Duho Kim

In an effort to develop high-energy-density cathodes for sodium-ion batteries (SIBs), low-cost, high capacity Na(Li_1/3 Mn_2/3 )O₂ is discovered, which utilizes the labile O 2p-electron for charge compensation during the intercalation process, inspired by Li₂ MnO₃ redox reactions. Na(Li_1/3 Mn_2/3 )O₂ is systematically designed by first-principles calculations considering the Li/Na mixing enthalpy based on the si

Neuromorphic computing has garnered significant attention because it can overcome the limitations of the current von-Neumann computing system. Analog synaptic devices are essential for realizing hardware-based artificial neuromorphic devices; however, only a few systematic studies in terms of both synaptic materials and device structures have been conducted so far, and thus, further research is required in this direction. In this study, we demonstrate the synaptic characteristics of a ferroelect

Through first-principles calculations and experimental observations, we first present the correlation between the Ni and Mn ratio and the redox behaviors of the layered NCM cathodes. The equilibrium potentials based on redox reactions of Ni2+/Ni3+ are highly dependent on the Mn ratio (NCM523 and NCM721: ∼3.7 and 3.5 V) because of a donor electron, in the eg band, transferred from Mn to Ni owing to their crystal field splitting (CFS) with different electronegativities, leading to oxidation states

Enhanced polysulfide conversion kinetics is essential for realizing lithium–sulfur batteries with high energy density and rate performance and promising cyclability. The modification of the local atomic structure of MNx active sites in single-atom M–N–C catalysts was proposed to improve their electrocatalytic activity for demanding reactions by fine-tuning the interaction with reaction intermediates. Here, we demonstrate that engineering the binding geometry of lithium polysulfides (LiPSs) by in

Oxygen 2p-electron, unhybridized with transition metals (TMs), is a critical species for the generation of an anion-based redox reaction of O2–/O– for high-energy-density cathodes in lithium-ion and sodium-ion batteries (LIBs and SIBs, respectively). More importantly, oxygen redox activity has been highlighted as a breakthrough to increase the intrinsic low redox potential for SIBs because its reaction theoretically and experimentally occurs at ≈4.2 V versus Na+/Na. Here, we present in detail th

Abstract The demands for higher energy density of rechargeable batteries have been continuously increasing recently, and cationic redox based current cathodes have little scope to further increase energy density since they already exhibit near‐theoretical specific capacities. In this regard, oxygen redox (OR) reactions have emerged as a promising breakthrough for sodium‐ion battery (SIB) cathodes. Most OR‐based layered oxides suffer from drastic hysteretic‐oxygen capacities upon discharging afte

Abstract Intercalation‐based cathodes typically rely on the cationic redox activity of transition metals to deliver capacity, but, recently, anionic redox chemistry has emerged as a way to increase the energy density of rechargeable batteries. However, the irreversible structural disorder and voltage fading accompanying oxygen release are major problems preventing commercial use. To overcome these limitations, the connection between structural stability and anionic redox activity must be underst

Critical degradation mechanism of many cathode materials for Li-ion batteries is closely related to phase transformations at the surface/interface. Li2MnO3 in x Li2MnO3 ⋅(1-x) LiMO2 (M=Ni, Co, Mn) provides high capacity, but the Li2MnO3 phase is known to degrade during cycling through phase transformation and O2 evolution. To resolve such degradation problems, it is critical to develop a fundamental understanding of the underlying mechanism. Using first-principles calculations, we identified the

Abstract An intriguing mechanism for enabling fast Na kinetics during oxygen redox (OR) is proposed to produce high‐power‐density cathodes for sodium‐ion batteries (SIBs) based on the P2‐type oxide models, Na 2/3 [Mn 6/9 Ni 3/9 ]O 2 (NMNO) and Na 2/3 [Ti 1/9 Mn 5/9 Ni 3/9 ]O 2 (NTMNO) using the “potential pillar” effect. The critical structural parameter of NTMNO lowers the Na migration barrier in the desodiated state because the electrostatic repulsion of O(2 p )O(2 p ) that occurs between tra

Abstract This study suggests a critical factor that regulates (in)homogeneous growth based on an in‐depth understanding of three alkali metal ((AM): Li, Na, and K) models using unified‐multiscale atomistic calculations. The importance of AM disordered phases as a transition state is covered with a thermodynamic energy dataset using density functional theory (DFT) calculations, which indicates that the disordered‐phase energy level (DPEL) plays a decisive role in controlling the degree of non‐hom

A combined study involving experiments and multiscale computational approaches is conducted to propose a theoretical solution for the suppression of the Jahn-Teller distortion which causes severe cyclic degradation. As-synthesized pristine and Al-doped Mn spinel compounds are the focus to understand the mechanism of the cyclic degradation in terms of the Jahn-Teller distortion, and the electrochemical performance of the Al-doped sample shows enhanced cyclic performance compared with that of the