Electrolyte additive for improving high-temperature storage gas production, electrolyte and lithium ion battery

Abstract

The invention provides an electrolyte additive for improving high-temperature storage gas production, an electrolyte and a lithium ion battery. The electrolyte additive comprises a first additive, a second additive and fluoroethylene carbonate, and the structural formula of the first additive is shown in the specification; and the second additive is or. The first additive forms an organic-inorganic hybrid CEI membrane on the positive electrode, the second additive forms a LiF-rich SEI membrane on the negative electrode, and the interface impedance is reduced through the cooperation of the two membranes, so that the dual protection effect on the battery is achieved, and the high-temperature performance of the battery is obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive for improving high-temperature storage gas production, an electrolyte and a lithium ion battery. BACKGROUND

[0002] With the rapid development of the new energy industry, the ternary soft-pack lithium ion battery has been widely used in key fields such as electric vehicles and energy storage systems due to its high energy density and flexible packaging. However, the inherent thermal stability defects of ternary materials (such as NCM811) make the performance degradation and safety risks in high-temperature environments become the core bottleneck restricting the development of the industry. The thermal decomposition temperature of ternary materials is only about 200℃, which is significantly lower than that of lithium iron phosphate (500-800℃), and the high-nickel component further reduces the thermal stability of the material, leading to problems such as lattice oxygen release, intensified Li / Ni ion mixing, and other problems at high temperatures, which cause the collapse of the positive electrode structure and the rapid increase of electrolyte side reactions. Therefore, improving the high-temperature resistance of ternary soft-pack batteries has become an urgent need in the industry. SUMMARY

[0003] In order to solve the problems of the prior art, the application provides an electrolyte additive for improving high-temperature storage gas production, an electrolyte and a lithium ion battery.

[0004] The application is achieved by the following technical solutions: In a first aspect, the application provides an electrolyte additive for improving high-temperature storage gas production, comprising: a first additive, a second additive and fluoroethylene carbonate, The structural formula of the first additive is shown as formula I, and the second additive is selected from formula II-1, formula II-2 and formula II-3.

[0005] Wherein, R is selected from substituted or unsubstituted alkyl, substituted phenyl and amine group.

[0006] The first additive adopted in the application contains unsaturated bond -C=C-, during the first charging of the battery, the unsaturated carbon-carbon double bond undergoes a reduction reaction, and a flexible interface film is formed on the negative electrode surface through free radical polymerization, the unsaturated double bond can capture the active oxygen free radicals of the positive electrode, slow down the oxidation ability of the positive electrode material, thereby inhibiting the oxidation of the electrolyte solvent by the positive electrode and reducing the gas production; in addition, the first additive can react with free acid and water in the battery, play a role in removing water and acid, and protect the positive electrode structure from corrosion; the second additive contains a cyano group, which complexes with transition metal ions at the positive electrode, preventing the migration of transition metal ions to the negative electrode, protecting the negative electrode interface, and the cyano group can capture moisture and free acid in the battery, in combination with the first additive, the first additive forms an organic-inorganic hybrid CEI film on the positive electrode, and the second additive builds a LiF-rich SEI film on the negative electrode, the double films synergistically reduce the interface impedance, and have a double protection effect on the battery, significantly improving the high-temperature performance of the battery. In some preferred embodiments of the application, the substituted or unsubstituted alkyl group is a substituted or unsubstituted C2-C4 alkyl group.

[0007] In some preferred embodiments of the application, the substituent in the substituted C2-C4 alkyl group is halogen.

[0008] In some preferred embodiments of the application, the first additive is one of the following compounds: .

[0009] In some preferred embodiments of the application, the mass ratio of the first additive to the second additive is (0.3-2):(0.3-3). More preferably, the mass ratio of the first additive to the second additive is (0.3-0.7):(0.3-0.5).

[0010] In some preferred embodiments of the application, the electrolyte additive further comprises a carbonate additive and a lithium salt additive.

[0011] Specifically, the carbonate additive includes fluoroethylene carbonate and vinylene carbonate.

[0012] The carbonate additive in the ternary battery forms a dense SEI film rich in LiF on the negative electrode and an oxidation-resistant CEI film on the positive electrode, thereby improving the interface stability.

[0013] Specifically, the lithium salt additive includes at least one of lithium difluorophosphate, lithium tetrafluoroborate and lithium bis(oxalato)borate. The lithium salt additive forms a high-stability interface film (rich in LiF, borate or polyphosphate) by decomposition in the ternary battery, alleviates the irreversible capacity loss by supplementing the active lithium source, and inhibits the oxidation decomposition of the electrolyte and the dissolution of transition metal, thereby significantly improving the performance of the battery.

[0014] In a second aspect, the present application provides an electrolyte, comprising: a carbonate organic solvent, a fluorine-containing lithium salt and the electrolyte additive as described above.

[0015] The carbonate organic solvent comprises ethylene carbonate, methyl ethyl carbonate and diethyl carbonate.

[0016] In some embodiments of the present application, the carbonate organic solvent comprises, based on the total volume of the carbonate organic solvent being 100%, methyl ethyl carbonate 50-70%, ethylene carbonate 15-20% and diethyl carbonate 10-20%.

[0017] In some preferred embodiments of the present application, the fluorine-containing lithium salt is one or a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide.

[0018] In some preferred embodiments of the present application, the concentration of the fluorine-containing lithium salt in the electrolyte is 1.0-1.3 mol / L.

[0019] In some preferred embodiments of the present application, the total amount of the electrolyte additive is 3.5-6% by mass in the electrolyte, and the balance is the carbonate organic solvent.

[0020] In a third aspect, the present application provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and the electrolyte as described above.

[0021] Compared with the prior art, the present application has the following beneficial effects: The first additive used in the present application contains an unsaturated bond -C=C-, which undergoes a reduction reaction during the first charging process of the battery, and forms a flexible interface film on the negative electrode surface through free radical polymerization. The unsaturated double bond can capture active oxygen radicals of the positive electrode, slow down the oxidation ability of the positive electrode material, thereby inhibiting the oxidation of the electrolyte solvent by the positive electrode and reducing the gas production. In addition, the first additive can react with free acid and water in the battery, thereby playing a role in removing water and acid and protecting the positive electrode structure from corrosion. The second additive contains a cyano group, which complexes with transition metal ions at the positive electrode, preventing the migration of transition metal ions to the negative electrode and protecting the negative electrode interface. The cyano group can also capture moisture and free acid in the battery. When used in combination with the first additive, the first additive forms an organic-inorganic hybrid CEI film on the positive electrode, and the second additive forms a LiF-rich SEI film on the negative electrode. The double films synergistically reduce the interface impedance and provide double protection for the battery, significantly improving the high-temperature performance of the battery. DETAILED DESCRIPTION

[0022] 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.

[0023] It should be noted that the process equipment or apparatus not specifically mentioned in the following embodiments are all conventional equipment or apparatus in the art.

[0024] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products, or apparatuses. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not intended to limit the order of the method steps or define the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0025] Example 1 This embodiment provides an electrolyte, which is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-1 (dimethyl(dimethylamino)vinylsilane), compound II-1 (4-acetyl-2,6-difluorobenzonitrile), fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of compound I-1 is 0.3%, the mass percentage of compound II-1 is 0.5%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 0.2%, the mass percentage of lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.1 mol / L; The organic solvent comprises, by volume percentage, 65% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, based on a total volume percentage of 100%.

[0026]

[0027] The electrolyte is prepared by the following method: under an argon atmosphere, compounds of formula I-1 and formula II-1, fluoroethylene carbonate, vinylene carbonate and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, and the mixture is stirred and mixed at 10°C for 3 hours to obtain the electrolyte.

[0028] Example 2 This embodiment provides an electrolyte, which differs from Example 1 only in that the amount of compound I-1 added in Example 1 is modified to 0.5%.

[0029] Specifically, the electrolyte described in this embodiment is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-1, compound II-1 (4-acetyl-2,6-difluorobenzonitrile), fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate, with the total mass of organic solvent and additive being 100%. The mass percentages of compound I-1, II-1, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate are 0.5%, 0.2%, and 0.8%, with the remainder being organic solvent. The concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L. The organic solvent comprises, by volume percentage, 65% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, based on a total volume percentage of 100%.

[0030] The electrolyte is prepared by the following method: under an argon atmosphere, compound I-1, compound II-1, fluoroethylene carbonate, vinylene carbonate and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, and the mixture is stirred and mixed at 10°C to obtain the electrolyte.

[0031] Example 3 This embodiment provides an electrolyte, which differs from Example 1 only in that the compound of formula I-1 in Example 1 is replaced with the compound of formula I-2.

[0032] Specifically, the electrolyte described in this embodiment is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of the compound shown in Formula I-2, the compound shown in Formula II-1, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of the compound in Formula I-2 is 0.5%, the mass percentage of the compound in Formula II-1 is 0.5%, the mass percentage of the fluoroethylene carbonate is 3%, the mass percentage of the vinylene carbonate is 0.2%, the mass percentage of the lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L; The organic solvent comprises, by volume percentage, 60% methyl ethyl carbonate, 20% ethylene carbonate, and 20% diethyl carbonate, based on a total volume percentage of 100%.

[0033]

[0034] The electrolyte is prepared by the following method: under an argon atmosphere, compounds of formula I-2, formula II-1, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate, and the mixture is stirred and mixed at 10°C for 3 hours to obtain the electrolyte.

[0035] Example 4 This embodiment provides an electrolyte that differs from Example 1 only in that the compound of formula I-1 in Example 1 is replaced with the compound of formula I-3.

[0036] Specifically, the electrolyte described in this embodiment is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-3, compound II-1, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of compound I-3 is 0.7%, the mass percentage of compound II-1 is 0.5%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 0.2%, the mass percentage of lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L. The organic solvent comprises, by volume percentage, 60% methyl ethyl carbonate, 20% ethylene carbonate, and 20% diethyl carbonate, based on a total volume percentage of 100%.

[0037]

[0038] The electrolyte is prepared by the following method: under an argon atmosphere, compounds of formula I-3, formula II-1, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate, and diethyl carbonate, and the mixture is stirred and mixed at 10°C for 3 hours to obtain the electrolyte.

[0039] Example 5 This embodiment provides an electrolyte that differs from Example 1 only in that the compound of formula II-1 in Example 1 is replaced with a compound of formula II-2. Specifically, the electrolyte is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-1, compound II-2, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of compound I-1 is 0.3%, the mass percentage of compound II-2 is 0.3%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 0.2%, the mass percentage of lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L; The organic solvent comprises, by volume percentage, 65% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, based on a total volume percentage of 100%.

[0040]

[0041] The electrolyte is prepared by the following method: under an argon atmosphere, compound I-1, compound II-2, fluoroethylene carbonate, vinylene carbonate and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, and the mixture is stirred at 10°C to obtain the electrolyte.

[0042] Example 6 This embodiment provides an electrolyte that differs from Example 1 only in that the compound of formula II-1 in Example 1 is replaced with a compound of formula II-2. Specifically, the electrolyte is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-1, compound II-2, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of compound I-1 is 0.3%, the mass percentage of compound II-2 is 0.7%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 0.2%, the mass percentage of lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L. The organic solvent comprises, by volume percentage, 65% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, based on a total volume percentage of 100%.

[0043]

[0044] The electrolyte is prepared by the following method: under an argon atmosphere, compound I-1, compound II-2, fluoroethylene carbonate, vinylene carbonate and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, and the mixture is stirred at 10°C to obtain the electrolyte.

[0045] Example 7 This embodiment provides an electrolyte that differs from Example 1 only in that the compound of formula II-1 in Example 1 is replaced with the compound of formula II-3. Specifically, the electrolyte is composed of an organic solvent, lithium hexafluorophosphate, and additives; The additive is composed of compound I-1, compound II-3, fluoroethylene carbonate, vinylene carbonate, and lithium difluorophosphate; based on the total mass of organic solvent and additives as 100%, the mass percentage of compound I-1 is 0.3%, the mass percentage of compound II-3 is 0.5%, the mass percentage of fluoroethylene carbonate is 3%, the mass percentage of vinylene carbonate is 0.2%, the mass percentage of lithium difluorophosphate is 0.8%, and the balance is organic solvent; the concentration of lithium hexafluorophosphate in the electrolyte is 1.2 mol / L. The organic solvent comprises, by volume percentage, 65% methyl ethyl carbonate, 20% ethylene carbonate, and 15% diethyl carbonate, based on a total volume percentage of 100%.

[0046]

[0047] The electrolyte is prepared by the following method: under an argon atmosphere, compound I-1, compound II-3, fluoroethylene carbonate, vinylene carbonate and lithium difluorophosphate are added to an organic solvent formed by mixing methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, and the mixture is stirred and mixed at 10°C to obtain the electrolyte.

[0048] Comparative Example 1 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain the first additive; otherwise, it is the same as Example 1.

[0049] Comparative Example 2 This comparative example provides an electrolyte that differs from Example 1 only in that it does not contain a second additive; otherwise, it is the same as Example 1.

[0050] The electrolytes from Examples 1-7 were assembled into lithium-ion batteries for performance testing. Graphite was used as the negative electrode active material, and NCM811 was used as the positive electrode active material. Lithium-ion battery assembly process: The negative electrode sheet can be prepared by the following steps: graphite, conductive agent acetylene black, binder CMC, and SBR are prepared into a negative electrode slurry in a mass ratio of 95.8:1.0:1.4:1.8. The negative electrode slurry is coated onto a copper foil current collector and vacuum dried to obtain the negative electrode sheet. The positive electrode sheet can be prepared by the following steps: positive electrode active material, conductive agent acetylene black, and binder PVDF (polyvinylidene fluoride) are prepared into a positive electrode slurry in a mass ratio of 95.5:2.2:2.3. The positive electrode slurry is coated onto an aluminum foil current collector and vacuum dried to obtain the positive electrode sheet. The electrolytes prepared in the examples and comparative examples are used to assemble the above-mentioned positive electrode sheet, negative electrode sheet, and separator into a pouch battery.

[0051] The electrical performance of the assembled pouch battery is then tested: (1) High-temperature cycling performance test At 45℃, the lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.25V, then charged at a constant voltage of 4.25V until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to a cutoff voltage of 2.8V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 300 charge-discharge cycles at 45℃ under the above conditions, and the capacity retention rate was calculated according to the following formula. The results are shown in Table 1.

[0052] Capacity retention rate (%) of a lithium-ion battery after N cycles = (Discharge capacity in the Nth cycle / Initial discharge capacity) × 100% Where N is the number of charge-discharge cycles.

[0053] (2) High-temperature storage gas generation test of lithium-ion batteries The lithium-ion battery was charged at a constant current of 1.0C (nominal capacity) to a voltage of 4.25V, then charged at a constant voltage of 4.25V until the current ≤0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to 2.8V. This constituted one charge-discharge cycle. The lithium-ion battery was subjected to three charge-discharge cycles at 25℃ with a charge-discharge rate of 1C, and then charged to full capacity at a 1C rate. The fully charged lithium-ion battery was stored at 60℃ for 14 days, and gas production was measured using the water displacement method. The gas production was recorded, and the results are shown in Table 1.

[0054] Table 1

[0055] Comparing Examples 1-7 and Comparative Examples 1-2, it can be seen that the electrolyte in Comparative Example 1 contains only the second additive, and the electrolyte in Comparative Example 2 contains only the first additive. Neither the first nor the second additive, used alone, can improve the high-temperature performance of the battery. However, by introducing functional additives as shown in formulas I-1, I-2, I-3, II-1, II-2, and II-3, the high-temperature gas generation during storage and the high-temperature cycling performance can be significantly improved. This is mainly because the first and second additives work synergistically to improve the high-temperature performance of the ternary lithium-ion battery.

Claims

1. An electrolyte additive for improving gas generation during high-temperature storage, characterized in that, include: The first additive, the second additive, and fluoroethylene carbonate, wherein the structural formula of the first additive is shown in Formula I, and the second additive is selected from Formula II-1, Formula II-2, and Formula II-3. Wherein, R is selected from substituted or unsubstituted alkyl groups, substituted phenyl groups, and amino groups.

2. The electrolyte additive for improving gas production during high-temperature storage according to claim 1, characterized in that, The substituted or unsubstituted alkyl group is a C2-C4 alkyl group.

3. The electrolyte additive for improving gas production during high-temperature storage according to claim 1, characterized in that, The substituents in the substituted C2-C4 alkyl groups are halogens.

4. The electrolyte additive for improving gas generation during high-temperature storage according to claim 1, characterized in that, The first additive is one of the following compounds: 。 5. The electrolyte additive for improving gas production during high-temperature storage according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is (0.3-2):(0.3-3).

6. The electrolyte additive for improving gas production during high-temperature storage according to claim 1, characterized in that, The electrolyte additives also include carbonate additives and lithium salt additives.

7. An electrolyte, characterized in that, include: Carbonate organic solvents, fluorinated lithium salts, and electrolyte additives for improving gas generation during high-temperature storage as described in any one of claims 1 to 6.

8. The electrolyte according to claim 7, characterized in that, The carbonate organic solvents include ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate.

9. The electrolyte according to claim 7, characterized in that, The fluorinated lithium salt is one or a combination of lithium hexafluorophosphate and lithium difluorosulfonylimide.

10. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, and the electrolyte as described in claim 7.

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