All-Solid-State Experimental Supercapacitors on the Basis of Advanced Superionic Conductors

In crystals of advanced superionic conductors (AdSICs), the hopping fast ionic transport (FIT) has record-braking low activation energy ≈ 0.1 eV while specific ionic conductivity (Ag+-or Cu+-ions) is at the level ≈ 0.2 Om-1cm-1 (300K), which is also characteristic of liquid electrolytes. All-solid-state and rather high-frequency supercapacitors on the basis of AdSICs (perspective, for example, for on-chip applications) are not presented in literature though could be demanded. In this work, the experimental SC with symmetrical functional heterojunctions, i.e., electronic conductor (EC) /AdSIC/ EC, were created by a method of crystallization of AdSIC-fusion on surfaces of macroscopically smooth ECs. The search for the states with FIT on EC/AdSIC het-erojunctions was fulfilled by the method of comparison of charge-discharge characteristics of EC/AdSIC/EC and standard capacitor, close in capacitance. Chemical compositions of EC and AdSIC were modified when developing of SC with acceptable characteristics. New AdSICs, i.e., solid solutions on the basis of CsAg4Br2.5I2.5 chemical compound in which a part of iodine was replaced by tellurium, were for the first time synthesized. These AdSICs provided in EC/AdSIC/EC (EC are alloys on the basis of Au) with volume of about 1 mm3 the record high specific capacitance δС > 100 μF cm-2 (at T = 300 K) for charge/discharge duration τ ∼ 50μs (for f recharge frequencies ∼104 Hz): the phenomenon can be caused by FIT in an electric double-layer (EDL). The capacitance δС > 100 μF cm-2 remained after 300 000 cycles of charge/discharge. The graphic scheme of distribution of charges explaining the nature of δС > 100 μF cm-2 is proposed. At an increase of τ to 5 s the capacitance of EC/AdSIC/EC increased up to δС ∼ 5000— 8000μF/cm2 what is explained with presence of pseudocapacitance. Further R & D are necessary as for creation of prototypes of EC/AdSIC/EC supercapacitors with δС > 100 μF cm-2 (300 K, τ ∼ 1 ÷ 10 μs) by methods of microelectronic technologies, and for increase of capacitance by use of EC having a large internal 3D surface.