A lithium secondary cell comprising a safe aqueous-solution electrolyte free from danger of firing and explosion and capable of supplying a high voltage of more than 3 V. The cell includes a positive plate having an active material absorbing/desorbing lithium ions and exhibiting a high voltage, a negative plate having an active material exhibiting a low voltage, a polymer solid electrolyte having a lithium-ionic conductivity, and an aqueous-solution electrolyte. The positive and negative plates are coated with a polymer solid electrolyte having an ionic conductivity and therefore isolated from the aqueous-solution electrolyte by the plate coating layers.