Y. Shaohorn et al., MICROSTRUCTURAL FEATURES OF ALPHA-MNO2 ELECTRODES FOR LITHIUM BATTERIES, Journal of the Electrochemical Society, 145(2), 1998, pp. 582-589
Citations number
22
Categorie Soggetti
Electrochemistry,"Materials Science, Coatings & Films
X-ray diffraction and transmission electron microscopy, including latt
ice imaging and convergent-beam electron diffraction, were used to stu
dy the microstructural features of alpha-MnO2 products that had been s
ynthesized from different precursors. The alpha-MnO2 products, which w
ere formed by acid digestion of Mn2O3 and Li2MnO3 oxide powders, conta
ined water molecules in the (2 x 2) channels of their hollandite-type
structures. The alpha-MnO2 crystals had a distinct rod-shaped morpholo
gy with the [001] crystallographic orientation parallel to the rod axi
s. Transmission electron microscopy data showed that the nature of the
precursor directly affects the grain morphology of the alpha-MnO2 pro
duct. The grain morphology of alpha-MnO2 electrodes plays an important
role in the electrochemical behavior of Li/alpha-MnO2 rechargeable ce
lls: crystals with a small aspect ratio have a large electrochemically
active surface [i.e., a large exposed (2 x 2) tunnel cross-sectional
area] per unit volume available for lithium insertion. Lattice imaging
and electron diffraction studies of chemically lithiated alpha-MnO2 p
roducts (LixMnO2: 0.4 < x < 0.5) confirmed that the alpha-MnO2 structu
re was unstable to chemical lithiation; the capacity loss that was obs
erved during the initial electrochemical cycling of Li/alpha-MnO2 cell
s is attributed to this structure instability.