**4.2 Sample preparation**

Prior to the preparation of the polymer electrolytes, Li2B4O7 was dried at 100 °C for 1 hour to eliminate trace amounts of water in the material. Appropriate amount of PVC, Li2B4O7 and PC were dissolved in anhydrous THF. The mixture was then stirred continuously for 24 hours at room temperature to achieve a homogenous solution. The resulting solution was cast on a Petri dish and was allowed to evaporate slowly in a fume hood. This procedure yields free standing films eventually. The designations of polymer film are listed in Table 1. The weight ratio of PVC (70%) to Li2B4O7 (30%) had achieved the maximum ionic conductivity in the preliminary step which is not being shown here. As a result, the ratio of PVC to Li2B4O7 was fixed as 70 wt% to 30 wt% in this study.


Table 1. The nomenclature of samples with different stoichiometric amounts of materials added into polymer electrolytes.
