Abstract
Stretchable batteries are needed to accommodate deformable geometries in tantalizing applications such as smart textiles, biomedical implants, and stretchable electronics. An increasing number of studies have focused on flexible and bendable batteries, but very few have investigated a stretchable lithium ion battery in which some or all components, including the electrodes, electrolyte, and encapsulation may be stretched. Here, we report the design, fabrication and characterization of a stretchable-sliding battery where the electrodes can slide, and the solid polymer electrolyte is stretched. The battery consists of a single solid polymer electrolyte film sandwiched between two sliding layered electrodes on each side. The two cathode layers are based on LiFePO4 active material, and the two anode layers are graphite based. The stretchable polymer electrolyte is composed of a specific blend of polyethylene oxide (PEO) of 100k and 600k molecular weights to enhance both the ionic conductivity and mechanical properties. Results show that the capacity of the stretchable-sliding battery increases at small tensile strains, but can degrade at larger strains. Tensile stress-strain curves of the stretchable battery and its components until failure are also presented. In situ strain-dependent electrochemical measurements provide critical insights on the stretching and sliding mechanisms in the battery. This study further validates the dual-functionality of the PEO solid electrolyte as both a stretchable film and a lithium ion conductor in a charged/discharged battery. This stretchable-sliding battery configuration can offer an experimental platform for in situ characterizations of solid polymer electrolyte films subjected to stretching inside an active electrochemical cell.
Highlights
Flexible and stretchable energy storage devices have attracted significant attention in recent years
Results in this study show an order of magnitude difference in ionic conductivity of 600k and 100k polyethylene oxide (PEO) electrolyte, which agrees well with previously reported values
Higher ionic conductivity in 100k PEO generally stems from higher degree of amorphicity and chain motion in the lower molecular weight polymer
Summary
Flexible and stretchable energy storage devices have attracted significant attention in recent years These multi-functional batteries can offer mechanical and electrochemical functionalities that address a wide range of applications such as smart suits, stretchable electronics and biomedical implants. Conventional batteries containing flammable organic liquid electrolyte are prone to leakage and thermal runaway that can lead to catastrophic failures.1–8 They are less suitable for special applications such as wearable, implantable, and deformable electronics where the mechanical and thermal stability requirements are critical. Ceramic electrolytes exhibit high ion conductivities, but are not suitable for stretchable applications.. Solid polymer electrolytes are mechanically flexible and stretchable, but provide lower ion conductivities. In 2016, Kammoun et al. fabricated a thin-film stretchable battery based on polymer electrolyte in a spiral configuration capable of large out-ofplane stretching up to 1300%. The battery shows high voltage retention over 9000 stretching cycles, and maintains stable capacity over 100 charge/discharge cycles
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