Modulating Ion Transport and Self-Assembly of Polymer Electrolytes via End-Group Chemistry

Abstract

We report a rational design of solid-state dry polymer electrolytes with high conductivity, high mechanical strength, and improved cation transference number. Thiol–ene click chemistry provided orthogonal control over the type and number of end groups in poly­(styrene-b-ethylene oxide) (PS-b-PEO) block copolymers. This approach permitted the synthesis of PEO chains with reduced crystallinity, reminiscent of PEO oligomers, thereby playing a key role in improving the room temperature conductivity. Intriguingly, the incorporation of diol or dicarboxylic acid end groups in PS-b-PEO produced a well-defined gyroid structure, leading to order of magnitude improvements in the storage modulus. Out of the various samples examined, the electrolytes bearing terminal diol displayed the highest ionic conductivity and a 2-fold increase in lithium transference number. The improvements in performance are attributed to the reduced interchain aggregation and the anion stabilization mediated by the terminal diol group. The fact that the dramatic changes in ion transport and mechanical properties of PS-b-PEO samples were brought about solely by the modification of single terminal group of the PEO unit confirmed end-group chemistry as a powerful tool for the design of efficient solid-state polymer electrolytes. This work should find applications in various emerging electrochemical technologies, namely those employed in energy storage and conversion.

Multivalent ion conduction in solid polymer systems

“…81 Further small improvements to the mechanical properties as well as the conductivity can be achieved through bi-continuous morphologies such as gyroid, which can be accessed through end-group modification for low molecular weight systems. [82][83] Similar studies on multivalent salts in BCPs have not been performed but would provide interesting comparisons in their effect on ionic conductivity and mechanical property retention as compared with lithium counterparts.…”

All‐Solid‐State Lithium–Organic Batteries Comprising Single‐Ion Polymer Nanoparticle Electrolytes

“…As an alternative, poly(ethylene oxide) (PEO)‐based electrolytes have been studied for decades because PEO electrolytes exhibit higher lithium‐ionic conductivities than other polymer electrolytes . However, despite the research efforts in this area, the reported conductivities are typically in the range of 10 −7 to 10 −4 S cm −1 at room temperature and the mechanical properties are sensitive to temperature, making these electrolytes unsuitable for practical applications. Therefore, most polymer electrolytes that have shown success in battery tests are so‐called gel polymer electrolytes, which contain excessive amounts of liquid additives .…”

Recent progress in block copolymer crystallization

“…Unfortunately, PEO is highly crystalline, and research shows that crystallinity inhibits the flow of Li + ions . BCPs are advantageous because the second block adds strength to the membrane, the BCP morphology can help direct ion flow and the second block can inhibit PEO crystallization . In BCPs, the salt concentration influences the morphology by changing the apparent volume fraction for the conductive block.…”

“…However, PEO crystallinity remained the same. In another study, the PEO end‐group chemistry in PS‐ b ‐PEO copolymer was altered between single or double carboxylic acid or hydroxyl groups . It was shown that the weaker primary alcohol association with Li + and a designed diol end‐group were both more favorable to improve conductivity in the PEO phase.…”