Synthesis of high-performance TiN based battery-type wire supercapacitors and their energy storage mechanisms

Abstract Battery-type supercapacitors that exhibit both high power density from capacitor-like behaviour, and high energy density from battery-like behaviour, have attracted significant interest recently. However, compared to conventional capacitor technology, these supercapacitors present new challenges for the design of the electrode materials, since they require not only high conductivity for fast electron transport, but also a suitable crystal structure for efficient ion intercalation. Here, we report a large-capacity wire supercapacitor, which is assembled by forming TiN nanowire arrays on carbonized cotton threads. The resulting structure is capable of both acting as the cathode and the anode, with specific capacities of 12.9 mAh cm−1 and 25.0 mAh cm−1 in Li-ion aqueous electrolyte, respectively. Sweep voltammetry analysis further reveals that the storage characteristics include both battery and capacitor-like behaviour, that is, 50–60% of the energy storage arises from the intercalation/deintercalation of Li/Na ions (battery-like) with the balance coming from the adsorption/desorption of electrolyte ions on the electrode surface (capacitor-like). Finally, two types of wire supercapacitors are assembled (lithium and sodium ion based), which exhibited excellent energy density of 52.5 μW h cm−2 for the lithium ion capacitor and 93.1 μW h cm−2 for the sodium ion capacitor, with 74.9% and 51.5% of the specific capacity retained after 10,000 cycles. This work demonstrates the possible application of these materials and structures in high-performance wearable energy storage systems.