Lithium ion battery electrolyte and application thereof

Abstract

The application provides a lithium ion battery electrolyte and application thereof. The electrolyte comprises the following components: a lithium salt, a solvent and an additive. The additive comprises a first additive, and a general structure of the first additive is as follows: A is selected from a cyclopentadienyl group or a phenyl group, X1 is selected from -S(=O)2- or -P(F)-, L1 is selected from one of C1-C4 amino-substituted alkylene which is unsubstituted or substituted by a first substituent, and amino-substituted (-C2H4-O-C2H4-)n1, R1 and R2 are each independently selected from one of a hydrogen atom, a halogen atom, an unsaturation degree of 0-2 and a carbon atom number of 1-4 alkyl, alkenyl or alkynyl which is unsubstituted or substituted by a second substituent, a carbonyl group, an ester group, an ether group, an amide group or a cyano group which has a carbon atom number of 2-4, and an unsubstituted or third substituent-substituted phenyl group, the first substituent, the second substituent and the third substituent are each selected from one of a halogen atom, and the third substituent has a substitution site of 1-2 in the phenyl group. The lithium ion battery electrolyte provided by the application can improve the cycle stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, specifically to a lithium-ion battery electrolyte and its application. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high safety, and long cycle life, and are widely used in consumer electronics, electric vehicles, and energy storage. Among them, high-nickel oxide-silicon systems have become one of the most promising high-energy-density technologies for lithium-ion batteries due to the high specific capacity of high-nickel oxide cathode materials and the advantages of silicon anode materials such as high theoretical capacity, good safety performance, and wide availability. However, silicon anode materials undergo numerous side reactions with the electrolyte, and continuous expansion and contraction during cycling leads to the rupture of the solid electrolyte interface (SEI) film on the anode surface, compromising the cycle stability of the high-nickel oxide-silicon system and thus limiting its development. Summary of the Invention

[0003] This invention proposes a lithium-ion battery electrolyte and its application. The lithium-ion battery electrolyte and its application provided by this invention can reduce battery impedance and improve battery cycle stability.

[0004] To address the aforementioned technical problems, the present invention provides a lithium-ion battery electrolyte, comprising at least the following components:

[0005] Lithium salts;

[0006] Solvent; and

[0007] The additive includes a first additive, the first additive having the following general structural formula:

[0008]

[0009] Wherein, A is selected from cyclopentadienyl or phenyl, X1 is selected from -S(=O)2- or -P(F)-, L1 is selected from unsubstituted or first-substituted C1-C4 amino-substituted alkylene, and amino-substituted (-C2H4-O-C2H4-)n1, n1 is selected from an integer from 1 to 10, R1 and R2 are each independently selected from hydrogen atom, halogen atom, unsubstituted or second-substituted alkyl, alkenyl or alkynyl with an unsaturation degree of 0-2 and a carbon number of 1-4, carbonyl, ester, ether, amide or cyano with a carbon number of 2-4, and unsubstituted or third-substituted phenyl, the first substituent, the second substituent and the third substituent are each independently selected from halogen atom, and the third substituent has 1-2 substitution sites in the phenyl.

[0010] In one embodiment of the present invention, in the general structural formula of the first additive, as a substituent group connected to the cyclic structure A: R1 is located at the ortho or meta position of the vinyl group on the cyclic structure A, and / or, the main chain having a sulfonamide structure is located at the ortho position of the vinyl group on the cyclic structure A.

[0011] In one embodiment of the present invention, the first additive is selected from:

[0012]

[0013] At least one of them.

[0014] In one embodiment of the present invention, the content of the first additive in the electrolyte is 0.1wt%-3wt%.

[0015] In one embodiment of the present invention, the additive further includes a second additive, the second additive being selected from at least one of vinyl sulfate, fluorovinyl carbonate, 1,3-propanesulfonic acid lactone, or trimethylsilyl phosphate.

[0016] In one embodiment of the present invention, the content of the second additive in the electrolyte is 0.3wt%-2wt%.

[0017] In one embodiment of the present invention, the additive further includes a third additive, which is selected from at least one of lithium difluorooxalate phosphate or lithium difluorooxalate borate, and the content of the third additive in the electrolyte is 0.2wt%-0.8wt%.

[0018] In one embodiment of the present invention, the solvent includes a first solvent, which is selected from at least one of ethylene carbonate or propylene carbonate, and the content of the first solvent in the electrolyte is 8wt%-15wt%.

[0019] In one embodiment of the present invention, the solvent further includes a second solvent, the second solvent being selected from at least one of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

[0020] The present invention also provides a lithium-ion battery, comprising at least:

[0021] The positive electrode sheet includes a positive electrode active material, wherein the structural formula of the positive electrode active material is Li. x [Ni y Co z Mn t M (1-y-z-t) O 2-δWherein, M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, 0.9 <x<1.1,0.65≤y<1.0,0≤z<0.5,0≤t<0.5,0≤δ≤0.1;

[0022] A negative electrode sheet, comprising a negative electrode active material, wherein the negative electrode active material comprises at least one of silicon-oxygen materials or silicon-carbon materials;

[0023] A diaphragm is disposed between the positive electrode and the negative electrode; and

[0024] The electrolyte is selected from the lithium-ion battery electrolytes mentioned above.

[0025] In summary, this invention proposes a lithium-ion battery electrolyte and its application. The first additive can reduce battery impedance and improve battery cycle stability. When the first and second additives are used together, they adsorb at the negative electrode interface and undergo free radical polymerization. The fluorine element in the generated polymer easily forms inorganic SEI substances such as lithium fluoride on the negative electrode surface, thereby effectively reducing unnecessary chemical reactions between the negative electrode and the electrolyte, further improving the safety and stability of the battery. Moreover, the first and third additives can form a hydrogen bond structure with excellent expansion characteristics through electrostatic interaction, thereby ensuring that the SEI film does not rupture during the expansion and contraction of the negative electrode, further improving the cycle stability of the battery. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0027] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0028] The technical solution of the present invention will be further described in detail below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention proposes a lithium-ion battery electrolyte, comprising at least a lithium salt, a solvent, and additives, wherein the additives include a first additive, the structural formula of which is: Wherein, A is selected from cyclopentadienyl or phenyl, X1 is selected from -S(=O)2- or -P(F)-, L1 is selected from unsubstituted or first-substituted C1-C4 amino-substituted alkylene groups, and amino-substituted (-C2H4-O-C2H4-)n1, where n1 is an integer from 1 to 10, R1 and R2 are each independently selected from hydrogen atoms, halogen atoms, unsubstituted or second-substituted alkyl, alkenyl or alkynyl groups with an unsaturation degree of 0-2 and 1-4 carbon atoms, carbonyl, ester, ether, amide or cyano groups with 2-4 carbon atoms, and unsubstituted or third-substituted phenyl groups, where the first, second and third substituents are each independently selected from halogen atoms, and the third substituent has 1-2 substitution sites in the phenyl group. In the lithium-ion battery electrolyte provided by this invention, the first additive can reduce the battery impedance and improve the battery cycle stability.

[0030] In one embodiment of the present invention, in Formula 1, as a substituent group connected to the cyclic structure A: R1 is located at the ortho or meta position of the vinyl group on the cyclic structure A, and / or, the main chain having a sulfonamide structure is located at the ortho position of the vinyl group on the cyclic structure A, and the structures of R1 and R2 may be the same or different. Further, in this embodiment, the first additive is selected, for example, from:

[0031]

[0032] At least one of the following. Because the first additive contains a -NH2 group, the positively charged H on the -NH2 group readily forms a hydrogen bond structure RH---F-R' with the highly electronegative -F substituent in the fluorinated substance of the electrolyte through electrostatic interaction. This hydrogen bond structure has excellent expansion characteristics, ensuring that the SEI film does not rupture during the expansion and contraction of the negative electrode, thereby improving the cycle stability of the battery. Wherein, RH is the structural formula of the first additive, and F-R' is the structural formula of the fluorinated substance in the electrolyte.

[0033] In one embodiment of the present invention, the content of the first additive in the electrolyte is, for example, 0.1wt%-3wt%, and further, for example, 0.5wt%-1.5wt%. By controlling the content of the first additive, the battery impedance can be reduced and the battery cycle stability can be improved.

[0034] In one embodiment of the present invention, the additive further includes a second additive, which is selected from at least one of ethylene sulfate (DTD), fluoroethylene carbonate (FEC), 1,3-propane sulfonate (PS), or trimethylsilyl phosphate (TMSP). The second additive and the first additive adsorb at the negative electrode interface and undergo a free radical polymerization reaction. The NF bonds in the resulting polymer, due to their low bond energy, break, and fluoride ions, after detaching from the polymer, easily form inorganic SEI substances such as lithium fluoride on the negative electrode surface. This protects the negative electrode, prevents unnecessary chemical reactions between the negative electrode and the electrolyte, and improves the safety and stability of the battery.

[0035] In one embodiment of the present invention, the content of the second additive in the electrolyte is, for example, 0.3wt%-2wt%, and further, for example, 0.5wt%-1wt%. By controlling the content of the second additive, the battery impedance can be reduced and the battery cycle stability can be improved.

[0036] In one embodiment of the present invention, the additive further includes a third additive, which is selected from at least one of lithium difluoro(oxalato)phosphate (LiODFP) or lithium difluoro(oxalato)borate (LiODFB). Because the third additive contains fluorine atoms, it readily forms a hydrogen bond structure RH-F-R' with the H atoms in the -NH2 group of the first additive through electrostatic interaction. This hydrogen bond structure has excellent expansion characteristics, ensuring that the SEI film does not rupture during the expansion and contraction of the negative electrode, thereby improving the cycle stability of the battery. Here, RH is the structural formula of the first additive, and F-R' is the structural formula of the third additive. The content of the third additive in the electrolyte is, for example, 0.2wt%-0.8wt%. By controlling the content of the third additive in the electrolyte, the cycle stability of the battery can be improved.

[0037] In one embodiment of the present invention, the solvent includes a first solvent, which is, for example, a cyclic carbonate, or at least one selected from ethylene carbonate (EC) or propylene carbonate (PC). The content of the first solvent in the electrolyte is, for example, 8 wt% to 15 wt%.

[0038] In one embodiment of the present invention, the solvent further includes a second solvent, which is, for example, a chain carbonate, or at least one selected from dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or diethyl carbonate (DEC), and the content of the second solvent in the electrolyte is, for example, 60wt%-80wt%.

[0039] In one embodiment of the present invention, the lithium salt is selected from at least one of lithium fluorosulfonylimide or lithium hexafluorophosphate (LiPF6), and the content of the lithium salt in the electrolyte is, for example, 10wt%-18wt%.

[0040] In one embodiment of the present invention, when preparing the electrolyte, a first solvent and a second solvent are mixed evenly in a glove box under a stable gas atmosphere such as argon according to a mass ratio to obtain a solvent. Lithium salt and additives are then added to the solvent and mixed evenly to prepare a lithium-ion battery electrolyte. The moisture content in the glove box is, for example, less than 10 ppm.

[0041] This invention also proposes a lithium-ion battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte. The separator is located between the positive and negative electrodes to prevent short circuits between them, allowing lithium ions to pass through. The electrolyte fills the space between the positive electrode, separator, and negative electrode, and is the aforementioned lithium-ion battery electrolyte, serving to conduct ions. The lithium-ion battery can be, for example, a primary or secondary battery. A secondary battery can be, for example, a pouch battery, a hard-case battery, or a cylindrical battery. This invention does not specifically limit the type or category of lithium-ion batteries.

[0042] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer coated on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric.

[0043] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a conductive agent, and a binder. The ratio of the positive electrode active material, the conductive agent, and the binder can be selected according to actual needs. In this embodiment, the positive electrode active material is, for example, a high-nickel oxide material, and the chemical formula of the high-nickel oxide material is, for example, Li. x [Ni y Co z Mn t M (1-y-z-t) ]O 2-δWherein, M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, 0.9 <x<1.1,0.65≤y<1.0,0≤z<0.5,0≤t<0.5,0≤δ≤0.1。

[0044] In one embodiment of the present invention, the conductive agent is selected from at least one of conductive carbon black (SuperP), acetylene black, carbon nanotubes, or graphene, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), poly(ethylene oxide) (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate (polyacrylate), polyvinyl ether (polyvinyl ether), polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexanefluoropropylene (polyhexafluoropropylene), or polymerized styrene-butadiene rubber (SBR).

[0045] In one embodiment of the present invention, the positive electrode current collector is, for example, aluminum foil, and the chemical formula of the positive electrode active material is, for example, LiNi. 0.9 Mn 0.05 Co 0.05 O2, a conductive agent such as acetylene black, and a binder such as PVDF are used. The positive electrode active material, conductive agent, and binder are mixed in a mass ratio of 95:3:2, dissolved in an organic solvent, and stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil, air-dried at room temperature, and then transferred to an oven for drying. After rolling and cutting, the positive electrode sheet is obtained. The organic solvent is, for example, N-methylpyrrolidone (NMP).

[0046] In one embodiment of the present invention, the negative electrode sheet includes, for example, a negative electrode current collector and a negative electrode active layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is selected from, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foamed copper current collector, or a stainless steel current collector.

[0047] In one embodiment of the present invention, the negative electrode active layer includes a negative electrode active material, a conductive agent, a binder, and a thickener. The proportions of the negative electrode active material, the conductive agent, and the binder can be selected according to actual needs. In this embodiment, the negative electrode active material includes at least one silicon material such as silicon oxide or silicon carbide; the silicon oxide material includes at least one silicon suboxide or silicon oxide; and the silicon carbide material includes silicon carbide. Further, the negative electrode active material also includes graphite, and the proportions of graphite and silicon materials in the negative electrode active material can be selected according to actual needs. Specifically, in this embodiment, the content of silicon material in the negative electrode active material is, for example, 2wt%-20wt%, and the content of graphite in the negative electrode active material is, for example, 80wt%-98wt%.

[0048] In one embodiment of the present invention, the binder is selected from at least one of PVDF, PEO, PA, polypropylene, polyacrylate, polyethylene ether, PMMA, polyhexamethylene propylene, or SBR. The conductive agent is selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, or graphene. The thickener is selected from, for example, sodium carboxymethyl cellulose (CNC-Na).

[0049] In one embodiment of the present invention, the negative electrode current collector is, for example, copper foil; the negative electrode active material is, for example, a mixture of silicon carbide and graphite, wherein the content of silicon carbide in the mixture is, for example, 6 wt%; the conductive agent is, for example, acetylene black; the thickener is, for example, CNC-Na; and the binder is, for example, SBR. Specifically, the negative electrode active material, conductive agent, thickener, and binder carbon are mixed in a mass ratio of 96.5:1:1:1.5, and deionized water solvent is added. The mixture is then thoroughly stirred and mixed uniformly under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, and after being dried at room temperature, it is transferred to an oven for drying. After processes such as rolling and cutting, a negative electrode sheet is obtained.

[0050] In one embodiment of the present invention, the separator is, for example, a conventional separator, a ceramic separator, a polymer separator, a non-woven fabric separator, or an inorganic-organic composite separator. Specifically, the separator is, for example, a single-layer polypropylene (PP) membrane, a single-layer polyethylene (PE) membrane, a double-layer PP / PE membrane, a double-layer PP / PP membrane, or a triple-layer PP / PE / PP membrane. In this embodiment, for example, a single-layer PP membrane is selected as the separator.

[0051] In one embodiment of the present invention, the above-mentioned positive electrode, separator and negative electrode are placed in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation, and is put into an aluminum-plastic film to obtain a dry cell. Then, the dry cell is baked at 80°C to remove water, the electrolyte is injected into the dry cell and sealed to obtain a lithium-ion battery.

[0052] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0053] Example 1

[0054] Preparation of positive electrode: LiNi 0.9 Mn 0.05 Co 0.05 O2, acetylene black and PVDF are mixed in a mass ratio of 95:3:2, dissolved in NMP organic solvent, and stirred in a vacuum mixer until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil, dried at room temperature, and then transferred to an oven for drying. After rolling and cutting, the positive electrode sheet is obtained.

[0055] Preparation of the negative electrode sheet: Silicon carbide and graphite are mixed to obtain the negative electrode active material, with the silicon carbide content in the negative electrode active material being 6 wt%. The negative electrode active material, acetylene black, and CMC are mixed at a mass ratio of 96:2:2, and deionized water solvent is added. The mixture is then thoroughly stirred and homogenized under vacuum to obtain a negative electrode slurry. The negative electrode slurry is coated onto copper foil, then air-dried at room temperature and transferred to an oven for drying. After rolling and cutting processes, the negative electrode sheet is obtained.

[0056] Electrolyte preparation: In an argon-atmospheric glove box with a moisture content of less than 1 ppm, the first solvent EC, the second solvent DMC, and the second solvent EMC were mixed evenly according to the electrolyte composition described in Table 1 to obtain a solvent. Then, the first additive compound 1 and lithium salt LiPF6 were added to the solvent and mixed evenly to prepare a lithium-ion battery electrolyte. The contents of EC, DMC, EMC, LiPF6, and compound 1 in the electrolyte were 17.9 wt%, 50.0 wt%, 20.0 wt%, 12 wt%, and 0.1 wt%, respectively.

[0057] Selection of diaphragm: Single-layer PP membrane is selected as the diaphragm.

[0058] Battery preparation: The positive electrode, separator and negative electrode are placed in sequence and put into an aluminum-plastic film to obtain a dry cell. Then, the dry cell is baked at 80°C to remove water. Electrolyte is injected into the dry cell and it is then packaged to obtain a lithium-ion battery.

[0059] Example 2

[0060] The contents of compound 1 and DMC in the electrolyte were 0.5 wt% and 49.6 wt%, respectively, and the other steps were the same as in Example 1.

[0061] Example 3

[0062] The contents of compound 1 and DMC in the electrolyte were 1.5 wt% and 48.6 wt%, respectively, and the other steps were the same as in Example 1.

[0063] Example 4

[0064] The contents of compound 1 and DMC in the electrolyte were 3 wt% and 47.1 wt%, respectively, and the other steps were the same as in Example 1.

[0065] Example 5

[0066] The contents of compound 1 and DMC in the electrolyte were 5 wt% and 45.1 wt%, respectively, and the other steps were the same as in Example 1.

[0067] Example 6

[0068] The first additive in the electrolyte is compound 3, and the other steps are the same as in Example 2.

[0069] Example 7

[0070] The first additive in the electrolyte is compound 5, and the other steps are the same as in Example 2.

[0071] Example 8

[0072] The first additive in the electrolyte is compound 6, and the other steps are the same as in Example 2.

[0073] Example 9

[0074] The first additive in the electrolyte is compound 7, and the other steps are the same as in Example 2.

[0075] Example 10

[0076] The electrolyte also contains a second additive, DTD, and the contents of DTD and DMC in the electrolyte are 0.1 wt% and 49.5 wt%, respectively. The other steps are the same as in Example 2.

[0077] Example 11

[0078] The contents of DTD and DMC in the electrolyte are 0.5 wt% and 49.1 wt%, respectively, and the other steps are the same as in Example 10.

[0079] Example 12

[0080] The contents of DTD and DMC in the electrolyte are 1 wt% and 48.6 wt%, respectively, and the other steps are the same as in Example 10.

[0081] Example 13

[0082] The contents of DTD and DMC in the electrolyte are 2 wt% and 47.6 wt%, respectively, and the other steps are the same as in Example 10.

[0083] Example 14

[0084] The contents of DTD and DMC in the electrolyte are 5 wt% and 44.6 wt%, respectively, and the other steps are the same as in Example 10.

[0085] Example 15

[0086] The contents of EC and DMC in the electrolyte are 8 wt% and 59.5 wt%, respectively, and the other steps are the same as in Example 2.

[0087] Example 16

[0088] The contents of EC and DMC in the electrolyte are 10 wt% and 57.5 wt%, respectively, and the other steps are the same as in Example 15.

[0089] Example 17

[0090] The contents of EC and DMC in the electrolyte are 15 wt% and 52.5 wt%, respectively, and the other steps are the same as in Example 15.

[0091] Example 18

[0092] The electrolyte also contains a third additive, LiODFP. The contents of LiODFP and DMC in the electrolyte are 0.2 wt% and 49.4 wt%, respectively. The other steps are the same as in Example 2.

[0093] Example 19

[0094] The contents of LiODFP and DMC in the electrolyte are 0.5 wt% and 49.1 wt%, respectively, and the other steps are the same as in Example 18.

[0095] Example 20

[0096] The contents of LiODFP and DMC in the electrolyte were 0.8 wt% and 48.8 wt%, respectively, and the other steps were the same as in Example 18.

[0097] Example 21

[0098] The electrolyte also contains a second additive, DTD, and a third additive, LiODFP. The contents of DMC, LiODFP, DTD, and DMC in the electrolyte are 48.6 wt%, 0.5 wt%, and 0.5 wt%, respectively. The other steps are the same as in Example 2.

[0099] Comparative Example 1

[0100] The contents of compound 1 and DMC in the electrolyte were 0 and 50.1 wt%, respectively, and the other steps were the same as in Example 2.

[0101] Comparative Example 2

[0102] The contents of compound 1 and DMC in the electrolyte were 0 and 49.6 wt%, respectively, and the other steps were the same as in Example 11.

[0103] Comparative Example 3

[0104] The contents of compound 1 and DMC in the electrolyte were 0 and 58 wt%, respectively, and the other steps were the same as in Example 16.

[0105] Comparative Example 4

[0106] The contents of compound 1 and DMC in the electrolyte were 0 and 49.6 wt%, respectively, and the other steps were the same as in Example 19.

[0107] Comparative Example 5

[0108] The first additive in the electrolyte is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the other steps are the same as in Example 2.

[0109] The content and mass ratio of raw material components required for the electrolytes prepared in each embodiment and comparative example are shown in Table 1. The content of each component is a mass percentage calculated based on the total mass of the electrolyte.

[0110] Table 1. Composition of electrolytes in Examples 1-21 and Comparative Examples 1-5

[0111]

[0112]

[0113] In this invention, the lithium-ion batteries prepared with different electrolyte ratios in Examples 1-21 and Comparative Examples 1-5 were subjected to performance tests, and the test results are shown in Table 2.

[0114] In one embodiment of the present invention, for example, an initial (Beginning of Life, BOL) direct current resistance (DCR) test is performed on a lithium-ion battery. Specifically, the temperature of the constant temperature chamber is adjusted to 25°C. After the lithium-ion battery is left to stand in the constant temperature chamber for 10 minutes, it is then charged at a constant current of 0.33C to 4.25V, and then charged at a constant current of 4.25V to 0.05C. After standing for 30 minutes, the battery is discharged at a constant current of 0.33C to 2.5V, and then stood for 10 minutes. This cycle is repeated twice to obtain the final discharge capacity C0. Then, the battery is charged at a constant current of 0.33C to 4.25V, and then charged at a constant voltage to 0.05C. After standing for 30 minutes, the battery is discharged at a constant current of 0.33C to (50% C0), and then stood for 1 hour. The voltage V0 at the end of the standing period is recorded. Then, the battery is discharged at a constant current of 4C0 for 30 seconds, and the voltage V1 is recorded. The BOL DCR is calculated according to the following formula:

[0115] BOL DCR=(V0-V1) / 4C0.

[0116] In one embodiment of the present invention, a high-temperature cycling performance test is performed on a lithium-ion battery, for example. Specifically, the temperature of the constant temperature chamber is adjusted to 45°C. After the lithium-ion battery is left to stand in the constant temperature chamber for 30 minutes, it is charged at a constant current of 1C to 4.25V, then charged at a constant voltage to a current of 0.05C. After standing for 10 minutes, the battery is discharged at a constant current of 1C to 2.5V, and the battery capacity C0 is recorded. The above charge and discharge steps are repeated 500 times, and the discharge capacity C1 of the battery after 500 cycles is recorded. The capacity retention rate of the battery after 500 cycles at 45°C is calculated according to the following formula:

[0117] Capacity retention rate = C1 / C0 * 100%.

[0118] Table 2. Performance test results of lithium-ion batteries in Examples 1-21 and Comparative Examples 1-5

[0119]

[0120] Please refer to Tables 1 and 2. Comparing Examples 1-5, Comparative Examples 1 and 5, it can be seen that when the electrolyte contains Compound 1, the battery capacity retention rate can be increased by more than 20%, and the BOL DCR is significantly reduced. This shows that Compound 1 can improve the kinetic performance of the electrolyte and can form a stable protective layer on the electrode surface, thereby improving the cycle performance of the battery.

[0121] Please refer to Tables 1 and 2. Comparing Examples 1-5, it can be seen that as the content of the first additive increases, the battery capacity first increases and then decreases, while the BOL DCR first decreases and then increases. This indicates that by controlling the content of the first additive to be 0.1wt%-3wt%, the kinetic performance of the electrolyte and the cycle stability of the battery can be improved.

[0122] Please refer to Tables 1 and 2. Comparing Examples 2 and 6-9, it can be seen that among the five first additives, compounds 1, 3, 5, 6, and 7, the BOL DCR of the battery is relatively low and the capacity retention rate is above 90% because cyclopentadiene or benzene rings contain F atom substituents. This shows that F atom-substituted unsaturated cyclic alkanes can effectively form a stable protective layer (LiF) on the electrode surface, thereby improving the cycle performance of the battery.

[0123] Please refer to Tables 1 and 2. Comparing Examples 10-14, Comparative Examples 1 and 2, it can be seen that when the electrolyte contains only the second additive and not the first additive, the battery capacity retention rate is slightly improved and the BOL DCR is slightly reduced. However, when the electrolyte contains both the first and second additives, the battery capacity retention rate is significantly improved and the BOL DCR is significantly reduced. This indicates that the synergistic effect of the first and second additives can significantly improve the kinetic performance of the electrolyte and the cycle performance of the battery.

[0124] Please refer to Tables 1 and 2. Comparing Examples 10-14, it can be seen that as the content of the second additive increases, the battery capacity first increases and then decreases, and the BOL DCR first decreases and then increases. This shows that by controlling the content of the second additive, the kinetic performance of the electrolyte and the cycle stability of the battery can be improved.

[0125] Please refer to Tables 1 and 2. Comparing Comparative Examples 1 and 3, it can be seen that when there is no first additive in the electrolyte, the BOL DCR of the battery decreases and the capacity retention rate increases with the increase of the first solvent content. However, comparing Examples 16 and 2, it can be seen that when the electrolyte contains the first additive, the BOL DCR of the battery decreases significantly and the capacity retention rate increases significantly with the increase of the first solvent content. This indicates that there is an interaction between the first additive and the first solvent, and their synergistic use can significantly improve the kinetic performance of the electrolyte and the cycle stability of the battery.

[0126] Please refer to Tables 1 and 2. Comparing Examples 15-17 and Example 2, it can be seen that as the content of the first solvent increases, the battery capacity retention rate improves and the BOL DCR decreases. Therefore, by controlling the content of the first solvent, the electrolyte viscosity can be reduced, thereby improving the electrolyte kinetics, reducing battery impedance, and also improving the battery cycle performance.

[0127] Please refer to Tables 1 and 2. Comparing Comparative Examples 1 and 4, it can be seen that when the electrolyte does not contain the first additive, adding the third additive to the electrolyte reduces both the BOLDCR and capacity retention of the battery. Comparing Examples 2 and 19, it can be seen that when the electrolyte contains the first additive, adding the third additive slightly increases the BOLDCR of the battery, but also increases the capacity retention. This indicates that the first and third additives work synergistically to form a hydrogen bond structure with excellent expansibility on the electrode surface, ensuring that the SEI film is not easily broken during battery cycling, thereby improving the battery cycling stability.

[0128] Please refer to Tables 1 and 2. Comparing Examples 18-20, it can be seen that as the content of the third additive increases, the battery capacity retention first increases and then decreases, while the BOL DCR first decreases and then increases. When the content of the third additive is 0.5 wt%, the battery capacity retention and BOL DCR reach their optimal values. Therefore, by controlling the content of the third additive, battery impedance can be minimized and battery cycle performance improved.

[0129] Please refer to Tables 1 and 2. Comparing Examples 2, 11, 19, 21, and Comparative Example 1, it can be seen that when the electrolyte contains the first additive, the second additive, and the third additive simultaneously, the battery exhibits the highest capacity retention and the lowest BOL DCR. Therefore, the first, second, and third additives can work synergistically to maximize the battery's cycle performance and the electrolyte's kinetic performance.

[0130] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0131] In summary, this invention proposes a lithium-ion battery electrolyte and its application. By introducing a first additive and a second additive into the electrolyte, the first and second additives work synergistically to facilitate the formation of inorganic SEI materials such as lithium fluoride on the negative electrode surface. This effectively reduces unnecessary chemical reactions between the negative electrode and the electrolyte, improving the safety and stability of the battery. Furthermore, the first and third additives interact electrostatically to form hydrogen bonds with excellent expansion characteristics, ensuring that the SEI film does not rupture during the expansion and contraction of the negative electrode, further improving the cycle stability of the battery.

[0132] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0133] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A lithium-ion battery electrolyte, characterized in that, It includes at least the following components: Lithium salts; Solvent; as well as The additive includes a first additive, the first additive having the following general structural formula: Wherein, A is selected from cyclopentadienyl or phenyl, X1 is selected from -S(=O)2- or -P(F)-, L1 is selected from unsubstituted or first-substituted C1-C4 amino-substituted alkylene, and amino-substituted (-C2H4-O-C2H4-)n1, n1 is selected from an integer from 1 to 10, R1 and R2 are each independently selected from hydrogen atom, halogen atom, unsubstituted or second-substituted alkyl, alkenyl or alkynyl with an unsaturation degree of 0-2 and a carbon number of 1-4, carbonyl, ester, ether, amide or cyano with a carbon number of 2-4, and unsubstituted or third-substituted phenyl, the first substituent, the second substituent and the third substituent are each independently selected from halogen atom, and the third substituent has 1-2 substitution sites in the phenyl.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, In the general structural formula of the first additive, as a substituent group connected to the cyclic structure A: R1 is located at the ortho or meta position of the vinyl group on the cyclic structure A, and / or, the main chain having a sulfonamide structure is located at the ortho position of the vinyl group on the cyclic structure A.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The first additive is selected from: Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 or At least one of compound 7.

4. The lithium-ion battery electrolyte according to claim 1, characterized in that, The content of the first additive in the electrolyte is 0.1wt%-3wt%.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive further includes a second additive, which is selected from at least one of vinyl sulfate, fluorovinyl carbonate, 1,3-propanesulfonic acid lactone, or trimethylsilyl phosphate.

6. The lithium-ion battery electrolyte according to claim 5, characterized in that, The content of the second additive in the electrolyte is 0.3wt%-2wt%.

7. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additive also includes a third additive, which is selected from at least one of lithium difluorooxalate phosphate or lithium difluorooxalate borate, and the content of the third additive in the electrolyte is 0.2wt%-0.8wt%.

8. The lithium-ion battery electrolyte according to claim 1, characterized in that, The solvent includes a first solvent, which is selected from at least one of ethylene carbonate or propylene carbonate, and the content of the first solvent in the electrolyte is 8wt%-15wt%.

9. The lithium-ion battery electrolyte according to claim 8, characterized in that, The solvent further includes a second solvent, which is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

10. A lithium-ion battery, characterized in that, include: The positive electrode sheet includes a positive electrode active material, wherein the structural formula of the positive electrode active material is Li. x [Ni y Co z Mn t M (1-y-z-t) O 2-δ Wherein, M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, or Zn, 0.9 <x<1.1,0.65≤y<1.0,0≤z<0.5,0≤t<0.5,0≤δ≤0.1; A negative electrode sheet, comprising a negative electrode active material, wherein the negative electrode active material comprises at least one of silicon-oxygen materials or silicon-carbon materials; A diaphragm is disposed between the positive electrode and the negative electrode; and The electrolyte is selected from the lithium-ion battery electrolyte according to any one of claims 1-9.

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