All-climate aqueous Na-ion batteries using "water-in-salt" electrolyte

Aqueous Na-ion batteries have been extensively studied for large-scale energy storage systems. However, their wide application is still limited by their inferior cycle stability (<3000 cycles) and poor temperature tolerance. Furthermore, many of the reported high rate behaviors are achieved at a low mass loading (<3 mg cm^-2) of the electrodes. Herein, we propose an aqueous Na-ion battery which includes a Ni-based Prussian blue (NiHCF) cathode, a carbonyl-based organic compound, 5,7,12,14-pentacenetetrone (PT) anode and a "water-in-salt" electrolyte (17 mol kg^-1 NaClO₄ in water). Its operation involves the reversible coordination reaction of the PT anode and the extraction/insertion of Na⁺ in the NiHCF cathode. It is demonstrated that the wide internal spaces of the PT anode and NiHCF cathode can not only buffer the volumetric change induced by Na⁺ storage, but also enable fast kinetics. The full cell exhibits a supercapacitor-like rate performance of 50 A g^-1 (corresponding to a discharge or charge within 6.3 s) and a super-long lifespan of 15,000 cycles. Moreover, the excellent rate performance can still be preserved even with a high mass loading of the electrodes (15 mg_NiHCF cm^-2 and 8 mg_PT cm^-2). Especially, the cell can work well in a wide temperature range, from -40 to 100 °C, showing a typical all-climate operation.