Biomineralization-inspired crystallization of monodisperse alpha -Mn2O3 octahedra and assembly of high-capacity lithium-ion battery anodes

Uniform colloidal building-blocks enable the creation of more stable, structurally sophisticated materials. Here we describe a simple polymer-mediated approach to generate grams of monodisperse, single-crystal alpha -Mn2O3 nanocrystals bound by {111} facets. The technique is inspired in part by biomineralization, where organisms use macromolecular matrices or compartments to trigger the oriented nucleation and growth of crystalline phases. Polyvinylpyrrolidone (PVP) behaves as a polymeric nano-reactor by coordinating to the manganese (Mn) precursor while recruiting the NOx oxidizing agent from solution to drive the co-precipitation of the manganese oxide. PVP also serves as a molecular template to guide the nucleation of trigonal bipyramids composed of Mn3O4. The porosity of the Mn3O4 particles indicates that they form non-classically via oriented attachment instead of atom-by-atom. The particles are further oxidized and transform into single-crystal alpha -Mn2O3 octahedra. This co-precipitation approach is advantageous because it can generate large amounts of monodisperse nanocrystals at low economic cost. alpha -Mn2O3 is an alternative lithium ion battery (LIB) anode material that is earth abundant and has similar to 2.7 times higher capacity than conventional graphite anodes. We assembled the monodisperse alpha -Mn2O3 octahedra into LIB anodes to examine their performance in a realistic device. The alpha -Mn2O3 octahedra exhibit good rate performance, cycling stability, coulombic efficiency and morphology retention during extended lithiation-delithiation cycles compared to previous reports for this material. We attribute the improved electrochemical performance of the alpha -Mn2O3 octahedra to the lack of agglomeration in the uniformly distributed electrode and improved lithiation of single crystalline alpha -Mn2O3 nanoparticles.