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Polyzwitterions (polyZIs), macromolecules with repeating ampholytic monomers, are a novel class of materials with attractive properties for battery electrolytes. In this study, we probe the ion transport characteristics and underlying mechanisms in two salt‐doped (Li⁺‐TFSI⁻) polyZIs of similar composition with contrasting zwitterion (ZI) ionic organization: pendant monomers organized via backbone‐anion‐cation (B‐ZI⁻‐ZI⁺, Motif B) and backbone‐cation‐anion (B‐ZI⁺‐ZI⁻, Motif C). Within both Motifs B and C, the counterion of the pendant‐end ZI moiety shows higher mobility. Similarly, when comparing Li⁺or TFSI⁻across motifs, it is seen that the respective pendant‐end counterion possesses higher mobility than its backbone‐adjacent counterpart. Furthermore, when comparing counterions to same‐position ZI moieties, TFSI⁻is seen to possess higher mobility than Li⁺in each case, a result rationalized by invoking the lower interaction strength between the TFSI⁻and ZI⁺. Analysis of ion‐transport mechanisms demonstrate that the mobility of countercharges to the pendant‐end ZI moiety correlates with the ion‐association relaxation timescale, similar to ideas noted in polymerized ionic liquids in past studies. However, the mobility of countercharges to the backbone‐adjacent ZI moiety is shown to be correlated with a cage relaxation time, which incorporates the combined effects of frustrated motion due to the presence of the polymer backbone and pendant‐end ZI moiety and the higher mobility in a population of lightly ZI‐coordinated ions. © 2020 Wiley Periodicals, Inc. J. Polym. Sci.2020,58, 578–588

 

Despite significant interest toward solid‐state electrolytes owing to their superior safety in comparison to liquid‐based electrolytes, sluggish ion diffusion and high interfacial resistance limit their application in durable and high‐power density batteries. Here, a novel quasi‐solid Li⁺ion conductive nanocomposite polymer electrolyte containing black phosphorous (BP) nanosheets is reported. The developed electrolyte is successfully cycled against Li metal (over 550 h cycling) at 1 mA cm⁻²at room temperature. The cycling overpotential is dropped by 75% in comparison to BP‐free polymer composite electrolyte indicating lower interfacial resistance at the electrode/electrolyte interfaces. Molecular dynamics simulations reveal that the coordination number of Li⁺ions around (trifluoromethanesulfonyl)imide (TFSI⁻) pairs and ethylene‐oxide chains decreases at the Li metal/electrolyte interface, which facilitates the Li⁺transport through the polymer host. Density functional theory calculations confirm that the adsorption of the LiTFSI molecules at the BP surface leads to the weakening of N and Li atomic bonding and enhances the dissociation of Li⁺ions. This work offers a new potential mechanism to tune the bulk and interfacial ionic conductivity of solid‐state electrolytes that may lead to a new generation of lithium polymer batteries with high ionic conduction kinetics and stable long‐life cycling.

 

We report a partial elucidation of the relationship between polymer polarity and ionic conductivity in polymer electrolyte mixtures comprising a homologous series of nine poly(vinyl ether)s (PVEs) and lithium bis(trifluoromethylsulfonyl)imide. Recent simulation studies have suggested that low dielectric polymer hosts with glass transition temperatures far below ambient conditions are expected to have ionic conductivity limited by salt solubility and dissociation. In contrast, high dielectric hosts are expected to have the potential for high ion solubility but slow segmental dynamics due to strong polymer–polymer and polymer–ion interactions. We report results for PVEs in the low polarity regime with dielectric constants of about 1.3 to 9.0. Ionic conductivity measured for the PVE and salt mixtures ranged from about 10–10 to 10–3 S/cm. In agreement with the predictions from computer simulations, the ionic conductivity increased with dielectric constant and plateaued as the dielectric approached 9.0, comparable to the dielectric constant of the widely used poly(ethylene oxide).