Layered H 2 Ti 6 O 13 -nanowires are prepared using a facile hydrothermal method and their Li-storage behavior is investigated in non-aqueous electrolyte. The achieved results demonstrate the pseudocapacitive characteristic of Li-storage in the layered H 2 Ti 6 O 13 -nanowires, which is because of the typical nanosize and expanded interlayer space. The as-prepared H 2 Ti 6 O 13 -nanowires have a high capacitance of 828 F g − 1 within the potential window from 2.0 to 1.0 V (vs. Li/Li + ). An asymmetric supercapacitor with high energy density is developed successfully using H 2 Ti 6 O 13 -nanowires as a negative electrode and ordered mesoporous carbon (CMK-3) as a positive electrode in organic electrolyte. The asymmetric supercapacitor can be cycled reversibly in the voltage range of 1 to 3.5 V and exhibits maximum energy density of 90 Wh kg − 1 , which is calculated based on the mass of electrode active materials. This achieved energy density is much higher than previous reports. Additionally, H 2 Ti 6 O 13 // CMK-3 asymmetric supercapacitor displays the highest average power density of 11 000 W kg − 1 . These results indicate that the H 2 Ti 6 O 13 //CMK-3 asymmetric supercapacitor should be a promising device for fast energy storage.

Unique nanorod-like mesocrystals constructed from ultrathin rutile TiO 2 nanowires were successfully fabricated for the first time using a low-temperature additive-free synthetic route, and the mesocrystal formation requirements and mechanism in the absence of polymer additives were discussed. The ultrathin nanowires were highly crystalline and their diameters were found to be ca. 3-5 nm. The rutile TiO 2 mesocrystals were formed through homoepitaxial aggregation of the ultrathin nanowires via faceto-face oriented attachment, accompanied and promoted by simultaneous phase transformation from the precursor hydrogen titanate to rutile TiO 2 . The rutile TiO 2 mesocrystals thus synthesized were subjected to detailed structural characterization by means of scanning and transmission electron microscopy (SEM/TEM) including high-resolution TEM (HRTEM) and selected area electron diffraction (SAED), X-ray diffraction (XRD) and Raman spectroscopy. The rutile TiO 2 mesocrystals were tested for lithium-ion intercalation and demonstrated large reversible charge-discharge capacity and excellent cyclic stability, which could be attributed to the intrinsic characteristics of the mesostructured TiO 2 constructed from ultrathin nanowires offering large specific surface area for intercalation reaction and easy mass and charge transport, as well as sufficient void space accommodating volume change.

Heteroatom-doping is a promising strategy to tuning the microstructure of carbon material toward improved electrochemical storage performance. However, it is a big challenge to control the doping sites for heteroatom-doping and the rational design of doping is urgently needed. Herein, S doping sites and the influence of interlayer spacing for two kinds of hard carbon, perfect structure and vacancy defect structure, are explored by the first-principles method. S prefers doping in the interlayer for the former with interlayer distance of 3.997 Å, while S is doped on the carbon layer for the latter with interlayer distance of 3.695 Å. More importantly, one step molten salts method is developed as a universal synthetic strategy to fabricate hard carbon with tunable microstructure. It is demonstrated by the experimental results that S-doping hard carbon with fewer pores exhibits a larger interlayer spacing than that of porous carbon, agreeing well with the theoretical prediction. Furthermore, the S-doping carbon with larger interlayer distance and fewer pores exhibits remarkably large reversible capacity, excellent rate performance, and long-term cycling stability for Na-ion storage. A stable and reversible capacity of ≈200 mAh g is steadily kept even after 4000 cycles at 1 A g .

No abstract

Complex spinel titanate Li 2 MTi 3 O 8 (M ¼ Co, Zn, Co 0.5 Zn 0.5 ) nanowires have been synthesized via a simple synthetic route using titanate nanowires as a precursor. The nanowires are highly crystalline and have been used for the first time as the anode material in a rechargeable lithium-ion battery. The battery has exhibited a highly reversible charge-discharge capacity and excellent cycling stability, even at a current density as high as 3.2 A g À1 . This result can be attributed to the intrinsic characteristics of spinel Li 2 MTi 3 O 8 nanowires. A three-dimensional network could provide a diffusion space for lithium ion insertion into and extraction from the anode material, resulting in very good cycle performance, even at a high rate.

A major obstacle in realizing Na-ion batteries (NIBs) is the absence of suitable anode materials. Herein, we firstly report the anatase TiO2 mesocages constructed by crystallographically oriented nanoparticle subunits as a high performance anode for NIBs. The mesocages with tunable microstructures, high surface area (204 m2 g−1) and uniform mesoporous structure were firstly prepared by a general synthesis method under the assist of sodium dodecyl sulfate (SDS). It’s notable that the TiO2 mesocages exhibit a large reversible capacity and good rate capability. A stable capacity of 93 mAhg−1 can be retained after 500 cycles at 10 C in the range of 0.01–2.5 V, indicating high rate performance and good cycling stability. This could be due to the uniform architecture of iso-oriented mesocage structure with few grain boundaries and nanoporous nature, allowing fast electron and ion transport, and providing more active sites as well as freedom for volume change during Na-ion insertion. CV measurements demonstrate that the sodium-ion storage process of anatase mesocages is mainly controlled by pseudocapacitive behavior, which is different from the lithium-ion storage and further facilitates the high rate capability.

No abstract

No abstract