a high conductivity of 0.46 mS cm −1 at room temperature because the three-dimensional pathways in the open framework benefi t the diffusion of Na ions. [ 5 ] Further improvement (60%, 0.74 mS cm −1 ) has been obtained by substitution of Si on P sites in 94Na 3 PS 4 -6Na 4 SiS 4 . [ 6 ] However, the ionic conductivity is still low in comparison to liquid electrolytes, and therefore SEs with higher ionic conductivity need to be sought.Tatsumisago and co-workers found that an appropriate diffusion channel size is critical for fast ion diffusion and anion substitutions have a greater effect on ionic diffusivity than cation substitutions. [ 7 ] Moreover, Se-substituted lithium sulfi des demonstrate an enhanced ionic conductivity in comparison with their pristine compounds. [ 8 ] The advantages of Se-doping lie in two aspects. On one hand, the atomic radius of Se is bigger than that of S, so Se substitution on S sites may expand the lattice. On the other hand, the higher polarizability of Se 2− may weaken the binding energy between the moving ion and the anion framework. These modifi cations may be benefi cial for Na + diffusion because of the big ionic radius of sodium. It is therefore highly interesting to synthesize Na 3 PSe 4 and evaluate its electrochemical performance.In this study, cubic Na 3 PSe 4 was synthesized for the fi rst time and its crystal structure, spectra, and electrochemical performance were investigated. A ionic conductivity of 1.16 mS cm −1 was observed; to the best of our knowledge, this is one of the best values among sodium ion conductors and is the highest value reported for sulfi des to date. Figure 1 a shows the X-Ray Diffraction (XRD) pattern of Na 3 PSe 4 . The halo patterns in both cases refl ect the polyimide fi lm. The crystal structure of Na 3 PSe 4 has not been reported yet. Here, the integrated intensities from powder XRD data were extracted by the Le Bail method using the FullProf program. The crystal structure was solved by using the direct space method and was then refi ned by the Rietveld method. The crystal structure was determined to be cubic with the space group I -43 m (No. 217) and Z = 2. The plots of the observed, calculated, and difference patterns from the Rietveld refi nement (Figure 1 a) evidence the formation of single-phase Na 3 PSe 4 . The refi ned crystallographic data are listed in Table 1 . The cell has a lattice parameter a = 7.3094(2) Å, which is much larger than that of Si-doped Na 3 PS 4 ( a = 6.9978 Å). [ 6 ] A negative isotropic atomic displacement parameter ( U iso ) for P atoms and large U iso values for Na and Se atoms are obtained, indicating large disorders in the crystal structure. Comparison of the XRD patterns of Na 3 PSe 4 before and after ball milling ( Figure S1, Supporting Information) shows that only peak broadening is observed. This observation is in accordance with Differential scanning calorimetry (DSC) results ( Figure S2,The development of large-scale energy-storage system attracts worldwide attention because of the rapidly increasing de...

In this work, MnO(2)/GO (graphene oxide) composites with novel multilayer nanoflake structure, and a carbon material derived from Artemia cyst shell with genetic 3D hierarchical porous structure (HPC), are prepared. An asymmetric supercapacitor has been fabricated using MnO(2)/GO as positive electrode and HPC as negative electrode material. Because of their unique structures, both MnO(2)/GO composites and HPC exhibit excellent electrochemical performances. The optimized asymmetric supercapacitor could be cycled reversibly in the high voltage range of 0-2 V in aqueous electrolyte, which exhibits maximum energy density of 46.7 Wh kg(-1) at a power density of 100 W kg(-1) and remains 18.9 Wh kg(-1) at 2000 W kg(-1). Additionally, such device also shows superior long cycle life along with ∼100% capacitance retention after 1000 cycles and ∼93% after 4000 cycles.

The high Li-ion conductivity of the argyrodite Li6PS5Cl makes it a promising solid electrolyte candidate for all-solid-state Li-ion batteries. For future application, it is essential to identify facile synthesis procedures and to relate the synthesis conditions to the solid electrolyte material performance. Here, a simple optimized synthesis route is investigated that avoids intensive ball milling by direct annealing of the mixed precursors at 550 °C for 10 h, resulting in argyrodite Li6PS5Cl with a high Li-ion conductivity of up to 4.96 × 10–3 S cm–1 at 26.2 °C. Both the temperature-dependent alternating current impedance conductivities and solid-state NMR spin–lattice relaxation rates demonstrate that the Li6PS5Cl prepared under these conditions results in a higher conductivity and Li-ion mobility compared to materials prepared by the traditional mechanical milling route. The origin of the improved conductivity appears to be a combination of the optimal local Cl structure and its homogeneous distribution in the material. All-solid-state cells consisting of an 80Li2S–20LiI cathode, the optimized Li6PS5Cl electrolyte, and an In anode showed a relatively good electrochemical performance with an initial discharge capacity of 662.6 mAh g–1 when a current density of 0.13 mA cm–2 was used, corresponding to a C-rate of approximately C/20. On direct comparison with a solid-state battery using a solid electrolyte prepared by the mechanical milling route, the battery made with the new material exhibits a higher initial discharge capacity and Coulombic efficiency at a higher current density with better cycling stability. Nevertheless, the cycling stability is limited by the electrolyte stability, which is a major concern for these types of solid-state batteries.

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The relation between the argyrodite solid-electrolyte morphology and solid-state Li-ion battery performance is investigated, suggesting different morphologies for the electrode in combination electrolyte regions.