Electrochrmica zyxwvutsrqponmlkjihgfedcbaZYXWVUTS Acta, Vol. 40. No. 17. pp. 2723 2729. 1995 Elwier Science Ltd. Printed m Great Brltam 013 4686195 169.50 + 0.00 Pergamon 0013-4686(95)00258-8 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR INFLUENCE OF CARBON BLACK TYPE ON ANODE AND CATHODE ELECTRICAL PROPERTIES IN LI/SOC12 BATTERIES M. JAKIE,* M. KOVAC, M. GABERSCEK, and S. PEJOVNIK National Institute of Chemistry, Hajdrihova 19, 61115 Ljubljana, Slovenia zyxwvutsrqponmlkjihgfed (Received 20 February 1995; in revisedform 23 May 1995) Abstract-The purpose of the work was to find the dependence of physical and electrical properties of Li/SOCl, cathodes on the type of carbon blacks used in cathode preparation. Additionally, we tried to evaluate the possible influence of the carbon black type on anode electrical properties. The separate investigation of cathode and anode electrical properties could be realised by implementing a reference lithium electrode into the Li/SOCI, batteries under investigation. It is shown that at low frequencies (below 100 Hz) the reference electrode may serve as a relevant tool for distinguishing between the cathode and anode electrical behaviour. Before battery discharge the electrical properties of both electrodes were studied using the impedance spectroscopy as a non-destructive method, while during the discharge the potential drop on each electrode was monitored as a function of time and current. The distribution and composition of discharge products was studied using SEM/EDS analysis. Key words: lithium battery, carbon cathode. electrochemical impedance spectroscopy, SOCI,, battery capacity, voltage delay effect INTRODUCTION The role of the porous carbon cathode in Li/SOCl, batteries is two-fold: on its surface the electrochemi- cal reduction of SOCl, takes place[l-41, while inside the pores crystalline products of the reduction process are deposited[5-81. Hence, a large specific surface area assuring a low charge transfer resist- ance, and a high porosity providing enough space for deposition of reduction products, are basic requirements for a good-quality carbon cathode. In this study we try to improve the cathode characteristics by adding acetylene black with large specific area (Ketjen) to the usually used acetylene black (Knapsack). The effect of this addition on cathode physical properties is checked using mercury porosimetry and BET. A true test of cathode improvement, however, rep- resents electrochemical measurements. Electrochemi- cal characteristics of a cathode may be tested either in specially designed electrochemical cells or in real batteries. The advantage of the investigations involv- ing special electrochemical cells is that the complex battery behaviour is divided into properties of indi- vidual battery elements, ie the properties of cathode, anode, electrolyte and separator. The disadvantage, however, is that the conditions in specially designed cells are usually essentially different from those in real batteries, so the results of a cell investigation can rarely be directly applied to real batteries. In the present work we try to combine the advantages of both approaches. We decided to implement into real * Author to whom correspondence should be addressed. batteries a third electrode, which should allow for separate studies of cathode and anode properties under real-battery conditions. The relevance of the reference electrode is tested using impedance spec- troscopy. It is shown that the suggested experimental setup allows separate studies of resistive (low-fre- quency) properties of the cathode and anode before and during the battery discharge. To obtain additional information about the dis- charge process we analyse the discharge products using scanning electron microscopy/energy disper- sive spectroscopy (SEM/EDS). EXPERIMENTAL Two types of cathodes were prepared: the first type (further designated as type A) was made from Knapsack acetylene black (Hoechst) and the second type (type B) was prepared from a mixture of 70% Knapsack acetylene black (Hoechst) and 30% Ketjen black EC (Akzo Chemie). In both cases the paste was prepared from a mixture of the selected carbon black, water, iso-propanol and Teflon binder (Fluon GP 1). The two types of paste were extruded and dried under the same regime: at least 2 h in a vacuum chamber at 100°C. Specific surface area and porosity measurements of Knapsack acetylene black and Ketjen black were accomplished using the single point BET method (Micromeritics-FlowSorb Z/2300; mixture NJHe = 70% : 30%) and by mercury porosimetry (Micromeritics-Autopicnometer 1320). The electrolyte was prepared by dissolving AlCl, in the middle fraction of SOCl, until the solution 2723