Ab Initio Tomography Analysis of Lithium Incorporation and Diffusion in Multidomain Silicon Suboxide Anode Materials

Abstract

Silicon is considered a promising anode material to supplant conventional graphite materials in lithium-ion batteries due to its higher theoretical energy-storage capacity compared to graphite. However, the widespread application of Si anodes has been hindered because the capacity of Si anodes decreases rapidly as the charge/discharge cycle proceeds. The controlled incorporation of oxygen into Si is often considered as a feasible approach for employing Si as an anode material in the form of silicon suboxide. Silicon suboxide exhibits a lower energy capacity compared to pure Si, but offers enhanced stability against volume expansion. Consequently, silicon suboxide materials have been commercialized by blending them with graphite. However, the blending ratio of silicon suboxide with graphite is limited to low levels due to its poor first-cycle efficiency, so-called initial Coulombic efficiency. In-depth understanding of the lithium interaction characteristics within multidomain silicon suboxide is indispensable for optimizing the electrochemical performance of silicon suboxide anode materials for lithium-ion batteries. In this study, we investigate the domain-dependent thermodynamic and kinetic properties of lithium atoms within systematically designed multidomain silicon suboxide models composed of Si, SiO2, and Si/SiO2 interface by performing a series of computational simulations combined with a unique tomography-like sampling scheme. We find that the Si/SiO2 interfacial region exhibits preferential thermodynamics and kinetics for lithiation and can serve as a critical lithium transport channel during charge-discharge cycles, while the SiO2 domain is likely to be excluded from lithiation due to its high resistance to lithium diffusion. Consequently, a significant fraction of lithium is expected to be trapped at the Si/SiO2 interface during the discharge process, which ultimately contributes to a low initial Coulombic efficiency. This theoretical understanding suggests that the formation of continuously connected lithium-transportable Si/SiO2 interfacial channels surrounding the Si domains, along with a well-structured shallow SiO2 framework through the use of appropriate synthesis methods, is essential for maximizing the electrochemical performance of silicon suboxide anode materials. Our theoretical approach offers new insights into the atomistic characteristics of silicon suboxide during lithiation/delithiation processes, ultimately enabling the identification of the origin of low ICE and strategies for addressing it.References(1) Chae, S.; Lim, H.-K.; Lee, S. Energy Landscapes for Lithium Incorporation and Diffusion in Multidomain Silicon Suboxide Anode Materials. ACS Applied Materials & Interfaces 2023, 15 (49), 57059-57069. DOI: 10.1021/acsami.3c12846. Figure 1