Self-combustion synthesis of dilithium cobalt bis(tungstate) decorated with silver nanoparticles for high performance hybrid supercapacitors

Oxide materials LixMy(XO4)z (M = Ni, Co, Fe, Mn...) and (X = P, W, Mo, As) with an open frame structure are of great interest for electrochemical energy storage. In this work, a high energy density Hybrid supercapacitor (HSC) was fabricated by combining a battery-type (faradaic) Li2Co(WO4)2@Ag electrode with an Activated carbon (AC) as a capacitive type electrode (non-faradaic). First, the dilithium cobalt bis(tungstate), Li2Co(WO4)2, material was prepared by a facile chemical method (self-combustion), followed by coating with silver nanoparticles (Ag NPs) through reduction of silver ions (Ag+) using ethanol containing Polyvinylpyrrolidone (PVP) to improve the conductivity of the composite. The Li2Co(WO4)2@Ag electrode delivered a specific capacity almost two-times greater (1192C/g at a current density of 1 A/g) compared to the electrode without silver (631.2 C/g at 1 A/g) in an electrolyte of 6 M KOH aqueous solution, and also exhibited an excellent retention capacity of 85.2% after 10,000 cycles at 20 A/g. Furthermore, Li2Co(WO4)2@Ag//AC hybrid supercapacitor was assembled and delivered a high energy density of 89.33 Wh/kg at the power density of 800 W/kg. At a maximum power density of 8 kW/kg, the HSC provided an energy density of 58.66 Wh/kg along with an excellent capacity retention (83.4%) after 10,000 charge-discharge cycles at 5 A/g.