LIMN2-XCUXO4 SPINELS LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5) - A NEW CLASS OF 5 V CATHODE MATERIALS FOR LI BATTERIES - I - ELECTROCHEMICAL, STRUCTURAL, AND SPECTROSCOPIC STUDIES
Y. Eineli et al., LIMN2-XCUXO4 SPINELS LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.5) - A NEW CLASS OF 5 V CATHODE MATERIALS FOR LI BATTERIES - I - ELECTROCHEMICAL, STRUCTURAL, AND SPECTROSCOPIC STUDIES, Journal of the Electrochemical Society, 145(4), 1998, pp. 1238-1244
Citations number
26
Categorie Soggetti
Electrochemistry,"Materials Science, Coatings & Films
A series of electroactive spinel compounds, LiMn2-xCuxO4 (0.1 less tha
n or equal to x less than or equal to 0.5), has been studied by crysta
llographic, spectroscopic, and electrochemical methods and by electron
microscopy. These LiMn2-xCuxO4, spinels are nearly identical in struc
ture to cubic LiMn2O4 and successfully undergo reversible Li intercala
tion. The electrochemical data show a remarkable reversible electroche
mical process at 4.9 V which is attributed to the oxidation of Cu2+ to
Cu3+. The inclusion of Cu in the spinel structure enhances the electr
ochemical stability of these materials upon cycling. The initial capac
ity of LiMn2-xCuxO4 spinels decreases with increasing x from 130 mAh/g
in LiMn2O4 (x=0) to 70 mAh/g in ''LiMn1.5Cu0.5O4'' (x=0.5). The data
also show slight shifts to higher voltage for the delithiation reactio
n that normally occurs at 4.1 V in standard Li1-xMn2O4 electrodes (1 g
reater than or equal to x greater than or equal to 0) corresponding to
the oxidation of Mn3+ to Mn4+. Although the powder X-ray diffraction
pattern of ''LiMn1.5Cu0.5O4'' shows a single-phase spinel product, neu
tron diffraction data show a small but significant quantity of an impu
rity phase, the composition and structure of which could not be identi
fied. X-ray absorption spectroscopy was used to gather information abo
ut the oxidation states of the manganese and copper ions. The composit
ion of the spinel component in the LiMn1.5Cu0.5O4 was determined from
X-ray diffraction and X-ray absorption near-edge spectroscopy to be Li
1.01Mn1.67Cu0.32O4, suggesting to a best approximation that the impuri
ty in the sample was a lithium-copper-oxide phase. The substitution of
manganese by copper enhances the reactivity of the spinel structure t
oward hydrogen: the compounds are more easily reduced at moderate temp
erature (similar to 200 degrees C) than LiMn2O4.