Phosphonate-Functionalized Ionic Liquid Gel Polymer Electrolyte with High Safety for Dendrite-Free Lithium Metal Batteries

Abstract

The conventional lithium-ion battery technology relies on the liquid carbonate-based electrolyte solution, which causes excessive side reactions, serious risk of electrolyte leakage, high flammability, and significant safety hazards. In this work, phosphonate-functionalized imidazolium ionic liquid (PFIL) is synthesized and used as a gel polymer electrolyte (GPE) to replace the organic carbonate-based electrolyte solution. The as-prepared ionic liquid-based gel polymer electrolyte (IL-GPE) shows low crystallinity, flame retardance, and excellent electrochemical performance. Thanks to the fast double channel transport of lithium ions in the IL-GPE electrolyte, a high ionic conductivity of 0.48 mS cm −1 and a lithium-ion transference number of 0.37 are exhibited. Symmetrical lithium cells with IL-GPE retain stable cycling even after 3000 h under 0.1 mA cm −2 . IL-GPE exhibits good compatibility toward lithium metal, yielding excellent long-term electrochemical kinetic stability. IL-GPE induces the formation of a uniform and robust SEI layer, inhibiting the growth of lithium dendrites and improving the rate performance and cycle stability. Furthermore, Li/LiFePO 4 cells exhibit a specific capacity of 63 mA h g −1 after 150 cycles at 5.0 C, with a capacity retention of 90.2%. It is foreseen that this GPE is a promising candidate to enhance the safety of high-performance lithium metal batteries.

A Review of the Relationship between Gel Polymer Electrolytes and Solid Electrolyte Interfaces in Lithium Metal Batteries

“…Commonly used lithium salts include LiPF 6 , lithium bis(trifluoromethanesulphonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), LiNO 3 , LiClO 4 , and LiBF 4 , etc. [23,32,33]. The plasticizers are linear carbonate (EMC, DMC, and DEC, etc.…”

Experimental and Theoretical Insight into the Ionic Liquid-Mediated Complexation of Trivalent Lanthanides with β-Diketone and Its Fluorinated Analogue

“…Ionic liquids are considered as potential ‘green’ alternatives to molecular diluents and find many applications in the field of liquid–liquid extraction of the f-cations relevant in nuclear industry, battery, and energy applications, membrane technology to achieve unconventional separations, stimuli-responsive membranes, dissolution of natural products, organic synthesis, etc . Covalently attached functional moieties have also been introduced onto the ionic liquids to induce task-specific applications and higher extraction efficiency/selectivity in the performance of ionic liquids . One of the most interesting dimensions of application of ionic liquids is their tunable physicochemical properties on slight structural modifications .…”

Non-flammable Gel Polymer Electrolyte for Enhancing the Safety and High-Temperature Performance of Lithium-Ion Batteries

“…To date, various approaches have been introduced for the development of nonflammable electrolytes, such as inorganic electrolytes, flame retardant additives and electrolytes, and solid-state and gel polymer electrolytes (GPEs). − Among them, chemically cross-linked GPEs can effectively immobilize flammable organic solvents within the polymer matrix and ensure good interfacial contacts between the electrolyte and electrodes as well as high ionic conductivity due to the presence of LEs. , Particularly, nonflammable GPEs employing a flame-retardant plasticizer or cross-linked polymer as flame-retardant materials are being extensively explored to enhance the battery safety. − When preparing a nonflammable GPE, organic phosphorus- and fluorinated-based flame-retardant solvents have been studied as plasticizers since they mitigate the risk of ignition of LEs. − For example, phosphorus compounds such as trimethyl phosphate, , triethyl phosphate, tripropyl phosphate, and dimethyl methylphosphonate are commonly employed due to their high fire-extinguishing property and high ionic conductivity. However, these phosphide compounds can trigger deleterious reactions at the graphite anode during cycling, leading to the formation of an unstable solid–electrolyte interface and degradation of the battery performance .…”

“…9−15 Among them, chemically cross-linked GPEs can effectively immobilize flammable organic solvents within the polymer matrix and ensure good interfacial contacts between the electrolyte and electrodes as well as high ionic conductivity due to the presence of LEs. 16,17 Particularly, nonflammable GPEs employing a flame-retardant plasticizer or cross-linked polymer as flame-retardant materials are being extensively explored to enhance the battery safety. 18−20 When preparing a nonflam-mable GPE, organic phosphorus-and fluorinated-based flameretardant solvents have been studied as plasticizers since they mitigate the risk of ignition of LEs.…”