A fundamental approach to design of injectable high-content gel polymer electrolyte for activated carbon electrode supercapacitors

Polymer Electrolytes for Supercapacitors

Because of safety concerns associated with the use of liquid electrolytes and electrolyte solutions, options for non-liquid materials like gels and polymers to be used as ion-conducting electrolytes have been explored intensely, and they attract steadily growing interest from researchers. The low ionic conductivity of most hard and soft solid materials was initially too low for practical applications in supercapacitors, which require low internal resistance of a device and, consequently, highly conducting materials. Even if an additional separator may not be needed when the solid electrolyte already ensures reliable separation of the electrodes, the electrolytes prepared as films or membranes as thin as practically acceptable, resistance may still be too high even today. Recent developments with gel electrolytes sometimes approach or even surpass liquid electrolyte solutions, in terms of effective conductance. This includes materials based on biopolymers, renewable raw materials, materials with biodegradability, and better environmental compatibility. In addition, numerous approaches to improving the electrolyte/electrode interaction have yielded improvements in effective internal device resistance. Reported studies are reviewed, material combinations are sorted out, and trends are identified.

Roles of gel polymer electrolytes for high-power activated carbon supercapacitors: ion reservoir and binder-like effects

Ion reservoir and binder-like effects of gel polymer electrolytes (GPEs) are suggested for working mechanisms to enhance rate capability and cycling stability of activated carbon (AC) supercapacitors (SCs) even at 3.4 V. Analysis on kinetics from cyclic voltammetry, electrochemical reactions through in situ Fourier-transform infrared spectroscopy, and differential information of galvanostatic curves reveals that the increased rate-capability is derived dominantly by an improved non-faradaic process by the ion reservoir effect of GPEs in the AC. Although the designed GPEs induce slightly higher bulk and diffusion resistance at the incipient stage, the GPEs play a binder-like function to suppress detachment of AC particles and aggravation of impedance parameters during cycling at 3.4 V.

Roles of gel polymer electrolytes (GPEs), ion reservoir and binder-like effects, are suggested for enhanced rate capability and high durability of supercapacitors at 3.4 V, surpassing the conventional liquid SCs.