Lithium ion battery electrolyte, lithium ion battery and electrical equipment

Abstract

The present application provides a lithium ion battery electrolyte, a lithium ion battery and an electrical device, belonging to the field of lithium ion battery manufacturing technology. The lithium ion battery electrolyte includes an organic solvent, a lithium salt and an additive, the additive including tetrakis (2-methyl-8-hydroxyquinoline) boron lithium and an additive S, the structural formula of the additive S is as shown in Formula I, wherein R1 and R2 in Formula I are independently selected from any one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group and a substituted silane group, and the electrolyte can improve the serious gas production problem of the corresponding lithium ion battery when applied under high voltage and high temperature conditions, so that the battery has relatively excellent cycle performance; at the same time, it can also reduce the charge transfer impedance of the corresponding battery at the interface, reduce the active lithium ion consumption in the formation stage, so that the battery has a higher first efficiency.

Description

Technical Field

[0001] The present application relates to the technical 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] Lithium-ion batteries are currently used as power batteries in new energy vehicles due to their environmentally friendly, high energy density, and long cycle life. Due to the high energy consumption, long driving range, and high and low-temperature operation requirements of new energy vehicles, high-voltage ternary and lithium nickel manganese oxide (LiMnO) cathode materials have become a hot topic in the development of new power batteries. However, when charging and discharging at high voltages (≥4.5V) and high temperatures (≥45°C), the organic solvents in existing commercial electrolytes are easily oxidized and decomposed at the cathode interface, generating large amounts of gas. This leads to a loss of active lithium ions at the cathode and a sharp decrease in the battery's cycle life. To suppress gassing during high-voltage and high-temperature operation, additives such as 1,3-propene sultone (PST) and maleic anhydride are currently used to improve battery performance. However, these additives are ineffective in improving high-temperature battery performance at high voltages above 4.5V, resulting in significant gassing issues when operating at high voltages and high temperatures. Furthermore, the interfacial film formed by these additives exhibits high impedance, which also affects the battery's initial efficiency. Summary of the Invention

[0003] The purpose of the present application is to provide a lithium-ion battery electrolyte, a lithium-ion battery and an electrical device, which can improve the serious gas production problem of the corresponding lithium-ion battery when used under high voltage and high temperature conditions, so that the battery has relatively excellent cycle performance; at the same time, it can also reduce the charge transfer impedance of the corresponding battery at the interface and reduce the consumption of active lithium ions in the formation stage, so that the battery has a higher initial efficiency.

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

[0005] In a first aspect, an embodiment of the present application provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises lithium tetrakis(2-methyl-8-hydroxyquinoline)borate and an additive S, wherein the structural formula of the additive S is as shown in Formula I:

[0006]

[0007] Wherein, R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group and a substituted silyl group.

[0008] In the above technical solution, the lithium-ion battery electrolyte contains the above-mentioned specific combination of additive components. On the one hand, the carboxylic anhydride in the above-mentioned specific structural additive S can form an interface film with good thermal stability on the surface of both the positive and negative electrodes, thereby effectively alleviating the problem of violent decomposition and gas production at the positive and negative electrode interfaces when the electrolyte is used under high voltage and high temperature conditions (helping to improve the battery's cycle performance); at the same time, the bipyridine ring in the structure has a weak alkaline property and can neutralize the hydrofluoric acid produced by the decomposition of the electrolyte, thereby further alleviating the problem of poor battery performance caused by gas production (also helping to improve the battery's cycle performance). Moreover, the bipyridine ring can also complex some metal ions dissolved from the positive electrode (such as manganese ions), thereby improving the problem of battery capacity decay caused by the deposition of dissolved metal ions at the negative electrode. On the other hand, tetrakis(2-methyl-8-hydroxyquinoline) boron lithium can also decompose at the positive electrode to form an interface film rich in boron oxide and alkyl lithium, which can synergistically decompose with the additive S to form an organic polymer-inorganic lithium salt composite interface film on the positive electrode surface, thereby further improving the thermal stability of the interface film formed by the battery at the positive electrode interface; at the same time, the formed organic polymer-inorganic lithium salt composite interface film can also reduce the charge transfer impedance of the battery at the positive electrode interface, reduce the active lithium ion consumption in the formation stage, and thus improve the first efficiency of the battery. In the embodiment of the present application, by using two additives with specific structures in combination, the problem of serious gas production when the corresponding lithium ion battery is used under high voltage and high temperature conditions can be improved, so that the battery has relatively excellent cycle performance; at the same time, it can also make the battery have a higher first efficiency.

[0009] In some optional embodiments, R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a propyl group, a trifluoromethyl group and trimethylsilane.

[0010] In the above technical solution, the structural selection of the additive S is further limited to a specific range, which helps to further improve the cycle performance and initial efficiency of the battery corresponding to the electrolyte when used at high voltage and high temperature.

[0011] In some optional embodiments, the mass percentage of the additive in the electrolyte is 0.2-3%.

[0012] In the above technical solution, the total amount of the additive is limited to a specific range, so that the battery corresponding to the electrolyte has relatively excellent cycle performance and first efficiency when used at high voltage.

[0013] In some optional embodiments, the electrolyte further includes an auxiliary additive, the auxiliary additive including at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

[0014] In the above technical solution, adding specific types of auxiliary additives to the electrolyte can give the electrolyte more functions, thereby more comprehensively improving the comprehensive electrical performance of the corresponding battery (such as safety performance and cycle performance, etc.).

[0015] In some optional embodiments, the mass percentage of the auxiliary additive in the electrolyte is 0.5-5%.

[0016] In the above technical solution, the amount of the auxiliary additive is limited to a specific range, so that the auxiliary additive has an appropriate amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0017] In some optional embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bisfluorosulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisoxalatoborate.

[0018] Optionally, the mass percentage of lithium salt in the electrolyte is 10-20%.

[0019] Among the above technical solutions, the technical solutions provided in the embodiments of the present application are applicable to a wide variety of lithium salts and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solutions provided in the present application.

[0020] Furthermore, limiting the amount of lithium salt to the above range can ensure that the lithium salt has an appropriate amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0021] In some optional embodiments, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0022] Among the above technical solutions, the technical solutions provided in the embodiments of the present application are applicable to a wide variety of organic solvents and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solutions provided in the present application.

[0023] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and the electrolyte provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; and the electrolyte is housed in the housing.

[0024] In the above technical solution, the lithium-ion battery includes the electrolyte provided in the embodiment of the first aspect. By taking advantage of the unique advantages of the electrolyte, the lithium-ion battery has relatively excellent cycle performance and higher initial efficiency when used under high voltage and high temperature conditions.

[0025] In some optional embodiments, in the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate and a transition metal oxide lithium salt.

[0026] Optionally, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

[0027] Among the above technical solutions, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple positive electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0028] In addition, the use of the above-mentioned specific type of positive electrode active material has the advantage of being more resistant to high voltage and high temperature compared to the use of other types of positive electrode active materials.

[0029] In some optional embodiments, 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.

[0030] Among the above technical solutions, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple negative electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0031] 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

[0032] 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.

[0033] 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”.

[0034] 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".

[0035] In the existing technology, high-voltage-resistant electrolyte additives usually use some organic substances, such as 1,3-propylene sultone or maleic anhydride. However, these additives are not effective in inhibiting gas production when used under high voltage and high temperature conditions, resulting in poor battery cycle performance. In addition, the interfacial film formed by these additives also has the problem of large interfacial impedance, resulting in poor initial efficiency of the battery.

[0036] The inventors have discovered that by using a composite system of an additive S containing a bipyridine ring and a specific anhydride skeleton and lithium tetrakis(2-methyl-8-hydroxyquinoline)borate as an additive, the problem of severe gas production when the corresponding lithium-ion battery is used under high voltage and high temperature conditions can be improved, so that the battery has relatively excellent cycle performance; at the same time, it can also make the battery have a higher initial efficiency.

[0037] The following is a detailed description of a lithium-ion battery electrolyte, a lithium-ion battery, and an electrical device according to an embodiment of the present application.

[0038] In a first aspect, an embodiment of the present application provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt, and an additive, wherein the additive comprises lithium tetrakis(2-methyl-8-hydroxyquinoline)borate and an additive S, wherein the structural formula of the additive S is as shown in Formula I:

[0039]

[0040] Wherein, R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group and a substituted silyl group.

[0041] In the present application, the lithium-ion battery electrolyte contains the above-mentioned specific combination of additive components. On the one hand, the carboxylic anhydride in the above-mentioned specific structural additive S can form an interface film with good thermal stability on the surface of both the positive and negative electrodes, thereby effectively alleviating the problem of violent decomposition and gas production at the positive and negative electrode interfaces when the electrolyte is used under high voltage and high temperature conditions (helping to improve the battery's cycle performance); at the same time, the bipyridine ring in the structure has a weak alkaline property and can neutralize the hydrofluoric acid produced by the decomposition of the electrolyte, thereby further alleviating the problem of poor battery performance caused by gas production (also helping to improve the battery's cycle performance), and the bipyridine ring can also complex some metal ions dissolved from the positive electrode (such as manganese ions), thereby improving the problem of battery capacity decay caused by the deposition of dissolved metal ions at the negative electrode. On the other hand, tetrakis(2-methyl-8-hydroxyquinoline) boron lithium can also decompose at the positive electrode to form an interface film rich in boron oxide and alkyl lithium, which can synergistically decompose with the additive S to form an organic polymer-inorganic lithium salt composite interface film on the positive electrode surface, thereby further improving the thermal stability of the interface film formed by the battery at the positive electrode interface; at the same time, the formed organic polymer-inorganic lithium salt composite interface film can also reduce the charge transfer impedance of the battery at the positive electrode interface, reduce the active lithium ion consumption in the formation stage, and thus improve the first efficiency of the battery. In the embodiment of the present application, by using two additives with specific structures in combination, the problem of serious gas production when the corresponding lithium ion battery is used under high voltage and high temperature conditions can be improved, so that the battery has relatively excellent cycle performance; at the same time, it can also make the battery have a higher first efficiency.

[0042] It should be noted that since there are many components in the electrolyte and the physical and chemical properties of each component are different, it is necessary to focus on whether the components are compatible with each other when selecting additives, that is, whether they will affect other components in the process of exerting their effects. This is one of the main reasons why there are many compounds with the same functional groups but few systems that can be used as composite additives. This is also a major difficulty in designing composite additive systems in this field.

[0043] As an example, R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a propyl group, a trifluoromethyl group and trimethylsilane.

[0044] In this embodiment, the structure of the additive S is further limited to a specific range, which helps to further improve the cycle performance and initial efficiency of the battery corresponding to the electrolyte when used at high voltage and high temperature.

[0045] In order to better understand the technical solution, some specific compound structures of the additive S are used as examples below.

[0046]

[0047]

[0048]

[0049] It should be noted that the effectiveness of additives is closely related to their dosage. Specifically, if the dosage is too low, the performance of the corresponding battery will not be effectively improved; if the dosage is too high, the interface film will be too thick, which will also affect the performance of the corresponding battery. Based on this, considering the ultimate performance of the corresponding battery, the dosage of the additive can be limited.

[0050] As an example, the mass percentage of the additive in the electrolyte is 0.2-3%, for example, but not limited to, any one of 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5% and 3% by mass, or a range between any two of them.

[0051] In this embodiment, the amount of the additive is limited to a specific range, so that the battery corresponding to the electrolyte has relatively excellent cycle performance and first efficiency when used at a high voltage.

[0052] As an example, the electrolyte further includes auxiliary additives, which include at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

[0053] In this embodiment, adding a specific type of auxiliary additive to the electrolyte can give the electrolyte more functions, thereby more comprehensively improving the comprehensive electrical performance of the corresponding battery (such as safety performance and cycle performance, etc.).

[0054] As an example, the mass percentage of the auxiliary additive in the electrolyte is 0.5-5%, for example, but not limited to, any one of 0.5%, 1%, 2%, 3%, 4% and 5% by mass, or a range between any two of them.

[0055] In this embodiment, the amount of the auxiliary additive is limited to a specific range, so that the auxiliary additive has a suitable amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0056] As an example, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bisfluorosulfonyl imide, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisoxalatoborate.

[0057] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to a wide variety of lithium salts and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the present application.

[0058] As an example, the mass percentage of lithium salt in the electrolyte is 10-20%, for example, but not limited to, any one of 10%, 12%, 14%, 16%, 18% and 20% by mass, or a range between any two of them.

[0059] In this embodiment, the amount of lithium salt is further limited to the above range, so that the lithium salt has an appropriate amount, thereby better improving the comprehensive electrical performance of the corresponding battery.

[0060] As an example, the organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0061] In this embodiment, the technical solution provided in the embodiment of the present application is applicable to a wide variety of organic solvents and can provide a wide variety of feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the present application.

[0062] It should be noted that the components and amounts in the electrolyte that are not specifically described or limited can be set according to conventional selection in the art.

[0063] In a second aspect, an embodiment of the present application provides a lithium-ion battery comprising a housing, an electrode assembly, and the electrolyte provided in the embodiment of the first aspect. The electrode assembly is housed in the housing; and the electrolyte is housed in the housing.

[0064] In the present application, the lithium-ion battery includes the electrolyte provided in the embodiment of the first aspect. By taking advantage of the unique advantages of the electrolyte, the lithium-ion battery has relatively excellent cycle performance and higher initial efficiency when used under high voltage and high temperature conditions.

[0065] As an example, in the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate and a transition metal oxide lithium salt.

[0066] In this embodiment, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple positive electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0067] As an example, the positive electrode active material includes at least one of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

[0068] In this embodiment, the use of the above-mentioned specific type of positive electrode active material has the advantage of being more resistant to high voltage and high temperature compared to the use of other types of positive electrode active materials.

[0069] As an example, 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.

[0070] In this embodiment, the technical solution provided in the embodiment of the present application can be applied to the above-mentioned multiple negative electrode active material systems, providing more feasible implementation plans, thereby facilitating the promotion and application of the technical solution provided in the embodiment of the present application.

[0071] It should be noted that any structure not specifically described in the battery may be configured according to conventional options in the art.

[0072] 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.

[0073] It should be noted that there is no limitation on the types of electrical equipment, such as mobile phones, portable devices, laptops, electric vehicles, electric cars, ships, electric aircraft, spacecraft, electric toys, energy storage devices and power tools.

[0074] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0075] Example 1

[0076] The present invention provides a method for preparing an electrolyte, comprising the following steps:

[0077] Ethylene carbonate (EC), diethyl carbonate (DEC) and methyl trifluoroethyl carbonate (FEMC) are mixed in a mass ratio of 3:4:3 to obtain a mixed organic solvent; then, lithium hexafluorophosphate (LiPF6), lithium tetrakis(2-methyl-8-hydroxyquinoline) boron 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: lithium tetrakis(2-methyl-8-hydroxyquinoline) boron: compound 1 = 89.8:10:0.1:0.1.

[0078] The preparation methods of the subsequent embodiments and comparative examples can all refer to Example 1. In order to better understand the differences between the various embodiments and comparative examples, they are summarized in Table 1 below.

[0079] Table 1

[0080]

[0081]

[0082]

[0083] Here, “—” indicates that the component is not contained, and the amount of the organic solvent is equal to 100 minus the remainder of the sum of the amounts of the other components.

[0084] Test Example 1

[0085] Electrical performance test

[0086] Test method:

[0087] The lithium-ion battery electrolytes prepared in Examples 1 to 13 and Comparative Examples 1 to 4 were assembled into batteries and numbered accordingly. Then, the batteries were tested for their initial efficiency at 25°C, capacity retention after 100 cycles at 25°C, capacity retention after 100 cycles at 45°C, and expansion rate after 15 days of storage at 45°C, and the data are summarized in Table 2.

[0088] The battery is assembled as follows:

[0089] S1 is mixed with LiNi in a mass ratio of 96:2:2 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.

[0090] 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 125μm.

[0091] S3: The prepared positive electrode sheet, negative electrode sheet and ion separator (PP / PE / PP three-layer composite separator) are wound to prepare a bare battery cell. Then, the bare battery cell and the shell, as well as the high-voltage electrolyte group prepared in Examples 1 to 13 and Comparative Examples 1 to 4, are injected into the dried battery. After packaging, standing, formation, shaping and capacity testing, the battery is assembled.

[0092] The test of the battery's electrical parameters and the corresponding calculation formulas are as follows:

[0093] (1) First efficiency test of battery:

[0094] Place the battery that has not been charged and activated after filling with liquid at 25℃, charge and discharge the battery once with a current of 0.1C in the charge and discharge voltage range of 3.5~4.85V, and record its charge and discharge capacity.

[0095] (2) Battery capacity retention test after 100 cycles at 25°C:

[0096] The battery was placed at 25°C and cycled at a current of 0.5C in the charge and discharge voltage range of 3.5 to 4.85V, and the discharge retention capacity at the 100th cycle was recorded.

[0097] (3) Battery capacity retention test after 100 cycles at 45°C:

[0098] The battery was placed at 45°C and cycled at a current of 0.5C in the charge and discharge voltage range of 3.5 to 4.85V, and the discharge retention capacity at the 100th cycle was recorded.

[0099] (4) Battery expansion rate test after 15 days of storage at 45°C:

[0100] The battery was charged and discharged three times at room temperature (25°C) with a current of 0.33C in the charge and discharge voltage range of 3.5-4.85V, and then fully charged with 0.33C. The thickness of the battery was tested at room temperature (25°C) before high-temperature storage. The battery was then placed at high temperature (45°C) for 15 days, then taken out and placed at room temperature (25°C) for 2 hours, and the thickness of the battery after high-temperature storage was tested.

[0101] The calculation formula is as follows:

[0102] First efficiency (%) = (first discharge capacity / first charge capacity) × 100%.

[0103] 100-cycle capacity retention rate (%) = (100th discharge retention capacity / 1st cycle discharge capacity) × 100%.

[0104] Expansion rate after storage at 45° C. for 15 days (%) = (battery thickness after high-temperature storage − battery thickness before high-temperature storage) / battery thickness before high-temperature storage × 100%.

[0105] Table 2

[0106]

[0107] Referring to Table 2, it can be seen from the test results of Examples 1 to 13 and Comparative Example 1 that the composite additives provided in the embodiments of the present application, compared with conventional additives, can provide batteries with better initial efficiency and cycle performance when used under high voltage and high temperature conditions.

[0108] It can be seen from the test results of Example 5 and Example 6 that when the upper limit of the total amount of additives is within a specific range, the battery corresponding to the former can have better initial efficiency and cycle performance when used under high voltage and high temperature conditions, compared with when it is not within the specific range.

[0109] It can be seen from the test results of Examples 7 and 12 to 13 that, on the basis of the electrolyte containing the composite additives provided in the embodiments of the present application, further adding the auxiliary additives provided in the embodiments of the present application can enable the corresponding battery to have better initial efficiency and cycle performance when used under high voltage and high temperature conditions.

[0110] It can be seen from the test results of Example 4 and Comparative Examples 2 to 3 that when the composite additives provided in the embodiments of the present application are used, compared with using only one of them, the battery corresponding to the former can have both better initial efficiency and cycle performance when used under high voltage and high temperature conditions.

[0111] It can be seen from the test results of Example 3 and Comparative Example 4 that when the composite additive provided in the embodiment of the present application is used, compared with replacing additive S with other conventional additives, the battery corresponding to the former can have both better initial efficiency and cycle performance when used under high voltage and high temperature conditions.

[0112] 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 an organic solvent, a lithium salt and an additive, wherein the additive comprises lithium tetrakis(2-methyl-8-hydroxyquinoline)borate and an additive S, and the structural formula of the additive S is as shown in Formula I: Formula I Wherein, R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a substituted or unsubstituted C1-C3 alkyl group and a substituted silyl group; The mass percentage of the additive in the electrolyte is 0.2-3%.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The R1 and R2 are independently selected from any one of a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a propyl group, a trifluoromethyl group and trimethylsilane.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that The electrolyte further includes an auxiliary additive, which includes at least one of vinyl sulfate, vinyl ethylene carbonate, 1,3-propane sultone, methylene disulfonate, 2-fluoropyridine, allyl isocyanate, triallyl isocyanurate, 2(5H)-furanone, tris(trimethylsilyl)phosphite and tripropylene phosphate.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that The mass percentage of the auxiliary additive in the electrolyte is 0.5-5%.

5. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium difluorobis(oxalatophosphate), lithium tetrafluorooxalatophosphate, lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(oxalatoborate).

6. The lithium-ion battery electrolyte according to claim 5, characterized in that The mass percentage of the lithium salt in the electrolyte is 10-20%.

7. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that The organic solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, 3,3,3-trifluoropropylene carbonate, methyl trifluoroethyl carbonate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

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 electrolyte according to any one of claims 1 to 7, wherein the electrolyte is contained in the housing.

9. The lithium-ion battery according to claim 8, characterized in that In the battery positive electrode of the electrode assembly, the positive electrode active material includes at least one of a transition metal phosphate and a transition metal oxide lithium salt.

10. The lithium-ion battery according to claim 9, characterized in that The positive electrode active material includes at least one of lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, and lithium cobalt oxide.

11. The lithium-ion battery according to claim 8, wherein 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.

12. An electrical device, characterized in that: The invention comprises a lithium ion battery as claimed in any one of claims 8 to 11.

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