IN-SITU MEASUREMENTS OF DRASTIC CHANGE OF ELECTRICAL-CONDUCTIVITY ANDSTRUCTURE UPON ELECTROCHEMICAL LITHIUM INTERCALATION IN PYROLYZED POLY(HYDRAZOCARBONYL-1-4-PHENYLENECARBONYL) FILM

Drastic changes of structure and electrical property of pyrolyzed poly mers based on poly(hydrazocarbonyl-1,4-phenylenecarbonyl) (poly(tereph thalohydrazide)) film have been investigated in an electrochemical cel l with 1 M LiClO4 in a 70:30 mixture of propylene carbonate and 1,2-di methoxyethane as the electrolyte, by means of in situ measurement tech niques using the four-probe conductivity measurement method and X-ray diffraction method with a beryllium window. In the first redox cycle, the highly crystallized graphite prepared by pyrolysis at 2800 degrees C exhibits large irreversible changes in both apparent conductivity a nd the layered structure, whereas the poorly crystallized carbon prepa red by pyrolysis at 1300 degrees C showed a good reversible change in structure but a large decrease in conductivity compared with that of t he pristine sample. The two characteristic X-ray diffraction peaks of the distorted graphite layer observed only in the first discharge are attributed to the decomposition reaction of electrolyte and lithium io ns in graphite layers. The passivation film formed on the surface by t he first discharge also affects the characteristics. In the film prepa red by pyrolysis at 1300 degrees C, damage of disordered carbon layer structures occurred in the first charge process. The apparent diffusio n coefficient of lithium in the disordered carbon was larger than that in graphite, and was activated with increasing number of cycles, whil e that of graphite was independent of the number of cycles.