NaTi2(PO4)3 nanoparticles embedded in double carbon networks as a negative electrode for an aqueous sodium-polyiodide flow battery

Abstract To demonstrate an aqueous sodium-polyiodide flow battery (SIFB) for the first time, sodium titanium phosphate (NaTi2(PO4)3) was utilized as the negative electrode and I−/I3− couple was adopted as the positive redox active species. SIFB not only shows advantages of cost-effectiveness and environmental friendliness based on earth-abundant elements of sodium and iodine, but also exhibits a high energy density due to the high solubility of sodium iodide (~12.3 M at room temperature). Although NaTi2(PO4)3 has several advantages such as high Na-ion conductivity and good structural stability, its use as a negative electrode is limited because of intrinsically low electrical conductivity. In this study, NaTi2(PO4)3 nanoparticles were embedded in double carbon networks comprising internal and external carbon layers. Individual effects by the internal and external carbon networks on the electrochemical performance of NaTi2(PO4)3 were clearly distinguished. With the simultaneous formation of the two carbon networks, a SIFB exhibited outstanding electrochemical performance (86.0 mAh•g−1 at a rate of 7 C) and a long cycle life (93.5% capacity retention after 100 cycles).