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Kim, Dong-Min

Publications and source records attributed to Kim, Dong-Min.

7 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Aqueous solution-based synthesis approach for carbon-disordered rocksalt composite cathode development and its limitations

Disordered rocksalt cathodes exhibit high specific capacities and high energy density; however, their low electronic conductivity poses a great challenge. Herein, we explored an aqueous-solution-based synthesis route that involves controlling the surface charges of Li 1.2 Mn 0.6 Ti 0.2 O 1.8 F 0.2 (LMTOF) to be anchored by a few-layer reduced graphene oxide (rGO) for the first time. The uniform rGO wrapping on the surface of the LMTOF particles is achieved by electrostatic attraction between the negatively charged rGO and positively charged LMTOF particles. Although the initial specific capacity of rGO-LMTOF composite increased by 58 % compared to the pristine LMTOF, the composite experienced a severe capacity fade over cycling. The synthesis process in an aqueous medium resulted in Li + /H + exchange and TM dissolution as evidenced from inductively coupled plasmon analysis and X-ray diffraction analysis. Therefore, this work suggests the search for alternative media or conditions for the synthesis of carbon-disordered rock salt cathode composite.

25 ENERGY STORAGE↗
DOE OSTI2024

Inverse Consequences of the SnO 2 Protection Layers on Pt/C Catalysts in Proton-Exchange Membrane Fuel Cells

Proton-exchange membrane fuel cells (PEMFCs) are promising energy-conversion systems, offering an appealing blend of high energy efficiency and low environmental impact. However, carbon corrosion of PEMFCs is known to significantly degrade their performance, remaining a critical challenge to overcome. In this study, we applied a Nb-doped SnO 2 (Nb-SnO 2 ) nanoparticle coating on Pt/C catalysts as a protective layer, with the Sn/C ratio in the precursors varying from 0.25:1 to 2.0:1. Contradictory behaviors of the coated Pt/C catalysts were observed at different Sn/C ratios. The Sn/C = 1.0 sample exhibited improved electrochemically active surface area retention after 500 cycles of accelerated stress testing (AST) but with more significant polarization and resistance increase observed in the polarization curves. In addition, agglomeration of Nb-SnO 2 particles was observed at a higher Sn/C ratio in the AST of a membrane electrode assembly, with less shrinkage of the total thickness of the Nb-SnO 2 -coated Pt/C electrode. We speculate that formation of Nb-SnO 2 agglomerates occurs once the protective layer is broken down or the unprotected carbon surface is corroded and that these Nb-SnO 2 agglomerates increase the tortuosity of the electron pathways and significantly increase the cell polarization.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2024

Quantifying the regime of thermodynamic control for solid-state reactions during ternary metal oxide synthesis

The success of solid-state synthesis often hinges on the first intermediate phase that forms, which determines the remaining driving force to produce the desired target material. Recent work suggests that when reaction energies are large, thermodynamics primarily dictates the initial product formed, regardless of reactant stoichiometry. Here, we validate this principle and quantify its constraints by performing in situ characterization on 37 pairs of reactants. These experiments reveal a threshold for thermodynamic control in solid-state reactions, whereby initial product formation can be predicted when its driving force exceeds that of all other competing phases by ≥60 milli–electron volt per atom. In contrast, when multiple phases have a comparable driving force to form, the initial product is more often determined by kinetic factors. Analysis of the Materials Project data shows that 15% of possible reactions fall within the regime of thermodynamic control, highlighting the opportunity to predict synthesis pathways from first principles.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Topological Considerations in Electrolyte Additives for Passivating Silicon Anodes with Hybrid Solid–Electrolyte Interphases

Unlike most anodes used in high energy density batteries, lithiated Si does not form long-lasting passivating solid-electrolyte interphases (SEI) during formation or on charge due to SEI delamination, reconstruction, or dissolution. As a result, electrolyte degradation is continuous and results in a permanent loss of the Li inventory, shortening the useful life of the battery. Here, in this study, we show that perfluoroether electrolyte additives featuring either sulfonyl fluorides or trifluorovinyl ethers, when introduced in prescribed amounts to locally superconcentrated electrolytes, exhibit preferential reactivity at Si during formation due to their higher reduction potential than salts and solvents, creating a hybrid SEI that is simultaneously enriched with LiF and organics tethered to the reactive functionality. While both reactive motifs are effective in creating a hybrid SEI, perfluoroether additives bearing sulfonyl fluorides show more substantial integration. More important, however, is the combined influence of additive topology on anchoring efficacy and tether flexibility between anchoring sites on SEI resiliency. Top-performing Si|LFP cells featuring ditopic additive-enriched SEI improve capacity retention by as much as 45% over 100 cycles when compared to additive-free cells.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1990

Satellite stabilization using space leeches

A control algorithm for satellite stabilization using a space leech is presented. The space leech is assumed to have n reaction wheels with known moments of inertia about their axis of rotation. All mass properties of the satellite are assumed to be unknown. The algorithm brings the satellite to a specified attitude trajectory. Simulations were performed to demonstrate the controller. The model parameters and specific algorithm used and the results obtained are presented.

Walker, Michael W.↗