Inho Nam

Transparent and ultra-bendable all-solid-state supercapacitors without percolation problems

A technological foundation for transparent and ultra-bendable supercapacitors without percolation effects and depth limitations is introduced, with demonstrated examples in in- and out-of-plain ultra-deformation states. This prototype system, built on large-scale interdigitated pattern type electrodes, constitutes significant advances over existing energy systems for optoelectronic systems in terms of electrochemical performance (capacitance ∼405 F g−1) and flexibility (bending radius ∼1.5 mm).

Hybrid MnO2 Film with Agarose Gel for Enhancing the Structural Integrity of Thin Film Supercapacitor Electrodes

We report on the fabrication of a robust hybrid film containing MnO2 for achieving large areal capacitances. An agarose gel, as an ion-permeable and elastic layer coated on a current collector, plays a key role in stabilizing the deposited pseudocapacitive MnO2. Cyclic voltammetry and electrochemical impedance spectroscopy data indicate that the hybrid electrode is capable of exhibiting a high areal capacitance up to 52.55 mF cm(-2), with its superior structural integrity and adhesiveness to the current collector being maintained, even at a high MnO2 loading.

Preferential growth of Co3O4 anode material with improved cyclic stability for lithium-ion batteries

A strategy for the synthesis of Co3O4 embedded in a carbonaceous matrix using an agarose gel template is described. The close-packed and porous structures were formed by a preferential growth mechanism within a short time. The resulting structured Co3O4 electrode had a long cycling stability and high conductivity.

Fabrication and design equation of film-type large-scale interdigitated supercapacitor chips.

We report large-scale interdigitated supercapacitor chips based on pseudo-capacitive metal oxide electrodes. A novel method is presented, which provides a powerful fabrication technology of interdigitated supercapacitors operated by a pseudo-capacitive reaction. Also, we empirically develop an equation that describes the relationship between capacitance, mass, and sweep rate in an actual supercapacitor system.

All-solid-state, origami-type foldable supercapacitor chips with integrated series circuit analogues

Patterning-assembly technology for energy storage systems can be a breakthrough for physicochemically limited energy storage systems. In this study, a concept of design with experimental proof is provided for an all-solid-state origami-type foldable supercapacitor by a novel patterning approach. The proposed system is composed of periodically assembled isolated electrodes (IEs) and sectionalized ion transferring paper (SITP), which are key factors for the densely packed series circuit analogues in the single system. The system shows a linear relationship between the potential window and the number of IEs, which does not have any limited asymptotic line. This system could increase energy and power simultaneously, which was conventionally not possible. Also, its folding characteristics accommodate highly stable stretching. These characteristics are proven by simulations based on ab-initio calculations and the finite-element method.

Interfacial Adsorption and Redox Coupling of Li4Ti5O12 with Nanographene for High-Rate Lithium Storage

Despite the many efforts to solve the problem associated with lithium storage at high rates, it is rarely achieved up until now. The design with experimental proof is reported here for the high rate of lithium storage via a core-shell structure composite comprised of a Li4Ti5O12 (LTO) core and a nanographene (NG) shell. The LTO-NG core-shell was synthesized via a first-principles understanding of the adsorption properties between LTO and NG. Interfacial reactions are considered between the two materials by a redox coupling effect. The large interfacial area between the LTO core and the NG shell resulted in a high electron-conducting path. It allowed rapid kinetics to be achieved for lithium storage and also resulted in a stable contact between LTO and NG, affording cyclic performance stability.

Nanoporous hexagonal TiO2 superstructure as a multifunctional material for energy conversion and storage

Tremendous efforts have been devoted for the development of rationally designed titanium dioxide (TiO2) nanostructures, because structural characteristics such as morphology, porosity, size, and crystal phase significantly affect the physical properties of TiO2. Despite the significant advances made in synthesis strategies over the past few decades, designing an innovative TiO2 nanostructure that overcomes the limitations that TiO2 encounters in various applications remains a great challenge. In this study, we demonstrate the synthesis of a hierarchically nanostructured TiO2 having a higher symmetry (hexagonal structure) than its own constituent tectons. Anatase TiO2 possesses only a primitive tetragonal unit cell, and there is no hexagonal symmetry axis. Thus, a hexagonal TiO2 superstructure is hardly obtainable without the multiple twinning of primitive units, which rarely occurs under conventional reaction conditions. Our exotic TiO2 nanostructure is synthesized by the calcination of a novel TiO2 precursor that is formed by a simple precipitation reaction and is utilized as an electrode material in energy conversion and storage devices. Due to the unique physical properties offered by this morphology, nanoporous hexagonal TiO2 is superior to conventionally used TiO2 in these applications, highlighting the benefits as an advanced, multifunctional electrode material.

Preparation via an electrochemical method of graphene films coated on both sides with NiO nanoparticles for use as high-performance lithium ion anodes

We report on a simple strategy for the direct synthesis of a thin film comprising interconnected NiO nanoparticles deposited on both sides of a graphene sheet via cathodic deposition. For the co-electrodeposition, graphene oxide (GO) is treated with water-soluble cationic poly(ethyleneimine) (PEI) which acts as a stabilizer and trapping agent to form complexes of GO and Ni2+. The positively charged complexes migrate toward the stainless steel substrate, resulting in the electrochemical deposition of PEI-modified GO/Ni(OH)2 at the electrode surface under an applied electric field. The as-synthesized film is then converted to graphene/NiO after annealing at 350 ° C. The interconnected NiO nanoparticles are uniformly deposited on both sides of the graphene surface, as evidenced by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectrometry. This graphene/NiO structure shows enhanced electrochemical performance with a large reversible capacity, good cyclic performance and improved electronic conductivity as an anode material for lithium ion batteries. A reversible capacity is retained above 586 mA h g−1 after 50 cycles. The findings reported herein suggest that this strategy can be effectively used to overcome a bottleneck problem associated with the electrochemical production of graphene/metal oxide films for lithium ion battery anodes.

Tuning the oxidation states of nanostructured amorphous Mn oxides for electrochemical applications

A simple precipitation method is proposed in order to maximize the electrochemical performance of nanostructured amorphous Mn oxide via the tuning of the oxidation states using various n-alcohol solvents with different lengths of alkyl chain.

Insights into the Li Diffusion Dynamics and Nanostructuring of H2Ti12O25 To Enhance Its Li Storage Performance

Dodecatitanate H2Ti12O25 crystal has a condensed layered structure and exhibits noteworthy Li storage performance that makes it an anode material with great potential for use in Li-ion batteries. However, an unknown Li diffusion mechanism and a sluggish level of Li dynamics through elongated diffusion paths inside this crystal has impeded any forward development in resolving its limited rate capability and cyclic stability. In this study, we investigated the Li diffusion dynamics inside the H2Ti12O25 crystal that play an essential role in Li storage performance. A study of density functional theory combined with experimental evaluation confirmed a strong dependence of Li storage performance on its diffusion. In addition, a nanostructured H2Ti12O25 containing a bundle of nanorods is developed via the introduction of a kinetic gap during the structural transformation, which conferred a significantly shortened diffusion time/length for Li in H2Ti12O25. The nanostructured H2Ti12O25 has high specific capacity (∼230 mAh g(-1)) and exhibits enhanced cyclic stability and rate capability compared with conventional bulky H2Ti12O25. The H2Ti12O25 proposed in this study has high potential for use as an anode material with excellent safety and stability.