PEO-Based Polymers As SOLID-State Electrolyte: Synthesis and Characterization

Due to the leakage and sealing problems of liquid electrolyte used in batteries or cells, the development of solid-sate electrolyte is important. Among all the alternatives, polymer electrolytes are of particular interests that attract lots of groups. Polymer electrolytes, especially poly(ethylene oxide) (PEO) based polymer electrolytes, have generated considerable research interests in lithium ion batteries, fuel cells, and other solid state electrochemical devices, mostly due to their unique properties, such as, high polarity to dissolve metal salt and excellent chemical stability.

In this work, we designed, synthesized and characterized several novel polymer electrolytes that consist of poly(ethylene oxide) (PEO) based polymer blended with LiI/I₂ to form a homogenous solid-state or quasi solid-state electrolyte used as the electrolyte in dye-sensitized solar cells (DSSCs). The high polarity of ethylene glycol repeating unit in polymers caused an ion-dipole interaction between lithium cation and oxygen atom, making cation be dissociated by the polymer network, resulted in a sovation-desolvation process, which provides a pathway for ion transportation in DSSCs.

As shown in Scheme 1, a series of poly(ethylene glycol) methyl ether mechacrylate (PEGMA) polymers with different length of PEO side chains were polymerized through Atom Radical Transfer Polymerization (ATRP). Electrolytes were later prepared from the functionalized PEGMA polymers and low-molecular weight (~500 g/mol) polyethylene glycol dimethyl ether (PEGDME500)  with the addition of LiI and I₂ as redox couple.

Upon the introduction of PEGMA, electrolytes became very viscous and gel-like. With the increase of PEO side chains, the viscosity of the electrolyte increased dramatically, among which, poly(PEGMA-1100) became solid-state. The room temperature conductivity of polymer electrolytes is in the range of 1.2×10^-4 to 1.5×10^-4 S/cm, slightly lower than the reference. Poly(PEGMA-475), with much higher viscosity, represented better ionic conductivity.

Acknowledgement

We thank the National Science Foundation (NSF-0934568) for funding this research.