Toward a low-cost high-voltage sodium aqueous rechargeable battery

Recent discovery of high-concentration electrolyte systems has opened a new avenue toward the high-voltage, safe, and low-cost aqueous rechargeable batteries. However, the need for generally high-cost organic solutes in the high-concentration electrolyte has become another major obstacle. Herein, we revisited all the commonly used low-cost solutes for high-concentration system and discovered that the use of NaClO4 solute effectively results in a wide electrochemical stability window by suppressing water decomposition and induces stable solid-electrolyte interphase (SEI) layer formation without involving the reduction of salt anions. The SEI layer, composed of Na2CO3 and Na-O compounds including NaOH, guarantees the excellent electrochemical storage stability of the full-cell composed of Na4Fe3(PO4)(2)(P2O7) cathode and NaTi2(PO4)(3 )anode for the extended period of time. This new class of electrolyte systems provides remarkable cycle stability and a coulombic efficiency of similar to 99% at 1C for over 200 cycles, which outperforms the state-of-the-art super-concentrated systems based on NaCF3SO3.