Anatase TiO2 Confined in Carbon Nanopores for High‐Energy Li‐Ion Hybrid Supercapacitors Operating at High Rates and Subzero Temperatures

Li-ion hybrid supercapacitors (Li-HSCs) hold great promise in future electrical energy storage due to their relatively high power and energy density. However, a major challenge lies in the slow kinetics of Li-ion intercalation/extraction within metal-oxide electrodes. Here, it is shown that ultrafast charge storage is realized by confining anatase TiO2 nanoparticles in carbon nanopores to enable a high-rate anode for Li-HSCs. The porous carbon with interconnected pore walls and open channels not only works as a conductive host to protect TiO2 from structural degradation but also provides fast pathways for ion/electron transport. As a result, the assembled cells exhibit remarkable rate capabilities with a specific capacity of approximate to 140 mAh g(-1) at a slow charge and approximate to 60 mAh g(-1) at a 3.5 s fast charge. While the charge/discharge process can be completed as fast as that of state-of-the-art electrical double-layer capacitors (EDLCs), the produced nanocomposites show three to seven times higher volumetric capacitance than activated carbons used in commercial EDLCs with acetonitrile-based electrolytes. Equally important for some applications in cold climates or the space, the Li-HSCs can operate at subzero temperatures as low as -40 degrees C, which is likely only limited by thermal properties of the acetonitrile (melting point of -45 degrees C).