Advanced energy storage device: a hybrid BatCap system consisting of battery–supercapacitor hybrid electrodes based on Li4Ti5O12–activated-carbon hybrid nanotubes

The battery–supercapacitor hybrid electrode, consisting of both faradaic rechargeable battery components and non-faradaic rechargeable supercapacitor components in a single electrode, is successfully developed using Li4Ti5O12–activated carbon (LTO–AC) hybrid nanotubes in a negative electrode for an advanced energy storage device. Li4Ti5O12 and PVA-derived activated carbon are hybridized with morphological control over the one-dimensional (1D) tubular structures via an in situ sol–gel reaction combined with electrospinning, followed by a hydrothermal reaction and appropriate heat treatment. The prepared LTO–AC hybrid nanotubes are tested at a variety of charge–discharge rates as anode materials for use in lithium-ion rechargeable batteries that deliver a specific capacity in the range of 128–84 mA h g−1 over a 100–4000 mA g−1 charge–discharge rate in the potential range 1.0–2.5 V vs. Li/Li+. The hybridized LTO–AC hybrid nanotubes electrode is included in a new type of hybrid energy storage cell, denoted as BatCap, as the negative electrode using commercialized activated carbon (AC) as the positive electrode. The hybrid BatCap cell exhibits a high energy density of 32 W h kg−1 and a high power density of 6000 W kg−1, comparable to the properties of a typical AC symmetric capacitor.