Achieving rapid Li-ion insertion kinetics in TiO2 mesoporous nanotube arrays for bifunctional high-rate energy storage smart windows

Smart electrochromic windows integrated with electrochemical energy storage capacity are receiving increasing interest for green buildings. However, the fabrication of bifunctional devices that demonstrate high-rate capability with stable and desirable optical modulation still remains a great challenge. Herein, a facile sacrificial template-accelerated hydrolysis approach is presented to prepare a designed lithium-ion insertion-type material layer on a fluorine-doped tin oxide substrate, with TiO2 mesoporous nanotube array (MNTA) film as an example, with rapid Li-ion insertion kinetics and without sacrificing window transparency, to meet requirements. A bifunctional device is assembled to exhibit the optical-electrochemical superiority of MNTA nanostructures. The as-assembled bifunctional smart window exhibits strong electrochromic contrast and high-rate capability in the fast galvanostatic charge/discharge process. For instance, at 1 A g(-1), it completes the charge or discharge process within only 232 s and delivers a high, reversible and stable specific capacity of 60 mA h g(-1), accompanying obvious transmittance modulation in the visible spectrum, with a typical value of ca. 30.4% at 700 nm, and strong color changes between deep blue and transparency.