Stress in 3-D nanoarchitectures distributes throughout core and shell

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 Defect-free single crystalline Si nanowires generate structural defects from stress when the Ge shell becomes thicker. The short lines in the Ge shell represent the induced defects. NW is nanowire.

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At fast charging rates, lithium ion battery anodes with silicon (Si) core and germanium (Ge) shell nanowire heterostructures have a higher storage capacity compared to anodes with Si nanowires alone. However, defect propagation limits the performance of these higher capacity lithium ion batteries. Center for Integrated Nanotechnologies (MPA-CINT) researchers and collaborators investigated the cause of this phenomenon and found, for the first time, that stress in a core/shell nanowire heterostructure is shared between the core and the shell.

The journal Nanoscale published the findings. The researchers performed an integrated study of structural characterization and electrochemical performance to determine the root cause of the defect propagation. The team showed that radial heteroepitaxial shell growth induced structural defects in the core nanowires, which relaxed strain in both the core and shell regions. The distributed stress in the shell and core differs from conventional thin films on substrates, where the stress is confined in the thin film. The induced structural defects affect the electrochemical performance of the combined core/shell nanowire heterostructure.

The investigators suggest that the induced defect in the core/shell structures causes the actual capacity of the lithium ion battery performance lower to be lower than the theoretical maximum. The induced defects observed in the research are crucial factors to be considered for nanodevices and battery electrode design. This work is the first observation of how strain relaxation in 3-D structures of nanomaterials impacts electrical energy storage. The concept of crossover defects provides a new tunable parameter and a novel factor for designing nanomaterials that improve electrical energy storage.

The Si/Ge core/shell nanowire heterostructure serves as a representative platform for these types of composition modulation studies. The team concludes that this type of strain relaxation in 3-D nanostructures, which does not occur in conventional thin films, should be considered in designing nanomaterials for nanodevices.

Reference: “Strain-Induced Structural Defects and their Effects on the Electrochemical Performances of Silicon Core/Germanium Shell Nanowire Heterostructures,” Nanoscale 9, 1213 (2017); doi: 10.1039/C6NR07681E. http://pubs.rsc.org/en/content/articlepdf/2017/nr/c6nr07681e. Authors: Researchers: Dongheun Kim, Nan Li, and Jinkyoung Yoo (Center for Integrated Nanotechnologies, MPA-CINT); Zhen Li and Shixiong Zhang (Indiana University – Bloomington); Binh-Minh Nguyen and Yung-Chen Lin (formerly MPA-CINT).

Funding and Mission

The research was performed in part at CINT, a DOE Office of Basic Energy Sciences User Facility jointly operated by Los Alamos and Sandia national laboratories. The DOE Basic Energy Sciences and its Scientific User Facilities Division funded the Los Alamos portion of the study. The work supports the Lab’s Energy Security mission area and its Materials for the Future science pillar. In studying the fundamental properties of materials, researchers aim to tune those properties and achieve controlled functionality, a central vision of the Laboratory’s materials strategy.

Technical contact: Jinkyoung Yoo