Secondary battery and electronic device

Abstract

This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector. The insulating layer comprises boehmite, the positive electrode material layer comprises lithium iron phosphate and lithium manganese oxide, the lithium iron phosphate comprising zirconium and boron, and the lithium manganese oxide comprising antimony. The electrolyte comprises lithium difluorophosphate. This application not only improves the float charging safety of the secondary battery but also reduces the particle breakage rate.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to a secondary battery and electronic device. Background Technology

[0002] Against the backdrop of rapid technological advancements and continuous improvement in living standards, rechargeable batteries, with their superior high energy density and convenient rechargeable / dischargeable characteristics, have become a core power source in key areas such as portable electronic devices and electric vehicles, highlighting their increasing importance. However, as application scenarios continue to expand and become more complex, more stringent requirements are being placed on the overall performance of rechargeable batteries. Summary of the Invention

[0003] This application's embodiments further enhance the overall stability of the secondary battery by adjusting the composition of the positive electrode and electrolyte. The inventors of this application discovered that the positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the current collector; the insulating layer includes boehmite, the positive electrode material layer includes lithium iron phosphate and lithium manganese oxide, the lithium iron phosphate includes zirconium and boron elements, the lithium manganese oxide includes antimony elements, and the electrolyte includes lithium difluorophosphate. This not only improves the safety of battery float charging but also reduces the particle breakage rate, thus completing this application.

[0004] Optionally, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content ratio of zirconium, boron and antimony is 1:(0.1~0.9):(0.01~0.5).

[0005] Optionally, the lithium difluorophosphate is 0.01 to 1 part by weight relative to 100 parts by weight of the electrolyte.

[0006] Optionally, the lithium difluorophosphate is 0.05 to 0.9 parts by weight relative to 100 parts by weight of the electrolyte.

[0007] Optionally, the lithium difluorophosphate is 0.09 to 0.6 parts by weight relative to 100 parts by weight of the electrolyte.

[0008] Alternatively, the insulating layer may include polyvinylidene fluoride and N-methylpyrrolidone.

[0009] Optionally, the electrolyte includes sodium dihydrogen phosphate, wherein the amount of sodium dihydrogen phosphate is from 0.03 to 0.7 parts by weight relative to 100 parts by weight of electrolyte.

[0010] Optionally, the electrolyte includes p-toluenesulfonyl isocyanate, wherein the p-toluenesulfonyl isocyanate is 0.01 to 3 parts by weight relative to 100 parts by weight of the electrolyte.

[0011] Optionally, the electrolyte comprises sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate, wherein sodium dihydrogen phosphate is a parts by mass and p-toluenesulfonyl isocyanate is b parts by mass relative to 100 parts by mass of electrolyte, and 0.01 ≤ a / b ≤ 0.95.

[0012] In another aspect of this application, an electronic device is provided that includes the secondary battery described in this application.

[0013] This application, by using a specific combination of positive electrode and electrolyte, can not only improve the safety of battery float charging, but also reduce the particle breakage rate.

[0014] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0015] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0016] Unless otherwise expressly stated, the terms used in this application shall have the meanings indicated below.

[0017] This application, by using a specific combination of positive electrode and electrolyte, can not only improve the safety of battery float charging, but also reduce the particle breakage rate.

[0018] In one embodiment, this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0019] I. Positive electrode

[0020] This application relates to a secondary battery and an electronic device. Specifically, this application provides a secondary battery comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector. The insulating layer includes boehmite, the positive electrode material layer includes lithium iron phosphate and lithium manganese oxide, and the electrolyte includes lithium difluorophosphate. This application not only improves the safety of battery float charging but also reduces the particle breakage rate.

[0021] The cathode material layer contains lithium iron phosphate and lithium manganese oxide, and the cathode material layer can be one or more layers.

[0022] The inventors of this application unexpectedly discovered in experiments that a cathode material layer containing lithium iron phosphate and lithium manganese oxide, along with an insulating layer containing boehmite, in an electrolyte system containing lithium difluorophosphate, can not only improve the safety of battery float charging but also reduce the particle breakage rate.

[0023] Boehmite, lithium iron phosphate, and lithium manganese oxide have significantly different crystallographic information. However, with the assistance of an electrolyte containing lithium difluorophosphate, the elemental sites in all three materials come into contact with lithium difluorophosphate. It is speculated that this forms a special structural channel in the secondary battery, which can not only improve the safety of battery float charging but also reduce the particle breakage rate.

[0024] Specifically, from the perspective of improving battery float charging safety and reducing particle breakage rate, lithium iron phosphate includes zirconium and boron, while lithium manganese oxide includes antimony. Specifically, from the perspective of reducing particle breakage rate, the mass ratio of zirconium, boron, and antimony is 1:(0.1~0.9):(0.01~0.5), preferably 1:(0.16~0.6):(0.02~0.25), and more preferably 1:(0.2~0.5):(0.03~0.2). When the mass ratio of zirconium, boron, and antimony meets the above range, battery float charging safety and particle breakage rate can be further improved. Introducing these elements into the crystal structures of lithium iron phosphate and lithium manganese oxide further enhances the compatibility of their unit cell parameters.

[0025] Specifically, from the viewpoint of improving battery float charging safety and reducing particle breakage rate, in some embodiments, based on the content of metal elements other than lithium in the cathode material layer, the mass content of zirconium is 1000ppm to 20000ppm, for example, values ​​within the range of 1000ppm, 2300ppm, 2600ppm, 5300ppm, 6300ppm, 7200ppm, 9500ppm, 10400ppm, 11700ppm, 13600ppm, 15000ppm, 15900ppm, 17900ppm, 19200ppm, 20000ppm, or any two of these. In some embodiments, from the viewpoint of improving battery float charging safety and reducing particle breakage rate, based on the content of metal elements other than lithium in the cathode material layer, the mass content of boron is from 500 ppm to 3000 ppm, for example, values ​​within the range of 500 ppm, 700 ppm, 1000 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1700 ppm, 1900 ppm, 2100 ppm, 2200 ppm, 2600 ppm, 3000 ppm, or any two of these. In some embodiments, from the viewpoint of improving battery float charging safety and reducing particle breakage rate, based on the content of metal elements other than lithium in the cathode material layer, the mass content of antimony is from 100 ppm to 1000 ppm, for example, values ​​within the range of 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, or any two of these.

[0026] There are no restrictions on the type of positive electrode conductive material; any known conductive material can be used. Examples of positive electrode conductive materials include, but are not limited to, carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; graphene, etc. The above-mentioned positive electrode conductive materials can be used alone or in any combination.

[0027] There are no restrictions on the type of solvent used to form the positive electrode slurry, as long as it can dissolve or disperse the positive electrode material, conductive material, and positive electrode binder. Examples of solvents used to form the positive electrode slurry can include any of aqueous solvents and organic solvents. Examples of aqueous media can include, but are not limited to, water and mixed media composed of alcohol and water. Examples of organic media can include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran; amides such as N-methylpyrrolidone, dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

[0028] The density of the active material layer in the positive electrode, excluding the current collector, is typically 3.5 g / cm³. 3 In order to further improve the battery capacity, a value of 4g / cm³ is preferred. 3 That's all. Furthermore, as an upper limit, 4.6 g / cm³ is preferred. 3 the following.

[0029] There are no particular limitations on the type of positive electrode current collector; it can be any material known to be suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum.

[0030] To reduce the electronic contact resistance between the positive current collector and the positive electrode material layer, the surface of the positive current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings may include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0031] From the perspective of improving battery float charging safety and reducing particle breakage rate, boehmite is included in the insulation layer.

[0032] Specifically, from the perspective of improving battery float charging safety and reducing particle breakage rate, the insulation layer includes polyvinylidene fluoride and N-methylpyrrolidone.

[0033] The positive electrode is made in the following way:

[0034] Boehmite, polyvinylidene fluoride, and N-methylpyrrolidone were mixed, and deionized water was added and mixed evenly to form slurry 1.

[0035] The above-mentioned positive electrode material, conductive agents such as acetylene black and carbon black, and binders such as polyvinylidene fluoride or polyacrylonitrile are mixed together, and high-boiling-point solvents such as N-methylpyrrolidone are added and kneaded to prepare slurry 2.

[0036] Slurry 1 and slurry 2 are coated in parallel onto the aluminum foil or other material of the current collector, then dried and pressurized to form the positive electrode.

[0037] II. Electrolyte

[0038] The electrolyte used in the secondary battery of this application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte of this application includes lithium difluorophosphate.

[0039] When lithium difluorophosphate is used in the secondary battery of this application, the inventors have found that with the addition of lithium iron phosphate, lithium manganese oxide and boehmite in the positive electrode, it can not only improve the safety of battery float charging, but also reduce the particle breakage rate.

[0040] Specifically, from the viewpoint of improving battery float charging safety and reducing particle breakage rate, the electrolyte includes lithium difluorophosphate, wherein, relative to 100 parts by mass of electrolyte, lithium difluorophosphate is 0.01 parts by mass or more, preferably 0.05 parts by mass or more, further preferably 0.09 parts by mass or more, more preferably 0.15 parts by mass or more, and particularly preferably 0.18 parts by mass or more. Furthermore, as an upper limit for the content of lithium difluorophosphate, from the viewpoint of improving battery float charging safety and reducing particle breakage rate, lithium difluorophosphate is 1 part by mass or less, preferably 0.9 parts by mass or less, particularly preferably 0.8 parts by mass or less, more preferably 0.7 parts by mass or less, further preferably 0.6 parts by mass or less, and particularly preferably 0.5 parts by mass or less. When within the above ranges, it helps to further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0041] Specifically, from the viewpoint of improving the float charging safety of secondary batteries and reducing the particle breakage rate, the electrolyte includes sodium dihydrogen phosphate. In some embodiments, relative to 100 parts by mass of the electrolyte, the sodium dihydrogen phosphate is 'a' parts by mass, where 'a' ranges from 0.03 to 0.7, for example, 'a' is a value within the range of 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or any combination thereof. When the mass fraction of sodium dihydrogen phosphate in the electrolyte is adjusted to meet the above range, the float charging safety of the secondary battery and the particle breakage rate can be further improved.

[0042] Specifically, from the viewpoint of improving the float charging safety of secondary batteries and reducing the particle breakage rate, the electrolyte includes p-toluenesulfonyl isocyanate. In some embodiments, the p-toluenesulfonyl isocyanate is b parts by mass relative to 100 parts by mass of the electrolyte, where b ranges from 0.01 to 3, for example, b is a value within the range of 0.01, 0.1, 0.2, 0.3, 0.7, 0.8, 1.1, 1.3, 1.6, 1.7, 2.0, 2.1, 2.4, 2.6, 3.0, or any combination thereof. When the mass fraction of p-toluenesulfonyl isocyanate in the electrolyte is controlled to meet the above range, the float charging safety of the secondary battery and the particle breakage rate can be further improved.

[0043] Specifically, from the viewpoint of improving the float charging safety of secondary batteries and reducing the particle breakage rate, the electrolyte includes sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate. In some embodiments, 0.01 ≤ a / b ≤ 0.95, for example, the value of a / b is within the range of 0.01, 0.06, 0.13, 0.19, 0.27, 0.37, 0.42, 0.46, 0.52, 0.63, 0.67, 0.75, 0.87, 0.88, 0.95, or any combination thereof. When the mass fractions of sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate in the electrolyte are controlled to satisfy the above relationship, their interaction and close cooperation can be promoted, thereby better improving the float charging safety of secondary batteries and reducing the particle breakage rate.

[0044] In some embodiments, the additives in the electrolyte comprise one or more of the following: ethylene glycol sulfate, 1,2-propanediol sulfate, 1,3-propanediol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 1,4-butanediol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, dimethyl sulfate, methyl ethyl sulfate, sulfur Diethyl fluorosulfonate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate, methyl 2-(methanesulfonyloxy)propionate, ethyl 2-(methanesulfonyloxy)propionate, 1-fluoro-1,3-propanesulfonate lactone, 2-fluoro-1,3-propanesulfonate lactone, 3-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 2-methyl-1,3-propanesulfonate lactone, 3-methyl-1, 3-Propanesulfonate lactone, 1-Propylene-1,3-sulfonate lactone, 2-Propylene-1,3-sulfonate lactone, 1-Fluoro-1-Propylene-1,3-sulfonate lactone, 2-Fluoro-1-Propylene-1,3-sulfonate lactone, 3-Fluoro-1-Propylene-1,3-sulfonate lactone, 1-Fluoro-2-Propylene-1,3-sulfonate lactone, 2-Fluoro-2-Propylene-1,3-sulfonate lactone, 3-Fluoro-2-Propylene-1,3-sulfonate lactone, 1-Methyl-1-Propylene-1,3-sulfonate lactone, 2-Methyl-1-Propylene-1,3-sulfonate lactone, 3-Methyl-1-Propylene-1,3-sulfonate lactone, 1-Methyl-2-Propylene-1,3-sulfonate lactone 2-Methyl-2-propene-1,3-sulfonyl lactone, 3-methyl-2-propene-1,3-sulfonyl lactone, 1,4-butanesulfonyl lactone, 1,5-pentanesulfonyl lactone, methanedisulfonate methanedisulfonate methanedisulfonate ethylene methanedisulfonate ... In some embodiments, the electrolyte further includes an ionizable lithium salt, which includes at least one selected from LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. For example, the lithium salt used in the electrolyte of this application includes LiPF6, and the content of LiPF6 is 9-15% by mass, preferably 9-13% by mass, and more preferably 9-12% by mass, based on the mass of the electrolyte. By setting the content within the above range, the effects of improving the float charging safety of the secondary battery and reducing the particle breakage rate can be more balanced.

[0045] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate borate) (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0046] In some embodiments, the additives in the electrolyte also include at least one of fluoroether compounds, fluorocarbonate compounds, and ether nitrile compounds, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), etc.

[0047] In some embodiments, the electrolyte may also include a non-aqueous solvent. The non-aqueous solvent may be selected from carbonate compounds, carboxylic acid ester compounds, ether compounds, phosphate ester compounds, other organic solvents, or combinations thereof.

[0048] Optionally, the carbonate compound may be a chain 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.

[0049] Specifically, examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene 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.

[0050] Specifically, examples of carboxylic acid ester compounds are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, methyl formate, or combinations thereof.

[0051] Specifically, examples of ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or combinations thereof.

[0052] Specifically, examples of phosphate ester compounds are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or combinations thereof.

[0053] Specifically, examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methylpyrrolidone, formamide, dimethylformamide, acetonitrile, or combinations thereof.

[0054] III. Negative electrode

[0055] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on the surface of the negative electrode current collector, the negative electrode material layer containing negative electrode material. In some embodiments, the rechargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0056] Furthermore, there are no particular limitations on anode materials; examples include carbon-based anode materials, metal-based anode materials, silicon-based anode materials, and anode materials that combine these materials.

[0057] Carbon-based anode materials

[0058] Here, carbon-based anode materials refer to active materials with carbon as the main framework that can insert lithium. Examples of carbon-based anode materials include carbonaceous materials and graphitic materials.

[0059] Examples of carbonaceous materials include easily graphitized carbon and difficult-to-graphitize carbon with a similar amorphous structure, such as glassy carbon. Among easily graphitized carbons, examples include carbon materials derived from petroleum or coal using tar pitch as a raw material. Specific examples include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, and pyrolysis-grown carbon fibers. Furthermore, examples of difficult-to-graphitize carbons include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0060] Furthermore, examples of graphitic materials include natural graphite and artificial graphite. Among these, examples of artificial graphite include: artificial graphite formed by heat-treating carbon containing easily graphitizable carbon primarily at temperatures above 2800°C; graphitic MCMB formed by heat-treating MCMB at temperatures above 2000°C; and graphitic mesophase pitch-based carbon fiber formed by heat-treating mesophase pitch-based carbon fiber at temperatures above 2000°C. Additionally, in this invention application, as a carbon-based negative electrode material, natural graphite whose surface is at least partially coated with amorphous carbon (amorphously coated natural graphite) can be used.

[0061] Furthermore, metal-based anode materials are active materials containing metals, typically referring to active materials whose structure contains elements capable of intercalating into or alloying with lithium, and whose theoretical current capacity per unit mass is 500 mAh / g or higher when intercalated into or alloyed with lithium. Examples of metal-based anode materials that can be used include: lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, active materials containing silicon (silicon-based anode materials) are preferred as metal-based anode materials. This is because using silicon-based anode materials enables high-capacity secondary batteries.

[0062] Examples of silicon-based anode materials include: silicon (Si), silicon-containing alloys, SiO, SiO2, and silicon-containing materials coated or composited with conductive carbon (silicon-carbon materials).

[0063] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as porous carbon-supported silicon composites.

[0064] In addition, a single negative electrode material can be used alone, or two or more materials can be used in any ratio.

[0065] Here, the volume average particle size of the negative electrode material is preferably 1 μm or more, more preferably 5 μm or more, more preferably 30 μm or less, and more preferably 20 μm or less. If the volume average particle size of the negative electrode material is above the above-mentioned lower limit, the heat generation during internal short circuit can be effectively suppressed. In addition, if the volume average particle size of the negative electrode material is below the above-mentioned upper limit, the increase in the initial resistance of the resulting battery can be effectively suppressed.

[0066] The negative electrode material layer may also include a negative electrode binder. The negative electrode binder improves the bonding between negative electrode material particles and the bonding between the negative electrode material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When a negative electrode slurry is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0067] As the current collector for retaining the negative electrode material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0068] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode material, resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0069] IV. Separating membrane

[0070] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0071] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0072] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0073] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0074] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the thin film form, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0075] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, as well as the DC resistance characteristics and energy density of the secondary battery.

[0076] This application also provides an electronic device that includes a secondary battery as described in this application.

[0077] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0078] Example

[0079] The following are embodiments of the secondary battery of this application, but this application is not limited to these embodiments.

[0080] Preparation of secondary batteries

[0081] The production of the positive electrode:

[0082] Boehmite and polyvinylidene fluoride were mixed in the mass ratio shown in Table 1, dissolved in N-methylpyrrolidone, and then deionized water was added and mixed evenly to prepare positive electrode slurry 1.

[0083] The positive electrode materials listed in Table 1—lithium iron phosphate (46 wt%), lithium manganese oxide (51 wt%), and conductive carbon black (1 wt%)—were mixed. Polyvinylidene fluoride (2 wt%) was dissolved in N-methylpyrrolidone, and the mixture was then combined to prepare positive electrode slurry 2. Slurry 1 was coated on the tab side, and slurries 1 and 2 were coated parallel to each other on an aluminum foil. The coated aluminum foil was dried, pressurized, and then cut to the specified size to fabricate the positive electrode.

[0084] Preparation of the isolation membrane: A 12μm thick polyethylene (PE) microporous membrane was selected as the isolation membrane.

[0085] Making the negative electrode:

[0086] A negative electrode slurry was prepared by mixing artificial graphite and SiO2 (90:10 by mass) at a ratio of 96 wt% and styrene-butadiene rubber at a ratio of 2 wt%, and adding the mixture to a solution obtained by dissolving lithium carboxymethyl cellulose at a ratio of 2 wt% in deionized water. This negative electrode slurry was then coated onto one side of a copper foil, dried, pressurized, and cut to the specified size to fabricate the negative electrode.

[0087] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, methyl ethyl carbonate, ethyl acetate and diethyl carbonate are mixed in a mass ratio of 1:1:1 to obtain a base solvent. Then, lithium salt LiPF6 and the additives shown in Table 1 are added to the base solvent and mixed evenly to obtain the electrolyte. The mass content of LiPF6 is 12% based on the mass of the electrolyte.

[0088] Battery making:

[0089] The positive electrode, separator, and negative electrode are stacked sequentially, with the separator acting as a barrier between the positive and negative electrodes. The electrode assembly is then wound up. After welding tabs, the electrode assembly is placed in an outer aluminum-plastic film package. Moisture is removed at 80°C, and the electrolyte is injected. Following vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained. This secondary battery is a pouch-shaped battery with dimensions of 30mm wide, 45mm high, and 5mm thick.

[0090] Table 1

[0091]

[0092] Test methods

[0093] Particle breakage change rate

[0094] The following steps were used to repeatedly charge and discharge two secondary batteries (numbered as battery X and battery Y) to conduct the test:

[0095] First, in an environment of 25℃, the first charge and discharge were carried out. The battery was first charged with a constant current of 0.5C until it reached 4.2V, and then charged with a constant voltage. Then, it was discharged with a constant current of 1C until it reached 2.8V. Then, the battery X was subjected to 200 charge and discharge cycles, and the battery Y was subjected to 400 charge and discharge cycles.

[0096] After disassembling the battery after the above cycle, the particle breakage change rate was obtained by cross-sectional polishing-scanning electron microscopy (CP-SEM) test on the positive electrode material layer = the first particle breakage percentage of battery X / the second particle breakage percentage of battery Y × 100%.

[0097] The following criteria are used for evaluation: the smaller the particle breakage rate, the higher the overall stability of the secondary battery in this application.

[0098] A: The particle breakage rate is less than 1.2%.

[0099] B: The particle breakage change rate is above 1.2 and less than 1.4.

[0100] C: The particle breakage change rate is above 1.4 and less than 1.8.

[0101] D: The particle breakage rate is above 1.8.

[0102] Float charging safety

[0103] The testing method is as follows:

[0104] The prepared secondary battery was placed in a 25°C constant temperature chamber and allowed to stand for 30 minutes to reach a constant temperature. It was then charged at a constant current of 1C until the voltage reached 4.2V, and then charged at a constant voltage until the current reached 0.05C. It was then discharged at a constant current of 1C until the voltage reached 2.8V. Afterward, it was charged at a constant current of 0.5C until the voltage reached 4.2V, and then charged at a constant voltage until the current reached 0.05C. The thickness of the secondary battery at this point was measured and recorded as the initial thickness. The secondary battery was transferred to a 45°C constant temperature chamber and charged at a constant voltage of 4.2V for 30 days. After 30 days, the secondary battery was transferred to a 25°C constant temperature chamber and allowed to stand for 60 minutes. It was then discharged at a constant current of 1C until the voltage reached 2.8V. It was then charged at a constant current of 1C until the voltage reached 4.2V, and then charged at a constant voltage until the current reached 0.05C. Finally, it was discharged at a constant current of 1C until the voltage reached 2.8V. The thickness of the lithium-ion battery was measured and recorded as the thickness after float charging.

[0105] Float charge thickness change rate = (Thickness after float charge - Initial thickness) / Initial thickness × 100%

[0106] The following benchmarks are used for evaluation: the smaller the value of the float charge thickness change rate, the higher the overall stability of the secondary battery in this application.

[0107] A: The change rate of float thickness is less than 22%.

[0108] B: The float thickness variation rate is above 22% and less than 28%.

[0109] C: The float thickness change rate is above 28% and less than 33%.

[0110] D: The float thickness variation rate is above 33%.

[0111] Test Results

[0112] In Table 1, " / " indicates that the substance was not added;

[0113] As shown in Table 1, the positive electrode of this application includes a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes lithium iron phosphate and lithium manganese oxide, and the electrolyte includes lithium difluorophosphate, which can not only improve the float charging safety of secondary batteries, but also reduce the particle breakage rate.

[0114] In particular, this application dops zirconium and boron into lithium iron phosphate and antimony into lithium manganese oxide, which can further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0115] Specifically, based on the content of metal elements other than lithium in the cathode material layer, the mass content ratio of zirconium, boron and antimony is 1:(0.1~0.9):(0.01~0.5), which can further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0116] In particular, the amount of lithium difluorophosphate is 0.01 to 1 part by mass relative to 100 parts by mass of the electrolyte, which can further improve the float charging safety of the secondary battery and reduce the particle breakage rate.

[0117] In particular, lithium difluorophosphate is more preferably 0.09 to 0.6 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the float charging safety of the secondary battery and reduce the particle breakage rate.

[0118] In particular, the insulation layer includes polyvinylidene fluoride and N-methylpyrrolidone, which can further improve the float charging safety of the secondary battery and reduce the particle breakage rate.

[0119] Specifically, the electrolyte includes sodium dihydrogen phosphate, and the amount of sodium dihydrogen phosphate is 0.03 to 0.7 parts by mass relative to 100 parts by mass of electrolyte, which can further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0120] In particular, the electrolyte includes p-toluenesulfonyl isocyanate. The amount of p-toluenesulfonyl isocyanate, ranging from 0.01 to 3 parts by weight relative to 100 parts by weight of electrolyte, can further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0121] Specifically, the electrolyte includes sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate. Relative to 100 parts by mass of electrolyte, sodium dihydrogen phosphate is a parts by mass and p-toluenesulfonyl isocyanate is b parts by mass. 0.01≤a / b≤0.95 can further improve the float charging safety of secondary batteries and reduce the particle breakage rate.

[0122] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0123] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A secondary battery, comprising: A positive electrode, a negative electrode, and an electrolyte, characterized in that the positive electrode comprises a positive electrode current collector and an insulating layer and a positive electrode material layer disposed on the positive electrode current collector; the insulating layer and the positive electrode material layer are disposed parallel to each other on the surface of the positive electrode current collector, and the insulating layer is located in the tab contact area; The insulating layer includes boehmite, the positive electrode material layer includes lithium iron phosphate and lithium manganese oxide, the lithium iron phosphate includes zirconium and boron, the lithium manganese oxide includes antimony, and the electrolyte includes lithium difluorophosphate. The electrolyte comprises p-toluenesulfonyl isocyanate, and the p-toluenesulfonyl isocyanate is from 0.01 parts by weight to 3 parts by weight relative to 100 parts by weight of the electrolyte; Based on the content of metal elements other than lithium in the cathode material layer, the mass content ratio of zirconium, boron and antimony is 1:(0.1~0.9):(0.01~0.5); Based on the content of metal elements other than lithium in the cathode material layer, the zirconium element has a mass content of 2000ppm to 5000ppm, the boron element has a mass content of 500ppm to 3000ppm, and the antimony element has a mass content of 100ppm to 1000ppm.

2. The secondary battery according to claim 1, characterized in that, The lithium difluorophosphate is 0.01 to 1 part by mass relative to 100 parts by mass of the electrolyte.

3. The secondary battery according to claim 1, characterized in that, The lithium difluorophosphate is 0.05 to 0.9 parts by weight relative to 100 parts by weight of the electrolyte.

4. The secondary battery according to claim 1, characterized in that, The lithium difluorophosphate is 0.09 to 0.6 parts by mass relative to 100 parts by mass of the electrolyte.

5. The secondary battery according to claim 1, characterized in that, The insulating layer comprises polyvinylidene fluoride and N-methylpyrrolidone.

6. The secondary battery according to claim 1, characterized in that, The electrolyte comprises sodium dihydrogen phosphate, wherein the sodium dihydrogen phosphate is 0.03 to 0.7 parts by weight relative to 100 parts by weight of the electrolyte.

7. The secondary battery according to claim 1, characterized in that, The electrolyte comprises sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate, wherein, relative to 100 parts by mass of the electrolyte, sodium dihydrogen phosphate is a parts by mass and p-toluenesulfonyl isocyanate is b parts by mass, and 0.01 ≤ a / b ≤ 0.

95.

8. An electronic device, characterized in that, It includes a secondary battery according to any one of claims 1 to 7.

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