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

Abstract

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.