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| Home > Publications database > Structural Origin of Reversible Li Insertion in Guest‐Free, Type‐II Silicon Clathrates |
| Journal Article | PUBDB-2021-04019 |
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2021
Wiley-VCH
Weinheim
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Please use a persistent id in citations: doi:10.1002/aesr.202000114 doi:10.3204/PUBDB-2021-04019
Abstract: The guest-free, type-II Si clathrate (Si$_{136}$) is an open cage polymorph of Si with structural features amenable to electrochemical Li storage. However, the detailed mechanism for reversible Li insertion and migration within the vacant cages of Si$_{136}$ is not established. Herein, X-ray characterization and density functional theory (DFT) calculations are used to understand the structural origin of electrochemical Li insertion into the type-II clathrate structure. At low Li content, instead of alloying with Si, topotactic Li insertion into the empty cages occurs at ≈0.3 V versus Li/Li$^+$ with a capacity of ≈231 mAh g$^{−1}$ (corresponding to composition Li$_{32}$Si$_{136}$). A synchrotron powder X-ray diffraction analysis of electrodes after lithiation shows evidence of Li occupation within the Si$_{20}$ and Si$_{28}$ cages and a volume expansion of 0.22%, which is corroborated by DFT calculations. Nudged elastic band calculations suggest a low barrier (0.2 eV) for Li migration through interconnected Si$_{28}$ cages, whereas there is a higher barrier for Li migration into Si$_{20}$ cages (2.0 eV). However, if Li is present in a neighboring cage, a cooperative migration pathway with a barrier of 0.65 eV is possible. The results show that the type-II Si clathrate displays unique electrochemical properties for potential applications as Li-ion battery anodes.
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