Electrolyte composition

Abstract

The present disclosure provides an "electrolyte composition". A lithium-ion battery having an electrode assembly is presented. The electrode assembly has a current collector and a positive active material layer on the current collector. The electrode assembly also has an electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8 M to 0.2 M and 7 wt% of an ethoxyphosphazene additive dissolved in a solvent mixture of ethylene carbonate and sulfolane in a volume ratio of 25 / 2. The electrolyte penetrates the surface of the positive active material layer to inhibit electrochemical oxidation of the positive active material layer during electrochemical cycling.

Description

Technical Field

[0001] This disclosure relates to electrolyte compositions for use in lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries require electrolytes that maintain high ionic conductivity and stability at elevated temperatures. Summary of the Invention

[0003] An electrode assembly includes: a current collector; a positive electrode active material layer on the current collector; and an electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8M to 0.2M, and 7% by weight of ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane in a volume ratio of 25 / 2. The electrolyte permeates the surface of the positive electrode active material layer and is configured to inhibit electrochemical oxidation of the positive electrode active material layer during electrochemical cycling of the positive electrode active material layer. The electrolyte may include 1% by weight of fluoroethylene carbonate. The electrolyte may also include 0.5% by weight of vinylene carbonate. In some configurations, the electrolyte may include 0.5% by weight of propylene sulfite. The electrolyte may also include 0.3% by weight of propylene sulfone. The electrolyte may also include 0.5% by weight of ethyl sulfate anhydride. In some configurations, the electrolyte may include 0.7% by weight of lithium difluoro(oxalate)phosphate. In other configurations, the electrolyte may include 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl sulfate anhydride, and 0.7% by weight of lithium difluoro(oxalate) phosphate.

[0004] A battery cell includes a negative electrode, a positive electrode, and an electrolyte. The electrolyte comprises lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8M to 0.2M, and 7% by weight of ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane. The electrolyte saturates the negative and positive electrodes such that lithium ions dissociated from the lithium bis(fluorosulfonyl)imide are stabilized by complexing with ethoxyphosphazene and sulfolane molecules. The electrolyte may include 1% by weight of fluoroethylene carbonate. The electrolyte may also include 0.5% by weight of vinylene carbonate. In some configurations, the electrolyte may include 0.5% by weight of propylene sulfite. The electrolyte may also include 0.3% by weight of propylene sulfone. The electrolyte may also include 0.5% by weight of ethyl sulfate anhydride. In some configurations, the electrolyte may include 0.7% by weight of lithium difluoro(oxalate)phosphate. In other configurations, the electrolyte may include 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl sulfate anhydride, and 0.7% by weight of lithium difluoro(oxalate) phosphate.

[0005] Another battery cell includes a negative electrode, a positive electrode, and an electrolyte comprising lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and an ethoxyphosphazene additive, all dissolved in a solvent of ethylene carbonate and sulfolane. The electrolyte saturates both the negative and positive electrodes, stabilizing lithium ions released from the lithium bis(fluorosulfonyl)imide through solvation with ethoxyphosphazene and sulfolane molecules. The ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide can be from 0.8M to 0.2M. The solvent of ethylene carbonate and sulfolane can have a volume ratio of 25 / 2. The electrolyte may comprise 7 wt% ethoxyphosphazene, 1 wt% fluoroethylene carbonate, 0.5 wt% ethylene carbonate, 0.5 wt% propylene sulfite, 0.3 wt% propylene sulfone, 0.5 wt% ethyl acetate anhydride, and 0.7 wt% lithium difluoro(oxalate)phosphate. Attached Figure Description

[0006] Figure 1 This is a table showing various electrolyte compositions;

[0007] Figure 2 It is a comparison Figure 1 A table of physical properties and flash points of the electrolyte composition;

[0008] Figure 3 The ignition time test results for the selected electrolyte composition are shown;

[0009] Figure 4 The results of the extinction time test for the selected electrolyte composition are shown;

[0010] Figure 5 and Figure 6 It is a graph showing the cycle life performance of the selected electrolyte composition;

[0011] Figure 7 The swelling ratio of a pouch cell containing a selected electrolyte composition is shown;

[0012] Figure 8 The capacity retention rate of a battery cell containing a selected electrolyte composition is shown; and

[0013] Figure 9 This is a schematic diagram of a battery cell, showing the positive electrode, negative electrode, separator, and liquid electrolyte that permeates the electrode and separator. Detailed Implementation

[0014] This document describes embodiments. However, it should be understood that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The drawings are not necessarily drawn to scale. Some features may be enlarged or minimized to show details of specific components. Therefore, the specific structural and functional details disclosed herein should not be construed as limiting, but merely as a representative basis for teaching those skilled in the art.

[0015] The various features shown and described with reference to any of the accompanying drawings may be combined with features shown in one or more other drawings to produce embodiments not explicitly shown or described. The combinations of features shown provide representative embodiments for typical applications. However, for a particular application or implementation, various combinations and modifications of features consistent with the teachings of this disclosure may be desired.

[0016] Unless otherwise expressly stated, all numerical values ​​and ranges relating to quantities, measurements, percentages, weights, and similar numerical references within this document should be understood as being preceded by the term "about". This applies even where the term "about" is not explicitly used. The intention is that all values ​​and ranges encompass variations that may arise from standard measurements, manufacturing processes, material properties, and the intended functionality of various aspects of this disclosure. For example, when a composition is described as having "5% by weight of component", it should be understood as "about 5% by weight of component". Furthermore, when numerical values ​​are presented as ranges such as "100 to 200 units", the range should be interpreted as actually meaning "about 100 to about 200 units". Such variations are implicitly incorporated within the scope of this disclosure.

[0017] This disclosure relates to heat-resistant electrolyte compositions that exhibit enhanced thermal stability by incorporating specific heat-resistant materials into a combination of ethoxy(pentafluoro)cyclotriphosphazene (PFPN) and sulfolane. The specific heat-resistant materials are fluorinated ester derivatives and fluorinated carbonate materials. When combined with PFPN and sulfolane, these additives contribute to increasing the activation point and overall heat resistance of the electrolyte.

[0018] This is likely due to the interaction between PFPN, sulfolane, and lithium cations as the temperature of the lithium-ion battery (LiB) cell increases. This interaction can promote the desorption of fluorine from both PFPN and certain heat-resistant materials, thereby increasing inhibition. The desorbed fluorine can act as an enhancer of the inhibitor.

[0019] The increased heat resistance of the proposed electrolyte composition was demonstrated in experimental comparisons. The proposed electrolyte composition has an activation point of 95°C or higher. Furthermore, the proposed electrolyte composition does not initiate under the same conditions regardless of the duration of exposure. This behavior is similar to that of ionic liquids, which are known for their heat resistance. However, unlike conventional ionic liquids, which require a presence quantity exceeding 20%, resulting in increased viscosity and performance trade-offs, the proposed electrolyte composition maintains an acceptable balance between viscosity and ionic conductivity.

[0020] Battery cells incorporating the proposed electrolyte composition exhibit equivalent cycle life performance at both room temperature and 45°C, with increased storage performance at 60°C. These properties make the proposed electrolyte composition suitable for high-capacity LiB batteries, particularly those used in automotive applications where high electrochemical performance may be required.

[0021] Figure 1 This is a table of compositions of various electrolytes. Each electrolyte includes a salt, a solvent system, and various additives, such as heat-resistant materials and free radical scavengers.

[0022] The first reference electrolyte (electrolyte #1) is a conventional LiB electrolyte containing 1.0 M lithium hexafluorophosphate (LiPF6) as the conductive salt. The solvent used is 25 vol% ethylene carbonate (EC) and 75 vol% ethyl methyl carbonate (EMC), with 0.5 wt% vinylene carbonate (VC), 1 wt% fluoroethylene carbonate (FEC), and amphoteric additives such as 0.5 wt% polystyrene (PS), 0.3 wt% 1,3-propenyl sulpholol (PRS), 0.5 wt% ethylene sulfate (ESA), and 1 wt% lithium difluorophosphate (LiPO2F2).

[0023] The second reference electrolyte (electrolyte #2) is also a conventional LiB electrolyte, containing 0.8 M LiPF6 and 0.2 M lithium bis(fluorosulfonyl)imide (LiFSI) as salts. The solvent is 25 vol% EC and 73 vol% EMC, with 2 vol% sulfolane (SFL) as a heat-resistant material. This electrolyte also includes 0.5 wt% VC, 1 wt% FEC, and amphoteric additives such as 0.5 wt% PS, 0.3 wt% PRS, 0.5 wt% ESA, and 0.7 wt% to 1 wt% LiPO2F2. Additionally, the electrolyte incorporates 7 wt% ethoxyphosphazene (PFPN) as a free radical scavenger to improve heat resistance.

[0024] Electrolyte 1 (Electrolyte #3) comprises 0.8 M LiPF6 and 0.2 M LiFSI, with 25 vol% EC and 43 vol% EMC content. The heat-resistant solvent is incorporated in the form of 2 vol% SFL and 30 vol% ethyl 2,2-difluoroacetate (DFEA). This additive composition remains similar to Electrolyte #2, containing 0.5 wt% VC, 1 wt% FEC, 0.5 wt% PS, 0.3 wt% PRS, 0.5 wt% ESA, and 0.7 wt% to 1 wt% LiPO2F2. The presence of PFPN is maintained at 7.0 wt%.

[0025] Electrolyte 2 (electrolyte #4) also contains 0.8 M LiPF6 and 0.2 M LiFSI, with 25 vol% EC, 73 vol% DFEA, and 2 vol%. The additive composition is 0.5 wt% VC, 1 wt% FEC, 0.5 wt% PS, 0.3 wt% PRS, 0.5 wt% ESA, and 0.7 wt% to 1 wt% LiPO2F2. The presence of PFPN is also maintained at 7.0 wt%.

[0026] The electrolyte used for comparisons 3 and 4 (electrolyte #5) contains 1.0 M LiPF6, similar to electrolyte #1, but with the carbonate solvent content reduced to 10 vol% EC and 30 vol% EMC. Instead, it incorporates 30 vol% DFEA and 20 vol% 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) as a heat-resistant material solvent. The additive composition may also vary, containing 10 wt% VC, 1 wt% FEC, 0.5 wt% PS, 0.3 wt% PRS, 0.5 wt% ESA, and 0.7 wt% to 1 wt% LiPO2F2.

[0027] Figure 2 yes Figure 1A table of physical properties and activation points of the electrolyte compositions described herein is provided. This table compares each formulation based on viscosity in centipoise (cP), ionic conductivity in millisiemens per centimeter (mS / cm), and activation point (°C). These parameters provide insight into the balance between the electrochemical performance and stability of the electrolyte compositions.

[0028] Electrolyte #1 (a conventional LiB electrolyte) has a minimum viscosity of 3.89 cP and a maximum ionic conductivity of 8.43 mS / cm. However, it also has a minimum activation point measured at 26.7 °C.

[0029] Electrolyte #2 (the previously developed electrolyte) has a viscosity of 4.45 cP and an ionic conductivity that is slightly reduced to 7.54 mS / cm. The activation point is 37.7 °C, indicating increased heat resistance compared to electrolyte #1.

[0030] Electrolyte #3 (one of the proposed electrolyte compositions) has a viscosity of 4.72 cP and an ionic conductivity of 7.34 mS / cm. Its activation point exceeds 95.0 °C. This increase indicates that electrolyte #3 exhibits high stability under standard test conditions.

[0031] Electrolyte #4 (another of the proposed electrolyte compositions) has a maximum viscosity of 5.36 cP and an ionic conductivity of 7.01 mS / cm. Similar to electrolyte #3, it has an activation point greater than 95.0 °C. Electrolyte #5 has a viscosity of 4.04 cP and a lower ionic conductivity of 6.22 mS / cm. Its activation point was measured at 35.0 °C, which is significantly lower than that of the proposed electrolyte compositions (electrolytes #3 and #4).

[0032] Figure 3 and Figure 4 The results (in seconds) of activation and inhibition time tests performed on electrolytes #2, #3, and #4 are shown. These tests assess heat resistance by measuring the time required for activation and the time taken for self-inhibition once activation occurs.

[0033] Figure 3 The activation times for each electrolyte in four tests are shown. Electrolyte #2 activated consistently, with activation times ranging from 45 to 61 seconds, indicating that while it exhibits some heat resistance, it remains reactivatable under prolonged exposure. Electrolyte #3 showed increased resistance, with activation times between 68 and 91 seconds, indicating an activation delay compared to electrolyte #2. Electrolyte #4 did not activate in any test, thus confirming its heat resistance.

[0034] Figure 4The inhibition time, or the duration of inhibition after activation, was measured. Electrolyte #2 exhibited the longest inhibition time, ranging from 35 to 42 seconds, indicating that once activated, this condition persisted until self-extinguishing. Electrolyte #3 showed a shortened inhibition time, with values ​​between 5 and 33 seconds, indicating increased inhibition. Electrolyte #4 did not activate under the test conditions, thus eliminating the need to measure the inhibition time.

[0035] for Figures 5 to 8 The nickel-rich lithium nickel cobalt manganese oxide (Ni 83%) and graphite (Gr) pouch cells were tested at a charge-discharge rate of 1 C, using 1.2 ampere-hours (Ah) and incorporating electrolytes #2, #3, and #4. The battery cells were charged to a cutoff current of 4.2 volts (V) with a tapered current of 0.02 C and discharged to 2.7 V.

[0036] Figure 5 and Figure 6 Electrolytes #2, #3, and #4 are shown in Figure 5 At room temperature and Figure 6 Cyclic life performance at 45°C. These graphs measure capacity retention (%) over multiple charge-discharge cycles, providing insights into the long-term electrochemical stability of each electrolyte.

[0037] exist Figure 5 The data show that all three electrolytes maintained nearly 100% capacity retention during the test period. The curves for electrolytes #2, #3, and #4 are closely aligned, indicating that the modification of the electrolyte composition does not negatively affect the cycling stability under standard temperature conditions. This result demonstrates that the upgraded electrolytes (electrolytes #3 and #4) exhibit equivalent electrochemical performance to the reference electrolyte (electrolyte #2) at room temperature, while also possessing increased heat resistance.

[0038] Figure 6 The results show that all three electrolytes exhibit high capacity retention, with a gradual decrease in capacity over the test period. The retention curves for electrolytes #3 and #4 are almost identical to those for electrolyte #2, confirming that the increased heat-resistant composition does not compromise cycle life even at elevated temperatures.

[0039] Figure 7 and Figure 8 The effects of high-temperature storage (60°C for one week) on electrolytes #2, #3, and #4 are shown. Figure 7 and Figure 8 The cell swelling behavior and capacity retention after prolonged exposure to elevated temperatures were evaluated to assess electrolyte stability and long-term battery performance.

[0040] Figure 7 The swelling ratios (%) of the pouch cells after one week of storage at 60°C are shown. Electrolyte #2 exhibits the highest swelling ratio, approaching 5%, indicating electrolyte decomposition and gas generation under high-temperature conditions. Electrolyte #3 shows a reduction in swelling, remaining below 1.5%, indicating improved thermal stability and reduced side reactions. Electrolyte #4 has an intermediate swelling ratio of approximately 3.5%, lower than Electrolyte #2 but higher than Electrolyte #3. These results indicate that Electrolyte #3 is the most resistant to gas formation and cell expansion under high-temperature storage conditions.

[0041] Figure 8 The capacity retention (%) after one week of storage at 60°C is shown. All three electrolytes maintained high capacity retention, with values ​​above 90%, indicating that the fundamental electrochemical properties remained stable despite differences in swelling behavior. Electrolytes #3 and #4 exhibited retention levels comparable to electrolyte #2, demonstrating that the increased heat-resistant composition did not negatively impact long-term charge retention at elevated temperatures.

[0042] Figure 9 A battery cell 10 is shown, having a positive electrode 12, a negative electrode 14, and a separator 16 positioned between the positive electrode 12 and the negative electrode 14, wherein a liquid electrolyte 18 permeates the positive electrode 12, the negative electrode 14, and the separator 16.

[0043] Liquid electrolyte 18 comprises 0.8 M LiPF6 and 0.2 M LiFSI as conductive salts. The solvent system comprises EC and EMC in a volume ratio of 25 / 75, which balances high ionic conductivity and electrochemical stability. Liquid electrolyte 18 also contains 1 wt% FEC, 1 wt% VC, and 0.7 wt% to 1 wt% LiPO2F2, which increases electrode passivation and cycle life. Additionally, liquid electrolyte 18 incorporates 2 vol% SFL and 30 vol% DFEA as heat-resistant solvents, which improves thermal stability while maintaining viscosity and conductivity. In another embodiment, liquid electrolyte 18 comprises 73 vol% DFEA without any EMC to further enhance its heat resistance properties.

[0044] The liquid electrolyte 18 is configured to saturate the positive electrode 12, the negative electrode 14, and the separator, thereby ensuring efficient ion transport and a stable electrode interface. The positive electrode 12 comprises a positive electrode active material layer 20, which interacts with the liquid electrolyte 18 to suppress electrochemical oxidation and reduce impedance growth. The combination of LiFSI, FEC, VC, and LiPO2F2 promotes the formation of a stable interface 22 on the positive electrode active material layer 20, thereby improving long-term electrochemical stability. Furthermore, the heat-resistant components of the liquid electrolyte 18 contribute to improved thermal stability without significantly affecting ionic conductivity.

[0045] The liquid electrolyte 18 also minimizes cell swelling under high-temperature storage conditions. When stored at 60°C for one week, the battery cell 10 containing this composition exhibits lower gas generation and reduced swelling, resulting in higher mechanical stability. Furthermore, when the battery cell 10 is cycled at 45°C, the liquid electrolyte 18 maintains high capacity retention and extended cycle life, thus performing comparable to or better than conventional electrolytes.

[0046] The liquid electrolyte 18 can also interact with the positive electrode active material layer 20 to alter the interface 22 by reducing impedance growth and improving electrochemical stability. The EC / EMC solvent mixture provides a balance between high ionic conductivity and electrolyte stability, thereby contributing to the overall performance and lifespan of the battery cell 10. The battery cell 10 is configured to maintain its capacity over extended cycles, exhibiting increased high-temperature storage characteristics at 45°C and increased cycle life performance, making it suitable for high-capacity LiB applications requiring durability.

[0047] While exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms covered by the claims. The language used in this specification is descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of this disclosure.

[0048] As previously described, features of various embodiments can be combined to form other embodiments of the invention that may not be explicitly described or shown. While various embodiments may have been described as offering advantages or preferences over other embodiments or prior art implementations in terms of one or more desired characteristics, those skilled in the art will recognize that one or more features or characteristics may be compromised to achieve desired overall system properties, depending on the specific application and implementation. Therefore, embodiments described as less desirable than those desired by other embodiments or prior art implementations in terms of one or more characteristics are within the scope of this disclosure and may be desirable for a particular application.

[0049] According to the present invention, an electrode assembly is provided comprising: a current collector; a positive electrode active material layer on the current collector; and an electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8M to 0.2M and 7% by weight of ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane in a volume ratio of 25 / 2, the electrolyte permeating the surface of the positive electrode active material layer and configured to inhibit electrochemical oxidation of the positive electrode active material layer during electrochemical cycling of the positive electrode active material layer.

[0050] According to an embodiment, the electrolyte further includes 1% by weight of fluoroethylene carbonate.

[0051] According to an embodiment, the electrolyte further includes 0.5% by weight of vinylene carbonate.

[0052] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfite.

[0053] According to an embodiment, the electrolyte further includes 0.3% by weight of propylene sulfone.

[0054] According to an embodiment, the electrolyte further includes 0.5% by weight of ethyl sulfate anhydride.

[0055] According to an embodiment, the electrolyte further includes 0.7% by weight of lithium difluoro(oxalate)phosphate.

[0056] According to an embodiment, the electrolyte further comprises 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl sulfate anhydride, and 0.7% by weight of lithium difluoro(oxalate)phosphate.

[0057] According to the present invention, a battery cell is provided, comprising: a negative electrode; a positive electrode; and an electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8M to 0.2M and 7% by weight of ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane, wherein the electrolyte saturates the negative electrode and the positive electrode such that lithium ions dissociated from the lithium bis(fluorosulfonyl)imide are stabilized by complexing with ethoxyphosphazene and sulfolane molecules.

[0058] According to an embodiment, the electrolyte further includes 1% by weight of fluoroethylene carbonate.

[0059] According to an embodiment, the electrolyte further includes 0.5% by weight of vinylene carbonate.

[0060] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfite.

[0061] According to an embodiment, the electrolyte further includes 0.3% by weight of propylene sulfone.

[0062] According to an embodiment, the electrolyte further includes 0.5% by weight of ethyl sulfate anhydride.

[0063] According to an embodiment, the electrolyte also contains 0.7% by weight of lithium difluoro(oxalate)phosphate.

[0064] According to an embodiment, the electrolyte further comprises 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl sulfate anhydride, and 0.7% by weight of lithium difluoro(oxalate)phosphate.

[0065] According to the present invention, a battery cell is provided, comprising: a negative electrode; a positive electrode; and an electrolyte comprising lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane, wherein the electrolyte saturates the negative electrode and the positive electrode.

[0066] According to the examples, the ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 0.8M to 0.2M.

[0067] According to the examples, the solvents of ethylene carbonate and sulfolane have a volume ratio of 25 / 2.

[0068] According to an embodiment, the electrolyte comprises 7% by weight of ethoxyphosphazene, 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl ester sulfate anhydride, and 0.7% by weight of lithium difluoro(oxalate)phosphate.

Claims

1. An electrode assembly comprising: Current collector; A positive electrode active material layer is provided on the current collector. as well as An electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8M to 0.2M and 7% by weight of ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane in a volume ratio of 25 / 2, wherein the electrolyte permeates the surface of the positive electrode active material layer and is configured to inhibit electrochemical oxidation of the positive electrode active material layer during electrochemical cycling of the positive electrode active material layer.

2. The electrode assembly of claim 1, wherein the electrolyte further comprises 1% by weight of ethylene fluorocarbonate.

3. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.5% by weight of vinylene carbonate.

4. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.5% by weight of propylene sulfite.

5. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.3% by weight of propylene sulfone.

6. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.5% by weight of ethyl sulfate anhydride.

7. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.7% by weight of lithium difluoro(oxalate)phosphate.

8. The electrode assembly of claim 1, wherein the electrolyte further comprises 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl ester sulfate anhydride and 0.7% by weight of lithium difluoro(oxalate) phosphate.

9. A battery cell comprising: negative electrode; Positive electrode; as well as An electrolyte comprising lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide in a ratio of 0.8 M to 0.2 M, and 7 wt% ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane, wherein the electrolyte saturates the negative electrode and the positive electrode such that lithium ions dissociated from the lithium bis(fluorosulfonyl)imide are stabilized by complexing with ethoxyphosphazene and sulfolane molecules.

10. The battery cell of claim 9, wherein the electrolyte further comprises 1% by weight of fluoroethylene carbonate.

11. The battery cell of claim 9, wherein the electrolyte further comprises 0.5% by weight of vinylene carbonate.

12. A battery cell comprising: negative electrode; Positive electrode; as well as An electrolyte comprising lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and ethoxyphosphazene additive, dissolved in a solvent of ethylene carbonate and sulfolane, wherein the electrolyte saturates the negative electrode and the positive electrode.

13. The battery cell of claim 12, wherein the ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 0.8M to 0.2M.

14. The battery cell of claim 12, wherein the solvents of ethylene carbonate and sulfolane have a volume ratio of 25 / 2.

15. The battery cell of claim 12, wherein the electrolyte comprises 7% by weight of ethoxyphosphazene, 1% by weight of fluoroethylene carbonate, 0.5% by weight of vinylene carbonate, 0.5% by weight of propylene sulfite, 0.3% by weight of propylene sulfone, 0.5% by weight of ethyl ester sulfate anhydride and 0.7% by weight of lithium difluoro(oxalate)phosphate.

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