LIGHTWEIGHT, STABLE, AND RECHARGEABLE BATTERY AND CAPACITOR WITH ACTIVATED CARBON FIBER ELECTRODE

Abstract

We made a rechargeable battery and an electric double layer capacitor by use of an activated carbon fiber as the electrode material. Recently, polyacetylene /1,2,3/ and poly-(p-phenylene) /4/ have been reported to be useful as the electrode material in rechargeable batteries. In the charge and discharge processes of these batteries, electrochemical doping and undoping of the material are involved. The large energy density of this kind of battery is due to the large specific surface area of polymer film. In a search for other electrode materials, we noticed that a special kind of activated carbon fiber (ACF) /5/ made from cellulose or phenolic resin has the following attractive properties as the electrode ater rial: (1) it has a much larger specific surface area (1500 2500 m2/g) than polyacetylene; ( 2 ) it has a high electrical conductivity of about 10 70 S c~n-l; (3) various types of ACF, such as felt, fiber, cloth, and paper sheet can be obtained commercially with low cost /6/; (4) it is quite a stable material in the air; (5) it has a small bulk density of 0.05 g/cm3 for a felt. We have made a rechargeable battery by use of a p-doped ACF as a cathode and lithium metal as an anode. We have also made an organic electrolyte capacitor by use of a p-doped ACF as a cathode and a n-doped ACF as an anode / 7 / . I RECHARGEABLE BATTERY 2 A felt of ACF (33 mg, 2.5 cm ) , type KF-1600 available from Toyobo Co. Ltd., and a strip of lithium were separated by a glass fiber filter of 0.25 mm thickness. They were then placed in a glass vessel containing a 1 mol dm-3 solution of LiC104 in a mixed solvent of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) in an argon atmosphere. Platinum wires attached to the ACF and lithium were connected to the positive and negative terminals of a D.C. power source, respectively. After passing 5.16 C, the battery, Li I LiC104 in PC-DYE I (ACF~+) (C104-),, was made. The molar ratio of dopant to carbon atom was . estimated to be a = 0.036 /8 / . The open circuit voltage (V,,) of 3.9 V and short-circuit current (I,,) of 203 nt4 were obtained, which correspond to a maximum power density of 20 kW/kg, based on the weight of the (ACF~') (C1O4-), and that of lithium consumed. Figure 1 shows the charge-discharqe characteristics of the ACF battery under a Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19833113