Optimizing interfacial stability of sulfurized polyacrylonitrile batteries by fluorinated composite polymer electrolytes

Abstract

Sulfurized polyacrylonitrile (SPAN) is a promising cathode to address the notorious polysulfide shuttle effect sluggish and reaction dynamics of traditional lithium-sulfur (Li–S) batteries through its conductive pyridinic framework. However, the stability of lithium anode interface remains a hot potato due to the high working current density. Herein, a new polymer electrolyte (PHL5) comprising poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP) polymer matrix and 5 % garnet-type Li₇La₃Zr₂O₁₂ (LLZO) filler is developed to regulate uniform Li⁺ deposition and enhance Li⁺ transport efficiency for Li-SPAN batteries. The Lewis acid-base interaction between PVDF-HFP and LLZO is verified through Raman. Theoretical calculations further reveal that PHL5 exhibits lower binding energy with Li⁺ while showing higher binding energy with PF₆⁻, thereby promoting lithium salt dissociation and facilitating enhanced ion transport kinetics. Distribution of relaxation times (DRT) and in situ microscopic-electrochemical battery test demonstrate that the incorporation of LLZO effectively regulates Li⁺ deposition. Specifically, Li/PHL5/SPAN battery presents a remarkable capacity of 1010.9 mAh g⁻¹ after 300 cycles at a high rate of 0.5C, higher than those of PVDF-HFP (PH) and liquid electrolyte counterparts (LE). Additionally, Li/PHL5/SPAN pouch battery maintains a stable voltage profile and operates reliably under extreme mechanical conditions, including hammering, folding and cutting. This strategy offers a novel approach for developing high-performance and practical Li–S battery technologies.