Intrinsic Nonflammable Ether Electrolytes for Ultrahigh‐Voltage Lithium Metal Batteries Enabled by Chlorine Functionality

Abstract

The issues of inherent low anodic stability and high flammability hinder the deployment of the etherbased electrolytes in practical high-voltage lithium metal batteries. Here, we report a rationally designed etherbased electrolyte with chlorine functionality on ether molecular structure to address these critical challenges. The chloroether-based electrolyte demonstrates a high Li Coulombic efficiency of 99.2 % and a high capacity retention > 88 % over 200 cycles for Ni-rich cathodes at an ultrahigh cut-off voltage of 4.6 V (stable even up to 4.7 V). The chloroether-based electrolyte not only greatly improves electrochemical stabilities of Ni-rich cathodes under ultrahigh voltages with interphases riched in LiF and LiCl, but possesses the intrinsic nonflammable safety feature owing to the flame-retarding ability of chlorine functional groups. This study offers a new approach to enable ether-based electrolytes for high energy density, long-life and safe Li metal batteries.

Monofluoro-ether electrolyte design with reduced Li+-anion coordination enables fast-charging ultrahigh-voltage lithium metal batteries

“…Figure 1a illustrates the molecular electrostatic potential (ESP) maps and theoretical oxidation potentials (Eox) derived from density functional theory (DFT) calculations, which show significant decreases in the electron cloud density of oxygen atoms due to the electron-withdrawing effect of both Cl and F atoms. 22,25 The increased theoretical oxidation potentials also indicate their improved oxidation stabilities compared to the parent molecule DEE. Thanks to the high salt solubility with monofluorination, LHCEs were formulated with LiFSI as the single salt and TTE as the non-solvating diluent.…”

“…3h-k). 22,37,38 A thinner and more uniform CEI of only 3 nm was observed in FDEE-LHCE by transmission electron microscopy (TEM), compared to the other electrolytes (Figure 3l). Given the fact that all the three LHCEs contain similar ratios of identical fluorinated species (LiFSI and TTE), it is very surprising to find the significant enrichment of LiF species with the FDEE-based electrolyte, where the CIP structure with low FSIcoordination in the inner solvation sheath is in dominance.…”

“…Recent studies have shown that introducing strong electron-withdrawing functional groups into the solvent structure can improve their inherent oxidation stability. [19][20][21][22] Several ether molecules with difluoro or trifluoro functional groups have demonstrated enhanced high voltage stabilities for LMBs (under 4.3~4.4 V). 23,24 Nevertheless, salt dissolution ability of the solvent would be compromised due to the existence of multi-fluorinated moieties at the vicinity of Li +coordination sites (e.g., oxygen atoms).…”

A Solution‐Processable High‐Modulus Crystalline Artificial Solid Electrolyte Interphase for Practical Lithium Metal Batteries

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Particularly, the issue originates from the high reactivity of Li metal and thus continuous parasitic reactions between Li and electrolyte components that finally result in a poorly passivating layer, known as solid-electrolyte interphase (SEI). [3][4][5][6] Generally, the native SEIs in conventional/ commercial carbonate electrolytes are mechanically brittle, heterogeneous in ionic conduction, and fail to passivate the Li surface during long-term cycling.To solve these issues associated with Li metal anodes, several strategies have been proposed, such as liquid electrolyte engineering, [7][8][9][10][11][12][13][14] solid-state electrolytes, [15][16][17][18] Li metal hosts, [5,19] or pretreatment of Li metal. [20][21][22] Artificial SEIs (ASEIs) [23][24][25][26][27][28] have garnered increasing attention due to their potential compatibility with commercial electrolytes [24] and the possibility for scalable manufacturing.

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“…To solve these issues associated with Li metal anodes, several strategies have been proposed, such as liquid electrolyte engineering, [7][8][9][10][11][12][13][14] solid-state electrolytes, [15][16][17][18] Li metal hosts, [5,19] or pretreatment of Li metal. [20][21][22] Artificial SEIs (ASEIs) [23][24][25][26][27][28] have garnered increasing attention due to their potential compatibility with commercial electrolytes [24] and the possibility for scalable manufacturing.…”