High capacity group-15 alloy anodes for Na-ion batteries: Electrochemical and mechanical insights

Significance Statement

Na-ion batteries (NIBs) have received increasing attention due to the abundance of Na, its environmental friendliness and its electrochemical similarity to Li. Among the potential anode candidates for Na-ion batteries, alloy anodes have attracted considerable interest as they provide high gravimetric capacities. Group-15 elements such as phosphorus, arsenic, antimony and bismuth, offer the prospect of serving as functional alloying elements for developing high-capacity anodes for Na-ion batteries (with capacities as large as 2560 mAh g-1). However, their practical application has largely been hindered by drastic volume expansion/contraction during sodiation/ desodiation resulting in cracking, pulverization and ultimately, a significant capacity fade. Using first principles calculations, we have obtained a full set of concentration-dependent elastic properties for a single crystal as well as a polycrystalline microstructure of sodium alloys with group-15 elements. These elastic properties are essential for developing analytical models that can describe the mechanistic behavior of these alloy anodes during cyclic sodiation and desodiation. In addition, we obtain concentration-dependent electrochemical properties of the alloys. We find that sodiation of these alloys results in their significant elastic softening by as large as 60 %. The operating voltage remains within a narrow range of 0.4 V – 1.2 V suitable for anode applications. Our results give crucial insights into the electrochemical and mechanical response of these alloys as a function of Na content. They also furnish a guide towards developing continuum models for predicting deformation and fracture behavior, which is  beneficial in the design of failure-resistant architectures of high capacity Na-ion batteries.

Journal Reference

Journal of Power Sources, Volume 285, 2015, Pages 29-36.

Majid Mortazavi, Qiongjie Ye, Nick Birbilis, Nikhil V. Medhekar

Department of Materials Engineering, Monash University, Clayton, Victoria 3800, Australia

Abstract

Group-15 elements phosphorus, arsenic, antimony and bismuth offer the prospect of serving as functional alloying elements for developing high-capacity alloy anodes for sodium-ion batteries (NIBs). Here we obtain concentration-dependent electrochemical properties of sodium (Na) alloys with group-15 elements using first principles calculations. Since Na intercalation in these alloys is accompanied by a substantial volume expansion that can lead to mechanical failure and loss of capacity, we have also obtained a full set of concentration-dependent elastic properties for a single crystal as well as a polycrystalline microstructure. We find that sodiation of these alloys results in their significant elastic softening by as large as 60%. In contrast to the group-14 alloys that are also being explored as anodes of Na-ion batteries, the elastic softening in group-15 alloys varies in a non-monotonic manner with Na concentration, and more importantly, the maximum degradation of elastic properties does not necessarily occur at full sodiation. Our results provide crucial insights into the electrochemical and mechanical response of these alloys to Na intercalation, thus contributing to the design of failure-resistant architectures of high capacity Na-ion batteries.

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High capacity group-15 alloy anodes Na-ion batterie Electrochemical mechanical insights. Advances In Engineering

 

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