Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. The secondary battery comprises: a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises a positive electrode current collector, and an insulating layer and a positive electrode material layer which are provided on the positive electrode current collector; and the insulating layer comprises boehmite, the positive electrode material layer comprises lithium iron phosphate and lithium manganate, and the electrolyte comprises lithium difluorophosphate. The present application not only improves the floating charge safety of secondary batteries, but also reduces the rate of particle fragmentation.

Description

Secondary battery and electronic device TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Under the background of rapid development of current technology and continuous improvement of life quality, secondary batteries have become the core power source in key fields such as portable electronic devices and electric vehicles due to their excellent high energy density characteristics and the convenience of cyclic charging and discharging, and their importance is increasingly prominent. However, as the application scenarios continue to expand and complicate, more stringent requirements are put forward for the comprehensive performance of secondary batteries. SUMMARY

[0003] The embodiments of the present application adjust the components of the positive electrode and the electrolyte in the secondary battery to further improve the comprehensive stability of the secondary battery. The present inventors have found that 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, and the positive electrode material layer includes lithium iron phosphate and lithium manganate; and the electrolyte includes lithium difluorophosphate, which not only improves the safety of battery floating charging, but also reduces the particle breakage rate, thereby completing the present application.

[0004] Optionally, the lithium iron phosphate includes zirconium elements and boron elements, and the lithium manganate includes antimony elements.

[0005] Optionally, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content ratio of zirconium elements, boron elements and antimony elements is 1:(0.1-0.9):(0.01-0.5).

[0006] Optionally, relative to 100 parts by mass of the electrolyte, the lithium difluorophosphate is 0.01 parts by mass to 1 part by mass.

[0007] Optionally, relative to 100 parts by mass of the electrolyte, the lithium difluorophosphate is 0.05 parts by mass to 0.9 parts by mass.

[0008] Optionally, relative to 100 parts by mass of the electrolyte, the lithium difluorophosphate is 0.09 parts by mass to 0.6 parts by mass.

[0009] Optionally, the insulating layer includes polyvinylidene fluoride and N-methyl pyrrolidone.

[0010] Optionally, the electrolyte includes sodium dihydrogen phosphate, and relative to 100 parts by mass of the electrolyte, the sodium dihydrogen phosphate is 0.03 parts by mass to 0.7 parts by mass.

[0011] Optionally, the electrolyte includes p-toluenesulfonyl isocyanate, and relative to 100 parts by mass of the electrolyte, the p-toluenesulfonyl isocyanate is 0.01 parts by mass to 3 parts by mass.

[0012] Optionally, the electrolyte comprises sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate, the sodium dihydrogen phosphate is a mass parts and the p-toluenesulfonyl isocyanate is b mass parts relative to 100 mass parts of the electrolyte, 0.01≤a / b≤0.95.

[0013] In another aspect of the present application, the present application provides an electronic device comprising the secondary battery described in the present application.

[0014] The present application can not only improve the floating safety of the battery, but also reduce the particle breakage rate by using the combination of the specific positive electrode and the electrolyte.

[0015] Additional aspects and advantages of embodiments of the present application will be described in part in the description that follows, will be apparent through use of the embodiments of the present application, and will be learned through practice of the embodiments of the present application. Embodiments of the present application

[0016] Embodiments of the present application will be described in detail below. Embodiments of the present application should not be construed as limiting the present application.

[0017] The following terms used in the present application have the meanings indicated below, unless explicitly stated otherwise.

[0018] The present application can not only improve the floating safety of the battery, but also reduce the particle breakage rate by using the combination of the specific positive electrode and the electrolyte.

[0019] In one embodiment, the present application provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte as described below.

[0020] I. Positive electrode

[0021] The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery comprising: a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising 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 comprising boehmite, the positive electrode material layer comprising lithium iron phosphate and lithium manganate, the electrolyte comprising lithium difluorophosphate. The present application can not only improve the floating safety of the battery, but also reduce the particle breakage rate.

[0022] The positive electrode material layer contains lithium iron phosphate and lithium manganate, and the positive electrode material layer can be one layer or multiple layers.

[0023] The present inventors have unexpectedly found in experiments that the positive electrode material layer containing lithium iron phosphate and lithium manganate and the insulating layer containing boehmite in the electrolyte system containing lithium difluorophosphate can not only improve the floating safety of the battery, but also reduce the particle breakage rate.

[0024] The crystallographic information of boehmite, lithium iron phosphate and lithium manganate is quite different, but in the presence of lithium difluorophosphate-containing electrolyte, the element sites in the three materials are in contact with lithium difluorophosphate, which is speculated to form a special structure channel in the secondary battery, thus not only improving the battery floating safety, but also reducing the particle breakage change rate.

[0025] Specifically, from the perspective of improving the battery floating safety and reducing the particle breakage change rate, lithium iron phosphate includes zirconium and boron elements, and lithium manganate includes antimony element. Among them, from the perspective of reducing the particle breakage change rate, the mass content ratio of zirconium, boron and antimony elements is 1:(0.1-0.9):(0.01-0.5), preferably 1:(0.16-0.6):(0.02-0.25), more preferably 1:(0.2-0.5):(0.03-0.2). When the mass content ratio of zirconium, boron and antimony elements meets the above range, the battery floating safety can be further improved and the particle breakage change rate can be further reduced. When the above elements are introduced into the crystal structure of lithium iron phosphate and lithium manganate, the lattice parameter matching degree between them is further improved.

[0026] Specifically, from the viewpoint of improving the safety of battery float charging and reducing the change rate of particle breakage, in some embodiments, the mass content of the zirconium element is 1000 ppm to 20000 ppm, for example, a value within a range consisting of 1000 ppm, 2300 ppm, 2600 ppm, 5300 ppm, 6300 ppm, 7200 ppm, 9500 ppm, 10400 ppm, 11700 ppm, 13600 ppm, 15000 ppm, 15900 ppm, 17900 ppm, 19200 ppm, 20000 ppm, or any two thereof, based on the content of metal elements other than lithium in the positive electrode material layer. In some embodiments, from the viewpoint of improving the safety of battery float charging and reducing the change rate of particle breakage, the mass content of the boron element is 500 ppm to 3000 ppm, for example, a value within a range consisting 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 thereof, based on the content of metal elements other than lithium in the positive electrode material layer. In some embodiments, from the viewpoint of improving the safety of battery float charging and reducing the change rate of particle breakage, the mass content of the antimony element is 100 ppm to 1000 ppm, for example, a value within a range consisting of 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm, or any two thereof, based on the content of metal elements other than lithium in the positive electrode material layer.

[0027] The kind of the positive electrode conductive material is not limited, and any known conductive material can be used. Examples of the positive electrode conductive material can include, but are not limited to, carbon black such as acetylene black; amorphous carbon such as needle coke; and the like. Carbon nanotubes; graphene; and the like. The above-described positive electrode conductive material can be used alone or in any combination.

[0028] The kind of solvent used to form the positive electrode slurry is not limited, as long as it is a solvent capable of dissolving or dispersing the positive electrode material, the conductive material, and the positive electrode binder. Examples of the solvent used to form the positive electrode slurry can include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium can include, but are not limited to, water and a mixed medium composed of alcohol and water, etc. Examples of the organic medium can include, but are not limited to, aliphatic hydrocarbons such as hexane, etc.; aromatic hydrocarbons such as benzene, toluene, xylene, methylnaphthalene, etc.; heterocyclic compounds such as quinoline, pyridine, etc.; ketones such as acetone, methyl ethyl ketone, cyclohexanone, etc.; esters such as methyl acetate, methyl acrylate, etc.; amines such as diethylenetriamine, N,N-dimethylaminopropylamine, etc.; ethers such as diethyl ether, propylene oxide, tetrahydrofuran, etc.; amides such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, etc.; aprotic polar solvents such as hexamethylphosphoramide, dimethyl sulfoxide, etc.

[0029] The density of the portion of the active material layer of the positive electrode other than the current collector is generally 3.5 g / cm 3 The density of the portion of the active material layer of the positive electrode other than the current collector is generally 3.5 g / cm 3 The density of the portion of the active material layer of the positive electrode other than the current collector is generally 3.5 g / cm 3 The density of the portion of the active material layer of the positive electrode other than the current collector is generally 3.5 g / cm

[0030] The kind of the positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. Examples of the positive electrode current collector can include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating layer, titanium, tantalum, etc.; carbon materials such as carbon cloth, carbon paper, etc. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0031] In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode material layer, the surface of the positive electrode current collector can include a conductive aid or a conductive coating. Examples of the conductive aid can include, but are not limited to, carbon and noble metals such as gold, platinum, silver, etc. Examples of the conductive coating can include a mixture layer containing inorganic oxide, conductive agent, binder.

[0032] From the viewpoint of improving the float safety of the battery and reducing the change rate of particle breakage, boehmite is contained in the insulating layer.

[0033] Specifically, from the viewpoint of improving the float safety of the battery and reducing the change rate of particle breakage, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone.

[0034] The positive electrode is produced by:

[0035] Boehmite, polyvinylidene fluoride, N-methylpyrrolidone are mixed, deionized water is added thereto and mixed uniformly to form slurry 1.

[0036] The positive electrode material described above, a conductive agent such as acetylene black, carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile are mixed, a high-boiling solvent such as N-methylpyrrolidone is added thereto, and kneading is performed to produce slurry 2.

[0037] The slurry 1 and the slurry 2 are applied in parallel on an aluminum foil or the like serving as a current collector, and then dried and pressed to form a positive electrode.

[0038] II. Electrolyte

[0039] The electrolyte used in the secondary battery of the present application includes an electrolyte and a solvent in which the electrolyte is dissolved. In some embodiments, the electrolyte of the present application includes lithium difluorophosphate.

[0040] When lithium difluorophosphate is used in the secondary battery in the present application, the inventors found that it not only improves the battery float safety but also reduces the particle breakage change rate under the addition of lithium iron phosphate and lithium manganese phosphate and boehmite in the positive electrode.

[0041] Specifically, from the viewpoint of improving the battery float safety and reducing the particle breakage change rate, the electrolyte includes lithium difluorophosphate, wherein the 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, particularly preferably 0.18 parts by mass or more, with respect to 100 parts by mass of the electrolyte. In addition, as the upper limit of the content of lithium difluorophosphate, from the viewpoint of improving the battery float safety and reducing the particle breakage change rate, the 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, particularly preferably 0.5 parts by mass or less. When it is within the above range, it is helpful to further improve the float safety of the secondary battery and reduce the particle breakage change rate.

[0042] Specifically, from the viewpoint of improving the float safety of the secondary battery and reducing the particle breakage change rate, the electrolyte includes sodium dihydrogen phosphate. In some embodiments, the sodium dihydrogen phosphate is a parts by mass with respect to 100 parts by mass of the electrolyte, and a has a value in the range of 0.03 to 0.7, for example, a is 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or a value within a range consisting of any two of them. When the mass fraction of sodium dihydrogen phosphate in the electrolyte is regulated to satisfy the above range, the float safety of the secondary battery can be further improved and the particle breakage change rate can be reduced.

[0043] Specifically, from the viewpoint of improving the float safety of the secondary battery and reducing the particle breakage change rate, the electrolyte includes p-toluenesulfonyl isocyanate. In some embodiments, the p-toluenesulfonyl isocyanate is b mass parts with respect to 100 mass parts of the electrolyte, and b is in the range of 0.01 to 3, for example, b is 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 a value in a range defined by any two of them. When the mass fraction of p-toluenesulfonyl isocyanate in the electrolyte is regulated to be in the above range, the float safety of the secondary battery and the particle breakage change rate can be further improved.

[0044] Specifically, from the viewpoint of improving the float safety of the secondary battery and reducing the particle breakage change rate, the electrolyte includes p-toluenesulfonyl isocyanate. In some embodiments, the p-toluenesulfonyl isocyanate is b mass parts with respect to 100 mass parts of the electrolyte, and b is in the range of 0.01 to 3, for example, b is 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 a value in a range defined by any two of them. When the mass fraction of p-toluenesulfonyl isocyanate in the electrolyte is regulated to be in the above range, the float safety of the secondary battery and the particle breakage change rate can be further improved.

[0045] In some embodiments, the additive in the electrolyte solution includes one or more of 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, diethyl sulfate, methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethylsulfonate, methyl 2-(methylsulfonyloxy)propionate, ethyl 2-(methylsulfonyloxy)propionate, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1-propenyl-1,3-propanesultone, 2-propenyl-1,3-propanesultone, 1-fluoro-1-propenyl-1,3-propanesultone, 2-fluoro-1-propenyl-1,3-propanesultone, 3-fluoro-1-propenyl-1,3-propanesultone, 1-fluoro-2-propenyl-1,3-propanesultone, 2-fluoro-2-propenyl-1,3-propanesultone, 3-fluoro-2-propenyl-1,3-propanesultone, 1-methyl-1-propenyl-1,3-propanesultone, 2-methyl-1-propenyl-1,3-propanesultone, 3-methyl-1-propenyl-1,3-propanesultone, 1-methyl-2-propenyl-1,3-propanesultone, 2-methyl-2-propenyl-1,3-propanesultone, 3-methyl-2-propenyl-1,3-propanesultone, 1,4-butanesultone, 1,5-pentanesultone, methanedisulfonate methylene, methanedisulfonate ethylene, dimethyl sulfite, methyl ethyl sulfite, diethyl sulfite, 1,2-ethanediol sulfite, 1,2-propanediol sulfite, 1,3-propanediol sulfite, 1,2-butanediol sulfite, 1,3-butanediol sulfite, 1,4-butanediol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, and the like. In some embodiments, the electrolyte solution further includes an ionizable lithium salt, which includes at least one of LiPF6, LiSbF6, LiAsF6, LiClO4, LiN(C2F5SO2)2, CF3SO3Li, LiC(CF3SO2)3, or LiC4BO8. For example, the lithium salt used in the electrolyte solution of the present application includes LiPF6, and the content of LiPF6is 9 to 15% by mass, preferably 9 to 13% by mass, and more preferably 9 to 12% by mass, based on the mass of the electrolyte solution. By setting the content within the above range, the effects of improving the float safety of the secondary battery and reducing the particle breakage rate can be more balanced.

[0046] In some embodiments, the electrolyte further includes at least one of lithium difluorophosphate (LiPO2F2), lithium difluoro oxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis-trifluoromethanesulfonimide (LiTFSI), lithium bisfluorosulfonimide (LiFSI).

[0047] In some embodiments, the additive in the electrolyte further includes at least one of a fluoroether compound, a fluoro-carbonate compound, an ether nitrile compound, such as hydrofluoroether (HFE-458), fluoroethylene carbonate (FEC), and the like.

[0048] In some embodiments, the electrolyte can further include a non-aqueous solvent. The non-aqueous solvent can be selected from a carbonate compound, a carboxylate compound, an ether compound, a phosphate compound, other organic solvents, or a combination thereof.

[0049] Alternatively, the carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof. In another aspect, the carbonate compound can also be a fluoro-carbonate compound, a non-fluoro-carbonate compound, or a combination thereof.

[0050] Specifically, examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or a combination thereof. Examples of the fluoro-carbonate compound 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-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, trifluoromethyl ethylene carbonate, or a combination thereof.

[0051] Specifically, examples of the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, hexalactone, methyl formate, or a combination thereof.

[0052] 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.

[0053] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0054] Specifically, examples of the other organic solvent are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidone, formamide, dimethylformamide, acetonitrile, or a combination thereof.

[0055] III, negative electrode

[0056] The negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on a surface of the negative electrode current collector, the negative electrode material layer including a negative electrode material. In some embodiments, the chargeable capacity of the negative electrode material is greater than the discharge capacity of the positive electrode material to prevent lithium metal from inadvertently depositing on the negative electrode during charging.

[0057] Further, as the negative electrode material, there is no particular limitation, and carbon-based negative electrode materials, metal-based negative electrode materials, silicon-based negative electrode materials, and negative electrode materials combining them, and the like can be cited.

[0058] Carbon-based negative electrode material

[0059] Here, the carbon-based negative electrode material refers to an active material that can intercalate lithium with a carbon-based skeleton, and as the carbon-based negative electrode material, for example, carbonaceous materials and graphitic materials can be cited.

[0060] As the carbonaceous material, for example, easy graphitizable carbon, difficult graphitizable carbon having a structure similar to an amorphous structure represented by glassy carbon, and the like can be cited. Here, as the easy graphitizable carbon, for example, carbon materials obtained from tar pitch as a raw material from petroleum or coal can be cited. When a specific example is cited, for example, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolytic vapor grown carbon fibers can be cited. Further, as the difficult graphitizable carbon, for example, phenol resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), hard carbon, and the like can be cited.

[0061] Further, as the graphitic material, for example, natural graphite, artificial graphite, and the like can be cited. Among them, as the artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing easy graphitizable carbon at 2800°C or higher, graphitic MCMB obtained by heat-treating MCMB at 2000°C or higher, graphitic mesophase pitch-based carbon fibers obtained by heat-treating mesophase pitch-based carbon fibers at 2000°C or higher, and the like can be cited. In addition, in the present application, as the carbon-based negative electrode material, natural graphite in which at least a part of the surface thereof is covered with amorphous carbon (amorphous-coated natural graphite) can be used.

[0062] Further, the metal-based negative electrode material is an active material including a metal, and generally refers to an active material including an element capable of intercalating lithium or alloying with lithium in the structure, in which case the theoretical current capacity per unit mass is 500 mAh / g or more. As the metal-based negative electrode material, for example, lithium metal, elemental metals that can form lithium alloys (for example, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, and the like), alloys thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof can be used. Among them, as the metal-based negative electrode material, an active material including silicon (silicon-based negative electrode material) is preferable. This is because, by using a silicon-based negative electrode material, it is possible to increase the capacity of the secondary battery.

[0063] As the silicon-based negative electrode material, for example, silicon (Si), an alloy including silicon, SiO, SiO2, a composite of a silicon-containing material and a conductive carbon in which the silicon-containing material is coated or compounded with the conductive carbon (silicon-carbon material) can be given.

[0064] From the viewpoint of increasing the capacity of the battery, a silicon-carbon material, for example, a composite of porous carbon supporting silicon, is preferable.

[0065] In addition, the negative electrode material can be used alone or two or more kinds can be used in combination at an arbitrary ratio.

[0066] Here, the volume average particle diameter of the negative electrode material is preferably 1 μm or more, more preferably 5 μm or more, and is preferably 30 μm or less, more preferably 20 μm or less. If the volume average particle diameter of the negative electrode material is equal to or greater than the lower limit value described above, it is possible to effectively suppress the heat generation at the time of internal short circuit. In addition, if the volume average particle diameter of the negative electrode material is equal to or less than the upper limit value described above, it is possible to effectively suppress the increase in the initial resistance of the obtained battery.

[0067] The negative electrode material layer can further include a negative electrode binder. The negative electrode binder can improve the binding between the negative electrode material particles and the binding between the negative electrode material and the current collector. The kind of the negative electrode binder is not particularly limited, and can be a material stable to the electrolyte or the solvent used at the time of manufacturing the electrode. In some embodiments, the negative electrode binder includes a resin binder. Examples of the resin binder include, but are not limited to, a fluorine resin, a polyacrylonitrile (PAN), a polyimide resin, an acrylic resin, a polyolefin resin, and the like. When the negative electrode binder is prepared using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, and the like.

[0068] As the current collector that holds the negative electrode material, a publicly known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0069] The negative electrode can be produced by coating a negative electrode mixture slurry containing a negative electrode material, a resin binder, and the like on a negative electrode current collector, drying, and then calendering to form a negative electrode material layer on both sides of the negative electrode current collector, whereby a negative electrode can be obtained.

[0070] IV. Separator

[0071] In order to prevent short-circuiting, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by permeating into the separator.

[0072] The material and shape of the separator are not particularly limited as long as the effects of the present application are not significantly impaired. The separator can be a resin, a glass fiber, an inorganic substance, or the like formed of a material stable to the electrolyte of the present application. In some embodiments, the separator includes a porous sheet or a nonwoven fabric-like substance having excellent liquid retention, or the like. Examples of the material of the resin or glass fiber separator can include, but are not limited to, polyolefin, aramid, polytetrafluoroethylene, polyethersulfone, and the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separator can be used alone or in any combination.

[0073] The separator can also be a material in which the above-mentioned materials are layered, examples of which include, but are not limited to, a three-layer separator in which polypropylene, polyethylene, and polypropylene are layered in this order, and the like.

[0074] Examples of the material of the inorganic substance can include, but are not limited to, oxides such as alumina and silica, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate. The form of the inorganic substance can include, but is not limited to, a granular or fibrous form.

[0075] The separator can be in a film form, examples of which include, but are not limited to, a nonwoven fabric, a woven fabric, and a microporous film. In the film form, the separator has a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent film-like separator, a separator in which a composite porous layer containing the above-mentioned inorganic substance particles is formed on the surface of the positive electrode and / or the negative electrode by using a resin-based adhesive can be used, for example, a separator in which 90% of alumina particles having a particle size of less than 1 μm are formed into a porous layer on both sides of the positive electrode using a fluororesin as an adhesive.

[0076] The thickness of the separator film is arbitrary. In some embodiments, the thickness of the separator film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator film is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator film is within the above range, the insulation and mechanical strength can be ensured, and the direct current resistance characteristics and energy density of the secondary battery can be ensured.

[0077] The present application also provides an electronic device comprising the secondary battery according to the present application.

[0078] The use of the secondary battery of the present application is not particularly limited, and it can be used in any electronic device known in the art. In some embodiments, the secondary battery of the present application can be used in, but not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium-ion capacitors, etc.

[0079] Embodiments

[0080] Hereinafter, embodiments of the secondary battery of the present application are shown, but the present application is not limited to these embodiments.

[0081] Preparation of the secondary battery

[0082] Preparation of the positive electrode:

[0083] Boehmite and polyvinylidene fluoride were mixed in the mass ratio shown in Table 1, dissolved in N-methylpyrrolidone, deionized water was added thereto and mixed uniformly to prepare a positive electrode slurry 1.

[0084] The positive electrode material lithium iron phosphate (46 wt%), lithium manganese oxide (51 wt%), conductive carbon black (1 wt%) in Table 1 were mixed, and a solution of polyvinylidene fluoride (2 wt%) dissolved in N-methylpyrrolidone was added thereto and mixed to prepare a positive electrode slurry 2. The slurry 1 was coated on the tab side, and the slurry 1 and the slurry 2 were coated in parallel on an aluminum foil. The coated aluminum foil was dried, subjected to pressure treatment, and cut into a predetermined size to prepare a positive electrode.

[0085] Preparation of the separator film: A 12 μm-thick polyethylene (PE) microporous film was selected as the separator film.

[0086] Preparation of the negative electrode:

[0087] A negative electrode slurry was prepared by mixing artificial graphite and SiO2 (mass ratio 90:10) 96 wt%, styrene-butadiene rubber 2 wt%, adding to a solution in which carboxymethyl cellulose lithium 2 wt% was previously dissolved in deionized water and mixing. The negative electrode slurry was coated on one side of a copper foil, dried, pressure treated, and then cut to a specified size to make a negative electrode.

[0088] Preparation of electrolyte: In an argon glove box with a water content of less than 10 ppm, methyl ethyl carbonate, ethyl acetate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 to obtain a base solvent, and then lithium salt LiPF6 and the additives shown in Table 1 were added to the base solvent. After mixing uniformly, an electrolyte was obtained, wherein the mass content of LiPF6 was 12% based on the mass of the electrolyte.

[0089] Battery preparation:

[0090] The positive electrode sheet, the separator, and the negative electrode sheet were sequentially stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to act as a barrier, and the electrode assembly was obtained by winding. After welding the tabs, the electrode assembly was placed in an outer packaging aluminum plastic film, and after removing the water at 80°C, the above-mentioned electrolyte was injected. After vacuum packaging, standing, formation, shaping, capacity testing, and other processes, a lithium ion battery was obtained. The secondary battery is a bag-shaped battery with a width of 30 mm, a height of 45 mm, and a thickness of 5 mm.

[0091] Table 1

[0092]

[0093] Test method

[0094] Particle breakage change rate

[0095] Two pieces of the prepared secondary batteries (labeled as battery X and battery Y, respectively) were subjected to repeated charging and discharging by the following steps, and the test method is as follows:

[0096] First, in an environment of 25°C, the first charging and discharging were performed, first using a current of 0.5C for constant current charging, then constant voltage charging after charging to 4.2V, and then constant current discharging at a current of 1C to 2.8V. Then, battery X was subjected to 200 cycles of charging and discharging, and battery Y was subjected to 400 cycles of charging and discharging.

[0097] The above-mentioned cycled batteries were disassembled, and the positive electrode material layer was tested by cross-section polishing-scanning electron microscopy (CP-SEM) to obtain the particle breakage change rate = first particle breakage percentage of battery X / second particle breakage percentage of battery Y x 100%.

[0098] The smaller the particle breakage change rate, the higher the comprehensive stability of the secondary battery in the present application.

[0099] A: The particle breakage change rate is less than 1.2.

[0100] B: The particle breakage change rate is 1.2 or more but less than 1.4.

[0101] C: The particle breakage change rate is 1.4 or more but less than 1.8.

[0102] D: The particle breakage change rate is 1.8 or more.

[0103] Floating safety

[0104] The test method is as follows:

[0105] The prepared secondary battery is placed in a 25°C constant temperature oven and allowed to stand for 30 minutes to allow the secondary battery to reach a constant temperature. It is charged at 1C constant current to a voltage of 4.2V, charged at constant voltage to a current of 0.05C, and then discharged at 1C constant current to a voltage of 2.8V. It is then charged at 0.5C constant current to a voltage of 4.2V, charged at constant voltage to a current of 0.05C, and the thickness of the secondary battery at this time is measured and recorded as the initial thickness. The secondary battery is transferred to a 45°C constant temperature oven and charged at 4.2V constant voltage for 30 days. After 30 days, the secondary battery is transferred to a 25°C constant temperature oven and allowed to stand for 60 minutes, and discharged at 1C constant current to a voltage of 2.8V. It is then charged at 1C constant current to a voltage of 4.2V, charged at constant voltage to a current of 0.05C, and then discharged at 1C constant current to 2.8V. The thickness of the lithium ion battery is measured as the thickness after floating.

[0106] Floating thickness change rate = (thickness after floating - initial thickness) / initial thickness x 100%

[0107] The smaller the value of the floating thickness change rate, the higher the comprehensive stability of the secondary battery in the present application.

[0108] A: The floating thickness change rate is less than 22%.

[0109] B: The floating thickness change rate is 22% or more but less than 28%.

[0110] C: The floating thickness change rate is 28% or more but less than 33%.

[0111] D: The floating thickness change rate is 33% or more.

[0112] Test results

[0113] In Table 1, " / " indicates that the substance is not added;

[0114] It can be known from Table 1 that the positive electrode includes a positive electrode current collector and an insulating layer and a positive electrode material layer arranged on the positive electrode current collector; the insulating layer includes boehmite, the positive electrode material layer includes lithium iron phosphate and lithium manganate, and the electrolyte includes lithium difluorophosphate, which can not only improve the floating safety of the secondary battery but also reduce the particle breakage change rate.

[0115] In particular, the zirconium element and the boron element are doped in the lithium iron phosphate, and the antimony element is doped in the lithium manganate, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0116] In particular, based on the content of the metal elements other than lithium in the positive electrode material layer, the mass content ratio of the zirconium element, the boron element and the antimony element is 1:(0.1-0.9):(0.01-0.5), which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0117] In particular, the lithium difluorophosphate is 0.01-1 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0118] In particular, the lithium difluorophosphate is more preferably 0.09-0.6 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0119] In particular, the insulating layer includes polyvinylidene fluoride and N-methylpyrrolidone, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0120] In particular, the electrolyte includes sodium dihydrogen phosphate, and the sodium dihydrogen phosphate is 0.03-0.7 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0121] In particular, the electrolyte includes p-toluenesulfonyl isocyanate, and the p-toluenesulfonyl isocyanate is 0.01-3 parts by mass relative to 100 parts by mass of the electrolyte, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0122] In particular, the electrolyte includes sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate, and the sodium dihydrogen phosphate is a parts by mass and the p-toluenesulfonyl isocyanate is b parts by mass relative to 100 parts by mass of the electrolyte, and 0.01≤a / b≤0.95, which can further improve the floating safety of the secondary battery and reduce the particle breakage change rate.

[0123] References throughout this specification to "an embodiment", "particular embodiments", "one embodiment", "another embodiment", "certain embodiments", "some embodiments", "one example" or "an example" mean that a particular feature, structure, material or characteristic is included in at least one embodiment or example of the present application. Thus, the appearances of the phrases such as "in some embodiments", "in an embodiment", "in one embodiment", "in another embodiment", "in one example", "in particular embodiments" or "in certain embodiments" in various places throughout this specification are not necessarily referring to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0124] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. A secondary battery comprising: The positive electrode, the negative electrode and the electrolyte are characterized in that the positive electrode comprises a positive electrode current collector and an insulating layer and a positive electrode material layer arranged on the positive electrode current collector; the insulating layer comprises boehmite, the positive electrode material layer comprises lithium iron phosphate and lithium manganate, and the electrolyte comprises lithium difluorophosphate.

2. The secondary battery according to claim 1, characterized by The lithium iron phosphate comprises a zirconium element and a boron element, and the lithium manganate comprises an antimony element.

3. The secondary battery according to claim 2, characterized by The mass content ratio of the zirconium element, the boron element and the antimony element is 1:(0.1-0.9):(0.01-0.5) based on the content of metal elements other than lithium in the positive electrode material layer.

4. The secondary battery according to any one of claims 1 to 3, characterized by The lithium difluorophosphate is 0.01-1 parts by mass relative to 100 parts by mass of the electrolyte.

5. The secondary battery according to any one of claims 1 to 3, characterized by The lithium difluorophosphate is 0.05-0.9 parts by mass relative to 100 parts by mass of the electrolyte.

6. The secondary battery according to any one of claims 1 to 3, characterized by The lithium difluorophosphate is 0.09-0.6 parts by mass relative to 100 parts by mass of the electrolyte.

7. The secondary battery according to any one of claims 1 to 3, characterized by The insulating layer comprises polyvinylidene fluoride and N-methylpyrrolidone.

8. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte comprises sodium dihydrogen phosphate, and the sodium dihydrogen phosphate is 0.03-0.7 parts by mass relative to 100 parts by mass of the electrolyte; or The electrolyte comprises p-toluenesulfonyl isocyanate, and the p-toluenesulfonyl isocyanate is 0.01-3 parts by mass relative to 100 parts by mass of the electrolyte.

9. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte comprises sodium dihydrogen phosphate and p-toluenesulfonyl isocyanate, and the sodium dihydrogen phosphate is a parts by mass and the p-toluenesulfonyl isocyanate is b parts by mass relative to 100 parts by mass of the electrolyte, and 0.01≤a / b≤0.

95.

10. An electronic device, comprising: The secondary battery comprises the secondary battery according to any one of claims 1-9.

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