Synergy of phase and interface engineering of manganese difluoride enable high-efficiency potassium-ion batteries

Abstract

Conversion-type materials are regarded as potential anodes for potassium-ion batteries, achieving high potassium storage capacity through conversion reactions to form K-rich compounds. However, the accompanying huge volume change often brings about the repeated destruction and formation of a thick solid electrolyte interphase (SEI), leading to electrode deterioration and pulverization. Herein, a synergistic strategy of phase and interface engineering is proposed for conversion anodes. We first uniformly embed ultrasmall MnF2 nanoparticles in carbon nanofibers (CNFs) through electrospinning and subsequent annealing. Phase regulation indicates that the rutile phase (R-MnF2) exhibits a smaller band gap and less volume variation compared to the fluorite phase. Additionally, cryo-electron microscopy studies show that the configuration of ultrafine MnF2 nanoparticles impregnated in CNFs can facilitate the generation of a robust KF-rich SEI. The obtained R-MnF2@CNFs demonstrate a high capacity of 407.4 mAh g−1 at 0.1 A g−1, superior rate capability of 252.1 mAh g−1 at 5 A g−1, and a high capacity retention of 82.6% after 5000 cycles at 1 A g−1. Notably, the carbon-coated KVPO4F||R-MnF2@CNFs full cell showcases stability close to the current state-of-the-art level and has a capacity decay rate of ~0.1‰ per cycle in a 2000-cycle test.