Electrolyte and battery

Abstract

The embodiment of the present application provides an electrolyte and a battery, the electrolyte comprises an additive, the additive comprises a first additive and a second additive, the first additive comprises a compound shown in formula (1), and the second additive comprises a compound shown in formula (2). The first additive can form a cathode electrolyte interface film (CEI film) and a solid electrolyte interface film (SEI film) containing an N-phenyl skeleton and Li2S2O4, Li2SO3 and the like, and the first additive participates in the repair of the film in the cycle process, thereby improving the cycle performance of the battery. The second additive is more prone to oxidizing and decomposing into a film on the positive electrode side in the high-voltage cycle process, thereby repairing and protecting the CEI film formed by the first additive in the formation stage, enhancing the stability of the whole CEI film, and synergistically promoting the formation of a more stable interface film, inhibiting the decomposition of the electrolyte, and improving the fast-charging cycle performance of the battery.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and in particular relates to an electrolyte and a battery. Background Art

[0002] In recent years, with the rapid development and widespread application of various portable electronic devices, new energy electric vehicles and energy storage systems, in order to meet the market demand for high-capacity batteries, current battery systems will increase battery capacity by increasing the upper cut-off voltage.

[0003] However, in the related art, during the battery charging and discharging process, physical or chemical changes that are detrimental to the battery performance may occur inside the battery, further deteriorating the battery's cycle performance, which needs to be further improved. Summary of the Invention

[0004] The embodiments of the present application provide an electrolyte and a battery, which aim to solve the aforementioned technical problems at least to a certain extent.

[0005] In a first aspect, an embodiment of the present application provides an electrolyte, comprising an additive, wherein the additive comprises a first additive and a second additive, wherein the first additive comprises a compound represented by formula (1), and the second additive comprises a compound represented by formula (2).

[0006] Formula (1),

[0007] Formula (2),

[0008] Wherein, in formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl ring group, a sulfonyl group, and derivatives thereof, and at least one of R7 and R9 is a phenyl ring group; R8 is selected from H, halogen, or a C1-C3 substituted or unsubstituted alkyl group;

[0009] In formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, halogen, C1-C3 substituted or unsubstituted alkyl, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy.

[0010] In one embodiment, in formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl group, a sulfonyl group, a sulfonyl chloride group, and a sulfonyl fluoride group, and at least one of R7 and R9 is a phenyl group, and / or R8 is selected from H, F, Cl, or an unsubstituted alkyl group of C3; and / or

[0011] In formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, F, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy group.

[0012] In one embodiment, the first additive includes at least one of the following compounds:

[0013] 、 、 、 、 、 、 、 .

[0014] In one embodiment, the second additive includes at least one of the following compounds:

[0015] 、 、 、 、 、 .

[0016] In one embodiment, the mass ratio of the first additive to the second additive is 0.005-500; and / or

[0017] The mass percentage of the first additive in the electrolyte is 0.05%-5%; and / or

[0018] The mass percentage of the second additive in the electrolyte is 0.01%-10%.

[0019] In one embodiment, the mass ratio of the first additive to the second additive is 0.1-30; and / or

[0020] The mass percentage of the first additive in the electrolyte is 0.5%-3%; and / or

[0021] The mass percentage of the second additive in the electrolyte is 0.1%-5%.

[0022] In one embodiment, the electrolyte further includes a solvent and / or an electrolyte salt.

[0023] In one embodiment, the mass percentage of the electrolyte salt in the electrolyte is 10%-18%; and / or

[0024] The electrolyte salt includes a lithium salt and / or a sodium salt.

[0025] In an embodiment, the lithium salt comprises at least one of LiPF6, LiFSI, LiTFSI, LiB(C2O4)2, LiBF2C2O4, LiPO2F2, LiPF2(C2O4)2; and / or

[0026] The sodium salt comprises at least one of NaPF6, NaAsF6, NaFSI, NaClO4, NaB(C2O4)2, NaBF2C2O4, NaN(SO2F)2, NaN(SO2CF3)2, NaPO2F2, NaPF2(C2O4)2, NaPF4C2O4.

[0027] In an embodiment, the solvent comprises at least one of carbonate solvents, carboxylate solvents, ether solvents.

[0028] In an embodiment, the solvent comprises at least one of vinyl carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and 2,2-difluoroethyl methyl carbonate.

[0029] In a second aspect, embodiments of the present application also provide a battery comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte as described above.

[0030] In an embodiment, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer comprising a positive electrode active material coated on at least one surface of the positive electrode current collector, the positive electrode active material being selected from lithium cobaltate, and the battery has a charge cut-off voltage ≥ 4.4 V.

[0031] Advantages of embodiments of the present application:

[0032] The electrolyte provided by the embodiment of the present application comprises an additive, the additive comprises a first additive and a second additive, the first additive comprises a compound shown in formula (1), and the second additive comprises a compound shown in formula (2). In the first aspect, the first additive has an N-SO2 group, and the first additive has a lower unoccupied molecular orbital (LUMO) energy level and a higher occupied molecular orbital (HOMO) energy level, so that the first additive preferentially undergoes a reduction reaction at a low voltage compared with a solvent, and therefore, in the formation stage of a battery having the electrolyte, the first additive can form a cathode electrolyte interface film (CEI film) and a solid electrolyte interface film (SEI film) containing components such as an N-phenyl skeleton, Li2S2O4 and Li2SO3, the CEI film and the SEI film have high electron conductivity and low impedance, and the first additive participates in the repair of the film during the cycle process, thereby improving the cycle performance of the battery. In the second aspect, the second additive can increase the wettability of the electrolyte, thereby helping to improve the uniformity of the formation of the SEI film, and meanwhile, in the actual battery cycle process, the second additive is more likely to be oxidized and decomposed into a film on the positive electrode side during high-voltage cycle, thereby repairing and protecting the CEI film formed by the first additive in the formation stage, enhancing the stability of the whole CEI film, retaining the high electron conductivity of the CEI film, reducing the impedance of the film, and synergistically forming a more stable interface film, inhibiting the decomposition of the electrolyte, reducing the contact between the electrolyte and the electrode material, and improving the fast-charging cycle performance of the battery. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person skilled in the art without creative labor fall within the scope of protection of the present application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application, and are not used to limit the present application. In the present application, the positional words such as “upper” and “lower” generally refer to the upper and lower positions of the device in the actual use or working state, and “inner” and “outer” refer to the outline of the device.

[0034] In the related art, a battery cannot have good fast-charging cycle performance and safety performance under high working voltage conditions, and needs to be further improved.

[0035] The electrolyte provided by the embodiment of the present application comprises an additive, the additive comprises a first additive and a second additive, the first additive comprises a compound shown in formula (1), and the second additive comprises a compound shown in formula (2),

[0036] Formula (1),

[0037] Formula (2),

[0038] In formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl group, a sulfonyl group, and derivatives thereof, and at least one of R7 and R9 is a phenyl group; R8 is selected from H, halogen, or a C1-C3 substituted or unsubstituted alkyl group;

[0039] In formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, halogen, C1-C3 substituted or unsubstituted alkyl, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy.

[0040] In this embodiment, the first additive has an N-SO2 group and has a lower unoccupied molecular orbital (LUMO) energy level and a higher occupied molecular orbital (HOMO) energy level, thereby undergoing a reduction reaction at low voltage in preference to the solvent. Therefore, during the formation stage of a battery containing this electrolyte, the first additive can form a cathode electrolyte interface film (CEI film) and a solid electrolyte interface film (SEI film) containing components such as an N-phenyl skeleton, Li2S2O4, and Li2SO3. The CEI film and SEI film have high conductivity and low impedance, and the first additive participates in the repair of the film during the cycle process, thereby improving the cycle performance of the battery. However, when the battery is under high voltage conditions, the CEI film formed by the first additive is easily decomposed at high voltage and has poor stability, resulting in increased battery impedance, deterioration of cycle performance and rate performance, and violent reaction of lithium dendrites precipitated on the negative electrode surface with the electrolyte to release heat, causing thermal runaway of the battery.

[0041] The second additive can increase the wettability of the electrolyte, thereby helping to improve the uniformity of SEI film formation. At the same time, in the actual battery cycle process, the second additive is more likely to be oxidized and decomposed into a film on the positive electrode side during the high-voltage cycle process, thereby repairing and protecting the CEI film originally formed by the first additive in the formation stage. A layer of CEI film containing a lithium salt compound of N and P elements is formed on the CEI film formed by the first additive in the formation stage, reducing the decomposition of N-phenyl at higher voltages, which is beneficial to maintaining the toughness and structural stability of the CEI film. At the same time, the high-conductivity electronic properties of the CEI film are retained, and the membrane impedance is reduced. The two synergistically promote the formation of a more stable interface film, inhibit the decomposition of the electrolyte, reduce the contact between the electrolyte and the electrode material, and improve the fast charge cycle performance of the battery;

[0042] Therefore, the first additive and the second additive work synergistically, so that the battery has both good fast charge cycle performance and safety performance under high operating voltage conditions.

[0043] In one embodiment, in formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl group, a sulfonyl group, a sulfonyl chloride group, and a sulfonyl fluoride group, and at least one of R7 and R9 is a phenyl group, and / or R8 is selected from H, F, Cl, or an unsubstituted alkyl group of C3.

[0044] In one embodiment, in formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, F, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy group.

[0045] In one embodiment, the first additive includes at least one of the following compounds:

[0046] 、 、 、 、 、 、 、 .

[0047] In particular, the FS direct bond of the first additive having the structure of Formula (1-1), Formula (1-2), Formula (1-3), Formula (1-4), and Formula (1-5) has a larger bond energy and is more resistant to high temperature and oxidation than other structural analogs with FCS bond. At the same time, its decomposition products can form a more stable interface film with better ion conductivity, while the interface film formed by the latter is mainly composed of organic products and has a higher SEI impedance.

[0048] In one embodiment, the second additive includes at least one of the following compounds:

[0049] 、 、 、 、 、 .

[0050] In one embodiment, the mass ratio of the first additive to the second additive is 0.005-500, preferably, the mass ratio of the first additive to the second additive is 0.1-30. Optionally, the mass ratio of the first additive to the second additive can be any one of 0.005, 0.1, 15, 30, 100, 250, 500, etc. or a range between any two, which is not limited here. In this embodiment, when the mass ratio of the first additive to the second additive is less than 0.005, it is easy to cause the CEI film formed by the first additive to be uneven, the protection of the CEI film to the positive electrode interface is not ideal, the electrolyte is prone to oxidative decomposition, and the battery performance is reduced; when the mass ratio of the first additive to the second additive is greater than 500, it is easy to cause the CEI film formed by the first additive to be too thick, and the transmission resistance of ions when deintercalating at the outer CEI film formed by the second additive is too large, thereby reducing the fast charging performance and cycle performance of the battery.

[0051] In one embodiment, the mass percentage of the first additive in the electrolyte is 0.05%-5%, preferably, the mass percentage of the first additive in the electrolyte is 0.5%-3%. Optionally, the mass percentage of the first additive in the electrolyte can be any one of 0.05%, 1.5%, 2%, 3%, 4%, 5%, etc. or a range between any two, which is not limited here. In this embodiment, when the mass percentage of the first additive in the electrolyte is less than 0.05%, the effect of the first additive in forming a complete SEI film and CEI film in the formation stage is irrational, and the electrolyte can still be in direct contact with the electrode interface. During the battery charge and discharge process, the parasitic side reactions and accumulated by-products occurring at the electrode interface lead to an increase in battery impedance, difficulty in deintercalation of conductive ions, and the appearance of dendrites at the negative electrode, degradation of battery cycle performance, and even thermal runaway. When the mass percentage of the first additive in the electrolyte is greater than 5%, the interface film formed by the first additive in the formation stage is too thick, which consumes active conductive ions excessively, resulting in increased battery impedance and restricted transmission dynamics of conductive ions, resulting in decreased battery cycle performance and increased safety risks.

[0052] In one embodiment, the mass percentage of the second additive in the electrolyte is 0.01%-10%, preferably 0.1%-5%. Optionally, the mass percentage of the second additive in the electrolyte can be any one of 0.01%, 0.1%, 2.5%, 5%, 7%, 10%, etc., or a range between any two of them, without limitation herein. In this embodiment, when the mass percentage of the second additive in the electrolyte is less than 0.01%, the flame retardant effect of the second additive is reduced. At the same time, the second additive has an unsatisfactory repair and protection effect on the CEI film originally formed by the first additive in the formation stage. When the mass percentage of the second additive in the electrolyte is greater than 10%, it is easy to cause a reduction in the content of conductive ions, thereby reducing the capacity performance of the battery. At the same time, when the mass percentage of the second additive in the electrolyte is too large, it is easy to cause the CEI film to be too thick, increase the impedance of the battery, affect the kinetic properties of lithium ions, and thus lead to a decrease in the battery cycle performance.

[0053] In one embodiment, the electrolyte further includes a solvent and / or an electrolyte salt.

[0054] In one embodiment, the mass percentage of the electrolyte salt in the electrolyte is 10%-18%. Alternatively, the mass percentage of the electrolyte salt in the electrolyte can be any one of 10%, 12%, 14%, 16%, 18%, or any range between two thereof, without limitation herein. In this embodiment, setting the mass percentage of the electrolyte salt in the electrolyte within the above range can result in the electrolyte having good ionic conductivity.

[0055] In one embodiment, the electrolyte salt includes a lithium salt and / or a sodium salt.

[0056] In one embodiment, the lithium salt includes at least one of LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bis(fluorosulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiB(C2O4)2 (lithium dioxalatoborate), LiBF2C2O4 (lithium difluorooxalatoborate), LiPO2F2 (lithium difluorophosphate), and LiPF2(C2O4)2 (lithium difluorobis(oxalatophosphate).

[0057] In one embodiment, the sodium salt includes at least one of NaPF6 (sodium hexafluorophosphate), NaAsF6 (sodium hexafluoroarsenate), NaFSI (sodium bis(fluorosulfonyl)imide), NaClO4 (sodium perchlorate), NaB(C2O4)2 (sodium dioxalatoborate), NaBF2C2O4 (sodium difluorooxalatoborate), NaPO2F2 (sodium difluorophosphate), NaPF2(C2O4)2 (sodium difluorobis(oxalatophosphate), and NaPF4C2O4 (sodium tetrafluorooxalatophosphate).

[0058] In one embodiment, the mass percentage of the solvent in the electrolyte is 60%-80%. Alternatively, the mass percentage of the solvent in the electrolyte can be any one of 60%, 65%, 70%, 75%, 80%, or any range between two thereof, without limitation herein. In this embodiment, setting the mass percentage of the solvent in the electrolyte within the above range can ensure that the electrolyte has an appropriate viscosity and promote sufficient dissolution of the lithium salt.

[0059] In one embodiment, the solvent includes at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent.

[0060] In one embodiment, the solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate and 2,2-difluoroethyl methyl carbonate.

[0061] The present application also provides a battery, comprising the electrolyte as described above. In this embodiment, the battery may comprise a lithium-ion battery or a sodium-ion battery, and the type of battery is not limited here.

[0062] An embodiment of the present application further provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the electrolyte as described above.

[0063] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector and containing a positive electrode active material, the positive electrode active material is selected from lithium cobalt oxide, and the charging cut-off voltage of the battery is ≥4.4V.

[0064] The present application also provides an electrical device, including the electrolyte described above, or including the battery described above. In this embodiment, the type of the electrical device is not limited, and the electrical device can be a car, a ship, an unmanned aerial vehicle, a fixed power source, a portable power source, etc.

[0065] The above scheme is further described below with reference to specific implementation examples. The embodiments of this application are described in detail as follows:

[0066] Example 1

[0067] 1. Preparation of electrolyte

[0068] In an argon atmosphere glove box (water content <1 ppm, oxygen content <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 15:20:15:50 to obtain a solvent, and lithium hexafluorophosphate (LiPF6), a first additive, and a second additive were added to the solvent, dissolved, and mixed uniformly to obtain an electrolyte; wherein:

[0069] The mass percentage of lithium hexafluorophosphate (LiPF6) in the electrolyte is 13.5%;

[0070] The first additive is a compound represented by formula (1-1), and the mass percentage of the first additive in the electrolyte is 1.5%;

[0071] The second additive is a compound represented by formula (2-1), and the mass percentage of the second additive in the electrolyte is 2.5%;

[0072] The rest is solvent.

[0073] 2. Preparation of positive electrode sheet

[0074] The positive electrode active material LiCoO2, the binder polyvinylidene fluoride PVDF, the conductive carbon black, and the conductive carbon nanotubes were mixed evenly in a weight ratio of 95:2.3:2:0.7, and N-methylpyrrolidone NMP was added and stirred under the action of a vacuum mixer until the mixed system became a positive electrode slurry with uniform fluidity; the positive electrode slurry was evenly coated on the positive electrode current collector aluminum foil with a coating amount of 35g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0075] 3. Preparation of negative electrode sheet

[0076] The negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber were mixed in a weight ratio of 95:1.5:1:2.5, and deionized water was added to obtain the negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil with a coating amount of 20g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0077] 4. Isolation film

[0078] A polyethylene isolation film with a thickness of 8 μm was selected.

[0079] 5. Preparation of LiCoO2 lithium-ion batteries

[0080] 1) The positive and negative electrode sheets, along with the separator, prepared according to the above process were wound into a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery was vacuum-baked at 75°C for 10 hours and then injected with the previously prepared electrolyte. After standing at 45°C for 12 hours, the battery was placed in a formation cabinet and charged at 0.1C (220 mA) to 4.53 V at 45°C and 3 kg of pressure. The battery was then allowed to stand at the same temperature and pressure for 24 hours (to fully activate the battery) to obtain a formation cell.

[0081] 2) Clamp the formed battery on the battery test cabinet and charge and discharge it at 0.2C (440mA), 0.5C (1100mA) and 1C (2200mA) in sequence. The charging process is constant current and constant voltage charging with a cut-off current of 0.05C. The discharging process is constant current discharge with a cut-off voltage of 3V. Finally, continue to charge and discharge at 1C for 3 cycles to obtain a fully charged capacity battery, that is, a lithium-ion battery.

[0082] The preparation methods of the lithium-ion batteries of Examples 2-28 and Comparative Examples 1-7 are the same as those of Example 1, except that the electrolyte compositions are different, as shown in Table 1.

[0083] Example 29

[0084] 1. Preparation of electrolyte

[0085] In an argon atmosphere glove box (water content <1 ppm, oxygen content <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 15:20:15:50 to obtain a solvent, and lithium hexafluorophosphate (LiPF6), a first additive, and a second additive were added to the solvent, dissolved, and mixed uniformly to obtain an electrolyte; wherein:

[0086] The mass percentage of lithium hexafluorophosphate (LiPF6) in the electrolyte is 13.5%;

[0087] The first additive is a compound represented by formula (1-1), and the mass percentage of the first additive in the electrolyte is 1.5%;

[0088] The second additive is a compound represented by formula (2-1), and the mass percentage of the second additive in the electrolyte is 2.5%;

[0089] The rest is solvent.

[0090] 2. Preparation of positive electrode sheet

[0091] The positive electrode active material LiNi 0.6 Co 0.1 Mn 0.3O2, binder polyvinylidene fluoride PVDF, conductive carbon black, and conductive carbon nanotubes are mixed evenly in a weight ratio of 95:1.5:3:0.5, and N-methylpyrrolidone NMP is added and stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil with a coating amount of 35g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0092] 3. Preparation of negative electrode sheet

[0093] The negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber were mixed in a weight ratio of 95:1.5:1.5:2, and deionized water was added to obtain the negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil with a coating amount of 20g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After striping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0094] 4. Isolation film

[0095] A polyethylene isolation film with a thickness of 8 μm was selected.

[0096] 5. Preparation of NCM613 lithium-ion batteries

[0097] 1) The positive and negative electrode sheets, along with the separator, prepared according to the above process were wound into a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery was vacuum-baked at 75°C for 10 hours and then injected with the previously prepared electrolyte. After standing at 45°C for 12 hours, the battery was placed in a formation cabinet and charged to 4.4 V at 0.1C (160 mA) at 45°C and 3 kg of pressure. The battery was then allowed to stand for 24 hours under the same temperature and pressure conditions (to fully activate the battery) to obtain a formation battery.

[0098] 2) Clamp the formed battery on the battery test cabinet and charge and discharge it at 0.2C (320mA), 0.5C (800mA) and 1C (1600mA) in sequence. The charging process is constant current and constant voltage charging with a cut-off current of 0.05C. The discharging process is constant current discharge with a cut-off voltage of 2.75V. Finally, continue to charge and discharge at 1C for 3 cycles to obtain a fully charged capacity battery, that is, a lithium-ion battery.

[0099] Example 30

[0100] 1. Preparation of electrolyte

[0101] In an argon atmosphere glove box (water content <1 ppm, oxygen content <1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed uniformly in a mass ratio of 15:20:15:50 to obtain a solvent, and lithium hexafluorophosphate (LiPF6), a first additive, and a second additive were added to the solvent, dissolved, and mixed uniformly to obtain an electrolyte; wherein:

[0102] The mass percentage of lithium hexafluorophosphate (LiPF6) in the electrolyte is 13.5%;

[0103] The first additive is a compound represented by formula (1-1), and the mass percentage of the first additive in the electrolyte is 1.5%;

[0104] The second additive is a compound represented by formula (2-1), and the mass percentage of the second additive in the electrolyte is 2.5%;

[0105] The rest is solvent.

[0106] 2. Preparation of positive electrode sheet

[0107] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2, binder polyvinylidene fluoride PVDF, conductive carbon black, and conductive carbon nanotubes are mixed evenly in a weight ratio of 95:1.2:2:1.8, and N-methylpyrrolidone NMP is added and stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil with a coating amount of 35g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the positive electrode sheet.

[0108] 3. Preparation of negative electrode sheet

[0109] The negative electrode active material graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber were mixed in a weight ratio of 95:1.5:1:2.5, and deionized water was added to obtain the negative electrode slurry under the action of a vacuum mixer; the negative electrode slurry was evenly coated on the negative electrode current collector copper foil with a coating amount of 20g / m 2 After drying at 85°C, cold pressing is performed, and edge trimming, cutting, and striping are performed. After stripping, it is dried at 85°C under vacuum conditions for 4 hours, and the tabs are welded to obtain the negative electrode sheet.

[0110] 4. Isolation film

[0111] A polyethylene isolation film with a thickness of 8 μm was selected.

[0112] 5. Preparation of NCM811 lithium-ion batteries

[0113] 1) The positive and negative electrode sheets, along with the separator, prepared according to the above process were wound into a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm, and a length of 60 mm. The battery was vacuum-baked at 75°C for 10 hours and then injected with the previously prepared electrolyte. After standing at 45°C for 12 hours, the battery was placed in a formation cabinet and charged to 4.25 V at 0.1C (200 mA) at 45°C and 3 kg of pressure. The battery was then allowed to stand at the same temperature and pressure for 24 hours (to fully activate the battery) to obtain a formation cell.

[0114] 2) Clamp the formed battery on the battery test cabinet and charge and discharge it at 0.2C (400mA), 0.5C (1000mA) and 1C (2000mA) in sequence. The charging process is constant current and constant voltage charging with a cut-off current of 0.05C. The discharging process is constant current discharge with a cut-off voltage of 2.75V. Finally, continue to charge and discharge at 1C for 3 cycles to obtain a fully charged capacity battery, that is, a lithium-ion battery.

[0115] Table 1

[0116]

[0117] Table 1

[0118]

[0119] Test Method

[0120] The electrochemical performance of the lithium-ion batteries prepared in Examples 1 to 30 and Comparative Examples 1 to 7 was tested as follows:

[0121] (1) Cyclic performance test at 25℃ under 3C / 1C:

[0122] The fully charged capacity-dividing batteries were placed in a constant temperature test cabinet at 25°C and first left for 5 minutes. Then, they were charged at a constant current and constant voltage of 3C to a specified voltage (the specified voltage of the battery samples of Examples 1-28 and Comparative Examples 1-7 was 4.53V, the specified voltage of the battery sample of Example 29 was 4.4V, and the specified voltage of the battery sample of Example 30 was 4.25V). The cutoff current of this process was 0.05C. After the battery was fully charged, it was left for another 5 minutes. Then, it was discharged at a constant current of 1C. The cutoff voltage was: the cutoff voltage of the battery samples of Examples 1-28 and Comparative Examples 1-7 was 3V, and the cutoff voltage of the battery samples of Examples 29 and Example 30 was 2.75V. In this manner, 800 cycles of charge and discharge tests were performed, and the discharge capacity of each cycle was recorded. The capacity retention rate after 500 cycles was calculated as follows:

[0123] Capacity retention after 800 cycles (%) = discharge capacity at the 500th cycle / discharge capacity at the 1st cycle × 100%.

[0124] (2) Cyclic performance test at 45°C under 3C / 1C:

[0125] The fully charged capacity-scaling batteries were placed in a 45°C constant temperature test cabinet and first left for 5 minutes. Then, they were charged at a constant current and constant voltage of 3C to a specified voltage (the specified voltage of the battery samples of Examples 1-28 and Comparative Examples 1-7 was 4.53V, the specified voltage of the battery sample of Example 29 was 4.4V, and the specified voltage of the battery sample of Example 30 was 4.25V). The cutoff current of this process was 0.05C. After the battery was fully charged, it was left for another 5 minutes and then discharged at a constant current of 1C. The cutoff voltage was: the cutoff voltage of the battery samples of Examples 1-28 and Comparative Examples 1-7 was 3V, and the cutoff voltage of the battery samples of Examples 29 and Example 30 was 2.75V. 500 cycles of charge and discharge tests were performed in this manner, and the discharge capacity of each cycle was recorded. The capacity retention rate after 500 cycles was calculated as follows:

[0126] Capacity retention after 500 cycles (%) = discharge capacity at the 500th cycle / discharge capacity at the 1st cycle × 100%.

[0127] (3) Hot box experiment

[0128] Fully charge the batteries at 0.5C, then hang them vertically in a heating chamber. Heat the chamber at a rate of 5°C / minute. After the furnace temperature reaches 135°C, hold the chamber at this temperature for one hour. Record whether the lithium-ion battery catches fire or explodes during this period. The test is considered a pass if the battery does not catch fire or explode during this period.

[0129] The test results are shown in Table 2 below:

[0130] Table 2

[0131]

[0132] Table 2

[0133]

[0134] As can be seen from the test results in Table 2, compared with Comparative Examples 1 to 7, the capacity retention rates at 25°C and 45°C of the lithium-ion batteries prepared in Examples 1 to 30 under fast charging conditions are improved. This indicates that by adding a first additive and a second additive to the electrolyte, the first additive includes a compound represented by formula (1), and the second additive includes a compound represented by formula (2), the first additive can form a cathode electrolyte interface film (CEI film) and a solid electrolyte interface film (SEI film) containing an N-phenyl skeleton and components such as Li2S2O4 and Li2SO3. The CEI film and SEI film have high electrical conductivity and low impedance, and the first additive participates in the repair of the film during the cycle, thereby improving the cycle performance of the battery. The second additive can increase the wettability of the electrolyte, thereby helping to improve the uniformity of SEI film formation. At the same time, during the actual battery cycle, the second additive is more easily oxidized and decomposed into a film on the positive electrode side during the high-voltage cycle, thereby repairing and protecting the CEI film originally formed by the first additive in the formation stage, thereby enhancing the overall stability of the CEI film, while retaining the high conductivity electronic properties of the CEI film and reducing the membrane impedance. The two work together to promote the formation of a more stable interface film, inhibit the decomposition of the electrolyte, reduce the contact between the electrolyte and the electrode material, and improve the battery's cycle performance.

[0135] From the comparison of Examples 1 to 22, Examples 29-30, Examples 23-24, and Examples 27-28, it can be seen that controlling the mass percentage of the first additive in the electrolyte within the range of 0.05%-5% can ensure that the battery has good cycle performance.

[0136] From the comparison of Examples 1 to 22, Examples 29-30 and Examples 25-28, it can be seen that controlling the mass percentage of the second additive in the electrolyte within the range of 0.01%-10% can ensure that the battery has good cycle performance.

[0137] From the comparison of Examples 1 to 22, Examples 29-30 and Examples 27-28, it can be seen that controlling the mass ratio of the first additive to the second additive in the range of 0.005-500 can ensure that the battery has good cycle performance.

[0138] From the comparison of Examples 1 to 16, Examples 29-30, Examples 17-18 and Examples 21-22, it can be seen that controlling the mass percentage of the first additive in the electrolyte within the range of 0.5%-3% can further improve the cycle performance and safety performance of the battery.

[0139] From the comparison of Examples 1 to 16, Examples 29-30, and Examples 19-22, it can be seen that controlling the mass percentage of the second additive in the electrolyte within the range of 0.1%-5% can further improve the cycle performance and safety performance of the battery.

[0140] The above detailed description of the embodiments of the present application is made with specific examples applied to the principles and implementation modes of the present application, and the above description of the embodiments is only used to help understand the method of the present application and its core idea; meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description of the present application should not be understood as a limitation of the present application.

Claims

1. An electrolyte, characterized in that: The additives include a first additive and a second additive, the first additive includes a compound represented by formula (1), the second additive includes a compound represented by formula (2), Formula (1), Formula (2), Wherein, in formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl ring group, a sulfonyl group, and derivatives thereof, and at least one of R7 and R9 is a phenyl ring group; R8 is selected from H, halogen, or a C1-C3 substituted or unsubstituted alkyl group; In formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, halogen, C1-C3 substituted or unsubstituted alkyl, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy; The mass ratio of the first additive to the second additive is 0.005-500; The mass percentage of the first additive in the electrolyte is 0.05%-5%; The mass percentage of the second additive in the electrolyte is 0.01%-10%.

2. The electrolyte according to claim 1, characterized in that In formula (1), R7 and R9 are each independently selected from at least one of H, a phenyl ring group, a sulfonyl group, a sulfonyl chloride group, and a sulfonyl fluoride group, and at least one of R7 and R9 is a phenyl ring group, and / or R8 is selected from H, F, Cl, or an unsubstituted alkyl group of C3; and / or In formula (2), R1, R2, R3, R4, R5, and R6 are each independently selected from at least one of H, F, and alkoxy, and at least one of R1, R2, R3, R4, R5, and R6 is an alkoxy group.

3. The electrolyte according to claim 1, characterized in that The first additive includes at least one of the following compounds: 、 、 、 、 、 、 、 。 4. The electrolyte according to claim 1, characterized in that The second additive includes at least one of the following compounds: 、 、 、 、 、 。 5. The electrolyte according to claim 1, characterized in that The mass ratio of the first additive to the second additive is 0.1-30; and / or The mass percentage of the first additive in the electrolyte is 0.5%-3%; and / or The mass percentage of the second additive in the electrolyte is 0.1%-5%.

6. The electrolyte according to any one of claims 1 to 4, characterized in that The electrolyte solution further includes a solvent and / or an electrolyte salt.

7. The electrolyte according to claim 6, characterized in that The mass percentage of the electrolyte salt in the electrolyte is 10%-18%; and / or, The electrolyte salt includes lithium salt and / or sodium salt, The lithium salts include LiPF6, LiFSI, LiTFSI, LiB(C2O4)2, LiBF2C2O4, LiPO2F 2、 At least one of LiPF2(C2O4)2; and / or The sodium salt includes at least one of NaPF6, NaAsF6, NaFSI, NaClO4, NaB(C2O4)2, NaBF2C2O4, NaN(SO2F)2, NaN(SO2CF3)2, NaPO2F2, NaPF2(C2O4)2, and NaPF4C2O4.

8. The electrolyte according to claim 6, characterized in that The solvent includes at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent.

9. The electrolyte according to claim 8, characterized in that The solvent includes at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyl trifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate and 2,2-difluoroethyl methyl carbonate.

10. A battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator placed between the positive electrode sheet and the negative electrode sheet, and the electrolyte according to any one of claims 1 to 9.

11. The battery according to claim 10, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector and containing a positive electrode active material. The positive electrode active material is selected from lithium cobalt oxide. The charging cut-off voltage of the battery is ≥4.4V.

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