An electrolyte and its preparation method and application

Abstract

The present invention discloses an electrolyte, a preparation method, and an application thereof. The electrolyte includes a solvent, wherein the solvent includes a fluoroether compound, a fluorocarboxylate, and a fluorocarbonate, wherein, based on the total mass of the electrolyte, the mass fraction X of the fluoroether compound is 0.1-30%, the mass fraction Y of the fluorocarboxylate is 0.1-60%, and the mass fraction Z of the fluorocarbonate is 0.1-40%. In the present invention, by introducing a novel fluorosolvent into the electrolyte, the resulting battery electrolyte not only exhibits excellent oxidation resistance and high-temperature performance, but also effectively maintains excellent cycle performance and can improve hot box performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries, and in particular relates to an electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, with their high operating voltage, long cycle life, high energy density, and environmentally friendly characteristics, are widely used in portable electronic devices, electric vehicles, and other fields. As one of the key materials in lithium-ion batteries, the electrolyte primarily transports lithium ions within the battery and is often referred to as the "blood" of the battery. The electrolyte primarily consists of a solvent, lithium salt, and additives. However, the solvent in traditional electrolytes is often easily oxidized, resulting in a decrease in the battery's cycle life. Summary of the Invention

[0003] The present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides an electrolyte having the characteristic of strong oxidation resistance.

[0004] The invention also provides a method for preparing the electrolyte.

[0005] The present invention also provides a secondary battery.

[0006] The present invention also provides the application of the electrolyte.

[0007] In a first aspect of the present invention, an electrolyte is provided, comprising a solvent, wherein the solvent comprises a fluoroether compound, a fluorocarboxylate and a fluorocarbonate, wherein, based on the total mass of the electrolyte: the mass fraction X of the fluoroether compound is 0.1-30%, the mass fraction Y of the fluorocarboxylate is 0.1-60%, and the mass fraction Z of the fluorocarbonate is 0.1-40%.

[0008] The electrolyte according to the embodiment of the present invention has at least the following beneficial effects:

[0009] The present invention introduces a new type of fluorinated solvent, which is a fluorinated solvent of a specific ratio range and type. The resulting battery electrolyte not only exhibits excellent oxidation resistance and high-temperature performance, but also effectively maintains excellent cycle performance and improves hot box performance. Specifically, after the H atoms in conventional solvents are replaced by F atoms, the F atoms have a strong electron-withdrawing effect, which can reduce the energy of the solvent's HOMO orbital, making it more difficult for electrons in its HOMO orbital to be captured. Therefore, the present invention uses a specific ratio and type of fluorinated solvent to significantly improve the solvent's oxidation resistance, thereby extending the battery's cycle life. The fluorinated solvents in the present invention also have good flame retardant properties, which can improve the battery's cycle performance, high-temperature performance, and hot box performance.

[0010] In some embodiments of the present invention, the fluoroether compound is represented by Formula I:

[0011]

[0012] Wherein, R1 and R2 are each independently selected from a substituted or unsubstituted alkyl or alkoxy group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

[0013] In some preferred embodiments of the present invention, the fluoroether compound comprises at least one of the compounds of formula I-1 to I-7:

[0014]

[0015] In some embodiments of the present invention, the mass fraction X of the fluoroether compound is 5-20%.

[0016] In some embodiments of the present invention, the mass fraction X of the fluoroether compound is 10-20%.

[0017] In some embodiments of the present invention, the fluorocarboxylate is represented by Formula II:

[0018]

[0019] Wherein, R3 and R4 are each independently selected from a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

[0020] In some preferred embodiments of the present invention, the carboxylic acid ester comprises at least one of the compounds of formula II-1 to II-4:

[0021]

[0022] In some embodiments of the present invention, the mass fraction Y of the fluorocarboxylate is 15-60%.

[0023] In some preferred embodiments of the present invention, the mass fraction Y of the fluorocarboxylate is 40-60%.

[0024] In some embodiments of the present invention, the fluorocarbonate comprises at least one of a compound of formula III or a compound of formula IV:

[0025]

[0026] Wherein, R5 to R8 are each independently selected from a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

[0027] In some preferred embodiments of the present invention, the compound of formula III includes at least one of the compounds of formula III-1 to III-3:

[0028]

[0029] In some preferred embodiments of the present invention, the compound of formula IV comprises at least one of the compounds of formula IV-1 to IV-3:

[0030]

[0031] In some embodiments of the present invention, the mass fraction Z of the fluorinated carbonate is 5-25%.

[0032] In some preferred embodiments of the present invention, the mass fraction Z of the fluorinated carbonate is 10-20%.

[0033] In some embodiments of the present invention, the relationships among X, Y, and Z satisfy equations (1) to (3):

[0034] 30%≤X+Y+Z≤90% (1);

[0035] 5%≤X+Y≤75% (2);

[0036] 0.2≤X / Y≤1 (3).

[0037] In some preferred embodiments of the present invention, 5%≤X+Y≤70%.

[0038] In some embodiments of the present invention, the electrolyte further includes a polynitrile compound.

[0039] In some preferred embodiments of the present invention, the polynitrile compound includes 1,3,6-hexanetrinitrile (HTCN).

[0040] In some preferred embodiments of the present invention, based on the total mass of the electrolyte, the mass fraction of the polynitrile compound is 0.1-4%.

[0041] In some embodiments of the present invention, the electrolyte further includes a lithium salt.

[0042] In some preferred embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) or lithium bis(fluorosulfonyl imide) (LiFSI).

[0043] In some preferred embodiments of the present invention, based on the total mass of the electrolyte, the mass fraction of the lithium salt is 0.1-20%.

[0044] In some more preferred embodiments of the present invention, the mass fraction of the lithium salt is 10-20% based on the total mass of the electrolyte.

[0045] In some embodiments of the present invention, the electrolyte further includes a film-forming additive.

[0046] Through the above-mentioned embodiment, the solvent (fluorinated) in the present invention works synergistically with the film-forming additive to form a LiF-rich solid electrolyte interface film (SEI) on the surface of the positive and negative electrodes. The interface film has a high Young's modulus and can effectively inhibit the formation of lithium dendrites.

[0047] In some preferred embodiments of the present invention, the film-forming additive includes at least one of a sulfonate compound, butylene sulfite (BS), vinyl sulfate (DTD), succinonitrile (SN), adiponitrile (ADN) or ethylene glycol bis(propionitrile) ether (EGBE).

[0048] In some more preferred embodiments of the present invention, the sulfonate compound includes 1,3-propane sultone (PS).

[0049] In some more preferred embodiments of the present invention, based on the total mass of the electrolyte, the mass fraction of the sulfonate compound is 0.1-7%.

[0050] In some preferred embodiments of the present invention, based on the total mass of the electrolyte, the mass fraction of the film-forming additive is 0.1-27%.

[0051] In some more preferred embodiments of the present invention, the mass fraction of the film-forming additive is 0.1-20% based on the total mass of the electrolyte. In a second aspect of the present invention, a method for preparing an electrolyte is provided, comprising the steps of: mixing a fluoroether compound, a fluorocarboxylate, and a fluorocarbonate to obtain a solvent, thereby obtaining the electrolyte.

[0052] In some embodiments of the present invention, the preparation method includes the following steps: mixing the solvent, lithium salt and polynitrile compound to obtain the electrolyte.

[0053] In some embodiments of the present invention, the preparation method includes the following steps: mixing the solvent, lithium salt, polynitrile compound and film-forming additive to obtain the electrolyte.

[0054] In some embodiments of the present invention, the preparation method comprises the following steps: mixing a fluoroether compound, a fluorocarboxylic acid ester and a fluorocarbonate, adding a lithium salt, a film-forming additive and a polynitrile compound to obtain the electrolyte.

[0055] According to a third aspect of the present invention, a secondary battery is provided, wherein the secondary battery comprises the above-mentioned electrolyte.

[0056] In some embodiments of the present invention, the secondary battery includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode current collector and a negative electrode membrane.

[0057] In some preferred embodiments of the present invention, the negative electrode current collector comprises copper foil.

[0058] In some preferred embodiments of the present invention, the negative electrode film includes a negative electrode active material, a negative electrode conductor and a negative electrode binder.

[0059] In some more preferred embodiments of the present invention, the negative electrode active material includes graphite; preferably, the graphite includes at least one of artificial graphite or natural graphite.

[0060] In some embodiments of the present invention, the secondary battery includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode membrane.

[0061] In some preferred embodiments of the present invention, the positive electrode current collector comprises aluminum foil.

[0062] In some preferred embodiments of the present invention, the positive electrode film includes a positive electrode active material, a positive electrode conductor and a positive electrode binder.

[0063] In some more preferred embodiments of the present invention, the positive electrode active material includes LiCoO2.

[0064] In some embodiments of the present invention, the secondary battery includes at least one of a lithium ion battery or a sodium ion battery.

[0065] The beneficial effects of the present invention include:

[0066] The present invention replaces the existing conventional solvent system by mixing different types of fluorinated solvents, and develops a new electrolyte system including fluorinated solvents, lithium salts, and film-forming additives to improve the oxidation resistance of the electrolyte. After the H atoms in the conventional solvents are replaced by F atoms, the F atoms have a strong electron-withdrawing effect, which can reduce the energy of the HOMO orbit of the solvent, and the electrons in its HOMO orbit are more difficult to be captured. Therefore, the fluorinated solvents used in the present invention can significantly improve the oxidation resistance of the solvent, thereby extending the cycle life of the battery. At the same time, the fluorinated solvents and the film-forming additives work synergistically to form a solid electrolyte interface film (SEI) rich in LiF on the surface of the positive and negative electrodes. The interface film has a high Young's modulus and can effectively inhibit the formation of lithium dendrites. At the same time, the fluorinated solvents in the present invention have good flame retardant properties, so they can improve the cycle performance, high temperature performance and hot box performance of the battery. DETAILED DESCRIPTION

[0067] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0068] The experimental methods in the following examples, for which specific conditions are not specified, are generally performed in accordance with conventional conditions in the art or conditions recommended by the manufacturers; the raw materials and reagents used, unless otherwise specified, are all commercially available from conventional markets.

[0069] Example 1

[0070] This embodiment discloses an electrolyte, the preparation process of which includes:

[0071] In an argon-filled glove box, the compounds of formulas I-1, II-1, and III-1 were mixed in a mass ratio of 2:6:2 to obtain a mixed solution (organic solvent). Lithium hexafluorophosphate (LiPF6) was then slowly added to the mixed solution, followed by the addition of 1,3-propane sultone (PS) and 1,3,6-hexane tricarbonitrile (HTCN). The mixture was stirred uniformly to obtain an electrolyte solution. The electrolyte solution contained 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexane tricarbonitrile (HTCN), with the remainder being the organic solvent, based on the total weight of the electrolyte.

[0072] Compound of formula I-1: Compound of formula II-1:

[0073] Compound of formula III-1:

[0074] This embodiment also discloses a lithium-ion battery, which is a soft-pack battery. The preparation process of the lithium-ion battery includes:

[0075] The positive electrode sheet (active material LiCoO2, Peking University Pioneer 983HA), the separator (Shenzhen Xingyuan Material SW09), and the negative electrode sheet (active material graphite, Shanshan Technology FSN-1) are stacked in order with the separator in the middle of the positive and negative electrode sheets, and the bare battery cell is wound to obtain the bare battery cell. The bare battery cell is placed in an aluminum-plastic film outer packaging, and the electrolyte prepared in this embodiment is injected into the dried battery cell. The battery cell is packaged, allowed to stand, formed, shaped, and capacity divided to obtain a lithium-ion battery.

[0076] Example 2

[0077] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-2 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0078] Among them, the compound of formula I-2:

[0079] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0080] Example 3

[0081] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-3 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0082] Among them, the compound of formula I-3:

[0083] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0084] Example 4

[0085] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-4 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0086] Among them, the compound of formula I-4:

[0087] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0088] Example 5

[0089] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-5 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0090] Among them, the compound of formula I-5:

[0091] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0092] Example 6

[0093] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-6 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0094] Among them, the compound of formula I-6:

[0095] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0096] Example 7

[0097] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula I-7 is used in this embodiment to replace the compound of formula I-1 in Example 1.

[0098] Among them, the compound of formula I-7:

[0099] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0100] Example 8

[0101] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula III-2 is used in this embodiment to replace the compound of formula III-1 in Example 1.

[0102] Among them, the compound of formula III-2:

[0103] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0104] Example 9

[0105] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula III-3 is used in this embodiment to replace the compound of formula III-1 in Example 1.

[0106] Among them, the compound of formula III-3:

[0107] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0108] Example 10

[0109] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula IV-1 is used in this embodiment to replace the compound of formula III-1 in Example 1.

[0110] Among them, the compound of formula IV-1:

[0111] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0112] Example 11

[0113] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula IV-2 is used in this embodiment to replace the compound of formula III-1 in Example 1.

[0114] Among them, the compound of formula IV-2:

[0115] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0116] Example 12

[0117] This embodiment discloses an electrolyte, which differs from Example 1 only in that an equal mass of the compound of formula IV-3 is used in this embodiment to replace the compound of formula III-1 in Example 1.

[0118] Among them, the compound of formula IV-3:

[0119] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0120] Example 13

[0121] This embodiment discloses an electrolyte solution, which differs from that of Example 1 only in that the electrolyte solution of this embodiment does not contain PS. Specifically, based on the total weight of the electrolyte solution, the electrolyte solution of this embodiment contains 14.5 wt% lithium hexafluorophosphate, 2 wt% 1,3,6-hexanetricarbonitrile (HTCN), and the balance an organic solvent. The composition of the organic solvent is the same as that of Example 1.

[0122] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0123] Example 14

[0124] This embodiment discloses an electrolyte solution, which differs from that of Example 1 in that the electrolyte solution of this embodiment does not contain HTCN. Specifically, based on the total weight of the electrolyte solution, the electrolyte solution of this embodiment contains 14.5 wt% lithium hexafluorophosphate, 4 wt% 1,3-propane sultone (PS), and the balance is an organic solvent. The composition of the organic solvent is the same as that of Example 1.

[0125] This embodiment also discloses a lithium-ion battery, which contains an electrolyte prepared in this embodiment, and other components and preparation steps are the same as those in Example 1.

[0126] Comparative Example 1

[0127] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetrionitrile (HTCN), and the remainder is an organic solvent, wherein EC (ethylene carbonate), DEC (diethyl carbonate) and PC (propylene carbonate) are mixed in a mass ratio of EC:DEC:PC=2:6:2 to obtain the organic solvent (mixed solution).

[0128] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0129] Comparative Example 2

[0130] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), and the remainder is an organic solvent, wherein the compound of formula I-1, DEC and PC are mixed in a mass ratio of compound of formula I-1:DEC:PC=2:6:2 to obtain the organic solvent (mixed solution).

[0131] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0132] Comparative Example 3

[0133] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), and the remainder is an organic solvent, wherein EC, a compound of formula II-1, and PC are mixed in a mass ratio of EC: compound of formula II-1: PC = 2:6:2 to obtain the organic solvent (mixed solution).

[0134] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0135] Comparative Example 4

[0136] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), and the remainder is an organic solvent, wherein EC, DEC and the compound of formula III-1 are mixed in a mass ratio of EC:DEC:compound of formula III-1=2:6:2 to obtain the organic solvent (mixed solution).

[0137] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0138] Comparative Example 5

[0139] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetricarbonitrile (HTCN), and the remainder is an organic solvent, wherein EC, DEC and the compound of formula IV-1 are mixed in a mass ratio of EC:DEC:compound of formula IV-1=2:6:2 to obtain the organic solvent (mixed solution).

[0140] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0141] Comparative Example 6

[0142] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetrionitrile (HTCN), and the remainder is an organic solvent, wherein EC, a compound of formula II-1, and a compound of formula III-1 are mixed in a mass ratio of EC: compound of formula II-1: compound of formula III-1 = 2:6:2 to obtain the organic solvent (mixed solution).

[0143] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0144] Comparative Example 7

[0145] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetrionitrile (HTCN), and the remainder is an organic solvent, wherein the compound of formula I-1, DEC and the compound of formula III-1 are mixed in a mass ratio of compound of formula I-1:DEC: compound of formula III-1 = 2:6:2 to obtain the organic solvent (mixed solution).

[0146] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0147] Comparative Example 8

[0148] This comparative example discloses an electrolyte, which differs from Example 1 only in that the composition of the organic solvent in the electrolyte of this comparative example is different from that of Example 1. Specifically, in this comparative example, based on the total weight of the electrolyte, the electrolyte contains 14.5 wt% of lithium hexafluorophosphate, 4 wt% of 1,3-propane sultone (PS), and 2 wt% of 1,3,6-hexanetrinitrile (HTCN), and the remainder is an organic solvent, wherein the compound of formula I-1, the compound of formula II-1, and PC are mixed in a mass ratio of formula I-1 compound: formula II-1 compound: PC = 2:6:2 to obtain the organic solvent (mixed solution).

[0149] This comparative example also discloses a lithium-ion battery, which contains an electrolyte prepared in this comparative example, and other components and preparation steps are the same as those in Example 1.

[0150] The composition and content of the organic solvent, lithium salt and additive (sulfonate compound, polynitrile compound) in the electrolyte in Examples 1-14 and Comparative Examples 1-8 are shown in Table 1 below. In Table 1, the content of each component is the mass percentage calculated based on the total mass of the electrolyte:

[0151] Table 1

[0152]

[0153]

[0154] Test example

[0155] This test example performed performance tests on the batteries obtained in the examples and comparative examples, specifically including:

[0156] 1. Room temperature cycle performance test: In a 25°C environment, charge the divided battery at a constant current and constant voltage of 1C to 4.50V, with a cut-off current of 0.05C, and then discharge it at a constant current of 0.7C to 3.0V. Repeat this cycle. After 500 cycles of charge and discharge, calculate the capacity retention rate at the 500th week. The calculation formula is as follows:

[0157] 500th cycle capacity retention rate (%) = (500th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0158] 2. High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.50V at a constant current and constant voltage of 1C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.7C. After 400 cycles of charge and discharge, the capacity retention rate at the 400th week is calculated. The calculation formula is as follows:

[0159] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%.

[0160] 3. 60℃ 14d high temperature storage test: The battery was placed at room temperature and charged and discharged once at 0.5C (4.50V-3.0V), and the discharge capacity C0 of the battery before storage was recorded. The battery was then charged to a fully charged state of 4.50V using a PPG battery thickness gauge (600g) to measure the thickness d1 of the battery before high temperature storage. The battery was placed in a 60℃ constant temperature box and stored for 14 days. After storage, the battery was taken out and the thermal thickness d2 of the battery after storage was measured. The thickness expansion rate of the battery after storage at 60℃ for 14 days was calculated. After the battery was cooled at room temperature for 24h, the battery was again discharged to 3.0V at 0.5C and then charged to 4.50V at 0.5C constant current and constant voltage. The discharge capacity C1 and charge capacity C2 of the battery after storage were recorded. The capacity remaining rate (retention rate) and recovery rate of the battery after storage at 60℃ for 14 days were calculated as follows:

[0161] Thickness expansion ratio after storage at 60°C for 14 days = (d2-d1) / d1×100%;

[0162] After 14 days of storage at 60°C, the remaining capacity is C1 / C0×100%.

[0163] After storage at 60°C for 14 days, the capacity recovery rate = C2 / C0×100%.

[0164] 4. Low temperature discharge performance test: Under 25℃ environmental conditions, discharge the divided battery at 0.5C to 3.0V and let it sit for 5 minutes; then charge it at 0.2C to 4.50V. When the cell voltage reaches 4.50V, change to 4.50V constant voltage charging until the charging current is less than or equal to the given cut-off current 0.05C and let it sit for 5 minutes; transfer the fully charged cell to a high and low temperature box, set to -10℃, and let it sit for 120 minutes after the box temperature reaches the target; then discharge it at 0.2C to a termination voltage of 3.0V and let it sit for 5 minutes; then adjust the high and low temperature box temperature to 25℃±1℃, and let it sit for 60 minutes after the box temperature reaches the target; charge it at 0.2C to 4.50V. When the cell voltage reaches 4.50V, change to 4.50V constant voltage charging until the charging current is less than or equal to the given cut-off current 0.05C; let it sit for 5 minutes; calculate the -10℃ low temperature discharge 3.0V capacity retention rate. The calculation formula is as follows:

[0165] Capacity retention rate at -10°C discharge to 3.0V (%) = (discharge capacity at -10°C discharge to 3.0V / discharge capacity at 25°C discharge to 3.0V) × 100%.

[0166] 5. Thermal shock performance (hot box test): Under 25℃ ambient conditions, discharge the battery to 3.0V at a given current of 0.2C; let it sit for 5 minutes; charge it to 4.50V at a charging current of 0.2C. When the battery cell voltage reaches 4.50V, change to 4.50V constant voltage charging until the charging current is less than or equal to the given cut-off current of 0.05C; after leaving it for 1 hour, place the battery cell in an oven, increase the oven temperature to 135±2℃ at a rate of 5±2℃ / min, and keep it for 30 minutes before stopping. The judgment standard is that the battery cell does not catch fire or explode.

[0167] The performance test results of the batteries in Examples 1-14 and Comparative Examples 1-8 are shown in Table 2 below:

[0168] Table 2

[0169]

[0170]

[0171] From the comparison of the test results of Comparative Examples 1-5 and Examples 1-12 in Table 2, it can be seen that replacing all carbonate and carboxylate solvents with fluorinated solvents in the examples can significantly improve the room temperature cycle performance, high temperature cycle performance, and hot box performance of the electrolyte, improve the charge retention rate and capacity recovery rate of the battery after high temperature storage, and inhibit the gas production of the battery after high temperature storage.

[0172] It can be seen from Example 1 and Comparative Examples 1-8 that the performance of any one or two types of fluorinated solvents among fluoroether compounds, fluorocarboxylates and fluorocarbonates is inferior to the performance of a mixture of three types of solvents (fluoroether compounds, fluorocarboxylates and fluorocarbonates). The three types of solvents can improve the comprehensive performance of the electrolyte through synergistic effects.

[0173] Examples 1, 13, and Comparative Example 2 demonstrate that the PS additive effectively improves the battery's cycling performance and high-temperature storage performance. PS forms films on both the positive and negative electrodes, with a greater impact on the positive electrode. Formation of the PS film on the positive electrode significantly improves the battery's cycle life and storage stability. Furthermore, as a film-forming additive, PS synergizes with fluorinated solvents to stabilize the negative electrode material and enhance battery performance.

[0174] By comparing Example 1 and Example 14, it can be seen that the additive HTCN can effectively improve the cycle performance and high temperature storage performance of the battery. HTCN is a nitrile containing multiple -CN groups, which can effectively complex the Co dissolved in the positive electrode active material LiCoO2. 3 + / Co 4+ , inhibiting the catalytic oxidation of the electrolyte and the malignant growth of SEI, thereby improving the cycle life and high and low temperature performance of the battery.

[0175] It should be noted that, unless otherwise specified, “room temperature” or “normal temperature” herein refers to approximately 25° C.; and “approximately” for numerical values ​​herein means an error of ±2%.

[0176] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A lithium ion battery electrolyte comprising a solvent, characterized in that: The solvent is composed of a fluoroether compound, a fluorocarboxylate and a fluorocarbonate, wherein, based on the total mass of the lithium-ion battery electrolyte: the mass fraction X of the fluoroether compound is 0.1-30%, the mass fraction Y of the fluorocarboxylate is 0.1-60%, and the mass fraction Z of the fluorocarbonate is 0.1-40%; The fluorocarbonate is a compound of formula IV: Wherein, R7 to R8 are each independently selected from a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that The fluoroether compound is shown in Formula I: Wherein, R1 and R2 are each independently selected from a substituted or unsubstituted alkyl or alkoxy group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

3. The lithium-ion battery electrolyte according to claim 2, characterized in that The fluoroether compound includes at least one of the compounds of formula I-1 to I-7:

4. The lithium-ion battery electrolyte according to claim 1, characterized in that The fluorocarboxylate is shown in Formula II: Wherein, R3 and R4 are each independently selected from a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, and when substituted, the substituent is selected from -F.

5. The lithium-ion battery electrolyte according to claim 4, characterized in that The fluorocarboxylate comprises at least one of the compounds of formula II-1 to II-4:

6. The lithium-ion battery electrolyte according to claim 1, characterized in that The compound of formula IV includes at least one of the compounds of formula IV-1 to IV-3:

7. The lithium-ion battery electrolyte according to claim 1, characterized in that The relationship between X, Y, and Z satisfies equations (1) to (3): 30%≤X+Y+Z≤90%(1); 5%≤X+Y≤75%(2); 0.2≤X / Y≤1(3) 8. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium ion battery electrolyte also includes a film-forming additive.

9. The lithium-ion battery electrolyte according to claim 8, characterized in that The film-forming additive includes at least one of sulfonate compounds, butylene sulfite, vinyl sulfate, succinonitrile, adiponitrile or ethylene glycol bis(propionitrile) ether.

10. The lithium-ion battery electrolyte according to claim 9, characterized in that The sulfonate compound includes 1,3-propane sultone.

11. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium ion battery electrolyte also includes polynitrile compounds.

12. The lithium-ion battery electrolyte according to claim 11, characterized in that The polynitrile compound includes 1,3,6-hexanetrinitrile.

13. The lithium-ion battery electrolyte according to claim 1, characterized in that The lithium ion battery electrolyte also includes lithium salt.

14. A secondary battery, characterized in that: The secondary battery comprises the lithium-ion battery electrolyte according to any one of claims 1 to 13, and the secondary battery is a lithium-ion battery.

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