Graphene-controlled FeSe nanoparticles embedded in carbon nanofibers for high-performance potassium-ion batteries

Iron selenide (FeSe) has drawn attention due to its resource-rich, environment-friendly, and low toxicity advantages. However, FeSe, like many transition metal selenides, has some limitations, including low conductivity and massive volume expansion during charge and discharge. Thus, graphene oxide-controlled FeSe nanoparticles embedded in carbon nanofibers were created using graphene oxide as an additive in the electrospinning precursor. The composites as the anodes for potassium-ion batteries (KIBs) can maintain an excellent capacity of 409 mA h g−1 at a current density of 0.2 A g−1 after 400 cycles with the capacity retention of nearly 100%. Even at 2 A g−1, the capacity can maintain 200 mA h g−1 after 1700 cycles with the capacity retention of about 80.9%. It was discovered that the addition of graphene oxide can reduce the diameter of FeSe nanoparticles and cause most nanoparticles to be wrapped in carbon fibers, which can relieve volume expansion and improve composite stability. Furthermore, the graphene and carbon fiber matrix can result in high K-ion diffusion kinetics, improved material conductivity, and enhanced pseudo-capacitance performance, endowing composites with excellent cycling and rate performance. The strategy of using graphene oxide to control the microstructure and improve the conductivity of carbon fiber composites may provide a new idea for future application and development of carbon fibers in other energy devices.