Current Collector Interface for Phase Changing Tin Anode in Sodium Ion Batteries: Insight from First Principles Calculations

Abstract

Performance of an efficient and high capacity Lithium-ion battery (LIB) and Sodium-ion battery (NIB) greatly depends upon electrode-current collector interface. While copper (Cu) is most extensively used current collector at the anode end, it has been associated with numerous functional issues such as debonding, corrosion, strain accommodation, low flexibility, and high cost and weight. In this work, we investigate the comparative performance of Graphene with Cu as the current collector for NIB anode. Graphene not only provides the battery system much-needed flexibility, cost, and weight efficiency but also imparts mechanical stability to the system during the sodiation and de-sodiation cycles. Tin (Sn) has been taken up as model anode material owing to its potential and promising high theoretical specific capacity of 994 mAh/g. However, the anodic performance of Sn is limited by its high-volume expansion and multiple phase changes which leads to subsequent mechanical failure. Therefore, the effect of mechanical strains and phase transitions during battery performance on the interface has been investigated in detail. We have employed vdW inclusive GGA based Density Functional Theory (DFT) implemented in VASP to study the effect of sodiation and de-sodiation on the mechanical integrity of anode and current collector interface. We report that Graphene is more efficient in combatting mechanical stresses generated in the anode during the performance and also allows easy expansion to Sn. We hope that this work will throw more light on the mechanics and chemistry that are prominent at the interface of an anode and current collector.