Stretching the c-axis of the Mn3O4 lattice with broadened ion transfer channels for enhanced Na-ion storage

Abstract

Mn₃O₄ is a typical electrode material for supercapacitors with high theoretical energy density. However, the electrochemical performance of Mn₃O₄ is hindered by the sluggish charge transfer kinetics and poor cycling lifetimes. Herein, Mn₃O₄ with c-axis stretched lattice distortion (oxygen vacancy, Ov-Mn₃O₄) was prepared through a simple sulfurization/desulfurization treatment. The resultant Ov-Mn₃O₄ displays a high capacity of 331.1 F g⁻¹ at 1 A g⁻¹, a significant rate capability of 258.2 F g⁻¹ at 20 A g⁻¹, and a promising cycling stability with 83% capacity retention after 15 000 cycles. An asymmetric supercapacitor with Ov-Mn₃O₄ as the cathode delivers an energy density of 52.5 W h kg⁻¹ at a power density of 1000 W kg⁻¹. In situ Raman results demonstrate that Ov-Mn₃O₄ can effectively suppress and accommodate the cooperative Jahn–Teller distortion, contributing to a prolonged cycling life. DFT results suggest that the c-axis stretched lattice distortion induces electron delocalization, thus facilitating the electron transfer. Moreover, Na⁺ exhibits accelerated transfer kinetics in c-axis stretched lattice distorted Ov-Mn₃O₄ with broadened ion transfer channels. This work highlights the advantage of c-axis stretched lattice distortion for Na ion storage in Mn₃O₄, which can be expanded to optimize the electronic configuration of other metal oxides.