Effect of electrolytic solutions on the electrochemical performance of binder-free VMnS electrode and its applications as an energy storage devices

Abstract

The electrolytes in supercapacitors (SCs) are essential in determining the capacity for storing energy. The durability of the electrolytic solution is determined by the operating potential of the SCs. And the power density of SCs is mainly dependent upon the electrolytic viscosity. This work presents an electrochemically stable ethylene glycol (EG)-derived electrolyte for electrochemical tests. The presence of lithium tetrafluoroborate (LiBF4) salt in EG decreases the viscosity. The effect of salt content on EG viscosity had been examined. The structure and surface analysis of vanadium sulfide (VS2), manganese sulfide (MnS), and vanadium manganese sulfide (VMnS) were carried out using X-ray diffractometry (XRD) and scanning electron microscope (SEM), respectively. The tensile strength measurements revealed that VMnS had a high mechanical tensile strength of 59.3. The maximum ionic conductivity of 7.32 mS/cm was achieved with 4 M LiBF4 in the EG electrolyte. The highest electrochemical performance of hydrothermally synthesized vanadium manganese sulfide (VMnS) electrodes was obtained with 4 M LiBF4-EG electrolyte. The VMnS in EG-based electrolyte delivered a specific capacity of 1615C/g. The supercapattery (VMnS//AC) was also developed with vanadium manganese sulfide and activated carbon as positive and negative electrodes. This supercapattery (VMnS//AC) can provide a capacity of 204.2C/g. The energy density of the VMnS/AC supercapattery reached 68.12 Wh/kg. The VMnS//AC asymmetric device was subjected to 10,000 consecutive cycles to check durability. After completing 10,000 cycles, this device can retain 80 % of its capacity. This study reveals that VMnS//AC asymmetric device with 4 M LiBF4-EG can be used in energy storage systems.