Stephen Dongmin Kang

All Publications

• Galvanostatic Intermittent Titration Technique Reinvented: Part II. Experiments JOURNAL OF THE ELECTROCHEMICAL SOCIETY Kang, S., Kuo, J., Kapate, N., Hong, J., Park, J., Chueh, W. C. 2021; 168 (12)

  View details for DOI 10.1149/1945-7111/ac3939

  View details for Web of Science ID 000727012800001

• Galvanostatic Intermittent Titration Technique Reinvented: Part I. A Critical Review JOURNAL OF THE ELECTROCHEMICAL SOCIETY Kang, S., Chueh, W. C. 2021; 168 (12)

  View details for DOI 10.1149/1945-7111/ac3940

  View details for Web of Science ID 000727014000001

• Electro-chemo-mechanical charge carrier equilibrium at interfaces. Physical chemistry chemical physics : PCCP Chen, C., Yin, Y., Kang, S. D., Cai, W., Chueh, W. C. 2021

  Abstract

  Electrochemical interfaces involving solids enable charge transfer, electrical transport, and mass storage in energy devices. One central concept that determines the interfacial charge carrier concentration is the space-charge field. The classical theory accounts for electrochemical equilibrium in the absence of mechanical effects; such effects have recently been found critical in many solids, such as materials for lithium-ion and solid-state batteries, perovskite solar cells, and fuel cells. Towards elucidating the interplay between charge carriers and mechanics, we establish a generalized electro-chemo-mechanical space-charge model and categorize the carriers into physically-meaningful four types, based on the signs of the charge number (i.e., polarity) and the partial molar volume (i.e., expansion coefficient). Beyond the electrostatic effects discussed in the literature, our work reveals the importance of elastic effects, as demonstrated by simulations of a composite beam bending experiment. The analysis highlights opportunities to systematically tune the interfacial electrical conductivity and the reaction kinetics of solids through mechanics. Our treatment provides a rational basis for understanding stress-driven phenomena at interfaces in a wide range of solids.

  View details for DOI 10.1039/d1cp02690a

  View details for PubMedID 34643199

• Fictitious phase separation in Li layered oxides driven by electro-autocatalysis. Nature materials Park, J., Zhao, H., Kang, S. D., Lim, K., Chen, C., Yu, Y., Braatz, R. D., Shapiro, D. A., Hong, J., Toney, M. F., Bazant, M. Z., Chueh, W. C. 2021

  Abstract

  Layered oxides widely used as lithium-ion battery electrodes are designed to be cycled under conditions that avoid phase transitions. Although the desired single-phase composition ranges are well established near equilibrium, operando diffraction studies on many-particle porous electrodes have suggested phase separation during delithiation. Notably, the separation is not always observed, and never during lithiation. These anomalies have been attributed to irreversible processes during the first delithiation or reversible concentration-dependent diffusion. However, these explanations are not consistent with all experimental observations such as rate and path dependencies and particle-by-particle lithium concentration changes. Here, we show that the apparent phase separation is a dynamical artefact occurring in a many-particle system driven by autocatalytic electrochemical reactions, that is, an interfacial exchange current that increases with the extent of delithiation. We experimentally validate this population-dynamics model using the single-phase material Lix(Ni1/3Mn1/3Co1/3)O2 (0.5

  View details for DOI 10.1038/s41563-021-00936-1

  View details for PubMedID 33686277

• Effect of two-dimensional crystal orbitals on Fermi surfaces and electron transport in three-dimensional perovskite oxides. Angewandte Chemie (International ed. in English) Dylla, M., Kang, S., Snyder, G. J. 2018

  Abstract

  Perovskite oxides are candidate materials in catalysis, fuel cells, thermoelectrics, and electronics, where electronic transport is vital to their use. While the fundamental transport properties of these materials have been heavily studied, there are still key features that are not well understood, including the temperature-squared behavior of their resistivities. Standard transport models fail to account for this atypical property because Fermi surfaces of many perovskite oxides are low-dimensional and distinct from traditional semiconductors. In this work, the low-dimensional Fermi surfaces of perovskite oxides are chemically interpreted in terms of two-dimensional crystal orbitals that form the conduction bands. Using SrTiO 3 as a case study, the d/p-hybridization that creates these low-dimensional electronic structures is reviewed and connected to its fundamentally different electronic properties. A low-dimensional band model explains several experimental transport properties, including the temperature and carrier-density dependence of the effective mass, the carrier-density dependence of scattering, and the temperature dependence of resistivity. This work highlights how chemical bonding influences semiconductor transport.

  View details for PubMedID 30589168

• Compliant and stretchable thermoelectric coils for energy harvesting in miniature flexible devices SCIENCE ADVANCES Nan, K., Kang, S., Li, K., Yu, K., Zhu, F., Wang, J., Dunn, A. C., Zhou, C., Xie, Z., Agne, M. T., Wang, H., Luan, H., Zhang, Y., Huang, Y., Snyder, G., Rogers, J. A. 2018; 4 (11): eaau5849

  Abstract

  With accelerating trends in miniaturization of semiconductor devices, techniques for energy harvesting become increasingly important, especially in wearable technologies and sensors for the internet of things. Although thermoelectric systems have many attractive attributes in this context, maintaining large temperature differences across the device terminals and achieving low-thermal impedance interfaces to the surrounding environment become increasingly difficult to achieve as the characteristic dimensions decrease. Here, we propose and demonstrate an architectural solution to this problem, where thin-film active materials integrate into compliant, open three-dimensional (3D) forms. This approach not only enables efficient thermal impedance matching but also multiplies the heat flow through the harvester, thereby increasing the efficiencies for power conversion. Interconnected arrays of 3D thermoelectric coils built using microscale ribbons of monocrystalline silicon as the active material demonstrate these concepts. Quantitative measurements and simulations establish the basic operating principles and the key design features. The results suggest a scalable strategy for deploying hard thermoelectric thin-film materials in harvesters that can integrate effectively with soft materials systems, including those of the human body.

  View details for DOI 10.1126/sciadv.aau5849

  View details for Web of Science ID 000452212000059

  View details for PubMedID 30406207

  View details for PubMedCentralID PMC6214638