A sodium-sulfur battery according to the present invention is provided with a reservoir space 100 that retains and solidifies a high-temperature molten material having flowed out of a cell 4, in order to prevent the high-temperature molten material from leaking out of a casing 1, even when an accident occurs to generate the high-temperature molten material inside the casing. The reservoir space 100 can be formed along a perimeter of the casing 1, or alternatively, can be formed inside the casing 1. The reservoir space 100 includes, for example, a composite member 15 of a rigid member 11, a heat-insulating material 12, and a heat-resisting material 13.

An electrochemical storage device has an anode chamber filled with anode material during operation, and a cathode chamber filled with cathode material. The anode chamber is separated from the cathode chamber by solid body electrolyte guiding ions, and the anode chamber is limited on one side by the solid body electrolyte, on another side by a wall at least partially surrounding the solid body electrolyte. The wall is surrounded by a head part of the device, by a base part arranged opposite the head part and/or by a lateral part arranged between the head and base part. The wall has an electrical conductive wall section as an anode to the anode chamber, an at least partially flat, electrical conductive line section electrically connected to the wall section by a surface, and conductivity per surface of the line section greater than conductivity of the wall per surface of the wall section.

A metal-ion accumulator, including a metal element of flat surface forming a current collector of an electrode of one polarity; an insulating layer, deposited on the metal element while defining an interlocking pattern; a layer forming a current collector of an electrode of opposite polarity to the one having the current collector formed by the metal element, the collector layer being deposited on the interlocking pattern of the insulating layer; an electrode layer, deposited on the metal element according to a pattern at least partly interlocked in the interlocking pattern; an electrode layer of opposite polarity to the one deposited on the metal element, the layer of opposite polarity being deposited on the collector layer according to the interlocking pattern; a layer of electrolyte deposited at least in the spaces between the two layers of active materials of opposite polarity.