Abstract
Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. However, in real batteries, lithiation occurs simultaneously in clusters of Si in a confined medium. Hence, understanding how the individual Si structures interact during lithiation in a closed space is necessary. Here, we demonstrate 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 at 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 study will contribute to improved design of Si structures at the electrode level for high-performance Li-ion batteries.
Highlights
Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics
Silicon (Si) has attracted great attention as a promising negative electrode material for Li-ion batteries due to its exceptional theoretical specific capacity of 3,578 mAh g À 1 for the Li15Si4 phase at room temperature[1,2,3,4,5]. Despite these preeminent theoretical properties, conventional Si anodes face significant challenges due to the large volume changes that accompany lithiation. These effects have limited the choice of Si as a commercial negative electrode because they can lead to the loss of electrical contact between active materials by mechanical fracture, accumulation of solid-electrolyte interphase layers, and rapid capacity fading during electrochemical cycling[6,7,8,9]
To mimic the cluster of crystalline Si particles in the confined volume in the negative electrode of a Li-ion battery, Si nanopillars with adjacent rigid walls were fabricated by e-beam lithography and dry etching of o1104 single crystalline Si wafer
Summary
Following an explosion of studies of silicon as a negative electrode for Li-ion batteries, the anomalous volumetric changes and fracture of lithiated single Si particles have attracted significant attention in various fields, including mechanics. Ex situ SEM and in situ TEM studies reveal that compressive stresses change the reaction kinetics so that preferential lithiation occurs at free surfaces when the pillars are mechanically clamped. Silicon (Si) has attracted great attention as a promising negative electrode material for Li-ion batteries due to its exceptional theoretical specific capacity of 3,578 mAh g À 1 for the Li15Si4 phase at room temperature[1,2,3,4,5] Despite these preeminent theoretical properties, conventional Si anodes face significant challenges due to the large volume changes that accompany lithiation. We show how mechanical interactions of neighbouring crystalline Si structures affect their reaction kinetics and fracture resistance during electrochemical lithiation, using ex situ scanning electron microscopy (SEM) and in situ TEM of Si nanopillar pairs
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