Surface-modified Manganese Dioxide for Alkaline-Manganese Battery
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The synthesis of SMMD was performed by mixing electrolytic manganese dioxide (EMD) powder into the aqueous solution which consists of 2M-H 2SO4 and 0.06M-Ti(SO 4)2, and stirring for a hour at 70 0C. Battery grade EMD of which average particle size is 40 g m, and reagent grade titanic sulfate (Ti(S0 4)2-9H 2 0) was used. After the treatment, the compound was filtered, washed with distilled water, neutralized by aqueous solution with potassium hydroxide, and then dried. Test conditions for the electrochemical behavior The discharge characteristic in alkaline aqueous solution of SMMD was tested by using half-cell. The cathode electrode was composed of the mixture of 0.1 g manganese dioxide and 0.01g acetylene black. The electrolyte was prepared by the solution of 9M-KOH with 0.3MZnO. The reference electrode was Hg/HgO electrode, and the counter electrode was Pt plate. It was tested under the condition of current density at 1.07mA/g in the room temperature. Characterization In order to investigate the characteristics of specimen, characterization was performed by following techniques. The distribution of Ti in SMMD particles was measured with EPMA (EDAX-DX4). Ti content was measured by fluorescent X-ray spectroscopy. XAFS measurement was carried out by fluorescent method at the Photon-factory of High Energy Accelerator Research Organization in Japan. Inter-atomic distances and coordination 109
Mat. Res. Soc. Symp. Proc. Vol. 575 ©2000Materials Research Society
numbers of the specimen were obtained from EXAFS(extended X-ray absorption fine structure) by using curve fitting. For Raman Spectroscopy measurement, Ramanor T-64000 (Jobin Yvon) and Ar laser as light source were used. ESR measurement was carried out at the temperature of 1OK, using ESP 350E (BRUKER). RESULTS AND DISCUSSION Content and distribution of Ti in SMMD particles Ti content in SMMD was 0.8 weight% from fluorescent X-ray spectroscopy measurement. Figure 1 shows SEM image and Ti distribution of SMMD particle section. In figure 1, Ti is distributed mainly on the surface of the particles. Discharge characteristic Figure 2 shows the discharge characteristic of SMMD and conventional EMD. At the potential range of -0.3V vs.Hg/HgO, the slight potential drop is observed in EMD, presumably due to a formation of Hetaerolite, while no potential drop can be seen in SMMD at the same potential. This contributes to the increase in the discharge capacity of SMMD. Characterization of SMMD The characterization of SMMD was carried out being compared with the mixture of 1.0 weight% Anatase type TiO 2 (Anatase-EMD mixture) and EMD ,and non-treated EMD.
SEM image
Ti distribution
Fig. 1 SEM image and Ti distribution of SlMD particles section 0.3 =- 0.1 >
Fig.2 Discharge curves of SMMD and END tested with cathode half-cell
Discharge end voltage ffor Alkaline manganese batt ttery
-0.1
"w -0.3 l_
•SMM"-.D --E:MD
O -0.5 -0.7
0
50
100
150 200 250 300 Discharge capacity (mAh/g)
110
350
400
1.4
220
1. 65 2
170
Ate--mixuAnatase-Er
0.2
s
1 20
0
-80
4960
