Large-scale electric energy storage is a key enabler for the use of renewable energy. Recently, the room-temperature Na-ion battery has been rehighlighted as an alternative low-cost technology for this application. However, significant challenges such as energy density and long-term stability must be addressed. Herein, we introduce a novel cathode material, Na1.5VPO4.8F0.7, for Na-ion batteries. This new material provides an energy density of ~600 Wh kg(-1), the highest value among cathodes, originating from both the multielectron redox reaction (1.2 e(-) per formula unit) and the high potential (~3.8 V vs Na(+)/Na) of the tailored vanadium redox couple (V(3.8+)/V(5+)). Furthermore, an outstanding cycle life (~95% capacity retention for 100 cycles and ~84% for extended 500 cycles) could be achieved, which we attribute to the small volume change (2.9%) upon cycling, the smallest volume change among known Na intercalation cathodes. The open crystal framework with two-dimensional Na diffusional pathways leads to low activation barriers for Na diffusion, enabling excellent rate capability. We believe that this new material can bring the low-cost room-temperature Na-ion battery a step closer to a sustainable large-scale energy storage system.

Insulation resistance degradation of dielectric BaTiO(3) is expected to be closely correlated to its defect structure frozen in from elevated processing temperatures. For BaTiO(3), respectively doped with variable-valence (Mn(Ti)) and fixed-valence acceptors (Al(Ti)), their defect structures were frozen in by quenching at different equilibrium oxygen activities in the range of -18 < log a(O(2))< or = 0 at 1000 and 900 degrees C, respectively, and their electrical conductivities were measured against temperature in the range of 200 < or =T/K < or = 494 by impedance spectroscopy. Frozen-in defect structures were calculated and compared with the conductivity as measured in the quenched state. A close correlation has been confirmed between the bulk conductivity as measured in the quenched state and the frozen-in defect structure as calculated. The effects of variable- and fixed-valence acceptor impurities on the defect structure and electrical conductivity in the quenched state are highlighted in the light of hole trapping, and the charge transport behavior in the quenched state is discussed.

We demonstrate here that an improvement in the green density leads to a great enhancement in the photovoltaic performance of CuInSe2 (CISe) solar cells fabricated with Cu-In nanoparticle precursor films via colloidal solution deposition. Cold-isostatic pressing (CIP) increases the precursor film density by ca. 20%, which results in an appreciable improvement in the microstructural features of the sintered CISe film in terms of a lower porosity, a more uniform surface morphology, and a thinner MoSe2 layer. The low-band-gap (1.0 eV) CISe solar cells with the CIP-treated films exhibit greatly enhanced open-circuit voltage (V(OC), typically from 0.265 to 0.413 V) and fill factor (FF, typically from 0.34 to 0.55), compared to the control devices. As a consequence, an almost 3-fold increase in the average efficiency, from 3.0 to 8.2% (with the highest value of 9.02%), is realized. Diode analysis reveals that the enhanced V(OC) and FF are essentially attributed to the reduced reverse saturation current density and diode ideality factor. This is associated with suppressed recombination, likely due to the reduction in recombination sites at grain/air surfaces, intergranular interfaces, and defective CISe/CdS junctions. From the temperature dependences of V(OC), it is revealed that CIP-treated devices suffer less from interface recombination.

A novel, Na-pillared LiMnPO4 with an alluaudite structure that allows fast lithium diffusion with stable electrochemical cycling as a cathode in lithium batteries.

On undoped polycrystalline BaTiO(3-delta) (99.9% nominal purity), that had been equilibrated and quenched at 1000 degrees C under different oxygen activities in the range of -19.4 < or = log a(O(2)) < 0.1, were measured optical reflectance spectra at 298 K and ac conductivity at 473, 523 and 573 K, respectively. It was observed that all specimens quenched at log a(O(2)) > -17 are electrically insulating and white in color, once powdered, and show optical absorption only at the absorption edge at approximately 3 eV. In contrast, those quenched at log a(O(2)) < -17 are electronically conducting and dark and exhibit a significant absorption in the IR region. This demarcating oxygen activity for the conductivity transition is ca. 13 orders of magnitude lower than that for the n-to-p type transition (delta = 0) in the equilibrium state, contrary to expectation. It is, thus, suggested that contrary to the textbook knowledge, the hole traps responsible for the conductivity transition in undoped BaTiO(3) may be variable-valent acceptor defects like Mn(Ti). The strong IR absorption in the semiconducting state is ascribed to small-polaron (Ti'(Ti)) hopping processes.