(323b) Effect of Lithium Salt Addition On Self-Assembly of Block Copolymer Electrolytes

Microphase separated mixtures of lithium salts and polystyrene-block-poly(ethylene oxide) block copolymers have the potential to serve as mechanically robust electrolytes for rechargeable lithium batteries.  The lithium salt molecules reside primarily in the poly(ethylene oxide) domains providing channels for ion transport while the polystyrene domains control the mechanical properties of the electrolyte. Both experiments and theories in current literature that the addition of lithium salts results in a linear increase in the effective Flory-Huggins interaction that controls the self-assembly the block copolymer/salt mixtures.  More detailed studies of the thermodynamics of these systems indicate that the addition of lithium salts results in a highly non-linear increase in the effective Flory-Huggins interaction which increases very rapidly at low salt concentrations, reaching a concentration-independent plateau over most of the concentration range relevant for battery operation.  It is also evident that this dependence if a strong function of block copolymer molecular weight.  In the presentation, we will attempt to reconcile the differences between the data described above and previously published results.