Key Takeaways & Executive Findings
- •• Fluorine-grafted quasi-solid-state composite electrolyte (F-QSCE)@30 exhibits high ionic conductivity of 1.21 mS cm–1 at 25 °C. • The inductive effect weakens the coordination between Li+ and TFSI‒, enhancing Li+ transport. • LiF in the solid electrolyte interphase of F-QSCE@30 comes from decomposed F segments, not TFSI‒. • F-QSCE@30 maintains stability with Li metal for over 4000 h and inhibits dendrite growth.
Abstract
Quasi-solid-state composite electrolytes (QSCEs) show promise for high-performance solid-state batteries, while they still struggle with interfacial stability and cycling performance. Herein, a F-grafted QSCE (F-QSCE) was developed via copolymerizing the F monomers and ionic liquid monomers. The F-QSCE demonstrates better overall performance, such as high ionic conductivity of 1.21 mS cm–1 at 25 °C, wide electrochemical windows of 5.20 V, and stable cycling stability for Li//Li symmetric cells over 4000 h. This is attributed to the significant electronegativity difference between C and F in the fluorinated chain (‒CF2‒CF‒CF3), which causes the electron cloud to shift toward the F atom, surrounding it with a negative charge and producing the inductive effect. Furthermore, the interactions between Li+ and F, TFSI‒, and C are enhanced, reducing ion pair aggregation (Li+‒TFSI‒‒Li+) and promoting Li+ transport. Besides, ‒CF2‒CF‒CF3 decomposes to form LiF preferentially over TFSI–, resulting in better interfacial stability for F-QSCE. This work provides a pathway to enable the development of high-performance Li metal batteries.
1. Introduction
With the rising need for energy and electric vehicles, developing high-performance and safe batteries has become particularly important [1]. Lithium metal, known for its remarkable specific capacity (3860 mAh g–1) [2–7], low density (0.53 g cm–3), and electrochemical potential (−3.04 V vs H+/H2) [8], is widely considered a promising anode for advancing high-performance Li metal batteries (LMBs) [9–12]. Despite the significant advantages of the Li metal itself, LMBs, based on commercial organic electrolytes, still present safety challenges linked to liquid leakage and high flammability [13, 14]. These issues have driven the rise of composite solid electrolytes (CSEs), which consist of a polymer backbone, filler, and Li salt. With their enhanced safety, superior thermal stability, and scalability, CSEs are regarded as potential candidates for future solid-state electrolytes [15]. However, inherent challenges, including low ionic conductivity and unstable interface, continue to limit the performance of CSEs [9, 16].
To address the challenges of CSEs, several strategies have been developed and implemented. For instance, the in situ polymerization strategy has been widely adopted to improve interfacial contact by forming a seamless electrode–electrolyte interface, while also enhancing the ionic conductivity [17, 18]. Adding buffer layers between the electrolyte and electrode has proven effective in mitigating interfacial reactions and reducing dendrite growth [19]. However, the added buffer layer also hinders the conduction of ions. Other approaches, such as electrolyte surface treatment and increasing stacking pressure, are simple modification methods, offering limited improvements. More advanced strategies, including constructing interfacial transition layers [20] and composite anodes, have shown promise in reducing interfacial resistance and enhancing cycling performance. However, these methods are often complex and costly, accompanied by insufficiently high ionic conductivity [21]. While these advancements have addressed some challenges of CSEs, further optimization is needed.
Quasi-solid-state composite electrolytes (QSCEs) incorporate a small amount of liquid into CSEs, offering the high ionic conductivity of liquids alongside the improved thermal stability, safety, and scalability of CSEs [15]. Although this combination improves the overall performance of the electrolytes compared to the traditional CSEs, it still fails to meet the performance requirements for applications, calling for further development [9]. Adding more liquids has been proposed to further develop, where the novel ionic liquids (ILs) have been extensively studied. The addition of ILs with high chemical stability and ionic conductivity (e.g., 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) [22] and n-propyl-n-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR13TFSI) [23]) can expand the electrochemical stability window and improve interfacial stability with the lithium metal [24]. However, to achieve sufficient ionic conductivity (>1.00 mS cm–1 at 25 °C), [25] th
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Haiman Hu, Jiajia Li, Fei Lin, Jiaqi Huang, Huaiyang Zheng, Haitao Zhang, Xiaoyan Ji (2025). Induction Effect of Fluorine-Grafted Polymer-Based Electrolytes for High-Performance Lithium Metal Batteries. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01738-9
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Frequently Asked Questions
What is the main innovation of this study?
The study introduces a fluorine-grafted quasi-solid-state composite electrolyte (F-QSCE) that leverages the inductive effect of fluorine to enhance lithium-ion transport and interfacial stability, achieving high ionic conductivity and long-term cycling performance.
How does the fluorine grafting improve electrolyte performance?
Fluorine grafting creates an inductive effect that weakens the coordination between Li+ and TFSI−, promoting Li+ transport. Additionally, the fluorinated segments decompose to form LiF preferentially, enhancing the solid electrolyte interphase stability.
What are the key performance metrics of the F-QSCE?
The F-QSCE exhibits an ionic conductivity of 1.21 mS cm−1 at 25 °C, an electrochemical window of 5.20 V, and stable cycling for over 4000 hours in Li//Li symmetric cells.
Why is the inductive effect important in this context?
The inductive effect, caused by the electronegativity difference between carbon and fluorine, shifts electron density towards fluorine, which enhances interactions with Li+ and reduces ion pair aggregation, thereby improving ion transport.
What are the potential applications of this research?
This research provides a pathway for developing high-performance lithium metal batteries with improved safety and cycling stability, which are crucial for electric vehicles and large-scale energy storage.
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