An electrolyte and a lithium-ion battery using the same.

Abstract

This invention provides a battery. The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode contains metallic Mn. The electrolyte includes a lithium salt, an organic solvent, and a first additive selected from fluorinated cyclic carboxylic acid esters. The fluorinated cyclic carboxylic acid esters form a stable interfacial film at the positive electrode, reducing side reactions between the electrolyte and the positive electrode interface and improving the stability of the positive electrode under high voltage. Furthermore, it increases the content of LiF and other elements in the SEI film, thereby improving the stability of the negative electrode, reducing the negative impact of metallic Mn in the negative electrode, and significantly improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, and specifically relates to a battery, particularly a battery with good high-temperature cycle performance and good high-temperature storage performance. Background Technology

[0002] Lithium-ion batteries possess advantages such as long cycle life, high energy density, and low self-discharge rate, and are widely used in various consumer electronics, electric vehicles, and energy storage devices. With the development of battery technology, the demand for high-energy-density batteries is increasing. Electrolytes, as a crucial component of lithium-ion batteries, play an indispensable role. Correspondingly, high-voltage electrolytes have become an important research direction in the field of lithium-ion batteries.

[0003] Currently, most commercial lithium-ion battery electrolytes consist of carbonate organic solvents and lithium hexafluorophosphate (LiPF6). However, carbonate solvents have low oxidation potentials and are prone to decomposition at operating voltages above 4.5V, leading to reduced lithium-ion battery performance. Furthermore, the presence of metallic Mn in the negative electrode also significantly degrades battery performance. Therefore, traditional electrolytes are insufficient for the requirements of high-voltage lithium-ion batteries, necessitating the development of suitable high-voltage electrolytes for batteries containing metallic Mn in the negative electrode. Adding additives to traditional carbonate electrolytes is a common method. Although researchers have attempted to develop different additives to improve the performance of high-voltage electrolytes, no ideal solution has yet been found. Therefore, continued active research and development in this area is still needed. Summary of the Invention

[0004] To improve the poor high-temperature cycle performance and high-temperature storage performance of batteries containing metallic Mn in the negative electrode under high voltage conditions, this invention provides a battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode contains metallic Mn, and the electrolyte comprises a fluorinated cyclic carboxylic acid ester compound. This battery effectively solves the problem of deteriorated high-temperature cycle performance and high-temperature storage performance caused by the presence of metallic Mn in the negative electrode under high voltage, providing a battery with good high-temperature cycle performance and high-temperature storage performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte; the negative electrode contains metallic Mn, and the electrolyte comprises a lithium salt, an organic solvent, and a first additive selected from fluorinated cyclic carboxylic acid esters.

[0007] According to embodiments of the present invention, it is well known that the presence of metallic Mn in the negative electrode deteriorates battery performance. The inventors of this application, through research, discovered that when fluorinated cyclic carboxylic acid esters are introduced into the electrolyte, these esters enable the battery to form a stable interfacial film at the positive electrode earlier during formation and charge / discharge processes. This reduces side reactions between the electrolyte and the positive electrode interface, improves the stability of the positive electrode at high voltage, and reduces electrolyte consumption and damage to the positive electrode structure during battery cycling. Simultaneously, the introduced fluorinated cyclic carboxylic acid esters can also increase the content of LiF and other elements in the negative electrode SEI film, reducing the impact of metallic Mn on battery performance. Therefore, the introduction of this additive can significantly improve the high-temperature cycling performance and high-temperature storage performance of batteries containing metallic Mn at high voltage, minimizing the impact of metallic Mn on battery performance.

[0008] According to an embodiment of the present invention, the battery satisfies the following relationship:

[0009] 0.1 <a<10;

[0010] 0.1 <a+b<55;

[0011] a / b > 0.002;

[0012] Where a% is the percentage of the mass of fluorinated cyclic carboxylic acid esters in the total mass of the electrolyte; b is the percentage of the mass of metallic Mn in the total mass of the negative electrode active material layer in the negative electrode sheet, in ppm.

[0013] According to an embodiment of the present invention, when the battery satisfies the above-mentioned relationship, the electrolyte additive can be well matched with the positive and negative electrodes. Firstly, it effectively improves the stability of the protective film on the positive electrode surface, thereby significantly improving the battery's high-temperature cycle performance and high-temperature storage performance under high voltage. Furthermore, within this range, it can improve the content of LiF and other elements in the SEI film on the negative electrode surface during formation and charge / discharge processes, increasing the stability of the negative electrode SEI film, reducing the negative impact of metallic Mn elements in the negative electrode sheet on the battery, and further improving the battery's high-temperature cycle performance and high-temperature storage performance under high voltage.

[0014] According to embodiments of the present invention, the fluorinated cyclic carboxylic acid ester compound accounts for 0.15% to 9.9% of the total mass of the electrolyte; preferably 0.5% to 6%. For example, it is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 3.0%, 3.4%, 3.5%, 4%, 4.5%, 4.8%, 5%, 6%, 7%, 8%, 9%, or 9.5%.

[0015] According to an embodiment of the present invention, the mass ratio of the metallic Mn element to the total mass of the negative electrode active material layer in the negative electrode sheet is 0.1ppm to 45ppm; preferably 0.2ppm to 40ppm. For example, it is 0.2ppm, 0.3ppm, 0.5ppm, 0.8ppm, 1ppm, 2ppm, 5ppm, 8ppm, 10ppm, 12ppm, 15ppm, 18ppm, 20ppm, 25ppm, 30ppm, 35ppm, 40ppm, or 45ppm.

[0016] According to an embodiment of the present invention, 0.5 ≤ a + b ≤ 50; preferably, 1.2 ≤ a + b ≤ 45; exemplaryly, a + b is 0.5, 0.6, 0.8, 0.9, 1, 1.2, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45 or 50.

[0017] According to an embodiment of the present invention, a / b ≥ 1; preferably, 25 ≥ a / b ≥ 5; exemplary, a / b is 0.125, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 2, 4, 5, 8, 10, 12, 15, 18, 20, 25, 30, 35, 40, 45 or 50.

[0018] According to embodiments of the present invention, the fluorocyclic carboxylic acid ester compound has at least one of the structural formulas shown in Formula I:

[0019]

[0020] In Formula I, R1 is absent or -CH2-; R2, R3, R4, R5, R6, and R7 are the same or different, and are independently selected from hydrogen, fluorine, alkyl, or fluorine-substituted alkyl, and at least one group among R2, R3, R4, R5, R6, and R7 is selected from fluorine or fluorine-substituted alkyl.

[0021] According to embodiments of the present invention, R2, R3, R4, R5, R6, and R7 may be the same or different, and are independently selected from hydrogen, fluorine, and C. 1-12 Alkyl, fluorine-substituted C 1-12 Alkyl group, and at least one of R2, R3, R4, R5, R6, R7 is selected from fluorine or fluorine-substituted C. 1-12 alkyl.

[0022] According to embodiments of the present invention, R2, R3, R4, R5, R6, and R7 may be the same or different, and are independently selected from hydrogen, fluorine, and C. 1-6 Alkyl, fluorine-substituted C 1-6Alkyl group, and at least one of R2, R3, R4, R5, R6, R7 is selected from fluorine or fluorine-substituted C. 1-6 alkyl.

[0023] According to embodiments of the present invention, R2, R3, R4, R5, R6, and R7 may be the same or different, and are independently selected from hydrogen, fluorine, and C. 1-3 Alkyl, fluorine-substituted C 1-3 Alkyl group, and at least one of R2, R3, R4, R5, R6, R7 is selected from fluorine or fluorine-substituted C. 1-3 alkyl.

[0024] According to embodiments of the present invention, the fluorocyclic carboxylic acid ester compound is selected from at least one of the compounds shown in Formula I-1 to Formula I-3:

[0025]

[0026] According to embodiments of the present invention, the fluorinated cyclic carboxylic acid ester compound can generate an SEI film containing LiF, etc. on the surface of the negative electrode, thereby improving the stability of the negative electrode, reducing the negative impact of the metal Mn element in the negative electrode sheet on the battery, and significantly improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

[0027] According to embodiments of the present invention, the fluorinated cyclic carboxylic acid ester compounds can be prepared using methods known in the art, or can be obtained commercially.

[0028] According to an embodiment of the present invention, the electrolyte further includes a second additive, the second additive being selected from at least one of 1,3,6-hexanetrionitrile, adiponitrile (ADN), succinic anhydride, fluoroethylene carbonate (FEC), 1,3-propanesulfonate lactone (PS), and 1,3-propenesulfonate lactone.

[0029] According to an embodiment of the present invention, the weight of the second additive is 8 wt% to 15 wt% of the total weight of the electrolyte, for example, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%. The introduction of the second additive can participate in the formation of the SEI film in the early stage of formation, playing a role in protecting the negative electrode and improving the electrochemical performance of the battery.

[0030] According to embodiments of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(trifluoromethanesulfonyl)imide, lithium difluorobis(oxalate)phosphate, lithium tetrafluoroborate, lithium bis(oxalate)borate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, lithium tri(trifluoromethanesulfonyl)methyl, or lithium di(trifluoromethanesulfonyl)imide.

[0031] According to embodiments of the present invention, the organic solvent is selected from carbonates and / or carboxylic esters, wherein the carbonate is selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), and methyl ethyl carbonate; and the carboxylic ester is selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, and ethyl butyrate.

[0032] According to an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material; the negative electrode active material contains metallic Mn element. That is, metallic Mn element is introduced into the negative electrode sheet through the negative electrode active material.

[0033] According to an embodiment of the present invention, the negative electrode containing the metal Mn element can be a negative electrode after formation or charge-discharge cycle (i.e., a negative electrode obtained after disassembling from a battery), or it can be a negative electrode obtained before being assembled into a battery; both types of negative electrode contain the metal Mn element, and the difference in the content of the metal Mn element is within 5%.

[0034] According to an embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer coated on one or both surfaces of the positive current collector, wherein the positive active material layer includes a positive active material, a conductive agent, and a binder.

[0035] According to an embodiment of the present invention, the negative electrode active material layer further includes a conductive agent and a binder.

[0036] According to an embodiment of the present invention, the mass percentage of each component in the positive electrode active material layer is: 80-99.8 wt% positive electrode active material, 0.1-10 wt% conductive agent, and 0.1-10 wt% binder.

[0037] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6 wt% positive electrode active material, 0.2-5 wt% conductive agent, and 0.2-5 wt% binder.

[0038] According to an embodiment of the present invention, the mass percentage of each component in the negative electrode active material layer is: 80-99.8 wt% negative electrode active material, 0.1-10 wt% conductive agent, and 0.1-10 wt% binder.

[0039] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6 wt% negative electrode active material, 0.2-5 wt% conductive agent, and 0.2-5 wt% binder.

[0040] According to an embodiment of the present invention, the negative electrode active material is selected from at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, soft carbon, and silicon-based negative electrode materials.

[0041] According to an embodiment of the present invention, the positive electrode active material is selected from one or more of transition metal lithium oxides, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate; the chemical formula of the transition metal lithium oxide is Li. 1+ x Ni y Co z M (1-y-z) O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0042] The beneficial effects of this invention are:

[0043] This invention provides a battery. The battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode contains metallic Mn, and the electrolyte includes a lithium salt, an organic solvent, and a first additive selected from fluorinated cyclic carboxylic acid esters. The fluorinated cyclic carboxylic acid esters introduced into the electrolyte enable the battery to form a stable interfacial film at the positive electrode earlier during formation and charge / discharge processes, reducing side reactions between the electrolyte and the positive electrode interface, improving the stability of the positive electrode at high voltage, reducing electrolyte consumption and damage to the positive electrode structure during battery cycling, and improving high-temperature cycle performance and high-temperature storage performance at high voltage. Furthermore, by adjusting the content of the fluorinated cyclic carboxylic acid esters in the electrolyte and their ratio with metallic Mn in the negative electrode, the battery can improve the content of LiF and other substances in the SEI film on the negative electrode surface during formation and charge / discharge processes, improving the stability of the negative electrode SEI film, and further improving the high-temperature cycle performance and high-temperature storage performance of the battery at high voltage. Detailed Implementation

[0044] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0045] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0046] In the description of this invention, it should be noted that the terms "first," "second," etc., are used for descriptive purposes only and are not intended to indicate or imply relative importance.

[0047] The negative electrode active material used in the following examples may be doped with a small amount of metallic Mn, which can degrade battery performance. By screening different batches of negative electrode active materials, negative electrode sheets with different amounts of metallic Mn (0 ppm, 0.2 ppm, 40 ppm, or 50 ppm) were obtained.

[0048] Examples 1-14 and Comparative Examples 1-6

[0049] The batteries of Examples 1-14 and Comparative Examples 1-6 were prepared by the following steps:

[0050] 1) Preparation of positive electrode sheet

[0051] Lithium cobalt oxide (LiCoO2), polyvinylidene fluoride (PVDF), super P (SP), and carbon nanotubes (CNT) were mixed in a mass ratio of 96:2:1.5:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried and then rolled and slit to obtain the desired positive electrode sheet.

[0052] 2) Preparation of negative electrode sheet

[0053] The negative electrode active materials, artificial graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs), were mixed in a mass ratio of 94.5:2.5:1.5:1:0.5. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode active slurry. The negative electrode active slurry was uniformly coated on both surfaces of a copper foil. The coated copper foil was dried at room temperature and then transferred to an 80°C oven for 10 hours. After cold pressing and slitting, the negative electrode sheet was obtained.

[0054] 3) Preparation of electrolyte

[0055] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP were mixed uniformly in a mass ratio of 10 / 20 / 40 / 30. Then, 1 mol / L of fully dried lithium hexafluorophosphate (LiPF6) was quickly added and dissolved. After dissolution, 12 wt% of fluoroethylene carbonate, 2 wt% of 1,3-propanesulfonate lactone, 2 wt% of 1,3,6-hexanetrionitrile, and fluorocyclic carboxylic acid esters were added based on the total mass of the electrolyte (specific amounts are shown in Table 1). The mixture was stirred evenly, and after passing the moisture and free acid tests, the desired electrolyte was obtained.

[0056] 4) Battery manufacturing

[0057] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting, a battery is obtained. The battery of this invention has a charge / discharge range of 3.0-4.5V.

[0058] The batteries obtained in the examples and comparative examples were subjected to high-temperature storage performance tests at 60°C and cycle performance tests at 45°C, respectively.

[0059] 1) 60℃ High Temperature Storage Performance Test

[0060] The batteries in Table 1 were charged at 25℃ at a rate of 1C to the cutoff voltage, with a cutoff current of 0.025C. After standing for 5 minutes, the thickness of the lithium-ion batteries was measured (this thickness was taken as the thickness before storage). The fully charged batteries were then left in an open circuit at (60±2)℃ for 35 days. After 35 days of storage, they were left in an open circuit at room temperature for 2 hours. The thickness after storage was measured, and the thickness expansion rate of the lithium-ion batteries was calculated.

[0061] Thickness expansion rate = [(thickness after storage - thickness before storage) / thickness before storage] × 100%

[0062] 2) 45℃ Cyclic Performance Test

[0063] The batteries in Table 1 were charged and discharged at 45°C at a rate of 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first week was measured as x1mAh, and the discharge capacity of the Nth week was measured as y1mAh. The capacity of the Nth week was divided by the capacity of the first week to obtain the cycle capacity retention rate R1 = y1 / x1. The number of cycles of the battery when the cycle capacity retention rate R1 was 80% was recorded.

[0064] 3) Scrape off the negative electrode active material layer from the negative electrode sheet, take 5mg of the negative electrode active material layer and add 3mL of concentrated sulfuric acid and 3mL of concentrated nitric acid in sequence, heat to 180℃ until the solution is clear and transparent, cool and add water to make up to 50mL, send the sample for testing, and use an ICP element analyzer to test the content of the metal Mn element.

[0065] Table 1. Composition of electrolyte additives in the batteries of the examples and comparative examples, and battery performance test results.

[0066]

[0067] Table 2 Comparison of Mn content in the negative electrode before and after cycling in Example 3 after formation.

[0068] Group Mn content (ppm) The battery after formation in Example 3 before cycling 0.20 The battery formed in Example 3 after cycling 0.18

[0069] As can be seen from the performance test results in Table 1, and from the comparison of Comparative Examples 1-4, the presence of metallic Mn in the negative electrode sheet degrades the battery's high-temperature cycle performance and high-temperature storage performance under high voltage. Comparative Examples 1 and 5-6 show that the fluorinated cyclic carboxylic acid esters introduced into the electrolyte enable the battery to form a stable interfacial film at the positive electrode earlier during formation and charge / discharge processes, reducing side reactions between the electrolyte and the positive electrode interface, improving the stability of the positive electrode under high voltage, reducing electrolyte consumption and damage to the positive electrode structure during battery cycling, and improving the battery's high-temperature cycle performance and high-temperature storage performance under high voltage.

[0070] As can be seen from the comparison of Examples 1-14, the introduction of fluorinated cyclic carboxylic acid esters can improve the deteriorating effect of the metallic Mn element contained in the negative electrode on the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage. In particular, by adjusting the content of the fluorinated cyclic carboxylic acid esters in the electrolyte and the ratio of the fluorinated cyclic carboxylic acid esters to the metallic Mn element in the negative electrode, the battery satisfies the following relationship: 0.1 <a<10;0.1<a+b<55;a / b> At 0.002, the content of LiF and other substances in the SEI film on the negative electrode surface can be improved during the formation and charge / discharge process of the battery, thereby improving the stability of the SEI film and further improving the high-temperature cycle performance and high-temperature storage performance of the battery under high voltage.

[0071] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A battery, characterized by, The battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the negative electrode active material in the negative electrode sheet contains a metal Mn element, the electrolyte comprises a lithium salt, an organic solvent and a first additive, the first additive is selected from fluorinated cyclic carboxylate compounds; The battery satisfies the following relationship: 0.1<a<10； 0.1 < a + b < 55; a / b > 0.002; Wherein, a% is the mass percentage of the fluorinated cyclic carboxylate compound in the total mass of the electrolyte; b is the mass proportion of the metal Mn element in the total mass of the negative electrode active material layer in the negative electrode sheet, unit ppm; The fluorinated cyclic carboxylate compound is selected from at least one of the compounds shown in formula I-1~formula I-3: Formula I-1 Formula I-2 Formula I-3.

2. The battery of claim 1, wherein, 0.15≤a≤9.9。 3. The battery of claim 2, wherein, 0.5≤a≤6。 4. The battery of claim 1, wherein, 0.5 ≤ a + b ≤ 50.

5. The battery of claim 4, wherein, 1.2 ≤ a + b ≤ 45.

6. The battery of claim 1, wherein, a / b ≥ 1.

7. The battery of claim 6, wherein, 25 ≥ a / b ≥ 5.

8. The battery of claim 1, wherein, The mass proportion of the metal Mn element in the total mass of the negative electrode active material layer in the negative electrode sheet is 0.1 ppm~45 ppm.

9. The battery of claim 8, wherein, The mass proportion of the metal Mn element in the total mass of the negative electrode active material layer in the negative electrode sheet is 0.2 ppm~40 ppm.

10. The battery according to any one of claims 1 to 9, characterized in that, The electrolyte further comprises a second additive, the second additive is selected from at least one of 1,3,6-hexane tricyanide, adiponitrile, butanedinitrile, fluorinated ethylene carbonate, 1,3-propane sulfone lactone and 1,3-propylene sulfone lactone.

11. The battery of claim 10, wherein, The weight of the second additive is 8wt%~15wt% of the total weight of the electrolyte.

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