NOVELTY - An improved battery comprising an electrolyte and at least 2 electrodes, comprises in the electrolyte a compound (I), which generates a fire-retardant gas on decomposition.    USE - In batteries used for back-up power, e.g. for telephone lines, or electric and hybrid vehicles, consumer electronics, e.g. video cameras, cellular telephones, personal data assistants, mini-disks and computers, and light-weight hand-held instruments, e.g. data loggers used in difficult environments. The electrolytes may also be used in capacitors, in surface treatment of metals, in situations where a non-oxidizing/inert environment is required, for building over-pressure in sealed containers, for storage of materials needing a gas blanket, preferably flammable materials, and as gas propellants in drug delivery.    ADVANTAGE - Unlike a fire-resistant electrolyte, which can lose its fire-resistant properties when it decomposes, the additive develops fire-retardant properties on decomposition, and it can produce fire-retardant gases other than carbon dioxide, which can have an adverse effect on certain types of cell. Adding (I) to an electrolyte can result in formation of an enhanced solid electrolyte interface (claimed) between the anode and the electrolyte, which reduces electrolyte breakdown and irreversible capacity loss.    DETAILED DESCRIPTION - In an improved battery comprising an electrolyte and at least 2 electrodes, the improvement comprises a compound which generates a fire-retardant gas on decomposition and has the formula (I);    X = N, C, S, NO, N2, CO or SO;    A = aryl, or alkyl, alkenyl, alkoxy or aralkylene, all 4 optionally heteroatom-substituted, or annulene (i.e. completely conjugated monocyclic polyenes), conjugated hydrocarbons (e.g. fulvene, calicene, fulvalene and methylenecyclopropene), fused ring systems (e.g. naphthalene, anthracene, naphthacene, phenanthrene, triphenylene, pyrene, perylene, butalene, pentalene, azulene, heptalene, biphenylene and acenaphtylene), heteroatoms (including halogen and alkali and transition metals), alcohol (e.g. phenol, ethanol and butanol), hydroxyl, acetal or ketal;    B1, B2 = H, oxygen or A', provided B1 or B2 is absent when X = nitrogen, A, B1 or B2 are not chalcogen when X = carbon and B1 and B2 are not oxygen when X = carbonyl; and    n, n' = 0-100, provided both are not zero simultaneously.