In order to enhance the ionic conductivity of PEO based polymer electrolytes and improve the stability of the interface between the lithium electrode and the polymer electrolyte

PEO／LiClO4/nano-SiO2 composite polymer electrolytes were prepared by adding self-synthesized nanometric SiO2(NMSIO) or commercial nanometric SiO2 (MN1P and modified MN1P) powder into the PEO／LiClO4 complex．There was 1～2 orders of magnitude increase in the ionic conductivities for these composite PEO electrolytes．It could reach as high as 1.24×10-5S／cm at room temperature．There are two reasons of the increase in ionic conductivity．First

the addition of SiO2 powder can suppress the crystallization of PEO．Secondly

the interface between the SiO2 powder and polymer electrolyte also makes a contribution to the increase in ionic conductivity．PEO based composite gel electrolytes were prepared by the addition of plasticizer PC(propylene carbonate)／EC(ethylene carbonate) into the PEO based composite electrolytes．The ionic conductivity was increased by another two orders of magnitude．The highest one reached 2×10-3 S／cm at room temperature．A half-cell of Li | composite gel electrolyte | Li was assembled with the above mentioned composite gel PEO electrolyte．The variation of the AC impedance spectra with post-preparing time of the half-cell was measured．It was found that the AC impedance of the passivation layer increased quickly within l44 h

but stabilized gradually in the following time．It revealed that SiO2 powder could suppress the growth of the passivation layer between the composite gel PEO electrolyte and the lithium electrode．