Construction of CoF2 nanoconfined in N-doped carbon matrix as high-capacity cathodes to boost reversibility of lithium-ion batteries

Abstract

Metal fluoride materials with high theoretical capacities are considered the next generation of Li-free conversion cathodes. However, the inherently sluggish reaction kinetics of metal fluorides result in unsatisfactory electrochemical performance. In this study, CoF₂ was combined with carbonaceous materials to obtain graphitic carbon-encapsulated CoF₂ nanoparticles uniformly embedded in an interconnected N-doped carbon matrix (CoF₂@NC), significantly boosting the inert kinetics and electronic conductivity. The CoF₂@NC nanocomposites exhibited a notable reversible capacity of 352.0 mAh·g⁻¹ at 0.2 A·g⁻¹. Notably, it maintained superior long-term cycling stability even at a high current density of 2 A·g⁻¹, with a capacity of 235.5 mAh·g⁻¹ after 1200 cycles, evidently exceeding that of commercially available CoF₂ electrodes. Kinetic analysis indicated that the enhanced electrochemical performance originated from the increased contribution of capacitive effects. Furthermore, in-situ electrochemical impedance spectroscopy (EIS) results verify that the improved cycling performance is associated with the enhanced interfacial stability of CoF₂@NC. This research not only proposes a solution for the challenges of conversion cathodes in lithium-ion batteries, but also offers novel synthesis strategies for designing high-energy metal fluoride materials.

Graphical Abstract