Boosting Sodium Storage in TiF3/Carbon Core/Sheath Nanofibers through an Efficient Mixed-Conducting Network

Sodium-ion batteries (SIBs) are considered to be promising energy storage devices for large-scale grid storage application due to the vast earth-abundance and low cost of sodium-containing precursors. Designing and fabricating a highly efficient anode is one of the keys to improve the electrochemical performance of SIBs. Recently, fluoride-based materials are found to show an exceptional anode function with high theoretical specific capacity, based on open-framework structure enabling Na insertion and also exhibiting improved safety. However, fluoride-based materials suffer from sluggish kinetics and poor capacity retention essentially due to low electric conductivity. Here, an efficient mixed-conducting network offering fast pathways is proposed to address these issues. This network relies on titanium fluoride subset of carbon (TiF3 subset of C) core/sheath nanofibers that are prepared via electrospinning. Such highly interconnected electrodes exhibit an enhanced and faster sodium storage performance. Carbon sheath nanofibers are key to an efficient ion- and electron-conducting network that enable Na+/e(-) transfer to reach the nanosized TiF3. In addition, in-situ-converted Ti and NaF particles embedded in the carbon matrix allow high reversible interfacial storage. As a result, the TiF3 subset of C core/sheath electrode exhibits a high capacity of 161 mAh g(-1) at a high current density of 1000 mA g(-1) over 2000 cycles