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Molybdenum trioxide (MoO 3 ) is known as a promising pseudocapacitive material, but low conductivity limits its applications. Hydrogenation is demonstrated to increase the conductivity of MoO 3 and hence improve its electrochemical performance. Hydrogenated MoO 3 (MoO 3 À x ) shows enhanced conductivity based on, both first principle calculations and single nanobelt measurements. Freestanding MoO 3 À x /carbon nanotubes (CNT) composite films have been fabricated and showed much improved electrochemical performance compared to composites of CNT and as-synthesized MoO 3 (MoO 3 /CNT). Electrodes showed a specific capacitance of 337 F/g (based on the mass of MoO 3 À x ) and a high volumetric capacitance of 291 F/cm 3 (based on the whole electrode) with excellent rate capability. Also we confirmed that the improved intercalation kinetics and the increased intercalation pseudocapacitance could be attributed to the higher electronic conductivity of MoO 3 À x , which results in better and faster intercalations http://dx.(J. Zhou). Nano Energy (2014) 9, 355-363 of Li + ions. This electrochemical behavior implies that MoO 3 À x can serve as a very good negative electrode with high capacitance at high mass loading levels.

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In order to restrict the polysulfide shuttle effect and enhance sulfur utilization of lithium–sulfur batteries (LSBs) especially at low charge/discharge rates, a facile hydrothermal synthesis and subsequent heating melting treatment are used to synthesize the heteroatom-doped carbon nanotubes/sulfur composite cathode. The composition analysis and structure characteristics of samples are examined by X-ray photoelectron spectroscopy, X-ray powder diffraction, and transmission electron microscopy. The electrochemical performances of samples are measured by cyclic voltammetry and charge/discharge experiments. The results show that N, B, S tridoped active carbon nanotubes (ACNTs) with abundant mesoporous structure enable fast Li+ transmittal and provide strong polysulfide adsorption ability. More importantly, they offer enough mechanical strength to support high sulfur loading (77 wt %) that maximizes their chemical role and can accommodate large volume changes. The N, B, S tridoped ACNTs/S composite exhibits a superb incipient capacity of 1166 mAh/g-S at 0.3 C and large reversible capacity of 881 mAh/g-S at the 700th cycle. To further promote the cyclic lifespan of LSB, the as-prepared N, B, S tridoped ACNTs acted as both sulfur matrix and spring functional layer and achieved a large reversible specific capacity of about 713 mAh/g-S at the 1400th cycle at lofty current density of 0.5 C with a slow capacity decay of 0.014% 1/cycle and a higher sulfur loading of 90 wt %. Accordingly, reasonable design for the heteroatom doping element in carbon material and separator modification will be distinctly vital for enhancing the electrochemical performance of the LSB and boosting its industrial application.