Abstract: AN electrochemical cell which comprises a conductive anode and cathode capable of mutual electrochemical reaction and separated by a solid electrolyte comprising:(a) a matrix of sheets of atoms, having side-chains linked to the sheets, which side chains comprise polar groups free from active hydrogen atoms,(b) a polar aprotic liquid dispersed in the matrix, and(c) a highly ionized ammonium or alkali metal salt dissolved in the matrix and/or liquid,a cathode therefor, the electrolyte per se, and processes for the preparation of the electrolyte and the cathode.