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Despite extensive effort during the past few decades, a comprehensive understanding of the key variables governing the electrochemical properties of cathode materials in Li-ion batteries is still far from complete. To elucidate the critical parameters affecting energy density (ED) and capacity (Q) retention in layer and spinel cathodes, we data-mine the existing experimental data via confirmatory factor analysis (CFA) based on a structural equation model (SEM), which is a proven, versatile tool in understanding complex problems in the social science. The data sets are composed of 18 and 15 parameters extracted from 38 layer and 33 spinel compounds, respectively. CFA reveals the irrelevance of Q retention to all the parameters we adopt, but it also reveals the sensitive variations of ED with specific parameters. We validate the usefulness of CFA in material science and pinpointed critical parameters for high-ED cathodes, hoping to suggest a new insight in materials design. [ABSTRACT FROM AUTHOR]

Poly(hexyl viologen dichloride) (PHV-Cl) is described as a high energy density (ED) material in magnesium-based electrolytes. When coupled with Mg metal in all phenyl complex (APC) electrolytes, PHV-Cl cathodes demonstrate anion-transport behaviors with the reduction/oxidation of viologen units. This dual-ion type cell delivers a relatively high ED with reasonable stability during repeated charge/discharge (C/D) when compared with previously reported inorganic/organic cathodes in magnesium-ion batteries (MIBs). PHV-Cl shows a capacity of 171 mAh g −1 at an average discharge potential of 1.33 V vs. Mg/Mg 2+ , resulting in a significantly high ED (227 mWh g −1 ). The high ED characteristics of PHV-Cl are retained during repeated C/D cycles (201 mWh g −1 after 50 C/D) in contrast to the relative instability of other previously reported organic cathodes. Herein, the electrochemical performance of PHV-Cl in various types of electrolytes is also described. This work suggests that viologen-based cathodes with anion-transport properties could be implemented to achieve high levels of ED and stability via a dual-ion mode in MIBs, particularly with currently available electrolytes that are compatible with magnesium metal. [ABSTRACT FROM AUTHOR]

Though redox-based electrode materials with a high surface-area are expected to bridge the gap between supercapacitors and rechargeable batteries in energy-storage applications, full utilization of the inherent electoactivity is frequently hindered by the limited diffusion of electrolytes, paricularly during high-rate charge/discharge. Here, we demonstrate the electrochemical properties of Ni(OH) 2 nanoplatelets that are vertically grown on graphene by employing poly(amidoamine) dendrimers as growth directing agents and as linkers. By virtue of the structural features, Ni(OH) 2 electrodes deliver a maximum specific capacity of 1226 Cg −1 (2043 Fg −1 ) at 5 mVs −1 . The electrodes also retain a substantial capacity at high charge/discharge rates (955 Cg −1 at 1 Ag −1 vs. 560 Cg −1 at 80 Ag −1 ). The cycability is also remarkable, exhibiting the capacity retention of 102% after 5000 cycles at 10 Ag −1 . These excellent electrochemical properties are contrasted with those of a composite prepared without dendrimers (496 Cg −1 at 5 mVs −1 ; 486 Cg −1 at 1 Ag −1 vs. 184 Cg −1 at 80 Ag −1 ; 78% retention). By virtue of Ni(OH) 2 nanoplatelets, an asymmetric full-cell coupled with a graphene electrode can deliver one of the highest energy densities ever reported (52–58 Whkg −1 ) with high power densities that range between 1.0 and 20.0 kWkg −1 . [ABSTRACT FROM AUTHOR]

BCC-based refractory complex concentrated alloys (RCCAs) are attracting attention as high-temperature materials because of their exceptional strength at high temperatures, but suffer from low tensile ductility. To search for alloys with improved ductility, it is necessary to investigate the properties of RCCA systems thoroughly, however, an experimental investigation of these vast constitutional spaces is impractical. This study employed data-driven approaches that combined first-principles calculations with machine learning. We first calculated the lattice parameters and elastic constants of 1693 ternary RCCAs, subsets of RCCAs alloys consisting of Ti, Zr, Hf, Nb, Mo, V, Ta, and W, using the exact muffin-tin orbitals method with coherent potential approximation (EMTO-CPA), and generated ductility-related parameters, including Pugh's ratio, Poisson's ratio, and Cauchy pressure. Machine learning models that could predict the three parameters were searched and trained using the generated data. Subsequently, an inverse design based on optimization algorithms was performed to identify optimal alloy systems with high Pugh's ratios. The ductility of the searched alloys was verified by calculating Pugh's ratio using EMTO-CPA, followed by thermodynamic calculations to investigate their structural stability. [Display omitted] • Ductility-related parameters of 1693 ternary RCCAs were calculated. • Machine learning and meta-heuristics search explored the alloys with high ductility. • First-principles and thermodynamic calculations validated the alloys explored. • The explored alloy with the highest expected ductility is Ti 91.2 Zr 1.0 Hf 7.8 [ABSTRACT FROM AUTHOR]

Abstract: SnO2 nanoparticles (SNPs) entrapped in a graphene framework are synthesized for use as an anode material in Li ion batteries. A framework is prepared by covalently linking SNPs-anchored graphene oxide layers with diboronic acids. The framework provides the SNPs with more effective buffering than thermally reduced graphene oxide. SNPs in a graphene framework maintain the initial particle size and morphology after repeated charge-discharge cycles, with no inter-particle aggregation. The volume increase of the composite, accompanied by Li+ insertion into SNPs, is also significantly suppressed. The isolation of an individual nanoparticle and the firmness of a framework, which are ascribed to densely cross-linked graphene layers, results in better cyclability and rate performance by comparison with thermally reduced SNPs-anchored graphene oxide. [Copyright &y& Elsevier]

The goal of the present investigation was to visualize the propagating crack in a mechano-luminescence (ML) material to enable the measurement of instantaneous R-curves and directly observe the bridging (shielding) stress in a fast-propagating crack system. The well-known ML compound, SrAl2O4: Eu2+, was used as a model test material. Two additional trivalent rare earth elements, Dy and Nd, were introduced as co-dopants to improve the luminescent efficiency. The initiation and growth of a crack from the mechanically machined sharp notch tip in a disc shaped compact tension (CT) specimen at a relatively high loading rate were found to be associated with the extent of light emission around the crack. An in-situ measurement of crack length and applied load for 0.3 sec yielded an instantaneous R-curve at the conventional crack propagation speed. [Copyright &y& Elsevier]

Herein is the first use of a CoSn(OH) 6 /graphene composites as a high-performance anode in lithium ion batteries (LIBs). CoSn(OH) 6 alone is found to be electrochemically active and to possess electrochemical properties that are superior to those displayed in its dehydrated form (CoSnO 3 ). In contrast to the formation of 3Li 2 O in CoSnO 3 during the first discharge (CoSnO 3 + 6Li + + 6e − → Co + Sn + 3Li 2 O), the production of 6 mol of LiOH in CoSn(OH) 6 (CoSn(OH) 6 + 6Li + + 6e − → Co + Sn + 6LiOH) seems to provide nanometric Co/Sn particles with more efficient reversibility for the subsequent Li + -insertion/de-insertion via conversion/alloy reactions. The electrochemical performance of CoSn(OH) 6 is further improved when composited with graphenes. This is accomplished by electrostatically combining negatively charged Co 2 + /Sn 2 + -anchored graphene oxide (GO) with positively charged amine-functionalized graphene (GN) in a solution. The subsequent hydrothermal reaction produces CoSn(OH) 6 nanocubes that are tightly held by graphene sheets (GO/CS/GN). The GO/CS/GN delivers unprecedentedly high capacity and excellent cyclability (discharge capacities of 1475 mAh·g − 1 for the 100th charge/discharge (C/D) cycles at a 0.1 A·g − 1 ). In contrast to the comparison materials (CoSnO 3 /graphene composites) the rate performance is also remarkable, delivering a capacity of 650 mAh·g − 1 at 2.0 A·g − 1 . [ABSTRACT FROM AUTHOR]

A thermally expanded graphene oxide (EGO) electrode is electrochemically activated to simultaneously introduce electrolyte-accessible mesopores and oxygen functional groups. The former is produced via O 2 evolution and the latter is incorporated by the intermediate hydroxyl radicals generated during the potentiostatic oxidation of H 2 O in 1 M H 2 SO 4 at 1.2 V (vs. Ag/AgCl). When applied as a supercapacitor, the potentiostatically treated EGO (EGO-PS) shows significant enhancement in an electric-double layer (EDL) process with a noticeable Faradaic reaction and delivers high capacitance at fast charge/discharge (C/D) rates (334 F g −1 at 0.1 A g −1 and 230 F g −1 at 50 A g −1 ). In contrast to EGO-PS, EGO that is oxidized potentiodynamically (EGO-PD) shows negligible enhancement in EDL currents. EGO that is subjected to successive potential pulses also shows behaviors similar to EGO-PD, which indicates the importance of hydroxyl radical accumulation via a potentiostatic method for simultaneous functionalization and microstructural control of graphenes. The potentiostatic post-treatment presented here is a convenient post-treatment strategy that could be used to readily increase capacitance and simultaneously improve the high-rate performance of carbon-based electrodes. [ABSTRACT FROM AUTHOR]

Na x Ca y CoO 2 (0.45 ≤ x ≤ 0.64, 0.02 ≤ y ≤ 0.10) is synthesized via a solid-state method and examined as a cathode material to improve the cyclability of sodium ion batteries (SIBs). The substitution of one Ca 2+ for two Na + does not alter the P2-phase of undoped Na 0.73 CoO 2 , accompanying the continuous contraction of the unit cell volume with Ca-doping. The existence of Ca 2+ in the prismatic sites between CoO 6 slabs also affects the phase transition behaviors during charge–discharge (C–D). The suppression of Na + -vacancy ordering, ascribed to the immobility of Ca 2+ in Na x Ca y CoO 2 , leads to continuous changes of the cell voltages with no abrupt voltage drops during C–D. The reduced cell dimension and the mitigation of distinctiveness between biphasic and solid-solution domains during C-D improve the cyclability of Na x Ca y CoO 2 in SIBs. As an example, the negligible capacity fading in Na 0.60 Ca 0.07 CoO 2 during 60 cycles (0.07 mAh g −1 cycle −1 ) is contrasted with a substantial decrease in the reversible capacity of Na 0.73 CoO 2 (0.56 mAh g −1 cycle −1 ). Furthermore, a slower Na + diffusion of Na x Ca y CoO 2 in Na + -vacancy ordering regions, is sufficiently offset by a more rapid diffusion in all the other regions, which results in an improved rate performance. The platform presented here (multi-valent cation substitution for Na + ) could be utilized in other layered cathode materials to improve the electrochemical performance of SIBs. [ABSTRACT FROM AUTHOR]

Lattice oxygen mechanism (LOM) is a promising pathway to circumvent sluggish oxygen evolution reaction (OER) for efficient water electrolysis. The iron (Fe)-based oxyhydroxide materials for OER catalysts by LOM is well known. However, dissolution of Fe atoms and promoting participation level of lattice oxygen at a practical and extremely high current density (> 1000 mA cm-2 for oxygen generation) should be resolved for high performance and long-term stability. Here, controlling the reduction of synthetic intermediates allowed amorphous BiFe (oxy)hydroxides with secondary bismuth (Bi) metal (BM/BiFeO x H y) heterogeneous structures with abundant lattice vacancies to be obtained. The BM/BiFeO x H y electrode exhibited low overpotential of 232 and 359 mV at a current density of 10 and 1000 mA cm-2, respectively. Moreover, the balanced hybridization of Bi/Fe-O was demonstrated to result in long-term catalytic stability without the dissolution of Fe atoms up to 1000 h at the extremely high current density of 1000 mA cm-2 with negligible degradation. We further showed that the excellent performance of the newly proposed BM/BiFeO x H y electrocatalysts is attributed to the utilization of Fe/Bi-O hybridization, the induced amorphous structure, and increased lattice vacancies, which are systematically demonstrated by the electrochemical and physicochemical analysis and theoretical density functional theory (DFT) calculation. Bi metal/BiFe (oxy)hydroxides (BM/BiFeO x H y) heterostructure with internal voids was obtained by simple solvothermal process under reduction environment. Oxygen evolution reaction (OER) of BM/BiFeO x H y evolved Bi metal into high valence state, which enables lattice oxygen mechanism (LOM). [Display omitted] • BM/BiFeO x H y with lattice vacancies was developed by a simple solvothermal synthesis. • Electrode shows the long-term OER operation at high current density of 1000 mA cm-2. • Fe/Bi-O hybridization and the induced amorphous structure increase the performance. • DFT has confirmed lattice oxygen mechanism (LOM) in the OER activity of BM/BiFeO x H y. [ABSTRACT FROM AUTHOR]

Abstract: SnO2/graphene nanocomposites were prepared from graphite oxide (GTO). Sn2+ precursors were impregnated between graphene layers of GTO and subsequently subjected to thermal treatment to produce nanocomposites consisting of SnO2 and reduced GTO (SnO2/rGTO). When thermally reduced, the pre-aligned nature of graphene layers in GTO produced densely packed and thick graphene stacks, in contrast to graphene layers in the SnO2 nanocomposites (SnO2/rGO) made from thermal reduction of mechanically exfoliated graphene oxide (GO). The surface area and void volume of the SnO2/rGTO nanocomposites (280m2 g−1 and 0.27cm3 g−1, respectively) were significantly decreased, by comparison with those of the SnO2/rGO nanocomposites (390m2 g−1 and 0.39cm3 g−1, respectively), which resulted in an enhanced dimensional-stability of SnO2 during the lithium alloying/dealloying processes. As a result, SnO2/rGTO proved to be superior to SnO2/rGO as an anode material in lithium ion batteries from the view-point of both reversible charge–discharge (C–D) capacity and cyclability. The simplification of the nanocomposite preparation process (the removal of mechanical exfoliation) is an additional benefit of using GTO as a template. [Copyright &y& Elsevier]

Abstract: W-doped LiW x Ni0.5Mn1.5−x O4 (x =0.00–0.10) are synthesized via a sol–gel method, and their electrochemical properties are investigated. During synthesis, W4+ is converted to W6+, the amount of which significantly affects the charge–discharge behaviors of LiW x Ni0.5Mn1.5−x O4. When limited to x ≤0.005, W-doping enhances the electrochemical activity of cathodes, leading to a greater discharge capacity and less capacity fading than LiNi0.5Mn1.5O4 at high C-rates. This is interesting since lowering the average valence state of Mn ions by incorporating W6+ can introduce structural instability, extending a 4V plateau (Mn3+/4+). The reasons for such behavior associated with W-doping are examined by electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and impedance spectroscopy. It is disclosed that the simultaneous increase in Lingth and decrease in transition metal-oxide bond length, while the unit cell volume is maintained almost invariant, provides LiW0.005Ni0.5Mn1.495O4 with optimal high rate performance. When W-doping exceeds x =0.01, 3 factors (intrinsically low electronic conductivity of W6+, the presence of tungsten oxide impurities, and an increase in the inter-metallic distance) aggravates electrochemical performance of LiW x Ni0.5Mn1.5−x O4. The last factor also induces structural instability during repeated cycling because of the expansion of a unit cell volume. [Copyright &y& Elsevier]

Abstract: The use of a mechanoluminescent (ML) paint enables a propagating crack and bridging stress distribution to be visualized. This technique was used to examine the mechanism of fracture in alumina ceramics. The mechanism appears to be inconsistent with currently accepted R-curve concepts. The magnitude and shape of the bridging stress distribution changes with the advancing crack. It continues to change as the applied load changes, even after the cessation of crack propagation. The measured R-curve increased dramatically up to . ML technology provides not only a versatile tool for the study of fracture mechanism, but also has the potential for use in the low-cost safety diagnosis of structural components or the visualization of microelectromechanical systems operations. [Copyright &y& Elsevier]

ZnO thin films were grown on c-plane sapphire and GaAs (001) substrates by metalorganic chemical vapor deposition. Atomic force microscopy and double-crystal X-ray diffractometry were utilized to investigate the structural properties of the ZnO films. The optical properties of ZnO films were also investigated in terms of time integrated and resolved photoluminescence (TIPL and TRPL). Large hexagonal crystallites and better crystalline quality were observed from the ZnO film on sapphire. Also, both the TIPL and TRPL showed a significant difference as the substrate changed. In particular, a detected sharp contrast in the result of TRPL measurement is due to the different defect structure and the lattice strain and stress of ZnO films on different substrates. [Copyright &y& Elsevier]

The development of electrode materials with higher energy/power densities is crucial for magnesium batteries to become a viable alternative to lithium-ion batteries. Herein, we describe a possible solution that involves high-voltage redox polymer (poly(vinyl carbazole), PVCz) cathodes and alloy-type anodes (3Mg/Mg 2 Sn) in Mg(TFSI) 2 /acetonitrile (TFSI = bis(trifluoromethanesulfonyl)imide). When low molecular weight PVCz is crosslinked (x-PVCz), the density of micro-to-macro pores and the electronic conductivity are remarkably enhanced, which enables the attainment of near theoretical capacities (122 mAh g−1) with a marginal voltage drop even at a rate of 2000 mA g−1 (14.3C). This corresponds to energy and power densities of 384 Wh kg−1 and 6300 W kg−1, respectively, which are incomparably high values for magnesium batteries. Their cyclic stability also is excellent, delivering 94.2% of the initial capacity during 2000 charge/discharge cycles. Magnesium-based dual ion batteries (MDIBs), which consist of de-magnesiated 3Mg/Mg 2 Sn anodes and x-PVCz cathodes in Mg(TFSI) 2 /acetonitrile, also retain the unique properties of x-PCVz. The discharge voltages are slightly decreased due to an alloy/de-alloy potential of 3Mg/Mg 2 Sn, but high energy/power densities and excellent cyclability are maintained. This work evidences the excellence of x-PVCz and hints the usefulness of MDIBs for the construction of viable magnesium batteries. [Display omitted] • Poly(vinyl carbazole) (PVCz) is used as an anion-insertion cathode for Mg batteries. • Crosslinking of PVCz (x-PVCz) significantly increases the porosity and conductivity. • x-PVCz∥Mg(TFSI) 2 /ACN∥3Mg/Mg 2 Sn shows astonishingly high energy/power densities. • Highest ED (394 Wh kg−1) and PD (5860 W kg−1) at 2.93 V are retained for 1000 cycles. • This work proves that dual-ion concept can make a breakthrough in Mg batteries. [ABSTRACT FROM AUTHOR]

The search for new materials that exhibit rapid Faradaic energy-storing behavior continues to be ever more important as they offer a promising alternative to battery technology because of their unrivalled ability to deliver large amounts of power along with large amounts of energy. Here, we present a reduced binary anion compound (r-BAC) as a first demonstration of redox-active materials, which are fabricated by a facile and direct activation synthetic method. The r-BAC exhibits excellent energy storage characteristics compared to non-reduced full binary anion compound (f-BAC). Based on the density functional theory (DFT) calculations and the ex-situ chemical study, it is found that the superior electrochemical performance is strongly attributed to not only the Ni cation sites (Ni2+/Ni3+ redox couple) that are energetically more activated by oxygen vacancies, but also to the additive electrochemical activity at the unsaturated sulfur sites (S4+/S6+ redox couple) in a binary anion. Thus, we expect that this study on the binary anion material and the corresponding anion-based charge transfer mechanisms may provide a new strategy for the efficient storage of charge in next-generation energy storage applications. • We first propose an electrochemically active binary anion compound. • A novel binary anion compound has the tailored oxygen vacancy site. • The electrode shows excellent electrochemical energy storage abilities. • The electrochemical features are highly dependent on anion-mediated active sites. • DFT calculations exhibit the possibility of anion-based Faradaic redox reactions. [ABSTRACT FROM AUTHOR]

A novel layered P2–K ~2/3 [Ni 1/3 Mn 2/3 ]O 2 (K 0·64 Na 0·04 [Ni 1/3 Mn 2/3 ]O 2 , KNMO) is presented as a high-performance cathode for K+-ion batteries. KNMO is prepared via an electrochemical ion-exchange of P2–Na 0.64 [Ni 1/3 Mn 2/3 ]O 2 (NNMO). During 50 charge/discharge (C/D) cycles within a P2-phase range, NNMO gradually turns to KNMO and finally reaches KNMO through a biphasic state. The as-prepared KNMO shows a P2–O2 transition at 4.65 V vs. K/K+, which implies that K+-preference in the prismatic sites of KNMO leads to the formation of O2-phases at higher voltages than that predicted from NNMO. Thanks to the retardation of the P2–O2 transition and fast diffusion during K+ extraction (0.57 × 10−11 cm2 s−1), KNMO can be quickly charged within the P2-phase region without a significant loss in discharge capacities. For example, comparable capacities of 82 and 75 mAh·g−1 during discharge (0.5C) are obtained after charging at 0.5 and 15C (2580 mA g−1), respectively. This behavior is contrasted with a significant reduction in capacities when cycled at the same C/D rates or when cycled at C/D rates of 0.5/15C, respectively. KNMO also shows excellent cyclability during fast charging, retaining a reversible capacity of 73 mAh·g−1 after 200C/D cycles (0.01 mAh·g−1·cycle−1). • P2–K ~2/3 [Ni 1/3 Mn 2/3 ]O 2 is prepared via ion-exchange from Na 0·64 [Ni 1/3 Mn 2/3 ]O 2. • K+-preference in prismatic sites renders P2–O2 transition to occur at higher voltage. • K+ diffusion during charge is 3-fold faster than that during discharge. • These contribute to fast-chargeable (15C) with a reasonable capacity (75 mAh·g−1). [ABSTRACT FROM AUTHOR]