The present invention relates to an apparatus, which works according to galvanic principles, in particular to a lithium-ion accumulator or, respectively, a lithium-ion cell, with at least two electrode devices (10; 20), in particular, a cathode and an anode, in particular, a separator device (30), arranged between two electrode devices, the apparatus (2) comprises, according to the invention, at least one or a plurality of glass fibers (18, 28, 38) which are configured or, respectively, operable as temperature sensor. It can comprise a net (16, 26, 36) formed by glass fibers, or an arrangement of a plurality of glass fibers, which are arranged substantially in parallel to each other, wherein at least one glass fiber (18, 28, 38) is configured or operable as temperature sensor. Such a glass fiber structure can be arranged at the surface of a separator device (30) and/or the cathode, respectively, anode device (10, 20) and can serve as carrier material for this device (30, 10, 20) or can be embedded into this device.