Enhancing metal ion battery longevity through minimized coordinating diluent

Abstract

Embodiments relate to an electrolyte composition including a cyclic fluorinated ether diluent configured to configured to control reactions between a metal anode of a metal ion battery and the electrolyte composition. Embodiments further relate to a solid electrolyte interphase (SEI) bilayer formed on a surface of the metal anode and to a metal ion battery including the cyclic fluorinated ether diluent and / or the SEI bilayer.

Description

ENHANCING METAL ION BATTERY LONGEVITY THROUGH MINIMIZEDCOORDINATING DILUENTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority of U.S. Provisional Application 63 / 632,611 , filed on April 1 1, 2024, the entire contents of which is incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH DEVELOPMENT

[0002] This invention was made with government support under Contract No. DE-AC05- 76RL01830 awarded by the Department of Energy. The Government has certain rights in the invention.FIELD

[0003] Embodiments relate to an electrolyte composition including a cyclic fluorinated ether diluent configured to control reactions between a metal anode of a metal ion battery and the electrolyte composition. Embodiments further relate to a solid electrolyte interphase (SEI) bilayer formed on a surface of the metal anode and to a metal ion battery including the cyclic fluorinated ether diluent and / or the SEI bilayer.BACKGROUND

[0004] Lithium (Li) metal has long been considered as a promising anode material for the next generation batteries. However, its practical application is impeded by poor cycling stability, primarily attributed to the inherent reactivity of Li metal. This reactivity induces undesirable parasitic reactions between the Li metal anode and electrolytes, resulting in the formation of unstable solid-electrolyte interphases (SEIs). Consequently, this leads to low Coulombicefficiencies (CEs), rapid depletion of electrolytes, reduced Li inventory, and ultimately, poor cycling life.SUMMARY

[0005] A stable SEI necessitates specific design features including the establishment of a uniform highly ionic conductive layer to facilitate uniform Li deposition and the creation of dense and electronically insulating passivation to impede electrolyte penetration and corrosion. Liquid electrolyte engineering is a promising approach to foster stable SEIs in durable Li metal batteries (LMBs), primarily by reducing electrolyte reactivity. This involves increasing electrolyte concentration to minimize solvent reactivity, selecting Li salts for anion derived SEIs, and replacing carbonate solvents with ether solvents. The use of a fluorinated ether co-solvent diluent is also widely used for further diminishing electrolyte reactivity and enhancing stability when in contact with Li metal. However, this fluorinated co-solvent diluent, traditionally deemed “non-coordinating” to Li-ions due to its heavily fluorinated C-H bonds, can exhibit electrochemical reactivity against Li metal. This reactivity leads to its decomposition, and participation in the SEI formation, potentially undermining the SEI robustness due to the increase of its organic components. Thus far, there has been no investigation into a co-solvent diluent with minimized coordinating capability that can efficiently curb its contribution in the SEI formation process to facilitate the creation of an exceptionally stable SEI layer for stabilizing Li metal anode.

[0006] We have developed fluorinated cyclic ethers configured to minimize coordination with Li-ions. In particular, 3,3,4,4,5,5-hexafluorotetrahydropyran (HFTHP) features a specific constrained conformation and may be employed as a diluent for a dual-salt ether-based electrolyte. HFTHP’s minimized coordination interaction with Li-ions enables mitigatedreactivity to Li metal and limited participation to SEI. More importantly, the use of HFTHP, which shows minimized coordination with Li-ion as the diluent, refines Li-ion solvation structure to result in an inner solvation sheath rich lithium oxide and an outer solvation sheath enriched with lithium fluoride.

[0007] Moreover, 3,3,4,4-tetrafluorotetrahydrofuran (TFTHF) may be employed as a diluent to foster an enhanced dipole-dipole interaction with the Li-ion-coordinated solvent, therefore greatly altering the solvation structures of Li-ions. This leads to the weakened coordination of Li-ions with the solvents while promoting intensified interaction between Li-ions and anions, facilitating the formation of a stable inorganic SEI layer.

[0008] In an exemplary embodiment, an electrolyte composition comprises an electrolyte comprising a first metal salt and a second metal salt; a solvent comprising at least one organic compound; and a diluent comprising a cyclic fluorinated ether.

[0009] In some embodiments, the cyclic fluorinated ether comprises 3, 3, 4, 4,5,5- hexafl uorotetrahy dropy ran .

[0010] In some embodiments, the cyclic fluorinated ether comprises 3, 3,4,4- tetrafluorotetrahydrofuran.

[0011] In some embodiments, the first metal salt is a metal oxide-forming salt, and wherein the second metal salt is a metal fluoride-forming salt.

[0012] In some embodiments, the first metal salt is metal difluoro(oxalato)borate.

[0013] In some embodiments, the second metal salt is metal tetrafluoroborate.

[0014] In some embodiments, the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a metal oxide-rich inner layer and a metal fluoride-rich outer layer.

[0015] In some embodiments, the first metal salt is a lithium oxide-forming salt, and wherein the second metal salt is a lithium fluoride-forming salt.

[0016] In some embodiments, the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a lithium oxide-rich inner layer and a lithium fluoride-rich outer layer.

[0017] In some embodiments, the at least one organic compound comprises dimethyl ether.

[0018] In an exemplary embodiment, a metal ion battery comprises an anode; a cathode; and an electrolyte composition comprising an electrolyte comprising a first metal salt and a second metal salt, a solvent comprising at least one organic compound, and a diluent comprising a cyclic fluorinated ether.

[0019] In some embodiments, the cyclic fluorinated ether comprises 3, 3, 4, 4,5,5- hexafl uorotetrahy dropy ran .

[0020] In some embodiments, the cyclic fluorinated ether comprises 3, 3,4,4- tetrafluorotetrahydrofuran.

[0021] In some embodiments, the first metal salt is a metal oxide-forming salt, and wherein the second metal salt is a metal fluoride-forming salt.

[0022] In some embodiments, the first metal salt is metal difluoro(oxalato)borate.

[0023] In some embodiments, the second metal salt is metal tetrafluorob orate.

[0024] In some embodiments, the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a metal oxide-rich inner layer and a metal fluoride-rich outer layer.

[0025] In some embodiments, the first metal salt is a lithium oxide-forming salt, and wherein the second metal salt is a lithium fluoride-forming salt.

[0026] In some embodiments, the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a lithium oxide-rich inner layer and a lithium fluoride-rich outer layer.

[0027] In some embodiments, the at least one organic compound comprises dimethyl ether.

[0028] In some embodiments, the anode comprises a carbon-based material.

[0029] In some embodiments, the anode comprises a metal selected from the group consisting of lithium, sodium, magnesium, potassium, aluminum, and zinc.

[0030] In some embodiments, the metal is lithium.

[0031] These and other embodiments shall be described in more detail herein and in the drawings that show exemplary embodiments. Therefore, other details, objects, and advantages will become apparent as the following description of certain present preferred embodiments thereof and certain present preferred methods of practicing the same proceeds.BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The above and other objects, aspects, features, advantages, and possible applications of embodiments of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0033] FIG. 1 shows a schematic representation of a fluorinated cyclic ether with minimized Li- ion coordination and the promoted stable SEI. The six-membered fluorinated cyclic ether shows minimized Li-ion coordination and thus tailors the proximity of dual anions around the Li-ions,resulting in the generation of a differentiated dual-anion derived SEI. The developed dual-salt electrolyte using the minimized Li-ion coordination diluent, promotes the formation of predominantly inorganic, bilayer SEI composed of an inner layer enriched with Li2O and an outer layer rich in LiF, collectively enhancing the reversibility and passivation of lithium metal anode.

[0034] FIG. 2 is a graph showing enhanced dipole-dipole interaction between solvent DME and non-Li-ion-coordinating diluent TFTHF was achieved and found to fine tune the Li-ion solvation structure in a binary salt electrolyte. This leads to weakened Li -ion- solvent coordination and strengthened Li-ion-anion interactions, facilitating the formation of a stable bi-layered SEI for significantly stabilizing Li metal anode.

[0035] FIG. 3 is a schematic representation of the tuned Li-ion solvation structure by enhanced dipole-dipole interactions between Li-ion-coordinated solvent and non-Li-ion-coordinating diluent in the binary salt electrolyte.

[0036] FIG. 4 includes graphs showing the19F NMR chemical shift differences for the electrolytes of D-BTFE (top left), D-TTE (top middle) and D-HFTHP (top right) with / without the dissolution of IM LiDFOB and 0.4M LiBF4.

[0037] FIG. 5 shows a schematic representation of the17O NMR chemical shift differences for the electrolytes of D-BTFE (bottom left), D-TTE (bottom middle) and D-HFTHP (bottom right) with / without the dissolution of IM LiDFOB and 0.4M LiBF4.

[0038] FIG. 6 includes top-view and cross-sectional SEM images on the deposited Li metal in electrolytes D-BTFE (top left, bottom left), D-TTE (top middle, bottom middle) and D-HFTHP(top right, bottom right).

[0039] FIG. 7 includes graphs showing high-resolution C is XPS spectra of the formed SEIs in electrolytes, after 20 cycles.

[0040] FIG. 8 shows high-resolution F Is depth profiling XPS spectra of the formed SEIs in the electrolytes of D-BTFE.

[0041] FIG. 9 shows high-resolution F Is depth profiling XPS spectra of the formed SEIs in the electrolytes of D-TTE

[0042] FIG. 10 shows high-resolution F Is depth profiling XPS spectra of the formed SEIs in the electrolytes of D-HFTHP.

[0043] FIG. 11 is a graph showing depth profiling of the absolute intensities of organic species, LiF and Li2O within the formed SEIs in the electrolytes of D-BTFE.

[0044] FIG. 12 is a graph showing depth profiling of the absolute intensities of organic species, LiF and Li2O within the formed SEIs in the electrolytes of D-TTE.

[0045] FIG. 13 is a graph showing depth profiling of the absolute intensities of organic species, LiF and Li2O within the formed SEIs in the electrolytes of D-HFTHP.

[0046] FIG. 14 is a cryo-TEM image of the SEI in D-HFTHP.

[0047] FIG. 15 shows zoomed-in cryo-TEM images of the SEI shown in FIG. 14.

[0048] FIG. 16 is a HAADF-STEM image along with the associated Li K-edge EELS spectra collected. The three boxed regions selected for the collection of Li K-edge spectra represent the deposited Li layer, the inner SEI layer, and the outer SEI layer.

[0049] FIG. 17 shows a chemical shift that may be provided in an exemplary embodiment. The figure shows negligible change (< 0.1 ppm) of chemical shifts for the carbonyl carbons between D-BTFE and D-TTE is observed in13C NMR.

[0050] FIG. 18 shows a chemical shift that may be provided in an exemplary embodiment using19F NMR. The figures shows chemical shift differences between the DFOB and BF4 anions of only 0.66 ppm and 0.98 ppm in D-BTFE and D-TTE, respectively. In contrast, a significant chemical shift difference of 1.97 ppm between the DFOB and BF4 anions was observed in D- HFTHP, indicating a substantially differentiated interaction between the DFOB

[0051] FIG. 19 is a graph showing the results of a test to identify the strongest interaction center(s).

[0052] FIG. 20 is a graph showing the results of a test to identify the strongest interaction center(s).

[0053] FIG. 21 is a graph showing leakage current testing of Li||NMC811 full cells in the presence of electrolytes.

[0054] FIG. 22 is a graph showing the voltage profile of the Li ||NMC811 full cells for the aging evaluation with the combined testing protocol between 2.8-4.3 V at room temperature, charging at 0.2C and resting for 24 hours then discharging at 0.5C.

[0055] FIG. 23 is a graph showing the cycling performance of the Li ||NMC811 full cells for the aging evaluation with the combined testing protocol between 2.8-4.3 V at room temperature, charging at 0.2C and resting for 24 hours then discharging at 0.5C.

[0056] FIG. 24 is a graph showing the cycling performance of the Li ||NMC811 full cells between 2.8-4.3 V under 60 °C, charging at 0.2C and discharging at 0.5C. Electrolyte / capacity (E / C) ratio of 10 pL / mAh and 50 pm-thick Li foil were used for all cases. 1C= 4 mA / cm2.

[0057] FIG. 25 is a graph showing the cycling performance of Li||NMC811 coin cells in electrolytes, E / C ratio of 10 pL / mAh and 50 pm-thick Li foil were used.

[0058] FIG. 26 includes bar graphs showing the retentions of electrolyte components in the electrolytes of D-BTFE, D-TTE and D-HFTHP after 200 cycles, determined by!H and19F NMR analysis.

[0059] FIG. 27 is a graph showing the cycling performance of Li ||NMC811 pouch cells between 2.8-4.3 V at room temperature and 2.4 g / Ah of D-HFTHP. 1C= 4 mA / cm2. The inset is the SEM image of the cycled Li metal anode after 460 cycles.

[0060] FIG. 28 includes graphs showing the 'H DOSY NMR spectra of DME / BTFE (right), DME / TTE (middle), and DME / TFTHF (right) mixtures.

[0061] FIG. 29 includes graphs showing the 'H DOSY NMR spectra of BTFE-E (right), TTE-E (middle), and TFTHF-E (right) electrolytes.

[0062] FIG. 30 is a graph showing diffusion coefficients of the solvents and diluents with and without the Li salts dissolution into the mixture of DME / BTFE. Toluene was used as the internal reference.

[0063] FIG. 31 is a graph showing diffusion coefficients of the solvents and diluents with and without the Li salts dissolution into the mixture of DME / TTE. Toluene was used as the internal reference.

[0064] FIG. 32 is a graph showing diffusion coefficients of the solvents and diluents with and without the Li salts dissolution into the mixture of DME / TFTHF. Toluene was used as the internal reference.

[0065] FIG. 33 shows17O characterization on the coordination behaviors of diluent TFTHF within the mixture of DME / TFTHF and electrolyte of TFTHF-E.

[0066] FIG. 34 shows19F NMR characterization on the coordination behaviors of diluentTFTHF within the mixture of DME / TFTHF and electrolyte of TFTHF-E.

[0067] FIG. 35 is a graph showing 2DJH-19F HOESY analysis of the dipole-dipole interactions between solvent DME and diluent TFTHF within the mixture of DME / TFTHF.

[0068] FIG. 36 is a graph showing 2D ^-^F HOESY analysis of the dipole-dipole interactions between solvent DME and diluent TFTHF within the mixture of electrolyte of TFTHF-E.

[0069] FIG. 37 is a graph showing SAXS analysis of the nanostructures in mixture of DME / BTFE, with and without the dual Li salts dissolution.

[0070] FIG. 38 is a graph showing SAXS analysis of the nanostructures in mixture of DME / TTE, with and without the dual Li salts dissolution.

[0071] FIG. 39 is a graph showing SAXS analysis of the nanostructures in mixture of DME / TFTHF, with and without the dual Li salts dissolution.

[0072] FIG. 40 is a graph showing viscosities of BTFE-E, TTE-E and TFTHF-E electrolytes at 25 °C.

[0073] FIG. 41 is a graph showing ionic conductivities of BTFE-E, TTE-E and TFTHF-E electrolytes at 25 and -30°C.

[0074] FIG. 42 is a graph showing LSV of BTFE-E, TTE-E and TFTHF-E electrolytes in Li||Al cells.

[0075] FIG. 43 is a graph showing Li-ion transference number measurement of BTFE-E electrolytes using Li||Li symmetric cells, with the EIS spectra before and after the polarization as the insets.

[0076] FIG. 44 is a graph showing Li-ion transference number measurement of TTE-E electrolytes using Li | |Li symmetric cells, with the EIS spectra before and after the polarization as the insets.

[0077] FIG. 45 is a graph showing Li-ion transference number measurement of TFTHF-E electrolytes using Li| |Li symmetric cells, with the EIS spectra before and after the polarization as the insets.

[0078] FIG. 46 is a graph showing high resolution C is spectrum of the formed SEIs in BTFE-E electrolyte.

[0079] FIG. 47 is a graph showing high resolution C is spectrum of the formed SEIs in TTE-E electrolyte.

[0080] FIG. 48 is a graph showing high resolution C is spectrum of the formed SEIs in TTE-E electrolyte.

[0081] FIG. 49 is a graph showing high resolution F Is XPS spectra of the formed SEIs in BTFE -E electrolyte.

[0082] FIG. 50 is a graph showing high resolution F Is XPS spectra of the formed SEIs in TTE- E electrolyte.

[0083] FIG. 51 is a graph showing high resolution F Is XPS spectra of the formed SEIs in TFTHF-E electrolyte.

[0084] FIG. 52 shows SEM images of Li metal anode after 200 cycles in Li||NMC811 cells inBTFE-E (left), TTE-E (middle), and TFTHF-E (right) electrolytes.

[0085] FIG. 53 shows cryo-TEM images of the formed SEIs in BTFE-E (left), TTE-E (middle), and TFTHF-E (right) electrolytes.

[0086] FIG. 54 shows a high-resolution TEM image and a HAADF-TEM image with Li K-edge EELS spectra of the formed SEI in TFTHF-E electrolyte.

[0087] FIG, 55 shows7Li NMR analysis on the solvation structures of Li-ions in the binary salt electrolytes.

[0088] FIG. 56 is a graph showing a self-discharge evaluation of Li||NMC811 cells.

[0089] FIG. 57 is a graph showing fast charge and discharge at 1C of Li||NMC811 cells.

[0090] FIG. 58 is a graph showing cycling stability of Li||NMC811 cells in TFTHF-E at 25 and -20°C, alternatively.

[0091] FIG. 59 is a graph showing cycling stability of Li||NMC811 cells in TFTHF-E at 65 °C.

[0092] FIG. 60 is a graph showing cycling stability of the Li (20 pm)||NMC811 (5 mAh / cm2) cell in TFTHF-E.

[0093] FIG. 61 is a graph showing cycling stability of Li||NMC811 cells at room temperature.

[0094] FIG. 62 is a graph showing cycling stability of Li||NMC811 pouch cell under practical conditions in TFTHF-E.DETAILED DESCRIPTION

[0095] The following description is of exemplary embodiments and methods of use that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of various aspects of the present invention. The scope of the present invention is not limited by this description.

[0096] Embodiments generally relate to electrolyte compositions configured to manage reactions at a metal anode of a metal ion battery and to stabilize a solid electrolyte interphase (SEI) layer formed on the surface of the metal anode.

[0097] As used herein, the phrase “metal ion battery” refers to a rechargeable battery where metal ions move between an anode and a cathode during charging and recharging. Metal ions may include, but are not limited to, lithium (lithium-ion battery), sodium (sodium-ion battery), magnesium (magnesium-ion battery), potassium (potassium-ion battery), aluminum (aluminum-ion battery), or zinc (zinc-ion battery). The battery may store and release energy by the flow of metal ions through an electrolyte composition. For example, metal ions may move from the anode to the cathode through the electrolyte composition during discharging, and the metal ions may move back from the cathode to the anode through the electrolyte composition during charging.

[0098] It is contemplated that an electrolyte composition may react with a metal anode, specifically during initial charging-discharging cycles, to form an SEI layer on the surface of the anode. The SEI may provide certain advantages to the battery, as it may protect the anode from direct contact with the electrolyte composition to help prevent harmful side reactions that could degrade the battery, it may stabilize the interface between the anode and the electrolyte composition to improve battery life, and it may allow metal ions to pass through it, thus enabling the battery to charge and discharge properly. However, the SEI may also be a source of inefficiency and reduce a battery’s performance by inhibiting or decreasing metal ion movement and / or increasing internal resistance. Accordingly, controlling the SEI formation process and ensuring that the resulting SEI is stable can be critical in achieving effective battery performance.

[0099] Embodiments therefore relate to electrolyte compositions configured to manage reactions at the anode and control the SEI formation process. The electrolyte compositions are specifically configured to facilitate formation of a stable SEI bilayer including a metal oxide rich inner layer and a metal fluoride rich outer layer. As used herein, the term “inner layer” refers to an anodefacing layer of the SEI (e.g., the layer of the SEI formed on an anode surface), and the term “outer layer” refers to an outward-facing layer of the SEI (e.g., the layer of the SEI opposite of the inner layer).

[0100] The electrolyte composition includes an electrolyte, a solvent, and a diluent. The electrolyte may include at least one metal salt. In some embodiments, the electrolyte may include dual metal salts, such as a metal oxide-forming salt and a metal fluoride-forming salt. As used herein, the term “metal oxide-forming salt” refers to a salt that may react with metal ions (e.g., Me+) to form a metal oxide compound (e.g., Me?©). As used herein, the term “metal fluoride- forming salt” refers to a salt that may react with metal ions (e.g., Me+) to form a metal fluoride compound (e.g., MeF).

[0101] In some embodiments, the metal oxide-forming salt may be metal difluoro(oxalato)borate (e.g., MeDFOB). For example, in embodiments in which the metal ion battery is a lithium ion battery, the metal oxide-forming salt may be lithium difluoro(oxalato)borate (e.g., LiDFOB). In some embodiments, the metal fluoride-forming salt may be metal tetrafluoroborate (e.g., MeBF4). For example, in embodiments in which the metal ion battery is a lithium ion battery, the metal oxide-forming salt may be lithium tetrafluoroborate (e.g., LiBF4).

[0102] The solvent may be a liquid or gel medium configured to dissolve the electrolyte such that metal ions may move freely through the electrolyte composition between the anode and cathode. The solvent may include at least one organic compound. Organic compounds may be selected from the group consisting of dimethyl ether (DME), ethylene carbonate (EC), dimethyl carbonate (DMC), or any other suitable organic compounds, and mixtures thereof.

[0103] The diluent may be an additional liquid or substance combined with the solvent. The diluent may be selected to regulate the participation of the electrolyte composition in formation of the SEI. In particular, the diluent may be selected to suppress interaction betweenthe anode and the diluent. The diluent therefore preferably has minimized metal ion coordination capability, and in some embodiments is electrochemically inert to the metal ions.

[0104] In some embodiments in which the electrolyte includes dual metal salts, the diluent may be configured to differentiate the contributions of the dual anions to the SEI, thus forming a SEI bilayer.

[0105] In some embodiments, referring to FIG. 1, the diluent may include or consist of a fluorinated cyclic ether. In one embodiment, the diluent may include or consist of 3, 3, 4, 4,5,5- hexafluorotetrahydropyran (HFTHP). HFTHP has a specific constrained conformation designed to minimize its interaction with metal ions, enabling mitigated reactivity to the metal anode and limited participation in formation of the SEI, as compared to linear ethers. HFTHP may further refine the structure of the SEI to result in an inner SEI layer rich in metal oxide and an outer SEI layer rich in metal fluoride.

[0106] In another embodiment, referring to FIGS. 2-3, the diluent may include 3, 3,4,4- tetrafluorotetrahydrofuran (TFTHF). TFTHF may similarly refine the structure of the SEI through enhanced dipole-dipole interactions between the metal ion-coordinated solvent and the metal ion-suppressed diluent. In particular, TFTHF may foster an enhanced dipole-dipole interaction with the solvent, therefore greatly altering the solvation structures of metal ions. This leads to the weakened coordination of metal ions with the solvents while promoting intensified interaction between metal ions and anions, facilitating the formation of a stable SEI bilayer.

[0107] Embodiments further relate to an SEI formed from reacting the above-described electrolyte composition with an anode. In particular, the SEI may be a bilayer including a metal oxide rich inner layer and a metal fluoride rich outer layer, which will be described in furtherdetail. For example, in embodiments in which the metal ion battery is a lithium ion battery, the inner SEI layer may be LiCh-rich, and the outer SEI layer may be LiF-rich.

[0108] The formed SEI may exhibit improved stability in comparison to SEIs formed using linear fluorinated ether diluent, thus stabilizing the metal anode. The formed SEIs may further minimize void formation in comparison to SEIs formed using linear fluorinated ether diluent. The formed SEIs may further exhibit reduced dendrite formation in comparison to SEIs formed using linear fluorinated ether diluent. For example, the formed SEI may reduce the surface area available for parasitic reactions between a metal anode and an electrolyte composition.

[0109] Embodiments further relate to a rechargeable metal ion battery (e g., battery cells, battery packs, etc.) including the above-described electrolyte composition and / or the abovedescribed SEI. Such rechargeable metal ion batteries may be used in applications such as, but not limited to, consumer electronics (e.g., smartphones, tablets, laptops, smartwatches, fitness trackers, portable game consoles, headphones, earbuds, other audio devices), electric vehicles (e.g., electric automobiles, electric bikes, electric scooters, electric motorcycles, autonomous delivery robots), energy storage systems (e g., solar energy storage systems, backup power suppliers, grid stabilization systems, off-grid power systems), power tools (e.g., cordless hand tools, lawn mowers, garden equipment, portable generators), medical devices (e.g., implantable devices such as pacemakers, portable medical equipment, wearable health monitoring devices, diagnostic equipment), droves and UAVs (e.g., personal drones such as for recreation, commercial drones such as for agriculture, surveying, or delivery), portable lighting (e.g., flashlights, lanterns, emergency lights, headlamps), consumer appliances (e.g., cordless vacuum cleaners, electric toothbrushes, smart home devices), sports and recreation equipment (e.g.,electric skateboards, electric scooters, electric bikes, electric surfboards, electric watercraft), aerospace and aviation (e.g., aircraft systems, spacecraft and satellite systems), toys (e.g., remote-controlled cards, remote-controlled planes, remote-controlled drones, interactive toys), electric heating systems (e.g., portable electric heaters, battery-powered warmers), computing and data centers, robotics, electric grid and renewable energy systems, etc.

[0110] In some embodiments, the metal ion battery may be a lithium-ion battery, sodium- ion battery, magnesium-ion battery, potassium-ion battery, aluminum-ion battery, zinc-ion battery ,or any other suitable metal-ion battery.

[0111] In some embodiments, the anode of the metal ion battery may include carbonbased materials, such as graphite. In some embodiments, the anode may alternatively, or additionally, include a metal, such as lithium, sodium, magnesium, potassium, aluminum, zinc, or any other suitable metal.

[0112] In some embodiments, the cathode of the metal ion battery may be nickel (Ni), aluminum (Al), . . .EXAMPLES

[0113] Example 1 : Lithium-ion battery including an electrolyte with HFTHP diluent

[0114] We compared the participation of the commonly used linear fluorinated ether diluents, such as bis(2,2,2-trifluoroethyl) ether (BTFE) and l,l,2,2-tetrafluoroethyl-2,2,3,3- tetrafluoropropyl ether (TTE) in the solvation sheath of the Li-ion with the participation of, HFTHP, a highly fluorinated six-membered cyclic ether whose interaction with metal ions can be effectively suppressed by the constrained conformation of the specific cyclic structure ofHFTHP.

[0115] To illustrate their differences in Li-ion coordinating behavior between fluorinated linear and cyclic ethers, we firstly utilized the19F nuclear magnetic resonance (NMR) technique to examine the coordination interactions between Li-ions and diluents BTFE, TTE, and HFTHP in the dual-salt electrolytes containing IM LiDFOB and 0.4M LiBF4 in DME / BTFE, DME / TTE, or DME / HFTHP (referred to as D-BTFE, D-TTE, D-HFTHP, respectively). An apparent upfield shift of 0.14 ppm for BTFE was observed in the electrolyte of D-BTFE upon dissolving IM LiDFOB and 0.4M LiBF4 (FIG. 4). Different upfield shifts of the F atoms were observed for TTE after dissolving the dual Li salts. The F atoms bonded to the ethyl structure moiety show upfield shifts of 0.14 ppm and 0.15 ppm, respectively, while the F atoms on the propyl moiety only show inappreciable upfield shifts (0.07 ppm and 0.03 ppm, respectively) (FIG. 4). In contrast, all the F atoms in HFTHP showed negligible upfield shifts (0.03 ppm and 0.02 ppm, respectively) (FIG. 4), suggesting the absence of coordination interaction between the F atoms in HFTHP and Li-ion. The17O NMR characterization was conducted to further elaborate on the participation of O atoms in coordination with Li-ions. The O atom in BTFE exhibits an apparent upfield shift of 1.61 ppm after dissolving dual salts (FIG. 4), confirming the clear coordination between the O atom in BTFE and Li-ion. In contrast, the O atoms in TTE and HFTHP only show shifts of 0.23 ppm (FIG. 4) and 0.04 ppm (FIG. 4), respectively, indicating negligible coordination interaction between the O atoms and Li-ion in the electrolytes of D-TTE and D- HFTHP. To enhance experimental NMR measurements evaluating the interactions between Li- ions and diluents, electronic structure calculations were additionally conducted within the framework of the density functional theory (DFT) approach. Through examination of a wide set of ion-molecular complexes, higher binding energies were found for geometries involving BTFE and TTE molecules compared to geometries with HFTHP. This tendency is particularly affectedby the presence of both counterions in proximity to the diluent molecules. On the other hand, a clear correlation of this behavior is also observed when explicitly considering the strength of the ion-molecular interactions probed by the17O NMR chemical shift. Here, a relatively lower distance of 0.22 nm was found for BTFE, while larger distances of 0.31 and 0.39 nm are attributed to the weak interactions between Li and TTE and HFTHP, respectively. Regarding the interactions with the F atoms of the diluent, they also follow the experimental behavior observed in19F NMR, while the mutual contribution of BF4 and DFOB is less pronounced compared to the role of each individual counterion. Collectively, the19F and17O NMR results indicate the formation of an enhanced tridentate coordination structure involving F and O atoms in BTFE (FIG. 5) and a distinct five-membered ring coordination structure involving only F atoms bonded to the ethyl moiety in TTE (FIG. 5), while confirming the absence of coordination between HFTHP and Li-ion in the electrolyte of D-HFTHP.

[0116] Linear sweep voltammetry (LSV) of Li||Al cells is carried out to evaluate the oxidation stability of electrolytes. The electrolyte without fluorinated ether diluent, IM LiDFOB and 0.4M LiBF4 in DME, delivers an inferior oxidation stability with oxidation potential <3.5 V (vs. Li+ / Li) as the oxidation current reaching 0.002 mA / cm2. The electrolytes of D-BTFE and D- TTE deliver slightly improved oxidation tolerance by giving oxidation potentials at ~4.0 V and ~4.3 V, respectively. In contrast, the electrolyte of D-HFTHP can deliver a considerably improved oxidation stability window of >6 V as the oxidation current reaches 0.002 mA / cm2. The enhanced oxidation stability of D-HFTHP is notably attributed to the reduced presence of uncoordinated DME solvent molecules in D-HFTHP because of the increased involvement ofDME in Li-ion solvation promoted by the non-coordinating feature of HFTHP with Li-ion. To evaluate the reversibility of Li metal anode in the D-HFTHP electrolytes under practicaloperating conditions, we conducted CE tests on the more demanding anode-free Cu||NMC811 (4.2 mAh / cm2) cells. Following an initial formation cycle at 0.1C for charging and C / 3 for discharging, the cells were cycled between 2.8-4.4 V at 0.2C for charging and C / 3 for discharging for the subsequent cycles. The D-BTFE and D-TTE electrolytes exhibit an average CE of 99.0% and 99.1%, respectively, while the D-HFTHP electrolyte demonstrates a considerable improvement with an average CE of 99.5% for the first 100 cycles, and a rapid ramp-up to >99.5% within just 2 cycles. Furthermore, D-HFTHP exhibits enhanced interfacial Li-ion transport kinetics, potentially leading to a more uniform Li deposition morphology, evidenced by the lower activation energy (Ea) of 38.0 kJ / mol for interfacial Li-ion transport in D- HFTHP, in contrast to the higher Eaobserved in D-BTFE (56.3 kJ / mol) and D-TTE (55.1 kJ / mol) electrolytes. Additionally, this is further substantiated by the lowest Li cycling overpotential observed in Li||Li symmetric cells when using D-HFTHP and consistent with the improved ionic conductivity in D-HFTHP.

[0117] The morphologies of electrodeposited Li metal with a 4.0 mAh / cm2areal capacity in the electrolytes of D-BTFE, D-TTE and D-HFTHP were first studied using scanning electron microscopy (SEM), as shown in FIG. 6. In the D-BTFE electrolyte, a porous and dendritic Li structure, featuring sporadic voids and loose structure within the bulk Li metal and with a thickness of approximately 30 pm, is observed. In the D-TTE electrolyte, Li dendrites still formed despite an increased granule size of the electrodeposited Li metal. The thickness of the Li metal decreased to ~28 pm, while still showing both loose structures and sporadic voids. In contrast, the D-HFTHP electrolyte promoted uniform and nodular Li deposition without dendrites or voids inside the deposited Li metal, with a thickness of ~21 pm, aligning closely with the theoretically calculated thickness of 19.4 pm. The morphological studies demonstratethat D-HFTHP can greatly facilitate uniform Li deposition and lead to a significant reduction in the surface area available for the parasitic reactions between the Li metal anode and electrolyte.

[0118] We next used the X-ray photoelectron spectroscopy (XPS) depth profiling analysis to deliberate on the interfacial chemical compositions of the formed SEIs on Li metal collected from Li (50 pm)||NMC811 (4.0 mAh / cm2) pouch cells after 20 cycles using the electrolytes of D-BTFE, D-TTE and D-HFTHP. The high-resolution C is XPS spectra (FIG. 7) reveal peaks of -CF3 (at -293.5 eV) and C-F (at -288.4 eV) and similarly, the high-resolution F Is XPS spectra (FIGS. 8-9) reveal the peaks of C-F (at -688.0 eV) for the SEIs in electrolytes of D-BTFE and D-TTE. The results collectively reveal that BTFE and TTE molecules decompose on the surface of Li metal anode during cycling, a process driven by their involvement in Li-ion solvation, as evidenced by the NMR data (FIGS. 4-5). More importantly, the depth profding of F Is XPS spectra shows a noticeable increase in LiF peak intensities when using D-HFTHP (at -684.8 eV) (FIG. 10), indicating a LiF-rich SEI formation on the Li metal, compared with D- BTFE and D-TTE. Moreover, depth profdes of the SEI components (e.g., organic species, Li2O and LiF) reveal that the electrolyte of D-BTFE promotes an organic-rich SEI layer (FIG. 11), while the electrolyte D-TTE promotes the formed SEI with an organic-rich outer layer and a Li2O-rich inner layer (FIG. 12). In contrast, the D-HFTHP electrolyte leads to the generation of an SEI layer that is dominated by inorganic components, with a LiF-rich outer layer and a Li2O- rich inner layer. (FIG. 13). Collectively, the XPS results demonstrate that the use of the D- HFTHP electrolyte reduces the content of organic species in SEI due to its minimized coordination with Li-ion and leads to the creation of a unique inorganic-dominant bilayer SEI onLi metal surface.

[0119] Cryogenic transmission electron microscopy (cryo-TEM) techniques are conducted to investigate the formed SEIs in electrolytes further, demonstrating significant differences in the nanostructural features and dominant components within SEI layers. The collected cryo-TEM image of the formed SEI layer using the electrolyte of D-HFTHP was depicted in FIG. 14. A distinctive and well-defined bilayer SEI rich in inorganic components is observed on the surface of the Li metal anode, exhibiting uniformity and dense passivation, with a thickness of approximately 30 nm. In the formed SEI layer, the { 111 } planes of LiF and Li2O were identified, exhibiting lattice spacings of 0.233 nm (FIG. 15) and 0.27 nm (FIG. 16), respectively. The microscopic results show Li2O is the dominant species in the inner SEI layer, while LiF dominates the outer layer, corroborating the results revealed by the XPS depth profiling results (FIG. 13). The Li2O-rich inner SEI layer enhances Li-ion distribution within the SEI, attributed to the low interfacial binding energy of Li-ions across the Li2O / Li2O boundaries, fostering uniform Li metal deposition. Concurrently, the LiF-rich outer SEI layer, characterized by its superior electronic insulation and mechanical properties, acts as an effective passivation film, preventing parasitic corrosion reactions between the Li metal anode and the electrolyte and improving the overall robustness of the SEI layer against degradation upon cycling. In contrast, the SEI formed in D-BTFE is notably thicker, with a thickness of approximately 40 nm, and is predominantly composed of an amorphous structure, containing sparsely distributed LiF / Li2O species. Likewise, the SEI formed in D-TTE, despite being thinner with a thickness of around 20 nm, also exhibits an amorphous dominant SEI with thinly dispersed LiF / Li2O species, aligning with the XPS depth profiling results (FIG. 12).

[0120] The unique bilayer SEI structure formed in the electrolyte of D-HFTHP was further verified by TEM characterization. High-angle annular dark-field scanning transmissionelectron microscopy (HAADF-STEM) was conducted to collect an image for the SEI formed inD-HFTHP, as depicted in FIG. 16. Pixel-by-pixel analysis was conducted on three designated regions of the deposited Li layer, inner SEI layer, and the outer SEI layer. The Li K-edge spectrum of electron energy loss spectroscopy (EELS) studies acquired from the top maroon designated region of the outer SEI layer shows a peak shape indicative of the high intensity of LiF, suggesting the presence of a LiF-rich fdm in the outer SEI layer. For the middle blue designated region, the peak shape aligns with Li2O, indicating the presence of a Li2O-rich inner SEI layer. Finally, the peak shape from the bottom cyan designated region matches the electrochemically deposited Li metal. Additionally, the energy dispersive X-ray spectroscopy (EDS) analysis results indicate that the SEI layer formed in the electrolyte of D-HFTHP is C-less but F-rich, confirming the formation of an inorganic-dominant SEI layer. These electron microscopic results coincide with the XPS data and further confirm the formation of a unique inorganic-dominant bilayer SEI composed of a Li2O-rich inner layer and a LiF-rich outer layer.

[0121] Given that the electrolyte formulations of D-BTFE, D-TTE, and D-HFTHP are similar, with the only difference being the diluent used, we deduce that the choice of diluent HFTHP can significantly impact the coordination interaction between the Li-ion and anions within Li-ion solvation structure, leading to corresponding unique bilayer SEI formation process. To uncover the underlying coordination between Li-ions and anions affected by the diluents, we utilized13C and19F NMR techniques to probe the anions to illustrate Li-ion solvation structure changes in the three electrolytes studied here. It has been found that the bidentate difluoro(oxalato)borate anion, DFOB , can coordinate with the Li-ion through its carbonyl oxygen atoms. Therefore, the coordination interaction between the Li-ion and DFOB anion can be studied by analyzing the chemical shifts of the carbonyl functional group in DFOB using13CNMR. As depicted in FIG. 17, negligible change (< 0.1 ppm) of chemical shifts for the carbonyl carbons between D-BTFE and D-TTE are observed in13C NMR, indicating very similar coordination interaction between the Li-ion and DFOB anion in these two electrolytes. However, the use of D-HFTHP with fluorinated cyclic ether HFTHP as the diluent shows a noticeable downfield chemical shift (0.20 ppm and 0.15 ppm, compared with D-BTFE and D- TTE, respectively), suggesting a stronger interaction between Li-ion and the carbonyl functional groups of DFOB . To investigate the coordination interactions between the DFOB and BF4 anions with the Li-ion,19F NMR is utilized (FIG. 18). The chemical shift differences between the DFOB and BF4 anions are only 0.66 ppm and 0.98 ppm in D-BTFE and D-TTE, respectively. In contrast, a significant chemical shift difference of 1.97 ppm between the DFOB and BF4 anions is observed in D-HFTHP, indicating a substantially differentiated interaction between the DFOB and BF4 anions with the Li-ion enabled by the minimized coordinating diluent HFTHP.

[0122] The molecular dynamics (MD) simulation was further conducted to explore the differentiated coordination of DFOB and BF4 with Li-ions following the13C and19F NMR studies. The strength of the interionic interactions and the coordination ability of Li+with DFOB and BF4 were tested. In the case of Li+-DFOB , we initially estimated the interactions between different electronegative atoms, namely ~O~, 0= and F, to identify the strongest interaction center (FIG. 19). As indicated by the resulting radial distributions, both O atoms interact slightly more strongly (0.17 nm) compared to the F atom (0.18 nm). This is also evident when comparing the intensities of the first peak, where Li---F is notably weaker than Li- -O. The negligible difference in Li—O strength may be attributed to the mutual coordination of both O atoms, although this is not reflected in the analysis of the respective running coordination numbers. A generally higher coordination number of Li — O- compared to Li— 0= led us toconsider the ether oxygen atom as a representative site for Li ---DFOB interactions. As depicted in FIG. 20, when comparing the interionic interactions of both DFOB and BF4 , it should be noted that the position of the first peak for DFOB is located at slightly shorter distances (0.17 nm) than that for BFi (0.18 nm), suggesting a difference in the strength between the two anions. Furthermore, by analyzing the Li+running coordination number, a predominant coordination of DFOB over BF4 is found. Interestingly, the diluent affects the Li+coordination ability differently, particularly for TTE and HFTHP. For both DFOB and BF4 , Li+exhibits stronger coordination in the BTFE environment. For DFOB , the HFTHP environment is more favorable for interionic coordination than TTE, while the opposite situation is observed for BF4 Together, the modelling results corroborate that using HFTHP enhances differentiated coordination of DFOB and BF4 .

[0123] Combining the13C,19F NMR results and the MD simulation, a clear differentiated coordination between dual anions with Li-ions is discovered in D-HFTHP, where there is an enhanced coordination between Li-ion and DFOB , while the coordination between Li-ion and BF4 anion is attenuated. The differentiated coordination of DFOB and BF4 with Li-ion enabled by HFTHP promotes the formation of a DFOB rich inner solvation sheath and a BF4 rich outer solvation sheath around the Li-ions. This tailored anion proximity around Li-ions leads to the creation of a Li2O-rich inner SEI layer, which is analogous to the SEI layer formed with only LiDFOB as the Li salt in electrolyte. Meanwhile, the weakly coordinating BF4 anion can undergo reductive decomposition, contributing to the creation of a LiF-rich outer SEI layer. However, the generation of LiF in the outer SEI layer does not entirely preclude the influence ofLiDFOB. Collectively, the developed fluorinated cyclic ether HFTHP with the minimized Li-ion coordination fundamentally alters dual anion solvation structures, facilitating the differentiateddecomposition of dual anions to generate the bilayer SEI formation process in D-HFTHP. The unique organic-less, inorganic-rich bilayer SEI with a Li2O-rich inner layer and a LiF-rich outer layer contributes to significant enhancement in the cycling stability and calendar life of Li metal anodes, as evidenced in the subsequent section.

[0124] After the elaboration on the compositions and nanostructures of the formed SEIs, the developed electrolyte of D-HFTHP is expected to stabilize the Li metal anodes. To assess the efficacy of the electrolytes of D-BTFE, D-TTE and D-HFTHP and the correspondingly formed SEIs in suppressing self-discharge of LMBs, the leakage current of Li (50 pm)||NMC811 (4.0 mAh / cm2) full cells charged at 4.3 V were measured (FIG. 21). The D-HFTHP electrolyte delivers the smallest leakage current, dropping to a stable value below 0.4 pA / cm2after the first 24 hours, compared to electrolytes of D-BTFE and D-TTE. Based on these results, a combined testing protocol has been developed by introducing a 24-hour resting period during cycling to comprehensively evaluate the aging of LMBs. After pre-cycling at 0.1C for one cycle, the combined testing protocol involves a repeated process that includes a 24-hour resting period after charging the Li||NMC811 full cells to 4.3 V at 0.2C, allowing the full occurrence of galvanic and chemical corrosion of the Li metal anodes, then the Li||NMC811 full cells are discharged at 0.5C to 2.8 V. As shown in FIGS. 22-23, the cells using electrolytes of D-BTFE and D-TTE experience rapid capacity decay, resulting in 80% capacity retention after merely 50 and 70 cycles, respectively. In contrast, the electrolyte of D-HFTHP deliver an 80% of capacity retention over 190 cycles after 245 days, demonstrating that the developed electrolyte can effectively suppress the self-discharge and calendar aging of Li||NMC811 cells, making it potentially useful in LMBs under practical conditions.

[0125] In addition to the challenge of self-discharge, the cycling stability of Li metal anodes remains a persistent issue, particularly when operating at high temperatures. This is due to the fast Li metal degradation resulting from the susceptibility of SEI layer and the aggravated parasitic reactions between the Li metal anode and electrolytes. The developed electrolyte of D- HFTHP, which benefits from the moderately high boiling point of diluent HFTHP (100°C), is further tested in LMBs at elevated temperatures. As shown in FIG. 24, when the Li||NMC811 full cells were evaluated at 60°C, those incorporating the electrolyte of D-HFTHP delivered greatly enhanced cycling stability, showing a capacity retention of 80% after 218 cycles, compared to the sharp capacity decay observed with the electrolytes of D-BTFE and D-TTE using linear fluorinated ether diluents. The substantially enhanced cycling stability observed at 60°C, as confirmed by the parallel cells, can be attributed to the electrochemical inertness of the fluorinated cyclic ether diluent HFTHP to the Li metal anode, and the formation of a robust inorganic-dominant bilayer SEI layer, as revealed by the results of XPS and electron microscopic characterization. Impressively, as shown in FIG. 25, the developed electrolyte D-HFTHP enables an unprecedented cycling performance of Li (50 pm)||NMC811 (4.0 mAh / cm2) full cells, with a capacity retention of 80% after 568 cycles at room temperature, as further confirmed by the parallel cells. In contrast, the electrolytes of D-BTFE and D-TTE showed inferior cycling performance, with 80% capacity retention after 252 cycles and 324 cycles, respectively. The ’H and19F quantitative NMR spectroscopic analysis was utilized to explore the electrolytes evolution after 20 cycles in Li||NMC811 full cells. As revealed by the NMR analysis in FIG. 26, the electrolyte of D-HFTHP demonstrates good retentions of diluent HFTHP (67.1%) and solvent DME (61.4%). In contrast, the electrolyte of D-BTFE shows substantial consumption of BTFE (0.9% retention) and solvent DME (17.8%), while the electrolyte of D-TTE exhibitsapparent consumption of TTE (10.3% retention) and solvent DME (28.9%). The19F quantitative NMR spectroscopic analysis was utilized to reveal the evolution of F-containing Li salts of LiDFOB and LiBF4. The developed electrolyte D-HFTHP can also clearly retards the consumption of LiDFOB (43.3% retention) and LiBF4 (64.3% retention), as revealed by the19F quantitative NMR spectroscopic analysis results. Collectively, the above quantitative NMR results suggest the evidently retarded decomposition of the developed electrolyte of D-HFTHP, enabling notably improved electrochemical performance of LMBs under practical conditions.

[0126] To evaluate the feasibility of the developed electrolyte of D-HFTHP, two parallel Li||NMC811 pouch cells were next fabricated and tested under challenge conditions (FIG. 27). The pouch cells exhibited a gravimetric energy density of as high as 410 Wh / kg, with calculations including the NMC811 cathode electrode, Li metal anode, electrolyte, and separator. As shown in FIG. 27, the newly developed D-HFTHP electrolyte exhibits excellent repeatability in tested pouch cells, delivering exceptional cycling stability with 80% capacity retention up to 470 cycles, when compared to literature reported Li||NMC811 pouch cells with high energy density (>300 Wh / kg). It is worthy to note that the Li metal anode still demonstrated a uniform morphology even after 460 cycles, as shown in the inset of FIG. 27. These results verify the effectiveness of the developed electrolyte in stabilizing Li metal anodes and demonstrate its promising potential for practical applications in LMBs.

[0127] In summary, we have demonstrated a strategy to develop superior liquid electrolytes for high-energy density LMBs by introducing minimized coordinating diluent of a highly fluorinated cyclic ether. Distinct from the widely used linear fluorinated ethers, such asBTFE and TTE, the developed fluorinated ether diluent HFTHP exhibits minimized coordination to Li-ion, enabling a distinctive coordination dynamic between Li-ion with DFOB over BFianion and the formation of a unique inorganic-dominant bilayer SEI with a Li2O-rich inner layer and a LiF-rich outer layer. Benefit from the electrochemical inertness of the diluent and the resultant robust SEI structure, high-energy-density Li metal battery pouch cells, pairing high Ni NMC81 1 cathode with Li metal anode, deliver exceptional long cycling life with improved selfdischarge and high-temperature performance. This study significantly advances the understanding of the solvation behavior of fluorinated ether diluents and provides a strategy in developing superior liquid electrolytes for Li metal batteries by introducing minimized coordinating diluent to facilitate the formation of stable SEI layer, thereby enabling extended longevity of Li metal batteries.

[0128] Materials

[0129] The NMC811 cathode electrode with an active material loading of -19.5 mg / cm2was acquired from Guangdong Canrd New Energy Technology Co., Ltd. The electrodes were punched into 10-mm-diameter discs for the Li||NMC811 coin cell assembly. The LiDFOB, LiBF4 and DME were purchased from Gotion. 2,2,3,3,4,4-Hexafluoro-l,5-pentanediol (>98%) was acquired from Matrix Scientific. BTFE and TTE were acquired from SynQuest and dried over 4 A molecular sieves before use. The Cu foil (9 pm thickness) for Cu||NMC811 anode-free cells was acquired from MTI. Free-standing Li foil (50 pm thickness) was acquired from Honjo and used as received. Celgard 2325 (25 pm thickness) was used as the separator for all cells. All electrolytes tested in this study were prepared inside an Ar-filled glovebox with Ch <0.1 ppm and H2O <0.1 ppm. To prepare the electrolytes D-BTFE, D-TTE, and D-HFTHP, the respective diluents (BTFE, TTE, and HFTHP) were added to a solution that initially contained 5M LiDFOB and 2M LiBF4 in DME, and the mixture was diluted to obtain a final solution with IM LiDFOBand 0.4M LiBF4. All remaining reagents acquired from Sigma-Aldrich were utilized in their received condition, except where noted differently.

[0130] Synthesis of HFTHP

[0131] A mixture of the 2,2,3,3,4,4-hexafluoro-l,5-pentanediol (21.2 g, 0.1 mole) and 98% sulfuric acid (2.5 g) was stirred in an oil-bath at 195 °C. The crude product HFTHP distilled over was dried with anhydrous K2CO3 overnight. After filtration to remove the K2CO3, the resultant filtrate was redistilled, with fractions collected in the temperature range of 99-100 °C, giving HFTHP (16.7 g) with an overall yield of 86%. The obtained HFTHP was further dried over 4 A molecular sieves before use.

[0132] Electrochemical Testing

[0133] All electrochemical evaluations of the cells were conducted on Landt battery testers. 50-pm-thick Li metal anodes and 27 pL of the corresponding electrolyte were used for assembly of Li||NMC811 CR2016 coin cells. The coin cells were tested under galvanostatic charging / discharging conditions. After one formation with both charging and discharging at 0.1C, the coin cells were then charged at 0.2C and discharged at 0.5C for cycling, within the voltage window of 2.8-4.3V. For Coulombic efficiency evaluation, all Cu||NMC811 anode-free cells were assembled using 14 pL of the corresponding electrolyte and tested at constant current and constant voltage charging protocol. Following the first cycle of formation with charging at C / 10 and discharging at C / 3, the anode-free cells were subjected to cycling, which involved charging at C / 5 to 4.3 V and holding at 4.3 V until the anodic current fell below C / 20, then discharging at C / 3 to 2.8 V. The linear sweep voltammetry (LSV) was measured in Li| | Al cells on Solartron ModuLab, with a scan rate 0.5 mV / s. The leakage current in the Li||NMC811 coin cells was measured by holding the cells at 4.3 V and monitoring the current generated.

[0134] Characterizations

[0135] All SEM images were collected using a Nova NanoSEM 630 instrument to elucidate the morphological evolution of both the Li metal anodes and the NMC811 cathodes.All XPS characterizations were conducted using a PHI VersaProbe II Scanning XPS Microprobe. The Li metal anodes used for XPS depth-profiling analysis, were harvested from the Li||NMC811 pouch cells after 20 cycles at 0.2C charging and 0.5C discharging after one formation cycle with both charging and discharging at 0.1C. For the XPS characterization, all the collected Li metal anodes were washed three times with DME to remove any electrolyte residues, followed by drying in vacuum for 10 minutes. All the 'H,13C, and19F NMR spectra were collected using a Bruker AVANCE NEO-500 instrument, and all the17O and7Li spectra were collected using a Bruker AVANCE NEO-400 instrument. To avoid the impact on solvation structure from the internal standard solution or the deuterated solvents, coaxial NMR tubes were used for the13C,19F,17O and7Li NMR studies on the electrolytes in this study. In the collected NMR spectra, the13C peaks are calibrated using DMSO as the internal reference at 8 = 39.40 ppm, the19F peaks are calibrated using hexafluorobenzene as the internal reference at 8 = - 164.90 ppm, the17O peaks are calibrated using D2O as the internal reference at 8 = 0 ppm, and the7Li peaks are calibrated using IM LiCl in D2O as the internal reference at 8 = 0 ppm. For the quantitative NMR analysis of electrolytes evolution, acetonitrile (3.0 pL) and hexafluorobenzene (2.0 pL) were employed as the internal references for quantitativeJH and19F NMR analysis, respectively. The Li||NMC811 coin cells with 20 pL of the corresponding electrolyte were disassembled in a glovebox after 200 cycles and rinsed thoroughly with approximately 2 mL ofDMSO-tL, and the resultant solutions were utilized for the quantitative NMR analysis. The electrochemical impedance spectroscopy (EIS) tests on the Li||Li symmetric cells in differentelectrolytes were performed at an amplitude of 10 mV in the frequency range of 1 MHz to 0.01 Hz.

[0136] Cry o-TEM Experiment

[0137] The Li samples for cryo-TEM characterization were produced by electroplating a 0.25 mAh / cm2Li onto bare Cu grids at 0.5 mA / cm2in the specified electrolyte. The resultant Li samples on Cu grids were washed with DME, dried in vacuum for 10 minutes and then used for the cryo-TEM analysis. A dual spherical aberration-corrected FEI Titan2 G2 60-300 STEM was used to collect the TEM and STEM images by operating at an accelerating voltage of 200 kV. A Gatan GIF Quantum ERS 966 system, with settings adjusted to an energy dispersion of 0.05 eV per channel, an exposure time of 0.1 s, and a maintained 10 nm pixel size, was utilized to collect the EELS spectra. The EDS mapping images were acquired using Bruker Super-X quad X-ray detectors with a beam current of 0.1 nA in 5 minutes.

[0138] Pouch Cell Fabrication and its Electrochemical Test

[0139] The pouch cells in this study were fabricated inside a glovebox by stacking a double-sided coated NMC811 electrode (39 mm length x 29 mm width), two pieces of 50 pm thick free-standing Li foil (40 mm length x 30 mm width each), and two pieces of Celgard 2325 separators (40 mm length x 30 mm width each). 210 mg of 1 M LiDFOB+ 0.4M LiBF4 in DME / HFTHP was utilized as electrolyte for every single pouch cell. Following a formation cycle with both charging and discharging at 0.1C, the assembled pouch cells were subjected to cycling, which involved charging at 0.2C to 4.3 V and maintaining at 4.3 V until the anodic current fell below 0.05C, then discharging at 0.5C to 2.8 V.

[0140] Computation Details

[0141] DFT calculations were performed for the set of ion and ion-molecular complexes optimized in gas phase using M06-2X / 6-311++G(d, p) level of theory using Gaussian code. For classical MD the OPLS-AA force field was utilized to adjust most of the intra- and interatomic potential parameters. The Coulomb interactions were described by CHELPG scheme using MP2 / aug-cc-pVTZ level of theory, preliminary optimized in gas phase using HF / aug-cc-pVTZ under Gaussian code, vl6. Optimized geometries were additionally checked to be in true minima by the absence of imaginary vibration frequencies. Missing interm olecul ar parameters for DFOB and TTE were derived using relaxed potential energy surface scan. The obtained potential parameters were validated against the experimental density, where for all systems the maximum deviations did not exceed 7%.

[0142] The initial coordinates of 64 LiBF4, 160 LiDFOB, 318 DME and 979 BTFE (D- BTFE), 837 TTE (D-TTE) and 1246 HFTHP (D-HFTHP), representing the considered experimentally electrolytes and neat mixtures, were generated using Packmol code and placed into orthorhombic supercell of 8 x 8 x 8 nm with three-dimensional periodic boundary conditions. All MD simulations were performed using GROMACS, v2016.3. The leap-frog algorithm was utilized to integrate the equations of motion, with a timestep of 0.5 fs. The electrostatic long-range interactions within the cut-off range of 1.4 nm were accounted by Particle Mesh Ewald algorithm, using the same cut-off distance for the real-space component. The conventional shifted force technique was utilized to treat the 12-6 Lennard-Jones interactions, with a switching region between 1.2 and 1.3 nm.

[0143] Each system was, firstly, minimized using steepest descent algorithm, following equilibration procedure in npT ensemble for 50 ns and nVT ensemble for additional 10 ns to collect the coordinates for the analysis under the target thermodynamic conditions of 298.15 Kand 1 bar using velocity-rescaling thermostat and Parrinello-Rahman barostat with coupling constants of 0.1 ps and 0.5 ps, respectively. All the analysis of MD trajectories was conducted using TRAVIS, code, version July 29, 2022.

[0144] Example 2: Lithium-ion battery including an electrolyte with TFTHF diluent

[0145] To elucidate the coordination interactions between Li-ions and the solvent DME, as well as fluorinated ether diluents bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1, 2, 2- tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and TFTHF within the binary salt electrolytes (BTFE-E: IM LiDFOB and 0.4M LiBF4in DME / BTFE; TTE-E: IM LiDFOB and 0.4M LiBF4in DME / TTE; and TFTHF-E: IM LiDFOB and 0.4M LiBF4in DME / TFTHF), we first utilized the1H diffusion-ordered spectroscopy (DOSY) nuclear magnetic resonance (NMR) technique. For the1H DOSY NMR characterization, toluene was selected as an internal reference due to its exceptionally low coordination capability to Li-ions. In principle, when the diffusion coefficient of a solvent approaches that of the internal reference toluene, it indicates a diminished coordination between the solvent and Li-ions, similar as toluene of exceptionally low Li-ion coordination within the electrolyte solution. As depicted in FIGS. 28-30, the diffusion coefficients of DME and BTFE decrease after IM LiDFOB and 0.4M LiBF4are added and dissolved in mixture of DME and BTFE. The diffusion coefficients of DME (2.59 * 10'9m2 / s) and BTFE (2.23 * 10'9m2 / s) decrease significantly to 0.58 x 10'9m2 / s and 1.17 x 10'9m2 / s, respectively, while the internal reference toluene shows a distinctly higher diffusion coefficient of 1.62 x 10’9m2 / s in the BTFE-E electrolyte. Similarly, the diffusion coefficients of DME and TTE are also affected upon the Li salts dissolution. As depicted in FIGS. 28, 29, and 31, the diffusion coefficients of DME (1.45 x 10'9m2 / s) and TTE (1.07 x 10’9m2 / s) significantly decreases to 0.31 x 10'9m2 / s and 0.51 x 10'9m2 / s, respectively, while the internal referencetoluene exhibits an apparently higher diffusion coefficient of 0.85 x 10’9m2 / s in the TTE-E electrolyte. Notably, the diffusion coefficients of DME (1.97 x 10'9m2 / s) and TFTHF (1.68 x 10'9m2 / s) decrease to 0.29 x 10'9m2 / s and 0.72 x 10'9m2 / s, respectively, upon the dissolution of Li salts (FIGS. 28, 29, and 32). Interestingly, the diffusion coefficients of TFTHF and the internal reference toluene (0.81 x 10'9m2 / s) are very similar in the TFTHF-E electrolyte, suggesting the non-Li-ion-coordinating feature of diluent TFTHF. Collectively, the1H DOSY NMR results indicate that DME predominantly solvates Li-ions in BTFE-E, TTE-E, and TFTHF-E electrolytes, with BTFE and TTE exhibiting appreciable coordination with Li-ions, consistent with our recent findings, while TFTHF shows no Li-ion coordination.

[0146] After the elucidation on the coordination interactions within the binary salt electrolytes by1H DOSY NMR characterization, we tried to further verify the non -coordinating capability of diluent TFTHF by using17O and19F NMR techniques. As depicted in FIG. 33, the17O chemical shifts of the O atom in TFTHF exhibited a negligible difference (0.03 ppm) after the dissolution of Li salts LiDFOB and LiBF4, confirming that the O atom in TFTHF hardly coordinates with Li-ions in electrolyte of TFTHF-E. Interestingly, the19F NMR analysis revealed an apparent downfield shift of 0.11 ppm for the F atoms in TFTHF upon the binary Li salts dissolution (FIG. 34), seemingly contradicting the non-Li-ion coordination of the diluent TFTHF as revealed by the1H DOSY NMR analysis. This is presumably attributed to the potential dipoledipole interaction between the F atoms in TFTHF and positively charged species, specifically the Li-ion-coordinated solvent DME, rather than the Li-ions as supported by the1H DOSY NMR characterization. To substantiate this hypothesis, the 2D ^-^F heteronuclear Overhauser spectroscopy (HOESY) technique was next utilized to explore the dipole-dipole interaction between the Li-ion coordinated solvent DME and diluent TFTHF (FIGS. 35-36). Given theinherent correlation between the H atoms (Ha) and F atoms (Fp) within the same TFTHF molecule (as shown in the insets of FIGS. 35-36), the intensity of this Ha-Fp correlation is used as a reference and set to 1.00. There is only a negligible correlation, with an intensity of 0.07, between the H atoms (labeled as Ht) at the terminal methyl group in DME and the Fp atoms in TFTHF within the DME / TFTHF mixture (FIG. 35). In contrast, a notably stronger correlation intensity of 0.15 was observed between the Htatoms in the solvent DME and the Fp atoms in TFTHF within the TFTHF-E electrolyte (FIG. 36), confirming apparently enhanced C~F H~C dipole-dipole interactions between the Li-ion-coordinated solvent DME and diluent TFTHF. These enhanced dipole-dipole interactions can enable weakened coordination between Li-ions and solvent DME while intensifying interactions between Li-ions and anions, thereby promising homogeneous solvation nanostructures, improved Li-ion transference number (H i ) and the formation of an anion-derived SEI in the electrolyte of TFTHF-E, as will be elaborated in detail in the following sections.

[0147] To explore the impact of enhanced dipole-dipole interactions on the solvation nanostructures of the binary salt electrolytes, small-angle X-ray scattering (SAXS) technique was applied, due to its effectiveness to study the long range solvation structures such as cluster or aggregate of battery liquid electrolytes. The SAXS profiles of the electrolytes of BTFE-E, TTE-E and TFTHF-E were collected and assessed against those of the corresponding pure solvent / diluent mixtures, as shown in FIGS. 37-39. For BTFE-E electrolyte, a pronounced intensity increase was observed in the q range of 0.1-1.1 A'1when compared to the mixture of DME / BTFE. In contrast, for the TTE-E and TFTHF-E electrolytes, the intensity remains nearly unchanged, indicating that these two electrolytes maintain greater homogeneity upon Li saltsaddition and supports the homogeneous solvation nanostructures in the developed TFTHF-E electrolyte.

[0148] The viscosities of the binary salt electrolytes of BTFE-E, TTE-E and TFTHF-E were measured at 25 °C, as shown in FIG. 40. TFTHF-E exhibited a moderate viscosity of 3.81 cP. Additionally, introduction of the cyclic fluorinated ether diluent TFTHF significantly enhanced ionic conductivity (FIG. 41), with the TFTHF-E electrolyte demonstrating a conductivity of 3.10 mS / cm at 25 °C and maintaining 1.92 mS / cm at -30 °C, underscoring its potential viability under low-temperature conditions. In contrast, both BTFE-E and TTE-E electrolytes showed inferior ionic conductivities at both 25 °C and -30 °C.

[0149] The electrolytes' oxidation stability was evaluated using linear sweep voltammetry (LSV) on Li 11 Al cells at a scan rate of 0.5 mV / s, as depicted in FIG. 42. The BTFE- E and TTE-E electrolytes exhibit inferior oxidation stability with oxidation potentials around 4.0 V and 4.2 V (v.s; Li+ / Li), respectively, when the oxidation current density reaches 1.3 pA / cm2. Notably, the TFTHF-E electrolyte demonstrates a substantially enhanced oxidation stability window exceeding 6 V, with an oxidation current density reaching 1.3 pA / cm2. The enhanced stability of TFTHF-E electrolyte against oxidation can be attributed to the introduction of the non-coordinating diluent TFTHF, which barely coordinates with Li ions, thereby mitigating the release of free DME solvent.

[0150] Based on the 2D 'H-19F HOESY analysis, an enhanced dipole-dipole interaction between diluent TFTHF and the Li-ion-coordinated DME was observed, promising an improved Tti+in the developed electrolyte of TFTHF-E. The T i+values of BTFE-E, TTE-E and TFTHF-E electrolytes were then measured by following a reported testing protocol,

[0037] as illustrated in FIGS. 43-45. The developed electrolyte of TFTHF-E exhibited a significantly higher TLI+valueof 0.82, in contrast to the lower TL values of 0.50 and 0.63 for electrolytes of BTFE-E and TTE-E, respectively. This elevated TL not only potentially accelerates Li-ion transfer kinetics, but also facilitates enhanced Li metal reversibility in the electrolyte of TFTHF-E.

[0038] To validate the Li metal plating / stripping reversibility in TFTHF-E electrolyte, Coulombic efficiencies (CEs) of anode-free Cu||NMC811 cells were measured. The TFTHF-E electrolyte demonstrates a notable improvement, achieving the highest average CE of 99.6%, in comparison to the BTFE-E and TTE-E electrolytes, which exhibit inferior average CEs of 99.0% and 99.1%, respectively.

[0151] The formed SEIs were analyzed using X-ray photoelectron spectroscopy (XPS) on cycled Li metal anodes to reveal their interfacial chemical compositions. As shown in FIGS. 46-47, high-resolution XPS spectra of C Is identify the presence of -CF3 (-293.8 eV) and C-F (-288.4 eV) within the SEIs formed in BTFE-E and TTE-E, confirming the electrochemical decomposition of cosolvents BTFE and TTE during cycling. This decomposition was further verified by the high-resolution F Is XPS spectra (FIGS. 49-50) which show peaks at -688.0 eV for C-F bonds, indicating the decomposition of BTFE and TTE during SEI formation. The electrochemical decomposition of BTFE and TTE can be attributed to their coordination to Li- ions, as revealed by the1H DOSY NMR results in FIGS. 28-32. In contrast, the non-coordinating diluent TFTHF demonstrates excellent electrochemical stability against Li metal anode, as evidenced by the absence of detectable C-F decomposition in the formed SEI, confirmed by high-resolution C is and F Is XPS analyses (FIGS. 48 and 51).

[0152] To further reveal the compositions distribution within the formed SEIs, the depth profiles of organic species, Li2O and LiF, were obtained from the XPS depth profiling results.Both BTFE-E and TTE-E electrolytes facilitate SEIs with an outer layer rich in organic components and an inner layer dominated by Li2O. In contrast, the TFTHF-E electrolytepromotes an inorganic-dominant SEI layer, with an outer layer enriched with LiF and an inner layer enriched with Li2O. Overall, the XPS data indicate that the TFTHF-E electrolyte promotes a robust SEI, characterized by an outer layer predominantly composed of LiF and an inner layer primarily consisting of Li2O. This formed bilayer SEI can promote uniform Li deposition and mitigate side reactions of Li metal anodes, as revealed by the scanning electron microscope (SEM) studies in FIG. 52.

[0153] The nanostructures of the SEIs were further explored using cryogenic transmission electron microscopy (cryo-TEM) technique. The formed SEI layer in BTFE-E is notably thick (~80 nm), and primarily consists of an amorphous structure (FIG. 53). Similarly, the formed SEI layer in TTE-E also displays a predominantly amorphous structure, though it is thinner at approximately 20 nm (FIG. 53). In contrast, the formed SEI in TFTHF-E appears thin, with a thickness of around 20 nm, and is featured by a dense and uniform structure (FIG. 53). A high-resolution cryo-TEM image of the TFTHF-E facilitated SEI was captured, as depicted in FIG. 54. The LiF { 111 } plane featuring a 0.233 nm lattice spacing (within the maroon-outlined region) and the Li2O { 111 } plane featuring a 0.27 nm lattice spacing (within the pink-outlined region) were observed within the formed SEI layer, along with the Li {200} plane featuring a 0.171 nm lattice spacing (within the yellow-outlined region). A prominent bilayer structured SEI with an outer layer predominantly composed of LiF and an inner layer primarily consisting of Li2O was characterized, confirming the results obtained from XPS depth profiling.

[0154] The nanostructures of the formed SEI facilitated by TFTHF-E were also explored by electron energy loss spectroscopy (EELS) techniques (FIG. 54). A high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM) image was captured, and three distinct regions, marked in maroon, pink and yellow, representing the outer SEI layer, innerSEI layer and deposited Li layer, respectively, were investigated by EELS. From the upper maroon region, the Li K-edge spectrum reveals the presence of LiF, confirming the formation of an outer SEI dominated in LiF. In the central pink region, the spectrum is consistent with Li2O, indicating an inner SEI layer predominantly composed of Li2O. The spectrum from the lower yellow region aligns with electrochemically deposited metallic Li. Taken together, these electron microscopic findings further confirm the creation of a distinctive bilayer SEI featuring an outer layer predominantly composed of LiF and an inner layer primarily consisting of Li2O in the developed TFTHF-E electrolyte.[00155J Achievement of the thin, inorganic-dominant SEI layer indicates a predominantly anion-derived SEI formation process in the TFTHF-E electrolyte. Thus, investigating the solvation structure of Li-ions can provide valuable insights into the underlying chemistry of the SEI formation process. To probe the solvation structures of Li-ions in the binary salt electrolytes,7Li NMR analysis was utilized. As illustrated in FIG. 55, using a solution of 0.1M LiCl in D2O as the internal reference (8 = 0 ppm), the addition of BTFE to the pre-diluted concentrated electrolyte of 5M LiDFOB and 2M LiBF4 in DME resulted in a downfield chemical shift from - 0.81 ppm to -0.73 ppm. The introduction of TTE caused a slight downfield shift to -0.78 ppm. These observations indicates that the addition of BTFE and TTE disrupts the pristine Li-ion solvation structures within the pre-diluted concentrated electrolyte of 5M LiDFOB and 2M LiBF4 in DME, leading to weakened interactions between the anions DFOB and BIT and the Li- ions in both the BTFE-E and TTE-E electrolytes. In contrast, a detectable upfield chemical shift (-0.87 ppm) was observed following the addition of the diluent TFTHF, suggesting intensified interactions between the Li-ions and the anions DFOB and BF4 within the TFTHF-E electrolyte, compared to the pre-diluted concentrated electrolyte of 5M LiDFOB and 2M LiBF4in DME. These enhanced Li-ion-anion interactions will facilitate the anion-derived SEI formation process in the TFTHF-E electrolyte, as elucidated by the XPS and cryo-TEM results. The creation of the bilayer SEI structure featuring an outer layer predominantly composed of LiF and an inner layer primarily consisting of Li2O facilitated by the developed TFTHF-E electrolyte, can be attributed to the stronger Li-ion coordination capability of DFOB anions over BF4 anions and the resultant preferentially electrochemical decomposition for SEI formation, as reported in the literature.

[0156] After revealing the influences of enhanced dipole-dipole interactions on the chemistry of electrolyte and SEI layer, we further conducted electrochemical evaluation of LMBs using the binary salt electrolytes of BTFE-E, TTE-E and TFTHF-E. To evaluate the reliability of these binary salt electrolytes in stabilizing Li metal anodes under practical operation, we adopted a testing protocol that incorporated a 24-hour rest interval between the charge and discharge cycles for the self-discharge evaluation. (FIG. 56). The developed electrolyte of TFTHF-E demonstrated 80% capacity retention after 225 cycles over 292 days for the Li||NMC811 full cells. In contrast, the cells using BTFE-E and TTE-E electrolytes experienced fast capacity loss, maintaining only 80% capacity after 51 and 65 cycles, respectively. These results indicate that the SEI layer facilitated by TFTHF-E can significantly mitigate Li metal corrosion and stabilize the Li metal anode, thus demonstrating its potential for improving the calendar life of LMBs.

[0157] Due to the readily Li dendrites formation and accumulation during fast charging and operation at low temperature, the performance of LMBs under these conditions remains challenging. Encouraged by the properties of the TFTHF-E electrolyte, including its moderated viscosity, high ionic conductivity and Li-ion transference number, as illustrated in FIGS, 40-45,it is reasonable to deduce its feasibility of enabling fast changing of LMBs. Hence, we evaluated the cycling stability of Li ||NMC811 full cells when charging and discharging at 1C. As depicted in FIG. 57, the cells using BTFE-E and TTE-E electrolytes experienced fast decay, with capacity retention of 80% after 27 and 43 cycles, respectively. In contrast, TFTHF-E demonstrated a greatly enhanced cycling longevity, with a capacity retention of 80% after 218 cycles.Furthermore, the Li|| NMC811 full cells cycled alternately at 25 °C and -20 °C, demonstrated stable cycling performance with a capacity retention of 80% after a total of 200 cycles in the TFTHF-E electrolyte (FIG. 58). Additionally, the cycling performance ofLi||NMC811 full cells at an elevated temperature of 65 °C was also assessed, delivering remarkable cycling stability with a capacity retention of 80% over 207 cycles in the TFTHF-E electrolyte. (FIG. 59). These results substantiate the promising practical application of the developed TFTHF-E electrolyte for LMBs under extreme conditions.

[0158] The cycling stability of full cell incorporated high-loading NMC811 (5.0 mAh / cm2) and thin Li metal anode (20 pm) with a low electrolyte / capacity (E / C) ratio of 6 pL / mAh, was further evaluated in the electrolyte of TFTHF-E (FIG. 60). The cell demonstrated a notable cycling stability, delivering a capacity retention of 80% over 445 cycles. Additionally, the Li||NMC811 full cell incorporated cathode with areal capacity of 4.0 mAh / cm2and 50 pm- thickness Li metal anode, demonstrated an exceptional cycling performance with a capacity retention of 80% over 600 cycles in TFTHF-E, compared to electrolytes of BTFE-E and TTE-E (FIG. 61). Furthermore, a double-layer Li||NMC811 pouch cell with a projected gravimetric energy density of 402 Wh / kg was fabricated to examine the practicality of TFTHF-E electrolyte. The pouch cell demonstrated state-of-the-art cycling performance in literature, offering 80% capacity retention over 606 cycles (FIG. 62). Collectively, the achieved electrochemicalevaluations of Li||NMC811 full cells across different demanding scenarios validates the efficacy of the developed TFTHF-E electrolyte, characterized by the enhanced dipole-dipole interactions between Li-ion coordinated DME and the diluent TFTHF, in achieving stable and long-life LMBs for practical applications.

[0159] In this example, we developed a strategy for creating a stable SEI to stabilize Li metal anode by modulating dipole-dipole interactions between the solvent and diluent. The resultant enhanced dipole-dipole interactions, fostered by the non-Li-ion-coordinating diluent TFTHF, can regulate the Li-ion solvation structures, weakening the Li-ion coordination of Li- ions with solvent DME while intensifying interactions between Li-ions and dual anions. Consequently, this facilitates the Li-ion transfer kinetics and, more importantly, actively promotes the generation of robust SEI layer, thereby significantly improving the electrochemical performance of high-energy density LMBs. This protocol demonstrates the potential and feasibility of regulating the dipole-dipole interactions between solvents and diluents, advancing the understanding of designing advanced liquid electrolytes for practical LMBs.

[0160] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. For instance, the number of components or parameters can be varied to meet a particular objective. As another example, component configurations may be varied to meet a particular set of design criteria.

[0161] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternative embodiments may include some or all of the features of the various embodiments disclosed herein. For instance, it is contemplated that a particular featuredescribed, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. The elements and acts of the various embodiments described herein can therefore be combined to provide further embodiments.

[0162] It is the intent to cover all such modifications and alternative embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. Thus, while certain exemplary embodiments of the apparatus and process and / or utilization and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

What is claimed is:

1. An electrolyte composition comprising: an electrolyte comprising a first metal salt and a second metal salt; a solvent comprising at least one organic compound; and a diluent comprising a cyclic fluorinated ether.

2. The electrolyte composition of claim 1, wherein the cyclic fluorinated ether comprises 3 , 3 ,4,4, 5 , 5 -hexafluorotetrahy dropy ran.

3. The electrolyte composition of claim 1, wherein the cyclic fluorinated ether comprises 3 , 3 ,4,4-tetrafluorotetrahy drofuran.

4. The electrolyte composition of claim 1, wherein the first metal salt is a metal oxideforming salt, and wherein the second metal salt is a metal fluoride-forming salt.

5. The electrolyte composition of claim 4, wherein the first metal salt is metal difluoro(oxal ato)b orate .

6. The electrolyte composition of claim 4, wherein the second metal salt is metal tetrafluoroborate.

7. The electrolyte composition of claim 1, wherein the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a metal oxide-rich inner layer and a metal fluoride-rich outer layer.

8. The electrolyte composition of claim 1, wherein the first metal salt is a lithium oxideforming salt, and wherein the second metal salt is a lithium fluoride-forming salt.

9. The electrolyte composition of claim 8, wherein the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a lithium oxide-rich inner layer and a lithium fluoride- rich outer layer.

10. The electrolyte composition of claim 1, wherein the at least one organic compound comprises dimethyl ether.

11. A metal ion battery comprising: an anode; a cathode; and an electrolyte composition comprising an electrolyte comprising a first metal salt and a second metal salt, a solvent comprising at least one organic compound, and a diluent comprising a cyclic fluorinated ether.

12. The metal ion battery of claim 11, wherein the cyclic fluorinated ether comprises3 , 3 ,4,4, 5 , 5 -hexafluorotetrahy dropyran .

13. The metal ion battery of claim 11, wherein the cyclic fluorinated ether comprises 3, 3,4,4- tetrafluorotetrahydrofuran.

14. The metal ion battery of claim 11, wherein the first metal salt is a metal oxide-forming salt, and wherein the second metal salt is a metal fluoride-forming salt.

15. The metal ion battery of claim 14, wherein the first metal salt is metal difluoro(oxalato)borate.

16. The metal ion battery of claim 14, wherein the second metal salt is metal tetrafluoroborate.

17. The metal ion battery of claim 11, wherein the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a metal oxide-rich inner layer and a metal fluoride-rich outer layer.

18. The metal ion battery of claim 11, wherein the first metal salt is a lithium oxide-forming salt, and wherein the second metal salt is a lithium fluoride-forming salt.

19. The metal ion battery of claim 18, wherein the electrolyte composition is configured to form a solid electrolyte interphase bilayer on a surface of a metal anode, wherein the solid electrolyte interphase bilayer comprises a lithium oxide-rich inner layer and a lithium fluoride- rich outer layer.

20. The metal ion battery of claim 11, wherein the at least one organic compound comprises dimethyl ether.

21. The metal ion battery of claim 11, wherein the anode comprises a carbon-based material.

22. The metal ion battery of claim 11, wherein the anode comprises a metal selected from the group consisting of lithium, sodium, magnesium, potassium, aluminum, and zinc.

23. The metal ion battery of claim 22, wherein the metal is lithium.

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