Flame retardant additives containing lithium phosphonate salts having enhanced safety and performance in rechargeable batteries

Abstract

Flame retardant ionic compositions can be used as additives in lithium-ion batteries. The compositions incorporate specific phosphorus (V) moieties into the structural backbone of the anion lithium salt. Methods of synthesizing these phosphonates and selectively dealkylating each one using a lithium halide salt are also contemplated.

Description

PCT PATENT APPLICATION Inventors: John Protasiewicz Anthony Komokovich Emalyn Delgado Rosario Judith Jeevarajan Wan Si Tang Vallabha Rao Rikka Docket No.: 12166-00224TITLE FLAME RETARDANT ADDITIVES CONTAINING LITHIUM PHOSPHONATE SALTS HAVING ENHANCED SAFETY AND PERFORMANCE IN RECHARGEABLE BATTERIESCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to United States provisional patent applications having serial numbers 63 / 771,272, filed on March 13, 2025, and 63 / 804,266, filed on May 12, 2025. Both of these applications are incorporated by reference in their entirety.TECHNICAL FIELD

[0002] The invention contemplates compositions, methods, and systems useful as additives in battery electrolytes and, more specifically, to lithium salts integrating phosphorus moieties that introduce flame retardant and other performance enhancing qualities while maintaining high energy and power densities for lithium-ion batteries.BACKGROUND

[0003] Lithium-ion batteries offer portability, long cycle life, high energy7density, and high specific power making them the preferred energy storage device of choice for many portable electronic devices and vehicles. Lithium-ion batteries are usually composed of a graphite anode, a lithium metal oxide cathode, and an electrolyte solution. The electrolyte solution are formed from lithium salts (typically lithium hexafluorophosphate or LiPFg) dissolved into organic alky l carbonate solvents, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and / or ethylene carbonate (EC). Lithium salts (LiX) are composed of a lithium cation (Li+) and a counter anion (X‘). A wide variety of counterions have been examined for the uses as lithium salts in battery electrolyte 137718301.1solutions, including tetrafluoroborate, oxolatoborates, fluorosulfonyl imides, and fluromethylsulonyl imides. Each lithium salts offers a different set of properties that include electrochemical and oxidative stability, ionic conductivity, electrode wettability, solid electrolyte interface (SEI) layer formation, improved compatibility with high-voltage cathodes, current collectors corrosion resistance, solubility, and overall thermal stability , etc.

[0004] Lithium-ion batteries are critical to a wide and growing range of applications, including consumer electronics and electric vehicles. Unsurprisingly, safety is a significant concern, particularly in large-scale applications, in view of enhanced risks posed by the use of flammable organic electrolyte solvents and reactive lithium. In particular, thermal runaway caused during abusive conditions (based on electrical, mechanical, or thermal events) can cause a series of exothermic reactions that ultimately lead to fires and explosions. For example, if battery puncture occurs, lithium can ignite the flammable battery components and / or release additional harmful materials or contribute to cascading abusive conditions. Furthermore, longer term degradation of the solid electrolyte interface (SEI) may oxidize the electrolyte and also culminate in hazardous events.

[0005] Some types of organophosphorus compounds are known to act as efficient flame retardants (via either forming char during combustion that produces an insulating barrier to heat and oxygen transfer or radical capture processes), but their adaption and engineering to the exigencies of lithium-ion batteries is rather limited. As an example, triethyl and trimethyl organophosphates additives have been examined, but they can have deleterious effects such as reduced battery capacity. Various forms halogenated phosphates have also been explored, but these can release highly toxic gases upon decomposition. Still other studies of lithium difluorophosphate and dimethyl phosphate additives have revealed similar drawbacks.

[0006] A small number of flame retardant ions based on bifunctional lithium borate salts have also been explored. However, these compounds relied on the chelating properties of the boron atom in order to incorporate halogens and, thus, suffered the same draw-backs as halogenated phosphates. Organophosphorus borate salts were also characterized, but these possessed limited solubility in alkyl carbonates which made them unlikely candidates for use in lithium-ion batten’ electrolytes.

[0007] Another approach involves the use of phosphonate-based salt additives as flame retardants in the electrolyte and / or battery structures, although these usually came with tradeoffs such as poor solubility in common electrolyte solvents and adverse impacts on battery¬ performance (further iterations of these compounds were also proposed for use in the recovery of lithium from alkaline media). Further reference is made to the following 237718301.1exemplary publications, all of which disclose the known limitations (in terms of solubility and electrochemical performance) of phosphorus-based flame-retardant additives: United States patent publications 2023 / 0155174A1 and 2010 / 0047695A1; United States patents 9,745,449, 10,903,522, and 11,404,723,; and international patent publication WO2018 / 054933A. These documents are all incorporated by reference herein.

[0008] Ion-exchanging polymers have also been proposed as complete replacements for conventional lithium-ion battery electrolytes. However, these materials are still comparatively new, unproven, and / or expensive. In some instances, they may also be unable to deliver the type of electrochemical performance characteristics now expected from conventional electrolyte batteries.

[0009] Any proposed additive for inhibiting flammability of the organic-based electrolyte system must still work in concert with the other chemical components of the battery system. Also, since introduction of such additives can displace working species present in the lithium-ion batteries, the additives must be highly effective so as to allow introduction at very low loading levels. Alternatively, if the additive could promote flame retardancy while also serving as a functional electrolyte component (e.g.. a lithium salt such as LiPFe that introduces lithium and provides ionic conductivity and other desired properties, such as promotion of a stabile SEI or cathode-electrolyte interface (CEI) formation, suppression of electrolyte solvents decomposition, broadening the operating voltage and / or temperature range, etc.), then the negative impact of decreased function and / or battery capacity caused by such a bifunctional additive would be minimized.

[0010] In short, flame retardant (FR) additives and lithium salts have been studied for their ability to enhance the thermal and electrochemical properties of the electrolyte. Various phosphorus compounds, such as trimethyl phosphate (TMP). triphenyl phosphate (TPP), and dimethyl methyl phosphonate (DMMP), have demonstrated significant flame retardancy, but at comparatively high concentrations that leads to decreased cell performance. These additives also exhibited poor compatibility with high energy7density anodes such as lithium-metal, graphite, and Si anodes. Lithium salts, such as lithium dimethyl phosphate (LiDMP), lithium bis(trimethylsilyl) phosphate (LiTMSP), and lithium bis(2,2,2-trifluoroethyl) phosphate [LiCUPCOCTLCFsh], are known to enhance solid electrolyte interface (SEI) film formation on the anode, improving lithium-ion battery performance through more ionic conductive passivation films. However, none of these solutions are known to deliver both flame retardance and acceptably improved functionality within an electrolyte component.337718301.1

[0011] In view of the foregoing, compositions and methods of synthesis for additives that could serve as such bifunctional additives would be welcomed.SUMMARY OF INVENTION

[0012] Novel organophosphorus compounds, hereafter referred to as flame retardant ions (FRIONs), are bifunctional lithium salts that are compatible with and useful in lithium-ion battery designs. In specific aspects, the bifunctional FRIONs incorporate specific phosphorus (V) moieties into or part of the structural backbone of the anion of the lithium salt, thereby seeking the lowest possible molecular weight of the anion in order to maximize % lithium in the salts. The synthesis of these phosphonates is achieved by selective dealkylating of various organophosphonates with a lithium halide salt to produce new lithium phosphonate salts such as: lithium ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate, lithium ethyl(2,6-difluorophenyl)phosphonate, lithium ethyl(2-bromophenyl)phosphonate, lithium ethyl phenyl phosponate, and lithium ethyl(2-hydroxyphenyl)phosphonate. Other short chain alkyls can be used in place of the ethyl group within the phosphonate and / or within the substitutions at the 5 position, and other halogens may prove useful in place of fluorine and bromine. Each of these compounds has been shown to enhance the thermal stability of the electrolyte solution without compromising the overall cell performance and safety.

[0013] FRION-based additives have excellent solubility in these and other common electrolyte solvents, in common electrolyte solvents (e.g., ethyl carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC)), allowing for seamless integration into electrolyte formulations. They also possess the desirable properties of being both low molecular weight (high percentage of Li content) and soluble in organic media. This enhanced solubility streamlines manufacturing processes and ensures homogeneous dispersion throughout the electrolyte, resulting in more effective flame retardancy.

[0014] Additionally, the aforementioned FRION-based additives significantly bolster the stability and uniformity of the solid electrolyte interface (SEI) layer. Theses additives simultaneously promote improved ionic conductivity while suppressing continued solvent decomposition by facilitating the rapid formation of the SEI layer. This dual-action mechanism not only advances safety measures but also unlocks fast-charging capabilities, even in the presence of high-volume change anode materials such as Si and Sn. These additives also contribute to superior electrochemical performance in lithium metal batteries437718301.1by addressing challenges associated with lithium stripping and plating, thereby reducing dendritic growth and enhancing cycling stability and safety

[0015] Finally, these additives remain effective across a wide temperature range, including challenging conditions commonly encountered by lithium-ion batter}7applications (e.g., from well below freezing up to 60°C). This wide range of temperatures allow for prospective adoption in lithium-metal and lithium-ion battery technologies that are particularly useful in electric vehicle applications.

[0016] Specific reference is made to the appended claims, drawings, and description below, all of which disclose elements of the invention. While specific embodiments are identified, it will be understood that elements from one described aspect may be combined with those from a separately identified aspect. In the same manner, a person of ordinary skill will have the requisite understanding of common processes, components, and methods, and this description is intended to encompass and disclose such common aspects even if they are not expressly identified herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 depicts the structure of earlier-developed FRIONs from the prior art.

[0018] Figure 2 is a schematic representation of FRIONs racemic structures attainable according to various aspects of the invention.

[0019] Figures 3A through 3C are representative synthesis routes for of selected FRIONs contemplated in Fig. 2.

[0020] With further reference to Table 1 below, Figure 4 is a graphical representation of the CV profiles of the baseline and FRION modified electroly tes.

[0021] With further reference to Table 1 below, Figure 5 is a graphical representation of the continuous charge-discharge cycles at Li-Li symmetnc cell of baseline and FRION-modified electrolytes.

[0022] With further reference to Table 1 below, Figures 6A and 6B are graphical representations of the EIS curves for the baseline and FRION-modified graphite half coin cells before and after three formation cycles at 0.05C rate.

[0023] With further reference to Table 1 below, Figures 7A through 7E are graphical representations of the initial formation cycles of baseline and FRION-modified electrolyte graphite half cells. Figure 7F is comparative analysis of Li+ content loss after first discharge and after formation cycle.537718301.1

[0024] With further reference to Table 1 below, Figure 8A is a graphical representation of charge-discharge current rates for selected FRIONs. Figure 8B is a graphical representation of voltage profiles over the charge-discharge cycles at different C-rates for the baseline and FRION-modified electrolyte graphite half cells.

[0025] With further reference to Table 1 below, Figures 9A through 9F are graphical representations of cyclic voltammetry of selected compositions disclosed herein.

[0026] Figure 10 is a thermogravimetric analysis of selected FRIONs contemplated herein.DETAILED DESCRIPTION

[0027] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. It is to be understood that other embodiments may be utilized and structural and functional changes may be made without departing from the respective scope of the invention. As such, the following description is presented by way of illustration only and should not limit in any way the various alternatives and modifications that may be made to the illustrated embodiments and still be within the spirit and scope of the invention.

[0028] As used herein, the words “example” and “exemplary” mean an instance, or illustration. The words “example” or “exemplary” do not indicate a key or preferred aspect or embodiment. The word “or” is intended to be inclusive rather an exclusive, unless context suggests otherwise. As an example, the phrase “A employs B or C,” includes any inclusive permutation (e.g., A employs B; A employs C; or A employs both B and C). As another matter, the articles “a” and “an” are generally intended to mean “one or more” unless context suggest otherwise.

[0029] Unless noted, all experiments were conducted in ambient conditions relying on common practices and methodologies (some of which can be informed by known testing standards published by organizations such as ASTM and / or by reference to procedures published by manufacturers of the applicable instrumentation and / or compositions used herein). Molecular weights may be weight average, and reference should be made to standard practices within the lithium-ion battery industry to better understand the following information.

[0030] The present invention relates to lithium phosphonate salts as additives in lithium-ion battery (LIB) electrolytes. Aspects of the inventive flame retardant ionic compositions (FRION) additives contemplated herein significantly improve the formation of the solid 637718301.1electrolyte interface (SEI) layer, enhancing utilization energy' density, cycle life, fastcharging capability, and reduced heat generation. These improvements are critical for maintaining the safety and efficiency of lithium-ion batteries under demanding conditions, especially those in electric vehicles and energy storage technology.

[0031] These salts have flame-retardant properties and maintain high electrochemical performance for both high energy density and high power density anode and cathode electrodes when added into lithium-ion battery electrolytes. Specifically, salts with high decomposition temperatures exceeding 200° C should be capable of prolonged usage in standard lithium-ion batteries, which are commonly designed for operation between -40° C up to 60° C.

[0032] To be clear, earlier types of FRIONs, such as the structure shown in Fig. 1, have been reported in the literature, and the use of bifunctional lithium borate and phosphate salts integrated with organophosphorus structure appeared to promote char formation upon combustion. However, difficulties in limited solubility7in alky l carbonates and higher molecular weights of these earlier FRIONs limited further consideration.

[0033] Here, the inventive, bifunctional FRIONs, including those depicted in Fig. 2, incorporate specific phosphorus (V) moieties into the structural backbone of the anion lithium salt. The inventive bifunctional FRIONs are further characterized by low molecular weight (in comparison to conventional electrolyte salts and earlier organophosphorus borate salts noted above) and lower cost (in comparison to other experimental or unproven alternatives). Often, these earlier organophosphorus borate salts were synthesized relying on chelation with tetraethyl diphosphinato catechol (DPC).

[0034] Using the synthesis and selective dealky lating of selected lithium halide salts described herein, new lithium phosphonate FRION salts attain increased solubility (in comparison to prior art inorganic and organic salts, such as those identified above). The most useful of these include: ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate, lithium ethyl(2,6-difluorophenyl)phosphonate, lithium ethyl(2-bromophenyl)phosphonate, lithium ethyl phenyl phosponate, and lithium ethyl(2-hydroxyphenyl)phosphonate. These novel compounds enhance the thermal stability of the electrolyte solution without compromising the overall cell performance. In some aspects, these lithium phosphonate salts that enhance both the fire-retardancy and electrochemical performance of LIBs. Overall, these innovations offer a promising solution to the ongoing challenges in lithium metal and lithium-ion battery technology for improving safety and fast charging capabilities.737718301.1

[0035] In one aspect, new and sufficiently soluble (for lithium-ion electrolyte purposes) FRIONs were made using a mono (P=0(0Et)2) functionalized precursor. This route produced combination lithium-phosphonate-borate compounds. More generally, synthesis can be effected from commercially available phenylphosphonate (Ph-P(=O)(OEt)2; commercially available phenols; or a multi-step process from commercially available aryl borates.

[0036] With reference to Figs. 2 and 3, the mono functionalized precursor was obtained by first generating the hydroxy phenylphosphonate. Phenol was then reacted with diethyl chlorophosphate (1 eq.) in the presence of triethyl amine. Then, with lithium diisopropylamide (LDA) generated in situ, a phospho-fries rearrangement produces as a clear yellow oil. Thereafter, one ethyl (Et) group is selectively replaced with lithium on the phosphonate moiety via exchange reaction with LiBr (2.5 eq) in the presence of acetonitrile (MeCN). All structures were confirmed via NMR spectroscopic and other analyses. Isopropyl bearing precursors can be synthesized in a similar manner, and other synthesis routes may be developed.

[0037] In various aspects, other short chain n-alkyl groups having fewer than 5 carbons could be used in place of the ethyl group on the phosphonate moiety. Methyl, n-propyl, and n-butyl are specifically contemplated.

[0038] Similarly, additional aspects of the invention could also incorporate short chain alky l groups in place of the isopropyl group at the 5 position of the phenyl ring. Here again, methyl, ethyl, propyl, and butyl groups are possible. Similarly, in some aspects, fluorine can be used in place of bromine, and other halogens may also prove useful.

[0039] As seen in Fig. 2, these additional aspects can be referred to as dual substituted lithium hydroxy and / or alkyl(phenyl)phosphonates, with R’ at the 2 position and R at the 5 position as shown or at the 6 position as indicated by X. R’ can be H, hydroxy, or a halogen and R can be H, branched alkyl group (e.g., 3 or 4 carbons), or a halogen. n-Alk refers to methyl, ethyl, n-propyl, or n-butyl.

[0040] Preparation of FRIONs involves dealkylation with LiBr or Lil (e.g., 2.5 equivalents of LiBr in refluxing acetonitrile). This produces lithium ethyl (2-bromophyenyl) phosponate. Similarly, lithium ethyl (5-isopropyl-2-hydroxyphenyl) phosphonate and lithium ethyl phenyl phosphonate can be synthesized in this manner based upon selection of starting materials.

[0041] Keeping in mind the goals of solubility, conductivity, and comparatively good resistance to thermal decomposition, especially within the conditions encountered in lithium-ion batteries, it should be understood that the specific compositions noted above are unique 837718301.1and useful. Nevertheless, this disclosure embraces minor substitutions (consistent with the aforementioned goals). Similarly, as with any synthesis process, yields in excess of 70%, 80%, or 90% are preferred, but it will be understood that minor impurities or remnants of the reactants may remain present without departing from the invention. In the same manner, those skilled in this field will appreciate purification and / or extraction techniques may further improve yields so as to allow even more complete realization of the goals and purposes of the invention described herein.

[0042] Further, with reference to Fig. 2, the methods reported herein tended to yield a racemic mixture of the desired FRIONs. Nevetheless, the invention contemplates all depicted structures.EXAMPLES

[0043] Exemplary Synthesis (lithium ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate)

[0044] A 50 mL round bottom flask was flame dried, charged with MeCN (25 mL) and placed under inert atmosphere. Under flowing N2, diethyl(5-isopropyl-2-hydroxyphenyl)phosphonate (5.015 g, 18.36 mmol) was added. LiBr (3.987 g, 45.91 mmol) was added under flow of N2. A condenser was affixed and the reaction was heated under reflux for 18 hrs. A cloudy solution was observed and the reaction was cooled to RT. The solvent was removed under reduced pressure and a white solid was observed. The solid was dissolved in fresh acetonitrile and the reaction was heated under reflux for an additional hour. The reaction was cooled to RT and the solvent was removed under reduced pressure. A white precipitate was obtained, washed. Adaptations can be made to attain the various FRIONs contemplated herein, as shown in Table 1 and Fig. 2.

[0045] Materials and Method for manufacturing electrolytes from FRIONs

[0046] A commercial electrolyte 1.2 M LiPFe in EC / EMC (3:7 wt) was obtained from TOMIYAMA PURE CHEMICAL INDUSTRIES, LTD. (“baseline electrolyte”) was used as the standard electrolyte. FRION electrolytes, as designated in Table 1 below, were prepared by adding 1 wt.% of each in-house synthesized lithium phosphonate salt: lithium ethyl(2-hydroxyphenyl) phosphonate, lithium ethyl (5-isopropyl-2-hydroxyphenyl) phosphonate, and lithium ethyl (2 -bromophenyl) phosphonate. The salts were gradually added into the standard electrolyte and mixed continuously in a sealed glass beaker at 500 rpm using a Tefloncoated magnetic stir bar on a magnetic hotplate stirrer (IKA C-Mag HS 7) at room temperature (23°C) for several hours until the homogeneous and transparent solution was obtained. All 937718301.1procedures were conducted in a glove box under an argon atmosphere, with O2 and H2O levels maintained below 1 ppm. The moisture content of the FRIONS electrolyte mixture was tested using Karl Fischer titration found to be under 40 ppm.

[0047] Flash Point (FP) test

[0048] The flash points (FP) of FRIONs were determined using a small-scale closed cup apparatus: the Seta Flash 82100-2 flash tester (SL 1096), in accordance with the screening method (ASTM D7236) and the fixed-temperature method (ASTM D3278). For each measurement, 2 mL of FRIONs were dispensed into the closed cup. The FP determination commenced at 5°C with a ramp rate of 2°C / min and continued until the flash point was identified.

[0049] Self-extinguishing time (SET) measurements

[0050] There are no standard protocols currently available for determining the selfextinguishing time (SET) of liquid samples. Most SET tests reported in the battery literature are adaptations of the standard UL 94 method, originally developed to assess solid materials' fire hazard, such as polymers and other non-metallic samples. In this study, SET tests were conducted directly on FR1ON electrolytes. For each test, 1 g of the FR1ON electrolyte sample was placed on a watch glass and ignited with a gas burner to get a flame for 3 seconds. Once ignition occurs and the flame is removed, the actual SET is expected to be independent of the ignition source.

[0051] Electrochemical measurement

[0052] The electrochemical impedance spectroscopy (EIS) measurements were carried out to determine the conductivity of the FRION electrolytes using a Gamry Potentiostat. The EIS measurements were conducted in the frequency range of 1MHz to 50 mHz at an AC bias of 5 VRMS. The obtained EIS data was fitted using EC -lab to calculate the solution resistance (Ro) and calculated the ionic conductivity of the FRIONs electrolytes.

[0053] The Cyclic Voltammetry (CV) measurements were performed in a Biologic battery tester to identify the electrochemical stability7of baseline electrolytes and FRION electrolytes. The CV experiments were conducted in the voltage range of 0-3 V for the anode electrodes and 2-4.5V for the cathode electrodes respectively at a voltage scan rate of 0.05 mV s-1. The EIS and CV measurements of FRION electrolytes were performed in a Swagelok cell, between stainless steel rods and calibrated using a standard NaCl electrolyte solution with a conductivity of 1431 uS / cm.

[0054] Structural characterization:1037718301.1

[0055] The chemical analysis of FRION electrolyte was studied using a Fourier-transform infrared spectroscopy (FTIR) Bruker VERTEX 80v under vacuum in attenuated total reflection mode (ATR) range 4000-400 cm'1with 64 scans per sample and a resolution of 2 cm'1. Thermogravimetric and differential scanning calorimeter (TG-DSC) analyses were performed on a CALVERT Pro system from room temperature to 600 °C at a heating rate of 5 °C / min under an Argon gas flow of 30 mL / min. The morphology and chemical composition of the samples were characterized using a tabletop SEM (Phenom XL, operating voltage. 15 kV). Rigaku X-ray powder diffraction (XRD) instrument (Cu Kot radiation, Z = 1.5418 A, scattering angles of 20-80° and step size of 0.5°).

[0056] Analysis

[0057] 1. Flash Point Test

[0058] The flash point test determined the flame retardancy of the baseline electrolyte and the modified electrolytes containing in-house synthesized FRION additives. The baseline electrolyte, consisting of 1.2 M LiPFe in a 3:7 volume ratio of ethylene carbonate (EC) and ethyl methyl carbonate (EMC), exhibited a flash point of 26 °C. In contrast, adding flameretardant additives increased the flash points of the baseline electrolyte. Even with as small an amount as 0.1 wt% of FRION additives, the flash point exceeded 26°C, indicating enhanced flame retardancy.

[0059] The improvement in flash points is attributed to the chemical structures of the FRION additives. The phosphonate group (-P(O)(OR)(OH)) in the synthesized FRION salts, including lithium ethyl(2-hydroxyphenyl)phosphonate and its derivatives, plays an important role in the enhancement of thermal properties. These lithium-phosphonate groups decompose under high-temperature conditions, releasing phosphoric acid derivatives that promote char layer formation. This char layer is a physical, thermal insulation barrier, reducing heat transfer. Additionally, hydroxyl (OH) groups contribute by forming hydrogen bonds with solvent molecules, decreasing the overall volatility. Bromine atoms in certain additives like lithium ethyl (2-bromophenyl) phosphonate exhibit radical quenching properties, effectively disrupting the combustion chain reactions by neutralizing free radicals.

[0060] Mechanistically, the decomposition of phosphonate additives generates polyphosphoric acid species, which act as dehydrating agents to convert surface hydrocarbons into char. Combined with radical scavenging by brominated compounds, this char formation mechanism ensures a two pronged approach to flame retardancy. The bulky isopropyl groups in some additives, such as lithium ethyl(5-isopropyl-2-1137718301.1hydroxyphenyl)phosphonate, further stabilize the system by increasing the steric hindrance, which reduces the decomposition rate of volatile components.

[0061] The flash point data, summarized in Table 1, clearly demonstrates the effectiveness of FRION additives. For example, the baseline electrolyte with 0.1 wt.% lithium ethyl (2 -bromophenyl) phosphonate exhibited a flash point increase to 27°C, while 0.1 wt.% lithium ethyl (5-isopropyl-2-hydroxyphenyl) phosphonate raised the flash point to 28°C. These results indicate the importance of the molecular structure and functional groups of FRION additives in enhancing flame retardancy.Table 1. Flashpoints for the baseline electrolyte (3:7 EC.EMC raito) and 0.1wt%> FRION additive contained baseline electrolyteDesignation Lithium Salt Flashpoint, ° C 26BASELINE ELECTROLYTE 1.2M LIPF6FRION-I modified baseline lithium ethyl phenyl 26.5Electrolyte phosphonateFRION-II modified baseline Lithium ethyl (2- 28Electrolyte hydroxyphenyl)phosphonateFRION-III modified baseline Lithium ethyl(5-isopropyl-2- 26.5Electrolyte hydroxyphenyl)phosphonateFRION-IV modified baseline Lithium Ethyl(2- 28Electrolyte bromophenyl)phosphonate

[0062] 2. Self-Extinguishing Time (SET) Measurements

[0063] Self-extinguishing time (SET) tests were performed to further evaluate the electrolytes' flame retardancy. For each test, 1 g of the electrolyte was ignited in open air, and the time required for the flame to extinguish was recorded. The baseline electrolyte exhibited a flame duration of approximately 40 seconds after ignition. In contrast, the modified electrolytes containing FRION additives showed significantly shorter flame durations, ranging from 20 to 25 seconds. .

[0064] The reduced flame duration observed with FRION additives is attributed to their ability to interfere with the combustion process. Ultimately, the decomposition of phosphonate groups at higher operating temperatures releases phosphoric acid derivatives,1237718301.1which catalyze the formation of a thermally stable char layer. This char layer acts as a thermal insulator barrier to oxygen diffusion and heat transfer, effectively reducing the intensity and duration of combustion. Hydroxyl functional groups stabilize combustion by forming hydrogen bonds with solvent molecules, reducing the system's volatility. Bromine atoms further inhibit combustion by scavenging free radicals, disrupting the exothermic reactions that sustain the flame

[0065] Interestingly, the baseline electrolyte was completely consumed during the SET test, leaving no residue in the sample container. In contrast, the FRION-containing electrolytes left a noticeable residue, indicating their capacity to form stable thermal degradation char products. These findings highlight the effectiveness of FRION additives in enhancing flame retardancy through mechanisms such as char formation and radical quenching.

[0066] 3. Electrochemical Stability Analysis of FRION electrolytes Using Cyclic Voltammetry

[0067] Cyclic voltammetry (CV) experiments were conducted on a CR2032 coin cell with lithium (Li) and nickel (Ni) metal electrodes to evaluate the electrochemical stability of the baseline electrolyte and the FRION additive-containing electrolyte. The measurements were performed in the voltage range of 0-3 V with a scan rate of 0.05 mV s '.

[0068] Fig. 4 shows the CV peaks of the baseline and FRION additive added electrolytes. The baseline electrolyte exhibited reduction peaks at ~1.4 V, and -0.8 V. which correspond to the reduction of solvents and salts, leading to irreversible reactions at the Ni and Li electrodes. In contrast, with the addition of FRION additives such as lithium ethyl(2-hydroxyphenyl)phosphonate, lithium ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate, and lithium ethyl(2-bromophenyl)phosphonate, a reduction peak above 2 V was observed. This peak is attributed to the selective reduction of the FRION additives, initiating SEI formation. The reduction of FRION additives likely follows a double-electron reaction mechanism due to the electron-withdrawing nature of the phosphonate groups, resulting in a stable and dense SEI layer, thereby protecting the electrode surface and enhancing electrochemical stability.

[0069] 4. Electrochemical Analysis with Lithium-Lithium Symmetric Cells

[0070] To determine the electrochemical stability of the FRION electrolytes in comparison with the baseline electrolyte, lithium-lithium symmetric CR2032 coin cells were fabricated. The Celgard separator was wetted with the baseline and FRION electrolytes, respectively. Herein. 16 mm diameter, 200 pm thick lithium strips were used as the working and counter electrodes for CR20232 lithium-lithium symmetric coin cells.1337718301.1

[0071] The lithium-lithium symmetric cells were cycled at a current density of 500 mA / cm2for 30 minutes of charge followed by 30 minutes of discharge, with no rest time between the charge-discharge cycles. Fig. 5 shows the charge-discharge voltage profiles of the lithium-lithium symmetric cells over 100 hours of cycling for both the baseline electrolyte and the FRION-modified electrolytes.

[0072] The baseline electrolyte-containing lithium-lithium symmetric cells showed stable voltage behavior during the initial few- cycles. However, after several cycles, the chargedischarge voltages started to increase, indicating electrolyte degradation and a loss of stability'. This behavior can be attributed to continuous lithium plating and stripping processes causing the formation of uneven lithium deposits, which further destabilize the electrolyte through repeated decomposition reactions.

[0073] In contrast, the FRION-electrolyte-containing symmetric cells exhibited a reduction in charge-discharge voltages during the initial few cycles, similar to the baseline electrolyte. However, unlike the baseline electrolyte, the FRION-electrolyte cells demonstrated stable charge-discharge voltage behavior over extended cycling. This stability can be explained by the FRION additives’ ability to control the electrolyte degradation and promote the formation of a more uniform and stable solid electrolyte interphase (SEI). Also, the reduced and stabilized voltage profiles suggest effective mitigation of lithium dendrite growth and improved plating-stripping efficiency.

[0074] The increasing and decreasing charge-discharge voltage trend in the baseline electrolyte indicates continuous electrolyte decomposition and an unstable SEI, which leads to irregular lithium deposition and stripping. Conversely, the stability observed with the FRION-modified electrolyte highlights its role in maintaining consistent lithium platingstripping processes, which is critical for long-term cycling stability in lithium-metal batteries.

[0075] 5. Electrochemical Analysis with Graphite Anode

[0076] To determine the stability of the baseline and FRION-modified electrolytes with graphite anodes, CR2032 coin half cells w ere fabricated. The graphite electrode composition consisted of 98% graphite active material and 2% PVDF binder. A 16 mm diameter graphite electrode served as the working electrode, while a 15 mm diameter lithium metal electrode was used as both the counter and reference electrode. After assembling the cells, they were soaked for 12 hours before conducting electrochemical impedance spectroscopy (EIS) and the SEI formation cycles tests.

[0077] Electrochemical Impedance Spectroscopy (EIS) Results1437718301.1

[0078] Figs. 6A and 6B show the EIS curves for the baseline and FRION-modified electrolyte graphite anode half-cells. Before the initial charge-discharge cycles (cell formation cycles), the EIS curves for both the baseline and FRION-modified electrolyte graphite half-cells exhibited one semicircle in the high-frequency region (1 MHz to 1 kHz) and a linear slope in the low-frequency region (1 kHz to 50 mHz). Typically , the intersection of the EIS curve with the real (X-axis) at high frequencies represents the solution resistance or ohmic resistance (R<>) of the cell. The diameter of the semicircle reflects the charge transfer resistance (Ret) in the medium-frequency range and the solid electrolyte interface resistance (RSEI) in the high-frequency range.

[0079] After three successive formation cycles, the EIS curves displayed a distinct change in trend. Two semicircles appeared in the high- to medium-frequency range (500 kHz to 1 kHz), followed by a linear slope in the low-frequency range. This change indicates modifications in interfacial and charge transfer properties during the formation cycles.

[0080] From the EIS measurement calculations, the solution resistance (Ro) and charge transfer resistance (Ret) were observed to be higher for the FRION-I, FRION-III, and FRION-1V modified electrolytes compared to the baseline electrolyte in the graphite anode half-cells, both before and after the formation cycles, as shown in Table 2.Table 2. EIS test data of baseline and FRION-modified electrolytesBssAiae 1 t.3S I LSIFRION-I. m.ads&ed efetaiyie 12.1 < 1FRR2N-H meddssd 244 2.45FRION-ili etefe&lyte 12.75 U4.2FRION-Fv' iKC'iiiSsd 12.34 3 31

[0081] This trend can be attributed to the interaction of FRION additives with the graphite surface and electrolyte, which facilitates the early-stage stabilization of the SEI layer. However, the Ro and Ret values were higher for the FRION-II electrolyte in the graphite half-cell compared to the baseline and the other three FRION-modified electrolyte graphite half-cells. This indicates that the FRION-II additive increased the electrolyte's dielectric properties, which controls the initial decomposition of electrolyte solvents and1537718301 1lithium salts. After three formation cycles, the diameter of the first semicircle (representing Ret) in the EIS curve decreased for the FRION-modified electrolyte graphite half-cells. Conversely, the diameter of the second semicircle (representing RSF.I) significantly increased for all FRION-modified electrolyte graphite half-cells. This suggests that a stable SEI layer formed on the graphite electrode, which resulted in a decrease in the charge transfer resistance (Rct) of the graphite half-cells.

[0082] Figs. 7A through 7E show the initial three formation charge-discharge cycles at a 0.05C rate for the baseline and FRION-modified electrolyte graphite half-cells. The Li+ content loss after the lithiation of the graphite electrode was higher for the baseline and FRION-II electrolyte graphite half-cells compared to the other FRION-modified electrolyte graphite half-cells, as shown in Fig. 7F. However, starting from the second formation cycle, the Li+loss for the FRION-II modified electrolyte significantly decreased, and the Li+content storage capacity recovered to 100%.

[0083] In contrast, for the baseline electrolyte graphite half-cells, Li+content loss continued throughout the initial three formation cycles, indicating incomplete and unstable SEI layer formation on the graphite electrode. This suggests that more formation cycles are required to develop a stable and uniform SEI layer for the baseline electrolyte.

[0084] For the FRION-modified electrolytes, the improved Li+content storage capacity can be attributed to the formation of a more stable and uniform SEI layer on the graphite electrode. This stability may be due to the decomposition products of FRION additives during the initial electrochemical formation cycles, including compounds such as Li2CO3, LiF, and phosphorus and borate-based lithium compounds. Without intendin to be bound by any theory, it is believed he uniform and stable SEI layer could act as an electrical insulator with good ionic conductivity.

[0085] The scanning electron microscopy (SEM)-Energy-Dispersive X-ray Spectroscopy (EDS) analysis supported a further finding that, unlike the baseline electrolyte (which produces a granular, porous, and carbon-rich SEI), the FRION electrolytes tend to create a dense, continuous interphase enriched in C, O, F, and Br species. These inorganic species originate from controlled early-cycle decomposition of the FRION additives, which rapidly establishes a mechanically robust and ionically conductive SEI that suppresses further solvent breakdown over the cycles. This compact morphology could promote uniform Li+transport and reduces charge-transfer resistance. Electrical impedance studies (as represented in Figs.8a-8b) help to confirm the resulting decrease in interfacial resistance and the sustained ionic conductivity enabled by the FRION -derived SEI.1637718301.1

[0086] To evaluate the electrochemical stability of the FRION-modified electrolytes and the stability of their SEI layer after the formation cycles, a rate capability test was conducted on the graphite half-cells, as shown in Figures 8A and 8B. Figure 8A presents the current vs. time curves, while Figure 8B illustrates the voltage vs. time curves for different chargedischarge current rates (C -rates). The rate capability test involved three continuous chargedischarge cycles at various C-rates in a sequential order: increasing from lower to higher C-rates and then decreasing back to the lower C-rates. The tested C-rates included 0.05C, 0.1C, 0.5C, and 1C.

[0087] The test results revealed that the FRION-modified electrolyte graphite half-cells exhibited excellent Li+ cycling reversibility across all tested C-rates. In contrast, the baseline electrolyte graphite half-cell showed higher Li+ irreversibility after the rate capability test. These findings suggest that the incorporation of FRION salts enhanced the electrochemical performance of the baseline electrolyte by improving the stability at low lithium reduction potentials, higher energy density7for anode electrodes, and optimizing electrode-electrolyte interface properties.

[0088] 6. Electrochemical Analysis with Cathode electrode

[0089] To evaluate the electrochemical stability of the baseline and FRION-modified electrolytes for high-operating-potential cathode electrodes, 2032-coin half-cells were fabricated using a LiNi{l-x-y}Co xAl yO2 (NCA) cathode electrode harvested from a commercial lithium-ion pouch cell (model SLPB 533459H4, Kokam Co., Ltd.). The NCA cathode disk had a diameter of 15 mm, while lithium metal with a diameter of 16 mm was used as both the counter and reference electrode. A Celgard separator wetted with either the baseline electrolyte or the FRION-modified electrolyte was used for cell assembly. Following fabrication, the cells were soaked for 12 hours to ensure proper wetting and interfacial stabilization before electrochemical testing.

[0090] Electrochemical Impedance Spectroscopy (EIS) Results

[0091] After 12 hours of electrolyte soaking, the NCA-CR2032 half-coin cells were subjected to electrochemical impedance spectroscopy (EIS) measurements before and after cyclic voltammetry (CV) tests. From the EIS measurements taken before the CV tests, the curves revealed that the solution resistance (Ro) and charge transfer resistance (Ret) were higher for the FRION-modified electrolytes compared to the baseline electrolyte. This behavior can be attributed to the molecular interactions between the FRION additives and electrolyte solvents and the initial stabilization of the cathode electrolyte interphase (CEI) layer on the NCA electrode surface.1737718301.1

[0092] After three successive CV cycles, both Ro and Ret decreased significantly for the FRION additive-based electrolytes. This reduction suggests improved ionic mobility’ and enhanced charge transfer kinetics at the electrode-electrolyte interface. Additionally, the decrease in Ret highlights the electrochemical stability of the FRION -modified electrolytes with the NCA electrode, with no evidence of electrolyte reduction at the higher operating voltages of the NCA cathode.

[0093] Cyclic Voltammetry (CV) Analysis

[0094] Cyclic voltammetry (CV) was conducted at a scan rate of 0.05 mV / s within a voltage range of 2.5 V to 4.3 V to determine the electrochemical voltage stability window. The CV results revealed identical redox potentials for both the baseline and FRION-modified electrolytes, with no additional redox peaks observed. This observation indicates that the FRION additives do not cause unwanted side reactions or degrade under high-voltage conditions, confirming their compatibility and stability with the NCA cathode. See Figs. 10a and 10b.

[0095] The absence of additional redox peaks underscores the chemical stability of the FRION-modified electrolytes, even at the high operating voltages required for NCA cathodes. These results indicate that FRION-modified electrolytes are not only compatible with high-voltage cathode materials but also maintain their electrochemical integrity during cycling.

[0096] The combined findings from the EIS and CV analyses demonstrate that FRION additives significantly enhance the electrochemical stability of lithium-ion battery electrolytes. The initially higher resistance values, which decrease over time, highlight the stabilizing effect of the additives on the SEI layer. Moreover, the chemical inertness of the FRION additives under high-voltage conditions further confirms their suitability for advanced lithium-ion battery applications, particularly for high-voltage cathode materials such as NCA and other high Ni-content cathode electrodes.

[0097] 7. Preparation of novel lithium salts

[0098] With reference to Fig. 3, the preparation of the new lithium salts 2a-d is achieved by reaction of previously reported phosphonates with LiBr or Lil to effect dealkylation. In one example, the reaction of the starting material with 2.5 equivalents of LiBr in refluxing acetonitrile leads to the generation of a precipitate of lithium ethyl(2-hydroxyphenyl)phosphonate. The white solid can be collected by vacuum filtration and dried under reduced pressure to give good yield (82%) (Scheme 1). Similarly, lithium ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate, lithium ethyl phenyl phosphonate and lithium 1837718301.1ethyl(2-bromophenyl)phosphonate were isolated as white solids in 70-79% yields. The reaction mechanism is schematically represented by

[0099] Scheme 1

[0100] The conversion of intermediaries was corroborated by the observation of upfield shifts for the31P{1H} NMR resonances upon formation of the lithium salts. For example, the31P{1H} NMR resonances for la (5 = 22.4 ppm) significantly downfield by 11.7 ppm relative to the resonance for 2a (5 = 11.6 ppm). The conversions of Ib-ld to 2b-2d were also accompanied by comparable upfield shifts of31PNMR resonances (11.0-11.9 ppm).

[0101] Lithium phosphonates displayed good thermal stability, as demonstrated by TGA in Fig. 10. FRION II begins to decompose above 240 °C. FRIONs I and IV are comparatively more stable and begin to decompose around 320 and 280 °C respectively. After each experiment a small residue, ca 28% by total mass, remains, which could indicate char formation.

[0102] Following synthesis and complete characterization, the new materials underwent electrochemical and flammability testing as lithium-ion battery electrolyte additives. Initial screening experiments showed that these salts have flame-retardant properties and maintain high electrochemical performance for both high energy density and high power density anode and cathode electrodes when added into lithium-ion battery electrolytes. They also significantly bolster the stability of the solid electrolyte interface (SEI) layer while concurrently enhancing ionic conductivity. Thermal gravimetric analysis data of various salts is depicted in Fig. 10.

[0103] Based on these findings, the foregoing FRION additives provide robust flameretardant properties and maintain and / or enhance the electrochemical performance of lithium-ion batteries. This dual benefit significantly advances existing solutions, offering a comprehensive approach to improving lithium-ion batteries including lithium metal-based lithium-ion batteries, safety, and performance.

[0104] Batteries and electrolytes based upon the various additives (i.e., the FRIONs and related derivatives) contemplated by this disclosure exhibit many unique and advantageous properties. For example, when added at between 0.01 to 5.00 wt.% (relative to the mass of the electrolyte), the additive can increase the flash point of the electrolyte by at least 1° C in comparison to the electrolyte when the additive is not present. At that amount, the additive also reduces the self-extinguishing time of the electrolyte by at least 20% (again, in comparison to the electrolyte when the additive is not present).1937718301.1

[0105] When used in combination with alkyl-carbonate solvent(s) and a conducting lithium salt, the additives will produce at 10 wt.% of char residues when combusted at temperatures in excess of 600° C. Additionally, this combination will exhibit a decomposition temperature of at least 200° C.

[0106] Methods of stabilizing the SEI and the cathode-electrolyte interface (CEI) are also contemplated. With respect to the former the additive will undergo preferential reduction above 1.5 V vs. Li / Li+reference, reduce charge-transfer resistance by at least 10% after three formation cycles, and suppress irreversible lithium loss during formation by at least 15%. The latter insures, at greater than or equal 4.2 V, the additive remains inert from 1.0 up to 4.5 V, particularly when: (a) he cathode comprises a positive-electrode active material selected from layered oxides (including NCA, NCM and high-nickel compositions), spinels (including LNMO and high-voltage spinels), olivines (including LFP and LMFP), polyanion cathodes, disordered rock-salt cathodes, lithium-rich or doped / coated derivatives, or combinations thereof, and / or (b) the anode comprises graphite, hard carbon, soft carbon, silicon-containing, tin-containing, lithium metal, lithium alloy, or combinations thereof.

[0107] Batteries constructed to incorporate the additive and / or electrolytes described herein enables stable plating and stripping for at least 100 hours at greater than or equal to 0.5 mA / cm2They also suppress dendritic lithium growth by forming a robust inorganic SEI. When the batteries are lithium-ion or lithium-metal based, the additive enables the cell to exhibit a flash-point increase of at least 1° C and a SET reduction of at least 10%, while separately maintaining operational stability from below freezing up to 60° C.

[0108] Generally speaking, these lithium-containing phosphonate salts increase flash point, reduce self-extinguishing time, and improve SEI and CEI stabilization. They also act as a flame retardant, and can even improve the fast-charging performance by enabling reversible Li+intercalation at t >1C. Separately, they produce at least a 5% reduction in polarization of the battery at 1C relative to an additive-free electrolyte.

[0109] Thus, in one aspect, a flame retardant ionic composition that is soluble in at least one alkyl carbonate is contemplated. That composition includes a cation and phosphonate-based anion having a structure selected from:£7 nli "V! ;

[0110] i) ; or2037718301.1R’ 0RxxU, .A'"I On-A!k

[0111] li) ; and

[0112] where R is H or an alkyl group with no more than 4 carbons; R’ is H, hydroxy, or a halogen; R"’ H or a halogen; and n-Alk is methyl, ethyl, n-propyl, or n-butyl group.

[0113] Additional aspects include any one or combination of the following additional features associated with or based upon the foregoing composition:• An electrolyte solution comprising the foregoing compositions that is dissolved in at least one non-aqueous organic solvent selected from at least one of: an alkyl carbonate, a fluorinated a carbonate, a cyclic carbonate, a linear carbonate, an ether, an ester, a nitnle, a sulfone, and combinations thereof;• An electrolyte solution comprising the foregoing compositions including up to 0.1 wt.% of the composition of claim 1 and at least one of: ethyl carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), a fluorinated carbonate, and combinations thereof;• An electrolyte solution comprising the foregoing compositions with greater than 0.1 wt.% of the composition of claim 1 and at least one of: EC, EMC, DEC, DMC, a fluorinated carbonate, and combinations thereof;• A lithium-based battery including any of the foregoing electrolyte solutions;• wherein the cation includes lithium;• wherein the cation consists of Li+;• wherein n-Alk is ethyl;• wherein the halogen is bromine and / or fluorine; and / or• wherein the phosphonate-based anion is selected from ethyl(5-isopropyl-2- hydroxyphenyl)phosphonate, ethyl(2,6-difluorophenyl)phosphonate, ethyl(2- bromophenyl)phosphonate, ethyl phenyl phosponate, and ethyl(2- hydroxyphenyl)phosphonate.

[0114] In a further aspect, a method of synthesizing the foregoing compositions is contemplated. The method starts by reacting a phenol with diethyl chlorophosphate in the presence of triethyl amine to produce a hydroxy phenylphosphonate precursor. Next, lithium is introduced to the hydroxy phenylphosphonate precursor and an alkyl group is introduced to the hydroxy phenylphosphonate precursor. After the lithium and alkyl group have been 2137718301.1introduced, an exchange reaction is initiated using a lithium halide to produce the composition. In these methods, tthe alkyl group is selected from an ethyl group and an isopropyl group and / or the lithium halide is selected from lithium bromide and lithium iodide and the exchange reaction occurs with acetonitrile. Separately, the introducing lithium may involve a rearrangement reaction including lithium diisopropylamide. LiBH4 can dissolved in a solvent, such as tetrahgydrofuran (THF), and the solvent is subsequently removed prior to producing the composition.

[0115] When the lithium-containing phosphonate salts were used as flame-retardant electrolyte additives, the inventors observed increased flash point, reduced self-extinguishing time, and improved SEI or CEI stability. Thus, the electrolytes, additives, and the compositions themselves may individually and collectively function simultaneously as a flame-retardant additive and a solid-electrolyte-interphase (SEI)-forming additive, thereby providing both flame-retardancy and SEI and CEI stabilization.

[0116] Additional aspects of the invention include flame retardant electrolytes and additives (that, in some aspects, include the specific FRIONs described above), as well as batteries that incorporating those electrolytes and additives. Numerous performance advantages are delivered by these electrolytes and additives. For example, when the additive is provided at 0.01-5 wt.% (relative to the electrolyte mass), the flash point of the electrolyte increases by at least 1 °C. The additive also reduces the self-extinguishing time (SET) of the electrolyte by at least 20%. When combined with an alkyl-carbonate solvent and a conducting lithium salt, the resulting electrolyte will produce at least 10 wt.% char residues at > 600 °C (i.e., when the electrolyte or battery undergoes thermal decomposition or rapid combustion), with the additive in that resulting electrolyte exhibiting a decomposition temperature of at least 200 °C.

[0117] Those advantages may also manifest in a number of ways when batteries rely on these electrolytes and additives. For example, any of the foregoing additives and electrolytes may serve: (i) as a way to stabilize the SEI and / or the cathode-electrolyte interface (CEI), (ii) as a way to enable stable plating and stripping for at least 100 hours at >0.5 mA / cm2, and (iii) as a way to suppress dendritic lithium growth through the formation of a robust inorganic SEI (in one aspect, the robust inorganic SEI does not include any discrete organic compounds). With regard to stabilizing the SEI, the method specifically includes introducing the additive / FRION to an electrolyte that undergoes preferential reduction above 1.5 V vs Li / Li+, which may also create an SEI that reduces charge-transfer resistance by at least 10% after three formation cycles and that suppress irreversible lithium loss during formation by at least 2237718301.115% (relative to the input of lithium). When the CEI is stabilized (at >4.2 V), the additive / FRION will remain inert from 1-4.5 V.

[0118] Specific examples of cathode materials that are particularly amenable to the advantages mentioned above include those w th a positive-electrode active material selected from layered oxides (including NCA, NCM and high-nickel compositions), spinels (including LNMO and high-voltage spinels), olivines (including LFP and LMFP), polyanion cathodes, disordered rock-salt cathodes, lithium-rich or doped / coated derivatives, or combinations thereof. Similarly, anodes may comprise graphite, hard carbon, soft carbon, silicon-containing, tin-containing, lithium metal, lithium alloy, or combinations thereof.

[0119] It will be understood that the emphasis of this research was in the context of lithium-ion batteries. Nevertheless, it will be understood that lithium-metal and other lithium-based battery systems may also rely on the same or similar electrolytes as those for which the FRIONs here have proven useful. Thus, any reference to lithium-ion batteries should not necessarily be considered as limited only to those systems.

[0120] In those aspects involving a lithium-ion or lithium-metal battery with an anode, a cathode, and an electrolyte containing the additive / FRION, the battery exhibits a flash-point increase of at least 1 °C and a SET reduction of at least 10%. These batteries also maintain operational stability7from below7zero degree Celsius to 60 °C.

[0121] A method of improving fast charging performance such batteries is also contemplated. When the additives and / or electrolytes are employed, reversible Li+intercalation at >1C is enabled. These batteries may also exhibit at least a 5% reduction in polarization at 1C relative to an additive-free electrolyte as part of that method.

[0122] Although the present embodiments have been illustrated in the accompanying drawings and described in the foregoing detailed description, it is to be understood that the invention is not to be limited to just the embodiments disclosed, and numerous rearrangements, modifications and substitutions are also contemplated. The exemplary embodiment has been described with reference to the preferred embodiments, but further modifications and alterations encompass the preceding detailed description. These modifications and alterations also fall within the scope of the appended claims or the equivalents thereof.2337718301.1

Claims

CLAIMSWhat is claimed is:

1. A flame retardant ionic composition that is soluble in at least one alkyl carbonate, the composition comprising:a cation; anda phosphonate-based anion having a structure selected from:7 9via1) ; orwherein R is H or an alkyl group with no more than 4 carbons; R‘ is H, hydroxy, or a halogen; R” H or a halogen; and n-Alk is methyl, ethyl, n-propyl. or n-butyl group.

2. An electrolyte solution comprising the composition of claim 1 dissolved in at least one non-aqueous organic solvent selected from at least one of: an alkyd carbonate, a fluorinated a carbonate, a cyclic carbonate, a linear carbonate, an ether, an ester, a nitrile, a sulfone, and combinations thereof.

3. The electrolyte solution of claim 2 includes up to 0.1 wt.% of the composition of claim 1 and at least one of: ethyl carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), a fluorinated carbonate, and combinations thereof.

4. The electrolyte solution of claim 2 includes greater than 0.1 wt.% of the composition of claim 1 and at least one of: EC, EMC, DEC, DMC, a fluorinated carbonate, and combinations thereof.

5. A method of synthesizing the composition of claim 1 wherein the phosphonate-based anion is selected from structure (i) or structure (ii) and the method includes:reacting a phenol with diethyl chlorophosphate in the presence of triethyl amine to produce a hydroxy phenylphosphonate precursor;introducing lithium to the hydroxy phenylphosphonate precursor;introducing an alky l group to the hydroxy phenylphosphonate precursor; and2437718301.1after the lithium and alkyl group have been introduced, initiating an exchange reaction using a lithium halide to produce the composition.

6. The method of claim 5 wherein the alkyl group is selected from an ethyl group and an isopropyl group.

7. The method of claim 5 wherein the lithium halide is selected from lithium bromide and lithium iodide and the exchange reaction occurs with acetonitrile.

8. The method of claim 5 wherein the introducing lithium involves a rearrangement reaction including lithium diisopropylamide.

9. The method of claim 5 wherein the LiBFE is dissolved in a solvent and the solvent is subsequently removed prior to producing the composition.

10. The method of claim 9 wherein the solvent is tetrahydrofuran (THF).

11. A lithium-based battery including the electrolyte solution of claim 2.

12. A lithium-based battery including the electrolyte solution of claim 3.

13. A lithium-based battery including the electrolyte solution of claim 4.

14. The composition of claim 1 wherein the cation includes lithium.

15. The composition of claim 1 wherein the cation consists of Li+.

16. The composition of claim 1 wherein n-Alk is ethyl.

17. The composition of claim 1 wherein the halogen is bromine and / or fluorine.

18. The composition of claim 1 wherein the phosphonate-based anion is selected from ethyl(5-isopropyl-2-hydroxyphenyl)phosphonate, ethyl(2.6-difluorophenyl)phosphonate. ethyl(2-bromophenyl)phosphonate, ethyl phenyl phosponate, and ethyl(2-hy dr oxy phenyl )phosphonate.

19. An electrolyte solution comprising the composition of claim 18 dissolved in at least one non-aqueous organic solvent selected from at least one of: an alkyl carbonate, a fluorinated a carbonate, a cyclic carbonate, a linear carbonate, an ether, an ester, a nitrile, a sulfone, and combinations thereof.

20. The electrolyte solution of claim 19 includes up to 0.1 wt.% of the composition and at least one of: ethyl carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), a fluorinated carbonate, and combinations thereof.

21. The electrolyte solution of claim 19 includes greater than 0.1 wt.% of the composition and at least one of: EC, EMC, DEC, DMC, a fluorinated carbonate, and combinations thereof.2537718301.1

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