Ultra-high rate capability of in-situ anchoring FeF3 cathode onto double-enhanced conductive Fe/graphitic carbon for high energy density lithium-ion batteries

The FeF3 cathode shows some promising potentials for lithium-ion batteries (LIBs) because of its high theoretical capacity induced by conversion reactions, but the poor electrical conductivity and inferior reaction kinetics severely limit battery performance. Herein, the FeF3 nanoparticles embedded in double Fe/graphitized carbon (GC) matrices (FeF3/Fe/GC) are fabricated using low-temperature fluorination, where the spongy structure originates from the unique self-expanding process. It was found that the pseudocapacitive contribution of the optimized FeF3/Fe/GC nanocomposite is as high as 98%, which contributes to a high specific capacity of 151.2 mA h g−1 at a high rate of 10 C after 1000 cycles, with a capacity decay rate of only 0.03% per cycle. Surprisingly, even at an ultra-high rate of 100 C, the composite cathode still delivers a discharge capacity as high as 106.7 mA h g−1, which is superior to those reported in the previous studies. The excellent cycle stability and ultra-high rate performance can be attributed to the intimate contact between double Fe/GC matrices and ultrafine FeF3 nanoparticles, which can effectively reduce the diffusion barrier of ions and electrons to enhance the redox pseudocapacitive process. It has been demonstrated that optimizing the pseudocapacitive behavior may be a simple yet effective strategy to obtain the cathode materials with ultra-high rate capability.