MGOS: A library for molecular geometry and its operating system

The geometry of atomic arrangement underpins the structural understanding of molecules in many fields. However, no general framework of mathematical/computational theory for the geometry of atomic arrangement exists. Here we present "Molecular Geometry (MG)'' as a theoretical framework accompanied by "MG Operating System (MGOS)'' which consists of callable functions implementing the MG theory. MG allows researchers to model complicated molecular structure problems in terms of elementary yet standard notions of volume, area, etc. and MGOS frees them from the hard and tedious task of developing/implementing geometric algorithms so that they can focus more on their primary research issues. MG facilitates simpler modeling of molecular structure problems; MGOS functions can be conveniently embedded in application programs for the efficient and accurate solution of geometric queries involving atomic arrangements. The use of MGOS in problems involving spherical entities is akin to the use of math libraries in general purpose programming languages in science and engineering. (C) 2019 The Author(s). Published by Elsevier B.V

Carbon-free high-performance cathode for solid-state Li-O-2 battery

The development of a cathode for solid-state lithium-oxygen batteries has been hindered in practice by a low capacity and limited cycle life despite their potential for high energy density. Here, a previously unexplored strategy is proposed wherein the cathode delivers a specific capacity of 200 milliampere hour per gram over 665 discharge/charge cycles, while existing cathodes achieve only similar to 50 milliampere hour per gram and similar to 100 cycles. A highly conductive ruthenium-based composite is designed as a carbon-free cathode by first-principles calculations to avoid the degradation associated with carbonaceous materials, implying an improvement in stability during the electrochemical cycling. In addition, water vapor is added into the main oxygen gas as an additive to change the discharge product from growth-restricted lithium peroxide to easily grown lithium hydroxide, resulting in a notable increase in capacity. Thus, the proposed strategy is effective for developing reversible solid-state lithium-oxygen batteries with high energy density

Preferential Positioning of gamma-Ray Treated Multi-Walled Carbon Nanotubes in Polyamide 6,6/Poly(p-phenylene ether) Blends

Morphological characteristics and electrical conductivity of polyamide 6,6/poly(p-phenylene ether)/multi-walled carbon nanotube (PA66/PPE/MWCNT) ternary nanocomposites were investigated. The MWCNTs were modified by 60Co gamma ray (γ-ray) irradiation under a dry condition and O2 atmosphere, which introduces oxygen-containing functional groups on the surfaces of the MWCNTs and thereby provides better compatibility with the hydrophilic PA66 phase. It was observed that the MWCNTs are preferentially positioned in the continuous PA66 matrix, whereas PPE domains are almost free of MWCNTs. Since PA66 consists of a continuous phase and the MWCNTs are preferentially positioned in the PA66 phase, electrical conductivity of PA66/PPE/MWCNT ternary composites is higher than that of PA66/MWCNT binary composites at the same MWCNT content. It was observed that raising the processing temperature and increasing the mixing time were effective means of improving the electrical conductivity of the composites, via enhancement of MWCNT dispersion. [Figure not available: see fulltext.] © 2013 The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht.

Mixed Ionic-Electronic Conductor of Perovskite Li(x)La(y)MO(3-)(delta)toward Carbon-Free Cathode for Reversible Lithium-Air Batteries

Mixed ionic-electronic conductors (MIECs) can play a pivotal role in achieving high energies and power densities in rechargeable batteries owing to their ability to simultaneously conduct ions and electrons. Herein, a new strategy is proposed wherein late 3d transition metals (TMs) are substituted into a perovskite Li-ion conductor to transform it into a Li-containing MIEC. First-principles calculations show that perovskite Li(x)La(y)MO(3)with late 3d TMs have a low oxygen vacancy formation energy, implying high electron carrier concentrations corresponding to high electronic conductivity. The activation barriers for Li diffusion in LixLayMO3(M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li-ion conductivity. The designed perovskites of Li(0.34)La(0.55)MnO(3-)(delta)experimentally prove to have high electronic (2.04 x 10(-3)S cm(-1)) and Li-ion (8.53 x 10(-5)S cm(-1)) conductivities, and when applied in a carbon-free cathode of a Li-air cell, they deliver superior reversibility at 0.21 mAh cm(-2)over 100 charge/discharge cycles while avoiding the degradation associated with carbonaceous materials. This strategy enables the effective design of Li-conducting MIEC and reversible Li-air batteries

Rapid oxygen diffusive lithium-oxygen batteries using a restacking-inhibited, free-standing graphene cathode film

© The Royal Society of Chemistry. A graphene-based porous electrode for a lithium-oxygen (Li-O 2 ) battery is investigated for use in next generation energy storage systems. The porosity of the cathode electrode in Li-O 2 batteries is a key factor in increasing their oxygen diffusion rate and electrochemical activity, and enables a longer cycle life. In addition, the adsorption behavior of the electrolyte is an important factor for the charging process and diffusion of oxygen. We report the fabrication of a restacking-inhibited film cathode using corrugated and highly porous reduced graphene flakes that have an outstanding capacity and cycle life. We have demonstrated a robust porous cathode film for the next generation Li-O 2 batteries, which provides (1) rich voids and spaces for oxygen-related reactions, (2) easy accessibility to the electrolyte and rapid oxygen diffusion. This study can be applied for the design of new solution-processed graphene and the development of Li-O 2 battery cathode

Flexible free-standing air electrode with bimodal pore architecture for long-cycling Li-O-2 batteries

Li-O-2 batteries have been proposed as next-generation energy-storage devices, but this technology is hindered by serious problems including parasitic reactions, degradation, and leakage of the electrolyte. Li-O-2 batteries are also currently designed to have a rigid bulky structure, which cannot satisfy the flexibility demands of modern electronics. Herein, we report the significant enhancement of the electrochemical performance and flexibility of a Li-O-2 battery by introducing a free-standing, binder-free carbon nanotube cathode with a bimodal pore architecture. This electrode structure imparted stability to active sites during the recovery of discharge products to the initial state, providing long-term cyclability of more than 100 cycles in a tetraethylene glycol dimethyl ether electrolyte system. The O-2 transportation and conductivity were also improved, yielding an increased discharge capacity of 5500 mAh g(-1) (nearly twice that of a non-porous cathode) and minimizing parasitic reactions. This novel bimodal-pore cathode exhibited an increased tri-phase boundary for the Li-O-2 reactive zone in the interconnected CNT network. The small pore structures (similar to 50 nm) accommodated Li2O2, and the large pore structures (similar to 385 nm) enabled effective oxygen diffusion without clogging the pores. Moreover, Li+ and oxygen diffusion were facilitated by the two independent channels provided by the pore structures. (C) 2017 Elsevier Ltd. All rights reserved.

Enhancing the cycle stability of Li-O-2 batteries via functionalized carbon nanotube-based electrodes

Achieving the high theoretical energy density (similar to 3500 W h kg(-1)) of Li-O-2 batteries involves maximizing the electrochemically active surface area (EASA) of the electrodes. Carbon nanotubes (CNTs) have been widely adopted for Li-O-2 electrodes but their EASA is limited by their electrolyte-phobic surface nature and the strong van der Waals interaction between CNTs. To increase the affinity between CNT-based electrodes and the electrolyte without decreasing CNT chemical stability, CNT buckypapers are functionalized with 3,5-bis(trifluoromethyl)phenylmaleimide. The solubility parameters of the electrolyte and CNTs are considered so that the maleimide groups increase the affinity between the electrode and electrolyte and the 3,5-bis(trifluoromethyl)phenyl groups protect the maleimide groups from decomposition. The functionalized CNT cathode exhibits a 58% greater discharge capacity and a 50% increased cyclability compared to the pristine CNT cathode when a 1 : 2.5 weight ratio of CNT to electrolyte was used due to an increased EASA and steric hindrance effect. Finally, a 3D folded Li-O-2 cell is fabricated using the functionalized CNT-based cathode and demonstrated 30 cycles at 100 W h kg(cell)(-1) cutoff. These results clearly show that high energy density and long cycling performance of Li-O-2 batteries can be achieved even with a much reduced amount of electrolyte by increasing the affinity between CNT-based electrodes and the electrolyte.