First-Principles Characterization of the Unknown Crystal Structure and Ionic Conductivity of Li₇P₂S₈I as a Solid Electrolyte for High-Voltage Li Ion Batteries

Using first-principles density functional theory calculations and ab initio molecular dynamics (AIMD) simulations, we demonstrate the crystal structure of the Li₇P₂S₈I (LPSI) and Li ionic conductivity at room temperature with its atomic-level mechanism. By successively applying three rigorous conceptual approaches, we identify that the LPSI has a similar symmetry class as Li₁₀GeP₂S₁₂ (LGPS) material and estimate the Li ionic conductivity to be 0.3 mS cm^–1 with an activation energy of 0.20 eV, similar to the experimental value of 0.63 mS cm^–1. Iodine ions provide an additional path for Li ion diffusion, but a strong Li–I attractive interaction degrades the Li ionic transport. Calculated density of states (DOS) for LPSI indicate that electrochemical instability can be substantially improved by incorporating iodine at the Li metallic anode via forming a LiI compound. Our methods propose the computational design concept for a sulfide-based solid electrolyte with heteroatom doping for high-voltage Li ion batteries

First-Principles Study on the Thermal Stability of LiNiO₂ Materials Coated by Amorphous Al₂O₃ with Atomic Layer Thickness

Using first-principles calculations, we study how to enhance thermal stability of high Ni compositional cathodes in Li-ion battery application. Using the archetype material LiNiO₂ (LNO), we identify that ultrathin coating of Al₂O₃ (0001) on LNO(012) surface, which is the Li de-/intercalation channel, substantially improves the instability problem. Density functional theory calculations indicate that the Al₂O₃ deposits show phase transition from the corundum-type crystalline (c-Al₂O₃) to amorphous (a-Al₂O₃) structures as the number of coating layers reaches three. Ab initio molecular dynamic simulations on the LNO(012) surface coated by a-Al₂O₃ (about 0.88 nm) with three atomic layers oxygen gas evolution is strongly suppressed at <i>T</i> = 400 K. We find that the underlying mechanism is the strong contacting force at the interface between LNO(012) and Al₂O₃ deposits, which, in turn, originated from highly ionic chemical bonding of Al and O at the interface. Furthermore, we identify that thermodynamic stability of the a-Al₂O₃ is even more enhanced with Li in the layer, implying that the protection for the LNO(012) surface by the coating layer is meaningful over the charging process. Our approach contributes to the design of innovative cathode materials with not only high-energy capacity but also long-term thermal and electrochemical stability applicable for a variety of electrochemical energy devices including Li-ion batteries

Universal Scaling Relationship To Screen an Efficient Metallic Adsorbent for Adsorptive Removal of Iodine Gas under Humid Conditions: First-Principles Study

Safe control and removal of radioactive iodine gases (I-129 and I-131) leaking from the accidents in chemical factories or nuclear industries are of importance because of their critical damage to the biosphere. We study the adsorptive removal of the off-gaseous iodine using transition metals of group 10 and group 11 under humid conditions. First-principles calculations enable to capture key adsorption natures of iodine and water molecules on the adsorbent surfaces. The underlying mechanism is analyzed by thermodynamic free energies, electronic structures, and surface work function changes. Our results unveil why silver metal shows notably outstanding efficiency for the iodine removal. We propose an innovative and insightful map to guide sorting out the best metal adsorbents and impregnants for dramatic improvement of the adsorptive removal of the radioactive iodine gas. Our study is useful for preventing critical risks from chemical and nuclear accidents

First-Principles Computational Screening of Highly Active Pyrites Catalysts for Hydrogen Evolution Reaction through a Universal Relation with a Thermodynamic Variable

Hydrogen gas has been regarded as a promising fuel for securing energy and environmental sustainability of our society. Accordingly, efficient and large scale production of hydrogen is central issue due to high activation barrier unless costly transition metal catalysts are used. Here, we screen optimum catalysts toward hydrogen evolution among cheap pyrites using first-principles density functional theory calculations and rigorous thermodynamic approach. A key thermodynamic state variable accurately describes the catalytic activity, of which the mechanism is unveiled by a universal linear correlation between kinetic exchange current density in hydrogen evolution reaction and thermodynamic adsorption energy of hydrogen atom over various pyrites. On the basis of the results, we propose a design principle for substantial tuning the catalytic performance

Effective Trapping of Lithium Polysulfides Using a Functionalized Carbon Nanotube-Coated Separator for Lithium–Sulfur Cells with Enhanced Cycling Stability

The critical issues that hinder the practical applications of lithium–sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium–sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g^–1 (corresponding to an areal capacity of 3.2 mAh cm^–2) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate