Journal Publication


Yongil Kim, Guk-Tae Kim, Sangsik Jeong, Xinwei Dou, Chenxi Geng, Youngsik Kim, and Stefano Passerini

Energy Storage Materials, 2018, accepted

img A new electrolyte (anolyte) for the negative electrode of seawater batteries, based on the combination of two ionic liquids (ILs), a sodium salt, and a SEI-forming additive, is herein reported. The quaternary anolyte is composed of N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide (0.6 mol fraction), N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl) imide) (0.3 mol fraction), and sodium bis(fluorosulfonyl)imide (0.1 mol fraction). Ethylene carbonate (5 wt% with respect to the ILs and salt mixture) is added to promote SEI formation. The thermal, physicochemical, and electrochemical characterization of the quaternary electrolyte indicate its suitability as an anolyte, as well as the formation of a highly stable interface with the negative (hard carbon) electrode. Lab-scale seawater full cells employing a hard carbon anode and the ionic liquid-based quaternary anolyte show remarkable results in terms of capacity, cyclability, and rate capability at room temperature. Additionally, these cells showed better energy efficiency (voltage efficiency) and cyclability than those based on a conventional organic carbonate-based anolyte.

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

Batteries & Supercaps, 2018, accepted

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, accepted

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.