Se-Hee Kim

Mechanically compliant and lithium dendrite growth-suppressing composite polymer electrolytes for flexible lithium-ion batteries

We demonstrate mechanically compliant and lithium dendrite growth-suppressing composite polymer electrolytes for use in flexible lithium-ion batteries. This new composite polymer electrolyte (referred to as “CPE”) is fabricated via an exquisite combination of UV (ultraviolet)-cured ethoxylated trimethylolpropane triacrylate macromer (serving as a mechanical framework) and Al2O3 nanoparticles (as a functional filler) in the presence of a high boiling point liquid electrolyte. A distinctive structural feature of the CPE is the close-packed Al2O3 nanoparticles in the liquid electrolyte-swollen ETPTA macromer matrix. Owing to this unique morphology, the CPE provides significant improvements in the mechanical bendability and suppression of lithium dendrite growth during charge–discharge cycling.

Compliant polymer network-mediated fabrication of a bendable plastic crystal polymer electrolyte for flexible lithium-ion batteries

We demonstrate a bendable plastic crystal polymer electrolyte (referred to as “B-PCPE”) for use in flexible lithium-ion batteries. The B-PCPE proposed herein is composed of a plastic crystal electrolyte (PCE, 1 M lithium bis-trifluoromethanesulphonimide (LiTFSI) in succinonitrile (SN)) and a UV (ultraviolet)-cured polymer network bearing long linear hydrocarbon chains (here, trimethylolpropane propoxylate triacrylate (TPPTA) polymer is exploited). The solid electrolyte characteristics of the B-PCPE are investigated in terms of plastic crystal behavior, mechanical bendability, ionic conductivity, and cell performance. Owing to the presence of long linear hydrocarbon chains attached to crosslinkable acrylate groups, the TPPTA polymer network in the B-PCPE acts as a compliant mechanical framework, thereby exerting a beneficial influence on bendability and also interfacial resistance with lithium metal electrodes. Meanwhile, the B-PCPE exhibits slightly lower ionic conductivity than a control sample (referred to as “R-PCPE”) incorporating a rigid and stiff polymer network of ethoxylated trimethylolpropane triacrylate (ETPTA). This unique behavior of the B-PCPE is discussed with an in-depth consideration of the polymer network structure and its specific interaction with the lattice defect phase of SN in the PCE. Although relatively sluggish ionic transport is observed in the B-PCPE, its intimate interfacial contact with electrodes (possibly due to the mechanically compliant TPPTA polymer network) may beneficially contribute to imparting satisfactory cycling performance.

A shape-deformable and thermally stable solid-state electrolyte based on a plastic crystal composite polymer electrolyte for flexible/safer lithium-ion batteries

A solid-state electrolyte with reliable electrochemical performance, mechanical robustness and safety features is strongly pursued to facilitate the progress of flexible batteries. Here, we demonstrate a shape-deformable and thermally stable plastic crystal composite polymer electrolyte (denoted as “PC-CPE”) as a new class of solid-state electrolyte to achieve this challenging goal. The PC-CPE is composed of UV (ultraviolet)-cured ethoxylated trimethylolpropane triacrylate (ETPTA) macromer/close-packed Al2O3 nanoparticles (acting as the mechanical framework) and succinonitrile-mediated plastic crystal electrolyte (serving as the ionic transport channel). This chemical/structural uniqueness of the PC-CPE brings remarkable improvement in mechanical flexibility and thermal stability, as compared to conventional carbonate-based liquid electrolytes that are fluidic and volatile. In addition, the PC-CPE precursor mixture (i.e., prior to UV irradiation) with well-adjusted rheological properties, via collaboration with a UV-assisted imprint lithography technique, produces the micropatterned PC-CPE with tunable dimensions. Notably, the cell incorporating the self-standing PC-CPE, which acts as a thermally stable electrolyte and also a separator membrane, maintains stable charge/discharge behavior even after exposure to thermal shock condition (=130 °C/0.5 h), while a control cell assembled with a carbonate-based liquid electrolyte and a polyethylene separator membrane loses electrochemical activity.

Flexible/shape-versatile, bipolar all-solid-state lithium-ion batteries prepared by multistage printing

Bipolar all-solid-state lithium-ion batteries (LIBs) have attracted considerable attention as a promising approach to address the ever-increasing demand for high energy and safety. However, the use of (sulfide- or oxide-based) inorganic solid electrolytes, which have been the most extensively investigated electrolytes in LIBs, causes problems with respect to mechanical flexibility and form factors in addition to their longstanding issues such as chemical/electrochemical instability, interfacial contact resistance and manufacturing processability. Here, we develop a new class of flexible/shape-versatile bipolar all-solid-state LIBs via ultraviolet (UV) curing-assisted multistage printing, which does not require the high-pressure/high-temperature sintering processes adopted for typical inorganic electrolyte-based all-solid-state LIBs. Instead of inorganic electrolytes, a flexible/nonflammable gel electrolyte consisting of a sebaconitrile-based electrolyte and a semi-interpenetrating polymer network skeleton is used as a core element in the printed electrodes and gel composite electrolytes (GCEs, acting as an ion-conducting separator membrane). Rheology tuning (toward thixotropic fluid behavior) of the electrode and GCE pastes, in conjunction with solvent-drying-free multistage printing, enables the monolithic integration of in-series/in-plane bipolar-stacked cells onto complex-shaped objects. Because of the aforementioned material and process novelties, the printed bipolar LIBs show exceptional flexibility, form factors, charge/discharge behavior and abuse tolerance (nonflammability) that far exceed those achievable with inorganic-electrolyte-based conventional bipolar cell technologies.