On-Chip Micro-Supercapacitor with High Areal Energy Density Based on Dielectrophoretic Assembly of Nanoporous Metal Microwire Electrodes.

Advances in the Internet of Things (IoT) technology have driven the demand for miniaturized electronic devices, prompting research on small-scale energy-storage systems. Micro-supercapacitors (MSCs) stand out in this regard because of their compact size, high power density, high charge-discharge rate, and extended cycle life. However, their limited energy density impedes commercialization. To resolve this issue, a simple and innovative approach is reported herein for fabricating highly efficient on-chip MSCs integrated with nanoporous metal microwires formed by dielectrophoresis (DEP)-driven gold nanoparticle (AuNP) assembly. Placing a water-based AuNP suspension onto interdigitated electrodes and applying an alternating voltage induces in-plane porous microwire formation in the electrode gap. The DEP-induced AuNP assembly and the gold microwire (AuMW) growth rate can be adjusted by controlling the applied alternating voltage and frequency. The microwire-integrated MSC (AuMW-MSC) electrically outperforms its unmodified counterpart and exhibits a 30% larger electrode area, along with 72% and 78% higher specific and areal capacitances, respectively, than a microwire-free MSC. Additionally, AuMW-MSC achieves maximum energy and power densities of 3.33 µWh cm-2 and 2629 µW cm-2, respectively, with a gel electrolyte. These findings can help upgrade MSCs to function as potent energy-storage devices for small electronics.

In Situ Conversion of Metal-Organic Frameworks into VO2 -V3 S4 Heterocatalyst Embedded Layered Porous Carbon as an "All-in-One" Host for Lithium-Sulfur Batteries.

Although lithium-sulfur batteries exhibit a fivefold higher energy density than commercial lithium-ion batteries, their volume expansion and insulating nature, and intrinsic polysulfide shuttle have hindered their practical application. An alternative sulfur host is necessary to realize porous, conductive, and polar functions; however, there is a tradeoff among these three critical factors in material design. Here, the authors report a layered porous carbon (LPC) with VO2 /V3 S4 heterostructures using one-step carbonization-sulfidation of metal-organic framework templates as a sulfur host that meets all the criteria. In situ conversion of V-O ions into V3 S4 nuclei in the confined 2D space generated by dynamic formation of the LPC matrix creates {200}-facet-exposed V3 S4 nanosheets decorated with tiny VO2 nanoparticles. The VO2 /V3 S4  @ LPC composite facilitates high sulfur loading (70 wt%), superior energy density (1022 mA h g-1 at 0.2 C, 100 cycles), and long-term cyclability (665 mA h g-1 at 1 C, 1000 cycles). The enhanced Li-S chemistry is attributed to the synergistic heterocatalytic behavior of polar VO2 and conductive V3 S4 in the soft porous LPC scaffold, which accelerates polysulfide adsorption, conversion, and charge-transfer ability simultaneously.

A Novel Time-Saving Synthesis Approach for Li-Argyrodite Superionic Conductor.

The wet-chemical synthetic approach for Li-argyrodite superionic conductors for all-solid-state batteries (ASSBs) is promising as it saves time, energy, and cost, while achieving scalable production. However, it faces certain commercialization issues such as byproduct generation, nucleophilic attack of the solvent, and long processing times. In this study, a facile and time-saving microwave-assisted wet synthesis (MW-process) approach is proposed for Li6 PS5 Cl (LPSC), which is completed in 3 h at the precursor-synthesis stage. The LPSC crystal obtained from the MW-process presents various advantages such as fast-PS4 3- generation, high solubility of LiCl, and low adverse effects from solvent molecules. These features help in achieving a high Li-ion conductivity (2.79 mS cm-1 ) and low electric conductivity (1.85×10-6 mS cm-1 ). Furthermore, the LPSC crystal is stable when reacting with Li metal (2000 h at 0.1 mA cm-2 ) and exhibits superior cyclability with LiNi0.6 Co0.2 Mn0.2 (NCM622) (145.5 mA h g-1 at 0.5 C, 200 cycles with 0.12% of capacity loss per cycle). The proposed synthetic approach presents new insights into wet-chemical engineering for sulfide-based solid-electrolytes (SEs), which is crucial for developing ASSBs from a commercial-scale perspective.

Synthesis of core/shell spinel ferrite/carbon nanoparticles with enhanced cycling stability for lithium ion battery anodes.

Monodispersed core/shell spinel ferrite/carbon nanoparticles are formed by thermolysis of metal (Fe3+, Co2+) oleates followed by carbon coating. The phase and morphology of nanoparticles are characterized by x-ray diffraction and transmission electron microscopy. Pure Fe3O4 and CoFe2O4 nanoparticles are initially prepared through thermal decomposition of metal­oleate precursors at 310 degrees C and they are found to exhibit poor electrochemical performance because of the easy aggregation of nanoparticles and the resulting increase in the interparticle contact resistance. In contrast, uniform carbon coating of Fe3O4 and CoFe2O4 nanoparticles by low-temperature (180 degrees C) decomposition of malic acid allowed each nanoparticle to be electrically wired to a current collector through a conducting percolative path. Core/shell Fe3O4/C and CoFe2O4/C nanocomposite electrodes show a high specific capacity that can exceed 700 mAh g(-1) after 200 cycles, along with enhanced cycling stability.

Superior long-term cycling stability of SnO2 nanoparticle/multiwalled carbon nanotube heterostructured electrodes for Li-ion rechargeable batteries.

We demonstrate the fabrication of hybrid nanocomposite electrodes with a combination of SnO(2) nanoparticles (NPs) and conducting multiwalled carbon nanotube (MWCNT) anodes (SnO(2)@CNT) through the direct anchoring of SnO(2) NPs on the surface of electrophoretically pre-deposited MWCNT (EPD-CNT) networks via a metal-organic chemical vapor deposition process. This SnO(2)@CNT nanocomposite displays large reversible capacities of over 780, 510, and 470 mA h g(-1) at 1 C after 100, 500, and 1000 cycles, respectively. This outstanding long-term cycling stability is a result of the uniform distribution of SnO(2) NPs (~8.5 nm), a nanoscale EPD-CNT network with good electrical conductivity, and the creation of open spaces that buffer a large volume change during the Li-alloying/dealloying reaction of SnO(2).

Enhanced Lithium Storage in Hierarchically Porous Carbon Derived from Waste Tea Leaves.

In this study, highly nanoporous carbon (HCl-TW-Car) was successfully synthesized using a facile procedure combining acid treatment with a carbonization process that uses waste tea leaves from spent tea bags as raw materials. The acid treatment not only promotes the efficient removal of unnecessary inorganic impurities but also increases the product porosity to enable synthesis of hierarchically porous carbon materials with various micro-, meso-, and macropores. When used as an anode material for lithium-ion batteries, HCl-TW-Car demonstrated a much higher discharge capacity than is theoretically possible using graphite [479 mAh g-1 after the 200th cycle at a rate of 0.2C (1C = 372 mA g-1)] and exhibited greater rate capabilities compared with those of carbonated products from tea waste without acid treatment. It was shown that the good electrochemical properties of HCl-TW-Car can be ascribed to large Brunauer-Emmett-Teller (BET) surface area, well-formed hierarchical pores, and the prevention of unexpected electrochemical reactions from the reduction of metallic atoms.

High-areal-capacity lithium storage of the Kirkendall effect-driven hollow hierarchical NiS(x) nanoarchitecture.

Three-dimensional (3-D) architectures can provide significant advantages as lithium ion microbattery electrodes by lengthening the vertical dimension. In addition, the nanoscale hierarchy and hollow properties are important factors for enhancing the performance. Here, we prepared a 3-D nickel sulfide nanoarchitecture via a facile low-temperature solution route. A Kirkendall effect-driven sulfidation of a 3-D nickel electrode was used to produce a hollow 3-D structure. Moreover, a nanoscale hierarchy can be formed with the use of highly concentrated sulfur species. The morphology, structure, and chemical composition of the 3-D nickel sulfide electrode are characterized in detail, and the formation mechanism is discussed based on a time-resolved study. The 3-D nickel sulfide electrodes show an outstanding areal capacity (1.5 mA h cm(-2) at a current rate of 0.5 mA cm(-2)), making this electrode a potential electrode for 3-D lithium ion microbatteries with a large energy density. Moreover, this strategy is expected to provide a general fabrication method for transition metal sulfide nanoarchitectures.

Three-dimensional hierarchical Li4Ti5O12 nanoarchitecture by a simple hydrothermal method.

The spinel Li4Ti5O12 (LTO) is a promising candidate as a superior electrode material for energy storage devices due to the extremely small volume expansion/contraction during the charge/discharge processes of a battery. There are various synthetic approaches for the nanostructured LTO electrode: sol-gel, sonochemical, solution-combustion, hydrothermal methods, and others. Herein, three-dimensional (3D) high-density heterogeneous LTO architectures are fabricated by employing the TiO2 nanorods (NRs) branched SnO2 nanowire (NW) arrays as the template. The TiO2 NRs were effectively converted by the hydrothermal method into the LTO NRs that have a width of 40-nm and length of 100-nm, which induce branch/backbone structured LTO-SnO2 composites. Interestingly, the 3D LTO architectures exhibit unique geometrical shapes because the NRs are surrounded by small nanoparticles. We also discuss how the temperature and solvent affect the LTO nanostructure formation in detail. These results suggest that using a template can provide a new method for designing and synthesizing various classes of 3D architecturing synthesis.

Scalable one-pot bacteria-templating synthesis route toward hierarchical, porous-Co3O4 superstructures for supercapacitor electrodes.

Template-driven strategy has been widely used to synthesize inorganic nano/micro materials. Here, we used a bottom-up controlled synthesis route to develop a powerful solution-based method of fabricating three-dimensional (3D), hierarchical, porous-Co3O4 superstructures that exhibit the morphology of flower-like microspheres (hereafter, RT-Co3O4). The gram-scale RT-Co3O4 was facilely prepared using one-pot synthesis with bacterial templating at room temperature. Large-surface-area RT-Co3O4 also has a noticeable pseudocapacitive performance because of its high mass loading per area (~10 mg cm(-2)), indicating a high capacitance of 214 F g(-1) (2.04 F cm(-2)) at 2 A g(-1) (19.02 mA cm(-2)), a Coulombic efficiency averaging over 95%, and an excellent cycling stability that shows a capacitance retention of about 95% after 4,000 cycles.

Electrochemical performance of NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire anodes for lithium-ion batteries.

NixCo1-xMoO4 (0 ≤ x ≤ 1) nanowire electrodes for lithium-ion rechargeable batteries have been synthesized via a hydrothermal method, followed by thermal post-annealing at 500°C for 2 h. The chemical composition of the nanowires was varied, and their morphological features and crystalline structures were characterized using field-emission scanning electron microscopy and X-ray powder diffraction. The reversible capacity of NiMoO4 and Ni0.75Co0.25MoO4 nanowire electrodes was larger (≈520 mA h/g after 20 cycles at a rate of 196 mA/g) than that of the other nanowires. This enhanced electrochemical performance of NixCo1-xMoO4 nanowires with high Ni content was ascribed to their larger surface area and efficient electron transport path facilitated by their one-dimensional nanostructure.