Solid-state ion dynamics refers to the motion of ions in solids, encompassing vibrational, reorientational, and translational motions (three degrees of freedom). Although typical solids exhibit only vibrational motion due to ions being constrained by three-dimensional bonding networks, chain-structured materials such as polymers allow reorientational motion above their glass transition temperatures. When ions diffuse rapidly in ionic solids, they are considered to exhibit translational motion, as observed in superionic conductors. In particular, vibrational motion can be described in terms of quasiparticles known as phonons. 

Ion dynamics in solids (or lattice dynamics) are closely related to charge transport properties. In inorganic semiconductors, lattice dynamics generally hinder electron transport through scattering, whereas in organic semiconductors, interactions between electrons and phonons lead to the formation of polarons as charge carriers. Ion dynamics are also associated with polarizability, which significantly affects exciton lifetimes—a property effectively utilized in metal halide perovskite semiconductors for applications such as solar cells and light-emitting diodes.  Furthermore, phonons play a crucial role in heat transport, as extensively studied in thermoelectric materials. 

Solid-state ion conductors (or solid-state electrolytes) with rapid ion diffusion are key enablers for future electronic and energy devices, such as solid-state battery systems, fuel cells, ion–electron mixed conductors for bioelectronics, and various healthcare sensor systems.In particular, as the importance of solid-state electrolytes becomes more pronounced in the field of solid-state batteries, understanding the fundamental mechanisms governing ion diffusion has become increasingly crucial. However, fast ion diffusion in solids (or superionic conductivity) remains poorly understood compared to electron transport. Unlike electrons, which can be treated as quasiparticles whose effective mass and energy band structures can be theoretically calculated using quantum mechanics, diffusing ions in solids cannot be regarded as quasiparticles because their hopping motion follows the principles of classical physics. Materials scientists believe that uncovering the principles governing ion diffusion in solids will lead to the development of high-performance superionic conductors. 

Additionally, ion dynamics are correlated with the mechanical properties of solids. The propagation or localization of lattice vibrations influences the mechanical brittleness and toughness of solids, while reorientational motions of solid frameworks generate mechanical softness and plasticity. Such reorientational motions can occur when solids are composed of isolated structural units, such as molecules or polymers, and the timescale of these dynamics is associated with the viscosity of the solids. 

It is clear that understanding solid-state ion dynamics is crucial for designing the electrical and mechanical properties of solids. For a deeper understanding of these dynamics, contemporary research aims to elucidate the relationships among different types of motion. Vibration is the fundamental motion in solids, initially activated as harmonic oscillations; as the temperature increases from 0 K, these vibrations become anharmonic. Anharmonic vibrations are believed to promote the diffusional motion of ions, while reorientational motions of the framework may enhance the translational motion of ions, although this relationship remains under debate. 

*Three motions of ion in solids :  vibration (harmonic + anharmonic oscillations), reorientation, translation 

*Diffusional motion :  reorientational + translational motions

Updated at Nov. 2025. Please contact I.Y. for any comments or discussions. 

A newly designed ionic solids requires an appropriate synthesis protocol. Although the theoretical thermodynamic stability of a proposed material can be calculated using DFT (e.g. energy above hull), this does not guarantee whether the material can be synthesized. The synthesis processes and conditions vary depending on the types of elements and structures involved, while both thermodynamic and kinetic factors must be considered simultaneously.

As the structures of new materials become more sophisticated, synthesis conditions must be controlled with greater precision due to their metastable nature. Over the past decades, many thermodynamically stable materials—mostly crystalline—have been predicted through theoretical calculations and successfully synthesized using straightforward methods. However, many emerging materials exhibit metastability. In the coming era, the theoretical design of new materials will be accelerated by artificial intelligence (AI), which is expected to propose unconventional or previously unthinkable structures. Therefore, a fundamental understanding of synthetic chemistry will become even more essential than before for designing synthesis processes for non-traditional materials. The conventional boundaries that categorize materials are expected to blur, leading to the convergence and continuous evolution of diverse synthesis methodologies 

Updated at Nov. 2025

Li-ion secondary battery systems provide physical flexibility, enabling the use of electronic devices anytime and anywhere. With the rapid growth of the electric vehicle (EV) market—largely driven by Tesla—the global battery market has expanded enormously over the past decade. Large-scale and efficient battery production has also facilitated the development of energy storage systems (ESS), which are essential for utilizing renewable energy. Since renewable energy systems can generate power only when the sun shines or the wind blows, ESS must be implemented to replace fossil fuel or nuclear power plants. The growing necessity of ESS has further increased market demand, establishing batteries as one of the core technologies supporting South Korea’s industrial development. 

A solid-state battery system uses solid electrolytes instead of the liquid electrolytes and the most significant advantage of solid electrolytes over liquid ones is their non-flammability. Current large-scale battery systems limit their charge rate due to the risk of short circuits and require additional safety mechanisms to mitigate fire hazards once ignition occurs. By eliminating flammable liquid components, solid-state batteries inherently improve operational safety and thermal stability. Furthermore, the use of solid electrolytes allows for the integration of high-capacity metallic anodes, such as lithium or sodium metal, which can significantly enhance the energy density of the system. This structural robustness also enables the design of compact, lightweight cells suitable for next-generation electric vehicles and portable electronics. As a result, solid-state batteries are expected to play a pivotal role in advancing safe and high-performance energy storage technologies.

Global battery companies are currently focused on developing oxide- and sulfide-based materials for demonstrating solid-state electrolytes; however, it remains unclear which class of materials will ultimately win the game. Among the various candidates—such as halides, nitrides, perovskites, and polymers—oxides and sulfides have been prioritized because they must simultaneously satisfy multiple requirements, including high ionic conductivity, suppression of lithium dendrite formation, compatibility with electrodes, good processability, and low operating pressure. Although several companies have begun producing prototype solid-state battery packs, solid-state batteries are unlikely to replace liquid-based systems in the near term due to the high cost of solid electrolytes and the complexity of their fabrication process. 

We are currently focused on developing low-cost and high-performance solid-state electrolytes for next-generation solid-state battery systems. To achieve this goal, our study begins with designing solid-state electrolytes (or superionic conductors) through structural manipulation using earth-abundant elements. This approach requires a comprehensive understanding of structure–property relationships, including electrochemical stability, ionic and electronic conductivity, as well as mechanical properties such as modulus and plasticity.

Updated at Nov. 2025