Résumé
In this work we report on the properties of three novel aqueous electrolytes containing 1 m (mol kg −1 ) of lithium formate, sodium formate and potassium formate in H 2 O. We show that these cheap and environmentally friendly electrolytes display high conductivity and low viscosity from 0 °C to 80 °C. When used in asymmetric supercapacitors (SCs) containing Manganese dioxide (MnO 2 ) as active material in the positive electrode and activated carbon (AC) as active material in the negative electrode, these electrolytes allow the design of devices with operating voltage up to 1.7 V. Asymmetric SC containing these novel electrolytes display good capacity (19 mAh g −1 , 18 mAh g −1 and 13 mAh g −1 in 1 m HCOOK in H 2 O, 1 m HCOOLi in H 2 O and 1 m HCOONa in H 2 O, respectively). The capacity retention after 10,000 cycles of the devices containing 1 m HCOOLi in H 2 O, 1 m HCOONa in H 2 O and 1 m HCOOK in H 2 O are all higher than 85%.