Regular Mesoporous Structural FeSe@C Composite with Enhanced Reversibility for Fast and Stable Potassium Storage

Due to the superior theoretical capacity, impressive operating potential, and environmental benignity, metal selenides as the promising candidates have attracted extensive interest in potassium-ion batteries (KIBs). However, structure collapse of the electrode and sluggish reaction kinetics restrict their application in KIBs owing to the volume expansion of metal selenides and the large radius of K+. Herein, we rationally select metal–organic framework (MOF) iron 1,3,5-benzenetricarboxylate (MIL-100­(Fe)) as the precursor on account of its microporous opening windows and mesoporous cages, which well-confined selenium (Se) and fabricated mesoporous structural FeSe@C (NFC) successfully. The mesoporous structural NFC electrode achieved 310 mA h g–1 at 500 mA g–1 over 1000 cycles with 98% coulombic efficiency and delivered excellent rate capacity (276 mA h g–1 at 1000 mA g–1 and 254 mA h g–1 at 2000 mA g–1), which could be attributed to the large surface area and mesoporous structural composite along with carbon framework coating. It can also be concluded that the pseudocapacitive contribution accelerates K+ transport and enable faster kinetics. Significantly, in situ X-ray diffraction (XRD) analysis revealed that the conversion reaction mechanism of FeSe (FeSe + 2K+ ↔ Fe + K2Se) occurs on reduction and oxidation reversibly. The superior electrochemical performance exhibits the great potential of the FeSe@C composite as a promising anode material for KIBs.