In situ strain dependent electrochemical characterization of a stretchable-sliding battery

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.