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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-TiO2-x/graphene (B-TiO2-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-TiO2-x nanosheets were self-assembled into three-dimensional (3D) interconnected B-TiO2-x/G aerogel. Owing to the rich active sites, high conductivity and fast kinetics, the B-TiO2-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-TiO2-x. The asymmetric LIC based on B-TiO2-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.

In the development of lithium-sulfur (Li-S) batteries, various approaches have been adopted to enhance the electronic conductivity of the sulfur cathode and alleviate the shuttle effect of polysulfides; however, the strategies providing efficient solutions are still limited. To further improve the electrochemical performance of Li-S batteries, in this work we propose a new strategy involving the incorporation of a three-dimensional functional spongy framework as polysulfide reservoir layer, with strong absorbability and electrocatalytic activity towards sulfur species. The spongy framework has a hierarchical architecture composed of highly conductive Ni foam/graphene/carbon nanotubes/MnO2 nanoflakes (NGCM). The strongly interconnected Ni foam, graphene, and carbon nanotubes of the NGCM sponge facilitate electron transfer during discharge/charge processes; moreover, the superlyophilic properties of the NGCM sponge ensure good wettability and interface contact with the Li-S electrolyte, and the porous MnO2 nanoflakes provide strong chemisorptive and electrocatalytic effects on polysulfides (as confirmed theoretically and experimentally). The NGCM sponge, serving as a polysulfide reservoir layer attached on a conventional sulfur-mixed carbon nanotubes (S/CNTs) cathode, can provide improved reversible capacity, rate capability (593 mAh·g–1 at 3.0 C), and cycling stability. In addition, the self-discharge rate is greatly reduced, owing to the efficient conservation of polysulfides in the NGCM spongy framework.