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

Abstract

The global pandemic of coronavirus has caused a huge blow to the whole human society. [1] In this regard, the development of renewable energy and corresponding energy Constructing ionic conductive hydrogels with diversified properties is crucial for portable zinc-ion hybrid supercapacitors (ZHSCs). Herein, a freezetolerant hydrogel electrolyte (AF PVA-CMC/Zn(CF 3 SO 3 ) 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(CF 3 SO 3 ) 2 aqueous solution. The semi-interpenetrating AF PVA-CMC/Zn(CF 3 SO 3 ) 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.

Kinetics‐Boosted Effect Enabled by Zwitterionic Hydrogel Electrolyte for Highly Reversible Zinc Anode in Zinc‐Ion Hybrid Micro‐Supercapacitors

“…It is worth mentioning that the DOD value (80.9%) of the Zn anode in PASHE is higher than that of recent reports with various strategies (Table S1, Supporting Information). The cumulative capacity of the Zn|PASHE|Zn cell at 20 mA cm −2 and 1 mAh cm −2 is superior to reported symmetrical cells with hydrogel electrolyte engineering (Figure 4i) [17,20,24,[53][54][55][56][57][58][59][60][61][62][63] and other strategies (Table S2, Supporting Information), respectively.…”

“…Hydrogel electrolytes with polymeric matrices, as distinct from LE, can capture electrolytes to guide their migration, immobilize free water molecules to abate their activity, and function as ion‐conduction separators, which are particularly advantageous for ZHMSCs to alleviate the mentioned issues. [ 17,18 ] Significantly, the H 2 O activity‐reduced effect of hydrogel electrolytes contributed by hydrophilic groups in polymeric matrices relieves H 2 O‐induced corrosion and H 2 evolution of the Zn anode. [ 11 ] Despite these superiorities, sluggish kinetics of Zn 2+ transport and desolvation of hydrated Zn 2+ in hydrogel electrolytes greatly weakens the capabilities of dendrite and parasitic reactions suppression for such electrolytes.…”

High‐Rate, Large Capacity, and Long Life Dendrite‐Free Zn Metal Anode Enabled by Trifunctional Electrolyte Additive with a Wide Temperature Range

“…Recently, the demand for commercial energy storage applications operated in extreme weather or low‐temperature conditions has risen. [ 34 , 35 , 36 ] For instance, AZIBs and Zn‐ion‐based capacitors that maintain stable performance under the subzero temperatures are urgently needed. [ 37 , 38 , 39 ] The aqueous electrolytes will freeze at low temperature (<0 °C), which not only decreases the migration rate of Zn 2+ , but also causes a sharp fluctuation in pH at the interface within the Zn electrode/aqueous electrolyte.…”

Multifunctional Quasi-Solid-State Zinc–Sulfur Battery

“…Next, 2 mL of the I 2 /W-EG solution was added to the PVA/zinc acetate dihydrate/W-EG solution (Figure S1), and the mixture was stirred at 70 °C for 24 h. The resultant viscous solution was then coated on the anode and cathode materials, sandwiched, and subjected to freeze/thaw cycles to solidify. During the freeze/thaw process, PVA chains with a 3D network (PVA crystalline domains) form by developing intermolecular hydrogen bonds between PVA chains and H 2 O and PVA chains and ethylene glycol components . According to the technique reported in ref , the ionic conductivity of the as-prepared electrolyte is 8.8 mS/cm.…”