For sodium (Na)‐rechargeable batteries to compete, and go beyond the currently prevailing Li‐ion technologies, mastering the chemistry and accompanying phenomena is of supreme importance. Among the crucial components of the battery system, the electrolyte, which bridges the highly polarized positive and negative electrode materials, is arguably the most critical and indispensable of all. The electrolyte dictates the interfacial chemistry of the battery and the overall performance, having an influence over the practical capacity, rate capability (power), chemical/thermal stress (safety), and lifetime. In‐depth knowledge of electrolyte properties provides invaluable information to improve the design, assembly, and operation of the battery. Thus, the full‐scale appraisal of both tailored electrolytes and the concomitant interphases generated at the electrodes need to be prioritized. The deployment of large‐format Na‐based rechargeable batteries also necessitates systematic evaluation and detailed appraisal of the safety‐related hazards of Na‐based batteries. Hence, this review presents a comprehensive account of the progress, status, and prospect of various Na⁺‐ion electrolytes, including solvents, salts and additives, their interphases and potential hazards.

Vanadium oxides have been recognized to be among the most promising positive electrode materials for aqueous zinc metal batteries (AZMBs). However, their underlying intercalation mechanisms are still vigorously debated. To shed light on the intercalation mechanisms, high-performance δ-V₂O₅ is investigated as a model compound. Its structural and electrochemical behaviors in the designed cells with three different electrolytes, i.e., 3 m Zn(CF₃SO₃)₂/water, 0.01 M H₂SO₄/water, and 1 M Zn(CF₃SO₃)₂/acetonitrile, demonstrate that the conventional structural and elemental characterization methods cannot adequately clarify the separate roles of H⁺ and Zn²⁺ intercalations in the Zn(CF₃SO₃)₂/water electrolyte. Thus, an operando pH determination method is developed and used toward Zn/δ-V₂O₅ AZMBs. This method indicates the intercalation of both H⁺ and Zn²⁺ into δ-V₂O₅ and uncovers an unusual H⁺/Zn²⁺-exchange intercalation–deintercalation mechanism. Density functional theory calculations further reveal that the H⁺/Zn²⁺ intercalation chemistry is a consequence of the variation of the electrochemical potential of Zn²⁺ and H⁺ during the electrochemical intercalation/release.

A novel lithium–oxygen battery exploiting PYR₁₄TFSI–LiTFSI as ionic liquid-based electrolyte medium is reported. The Li/PYR₁₄TFSI–LiTFSI/O₂ battery was fully characterized by electrochemical impedance spectroscopy, capacity-limited cycling, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results of this extensive study demonstrate that this new Li/O₂ cell is characterized by a stable electrode–electrolyte interface and a highly reversible charge–discharge cycling behavior. Most remarkably, the charge process (oxygen oxidation reaction) is characterized by a very low overvoltage, enhancing the energy efficiency to 82%, thus, addressing one of the most critical issues preventing the practical application of lithium–oxygen batteries.