Delicately Tailored Ternary Phosphate Electrolyte Promotes Ultrastable Cycling of Na₃V₂(PO₄)₂F₃-Based Sodium Metal Batteries

Abstract

High-voltage sodium metal batteries are a highly intriguing battery technology in view of their resource sustainability, cost efficiency, and ultrahigh energy density. However, developing a high-performance electrolyte, compatible with both high-voltage cathodes and highly reactive sodium metal anodes, is extremely challenging. In this work, we delicately formulate a ternary phosphate electrolyte, composing of a cost-effective sodium bis(trifluoromethane sulfonyl) imide salt, a nonflammable triethyl phosphate (TEP) solvent, and a fluoroethylene carbonate (FEC) co-solvent. By rationally tailoring the TEP/FEC ratio, the ternary phosphate electrolyte displays a wellbalanced performance, not only enabling highly efficient sodium deposition (an average Coulombic efficiency of 95.7% for Na//Cu cells) but also inheriting the intrinsic anodic stability (≥4.5 V vs Na + / Na) and nonflammability of phosphates. As a consequence, highvoltage Na 3 V 2 (PO 4 ) 2 F 3 cathode-based sodium metal cells (Na 3 V 2 (PO 4 ) 2 F 3 //Na) deliver remarkable cyclic stability (97.9% capacity retention after 300 cycles), which is among the best for Na 3 V 2 (PO 4 ) 2 F 3 -based batteries. This work may guide the electrolyte design principles and is highly enlightening in developing high energy density sodium-based batteries. KEYWORDS: phosphate electrolyte, high voltage, Na 3 V 2 (PO 4 ) 2 F 3 cathode, nonflammable, sodium metal batteries

A rooted interphase on sodium via in situ pre-implantation of fluorine atoms for high-performance sodium metal batteries

“…Among them, the signal of the (110) crystal plane is the most intense, indicating that this crystal plane is the main crystal plane of Na metal. 19,20,39 The C-F bond preferentially decomposes on Na (110). Dissociative adsorption is thermodynamically favourable because this mode of action is expected to change the charge state of Na (110).…”

“…The structure, composition, and properties of an SEI are closely related to the electrolyte. 5,[17][18][19][20][21][22] An ideal SEI not only has a superior structure and beneficial composition but also, more importantly, achieves a tight connection with the metal electrode to facilitate a fast and intensive sodium plating/ stripping process. 6,[23][24][25][26] In recent years, many improvements have been proposed to construct a suitable layer of the SEI.…”

Revealing the importance of suppressing formation of lithium hydride and hydrogen in Li anode protection

“…Analogously, it is noted here that efforts are also required to clarify the role and formation of sodium hydride (NaH) in the SEI layer of Na metal anode. [64,65] Finally, we hope our unusual concept of suppressing the formation of LiH and H 2 will serve as a modest spur to draw forth more insightful efforts to realize excellent Li anode protection and the ultimate practical applications of "holy grail" LMBs.…”

Formation of NaF‐Rich Solid Electrolyte Interphase on Na Anode through Additive‐Induced Anion‐Enriched Structure of Na+Solvation

“…To obtain stable SEIs, many methods such as electrolyte engineering, artificial SEI and polymer membrane, are used [16–19] . Electrolyte engineering is the most convenient and efficient strategy which can form homogeneous and stable SEIs [20, 21] . To date, there are thousands of reports on the performance enhancement of metal anodes by controlling the electrolyte solvents, additives and salts.…”

“…[16][17][18][19] Electrolyte engineering is the most convenient and efficient strategy which can form homogeneous and stable SEIs. [20,21] To date, there are thousands of reports on the performance enhancement of metal anodes by controlling the electrolyte solvents, additives and salts. Fluorides (MF: M = Li, Na, K, etc.)…”