Aprotic Li-O batteries represent promising alternative devices for electrical energy storage owing to their extremely high energy densities. Upon discharge, insulating solid LiO forms on cathode surfaces, which is usually governed by two growth models, namely the solution model and the surface model. These LiO growth models can largely determine the battery performances such as the discharge capacity, round-trip efficiency and cycling stability. Understanding the LiO formation mechanism and controlling its growth are essential to fully realize the technological potential of Li-O batteries. In this review, we overview the recent advances in understanding the electrochemical and chemical processes that occur during the LiO formation. In the beginning, the oxygen reduction mechanisms, the identification of O/LiO intermediates, and their influence on the LiO morphology have been discussed. The effects of the discharge current density and potential on the LiO growth model have been subsequently reviewed. Special focus is then given to the prominent strategies, including the electrolyte-mediated strategy and the cathode-catalyst-tailoring strategy, for controlling the LiO growth pathways. Finally, we conclude by discussing the profound implications of controlling LiO formation for further development in Li-O batteries.

To investigate the influence of surface-functionalized substrates with nanostructures on the behaviors of mesenchymal stem cells, we conjugated bone morphogenetic protein 2 (BMP2) onto TiO(2) nanotubes with different diameter sizes of 30, 60, and 100 nm for in vitro study. Polydopamine was employed as the intermediate layer for the conjugation of BMP2. The successful conjugation of BMP2 onto TiO(2) nanotubes was revealed by field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. Immunofluorescence staining of vinculin, osteocalcin (OCN), and osteopontin (OPN) revealed that BMP2-functionalized TiO(2) nanotubes was favorable for cell growth. More importantly, MSCs cultured onto BMP2-functionalized TiO(2) nanotubes displayed significantly higher (p < 0.05 or p < 0.01) differentiation levels of ALP and mineralization after 7 and 14 day cultures, respectively. The results suggested that surface functionalization of TiO(2) nanotubes with BMP2 was beneficial for cell proliferation and differentiation. The approach presented here has potential application for the development of titanium-based implants for enhanced bone osseointegration.

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