Electrolyte additive and preparation method therefor, secondary battery, and electronic device

Abstract

Embodiments of the present application relate to the technical field of batteries. Provided are an electrolyte additive and a preparation method therefor, a secondary battery, and an electronic device. The electrolyte additive not only comprises fluorine atoms or a fluorine-containing substituent, but also comprises a cyano group, and can be used to generate a solid electrolyte interface film having rich inorganic components. The ionic conductivity and the stability of the solid electrolyte interface film are improved. Thus, the cycle performance and the high-temperature storage performance of batteries can be improved, accordingly.

Description

Electrolyte additive and preparation method thereof, secondary battery and electronic device

[0001] The present application claims priority from the Chinese patent application No. 202410741006.8 filed on June 7, 2024, and entitled "Electrolyte additive and preparation method thereof, secondary battery and electronic device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of batteries, in particular to an electrolyte additive and a preparation method thereof, a secondary battery and an electronic device. BACKGROUND

[0003] With the development of economy and technology, most electronic devices (such as portable electronic devices, unmanned aerial vehicles, electric vehicles, etc.) urgently need energy storage devices such as batteries with higher energy density, higher power density, longer cycle life and higher safety. Electrolyte is essential for the stable operation of the battery as it conducts ions and stabilizes the positive and negative electrode interfaces.

[0004] Generally, some additives such as fluoroethylene carbonate, vinylene carbonate and vinyl sulfate are added to the electrolyte. The additives can form a SEI (Solid Electrolyte Interphase) film on the surface of the positive and negative electrodes during formation or partitioning to avoid the reduction and decomposition of the solvent in the electrolyte, thereby improving the cycle life of the battery.

[0005] Due to the higher specific capacity of alloy anodes (silicon, phosphorus, etc.) and lithium metal anodes, volume expansion and repeated rupture of the SEI film and interface layer thickening occur. Therefore, a high content of additives is required to maintain the later cycle repair of the SEI film, but high content of additives not only increases the interface impedance, but also affects the long cycle performance of the battery system. SUMMARY

[0006] The present application provides an electrolyte additive and a preparation method thereof, an electrolyte containing the electrolyte additive, a secondary battery containing the electrolyte, and an electronic device containing the secondary battery. The electrolyte additive not only includes fluorine atoms or fluorine-containing substituent groups, but also includes cyano groups, which can generate a solid electrolyte interface film rich in inorganic components, thereby improving the ionic conductivity and stability of the solid electrolyte interface film. Thus, the cycle performance and high-temperature storage performance of the battery can be improved subsequently.

[0007] To achieve the above-mentioned purpose, the embodiments of the present application adopt the following technical solutions:

[0008] In a first aspect, an electrolyte additive is provided, the electrolyte additive comprising a first additive and / or a second additive;

[0009] The first additive has a general structure of Formula (1) as follows: R1-S(=O) x -N(-R3)-R2 Formula (1);

[0010] The second additive has a general structure of Formula (2) as follows: R1-S(=O) x -N(-R3)-S(=O) y -R4 Formula (2);

[0011] R1 and R4 are independently selected from one of a fluorine atom or a fluorine-containing substituent group;

[0012] R2 and R3 are independently selected from one of a substituted or unsubstituted alkylene nitrile group, a substituted or unsubstituted alkyloxy nitrile group, a substituted or unsubstituted alkenylene nitrile group, a substituted or unsubstituted alkenyloxy nitrile group, a substituted or unsubstituted arylene nitrile group, or a substituted or unsubstituted aryloxy nitrile group;

[0013] x is 1 or 2, and y is 1 or 2.

[0014] Thus, in one aspect, R1 and R4 in the electrolyte additive provided by the embodiments of the present application can be selected from one of a fluorine atom or a fluorine-containing substituent group, which can form inorganic component compounds such as lithium fluoride, lithium nitride, and sulfide on the surface of the positive and negative electrodes, and can generate a solid electrolyte interface film with high conductivity and high stability. Further, the dissolution of CEI and SEI is reduced, and the interface impedance is reduced. Subsequently, the rate performance and transmission performance of the battery can be improved.

[0015] On the other hand, R2 and R3 include a nitrile group substituent, such as a substituted nitrile group. The nitrile group substituent includes a cyano group (-CN), which can preferentially complex with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of transition metal ions, reduce the side reaction of the electrolyte with the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, thereby improving the high-voltage stability of the electrolyte.

[0016] At the same time, when a high-capacity (such as silicon) negative electrode material is used in the negative electrode, the electrolyte with the electrolyte additive can form a solid electrolyte interface film with high stability, and has stronger resistance to the expansion of the negative electrode material, and can also improve the compatibility with the negative electrode material. Thus, the electrolyte additive provided by the embodiments of the present application can improve the stability and ionic conductivity of the electrolyte at high voltage, thereby improving the high-temperature storage performance and cycle performance of the battery.

[0017] In some implementable manners, the fluorine-containing substituent group comprises a fluorine-substituted alkyl group, a fluorine-substituted alkoxy group, a fluorine-substituted alkenyl group, a fluorine-substituted alkenyloxy group, a fluorine-substituted aryl group, or a fluorine-substituted aryloxy group.

[0018] Thus, when the substituent group in the electrolyte additive provided by the embodiments of the present application is a fluorine-containing group, the interface film formed on the surface of the electrode contains a certain amount of stable fluoride, which is beneficial to effectively protecting the electrode. Thus, the stability of the interface film is improved, and the cycle performance and high-temperature storage performance of the battery are further improved.

[0019] In some implementable manners, the fluorine-substituted alkyl group and the fluorine-substituted alkoxy group correspond to 1-20 carbon atoms, the fluorine-substituted alkenyl group and the fluorine-substituted alkenyloxy group correspond to 2-20 carbon atoms, the fluorine-substituted aryl group, the fluorine-substituted aryloxy group, the substituted or unsubstituted arylene nitrile group, and the substituted or unsubstituted aryloxy nitrile group correspond to 6-20 carbon atoms, the substituted or unsubstituted alkylene nitrile group and the substituted or unsubstituted alkoxy nitrile group correspond to 2-20 carbon atoms, and the substituted or unsubstituted alkenylene nitrile group and the substituted or unsubstituted alkenyloxy nitrile group correspond to 3-20 carbon atoms. Thus, a smaller number of carbon atoms can be beneficial to controlling the molecular weight of the additive, thereby facilitating better subsequent control of the viscosity of the electrolyte.

[0020] In some implementable manners, the substituent group in the substituted alkylene nitrile group, the substituted alkoxy nitrile group, the substituted alkenylene nitrile group, the substituted alkenyloxy nitrile group, the substituted arylene nitrile group, and the substituted aryloxy nitrile group is independently selected from one or more of fluorine, chlorine, bromine, iodine, an alkyl group, a halogenated alkyl group, an alkoxy group, a halogenated alkoxy group, an alkenyl group, a halogenated alkenyl group, an alkenyloxy group, a halogenated alkenyloxy group, an aryl group, a halogenated aryl group, an aryloxy group, or a halogenated aryloxy group.

[0021] Specifically, the halogen in the halogenated alkyl group, the halogenated alkoxy group, the halogenated alkenyl group, the halogenated alkenyloxy group, the halogenated aryl group, or the halogenated aryloxy group is independently selected from one or more of fluorine, chlorine, bromine, and iodine.

[0022] Therefore, the alkylene nitrile group, the alkyleneoxy nitrile group, the alkenylene nitrile group, the alkenyloxy nitrile group, the arylene nitrile group and the aryloxy nitrile group in the structure of the electrolyte additive in the embodiments of the present application include the above-mentioned substituent groups. The above-mentioned groups include the cyano group (-CN), which can preferentially complex with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of the transition metal ions, reduce the side reaction between the electrolyte and the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, thereby improving the high-voltage stability of the electrolyte. Therefore, the cycle performance and the high-temperature storage performance of the battery are improved.

[0023] In some implementations, the electrolyte additive includes at least one of the structures shown in the following formulas (3)-(10):

[0024] Therefore, the electrolyte additive in the embodiments of the present application includes at least one of the above-mentioned structures, which can enable the electrolyte to form a solid electrolyte interface film with high stability on the surface of the positive and negative electrodes. Meanwhile, when a high-capacity (such as silicon) negative electrode material is used in the negative electrode, the solid electrolyte interface film has stronger resistance to the expansion of the negative electrode material, and can also improve the compatibility with the negative electrode material. Therefore, the cycle performance and the high-temperature storage performance of the battery are improved.

[0025] In a second aspect, the embodiments of the present application also provide a preparation method of the electrolyte additive, which includes the following steps:

[0026] Mixing the acid-binding agent and the solvent to obtain a first solution.

[0027] Providing a first reaction substrate, which includes at least one of the following: a substituted or unsubstituted alkylene nitrile group compound, a substituted or unsubstituted alkyleneoxy nitrile group compound, a substituted or unsubstituted alkenylene nitrile group compound, a substituted or unsubstituted alkenyloxy nitrile group compound, a substituted or unsubstituted arylene nitrile group compound, and a substituted or unsubstituted aryloxy nitrile group compound.

[0028] Providing a second reaction substrate, which includes a fluorine-containing substituent group compound.

[0029] Reacting the first reaction substrate, the second reaction substrate and the first solution to obtain the electrolyte additive described in the first aspect.

[0030] Thus, the electrolyte additive prepared by the above method can form inorganic component compounds such as lithium fluoride, lithium nitride and sulfide on the surface of the positive and negative electrodes, and can generate a solid electrolyte interface film with high conductivity and high stability. At the same time, the electrolyte additive can be preferentially complexed with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of transition metal ions, reduce the side reaction of the electrolyte with the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, thereby improving the high-voltage stability of the electrolyte.

[0031] In a third aspect, the embodiments of the present application also provide a battery electrolyte, comprising: an electrolyte salt, an organic solvent and the electrolyte additive described above.

[0032] Thus, the electrolyte provided by the embodiments of the present application can form a solid electrolyte interface film with high conductivity and high stability on the surface of the positive and negative electrodes. The electrolyte additive in the electrolyte can be preferentially complexed with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of transition metal ions, reduce the side reaction of the electrolyte with the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, so that the electrolyte has higher high-voltage stability. At the same time, the electrolyte has stronger resistance to negative electrode material expansion and can also improve the compatibility with the negative electrode material. Thus, the high-temperature storage performance and cycle performance of the battery are improved.

[0033] In some implementable manners, the mass percentage content of the electrolyte additive in the electrolyte is 0.05%-10%.

[0034] Specifically, the mass percentage content of the electrolyte additive in the electrolyte is 0.05%-5%.

[0035] Thus, the embodiments of the present application can keep the content of the electrolyte additive in the electrolyte within an appropriate range by regulating the content of the electrolyte additive, so as to promote the electrolyte to form a solid electrolyte interface film with high stability on the surface of the positive and negative electrodes. Thus, the rate performance, cycle performance and high-temperature storage performance of the subsequent battery are improved.

[0036] In some implementable manners, the organic solvent comprises one or more of a carbonate solvent, a carboxylic acid ester solvent or an ether solvent, and the carbonate solvent comprises one or more of a cyclic carbonate solvent or a linear carbonate solvent.

[0037] In some implementable manners, the mass percentage content of the cyclic carbonate solvent in the electrolyte is 10%-50%.

[0038] Specifically, the mass percentage content of the cyclic carbonate solvent in the electrolyte is 20%-40%.

[0039] Therefore, the embodiments of the present application control the mass percentage of the cyclic carbonate solvent, so that the content of the cyclic carbonate in the electrolyte is appropriate, the viscosity of the electrolyte is prevented from being too large, and the slow ion transmission in the electrolyte is avoided to reduce the cycle performance of the battery.

[0040] In some implementable manners, the mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.01:1 to 0.5:1.

[0041] Specifically, the mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.02:1 to 0.3:1.

[0042] Therefore, the embodiments of the present application control the mass ratio of the electrolyte additive to the cyclic carbonate solvent, so that the content of the cyclic carbonate in the electrolyte is appropriate, the viscosity of the electrolyte is prevented from being too large, and the slow ion transmission in the electrolyte is avoided to reduce the cycle performance of the battery.

[0043] In some implementable manners, the molar concentration of the electrolyte salt in the electrolyte is 0.01 mol / L-5.0 mol / L.

[0044] In some implementable manners, the electrolyte salt includes one or more of lithium salt, sodium salt, potassium salt, magnesium salt, zinc salt or aluminum salt.

[0045] In some implementable manners, the electrolyte salt includes one or more of MClO4, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C2O4)2, MBF2C2O4, M[(CF3SO2)2N], M[(FSO2)2N] or M[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein M is lithium, sodium or potassium, and m and n are natural numbers.

[0046] In some implementable manners, the electrolyte additive further includes other additives, and the other additives include one or more of film-forming additives, overcharge-preventing additives, wetting agents, and flame retardants.

[0047] In some implementations, the other additives include one or more of biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, methylene methane disulfonate, butanedinitrile, hexanedinitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetricarbonitrile, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, triethyl phosphite, (ethoxy)pentakisfluorocyclotriphosphazene, hexafluorocyclotriphosphazene, tris(trimethylsilyl)phosphate, tris(trimethylsilyl)borate.

[0048] In a fourth aspect, the embodiments of the present application further provide a secondary battery, including a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the electrolyte of the third aspect, the electrolyte being filled between the positive electrode and the negative electrode.

[0049] In a fifth aspect, the embodiments of the present application further provide an electronic device, including a shell, and electronic components and a battery accommodated in the shell, the battery being used to supply power for the electronic components, and the battery including the secondary battery of the fourth aspect. BRIEF DESCRIPTION OF DRAWINGS

[0050] FIG. 1 is a structural schematic diagram of a lithium ion battery according to an embodiment of the present application;

[0051] FIG. 2 is a schematic diagram of test results of Example 1 and Comparative Examples 1, 2 and 3 according to an embodiment of the present application;

[0052] FIG. 3 is a schematic diagram of test results of Example 3 and Comparative Examples 4 and 5 according to an embodiment of the present application;

[0053] FIG. 4 is a structural schematic diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0054] The technical solutions in the embodiments of the present application will be described below with reference to the drawings in the embodiments of the present application. In the description of the present application, unless otherwise specified, " / " represents an "or" relationship between the objects before and after the " / ", for example, A / B can represent A or B; "and / or" in the present application is only a description of the relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which means that there are three cases of A alone, A and B together, and B alone, where A and B can be singular or plural. In the description of the present application, unless otherwise specified, "multiple" means two or more than two. "At least one of the following" or the like means any combination of the items, including any combination of single or multiple items. For example, at least one of a, b, or c can mean a, b, c, a-b, a-c, b-c, or a-b-c, where a, b, and c can be single or multiple. In addition, in order to clearly describe the technical solutions of the embodiments of the present application, in the embodiments of the present application, "first", "second", and the like are used to distinguish the same items or similar items with basically the same function and effect.

[0055] Those skilled in the art can understand that the "first", "second", and the like do not limit the quantity and execution order, and the "first", "second", and the like do not necessarily mean different. At the same time, in some embodiments of the present application, the words "exemplary" or "for example" are used to represent an example, illustration or description. Any embodiment or design scheme described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. Rather, the words "exemplary" or "for example" are intended to present the relevant concept in a specific manner, for ease of understanding.

[0056] For ease of understanding, some descriptions of concepts related to the embodiments of the present application are given as examples for reference. As shown below:

[0057] Rechargeable battery, also known as secondary battery or storage battery, refers to a battery that can be activated by charging after discharging to continue to use.

[0058] Cathode: In a primary cell, the electrode with a higher potential for current flow is the positive electrode, which acts as a reducing agent. In an electrolytic cell, the positive electrode is the electrode connected to the positive pole of the power source, which loses electrons and acts as an oxidizing agent.

[0059] Anode: In a primary cell, the electrode with a lower potential for current flow is the negative electrode, which loses electrons and acts as an oxidizing agent. In an electrolytic cell, the negative electrode is the electrode connected to the negative pole of the power source, which gains electrons and acts as a reducing agent.

[0060] Electrolyte: A medium that provides ion exchange between the positive and negative electrodes of a battery.

[0061] Separator: The main function of the separator is to separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting, and in addition, to have the function of allowing electrolyte ions to pass through.

[0062] Additive: A class of substances that preferentially decompose on the surface of the material to form an interfacial film in organic solvents, which can significantly improve the performance of the battery.

[0063] Solid Electrolyte Interphase (SEI) film: During the first charge and discharge process of the battery, the electrode material reacts with the electrolyte at the solid-liquid interface to form a passivation layer covering the surface of the electrode material. In the case of lithium-ion batteries, this passivation layer is an interfacial layer with the characteristics of a solid electrolyte, which is an electronic insulator but a good conductor of Li+, and Li+ can freely insert and extract through the passivation layer.

[0064] Cathode Electrolyte Interphase (CEI), which represents the interface protection film or cathode electrolyte interface (film), refers to a passivation film layer with solid electrolyte properties.

[0065] With the development of economy and technology, most electronic devices (such as portable electronic devices, drones, electric vehicles, etc.) urgently need energy storage devices such as batteries with higher energy density, higher power density, longer cycle life, and higher safety. Electrolyte, as a component that conducts ions and stabilizes the positive and negative electrode interfaces in the battery, is crucial for stable operation of the battery. However, with the use of higher voltage positive electrodes (such as high voltage lithium cobalt oxide positive electrodes) and higher gram capacity negative electrodes (such as silicon negative electrodes / lithium metal negative electrodes), on the one hand, the high voltage lithium cobalt oxide material will have serious side reactions with the electrolyte, and on the other hand, the large volume expansion of such negative electrode materials during cycling will cause the SEI film to continuously break / recombine and the interface layer to thicken, thus requiring more or more effective film-forming additives to form an interface film to maintain cycle stability.

[0066] To solve the above technical problems, the embodiments of the present application propose an electrolyte additive, which comprises a first additive and / or a second additive.

[0067] The structural general formula of the first additive is as follows: R1-S(=O) x -N(-R3)-R2 Formula (1);

[0068] The second additive has a general structure of formula (2) as follows: R1-S(=O) x -N(-R3)-S(=O) y -R4 Formula (2);

[0069] R1 and R4 are independently selected from one of a fluorine atom or a fluorine-containing substituent group;

[0070] R2 and R3 are independently selected from one of a substituted or unsubstituted alkylene nitrile group, a substituted or unsubstituted alkyloxy nitrile group, a substituted or unsubstituted alkenylene nitrile group, a substituted or unsubstituted alkenyloxy nitrile group, a substituted or unsubstituted arylene nitrile group, and a substituted or unsubstituted aryloxy nitrile group. x is 1 or 2, and y is 1 or 2.

[0071] In one aspect, R1 and R4 in the electrolyte additive provided by the embodiments of the present application can be selected from one of a fluorine atom or a fluorine-containing substituent group, and can form inorganic component compounds such as lithium fluoride, lithium nitride, and sulfide on the surface of the positive and negative electrodes, so as to generate a solid electrolyte interface film with high conductivity and high stability. In this way, the dissolution of CEI and SEI is reduced, and the interface impedance is reduced. Subsequently, the rate performance and transmission performance of the battery can be improved.

[0072] On the other hand, R2 and R3 include a nitrile group substituent, such as a substituted nitrile group. The nitrile group substituent includes a cyano group (-CN), which can preferentially complex with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of the transition metal ions, reduce the side reaction of the electrolyte with the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, thereby improving the high-voltage stability of the electrolyte. The side reaction can be, for example, the generation of a large amount of gas, which can cause the electrolyte to deteriorate in wetting between the separator and the positive and negative electrodes, resulting in battery volume expansion, electrode / separator misalignment, and increased battery polarization. The oxidative decomposition of the electrolyte can be, for example, the generation of oxygen and the generation of Co 3+ / Ni 4+ , which can cause the electrolyte to continuously decompose on the surface of the positive and negative electrodes, resulting in increased battery impedance and capacity degradation.

[0073] Meanwhile, when a high-capacity (such as silicon) negative electrode material is used in the negative electrode, the electrolyte with the electrolyte additive can form a solid electrolyte interface film with high stability, and has stronger resistance to the expansion of the negative electrode material, and can also improve the compatibility with the negative electrode material. Thus, the electrolyte additive provided by the embodiments of the present application can improve the stability and ionic conductivity of the electrolyte at high voltage, thereby improving the high-temperature storage performance and cycle performance of the battery.

[0074] FIG. 1 is a structural schematic diagram of a lithium ion battery provided by an embodiment of the present application. As shown in FIG. 1, the lithium ion battery includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40, wherein the separator 30 is arranged between the positive electrode 10 and the negative electrode 20, and the electrolyte 40 is filled between the positive electrode 10 and the negative electrode 20 and infiltrates the separator 30. During charging, lithium ions are released from a positive electrode active material 102 of the positive electrode 10, pass through the electrolyte 40, and are inserted into a negative electrode active material 202 of the negative electrode 20; during discharging, lithium ions are released from the negative electrode active material 202, pass through the electrolyte 40, and are inserted into the positive electrode active material 102.

[0075] As shown in FIG. 1, the positive electrode 10 includes a positive electrode current collector 101 and a positive electrode material layer coated on a surface of the positive electrode current collector 101. The positive electrode material layer can include, in addition to the positive electrode active material 102, a certain amount of a binder, a conductive agent, and the like.

[0076] The positive electrode current collector 101 can be a metal foil (for example, an aluminum foil, a gold foil, a platinum foil, or the like), a carbon-coated metal foil, or the like. The positive electrode active material 102 is capable of reversibly intercalating / deintercalating active ions (such as lithium ions, sodium ions, potassium ions, magnesium ions, zinc ions, or aluminum ions, or the like). The positive electrode active material 102 includes, but is not limited to, at least one of transition metal oxides of lithium, sodium, potassium, magnesium, zinc, and aluminum, Prussian blue (white) compounds, polyanionic compounds of lithium, sodium, potassium, magnesium, zinc, and aluminum, or the like. The positive electrode active material 102 can be, for example, lithium cobaltate (LiCoO2, abbreviated as LCO).

[0077] The positive electrode active material 102 can also include at least one of lithium cobaltate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium nickel manganese oxide, and lithium nickel oxide. The binder can be, for example, poly 1,1-difluoroethylene (PVDF), and the conductive agent can be, for example, super P, amorphous carbon, carbon nanotubes, carbon fibers, graphene, or the like. The above-mentioned positive electrode current collector 101, positive electrode active material 102, binder, and conductive agent used for preparing the positive electrode 10 are only exemplary and are not limited by the embodiments of the present application. Taking the positive electrode active material 102 as an example, in theory, it is a compound capable of reversibly intercalating / deintercalating active ions.

[0078] Continuing to refer to FIG. 1, in the lithium ion battery provided by the embodiment of the present application, the negative electrode 20 includes a negative electrode current collector 201 and a negative electrode material layer coated on a surface of the negative electrode current collector 201. The negative electrode material layer can include, in addition to the negative electrode active material 202, a certain amount of a binder, a conductive agent, and the like.

[0079] The negative current collector 201 can be a metal foil (e.g., copper foil, aluminum foil, gold foil, platinum foil, etc.), a carbon-coated metal foil, or the like. The negative active material 202 can include at least one of natural graphite, artificial graphite, meso-carbon microbead, hard carbon, soft carbon, porous carbon material, or the like. The negative active material 202 can be one or more of a carbon-based material capable of intercalation and deintercalation of active ions, a tin-based material, a silicon-based material, a phosphorus-based material, a lithium titanate (Li4Ti5O12) material, a lithium material, a sodium material, a potassium material, a magnesium material, a zinc material, or an aluminum material. The carbon-based material includes, but is not limited to, one or more of graphite, hard carbon, soft carbon, meso-carbon microbead, graphene, porous carbon. The tin-based material includes, but is not limited to, one or more of tin, tin-carbon, tin-oxygen, tin metal compound; the phosphorus-based material includes, but is not limited to, one or more of red phosphorus, black phosphorus, phosphorus compound; the sodium material includes, but is not limited to, metallic sodium or sodium alloy. The silicon-based material includes one or more of silicon, silicon-carbon, silicon-oxygen, or silicon metal compound. The lithium material includes metallic lithium or lithium alloy. The lithium alloy includes at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. The potassium material includes metallic potassium or potassium alloy. The magnesium material includes metallic magnesium or magnesium alloy. The zinc material includes metallic zinc or zinc alloy. The aluminum material includes metallic aluminum or aluminum alloy. 12 ) material, a lithium material, a sodium material, a potassium material, a magnesium material, a zinc material, or an aluminum material. The carbon-based material includes, but is not limited to, one or more of graphite, hard carbon, soft carbon, meso-carbon microbead, graphene, porous carbon. The tin-based material includes, but is not limited to, one or more of tin, tin-carbon, tin-oxygen, tin metal compound; the phosphorus-based material includes, but is not limited to, one or more of red phosphorus, black phosphorus, phosphorus compound; the sodium material includes, but is not limited to, metallic sodium or sodium alloy. The silicon-based material includes one or more of silicon, silicon-carbon, silicon-oxygen, or silicon metal compound. The lithium material includes metallic lithium or lithium alloy. The lithium alloy includes at least one of lithium-silicon alloy, lithium-sodium alloy, lithium-potassium alloy, lithium-aluminum alloy, lithium-tin alloy, and lithium-indium alloy. The potassium material includes metallic potassium or potassium alloy. The magnesium material includes metallic magnesium or magnesium alloy. The zinc material includes metallic zinc or zinc alloy. The aluminum material includes metallic aluminum or aluminum alloy.

[0080] The binder can be, for example, one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), lithium polyacrylate (LiPAA). The conductive agent can be, for example, super P, acetylene black, carbon nanotube, graphene, amorphous carbon, or the like. The above-mentioned negative current collector 201, negative active material 202, binder, and conductive agent used for preparing the negative electrode 20 are merely exemplary and are not limited in the embodiments of the present application.

[0081] Referring back to FIG. 1, in the lithium ion battery provided by the embodiments of the present application, the separator 30 blocks the passage of electrons and allows the passage of ions. The separator 30 includes, but is not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, ceramic-coated PE, and solid electrolyte-coated PE, or the like.

[0082] As shown in FIG. 1, in the lithium ion battery, the electrolyte 40 is a transport medium for lithium ions to transport between the positive electrode 10 and the negative electrode 20. In an embodiment of the present application, the electrolyte 40 includes an organic solvent, an electrolyte salt, and an electrolyte additive. The electrolyte salt and the electrolyte additive are both dissolved in the organic solvent.

[0083] In some embodiments of the present application, the organic solvent can be a non-aqueous organic solvent, and the organic solvent can include, but is not limited to, at least one of a carbonate solvent, a carboxylic acid ester solvent, and an ether solvent.

[0084] The carbonate solvent includes, but is not limited to, one or more of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, trifluoromethyl ethylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and (2,2,2-trifluoroethyl) methyl carbonate. The ether solvent includes, but is not limited to, one or more of tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diglyme, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether. The carboxylic acid ester solvent includes, but is not limited to, one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate.

[0085] The carbonate solvent can further include a cyclic carbonate solvent and a linear carbonate solvent. The cyclic carbonate solvent includes, but is not limited to, one or more of ethylene carbonate (EC), propylene carbonate (PC), and trifluoromethyl ethylene carbonate. The linear carbonate solvent includes, but is not limited to, one or more of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), bis(2,2,2-trifluoroethyl) carbonate, and (2,2,2-trifluoroethyl) methyl carbonate. The introduction of the linear carbonate solvent is more helpful to reduce the viscosity of the battery electrolyte, and the linear carbonate solvent has higher compatibility with the cyclic carbonate solvent.

[0086] In some embodiments of the present application, the mass percentage of the cyclic carbonate solvent in the electrolyte is 10% to 50%. Specifically, the mass percentage of the cyclic carbonate solvent in the electrolyte is 20% to 40%.

[0087] As an example, the value of the cyclic carbonate solvent can be, for example, 10%, 20%, 30%, 40%, 50%, and a number between any two of the above values, all of which are within the range of values that can be taken.

[0088] In this way, the embodiments of the present application control the mass percentage of the cyclic carbonate solvent, so that the content of the cyclic carbonate in the electrolyte is appropriate, the viscosity of the electrolyte is prevented from being too large, and the slow ion transmission in the electrolyte is avoided to reduce the cycle performance of the battery.

[0089] In some embodiments of the present application, the mass percentage of the electrolyte additive in the electrolyte is 0.05% to 10%.

[0090] Specifically, the mass percentage content of the electrolyte additive in the electrolyte is 0.5%-5%.

[0091] For example, the content of the electrolyte additive in the electrolyte can be 0.05%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 8.0%, 10%, or a number between any two of the above values.

[0092] Therefore, the content of the electrolyte additive in the electrolyte is controlled to be in an appropriate range, which promotes the formation of a high-stability solid electrolyte interface film on the surface of the positive and negative electrodes. As a result, the rate performance, cycle performance, and high-temperature storage performance of the subsequent battery are improved.

[0093] In some embodiments of the present application, the mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.01:1 to 0.5:1. Specifically, the mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.02:1 to 0.3:1.

[0094] The mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.01:1 to 0.5:1. The value of the ratio can be, for example, 0.01:1, 0.05:1, 0.08:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, or a number between any two of the above values.

[0095] Therefore, the content of the electrolyte additive in the electrolyte is controlled to be in an appropriate range, which promotes the formation of a high-stability solid electrolyte interface film on the surface of the positive and negative electrodes. As a result, the rate performance, cycle performance, and high-temperature storage performance of the subsequent battery are improved.

[0096] It should be noted that the type and amount of components in the organic solvent are not specifically limited, and the mass percentage content of each component in the electrolyte is also not specifically limited.

[0097] In some embodiments of the present application, the electrolyte salt comprises one or more of a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a zinc salt, or an aluminum salt.

[0098] The electrolyte salt comprises, but is not limited to, one or more of MCIO4, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C2O4)2, MBF2C2O4, M[(CF3SO2)2N], M[(FSO2)2N], or M[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein M is lithium, sodium, or potassium, and m and n are natural numbers.

[0099] In an embodiment of the electrolyte of the present application, the molar concentration of the electrolyte salt can be 0.01 mol / L-5.0 mol / L.

[0100] For example, the molar concentration of the electrolyte salt can be 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, or 5.0 mol / L, and any value between 0.01 mol / L and 5.0 mol / L, which is not listed here. It should be understood that the concentration range of the electrolyte salt in the electrolyte can allow for certain measurement system errors in practical applications, and the values within the system error range are all within the range defined by the embodiments of the present application.

[0101] In some embodiments of the present application, the electrolyte additive can comprise at least one of a first additive or a second additive, the first additive can refer to formula (1) described above, and the second additive can refer to formula (2) described above.

[0102] In formula (1) and formula (2), the fluorine-substituted alkyl group, the fluorine-substituted alkoxy group, the fluorine-substituted alkenyl group, the fluorine-substituted alkenyloxy group, the fluorine-substituted aryl group, or the fluorine-substituted aryloxy group can be linear or branched.

[0103] In formula (1) and formula (2), the fluorine-substituted alkyl group, the fluorine-substituted alkoxy group, the fluorine-substituted alkenyl group, the fluorine-substituted alkenyloxy group, the fluorine-substituted aryl group, or the fluorine-substituted aryloxy group can be linear or branched.

[0104] Specifically, the number of carbon atoms of the fluorine-substituted alkyl group and the fluorine-substituted alkoxy group is 1-20, the number of carbon atoms of the fluorine-substituted alkenyl group and the fluorine-substituted alkenyloxy group is 2-20, and the number of carbon atoms of the fluorine-substituted aryl group and the fluorine-substituted aryloxy group is 6-20.

[0105] Further, the number of carbon atoms of the fluorine-substituted alkyl group and the fluorine-substituted alkoxy group can be 1-10, specifically, the number of carbon atoms is, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. The number of carbon atoms of the fluorine-substituted alkenyl group and the fluorine-substituted alkenyloxy group can be 2-6, specifically, the number of carbon atoms is, for example, 2, 3, 4, 5, or 6. The number of carbon atoms of the fluorine-substituted aryl group and the fluorine-substituted aryloxy group can be 6-10, specifically, the number of carbon atoms is, for example, 6, 7, 8, 9, or 10. A smaller number of carbon atoms can be conducive to controlling the molecular weight of the additive, thereby facilitating better control of the viscosity of the electrolyte subsequently.

[0106] In this way, when the substituent group in the electrolyte additive provided in the embodiments of the present application is a fluorine-containing group, the interface film formed on the surface of the electrode contains a certain amount of stable fluoride, which is conducive to effectively protecting the electrode. This improves the stability of the interface film, and further improves the cycle performance and high-temperature storage performance of the battery.

[0107] In some embodiments of the present application, the substituent group in the substituted alkylene nitrile group, the substituted alkyloxy nitrile group, the substituted alkenylene nitrile group, the substituted alkenyloxy nitrile group, the substituted arylene nitrile group, and the substituted aryloxy nitrile group is independently selected from one or more of fluorine, chlorine, bromine, iodine, an alkyl group, a halogenated alkyl group, an alkoxy group, a halogenated alkoxy group, an alkenyl group, a halogenated alkenyl group, an alkenyloxy group, a halogenated alkenyloxy group, an aryl group, a halogenated aryl group, an aryloxy group, or a halogenated aryloxy group. The above-mentioned halogenation can be total halogenation or partial halogenation. The above-mentioned substituent group can be linear, branched, or cyclic.

[0108] Specifically, the halogen in the halogenated alkyl group, the halogenated alkoxy group, the halogenated alkenyl group, the halogenated alkenyloxy group, the halogenated aryl group, or the halogenated aryloxy group is independently selected from one or more of fluorine, chlorine, bromine, and iodine.

[0109] Thus, R2and R3in the embodiments of the present application can be independently selected from substituted or unsubstituted alkylene nitrile groups, substituted or unsubstituted alkyloxy nitrile groups, substituted or unsubstituted alkenylene nitrile groups, substituted or unsubstituted alkenyloxy nitrile groups, substituted or unsubstituted arylene nitrile groups, and substituted or unsubstituted aryloxy nitrile groups. The above groups include a cyano group (-CN), which can preferentially complex with transition metal ions in the high-voltage positive electrode material, inhibit the dissolution of transition metal ions, reduce the side reaction of the electrolyte with the positive electrode material, and inhibit the further oxidative decomposition of the electrolyte, thereby improving the high-voltage stability of the electrolyte. Thus, the cycle performance and high-temperature storage performance of the battery are improved.

[0110] In some embodiments of the present application, the substituted or unsubstituted alkylene nitrile groups and the substituted or unsubstituted alkyloxy nitrile groups correspond to 2-20 carbon atoms, the substituted or unsubstituted alkenylene nitrile groups and the substituted or unsubstituted alkenyloxy nitrile groups correspond to 3-20 carbon atoms, and the substituted or unsubstituted arylene nitrile groups and the substituted or unsubstituted aryloxy nitrile groups correspond to 6-20 carbon atoms.

[0111] Further, the substituted or unsubstituted alkylene nitrile groups and the substituted or unsubstituted alkyloxy nitrile groups can correspond to 2-10 carbon atoms, and specifically, the number of carbon atoms can be, for example, 2, 3, 4, 5, 6, 7, 8, 9, or 10. The substituted or unsubstituted alkenylene nitrile groups and the substituted or unsubstituted alkenyloxy nitrile groups can correspond to 3-6 carbon atoms, and specifically, the number of carbon atoms can be, for example, 3, 4, 5, or 6. The substituted or unsubstituted arylene nitrile groups and the substituted or unsubstituted aryloxy nitrile groups can correspond to 6-10 carbon atoms, and specifically, the number of carbon atoms can be, for example, 6, 7, 8, 9, or 10. A smaller number of carbon atoms can be beneficial for controlling the molecular weight of the additive, thereby facilitating better control of the viscosity of the electrolyte.

[0112] In some embodiments of the present application, the substituted or unsubstituted alkylene nitrile groups, the substituted or unsubstituted alkyloxy nitrile groups, the substituted or unsubstituted alkenylene nitrile groups, the substituted or unsubstituted alkenyloxy nitrile groups, the substituted or unsubstituted arylene nitrile groups, or the substituted or unsubstituted aryloxy nitrile groups can be linear or branched.

[0113] In some embodiments of the present application, the electrolyte additive includes at least one of the structures represented by the following formula (3) to formula (10):

[0114] Therefore, the electrolyte additive in the embodiments of the present application includes at least one of the above structures, which can enable the electrolyte to form a solid electrolyte interface film with high stability on the positive and negative electrode surfaces. Meanwhile, when a high-capacity (such as silicon) negative electrode material is used in the negative electrode, the solid electrolyte interface film has stronger resistance to the expansion of the negative electrode material, and can also improve the compatibility with the negative electrode material. Thus, the cycle performance and high-temperature storage performance of the battery are improved.

[0115] In some embodiments of the present application, the electrolyte additive further includes other additives, which include one or more of a film-forming additive, an overcharge-preventing additive, a wetting agent, a flame retardant, and the like. The film-forming additive can include, but is not limited to, one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), 1,4-butane sultone (BS), vinyl sulfate (DTD), ethylene sulfite (ES), methane disulfonate (MMDS), dimethyl sulfate, dimethyl sulfite (DS), diethyl sulfite, diethyl sulfate, 4-methyl ethylene sulfite, tris(trimethylsilyl)borate, and the like. The overcharge-preventing additive can include one or more of biphenyl (BP), succinonitrile (SN), glutaronitrile, adiponitrile (ADN), 1,2-bis(2-cyanoethoxy)ethane (DENE), 1,3,6-hexanetricarbonitrile (HTCN), and the like, which generally also have the effect of improving the high-voltage performance of the battery. The wetting agent can improve the wettability of the electrolyte of the battery to the electrode sheet, and exemplary wetting agents can include fluorobenzene and the like. Exemplary flame retardants can include one or more of phosphate ester substances (such as trimethyl phosphate, triethyl phosphate, tris(trimethylsilyl)phosphate), phosphite ester substances (such as trimethyl phosphite, triethyl phosphite), cyclotriphosphazene substances (such as (ethoxy) pentafluorocyclotriphosphazene, hexafluorocyclotriphosphazene).

[0116] In the embodiments of the present application, the electrolyte additive represented by the above formula (1) or formula (2) can be prepared by different methods, and the specific preparation method is not limited.

[0117] In some embodiments of the present application, the electrolyte additive can be prepared in the following manner: the method includes:

[0118] mixing the acid-binding agent with the solvent to obtain a first solution;

[0119] A first reaction substrate is provided, the first reaction substrate including at least one of a substituted or unsubstituted alkylidene nitrile group compound, a substituted or unsubstituted alkyleneoxy nitrile group compound, a substituted or unsubstituted alkenylidene nitrile group compound, a substituted or unsubstituted alkenyloxy nitrile group compound, a substituted or unsubstituted arylidene nitrile group compound, and a substituted or unsubstituted aryloxy nitrile group compound.

[0120] A second reaction substrate is provided, the second reaction substrate including a fluorine-containing substituent group compound.

[0121] The first reaction substrate, the second reaction substrate, and the first solution are reacted to produce an electrolyte additive provided by the embodiments of the present application.

[0122] In some embodiments of the present application, the acid-binding agent includes at least one of an inorganic base and an organic base compound, and specifically includes, but is not limited to, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium phosphate, potassium phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, triethylamine, N,N-dimethylcyclohexylamine, pyridine, pyrimidine, quinoline, and the like. The solvent includes, but is not limited to, one or more of ethane, cyclohexane, dichloromethane, trichloromethane, diethyl ether, petroleum ether, benzene, toluene, chlorobenzene, fluorobenzene, acetone, acetonitrile, methanol, ethanol, tetrahydrofuran, nitromethane, dimethyl sulfoxide, N,N-dimethylformamide, ethyl acetate, and butyl acetate. It should be noted that the type and content of the solvent are not specifically limited in the embodiments of the present application.

[0123] In some embodiments of the present application, the first reaction substrate can include, but is not limited to, at least one of imidoyl diacetonitrile, imidoyl (1-acetonitrile)-2-propionitrile, and imidoyl (1-acetonitrile)-p-toluenemethylene cyanide. The second reaction substrate can include, but is not limited to, at least one of trifluoromethyl sulfonic anhydride, trifluoroethyl sulfonic anhydride, fluorosulfonic anhydride, and fluorosulfinic anhydride. It should be noted that the type and content of the first reaction substrate and the second reaction substrate are not specifically limited in the embodiments of the present application.

[0124] For example, 40 mmol of triethylamine (4.048 g) is weighed and mixed with 50 mL of dichloromethane to obtain a first solution, which is added to a 250 mL round-bottom flask. Then, 40 mmol of imidoyl diacetonitrile (4.138 g) is weighed and mixed with 50 mL of dichloromethane and added to the round-bottom flask, and a magnetic stirrer is placed in the round-bottom flask. Then, 40 mmol of trifluoromethyl sulfonic anhydride (11.285 g) is weighed and mixed with 25 mL of dichloromethane and added to a 50 mL constant-pressure dropping funnel, which is combined with the round-bottom flask, and the system is closed after nitrogen is introduced into the system.

[0125] Then, the system is placed in an atmosphere of -15 degrees Celsius for a period of time to wait for the system to cool down. After the temperature of the system is stable, triflic anhydride and dichloromethane mixture (1 drop / second) is added at a constant speed. After the titration is completed, the system is transferred to a room temperature environment and stirred overnight. Then, the next day, the product is transferred to a 250 mL separatory funnel, and 50 mL of ultrapure water is added for quenching. After stirring and standing, the upper liquid phase is separated from the system, and pH test paper is used for acidity test. The above steps (quenching process, separation of the upper liquid phase, and acidity test) are repeated multiple times until the upper liquid phase is not acidic.

[0126] Then, 50 mL of saturated brine is added to the system and stirred and allowed to stand. After the layers are separated, the lower organic phase is removed, and an appropriate amount of sodium sulfate is added to the organic phase for drying and water removal. Then, the organic phase after water removal is added to a 250 mL chicken heart bottle for rotary evaporation under reduced pressure to remove dichloromethane. Then, after removing the dichloromethane, the crude product is obtained, and the electrolyte additive (see formula 3 above) is obtained after recrystallization of the crude product (conditions: 65 degrees Celsius, tetrahydrofuran: n-hexane ratio equal to 1:5).

[0127] The application also provides a preparation method of an electrolyte, which comprises: preparing the above-mentioned required organic solvent in an inert or closed environment, and then dissolving the fully dried electrolyte salt in the organic solvent and stirring and mixing to form a uniform solution. Then, the electrolyte additive is added to the uniform solution, and the electrolyte is prepared after mixing uniformly.

[0128] It should be noted that the mass percentage of the above-mentioned organic solvent, electrolyte salt, electrolyte additive in the electrolyte, and the mass ratio between the organic solvent and the electrolyte additive are allowed to have a certain measurement error due to the formation of the interface film after the actual battery formation, distribution or circulation, and the values within the error range can be understood as the range defined in the application embodiment, or the value range of the mass percentage of the electrolyte solvent and the additive after the formation, distribution or circulation test is still within the above-mentioned range, which can be understood as the range defined in the application embodiment.

[0129] It can be understood that the calculated value of the above-mentioned numerical ratio can have a certain measurement system error in the actual test operation, and the values within the system error range can be understood as the range defined in the application embodiment.

[0130] The following describes the above-mentioned electrolyte additive, lithium secondary battery containing the electrolyte additive, and lithium secondary battery prepared by the electrolyte prepared in the examples, and tests the performance of various lithium secondary batteries.

[0131] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive A (see formula 3 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the above solution respectively, and mixed uniformly to obtain a lithium secondary battery electrolyte (Example 1). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of electrolyte additive A, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0132] The lithium secondary battery is prepared by the following method:

[0133] The mass percentage of 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobaltate (LiCoO2) is weighed and added to N-methyl pyrrolidone (NMP) in turn, and then fully stirred and mixed uniformly. The slurry is coated on an aluminum foil current collector, dried, cold pressed and cut to obtain a positive electrode sheet.

[0134] The mass percentage of 1.5% CMC, 2.5% SBR, 1% carbon nanotube and 95% graphite is weighed and added to deionized water in turn, and then fully stirred and mixed uniformly. The slurry is coated on a copper foil current collector, dried, cold pressed and cut to obtain a negative electrode sheet.

[0135] The above prepared positive electrode sheet, negative electrode sheet and PE separator are made into an electric core, packaged with a polymer, filled with the lithium secondary battery electrolyte prepared in Example 1 above, and then processed by formation to obtain a 4Ah soft package lithium secondary battery.

[0136] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution by stirring. Then, electrolyte additive D (formula 6 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the above solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 2). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of electrolyte additives D, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0137] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 2, and the preparation method is the same as that in Example 1.

[0138] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution by stirring. Then, electrolyte additive F (formula 8 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the above solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 3). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of electrolyte additives F, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0139] A lithium secondary battery is prepared using the following preparation method: 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobaltate (LiCoO2) are weighed and added to N-methyl pyrrolidone (NMP) in sequence, and then fully stirred and mixed uniformly. The slurry is coated on an aluminum foil current collector, dried, cold-pressed and cut to prepare a positive electrode sheet.

[0140] 1.5% CMC, 2.5% SBR, 1% carbon nanotube and 95% silicon carbon are weighed and added to deionized water in sequence, and then fully stirred and mixed uniformly. The slurry is coated on a copper foil current collector, dried, cold-pressed and cut to prepare a negative electrode sheet.

[0141] The positive electrode sheet, the negative electrode sheet and the PE separator prepared above are made into an electric core, a polymer package is adopted, the lithium secondary battery electrolyte prepared in Example 3 is filled, and after a formation process, a soft package lithium secondary battery of 4 Ah is prepared.

[0142] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive F (Formula 8) is added to the solution, and the mixture is stirred to obtain a lithium secondary battery electrolyte (Example 4). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, and the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 18%, 12.5% and 30%, respectively. The mass percentage of F, FEC and PS in the electrolyte is 4%, 5% and 3%, respectively.

[0143] The lithium secondary battery electrolyte prepared in Example 4 is used to prepare a lithium secondary battery, and the preparation method is the same as that of Example 3.

[0144] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive G (Formula 9) is added to the solution, and the mixture is stirred to obtain a lithium secondary battery electrolyte (Example 5). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, and the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30%, respectively. The mass percentage of G, FEC and PS in the electrolyte is 2%, 5% and 3%, respectively.

[0145] The lithium secondary battery electrolyte prepared in Example 5 is used to prepare a lithium secondary battery, and the preparation method is the same as that of Example 3.

[0146] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then electrolyte additive H (formula 10 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 6). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of H, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0147] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 6, and the preparation method is the same as that in Example 3.

[0148] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then electrolyte additive A (formula 3 above), electrolyte additive F (formula 8 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 7). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 18%, 12.5% and 30% respectively, and the mass percentage of A, F, FEC and PS in the electrolyte is 2%, 2%, 5% and 3% respectively.

[0149] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 7, and the preparation method is the same as that in Example 3.

[0150] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then electrolyte additive G (formula 9 above), electrolyte additive H (formula 10 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 8). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of G, H, FEC and PS in the electrolyte is 1%, 1%, 5% and 3% respectively.

[0151] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 8, and the preparation method is the same as that in Example 3.

[0152] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then electrolyte additive G (formula 9 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 9). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 20%, 10%, 30% and 19% respectively, and the mass percentage of G, FEC and PS in the electrolyte is 0.5%, 5% and 3% respectively.

[0153] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 9, and the preparation method is the same as that in Example 3.

[0154] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive G (formula 9 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to obtain a lithium secondary battery electrolyte (Example 10). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 5%, 24.5%, 5% and 40% respectively, and the mass percentage of G, FEC and PS in the electrolyte is 5%, 5% and 3% respectively.

[0155] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 10, and the preparation method is the same as that in Example 3.

[0156] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive G (formula 9 above), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to obtain a lithium secondary battery electrolyte (Example 10). In this example, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 5%, 24.5%, 5% and 40% respectively, and the mass percentage of G, FEC and PS in the electrolyte is 5%, 5% and 3% respectively.

[0157] A lithium secondary battery is prepared using the following preparation method: 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobaltate (LiCoO2) are weighed and added to N-methyl pyrrolidone (NMP) in sequence, and then fully stirred and mixed uniformly. The slurry is coated on an aluminum foil current collector, dried, cold-pressed and cut to obtain a positive electrode sheet.

[0158] 1.5% CMC, 2.5% SBR, 1% carbon nanotube and 95% silicon carbon are weighed and added to deionized water in sequence, and then fully stirred and mixed uniformly. The slurry is coated on a copper foil current collector, dried, cold-pressed and cut to obtain a negative electrode sheet.

[0159] The positive electrode sheet, the negative electrode sheet and the PE separator prepared above are made into an electric core, a polymer package is adopted, the lithium secondary battery electrolyte prepared in Example 11 is filled, and after a process such as formation, a soft package lithium secondary battery of 4 Ah is prepared.

[0160] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro oxalate borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive G (formula 9) above, fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 12). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 5%, 23.5%, 5% and 40% respectively, and the mass percentage of G, FEC and PS in the electrolyte is 6%, 5% and 3% respectively.

[0161] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 12, and the preparation method is the same as that in Example 11.

[0162] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro oxalate borate (LiDFOB) are dissolved in the organic solvent to form a uniform solution. Then, electrolyte additive F (formula 8) above, vinylene carbonate (VC) and vinyl sulfate (DTD) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Example 13). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of F, VC and DTD in the electrolyte is 2%, 5% and 3% respectively.

[0163] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Example 13, and the preparation method is the same as that in Example 11.

[0164] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro oxalate borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then butanedinitrile (SN), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to obtain a lithium secondary battery electrolyte (Comparative Example 1). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of SN, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0165] The structural formula of butanedinitrile (SN) is:

[0166] The lithium secondary battery is prepared by the following method: 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobaltate (LiCoO2) are weighed and added to N-methyl pyrrolidone (NMP) in sequence, and then stirred and mixed uniformly. The slurry is coated on an aluminum foil current collector, dried, cold-pressed, and cut to obtain a positive electrode sheet.

[0167] 1.5% CMC, 2.5% SBR, 1% carbon nanotube and 95% graphite are weighed and added to deionized water in sequence, and then stirred and mixed uniformly. The slurry is coated on a copper foil current collector, dried, cold-pressed, and cut to obtain a negative electrode sheet.

[0168] The above-prepared positive electrode sheet, negative electrode sheet and PE separator are made into an electric core, and a polymer package is used to fill the lithium secondary battery electrolyte prepared in Comparative Example 1. After the formation process, a 4Ah soft-pack lithium secondary battery is prepared.

[0169] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, N,N-dimethyl-trifluoromethyl sulfonamide (I), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 2). In the electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of N,N-dimethyl-trifluoromethyl sulfonamide (I), FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0170] The structural formula of N,N-dimethyl-trifluoromethyl sulfonamide (I) is as follows:

[0171] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 2, and the preparation method is the same as that in Comparative Example 1.

[0172] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, N,N-dimethyl-trifluoromethyl sulfonamide (I), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 2). In the electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of N,N-dimethyl-trifluoromethyl sulfonamide (I), FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0173] The structural formula of N,N-dimethyl-trifluoromethyl sulfonamide (I) is as follows:

[0174] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 3, and the preparation method is the same as that in Comparative Example 1.

[0175] In some embodiments of the present application, in an argon-filled glove box, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then 1,2-bis(2-cyanoethoxy)ethane (DENE), fluoroethylene carbonate (FEC) and 1,3-propanesultone (PS) are added to the solution respectively, and mixed uniformly to obtain a lithium secondary battery electrolyte (Comparative Example 4). The concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of DENE, FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0176] The structural formula of 1,2-bis(2-cyanoethoxy)ethane (DENE) is:

[0177] The lithium secondary battery is prepared by the following method: 2% polyvinylidene fluoride (PVDF), 2% conductive agent super P and 96% lithium cobaltate (LiCoO2) are weighed and added to N-methyl pyrrolidone (NMP) in sequence, and then stirred and mixed uniformly. The slurry is coated on an aluminum foil current collector, dried, cold-pressed, and cut to obtain a positive electrode sheet.

[0178] 1.5% CMC, 2.5% SBR, 1% carbon nanotube and 95% silicon carbon are weighed and added to deionized water in sequence, and then stirred and mixed uniformly. The slurry is coated on a copper foil current collector, dried, cold-pressed, and cut to obtain a negative electrode sheet.

[0179] The above prepared positive electrode sheet, negative electrode sheet and PE separator are made into a battery cell, and the lithium secondary battery electrolyte prepared in Comparative Example 1 is filled in the battery cell, and then a 4Ah soft package lithium secondary battery is prepared after formation and other processes.

[0180] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, N,N-dimethyl-fluorosulfamide (J), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 5). In the electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of N,N-dimethyl-fluorosulfamide (J), FEC and PS in the electrolyte is 2%, 5% and 3% respectively.

[0181] The structural formula of N,N-dimethyl-fluorosulfamide (J) is as follows:

[0182] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 5, and the preparation method is the same as that of Comparative Example 4.

[0183] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, N,N-dimethyl-fluorosulfamide (J), 1,2-bis(2-cyanoethoxy)ethane (DENE), fluoroethylene carbonate (FEC) and 1,3-propane sultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 6). In the electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 18%, 12.5% and 30% respectively, and the mass percentage of N,N-dimethyl-fluorosulfamide (J), DENE, FEC and PS in the electrolyte is 2%, 2%, 5% and 3% respectively.

[0184] The structural formula of 1,2-bis(2-cyanoethoxy)ethane (DENE) is as follows:

[0185] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 6, and the preparation method is the same as that of Comparative Example 4.

[0186] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, succinonitrile (SN), 1,2-bis(2-cyanoethoxy)ethane (DENE), fluoroethylene carbonate (FEC) and 1,3-propanesultone (PS) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 7). In the lithium secondary battery electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 18%, 12.5% and 30% respectively, and the mass percentage of SN, DENE, FEC and PS in the electrolyte is 2%, 2%, 5% and 3% respectively.

[0187] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 7, and the preparation method is the same as that in Comparative Example 4.

[0188] In some embodiments of the present application, ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) and propyl propionate (PP) are mixed to form an organic solvent in an argon-filled glove box, and then fully dried lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB) are dissolved in the organic solvent, and stirred to form a uniform solution. Then, N,N-dimethyl-fluorosulfamide (J), vinylene carbonate (VC) and vinyl sulfate (DTD) are added to the solution respectively, and mixed uniformly to prepare a lithium secondary battery electrolyte (Comparative Example 8). In the lithium secondary battery electrolyte, the concentration of LiPF6 is 1.0 mol / L, the concentration of LiDFOB is 0.05 mol / L, the mass percentage of EC, DEC, PC and PP in the electrolyte is 15%, 20%, 12.5% and 30% respectively, and the mass percentage of N,N-dimethyl-fluorosulfamide (J), VC and DTD in the electrolyte is 2%, 5% and 3% respectively.

[0189] The structural formula of N,N-dimethyl-fluorosulfamide (J) is as follows:

[0190] A lithium secondary battery is prepared using the lithium secondary battery electrolyte prepared in Comparative Example 8, and the preparation method is the same as that in Comparative Example 4.

[0191] The lithium secondary batteries prepared in Examples 1-13 and Comparative Examples 1-8 are respectively subjected to performance tests. See the following test methods:

[0192] 25℃ cycle performance test: the lithium secondary batteries prepared by examples 1-13 and comparative examples 1-8 were placed in an oven with a constant temperature of 25±3℃, and charged at a current of 1.0C to 4.6V, and then charged at a constant voltage until the current decreased to 0.025C, and then rested for 5min. Then discharged at a current of 1.0C to 3.0V, and so on for 300 cycles, and the discharge capacity of the first cycle and the 300th cycle were recorded, and the capacity retention rate was calculated according to the following formula, and the test results are shown in Table 1.

[0193] wherein the capacity retention rate (%) = the discharge capacity of the 300th cycle / the discharge capacity of the first cycle x 100%.

[0194] 60℃ storage for 7 days performance test: under room temperature conditions (25℃±3℃), the lithium secondary batteries assembled by examples 1-13 and comparative examples 1-8 were charged at a constant current of 0.2C to 4.6V, and then charged at a constant voltage until the current was less than or equal to 0.025C, and stopped charging. Rest for 5min between charging and discharging, and then discharge at a constant current of 0.5C to a cut-off voltage of 3.0V, and record the capacity as the initial capacity. The battery was again charged according to the above charging method, and then placed in a 60℃ constant temperature oven for 7 days, and then placed at room temperature for 2 hours before discharging at a constant current of 0.5C to a cut-off voltage of 3.0V, and recorded as the remaining capacity, and the storage capacity retention rate was calculated according to the following formula, and the test results are shown in Table 1.

[0195] wherein the capacity retention rate (%) = the discharge capacity of the 300th cycle / the discharge capacity of the first cycle x 100%.

[0196] Table 1: 25℃ cycle and 60℃ storage test results of examples 1-13 and comparative examples 1-8

[0197] From the test results of Table 1 and Figure 2, it can be seen that the 25℃ cycle capacity retention rate of the lithium secondary batteries in examples 1-2 of the present application is 86.1%-86.3%, and the 60℃ storage capacity retention rate is 91.3%-91.8%. Both are higher than the 25℃ cycle capacity retention rate (81.4%-83.4%) and the 60℃ storage capacity retention rate (85.1%-86.6%) of the lithium secondary batteries in comparative examples 1-3. Therefore, it can be shown that the use of the electrolyte additive provided in the present application can significantly improve the cycle performance and high temperature storage performance of the battery.

[0198] Specifically, for Example 1, one end of the structure of electrolyte additive A is a trifluoromethyl substituent group, which can form a stable interface film containing lithium fluoride, lithium nitride and sulfide compounds on the surface of the positive material LCO and the graphite negative electrode, can reduce the side reaction of electrolyte with positive and negative electrodes, improve the battery coulomb efficiency and cycle performance. At the same time, the structure of the electrolyte additive A includes a nitrile group (-CN), which can complex with Co ions in the positive material LCO, inhibit the dissolution of transition metal ions, inhibit the further oxidation and decomposition of the electrolyte, improve the high voltage stability of the electrolyte, and thus improve the high temperature storage performance and cycle performance of the battery.

[0199] While butanedinitrile (SN) used in Comparative Example 1 can complex with Co ions in the positive material LCO, it cannot form a stable and higher interface film. N,N-dimethyl-trifluoromethylsulfonamide (I) used in Comparative Example 2 can form an interface film on the surface of the positive and negative electrodes, but it does not contain a nitrile group, and cannot complex with Co ions in the positive material LCO, so it cannot effectively inhibit the dissolution of transition metal ions and reduce the stability of the interface film. The combination of N,N-dimethyl-trifluoromethylsulfonamide and butanedinitrile used in Comparative Example 3 will cause an increase in battery impedance by using a combination of multiple additives. At the same time, there will be competitive chemical / electrochemical reactions between different additives, which will reduce the stability of the interface film. Therefore, the high temperature storage performance and cycle performance of the batteries corresponding to Comparative Examples 1-3 are poor.

[0200] From the test results of Table 1 and Figure 3, it can be seen that the 25°C cycle capacity retention rate of the lithium secondary batteries in Examples 3-10 of the present application is 84.1%-85.9%, and the 60°C storage capacity retention rate is 87.2%-91.1%. Both are higher than the 25°C cycle capacity retention rate (79.9%-82.1%) and the 60°C storage capacity retention rate (81.9%-84.7%) of the lithium secondary batteries in Comparative Examples 4-7. This shows that the use of the electrolyte additive of the present application can significantly improve the cycle performance and high temperature storage performance of the battery.

[0201] Specifically, for Example 3, one end of the structure of electrolyte additive F is a fluorine substituent group, which can form a stable interface film containing lithium fluoride, lithium nitride and sulfide compounds on the surface of the positive material LCO and the silicon-carbon negative electrode, can reduce the side reaction of electrolyte with positive and negative electrodes, improve the battery coulomb efficiency and cycle performance. At the same time, the structure of the electrolyte additive F includes a nitrile group, which can complex with Co ions in the positive material LCO, inhibit the dissolution of transition metal ions, inhibit the further oxidation and decomposition of the electrolyte, improve the high voltage stability of the electrolyte, and thus improve the high temperature storage performance and cycle performance of the battery.

[0202] While the use of 1,2-bis(2-cyanoethoxy)ethane (DENE) in Comparative Example 4 can complex with Co ions in the positive electrode material LCO, it cannot form a stable and high interface film. While the use of N,N-dimethyl-fluorosulfamide (J) in Comparative Example 5 can form an interface film on the positive and negative electrode surfaces, it does not contain a nitrile group and cannot complex with Co ions in the positive electrode material LCO, so it cannot effectively inhibit the elution of transition metal ions and reduce the stability of the interface film. Thus, the high-temperature storage performance and cycle performance of the batteries corresponding to Comparative Examples 4 and 5 are poor.

[0203] As can be known from the test results in Table 1, the 25°C cycle capacity retention rate of the lithium secondary battery in Example 4 of the present application is 85.6%, and the 60°C storage capacity retention rate is 90.8%. Both are higher than the 25°C cycle capacity retention rate (82.1%) and the 60°C storage capacity retention rate (84.2%) of the lithium secondary battery in Comparative Example 6.

[0204] Example 4 is the same as Example 3 described above. The structure of the electrolyte additive F has a fluorine substituent group at one end and a cyano group at the other end. It can improve the high-voltage stability of the electrolyte and form a high-stability interface film on the positive and negative electrode surfaces. Thus, the high-temperature storage performance and cycle performance of the battery are improved. While the use of N,N-dimethyl-fluorosulfamide and 1,2-bis(2-cyanoethoxy)ethane in Comparative Example 6 causes an increase in battery impedance by using multiple additives in combination. At the same time, there are also competitive chemical / electrochemical reactions between different additives, which reduces the stability of the interface film. Thus, the high-temperature storage performance and cycle performance of the battery corresponding to Comparative Example 6 are poor.

[0205] As can be known from the test results in Table 1, the 25°C cycle capacity retention rate of the lithium secondary battery in Example 7 of the present application is 85.9%, and the 60°C storage capacity retention rate is 91.1%. Both are higher than the 25°C cycle capacity retention rate (81.8%) and the 60°C storage capacity retention rate (84.7%) of the lithium secondary battery in Comparative Example 7.

[0206] Specifically, by combining electrolyte additive A and electrolyte additive F in Example 7, the two do not undergo chemical reactions and do not increase the impedance of the battery, while improving the high-voltage stability of the electrolyte and forming a high-stability interface film on the positive and negative electrode surfaces. Thus, the high-temperature storage performance and cycle performance of the battery are improved.

[0207] While the use of succinonitrile (SN) and 1,2-bis(2-cyanoethoxy)ethane in Comparative Example 7 can complex with Co ions in the positive electrode material LCO and inhibit the elution of transition metal ions, it cannot form a high-stability solid electrolyte interface film.

[0208] From the test results of Table 1, it can be seen that the lithium secondary battery in Example 9 has a 25°C cycle capacity retention rate of 84.1% and a 60°C storage capacity retention rate of 87.2%. Both are higher than the 25°C cycle capacity retention rate (83.6%) and the 60°C storage capacity retention rate (86.8%) of the lithium secondary battery in Example 11.

[0209] Specifically, the mass ratio of the electrolyte additive G to the cyclic carbonate (EC+PC) in Example 9 is 0.01:1, which meets the appropriate range of 0.01:1 to 0.5:1, avoiding the reaction between the electrolyte and the positive and negative electrodes to produce a large amount of gas. At the same time, it can act with complex Co ions, effectively inhibit the dissolution of transition metal ions, and form a high-stability and high-conductivity interface film at the positive and negative electrodes. Thus, the high-temperature storage performance and cycle performance of the battery are improved.

[0210] From the test results of Table 1, it can be seen that the lithium secondary battery in Example 10 has a 25°C cycle capacity retention rate of 84.8% and a 60°C storage capacity retention rate of 88.7%. Both are higher than the 25°C cycle capacity retention rate (83.9%) and the 60°C storage capacity retention rate (87.1%) of the lithium secondary battery in Example 12.

[0211] Specifically, the mass ratio of the electrolyte additive G to the cyclic carbonate (EC+PC) in Example 10 is 0.5:1, which meets the appropriate range of 0.01:1 to 0.5:1. This makes the content of cyclic carbonate in the electrolyte appropriate, preventing the electrolyte viscosity from being too large. At the same time, it is also beneficial to the electrolyte additive participating in the formation of a high-stability interface film on the electrode surface. Thus, the cycle performance and high-temperature storage performance of the battery are improved.

[0212] From the test results of Table 1, it can be seen that the lithium secondary battery in Example 13 has a 25°C cycle capacity retention rate of 84.9% and a 60°C storage capacity retention rate of 89.5%. Both are higher than the 25°C cycle capacity retention rate (78.8%) and the 60°C storage capacity retention rate (81.1%) of the lithium secondary battery in Comparative Example 8.

[0213] Specifically, the structure of the electrolyte additive F in Example 13 has a fluorine-substituted group at one end, which can form a stable interface film on the surface of the positive electrode material LCO and the silicon-carbon negative electrode, reduce the side reaction of the electrolyte with the positive and negative electrodes, and improve the battery coulomb efficiency and cycle performance. At the same time, the structure of the electrolyte additive F includes a nitrile group, which can complex with Co ions in the positive electrode material LCO, inhibit the dissolution of transition metal ions, inhibit the further oxidation and decomposition of the electrolyte, improve the high-voltage stability of the electrolyte, and thus improve the high-temperature storage performance and cycle performance of the battery. However, the use of N,N-dimethyl-fluorosulfamide (J) in Comparative Example 8 can form an interface film on the surface of the positive and negative electrodes, but it does not contain a nitrile group and cannot complex with Co ions in the positive electrode material LCO, so it cannot effectively inhibit the dissolution of transition metal ions and reduce the stability of the interface film.

[0214] From the test results in Table 1, it can be seen that Examples 3 and 13 are used as examples. The electrolyte additive used in Example 3 is electrolyte additive F, fluoroethylene carbonate (FEC), and 1,3-propanesulfonic acid lactone (PS). The electrolyte additive used in Example 13 is electrolyte additive F, vinylene carbonate (VC), and vinyl sulfate (DTD). The lithium secondary batteries corresponding to Examples 3 and 13 both have high 25°C cycle capacity retention rate and 60°C storage capacity retention rate. That is, the first additive and / or the second additive proposed in the embodiments of the present application can be combined with other types of electrolyte additives to improve the high-temperature storage performance and cycle performance of the battery.

[0215] It should be noted that the embodiments of the present application do not specifically limit the specific type and content of the electrolyte additive combined with the first additive and / or the second additive.

[0216] The embodiments of the present application also provide a secondary battery, which includes a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the above-mentioned electrolyte, the electrolyte being filled between the positive electrode and the negative electrode.

[0217] In some examples, the secondary battery can include a lithium secondary battery, a potassium secondary battery, a sodium secondary battery, a magnesium secondary battery, a zinc secondary battery, or an aluminum secondary battery.

[0218] The embodiments of the present application also provide an electronic device, which includes a housing, and electronic components and a battery received in the housing, the battery powering the electronic components, and the battery including the above-mentioned secondary battery.

[0219] Referring to FIG. 4, the electronic device may, for example, be a mobile phone 1100, and may also include a smart screen, a tablet computer, a personal computer (PC), a personal digital assistant (PDA), a smart watch, a mobile power supply, a netbook, a wearable device, an augmented reality (AR) device, a virtual reality (VR) device, a vehicle-mounted device, an energy storage device, a base station, a vehicle, and the like. The specific form of the electronic device is not particularly limited in the embodiments of the present application.

[0220] In some schemes, multiple embodiments of the present application can be combined, and the combined scheme can be implemented. Optionally, some operations in the flow of each method embodiment are optionally combined, and / or the order of some operations is optionally changed. In addition, the execution order between the steps of each flow is only exemplary and does not constitute a limitation on the execution order between the steps, and other execution orders between the steps can also be used. It is not intended to indicate the only execution order in which these operations can be performed.

[0221] A person of ordinary skill in the art will think of various ways to reorder the operations described in the embodiments of the present application. In addition, it should be pointed out that the process details involved in some embodiments of the present application are also applicable in a similar manner to other embodiments, or different embodiments can be combined for use.

[0222] In addition, some steps in the method embodiments can be equivalently replaced by other possible steps. Alternatively, some steps in the method embodiments can be optional and can be deleted in some use scenarios. Alternatively, other possible steps can be added to the method embodiments.

[0223] In addition, each method embodiment can be implemented individually or in combination.

[0224] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or replacements within the technical scope disclosed in the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. An electrolyte additive characterized in that, The electrolyte additive comprises a first additive and / or a second additive; The first additive has a general structure of formula (1) as follows: R1-S(=O) x -N(-R3)-R2 Formula (1); The second additive has a general structure of formula (2) as follows: R1-S(=O) x -N(-R3)-S(=O) y -R4 Formula (2); R1 and R4 are independently selected from one of a fluorine atom or a fluorine-containing substituent group; R2 and R3 are independently selected from one of a substituted or unsubstituted alkylene nitrile group, a substituted or unsubstituted alkyloxy nitrile group, a substituted or unsubstituted alkenylene nitrile group, a substituted or unsubstituted alkenyloxy nitrile group, a substituted or unsubstituted arylene nitrile group, or a substituted or unsubstituted aryloxy nitrile group; x is 1 or 2, and y is 1 or 2.

2. The electrolyte additive according to claim 1, characterized in that, The fluorine-containing substituent group comprises a fluorine-substituted alkyl group, a fluorine-substituted alkoxy group, a fluorine-substituted alkenyl group, a fluorine-substituted alkenyloxy group, a fluorine-substituted aryl group, or a fluorine-substituted aryloxy group.

3. The electrolyte additive according to claim 2, characterized in that The fluorine-substituted alkyl group and the fluorine-substituted alkoxy group correspond to a carbon atom number of 1-20, the fluorine-substituted alkenyl group and the fluorine-substituted alkenyloxy group correspond to a carbon atom number of 2-20, the fluorine-substituted aryl group, the fluorine-substituted aryloxy group, the substituted or unsubstituted arylene nitrile group, and the substituted or unsubstituted aryloxy nitrile group correspond to a carbon atom number of 6-20, the substituted or unsubstituted alkylene nitrile group and the substituted or unsubstituted alkyloxy nitrile group correspond to a carbon atom number of 2-20, and the substituted or unsubstituted alkenylene nitrile group and the substituted or unsubstituted alkenyloxy nitrile group correspond to a carbon atom number of 3-20.

4. The electrolyte additive according to any one of claims 1 to 3, characterized in that The substituent group in the substituted alkylene nitrile group, the substituted alkyloxy nitrile group, the substituted alkenylene nitrile group, the substituted alkenyloxy nitrile group, the substituted arylene nitrile group, and the substituted aryloxy nitrile group is independently selected from one or more of fluorine, chlorine, bromine, iodine, an alkyl group, a halogenated alkyl group, an alkoxy group, a halogenated alkoxy group, an alkenyl group, a halogenated alkenyl group, an alkenyloxy group, a halogenated alkenyloxy group, an aryl group, a halogenated aryl group, an aryloxy group, or a halogenated aryloxy group.

5. The electrolyte additive according to claim 4, characterized in that The halogen in the halogenated alkyl group, the halogenated alkoxy group, the halogenated alkenyl group, the halogenated alkenyloxy group, the halogenated aryl group, or the halogenated aryloxy group is independently selected from one or more of fluorine, chlorine, bromine, and iodine.

6. The electrolyte additive according to any one of claims 1 to 5, characterized in that, The electrolyte additive includes at least one of structures represented by the following formula (3) to formula (10):

7. A method of preparing an electrolyte additive, characterized by, The method comprises: mixing the acid-binding agent with a solvent to obtain a first solution; providing a first reaction substrate, wherein the first reaction substrate comprises at least one of a substituted or unsubstituted alkylene nitrile group compound, a substituted or unsubstituted alkyloxy nitrile group compound, a substituted or unsubstituted alkenylene nitrile group compound, a substituted or unsubstituted alkenyloxy nitrile group compound, a substituted or unsubstituted arylene nitrile group compound, or a substituted or unsubstituted aryloxy nitrile group compound; providing a second reaction substrate, wherein the second reaction substrate comprises a fluorine-containing substituent group compound; and mixing the first solution and the second reaction substrate to obtain a second solution. reacting the first reaction substrate, the second reaction substrate and the first solution to produce the electrolyte additive of any one of claims 1-6.

8. A battery electrolyte, characterized by, comprising: an electrolyte salt, an organic solvent and the electrolyte additive of any one of claims 1-6.

9. The electrolyte of claim 8, wherein, The mass percentage content of the electrolyte additive in the electrolyte is 0.05%-10%.

10. The electrolyte according to claim 8 or 9, characterized in that, The mass percentage content of the electrolyte additive in the electrolyte is 0.05%-5%.

11. The electrolyte according to any one of claims 8 to 10, characterized in that, The molar concentration of the electrolyte salt in the electrolyte is 0.01mol / L-5.0mol / L.

12. The electrolyte according to any one of claims 8 to 11, characterized in that, The organic solvent comprises one or more of a carbonate solvent, a carboxylic acid ester solvent or an ether solvent, the carbonate solvent comprises one or more of a cyclic carbonate solvent or a linear carbonate solvent.

13. The electrolyte of claim 12, wherein, The mass percentage content of the cyclic carbonate solvent in the electrolyte is 10%-50%.

14. The electrolyte according to claim 12 or 13, characterized in that, The mass percentage content of the cyclic carbonate solvent in the electrolyte is 20%-40%.

15. The electrolyte according to any one of claims 12 to 14, characterized in that, The mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.01:1 to 0.5:

1.

16. The electrolyte according to any one of claims 12 to 15, characterized in that, The mass ratio of the electrolyte additive to the cyclic carbonate solvent is 0.02:1 to 0.3:

1.

17. The electrolyte according to any one of claims 8 to 16, characterized in that, The electrolyte salt comprises one or more of a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a zinc salt or an aluminum salt.

18. The electrolyte according to any one of claims 8 to 17, characterized in that, The electrolyte salt includes one or more of MCI04, MBF4, MPF6, MAsF6, MPO2F2, MCF3SO3, MTDI, MB(C204)2, MBF2C204, M[(CF3SO2)2N], M[(FSO2)2N], or M[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N] wherein M is lithium, sodium, or potassium, and m and n are natural numbers.

19. The electrolyte according to any one of claims 8-18, characterized in that, The electrolyte additive further comprises one or more of a film-forming additive, an overcharge-preventing additive, a wetting agent, a flame retardant.

20. A secondary battery characterized by comprising: comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and the electrolyte of any one of claims 8-19, the electrolyte being filled between the positive electrode and the negative electrode.

21. An electronic device, comprising: The electronic device comprises a housing, and electronic components and a battery accommodated in the housing, the battery powering the electronic components, the battery comprising the secondary battery of claim 20.

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