김형섭 교수

Grid‐scale energy storage systems (ESSs) that can connect to sustainable energy resources have received great attention in an effort to satisfy ever‐growing energy demands. Although recent advances in Li‐ion battery (LIB) technology have increased the energy density to a level applicable to grid‐scale ESSs, the high cost of Li and transition metals have led to a search for lower‐cost battery system alternatives. Based on the abundance and accessibility of Na and its similar electrochemistry to t

New iron-based mixed-polyanion compounds Li(x)Na(4-x)Fe(3)(PO(4))(2)(P(2)O(7)) (x = 0-3) were synthesized, and their crystal structures were determined. The new compounds contained three-dimensional (3D)sodium/lithium paths supported by P(2)O(7) pillars in the crystal. First principles calculations identified the complex 3D paths with their activation barriers and revealed them as fast ionic conductors. The reversible electrode operation was found in both Li and Na cells with capacities of one-e

Compounds with a mixed polyanion framework have recently gained attention as a new class of compounds for material exploration. The potential tunability of the structure by using various combinations of polyanions can potentially lead to a novel cathode. However, the redox reaction in complex structures often involves complex structural evolutions during the electrochemical reaction, which require careful analysis. We investigated the electrochemical mechanism of Na x Fe 3 (PO 4 ) 2 (P 2 O 7 ) (

We report a 3.8 V manganese-based mixed-phosphate cathode material for applications in sodium rechargeable batteries; i.e. , Na 4 Mn 3 (PO 4 ) 2 (P 2 O 7 ).

Abstract Layered lithium–nickel–cobalt–manganese oxide (NCM) materials have emerged as promising alternative cathode materials owing to their high energy density and electrochemical stability. Although high reversible capacity has been achieved for Ni‐rich NCM materials when charged beyond 4.2 V versus Li + /Li, full lithium utilization is hindered by the pronounced structural degradation and electrolyte decomposition. Herein, the unexpected realization of sustained working voltage as well as im

Structural characterization of Li 2– x MP 2 O 7 (M = Fe, Co) was carried out using neutron diffraction (ND) and X-ray diffraction (XRD) analyses to elucidate structural information and structural changes during an electrochemical reaction. The crystal system and space group were determined to be monoclinic P 2 1 / c for both materials with a = 11.0192 (4) Å, b = 9.7488 (3) Å, c = 9.8057 (4) Å, and β = 101.569 (3)° for Li 2– x FeP 2 O 7 and a = 10.9574 (3), b = 9.6921 (3), c = 9.7611 (3), and β =

The development of long-lasting and low-cost rechargeable batteries lies at the heart of the success of large-scale energy storage systems for various applications. Here, we introduce Fe- and Mn-based Na rechargeable battery cathodes that can stably cycle more than 3000 times. The new cathode is based on the solid-solution phases of Na 4 Mn x Fe 3– x (PO 4 ) 2 (P 2 O 7 ) ( x = 1 or 2) that we successfully synthesized for the first time. Electrochemical analysis and ex situ structural investigati

In this study, a one-step process to fabricate "Janus"-structured nanocomposites with iron oxide (Fe₃O₄) nanoparticles (Fe₃O₄ NPs) and polydopamine (PDA) on each side of a graphene oxide (GO) nanosheet using the Langmuir-Schaefer technique has been proposed. The Fe₃O₄ NPs-GO hybrid is used as a high-capacity active material, while PDA is added as a binder due to its unique wet-resistant adhesive property. The transmission electron

With continuous dimensional scaling of high-performance transistors, high-k dielectrics are emerging as a very important research area in Si-based FET (field effect transistor) devices. Additionally, due to the uniquely high film quality, easy thickness controllability down to the nm range, and near perfect conformality, the ALD (atomic layer deposition) technique is also emerging as a future deposition technique for various applications. By combining these two promising areas, it is quite possi

Abstract Li‐rich layered oxide materials are considered promising candidates for high‐capacity cathodes for battery applications and improving the reversibility of the anionic redox reaction is the key to exploiting the full capacity of these materials. However, permanent structural change of the electrode occurring upon electrochemical cycling results in capacity and voltage decay. In view of these factors, Ti 4+ ‐substituted Li 2 IrO 3 (Li 2 Ir 0.75 Ti 0.25 O 3 ) is synthesized, which undergoe