Reversible Changes in a Block Copolymer Electrolyte with Temperature

Polymer electrolytes have received special attention because of their high thermal stability, high safety, flexibility of battery configuration, and low cost. The use of block copolymer electrolyte materials in solid polymer electrolytes can improve the mechanical strength and ionic conductivity of the electrolyte, and is conducive to the packaging and integration of battery components. Some studies have shown that the grain structure of block copolymers is affected by both thermodynamics and kinetics. 

And a recent study reported the phase behavior of a triblock organic-inorganic hybrid copolymer, poly(polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS)/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixture, as a function of temperature.

The researchers found that the polymer exhibits a lamellar morphology both in the neat state and in the presence of salt. However, the average grain size increases substantially when the electrolyte is heated above 113 °C. The grain structure of this sample changes reversibly with temperature, that is, smaller grains reappear when the electrolyte is cooled below 113 °C. While annealing block copolymers at high temperatures often leads to an increase in the grain size, this change is generally irreversible.

The researchers discussed reason for the reversible change in the grain structure of the POSS-PEO-POSS/LiTFSI electrolyte. They also found the ionic conductivity of the electrolyte also exhibits reversible changes in this temperature window.

Knowledge of the grain structure is crucial for understanding ion transport in nanostructured electrolytes.

Reference: saheli Chakraborty, et al, reversible changes in the grain structure and conductivity in a block, copolymer, electrocule, 2020. Doi: 10.1021/ acs.macromol .0c00466