Evolution of Morphology, Modulus, and Conductivity in Polymer Electrolytes Prepared via Polymerization-Induced Phase Separation

Abstract

Polymer electrolytes are alternatives to liquid electrolytes traditionally used in electrochemical devices such as lithium-ion batteries and fuel cells. In particular, block polymer electrolytes are promising candidates because they self-assemble into well-defined microstructures, in which orthogonal properties can be integrated into a single material (e.g., high modulus in domain A, fast ion transport in domain B). However, the performance of block polymer electrolytes often falls short, due to the lack of long-range continuity of both domains and relatively low strength. We recently reported a simple, one-pot synthetic strategy to prepare polymer electrolytes with the highest reported combination of modulus and ionic conductivity, attributes enabled by a co-continuous, cross-linked network morphology. In this work we aim to understand the mechanism by which this nanoscale morphology is formed by performing a series of in situ, time-resolved experimentssmall-angle X-ray scattering, conductivity, rheology, and reaction kineticsto monitor the electrolyte as it transitions from a macroscopically homogeneous liquid to a microphase-separated solid. The results suggest that the chain connectivity of the diblock gives rise to isotropic concentration fluctuations that increase in amplitude and coherence such that the network morphology is ultimately produced. The kinetic trapping of this network morphology by chemical cross-linking prior to the ordering transition is shown to be critically important to the resulting advantageous bulk electrolyte properties.

Brush polymer ion gels

“…Conductivity decreases with increasing N A : N B block ratios and polymer concentration but generally remains near neat [BMI][TFSI] ( σ gel / σ IL ∼ 0.2–0.8). Ion gels and related IL‐incorporating polymers provide extraordinary opportunities to specifically tailor materials for technological applications. Appreciating the connection between polymer architecture and properties may facilitate the development of designer materials with improved function.…”

Ion Conduction and Viscoelastic Response of Epoxy‐Based Solid Polymer Electrolytes Containing Solvating Plastic Crystal Plasticizer

“…This cross‐linked material exhibited high‐temperature stability and a bicontinuous morphology. Hillmyer and co‐workers extended this PIPS approach to generate nanostructured polymer electrolyte membranes through the integration of ionic liquid and Li‐salt as the liquid precursor, and these membranes showed high‐temperature stability, modulus, and ionic conductivity . Shirshova et al reported multifunctional, structural electrolytes using an epoxy resin (where epoxides have the ability to form bicontinuous structure via PIPS) and a liquid electrolyte comprising an ionic liquid (possessing high ionic conductivity and thermal stability) and a lithium salt.…”

Structure, viscoelasticity, and interfacial dynamics of a model polymeric bicontinuous microemulsion

“…[1][2][3][4][5][6][7] To date, a host of ingredients (metals, 8 oxides, 9,10 surfactants, 6 and polymers 3 ) and processing strategies (both kinetic 11,12 and thermodynamic 3,6 ) have been exploited to control the characteristic length scale and physical properties of such co-continuous structures. 3,4,12,[15][16][17][18][19][20][21] For example, recent work has shown that a kinetically controlled co-continuous structure with nanometer scale features can be trapped by in situ cross-linking through a process called polymerization-induced microphase separation. 13,14 A variety of approaches afford access to characteristic length scales in co-continuous polymeric systems that range from nanometers to millimeters.…”

“…Polymers are particularly attractive for this purpose. 12,20,22 In contrast, coarsening of a two-phase morphology generated by spinodal decomposition of polymer/solvent blends can lead to bicontinuous structures with micrometer, and even millimeter size domains. 3,4,12,[15][16][17][18][19][20][21] For example, recent work has shown that a kinetically controlled co-continuous structure with nanometer scale features can be trapped by in situ cross-linking through a process called polymerization-induced microphase separation.…”