Enhanced Conductivity of Block Copolymer Electrolytes for Lithium Batteries
University of Delaware
Polymers are promising materials for ion conducting membranes in lithium and lithium ion batteries due to their mechanical strength and thermal and electrochemical stability. Poly(ethylene oxide) (PEO) based polymer electrolytes are candidates for this application; however, they show a discontinuity in conductivity around 60 °C due to crystallization. Below this temperature, the conductivity is markedly lower reducing the performance at room temperature. In this work, we explored two strategies for increasing the room temperature conductivity of PEO based electrolytes by inhibiting crystallization. The first approach was forming copolymer/copolymer blends with polystyrene-b-poly(ethylene oxide) (PS-PEO) and polystyrene-b-poly(oligo(oxyethylene) methacrylate) (PS-POEM). We found that the PS-POEM did not inhibit crystallization of PEO. However, due to its amorphous nature, PS-POEM was three orders of magnitude more conductive than PS-PEO. The second approach was adding titania nanoparticles to polystyrene-b-poly(ethylene oxide)-b-polystyrene (PS-PEO-PS). We found that the addition of titania nanoparticles reduced the crystallinity of the PEO block by 10% regardless of the titania to ethylene oxide ratio. Additionally, the room temperature conductivity increased upon nanoparticles addition. This increase was dependent upon composition, with highest increase noted for a doping ratio of 10:1 followed by 5:1 then 20:1.