Min Sik Park

A Highly Reversible Lithium Metal Anode

Lithium metal has shown a lot of promise for use as an anode material in rechargeable batteries owing to its high theoretical capacity. However, it does not meet the cycle life and safety requirements of rechargeable batteries owing to electrolyte decomposition and dendrite formation on the surfaces of the lithium anodes during electrochemical cycling. Here, we propose a novel electrolyte system that is relatively stable against lithium metal and mitigates dendritic growth. Systematic design methods that combined simulations, model-based experiments, and in situ analyses were employed to design the system. The reduction potential of the solvent, the size of the salt anions, and the viscosity of the electrolyte were found to be critical parameters determining the rate of dendritic growth. A lithium metal anode in contact with the designed electrolyte exhibited remarkable cyclability (more than 100 cycles) at a high areal capacity of 12u2005mAh cm−2.

Effective passivation of a high-voltage positive electrode by 5-hydroxy-1H-indazole additives

5-Hydroxy-1H-indazole (HI) is investigated as an effective film-forming additive for an over-lithiated layered oxide (OLO) positive electrode. The protective film that is generated by oxidative decomposition of the additive (HI) prior to the carbonate electrolyte is thin and less resistive. As a result, a full cell comprised of OLO/graphite in the HI-added electrolyte gives a better cycling performance.

A search map for organic additives and solvents applicable in high-voltage rechargeable batteries

Chemical databases store information such as molecular formulas, chemical structures, and the physical and chemical properties of compounds. Although the massive databases of organic compounds exist, the search of target materials is constrained by a lack of physical and chemical properties necessary for specific applications. With increasing interest in the development of energy storage systems such as high-voltage rechargeable batteries, it is critical to find new electrolytes efficiently. Here we build a search map to screen organic additives and solvents with novel core and functional groups, and thus establish a database of electrolytes to identify the most promising electrolyte for high-voltage rechargeable batteries. This search map is generated from MAssive Molecular Map BUilder (MAMMBU) by combining a high-throughput quantum chemical simulation with an artificial neural network algorithm. MAMMBU is designed for predicting the oxidation and reduction potentials of organic compounds existing in the massive organic compound database, PubChem. We develop a search map composed of ∼1u2009000u2009000 redox potentials and elucidate the quantitative relationship between the redox potentials and functional groups. Finally, we screen a quinoxaline compound for an anode additive and apply it to electrolytes and improve the capacity retention from 64.3% to 80.8% near 200 cycles for a lithium ion battery in experiments.

Tetrathiafulvalene as a Conductive Film-Making Additive on High-Voltage Cathode

Tetrathiafulvalene (TTF) is investigated as a conductive film-making additive on an overlithiated layered oxide (OLO) cathode. When the OLO/graphite cell is cycled at high voltage, carbonate-based electrolyte without the additive decomposes continuously to form a thick and highly resistant surface film on the cathode. In contrast, TTF added into the electrolyte becomes oxidized before the electrolyte solvents, creating a thinner film on the cathode surface. This film inhibits further electrolyte decomposition through cycling and stabilizes the interface between the cathode and the electrolyte. The cells containing the OLO cathode with TTF-added electrolyte afforded enhanced capacity retention and rate capability, making TTF a prospective electrolyte additive for higher energy density lithium-ion cells.

Topmost Atomistic Li Structures and Native Point Defects in the Li (001) Surface

To elucidate the atomic scale mechanism of the dendrite growth in the Li metal anode under the electrochemical condition, the formations of native point defects and topmost atomistic Li structures in the surface of Li metal were studied by using the firstprinciples calculation. In the (001) surface, vacancies are dominant and mainly confined in the surface, and moreover, the vacancy clustering is not favorable. Li interstitials near the surface always migrate to the top of the surface. Such native point defects without clustering effects near the surface, therefore, cannot be the initial step of dendrite growth. On the surface, the formations of atomistic Li structures with low coordination numbers, such as bridge-, tetrahedron-, pyramid-types and c-directional chain structures, were studied. It is found that the local electric potentials deviation of ~1V can initiate filamentary type dendrite growths in the electrochemical charging process of rechargeable batteries.