LiFePO4 nanopowders (50 nm) were prepared through a simple hydrothermal process. Poly vinylidene fluoride (PVDF): LiFePO4 complex membranes as solid polymer electrolytes were characterized. X-ray diffraction (XRD) and differential scanning calorimetric (DSC) studies show a decrease in crystalline size and crystallinity of the polymer PVDF with increasing LiFePO4 concentration. Scanning electron micrographs show smaller spherical domains in the dry film with increased LiFePO4 nanopowder content. Impedance measurements suggest that the ionic conductivity of (PVDF + LiFePO4) increases with increased temperature and lithium powder concentration.