Y. Shaohorn et al., MORPHOLOGY MODIFICATION AND DELITHIATION MECHANISMS OF LIMN2O4 AND LI2MNO3 BY ACID DIGESTION, Journal of the Electrochemical Society, 145(1), 1998, pp. 16-23
Citations number
22
Categorie Soggetti
Electrochemistry,"Materials Science, Coatings & Films
The structural features of equilibrium phases, LiMn2O4 and Li2MnO3, an
d their acid-delithiated products (MnO2) are compared using x-ray diff
raction and electron microscopy. The observed morphological changes as
sociated with acid-delithiated Li0.1Mn2O4 confirm the acid digestion m
echanism proposed by Hunter. Three delithiated phases including alpha-
, gamma-, and beta-MnO2-like phases can be derived from Li2MnO3 under
different acid digestion conditions. An acid-delithiation mechanism co
nverting Li2MnO3 to alpha- and gamma-MnO2 is proposed. This mechanism
involves an acid-dissolution and precipitation process. A related sche
me is also proposed for the formation of beta-MnO2-like materials from
alpha- and gamma-MnO2 phases. The crystallography of the alpha-MnO2 s
tructure is related to the grain/crystal geometry of alpha-MnO2 on the
basis of convergent-beam electron diffraction and lattice imaging ana
lysis. An in situ heating experiment in a transmission electron micros
cope demonstrates that heat-treatment of hydrated alpha-MnO2 at simila
r to 300 degrees C develops porosity within grains/crystals. It is pro
posed that the microstructural changes induced by acid delithiation ma
y contribute to the reported difference in the initial electrochemical
behavior of acid delithiated Li0.1Mn2O4 and equilibrium LiMn2O4. The
delithiated product derived from Li2MnO3 at similar to 115 degrees C f
or 4-6 h, having gamma-MnO2 as the major phase, demonstrates superior
electrochemical properties.