Yoon Hwa

Arizona State University | ASU · School of Electrical, Computer and Energy Engineering

SiOx is considered a promising alternative anode material for Li-ion batteries because of its higher theoretical capacity and safety compared with those of carbonaceous materials. In this study, SiOx with N-doped carbon containing Fe2O3 (Fe2O3/N-C@SiOx) was synthesized through mechanical milling, and its electrochemical properties and applicability...

As representative next-generation secondary battery systems, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are key candidates to achieve zero-carbon emission. Herein, we introduce a versatile GaSb nanocomposite anode for SIBs and PIBs. The performance and phase transition mechanism for GaSb, pure Ga, and Sb with Na and K ions are e...

The high theoretical specific energy of lithium/sulfur (Li/S) cells (2600 Wh/kg) has positioned the Li/S cell as one of the most promising candidates for the beyond lithium‐ion cell. Despite the evident advantages, there are remaining problems mainly associated with the unique solution‐based reaction chemistry involving lithium polysulfide (Li‐PS)...

Lithium/sulfur (Li/S) cells that offer an ultrahigh theoretical specific energy of 2600 Wh/kg are considered one of the most promising next-generation rechargeable battery systems for the electrification of transportation. However, the commercialization of Li/S cells remains challenging, despite the recent advancements in materials development for...

Laser three-dimensional (3D) manufacturing technologies have gained substantial attention to fabricate 3D structured electrochemical rechargeable batteries. Laser 3D manufacturing techniques offer excellent 3D microstructure controllability, good design flexibility, process simplicity, and high energy and cost efficiencies, which are beneficial for...

The localized corrosion of laser surface melted (LSM) 316L stainless steel is investigated by a combination of potentiodynamic anodic polarization in 0.1M HCl and microscopic investigation of the initiation and propagation of localized corrosion. The pitting potential of LSM 316L is significantly lower than the pitting potential of wrought 316L. Th...

Lithium (Li) ion batteries have been regarded as major contributors to the energy solution and they have been intensively developed in terms of performance, cost and lifetime to meet the demands of emerging applications such as electric vehicle and energy storage systems for power grids. One of major goals of Li rechargeable battery development is...

The development of high-capacity and high-power lithium-ion batteries (LIBs) is a key challenge to meet the increasing demand for advanced mobile electronics and electric vehicles. A novel high-capacity and high-power...

Lithium/sulfur (Li/S) cells that offer high theoretical specific energy (2600 Wh/kg) have been considered for emerging high energy applications. Significant progress in improving the electrochemical performance of Li/S cells has been made based on the development strategies of the nano‐structured sulfur‐based electrodes: (i) improving the electrica...

The microstructures of 316 L stainless steel created by rapid solidification are investigated by comparing the similar microstructures of individual hatches of directed energy deposition additive manufacturing (DED-AM) and those of single, laser surface-melted tracks formed on a solid plate. High recoil pressure, which is exponentially dependent on...

To design a high-performance sodium-ion battery (SIB) anode, binary zinc phosphides (ZnP2 and Zn3P2) were synthesized by a facile solid-state heat treatment process, and their Na storage characteristics were evaluated. The Na reactivity of ZnP2 was better than that of Zn3P2. Therefore, a C-modified ZnP2-based composite (ZnP2–C) was fabricated to ac...

Understanding of lithium polysulfide (Li-PS) formation and the shuttle phenomenon is essential for practical application of the lithium/sulfur (Li/S) cell, which has superior theoretical specific energy (2600 Wh/kg). However, it suffers from the lack of direct observation on behaviors of soluble Li-PS in liquid electrolytes. Using in situ graphene...

The micrometer-scale reticulated structure of highly sulfur-phillic nitrogen-doped graphene oxide (NrGO) that is produced by chemically-controlled nitrogen-doping improves the chemical and electrochemical stability of the active sulfur while providing sufficient...

To date, Li2S has drawn significant attention as a positive electrode active material for rechargeable lithium cells due to its high theoretical specific capacity and capability of pairing with a lithium-free anode which can obviate any safety concern of the lithium metal anode when using sulfur. In recent years, various approaches have been employ...

Rational design of sulfur electrodes is exceptionally important in enabling a high performance lithium/sulfur cell. Constructing a continuous pore structure of the sulfur electrode that enables facile lithium ion transport into the electrode and mitigates the reconstruction of sulfur is a key factor for enhancing the electrochemical performance. He...

A novel ionic liquid-containing electrolyte has been demonstrated to improve charging efficiency, lifetime and safety of Li/S cells. However, the high viscosity of the ionic liquid can reduce the kinetics of the electrochemical process and degrade the wettability the S electrode by the electrolyte, which limits electrochemical utilization of the ac...

Lithium/Sulfur (Li/S) cells are a promising chemistry with potential to deliver a step-change in energy density compared to state-of-the-art Li-ion batteries. To minimize the environmental impact of the Li/S cell manufacturing and to compete with Li-ion cells in both performance and cost, electrodes cast using an aqueous process are highly desirabl...

The ambient-temperature rechargeable lithium/sulfur (Li/S) cell is a strong candidate for the beyond lithium ion cell, since significant progress on developing advanced sulfur electrodes with high sulfur loading has been made. Here we report on a new sulfur electrode active material consisting of a cetyltrimethylammonium bromide-modified sulfur-gra...

?-Stacked perylene bisimide (PBI) molecules are implemented here as highly networked, redox-active supramolecular polymer binders in sulfur cathodes for lightweight and energy-dense Li?S batteries. We show that the in operando reduction and lithiation of these PBI binders sustainably reduces Li?S cell impedance relative to non-redox active conventi...

Fully lithiated lithium sulfide (Li2S) has become a promising cathode material for Li/S cells due to its high theoretic capacity (1166 mA·h g-1) and specific energy (2600 W·h kg-1). However, low utilization of sulfur and poor rate capability still hinder the practical application of Li/S cells. In this paper, a carbon coated Li2S/graphene composite...

Light metals have been widely used as electrode materials for batteries owing to their low standard redox potential, their low equivalent weight, large specific capacity, and great abundance. Both primary and secondary cells including light metals as electrode material have influenced all aspects of our lives, e.g., electrically operated toys, powe...

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W⋅h kg-1, which is much higher than that of Li ion cells (400-600 W⋅h kg-1). However, problems of the S cathode such as highly soluble intermediate species...

We report a new method to generate a thin carbon layer on active materials for electrochemical energy storage. A solid precursor can be simply placed on the target material in a tailored vertical quartz tube and sublimated at a slightly high temperature. The carbon source gas remains around the target material during the heat treatment because of t...

Electrochemical behaviors of milled Si using high energy mechanical milling (HEMM) process are characterized with a degree of amorphization. The amount of amorphous Si increases with milling time, and Si crystallites are embedded in the amorphous Si matrix. Unlike crystallite Si, partially amorphous Si starts to react with Li near 0.32 V. An interm...

SnO2@Co3O4 hollow nano-spheres have been prepared using the template-based sol-gel coating technique and their electrochemical performance as an anode for lithium-ion battery (LIB) was investigated. The size of synthesized hollow spheres was about 50 nm with the shell thickness of 7-8 nm. The fabricated SnO2@Co3O4 hollow nano-sphere electrode exhib...

A new method for a facile synthesis of nano-silicon/carbon mesoporous composite is proposed. Silicon nanoparticles can be obtained through the magnesium silicide reduction of amorphous silica using high energy mechanical milling process. And mesoporous carbon matrix is fabricated via simple carbon coating method on Si nanoparticles followed by chem...

The silicon nanostructure is a promising candidate for an anode of Li-ion batteries due to its high theoretical capacity. In this work, we have demonstrated the scalable synthesis of Si nanosheets from natural sand by magnesiothermic reduction, and suggested a new formation mechanism for Si nanosheets. In the suggested mechanism, an Mg2Si intermedi...

Unlike previous HF etching of Si oxides to produce porous Si a new concept for the preparation of porous SiOx was suggested adopting Si as a pore generating agent and Si oxides as template using NaOH solution. The heat treatment of pristine SiO at 900 °C provided nano-crystalline Si within the SiOx matrix. The nano-crystalline Si was dissolved to p...

A nano-Si/TiO2 core–shell nanostructured electrode was synthesized using sol–gel method. The TiO2 shells were made with 10-nm thickness, and were structurally stable upon the intercalation/deintercalation of Li+, improve the cyclability of the Si electrode during cycling. The nano-Si/TiO2 core–shell nanostructured electrode showed a reversible capa...

The synthesis of nano-sized Si with various microstructures has been studied intensively to produce anode materials for Li-rechargeable batteries. Methods such as chemical/physical vapor deposition (CVD/PVD) and wet-chemical processes are currently used to produce nano-sized Si; however, the complicated synthesis procedures and low production yield...

Oxide thickness controlled amorphous SiO2/nano-Si core–shell structure anode for Li ion batteries was easily prepared by etching with NaOH solution using commercial nano-Si with a native oxide. Based on X-ray diffraction patterns and analysis of high resolution transmission microscope images, the electrode which consists of amorphous SiO2/amorphous...

A nano-Si/Co3O4 core–shell nanostructured material has been successfully prepared using the sol–gel method. The reaction mechanism between Li and the nano-Si/Co3O4 core–shell nanostructured electrode was investigated by ex situ analyses. Metallic Co, Li21Si8, and amorphous Li2O phases were formed when fully lithiated, and an amorphous Si, Co3O4, an...

SiO has been considered as one of the most promising anodes, the reaction mechanism of SiO with Li is still not well understood. High energy mechanical milling (HEMM) followed by etching of the SiO surface with NaOH solution was carried out in this study to enhance cycle performance. X-ray photoelectron spectroscopy (XPS) analyses showed the differ...

Nano-sized SnO2 hollow spheres are facilely synthesized by sol–gel method using the SiO2 nanospheres as sacrificed templates, and their electrochemical properties are investigated as an anode application for lithium ion battery (LIB). The size of the hollow spheres is controlled by using different-sized templates. As-coated SnO2 shell is almost amo...

A core–shell nanostructured composite material consisting of nano-Si as the core and SnO2 as the shell is synthesized by a sol–gel method. The reaction mechanism between Li and a nano-Si/SnO2 core–shell nanostructured electrode is investigated, the partial reversible reaction between Li and SnO2 during the first cycle is identified, and the reactiv...

An anode material with improved electrochemical performances for Li-ion batteries is prepared using the disproportionation reaction of SiO followed by a high energy mechanical milling process. The modified SiO is composed of embedded Si nano-crystallites in a Si-oxide matrix. Si-oxide matrix could be divided into two parts by reactivity with Li-ion...

A Si–TiFeSi2 composite was synthesized in large-scale using arc melting followed by rapid quenching. The composite showed that active Si nanocrystallites of approximately 50 nm were embedded in an inactive TiFeSi2 hard matrix. Crystalline Si reacted with Li to form the Li21Si8 phase and transformed into amorphous Si when Li was extracted, while the...

The mechanism of the electrochemical reaction of Zn with Li was investigated by ex situ X-ray diffraction (XRD) analysis combined with a differential capacity plot of the Zn electrode at a low current of 10 mA g−1. The pure Zn electrode showed a high reactivity with Li, with first discharge and charge capacities of 574 and 351 mA h g−1, respectivel...

Core–shell structured nano-Si/C (n-Si/C) anode material for Li ion batteries was prepared by substrate induced coagulation (SIC) method with nano-Si (n-Si) as core component and amorphous carbon as shell. The electronic conducting amorphous carbon shell of 5–10 nm thickness which connected each n-Si particle like frog spawn shape not only buffered...

The suitability of silver sulfide (Ag2S) and its nanocomposite Ag2S/C, prepared by simple solid-state synthetic routes such as high-energy mechanical milling and heat treatment, for use as anode materials in rechargeable Li-ion batteries has been investigated. A well-developed Ag2S phase is identified from X-ray diffraction (XRD) patterns, and XRD...

A nanosize Si embedded in super-elastic Nitinol alloy matrix composite was synthesized in large-scale using arc melting followed by a rapid quenching method. Both X-ray diffraction and high resolution transmission electron microscope with energy dispersive spectroscopy analyses confirmed that approximately 50 nm Si crystallites were surrounded by t...

Sn2Fe/Al2O3/C nanocomposites are synthesized using a high-energy, mechanical milling method with thermally synthesized Sn2Fe, Al2O3 and carbon (Super P) powders. The effect of Al2O3 addition on the microstructure of the Sn2Fe/Al2O3/C nanocomposites is examined. The electrochemical characteristics of the material as an anode in lithium-ion batteries...

Commercially available solid SiO is composed of amorphous Si with silicon suboxides of various valence states. Solid SiO is thermodynamically unstable at all temperatures, which would disproportionate to Si and SiO2. Disproportionation of SiO at several temperatures was characterized with various analytical techniques, such as XRD, XPS, NMR and HRT...

A Ge/Cu3Ge/C composite, prepared by pyrolysis and a high energy mechanical milling process, was investigated as an anode material for Li-ion batteries. Electron probe micro-analyzer images showed that Ge and Cu3Ge were well dispersed in the carbon matrix. Various analytical techniques were carried out to clarify the reaction mechanism of the Cu3Ge...

Orthorhombic Sb2S3 (stibnite) and its amorphous Sb2S3/C composite were synthesized by solid-state routes, such as heat treatment and high energy mechanical milling (HEMM). X-ray diffraction, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy confirmed that the amorphous Sb2S3/C composite was composed of amorphous...