Research

Research Goals and Strategies

As global warming, environmental pollution, and depletion of fossil fuels are emerging as global issues, the significance of energy storage technology is rapidly increasing for efficient energy usage. Expansion of the application of the wireless electrical energy from small electronic devises to energy storage system or electric vehicles moves up the energy ubiquitous era in which the electrical energy can be used anywhere, anytime, without being constrained by time and space. At the same time, one of the recent biggest issues of unusual climate change or global warming accelerates the development of efficient energy storage system for carbon-neutral energy cycles. Those changes in energy and environmental technologies highly requests on the development of sustainable energy storage and conversion devices with high energy density. 

In response to the requests, we are mainly trying to design and discover advanced new energy materials by exploring including non-equilibrium thermodynamic chemical spaces. Based on the novel material synthesis, we systematically study on the material characterization and finally apply the material to the fabrication of electrochemical devices to bridge the fundamental discovery and knowledge to the energy storage and conversion technologies. We are focusing on the defining the key question with "What" and "How" and solving the core issues in energy research fields.

Research Themes

1. Designing and exploring new materials for energy storage and conversion

Reversible storage of lithium ions in electrode materials is the fundamental principle that enables electrical energy storage in lithium ion batteries, and electrode materials are thus at the heart of advanced lithium rechargeable battery technology. Generally, lithium ions are initially contained in a host crystal of positive electrode materials, and upon charge (or discharge), are extracted from (or reinserted into) the host crystal. Intrinsic lithium and a lithium conduction path are therefore regarded as essential characteristics of the positive electrode material. Based on this criteria, LiCoO2, polyanion compounds like LiFePO4, and spinel are developed. Unfortunately, this material group consists of only a tiny fraction of the existing transition metal compounds in nature. This constraint has significantly limited the choice of materials and retarded the development of new positive electrodes in lithium ion batteries. Here, we suggested a new design principle for cathode materials composed of nanocomposite with lithium and transition metal compounds (LiY, Y=anion), that various transition metal compounds (MX, M=metal, X=anion) are now viable positive electrode materials, regardless of their crystal structure, bringing a new material group into lithium ion battery development. In this research theme, we are exploring not only new electrode materials but also new energy storage mechanism determining the electrochemical reaction such as surface conversion (S.-K. Jung et al., Nat. Energy 2017 and S.-K. Jung et al., Adv. Energy Mater. 2019), and host formation reaction (S.-K. Jung et al. Chem. Mater. 2018).

Mechanochemical mixing is also an effective synthetic method in terms of designing and discovering of new solid electrolyte materials for solid-state batteries. It enables to explore non-equilibrium thermodynamic chemical space for searching new materials. In fact, various solid electrolyte materials including sulfide, oxide, halide and dispersed solid electrolytes have been discovered with mechanochemical reaction. Using this approach, we successfully synthesized new type of clay-like solid electrolyte material by formation of Ga containing complex anion group with halide ion (xLiCl-GaF3), that can be a solution for challenging issue of intimate contact with the rigid cathode in solid-state batteries (S.-K. Jung et al., ACS Energy Lett. 2021). Because mechanochemical mixing also can induce chemical variation or formation of space charge layer at the near the surface region that enhance the ionic conductivity of lithium compounds, therefore, new dispersed solid electrolytes with high ionic conductivity and wide electrochemical stability window can be designed. Further, chemical space of new solid electrolyte can be explored.

Selected Publication

Sung-Kyun Jung, Hyunchul Kim, Min Gee Cho, Sung-Pyo Cho, Byungju Lee, Hyungsub Kim, Young-Uk Park, Jihyun Hong, Kyu-Young Park, Gabin Yoon, Won Mo Seong, Yongbeom Cho, Myoung Hwan Oh, Haegyeom Kim, Hyeokjo Gwon, Insang Hwang, Taeghwan Hyeon, Won-Sub Yoon*, and Kisuk Kang*, "Lithium-free transition metal monoxides for positive electrodes in lithium-ion batteries" Nature Energy 2, 1-9 (2017) 

Sung‐Kyun Jung†, Insang Hwang†, Il Rok Choi†, Gabin Yoon, Joo Ha Park, Kyu‐Young Park, and Kisuk Kang*, "Chemical Origins of Electrochemical Overpotential in Surface‐Conversion Nanocomposite Cathodes" Advanced Energy Materials 9, 1900503 (2019)

Sung-Kyun Jung, Insang Hwang, Sung-Pyo Cho, Kyungbae Oh, Kyojin Ku, Il Rok Choi, and Kisuk Kang*, "New iron-based intercalation host for lithium-ion batteries" Chemistry of Materials 30, 1956-1964 (2018)

Sung-Kyun Jung†,*, Hyeokjo Gwon†,*, Gabin Yoon, Lincoln J. Miara, Valentina Lacivita, and Ju-Sik Kim, "Pliable Lithium Superionic Conductor for All-Solid-State Batteries" ACS Energy Letters 6, 2006-2015 (2021)

2. Advanced X-ray characterization for probing interfacial phenomena

Fundamental understanding on reaction mechanism and physical or chemical change is being studied with advanced X-ray characterization technique. Full-field transmission X-ray microscopy (TXM) is analyzing tool measuring the electronic state using hard X-ray with hundreds nanometer scale spatial resolution. Likewise, scanning transmission X-ray microscopy (STXM) and ptychography is also electronic state measuring tool using soft X-ray with a few nanometer scale spatial resolution. STXM and ptychography is powerful tool to investigate light element with high resolution compared to TXM. Using those techniques, we are studying the fundamental understanding on interfacial phenomena in all-solid-state batteries and reaction mechanism in nanocomposite cathode materials.

Selected Publication

Sung-Kyun Jung†,*, Hyungsub Kim†, Seok Hyun Song, Seongsu Lee, Jongsoon Kim and Kisuk Kang*, "Unveiling the role of transition-metal ion in the thermal degradation of layered Ni–Co–Mn cathodes for lithium rechargeable batteries", Advanced Functional Materials 32, 2108790 (2022)

Sangpyo Lee†, Youngkyung Kim†, Chanhyun Park, Jihye Kim, Jae-Seung Kim, Hyoi Jo, Chang Ju Lee, Sinho Choi, Dong-Hwa Seo and Sung-Kyun Jung*, "Interplay of cathode–halide solid electrolyte in enhancing thermal stability of charged cathode material in all-solid-state batteries", ACS Energy Letters 9, 1369 (2024)

3. Fabrication and Characterization of Solid-State Battery

The key challenge in all-solid-state batteries (ASSBs) is establishing and maintaining perfect physical contact between rigid components for facile interfacial charge transfer, especially between the solid electrolyte and anode/cathode. Anode-solid electrolyte interface, represented by a metal–ceramic interface, maintains intimate contact relatively easily, regardless of the type of electrolyte, owing to the ductile nature of lithium metal. Meanwhile, because cathodes have a random porous structure, forming a well-defined cathode–electrolyte interface fully covered by a solid electrolyte is difficult, which can result in inhomogeneous electronic and ionic conduction in the cathode. Further, this interface is a rigid ceramic–ceramic contact, making it more challenging to establish and maintain intimate contact. In addition to physical interfacial issue, chemical reaction between cathode and solid electrolyte is complexly intertwined in interfacial phenomena (S.-K. Jung et al., J. Mater. Chem. A 2019). Although chemical reaction could be accelerated at high voltage and degradation product could be altered, the systematic investigation of interfacial chemical degradation as state of charge is currently overlooked.

Current solid electrolyte systems that are considered promising candidates in terms of lithium ion conductivity (e.g., garnet or argyrodite) require additional engineering for intimate cathode–electrolyte contact, such as co-sintering, maintaining external pressure, or adding an ionic liquid. However, co-sintering can cause thermal decomposition or chemical diffusion, and incorporating a device to apply pressure can occupy considerable space, thus decreasing the volumetric energy density. In particular, because these materials are in the class of inorganic solids, their deformability is limited, which makes it challenging to maintain close contact at the solid–solid interface. Meanwhile, solid polymer electrolytes satisfy the requirements of deformability, but their low ionic conductivity and safety concern regarding thermal vulnerability remain critical issues.

In this research theme, we have interest in fabrication of ASSBs for maintaining intimate contact between solid electrolyte and electrode in both physical and chemical perspective depending on the types of solid electrolytes (S.-K. Jung et al., ACS Energy Lett. 2021). In addition, we are investigating complex interfaical phenomena in ASSBs using combined analysis with electrochemical impedance spectroscopy modeling and advanced characterization.

Selected Publication

Sung-Kyun Jung†, Hyeokjo Gwon†, Seok-Soo Lee, Hyunseok Kim, Jae Cheol Lee, Jae Gwan Chung, Seong Yong Park, Yuichi Aihara, and Dongmin Im*, "Understanding the effects of chemical reactions at the cathode–electrolyte interface in sulfide based all-solid-state batteries" Journal of Materials Chemistry A 7, 22967-22976 (2019)

Sung-Kyun Jung†,*, Hyeokjo Gwon†,*, Gabin Yoon, Lincoln J. Miara, Valentina Lacivita, and Ju-Sik Kim, "Pliable Lithium Superionic Conductor for All-Solid-State Batteries" ACS Energy Letters 6, 2006-2015 (2021)

Sung-Kyun Jung†,*, Hyeokjo Gwon†,*, Hyungsub Kim, Gabin Yoon, Dongki Shin, Jihyun Hong, Changhoon Jung, and Ju-Sik Kim, "Unlocking the hidden chemical space in cubic-phase garnet solid electrolyte for efficient quasi-all-solid-state lithium batteries" Nature Communications 13, 7638 (2022)

Chanhyun Park, Juho Lee, Sangpyo Lee, Yu Jin Han, Jinsoo Kim*, and Sung-Kyun Jung*, "Organic-additive-derived cathode electrolyte interphase layer mitigating intertwined chemical and mechanical degradation for sulfide-based solid-state batteries" Advanced Energy Materials 13, 2203861 (2023)

4. New system of energy storage and conversion: Fluoride ion battery

Fluoride-ion batteries (FIBs), firstly proposed in 2011, are energy storage system using the charge carrier ion as fluoride anion. It is potential candidate for next generation solid-state battery thanks to the large volumetric energy density up to theoretically three or four times higher than lithium ion batteries. High volumetric energy is expected by multi-redox reaction from reversible conversion reaction of metal fluoride (Cathode: MFx + xe- -> M + xF- / Anode: M’ + yF- -> MFy + ye-). Currently, FIB is operated using La1-xBaxF3-x solid electrolyte at 170 ~ 180 °C due to the low ionic conductivity at room temperature compared to lithium conducting solid electrolytes. In addition, large volumetric change due to the conversion reaction is critical issues on poor cycle life performance, which is analogous to one of the reason for cycle degradation of current Li-ion based all-solid-state batteries. Therefore, not only the material discovery for solid electrolyte and electrode but also fundamental study on interfacial phenomena at high temperature have to be preceded. In this research theme, we have interest in designing not only electrode materials but also solid electrolytes for fluoride ion storage and conduction. Designing the electrode materials that can reversibly intercalate and deintercalate fluoride ion could be beneficial for cycle life performance due to the decrease of volume changes compared to conversion reaction. Furthermore, as confirmed in nanocomposite cathode, nanoparticles of MnO can adsorb the fluorine ion on the surface, which means that it can be applied to FIBs system.