Microstructural features of α-MnO < inf> 2 electrodes for lithium batteries

Document Type

Article

Publication Date

1-1-1998

Abstract

X-ray diffraction and transmission electron microscopy, including lattice imaging and convergent-beam electron diffraction, were used to study the microstructural features of α-MnO2 products that had been synthesized from different precursors. The α-MnO2 products, which were formed by acid digestion of Mn2O3 and Li2MnO3 oxide powders, contained water molecules in the (2 × 2) channels of their hollandite-type structures. The α-MnO2 crystals had a distinct rod-shaped morphology with the [001] crystallographic orientation parallel to the rod axis. Transmission electron microscopy data showed that the nature of the precursor directly affects the grain morphology of the α-MnO2 product. The grain morphology of α-MnO2 electrodes plays an important role in the electrochemical behavior of Li/α-MnO2 rechargeable cells: crystals with a small aspect ratio have a large electrochemically active surface [i.e., a large exposed (2 × 2) tunnel cross-sectional area] per unit volume available for lithium insertion. Lattice imaging and electron diffraction studies of chemically lithiated α-MnO2 products (LixMnO2: 0.4 < x < 0.5) confirmed that the α-MnO2 structure was unstable to chemical lithiation; the capacity loss that was observed during the initial electrochemical cycling of Li/α-MnO2 cells is attributed to this structure instability.

Publication Title

Journal of the Electrochemical Society

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