The Effect of Various Contents of PTFE on the electrochemical performance of the Acetylen Black-Polytetrafluoroethylene Composite Cathode in Lithium- Thionyl Chloride Batteries

Lithium-thionyl chloride cell (Li-SOCl2) has a metallic lithium anode and a liquid cathode comprising a porous carbon current collector filled with thionyl chloride. It delivers a voltage of 3.6V and is cylindrical in shape, in 1/2AA to D size, with spiral electrodes for power applications and bobbin construction for prolonged discharge. Among of all primary batteries, lithium thionyl chloride batteries have the highest voltage and energy, longest storage period, and the least selfdischarge rate. Those batteries are suitable for such long-term applications as power for electric devices and electric power, water and gas meters, and especially as a backup power source for memory ICs. The cathode is made of highly porous Teflon-bonded carbon black whose electronic conductivity is needed for the charge transfer to take place. Thionyl chloride cathodic reduction is catalyzed by the cathode surface when a load is connected. The pores of the carbon cathode retain both the reactants and the products of this process. It is well known that in case of discharge, reaction products of LiCl, SO2 and S are created caused by chemical reaction [1]. Lithium chloride and Sulfur in a solid phase deposited to porous carbon cathode. Therefore, cathode should provide enough pore space until completion of discharge and efficient structural design is required because speed of reaction products deposition is different according to discharge current. PTFE increases the mechanical strength of porous carbon cathode but also decreases the electrical conductivity of positive electrode and it occupies the pores of acetylene black, that it can cause a drastic failure in the performance of the battery [2]. The chief objective of this work is to evaluate the effect of various contents of polytetrafluoroethylene on electrochemical performance of positive electrode in lithium thionyl chloride battery. Polarization curves indicate that the performance of a Li/SOCl2 battery is 269 sensitive to the Acetylen-Black: PTFE (AB/P) ratio in the cathode. All electrochemical characteristics were measured by SCRIBNER 850E test station. The electrochemical measurements were carried out in a designed test cell which made by PTFE and 316 stainless steel. An optimal value of 40 wt. % PTFE in Acetylen-Black was found to be the best to balance the structural strength of cathode and the battery electrochemical performance based on polarization curve and discharge profile. Figure 8. Voltage plateau versus Current at mid-discharge for various kinds of cathode composites