Effects of Inorganic Fillers on Electrochemical and Rheological Properties of Composite Polymer Electrolytes

摘要

Composite polymer electrolytes (CPEs) with significant lithium-ion conductivity, enhanced ion-transport properties, and good compatibility with lithium metal electrodes have attracted attention for rechargeable lithium batteries. Conventional CPEs are normally formed by dispersing ceramic fillers (e.g., A1_2O_3, TiO_2) into high-molecular weight (MW) poly(ethylene oxide) (PEO) polymers doped with lithium salts. Our group, however, is developing a new type of CPE based on low-MW PEO with fumed silica (SiO_2) fillers. Our CPEs yield a much higher conductivity (>10~(-3) S/cm at room-temperature) than conventional CPEs {I0~(-5) to 10~(-4) S/cm at room-temperature) due to less rigidity of the polymer chain. Solid-like mechanical strength (elastic modulus G'>10~5 Pa) and a significant improvement of lithium interfacial stability with incorporation of the fumed silica is also observed during cell cycling. The purpose of this work is to investigate the effects of varied inorganic fillers such as Al_2O_3, TiO_2, and mixtures of A1_2O_3 and SiO_2 on electrochemical and rheological properties of CPEs. One common feature of above-mentioned fillers and fumed silica is that they all have hydroxyl surface groups that may allow them to flocculate or form three-dimensional networks through hydrogen bonds. In addition, their surface chemistry can be modified by replacing these hydroxyl groups with other functional groups through chemical reactions. The ultimate purpose of this work is to explore the underlying mechanism that determines the effects of fillers on performance of composites and further optimize the properties of the composites.