In situ synthesis of Fe7Se8 with a yolk-shell structure achieves fast and stabilized potassium storage

Abstract

Iron-based selenides are considered one of the most promising candidates for anode materials in potassium-ion batteries due to their impressive theoretical capacities. However, the challenges of enormous volume expansion and low intrinsic conductivity result in suboptimal electrochemical performance. Here, an iron selenide (Fe₇Se₈) with a yolk-shell structure (Fe₇Se₈/C@NC) is designed that effectively improves structural stability, relieves volume expansion, enhances ionic conductivity via carbon-shell construction, and prevents architecture damage caused by Fe₇Se₈ aggregation. Because of these advantages, the electrode presents a satisfactory cycling stability (206.6 mAh g⁻¹ after 3,200 cycles at 1 A g⁻¹) and an excellent rate capacity (205.2 mAh g⁻¹ at 5 A g⁻¹). In situ X-ray diffraction and ex situ transmission electron microscopy characterizations elucidate the potassium storage mechanism of Fe₇Se₈. The electrochemical performance of the composites positions them as promising electrode materials.