The role of crystallographic orientation on surface properties and ion transport in lithium germanate (Li2GeO3) anodes: A computational approach

Abstract

The performance of lithium-ion batteries (LIBs) hinges on the surface properties of their anodes. Compared to the bulk material, the anode surface is more susceptible to environmental changes during lithium (Li) intake and release, directly impacting factors like capacity, cycling stability, and charge/discharge rates. Lithium germanate (Li2GeO3, LGO) has emerged as a promising anode material due to its fast Li-ion conduction. While numerous studies have explored performance improvements through various methods, including defect engineering. However, there is currently a lack of atomistic-level understanding of the surface structure. Consequently, despite the importance of precisely understanding the surface to manipulate its different properties, specific surface details of LGO remain unclear. This knowledge gap hinders precise manipulation of surface properties for optimal performance.This study addresses this critical need by employing theoretical calculations to predict the structural, electrochemical characteristics, and Li-ion transport behavior in LGO surfaces. Our results indicate that polar surfaces exhibit lower formation energies compared to non-polar surfaces. Further investigation revealed that Li-terminated surfaces possess the lowest surface energy among various surface terminations. Interestingly, the work function calculations displayed an opposite trend to surface formation energy, with polar surfaces exhibiting the lowest work function values.To explore Li-ion transport, we employed ab initio molecular dynamics simulations. Notably, the (003) surface displayed the highest Li-ion diffusion rate among all considered surfaces.Further analysis of the (001) surface, which exhibited similar diffusion pathways to the (003) surface, revealed a lower diffusion rate.To understand this disparity, nudged elastic band (NEB) simulations were used to estimate the energy barriers for Li-ion migration along each pathway in both structures. Despite sharing similar pathways, the energy barriers in the (003) surface were significantly lower than those in the (001) surface. This finding suggests that the intrinsic energy landscape of the surface plays a crucial role in dictating Li-ion transport behavior.