Journal Publication


Wooseok Go, Minho Kim, Jehee Park, Chek Hai Lim, Sang Hoon Joo, Youngsik Kim, and Hyun-Wook Lee

Nano Letters, Nano Letters, 19 (3) 1504-1511 (2019). (Selected as a Supplementary Cover page on Nano Letters, March 2019 issue) (Website link)

img The metallic lithium (Li) and sodium (Na) anodes have great attention as ideal anodes to meet the needs for high energy density batteries due to their highest theoretical capacities. Although many approaches have successfully improved the performances of Li or Na metal anodes, many of these methods are difficult to scale up and thus cannot be applied in the production of batteries in practice. In this work, we introduce nanocrevasses in a carbon fiber scaffold which can facilitate the penetration of molten alkali metal into a carbon scaffold by enhancing its wettability for Li/Na metal. The resulting alkali metal/carbon composites exhibit stable long-term cycling over hundreds of cycles. The facile synthetic method enables for scalable production using recycled metal waste. Thus, the addition of nanocrevasses to carbon fiber as a scaffold for alkali metals can generate environmentally friendly and cost-effective composites for practical electrode applications.

Ziyauddin Khan, Sung O Park, Juchan Yang, Seungyoung Park, Ravi Shanker, Hyun-Kon Song, Youngsik Kim, Sang Kyu Kwak and Hyunhyub Ko

Journal of Materials Chemistry A, 2018, 6, 24459-24467 (Website link)

img Cost-effective and environmentally friendly seawater-electrolyte-based batteries exhibit high energy density and demonstrate immense potential for use in future energy storage devices; however, lack of high-performance negative and positive electrodes significantly challenges their practical applications. In this study, N-doped and N,S-doped carbon nanospheres (referred to as NCSs and NSCSs, respectively) are synthesized via the pyrolysis of melanosomes, which is a bio-inspired polymer. Electrocatalytic activity measurements reveal the bifunctionality of the prepared catalysts. NSCSs exhibit a distinctively higher performance than NCSs when used as an air electrode in seawater batteries under ambient conditions (referred to as static mode hereafter). Further, due to the introduction of air flow into the seawater electrolyte (referred to as flow mode hereafter), NSCSs exhibit an improved cell discharge potential. The high performance of the cell is attributed to the high surface area, bifunctional electrocatalytic activity, generation of new active sites, improvement of spin density in NSCSs, and continuous flow of air to the electrolyte. The cell in the flow mode exhibits an overpotential gap of 0.56 V, a round-trip efficiency of 84%, a maximum power density of 203 mW g−1, and an outstanding cycling stability up to 100 cycles. The developed synthetic method provides an effective, scalable approach for doping binary or ternary atoms into the carbon host matrix, which can motivate further experimental and theoretical studies of electrode materials in various energy storage devices. In addition, the concept and results obtained by the introduction of air flow into the electrolyte can lead to the improvement of cell performance in terms of electrical energy efficiency, which can be exploited in various metal–air batteries.

Do Hyeong Kim, Hongkyw Choi , Dae Yeon Hwang, Jaehyun Park, Keun Soo Kim, Seokhoon Ahn, Youngsik Kim, Sang Kyu Kwak, Young-Jun Yu and Seok Ju Kang

J. Mater. Chem. A, 2018, 6, 19672-19680 (Website link)

img Seawater battery, which consists of a Na metal anode and a seawater cathode, has highly attractive features because of eco-friendliness in use of seawater and cost-effectiveness in use of Na, the 6th most abundant element of the Earth’s crust. Here, we demonstrate a reliable Na metal anode for the seawater battery by covering the Cu current collector with graphene monolayer. The surface of chemically uniform graphene-coated current collector facilitates to control the nucleation rate of surfacial Na metal at the initial stage and enhances the Coulombic efficiency in current collector׀separator׀Na metal cells by lowering nucleation and plating potentials. Further deliberate modification of the graphene surface by using O2 plasma and thermal treatments supports the significance of homogeneity of the interface of the current collector. Problematically, heterogeneous Cu surfaces covering with islands of oxide layers significantly altered the surface morphology of plated Na metal and consequently resulted in the drop of the electrochemical performance due to the impeding effect on Na ion diffusion near the current collector surface. By successful implantation of the graphene-coated Cu current collector as an anode into seawater battery, battery performance has been drastically improved, which was confirmed by monitoring the discharge/charge performance and durability of LED lighting.

Yanjun Zhang, Jeongsun Park, Sirugaloor Thangavel Senthilkumar, Youngsik Kim

Journal of Power Source, 2018, 400, 478-484 (Website link)

img A novel rechargeable hybrid Na-seawater flow battery, using natural seawater as an abundant source of active materials, have been developed recently. In this kind of metal-air battery, electrochemical oxygen evolution and reduction are the two key processes taking place during charging and discharging, respectively. In general, powder form of electrocatalysts are attached to the current collectors by using inactive and insulating polymer binders, which inevitably impede the overall performance, and increase the manufacturing costs of the battery. Therefore, a simple way to construct the 3D current collector combined with efficient electrocatalytic activities remains a big challenge. In this work, a 3D macroporous carbon sponge is prepared by the direct carbonization of commercially available polymer “Magic Eraser”. The obtained carbon sponge has interconnected macroporous open 3D scaffold structure and exhibits good flexibility and tailorability. The 3D macroporous carbon sponge shows good bifunctional electrocatalytic activities toward oxygen evolution and reduction reactions in seawater. The fabricated hybrid Na-seawater flow battery using 3D macroporous carbon sponge as cathode current collector displays small charge-discharge voltage gap with high voltage efficiency, excellent rechargeability, and long-term cycling stability.

Ji-Eun Lim, Jeha Kim, Youngsik Kim, Jae-Kwang Kim

Electrochimica Acta, 2018, 282, 270-275 (Website link)

img We have developed a new binder-free hybrid anode material for lithium-ion batteries, by directly coating spinel Li4Ti5O12 particles using in-situ polymerization of styrenesulfonate (SS) to form a core-shell structure. The resulting hybrid anode has significantly improved electrochemical performance, with higher reversible capacity, rate-capability, and capacity value compared with pure Li4Ti5O12. Of the initial discharge capacity of 239.2 mAh g1, 95.6% was retained after 100 cycles at 0.1 C-rate. The high cycle performance with increased discharge capacity is attributed to the coated poly (styrenesulfonate) (PSS) shell, which takes part in lithium ion storage and prevents the growth of a solid electrolyte interface (SEI) layer. The fast electron transfer in PSS also allows high rate-capability. Moreover, we clarify the contribution of carbon conductor in the range of 0.01 Ve1.0 V.

Palanisamy Manikandan, Koshal Kishor, Jinhyup Han, and Youngsik Kim

Journal of Materials Chemistry A, 2018, 6, 11012-11021 (Website link)

img Electrical energy storage on large-scale is very essential to the ultimate use of natural and clean renewable energy sources. Recently, research and development attempts on room-temperature seawater battery (SWB) have been rejuvenated, as SWBs are considered capable, low-cost substitutes to the existing Li-ion battery technology for large-scale uses. In this work, P2-type layered Na0.5Co0.5Mn0.5O2 oxide have been discovered for the first time as a new option of bifunctional cathode electrocatalyst material for aqueous SWB which admits two kinds of voltage profiles such as slope and flat voltage region corresponding to Na+ ion intercalation- deintercalation reaction and OER/ORR catalytic activities in comparison with carbon felt substrate and 20% Pt/C catalyst. Developed electrocatalyst for cathode of SWB demonstrates excellent activity and provides discharge capacity of ~ 30 mAh g–1 ascribed to Na+ ion intercalation - deintercalation reaction and cyclic voltammetric analysis corroborated with the redox peak at 3.31/3.04 V for Co3+/4+ redox species in comparison with carbon felt substrate. Further, OER and ORR catalytic activities of electrocatalyst were confirmed with full-cell seawater battery, exhibited less voltage difference 0.36 V and delivered hard carbon discharge capacity 183 mAh g–1 at 0.1 mA. Consequently, this cathode was demonstrated integrated voltage profile for seawater battery, shows potential to work on commercial scale.

Yanjun Zhang, Sirugaloor Thangavel Senthilkumar, Jeongsun Park, Jehee Park, and Youngsik Kim

Batteries & Supercaps, 2018, 1, 1-6

img The exploitation and utilization of seawater resources has become a significant research topic nowadays. In this communication, we report a rechargeable desalination battery system for the first time. This design can integrate the electrochemical battery, seawater desalination, and acid-alkali production in one system. The basic working principle of the designed system was illustrated, and further proved by the results of experiment. Furthermore, future research directions and outlooks of this system were prospected. This conceptual work provides a promising technology for utilization of natural seawater resources.

Sirugaloor Thangavel Senthilkumar, Hyuntae Bae, Jinhyup Han, and Youngsik Kim

Angewandte Chemie, 2018, 57, 5335-5339 (Website link)

img We describe a new strategy to increase charge storage in a dual electrolyte Na-ion battery (DESIB) by combining the redox chemistry of the electrolyte with a Na+ ion de-insertion/insertion cathode. Conventional electrolytes do not contribute to charge storage in battery systems, but redox-active electrolytes augment this property via charge transfer reactions at the electrode-electrolyte interface. Hence, the capacity of the cathode combined with that provided by the electrolyte redox reaction increases overall charge storage. We employ an aqueous sodium hexacyanoferrate (Na4Fe(CN)6) solution as the redox-active electrolyte (Na-FC) and sodium nickel Prussian blue (Nax-NiBP) as the Na+ ion insertion/de-insertion cathode. The capacity of DESIB with Na-FC electrolyte is twice that of a battery using conventional (Na2SO4) electrolyte. The use of redox-active electrolytes in batteries of any kind is an efficient and scalable approach to develop advanced high-energy-density storage systems.

Yongil Kim, Soo Min Hwang, Hyein Yu and Youngsik Kim

Journal of Materials Chemistry A, 2018, 6, 3046-3054 (Website link)

img A new energy conversion and storage system, named the ‘seawater battery’, has recently been the subject of research in the field of electrochemistry. Using natural seawater as the catholyte in an open-structured cathode, the battery stores sodium (Na) ions from the seawater into the anode side during charging, and then delivers electricity by discharging on demand. Herein, we report on an amorphous red phosphorus/carbon composite anode material which was successfully employed as the anode of a seawater battery. It exhibited a stable cycling performance with a high reversible capacity exceeding 920 mAh g-1composite with a coulombic efficiency of more than 92% over 80 cycles, as well as good rate capabilities. In terms of the full-cell performance of lithium ion and sodium ion batteries, the seawater batteries with the amorphous red phosphorus/carbon composite anode exhibited the highest reversible capacity and energy density. These results indicate that the use of an open-structured cathode system, which provides the anode with an unlimited supply of Na ions, would allow a seawater battery to overcome the limitations associated with the high-capacity alloying reaction-based anodes used in conventional batteries with a closed system.

Yongil Kim, Jae-Kwang Kim, Christoph Vaalma, Geun Hyeong Bae, Guk-Tae Kim, Stefano Passerini and Youngsik Kim

Carbon, 2018, 129, 564-571 (Website link)

img The recently introduced seawater battery concept is an eco-friendly energy storage system that offers appealing electrochemical performance. Its radically innovative design, compared to conventional lithium-ion batteries, makes use of seawater as an almost infinite sodium reservoir for the positive electrode and, thereby, avoids the use of expensive, scarce, and toxic elements like nickel and cobalt. So far, the problems identified mostly originate from the available negative electrode active materials. In this study, a starch-derived hard carbon was used to optimize the system. Due to its improved disordered structure compared with commercial hard carbon, the starch hard carbon exhibits an increased reversible capacity, current-rate capability, and cycling ability. The material, in fact, depicts a high maximum power density of 700 W kg -1­ (based on hard carbon weight) upon discharge at 900 mA g-1, while still being active at 2700 mA g-1. These results represent an important step toward practical application of the sodium-based seawater battery technology.

Junsoo Kim, Donghyeok Shin, Youngjae Jung, Soo Min Hwang, Taeseup Song, Youngsik Kim and Ungyu Paik

Journal of Power Sources, 2018, 377, 87-92 (Website link)

img Liquid metal batteries (LMBs) are attractive energy storage device for large-scale energy storage system (ESS) due to the simple cell configuration and their high rate capability. The high operation temperature caused by high melting temperature of both the molten salt electrolyte and metal electrodes can induce the critical issues related to the maintenance cost and degradation of electrochemical properties resulting from the thermal corrosion of materials. Here, we report a new chemistry of LiCl-LiI electrolyte and Bi-Pb positive electrode to lower the operation temperature of Li-based LMBs and achieve the long-term stability. The cell (Li|LiCl-LiI|Bi-Pb) is operated at 410 ˚C by employing the LiCl-LiI (LiCl:LiI = 36:64 mol %) electrolyte and Bi-Pb alloy (Bi:Pb = 55.5:44.5 mol %) positive electrode. The cell shows excellent capacity retention (86.5 %) and high Coulombic efficiencies over 99.3 % at a high current density of 52 mA cm-2 during 1000th cycles.

Jinhyup Han, Soo Min Hwang, Wooseok Go, S.T. Senthilkumar, Donghoon Jeon, and Youngsik Kim

Journal of Power Sources, 2018, 374, 24-30 (Website link)

img Cell design and optimization of the components, including active materials and passive components, play an important role in constructing robust, high-performance rechargeable batteries. Seawater batteries, which utilize earth-abundant and natural seawater as the active material in an open-structured cathode, require a new platform for building and testing the cells other than typical Li-ion coin-type or pouch-type cells. Herein, we present new findings based on our optimized cell. Engineering the cathode components—improving the wettability of cathode current collector and seawater catholyte flow—improves the battery performance (voltage efficiency). Optimizing the cell component and design is the key to identifying the electrochemical processes and reactions of active materials. Hence, the outcome of this research can provide a systematic study of potentially active materials used in seawater batteries and their effectiveness on the electrochemical performance.