J. Kim et A. Manthiram, SYNTHESIS, CHARACTERIZATION, AND ELECTROCHEMICAL PROPERTIES OF AMORPHOUS CRO2-DELTA -THAN-OR-EQUAL-TO-DELTA-LESS-THAN-OR-EQUAL-TO-0.5) CATHODES, Journal of the Electrochemical Society, 144(9), 1997, pp. 3077-3081
Amorphous chromium oxides CrO2-delta (0 less than or equal to delta le
ss than or equal to 0.5) have been synthesized by a reduction of K2CrO
4 with KBH4 in aqueous solutions. The samples have been characterized
by x-ray diffraction, differential scanning calorimetry, thermogravime
tric analysis, transmission electron microscopy, and iodometric titrat
ion. The oxidation state of Cr and the total oxygen content (2-delta)
generally decrease with increasing volume of KBH4 at a given pH or wit
h increasing pH at a given volume of KBH4. The amorphous CrO2-delta sa
mples lose oxygen sharply at 400 < T < 600 degrees C to give crystalli
ne Cr2O3; the temperature at which oxygen loss occurs increases from a
bout 400 degrees C for delta approximate to 0 to about 600 degrees C f
or delta approximate to 0.5. The capacity of the amorphous CrO2-delta
cathodes decreases with increasing delta due to a decreasing oxidation
state of Cr. Amorphous CrO2 shows a maximum initial capacity of 180 m
Ah/g in the range 3.3 to 2.3 V for a current density of 0.1 mA/cm(2).
Although the capacity declines during the initial cycles, it becomes s
table after about 20 cycles, for example, at about 90 mAh/g for 0.5 mA
/cm(2).