COMPOSITE POLYMER ELECTROLYTES WITH IMPROVED LITHIUM METAL-ELECTRODE INTERFACIAL PROPERTIES - I - ELECTROCHEMICAL PROPERTIES OF DRY PEO-LIXSYSTEMS

Several types of lithium ion conducting polymer electrolytes have been synthesized by hot-pressing homogeneous mixtures of the components, n amely, poly(ethylene oxide) (PEO) as the polymer matrix, lithium trifl uoromethane sulfonate (LiCF3SO3), and lithium tetrafluoborate (LiBF4), respectively, as the lithium salt, and lithium gamma-aluminate gamma- LiAlO2, as a ceramic filler. This preparation procedure avoids any ste p including liquids so that plasticizer-free, composite polymer electr olytes can be obtained. These electrolyte have enhanced electrochemica l properties, such as an ionic conductivity of the order of 10(-4) S c m(-1) at 80-90 degrees C and an anodic breakdown voltage higher than 4 V vs. Li. In addition, and most importantly, the combination of the d ry feature of the synthesis procedure with the dispersion of the ceram ic powder, concurs to provide these composite electrolytes with an exc eptionally high stability with the lithium metal electrode. In fact, t his electrode cycles in these dry polymer electrolytes with a very hig h efficiency, i.e., approaching 99%. This in turn suggests the suitabi lity of the electrolytes for the fabrication of improved rechargeable lithium polymer batteries.