Long-Range Cation Disorder Enhances Comprehensive Performance in Mn-Rich Layered Sodium Cathodes.

Abstract

Mn-rich layered oxides (MRLOs) are promising low-cost cathode materials for sustainable sodium-ion batteries (SIBs). However, the low Mn⁴⁺/Mn³⁺ redox potential limits their energy densities, and the Jahn-Teller distortion that occurs surrounding Mn³⁺ at low voltages destabilizes the structure. Additionally, complex ordered structures inherently present in MRLOs hinder Na⁺ migration. In this study, new types of cation ordering structures are discovered in common MRLOs. By regulating oxygen vacancy formation, the transition from short-range to long-range cation ordering is disrupted, effectively mitigating cooperative Jahn-Teller distortion and achieving a 95.3% capacity retention over 1 000 cycles at 8 C. The maximum entropy method (MEM) analysis is performed based on neutron diffraction data, which visualizes significantly optimized Na⁺ diffusion pathways in long-range disordered cathode with enhanced Na⁺ diffusion kinetics. Furthermore, the formation of oxygen vacancy elevates the Mn⁴⁺/Mn³⁺ redox potential, resulting in a competitive energy density of 626 Wh kg^-1 within 1.5-4.5 V in a half-cell configuration. This work offers a multiscale approach to precise elucidation of the cathode crystal structure and provides a feasible pathway to optimize sodium-ion cathodes by disrupting long-range cation ordering, ultimately facilitating substantial improvements in electrochemical performance.