Efficient Stabilization of Na Storage Reversibility by Ti Integration into O′3-Type NaMnO 2

Abstract

The development of an energy storage system with abundant elements is a key challenge for a sustainable society, and the interest of Na intercalation chemistry is extending throughout the research community. Herein, the impact of Ti integration into NaMnO₂ in a binary system of NaMnO₂–() TiO₂ () is systematically examined for rechargeable Na battery applications. Stoichiometric NaMnO₂, which is classified as an in-plane distorted O3-type layered structure, delivers a large initial discharge capacity of approximately 200 mAh g^-1, but insufficient capacity retention is observed, most probably associated with dissolution of Mn ions on electrochemical cycles. Ti-substituted samples show highly improved electrode performance as electrode materials. However, the appearance of a sodium-deficient phase, Na₄Mn₄Ti₅O₁₈ with a tunnel-type structure, is observed for Ti-rich phases. Among the samples in this binary system, Na_0.8Mn_0.8Ti_0.2O₂ (), which is a mixture of a partially Ti-substituted O3-type layered oxide (Na_0.88Mn_0.88Ti_0.12O₂) and tunnel-type...