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Six molecular ionic composite electrolyte films were produced by combining a rigid-rod polyelectrolyte and various ionic liquids. These electrolytes exhibit both higher modulus and room temperature ionic conductivity than other polymer-based electrolytes.

A critical challenge for next-generation lithium-based batteries lies in development of electrolytes that enable thermal safety along with the use of high-energy-density electrodes. We describe molecular ionic composite electrolytes based on an aligned liquid crystalline polymer combined with ionic liquids and concentrated Li salt. This high strength (200 MPa) and non-flammable solid electrolyte possesses outstanding Li+ conductivity (1 mS cm−1 at 25 °C) and electrochemical stability (5.6 V versus Li|Li+) while suppressing dendrite growth and exhibiting low interfacial resistance (32 Ω cm2) and overpotentials (≤120 mV at 1 mA cm−2) during Li symmetric cell cycling. A heterogeneous salt doping process modifies a locally ordered polymer–ion assembly to incorporate an inter-grain network filled with defective LiFSI and LiBF4 nanocrystals, strongly enhancing Li+ conduction. This modular material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer electrolytes. Developing safe electrolytes compatible with high-energy-density electrodes is key for the next generation of lithium-based batteries. Stable solid-state rigid-rod polymer composite electrolytes with nanocrystalline lithium ion pathways are now proposed.

We report irreversible, shear-activated gelation in liquid crystalline solutions of a rigid polyelectrolyte that forms rodlike assemblies (rods) in salt-free solution. At rest, the liquid crystalline solutions are kinetically stable against gelation and exhibit low viscosities. Under steady shear at, or above, a critical shear rate, a physically cross-linked, nematic gel network forms due to linear growth and branching of the rods. Above a critical shear rate, the time scale of gelation can be tuned from hours to nearly instantaneously by varying the shear rate and solution concentration. The shear-activated gels are distinct in their structure and rheological properties from thermoreversible gels. At a fixed concentration, the induction time prior to gelation decreases exponentially with the shear rate. This result indicates that shear-activated thermalization of the electrostatically stabilized rods overcomes the energy barrier for rod-rod contact, enabling rod fusion and subsequent irreversible network formation.

Polymer electrolytes show promise as alternatives to conventional electrolytes in energy storage and conversion devices but have been limited due to their inverse correlation between ionic conductivity and modulus. In this study, we examine surface morphology, linear viscoelastic, dielectric and diffusive properties of molecular ionic composites (MICs), materials produced through the combination of a rigid and charged double helical polymer, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), and ionic liquids (ILs). To probe temperature extremes, we incorporate a non-crystallizable IL to allow measurements from −90 to 200 °C. As we increase the PBDT weight percentage, shear moduli increase and do not decay up to 200 °C while maintaining room temperature ionic conductivity within a factor of 2 of the neat IL. We connect diffusion coefficients of IL ions with ionic conductivity through the Haven ratio across a wide temperature range and analyze trends in ion transport based on a relatively high an...

Molecular ionic composites (MICs) are a new class of solid electrolyte materials developed recently in our group. These materials are constructed from various ionic liquids and a highly charged rigid rodlike polymer, poly(2,2′-disulfonyl-4,4′-benzideneterephthalamide) (PBDT). MICs demonstrate an unprecedented combination of thermal properties (stability up to 300 °C), mechanical properties (E′ up to ~ 1 GPa), and ion transport properties (ionic conductivity up to 8 mS/cm).[1-3] Here we present preparation and characterization of a MIC membrane based on the PBDT polymer, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Pyr14TFSI) and LiTFSI. This MIC membrane is robust and flexible, and exhibits ionic conductivity ~ 0.2 mS/cm at room temperature. Due to the electrochemical and mechanical stability of the MIC membrane at elevated temperature, Li/MIC/LiFePO4 coin cells demonstrate excellent cycling performance over a wide temperature range from 20 to 150 °C. This study demonstrates that MIC materials represent a promising electrolyte platform for safe and wide-temperature-range lithium batteries. References: [1] Y. Wang, Y. Chen, J. W. Gao, H. G. Yoon, L. Y. Jin, M. Forsyth, T. J. Dingemans, L. A. Madsen, Adv. Mater. 2016, 28, 2571. [2] J. E. Bostwick, C. J. Zanelotti, C. Iacob, A. G. Korovich, L. A. Madsen, R. H. Colby, Macromolecules 2020, 53, 1405. [3] R. J. Fox, D. Yu, M. Hegde, A. S. Kumbhar, L. A. Madsen, T. J. Dingemans, ACS Appl. Mater. Interfaces 2019, 11, 40551. Figure 1. Cycling performance of Li/MIC/LiFePO4 coin cell at 150 °C. Inset image is a MIC membrane. Figure 1

The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While double and multiple helix structures appear widely in nature, only rarely are these found in synthetic non-chiral macromolecules. Here we report a double helical conformation in the densely charged aromatic polyamide poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) or PBDT. This double helix macromolecule represents one of the most rigid simple molecular structures known, exhibiting an extremely high axial persistence length (~1 micrometer). We present X-ray diffraction, NMR spectroscopy, and molecular dynamics (MD) simulations that reveal and confirm the double helical conformation. The discovery of this extreme rigidity in combination with high charge density gives insight into the self-assembly of molecular ionic composites with high mechanical modulus (~ 1 GPa) yet with liquid-like ion motions inside, and provides fodder for formation of other 1D-reinforced composites., Double helix structures appear widely in nature, but only rarely in synthetic non-chiral macromolecules. Here the authors describe a double helix in a densely charged aromatic polyamide, which exhibits an axial rigidity persistence length of ~ 1 μm, much higher than that of DNA (~ 50 nm).