Enhancing Li cycling coulombic efficiency while mitigating “shuttle effect” of Li-S battery through sustained release of LiNO₃

In practical lithium-sulfur batteries (LSBs), the shuttle effect and Li cycling coulombic efficiency (CE) are strongly affected by the physicochemical properties of solid electrolyte interphase (SEI). LiNO₃ is widely used as an additive in electrolytes to build a high-quality SEI, but its self-sacrificial nature limits the ability to mitigate the shuttle effect and stabilize Li anode during long-term cycling. To counteract LiNO₃ consumption during long-term cycling without using a high initial concentration, inspired by sustained-release drugs, we encapsulated LiNO₃ in lithiated Nafion polymer and added an electrolyte co-solvent (1,1,2,2-tetrafluoroethylene 2,2,2-trifluoromethyl ether) with poor LiNO₃ solubility to construct high-quality and durable F- and N-rich SEI. Theoretical calculations, experiments, multiphysics simulations, and in-situ observations confirmed that the F- and N-rich SEI can modulate lithium deposition behavior and allow persistent repair of SEI during prolonged cycling. Hence, the F- and N-rich SEI improves the Li anode cycling CE to 99.63% and alleviates the shuttle effect during long-term cycling. The lithium anode with sustainable F- and N-rich SEI shows a stable Li plating/stripping over 2000 h at 1 mA cm⁻². As expected, Li||S full cells with this SEI achieved a long lifespan of 250 cycles, far exceeding cells with a routine SEI. The Li||S pouch cell based on F- and N-rich SEI also can achieve a high energy density of about 300 Wh kg⁻¹ at initial cycles. This strategy provides a novel design for high-quality and durable SEIs in LSBs and may also be extendable to other alkali metal batteries.