High-performance aqueous sodium-ion battery using a hybrid electrolyte with a wide electrochemical stability window

The practical application of aqueous sodium-ion batteries (ASIBs) is limited by the electrolysis of water, which results in a low working voltage and energy density of ASIBs. Here, a NaClO₄-based acetonitrile/water hybrid electrolyte (NaClO₄(H₂O)₂AN_2.4) is applied to ASIBs for the first time, which effectively extends the electrochemical stability window (ESW) to 3.0 V and reduces the internal resistance of the battery. Based on this hybrid electrolyte, an ASIB full cell using carbon coated Na_2.85K_0.15V₂(PO₄)₃ and NaTi₂(PO₄)₃ as the cathode and anode materials, respectively, can afford a discharge capacity and energy density of 52 mA h g^-1 and 51 W h kg^-1, respectively, at a current density of 1 A g^-1. The energy density of this battery exceeds almost all reported traditional ASIBs.