Three-Dimensionally Ordered Macroporous Lithium Manganese Oxide for Rechargeable Lithium Batteries

Three-dimensionally ordered macroporous (3DOM) LiMn 2 O 4 spinel was prepared by a colloidal templating process. An opal structure consisting of monodispersed poly[styrene- co -methacrilic acid] beads (380 nm in diameter) was used as a template. After infiltration of Li and Mn nitrates, the assembly was calcined in air at temperatures between 500 and 700 °C. Chemical processes were studied by means of thermal analysis, X-ray diffraction (XRD), and solid-state nuclear magnetic resonance (NMR). Morphological and microstructural characterizations were carried out by scanning and transmission electron microscopy (SEM, TEM) and by gas adsorption volumetry. Despite the simple preparation procedure, several steps are detected, which prove to be critical for the successful formation of high-quality 3DOM materials. Optimization of the preparation conditions gave extended macroporous networks with relatively smooth nanocrystalline spinel walls and a surface area of 24 m 2 /g. Porosity results from three ranges of pores: (1) the macroporous sublattice (replica of the opal lattice), (2) the pores formed after mineralization of the tetrahedral and octahedral holes of the template, and (3) the porosity from the nanocrystallites forming roughened macroporous walls. Films of 3DOM LiMn 2 O 4 were prepared on conductive substrates and used as electrodes, showing fast and reversible lithium deinsertion over a large number of cycles without suffering significant morphological or electrochemical degradation.