A lithium conducting phase (Li₂Te) can obviate need for nanocrystallites in the lithiation/de-lithiation of Germanium

Mainstream rechargeable lithium battery materials research of the past 20 years has focused on nano-particulate materials, where Li⁺-diffusion lengths exceeded at designated cycling rates the particle radii, and where the particles slipped rather than broke upon their expansion and shrinkage in lithiation/de-lithiation cycles. Here we show that in intrinsically rapidly Li⁺-transporting macrocrystalline germanium and even more so in a dispersion of non-cycling Li₂Te in macrocrystalline germanium it is unnecessary to use nanocrystalline materials and that Li₂Te increases the retained capacity at 1C rate after 500 cycles. Dispersions of 10-30 atom % of crystalline GeTe in 90-70 atom % crystalline Ge were synthesized by quenching from the melt followed by high energy ball milling to 1μm-5μm particle size. The particles, as well as similarly made and similarly sized pure Ge particles were incorporated in electrodes, which were galvanostatically lithiated/de-lithiated. In the initial cycle, GeTe is reduced to Li[subscript x]Ge alloys and Li₂Te. In 500 1C cycles of Li[subscript x]Ge de-lithiation/Ge lithiation the capacity of the pure Ge faded more rapidly than that of the Ge electrodes containing Li₂Te, which retained 94-96 % of their initial capacity after 500 cycles at 1C rate.