High Lithium Concentrations in Covalently Bonded Germanium Nanoparticle Assembled Layers

Germanium nanoparticles have impressive potential for use in Li-batteries due to their extremely high volumetric Li absorption capacity. By reducing the size of the nanoparticles, the embrittlement associated with Li absorption is reduced due to their ability to “breath,” accommodating for lattice expansion. This raises the question at which lithium concentration the nanoparticles start cracking and fragmenting. In this work, very small and ultra clean germanium nanoparticles were fabricated by magnetron sputtering and investigated with a suite of techniques. The invisibility of highly disordered germanium oxide for Raman spectroscopy, complemented with the oxide sensitive X-ray absorption spectroscopy (XAFS), provided differentiated information about the crystalline and oxidized states of both the pre- and post-lithiation, respectively. A current-density limit for lithium absorption was found to preserve the integrity of the germanium nanoparticles, after which the nanoparticles cracked and dislodged into the electrolytic solution. The ability to follow the process of lithiation ex situ with complementary techniques considerably simplify future experimentation on similar systems.