Selective Transporting of Lithium Ion by Shape Selective Molecular Sieves ZSM-5 in PEO-Based Composite Polymer Electrolyte

To elucidate the mechanism of the enhancement of lithium ion transference numbers, TLi+, induced by ZSM-5 in PEO-based composite polymer electrolyte, different types of other fillers, such as ceramic fillers (SiO2 and Al2O3), solid superacid (SO42-/ZrO2), layered materials (montmorillonite), and mesoporous materials (MCM-41, HMS, and SBA-15), are selected to compare with ZSM-5 molecular sieves. The experimental results suggest that ZSM-5 may enhance the TLi+ of PEO-based composite polymer electrolytes in three ways: (1) Lewis acid−base interactions, resulting in the release of more "free" Li+ cations; (2) selective passing of Li+ cations due to the special pore size of ZSM-5 and electrostatic repulsion for ClO4- anions due to the negative environment in the channels of ZSM-5; (3) the cation-exchange centers in the framework of ZSM-5, suggesting that the Li+ cation can be ion-exchanged into the channels for charge balance, namely, provide a special conducting pathway for Li+ cation. In addition, room temperature ionic conductivity of the composite polymer electrolyte can also be increased by about 2 orders of magnitude. The high lithium ion transference numbers combined with a suitable ionic conductivity of PEO−LiClO4−ZSM5 composite polymer electrolyte suggest that it can be used as candidate electrolyte material for all solid-state rechargeable lithium polymer batteries.