Electrochemical devices and electronic devices

Abstract

The application discloses an electrochemical device and an electronic device, and the electrochemical device comprises a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises a compound shown in formula I: wherein the compound shown in formula I accounts for A% of the total mass of the electrolyte, A is 0.3-40; R1 and R2 are each independently selected from hydrogen, halogen, alkyl with 1-5 carbon atoms, alkyl with 1-5 carbon atoms substituted by halogen, alkenyl with 1-5 carbon atoms or alkenyl with 1-5 carbon atoms substituted by halogen; and at least one of R1 and R2 contains halogen; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the tensile strength of the positive electrode current collector is B MPa, and 2<=B / A<=750. The application can improve the cycle performance and over-discharge storage performance of the electrochemical device, and the electrochemical device can maintain good safety performance after long-time cycle.

Description

[0001] This application is a divisional application of the application for patent with the application number 202110340358.9, the title of which is "Electrochemical device and electronic device", and the filing date of which is March 30, 2021. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to an electrochemical device and an electronic device. BACKGROUND

[0003] Electrochemical devices (for example: lithium ion batteries) are widely used in electronic devices in various fields. With the development of electronic devices, people have higher requirements for the energy density of electrochemical devices.

[0004] On the other hand, various electronic products have safety problems, not only the service life of the electrochemical device needs to be considered, but also its safety needs to be concerned. Therefore, how to ensure the cycle performance of the electrochemical device while improving the safety of the electrochemical device has become a problem to be solved urgently. SUMMARY

[0005] The present application provides an electrochemical device and an electronic device, which can improve the cycle performance and over-discharge storage performance of the electrochemical device, reduce the corrosion of the electrolyte to the positive current collector, and ensure the safety performance of the electrochemical device.

[0006] In some embodiments of the present application, an electrochemical device is provided, which comprises a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises a compound represented by Formula I:

[0007]

[0008] wherein the compound represented by Formula I accounts for A% of the total mass of the electrolyte, A is 0.3 to 40; R1 and R2 are each independently selected from hydrogen, halogen, an alkyl group with 1 to 5 carbon atoms, an alkyl group with 1 to 5 carbon atoms substituted by halogen, an alkenyl group with 1 to 5 carbon atoms, or an alkenyl group with 1 to 5 carbon atoms substituted by halogen, an alkynyl group with 1 to 5 carbon atoms, or an alkynyl group with 1 to 5 carbon atoms substituted by halogen; and at least one of R1 and R2 contains halogen; the positive electrode comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, the tensile strength of the positive current collector is B MPa, and 2≤B / A≤750.

[0009] In some embodiments of the present application, the compound represented by Formula I comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroethylene carbonate or 4-fluoro-5-methyl ethylene carbonate.

[0010] In some embodiments of the present application, at least one of the following conditions (a) to (d) is met:

[0011] (a) The electrolyte further comprises a dinitrile compound;

[0012] (b) The electrolyte further comprises a polynitrile compound with a number of cyano groups equal to or greater than 3;

[0013] (c) The electrolyte further comprises a compound containing a S=O double bond;

[0014] (d) The electrolyte further comprises an oxygen heterocyclic compound.

[0015] In some embodiments of the present application, the dinitrile compound accounts for C% of the total mass of the electrolyte, the polynitrile compound accounts for D% of the total mass of the electrolyte, and 0.5≤D / C≤20;

[0016] In some embodiments of the present application, the dinitrile compound accounts for C% of the total mass of the electrolyte, and 0.5≤C≤7 is met.

[0017] In some embodiments of the present application, the polynitrile compound accounts for D% of the total mass of the electrolyte, and 0.1≤D≤4 is met.

[0018] In some embodiments of the present application, the compound of formula I and the polynitrile compound meet 0.02≤A / D≤130.

[0019] In some embodiments of the present application, the dinitrile compound includes at least one of butanedinitrile, pentanedinitrile, hexanedinitrile, heptanedinitrile, octanedinitrile, nonanedinitrile, decanedinitrile, ethylene glycol (bispropionitrile) ether (nitrile ether), or fumaronitrile;

[0020] In some embodiments of the present application, the polynitrile compound includes at least one of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, nonanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-benzene tricyano, or 1,2,3-tris(2-cyanooxy)propane.

[0021] In some embodiments of the present application, the compound containing a S=O double bond includes at least one of 1,3-propane sulfone, 2,4-butane sulfone, 1,4-butane sulfone, methane dithioformate, ethylene sulfate, sulfolane, propylene sulfate, 4-methyl ethylene sulfite, or 5-methyl oxathiane 2,2-dioxide.

[0022] In some embodiments of the present application, the compound containing a S=O double bond accounts for 0.1% to 7% of the total mass of the electrolyte.

[0023] In some embodiments of the present application, the oxygen-containing heterocyclic compound includes at least one of 1,3-dioxane, dioxolane, 4-methyl-1,3-dioxane, tetrahydropyran, tetrahydrofuran or 1,2-epoxybutane.

[0024] In some embodiments of the present application, the oxygen-containing heterocyclic compound accounts for 0.01% to 3% of the total mass of the electrolyte.

[0025] In some embodiments of the present application, the tensile strength of the positive current collector is B MPa, satisfying B>100.

[0026] In some embodiments of the present application, the positive current collector satisfies at least one of conditions (e) to (j):

[0027] (e) the positive current collector contains aluminum;

[0028] (f) the thickness of the positive current collector is 5 μm to 20 μm;

[0029] (g) the positive current collector contains an M element, the M element including at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium and vanadium, the percentage of the M element in the total weight of the positive current collector being not more than 2%;

[0030] (h) the positive current collector has a unit area weight of 15 g / m 2 to 100 g / m 2 ;

[0031] (i) the positive current collector has an elongation rate ≥1%;

[0032] (j) the positive current collector has a welding area, the area of the welding area being F cm 2 , 1≤F≤50.

[0033] In some embodiments of the present application, the negative electrode includes a negative current collector and a negative active material layer, the negative active material layer including a negative material, the negative material including a silicon-based material, at least a part of the surface of the silicon-based material having a protective layer.

[0034] In some embodiments of the present application, the protective layer includes a carbon material or Me x O y , wherein Me includes at least one of Al, Si, Mn, V, Cr, Co or Zr, x is 1-2 and y is 1-3.

[0035] Some embodiments of the present application provide an electronic device including the above-described electrochemical device.

[0036] The electrochemical device provided by the embodiments of the present application comprises the compound shown in Formula I. The compound shown in Formula I can continuously repair the negative electrode SEI (solid electrolyte interphase) film during over-discharge storage of the electrochemical device, effectively improve the negative electrode interface, reduce over-discharge storage swelling, and improve the cycle performance. In addition, by controlling the ratio of the tensile strength of the positive electrode current collector and the content of the compound shown in Formula I within a certain range, the cycle performance and over-discharge storage performance of the electrochemical device can be ensured, and the safety performance of the electrochemical device can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0037] The above and other features, advantages, and aspects of the embodiments of the present disclosure will become more apparent with reference to the following detailed description in conjunction with the accompanying drawings. Throughout the drawings, same or similar reference numerals can represent same or similar elements. It should be understood that the drawings are schematic and elements and features are not necessarily drawn to scale.

[0038] Figure 1 FIG. 1 is a schematic diagram of the connection of a positive electrode and a tab according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0039] Embodiments of the present application will be described in more detail below. The present application can be implemented in various forms, and should not be interpreted as being limited to the embodiments set forth herein, but rather, the embodiments are provided so that the present application can be more thoroughly and completely understood.

[0040] In the related art, a fluorine-containing additive, such as FEC, is added to the electrolyte to improve the cycle performance of the negative electrode system electrochemical device. However, FEC can react with lithium hexafluorophosphate to generate a corrosive component that corrodes the positive electrode current collector, such as an aluminum foil, resulting in a decrease in the safety performance, such as drop performance and impact performance, of the electrochemical device.

[0041] To at least partially solve the above problems, some embodiments of the present application provide an electrochemical device, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte comprises a compound shown in Formula I:

[0042]

[0043] wherein the compound of Formula I is present in the electrolyte in an amount of A% of the total mass of the electrolyte, A is 0.3 to 40; R1, R2 are each independently selected from hydrogen, halogen, alkyl having 1 to 5 carbon atoms, alkyl having 1 to 5 carbon atoms substituted with halogen, alkenyl having 1 to 5 carbon atoms or alkenyl having 1 to 5 carbon atoms substituted with halogen, alkynyl having 1 to 5 carbon atoms or alkynyl having 1 to 5 carbon atoms substituted with halogen; and at least one of R1 and R2 contains halogen; the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode current collector has a tensile strength of B MPa, and 2≤B / A≤750. In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0044] In some embodiments of the present application, on one hand, by adding the compound of Formula I to the electrolyte, the SEI film of the negative electrode can be continuously repaired during over-discharge storage of the electrochemical device, the negative electrode interface can be effectively improved, over-discharge storage swelling can be reduced, and the cycle performance can be improved. On the other hand, in order to solve the problem of reduced safety performance caused by the corrosion of the product after the reaction of the compound of Formula I with water to the positive electrode current collector, the ratio of the tensile strength of the positive electrode current collector to the content of the compound of Formula I is controlled in the present application, the positive electrode current collector can maintain a certain tensile strength, and the drop performance and impact performance of the electrochemical device after cycling can be improved. Therefore, the electrochemical device proposed in the present application can ensure the cycle performance and over-discharge storage performance of the electrochemical device, reduce the corrosion of the electrolyte to the positive electrode current collector, and enable the positive electrode current collector to maintain a certain tensile strength for a long time under high temperature, thereby improving the safety performance of the electrochemical device.

[0045] In some embodiments of the present application, the compound of Formula I includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroethylene carbonate, or 4-fluoro-5-methyl ethylene carbonate. In some embodiments of the present application, the content of the compound of Formula I is 0.1% to 40%. In some embodiments of the present application, the content of the compound of Formula I is 1% to 20%. In some embodiments of the present application, the content of the compound of Formula I is 4% to 20%. The above-mentioned compounds can preferentially form stable SEI films with the negative electrode active material layer, thereby protecting the negative electrode active material layer.

[0046] In some embodiments of the present application, the electrolyte further includes a dinitrile compound.

[0047] In some embodiments of the present application, the electrolyte further includes a multi-nitrile compound having a number of cyano groups greater than or equal to 3.

[0048] In some embodiments, the cyano group has high bond energy and is not easily oxidized, and the nitrile compound has good stability on the positive electrode and strong resistance to oxidation. In addition, the cyano group has strong coordination ability and can bind to active sites on the surface of the positive active material layer, reducing the decomposition of the electrolyte by the positive active material layer and enhancing the resistance of the electrolyte to oxidation by the positive active material layer, thereby improving the cycle life of the electrolyte at high voltage. The multiple nitrile compound has more cyano groups, which can improve the cycle performance of the electrochemical device, but can cause a storage pressure drop of the electrochemical device. The use of a certain dinitrile compound can inhibit the influence on the pressure drop.

[0049] In some embodiments of the present application, the electrolyte further comprises a compound containing a S=O double bond. In some embodiments, the compound containing a S=O double bond can form a relatively stable protective layer on the positive active material layer and the negative active material layer, thereby improving the cycle performance and storage performance of the electrochemical device.

[0050] In some embodiments of the present application, the electrolyte further comprises an oxygen heterocycle-containing compound. In some embodiments, the oxygen heterocycle-containing compound can form a relatively stable protective layer on the positive active material layer and the negative active material layer, thereby improving the cycle performance and storage performance of the electrochemical device.

[0051] In some embodiments of the present application, the dinitrile compound accounts for C% of the total mass of the electrolyte, and the multiple nitrile compound accounts for D% of the total mass of the electrolyte, and 0.5≤D / C≤20. In some embodiments, when the value of D / C is greater than 20, the storage pressure drop of the electrochemical device is larger, and when the value of D / C is less than 0.5, the cycle performance of the electrochemical device is poor. The possible reason is that when the value of D / C is greater than 20, the content of the trinitrile compound is high. Although the trinitrile compound significantly improves the electrical performance, it affects the storage pressure drop of the electrochemical device. Therefore, when a certain content of trinitrile compound is added, a part of dinitrile compound needs to be added to inhibit the influence of trinitrile compound on the storage pressure drop. At the same time, the addition of dinitrile compound also significantly improves the cycle performance. When the value of D / C is less than 0.5, the low content of trinitrile has no significant improvement on the cycle. Therefore, in some embodiments, 0.5≤D / C≤20 is controlled.

[0052] In some embodiments of the present application, the dinitrile compound accounts for C% of the total mass of the electrolyte, and 0.5≤C≤7 is satisfied.

[0053] In some embodiments of the present application, the multiple nitrile compound accounts for D% of the total mass of the electrolyte, and 0.1≤D≤4 is satisfied.

[0054] In some embodiments of the present application, the compound of Formula I and the polycarbonic compound satisfy: 0.02≤A / D≤130. In some embodiments of the present application, the compound of Formula I and the polycarbonic compound satisfy: 0.1≤A / D≤130. In some embodiments of the present application, the compound of Formula I and the polycarbonic compound satisfy: 1≤A / D≤130. In some embodiments of the present application, the compound of Formula I and the polycarbonic compound satisfy: 5≤A / D≤130. In some embodiments, when A / D is less than 0.02, the cycle performance and over-discharge storage performance of the electrochemical device are both poor, and when A / D is greater than 130, the cycle performance of the electrochemical device is poor. In some embodiments, when 0.1≤A / D≤130, the cycle performance of the electrochemical device is more excellent.

[0055] In some embodiments of the present application, the dinitrile compound includes at least one of butanedinitrile, pentanedinitrile, hexanedinitrile, heptanedinitrile, octanedinitrile, nonanedinitrile, decanedinitrile, ethylene glycol (bispropionitrile) ether (nitrile ether), or maleonitrile.

[0056] In some embodiments of the present application, the polycarbonic compound includes at least one of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, nonanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-benzene tricyano, or 1,2,3-tris(2-cyanooxy)propane.

[0057] In some embodiments of the present application, the compound containing S=O double bond includes at least one of 1,3-propane sulfone, 2,4-butane sulfone, 1,4-butane sulfone, methane dithioformate, ethylene sulfate, sulfolane, propylene sulfate, 4-methyl ethylene sulfite, or 5-methyl oxathiane 2,2-dioxide.

[0058] In some embodiments of the present application, the compound containing S=O double bond accounts for 0.01% to 3% of the total mass of the electrolyte.

[0059] In some embodiments of the present application, when the compound containing S=O double bond includes 1,3-propane sulfone, the 1,3-propane sulfone accounts for 0.1% to 1% of the total mass of the electrolyte.

[0060] In some embodiments of the present application, the oxygen heterocyclic compound includes at least one of 1,3-dioxane, dioxolane, 4-methyl-1,3-dioxane, tetrahydropyran, tetrahydrofuran, or 1,2-epoxybutane.

[0061] In some embodiments of the present application, the oxygen heterocyclic compound accounts for 0.01% to 3% of the total mass of the electrolyte.

[0062] In some embodiments of this application, the tensile strength of the positive current collector is B MPa, satisfying B>100.

[0063] In some embodiments of this application, the positive electrode current collector comprises aluminum. In some embodiments, the positive electrode current collector is aluminum foil, which has low density and high strength, which is beneficial for ensuring safety performance while reducing the number of electrochemical devices.

[0064] In some embodiments of this application, the thickness of the positive electrode current collector is from 5 μm to 20 μm. In some embodiments, when the thickness of the positive electrode current collector is less than 5 μm, it may cause the positive electrode current collector to be easily corroded or broken, resulting in a reduction in safety performance. When the thickness of the positive electrode current collector is greater than 20 μm, it may cause a reduction in the energy density of the electrochemical device.

[0065] In some embodiments of this application, the positive electrode current collector contains element M, which includes at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium, and vanadium. The percentage of element M in the total weight of the positive electrode current collector is no more than 2%. In some embodiments, when the percentage of element M in the total weight of the positive electrode current collector is greater than 2%, it will cause a decrease in the strength of the positive electrode current collector, resulting in a decrease in the drop performance of the electrochemical device.

[0066] In some embodiments of this application, the weight per unit area of ​​the positive current collector is 15 g / m². 2 -100g / m 2 In some embodiments, an insufficient weight per unit area of ​​the positive electrode current collector may result in insufficient strength of the positive electrode current collector, while an excessive weight per unit area of ​​the positive electrode current collector may result in an increase in the weight of the electrochemical device.

[0067] In some embodiments of this application, the elongation of the positive current collector is ≥1%. In some embodiments, an elongation of less than 1% of the positive current collector may cause it to break easily, reducing safety performance.

[0068] In some embodiments of this application, the positive current collector has a solder area, the area of ​​which is F cm². 2 , 1≤F≤50. In some embodiments, such as Figure 1 As shown, Figure 1 The diagram illustrates the connection between the positive electrode and the tab. The positive electrode includes a positive current collector 2 and a positive active material layer 1 located on the positive current collector 2. The blank area of ​​the positive current collector 2 has a solder area 4 (shown in the dashed box). The solder area 4 is formed after the tab 3 is welded to the positive current collector 2. It is a region defined by the solder joint. The positive current collector needs to be welded to the tab. When the area of ​​the solder area is too small, the connection strength of the solder joint may be insufficient. When the area of ​​the solder area is too large, the solder joint is more easily corroded by the electrolyte, resulting in a deterioration of the drop performance.

[0069] In some embodiments of the present application, the number of the welding mark regions is greater than or equal to 2. When the number of the welding mark regions is greater than or equal to 2, the area of the welding mark regions is the sum of the areas of all the welding mark regions.

[0070] In some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer includes a negative electrode material, the negative electrode material includes a silicon-based material, and at least a portion of the surface of the silicon-based material has a protective layer. The theoretical specific capacity of the silicon-based material reaches 4200 mAh / g, which is much higher than the theoretical specific capacity of carbon materials. By adding the silicon-based material to the negative electrode material, the specific capacity of the negative electrode material can be improved. However, the silicon-based material will have a large volume expansion during the charging and discharging process. Therefore, at least a portion of the surface of the silicon-based material has a protective layer, thereby reducing the volume expansion of the silicon-based material and reducing the volume change of the electrochemical device during the charging and discharging process.

[0071] In some embodiments of the present application, the protective layer includes a carbon material or Me x O y , Me includes at least one of Al, Si, Mn, V, Cr, Co, or Zr, x is 1 to 2, and y is 1 to 3. In some embodiments, the carbon material itself can accommodate lithium ions. When the protective layer includes the carbon material, on the one hand, the expansion of the silicon-based material can be inhibited, and on the other hand, the capacity of the negative electrode material can be improved. When the protective layer includes Me x O y , since Me x O y is a metal oxide, it has a high strength and can well inhibit the expansion of the silicon-based material.

[0072] In some embodiments, the positive electrode current collector can be an Al foil, and of course, other positive electrode current collectors commonly used in the art can also be used. In some embodiments, the thickness of the positive electrode current collector can be 1 μm to 50 μm. In some embodiments, the positive electrode active material layer can be coated only on a portion of the positive electrode current collector. In some embodiments, the thickness of the positive electrode active material layer can be 10 μm to 500 μm. It should be understood that these are only exemplary, and other suitable thicknesses can be used.

[0073] In some embodiments, the separator film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultrahigh molecular weight polyethylene. In particular, polyethylene and polypropylene have good effects on preventing short circuits and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the separator film is in the range of about 3 μm to 50 μm.

[0074] In some embodiments, the surface of the separator film can further include a porous layer disposed on at least one surface of the separator film, the porous layer including inorganic particles and a binder, the inorganic particles being selected from at least one of aluminum oxide (AI2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer of the surface of the separator film can improve the heat resistance, oxidation resistance, and electrolyte impregnation properties of the separator film, and enhance the adhesion between the separator film and the electrode sheet.

[0075] In some embodiments of the present application, the electrochemical device is a jelly-roll or a stack.

[0076] In some embodiments, the electrochemical device includes a lithium ion battery, but the present application is not limited thereto. In some embodiments, the electrochemical device can further include an electrolyte. The electrolyte can be one or more of a gel electrolyte, a solid-state electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent. The lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF + , LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, or lithium difluoroborate. For example, the lithium salt is selected as LiPF6because it can give a high ionic conductivity and improve the cycle characteristics.

[0077] The non-aqueous solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0078] The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof.

[0079] Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and a combination thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or a combination thereof.

[0080] Examples of the carboxylic acid ester compound are ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decanolide, valerolactone, methylvaleronolactone, caprolactone, or a combination thereof.

[0081] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0082] Examples of the other organic solvent are dimethyl sulfoxide, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid ester, or a combination thereof.

[0083] Embodiments of the present application also provide an electronic device comprising the above-mentioned electrochemical device. The electronic device of embodiments of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor, etc.

[0084] For the purpose of clarity, technical solutions and advantages of the present application will be further described below in conjunction with specific embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the technical solutions provided by the present application and the embodiments given, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0085] Preparation of the positive electrode sheet: the positive electrode material lithium cobaltate, polyvinylidene fluoride (PVDF), and Super-P were dissolved in N-methyl pyrrolidone (NMP) at a mass ratio of 96:2:2 to uniformly mix and prepare a positive electrode slurry. The positive electrode slurry was uniformly coated on a positive electrode current collector aluminum foil with a thickness of 12 μm, baked at 120°C for 1 h, and then subjected to compaction, slitting, and welding of the tabs to obtain a positive electrode sheet;

[0086] Negative electrode sheet preparation: the negative electrode material, sodium carboxymethyl cellulose (CMC), and butadiene-styrene rubber were dissolved in water at a mass ratio of 85:2:13, and were fully mixed and stirred to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a negative electrode current collector copper foil with a thickness of 12 μm, and was baked at 120°C for 1 h to obtain a negative electrode active material layer. Then, the negative electrode sheet was obtained by compaction, slitting, and welding of the tab.

[0087] Lithium ion battery preparation: a 12 μm polypropylene film was used as a separator. The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, and then were wound into a bare cell. The bare cell was placed in an aluminum foil packaging bag, and was baked at 80°C to remove water to obtain a dry cell. The dry cell was injected with a corresponding electrolyte, and was subjected to vacuum packaging, standing, formation, shaping, and other processes to complete the preparation of the lithium ion battery.

[0088] Electrolyte preparation: ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed at a mass ratio of 3:1:6, and then different contents of other additives and lithium salts were added to the above electrolyte to obtain the electrolyte used in each example.

[0089] The test methods for the high-temperature cycle performance and safety performance of the lithium ion batteries prepared in each example and the comparative example were as follows:

[0090] Cycle performance test: the battery was charged at a constant current of 1C to 4.45V at 45°C, was allowed to stand for 30 min, was discharged at 1C to 3.0V, was cycled for 500 times, and the discharge capacity during the cycle was recorded.

[0091] Cycle capacity retention rate (%) = 500th discharge capacity / initial discharge capacity x 100%.

[0092] Over-discharge storage test: the battery was placed in a 25°C constant temperature box, was discharged at a constant current of 0.5C to 2.0V, and the thickness of the battery was tested. Then, the battery was stored in a 60°C high-temperature oven for 15 days, and the thickness of the battery after storage was tested.

[0093] Over-discharge storage thickness growth rate (%) = (thickness of the battery after storage-thickness of the battery before storage) / thickness of the battery before storage x 100%.

[0094] 60°C storage pressure drop test: the battery was placed in a 25°C constant temperature box, was charged at a constant current of 0.5C to 4.45V, and was charged at a constant voltage until the current was 0.05C. The battery was stored in a 60°C high-temperature oven for 30 days, and the voltage value of the lithium ion battery after storage was recorded.

[0095] 60°C storage pressure drop = 4.45V-voltage value of the lithium ion battery after storage.

[0096] Drop performance test: after high temperature cycling at 45℃, the battery was placed in a constant temperature oven at 25℃, charged to 4.45V at a constant current of 0.5C, then charged at a constant voltage until the current was 0.05C, and the battery was placed in an environment at 25℃ for drop test. The battery was dropped from a height of 1 meter to the concrete floor, and 1 battery was repeated for 3 times. Ensure that each random direction is impacted during the drop. If there is leakage, fire or explosion, it is determined to be invalid. 20 batteries were tested in each group.

[0097] Drop pass rate (%) = number of failed batteries / 20 x 100%.

[0098] Positive current collector test as follows:

[0099] Aluminum foil thickness test: measure 5 points and take the average value.

[0100] Unit area mass: cut the aluminum foil into 100mm x 100mm pieces and weigh them to calculate the unit area mass. Take 5 samples and calculate the average value. Unit area mass = weight / area.

[0101] Tensile strength test: use a tensile testing machine to test. The sample length is 200±0.5mm, the width is 15±0.25mm, the tensile speed is set to 50mm / min, the distance between the testing machine clamps is 125±0.1mm, the sample is stretched to break and the test is stopped, and the tensile strength value is read. Test 5 parallel samples and take the average value as the test result. The sample length direction is parallel to the clamp axis during testing, and the sample is kept straight. The experimental temperature is 20±5℃.

[0102] Elongation test: use a tensile testing machine to test. The sample length is 200±0.5mm, the width is 15±0.25mm, the tensile speed is set to 50mm / min, the distance between the testing machine clamps is 125±0.1mm, the sample is stretched to break and the test is stopped, and the tensile length is recorded. Test 5 parallel samples and take the average value as the test result. The sample length direction is parallel to the clamp axis during testing, and the sample is kept straight. The experimental temperature is 20±5℃. Elongation = tensile length / sample length.

[0103] The electrical performance test data is shown below:

[0104] Table 1 shows the electrolyte used in Comparative Examples 1 to 3, and Examples 1 to 13, and the performance test results. The positive electrode material used in Comparative Examples 1 to 3, and Examples 1 to 13 shown in Table 1 is lithium cobalt oxide, the negative electrode material is a mixture of silicon-based material and graphite, and the silicon-based material is silicon oxide, and the mass ratio of silicon-based material to graphite is 1:9; the aluminum foil thickness is 10μm, the elongation is ≥1%, and the unit area weight is 67g / m 2, the percentage of Cu element in the total weight of the positive electrode current collector is 0.1%, the area F of the welding mark is 1.2 cm 2 , the content of the compound represented by formula I is A%, the tensile strength of the positive electrode current collector is 80 MPa, the fluorine-containing lithium salt in the electrolyte is lithium hexafluorophosphate, and the content is 12.5%.

[0105] Table 1

[0106]

[0107] As can be seen from the comparative example 1 and examples 1 to 13 in Table 1, when the compound represented by formula I is added to the electrolyte, the cycle capacity retention rate of the lithium ion battery is increased, the thickness growth rate during over-discharge storage is reduced, and the drop pass rate is improved, that is, the cycle performance and storage performance of the lithium ion battery are obviously improved. This is because the compound represented by formula I in examples 1 to 13 contains F element and carbonate group, which can continuously form LiF protective layer on the negative electrode during the cycle process, improve the stability of the negative electrode interface, and thus significantly improve the cycle performance of the lithium ion battery. At the same time, when the lithium ion battery is in over-discharge state, the negative electrode potential is improved, and the instability is enhanced. Since the compound represented by formula I can effectively repair the negative electrode, the gas production during over-discharge storage is significantly reduced, and the safety performance of the lithium ion battery is improved.

[0108] As can be seen from the comparative example 2, when the content of the compound represented by formula I is less than 0.3 and the value of B / A is large, the thickness growth rate of the lithium ion battery during over-discharge storage is still large, and the storage performance is poor. This may be because the content of the compound represented by formula I is too small to improve the effect obviously. As can be seen from examples 1 to 6 and comparative example 3, with the increase of the content of the compound represented by formula I, the cycle performance and storage performance of the lithium ion battery are significantly improved, but the drop pass rate may be reduced, starting from the initial pass rate of 100%. As shown in comparative example 3, when the content of the compound represented by formula I reaches 41%, the drop pass rate is only 70%. This is because at high temperature, the compound represented by formula I in the lithium ion battery generates a large amount of HF by defluorination, which continuously corrodes the surface layer of the aluminum foil, causing the strength of the aluminum foil to decrease, and finally leading to the drop pass rate to decrease to 70%, which seriously affects the safety of the lithium ion battery during use. Therefore, in some examples, A is controlled to be 0.3 to 40, and 2≤B / A≤750.

[0109] As can be seen from examples 7 to 13, when the compound satisfying the structural formula of formula I is used alone or different types of compounds satisfying the structural formula of formula I are mixed, the cycle performance of the lithium ion battery can be ensured while the safety performance of the lithium ion battery is improved.

[0110] Table 2 shows the electrolyte used in Examples 14-25 and the performance test results, the positive electrode material used in each example in Table 2 is lithium cobaltate, the negative electrode material is a mixture of silicon-based material and graphite, the silicon-based material is coated with a carbon layer on the surface, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to graphite is 1:9, the thickness of the aluminum foil is 10 pm, the elongation is >1%, the weight per unit area is 67 g / m 2 , the percentage of Cu element in the total weight of the positive electrode current collector is 0.1%, the area F of the welding area is 1.2 cm 2 , the content of the compound represented by Formula I is A%, the tensile strength of the positive electrode current collector is B MPa, the mass content of the dinitrile compound in the electrolyte is 1%, the mass content of the polynitrile compound is 1,3,6-hexanetricarbonitrile is 2%, the fluorine-containing lithium salt is lithium hexafluorophosphate, and the content is 12.5%.

[0111] Table 2

[0112]

[0113]

[0114] As can be seen from the examples 14-20 shown in Table 2, as the tensile strength of the aluminum foil increases, when the value of B / A is in the range shown in Examples 16-25, the cycle performance, storage performance and drop performance of the lithium ion battery are all better.

[0115] In order to ensure the electrical performance and safety performance of the lithium ion battery at the same time, it is necessary to control the value of B / A within a certain range, so in some embodiments of the present application, 2≤B / A≤750 is controlled.

[0116] Table 3 shows the electrolyte used in Examples 26-38 and the performance test results, the positive electrode material used in Table 3 is lithium cobaltate, the negative electrode material is a mixture of silicon-based material and graphite, and the silicon-based material is coated with a carbon layer on the surface, and the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to graphite is 1:9, the content of the compound represented by Formula I in the electrolyte is A%, the tensile strength of the positive electrode current collector is 160 MPa, the thickness of the aluminum foil is 10 pm, the elongation is >1%, the weight per unit area is 67 g / m 2 , the percentage of Cu element in the total weight of the positive electrode current collector is <1%, the area F of the welding area is 1.2 cm 2 , the fluorine-containing lithium salt is lithium hexafluorophosphate, and the content is 12.5%.

[0117] Table 3

[0118]

[0119]

[0120] As can be seen from Examples 35 to 38 in Table 3, when the electrolyte only includes a trinitrile compound, the 60°C storage pressure drop of the lithium ion battery is relatively large. As can be seen from Examples 26 to 34 in Table 3, when the electrolyte includes both a dinitrile compound and a trinitrile compound, the 60°C storage pressure drop of the lithium ion battery can be reduced.

[0121] As can be seen from Comparative Examples 26 to 34, when the value of D / C is greater than 20, the 60°C storage pressure drop of the lithium ion battery is relatively large, and when the value of D / C is less than 0.5, the cycle performance of the lithium ion battery is relatively poor, which can be because the trinitrile compound, although significantly improving the electrical performance, is prone to causing an increase in the storage pressure drop, so when the value of D / C is greater than 20, the 60°C storage pressure drop is relatively large; in order to suppress the influence of the trinitrile compound on the storage pressure drop, the dinitrile compound is added, and when the value of D / C is less than 0.5, the trinitrile compound in too low a content does not significantly improve the cycle performance, causing the cycle performance to decrease. Therefore, in some examples, 0.5≤D / C≤20 is defined, so as to reduce the storage pressure drop while ensuring the cycle performance.

[0122] Table 4 shows the electrolytes used in Examples 39 to 50 and the performance test results. In Table 4, the positive electrode material is lithium cobaltate, the negative electrode material is a mixture of a silicon-based material and graphite, the silicon-based material has a carbon layer on the surface, the silicon-based material is silicon oxide, the mass ratio of the silicon-based material to graphite is 1:9, the thickness of the aluminum foil is 10 μm, the elongation is ≥1%, the weight per unit area is 67 g / m 2 , the content of element M is <1%, the area F of the welding mark area is 1.2 cm 2 , the content of the compound represented by Formula I is A%, the tensile strength of the positive electrode current collector is 100 MPa, the compound represented by Formula I contained in the electrolyte in the examples shown in Table 4 is fluoroethylene carbonate, and the content is 5%, the dinitrile compound contained in the electrolyte is butanedinitrile and hexanedinitrile, and the mass contents are 1% and 0.5%, respectively, the trinitrile compound contained in the electrolyte is 1,3,6-hexanetristrile, and the mass content is 2%, the fluorine-containing lithium salt is lithium hexafluorophosphate, and the content is 12.5%.

[0123] Table 4

[0124]

[0125]

[0126] As can be seen from Examples 39 to 44, when the electrolyte contains a compound containing S=O double bond or an oxygen-containing heterocyclic compound, the cycle capacity retention of the lithium ion battery is higher, the thickness growth rate of over-discharge storage is lower, and the pressure drop at 60°C storage is smaller, i.e. the electrical performance of the lithium ion battery can be improved when the electrolyte contains a compound containing S=O double bond or an oxygen-containing heterocyclic compound, which may be because the compound containing S=O double bond or the oxygen-containing heterocyclic compound can form a stable SEI film on the positive and negative electrodes, thereby improving the protection of the positive and negative electrodes, and ultimately improving the electrical performance of the lithium ion battery. As can be seen from Examples 45 to 50, when the electrolyte contains both a compound containing S=O double bond and an oxygen-containing heterocyclic compound, the cycle capacity retention of the lithium ion battery is higher, and the thickness growth rate of over-discharge storage is lower, and the pressure drop at 60°C storage is smaller.

[0127] Table 5 shows the electrolytes used in Examples 51 to 58 and the performance test results. In Table 5, the positive electrode material is lithium cobaltate, the negative electrode is a mixture of silicon-based material and graphite, the silicon-based material is silicon oxide, the mass ratio of silicon-based material to graphite is 2:8, the thickness of aluminum foil is 10 μm, the elongation is ≥1%, the areal weight is 67 g / m 2 , the tensile strength of the positive electrode current collector is 160 MPa, the compound represented by Formula I contained in the electrolyte in each example in Table 5 is fluoroethylene carbonate, the mass content is 5%, the dinitrile compound contained in the electrolyte is butanedinitrile and hexanedinitrile, the mass contents are 1% and 0.5% respectively, the tri-nitrile contained in the electrolyte is 1,3,6-hexanetri-nitrile, the mass content is 2%, the fluorine-containing lithium salt is lithium hexafluorophosphate, the content is 12.5%, and M is Cu element.

[0128] Table 5

[0129]

[0130]

[0131] As can be seen from Comparative Examples 51 to 53, when the mass content of M element in the aluminum foil is >2%, the drop passing rate of the lithium ion battery decreases, which may be because when the content of M element is >2%, the strength of the aluminum foil is reduced, and finally the drop performance is deteriorated.

[0132] As can be seen from Comparative Examples 54 to 58, when the area of the welding mark gradually increases, the drop passing rate of the lithium ion battery decreases significantly, which may be because the welding point is more easily corroded by the electrolyte, and the drop performance is deteriorated.

[0133] As can be seen from Comparative Example 51 and Example 57, when the negative electrode material uses a silicon material without a coating layer, the cycle capacity retention of the lithium ion battery is significantly reduced, and the over-discharge storage thickness growth rate is significantly increased, thus it can be seen that using a silicon material with a coating layer can significantly improve the electrical performance of a lithium ion battery using a silicon material negative electrode.

[0134] The above description is merely the preferred embodiments of the present application and the technical principles used. Those skilled in the art should understand that the disclosed range in the present application is not limited to the technical solutions formed by the specific combinations of the above technical features, and should also cover other technical solutions formed by any combinations of the above technical features or equivalent features. For example, the above features and the technical features with similar functions disclosed in the present application are replaced with each other to form technical solutions.

Claims

1. An electrochemical device, characterized by, The electrochemical device comprises: a positive electrode, a negative electrode, a separator, and an electrolyte; the electrolyte comprises a compound represented by Formula I: wherein the compound represented by Formula I accounts for A% of the total mass of the electrolyte, A is 0.3 to 40; R1 and R2 are each independently selected from hydrogen, halogen, an alkyl group having 1 to 5 carbon atoms, an alkyl group having 1 to 5 carbon atoms substituted with halogen, an alkenyl group having 1 to 5 carbon atoms, an alkenyl group having 1 to 5 carbon atoms substituted with halogen, an alkynyl group having 1 to 5 carbon atoms, or an alkynyl group having 1 to 5 carbon atoms substituted with halogen; and at least one of R1 and R2 contains halogen; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, the positive electrode current collector has a tensile strength of B MPa, and 20≤B / A≤550; wherein the electrolyte further comprises a dinitrile compound and a multi-nitrile compound having a number of cyano groups of 3 or more; the dinitrile compound accounts for C% of the total mass of the electrolyte, the multi-nitrile compound accounts for D% of the total mass of the electrolyte, and 3≤D / C≤20; and the electrochemical device satisfies at least one of the following conditions (a) and (b): (a) the electrolyte further comprises a compound containing a S=O double bond; (b) the electrolyte further comprises an oxygen heterocycle compound.

2. The electrochemical device of claim 1, wherein The compound represented by Formula I comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, methyl fluoroethylene carbonate, or 4-fluoro-5-methyl ethylene carbonate.

3. The electrochemical device according to claim 1, The compound represented by Formula I and the multi-nitrile compound satisfy 0.02≤A / D≤130.

4. The electrochemical device according to claim 1, The dinitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, sebaconitrile, ethyleneglycol (dipropionitrile) ether (nitrile ether), or fumaronitrile; and / or, The multi-nitrile compound comprises at least one of 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile, 1,3,5-pentanetricarbonitrile, nonanetricarbonitrile, 1,3,5-benzenetricarbonitrile, 2,4,6-trifluorobenzene-1,3,5-tricarbonitrile, 1,3,5-cyclohexanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-benzene tricyano, or 1,2,3-tris(2-cyanato)propane.

5. The electrochemical device according to claim 1, The compound containing a S=O double bond comprises at least one of 1,3-propane sulfone, 2,4-butane sulfone, 1,4-butane sulfone, methylene methane disulfonate, ethylene sulfate, sulfolane, propylene sulfate, 4-methyl ethylene sulfite, or 5-methyl oxathiane 2,2-dioxide; and / or, The oxygen heterocycle compound comprises at least one of 1,3-dioxane, dioxolane, 4-methyl-1,3-dioxane, tetrahydropyran, tetrahydrofuran, or 1,2-epoxybutane.

6. The electrochemical device of claim 1, wherein The positive electrode current collector satisfies at least one of the following conditions (e) to (j): (e) the positive electrode current collector comprises aluminum; (f) the positive electrode current collector has a thickness of 5 μm to 20 μm; (g) the positive electrode current collector contains an M element, the M element including at least one of silicon, copper, manganese, iron, zinc, magnesium, titanium, and vanadium, the percentage of the M element in the total weight of the positive electrode current collector being not more than 2%; (h) the positive electrode current collector has a unit area weight of 15 g / m 2 to 100 g / m 2 ; (i) the positive electrode current collector has an elongation of ≥ 1 %; (j) the positive current collector has a weld print area thereon, the weld print area having an area of F cm 2 , 1 < F < 50.

7. The electrochemical device of claim 1, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including a negative electrode material, the negative electrode material including a silicon-based material, at least a part of the surface of a particle of the silicon-based material having a protective layer thereon.

8. The electrochemical device of claim 7, wherein, The protective layer includes: a carbon material or Me x O y wherein Me includes at least one of Al, Si, Mn, V, Cr, Co, or Zr, x is 1 to 2, and y is 1 to 3.

9. An electronic device, comprising: An electrochemical device including the electrochemical device as described in any one of claims 1 to 8.

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