Nan Lu,Ruiqi Na,Leibo Li,Chongyang Zhang,Zhuoqi Chen,Shuling Zhang,Jiashuang Luan,Guibin Wang
Hydrogel electrolytes have gained significant attention in the field of flexible supercapacitors for their intrinsic safety, high flexibility, and superior ionic conductivity. However, the water-rich structures of traditional hydrogel electrolytes inevitably cause them to freeze at subfreezing temperatures, which therefore limits the application of flexible supercapacitors at extremely cold temperatures. Herein, an organohydrogel electrolyte was successfully fabricated by displacing a portion of water molecules from hydroxypropyl cellulose/poly(vinyl alcohol) (HPC/PVA) hydrogel with LiClO4 water/glycerol mixture solution. The introduction of glycerol and inorganic salt into the hydrogel matrix can effectively preclude the ice formation of water at subfreezing temperatures. The flexible supercapacitor comprising the optimal antifreezing organohydrogel electrolyte exhibited excellent mechanical and electrochemical stability at subfreezing temperatures. Even if the temperature decreased to −40 °C, the supercapacitor could also deliver a specific capacitance of 143.6 F g–1 (73.75% of the one delivered at 20 °C) with Coulombic efficiency approaching ∼100%. Meanwhile, the electrochemical performance of the supercapacitor could also be well maintained under different bending conditions. It is believed that this work will play an exemplary role for designing antifreezing gel electrolytes for flexible energy storage devices using at extremely cold environments.
Solid polymer electrolyte based on the random copolymer PGO from the monomers of glycidyl methacrylate (GMA) and oligo (ethylene oxide) methyl ether methacrylate (OE) was successfully synthesized and investigated in detail aiming at applications in all solid lithium ion battery . Namely, four polymers PGO-60, PGO-70, PGO-80, PGO-90 with numbers indicating the percentage molar ratio of OE were mixed with LiClO 4 , and studied for their Li conductivity and other electrochemical properties in order to understand the effects from the polar glycidyl moieties. Polymer PGO-70 showed the highest ionic conductivity of 2.08 × 10 −5 S/cm when the LiClO 4 content was 50% and at 50 °C. PGO-60 had the largest lithium ion transference number of 0.549, and exhibited electrochemical stability up to 4.4 V vs. Li + /Li. When the epoxy groups in the polymer were hydrolyzed, two hydroxyl groups as side chain pendants were obtained. When tested, the ring-opening membrane HPGO-70 showed significantly higher ionic conductivity (2.26 × 10 −6 S/cm, LiClO 4 = 30%) than the corresponding PGO-70 (2.58 × 10 −7 S/cm, LiClO 4 = 30%) at room temperature . The maximum lithium ion transport number of ring-opening polymers is 0.693 for HPGO-60, however, it's stability was a little lowered to 4.0 V vs. Li + /Li. Generally, compared with the polymer electrolyte membrane before ring opening, the lithium ion conductivity and lithium ion transference number of the ring-opening polymer electrolyte membrane were improved, however, the electrochemical stability window was slightly reduced. In the preliminary test of the assembled half cell battery using HPGO-60 as the polymer electrolyte and LiFePO 4 as the anode, fairly good charge/discharge cycling can be achieved at 25 °C, but the capacity remained quite low (around 20 mAh/g). When temperature increased to 70 °C, the capacity increased considerably to 99 mAh/g at the first cycle, but quickly decreased to around 50 mAh/g.
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