Inherent limitations of the hydrogen-bonding UPy motif as self-healing functionality for polymer electrolytes†

The development of advanced materials displaying reversible functionalities, such as self-healing is particularly desirable for energy storage devices, since the cycle life of many rechargeable batteries is limited due to the irreversible mechanical damages over the cycling processes. Hydrogen-bonding self-healing polymers functionalized with ureido pyrimidinone (UPy) has received great interest for energy storage applications, particularly for polymer electrolytes. Herein, we design a star-branched poly(ε-caprolactone-co-trimethylene carbonate) end-capped with UPy groups for both reinforced mechanical and desired self-healing properties in the polymer electrolytes. Despite the versatile implementation and strong bonding association, the benefits of hydrogen-bonding UPy functionalities are diminished after the dissolution of LiTFSI salt in the self-healing polymer matrix. Experimental analysis and molecular dynamics simulations were performed to gain insight into the dynamics of the self-healing polymer electrolyte system. FTIR shows a dramatic decrease in the intensities of the hydrogen-bonded CO signals belonging to UPy motifs after adding LiTFSI salt, indicative of a significant reduction in the total number of hydrogen-bonding and more loosened cross-linked polymer network. This is also noticed as a simultaneous deterioration of the mechanical properties. Molecular dynamics simulations reveal that the complex interplay of CO--Li⁺ coordination bonds and hydrogen bonding between TFSI anions and UPy motifs are responsible for the mechanical deterioration of the self-healing polymer electrolytes.