Biofunctional hollow γ-MnO 2 microspheres by a one-pot collagen-templated biomineralization route and their applications in lithium batteries.

γ-MnO 2 nanomaterials play an essential role in the development of advanced electrochemical energy storage and conversion devices with versatile industrial applications. Herein, novel dandelion-like hollow microspheres of γ-MnO 2 mesocrystals have been fabricated for the first time by a one-pot biomineralization route. Recombinant collagen with unique rod-like structure has been demonstrated as a robust template to tune the morphologies of γ-MnO 2 mesocrystals, and a very low concentration of collagen can alter the nanostructures of γ-MnO 2 from nanorods to microspheres. The as-prepared γ-MnO 2 mesocrystals formed well-ordered hollow microspheres composed of delicate nanoneedle-like units. Among all the reported γ-MnO 2 with various nanostructures, the γ-MnO 2 microspheres showed the most prowess to maintain high discharge capacities after 100+ cycles. The superior electrochemical performance of γ-MnO 2 likely results from its unique hierarchical micro-nano structure. Notably, the γ-MnO 2 mesocrystals display high biocompatibility and cellular activity. Collagen plays a key dual role in mediating the morphology as well as endowing the biofunction of the γ-MnO 2 mesocrystals. This environmentally friendly biomineralization approach using rod-like collagen as the template, provides unprecedented opportunity for the production of novel nanostructured metal oxides with superior biocompatibility and electrochemical performance, which have great potential in advanced implantable and wearable health-care electronic devices.