Publications by authors named "Yang-Kook Sun"

103 Publications

Critical Role of Functional Groups Containing N, S, and O on Graphene Surface for Stable and Fast Charging Li-S Batteries.

Small 2021 Apr 14;17(17):e2007242. Epub 2021 Mar 14.

Department of Physics, Chalmers University of Technology, Göteborg, 41296, Sweden.

Lithium-sulfur (Li-S) batteries are considered one of the most promising energy storage technologies, possibly replacing the state-of-the-art lithium-ion (Li-ion) batteries owing to their high energy density, low cost, and eco-compatibility. However, the migration of high-order lithium polysulfides (LiPs) to the lithium surface and the sluggish electrochemical kinetics pose challenges to their commercialization. The interactions between the cathode and LiPs can be enhanced by the doping of the carbon host with heteroatoms, however with relatively low doping content (<10%) in the bulk of the carbon, which can hardly interact with LiPs at the host surface. In this study, the grafting of versatile functional groups with designable properties (e.g., catalytic effects) directly on the surface of the carbon host is proposed to enhance interactions with LiPs. As model systems, benzene groups containing N/O and S/O atoms are vertically grafted and uniformly distributed on the surface of expanded reduced graphene oxide, fostering a stable interface between the cathode and LiPs. The combination of experiments and density functional theory calculations demonstrate improvements in chemical interactions between graphene and LiPs, with an enhancement in the electrochemical kinetics, power, and energy densities.
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http://dx.doi.org/10.1002/smll.202007242DOI Listing
April 2021

In Situ Oriented Mn Deficient ZnMnO@C Nanoarchitecture for Durable Rechargeable Aqueous Zinc-Ion Batteries.

Adv Sci (Weinh) 2021 Feb 4;8(4):2002636. Epub 2021 Jan 4.

Department of Materials Science and Engineering Chonnam National University Gwangju 500-757 South Korea.

Manganese (Mn)-based cathode materials have garnered huge research interest for rechargeable aqueous zinc-ion batteries (AZIBs) due to the abundance and low cost of manganese and the plentiful advantages of manganese oxides including their different structures, wide range of phases, and various stoichiometries. A novel in situ generated Mn-deficient ZnMnO@C (Mn-d-ZMO@C) nanoarchitecture cathode material from self-assembly of ZnO-MnO@C for rechargeable AZIBs is reported. Analytical techniques confirm the porous and crystalline structure of ZnO-MnO@C and the in situ growth of Mn deficient ZnMnO@C. The Zn/Mn-d-ZMO@C cell displays a promising capacity of 194 mAh g at a current density of 100 mA g with 84% of capacity retained after 2000 cycles (at 3000 mA g rate). The improved performance of this cathode originates from in situ orientation, porosity, and carbon coating. Additionally, first-principles calculations confirm the high electronic conductivity of Mn-d-ZMO@C cathode. Importantly, a good capacity retention (86%) is obtained with a year-old cell (after 150 cycles) at 100 mA g current density. This study, therefore, indicates that the in situ grown Mn-d-ZMO@C nanoarchitecture cathode is a promising material to prepare a durable AZIB.
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http://dx.doi.org/10.1002/advs.202002636DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7887583PMC
February 2021

Electrolyte-Mediated Stabilization of High-Capacity Micro-Sized Antimony Anodes for Potassium-Ion Batteries.

Adv Mater 2021 Feb 20;33(8):e2005993. Epub 2021 Jan 20.

State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, CAS, Changchun, 130022, China.

Alloying anodes exhibit very high capacity when used in potassium-ion batteries, but their severe capacity fading hinders their practical applications. The failure mechanism has traditionally been attributed to the large volumetric change and/or their fragile solid electrolyte interphase. Herein, it is reported that an antimony (Sb) alloying anode, even in bulk form, can be stabilized readily by electrolyte engineering. The Sb anode delivers an extremely high capacity of 628 and 305 mAh g at current densities of 100 and 3000 mA g , respectively, and remains stable for more than 200 cycles. Interestingly, there is no need to do nanostructural engineering and/or carbon modification to achieve this excellent performance. It is shown that the change in K solvation structure, which is tuned by electrolyte composition (i.e., anion, solvent, and concentration), is the main reason for achieving this excellent performance. Moreover, an interfacial model based on the K -solvent-anion complex behavior is presented. The electronegativity of the K -solvent-anion complex, which can be tuned by changing the solvent type and anion species, is used to predict and control electrode stability. The results shed new light on the failure mechanism of alloying anodes, and provide a new guideline for electrolyte design that stabilizes metal-ion batteries using alloying anodes.
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http://dx.doi.org/10.1002/adma.202005993DOI Listing
February 2021

WO Nanowire/Carbon Nanotube Interlayer as a Chemical Adsorption Mediator for High-Performance Lithium-Sulfur Batteries.

Molecules 2021 Jan 13;26(2). Epub 2021 Jan 13.

Department of Energy Engineering, Hanyang University, Seoul 04763, Korea.

We developed a new nanowire for enhancing the performance of lithium-sulfur batteries. In this study, we synthesized WO nanowires (WNWs) via a simple hydrothermal method. WNWs and one-dimensional materials are easily mixed with carbon nanotubes (CNTs) to form interlayers. The WNW interacts with lithium polysulfides through a thiosulfate mediator, retaining the lithium polysulfide near the cathode to increase the reaction kinetics. The lithium-sulfur cell achieves a very high initial discharge capacity of 1558 and 656 mAh g at 0.1 and 3 C, respectively. Moreover, a cell with a high sulfur mass loading of 4.2 mg cm still delivers a high capacity of 1136 mAh g at a current density of 0.2 C and it showed a capacity of 939 mAh g even after 100 cycles. The WNW/CNT interlayer maintains structural stability even after electrochemical testing. This excellent performance and structural stability are due to the chemical adsorption and catalytic effects of the thiosulfate mediator on WNW.
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http://dx.doi.org/10.3390/molecules26020377DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7828354PMC
January 2021

Engineering Sodium-Ion Solvation Structure to Stabilize Sodium Anodes: Universal Strategy for Fast-Charging and Safer Sodium-Ion Batteries.

Nano Lett 2020 May 27;20(5):3247-3254. Epub 2020 Apr 27.

State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, CAS, Changchun 130022, China.

Sodium-ion batteries are promising alternatives for lithium-ion batteries due to their lower cost caused by global sodium availability. However, the low Coulombic efficiency (CE) of the sodium metal plating/stripping process represents a serious issue for the Na anode, which hinders achieving a higher energy density. Herein, we report that the Na solvation structure, particularly the type and location of the anions, plays a critical role in determining the Na anode performance. We show that the low CE results from anion-mediated corrosion, which can be tackled readily through tuning the anion interaction at the electrolyte/anode interface. Our strategy thus enables fast-charging Na-ion and Na-S batteries with a remarkable cycle life. The presented insights differ from the prevailing interpretation that the failure mechanism mostly results from sodium dendrite growth and/or solid electrolyte interphase formation. Our anionic model introduces a new guideline for improving the electrolytes for metal-ion batteries with a greater energy density.
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http://dx.doi.org/10.1021/acs.nanolett.9b05355DOI Listing
May 2020

Density Functional Theory Investigation of Mixed Transition Metals in Olivine and Tavorite Cathode Materials for Li-Ion Batteries.

ACS Appl Mater Interfaces 2020 Apr 30;12(14):16376-16386. Epub 2020 Mar 30.

Department of Materials Science and Engineering, Chonnam National University, 300 Yongbong-dong, Bukgu, Gwangju 61186, Republic of Korea.

Lithium-ion batteries (LIBs) are widely used in various electronic devices and have garnered a huge amount of attention. In addition, evaluation of the intrinsic properties of LIB cathode materials is of considerable interest for practical applications. Therefore, through first-principles calculations based on the density functional theory, we investigated the structural, electronic, electrochemical, and kinetic properties of mixed transition metals, that is, Ni-substituted LiMnPO (LMP) and LiMnPOF (LMPF) cathode materials, that is, LiMnNiPO (LMNP) and LiMnNiPOF (LMNPF), respectively, which have not been extensively studied. We also evaluated their delithiated phases, that is, MnNiPO (MNP) and MnNiPOF (MNPF). Our calculations suggest that Ni substitution significantly affected the structural and electrochemical properties. After Li insertion, the MNPF unit-cell volume increased by about 8%, lower than that of pristine MnPOF. The Li intercalation voltage also increased in LMNP (4.27 V) and LMNPF (5.23 V). In addition, the migration barrier was calculated to be 0.4 eV for LMNPF, lower than that of LMPF. This study may provide insights for developing LMNP and LMNPF cathode materials in LIB applications.
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http://dx.doi.org/10.1021/acsami.9b23367DOI Listing
April 2020

Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future.

Chem Rev 2020 Jul 5;120(14):6626-6683. Epub 2020 Mar 5.

Department of Chemistry, Bar-Ilan University, Ramat Gan 5290002, Israel.

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal-air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal-air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li-O cells but include Na-O, K-O, and Mg-O cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li-O cells.
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http://dx.doi.org/10.1021/acs.chemrev.9b00609DOI Listing
July 2020

Nano/Microstructured Silicon-Carbon Hybrid Composite Particles Fabricated with Corn Starch Biowaste as Anode Materials for Li-Ion Batteries.

Nano Lett 2020 Jan 17;20(1):625-635. Epub 2019 Dec 17.

Center for Energy Storage Research , Korea Institute of Science and Technology , Seoul 02792 , Republic of Korea.

Silicon has a great potential as an alternative to graphite which is currently used commercially as an anode material in lithium-ion batteries (LIBs) because of its exceptional capacity and reasonable working potential. Herein, a low-cost and scalable approach is proposed for the production of high-performance silicon-carbon (Si-C) hybrid composite anodes for high-energy LIBs. The Si-C composite material is synthesized using a scalable microemulsion method by selecting silicon nanoparticles, using low-cost corn starch as a biomass precursor and finally conducting heat treatment under CH gas. This produces a unique nano/microstructured Si-C hybrid composite comprised of silicon nanoparticles embedded in micron-sized amorphous carbon balls derived from corn starch that is capsuled by thin graphitic carbon layer. Such a dual carbon matrix tightly surrounds the silicon nanoparticles that provides high electronic conductivity and significantly decreases the absolute stress/strain of the material during multiple lithiation-delithiation processes. The Si-C hybrid composite anode demonstrates a high capacity of 1800 mAh g, outstanding cycling stability with capacity retention of 80% over 500 cycles, and fast charge-discharge capability of 12 min. Moreover, the Si-C composite anode exhibits good acceptability in practical LIBs assembled with commercial Li[NiCoMn]O and Li[NiCoAl]O cathodes.
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http://dx.doi.org/10.1021/acs.nanolett.9b04395DOI Listing
January 2020

Layered KMnO·0.15HO as a Cathode Material for Potassium-Ion Intercalation.

ACS Appl Mater Interfaces 2019 Nov 7;11(46):43312-43319. Epub 2019 Nov 7.

Department of Nanotechnology and Advanced Materials Engineering & Sejong Battery Institute , Sejong University , Seoul 05006 , South Korea.

Here, we present KMnO·0.15HO, which has a two-dimensional open framework, as an intercalation host for potassium ions. KMnO·0.15HO has a layered structure consisting of edge-sharing MnO octahedra with a large basal spacing of ∼7.3 Å, which facilitates K-ion mobility. Water molecules in the interlayers between the MnO layers play an important role as a pillar to support the structure during repetitive de/potassiation cycles, as confirmed by an operando X-ray diffraction study. As a result, the large K ions readily migrate into the crystal structure, resulting in satisfactory electrochemical performance in K-cells. With the aid of the structural pillar, the KMnO·0.15HO cathode delivers a high reversible capacity of 150 mA h g over 100 cycles at a rate of 0.1 C (15 mA g), with acceptable power capability up to 5 C-rates.
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http://dx.doi.org/10.1021/acsami.9b18540DOI Listing
November 2019

A 4 V Class Potassium Metal Battery with Extremely Low Overpotential.

ACS Nano 2019 Aug 15;13(8):9306-9314. Epub 2019 Aug 15.

Department of Energy Engineering , Hanyang University , Seoul 133-791 , South Korea.

K metal anodes usually have a low Coulombic efficiency and poor safety owing to their large volume variation and high chemical reactivity. In this study, a three-dimensional K (3D-K) anode is formed by plating metallic K into hollow N-doped C polyhedrons/graphene (HNCP/G). Then a Sn-based solid-electrolyte interphase layer is conformably coated onto the surface of 3D-K to construct Sn@3D-K. Compared with the typical K-foil anode, the Sn@3D-K anode can significantly reduce the interfacial resistance, improve the K ion transport mobility, reduce parasitic reactions, and suppress the formation of K dendrites. Meanwhile, HNCP/G serves as a chemically stable, conductive host to accommodate the volume expansion/shrinkage of Sn@3D-K. Owing to these merits, the symmetric Sn@3D-K cell exhibits low voltage hysteresis (9 mV at 0.2 mA cm after 500 h; 31 mV at 1 mA cm after 100 h). When paired with a Prussian blue (PB)/graphene cathode, the KMn[Fe(CN)]/G∥Sn@3D-K battery delivers an average discharge plateau of 4.02 V, an ultralow overpotential of 0.01 V, and a high specific capacity of 147.2 mAh g, approaching the theoretical value of KMnFe(CN) (156 mAh g). A 4 V class K metal battery that exhibits extremely low overpotential and high specific capacity, which are the best among previously reported PB-based K batteries, is proposed.
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http://dx.doi.org/10.1021/acsnano.9b03915DOI Listing
August 2019

Degradation Mechanism of Highly Ni-Rich Li[NiCoMn]O Cathodes with > 0.9.

ACS Appl Mater Interfaces 2019 Aug 16;11(34):30936-30942. Epub 2019 Aug 16.

Department of Energy Engineering , Hanyang University , Seoul 04763 , Republic of Korea.

A series of Ni-rich Li[NiCoMn]O ( = 0.9, 0.92, 0.94, 0.96, 0.98, and 1.0) (NCM) cathodes are prepared to study their capacity fading behaviors. The intrinsic trade-off between the capacity gain and compromised cycling stability is observed for layered cathodes with ≥ 0.9. The initial specific capacities of LiNiO and Li[NiCoMn]O are 245 mAh g (91% of the theoretical capacity) and 230 mAh g, and their corresponding capacity retentions are 72.5% and 88.4%. However, the capacity retention characteristic deteriorates at an increasingly faster rate for > 0.95, in contrast with the nearly linear increase of specific capacity. The fast capacity fading stems from the chemical attack of the cathode by the electrolyte infiltrated through the microcracks, resulting from the mechanical instability inflicted by the anisotropic internal strain caused by the H2 ⇆ H3 phase transition. Thus, the capacity fading of the NCM cathodes for > 0.9 critically depends on the extent of the H2 → H3 phase transition. Retardation or protraction of the H2 ⇆ H3 phase transition by engineering the microstructure should improve the cycle life of these highly Ni-enriched NCM cathodes.
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http://dx.doi.org/10.1021/acsami.9b09754DOI Listing
August 2019

Deactivation of redox mediators in lithium-oxygen batteries by singlet oxygen.

Nat Commun 2019 03 26;10(1):1380. Epub 2019 Mar 26.

Department of Energy Engineering, Hanyang University, Seoul, 04763, Republic of Korea.

Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. However, the gradual deactivation of redox mediators during repeated cycling has not conclusively been explained. Here, we show that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. The reduced form of the mediator is markedly more reactive towards singlet oxygen than the oxidized form, from which we derive reaction mechanisms supported by density functional theory calculations. Redox mediators must thus be designed for stability against singlet oxygen.
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http://dx.doi.org/10.1038/s41467-019-09399-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6435713PMC
March 2019

Nano/Microstructured Silicon-Graphite Composite Anode for High-Energy-Density Li-Ion Battery.

ACS Nano 2019 Feb 15;13(2):2624-2633. Epub 2019 Feb 15.

Department of Energy Engineering , Hanyang University , Seoul 133-791 , Republic of Korea.

With the ever-increasing demand for lithium-ion batteries (LIBs) with higher energy density, tremendous attention has been paid to design various silicon-active materials as alternative electrodes due to their high theoretical capacity (ca. 3579 mAh g). However, totally replacing the commercially utilized graphite with silicon is still insurmountable owing to bottlenecks such as low electrode loading and insufficient areal capacity. Thus, in this study, we turn back to enhanced graphite electrode through the cooperation of modified silicon via a facile and scalable blending process. The modified nano/microstructured silicon with boron doping and carbon nanotube wedging (B-Si/CNT) can provide improved stability (88.2% retention after 200 cycles at 2000 mA g) and high reversible capacity (∼2426 mAh g), whereas the graphite can act as a tough framework for high loading. Owing to the synergistic effect, the resultant B-Si/CNT-graphite composite (B-Si/CNT@G) shows a high areal capacity of 5.2 mAh cm and excellent cycle retention of 83.4% over 100 cycles, even with ultrahigh active mass loading of 11.2 mg cm,which could significantly surpass the commercially used graphite electrode. Notably, the composite also exhibits impressive application in Li-ion full battery using 2 mol % Al-doped full-concentration-gradient Li[NiCoMn]O (Al2-FCG76) as the cathode with excellent capacity retention of 82.5% even after 300 cycles and an outstanding energy density (8.0 mWh cm) based on the large mass loading of the cathode (12.0 mg cm).
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http://dx.doi.org/10.1021/acsnano.9b00169DOI Listing
February 2019

Microstructural Degradation of Ni-Rich Li[Ni Co Mn ]O Cathodes During Accelerated Calendar Aging.

Small 2018 Nov 14;14(45):e1803179. Epub 2018 Sep 14.

Department of Energy Engineering, Hanyang University, Seoul, 133-791, South Korea.

Because electric vehicles (EVs) are used intermittently with long resting periods in the fully charged state before driving, calendar aging behavior is an important criterion for the application of Li-ion batteries used in EVs. In this work, Ni-rich Li[Ni Co Mn ]O (x = 0.8 and 0.9) cathode materials with high energy densities, but low cycling stabilities are investigated to characterize their microstructural degradation during accelerated calendar aging. Although the particles seem to maintain their crystal structures and morphologies, the microcracks which develop during calendar aging remain even in the fully discharged state. An NiO-like phase rock-salt structure of tens of nanometers in thickness accumulates on the surfaces of the primary particles through parasitic reactions with the electrolyte. In addition, the passive layer of this rock-salt structure near the microcracks is gradually exfoliated from the primary particles, exposing fresh surfaces containing Ni to the electrolyte. Interestingly, the interior primary particles near the microcracks have deteriorated more severely than the outer particles. The microstructural degradation is worsened with increasing Ni contents in the cathode materials, directly affecting electrochemical performances such as the reversible capacities and voltage profiles.
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http://dx.doi.org/10.1002/smll.201803179DOI Listing
November 2018

High-Performance Cells Containing Lithium Metal Anodes, LiNiCoMnO (NCM 622) Cathodes, and Fluoroethylene Carbonate-Based Electrolyte Solution with Practical Loading.

ACS Appl Mater Interfaces 2018 Jun 31;10(23):19773-19782. Epub 2018 May 31.

Department of Chemistry , Bar-Ilan University , Ramat Gan 52900 , Israel.

We report on the highly stable lithium metal|LiNiCoMnO (NCM 622) cells with practical electrodes' loading of 3.3 mA h g, which can undergo many hundreds of stable cycles, demonstrating high rate capability. A key issue was the use of fluoroethylene carbonate (FEC)-based electrolyte solutions (1 M LiPF in FEC/dimethyl carbonate). Li|NCM 622 cells can be cycled at 1.5 mA cm for more than 600 cycles, whereas symmetric Li|Li cells demonstrate stable performance for more than 1000 cycles even at higher areal capacity and current density. We attribute the excellent performance of both Li|NCM and Li|Li cells to the formation of a stable and efficient solid electrolyte interphase (SEI) on the surface of the Li metal electrodes cycled in FEC-based electrolyte solutions. The composition of the SEI on the Li and the NCM electrodes is analyzed by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. A drastic capacity fading of Li|NCM cells is observed, followed by spontaneous capacity recovery during prolonged cycling. This phenomenon depends on the current density and the amount of the electrolyte solution and relates to kinetic limitations because of SEI formation on the Li anodes in the FEC-based electrolyte solution.
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http://dx.doi.org/10.1021/acsami.8b07004DOI Listing
June 2018

A 4 V Li-Ion Battery using All-Spinel-Based Electrodes.

ChemSusChem 2018 Jul 30;11(13):2165-2170. Epub 2018 May 30.

Center for Energy Storage Research, Green City Technology Institute, Korea Institute of Science and Technology, Seoul, 02792, Republic of Korea.

Boosting the performance of rechargeable lithium-ion batteries (LIBs) beyond the state-of-the-art is mandatory toward meeting the future energy requirements of the consumer mass market. The replacement of conventional graphite anodes with conversion-type metal-oxide anodes is one progressive approach toward achieving this goal. Here, a LIB consisting of a highcapacity spinel NiMn O anode and a high-voltage spinel LiNi Mn O cathode was proposed. Polyhedral-shaped NiMn O powder was prepared from a citrate precursor via the sol-gel method. Electrochemical tests showed that the NiMn O in a half-cell configuration could deliver reversible capacities of 750 and 303 mAh g at 0.1 and 3 C rates. Integrating the NiMn O anode into a full-cell configuration provided an estimated energy density of 506 Wh kg (vs. cathode mass) upon 100 cycles and excellent cycling performance over 150 cycles at the 0.1 C rate, which can be considered promising in terms of satisfying the demands for high energy densities in large-scale applications.
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http://dx.doi.org/10.1002/cssc.201800579DOI Listing
July 2018

Pyrosynthesis of Na V (PO ) @C Cathodes for Safe and Low-Cost Aqueous Hybrid Batteries.

ChemSusChem 2018 Jul 21;11(13):2239-2247. Epub 2018 Jun 21.

Department of Materials Science and Engineering, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju, 61186, Republic of Korea.

Rechargeable hybrid aqueous batteries (ReHABs) have emerged as promising sustainable energy-storage devices because all components are environmentally benign and abundant. In this study, a carbon-wrapped sponge-like Na V (PO ) nanoparticle (NVP@C) cathode is prepared by a simple pyrosynthesis for use in the ReHAB system with impressive rate capability and high cyclability. A high-resolution X-ray diffraction study confirmed the formation of pure Na ion superionic conductor (NASICON) NVP with rhombohedral structure. When tested in the ReHAB system, the NVP@C demonstrated high rate capability (66 mAh g at 32 C) and remarkable cyclability over 1000 cycles (about 72 % of the initial capacity is retained at 30 C). Structural transformation and oxidation change studies of the electrode evaluated by using in situ synchrotron X-ray diffraction and ex situ X-ray photoelectron spectroscopy, respectively, confirmed the high reversibility of the NVP@C electrode in the ReHAB system through a two-phase reaction. The combined strategy of nanosizing and carbon-wrapping in the NVP particles is responsible for the remarkable electrochemical properties. The pyrosynthesis technique appears to be a promising and feasible approach to prepare a high-performance electrode for safe and low-cost ReHAB systems as nextgeneration large-scale energy storage devices.
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http://dx.doi.org/10.1002/cssc.201800724DOI Listing
July 2018

Stabilization of Lithium-Metal Batteries Based on the in Situ Formation of a Stable Solid Electrolyte Interphase Layer.

ACS Appl Mater Interfaces 2018 May 15;10(21):17985-17993. Epub 2018 May 15.

Center for Energy Convergence, Green City Technology Institute , Korea Institute of Science and Technology , Hwarangno 14 gil 5, Seongbuk-gu , Seoul 136-791 , Republic of Korea.

Lithium (Li) metals have been considered most promising candidates as an anode to increase the energy density of Li-ion batteries because of their ultrahigh specific capacity (3860 mA h g) and lowest redox potential (-3.040 V vs standard hydrogen electrode). However, unstable dendritic electrodeposition, low Coulombic efficiency, and infinite volume changes severely hinder their practical uses. Herein, we report that ethyl methyl carbonate (EMC)- and fluoroethylene carbonate (FEC)-based electrolytes significantly enhance the energy density and cycling stability of Li-metal batteries (LMBs). In LMBs, using commercialized Ni-rich Li[NiCoMn]O (NCM622) and 1 M LiPF in EMC/FEC = 3:1 electrolyte exhibits a high initial capacity of 1.8 mA h cm with superior cycling stability and high Coulombic efficiency above 99.8% for 500 cycles while delivering a unprecedented energy density. The present work also highlights a significant improvement in scaled-up pouch-type Li/NCM622 cells. Moreover, the postmortem characterization of the cycled cathodes, separators, and Li-metal anodes collected from the pouch-type Li/NCM622 cells helped identifying the improvement or degradation mechanisms behind the observed electrochemical cycling.
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http://dx.doi.org/10.1021/acsami.8b04592DOI Listing
May 2018

NaVO·3HO Barnesite Nanorod: An Open Door to Display a Stable and High Energy for Aqueous Rechargeable Zn-Ion Batteries as Cathodes.

Nano Lett 2018 04 29;18(4):2402-2410. Epub 2018 Mar 29.

Department of Materials Science and Engineering , Chonnam National University , Gwangju 500-757 , South Korea.

Owing to their safety and low cost, aqueous rechargeable Zn-ion batteries (ARZIBs) are currently more feasible for grid-scale applications, as compared to their alkali counterparts such as lithium- and sodium-ion batteries (LIBs and SIBs), for both aqueous and nonaqueous systems. However, the materials used in ARZIBs have a poor rate capability and inadequate cycle lifespan, serving as a major handicap for long-term storage applications. Here, we report vanadium-based NaVO·3HO nanorods employed as a positive electrode for ARZIBs, which display superior electrochemical Zn storage properties. A reversible Zn-ion (de)intercalation reaction describing the storage mechanism is revealed using the in situ synchrotron X-ray diffraction technique. This cathode material delivers a very high rate capability and high capacity retention of more than 80% over 1000 cycles, at a current rate of 40C (1C = 361 mA g). The battery offers a specific energy of 90 W h kg at a specific power of 15.8 KW kg, enlightening the material advantages for an eco-friendly atmosphere.
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http://dx.doi.org/10.1021/acs.nanolett.7b05403DOI Listing
April 2018

Shedding Light on the Oxygen Reduction Reaction Mechanism in Ether-Based Electrolyte Solutions: A Study Using Operando UV-Vis Spectroscopy.

ACS Appl Mater Interfaces 2018 Apr 20;10(13):10860-10869. Epub 2018 Mar 20.

Department of Chemistry and BINA (BIU Institute of Nanotechnology and Advanced Materials) , Bar Ilan University , Ramat-Gan 5290002 , Israel.

Using UV-vis spectroscopy in conjunction with various electrochemical techniques, we have developed a new effective operando methodology for investigating the oxygen reduction reactions (ORRs) and their mechanisms in nonaqueous solutions. We can follow the in situ formation and presence of superoxide moieties during ORR as a function of solvent, cations, anions, and additives in the solution. Thus, using operando UV-vis spectroscopy, we found evidence for the formation of superoxide radical anions during oxygen reduction in LiTFSI/diglyme electrolyte solutions. Nitro blue tetrazolium (NBT) was used to indicate the presence of superoxide moieties based on its unique spectral response. Indeed, the spectral response of NBT containing solutions undergoing ORR could provide a direct indication for the level of association of the Li cations with the electrolyte anions.
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http://dx.doi.org/10.1021/acsami.7b18376DOI Listing
April 2018

Clarification of Solvent Effects on Discharge Products in Li-O Batteries through a Titration Method.

ACS Appl Mater Interfaces 2018 Jan 28;10(1):526-533. Epub 2017 Dec 28.

Department of Energy Engineering, Hanyang University , Seoul 04763, Republic of Korea.

As a substitute for the current lithium-ion batteries, rechargeable lithium oxygen batteries have attracted much attention because of their theoretically high energy density, but many challenges continue to exist. For the development of these batteries, understanding and controlling the main discharge product LiO (lithium peroxide) are of paramount importance. Here, we comparatively analyzed the amount of LiO in the cathodes discharged at various discharge capacities and current densities in dimethyl sulfoxide (DMSO) and tetraethylene glycol dimethyl ether (TEGDME) solvents. The precise assessment entailed revisiting and revising the UV-vis titration analysis. The amount of LiO electrochemically formed in DMSO was less than that formed in TEGDME at the same capacity and even at a much higher full discharge capacity in DMSO than in TEGDME. On the basis of our analytical experimental results, this unexpected result was ascribed to the presence of soluble LiO-like intermediates that remained in the DMSO solvent and the chemical transformation of LiO to LiOH, both of which originated from the inherent properties of the DMSO solvent.
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http://dx.doi.org/10.1021/acsami.7b14279DOI Listing
January 2018

Microsphere Na[NiCoMn]O Cathode Material for High-Performance Sodium-Ion Batteries.

ACS Appl Mater Interfaces 2017 Dec 15;9(51):44534-44541. Epub 2017 Dec 15.

Department of Energy Engineering, Hanyang University , Seoul 04763, South Korea.

P2-type layered oxides have been considered promising candidates as cathodes for sodium-ion batteries (SIBs) owing to their high capacity and high rate capability. However, because of the difficulty involved in forming hierarchical microstructures, it remains challenging to develop high energy density P2-type layered oxides with good electrochemical performance and high electrode density. In this study, we demonstrate the feasibility of P2-type Na[NiCoMn]O as a very efficient cathode material for high energy density SIBs by synthesizing a micron-sized hierarchical structure via the coprecipitation route. The as-prepared P2-type microsphere cathode constructed from nanoscale primary particles provides a sufficient interface between the electrodes and the electrolyte solution, which enables to shorten the transport pathways for Na ions and electrons. Simultaneously, the hierarchical microstructure enhances the structural stability and high tap density (∼1.18 g cm). Benefiting from these merits, the proposed P2-type microsphere Na[NiCoMn]O displays a high discharge capacity of 187 mA h g at 12 mA g and an exceptional cycle retention of 74.7% after 500 cycles, even at the high current density of 600 mA g. In addition, the high tap density of this P2-type microsphere enhances the density of composite cathodes, which translates to a high volumetric energy density of 340 W h L based on the overall volume of the cathode active mass and the aluminum foil current collector.
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http://dx.doi.org/10.1021/acsami.7b15267DOI Listing
December 2017

Redox Mediators for Li-O Batteries: Status and Perspectives.

Adv Mater 2018 Jan 27;30(1). Epub 2017 Nov 27.

Department of Energy Engineering, Hanyang University, Seoul, 133-791, South Korea.

Li-O batteries have received much attention due to their extremely large theoretical energy density. However, the high overpotentials required for charging Li-O batteries lower their energy efficiency and degrade the electrolytes and carbon electrodes. This problem is one of the main obstacles in developing practical Li-O batteries. To solve this problem, it is important to facilitate the oxidation of Li O upon charging by using effective electrocatalysis. Using solid catalysts is not too effective for oxidizing the electronically isolating Li-peroxide layers. In turn, for soluble catalysts, red-ox mediators (RMs) are homogeneously dissolved in the electrolyte solutions and can effectively oxidize all of the Li O precipitated during discharge. RMs can decompose solid Li O species no matter their size, morphology, or thickness and thus dramatically increase energy efficiency. However, some negative side effects, such as the shuttle reactions of RMs and deterioration of the Li-metal occur. Therefore, it is necessary to study the activity and stability of RMs in Li-O batteries in detail. Herein, recent studies related to redox mediators are reviewed and the mechanisms of redox reactions are illustrated. The development opportunities of RMs for this important battery technology are discussed and future directions are suggested.
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http://dx.doi.org/10.1002/adma.201704162DOI Listing
January 2018

Effect of Mn in LiVMn(PO) as High Capacity Cathodes for Lithium Batteries.

ACS Appl Mater Interfaces 2017 Nov 7;9(46):40307-40316. Epub 2017 Nov 7.

Department of Nanotechnology and Advanced Materials Engineering & Sejong Battery Institute, Sejong University , Seoul 05006, South Korea.

LiVMn(PO) (x = 0, 0.05) cathode materials, which allow extraction of 3 mol of Li from the formula unit, were investigated to achieve a high energy density utilizing multielectron reactions, activated by the V redox reaction. Structural investigation demonstrates that V was replaced by equivalent Mn, as confirmed by Rietveld refinement of the X-ray diffraction data and X-ray absorption near edge spectroscopy. The substitution simultaneously lowered the band gap energy from 3.4 to 3.2 eV, according to a density functional theory calculation. In addition to the effect of Mn doping, surface carbonization of LiVMn(PO) (x = 0, 0.05) dramatically increased the electric conductivity up to 10 S cm. As a result, the carbon-coated LiVMn(PO) (x = 0.05) delivered a high discharge (reduction) capacity of approximately 180 mAh g at a current of 20 mA g (0.1 C rate) with excellent retention, delivering approximately 163 mAh g at the 200th cycle. Even at 50 C (10 A g), the electrode afforded a discharge capacity of 68 mAh g and delivered approximately 104 mAh g (1 C) at -10 °C with the help of Mn doping and carbon coating. The synergetic effects such as a lowered band gap energy by Mn doping and high electric conductivity associated with carbon coating are responsible for the superior electrode performances, including thermal properties with extremely low exothermic heat generation (<0.4 J g for LiVMn(PO)), which is compatible with the layered high energy density of LiNiCoAlO and LiNiCoMnO materials.
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http://dx.doi.org/10.1021/acsami.7b13128DOI Listing
November 2017

Micro-Intertexture Carbon-Free Iron Sulfides as Advanced High Tap Density Anodes for Rechargeable Batteries.

ACS Appl Mater Interfaces 2017 Nov 1;9(45):39416-39424. Epub 2017 Nov 1.

Department of Energy Engineering, Hanyang University , Seoul 133-791, Republic of Korea.

Numerous materials have been considered as promising electrode materials for rechargeable batteries; however, developing efficient materials to achieving good cycling performance and high volumetric energy capacity simultaneously remains a great challenge. Considering the appealing properties of iron sulfides, which include low cost, high theoretical capacity, and favorable electrochemical conversion mechanism, in this work, we demonstrate the feasibility of carbon-free microscale FeS as high-efficiency anode materials for rechargeable batteries by designing hierarchical intertexture architecture. The as-prepared intertexture FeS microspheres constructed from nanoscale units take advantage of both the long cycle life of nanoscale units and the high tap density (1.13 g cm) of the micro-intertexture FeS. As a result, high capacities of 1089.2 mA h g (1230.8 mA h cm) and 624.7 mA h g (705.9 mA h cm) were obtained after 100 cycles at 1 A g in Li-ion and Na-ion batteries, respectively, demonstrating one of the best performances for iron sulfide-based electrodes. Even after deep cycling at 20 A g, satisfactory capacities could be retained. Related results promote the practical application of metal sulfides as high-capacity electrodes with high rate capability for next-generation rechargeable batteries.
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http://dx.doi.org/10.1021/acsami.7b13239DOI Listing
November 2017

Electrochemical Properties of Sulfurized-Polyacrylonitrile Cathode for Lithium-Sulfur Batteries: Effect of Polyacrylic Acid Binder and Fluoroethylene Carbonate Additive.

J Phys Chem Lett 2017 Nov 19;8(21):5331-5337. Epub 2017 Oct 19.

Department of Energy Engineering, Hanyang University , Seoul 04763, South Korea.

Sulfurized carbonized polyacrylonitrile (S-CPAN) is a promising cathode material for Li-S batteries owing to the absence of polysulfide dissolution phenomena in the electrolyte solutions and thus the lack of a detrimental shuttle mechanism. However, challenges remain in achieving high performance at practical loading because of large volume expansion of S-CPAN electrodes and lithium anode degradation at high current densities. To mitigate this problem, we propose a novel cell design including poly(acrylic acid) (PAA) binder for improved integrity of the composite electrodes and fluoroethylene carbonate (FEC) as additive in the electrolyte solutions for stabilizing the lithium metal surface. As a result, these cells delivered high initial discharge capacity of 1500 mAh g and a superior cycling stability ∼98.5% capacity retention after 100 cycles, 0.5 C rate, and high sulfur loading of 3.0 mg cm. Scaled-up 260 mAh pouch cells are working very well, highlighting the practical importance of this work.
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http://dx.doi.org/10.1021/acs.jpclett.7b02354DOI Listing
November 2017

Low-Polarization Lithium-Oxygen Battery Using [DEME][TFSI] Ionic Liquid Electrolyte.

ChemSusChem 2018 01 23;11(1):229-236. Epub 2017 Nov 23.

Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via Fossato di Mortara, 44121, Ferrara, Italy.

The room-temperature molten salt mixture of N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethanesulfonyl) imide ([DEME][TFSI]) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt is herein reported as electrolyte for application in Li-O batteries. The [DEME][TFSI]-LiTFSI solution is studied in terms of ionic conductivity, viscosity, electrochemical stability, and compatibility with lithium metal at 30 °C, 40 °C, and 60 °C. The electrolyte shows suitable properties for application in Li-O battery, allowing a reversible, low-polarization discharge-charge performance with a capacity of about 13 Ah g-1carbon in the positive electrode and coulombic efficiency approaching 100 %. The reversibility of the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) is demonstrated by ex situ XRD and SEM studies. Furthermore, the study of the cycling behavior of the Li-O cell using the [DEME][TFSI]-LiTFSI electrolyte at increasing temperatures (from 30 to 60 °C) evidences enhanced energy efficiency together with morphology changes of the deposited species at the working electrode. In addition, the use of carbon-coated Zn Fe O (TMO-C) lithium-conversion anode in an ionic-liquid-based Li-ion/oxygen configuration is preliminarily demonstrated.
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http://dx.doi.org/10.1002/cssc.201701696DOI Listing
January 2018

Self-Rearrangement of Silicon Nanoparticles Embedded in Micro-Carbon Sphere Framework for High-Energy and Long-Life Lithium-Ion Batteries.

Nano Lett 2017 09 31;17(9):5600-5606. Epub 2017 Aug 31.

Center for Energy Convergence Research, Green City Technology Institute, Korea Institute of Science and Technology , Seoul 02792, Republic of Korea.

Despite its highest theoretical capacity, the practical applications of the silicon anode are still limited by severe capacity fading, which is due to pulverization of the Si particles through volume change during charge and discharge. In this study, silicon nanoparticles are embedded in micron-sized porous carbon spheres (Si-MCS) via a facile hydrothermal process in order to provide a stiff carbon framework that functions as a cage to hold the pulverized silicon pieces. The carbon framework subsequently allows these silicon pieces to rearrange themselves in restricted domains within the sphere. Unlike current carbon coating methods, the Si-MCS electrode is immune to delamination. Hence, it demonstrates unprecedented excellent cyclability (capacity retention: 93.5% after 500 cycles at 0.8 A g), high rate capability (with a specific capacity of 880 mAh g at the high discharge current density of 40 A g), and high volumetric capacity (814.8 mAh cm) on account of increased tap density. The lithium-ion battery using the new Si-MCS anode and commercial LiNiCoMnO cathode shows a high specific energy density above 300 Wh kg, which is considerably higher than that of commercial graphite anodes.
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http://dx.doi.org/10.1021/acs.nanolett.7b02433DOI Listing
September 2017

Synthetic Control of Kinetic Reaction Pathway and Cationic Ordering in High-Ni Layered Oxide Cathodes.

Adv Mater 2017 Oct 25;29(39). Epub 2017 Aug 25.

Sustainable Energy Technologies Department, Brookhaven National Laboratory, Upton, NY, 11973, USA.

Nickel-rich layered transition metal oxides, LiNi (MnCo) O (1-x ≥ 0.5), are appealing candidates for cathodes in next-generation lithium-ion batteries (LIBs) for electric vehicles and other large-scale applications, due to their high capacity and low cost. However, synthetic control of the structural ordering in such a complex quaternary system has been a great challenge, especially in the presence of high Ni content. Herein, synthesis reactions for preparing layered LiNi Mn Co O (NMC71515) by solid-state methods are investigated through a combination of time-resolved in situ high-energy X-ray diffraction and absorption spectroscopy measurements. The real-time observation reveals a strong temperature dependence of the kinetics of cationic ordering in NMC71515 as a result of thermal-driven oxidation of transition metals and lithium/oxygen loss that concomitantly occur during heat treatment. Through synthetic control of the kinetic reaction pathway, a layered NMC71515 with low cationic disordering and a high reversible capacity is prepared in air. The findings may help to pave the way for designing high-Ni layered oxide cathodes for LIBs.
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http://dx.doi.org/10.1002/adma.201606715DOI Listing
October 2017

2,4-Dimethoxy-2,4-dimethylpentan-3-one: An Aprotic Solvent Designed for Stability in Li-O Cells.

J Am Chem Soc 2017 08 18;139(34):11690-11693. Epub 2017 Aug 18.

Department of Chemistry and BINA (BIU Institute for Nano-Technology and Advanced Materials), Bar Ilan University , Ramat-Gan 5290002, Israel.

In this study, we present a new aprotic solvent, 2,4-dimethoxy-2,4-dimethylpentan-3-one (DMDMP), which is designed to resist nucleophilic attack and hydrogen abstraction by reduced oxygen species. Li-O cells using DMDMP solutions were successfully cycled. By various analytical measurements, we showed that even after prolonged cycling only a negligible amount of DMDMP was degraded. We suggest that the observed capacity fading of the Li-O DMDMP-based cells was due to instability of the lithium anode during cycling. The stability toward oxygen species makes DMDMP an excellent solvent candidate for many kinds of electrochemical systems which involve oxygen reduction and assorted evaluation reactions.
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http://dx.doi.org/10.1021/jacs.7b06414DOI Listing
August 2017