Electrolyte and secondary battery

Abstract

The invention belongs to the technical field of power batteries, and particularly discloses an electrolyte and a secondary battery. The electrolyte comprises an electrolyte, a solvent and an additive, wherein the additive at least comprises a first additive; the first additive is an amide organic compound of which the chemical general formula is as shown in formula (I): in the formula (I), R1 is selected from any one of substituent groups of which the number of hydrogen atoms or carbon atoms is 1-6, the degree of unsaturation is 0-4 and the number of heteroatoms is 0-3; r2 and R3 are respectively selected from any one of substituent groups with the carbon atom number of 1-6, the unsaturation degree of 0-4 and the heteroatom number of 0-3; the heteroatom is selected from at least one of oxygen, nitrogen, sulfur or phosphorus. The new additive is added into the electrolyte and then applied to the secondary battery, so that the high and low temperature performance and the like of the battery are improved, and the overall performance and the safety of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of power battery technology, and in particular to an electrolyte and a secondary battery. Background Technology

[0002] Faced with surging global demand for electric vehicles and portable electronic devices, lithium-ion battery technology is evolving at an unprecedented pace, making the enhancement of its core competitiveness particularly crucial. In the composition of lithium-ion batteries, the cathode material not only accounts for more than half of the overall weight and cost, but also directly determines the battery's energy density and cost control capabilities, becoming a core element driving technological breakthroughs.

[0003] Among the many cathode material systems under active exploration, high-nickel cathode material LiNi... x M 1-x O2 (where M represents transition metal elements such as Mn, Co, and Al) has emerged as a highly promising research subject due to its exceptional potential. These materials can achieve energy densities ranging from 650 Wh / kg to over 850 Wh / kg, greatly satisfying market demands for extended battery life. Furthermore, their cycle stability is remarkable, capable of withstanding approximately 3000 charge-discharge cycles, providing a strong guarantee for long battery life.

[0004] However, the widespread application of high-nickel cathode materials is also accompanied by significant safety challenges, particularly the problem of significant gas generation. This problem mainly stems from two complex side reactions. One is that lithium compounds remaining on the cathode surface (such as LiOH, LiHCO3, Li2CO3, etc.) decompose under certain conditions or interact with the acidic environment inside the battery. For example, this can cause transition metal ions to dissolve and diffuse to the negative electrode, resulting in reduction and causing an internal short circuit. This leads to a significant reduction in battery life and even serious safety issues, such as battery explosions, severely restricting the large-scale commercial application of high-nickel cathode materials.

[0005] Furthermore, the electrolyte commonly used in lithium-ion batteries currently primarily consists of lithium hexafluorophosphate (LiPF6) as the electrolyte salt, combined with a mixed organic solvent composed of cyclic and chain carbonates. However, this electrolyte has some shortcomings in practical applications. In particular, during the charging and discharging process of lithium batteries, the generation of a large amount of gas can reduce the contact area between the electrodes and the electrolyte, thereby decreasing the battery's charging and discharging efficiency. In addition, the presence of gas can interfere with the internal electrochemical reactions of the battery, further reducing the battery's energy density and power output, and severely impacting its cycle life. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an electrolyte and a secondary battery. By adding new additives to the electrolyte and then applying it to the secondary battery, the high and low temperature performance of the battery can be improved, thereby enhancing the overall performance and safety of the battery and solving the gas generation problem caused by the application of high-nickel cathode materials, thus improving the prospects for large-scale commercialization of high-nickel cathode materials.

[0007] To achieve the above and other related objectives, the present invention provides an electrolyte comprising an electrolyte, a solvent, and an additive, wherein the additive comprises at least a first additive;

[0008] The first additive is an amide organic compound with the general chemical formula shown in formula (I):

[0009]

[0010] In formula (Ⅰ), R1 is selected from hydrogen atoms, or any one of the following substituents having 1 to 6 carbon atoms, an unsaturation degree of 0 to 4, and a heteroatom number of 0 to 3;

[0011] R2 and R3 are selected from any one of the substituents having 1 to 6 carbon atoms, an unsaturation degree of 0 to 4, and a heteroatom number of 0 to 3;

[0012] The heteroatom is selected from at least one of oxygen, nitrogen, sulfur or phosphorus.

[0013] Furthermore, the additive also includes a first additive, and the second additive is lithium difluorobis(oxalato)phosphate (LiODFP).

[0014] Furthermore, in formula (Ⅰ), R1, R2 and R3 are selected from any one of the following substituents: alkyl, alkenyl, alkynyl, carbonyl, ester, alkoxy, amino, amino, phosphorooxyheterocyclic, furan, thiophene, pyrrole, thiazole, imidazole, pyridine, pyrazine, pyrimidine or pyridazine.

[0015] Furthermore, the first additive is selected from at least one of compound 1, compound 2, compound 3, compound 4, compound 5, or compound 6.

[0016] The chemical structural formula of compound 1 is as follows:

[0017] The chemical structural formula of compound 2 is as follows:

[0018] The chemical structural formula of compound 3 is as follows:

[0019] The chemical structural formula of compound 4 is as follows:

[0020] The chemical structural formula of compound 5 is as follows:

[0021] The chemical structural formula of compound 6 is as follows:

[0022] Furthermore, based on the total mass of the electrolyte, the mass percentage of the first additive is 0.05% to 3%, preferably 0.1% to 0.5%.

[0023] Furthermore, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.05% to 1%.

[0024] Furthermore, the electrolyte is a lithium salt, which is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, or lithium trifluoromethylsulfonate.

[0025] Furthermore, based on the total mass of the electrolyte, the mass percentage of the electrolyte is 12% to 16%.

[0026] Furthermore, the solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents.

[0027] Furthermore, based on the total mass of the electrolyte, the solvent accounts for 70% to 80% by mass.

[0028] Furthermore, the additive also includes a third additive selected from at least one of fluoroethylene carbonate, propylene-1,3-sulfonyl lactone, or tetravinylsilane.

[0029] The present invention also provides a secondary battery comprising the electrolyte as described above.

[0030] As described above, the electrolyte and secondary battery of the present invention have the following beneficial effects:

[0031] 1. In a fully charged state, if the positive electrode material is subjected to protons H... + After an attack, the battery will collapse, and transition metal ions will overflow. This invention adds a first additive to the electrolyte to capture the escaped transition metal ions, preventing them from diffusing to the negative electrode and causing reduction, which would result in a micro-short circuit inside the battery. This improves the battery's low-temperature performance, extends its cycle life, and enhances its safety performance.

[0032] 2. This invention also proposes adding a second additive, LiODFP, to the electrolyte. LiODFP, as an additive with both positive and negative electrode film-forming capabilities, can significantly reduce the battery's impedance level, thereby enhancing overall battery performance, particularly its performance at low temperatures. However, it is worth noting that the relatively limited solubility of LiODFP in carbonate solvents has become a bottleneck to its full low-temperature performance, limiting its potential under extreme temperature conditions. However, this invention combines LiODFP with a first additive, which assists in the dissolution of LiODFP, thus improving its low-temperature performance.

[0033] 3. This invention also limits the amount of additives in the electrolyte. By reasonably controlling the amount of the first additive and the second additive within a specific range, it is possible to prevent the dissolution of transition metal ions and their diffusion to the negative electrode to cause reduction and internal short circuits, improve the film-forming ability of the positive and negative electrodes, significantly reduce the battery impedance level, promote the dissolution of LiODFP to improve its low-temperature performance, and ensure that the best balance point is found between battery performance, thereby effectively improving the overall performance and safety of the battery.

[0034] In summary, applying the electrolyte provided by this invention to secondary batteries such as lithium-ion batteries can effectively improve the overall performance and safety of the battery, and also solve the gas generation problem caused by the application of high-nickel cathode materials, thereby improving the prospects for large-scale commercialization of high-nickel cathode materials. Detailed Implementation

[0035] 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.

[0036] In this invention, unless otherwise stated, the term "multiple" means two or more.

[0037] The character " / " indicates that the objects before and after it are in an "or" relationship. For example, A / B means: A or B.

[0038] The term "and / or" describes an association between objects, indicating that three relationships can exist. For example, A and / or B means: A or B, or A and B.

[0039] One embodiment of the present invention provides an electrolyte comprising an electrolyte, a solvent, and an additive, wherein the additive comprises at least a first additive;

[0040] The first additive is an amide organic compound with the general chemical formula shown in formula (I):

[0041]

[0042] In formula (Ⅰ), R1 is selected from hydrogen atoms, or any one of the substituents with 1 to 6 carbon atoms, 0 to 4 degrees of unsaturation, and 0 to 3 heteroatoms; R2 and R3 are selected from any one of the substituents with 1 to 6 carbon atoms, 0 to 4 degrees of unsaturation, and 0 to 3 heteroatoms, respectively.

[0043] The heteroatom is selected from at least one of oxygen, nitrogen, sulfur or phosphorus.

[0044] In some embodiments, in formula (I), R1, R2 and R3 are selected from any one of alkyl, alkenyl, alkynyl, carbonyl, ester, alkoxy, amino, amino, phosphorooxyheterocyclic, furan, thiophene, pyrrole, thiazole, imidazole, pyridine, pyrazine, pyrimidine or pyridazine substituents.

[0045] In some embodiments, the first additive is selected from at least one of compound 1, compound 2, compound 3, compound 4, compound 5, or compound 6.

[0046] The chemical structural formula of compound 1 is as follows:

[0047] The chemical structural formula of compound 2 is as follows:

[0048] The chemical structural formula of compound 3 is as follows:

[0049] The chemical structural formula of compound 4 is as follows:

[0050] The chemical structural formula of compound 5 is as follows:

[0051] The chemical structural formula of compound 6 is as follows:

[0052] In secondary batteries, the electrolyte plays a crucial role in conducting ions, providing ion channels, and maintaining chemical stability. The various components of the electrolyte can be categorized according to their function and dosage as lithium salts, solvents, and additives. Lithium salts primarily provide lithium ions to form ion channels. In the entire electrochemical system of the battery, the directional movement of lithium ions and electrons generates electricity. Lithium salts have a significant impact on the energy density, power density, wide electrochemical window, cycle life, and safety performance of lithium batteries. Solvents are used to dissolve lithium salts and additives within the electrolyte. Additives, added in small amounts to the electrolyte, are numerous and each plays a different role, such as improving the battery's high and low temperature performance, cycle performance, and film-forming properties.

[0053] In a fully charged state, if the cathode material is subjected to protons H... + After an attack, the battery will collapse, and transition metal ions will overflow. The above implementation method / example adds a first additive to the electrolyte to capture the escaped transition metal ions and prevent them from diffusing to the negative electrode and causing reduction, which would cause micro-short circuits inside the battery. This improves the low-temperature performance of the battery, extends the cycle life of the battery, and improves the safety performance.

[0054] In some embodiments, the mass percentage of the first additive is 0.05% to 3% based on the total mass of the electrolyte, preferably 0.1% to 0.5%, for example 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 1.8%, 2.0%, 2.2%, 2.5%, 2.8%, 3.0%, etc.

[0055] The dosage of additives in the electrolyte needs to be precisely controlled. Experiments have shown that if the dosage of the first additive is excessive, exceeding the 3% limit, the excess additive may transform into a nucleophilic attacking agent, undergoing a ring-opening polymerization reaction with the cyclic electrolyte components in the battery system. This reaction not only consumes large amounts of solvents such as ethylene carbonate (EC), but may also adversely affect the battery's kinetic characteristics and high-temperature performance, thus impacting battery performance.

[0056] Conversely, if the amount of the first additive is too small, i.e. below the critical value of 0.05%, its ability to neutralize transition metal ions will be insufficient, and it will be unable to effectively inhibit the dissolution and migration of transition metal ions, and it will also be unable to fully play its expected role in preventing micro-short circuits and protecting the integrity of the battery structure.

[0057] Therefore, by reasonably controlling the amount of the first additive within the scope defined in the above embodiments, the best balance can be found between preventing the dissolution of transition metal ions and ensuring battery performance, which is also a key point in improving the overall performance and safety of the battery.

[0058] In some embodiments, the additive further includes a first additive, and the second additive is LiODFP.

[0059] In the above embodiments, LiODFP is used as an additive with both positive and negative electrode film-forming capabilities, which can significantly reduce the battery impedance level, thereby enhancing the overall battery performance, especially its performance at low temperatures. However, it is worth noting that due to the relatively limited solubility of LiODFP in carbonate solvents, this characteristic has become a bottleneck to its full low-temperature performance, limiting the full realization of its potential under extreme temperature conditions. However, this invention combines LiODFP with a first additive, which can assist in the dissolution of LiODFP, thereby improving its low-temperature performance. The specific reason is as follows:

[0060] The first additive is an organic compound containing an amide structure. The lone pair of electrons on the nitrogen atom in its molecule can form a conjugated system with the π electrons of the carbonyl group, reducing the electron cloud density on the nitrogen atom and thus weakening its ability to accept protons. Consequently, the CN bond exhibits a certain degree of double bond behavior. At the same time, the reduced electron cloud density on the nitrogen atom also increases the polarity of the NH bond. In this case, the first additive can assist in the dissolution of LiODFP, thereby improving its low-temperature performance.

[0061] In some embodiments, the mass percentage of the second additive is 0.05% to 1% based on the total mass of the electrolyte, for example, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, etc.

[0062] The present invention has found through experiments that if the amount of the second additive is too large, that is, exceeds the limit of 1%, the high-temperature cycle performance of the battery will be affected.

[0063] Conversely, if the amount of the second additive is too small, i.e. below the critical value of 0.05%, its ability to improve the film formation of the positive and negative electrodes and reduce the battery impedance level is insufficient, thus failing to enhance the overall performance of the battery and also failing to fully realize its expected role in improving its performance in low-temperature environments.

[0064] Therefore, within the scope defined in the above embodiments, reasonable control of the dosage of the first additive and the second additive is necessary to prevent the dissolution and diffusion of transition metal ions to the negative electrode, which would cause reduction and internal short circuits, improve the film-forming ability of the positive and negative electrodes, significantly reduce the battery impedance level, promote the dissolution of LiODFP to improve its low-temperature performance, and ensure that the battery performance finds the best balance point. This is also a key point in improving the overall performance and safety of the battery.

[0065] In some embodiments, the electrolyte is a lithium salt selected from at least one of lithium hexafluorophosphate, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, or lithium trifluoromethylsulfonate, and the mass percentage of the electrolyte is 12% to 16% based on the total mass of the electrolyte. The present invention does not limit the type of lithium salt; a single lithium salt or a mixture of lithium salts may be used. Further, in some embodiments, the lithium salt is selected, for example, from lithium hexafluorophosphate and lithium bis(trifluoromethyl)sulfonylimide, and the mass ratio of lithium hexafluorophosphate to lithium bis(trifluoromethyl)sulfonylimide is, for example, 13-14:1-2.

[0066] In some embodiments, the solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents, and the solvent accounts for 70% to 80% of the total mass of the electrolyte. Examples of carbonate solvents include ethylene carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, and polycarbonate; examples of carboxylic acid ester solvents include ethyl formate, ethyl acetate, propyl acetate, ethyl propionate, and propyl propionate; examples of ether solvents include ethylene glycol dimethyl ether and diethanol diethyl ether; and examples of nitrile solvents include acetonitrile, propionitrile, butyronitrile, and valerate. This invention does not limit the type of solvent; a single solvent or a mixture of solvents can be used.

[0067] In some embodiments, the additive further includes a third additive selected from at least one of fluoroethylene carbonate, propylene-1,3-sulfonyl lactone, or tetravinylsilane. Adding the third additive to the electrolyte, acting in conjunction with the first additive at the positive and negative electrode interfaces, can improve the stability of the CEI (Cathode Electrolyte Interphase) / SEI (Solid Electrolyte Interphase) composite component, further improving battery cycle performance and high-temperature performance, thereby enhancing the overall performance and safety of the battery.

[0068] Another embodiment of the present invention provides a secondary battery comprising the electrolyte as described in the above embodiments / examples.

[0069] In some embodiments, the secondary battery may be, for example, a lithium-ion battery, a sodium-ion battery, a potassium-ion battery, etc., but is not limited thereto.

[0070] In some embodiments, the secondary battery is a lithium-ion battery, including the electrolyte as described in the above embodiments / examples, and also including a casing and a bare cell disposed in the casing. The bare cell includes a positive electrode, a separator and a negative electrode.

[0071] In one specific embodiment, the method for preparing the lithium-ion battery includes the following steps: stacking a positive electrode, a separator, and a negative electrode sequentially, ensuring that a separator is present between any positive and negative electrode; obtaining a multi-layered stack by winding; and inserting this stack as a bare cell into a battery casing. Finally, injecting electrolyte into the casing once or in multiple stages, so that the bare cell is completely immersed in the electrolyte. In other words, the electrolyte is injected and fills the entire internal space of the battery, and the positive electrode, separator, and negative electrode are completely immersed in the electrolyte.

[0072] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer coated at least on one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric. The thickness of the positive current collector is, for example, 8 μm to 15 μm. Further, in a specific embodiment, the positive current collector is, for example, an aluminum foil, and the thickness of the aluminum foil is, for example, 13 μm.

[0073] In some embodiments, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent, etc., and the mass ratio of the positive electrode active material, the conductive agent, and the binder can be, for example, (90-98):(1-5):(1-5). The positive electrode active material can be selected from high-energy-density ternary materials, lithium cobalt oxide, or lithium iron phosphate, etc. Further, in some embodiments, the positive electrode active material is, for example, Li. x [Ni y Co z Mn t M (1-y-z-t) O 2-δ, where M is selected from at least one of Cr, Zr, Ca, Mg, Cu, Ti, Al, Mo, W, Zn, etc., 0.9 < x < 1.1, 0.65 ≤ y < 1.0, 0 ≤ z < 0.5, 0 ≤ t < 0.5, 0 ≤ δ ≤ 0.1, to improve the energy density and cycle life of the lithium-ion battery. The binder is, for example, selected from any one or more of Polyvinylidene Fluoride (PVDF), Poly(ethylene oxide) (PEO), Polyamide (PA), Polyacrylonitrile (PAN), Polyacrylate, Polyvinylether, Polymethyl Methacrylate (PMMA), Ethylene-Propylene-Diene Terpolymer (EPDM), Polyhexafluoropropylene, or Polymerized Styrene Butadiene Rubber (SBR), etc. The conductive agent is, for example, selected from any one or more of Super P, acetylene black, carbon nanotubes, or graphene, etc.

[0074] In a specific embodiment, the positive electrode active material is, for example, LiNi 0.9 Mn 0.05 Co 0.05 O2, the binder is, for example, selected from Polyvinylidene Fluoride, and the conductive agent is, for example, selected from Super P. After mixing the positive electrode active material, the conductive agent, and the binder, for example, in a mass ratio of 98:1:1, an organic solvent is added, and the mixture is stirred under a vacuum mixer until the system becomes homogeneous to obtain a positive electrode slurry. Among them, the organic solvent is, for example, selected from N-Methylpyrrolidone (NMP). The positive electrode slurry is uniformly coated on an aluminum foil, then air-dried at room temperature and transferred to an oven for drying, and a positive electrode sheet is obtained through processes such as cold pressing and slitting. In other embodiments, the positive electrode sheet can also be obtained by any other method of forming a positive electrode sheet.

[0075] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated at least on one side surface of the negative electrode current collector. Among them, the negative electrode current collector is, for example, selected from any one of copper foil current collectors, composite copper foil current collectors, carbon current collectors, foam copper current collectors, or stainless steel current collectors, etc., and the thickness of the negative electrode current collector is, for example, 8 μm to 15 μm. In a specific embodiment, the negative electrode current collector is, for example, a copper foil, and the thickness of the copper foil is, for example, 13 μm.

[0076] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder, a thickening agent, etc. The mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent can be, for example, (90 - 96):(1 - 2):(1 - 3):(2 - 5). Among them, the negative electrode active material is a compound capable of intercalating and deintercalating lithium ions, and for example, includes at least one of graphite, silicon oxide material (SiO x , 0 < x < 2), or silicon carbide material. The conductive agent is, for example, selected from any one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, or graphene, etc. The binder is, for example, selected from any one or more of polyvinylidene fluoride, polyethylene oxide, polyamide, polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene, or styrene-butadiene rubber, etc. The thickening agent is, for example, selected as sodium carboxymethyl cellulose (Carboxymethyl Cellulose Sodium, CMC-Na), etc.

[0077] In a specific embodiment, the negative electrode active material is, for example, selected from graphite and silicon oxide material, and the mass ratio of the silicon oxide material to graphite is, for example, 5:95 to 10:90. The conductive agent is, for example, selected from conductive carbon black, the binder is, for example, selected from styrene-butadiene rubber, and the thickening agent is, for example, selected from sodium carboxymethyl cellulose. The negative electrode active material, the conductive agent, the binder, and the thickening agent are mixed, for example, according to a mass ratio of 96:1:1:2, deionized water is added, and they are mixed evenly under the action of a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry is coated on a copper foil, then dried at room temperature and transferred to an oven for drying, and after processes such as cold pressing and slitting, a negative electrode plate is obtained. In other embodiments, the negative electrode plate can also be obtained by choosing any other method of forming a negative electrode plate.

[0078] In some embodiments, the separator is, for example, a polyethylene (PE) membrane, a polypropylene (PP) membrane, a glass fiber membrane, or a composite membrane, etc., and the thickness of the separator is, for example, 9 μm to 15 μm.

[0079] In some embodiments, the separator includes a base film and a coating applied on the base film. Among them, the base film is, for example, a PE membrane, a PP membrane, a glass fiber membrane, or a composite membrane, etc., and the thickness of the separator is, for example, 8 μm to 10 μm; the coating is, for example, a nano-aluminum oxide coating, and the coating thickness is, for example, 2 μm to 4 μm.

[0080] The following specific examples illustrate the present invention in detail. It should also be understood that the following examples are only for specific illustrative purposes and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0081] According to the types and amounts of the first and second additives in the electrolytes of Examples 1-13 and Comparative Examples 1-2 shown in Table 1, and the electrolytes, positive electrode plates, negative electrode plates and separators were prepared according to the following methods, and then lithium-ion batteries were made. Performance tests were conducted, and the test results are shown in Table 1.

[0082] 1. Preparation of electrolyte:

[0083] In an argon-filled glove box with a moisture content of less than 0.1 ppm and an oxygen content of less than 0.1 ppm, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly at a mass ratio of 3:5:2 to obtain a mixed solvent. Then, dried lithium hexafluorophosphate, along with a first additive and / or a second additive, were added to the mixed solvent and mixed thoroughly to obtain an electrolyte. In the obtained electrolyte, based on a total electrolyte mass percentage of 100%, the mass percentage of lithium hexafluorophosphate was 12.5%, and the mass percentage of the mixed solvent was adjusted according to the amounts (i.e., mass percentages) of the first and second additives.

[0084] 2. Preparation of the positive electrode sheet:

[0085] LiNi 0.9 Mn 0.05 Co 0.05 O2, polyvinylidene fluoride, and conductive carbon black were mixed in a mass ratio of 98:1:1, and N-methylpyrrolidone was added. The mixture was stirred under vacuum until the system was homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 13 μm, then air-dried at room temperature and transferred to an oven for drying. After cold pressing and slitting, the positive electrode sheet was obtained.

[0086] 3. Preparation of the negative electrode sheet:

[0087] The negative electrode active material, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber were mixed in a mass ratio of 96:1:1:2. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry. The negative electrode slurry was coated onto a 13 μm thick copper foil, then air-dried at room temperature before being transferred to an oven for drying. After cold pressing and slitting, the negative electrode sheet was obtained. The negative electrode active material was a mixture of SiO and graphite, with a mass ratio of SiO to graphite of 5:95.

[0088] 4. Preparation of the diaphragm:

[0089] An 8μm polyethylene membrane was selected as the base membrane, and a 3μm thick nano-alumina coating was coated on the base membrane to obtain the separator.

[0090] 5. Battery manufacturing:

[0091] The positive electrode, separator, and negative electrode are wound sequentially, with the separator positioned between the positive and negative electrodes to act as a separator, resulting in a cylindrical bare cell. This cell is then placed in a circular casing, dried in a vacuum oven, injected with the electrolyte prepared above, and sealed to allow electrolyte formation, thus obtaining a lithium-ion battery.

[0092] 6. Performance testing methods:

[0093] 6.1 Direct Current Resistance (DCR) at -20℃:

[0094] Adjust the temperature of the constant temperature chamber to -20℃, let it stand for 2 hours, charge at a constant current of 0.33C to 4.25V, then charge at a constant voltage of 4.25V to 0.05C cutoff, let it stand for 30 minutes, then discharge at a constant current of 0.33C to 2.5V; repeat the 0.33C charge-discharge cycle twice, and record the discharge capacity of the last discharge as C0; after standing for 30 minutes, discharge at 0.33C to 50% C0, adjust the battery SOC (State of Charge) to 50%, let it stand for 30 minutes, and record the voltage V1 at the end of the standing period, discharge at a constant current of C0 for 30 seconds, and record the voltage V2 and current I at the end of the standing period. Calculate DCR according to the following formula:

[0095] DCR=(V1-V2) / I

[0096] 6.2 Capacity retention during high-temperature cycling at 45℃:

[0097] Set the ambient temperature to 45℃ and let it stand for 1 hour. Charge the lithium-ion battery at a constant current of 0.5C to 4.4V, then charge it at a constant voltage of 4.4V until the current is less than 0.05C. Let it rest for 10 minutes, then discharge it at a constant current of 1.0C to 2.8V. Let it rest for 10 minutes, and record the discharge capacity of the lithium-ion battery at this point. This is the discharge capacity of the first cycle. Perform multiple cycles under the above conditions and calculate the capacity retention rate after 800 cycles. Calculate the capacity retention rate relative to the cycle using the following formula:

[0098] Capacity retention rate (%) = (Discharge capacity after 800 cycles / Discharge capacity during the first cycle) × 100%.

[0099] Table 1 shows the types and amounts of the first and second additives in the electrolytes of Examples 1-13 and Comparative Examples 1-2, and the battery performance test results.

[0100]

[0101]

[0102] From the data in Table 1, the following conclusions can be drawn:

[0103] Comparing Examples 1 and 13 with Comparative Examples 1 and 2, it can be seen that, compared with Comparative Example 1, Examples 1, 13, and Comparative Example 2 all reduced the DCR growth of lithium-ion batteries under low-temperature conditions and improved the capacity retention rate after high-temperature cycling. However, Example 1 showed the best effect, followed by Example 13, and Comparative Example 2 showed the worst effect. This indicates that adding a first additive to the electrolyte, or simultaneously adding the first additive and the second additive, can effectively reduce the DCR growth of lithium-ion batteries under low-temperature conditions and improve the capacity retention rate after high-temperature cycling. Furthermore, the combined use of the first additive and the second additive can better improve the low-temperature performance and high-temperature cycle life of lithium-ion batteries, thereby improving the overall performance and safety of the battery.

[0104] The first additives in Examples 1-4 were compounds 1-4, respectively. Compared with Comparative Example 1, they all significantly reduced the DCR growth of lithium-ion batteries under low-temperature conditions and improved the capacity retention rate after high-temperature cycling. Although there were some differences, they were very small. This indicates that selecting the amide-based organic compound shown in formula (I) as the first additive can effectively improve the low-temperature performance and high-temperature cycle life of lithium-ion batteries, thereby improving the overall performance and safety of the battery.

[0105] Comparing Examples 1, 6-10 with Comparative Example 2, it can be seen that the mass percentage of the first additive in Examples 9 and 10 is less than 0.05% and more than 3%, respectively. Although these examples improve the low-temperature performance and high-temperature cycle life of the battery compared to Comparative Example 2, they cannot compare with Examples 1, 6-8. This indicates that controlling the amount of the first additive within the range of 0.05% to 3% is necessary to better improve the low-temperature performance and high-temperature cycle life of lithium-ion batteries, thereby resulting in better overall battery performance and higher safety.

[0106] A comparison of Examples 1, 5, and 11-13 shows that the mass percentages of the second additive in Examples 11 and 12 are less than 0.5% and more than 1%, respectively. While these additives improve the high-temperature cycle life and low-temperature performance of the battery compared to Example 13, they cannot match the performance of Examples 1 and 5. This indicates that controlling the amount of the second additive within the range of 0.5% to 1% is necessary to better improve the low-temperature performance and high-temperature cycle life of lithium-ion batteries, thereby resulting in better overall battery performance and higher safety.

[0107] In Examples 1-13, the addition of the first additive, the combined use of the first and second additives, and the control of their dosages have been explained in more detail above, and will not be repeated here.

[0108] The electrolytes in Examples 1-13 were all mixed with the high-nickel cathode material LiNi. 0.9 Mn 0.05 Co 0.05 The use of O2 can solve the gas generation problem in the application of high-nickel cathode materials, thereby improving the prospects for large-scale commercialization of high-nickel cathode materials. The specific mechanism has been explained above and will not be repeated here.

[0109] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An electrolyte, characterized in that, It includes electrolytes, solvents, and additives, wherein the additives include at least a first additive; The first additive is an amide organic compound with the general chemical formula shown in formula (I): In formula (Ⅰ), R1 is selected from hydrogen atoms, or any one of the following substituents having 1 to 6 carbon atoms, an unsaturation degree of 0 to 4, and a heteroatom number of 0 to 3; R2 and R3 are selected from any one of the substituents having 1 to 6 carbon atoms, an unsaturation degree of 0 to 4, and a heteroatom number of 0 to 3; The heteroatom is selected from at least one of oxygen, nitrogen, sulfur, or phosphorus.

2. The electrolyte according to claim 1, characterized in that: The additive also includes a first additive, and the second additive is lithium difluorodioxazophosphate.

3. The electrolyte according to claim 1, characterized in that: In formula (Ⅰ), R1, R2 and R3 are selected from any one of the following substituents: alkyl, alkenyl, alkynyl, carbonyl, ester, alkoxy, amino, amino, phosphoroxane, furan, thiophene, pyrrole, thiazole, imidazole, pyridine, pyrazine, pyrimidine or pyridazine.

4. The electrolyte according to claim 1, characterized in that: The first additive is selected from at least one of compound 1, compound 2, compound 3, compound 4, compound 5, or compound 6. The chemical structural formula of compound 1 is as follows: The chemical structural formula of compound 2 is as follows: The chemical structural formula of compound 3 is as follows: The chemical structural formula of compound 4 is as follows: The chemical structural formula of compound 5 is as follows: The chemical structural formula of compound 6 is as follows:

5. The electrolyte according to claim 1, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the first additive is 0.05% to 3%.

6. The electrolyte according to claim 2, characterized in that: Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.05% to 1%.

7. The electrolyte according to claim 1, characterized in that: The electrolyte is a lithium salt, which is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonylimide, lithium acetate, lithium methanesulfonate, or lithium trifluoromethylsulfonate. And / or, based on the total mass of the electrolyte, the mass percentage of the electrolyte is 12% to 16%.

8. The electrolyte according to claim 1, characterized in that: The solvent is selected from at least one of carbonate solvents, carboxylic acid ester solvents, ether solvents, or nitrile solvents; And / or, based on the total mass of the electrolyte, the solvent accounts for 70% to 80% by mass.

9. The electrolyte according to any one of claims 1 to 8, characterized in that: The additive also includes a third additive selected from at least one of fluoroethylene carbonate, propylene-1,3-sulfonyl lactone, or tetravinylsilane.

10. A secondary battery, characterized in that: Includes the electrolyte as described in any one of claims 1 to 9.

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