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

Abstract

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 α-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 α-Mn2O3 octahedra. This co-precipitation approach is advantageous because it can generate large amounts of monodisperse nanocrystals at low economic cost. α-Mn2O3 is an alternative lithium ion battery (LIB) anode material that is earth abundant and has ∼2.7 times higher capacity than conventional graphite anodes. We assembled the monodisperse α-Mn2O3 octahedra into LIB anodes to examine their performance in a realistic device. The α-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 α-Mn2O3 octahedra to the lack of agglomeration in the uniformly distributed electrode and improved lithiation of single crystalline α-Mn2O3 nanoparticles.