Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device, the secondary battery comprising an electrolyte and a separator, the separator comprising a polyolefin base material and a coating layer provided on at least one surface of the polyolefin base material, the coating layer comprising inorganic particles, and the electrolyte containing ether nitrile, butanedione, propionate and a lithium salt containing boron in specific amounts. By setting the total content of ether nitrile, butanedione and propionate in the electrolyte to a specific range, and setting the total content of butanedione and the lithium salt containing boron to a specific range, the present application inhibits the decomposition of ether nitrile and propionate, helps to form a stable coating film on the positive electrode surface, thereby not only improving the heat resistance of the separator, but also significantly improving the safety performance and vibration resistance of the secondary battery.

Description

[0001] This application is a divisional application of the patent application filed on June 14, 2024, with application number 2024107693283 and title "Secondary Battery and Electronic Device". Technical Field

[0002] This application relates to the field of energy storage, specifically 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, with the application of rechargeable batteries, issues such as lifespan and safety have been exposed. Therefore, consumers are placing higher demands on the overall performance of rechargeable batteries, such as simultaneously possessing high energy density, good high-temperature storage performance, cycle performance, and safety performance.

[0004] However, current traditional methods to improve the energy density of secondary batteries include increasing coating weight, increasing electrode compaction density, and increasing voltage. But while these methods improve the energy density of secondary batteries, they also reduce their safety performance. Therefore, ensuring the safety performance of high-energy-density secondary batteries is an urgent problem that the battery industry needs to solve. Summary of the Invention

[0005] The embodiments of this application address, to some extent, the problems existing in the prior art by adjusting the composition of the separator and the components of the electrolyte used in secondary batteries.

[0006] One embodiment of this application proposes a secondary battery, including an electrolyte and a separator; the separator includes a polyolefin substrate and a coating disposed on at least one surface of the polyolefin substrate, the coating including inorganic particles. Based on the total mass of the electrolyte, the electrolyte contains: (I) ether nitrile in a content of 0.01% by mass or more and 2% by mass or less, (II) succinate in a content of 0.01% by mass or more and 2% by mass or less, (III) propionate in a content of 25% by mass or more and 65% by mass or less, and (IV) boron-containing lithium salt in a content of 0.01% by mass or more and 3% by mass or less; the total content of the above ether nitrile, succinate and propionate is 25.02% by mass or more and 67.9% by mass or less, and the total content of the above succinate and boron-containing lithium salt is 0.02% by mass or more and 4.6% by mass or less. Boron-containing lithium salts include lithium tetrafluoroborate [CAS:14283-07-9], lithium difluorooxalate borate [CAS:409071-16-5], lithium bis(oxalate borate [CAS:244761-29-3], lithium tetracyanoborate [CAS:294867-26-8], lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate [CAS:390750-38-6], and lithium pentafluoroethyltrifluoroborate [CAS:390750-4]. 3-3], Lithium dicyanooxalate borate [CAS: 1390624-95-9], Lithium dimalonate borate [CAS: 291298-96-9], Lithium (2-fluoromalonate) difluoroborate [CAS: 1604746-55-5], Lithium malonate oxalate borate [CAS: 383187-24-4], Lithium bis(salicylate) borate [CAS: 161589-07-7], Lithium bis(catechol) borate [CAS: 156762- [86-6], Lithium methoxytricyanoborate, Lithium ethoxytricyanoborate [CAS:1390624-92-6], Lithium tetramethoxyborate [CAS:6867-35-2], Lithium tetraethoxyborate [CAS:66350-36-5], Lithium tetra(trifluoromethoxy)borate [CAS:291541-83-8], Lithium tetra(2,2,2-trifluoroethoxy)borate [CAS:291541-84-9], Polytetra(hydroquinoneoxy)lithium borate, Di(trifluoroboric acid) sulfate At least one of the following: lithium difluoroborate [CAS: 2295884-18-1], lithium difluoroborate [CAS: 288611-80-3], lithium difluoroborate dimethyl disulfonate [CAS: 1630816-00-0], lithium difluorophosphoroxy trifluoroborate [CAS: 1253288-53-7], lithium di(difluorophosphoroxy)difluoroborate [CAS: 1253288-56-0], or lithium tetra(difluorophosphoroxy)borate [CAS: 1253288-57-1].

[0007] The inventors discovered that coating inorganic particles onto a separator substrate can improve battery safety. When the electrolyte contains specific amounts of ether nitrile, succinic acid nitrile, propionate ester, and boron-containing lithium salts, a stable coating can be formed on the positive electrode surface. This not only improves the heat resistance of the separator but also significantly enhances the safety performance and vibration resistance of the secondary battery. Adding the aforementioned boron-containing lithium salts to the electrolyte results in a coating with excellent stability, further improving battery performance. The boron-containing lithium salts can be one type, or two or more types.

[0008] In some embodiments, the inorganic particles include at least one selected from aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, or antimony. Further, the inorganic particles are selected from at least one selected from alumina, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, or antimony trioxide. By coating the aforementioned inorganic particles onto the substrate of the separator, the safety of the battery can be significantly improved.

[0009] In some embodiments, the ether nitrile includes at least one selected from ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane. By adding the above-mentioned ether nitrile to the electrolyte, the swelling of the polyolefin substrate of the separator in the electrolyte can be suppressed.

[0010] In some embodiments, the propionate ester includes at least one selected from methyl propionate, ethyl propionate, propyl propionate, or butyl propionate. By adding the aforementioned propionate ester to the electrolyte, swelling of the polyolefin substrate of the separator in the electrolyte can be suppressed.

[0011] In some embodiments, the electrolyte includes ether nitrile in a content of 0.01% by mass and less than 1% by mass, based on the total mass of the electrolyte. By adjusting the content of ether nitrile in the electrolyte to within the above range, the swelling of the polyolefin substrate of the separator in the electrolyte can be further suppressed.

[0012] In some embodiments, the electrolyte includes ether nitrile at a content of 0.4% by mass or more and 0.8% by mass or less, based on the total mass of the electrolyte. By adjusting the content of ether nitrile in the electrolyte to within the above range, the swelling of the polyolefin substrate of the separator in the electrolyte can be further suppressed.

[0013] In some embodiments, the electrolyte includes succinic anionylene at a content of 1.2% by mass or more and 1.8% by mass or less, based on the total mass of the electrolyte. By adjusting the succinic anionylene content in the electrolyte within the above range, the heat resistance of the diaphragm and the suppression of heat generation during internal short circuits can be improved.

[0014] In some embodiments, the electrolyte includes propyl propionate in a concentration of 25% to 65% by mass, based on the total mass of the electrolyte. Adding propyl propionate to the electrolyte in a concentration within this range results in a coating with excellent stability and further improves battery performance.

[0015] In some embodiments, the electrolyte includes ethyl propionate in a concentration of 25% to 65% by mass, based on the total mass of the electrolyte. Adding ethyl propionate to the electrolyte in a concentration within this range results in a coating with excellent stability and further improves battery performance.

[0016] In some embodiments, the electrolyte comprises propyl propionate and ethyl propionate. Adding a mixture of propyl propionate and ethyl propionate to the electrolyte results in a more stable coating and further enhances battery performance.

[0017] In some embodiments, the electrolyte further comprises other nitrile compounds, including at least one selected from adiponitrile, cis-butenedionitrile, trans-butenedionitrile, 1,3,5-pentanetricarbonyl nitrile, 1,2,3-propanetricarbonyl nitrile, 1,3,6-hexanetricarbonyl nitrile, or 1,2,6-hexanetricarbonyl nitrile; the content of the other nitrile compounds is 0.1% by mass and 8% by mass or less based on the total mass of the electrolyte. These other nitrile compounds can improve the stability of the aforementioned coating, enhance lithium-ion charge transport, and improve vibration resistance.

[0018] In some embodiments, the adiponitrile content is 0.1% by mass or more and 1% by mass or less, based on the total mass of the electrolyte. By adjusting the adiponitrile content in the electrolyte to within the above range, the stability of the aforementioned coating can be further improved, lithium-ion charge transport can be enhanced, and vibration resistance can be improved.

[0019] In some embodiments, the adiponitrile content is 2.1% by mass or more and 4% by mass or less, based on the total mass of the electrolyte. By adjusting the adiponitrile content in the electrolyte to within the above range, the stability of the aforementioned coating can be further improved, lithium-ion charge transport can be enhanced, and vibration resistance can be improved.

[0020] In some embodiments, the content of 1,3,6-hexanetrionitrile is 0.3% by mass or more and 0.9% by mass or less, based on the total mass of the electrolyte. By adjusting the content of 1,3,6-hexanetrionitrile in the electrolyte within the above range, the stability of the aforementioned coating can be further improved, lithium-ion charge transport can be enhanced, and vibration resistance can be improved.

[0021] In some embodiments, the content of the aforementioned 1,3,6-hexanetricarbonyl nitrile is 1.7% by mass or more and 3.1% by mass or less, based on the total mass of the electrolyte. By adjusting the content of 1,3,6-hexanetricarbonyl nitrile in the electrolyte within the above range, the stability of the aforementioned coating can be further improved, lithium-ion charge transport can be enhanced, and vibration resistance can be improved.

[0022] In some embodiments, the electrolyte further includes other additives, including at least one of fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, 1,3-propanediol cyclosulfonate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane)phosphate, or tris(trimethylsilane)borate; the content of the other additives is 0.01% by mass or more and 10% by mass or less based on the total mass of the electrolyte. These other additives can inhibit the decomposition and regeneration of the coating formed by the reaction of the aforementioned substances (I) to (IV) with the active portion of the positive electrode surface during the charge-discharge process, thereby further reducing the positive electrode resistance and improving vibration resistance.

[0023] In some embodiments, the content of the aforementioned fluoroethylene carbonate is 0.01% by mass and 3% by mass or less, based on the total mass of the electrolyte. By adjusting the content of fluoroethylene carbonate in the electrolyte within the above range, vibration resistance characteristics can be improved.

[0024] In some embodiments, the content of the aforementioned fluoroethylene carbonate is 4.1% by mass and 6.9% by mass, based on the total mass of the electrolyte. By adjusting the content of fluoroethylene carbonate in the electrolyte within the above range, vibration resistance characteristics can be improved.

[0025] In some embodiments, the content of lithium difluorophosphate is 0.01% by mass and 0.3% by mass or less, based on the total mass of the electrolyte. By adjusting the content of lithium difluorophosphate in the electrolyte within the above range, vibration resistance characteristics can be improved.

[0026] In some embodiments, the content of vinyl sulfate is 0.01% by mass and 0.4% by mass, based on the total mass of the electrolyte. By adjusting the content of vinyl sulfate in the electrolyte to within the above range, vibration resistance characteristics can be improved.

[0027] Another aspect of this application provides an electronic device that includes the secondary battery described above.

[0028] Based on the secondary battery and electronic device of this application embodiment, since the ether nitrile and propionate in the electrolyte can inhibit the swelling of the polyolefin substrate in the electrolyte, but the presence of inorganic particles will catalyze the decomposition of ether nitrile and propionate on the positive electrode surface, the embodiments of this application add a specific amount of succinic anion and boron-containing lithium salt to the electrolyte so that it can just inhibit the decomposition of ether nitrile and propionate, forming a stable coating on the positive electrode surface, thereby not only improving the heat resistance of the separator, but also significantly improving the safety performance and vibration resistance of the secondary battery.

[0029] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0030] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0031] Secondary batteries

[0032] Unless otherwise expressly stated, the terms used in this application shall have the meanings indicated below.

[0033] By using a specific combination of separator composition and electrolyte, this application not only improves the heat resistance of the separator, but also significantly enhances the safety performance and vibration resistance of the secondary battery.

[0034] In one embodiment, the first aspect of this application provides a secondary battery, which includes an electrolyte, a separator, a positive electrode, and a negative electrode as described below.

[0035] I. Electrolyte

[0036] The electrolyte used in the secondary battery embodiments of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte includes ether nitrile, succinic acid nitrile, propionate ester, and boron-containing lithium salt.

[0037] The separator used in secondary batteries comprises a polyolefin substrate and a coating on the substrate. The addition of inorganic particles to the coating significantly improves the separator's heat resistance, thereby enhancing battery safety. The inventors unexpectedly discovered that ether nitrile and propionate in the electrolyte can inhibit the swelling of the polyolefin substrate in the electrolyte. However, the presence of inorganic particles catalyzes the decomposition of ether nitrile and propionate on the positive electrode surface. A specific amount of succinic anionylene and boron-containing lithium salt can precisely inhibit the decomposition of ether nitrile and propionate, forming a stable coating on the positive electrode surface. Using this design not only improves the separator's heat resistance but also significantly enhances the safety performance and vibration resistance of the secondary battery.

[0038] In some embodiments, the ether nitrile includes at least one selected from ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane. Due to the excellent stability of the formed coating, battery performance is further improved. Only one ether nitrile may be used, or two or more may be used. Ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, or 3-methyl-1,3,5-tris(cyanoethoxy)pentane are preferred.

[0039] Specifically, from the viewpoint of improving the heat resistance of the diaphragm, the content of ether nitrile, based on the total mass of the electrolyte, is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.4% by mass or more. Furthermore, as an upper limit for the mass content of ether nitrile, from the viewpoint of suppressing heat generation during internal short circuits, the mass content of ether nitrile is 2% by mass or less, preferably 1.9% by mass or less, more preferably 1.6% by mass or less, even more preferably 1.2% by mass or less, and particularly preferably 1% by mass or less. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[0040] In some embodiments, the content of ether nitrile is set as a1% by mass, where a1 is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 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, 0.05 to 0.1, 0.1 to 0.8, 0.5 to 1.2, 0.7 to 1.9. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[0041] Specifically, from the viewpoint of improving the heat resistance of the diaphragm, the mass content of succinic acid (SNA) based on the total mass of the electrolyte is 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.08% by mass or more. Furthermore, as an upper limit for the SNA mass content, from the viewpoint of suppressing heat generation during internal short circuits, the SNA mass content is 2% by mass or less, preferably 1.8% by mass or less, more preferably 1.6% by mass or less, even more preferably 1.4% by mass or less, and particularly preferably 1.2% by mass or less. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[0042] In some embodiments, the succinic acid content is set as a2% by mass, where a2 is 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 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, 0.05 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 suppress heat generation during internal short circuits.

[0043] In some embodiments, the propionate ester includes at least one selected from methyl propionate, ethyl propionate, propyl propionate, or butyl propionate. Only one type of propionate may be used, or two or more types may be used. Due to the excellent stability of the formed coating, battery performance is further improved; ethyl propionate and propyl propionate are preferred.

[0044] Specifically, from the viewpoint of improving the vibration resistance of secondary batteries, the propionate content, based on the total mass of the electrolyte, is 25% by mass or more, preferably 28% by mass or more, more preferably 30% by mass or more, and even more preferably 35% by mass or more. Furthermore, as an upper limit for the propionate content, from the viewpoint of suppressing heat generation during internal short circuits, the propionate content is 65% by mass or less, preferably 60% by mass or less, more preferably 56% by mass or less, even more preferably 53% by mass or less, and particularly preferably 48% by mass or less. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[0045] In some embodiments, the propionate content is set to a3% by mass, where a3 is 25, 28, 29, 30, 32, 33, 35, 39, 40, 42, 45, 48, 50, 53, 56, 60, 63, 65, or within a range consisting of any two of the above values. For example, 25 to 28, 28 to 36, 33 to 45, 40 to 53, 50 to 65, when within the above ranges, helps to further suppress heat generation during internal short circuits.

[0046] In some embodiments, boron-containing lithium salts include lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium tetracyanoborate, (3-methyl-2,4-pentanedione)oxalate borate (MOAB), lithium tetra(trifluoromethyl)borate, lithium (trifluoromethyl)trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyltrifluoroborate, lithium dicyanooxalate borate, lithium bis(malonate)borate, lithium (2-fluoromalonate)difluoroborate, lithium malonate oxalate borate, lithium bis(catechol)borate, and lithium bis(catechol)borate. At least one of lithium boron salts, including lithium methoxytricyanoborate, lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetra(trifluoromethoxy)borate, lithium tetra(2,2,2-trifluoroethoxy)borate, lithium polytetrafluoro(hydroquinoneoxy)borate, lithium di(trifluoroborate)sulfate, lithium difluoroborate, lithium methane disulfonate difluoroborate, lithium difluorophosphoryloxytrifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate, or lithium tetra(difluorophosphoryloxy)borate, is used. 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), lithium difluorooxalatoborate (LiDFOB), or (3-methyl-2,4-pentanedione) oxalatoborate ester (MOAB).

[0048] Specifically, from the viewpoint of improving the vibration resistance characteristics of secondary batteries, the mass content of boron-containing lithium salt, based on the total mass of the electrolyte, is 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.06% by mass or more, and even more preferably 0.1% by mass or more. Furthermore, as an upper limit for the mass content of boron-containing lithium salt, from the viewpoint of suppressing heat generation during internal short circuits, the mass content of boron-containing lithium salt is 3% by mass or less, preferably 2.3% by mass or less, more preferably 1.5% by mass or less, even more preferably 1.1% by mass or less, and particularly preferably 0.7% by mass or less. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[0049] In some embodiments, the content of the boron-containing lithium salt is set to a4% by mass, 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 consisting 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 range, it helps to further suppress heat generation during internal short circuits.

[0050] Furthermore, from the viewpoint of suppressing heat generation during internal short circuits, based on the electrolyte mass, the total mass content of (I) ether nitrile, (II) succinate, and (III) propionate is 25.02% by mass or more, preferably 30.3% by mass or more. In addition, the upper limit for the total content of (I) ether nitrile, (II) succinate, and (III) propionate is 67.9% by mass or less, preferably 58.3% by mass or less.

[0051] In some embodiments, the total mass content of (I) ether nitrile, (II) succinate, and (III) propionate is a1+a2+a3 mass%, where a1+a2+a3 is 25.02, 28.18, 30.3, 35.6, 39.9, 43.2, 49.7, 55, 58.3, 62.6, 67.9, or within any two of the above values. For example, 25.02 to 39.9, 28.18 to 49.7, 30.3 to 55, 35.6 to 58.3, and 39.9 to 67.9, when within the above ranges, helps to further suppress heat generation during internal short circuits.

[0052] Furthermore, from the viewpoint of suppressing heat generation during internal short circuits, based on the electrolyte mass, the total mass content of (II) succinic acid and (IV) boron-containing lithium salt is 0.02% by mass or more, preferably 0.12% by mass or more. In addition, the upper limit of the total content of (II) succinic acid and (IV) boron-containing lithium salt is 4.6% by mass or less, preferably 3.9% by mass or less.

[0053] In some embodiments, the total mass content of (II) succinic anion and (IV) boron-containing lithium salt is a2+a4 mass%, where a2+a4 is 0.02, 0.12, 0.26, 0.5, 1, 1.5, 2.3, 2.9, 3.9, 4.6, or within a range of any two of the above values. For example, 0.02 to 0.12, 0.12 to 0.5, 0.26 to 1.5, 1 to 2.9, 1.5 to 4.6. When within the above ranges, it helps to further suppress heat generation during internal short circuits.

[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, enhance lithium-ion charge transport, and improve vibration resistance.

[0055] Other nitrile compounds include at least one of adiponitrile, cis-butenedionitrile, trans-butenedionitrile, 1,3,5-pentanetricarbonyl nitrile, 1,2,3-propanetricarbonyl nitrile, 1,3,6-hexanetricarbonyl nitrile, or 1,2,6-hexanetricarbonyl nitrile. There may be only one or more of the aforementioned other nitrile compounds.

[0056] Specifically, from the viewpoint of improving the vibration resistance of the secondary battery, based on the total mass of the electrolyte, the content of other nitrile compounds is 0.1% by mass or more, preferably 0.3% by mass or more, more preferably 0.6% by mass or more, further preferably 0.9% by mass or more, and particularly preferably 1.4% by mass or more. Furthermore, from the viewpoint of suppressing internal short-circuit heat release, as an upper limit for the content of other nitrile compounds, the content of other nitrile compounds is 8% by mass or less, preferably 7.9% by mass or less, more preferably 7.1% by mass or less, further preferably 6.2% by mass or less, and particularly preferably 5.3% by mass or less.

[0057] In some embodiments, the total content of other nitrile compounds is b% by mass, where b is 0.1, 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, 0.1 to 7.1, 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 vibration resistance characteristics of the secondary battery.

[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 coating formed by the reaction of the aforementioned substances (I) to (IV) with the active part of the positive electrode surface during the charging and discharging process, thereby further reducing the positive electrode resistance and improving the vibration resistance characteristics.

[0059] Other additives include at least one of the following: fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 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 vibration resistance, based on the total mass of the electrolyte, the content of other additives is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1.6% by mass or more, and more preferably 2.8% by mass or more.

[0061] Furthermore, from the viewpoint of improving vibration resistance, the content of other additives is 10% by mass or less, preferably 9.7% by mass or less, more preferably 8.2% by mass or less, even more preferably 7.1% by mass or less, and particularly preferably 6.7% by mass or less.

[0062] In some embodiments, the total content of other additives is c% by mass, 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, values ​​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, help to further improve vibration resistance characteristics.

[0063] 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 9-15% by mass, preferably 9-13% by mass, and more preferably 9-12% by mass. By setting the content within the above range, the effect of improving high-temperature and low-temperature characteristics can be more balanced.

[0064] The electrolyte of this application may further comprise any non-aqueous solvent known in the prior art that can be used as an electrolyte solvent. Examples include chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, and chain ethers. Chain carboxylic acid esters, such as ethyl acetate and ethyl fluorocarbonate, are preferred.

[0065] II. Diaphragm

[0066] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0067] In some embodiments, from the viewpoint of improving the heat resistance of the diaphragm, the diaphragm includes a polyolefin substrate and a coating on the substrate, the coating including inorganic particles.

[0068] In some embodiments, the polyolefin is polyethylene or polypropylene. The separator may also be a material formed by laminating the above materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0069] Specifically, the metallic element in the inorganic particles includes at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, or antimony. For example, the inorganic particles may be selected from at least one of alumina, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, or antimony trioxide.

[0070] 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.

[0071] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0072] III. Positive electrode

[0073] 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.

[0074] 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.

[0075] For example, as the positive electrode active material for a secondary battery, a composite metal oxide of lithium containing one or more selected from the group consisting of cobalt, manganese, and nickel, or a lithium-containing olivine-type phosphate containing one or more selected from iron, cobalt, nickel, and manganese is used. These positive electrode active materials can be used alone or in combination of two or more.

[0076] As such a lithium composite metal oxide, for example, those selected from LiCoO2, LiMn2O4, LiNiO2, LiCo 1-x Ni x O2 (0.01 < x < 1), LiNi x Mn y Co z O2 (x + y + z = 1), a solid solution of 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 FexPO4 (0.01 < x < 1), and more preferably two or more. A part of these composite metal oxides of lithium or lithium-containing olivine-type phosphates 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.

[0077] As the voltage during charging, from the viewpoint 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.

[0078] The conductive agent for the positive electrode is not particularly limited as long as it is an electron-conducting material that does not cause a chemical change. Examples include natural graphite (such as flake graphite), artificial graphite, etc., graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, or carbon black such as 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% by mass, and particularly preferably 1.5 to 5% by mass.

[0079] The positive electrode can be manufactured as follows: The above-mentioned positive electrode active material is mixed with conductive agents such as acetylene black and carbon black, and binders such as polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, copolymer of styrene and butadiene, and carboxymethyl cellulose. A high-boiling-point solvent such as 1-methyl-2-pyrrolidone is added and the mixture is kneaded to form a positive electrode slurry. This slurry is then coated onto aluminum foil or other materials used as a positive electrode current collector, dried, and pressurized to form a positive electrode slurry layer.

[0080] The density of the portion of the positive electrode excluding the positive current collector is typically 3.5 g / cm³. 3 In order to further improve the battery capacity, a value of 3.8 g / cm³ is preferred. 3 The above, more preferably 4g / cm 3 The above is further optimized to 4.1 g / cm³. 3 That's all. Furthermore, as an upper limit, 4.6 g / cm³ is preferred. 3 the following.

[0081] There are no particular limitations on the type of positive electrode current collector; it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may 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.

[0082] 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.

[0083] 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.

[0084] IV. Negative electrode

[0085] 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.

[0086] 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.

[0087] Carbon-based anode active materials refer to active materials with a carbon-based backbone that can insert lithium. Examples of carbon-based anode active materials include carbonaceous materials and graphitic materials.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0093] In addition, the negative electrode active material can be used alone or in combination of two or more in any ratio.

[0094] 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.

[0095] 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.

[0096] The negative electrode can be prepared by the following method: 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.

[0097] Electronic devices

[0098] A second aspect of this application provides an electronic device that includes a secondary battery as described in this application.

[0099] 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.

[0100] 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.

[0101] Example: Preparation and performance testing of secondary batteries

[0102] The following are examples of non-aqueous electrolytes of this application, but this application is not limited to these examples.

[0103] 1. Positive electrode production

[0104] Lithium cobalt oxide (97% by mass) and acetylene black (1.5% by mass) were mixed and added to a solution obtained by dissolving polyacrylonitrile (1.5% by mass) in 1-methyl-2-pyrrolidone, and then mixed to prepare a positive electrode paste. This positive electrode paste was then coated onto one side of an aluminum foil (current collector), dried, pressurized, and cut to the specified size to fabricate the positive electrode.

[0105] 2. Negative electrode fabrication

[0106] Artificial graphite and silicon carbon (mass ratio 90:10, totaling 96% by mass) and styrene-butadiene rubber (2% by mass) were mixed and added to a solution obtained by dissolving lithium carboxymethyl cellulose (2% by mass) in deionized water, and then mixed to prepare a negative electrode paste. This negative electrode paste was coated onto one side of a copper foil (current collector), dried, pressurized, and then cut to the specified size to fabricate the negative electrode.

[0107] 3. Diaphragm fabrication

[0108] A 5μm porous polyethylene membrane was used as the diaphragm substrate. Deionized water and the inorganic particles listed in Table 1-1 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 an inorganic particle slurry with a solid content of 3%, wherein the inorganic particles accounted for 2% of the total weight of the slurry, and sodium carboxymethyl cellulose accounted for 1% of the total weight of the slurry. The inorganic particle slurry was then coated onto one side of the 5μm porous polyethylene membrane using a printing coating method and dried to obtain the diaphragm with an inorganic particle layer thickness of 1.5μm.

[0109] 4. Electrolyte preparation

[0110] LiPF6, serving as the supporting electrolyte, was dissolved in a solution containing (I) ether nitrile, (II) succinate, (III) propionate, (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 1-2 and 1-3. The content of LiPF6 was 14%, with the remainder being ethylene carbonate and propylene carbonate (mass ratio 1.2:1).

[0111] 5. Battery manufacturing

[0112] The positive and negative electrodes, as prepared above, are each connected to a wire. The electrodes are then layered and wound using the aforementioned separator. The wound assembly, along with 3.2g of electrolyte, is then housed within an aluminum laminated casing. The opening of the casing is heat-sealed, and a secondary battery is manufactured through formation and capacity testing. This secondary battery is a pouch-shaped secondary battery with a width of 35mm, a height of 48mm, and a thickness of 5mm.

[0113] Table 1-1 Types of diaphragms

[0114] Diaphragm number Inorganic particulate components Diaphragm 1 Alumina Diaphragm 2 Boehmite Diaphragm 3 Alumina and boehmite (mass ratio 1:1.2) Diaphragm 4 Magnesium hydroxide Diaphragm 5 Magnesium hydroxide and boehmite (mass ratio 1:1.2) Diaphragm 6 Titanium dioxide Diaphragm 7 Zirconium dioxide Diaphragm 8 Niobium trioxide Diaphragm 9 Indium trioxide Diaphragm 10 Tungsten trioxide Diaphragm 11 Tin dioxide Diaphragm 12 Antimony trioxide Diaphragm 13 none

[0115] Table 1-2 Electrolyte Types

[0116]

[0117]

[0118] *In the table above: a1 represents the content of (I) ether nitrile, a2 represents the content of (II) succinic anion, a3 represents the content of (III) propionate, a4 represents the total content of (IV) boron-containing lithium salt, b represents the total content of other nitrile compounds, and c represents the total content of other additives.

[0119] Table 1-3 Electrolyte Component Codes

[0120] 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 1,3,6-hexanetricarbonitrile B6 Lithium tetrakis(2,2,2-trifluoroethoxy)borate N6 cis-butenedionitrile B7 Lithium bis(trifluoromethyl)difluoroborate N7 trans-butenedionitrile B8 Lithium dicyanooxalate borate N8 1,3,5-pentanetricarbonyl nitrile B9 Dilithium di(trifluoroboronic acid) sulfate P1 Propyl propionate B10 Lithium malonate oxalate oxalate borate P2 Ethyl propionate C1 Fluoroethylene carbonate C7 fluorobenzene C2 Lithium difluorophosphate C8 Cyclohexylbenzene C3 vinyl sulfate C9 Biphenyl 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

[0121] 6. Testing Methods

[0122] According to Table 2, the electrolytes prepared using electrolytes numbered 1 to 35 in the above steps were matched with the membranes prepared using membranes numbered 1 to 12 to prepare secondary batteries, resulting in Examples 1 to 35; the electrolytes prepared using electrolytes numbered 36 to 43 in the above steps were matched with the membrane prepared using membrane 1 to prepare secondary batteries, resulting in Comparative Examples 1 to 8; the electrolyte prepared using electrolyte 43 in the above steps was matched with the membrane prepared using membrane 13 to prepare secondary batteries, resulting in Comparative Example 9; and the electrolyte prepared using electrolyte 1 in the above steps was matched with the membrane prepared using membrane 13 to prepare secondary batteries, resulting in Comparative Example 10.

[0123] The secondary batteries prepared in Examples 1 to 35 and Comparative Examples 1 to 9 were tested for their heat resistance, safety, and vibration resistance using the following methods. The test results are shown in Table 2.

[0124] 6.1 Heat Shrinkage Resistance Test in Electrolyte

[0125] The negative electrode and separator obtained in the examples and comparative examples were cut into slices 50 mm wide and 50 mm long. The negative electrode slices and separator slices were overlapped and pressed using a roller press under conditions of 10 kN / m load and 80°C to obtain a test piece integrating the negative electrode slices and separator slices.

[0126] The test piece and the electrolyte specified above were sealed in a laminated packaging material to obtain the sample. The amount of electrolyte was set to be 4 g / Ah relative to the negative electrode capacity. After heating the obtained sample at 140°C for 1 hour, the laminated packaging material was opened and the test piece was removed. The dimensions of the diaphragm on the test piece were measured. Based on the area A0 of the diaphragm before heating and the area A1 of the diaphragm after heating, the shrinkage rate of the diaphragm ((A0-A1) / A0)×100 (%) was calculated.

[0127] A: Shrinkage rate is less than 0.5%.

[0128] B: Shrinkage rate is greater than 0.5% and less than 1.0%.

[0129] C: Shrinkage rate is greater than 1.0% and less than 5.0%.

[0130] D: Shrinkage rate is 5.0% or more but less than 10.0%.

[0131] E: Shrinkage rate is above 10.0%.

[0132] 6.2 Safety Test for Suppression of Heat Exhaust During Internal Short Circuit (Forced Internal Short Circuit Test)

[0133] The secondary batteries prepared in the examples and comparative examples were subjected to constant current (CC-CV) charging at 0.2C (upper limit cell voltage 4.6V) and constant current (CC-CV) discharging at 0.2C to 3.0V. This 0.2C charge-discharge cycle was repeated three times. Then, under an atmosphere of 25°C, the batteries were charged at a charge rate of 0.2C using constant voltage-constant current (CC-CV) to 4.6V (termination condition: 0.02C). Then, near the center of the secondary battery, a 3mm diameter, 10cm long iron nail was forcibly short-circuited by penetrating it at a speed of 5m / min. This forced short-circuiting was performed on five secondary batteries prepared using the same procedure, and the batteries were evaluated according to the following criteria based on the number of test specimens that did not rupture or ignite. The greater the number of test specimens that did not rupture or ignite, the better the heat release suppression performance of the secondary battery during internal short circuit.

[0134] A: The number of test subjects that did not rupture or catch fire was 4 or 5.

[0135] B: The number of test subjects that did not crack or catch fire was 3.

[0136] C: The number of test subjects that did not crack or catch fire was 2.

[0137] D: The number of test subjects that neither cracked nor caught fire is 1 or 0.

[0138] 6.3 Capacity retention test after vibration test

[0139] For the secondary batteries obtained in the examples and comparative examples, a charge-discharge test was performed five times, consisting of charging to 4.6V at 60°C using a constant current method with a charging rate of 0.1C, followed by discharging to 3.0V at a discharging rate of 0.1C. The discharge capacity of the fifth cycle was taken as the initial capacity. Next, the secondary battery was fixed on a sieve with an inner diameter of 200mm and vibrated for 1 hour using a Ro-tap type sieve vibrator. The same charge-discharge test as described above was then performed, and the discharge capacity after the vibration test was measured. The ratio of the discharge capacity after the vibration test to the initial discharge capacity was calculated as the capacity retention rate. The larger this value, the less capacity loss caused by the vibration test.

[0140] A: Capacity retention rate is over 95%.

[0141] B: Capacity retention rate is above 90% and below 95%.

[0142] C: Capacity retention rate is above 85% and less than 90%.

[0143] D: Capacity retention rate is less than 85%.

[0144] Table 2

[0145]

[0146]

[0147] 7. Test Results

[0148] As shown in Table 2 above, in Examples 1 to 35, when the separator includes a polyolefin substrate and the coating on the separator substrate includes inorganic particles, the electrolyte contains specific amounts of ether nitrile, succinic acid ester, propionate, and boron-containing lithium salt provided in this application. The total content of ether nitrile, succinic acid ester, and propionate in the electrolyte is set to a specific range, and the total content of succinic acid ester and boron-containing lithium salt is set to a specific range. By using this design, not only can the heat resistance of the separator be improved, but the safety performance and vibration resistance of the secondary battery can also be significantly improved.

[0149] In particular, using a mixture of propyl propionate and ethyl propionate in the electrolyte can significantly improve heat resistance. Furthermore, when the contents of ether nitrile, succinic acid, propionate, and boron-containing lithium salt in the electrolyte are within the ranges provided in this application, the resulting secondary battery separator exhibits good heat resistance and significantly improves the safety performance and vibration resistance of the secondary battery.

[0150] In particular, when the electrolyte also contains other nitrile compounds, the impedance of the coating can be reduced, further improving the safety performance and vibration resistance of the secondary battery. Furthermore, when the mass content of other nitrile compounds in the electrolyte meets the above-mentioned range, the impedance of the coating can be further reduced, improving vibration resistance.

[0151] 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 charge and discharge, thereby further improving the safety performance and vibration resistance of the secondary battery. Specifically, when the mass content of other additives in the electrolyte meets the aforementioned range, it can further inhibit the decomposition and regeneration of the coating during charge and discharge, thereby significantly improving the safety performance and vibration resistance of the secondary battery.

[0152] 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.

[0153] 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, Includes positive electrode, negative electrode, electrolyte, and separator; The diaphragm includes a polyolefin substrate and a coating disposed on at least one surface of the polyolefin substrate, the coating including inorganic particles; the inorganic particles are selected from at least one of alumina, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, or antimony trioxide; Based on the total mass of the electrolyte, the electrolyte contains: (I) Etheronitriles with a content of 0.01% by mass or more and 2% by mass or less (II) Butadionitrile with a content of 0.01% by mass or more and 2% by mass or less (III) Propionate esters with a content of 25% by mass or more and 65% by mass or less (IV) Boron-containing lithium salts with a content of 0.01% by mass or more and 3% by mass or less; The total content of the ether nitrile, the succinic anion, and the propionate is 25.02% by mass or more and 67.9% by mass or less, and the total content of the succinic anion and the boron-containing lithium salt is 0.02% by mass or more and 4.6% by mass or less. 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. At least one of 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. The electrolyte further comprises other nitrile compounds, including at least one of adiponitrile, cis-butenedionitrile, trans-butenedionitrile, 1,3,5-pentanetricarbonyl, 1,2,3-propanetricarbonyl, 1,3,6-hexanetricarbonyl or 1,2,6-hexanetricarbonyl.

2. The secondary battery according to claim 1, characterized in that, The ether nitrile includes at least one selected from ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, or 1,2,5-tris(cyanoethoxy)pentane.

3. The secondary battery according to claim 1, characterized in that, The propionate includes at least one of methyl propionate, ethyl propionate, propyl propionate, or butyl propionate.

4. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes ether nitrile in a content of more than 0.01% by mass and less than 1% by mass.

5. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes ether nitrile in a content of more than 0.4% by mass and less than 0.8% by mass.

6. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes succinate in a content of 1.2% by mass or more and 1.8% by mass or less.

7. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes propyl propionate in a content of 25% by mass or more and 65% by mass or less.

8. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the electrolyte includes ethyl propionate in a content of 25% by mass or more and 65% by mass or less.

9. The secondary battery according to claim 1, characterized in that, The electrolyte includes propyl propionate and ethyl propionate.

10. The secondary battery according to claim 1, characterized in that, Based on the total mass of the electrolyte, the content of the other nitrile compounds is 0.3% by mass or more and 7.9% by mass or less.

11. The secondary battery according to claim 10, characterized in that, The electrolyte includes adiponitrile, and the content of adiponitrile is more than 0.1% by mass and less than 1% by mass based on the total mass of the electrolyte.

12. The secondary battery according to claim 10, characterized in that, The electrolyte comprises adiponitrile, and the content of adiponitrile is more than 2.1% by mass and less than 4% by mass based on the total mass of the electrolyte.

13. The secondary battery according to claim 10, characterized in that, The electrolyte comprises 1,3,6-hexanetricarbonyl nitrile, and the content of 1,3,6-hexanetricarbonyl nitrile is 0.3% by mass or more and 0.9% by mass or less, based on the total mass of the electrolyte.

14. The secondary battery according to claim 10, characterized in that, The electrolyte comprises 1,3,6-hexanetricarbonyl nitrile, and the content of 1,3,6-hexanetricarbonyl nitrile is more than 1.7% by mass and less than 3.1% by mass based on the total mass of the electrolyte.

15. The secondary battery according to claim 1, characterized in that, The electrolyte further includes other additives, including at least one selected from the following: fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, 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% by mass and less than 10% by mass.

16. The secondary battery according to claim 15, characterized in that, The electrolyte includes fluoroethylene carbonate, and the content of fluoroethylene carbonate is more than 0.01% by mass and less than 3% by mass based on the total mass of the electrolyte.

17. The secondary battery according to claim 15, characterized in that, The electrolyte includes fluoroethylene carbonate, and the content of the fluoroethylene carbonate is 4.1% by mass or more and 6.9% by mass or less, based on the total mass of the electrolyte.

18. The secondary battery according to claim 15, characterized in that, The electrolyte includes lithium difluorophosphate, and the content of lithium difluorophosphate is more than 0.01% by mass and less than 0.3% by mass based on the total mass of the electrolyte.

19. The secondary battery according to claim 15, characterized in that, The electrolyte includes vinyl sulfate, and the content of vinyl sulfate is more than 0.01% by mass and less than 0.4% by mass based on the total mass of the electrolyte.

20. An electronic device, characterized in that, Includes the secondary battery according to any one of claims 1 to 19.

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