Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device, the secondary battery including an electrolyte and a separator, the separator including a polyolefin substrate and a coating layer disposed on at least one surface of the polyolefin substrate, the coating layer including inorganic particles, the electrolyte containing specific amounts of ether nitrile, butanedinitrile, propionate, and a boron-containing lithium salt. The total content of ether nitrile, butanedinitrile and propionate in the electrolyte is set to be in a specific range, the total content of butanedinitrile and boron-containing lithium salt is set to be in a specific range, decomposition of ether nitrile and propionate is inhibited, and formation of a stable coating film on the surface of the positive electrode is facilitated, so that the heat resistance of the diaphragm can be improved, and the service life of the diaphragm is prolonged. And the safety performance and the vibration resistance of the secondary battery can also be obviously improved.

Description

[0001] This application is a divisional application of a patent application with an application date of June 14, 2024, application number 2024107693283, and invention name “Secondary battery and electronic device”. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a secondary battery and an electronic device. Background Art

[0003] Secondary batteries have the advantages of high energy storage density, high open circuit voltage, low self-discharge rate, long cycle life, and good safety, and are widely used in various fields such as portable power storage, electronic equipment, and electric vehicles. However, with the application of secondary batteries, they have exposed problems such as life and safety. Therefore, consumers have higher requirements for the comprehensive performance of secondary batteries, such as high energy density, good high-temperature storage performance, cycle performance, and safety performance.

[0004] However, the current traditional methods for improving the energy density of secondary batteries include increasing the coating weight, increasing the compaction density of the electrode, and increasing the voltage. However, the above methods reduce the safety performance of the secondary battery while increasing the energy density of the secondary battery. Therefore, for high-energy-density secondary batteries, how to ensure their safety performance is an urgent problem that the battery industry needs to solve. Summary of the invention

[0005] The embodiments of the present application solve the problems existing in the prior art to some extent by adjusting the composition of the separator used in the secondary battery and the components in the electrolyte.

[0006] In one aspect, an embodiment of the present application provides a secondary battery, comprising 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 inorganic particles. Based on the total mass of the electrolyte, the electrolyte contains: (I) ether nitrile having a content of 0.01 mass % or more and 2 mass % or less, (II) succinonitrile having a content of 0.01 mass % or more and 2 mass % or less, (III) propionate having a content of 25 mass % or more and 65 mass % or less, (IV) boron-containing lithium salt having a content of 0.01 mass % or more and 3 mass % or less; the total content of the above-mentioned ether nitrile, succinonitrile and the above-mentioned propionate is 25.02 mass % or more and 67.9 mass % or less, and the total content of the above-mentioned succinonitrile and the above-mentioned boron-containing lithium salt is 0.02 mass % or more and 4.6 mass % or less. Boron-containing lithium salts include lithium tetrafluoroborate [CAS: 14283-07-9], lithium difluorooxalatoborate [CAS: 409071-16-5], lithium bis(oxalatoborate) [CAS: 244761-29-3], lithium tetracyanoborate [CAS: 294867-26-8], lithium tetrakis(trifluoromethyl)borate, lithium (trifluoromethyl) trifluoroborate, lithium bis(trifluoromethyl) difluoroborate [CAS: 390750-38-6], lithium pentafluoroethyl trifluoroborate [CAS: 390750-4 3-3], lithium dicyanooxalatoborate [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 di(salicylate) borate [CAS: 161589-07-7], lithium di(catecholate) 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 tetrakis(trifluoromethoxy)borate [CAS: 291541-83-8], lithium tetrakis(2,2,2-trifluoroethoxy)borate [CAS: 291541-84-9], lithium polytetrakis(hydroquinone)borate, di(trifluoroboric acid) sulfate ) dilithium [CAS: 2295884-18-1], lithium difluoroborate [CAS: 288611-80-3], methanedisulfonato lithium difluoroborate [CAS: 1630816-00-0], difluorophosphoryloxy lithium trifluoroborate [CAS: 1253288-53-7], bis(difluorophosphoryloxy) lithium difluoroborate [CAS: 1253288-56-0] or tetrakis(difluorophosphoryloxy) lithium borate [CAS: 1253288-57-1].

[0007] The inventors found that coating inorganic particles on the diaphragm substrate can improve the safety of the battery. When the electrolyte contains a specific amount of ether nitrile, succinonitrile, propionate and boron-containing lithium salt, a stable coating can be formed on the positive electrode surface, which can not only improve the heat resistance of the diaphragm, but also significantly improve the safety performance and vibration resistance of the secondary battery. When the above-mentioned boron-containing lithium salt is added to the electrolyte, the stability of the coating formed is excellent, and the battery performance is further improved. The boron-containing lithium salt can be only one, or it can be more than two or more than three.

[0008] In some embodiments, the inorganic particles include at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc or antimony. Further, the inorganic particles are selected from at least one of aluminum oxide, 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 above inorganic particles on the substrate of the diaphragm, the safety of the battery can be significantly improved.

[0009] In some embodiments, the ether nitrile includes at least one of 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 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 of methyl propionate, ethyl propionate, propyl propionate or butyl propionate. By adding the propionate ester to the electrolyte, the swelling of the polyolefin substrate of the separator in the electrolyte can be suppressed.

[0011] In some embodiments, the electrolyte includes ether nitrile in an amount of 0.01 mass % or more and 1 mass % or less based on the total mass of the electrolyte. By adjusting the content of ether nitrile in the electrolyte 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 in an amount of 0.4 mass % or more and 0.8 mass % or less based on the total mass of the electrolyte. By adjusting the content of ether nitrile in the electrolyte 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 succinonitrile in an amount of 1.2 mass % or more and 1.8 mass % or less based on the total mass of the electrolyte. By adjusting the content of succinonitrile in the electrolyte within the above range, the heat resistance of the separator can be improved and heat generation during internal short circuit can be suppressed.

[0014] In some embodiments, the electrolyte includes propyl propionate in an amount of 25 mass % or more and 65 mass % or less based on the total mass of the electrolyte. When propyl propionate is added to the electrolyte in an amount within the above range, the stability of the formed coating is excellent, and the battery performance is further improved.

[0015] In some embodiments, the electrolyte includes ethyl propionate in an amount of 25 mass % or more and 65 mass % or less based on the total mass of the electrolyte. When ethyl propionate is added to the electrolyte in an amount within the above range, the stability of the formed coating is excellent, and the battery performance is further improved.

[0016] In some embodiments, the electrolyte includes propyl propionate and ethyl propionate. When a mixture of propyl propionate and ethyl propionate is added to the electrolyte, the stability of the formed coating is more excellent, and the battery performance is further improved.

[0017] In some embodiments, the electrolyte further comprises other nitrile compounds, including at least one of adiponitrile, cis-butylene dinitrile, trans-butylene dinitrile, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexatriconitrile or 1,2,6-hexatriconitrile; based on the total mass of the electrolyte, the content of the other nitrile compounds is 0.1% by mass or more and 8% by mass or less. Other nitrile compounds can improve the stability of the aforementioned coating, improve lithium ion charge transfer, and improve vibration resistance.

[0018] In some embodiments, the content of adiponitrile is greater than 0.1 mass % and less than 1 mass % based on the total mass of the electrolyte. By adjusting the content of adiponitrile in the electrolyte within the above range, the stability of the coating can be further improved, the lithium ion charge transfer can be improved, and the vibration resistance can be improved.

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

[0020] In some embodiments, based on the total mass of the electrolyte, the content of the 1,3,6-hexanetricarboxylic acid nitrile is greater than 0.3 mass % and less than 0.9 mass %. By adjusting the content of the 1,3,6-hexanetricarboxylic acid nitrile in the electrolyte within the above range, the stability of the aforementioned coating can be further improved, the lithium ion charge transfer can be improved, and the vibration resistance characteristics can be improved.

[0021] In some embodiments, the content of 1,3,6-hexanetricarboxylic acid nitrile is 1.7 mass % or more and 3.1 mass % or less based on the total mass of the electrolyte. By adjusting the content of 1,3,6-hexanetricarboxylic acid nitrile in the electrolyte within the above range, the stability of the aforementioned coating can be further improved, the lithium ion charge transfer can be improved, and the vibration resistance characteristics 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-propane sultone, 1,3-propylene sultone, vinyl sulfate, 1,3-propylene glycol cyclosulfate, 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 0.01% by mass or more and 10% by mass or less. Other additives can inhibit the decomposition and regeneration of the aforementioned (I) to (IV) substances in the charge and discharge process by reacting with the active part of the positive electrode surface to form a coating, thereby further reducing the positive electrode resistance and improving the vibration resistance characteristics.

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

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

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

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

[0027] Another aspect of an embodiment of the present application provides an electronic device, which includes the secondary battery described above in the present application.

[0028] Based on the secondary battery and electronic device of the embodiment of the present application, 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 the ether nitrile and propionate on the positive electrode surface, the embodiment of the present application adds a specific amount of succinonitrile and boron-containing lithium salt to the electrolyte, so that the decomposition of the ether nitrile and propionate is just inhibited, and a stable coating is formed on the positive electrode surface, thereby not only improving the heat resistance of the diaphragm, but also significantly improving the safety performance and vibration resistance of the secondary battery.

[0029] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0031] Secondary battery

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

[0033] The present application uses a specific combination of a separator structure and an electrolyte solution. This design can not only improve the heat resistance of the separator, but also significantly improve the safety performance and vibration resistance characteristics of the secondary battery.

[0034] In one embodiment, a first aspect of the embodiment of the present 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 of the embodiment of the present application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte includes ether nitrile, succinonitrile, propionate, and boron-containing lithium salt.

[0037] The diaphragm used in the secondary battery includes a polyolefin substrate and a coating on the substrate. The addition of inorganic particles to the coating can significantly improve the heat resistance of the diaphragm, thereby improving the safety of the battery. The inventor unexpectedly discovered that 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 the ether nitrile and propionate on the positive electrode surface, and a specific amount of succinonitrile and boron-containing lithium salt can just inhibit the decomposition of the ether nitrile and propionate, forming a stable coating on the positive electrode surface. By using this design, not only can the heat resistance of the diaphragm be improved, but also the safety performance and vibration resistance of the secondary battery can be significantly improved.

[0038] In some embodiments, the ether nitrile includes at least one of 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 film, the battery performance is further improved. As an ether nitrile, it can be only one or more than two. Preferably, ethylene glycol di(propionitrile) ether, 1,2,3-tris(2-cyanoethoxy) propane or 3-methyl-1,3,5-tris(cyanoethoxy) pentane.

[0039] Specifically, from the viewpoint of improving the heat resistance of the separator, the content of ether nitrile is 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and further preferably 0.4% by mass or more, based on the total mass of the electrolyte. In addition, as the upper limit of the mass content of ether nitrile, from the viewpoint of suppressing heat generation during internal short circuit, 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, further preferably 1.2% by mass or less, and particularly preferably 1% by mass or less. When within the above range, it helps to further suppress heat generation during internal short circuit.

[0040] In some embodiments, the content of ether nitrile is set to a1 mass %, and 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 in the 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 it is within the above range, it helps to further suppress the heat generation during internal short circuit.

[0041] Specifically, from the viewpoint of improving the heat resistance of the separator, based on the total mass of the electrolyte, the mass content of succinonitrile is 0.01 mass % or more, preferably 0.03 mass % or more, more preferably 0.05 mass % or more, and further preferably 0.08 mass % or more. In addition, as the upper limit of the mass content of succinonitrile, from the viewpoint of suppressing heat generation during internal short circuit, the mass content of succinonitrile is 2 mass % or less, preferably 1.8 mass % or less, more preferably 1.6 mass % or less, further preferably 1.4 mass % or less, and particularly preferably 1.2 mass % or less. When within the above range, it helps to further suppress heat generation during internal short circuit.

[0042] In some embodiments, the content of succinonitrile is set to a2 mass %, and 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 in the 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 range, it helps to further suppress the heat generation during the internal short circuit.

[0043] In some embodiments, the propionate ester includes at least one of methyl propionate, ethyl propionate, propyl propionate or butyl propionate. The propionate ester may be only one or more than two. Since the stability of the formed film is excellent, the battery performance is further improved, and ethyl propionate and propyl propionate are preferred.

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

[0045] In some embodiments, the content of propionate is set to a3 mass %, and 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 range, it helps to further suppress heat generation during internal short circuit.

[0046] In some embodiments, the boron-containing lithium salt includes lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium tetracyanoborate, (3-methyl-2,4-pentanedione) oxalatoborate (MOAB), lithium tetrakis(trifluoromethyl)borate, lithium (trifluoromethyl) trifluoroborate, lithium bis(trifluoromethyl) difluoroborate, lithium pentafluoroethyl trifluoroborate, lithium dicyanoborate, lithium bismalonate borate, lithium (2-fluoromalonate) difluoroborate, lithium malonate oxalatoborate, lithium di(salicylate)borate, di(catecholate) borate At least one of lithium borate, methoxy tricyanoborate, ethoxy tricyanoborate, tetramethoxyborate, tetraethoxyborate, tetrakis(trifluoromethoxy)borate, tetrakis(2,2,2-trifluoroethoxy)borate, polytetrakis(hydroquinone oxygen)borate, dilithium sulfate (trifluoroborate), lithium difluoroborate, methanedisulfonate difluoroborate, difluorophosphoryloxy trifluoroborate, di(difluorophosphoryloxy) difluoroborate or tetrakis(difluorophosphoryloxy)borate, at this time, the stability of the formed film is excellent, and the battery performance is further improved. The boron-containing lithium salt can be only one, or two or more, or three or more.

[0047] In some embodiments, the boron-containing lithium salt preferably includes at least one of lithium tetrafluoroborate, lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), or (3-methyl-2,4-pentanedione) oxalatoborate (MOAB).

[0048] Specifically, from the viewpoint of improving the vibration resistance of the secondary battery, based on the total mass of the electrolyte, the mass content of the boron-containing lithium salt is 0.01% by mass or more, preferably 0.02% by mass or more, more preferably 0.06% by mass or more, and further preferably 0.1% by mass or more. In addition, as the upper limit of the mass content of the boron-containing lithium salt, from the viewpoint of suppressing heat generation during internal short circuit, the mass content of the 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, further preferably 1.1% by mass or less, and particularly preferably 0.7% by mass or less. When within the above range, it helps to further suppress heat generation during internal short circuit.

[0049] In some embodiments, the content of the boron-containing lithium salt is set to a4 mass %, and 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, such as 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 circuit.

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

[0051] In some embodiments, the total mass content of (I) ether nitrile, (II) succinonitrile and (III) propionate is a1+a2+a3 mass %, and 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 in the range consisting of 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, 39.9 to 67.9. When it is within the above range, it helps to further suppress the heat generation during internal short circuit.

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

[0053] In some embodiments, the total mass content of (II) succinonitrile and (IV) boron-containing lithium salt is a2+a4 mass%, and a2+a4 is 0.02, 0.12, 0.26, 0.5, 1, 1.5, 2.3, 2.9, 3.9, 4.6, or in the range consisting 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 it is within the above range, it helps to further suppress the heat generation during internal short circuit.

[0054] In addition, the electrolyte may also include other nitrile compounds. The inventors have also unexpectedly discovered that other nitrile compounds can improve the stability of the aforementioned coating, enhance lithium ion charge transfer, and improve vibration resistance.

[0055] The other nitrile compounds include at least one of adiponitrile, cis-butenedinitrile, trans-butenedinitrile, 1,3,5-pentanetricarboxylonitrile, 1,2,3-propanetricarboxylonitrile, 1,3,6-hexatricarboxylonitrile or 1,2,6-hexatricarboxylonitrile. The other nitrile compounds may be only one or more.

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

[0057] In some embodiments, the total content of other nitrile compounds is b mass %, and 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 in the 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 range, 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 have also unexpectedly discovered that other additives can inhibit the decomposition and regeneration of the aforementioned (I) to (IV) substances that react with the active parts of the positive electrode surface to form a film during the charge and discharge process, thereby further reducing the positive electrode resistance and improving the vibration resistance.

[0059] Other additives include at least one of fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, 1,3-propylene glycol cyclosulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane)phosphate or tris(trimethylsilane)borate. The other additives may be only one or more.

[0060] Specifically, from the viewpoint of improving vibration resistance, the content of other additives is 0.01 mass % or more, preferably 0.1 mass % or more, preferably 1.6 mass % or more, and more preferably 2.8 mass % or more, based on the total mass of the electrolyte.

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

[0062] In some embodiments, the total content of other additives is c mass %, and 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 the range consisting of any two of the above values. For example, 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, it helps to further improve the vibration resistance characteristics.

[0063] The lithium salt used in the electrolyte of the present application includes lithium hexafluorophosphate, and the content of lithium hexafluorophosphate is 9 to 15% by mass, preferably 9 to 13% by mass, and more preferably 9 to 12% by mass based on the total mass of the electrolyte. By setting the content range as above, the effect of improving high temperature and low temperature characteristics can be more balanced.

[0064] The electrolyte of the present application may further contain any non-aqueous solvent known in the prior art that can be used as a solvent for the electrolyte, such as chain carbonate, cyclic carboxylic acid ester, chain carboxylic acid ester, cyclic ether, chain ether. Chain carboxylic acid ester is preferred, such as ethyl acetate, ethyl fluoroacetate.

[0065] II. Diaphragm

[0066] In order to prevent short circuit, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by infiltrating the separator.

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

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

[0069] Specifically, the metal 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 are selected from at least one of aluminum oxide, 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 may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. In the thin film form, 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: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with alumina particles having a particle size (Dv90) of 90% less than 1 μm.

[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 range, 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 mixture layer disposed on a surface of the positive electrode current collector.

[0074] The positive electrode mixture layer contains positive electrode active material, and the positive electrode mixture layer can be one layer or multiple layers. The positive electrode active material is any material that can reversibly insert and release 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), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn 1-x FexPO4 (0.01 < x < 1), and more preferably two or more of them. A part of these composite metal oxides of lithium or lithium-containing olivine-type phosphates can be replaced with other elements, or a part of cobalt, nickel, manganese, and iron can be replaced 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 made according to the following method: the above-mentioned positive electrode active material is mixed with a conductive agent such as acetylene black, carbon black, and a binder such as polytetrafluoroethylene, polyvinylidene fluoride, polyacrylonitrile, a copolymer of styrene and butadiene, and carboxymethyl cellulose, and a high-boiling point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to form a positive electrode mixture slurry, which is then applied to an aluminum foil of a positive electrode current collector, etc., dried, and pressed to form a positive electrode mixture layer, thereby making it.

[0080] The density of the positive electrode excluding the positive electrode current collector is usually 3.5 g / cm 3 In order to further increase the capacity of the battery, it is preferably 3.8 g / cm 3 More preferably 4 g / cm 3 More preferably, 4.1 g / cm 3 In addition, the upper limit is preferably 4.6 g / cm 3 the following.

[0081] The type of positive electrode current collector is not particularly limited, and 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, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0082] In order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode mixture layer, the surface of the positive electrode current collector may include a conductive additive or a conductive coating. Examples of conductive additives may 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 an inorganic oxide, a conductive agent, and a binder.

[0083] The positive electrode can be made by forming a positive electrode mixture layer containing a positive electrode active material and a binder on the positive electrode current collector. The manufacture of the positive electrode using the positive electrode active material can be carried out by conventional methods, that is, the positive electrode active material and the binder, as well as the conductive material and the thickener as needed, are dry-mixed to form a sheet, and the obtained sheet is pressed onto the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode mixture layer on the positive electrode current collector, thereby obtaining a positive electrode.

[0084] IV. Negative electrode

[0085] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the surface of the negative electrode current collector, wherein the negative electrode mixture layer contains a negative electrode active material. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent lithium metal from being accidentally precipitated on the negative electrode during charging.

[0086] The negative electrode active material is not particularly limited, and examples thereof include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials obtained by combining these.

[0087] Carbon-Based Negative Electrode Active Material Here, the carbon-based negative electrode active material refers to an active material having a carbon-based skeleton into which lithium can be inserted. Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0088] As carbonaceous materials, for example, graphitizable carbon, non-graphitizable carbon with amorphous structure represented by glassy carbon, etc. can be cited. Here, as graphitizable carbon, for example, carbon materials obtained from petroleum or coal using tar pitch as raw material can be cited. When giving specific examples, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers can be cited. In addition, as non-graphitizable carbon, for example, phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), hard carbon, etc. can be cited.

[0089] Furthermore, as graphite materials, for example, natural graphite, artificial graphite, etc. can be cited. Among them, as artificial graphite, for example: artificial graphite obtained by heat-treating carbon containing graphitized carbon mainly at 2800°C or above, graphite MCMB obtained by heat-treating MCMB at 2000°C or above, graphite mesophase pitch-based carbon fiber obtained by heat-treating mesophase pitch-based carbon fiber at 2000°C or above, etc. can be cited. In addition, in the present application, as a carbon-based negative electrode active material, natural graphite (amorphous coated natural graphite) in which at least a portion of its surface is coated with amorphous carbon can be used.

[0090] In addition, the metal-based negative electrode active material is an active material containing a metal, generally referring to an active material having an element capable of inserting lithium or alloying with lithium in the structure, and a theoretical current capacity of 500 mAh / g or more per unit mass when inserting lithium or alloying with lithium. As a metal-based negative electrode active material, for example, lithium metal, a single metal that can form a lithium alloy (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and its alloy, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. can be used. Among them, as a metal-based negative electrode active material, an active material containing silicon (silicon-based negative electrode active material) is preferably used. This is because the use of a silicon-based negative electrode active material can increase the capacity of a lithium-ion secondary battery.

[0091] Examples of the silicon-based negative electrode active material include silicon (Si), alloys containing silicon, silicon oxides, and composites of a silicon-containing material and conductive carbon in which a silicon-containing material is coated with conductive carbon or composited with conductive carbon.

[0092] From the viewpoint of improving battery capacity, a silicon-carbon material, for example, a porous carbon-supported silicon composite material is preferred.

[0093] The negative electrode active material may be used alone or in combination of two or more at any ratio.

[0094] The negative electrode mixture layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the solvent used in the electrolyte or electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0095] As the negative electrode current collector for holding the negative electrode active material, any known current collector can be used. Examples of the negative electrode current collector include, but are not limited to, metal 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 applying a negative electrode mixture slurry containing a negative electrode active material, a resin binder, etc. on a negative electrode current collector, drying it, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode current collector, thereby obtaining a negative electrode.

[0097] Electronic Devices

[0098] A second aspect of the embodiments of the present application provides an electronic device, which includes the secondary battery described in the present application.

[0099] The use of the secondary battery of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the secondary battery of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0100] The preparation of the secondary battery is described below in conjunction with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0101] Preparation and performance testing of secondary batteries

[0102] Examples of the nonaqueous electrolyte solution of the present application are shown below, but the present application is not limited to these examples.

[0103] 1. Cathode production

[0104] The positive electrode active material lithium cobalt oxide (97 mass%) and acetylene black (1.5 mass%) were mixed, added to a solution prepared by dissolving polyacrylonitrile (1.5 mass%) in 1-methyl-2-pyrrolidone in advance, and mixed to prepare a positive electrode mixture paste. The positive electrode mixture paste was applied to one side of an aluminum foil (current collector), dried, pressurized, and then cut into a specified size to prepare a positive electrode.

[0105] 2. Negative electrode preparation

[0106] The negative electrode active material artificial graphite and silicon carbon (mass ratio 90:10, total 96 mass%) and styrene-butadiene rubber (2 mass%) were mixed and added to a solution obtained by dissolving lithium carboxymethyl cellulose (2 mass%) in deionized water in advance and mixed to prepare a negative electrode mixture paste. The negative electrode mixture paste was applied to one side of a copper foil (current collector), dried, pressurized, and then cut into a specified size to make a negative electrode.

[0107] 3. Diaphragm production

[0108] A 5 μm polyethylene porous film was used as a diaphragm substrate; deionized water and inorganic particles in Table 1-1 were added to a double planetary mixer and dispersed at high speed for 1 hour at 40°C; then a binder, sodium carboxymethyl cellulose, was added and stirred at low speed for 1 hour at room temperature 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 the sodium carboxymethyl cellulose accounted for 1% of the total weight of the slurry. Then, the inorganic particle slurry was coated on one side of the 5 μm polyethylene porous film by printing and coating, and dried to obtain a diaphragm with an inorganic particle layer thickness of 1.5 μm.

[0109] 4. Preparation of electrolyte

[0110] LiPF6 as a supporting electrolyte is dissolved in a solution containing (I) ether nitrile, (II) succinonitrile, (III) propionate, (IV) boron-containing lithium salt, other nitrile compounds, and other additives. Based on 100 parts by weight of the total mass of the electrolyte, the contents and components of (I) to (IV), other nitrile compounds, and other additives are shown in Tables 1-2 and 1-3, with the content of LiPF6 being 14%, and the rest being ethylene carbonate and propylene carbonate (mass ratio 1.2:1).

[0111] 5. Battery production

[0112] The positive electrode and negative electrode prepared as above are connected to the lead wires respectively. The layers are wound via the above-mentioned separator. Then, the wound body is stored in an aluminum laminated shell together with 3.2g of electrolyte. The opening of the shell is heat-sealed, and a secondary battery is made through the steps of formation and capacity. The secondary battery is a bag-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 No. Inorganic particle 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 Types of electrolytes

[0116]

[0117]

[0118] *In the above table: a1 represents (I) the content of ether nitrile, a2 represents (II) the content of succinonitrile, a3 represents (III) the content of propionate, a4 represents (IV) the total content of 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 code

[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 bis(oxalatoborate) N3 3-Methyl-1,3,5-tri(cyanoethoxy)pentane B4 Lithium tetracyanoborate N4 Adiponitrile B5 Lithium Tetramethoxyborate N5 1,3,6-hexanetricarbonitrile B6 Lithium tetrakis(2,2,2-trifluoroethoxy)borate N6 Cis-Butene dinitrile B7 Lithium bis(trifluoromethyl)difluoroborate N7 Trans-Butene dinitrile B8 Lithium dicyanoborate N8 1,3,5-Pentatricarboxynitrile B9 Dilithium bis(trifluoroborate) sulfate P1 Propyl Propionate B10 Lithium Malonate Oxalate Borate P2 Ethyl propionate C1 Fluoroethylene carbonate C7 Fluorobenzene C2 Lithium difluorophosphate C8 Cyclohexylbenzene C3 Vinyl Sulfate C9 Biphenyl C4 Vinylene carbonate C10 Tris(trimethylsilyl)phosphate C5 1,3-Propane sultone C11 Tris(trimethylsilyl)borate C6 1,3-Propene sultone C12 Lithium Fluorosulfate

[0121] 6. Test Methods

[0122] According to Table 2, the electrolytes numbered electrolytes 1 to 35 prepared in the above steps were matched with the diaphragms numbered 1 to 12, and secondary batteries were respectively prepared to obtain Examples 1 to 35; the electrolytes numbered electrolytes 36 to 43 prepared in the above steps were matched with the diaphragms numbered 1, and secondary batteries were respectively prepared to obtain Comparative Examples 1 to 8; the electrolyte numbered electrolyte 43 prepared in the above steps was matched with the diaphragm numbered 13, and a secondary battery was prepared to obtain Comparative Example 9; the electrolyte numbered electrolyte 1 prepared in the above steps was matched with the diaphragm numbered 13, and a secondary battery was prepared to obtain Comparative Example 10.

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

[0124] 6.1 Thermal shrinkage resistance test in electrolyte

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

[0126] Seal the test piece and the electrolyte specified above in a laminated packaging material to obtain a sample. The amount of electrolyte is set to 4 g / Ah relative to the negative electrode capacity. After heating the obtained sample at 140°C for 1 hour, unseal the laminated packaging material and take out the test piece. Measure the size of the diaphragm on the test piece. Based on the area A0 of the diaphragm before heating and the area A1 of the diaphragm after heating, calculate the shrinkage rate of the diaphragm ((A0-A1) / A0)×100(%).

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

[0128] B: The shrinkage rate is 0.5% or more and less than 1.0%.

[0129] C: The shrinkage rate is 1.0% or more and less than 5.0%.

[0130] D: The shrinkage rate is 5.0% or more and less than 10.0%.

[0131] E: The shrinkage rate is 10.0% or more.

[0132] 6.2 Safety test of heat release suppression during internal short circuit (forced internal short circuit test)

[0133] The secondary batteries made in the examples and comparative examples were charged by CC-CV at a constant current method of 0.2C (the upper limit of the battery cell voltage was 4.6V), and CC discharged to 3.0V at a constant current method of 0.2C. The 0.2C charge and discharge were repeated 3 times. Then, in an atmosphere of 25°C, the battery was charged to 4.6V by constant voltage and constant current (CC-CV) at a charge rate of 0.2C (termination condition: 0.02C). Then, near the center of the secondary battery, an iron nail with a diameter of 3mm and a length of 10cm was penetrated at a speed of 5m / min to force it to short-circuit. This forced short-circuiting was performed on 5 secondary batteries made by the same operation, and the evaluation was performed according to the following criteria based on the number of test bodies that did not rupture or catch fire. The more test bodies that did not rupture or catch fire, the better the heat release suppression performance of the secondary battery during internal short circuit.

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

[0135] B: The number of test pieces that neither cracked nor caught fire was 3.

[0136] C: The number of test pieces that neither cracked nor caught fire was 2.

[0137] D: The number of test pieces that did not crack or catch fire was 1 or 0.

[0138] 6.3 Capacity retention test after vibration test

[0139] For the secondary batteries obtained in the embodiments and comparative examples, the following cycle charge and discharge test was repeated 5 times. The above cycle is to charge to 4.6V at 60°C by constant current method with a charge rate of 0.1C, and then discharge to 3.0V at a discharge rate of 0.1C. The discharge capacity for the 5th time is taken as the initial capacity. Next, the secondary battery is fixed on a sieve with an inner diameter of 200mm, and after vibrating for 1 hour with a Ro-tap type sieve oscillator, the same charge and discharge test as above is carried out to measure the discharge capacity after the vibration test. The ratio of the discharge capacity after the vibration test to the initial discharge capacity is calculated as the capacity retention rate. The larger the value, the less the capacity reduction caused by the vibration test.

[0140] A: The capacity retention rate is 95% or more.

[0141] B: The capacity retention rate is 90% or more and less than 95%.

[0142] C: The capacity retention rate is 85% or more and less than 90%.

[0143] D: The 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 diaphragm includes a polyolefin substrate and the coating on the diaphragm substrate includes inorganic particles, the electrolyte contains a specific amount of ether nitrile, succinonitrile, propionate, and boron-containing lithium salt provided in the present application, and the total content of ether nitrile, succinonitrile and propionate in the above electrolyte is set to a specific range, and the total content of succinonitrile and boron-containing lithium salt is set to a specific range. By using this design, not only the heat resistance of the diaphragm can be improved, but also the safety performance and vibration resistance characteristics of the secondary battery can be significantly improved.

[0149] In particular, the use of a mixture of propyl propionate and ethyl propionate in the electrolyte can significantly improve heat resistance. Further, when the content of ether nitrile, succinonitrile, propionate and boron-containing lithium salt in the electrolyte is within the above range provided in the present application, the obtained secondary battery separator has good heat resistance and significantly improves the safety performance and vibration resistance of the secondary battery.

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

[0151] In particular, when the electrolyte also contains other additives, the inventors unexpectedly discovered that the other additives can inhibit the decomposition and regeneration of the coating during the charge and discharge process, thereby further improving the safety performance and vibration resistance of the secondary battery. In particular, the mass content of other additives in the electrolyte satisfies the above range, which can further inhibit the decomposition and regeneration of the coating during the charge and discharge process, thereby significantly improving the safety performance and vibration resistance of the secondary battery.

[0152] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics in the present application may be combined in one or more embodiments or examples in any suitable manner.

[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 limitations on the present application, and that changes, substitutions and modifications may 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: Including positive electrode, negative electrode, electrolyte and separator; The separator includes a polyolefin substrate and a coating disposed on at least one surface of the polyolefin substrate, wherein the coating includes inorganic particles; Based on the total mass of the electrolyte, the electrolyte contains: (I) ether nitrile in an amount of 0.01% by mass or more and 2% by mass or less, (II) succinonitrile in an amount of 0.01% by mass or more and 2% by mass or less, (III) a propionic acid ester having a content of 25% by mass or more and 65% by mass or less, (IV) a boron-containing lithium salt having a content of 0.01 mass % to 3 mass %; The total content of the ether nitrile, the succinonitrile and the propionate is 25.02 mass % or more and 67.9 mass % or less, and the total content of the succinonitrile and the boron-containing lithium salt is 0.02 mass % or more and 4.6 mass % or less; The boron-containing lithium salts include lithium tetrafluoroborate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium tetracyanoborate, lithium tetrakis(trifluoromethyl)borate, lithium (trifluoromethyl) trifluoroborate, lithium bis(trifluoromethyl)difluoroborate, lithium pentafluoroethyl trifluoroborate, lithium dicyanooxalatoborate, lithium bismalonate borate, lithium (2-fluoromalonate) difluoroborate, lithium malonate oxalatoborate, lithium bis(salicylate)borate, lithium bis(catecholate)borate, At least one of lithium methoxytricyanoborate, lithium ethoxytricyanoborate, lithium tetramethoxyborate, lithium tetraethoxyborate, lithium tetrakis(trifluoromethoxy)borate, lithium tetrakis(2,2,2-trifluoroethoxy)borate, lithium polytetrakis(hydroquinone)borate, lithium di(trifluoroborate) sulfate, lithium difluoroborate, lithium methanedisulfonate difluoroborate, lithium difluorophosphoryloxy trifluoroborate, lithium di(difluorophosphoryloxy)difluoroborate or lithium tetrakis(difluorophosphoryloxy)borate; The electrolyte further includes other additives, and the other additives include at least one of fluoroethylene carbonate, vinylene carbonate, lithium difluorophosphate, lithium fluorosulfonate, 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, 1,3-propylene glycol cyclosulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate or tris(trimethylsilyl)borate.

2. The secondary battery according to claim 1, characterized in that: The inorganic particles include at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc or antimony.

3. The secondary battery according to claim 1, characterized in that: The inorganic particles are selected from at least one of aluminum oxide, 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.

4. The secondary battery according to claim 1, characterized in that: The ether nitrile includes at least one of 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.

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

6. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes ether nitrile in an amount of 0.01 mass % or more and 1 mass % or less based on the total mass of the electrolyte.

7. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes ether nitrile in an amount of 0.4 mass % or more and 0.8 mass % or less based on the total mass of the electrolyte.

8. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes succinonitrile in an amount of 1.2 mass % or more and 1.8 mass % or less based on the total mass of the electrolyte.

9. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes propyl propionate in an amount of 25 mass % or more and 65 mass % or less based on the total mass of the electrolyte.

10. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes ethyl propionate in an amount of 25 mass % or more and 65 mass % or less based on the total mass of the electrolyte.

11. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte includes propyl propionate and ethyl propionate.

12. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte further comprises other nitrile compounds, and the other nitrile compounds include at least one of adiponitrile, cis-butenedinitrile, trans-butenedinitrile, 1,3,5-pentanetricarboxylonitrile, 1,2,3-propanetricarboxylonitrile, 1,3,6-hexatricarboxylonitrile or 1,2,6-hexatricarboxylonitrile; The content of the other nitrile compound is 0.1 mass % or more and 8 mass % or less based on the total mass of the electrolyte.

13. The secondary battery according to claim 12, characterized in that: The electrolyte includes adiponitrile, and the content of the adiponitrile is 0.1 mass % or more and 1 mass % or less based on the total mass of the electrolyte.

14. The secondary battery according to claim 12, characterized in that: The electrolyte includes adiponitrile, and the content of the adiponitrile is 2.1 mass % or more and 4 mass % or less based on the total mass of the electrolyte.

15. The secondary battery according to claim 12, characterized in that: The electrolyte includes 1,3,6-hexanetricarboxylic acid nitrile, and the content of the 1,3,6-hexanetricarboxylic acid nitrile is 0.3 mass % or more and 0.9 mass % or less based on the total mass of the electrolyte.

16. The secondary battery according to claim 12, characterized in that: The electrolyte includes 1,3,6-hexanetricarboxylic acid nitrile, and the content of the 1,3,6-hexanetricarboxylic acid nitrile is 1.7 mass % or more and 3.1 mass % or less based on the total mass of the electrolyte.

17. The secondary battery according to claim 1 or 2, characterized in that: The content of the other additives is 0.01 mass % or more and 10 mass % or less based on the total mass of the electrolyte.

18. The secondary battery according to claim 17, characterized in that: The electrolyte includes fluoroethylene carbonate, and the content of the fluoroethylene carbonate is 0.01 mass % or more and 3 mass % or less based on the total mass of the electrolyte.

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

20. The secondary battery according to claim 17, characterized in that: The electrolyte includes lithium difluorophosphate, and the content of the lithium difluorophosphate is 0.01 mass % or more and 0.3 mass % or less based on the total mass of the electrolyte.

21. The secondary battery according to claim 17, characterized in that: The electrolyte includes vinyl sulfate, and the content of the vinyl sulfate is 0.01 mass % or more and 0.4 mass % or less based on the total mass of the electrolyte.

22. An electronic device, characterized in that: Includes the secondary battery according to any one of claims 1 to 21.

Images