Journal
JOURNAL OF MATERIALS CHEMISTRY A
Volume 2, Issue 34, Pages 13976-13982Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c4ta01614a
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Improvements in the electrical conductivity and lithium (Li) mobility for Li ion batteries are of particular importance for their high-power applications. Mapping of electron energy loss spectroscopy shows that the electrochemical reaction front region is under electron-rich conditions during lithiation. In this paper, the electron-rich effect on the diffusion behaviors of Li in pristine and phosphorus-doped group IVA elements, e. g., silicon, germanium and tin, were investigated using the first principles density functional theory (DFT) calculations in combination with a climbing-image nudged elastic band and ab initio DFT molecular dynamics. Phosphorus doping was found to be a non-critical factor for enhanced Li diffusion into Si. Instead, the results showed that the diffusion barriers and diffusivity of Li are mainly affected by the electron-rich effect, i.e. the energy barriers decrease and diffusivity increases in an electron-rich environment. The decrease in diffusion barriers was attributed to the relaxation of Si-Si bonds with extra electrons, which can also apply to the case of Ge but not for metallic Sn. These new findings provide a theoretical and experimental basis for the design and fabrication of next generation batteries with a high power density.
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