Solid-State Double-Network Hydrogel Redox Electrolytes for High-Performance Flexible Supercapacitors

Self-healing, deformable and safe integrated supercapacitor enabled by synergistic effect of multiple physical interactions in gel polymer electrolyte with dual-role Co2

With the rapid development of wearable electronic devices, flexible supercapacitors have gained strong interest. However, traditional sandwich supercapacitors have weak interfacial binding, resulting in high interface resistance and poor deformability. Herein, a self-healing integrated supercapacitor based on a polyacrylic acid-polyisodecyl methacrylate-CoSO4 gel polymer electrolyte (GPE) was developed. By incorporating ion coordination into a hydrophobic association network, a double network structure was formed, endowing the GPE with remarkable mechanical properties and self-healing abilities. Specifically, Co2+ ions functioned both as charge carrier and crosslinker, simultaneously enhancing the electrochemical (2.87 S/m) and mechanical (0.262 MPa) properties of the GPE. In situ growth of polyaniline electrode material on the GPE surface resulted in an integrated supercapacitor with a continuous morphology at the electrode/electrolyte interface, minimizing interface resistance and improving electrochemical performance. The supercapacitor exhibits high specific capacitance, exceptional cyclic stability, superior deformability and security due to the unique integrated structure. Furthermore, it demonstrates remarkable electrochemical and self-healing properties even at quite low temperature. Overall, this work offers a promising approach for reliable self-healing energy storage devices with high performance and adaptability to complex usage conditions.

Recent Advancements in Gel Polymer Electrolytes for Flexible Energy Storage Applications

Since the last decade, the need for deformable electronics exponentially increased, requiring adaptive energy storage systems, especially batteries and supercapacitors. Thus, the conception and elaboration of new deformable electrolytes becomes more crucial than ever. Among diverse materials, gel polymer electrolytes (hydrogels, organogels, and ionogels) remain the most studied thanks to the ability to tune the physicochemical and mechanical properties by changing the nature of the precursors, the type of interactions, and the formulation. Nevertheless, the exploitation of this category of electrolyte as a possible commercial product is still restrained, due to different issues related to the nature of the gels (ionic conductivity, evaporation of filling solvent, toxicity, etc.). Therefore, this review aims to resume different strategies to tailor the properties of the gel polymer electrolytes as well as to provide recent advancements in the field toward the elaboration of deformable batteries and supercapacitors.

Impact-resistant supercapacitor by hydrogel-infused lattice

The safety of energy storage devices is increasingly crucial due to the growing requirements for application under harsh conditions. Effective methods for enhancing robustness without compromising functionality are necessary. Here we present an impact-resistant, ready-to-use supercapacitor constructed from self-healable hydrogel electrolyte-infused lattice electrodes. Three-dimensional-printed carbon-coated silicon oxycarbide current collectors provide mechanical protection, with compressive stress, Young's modulus, and energy absorption up to 70.61 MPa, 2.75 GPa, and 92.15 kJ/m3, respectively. Commercially viable polyaniline and self-healable polyvinyl alcohol hydrogel are used as active coatings and electrolytes. I-wrapped package structured supercapacitor electrode exhibits a static specific capacitance of 585.51 mF/cm3 at 3 mA/cm3, with an energy density of 97.63 μWh/cm3 at a power density of 0.5 mW/cm3. It maintains operational integrity under extreme conditions, including post-impact with energy of 0.3 J/cm3, dynamic loading ranging from 0 to 18.83 MPa, and self-healing after electrolyte damage, demonstrating its promise for applications in extreme environments.

Reversibly Stretchable Organohydrogel-Based Soft Electronics with Robust and Redox-Active Interfaces Enabled by Polyphenol-Incorporated Double Networks

Hydrogel electrolytes as soft ionic conductors have been extensively exploited to establish skinlike and biocompatible devices. However, in many common hydrogels, there exists irreversible elongation upon prolonged stretching cycles and poor interfacial contact, which have significantly hindered their practical applications where long-term operation at large deformations is needed. Herein, multifunctional soft electronic devices with reversible stretchability and improved electrode/electrolyte interfaces are demonstrated by employing polyacrylamide-based double-network organohydrogel electrolytes soaked with a high content of tannic acid (TA) that affords multiple noncovalent interactions and redox activity. Performances of the TA-rich gels are evaluated for the first time in realizing shape-recoverable stretchable devices against repeated deformations to 500% strain, with superior gel-electrode interfaces exhibiting both intimate adhesion and boosted electrochemical capacitance of >200 mF·cm^-2. A maximal 4-fold higher capacitance can be achieved by introducing TA and ethylene glycol (EG) into hydrogels. Moreover, a soft electronic system consisting of stretchable supercapacitors and gel-based microsensors was demonstrated, in which the electronic performance of these devices can be well preserved after >1000 repeated cycles at strains of up to 200%, without obvious residual strain or electrode delamination. This could pave a route to the design of multifunctional gel networks tackling both the mechanical and interfacial issues in soft and biocompatible devices.

Nitrogen-Doped Nanoporous Anodic Stainless Steel Foils towards Flexible Supercapacitors

In this work, we report the fabrication and enhanced supercapacitive performance of nitrogen-doped nanoporous stainless steel foils, which have been prepared by electrochemical anodization and subsequent thermal annealing in ammonia atmosphere. The nanoporous oxide layers are grown on type-304 stainless steel foil with optimal thickness ~11.9 μm. The N-doped sample exhibits high average areal capacitance of 321.3 mF·cm⁻² at a current density of 1.0 mA·cm⁻², 3.6 times of increment compared with untreated one. Structural and electrochemical characterizations indicate that the significant enhancement is correlated to the high charge transfer efficiency from nitriding nanosheet products Fe₃N. Our report here may provide new insight on the development of high-performance, low-cost and binder-free supercapacitor electrodes for flexible and portable electronic device applications with multiple anions.