Rigid-spring-network in P2-type binary Na layered oxides for stable oxygen redox

Abstract

Recently, utilizing oxygen redox (OR) reaction has emerged as a promising strategy to increase specific capacity as well as reaction voltage of cathodes, eventually increasing energy density of rechargeable batteries. However, due to irreversible structural disorder and oxygen release during OR, OR-based cathodes suffer from severe capacity fading and large voltage hysteresis. Herein, we present stable and nonhysteretic Ti-substituted Na layered oxide (NTMNO) with higher capacity and enhanced cyclability. Combined studies of experiments and first-principles calculations discovered the role of redox-inactive Ti within the stable crystal structure of the cathode upon cycling. It is found that OR participation is more significant for NTMNO than Na layered oxide without Ti substitution, which coincides with the comparison of the specific capacities. Moreover, incorporating Ti into the P2-type layered cathode improves the sluggish kinetics of Na-ions during the cycling. In this study, we present a novel concept of the "rigid-spring-network " as an origin of the reversible OR-based layered oxides.