High-entropy perovskite fluoride ultrasmall nanoparticles embedded in carbon nanofibers enable accelerated redox kinetic for K storage†

With the development of potassium-ion batteries, perovskite fluorides with three-dimensional framework structures and high theoretical capacities are attracting increasing attention. However, their intrinsically low electronic conductivities and high K⁺ diffusion barriers hinder the release of their potential capabilities. Herein, the embedding of ultrasmall perovskite fluoride nanoparticles (∼10 nm) in carbon nanofibers, along with a high-entropy strategy, is pioneered to strengthen structural stability, enhance electronic conductivity, and lower the K⁺ diffusion barrier. The high-entropy leads to a high reactivity and bonding effect between the fluoride surface and carbon nanofiber matrix that controls the growth of fluoride grains. The obtained high-entropy KMg_0.2Mn_0.2Fe_0.2Co_0.2Ni_0.2F₃-embedded carbon nanofiber cathode delivers a high reversible capacity of 122 mA h g⁻¹ at 20 mA g⁻¹ and an outstanding cycling life of over 5000 cycles at 500 mA g⁻¹. More importantly, the robust high-entropy structure suppresses the fluoride conversion reaction and exhibits a low-strain intercalation reaction mechanism, which fully exerts the positive effect of high entropy during the entire cycle life.