Self-adhesive, freeze-tolerant, and strong hydrogel electrolyte containing xanthan gum enables the high-performance of zinc-ion hybrid supercapacitors.

Hydrogel electrolyte is an ideal candidate material for flexible energy storage devices due to its excellent softness and conductivity properties. However, challenges such as the inherent mechanical weakness, the susceptibility to be frozen in low-temperature environments, and the insufficiency of hydrogel-electrode contact persist. Herein, a "Multi in One" strategy is employed to effectively conquer these difficulties by endowing hydrogels with high strength, freeze-resistance, and self-adhesive ability. Multiple hydrogen bond networks and ion crosslinking networks are constructed within the hydrogel electrolyte (PVA/PAAc/XG) containing polyvinyl alcohol (PVA), acrylic acid (AAc), and xanthan gum (XG), promoting the enhanced mechanical property, and the adhesion to electrode materials is also improved through abundant active groups. The introduction of zinc ions provides the material with superior frost resistance while also promoting electrical conductivity. Leveraging its multifunction of superior mechanical strength, anti-freeze property, and self-adhesive characteristic, the PVA/PAAc/XG hydrogel electrolyte is employed to fabricate zinc ion hybrid supercapacitors (ZHS). Remarkably, ZHS exhibits outstanding electrochemical performance and cycle stability. A remarkable capacity retention rate of 83.86 % after 10,000 charge-discharge cycles can be achieved at high current densities, even when the operational temperature decreases to -60 °C, showing great potential in the field of flexible energy storage devices.

Zhou Y ，Liu H ，Zhou X ，Lin X ，Cai Y ，Shen M ，Huang X ，Liu H ，Xu X ... -  《-》

Freeze-Tolerant Hydrogel Electrolyte with High Strength for Stable Operation of Flexible Zinc-Ion Hybrid Supercapacitors.

Constructing ionic conductive hydrogels with diversified properties is crucial for portable zinc-ion hybrid supercapacitors (ZHSCs). Herein, a freeze-tolerant hydrogel electrolyte (AF PVA-CMC/Zn(CF3 SO3 )2 ) is developed by forming a semi-interpenetrating anti-freezing polyvinyl alcohol-carboxymethyl cellulose (AF PVA-CMC) network filled with the ethylene glycol (EG)-containing Zn(CF3 SO3 )2 aqueous solution. The semi-interpenetrating AF PVA-CMC/Zn(CF3 SO3 )2 possesses enhanced mechanical properties, realizes the uniform zinc deposition, and impedes the dendrite growth. Notably, the interaction between PVA and EG suppresses the ice crystal formation and prevents freezing at -20 °C. Due to these advantages, the designed hydrogel owns high ionic conductivity of 1.73/0.75 S m-1 at 20/-20 °C with excellent tensile/compression strength at 20 °C. Impressively, the flexible AF quasi-solid-state ZHSC employing the hydrogel electrolyte achieves a superior energy density at 20/-20 °C (87.9/60.7 Wh kg-1 ). It maintains nearly 84.8% of the initial capacity after 10 000 cycles and a low self-discharge rate (1.77 mV h-1 ) at 20 °C, together with great tolerance to corrosion. Moreover, this device demonstrates a stable electrochemical performance at -20 °C under deformation. The obtained results provide valuable insights for constructing durable hydrogel electrolytes in cold environments.

Zhu X ，Ji C ，Meng Q ，Mi H ，Yang Q ，Li Z ，Yang N ，Qiu J ... -  《-》

Dual-network polyvinyl alcohol/polyacrylamide/xanthan gum ionic conductive hydrogels for flexible electronic devices.

Ionic conductive hydrogels (ICHs) have received widespread attention as an ideal candidate for flexible electronic devices. However, conventional ICHs failed in widespread applications due to their inability to simultaneously possess high toughness, high ionic conductivity, and anti-freezing properties. Here, polyvinyl alcohol (PVA) and polyacrylamide (PAAm) were first dissolved in the zinc chloride solution, in which zinc ions (Zn2+) act as ionic cross-linkers and conducting ions, followed by the introduction of xanthan gum (XG) with a unique structure of trisaccharide side chains into the PVA/PAAm semi-interpenetrating network to prepare a dual-network ICHs (refers as PPXZ). Enabled by the synergistic effect of intermolecular chemical covalent cross-linking and physical cross-linking, PPXZ hydrogels exhibit significantly improved mechanical properties without sacrificing electrical conductivity. Furthermore, PPXZ hydrogels are successfully applied to flexible electronic devices, such as strain sensors and zinc ion hybrid supercapacitors, exhibiting satisfactory sensing sensitivity and cycling stability at a wide temperature range, respectively. Even at a high current density (10 A g-1), the capacity of the supercapacitor retains 88.24 % after 10,000 cycles. This strategy provides new insight for ICHs in wide temperature-applied flexible electronic devices.

Zhou Y ，Zhang L ，Lin X ，Lu J ，Huang Z ，Sun P ，Zhang Y ，Xu X ，Li Q ，Liu H ... -  《-》

A Powder Self-Healable Hydrogel Electrolyte for Flexible Hybrid Supercapacitors with High Energy Density and Sustainability.

Ionic conductive hydrogel electrolyte is considered to be an ideal electrolyte candidate for flexible supercapacitor due to its flexibility and high conductivity. However, due to the lack of effective recycling methods, a large number of ineffective flexible hydrogel supercapacitors caused by some irreversible damages and dryness of hydrogel electrolyte are abandoned, which would induce heavy economic and environmental protection problems. Herein,a smart ionic conductive hydrogel (SPMA-Zn: ZnSO4 /sodium alginate/polymethylacrylic acid) is developed for flexible hybrid supercapacitor (SPMA-ZHS). The SPMA-Zn exhibits an excellent self-healing ability and can recover its electrochemical performance after multiple mechanical damages. More importantly, it possesses an outstanding powder self-healable property, which could easily regenerate the hydrogel electrolyte after powdering, and maintain stable electrochemical performance of SPMA-ZHS. Besides, the SPMA-ZHS displays excellent electrochemical performance with a wide and stable working voltage range of 0-2.2 V, high energy density of 164.13 Wh kg-1 at the power density of 1283.44 Wh kg-1 and good stability with a capacity retention of 95.3% after 5000 charge/discharge cycles at 10 A g-1 . The strategy in this work would provide a new insight in exploring flexible hydrogel electrolyte-based supercapacitor with good sustainability and high energy density for flexible wearable electronic devices.

Huang H ，Han L ，Fu X ，Wang Y ，Yang Z ，Pan L ，Xu M ... -  《-》

Nucleotide-Tackified Organohydrogel Electrolyte for Environmentally Self-Adaptive Flexible Supercapacitor with Robust Electrolyte/Electrode Interface.

Hydrogel electrolytes have attracted enormous attention in flexible and safe supercapacitors. However, the interfacial contact problem between hydrogel electrolyte and electrodes, and the environmental instability are the key factors restricting the development of hydrogel-based supercapacitors. Here, a nucleotide-tackified adhesive organohydrogel electrolyte is successfully constructed and exhibits freezing resistance and water-holding ability based on the water/glycerol binary solvent system. Adenosine monophosphate enables the organohydrogels to possess outstanding adhesion and mechanical robustness. The robust adhesion can ensure close contact between the organohydrogel electrolyte and electrodes for constructing an all-in-one supercapacitor with low interfacial contact resistance. Impressively, the integrated organohydrogel-based supercapacitors display an areal specific capacitance of 163.6 mF cm-2 . Besides, the supercapacitors feature prominent environmental stability with capacitance retention of 90.6% after 5000 charging/discharging cycles at -20 °C. Furthermore, based on the strong interfacial adhesion, the supercapacitors present excellent electrochemical stability without delamination/displacement between electrolyte and electrodes even under severe deformations such as bending and twisting. It is anticipated that this work will provide an encouraging way for developing flexible energy storage devices with electrochemical stability and environmental adaptability.

Zhang Q ，Hou X ，Liu X ，Xie X ，Duan L ，Lü W ，Gao G ... -  《-》