Promoting cationic redox and stabilizing lattice oxygen in an Fe-based DRX cathode by the synergy of initial Li deficiency and 3D hierarchical porous architecture

Abstract

Anionic and cationic redox chemistries boost the ultrahigh specific capacity of Fe-based disordered rock salt (DRX) Li₂FeTiO₄. However, the sluggish kinetics and high O redox activity result in continuous capacity decay and poor rate performance. Herein, 3D hierarchical porous Li₂FeTiO₄ (H-Ca-LFT) with initial Li-deficiency is successfully prepared using an acid-assisted CaCO₃ template method. By introducing Li deficiency, the local electronic structure of Li₂FeTiO₄ is modulated to facilitate Li⁺ diffusion and regulate the redox activity. Specifically, Li deficiency reduces the density of states in the O 2p band, Li⁺ diffusion barrier, and band gap, thereby suppressing the high activity of oxygen and improving transport dynamics and electron conductivity. Moreover, the 3D hierarchical porous structure provides abundant channels and active sites for ion diffusion and electrochemical reaction. The synergistic effect of Li deficiency and the 3D hierarchical porous structure is revealed by various in/ex situ characterizations and DFT calculations, which promotes cationic redox and stabilizes anionic redox. Consequently, H-Ca-LFT demonstrates a high initial capacity (209.3 mA h g⁻¹ at 50 mA g⁻¹), remarkable rate capability (130.4 mA h g⁻¹ at 1 A g⁻¹), and outstanding long-term cycling stability. This work offers a new insight into stabilizing anionic redox through the design of initial Li deficiency and 3D hierarchical porous architecture for high-performance DRX cathodes.