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.

Electrolytes are critical for the reversibility of various electrochemical energy storage systems. The recent development of electrolytes for high-voltage Li-metal batteries has been counting on the salt anion chemistry for building stable interphases. Herein, we investigate the effect of the solvent structure on the interfacial reactivity and discover profound solvent chemistry of designed monofluoro-ether in anion-enriched solvation structures, which enables enhanced stabilization of both high-voltage cathodes and Li-metal anodes. Systematic comparison of different molecular derivatives provides an atomic-scale understanding of the unique solvent structure-dependent reactivity. The interaction between Li + and the monofluoro (−CH 2 F) group significantly influences the electrolyte solvation structure and promotes the monofluoro-ether-based interfacial reactions over the anion chemistry. With indepth analyses of the compositions, charge transfer, and ion transport at interfaces, we demonstrated the essential role of the monofluoro-ether solvent chemistry in tailoring highly protective and conductive interphases (with enriched LiF at full depths) on both electrodes, as opposed to the anion-derived ones in typical concentrated electrolytes. As a result, the solvent-dominant electrolyte chemistry enables a high Li Coulombic efficiency (∼99.4%) and stable Li anode cycling at a high rate (10 mA cm −2 ), together with greatly improved cycling stability of 4.7 V-class nickel-rich cathodes. This work illustrates the underlying mechanism of the competitive solvent and anion interfacial reaction schemes in Li-metal batteries and offers fundamental insights into the rational design of electrolytes for future high-energy batteries.

Albeit ethers are favorable electrolyte solvents for lithium (Li) metal anode, their inferior oxidation stability (< 4.0 V vs. Li/Li + ) is problematic for highvoltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we unveil the crucial effect of ion coordination configuration on oxidation stability by varying the ether backbone structure. The designed 1,3dimethoxypropane (DMP, C3) forms a unique sixmembered chelating complex with Li + , whose stronger solvating ability suppresses oxidation side reactions. In addition, the favored hydrogen transfer reaction between C3 and anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7 %) on the cathode surface. As a result, the C3-based electrolyte enables greatly improved cycling of nickel-rich cathodes under 4.7 V. This study offers fundamental insights into rational electrolyte design for developing high-energy-density batteries.

Nonflammable electrolytes are critical for the safe operation of high-voltage lithium-ion batteries (LIBs). Although organic phosphates are effective flame-retardants, their poor electrochemical stability with graphite (Gr) anode and Ni-rich cathodes...

Ethers are promising electrolytes for lithium (Li) metal batteries (LMBs) because of their unique stability with Li metal. Although intensive research on designing anion-enriched electrolyte solvation structures has greatly improved their electrochemical stabilities, ether electrolytes are approaching an anodic bottleneck. Herein, we reveal the strong correlation between electrolyte solvation structure and oxidation stability. In contrast to previous designs of weakly solvating solvents for enhanced anion reactivities, the triglyme (G3)-based electrolyte with the largest Li + solvation energy among different linear ethers demonstrates greatly improved stability on Ni-rich cathodes under an ultrahigh voltage of 4.7 V (93% capacity retention after 100 cycles). Ether electrolytes with a stronger Li + solvating ability could greatly suppress deleterious oxidation side reactions by decreasing the lifetime of free labile ether molecules. This study provides critical insights into the dynamics of the solvation structure and its significant influence on the interfacial stability for future development of high-efficiency electrolytes for high-energy-density LMBs.

Ethers with distinctive reduction stability are emerging as the promising solution to the issues of lithium (Li) metal anode. However, their inferior oxidation stability (<4.0 V vs. Li/Li+) cannot meet the ever-growing needs of high-voltage cathodes. Studies of ether electrolytes have been focusing on the archetype glyme structure with ethylene oxide moieties. Herein, we systematically vary the methylene units in the ether backbone and unveil the crucial effect of ion-ether coordination configuration on the electrolyte oxidation stability. The 1,3-dimethoxypropane (DMP, C3) molecule forms a unique six-membered chelating complex with Li+, whose stronger solvating ability suppresses undesired oxidation side reactions. In addition, the favored hydrogen transfer reaction between DMP and salt anion induces a dramatic enrichment of LiF (a total atomic ratio of 76.7%) on the cathode surface. As a result, the DMP-based electrolyte demonstrates stable cycling of nickel-rich cathodes under a high voltage of 4.7 V (87% capacity retention after 150 cycles). This study offers fundamental insights into rational electrolyte design with wide electrochemical stability window for developing high-energy-density batteries.

Ether-based electrolytes are particularly useful for lithium metal batteries (LMBs) and have shown improved anodic stability with the high concentration design. Nevertheless, the vaunted anion-reinforced solvation in concentrated electrolytes has non-negligible adverse effect on ion conduction and battery rate performance. Here, we propose a new solvent design strategy of ether monofluorination to tune the Li+-anion interaction for fast-charging LMBs. With the highly polar monofluoro functional groups, the ether-based electrolyte not only exhibits excellent high oxidation stability due to the strong electron-withdrawing effect of F, but also has a greatly increased ionic conductivity because of reduced anion coordination. The unique solvation structure also enables the formation of robust and highly conductive interphases at both the Li anode and NMC811 surfaces. High Li CEs (~99.4%) and stable long-term cycling with low overpotential under ultrahigh current densities (10 mA cm-2) could be achieved for Li anode. Li||NMC811 cells exhibit outstanding cycling performance under ultrahigh cut-off voltages of 4.6 V and 4.7 V, or at high current densities (5.1 mA cm-2). This work provides critical insights into the ion-solvent interactions in the solvation complex and their profound influence on the battery electrochemical performances.

Ether-based electrolytes are particularly useful for lithium metal batteries (LMBs) and have shown improved anodic stability with the high concentration design. Nevertheless, the vaunted anion-reinforced solvation in concentrated electrolytes has non-negligible adverse effect on ion conduction and battery rate performance. Here, we propose a new solvent design strategy of ether monofluorination to tune the Li+-anion interaction for fast-charging LMBs. With the highly polar monofluoro functional groups, the ether-based electrolyte not only exhibits excellent high oxidation stability due to the strong electron-withdrawing effect of F, but also has a greatly increased ionic conductivity because of reduced anion coordination. The unique solvation structure also enables the formation of robust and highly conductive interphases at both the Li anode and NMC811 surfaces. High Li CEs (~99.4%) and stable long-term cycling with low overpotential under ultrahigh current densities (10 mA cm-2) could be achieved for Li anode. Li||NMC811 cells exhibit outstanding cycling performance under ultrahigh cut-off voltages of 4.6 V and 4.7 V, or at high current densities (5.1 mA cm-2). This work provides critical insights into the ion-solvent interactions in the solvation complex and their profound influence on the battery electrochemical performances.