Lithium ion battery electrolyte and application thereof

Abstract

The invention provides a lithium ion battery electrolyte and application thereof. The electrolyte comprises: a non-aqueous solvent; a lithium salt; the additives comprise a first additive and a second additive, the first additive comprises lithium difluoro-bis (oxalate) phosphate, the second additive comprises methylene methanedisulfonate, the content of the first additive in the electrolyte is Mwt%, the content of the second additive in the electrolyte is Nwt%, A = 2 * M / 100 + 0.5 * N / 100 < = 0.015, B = 80 * M / 100 + 170 * N / 100 > = 1, and M is a positive integer. C = M + N < = 1.5. According to the lithium ion battery electrolyte and the application thereof provided by the invention, the problem of R angle wrinkles caused by formation gas production of a soft package battery can be effectively solved, and a large-size lithium ion battery with low formation gas production and excellent cycle performance is obtained.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, specifically to a lithium-ion battery electrolyte and its application. Background Technology

[0002] Lithium-ion batteries, due to their advantages such as high energy density, long cycle life, and no memory effect, have been widely used in mobile communication devices, electric vehicles, and energy storage systems. Among the various packaging forms of lithium-ion batteries, pouch lithium-ion batteries, with their flexible shape design, high energy density, and good safety performance, occupy an increasingly important market share. However, after formation, pouch lithium-ion batteries often develop wrinkles at the rounded corners (R-corners) of the cell edges. These wrinkles not only affect the uniformity of the battery's appearance but may also lead to uneven stress distribution and poor alignment between the internal electrodes and separator. Under long-term use, this may cause excessive local current density or even puncture the separator, posing potential safety hazards and seriously affecting the product's yield and reliability. Summary of the Invention

[0003] This invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by this invention can effectively solve the R-corner wrinkling problem caused by gas generation during formation in soft-pack batteries, while ensuring that the battery has good cycle performance, and obtain large-size lithium-ion batteries with low formation gas generation and excellent cycle performance.

[0004] To solve the above-mentioned technical problems, the present invention provides a lithium-ion battery electrolyte, comprising:

[0005] Non-aqueous solvents;

[0006] Lithium salts; and

[0007] The additives, comprising a first additive and a second additive, wherein the first additive comprises lithium difluorodioxazophosphate, and the second additive comprises methylene disulfonate, wherein the content of the first additive in the electrolyte is Mwt%, and the content of the second additive in the electrolyte is Nwt%, satisfying the following:

[0008] A = 2*M / 100 + 0.5*N / 100 ≤ 0.015, B = 80*M / 100 + 170*N / 100 ≥ 1, C = M + N ≤ 1.5. In one embodiment of the present invention, the content of the first additive in the electrolyte is not less than 0.1 wt%; and / or, the content of the second additive in the electrolyte is not less than 0.1 wt%.

[0009] In one embodiment of the present invention, the non-aqueous solvent includes ethylene carbonate, and the content of ethylene carbonate in the electrolyte is 10 wt% to 20 wt%.

[0010] In one embodiment of the present invention, the non-aqueous solvent further includes at least one of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate.

[0011] In one embodiment of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or lithium dioxalatoborate.

[0012] In one embodiment of the present invention, the content of the lithium salt in the electrolyte is 10wt%-20wt%.

[0013] The present invention also provides a lithium-ion battery, characterized in that it comprises:

[0014] case;

[0015] An electrode assembly disposed within the housing is formed by winding or stacking positive electrode sheets, a separator, and a negative electrode sheet; and

[0016] An electrolyte is filled within the electrode assembly and within the electrode assembly and the housing, wherein the electrolyte is selected from the lithium-ion battery electrolytes described above.

[0017] In one embodiment of the present invention, the width of the electrode assembly is greater than or equal to 80 mm, and the thickness of the electrode assembly is greater than or equal to 10 mm.

[0018] In one embodiment of the present invention, the positive electrode sheet includes a positive electrode active material, wherein the positive electrode active material is LiNi. x Co y M z O2, where 0.3≤x≤0.7, 0.15≤y≤0.35, and 0.15≤z≤0.35;

[0019] And / or, the negative electrode sheet includes a negative electrode active material, which is graphite or a graphite-doped silicon compound.

[0020] The present invention also provides an electronic device comprising the lithium-ion battery described above.

[0021] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By adding a first additive and a second additive to the electrolyte, studying the formation reaction mechanism of the first and second additives, understanding the consumption and gas generation patterns of the additives, optimizing the content of easily formed gas-generating components in the electrolyte, and constraining the dosage of the first and second additives, the R-corner wrinkling problem caused by formation gas generation in pouch batteries can be effectively solved, while ensuring good cycle performance of the battery. Ultimately, a large-size lithium-ion battery with low formation gas generation and excellent cycle performance is obtained. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0024] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In-depth research revealed that the root cause of the R-corner wrinkles is gas generation during the formation process. Simultaneously with the formation of the solid electrolyte interface (SEI), the solvent and certain functional additives in the electrolyte undergo unavoidable side reactions, decomposing and generating gases (such as H2, CO2, and C2H4). These gases accumulate within the sealed aluminum-plastic film packaging, creating internal pressure. Due to the limited size of the cell's gas bag, gas accumulation leads to significant deformation of the bag. Since the structural support at the R-corner of a pouch battery is relatively weak, the aluminum-plastic film at the R-corner also undergoes irreversible plastic deformation under the influence of the gas bag deformation. Even after removing most of the gas in the subsequent degassing process, the deformed R-corner cannot be completely restored to its original smoothness, ultimately forming permanent wrinkles. Among various commonly used electrolyte solvents and additives in the industry, different additive components have varying effects on gas generation during formation. This invention proposes a lithium-ion battery electrolyte. By studying the formation reaction mechanism of additives, understanding the consumption and gas generation patterns of additives, optimizing the content of easily formed and gas-generating components in the electrolyte, and imposing secondary constraints on the additive content, the R-angle wrinkling problem is significantly improved, ultimately achieving the effect of low formation gas generation and excellent cycle performance.

[0026] This invention proposes a lithium-ion battery electrolyte, comprising a non-aqueous solvent, a lithium salt, and additives. The additives include a first additive and a second additive. The first additive includes, for example, lithium difluorodioxanol phosphate (LiODFP), and the second additive includes, for example, methylene methanedisulfonate (MMDS). The first additive primarily acts on the positive electrode interface while also providing some negative electrode protection. The second additive primarily acts on the negative electrode interface, focusing on building a dense and stable SEI film to reduce electrolyte consumption on the negative electrode side and indirectly reduce electrolyte oxidation pressure at the positive electrode interface. Therefore, the synergistic effect of the first and second additives achieves "co-stabilization of the positive and negative electrode interfaces," significantly improving the battery's cycle stability, rate performance, and safety performance.

[0027] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, Mwt%, and the content of the second additive in the electrolyte is, for example, Nwt%, satisfying: A = 2*M / 100 + 0.5*N / 100 ≤ 0.015, B = 80*M / 100 + 170*N / 100 ≥ 1, and C = M + N ≤ 1.5. By defining three additive content constraint parameters A, B, and C, where A is related to the gas production content of the additive during formation, and by studying the consumption and gas production patterns of the first and second additives during the formation stage, it was found that the gas production (mL / Ah) of the additives during formation has a positive proportional relationship with its addition amount to varying degrees; B is related to the influence of the first and second additives on the battery cycle life, with different additives having different influence weights on cycle life; furthermore, the study found that the total amount of additives added, C, also affects the battery cycle life. Therefore, by constraining the dosage of the first and second additives under these three conditions, the R-corner wrinkling problem caused by gas production during formation in pouch batteries can be effectively solved, while ensuring good battery cycle performance.

[0028] In one embodiment of the present invention, the content of the first additive in the electrolyte is not less than 0.1 wt%, and the content of the second additive in the electrolyte is not less than 0.1 wt%. This effectively forms a film covering the solid-liquid interface, while exerting a good synergistic effect and improving the cycle performance of the battery.

[0029] In one embodiment of the present invention, the lithium salt includes, for example, at least one selected from lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium dioxolaneborate (LiBOB). The content of the lithium salt in the electrolyte is, for example, 10 wt% to 20 wt%.

[0030] In one embodiment of the invention, the non-aqueous solvent includes, for example, ethylene carbonate (EC), and the content of ethylene carbonate in the electrolyte is, for example, 10 wt% to 20 wt%. Ethylene carbonate has a high dielectric constant, moderate viscosity, and high boiling point, which ensures the dissolution of lithium salt, constructs a stable SEI film, and protects the electrode. Simultaneously, controlling the content of ethylene carbonate in the electrolyte reduces gas generation, balancing the gas generation performance of the electrolyte and the cycle performance of the battery.

[0031] In one embodiment of the present invention, the non-aqueous solvent further includes at least one selected from propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). In one embodiment of the present invention, the total content of the non-aqueous solvent in the electrolyte is, for example, 70 wt% to 90 wt%.

[0032] In one embodiment of the present invention, when preparing the electrolyte, the solvent is mixed uniformly in a glove box with an inert gas atmosphere such as argon, where the moisture content and oxygen content are both less than or equal to 10 ppm. The lithium salt and additives are then added to the solvent and mixed uniformly to prepare a lithium-ion battery electrolyte. The contents described in this application are weight percentages calculated based on the total weight of the electrolyte.

[0033] This invention also proposes a lithium-ion battery, comprising a casing and an electrode assembly disposed within the casing. The electrode assembly is formed by layering a positive electrode, a separator, and a negative electrode, followed by winding or stacking. An electrolyte fills the electrode assembly and the casing. The electrolyte is selected from the aforementioned electrolytes. The separator prevents short circuits between the positive and negative electrodes, allowing lithium ions to pass through. Specifically, the positive electrode, separator, and negative electrode are sequentially stacked to ensure that a separator is provided between any positive and negative electrode. The electrode assembly is obtained by winding or folding and then installed in the battery casing. Finally, electrolyte is injected into the casing once or in multiple stages to completely immerse the electrode assembly in the electrolyte, thereby conducting ions between the positive and negative electrodes. In one embodiment of this invention, the lithium-ion battery is, for example, a secondary battery, which may be, for example, a pouch battery, a prismatic battery, or a cylindrical battery. This invention does not specifically limit the type of lithium-ion battery.

[0034] In one embodiment of the present invention, the lithium-ion battery is, for example, a pouch cell, and the width of the electrode assembly is, for example, greater than or equal to 80 mm, and the thickness of the electrode assembly is, for example, greater than or equal to 10 mm. When the electrode assembly is small, the formation gas production is small, and the problem of R-corner wrinkles is less likely to occur. Therefore, for large-size electrode assemblies, the gas production volume increases during battery formation, and R-corner wrinkles increase. Using the electrolyte provided by the present invention can reduce the R-corner wrinkles of large-size batteries.

[0035] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. The thickness of the positive current collector is, for example, 8 μm to 20 μm. In this embodiment, the positive current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0036] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes, for example, LiNi. x Co y M z O2, wherein 0.3≤x≤0.7, 0.15≤y≤0.35, and 0.15≤z≤0.35, is used to improve the operating voltage of the lithium-ion battery. In one embodiment of the present invention, the upper limit of the operating voltage of the lithium-ion battery is, for example, not less than 4.35V. The binder is selected from, for example, any one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer (ETFE), ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer (TFE-HFP-VDF), or ethylene-hexafluoropropylene copolymer (FEP). The conductive agent is selected from, for example, any one or more of conductive carbon black (Super P), acetylene black, or Ketjen black. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active layer is, for example, (94 to 98):(1 to 3):(1 to 3).

[0037] In one embodiment of the present invention, the positive electrode active material is, for example, LiNi. 0.6 Co 0.2 Mn 0.2O2, a conductive agent (e.g., conductive carbon black), and a binder (e.g., polyvinylidene fluoride) are mixed in a mass ratio of 98:1:1, and an organic solvent is added. The mixture is stirred thoroughly to obtain a positive electrode slurry. The organic solvent is, for example, N-methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated onto aluminum foil, then dried in a vacuum drying oven. The positive electrode sheet is obtained through cold pressing, edge trimming, cutting, and slitting processes. This application does not limit the method of preparing the positive electrode sheet; in other embodiments, the positive electrode sheet can also be obtained by any other method of forming a positive electrode sheet.

[0038] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative current collector and a negative active layer coated at least on one surface of the negative current collector. The negative current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector, and the thickness of the negative current collector is, for example, 6 μm to 15 μm. In this embodiment, the negative current collector is, for example, copper foil, and the thickness of the copper foil is, for example, 8 μm.

[0039] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The negative electrode active material includes, for example, at least one of graphite or a graphite-doped silicon compound, or for example, a graphite-doped silicon oxide compound, a graphite-doped silicon carbon compound, or graphite-doped silicon. In this embodiment, the negative electrode active material is, for example, a combination of graphite and silicon carbon materials or graphite and silicon oxide materials, and the content of silicon carbon materials or silicon oxide materials in the negative electrode active material is, for example, 2 wt% to 20 wt%, to improve the energy density and operating voltage of the lithium-ion battery. The binder is selected from at least one of the following: polymerized styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylic acid (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), or carboxymethyl chitosan (CMCS). The thickener is selected from, for example, sodium carboxymethyl cellulose (CMC-Na). The conductive agent is selected from, for example, any one or more of conductive carbon black, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers. The mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode active layer is, for example, (94 to 97):(1 to 2):(1 to 2):(1 to 2).

[0040] In one embodiment of the present invention, the negative electrode active material is selected from artificial graphite, the conductive agent is selected from conductive carbon black, the thickener is selected from sodium carboxymethyl cellulose, and the binder is selected from styrene-butadiene rubber. The negative electrode active material, conductive agent, thickener, and binder are mixed in a mass ratio of 96:1:1:2, deionized water is added, and the mixture is thoroughly stirred to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, dried in a vacuum drying oven, and then subjected to cold pressing, edge trimming, cutting, and slitting processes to obtain the negative electrode sheet. In other embodiments, the negative electrode sheet can also be obtained by any other method of forming the negative electrode sheet.

[0041] In one embodiment of the present invention, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, and the thickness of the separator is, for example, 9 μm to 15 μm. In another embodiment of the present invention, the separator is, for example, selected as a polyethylene base membrane with a thickness of 8 μm to 10 μm, and a nano-alumina coating with a thickness of 2 μm to 4 μm is coated on at least one side of the base membrane.

[0042] In one embodiment of the present invention, the positive electrode, separator, and negative electrode are placed sequentially, with the separator positioned between the positive and negative electrode to act as a separator. An electrode assembly is obtained by winding or stacking the electrodes. The electrode assembly is then placed in a housing such as an aluminum-plastic film, baked at 80°C to 120°C to remove moisture, injected with electrolyte, and sealed. Following these processes, a lithium-ion battery is obtained through standing, hot and cold pressing, formation, clamping, and capacity testing.

[0043] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0044] Example 1

[0045] Electrolyte preparation: In an argon-filled glove box with an oxygen content of less than 10 ppm and a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed uniformly in a specific mass ratio. Then, dried LiPF6, LiODFP, and MMDS were added. Based on the total weight of the electrolyte, the contents of EC were 18 wt%, PC 4 wt%, EMC 63 wt%, LiPF6 14 wt%, LiODFP 0.5 wt%, and MMDS 0.5 wt%.

[0046] Preparation of positive electrode: LiNi 0.6 Co 0.2 Mn 0.2 O2, conductive carbon black, and polyvinylidene fluoride were mixed in a mass ratio of 98:1:1, and NMP was added. The mixture was stirred thoroughly to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 13μm aluminum foil, then dried in a vacuum drying oven. After cold pressing, edge trimming, cutting, and slitting, the positive electrode sheet was obtained.

[0047] Preparation of negative electrode sheet: Artificial graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber are mixed in a mass ratio of 96:1:1:2, deionized water is added, and the mixture is stirred and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on an 8μm copper foil and then dried in a vacuum drying oven. After cold pressing, edge trimming, cutting and slitting, the negative electrode sheet is obtained.

[0048] Selection of diaphragm: A 12μm thick polypropylene membrane was selected as the diaphragm.

[0049] Battery fabrication: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The stacked electrodes form an electrode assembly with a width of 96 mm and a thickness of 12 mm. The electrode assembly is then placed in an aluminum-plastic film, baked at 120°C to remove moisture, and then injected with electrolyte at a rate of 2.5 g / Ah before sealing. Following static settling, hot and cold pressing, formation, clamping, and capacity testing, a 125 Ah soft-pack lithium-ion battery is obtained.

[0050] Example 2

[0051] In the electrolyte, the content of EC is 20 wt% and the content of EMC is 61 wt%, and the other steps are consistent with those in Example 1.

[0052] Example 3

[0053] In the electrolyte, the content of EC is 10 wt% and the content of EMC is 71 wt%, and the other steps are consistent with those in Example 1.

[0054] Example 4

[0055] The electrolyte contained 0.5 wt% LiODFP, 1 wt% MMDS, and 62.5 wt% EMC, with other steps consistent with Example 1.

[0056] Example 5

[0057] In the electrolyte, no LiODFP was added, the MMDS content was 0.6 wt%, the EMC content was 63.4 wt%, and the other steps were consistent with those in Example 1.

[0058] Example 6

[0059] In the electrolyte, no LiODFP was added, the MMDS content was 1.5 wt%, the EMC content was 62.5 wt%, and the other steps were consistent with those in Example 1.

[0060] Example 7

[0061] The electrolyte contained 0.65 wt% LiODFP and 0.35 wt% MMDS, and the other steps were consistent with those in Example 1.

[0062] Example 8

[0063] In the electrolyte, the content of EC was 22 wt% and the content of EMC was 59 wt%, and the other steps were consistent with those in Example 1.

[0064] Example 9

[0065] In the electrolyte, the content of EC is 8 wt% and the content of EMC is 73 wt%, and the other steps are consistent with those in Example 1.

[0066] Comparative Example 1

[0067] The electrolyte contained 0.7 wt% LiODFP and 0.3 wt% MMDS, and the other steps were consistent with those in Example 1.

[0068] Comparative Example 2

[0069] The electrolyte contained 1 wt% LiODFP, no MMDS was added, and the other steps were the same as in Example 1.

[0070] Comparative Example 3

[0071] The electrolyte contained 0.2 wt% LiODFP, 1.8 wt% MMDS, and 62 wt% EMC, with other steps consistent with Example 1.

[0072] Comparative Example 4

[0073] The electrolyte contained 0.5 wt% LiODFP and 0.4 wt% MMDS. 1,3,2-Dioxathiolane 2,2-Dioxide (DTD) was also added to the electrolyte, with a DTD content of 0.2 wt% and an EMC content of 62.9 wt%. Other steps were consistent with those in Example 1.

[0074] Comparative Example 5

[0075] The electrolyte contains 1 wt% LiODFP and no MMDS is added; the electrode assembly has a width of 70 mm and a thickness of 12 mm, and other steps are consistent with those in Example 1.

[0076] Comparative Example 6

[0077] The electrolyte contains 1 wt% LiODFP and no MMDS is added; the electrode assembly has a width of 96 mm and a thickness of 8 mm, and other steps are consistent with those in Example 1.

[0078] In this invention, lithium-ion batteries were prepared using different electrolytes in Examples 1 to 9 and Comparative Examples 1 to 6. Some characteristics of the electrolytes are shown in Table 1, and the performance of the lithium-ion batteries was tested. The test results are shown in Table 2.

[0079] Table 1. Partial characteristics of the electrolytes in Examples 1 to 9 and Comparative Examples 1 to 6

[0080]

[0081] In one embodiment of the present invention, the cyclic test is performed in an oven at 25°C with a current of 1C within a range of 2.8V to 4.4V, and the discharge capacity of each cycle is recorded. The test ends when the battery capacity reaches 90% of the capacity of the first cycle (90% SOH), and the number of cycles is recorded.

[0082] In one embodiment of the present invention, the volume difference of the cell before and after formation is tested using the water displacement method, and the result is counted as the formation gas production. This gas production is then divided by the battery capacity to calculate the formation gas production per Ah capacity (mL).

[0083] In one embodiment of the present invention, after the lithium-ion battery is formed, it is disassembled to observe and measure the height of wrinkles at the rounded corners (R-corners) of the electrode assembly. The wrinkle height is defined as the maximum vertical distance a single wrinkle protrudes from a flat surface. The thickness of the air pocket at the wrinkle and the thickness of the air pocket at the flat surface are measured using calipers and denoted as a and b, respectively. The wrinkle height is defined as c = ab. Specifically, when c < 1 mm, it is considered normal; when 1 ≤ c ≤ 3 mm, it is considered slight wrinkling; when 3 ≤ c ≤ 8 mm, it is considered significant wrinkling; and when c ≥ 8 mm, it is considered severe wrinkling.

[0084] Table 2, Test Results of Examples 1 to 9 and Comparative Examples 1 to 6

[0085]

[0086] Please refer to Table 1. Comparing Examples 1-3 and 8-9, it can be seen that as the EC content increases, the gas production rate increases, the R-corner wrinkles change from normal to slight wrinkles, and the cycle performance improves. This is because EC is the main solvent consumed in the formation process, and EC will be reduced to form ethylene, causing gas production. Therefore, by reasonably adjusting the amount of EC, the gas production in the formation can be controlled within a reasonable range, ensuring that the R-corner does not wrinkle, while maintaining good cycle performance.

[0087] Please refer to Table 1. Comparing Examples 1, 4-7, and Comparative Examples 1-3, it can be seen that in lithium-ion batteries, the amounts of LiODFP and MMDS have a significant impact on formation gas generation and cycle performance, and the effects of LiODFP and MMDS on gas generation and cycle performance are slightly different. Specifically, LiODFP contributes more to formation gas generation than MMDS, while MMDS has a greater impact on cycle performance than LiODFP. If the amounts of both do not meet the restrictions of A≤0.015 and / or B≥1, it will cause R-angle wrinkling and deterioration of cycle performance. Therefore, controlling the amounts of LiODFP and MMDS and coordinating their amounts is crucial to simultaneously improve gas generation and cycle performance.

[0088] Please refer to Table 1. Comparing Examples 1, 4, 6 and Comparative Example 3, it can be seen that the total amount of LiODFP and MMDS must also satisfy C≤1.5. This is because within a wide range of content, the content of the first and second additives and the formation gas production, i.e., A and B, both meet the limitations of this application. However, when the content of the first and second additives reaches a certain limit, an extreme value will appear between the content and the cycle performance. At this point, further increasing the content of the first and second additives will worsen the cycle performance.

[0089] Please refer to Table 1. Comparing Example 1 and Comparative Example 4, it can be seen that when A is not satisfied, adding a small amount of DTD to the electrolyte will significantly increase the formation gas production, leading to R-angle wrinkling. The addition of DTD does not significantly improve the cycle performance. Therefore, the present invention can completely abandon the use of DTD.

[0090] Please refer to Table 1. Comparing Example 1 and Comparative Examples 2 and 5-6, it can be seen that when the electrode assembly size does not meet the requirements of width ≥ 80 mm and thickness ≥ 10 mm, the battery capacity is relatively small. Even if the formation gas production per unit Ah is large, the total formation gas production will be very low, thus avoiding the problem of R-corner wrinkles. Therefore, the electrolyte of the present invention is suitable for solving the R-corner wrinkle problem in larger-sized battery cells.

[0091] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0092] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By adding a first additive and a second additive to the electrolyte, studying the formation reaction mechanism of the first and second additives, understanding the consumption and gas generation patterns of the additives, optimizing the content of easily formed gas-generating components in the electrolyte, and constraining the dosage of the first and second additives, the R-corner wrinkling problem caused by formation gas generation in pouch batteries can be effectively solved, while ensuring good cycle performance of the battery. Ultimately, a large-size lithium-ion battery with low formation gas generation and excellent cycle performance is obtained.

[0093] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0094] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, include: Non-aqueous solvents; Lithium salts; as well as The additives, comprising a first additive and a second additive, wherein the first additive comprises lithium difluorodioxazophosphate, and the second additive comprises methylene disulfonate, wherein the content of the first additive in the electrolyte is Mwt%, and the content of the second additive in the electrolyte is Nwt%, satisfying the following: A=2*M / 100+0.5*N / 100≤0.015, B=80*M / 100+170*N / 100≥1, C=M+N≤1.

5.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is not less than 0.1 wt%; and / or, the content of the second additive in the electrolyte is not less than 0.1 wt%.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The non-aqueous solvent includes ethylene carbonate, and the content of ethylene carbonate in the electrolyte is 10 wt% to 20 wt%.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The non-aqueous solvent also includes at least one of propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or lithium dioxalatoborate.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt content in the electrolyte is 10wt%-20wt%.

7. A lithium-ion battery, characterized in that, include: case; The electrode assembly disposed within the housing is formed by winding or stacking positive electrode sheets, a separator and negative electrode sheets; as well as An electrolyte is filled within the electrode assembly and within the electrode assembly and the housing, wherein the electrolyte is selected from the lithium-ion battery electrolyte according to any one of claims 1-6.

8. The lithium-ion battery according to claim 7, characterized in that, The width of the electrode assembly is greater than or equal to 80 mm, and the thickness of the electrode assembly is greater than or equal to 10 mm.

9. The lithium-ion battery according to claim 7, characterized in that, The positive electrode includes a positive active material, namely LiNi. x Co y M z O2, where 0.3≤x≤0.7, 0.15≤y≤0.35, and 0.15≤z≤0.35; And / or, the negative electrode sheet includes a negative electrode active material, which is graphite or a graphite-doped silicon compound.

10. An electronic device, characterized in that, Includes the lithium-ion battery as described in any one of claims 7-9.

Images