Exploring Li-ion conductivity in cubic, tetragonal and mixed-phase Al-substituted Li7La3Zr2O12 using atomistic simulations and effective medium theory

Garnet Li7La3Zr2O12 (LLZO) is a promising solid electrolyte candidate for solid-state Li-ion batteries, but at room temperature it crystallizes in a poorly Li-ion conductive tetragonal phase. To this end, partial substitution of Li+ by Al3+ ions is an effective way to stabilize the highly conductive cubic phase at room temperature. Yet, fundamental aspects regarding this aliovalent substitution remain poorly understood. In this work, we use molecular dynamics and advanced hybrid Monte Carlo methods for systematic study of the room temperature Li-ion diffusion in tetragonal and cubic LLZO to shed light on important open questions. We find that Al substitution in tetrahedral sites of the tetragonal LLZO allows previously inaccessible sites to become available, which enhances Li-ion conductivity. In contrast, in the cubic phase Li-ion diffusion paths become blocked in the vicinity of Al ions, resulting in a decrease of Li-ion conductivity. Moreover, combining the conductivities of individual phases through an effective medium approximation allowed us to estimate the conductivities of cubic/tetragonal phase mixtures that are in good agreement with those reported in several experimental works. This suggests that phase coexistence (due to phase equilibrium or gradients in Al content within a sample) could have a significant impact on the conductivity of Al-substituted LLZO, particularly at low contents of Al3+. Overall, by making a thorough comparison with reported experimental data, the theoretical study and simulations of this work advance our current understanding of Li-ion mobility in Al-substituted LLZO garnets and might guide future in-depth characterization experiments of this relevant energy storage material.MINECO ENE2016-81020-R. SGI/IZO-SGIker UPV/EHU. the i2BASQUE academic network. Barcelona Supercomputer Center (QCM-2016-450 3-0002)

Atomistic Insight into Ion Transport and Conductivity in Ga/Al-Substituted Li7_7La3_3Zr2_2O12_{12} Solid Electrolytes

Garnet-structured Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$ is a promising solid electrolyte for next-generation solid-state Li batteries. However, sufficiently fast Li-ion mobility required for battery applications only emerges at high temperatures, upon a phase transition to cubic structure. A well-known strategy to stabilize the cubic phase at room temperature relies on aliovalent substitution; in particular, the substitution of Li$^{+}$ by Al$^{3+}$ and Ga$^{3+}$ ions. Yet, despite having the same formal charge, Ga$^{3+}$ substitution yields higher conductivities ($10^{-3}$~S/cm) than Al$^{3+}$ ($10^{-4}$~S/cm). The reason of such difference in ionic conductivity remains a mystery. Here we use molecular dynamic simulations and advanced sampling techniques to precisely unveil the atomistic origin of this phenomenon. Our results show that Li$^{+}$ vacancies generated by Al$^{3+}$ and Ga$^{3+}$ substitution remain adjacent to Ga$^{3+}$ and Al$^{3+}$ ions, without contributing to the promotion of Li$^{+}$ mobility. However, while Ga$^{3+}$ ions tend to allow limited Li$^{+}$ diffusion within their immediate surroundings, the less repulsive interactions associated with Al$^{3+}$ ions lead to a complete blockage of neighboring Li$^{+}$ diffusion paths. This effect is magnified at lower temperatures, and explains the higher conductivities observed for Ga-substituted systems. Overall this study provides a valuable insight into the fundamental ion transport mechanism in the bulk of Ga/Al-substituted Li$_{7}$La$_{3}$Zr$_{2}$O$_{12}$ and paves the way for rationalizing aliovalent substitution design strategies for enhancing ionic transport in these materials.ENE2016-81020-R (MINECO

Unveiling Interfacial Li-Ion Dynamics in Li7La3Zr2O12/PEO(LiTFSI) Composite Polymer-Ceramic Solid Electrolytes for All-Solid-State Lithium Batteries

Unlocking the full potential of solid-state electrolytes (SSEs) is key to enabling safer and more-energy dense technologies than today’s Li-ion batteries. In particular, composite materials comprising a conductive, flexible polymer matrix embedding ceramic filler particles are emerging as a good strategy to provide the combination of conductivity and mechanical and chemical stability demanded from SSEs. However, the electrochemical activity of these materials strongly depends on their polymer/ceramic interfacial Li-ion dynamics at the molecular scale, whose fundamental understanding remains elusive. While this interface has been explored for nonconductive ceramic fillers, atomistic modeling of interfaces involving a potentially more promising conductive ceramic filler is still lacking. We address this shortfall by employing molecular dynamics and enhanced Monte Carlo techniques to gain unprecedented insights into the interfacial Li-ion dynamics in a composite polymer-ceramic electrolyte, which integrates polyethylene oxide plus LiN(CF3SO2)2 lithium imide salt (LiTFSI), and Li-ion conductive cubic Li7La3Zr2O12 (LLZO) inclusions. Our simulations automatically produce the interfacial Li-ion distribution assumed in space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and experimental measurements of tensile strength and ionic conductivity, we are able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold. Our results pave the way for the computational modeling of other conductive filler/polymer combinations and the rational design of composite SSEs.-Juan de la Cierva grant IJC2018-037214-I, -PID2019-106519RB-I00, as -HPC-Europa3 grant HPC17ERWTO -AI in BCAM, EXP. 2019/004

Low critical micelle concentration discrepancy between theory and experiment

10.1021/jz500790

Consenso colombiano de atención, diagnóstico y manejo de la infección por SARS-COV-2/COVID-19 en establecimientos de atención de la salud Recomendaciones basadas en consenso de expertos e informadas en la evidencia

The “Asociación Colombiana de Infectología” (ACIN) and the “Instituto de Evaluación de Nuevas Tecnologías de la Salud” (IETS) created a task force to develop recommendations for Covid 19 health care diagnosis, management and treatment informed, and based, on evidence. Theses reccomendations are addressed to the health personnel on the Colombian context of health services. © 2020 Asociacion Colombiana de Infectologia. All rights reserved