Hybrid Polyvinyl Alcohol/Silicon Nanofiber Anodes with High Concentrated Graphene Nanoribbons for Rechargeable Lithium-ion Batteries

Abstract

Despite the highest theoretical capacity of 3579 mAh/g in lithium–ion batteries,[1,2] silicon (Si) anodes have been still suffered from severe capacity fading, because of two kinds of drawbacks such as (i) dramatic volume expansion called pulverization leading to electrical disconnection as well as (ii) formation of solid–electrolyte interface on their surfaces.Herein, we prepared an organic/inorganic hybrid anode of polyvinyl alcohol (PVA)/Si nanoparticles (NPs)/graphene nanoribbons (GNRs) nanofibers via electrospinning process. Since PVA polymer could be dissolved in water, our hybrid nanofibers have been made via water‒based electrospinning, which means that toxic solvents like N–Methyl–2–pyrrolidone (NMP) do not need to be used for preparing the electrodes. Furthermore, the PVA polymer as a good dispersant can effectively help to disperse high‒concentrated GNRs (20 mg/ml) under water, which are unzipped from multiwall carbon nanotubes for better dispersion ability. The battery cells using the hybrid PVA/Si/GNRs nanofibers exhibited an initial high discharge capacity of over 5000 mAh/g at 0.1C because of the contribution of well–dispersed GNRs and Si NPs, while only Si NPs have the first discharge capacity of ca. 2500 mAh/g. At even 1C (3.6 A/g), they showed a high reversible capacity of around 1800 mAh/g owing to highly–conductive GNRs within the hybrid nanofibers. Moreover, the nanofibers retained very stable cycle retention of over 90% during 200 cycles. Such excellent cycle retention should be attributed by cross–linked and stabilized PVA nanofibers covering Si NPs, available to not only prohibit the volume expansion but also alleviate the formation of SEI layers. In terms of electrochemical properties, the hybrid nanofibers represented much less charge transport resistance from electrochemical impedance spectroscopy and higher peak current density from cyclic voltammetry than only Si NPs, because the GNRs as electrical conductors in the electrodes must be well–distributed between Si NPs. As a result, we demonstrated an outstanding battery performance through a novel hybrid PVA/Si/GNRs nanofibers directly fabricated via water–based spinning.