Noncoordinating Flame-Retardant Functional Electrolyte Solvents for Rechargeable Lithium-Ion Batteries

Abstract

In Li-ion batteries, functional cosolvents could significantly improve the specific performance of the electrolyte, for example, the flame retardancy. In case the cosolvent shows strong Li+-coordinating ability, it could adversely influence the electrochemical Li+-intercalation reaction of the electrode. In this work, a noncoordinating functional cosolvent was proposed to enrich the functionality of the electrolyte while avoiding interference with the Li storage process. Hexafluorocyclotriphosphazene, an efficient flame-retardant agent with proper physicochemical properties, was chosen as a cosolvent for preparing functional electrolytes. The nonpolar phosphazene molecules with low electron-donating ability do not coordinate with Li+ and thus are excluded from the primary solvation sheath. In graphite-anode-based Li-ion batteries, the phosphazene molecules do not cointercalate with Li+ into the graphite lattice during the charging process, which helps to maintain integral anode structure and interface and contributes to stable cycling. The noncoordinating cosolvent was also applied to other types of electrode materials and batteries, paving a new way for high-performance electrochemical energy storage systems with customizable functions.

High-safety and high-efficiency electrolyte design for 4.6 V-class lithium-ion batteries with a non-solvating flame-retardant

“…Very recently, fluorophosphazenes have demonstrated improved electrochemical performances for Gr and Li metal anodes as the diluent of LHCEs. 11,43 However, this study of E-PFPN first proves the advantages of such nonflammable electrolyte design in terms of the long-term stability Gr‖NMC811 full cells at such high voltages and temperatures over other reported electrolytes (Fig. 2h).…”

“…This difference with the recent result of hexafluorocyclotriphosphazene on Gr anode may be due to the additional ethoxy functional group of PFPN and the reaction intermediates from decompositions of carbonate/ether solvents. 43 Based on the above analysis, the thin, robust SEI formed in the E-PFPN by the synergy of FEC and LiFSI can hinder solvent co-intercalation into the Gr and enable the long-term cycling performance of Gr anodes (Fig. 6).…”

Single-Ion Conducting Polymeric Protective Interlayer for Stable Solid Lithium-Metal Batteries

“…The traditional liquid-electrolyte-based lithium-ion batteries cannot achieve next-generation energy storage devices due to their limited safety and energy density. − Developing solid-state Li-metal batteries (LMBs) with combined solid electrolytes and high-capability Li-metal anodes is especially attractive due to high energy density (bipolar stacking and high capacity metal anode), improved safety (the absence of liquid components), and prolonged lifetime (dendrite-free anode). − Solid-state electrolytes, as high-priority materials for solid-state LMBs, can be generally classified into two distinct families: inorganic/ceramic electrolytes and polymer electrolytes. , With high ionic conductivity, mechanical robustness, and unit cationic transport number, inorganic electrolytes are usually fragile and brittle with poor interfacial contact with electrodes . In contrast, the polymer electrolyte exhibits several merits such as good compatibility with the electrode, mechanical flexibility, improved processibility for large-scale manufacturing, and easy-to-deform characteristic for emerging applications .…”

Tuning the Li+ Solvation Structure by a “Bulky Coordinating” Strategy Enables Nonflammable Electrolyte for Ultrahigh Voltage Lithium Metal Batteries

“…As shown in Figure 1a, the fluorinated cyclotriphosphazene ring in PFPN is responsible for flame-retardant and film-forming functions, while it is almost noncoordinating with Li + due to its low polarity. 39 The ethoxy group in PFPN provides the coordinating site and the synergistic effect of oxygen and nitrogen atoms realizing its stable coordination with Li + . Therefore, PFPN can enter the solvation shell, and the steric hindrance from the bulky cyclotriphosphazene group will potentially reconstruct the Li + solvation.…”