Electrolyte for improving cycle performance of lithium ion battery and preparation method thereof, Secondary battery

Abstract

The application belongs to the technical field of secondary batteries, and particularly relates to an electrolyte for improving the cycle performance of a lithium ion battery, which comprises an organic solvent, a lithium salt and an additive, the weight percentage of the organic solvent is 70-88%, the weight percentage of the lithium salt is 8-18%, and the additive is 0.01-10%, wherein the additive comprises bis(dioxidosulfur)-1,4-diazabicyclo[2,2,2]octane adduct and a compound containing a perfluorosulfonyl fluoride structure. The electrolyte can generate a solid electrolyte layer on the surface of an electrode sheet, prevent the destruction of an interface layer, realize the storage stability of the electrolyte, and improve the service life of the battery.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to an electrolyte for improving the cycle performance of lithium-ion batteries, its preparation method, and a secondary battery. Background Technology

[0002] As one of the key materials in lithium-ion batteries, lithium-ion battery electrolytes are used to improve the performance of lithium-ion batteries. In addition to focusing on the performance and characteristics of positive and negative electrode materials, researchers also strive to improve the formulation and preparation methods of lithium-ion battery electrolytes.

[0003] Typically, lithium-ion battery electrolytes consist of three main components: lithium salts, organic solvents, and additives. Lithium hexafluorophosphate is the primary lithium salt, supplemented by other lithium salts. The choice of organic solvents varies depending on the application and the specific lithium-ion battery system, selecting different types and appropriate proportions. Although additives constitute a small percentage of the electrolyte, their significant functions have led to their widespread use and extensive research and development.

[0004] Gaseous additives, such as carbon dioxide, carbon monoxide, and sulfur dioxide, have been validated in the laboratory. However, since lithium-ion battery electrolytes are liquids, and these gases are gases under normal conditions, their solubility in liquids is relatively low, and their concentrations may vary due to environmental and storage conditions. This results in unsatisfactory product consistency when used as additives in the electrolyte. To improve the effectiveness of these additives, some technicians have used liquid or solid compounds of these additives for further addition. However, limitations in technology exist. For example, when using lithium carbonate as an additive, its low solubility in the electrolyte and potential stratification at the bottom of the electrolyte packaging also affect the routine use of such additives. Summary of the Invention

[0005] One of the objectives of this invention is to provide an electrolyte that improves the cycle performance of lithium-ion batteries, addressing the shortcomings of existing technologies. This electrolyte can generate a solid electrolyte layer on the electrode surface, preventing interface layer damage, while also achieving stable electrolyte storage and improving battery lifespan.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] An electrolyte for improving the cycle performance of lithium-ion batteries includes an organic solvent, a lithium salt, and additives. The organic solvent is 70% to 88% by weight, the lithium salt is 8% to 18% by weight, and the additives are 0.01% to 10% by weight. The additives include bis(sulfur dioxide)-1,4-diazabicyclo[2,2,2]octane adducts and compounds containing perfluorosulfonyl fluoride structures.

[0008] The organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethyl acetate.

[0009] The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxaborate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0010] The compounds containing perfluorosulfonyl fluoride structures include one or more of perfluorobutylsulfonyl fluoride, perfluorohexylsulfonyl fluoride, and perfluorooctylsulfonyl fluoride.

[0011] The additives also include one or more of the following: vinylene carbonate, fluorovinyl carbonate, biphenyl, cyclohexylbenzene, propane sulfonate lactone, succinate, and ethylene nitrile.

[0012] The second objective of this invention is to provide a method for preparing an electrolyte that improves the cycle performance of lithium-ion batteries, addressing the shortcomings of existing technologies. This method is simple to implement.

[0013] To achieve the above objectives, the present invention adopts the following technical solution:

[0014] A method for preparing an electrolyte to improve the cycle performance of lithium-ion batteries includes the following steps:

[0015] Step S1: Take the above-mentioned parts by weight of organic solvent and mix them thoroughly in a container;

[0016] Step S2: Add the lithium salt in the above weight proportions to the above container and stir to dissolve;

[0017] Step S3: Take the above-mentioned amount of additive by weight and stir to obtain the final product.

[0018] The third objective of this invention is to provide a secondary battery with good cycle performance, addressing the shortcomings of existing technologies.

[0019] To achieve the above objectives, the present invention employs the following technical description:

[0020] A secondary battery includes a positive electrode, a negative electrode, a separator, a housing, and the electrolyte described above for improving the cycle performance of a lithium-ion battery. The separator is used to separate the positive electrode and the negative electrode, and the housing is used to house the positive electrode, the negative electrode, the separator, and the electrolyte.

[0021] The negative electrode sheet includes a negative current collector and a negative active coating disposed on at least one surface of the negative current collector. The negative active coating includes a negative active material, which includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese oxide, and lithium nickel oxide, or a composite compound LiM1. x M2 y O2, where M1 and M2 are metallic elements, and x and y are rational numbers from 0 to 2.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: The electrolyte of the present invention for improving the cycle performance of lithium-ion batteries can generate a solid electrolyte layer on the electrode surface, prevent the interface layer from being damaged, and at the same time achieve stable electrolyte storage and improve battery life. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0024] An electrolyte for improving the cycle performance of lithium-ion batteries includes an organic solvent, a lithium salt, and additives. The organic solvent is 70% to 88% by weight, the lithium salt is 8% to 18% by weight, and the additives are 0.01% to 10% by weight. The additives include bis(sulfur dioxide)-1,4-diazabicyclo[2,2,2]octane adducts and compounds containing perfluorosulfonyl fluoride structures.

[0025] The electrolyte of the present invention can be formulated in a measured manner according to the formulation design concept, thereby ensuring that the electrolyte has good performance and stability.

[0026] The electrolyte of the present invention improves the cycle performance of lithium-ion batteries, which can generate a solid electrolyte layer on the electrode surface, prevent the interface layer from being damaged, and also improves the stability of the battery.

[0027] The organic solvent includes one or a mixture of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethyl acetate.

[0028] The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxaborate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

[0029] The compounds containing perfluorosulfonyl fluoride structures include one or more of perfluorobutylsulfonyl fluoride, perfluorohexylsulfonyl fluoride, and perfluorooctylsulfonyl fluoride.

[0030] The additives also include one or more of the following: vinylene carbonate, fluorovinyl carbonate, biphenyl, cyclohexylbenzene, propane sulfonate lactone, succinate, and ethylene nitrile.

[0031] Solid sulfur dioxide (DABSO), bis(sulfur dioxide)-1,4-diazabicyclo[2,2,2]octane adduct, also known as DABCO-bis(sulfur dioxide), is a colorless solid containing two sulfur dioxide atoms per molecule. It is stable and can replace gaseous sulfur dioxide in various organic synthesis reactions. Solid sulfur dioxide (DABSO) is chosen as an additive because it contains nitrogen to compensate for phosphorus or boron in lithium salts. As a neutral substance, DABSO does not affect the pH of the electrolyte, thus maintaining its quality. The introduction of fluorinated surfactants such as perfluorosulfonyl fluoride (PFSF), which contains both sulfur dioxide and fluorine, improves the permeability of the electrolyte and increases its fluorine content. Examples of PFSF include perfluorohexyl sulfonyl fluoride, perfluorohexyl sulfonyl fluoride, and perfluorobutyl sulfonyl fluoride.

[0032] The additive uses solid sulfur dioxide (DABSO) and perfluoroethylene propylene (PFEP). The structural formula of solid sulfur dioxide (DABSO) is as follows: It possesses a sulfone group and incorporates the fluorinated surfactant perfluorosulfonyl fluoride. As a fluorinated surfactant, perfluorosulfonyl fluoride contains both sulfur dioxide and fluorine elements, which helps improve the permeability of the electrolyte and simultaneously increase its fluorine content. For example, perfluorobutylsulfonyl fluoride (structural formula...) ), perfluorohexylsulfonyl fluoride (structural formula) ), perfluorooctyl sulfonyl fluoride (structural formula) The additives used in this invention are a mixture of one or more perfluorosulfonyl fluorides and their homologues.

[0033] Although special additives are not frequently used in battery manufacturing, their use can improve performance, such as lifespan, high discharge rate at low temperatures, high temperature stability, and prevention of overcharging and expansion at high temperatures, thereby increasing the lifespan of lithium-ion batteries.

[0034] A method for preparing an electrolyte that improves the cycle performance of lithium-ion batteries, characterized by its simplicity.

[0035] The present invention provides a method for preparing an electrolyte to improve the cycle performance of lithium-ion batteries, comprising the following steps:

[0036] Step S1: Take the above-mentioned parts by weight of organic solvent and mix them thoroughly in a container;

[0037] Step S2: Add the lithium salt in the above weight proportions to the above container and stir to dissolve;

[0038] Step S3: Take the above-mentioned amount of additive by weight and stir to obtain the final product.

[0039] A secondary battery with good cycle performance. The secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, a housing, and the aforementioned electrolyte for improving the cycle performance of a lithium-ion battery. The separator separates the positive electrode and the negative electrode, and the housing houses the positive electrode, the negative electrode, the separator, and the electrolyte.

[0040] The negative electrode sheet includes a negative current collector and a negative active coating disposed on at least one surface of the negative current collector. The negative active coating includes a negative active material, which includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese oxide, and lithium nickel oxide, or a composite compound LiM1. x M2 y O2, where M1 and M2 are metallic elements, and x and y are rational numbers from 0 to 2.

[0041] The positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one surface of the positive current collector. The positive active coating includes a positive active material, which includes crystalline carbon or amorphous carbon.

[0042] The negative electrode sheet includes a negative current collector and a negative active coating disposed on at least one surface of the negative current collector. The negative active coating includes a negative active material, which includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese oxide, and lithium nickel oxide, or a composite compound LiM1. x M2 y O2, where M1 and M2 are metallic elements, and x and y are rational numbers from 0 to 2.

[0043] The material of the separator is one or more of polypropylene, polyethylene, and polyethylene naphthalate.

[0044] Example 1:

[0045] Step 1: Take the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a 5:3:4 ratio by weight and mix them thoroughly in a container.

[0046] Step 2: Then slowly add 12.5% ​​by weight of LiPF6 lithium salt and stir until fully dissolved;

[0047] Step 3: Add 1.8% by weight of vinylene carbonate (VC), 0.1 wt.% of solid sulfur dioxide DABSO, and 3% of 1,3-propanesulfonyl lactone (PS), and stir thoroughly.

[0048] Step 4: Take the manufactured model (48mm*44mm*6.1 mm), 1300mAh nominal capacity aluminum-cased battery, and vacuum bake it at 80±5℃ for 24 hours. Every 0.5~2 hours, replace the atmosphere in the oven with anhydrous nitrogen, and then continue vacuum baking. Inject the prepared electrolyte.

[0049] Step 5: The battery prepared in the above embodiment is charged under constant current-constant voltage (CC-CV) conditions. The charging current is 0.05C for 180 minutes, then charged at 0.2C to 3.9V, and the constant voltage charging ends at 0.02C. After pressing the steel column, it is charged under 0.5C constant current-constant voltage (CC-CV) conditions to 4.2V, ending at a cutoff current of 0.02C. Then, it is charged and discharged under 1C constant current-constant voltage (CC-CV) conditions. The discharge cutoff voltage is 3.0V.

[0050] Example 2

[0051] The difference from Example 1 is that the additive is 0.5 wt% solid sulfur dioxide DABSO.

[0052] Example 3

[0053] The difference from Example 1 is that the additive is 0.1 wt% perfluorobutyl sulfonyl fluoride.

[0054] Example 4

[0055] The difference from Example 1 is that the additive is 0.5 wt% perfluorobutyl sulfonyl fluoride.

[0056] Example 5

[0057] The difference from Example 1 is that the additive is 0.1 wt% perfluorohexyl sulfonyl fluoride.

[0058] Example 6

[0059] The difference from Example 1 is that the additive is 0.5 wt% perfluorohexyl sulfonyl fluoride.

[0060] Example 7

[0061] The difference from Example 1 is that the additive is 0.1 wt% perfluorooctyl sulfonyl fluoride.

[0062] The rest is the same as in Example 1, and will not be repeated here.

[0063] Example 8

[0064] The difference from Example 1 is that the additive is 0.5 wt% perfluorooctyl sulfonyl fluoride.

[0065] Example 9

[0066] The difference from Example 1 is that the additive is 0.1 wt% solid sulfur dioxide DABSO and 0.1 wt% perfluorobutyl sulfonyl fluoride.

[0067] Example 10

[0068] The difference from Example 1 is that the additive is 0.5 wt% solid sulfur dioxide DABSO and 0.5 wt% perfluorobutyl sulfonyl fluoride.

[0069] Example 11

[0070] The difference from Example 1 is that the additive is 0.1 wt% solid sulfur dioxide DABSO and 0.1 wt% perfluorohexyl sulfonyl fluoride.

[0071] Example 12

[0072] The difference from Example 1 is that the additive is 0.5 wt% solid sulfur dioxide DABSO and 0.5 wt% perfluorohexyl sulfonyl fluoride.

[0073] Example 13

[0074] The difference from Example 1 is that the additive is 0.1 wt% solid sulfur dioxide DABSO and 0.1 wt% perfluorooctyl sulfonyl fluoride.

[0075] Example 14

[0076] The difference from Example 1 is that the additive is 0.5 wt% solid sulfur dioxide DABSO and 0.5 wt% perfluorooctyl sulfonyl fluoride.

[0077] Example 15

[0078] The difference from Example 1 is that the additives are 0.1 wt% solid sulfur dioxide DABSO, 0.1 wt% perfluorobutyl sulfonyl fluoride, 0.1 wt% perfluorohexyl sulfonyl fluoride, and 0.1 wt% perfluorooctyl sulfonyl fluoride.

[0079] Example 16

[0080] The difference from Example 1 is that the additives are 0.5 wt% solid sulfur dioxide DABSO, 0.5 wt% perfluorobutyl sulfonyl fluoride, 0.5 wt% perfluorohexyl sulfonyl fluoride, and 0.5 wt% perfluorooctyl sulfonyl fluoride.

[0081] Comparative Example 1

[0082] Step 1: Take the organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a 5:3:4 ratio by weight and mix them thoroughly in a container.

[0083] Step 2: Then slowly add 12.5% ​​by weight of LiPF6 lithium salt and stir until fully dissolved;

[0084] Step 3: Add 2.0% by weight of the additive vinylene carbonate (VC) and 3% by weight of 1,3-propanesulfonate lactone (PS), and stir thoroughly.

[0085] Step 4: Take the manufactured model (48mm*44mm*6.1 mm), 1300mAh nominal capacity aluminum-cased battery, and vacuum bake it at 80±5℃ for 24 hours. Every 0.5~2 hours, replace the atmosphere in the oven with anhydrous nitrogen, and then continue vacuum baking. Inject the prepared electrolyte.

[0086] Step 5: The battery prepared in the above embodiment is charged under constant current-constant voltage (CC-CV) conditions. The charging current is 0.05C for 180 minutes, then charged at 0.2C to 3.9V, and the constant voltage charging ends at 0.02C. After pressing the steel column, it is charged under 0.5C constant current-constant voltage (CC-CV) conditions to 4.2V, ending at a cutoff current of 0.02C. Then, it is charged and discharged under 1C constant current-constant voltage (CC-CV) conditions. The discharge cutoff voltage is 3.0V.

[0087] The electrolytes of Examples 1-16 and Comparative Example 1 were applied to the battery for 300 charge-discharge cycles, and the test results were recorded in Table 1.

[0088] Table 1

[0089]

[0090] The charge-discharge cycle performance test data of the batteries in the various embodiments and comparative examples in the table show that the electrolyte prepared by the present invention, when injected into lithium-ion batteries, has a significantly better cycle life at a charge-discharge rate of 0-4.2V and 1C than the batteries prepared by the comparative non-aqueous electrolyte.

[0091] Furthermore, the electrolyte formulated with the single-component additives used in this invention exhibits superior battery electrical performance compared to electrolytes without additives. Combining these additives in a synergistic effect can further enhance the battery's cycle performance.

[0092] The experiment used compounds containing sulfone groups (-SO2-) and combinations thereof with perfluoroethylene propylene structures as additives, which facilitated the quantitative addition of sulfur dioxide. Sulfonyl fluoride, as a basic raw material for fluorinated surfactants, combined with its chain-like fluorine structure, improved the electrolyte penetration into the battery, thereby enhancing battery performance.

[0093] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. An electrolyte for improving the cycle performance of a lithium ion battery, characterized by comprising: It includes an organic solvent, a lithium salt, and additives, wherein the organic solvent comprises 70% to 88% by weight, the lithium salt comprises 8% to 18% by weight, and the additives comprise 0.01% to 10% by weight. The additives include bis(sulfur dioxide)-1,4-diazabicyclo[2,2,2]octane adducts and compounds containing perfluorosulfonyl fluoride structures.

2. The electrolyte for improving cycle performance of a lithium-ion battery according to claim 1, characterized by, The organic solvent includes one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and ethyl acetate.

3. The electrolyte for improving cycle performance of a lithium-ion battery according to claim 1, wherein The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium dioxaborate, lithium difluorooxaborate, lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate.

4. The electrolyte for improving cycle performance of a lithium-ion battery according to claim 1, wherein The compounds containing perfluorosulfonyl fluoride structures include one or more of perfluorobutylsulfonyl fluoride, perfluorohexylsulfonyl fluoride, and perfluorooctylsulfonyl fluoride.

5. The electrolyte for improving cycle performance of a lithium-ion battery according to claim 1, wherein The additives also include one or more of the following: vinylene carbonate, fluorovinyl carbonate, biphenyl, cyclohexylbenzene, propane sulfonate lactone, succinate, and ethylene nitrile.

6. The method for preparing an electrolyte for improving cycle performance of a lithium ion battery according to any one of claims 1 to 5, wherein Includes the following steps: Step S1: Take the above-mentioned parts by weight of organic solvent and mix them in a container; Step S2: Add the above-mentioned weight proportions of lithium salt to the above container and stir to dissolve; Step S3: Take the above-mentioned amount of additive by weight and stir to obtain the final product.

7. A secondary battery characterized by comprising: The battery comprises a positive electrode, a negative electrode, a separator, a housing, and an electrolyte according to any one of claims 1 to 5 for improving the cycle performance of a lithium-ion battery. The separator is used to separate the positive electrode and the negative electrode, and the housing is used to house the positive electrode, the negative electrode, the separator, and the electrolyte.

8. The secondary battery according to claim 7, characterized by The negative electrode sheet includes a negative electrode current collector and a negative electrode active coating layer provided on at least one surface of the negative electrode current collector, the negative electrode active coating layer including a negative electrode active material, the negative electrode active material including one or several of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganate, lithium nickelate, or a composite compound LiM1 x M2 y O2, wherein M1 and M2 are metal elements, and x and y are rational numbers between 0 and 2.

Images