Preparation And Functionalization Of Alkaline Hydrogels And Their Application In Zinc-based Hybrid Supercapacitors

The fast-growing development of flexible artificial intelligence and wearable electronic devices have brought widespread attention to flexible energy storage devices.Electrolytes play an indispensable part of energy storage devices.Among many electrolyte materials,hydrogels are considered to be one of the most potential candidates for supercapacitor electrolytes due to their excellent flexibility,high electrical conductivity,low leakage and safety.In this paper,to address the issues such as low energy density and poor mechanical properties of current flexible supercapacitors,a series of functional hydrogel electrolytes are designed and studied.The details are as follows:1.An alkaline ionic conductive hydrogel（PEGMA）was prepared by copolymerization of poly（ethylene glycol）methyl ether acrylate（PEGA）,2-methoxyethyl acrylate（MEA）and acrylamide（AM）,and potassium hydroxide（KOH）was selected as conductive substance to form hydrogel electrolyte for the flexible hybrid supercapacitors.A supercapacitor（PEGMA-ZHS）was assembled with the alkaline hydrogel as electrolyte,zinc foil as the negative electrode and activated carbon as the positive electrode.The specific capacity can reach 134.8 m Ah g^-1.The power density was 2647.4 W kg^-1 at the energy density of 356.6 Wh kg^-1.In addition,PEGMA-ZHS exhibited excellent electrochemical stability.The capacity retention and Coulombic efficiency can still retain 100%after 10,000 charge-discharge cycles.2.By introducing sodium carboxymethyl cellulose as the second network,a double network hydrogel was prepared.The mechanical properties of the hydrogel were greatly improved,which the breaking strength increased from 0.0102 MPa to 0.110MPa and the elongation at break increased from 608%to 1425%.The hydrogel maintains its integrity even when it is compressed by 80%and can quickly return to its original shape after removing the external force.A zinc-based hybrid supercapacitor was assembled using the hydrogel film,and the specific capacitance of the supercapacitor could reach 100.1 m Ah g^-1.Benefiting from the decent adhesion of the hydrogel to the electrode,the hydrogel supercapacitor could keep excellent capacity retention under various bending angles.3.In the purpose of enhancing the flexibility of the hydrogel at low temperature,a hard hydrogel was prepared by using N,N’-methylenebisacrylamide to crosslink CMC-PEGMA hydrogel.Then soak it in concentrated KOH solution and an alkaline antifreezing hydrogel（CPMA）was prepared.The freezing point of CPMA was lowered to-34.3°C.The CPMA-SC supercapacitor assembled with CPMA can achieve a specific capacity of 182.13 m Ah g^-1 under a voltage window of 2 V and a specific capacity of 107.31 m Ah g^-1 at-20℃.And after 5000 cycles at-20°C,the cycle performance of the device is as high as 89.37%.