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 NO_x 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.