Electrolytes for Lithium-ion Batteries Under Extreme Operating Conditions

Abstract

The present disclosure relates to electrolyte compositions for Li-ion batteries, the preparation of such batteries, and their uses. Exemplary electrolyte compositions disclosed herein enable the use of Li-ion batteries in extreme operating conditions over a wide temperature range, allowing for efficient use at both high and low temperatures.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Patent Application No. 63 / 384,048, filed November 16, 2022, the entire contents of which are incorporated herein by reference.

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This invention was made with government support under DSC0012704 awarded by the USDepartment of Energy. The government has certain rights in this invention.

[0003] The field of the invention relates generally to electrochemical cells, and more particularly to electrolytes and electrolyte designs for electrochemical cells such as lithium ion batteries. [Background technology]

[0004] This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily made, nor should be construed, that any information disclosed herein constitutes prior art against the present invention.

[0005] State-of-the-art electrolytes based on carbonate esters cannot meet most of the requirements for extreme Li-ion batteries (LIBs) because their voltage window is limited to 4.3 V, they have a narrow operating temperature range of -20 to +50 °C, and they are highly flammable. Enabling low-temperature operation has previously been achieved by lowering the freezing point of the electrolyte through the introduction of a series of cosolvents with low freezing points, such as linear carboxylate esters and ethers. However, the narrower electrochemical stability of these esters and ethers, between 1.5 and 4.7 V (vs. Li+ / Li), sets an upper limit on battery voltage. Recent breakthroughs in low-temperature batteries via liquefied gas electrolytes have enabled the retention of over 60% of room-temperature capacity even at -60 °C, but the low boiling points of these volatile solvents necessitate the redesign of gas-tight cells at the pressures required for gas liquefaction.

[0006] In addition to ionic conductivity, interfacial / interphasial resistance is also a factor in electrolytes with low Li + The desolvation energy is dominant at low temperatures, which requires the presence of large charge transfer and low ionic conductivity below -20 °C. The high overpotential reduces the accessible capacity and causes Li to adhere to the graphite surface. 0 Resulting in plating of Li on graphite 0 Plating accelerates capacity fade and reduces the coulombic efficiency (CE) to <99.5%. Furthermore, Li dendrite growth can short out the cell, which represents a safety hazard. Li on graphite at low temperatures 0To avoid plating, a common practice is to use a relatively high N / P capacity ratio in commercial LIBs, which guarantees better safety at the expense of overall energy density. However, due to the different charge / discharge kinetics between graphite anodes and NMC cathodes, Li dendrites can still form during fast charging or at extremely low temperatures (<-20 °C). Because the charge / discharge kinetics of electrodes are primarily controlled by the interphase, an ideal low-temperature electrolyte should form a kinetically matched interphase on both electrodes to achieve low equivalent overpotentials at different temperatures and currents.

[0007] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. [Brief explanation of the drawings]

[0008] [Figure 1] Electrolyte Design Strategy. Figure 1A shows the illustration of soft solvation between soft solvents and Li ions, rapid Li ion transport, and wide temperature (±60 °C) stability. Figure 1B shows the solvent diagram of donor number versus dielectric constant. Solvents located in zone IV are designated as soft solvents, where the lower donor number and higher dielectric constant effectively reduce Li+-solvent affinity without sacrificing kinetic transport. Figure 1C shows the Li+-solvent binding energy from DFT calculations versus experimental dielectric constant. Figure 1D shows the chemical structure of soft solvation solvents. [Figure 2A] Physical properties of the electrolyte. Figure 2A shows the Raman spectra of 1 M LiTFSI in different solvents. [Figure 2BCDE]Physical properties of electrolytes. Figure 2B shows an overview of Δδ (C NMR spectra of carbonyl carbon) in different solvents with and without LiTFSI. Figure 2C shows the temperature dependence of the conductivity of different electrolytes. For comparison, red stars represent the conductivity values ​​predicted by molecular dynamics (MD). Figure 2D shows the DSC cooling and heating curves of different electrolytes. Figure 2E shows the PDF data of 1 M LiTFSI MDFA / MDFSA-TTE electrolyte and single solvent. Gray lines: experimental data; red lines: MD simulation predictions. [Figure 2FGH] Physical properties of the electrolyte. Figures 2F–H show MD simulation results. In Figure 2F, LiTFSI-MDFA is highlighted by a yellow isosurface, while TTE and MDFSA are highlighted by blue isosurfaces. Figure 2G shows a representative ionic aggregate from an MD simulation at 25 °C. The Jmol color scheme is used: Li-purple, N-blue, F-green, S-yellow, C-gray, O-red, and H-white. Figure 2H shows the fraction of free Li and TFSI, defined as ions not coordinated to a counterion within 5.0 Å of Li-N(TFSI), and the uncorrelated mobility (ionicity) from an MD simulation of 1 M LiTFSI in MDFA / MDFSA-TTE electrolyte. [Figure 3AB] Electrochemical performance of NMC811|| graphite full cells. Figure 3A shows the cycling performance at 0.5 C under 25 °C. Figure 2B shows the rate performance at 25 °C. [Figure 3CD] Electrochemical performance of NMC811|| graphite full cells. Figure 3C shows the corresponding voltage profile of Figure 3B. Figure 3D shows the long-term cycling performance at 0.2 C under -30 / -40 °C. [Figure 3EF] Electrochemical performance of NMC811|| graphite full cells. Figure 3E shows the 0.1C cycling performance at different temperatures (60°C, 25°C, 0°C, -20°C, -30°C, -40°C, -50°C, and -60°C). Figure 3G shows the corresponding voltage profile of the cell in Figure 3E using 1M LiTFSI MDFA / MDFSA-TTE electrolyte. [Figure 3G]Electrochemical performance of NMC811|| graphite full cells. Figure 3G shows pouch cell performance at -30 °C and 0.2 C rate using 2.5 g / Ah or 3.5 g / Ah electrolyte. Rate performance was performed using cells with 3.5 g / Ah electrolyte at different C rates (5 cycles at 0.2 C, 5 cycles at 0.3 C, 5 cycles at 0.4 C, and 345 cycles at 0.2 C) (red line). The inset shows a photograph of the 4.5 V pouch cell. [Figure 4AB] Characterization of the SEI layer on the graphite anode after cycling at -30 °C. Figure 4A shows an HRTEM image with 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. Figure 4B shows an HRTEM image with 1 M LiPF6 EC / DEC electrolyte. [Figure 4CDE] Characterization of the SEI layer on the graphite anode after cycling at -30 °C. Figures 3C-D show the morphology of the graphite electrode before and after cycling in 1 M LiPF6 EC / DEC electrolyte, respectively. Figure 4E shows the morphology of the graphite electrode after cycling in 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. Comparison of AFM roughness (R) over a 0.5 μm × 0.5 μm area. [Figure 4FGH] Characterization of the SEI layer on a graphite anode after cycling at -30 °C. Figures 4F-H show the XPS results of the SEI on cycled graphite in 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. Figure 4F shows the quantified atomic ratios of elements in the SEI. Figures 4G-H display the C 1s spectrum and F 1s spectrum, respectively, displayed in the corresponding depth profiling results column. [Figure 5AB] Illustration of capacitance and kinetic matching. Figure 5A shows a thick interface between a commercial carbonate-based electrolyte and a lithiated graphite anode. Figure 5B shows a self-limiting interface between a designed electrolyte and a lithiated graphite anode. [Figure 5CDE]5C-E show schematic diagrams of capacitance mismatch as a function of charge rate or charge temperature, capacitance matching as a function of charge rate or charge temperature, and resistance matching between the anode and cathode, respectively. [Figure 6AB] Figure 6A shows the X-ray measurements. Figure 6B shows the MD simulation results. The structure factor S(Q) from X-ray measurements (black solid line) and MD simulations (blue dashed line) for 1 M LiTFSI in the MDFA / MDFSA-TTE electrolyte and the two dominant solvents, MDFA and TTE. The S(Q) of MDFA and TTE shifted by -1.5 and 3.0, respectively. [Figure 7ABC] MD simulation results. Figures 7A-B display snapshots of the MD simulation boxes for LiTFSI in MDFA and 1 M LiTFSI in MDFA / MDFSA-TTE, respectively, from MD simulations at 25 °C. The solvent is shown as a wireframe. Figure 7C shows the structure of Li(MDFA)4 free Li (solvent separated from TFSI) from the MD simulation of 1 M LiTFSI in MDFA / MDFSA-TTE at 25 °C (Figure 7B). The Jmol color scheme is used: Li - purple, N - blue, F - green, S - yellow, C - gray, O - red, H - white. [Figure 7DE] MD simulation results. Figure 7D shows the ion and solvent self-diffusion coefficients from MD simulation of 1 M LiTFSI in MDFA / MDFSA-TTE electrolyte. Figure 7E shows the conductivity of 1 M LiTFSI in MDFA-MDFSA-TTE electrolyte from MD simulation and experiment. [Figure 8AB] Rate performance of polycrystalline NMC811|| graphite pouch cells at 25 °C. Pouch cells with different amounts of 1 M LiTFSI MDFA / MDFSA-TTE electrolyte under 3C and 4C. Figure 8A shows the 3.5 g / Ah electrolyte at 3C. Figure 8B shows the 3.5 g / Ah electrolyte at 4C. [Figure 8CD]Rate performance of polycrystalline NMC811|| graphite pouch cells at 25 °C. Pouch cells with different amounts of 1 M LiTFSI MDFA / MDFSA-TTE electrolyte at 3C and 4C. Figure 8C shows the 3.0 g / Ah electrolyte at 3C. Figure 8D shows the 3.0 g / Ah electrolyte at 4C. [Figure 8EF] Rate performance of polycrystalline NMC811||graphite pouch cells at 25 °C. Pouch cells with different amounts of 1 M LiTFSI MDFA / MDFSA-TTE electrolyte at 3C and 4C. Figure 8E shows the 2.5 g / Ah electrolyte at 3C. Figure 8F shows the 2.5 g / Ah electrolyte at 4C. [Figure 9] NMC811||Cycle performance of graphite full cell at -50 / 60℃ and 0.1C. [Figure 10AB] Kinetic analysis of low-temperature processes. Figure 10A shows the three-electrode cell diagram set up for kinetic analysis. Figure 10B shows the cell voltage and electrode potential of the NMC811|| graphite pouch cell at -30°C and 0.2C. [Figure 10CD] Kinetic analysis of the low-temperature process. Figures 10C-D show Nyquist impedance plots and fitted lines using an equivalent circuit for a three-electrode cell containing 1 M LiTFSI MDFA / MDFSA-TTE electrolyte at 25 °C and -30 °C, respectively. Impedance spectra were obtained at 50% SOC. [Figure 11ABC] DFT calculations of reaction energies. Figures 11A-C show the reaction energies from PBE+U (red) and SCAN (blue) (units: eV) for the dehydrogenation of MDFA on Li0.5NiO2, TTE on Li0.5NiO2, and Li+-MDFSA on Li1.0NiO2, respectively. In Figure 11C, a single F- ion is also present on the surface to neutralize the cell. [Figure 12ABC]Figure 12A shows the binding energies for Li(MDFA)(solvent) solvates versus Li(solvent) for the indicated solvents in the implicit ethereal solvent. Figure 12B shows the difference in Li(MDFA)(solvent) and Li(solvent) binding energies, indicating steric hindrance and cross-interactions between solvents in Li(MDFA)(solvent) solvates, which tend to increase as molecular size and the number of solvating groups increase. Figure 12C shows the Li(MDFA)(solvent) binding energy from DFT calculations versus experimental dielectric constant. [Figure 13AB] Figure 10A shows the independent CV profiles of a graphite electrode in different electrolytes. Figure 10B shows the CV of 1 M LiTFSI in MDFA-TTE. Figure 10B shows the CV of 1 M LiTFSI in MDFA / MDFSA-TTE. The inset in Figure 10B shows the enlarged region from 2.0 to 2.5 V, revealing a small reduction peak at approximately 2.2 V. This higher voltage reduction peak is absent in the MDFA-free electrolyte and can be assigned to MDFA reduction according to the QC results. [Figure 13CD] Figure 10 shows independent CV profiles of a graphite electrode in different electrolytes. Figure 10C shows the CV of 1 M LiTFSI in EDFA / MDFSA-TTE. Figure 10D shows the CV of 1 M LiTFSI in M4FP / MDFSA-TTE. [Figure 14] Photographs of flammability tests of glass fibers saturated with electrolytes having different volume ratios of TTE are shown. [Figure 15AB] Figure 15A shows the Raman spectra of MDFA-based electrolytes with different LiTFSI concentrations, and Figure 15B shows the Raman spectrum of 1 M LiFSI in a weakly solvating solvent. [Figure 16AB] Figure 16A shows the C NMR spectra of LiTFSI saturated MA and neat MA solvents, and Figure 16B shows the C NMR spectra of LiTFSI saturated EDFA and neat EDFA solvents. [Figure 16CD]Figure 16C shows the C NMR spectra of LiTFSI saturated MDFA and neat MDFA solvents, and Figure 16D shows the C NMR spectra of LiTFSI saturated M4FP and neat M4FP solvents. [Figure 17AB] Figure 17A shows the 17O NMR spectra of LiTFSI saturated MDFA and neat MDFA solvents, and Figure 17B shows the 17O NMR spectra of LiTFSI saturated EDFA and neat EDFA solvents. [Figure 17CD] Figure 17C shows the 17O NMR spectra of LiTFSI saturated MTFP and neat MTFP solvents, and Figure 17D shows a summary of Δδ (17O NMR spectra of carbonyl oxygen) in different solvents with and without LiTFSI. [Figure 18AB] Figure 18A shows optical images of different electrolytes after overnight storage at -30°C. Figure 18B shows optical images of different electrolytes after overnight storage at 90°C. [Figure 19AB] Figure 19A shows the oxidative stability of different electrolytes evaluated on a Pt electrode at a scan rate of 1 mV / s. Figure 19B shows the floating test of 1 M LiTFSI MDFA / MDFSA-TTE and 1 M LiTFSI M4FP / MDFSA-TTE electrolytes. [Figure 19CDE] Figure 19C shows an SEM image of the new aluminum foil. Figure 19D displays an SEM image of the aluminum foil after 24 hours at 4.5 V in 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. Figure 19E displays an SEM image of the aluminum foil after 48 hours at 4.5 V in 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. [Figure 20] 1 shows Walden plots for molar conductivity (Λ) and fluidity (inverse viscosity (1 / η)) for LiTFSI in MDFA and MDFA / MDFSA-TTE electrolytes from MD simulations and experiments. [Figure 21AB]FIG. 21A shows the polarization curve of a Li||Li cell with 1M LiTFSI MDFA / MDFSA-TTE electrolyte with an applied voltage of 5 mV. I0 indicates the initial current, and Iss indicates the steady-state current. FIG. 21B shows the impedance spectra before and after polarization. Without wishing to be bound by any particular theory, for a conventional 1M LiPF6 EC / DEC electrolyte, using the same potentiostatic polarization method, a transference number (t+) of 0.33 is calculated by: t+=Iss(ΔV-I0R0) / I0(ΔV-IssRss) [Figure 22AB] Figure 22A shows the ion and solvent self-diffusion coefficients from MD simulations of 1 M LiTFSI in MDFA / MDFSA-TTE electrolyte, and Figure 22B shows the conductivity of 1 M LiTFSI in MDFA-MDFSA-TTE electrolyte from MD simulations and experiments. [Figure 23AB] Figure 23A shows a typical voltage profile for the first formation cycle of an NMC811|| graphite full cell with 1 M LiTFSI MDFA / MDFSA-TTE electrolyte at 0.2 C. Figure 23B shows selected voltage profiles for the 1st, 100th, and 400th cycles of an NMC811|| graphite full cell with 1 M LiTFSI MDFA / MDFSA-TTE electrolyte at 0.5 C. [Figure 24] Cycling performance of NMC811|| graphite full cells with 1M LiTFSI MDFA-TTE electrolyte at 25°C and 0.5C. [Figure 25] This figure shows the cycling performance of NMC811|| graphite full cells with 1M LiTFSI MDFA / MTFSP-TTE or 1M LiTFSI MDFA / NFSF-TTE electrolytes at 25°C and 0.5C, with illustrations of the molecular structures of MDFA, MDFSA, methyl 2,3,3,3-tetrafluoro-2-(fluorosulfonyl)propionate (MTFSP), and nonafluorobutanesulfonyl fluoride (NFSF) with the same fluorosulfonyl group. [Figure 26AB]Figure 26A shows a photograph of the EL-CELL device, and Figure 26B shows the pressure change through an NMC811|| graphite full cell cycled at 0.5 C containing 1 M LiTFSI MDFA / MDFSA-TTE and 1 M LiPF6 EC / DEC electrolyte with a cutoff voltage of either 4.3 V or 4.5 V. [Figure 27] Figure 1 shows typical charge / discharge voltage profiles at different C-rates for an NMC811|| graphite full cell with 1M LiPF6 EC / DEC electrolyte. [Figure 28] Figure 28A shows a typical SEM image of single crystal NMC811. Figure 28B shows a typical SEM image of single crystal NMC811. Figure 28C shows a typical SEM image of polycrystalline NMC811. Figure 28D shows a typical SEM image of polycrystalline NMC811. [Figure 29AB] Figure 29A shows the rate performance of an NMC 811 / Li half-cell containing 1 M LiTFSI MDFA / MDFSA-TTE electrolyte, and Figure 29B shows the rate performance of a graphite / Li half-cell containing 1 M LiTFSI MDFA / MDFSA-TTE electrolyte. [Figure 29CD] Figure 29C shows the N / P ratio at different C rates: 1C = 2.5 mA / cm, 2C = 5.0 mA / cm, 3C = 7.5 mA / cm, 4C = 10 mA / cm. Figure 29D shows a photograph of the graphite anode from an exploded pouch cell cycled at -30 °C. [Figure 30AB] Figure 30A shows the cycling performance of NMC811|| graphite full cells with different electrolytes at 60 °C and 0.5 C. Figure 30B shows the cycling performance of NMC811|| graphite pouch cells with various amounts of 1 M LiTFSI MDFA / MDFAS-TTE electrolyte (3.5, 3.0, and 2.5 g / Ah) at 60 °C and 4 C. [Figure 31AB]Figure 31A shows the Nyquist impedance plot of the three-electrode cell containing 1M LiPF6 EC / DEC electrolyte at 25° C. Figure 31B shows the Nyquist impedance plot of the three-electrode cell containing 1M LiPF6 EC / DEC electrolyte at −30° C. Impedance spectra were obtained at 50% SOC. [Figure 32AB] Figure 32A shows the XRD patterns of graphite anodes collected from NMC811|| graphite full cells containing 1M LiPF6 EC / DEC after 20 cycles at -30°C and 0.2C, and Figure 32B shows the XRD patterns of graphite anodes collected from NMC811|| graphite full cells containing 1M LiTFSI MDFA / MDFSA-TTE after 20 cycles at -30°C and 0.2C. [Figure 33ABC] Figure 33A shows SEM images of a pristine graphite anode. Figure 33B shows a cycled graphite anode collected from an NMC811|| graphite full cell containing 1M LiPF6 EC / DEC after 20 cycles at -30°C and 0.2C. Figure 33C shows a cycled graphite anode collected from an NMC811|| graphite full cell containing 1M LiTFSI MDFA / MDFSA-TTE after 20 cycles at -30°C and 0.2C. [Fig. 34AB] Figure 34A shows the surface morphology of a cycled graphite anode using 1 M LiTFSI MDFA / MDFSA-TTE electrolyte for TOF-SIMS analysis over a 2 × 2 μm raster size. Figure 34B shows the mapping of F on the cycled graphite anode. [Figure 34C] Corresponding TOF-SIMS depth profiles of O-, F-, and C- secondary ions on a cycled graphite anode are shown. [Figure 35AB]XPS characterization of the SEI formed on graphite cycled using 1M LiPF EC / DEC electrolyte. Figure 35A shows the quantified atomic ratios of elements in the SEI. Figure 35B shows the C 1s spectrum, O 1s spectrum, and F 1s spectrum, respectively, displayed in the corresponding depth profiling results column. [Figure 35CD] XPS characterization of the SEI formed on graphite cycled using 1 M LiPF EC / DEC electrolyte. Figures 35C-D show the C 1s spectrum, O 1s spectrum, and F 1s spectrum, respectively, displayed in the corresponding depth profiling results column. [Figure 36] 1 shows the XRD patterns of a pristine NMC811 cathode, a cathode cycled with 1M LiPF 6 EC / DEC, and a cathode cycled with 1M LiTFSI MDFA / MDFSA-TTE electrolyte. [Figure 37A] HRTEM image of NMC811 cathode cycled at −30° C. with 1M LiTFSI MDFA / MDFSA-TTE electrolyte. [Figure 37B] Figure 1 shows HRTEM images of NMC811 cathodes cycled at -30°C with 1M LiPF6 EC / DEC electrolyte. [Figure 38AB] Figure 38A shows XPS characterization of CEI formed on cycled NMC811 using 1M LiTFSI MDFA / MDFSA-TTE electrolyte with C 1s spectra shown in the corresponding depth profiling results column. Figure 38B shows XPS characterization of CEI formed on cycled NMC811 using 1M LiTFSI MDFA / MDFSA-TTE electrolyte with F 1s spectra shown in the corresponding depth profiling results column. [Figure 39AB]Figure 39A shows the surface morphology of a cycled NMC811 cathode using 1 M LiTFSI MDFA / MDFSA-TTE electrolyte for TOF-SIMS analysis over a 2 × 2 μm raster size. Figure 39B shows the mapping of F on the cycled NMC811. [Figure 39C] The corresponding TOF-SIMS depth profiles of O-, F-, and C- secondary ions on the cycled NMC811 are shown. [Figure 40AB] Figure 40A shows the partial density of states of LiNiO2 (U=5.96 eV for Ni) from PBE+U. Figure 40B shows the partial density of states of LiNiO2 from SCAN. [Figure 40CD] Figure 40C shows the partial density of states of Li0.5NiO2 from PBE+U. Figure 40D shows the partial density of states of Li0.5NiO2 from SCAN. Structure from single point energy optimization using PBE+U with a 520 eV cutoff, SCAN with an 800 eV cutoff. DETAILED DESCRIPTION OF THE INVENTION

[0009] 1.0 Definition For the purposes of promoting an understanding of the principles of the invention, reference will be made herein to particular embodiments and specific language will be used to describe the same. Nevertheless, it will be understood that no limitation of the scope of the invention is thereby intended, and that changes and modifications in the illustrated invention, and further applications of the principles of the invention as set forth therein, are contemplated herein as would normally occur to one skilled in the art to which the invention pertains.

[0010] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0011] For purposes of interpreting this specification, the following definitions shall apply, and where appropriate, terms used in the singular shall also include the plural and vice versa. In the event that any definition set forth below conflicts with the usage of that word in any other document, including any document incorporated herein by reference, the definition set forth below shall always control for purposes of interpreting this specification and its associated claims, unless a contrary meaning is clearly intended (e.g., in the document in which the term is first used).

[0012] The use of "or" means "and / or" unless otherwise stated.

[0013] The use of "a" or "an" herein means "one or more" unless otherwise specified or unless the use of "one or more" is clearly inappropriate.

[0014] The use of "comprise," "comprises," "comprising," "include," "includes," and "including" are interchangeable and are not intended to be limiting. Additionally, when a description of one or more embodiments uses the term "comprising," those skilled in the art will understand that in some specific instances, one or more embodiments may alternatively be described using the terms "consisting essentially of" and / or "consisting of."

[0015] As used herein, the term "about" refers to a ±10% variation from the nominal value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

[0016] Any range expressed in either absolute or approximate terms is intended to be inclusive, and any definitions used herein are intended to be descriptive, not limiting. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values ​​set forth in the specific examples are reported as precisely as possible. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein, including all fractional and whole values.

[0017] As used herein, the term "NMC811" refers to LiNi 0.8 Mn 0.1- Co 0.1 Refers to a chemical composition that includes O2.

[0018] As used herein, the term "M3FP" refers to methyl 3,3,3-trifluoropropionate.

[0019] As used herein, the term "M4FP" refers to methyl-2,3,3,3-tetrafluoropropionate.

[0020] As used herein, the term "MDFA" refers to methyl difluoroacetate.

[0021] As used herein, the term "MDFSA" refers to methyl-2,2-difluoro-2-(fluorosulfonyl)acetate.

[0022] As used herein, the term "EDFA" refers to ethyl difluoroacetate.

[0023] As used herein, the term "TTE" refers to 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0024] As used herein, the term "LiTFSI" refers to the salt lithium bis(trifluoromethanesulfonyl)imide, also known as lithium bistriflimide.

[0025] As used herein, the term "SEI" refers to a solid electrolyte interphase layer. Typically, the layer forms during the initial cycles of a battery on the surface of the anode material due to partial electrolyte decomposition.

[0026] As used herein, the term "CEI" refers to a cathode-electrolyte interphase layer.

[0027] As used herein, the term "PVDF" refers to polyvinylidene fluoride.

[0028] 2.0 Electrolyte Design for Li-ion Batteries under Extreme Operating Conditions

[0029] The widely used LiNi 0.8 Mn 0.1 Co 0.1 An ideal electrolyte for O2(NMC811)|| graphite Li-ion batteries is expected to have the ability to support higher voltages (≥ 4.5 V), rapid charging (≤ 15 min), charge / discharge over a wide temperature range (± 60 °C) without Li plating, and non-flammability. No existing electrolyte simultaneously meets all these requirements, and electrolyte design is hindered by the lack of effective guiding principles that address the relationship between battery performance, solvation structure, and solid electrolyte-interphase chemistry. Herein, we propose a weak Li-ion electrolyte to meet all the above requirements. + A strategy for electrolyte design based on a group of soft solvents that balances between -solvent interactions, sufficient salt dissociation, and desired electrochemistry is reported and validated. Remarkably, an areal capacity of 2.5 mAh / cm was achieved. 2NMC811|| graphite coin cells at over 4.5 V retain 75% (54%) of their room-temperature capacity when these cells are charged and discharged at 0.1 C at -50 °C (-60 °C), while NMC811|| graphite pouch cells with dilute electrolyte (2.5 g / Ah) achieve stable cycling with an average coulombic efficiency of over 99.9% at -30 °C. Comprehensive analysis further reveals impedance matching between the NMC811 cathode and graphite anode, which is attributed to the formation of a similar LiF-rich interphase phase, thus effectively avoiding lithium plating at low temperatures. The new electrolyte design principle can be extended to other alkali metal-ion batteries operating under extreme conditions.

[0030] 2.1 Non-Limiting Embodiments

[0031] One aspect of the present invention relates to an electrolyte composition comprising a lithium salt dissolved in one or more solvents, the solvents having a donor number less than 10, a dielectric constant greater than 5, a boiling point greater than 60° C., and a melting point less than −60° C. The electrolyte composition may be comprised of a soft solvent. Without wishing to be limited to any particular theory, it is believed that the solvent may provide sufficient lithium saturation dissociation, but the Li + It is contemplated that the solvent and the lithium salt interact in an intermediate manner so that weak lithium salt solution interactions can also be minimized. Examples of solvents that can be used in the electrolyte compositions disclosed herein include MDFA, MDFSA, M4FP, EDFA, and M3FP, or combinations thereof. In some embodiments, the solvent in the electrolyte composition is MDFA. In other embodiments, the solvent in the electrolyte composition is a mixture of MDFA and MDFSA. In further embodiments, the electrolyte composition includes a mixture of MDFA, MDFSA, and TTE.

[0032] In some embodiments, the electrolyte composition comprises MDFA in an amount ranging from about 20% to about 50%. In some embodiments, the electrolyte composition comprises MDFSA in an amount ranging from about 10% to about 25%. In some embodiments, the electrolyte composition comprises TTE in an amount ranging from about 30% to about 60%. In further embodiments, the electrolyte composition comprises at least 40% by volume of TTE. In some embodiments, the electrolyte composition comprises MDFA, MDFSA, and TTE, respectively (e.g., in a volume ratio of 4:1:5).

[0033] The electrolyte composition may also include a lithium salt. Examples of lithium salts that can be used include LiTFSI, LiClO4, LiI, LiBF4, LiCF3SO3, LiNO3, LiBr, and LiCF3CO2, or combinations thereof. In some embodiments, the lithium salt in the electrolyte composition is LiTFSI.

[0034] In some embodiments, the lithium salt in the electrolyte composition has a concentration ranging from about 0.5 M to about 4 M. In some embodiments, the lithium salt in the electrolyte composition has a concentration ranging from about 1 M to about 2 M. In further embodiments, the lithium salt in the electrolyte composition has a concentration of about 1 M.

[0035] In some embodiments, the electrolyte composition comprises about 1 M LiTFSI in a mixture of MDFA, MDFSA, and TTE solvents in a volume ratio of about 4:1:5.

[0036] Another aspect of the present invention relates to a Li-ion battery that can include the cathode, anode, and electrolyte described in any of the preceding embodiments. In some embodiments, the cathode includes NMC811. In some embodiments, the cathode includes NMC811 and further includes a mixture of PVDF and carbon black. In some embodiments, the cathode includes about 80% to about 98% NMC811, about 1% to about 10% PVDF, and about 1% to about 10% carbon black. In some embodiments, the cathode includes about 90% to about 95% NMC811, about 3% to about 5% PVDF, and about 2% to about 5% carbon black. In some embodiments, the cathode includes about 90% to about 95% NMC811, about 2.5% to about 5% PVDF, and about 2.5% to about 5% carbon black. In a further embodiment, the cathode comprises about 94% NMC811, about 3% PVDF, and about 3% carbon black.

[0037] In some embodiments, the anode of a Li-ion battery comprises graphite. In some embodiments, the anode comprises graphite and further comprises a mixture of PVDF and carbon black. In some embodiments, the anode comprises about 80% to about 98% graphite, about 1% to about 10% PVDF, and about 1% to about 10% carbon black. In some embodiments, the anode comprises about 90% to about 95% graphite, about 4% to about 7% PVDF, and about 1% to about 3% carbon black. In some embodiments, the anode comprises about 90% to about 95% graphite, about 3% to about 5% PVDF, and about 2% to about 5% carbon black. In further embodiments, the anode comprises about 92% by weight graphite, about 6% by weight PVDF, and about 2% by weight carbon black.

[0038] In some embodiments of the invention, the battery has an operating charge and discharge temperature in the range of about −120° C. to about 120° C. In further embodiments, the battery has an operating charge and discharge temperature in the range of about −90° C. to about 90° C., or about −60° C. to about 60° C., or about −30° C. to about 30° C.

[0039] A further aspect of the present invention relates to a method for assembling a Li-ion battery, comprising preparing multiple layers of a cathode, an electrolyte, and an anode. For example, the method comprises stacking a cathode disclosed herein, a separator material disclosed herein, an anode disclosed herein, and an electrolyte composition disclosed herein. In some embodiments, the separator material is CELGARD 2325®, CELGARD 3501®, CELGARD 2500®, or CELGARD PP1410®. In further embodiments, the amount of electrolyte composition used ranges from about 20 μL to about 80 μL, or from about 30 μL to about 70 μL, or from about 40 to about 60 μL.

[0040] In some embodiments, the battery is a coin cell battery. In some embodiments, the cathode is coated on a metal, such as aluminum foil. The anode may also be coated on a metal, such as Cu foil.

[0041] In some embodiments, the battery is a pouch cell battery. In some embodiments, the cathode disclosed herein is attached (e.g., via an electrode tab) to a metal strip (e.g., an aluminum strip). The anode may be attached (e.g., via an electrode tab) to a metal strip (e.g., a nickel strip). In further embodiments, the amount of the electrolyte composition of the foregoing embodiments used ranges from about 2 g / Ah to about 8 g / Ah, or from about 2.5 g / Ah to about 6.5 g / Ah, or from about 3 g / Ah to about 5 g / Ah.

[0042] A further aspect of the invention relates to a method of using the Li-ion batteries described herein to provide electrical power, the method comprising using the batteries disclosed herein to provide a voltage in the range of about 2 V to about 5 V. In some embodiments, the batteries are discharged at a voltage in the range of about 2 V to about 5 V, or discharged at a voltage in the range of about 3 V to about 5 V, or discharged at a voltage in the range of about 2.5 V to about 4.5 V, or discharged at about 4.5 V. In further embodiments of the invention, the batteries are charged or discharged at an operating temperature in the range of about −60° C. to about 60° C.

[0043] Enumeration of Embodiments The following is a list of non-limiting embodiments: 1. An electrolyte composition comprising a lithium salt dissolved in one or more solvents, the solvents having a donor number less than 10, a dielectric constant greater than 5, a boiling point greater than 60° C., and a melting point less than −60° C. The electrolyte composition may be a soft solvated electrolyte. 2. The electrolyte composition of embodiment 1, wherein the solvent is selected from MDFA, MDFSA, M4FP, EDFA, TTE and M3FP, or a combination thereof. 3. The electrolyte composition of embodiment 1, wherein the solvent is MDFA. 4. The electrolyte composition of embodiment 1, wherein the electrolyte comprises a mixture of MDFA and MDFSA. 5. The electrolyte composition of embodiment 4, comprising MDFA, MDFSA, and TTE. 6. The electrolyte composition of embodiment 3 or 4, comprising about 20% to about 50% MDFA. 7. The electrolyte composition of embodiment 4, comprising about 10% to about 25% MDFSA. 8. The electrolyte composition of embodiment 5, comprising about 30% to about 60% TTE. 9. The electrolyte composition of embodiment 5, wherein the TTE comprises from about 40% to about 60% by volume, or from about 40% to about 50% by volume of the electrolyte. 10. The electrolyte composition of embodiment 5, wherein the solvent volume ratio is 4:1:5 for MDFA, MDFSA, and TTE, respectively. 11. The electrolyte composition of embodiment 1, wherein the lithium salt is selected from LiTFSI, LiClO4, LiI, LiBF4, LiCF3SO3, LiNO3, LiBr, and LiCF3CO2, or a combination thereof. 12. The electrolyte composition of embodiment 1, wherein the lithium salt is LiTFSI. 13. The electrolyte composition of embodiment 1, wherein the lithium salt is present at a concentration ranging from about 0.5M to about 4M. 14. The electrolyte composition of embodiment 13, wherein the lithium salt is present at a concentration ranging from about 1M to about 2M. 15. The electrolyte composition of embodiment 13, wherein the concentration of the lithium salt is about 1 M. 16. The electrolyte composition of embodiment 1, wherein the electrolyte comprises about 1 M LiTFSI in a MDFA / MDFSA / TTE mixture in a volume ratio of about 4:about 1:about 5. 17. A Li-ion battery comprising a cathode, an anode, and an electrolyte according to any of the previous embodiments. 18. The Li-ion battery of embodiment 17, wherein the cathode comprises NMC811. 19. The Li-ion battery of embodiment 17, wherein the cathode comprises NMC811, PVDF, and carbon black. 20. The Li-ion battery of embodiment 19, wherein the cathode comprises about 80% to about 98% by weight of said NMC811, about 1% to about 10% by weight of said PVDF, and about 1% to about 10% by weight of said carbon black. 21. The Li-ion battery of embodiment 20, wherein the cathode comprises about 90% to about 95% by weight of said NMC811, about 3% to about 5% by weight of said PVDF, and about 2% to about 5% by weight of said carbon black. 22. The Li-ion battery of embodiment 20, wherein the cathode comprises about 90% to about 95% by weight of said NMC811, about 2.5% to about 5% by weight of said PVDF, and about 2.5% to about 5% by weight of said carbon black. 23. The Li-ion battery of embodiment 20, wherein the cathode comprises about 94% by weight NMC811, about 3% by weight PVDF, and about 3% by weight carbon black. 24. The Li-ion battery of embodiment 17, wherein the anode comprises graphite. 25. The Li-ion battery of embodiment 17, wherein the anode comprises graphite, PVDF, and carbon black. 26. The Li-ion battery of embodiment 25, wherein the anode comprises about 80% to about 98% by weight of the graphite, about 1% to about 10% by weight of the PVDF, and about 1% to about 10% by weight of the carbon black. 27. The Li-ion battery of embodiment 25, wherein the anode comprises about 90% to about 95% by weight of the graphite, about 4% to about 7% by weight of the PVDF, and about 1% to about 3% by weight of the carbon black. 28. The Li-ion battery of embodiment 17, wherein the anode comprises about 90% to about 95% by weight of the graphite, about 3% to about 5% by weight of the PVDF, and about 2% to about 5% by weight of the carbon black. 29. The Li-ion battery of embodiment 17, wherein the anode comprises about 92 wt. % of said graphite, 6 wt. % of said PVDF, and 2 wt. % of said carbon black. 30. The Li-ion battery of embodiment 17, having an operating charge and discharge temperature in the range of about -120°C to about 120°C, or about -90°C to about 90°C, or about -60°C to about 60°C, or about -30°C to about 30°C. 31. The Li-ion battery of embodiment 30, wherein the operating charge and discharge temperature of the battery is in the range of about -40°C to about 50°C. 32. The battery of any of the previous embodiments, which is a coin cell battery. 33. The battery of any of the previous embodiments, wherein the cathode is coated on Al foil. 34. The battery of any of the previous embodiments, wherein the anode is coated on a Cu foil. 35. The battery of any of the previous embodiments, which is a pouch cell battery. 36. The battery of embodiment 17, wherein the cathode is attached to the aluminum strip via an electrode tab. 37. The battery of embodiment 17, wherein the anode is attached to the nickel strip via an electrode tab. 38. The battery of embodiment 17, wherein the separator material is CELGARD 2325®, CELGARD 3501®, CELGARD 2500®, or CELGARD PP1410®. 39. The battery of embodiment 17, wherein the electrolyte is present in an amount ranging from about 20 μL to about 80 μL, or from about 30 μL to about 70 μL, or from about 40 μL to about 60 μL for a coin cell battery. 40. The battery of embodiment 17, wherein the electrolyte is present in a range of from about 2 g / Ah to about 8 g / Ah, or from about 2.5 g / Ah to about 6.5 g / Ah, or from about 3 g / Ah to about 5 g / Ah for a pouch cell battery. 41. A method of assembling a Li-ion battery according to any of the preceding embodiments, comprising stacking a cathode according to any of the preceding embodiments, a separator material, an anode according to any of the preceding embodiments, and an electrolyte composition according to any of the preceding embodiments. 42. The method of any of the preceding embodiments, wherein the battery is a coin cell battery. 43. The method of any of the previous embodiments, wherein the cathode is coated on an Al foil. 44. The method of any of the previous embodiments, wherein the anode is coated on a Cu foil. 45. The method of any of the previous embodiments, wherein the battery is a pouch cell battery. 46. ​​The method of embodiment 32, wherein the cathode is attached to the aluminum strip via an electrode tab. 47. The method of embodiment 32, wherein the anode is attached to the nickel strip via an electrode tab. 48. The method of embodiment 32, wherein the separator material can be CELGARD 2325®, CELGARD 3501®, CELGARD 2500®, or CELGARD PP1410®. 49. The method of embodiment 32, wherein the electrolyte is present in an amount ranging from about 20 μL to about 80 μL, or from about 30 μL to about 70 μL, or from about 40 μL to about 60 μL for a coin cell battery. 50. The method of embodiment 32, wherein the electrolyte is present in a range of from about 2 g / Ah to about 8 g / Ah, or from about 2.5 g / Ah to about 6.5 g / Ah, or from about 3 g / Ah to about 5 g / Ah for a pouch cell battery. 51. A method of providing power using a battery according to any of the preceding embodiments, comprising using a battery according to any of the preceding embodiments to generate an electrical flow and current such that the battery charges or discharges, wherein the battery discharges at a voltage in the range of about 2V to about 5V. 52. The method of any of the preceding embodiments, wherein the discharge voltage can be in the range of about 3V to about 5V. 53. The method of any of the preceding embodiments, wherein the discharge voltage can be in the range of about 2.5 to about 4.5 V. 54. The method according to any of the preceding embodiments, wherein the discharge voltage can be about 4.5V. 55. The method of any of the preceding embodiments, wherein charging or discharging the battery may be operable at temperatures ranging from about -60°C to about 60°C.

[0044] 3.0 Working Example

[0045] The following examples are provided solely to illustrate the present invention and are not intended to limit the scope of the invention described herein.

[0046] Example 1. Balanced electrolyte design principle

[0047] While a low freezing point but moderate boiling point and a wide electrochemical stability window set the primary criteria for solvent selection (Table 1), a secondary criterion is low Li without sacrificing much ion dissociation ability. + The ion desolvation energy should be soft solvation ability to ensure (Figure 1A). DN and Li from density functional theory (DFT) calculations +The Li-solvent binding energies reveal a close correlation between them (Figure 1B-1C), making DFT a useful method for screening solvation capabilities. + Including cross-interactions and steric hindrance between solvates in the first solvation shell yields a similar picture, as shown in Figure 12. Other parameters, such as BF affinity and Li cation basicity for various solvents, are listed in Table 2 and demonstrate similar trends. Among these, DN is the most widely used and available physical parameter. Therefore, DN should serve as the primary descriptor for evaluating lithium solvation capacity. Most known polar solvents with high salt dissociation capacity have a high donor number (DN > 10) (zones I and II in Figure 1B), while polar solvents with low DN and low dielectric constants have low salt dissociation capacity (zone III in Figures 1B-1C), corresponding to nonsolvating diluents. However, moderate Li + There appears to be an equilibrium region (Zone IV) containing low DN solvents with intermediate dielectric constants that result in -solvent binding energies and salt dissociation.

[0048] [Table 1]

[0049] Relative permittivity and DN values ​​(in bold) are determined from capacitance and calorimetry measurements, respectively.

[0050] [Table 2]

[0051] Applying these two criteria to several solvents (Figure 1A-1C), we identified a family of fluorinated esters (EDFA, M4FP, MDFA, and MDFSA) as prime candidates. The chemical structures of these species are shown in Figure 1D. One Zone IV solvent, methyl 3,3,3-trifluoropropionate (M3FP), has previously shown promising results in Li-metal batteries at temperatures as low as -60 °C, providing further support for the proposed criteria. Compared to non-fluorinated ester solvents, the fluorinated counterparts (MDFA, EDFA, M4FP) have a wider electrochemical stability window, greater thermal stability, and an ultra-low freezing point (Table 1).

[0052] To maximize ionic conductivity, a soft solvent must be combined with a highly dissociated and soluble lithium salt. Studies of (glyme)-LiX electrolytes have shown that salt dissociation follows the order LiTFSI > LiClO4, LiI > LiBF4 > LiCF3SO3 > LiNO3, LiBr > LiCF3CO2, which is consistent with the DN values ​​of some anions in TFSI. - , 5.4, CF3SO3 - , 16.9, Br - , 33.7). LiTFSI is a weak Li + It is a good choice due to its low binding energy and high solubility of 5.0, 4.5, and 3.0 M in MDFA, EDFA, and M4FP solvents, respectively.

[0053] Soft solvating solvents are also solvents and Li + The high reduction potential observed in DFT screening of LiF-solvent complexes promotes the formation of LiF-rich SEI and CEI (see Example 10). These solvents inherently favor the formation of predominant ion pairs and aggregates in solution, which is beneficial for the formation of anion-derived LiF-rich interphases. The addition of MDFSA (fluorosulfonyl-substituted MDFA, molecular structure shown in Figure 1D), which has a high reduction potential of 2.2 V, as a cosolvent allowed the formation of (1) LiF-rich SEI and CEI. +(2) the formation of LiF-rich SEI and LiF-rich CEI was enhanced. The addition of TTE diluent made the electrolyte nonflammable when the volume ratio of TTE in the mixed solvent was greater than 40%.

[0054] Both the graphite anode and NMC811 cathode undergo relatively small volume changes during lithiation / delithiation, which can be tolerated by the elastic inorganic-organic interphase, resulting in excellent cycle life (Figure 5). Because the organic interphase has a higher activation energy, higher electronic conductivity, higher electrolyte solubility, and lower high-voltage stability than LiF, minimizing the organic content at the interface is still desirable. Increasing the LiF content is expected to reduce the SEI thickness during the self-limiting formation process, resulting in a lower area-specific resistance even at low temperatures (Figure 5B). Similar LiF-rich compositions of both the SEI and CEI also improve the overpotential and capacity and kinetic matching between the graphite anode and NMC811 cathode at different currents and temperatures (Figure 5D), thereby controlling the cell voltage and thus the maximum cell capacity and LiF content. 0 This allows for the prevention of Li-ion plating (Figure 5E). In comparison, the inorganic-organic SEI / CEI formed in conventional carbonate electrolytes leads to capacity mismatch and overpotential between the anode and cathode (Figure 5C), thus affecting the high-rate and low-temperature performance of full cells. By balancing the thermodynamic (capacity) and kinetic (interfacial resistance) match between the graphite anode and NMC811 cathode, Li-ion charging can be achieved during fast charging at room temperature and operation at low temperatures. 0 The high modulus hydrophobic LiF-rich interphase effectively suppresses local Li plating under extreme conditions. 0 Even if plating occurs, it mitigates the growth of lithium dendrites.

[0055] Example 2. Physicochemical properties and solvation structure

[0056] LiTFSI was dissolved in different solvents and then analyzed using Raman spectroscopy. - ...Li +The coordination was characterized. Among all electrolytes with commonly used solvents, the TFSI anion peak corresponding to S-N-S bending / vibration in the 1M LiTFSI-MDFA electrolyte - exhibits the smallest red shift (2 cm -1 ), when referenced to crystalline LiTFSI (748.5 cm -1 ), indicating that MDFA has the lowest solvation ability. The increase in LiTFSI salt concentration and the addition of TTE further reduce the Li + -solvent coordination, leading to a higher population of ion aggregation. Since some solvents can only dissolve LiFSI salt, the Raman spectra of 1M LiFSI in different solvents were also compared in Fig. 15B, which shows a similar trend to 1M LiTFSI. When LiFSI is dissolved in the MDFA solvent, the S-N-S bending peak of the LiFSI crystal at 774.5 cm -1 experiences a minimum shift to 750.1 cm -1 , suggesting a smaller Li + -solvent binding energy than all reported weakly solvating solvents (diethyl ether, 1,4-dioxane).

[0057] The solvation structures of electrolytes using different solvents (MA, EDFA, MDFA, M4FP) were also investigated using nuclear magnetic resonance (NMR). The chemical shift of the carbonyl (C=O) carbon of the solvent in the presence of the LiTFSI salt was referenced to its corresponding neat solvent, and the difference was denoted as Δδ (Δδ = δ Li、溶媒 - δ 溶媒 ). Here, δ Li、溶媒 and δ 溶媒 represent the corresponding chemical shifts in the LiTFSI saturated electrolyte and the neat solvent, respectively. All carbonyl 13 C is expected to experience an upshift due to better shielding caused by the Li + -solvent interaction upon the addition of the LiTFSI salt. 13 Details of the C and 17 O NMR spectra are shown in Figs. 16 - 17. A similar trend in chemical shifts is observed in the order of M4FP < MDFA < EDFA 17The minimum Δδ of 2.0 ppm for M4FP (Figure 2B) is also observed in the O NMR spectrum, consistent with the DN value, indicating the weakest Li + -solvent interactions.

[0058] The ionic conductivities of the prepared soft electrolytes are summarized in Figure 2C. As expected, the M4FP-based electrolyte has the lowest ionic conductivity due to its lowest DN and dielectric constant. At 20 °C, the ionic conductivities of the proposed soft electrolytes are 1.8 mS / cm for EDFA, 1.7 mS / cm for MDFA, and 0.6 mS / cm for M4FP, slightly lower than that of the EC / DEC electrolyte (6.4 mS / cm). However, at temperatures below -20 °C, the ionic conductivity of the MDFA-based electrolyte exceeds that of the EC / DEC electrolyte (Figure 2C). The sudden decrease in the ionic conductivity of the EC / DEC electrolyte near -20 °C is attributed to the solidification of the electrolyte. This phase transition of the EC / DEC electrolyte was identified by differential scanning calorimetry (DSC) (Figure 2D), which showed two observable endothermic peaks near -4.0 °C and -18.6 °C. DSC also demonstrated that none of the soft-solvent-based electrolytes underwent a phase change over the temperature range of -90°C to +90°C. These DSC results are supported by visual observation of the electrolytes when stored at -30°C and -90°C, respectively. While the EC / DEC electrolyte was found to freeze below -30°C (Figure 18A), the MDFA-based electrolyte maintained a liquid state even at storage temperatures as low as -90°C (Figure 18B). The electrolyte oxidation potentials of the designed 1M LiTFSI MDFA / MDFSA-TTE and 1M LiTFSI M4FP / MDFSA-TTE electrolytes were >4.8 V (Figure 19A), enabling the NMC811 cathode to operate at 4.5 V. For the 1M LiTFSI EDFA / MDFSA-TTE electrolyte, the oxidation current began to increase sharply at 4.3 V, indicating its unsuitability for high-voltage operation. More aggressive floating tests further confirmed the high stability of the designed electrolytes at high voltages. At 4.5 V or 4.6 V, the minimum leakage current of the 1M LiTFSI MDFA / MDFSA-TTE electrolyte was smaller than that of the 1M LiTFSI M4FP / MDFSA-TTE electrolyte (Figure 19B). Furthermore, the 1M LiTFSI MDFA / MDFSA-TTE electrolyte showed high inhibition of aluminum corrosion due to the formation of a surface layer (Figures 19C-19E). +Considering all the above factors, including the -solvent binding energy, ionic conductivity, and electrochemical stability window, the 1 M LiTFSI MDFA / MDFSA-TTE soft electrolyte is selected for further study.

[0059] The solvation structure of the 1M LiTFSI MDFA / MDFSA-TTE electrolyte was further analyzed using X-ray pair distribution functions (PDFs). The experimental results agreed well with molecular dynamics (MD) simulations in both R-space (Figure 2E) and Q-space (Figure 6), validating the MD simulation predictions of the electrolyte structure. Snapshots of the MD simulation box (Figure 2F and Figures 7A-7B) show that the addition of TTE and MDFA promotes ion aggregation. In the mixed MDFA / MDFSA-TTE solvent electrolyte, Li + Mainly 1.92 MDFA and 1.66 TFSI - It is coordinated by anions, with a contribution from MDFSA of only 0.09 (Figure 2G). - Free Li isolated from + The ionic solvent is primarily coordinated by 4MDFA (Figure 7C). In 1M LiTFSI in MDFA, 10% free Li + and 3% free TFSI. - was observed at room temperature. Upon dilution with TTE and MDFSA, free Li + The proportion of free TFSI decreased to 2–7% depending on the temperature. - The proportion of is less than 0.4%, which means that almost all TFSI - This indicates that anions are involved in the aggregation (Fig. 2F), which is consistent with the trend of the Walden plot (Fig. 2C) and the high Li + Transference number (t + ) as evidenced by the TFSI - Priority Li for transportation + Therefore, the 1M LiTFSI MDFA / MDFSA-TTE electrolyte also exhibits a high t + (Figure 21). When the temperature is lowered, the free Li +Although the proportion of ionic conductivity increases slightly, the ionicity (inverse Haven ratio) remains roughly the same and further decreases slightly below -30 °C (Figure 2H), with a more pronounced decrease in conductivity in this region (Figures 7D-7E).

[0060] Example 3. Electrochemical Performance of 4.5V NMC811||Graphite Full Cell

[0061] 2.5mAhcm in different electrolytes -2The cycling and rate performance of NMC811|| graphite full cells with an areal capacitance of 0.2 V and an N / P ratio of 1.1 were investigated in the voltage range of 2.5 to 4.5 V. Figure 3A shows that the performance of full cells in 1M LiTFSI MDFA / MDFSA-TTE electrolyte is superior to that of EC / DEC-based electrolytes. Specifically, full cells in 1M LiTFSI MDFA / MDFSA-TTE electrolyte exhibit a capacity retention of 80.1% after 400 cycles, with an average CE of 99.94%. The first charge / discharge formation cycle of the NMC811|| graphite full cell at 0.2 C shows a high initial CE of 87.2% (Figure 23A). The voltage profiles of the NMC811|| graphite full cell at 0.5 C for the 1st, 100th, and 400th cycles can be seen in Figure 23B. In comparison, the full cell with 1M LiTFSI MDFA-TTE in Figure 24 exhibits faster capacity fade (52.8% retention after 200 cycles), verifying the role of the MDFA cosolvent in forming a LiF-rich interphase and thus stabilizing cycling performance. Stable cycling performance could also be achieved using other cosolvents with fluorosulfonyl functional groups (Figure 25), suggesting this is a universal strategy. Furthermore, the potential gas pressure changes of NMC811|| graphite full cells during charge / discharge cycling in 1M LiTFSI MDFA / MDFSA-TTE and 1.0M LiPF6EC / DEC were simultaneously monitored by the EL-Cell device. The pressure change in the 1M LiTFSI MDFA / MDFSA-TTE electrolyte is almost negligible compared to the increased pressure in the EC / DEC-based electrolyte at a high cutoff voltage of 4.5 V (Figure 26).

[0062] The improvement in rate performance over 1M LiPF6EC / DEC is shown in Figure 3B for an NMC811||| graphite full cell with 1M LiTFSI MDFA / MDFSA-TTE electrolyte, delivering capacities of 202 mAh / g at 1C, 185 mAh / g at 2C, 169 mAh / g at 3C, and 140 mAh / g at 4C. The corresponding charge / discharge voltage profiles of the cell at different C rates with 1M LiTFSI MDFA / MDFSA-TTE are shown in Figure 3C. The rate performance is further improved by employing polycrystalline NMC811, demonstrating the stable cycling performance of the NMC811||| graphite pouch cell with dilute electrolyte at high rates of 3-4C (Figure 8). Furthermore, the capacity is consistent between the graphite anode and NMC811 cathode at different C rates. The capacities of the NMC811 cathode (Figure 29A) and graphite anode (Figure 29B), measured separately in half cells using a Li counter electrode, ensured that the N / P ratio was slightly greater than 1 as the C rate increased from 1 C to 4 C (Figure 29C), effectively avoiding lithium plating. Photographs of the graphite anode from an exploded pouch cell cycled at -30°C also confirmed the absence of obvious lithium plating on the graphite anode (Figure 29D). This excellent rate performance is attributable to rapid LiF transport across the LiF-rich interphase in both the anode and cathode. + Low Li induced by diffusion and inherent solvation structure + This is due to the desolvation energy as well as the high transference number of the designed electrolytes.

[0063] In addition to excellent performance at room temperature, the NMC811|| graphite full cell also exhibited excellent performance at low temperatures. Figure 3D shows the cycling stability of an NMC811|| graphite full cell with 1M LiTFSI MDFA / MDFSA-TTE electrolyte at 0.2°C, -30°C, and -40°C. At -30°C, 93.9% of the capacity is retained after 260 cycles, with an average coulombic efficiency of 99.98%. At lower temperatures, down to -50 / -60°C, a slightly faster capacity fade is observed (Figure 9). Figure 3E compares the performance of the NMC811|| graphite full cell in the two electrolytes at different temperatures. The NMC811|| graphite full cell with EC / DEC electrolyte cannot operate at -30°C due to solidification of the electrolyte. In contrast, the capacities of NMC811|| graphite full cells with 1M MDFA / MDFSA-TTE electrolyte show high retention of their room temperature capacity at low temperatures: 206.8 (95%), 194.5 (90%), 188.7 (87%), 184.6 (85%), 161.0 (75%), and 115.5 (54%) mAh / g when cycled at 0°C, -20°C, -30°C, -40°C, -50°C, and -60°C, respectively. Representative voltage curves of full cells with 1M LiTFSI MDFA / MDFSA-TTE electrolyte at different temperatures are shown in Figure 3F. NMC811|| graphite full cells with 1M MDFA / MDFSA-TTE electrolyte can fully recover their original capacity at 25°C even after ultra-low temperature operation at -60°C, indicating that the LiF-rich interphase is LiF-rich. 0 This suggests that the coating is robust enough to mitigate plating and dendrites.

[0064] To better represent practical conditions, an NMC811|| graphite pouch cell was evaluated (Figure 3G), delivering a charge / discharge capacity of 160.2 mAh / g at 0.2 C at -30 °C, similar to the charge / discharge capacity of a coin cell under the same conditions. Even with a dilute electrolyte of 2.5 g / Ah, no obvious capacity fade was observed (Figure 3G). At higher C rates of 0.4 C and 0.5 C, the pouch cell exhibited capacities of 152.6 mAh / g and 134.6 mAh / g, respectively. The NMC811|| graphite pouch cell maintained 80% of its capacity after 360 cycles. Performing both charge and discharge tests on the pouch cell at the same low temperature is a very aggressive protocol, especially at very low temperatures at typical 0.2–0.3 C rates. Previous reports in the literature have shown that almost all full cells using graphite anodes were initially charged at room temperature and then discharged at low temperatures to achieve high charge capacities and avoid Li plating. Some electrolytes that enable Li metal batteries can charge / discharge at low temperatures but cannot support high-voltage NMC811 cathodes. To date, it remains impossible to charge / discharge NMC811|| graphite full cells with practical areal capacities and N / P ratios. However, we surprisingly found that by using a rational design of advanced electrolytes, we were able to demonstrate exceptional performance of NMC811|| graphite full cells in both coin and pouch cell formats using the most aggressive charge / discharge protocols at the same low temperature, even at -60 °C. A quantitative comparison (areal capacity, operating voltage, operating temperature range, low-temperature charge capacity, rate capability, and safety) of Li-ion batteries using graphite anodes but different cathodes under practical applications is listed in Table 3.

[0065] [Table 3]

[0066] In addition to exceptional low-temperature performance, the 1M MDFA / MDFSA-TTE electrolyte also demonstrated that NMC811|| graphite full cells achieved improved capacity at high temperatures because the LiF-rich SEI and CEI formed were less soluble in the electrolyte. As shown in Figure 30A, the NMC811|| graphite full cell with 1M LiTFSI MDFA / MDFSA-TTE electrolyte retains 73.1% of its capacity after 180 cycles at 60 °C. Notably, the NMC811|| graphite pouch cell with a dilute electrolyte (2.5 g / Ah) retains 92% after 200 cycles at 4 C under 60 °C (Figure 30B). In contrast, the capacity of the NMC811|| graphite full cell with an EC / DEC-based electrolyte fades rapidly at 60 °C. + The high operating voltage of up to 4.6 V vs. θ exceeds the stability limits of not only EC / DEC-based electrolytes but also organic-rich SEI / CEI at high temperatures, especially in the presence of LiPF6.

[0067] To quantitatively analyze the improved low-temperature performance, a three-electrode pouch cell was used to simultaneously monitor the behavior of the anode and cathode (Figure 10A), and the cell voltage (U), the potential of the NMC811 cathode (E (+) ), and the potential of the graphite anode (E (-) The potential of the graphite anode was measured at -30°C. + It can be seen that the SEI resistance, R, of both the cathode and anode decreases as the temperature decreases from 25°C to -30°C. SEI and charge transfer resistance R ct The SEI resistance and charge transfer (R SEI , cathode=4.8, R SEI , anode=5.6, R ct , cathode=22.5, Rct , anode = 25.2) is R at -30°C SEIカソード =72.3, R SEIアノード =81.5, R ctカソード =228.5, R ctアノード = 241.2 (Figure 10). The nearly identical impedance values ​​of the cathode and anode at different temperatures indicate that impedance matching was successfully achieved by adjusting the interphase chemistry. In contrast, the overall resistance of the cell in the EC / DEC electrolyte, especially R ct increased as the temperature decreased from 25 °C to -30 °C due to solidification of the electrolyte and kinetic slowdown across the interphase (Figure 31). Furthermore, the impedance ratio between the NMC811 cathode and the graphite anode also changed significantly, from a predominant NMC811 impedance at 25 °C to a predominant graphite anode impedance at -30 °C.

[0068] Example 4. Characterization of electrode and interphase chemistry

[0069] To identify the interphase chemistry, the morphology and composition of the SEI on the graphite anode were systematically investigated. Under high-resolution transmission electron microscopy (HRTEM), a uniform and thin SEI of approximately 2 nm was observed on the graphite anode after 20 cycles in an MDFA / MDFSA-based electrolyte (Figure 4A). Such thinness approaches the theoretical lower limit of the interphase and reflects the effectiveness of the LiF-based interphase in insulating electron tunneling. In contrast, a much thicker SEI layer of approximately 14 nm was observed in an EC / DEC-based electrolyte (Figure 4B). The roughness and thickness of the SEI were also studied by electrochemical atomic force microscopy (AFM). As shown in Figures 4C-E, pristine graphite particles have a smooth surface with a roughness of approximately 0.233 nm. In good agreement with the HRTEM observations, the roughness of the cycled graphite in the MDFA / MDFSA-based electrolyte obtained by AFM increased to approximately 3.0 nm (Figure 4E), much smaller than the value of approximately 11.8 nm in the EC / DEC-based electrolyte (Figure 4D). X-ray diffraction (XRD) and SEM were also used to characterize the graphite anode after 20 cycles at -30 °C. According to the XRD patterns (Figure 32), graphite cycled in both the MDFA / MDFSA and EC / DEC-based electrolytes shows negligible changes from its initial state, verifying its structural integrity after cycling. According to SEM, it is clear that the surface of graphite with the EC / DEC-based electrolyte is covered with a thick SEI, whereas a much thinner SEI is observed in the MDFA / MDFSA-based electrolyte (Figure 33).

[0070] To identify the chemical composition of the SEI on the cycled graphite anode, Ar +X-ray photoelectron spectroscopy (XPS) using sputtering depth profiling was performed. The elements and their associated atomic ratios detected in the SEI on graphite recovered from 1M LiTFSI MDFA / MDFSA-TTE electrolyte are summarized in Figure 4F, and the C 1s and F 1s spectra are shown in Figure 4G and Figure 4H, respectively. The top surface of the SEI is composed of both organic (CO2CF2) and inorganic (LiF, Li2CO3) components. N and S were found in the SEI from the MDFA / MDFSA-based electrolyte, which is consistent with the TFSI. - This arises from the decomposition of the anions and the MDFA cosolvent. In the C 1s spectrum (Figure 4G), the organic signals (CO, CO2CF2) drop to the noise level at 300 s of sputtering, whereas the LiF signal persists throughout the sputtering process (Figure 4H). Combining the results from the C 1s and F 1s spectra, we conclude that a robust bilayer SEI with a LiF-rich inner layer and an organic-rich outer layer was formed. The formation of the LiF-rich SEI was verified by time-of-flight secondary ion mass spectrometry (TOF-SIMS) spectra collected with negative polarity in the 5-60 m / z range (Figure 4F).

[0071] The XPS spectrum from the EC / DEC-based electrolyte (Figure 35) shows that the SEI composition on graphite is significantly different from that of the MDFA / MDFSA-based electrolyte. The LiPF salt-derived SEI still exhibited a P signal after 480 seconds of etching, indicating that it was much thicker than the SEI produced in the MDFA / MDFSA-based electrolyte. In the EC / DEC-based electrolyte, the signal intensity was low for LiF but high for C=O / PO and CO-containing species, suggesting that the SEI is composed of more organic compounds than LiF. While the Ni 2p signal can be seen on graphite cycled in the EC / DEC-based electrolyte, apparently due to the dissolution of active species from the NMC811 cathode, the Ni 2p signal was absent on the SEI on graphite cycled in the MDFA / MDFSA-based electrolyte, demonstrating that the MDFA / MDFSA-based electrolyte produces a better CEI and suppresses such parasitic dissolution even at such a high cutoff voltage of 4.5 V.

[0072] Characterization of the NMC811 cathode interphase also revealed the formation of a LiF-rich inner layer and an organic-rich outer layer, the CEI, in the MDFA / MDFSA-based electrolyte. The (003) reflection at 19.0 2-theta of NMC811 recovered from the EC / DEC electrolyte shifted slightly to lower scattering angles (Figure 36, marked by the dotted line), reflecting a decrease in the degree of lithiation. This is because the organic-rich CEI formed in the EC / DEC electrolyte cannot effectively protect NMC811, leading to the dissolution of Ni, Mn, and Co from NMC811 and inducing a phase change on the NMC811 surface. The LiF-rich CEI formed in the MDFA / MDFSA-based electrolyte builds a denser, more compact, and thinner (approximately 9 nm) barrier than the approximately 24 nm barrier formed in the EC / DEC-based electrolyte (Figure 37). This CEI effectively passivates NMC811 and stabilizes its structure. The formation of a bilayer CEI with a LiF-rich inner layer and an organic-rich outer layer is supported by the XPS characterization in Figure 38 and the TOF-SIMS results shown in Figure 39.x DFT calculations of the reaction energies of MDFA, TTE, and MDFSA on a four-layer slab model of NiO2(104) support these observations. At high potentials, surface oxygen becomes highly reactive, and electrolyte species in contact with these surfaces undergo dehydrogenation, which sets an upper limit on the anodic stability window. On semilithiated surfaces, dehydrogenation of MDFA without radical chemisorption on the CF2 carbon was found to be energetically favorable, with a reaction energy of -0.49 eV using PBE+U and a similar energy of -0.45 eV using the SCAN function (Figure 11A). Li 0.5 Dehydrogenation of TTE on NiO2 may also be possible, proceeding with a much smaller reaction energy of -0.05 eV via PBE+U. This reaction is slightly more favorable when considering the SCAN function, which gives an energy of -0.31 eV (Figure 11B). Finally, the cluster calculations discussed earlier suggest that the Li + The high reduction potentials calculated for these reactions are not only related to SEI formation, but also account for CEI formation at low states of charge or open circuit voltages when the cathode is in a discharged state. 1.0 For NiO2, PBE+U requires Li to form the SO2F product. + While we predict a reaction energy of 0.50 eV for -MDFSA, a significant shift to -1.03 eV is observed for the same configuration when using SCAN (Figure 11C). The difference in reaction energy between the PBE+U and SCAN methods can be attributed to the low density of states of the Ni 3d electrons near the Fermi energy, which is a result of the Hubbard correction required to localize the electron density on the transition metal. This difference can be seen in Figure 40, where the Li 0.5 NiO2 and Li 1.0 This is best illustrated in the partial density of states of bare NiO2 surfaces. 1.0The Hubbard-corrected PBE function for NiO2 underestimates the Ni3dO2p hybridization, which makes Ni less oxidizable and tends to result in a positive reaction energy. These differences are due to the Li 0.5 For NiO2, it decreases. In both cases, the Hubbard term is not used for O 2p, so the O 2p density of states near the Fermi energy is similar between the functions. 1.0 In the NiO2 structure, the SCAN function better reproduces the hybridization behavior and increases the density of states of Ni 3d electrons near the Fermi energy. The downstream decomposition of the SO2F product is the most likely source of the LiF-rich thin layer in the inner part of the CEI, while the byproducts of MDFA and TTE dehydrogenation and radical condensation comprise the fluorine-rich organic outer layer.

[0073] Example 5. Materials and Methods

[0074] Methyl difluoroacetate (MDFA), methyl 2,2-difluoro-2(fluorosulfonyl)acetate (MDFSA), methyl 2,3,3,3-tetrafluoropropionate (M4FP), ethyl difluoroacetate (EDFA), and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) were purchased from SynQuest Labs, Inc. and used after dehydration with 4Å molecular sieves. In an argon-filled glove box, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) purchased from Gotion Inc. was dissolved in a solvent mixture of the specified concentration (MDFA:MDFSA:TTE = 4:1:5, volume ratio). The water content of the solution was measured using a Karl Fischer moisture meter and was below 5 ppm. For comparison, a solution of 1M LiPF6 in EC / DEC = 50 / 50 (v / v), battery grade (Sigma Inc.) was used as received. The ionic conductivity of the electrolyte was calculated from the high-frequency intercept of the EIS impedance spectrum measured in a symmetric Pt|Pt Swagelok blocking cell at various temperatures (-60 °C to +60 °C). Each sample subjected to differential scanning calorimetry (DSC) measurements was packed into a stainless steel pan and crimp-sealed in an argon-filled glove box. All DSC experiments were performed at a cooling / heating rate of 5 °C / min.

[0075] NMC811(LiNi) on Al foil 0.8 Mn 0.1 Co 0.1 The cathode coating of O2 was kindly provided by Saft America Inc. These electrodes consisted of 94 wt% NMC811, 3 wt% carbon, and 3 wt% PVDF, with approximately 30% porosity and 2.5 mAhcm -2 Area capacitance (mass loading) of approximately 11.5 mg / cm 2Graphite powder within a narrow size distribution (3.5±1.5 μm) was obtained from China Steel Chemical Corp. Graphite electrodes were prepared by mixing graphite with carbon black and PVDF in a weight ratio of 92:2:6 using N-methylpyrrolidinone as the solvent, cast onto copper (Cu) foil, and dried overnight at 80°C under vacuum. The areal capacity of the graphite electrode was 2.7 mAhcm. -2 This corresponds to an N / P ratio of 1.08. 2 The sheets were cut into 100 mm thick sheets and dried in vacuum at 80°C for 24 hours before assembly.

[0076] Example 6. Electrochemical measurements

[0077] CR2032 coin-type full cells were assembled by sandwiching a Celgard 2325 separator between a graphite anode and an NMC811 cathode. For consistency, all cells were filled with a fixed volume (40 μL) of liquid electrolyte, and the Li-ion cells were cycled twice between 2.5 V and 4.5 V at 0.2 C before testing. The 2.5 mAh cm in the different electrolytes was used. -2 The cycling and rate performance of NMC811|| graphite full cells with an areal capacity of 1.1 and an N / P ratio of 1.1 were tested over a voltage range of 2.5 to 4.5 V. The cycling conditions for each test are described in the description section or figure captions. The C rate was determined by the charging time, e.g., 1 C, which is equivalent to 1 h. For the pouch cells, aluminum and nickel strips were attached to the sides of the cathode and anode, respectively, as electrode tabs. The electrodes, separator, and liquid electrolyte were all the same as those used in the coin cells. All single-layer pouch cells (5 cm x 7 cm) were vacuum-sealed in a Saft Corporation dry room without electrolyte and then shipped to the University of Maryland for electrolyte infiltration. For comparison, various amounts of electrolyte (3.5, 3.0, and 2.5 g / Ah) were injected into the packages. Similar to the coin cells, the same N / P ratio of 1.1 and 2.5 mAh cm were used.-2 The pouch full cell, with an areal capacity of 1000 mAh, was charged / discharged at the same temperature for all tests. The impedance spectrum of the three-electrode cell was tested over a frequency range of 0.01 to 1,000,000 Hz using a pouch cell incorporating a small piece of lithium metal as a reference electrode.

[0078] Example 7. Molecular dynamics simulation.

[0079] The MD simulation cell for LiTFSI in the MDFA / MDFSA-TTE contained 330 MDFAs, 75 MDFSAs, 380 TTEs, and 96 LiTFSIs, while the LiTFSI in the MDFA cell contained 1100 MDFAs and 96 LiTFSIs. The polarization force field APPLE&P with the previously developed LiTFSI and TTE parameters was used. + (MDFA) and Li + The (MDFSA) interactions, solvent charge, and polarizability were calculated using the methodology from previous studies, but MP2 / aug-cc-pvTz was used to calculate the electrostatic potential on the lattice surrounding the solvent, and PBE / 6-31+G(d,p) was used to fit the charge on the lattice surrounding the solvent. + Calculate the binding energies and polarizabilities of Li relative to the solvent using G4MP2. + The binding energies were calculated to obtain the most favorable geometries.

[0080] The lengths of the equilibration and production runs, the simulation temperatures, densities, and the number of independently simulated replicas are summarized in Table 4. The equations of motion were solved using a time-reversible (RESPA) integrator over the following time resolutions: i) bond and angular contributions to the forces were calculated at any 0.5 femtosecond (fs), ii) dihedral and non-bond force contributions within an 8 Å cutoff were updated at any 1.5 fs, and iii) the force remainder (k = 8 3 Reciprocal space Ewald using vectors and non-bonded forces within a 12 or 14 Å cutoff was updated at an arbitrary 3 fs interval. -1A Nose-Hoover thermostat was used for temperature control with a relevant frequency of .

[0081] [Table 4]

[0082] Example 8. Li + Quantum chemical calculations of solvation

[0083] Li + The binding energies of (solvent) (shown in Figure 1C) were calculated using DFT with the PBE functional, 6-31+G(d,p) basis set, to determine the binding energy between the solvent and Li + (solvates) were calculated in an implicit solvent modeled using PCM(ether) implemented in the Gaussian software package.

[0084] The reduction potential of the complex of interest, designated as complex A, is calculated by the ratio of A in solution to the - The negative free energy of formation [ΔG S 298 =G S 298 (A - )-G S 298 (A)] divided by Faraday's constant. G red =-(ΔG S 298K ) / F-1.4V

[0085] 1.4V Li + The difference between the / Li and the absolute reduction potential was subtracted, and the results were compared with Li as extensively discussed elsewhere. + Converted to / Li scale.

[0086] Example 9. Modeling surface reactions

[0087] Calculations to determine the reaction energy of the decomposition reaction in a four-layer slab model of LiNiO2 (1 0 4) were performed using VASP5.4. All geometry optimizations were performed using PBE+U (U = 5.96 eV for Ni) and _sv and _pv potentials for Li and Ni, respectively. Only gamma points are considered for surface calculations. Single-point energies were also calculated using the SCAN function. The plane wave basis was extended to 520 eV for the PBE method and 800 eV for SCAN. Dipole corrections were also used for optimizations and single-point energy calculations. Li + -MDFA calculations use a single F - Ions were added elsewhere on the surface to neutralize the cell. The reactant state used here is the minimum-energy physisorbed state. Calculations were prepared using the Atomic Simulation Environment, and the density of states was analyzed using the VASP plugin in pymatgen. Images were generated using VESTA.

[0088] Example 10. Solvent reduction stability screening using density functional theory.

[0089] Density functional theory (DFT) and three models were used to calculate the reduction stability of the electrolyte solvent. The three models, in order of increasing complexity and computational cost, are a) isolated solvent, b) Li + (solvent) and c) Li + The (MDFA)3(solvent) cluster. All solvents / solvates were immersed in implicit solvent using diethyl ether parameters. A polarizable continuum model with solvents, except for the surface PCM (SES), was used for high-throughput screening. Li was added to the isolated solvent and to all oxygen, nitrogen, and fluorine atoms in the solvent. + Li bonded to + All conformers of the (solvent) complex were screened (>10,000 calculations) and the results for the most energetically stable configurations are reported in Table 5. As shown in Table 6, Li + By replacing one MDFA in (MDFA)4 with the test solvent, Li +To generate the initial structure of (MDFA)3(solvent), Li + Up to five of the most stable configurations of the (solvent) complex were used.

[0090] The screening is performed by the vertical reduction energy (E vert ), which is the fastest calculation because it does not require geometric optimization of the reduced complex. On the other hand, it does not account for molecular deformation, including bond breaking, that may occur as a result of reduction. The vertical reduction energy shows that MDFSA has the highest reduction potential, followed by fluorinated esters (M3FA, MDFA, EDFA), and ethers such as DME and THF have the lowest reduction potential. The adiabatic reduction energy (E red ) and free energy (G red ) and fluorinated esters are Li / Li + It is shown that not only do they have reduction free energies above 0 V relative to the SiO2 complex, but they also undergo energetically favorable C-F bond breaking after reduction, leading to higher reduction potentials. TTE and MDFSA also exhibit C-O and C-S bond breaking, respectively, in addition to C-F bond breaking during geometry optimization of the reduced complex, suggesting that these molecules are the catalysts for SEI formation. - and has been shown to be a good source of highly fluorinated fragments.

[0091] Li to the reducing solvent + The binding of Li results in solvent polarization due to strong interactions with excess electrons in the reducing solvent, leading to higher reduction potentials of 0.5–1.9 V. The reduction free energies are in good agreement with available experimental values. +The reduction free energy of DMFSA ranges from 4 V with C-S bond breaking and LiSOF formation to LiF formation in the range of 2.3–3 V. Semifluorinated esters exhibit the next highest reduction potentials, ranging from 1–1.73 V, with no bond breaking occurring until 2.0–2.6 V, at which point C-F bond breaking occurs during reduction to form LiF. The latter process requires more reorganization energy and is kinetically predicted (by Marcus theory) to be much slower than reduction without bond breaking.

[0092] Using MFDA as the primary solvent, Li was measured for a small subset of the solvents listed in Table 6. + The reduction of (MDFA)3(solvent) clusters was investigated. + (MDFA)3(MDFSA) and Li + For all solvates except (MDFA)3(M4FP), the MDFA solvent underwent reduction, while the other solvents (EC, ACN, DMC, DMC, MA, EA, MB, M3FP, EFA, TTE, EDFA, EFA, DOL, EP, EMC) remained neutral. + The reduction potential of (DMFA)4 ranged from 1.17 to 1.51 V, which is consistent with the reduction peak at 1.3 V observed in the CV of Figure 13. If C-F bond breaking is associated with the reduction, the reduction potential of these solvates was slightly higher, at 1.65 to 2.05 V, but F - The reorganization energy is expected to be larger and the kinetics is expected to be slower. 2 Carbon (fluorine atom and oxygen) 2 C(sp 3 This behavior is demonstrated by the Li ions shown in Table 5. + The lower Li of these solvents compared to MDFA + (solvent) reduction potential [no bond breaking]. +For the (MDFA)3(M4FP) solvate, the reduction of both MDFA and M4FP was observed at similar reduction potentials, which is shown in Table 5. + (MDFA) and Li + This is consistent with the similar reduction potential for (M4FP). + The reduction of (MDFA)(MDFSA) yielded potentials ranging from 1.76 to 2.05 V for MDFA reduction with C-F bond rupture and for MDFSA reduction with C-S bond rupture, which occurred at 3.70 to 3.93 V. The high reduction potential within the cathodic cycle makes MDFSA a good candidate as an additive / co-solvent for forming CEI on the cathode surface. Similar conclusions were reached by considering MDFA and MDFSA solvates when the C-F and C-S bonds were manually cleaved.

[0093] [Table 5]

[0094] a During reduction, bond rupture occurs, resulting in multiple reduction products. Only the most stable ones are listed.

[0095] [Table 6]

[0096] [Table 7]

[0097] All publications mentioned herein are incorporated by reference to the extent that they support the present invention.

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Claims

1. 1. An electrolyte composition comprising a lithium salt dissolved in one or more solvents, the solvents having a donor number less than 10, a dielectric constant greater than 5, a boiling point greater than 60°C, and a melting point less than -60°C.

2. 2. The electrolyte composition of claim 1, wherein the solvent is selected from MDFA, MDFSA, M4FP, EDFA, TTE and M3FP, or combinations thereof.

3. 10. The electrolyte composition of claim 1, wherein the electrolyte comprises MDFA and MDFSA.

4. 4. The electrolyte composition of claim 3 comprising MDFA, MDFSA and TTE.

5. 5. The electrolyte composition of claim 4, comprising the MDFA in an amount of about 20% to about 50%, the MDFSA in an amount of about 10% to about 25%, and the TTE in an amount of about 30% to about 60%.

6. 2. The electrolyte composition of claim 1, wherein the lithium salt is selected from LiTFSI, LiClO4, LiI, LiBF4, LiCF3SO3, LiNO3, LiBr, and LiCF3CO2, or combinations thereof.

7. 2. The electrolyte composition of claim 1, wherein the lithium salt is LiTFSI.

8. 10. The electrolyte composition of claim 1, wherein the lithium salt is present at a concentration ranging from about 0.5M to about 4M.

9. A Li-ion battery comprising a cathode, an anode, and an electrolyte according to any one of claims 1 to 8.

10. 10. The Li-ion battery of claim 9, wherein the cathode comprises NMC811, PVDF, and carbon black.

11. 10. The Li-ion battery of claim 9, wherein the cathode comprises about 80% to about 98% by weight of the NMC811, about 1% to about 10% by weight of the PVDF, and about 1% to about 10% by weight of the carbon black.

12. 10. The Li-ion battery of claim 9, wherein the cathode comprises about 90% to about 95% by weight of the NMC811, about 3% to about 5% by weight of the PVDF, and about 2% to about 5% by weight of the carbon black.

13. 10. The Li-ion battery of claim 9, wherein the anode comprises graphite, PVDF, and carbon black.

14. 10. The Li-ion battery of claim 9, wherein the anode comprises about 80% to about 98% by weight of the graphite, about 1% to about 10% by weight of the PVDF, and about 1% to about 10% by weight of the carbon black.

15. 10. The Li-ion battery of claim 9, wherein the anode comprises about 90% to about 95% by weight of the graphite, about 4% to about 7% by weight of the PVDF, and about 1% to about 3% by weight of the carbon black.

16. 16. The Li-ion battery of any one of claims 1 to 15, wherein the battery has an operating charge and discharge temperature in the range of about -120°C to about 120°C.

17. 17. A method of assembling a Li-ion battery according to any one of claims 1 to 16, comprising stacking a cathode according to any one of claims 1 to 16, a separator material, an anode according to any one of claims 1 to 16, and an electrolyte composition according to any one of claims 1 to 16.

18. 18. The method of claim 17, wherein the battery is a coin cell battery, the cathode is coated on Al foil, the anode is coated on Cu foil, the separator material is Celgard 2325, and the amount of electrolyte used is about 40 μL.

19. 18. The method of claim 17, wherein the battery is a pouch cell type battery, the cathode is attached to an Al strip via an electrode tab, the anode is attached to a Ni strip via an electrode tab, and the amount of electrolyte is present in an amount ranging from about 2 g / Ah to about 4 g / Ah.

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