<i>In Situ</i> Mn K-edge X-ray Absorption Spectroscopy Studies of Electrodeposited Manganese Oxide Films for Electrochemical Capacitors

In situ Mn K-edge fluorescence X-ray absorption spectroscopy (XAS) was used to analyze the manganese oxides electrodeposited on a porous carbon paper substrate for use in electrochemical capacitors in order to determine the local and electronic structural changes in the material as a function of the applied potential in a neutral electrolyte. Within the potential range from +0.1 to +0.8 V vs SCE (reversible region), the cyclic voltammogram (CV) showed ideal capacitive characteristics. On the other hand, large current tails were observed at near both ends of the potential window in the CV when the upper and lower potential limits were expanded to +1.0 and −0.3 V vs SCE (irreversible region), which is indicative of an irreversible reaction. According to the in situ X-ray absorption near-edge structure (XANES) results, the capacitive currents of the manganese oxides in 2 M KCl in the reversible region originated from the Faradaic pseudocapacitance. The average oxidation state and local structure of the manganese oxide changed reversibly during charging/ discharging within the reversible region. On the other hand, the local and electronic structure of manganese oxide changed in an irreversible manner in the irreversible region, particularly during the redox reaction within the potential range between +0.1 to −0.3 V vs SCE. This irreversible feature of the local and electronic structure changes was attributed to the formation of the electrochemically irreversible low valence manganese oxides such as Mn2O3 and Mn3O4, and the dissolution of Mn species from the electrode

Template-Free Synthesis of Ruthenium Oxide Nanotubes for High-Performance Electrochemical Capacitors

One-dimensional, hydrous ruthenium oxide nanotubes (RuO₂·1.84H₂O) have been successfully achieved using a template-free, microwave-hydrothermal process. These were found to be amorphous in nature and have a large specific surface area of 250 m²·g^–1, producing a specific and volumetric capacitance of 511 F·g^–1 and 531 F·cm^–3, respectively, at a discharging current density of 0.5 A·g^–1. When used as an electrode material in an electrochemical capacitor or ultracapacitor, they produced a significant improvement in capacitance, rate capability, and cyclability that can be attributed to the hollow nature of tubes allowing greater contact between the active surface of the electrode and the electrolyte

Fe³⁺-Derived Boosted Charge Transfer in an FeSi₄P₄ Anode for Ultradurable Li-Ion Batteries

Ion and electron transportation determine the electrochemical performance of anodes in metal-ion batteries. This study demonstrates the advantage of charge transfer over mass transport in ensuring ultrastable electrochemical performance. Additionally, charge transfer governs the quality, composition, and morphology of a solid–electrolyte interphase (SEI) film. We develop FeSi4P4-carbon nanotube (FSPC) and reduced-FeSi4P4-carbon nanotube (R-FSPC) heterostructures. The FSPC contains abundant Fe3+ cations and negligible pore contents, whereas R-FSPC predominantly comprises Fe2+ and an abundance of nanopores and vacancies. The copious amount of Fe3+ ions in FSPC significantly improves charge transfer during Li-ion battery tests and leads to the formation of a thin monotonic SEI film. This prevents the formation of detrimental LiP and crystalline-Li3.75Si phases and the aggregation of discharging/recharging products and guarantees the reformation of FeSi4P4 nanocrystals during delithiation. Thus, FSPC delivers a high initial Coulombic efficiency (>90%), exceptional rate capability (616 mAh g–1 at 15 A g–1), and ultrastable symmetric/asymmetric cycling performance (>1000 cycles at ultrahigh current densities). This study deepens our understanding of the effects of electron transport on regulating the structural and electrochemical properties of electrode materials in high-performance batteries

Magnéli Phase Titanium Oxide as a Novel Anode Material for Potassium-Ion Batteries

Recently, K-ion batteries (KIBs) have attracted attention for potential applications in next-generation energy storage devices principally on the account of their abundancy and lower cost. Herein, for the first time, we report an anatase TiO2-derived Magnéli phase Ti6O11 as a novel anode material for KIBs. We incorporate pristine carbon nanotube (CNT) on the TiO2 host materials due to the low electronic conductivity of the host materials. TiO2 transformed to Magnéli phase Ti6O11 after the first insertion/deinsertion of K ions. From the second cycle, Magnéli phase Ti6O11/CNT composite showed reversible charge/discharge profiles with ∼150 mA h g–1 at 0.05 A g–1. Ex situ X-ray diffraction and transmission electron microscopy analyses revealed that the charge storage process of Magnéli phase Ti6O11 proceeded via the conversion reaction during potassium ion insertion/deinsertion. The Magnéli phase Ti6O11/CNT composite electrode showed long-term cycling life over 500 cycles at 200 mA g–1, exhibiting a capacity retention of 76% and a high Coulombic efficiency of 99.9%. These salient results presented here provide a novel understanding of the K-ion storage mechanisms in the extensively investigated oxide-based material for Li-ion batteries and Na-ion batteries, shedding light on the development of promising electrode materials for next-generation batteries

Ultra-fast shock-wave combustion synthesis of nanostructured silicon from sand with excellent Li storage performance

The available technologies used for the preparation of elemental silicon (Si), including the traditional carbothermal technology of producing bulk Si, pyrolysis-based methods of producing Si nanoparticles and the metallothermic fabrication of state-of-the-art nanostructured Si powder are all considered energy- and time-intensive processes, with associated environmental issues. Herein, for the first time, a combustion synthesis methodology, involving the occurrence of an ignition event followed by the immediate completion of the process, is used for the preparation of nanostructured Si for energy applications. In this process, Si powders are directly extracted from sea sand by a novel ultra-fast shock-wave combustion synthesis (SWCS), in which KClO . The reaction is completed at an ignition temperature of about 550 °C, requiring virtually no dwell time. The process is scalable, green and carbon-free with a low energy consumption of about 100 kW h per ton, less than one percent of that of the current technologies. The Si product possesses a nanostructured mesoporous integrated sheet-like (NMIS) morphology, with an excellent and stable Li storage performance. The mechanism involved in the proposed method is also discussed. The feasibility of the SWCS approach for the preparation of Si is demonstrated in this article, based on which a variety of nanostructured materials is expected to be produced by this method.</p

Phase Transition Method To Form Group 6A Nanoparticles on Carbonaceous Templates

Considerable effort has been made to develop unique methods of preparing and characterizing nanoparticles and nanocomposites in order to exploit the true potential of nanotechnology. We used a facile, versatile phase-transition method for forming Group 6A nanoparticles on carbonaceous templates to produce homogeneous 5–10 nm diameter Group 6A nanoparticles on carbon nanotubes (CNTs) and reduced graphene oxide (RGO), to obtain nanocomposites. The method involved melting and recrystallizing mixtures of elemental sulfur and either CNTs or RGO on carbonaceous templates. The surface tension and hydrophilicity of the molten Group 6A species surfaces and the oxygen functional groups on the carbonaceous template surfaces were considered in depth to provide important guidelines for forming Group 6A nanoparticles on carbonaceous templates. The surface tension of the molten Group 6A species should be intrinsically low, leading to effective wetting on the carbonaceous template. In addition, the molten Group 6A species hydrophilic surfaces were essential for enabling hydrophilic–hydrophilic interaction for selective wetting at the oxygen functional groups on the carbonaceous template, leading to the heterogeneous nucleation of nanoparticles. Furthermore, the size and morphology (isolated <i>vs</i> layer-like) of the Group 6A nanoparticles were tuned by adjusting the oxidation state of the carbonaceous template. We investigated the potential application of the nanocomposites prepared using this method to cathode materials in lithium–sulfur secondary batteries

Hybrid Thin-Film Encapsulation for All-Solid-State Thin-Film Batteries

All-solid-state thin-film batteries have been actively investigated as a power source for various microdevices. However, insufficient research has been conducted on thin-film encapsulation, which is an essential element of these batteries as solid electrolytes and Li anodes are vulnerable to moisture in the atmosphere. In this study, a hybrid thin-film encapsulation structure of hybrid SiOy/SiNxOy/a-SiNx:H/Parylene is suggested and investigated. The water-vapor transmission rate of hybrid thin-film encapsulation is estimated to be 4.9 × 10–3 g m–2·day–1, a value that is applicable to batteries as well as flexible solar cells, thin-film transistor liquid-crystal display, and E-papers. As a result of hybrid thin-film encapsulation, it is confirmed that the all-solid-state thin-film batteries are stable even after 100 charge/discharge cycles in the air atmosphere for 30 days and present a Coulombic efficiency of 99.8% even after 100 cycles in the air atmosphere. These results demonstrate that the thin-film encapsulation structure of hybrid SiOy/SiNxOy/a-SiNx:H/Parylene can be employed in thin-film batteries while retaining long-term stability

In Situ Synthesis of Three-Dimensional Self-Assembled Metal Oxide–Reduced Graphene Oxide Architecture

The fabrication of self-assembled, three-dimensional (3-D) graphene structures is recognized as a powerful technique for integrating various nanostructured building blocks into macroscopic materials. In this way, nanoscale properties can be harnessed to provide innovative functionalities of macroscopic devices with hierarchical microstructures. To this end, we report on the fabrication of a three-dimensional (3-D) metal oxide (MO)–reduced graphene oxide (RGO) architecture by controlling the reduction conditions of graphene oxide. In this structure, SnO₂ nanoparticles with dimensions of 2–3 nm are uniformly anchored and supported on a 3-D RGO structure. The resulting composite exhibits excellent rate capability as a binder-free electrode and shows great potential for use in Li-ion batteries. Furthermore, the proposed reduction synthesis can also be applied to the study of the synergetic properties of other 3-D MO–RGO architectures

Spray-Assisted Deep-Frying Process for the In Situ Spherical Assembly of Graphene for Energy-Storage Devices

To take full advantage of graphene in macroscale devices, it is important to integrate two-dimensional graphene nanosheets into a micro/macrosized structure that can fully utilize graphene’s nanoscale characteristics. To this end, we developed a novel spray-assisted self-assembly process to create a spherically integrated graphene microstructure (graphene microsphere) using a high-temperature organic solvent in a manner reminiscent of deep-frying. This graphene microsphere improves the electrochemical performance of supercapacitors, in contrast to nonassembled graphene, which is attributed to its structural and pore characteristics. Furthermore, this synthesis method can also produce an effective graphene-based hybrid microsphere structure, in which Si nanoparticles are efficiently entrapped by graphene nanosheets during the assembly process. When used in a Li-ion battery, this material can provide a more suitable framework to buffer the considerable volume change that occurs in Si during electrochemical lithiation/delithiation, thereby improving cycling performance. This simple and versatile self-assembly method is therefore directly relevant to the future design and development of practical graphene-based electrode materials for various energy-storage devices