NOVELTY - The electrochemical accumulator comprises an electrochemical cell (2), latent heat accumulator jackets (3) that partially surround the cell and are present in thermally conductive contact with the cell, and operating gas channels (4, 5) delimited by the accumulator jacket and the cell, where an operating gas such as air of the cell together with a gaseous reaction partner flows toward the cell and away from the cell through the gas channel. The accumulator jacket: is formed in box-shape; and in its cross-section, is thermally conductively contacted to the electrochemical cell.    USE - Used as an electrochemical accumulator.    ADVANTAGE - The electrochemical accumulator exhibits high energy efficiency and reduced temperature fluctuations and temperature gradients.    DETAILED DESCRIPTION - The electrochemical accumulator comprises an electrochemical cell (2), latent heat accumulator jackets (3) that partially surround the cell and are present in thermally conductive contact with the cell, and operating gas channels (4, 5) delimited by the accumulator jacket and the cell, where an operating gas such as air of the cell together with a gaseous reaction partner flows toward the cell and away from the cell through the gas channel. The accumulator jacket: is formed in box-shape; in its cross-section, is thermally conductively contacted to the electrochemical cell at three inner sides of the jacket; and comprises a phase change material and a porous support structure in which the phase change material is introduced. The accumulator jackets are arranged in a matrix form and formed in one-piece. A part of the accumulator jacket is arranged between one of the operation gas channels, by which the operation gas flows to the cell, and another operation gas channel, by which the operation is divertable from the cell. The electrochemical accumulator is formed as a sandwich-like stack, in which the accumulator jacket is formed of layers, between which one of the electrochemical cells is arranged. The phase change material comprises a salt, a mixture of salts, a metal and/or an alloy so that the corresponding melting temperature lies between the desired charge- and discharge temperature of the electrochemical cell. A portion of the phase change material, during the discharge of the electrochemical cell, experiences a phase transition. The electrochemical cell is: more rechargeable; and a fuel cell that is operable as an electrolyzer. The gaseous reactant is oxygen.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of an electrochemical accumulator.    Electrochemical cell (2)    Latent heat accumulator jackets (3)    Operating gas channels (4, 5)    Latent heat accumulator body (8)    Cuboidal chambers. (9)