disorder in LiNixCoyMnzO2 for the development of high energy density Li-ion batteries.