Composite electrolyte, application thereof and lithium ion battery

Abstract

The application relates to the field of lithium ion batteries, in particular to a composite electrolyte, application of the composite electrolyte and a lithium ion battery, wherein the composite electrolyte comprises a lithium salt, an organic solvent and a modifier, and the modifier comprises at least one compound with the structure of formula 1 ( ). Researches show that the compound with the formula 1 and a special tricyclic structure is used as an electrolyte modifier, an SEI / CEI film with a special physical and chemical structure can be constructed in situ, and the electrochemical performance of the electrolyte under high voltage (>=4.5V) and wide temperature range (-25 DEG C~60 DEG C) conditions can be effectively improved.

Description

Technical Field

[0001] This invention relates to the field of electrolytes, and more specifically to composite electrolytes and their applications, and to the field of lithium-ion batteries. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, high energy density, long cycle life, and low self-discharge rate, are widely used in consumer electronics, electric vehicles, and energy storage systems. The electrolyte, as the "blood" of a lithium-ion battery, plays a crucial role in transporting lithium ions between the positive and negative electrodes. Its composition directly determines the battery's rate performance, cycle stability, and safety. In practical applications, lithium-ion batteries often need to operate stably within a wide temperature range (-25℃ to 60℃). However, traditional electrolytes exhibit increased viscosity and a sharp drop in conductivity at low temperatures, and are prone to oxidation and decomposition at high voltages, leading to increased interfacial impedance and rapid capacity decay. Adding functional additives is one of the most economical and effective methods to optimize electrolyte performance and improve electrode / electrolyte interfacial compatibility.

[0003] To improve performance in wide-temperature applications, existing technologies have provided numerous electrolyte additives. For example, patent document CN107849004A discloses a method for manufacturing fluorinated cyclic carbonates and their use in lithium-ion batteries. Specifically, it reports the use of fluorinated cyclic carbonates (e.g., fluoroethylene carbonate and difluoroethylene carbonate) as electrolyte additives to improve performance in wide-temperature applications. Chinese patent document CN103618110A discloses a lithium-ion secondary battery and its electrolyte. The disclosed electrolyte includes lithium salts, a non-aqueous organic solvent, and additives. The additives contain a first additive and a second additive. The first additive is 1,3-propanesulfonyl lactone (PS), and the second additive is 4-methylene-1,3-dioxapentane-2-one and its derivatives having structural formula 1, and / or 4,5-dimethylene-1,3-dioxapentane-2-one and its derivatives having structural formula 2. This technical solution uses PS combined with carbonate derivatives to improve low-temperature performance.

[0004] In summary, the existing technology discloses many electrolyte modification schemes, but there is still room for improvement in the existing schemes that can take into account both high voltage (≥4.5V) and wide temperature range conditions. Summary of the Invention

[0005] In view of the problems existing in the prior art, the primary objective of this invention is to provide a composite electrolyte, which aims to improve the compatibility of the electrolyte with high-voltage positive electrodes and improve high-voltage and wide-temperature performance.

[0006] The second objective of this invention is to provide applications of composite electrolytes.

[0007] A third objective of this invention is to provide a lithium-ion battery comprising a composite electrolyte.

[0008] A composite electrolyte includes a lithium salt, an organic solvent, and a modifier, wherein the modifier includes at least one compound having the structure of Formula 1;

[0009] Formula 1

[0010] R1 and R2 are individually H, C1-C4 alkyl, or C1-C4 alkoxy; Ar is an aromatic ring with or without substituents; R3 is H, C1-C4 alkyl, C1-C4 alkylyl, C1-C4 ester, or benzyl.

[0011] The present invention demonstrates that using a compound of formula 1 with a special tricyclic structure as an electrolyte modifier can enable the in-situ construction of an SEI / CEI film with a special physicochemical structure, effectively improving the electrochemical performance of the electrolyte under high voltage (≥4.5V) and wide temperature range (-25℃~60℃).

[0012] The unique tri-ring structure of Formula 1 of this invention is adaptable to high-voltage battery systems, effectively neutralizing HF in the electrolyte, complexing transition metal ions dissolved from the positive electrode, and effectively complexing PF6. - This invention promotes lithium salt dissociation and participates in the formation of a low-impedance interfacial film rich in BO species on the cathode surface. Furthermore, it possesses an excellent rigid framework and π-π stacking ability, enhancing the adsorption stability of molecules on the cathode surface. The special tricyclic linkage structure described in this invention enables intramolecular synergy, allowing this type of additive to construct a stable, low-impedance interfacial protective layer under high voltage and wide temperature range conditions.

[0013] R1 and R2 are methyl or ethyl;

[0014] The Ar is a benzene ring, a pyridine ring, or a m-diazine.

[0015] The present invention demonstrates that preferred substituents can enhance electron-donating ability, which is beneficial to improving the formation efficiency of interfacial films; they can also balance adsorption stability and molecular flexibility; and thus help to further synergistically improve high-voltage and wide-temperature stability.

[0016] The modifier includes at least one of compound 1 to compound 12;

[0017]

[0018] Compound 1 Compound 2 Compound 3

[0019]

[0020] Compound 4 Compound 5

[0021]

[0022] Compound 6 Compound 7

[0023]

[0024] Compound 8, Compound 9, Compound 10

[0025]

[0026] Compound 11 Compound 12.

[0027] Preferably, the modifier is two or three of compound 1, compound 6, and compound 8; further, the modifier is compound 1 and compound 8 in a mass ratio of 1~2:1~2; or, the modifier is compound 1 and compound 6 in a mass ratio of 1~2:1~2; or, the modifier is compound 6 and compound 8 in a mass ratio of 1~2:1~2.

[0028] The composite electrolyte has a modifier content of 0.1wt% to 5.0wt%, preferably 0.3wt% to 2.0wt%, and more preferably 0.4wt% to 1wt%.

[0029] The electrolyte also contains additives (auxiliary modifiers), which are selected from at least one of sulfur-containing additives, fluorine-containing additives, and nitrile additives;

[0030] Preferably, the sulfur-containing additive is selected from at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, and methylene disulfonate;

[0031] The fluorinated additive is selected from at least one of fluoroethylene carbonate and difluoroethylene carbonate;

[0032] The nitrile additive is selected from at least one of butadionitrile, adiponitrile, and 1,3,6-hexanetrionitrile.

[0033] The mass ratio of the modifier to the additive is 1:5 to 5:1, and may further be 1:2:1.

[0034] The solvent is selected from at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate.

[0035] The lithium salt is selected from at least one of LiPF6, LiFSI, LiTFSI, LiBF4, and LiClO4, and may further be LiPF6;

[0036] The lithium salt concentration is 0.5~2.0 mol / L, and can be further 0.8~1.5 mol / L.

[0037] The present invention also provides an application of the aforementioned composite electrolyte in the preparation of lithium-ion batteries.

[0038] The present invention also provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the composite electrolyte described above;

[0039] Preferably, the positive electrode material in the positive electrode sheet is at least one of lithium nickel manganese oxide, lithium cobalt oxide, nickel-cobalt-manganese ternary material, and lithium-rich manganese-based material;

[0040] The negative electrode material in the negative electrode sheet is selected from at least one of graphite, silicon-based materials, lithium metal, niobium titanium oxide, and lithium titanate.

[0041] Beneficial effects

[0042] This invention demonstrates that using a special tricyclic compound of Formula 1 as a modifier for the electrolyte can achieve synergistic effects, enabling the in-situ construction of a SEI structure with a unique physicochemical structure, thereby effectively improving the long-cycle performance of the electrolyte under high voltage. Furthermore, the use of combined modifiers and / or modifier-auxiliary additive combinations further enhances the synergistic effect, strengthening the long-cycle performance of the electrolyte under high voltage. Attached Figure Description

[0043] Figure 1 SEM image of NCM811 cathode particles after 200 cycles at 45°C / 4.5V for the battery assembled in Example 4;

[0044] Figure 2 SEM image of NCM811 cathode particles after 200 cycles at 45℃ / 4.5V for the battery assembled for Comparative Example 1. Detailed Implementation

[0045] Example 1

[0046] In a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly in a mass ratio of 1:1:1. LiPF6 was slowly added until the concentration reached 1.0 mol / L, and the mixture was stirred until completely dissolved. Then, a modifier (compound of formula 1, specifically compound 1 in this case) was added at an amount of 0.5 wt% of the total electrolyte mass, and the mixture was stirred until completely dissolved to obtain the composite electrolyte.

[0047] The positive electrode sheet is made by coating an aluminum foil with a nickel-cobalt-manganese ternary material (NCM811) as the positive electrode active material, acetylene black as the conductive agent, and PVDF as the binder in a mass ratio of 8:1:1; a lithium metal sheet is used as the negative electrode; Celgard 2400 is used as the separator; and CR2032 button cells are assembled in a glove box.

[0048] The lithium-ion batteries obtained above were subjected to lithium-ion battery performance tests, including the following performance tests:

[0049] Test 1: High voltage cycle test: At 45℃, perform 200 charge-discharge cycles with a 1C / 1C current density in the voltage range of 3.0V~4.5V, and record the capacity retention rate.

[0050] Test 2: Wide temperature range cycling test: 100 charge-discharge cycles were performed at -25℃, 25℃, and 60℃ respectively, with a current density of 1C / 1C in the voltage range of 3.0V~4.3V, and the capacity retention rate was recorded.

[0051] Example 2

[0052] Compared with Example 1, the only difference is that the modifier of Formula 1 is changed. The total amount of modifier and other operations and parameters are the same as in Example 1. The experimental groups are as follows:

[0053] Group A: The modifier is compound 4;

[0054] Group B: The modifier is compound 6;

[0055] Group C: The modifier is compound 8;

[0056] Group D: The modifier is compound 10;

[0057] All other operations and parameters are the same as in Example 1.

[0058] Example 3

[0059] Compared with Example 1, the only difference is that the modifier of Formula 1 is used, the total amount of modifier and other operations and parameters are the same as in Example 1, and the experimental groups are as follows:

[0060] Group A: The modifiers are compound 1 and compound 6 in a mass ratio of 1:1;

[0061] Group B: The modifiers are compound 1 and compound 8 in a mass ratio of 1:1;

[0062] Group C: The modifiers are compound 6 and compound 8 in a mass ratio of 1:1;

[0063] The total amount of modifier and other operations and parameters are the same as in Example 1.

[0064] Example 4

[0065] Compared with Example 1, the only difference is that an auxiliary additive, 1,3-propanesulfonyl lactone, is added to the electrolyte. The amount of the auxiliary additive added to the electrolyte is 0.5 wt%. All other operations and parameters are the same as in Example 1.

[0066] Example 5

[0067] Compared with Example 4, the only difference is that the concentration of lithium hexafluorophosphate (LiPF6) is changed to 1.2 mol / L, the weight ratio of Formula 1 compound and auxiliary additive is 2:1, and the amount of total additive (referring to the total amount of Formula 1 modifier and auxiliary additive) is 1.5 wt.%, while other operations and parameters are the same as in Example 4.

[0068] Comparative Example 1

[0069] Compared with Example 1, the only difference is that the electrolyte lacks the modifier of Formula 1, while the other operations and parameters are the same as in Example 1.

[0070] Comparative Example 2

[0071] Compared with Example 1, the only difference is that the following component is used to replace the modifier 1, and the amount of modifier and other operations and parameters are the same as in Example 1.

[0072] Group A: ;

[0073] Group B: ;

[0074] Group C: An equimolar mixture of additives from Groups A and B;

[0075] Group D: ;

[0076] Group E: 1,3-propanesulfonyl lactone;

[0077] The high-voltage test data for each case are shown in Table 1; the wide-temperature test results are shown in Table 2.

[0078] Table 1: High-pressure cycle test results for each case:

[0079]

[0080] Note: The cycle retention rate in Table 1 refers to the capacity after 200 cycles / the capacity after the 3rd cycle × 100%.

[0081] Table 2: Wide-temperature-range cycling test results for each case:

[0082]

[0083] Note: The cycle retention rate in Table 2 refers to the capacity of 100 cycles / the capacity of the 3rd cycle × 100%.

[0084] As shown in Tables 1 and 2, using the special tricyclic compound of Formula 1 as an electrolyte additive achieves synergistic effects, enabling the in-situ construction of a SEI structure with a special physicochemical structure, thereby effectively improving the long-cycle performance of the electrolyte under high voltage. Furthermore, as shown in Examples 1-5, the composite additive described in this invention can further synergistically enhance high-voltage and wide-temperature performance.

Claims

1. A composite electrolyte, comprising a lithium salt, an organic solvent, and a modifier, characterized in that, Modifiers include at least one compound having the structure of Formula 1; Formula 1 R1 and R2 are individually H, C1-C4 alkyl, or C1-C4 alkoxy; Ar is an aromatic ring with or without substituents; R3 is H, C1-C4 alkyl, C1-C4 alkylyl, C1-C4 ester, or benzyl.

2. The composite electrolyte as described in claim 1, characterized in that, R1 and R2 are methyl or ethyl; The Ar is a benzene ring, a pyridine ring, or a m-diazine.

3. The composite electrolyte as described in claim 1, characterized in that, The modifier includes at least one of compound 1 to compound 12; ； Compound 1 Compound 2 Compound 3 ； Compound 4 Compound 5 ； Compound 6 Compound 7 ； Compound 8, Compound 9, Compound 10 ； Compound 11 Compound 12.

4. The composite electrolyte as described in claim 3, characterized in that, The modifier is two or three of compound 1, compound 6, and compound 8.

5. The composite electrolyte according to any one of claims 1 to 4, characterized in that, The modifier has a content of 0.1wt% to 5.0wt% in the electrolyte, preferably 0.3wt% to 2.0wt%.

6. The composite electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte also contains additives, which are selected from at least one of sulfur-containing additives, fluorine-containing additives, and nitrile additives. Preferably, the sulfur-containing additive is selected from at least one of 1,3-propanesulfonyl lactone, vinyl sulfate, and methylene disulfonate; The fluorinated additive is selected from at least one of fluoroethylene carbonate and difluoroethylene carbonate; The nitrile additive is selected from at least one of butadionitrile, adiponitrile, and 1,3,6-hexanetrionitrile.

7. The composite electrolyte as described in claim 6, characterized in that, The mass ratio of the modifier to the additive is 1:5 to 5:

1.

8. The composite electrolyte as described in claim 1, characterized in that, The solvent is selected from at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, and fluoroethylene carbonate. The lithium salt is selected from at least one of LiPF6, LiFSI, LiTFSI, LiBF4, and LiClO4; The lithium salt concentration is 0.5~2.0 mol / L.

9. The application of the composite electrolyte according to any one of claims 1 to 8, characterized in that, It is used to manufacture lithium-ion batteries.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that the electrolyte is a composite electrolyte according to any one of claims 1 to 8; Preferably, the positive electrode material in the positive electrode sheet is at least one of lithium nickel manganese oxide, lithium cobalt oxide, nickel-cobalt-manganese ternary material, and lithium-rich manganese-based material; The negative electrode material in the negative electrode sheet is selected from at least one of graphite, silicon-based materials, lithium metal, niobium titanium oxide, and lithium titanate.

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