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

Niobium tungsten oxides (Nb-W-O) have been verified as promising Li storage anodes because of their similar working voltage and cycling stability to Li 4 Ti 5 O 12 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 Nb 14 W 3 O 44 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 Nb 14 W 3 O 4 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 Nb 14 W 3 O 44 can be a very promising anode material for both Li-ion batteries and Li-ion hybrid capacitors towards high energy-power outputs.