Mixed-valence Keggin-type lithium polyoxometalates (POMs) were used as the electrolytes of polyacenic semiconductor (PAS) secondary batteries substituting for LiClO4 for the first time. The discharging, cycle and self-discharging properties of these PAS/Li secondary batteries and the effect of current density and temperature on the properties of the batteries have been investigated. The results indicate not only that the lithium POMs can overcome the disadvantages of LiClO4, which is apt to explode when heated or rammed, but also that some of the PAS/Li secondary batteries assembled with the novel electrolytes have larger capacity and smaller self-discharging than that assembled with LiClO4. Therefore, it is believed that Keggin-type mixed-valence lithium POMs are novel and better electrolytes of PAS secondary batteries and exhibit promising practical application. (C) 2003 Elsevier Science B.V. All rights reserved.