First principle calculations on structural, electronic and transport properties of Li2TiS3 and Li3NbS4 positive electrode materials

Thiyagarajan Gnanapoongothai,Balasubramaniam Rameshe,Balan Palanivel,Ramaswamy Murugan,Kaliaperumal Shanmugapriya

doi:10.1007/s40243-016-0072-2

Abstract

First principle calculations based on density functional theory have been performed on lithium containing transition metal sulfides Li2TiS3 and Li3NbS4 which are recently identified as novel positive electrode materials for rechargeable Li+ batteries. The calculations were performed to investigate the structural stability, electronic and transport properties of Li2TiS3 and Li3NbS4 along with their corresponding delithiated phases LiTiS3 and Li2NbS4. In this study it has been observed that these lithium containing sulfur materials maintain their face-centered cubic structure upon extraction of Li+. To calculate the structural stability and volume change due to lithium extraction, the total energies of Li2TiS3, Li3NbS4 and their corresponding delithiated phases LiTiS3 and Li2NbS4 have been computed by applying full potential linearized augmented plane wave (FP-LAPW) method implemented in WIEN2K. The equilibrium structural parameters for all the phases were determined by achieving total energy convergence. These electrode materials exhibit very small percentage of volume change with change in Li+ concentration which accounts for excellent structural stability. The computed band structure along high symmetry lines in the Brillouin zone, total and partial density of states clearly reveals that the extraction lithium from these electrode materials does not change their metallic nature. The electronic conductivities of both lithiated and delithiated phases have been calculated by employing BoltzTrap which can be interfaced with WIEN2K. The topological distributions of electron charge density at various critical points within the system were analyzed with the use of CRITIC code which is based on Bader’s theory of atoms in molecules (AIM). From the charge density calculations, it was observed that, there is strong ionic bond and weak covalent bond between atoms of the compounds Li2TiS3 and Li3NbS4. But the ionic bond nature was found to decrease in the delithiated phases LiTiS3 and Li2NbS4. The calculated values of electronic conductivities and discharge voltages for both electrodes are found to be in accordance with the recent experimental reports.

Highlights

Li? batteries are the most significant rechargeable power sources which are being successful in powering portable consumer electronic devices
First principle calculations based on density functional theory have been performed on lithium containing transition metal sulfides Li2TiS3 and Li3NbS4 which are recently identified as novel positive electrode materials for rechargeable Li? batteries
To find the imbalanced redox potential in the delithiated phases, we have considered electron self-interaction (SIC) and employed local density approximation (LDA) ? U method with three different selfinteraction corrections to obtain the ionic charge distribution inside the atomic basins for the electrodes Li2TiS3 and Li3NbS4 as well as for their delithiated phases

Summary

Introduction

Li? batteries are the most significant rechargeable power sources which are being successful in powering portable consumer electronic devices. Transportation rate and specific capacities are mainly determined by the positive electrode materials [1]. The practical reversible capacities of conventional positive electrode materials with layered structure and olivine. Even though the olivine LiMPO4 and spinel LiMn2O4 were proposed as the positive electrode materials with better cyclic performance and low cost, they have lower electronic conductivity [3,4,5,6,7,8,9,10,11,12,13,14,15]. Li2S, Li2Se and Li2O exhibit high capacities due to multi electron reaction [19,20,21]. It is clear that electrodes involved in multi electron reactions exhibit high specific capacity

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