Carbon Nanofiber Composites As Anode Materials in Li+ and Na+ Batteries

Abstract

Carbon nanofibers (CNFs) are well known by their one-dimensional (1D) nanostructure, high conductivity and large surface area, which can provide direct and short pathways for ion transport. These unique properties have facilitated their application as anode materials in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Electrospinning, as a versatile and controllable method of CNFs manufacturing, has been widely investigated in the battery field. Electrospun CNFs still have limited capacity and rate capability. To further improve their performance, additives such as nickel metal nanoparticles and macromolecular Pluronic were added in this work. Pure CNFs derived from polyacrylonitrile (PAN) and two composite systems: CNFs/Ni and CNFs/Pluronic were synthesized. Morphology of the electrospun fibers and their electrochemical performance in both LIBs and SIBs were studied. Metallic nickel plays the role of an electronic conducting agent, while Pluronic serves as a template to generate micropores, which is favorable for sodium ion transport. Nanofibers with diameters around 200 nm were successfully prepared. Nanoparticles of nickel were observed on the surface of these CNFs by scanning electrode microscope (SEM). A high capacity of 460 mA h g-1 of pure CNFs when cycled at 100 mA g-1 in LIBs has been achieved with an outstanding stability. After 300 cycles, the capacity stays above 400 mA h g-1. With the addition of nickel particles, an even higher capacity of around 800 mA h g-1 was obtained. CNFs/Pluronic showed the best capacity retention among all composites with a steady capacity at around 600 mA h g-1. The influence of porosity and carbonization temperature on overall electrochemistry performance in LIBs and NIBs are being investigated. In summary, introduction of additives of Ni and micropores can effectively improve capacity of CNFs as anode materials. Charge/discharge profiles did not vary a lot which can prove that the additives are electrochemically inert. Electrospinning is a flexible method to develop 1D nanostructured electrode materials for both LIBs and SIBs. The outstanding electrochemical properties of such electrospun anodes will further stimulate their applications in LIBs and SIBs.