High-voltage and long-lasting aqueous chlorine-ion battery by virtue of "water-in-salt" electrolyte.

Chloride-ion battery (CIB) is regarded as a promising electrochemical storage device due to their high theoretical volumetric capacities, low cost, and high abundance. However, low-cycle life limits its application in the energy storage field. Herein, we report a rechargeable CIB composed of a "water-in-salt" electrolyte, a zinc anode, and a carbon cathode (graphene, carbon nanotubes, carbon black). These cathodes exhibit initial reversible specific capacities of 136, 108, and 102 mAh g-1, respectively. Especially, a reversible discharge capacity of 95 mAh g-1 was retained after 2000 cycles when graphene is used as the cathode. Such high cycling stability was first reported in CIBs. Furthermore, the use of "water-in-salt" electrolytes has improved the discharge platform of aqueous CIBs to 2.6V. The charge and discharge mechanism of the carbon cathode was investigated by TEM, FTIR, Raman, and XPS, proving the chloride ions reversible absorption/desorption in carbon cathodes.