Tough‐Hydrogel Reinforced Low‐Tortuosity Conductive Networks for Stretchable and High‐Performance Supercapacitors

Abstract

All‐solid‐state supercapacitors are seeing emerging applications in flexible and stretchable electronics. Supercapacitors with high capacitance, high power density, simple form factor, and good mechanical robustness are highly desired, which demands electrode materials with high surface area, high mass loading, good conductivity, larger thickness, low tortuosity, and high toughness. However, it has been challenging to simultaneously realize them in a single material. By compositing a superficial layer of tough hydrogel on conductive and low tortuous foams, a thick capacitor electrode with large capacitance (5.25 F cm‐2), high power density (41.28 mW cm‐2), and good mechanical robustness (ε = 140%, Γ = 1000 J m‐2) is achieved. The tough hydrogel serves as both a load‐bearing layer to maintain structural integrity during deformation and a permeable binder to allow interaction between the conductive electrode and electrolyte. It is shown that the tough hydrogel reinforcement is beneficial for both electrical and mechanical stability. With a simple design and facile fabrication, this strategy is generalizable for various conductive materials.

Highly Flexible and Broad-Range Mechanically Tunable All-Wood Hydrogels with Nanoscale Channels via the Hofmeister Effect for Human Motion Monitoring

“…Induced by the Hofmeister effect, crystal domains and numerous hydrogen bonds are formed in the hydrogel network, resulting in the high mechanical strength of the all-wood hydrogels [ 35 , 38 , 47 – 49 ]. The effects of lignin content, PVA content, and salting time on the tensile strength of all-wood hydrogels in the L-directional are further investigated.…”

“…The excellent mechanical properties of allwood hydrogels are mainly attributed to the strong hydrogen bonding, physical entanglement, and van der Waals forces between cellulose nanofibers, lignin molecules, and PVA chains, and the toughening effect of cellulose nanofibers. Induced by the Hofmeister effect, crystal domains and numerous hydrogen bonds are formed in the hydrogel network, resulting in the high mechanical strength of the allwood hydrogels [35,38,[47][48][49]. The effects of lignin content, PVA content, and salting time on the tensile strength of all-wood hydrogels in the L-directional are further 1 3 investigated.…”

“…Different salts show distinguishable abilities to precipitate proteins/polymers from aqueous solutions, which is defined as the Hofmeister effect [35][36][37]. Some reports discussed the relationship between various ions and the solubility of the polymers (e.g., poly(vinyl alcohol) (PVA)) and made it possible to use different ions to obtain hydrogels with tunable mechanical properties [36,38]. With these considerations and inspirations from the ion-specific phenomena, we design a PVAreinforced all-wood hydrogel by constructing microstructure between cellulose fibers, PVA chains, and lignin molecules using the Hofmeister effect without modifications for the raw materials and any chemical cross-linking agent (Fig.…”

Correlating Ionic Conductivity and Microstructure in Polyelectrolyte Hydrogels for Bioelectronic Devices

“…Various definition and measurements of tortuosity have been reported from the perspective of engineers geologists and chemists, [34,35] but rarely studied for hydrogels. In fact, hydrogels with low tortuosity are desired for supercapacitors [36] and ion-based bioelectronic devices, so the investigation on the hydrogel tortuosity is in demand. Figure 4l shows the definition of tortuosity: the ratio of the actual distance that ions travel between two points by following the microchannel of the hydrogel to the straight-line distance between the two points (Equation 8).…”

Interface Engineering on Cellulose‐Based Flexible Electrode Enables High Mass Loading Wearable Supercapacitor with Ultrahigh Capacitance and Energy Density

“…Recent studies have demonstrated that aligning internal constructions and creating available pore channels for lower tortuosity can effectively regulate the ion transport. [19][20][21][22] Taking these advances, greatly improved device performance has been achieved with high mass loading electrode. However, such achievements can only be valid for specific materials and special equipment, and do not apply to flexible electrodes.…”