Miniature all-solid-state heterostructure nanowire Li-ion batteries as a tool for engineering and structural diagnostics of nanoscale electrochemical processes.

Complex interfacial phenomena and phase transformations that govern the operation of Li-ion batteries require detailed nanoscale 3D structural and compositional characterization that can be directly related to their capacity and electrical transport properties. For this purpose, we have designed model miniature all solid-state radial heterostructure Li-ion batteries composed of LiCoO2 cathode, LiPON electrolyte and amorphous Si anode shells, which were deposited around metallized high-aspect-ratio Si nanowires as a scaffolding core. Such diagnostic batteries, the smallest, complete secondary Li-ion batteries realized to date, were specifically designed for in situ electrical testing in a field-emission scanning electron microscope and/or transmission electron microscope. The results of electrochemical testing were described in detail in a previous publication (Nano Lett., 2012, 12, 505-511). The model Li-ion batteries allow analysis of the correlations between electrochemical properties and their structural evolution during cycling in various imaging, diffraction and spectroscopic modes down to the atomic level. Employing multimode analytical scanning/transmission electron microscopy imaging coupled with correlative multivariate statistical analysis and tomography, we have analyzed and quantified the 3D morphological and structural arrangement of the batteries, including textured platelet-like LiCoO2 nanocrystallites, buried electrode-electrolyte interfaces and hidden internal defects to clarify effects of scaling on a battery's electrochemical performance. Characterization of the nanoscale interfacial processes using model heterostructure nanowire-based Li-ion batteries provides useful guidelines for engineering of prospective nano-sized building blocks in future electrochemical energy storage systems.