Interpenetrating network of titania and carbon ultrafine fibers as hybrid anode materials for high performance sodium-ion batteries

Interpenetrating networks (IPNs) of titania, having high cycling stability and rate capability, and carbon, having high electrical conductivity and capacity, ultrafine fibers were fabricated by a co-electrospinning technique in opposite directions. The IPN structure promoted a contact between titania and carbon fibers, minimized strain during ion de-insertion, and prevented agglomeration that shortened the cycling stability. Images from scanning electron microscopy with backscattering electron detector and X-ray diffraction spectra confirm the existence of the IPN structure of both types of fibers. Thermogravimetric analysis and Raman spectroscopy of the composite fibers reveal their 37 wt% of titania content and 1.2 ratio between disorder and graphitic carbon (ID/IG). A galvanostatic curve displays stable reversible capacities of 202 and 247 mA h g−1 for charge and discharge after the fifth cycle at a current density of 25 mA g−1. The material had a superior discharge capacity of 151 and 123 mA h g−1 at 125 and 250 mA g−1, respectively. Moreover, the discharge capacity could be maintained at 134 mA h g−1 after 100 cycles at 125 mA g−1 with a Coulombic efficiency of more than 98%, presenting a long life cycle of batteries. Therefore, the prepared IPN composite fibers can be an efficient anode for sodium-ion batteries.