Theoretical Evidence for Low Charging Overpotentials of Superoxide Discharge Products in Metal–Oxygen Batteries

Li–oxygen and Na–oxygen batteries are some of the most promising next-generation battery systems because of their high energy densities. Despite the chemical similarity of Li and Na, the two systems exhibit distinct characteristics, especially the typically higher charging overpotential observed in Li–oxygen batteries. In previous theoretical and experimental studies, this higher charging overpotential was attributed to factors such as the sluggish oxygen evolution or poor transport property of the discharge product of the Li–oxygen cell; however, a general understanding of the interplay between the discharge products and overpotential remains elusive. Here, we investigated the charging mechanisms with respect to the oxygen evolution reaction (OER) kinetics, charge-carrier conductivity, and dissolution property of various discharge products reported in Li–oxygen and Na–oxygen cells. The OER kinetics were generally faster for superoxides (i.e., LiO₂ and NaO₂) than for peroxides (i.e., Li₂O₂ and Na₂O₂). The electronic and ionic conductivities were also predicted to be significantly higher in superoxide phases than in peroxide phases. Moreover, systematic calculations of the dissolution energy of the discharge products in the electrolyte, which mediate a solution-based OER reaction, revealed that the superoxide phases, particularly NaO₂, exhibited markedly low dissolution energy compared with the peroxide phases. These results imply that the formation of superoxides instead of peroxides during discharge may be the key to improving the energy efficiency of metal–oxygen batteries in general

Ultrahigh Tensile Strength Nanowires with a Ni/Ni–Au Multilayer Nanocrystalline Structure

Superior mechanical properties of nanolayered structures have attracted great interest recently. However, previously fabricated multilayer metallic nanostructures have high strength under compressive load but never reached such high strength under tensile loads. Here, we report that our microalloying-based electrodeposition method creates a strong and stable Ni/Ni–Au multilayer nanocrystalline structure by incorporating Au atoms that makes nickel nanowires (NWs) strongest ever under tensile loads even with diameters exceeding 200 nm. When the layer thickness is reduced to 10 nm, the tensile strength reaches the unprecedentedly high 7.4 GPa, approximately 10 times that of metal NWs with similar diameters, and exceeding that of most metal nanostructures previously reported at any scale

Ultrahigh Tensile Strength Nanowires with a Ni/Ni–Au Multilayer Nanocrystalline Structure

Superior mechanical properties of nanolayered structures have attracted great interest recently. However, previously fabricated multilayer metallic nanostructures have high strength under compressive load but never reached such high strength under tensile loads. Here, we report that our microalloying-based electrodeposition method creates a strong and stable Ni/Ni–Au multilayer nanocrystalline structure by incorporating Au atoms that makes nickel nanowires (NWs) strongest ever under tensile loads even with diameters exceeding 200 nm. When the layer thickness is reduced to 10 nm, the tensile strength reaches the unprecedentedly high 7.4 GPa, approximately 10 times that of metal NWs with similar diameters, and exceeding that of most metal nanostructures previously reported at any scale

Dehydrogenation Reaction Pathway of the LiBH₄–MgH₂ Composite under Various Pressure Conditions

This paper investigates dehydrogenation reaction behavior of the LiBH₄–MgH₂ composite at 450 °C under various hydrogen and argon back-pressure conditions. While the individual decompositions of LiBH₄ and MgH₂ simultaneously occur under 0.1 MPa H₂, the dehydrogenation of MgH₂ into Mg first takes place and subsequent reaction between LiBH₄ and Mg into LiH and MgB₂ after an incubation period under 0.5 MPa H₂. Under 1 MPa H₂, enhanced dehydrogenation kinetics for the same reaction pathway as that under 0.5 MPa H₂ is obtained without the incubation period. However, the dehydrogenation reaction is significantly suppressed under 2 MPa H₂. The formation of Li₂B₁₂H₁₂ as an intermediate product during dehydrogenation seems to be responsible for the incubation period. The degradation in hydrogen capacity during hydrogen sorption cycles is not prevented with the dehydrogenation under 1 MPa H₂, which effectively suppresses the formation of Li₂B₁₂H₁₂. The overall dehydrogenation behavior under argon pressure conditions is similar to that at hydrogen pressure conditions, except that under 2 MPa Ar

A Half Millimeter Thick Coplanar Flexible Battery with Wireless Recharging Capability

Most of the existing flexible lithium ion batteries (LIBs) adopt the conventional cofacial cell configuration where anode, separator, and cathode are sequentially stacked and so have difficulty in the integration with emerging thin LIB applications, such as smart cards and medical patches. In order to overcome this shortcoming, herein, we report a coplanar cell structure in which anodes and cathodes are interdigitatedly positioned on the same plane. The coplanar electrode design brings advantages of enhanced bending tolerance and capability of increasing the cell voltage by in series-connection of multiple single-cells in addition to its suitability for the thickness reduction. On the basis of these structural benefits, we develop a coplanar flexible LIB that delivers 7.4 V with an entire cell thickness below 0.5 mm while preserving stable electrochemical performance throughout 5000 (un)­bending cycles (bending radius = 5 mm). Also, even the pouch case serves as barriers between anodes and cathodes to prevent Li dendrite growth and short-circuit formation while saving the thickness. Furthermore, for convenient practical use wireless charging via inductive electromagnetic energy transfer and solar cell integration is demonstrated

A Half Millimeter Thick Coplanar Flexible Battery with Wireless Recharging Capability

Most of the existing flexible lithium ion batteries (LIBs) adopt the conventional cofacial cell configuration where anode, separator, and cathode are sequentially stacked and so have difficulty in the integration with emerging thin LIB applications, such as smart cards and medical patches. In order to overcome this shortcoming, herein, we report a coplanar cell structure in which anodes and cathodes are interdigitatedly positioned on the same plane. The coplanar electrode design brings advantages of enhanced bending tolerance and capability of increasing the cell voltage by in series-connection of multiple single-cells in addition to its suitability for the thickness reduction. On the basis of these structural benefits, we develop a coplanar flexible LIB that delivers 7.4 V with an entire cell thickness below 0.5 mm while preserving stable electrochemical performance throughout 5000 (un)­bending cycles (bending radius = 5 mm). Also, even the pouch case serves as barriers between anodes and cathodes to prevent Li dendrite growth and short-circuit formation while saving the thickness. Furthermore, for convenient practical use wireless charging via inductive electromagnetic energy transfer and solar cell integration is demonstrated

Large-Scale, Lightweight, and Robust Nanocomposites Based on Ruthenium-Decorated Carbon Nanosheets for Deformable Electrochemical Capacitors

Despite the increase in demand for deformable electrochemical capacitors as a power source for wearable electronics, significant obstacles remain in developing these capacitors, including their manufacturing complexity and insufficient deformability. With recognition of these challenges, a facile strategy is proposed to fabricate large-scale, lightweight, and mechanically robust composite electrodes composed of ruthenium nanoparticles embedded in freestanding carbon nanotube (CNT)-based nanosheets (Ru@a-CNTs). Surface-modified CNT sheets with hierarchical porous structures can behave as an ideal platform to accommodate a large number of uniformly distributed Ru nanoparticles (Ru/CNT weight ratio of 5:1) while improving compatibility with aqueous electrolytes. Accordingly, Ru@a-CNTs offer a large electrochemically active area, showing a high specific capacitance (∼253.3 F g–1) and stability for over 2000 cycles. More importantly, the exceptional performance and mechanical durability of quasi-solid-state capacitors assembled with Ru@a-CNTs and a PVA-H3PO4 hydrogel electrolyte are successfully demonstrated in that 94% of the initial capacitance is retained after 100 000 cycles of bending deformation and a commercial smartwatch is charged by multiple cells. The feasible large-scale production and potential applicability shown in this study provide a simple and highly effective design strategy for a wide range of energy storage applications from small- to large-scale wearable electronics

A Half Millimeter Thick Coplanar Flexible Battery with Wireless Recharging Capability

Most of the existing flexible lithium ion batteries (LIBs) adopt the conventional cofacial cell configuration where anode, separator, and cathode are sequentially stacked and so have difficulty in the integration with emerging thin LIB applications, such as smart cards and medical patches. In order to overcome this shortcoming, herein, we report a coplanar cell structure in which anodes and cathodes are interdigitatedly positioned on the same plane. The coplanar electrode design brings advantages of enhanced bending tolerance and capability of increasing the cell voltage by in series-connection of multiple single-cells in addition to its suitability for the thickness reduction. On the basis of these structural benefits, we develop a coplanar flexible LIB that delivers 7.4 V with an entire cell thickness below 0.5 mm while preserving stable electrochemical performance throughout 5000 (un)­bending cycles (bending radius = 5 mm). Also, even the pouch case serves as barriers between anodes and cathodes to prevent Li dendrite growth and short-circuit formation while saving the thickness. Furthermore, for convenient practical use wireless charging via inductive electromagnetic energy transfer and solar cell integration is demonstrated

Large-Scale, Lightweight, and Robust Nanocomposites Based on Ruthenium-Decorated Carbon Nanosheets for Deformable Electrochemical Capacitors

Despite the increase in demand for deformable electrochemical capacitors as a power source for wearable electronics, significant obstacles remain in developing these capacitors, including their manufacturing complexity and insufficient deformability. With recognition of these challenges, a facile strategy is proposed to fabricate large-scale, lightweight, and mechanically robust composite electrodes composed of ruthenium nanoparticles embedded in freestanding carbon nanotube (CNT)-based nanosheets (Ru@a-CNTs). Surface-modified CNT sheets with hierarchical porous structures can behave as an ideal platform to accommodate a large number of uniformly distributed Ru nanoparticles (Ru/CNT weight ratio of 5:1) while improving compatibility with aqueous electrolytes. Accordingly, Ru@a-CNTs offer a large electrochemically active area, showing a high specific capacitance (∼253.3 F g–1) and stability for over 2000 cycles. More importantly, the exceptional performance and mechanical durability of quasi-solid-state capacitors assembled with Ru@a-CNTs and a PVA-H3PO4 hydrogel electrolyte are successfully demonstrated in that 94% of the initial capacitance is retained after 100 000 cycles of bending deformation and a commercial smartwatch is charged by multiple cells. The feasible large-scale production and potential applicability shown in this study provide a simple and highly effective design strategy for a wide range of energy storage applications from small- to large-scale wearable electronics