Electrochemical devices and electronic devices

Abstract

The present application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte includes a first additive and a second additive: the first additive includes at least one of the compound shown in Formula I and the compound shown in Formula II: the second additive includes a polynitrile compound shown in Formula III: wherein M1 and M2 are independently selected from halogen, Formula IV, and Formula V; wherein α and γ are independently selected from 0 or 1, and β is independently selected from 0, 1, and 2. The electrolyte is suitable for use in an electrochemical device, and can effectively improve the cycle stability and high-temperature storage performance of the electrochemical device, and enhance safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device. Background Art

[0002] With the rapid development of new energy technologies, the development trend of electrification, intelligence and sharing will promote a comprehensive change in energy. Rechargeable lithium-ion batteries are widely considered to be the most promising power source for daily portable devices due to their high specific capacity, low cost and non-toxicity. With the development of electronic devices, the development of high energy density batteries is becoming increasingly urgent. At present, the main way to improve energy density is to increase the charging cut-off voltage of the positive electrode, but increasing the charging cut-off voltage leads to rapid deterioration of storage and cycle. Therefore, improving the high temperature storage and cycle stability of lithium-ion batteries has become an urgent problem to be solved. Summary of the invention

[0003] In view of the problems existing in the background technology, the purpose of the present application is to provide an electrochemical device and an electronic device.

[0004] In order to achieve the above object, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte includes a first additive and a second additive:

[0005] The first additive includes at least one of the compound represented by Formula I and the compound represented by Formula II:

[0006]

[0007] Among them, R1-R 11 independently selected from hydrogen, halogen, cyano, nitro, sulfonic acid, aldehyde, hydroxyl, amino, carboxyl, silicon, substituted or unsubstituted C 1-6 Alkoxy, substituted or unsubstituted C 1-6 Alkyl, substituted or unsubstituted C 2-6 Alkenyl, substituted or unsubstituted C 2-6 Alkynyl or substituted or unsubstituted C 6-12 at least one of aryl groups, wherein, when substituted, the substituent is a halogen;

[0008] The second additive comprises a polynitrile compound represented by formula III:

[0009]

[0010] Wherein, M1 and M2 are independently selected from halogen, Formula IV, and Formula V;

[0011]

[0012] wherein α and γ are independently selected from 0 or 1, and β is independently selected from 0, 1, and 2;

[0013] R 12 , R 13 are each independently selected from hydrogen, halogen, substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The ring group, substituted or unsubstituted C 2-10 A functional group containing a heteroatom, wherein the substituents are each independently selected from halogen; R 14 , R 15 Each independently selected substituted or unsubstituted C 1-10 Alkylene, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The ring group, substituted or unsubstituted C 2-10 The functional group containing heteroatoms, the substituents are each independently selected from halogens; wherein the cyclic group includes at least one of an alicyclic group and a heterocyclic group.

[0014] In some embodiments, the first additive includes at least one of the following compounds:

[0015]

[0016]

[0017] In some embodiments, the second additive includes at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, 1,2,3-tris(2-cyano)propane, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene, 1,2-bis(cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile or 1,2,6-hexanetricarbonitrile.

[0018] In some embodiments, based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.01-5%, and / or the mass percentage B% of the second additive is 0.5-10%.

[0019] In some embodiments, the mass percentage of the first additive and the mass percentage of the second additive satisfy the following relationship: 0.005≤A / B≤10.

[0020] In some embodiments, the electrolyte further includes a third additive, the third additive including at least one of fluoroethylene carbonate, vinyl ethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-dioxane, 1,4-dioxane, lithium dioxalatoborate, and lithium tetrafluoroborate; based on the total weight of the electrolyte, the mass percentage C of the third additive is 0.5-10%.

[0021] In some embodiments, the positive electrode plate comprises a positive electrode active material; the positive electrode active material comprises a doping element: at least one of aluminum, cerium, titanium, zirconium, niobium, and manganese.

[0022] In some embodiments, based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0<X≤3.

[0023] In some embodiments, the doping amount X% of the doping element and the mass percentage A% of the first additive satisfy the following relationship: 0<X / A≤100.

[0024] In some embodiments, the electrochemical device satisfies one of the following conditions:

[0025] (1) Based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.1%-3%,

[0026] (2) Based on the total weight of the electrolyte, the mass percentage B% of the second additive is 1%-5%,

[0027] (3) Based on the total weight of the electrolyte, the mass percentage content A% of the first additive and the mass percentage content B% of the second additive satisfy the following relationship: 0.05≤A / B≤5,

[0028] (4) Based on the total weight of the electrolyte, the mass percentage C% of the third additive is 1%-5%,

[0029] (5) Based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0.5≤X≤2,

[0030] (6) The doping amount X% of the doping element and the mass percentage A% of the first additive satisfy the following relationship: 0.5≤X / A≤30.

[0031] In some embodiments, the present application also provides an electronic device, which includes the above-mentioned electrochemical device.

[0032] This application has at least the following beneficial effects:

[0033] The electrolyte in the present application can effectively improve the cycle stability and high-temperature storage performance of the electrochemical device, and enhance the safety performance of the electrochemical device. DETAILED DESCRIPTION

[0034] It will be understood that the disclosed embodiments are merely examples of the present application, which can be implemented in various forms, and therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as the basis for the claims and as a representative basis for teaching one of ordinary skill in the art to implement the present application in various ways.

[0035] In the description of this application, unless otherwise clearly specified and limited, the terms "Formula I", "Formula II", "Formula III", "Formula IV", "Formula V", "first additive", "second additive", "third additive", etc. are used for illustrative purposes only and are not to be understood as indicating or implying relative importance and mutual relationship.

[0036] In the description of the present application, unless otherwise specified, the functional groups of all compounds may be substituted or unsubstituted.

[0037] (Electrolyte)

[0038] [First additive]

[0039] In some embodiments, the electrolyte comprises a first additive and a second additive:

[0040] The first additive includes at least one of the compound represented by Formula I and the compound represented by Formula II:

[0041]

[0042] Among them, R1-R 11 independently selected from hydrogen, halogen, cyano, nitro, sulfonic acid, aldehyde, hydroxyl, amino, carboxyl, silicon, substituted or unsubstituted C 1-6 Alkoxy, substituted or unsubstituted C 1-6 Alkyl, substituted or unsubstituted C 2-6 Alkenyl, substituted or unsubstituted C 2-6 Alkynyl or substituted or unsubstituted C 6-12 at least one of aryl groups, wherein, when substituted, the substituent is a halogen;

[0043] The second additive comprises a polynitrile compound represented by formula III:

[0044]

[0045] Wherein, M1 and M2 are independently selected from halogen, Formula IV, and Formula V;

[0046]

[0047] wherein α and γ are independently selected from 0 or 1, and β is independently selected from 0, 1, and 2;

[0048] R 12 , R 13 are each independently selected from hydrogen, halogen, substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The ring group, substituted or unsubstituted C 2-10 A functional group containing a heteroatom, wherein the substituents are each independently selected from halogen; R 14 , R 15 Each independently selected substituted or unsubstituted C 1-10 Alkylene, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The ring group, substituted or unsubstituted C 2-10 The functional group containing heteroatoms, the substituents are each independently selected from halogens; wherein the cyclic group includes at least one of an alicyclic group and a heterocyclic group.

[0049] The polynitrile compound shown in formula III can effectively improve the stability of the positive electrode interface, but it has a certain destructive effect on the stability of the SEI film of the negative electrode. The anhydride compound shown in formula I or formula II can itself be used as a negative electrode interface protective substance. It will form a dense SEI film at the negative electrode interface, which can prevent the polynitrile compound additive from damaging the negative electrode interface and reduce the negative electrode interface side reactions. The combination of the two can not only stabilize the positive electrode interface, but also protect the negative electrode interface, thereby achieving the effect of improving the long-cycle stability of lithium-ion batteries.

[0050] Therefore, the first additive can form a stable passivation film at the negative electrode interface, inhibiting the damage of the polynitrile compound additive to the negative electrode interface. The two are used together to inhibit the flatulence of lithium-ion batteries under high-temperature storage, and ensure the long-cycle stability of lithium-ion batteries, thereby improving the safety performance of lithium-ion batteries.

[0051] In some embodiments, the first additive includes at least one of the following compounds:

[0052]

[0053] In some embodiments, the second additive includes at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, 1,2,3-tris(2-cyano)propane, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene, 1,2-bis(cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile or 1,2,6-hexanetricarbonitrile.

[0054] In some embodiments, based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.01-5%. In some embodiments, based on the total weight of the electrolyte, the content of the first additive in the electrolyte may be 0.01%, 0.1%, 0.2%, 0.5%, 1.0%, 3.0%, 5.0% or a range consisting of any two values. In some embodiments, based on the total weight of the electrolyte, the mass percentage B of the second additive is 0.5-10%. In some embodiments, based on the total weight of the electrolyte, the content of the second additive in the electrolyte may be 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 7.0%, 10% or a range consisting of any two values. In some embodiments, the content of the first additive and the second additive satisfies the following relationship: 0.005≤A / B≤10. The contents of the first additive and the second additive satisfy the following relationship and can be 0.005, 0.1, 0.2, 0.25, 0.5, 1.0, 1.5, 2.5, 3.0, and 10. Combining the additives within the above range can significantly improve the capacity retention rate, high temperature storage expansion rate, and safety performance of the lithium-ion battery.

[0055] In some embodiments, the electrolyte further includes a third additive, and the third additive includes at least one of fluoroethylene carbonate, vinyl ethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-dioxane, 1,4-dioxane, lithium dioxalatoborate, and lithium tetrafluoroborate.

[0056] On the basis of adding the first additive and the second additive to the electrolyte, the third additive is introduced, the cycle retention rate of the lithium-ion battery is significantly increased, and the expansion during high-temperature storage is significantly improved. The reason may be that the third additive, as a negative electrode protection additive, will generate a dense and flexible SEI film at the negative electrode, which can be quickly repaired during the cycle, effectively preventing the damage of the polynitrile compound additive to the negative electrode, reducing the negative electrode interface side reactions, and achieving the effect of improving the long-cycle stability of the lithium-ion battery and improving the high-temperature storage performance of the lithium-ion battery, thereby improving the safety performance of the lithium-ion battery.

[0057] In some embodiments, based on the total weight of the electrolyte, the mass percentage C of the third additive is 0.5-10%. In some embodiments, based on the total weight of the electrolyte, the content of the third additive in the electrolyte may be 0.5%, 0.8%, 1.0%, 1.5%, 2.0%, 3.0%, 5.0%, 8.0%, 10% or a range consisting of any two values. When the mass percentage of the third additive is within the above range, the effect of improving the long cycle stability and safety performance of the lithium ion battery and improving the high temperature storage performance of the lithium ion battery can be achieved.

[0058] In some embodiments, at least one of the following conditions is met:

[0059] (1) Based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.1%-3%,

[0060] (2) Based on the total weight of the electrolyte, the mass percentage B% of the second additive is 1%-5%,

[0061] (3) Based on the total weight of the electrolyte, the mass percentage content A% of the first additive and the mass percentage content B% of the second additive satisfy the following relationship: 0.05≤A / B≤5,

[0062] (4) Based on the total weight of the electrolyte, the mass percentage C% of the third additive is 1%-5%.

[0063] In some embodiments, the electrolyte further includes an organic solvent and a lithium salt, wherein the types of the organic solvent and the lithium salt are not subject to specific restrictions and can be selected according to needs.

[0064] In some embodiments, the lithium salt includes but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), and lithium dioxalatoborate (LiBOB).

[0065] In some embodiments, the organic solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, and a sulfone compound. The organic solvent includes but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), cyclopentane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), diethyl sulfone (ESE), 1,3-dioxolane (DOL), and dimethyl ether (DME).

[0066] (Electrochemical Device)

[0067] The electrochemical device of the present application is, for example, a primary battery or a secondary battery. The secondary battery is, for example, a lithium secondary battery, which includes but is not limited to a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0068] In some embodiments, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described above in the present application.

[0069] [Positive electrode]

[0070] The positive electrode sheet is a positive electrode sheet that can be used in an electrochemical device and is well known in the art. In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer. The positive active material layer is disposed on the surface of the positive current collector. The positive active material layer includes a positive active material, and the positive active material includes but is not limited to lithium cobalt oxide, lithium nickel cobalt manganese ternary material, lithium nickel cobalt aluminum ternary material, lithium iron phosphate, lithium-rich manganese-based material, and at least one of their respective modified compounds. The positive active material may also include a conductive agent and a binder.

[0071] In some embodiments, the positive electrode active material contains doping elements: at least one of aluminum, cerium, titanium, zirconium, niobium, and manganese. When a high-valent metal element is used to modify the positive electrode material, the cycle performance and high-temperature storage of the lithium-ion battery are significantly improved. The reason may be that the high-valent metal element ions with a larger ion radius increase the intercrystalline spacing of the positive electrode material particles after doping and coating, which is more conducive to the transmission of lithium ions. After the high-valent metal ions are doped into the lattice of the positive electrode main material, the particle size of the positive electrode main material is well maintained during the cycle, thereby reducing the side reaction between the positive electrode material and the electrolyte, improving the cycle stability and high-temperature storage performance of the lithium-ion battery, and thus improving its safety performance.

[0072] In some embodiments, based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0<X≤3. The range of X can be any value among 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0. Introducing an appropriate amount of doping elements into the lattice of the positive electrode active material can reduce the breakage of the positive electrode particles during the cycle, reduce the side reaction between the positive electrode material and the electrolyte, and improve the cycle stability of the electrochemical device. In some embodiments, the doping amount X% of the doping element and the mass percentage A% of the first additive satisfy the following relationship: 0<X / A≤100. X / A can be any value among 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, and 3.2.

[0073] In some embodiments, at least one of the following conditions is met:

[0074] (5) Based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0.5≤X≤2,

[0075] (6) The doping amount X% of the doping element and the mass percentage A% of the first additive satisfy the following relationship: 0.5≤X / A≤30.

[0076] In some embodiments, the conductive agent includes but is not limited to at least one of conductive graphite, superconducting carbon, acetylene black, conductive carbon black (Super-P), Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0077] In some embodiments, the binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinyl alcohol (PVA).

[0078] [Negative electrode]

[0079] The negative electrode sheet is a negative electrode sheet that can be used in an electrochemical device as known in the art. In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material includes but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured Li4Ti5O 12 , Li-Al alloy.

[0080] In some embodiments, the structure of the negative electrode sheet is a structure of a negative electrode sheet that is well known in the art and can be used in an electrochemical device.

[0081] In some embodiments, the negative electrode membrane further comprises a negative electrode binder. In some embodiments, the negative electrode binder comprises at least one of difluoroethylene-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon.

[0082] In some embodiments, the negative electrode membrane further comprises a thickener. The specific type of the thickener is not subject to specific restrictions and can be selected according to needs. For example, the thickener includes but is not limited to sodium carboxymethyl cellulose (CMC).

[0083] In some embodiments, the method for preparing the negative electrode sheet is a method for preparing the negative electrode sheet that is well known in the art and can be used for an electrochemical device. In some embodiments, the negative electrode active material, the negative electrode binder, and the optional conductive material and thickener as needed are dissolved or dispersed in a solvent to form a negative electrode slurry, and the negative electrode slurry is coated on the negative electrode collector, and then dried, rolled, and cut to obtain a negative electrode sheet. It should be noted that in the obtained negative electrode sheet, the portion containing the negative electrode active material on the surface of the negative electrode collector is a negative electrode film.

[0084] [Isolation film]

[0085] The separator is disposed between the positive electrode sheet and the negative electrode sheet to prevent a short circuit between the positive electrode sheet and the negative electrode sheet.

[0086] In some embodiments, the isolation film may include a substrate layer and an optional surface treatment layer. The substrate layer may include a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. As an example, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0087] The surface of the substrate layer may or may not be provided with a surface treatment layer. In some embodiments, at least one surface of the substrate layer is provided with a surface treatment layer, which may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material.

[0088] In some embodiments, the inorganic layer includes inorganic particles and a binder, and the inorganic particles include but are not limited to at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes but is not limited to at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0089] In some embodiments, the polymer material in the polymer layer includes at least one of polyacrylonitrile, polyacrylic acid salt, polyamide, polyvinylidene fluoride, and polyvinyl pyrrolidone.

[0090] [case]

[0091] In some embodiments, the positive electrode sheet, the isolation membrane and the negative electrode sheet are stacked in order so that the isolation membrane is between the positive electrode sheet and the negative electrode sheet, and then a wound battery cell (or electrode assembly) is obtained by winding. The battery cell is placed in a shell and injected with electrolyte. After vacuum packaging, standing, formation, shaping, capacity division and other processes, an electrochemical device can be obtained.

[0092] In other embodiments, the battery cells are stacked.

[0093] In other embodiments, the electrochemical device is used in conjunction with a circuit protection board.

[0094] The housing is a hard shell housing or a flexible shell. The material of the hard shell is, for example, metal. The flexible shell is, for example, a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0095] (Electronic Devices)

[0096] The electronic device of the present application is any electronic device, such as but not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor. It is noted that the electrochemical device of the present application is applicable to energy storage power stations, marine vehicles, and air vehicles in addition to the electronic devices listed above. Air vehicles include air vehicles within the atmosphere and air vehicles outside the atmosphere.

[0097] In some embodiments, the electronic device comprises the electrochemical device described above in the present application.

[0098] [test]

[0099] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0100] The lithium ion batteries of Examples 1-1 to 1-19, Examples 2-1 to 2-11, Examples 3-1 to 3-11 and Comparative Example 1-3 were prepared according to the following method:

[0101] (1) Preparation of positive electrode

[0102] The positive electrode active material lithium cobalt oxide (molecular formula LiCoO2), binder polyvinylidene fluoride (PVDF), and conductive agent Super-P are dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2 and mixed evenly to form a positive electrode slurry. The positive electrode slurry is evenly coated on a positive electrode current collector aluminum foil with a thickness of 12μm, and baked at 120℃ for 1h to obtain a positive electrode film, which is then compacted and cut to obtain a positive electrode sheet.

[0103] (2) Preparation of negative electrode

[0104] The negative electrode active material artificial graphite powder, sodium carboxymethyl cellulose thickener (CMC), and binder styrene-butadiene rubber are dissolved in water at a mass ratio of 96:2:2, and the mixture is fully mixed and stirred to obtain a negative electrode slurry. The negative electrode slurry is evenly coated on a negative electrode current collector copper foil with a thickness of 12 μm, and baked at 120°C for 1 h to obtain a negative electrode film, which is then compacted and cut to obtain a negative electrode sheet.

[0105] (3) Preparation of electrolyte

[0106] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate, propylene carbonate, and diethyl carbonate are mixed in a mass ratio of 2:2:6 to obtain an organic solvent, and then lithium salt LiPF6 is added to the organic solvent and mixed to obtain a basic electrolyte, wherein the mass percentage of the lithium salt is 12.5% ​​based on the mass of the electrolyte. A certain amount of the first additive, the second additive, or the third additive is added to the basic electrolyte.

[0107] (4) Preparation of isolation membrane

[0108] <Preparation of Separator Film>

[0109] A porous polyethylene film with a thickness of 12 μm (provided by Celgard Company) was used as the isolation membrane.

[0110] (5) Preparation of lithium-ion batteries

[0111] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator placed between the positive and negative electrodes to play a role of isolation, and then wound into a square bare cell. The bare cell is placed in an aluminum foil packaging bag, baked at 80°C to remove water, and a dry cell is obtained. The corresponding electrolyte is injected, and the preparation of the lithium-ion battery is completed after vacuum packaging, standing, formation, shaping, and other processes.

[0112] In Examples 1-1 to 1-19, Examples 2-1 to 2-11, Examples 3-1 to 3-11 and Comparative Example 1-3, the types and contents of the additives used are shown in the data in Tables 1 to 3, wherein the content of each additive is the mass percentage calculated based on the total mass of the electrolyte.

[0113] Next, the performance test process and test results of lithium-ion batteries are described.

[0114] (1) Cyclic performance test

[0115] At 45°C, charge the lithium-ion battery at 1C constant current to 4.45V, then charge at constant voltage to a current of 0.5C, at which point the battery is fully charged; let the battery rest for 30 minutes, then discharge at 1C constant current to 3.0V, and let it rest for 30 minutes, this is a cycle charge and discharge process, record the discharge capacity at this time, which is the first cycle discharge capacity. Perform a cyclic charge and discharge test on the lithium-ion battery according to the above method, record the discharge capacity after each cycle, until the cycle reaches 300, stop the test, and record the discharge capacity at this time, which is the discharge capacity of the 300th cycle.

[0116] Lithium-ion battery capacity retention rate (%) = discharge capacity after 300 cycles / first cycle discharge capacity × 100%.

[0117] (2) High temperature storage performance test

[0118] At 25°C, the lithium-ion battery is charged to 3.95V at 1C constant current, then charged to 0.5C at constant voltage, the lithium-ion battery is half-charged, and the thickness of the battery at this time is recorded as t mm; then charged to 4.45V at 1C constant current, then charged to 0.5C at constant voltage, the lithium-ion battery is fully charged, the battery is placed in a 60°C constant temperature box for high-temperature storage, taken out after 15 days of storage, cooled to 25°C, and the lithium-ion battery is tested for thickness, and the thickness of the battery at this time is recorded as T mm. Lithium-ion battery thickness expansion rate (%) = (Tt) / t×100%.

[0119] Table 1 Parameters of Examples 1-1 to 1-19 and Comparative Examples 1-1 to 1-3

[0120]

[0121]

[0122] It can be seen from Comparative Examples 1-1 to 1-3 and Examples 1-1 to 1-20 in Table 1 that increasing the content of anhydride compounds in the electrolyte significantly improves the cycle performance of lithium-ion batteries; as the content of polynitrile compounds increases, the high-temperature storage expansion rate of lithium-ion batteries is affected; the combination of the first additive and the second additive within the preferred range has a significant improvement effect on the capacity retention rate and the high-temperature storage expansion rate. The combination of the two can achieve the effect of improving the long-cycle stability of lithium-ion batteries and improving the high-temperature storage performance of lithium-ion batteries. The protective effect of anhydride compounds and polynitrile compounds on the negative and positive electrode interfaces can prevent the internal active materials of lithium-ion batteries from contacting with the current collector in a high-temperature environment to generate sparks, ignite the electrolyte, and thus improve the safety performance of lithium-ion batteries.

[0123] Table 2 Parameters of Examples 1-3, 2-1 to 2-11

[0124]

[0125]

[0126] It can be seen from Examples 1-3, 2-1 to 2-11 in Table 2 that, after the third additive is introduced into the electrolyte on the basis of adding the first additive and the second additive, the long cycle retention rate of the lithium ion battery is significantly increased, and the expansion of the lithium ion battery during high temperature storage is significantly reduced. The third additive, as a negative electrode protection additive, will generate a dense and flexible SEI film at the negative electrode, which is quickly repaired during the cycle, effectively preventing the multinitrile compound from damaging the negative electrode interface, reducing the negative electrode interface side reactions, and achieving the effect of improving the long cycle stability of the lithium ion battery and improving the high temperature storage performance, thereby improving the safety performance of the lithium ion battery.

[0127] Table 3 Parameters of Examples 1-3 and Examples 3-1 to 3-11

[0128]

[0129]

[0130] It can be seen from Examples 1-3 and Examples 3-1 to 3-11 in Table 3 that when a high-valent metal element is used to modify the positive electrode material, it is more conducive to the transmission of lithium ions inside the lithium-ion battery, reduces the side reaction between the positive electrode material and the electrolyte, and achieves the effect of improving the long-cycle stability and high-temperature storage performance of the lithium-ion battery, as well as enhancing the safety performance of the lithium-ion battery.

[0131] The above disclosed features are not intended to limit the scope of implementation of the present disclosure. Therefore, all equivalent changes made to the contents described in the claims of the present disclosure should be included in the scope of the claims of the present disclosure.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a first additive and a second additive: The first additive comprises at least one of the following compounds: The second additive comprises a polynitrile compound represented by formula III: in, M1, M2 are independently selected from halogen, formula IV, formula V; wherein α and γ are independently selected from 0 or 1, and β is independently selected from 0, 1, and 2; R 12 , R 13 are each independently selected from hydrogen, halogen, substituted or unsubstituted C 1-10 Alkyl, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The substituents are each independently selected from halogen; R 14 , R 15 Each independently selected substituted or unsubstituted C 1-10 Alkylene, substituted or unsubstituted C 2-10 Alkenyl, substituted or unsubstituted C 2-10 Alkynyl, substituted or unsubstituted C 2-10 The ring group of is independently selected from halogen; The cyclic group includes at least one of an alicyclic group and a heterocyclic group; Based on the total weight of the electrolyte, the mass percentage of the first additive is A%, and the mass percentage of the second additive is B%. The mass percentage content of the first additive and the mass percentage content of the second additive satisfy the following relationship: 0.005≤A / B≤10.

2. The electrochemical device according to claim 1, wherein: The second additive includes at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, suberonitrile, 1,2,3-tris(2-cyano)propane, 1,3,6-hexanetrinitrile, 1,4-dicyano-2-butene, 1,2-bis(cyanoethoxy)ethane, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile or 1,2,6-hexanetricarbonitrile.

3. The electrochemical device according to claim 1, wherein Based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.01%-5%, and / or The mass percentage B% of the second additive is 0.5%-10%.

4. The electrochemical device according to claim 1, wherein The electrolyte further comprises a third additive, The third additive includes at least one of fluoroethylene carbonate, vinyl ethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,3-dioxane, 1,4-dioxane, lithium bis(oxalato)borate, and lithium tetrafluoroborate; based on the total weight of the electrolyte, The mass percentage C% of the third additive is 0.5%-10%.

5. The electrochemical device according to claim 1, wherein The positive electrode comprises a positive electrode active material; The positive electrode active material contains a doping element: at least one of aluminum, cerium, titanium, zirconium, niobium, and manganese; Based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0<X≤3.

6. The electrochemical device according to claim 5, wherein: Based on the total weight of the electrolyte, the mass percentage of the first additive is A%, The doping amount X% of the doping element and the mass percentage content A% of the first additive satisfy the following relationship: 0<X / A≤100.

7. The electrochemical device according to any one of claims 1 to 6, satisfying one of the following conditions: (1) Based on the total weight of the electrolyte, the mass percentage A% of the first additive is 0.1%-3%, (2) Based on the total weight of the electrolyte, the mass percentage B% of the second additive is 1%-5%, (3) Based on the total weight of the electrolyte, the mass percentage A% of the first additive and the mass percentage B% of the second additive satisfy the following relationship: 0.05≤A / B≤5.

8. The electrochemical device according to claim 4, satisfying the following conditions: (4) Based on the total weight of the electrolyte, the mass percentage C% of the third additive is 1%-5%.

9. The electrochemical device according to claim 5, satisfying the following conditions: (5) Based on the total mass of the positive electrode active material, the doping amount of the doping element is X%, and the range of X is 0.5≤X≤2.

10. The electrochemical device according to claim 6, satisfying the following conditions: (6) The doping amount X% of the doping element and the mass percentage A% of the first additive satisfy the following relationship: 0.5≤X / A≤30.

11. An electronic device comprising the electrochemical device according to any one of claims 1 to 10.

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