In Situ Engineering Toward Core Regions: A Smart Way to Make Applicable FeF@Carbon Nanoreactor Cathodes for Li-Ion Batteries.

Iron fluorides (FeF) have attracted great interest in Li-ion batteries due to their high theoretical capacity, low cost, and preferable cell safety. However, their practical utilization is severely impeded by inferior electrode kinetics, leading to poor electrode cyclability and rate capabilities. The major bottleneck should be lack of any effective engineering techniques to make reliable encapsulation and conducting matrix on soluble FeF species. Herein, we propose an applicable synthetic strategy where the massive production of FeF@carbon nanoreactors (total size: ∼60 nm) can be easily achieved by in situ engineering toward the core regions in hybrids, with the iron rust wastes and common solvents as raw materials. Such functionalized configurations can well make up for the shortcomings of FeF species, enabling them with outstanding cathode behaviors involving excellent reversible capacity retention (∼270% higher than that of a bare FeF electrode after 600 cycles) and drastically enhanced rate performance. This paradigm work provides a facile and scalable method to make superior and sustainable cathodes and, moreover, offers a feasible engineering protocol to make water-soluble species encapsulated into carbon matrix, not merely for batteries but also for other wide range of fields like catalysis, nanomedicine, etc.