A high performance TiNb 2 O 7 anode material with a nanoporous nature, which was prepared by a facile approach, exhibits an average storage voltage of 1.66 V, a reversible capacity of 281 mA h g À1 , and an 84% capacity retention after 1000 cycles, and may be suitable for long-life stationary lithium-ion batteries.

Room-temperature sodium-ion batteries attract increasing attention for large-scale energy storage applications in renewable energy and smart grid. However, the development of suitable anode materials remains a challenging issue. Here we demonstrate that the spinel Li 4 Ti 5 O 12 , well-known as a 'zero-strain' anode for lithium-ion batteries, can also store sodium, displaying an average storage voltage of 0.91 V. With an appropriate binder, the Li 4 Ti 5 O 12 electrode delivers a reversible capacity of 155 mAh g À 1 and presents the best cyclability among all reported oxide-based anode materials. Density functional theory calculations predict a three-phase separation mechanism, 2Li 4 Ti 5 O 12 þ 6Na þ þ 6e À 2Li 7 Ti 5 O 12 þ Na 6 LiTi 5 O 12 , which has been confirmed through in situ synchrotron X-ray diffraction and advanced scanning transmission electron microscope imaging techniques. The three-phase separation reaction has never been seen in any insertion electrode materials for lithium-or sodium-ion batteries. Furthermore, interfacial structure is clearly resolved at an atomic scale in electrochemically sodiated Li 4 Ti 5 O 12 for the first time via the advanced electron microscopy.

Key indicators: single-crystal X-ray study; T = 293 K; mean (P-O) = 0.001 A ˚ ; disorder in solvent or counterion; R factor = 0.032; wR factor = 0.075; data-to-parameter ratio = 36.0. Single crystals of the title compound, trisodium divanadium-(III) tris(orthophosphate), were grown from a self-flux in the system Na 4 P 2 O 7-NaVP 2 O 7. Na 3 V 2 (PO 4) 3 belongs to the family of NASICON-related structures and is built up from isolated [VO 6 ] octahedra (3. symmetry) and [PO 4 ] tetrahedra (.2 symmetry) interlinked via corners to establish the framework anion [V 2 (PO 4) 3 ] 3À. The two independent Na + cations are partially occupied [site-occupancy factors = 0.805 (18) and 0.731 (7)] and are located in channels with two different oxygen environments, viz sixfold coordination for the first (3. symmetry) and eightfold for the second (.2 symmetry) Na + cation. Related literature For structures and properties of complex phosphates with general formula Na 3 M III 2 (PO 4) 3 (M III = Sc, Fe, Cr), see: Collin et al. (1986); Genkina et al. (1991); Lazoryak et al. (1980); Lucazeau et al. (1986); Masquelier et al. (1992); Susman et al. (1983). For preparation of NaVP 2 O 7 which was used as an educt for crystal growth of the title compound, see: Zatovsky et al. (1999). Experimental Crystal data Na 3 V 2 (PO 4) 3 M r = 455.76 Trigonal, R3c a = 8.7288 (2) A ˚ c = 21.8042 (7) A ˚ V = 1438.73 (7) A ˚ 3 Z = 6 Mo K radiation = 2.66 mm À1 T = 293 K 0.20 Â 0.15 Â 0.10 mm Data collection Oxford Diffraction Xcalibur-3 CCD diffractometer Absorption correction: multi-scan (Blessing, 1995) T min = 0.635, T max = 0.780 12580 measured reflections 1331 independent reflections 1153 reflections with I > 2(I) R int = 0.063

The full static picture of Li storage in Li(4)Ti(5)O(12) is derived using the latest spherical aberration-corrected scanning transmission electron microscopy and first-principles calculations. The accommodation of the additional Li(+) is directly visualized and the distribution of electrons introduced by lithium insertion deduced. Moreover, Li(4)Ti(5)O(12) is found to transform into Li(7)Ti(5)O(12) on lithiation by developing a dislocation-free coherent hetero-interface.

The mechanism of high-temperature superconductivity in the iron-based superconductors remains an outstanding issue in condensed matter physics. The electronic structure plays an essential role in dictating superconductivity. Recent revelation of distinct electronic structure and high-temperature superconductivity in the single-layer FeSe/SrTiO3 films provides key information on the role of Fermi surface topology and interface in inducing or enhancing superconductivity. Here we report high-resolution angle-resolved photoemission measurements on the electronic structure and superconducting gap of an FeSe-based superconductor, (Li0.84Fe0.16)OHFe0.98Se, with a Tc at 41 K. We find that this single-phase bulk superconductor shows remarkably similar electronic behaviours to that of the superconducting single-layer FeSe/SrTiO3 films in terms of Fermi surface topology, band structure and the gap symmetry. These observations provide new insights in understanding high-temperature superconductivity in the single-layer FeSe/SrTiO3 films and the mechanism of superconductivity in the bulk iron-based superconductors.

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Direct observation of delithiated structures of LiCoO(2) at atomic scale has been achieved using spherical aberration-corrected scanning transmission electron microscopy (STEM) with high-angle annular-dark-field (HAADF) and annular-bright-field (ABF) techniques. The ordered Li, Co, and O columns for LiCoO(2) nanoparticles are clearly identified in ABF micrographs. Upon the Li ions extraction from LiCoO(2), the Co-contained (003) planes distort from the bulk to the surface region and the c-axis is expanded significantly. Ordering of lithium ions and lithium vacancies has been observed directly and explained by first-principles simulation. On the basis of HAADF micrographs, it is found that the phase irreversibly changes from O3-type in pristine LiCoO(2) to O1-type Li(x)CoO(2) (x ≈ 0.50) after the first electrochemical Li extraction and back to O2-type Li(x)CoO(2) (x ≈ 0.93) rather than to O3-stacking after the first electrochemical lithiation. This is the first report of finding O2-Li(x)CoO(2) in the phase diagram of O3-LiCoO(2), through which the two previously separated LiCoO(2) phases, i.e. O2 and O3 systems, are connected. These new investigations shed new insight into the lithium storage mechanism in this important cathode material for Li-ion batteries.

Aqueous sodium-ion batteries have shown desired properties of high safety characteristics and low-cost for large-scale energy storage applications such as smart grid, because of the abundant sodium resources as well as the inherently safer aqueous electrolytes. Among various Na insertion electrode materials, tunnel-type Na 0.44 MnO 2 has been widely investigated as a positive electrode for aqueous sodium-ion batteries. However, the low achievable capacity hinders its practical applications. Here, a novel sodium rich tunneltype positive material with a nominal composition of Na 0.66 [Mn 0.66 Ti 0.34 ]O 2 is reported. The tunnel-type structure of Na 0.44 MnO 2 obtained for this compound is confi rmed by X-ray diffraction and atomic-scale spherical aberrationcorrected scanning transmission electron microscopy/electron energy-loss spectrum. When cycled as positive electrode in full cells using NaTi 2 (PO 4 ) 3 /C as negative electrode in 1 M Na 2 SO 4 aqueous electrolyte, this material shows the highest capacity of 76 mAh g −1 among the Na insertion oxides with an average operating voltage of 1.2 V at a current rate of 2 C. These results demonstrate that Na 0.66 [Mn 0.66 Ti 0.34 ]O 2 is a promising positive electrode material for rechargeable aqueous sodium-ion batteries.