Electrolyte design is critical for enabling next-generation batteries with higher energy densities. Hydrofluoroether (HFE) solvents have drawn a lot of attention as the electrolytes based on HFEs showed great promise to deliver highly desired properties, including high oxidative stability, ionic conductivity, as well as enhanced lithium metal compatibility. However, the structure-dynamics-properties relationships and design principles for high-performance HFE solvents are still poorly understood. Herein, we proposed four novel asymmetric HFE designs by systematically varying polyether and fluorocarbon structural building blocks. By leveraging molecular dynamics (MD) modeling to analyze the solvation structures and predict the properties of the corresponding 1 M lithium bis(fluorosulfonyl)imide (LiTFSI) solutions, we downselected the most promising candidate based on high conductivity, solvation species distribution, and oxidative stability for extensive electrochemical characterizations. The formulated electrolyte demonstrated properties consistent with the predictions from the simulations and showed muchimproved capacity retention as well as Coulombic efficiency compared to the baseline electrolytes when cycled in lithium metal cells. This work exemplifies the construction of candidate electrolytes from building block functional moieties to engineer fundamental solvation structures for desired electrolyte properties and guide the discovery and rational design of new solvent materials.

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For wearable and implantable electronics applications, developing intrinsically stretchable polymer semiconductor is advantageous, especially in the manufacturing of large-area and high-density devices. A major challenge is to simultaneously achieve good electrical and mechanical properties for these semiconductor devices. While crystalline domains are generally needed to achieve high charge carrier mobilities, amorphous domains are necessary to impart stretchability. Recent progresses in the design of high-performance donor-acceptor polymers which exhibited low degrees of energetic disorder, while having high fraction of amorphous morphology, appears promising for polymer semiconductors. Here, a low crystalline, i.e. near-amorphous, indacenodithiophene-co-benzothiadiazole (IDTBT) polymer and a semi-crystalline thieno[3,2-b]thiophene-diketopyrrolopyrrole (DPPTT) are compared, for mechanical properties and electrical performance under applied strains. It is observed that the low crystalline IDTBT is able to achieve both high modulus and high fracture strain, and to preserve electrical functionality under high strain. Next, fully stretchable transistors are fabricated using the IDTBT polymer, and observed mobility ~0.6 cm 2 V-1 s-1 at 100% strain along stretching direction. In addition, the morphological evolution of the stretched IDTBT films is investigated by polarized UV-Vis and GIXD to elucidate the molecular origins of high ductility. In summary, the nearamorphous IDTBT polymer signifies a promising direction regarding molecular design principles toward intrinsically stretchable high-performance polymer semiconductor.

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