Customized Design of LiF-Rich SEI Layer on Lithium Metal Anode for High Flame Retardant Electrolyte

Abstract

Gel polymer electrolytes (GPEs) with high flame-retardant concentration can remarkably reduce the thermal runaway risk of lithium metal batteries (LMBs). However, higher flame-retardant content in GPEs always leads to increased leakage of active component and severe lithium corrosion, which greatly hinders the service life of LMBs. Herein, GPEs with high-loading triphenyl phosphate (TPP) are originally fabricated by coaxial electrospinning and stabilized by dual confinement effects, including chemisorption of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and physical encapsulation of polyacrylonitrile (PAN)/PVDF-HFP. These effects arise from the strong polar interactions between the −CF₃ group in PVDF-HFP and P=O group in TPP, as well as the superior anti-swelling property of PAN. To mitigate TPP-induced corrosion during cycling, the optimized Li anode is armored with LiF-rich solid electrolyte interphase (SEI) layer through immersing it in fluoroethylene carbonate-containing electrolyte. As expected, the corresponding Li||Li symmetric cells deliver long-term stable cycling behavior over 2400 h at 0.5 mA cm⁻², and the LiFePO₄||Li batteries hold a high-capacity retention ratio of 81.7% after 6000 cycles at 10 C with excellent flame retardancy. These findings offer new insight into designing the SEI layer for lithium metal in flame-retardant electrolytes, thus promoting the development and application of high-security LMBs.

Keywords

dual confinement effects / gel polymer electrolyte / lithium metal batteries / solid electrolyte interphase layer

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