Electrolytes play a pivotal role in determining the electrochemical performance of anode-free sodium metal batteries. Ether-based electrolytes exhibit superior compatibility with sodium metal anode, while their poor oxidation stability has historically restricted their application in high-voltage systems. Although high concentration and localized high concentration strategies have been employed to improve the oxidation resistance, their high costs and complexity remain significant barriers. Herein, a low-cost, standard-concentration (1 M) ether-based electrolyte that achieved exceptional high-voltage stability was developed. The extended ether chains endow tetraethylene glycol dimethyl ether with intrinsically enhanced oxidation resistance by lowering its highest occupied molecular orbital energy level, while maintaining excellent reduction stability. Furthermore, the BF₄⁻ anions preferentially decompose to form a robust boride- and fluoride-rich interphase at the cathode surface. This synergistic effect between the solvent and anion enables an anode-free Al@C||Na₂Fe₂(SO₄)₃ battery to deliver 500 stable cycles at a high charging cut-off voltage of 4.5 V, with an average discharging voltage of 3.8 V. This work not only demonstrates the feasibility of high-voltage ether-based electrolytes at standard concentrations, but also provides critical insights and references for the development of advanced electrolytes for next-generation batteries.

Zn-based batteries have attracted extensive attention due to their high theoretical energy density, safety, abundant resources, environmental friendliness, and low cost. They are a new energy storage and conversion technology with significant development potential and have been widely used in renewable energy and portable electronic devices. Considerable attempts have been devoted to improving the performance of Zn-based batteries. Specifically, battery cycle life and energy efficiency can be improved by electrolyte modification and the construction of highly efficient rechargeable Zn anodes. This review compiles the progress of the research related to Zn anodes and electrolytes, especially in the last five years. This review will introduce fundamental concepts, summarize recent development, and inspire further systematic research for high-performance Zn-based batteries in the future.