Multicore–shell iron fluoride@carbon microspheres as a long-life cathode for high-energy lithium batteries

Abstract

The study of multi-electron conversion cathodes is an important direction for developing next-generation rechargeable batteries. Iron fluoride (FeF₃), in particular, has a high theoretical specific capacity (712 mA h g⁻¹) and a low cost for Li storage. However, the FeF₃ material suffers from poor conductivity, volume change and active material dissolution, resulting in voltage hysteresis and poor cycling and rate performance during electrochemical reactions. Here novel multicore–shell FeF₃@carbon (C) composite microspheres with FeF₃ nanoparticles embedded in carbon shells are developed through a bottom-up method and demonstrate smaller FeF₃ particle size, a good carbon coating and superior maintenance of carbon shell integrity after fluorination and cycling as well. The FeF₃@C/Li cells exhibit excellent electrochemical properties, offering a reversible capacity of 511.4 mA h g⁻¹ at 0.2C after 250 cycles and outstanding cycle stability for 3500 cycles, with a capacity retention of 81% at 1C. It is worth noting that the carbon shell effectively inhibits the dissolution and diffusion of the active material and enhances the electrode reaction kinetics during charge/discharge reactions together with reduced core size. Overall, the sophisticatedly designed multicore–shell structure not only effectively improves the electrochemical properties of FeF₃ but also offers a new idea for refining transition metal-based electrode materials.