Lithium ion battery electrolyte

Abstract

The present disclosure provides a lithium ion battery electrolyte. An electrode is presented. The electrode has a current collector and a positive electrode active material layer provided on the current collector. The electrode includes an electrolyte. The electrolyte composition includes 1 M of a lithium hexafluorophosphate salt and 0.5 wt% of vinylene carbonate dissolved in a solvent mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 25 / 75. The electrolyte permeates the surface of the positive electrode active material layer, thereby effectively suppressing electrochemical oxidation during an electrochemical cycle process, and thus improving stability and performance of the electrode assembly.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to electrolyte materials for lithium-ion batteries. BACKGROUND

[0002] Layered transition metal oxides are used as cathode materials due to their high energy density and good cycling stability. These materials have a combination of transition metals such as nickel, cobalt, and manganese, and lithium ions that intercalate between the layers during the charging and discharging process. However, increasing the nickel content in layered transition metal oxide cathodes can lead to structural instability, particularly during extended cycling or exposure to high temperatures. This instability can impact the performance of the battery. SUMMARY

[0003] In one aspect of the present disclosure, an electrode assembly is presented. The electrode assembly includes: a current collector; a positive active material layer on the current collector; and an electrolyte including 1 M lithium hexafluorophosphate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 25 / 75, to penetrate to a surface of the positive active material layer, and configured to inhibit electrochemical oxidation of the positive active material layer during an electrochemical cycling process of the positive active material layer. The current collector can be aluminum. The electrolyte can further include 0.5 wt% of propene sulfone. The electrolyte can also include 0.3 wt% of 1,3-propene sultone. The positive active material layer can be lithium nickel manganese cobalt oxide. The electrolyte can further include 0.5 wt% of vinyl sulfate. The electrolyte can further include 1 wt% of fluoroethylene carbonate. The electrolyte can further include 1 wt% of lithium difluorophosphate.

[0004] In another aspect of the disclosure, a battery cell is presented. The battery cell includes a negative electrode, a positive electrode, and an electrolyte including lithium hexafluorophosphate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30 to saturate the negative electrode and the positive electrode such that lithium ions that dissociate from the lithium hexafluorophosphate are stabilized by complexing with the vinylene carbonate molecules to mitigate electrochemical oxidation of the positive electrode. The electrolyte of the battery cell can further include 1M lithium hexafluorophosphate and 0.3M lithium bis(fluorosulfonyl)imide. The solvent of the battery cell can include ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30. The electrolyte of the battery cell can further include 0.5 wt% of propene sulfone. In other configurations, the electrolyte of the battery cell can further include 0.3 wt% of 1,3-propene sultone. In further configurations, the electrolyte of the battery cell includes 0.5 wt% of ethylene sulfate. In other configurations, the electrolyte of the battery cell further includes 1 wt% of lithium difluorophosphate. The capacity retention of the battery cell after 200 charge-discharge cycles can be greater than 80%.

[0005] In yet another aspect of the disclosure, a battery cell is presented. The battery cell includes a negative electrode, a positive electrode, and an electrolyte including 1M lithium hexafluorophosphate and 1 wt% fluoroethylene carbonate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30 to saturate the negative electrode and the positive electrode such that lithium ions that dissociate from the lithium hexafluorophosphate are stabilized by solvation with the vinylene carbonate molecules resulting in a direct current impedance of the battery cell for a given state of charge that is less than a direct current impedance of an otherwise identical battery cell without the vinylene carbonate. The direct current impedance of the battery cell can be at least 10% less than a direct current impedance of an otherwise identical battery cell without the vinylene carbonate. The electrolyte of the battery cell can further include 0.5 wt% of propene sulfone and 0.3 wt% of 1,3-propene sultone. In other configurations, the electrolyte of the battery cell further includes 0.5 wt% of ethylene sulfate and 1 wt% of lithium difluorophosphate. BRIEF DESCRIPTION OF DRAWINGS

[0006] Figure 1 is a table of test methods and descriptions;

[0007] Figure 2 is a table of electrolyte samples and their compositions according to one or more aspects of the disclosure;

[0008] Figure 3 is a table of solvent properties according to one or more aspects of the disclosure;

[0009] Figure 4is a table of performance characteristics of electrolyte samples according to one or more aspects of the present disclosure;

[0010] Figure 5 is a table of performance characteristics of electrolyte samples according to one or more aspects of the present disclosure;

[0011] Figure 6 is a plot of retention properties of electrolyte samples according to one or more aspects of the present disclosure;

[0012] Figure 7 shows a plot of swelling properties of electrolyte samples according to one or more aspects of the present disclosure;

[0013] Figure 8 is a plot of DC internal resistance properties of electrolyte samples according to one or more aspects of the present disclosure;

[0014] Figure 9 is a plot of charge retention properties of electrolyte samples according to one or more aspects of the present disclosure;

[0015] Figure 10 is a plot of discharge retention properties of electrolyte samples according to one or more aspects of the present disclosure;

[0016] Figure 11 is a plot of swelling rate properties of electrolyte samples according to one or more aspects of the present disclosure;

[0017] Figure 12 is a plot of DC internal resistance properties of electrolyte samples at a given state of charge according to one or more aspects of the present disclosure;

[0018] Figure 13 is a table of performance characteristics of electrolyte samples according to one or more aspects of the present disclosure;

[0019] Figure 14 is a plot of charge rate properties of electrolyte samples according to one or more aspects of the present disclosure;

[0020] Figure 15 is a plot of discharge rate properties of electrolyte samples according to one or more aspects of the present disclosure;

[0021] Figure 16 is a plot of retention properties of electrolyte samples according to one or more aspects of the present disclosure;

[0022] Figure 17 is a plot of swelling properties of electrolyte samples according to one or more aspects of the present disclosure;

[0023] Figure 18is a plot of the DC internal resistance properties of an electrolyte sample at a given state of charge according to one or more aspects of the present disclosure;

[0024] Figure 19 is a table of performance characteristics of an electrolyte sample according to one or more aspects of the present disclosure;

[0025] Figure 20 is a plot of the retention properties of an electrolyte sample according to one or more aspects of the present disclosure;

[0026] Figure 21 is a plot of the swelling properties of an electrolyte sample according to one or more aspects of the present disclosure;

[0027] Figure 22 is a plot of the DC internal resistance properties of an electrolyte sample at a given state of charge according to one or more aspects of the present disclosure;

[0028] Figure 23 is a table of performance characteristics of an electrolyte sample according to one or more aspects of the present disclosure;

[0029] Figure 24 is a plot of the storage retention properties of an electrolyte sample at a given temperature according to one or more aspects of the present disclosure;

[0030] Figure 25 is a table of retention properties of an electrolyte sample according to one or more aspects of the present disclosure;

[0031] Figure 26 is a plot of the storage recovery capacity of an electrolyte sample at a given temperature according to one or more aspects of the present disclosure;

[0032] Figure 27 is a table of recovery properties of an electrolyte sample according to one or more aspects of the present disclosure;

[0033] Figure 28 is a plot of the storage thickness change of an electrolyte sample at a given temperature according to one or more aspects of the present disclosure;

[0034] Figure 29 is a table of thickness properties of an electrolyte sample according to one or more aspects of the present disclosure;

[0035] Figure 30 is a plot of the DC internal resistance increase of an electrolyte sample at a given temperature according to one or more aspects of the present disclosure;

[0036] Figure 31 is a table of thickness properties of an electrolyte sample according to one or more aspects of the present disclosure; and

[0037] Figure 32 is a schematic illustration of a battery having an electrolyte in accordance with one or more aspects of the present disclosure. DETAILED DESCRIPTION

[0038] Detailed embodiments of the present application are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the present application which can be embodied in various forms and alternative forms. The accompanying drawings are not necessarily to scale; some features can be exaggerated or minimized for the purpose of clarity. Specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to employ the present application in a variety of ways.

[0039] Unless otherwise expressly stated, all numerical values and ranges

[0040] High nickel layered oxide batteries, particularly those using nickel manganese cobalt and nickel cobalt aluminum chemistries, are being considered for lithium ion battery technology. These batteries have high energy density, high cycle life, and high performance characteristics.

[0041] The high nickel content, typically greater than 60%, in these batteries increases the energy density. This is because nickel helps enable higher capacity by allowing more lithium ions to be intercalated into the cathode structure during charging. However, increasing the nickel content also presents challenges. Rich nickel cathodes tend to be more reactive, especially at high voltages.

[0042] The electrolyte in high nickel layered oxide batteries plays a role in the performance of the battery. The electrolyte can be composed of a lithium salt, such as LiPF6, dissolved in a mixture of organic solvents, such as ethylene carbonate and ethyl methyl carbonate. In certain situations, this combination provides a balance of ionic conductivity and electrochemical stability.

[0043] A problem with high voltage operation is the decomposition of the electrolyte, which can lead to the formation of a resistive layer on the surface of the electrode, called the solid- electrolyte interface. This layer can hinder the movement of lithium ions, thus reducing the performance characteristics of the battery. To mitigate this, additives such as fluoroethylene carbonate and vinylene carbonate can be included, which form a more stable solid- electrolyte interface layer.

[0044] High nickel content lithium nickel cobalt manganese oxide refers to transition metal oxides with a layered structure and a nickel content of 80% or higher. Nickel, cobalt, and manganese are cathode materials in batteries. Increasing the nickel content in high nickel content lithium nickel cobalt manganese doubles the amount of lithium that goes into the lithium layer, resulting in higher capacity.

[0045] High nickel nickel manganese cobalt batteries provide high capacity without increasing the operating voltage due to their lithium-rich layered oxide structure. It also exhibits high electrical conductivity and minimal capacity loss at high charge / discharge rates (C-rates). Challenges include reduced reaction stability due to residual lithium and performance degradation. High nickel content nickel cobalt manganese has low thermal stability and high gas generation, affecting cycle life at room temperature and high temperature. Aspects of the present disclosure are directed to improving high nickel - nickel cobalt manganese battery performance through electrolyte composition.

[0046] The electrolyte composition presented plays a role in the performance of lithium ion batteries. The electrolyte composition includes 1.0 mole (M) of lithium hexafluorophosphate salt dissolved in a solvent mixture of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume (v / v / v) ratio of 25 / 45 / 30. The electrolyte also contains various additives, including 1 wt% of fluoroethylene carbonate, 0.5 wt% of vinylene carbonate, 0.5 wt% of propane sulfone, 0.3 wt% of 1,3- propene sulfone, 0.5 wt% of ethylene sulfite, and 1 wt% of lithium difluorophosphate.

[0047] The solvents utilized contribute to the performance of the proposed electrolyte. Ethylene carbonate, a cyclic carbonate with a high dielectric constant, is used to increase the solubility of the lithium hexafluorophosphate salt. Straight-chain carbonates, such as ethyl methyl carbonate and diethyl carbonate, are used to improve ionic conductivity by reducing the viscosity of the electrolyte. Diethyl carbonate exhibits suitable high-temperature performance due to its high boiling point. Lithium hexafluorophosphate is used as a salt in lithium ion battery electrolytes due to its electrochemical properties. It provides suitable solubility and high ionic conductivity in non-aqueous solvents, facilitates the formation of a stable passivation layer on the surface of the aluminum foil housing, and facilitates the formation of a stable solid- electrolyte interface on the electrode surface in the presence of carbonate solvents.

[0048] The electrolyte also incorporates various additives to achieve better battery performance and stability. Vinylene carbonate is added to promote the formation of a stable film on the anode surface, which improves ionic conductivity and prevents unwanted side reactions. Fluoroethylene carbonate is included to improve cycling performance and direct current internal resistance (DC-IR) properties, while preventing electrolyte oxidation. 1,3-propane sultone is used to form a stable layer on the cathode surface, while 1,3-propene sultone helps to suppress gas generation and improve high-temperature storage stability. Vinyl ethylene sulfite is incorporated to prevent corrosion and improve low-temperature performance. Lithium difluorophosphate is added to reduce the viscosity of the electrolyte, thereby improving ionic conductivity, increasing battery life at high voltage, and slowing the rate of electrolyte decomposition.

[0049] The combination of these selected solvents, salts, and additives in the electrolyte composition improves the performance and stability of high-nickel-nickel manganese cobalt cathode materials in lithium-ion batteries. The electrolyte formulation addresses challenges such as ionic conductivity, solid-electrolyte interphase formation, gas generation, and high-temperature stability, which contribute to the successful implementation of high-nickel-nickel manganese cobalt cathodes in advanced battery applications.

[0050] Figures 1 to 23 The composition of electrolyte samples, their performance characteristics, and physical properties according to one or more aspects of the present disclosure are shown. Figure 1 The tables showing the test methods and their corresponding descriptions are shown. The types of tests include constant current cycling (C / C), evaluation of high C-rate characteristics, fast charge cycling, and high-temperature storage (HTS). For the C / C tests, the descriptions specify the cycling conditions at various temperatures: 0.3C / 1C (C / D) at 25°C, 0.3C / 1C (C / D) at 45°C, and 1C / 1C (C / D) at 45°C. The high C-rate characteristics evaluation test includes charge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C at 25°C, and discharge rates of 0.1C, 0.2C, 0.5C, 1C, 2C, 3C, and 5C at 25°C. The fast charge cycling test is performed at 2C / 0.5C cycle life at 25°C. The HTS test involves storing the sample at 60°C for 8 weeks at SOC 100%. These test methods and conditions are used to evaluate the performance and characteristics of the electrolyte samples.

[0051] Figure 2is a table of electrolyte samples and their composition according to one or more aspects of the present disclosure. The reference sample includes 1 M lithium hexafluorophosphate, ethylene carbonate / ethyl methyl carbonate (25 / 75 v / v), 1 wt% fluoroethylene carbonate, 0.5 wt% vinylene carbonate, 0.5 wt% prop-1 -ene-1,3-sultone, 0.3 wt% propane sultone, 0.5 wt% ethyl sulfite, and 1 wt% lithium difluoro(oxalato)phosphate. The first electrolyte sample has a different solvent ratio of ethylene carbonate / ethyl methyl carbonate / diethyl carbonate (25 / 45 / 30 v / v / v). The second and third electrolyte samples introduce an additional salt, lithium bis(fluorosulfonyl)imide, at a concentration of 0.3 M, while maintaining the same solvent ratio and additive concentrations as the first electrolyte sample, except that lithium difluoro(oxalato)phosphate is excluded from the third electrolyte sample. The fourth electrolyte sample also includes 0.3 M lithium bis(fluorosulfonyl)imide, but has a higher concentration of fluoroethylene carbonate at 1.5 wt%, and does not include the additives propane sultone, ethyl sulfite, and lithium difluoro(oxalato)phosphate.

[0052] Figure 3 is a table of solvent properties of diethyl carbonate and ethyl methyl carbonate. Diethyl carbonate has a viscosity of 0.747 centipoise (cP) and a boiling point of 126 °C. Ethyl methyl carbonate has a viscosity of 0.65 cP and a boiling point of 107.5 °C.

[0053] Figure 4 is a table of performance characteristics of electrolyte samples according to one or more aspects of the present disclosure. The table includes data for a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4).

[0054] The table presents formation charge / discharge values, standard charge / discharge values at 0.3 C / 0.3 C rate, and DC-IR measured in milli-Ohm (mOhm) and at 20% state of charge (SOC).

[0055] For formation charge / discharge, charge capacity (ampere hours; Ah), discharge capacity (Ah), and efficiency (%) are provided. The reference sample shows a charge capacity of 3.893 Ah, a discharge capacity of 3.334 Ah, and an efficiency of 85.60%. The electrolyte samples EL1, EL2, EL3, and EL4 have similar charge capacities ranging from 3.879 Ah to 3.917 Ah, discharge capacities from 3.288 Ah to 3.316 Ah, and efficiencies between 84.10% and 85.10%.

[0056] Charged capacity (Ah), discharged capacity (Ah), and efficiency (%) are also provided for standard charge / discharge at 0.3C / 0.3C rate. The reference sample has a charged capacity of 3.420 Ah, a discharged capacity of 3.354 Ah, and an efficiency of 98.10%. The electrolyte samples show a charged capacity ranging from 3.388 Ah to 3.402 Ah, a discharged capacity from 3.33 Ah to 3.344 Ah, and an efficiency between 97.90% and 98.40%.

[0057] DC-IR measured in mOhm at 20% SOC is also listed for each sample. The reference sample has a DC-IR of 25.08 mOhm, while the electrolyte samples have DC-IR values ranging from 25.59 mOhm to 25.80 mOhm.

[0058] Figure 5 Table 1 is a table showing performance characteristics of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) under 25 °C cycling tests at 0.3C / 1C rate. The table includes data regarding the retention percentage, swelling percentage, and DC-IR percentage for each sample after the test. The reference sample exhibits a retention of 100.6%, a swelling of 107%, and a DC-IR of 103%. The electrolyte samples show a retention percentage ranging from 100.6% to 101.2%, a swelling percentage from 98% to 113%, and a DC-IR percentage between 101% and 104%.

[0059] The 25 °C cycling tests reveal several findings regarding the performance of the electrolyte samples. First, EL1 and EL2 exhibit a reduced DC-IR increase and less swelling during RT cycling (@ 300 cycles) compared to the reference sample. Second, all samples exhibit a 3% increase in capacity retention up to the 150th cycle, even under 25 °C cycling. Finally, the electrolyte samples still show positive results in 25 °C cycling (0.3C / 1C) performance and DC-IR despite a 30% reduction in diethyl carbonate content. These findings highlight the improved performance characteristics of the electrolyte samples compared to the reference sample, particularly in DC-IR, swelling, and capacity retention.

[0060] Figure 6 Figure 1 is a graph showing the retention properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) over 300 cycles, in accordance with one or more aspects of the present disclosure. The graph presents the capacity retention percentage on the y-axis and the number of cycles on the x-axis.

[0061] The graph indicates that all samples exhibit an initial increase in capacity retention, peaking around the 50th cycle. The reference sample shows the highest peak retention at around 102.5%, while the electrolyte samples have slightly lower peak retention ranging from 101.5% to 102%. After the peak, all samples exhibit a gradual decrease in capacity retention over the remaining cycles.

[0062] EL1 and EL2 show the best overall retention performance, maintaining a higher capacity retention throughout the 300 cycles compared to the reference sample and the other electrolyte samples. EL3 and EL4 exhibit slightly lower retention than EL1 and EL2 but still outperform the reference sample. At the end of 300 cycles, all electrolyte samples maintain a capacity retention above 99%, while the retention of the reference sample drops below 99%.

[0063] Figure 7 A graph showing the swelling properties of the reference sample (Ref.) and the four electrolyte samples (EL1, EL2, EL3, and EL4) over 400 cycles is presented. The graph displays the percentage of swelling on the y-axis and the number of cycles on the x-axis.

[0064] The graph shows that the percentage of swelling increases for all samples as the number of cycles increases. However, the rate of swelling varies between samples. The reference sample exhibits the highest percentage of swelling, reaching around 113% at the end of 400 cycles. In contrast, the electrolyte samples exhibit better resistance to swelling, with EL1 and EL2 showing the lowest percentages of swelling at around 105% and 103%, respectively.

[0065] EL3 and EL4 also show improved resistance to swelling compared to the reference sample, with percentages of swelling at around 109% and 107%, respectively, by the 400th cycle. The graph highlights the superior resistance to swelling of the electrolyte samples, particularly EL1 and EL2, which maintain significantly lower percentages of swelling throughout the cycles compared to the reference sample.

[0066] The improved resistance to swelling of the electrolyte samples can be attributed to their optimized composition, which can contribute to better stability and reduced gas generation during prolonged cycling. The results suggest that the electrolyte formulations, especially those of EL1 and EL2, have the potential to enhance the performance and lifespan of lithium-ion batteries by minimizing swelling-related issues.

[0067] Figure 8A graph depicting the DC-IR properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) over 400 cycles is plotted in accordance with one or more aspects of the present disclosure. The graph presents the DC-IR percentage on the y-axis and the cycle number on the x-axis.

[0068] The graph indicates that the DC-IR percentage of all samples increases as the cycle number increases. However, the electrolyte samples exhibit better DC-IR performance compared to the reference sample. The reference sample shows the highest DC-IR percentage, reaching about 104.5% at the end of 400 cycles. In contrast, EL1 and EL2 exhibit the lowest DC-IR percentage, maintaining values below 102% throughout the cycles.

[0069] EL3 and EL4 also show improved DC-IR performance compared to the reference sample, with DC-IR percentages of about 103% and 102.5% by the 400th cycle, respectively. The graph highlights the superior DC-IR stability of the electrolyte samples, particularly EL1 and EL2, which maintain significantly lower DC-IR percentages throughout the cycles compared to the reference sample.

[0070] The improved enhanced DC-IR stability of the electrolyte samples can be attributed to their optimized composition, which can contribute to reduced internal resistance growth and increased ionic conductivity during prolonged cycling. The results suggest that the electrolyte formulations, especially those of EL1 and EL2, have the potential to enhance the performance and efficiency of lithium-ion batteries by minimizing DC-IR-related losses and maintaining lower internal resistance during battery life.

[0071] Figure 9 is a graph depicting the charge retention properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) over 500 cycles in accordance with one or more aspects of the present disclosure. The graph presents the capacity retention percentage on the y-axis and the cycle number on the x-axis.

[0072] The graph indicates that all samples exhibit an initial increase in capacity retention, reaching a peak around the 50th cycle. After the peak, all samples show a gradual decrease in capacity retention over the remaining cycles. EL1 and EL2 show the best overall retention performance, maintaining a higher capacity retention throughout the 500 cycles compared to the reference sample and the other electrolyte samples. EL3 and EL4 are also superior to the reference sample, exhibiting slightly lower retention rates than EL1 and EL2.

[0073] At the end of 500 cycles, EL1 and EL2 maintained a capacity retention higher than 90%, while the retention of the reference sample decreased to about 88%. EL3 and EL4 exhibited a capacity retention of about 89% at the 500th cycle. The graph highlights the superior charge retention properties of the electrolyte samples, particularly EL1 and EL2, compared to the reference sample over an extended number of cycles.

[0074] Figure 10 is a graph showing the discharge retention properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) over 500 cycles in accordance with one or more aspects of the present disclosure. The graph presents the capacity retention percentage on the y-axis and the number of cycles on the x-axis.

[0075] The graph indicates that, as the number of cycles increases, all samples exhibit a gradual decrease in discharge capacity retention. However, the electrolyte samples exhibit better discharge retention performance compared to the reference sample. EL1 and EL2 show the highest discharge retention percentage throughout the 500 cycles, maintaining values higher than 95% at the end of the cycling process.

[0076] EL3 and EL4 also show improved discharge retention compared to the reference sample, with retention percentages of about 93% and 94%, respectively, at the 500th cycle. In contrast, the reference sample exhibits the lowest discharge retention, decreasing to about 91% at the end of 500 cycles.

[0077] Figure 11 is a graph depicting the swelling rate properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) over 500 cycles in accordance with one or more aspects of the present disclosure. The graph presents the thickness increase percentage on the y-axis and the number of cycles on the x-axis.

[0078] The graph indicates that, as the number of cycles increases, the swelling rate of all samples increases. However, the electrolyte samples exhibit significantly lower swelling rates compared to the reference sample. The reference sample exhibits the highest swelling rate, reaching a thickness increase of about 45% at the end of 500 cycles.

[0079] In contrast, EL2 shows the lowest swelling rate, maintaining a thickness increase lower than 15% throughout the cycling process. EL1, EL3, and EL4 also show improved resistance to swelling compared to the reference sample, with swelling rates of about 20%, 25%, and 30%, respectively, at the 500th cycle.

[0080] The graph highlights the superior resistance to swelling of the electrolyte samples, particularly EL2, which maintain very low swelling rates throughout the extended cycling. This indicates the optimized composition of the electrolyte samples, particularly EL2, which helps to enhance dimensional stability and reduce gas generation during long duration battery operation.

[0081] Figure 12 is a graph of the DC-IR properties of a reference sample (Ref.) and four electrolyte samples (EL1, EL2, EL3, and EL4) according to one or more aspects of the present disclosure at 20% SOC over 500 cycles. The graph presents the DC-IR values in mOhm on the y-axis and cycle number on the x-axis.

[0082] The graph indicates that the DC-IR values of all samples increase as the cycle number increases. However, the electrolyte samples exhibit significantly lower DC-IR growth compared to the reference sample. The reference sample exhibits the highest DC-IR values, reaching about 700 mOhm at the end of 500 cycles.

[0083] In contrast, EL2 shows the lowest DC-IR growth, thereby maintaining values below 200 mOhm throughout the cycling. EL1, EL3, and EL4 also show improved DC-IR stability compared to the reference sample, with DC-IR values of about 300 mOhm, 400 mOhm, and 500 mOhm, respectively, by the 500th cycle.

[0084] Figure 13 is a table of performance metrics between the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) after undergoing 45°C 1C / 1C cycling tests. This high-temperature cycling test provides valuable insights into how different electrolyte compositions hold up under more challenging conditions compared to the 25°C tests discussed previously in the specification.

[0085] In terms of retention %, EL1 shows the highest capacity retention of 89.31%, which is a significant improvement compared to the reference. EL3 is the next best with 78.74%. Notably, retention data is not provided for EL2 and EL4. In terms of swelling %, all four modified electrolytes exhibit reduced swelling compared to the reference of 29%. EL1 has the lowest swelling of 116%, followed closely by EL2 with 121%. EL3 and EL4 have slightly higher swellings of 127% and 128%, respectively, but are still much better than the reference.

[0086] Compared to the very high increase of 2349% seen in the reference electrolyte, EL1 showed a lower DC-IR increase of only 8%. EL3 followed closely with a DC-IR increase of 37%. Interestingly, EL2 showed a significantly higher DC-IR increase of 2780%, even exceeding the reference, while EL4 was also high at 1762%.

[0087] Figures 14 to 15 These are graphs showing the charge and discharge rate performance of the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) in the C-rate range from 0.1C to 5.0C. These graphs provide valuable insights into how different electrolyte compositions behave at varying current densities.

[0088] Focusing on charging rate Figure 14 In the tests, the reference electrolyte exhibited higher charging capacity at all C-rates compared to the modified electrolyte. Among the modified formulations, EL2 stood out due to its similar charging capacity to the reference at higher C-rates of 3C and 5C. This suggests that the composition of EL2 may be particularly well-suited for fast-charging applications.

[0089] Figure 15 The discharge rate performance is shown, and here EL1 exhibits a higher discharge capacity compared to the reference electrolyte within the tested discharge rate range. This indicates that the modifications made to EL1 are beneficial for maintaining discharge capacity at increased current densities.

[0090] The provided background information further clarifies these results. It should be noted that performance remains consistent up to a 3C discharge rate, but a significant drop is observed starting at 1C during charging. This highlights the challenge of maintaining performance at high charge rates and suggests that C-rate control may be necessary to mitigate capacity loss during fast charging.

[0091] Figures 16 to 19 The results of 45°C cycling tests performed on the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) at 0.3C / 1C charge / discharge rates are shown.

[0092] Figure 16 This is a graph showing the percentage capacity retention of the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) over 300 cycles. The reference shows the lowest retention rate, dropping to approximately 88% by cycle 300. EL1 and EL2 show the highest retention rates, maintaining above 90% at cycle 300. EL3 and EL4 also outperform the reference, with a retention rate of approximately 89% at the end of the cycle test.

[0093] Figure 17 This is a graph showing the percentage of swelling over 300 cycles. The reference electrolyte shows a sharp increase in swelling, reaching approximately 18% at 300 cycles. In contrast, the modified electrolytes exhibit significantly improved anti-swelling properties. EL2 exhibits the lowest swelling rate, remaining below 5% throughout the test. By 300 cycles, EL1, EL3, and EL4 also maintain low swelling rates of approximately 5% to 7%, thus demonstrating superior dimensional stability compared to the reference.

[0094] Figure 18 This is a graph showing the DC-IR measured in mOhms at 20% SOC over 300 cycles. The reference electrolyte showed the highest DC-IR growth, increasing from approximately 19 mOhms initially to over 22 mOhms by 300 cycles, a change of 104.1%. Figure 19 As shown in the figure, all modified electrolytes exhibited low increases in DC-IR. EL1 showed the smallest change at 102%, with a DC-IR of 20.65 mOhm at 300 cycles. EL2, EL3, and EL4 showed modest increases to 21.26 mOhm, 21.32 mOhm, and 20.85 mOhm, respectively, corresponding to 103% to 105% of their initial values.

[0095] Figure 19 This table shows the results from 300 cycles of testing, including capacity retention, thickness change, and percentage change in DC-IR. For capacity retention, EL2 achieved the highest at 93.4%, but showed a slightly higher swelling percentage of 104.3% and a 105% increase in DC-IR compared to EL1. EL1 had the second-best capacity retention of 91.3% relative to the other samples, while maintaining the lowest DC-IR increase of 102% and a relatively low swelling percentage of 104.4%. Overall, EL1 and EL2 appear to offer the best balance of performance across the three measurement parameters over extended cycles.

[0096] Figures 20 to 23 The results of 45°C cycling tests performed on the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) at 1C / 1C charge / discharge rates are shown.

[0097] Figure 20 This is a graph showing the percentage capacity retention of the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) over 600 cycles. The reference shows the lowest retention, dropping to approximately 88% by cycle 600. EL1 and EL2 show the highest retention, maintaining above 90% at cycle 600. EL3 and EL4 also outperform the reference, with a retention of approximately 89% at the end of the cycle test.

[0098] Figure 21 This is a graph showing the percentage of swelling over 600 cycles. The reference electrolyte shows a sharp increase in swelling, reaching approximately 18% at 600 cycles. In contrast, the modified electrolytes exhibit significantly improved anti-swelling properties. EL2 exhibits the lowest swelling rate, remaining below 5% throughout the test. By 600 cycles, EL1, EL3, and EL4 also maintain low swelling rates of approximately 5% to 7%, thus demonstrating superior dimensional stability compared to the reference.

[0099] Figure 22 This is a graph showing the DC-IR measured in mOhms at 20% SOC over 600 cycles. The reference electrolyte exhibits the highest DC-IR growth, increasing from approximately 19 mOhms initially to over 22 mOhms by 600 cycles, a change of 104.1%. Figure 19 As shown in the figure, all modified electrolytes exhibited low increases in DC-IR. EL1 showed the smallest change at 102%, with a DC-IR of 20.65 mOhm at 600 cycles. EL2, EL3, and EL4 showed modest increases to 21.26 mOhm, 21.32 mOhm, and 20.85 mOhm, respectively, corresponding to 103% to 105% of their initial values.

[0100] Figures 23 to 31 This table shows the results from 600 cycles of testing, including capacity retention, thickness change, and percentage change in DC-IR. For capacity retention, EL2 achieved the highest at 93.4%, but showed a slightly higher swelling percentage of 104.3% and a 105% increase in DC-IR compared to EL1. EL1 had the second-best capacity retention of 91.3% relative to the other samples, while maintaining the lowest DC-IR increase of 102% and a relatively low swelling percentage of 104.4%. Overall, EL1 and EL2 appear to offer the best balance of performance across the three measurement parameters over extended cycles.

[0101] Figure 24 The results of 60°C storage tests performed on the reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) over an 8-week period are shown.

[0102] Figure 25 This is a graph showing the percentage of capacity retention for a reference electrolyte (Ref) and four modified electrolyte formulations (EL1, EL2, EL3, EL4) over an 8-week period. The reference electrolyte showed the lowest retention rate, decreasing to approximately 84.6% by week 8. EL2 and EL3 showed the highest retention rates, remaining above 88% by week 8. EL1 and EL4 also outperformed the reference electrolyte, with a retention rate of approximately 87% at the end of the storage period.

[0103] Figure 26 This is a table showing capacity retention rates and percentages in Ah over an 8-week period. Initial capacity values ​​were normalized to 100%. EL2 shows the highest retention percentage at 88.3% in week 8, while the reference decreases to 84.6%.

[0104] Figure 27 This is a graph showing the percentage of volume recovery over an 8-week period. The reference electrolyte showed the lowest recovery rate, decreasing to 82.4% by week 8. EL3 and EL2 showed an excellent recovery percentage of approximately 90% at the end of this period. EL1 and EL4 also showed better recovery rates compared to the reference.

[0105] Figure 28 This is a table showing the capacity recovery rate in Ah and as a percentage over an 8-week period. Initial recovery values ​​were normalized to 100%. EL3 showed the highest recovery percentage at week 8, at 90.5%, while the reference decreased to 82.4%.

[0106] Figure 29 This is a graph showing the percentage change in thickness over an 8-week period. EL2 shows the highest thickness increase, reaching approximately 105.6% by week 8. EL1 exhibits the most stable thickness, maintaining close to 100.1% throughout the storage period.

[0107] Figure 30 This table shows the thickness and percentage change in millimeters (mm) over an 8-week period. The initial thickness values ​​were normalized to 100%. EL2 showed the highest thickness change at week 8, at 105.6%, while EL1 remained the most stable at 100.1%.

[0108] Figure 31 This is a graph showing the percentage increase in DC-IR over an 8-week period. EL4 exhibits the highest DC-IR increase, reaching approximately 175.3% by week 8. EL1 shows the most stable DC-IR value, remaining close to 114.9% throughout the storage period.

[0109] Figure 32 This is a table showing the DC-IR and percentage increase in mOhms over an 8-week period. Initial DC-IR values ​​were normalized to 100%. EL4 showed the highest DC-IR increase at week 8, at 175.3%, while EL1 remained the most stable at 114.9%.

[0110] ​A battery cell 10 is shown, having a positive electrode 12, a negative electrode 14, and a current collector 16. The positive electrode 12 comprises a positive electrode active material 18 forming a layer of the positive electrode 12. The battery cell 10 comprises a liquid electrolyte 20. The liquid electrolyte 20 permeates the surface of the positive electrode active material layer and comprises 1M lithium hexafluorophosphate and 0.5% by weight vinylene carbonate, dissolved in a solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 25 / 75. This specific composition of the liquid electrolyte 20 is configured to suppress the electrochemical oxidation of the positive electrode active material layer 18 during electrochemical cycling. The liquid electrolyte 20 may also include various additives to enhance battery performance. For example, the liquid electrolyte 20 may also include 0.5% by weight propylene sulfone to improve high-temperature performance and cycle stability, or include 0.3% by weight 1,3-propenesulfonyl lactone to enhance the formation of a stable solid-electrolyte interface on the electrode surface, thereby reducing impedance and improving cycle life. Additionally, 0.5% by weight of ethylene sulfate can be added to further stabilize the liquid electrolyte 20 and suppress side reactions that may degrade the performance of the battery cell 10 over time. Including 1% by weight of fluoroethylene carbonate provides additional stability to the solid-electrolyte interface layer and improves the overall performance and stability of the battery cell 10. Furthermore, 1% by weight of lithium difluorophosphate can be included to increase the thermal stability and ionic conductivity of the liquid electrolyte 20, thereby contributing to improved battery performance under various operating conditions. The liquid electrolyte 20 saturates the positive electrode 12 and the negative electrode 14, such that lithium ions separated from lithium hexafluorophosphate are stabilized by molecular complexation with ethylene carbonate to mitigate electrochemical oxidation of the positive electrode 12, resulting in a lower DC-IR for a given state of charge than that of a battery cell with the same properties without ethylene carbonate.

[0111] In another embodiment, the liquid electrolyte 20 comprises 1 M lithium hexafluorophosphate and 0.3 M lithium bis(fluorosulfonyl)imide, dissolved in a solvent mixture of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 25 / 75, which saturates the positive electrode 12 and the negative electrode 14. Lithium ions from lithium hexafluorophosphate can be stabilized by complexing with ethylene carbonate molecules to mitigate electrochemical oxidation of the positive electrode 12. In yet another embodiment, the solvent mixture comprises ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30 to provide a balance between high ionic conductivity and stability, thereby improving the performance and cycle life of the battery cell 10. The current collector 16 may be made of aluminum, which provides conductivity and stability in the battery 10. The positive electrode active material layer 18 may be composed of lithium nickel manganese cobalt oxide, which provides high capacity and thermal stability, thus contributing to the overall performance and stability of the battery cell 10. In addition, the battery cell 10 is configured to maintain its capacity for a long time, wherein the capacity retention rate of the battery cell 10 is greater than 80% after 200 charge-discharge cycles.

[0112] While exemplary embodiments have been described above, these embodiments are not intended to describe all possible forms of the invention. Rather, the terms used in this specification are descriptive rather than restrictive, and it should be understood that various changes may be made without departing from the spirit and scope of the invention. Furthermore, features of various embodiments may be combined to form other embodiments of the invention.

[0113] 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 1 M lithium hexafluorophosphate and 0.5 wt% vinylene carbonate, dissolved in a solvent of ethylene carbonate and methyl ethyl carbonate in a volume ratio of 25 / 75, thereby penetrating to the surface of the positive electrode active material layer and configured to suppress the electrochemical oxidation of the positive electrode active material layer during electrochemical cycling.

[0114] According to an embodiment, the current collector is made of aluminum.

[0115] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfone.

[0116] According to an embodiment, the electrolyte further includes 0.3% by weight of 1,3-propenylsulfonyl lactone.

[0117] According to an embodiment, the positive electrode active material layer is lithium nickel manganese cobalt oxide.

[0118] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfite.

[0119] According to an embodiment, the electrolyte further includes 1% by weight of fluoroethylene carbonate.

[0120] According to an embodiment, the electrolyte further includes 1% by weight of lithium difluorophosphate.

[0121] According to the present invention, a battery cell is provided, comprising: a negative electrode; a positive electrode; and an electrolyte comprising lithium hexafluorophosphate and 0.5% by weight of vinylene carbonate, which are dissolved in a solvent of ethylene carbonate and methyl ethyl carbonate, thereby saturating the negative electrode and the positive electrode, such that lithium ions separated from the lithium hexafluorophosphate are stabilized by molecular complexation with vinylene carbonate to mitigate electrochemical oxidation of the positive electrode.

[0122] According to an embodiment, the electrolyte further includes 1M lithium hexafluorophosphate and 0.3M lithium bis(fluorosulfonyl)imide.

[0123] According to an embodiment, the solvent comprises ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30.

[0124] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfone.

[0125] According to an embodiment, the electrolyte further includes 0.3% by weight of 1,3-propenylsulfonyl lactone.

[0126] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfite.

[0127] According to an embodiment, the electrolyte further includes 1% by weight of lithium difluorophosphate.

[0128] According to the embodiment, the battery cell retains more than 80% of its capacity after 200 charge-discharge cycles.

[0129] According to the present invention, a battery cell is provided having: a negative electrode; a positive electrode; and an electrolyte comprising 1 M lithium hexafluorophosphate and 1 wt% fluoroethylene carbonate and 0.5 wt% vinylene carbonate, dissolved in a solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 25 / 45 / 30, thereby saturating the negative electrode and the positive electrode, such that lithium ions released from the lithium hexafluorophosphate are stabilized by solvation with the vinylene carbonate molecules, resulting in a DC impedance of the battery cell for a given state of charge that is less than the DC impedance of a battery cell otherwise identical without the vinylene carbonate.

[0130] According to an embodiment, the DC impedance is at least 10% lower than that of a battery cell that is otherwise identical without the vinylene carbonate.

[0131] According to an embodiment, the electrolyte further includes 0.5% by weight of propylene sulfone and 0.3% by weight of 1,3-propenesulfonyl lactone.

[0132] According to an embodiment, the electrolyte further includes 0.5% by weight of vinyl sulfate and 1% by weight of lithium difluorophosphate.

Claims

1. An electrode assembly comprising: a current collector; a positive active material layer on the current collector; and an electrolyte comprising 1 M lithium hexafluorophosphate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 25 / 75, permeating to a surface of the positive active material layer, and configured to inhibit electrochemical oxidation of the positive active material layer during an electrochemical cycling process of the positive active material layer.

2. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.5 wt% of propene sulfone.

3. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.3 wt% of 1,3-propene sultone.

4. The electrode assembly of claim 1, wherein the electrolyte further comprises 0.5 wt% of vinyl sulfate.

5. The electrode assembly of claim 1, wherein the electrolyte further comprises 1 wt% of fluoroethylene carbonate.

6. The electrode assembly of claim 1, wherein the electrolyte further comprises 1 wt% of lithium difluorophosphate.

7. A battery cell comprising: a negative electrode; a positive electrode; and an electrolyte comprising lithium hexafluorophosphate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate and ethyl methyl carbonate, saturating the negative electrode and the positive electrode, such that lithium ions dissociating from the lithium hexafluorophosphate are stabilized by molecular complexation with the vinylene carbonate to mitigate electrochemical oxidation of the positive electrode.

8. The battery cell of claim 7, wherein the electrolyte further comprises 1 M lithium hexafluorophosphate and 0.3 M lithium bis(fluorosulfonyl)imide.

9. The battery cell of claim 7, wherein the solvent comprises ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30.

10. The battery cell of claim 7, wherein the electrolyte further comprises 0.5 wt% of propene sulfone.

11. The battery cell of claim 7, wherein the electrolyte further comprises 0.3 wt% of 1,3-propene sultone.

12. The battery cell of claim 7, wherein the electrolyte further comprises 0.5 wt% of vinyl sulfates.

13. The battery cell of claim 7, wherein the electrolyte further comprises 1 wt% of lithium difluorophosphate.

14. A battery cell comprising: a negative electrode; a positive electrode; and an electrolyte comprising 1 M lithium hexafluorophosphate and 1 wt% fluoroethylene carbonate and 0.5 wt% vinylene carbonate dissolved in a solvent of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 25 / 45 / 30, saturating the negative electrode and the positive electrode, such that lithium ions dissociating from the lithium hexafluorophosphate are stabilized by solvation with the vinylene carbonate molecules, resulting in a direct current impedance of the battery cell for a given state of charge that is less than a direct current impedance of an otherwise identical battery cell without the vinylene carbonate. ​ ​ ​ 15. The battery cell of claim 14, wherein the electrolyte further comprises 0.5 wt% of vinyl sulfonic acid and 1 wt% of lithium difluorophosphate.

Images