Lithium metal anode holds great promises for next‐generation battery technologies but is notoriously difficult to work with. The key to solving this challenge is believed to lie in the ability of forming stable solid‐electrolyte interphase (SEI) layers. To further address potential safety issues, it is critical to achieve this goal in nonflammable electrolytes. Building upon previous successes in forming stable SEI in conventional carbonate‐based electrolytes, here we report that reversible Li stripping/plating could be realized in triethyl phosphate (TEP), a known flame retardant. The critical enabling factor of our approach was the introduction of oxygen, which upon electrochemical reduction induces the initial decomposition of TEP and produces Li3PO4 and poly‐phosphates. Importantly, the reaction was self‐limiting, and the resulting material regulated Li plating by limiting dendrite formation. In effect, we obtained a functional SEI on Li metal in a nonflammable electrolyte. When tested in a symmetric Li∥Li cell, more than 300 cycles of stripping/plating were measured at a current density of 0.5 mA cm−2. Prototypical Li‐O2 and Li‐ion batteries were also fabricated and tested to further support the effectiveness of this strategy. The mechanism by which the SEI forms was studied by density functional theory (DFT), and the predictions were corroborated by the successful detection of the intermediates and products.

An important challenge in the direct utilization of Li metal as an anode material for next‐generation batteries is the lack of stable solid electrolyte interphase layers. The problem is even more acute when non‐flammable electrolytes, such as organic phosphates, are used. In their Research Article on page 19183, Dunwei Wang and co‐workers report a new strategy that helps solve this issue. By introducing oxygen, the authors were able to induce unique chemical reactions that lead to safe operations of Li metal batteries that are flame‐resistant.

Lithium metal anode holds great promises for next‐generation battery technologies but is notoriously difficult to work with. The key to solving this challenge is believed to lie in the ability of forming stable solid‐electrolyte interphase (SEI) layers. To further address potential safety issues, it is critical to achieve this goal in nonflammable electrolytes. Building upon previous successes in forming stable SEI in conventional carbonate‐based electrolytes, here we report that reversible Li stripping/plating could be realized in triethyl phosphate (TEP), a known flame retardant. The critical enabling factor of our approach was the introduction of oxygen, which upon electrochemical reduction induces the initial decomposition of TEP and produces Li3PO4 and poly‐phosphates. Importantly, the reaction was self‐limiting, and the resulting material regulated Li plating by limiting dendrite formation. In effect, we obtained a functional SEI on Li metal in a nonflammable electrolyte. When tested in a symmetric Li∥Li cell, more than 300 cycles of stripping/plating were measured at a current density of 0.5 mA cm−2. Prototypical Li‐O2 and Li‐ion batteries were also fabricated and tested to further support the effectiveness of this strategy. The mechanism by which the SEI forms was studied by density functional theory (DFT), and the predictions were corroborated by the successful detection of the intermediates and products.

Eine zentrale Herausforderung für die direkte Nutzung von Li‐Metall als Batterieanodenmaterial ist der Mangel an stabilen Festelektrolyt‐Zwischenschichten. Das Problem ist sogar noch akuter, wenn nichtbrennbare Elektrolyte, wie z. B. organische Phosphate, verwendet werden. In ihrem Forschungsartikel auf S. 19332 berichten Dunwei Wang und Mitarbeiter von einer neuen Strategie, die dieses Problem lösen könnte. Durch die Einführung von Sauerstoff gelang es, einzigartige chemische Reaktionen zu induzieren, die zu einem sicheren Betrieb schwer entflammbarer Li‐Metall‐Batterien führen.