Details

Autor(en) / Beteiligte

• Jung, Hyeyoung
• Allan, Phoebe K
• Hu, Yan-Yan
• Borkiewicz, Olaf J
• Wang, Xiao-Liang
• Han, Wei-Qiang
• Du, Lin-Shu
• Pickard, Chris J
• Chupas, Peter J
• Chapman, Karena W
• Morris, Andrew J
• Grey, Clare P

Titel

Elucidation of the Local and Long-Range Structural Changes that Occur in Germanium Anodes in Lithium-Ion Batteries

Ist Teil von

• Chemistry of materials, 2015-02, Vol.27 (3), p.1031-1041

Ort / Verlag

American Chemical Society

Erscheinungsjahr

2015

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Metallic germanium is a promising anode material in secondary lithium-ion batteries (LIBs) due to its high theoretical capacity (1623 mAh/g) and low operating voltage, coupled with the high lithium-ion diffusivity and electronic conductivity of lithiated Ge. Here, the lithiation mechanism of micron-sized Ge anodes has been investigated with X-ray diffraction (XRD), pair distribution function (PDF) analysis, and in-/ex-situ high-resolution 7Li solid-state nuclear magnetic resonance (NMR), utilizing the structural information and spectroscopic fingerprints obtained by characterizing a series of relevant Li x Ge y model compounds. In contrast to previous work, which postulated the formation of Li9Ge4 upon initial lithiation, we show that crystalline Ge first reacts to form a mixture of amorphous and crystalline Li7Ge3 (space group P3212). Although Li7Ge3 was proposed to be stable in a recent theoretical study of the Li–Ge phase diagram ( Morris, A. J. ; Grey, C. P. ; Pickard, C. J. Phys. Rev. B: Condens. Matter Mater. Phys. 2014, 90, 054111 ), it had not been identified in prior experimental studies. Further lithiation results in the transformation of Li7Ge3, via a series of disordered phases with related structural motifs, to form a phase that locally resembles Li7Ge2, a process that involves the gradual breakage of the Ge–Ge bonds in the Ge–Ge dimers (dumbbells) on lithiation. Crystalline Li15Ge4 then grows, with an overlithiated phase, Li15+δGe4, being formed at the end of discharge. This study provides comprehensive experimental evidence, by using techniques that probe short-, medium-, and long-range order, for the structural transformations that occur on electrochemical lithiation of Ge; the results are consistent with corresponding theoretical studies regarding stable lithiated Li x Ge y phases.