A THEORETICAL-MODEL FOR COMPOSITE ELECTROLYTES .2. PERCOLATION MODEL FOR IONIC-CONDUCTIVITY ENHANCEMENT

A novel method of a combination of a percolation model with the space charge layer model is derived. For the first time, this gives an analytical solution for the ionic-conductivity enhancement of composite electrolytes, The conductivity enhancement is directly related to the size of second phase particles and matrix particles, the density of the defects as charge carriers and temperature. The theoretical optimum-content of the second phase with an ideal random distribution is solved as 40 vol%. At the optimum-content, the ionic conductivity of the composite electrolytes reaches the maximum. With the introduction of the non-ideal random distribution of matrix particles or second phase particles, an analytical solution based on the percolation model was derived. The theoretical results fit the experimental data quantitatively very well for LiI/Al2O3 and CuCl/Al2O3 systems in the whole range of the second phase content admired in the matrix. The shift effect of optimum-content away from the theoretical optimum-content of 40 vol%, the reason for which is unknown so far, is caused by the non-uniform distribution of either matrix particles or second phase particles and this non-uniform distribution always degenerates the conductivity enhancement seriously.