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The performances of a Li-O battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, LiO forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO, which subsequently disproportionates into LiO and O. The release of O creates a hollow nanostructure with LiO outer-shell and LiO inner-shell surfaces. Our findings show that, in general, the way the released O is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O cells.

Aggregation-induced emission (AIE) has, since its discovery, become a valuable tool in the field of nanoscience. AIEgenic molecules, which display highly stable fluorescence in an assembled state, have applications in various biomedical fields—including photodynamic therapy. Engineering structure-inherent, AIEgenic nanomaterials with motile properties is, however, still an unexplored frontier in the evolution of this potent technology. Here, we present phototactic/phototherapeutic nanomotors where biodegradable block copolymers decorated with AIE motifs can transduce radiant energy into motion and enhance thermophoretic motility driven by an asymmetric Au nanoshell. The hybrid nanomotors can harness two photon near-infrared radiation, triggering autonomous propulsion and simultaneous phototherapeutic generation of reactive oxygen species. The potential of these nanomotors to be applied in photodynamic therapy is demonstrated in vitro, where near-infrared light directed motion and reactive oxygen species induction synergistically enhance efficacy with a high level of spatial control.

Designer particles that are embued with nanomachinery for autonomous motion have great potential for biomedical applications; however, their development is highly demanding with respect to biodegradability/compatibility. Previously, biodegradable propulsive machinery based on enzymes has been presented. However, enzymes are highly susceptible to proteolysis and deactivation in biological milieu. Biodegradable hybrid nanomotors powered by catalytic inorganic nanoparticles provide a proteolytically stable alternative to those based upon enzymes. Herein we describe the assembly of hybrid biodegradable nanomotors capable of transducing chemical energy into motion. Such nanomotors are constructed through a process of compartmentalized synthesis of inorganic MnO 2 nanoparticles (MnPs) within the cavity of organic stomatocytes. We show that the nanomotors remain active in cellular environments and do not compromise cell viability. Effective tumor penetration of hybrid nanomotors is also demonstrated in proof-of-principle experiments. Overall, this work represents a new prospect for engineering of nanomotors that can retain their functionality within biological contexts.

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Instability of carbon-based oxygen electrodes and incomplete decomposition of LiCO during charge process are critical barriers for rechargeable Li-O batteries. Here we report the complete decomposition of LiCO in Li-O batteries using the ultrafine iridium-decorated boron carbide (Ir/BC) nanocomposite as a noncarbon based oxygen electrode. The systematic investigation on charging the LiCO preloaded Ir/BC electrode in an ether-based electrolyte demonstrates that the Ir/BC electrode can decompose LiCO with an efficiency close to 100% at a voltage below 4.37 V. In contrast, the bare BC without Ir electrocatalyst can only decompose 4.7% of the preloaded LiCO. Theoretical analysis indicates that the high efficiency decomposition of LiCO can be attributed to the synergistic effects of Ir and BC. Ir has a high affinity for oxygen species, which could lower the energy barrier for electrochemical oxidation of LiCO. BC exhibits much higher chemical and electrochemical stability than carbon-based electrodes and high catalytic activity for Li-O reactions. A Li-O battery using Ir/BC as the oxygen electrode material shows highly enhanced cycling stability than those using the bare BC oxygen electrode. Further development of these stable oxygen-electrodes could accelerate practical applications of Li-O batteries.

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