A secondary battery and an electronic device

Abstract

The application discloses a secondary battery and an electronic device, and relates to the technical field of new energy sources. The secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm. The diaphragm comprises a polyolefin base material and a coating layer arranged on at least one surface of the polyolefin base material, wherein the coating layer comprises boehmite. The electrolyte contains a specific amount of 1,3-propanesultone, 1,3,6-hexanetricarbonitrile, lithium difluorophosphate, a boron-containing lithium salt and adiponitrile. The total amount of 1,3-propanesultone and 1,3,6-hexanetricarbonitrile, the total amount of lithium difluorophosphate and the boron-containing lithium salt and adiponitrile are within specific ranges, so that the secondary battery can have high energy density, good high-voltage life and good safety.

Description

[0001] This application is a divisional application of the patent application filed on June 14, 2024, with application number 202410770399.5 and invention title "A Secondary Battery and Electronic Device". Technical Field

[0002] This application relates to the field of new energy technology, and in particular to a secondary battery and electronic device. Background Technology

[0003] Rechargeable batteries have advantages such as high energy density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety, and are widely used in portable energy storage, electronic devices, electric vehicles, and other fields. However, rechargeable batteries have also revealed issues such as lifespan and safety during use. Therefore, consumers are placing higher demands on the overall performance of rechargeable batteries, such as those that simultaneously possess good safety, high energy density, and long cycle life.

[0004] Current traditional methods for improving the energy density of rechargeable batteries include increasing coating weight, increasing electrode compaction density, and increasing voltage. However, while these methods improve energy density, they also reduce the battery's safety performance and high-potential lifespan. Therefore, ensuring the high-potential lifespan and safety of high-energy-density rechargeable batteries is a pressing issue that the battery industry needs to address. Summary of the Invention

[0005] This application provides a secondary battery and an electronic device that enables the secondary battery to maintain high energy density while also having good high-potential lifespan and good safety.

[0006] In a first aspect, this application provides a secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator; the separator comprises a polyolefin substrate and a coating disposed on at least one surface of the polyolefin substrate, the coating comprising boehmite. Based on the total mass of the electrolyte, the electrolyte satisfies the following: (I) comprising 1,3-propanesulfonic acid lactone in a content of 1.3 wt% or more and 2.7 wt% or less; (II) comprising lithium difluorophosphate in a content of 0.01 wt% or more and 2 wt% or less; (III) comprising 1,3,6-hexanetrionitrile in a content of 1.6 wt% or more and 3.9 wt% or less; (IV) comprising boron-containing lithium salt in a content of 0.01 wt% or more and 3 wt% or less. The combined content of 1,3-propanesulfonic acid lactone and 1,3,6-hexanetrionitrile is 1.61 wt% or more and 6 wt% or less, and the combined content of lithium difluorophosphate and boron-containing lithium salt is 0.02 wt% or more and 5 wt% or less.

[0007] Based on the secondary battery of this application, the total content of 1,3-propanesulfonic acid lactone and 1,3,6-hexanetrionitrile, the total content of lithium difluorophosphate and boron-containing lithium salt, and the individual content of the four substances are controlled within specific ranges. When used in conjunction with a polyolefin substrate separator containing boehmite, it can not only improve the adhesion of the separator after being wetted by the electrolyte, but also improve the high-potential life and low-temperature output characteristics of the secondary battery, and also has good safety performance. Boehmite in the surface coating of polyolefin substrates significantly improves battery safety. Furthermore, the inventors unexpectedly discovered that the presence of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile in the electrolyte inhibits the swelling of the polyolefin substrate in the electrolyte; however, the presence of boehmite catalyzes the decomposition of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile on the negative electrode surface. Subsequently, the inventors found that specific amounts of lithium difluorophosphate and boron-containing lithium salts can precisely inhibit the decomposition of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile, forming a stable coating on the negative electrode surface. Using this design not only improves the adhesion of the separator after electrolyte immersion but also significantly enhances the high-potential life and low-temperature output characteristics of the secondary battery.

[0008] In some embodiments, the boron-containing lithium salt includes lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanoborate borate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(salicylate)borate, and lithium bis(catechol)borate. The lithium borate salt comprises at least one of the following: lithium methoxytricyanoborate, lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetra(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, or lithium tetra(difluorophosphoryloxy)borate. In the embodiments of this application, when the boron-containing lithium salt includes the above-mentioned materials, the secondary battery exhibits better safety performance, energy density, high-potential life, and low-temperature output performance.

[0009] In some of these embodiments, the electrolyte comprises 1,3-propanesulfonic acid lactone in a content of 1.3 wt% or more and 2.7 wt% or less, based on the total mass of the electrolyte.

[0010] In some of these embodiments, the electrolyte comprises 1,3-propanesulfonic acid lactone in a content of 2.6 wt% to 2.9 wt% based on the total mass of the electrolyte.

[0011] Based on the above embodiments, controlling the content of 1,3-propanesulfonic acid lactone within the above range can effectively suppress the swelling of the polyolefin substrate, thereby improving the safety performance of the secondary battery.

[0012] In some embodiments, the electrolyte comprises lithium difluorophosphate in a content of more than 0.07 wt% and less than 0.91 wt%, based on the total mass of the electrolyte.

[0013] In some embodiments, the electrolyte comprises lithium difluorophosphate in a content of more than 0.01 wt% and less than 0.11 wt%, based on the total mass of the electrolyte.

[0014] In some embodiments, the electrolyte comprises lithium difluorophosphate in a content of more than 0.11 wt% and less than 0.59 wt%, based on the total mass of the electrolyte.

[0015] Based on the above embodiments, the content of lithium difluorophosphate is controlled within the above range, which can effectively inhibit the decomposition of 1,3-propanesulfonic acid lactone and 1,3,6-hexanetrionitrile, thereby effectively inhibiting the swelling of polyolefin substrate and improving the safety performance of secondary batteries.

[0016] In some embodiments, the electrolyte includes 1,3,6-hexanetrionitrile at a content of 1.6 wt% to 2.8 wt%, based on the total mass of the electrolyte. Controlling the content of 1,3,6-hexanetrionitrile within this range effectively suppresses the swelling of the polyolefin substrate, thereby improving the safety performance of the secondary battery.

[0017] In some embodiments, the electrolyte also contains other nitrile compounds, including at least one selected from butadionitrile, adiponitrile, ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tris(cyanoethoxy)pentane; the content of the other nitrile compounds is 0.3 wt% to 8 wt% based on the total mass of the electrolyte. The inventors unexpectedly discovered that the other nitrile compounds can improve the stability of the formed coating, thereby further improving the high-potential life and low-temperature output characteristics of the secondary battery.

[0018] In some embodiments, the succinic acid content is 1.7 wt% or more and 5.5 wt% or less, based on the total mass of the electrolyte. When the electrolyte contains succinic acid within the above range, the low-temperature output characteristics of the secondary battery can be further improved.

[0019] In some embodiments, the adiponitrile content is 2.3 wt% or more and 4 wt% or less based on the total mass of the electrolyte. When the electrolyte contains adiponitrile within the above range, the high-potential life and low-temperature output characteristics of the secondary battery can be further improved.

[0020] In some embodiments, the content of ethylene glycol di(propionitrile) ether is 0.3 wt% or more and 0.9 wt% or less, based on the total mass of the electrolyte. When the electrolyte contains ethylene glycol di(propionitrile) ether within the above range, the low-temperature output characteristics of the secondary battery can be further improved.

[0021] In some embodiments, the content of 1,2,3-tris(2-cyanoethoxy)propane is 0.4 wt% or more and 2.3 wt% or less, based on the total mass of the electrolyte. When the electrolyte contains 1,2,3-tris(2-cyanoethoxy)propane within the above range, the low-temperature output characteristics of the secondary battery can be further improved.

[0022] In some embodiments, the electrolyte also includes other additives, including at least one selected from 2-ethyl-1-hexyl difluorophosphite, 4-methyl-2-pentyl difluorophosphite, pentyl difluorophosphite, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, vinyl sulfate, 1,3-propanediol cyclosulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate; the content of the other additives is 0.01 wt% or more and 10 wt% or less based on the total mass of the electrolyte. The inventors unexpectedly discovered that the other additives can inhibit the decomposition and regeneration of the aforementioned coating during charge and discharge processes, thereby further improving the high-potential life and low-temperature output characteristics of the secondary battery.

[0023] In some embodiments, the content of fluoroethylene carbonate is 0.01 wt% or more and 3 wt% or less, based on the total mass of the electrolyte.

[0024] In some embodiments, the content of fluoroethylene carbonate is 4.1 wt% or more and 6.9 wt% or less, based on the total mass of the electrolyte.

[0025] Based on the above embodiments, when the electrolyte contains the above-mentioned amount of fluoroethylene carbonate, the high-potential life and low-temperature output characteristics of the secondary battery are further improved.

[0026] In some embodiments, the content of vinyl sulfate is 0.01 wt% to 0.3 wt% based on the total mass of the electrolyte. When the electrolyte contains the above-mentioned amount of vinyl sulfate, the high-potential life and low-temperature output characteristics of the secondary battery are further improved.

[0027] In some embodiments, the content of 2-ethyl-1-hexyl difluorophosphite is 0.01 wt% to 1.4 wt% or less based on the total mass of the electrolyte. When the electrolyte contains the above-mentioned amount of 2-ethyl-1-hexyl difluorophosphite, the high-potential life and low-temperature output characteristics of the secondary battery are further improved.

[0028] Secondly, embodiments of this application provide an electronic device including any of the secondary batteries described in the first aspect. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. The embodiments of this application will be described in detail below. The embodiments of this application should not be construed as limiting the application. Unless otherwise expressly stated, the following terms used in this application have the meanings indicated below.

[0030] By using a specific combination of diaphragm composition and electrolyte, this application not only improves the adhesion of the diaphragm after electrolyte impregnation, but also significantly enhances the high-potential life and low-temperature output characteristics of the secondary battery.

[0031] In one embodiment, this application provides a secondary battery comprising an electrolyte, a separator, a positive electrode, and a negative electrode.

[0032] I. Electrolyte

[0033] The electrolyte used in the secondary battery of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte of this application includes:

[0034] (I) 1,3-propanesulfonic acid lactone in a content of 1.3 wt% or more and 2.7 wt% or less;

[0035] (II) Lithium difluorophosphate with a content of 0.01 wt% or more and 2 wt% or less;

[0036] (III) 1,3,6-hexanetrionitriles in a content of 1.6 wt% or more and 3.9 wt% or less;

[0037] (IV) Boron-containing lithium salts with a content of 0.01 wt% or more and 3 wt% or less.

[0038] The total content of 1,3-propanesulfonic acid lactone and 1,3,6-hexanetrionitrile is 1.61 wt% or more and 6 wt% or less, and the total content of lithium difluorophosphate and boron-containing lithium salt is 0.02 wt% or more and 5 wt% or less.

[0039] The separator used in the secondary battery of this application comprises a polyolefin substrate and a coating on at least one surface of the polyolefin substrate, the coating including boehmite, which can significantly improve the safety of the battery. The inventors unexpectedly discovered that 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile in the electrolyte can inhibit the swelling of the polyolefin substrate in the electrolyte; however, the presence of boehmite catalyzes the decomposition of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile on the negative electrode surface. A specific amount of lithium difluorophosphate and boron-containing lithium salt can precisely inhibit the decomposition of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile, forming a stable coating on the negative electrode surface. By using this design, not only can the adhesion of the separator after electrolyte immersion be improved, but the high-potential life and low-temperature output characteristics of the secondary battery are also significantly improved.

[0040] Specifically, from the viewpoint of improving the adhesion of the diaphragm after electrolyte impregnation, the content of 1,3-propanesulfonate lactone is 1.3 wt% or more based on the total mass of the electrolyte. Furthermore, as an upper limit for the mass content of 1,3-propanesulfonate lactone, from the viewpoint of improving the lifetime in the high-potential region, the mass content of 1,3-propanesulfonate lactone is 2.7 wt% or less, preferably 2.4 wt% or less, and more preferably 1.6 wt% or less. When within the above range, it helps to further improve the lifetime in the high-potential region.

[0041] In some embodiments, the content of 1,3-propanesulfonic acid lactone is set as a1wt%, where a1 is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.4, 2.6, 2.7, 2.8, 2.9, or within a range consisting of any two of the above values. For example, values ​​of 0.01 to 0.09, 0.01 to 1.3, 0.05 to 0.1, 0.1 to 0.8, 0.5 to 1.2, 0.7 to 1.9, 1.3 to 2.7, and 1.1 to 2.9, when within the above ranges, help to further improve the lifetime of the high potential region.

[0042] Specifically, from the viewpoint of improving the adhesion of the diaphragm after electrolyte impregnation, the lithium difluorophosphate content is 0.01 wt% or more based on the total mass of the electrolyte, preferably 0.02 wt% or more, more preferably 0.07 wt% or more, and more preferably 0.11 wt% or more. Furthermore, as an upper limit for the lithium difluorophosphate content, from the viewpoint of improving the lifetime in the high-potential region, the lithium difluorophosphate content is 2 wt% or less, preferably 1.8 wt% or less, more preferably 1.6 wt% or less, further preferably 1.3 wt% or less, particularly preferably 1.2 wt% or less, and even more particularly preferably 0.91 wt% or less. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0043] In some embodiments, the lithium difluorophosphate content is set to a2wt%, where a2 is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or within a range consisting of any two of the above values. For example, 0.01 to 0.09, 0.01 to 0.11, 0.05 to 0.1, 0.1 to 0.8, 0.6 to 1.2, 0.8 to 1.8. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0044] Specifically, from the viewpoint of improving the low-temperature output characteristics of secondary batteries, based on the total mass of the electrolyte, the content of 1,3,6-hexanetrionitrile is 1.6 wt% or more, preferably 1.8 wt% or more, more preferably 2.1 wt% or more, and even more preferably 2.4 wt% or more. Furthermore, as an upper limit for the mass content of 1,3,6-hexanetrionitrile, from the viewpoint of improving the lifetime in the high-potential region, the mass content of 1,3,6-hexanetrionitrile is 3.9 wt% or less, preferably 3.7 wt% or less, more preferably 3.5 wt% or less, even more preferably 3.3 wt% or less, and particularly preferably 3.1 wt% or less. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0045] In some embodiments, the content of 1,3,6-hexanetrionitrile is set to a3wt%, where a3 is 1.6, 1.8, 2.0, 2.3, 2.6, 2.8, 3.1, 3.3, 3.5, 3.7, 3.9, or within a range of any two of the above values. For example, 1.6 to 2.8, 1.8 to 3.3, 2.0 to 3.5, 2.3 to 3.7, and 1.6 to 2.3. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0046] In some embodiments, boron-containing lithium salts include lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanoborate borate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(salicylate)borate, lithium bis(catechol)borate, lithium methoxytricyanoborate, and ethyl... The lithium tricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetra(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, or lithium tetra(difluorophosphoryloxy)borate are selected as the primary boron salts. In this case, the formed coating exhibits excellent stability, and the battery performance is further improved. The boron-containing lithium salt can be only one type, or it can be two or more types, or three or more types.

[0047] In some embodiments, the boron-containing lithium salt preferably includes at least one of lithium tetrafluoroborate, lithium bis(oxalato)borate (LiBOB), and lithium di(fluorooxalato)borate (LiDFOB).

[0048] Specifically, from the viewpoint of improving the low-temperature output characteristics of secondary batteries, based on the total mass of the electrolyte, the mass content of boron-containing lithium salt is 0.01 wt% or more, preferably 0.02 wt% or more, more preferably 0.06 wt% or more, and even more preferably 0.1 wt% or more. Furthermore, as an upper limit for the mass content of boron-containing lithium salt, from the viewpoint of improving the lifetime in the high-potential region, the mass content of boron-containing lithium salt is 3 wt% or less, preferably 2.3 wt% or less, more preferably 1.5 wt% or less, even more preferably 1.1 wt% or less, and particularly preferably 0.7 wt% or less. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0049] In some embodiments, the content of the boron-containing lithium salt is set to a4wt%, where a4 is 0.01, 0.02, 0.06, 0.1, 0.4, 0.7, 1.1, 1.5, 2.3, 2.8, 3, or within a range of any two of the above values. For example, 0.01 to 0.1, 0.1 to 0.7, 0.4 to 1.1, 0.7 to 2.3, 1.5 to 3. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0050] Furthermore, from the viewpoint of improving the lifetime in the high-potential region, based on the electrolyte mass, the total mass content of (I) and (III) is 1.61 wt% or more, preferably 1.85 wt% or more. Moreover, from the viewpoint of improving electrochemical characteristics under low-temperature conditions, the upper limit of the total content of (I) and (III) is 6 wt% or less, preferably 5.7 wt% or less.

[0051] In some embodiments, the total mass content of (I) and (III) is a1+a3wt%, where a1+a3 is 1.61, 1.85, 2.18, 2.4, 2.8, 3.4, 4, 4.7, 5.2, 5.7, 6, or within a range of any two of the above values. For example, 1.61 to 2.8, 1.85 to 5.2, 1.61 to 2.18, 1.85 to 3.4, 2.4 to 4.7, 2.8 to 5.7, when within the above ranges, helps to further improve the lifetime in the high-potential region.

[0052] Furthermore, from the viewpoint of improving the lifetime in the high-potential region, based on the electrolyte mass, the total mass content of (II) and (IV) is 0.02 wt% or more, preferably 0.14 wt% or more. Moreover, as an upper limit for the total content of (II) and (IV), from the viewpoint of improving electrochemical characteristics at low temperatures, it is 5 wt% or less, preferably 4.4 wt% or less.

[0053] In some embodiments, the total mass content of (II) and (IV) is a2+a4wt%, where a2+a4 is 0.02, 0.04, 0.09, 0.14, 0.47, 0.66, 0.81, 1.12, 1.33, 1.56, 1.88, 2.21, 2.34, 2.56, 2.88, 3.12, 3.35, 3.78, 4.11, 4.4, 4.7, or 5, or within a range consisting of any two of the above values. For example, 0.02 to 0.14, 0.09 to 0.66, 0.47 to 1.56, 1.12 to 2.88, and 1.56 to 4.7wt%. When within the above ranges, it helps to further improve the lifetime in the high-potential region.

[0054] In addition, the electrolyte may also include other nitrile compounds. The inventors also unexpectedly discovered that other nitrile compounds can improve the stability of the aforementioned coating, improve lithium-ion charge transport, improve the high-potential life of the secondary battery, and improve low-temperature output characteristics.

[0055] Other nitrile compounds include at least one of butadionitrile, adiponitrile, ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tris(cyanoethoxy)pentane. There may be only one or more of the aforementioned other nitrile compounds.

[0056] Specifically, from the viewpoint of improving the low-temperature output characteristics of secondary batteries, based on the total mass of the electrolyte, the content of other nitrile compounds is 0.3 wt% or more, preferably 0.6 wt% or more, more preferably 0.9 wt% or more, and even more preferably 1.4 wt% or more. Furthermore, as an upper limit for the content of other nitrile compounds, the content is 8 wt% or less, preferably 7.9 wt% or less, more preferably 7.1 wt% or less, even more preferably 6.2 wt% or less, and particularly preferably 5.3 wt% or less.

[0057] In some embodiments, the total content of other nitrile compounds is bwt%, where b is 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.4, 1.5, 2, 2.5, 3, 3.1, 3.6, 3.9, 4, 4.6, 5.3, 6.2, 7.1, 7.9, 8, or within a range consisting of any two of the above values. For example, 0.3 to 5.3, 0.6 to 4.6, 0.9 to 3.1, 0.4 to 2, 0.45 to 3.6, 0.8 to 2.5, 1.4 to 3.9, 2.5 to 8, 0.9 to 6.2, 0.45 to 5.3, 0.6 to 1.4. When within the above ranges, it helps to further improve the low-temperature output characteristics of the secondary battery. Specifically, the content of succinic anion is 1.7 wt% or more and 5.5 wt% or less, or the content of adiponitrile is 2.3 wt% or more and 4 wt% or less, or the content of ethylene glycol di(propionitrile) ether is 0.3 wt% or more and 0.9 wt% or less, or the content of 1,2,3-tris(2-cyanoethoxy)propane is 0.4 wt% or more and 2.3 wt% or less.

[0058] In addition, the electrolyte may also include other additives. The inventors also unexpectedly discovered that other additives can inhibit the decomposition and regeneration of the aforementioned coating during the charging and discharging process, thereby further improving the high-potential life and low-temperature output characteristics of the secondary battery.

[0059] Other additives include at least one of 2-ethyl-1-hexyl difluorophosphite, 4-methyl-2-pentyl difluorophosphite, pentyl difluorophosphite, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, vinyl sulfate, 1,3-propanediol cyclosulfonate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate. There may be only one of the above-mentioned other additives, or there may be two or more.

[0060] Specifically, from the viewpoint of improving low-temperature output characteristics, based on the total mass of the electrolyte, the content of other additives is 0.01 wt% or more, preferably 0.1 wt% or more, more preferably 1.6 wt% or more, and more preferably 2.8 wt% or more. Furthermore, from the viewpoint of improving low-temperature output characteristics, the content of other additives is 10 wt% or less, preferably 9.7 wt% or less, more preferably 8.2 wt% or less, even more preferably 7.1 wt% or less, and particularly preferably 6.7 wt% or less.

[0061] In some embodiments, the total content of other additives is cwt%, where c is 0.01, 0.03, 0.1, 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 1.6, 2, 2.5, 2.9, 3, 3.5, 3.9, 4, 4.5, 5, 5.7, 6, 6.5, 7.1, 7.5, 8.2, 8.6, 9, 9.3, 9.7, 10, or within a range consisting of any two of the above values. For example, concentrations of 0.3 to 18.2, 0.45 to 7.5, 0.6 to 9.7, 5.5 to 9.7, 6 to 8.6, 2.8 to 6.5, 1 to 6.5, 0.7 to 7.1, 1.5 to 9.3, 0.45 to 3.9, and 0.7 to 4.5, when within the above ranges, contribute to further improvement in low-temperature output characteristics. Specifically, the content of fluoroethylene carbonate is 4.1 wt% or more and 6.9 wt% or less, or the content of ethylene sulfate is 0.01 wt% or more and 0.3 wt% or less, or the content of 2-ethyl-1-hexyl difluorophosphite is 0.01 wt% or more and 1.4 wt% or less.

[0062] The lithium salt used in the electrolyte of this application includes lithium hexafluorophosphate. Based on the total mass of the electrolyte, the content of lithium hexafluorophosphate is 9 to 15 wt%, preferably 9 to 13 wt%, and more preferably 9 to 12 wt%. By setting the content within the above range, the low-temperature characteristics can be improved.

[0063] The electrolyte of this application may further comprise any non-aqueous solvent known in the art that can be used as an electrolyte. Examples include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents. Chain carboxylic acid esters are preferred, such as ethyl acetate, ethyl fluoroacetate, ethyl propionate, and propyl propionate.

[0064] II. Diaphragm

[0065] To prevent short circuits, a diaphragm is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after permeating into the diaphragm.

[0066] In some embodiments, from the viewpoint of improving the adhesion of the diaphragm after electrolyte impregnation, the diaphragm includes a polyolefin substrate and a coating on the substrate, the coating including boehmite.

[0067] In some embodiments, the polyolefin is polyethylene or polypropylene. The diaphragm may also be a material formed by laminating the above materials, examples of which include, but are not limited to, a three-layer diaphragm formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0068] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size (diameter) of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators can also be used: separators formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive and / or negative electrodes, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size (Dv90) of less than 1 μm on both sides of the positive electrode.

[0069] The thickness of the separator is arbitrary. In some embodiments, the separator thickness is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator thickness is less than 50 μm, less than 40 μm, or less than 30 μm. When the separator thickness is within the above ranges, insulation and mechanical strength can be ensured, as well as the rate performance and energy density of the secondary battery.

[0070] III. Positive electrode

[0071] The positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on the surface of the positive electrode current collector.

[0072] The positive electrode flux layer contains the positive electrode active material, and the positive electrode flux layer can be one or more layers. The positive electrode active material is any material capable of reversibly inserting and deintercalating lithium ions.

[0073] For example, as positive electrode active materials for secondary batteries, lithium-containing composite metal oxides containing one or more of the group consisting of cobalt, manganese, and nickel, or lithium-containing olivine-type phosphates containing one or more of the group consisting of iron, cobalt, nickel, and manganese are used. These positive electrode active materials can be used alone or in combination of two or more.

[0074] Suitable examples of such lithium composite metal oxides include, for instance, those selected from LiCoO2, LiMn2O4, LiNiO2, and LiCo. 1-x NixO2 (0.01) <x<1)、LiNi x Mn y Co zA solid solution of O2 (x + y + z = 1), Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe, etc.), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn 1-x Fe x PO4 (0.01 < x < 1), and more preferably two or more. A part of these composite metal oxides with lithium or olivine-type phosphates containing lithium can be substituted with other elements, or a part of cobalt, nickel, manganese, and iron can be substituted with one or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or coated with a compound containing these other elements or a carbon material.

[0075] As the voltage during charging, from the perspective of increasing the voltage, the positive electrode potential is preferably 4.4 V (vs. Li / Li+) or more, more preferably 4.5 V (vs. Li / Li+) or more, and particularly preferably 4.6 V (vs. Li / Li+) or more.

[0076] The conductive agent of the positive electrode is not particularly limited as long as it is an electron-conducting material that does not cause chemical changes. Examples include natural graphite (such as flake graphite), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking carbon black. In addition, graphite and carbon black can be appropriately mixed and used. The mass content of the conductive agent in the positive electrode mixture is preferably 1 to 10 wt%, and particularly preferably 1.5 to 5 wt%.

[0077] The positive electrode can be produced as follows: Mix the above positive electrode active material with a conductive agent such as acetylene black and carbon black, and a binder such as polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, a copolymer of styrene and butadiene, and carboxymethyl cellulose. Add a high-boiling solvent such as 1-methyl-2-pyrrolidone and knead to form a positive electrode mixture slurry, then coat it on an aluminum foil or the like of the positive electrode current collector, dry, and press to form a positive electrode mixture layer.

[0078] The density of the part of the positive electrode other than the positive electrode current collector is usually 3.5 g / cm 3 or more. To further increase the capacity of the battery, it is preferably 3.8 g / cm 3 or more, more preferably 4 g / cm 3 or more, further preferably 4.1 g / cm 3 or more. In addition, as its upper limit, it is preferably 4.6 g / cm 3 or less.

[0079] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0080] To reduce the electronic contact resistance between the positive current collector and the positive electrode binder layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0081] The positive electrode can be manufactured by forming a positive electrode mixture layer containing positive electrode active material and binder on the positive electrode current collector. The manufacture of a positive electrode using positive electrode active material can be carried out by conventional methods, namely, dry mixing the positive electrode active material, binder, and conductive material and thickener as needed, forming a sheet, and pressing the resulting sheet onto the positive electrode current collector; or dissolving or dispersing these materials in a liquid medium to form a slurry, coating the slurry onto the positive electrode current collector and drying it, thereby forming a positive electrode mixture layer on the positive electrode current collector, thus obtaining the positive electrode.

[0082] IV. Negative electrode

[0083] The negative electrode includes a negative electrode current collector and a negative electrode additive layer disposed on the surface of the negative electrode current collector, the negative electrode additive layer containing a negative electrode active material. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0084] Furthermore, there are no particular limitations on the negative electrode active material; examples include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that combine these elements.

[0085] Carbon-based anode active materials

[0086] Here, carbon-based anode active materials refer to active materials with carbon as the main framework that can insert lithium. Examples of carbon-based anode active materials include carbonaceous materials and graphitic materials.

[0087] Examples of carbonaceous materials include easily graphitized carbon and non-graphitized carbon with a similar amorphous structure, such as glassy carbon. Among easily graphitized carbons, examples include carbon materials derived from petroleum or coal using tar pitch as a raw material. Specific examples include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, and pyrolysis-grown carbon fibers. Furthermore, examples of non-graphitized carbons include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0088] Furthermore, examples of graphitic materials include natural graphite and artificial graphite. Among these, examples of artificial graphite include: artificial graphite formed by heat-treating carbon containing easily graphitizable carbon primarily at temperatures above 2800°C; graphitic MCMB formed by heat-treating MCMB at temperatures above 2000°C; and graphitic mesophase pitch-based carbon fiber formed by heat-treating mesophase pitch-based carbon fiber at temperatures above 2000°C. Additionally, in this application, natural graphite (amorphously coated natural graphite) can be used as the carbon-based negative electrode active material, where at least a portion of its surface is coated with amorphous carbon.

[0089] Furthermore, metal-based anode active materials are active materials containing metals, generally referring to active materials whose structure contains elements capable of intercalating into or alloying with lithium, and whose theoretical current capacity per unit mass is 500 mAh / g or more when intercalated into or alloyed with lithium. Examples of metal-based anode active materials include: lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, active materials containing silicon (silicon-based anode active materials) are preferred as metal-based anode active materials. This is because using silicon-based anode active materials enables high-capacity lithium-ion secondary batteries.

[0090] Examples of silicon-based anode active materials include: silicon (Si), silicon-containing alloys, silicon oxides, and silicon-containing materials coated or composited with conductive carbon.

[0091] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0092] In addition, the negative electrode active material can be used alone or in combination of two or more in any ratio.

[0093] The negative electrode mixture layer may also include a negative electrode binder. The negative electrode binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode mixture slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0094] As the negative electrode current collector for maintaining the negative electrode active material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0095] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode active material, resin binder, etc. onto the negative electrode current collector, drying it, and then calendering it to form a negative electrode slurry layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0096] This application also provides an electronic device that includes a secondary battery according to this application.

[0097] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0098] The preparation of secondary batteries is described below with reference to specific embodiments. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0099] Example

[0100] The following are examples of non-aqueous electrolytes of this application, but this application is not limited to these examples.

[0101] Manufacturing of secondary batteries

[0102] Lithium cobalt oxide (97 wt%) and acetylene black (1.5 wt%), the positive electrode active materials, were mixed and added to a solution obtained by dissolving polyacrylonitrile (1.5 wt%) in 1-methyl-2-pyrrolidone. This mixture was then used to prepare a positive electrode paste. The paste was coated onto aluminum foil, dried, pressurized, and then cut to the specified size to fabricate the positive electrode.

[0103] Artificial graphite and silicon carbon (mass ratio 90:10, totaling 96 wt%), along with styrene-butadiene rubber (2 wt%), were mixed and added to a solution obtained by dissolving lithium carboxymethyl cellulose (2 wt%) in deionized water. This mixture was then used to prepare a negative electrode paste. The negative electrode paste was coated onto copper foil, dried, pressurized, and then cut into specified sizes to fabricate the negative electrode.

[0104] A 5μm porous polyethylene membrane was used as the membrane substrate. Deionized water and boehmite were added to a dual planetary mixer and dispersed at high speed at 40°C for 1 hour. Then, sodium carboxymethyl cellulose binder was added, and the mixture was stirred at low speed at room temperature for 1 hour to obtain a boehmite slurry with a solid content of 3%, where boehmite accounted for 2% of the total slurry weight and sodium carboxymethyl cellulose accounted for 1%. The boehmite slurry was then coated onto one side of the 5μm porous polyethylene membrane using a printing coating method and dried to obtain membrane 1 with a boehmite layer thickness of 1.5μm. The membrane substrate without a boehmite layer is designated as membrane 2.

[0105] The positive and negative electrodes prepared as described above are each connected to a wire. The electrodes are then layered and wound via the aforementioned diaphragm. Furthermore, LiPF6, serving as the supporting electrolyte, is dissolved in a solution containing (I) 1,3-propanesulfonate lactone, (II) lithium difluorophosphate, (III) 1,3,6-hexanetrionitrile, (IV) boron-containing lithium salt, other nitrile compounds, and other additives. Based on 100 parts by mass of the total electrolyte, the contents and composition of (I) to (IV), other nitrile compounds, and other additives are shown in Tables 1-1 and 1-2. The content of LiPF6 is 14%, with the remainder being ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate (mass ratio 0.8:1:2:0.5).

[0106] The wound body and 3.2g of electrolyte are then housed together in an aluminum laminated casing. The opening of the casing is heat-sealed, and a secondary battery is manufactured through formation, capacity testing, and other steps. This secondary battery is a pouch-shaped secondary battery with a width of 35mm, a height of 48mm, and a thickness of 5mm.

[0107] In the above-mentioned secondary batteries, the characteristics of membrane 1 and membrane 2 are shown in Table 1-1, and some components of the electrolyte are shown in Table 1-2 and Table 1-3.

[0108] Table 1-1 Types of diaphragms

[0109] serial number feature Diaphragm 1 With boehmite slurry coating Diaphragm 2 Boehmite-free slurry coating

[0110] Table 1-2 Partial Components of Electrolyte

[0111]

[0112]

[0113] In Table 1-2, a1 represents the content of (I) 1,3-propanesulfonic acid lactone, a2 represents the content of (II) lithium difluorophosphate, a3 represents the content of (III) 1,3,6-hexanetrionitrile, a4 represents the total content of (IV) boron-containing lithium salts, b represents the total content of other nitrile compounds, and c represents the total content of other additives; the code explanations are as follows:

[0114] Table 1-3 Electrolyte Component Codes

[0115] code Substance Name code Substance Name B1 Lithium tetrafluoroborate N1 Ethylene glycol di(propionitrile) ether B2 Lithium difluorooxalate borate N2 1,2,3-Tris(2-cyanoethoxy)propane B3 Lithium dioxalate borate N3 3-Methyl-1,3,5-tris(cyanoethoxy)pentane B4 Lithium tetracyanoboronate N4 adiponitrile B5 Lithium tetramethoxyborate N5 Succinic acid B6 Lithium tetrakis(2,2,2-trifluoroethoxy)borate B7 Lithium bis(trifluoromethyl)difluoroborate B8 Lithium dicyanooxalate borate B9 Dilithium di(trifluoroboronic acid) sulfate B10 Lithium malonate oxalate oxalate borate C1 Fluoroethylene carbonate C7 2-Ethyl-1-hexyl difluorophosphite C2 Lithium difluorophosphate C8 4-Methyl-2-pentyl difluorophosphite C3 vinyl sulfate C9 Pentyl difluorophosphite C4 Vinyl carbonate C10 Tris(trimethylsilane) phosphate C5 1,3-Propanesulfonate lactone C11 Tris(trimethylsilane)boronic acid ester C6 1,3-Propylenesulfonate lactone C12 Lithium fluorosulfonate

[0116] Test methods

[0117] Adhesion properties after electrolyte impregnation (wet adhesion)

[0118] The positive electrode and separator (with boehmite layers on both sides) prepared in the examples and comparative examples were cut into pieces 50 mm long and 10 mm wide. The cut positive electrode and separator were then reassembled and laminated. The resulting laminate was pressed using a roller press at 25°C and a load of 10 kN / m at a pressing speed of 30 m / min to obtain a test piece. This test piece was immersed in an electrolyte at 60°C for 72 hours. Here, the electrolyte used was a solution containing 14 wt% LiPF6 as the supporting electrolyte in ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate (mass ratio 0.8:1:2:0.5). The immersed test piece was removed from the electrolyte, and the electrolyte on the surface of the test piece was wiped off. The test piece was then pressed again under conditions of 1 MPa, 80°C, and 3 minutes. With the current collector side of the positive electrode facing down, the positive electrode of the re-pressed test piece was placed on the surface of the positive electrode, and transparent tape (the transparent tape specified in JIS Z1522) was attached. The transparent tape was pre-fixed to a horizontal test bench. Then, the stress was measured when one end of the diaphragm was stretched vertically at a tensile speed of 50 mm / min and peeled off. This measurement was performed three times. Furthermore, a laminate of the negative electrode and diaphragm was obtained in the same manner as described above, and this laminate was pressed to obtain a test piece. Then, a re-pressed test piece was obtained in the same manner as when using the positive electrode described above, and the stress after electrolyte impregnation was measured three times.

[0119] By measuring the positive and negative electrodes as described above, the average value of the stress obtained from a total of 6 measurements was calculated as the peel strength (N / m). This value was used to evaluate the process adhesion between the electrode and the separator separated by the boehmite layer after electrolyte impregnation, according to the following criteria. A higher peel strength indicates better wet adhesion, higher separator strength, higher safety performance of the secondary battery, and better assurance of energy density.

[0120] A: Peel strength is above 12.0 N / m.

[0121] B: Peel strength is above 8.0 N / m and less than 12.0 N / m.

[0122] C: Peel strength is above 5.0 N / m and less than 8.0 N / m.

[0123] D: Peel strength is less than 5.0 N / m.

[0124] High potential lifetime characteristics

[0125] For the fabricated secondary battery, the operation of charging to 4.7V at 0.2C and discharging to 3.0V was repeated three times at 25°C. Then, the operation of charging to 4.7V at 1C and discharging to 3.0V at 1C was repeated 100 times at 45°C. The ratio of the discharge capacity of the 100th discharge to the discharge capacity of the 1st discharge was then calculated and evaluated according to the following criteria. A higher discharge capacity ratio indicates better high-potential lifetime characteristics.

[0126] A: The ratio is over 85%.

[0127] B: The ratio is above 80% but less than 85%.

[0128] C: The ratio is above 75% but less than 80%.

[0129] D: The ratio is above 70% but less than 75%.

[0130] E: The ratio is less than 70%.

[0131] Low temperature output characteristics

[0132] The prepared secondary battery was charged to 4.7V using a constant current constant voltage (CCCV) method at 25°C to prepare battery cells. The prepared battery cells were then discharged to 3.0V using a constant current method at 0.2C and 1C at -20°C, and the capacity was calculated. Then, the discharge capacity retention rate, expressed as the ratio of capacitance (=(capacity at 1C / capacity at 0.2C)×100(%)), was calculated. These measurements were performed on five battery cells, and the average of the calculated discharge capacity retention rates was used as the output characteristic, evaluated according to the following criteria. A higher value indicates better output characteristics.

[0133] A: The average discharge capacity retention rate is over 85%.

[0134] B: The average discharge capacity retention rate is above 80% and less than 85%.

[0135] C: The average discharge capacity retention rate is above 75% and less than 80%.

[0136] D: The average discharge capacity retention rate is less than 75%.

[0137] The test results are shown in Table 2:

[0138] Table 2

[0139]

[0140]

[0141] As shown in Table 2, when the separator includes a polyolefin substrate and a coating on the substrate, and the coating includes boehmite, by using an electrolyte containing specific amounts of 1,3-propanesulfonate lactone, lithium difluorophosphate, 1,3,6-hexanetrionitrile, and boron-containing lithium salt, and setting the total content of 1,3-propanesulfonate lactone and 1,3,6-hexanetrionitrile in the electrolyte to a specific range, it is possible not only to improve the safety of the secondary battery, but also to significantly improve the high-potential life and low-temperature output characteristics of the secondary battery while maintaining high energy density.

[0142] In particular, when the electrolyte also contains other nitrile compounds, it can reduce the impedance of the coating and further improve the high-potential life and low-temperature output characteristics of the secondary battery.

[0143] In particular, when the electrolyte also contains other additives, the inventors unexpectedly discovered that these additives can inhibit the decomposition and regeneration of the coating during the charging and discharging process, thereby further improving the high-potential life and low-temperature output characteristics of the secondary battery.

[0144] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0145] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A secondary battery, characterized in that, It includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator includes a polyolefin substrate and a coating disposed on at least one surface of the substrate, the coating including boehmite; Based on the total mass of the electrolyte, the electrolyte satisfies: (I) Includes 1,3-propanesulfonic acid lactone in a content of 1.3 wt% or more and 2.7 wt% or less; (II) Includes lithium difluorophosphate in a content of 0.01 wt% or more and 2 wt% or less; (III) Includes 1,3,6-hexanetrionitriles in a content of 1.6 wt% or more and 3.9 wt% or less; (IV) Includes boron-containing lithium salts with a content of 0.01 wt% or more and 3 wt% or less; The total content of the 1,3-propanesulfonic acid lactone and the 1,3,6-hexanetrionitrile is more than 1.61 wt% and less than 6 wt%. The total content of the lithium difluorophosphate and the boron-containing lithium salt is more than 0.02 wt% and less than 5 wt%. The electrolyte also includes ethylene glycol di(propionitrile) ether.

2. The secondary battery according to claim 1, characterized in that, The boron-containing lithium salts include lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanoborate borate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(salicylate)borate, and lithium bis(catechol)borate. The lithium methoxytricyanoborate, lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetra(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, or lithium tetra(difluorophosphoryloxy)borate.

3. The secondary battery according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes lithium difluorophosphate in a content of more than 0.01 wt% and less than 0.11 wt%.

4. The secondary battery according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes lithium difluorophosphate in a content of more than 0.11 wt% and less than 0.59 wt%.

5. The secondary battery according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte, the electrolyte comprises 1,3,6-hexanetrionitrile in a content of more than 1.6 wt% and less than 2.8 wt%.

6. The secondary battery according to claim 1 or 2, characterized in that, The electrolyte also contains other nitrile compounds, including at least one selected from succinic anionyl nitrile, 1,2,3-tris(2-cyanoethoxy)propane, and 3-methyl-1,3,5-tris(cyanoethoxy)pentane; based on the total mass of the electrolyte, the content of the other nitrile compounds is more than 0.3 wt% and less than 8 wt%.

7. The secondary battery according to claim 6, characterized in that, The electrolyte includes succinic acid, and the content of succinic acid is more than 1.7 wt% and less than 5.5 wt% based on the total mass of the electrolyte.

8. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the content of ethylene glycol di(propionitrile) ether is 0.3 wt% or more and 0.9 wt% or less.

9. The secondary battery according to claim 6, characterized in that, The electrolyte contains 1,2,3-tris(2-cyanoethoxy)propane, and the content of 1,2,3-tris(2-cyanoethoxy)propane is more than 0.4 wt% and less than 2.3 wt% based on the total mass of the electrolyte.

10. The secondary battery according to claim 1 or 2, characterized in that, The electrolyte also includes other additives, including at least one of 2-ethyl-1-hexyl difluorophosphite, 4-methyl-2-pentyl difluorophosphite, pentyl difluorophosphite, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, vinyl sulfate, 1,3-propanediol cyclosulfonate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate; based on the total mass of the electrolyte, the content of the other additives is more than 0.01 wt% and less than 10 wt%.

11. The secondary battery according to claim 10, characterized in that, The electrolyte contains fluoroethylene carbonate, and the content of the fluoroethylene carbonate is more than 0.01 wt% and less than 3 wt% based on the total mass of the electrolyte.

12. The secondary battery according to claim 10, characterized in that, The electrolyte includes fluoroethylene carbonate, and the content of the fluoroethylene carbonate is 4.1 wt% or more and 6.9 wt% or less based on the total mass of the electrolyte.

13. The secondary battery according to claim 10, characterized in that, The electrolyte includes vinyl sulfate, and the content of vinyl sulfate is more than 0.01 wt% and less than 0.3 wt% based on the total mass of the electrolyte.

14. The secondary battery according to claim 10, characterized in that, The electrolyte includes 2-ethyl-1-hexyl difluorophosphite, and the content of 2-ethyl-1-hexyl difluorophosphite is more than 0.01 wt% and less than 1.4 wt% based on the total mass of the electrolyte.

15. An electronic device comprising a secondary battery according to any one of claims 1 to 14.

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