Sodium-ion batteries are potential alternatives in the lithium-ion battery territory. However, developing practical Na+ storage devices that offer high capacity, superior rate performance, and durability remains a significant challenge. Herein, a cyanide-to-oxide substitution strategy was developed via a two-step annealing process, converting Prussian blue analogues to a novel Fe-Mn oxide (HNMFO). The obtained material exhibits a unique phase configuration with an expanded Na+ diffusion channel and exceptionally ordered transition metal framework, effectively mitigating the intrinsic limitations of conventional cathodes. The HNMFO cathode delivers a high specific capacity of 171.9 mAh g-1 at 100 mA g-1 from 2.0 to 4.2 V, surpassing most previously reported Fe-Mn-based analogues. Crucially, the deep Mn3+/Mn4+ redox activity was successfully activated, synergistically enhancing both the capacity and stability. Pseudocapacitive analysis, density functional theory, and ab initio molecular dynamics simulations corroborate that the NaO2 layer elongation expands the interlayer spacing, contributes to electron delocalization, and reduces the energy barrier for Na+ diffusion, thereby accelerating ion transport and enhancing overall electrochemical performance. These theoretical insights align with experimental observations and validate the critical role of structural engineering in optimizing electrode kinetics.
Wang et al. (Mon,) studied this question.