In Situ Transmission Electron Microscopy Studies on Silicon Anodes in Lithium Ion Batteries

Abstract

Extensive research for new energy storage materials has created a high demand for experimental techniques that can provide real-time, single-particle-level information on the dynamic electrochemical processes taking place at the electrode materials during battery charge/discharge cycles. In situ transmission electron microscopy (TEM) on lithium ion batteries has been offered exceptional opportunities for monitoring the dynamic processes of electrode materials during electrochemical reaction at both spatial and temporal resolution.In this talk, I will introduce in situ TEM studies on Si anodes which suffers the anomalous volumetric changes and fracture during lithiation process. Previously, the lithiation behaviour of a single Si particle has been explained in detail by simulation data and experimental observation. However, in real batteries, since lithiation occurs simultaneously in clusters of Si in a confined medium, understanding how the individual Si structures interact during lithiation in a closed space is necessary. In this regard, I demonstrated physical and mechanical interactions of swelling Si structures during lithiation using well-defined Si nanopillar pairs. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs on free surfaces when the pillars are mechanically clamped. Such mechanical interactions enhance the fracture resistance of lithiated Si by lessening the tensile stress concentrations in Si structures. This experiment reveals the surprising effects of nanostructure shape, size, and void space for lithiation and the results will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.