High-safety lithium ion battery and preparation method thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-safety lithium ion battery and a preparation method thereof.The high-safety lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm and electrolyte; a positive active material of the positive pole piece comprises lithium cobalt oxide, the lithium cobalt oxide also contains M ppm of magnesium element, and M is more than or equal to 50 and less than or equal to 300; the electrolyte comprises a compound and a fluorinated compound; according to the high-safety lithium ion battery, the Mg element is used for inhibiting the structural change of lithium cobalt oxide under high voltage so as to improve the high-temperature cycling stability, and under the catalysis of Mg, a compound is dissolved prior to an electrolyte and is oxidized to generate a lithium sulfonate compound, so that the corrosion problem of aluminum plastic film packaging is inhibited; and meanwhile, under the condition that a limited relational expression is met, the compound and the fluorinated compound can form a more stable lithium ion transmission interface film, so that the efficiency of the lithium ion battery is improved, and the safety is also greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a high-safety lithium ion battery and a preparation method thereof. Background Art

[0002] Lithium-ion batteries with high energy density, long service life and low self-discharge have been widely used in 3C digital, electric vehicles, drones, electric ships, large and outdoor energy storage and other fields. Lithium-ion batteries are composed of four main materials: positive electrode, negative electrode, diaphragm and electrolyte. Lithium cobalt oxide positive electrode materials are used in mobile phones, laptops and other energy storage devices with high volume requirements due to their high compaction density and energy density.

[0003] In order to further improve the energy density of lithium-ion batteries and thus extend the battery life of the device, the operating voltage of lithium-ion batteries is also constantly increasing. However, the electrolyte has poor stability under high voltage, which easily leads to decomposition and gas production, thereby seriously deteriorating the cycle performance, especially at high temperatures. At the same time, the positive electrode also has problems such as oxygen evolution and crystal structure collapse under high voltage, which will further lead to the attenuation of cycle performance. In addition, in order to increase the energy density of the battery, it is a commonly used method to use aluminum-plastic film instead of aluminum shell to reduce the weight of inactive substances in the battery. However, the packaging of aluminum-plastic film is sealed by thermal compounding, which is affected to a certain extent by the components of the electrolyte. When the electrolyte contains highly acidic components, it will lead to insufficient packaging strength, resulting in serious safety problems.

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

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

[0006] The embodiments of the present disclosure at least provide a high-safety lithium-ion battery and a method for preparing the same.

[0007] In a first aspect, an embodiment of the present disclosure provides a lithium-ion battery, comprising: a positive electrode plate, a negative electrode plate, a separator and an electrolyte; the positive electrode active material of the positive electrode plate comprises lithium cobalt oxide, and the lithium cobalt oxide also 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 to 5 carbon atoms, or a halogenated hydrocarbon group with 1 to 5 carbon atoms, and R2, R3, and R4 are independently selected from Any one of the above, and R2, R3, and R4 are not selected at the same time Furthermore, the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1≤C2 / Cl≤10.

[0008] In an optional embodiment, the mass percentage C1 of the compound in the electrolyte is in the range of 0.3% to 4%; the mass percentage C2 of the fluorinated compound in the electrolyte is in the range of 3% to 15%.

[0009] In an optional embodiment, the fluorinated compound includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluorobenzene, trifluoromethylethylene carbonate, and ethoxypentafluorophosphazene.

[0010] In an optional embodiment, the content of ethanol in the compound does not exceed 20 ppm; the content of hydrofluoric acid in the fluorinated compound does not exceed 30 ppm.

[0011] In an optional embodiment, R1 includes any one of hydrogen, halogen, methyl, ethyl, n-propyl, isopropyl, butyl, pentyl, hexyl, halomethyl, haloethyl, halo-n-propyl, haloisopropyl, halobutyl, halopentyl and halohexyl.

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

[0013]

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

[0015] In an optional embodiment, the electrolyte further includes an electrolyte salt, and the mass proportion of the electrolyte salt in the electrolyte is 10% to 20%.

[0016] In an optional embodiment, the electrolyte further includes an additive, and the mass proportion of the additive in the electrolyte is 1% to 10%; the additive includes at least one of vinylene carbonate, methylene disulfonate, 1,3-propane sultone, glycerol trinitrile, succinonitrile, adiponitrile, 1,3,6-hexane trinitrile, fluoroethylene carbonate, lithium bis(fluorooxalatoborate), lithium bis(oxalatoborate), lithium tetrafluoroborate and lithium bis(fluorobis(oxalatophosphate)).

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

[0018] The beneficial effects of the present invention are that the high-safety lithium-ion battery and the preparation method thereof utilize the Mg element to inhibit the structural change of lithium cobalt oxide under high voltage to improve the high-temperature cycle stability, and under the catalysis of Mg, the compound will be dissolved in the electrolyte first and oxidized to generate lithium sulfonate compounds, thereby inhibiting the corrosion problem of the aluminum-plastic film packaging; at the same time, under the condition of satisfying the restricted 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.

[0019] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description.

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below for detailed description as follows. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In this document, a single "compound" refers specifically to The specific structures of its different substituents can also be referred to as Formula 1 in specific embodiments, and do not refer to all compounds.

[0023] As used herein, the phrases "in one embodiment," "according to one embodiment," "in some embodiments," and the like generally refer to the fact that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present disclosure. Therefore, a particular feature, structure, or characteristic may be included in more than one embodiment of the present disclosure, so that these phrases do not necessarily refer to the same embodiment. As used herein, the terms "example," "exemplary," and the like are used to "serve 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 superior to other implementations, aspects, or designs. On the contrary, the use of the terms "example," "exemplary," and the like is intended to present concepts in a concrete manner.

[0024] In this document, as used herein, expressions such as "at least one of..." when following a list of elements modify the entire list of elements rather than modifying the individual elements in the list. For example, the expression "at least one of a, b, and c" should be understood to include only a, only b, only c, both a and b, both a and c, both b and c, or all of a, b, and c.

[0025] The terms used herein are only used to describe specific exemplary configurations and are not intended to be limited. As used herein, the singular articles "one", "an" and "the" may also be intended to include plural forms, unless it is clearly indicated above that this is not the case. The terms "comprise", "include" and "have" are inclusive, and therefore specify the presence of features, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, elements, components and / or combinations thereof. The method steps, processes and operations described herein should not be interpreted as necessarily requiring them to be performed in the specific order discussed or shown, unless specifically identified as an execution order. Additional or alternative steps may be adopted.

[0026] Lithium cobalt oxide has a high energy density under high voltage. The doping or coating of Mg element can significantly inhibit the structural changes of lithium cobalt oxide under high voltage, thereby improving the high-temperature cycle stability. However, too little Mg will not significantly improve the structural changes of lithium cobalt oxide, 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 cobalt oxide, and can be adsorbed on the surface of the positive electrode active material after the battery is injected with electrolyte. However, the inventors found that the hydrofluoric acid in the fluorinated compounds will have a certain corrosive effect on the interface film, resulting in increased impedance and rapid reduction of the cycle. The compounds in the present application can be oxidized to generate lithium sulfonate compounds under the catalysis of Mg in lithium cobalt oxide in preference to the electrolyte solvent.

[0027] In addition, the inventors found that the ethanol in the compound of the present application would seriously hinder the formation of the interface film, resulting in the failure to exert the improved performance of the compound. Therefore, the combined use of the fluorinated compound and the compound can form an interface film of a mixture of fluoride and lithium sulfonate compounds.

[0028] The inventors also found that when the amount of compound added and the Mg content in lithium cobalt oxide meet the formula 0.002% ≤ M*Cl ≤ 0.1%, a more stable interface film that is conducive to lithium ion transmission can be formed. On the other hand, since high-voltage lithium cobalt oxide easily catalyzes the decomposition of lithium salts in the electrolyte to form highly acidic substances during the charging process, the packaging strength is insufficient when the battery is vented and packaged after formation, resulting in a large voltage at the battery side, which is easy to cause safety problems such as battery leakage. The electrolyte provided by the present invention can prevent the formation of acidic substances in the electrolyte, significantly improve the packaging performance of the battery, and enhance the safety performance of the battery.

[0029] The defects existing in the above solutions are the results obtained by the inventor after practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed by the present disclosure for the above problems below should be the contributions made by the inventor to the present disclosure during the disclosure process.

[0030] Some embodiments of the present invention are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0031] The embodiment of the present disclosure provides a high-safety lithium-ion battery, comprising: a positive electrode plate, a negative electrode plate, a separator and an electrolyte; the positive electrode active material of the positive electrode plate comprises lithium cobalt oxide, and the lithium cobalt oxide also contains magnesium in an amount 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 to 5 carbon atoms, or a halogenated hydrocarbon group with 1 to 5 carbon atoms, and R2, R3, and R4 are independently selected from Any one of the above, and R2, R3, and R4 are not selected at the same time Furthermore, the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1≤C2 / Cl≤10.

[0032] Specifically, the magnesium content is tested by inductively coupled plasma emission spectrometry.

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

[0034] In some embodiments, specifically, the fluorinated compound includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluorobenzene, trifluoromethylethylene carbonate, and ethoxypentafluorophosphazene.

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

[0036] Specifically, the ethanol content is determined by gas chromatography, and the hydrofluoric acid content is determined by a NaOH-bromothymol 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 sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector, wherein the positive electrode active material layer includes 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 may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material base and a metal layer formed on at least one side of the polymer material base. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like.

[0043] Optionally, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is arranged 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, and 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, and polyurethane.

[0046] In some embodiments, specifically, the mass ratio of the positive electrode 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 sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes at least one of a second binder and a second conductive agent and a negative electrode active material.

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

[0049] Optionally, the negative electrode active material may include at least one of the following materials: graphite, soft carbon, hard carbon, silicon-based materials, etc., preferably graphite or silicon-based materials, which have excellent cycle life, thereby improving the cycle performance and service life of the battery.

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

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

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

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

[0054] In some embodiments, specifically, the mass ratio of the negative electrode 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 proportion of the electrolyte salt in the electrolyte is 10% to 20%; optionally, the electrolyte salt is preferably a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0056] In some embodiments, specifically, the electrolyte also includes a solvent, and the solvent includes at least one of carbonates (such as cyclic carbonates, chain carbonates), carboxylates (such as cyclic carboxylates, chain carboxylates), ether compounds (such as cyclic ether compounds, chain ether compounds), phosphorus-containing compounds, sulfur-containing compounds and aromatic fluorine-containing compounds.

[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), and γ-T lactone.

[0058] In some embodiments, specifically, the electrolyte further includes an additive, and the mass proportion of the additive in the electrolyte is 1% to 10%; the additive includes at least one of vinylene carbonate, methylene disulfonate, 1,3-propane sultone, glycerol trinitrile, succinonitrile, adiponitrile, 1,3,6-hexane trinitrile, fluoroethylene carbonate, lithium bis(fluorooxalatoborate), lithium bis(oxalatoborate), lithium tetrafluoroborate and lithium bis(fluorobis(oxalatophosphate)).

[0059] In some embodiments, specifically, the battery further includes a separator, which 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 aluminum-plastic film packaging.

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

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

[0063] Example 1

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

[0065] (2) Preparation of positive electrode sheets: Lithium cobalt oxide containing 80 ppm of Mg, acetylene black and polyvinylidene fluoride are dispersed in N-methylpyrrolidone (NMP) solvent in a mass ratio of 97:1:2, and the mixture is stirred thoroughly to form a uniform positive electrode slurry, which is then evenly coated on the positive electrode current collector aluminum foil. After drying, rolling and slitting, the positive electrode sheets are obtained.

[0066] (3) Preparation of negative electrode sheets: 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, and the mixture is stirred thoroughly to form a uniform negative electrode slurry, which is then evenly coated on the negative electrode current collector copper foil. After drying, rolling and slitting, the negative electrode sheets are obtained.

[0067] (4) Preparation of battery: stack the positive electrode sheet, separator and negative electrode sheet in order, place the separator between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wind to obtain a bare cell, and place the bare cell in an aluminum plastic film packaging shell, and after drying, inject the electrolyte prepared in step (1), the total mass of the electrolyte is 7.7g. After vacuum packaging, standing, formation, secondary packaging and other processes, the battery is prepared, and its rated capacity is 5.5Ah. The charge and discharge voltage range of this battery is 3.0~4.45V.

[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 bisfluoroethylene 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] The difference between Example 10 and Example 1 is that the fluorinated compound used in Example 10 is trifluoromethylethylene carbonate.

[0086] Embodiment 11

[0087] The difference between Example 11 and Example 1 is that the fluorinated compound used in Example 11 is ethoxypentafluorophosphazene.

[0088] Example 12

[0089] The difference between Example 12 and Example 1: The Mg content in the lithium cobalt oxide of Example 12 is 50 ppm.

[0090] Example 13

[0091] The difference between Example 13 and Example 1: The Mg content in the lithium cobalt oxide of Example 13 is 300 ppm.

[0092] Embodiment 14

[0093] The difference between Example 14 and Example 1: The Mg content in the lithium cobalt oxide of Example 14 is 400 ppm.

[0094] Embodiment 15

[0095] The difference between Example 15 and Example 1: The ethanol content in the compound of formula 1 in Example 15 is 18 ppm.

[0096] Example 16

[0097] The difference between Example 16 and Example 1: The ethanol content in the compound of formula 1 in Example 16 is 33 ppm.

[0098] Embodiment 17

[0099] The difference between Example 17 and Example 1: The mass proportion C1 of the compound of formula 1-1 in Example 17 is 0.8wt%.

[0100] Embodiment 18

[0101] The difference between Example 18 and Example 1: The mass proportion C1 of the compound of formula 1-1 in Example 18 is 4wt%.

[0102] Embodiment 19

[0103] The difference between Example 19 and Example 1: The mass proportion C1 of the compound of formula 1-1 in Example 19 is 6wt%.

[0104] Embodiment 20

[0105] The difference between Example 20 and Example 1 is that the hydrofluoric acid content in the fluoroethylene carbonate of Example 20 is 10 ppm.

[0106] Embodiment 21

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

[0108] Embodiment 22

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

[0110] Embodiment 23

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

[0112] Embodiment 24

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

[0114] Embodiment 25

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

[0116] Embodiment 26

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

[0118] Comparative Example 1

[0119] The difference between Comparative Example 1 and Example 1 is that the compound represented by Formula 1 is not added to the electrolyte of Comparative Example 1.

[0120] Comparative Example 2

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

[0122] Comparative Example 3

[0123] The difference between Comparative Example 3 and Example 1 is that the compound represented by Formula 1 and the fluorinated compound are not added to the electrolyte of Comparative Example 3.

[0124] Comparative Example 4

[0125] The difference between Comparative Example 4 and Example 1 is that the content of Mg in the lithium cobalt oxide is 50 ppm, the mass proportion C1 of the compound of Formula 1-1 is 0.3 wt %, and the mass proportion C2 of the fluorinated compound is 2 wt %.

[0126] Comparative Example 5

[0127] The difference between Comparative Example 5 and Comparative Example 4 is that the mass proportion C2 of the fluorinated compound is 7 wt %.

[0128] Comparative Example 6

[0129] The difference between Comparative Example 6 and Comparative Example 5 is that the content of Mg in the lithium cobalt oxide is 80 ppm.

[0130] The electrolytes and positive electrode active materials of Examples 1-26 and Comparative Examples 1-6 are different, as shown in Table 1.

[0131] Table 1

[0132]

[0133]

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

[0135] High temperature cycle test: Place the battery at 45°C and use 1C current for charge and discharge cycles. Record the maximum capacity of the first three times as Q, select the capacity after 500 cycles as Q2, and calculate the capacity retention rate of the battery after high temperature cycling by the following formula: Capacity retention rate (%) = Q2 / Q×100.

[0136] Edge voltage test: Use a multimeter to test the voltage between the positive electrode and the aluminum foil of the aluminum-plastic film.

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

[0138] Table 2

[0139]

[0140]

[0141] It can be seen from the data in Table 2 that the high-temperature cycle retention rate and the edge voltage of the batteries of Examples 1-26 are significantly improved compared with the batteries of Comparative Examples 1 to 3 which do not add the compound shown in Formula 1 or / and the fluorinated compound. In particular, although Comparative Examples 4 and 5 add the compound shown in Formula 1 and the fluorinated compound, the value calculated by the formula M*C1 is not between 0.002% and 0.1%, and the value calculated by the formula C2 / C1 of Comparative Examples 5 and 6 is not between 1 and 10. The high-temperature cycle retention rate and the edge voltage of the batteries are also much worse than those of Examples 1-26, indicating that the electrolyte of the present application not only needs to add the compound shown in Formula 1 and the fluorinated compound, but also needs to satisfy the formulas 0.002%≤M*Cl≤0.1% and 1≤C2 / Cl≤10, and the final battery has excellent low and high temperature cycle stability and safety performance.

[0142] In summary, the high-safety lithium-ion battery and its preparation method utilize the Mg element to inhibit the structural change of lithium cobalt oxide under high voltage to improve the high-temperature cycle stability, and under the catalysis of Mg, the compound will be oxidized to form lithium sulfonate compounds before the electrolyte is dissolved, thereby inhibiting the corrosion problem of the aluminum-plastic film packaging; at the same time, under the condition of satisfying the limited 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 of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A lithium ion battery, characterized in that: include: Positive electrode sheet, negative electrode sheet, separator and electrolyte; The positive electrode active material of the positive electrode plate includes lithium cobalt oxide, and the lithium cobalt oxide also contains magnesium element with a content of Mppm, and satisfies 50≤M≤300; The electrolyte includes a compound and a fluorinated compound, wherein 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 having 1 to 5 carbon atoms, or a halogenated hydrocarbon group having 1 to 5 carbon atoms, and R2, R3, and R4 are independently selected from Any one of the above, and R2, R3, and R4 are not selected at the same time Furthermore, the mass percentage C2 of the fluorinated compound in the electrolyte satisfies 1≤C2 / Cl≤10.

2. The lithium-ion battery according to claim 1, characterized in that The mass percentage C1 of the compound in the electrolyte is in the range of 0.3% to 4%; The mass percentage C2 of the fluorinated compound in the electrolyte is in the range of 3% to 15%.

3. The lithium ion battery according to claim 1, characterized in that The fluorinated compound includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, fluorobenzene, trifluoromethylethylene carbonate, and ethoxy pentafluorophosphazene.

4. The lithium ion battery according to claim 1, characterized in that The content of ethanol in the compound does not exceed 20 ppm; The content of hydrofluoric acid in the fluorinated compound does not exceed 30 ppm.

5. The lithium ion battery according to claim 1, characterized in that The 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.

6. The lithium ion battery according to claim 1, characterized in that The compound comprises at least one of the following compounds:

7. The lithium ion battery according to claim 1, characterized in that The negative electrode active material of the negative electrode plate includes graphite or silicon-based material.

8. The lithium ion battery according to claim 1, characterized in that The electrolyte solution further includes an electrolyte salt, and the mass proportion of the electrolyte salt in the electrolyte solution is 10% to 20%.

9. The lithium ion battery according to claim 1, characterized in that The electrolyte further includes an additive, and the mass proportion of the additive in the electrolyte is 1% to 10%; The additive includes at least one of vinylene carbonate, methylene methanedisulfonate, 1,3-propane sultone, glycerol trinitrile, succinonitrile, adiponitrile, 1,3,6-hexane trinitrile, fluoroethylene carbonate, lithium bisfluorooxalatoborate, lithium bisoxalatoborate, lithium tetrafluoroborate and lithium bisfluorobisoxalatophosphate.

10. A method for preparing a lithium ion battery according to any one of claims 1 to 9, characterized in that: The steps include: (1) Preparation of electrolyte, namely, mixing ethylene carbonate, propyl propionate and diethyl carbonate, adding lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and then adding compound and fluorinated compounds; (2) Preparation of positive electrode sheet, i.e., dispersing magnesium-containing lithium phosphate, acetylene black and polyvinylidene fluoride in N-methylpyrrolidone and coating the dispersed materials on positive electrode current collector aluminum foil; (3) Preparation of negative electrode sheet, i.e., dispersing graphite, acetylene black, sodium carboxymethyl cellulose and styrene-butadiene rubber in deionized water and coating the resulting mixture on the negative electrode current collector aluminum foil; (4) Preparation of a battery, i.e., stacking the positive electrode sheet, the separator and the negative electrode sheet in order, placing the separator between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then winding to obtain a bare cell, placing the bare cell in an aluminum-plastic film packaging shell, and after drying, injecting the electrolyte prepared in step (1), and completing the battery preparation through vacuum packaging, standing, formation, secondary packaging and other processes.

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