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 NaClO 4 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 Na 2 CO 3 and Na–O compounds including NaOH, guarantees the excellent electrochemical storage stability of the full-cell composed of Na 4 Fe 3 (PO 4 ) 2 (P 2 O 7 ) cathode and NaTi 2 (PO 4 ) 3 anode for the extended period of time. This new class of electrolyte systems provides remarkable cycle stability and a coulombic efficiency of ∼99% at 1C for over 200 cycles, which outperforms the state-of-the-art super-concentrated systems based on NaCF 3 SO 3 . 2019 The Authors. Published by Elsevier Ltd.