Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. The secondary battery comprises a positive electrode, a negative electrode and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode material layer, wherein the positive electrode material layer comprises a first material layer and a second material layer; the second material layer is arranged between the positive electrode current collector and the first material layer; the first material layer comprises lithium cobalt oxide, the lithium cobalt oxide comprises a first element, and the first element comprises magnesium, titanium and aluminum; and the second material layer comprises an inorganic additive. The electrolyte comprises a tricarbonitrile compound. Based on the total mass of the positive electrode material, the mass content of the first element is n1, wherein 800 ppm≤n1≤10000 ppm.

Description

Secondary battery and electronic device Technical Field

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, also known as rechargeable batteries, are batteries that can be repeatedly charged and discharged. Lithium-ion batteries, due to their compact size and light weight, are widely used in portable electronic devices, electric vehicles, and other fields. With the advancement of technology and improvements in living standards, the use of lithium-ion batteries in daily life has become more diverse, and people's demand for their performance has also continued to increase. Summary of the Invention

[0003] In view of this, the present application provides a secondary battery and an electronic device, which produce a synergistic effect by combining lithium cobalt oxide and inorganic additives in the positive electrode plate with additives in the electrolyte to jointly improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0004] In a first aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode material layer, the positive electrode material layer comprising a first material layer and a second material layer, the second material layer being disposed between the positive electrode current collector and the first material layer; the first material layer comprises lithium cobalt oxide, the lithium cobalt oxide comprising a first element, the first element comprising magnesium, titanium, and aluminum; the second material layer comprises an inorganic additive; the electrolyte comprises a trinitrile compound; and the mass content of the first element, based on the total mass of the positive electrode material, is n1, where 800 ppm ≤ n1 ≤ 10,000 ppm.

[0005] The inorganic additives contained in the positive electrode of the secondary battery provided in the present application and the lithium cobalt oxide added with magnesium, titanium and aluminum elements strengthen its structure. When combined with the trinitrile compound with an appropriate content in the electrolyte, they can play a synergistic role to improve the stability of the positive electrode material and improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0006] In some embodiments, the secondary battery satisfies the following conditions: based on the total mass of the positive electrode material, the mass content of the first element is n1, 800ppm≤n1≤10000ppm. Exemplarily, the mass content of the first element n1 is selected from 800ppm, 1000ppm, 1785ppm, 2651ppm, 3637ppm, 4924ppm, 6182ppm, 6658ppm, 7000ppm, 7771ppm, 8233ppm, 10000ppm or a range consisting of any two of the above values. When the mass content of the first element in the positive electrode material meets the above range, the high temperature storage performance and penetration resistance of the secondary battery can be further improved.

[0007] In some embodiments, the inorganic additive includes a second element, and the second element includes at least one of chromium, zirconium, lanthanum, niobium, indium, tin, zinc, or antimony. Inorganic additives that meet this condition can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0008] In some embodiments, the second element includes indium, tin, and antimony, which can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0009] In some embodiments, the lithium cobalt oxide includes tungsten. Adding tungsten to the lithium cobalt oxide can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0010] In some embodiments, the trinitrile compound includes at least one of 1,3,5-pentanetricarboxylic acid nitrile, 1,2,3-propanetricarboxylic acid nitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 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.

[0011] In some embodiments, the secondary battery satisfies the following condition: among the first elements, the mass content ratio of magnesium, titanium, and aluminum is 1:(0.8-1.2):(1.5-2). This ratio of magnesium, titanium, and aluminum can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0012] In order to further improve the high-temperature storage performance and penetration resistance of the secondary battery, the secondary battery in this application satisfies: 1000ppm≤n1≤7000ppm.

[0013] In some embodiments, based on the total mass of the positive electrode material, the mass content of the second element is n2, 1ppm≤n2≤6000ppm. The second element at this mass content can closely cooperate with the electrolyte in the inorganic additive, exert a good enhancement effect, ensure the high temperature storage performance of the secondary battery and reduce the penetration resistance. Exemplarily, the mass content n2 of the second element is selected from 1ppm, 641ppm, 1356ppm, 1940ppm, 2446ppm, 3384ppm, 3992ppm, 4922ppm, 5152ppm, 5935ppm, 6000ppm or a range consisting of any two of the above values.

[0014] In some embodiments, when the second element includes indium, tin, and antimony, the mass ratio of indium, tin, and antimony is 1:(0.6-1.4):(0.6-1.4). This ratio of indium, tin, and antimony can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0015] In some embodiments, based on the total mass content of the positive electrode material, the mass content of the tungsten element is n3, 5ppm≤n3≤1000ppm. By controlling the mass content of the tungsten element, the high-temperature storage performance and penetration resistance of the secondary battery can be further improved. Exemplarily, the mass content n3 of the third element is selected from 5ppm, 124ppm, 213ppm, 338ppm, 406ppm, 544ppm, 630ppm, 754ppm, 886ppm, 1000ppm, or a range consisting of any two of the above values.

[0016] In some embodiments, the negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a silicon-based material. A secondary battery meeting the above conditions can further improve the high-temperature storage performance of the secondary battery.

[0017] In some embodiments, the electrolyte further includes lithium bis(oxalatoborate), and the mass content of lithium bis(oxalatoborate) is 0.01% to 2% based on the mass of the electrolyte. By further adding lithium bis(oxalatoborate) to the electrolyte for coordination, it is beneficial to further improve the high temperature storage performance and penetration resistance of the secondary battery. Exemplarily, based on the mass of the electrolyte, the mass content of lithium bis(oxalatoborate) is selected from 0.01%, 0.24%, 0.42%, 0.61%, 0.82%, 1.14%, 1.24%, 1.48%, 1.63%, 1.89%, 2% or a range consisting of any two of the above values.

[0018] In some embodiments, the electrolyte further comprises phosphazene, and the mass content of phosphazene is 0.01% to 1.5% based on the mass of the electrolyte. The addition of an appropriate amount of phosphazene can further improve the high-temperature storage performance and penetration resistance of the secondary battery. Exemplarily, the mass content of phosphazene is selected from 0.01%, 0.17%, 0.34%, 0.53%, 0.61%, 0.85%, 0.94%, 1.20%, 1.23%, 1.46%, 1.5%, or a range consisting of any two of the above values, based on the mass of the electrolyte.

[0019] In some embodiments, the weight percentage of the trinitrile compound is 0.1% to 6% based on the weight of the electrolyte. Secondary batteries meeting this condition have better high-temperature storage performance and lower penetration resistance. For example, the weight percentage of the trinitrile compound is selected from 0.1%, 0.8%, 1.4%, 2.0%, 2.8%, 3.5%, 4.2%, 5.0%, 5.5%, 6%, or a range consisting of any two of these values, based on the weight of the electrolyte.

[0020] In a second aspect, the present application further provides an electronic device comprising any one of the above-mentioned secondary batteries.

[0021] The secondary battery and electronic device provided in this application have the following beneficial effects:

[0022] In the present application, magnesium, titanium and aluminum elements are added to lithium cobalt oxide to strengthen its structure. When combined with inorganic additives and trinitrile compounds with appropriate content in the electrolyte, they can play a synergistic role in improving the stability of the positive electrode material. The trinitrile compound can form a uniform protective film at the positive electrode interface in the present application, and cooperate with the first material layer and the second material layer in the positive electrode to stabilize the positive electrode and the electrolyte, so that the secondary battery has better high-temperature storage performance and lower penetration resistance. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0024] To address the problems in the prior art, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode material layer, the positive electrode material layer comprising a first material layer and a second material layer, the second material layer being disposed between the positive electrode current collector and the first material layer; the first material layer comprises lithium cobalt oxide, the lithium cobalt oxide comprising a first element, the first element comprising magnesium, titanium, and aluminum; the second material layer comprises an inorganic additive; the electrolyte comprises a trinitrile compound; and the mass content of the first element, based on the total mass of the positive electrode material, is n1, where 800 ppm ≤ n1 ≤ 10,000 ppm.

[0025] In some embodiments, lithium cobalt oxide is prepared by a method comprising the following steps: mixing Co3O4, Li2CO3, an aluminum source, a magnesium source, and a titanium source according to a ratio, and then calcining in a furnace at 700-1200°C for 7-20 hours to obtain lithium cobalt oxide doped with a first element.

[0026] In some embodiments, Co3O4, Li2CO3, an aluminum source, a magnesium source, a titanium source and a raw material providing tungsten element may be mixed according to a ratio to prepare lithium cobalt oxide doped with the first element and tungsten element.

[0027] In the present application, the inorganic additive is selected from inorganic metal oxides and / or inorganic metal hydroxides, such as 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, and antimony trioxide.

[0028] In the present application, a trinitrile compound refers to an organic compound containing a hydrocarbon group and three cyano groups (-CN) connected by carbon atoms.

[0029] In some embodiments, the electrolyte further comprises an ionizable lithium salt, and the ionizable lithium salt comprises at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. In the present application, the concentration of the ionizable lithium salt in the electrolyte is not particularly limited, and is preferably 0.5 mol / L or more, more preferably 0.8 mol / L or more, and further preferably 1.0 mol / L or more. In addition, it is preferably 3 mol / L or less, more preferably 2 mol / L or less, further preferably 1.8 mol / L or less, and particularly preferably 1.6 mol / L or less. If the concentration of these ionizable lithium salts is too low, the conductivity of the electrolyte may be insufficient. On the other hand, if the concentration of these ionizable lithium salts is too high, the viscosity of the electrolyte may increase, thereby reducing the conductivity, which may lead to reduced performance of the electrochemical device.

[0030] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiSO3F), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI).

[0031] In some embodiments, the additive in the electrolyte further includes at least one of a fluoroether compound, a fluorocarbonate compound, and an ether nitrile compound, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), ethylene glycol bis(propionitrile) ether (DENE), and the like.

[0032] In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent may be selected from carbonate compounds, carboxylate compounds, ether compounds, phosphate compounds, other organic solvents, or combinations thereof.

[0033] Alternatively, the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, or a combination thereof. Alternatively, the carbonate compound may be a fluorinated carbonate compound, a non-fluorinated carbonate compound, or a combination thereof.

[0034] The example of chain carbonate compound is diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) and its combination. The example of cyclic carbonate compound is ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC) or its combination. The example of fluorocarbonate compound is fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or its combination.

[0035] Specifically, examples of the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0036] Specifically, examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0037] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0038] Specifically, examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, or a combination thereof.

[0039] The present application also provides an electrochemical device comprising the aforementioned electrolyte. In some embodiments, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, and a separator, wherein the positive electrode sheet and the negative electrode sheet are separated by the separator disposed therebetween. In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed thereon, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed thereon.

[0040] In some embodiments, the negative electrode plate may include a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector. The negative electrode material layer may be disposed on one or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of copper foil, nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode material layer may be coated only on a partial area of ​​the negative electrode current collector. In some embodiments, the thickness of the negative electrode material layer may be 10 μm to 100 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be used.

[0041] In some embodiments, as described above, the negative electrode material layer includes a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy. In some embodiments, the negative electrode material includes a combination of a silicon-based material and a carbon material in a weight ratio of 1:(5-12).

[0042] In some embodiments, the negative electrode sheet is prepared using a method comprising the following steps: mixing a negative electrode material, a negative electrode binder, and deionized water to prepare a negative electrode slurry; applying the negative electrode slurry to the surface of the negative electrode current collector; and drying, cold pressing, cutting, and welding the tabs to obtain the negative electrode sheet.

[0043] In some embodiments, the negative electrode material layer may further include a negative electrode conductor and / or a negative electrode binder. The negative electrode conductor may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the negative electrode binder may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyacrylate, polyvinyl pyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are merely exemplary, and the negative electrode material layer may be made of any other suitable material.

[0044] In some embodiments, the mass ratio of the negative electrode material, the negative electrode conductor and the negative electrode binder in the negative electrode material layer can be (80-99):(0.5-10):(0.5-10). It should be understood that this is only exemplary and not intended to limit the present application.

[0045] In some embodiments, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector. The positive electrode material layer may be located on one side or both sides of the positive electrode current collector. In some embodiments, the positive electrode current collector may be made of aluminum foil. Of course, other positive electrode current collectors commonly used in the art may also be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. In some embodiments, the positive electrode material layer may be coated only on a partial area of ​​the positive electrode current collector. In some embodiments, the thickness of the positive electrode material layer may be 10 μm to 90 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be used.

[0046] In some embodiments, as described above, the positive electrode material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the above positive electrode materials may be doped and / or coated.

[0047] In some embodiments, the positive electrode material layer also includes a positive electrode binder and a positive electrode conductor. In some embodiments, the positive electrode binder may include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinyl pyrrolidone, polyvinyl ether, polytetrafluoroethylene or polyhexafluoropropylene at least one. In some embodiments, the positive electrode conductor may include at least one of conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes or carbon fibers. In some embodiments, the mass ratio of the positive electrode material, positive electrode conductor and positive electrode binder in the positive electrode material layer may be (80-98): (0.5-10): (0.5-10). It should be understood that the above is only an example, and the positive electrode material layer may include any other suitable material, thickness and mass ratio.

[0048] In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve battery safety through a shutdown effect.

[0049] In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer being disposed on at least one surface of the isolation membrane, the porous layer comprising at least one of inorganic particles or a binder, the inorganic particles being selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the isolation membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the electrode.

[0050] In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto.

[0051] In some embodiments of the present application, taking lithium-ion batteries as an example, the positive electrode sheet, the separator, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in a shell such as an aluminum-plastic film, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0052] The embodiments of the present application also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor, etc.

[0053] The following are some specific examples and comparative examples to better illustrate the present application, wherein lithium-ion batteries are used as examples. Unless otherwise specified, the raw materials used in the following examples are all commercially available products, and the devices and equipment used are all purchased from conventional commercial sales channels.

[0054] Example 1

[0055] The secondary battery of this embodiment includes a positive electrode plate and an electrolyte. The positive electrode plate includes a positive electrode material layer, the positive electrode material layer includes a first material layer and a second material layer, the second material layer being disposed between the positive electrode current collector and the first material layer. The first material layer includes lithium cobalt oxide, the lithium cobalt oxide includes a first element, the first element including magnesium, titanium, and aluminum. The second material layer includes an inorganic additive, the inorganic additive being magnesium oxide. Based on the total mass of the positive electrode material, the mass contents of the first element, the titanium element, and the aluminum element are 600 ppm, 600 ppm, and 1000 ppm, respectively (in a mass ratio of 1:1:1.67), and the total mass content of the first element is n1 = 2200 ppm. The electrolyte includes a trinitrile compound, which is 1,2,3-tris(2-cyanoethoxy)propane. The mass content of 1,2,3-tris(2-cyanoethoxy)propane is 0.1% based on the electrolyte.

[0056] The secondary battery of this embodiment is prepared by a method comprising the following steps:

[0057] Preparation of lithium cobalt oxide: 8.19 g of Co3O4, 3.74 g of Li2CO3 and 1000 ppm of aluminum element (aluminum source: Al2O3), 600 ppm of magnesium element, and 600 ppm of titanium element (titanium source: TiO2) are mixed, and then calcined in a furnace at 1000°C for 10 hours to prepare lithium cobalt oxide, wherein the lithium cobalt oxide is doped with aluminum element, magnesium element and titanium element.

[0058] Preparation of positive electrode:

[0059] Magnesium oxide was used as an inorganic additive. 65% by mass of magnesium oxide, 15% by mass of acetylene black, and 15% by mass of PVDF were mixed, and deionized water was added to the mixture to mix evenly. This slurry was then coated on both sides of a 10 μm thick aluminum foil for the positive electrode current collector and dried to form the second material layer.

[0060] Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.6:1.5:1.9, and N-methylpyrrolidone (NMP) was added and stirred uniformly in a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was evenly coated on the surface of the second material layer on one side of the positive electrode current collector aluminum foil and dried at 120°C to obtain a positive electrode sheet coated with an 80 μm thick first material layer on one side. The above steps were repeated on the surface of the second material layer on the other side of the positive electrode current collector aluminum foil to obtain a positive electrode sheet coated with the first material layer on both sides. The sheet was then cold pressed, cut, and slit to obtain a positive electrode sheet with a size of 470 mm × 92 mm.

[0061] Preparation of the negative electrode sheet: Artificial graphite (negative electrode material), conductive carbon black (conductive agent), styrene-butadiene rubber (SBR) (binder), and carboxymethyl cellulose (CMC) (thickener) were mixed in a weight ratio of 96.5:1.5:1:1. Deionized water was added and the mixture was stirred uniformly in a vacuum mixer to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was evenly applied to one surface of a negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated on one side with a 90 μm thick negative electrode material layer. The above steps were repeated on the other side of the negative electrode current collector copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. The sheet was then cold pressed, cut, and slit to obtain a negative electrode sheet with a size of 476 mm × 93.5 mm.

[0062] Preparation of isolation membrane: A 10 μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0063] Preparation of the electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), and diethyl carbonate (abbreviated as DEC) are mixed in a mass ratio of 1:1:1 to obtain a base solvent. Then, lithium salt LiPF6 and a trinitrile compound are added to the base solvent and mixed uniformly to obtain an electrolyte, wherein the mass content of LiPF6 is 12.5% ​​based on the mass of the electrolyte. In this embodiment, the trinitrile compound is 1,2,3-tris(2-cyanoethoxy)propane, and the mass content of 1,2,3-tris(2-cyanoethoxy)propane is 0.1% based on the total mass of the electrolyte.

[0064] Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator placed between the positive and negative electrode sheets to act as an isolater, and then wind them to obtain an electrode assembly. After welding the tabs, the electrode assembly is placed in an outer packaging aluminum-plastic film. After dehydration at 80°C, the above-mentioned electrolyte is injected. After vacuum packaging, standing, formation, shaping, capacity testing and other processes, a lithium-ion battery is obtained.

[0065] The secondary batteries of Examples 2 to 10 differ from Example 1 only in that the total mass content of the first element n1 is 3000 ppm based on the total mass of the lithium cobalt oxide. The types and mass contents of the trinitrile compounds in the electrolyte are different, as shown in Table 1.

[0066] The secondary batteries of Examples 11 to 15 differ from Example 2 only in that the total mass content of the first element in the lithium cobalt oxide and the mass content of the trinitrile compound in the electrolyte are different, as shown in Table 1.

[0067] In the examples and comparative examples, when the total mass content of the first element in the lithium cobalt oxide is adjusted on the basis of Example 1, the mass content ratios of magnesium, titanium and aluminum in the first element are controlled to be the same as that in Example 1.

[0068] Example 16

[0069] The secondary battery of this embodiment differs from that of Example 1 only in that tin dioxide is used as the inorganic additive, i.e., the inorganic additive includes a second element, which includes tin. The mass content of the second element, n2, is 500 ppm, based on the total mass of the positive electrode material. The electrolyte includes 1,2,3-tris(2-cyanoethoxy)propane, and the mass content of 1,2,3-tris(2-cyanoethoxy)propane is 1.2%, based on the electrolyte.

[0070] Example 17

[0071] The secondary battery of this embodiment differs from that of Example 1 only in that the inorganic additive is niobium oxide. The mass content of the second element, n2, is 500 ppm, based on the total mass of the positive electrode material. The electrolyte contains 1,2,3-tris(2-cyanoethoxy)propane, with a mass content of 1.2% based on the electrolyte.

[0072] Example 18

[0073] The secondary battery of this embodiment differs from that of Example 1 only in that the lithium cobalt oxide also contains tungsten. The mass content of tungsten, n3, is 300 ppm, based on the total mass of the positive electrode material. The electrolyte contains 1,2,3-tris(2-cyanoethoxy)propane, with a mass content of 1.2% based on the electrolyte.

[0074] The preparation of the lithium cobalt oxide of this embodiment includes the following steps: 8.19 g of Co3O4, 3.74 g of Li2CO3 and 1000 ppm of aluminum (aluminum source: Al2O3), 600 ppm of magnesium, 600 ppm of titanium (titanium source: TiO2), and 300 ppm of tungsten (tungsten source: WO3) are mixed, and then calcined in a furnace at 1000°C for 10 hours to prepare lithium cobalt oxide, wherein the lithium cobalt oxide is doped with aluminum, magnesium, titanium, and tungsten.

[0075] Example 19

[0076] The secondary battery of this embodiment is different from that of the first embodiment only in that the negative electrode plate includes a negative electrode material layer, and the negative electrode material layer includes artificial graphite and silicon dioxide.

[0077] The preparation of the negative electrode sheet of this embodiment includes the following steps: preparing a first negative electrode material composed of artificial graphite and silicon oxide (SiO2) in a weight ratio of 9:1; then mixing the first negative electrode material, styrene-butadiene rubber, and lithium carboxymethyl cellulose in deionized water in a mass ratio of 96.5%:2.5%:1% and stirring evenly to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on one surface of an 8μm-thick negative electrode current collector copper foil, then dried at 110°C. The above steps are repeated on the other surface of the negative electrode current collector, followed by cold pressing, cutting, and welding the tabs to obtain a negative electrode sheet.

[0078] Example 20

[0079] The secondary battery of this embodiment is different from that of embodiment 1 only in that the electrolyte further includes lithium bis(oxalatoborate), and the mass content of lithium bis(oxalatoborate) is 0.3% based on the mass of the electrolyte.

[0080] Example 21

[0081] The secondary battery of this embodiment is different from that of embodiment 1 only in that the electrolyte further includes phosphazene, and the mass content of phosphazene is 0.5% based on the mass of the electrolyte.

[0082] Example 22

[0083] The secondary battery of this embodiment differs from that of Example 1 only in that the inorganic additives are indium oxide, tin oxide, and antimony oxide. The mass content of the second element, n2, is 1500 ppm, based on the total mass of the positive electrode material. The mass ratio of indium, tin, and antimony is 1:1:1. The electrolyte contains 1,2,3-tris(2-cyanoethoxy)propane, with a mass content of 1.2% based on the electrolyte.

[0084] Comparative Example 1

[0085] The secondary battery of this comparative example is different from that of Example 1 only in that the mass content of 1,2,3-tris(2-cyanoethoxy)propane is 0.05% based on the electrolyte.

[0086] Comparative Example 2

[0087] The secondary battery of this comparative example is different from that of Example 1 only in that the mass content of 1,2,3-tris(2-cyanoethoxy)propane is 10% based on the electrolyte.

[0088] Comparative Example 3

[0089] The secondary battery of this comparative example differs from that of Example 1 only in that the lithium cobalt oxide does not contain the first element. The lithium cobalt oxide preparation method includes the following steps: mixing 8.19 g of Co₃O₄ and 3.74 g of Li₂CO₃, and then calcining the mixture in a furnace at 1000°C for 10 hours to prepare the lithium cobalt oxide.

[0090] The test methods for the various performance parameters involved are as follows:

[0091] (1) High temperature storage test

[0092] Take 4 lithium-ion secondary batteries from each group and, in an environment of 60°C, first use a current of 0.5C for constant current charging. After charging to 4.5V, perform constant voltage charging. Then, perform constant current discharge at a current of 1C and discharge to 2.8V. Record the discharge capacity and record it as the capacity before storage. Charge to 3.99V with a constant current of 0.5C, charge at a constant voltage until the current is lower than 0.05C, place the battery in a 60°C oven for 14D, and then perform constant current discharge at a discharge current of 1C and discharge to 2.8V. Then, perform constant current and constant voltage charging at a charging current of 0.5C until the upper limit voltage is 4.5V. Then, perform constant current discharge at a discharge current of 1C and discharge to 2.8V. Record the discharge capacity and record it as the capacity after storage.

[0093] 60° C. high-temperature storage capacity retention rate=capacity after storage / capacity before storage×100%. The high-temperature storage performance thus obtained was evaluated according to the following evaluation criteria.

[0094] A: Capacity retention rate is greater than 85%;

[0095] B: Capacity retention rate is greater than or equal to 80% and less than 85%;

[0096] C: Capacity retention rate is greater than or equal to 75% and less than 80%;

[0097] D: Capacity retention rate is less than 75%.

[0098] (2) Penetration resistance test

[0099] The positive electrode sheet was punched out into a circle with a diameter of 12 mm, and the thickness d (μm) of the punched test piece and the area S of the positive electrode composite material layer were measured. The test piece was clamped in the fixture of a tensile compression testing machine (manufactured by Imada Manufacturing Co., Ltd., product name "SV-301NA") and pressurized to a pressure of 20 MPa. A double-terminal clamp was connected to the fixture, and the measuring cable was connected to an automatic polarization system (manufactured by Hokuto Denko Co., Ltd., product name "HSV-110"). Using the chronopotentiometry mode, a constant current I = 10 mA was passed through the fixture for 10 minutes, and the voltage V (V) at this time was measured. According to Ohm's law, the resistance R (Ω) = V / I was calculated, and the volume resistivity ρ (Ω·cm) = R×S / d was further calculated to obtain the volume resistivity ρ of the penetration method. The volume resistivity ρ thus obtained was evaluated according to the following evaluation criteria.

[0100] A: Volume resistivity ρ is less than 15Ω·cm;

[0101] B: Volume resistivity ρ is greater than or equal to 15Ω·cm and less than 25Ω·cm;

[0102] C: Volume resistivity ρ is greater than or equal to 25Ω·cm and less than 40Ω·cm;

[0103] D: Volume resistivity ρ is 40 Ω·cm or more.

[0104] Table 1 shows various parameters and evaluation results of Examples and Comparative Examples.

[0105] Table 1

[0106] In Table 1, “ / ” indicates that the substance was not added; N1: 1,2,3-tris(2-cyanoethoxy)propane; N2: 1,2,4-tris(2-cyanoethoxy)butane; N3: 1,1,1-tris(cyanoethoxymethylene)ethane; N4: 1,1,1-tris(cyanoethoxymethylene)propane; N5: 3-methyl-1,3,5-tris(cyanoethoxy)pentane; N6: 1,2,7-tris(cyanoethoxy)heptane; N7: 1,2,6-tris(cyanoethoxy)hexane; N8: 1,2,5-tris(cyanoethoxy)pentane; N9: 1,3,5-pentanetricarbonitrile; N10: 1,3,6-hexanetricarbonitrile.

[0107] As can be seen from Table 1, the lithium cobalt oxide doped with magnesium, titanium and aluminum elements in the present application cooperates with the inorganic additives and the trinitrile compound in the electrolyte to produce a synergistic effect, wherein the total mass content of magnesium, titanium and aluminum elements based on the total mass of the positive electrode material is n1, 800ppm≤n1≤10000ppm. The secondary battery that meets the above conditions can greatly improve the stability of the positive electrode material, thereby improving the high-temperature storage and penetration resistance of the secondary battery.

[0108] In particular, the present application further dopes tungsten into lithium cobalt oxide on the basis of doping the first element with a certain proportion of trinitrile compound, which can further improve the high-temperature storage and penetration resistance of the secondary battery.

[0109] In particular, the inorganic additive of the present application includes a second element, which can further improve the high-temperature storage and penetration resistance of the secondary battery.

[0110] In particular, the second element includes indium, tin, and antimony, which can further improve the high-temperature storage performance and penetration resistance of the secondary battery.

[0111] In particular, the use of a negative electrode material containing a silicon-based material in combination with a trinitrile compound added to the electrolyte can further improve the high-temperature storage of the secondary battery.

[0112] In particular, the combination of lithium cobalt oxide with trinitrile compounds and lithium bis(oxalatoborate) in the electrolyte can improve the high-temperature storage and penetration resistance of the secondary battery.

[0113] In particular, by adding phosphazene to the coordination of lithium cobalt oxide and trinitrile compounds in the electrolyte, the high-temperature storage and penetration resistance of the secondary battery can be further improved.

[0114] The above description is merely a preferred embodiment of the present application and an illustration of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by a specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or their equivalents. For example, a technical solution formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The positive electrode includes a positive electrode current collector and a positive electrode material layer, the positive electrode material layer includes a first material layer and a second material layer, and the second material layer is arranged between the positive electrode current collector and the first material layer; The first material layer includes lithium cobalt oxide, the lithium cobalt oxide includes a first element, and the first element includes magnesium, titanium, and aluminum; The second material layer includes an inorganic additive; The electrolyte includes a trinitrile compound; Based on the total mass of the positive electrode material, the mass content of the first element is n1, 800ppm≤n1≤10000ppm.

2. The secondary battery according to claim 1, wherein The inorganic additive includes a second element, and the second element includes at least one of chromium, zirconium, lanthanum, niobium, indium, tin, zinc, or antimony.

3. The secondary battery according to claim 2, wherein The second element includes indium, tin and antimony.

4. The secondary battery according to claim 1, wherein The lithium cobalt oxide further includes tungsten element.

5. The secondary battery according to any one of claims 1 to 4, characterized in that The trinitrile compound includes at least one of 1,3,5-pentanetricarboxylic acid nitrile, 1,2,3-propanetricarboxylic acid nitrile, 1,3,6-hexanetrinitrile, 1,2,6-hexanetrinitrile, 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.

6. The secondary battery according to any one of claims 1 to 4, characterized in that In the first element, the mass content ratio of magnesium, titanium and aluminum is 1:(0.8-1.2):(1.5-2).

7. The secondary battery according to any one of claims 1 to 4, characterized in that The secondary battery satisfies: 1000ppm≤n1≤7000ppm.

8. The secondary battery according to claim 2 or 3, characterized in that Based on the total mass of the positive electrode material, the mass content of the second element is n2, 1ppm≤n2≤6000ppm.

9. The secondary battery according to claim 4, wherein Based on the total mass content of the positive electrode material, the mass content of the tungsten element is n3, 5ppm≤n3≤1000ppm.

10. The secondary battery according to any one of claims 1 to 4, characterized in that The negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a silicon-based material.

11. The secondary battery according to any one of claims 1 to 4, characterized in that The electrolyte further comprises lithium bis(oxalatoborate), and the mass percentage of the lithium bis(oxalatoborate) is 0.01% to 2% based on the mass of the electrolyte.

12. The secondary battery according to any one of claims 1 to 4, characterized in that The electrolyte further includes phosphazene, and based on the mass of the electrolyte, the mass percentage of the phosphazene is 0.01% to 1.5%.

13. The secondary battery according to any one of claims 1 to 4, characterized in that Based on the mass of the electrolyte, the mass percentage of the trinitrile compound is 0.1% to 6%. 14 . An electronic device comprising the secondary battery according to claim 1 .

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