Stretchability enhancement of buckled polypyrrole electrodes for stretchable supercapacitors via engineering substrate surface roughness

Polyacrylate-graft-polypyrrole Copolymer as Intrinsically Elastic Electrodes for Stretchable Supercapacitors

Constructing elastic electrodes with high mechanical and electrochemical stability remains a challenge in developing flexible supercapacitors. Instability of elastic composite electrodes stems from detachment of noncovalently associated electroactive components from elastic substrates under cyclic deformations. Herein, a novel all-organic copolymer consisting of polypyrrole grafted from a polyacrylate elastomer is proposed as elastic electrodes for stretchable supercapacitors. The single copolymer is obtained by graft polymerization in the swollen state, characterized by a wrinkled polypyrrole coating covalently attached on an elastic core. The copolymer is intrinsically elastic and maintains structural integrity under bending, twisting, and stretching deformations to ensure stable electrochemical performance. In addition, the grafted polypyrrole aggregates densely under the constraint of the backbone and gives a competitive conductivity of 41.6 S cm-1. A stretchable supercapacitor is constructed using the copolymer as electrodes and an acid hydrogel as an electrolyte, resulting in a specific capacitance of 430 mF cm-2. The supercapacitor delivers a capacitance retention of 100% after 1000 stretching-releasing cycles, exhibiting mechanical and electrochemical reliability under elastic deformations.

Re-Stickable Yarn Supercapacitors with Vaper Phase Polymerized Multi-Layered Polypyrrole Electrodes for Smart Garments

Yarn supercapacitors have attracted significant attention for wearable energy storage due to their ability to be directly integrated with garments. Conducting polymer polypyrrole (PPy) based yarn supercapacitors show limited cycling stability because of the huge volume changes during the charge-discharge processes. In addition, laundering may cause damage to such yarn supercapacitors. Here, the fabrication of PPy-based re-stickable yarn supercapacitors is reported with good cycling stability by employing vapor phase polymerization (VPP) and water-soluble polyethylene oxide (PEO) film as the adhesive layer. VPP duration and cycle are controlled to achieve multi-layered PPy electrodes. The assembled yarn supercapacitors show a good cycling stability with capacitance retention of 79.1% after 5000 charge-discharge cycles. The energy stored in the yarn supercapacitor is sufficient to power a photodetector. After gluing the yarn supercapacitors onto a PEO film, the devices can be stunk on and peeled off the garment to avoid the mechanical stresses during the washing process. Three yarn supercapacitors connected in parallel on PEO film show negative changes in electrochemical performance after 5 sticking-peeling cycles. This work provides a facile way to fabricate PPy-based re-stickable energy storage devices with high cycling stability for smart garments.

Advanced materials and technologies for supercapacitors used in energy conversion and storage: a review

Supercapacitors are increasingly used for energy conversion and storage systems in sustainable nanotechnologies. Graphite is a conventional electrode utilized in Li-ion-based batteries, yet its specific capacitance of 372 mA h g−1 is not adequate for supercapacitor applications. Interest in supercapacitors is due to their high-energy capacity, storage for a shorter period and longer lifetime. This review compares the following materials used to fabricate supercapacitors: spinel ferrites, e.g., MFe2O4, MMoO4 and MCo2O4 where M denotes a transition metal ion; perovskite oxides; transition metals sulfides; carbon materials; and conducting polymers. The application window of perovskite can be controlled by cations in sublattice sites. Cations increase the specific capacitance because cations possess large orbital valence electrons which grow the oxygen vacancies. Electrodes made of transition metal sulfides, e.g., ZnCo2S4, display a high specific capacitance of 1269 F g−1, which is four times higher than those of transition metals oxides, e.g., Zn–Co ferrite, of 296 F g−1. This is explained by the low charge-transfer resistance and the high ion diffusion rate of transition metals sulfides. Composites made of magnetic oxides or transition metal sulfides with conducting polymers or carbon materials have the highest capacitance activity and cyclic stability. This is attributed to oxygen and sulfur active sites which foster electrolyte penetration during cycling, and, in turn, create new active sites.

Stretchable Supercapacitors: From Materials and Structures to Devices

Stretchable supercapacitors have received widespread attention due to their potential applications in wearable electronics and health monitoring. Stretchable supercapacitors not only possess advantages such as high power density, long cycle life, safety, and low cost of conventional supercapacitors but also have excellent flexibility and stretchability, which make them well integrated with other wearable systems. In this review, various strategies to fabricate stretchable supercapacitors are focused. The preparation methods for stretchable electrodes/devices in the literature are carefully classified and analyzed. Three strategies for preparing stretchable electrodes/devices are summarized in detail-the design of elastic polymer substrates, stretchable electrode structures, and composite electrodes combined with elastic polymers and stretchable structures. Meanwhile, the interface problem of electrodes/devices in the stretching process is studied in depth. The research progress of multifunctional stretchable supercapacitors is also introduced. Finally, challenges and possible solutions that still need to be addressed in the future development of stretchable supercapacitors are highlighted and prospected. This review comprehensively discusses the latest research progress in the field of stretchable supercapacitors and systematically elucidates the electrochemical and mechanical properties of these devices, hoping to improve the roadmap for scientists and engineers to develop supercapacitors with high electrochemical performance and good stretchability.