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1. Linking Electric Double Layer Formation to Electrocatalytic Activity

   https://doi.org/10.1021/acscatal.3c04255  

   Gebbie, Matthew A.; Liu, Beichen; Guo, Wenxiao; Anderson, Seth R.; Johnstone, Samuel G. (December 2023, ACS Catalysis)

   Electric double layers form at electrode-electrolyte interfaces and often play defining roles in governing electrochemical reaction rates and selectivity. While double layer formation has remained an active area of research for more than a century, most frameworks used to predict electric double layer properties, such as local ion concentrations, potential gradients, and reactant chemical potentials, remain rooted in classical Gouy-Chapman-Stern theory, which neglects ion-ion interactions and assumes non-reactive interfaces. Yet, recent findings from the surface forces and electrocatalysis communities have highlighted how the emergence of ion-ion interactions fundamentally alters electric double layer formation mechanisms and interface properties. Notably, recent studies with ionic liquids show that ionic correlations and clustering can substantially alter reaction rates and selectivity, especially in concentrated electrolytes. Further, emerging studies suggest that electric double layer structures and dynamics significantly change at potentials where electrocatalytic reactions occur. Here, we provide our perspective on how ion-ion interactions can impact electric double layer properties and contribute to modulating electrocatalytic systems, especially under conditions where high ion concentrations and large applied potentials cause deviations from classical electrolyte theory. We also summarize growing questions and opportunities to further explore how electrochemical reactions can drastically alter electric double layer properties. We conclude with a perspective on how these findings open the door to using electrocatalytic reactions to study electric double layer formation and achieve electrochemical conversion by engineering electrode-electrolyte interfaces. 

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2. In Situ Formation of Polymer-Inorganic Solid-Electrolyte Interphase for Stable Polymeric Solid-State Lithium Metal Batteries

   https://doi.org/10.1016/j.chempr.2021.06.019  

   Deng, Tao; Cao, Longsheng; He, Xinzi; Li, Ai-Min; Li, Dan; Xu, Jijian; Liu, Sufu; Bai, Panxing; Jin, Ting; Ma, Lin; et al (January 2021, Chem)

   null (Ed.)

   Composite polymer electrolytes (CPEs) for solid-state Li metal batteries (SSLBs) still suffer from gradually increased interface resistance and unconstrained Li dendrite growth. Herein, we addressed the challenges by designing a LiF-rich inorganic solid-electrolyte interphase (SEI) through introducing a fluoride-salt concentrated interlayer on CPE film. The rigid and flexible CPE helps accommodate the volume change of electrodes, while the polymeric high-concentrated electrolyte (PHCE) surface-layer regulates Li-ion flux due to the formation of a stable LiF-rich SEI via anion reduction. The designed CPE-PHCE presents enhanced ionic conductivity and high oxidation stability of > 5.0V (vs. Li/Li+). What’s more, it dramatically reduces the interfacial resistance and achieves a high critical current density of 4.5 mA cm-2 for dendrite-free cycling. The SSLBs, fabricated with thin CPE-PHCE membrane (< 100 μm) and Co-free LiNiO2 cathode, exhibit exceptional electrochemical performance and long cycling stability. This approach of SEI design can also be applied to other types of batteries. 

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3. Highly‐Cyclable Room‐Temperature Phosphorene Polymer Electrolyte Composites for Li Metal Batteries

   https://doi.org/10.1002/adfm.201910749  

   Rojaee, Ramin; Cavallo, Salvatore; Mogurampelly, Santosh; Wheatle, Bill K.; Yurkiv, Vitaliy; Deivanayagam, Ramasubramonian; Foroozan, Tara; Rasul, Md Golam; Sharifi‐Asl, Soroosh; Phakatkar, Abhijit H.; et al (June 2020, Advanced Functional Materials)

   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(-2) at 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. 

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4. Relationship between Ionic Conductivity, Glass Transition Temperature, and Dielectric Constant in Poly(vinyl ether) Lithium Electrolytes

   https://doi.org/10.1021/acsmacrolett.1c00305  

   Imbrogno, Jennifer; Maruyama, Kazuya; Rivers, Frederick; Baltzegar, Jacob R.; Zhang, Zidan; Meyer, Paul W.; Ganesan, Venkat; Aoshima, Sadahito; Lynd, Nathaniel A. (July 2021, ACS Macro Letters)

   null (Ed.)

   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). 

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5. Ion Channels in Sulfonated Copolymer-Grafted Nanoparticles in Ionic Liquid

   https://doi.org/10.1039/D2SM00725H  

   Li, Ruhao; Han, Yuke; Akcora, Pinar (June 2022, Soft Matter)

   The use of ionic liquids as solvent for polymers or polymer-grafted nanoparticles provides an exciting feature to explore electrolyte-polymer interaction. 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HMIm-TFSI) holds specific interactions with the polymer through ion-dipole or hydrogen bonding. For this work, poly(methyl methacrylate)-b-poly(styrene sulfonate) (PMMA-b-PSS) copolymer-grafted Fe3O4 nanoparticles with different sulfonation levels (~4.9-10.9 mol% SS) were synthesized and their concentration dependent ionic conductivities were reported in acetonitrile and HMIm-TFSI/acetonitrile mixture. We found that conductivity enhancement with the particle concentration in acetonitrile was due to the aggregation of grafted particles, hence sulfonic domain connectivity. The ionic conductivity was found to be related to the effective hopping transfer within ionic channels. To the contrary, the conductivity decreased or remained constant with increasing particle concentration in HMIm-TFSI/acetonitrile. This result was attributed to the ion coupling between ionic liquid and copolymer domains. 

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