Aqueous Sodium–Lithium Engineering-Grade Pouch Cell with Good Environmental Adaptability under a Wide Voltage Window

Aqueous sodium–lithium-ion batteries (ASLIBs) represent an economically viable, efficient, safe, and reliable technology for large-scale grid energy storage in the context of transitioning toward a low-carbon society. Nevertheless, the development of engineering-grade ASLIBs simultaneously featuring a wide voltage window and robust environmental adaptability remains a substantial challenge. In this study, a novel aqueous sodium–lithium-ion battery strategy is proposed wherein a mixture of trimethyl phosphate (TMP) and water (with a volume ratio of 8:2) acts as the solvent, with 0.8 mol/L NaBF4 and 0.2 mol/L LiBF4 dissolved therein to enhance the voltage window and environmental adaptability. The P═O moieties in TMP form strong hydrogen-bonding interactions with H2O, which significantly elevate the corrosion potential, reinforce the shielding effect, reduce the contact angle with the cathode material, and diminish the interfacial charge transfer resistance. Molecular dynamics simulations confirm the formation of a TMP-dominated water-lean solvation structure. Therefore, a high TMP content can notably expand the electrochemical window to 3.1 V. The battery retains over 60% of its theoretical capacity within the temperature range of −12 to 38 °C, meeting the requirements of Chinese national standards (SJ/T 11893-2023) for batteries and exhibiting favorable environmental adaptability. The battery’s Coulombic efficiency exceeds 96.5% across a temperature range of −20 to 50 °C. Furthermore, at 20 °C, the charging rate is 0.3 C, and the battery exhibits extremely high cycling stability, with a maximum temperature difference on its surface of only 0.5 °C. This novel electrolyte strategy provides a feasible approach for the practical application of engineering-grade aqueous sodium–lithium-ion batteries.