PVDF-HFP-modified ionic liquid-based gel polymer electrolytes for enhanced conductivity and long-term interfacial stability in lithium-ion batteries

The advancement of lithium-ion batteries (LIBs) necessitates the development of high-performance and safer electrolytes. This study introduces an ionic liquid-based gel polymer electrolyte (IL-GPE) prepared via a low-to-high controlled-temperature solution casting strategy, incorporating poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), 1‑butyl‑3-methylimidazolium bis (trifluoromethylsulfonyl)imide (BMIM[TFSI]), and lithium bis (trifluoromethanesulfonyl)imide (LiTFSI). This strategic composition leverages ionic liquid (IL) engineering to enhance ion transport dynamics and promote effective polymer-IL interactions, thereby ensuring a well-balanced synergy between mechanical integrity and electrochemical performance. The optimized IL-GPE demonstrates enhanced ion transport capability, achieving a conductivity of 3.31 × 10⁻³ S cm⁻¹ at 25 °C, maintains electrochemical stability window up to 5.3 V, and offers high thermal resilience with an onset decomposition temperature of 339 °C. Additionally, its inherent flame-retardant characteristics that further ensure safety during high-temperature conditions. The Li/IL-GPE/Li symmetric cells maintain stable performance beyond 30,000 charge-discharge cycles (1418 h), while Li/IL-GPE/LFP-GO full cells achieve a high-discharge capacity of 147.7 mAh g⁻¹ at 1C with 82.17 % retention and up to 99 % coulombic efficiency (CE) over 200 cycles. XPS analysis indicate a well-formed solid electrolyte interphase (SEI) layer that efficiently suppresses lithium dendrite propagation. These findings highlight IL-GPE as a promising potential electrolyte candidate for advanced high-energy-density LIBs. Description: The graphical abstract visually summarizes the key features of the developed IL-GPE, illustrating its composition using BMIM[TFSI], PVDF-HFP, and LiTFSI, and highlighting its high ionic conductivity (3.31–5.45 mS cm⁻¹), excellent flame-retardant behaviour, and stable electrochemical performance even at elevated temperatures in Li-ion batteries. It also demonstrates superior cycling stability with a discharge capacity of 147.7 mAh g⁻¹ (at 1C) and 82.17 % retention over 200 cycles, underscoring its applicability in high-voltage cathode systems.