Secondary battery and electronic device

Abstract

A secondary battery and an electronic device. By adjusting the components of a positive electrode and an electrolyte in the secondary battery, the discharge performance is improved. The secondary battery comprises a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises a positive electrode current collector, and a titanium dioxide material layer and a positive electrode material layer which are disposed on the positive electrode current collector; the positive electrode material layer comprises lithium iron phosphate and lithium manganese oxide, and the electrolyte comprises ethylene glycol bis(propionitrile)ether; the lithium iron phosphate is doped with a boron element, and the lithium manganese oxide is doped with a copper element and a tin element.

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] Secondary batteries have been widely applied to portable electronic devices and electric vehicles and other fields due to their core advantages of high energy density and cyclic charge-discharge capability. With the progress of technology and the upgrading of consumer demand, the application boundary of secondary batteries is also expanding, prompting the industry to continue to focus on the innovative research and development of key materials of batteries: positive electrode, negative electrode, separator and electrolyte. In this process, improving the discharge performance of secondary batteries has become one of the urgent needs in the current application of secondary batteries. SUMMARY

[0003] The embodiments of the present application further improve the discharge performance by adjusting the composition of the positive electrode and the electrolyte in the secondary battery. The present inventors have found that the positive electrode includes a positive electrode current collector and a titanium dioxide material layer and a positive electrode material layer disposed on the positive electrode current collector; the positive electrode material layer includes lithium iron phosphate and lithium manganate, the electrolyte includes ethylene glycol di (propyl cyanide) ether, the lithium iron phosphate is doped with boron elements, and the lithium manganate is doped with copper elements and tin elements, which can improve the discharge performance of the battery, thereby completing the present application.

[0004] In some embodiments, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content ratio of boron elements, copper elements and tin elements is 130: (1-4): (0.05-0.9).

[0005] In some embodiments, relative to 100 parts by mass of the electrolyte, ethylene glycol di (propyl cyanide) ether is 0.01 parts by mass to 1 part by mass.

[0006] In some embodiments, relative to 100 parts by mass of the electrolyte, ethylene glycol di (propyl cyanide) ether is 0.05 parts by mass to 0.9 parts by mass.

[0007] In some embodiments, relative to 100 parts by mass of the electrolyte, ethylene glycol di (propyl cyanide) ether is 0.09 parts by mass to 0.6 parts by mass.

[0008] In some embodiments, the titanium dioxide material layer is also doped with di-niobium trioxide.

[0009] In some embodiments, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate, and relative to 100 parts by mass of the electrolyte, 2,4,6-trimethoxyphenyl isocyanate is 0.01 parts by mass to 2 parts by mass.

[0010] In some embodiments, the electrolyte includes 2,4,6-trifluorophenyl isocyanate, and the 2,4,6-trifluorophenyl isocyanate is 0.1 to 4 parts by mass relative to 100 parts by mass of the electrolyte.

[0011] In some embodiments, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate and 2,4,6-trifluorophenyl isocyanate, and the 2,4,6-trimethoxyphenyl isocyanate is a parts by mass and the 2,4,6-trifluorophenyl isocyanate is b parts by mass relative to 100 parts by mass of the electrolyte, and 0.1≤a / b≤0.5.

[0012] In another aspect of the present application, the present application provides an electronic device including the secondary battery described in the present application.

[0013] The present application can improve the discharge performance of the battery by using the combination of the specific positive electrode and the electrolyte.

[0014] Additional aspects and advantages of embodiments of the present application will be described in part below. Embodiments of the present application

[0015] Embodiments of the present application will be described in detail below. Embodiments of the present application should not be interpreted as limiting the present application.

[0016] The following terms used in the present application have the meanings indicated below, unless explicitly stated otherwise.

[0017] The present application can improve the discharge performance of the battery by using the combination of the specific positive electrode and the electrolyte.

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

[0019] I. Positive electrode

[0020] The present application relates to a secondary battery and an electronic device. Specifically, the present application provides a secondary battery including: a positive electrode, a negative electrode, and an electrolyte, the positive electrode including a positive electrode current collector and a titanium dioxide material layer and a positive electrode material layer disposed on the positive electrode current collector; the positive electrode material layer including lithium iron phosphate and lithium manganate, and the electrolyte including ethylene glycol bis (propionitrile) ether. The present application can improve the discharge performance of the battery.

[0021] 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.

[0022] The inventors of the present application accidentally discovered in experiments that the positive electrode material layer containing lithium iron phosphate and lithium manganate can cooperate with the titanium dioxide material layer, and in the electrolyte system containing ethylene glycol bis (propyl nitrile) ether, the self-discharge performance and low-temperature discharge performance of the battery can be improved. The principle is speculated that ethylene glycol bis (propyl nitrile) ether and titanium in titanium dioxide can enhance the crystal structure stability of the lithium iron phosphate and lithium manganate mixed positive electrode system.

[0023] Specifically, from the perspective of improving the discharge performance of the battery, the lithium iron phosphate includes boron elements, and the lithium manganate includes copper elements and tin elements. Among them, from the perspective of improving the self-discharge performance of the battery, the mass content ratio of boron elements, copper elements and tin elements is 130: (1-4): (0.05-0.9), preferably 130: (1-4): (0.1-0.6). When the mass content ratio of boron elements, copper elements and tin elements meets the above range, the discharge performance of the battery can be further improved.

[0024] Specifically, from the perspective of improving the discharge performance of the battery, in some embodiments, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content of boron elements is 1000 ppm to 25000 ppm, such as 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, 25000 ppm or a value within a range consisting of any two of them. In some embodiments, from the perspective of improving the discharge performance of the battery, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content of copper elements is 100 ppm to 2000 ppm, such as 100 ppm, 300 ppm, 500 ppm, 700 ppm, 1000 ppm, 1200 ppm, 1400 ppm, 1500 ppm, 1700 ppm, 1900 ppm, 2000 ppm or a value within a range consisting of any two of them. In some embodiments, from the perspective of improving the discharge performance of the battery, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content of tin elements is 5 ppm to 1000 ppm, such as 5 ppm, 10 ppm, 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, 700 ppm, 800 ppm, 900 ppm, 1000 ppm or a value within a range consisting of any two of them.

[0025] 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-mentioned positive electrode conductive material can be used alone or in any combination.

[0026] The kind of the solvent used for forming 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 for forming 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 an alcohol and water; and the like. Examples of the organic medium 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; and the like.

[0027] The density of the active material layer of the positive electrode other than the current collector is generally 2.5 g / cm 3 The density of the active material layer of the positive electrode other than the current collector is generally 2.5 g / cm 3 The density of the active material layer of the positive electrode other than the current collector is generally 2.5 g / cm 3 The density of the active material layer of the positive electrode other than the current collector is generally 2.5 g / cm

[0028] 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, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0029] 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, and silver. Examples of the conductive coating can include a mixture layer containing inorganic oxides, conductive agents, and binders.

[0030] From the viewpoint of improving the discharge performance of the battery, the titanium dioxide material layer further includes di-niobium trioxide.

[0031] The positive electrode is produced by:

[0032] A slurry 1 was prepared by mixing an inorganic additive such as titanium dioxide, a conductive agent such as acetylene black or carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and then adding deionized water thereto and mixing them uniformly.

[0033] A slurry 2 was prepared by mixing a cathode material, a conductive agent such as acetylene black or carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and then adding a high-boiling solvent such as N-methylpyrrolidone thereto and mixing them.

[0034] The slurry 1 and the slurry 2 were respectively applied to an aluminum foil or the like serving as a current collector, dried, and pressed to form a cathode.

[0035] II. Electrolyte

[0036] 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 ethylene glycol bis (propionitrile) ether.

[0037] When ethylene glycol bis (propionitrile) ether is used in the battery in the present application, the inventors found that it can improve the discharge performance of the battery with the addition of lithium iron phosphate and lithium manganese oxide and titanium dioxide in the cathode.

[0038] Specifically, from the viewpoint of improving the discharge performance of the secondary battery, the electrolyte includes ethylene glycol bis (propionitrile) ether, wherein the ethylene glycol bis (propionitrile) ether is 0.01 parts by mass or more, preferably 0.05 parts by mass or more, and further preferably 0.09 parts by mass or more, and more preferably 0.15 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 ethylene glycol bis (propionitrile) ether, the ethylene glycol bis (propionitrile) ether is 1 part by mass or less, preferably 0.9 parts by mass or less, and particularly preferably 0.6 parts by mass or less, from the viewpoint of improving the discharge performance of the secondary battery. When it is within the above range, it is helpful to further improve the discharge performance of the secondary battery.

[0039] Specifically, from the viewpoint of improving the discharge performance of the secondary battery, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate. In some embodiments, the 2,4,6-trimethoxyphenyl isocyanate is a parts by mass with respect to 100 parts by mass of the electrolyte, and a is in the range of 0.01 to 2, for example, a is 0.01, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.9, 1, 2, or a value within a range consisting of any two of them. When the mass fraction of 2,4,6-trimethoxyphenyl isocyanate in the electrolyte is regulated to satisfy the above range, the discharge performance of the secondary battery can be further improved.

[0040] Specifically, from the viewpoint of improving the discharge performance of the secondary battery, the electrolyte includes 2,4,6-trifluorophenyl isocyanate. In some embodiments, the 2,4,6-trifluorophenyl isocyanate is b mass parts with respect to 100 mass parts of the electrolyte, and b ranges from 0.1 to 4, for example, b is 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, 4.0, or a value within a range defined by any two of these values. When the mass fraction of 2,4,6-trifluorophenyl isocyanate in the electrolyte is regulated to satisfy the above range, the discharge performance of the secondary battery can be further improved.

[0041] Specifically, from the viewpoint of improving the discharge performance of the secondary battery, the electrolyte includes 2,4,6-trifluorophenyl isocyanate. In some embodiments, the 2,4,6-trifluorophenyl isocyanate is b mass parts with respect to 100 mass parts of the electrolyte, and b ranges from 0.1 to 4, for example, b is 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, 4.0, or a value within a range defined by any two of these values. When the mass fraction of 2,4,6-trifluorophenyl isocyanate in the electrolyte is regulated to satisfy the above range, the discharge performance of the secondary battery can be further improved.

[0042] In some embodiments, the additive in the electrolyte solution comprises 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 comprises 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 effect of improving the discharge performance of the battery can be more balanced.

[0043] In some embodiments, the electrolyte further includes at least one of ethylene glycol bis (propionitrile) ether (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI).

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Specifically, examples of the phosphate compound are trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or a combination thereof.

[0051] 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.

[0052] III, negative electrode

[0053] 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.

[0054] 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.

[0055] Carbon-based negative electrode material

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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, and having a theoretical current capacity of 500 mAh / g or more per unit mass in the case of intercalating lithium or alloying with lithium. As the metal-based negative electrode material, for example, 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, 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 the use of the silicon-based negative electrode material enables high capacity of the secondary battery.

[0060] 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.

[0061] From the viewpoint of battery capacity improvement, a silicon-carbon material, for example, a composite of porous carbon supporting silicon, is preferable.

[0062] In addition, the negative electrode material can be used alone or two or more kinds can be used in combination at an arbitrary ratio.

[0063] 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.

[0064] 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 is a material stable to an electrolyte or a solvent used at the time of electrode production. 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 a water-based solvent is used to prepare a negative electrode binder slurry, 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.

[0065] 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, nickel-plated steel, and the like. In some embodiments, the negative electrode current collector is copper.

[0066] 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.

[0067] IV. Separation Film

[0068] In order to prevent short-circuiting, a separation film is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte solution of the present application is generally used by permeating into the separation film.

[0069] The material and shape of the separation film are not particularly limited as long as the effects of the present application are not significantly impaired. The separation film can be a resin, a glass fiber, an inorganic substance, or the like formed of a material stable to the electrolyte solution of the present application. In some embodiments, the separation film 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 separation film 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 separation film can be used alone or in any combination.

[0070] The separation film 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 separation film in which polypropylene, polyethylene, and polypropylene are layered in this order, and the like.

[0071] 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 (e.g., barium sulfate, calcium sulfate, and the like). The form of the inorganic substance can include, but is not limited to, a granular or fibrous form.

[0072] The shape of the separation film can be a film shape, examples of which include, but are not limited to, a nonwoven fabric, a woven fabric, a microporous film, and the like. In the film shape, the separation film 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-shaped separation film, a separation film formed by forming a composite porous layer containing the above-mentioned inorganic substance particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive can also be used, for example, a separation film 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.

[0073] 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, then the insulation and mechanical strength can be ensured, and the direct current resistance characteristics and energy density of the secondary battery can be ensured.

[0074] The present application also provides an electronic device including the secondary battery according to the present application.

[0075] 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.

[0076] Embodiments

[0077] Hereinafter, embodiments of the secondary battery of the present application are shown, but the present application is not limited to these embodiments.

[0078] Preparation of the secondary battery

[0079] Preparation of the positive electrode:

[0080] A positive electrode slurry 1 was prepared by mixing titanium dioxide 70 mass%, acetylene black 10 wt%, and polyvinylidene fluoride 20 wt% with deionized water, mixing uniformly, and adding deionized water thereto. The positive electrode slurry 1 was coated on both sides of a positive electrode current collector aluminum foil having a thickness of 10 μm, dried, and a titanium dioxide material layer was formed.

[0081] A positive electrode slurry 2 was prepared by mixing acetylene black (1 wt%), and polyvinylidene fluoride (2 wt%) dissolved in N-methylpyrrolidone and mixing. The positive electrode slurry 2 was uniformly coated on the surface of the titanium dioxide material layer on both sides of the positive electrode current collector aluminum foil, and then, after cold pressing, cutting, and slitting, a positive electrode was obtained.

[0082] Preparation of the separator film: A 12 μm thick polyethylene (PE) microporous film was selected as the separator film.

[0083] Preparation of the negative electrode:

[0084] 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 prescribed size to produce a negative electrode.

[0085] Preparation of electrolyte: In an argon glove box with a water content of less than 10 ppm, methyl ethyl carbonate, ethyl acetate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain a base solvent, and then LiPF6 and the additives shown in Table 1 were added to the base solvent. After mixing, an electrolyte was obtained, wherein the mass content of LiPF6 was 12% based on the mass of the electrolyte.

[0086] Battery production:

[0087] 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 serve as a separator, 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 moisture at 80°C, the electrolyte described above was injected. After vacuum packaging, standing, formation, shaping, capacity testing, and other processes, a lithium ion battery was obtained. The secondary battery was a bag-shaped battery with a width of 30 mm, a height of 45 mm, and a thickness of 5 mm.

[0088] Table 1

[0089]

[0090] Test method

[0091] Discharge performance at room temperature

[0092] A reference battery for reference was produced. The reference battery was the same as the battery of Example 1, except that it did not contain a titanium dioxide material layer, did not contain ethylene glycol bis (propionitrile) ether, and the positive electrode material did not contain lithium iron phosphate (only contained lithium manganate). The obtained reference battery was charged at a constant current of 0.05C until the battery voltage became 3.6V in a temperature environment of 25°C. Then, it was discharged at a constant current of 0.05C until the battery voltage reached 2.5V, and the charge-discharge curve was obtained. The open-circuit state was maintained for 20 minutes between charging and discharging.

[0093] Each of the prepared example and comparative example batteries was held with a jig composed of a pair of stainless steel (thickness 2 mm) at a pressure of 0.2 MPa. First, the battery was subjected to constant current charging at a current of 0.3 C until the voltage became 3.6 V at a temperature of 25°C, and then subjected to constant voltage charging at a constant voltage of 3.6 V until the current became 0.02 C. Next, the battery was stored in a temperature environment of 25°C, and the battery voltage VI after 48 hours and the battery voltage V2 after 72 hours were measured.

[0094] Based on the charging / discharging curve of the reference battery, the state of charge SOC1 after 48 hours and the state of charge SOC2 after 72 hours were calculated from the battery voltages VI and V2. Next, the self-discharge rate sd per day was derived based on the following equation, and the evaluation was performed.

[0095] Self-discharge rate sd (% / day) = SOC1 (%) - SOC2 (%).

[0096] The smaller the self-discharge rate, the better the secondary battery discharge performance in the present application.

[0097] A: The self-discharge rate sd (% / day) is less than 2.

[0098] B: The self-discharge rate sd (% / day) is 2 or more and less than 4.

[0099] C: The self-discharge rate sd (% / day) is 4 or more and less than 7.

[0100] D: The self-discharge rate sd (% / day) is 7 or more.

[0101] Low temperature discharge performance

[0102] The lithium ion battery was subjected to constant current charging at a constant current of 990 mA (0.3 hour rate) to 3.6 V, and then subjected to constant voltage charging at a constant voltage of 3.6 V with a termination current of 66 mA. Then, the battery was subjected to constant current discharging at a constant current of 3300 mA (1.0 hour rate) to 2.5 V, and the discharge capacity at that time was measured as the battery capacity at 25°C. Then, the battery was subjected to constant current charging at a constant current of 990 mA (0.3 hour rate) to 3.6 V at an ambient temperature of 25°C, and then subjected to constant voltage charging at a constant voltage of 3.6 V with a termination current of 66 mA, and then left in an environment of -10°C for 2 hours. Then, the battery was subjected to constant current discharging at a constant current of 3300 mA (1.0 hour rate) to 2.5 V at an ambient temperature of -10°C, and the discharge capacity at that time was measured as the battery capacity at -10°C. The capacity retention rate at -10°C was calculated by the following equation: Capacity retention rate at -10°C (%) = (-10°C battery capacity / 25°C battery capacity) x 100%.

[0103] The calculated -10 DEG C discharge capacity retention rate is used to evaluate the low-temperature discharge performance of the lithium ion battery, and the higher the low-temperature discharge capacity retention rate, the better the low-temperature discharge performance of the lithium ion battery.

[0104] A: -10 DEG C discharge capacity retention rate (%) is 85 or more.

[0105] B: -10 DEG C discharge capacity retention rate (%) is 80 or more and less than 85.

[0106] C: -10 DEG C discharge capacity retention rate (%) is 72 or more and less than 80.

[0107] D: -10 DEG C discharge capacity retention rate (%) is less than 72.

[0108] Test results

[0109] In Table 1, " / " indicates that the substance is not added;

[0110] As can be seen from Table 1, the positive electrode of the application includes a positive electrode current collector and a titanium dioxide material layer and a positive electrode material layer arranged on the positive electrode current collector; the positive electrode material layer includes lithium iron phosphate and lithium manganate, and the electrolyte includes ethylene glycol di (propyl nitrile) ether, which can improve the discharge performance of the battery.

[0111] In particular, the application dopes boron elements in lithium iron phosphate and dopes copper elements and tin elements in lithium manganate, which can further improve the discharge performance of the battery.

[0112] In particular, based on the content of metal elements other than lithium in the positive electrode material layer, the mass content ratio of boron elements, copper elements and tin elements is 130: (1-4): (0.05-0.9), which can further improve the discharge performance of the battery.

[0113] In particular, relative to 100 parts by mass of the electrolyte, ethylene glycol di (propyl nitrile) ether is 0.01 parts by mass to 1 parts by mass, which can further improve the discharge performance of the battery.

[0114] In particular, relative to 100 parts by mass of the electrolyte, ethylene glycol di (propyl nitrile) ether is more preferably 0.09 parts by mass to 0.6 parts by mass, which can further improve the discharge performance of the battery.

[0115] In particular, the electrolyte includes other additives, which can further improve the discharge performance of the battery.

[0116] In particular, the titanium dioxide material layer further includes di-niobium trioxide, which can further improve the discharge performance of the battery.

[0117] In particular, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate, and 0.01 parts by mass to 2 parts by mass of 2,4,6-trimethoxyphenyl isocyanate with respect to 100 parts by mass of the electrolyte can further improve the discharge performance of the battery.

[0118] In particular, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate, and 0.01 parts by mass to 2 parts by mass of 2,4,6-trimethoxyphenyl isocyanate with respect to 100 parts by mass of the electrolyte can further improve the discharge performance of the battery.

[0119] In particular, the electrolyte includes 2,4,6-trimethoxyphenyl isocyanate, and 0.01 parts by mass to 2 parts by mass of 2,4,6-trimethoxyphenyl isocyanate with respect to 100 parts by mass of the electrolyte can further improve the discharge performance of the battery.

[0120] Throughout this specification the use of "example", "particular example", "one example", "another example", "some examples" or "one particular example" can indicate that a particular feature, structure, material or characteristic is included in at least one example or example of the application. Thus, appearances of these phrases in various places throughout this specification are not necessarily referring to the same example or example of the application. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more examples or examples of the application.

[0121] While the illustrative embodiments have been demonstrated and described, it will be understood by those skilled in the art that the above-described embodiments are not to be interpreted in a limiting sense, and that various changes 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: A positive electrode, a negative electrode and an electrolyte, characterized in that The positive electrode comprises a positive electrode current collector and a titanium dioxide material layer and a positive electrode material layer arranged on the positive electrode current collector; the titanium dioxide material layer is located between the positive electrode current collector and the positive electrode material layer, the positive electrode material layer comprises lithium iron phosphate and lithium manganate, and the electrolyte comprises ethylene glycol di (propionitrile) ether.

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

3. The secondary battery according to claim 2, characterized by The mass content ratio of the boron element, the copper element and the tin element is 130: (1-4): (0.05-0.9) 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 ethylene glycol di (propionitrile) ether 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 ethylene glycol di (propionitrile) ether 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 ethylene glycol di (propionitrile) ether 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 titanium dioxide material layer further comprises di-niobium trioxide.

8. The secondary battery according to any one of claims 1 to 3, characterized by The electrolyte comprises 2,4,6-trimethoxyphenyl isocyanate, and the 2,4,6-trimethoxyphenyl isocyanate is 0.01-2 parts by mass relative to 100 parts by mass of the electrolyte; or The electrolyte comprises 2,4,6-trifluorophenyl isocyanate, and the 2,4,6-trifluorophenyl isocyanate is 0.1-4 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 2,4,6-trimethoxyphenyl isocyanate and 2,4,6-trifluorophenyl isocyanate, and the 2,4,6-trimethoxyphenyl isocyanate is a parts by mass and the 2,4,6-trifluorophenyl isocyanate is b parts by mass relative to 100 parts by mass of the electrolyte, and 0.1≤a / b≤0.

5.

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

Images