First-principles insights into lithium and magnesium ion dynamics for high-performance silicon and silicon-germanium anodes

Abstract

Silicon (Si) anodes offer high theoretical capacity for lithium-ion batteries but suffer from severe volume expansion, leading to structural degradation and capacity loss. This study explores silicon-germanium (SiGe) composites as an alternative anode material using Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD) simulations to evaluate thermodynamic stability, structural adaptability, and charge transport behavior under ion insertion.

The results show that Ge incorporation lowers formation energy barriers, facilitating Li and Mg insertion while reducing mechanical stress and volume expansion. The SiGe framework exhibits greater flexibility, enabling superior Li-ion mobility, while Mg-ion diffusion remains constrained due to stronger electrostatic interactions. Extended AIMD simulations at 300 K, 750 K, and 1200 K further confirm SiGe's structural resilience and improved ion transport. Projected Density of States (PDOS) calculations, along with Electron Localization Function (ELF) analysis, reveal enhanced charge distribution in SiGe, supporting its stability during cycling.

By offering greater thermodynamic stability, reduced volumetric strain, and enhanced ion transport, SiGe presents a promising anode material for next-generation lithium- and magnesium-ion batteries. These findings provide valuable insights into alloy design strategies, bridging the gap between fundamental materials science and practical energy storage applications.