Lithium/air batteries have a much higher specific energy than most available primary and rechargeable batteries. However, to produce lithium/air batteries with energy density in the 1,000-2,000 Wh/kg range will require a polymer electrolyte with high ionic conductivity and stability over the course of thousands of cycles. Polysiloxane grafted with short oligooxyethylene units are among the most promising class of materials as electrolytes in lithium/air batteries. Two types of the siloxane based polymers are (a) Poly[?-methoxyhepta(oxyethylene)ethoxy]methoxy-siloxane   and (b) poly[?-methoxyoligo(oxyethylene)propyl] methyl-siloxane. The siloxane based electrolytes are relatively easy to synthesize and purify. For example, poly[?-methoxyhepta(oxyethylene)ethoxy]methoxy-siloxane was prepared by reacting a 20% THF solution of poly(hydrogenmethylsiloxane) with a 5-10% excess of methoxypolyehylene glycol (Mn = 350) at 60o C for 48 h using zinc octanoate as catalyst (0.002 M per mole of SiH). The siloxane polymer/lithium perchlorate complexes display ionic conductivity values of 10-4 S cm-1 at room temperatures and thus meet the ionic conductance necessary for lithium/air batteries. Furthermore, elastomeric blend systems of poly(ethylene oxide)/poly(2-or 4-vinylprydine)/LiClO4 are characterized by not only high ionic conductivities but also the conductivities stayed high over a wider lithium ion concentration range. These observations in the polyblends can be attributed to having more mobile lithium ions over the wider concentration range. The blend system is interesting in that it is able to control the aggregation of lithium ions in the system by dispersing the ions effectively in the polymer matrix. This dispersion is possible because the lithium ion simultaneously interacts with both the oxygen of the ethylene oxide and nitrogen of the vinylpyridine polymer.  The interrelationship among the structure of the electrolytes (molecular structure, morphology including microphase and nanostructure), segmental motion of the polymer chains and nature of ion-pairing/aggregates of the lithium ions necessary for the most appropriate electrolytes will be presented.

Polysiloxane grafted with short oligo(oxyethylene) side chains/lithium perchlorate complexes and poly(vinylpyridine)/poly(ethylene oxide)/lithium perchorate blends: Electrolytes for high energy density batteries

246th National Meeting (2013)

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