Optimized lithium salt electrolytes for lithium-sulfur batteries

Abstract

Lithium-sulfur batteries offer theoretical energy densities approaching 2600 Wh / kg—nearly three times higher than conventional lithium-ion batteries. The present disclosure provides co-salt electrolyte compositions combining two or more lithium salts selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts to achieve synergistic performance improvements unattainable with single-salt formulations. These co-salt systems deliver enhanced capacity, superior coulombic efficiency retention, extended cycle life, and reduced self-discharge, enabling lithium-sulfur batteries to meet demanding requirements of next-generation applications including electric aviation, electric vehicles, and grid-scale energy storage. The disclosed formulations address environmental concerns by enabling reduced polyfluorinated substance content while maintaining electrochemical performance. By tailoring co-salt composition in conjunction with cathode design parameters, the technology enables application-specific optimization maximizing energy density or longevity. The result is a versatile electrolyte platform bridging the gap between the theoretical promise of lithium-sulfur chemistry and practical commercial performance requirements.

Description

DOCKET: LYT1P125P / LYTEP309WOOPTIMIZED LITHIUM SALT ELECTROLYTES FOR LITHIUM-SULFUR BATTERIESCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority to U.S. Provisional Patent Application No. 63 / 803,295, filed on 5 / 9 / 2025, entitled “OPTIMIZED LITHIUM SALT ELECTROLYTES FOR LITHIUM-SULFUR BATTERIES,” and U.S. Provisional Patent Application No. 63 / 760,020, filed 2 / 18 / 2025, entitled “OPTIMIZED LITHIUM SALT ELECTROLYTES FOR LITHIUM-SULFUR BATTERIES,” the contents of all of which are hereby incorporated by reference for all purposes.

[0002] Additionally, the present application is related to U.S. Patent Application 18 / 765,011, filed on 7 / 5 / 2024, entitled “ELECTROLYTE SYSTEMS INCLUDING ELECTRON WITHDRAWING COMPOUNDS WITH AN ALPHA-BETA MOTIF FOR IMPROVING PERFORMANCE OF LITHIUM-BASED SECONDARY BATTERIES,” the contents of which are hereby incorporated by reference for all purposes.FIELD OF THE INVENTION

[0003] The present disclosure relates to lithium-sulfur battery systems, and more particularly to optimizing lithium salt compositions.BACKGROUND

[0004] Lithium-sulfur batteries have garnered significant attention in the field of energy storage due to their high theoretical energy density, which exceeds that of conventional lithium-ion batteries. This potential for increased energy storage capacity makes lithium-sulfur batteries promising candidates for applications ranging fromelectric vehicles to portable electronics. However, the practical implementation of lithium-sulfur batteries faces several challenges that limit their widespread adoption and commercial viability.

[0005] Existing lithium-sulfur battery systems encounter numerous obstacles that hinder their performance and longevity. These include the polysulfide shuttle effect, where soluble lithium polysulfides migrate between the cathode and anode, leading to active material loss and capacity fading. Additionally, lithium- sulfur batteries often suffer from rapid capacity decay, poor rate capability, and limited cycle life. The highly reactive nature of lithium metal anodes also presents safety concerns, as it can lead to dendrite formation and potential short-circuits.

[0006] Further, existing lithium-sulfur battery systems have predominantly relied on lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the primary lithium salt in the electrolyte formulation. While EiTFSI provides reasonable ionic conductivity and electrochemical stability, this salt presents several challenges including high molecular weight that increases the overall density of the electrolyte package, classification as a polyfluorinated substance (PFAS) which raises environmental and regulatory concerns, and relatively high cost that impacts the commercial viability of lithium-sulfur battery systems. Earlier lithium salts employed in lithium secondary batteries, such as lithium hexafluoroarsenate, lithium hexafluorophosphate, and lithium tetrafluoroborate, have proven unsuitable for lithium-sulfur applications due to their toxicity from hydrogen fluoride release and incompatibility with lithium polysulfide species generated during cell operation.

[0007] Alternative lithium salts have been investigated as potential replacements or supplements to EiTFSI in lithium-sulfur electrolytes. However, these salts have presented fundamental challenges in achieving satisfactory performance in lithiumsulfur systems when used individually, leading researchers to continue relying on LiTFSI despite its drawbacks. For instance, single-salt electrolyte formulations may exhibit inadequate ionic conductivity at certain concentrations, insufficient solid electrolyte interphase formation on the lithium anode, or poor kinetics during charge and discharge processes. Additionally, the relationship between lithium salt selection and cathode loading levels, as well as the potential synergistic effects of combining multiple lithium salts in co-salt systems, remains an area where further developmentmay yield improvements in lithium- sulfur battery performance characteristics such as capacity retention, coulombic efficiency, and self-discharge behavior.

[0008] As such, there is thus a need for addressing these and / or other issues associated with the prior art.SUMMARY

[0009] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0010] The lithium-sulfur battery system includes a cathode, an anode, a separator disposed between the cathode and the anode, and an electrolyte comprising a lithium salt and a solvent. The lithium salt comprises at least one of lithium bromide (LiBr), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium triflate (LiOTf), and / or lithium iodide (Lil), and is present at a concentration between 0.1 M and 3.0 M.

[0011] The lithium- sulfur battery system includes a cathode containing sulfur, a lithium metal anode, a separator between the cathode and the anode, and an electrolyte comprising a solvent and a lithium salt mixture. The lithium salt mixture comprises lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and at least one additional lithium salt selected from the group consisting of lithium bromide (LiBr), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium iodide (Lil). The lithium salt mixture is present at a total concentration between 0.5 M and 5.0 M, and the additional lithium salt comprises between 1 % and 50% by weight of the total lithium salt mixture.

[0012] The lithium-sulfur battery system includes a cathode comprising sulfur, an anode comprising lithium metal, a porous separator between the cathode and the anode, and an electrolyte comprising an organic solvent and a lithium salt composition. The lithium salt composition comprises at least two different lithium salts, wherein at least one of the lithium salts is selected from the group consisting of lithium bromide (LiBr), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium iodide (Lil). The lithium salt composition is configured to reduce at least one of polysulfide shuttle effect, electrolyte dryout, or dendrite formation compared to a system using only lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt.

[0013] According to an aspect of the present disclosure, various electrolyte compositions for a lithium- sulfur battery is provided. The electrolyte composition includes a solvent system comprising 1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), and l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The electrolyte composition further includes a co-salt system comprising at least two lithium salts wherein the at least two lithium salts are each independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts. For example, the at least two lithium salts may include, but not be limited solely to, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium iodide (Lil), and / or lithium perchlorate (LiC104). In some instances, the electrolyte composition may also include lithium nitrate (LiNO3) and dicyandiamide (DCDA).

[0014] According to other aspects of the present disclosure, the electrolyte composition may include one or more of the following features. The co-salt system may comprise LiTFSI at a concentration of 0. IM to 1 ,2M and Lil at a concentration of 0. IM to 1.0M. The co-salt system may comprise LiTFSI at a concentration of 0.1M to 1.0M and LiFSI at a concentration of 0.1M to 0.8M, wherein a ratio of LiFSI to LiTFSI is between 1:5 and 3:1. The solvent system may comprise DME, DOL, and TTE at a volume ratio where DME is present at 50% to 80%, DOL is present at 10% to 35%, and TTE is present at 5% to 30%. The co-salt system may comprise LiClO4 at a concentration of 0.1M to 1.0M and LiFSI at a concentration of 0.1M to 0.8M.

[0015] According to another aspect of the present disclosure, a method of operating a lithium-sulfur battery is provided. The method includes providing a cathode comprising sulfur. The method further includes providing a lithium-containing anode. The method also includes providing an electrolyte disposed between the cathode and the anode. The electrolyte comprises a solvent system comprising at least one ether, at least one cyclic ether, and at least one fluorinated ether. The electrolyte further comprises a first lithium salt selected from the group consisting of lithium imide salts, lithium halide salts, and lithium oxyanion salts. The electrolyte also comprises a second lithium salt different from the first lithium salt, the second lithium salt selected from the group consisting of lithium imide salts, lithium halide salts, and lithium oxyanion salts.

[0016] According to another aspect of the present disclosure, a lithium-sulfur battery system is provided. The lithium-sulfur battery system includes a cathode comprising sulfur disposed on a carbon-containing material. The lithium-sulfur battery system further includes an anode comprising lithium. The lithium-sulfur battery system also includes a separator disposed between the cathode and the anode. The lithiumsulfur battery system includes an electrolyte in contact with the cathode, the anode, and the separator. In some embodiments, the electrolyte comprises a solvent mixture comprising at least one ether and at least one cyclic ether. The electrolyte further comprises a co-salt combination comprising at least two lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxy anion salts, wherein a first lithium salt is present at a concentration of 0.1 M to 1.2M and a second lithium salt is present at a concentration of 0.1M to 1.0M. The electrolyte may also comprise lithium nitrate (LiNO3) at a concentration of 0.1M to 1.0M and dicyandiamide (DCDA) at a concentration of 0.05M to 0.5M.

[0017] In various embodiments, the lithium-sulfur battery system may be cycled via constant current charge and discharge protocols. During discharge, the voltage may begin at a beginning of discharge voltage and decrease to a discharge cutoff voltage in the range of 1.5V to 2.0V. During charge, the voltage may begin at a beginning of charge voltage and increase to a charge cutoff voltage in the range of 2.3V to 2.6V. The constant current cycling protocol may employ discharge rates ranging from 0.1C to 2C and charge rates ranging from 0.1C to 1C, where the C-rate is defined rclalivc to the theoretical capacity of the sulfur active material within the cathode. The voltage profile during discharge may exhibit characteristic plateaus associated with the electrochemical conversion of sulfur to lithium polysulfide intermediates and ultimately to lithium sulfide, while the voltage profile during charge may exhibit corresponding plateaus associated with the reverse conversion reactions. The co-salt electrolyte compositions described in Table 1 may affect the voltage characteristics during cycling, where certain co-salt combinations may provide reduced voltage hysteresis between charge and discharge, improved voltage stability over extended cycling, or enhanced rate capability at higher C-rates. The cycling performance of the lithium-sulfur battery system, including capacity retention, coulombic efficiency, and voltage characteristics, may be evaluated over hundreds or thousands of chargedischarge cycles to assess the long-term stability of the co-salt electrolyte formulations.

[0018] The foregoing general description of the illustrative embodiments and the following detailed description thereof are merely exemplary aspects of the teachings of this disclosure and are not restrictive.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Non-limiting and non-exhausli vc examples are described with reference to the following figures.

[0020] FIG. 1 illustrates a block diagram of a battery system, according to aspects of the present disclosure.

[0021] FIG. 2 depicts an exploded view of a battery cell, according to an embodiment.

[0022] FIG. 3 shows a graph of voltage versus charge / discharge characteristics for different lithium salt electrolyte compositions, according to aspects of the present disclosure.

[0023] FIG. 4 illustrates a cyclic voltammetry graph for different lithium salt compositions, according to an embodiment.

[0024] FIG. 5 depicts a graph of voltage versus charge-discharge characteristics for various lithium salt compositions, according to aspects of the present disclosure.

[0025] FIG. 6 shows a cyclic voltammetry graph for different lithium salt compositions, according to an embodiment.

[0026] FIG. 7 illustrates a graph of discharge capacity versus C-rate for different battery configurations, according to aspects of the present disclosure.

[0027] FIG. 8 depicts a graph of cycling performance data for different lithium salt compositions, according to an embodiment.

[0028] FIG. 9 shows a graph of discharge capacity measurements at different C-rates for various battery configurations, according to aspects of the present disclosure.

[0029] FIG. 10 illustrates a graph of discharge capacity versus cycle number for different lithium salt compositions, according to an embodiment.

[0030] FIG. 11 depicts a set of graphs showing battery performance characteristics, according to aspects of the present disclosure.

[0031] FIG. 12 shows a set of performance graphs displaying battery characteristics over multiple cycles, according to an embodiment.

[0032] FIG. 13 illustrates a schematic diagram of a lithium-sulfur battery system, according to aspects of the present disclosure.

[0033] FIG. 14 illustrates performance graphs showing electrochemical characteristics of lithium-sulfur battery cells with varying LiTFSI concentrations, according to aspects of the present disclosure.

[0034] FIG. 15 illustrates a voltage drop graph showing voltage drop for different LiTFSI concentrations, according to aspects of the present disclosure.

[0035] FIG. 16 illustrates a graph showing discharge capacity versus cycle number for varying lithium iodide concentrations, according to aspects of the present disclosure.

[0036] FIG. 17 illustrates a graph showing coulombic efficiency versus cycle number for varying lithium iodide concentrations, according to aspects of the present disclosure.

[0037] FIG. 18 illustrates a graph showing discharge capacity versus C-rate for different lithium iodide concentrations, according to aspects of the present disclosure.

[0038] FIG. 19 illustrates performance graphs showing coulombic efficiency and discharge capacity for different baseline salt concentrations, according to aspects of the present disclosure.

[0039] FIG. 20 illustrates performance graphs showing coulombic efficiency and discharge capacity for LiTFSI and LiClO4 compositions, according to aspects of the present disclosure.

[0040] FIG. 21 illustrates performance graphs showing coulombic efficiency and discharge capacity for LiClO4 and LiTFSI co-salt compositions, according to aspects of the present disclosure.

[0041] FIG. 22 illustrates performance graphs showing coulombic efficiency and discharge capacity for LiTFSI and LiFSI co-salt compositions, according to aspects of the present disclosure.

[0042] FIG. 23 illustrates performance graphs showing cycling performance for Lil and LiFSI co-salt compositions, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0043] The present disclosure relates to the field of lithium-sulfur battery systems, specifically focusing on optimizing lithium salt compositions in electrolytes to enhance battery performance, stability, and longevity. This technology has applications ranging from electric vehicles to portable electronics, where high energy density and long-lasting power sources are crucial.

[0044] Current lithium-sulfur battery systems face significant challenges that limit their widespread adoption and commercial viability. These include the polysulfide shuttle effect, rapid capacity decay, poor rate capability, limited cycle life, and safety concerns related to dendrite formation in lithium metal anodes. For instance, in electric vehicle applications, existing lithium-sulfur batteries struggle to maintain consistent performance over extended cycling, limiting their practical energy density and driving range.

[0045] The present disclosure introduces novel electrolyte compositions utilizing co-salt systems comprising at least two lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts. By way of example, and not to be limited solely thereto, the lithium imide salts may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI), the lithium halide salts may include lithium iodide (Lil) and lithium bromide (LiBr), and the lithium oxyanion salts may include lithium perchlorate (LiClO4). These optimized electrolyte formulations significantly improve power capability, energy density, and cycle life of lithium-sulfur cells while mitigating issues such as the polysulfide shuttle effect, electrolyte dryout, and dendrite formation.

[0046] The problem of improved electrochemical characteristics in lithium-sulfur batteries has been explored by many researchers, but often in an incomplete manner. There exists a "triad" of lithium-sulfur battery metrics: charge / discharge rate (power), energy density, and cycle life. All three metrics are needed for commercialization of a lithium-sulfur battery; however, most approaches focus on only one metric at a time. The present disclosure addresses this limitation by providing electrolyte compositions that may simultaneously improve all three metrics. By replacing the incumbent LiTFSI with other salts that may be more power capable or more stable towards a lithium anode, the disclosed systems may achieve better chemical and electrochemical stability and performance - a stark contrast and improvement to conventional systems.

[0047] Furthermore, the present disclosure incorporates a comprehensive approach to electrolyte optimization, exploring various salt concentrations and combinations to achieve superior electrochemical performance. The disclosed battery systems demonstrate enhanced cycling stability, improved rate capability across different C-rates, and higher coulombic efficiency compared to conventional lithium-sulfur batteries. Additionally, the optimized electrolyte compositions offer potential cost advantages and increased safety, making them particularly suitable for large-scale energy storage applications and consumer electronics.

[0048] Still yet, the practical implementation of lithium-sulfur batteries in conventional systems has been hindered by several degradation mechanisms and electrolyte-related challenges. Fxisling lithium-sulfur battery systems have predominantly relied on lithium bis(trifhioromethanesulfonyl)imide (LiTFSI) as the primary lithium salt in the electrolyte formulation, which presents challenges including high molecular weight that increases the overall density of the electrolyte package, classification as a polyfluorinated substance (PFAS) raising environmental and regulatory concerns, and relatively high cost that impacts commercial viability. Additionally, single-salt electrolyte formulations may exhibit inadequate ionic conductivity at certain concentrations, insufficient solid electrolyte interphase formation on the lithium anode, or poor kinetics during charge and discharge processes, while the lithium polysulfide shuttle effect, electrolyte dryout, and dendrite formation collectively limit the achievable energy density, cycle life, and overall performance of these battery systems.

[0049] The present disclosure addresses these challenges through optimized lithium salt compositions employing co-salt systems that combine two or more lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts. These co-salt electrolyte formulations provide synergistic performance improvements over single-salt systems, including enhanced capacity, improved coulombic efficiency retention, extended cycle life, and reduced self-discharge behavior. The electrolyte compositions utilize solvent systems comprising at least one ether, at least one cyclic ether, and at least one fluorinated ether, along with addi lives to further enhance electrochemical performance. By way of example, the lithium imide salts may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium triflate (LiOTf), and lithium bis(fluorosulfonyl)imide (LiFSI), the lithium halide salts may include lithium iodide (Lil) and lithium bromide (LiBr), and the lithium oxyanion saltsmay include lithium perchlorate (LiC104). By way of further example, the ether may include 1 ,2-dimethoxyethane (DME), the cyclic ether may include 1,3-dioxolane (DOL), the fluorinated ether may include l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) or bis(2,2,2-trifluoroethyl) ether (BTFE), and the additives may include lithium nitrate (LiN03) and dicyandiamide (DCDA).

[0050] Furthermore, the present disclosure provides electrolyte formulations that enable reduced PFAS content by incorporating alternative salts such as LiFSI and Lil, which have lower molecular weight and density compared to LiTFSI while maintaining or improving ionic conductivity and cell performance. The co-salt combinations demonstrate unexpected benefits including significantly reduced voltage drop and selfdischarge (such as but not limited to when Lil is incorporated), improved coulombic efficiency retention (such as but not limited to when LiFSI is added to LiC104-based systems), and enhanced capacity delivery (such as but not limited to when LiTFSI and LiFSI are combined at specific ratios), all of which are exemplified and described in greater detail below. Additionally, the relationship between cathode loading levels and optimal salt selection enables tailored electrolyte-cathode pairing for specific applications, where lower loading cathodes paired with Lil-based electrolytes demonstrate improved cycle life and energy retention compared to higher loading configurations with conventional electrolyte formulations.Definitions and Use of Figures

[0051] Some of the terms used in this description are defined below for easy reference. The presented terms and their respective definitions are not rigidly restricted to these definitions — a term may be further defined by the term’s use within this disclosure. The term “exemplary” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Rather, use of the word exemplary is intended to present concepts in a concrete fashion. As used in this application and the appended claims, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or”. That is, unless specified otherwise, or is clear from the context, “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, if X employs A, X employs B, or X employs both A and B, then “X employs A or B” is satis lied under any of the foregoing instances. As used herein, at least one of A or B means at least one of A, or at least one of B, or at least one of both A and B. In other words, this phrase is disjunctive. The articles “a”and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or is clear from the context to be directed to a singular form.

[0052] Various embodiments are described herein with reference to the figures. It should be noted that the figures are not necessarily drawn to scale, and that elements of similar structures or functions are sometimes represented by like reference characters throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the disclosed embodiments — I hey are not representative of an exhaustive treatment of all possible embodiments, and they are not intended to impute any limitation as to the scope of the claims. In addition, an illustrated embodiment need not portray all aspects or advantages of usage in any particular environment.

[0053] An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated. References throughout this specification to “some embodiments” or “other embodiments” refer to a particular feature, structure, material or characteristic described in connection with the embodiments as being included in at least one embodiment. Thus, the appearance of the phrases “in some embodiments” or “in other embodiments” in various places throughout this specification are not necessarily referring to the same embodiment or embodiments. The disclosed embodiments are not intended to be limiting of the claims.Descriptions of Exemplary Embodiments

[0054] FIG. 1 illustrates a block diagram of a battery system 100, in accordance with one embodiment. As an option, the battery system 100 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the battery system 100 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0055] The battery system 100 includes a lithium-sulfur battery 102. The lithiumsulfur battery 102 comprises a cathode 104, an anode 106, and an electrolyte 108. The cathode 104 and anode 106 are arranged to enable electrochemical reactions within the lithium-sulfur battery 102, with the electrolyte 108 facilitating ion transport between them. Additionally (although not shown), the system may include a separator disposed between the cathode and the anode.

[0056] In some cases, the cathode 104 may be a carbon-sulfur composite cathode. The carbon-sulfur composite cathode may provide enhanced conductivity and sulfur utilization, potentially leading to improved battery performance.

[0057] The electrolyte 108 contains a lithium salt composition 110. The lithium salt composition 110 includes at least one of lithium bromide (LiBr), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), or lithium iodide (Lil). These allcrnalivc lithium salts may offer advantages over conventional lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in terms of electrochemical stability and performance.

[0058] The lithium salt composition 110 in the electrolyte 108 is present within a concentration range 112. The concentration range 112 indicates that the lithium salt may be present at a concentration between 0.1 M and 3.0 M in the electrolyte 108. This range of concentrations may allow for optimization of ionic conductivity and electrochemical performance.

[0059] In various embodiments, the electrolyte may contain one or more lithium salts at a total lithium ion concentration ranging from 0.5M to 2.0M. In some cases, a baseline lithium ion concentration ranging from 0.3M to 1.0M may be used. Testing has demonstrated that the lithium- sulfur cell may perform effectively at salt concentrations ranging from 0.1M to 3.0M per lithium salt, with cumulative concentrations potentially exceeding 4.0M. This broad concentration range may provide flexibility in optimizing the electrolyte composition for specific applications and cell formats.

[0060] In various embodiments, the lithium salt composition 110 may include combinations of two or more lithium salts. For example, the electrolyte 108 may contain a mixture of LiTFSI and one of the alternative lithium salts. This approach may allow for fine-tuning of the electrolyte properties to achieve desired performance characteristics. In various embodiments, the concentration range 112 of the lithium salt composition 110 may be adjusted based on the specific cell format or application requirements. For instance, higher concentrations may be used in larger format cells to compensate for increased internal resistance, while lower concentrations may be suitable for smaller, high-power applications.

[0061] In various embodiments, the lithium salts may be ranked based on their performance characteristics in the electrochemical system. For example, the lithium salts may be ranked depending on the specific performance metric being optimized.such as power capability, energy density, or cycle life. In some cases, the electrolyte may comprise dual-salt systems where LiTFSI is combined with one of the alternative lithium salts. Incorporating a dual-salt electrolyte system may provide enhanced ionic conductivity and stability, with improved power performance and reduced shuttle effect.

[0062] More illustrative information will now be set forth regarding various optional architectures and uses in which the foregoing method may or may not be implemented, per the desires of the user. It should be strongly noted that the following information is set forth for illustrative purposes and should not be construed as limiting in any manner. Any of the following features may be optionally incorporated with or without the exclusion of other features described.

[0063] FIG. 2 illustrates an exploded view of a battery cell 200, in accordance with one embodiment. As an option, the battery cell 200 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the battery cell 200 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the descriplion below.

[0064] The battery cell 200 comprises multiple components arranged in a layered configuration. These components include a composite cathode 202, a separator 204, a copper collector 206, a lithium anode 208, and an aluminum collector 210.

[0065] The composite cathode 202 may be positioned at one end of the battery cell 200. In some cases, the composite cathode 202 may contain sulfur as the active material, which may participate in electrochemical reactions during battery operation. The composite cathode 202 may also include conductive additives and binders to enhance electrical conductivity and structural integrity.

[0066] Adjacent to the composite cathode 202, a separator 204 may be placed. The separator 204 may serve as an electrically insulating barrier between the cathode and anode while allowing ion transport. In some cases, the separator 204 may be made of a porous polymer material that may be permeable to the electrolyte.

[0067] On the opposite side of the separator 204, a lithium anode 208 may be positioned. The lithium anode 208 may serve as the source of lithium ions during battery discharge and may accept lithium ions during charging. In some cases, the lithium anode 208 may be composed of lithium metal or a lithium-containing alloy.

[0068] The batery cell 200 may also include current collectors on both sides of the electrode assembly. A copper collector 206 may be placed adjacent to the lithium anode 208. The copper collector 206 may facilitate electron transfer between the external circuit and the anode during battery operation.

[0069] An aluminum collector 210 may be positioned on the opposite end of the battery cell 200, adjacent to the composite cathode 202. The aluminum collector 210 may serve a similar function to the copper collector 206, but for the cathode side of the cell.

[0070] In various embodiments, the solvent ratios and lithium salt ratios in the electrolyte may be changed simultaneously to optimize performance. For example, the salt content may be increased while decreasing the fluoroether content (such as BTFE), or vice versa. Alternatively, the salt content may be increased while adding more DME and reducing the amount of DOL in the solvent mixture. These adjustments may allow for fine-tuning of the electrolyte properties to address specific degradation mechanisms or to optimize performance for particular applications.

[0071] The arrangement of these components within the battery cell 200 may allow for efficient electrochemical reactions and ion transport. During discharge, lithium ions may move from the lithium anode 208 through the separator 204 to the composite cathode 202, while electrons flow through the external circuit. The process may be reversed during charging.

[0072] In various embodiments, the composite cathode 202 may be modified to include different sulfur-containing compounds or additives to enhance performance. For example, the composite cathode 202 may incorporate conductive carbon materials or metal oxides to improve electrical conductivity and sulfur utilization.

[0073] In various embodiments, the separator 204 may be coated or modified to enhance its properties. For instance, the separator 204 may be coated with ceramic particles or polymers to improve thermal stability and reduce the risk of internal short circuits. In various embodiments, the lithium anode 208 may be protected or modified to enhance its stability and reduce dendrite formation. For example, the lithium anode 208 may be coated with a protective layer or alloyed with other metals to improve its cycling performance and safety.

[0074] In various embodiments, the electrolyte may comprise a solvent package including at least one ether, at least one cyclic ether, and at least one fluorinated ether. These solvents may be present in various volume ratios, such as described in Table 2hereinbelow. The electrolyte may further comprise lithium nitrate (LiN03) at a concentration ranging from 0.1M to 1.0M and dicyandiamide (DCDA) at a concentration ranging from 0.05M to 0.5M. In some embodiments, the lithium nitrate may serve as an additive to help form a stable solid electrolyte interphase (SEI) on the lithium anode surface, while the dicyandiamide may function as an additional stabilizing agent in the electrolyte composition. The co-salt compositions within the electrolyte may comprise two or more lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxy anion salts at various concentration combinations, such as described in Table 1 hereinbelow. The solvent formulations and co-salt compositions described in Tables 1 and 2 may be combined in various configurations to achieve the enhanced performance characteristics, including improved capacity, enhanced coulombic efficiency, extended cycle life, and reduced self-discharge.

[0075] FIG. 3 illustrates a graph 300 showing voltage versus charge / discharge characteristics for different lithium salt electrolyte compositions in a battery system 100, in accordance with one embodiment. As an option, the graph 300 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 300 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0076] The graph 300 displays multiple overlapping curves representing the electrochemical performance during both discharge and charge cycles for various lithium salt compositions in the electrolyte 108. The x-axis of the graph 300 shows charge / discharge capacity in mAh, while the y-axis shows voltage in V. These curves provide insights into the behavior of different lithium salt compositions within the concentration range 112 of the battery system 100.

[0077] FIG. 4 illustrates a cyclic voltammetry graph 400 showing electrochemical performance data for different lithium salt compositions in a lithium-sulfur battery system, in accordance with one embodiment. As an option, the cyclic voltammetry graph 400 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the cyclic voltammetry graph 400 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0078] The cyclic voltammetry graph 400 shows reduction and oxidation peaks for different lithium salt compositions in a lithium-sulfur battery system, in accordance with one embodiment. The cyclic voltammetry graph 400 displays current response as a function of applied voltage, where the reduction peaks correspond to the electrochemical conversion of sulfur species during discharge and the oxidation peaks correspond to the reverse conversion reactions during charge. The position, intensity, and shape of the redox peaks may provide insight into the reaction kinetics, reversibility, and electrochemical stability of the different lithium salt compositions within the electrolyte. In various embodiments, co-salt electrolyte formulations as described in Table 1 may exhibit different redox peak characteristics compared to single-salt formulations, where the presence of multiple lithium salt species may affect the peak separation, peak current density, or onset potential of the reduction and oxidation reactions.

[0079] The cyclic voltammetry graph 400 displays multiple overlaid cyclic voltammetry curves plotted with current on the y-axis versus potential on the x-axis. The curves show distinct oxidation and reduction peaks for various lithium salt compositions in the electrolyte of the lithium-sulfur battery system. The graph 400 includes a legend identifying different electrolyte formulations labeled as composition_l, coinposilion_2, composition_3, composition_4, and composition_5.

[0080] In some cases, the cyclic voltammetry graph 400 may reveal improved power capabilities and kinetics for certain salt compositions compared to others. For example, the curves corresponding to composition_2 and composition_5 may exhibit sharper and more pronounced peaks, indicating enhanced electrochemical activity and faster reaction kinetics.

[0081] In some cases, certain lithium salt compositions may exhibit different selfdischarge characteristics when cells are allowed to rest before discharge. For example, cells containing lithium iodide or lithium bromide in the electrolyte may show reduced open-circuit voltage after extended rest periods compared to cells containing only LiTFSI. Despite this initial voltage reduction, the charge and cyclic voltammetry characteristics of these cells may remain favorable, suggesting that certain lithium salt compositions may be suitable for applications where extended storage periods between charge and discharge cycles are expected.

[0082] The oxidation peaks in the cyclic voltammetry graph 400 may correspond to the conversion of lithium sulfides to higher-order polysulfides and elemental sulfurduring the charging process. Conversely, the reduction peaks may represent the stepwise reduction of sulfur to lower-order polysulfides and ultimately to lithium sulfide during discharge.

[0083] As shown, the labeled steps 1-4 may correspond to key redox reactions during battery operation. Step 1 may represent the initial reduction of elemental sulfur to higher-order lithium polysulfides during discharge, characterized by a cathodic peak. Step 2 may indicate further reduction to lower-order polysulfides, potentially shown as a second cathodic peak or shoulder. During charging, step 3 may correspond to the oxidation of lithium sulfide and lower-order polysulfides back to higher-order polysulfides, typically represented by an anodic peak. Step 4 may represent the final oxidation back to elemental sulfur, completing the charge cycle and usually characterized by a second anodic peak. The graph's annotations of improved power and kinetics for certain regions may suggest that some lithium salt compositions enhance the rate or efficiency of these electrochemical processes. The variations in peak heights, shapes, and positions between different electrolyte formulations (composition_l , composition_2, composilion_3, composition_4, composition s) may provide insights into how various lithium salts affect the redox reactions in the system.

[0084] FIG. 5 illustrates a graph 500 showing voltage versus charge-discharge characteristics for different lithium salt compositions in a battery system 100, in accordance with one embodiment. As an option, the graph 500 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 500 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0085] The graph 500 displays multiple curves representing the electrochemical performance of various electrolyte formulations, with the x-axis showing discharge / charge capacity and the y-axis showing potential. These curves provide insights into the behavior of different lithium salt compositions within the concentration range 112 of the battery system 100.

[0086] In various embodiments, the open-circuit voltage (OCV) may indicate a measure of the potential difference between the electrodes when no current is flowing. In some cases, lower OCV values may indicate changes in the electrochemical state of the battery or the presence of self-discharge mechanisms. The "Low OCV" annotation may suggest that one or more of the tested electrolyte compositions result in a reducedopen-circuit voltage compared to the baseline or other formulations. This could be due to factors such as increased solubility of polysulfides in the electrolyte or changes in the cathode-electrolyte interface. The "Really Low OCV" annotation may indicate an even more pronounced reduction in open-circuit voltage for a particular electrolyte composition, potentially signaling more significant changes in the cell chemistry or increased self-discharge rates.

[0087] In various embodiments, the electrolyte may include a solid electrolyte interface (SEI) forming additive to provide enhanced anode protection. The SEL forming additive may help reduce dendrite formation on the lithium anode surface and improve cycling stability over extended charge-discharge cycles. In some cases, the SEI-forming additive may comprise lithium nitrate, which may react with the lithium metal surface to form a protective layer that inhibits further electrolyte decomposition and reduces the growth of lithium dendrites.

[0088] Additionally, in various embodiments, the electrolyte may comprise a concentration gradient of the lithium salt across the separator. The concentration of the lithium salt may be higher near the cathode than near the anode, or alternatively, higher near the anode than near the cathode. The concenlralion gradient may be linear or nonlinear across the separator. In some cases, the electrolyte may comprise a first layer with a first concentration of the lithium salt and a second layer with a second concentration of the lithium salt, the first concentrarion being different from the second concentration. A third layer of electrolyte with a third concentration may also be included. The concentration gradient of the lithium salt may be configured to optimize ion transport across the cell and improve at least one of power capability, energy density, or cycle life of the lithium-sulfur battery system.

[0089] FIG. 6 illustrates a cyclic voltammetry graph 600 showing electrochemical performance characteristics of different lithium salt compositions in a lithium-sulfur battery system, in accordance with one embodiment. As an option, the cyclic voltammetry graph 600 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the cyclic voltammetry graph 600 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0090] The cyclic voltammetry graph 600 displays current on the y-axis versus electrode potential on the x-axis, with multiple overlaid curves representing differentlithium salt electrolyte formulations. The graph 600 includes annotations indicating regions of improved power and improved kinetics for various voltage ranges during both charging and discharging cycles.

[0091] In some cases, the cyclic voltammetry graph 600 may reveal distinct differences in the electrochemical behavior of various lithium salt compositions within the concentration range of the battery system. For example, curves representing lithium iodide (Lil) at concentrations between 0.1 M and 2.0 M may exhibit sharper and more pronounced peaks compared to other salt compositions, indicating enhanced electrochemical activity and faster reaction kinetics.

[0092] The oxidation peaks in the cyclic voltammetry graph 600 may correspond to the conversion of lithium sulfides to higher-order polysulfides and elemental sulfur during the charging process. Conversely, the reduction peaks may represent the stepwise reduction of sulfur to lower-order polysulfides and ultimately to lithium sulfide during discharge. The position and intensity of these peaks may provide insights into the electrochemical behavior of different lithium salt compositions in the electrolyte.

[0093] In some cases, the cyclic voltammetry graph 600 may show improved power capabilities for certain lithium salt compositions. This improvement may be evidenced by higher peak currents and steeper slopes in the voltammogram curves. For instance, lithium perchlorate (LiClO4) at concentrations between 0.1 M and 2.0 M may demonstrate higher peak currents during both oxidation and reduction processes, suggesting enhanced charge transfer kinetics and potentially improved power performance in the battery system.

[0094] In some cases, the addition of lithium bromide or lithium iodide to the electrolyte may help improve kinetics and power capability compared to electrolytes containing only LiTFSI.

[0095] The regions of improved kinetics annotated in the cyclic voltammetry graph 600 may indicate voltage ranges where certain lithium salt compositions facilitate faster electrochemical reactions. These regions may be characterized by narrower peak separations between the oxidation and reduction processes, suggesting more reversible and efficient conversion of active materials in the cathode and anode of the battery cell.

[0096] FIG. 7 illustrates a graph 700 showing discharge capacity versus C-rate for different battery configurations, in accordance with one embodiment. As an option, the graph 700 may be implemented in the context of any one or more of the embodimentsset forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 700 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0097] The graph 700 displays multiple box plots comparing discharge capacity in mAh_g across three different C-rates (0.33C, 0.5C, and 1C) for various battery configurations. The discharge capacity values range from approximately 0 to 600 mAh_g on the verdeal axis. These box plots provide insights into the performance of different lithium salt compositions within the concentration range 112 of the battery system 100 under various discharge rates.

[0098] In some cases, the graph 700 may reveal distinct differences in the discharge capacity of various lithium salt compositions across different C-rates. For example, box plots representing lithium iodide (Lil) at concentrations between 0.1 M and 2.0 M may exhibit higher median discharge capacities compared to other salt compositions, particularly at higher C-rates.

[0099] The battery system 100 may be tested using a rate testing protocol to evaluate the performance of different electrolyte 108 formulations under various discharge rates. This protocol may involve cycling the battery cell 200 at different C-rates to assess how the discharge capacity changes with increasing current demands.

[0100] In some cases, the lithium salt composition 110 comprising lithium perchlorate (LiClO4) at concentrations between 0.1 M and 2.0 M may demonstrate superior rate capability. The graph 700 may show how LiClO4 affects the discharge capacity of the battery system 100 at different C-rates, potentially revealing better capacity retention at higher discharge rates compared to other salt compositions.

[0101] In some cases, the performance at higher C-rates may reveal significant differences between lithium salt compositions. Co-salt electrolyte formulations comprising lithium halide salts may demonstrate improved power capability compared to single-salt electrolyte formulations. This enhanced power performance may be a desired characteristic for applications requiring high discharge rates, such as electric aviation, electric vehicles during acceleration events, or grid storage systems providing frequency regulation services. The improved power capability provided by certain cosalt combinations may also enable optimization of other cell design parameters, potentially contributing to improved gravimetric energy density in practicalapplications. The various co-salt configurations that may provide enhanced power capability are described in Table 1, provided hereinbelow.

[0102] The performance of the battery system 100 at different C -rates may be influenced by factors such as the ionic conductivity of the electrolyte 108 and the kinetics of the electrochemical reactions at the composite cathode 202 and lithium anode 208. Higher C-rates may lead to increased polarization and reduced sulfur utilization, resulting in lower discharge capacities.

[0103] FIG. 8 illustrates a graph 800 showing cycling performance data for different lithium salt compositions in a battery system, in accordance with one embodiment. As an option, the graph 800 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 800 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0104] The graph 800 plots coulombic efficiency (CE) versus cycle number, with multiple data series represented by different colored points and lines tracking the performance over a wide range of cycles. The graph 800 shows several distinct performance curves that demonstrate varying degrees of stability and efficiency for different lithium salt compositions in the electrolyte of the battery system.

[0105] In some cases, the graph 800 may reveal that certain lithium salt compositions in the electrolyte maintain higher coulombic efficiency values near 1.0 over the course of cycling. For example, a lithium salt composition comprising lithium bis(fluorosulfonyl)imide (LiFSI) at a concentration between 0.1 M and 2.0 M may exhibit a more stable coulombic efficiency curve compared to other compositions.

[0106] In some cases, the coulombic efficiency may be highest with electrolytes containing lithium bis(fluorosulfonyl)imide (LiFSI), which may indicate improved reversibility of the electrochemical reactions. Doping a small amount of LiFSI into the electrolyte may be helpful for maintaining long cycle life while achieving high coulombic efficiency. Conversely, lithium bromide at certain concentrations may increase the polysulfide shuttle effect, resulting in a decrease in coulombic efficiency. These observations may suggest that the selection of lithium salt composition should be tailored to the specific performance requirements of the intended application.

[0107] The graph 800 may also indicate that some lithium salt compositions result in declining coulombic efficiency over the cycling period. For instance, a lithium saltcomposition containing lithium bromide (LiBr) at a concentration between 0.1 M and 3.0 M may show a gradual decrease in coulombic efficiency as the cycle number increases.

[0108] FIG. 9 illustrates a graph 900 showing discharge capacity measurements at different C-rates for various battery configurations, in accordance with one embodiment. As an option, the graph 900 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 900 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0109] The graph 900 displays box plot data comparing discharge capacity in mAh / g across three different C-rates (0.33C, 0.5C, and 1C) for multiple electrolyte formulations in the battery system. The discharge capacity values are shown on the vertical axis, while the C-rate values are displayed on the horizontal axis. This visualization allows for a comprehensive analysis of how various lithium salt compositions within the concentration range of the electrolyte perform under different discharge rates.

[0110] FIG. 10 illustrates a graph 1000 showing discharge capacity versus cycle number for different lithium salt compositions in a battery system, in accordance with one embodiment. As an option, the graph 1000 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 1000 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0111] The graph 1000 illustrates the cycling performance of multiple cells over a wide range of cycles, with the discharge capacity measured in mAh / g plotted on the vertical axis and the cycle number plotted on the horizontal axis. The graph 1000 displays several distinct curves representing different electrolyte formulations, with each curve showing a characteristic capacity fade profile over the cycling period.

[0112] In some cases, the graph 1000 may reveal that certain lithium salt compositions in the electrolyte maintain higher discharge capacities over the course of cycling. For example, a lithium salt composition comprising lithium iodide (Lil) at a concentration between 0.1 M and 2.0 M may exhibit a more stable capacity retention curve compared to other compositions.

[0113] In some cases, lithium iodide-based electrolytes may demonstrate unexpectedly high capacity retendon and cycling stability. The complete replacement of LiTFSI with alternative lithium salts, rather than merely supplementing LiTFSI with co- salts, may provide superior power capability in certain applications. These observations may suggest that full replacement of the incumbent lithium salt may be more effective than partial replacement for achieving optimal performance in lithiumsulfur battery systems.

[0114] The graph 1000 may also indicate that some lithium salt compositions result in more rapid capacity fade over the cycling period. For instance, a lithium salt composition containing lithium bromide (LiBr) at a concentration between 0.1 M and 3.0 M may show a steeper decline in discharge capacity as the cycle number increases.

[0115] FIG. 11 illustrates a set of graphs 1100 showing battery performance characteristics, in accordance with one embodiment. As an option, the set of graphs 1100 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the set of graphs 1100 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0116] The set of graphs 1100 includes four separate plots displaying discharge capacity, coulombic efficiency, average potential, and discharge capacity versus C-rate for different lithium salt electrolyte compositions in the battery system. These graphs track performance metrics over multiple charge-discharge cycles, with different colored traces representing various electrolyte formulations as indicated in the legend.

[0117] In some cases, the discharge capacity plot in the set of graphs 1100 may reveal distinct differences in capacity retention for various lithium salt compositions within the concentration range of the electrolyte. For example, certain electrolyte formulations may exhibit higher initial discharge capacities and better capacity retention over cycling compared to others. These differences may be attributed to variations in the ionic conductivity and electrochemical stability of the different lithium salt compositions in the electrolyte.

[0118] The coulombic efficiency plot in the set of graphs 1100 may provide insights into the reversibility of the electrochemical reactions occurring within the battery cell. Higher and more stable coulombic efficiency values may indicate more efficient utilization of active materials and reduced parasitic reactions. In some cases, certainlithium salt compositions in the electrolyte may demonstrate consistently higher coulombic efficiency values, suggesting improved overall battery performance and longevity.

[0119] The average potential plot in the set of graphs 1100 may show how different lithium salt compositions in the electrolyte affect the operating voltage of the battery system over multiple cycles. Variations in average potential may be indicative of changes in the electrochemical processes occurring at the composite cathode and lithium anode. In some cases, certain electrolyte formulations may maintain a more stable average potential over cycling, which may be desirable for consistent battery performance in various applications.

[0120] In various embodiments, changes in the average potential during charge and discharge may also infer that the resistance of the cell has changed or that the speciation of the lithium polysulfide redox reactions has been altered. The co-salt electrolyte compositions described in Table 1 may be configured to reduce and oxidize lithium polysulfides more efficiently compared to single-salt formulations, potentially contributing to improved voltage stability and reduced polarization over extended cycling.

[0121] The discharge capacity versus C-rate plot in the set of graphs 1100 may illustrate the rate capability of the battery system with different lithium salt compositions in the electrolyte. This plot may reveal how well various electrolyte formulations maintain discharge capacity at higher C-rates, which is crucial for applications requiring rapid charge and discharge capabilities. In some cases, certain lithium salt compositions may demonstrate superior rate performance, maintaining higher discharge capacities across a range of C-rates compared to other formulations.

[0122] In various embodiments, the voltage profile during discharge may exhibit characteristic plateaus corresponding to different stages of the sulfur reduction process. The first plateau, typically occurring at higher voltages around 2.3 V, may correspond to the reduction of elemental sulfur to higher-order polysulfides. The second plateau, typically occurring at lower voltages around 2.1 V, may correspond to the further reduction of polysulfides to lithium sulfide. At higher discharge rates, electrolytes containing only LiTFSI may begin to lose the second voltage plateau, indicating incomplete sulfur utilization. Electrolytes containing alternative lithium salts such as lithium iodide or lithium perchlorate may maintain both voltage plateaus even atelevated discharge rates, suggesting improved reaction kinetics and / or altered reduction pathways that enable more complete sulfur utilization.

[0123] FIG. 12 illustrates a set of performance graphs 1200 showing battery characteristics over multiple cycles, in accordance with one embodiment. As an option, the performance graphs 1200 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 1200 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0124] The performance graphs 1200 include four separate plots displaying discharge capacity, coulombic efficiency, average potential, and discharge capacity versus C-rate for various electrolyte compositions in the battery system 100. The graphs 1200 track performance metrics across a wide range of cycles, with different colored traces representing different electrolyte formulations being tested.

[0125] In some cases, the discharge capacity plot in the performance graphs 1200 may reveal distinct differences in capacity retention among various lithium salt compositions within the concentration range 112 of the electrolyte 108. For example, certain electrolyte formulations may exhibit more stable capacity retention over the extended cycling period, while others may show more rapid capacity fade.

[0126] The coulombic efficiency plot in the performance graphs 1200 may provide insights into the reversibility of the electrochemical reactions occurring within the battery cell 200 over extended cycling. Electrolyte compositions that maintain higher and more stable coulombic efficiency values may indicate reduced side reactions and improved long-term stability of the battery system 100.

[0127] In some cases, the average potential plot in the performance graphs 1200 may demonstrate how different lithium salt compositions in the electrolyte 108 affect the overall cell voltage during extended cycling. Changes in average potential over time may be indicative of shifts in the electrochemical behavior of the composite cathode 202 or lithium anode 208.

[0128] In various embodiments, the different behaviors observed for various lithium salt compositions may inform the selection of electrolyte formulations for specific applications. For applications requiring high power capability and rapid charge-discharge rates, lithium iodide-based electrolytes may be preferred. For applications requiring high coulombic efficiency and minimal self-discharge, lithiumbis(fluorosulfonyl)imide-based electrolytes may be more suitable. For applications requiring a balance of performance characteristics, dual-salt systems combining LiTFSI with one or more alternative lithium salts may provide optimal results. The selection of lithium salt composition may also be influenced by cost considerations, safety requirements, and compatibility with other cell components.

[0129] The discharge capacity versus C-rate plot in the performance graphs 1200 may illustrate how the rate capability of the battery system 100 evolves over extended cycling for different electrolyte formulations. This information may be valuable for understanding how various lithium salt compositions in the electrolyte 108 maintain power performance over the battery's lifetime.

[0130] The extended cycling data presented in the performance graphs 1200 may be used to identify potential degradation mechanisms associated with different lithium salt compositions in the electrolyte 108. For instance, a gradual decrease in discharge capacity coupled with declining coulombic efficiency may indicate ongoing side reactions or active material loss in the composite cathode 202 or lithium anode 208.

[0131] In various embodiments, the salt content in the lithium salt composition 110 may be increased while simultaneously adjusting the solvent ratios in the electrolyte 108. For example, the concentration of lithium salts may be increased while adding more 1 ,2-dimethoxyethane (DME) and reducing the amount of 1,3-dioxolane (DOL) in the solvent mixture. This modification may potentially enhance the ionic conductivity and long-term stability of the electrolyte 108, leading to improved cycling performance as observed in the performance graphs 1200.

[0132] In various embodiments, the solvent ratios and lithium salt ratios in the electrolyte 108 may be changed simultaneously to optimize the long-term performance of the battery system 100. For instance, the salt content may be increased while decreasing the content of bis(2,2,2-trifluoroethyl) ether (BTFE) or 1, 1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in the solvent mixture, or vice versa. These adjustments may allow for fine-tuning of the electrolyte properties to address specific degradation mechanisms observed during extended cycling, potentially leading to enhanced performance across the metrics displayed in the performance graphs 1200.

[0133] The present disclosure addresses significant challenges in lithium-sulfur battery technology that have long hindered its widespread adoption and commercial viability. Prior art solutions have struggled to effectively mitigate issues such as thepolysulfide shuttle effect, rapid capacity decay, poor rate capability, and limited cycle life. Conventional lithium-sulfur battery systems often face limitations in maintaining consistent performance over extended cycling, particularly in applications requiring high energy density and long-term stability. As a result, they frequently fail to achieve the theoretical energy density of 2600 Wh / kg, limiting their practical implementation in electric vehicles, portable electronics, and large-scale energy storage systems.

[0134] The disclosed lithium-sulfur battery system overcomes these deficiencies through a novel approach that optimizes the lithium salt composition in the electrolyte. By incorporating alternative lithium salts such as LiBr, LiC104, LiFSI, and Lil, either individually or in combination with conventional LiTFSI, the system achieves a level of electrochemical performance previously unattainable. The optimized electrolyte formulations significantly improve power capability, energy density, and cycle life while mitigating issues such as the polysulfide shuttle effect, electrolyte dryout, and dendrite formation. This innovative approach not only enhances the practical energy density of lithium-sulfur batteries but also leads to improved cycling stability, better rate capability across different C-rates, and higher coulombic efficiency. By addressing multiple degradation mechanisms simultaneously, the present disclosure effectively resolves the longstanding issues of performance inconsistency and limited longevity that have plagued prior art lithium-sulfur battery systems.

[0135] In various embodiments, the high power performance demonstrated by certain lithium salt compositions may directly enable higher practical energy densities in lithium-sulfur battery systems. Co-salt electrolyte formulations as described in Table 1 that maintain high discharge capacity at elevated C-rates may provide flexibility in cell design optimization, potentially enabling configurations that balance power capability with gravimetric energy density (Wh / kg). This relationship between power capability and practical energy density may be particularly relevant for applications such as electric vehicles and portable electronics, where both high power and high energy density are desired.

[0136] FIG. 13 illustrates a lithium-sulfur battery system 1300, in accordance with one embodiment. As an option, the lithium-sulfur battery system 1300 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the lithium-sulfur battery system 1300 may be implemented in the context of any desiredenvironment. Further, the aforementioned definitions may equally apply to the description below.

[0137] The lithium-sulfur battery system 1300 includes a sulfur-based cathode 1302, a separator / electrolyte region 1304, and a lithium-based anode 1306. The sulfurbased cathode 1302 is positioned on one side of the lithium-sulfur battery system 1300 and contains sulfur particles distributed within a matrix structure. In some cases, the sulfur-based cathode 1302 may include conductive carbon materials to enhance electrical conductivity and sulfur utilization throughout the electrode structure.

[0138] In various embodiments, the conductive carbon materials within the sulfurbased cathode 1302 may comprise three-dimensional (3D) graphene structures. The 3D graphene may provide a high surface area scaffold for hosting the sulfur particles, where interconnected graphene sheets form a porous network that facilitates electron transport and electrolyte infiltration throughout the cathode structure. The 3D graphene architecture may comprise graphene sheets arranged in various orientations, including curved, folded, and interconnected configurations that create hierarchical porosity within the sulfur-based cathode 1302. The porous nature of the 3D graphene scaffold may enable higher sulfur loading while maintaining adequate electrochemical accessibility of the sulfur active material, as the interconnected pore network provides pathways for lithium ion transport during charge and discharge cycles. In some cases, the 3D graphene may help contain sulfur and lithium polysulfide species within the sulfur-based cathode 1302, potentially reducing the migration of polysulfides into the separator / electrolyte region 1304 and mitigating the polysulfide shuttle effect. The combination of 3D graphene cathode structures with the co-salt electrolyte formulations described in Table 1 may provide synergistic benefits, where the enhanced polysulfide containment provided by the 3D graphene architecture complements the voltage drop reduction and coulombic efficiency improvements provided by the co-salt systems within the separator / electrolyte region 1304.

[0139] Further, the 3D graphene structures and methods of making the same as described in U.S. Patent No. 11,656,070, which is hereby incorporated by reference in its entirety, may be equally applied to the sulfur-based cathode 1302 of the present disclosure.

[0140] The lithium-based anode 1306 is positioned on the opposite side of the lithium-sulfur battery system 1300 from the sulfur-based cathode 1302. The lithium-based anode 1306 features a layered structure that serves as the source of lithium ions during battery discharge and accepts lithium ions during charging operations.

[0141] The separator / electrolyte region 1304 is disposed between the sulfur-based cathode 1302 and the lithium-based anode 1306. The separator / electrolyte region 1304 facilitates ion transport between the sulfur-based cathode 1302 and the lithium-based anode 1306 during charge and discharge cycles of the lithium-sulfur battery system 1300. Within the separator / electrolyte region 1304, a lithium co-salt mixture is present, depicted as molecular structures with positive and negative charge indicators representing the ionic species in the electrolyte.

[0142] The separator / electrolyte region 1304 may contain various solvent systems to support the lithium co-salt mixture and facilitate electrochemical reactions. In some cases, the lithium-sulfur battery system 1300 may utilize a solvent system comprising at least one ether, at least one cyclic ether, and at least one fluorinated ether at various volume ratios as described in Table 2, hereinbelow. By way of example, the solvent system may comprise 1 ,2-dimethoxyethane (DME) as the ether, 1,3-dioxolane (DOL) as the cyclic ether, and l,l,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) or bis(2,2,2-trifluoroethyl) ether (BTFE) as the fluorinated ether.

[0143] In some cases, the lithium-sulfur battery system 1300 may utilize a solvent system comprising at least one ether, at least one cyclic ether, and at least one fluorinated ether at various volume ratios. The ether component may be present at 50% to 80% by volume, the cyclic ether component may be present at 10% to 35% by volume, and the fluorinated ether component may be present at 5% to 30% by volume. The selection of solvent ratios may affect overall cell performance, and salt concentration optimization may differ between various solvent configurations. In other cases, the lithium-sulfur battery system 1300 may utilize binary solvent systems comprising an ether and a fluorinated ether without a cyclic ether component, where the ether may be present at 50% to 80% by volume and the fluorinated ether may be present at 20% to 50% by volume.

[0144] Additionally, the separator / electrolyte region 1304 may utilize solvent systems comprising two, three, or four solvent components selected from ethers, cyclic ethers, and fluorinated ethers. The separator / electrolyte region 1304 may comprise a primary lithium salt selected from lithium imide salts, lithium halide salts, or lithium oxyanion salts at a concentration ranging from 0.1M to 1.5M. In some cases, the primary lithium salt may be combined with one or more addilional lithium salts to formco-salt systems that provide enhanced coulombic efficiency and capacity retention. The various co-salt system configurations are described in Table 1, also hereinbelow.

[0145] In some embodiments, the separator / electrolyte region 1304 may include lithium nitrate (LiNO3) at a concentration ranging from 0.1M to 1.0M as an additive. The lithium nitrate may serve to form a stable solid electrolyte interphase on the surface of the lithium-based anode 1306, which may inhibit further electrolyte decomposition and reduce the growth of lithium dendrites during cycling. Additionally, the separator / electrolyte region 1304 may include dicyandiamide (DCDA) at a concentration ranging from 0.05M to 0.5M as an additive. The dicyandiamide may function as a stabilizing agent in the electrolyte composition, potentially contributing to improved cycling stability and reduced degradation of the electrolyte over extended charge-discharge cycles.

[0146] The lithium-sulfur battery system 1300 may be configured in various cell formats depending on the intended application and testing requirements. In some cases, the lithium-sulfur battery system 1300 may be configured as a coin cell for initial screening and development purposes. In other cases, the lithium-sulfur battery system 1300 may be configured as a multi-layer pouch cell, which may provide a larger form factor suitable for validation testing. In further cases, the lithium-sulfur battery system 1300 may be configured as an amp-hour level cell, which may enable evaluation of electrolyte performance at scales more representative of commercial applications.

[0147] For pouch cell configurations, the lithium-sulfur battery system 1300 may operate under applied pressure ranging from 10 psi to 100 psi. In some cases, an applied pressure of 30 psi to 50 psi may help maintain intimate contact between the sulfurbased cathode 1302, the separator / electrolyte region 1304, and the lithium-based anode 1306 throughout cycling. The applied pressure may also help mitigate volume changes that occur during the conversion reactions between sulfur and lithium sulfide, potentially improving capacity retention and cycle life of the lithium-sulfur battery system 1300.

[0148] The lithium co-salt mixture within the separator / electrolyte region 1304 provides enhanced benefits to the lithium-sulfur battery system 1300. For example, as illustrated in FIG. 13, these enhanced benefits include improved capacity, enhanced coulombic efficiency, extended cycle life, and reduced self-discharge. The improved capacity may result from synergistic interactions between the multiple lithium salts in the co-salt mixture, which may facilitate more complete ulilizalion of the sulfur activematerial in the sulfur-based cathode 1302. The enhanced coulombic efficiency may arise from reduced parasitic reactions and improved reversibility of the electrochemical processes occurring at both the sulfur-based cathode 1302 and the lithium-based anode 1306.

[0149] The extended cycle life provided by the lithium co-salt mixture may result from improved stability of the solid electrolyte interphase on the lithium-based anode 1306 and reduced degradation of the electrolyte components over repeated chargedischarge cycles. The reduced self-discharge may be attributed to decreased polysulfide shuttle effect, where the lithium co-salt mixture may help suppress the migration of dissolved polysulfide species from the sulfur-based cathode 1302 to the lithium-based anode 1306 during rest periods.

[0150] The lithium-sulfur battery system 1300 addresses challenges that have limited the practical implementation of lithium-sulfur battery technology. Prior approaches using single-salt electrolyte formulations have struggled to simultaneously achieve high capacity, high coulombic efficiency, long cycle life, and low selfdischarge. The co-salt approach employed in the lithium-sulfur battery system 1300 enables optimization of multiple performance parameters through careful selection of salt combinations and concentration ratios, providing a pathway toward practical lithium-sulfur batteries with energy densities approaching the theoretical limit of 2600 Wh / kg.

[0151] In various embodiments, the solvent ratios within the separator / electrolyte region 1304 may be adjusted based on the specific lithium salt combination employed. For example, when using lithium halide salt-based co-salt systems, certain solvent ratios may provide different performance characteristics compared to other ratios. The relationship between solvent composition and salt selection may enable further optimization of the lithium-sulfur battery system 1300 for specific applications.

[0152] In various embodiments, the cathode loading in the sulfur-based cathode 1302 may influence the selection of lithium salt combinations within the separator / electrolyte region 1304. Lower loading cathodes in the range of 2.0 to 4.0 mg / cm2 may demonstrate improved performance with lithium halide salt-based electrolytes compared to higher loading cathodes in the range of 4.0 to 7.0 mg / cm2. Conversely, higher loading cathodes may demonstrate improved performance with lithium imide salt-based electrolytes. This relationship between cathode loading andelectrolyte salt selection may enable tailored electrolyte-cathode pairing for specific applications requiring either maximized energy density or extended cycle life.

[0153] In various embodiments, the lithium-sulfur battery system 1300 may incorporate three-salt, four-salt, or five-salt combinations within the separator / electrolyte region 1304 to achieve cumulative benefits from each salt's properties. For example, a combination of lithium salts selected from lithium imide salts, lithium halide salts, and lithium oxy anion salts at various concentration ratios may provide a balance of capacity, coulombic efficiency, and cycle life characteristics.

[0154] As shown below, the multi-salt configurations are described in Table 1. The multi-salt approach may enable broader operating windows and more robust performance across varying temperature and rate conditions compared to single-salt or dual-salt formulations. In various embodiments, the co-salt composition within the electrolyte may comprise two or more lithium salts selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts at various concentration combinations.

[0155] As such, Table 1 provides exemplary co-salt electrolyte formulations showing representative single-salt, two-salt, three-salt, and four-salt systems with corresponding concentrations for each lithium salt component. The lithium imide salts may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and / or lithium triflate (LiOTf). The lithium halide salts may include lithium iodide (Lil) and lithium bromide (LiBr). The lithium oxyanion salts may include lithium perchlorate (LiClO4). The formulations shown in Table 1 are exemplary and non-limiting, and other concentration combinations within the ranges disclosed herein may be employed. In some cases, the total lithium salt concentration may range from 0.5M to 1.2M, though concentrations outside this range may also be suitable for particular applications.TABLE 1: CO-SALT ELECTROLYTE FORMULATIONS

[0156] In various embodiments, the solvent system within the electrolyte may comprise one or more organic solvents selected from ethers, fluorinated ethers, and cyclic ethers at various volume ratios. Table 2 provides exemplary solvent formulations showing representative binary, ternary, and quaternary solvent systems with corresponding volume percentages for each solvent component.

[0157] In various embodiments, the ethers may include 1 ,2-dimethoxyethane (DME). The cyclic ethers may include 1,3 -dioxolane (DOL). The fluorinated ethers may include bis(2,2,2-trifluoroethyl) ether (BTFE) and l,l,2,2-tetrafhioroethyl-2,2,3,3-tetrafluoropropyl ether (TTE). The formulations shown in Table 2 are exemplary and non-limiting, and other volume ratios within the ranges disclosed herein may be employed. In some cases, the DME content may range from 50% to 80% by volume, the DOL content may range from 0% to 30% by volume, and the fluorinated ether content may range from 10% to 30% by volume, though compositions outside these ranges may also be suitable for particular applications.TABLE 2: SOLVENT SYSTEM FORMULATIONS

[0158] FIG. 14 illustrates performance graphs 1400 showing electrochemical characteristics of lithium-sulfur battery cells with varying concentrations of LiTFSI salt in the electrolyte, in accordance with one embodiment. As an oplion, the performance graphs 1400 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 1400 may be implemented in the context of any desired environment. Further, the aforementioned del'inilions may equally apply to the description below.

[0159] As shown, FIG. 14 illustrates performance graphs 1400 showing electrochemical characteristics of lithium-sulfur battery cells with varying concentrations of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in the electrolyte. The performance graphs 1400 compare five different electrolyte compositions, where composition_l represents a baseline concenlralion of LiTFSI, composition_2 represents an increased concentration of LiTFSI, composition ^ represents a further increased concenlralion of LiTFSI, composition_4 represents a further increased concentration of LiTFSI, and composition_5 represents a further increased concentration of LiTFSI.

[0160] An upper left plot shows specific capacity in mAh / g as a function of cycle number, demonstrating that higher LiTFSI concentrations provide higher capacity over cycling. This result was unexpected, as conventional understanding would suggest that increasing salt concentration beyond a certain threshold would negatively impact cell performance due to increased viscosity and reduced ionic mobility.

[0161] An upper right plot displays coulombic efficiency as a function of cycle number, showing that coulombic efficiency trends with LiTFSI content, with higher concentrations maintaining efficiency closer to unity over extended cycling.

[0162] A lower left plot presents average potential as a function of cycle number, indicating voltage characteristics across the different salt concentrations. A lower right plot shows specific capacity in mAh / g as a function of C-rate, with data points at various discharge rates demonstrating rate capability performance for the various electrolyte compositions.

[0163] The performance graphs 1400 demonstrate that increasing the concentration of LiTFSI within the electrolyte formulation unexpectedly provides improved capacity compared to lower concentrations, while coulombic efficiency retention trends with LiTFSI content. The data indicates that an intermediate -to-higher concentration range may represent an optimal configuration for delivered capacity over cycling, though the specific optimal concentration may vary depending on other cell parameters such as cathode loading, solvent composition, and cell format.

[0164] The results presented in the performance graphs 1400 support the selection of lithium salt concentrations within the ranges described in Table 1 to achieve desired performance characteristics for specific applications.

[0165] Still yet, the performance graphs 1400 demonstrate that the relationship between LiTFSI concentration and electrochemical performance in the lithium-sulfur battery system 1300 is non-linear and may exhibit an optimum within the tested concentration range. The unexpected capacity improvements at higher LiTFSI concentrations may be attributed to enhanced solid electrolyte interphase formation on the lithium-based anode 1306, improved polysulfide management within the separator / electrolyte region 1304, changes in the solvation structure of lithium ions that affect reaction kinetics at the sulfur-based cathode 1302, or combinations thereof.

[0166] FIG. 15 illustrates a voltage drop graph 1500 of voltage drop measurements for different LiTFSI conccnlralions in the electrolyte, in accordance with one embodiment. As an option, the voltage drop graph 1500 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the voltage drop graph 1500 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0167] As shown, the voltage drop graph 1500 displays voltage drop over a prescribed rest period measured in volts on the vertical axis as a function of composition for different LiTFSI conccnlralions in the separator / electrolyte region 1304. The vertical axis of the voltage drop graph 1500 ranges from approximately 0.84 V to 0.92V, providing resolution to distinguish between the voltage drop characteristics of different electrolyte formulations. The horizontal axis of the voltage drop graph 1500 represents composition, with four different electrolyte compositions shown as bar representations corresponding to varying LiTFSI concentrations.

[0168] The voltage drop measurement serves as a performance metric for selfdischarge evaluation in the lithium-sulfur battery system 1300. Self-discharge in lithium-sulfur batteries may result from the polysulfide shuttle effect, where dissolved polysulfide species migrate from the sulfur-based cathode 1302 through the separator / electrolyte region 1304 to the lithium-based anode 1306 during rest periods. Additionally, voltage drop may result from the formation of cathode electrolyte interphase (CEI) on the sulfur-based cathode 1302 and solid electrolyte interphase (SEI) on the lithium-based anode 1306, which may change the difference in energy between the electrodes and contribute to the observed voltage reduction during rest periods.

[0169] As shown, a first composition in the voltage drop graph 1500 corresponds to a baseline concentration of LiTFSI and exhibits a voltage drop of approximately 0.90 V. A second composition corresponds to an increased concentration of LiTFSI and exhibits a voltage drop of approximately 0.89 V, which is comparable to the baseline concentration. A third composition corresponds to a further increased concentration of LiTFSI and exhibits the highest voltage drop of approximately 0.91 V among the compositions tested. A fourth composition corresponds to a further increased concentration of LiTFSI and exhibits the lowest voltage drop of approximately 0.88 V.

[0170] The voltage drop graph 1500 illustrates that varying the LiTFSI concentration in the separator / electrolyte region 1304 affects the voltage drop behavior of the lithium-sulfur battery system 1300. The fourth composition showing reduced voltage drop compared to the other compositions tested indicates that certain LiTFSI concentrations may provide improved self-discharge characteristics. Further, the reduced voltage drop observed for certain compositions may be attributed to improved self-discharge characteristics, enhanced solid electrolyte interphase (SEI) formation on the lithium-based anode 1306, or a combination of both mechanisms.

[0171] The observation that the third composition exhibits the highest voltage drop while the fourth composition exhibits the lowest voltage drop suggests a nonmonotonic relationship between LiTFSI concentration and self-discharge behavior in the lithium-sulfur battery system 1300. This non-monotonic relationship may indicate that competing mechanisms influence self-discharge at different concentration regimes,where increased salt concentration may initially promote polysulfide dissolution and shuttle but at higher concentrations may suppress shuttle through viscosity effects or modified polysulfide speciation. In some embodiments, this non-monotonic relationship represents an unexpected result, as conventional understanding would suggest a more linear relationship between salt concentrarion and self-discharge behavior. The reduced voltage drop at certain concentrations may indicate a favorable balance where improved self-discharge characteristics, enhanced solid electrolyte interphase (SEI) formation, or a combination of both mechanisms contribute to the observed performance improvement.

[0172] FIG. 16 illustrates a graph 1600 showing discharge capacity in mAh / g as a function of cycle number for lithium-sulfur battery cells with varying lithium iodide concentrations in the electrolyte, in accordance with one embodiment. As an option, the graph 1600 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 1600 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0173] As shown, two curves are provided in the graph 1600 representing different electrolyte compositions with varying concentrations of lithium iodide (Eil) as a single salt system within the separator / electrolyte region 1304 of the lithium- sulfur battery system 1300. A solid line in the graph 1600 corresponds to a baseline concentration of Eil, a long-dashed line corresponds to an increased concentration of Lil, and a short-dashed line corresponds to a further increased concentration of Lil. The vertical axis of the graph 1600 represents discharge capacity ranging from approximately 200 mAh / g to 600 mAh / g, while the horizontal axis represents cycle number extending over an extended cycling period.

[0174] The separator / electrolyte region 1304 may include lithium iodide (Lil) at various concentrations as a single salt system. As shown in the graph 1600, composition_l represents a baseline concentration of Lil for evaluating the effects of lithium iodide concentration on electrochemical performance in the lithium-sulfur battery system 1300. Composition_2 represents an increased concentration of Lil compared to composition_l. Composition_2 provides intermediate performance characteristics between the baseline concentration and the further increased concentration. The graph 1600 demonstrates that composition_2 maintains higherdischarge capacity over extended cycling compared to composition !, indicating improved capacity retention at the increased concentrarion level.

[0175] The relationship between Lil concentration and electrochemical performance in the lithium- sulfur battery system 1300 exhibits concentrationdependent behavior where increasing Lil concentration decreases voltage drop and increases coulombic efficiency (CE) retention. The decreased voltage drop observed at higher Lil concentrations may be attributed to improved kinetics facilitated by the iodide anion, which may participate in redox mediator reactions that enhance charge transfer at the sulfur-based cathode 1302. The increased CE retention at higher Lil concentrations may result from reduced polysulfide shuttle effect, where the lithium iodide may help suppress the migration of dissolved polysulfide species from the sulfurbased cathode 1302 to the lithium-based anode 1306 during cycling.

[0176] The graph 1600 demonstrates that all two Lil concentrations achieve similar initial discharge capacities near 600 mAh / g during early cycling, indicating that the initial sulfur utilization is comparable across the concentration range tested.

[0177] FIG. 17 illustrates a graph 1700 showing Coulombic Efficiency as a function of Cycle for lithium-sulfur battery cells with varying concentrations of lithium iodide (Lil) in the electrolyte, in accordance with one embodiment. As an option, the graph 1700 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 1700 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0178] The graph 1700 displays Coulombic Efficiency on the vertical axis with values ranging from 0.7 to 1.00, while the horizontal axis represents Cycle number extending over an extended cycling period. Three curves are shown in the graph 1700, each corresponding to a different electrolyte composition within the separator / electrolyte region 1304 of the lithium-sulfur battery system 1300. A solid line in the graph 1700 represents a baseline concentration of Lil composition_l, a long-dashed line represents an increased concentration of Lil composition_2, and a short-dashed line represents a further increased concentration of Lil composition_3.

[0179] The graph 1700 demonstrates that all three Lil compositions begin with Coulombic Efficiency values near 1.00 at early cycles, indicating comparable initial reversibility of the electrochemical reactions occurring at the sulfur-based cathode 1302and the lithium-based anode 1306. As cycling progresses, the Coulombic Efficiency decreases for all compositions, with the baseline concentration of Lil at composition_l showing the most rapid decline in Coulombic Efficiency over the cycling period. The composition with the further increased concentration of Lil at composition_3 maintains higher Coulombic Efficiency retention over extended cycling compared to the other compositions tested.

[0180] FIG. 18 illustrates a graph 1800 showing discharge capacity in mAh / g as a function of C-Rate for three different electrolyte compositions with varying concentrations of lithium iodide (Lil), in accordance with one embodiment. As an option, the graph 1800 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the graph 1800 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0181] The graph 1800 presents data at three C-Rates along the horizontal axis: 0.2C, 0.5C, and 1C, with discharge capacity values ranging from approximately 480 mAh / g to 600 mAh / g along the vertical axis. Three compositions are compared in the graph 1800: a first composition representing a baseline concentration of Lil composition_l shown with unfilled rectangular bars, a second composition representing an increased concentration of Lil composition_2 shown with diagonal line-filled bars, and a third composition representing a further increased concentration of Lil composition_3 shown with crosshatch-filled bars. The graph 1800 enables evaluation of how the lithium-sulfur battery system 1300 performs at rates up to 1C for high-rate performance evaluation across the different Lil concentrations within the separator / electrolyte region 1304.

[0182] At 0.2C, the discharge capacity values shown in the graph 1800 are highest for all three compositions, with the second composition Lil composition_2 and the third composition Lil composition_3 showing higher capacity than the first composition Lil composition_l.

[0183] At 0.5C the discharge capacity decreases for all compositions compared to 0.2C, with the second composition Lil composition_2 and the third composition Lil composition_3 again demonstrating higher capacity than the first composition Lil composition_l.

[0184] At 1C, the discharge capacity shown in the graph 1800 is lowest for all compositions, though the second composition Lil composition_2 and the third composition Lil composilion_3 continue to exhibit higher capacity than the first composition Lil composition_l.

[0185] The graph 1800 demonstrates that increasing Lil concentration increases capacity at each discharge rate tested within the lithium-sulfur battery system 1300. At 0.2C, the capacity increase from the baseline Lil composition_l to the Lil composition_3 is most pronounced, while at 1C the capacity increase is reduced but still measurable. This rate-dependent behavior may be attributed to the mechanism by which lithium iodide enhances electrochemical performance within the separator / electrolyte region 1304, where the iodide species may participate in redox mediator reactions that facilitate charge transfer at the sulfur-based cathode 1302. At higher discharge rates, the kinetic demands may exceed the rate at which the iodidemediated reactions can proceed, resulting in diminished capacity enhancement compared to lower rates.

[0186] In various embodiments, the rate capability characteristics observed in the graph 1800 may inform the selection of Lil concentrations for applications requiring both high energy density and high power capability.

[0187] FIG. 19 illustrates performance graphs 1900 depicting coulombic efficiency and discharge capacity characteristics for lithium- sulfur battery electrolyte compositions with different baseline salt concentrations, in accordance with one embodiment. As an option, the performance graphs 1900 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 1900 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0188] The performance graphs 1900 include an upper graph showing coulombic efficiency plotted against cycle number, where three compositions are compared within the separator / electrolyte region 1304 of the lithium-sulfur battery system 1300. A solid line in the performance graphs 1900 represents a first composition with a baseline concentration of LiTFSI, a long-dashed line represents a second composition with a baseline concentration of Lil, and a short-dashed line represents a third composition with a baseline concentration of both LiTFSI and Lil combined as a co-salt system. The coulombic efficiency values in the upper graph of the performance graphs 1900 rangefrom approximately 0.80 to 1.00, with all three compositions starting near 1.00 and decreasing over cycling.

[0189] The performance graphs 1900 also include a lower graph displaying discharge capacity in mAh / g as a function of C-rate, with measurements taken at 0.20C, 0.33C, 0.5C, and 1C rates. The discharge capacity values in the lower graph of the performance graphs 1900 range from approximately 450 mAh / g to 650 mAh / g, with the first composition shown as unfilled bars, the second composition shown as diagonal-hatched bars, and the third composition shown as cross-hatched bars. The lower graph of the performance graphs 1900 demonstrates varying performance across the different C-rates, where higher discharge capacities are generally observed at lower C-rates for all three compositions tested.

[0190] With continued reference to the upper graph of the performance graphs 1900, the first composition with baseline LiTFSI and the third composition with combined LiTFSI and Lil exhibit better coulombic efficiency retendon compared to the second composition with baseline Lil alone. The comparison between these two baseline formulations as well as an experimental formulation within the separator / electrolyte region 1304 reveals that while Lil provides benefits for voltage drop reduction and capacity enhancement as demonstrated in the graph 1600, the graph 1700, and the graph 1800, the coulombic efficiency retention of Lil alone may be inferior to formulations containing LiTFSI. The third composition combining both salts demonstrates that the co-salt approach may provide a balance of the benefits from each individual salt species.

[0191] As can be seen, the performance graphs 1900 demonstrate that adding too much Lil may drastically reduce the capacity of the lithium-sulfur battery system 1300, but by carefully adding LiTFSI back into the formulation, the capacity and cycle life may be recovered. The co-salt approach enables optimization of the separator / electrolyte region 1304 by leveraging the voltage drop reduction and kinetic enhancement benefits of lithium iodide while incorporating the capacity and coulombic efficiency retention benefits of lithium bis(trifluoromethanesulfonyl)imide. The careful balancing of Lil and LiTFSI concentrations within the co-salt system allows the lithium-sulfur battery system 1300 to achieve performance characteristics that exceed what is attainable with either salt alone.

[0192] The lower graph of the performance graphs 1900 illustrates that the discharge capacity at each C-rate varies among the three baseline compositions tested.At 0.20C, all three compositions achieve discharge capacities in the range of approximately 600 mAh / g to 650 mAh / g, with the combined LiTFSI-Lil composition demonstrating compclili ve capacity compared to the single-salt formulations. As the C-rate increases to 0.33C, 0.5C, and 1C, the discharge capacity decreases for all compositions, with the relative performance of the three formulations varying depending on the specific rate condition.

[0193] Notably, the combined LiTFSI-Lil composition demonstrates performance improvements that exceed the individual contributions of either single-salt baseline, particularly at higher C-rates such as 1C. This observation indicates that the co-salt system provides synergistic benefits rather than merely additive effects, where the combination of lithium imide salts and lithium halide salts within the separator / electrolyte region 1304 produces enhanced electrochemical performance that neither salt achieves independently. The synergistic behavior observed in the performance graphs 1900 supports the use of co-salt electrolyte formulations as described in Table 1 for applications requiring high power capability.

[0194] In various embodiments, the co-salt formulations combining Lil with LiTFSI within the separator / electrolyte region 1304 may be further optimized by adjusting the ratio of the two salts based on the specific performance requirements of the intended application. For applications where reduced self-discharge is prioritized, co-salt formulations comprising a lithium halide salt at a lower concentrad on combined with a lithium imide salt at a higher concentration may provide an appropriate balance of self-discharge reduction and capacity retention. For applications where enhanced kinetics and voltage drop reduction are prioritized, co-salt formulations with higher lithium halide salt content relative to the lithium imide salt content may be more suitable. The specific concentration ratios may be selected from the formulations described in Table 1 based on the performance requirements of the target application.

[0195] In various embodiments, the relationship between Lil and LiTFSI concentrations within the co-salt system may be influenced by other components of the separator / electrolyte region 1304, including the solvent system composition and the presence of additives such as lithium nitrate and dicyandiamide.

[0196] In various embodiments, the co-salt formulations demonstrated in the performance graphs 1900 may be extended to incorporate additional lithium salts beyond Lil and LiTFSI, creating three-salt or four-salt systems within the separator / electrolyte region 1304 (as found in Table 1 hereinabove). The synergisticbenefits observed when combining Lil with LiTFSI suggest that further combinations incorporating LiFSI or LiC104 may provide additional performance enhancements or enable optimization for specific application requirements.

[0197] FIG. 20 illustrates performance graphs 2000 showing coulombic efficiency and discharge capacity characteristics for LiTFSI and LiClO4 compositions in the lithium-sulfur battery system 1300, in accordance with one embodiment. As an option, the performance graphs 2000 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 2000 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0198] The performance graphs 2000 include an upper portion showing coulombic efficiency on the vertical axis ranging from approximately 0.80 to 1.00 plotted against cycle number on the horizontal axis. Four different electrolyte compositions are represented by distinct line styles within the performance graphs 2000, with a solid line representing composition_l having a baseline concentration of LiTFSI, a long-dashed line representing composition_2 having an increased concentration of LiTFSI, a short-dashed line representing composition_3 having a baseline concentration of LiClO4, and a dotted line representing composition_4 having an increased concentration of LiClO4. The coulombic efficiency data in the performance graphs 2000 demonstrates that the various compositions exhibit different retention characteristics over cycling, with some compositions maintaining higher efficiency values than others as cycle number increases.

[0199] The separator / electrolyte region 1304 may include LiClO4 at various concentrations as a single salt system. Composition_3 represents a baseline concentration of LiClO4 for evaluating the effects of lithium perchlorate as an alternative lithium salt within the lithium-sulfur battery system 1300. As shown in the performance graphs 2000, composition_3 exhibits coulombic efficiency values that begin near 1.00 at early cycles and decrease over extended cycling, with the rate of coulombic efficiency decline being more rapid compared to the LiTFSI compositions at comparable concentrations.

[0200] Composition_4 represents an increased concentration of LiClO4 compared to composition_3, enabling evaluation of concentration-dependent effects for lithium perchlorate within the separator / electrolyte region 1304. The performance graphs 2000demonstrate that composition_4 exhibits similar coulombic efficiency retention characteristics to composition_3, with both LiC104 formulations showing shorter cycle life compared to the LiTFSI formulations regardless of concentration.

[0201] The lower portion of the performance graphs 2000 displays discharge capacity in mAh / g on the vertical axis, plotted against C-rate on the horizontal axis at various discharge rates. Bar chart representations for each of the four compositions at each C-rate show that discharge capacity generally decreases as C-rate increases, with all compositions delivering higher capacity at lower C-rates and reduced capacity at higher C-rates. The discharge capacity data in the performance graphs 2000 indicates that the LiClO4 compositions provide comparable capacity to the LiTFSI compositions across the range of C-rates tested, despite the shorter cycle life characteristics observed in the coulombic efficiency data.

[0202] The comparison between LiTFSI and LiClO4 compositions in the performance graphs 2000 reveals that capacity performance at various discharge rates is comparable between the two salt types, while the cycling stability differs substantially. Composition_3 and composition_4 demonstrate the ability to deliver discharge capacity comparable to composition_l and composition_2 at rates ranging from low to high C-rates, indicating that lithium perchlorate provides sufficient ionic conductivity and reaction kinetics to support electrochemical performance across the tested rate range within the separator / electrolyte region 1304.

[0203] Additionally, the shorter cycle life exhibited by the LiClO4 compositions compared to the LiTFSI compositions may be attributed to differences in the solid electrolyte interphase formation characteristics on the lithium-based anode 1306, variations in the stability of the salt species within the separator / electrolyte region 1304 during extended cycling, or differences in the interaction between the salt anions and the polysulfide species generated at the sulfur-based cathode 1302.

[0204] FIG. 21 illustrates performance graphs 2100 showing coulombic efficiency and discharge capacity characteristics for LiClO4 and LiTFSI co-salt compositions in the lithium-sulfur battery system 1300, in accordance with one embodiment. As an option, the performance graphs 2100 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 2100 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0205] The performance graphs 2100 include an upper portion showing coulombic efficiency on the vertical axis ranging from 0.80 to 1.00 plotted against cycle number on the horizontal axis. Two curves are presented in the upper portion of the performance graphs 2100, with a solid line representing a first composition having a baseline concentration of LiClO4 composition_l as a single salt system, and a dashed line representing a second composition having a baseline concentration of LiClO4 combined with LiTFSI composition_2 as a co-salt system. The dashed line corresponding to the co-salt system of LiClO4 and LiTFSI demonstrates higher coulombic efficiency retention over cycling compared to the solid line representing Li Cl 04 alone within the separator / electrolyte region 1304.

[0206] The lower portion of the performance graphs 2100 displays discharge capacity in mAh / g on the vertical axis ranging from 400 to 600 plotted against C-rate on the horizontal axis at values of 0.20C, 0.33C, 0.5C, and 1C. Bar representations in the lower portion of the performance graphs 2100 show the discharge capacity performance at each C-rate, with open bars corresponding to the first composition containing LiClO4 composition_l alone and hatched bars corresponding to the second composition containing the LiClO4 combined with LiTFSI composition_2 co-salt system. The discharge capacity data demonstrates that the co-salt system maintains comparable or improved discharge capacity across the range of C-rates tested within the lithium- sulfur battery system 1300.

[0207] The composition_2 co-salt formulation increases total capacity delivered by increasing cycle life compared to the single salt LiClO4 formulation. The addition of LiTFSI to the LiClO4 base formulation provides enhanced cycling stability while maintaining the rate capability characteristics contributed by the lithium perchlorate component.

[0208] The performance graphs 2100 demonstrate that adding amounts of LiTFSI to a LiClO4-containing electrolyte allows the lithium-sulfur battery system 1300 to increase total capacity delivered by increasing cycle life. The upper portion of the performance graphs 2100 shows that the co-salt system maintains higher coulombic efficiency values over extended cycling compared to the single salt LiClO4 formulation, with the differentiation between the two formulations becoming more pronounced at later cycles.

[0209] The lower portion of the performance graphs 2100 illustrates that at all rates tested, the LiTFSI combined with LiClO4 co-salt system provides discharge capacitythat is comparable to or exceeds the discharge capacity of the single salt LiC104 formulation.

[0210] The co-salt approach demonstrated in the performance graphs 2100 addresses the cycle life limitations of single salt LiClO4 formulations that were identified in the performance graphs 2000. While the performance graphs 2000 showed that LiClO4 provides comparable rate capability to LiTFSI but exhibits shorter cycle life regardless of concentration, the performance graphs 2100 demonstrate that the incorporation of LiTFSI into the LiClO4-based electrolyte extends the cycle life and improves coulombic efficiency retention. This finding indicates that the co-salt approach enables the lithium-sulfur battery system 1300 to leverage the rate capability benefits of lithium perchlorate while midgating the cycle life limitations through the complementary contributions of lithium bis(trifluoromethanesulfonyl)imide.

[0211] In various embodiments, the ratio of LiTFSI to LiClO4 within the co-salt system may be adjusted based on the specific performance requirements of the intended application. Additionally, the co-salt formulations combining LiClO4 with LiTFSI may be further modified by adjusting the total salt concentration or by incorporating additional lithium salts to create three-salt or four-salt systems.

[0212] FIG. 22 illustrates performance graphs 2200 showing coulombic efficiency and discharge capacity characteristics for LiTFSI and LiFSI co-salt compositions in the lithium-sulfur battery system 1300, in accordance with one embodiment. As an option, the performance graphs 2200 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 2200 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0213] The performance graphs 2200 include an upper portion showing coulombic efficiency on the vertical axis ranging from approximately 0.80 to 1.00 plotted against cycle number on the horizontal axis. Two curves are presented in the upper portion of the performance graphs 2200, with a solid line representing a first composition having a baseline concentration of LiTFSI composition_l as a single salt system, and a dashed line representing a second composition having a baseline concentration of LiTFSI combined with LiFSI composition_2 as a co-salt system. The dashed line corresponding to the co-salt system of LiTFSI and LiFSI demonstrates higher coulombic efficiencyvalues compared to the solid line representing LiTFSI alone within the separator / electrolyte region 1304 of the lithium-sulfur battery system 1300.

[0214] The lower portion of the performance graphs 2200 displays discharge capacity in mAh / g on the vertical axis ranging from approximately 550 to 650 mAh / g plotted against C-rate on the horizontal axis at values of 0.20C, 0.33C, 0.5C, and 1C. Bar chart representations in the lower portion of the performance graphs 2200 show unfilled bars representing the first composition containing LiTFSI alone and hatched bars representing the second composition containing the LiTFSLLiFSI co-salt system. The discharge capacity data indicates that the second composition composition_2 achieves higher discharge capacity than the first composition composition_l at all C-rates. This improvement in discharge capacity across all C-rates is larger than would be expected from simply increasing the concentration of either salt individually, indicating synergistic benefits from the LiTFSLLiFSI co-salt combination. The synergistic behavior suggests that the interaction between the two lithium imide salts within the separator / electrolyte region 1304 provides enhanced electrochemical performance that exceeds the additive contributions of each salt species.

[0215] Overall, the addition of LiFSI to LiTFSI improves coulombic efficiency and reduces voltage drop compared to LiTFSI alone within the separator / electrolyte region 1304.

[0216] In various embodiments, the LiTFSLLiFSI co-salt combination may be suitable for high-energy applications such as drones due to less than 4% change (as an example) in total delivered capacity over the cycle life of the lithium- sulfur battery system 1300. The performance graphs 2200 demonstrate that the co-salt system provides much higher capacity when adding LiFSI to LiTFSI while maintaining stable capacity delivery over extended cycling. The less than 4% change in total delivered capacity indicates that the LiTFSLLiFSI co-salt system provides consistent energy delivery characteristics that may be advantageous for applications requiring predictable power availability, such as unmanned aerial vehicles and other e-mobility devices.

[0217] In various embodiments, the LiTFSLLiFSI co-salt formulations within the separator / electrolyte region 1304 may be further optimized by adjusting the ratio of the two salts based on the specific performance requirements of the intended application. For applications where high initial coulombic efficiency is prioritized, formulations with higher LiFSI ratios such as 2:1 or 3:1 may provide enhanced performance. For applications where compatibility with established LiTFSLbased electrolyte systems isdesired, formulations with lower LiFSI ratios such as 1:2 or 1:3 may provide incremental improvements while maintaining similarity to baseline formulations.

[0218] In various embodiments, the LiTFSI-LiFSI co-salt formulations may provide advantages for applications where reduced PF AS content is desired. While both LiTFSI and LiFSI contain fluorine atoms, LiFSI has a lower molecular weight and may be considered to have reduced PFAS characteristics compared to LiTFSI. The incorporation of LiFSI into co-salt formulations within the separator / electrolyte region 1304 may enable partial reduction of LiTFSI content while maintaining or improving electrochemical performance of the lithium- sulfur battery system 1300.

[0219] FIG. 23 illustrates performance graphs 2300 comparing cycling performance of lithium-sulfur battery cells with different electrolyte compositions containing Lil and LiFSI, in accordance with one embodiment. As an option, the performance graphs 2300 may be implemented in the context of any one or more of the embodiments set forth in any previous and / or subsequent Figures and / or description thereof. Of course, however, the performance graphs 2300 may be implemented in the context of any desired environment. Further, the aforementioned definitions may equally apply to the description below.

[0220] The performance graphs 2300 include an upper graph showing Coulombic Efficiency on the y-axis ranging from approximately 0.80 to 1.00 plotted against Cycle on the x-axis, and a lower graph showing Discharge Capacity in mAh / g on the y-axis ranging from approximately 400 to 600 plotted against Cycle on the x-axis. A solid line in the performance graphs 2300 represents a first composition with a baseline concentration of Lil composition_l as a single salt system, while a dashed line represents a second composition with a baseline concentration of Lil combined with LiFSI composition_2 as a co-salt system within the separator / electrolyte region 1304 of the lithium-sulfur battery system 1300.

[0221] The upper graph of the performance graphs 2300 demonstrates that both compositions initially exhibit Coulombic Efficiency near 1.00, with the Lil plus LiFSI composition_2 composition maintaining slightly higher efficiency over cycling before both compositions show declining efficiency at later cycles. The addition of LiFSI to Lil provides improved Coulombic Efficiency characteristics compared to the single salt Lil formulation, indicating that the LiFSI component contributes complementary benefits to the electrochemical performance of the separator / electrolyte region 1304. The enhanced Coulombic Efficiency retention observed with the co-salt system may beattributed, in one possible embodiment, to improved solid electrolyte interphase formation characteristics on the lithium-based anode 1306 or modified ionic transport properties within the separator / electrolyte region 1304.

[0222] The lower graph of the performance graphs 2300 illustrates that both compositions achieve initial discharge capacities near 600 mAh / g, with the Lil plus LiFSI composition_2 composition showing higher capacity retention through midcycling before both compositions exhibit capacity fade at extended cycles. The addition of LiFSI to Lil provides a significant gain in capacity delivered over the lifetime of the cell compared to the single salt Lil formulation within the lithium-sulfur battery system 1300. This capacity gain represents a substantial improvement in total energy delivery from the lithium-sulfur battery system 1300 over the battery lifetime, which may be particularly relevant for applications where cumulative energy delivery determines the practical utility of the battery system.

[0223] The performance graphs 2300 indicate that the Lil-LiFSI co-salt system experiences some additional voltage decay compared to the single salt Lil formulation. The voltage decay observed with the co-salt system may be addressed through the addition of further lithium salts to create three-salt or four-salt electrolyte systems within the separator / electrolyte region 1304. The incorporation of additional salt species may provide complementary benefits that mitigate the voltage decay while preserving the capacity retention improvements demonstrated in the performance graphs 2300.

[0224] In various embodiments, the LiClO4-LiFSI co-salt formulations may provide advantages for applications where reduced PFAS content is desired. The combination of lithium perchlorate, which contains no fluorine atoms, with lithium bis(fluorosulfonyl)imide, which has a lower molecular weight than LiTFSI, may enable formulation of electrolytes with reduced overall PFAS content compared to conventional LiTFSI-based electrolytes while maintaining or improving electrochemical performance. The improved coulombic efficiency retention and extended cycle life demonstrated by the LiClO4-LiFSI co-salt systems indicate that these formulations may serve as alternatives to LiTFSI-based electrolytes for applications where environmental or regulatory considerations favor reduced fluorinated compound content.ADDITIONAL EMBODIMENTS

[0225] Taking a step back, in various embodiments, the separator / electrolyte region may include co-salt systems combining lithium imide salts with lithium oxyanion salts for pouch cell applications. Such co-salt formulations may combine the salts at various concentration ratios, resulting in total lithium salt concentrations ranging from 0.5M to 1.5M within the separator / electrolyte region. These formulations provide co-salt configurations for pouch cell implementations where the rate capability characlcrislics contributed by the lithium oxyanion salt component may be combined with the cycling stability benefits of the lithium imide salt component. The pouch cell format enables evaluation of co-salt system performance under conditions more rcprcscnlalivc of commercial applications compared to coin cell testing. In addition to pouch cell configurations, the co-salt electrolyte formulations described herein may be equally applied to cylindrical cell and prismatic cell formats. These alternative cell formats may provide different form factors and packaging configurations suitable for various commercial applications, and the co-salt systems described in Table 1 may be implemented across these cell formats to achieve the enhanced performance characteristics disclosed herein.

[0226] In various embodiments, the separator / electrolyte region may include multisalt systems combining three or more lithium salts selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts. Such multi-salt formulations may combine the salts at equal or varying concentration ratios, resulting in total lithium salt concentrations ranging from 0.6M to 1.5M within the separator / electrolyte region. The multi-salt systems enable the lithium-sulfur battery to leverage cumulative benefits from each salt species, where different salt components contribute cycling stability, voltage drop reduction, kinetic enhancement, and rate capability characlcrislics. Multisalt configurations may provide a balanced approach to electrolyte formulation, potentially enabling broader operating windows and more robust performance across varying temperature and rate conditions. The various multi-salt configurations have been described hereinabove in Table 1.

[0227] In various embodiments, the sulfur-based cathode may have a loading ranging from 2.0 mg / cm2 to 7.0 mg / cm2. Lower cathode loadings in the range of 2.0 mg / cm2 to 4.0 mg / cm2 may provide improved electrochemical accessibility and ulilizalion of the sulfur active material, while higher cathode loadings in the range of 4.0 mg / cm2 to 7.0 mg / cm2 may provide increased energy density per cell. The relationship between cathode loading and electrolyte salt selection affects the overallperformance characteristics of the lithium-sulfur battery, where lower loading configurations may demonstrate synergistic relationships with lithium halide salt-based electrolyte formulations, and higher loading configurations may demonstrate improved performance with lithium imide salt-based electrolyte formulations.

[0228] In various embodiments, the carbon-containing material within the sulfurbased cathode may comprise three-dimensional (3D) graphene structures. The 3D graphene may provide a high surface area scaffold for hosting the sulfur acli vc material, where the interconnected graphene sheets form a porous network that facilitates electron transport and electrolyte infiltration throughout the cathode thickness. The 3D graphene architecture may comprise graphene sheets arranged in various orientations, including curved, folded, and interconnected configurations that create hierarchical porosity within the cathode structure. The porous nature of the 3D graphene scaffold may enable higher sulfur loading while maintaining adequate electrochemical accessibility of the sulfur active material, as the interconnected pore network provides pathways for lithium ion transport during charge and discharge cycles. In some cases, the 3D graphene may help contain sulfur and lithium polysulfide species within the cathode structure, potentially reducing the migration of polysulfides into the separator / electrolyte region and mitigating the polysulfide shuttle effect. The combination of 3D graphene cathode structures with the co-salt electrolyte formulations described in Table 1 may provide synergistic benefits, where the enhanced polysulfide containment provided by the 3D graphene architecture complements the voltage drop reduction and coulombic efficiency improvements provided by the co-salt systems. The 3D graphene may be produced through various synthesis methods, including chemical vapor deposition, template-assisted growth, or reduction of graphene oxide precursors, and the specific morphology and porosity characteristics may be tailored based on the target cathode loading and application requirements.

[0229] In various embodiments, the sulfur-based cathode may have a density ranging from 0.6 g / cc to 1.8 g / cc. This cathode density range represents electrode structures that balance mechanical integrity with porosity for electrolyte infiltration. Lower densities within this range may provide increased void volume for electrolyte access to the sulfur active material, while higher densities may provide improved structural stability and volumetric energy density. The cathode density may be selected in conjunction with cathode loading and electrolyte salt composition to achieve optimized performance for specific applications.

[0230] In various embodiments, the lithium-sulfur battery may operate with an electrolyte-to-sulfur (E / S) ralio ranging from 2.0 to 10.0. Lower E / S ralios in the range of 2.0 to 4.0 enable higher gravimetric energy density by minimizing the electrolyte contribution to the overall cell mass, though the reduced electrolyte volume may affect capacity retention and cycle life characteristics depending on the specific electrolyte salt composition employed. Higher E / S ratios in the range of 5.0 to 10.0 provide increased electrolyte volume to accommodate the dissolution and precipitation of polysulfide species during charge and discharge cycles, potentially improving cycle life at the expense of gravimetric energy density. The E / S ralio may be selected in conjunction with cathode loading and electrolyte salt composition to achieve the desired balance of energy density, power capability, and cycle life for target applications. In some cases, an E / S ratio of approximately 2.5 to 3.5 may be employed for pouch cell configurations, representing a balance between gravimetric energy density and electrochemical performance suitable for commercial applications. Higher E / S ratios used in coin cell testing for screening and development purposes may not be representative of the E / S ratios employed in production pouch cells.

[0231] In various embodiments, the relationship between cathode loading and optimal electrolyte salt selection may enable application-specific optimization of the lithium-sulfur battery. Lower cathode loadings combined with lithium halide salt-based electrolytes may provide longer cycle life and improved capacity retention compared to higher loading cathodes with the same electrolyte formulations. Conversely, higher cathode loadings may be preferred for lithium imide salt-based electrolyte systems. The synergistic relationship between cathode loading and electrolyte salt selection indicates that the optimization of electrolyte salt composition should be conducted in conjunction with cathode design parameters, enabling tailored electrolyte-cathode pairing for specific applications. As such, the exact configuration of the electrolyte salt may be configured based on the intended use of the battery.

[0232] In various embodiments, the lithium-sulfur battery system may substitute lithium iodide (Lil) with lithium bromide (LiBr) as an alternative lithium halide salt within the separator / electrolyte region. It is to be appreciated that other substitutions are envisioned with other similar compounds.

[0233] In various embodiments, the separator / electrolyte region may include cosalt systems combining lithium imide salts with lithium bromide at various concentration ralios as described in Table 1. Such co-salt formulations enable directcomparison with other co-salt systems at equivalent total salt concentrations, allowing evaluation of how the choice of halide anion affects co-salt system performance. The combination of lithium imide salts with lithium bromide may provide kinetic enhancement benefits from the bromide anion while incorporating the cycling stability contributions of the lithium imide salt component. In various embodiments, the separator / electrolyte region may include lithium bromide as a single salt system at concentrations ranging from 0.3M to 1.5M.

[0234] In various embodiments, the co-salt electrolyte formulations provide PFAS-reduced or PFAS-free alternatives by incorporating lithium salts that contain no fluorine atoms or reduced fluorine content as alternatives to conventional lithium imide salts within the separator / electrolyte region. The incorporation of allcrnalivc lithium salts such as lithium halide salts and lithium oxyanion salts, which contain no fluorine atoms, or certain lithium imide salts with reduced fluorine content, enables formulation of electrolytes with reduced overall PFAS content compared to conventional electrolytes.

[0235] In various embodiments, lithium halide salts such as lithium iodide and lithium bromide contain no fluorine atoms and therefore do not contribute to the PFAS content of the electrolyte formulation. Co-salt systems that combine lithium halide salts with lithium imide salts at various ratios as described in Table 1 may reduce the lithium imide salt content compared to baseline single-salt formulations while maintaining or improving electrochemical performance. The percentage reduction in PFAS content achieved by these co-salt formulations depends on the specific ratio of lithium halide salt to lithium imide salt employed, where higher lithium halide salt proportions provide greater PFAS reduction. In some cases, complete replacement of lithium imide salts with lithium halide salts or lithium oxyanion salts may provide PFAS-free electrolyte formulations.

[0236] In various embodiments, certain lithium imide salts may have lower molecular weight and may be considered to have reduced PFAS characteristics due to the absence of perfluorinated carbon chains in the molecular structure. Co-salt systems that combine such lithium imide salts with lithium halide salts provide electrolyte compositions with substantially reduced PFAS content compared to conventional electrolytes while achieving enhanced capacity delivery and coulombic efficiency retendon. The various PFAS-reduced co-salt configurations are described in Table 1.USE CASE SCENARIO

[0237] By way of a use-case scenario, and in various embodiments, a battery manufacturer implements the co-salt electrolyte formulations disclosed herein for production of lithium-sulfur battery cells intended for electric vertical takeoff and landing (eVTOL) aircraft applications. The manufacturer selects a co-salt system comprising at least two lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts within a solvent mixture comprising ethers and fluorinated ethers, along with additives that promote solid electrolyte interphase formation. The sulfur-based cathode is paired with a lithium-containing anode and assembled in a pouch cell format with an electrolyte-to-sulfur ratio selected to maximize gravimetric energy density. During operation, the eVTOL aircraft battery pack cycles through repeated charge and discharge cycles at elevated rates during takeoff and landing phases, where the co-salt system provides stable capacity delivery over the cycle life while maintaining high coulombic efficiency during cycling periods. The reduced voltage drop characlcrislics of the co-salt formulation minimize selfdischarge during periods when the aircraft is parked between flights, preserving available energy for subsequent missions. This implementation enables the eVTOL aircraft to achieve the high energy density approaching the theoretical limit of lithiumsulfur chemistry while maintaining the cycling stability and power capability required for aviation applications.

[0238] By way of another use-case scenario, and in various embodiments, an automotive manufacturer implements the co-salt electrolyte formulations disclosed herein for production of lithium-sulfur battery packs intended for electric vehicle applications. The manufacturer selects a co-salt system comprising at least two lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts, where the specific salt combination is tailored to provide extended cycle life and consistent capacity retention over thousands of charge-discharge cycles representative of vehicle lifetime requirements. The sulfur-based cathode loading and electrolyte-to-sulfur ratio are selected to balance energy density with longevity, enabling the electric vehicle to achieve driving ranges compclili ve with or exceeding conventional internal combustion vehicles. During operation, the electric vehicle battery pack experiences variable discharge rates ranging from moderate rates during highway cruising to elevated rates during acceleration events, where the co-salt system maintains stable voltage characteristics and consistent power delivery across the operaring envelope. The synergistic combination of lithium salts within the electrolytereduces capacity fade mechanisms including polysulfide shuttle and electrolyte degradation, enabling the battery pack to retain sufficient capacity throughout the vehicle warranty period. This implementation enables the electric vehicle manufacturer to leverage the high theoretical energy density of lithium-sulfur chemistry while meeting the durability and reliability requirements expected by automotive consumers.

[0239] By way of another use-case scenario, and in various embodiments, a grid storage system integrator implements the co-salt electrolyte formulations disclosed herein for production of lithium-sulfur battery modules intended for stationary energy storage applications. The integrator selects a co-salt system comprising at least two lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxyanion salts, where the specific salt combination is tailored to minimize selfdischarge during extended storage periods and provide consistent round-trip efficiency over the operational lifetime of the installation. The sulfur-based cathode configuration and electrolyte composition are selected to prioritize calendar life and cycling stability over gravimetric energy density, as weight constraints are less critical in stationary applications compared to mobile applications. During operation, the grid storage system cycles through daily charge and discharge cycles to support renewable energy integration, peak shaving, or frequency regulation services, where the co-salt system provides stable capacity delivery and maintains high coulombic efficiency across varying depths of discharge and cycling rates. The reduced self-discharge characteristics of the co-salt formulation preserve stored energy during periods of grid stability when the battery system remains idle, maximizing the economic value of the stored energy. This implementation enables the grid storage integrator to deploy lithium-sulfur battery systems that provide cost-effective energy storage with reduced environmental impact compared to conventional battery chemistries, while meeting the long operational lifetime requirements of utility-scale installations.IMPROVEMENTS OVER EXISTING SYSTEMS

[0240] The present disclosure addresses significant challenges in lithium-sulfur battery technology that have long hindered the practical implementation and commercial viability of these high-energy-density systems. Prior art solutions have predominantly relied on lithium bis(trifhioromethanesulfonyl)imide (LiTFSI) as the primary lithium salt in electrolyte formulations, which presents multiple deficiencies including high molecular weight that increases the overall density of the electrolyte package, classification as a polyfluorinated substance (PFAS) raising environmentaland regulatory concerns, and relatively high cost that impacts commercial viability. Furthermore, single-salt electrolyte formulations have struggled to simultaneously address the multiple degradation mechanisms affecting lithium-sulfur batteries, including the lithium polysulfide shuttle effect that causes self-discharge and capacity fade, electrolyte dryout during extended cycling, and dendrite formation on the lithium anode surface. Earlier alternative lithium salts such as lithium hexafluoroarsenate, lithium hexafluorophosphate, and lithium tetrafluoroborate proved unsuitable due to toxicity from hydrogen fluoride release and incompatibility with lithium polysulfide species, while other alternatives including lithium imide salts, lithium halide salts, and lithium oxyanion salts presented fundamental challenges when used individually, exhibiting inadequate ionic conductivity at certain concentrations, insufficient solid electrolyte interphase formation, or poor kinetics during charge and discharge processes.

[0241] The disclosed co-salt electrolyte systems overcome these deficiencies through optimized combinations of two or more lithium salts independently selected from lithium imide salts, lithium halide salts, and lithium oxy anion salts at concentration ratios that provide synergistic performance improvements unattainable with single-salt formulations. The lithium imide salts may include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium bis(fluorosulfonyl)imide (LiFSI). The lithium halide salts may include lithium iodide (Eil) and lithium bromide (EiBr). The lithium oxyanion salts may include lithium perchlorate (EiC104). Other similar compounds are envisioned to be feasibly used.

[0242] The addition of lithium halide salts to lithium imide salt-based electrolytes may drastically reduce voltage drop and self-discharge while increasing capacity, with co-salt formulations demonstrating significantly reduced voltage drop (such as over 24 hours) compared to baseline single-salt electrolytes. The combination of two lithium imide salts at various ratios improves coulombic efficiency retention and reduces voltage drop, achieving reduced change in total delivered capacity over the cycle life, making such formulations suitable for high-energy applications. The combination of lithium oxyanion salts with lithium imide salts addresses the cycle life limitations of single-salt lithium oxyanion lormulalions by incorporating the lithium imide salt to improve coulombic efficiency retention while preserving the rate capability characteristics of the lithium oxyanion salt. Additionally, the disclosed formulations enable reduced PFAS content by incorporating alternative salts such as lithium halidesalts and certain lithium imide salts, which have lower molecular weight and density compared to conventional lithium salts, addressing environmental and regulatory concerns while maintaining or improving ionic conductivity and cell performance.

[0243] The relationship between cathode loading levels and optimal salt selection further enables tailored electrolyte-cathode pairing, where lower loading cathodes paired with lithium halide salt-based electrolytes demonstrate improved cycle life and energy retendon compared to higher loading configurations with conventional electrolyte formulations, effectively resolving the longstanding issues of performance inconsistency and limited longevity that have plagued prior art lithium-sulfur battery systems. The co-salt systems may be employed in various cell formats including coin cells for screening and development purposes and pouch cells for validation under conditions more representative of commercial applications, where the larger form factor of pouch cells may reveal performance characteristics that inform the selection of co-salt compositions and cathode configurations for target applications. The electrolyte-to-sulfur (E / S) ratio may be selected based on the balance between gravimetric energy density and electrochemical performance requirements, where lower E / S ratios provide higher energy density while higher E / S ratios may provide improved capacity retention and cycle life characteristics.

[0244] As such, the disclosed co-salt electrolyte formulations provide enhanced benefits including improved capacity, enhanced coulombic efficiency, extended cycle life, and reduced self-discharge compared to single-salt electrolyte systems.SYSTEM IMPLEMENTATION EMBODIMENTS

[0245] A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.

[0246] The use of the terms "a" and "an" and "the" and similar referents in the context of describing the subject matter (particularly in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. Furthermore, the foregoing description is for the purpose of illustration only,and not for the purpose of limitation, as the scope of protection sought is defined by the claims as set forth hereinafter together with any equivalents thereof entitled to. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illustrate the subject matter and does not pose a limitation on the scope of the subject matter unless otherwise claimed. The use of the term “based on” and other like phrases indicating a condition for bringing about a result, both in the claims and in the written description, is not intended to foreclose any other conditions that bring about that result. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention as claimed.

[0247] The embodiments described herein included the one or more modes known to the inventor for carrying out the claimed subject matter. Of course, variations of those embodiments will become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the claimed subject matter to be practiced otherwise than as specifically described herein. Accordingly, this claimed subject matter includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed unless otherwise indicated herein or otherwise clearly contradicted by context.

Claims

CLAIMSWhat is claimed is:

1. A lithium-sulfur battery system comprising:a cathode;an anode;a separator disposed between the cathode and the anode; andan electrolyte comprising a lithium salt and a solvent,wherein the lithium salt comprises at least one of lithium bromide (LiBr), lithium perchlorate (LiC104), lithium bis(fluorosulfonyl)imide (LiFSI), or lithium iodide (Lil), andwherein the lithium salt is present at a concentration between 0.1 M and 3.0 M.

2. The lithium-sulfur battery system of claim 1, wherein the lithium salt comprises lithium iodide (Lil) at a concentration between 0.5 M and 2.0 M.

3. The lithium-sulfur battery system of claim 1, wherein the lithium salt comprises lithium perchlorate (LiC104) at a concentration between 0.3 M and 1.5 M.

4. The lithium-sulfur battery system of claim 1, wherein the lithium salt comprises a combination of lithium bis(trifhioromethanesulfonyl)imide (LiTFSI) and at least one of lithium iodide (Lil), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), or lithium bromide (LiBr).

5. The lithium-sulfur battery system of claim 4, wherein:the LiTFSI is present at a concentration between 0.2 M and 1.0 M; and the at least one of Lil, LiClO4, LiFSI, or LiBr is present at a concentration between 0.1 M and 1.0 M.

6. The lithium-sulfur battery system of claim 1, wherein the solvent comprises a mixture of 1 ,2-dimethoxyethane (DME), 1,3-dioxolane (DOL), and bis(2,2,2-trifluoroethyl) ether (BTFE).

7. The lithium-sulfur battery system of claim 6, wherein:the DME, DOL, and BTFE are present in a volume ratio of 2: 1 : 1 ; and the electrolyte further comprises 0.5 M lithium nitrate (LiNO3) and 0.15 M dicyandiamide (DCDA).

8. The lithium-sulfur battery system of claim 1, wherein the cathode comprises a carbon-sulfur composite material.

9. The lithium-sulfur battery system of claim 8, wherein:the carbon-sulfur composite material comprises a nanostructured 3D graphene material; andthe nanostructured 3D graphene material is configured to midgate polysulfide shuttle effect and provide high conductivity for charge and discharge rates.

10. The lithium-sulfur battery system of claim 1, wherein the anode comprises lithium metal.

11. The lithium-sulfur battery system of claim 10, wherein:the anode comprises a lithium metal composite structure; andthe lithium metal composite structure is configured to mitigate anode degradation.

12. The lithium-sulfur battery system of claim 1, wherein the separator comprises a porous polymer material.

13. The lithium-sulfur battery system of claim 12, wherein:the porous polymer material is coated with ceramic particles; andthe ceramic particles are configured to improve thermal stability and reduce the risk of internal short circuits.

14. The lithium-sulfur battery system of claim 1, wherein the lithium salt composition is configured to reduce at least one of polysulfide shuttle effect, electrolyte dryout, or dendrite formation compared to a system using only lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt.

15. The lithium-sulfur battery system of claim 1, further comprising:a copper current collector adjacent to the anode; andan aluminum current collector adjacent to the cathode.

16. The lithium-sulfur battery system of claim 1, wherein:the cathode has a sulfur loading between 3 mg / cm2 and 6 mg / cm2; and the electrolyte to sulfur (E / S) ratio is between 3 pL / mg and 7 pL / mg.

17. The lithium-sulfur battery system of claim 1, further comprising a battery management system configured to:monitor and control charging and discharging of the system;balance individual cells within the system; andprovide thermal management for the system during operation.

18. A lithium-sulfur battery system comprising:a cathode;an anode;a separator disposed between the cathode and the anode; andan electrolyte comprising a co-salt composition and a solvent,wherein the co-salt composition comprises at least two lithium salts, andwherein the at least two lithium salts are each independently selected from lithium imide salts, lithium halide salts, and lithium oxy anion salts.

19. The lithium-sulfur battery system of claim 18, wherein the lithium imide salts comprise at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI).

20. The lithium-sulfur battery system of claim 18, wherein the lithium halide salts comprise at least one of lithium iodide (Lil) or lithium bromide (LiBr).

21. The lithium-sulfur battery system of claim 18, wherein the lithium oxyanion salts comprise lithium perchlorate (LiC104).

22. The lithium-sulfur battery system of claim 18, wherein:the at least two lithium salts comprise a first lithium salt and a second lithium salt;the first lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); andthe second lithium salt is lithium iodide (Lil).

23. The lithium-sulfur battery system of claim 22, wherein:the LiTFSI is present at a concentration of 0.3M to 0.8M; andthe Lil is present at a concentration of 0.2M to 0.7M.

24. The lithium-sulfur battery system of claim 23, wherein:a ratio of Lil to LiTFSI is between 1 :5 and 1:1; anda total concentration of the LiTFSI and the Lil is between 0.6M and 1.2M.

25. The lithium-sulfur battery system of claim 18, wherein:the at least two lithium salts comprise a first lithium salt and a second lithium salt;the first lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); andthe second lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI).

26. The lithium-sulfur battery system of claim 25, wherein a ratio of LiFSI to LiTFSI is between 1:5 and 4:1.

27. The lithium-sulfur battery system of claim 26, wherein the ratio of LiFSI to LiTFSI is between 1:1 and 3:1.

28. The lithium-sulfur battery system of claim 18, wherein:the at least two lithium salts comprise a first lithium salt and a second lithium salt;the first lithium salt is lithium perchlorate (LiC104); andthe second lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI).

29. The lithium-sulfur battery system of claim 28, wherein:the LiC104 is present at a concentration of 0.4M to 1.0M; andthe LiFSI is present at a concentration of 0.2M to 0.6M.

30. The lithium-sulfur battery system of claim 18, wherein the co-salt composition comprises at least three lithium salts.

31. The lithium-sulfur battery system of claim 30, wherein the at least three lithium salts comprise lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium iodide (Lil), and lithium perchlorate (LiC104).

32. The lithium-sulfur battery system of claim 18, wherein the solvent comprises:1.2-dimethoxyethane (DME);1.3-dioxolane (DOL); anda fluorinated ether.

33. The lithium-sulfur battery system of claim 32, wherein:the fluorinated ether comprises l,l,2,2-tetrafhioroethyl-2,2,3,3-tetrafluoropropyl ether (TTE); andthe DME, DOL, and TTE are present at a volume ratio of approximately 50:25:25 or approximately 70:15:15.

34. The lithium-sulfur battery system of claim 18, wherein the electrolyte further comprises:lithium nitrate (LiNO3) at a concentration of 0.2M to 0.6M; and dicyandiamide (DCDA) at a concentration of 0.1 M to 0.2M.

35. The lithium-sulfur battery system of claim 18, wherein the co-salt composition provides enhanced coulombic efficiency retention over cycling compared to a singlesalt electrolyte composition at an equivalent total lithium salt concentration.

36. The lithium-sulfur battery system of claim 18, wherein the co-salt composition comprises at least one lithium salt that contains no fluorine atoms, wherein:the at least one lithium salt that contains no fluorine atoms comprises at least one of lithium iodide (Lil), lithium bromide (LiBr), or lithium perchlorate (LiC104); andthe co-salt composition has a reduced polyfluorinated substance (PFAS) content compared to a single-salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte at an equivalent total lithium salt concentration.

37. The lithium-sulfur battery system of claim 18, wherein the anode comprises a lithium alloy.

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