Application of potentially biodegradable polyamide and polyester containing disulfide bonds to positive active materials
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Introduction Light and high power secondary batteries are important devices for lightening potable electrical equipment, such as cellular phone, portable computer. Lithium or lithium-ion batteries are powerful candidates. Lithium cobalt oxide (LiCoO2) is used for a positive active material of lithium-ion practical secondary batteries[l]. However, estimated amount of cobalt (25 ppm) in the earth's crust is lower than that of iron (5.63 %), manganese (950 ppm), sulfur (260 ppm), and
carbon (200 ppm) [2]. New positive active material not based on cobalt for lithium or lithium-ion batteries is indispensable to construct a practical high power secondary battery in future. Use of organosulfur compounds, such as 2, 5-dimercapt-1, 3, 4-thiadiazole (DMcT), for positive active material of high power secondary lithium batteries have been also investigated and reported by Visco's [3-5] and Oyama's groups [6-8]. The theoretical capacity of DMcT is 362 Ah kg" 1 . Furthermore, the redox reaction of organosulfur compounds (R-S-S-R + 2e- = 2(RS-)) is usually reversible. We have investigated other organosulfur polymers which can be used as a positive active material for lithium batteries [9-12]. We think that the advantage of the organosulfur compounds is not only their high energy capacity but also their biodegradability. About 6 billion cells were produced in Japan on 1995 [13]. Wastes of batteries have also increased. Usual rechargeable batteries, such as lead-acid, nickel-cadmium, lithium-ion battery, contain heavy metals which are expected to pollute our environment. Recycling of the metals has been investigated. However, those materials is not recycled perfectly. Secondary batteries containing biodegradable materials are preferable for the natural environment. In this paper we propose that polyamide and polyester containing disulfide bonds are not only prefer to the positive active materials of lithium secondary batteries with high capacity and but also to the biodegradative electrode materials. Figure 1 shows their structures and their theoretical capacities. The disulfide bonds in the polyamide or polyester act as redox centers for battery reaction and the amide or ester bonds in the chain are hydrolyzed in the outdoor environment. The polyamide and polyester has intrinsic electric conductivity. Thus polymergraphite mixtures were prepared and used for all the electrochemical measurements.
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Mat. Res. Soc. Symp. Proc. Vol. 496 01998 Materials Research Society
-(NH
-C-CH2 -0H 2 -S-S-CH2-CH 2-C-NH -CH 2-CH 2 -S-S-CH2-CH
6
6
2
n
PIDI (328 Ah kg- 1 ) O-C-CH2 -CH 2 -S-S-CH2 -CH 2 -C-O- CH 2
/
CH 2
0n
0
PODOM (172 Ah kg 1 )
O\
C -CH2-CH2-S-S--CH 2-CH2-G-O-CH 2-O)2 --'_G...-CH nIl 11 11 0 0 o 0
p
1
c-PODOM (135 Ah kg ) Figure 1. Structures of PIDI, PODOM, and c-PODOM, and their theoretical capacities. EXPERIMENT Materials 3, Y-Dithiodipropionic acid (Aldrich), cystamine (Ishizu), 1, 4-benzenedimethanol (Ishizu), and acetonitrile (HPLC grade, Ishizu) were used as received. Propylene carbonate (PC) and 1, 2-dimeth
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