Ethylene carbonate compound, method for preparing the same, positive electrode slurry, and secondary battery

Abstract

The application provides an ethylene carbonate compound, a preparation method of the ethylene carbonate compound, a positive electrode slurry and a secondary battery. A structural formula of the ethylene carbonate compound is shown in formula I. The positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder, the ethylene carbonate compound and a solvent. The ethylene carbonate compound is used in a positive electrode sheet, can induce electrolyte to be soaked, improves the problem that the electrolyte is poorly soaked into the electrode, reduces the soaking time of the electrolyte, and improves the cycle performance and the rate performance.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and more particularly to a positive electrode auxiliary material, and even more particularly to cyclic ethylene carbonate compounds and their preparation methods, positive electrode slurries and secondary batteries. Background Technology

[0002] Rechargeable battery technology has made significant progress in recent years, particularly in improving volumetric and gravimetric energy densities. Currently, high areal density and high compaction electrode designs have become a crucial approach to enhancing battery energy density, especially in automotive power and large-scale energy storage, where higher proportions and densities of electrode active materials have become a major development trend. However, this design also introduces problems such as poor electrolyte wetting, leading to uneven current density distribution, SEI film instability, and lithium deposition on the negative electrode, thus affecting battery performance and safety.

[0003] To address the problem of poor electrolyte wetting of electrodes in secondary batteries, there are three main methods: (1) Adding wetting additives, such as fluorobenzene and fluoroethers, to the electrolyte to reduce the surface energy of the electrolyte and allow the electrolyte to better wet the electrodes. This method requires a large amount of wetting additives to be added to the electrolyte to achieve the desired effect, which not only increases the cost but also has unpredictable effects on battery performance, such as high-temperature cycling gas generation and capacity decay, posing certain risks. (2) Increasing the temperature or extending the battery's static aging time to allow the electrolyte to wet the electrodes more fully. This approach increases production energy consumption and costs, and the extended time also reduces production efficiency. Since the contact interface between the electrode and the electrolyte does not change fundamentally, the rate performance of the battery cannot be guaranteed. (3) Using mechanical, ultrasonic, or laser methods to process the electrode surface, forming small grooves or holes on the electrode surface, increasing the contact area between the electrolyte and the electrode, and improving the wetting effect of the electrolyte on the electrode. This type of method has high requirements for equipment and process control, which increases production costs. Furthermore, since it can only be processed on the surface of the electrode, it has limited effect on improving the contact between the electrolyte and the electrode.

[0004] Therefore, there is an urgent need to provide a new method to improve the wetting effect of electrolyte on the electrode in secondary batteries, so as to improve the lithium plating problem and improve cycle and rate performance. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide a cyclic ethylene carbonate compound, its preparation method, a positive electrode slurry, and a secondary battery. Using the cyclic ethylene carbonate compound in the positive electrode sheet can induce electrolyte wetting, improving the problem of poor electrolyte wetting of the electrode, reducing electrolyte run-in time, and enhancing cycle performance and rate performance.

[0006] To achieve the above objectives, the first aspect of the present invention provides a cyclic ethylene carbonate compound with the structural formula shown in Formula 1.

[0007]

[0008] The cycloethylene carbonate compound of this invention can be dissolved or dispersed in the positive electrode slurry and is also soluble in the electrolyte. It possesses good stability to water and air, thus preventing agglomeration in the positive electrode slurry. The solvent in the slurry allows for slurry formation, resulting in a stable positive electrode slurry. The positive electrode slurry containing the cycloethylene carbonate compound is used to make a positive electrode sheet. Upon contact with the electrolyte, the cycloethylene carbonate compound dissolves in the electrolyte, forming pores and channels within the positive electrode sheet. These pores and channels can induce more electrolyte wetting, thereby improving the problem of poor electrolyte wetting of the electrode.

[0009] As a technical solution of the present invention, the solubility of the cyclic ethylene carbonate compound in organic solvents is not less than 15 wt.%.

[0010] As one technical solution of the present invention, the organic solvent includes carbonates and / or carboxylic acid esters.

[0011] As one technical solution of the present invention, the organic solvent includes one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0012] As a technical solution of the present invention, the cyclic ethylene carbonate compound is soluble or dispersed in N-methylpyrrolidone and / or N-vinylpyrrolidone.

[0013] A second aspect of this invention provides a method for preparing cyclic ethylene carbonate compounds, comprising the steps of: mixing mannitol and dimethyl carbonate, using potassium carbonate as a catalyst, and refluxing at 70–100°C for transesterification followed by purification. The preparation method of this invention is simple, as it can be obtained by transesterification of mannitol and dimethyl carbonate.

[0014] A third aspect of this invention provides a positive electrode slurry, comprising a positive electrode active material, a conductive agent, a binder, an additive, and a solvent. The additive includes the aforementioned cyclic ethylene carbonate compound or a cyclic ethylene carbonate compound prepared by the aforementioned method for preparing the cyclic ethylene carbonate compound. The cyclic ethylene carbonate compound can be dissolved or dispersed in the positive electrode slurry, is stable to water and air, and does not agglomerate in the slurry; therefore, it does not affect the performance of the electrode itself after it is formed into an electrode sheet.

[0015] As one technical solution of the present invention, the mass of the positive electrode active material, the conductive agent, the binder and the additive is m, the mass of the cycloethylene carbonate compound is n, and the proportion of n in m is 0.1-3.0%.

[0016] As a technical solution of the present invention, the positive electrode active material includes at least one of lithium cobalt oxide positive electrode material, lithium iron phosphate positive electrode material, lithium manganese iron phosphate positive electrode material, lithium nickel cobalt manganese oxide positive electrode material and lithium nickel cobalt aluminum oxide positive electrode material; the conductive agent includes at least one of acetylene black, Ketjen black, carbon black, conductive graphite, carbon fiber and carbon nanotube; the binder includes polyvinylidene fluoride and / or polytetrafluoroethylene; and the solvent includes N-methylpyrrolidone and / or N-vinylpyrrolidone.

[0017] The fourth aspect of the present invention provides a positive electrode sheet obtained by coating, drying and rolling the aforementioned positive electrode slurry.

[0018] The fifth aspect of the present invention provides a secondary battery, comprising a negative electrode, a separator, an electrolyte, and the aforementioned positive electrode. Attached Figure Description

[0019] Figure 1 This is the proton NMR spectrum of a cyclic ethylene carbonate compound.

[0020] Figure 2 This is the carbon spectrum of a cyclic ethylene carbonate compound. Detailed Implementation

[0021] The cyclic ethylene carbonate compound of the present invention can be used in secondary batteries. In particular, the cyclic ethylene carbonate compound is used as a positive electrode additive. When the cyclic ethylene carbonate compound is used in the positive electrode sheet, it can induce electrolyte wetting, improve the problem of poor electrolyte wetting of the electrode, reduce the electrolyte pouring time, and improve cycle performance and rate performance.

[0022] A secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is made by coating, drying, and rolling a positive electrode slurry. The negative electrode is made by coating, drying, and rolling a negative electrode slurry.

[0023] The cathode slurry includes the cathode active material, conductive agent, binder, additives, and solvent. The cathode active material includes at least one of the following: lithium cobalt oxide-based cathode materials, lithium iron phosphate-based cathode materials, lithium manganese iron phosphate-based cathode materials, lithium nickel cobalt manganese oxide-based cathode materials, and lithium nickel cobalt aluminum oxide-based cathode materials. Lithium cobalt oxide-based cathode materials refer to lithium cobalt oxide, doped lithium cobalt oxide, or coated lithium cobalt oxide, with lithium cobalt oxide as the main material. Similarly, lithium iron phosphate-based cathode materials refer to lithium iron phosphate, doped lithium iron phosphate, or coated lithium iron phosphate. Lithium manganese iron phosphate-based cathode materials refer to lithium manganese iron phosphate, doped lithium manganese iron phosphate, or coated lithium manganese iron phosphate. Lithium nickel cobalt manganese oxide-based cathode materials refer to lithium nickel cobalt manganese oxide, doped lithium nickel cobalt manganese oxide, or coated lithium nickel cobalt manganese oxide. Lithium nickel cobalt aluminum oxide-based cathode materials refer to lithium nickel cobalt aluminum oxide, doped lithium nickel cobalt aluminum oxide, or coated lithium nickel cobalt aluminum oxide. The conductive agent can be any conductive material known in the industry that can be used in the positive electrode, including at least one of acetylene black, Ketjen black, carbon black, conductive graphite, carbon fiber, and carbon nanotubes. The binder can be any material known in the industry that can be used to bond the positive electrode components together, including polyvinylidene fluoride and / or polytetrafluoroethylene. The solvent includes N-methylpyrrolidone and / or N-vinylpyrrolidone. The additives include cyclovinyl carbonate compounds. The total mass of the positive electrode active material, conductive agent, binder, and additives is 100%. The binder content is 1% to 10%, and for example, it can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. The conductive agent content is 1% to 10%, and for example, it can be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. The content of cycloethylene carbonate compound is 0.1% to 3.0%, and for example, it may be, but is not limited to, 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%.

[0024] The negative electrode slurry includes a negative electrode active material, a conductive agent, a binder, an additive, and a solvent. The negative electrode active material includes at least one of carbon-based materials, silicon-based materials, lithium titanate, and tin-based materials. The carbon-based material may include, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The silicon-based material may include, but is not limited to, at least one of elemental silicon, silicon-oxygen composite materials, silicon-carbon composite materials, and silicon alloy materials. The tin-based material may include elemental tin, tin-carbon composite materials, tin-oxygen composite materials, and tin alloy compounds. The conductive agent may be any conductive material known in the industry that can be used for the negative electrode, including at least one of acetylene black, Ketjen black, carbon black, conductive graphite, carbon fiber, and carbon nanotubes. The binder may be any material known in the industry that can be used to bind the negative electrode components together, including styrene-butadiene rubber and sodium carboxymethyl cellulose. The solvent includes water. The total mass of the negative electrode active material, conductive agent, and binder is 100%. The binder content is 1% to 6%, and for example, it may be, but is not limited to, 1%, 2%, 3%, 4%, 5%, or 6%. The conductive agent content is 1% to 6%, and for example, it may be, but is not limited to, 1%, 2%, 3%, 4%, 5%, or 6%.

[0025] The electrolyte comprises an electrolyte salt, an organic solvent, and additives. The electrolyte salt may be, but is not limited to, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, and lithium difluorobis(oxalate phosphate). The organic solvent is selected from carbonates and / or carboxylic acid esters. Further organic solvents are selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (PC), propylene carbonate (PC), butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate, and ethyl butyrate. The additives are conventional additives, such as fluoroethylene carbonate, vinylene carbonate, 1,3-propanesulfonate lactone, vinyl sulfate, etc.

[0026] The separator can be a polyethylene separator, a polypropylene separator, a polyethylene separator with a porous ceramic layer on the surface, or a polypropylene separator with a porous ceramic layer on the surface.

[0027] The structural formula of the cyclic ethylene carbonate compound is shown in Formula 1. The cyclic ethylene carbonate compound is soluble or dispersed in N-methylpyrrolidone and / or N-vinylpyrrolidone. Therefore, when the cyclic ethylene carbonate compound is used to prepare a positive electrode slurry, its solubility in the solvents N-methylpyrrolidone and / or N-vinylpyrrolidone allows for slurry formation of a stable positive electrode slurry. Furthermore, the solubility of the cyclic ethylene carbonate compound in organic solvents is not less than 15 wt.%. Organic solvents include carbonates and / or carboxylic acid esters; furthermore, the organic solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (PC), propylene carbonate (PC), butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate, and ethyl butyrate. The solubility of cycloethylene carbonate compounds in organic solvents is not less than 15 wt.%, so when in contact with electrolyte, they can quickly dissolve in the electrolyte and form pores and channels inside the positive electrode, thereby inducing more electrolyte to wet the positive electrode and thus improving the problem of poor electrolyte wetting of the electrode.

[0028]

[0029] A method for preparing cyclic ethylene carbonate compounds includes the following steps: mixing mannitol and dimethyl carbonate, using potassium carbonate as a catalyst, and refluxing at 70–100°C for transesterification followed by purification. Cyclic ethylene carbonate compounds can be obtained by transesterification of mannitol and dimethyl carbonate. The purification step can involve washing with dimethyl carbonate followed by vacuum drying.

[0030] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0031] Part 1: Preparation of Cycloethylene Carbonate Compounds

[0032] The preparation method of the cyclic ethylene carbonate compound with the structural formula shown in Formula 1 includes the following steps: mixing mannitol and dimethyl carbonate, using potassium carbonate as a catalyst, and refluxing at 90°C to carry out a transesterification reaction to obtain cyclic ethylene carbonate; washing with dimethyl carbonate and drying to obtain purified cyclic ethylene carbonate with a yield of 75%. Its proton and carbon spectra are shown below. Figure 1 and Figure 2 As shown in the spectrum, cyclic ethylene carbonate compounds with the structural formula shown in Formula 1 can be synthesized.

[0033] Part Two: Applications of Cycloethylene Carbonate Compounds in Batteries

[0034] Example 1

[0035] This embodiment describes the preparation of a secondary battery, which includes the following steps.

[0036] (1) Preparation of positive electrode

[0037] LiFePO4, the cyclic ethylene carbonate compound prepared in Part 1, conductive carbon Super P, and PVDF were dissolved in N-methylpyrrolidone at a weight ratio of 95.0%:1.0%:2.0%:2.0%. A homogeneous positive electrode slurry was obtained by stirring. The positive electrode slurry was then coated on both sides of an aluminum foil substrate, with a compaction density of 2.5 g / cm³. 3 Its surface density is 35.0 mg / cm³. 2 After drying and rolling, the positive electrode sheets are cut into the required width and shape.

[0038] (2) Preparation of negative electrode

[0039] Artificial graphite, conductive carbon Super P, and PVDF (at a weight ratio of 95%:2%:3%) were dissolved in N-methylpyrrolidone, and a homogeneous negative electrode slurry was obtained by stirring. The negative electrode slurry was then uniformly coated onto the surface of a copper foil substrate, with double-sided coating and a compaction density of 1.5 g / cm³. 3 Its surface density is 16.0 mg / cm³. 2 After drying and rolling, the negative electrode sheets are cut into the required width and shape.

[0040] (3) Preparation of the separating membrane

[0041] The separation membrane is prepared using conventional techniques. The base membrane is a PE membrane with a ceramic layer coated on the surface, and it is cut into the required shape as needed.

[0042] (4) Battery manufacturing

[0043] The obtained negative electrode, positive electrode, and separator are wound together to form a core, which is then assembled, injected with electrolyte (and the injection time is recorded), and subjected to composition and capacity testing. The electrolyte solvent is EC:EMC = 1:1, and the lithium salt solute is LiPF6 with a molar concentration of 1M.

[0044] Example 2

[0045] This embodiment describes the preparation of a secondary battery, which includes the following steps.

[0046] (1) Preparation of positive electrode

[0047] LiFePO4, the cyclic ethylene carbonate compound prepared in Part 1, conductive carbon Super P, and PVDF were dissolved in N-methylpyrrolidone at a weight ratio of 95.0%:2.5%:1.0%:1.5%. A homogeneous positive electrode slurry was obtained by stirring. This slurry was then coated on both sides of an aluminum foil substrate, with a compaction density of 2.5 g / cm³. 3 Its surface density is 35.0 mg / cm³. 2 After drying and rolling, the positive electrode sheets are cut into the required width and shape.

[0048] (2) Preparation of negative electrode

[0049] Artificial graphite, conductive carbon Super P, and PVDF (at a weight ratio of 95%:2%:3%) were dissolved in N-methylpyrrolidone, and a homogeneous negative electrode slurry was obtained by stirring. The negative electrode slurry was then uniformly coated onto the surface of a copper foil substrate, with double-sided coating and a compaction density of 1.5 g / cm³. 3 Its surface density is 16.0 mg / cm³. 2 After drying and rolling, the negative electrode sheets are cut into the required width and shape.

[0050] (3) Preparation of the separating membrane

[0051] The separation membrane is prepared using conventional techniques. The base membrane is a PE membrane with a ceramic layer coated on the surface, and it is cut into the required shape as needed.

[0052] (4) Battery manufacturing

[0053] The obtained negative electrode, positive electrode, and separator are wound together to form a core, which is then assembled, injected with electrolyte (and the injection time is recorded), and subjected to composition and capacity testing. The electrolyte solvent is EC:EMC = 1:1, and the lithium salt solute is LiPF6 with a molar concentration of 1M.

[0054] Comparative Example 1

[0055] This comparative example describes the preparation of a secondary battery, which includes the following steps.

[0056] (1) Preparation of positive electrode

[0057] LiFePO4, conductive carbon Super P, and PVDF were dissolved in N-methylpyrrolidone at a weight ratio of 95.0%:3.0%:2.0%, and a homogeneous positive electrode slurry was obtained by stirring. The positive electrode slurry was then coated on both sides of an aluminum foil substrate, with a compaction density of 2.5 g / cm³. 3 Its surface density is 35.0 mg / cm³. 2 After drying and rolling, the positive electrode sheets are cut into the required width and shape.

[0058] (2) Preparation of negative electrode

[0059] Artificial graphite, conductive carbon Super P, and PVDF (at a weight ratio of 95%:2%:3%) were dissolved in N-methylpyrrolidone, and a homogeneous negative electrode slurry was obtained by stirring. The negative electrode slurry was then uniformly coated onto the surface of a copper foil substrate, with double-sided coating and a compaction density of 1.5 g / cm³. 3 Its surface density is 16.0 mg / cm³. 2 After drying and rolling, the negative electrode sheets are cut into the required width and shape.

[0060] (3) Preparation of the separating membrane

[0061] The separation membrane is prepared using conventional techniques. The base membrane is a PE membrane with a ceramic layer coated on the surface, and it is cut into the required shape as needed.

[0062] (4) Battery manufacturing

[0063] The obtained negative electrode, positive electrode, and separator are wound together to form a core, which is then assembled, injected with electrolyte (and the injection time is recorded), and subjected to composition and capacity testing. The electrolyte solvent is EC:EMC = 1:1, and the lithium salt solute is LiPF6 with a molar concentration of 1M.

[0064] Comparative Example 2

[0065] This comparative example describes the preparation of a secondary battery, which includes the following steps.

[0066] (1) Preparation of positive electrode

[0067] LiFePO4, conductive carbon Super P, and PVDF were dissolved in N-methylpyrrolidone at a weight ratio of 95.0%:3.0%:2.0%, and a homogeneous positive electrode slurry was obtained by stirring. The positive electrode slurry was then coated on both sides of an aluminum foil substrate, with a compaction density of 2.5 g / cm³. 3 Its surface density is 35.0 mg / cm³. 2 After drying and rolling, the positive electrode sheets are cut into the required width and shape.

[0068] (2) Preparation of negative electrode

[0069] Artificial graphite, conductive carbon Super P, and PVDF (at a weight ratio of 95%:2%:3%) were dissolved in N-methylpyrrolidone, and a homogeneous negative electrode slurry was obtained by stirring. The negative electrode slurry was then uniformly coated onto the surface of a copper foil substrate, with double-sided coating and a compaction density of 1.5 g / cm³. 3 Its surface density is 16.0 mg / cm³. 2 After drying and rolling, the negative electrode sheets are cut into the required width and shape.

[0070] (3) Preparation of the separating membrane

[0071] The separation membrane is prepared using conventional techniques. The base membrane is a PE membrane with a ceramic layer coated on the surface, and it is cut into the required shape as needed.

[0072] (4) Battery manufacturing

[0073] The obtained negative electrode, positive electrode, and separator are wound together to form a core, which is then assembled, injected with electrolyte (and the injection time is recorded), and subjected to composition and capacity testing. The electrolyte solvent is EC:EMC = 1:1, the lithium salt solute is LiPF6 with a molar concentration of 1M, and the electrolyte also contains 1% by mass of the cyclic ethylene carbonate compound prepared in the first part.

[0074] The electrolyte injection times for Examples 1-2 and Comparative Examples 1-2 are shown in Table 1. The results show that adding the ethylene carbonate compound prepared in Part 1 to the positive electrode significantly shortens the electrolyte injection time. This is because after the ethylene carbonate compound forms the positive electrode and comes into contact with the electrolyte, it dissolves in the electrolyte, thus forming pores and channels inside the positive electrode. These pores and channels can induce more electrolyte to penetrate, thereby improving the problem of poor electrolyte wetting of the electrode. Although the battery in Comparative Example 2 also contains ethylene carbonate compound, it is present in the electrolyte and does not help with electrolyte injection.

[0075] Table 1. Liquid dispensing times for Examples 1-2 and Comparative Examples 1-2

[0076]

[0077]

[0078] The batteries prepared in Examples 1-2 and Comparative Examples 1-2 were divided into two batches. The first batch of batteries underwent rate testing at 25°C under the following charge-discharge conditions: charged at 2.5C to 3.65V, then charged at a constant voltage to 0.05C, and then discharged at 2.5C to 2.8V, for 10 cycles. The second batch of batteries underwent cycle testing at 25°C under the following charge-discharge conditions: charged at 1C to 3.65V, then charged at a constant voltage to 0.05C, and then discharged at 1C to 2.8V, for 200 cycles. The results of the rate and cycle tests are shown in Table 2.

[0079] Table 2. Magnification and Cyclic Test Results of Examples 1-2 and Comparative Examples 1-2

[0080]

[0081] As shown in Table 2, Examples 1 and 2 exhibited superior rate performance and cycle performance. This is because the ethylene carbonate compound improved the poor electrolyte wetting of the electrodes, thus providing more lithium-ion transport channels and enhancing rate performance. Furthermore, the ethylene carbonate compound dissolved in the organic solvent can undergo an electrochemical reaction on the surfaces of the positive and negative electrodes to form a stable and dense SEI film, thereby improving cycle performance. In Comparative Example 2, an ethylene carbonate compound was added to the electrolyte, which also underwent an electrochemical reaction on the surfaces of the positive and negative electrodes to form a stable and dense SEI film, resulting in superior cycle performance as well.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A secondary battery comprising a negative electrode sheet, a separator, an electrolyte, and a positive electrode sheet, the positive electrode sheet being produced by coating, drying, and rolling a positive electrode slurry, characterized in that, The positive electrode slurry comprises a positive electrode active material, a conductive agent, a binder, an additive, and a solvent, the additive is selected from a cyclic carbonate vinyl ester compound, a structural formula of the cyclic carbonate vinyl ester compound is shown as Formula I, the cyclic carbonate vinyl ester compound is dissolved or dispersed in N-methyl pyrrolidone and / or N-vinyl pyrrolidone, a solubility of the cyclic carbonate vinyl ester compound in the organic solvent is not less than 15 wt.%, the electrolyte comprises an electrolyte salt, an additive, and an organic solvent selected from a carbonate and / or a carboxylic acid ester, Formula I.

2. The secondary battery according to claim 1, characterized by A preparation method of the cyclic carbonate vinyl ester compound comprises the following steps: mixing mannitol and dimethyl carbonate, performing an ester exchange reaction under reflux at 70-100 DEG C with potassium carbonate as a catalyst, and then performing a purification treatment.

3. The secondary battery according to claim 1, characterized by A mass of the positive electrode active material, the conductive agent, the binder, and the additive is m, a mass of the cyclic carbonate vinyl ester compound is n, and a proportion of n in m is 0.1-3.0%.

4. The secondary battery according to claim 1, characterized by The positive electrode active material is selected from at least one of a lithium cobaltate system positive electrode material, a lithium iron phosphate system positive electrode material, a lithium manganese iron phosphate system positive electrode material, a lithium nickel cobalt manganese phosphate system positive electrode material, and a lithium nickel cobalt aluminum phosphate system positive electrode material, the conductive agent is selected from at least one of acetylene black, ketjen black, carbon black, conductive graphite, carbon fiber, and carbon nanotube, and the binder is selected from polyvinylidene fluoride and / or polytetrafluoroethylene.

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