Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device, the 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 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, the first element comprises magnesium, titanium and aluminum; the second material layer comprises an inorganic additive; the electrolyte comprises 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. The secondary battery in the present application has good high temperature storage performance and low penetration resistance.

Description

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 charged and discharged repeatedly. Among them, lithium-ion batteries are widely used in portable electronic devices, electric vehicles and other fields due to their small size and light weight. With the development of science and technology and the improvement of 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 comprises a first material layer and a second material layer, the second material layer is disposed 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, the first element comprises magnesium, titanium and aluminum; the second material layer comprises an inorganic additive; the electrolyte comprises 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.

[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 a suitable 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 condition: based on the total mass of the positive electrode material, the mass content of the above-mentioned first element is n1, 800ppm≤n1≤10000ppm. Exemplarily, the mass content n1 of the first element 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 satisfies 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 element, and adding tungsten element 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-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 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 condition that, among the first elements, the mass content ratio of magnesium, titanium and aluminum is 1:(0.8-1.2):(1.5-2). The magnesium, titanium and aluminum elements in this ratio 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 the present 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 be closely matched with the electrolyte in the inorganic additive, exerting a good enhancement effect, ensuring the high temperature storage performance of the secondary battery and reducing 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). Indium, tin and antimony in this ratio 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 includes phosphazene, and the mass content of phosphazene is 0.01% to 1.5% based on the mass of the electrolyte. The high temperature storage performance and penetration resistance of the secondary battery can be further improved by adding an appropriate amount of phosphazene. Exemplarily, based on the mass of the electrolyte, 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.

[0019] In some embodiments, based on the mass of the electrolyte, the mass percentage of the trinitrile compound is 0.1% to 6%. The secondary battery meeting this condition has better high temperature storage performance and lower penetration resistance. Exemplarily, based on the mass of the electrolyte, the mass content 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 the above values.

[0020] In a second aspect, the present application also provides an electronic device, which includes 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. After being combined with inorganic additives and trinitrile compounds with appropriate contents in the electrolyte, a synergistic effect can be achieved to jointly improve 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 solution and advantages of the present application more clear, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described here are only used to explain the present application and are not used to limit the present application.

[0024] In order to solve the problems in the prior art, the present application provides a secondary battery, including a positive electrode, a negative electrode and an electrolyte. 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, 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, 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.

[0025] In some embodiments, lithium cobalt oxide is prepared by a method comprising the following steps: Co3O4, Li2CO3, an aluminum source, a magnesium source and a titanium source are mixed according to a ratio, and then calcined 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 the tungsten element may be mixed according to a ratio to prepare lithium cobalt oxide doped with the first element and the 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, antimony trioxide.

[0028] In the present application, the 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 includes an ionizable lithium salt, and the ionizable lithium salt includes 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, it may result in insufficient conductivity of the electrolyte. On the other hand, if the concentration of these ionizable lithium salts is too high, it may result in an increase in the viscosity of the electrolyte, thereby decreasing the conductivity, which may result in reduced performance of the electrochemical device.

[0030] In some embodiments, the electrolyte also 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] Optionally, the carbonate compound may be a linear carbonate compound, a cyclic carbonate compound or a combination thereof. On the other hand, the carbonate compound may also be a fluorinated carbonate compound, a non-fluorinated carbonate compound or a combination thereof.

[0034] Specifically, examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC) or combinations thereof. Examples of fluorinated carbonate compounds are 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 combinations thereof.

[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 above-mentioned 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 a separator disposed therebetween. In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on the negative electrode current collector.

[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 side or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of a copper foil, a 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 exemplary only 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-oxygen compound, 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 by a method comprising the following steps: mixing a negative electrode material, a negative electrode binder and deionized water to obtain a negative electrode slurry, coating the negative electrode slurry on the surface of the negative electrode current collector, and then 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, polyacrylic acid salt, polyacrylate, polyvinyl pyrrolidone, polyimide, polysiloxane, or styrene-butadiene rubber. It should be understood that the materials disclosed above are only 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, and 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 exemplary only, 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 further includes a positive electrode binder and a positive electrode conductor. In some embodiments, the positive electrode binder may include at least one of 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. 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, the positive electrode conductor and the 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 isolation film 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. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the safety of the battery through the shutdown effect.

[0049] In some embodiments, the surface of the isolation membrane may further include a porous layer, which is disposed on at least one surface of the isolation membrane, and the porous layer includes at least one of inorganic particles or binders, and the inorganic particles are selected from 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 isolation membrane, and the negative electrode sheet are wound or stacked in sequence to form an electrode assembly, and then placed in a shell such as an aluminum-plastic film for packaging, and the electrolyte is injected, formed, and packaged to make a lithium-ion battery.

[0052] Embodiments of the present application also provide electronic devices including the above-mentioned electrochemical devices. The electronic devices of the embodiments of the present application are not particularly limited, and they can be any electronic devices 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] Some specific examples and comparative examples are listed below to better illustrate the present application, wherein a lithium-ion battery is used as an example. Unless otherwise specified, the raw materials used in the following examples are all from common commercial products, and the devices or equipment used are all purchased from conventional market 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, 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, and the inorganic additive is magnesium oxide; wherein, based on the total mass of the positive electrode material, the mass contents of magnesium, titanium and aluminum in the first element are 600ppm, 600ppm and 1000ppm respectively (the mass content ratio is 1:1:1.67), and the total mass content of the first element n1=2200ppm. The electrolyte includes a trinitrile compound, and the trinitrile compound is 1,2,3-tris(2-cyanoethoxy)propane. Based on the electrolyte, the mass content of 1,2,3-tris(2-cyanoethoxy)propane is 0.1%.

[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, 1000 ppm of aluminum (aluminum source: Al2O3), 600 ppm of magnesium, and 600 ppm of titanium (titanium source: TiO2) were mixed and then calcined in a furnace at 1000°C for 10 hours to prepare lithium cobalt oxide, wherein the lithium cobalt oxide was doped with aluminum, magnesium and titanium.

[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, deionized water was added thereto and mixed evenly, and after preparing a slurry, the slurry was coated on both sides of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried to form a second material layer.

[0060] Lithium cobalt oxide, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96.6:1.5:1.9, N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry, wherein the solid content of the positive electrode slurry was 75wt%. 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 a first material layer with a thickness of 80μm on one side, and 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, and then after cold pressing, cutting, and slitting, a positive electrode sheet with a specification of 470mm×92mm was obtained.

[0061] Preparation of negative electrode sheet: artificial graphite of negative electrode material, conductive carbon black of conductive agent, styrene-butadiene rubber (SBR) of binder and carboxymethyl cellulose (CMC) of thickener are mixed in a weight ratio of 96.5:1.5:1:1, deionized water is added, and the mixture is stirred evenly under the action of a vacuum mixer to obtain negative electrode slurry, wherein the solid content of the negative electrode slurry is 75wt%. The negative electrode slurry is evenly coated on one side of the negative electrode current collector copper foil, and dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer with a thickness of 90μm on one side, and the above steps are repeated on the other side of the negative electrode current collector copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides, and then after cold pressing, cutting and slitting, a negative electrode sheet with a specification of 476mm×93.5mm is obtained.

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

[0063] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10ppm, 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 basic solvent, and then lithium salt LiPF6 and trinitrile compounds are added to the above-mentioned basic solvent, and the electrolyte is obtained after uniform mixing, 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, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and wind them to obtain an electrode assembly. After welding the pole ears, place the electrode assembly in an outer packaging aluminum-plastic film, remove moisture at 80°C, inject the above-mentioned electrolyte, and obtain a lithium-ion battery through vacuum packaging, standing, formation, shaping, capacity testing and other processes.

[0065] The secondary batteries of Examples 2 to 10 are different 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 are different from those of Example 2 only in that the total mass content of the first element in the lithium cobalt oxide is different from the mass content of the trinitrile compound in the electrolyte, as shown in Table 1.

[0067] When the total mass content of the first element in the lithium cobalt oxide is adjusted in the embodiment and the comparative example on the basis of the embodiment 1, the mass content ratio of the magnesium element, the titanium element and the aluminum element in the first element is controlled to be the same as that in the embodiment 1.

[0068] Example 16

[0069] The secondary battery of this embodiment is different from that of Embodiment 1 only in that the inorganic additive uses tin dioxide, that is, the inorganic additive includes a second element, and the second element includes tin. Based on the total mass of the positive electrode material, the mass content of the second element n2=500ppm. 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] Embodiment 17

[0071] The secondary battery of this embodiment is different from that of embodiment 1 only in that the inorganic additive is niobium oxide. Based on the total mass of the positive electrode material, the mass content of the second element n2=500ppm. 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.

[0072] Embodiment 18

[0073] The secondary battery of this embodiment is different from that of Embodiment 1 only in that the lithium cobalt oxide further includes tungsten. Based on the total mass of the positive electrode material, the mass content of tungsten is n3=300ppm. 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.

[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 element (aluminum source: Al2O3), 600 ppm of magnesium element, 600 ppm of titanium element (titanium source: TiO2), and 300 ppm of tungsten element (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 element, magnesium element, titanium element and tungsten element.

[0075] Embodiment 19

[0076] The secondary battery of this embodiment is different from that of Embodiment 1 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, and then mixing the first negative electrode material, styrene-butadiene rubber and lithium carboxymethyl cellulose with deionized water in a mass ratio of 96.5%:2.5%:1%, stirring evenly, and obtaining a negative electrode slurry. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8 μm, and then dried at 110°C, and the above steps are repeated on the other surface of the negative electrode current collector, cold pressing, cutting, and welding the pole ears to obtain a negative electrode sheet.

[0078] Embodiment 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] Embodiment 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] Embodiment 22

[0083] The secondary battery of this embodiment is different from that of Embodiment 1 only in that the inorganic additives are indium oxide, tin oxide and antimony oxide. Based on the total mass of the positive electrode material, the mass content of the second element n2=1500ppm, wherein the mass ratio of indium element, tin element and antimony element is 1:1:1. 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.

[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 is different from that of Example 1 only in that the lithium cobalt oxide does not contain the first element. The preparation method of the lithium cobalt oxide comprises the following steps: 8.19 g of Co3O4 and 3.74 g of Li2CO3 are mixed, and then calcined 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 to perform constant current charging, charge to 4.5V, then perform constant voltage charging, and then perform constant current discharge at a current of 1C, 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, 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, and then perform constant current discharge at a discharge current of 1C, 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 is punched 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 are measured. The test piece is clamped in the fixture of the 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 is connected to the fixture, and the measuring cable is connected to the automatic polarization system (manufactured by Hokuto Denko Co., Ltd., product name "HSV-110"). Using the chronopotentiometry mode, a constant current I = 10 mA is passed through the fixture for 10 minutes, and the voltage V (V) at this time is measured. According to Ohm's law, the resistance R (Ω) = V / I is calculated, and the volume resistivity ρ (Ω·cm) = R×S / d is further calculated to obtain the volume resistivity ρ of the penetration method. The volume resistivity ρ thus obtained is 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: The volume resistivity ρ is greater than or equal to 40 Ω·cm.

[0104] Table 1 shows various parameters and evaluation results of the embodiments and comparative examples.

[0105] Table 1

[0106]

[0107] 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.

[0108] It can be seen from Table 1 that 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, and 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.

[0109] In particular, the present application further dopes tungsten element 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.

[0110] 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.

[0111] 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.

[0112] 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.

[0113] 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.

[0114] In particular, by adding phosphazene to the combination of lithium cobalt oxide and trinitrile compound in the electrolyte, the high-temperature storage and penetration resistance of the secondary battery can be further improved.

[0115] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features. For example, the above features are replaced with the technical features with similar functions disclosed in the present application.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that: The positive electrode comprises a positive electrode current collector and a positive electrode material layer, the positive electrode material layer comprises 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 is doped with a first element, the first element includes magnesium, titanium and aluminum; in the first element, the mass content ratio of magnesium, titanium and aluminum is 1:(0.8-1.2):(1.5-2); The second material layer includes an inorganic additive; the inorganic additive includes a second element, the second element includes indium, tin and antimony, and the mass ratio of indium, tin and antimony is 1:(0.6~1.4):(0.6~1.4); based on the total mass of the positive electrode material, the mass content of the second element is n2, 500ppm≤n2≤1500ppm; indium, tin and antimony exist in the form of indium trioxide, tin dioxide and antimony trioxide; The electrolyte includes a trinitrile compound; the trinitrile compound includes 1,2,3-tris(2-cyanoethoxy)propane; based on the mass of the electrolyte, the mass percentage of the trinitrile compound is 0.8%-1.2%; Based on the total mass of the positive electrode material, the mass content of the first element is n1, 2200ppm≤n1≤6000ppm.

2. The secondary battery according to claim 1, characterized in that: The lithium cobalt oxide is further doped with tungsten element.

3. The secondary battery according to claim 2, characterized in that: Based on the total mass content of the positive electrode material, the mass content of the tungsten element is n3, 5ppm≤n3≤1000ppm.

4. The secondary battery according to claim 1 or 2, characterized in that: The negative electrode includes a negative electrode material layer, and the negative electrode material layer includes a silicon-based material.

5. The secondary battery according to claim 1 or 2, 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.

6. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte also includes phosphazene, and the mass percentage of the phosphazene is 0.01% to 1.5% based on the mass of the electrolyte. 7 . An electronic device comprising the secondary battery according to claim 1 .

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