A battery-supercapacitor hybrid energy storage device that directly uses seawater or saltwater lake water

Rechargeable seawater batteries (RSWBs) are highly attractive for grid storages, because seawater is free of charge, eco-friendly, and sustainable. A common route to achieve a balanced comprehensive performance for electrochemical energy storages is to combine the battery-supercapacitor behaviors, which has not been tried for RSWBs. Herein, we propose a seawater battery-supercapacitor hybrid device, which is constructed by a pseudocapacitive amorphous MoO x anode and an intercalation-type Prussian blue analogue cathode, to achieve high overall performances. Both the anode and cathode demonstrate high specific capacities, excellent rate performances, and high reversibility, due to pseudocapacitive characteristic of the anode and the open framework crystallographic structure of the cathode. The hybrid device displays a high specific energy of 41.2 Wh/kg at a high specific power of 519 W/kg and a high energy efficiency up to 76.8 %. By using directly salt-lake water (Qinghai Lake and Yuncheng Salt Lake) as electrolyte, the hybrid device also displays excellent electrochemical performances. This work provides a new avenue for developing high-performance sustainable energy storage devices.