Design of one dimensional (1D) nanofiber web structures and their applications for next-generation battery electrodes

Abstract

Poor electrochemical performances of materials in commercial lithium-ion batteries (LIBs) make it difficult to realize battery technologies for future electric power applications such as energy storage systems and electric vehicles. To reach beyond the horizon of state-of-the-art LIBs, the exploration of next generation batteries (Li-ion batteries, Na-ion batteries (SIBs) and $Li-O_2$ batteries (LOBs)) composed of rationally designed nanomaterials in consideration of the structure, phase and element influencing the battery performance is critical. By virtue of the simple set-up, versatility, size controllability and mass-productivity of electrospinning, one-dimensional (1D) nanofibers (NFs) produced via electrospinning are attractive candidates for the construction of advanced secondary batteries. In this dissertation, considering three different next-generation rechargeable systems (LIBs, SIBs and LOBs), 1D electrospun NFs were appropriately designed and applied as high performance anode and cathode materials. Firstly, for LIBs, 1D electrospun Si-based metallic glass alloy nanofibers (NFs) with an optimized composition of $Si_{60}Sn_{12}Ce_{18}Fe_5Al_3Ti_2$ were investigated. On the basis of careful compositional tailoring of Si alloy NFs, we found that Ce plays the most important role as a glass former in the formation of the metallic glass alloy. Moreover, Si-based metallic glass alloy NFs were wrapped by reduced graphene oxide sheets $(specifically Si_{60}Sn_{12}Ce_{18}Fe_5Al_3Ti_2 NFs@rGO)$, which can prevent the direct exposure of a-Si alloy NFs to the liquid electrolyte and stabilize the solid-electrolyte interphase (SEI) layers on the surfaces of rGO sheets while facilitating electron transport. Secondly, for SIBs, dimensional effects of $MoS_2$ nanoplates randomly embedded in twisted mesoporous carbon nanofibers $(MoS_2@MCNFs)$ on Li and Na storage properties were investigated. Considering dimensions of the $MoS_2$ nanoplates (e.g., interlayer, lateral distance, and slabs of stacking in number), thermolysis temperature to synthesize the $MoS_2$ nanoplates with different geometry and optimize them in the hybrid anode for delivering high performance was controlled. Finally, for LABs, the use of surface protection layers for improving the cycling stability of porous carbon-based LOB cathode were studied. Atomic layer deposition (ALD) for conformal coating of two types of overlayers $(In_2O_3 and TiN)$, i.e., oxide and nitride thin film, on an electrospun carbon nanopaper(CNp) membrane was employed. Using the proposed 1D NF electrodes, it was confirmed that electrochemical performance of next-generation rechargeable batteries has been remarkably enhanced.