High safety lithium ion battery and preparation method thereof

Abstract

The application belongs to the technical field of lithium ion batteries, and particularly relates to a high-safety lithium ion battery and a preparation method thereof, which comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte; a positive electrode active material of the positive electrode sheet comprises lithium cobaltate, and the lithium cobaltate further contains magnesium elements with a content of M ppm, and satisfies 50<=M<=300; the electrolyte comprises a compound and a fluorinated compound; the high-safety lithium ion battery utilizes the Mg elements to inhibit the structural change of the lithium cobaltate under high voltage to improve the high-temperature cycle stability, and under the catalysis of the Mg, the compound will be preferentially dissolved and oxidized to generate lithium sulfonate compounds to inhibit the corrosion problem of the aluminum plastic film packaging; meanwhile, under the condition of satisfying the defined relationship, the compound and the fluorinated compound can form a more stable lithium ion transmission interface film to improve the efficiency of the lithium ion battery and greatly increase the safety.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a high-safety lithium ion battery and a preparation method thereof. BACKGROUND

[0002] Lithium ion batteries with high energy density, long service life and low self-discharge have been widely used in 3C digital, electric vehicles, unmanned aerial vehicles, electric ships, large and outdoor energy storage, etc. fields. Lithium ion batteries are composed of four main materials, namely, positive electrode, negative electrode, separator and electrolyte. Lithium cobaltate positive electrode material is used in mobile phones, notebook computers and other energy storage devices with high volume requirements due to its high compaction density and energy density.

[0003] In order to further improve the energy density of lithium ion batteries and prolong the endurance time of the equipment, the working voltage of lithium ion batteries is also continuously improved. However, the electrolyte has poor stability under high voltage, which can easily lead to decomposition and gas production, thereby seriously deteriorating the cycle performance, especially at high temperature. At the same time, under high voltage, the positive electrode also has problems such as oxygen evolution and collapse of crystal structure, which can further cause the cycle performance to decay. In addition, in order to improve the energy density of the battery, it is a common method to use aluminum plastic film to replace aluminum shell to reduce the weight of non-active materials of the battery. However, the packaging of aluminum plastic film is sealed by heat compounding, which is affected to some extent by the electrolyte components. When the electrolyte contains components with strong acidity, it can cause insufficient packaging strength, thereby causing serious safety problems.

[0004] Therefore, how to overcome the corrosion of acidic components in lithium ion batteries to the packaging of aluminum plastic film is a technical problem that needs to be solved in the field.

[0005] It should be noted that the above information disclosed in the background section is only used to understand the background of the present application, and therefore, the above description is not considered to constitute prior art information. SUMMARY

[0006] The present application provides at least a high-safety lithium ion battery and a preparation method thereof.

[0007] In a first aspect, the present application provides a lithium ion battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode active material of the positive electrode sheet comprises lithium cobaltate, and the lithium cobaltate further contains magnesium element with a content of M ppm, and satisfies 50≤M≤300; the electrolyte comprises a compound and a fluorinated compound, and the mass percentage of the compound in the electrolyte is C1, and satisfies 0.002%≤M*C1≤0.1%; wherein R0 is a single bond or a methylene group, R1 is any one of hydrogen, halogen, a hydrocarbon group with 1-5 carbon atoms or a halogenated hydrocarbon group with 1-5 carbon atoms, R2, R3 and R4 are independently selected from , and R5 is a hydrocarbon group with 1-5 carbon atoms or a halogenated hydrocarbon group with 1-5 carbon atoms. R2, R3, and R4 are independently selected from any one of H, F, Cl, Br, I, CN, CF3, CCl3, CBr3, CI, OCF3, OCHF2, OCH2F, OCN, SCN, N02, NCO, NCS, N3, and SH, and R2, R3, and R4 are not simultaneously selected and the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1≤C2 / Cl≤10.

[0008] In an alternative embodiment, the mass percentage Cl of the compound in the electrolyte ranges from 0.3% to 4%; and the mass percentage C2 of the fluorinated compound in the electrolyte ranges from 3% to 15%.

[0009] In an alternative embodiment, the fluorinated compound includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluorobenzene, trifluoromethyl ethylene carbonate, and ethoxy pentafluorophosphazene.

[0010] In an alternative embodiment, the content of ethanol in the compound is not more than 20 ppm; and the content of hydrofluoric acid in the fluorinated compound is not more than 30 ppm.

[0011] In an alternative embodiment, the R1 includes any one of H, F, Cl, Br, I, CN, CF3, CCl3, CBr3, CI, OCF3, OCHF2, OCH2F, OCN, SCN, N02, NCO, NCS, N3, and SH.

[0012] In an alternative embodiment, the compound includes at least one of the following compounds:

[0013]

[0014] In an alternative embodiment, the negative active material of the negative electrode sheet includes graphite or silicon-based material.

[0015] In an alternative embodiment, the electrolyte further includes an electrolyte salt, and the mass percentage of the electrolyte salt in the electrolyte ranges from 10% to 20%.

[0016] In an alternative embodiment, the electrolyte further includes an additive, and the mass percentage of the additive in the electrolyte ranges from 1% to 10%; and the additive includes at least one of vinylene carbonate, methylene dimalonate, 1,3-propane sultone, glycerol trinitrile, butanedinitrile, hexanedinitrile, 1,3,6-hexanetrinitrile, fluoroethylene carbonate, lithium bisfluorograc oxide borate, lithium bisoxalate borate, lithium tetrafluoroborate, and lithium bisfluorobisoxalate phosphate.

[0017] In a second aspect, the present disclosure provides a preparation method of the lithium ion battery as described above, comprising the following steps: (1) preparation of the electrolyte, i.e., mixing ethylene carbonate, propyl propionate and diethyl carbonate, then adding lithium bisfluorosulfonylimide and lithium hexafluorophosphate, and then adding the compound and the fluorinated compound; (2) preparation of the positive electrode sheet, i.e., dispersing lithium-containing lithium phosphate, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone, and then coating on the positive current collector aluminum foil; (3) preparation of the negative electrode sheet, i.e., dispersing graphite, acetylene black, sodium carboxymethyl cellulose and butadiene-styrene rubber in deionized water, and then coating on the negative current collector aluminum foil; (4) preparation of the battery, i.e., stacking the above positive electrode sheet, the separator and the above negative electrode sheet in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then winding to obtain a bare cell, and placing the bare cell in an aluminum-plastic film packaging shell, drying, injecting the electrolyte prepared in step (1), and then performing vacuum packaging, standing, formation, secondary packaging and other processes to complete the preparation of the battery.

[0018] The present application has the advantages that the high-safety lithium ion battery and the preparation method thereof utilize the Mg element to inhibit the structural change of lithium cobaltate at high voltage to improve the high-temperature cycle stability, and under the catalysis of Mg, the compound will be preferentially oxidized to generate lithium sulfonate compounds to inhibit the corrosion problem of the aluminum-plastic film packaging; meanwhile, under the condition of satisfying the defined relationship, the compound and the fluorinated compound can form a more stable lithium ion transmission interface film to improve the efficiency of the lithium ion battery and greatly increase the safety.

[0019] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application will be realized and achieved by the structures particularly pointed out in the description.

[0020] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the following preferred embodiments are specifically described as follows. DETAILED DESCRIPTION

[0021] In order to make the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the present application will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0022] In this document, the term "compound" alone refers to and the specific structures of different substituents, which can also be referred to as formula 1 in the specific embodiments, but not all compounds.

[0023] As used herein, the phrases "in one embodiment," "according to one embodiment," "in some embodiments," and the like generally mean the particular feature, structure, or characteristic following the phrase is included in at least one embodiment of the present disclosure. Thus, appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment. As used herein, the term "example" or "exemplary" means "serving as an example, instance, or illustration." Any implementation, aspect or design described herein as "example" or "exemplary" is not necessarily to be construed as preferred or advantageous over other implementations, aspects or designs. Rather, the use of the terms "example" or "exemplary" is intended to present concepts in a concrete manner.

[0024] In this document, relational terms such as "at least one of" or "one or more of" are used to indicate an inclusion, such as in a set of items, having one or more members of a common group. For example, "at least one of a, b, and c" is intended to mean: a alone, b alone, c alone, a and b together, a and c together, b and c together, or a, b, and c together. Likewise, "one or more of a, b, and c" is intended to convey the same meaning as "at least one of a, b, and c."

[0025] The terminology used herein is for the purpose of describing particular example configurations only and is not intended to be limiting. As used herein, the singular articles "a," "an," and "the" can be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises," "comprising," "including," and "having" are inclusive and therefore specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order

[0026] Lithium cobaltate has high energy density at high voltage, and doping or coating with Mg element can significantly inhibit the structural change of lithium cobaltate at high voltage, thereby improving the high-temperature cycle stability. However, too little Mg cannot significantly improve the structural change of lithium cobaltate, and too much Mg will hinder the transmission of lithium ions and deteriorate the cycle performance. Fluorinated compounds have strong polarity and strong complexation with Co in lithium cobaltate, and can be adsorbed on the surface of the positive active material after the battery is injected with electrolyte. However, the inventors have found that the hydrofluoric acid in the fluorinated compound has a certain corrosion effect on the interface film, resulting in increased impedance and rapid cycle decay. However, the compound in the present application can be preferentially oxidized to form a lithium sulfonate compound in lithium cobaltate under the catalysis of Mg.

[0027] In addition, the inventors found that the ethanol in the compound in the present application can seriously hinder the formation of the interface film, resulting in the failure of the compound to exert its improved performance. Therefore, the combination of the fluorinated compound and the compound can form an interface film mixed with fluorides and lithium sulfonate compounds.

[0028] The inventors also found that when the amount of the compound added and the content of Mg in the lithium cobaltate satisfy the formula 0.002%≤M*Cl≤0.1%, a more stable interface film that is conducive to the transmission of lithium ions can be formed. On the other hand, due to the high voltage of the lithium cobaltate, it is easy to catalyze the decomposition of lithium salts in the electrolyte to form a strong acid substance during the charging process, which can cause insufficient sealing strength during the exhaust sealing after the battery formation, resulting in a large edge voltage of the battery and easily leading to battery leakage and other safety problems. The electrolyte provided by the present application can prevent the formation of acidic substances in the electrolyte, significantly improve the sealing performance of the battery, and improve the safety performance of the battery.

[0029] The above-mentioned defects are the results of the inventors' practice and careful research, and therefore, the discovery process of the above-mentioned problems and the solutions proposed by the present disclosure to solve the above-mentioned problems should be the contributions of the inventors to the present disclosure during the process of the present disclosure.

[0030] Some embodiments of the present application will be described in detail below. In the case of no conflict, the embodiments described below and the features in the embodiments can be combined with each other.

[0031] The present disclosure provides a high-safety lithium ion battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the positive electrode active material of the positive electrode sheet comprises lithium cobaltate, and the lithium cobaltate further contains a magnesium element with a content of M ppm, and satisfies 50≤M≤300; the electrolyte comprises a compound and a fluorinated compound, and the mass percentage of the compound in the electrolyte is C1%, and satisfies 0.002%≤M*C1≤0.1%; wherein R0 is a single bond or a methylene group, R1 is any one of hydrogen, halogen, a hydrocarbon group with 1-5 carbon atoms or a halogenated hydrocarbon group with 1-5 carbon atoms, R2, R3 and R4 are independently selected from any one of , and R2, R3 and R4 are not simultaneously selected from , and the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1≤C2 / C1≤10.

[0032] Specifically, the content of the magnesium element is tested by an inductively coupled plasma emission spectrometer.

[0033] In some embodiments, specifically, the mass percentage C1 of the compound in the electrolyte ranges from 0.3% to 4%; the mass percentage C2 of the fluorinated compound in the electrolyte ranges from 3% to 15%.

[0034] In some embodiments, specifically, the fluorinated compound includes at least one of fluoroethylene carbonate, bis-fluoroethylene carbonate, fluorobenzene, trifluoromethyl fluoroethylene carbonate, and ethoxy pentafluorophosphazene.

[0035] In some embodiments, specifically, the content of ethanol in the compound is not more than 20 ppm; the content of hydrofluoric acid in the fluorinated compound is not more than 30 ppm.

[0036] Specifically, the content of ethanol is determined by gas chromatography, and the content of hydrofluoric acid is determined by NaOH-bromine bromophenol blue indicator method.

[0037] In some embodiments, specifically, R1 includes any one of hydrogen, halogen, methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, halogenated methyl, halogenated ethyl, halogenated n-propyl, halogenated isopropyl, halogenated butyl, halogenated pentyl, and halogenated hexyl.

[0038] In some embodiments, specifically, the compound includes at least one of the following compounds:

[0039]

[0040]

[0041] Specifically, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector, the positive electrode active material layer including at least one of a first binder and a first conductive agent and a positive electrode active material.

[0042] In some embodiments, specifically, the positive electrode current collector can include a metal foil or a composite positive electrode current collector. For example, the metal foil can be an aluminum foil. The composite positive electrode current collector can include a polymer material base layer and a metal layer formed on at least one side surface of the polymer material base layer, for example, the composite negative electrode current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

[0043] Optionally, the positive electrode current collector has two opposite surfaces in the thickness direction of itself, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0044] In some embodiments, specifically, the first conductive agent includes at least one of carbon black, acetylene black, graphene, ketjen black, carbon fiber.

[0045] In some embodiments, specifically, the first binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane.

[0046] In some embodiments, specifically, the mass ratio of the positive active material, the first conductive agent, and the first binder is (90-99.5):(0.25-5):(0.25-5).

[0047] Specifically, the negative electrode tab includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, the negative active material layer including at least one of a second binder and a second conductive agent and a negative active material.

[0048] In some embodiments, specifically, the negative active material can be a negative active material for a battery known in the art.

[0049] Optionally, the negative active material can include at least one of graphite, soft carbon, hard carbon, silicon-based material, etc., and preferably graphite or a silicon-based material, which has excellent cycle life, thereby improving the cycle performance and service life of the battery.

[0050] Optionally, the silicon-based material can include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys.

[0051] In some embodiments, specifically, the negative current collector can be a metal foil or a composite current collector. Optionally, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.

[0052] In some embodiments, specifically, the second binder can include at least one of sodium carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, oxirane-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide imide, polyvinyl alcohol, sodium polyacrylate.

[0053] In some embodiments, specifically, the second conductive agent can include at least one of natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, graphene.

[0054] In some embodiments, specifically, the mass ratio of the negative active material, the second conductive agent, and the second binder is (90-99):(0-5):(1-10).

[0055] In some embodiments, specifically, the electrolyte further includes an electrolyte salt, and the mass ratio of the electrolyte salt in the electrolyte is 10%-20%; optionally, the electrolyte salt is preferably a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bisfluorosulfonylimide (LiFSI), or lithium bis-trifluoromethanesulfonylimide (LiTFSI).

[0056] In some embodiments, specifically, the electrolyte further includes a solvent, and the solvent includes at least one of a carbonate (such as a cyclic carbonate, a chain carbonate), a carboxylate (such as a cyclic carboxylate, a chain carboxylate), an ether compound (such as a cyclic ether compound, a chain ether compound), a phosphorus-containing compound, a sulfur-containing compound, and an aromatic fluorine-containing compound.

[0057] Optionally, the solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), propyl butyrate (PB), ethyl butyrate (EB), propyl propionate (PP), ethyl propionate (EP), methyl propionate (MP), propyl acetate (PA), ethyl acetate (EA), methyl acetate (MA), propyl formate (PF), ethyl formate (EF), methyl formate (MF), γ-T lactone.

[0058] In some embodiments, specifically, the electrolyte further includes an additive, and the mass ratio of the additive in the electrolyte is 1%-10%; the additive includes at least one of vinylene carbonate, methylene methane disulfonate, 1,3-propane sultone, glycerol trinitrile, butanedinitrile, hexanedinitrile, 1,3,6-hexanetricarbonitrile, fluoroethylene carbonate, lithium bisfluoroxalate borate, lithium bisoxalate borate, lithium tetrafluoroborate, and lithium bisfluorobisoxalate phosphate.

[0059] In some embodiments, specifically, the battery further includes a separator film, and the separator film includes but is not limited to glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0060] In some embodiments, specifically, the high-safety lithium ion battery is sealed by an aluminum-plastic film package.

[0061] In some embodiments, specifically, the upper limit charging voltage of the high-safety lithium-ion battery is ≥4.45V.

[0062] This disclosure provides a method for preparing a lithium-ion battery as described above, comprising the following steps: (1) preparation of an electrolyte, namely, mixing ethylene carbonate, propyl propionate and diethyl carbonate, adding lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and then adding a compound. (2) Preparation of positive electrode sheet: dispersing magnesium-containing lithium phosphate, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone and coating it onto the aluminum foil of the positive electrode current collector; (3) Preparation of negative electrode sheet: dispersing graphite, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber in deionized water and coating it onto the aluminum foil of the negative electrode current collector; (4) Preparation of battery: stacking the above positive electrode sheet, separator and the above negative electrode sheet in sequence, so that the separator is between the positive electrode sheet and the negative electrode sheet to play a role in isolation, then winding to obtain bare battery cell, placing the bare battery cell in aluminum-plastic film packaging shell, drying it, injecting the electrolyte prepared in step (1), and completing the battery preparation through vacuum sealing, standing, formation, secondary sealing and other processes.

[0063] Example 1

[0064] (1) Preparation of electrolyte: Under an inert atmosphere (moisture < 0.1 ppm, oxygen < 1 ppm), ethylene carbonate (EC), propyl propionate (PP), and diethyl carbonate (DEC) were mixed at a mass ratio of EC:PP:DEC = 3:3:4. After thorough mixing, lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6) were added. The mass percentage of LiFSI in the electrolyte was 1 wt%, and the mass percentage of LiPF6 in the electrolyte was 15 wt%. Then, compound of formula 1-1 with an ethanol content of 10 ppm and fluoroethylene carbonate with a hydrofluoric acid content of 20 ppm were added. Based on the total mass of the electrolyte, the mass percentage of compound of formula 1-1 (C1) was 2 wt%, and the mass percentage of fluoroethylene carbonate (C2) was 7 wt%.

[0065] (2) Preparation of positive electrode sheet: Lithium cobalt oxide containing 80 ppm Mg, acetylene black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone (NMP) solvent at a mass ratio of 97:1:2. After being thoroughly stirred and mixed to form a homogeneous positive electrode slurry, it is uniformly coated on the positive electrode current collector aluminum foil. After drying, rolling and cutting, the positive electrode sheet is obtained.

[0066] (3) Preparation of negative electrode sheet: Graphite, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber (SBR) are dispersed in an appropriate amount of deionized water at a mass ratio of 95:2:2:1. After being thoroughly stirred and mixed to form a uniform negative electrode slurry, it is uniformly coated on the copper foil of the negative electrode current collector. After drying, rolling and cutting, the negative electrode sheet is obtained.

[0067] (4) Preparation of the battery: the above positive electrode sheet, the separator and the above negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, then the naked battery is obtained by winding, and the naked battery is placed in an aluminum plastic film packaging shell, dried, and then the electrolyte prepared in step (1) is injected, and the total mass of the electrolyte is 7.7 g. After vacuum packaging, standing, formation, secondary packaging and other processes, the preparation of the battery is completed, and the rated capacity is 5.5 Ah. The charge-discharge voltage range of this battery is 3.0-4.45 V.

[0068] Example 2

[0069] The difference between Example 2 and Example 1: the compound represented by formula 1 used in Example 2 is formula 1-2.

[0070] Example 3

[0071] The difference between Example 3 and Example 1: the compound represented by formula 1 used in Example 3 is formula 1-3.

[0072] Example 4

[0073] The difference between Example 4 and Example 1: the compound represented by formula 1 used in Example 4 is formula 1-4.

[0074] Example 5

[0075] The difference between Example 5 and Example 1: the compound represented by formula 1 used in Example 5 is formula 1-5.

[0076] Example 6

[0077] The difference between Example 6 and Example 1: the compound represented by formula 1 used in Example 6 is formula 1-6.

[0078] Example 7

[0079] The difference between Example 7 and Example 1: the compound represented by formula 1 used in Example 7 is formula 1-7.

[0080] Example 8

[0081] The difference between Example 8 and Example 1: the fluorinated compound used in Example 8 is difluoroethylene carbonate.

[0082] Example 9

[0083] The difference between Example 9 and Example 1: the fluorinated compound used in Example 9 is fluorobenzene.

[0084] Example 10

[0085] Example 10 differs from Example 1 in that the fluorinated compound used in Example 10 is ethylene carbonate with a trifluoromethyl group.

[0086] Example 11

[0087] Example 11 differs from Example 1 in that the fluorinated compound used in Example 11 is ethoxy pentafluorophosphazene.

[0088] Example 12

[0089] Example 12 differs from Example 1 in that the content of Mg in the lithium cobaltate of Example 12 is 50 ppm.

[0090] Example 13

[0091] Example 13 differs from Example 1 in that the content of Mg in the lithium cobaltate of Example 13 is 300 ppm.

[0092] Example 14

[0093] Example 14 differs from Example 1 in that the content of Mg in the lithium cobaltate of Example 14 is 400 ppm.

[0094] Example 15

[0095] Example 15 differs from Example 1 in that the content of ethanol in the compound of Formula 1 of Example 15 is 18 ppm.

[0096] Example 16

[0097] Example 16 differs from Example 1 in that the content of ethanol in the compound of Formula 1 of Example 16 is 33 ppm.

[0098] Example 17

[0099] Example 17 differs from Example 1 in that the mass percentage C1 of the compound of Formula 1-1 of Example 17 is 0.8 wt%.

[0100] Example 18

[0101] Example 18 differs from Example 1 in that the mass percentage C1 of the compound of Formula 1-1 of Example 18 is 4 wt%.

[0102] Example 19

[0103] Example 19 differs from Example 1 in that the mass percentage C1 of the compound of Formula 1-1 of Example 19 is 6 wt%.

[0104] Example 20

[0105] Example 20 differs from Example 1 in that the content of hydrofluoric acid in the fluorinated ethylene carbonate of Example 20 is 10 ppm.

[0106] Example 21

[0107] The difference between Example 21 and Example 1: the hydrogen fluoride content in the fluoroethylene carbonate of Example 21 is 50 ppm.

[0108] Example 22

[0109] The difference between Example 22 and Example 1: the mass fraction C2 of the fluoroethylene carbonate of Example 22 is 3 wt%.

[0110] Example 23

[0111] The difference between Example 23 and Example 1: the mass fraction C2 of the fluoroethylene carbonate of Example 23 is 15 wt%.

[0112] Example 24

[0113] The difference between Example 24 and Example 1: the mass fraction C2 of the fluoroethylene carbonate of Example 23 is 1 wt%.

[0114] Example 25

[0115] The difference between Example 25 and Example 1: the mass fraction C2 of the fluoroethylene carbonate of Example 25 is 18 wt%.

[0116] Example 26

[0117] The difference between Example 26 and Example 1: 4 wt% of 1.3.6-hexanetricarbonitrile is further added to the electrolyte of Example 26.

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1: no compound shown as Formula 1 is added to the electrolyte of Comparative Example 1.

[0120] Comparative Example 2

[0121] The difference between Comparative Example 2 and Example 1: no fluoro compound is added to the electrolyte of Comparative Example 2.

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1: no compound shown as Formula 1 and no fluoro compound are added to the electrolyte of Comparative Example 3.

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1: the content of Mg in the lithium cobaltate is 50 ppm, the mass fraction C1 of the compound of Formula 1-1 is 0.3 wt%, and the mass fraction C2 of the fluoro compound is 2 wt%.

[0126] Comparative Example 5

[0127] Difference between Comparative Example 5 and Comparative Example 4: the mass fraction of fluorinated compound C2 was 7wt%.

[0128] Comparative Example 6

[0129] Difference between Comparative Example 6 and Comparative Example 5: the content of Mg in lithium cobaltate was 80ppm.

[0130] The electrolyte and the positive active material of Examples 1-26 and Comparative Examples 1-6 were different, and details can be seen in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] The batteries prepared from Examples 1-26 and Comparative Examples 1-6 were subjected to high-temperature cycle test and low-temperature discharge performance test, and the specific test conditions were as follows:

[0135] High-temperature cycle test: the battery was placed at 45℃, and was subjected to charge-discharge cycle using 1C current, and the maximum capacity of the first three times was recorded as Q, and the capacity of the cycle to 500 times was selected as Q2, and the capacity retention rate of the battery after high-temperature cycle was calculated by the following formula: capacity retention rate (%) = Q2 / Q x 100.

[0136] Edge voltage test: the voltage between the positive electrode and the aluminum plastic film aluminum foil was tested by a multimeter.

[0137] The batteries prepared from Examples 1-26 and Comparative Examples 1-6 were subjected to high-temperature cycle test and edge voltage test, and the test results were shown in Table 2.

[0138] Table 2

[0139]

[0140]

[0141] From the data of Table 2, the high-temperature cycle retention rate and edge voltage of the batteries of Examples 1-26 are significantly improved compared to the batteries of Comparative Examples 1-3 without adding the compound of Formula 1 and / or the fluorinated compound. In particular, the values calculated by Formula M*C1 of Comparative Examples 4 and 5 are not between 0.002% and 0.1%, and the values calculated by Formula C2 / C1 of Comparative Examples 5 and 6 are not between 1 and 10. The high-temperature cycle retention rate and edge voltage of the batteries of Comparative Examples 4-6 are much worse than those of Examples 1-26, indicating that not only the compound of Formula 1 and the fluorinated compound should be added to the electrolyte, but also the Formula 0.002%≤M*Cl≤0.1% and 1≤C2 / Cl≤10 should be satisfied. Ultimately, the batteries obtained have excellent high-temperature cycle stability and safety performance.

[0142] In summary, the high-safety lithium ion battery and the preparation method thereof utilize Mg element to inhibit the structural change of lithium cobaltate at high voltage to improve the high-temperature cycle stability. Under the catalysis of Mg, the compound is preferentially dissolved and oxidized to form lithium sulfonate compounds, thereby inhibiting the corrosion problem of the aluminum plastic film package. Meanwhile, under the condition of satisfying the defined relationship, the compound and the fluorinated compound can form a more stable lithium ion transmission interface film, thereby improving the efficiency of the lithium ion battery and greatly increasing the safety.

[0143] Based on the above ideal embodiments according to the present application, through the above description, relevant personnel can make various changes and modifications without deviating from the technical idea of the present application. The technical scope of the present application is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. A lithium-ion battery, characterized in that, include: Positive electrode, negative electrode, separator, and electrolyte; The positive electrode active material of the positive electrode sheet includes lithium cobalt oxide, and the lithium cobalt oxide also contains magnesium element with a content of M ppm, and satisfies 50≤M<300; The electrolyte contains compounds The compound is a fluorinated compound, wherein the mass percentage of the compound in the electrolyte is C1, and the mass percentage satisfies 0.002% ≤ M*C1 ≤ 0.1%. Wherein, R0 is a single bond or a methylene group, R1 is any one of hydrogen, halogen, a hydrocarbon group with 1 to 5 carbon atoms, or a haloalkyl group with 1 to 5 carbon atoms, and R2, R3, and R4 are each independently selected from... Any one of them, and R2, R3, and R4 are not selected simultaneously. Furthermore, the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1 ≤ C2 / Cl ≤ 10; The ethanol content in the compound does not exceed 20 ppm; The content of hydrofluoric acid in the fluorinated compound does not exceed 30 ppm; The electrolyte also includes additives, and the mass percentage of the additives in the electrolyte is 1% to 10%. The additives include at least one of the following: vinylene carbonate, methylene disulfonate, 1,3-propanesulfonate lactone, triglyceride, succinate, adiponitrile, 1,3,6-hexanetrionitrile, fluoroethylene carbonate, lithium difluorooxalate borate, lithium dioxalate borate, lithium tetrafluoroborate, and lithium difluorobis(oxalate) phosphate. The upper limit of the charging voltage of the lithium-ion battery is ≥4.45V.

2. The lithium-ion battery as described in claim 1, characterized in that, The mass percentage (C1) of the compound in the electrolyte ranges from 0.3% to 4%. The mass percentage (C2) of the fluorinated compound in the electrolyte ranges from 3% to 15%.

3. The lithium-ion battery as described in claim 1, characterized in that, The fluorinated compound includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, fluorobenzene, trifluoromethyl ethylene carbonate, and ethoxypentafluorophosphazene.

4. The lithium-ion battery as described in claim 1, characterized in that, The R1 includes any one of hydrogen, halogen, methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, halomethyl, haloethyl, halon-propyl, haloisopropyl, halobutyl, halopentyl, and halohexyl.

5. The lithium-ion battery as described in claim 1, characterized in that, The compound includes at least one of the following compounds:

6. The lithium-ion battery as described in claim 1, characterized in that, The negative electrode active material of the negative electrode sheet includes graphite or silicon-based materials.

7. The lithium-ion battery as described in claim 1, characterized in that, The electrolyte also includes an electrolyte salt, and the electrolyte salt accounts for 10% to 20% of the mass of the electrolyte.

8. A method for preparing a lithium-ion battery as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Preparation of electrolyte: ethylene carbonate, propyl propionate, and diethyl carbonate are mixed, then lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate are added, followed by the addition of compound... and fluorinated compounds; (2) Preparation of positive electrode sheet: magnesium-containing lithium cobalt oxide, acetylene black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone and then coated onto the positive electrode current collector aluminum foil. (3) Preparation of negative electrode sheet: graphite, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber are dispersed in deionized water and then coated onto the aluminum foil of the negative electrode current collector. (4) Battery preparation: The above positive electrode, separator and negative electrode are stacked in sequence, with the separator between the positive electrode and the negative electrode to play a role in isolation. Then, the battery is wound to obtain a bare cell, and the bare cell is placed in an aluminum-plastic film packaging shell. After drying, the electrolyte prepared in step (1) is injected. After vacuum sealing, standing, formation and secondary sealing, the battery preparation is completed.

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