Yoon-Sok Kang

Continuous activation of Li2MnO3 component upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material for lithium ion batteries

Li-rich layered cathode materials are very promising candidates for next generation high energy lithium ion batteries. One of the Li-rich layered cathode materials, Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 is prepared by a co-precipitation method. In this report, we focus on anomalous changes upon cycling in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material in a voltage range of 2.0–4.55 V at room temperature. The structural transitions upon cycling are analyzed by ex situ X-ray diffraction. In addition, the changes in local structure during cycling are studied by X-ray absorption near edge structure. With differential capacity plots by controlling the cut-off voltage, the voltage decay during cycling is intensively studied. The continuous activation process of the residual Li2MnO3 component during cycling is correlated with voltage decay during cycling, and increasing capacity during the initial several cycles. Also, the electrochemical performance in Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 cathode material below 4.4 V is discussed. Furthermore, cycle performance is improved by reassembling Li1.167Ni0.233Co0.100Mn0.467Mo0.033O2 into another cell after washing.

Silicon/Carbon Nanotube/BaTiO3 Nanocomposite Anode: Evidence for Enhanced Lithium-Ion Mobility Induced by the Local Piezoelectric Potential

We report on the synergetic effects of silicon (Si) and BaTiO3 (BTO) for applications as the anode of Li-ion batteries. The large expansion of Si during lithiation was exploited as an energy source via piezoelectric BTO nanoparticles. Si and BTO nanoparticles were dispersed in a matrix consisting of multiwalled carbon nanotubes (CNTs) using a high-energy ball-milling process. The mechanical stress resulting from the expansion of Si was transferred via the CNT matrix to the BTO, which can be poled, so that a piezoelectric potential is generated. We found that this local piezoelectric potential can improve the electrochemical performance of the Si/CNT/BTO nanocomposite anodes. Experimental measurements and simulation results support the increased mobility of Li-ions due to the local piezoelectric potential.

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 ∼1 000 000 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.