High performance Li-ion hybrid capacitors with micro-sized Nb14W3O44 as anode

Abstract Niobium tungsten oxides (Nb-W-O) have been verified as promising Li storage anodes because of their similar working voltage and cycling stability to Li4Ti5O12 but higher specific capacity than the latter. However, the phase and microstructural evolutions of a designated Nb-W-O compound during sintering as well as its possible application in Li-ion hybrid capacitors have not been reported. In this work, micro-sized phase pure Nb14W3O44 is obtained by sintering a solvothermal-derived precursor at about 1050°C, which as a Li-ion insertion host exhibits not only high reversible specific capacity up to 226 mAh g−1 at 0.04 A g−1, but outstanding rate capability (137 mAh g−1 at 6 A g−1) and cycle stability (74.2% capacity retention at 2 A g−1 after 1000 cycles). Such an excellent rate capability enables the Nb14W3O4 anode highly matchable to the capacitive cathode and yields high energy densities of 64.6 and 29.2 Wh kg−1 at 198.9 and 14,576 W kg−1, respectively, in Li-ion hybrid capacitors, along with a high capacity retention of 83.9% after 3,000 cycles at 1 A g−1. With these excellent electrochemical energy storage performances and a high packing density, the micro-sized Nb14W3O44 can be a very promising anode material for both Li-ion batteries and Li-ion hybrid capacitors towards high energy-power outputs.