Termodinâmica e cinética de portadores de carga iônica no cátodo Li2S

Abstract

Batteries are systems that store electrochemical energy and may be rechargeable or non-rechargeable. Lithium-ion batteries are rechargeable and have been applied very efficiently, mainly in electronic equipment, due to their high power and high gravimetric and volumetric energy density. In recent years, attention has focused on the development of electric vehicles, in which lithium-ion batteries based on LiNi1-x-yMnxCoyO2 (NMC), LiNi1-x-yCoxAlyO2 (NCA) or LiFePO4 (LFP) cathodes provide energy for the vehicle's electric motor, without emission of pollutants into the atmosphere. The electric vehicles are a multi-billion dollar market, with an investment perspective of 70 billion dollars for 2026. However, for application in electric vehicles, lithium-ion batteries still fall short in terms of energy density and manufacturing cost. Recently, lithium-sulfur (Li-S) batteries have stood out because of their enhanced energy density, both gravimetric (2500 Wh/kg) and volumetric (2800 Wh/L). However, they present some problems related to the dissolution of polysulfides in the electrolyte, formation of dendrites at the anode, and low ionic and electronic conductivities of the cathode (typically S8). In this work, we study the Li2S cathode (theoretical specific capacity of 1166 mAh/g) for application in Li-S batteries, qualitatively and quantitatively investigating the charge carriers and transport mechanisms relevant to Li+ ionic conductivity, through a combination of classical computational modeling – based on a force-field, using the GULP program – and analytical calculations of statistical and kinetic thermodynamics. We also investigated the feasibility of applying biaxial strain as an alternative to improve the ionic conductivity of Li2S, which is essential for it to be commercially applied.