Lithium Dendrite Growth in Glassy and Rubbery Nanostructured Block Copolymer Electrolytes

Enabling the use of lithium metal anodes is a critical step required to dramatically increase the energy density of rechargeable batteries. However, dendrite growth in lithium metal batteries, and a lack of fundamental understanding of the factors governing this growth, is a limiting factor preventing their adoption. Herein we present the effect of battery cycling temperature, ranging from 90 to 120°C, on dendrite growth through a polystyrene-block-poly(ethylene oxide)-based electrolyte. This temperature range encompasses the glass transition temperature of polystyrene (107°C). A slight increase in the cycling temperature of symmetric lithium-polymer-lithium cells from 90 to 105°C results in a factor of five decrease in the amount of charge that can be passed before short circuit. Synchrotron hard X-ray microtomography experiments reveal a shift in dendrite location from primarily within the lithium electrode at 90°C, to primarily within the electrolyte at 105°C. Rheological measurements show a large change in mechanical properties over this temperature window. Time-temperature superposition was used to interpret the rheological data. Dendrite growth characteristics and cell lifetimes correlate with the temperature-dependent shift factors used for time-temperature superposition. Our work represents a step toward understanding the factors that govern lithium dendrite growth in viscoelastic electrolytes

Light-controllable ionic conductivity in a polymeric ionic liquid

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light-responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light-mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light-responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light-controlled electrical circuits and wearable photodetectors

Light‐Controllable ionic conductivity in a polymeric ionic liquid

Polymeric ionic liquids (PILs) have attracted considerable attention as electrolytes with high stability and mechanical durability. Light‐responsive materials are enabling for a variety of future technologies owing to their remote and noninvasive manipulation, spatiotemporal control, and low environmental impact. To address this potential, responsive PIL materials based on diarylethene units were designed to undergo light‐mediated conductivity changes. Key to this modulation is tuning of the cationic character of the imidazolium bridging unit upon photoswitching. Irradiation of these materials with UV light triggers a circa 70 % drop in conductivity in the solid state that can be recovered upon subsequent irradiation with visible light. This light‐responsive ionic conductivity enables spatiotemporal and reversible patterning of PIL films using light. This modulation of ionic conductivity allows for the development of light‐controlled electrical circuits and wearable photodetectors

Ion Transport in Dynamic Polymer Networks Based on Metal–Ligand Coordination: Effect of Cross-Linker Concentration

The development of high-performance ion conducting polymers requires a comprehensive multiscale understanding of the connection between ion–polymer associations, ionic conductivity, and polymer mechanics. We present polymer networks based on dynamic metal–ligand coordination as model systems to illustrate this relationship. The molecular design of these materials allows for precise and independent control over the nature and concentration of ligand and metal, which are molecular properties critical for bulk ion conduction and polymer mechanics. The model system investigated, inspired by polymerized ionic liquids, is composed of poly­(ethylene oxide) with tethered imidazole moieties that facilitate dissociation upon incorporation of nickel­(II) bis­(trifluoro­methylsulfonyl)­imide. Nickel–imidazole interactions physically cross-link the polymer, increase the number of elastically active strands, and dramatically enhance the modulus. In addition, a maximum in ionic conductivity is observed due to the competing effects of increasing ion concentration and decreasing ion mobility upon network formation. The simultaneous enhancement of conducting and mechanical properties within a specific concentration regime demonstrates a promising pathway for the development of mechanically robust ion conducting polymers

Decoupling Bulk Mechanics and Mono- and Multivalent Ion Transport in Polymers Based on Metal�Ligand Coordination

Decoupling bulk mechanics and ion conduction in conventional ion conducting polymers is challenging due to their mutual dependence on segmental chain dynamics. Polymers based on dynamic metal–ligand coordination are promising materials toward this aim. This work examines the effect of the nature and concentration of metal bis­(trifluoromethyl­sulfonyl)­imide (MTFSI) salts on the mechanical properties and ionic conductivity of poly­[(ethylene oxide)-<i>stat</i>-(allyl glycidyl ether)] functionalized with tethered imidazole ligands (PIGE). Varying the cation identity of metal salts mixed in PIGE enables dramatic tunability of the zero-frequency viscosity from 0.3 to 100 kPa s. The ionic conductivity remains comparable at approximately 16 μS cm^–1 among mono-, di-, and trivalent salts at constant metal-to-ligand molar ratios due to negligible changes in glass transition temperatures at low ion concentrations. Thus, polymers based on metal–ligand coordination enable decoupling of polymer zero-frequency viscosity from ion conduction. Pulsed-field-gradient NMR on PIGE containing Li⁺ or Zn²⁺ salts complement electrochemical impedance spectroscopy to demonstrate that both the anion and cation contribute to ionic conductivity