Lithium ion battery, preparation method thereof and electronic device

Abstract

The invention discloses a lithium ion battery, a preparation method thereof and an electronic device, the lithium ion battery comprises a positive plate, a diaphragm, a negative plate and an electrolyte, and the diaphragm is clamped between the positive plate and the negative plate; the positive plate comprises a positive current collector and a positive material layer arranged on at least one side surface of the positive current collector, the positive material layer comprises an organic phosphide and a positive active material containing a cobalt element, the organic phosphide contains at least one P-A bond, and A is selected from at least one of S, N and O; the electrolyte contains an organic fluorine compound; the mass percentage X of the cobalt element in the positive electrode material layer, the mass percentage Y of the organic phosphide and the mass percentage T of the organic fluorine compound in the electrolyte meet the conditions that X / Y is more than or equal to 25 and less than or equal to 70, and X / (Y + T) is more than or equal to 10 and less than or equal to 18. The lithium ion battery has excellent high-temperature cycle performance, storage performance and safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery, a preparation method thereof, and an electronic device. Background Art

[0002] Lithium-ion batteries, due to their advantages such as high specific energy, high operating voltage, low self-discharge rate, compact size, and light weight, are widely used in various fields such as energy storage, portable electronic devices, and electric vehicle power supply. However, as the scope of use of lithium-ion batteries continues to expand, the market has placed higher requirements on lithium-ion batteries, such as requiring lithium-ion batteries to have high stability in high-temperature environments.

[0003] However, current lithium-ion batteries typically experience significant capacity decay at high temperatures. This is because the cathode active material in existing lithium-ion batteries is susceptible to severe side reactions with the electrolyte at high temperatures, leading to the dissolution of transition metals and the oxidative decomposition of electrolyte components. This can cause rapid deterioration in battery performance and even lead to serious consequences such as battery fires and explosions. Therefore, there is an urgent need to develop batteries with long service life, high cycle stability, and high safety at high temperatures. Summary of the Invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a lithium ion battery and a preparation method thereof and an electronic device.

[0005] In a first aspect of the present invention, a lithium-ion battery is provided, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the separator is sandwiched between the positive electrode sheet and the negative electrode sheet;

[0006] The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one side of the positive electrode current collector; the positive electrode material layer includes an organic phosphide and a positive electrode active material containing a cobalt element, the organic phosphide contains at least one PA bond, wherein A is selected from at least one of S, N, and O; the electrolyte includes an organic fluorine compound;

[0007] The mass percentage of the cobalt element in the positive electrode material layer is X, the mass percentage of the organic phosphide in the positive electrode material layer is Y, and the mass percentage of the organic fluorine compound in the electrolyte is T. X, Y, and T simultaneously satisfy: 25≤X / Y≤70 and 10≤X / (Y+T)≤18.

[0008] According to an embodiment of the present invention, a lithium-ion battery has at least the following beneficial effects: a positive electrode active material containing cobalt is used in the positive electrode material layer of the positive electrode sheet of the lithium-ion battery, and an organic phosphide containing at least one PA bond (A is selected from at least one of S, N, and O) is added, and the cobalt content X and the organic phosphide content Y in the positive electrode material layer are controlled to satisfy 25≤X / Y≤70. The organic phosphide can minimize the dissolution of transition metals from the positive electrode material at high temperatures. It can act as a sacrificial agent to complex with the transition metal, preventing the dissolution of high-valent transition metals from undergoing oxidative side reactions with the electrolyte. Moreover, the generated organic phosphide complex can be in-situ coated on the surface of the positive electrode material, acting as a protective layer and further isolating the positive electrode material from side reactions with the electrolyte. In addition, organic fluorine compounds are added to the electrolyte, and the content T of the organic fluorine compounds and the cobalt content X and the organic phosphide content Y in the positive electrode material layer are controlled to satisfy 10≤X / (Y+T)≤18. The organic fluorine compounds can form a very stable SEI film on the surface of the negative electrode sheet, which can effectively reduce the impedance growth during the battery cycle, inhibit the generation of hydrogen fluoride, and reduce the reaction between hydrogen fluoride and the positive electrode material. This can also cooperate with the complex of the organic phosphide on the surface of the positive electrode material layer to jointly improve the interface contact between the electrode and the electrolyte, thereby improving the high-temperature cycle performance, storage performance and safety performance of the lithium-ion battery.

[0009] In some embodiments of the present invention, the ratio (X / Y) of the mass percentage X of the cobalt element in the positive electrode material layer to the mass percentage Y of the organic phosphide can be controlled to be any value among 25, 26, 28, 29, 29.1, 30, 30.5, 32, 33, 35, 36, 38, 38.7, 39, 40, 42, 43, 45, 45.5, 47, 49, 50, 52, 55, 58, 58.1, 60, 63, 65, 67, 68, 70 or any two ranges of values. Among them, if the X / Y ratio is too large, the amount of organic phosphide added is too low, and it is impossible to complex all the dissolved transition metals. The uncomplexed high-valent transition metals will still react with the electrolyte, deteriorating the performance; and when the X / Y ratio is too small, the amount of organic phosphide added is too large. Although all the dissolved transition metals can be complexed, the excess organic phosphide will be enriched on the surface of the positive electrode, increasing the battery impedance and causing performance degradation.

[0010] Adding organic fluorine compounds to the electrolyte can increase the content of the inorganic component LiF in the SEI film on the surface of the negative electrode. Since LiF is very stable, the higher its content, the more stable the SEI film formed. In addition, LiF can inhibit the decomposition of lithium salts (such as LiPF6) in the electrolyte to a certain extent, effectively reducing the generation of hydrogen fluoride and reducing the reaction between hydrogen fluoride and the organic phosphide complex on the surface of the positive electrode material. In some embodiments of the present invention, the ratio of the cobalt element content X in the positive electrode material layer to the sum of the organic fluorine compound content T in the electrolyte and the organic phosphide content Y in the positive electrode material layer (i.e., X / (Y+T)) can be controlled to be any one of 10, 10.2, 10.6, 10.8, 11, 11.1, 11.6, 12, 12.5, 12.9, 13, 13.1, 13.5, 14, 14.5, 15, 15.5, 16, 16.6, 17, 17.3, 17.5, 17.8, and 18, or a range of any two of them. Among them, if X / (Y+T) is too large, the organic phosphide complexes the transition metal insufficiently, and the content of organic fluorine compounds in the electrolyte is low, which cannot effectively inhibit the decomposition of lithium salts and reduce the generation of hydrogen fluoride. The generated hydrogen fluoride will destroy the complex of the organic phosphide, causing the high-valent transition metal to dissolve and react with the electrolyte, thereby deteriorating the performance; and if X / (Y+T) is too small, there will be too much organic phosphide, and the excess organic phosphide will be enriched on the surface of the positive electrode sheet, increasing the positive electrode impedance. In addition, if there are too many organic fluorine compounds in the electrolyte, the excess organic fluorine compounds will increase the diffusion rate of lithium ions in the electrolyte, further increasing the battery impedance and thus deteriorating the performance.

[0011] Therefore, by controlling X, Y, and T to simultaneously satisfy: 25≤X / Y≤70 and 10≤X / (Y+T)≤18, it is possible to ensure that the lithium-ion battery has excellent high-temperature cycle performance, storage performance, and safety performance.

[0012] In some embodiments of the present invention, the lithium ion battery satisfies at least one of the following conditions:

[0013] The X satisfies: 50%≤X≤60%;

[0014] The Y satisfies: 1%≤Y≤2%

[0015] The T satisfies: 2%≤T≤4%;

[0016] X / Y=29.1-58.1;

[0017] The X / (Y+T)=10.6-16.6.

[0018] For example, X may be any value selected from 50%, 52%, 53%, 55%, 56.5%, 57%, 58.11%, 59%, and 60%, or a range of any two of them; Y may be any value selected from 1%, 1.2%, 1.35%, 1.5%, 1.6%, 1.7%, 1.8%, and 2%, or a range of any two of them; and T may be any value selected from 2%, 2.3%, 2.5%, 2.55%, 2.6%, 2.8%, 3%, 3.1%, 3.25%, 3.4%, 3.5%, 3.6%, 3.75%, 3.8%, 3.9%, and 4%, or a range of any two of them.

[0019] In some embodiments of the present invention, the organic phosphorus compound is selected from at least one of an organic phosphorus compound, a thiophosphoramide, and defoliant phosphorous, wherein the organic phosphorus compound is an organic phosphorus compound containing a phosphoric acid group.

[0020] In some embodiments of the present invention, the organic phosphoric acid compound is selected from at least one of phytate, phosphonate, phosphoramide, pyrophosphonate, pyrophosphamide, fenthion, and glycerophosphate. Among them, the phytate can be at least one of lithium phytate and sodium phytate.

[0021] In some embodiments of the present invention, the cobalt-containing positive electrode active material is selected from at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich cobalt-based positive electrode materials.

[0022] In some embodiments of the present invention, the organic fluorine compound is selected from at least one of a monofluorine compound, a difluorine compound, a trifluorine compound, and a polyfluorine compound; the monofluorine compound contains one carbon-fluorine bond, the difluorine compound contains two carbon-fluorine bonds, the trifluorine compound contains three carbon-fluorine bonds, and the polyfluorine compound contains four or more carbon-fluorine bonds;

[0023] Alternatively, the chemical formula of the organic fluorine compound is: RF n wherein n=1, 2, or 3; and R is selected from a Cl-substituted or unsubstituted C1-C10 alkyl group, a Cl-substituted or unsubstituted C2-C10 alkenyl group, a Cl-substituted or unsubstituted C2-C10 alkynyl group, a Cl-substituted or unsubstituted C5-C10 heteroaryl group, or a Cl-substituted or unsubstituted C6-C10 aryl group. Furthermore, in the organofluorine compound of the above chemical formula, the n F atoms may be attached to the same carbon atom or to different carbon atoms in the R group.

[0024] In some embodiments of the present invention, the monofluorinated compound is selected from at least one of fluoroethylene carbonate (CAS No.: 114435-02-8), 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, fluorodimethyl carbonate (CAS No.: 1983-85-3), and fluoroethyl acetate (CAS No.: 459-72-3);

[0025] The difluoro compound is at least one selected from bisfluoroethylene carbonate (CAS No.: 311810-76-1), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, p-difluorobenzene (CAS No.: 540-36-3), 3,4-difluoropyridine (CAS No.: 82878-63-5), 2,5-difluoropyridine (CAS No.: 84476-99-3), and lithium bisfluorooxalatoborate (CAS No.: 409071-16-5);

[0026] The trifluoro compound is at least one selected from 1,1,2-trifluoroethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, 1,3,5-trifluorobenzene (CAS No.: 372-38-3), methyl trifluoroacetate (CAS No.: 431-47-0), methyl trifluoropropionate (CAS No.: 378-75-4), and lithium trifluoromethanesulfonate (CAS No.: 90076-65-6);

[0027] The polyfluorinated compound is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (CAS No.: 1550-83-0), tetrafluorosulfolane (CAS No.: 1690-45-3), lithium bis(trifluoromethanesulfonyl)amide (CAS No.: 90076-65-6), and ethyl pentafluoropropionate (CAS No.: 358-54-1).

[0028] In some embodiments of the present invention, the positive electrode material layer further includes a conductive agent and a binder.

[0029] In some embodiments of the present invention, the mass percentage of the conductive agent in the positive electrode material layer is 0.5 wt % to 5 wt %. For example, the mass percentage of the conductive agent in the positive electrode material layer can be any one of 0.5 wt %, 0.8 wt %, 1 wt %, 1.2 wt %, 1.5 wt %, 1.6 wt %, 1.8 wt %, 2 wt %, 2.1 wt %, 2.3 wt %, 2.5 wt %, 2.6 wt %, 2.8 wt %, 3 wt %, 3.2 wt %, 3.5 wt %, 3.7 wt %, 4 wt %, 4.2 wt %, 4.5 wt %, 4.8 wt %, or 5 wt %, or any two of the ranges thereof.

[0030] The addition of a conductive agent in the positive electrode material layer can improve the conductivity. There is no restriction on the type of the conductive agent, and any known conductive agent can be used. In some embodiments of the present invention, the conductive agent in the positive electrode material layer is selected from at least one of natural graphite, artificial graphite, conductive carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, carbon fiber, conductive polymer, and metal powder.

[0031] In some embodiments of the present invention, the binder has a mass percentage in the positive electrode material layer of 0.5 wt % to 2 wt %. For example, the binder has a mass percentage in the positive electrode material layer of 0.5 wt %, 0.55 wt %, 0.6 wt %, 0.7 wt %, 0.75 wt %, 0.8 wt %, 0.9 wt %, 1 wt %, 1.2 wt %, 1.4 wt %, 1.5 wt %, 1.55 wt %, 1.6 wt %, 1.65 wt %, 1.7 wt %, 1.8 wt %, 1.85 wt %, 1.9 wt %, or 2 wt %, or any two of the ranges thereof.

[0032] The addition of the binder in the positive electrode material layer plays a role in bonding the material components and bonding to the current collector, wherein there is no restriction on the type of binder, and any known binder can be used. In some embodiments of the present invention, the binder in the positive electrode material layer is selected from polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polytetrafluoroethylene, polyacrylonitrile, polyethylene oxide, styrene-butadiene rubber, polyacrylate, polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, carboxymethyl cellulose, cellulose, nitrocellulose, acrylonitrile-butadiene rubber, fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber, styrene-butadiene-styrene block copolymer or its hydride, ethylene-propylene-diene terpolymer, styrene-ethylene-butadiene-ethylene copolymer, styrene-isoprene-styrene block copolymer, syndiotactic 1,2 polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, propylene-alpha olefin copolymer, fluorinated polyvinylidene fluoride, polytetrafluoroethylene-ethylene copolymer at least one.

[0033] In some embodiments of the present invention, the positive electrode material layer is provided on both side surfaces of the positive electrode current collector.

[0034] In some embodiments of the present invention, the positive electrode current collector may be made of at least one of aluminum, copper, platinum, and silver.

[0035] In some embodiments of the present invention, the electrolyte further comprises a lithium salt and an organic solvent.

[0036] In some embodiments of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium trifluoromethanesulfonate (LiCF3SO3), 2-trifluoromethyl-4,5-dicyanoimidazole lithium (C6F3LiN4), lithium difluorooxalatoborate (LiODFB), lithium bis(oxalato)borate (LiBOB), lithium bis(trifluoromethanesulfonyl imide (LiN(SO2CF3)2), and lithium bis(fluorosulfonyl imide) (LiN(SO2F)2).

[0037] In some embodiments of the present invention, the organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, γ-butyrolactone, 1,3-propane sultone, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, 1,3-dioxolane, and ethylene glycol dimethyl ether.

[0038] In some embodiments of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one side surface of the negative electrode current collector.

[0039] In some embodiments of the present invention, the negative electrode current collector may be made of at least one of copper, nickel, iron, silver, titanium, and platinum.

[0040] In some embodiments of the present invention, the negative electrode material layer includes a negative electrode active material, which is a carbon material or a non-carbon material that can be embedded in lithium, wherein the carbon material can be at least one of natural graphite, artificial graphite, soft carbon, hard carbon, and mesophase carbon microbeads, and the non-carbon material can be at least one of lithium, silicon element, silicon compound, tin element, tin compound, lithium titanium phosphate, and lithium titanate.

[0041] In some embodiments of the present invention, the negative electrode material layer further includes a binder, and the binder may be at least one of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, and polyvinyl alcohol.

[0042] In some embodiments of the present invention, the negative electrode material layer further includes a conductive agent, which may be at least one of graphite, carbon black, graphene, carbon nanotubes, and carbon nanofibers.

[0043] In some embodiments of the present invention, the negative electrode material layer further includes a thickener.

[0044] In some embodiments of the present invention, the lithium-ion battery further comprises a packaging shell, wherein the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte are contained in the packaging shell.

[0045] In some embodiments of the present invention, the positive electrode sheet, the separator, and the negative electrode sheet are wound to form a bare battery core, and the bare battery core and the electrolyte are contained in the packaging shell.

[0046] In a second aspect of the present invention, a method for preparing any of the aforementioned lithium-ion batteries of the present invention is provided, comprising the following steps:

[0047] A positive electrode raw material comprising an organic phosphide and a positive electrode active material containing a cobalt element is mixed with a solvent to prepare a positive electrode slurry, which is then applied to at least one side of a positive electrode current collector and dried to produce a positive electrode sheet; wherein the organic phosphide contains at least one PA bond, wherein A is selected from at least one of S, N, and O;

[0048] The electrolyte is prepared by using electrolyte raw materials including organic fluorine compounds;

[0049] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to obtain a lithium ion battery.

[0050] The above preparation method is simple to operate. In the process of preparing the positive electrode sheet, the organic phosphide is directly added to the positive electrode raw material by physical mixing, and the content X of the cobalt element and the content Y of the organic phosphide in the positive electrode material layer are controlled to satisfy 25≤X / Y≤70. The organic phosphide can minimize the dissolution of excessive metals in the positive electrode material at high temperature. It can act as a sacrificial agent to complex with the transition metal, preventing the dissolution of high-valent transition metals and the oxidation side reaction with the electrolyte. In addition, the generated organic phosphide complex can be in situ coated on the surface of the positive electrode material, acting as a protective layer, further isolating the side reaction with the electrolyte. In addition, an organic fluorine compound is added to the electrolyte, and the content T of the organic fluorine compound, the cobalt element content X, and the organic phosphide content Y in the positive electrode material layer are controlled to satisfy 10≤X / (Y+T)≤18. The organic fluorine compound can form a very stable SEI film on the surface of the negative electrode sheet, which can effectively reduce the impedance growth during the battery cycle, inhibit the generation of hydrogen fluoride, and reduce the reaction between hydrogen fluoride and the positive electrode material. It can also cooperate with the complex of the organic phosphide on the surface of the positive electrode material layer to jointly improve the interface contact between the electrode and the electrolyte, thereby improving the high-temperature cycle performance, storage performance, and safety performance of the lithium-ion battery.

[0051] In some embodiments of the present invention, the drying temperature of the positive electrode sheet preparation process is 100°C to 150°C. For example, the drying temperature may be any value among 100°C, 105°C, 110°C, 112°C, 115°C, 118°C, 120°C, 125°C, 130°C, 135°C, 140°C, 146°C, and 150°C, or a range of any two of them.

[0052] In some embodiments of the present invention, the drying time of the positive electrode sheet preparation process is 6 hours to 10 hours. For example, the drying time can be any value among 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, 8.5 hours, 9 hours, and 10 hours, or a range of any two of the values.

[0053] In some embodiments of the present invention, the positive electrode sheet preparation process further includes rolling and slitting after drying.

[0054] In some embodiments of the present invention, assembling the positive electrode sheet, the negative electrode sheet, the separator and the electrolyte to obtain a lithium-ion battery includes: stacking and winding the positive electrode sheet, the separator and the negative electrode sheet to form a bare battery cell, and then placing the bare battery cell in a packaging shell and injecting the electrolyte to obtain a lithium-ion battery.

[0055] In some embodiments of the present invention, during the process of assembling a lithium-ion battery, after injecting the electrolyte, the battery is further subjected to vacuum packaging, standing, forming, and shaping steps to obtain a lithium-ion battery.

[0056] In a third aspect of the present invention, an electronic device is provided, comprising any one of the aforementioned lithium-ion batteries of the present invention or a lithium-ion battery manufactured by any one of the aforementioned methods for manufacturing a lithium-ion battery of the present invention. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0058] Example 1

[0059] This embodiment provides a lithium-ion battery comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte, wherein the separator is sandwiched between the positive and negative electrode sheets. The positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer disposed on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil, and the positive electrode material layer comprises a cobalt-containing positive electrode active material, an organic phosphide, a binder polyvinylidene fluoride (PVDF), and a conductive agent carbon nanotubes (CNTs) in a mass ratio of 96.5:1.5:1:1. The cobalt-containing positive electrode active material is lithium cobaltate, and the mass percentage (X) of cobalt in the positive electrode material layer is 58.11%. The organic phosphide is an organophosphate compound, lithium phytate, and its mass percentage (Y) in the positive electrode material layer is 1.5%. The electrolyte contains an organic fluorine compound, a lithium salt, and an organic solvent. The organic fluorine compound is fluoroethylene carbonate, and its mass percentage T in the electrolyte is 3%; the lithium salt is LiPF6, and its mass percentage in the electrolyte is 15%; the organic solvent is ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and dimethyl carbonate (DMC) in a mass ratio of 20:10:10:10:50. In this lithium-ion battery, X, Y, and T satisfy the following conditions: 25 < X / Y = 38.7 < 70 and 10 < X / (Y+T) = 12.9 < 18.

[0060] The lithium-ion battery is prepared by a preparation method comprising the following steps:

[0061] Preparation of positive electrode sheet: The cobalt-containing positive electrode active material (lithium cobaltate), organic phosphide (lithium phytate), binder and conductive agent are mixed in a mass ratio of 96.5:1.5:1:1, N-methylpyrrolidone (NMP) is added, and stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil; the above-mentioned coated aluminum foil is baked in an oven with 5 different temperature gradients (100℃, 110℃, 120℃, 110℃, 100℃), and the baking time is determined according to the actual situation on site, and it can be dried without cracking; then it is dried in an oven at 120℃ for 8h, and then rolled and cut to obtain the positive electrode sheet.

[0062] Preparation of negative electrode sheet: The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly stirred and mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5, and then coated on the negative electrode current collector Cu foil. After drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0063] Preparation of the electrolyte: In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and dimethyl carbonate (DMC) are uniformly mixed in a mass ratio of 20:10:10:10:50 to obtain a non-aqueous solvent; then, a lithium salt (LiPF6) accounting for 15% of the total mass of the electrolyte is slowly added to the mixed solution and stirred until it is completely dissolved, and then an organic fluorine compound (fluoroethylene carbonate) accounting for 3.0% of the total mass of the electrolyte is added to obtain an electrolyte.

[0064] Assembly of lithium-ion batteries: Using a polyethylene (PE) porous polymer film as an isolation membrane, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrodes to act as an isolation membrane. The bare cell is then wound and placed in a packaging shell. The prepared electrolyte is injected, and the lithium-ion battery is produced through processes such as vacuum packaging, standing, formation, and shaping.

[0065] Example 2 group

[0066] This embodiment group includes embodiments 2a to 2b, and embodiments 2a to 2b respectively provide a lithium ion battery. The difference between them and embodiment 1 is that: the mass percentage Y of the organic phosphide lithium phytate in the positive electrode material layer of the lithium ion batteries of embodiments 2a to 2b is adjusted from 1.5% in embodiment 1 to 1% and 2%, respectively, and further, in the lithium ion batteries of embodiments 2a to 2b, X / Y is equal to 58.1 and 29.1, respectively, both satisfying 25<X / Y<70; X / (Y+T) is equal to 14.5 and 11.6, respectively, both satisfying 10<X / (Y+T)<18; otherwise, they are the same as the lithium ion battery of embodiment 1, see Table 1 for details.

[0067] Example 3 group

[0068] This embodiment group includes embodiments 3a to 3c, and embodiments 3a to 3c respectively provide a lithium ion battery. The difference between them and embodiment 1 is that the mass percentage T of the organic fluorine compound fluoroethylene carbonate in the electrolyte of the lithium ion batteries of embodiments 3a to 3c is adjusted from 3% in embodiment 1 to 2%, 3.5%, and 4%, respectively, and further, X / (Y+T) in the lithium ion batteries of embodiments 3a to 3c is equal to 16.6, 11.6, and 10.6, respectively, all satisfying 10<X / (Y+T)<18; otherwise, they are the same as the lithium ion battery of embodiment 1, see Table 1 for details.

[0069] Example 4 Group

[0070] This embodiment group includes embodiments 4a to 4c, and embodiments 4a to 4c respectively provide a lithium ion battery. The difference between them compared with embodiment 1 is that the organic phosphide in the positive electrode material layer of the lithium ion battery of embodiments 4a to 4e is adjusted from the lithium phytate in embodiment 1 to phosphonate, phosphoramide, glycerophosphate, thiophosphoramide, and defoliated phosphorous, respectively. The rest is the same as the lithium ion battery of embodiment 1. See Table 1 for details.

[0071] Example 5 Group

[0072] This embodiment group includes embodiments 5a to 5c. Embodiments 5a to 5c respectively provide a lithium ion battery. The difference between them and embodiment 1 is that the organic fluorine compound in the electrolyte of the lithium ion battery of embodiments 5a to 5c is adjusted from the fluoroethylene carbonate in embodiment 1 to difluoroethylene carbonate, 1,2-difluoroethylene carbonate, and 1,1,2-trifluoro-2-methylethylene carbonate, respectively. The rest is the same as the lithium ion battery of embodiment 1. See Table 1 for details.

[0073] Example 6

[0074] This embodiment group includes embodiments 6a to 6c, and embodiments 6a to 6c respectively provide a lithium ion battery. The difference between them and embodiment 1 is that the mass percentage X of lithium cobalt oxide in the positive electrode material layer of the lithium ion battery of embodiments 6a to 6c is adjusted from 58.11% in embodiment 1 to 55%, 59%, and 50%, respectively; accordingly, in the positive electrode sheet preparation process of embodiments 6a to 6c, the mass ratio of lithium cobalt oxide, lithium phytate, binder and conductive agent in the preparation of the positive electrode slurry is adjusted from 9 in embodiment 1 to 55%. The ratio of 6.5:1.5:1:1 is adjusted to 91.3:1.5:1:1, 98:1.5:1:1, and 83.1:1.5:1:1, respectively. Furthermore, in the lithium ion batteries of Examples 6a to 6c, X / Y is equal to 36.7, 39.3, and 33.3, respectively, all satisfying 25<X / Y<70; X / (Y+T) is equal to 12.2, 13.1, and 11.1, respectively, also satisfying 10<X / (Y+T)<18. Other aspects are the same as those of the lithium ion battery of Example 1. For details, see Table 1.

[0075] Comparative Example 1

[0076] This comparative example provides a lithium-ion battery, which differs from Example 1 in that the positive electrode material layer of this comparative example does not contain an organic phosphide, and the electrolyte does not contain an organic fluorine compound. Otherwise, it is the same as the lithium-ion battery in Example 1. For details, see Table 1.

[0077] Comparative Example 2

[0078] This comparative example group includes comparative examples 2a to 2b, and comparative examples 2a to 2b respectively provide a lithium ion battery. The difference between them compared with Example 1 is that the positive electrode material layer of the lithium ion battery of comparative example 2a does not contain an organic phosphide, and the electrolyte of the lithium ion battery of comparative example 2b does not contain an organic fluorine compound. Otherwise, they are the same as the lithium ion battery of Example 1. For details, see Table 1.

[0079] Comparative Example 3

[0080] This comparative example group includes comparative examples 3a to 3d, and comparative examples 3a to 3d respectively provide a lithium ion battery. The difference between them and Example 1 is that X, Y, and T in the lithium ion batteries of comparative examples 3a to 3d do not satisfy 10≤X / (Y+T)≤18.

[0081] Specifically, the mass percentage Y of the organic phosphide lithium phytate in the positive electrode material layer of the lithium ion batteries of Comparative Examples 3a to 3d was adjusted to 2.2%, 2.2%, 0.9%, and 0.9%, respectively, and the mass percentage T of the organic fluorine compound fluoroethylene carbonate in the electrolyte was adjusted to 0.1%, 4%, 0.5%, and 6%, respectively. Furthermore, in the lithium ion batteries of Comparative Examples 3a to 3d, X / Y was equal to 26.4, 26.4, 64.6, and 64.6, respectively, all satisfying 25<X / Y<70; X / (Y+T) was equal to 25.3, 9.4, 41.5, and 8.4, respectively, all not satisfying 10≤X / (Y+T)≤18. Otherwise, the conditions were the same as those of the lithium ion battery of Example 1. See Table 1 for details.

[0082] Comparative Example 4

[0083] This comparative example group includes comparative examples 4a to 4d, and comparative examples 4a to 4d respectively provide a lithium ion battery. The difference between them and Example 1 is that X, Y, and T in the lithium ion batteries of comparative examples 4a to 4d do not satisfy 25≤X / Y≤70 and 10≤X / (Y+T)≤18.

[0084] Specifically, the mass percentage Y of the organic phosphide lithium phytate in the positive electrode material layer of the lithium ion batteries of Comparative Examples 4a to 4d was adjusted to 0.8%, 0.8%, 2.4%, and 2.4%, respectively, and the mass percentage T of the organic fluorine compound fluoroethylene carbonate in the electrolyte was adjusted to 2.3%, 5.2%, 0.8%, and 3.5%, respectively. Furthermore, the X / Y in the lithium ion batteries of Comparative Examples 4a to 4d was equal to 72.6, 72.6, 24.2, and 24.2, respectively, which did not satisfy 25≤X / Y≤70; and X / (Y+T) was equal to 18.7, 9.7, 18.2, and 9.8, respectively, which did not satisfy 10≤X / (Y+T)≤18. Otherwise, the conditions were the same as those of the lithium ion battery of Example 1. See Table 1 for details.

[0085] Comparative Example 5

[0086] This comparative example group includes comparative examples 5a to 5d. Comparative examples 5a to 5d respectively provide a lithium ion battery. The difference between them and Example 1 is that X and Y in the lithium ion batteries of comparative examples 5a to 5b do not satisfy 25≤X / Y≤70.

[0087] Specifically, the mass percentage Y of the organic phosphide lithium phytate in the positive electrode material layer of the lithium ion batteries of Comparative Examples 5a to 5d was adjusted to 0.8%, 2.4%, 0.8%, and 2.4%, respectively, and the mass percentage T of the organic fluorine compound fluoroethylene carbonate in the electrolyte was adjusted to 4.9%, 3.3%, 2.5%, and 0.9%, respectively. Furthermore, X / Y in the lithium ion batteries of Comparative Examples 5a to 5d was equal to 72.6, 24.2, 72.6, and 24.2, respectively, which did not satisfy 25≤X / Y≤70; X / (Y+T) was equal to 10.2, 10.2, 17.6, and 17.6, respectively, all satisfying 10≤X / (Y+T)≤18. Otherwise, it was the same as the lithium ion battery of Example 1. For details, see Table 1.

[0088] Table 1

[0089]

[0090]

[0091] Performance Testing

[0092] (1) Cycle life test

[0093] The lithium-ion battery was placed in a constant temperature environment of 45°C and charged and discharged at a rate of 1.0C / 1.0C. The charge cut-off voltage was 4.5V, the discharge cut-off voltage was 3.0V, and the charge and discharge cycles were repeated 500 times. The cycle discharge capacity was recorded and divided by the discharge capacity of the first cycle to obtain the cycle capacity retention rate. The results are shown in Table 2.

[0094] (2) 85℃ high temperature storage test

[0095] The lithium-ion battery was first placed in a 25°C environment and charged at 0.7C to 4.5V, then discharged at 0.2C to 3.0V, and the initial discharge capacity was recorded. The battery was then charged to full charge (100% SOC) and stored in an 85°C constant temperature box for 24 hours. After the storage time was up, the battery cell was taken out and cooled to room temperature, and then discharged at 0.2C to 0% SOC. The discharge capacity after storage was recorded and divided by the initial discharge capacity to obtain the residual capacity retention rate. The results are shown in Table 2.

[0096] (3) 134℃ hot box test

[0097] At 25°C, charge the battery at a constant current of 0.5C to 4.5V, then charge it at a constant voltage to a cutoff current of 0.025C. Let it rest for 2 hours. Place the fully charged battery in a hot box and heat it from room temperature to 134°C at a heating rate of 5°C / min for 60 minutes. If the battery does not explode or catch fire, it is considered passed. Otherwise, it is considered failed.

[0098] The performance of the lithium-ion batteries of the embodiments and comparative examples were tested according to the above method, and the results are shown in Table 2.

[0099] Table 2

[0100]

[0101] According to Table 2, compared with the comparative examples and embodiments, in the lithium ion batteries of the above embodiments, a positive electrode active material containing cobalt is used in the positive electrode material layer, an organic phosphide is added, and an organic fluorine compound is added to the electrolyte. At the same time, the content X of the cobalt element in the positive electrode active material layer and the content Y of the organic phosphide and the content T of the organic fluorine compound in the electrolyte are controlled to simultaneously satisfy: 25≤X / Y≤70 and 10≤X / (Y+T)≤18. The synergistic effect of the organic phosphide and cobalt element in the positive electrode material layer and the organic fluorine compound in the electrolyte effectively suppresses the side reaction at the interface between the positive electrode active material and the electrolyte, and the safety performance, cycle capacity retention rate and high temperature storage residual capacity retention rate of the lithium ion battery are significantly improved.

[0102] Specifically, by comparing Example 1 with Comparative Examples 1 and 2 (i.e., Comparative Examples 2a-2b), it can be seen that in Example 1, when an organic phosphide is added to the positive electrode material layer and an organic fluorine compound is added to the electrolyte, the cycle capacity retention rate and the high-temperature storage residual capacity retention rate of the lithium-ion battery are significantly improved. Combining Comparative Example 3 (i.e., Comparative Examples 3a-3d), Comparative Example 4 (i.e., Comparative Examples 4a-4d), Comparative Example 5 (i.e., Comparative Examples 5a-5d) and each embodiment (especially Example 1), it can be seen that when the content X of the cobalt element in the positive electrode material layer of the lithium-ion battery, the content Y of the organic phosphide, and the content T of the organic fluorine compound in the electrolyte simultaneously meet the conditions of 25≤X / Y≤70 and 10≤X / (Y+T)≤18, the safety performance of the battery is significantly improved, and the cycle capacity retention rate and the high-temperature storage residual capacity retention rate of the battery are further improved.

[0103] The above lithium-ion batteries can be used in electronic devices. The present invention further proposes an electronic device, which includes but is not limited to laptop computers, e-book players, portable phones, portable printers, clocks, game consoles, toys, lighting equipment, calculators, video recorders, radios, portable power supplies, automobiles, motorcycles, large household batteries, etc.

[0104] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that: It includes a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, wherein the separator is sandwiched between the positive electrode sheet and the negative electrode sheet; The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one side of the positive electrode current collector; the positive electrode material layer includes an organic phosphide and a positive electrode active material containing a cobalt element, the organic phosphide contains at least one PA bond, wherein A is selected from at least one of S, N, and O; the electrolyte includes an organic fluorine compound; The mass percentage of the cobalt element in the positive electrode material layer is X, the mass percentage of the organic phosphide in the positive electrode material layer is Y, and the mass percentage of the organic fluorine compound in the electrolyte is T. X, Y, and T simultaneously satisfy: 25≤X / Y≤70 and 10≤X / (Y+T)≤18.

2. The lithium-ion battery according to claim 1, wherein At least one of the following conditions is met: The X satisfies: 50%≤X≤60%; The Y satisfies: 1%≤Y≤2%; The T satisfies: 2%≤T≤4%; X / Y=29.1-58.1; The X / (Y+T)=10.6-16.

6.

3. The lithium-ion battery according to claim 1, wherein The organic phosphorus compound is selected from at least one of organic phosphoric acid compounds, thiophosphoramides, and defoliant phosphorous.

4. The lithium-ion battery according to claim 3, characterized in that The organic phosphoric acid compound is at least one selected from phytate, phosphonate, phosphoramide, pyrophosphonate, pyrophosphamide, thiophene, and glycerophosphate.

5. The lithium-ion battery according to claim 1, wherein The positive electrode active material containing cobalt element is selected from at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium-rich cobalt-based positive electrode materials.

6. The lithium-ion battery according to claim 1, wherein The organic fluorine compound is selected from at least one of a monofluorine compound, a difluorine compound, a trifluorine compound and a polyfluorine compound; the monofluorine compound contains one carbon-fluorine bond, the difluorine compound contains two carbon-fluorine bonds, the trifluorine compound contains three carbon-fluorine bonds, and the polyfluorine compound contains four or more carbon-fluorine bonds; Alternatively, the chemical formula of the organic fluorine compound is: RF n ; wherein n=1, 2 or 3; R is selected from C1-C10 alkyl substituted or unsubstituted by Cl element, C2-C10 alkenyl substituted or unsubstituted by Cl element, C2-C10 alkynyl substituted or unsubstituted by Cl element, C5-C10 heteroaryl substituted or unsubstituted by Cl element, C6-C10 aryl substituted or unsubstituted by Cl element.

7. The lithium-ion battery according to claim 6, characterized in that The monofluorinated compound is selected from at least one of fluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, fluorodimethyl carbonate, and fluoroethyl acetate; The difluoro compound is at least one selected from bisfluoroethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, p-difluorobenzene, 3,4-difluoropyridine, 2,5-difluoropyridine, and lithium bisfluorooxalatoborate; The trifluoro compound is at least one selected from 1,1,2-trifluoroethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, 1,3,5-trifluorobenzene, methyl trifluoroacetate, methyl trifluoropropionate, and lithium trifluoromethanesulfonate; The polyfluorinated compound is at least one selected from 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, tetrafluorosulfolane, lithium bis(trifluoromethanesulfonyl)amide, and ethyl pentafluoropropionate.

8. The lithium-ion battery according to any one of claims 1 to 7, characterized in that The positive electrode material layer further includes a conductive agent and a binder; and / or the electrolyte further includes a lithium salt and an organic solvent.

9. The method for preparing a lithium ion battery according to any one of claims 1 to 8, characterized in that: The following steps are involved: A positive electrode slurry is prepared by mixing a positive electrode raw material including an organic phosphide and a positive electrode active material containing a cobalt element with a solvent, and then the positive electrode slurry is applied to at least one side of a positive electrode current collector and dried to obtain a positive electrode sheet; The electrolyte is prepared by using electrolyte raw materials including organic fluorine compounds; The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to obtain a lithium ion battery.

10. An electronic device, characterized in that: A lithium ion battery comprising the lithium ion battery according to any one of claims 1 to 8 or a lithium ion battery prepared by the preparation method of the lithium ion battery according to claim 9.

Images