Using first-principles simulations, we predict a high-performance solid electrolyte with composition Na 10 GeP 2 S 12 for use in sodium-sulfur (Na-S) batteries. The thermodynamic stability of its structure is established through determination of decomposition reaction energies and phonons, while Na-ionic conductivity is obtained using ab initio molecular dynamics at elevated temperatures. Our estimate of the room-temperature (RT) conductivity is 4.7 Â 10 À3 S cm À1 , which is slightly higher than those of other superionic solid electrolytes such as b 00 -alumina and Na 3 Zr 2 Si 2 PO 12 , currently used in practical hightemperature Na-S batteries. Activation energy obtained from the Arrhenius plot (in the range 800-1400 K) is 0.2 eV, which is slightly lower than the typical values exhibited by other ceramic conductors (0.25-1 V) (Hueso et al., Energy Environ. Sci., 2013, 6, 734). We show that soft Na-S phonon modes are responsible for its thermodynamic stability and the lower activation barrier for diffusion of Na-ions.Finally, the calculated electronic bandgap of 2.7 eV (a wide electrochemical window) augurs well for its safe use in sodium batteries. Opening up a possibility for realizing RT operation of Na-S batteries, our prediction of a new phase in the Na-Ge-P-S system will stimulate experimental studies of the material.

Structural and kinetic behavior of lithium-vanadium-oxide (Li x V 3 O 8 ) cathode is studied as lithium-ion battery electrode. The morphology of Li x V 3 O 8 is found to be nanoplates with nanorods as minor constituents. Theoretical prediction shows such a nanoplate morphology will have almost thirty four times faster lithium diffusion than spherical particle of same volume. In the present study, experimental and theoretical observation of Fourier transform infrared spectroscopy (FT-IR) is compared to investigate the vibrational mode of V-O bond. Li x V 3 O 8 cathode, delivers a high discharge capacity of 270 mAh g −1 at 200 mA g −1 and as high as 200 mAh g −1 , 135 mAh g −1 , and 100 mAh g −1 at 1000 mA g −1 , 2000 mA g −1 , and 3000 mA g −1 current rates respectively. A detailed electrode kinetic study using galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS) are performed to establish the relationship between high rate capability with kinetic parameters. The diffusion co-efficient (D Lithium ) value of Li x V 3 O 8 is estimated to be ∼ 10 −15 −10 −13 cm 2 s −1 and 10 −13 −10 −11 cm 2 s −1 in the single phase region (0 ≤ x ≤ 1.7) during discharge and charge processes respectively. Further, ex situ XRD is performed on Li x V 3 O 8 cathode material to study the phase transformation during charge/discharge process.

Solid‐state electrochemistry is drawing considerable interest as the interconversion of O2 and water playing an important role in energy conversion and storage technologies. With the aim of developing an efficient bifunctional catalyst by tuning the electronic properties and local structure around the 3d metal in CoWO4, solid solutions of Co1−xMnxWO4 are investigated. Nanocrystalline Co1−xMnxWO4 (x=0 to 1) phases with a unique exposure of low surface energy planes are synthesized by hydrothermal methods. Replacing an optimum amount of Co with Mn to enhance the catalytic activity leads a observation of a negative shift in the Co2+/3+ redox wave and onset of the oxygen evolution reaction (OER), indicating a strong electronic interaction between the two elements. The composition corresponding to Co0.5Mn0.5WO4 has demonstrated great ability to catalyze both the OER and oxygen reduction reaction (ORR) with a combined overpotential of 0.89 V. It exhibited an OER current density of 10 mA cm−2 at an overpotential of 400 mV. Whereas ORR current density of 3 mA cm−2 is reached at a potential of 0.74 V versus reversible hydrogen electrode (RHE). The density functional theory revealed that the substitution of Mn in CoWO4 elevate the 3d metal d band center closer to the Fermi energy and hence ease the electron transfer to facilitate ORR and OER.

Sodium-ion battery (NIB) cathode performance based on ammonium vanadate is demonstrated here as having high capacity, long cycle life and good rate capability. The simple preparation process and morphology study enable us to explore this electrode as suitable NIB cathode. Furthermore, density functional theory (DFT) calculation is envisioned for the NH4V4O10 cathode, and three possible sodium arrangements in the structure are depicted for the first time. Relevant NIB-related properties such as average voltage, lattice constants, and atomic coordinates have been derived, and the estimated values are in good agreement with the current experimental values. A screening study shows ammonium vanadate electrodes prepared on carbon coat onto Al-current collector exhibits a better electrochemical performance toward sodium, with a sustained reversible capacity and outstanding rate capability. With the current cathode with nanobelt morphology, a reversible capacity of 190 mAh g(-1) is attained at a charging rate of 200 mA g(-1), and a stable capacity of above 120 mAh g(-1) is retained for an extended 50 cycles tested at 1000 mA g(-1) without the addition of any expensive electrolyte additive.

We review our studies of the initial oxidation stages of Cu(001) thin films as investigated by in situ ultra-high vacuum transmission electron microscopy. We present our observations of surface reconstruction and the nucleation to coalescence of copper oxide during in situ oxidation in O2. We have proposed a semi-quantitative model, where oxygen surface diffusion is the dominant mechanism of the initial oxidation stages of Cu. We have also investigated the effect of water vapor on copper oxidation. We have observed that the presence of water vapor in the oxidizing atmosphere retards the rate of Cu oxidation and Cu2O is reduced when exposed directly to steam.