STRESS IN CARBON-FILM ELECTRODES DURING LI+ ELECTROCHEMICAL INTERCALATION

The mechanical deformation of thin films and membrane carbon electrode s during galvanostatic charge-discharge cycles has been measured by a simple optical technique. We have considered the deformations of coke and of graphite membrane electrodes to be due to the variations in the volume of grains and to the surface forces resulting from the electro chemical double layer. For such composite electrodes the minimum stres s can be associated with the potential of zero charge of the electrode . The results show that the stress Is due mainly to variations of volu me in nonporous electrodes, to surface forces, and to the presence of passivating layers in very porous electrodes. The stress observed in t he membrane electrodes after Li+ intercalation consists of an irrevers ible compressive tension and results in a permanent deformation of the electrodes.