Amorphous Germanium as a Promising Anode Material for Sodium Ion Batteries: A First Principle Study

TL;DR

This study uses first-principles simulations to explore amorphous germanium as an anode material for sodium-ion batteries, revealing atomic-scale insights into capacity, diffusion, and structural changes to guide experimental development.

Contribution

It provides a systematic atomistic analysis of sodiation in amorphous germanium, including capacity-voltage correlation, microstructural evolution, and diffusion kinetics, which was previously lacking.

Findings

Intercalation potential and capacity are correlated with intermediate structures.

Sodiation causes microstructural changes in amorphous Ge.

Sodium diffusivity and volume expansion trends are characterized.

Abstract

The abundance of Sodium (Na), its low-cost, and low reduction potential provide a lucrative inexpensive, safe, and environmentally benign alternative to Lithium Ion Batteries (LIBs). The significant challenges in advancing Sodium Ion Battery (NIB) technologies lies in finding the better electrode materials. Experimental investigations revealed the real potency of Germanium (Ge) as suitable anode materials for NIBs. However, a systematic atomistic study is necessary to understand the fundamental aspects of capacity-voltage correlation, microstructural changes of Ge, as well as diffusion kinetics. We, therefore, performed the Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD) simulation to investigate the sodiation-desodiation kinetics in Germanium-Sodium system (Na64Ge64). We analyzed the intercalation potential and capacity correlation for intermediate equilibrium structures and compared our data with the experimental results. Effect of sodiation on inter-atomic distances within Na-Ge system is analyzed by means of Pair Correlation Function (PCF). This provides insight into possible microstructural changes taking place during sodiation of amorphous Ge (a-Ge). We further investigated the diffusivity of sodium in a-Ge electrode material and analyzed the volume expansion trend for Na64Ge64 electrode system. Our computational results provide the fundamental insight into the atomic scale and help experimentalists design Ge based NIBs for real-life applications.