A lithium-ion battery electrolyte, a lithium-ion battery, and an electrical device

Abstract

The present application provides a lithium-ion battery electrolyte, a lithium-ion battery, and electrical equipment, belonging to the field of lithium-ion battery manufacturing. The lithium-ion battery electrolyte includes a fluorinated organic solvent, a lithium salt, and a lithium salt additive, wherein the lithium salt additive has a pyridyl salt of the structural formula shown in Formula I and / or Formula II, and the pyridyl salt includes lithium pyridyl borate and / or lithium pyridyl phosphate: wherein R1 to R3 are independently selected from one of a fluorinated C1 to C6 chain alkyl group, a C2 to C6 olefin group, a C2 to C6 alkyne group, a C6 to C12 cyclic olefin group, a cyano group, and a C1 to C5 nitrile group. By using this lithium-ion battery electrolyte, the cycle performance of the lithium-ion battery at high voltage can be improved to a certain extent.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion battery manufacturing, and in particular to a lithium-ion battery electrolyte, a lithium-ion battery, and electrical equipment. Background Art

[0002] In the prior art, commonly used lithium salt additives (such as lithium difluorooxalatoborate, lithium difluorophosphate, and lithium bis(oxalatoborate)) have the problem of poor cycling performance of corresponding lithium-ion batteries when used at high voltages (above 4.5V), especially when the application voltage is above 4.8V. Summary of the Invention

[0003] The purpose of this application is to provide a lithium-ion battery electrolyte, a lithium-ion battery and an electrical device, which can improve the cycle performance of the lithium-ion battery under high voltage to a certain extent.

[0004] The embodiment of the present application is implemented as follows:

[0005] In a first aspect, embodiments of the present application provide a lithium-ion battery electrolyte comprising a fluorinated organic solvent, a lithium salt, and a lithium salt additive. The lithium salt additive comprises a pyridyl salt having a general structural formula as shown in Formula I and / or Formula II, wherein the pyridyl salt comprises lithium pyridyl borate and / or lithium pyridyl phosphate:

[0006]

[0007] Wherein, R1 to R3 are independently selected from one of fluorine-substituted C1 to C6 chain alkyl groups, C2 to C6 olefin groups, C2 to C6 alkynyl groups, C6 to C12 cyclic olefin groups, cyano groups and C1 to C5 nitrile groups.

[0008] In the above technical solution, the lithium salt additive pyridyl salt having the above structural formula in the battery electrolyte, compared with the existing lithium salt additives (the existing lithium salt additives have low solubility in fluorinated organic solvents and low film-forming potential, resulting in lithium deficiency in the SEI film formed at the negative electrode), the lithium salt additive provided in the embodiment of the present application has a higher solubility in fluorinated organic solvents, coupled with its high film-forming potential, so that the negative electrode of the battery in a high-voltage application environment can form a lithium-rich SEI film, thereby improving the problem of lithium deficiency in the SEI film formed at the negative electrode of the battery under high voltage to a certain extent, thereby improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0009] In some optional embodiments, the lithium salt additive includes one or more of the following compound structures:

[0010]

[0011]

[0012] Compared with lithium salt additives with other structural formulas, the lithium salt additive with the above structural formula can better increase the lithium content in the SEI film formed at the battery negative electrode under high voltage, thereby better improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0013] In some alternative embodiments, the lithium salt additive includes lithium pyridylborate and lithium pyridylphosphate.

[0014] In the above technical solution, the lithium salt additive contains pyridinyl salts of two structural systems at the same time, which can more comprehensively improve the battery cycle performance compared to pyridinyl salts containing only one of the structural systems (when there is only pyridinyl salts of one of the structural systems, the overall battery performance can be improved, but some performance improvements are insufficient, and the performance improvement of the pyridinyl salts of the two structural systems is not exactly the same).

[0015] In some optional embodiments, in the lithium ion battery electrolyte, the mass ratio of lithium pyridyl borate to lithium pyridyl phosphate is 1:(1-2).

[0016] In the above technical solution, when lithium salt additives of two structural systems coexist, the mass proportion of lithium pyridyl phosphate is slightly higher, which can significantly improve the comprehensive electrical performance of the battery at high temperature.

[0017] In some optional embodiments, the mass percentage of the lithium salt additive in the lithium ion battery electrolyte is 0.1 to 5%;

[0018] Optionally, the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte is 0.5-2%.

[0019] In the above technical solution, the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte is limited to the range of 0.1-5%, which can ensure that the SEI film formed on the negative electrode has an appropriate content of lithium, thereby enabling the corresponding battery to have better cycle performance under high voltage.

[0020] Furthermore, limiting the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte to a range of 0.5 to 2% can enable the corresponding battery to have better cycle performance under high voltage.

[0021] In some optional embodiments, the mass percentage of lithium salt in the lithium-ion battery electrolyte is 12-15%.

[0022] In the above technical solution, limiting the amount of lithium salt to the above range can ensure that the lithium salt in the electrolyte has an appropriate amount, thereby enabling the corresponding battery to have better cycle performance under high voltage.

[0023] In some optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium bistrifluoromethanesulfonyl imide.

[0024] The solution of the present application can be well applied to the above-mentioned various lithium salt systems, providing more feasible implementation plans, thereby facilitating promotion and application; in addition, compared with the use of other types of lithium salts (such as lithium perchlorate, lithium difluorophosphate, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium hexafluoroaluminate, lithium hexafluoroarsenate and perfluoroalkylsulfonylmethyl lithium), the use of the lithium salts provided in the embodiments of the present application can enable the corresponding battery to have better cycle performance under high voltage.

[0025] In some optional embodiments, the fluorinated organic solvent includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluoropropylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, fluoroethyl acetate, fluoropropyl acetate, fluoroethyl propionate and fluoropropyl propionate.

[0026] The solution of the present application can be well applied to the above-mentioned various fluorinated organic solvent systems, and provides more feasible implementation plans, thereby facilitating promotion and application.

[0027] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and the lithium-ion battery electrolyte provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; the lithium-ion battery electrolyte is housed in the housing.

[0028] In this embodiment, the lithium-ion battery includes the lithium-ion battery electrolyte provided in the first embodiment. When used under high voltage, it can form a lithium-rich SEI film on the negative electrode of the battery, thereby improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0029] In some optional embodiments, the electrode assembly satisfies the following conditions (a) and / or (b);

[0030] (a) In the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate, a transition metal oxide lithium salt, and a transition metal sulfide;

[0031] Optionally, the positive electrode active material includes lithium nickel manganese oxide having a spinel structure;

[0032] (b) In the battery negative electrode of the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

[0033] The solution of the present application can be well applied to the above-mentioned multiple positive electrode active material systems and negative electrode active material systems, providing more feasible implementation plans, thereby facilitating promotion and application; among them, due to the spinel structure of lithium nickel manganese oxide (such as LiNi 0.5 Mn 1.5 O4) usually needs to delithiate and participate in the negative electrode film formation when the voltage reaches 3.5V or above, while the film formation voltage of conventional lithium salt additives is relatively low, which makes the SEI film formed under high voltage of this type of battery have a more serious lithium deficiency problem. Therefore, the solution of this application is particularly suitable for positive electrode active material batteries with spinel structure lithium nickel manganese oxide.

[0034] In a third aspect, an embodiment of the present application provides an electrical device, comprising a lithium-ion battery as provided in the embodiment of the second aspect. DETAILED DESCRIPTION

[0035] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0036] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to three situations: “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0037] In addition, in the description of this application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a to value b" includes the two end values "a" and "b", and the "unit of measurement" in "value a to value b+unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0038] In the prior art, to meet the cycling performance requirements of lithium-ion batteries when used in high-voltage environments, high-voltage-resistant fluorinated organic solvents are generally used. At the same time, lithium salt additives are added to the electrolyte to form an SEI film at the battery's negative electrode to optimize battery performance. However, current lithium salt additives (such as lithium difluorooxalatoborate, lithium difluorophosphate, and lithium bisoxalatoborate) have low solubility in fluorinated organic solvents (the solubility is typically less than 0.2%). Furthermore, these lithium salt additives have a low film-forming voltage, typically around 2.0V (i.e., the residual content is low at high voltage). This results in a lithium deficiency problem in the SEI film formed at the battery's negative electrode. This is particularly true for lithium-ion batteries operating at voltages of 4.5V and above, resulting in poor cycling performance of batteries containing these lithium salt additives at high voltages.

[0039] Based on this, the inventors discovered that using a pyridyl salt with a specific structural system as a lithium salt additive not only has a high solubility in fluorinated organic solvents, but also has a high film-forming voltage, which can enable the negative electrode of the battery to form a lithium-rich SEI film in a high-voltage application environment, thereby improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0040] In a first aspect, embodiments of the present application provide a lithium-ion battery electrolyte comprising a fluorinated organic solvent, a lithium salt, and a lithium salt additive. The lithium salt additive comprises a pyridyl salt having a general structural formula as shown in Formula I and / or Formula II, wherein the pyridyl salt comprises lithium pyridyl borate and / or lithium pyridyl phosphate:

[0041]

[0042] Wherein, R1 to R3 are independently selected from one of fluorine-substituted C1 to C6 chain alkyl groups, C2 to C6 olefin groups, C2 to C6 alkynyl groups, C6 to C12 cyclic olefin groups, cyano groups and C1 to C5 nitrile groups.

[0043] In the present application, the lithium salt additive pyridyl salt having the above-mentioned general structural formula in the battery electrolyte has a higher solubility in fluorinated organic solvents and a lower film-forming potential than the existing lithium salt additives (the existing lithium salt additives have a lower solubility in fluorinated organic solvents and a lower film-forming potential). In addition, its film-forming potential is higher, so that the negative electrode of the battery in a high-voltage application environment can form a lithium-rich SEI film, thereby improving the problem of lithium deficiency in the SEI film formed at the negative electrode of the battery under high voltage to a certain extent, thereby improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0044] As an example, the lithium salt additive includes one or more of the following compound structures:

[0045]

[0046]

[0047] In this embodiment, the lithium salt additive with the above structural formula can better increase the lithium content in the SEI film formed at the negative electrode of the battery under high voltage, compared with the lithium salt additive with other structural formulas, thereby better improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0048] It is understandable that pyridyl salts of different structural systems have some differences in physical and chemical properties, which will accordingly lead to slightly different effects on improving the cycle performance of the battery. In order to more comprehensively improve the cycle performance of the corresponding battery, the composition of the lithium salt additive can be adjusted.

[0049] As an example, the lithium salt additive includes lithium pyridylborate and lithium pyridylphosphate.

[0050] In this embodiment, the lithium salt additive contains pyridyl salts of two structural systems at the same time, which can more comprehensively improve the cycle performance of the battery compared to pyridyl salts containing only one of the structural systems (when there is only pyridyl salts of one of the structural systems, the overall battery performance can be improved, but some performance improvements are insufficient, and the performance improvement of the pyridyl salts of the two structural systems is not exactly the same).

[0051] It should be noted that when two pyridyl salts of the structural system coexist, the mass ratio between the two is not limited and can be adjusted according to actual needs.

[0052] As an example, in the lithium-ion battery electrolyte, the mass ratio of lithium pyridyl borate to lithium pyridyl phosphate is 1:(1-2), for example, but not limited to, the mass ratio is any one of 1:1, 1:1.2, 1:1.4, 1:1.6, 1:1.8 and 1:2, or a range between any two of them.

[0053] In this embodiment, when the lithium salt additives of the two structural systems coexist, the mass proportion of lithium pyridyl phosphate is slightly higher, which can significantly improve the comprehensive electrical performance of the battery at high temperature.

[0054] It should be noted that the amount of the lithium salt additive in the electrolyte is not limited and can be adjusted according to actual needs.

[0055] As an example, the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte is 0.1-5%, for example, but not limited to, any one of 0.1%, 0.5%, 1%, 2%, 3%, 4% and 5% by mass, or a range between any two of them.

[0056] Optionally, the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte is 0.5-2%, for example but not limited to any one of 0.5%, 1%, 1.5% and 2% by mass, or a range between any two of them.

[0057] In this embodiment, the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte is limited to the range of 0.1-5%, so that the SEI film formed on the negative electrode has an appropriate content of lithium, thereby making the corresponding battery have better cycle performance under high voltage.

[0058] Furthermore, limiting the mass percentage of the lithium salt additive in the lithium-ion battery electrolyte to a range of 0.5 to 2% can enable the corresponding battery to have better cycle performance under high voltage.

[0059] It should be noted that the amount of lithium salt in the electrolyte is not limited and can be adjusted according to actual needs.

[0060] As an example, the mass percentage of lithium salt in the lithium-ion battery electrolyte is 12-15%, for example, but not limited to, any one of 12%, 13%, 14% and 15% by mass, or a range between any two of them.

[0061] In this embodiment, the amount of lithium salt is limited to the range of 12-15%, so that the lithium salt in the electrolyte has an appropriate amount, thereby making the corresponding battery have better cycle performance under high voltage.

[0062] It should be noted that the type of lithium salt is not limited and can be adjusted according to actual needs.

[0063] As an example, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, and lithium bistrifluoromethanesulfonyl imide.

[0064] In this embodiment, the solution of the present application can be well applied to the above-mentioned multiple lithium salt systems, providing more feasible implementation plans, thereby facilitating promotion and application; in addition, compared with the use of other types of lithium salts (such as lithium perchlorate, lithium difluorophosphate, lithium dioxalatoborate, lithium difluorooxalatoborate, lithium hexafluoroaluminate, lithium hexafluoroarsenate and perfluoroalkylsulfonylmethyl lithium), the use of the lithium salt provided in the embodiment of the present application can enable the corresponding battery to have better cycle performance under high voltage.

[0065] It should be noted that the type of fluorinated organic solvent is not limited and can be adjusted according to actual needs.

[0066] As an example, the fluorinated organic solvent includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluoropropylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, fluoroethyl acetate, fluoropropyl acetate, fluoroethyl propionate and fluoropropyl propionate.

[0067] In this embodiment, the solution of the present application can be well applied to the above-mentioned multiple fluorinated organic solvent systems, providing more feasible implementation plans, thereby facilitating promotion and application; at the same time, the above-mentioned types of fluorinated organic solvents have good high-pressure resistance.

[0068] In other possible embodiments, the lithium-ion battery electrolyte further includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methylpropyl carbonate.

[0069] In this embodiment, the lithium-ion battery electrolyte includes some other types of organic solvents, which can more comprehensively improve the cycle performance of the battery under high voltage.

[0070] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and the lithium-ion battery electrolyte provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; the lithium-ion battery electrolyte is housed in the housing.

[0071] In the present application, the lithium-ion battery includes the lithium-ion battery electrolyte provided in the first embodiment. When used under high voltage, it can form a lithium-rich SEI film on the negative electrode of the battery, thereby improving the cycle performance of the corresponding lithium-ion battery under high voltage.

[0072] It should be noted that the types of positive electrode active materials and negative electrode active materials are not limited and can be adjusted according to actual needs.

[0073] As an example, the electrode assembly satisfies the following conditions (a) and / or (b);

[0074] (a) In the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate, a transition metal oxide lithium salt, and a transition metal sulfide.

[0075] (b) In the battery negative electrode of the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxides, and silicon-carbon composites.

[0076] In this embodiment, the solution of the present application can be well applied to the above-mentioned multiple positive electrode active material systems and negative electrode active material systems, providing more feasible implementation plans, thereby facilitating promotion and application.

[0077] As an example, the positive electrode active material includes lithium nickel manganese oxide having a spinel structure.

[0078] In this embodiment, the spinel structure of lithium nickel manganese oxide (such as LiNi 0.5 Mn 1.5 O4) is used as the positive electrode active material because this type of positive electrode active material usually needs to delithiate and participate in the negative electrode film formation under the condition of voltage reaching 3.5V or above. In addition, the film formation voltage of conventional lithium salt additives is relatively low (usually around 2.0V), which makes the SEI film formed by this type of battery under high voltage have a more serious lithium deficiency problem. Therefore, the solution of this application is particularly suitable for positive electrode active material batteries with spinel structure lithium nickel manganese oxide.

[0079] It should be noted that any structure not specifically described in the lithium-ion battery may be configured according to conventional selections in the art.

[0080] In a third aspect, an embodiment of the present application provides an electrical device, comprising a lithium-ion battery as provided in the embodiment of the second aspect.

[0081] It should be noted that there is no restriction on the type of electrical equipment, such as mobile phones, portable devices, laptops, electric vehicles, electric vehicles, ships, spacecraft, electric toys, energy storage devices and power tools.

[0082] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0083] Example 1

[0084] The present invention provides a method for preparing a lithium-ion battery electrolyte, comprising the following steps:

[0085] Ethylene carbonate (EC) and fluoroethyl methyl carbonate (FEMC) are mixed in a ratio of 2:8 to obtain a mixed organic solvent; then, lithium hexafluorophosphate (LiPF6) and compound 1 are added to the mixed organic solvent and mixed evenly to obtain a lithium-ion battery electrolyte; wherein, in terms of mass percentage, the mixed organic solvent: lithium hexafluorophosphate: compound 1 = 87.9:12:0.1.

[0086] Example 2

[0087] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that the ratio of mixed organic solvent: lithium hexafluorophosphate: compound 1 is 80:15:5.

[0088] Example 3

[0089] The embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that the mass percentage of Compound 1 is 0.05%, and the change in the mass of Compound 1 is adjusted by the amount of fluoroethyl methyl carbonate (FEMC).

[0090] Example 4

[0091] The embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 2 only in that the mass percentage of Compound 1 is 8%, and the change in the mass of Compound 1 is adjusted by the amount of fluoroethyl methyl carbonate (FEMC).

[0092] Example 5

[0093] The embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that the mass percentage of Compound 1 is 0.5%, and the change in the mass of Compound 1 is adjusted by the amount of fluoroethyl methyl carbonate (FEMC).

[0094] Example 6

[0095] The embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 2 only in that the mass percentage of Compound 1 is 2%, and the change in the mass of Compound 1 is adjusted by the amount of fluoroethyl methyl carbonate (FEMC).

[0096] Example 7

[0097] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 2.

[0098] Example 8

[0099] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 3.

[0100] Example 9

[0101] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 4.

[0102] Example 10

[0103] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced with 0.25% of Compound 1 and 0.25% of Compound 2.

[0104] Example 11

[0105] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 5.

[0106] Example 12

[0107] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 6.

[0108] Example 13

[0109] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 7.

[0110] Example 14

[0111] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 8.

[0112] Example 15

[0113] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 5 only in that Compound 1 is replaced with 0.25% of Compound 1 and 0.25% of Compound 5.

[0114] Example 16

[0115] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 14 only in that Compound 1 is replaced with 0.2% of Compound 1 and 0.3% of Compound 5.

[0116] Example 17

[0117] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that lithium hexafluorophosphate (LiPF6) is replaced by lithium hexafluoroaluminate (LiAlF6).

[0118] Comparative Example 1

[0119] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by lithium difluorooxalatoborate (C2BF2LiO4).

[0120] Comparative Example 2

[0121] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 9 having the following compound structure.

[0122]

[0123] Comparative Example 3

[0124] This embodiment of the present application provides a method for preparing a lithium-ion battery electrolyte, which differs from Example 1 only in that Compound 1 is replaced by Compound 10 having the following compound structure.

[0125]

[0126] In order to better understand the technical solution, the specific composition ratios of Examples 1 to 17 and Comparative Examples 1 to 3 are shown in Table 1.

[0127] Table 1 Component ratio of lithium-ion battery electrolyte

[0128]

[0129]

[0130] It should be noted that the remainder in Table 1 refers to the mass percentage remaining after deducting the mass percentage of lithium salt and lithium salt additive from 100.

[0131] Test Example 1

[0132] Electrical performance test

[0133] Test method:

[0134] The lithium-ion battery electrolytes prepared in Examples 1 to 17 and Comparative Examples 1 to 3 were assembled into batteries and numbered accordingly. Then, the capacity retention rate of the batteries after 300 cycles at 25°C and 45°C, and the capacity retention rate, capacity recovery rate, and thickness expansion rate after 7 days of storage at 60°C were tested.

[0135] in,

[0136] The battery is assembled as follows:

[0137] S1 is mixed with LiNi in a mass ratio of 96.8:2.0:1.2 0.5 Mn 1.5 O4 (positive electrode active material), conductive carbon black (conductive agent) and polyvinylidene fluoride (binder) are dispersed in N-methyl-2-pyrrolidone to obtain positive electrode slurry; then, the positive electrode slurry is evenly coated on both sides of the aluminum foil; then, after drying, calendering and vacuum drying in sequence, an aluminum lead wire is welded with an ultrasonic welder to obtain a positive electrode sheet with a thickness of 125μm.

[0138] S2 is mixed with graphite (negative electrode active material), conductive carbon black (conductive agent), styrene-butadiene rubber and carboxymethyl cellulose (binder) in a mass ratio of 95:1.5:1.5:2, and dispersed in deionized water to obtain a negative electrode slurry; then, the negative electrode slurry is coated on both sides of the copper foil; then, after drying, calendering and vacuum drying in sequence, a nickel lead wire is welded with an ultrasonic welder to obtain a negative electrode sheet with a thickness of 150μm.

[0139] S3: The prepared positive electrode sheet, negative electrode sheet and ion separator (16 μm thick PE ceramic separator) are wound to prepare a bare battery cell. Then, the bare battery cell and the shell and the lithium-ion battery electrolyte prepared in Examples 1 to 17 and Comparative Examples 1 and 2 are assembled into a battery.

[0140] The test of the battery's electrical parameters and the corresponding calculation formulas are as follows:

[0141] Battery capacity retention test after 300 cycles at 25°C: Place the lithium-ion battery at room temperature, then perform 300 charge and discharge cycles on the lithium-ion battery at 0.33C current. The test voltage window is 3.0~4.9V, and the discharge retention capacity at the 300th cycle is recorded.

[0142] Battery capacity retention test after 300 cycles at 45°C: Place the lithium-ion battery in a 45°C constant temperature box for 4 hours, then perform 300 charge and discharge cycles on the lithium-ion battery at a current of 0.33C. The test voltage window is 3.0~4.9V, and the discharge retention capacity at the 300th cycle is recorded.

[0143] Battery storage thickness expansion rate, capacity retention and capacity recovery test at 60°C for 7 days: Test and record the initial thickness and 0.33C discharge initial capacity of the lithium-ion battery; then charge the battery to 4.9V at a constant current and constant voltage at 0.33C, place it in a 60°C explosion-proof oven, and test the battery thermal thickness after storage for 7 days in the oven. Then, take out the battery and cool it to room temperature, and test its discharge retention capacity and recovery capacity at 0.33C discharge to 3.0V.

[0144] The calculation formula is as follows:

[0145] 300-cycle capacity retention rate (%) = (300th discharge retention capacity / 1st cycle discharge capacity) × 100%;

[0146] Storage capacity retention rate (%) = retention capacity / initial capacity × 100%;

[0147] Capacity recovery rate (%) = recovery capacity / initial capacity × 100%;

[0148] Thickness expansion ratio (%) = (thermal thickness - initial thickness) / initial thickness × 100%.

[0149] Table 2 Electrical performance test results

[0150]

[0151] Referring to Table 2, it can be seen from the test results of Example 1, Examples 7 to 9, Examples 11 to 14, and Comparative Example 1 that the use of the pyridinium salt provided in the examples of the present application as a lithium salt additive has better cycle performance at high voltage than the use of conventional lithium salt additives.

[0152] From the test results of Examples 1-2 and Examples 3-4, it can be seen that limiting the amount of pyridinium salt to the preferred range (i.e., 0.1-5%), compared with not being within the preferred range, the lithium-ion battery corresponding to the former has better cycle performance at high voltage.

[0153] The test results of Examples 1-2 and 5-6 show that limiting the amount of pyridinium salt to a more preferred range (i.e., 0.5-2%) results in a lithium-ion battery having better cycle performance at high voltage compared to batteries not within the more preferred range.

[0154] From the test results of Examples 1, 7 to 8, and 11 to 14, it can be seen that when the amount of pyridinium salt added is constant, the addition of a pyridyl borate or a pyridyl phosphate provided in the embodiments of the present application, the corresponding lithium ion battery has a relatively close cycle performance at high voltage, but the former corresponds to a lithium ion battery with better cycle performance at room temperature (due to the stronger reducing property of the boron element, it is easier to reduce to form a film at room temperature), while the latter corresponds to a lithium ion battery with better cycle performance at high temperature (due to the large radius of the phosphorus atom and the strong bond energy, the organic SEI film compound formed is more stable at high temperature).

[0155] It can be seen from the test results of Examples 5 and 10 that when the amount of pyridinium salt added is constant, adding one or more pyridinyl borates provided in the embodiments of the present application, the corresponding lithium-ion batteries have good cycle performance at high voltage and the cycle performance is close.

[0156] It can be seen from the test results of Examples 5 and 15 that when the amount of pyridinium salt added is constant, when the pyridyl borate and pyridyl phosphate provided in the embodiments of the present application are used together, compared with using only one of them as a lithium salt additive, due to the complementary effect between the two, the corresponding lithium-ion battery has better cycle performance at high voltage.

[0157] From the test results of Example 15 and Example 16, it can be seen that when pyridyl borate and pyridyl phosphate are used together, the amount of pyridyl phosphate used is larger, and the corresponding lithium-ion battery has better cycle performance at high temperature.

[0158] It can be seen from the test results of Example 1 and Example 17 that the lithium ion battery using the lithium salt provided in the examples of the present application has better cycle performance at high voltage compared to the conventional lithium salt.

[0159] It can be seen from the test results of Example 1 and Example 17 that the lithium ion battery using the lithium salt provided in the examples of the present application has better cycle performance at high voltage compared to the conventional lithium salt.

[0160] It can be seen from the test results of Examples 1, 7 to 9, 11 to 14 and Comparative Examples 2 and 3 that the lithium-ion battery corresponding to the pyridinium salt with a specific structure provided in the embodiments of the present application has better cycle performance at high voltage than the lithium-ion battery corresponding to the pyridinium salt with a conventional structure.

[0161] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A lithium ion battery electrolyte, characterized in that The method comprises a fluorinated organic solvent, a lithium salt and a lithium salt additive, wherein the lithium salt additive has a pyridyl salt of the general structural formula shown in Formula I and / or Formula II, and the pyridyl salt comprises lithium pyridyl borate and / or lithium pyridyl phosphate: Formula I Formula II wherein R1 to R3 are independently selected from one of hydrogen, fluorine-substituted C1 to C6 chain alkyl, C2 to C6 olefin, C2 to C6 alkynyl, C6 to C12 cyclic olefin, and C1 to C5 nitrile; The lithium salt additive includes the lithium pyridyl borate and the lithium pyridyl phosphate; The mass percentage of the lithium salt additive in the lithium ion battery electrolyte is 0.1-5%.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium salt additive includes one or more of the following compound structures: Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 Compound 7 Compound 8.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that In the lithium-ion battery electrolyte, the mass ratio of the lithium pyridyl borate to the lithium pyridyl phosphate is 1:(1-2).

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The mass percentage of the lithium salt additive in the lithium ion battery electrolyte is 0.5-2%.

5. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The mass percentage of the lithium salt in the lithium-ion battery electrolyte is 12-15%.

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

7. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The fluorinated organic solvent includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluoropropylene carbonate, fluoroethyl methyl carbonate, fluorodimethyl carbonate, fluorodiethyl carbonate, fluoroethyl acetate, fluoropropyl acetate, fluoroethyl propionate and fluoropropyl propionate.

8. A lithium-ion battery, characterized in that: include: case; an electrode assembly, the electrode assembly being accommodated in the housing; as well as The lithium-ion battery electrolyte according to any one of claims 1 to 7, wherein the lithium-ion battery electrolyte is contained in the housing.

9. The lithium-ion battery according to claim 8, characterized in that The electrode assembly satisfies the following conditions (a) and / or (b); (a) In the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate, a transition metal oxide lithium salt, and a transition metal sulfide; (b) In the battery negative electrode of the electrode assembly, the negative electrode active material includes at least one of graphite, soft carbon, hard carbon, silicon, silicon oxide, and silicon-carbon composite.

10. The lithium-ion battery according to claim 9, characterized in that The positive electrode active material includes lithium nickel manganese oxide having a spinel structure.

11. An electrical device, characterized in that: The electrical device comprises a lithium-ion battery according to any one of claims 8 to 10.

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