High-performance Li-ion capacitor based on black-TiO_2−x/graphene aerogel anode and biomass-derived microporous carbon cathode

Lithium-ion capacitor (LIC) has been regarded as a promising energy storage system with high powder density and high energy density. However, the kinetic mismatch between the anode and the cathode is a major issue to be solved. Here we report a high-performance asymmetric LIC based on oxygen-deficient black-TiO_2−x/graphene (B-TiO_2−x/G) aerogel anode and biomass derived microporous carbon cathode. Through a facile one-pot hydrothermal process, graphene nanosheets and oxygen-vacancy-rich porous B-TiO_2−x nanosheets were self-assembled into three-dimensional (3D) interconnected B-TiO_2−x/G aerogel. Owing to the rich active sites, high conductivity and fast kinetics, the B-TiO_2−x/G aerogel exhibits remarkable reversible capacity, high rate capability and long cycle life when used as anode material for lithium ion storage. Moreover, density functional theory (DFT) calculation reveals that the incorporation of graphene nanosheets can reduce the energy barrier of Li⁺ diffusion in B-TiO_2−x. The asymmetric LIC based on B-TiO_2−x/G aerogel anode and naturally-abundant pine-needles derived microporous carbon (MPC) cathode work well within a large voltage window (1.0-4.0 V), and can deliver high energy density (166.4 Wh∙kg⁻¹ at 200 mA∙g⁻¹), and high power density (7.9 kW∙kg⁻¹ at 17.1 Wh∙kg⁻¹). Moreover, the LIC shows a high capacitance retention of 87% after 3, 000 cycles at 2, 000 mA∙g⁻¹. The outstanding electrochemical performances indicate that the rationally-designed LICs have promising prospect to serve as advanced fast-charging energy storage devices.