Synthesis of a Li−Mn-oxide with Disordered Layer Stacking through Flocculation of Exfoliated MnO₂ Nanosheets, and Its Electrochemical Properties

Abstract

A new type of layered Li−Mn-oxide with heavy stacking faults has been synthesized via flocculation of delaminated MnO 2 nanosheets with Li ions. Flocculated products were characterized by powder X-ray diffraction, thermal analysis, scanning electron microscopy, transmission electron microscopy, chemical analysis, N 2 adsorption, and electrochemical measurements. Chemical analysis and X-ray diffraction results indicated that the colloidal MnO 2 nanosheets were restacked to produce a lamellar material Li 0.36 MnO 2 ·1.15H 2 O with a basal distance of 0.72 nm. Simulation of the X-ray diffraction profile suggested that the sheet-to-sheet registry was nearly random with partial order (20−40%) involving a shift vector of ( 1 / 3, 2 / 3, 1). A disordered mesoporous texture was resulted via the stacking of a limited number of the sheets and irregular aggregation of the resulting restacked crystallites. The structure proved to be stable during low-temperature soft-chemical synthetic processes while thermo-metastable upon heat treatment. A dehydrated sample of this new layered Li−Mn-oxide underwent electrochemical Li + insertion/extraction behavior with smooth cycling curves.