Electrolyte additive, electrolyte, battery, and electronic device

Abstract

The application relates to an electrolyte additive, an electrolyte, a battery and an electronic device. The electrolyte additive comprises a first additive; the first additive comprises a nitrogen-containing compound and a polynitrile compound, the polynitrile compound comprises a first nitrile additive and / or a second nitrile additive; wherein the structural formula of the nitrogen-containing compound is shown as formula 1; the structural formula of the first nitrile additive is shown as formula 2; and the structural formula of the second nitrile additive is shown as formula 3. The scheme provided by the application can make the battery present excellent cycle performance and storage performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrolyte additive, an electrolyte, a battery and an electronic device. BACKGROUND

[0002] Lithium ion batteries are widely used in consumer electronics, new energy vehicles and energy storage fields. With the rapid development of the new energy vehicle industry, consumers have higher requirements for the driving range and application scenarios, that is, the battery has higher energy density.

[0003] In order to improve the energy density of the battery, one of the methods is to improve the working voltage of the battery. However, under high working voltage, some side reactions occur inside the battery, such as structural phase transition of the positive active material, transition metal dissolution, intensified interface side reactions between the positive active material and the electrolyte, and decomposition of the positive and negative electrode interface film due to insufficient stability, thereby causing the cycle performance and storage performance of the battery to deteriorate. At present, a large number of additives have been reported to solve the above problems, such as ethylene carbonate, 1,3-propane sulfone, fluoroethylene carbonate and adiponitrile, but these additives cannot completely inhibit the above side reactions.

[0004] Therefore, the technical personnel in the art urgently need to develop an electrolyte additive capable of improving the cycle performance and storage performance of the battery under high voltage. SUMMARY

[0005] In order to solve or partially solve the problems in the related art, the present application provides an electrolyte additive, an electrolyte, a battery and an electronic device, which can improve the cycle performance and storage performance of the battery.

[0006] The first aspect of the present application provides an electrolyte additive, wherein the electrolyte additive comprises a first additive; the first additive comprises a nitrogen-containing compound and a polycarbonitrile compound, the polycarbonitrile compound comprises a first nitrile additive and / or a second nitrile additive; wherein,

[0007] The structure formula of the nitrogen-containing compound is as follows:

[0008]

[0009] Formula 1

[0010] wherein R1, R2 are each independently selected from one of H atom and C1-C8 alkyl;

[0011] The structure formula of the first nitrile additive is as follows:

[0012]

[0013] Formula 2

[0014] In Formula 2, R3, R4, R5 are each independently selected from substituted or unsubstituted C1-C8 alkylene, wherein the substituent is selected from C1-C8 alkyl, alkoxy, and cyano.

[0015] The second nitrile-based additive has the following structural formula:

[0016]

[0017] Formula 3

[0018] In Formula 3, R6 is selected from substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C2-C10 alkenylene, wherein the substituent is selected from at least one of C1-C8 alkyl, C2-C8 alkenyl, and cyano.

[0019] The electrolyte additive as described above, wherein the nitrogen-containing compound comprises a compound represented by Formula 1-1 and / or Formula 1-2:

[0020]

[0021] Formula 1-1

[0022]

[0023] Formula 1-2;

[0024] And / or, the first nitrile-based additive of Formula 2 comprises a compound represented by Formula 2-1 and / or Formula 2-2:

[0025]

[0026] Formula 2-1

[0027]

[0028] Formula 2-2.

[0029] And / or, the second nitrile-based additive of Formula 3 comprises at least one of compounds represented by Formula 3-1 to Formula 3-10:

[0030]

[0031] Formula 3-1

[0032]

[0033] Formula 3-2

[0034]

[0035] Formula 3-3

[0036]

[0037] Formula 3-4

[0038]

[0039] Formula 3-5

[0040]

[0041] Formula 3-6

[0042]

[0043] Formula 3-7

[0044]

[0045] Formula 3-8

[0046]

[0047] Formula 3-9

[0048]

[0049] Formula 3-10.

[0050] The electrolyte additive as described above, wherein the mass percentage of the nitrogen-containing compound in the electrolyte is 0.1% to 4%;

[0051] The mass percentage of the polycarbonitrile compound in the electrolyte is 2% to 6%.

[0052] The electrolyte additive as described above, wherein the mass percentage of the first nitrile additive in the electrolyte is 0.1% to 2%;

[0053] The mass percentage of the second nitrile additive in the electrolyte is 2% to 6%.

[0054] The electrolyte additive as described above, wherein the electrolyte additive further comprises a second additive, and the second additive comprises a compound shown in Formula 4:

[0055]

[0056] Formula 4

[0057] wherein R7, R8 are each independently selected from H, a substituted or unsubstituted cyclic carbonate group, a substituted or unsubstituted cyclic sulfate group.

[0058] The electrolyte additive as described above, wherein the second additive comprises at least one of the compounds shown in Formula 4-1 to Formula 4-5:

[0059]

[0060] Formula 4-1

[0061]

[0062] Formula 4-2

[0063]

[0064] Formula 4-3

[0065]

[0066] Formula 4-4

[0067]

[0068] Formula 4-5.

[0069] The electrolyte additive as described above, wherein a mass ratio of the first additive and the second additive is (0.1-8):(0.1-8); preferably, a mass ratio of the first additive and the second additive is (1-4):(1-4).

[0070] The electrolyte additive as described above, wherein further comprising one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, propylene sultone, methane disulfonate methylene, ethylene glycol bis(propionitrile) ether, pentafluoroethoxy phosphazene, dicyclohexyl carbonyl, phosphoric acid trimethyl imide, hexamethylene diisocyanate.

[0071] The second aspect of the present application provides an electrolyte, wherein comprising an organic solvent, an electrolyte additive and an electrolyte salt, the electrolyte additive adopts the electrolyte additive as described above.

[0072] The electrolyte as described above, wherein a mass percentage content of the organic solvent in the electrolyte is 20%-80%; and / or,

[0073] The organic solvent comprises one or more of vinyl carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, fluoroethyl acetate, fluoro methyl ethyl carbonate, fluoro dimethyl carbonate, fluoro propylene carbonate, γ-butyrolactone, cyclobutane sulfone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl n-butyrate, methyl acrylate, ethyl acrylate, etc.; and / or,

[0074] The mass percentage content of the electrolyte salt in the electrolyte is 10% to 30%; and / or,

[0075] The electrolyte salt comprises one or more of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorodicyanophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium cyano(trifluoromethanesulfonyl)imide; and / or,

[0076] The mass percentage content of the electrolyte additive in the electrolyte is 5% to 35%.

[0077] The battery as described above, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer comprises a positive electrode active material, and the positive electrode active material comprises at least one of lithium cobaltate, lithium manganate and lithium nickel cobalt manganate.

[0078] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of graphite, hard carbon, silicon, silicon oxide compound and silicon carbon compound.

[0079] The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of graphite, hard carbon, silicon, silicon oxide compound and silicon carbon compound.

[0080] The technical scheme provided by the present application can include the following beneficial effects: when the electrolyte additive comprises a first additive, and the first additive comprises a nitrogen-containing compound with structural formula 1 and a polynitrile compound, the polynitrile compound comprises a first nitrile additive with structural formula 2 and / or a second nitrile additive with structural formula 3, the nitrogen-containing compound and the polynitrile compound synergize, on the one hand, the nitrogen heterocyclic structure contained in the nitrogen-containing compound can undergo ring-opening reaction and participate in the construction of the negative electrode interface film, effectively promoting the increase of inorganic matter content in the negative electrode interface film, improving the mechanical strength and lithium ion migration rate of the negative electrode interface film, thereby improving the structural stability of the SEI film under high working voltage, avoiding the rupture of the SEI film to cause the contact of the electrolyte with the negative electrode active material, thereby avoiding the production gas problem caused by the side reaction, and at the same time, the low film formation resistance of the compound can effectively improve the lithium ion migration rate, reduce the internal resistance of the battery and improve the cycle performance of the battery; on the other hand, the polynitrile compound can complex and adsorb transition metals in the positive electrode active material, avoid the dissolution of the transition metals, improve the stability of the positive electrode active material, reduce the production gas caused by the oxidative decomposition of the electrolyte on the surface of the positive electrode active material, and avoid the migration of the transition metals to the negative electrode active material to cause the damage of the negative electrode interface film, thereby improving the cycle performance and storage performance of the battery.

[0081] It is to be understood that the foregoing general description and the following detailed description are only exemplary and explanatory and are not restrictive of the application. DETAILED DESCRIPTION

[0082] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0083] It should be understood that although the terms "first", "second", "third", etc. can be employed in this application to describe various information, such information should not be limited by these terms. These terms are only used to distinguish one piece of information from another. For example, a first information can also be termed a second information, similarly, a second information can also be termed a first information, without departing from the scope of the present application. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0084] In the related art, in a high-voltage environment, the side reaction of the positive active material increases, for example, the positive active material has a structure phase change, transition metal dissolution, the interface side reaction between the positive active material and the electrolyte is intensified, the positive and negative electrode interface film stability is insufficient, decomposition occurs, and the like, thereby causing the cycle performance and storage performance of the battery to deteriorate.

[0085] To solve the above problems, the embodiments of the present application provide an electrolyte additive, the electrolyte additive comprises a first additive; the first additive comprises a nitrogen-containing compound and a polynitrile compound, the polynitrile compound comprises a first nitrile additive and / or a second nitrile additive; wherein,

[0086] The structural formula of the nitrogen-containing compound is as follows:

[0087]

[0088] Formula 1

[0089] In formula 1, R1, R2 are each independently selected from one of H atom and C1-C8 alkyl;

[0090] The structural formula of the first nitrile additive is as follows:

[0091]

[0092] Formula 2

[0093] In Formula 2, R3, R4, R5 are each independently selected from substituted or unsubstituted C1-C8 alkylene, wherein the substituent is selected from C1-C8 alkyl containing cyano and alkoxy;

[0094] The structural formula of the second nitrile-based additive is as follows:

[0095]

[0096] Formula 3

[0097] In Formula 3, R6 is selected from substituted or unsubstituted C1-C10 alkylene, substituted or unsubstituted C2-C10 alkenylene, wherein the substituent is selected from at least one of C1-C8 alkyl, C2-C8 alkenyl, cyano.

[0098] The nitrogen-containing compound of the present application can refer to a compound including an azacyclic structure, such as an oxazolidinone compound; the first nitrile-based additive of the present application can refer to an additive including a cyano group and an ether group; and the second nitrile-based additive of the present application can refer to an additive including a dicyano group.

[0099] The C1-C8 alkyl of the present application refers to an alkyl group having 1 to 8 carbon atoms. The substituted or unsubstituted C1-C8 alkylene of the present application refers to an alkylene group having 1 to 8 carbon atoms with or without a substituent, and the C1-C8 alkyl containing cyano and alkoxy refers to an alkyl group having 1 to 8 carbon atoms including both cyano and alkoxy as substituents; for example, R3, R4, R5 can be selected from -CH2-, -C2H4-, -C3H6-, -CH-OCH2CN, -CH-OC2H4CN, -CH-OC3H6CN, -CH-OC4H8CN, etc.

[0100] The substituted or unsubstituted C1-C10 alkylene of the present application refers to an alkylene group having 1 to 10 carbon atoms with or without a substituent, and the substituted or unsubstituted C2-C10 alkenylene refers to an alkenylene group having 2 to 10 carbon atoms with or without a substituent; wherein the substituent of the alkyl and alkenyl is selected from at least one of C1-C8 alkyl, C1-C8 alkenyl, cyano. For example, R6 can be selected from -CH2-, -C2H4-, -C3H6-, -CH=CH-, -CH2CH=CH-, -CH(CN)-, -CH2CH=C(CN)-, etc.

[0101] According to the above scheme provided in the present application, after the electrolyte additive is added into the electrolyte and applied in the battery, the battery has excellent cycle performance and storage performance. The applicant analyzes the principle and considers that the reason is that the nitrogen-containing compound and the polynitrile compound have a synergistic effect. On the one hand, the nitrogen heterocyclic structure contained in the nitrogen-containing compound can undergo ring-opening reaction, and the oxygen in the nitrogen heterocyclic structure can coordinate with lithium ions more quickly to participate in the construction of the negative electrode interface film, effectively promote the increase of inorganic matter content in the negative electrode interface film, improve the mechanical strength and lithium ion migration rate of the negative electrode interface film, thereby improving the structural stability of the SEI film under high working voltage, avoiding the rupture of the SEI film to make the electrolyte contact with the negative active material, thereby avoiding the side reaction to cause the gas production problem, and at the same time, the film forming resistance of the compound is low, which can effectively improve the lithium ion migration rate and improve the cycle performance of the battery; on the other hand, the polynitrile compound can be complexed and adsorbed with transition metals in the positive active material, avoiding the dissolution of the transition metals, improving the stability of the positive active material, reducing the gas production caused by the oxidative decomposition of the electrolyte on the surface of the positive active material, and avoiding the migration of the transition metals to the negative active material to cause the damage of the negative electrode interface film, thereby improving the cycle performance and storage performance of the battery.

[0102] In a specific embodiment, the nitrogen-containing compound includes a compound represented by Formula 1-1 and / or Formula 1-2:

[0103] (CAS: 5840-76-6)

[0104] Formula 1-1

[0105] (CAS: 51784-00-0)

[0106] Formula 1-2.

[0107] When the nitrogen-containing compound is selected from the compound represented by Formula 1-1 and / or Formula 1-2, the nitrogen-containing additive can participate in the construction of the negative electrode interface film, further improve the mechanical properties and lithium ion conductivity of the negative electrode interface film, avoid the side reaction of the negative active material with the electrolyte to cause the decomposition of the electrolyte to produce gas, and thereby further improve the cycle performance and storage performance of the battery.

[0108] In a specific embodiment, the first nitrile additive of Formula 2 includes a compound represented by Formula 2-1 and / or Formula 2-2:

[0109] (CAS: 3386-87-6)

[0110] Formula 2-1

[0111] (CAS: 2465-93-2)

[0112] Formula 2-2.

[0113] When the nitrile additive is selected from the compounds shown in Formula 2-1 to Formula 2-2, the transition metal in the positive active material can be better complexed and adsorbed, avoiding the dissolution of the transition metal in the positive active material. At the same time, the nitrile additive can participate in the construction of the positive electrode interface film, improving the stability of the positive electrode interface film, thereby further improving the cycle performance and storage performance of the battery.

[0114] In a specific embodiment, the second nitrile additive of Formula 3 includes at least one of the compounds shown in Formula 3-1 to Formula 3-10:

[0115] (CAS: 110-61-2)

[0116] Formula 3-1

[0117] (CAS: 544-13-8)

[0118] Formula 3-2

[0119] (CAS: 111-69-3)

[0120] Formula 3-3

[0121] (CAS: 4553-62-2)

[0122] Formula 3-4

[0123] (CAS: 18715-38-3)

[0124] Formula 3-5

[0125] (CAS: 1572-52-7)

[0126] Formula 3-6

[0127] (CAS: 646-20-8)

[0128] Formula 3-7

[0129] (CAS: 629-40-3)

[0130] Formula 3-8

[0131] (CAS: 1675-69-0)

[0132] Formula 3-9

[0133] (CAS: 1772-25-4)

[0134] Formula 3-10.

[0135] When the second nitrile-based additive is selected from the compounds shown in Formula 3-1 to Formula 3-10, the second nitrile-based additive can better complex and adsorb the transition metal in the positive active material, avoid the dissolution of the transition metal in the positive active material, avoid the damage of the negative electrode interface film and the decomposition of the electrolyte, thereby further improving the cycle performance and storage performance of the battery.

[0136] In a specific embodiment, the mass percentage of the nitrogen-containing compound in the electrolyte is 0.1% to 4%, for example, the mass percentage of the nitrogen-containing compound in the electrolyte can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%, etc.; the mass percentage of the multi-nitrile compound in the electrolyte is 2% to 6%, for example, the mass percentage of the multi-nitrile compound in the electrolyte can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%, etc. When the mass percentages of the nitrogen-containing compound and the multi-nitrile compound in the electrolyte are within the above ranges, the nitrogen-containing compound and the multi-nitrile compound can better synergize, further improve the stability of the positive and negative electrode interface film and the lithium ion migration rate, and better complex and adsorb the transition metal in the positive active material, thereby reducing the side reactions of the battery and further improving the cycle performance and storage performance of the battery.

[0137] In a specific embodiment, the mass percentage of the first nitrile-based additive in the electrolyte is 0.1% to 2%, for example, the mass percentage of the first nitrile-based additive in the electrolyte is 0.1%, 0.5%, 1%, 1.5%, or 2%, etc.; the mass percentage of the second nitrile-based additive in the electrolyte is 2% to 6%, for example, the mass percentage of the second nitrile-based additive in the electrolyte is 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, or 6%, etc. When the mass percentages of the first nitrile-based additive and the second nitrile-based additive in the electrolyte are within the above ranges, the first nitrile-based additive and the second nitrile-based additive can synergize, better complex and adsorb the transition metal in the positive active material, reduce the dissolution of the transition metal, further improve the stability of the positive active material, and better improve the stability of the positive electrode interface, thereby making the cycle performance and storage performance of the battery better.

[0138] In a specific embodiment, the electrolyte additive further includes a second additive, and the second additive includes a compound shown in Formula 4:

[0139]

[0140] Formula 4

[0141] wherein R7, R8 are each independently selected from H, a substituted or unsubstituted cyclic carbonate group, a substituted or unsubstituted cyclic sulfate group.

[0142] The substituted or unsubstituted cyclic carbonate group of the present application refers to a group including -O-C(=O)-O- with or without substitution, for example , , , and the like. The substituted or unsubstituted cyclic sulfate group of the present application refers to a group including -O-S(=O)2-O- with or without substitution, for example , , and the like.

[0143] The second additive of the present application includes a cyclic carbonate group, a cyclic sulfate group, which can participate in the formation of the positive and negative electrode interface film, and improve the stability of the positive and negative electrode interface film. When the second additive is selected from the compound of Formula 4, the first additive and the second additive can synergistically generate a positive and negative electrode interface film with more optimal stability, improve the stability of the positive and negative electrode active material, and avoid the problem of decomposition gas generation. At the same time, the second additive has high compatibility with the electrolyte, so that the stability of the electrolyte is more optimal, and the redox reaction of the electrolyte on the surface of the positive and negative electrode active material is avoided, thereby greatly improving the cycle performance and storage performance of the battery.

[0144] In a specific embodiment, the second additive includes at least one of the compounds shown in Formula 4-1 to Formula 4-5:

[0145] (CAS: 2507955-35-1)

[0146] Formula 4-1

[0147] (CAS: 2520352-90-1)

[0148] Formula 4-2

[0149] (CAS: 2520352-90-1)

[0150] Formula 4-3

[0151] (CAS: 2520352-94-5)

[0152] Formula 4-4

[0153] (CAS: 2520352-91-2)

[0154] Formula 4-5.

[0155] When the second additive is selected from the compounds shown in Formula 4-1 to Formula 4-5, the synergistic effect of the first additive and the second additive is higher, the stability of the negative electrode interface film is more optimal, the protection of the positive and negative electrode active materials is higher, the side reactions of the positive and negative electrode active materials are avoided, and the stability of the electrolyte can be further improved, the decomposition of the electrolyte is avoided, the gas production is avoided, and the cycle performance and storage performance of the battery are more optimal.

[0156] In a specific embodiment, the mass ratio of the first additive and the second additive is (0.1-8):(0.1-8), preferably, the mass ratio of the first additive and the second additive is (1-4):(1-4), for example, the mass ratio is 0.1:0.5, 0.1:1, 0.1:2, 0.1:4, 0.1:8, 8:0.1, 4:0.4, 2:0.1, 0.5:0.1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 2:3, 3:2, etc. When the mass ratio of the first additive and the second additive is within the above range, the synergistic effect of the first additive and the second additive is more optimal, the mechanical properties of the negative electrode interface film generated by the first additive and the second additive are higher, the impedance is lower, and the complexation and adsorption of the positive electrode transition metal are better, the dissolution of the transition metal is avoided, the stability of the positive and negative electrode active materials is improved, and the stability of the electrolyte can be improved, the decomposition of the electrolyte is avoided, and the cycle performance and storage performance of the battery are excellent.

[0157] In a specific embodiment, the mass percentage of the first additive in the electrolyte is 0.1%-8%, for example, the mass percentage is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc. When the mass percentage of the first additive is within the above range, the stability of the negative electrode interface film formed by the first additive and the second additive is more optimal, the impedance is lower, and the complexation and adsorption of the positive electrode transition metal are more optimal, which is beneficial to reduce the dissolution of the transition metal, improve the stability of the positive and negative electrodes, and effectively improve the cycle performance and storage performance of the battery. Preferably, the mass percentage of the first additive in the electrolyte is 1%-4%.

[0158] In an embodiment, the second additive has a mass percentage in the electrolyte of 0.1% to 8%, such as 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, or 8%, etc. When the mass percentage of the second additive is within the above range, the second additive has a better synergy with the first additive, the mechanical property and lithium-ion conductivity of the generated negative electrode interface film are higher, and the stability of the electrolyte is higher, which is beneficial to reduce the decomposition of the electrolyte on the surface of the positive and negative electrodes and avoid the deterioration of the cycle performance and storage performance of the battery. Preferably, the mass percentage of the second additive in the electrolyte is 1% to 4%.

[0159] In an embodiment, the electrolyte additive further comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfone lactone, vinyl sulfate, propylene sulfone lactone, methane disulfide methylene, ethylene glycol bis(propionitrile) ether, pentafluoroethoxy phosphazene, dicyclohexyl carbonyl, phosphazene trimethyl imide, hexamethylene diisocyanate, etc. Preferably, the electrolyte additive comprises fluoroethylene carbonate. When the electrolyte additive further comprises the above-mentioned compounds, the above-mentioned compounds can have a synergy with the first additive and the second additive, further improve the stability and lithium-ion conductivity of the negative electrode interface film, and thus better protect the negative electrode active material and the electrolyte, avoid side reactions of the negative electrode active material and the electrolyte, and make the cycle performance and storage performance of the battery better.

[0160] The second aspect of the present application provides an electrolyte comprising the above-mentioned electrolyte additive. The application of the electrolyte to the battery can improve the cycle performance and storage performance of the battery.

[0161] In an embodiment, the electrolyte comprises an organic solvent, and the organic solvent comprises at least one of vinyl carbonate, propylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, fluoroethyl acetate, fluoro methyl ethyl carbonate, fluoro dimethyl carbonate, fluoro propylene carbonate, γ-butyrolactone, cyclobutane sulfone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, methyl propionate, methyl butyrate, ethyl butyrate, methyl acrylate, ethyl acrylate, and the mass percentage of the organic solvent in the electrolyte is 20% to 80%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%, etc. When the organic solvent of the electrolyte is selected from the above-mentioned organic solvents, the viscosity of the electrolyte is lower and the ionic conductivity is higher, which is beneficial to improve the migration rate of lithium ions, and the above-mentioned organic solvents can improve the stability of the electrolyte and avoid decomposition reactions of the electrolyte, thereby further improving the cycle performance and storage performance of the battery.

[0162] In an embodiment, the electrolyte includes an electrolyte salt, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorodioxalate phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium cyano(trifluoromethanesulfonyl)imide; the mass percentage of the electrolyte salt in the electrolyte is 10% to 30%, for example, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28% or 30%, etc. When the electrolyte salt is selected and the mass percentage is within the above range, the conductivity and stability of the electrolyte can be further improved, thereby further improving the cycle performance and storage performance of the battery.

[0163] In an embodiment, the mass percentage of the electrolyte additive in the electrolyte is 5% to 35%, for example, the mass percentage is 5%, 10%, 15%, 20%, 25%, 30% or 35%, etc. When the electrolyte additive is selected and the mass percentage is within the above range, the electrolyte additive can fully exert its performance, improve the stability and lithium-ion conductivity of the positive and negative electrode interface film, and at the same time improve the stability of the positive electrode active material, thereby better protecting the positive and negative electrode active materials and the electrolyte, avoiding the side reactions of the positive electrode active material, the negative electrode active material and the electrolyte, and making the cycle performance and storage performance of the battery more excellent.

[0164] The third aspect of the present application provides a battery including the above-mentioned electrolyte. The battery exhibits excellent cycle performance and storage performance.

[0165] In an embodiment, the battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes at least one of lithium cobaltate, lithium manganate and lithium nickel cobalt manganate. Preferably, the positive electrode active material includes lithium cobaltate and / or lithium nickel cobalt manganate. When the positive electrode active material is selected from the above-mentioned compounds, the positive electrode active material can fully exert its performance, thereby improving the electrochemical performance of the battery.

[0166] In the embodiments of the present application, the type of the positive electrode current collector is not particularly limited, and it can be any known material suitable for use as a positive electrode current collector. In an embodiment, the positive electrode current collector includes metal materials such as aluminum, stainless steel, nickel plating layer, titanium, tantalum, etc., and carbon materials such as carbon cloth and carbon paper. Preferably, the positive electrode current collector is a metal material.

[0167] In one specific embodiment, the battery further comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material, a conductive agent, and a binder. The negative electrode active material comprises at least one of graphite, hard carbon, silicon, a silicon oxide compound, and a silicon carbon compound. Preferably, the negative electrode active material comprises silicon.

[0168] The negative electrode current collector of the embodiments of the present application is not particularly limited as long as the purpose of the present application can be achieved, and can be, for example, a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector.

[0169] The conductive agent and the binder in the positive electrode active material layer and the negative electrode active material layer of the embodiments of the present application can each be a conventional material in the art.

[0170] In one specific embodiment, the battery further comprises a separator. The material and shape of the separator of the embodiments of the present application are not particularly limited as long as the effect of the present application is not significantly impaired, and can include, for example, a porous sheet or nonwoven fabric-like substance having excellent liquid retention, and the material of the resin or glass fiber separator includes, but is not limited to, polyolefin, aramid, polytetrafluoroethylene, polyether sulfone, and the like, and can be set as needed.

[0171] Hereinafter, the present application will be further described in detail through specific examples.

[0172] Example 1

[0173] 1. Preparation of the positive electrode sheet

[0174] The positive electrode active material lithium cobalt oxide (LCO), the conductive agent CNT, and the binder PVDF were mixed in a weight ratio of 97:1.5:1.5 in an NMP solvent, and the slurry was coated on an aluminum foil having a safety primer, and then subjected to processes such as drying, cold pressing, slitting, sheet making, welding of tabs, and taping to manufacture a positive electrode sheet satisfying the winding requirements.

[0175] 2. Preparation of the negative electrode sheet

[0176] The negative electrode active material (graphite and carbon-coated silicon material, in which the silicon content is 10%) and the binder (SBR-CMC) and the conductive agent (carbon black) were added to water as a solvent in a weight ratio of 95:3.5:1.5 to prepare a negative electrode slurry. The slurry was coated on a negative electrode current collector Cu foil, and then subjected to processes such as drying, cold pressing, slitting, sheet making, welding of tabs, and taping to manufacture a negative electrode sheet satisfying the winding requirements.

[0177] 3. Preparation of the electrolyte

[0178] Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a mass ratio of 1.5:1.5:4:3 to form a mixed solvent, 16% lithium hexafluorophosphate (LiPF6) was added and mixed uniformly, 10% fluoroethylene carbonate (FEC) was added based on the total mass of the electrolyte, and the first and second additives (the types and amounts of the additives are shown in Table 1) were added to obtain the electrolyte of each example and the comparative example.

[0179] 4. Preparation of a lithium ion battery

[0180] The positive electrode sheet, the separator, and the negative electrode sheet were wound to obtain a bare cell. The bare cell was placed in an aluminum-plastic film that had been punched, and top-side sealing was completed. After high-temperature baking, the prepared electrolyte was injected, and the battery was prepared after the processes of standing, formation, capacity distribution, and detection.

[0181] The preparation method of the battery provided in Examples 2-56 and Comparative Examples 1-31 was basically the same as that of Example 1, and the specific parameters are shown in Table 1.

[0182] Table 1

[0183]

[0184] Test Example

[0185] Battery performance test:

[0186] 45℃ cycle test: the battery was placed at 45℃ for 4h, charged at 1C constant current to 4.53V, the cutoff current was 0.05C, and the initial internal resistance R0, full charge thickness, and charge capacity were tested after standing for 10min. The battery was discharged at 0.5C to 3.0V, and the discharge capacity C0 was recorded as the initial value. The full charge internal resistance and full charge thickness were tested every 100 cycles for 200 cycles. The capacity C after 200 cycles was obtained. 200 , internal resistance R 200 , thickness D 200 , then, the capacity retention rate = C 200 / C0, the internal resistance growth rate = R 200 / R0-1, the thickness change rate = D 200 / D0-1, and the results are shown in Table 2.

[0187] 80℃ storage test: the battery was charged at 0.5C constant current to 4.53V, the cutoff current was 0.05C, and the full charge thickness D0 was tested after standing for 10min. The battery was left to stand at 85±2℃ for 6h, and the hot-state thickness D1 was tested immediately after the battery was taken out of the oven. The thickness change rate = D1 / D0-1.

[0188] Table 2

[0189]

[0190] From Table 2, according to the comparison of Examples 1-13 and Comparative Examples 1, 2-16, and the comparison of Example 12 and Comparative Example 26, it can be seen that when the first additive comprises a nitrogen-containing compound and a polycarbonyl compound, the cycle performance and storage performance of the battery are improved.

[0191] According to the comparison of Examples 14-17 and Comparative Examples 17, 18, it can be seen that when the mass percentage content of the nitrogen-containing compound in the electrolyte is 0.1%-4%, the nitrogen-containing compound can improve the mechanical strength and lithium ion transference rate of the negative electrode interface film, thereby improving the cycle performance and storage performance of the battery.

[0192] According to the comparison of Examples 18-20 and Comparative Examples 19, 20, it can be seen that when the mass percentage content of the polycarbonyl compound in the electrolyte is 2%-6%, the polycarbonyl compound can complex and adsorb transition metals in the positive electrode active material, avoid the dissolution of transition metals, improve the stability of the positive electrode active material, and make the cycle performance and storage performance of the battery better.

[0193] According to the comparison of Examples 21-24 and Comparative Examples 21, 22, it can be seen that when the mass percentage content of the first carbonyl additive in the electrolyte is 0.1%-2%, the cycle performance and storage performance of the battery are better.

[0194] According to the comparison of Examples 25-27 and Comparative Examples 23, 24, it can be seen that when the mass percentage content of the second carbonyl additive in the electrolyte is 2%-6%, the cycle performance and storage performance of the battery can be further improved.

[0195] According to the comparison of Examples 28-33 and Comparative Examples 25, 26, and the comparison of Examples 45 and Comparative Examples 28, 29, it can be seen that when the mass percentage content of the first additive in the electrolyte is 0.1%-8%, the cycle performance and storage performance of the battery can be improved to a greater extent.

[0196] According to the comparison of Examples 34-46 and Examples 1-13, it can be seen that when the first additive and the second additive synergistically act, the cycle performance and storage performance of the battery are improved.

[0197] According to the comparison of Examples 47-52 and Comparative Examples 30, 31, it can be seen that when the mass percentage content of the second additive in the electrolyte is 0.1%-8%, the cycle performance and storage performance of the battery are better.

[0198] As can be seen from the comparison of Examples 53 to 56, when the second additive is selected from the compounds represented by Formula 4-1 to Formula 4-5, the synergistic effect of the first additive and the second additive is higher, the stability of the negative electrode interface film is more optimal, and the cycle performance and storage performance of the battery are more optimal.

[0199] The above has described various embodiments of the present application, and the above description is exemplary and is not exhaustive, and is also not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The selection of the terms used herein is intended to best explain the principles of the embodiments, practical applications, or improvements to the technology in the market, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. An electrolyte additive characterized in that, The electrolyte additive comprises a first additive; the first additive comprises a nitrogen-containing compound and a polynitrile compound, the polynitrile compound comprises a first nitrile additive and / or a second nitrile additive; wherein, The structure formula of the nitrogen-containing compound is as follows: Formula 1 In formula 1, R1, R2 are each independently selected from one of H atom and C1-C8 alkyl group; The structure formula of the first nitrile additive is as follows: Formula 2 In formula 2, R3, R4, R5 are each independently selected from substituted or unsubstituted C1-C8 alkylene group, wherein the substituent group is selected from C1-C8 alkyl group containing cyano and alkoxy group; The structure formula of the second nitrile additive is as follows: Formula 3 In formula 3, R6 is selected from substituted or unsubstituted C1-C10 alkylene group, substituted or unsubstituted C2-C10 alkenylene group, wherein the substituent group is selected from at least one of C1-C8 alkyl group, C2-C8 alkenyl group, cyano.

2. The electrolyte additive according to claim 1, characterized in that, The nitrogen-containing compound comprises a compound shown in formula 1-1 and / or formula 1-2: Formula 1-1 Formula 1-2; And / or, the first nitrile additive of formula 2 comprises a compound shown in formula 2-1 and / or formula 2-2: Formula 2-1 Formula 2-2; And / or, the second nitrile additive of formula 3 comprises at least one of compounds shown in formula 3-1 to formula 3-10: Formula 3-1 Formula 3-2 Formula 3-3 Formula 3-4 Formula 3-5 Formula 3-6 Formula 3-7 Formula 3-8 Formula 3-9 Formula 3-10.

3. The electrolyte additive according to claim 1, characterized in that, The mass percentage content of the nitrogen-containing compound in the electrolyte is 0.1%-4%; The mass percentage content of the polynitrile compound in the electrolyte is 2%-6%.

4. The electrolyte additive according to claim 1, characterized in that, The mass percentage content of the first nitrile additive in the electrolyte is 0.1%-2%; The mass percentage content of the second nitrile additive in the electrolyte is 2%-6%.

5. The electrolyte additive according to claim 1, characterized in that, The electrolyte additive further comprises a second additive, the second additive comprises a compound shown in formula 4: Formula 4 Wherein, R7, R8 are each independently selected from H, substituted or unsubstituted cyclic carbonate group, substituted or unsubstituted cyclic sulfate group.

6. The electrolyte additive according to claim 5, characterized in that, The second additive comprises at least one of compounds shown in formula 4-1 to formula 4-5: Formula 4-1 Formula 4-2 Formula 4-3 Formula 4-4 Formula 4-5.

7. The electrolyte additive according to any one of claims 5 to 6, characterized in that, The mass ratio of the first additive and the second additive is (0.1-8):(0.1-8).

8. The electrolyte additive according to claim 7, characterized in that The mass ratio of the first additive and the second additive is (1-4):(1-4).

9. The electrolyte additive according to any one of claims 1 to 5, characterized in that, Further comprising one or more of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfone lactone, vinyl sulfate, propylene sulfone lactone, methane disulfide methylene, ethylene glycol bis(propionitrile) ether, pentafluoroethoxy phosphazene, dicyclohexyl carbonyl, phosphoric acid trimethyl imide, hexamethylene diisocyanate.

10. An electrolyte, characterized by, It comprises an organic solvent, an electrolyte additive and an electrolyte salt, the electrolyte additive adopts the electrolyte additive according to any one of claims 1-9.

11. The electrolyte of claim 10, wherein, The mass percentage content of the organic solvent in the electrolyte is 20%-80%; and / or, The organic solvent includes one or more of vinyl carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, ethyl propionate, propyl propionate, ethyl fluoroacetate, methyl ethyl fluoroacetate, dimethyl fluoroacetate, propylene fluoroacetate, gamma-butyrolactone, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl propionate, methyl butyrate, ethyl n-butyrate, methyl acrylate, ethyl acrylate, etc.; and / or, The mass percentage content of the electrolyte salt in the electrolyte is 10%-30%; and / or, The electrolyte salt includes one or more of lithium hexafluorophosphate, lithium difluoro oxalate borate, lithium bisoxalate borate, lithium difluoro di-oxalate phosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium cyano(trifluoromethanesulfonyl)imide; and / or, The mass percentage content of the electrolyte additive in the electrolyte is 5%-35%.

12. A battery, characterized by The positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte according to any one of claims 9 to 11.

13. The battery of claim 12, wherein, The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, the positive electrode active material including at least one of lithium cobaltate, lithium manganate, and lithium nickel cobalt manganate; The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, the negative electrode active material layer including a negative electrode active material, the negative electrode active material including at least one of graphite, hard carbon, silicon, silicon oxide compounds, and silicon carbon compounds.

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