Rechargeable Li-ion battery anode of indium oxide with visible to infra-red transparency

Unique bimodal distributions of single crystal epitaxially grown In ₂O₃ nanodots on silicon are shown to have excellent IR transparency greater than 87% at 4 μm without sacrificing transparency in the visible region. These broadband antireflective nanodot dispersions are grown using a two-step metal deposition and oxidation by molecular beam epitaxy, and backscattered diffraction confirms a dominant (111) surface orientation. We detail the growth of a bimodal size distribution that facilitates good surface coverage (80%) while allowing a significant reduction in In₂O ₃ refractive index. The (111) surface orientation of the nanodots, when fully ripened, allows minimum lattice mismatch strain between the In ₂O₃ and the Si surface. This helps to circumvent potential interfacial weakening caused by volume contraction due to electrochemical reduction to indium, or expansion during lithiation. Cycling under potentiodynamic conditions shows that the transparent anode of nanodots reversibly alloys lithium with good Coulombic efficiency, buffered by co-insertion into the silicon substrate. These properties could potentially lead to further development of similarly controlled dispersions of a range of other active materials to give transparent battery electrodes or materials capable of non-destructive in-situ spectroscopic characterization during charging and discharging.