Aligned titania nanotubes as an intercalation anode material for hybrid electrochemical energy storage

A new hybrid electrochemical cell incorporating aligned titania nanotubes (ATNTs) as the anode and ordered mesoporous carbon (OMC) as the cathode is demonstrated. The concept is characterized by the optimization of ionic transport in the anode and ionic uptake in the cathode. The ionic transport in the anode can be enhanced by reducing the tube length and wall thickness of the ATNTs. The ionic transport and uptake at the cathode is significantly improved by the combination of ordered mesopores and high specific surface area in the OMC. Remarkably, these hybrid electrochemical energy storage cells are capable of delivering a high energy density of 25 W h kg^-1 and a high power density of 3000 W kg^-1 at a short current-draining time of 30 s, more than two times higher than in previously reported hybrid cells. Another advantage of these hybrid cells is that they are safe and stable for long periods of operation owing to the absence of dendrite lithium metal and a solid electrolyte interphase. In terms of the fundamental electrochemistry, the superior performance of the hybrid cells is attributed to shortened electrolyte penetration depth and lithium ion diffusion distance in the ATNT anode, facilitating an effective lithiation anode process, and to the fast anion uptake at the cathode.