Electrolyte additive, electrolyte and battery

Abstract

The invention belongs to the technical field of batteries, and provides an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a first additive and a second additive, wherein the first additive comprises a compound as shown in a formula I; the second additive comprises a compound shown in the formula II, A1 and A2 are independently selected from CxH2xOy, x = 0 or 1 and y = 0 or 1 respectively, the electrolyte additive is applied to the battery, and the circulation and storage performance of the battery under the high-temperature and high-pressure conditions can be improved, and # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of batteries, and specifically, to electrolyte additives, electrolytes, and batteries. Background Art

[0002] Currently, improving the energy density of commercial lithium-ion batteries is mainly limited by the performance of the cathode material. Using a cathode material with a higher working voltage or a larger theoretical specific capacity is a key method to effectively increase the energy density of lithium-ion batteries.

[0003] Among them, lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) with a spinel structure has received wide attention due to its high working voltage and low cost. However, while increasing the working voltage to increase the energy density, it will also cause conventional carbonate-based electrolytes to be more prone to oxidation on the electrode surface. In addition, traditional lithium hexafluorophosphate (LiPF6) electrolytes have poor thermal stability. At high temperatures, they will undergo complex autocatalytic decomposition reactions, and the by-product hydrofluoric acid (HF) generated will damage the solid electrolyte interface (SEI) film on the anode surface and the crystal structure of the electrode material. This will cause the impedance of the lithium battery to rise sharply and the capacity to decay rapidly during high-temperature cycling and storage, seriously damaging the cycle life and safety performance of the battery.

[0004] In view of the above problems, there is an urgent need to develop an electrolyte with high temperature and high voltage resistance performance. Summary of the Invention

[0005] The present application aims to solve at least one of the technical problems existing in the prior art to some extent.

[0006] In a first aspect of the present application, an electrolyte additive is proposed. According to an embodiment of the present application, the electrolyte additive includes: a first additive, the first additive includes a compound represented by Formula I; and a second additive, the second additive includes a compound represented by Formula II,

[0007]

[0008] wherein, A1 and A2 are each independently selected from C x H 2x O y , x = 0 or 1, y = 0 or 1.

[0009] In the embodiments of the present application, the first additive enhances the high-temperature and high-pressure performance of the battery by forming an interfacial film of carbonate substances rich in benzene ring groups on the electrode surface. However, the boron-oxygen-containing compound formed by the decomposition of the first additive when attacked by electrons has strong reducibility and is easily consumed and reduced in large amounts on the negative electrode surface to participate in the film-forming process. Therefore, when the amount of the first additive is excessive, the SEI film formed during the first charge and discharge process is likely to be too thick, and the lithium-ion conductivity of the carbonate compound containing benzene ring groups is poor, resulting in an increase in battery impedance and capacity loss. When the amount is too small, an effective CEI film cannot be formed on the positive electrode surface, resulting in poor cycle and storage performance of the battery under high temperature and high pressure. The second additive has a relatively high reduction potential and can preferentially form a sulfur-containing compound with good lithium-ion conductivity on the negative electrode surface during the first cycle of the battery. When the second additive is attacked by electrons, S-O will preferentially break and decompose to generate sulfonyl radicals, and these radicals can form anions through proton transfer to attack EC (ethylene carbonate), and trigger the decomposition of EC, thereby polymerizing to form an SEI film on the negative electrode surface and reducing the consumption of the first additive at the negative electrode, enabling the first additive to participate more in the formation of the CEI film. Thus, the combined use of the two can effectively improve the cycle and storage performance of lithium-ion batteries under high temperature and high pressure conditions.

[0010] According to the embodiments of the present application, the electrolyte additive further includes at least one of the following additional technical features:

[0011] According to the embodiments of the present application, the mass ratio of the first additive to the second additive is (1 - 30):1. Thus, by making the mass ratio of the first additive to the second additive within the above range, they can better play their roles together, enhancing the high-temperature and high-pressure performance of lithium-ion batteries while reducing the impedance of the SEI film, reducing the irreversible capacity loss during the first cycle, and improving the capacity retention rate of the battery. According to the embodiments of the present application, the mass ratio of the first additive to the second additive is (1 - 10):1.

[0012] According to the embodiments of the present application, the second additive includes at least one of the following substances:

[0013]

[0014] Thus, the second additive of the above type can preferentially form a sulfur-containing compound with good lithium conduction performance on the surface of the negative electrode, optimize the components of the interfacial film, thereby effectively reducing the impedance of the SEI film, and can effectively reduce the consumption of the first additive at the negative electrode, and reduce the irreversible capacity loss in the first cycle of the battery and improve the capacity retention rate. Among them, the increase in the number of O atoms in the structure of Compound 2-1 can, on the one hand, effectively slow down the decomposition process of the second additive, making the generated SEI film more complete. On the other hand, it can make it more inclined to generate interfacial film components such as ROSO3Li, ROSO2Li, and Li2SO3, reduce the impedance of the SEI film, reduce the irreversible capacity loss in the first cycle, and improve the capacity retention rate of the battery.

[0015] In the second aspect of the present application, the present application proposes an electrolyte solution. According to an embodiment of the present application, the electrolyte solution includes the electrolyte additive described in the first aspect. Thus, adding this electrolyte solution to a secondary battery can form a stable carbonate-based interfacial film on the electrode surface, enhance the high-temperature and high-pressure performance of the battery, while reducing the impedance of the SEI film, reducing the irreversible capacity loss in the first cycle, and improving the capacity retention rate of the battery.

[0016] According to an embodiment of the present application, the electrolyte solution further includes at least one of the following additional technical features:

[0017] According to an embodiment of the present application, based on the total mass of the electrolyte solution, the mass ratio of the first additive is 1-5%. Thus, within the above mass ratio range, the first additive can form a benzene ring-containing carbonate-based interfacial film on the electrode surface, improving the storage and cycling performance of the battery under high-temperature and high-pressure conditions while reducing the negative impact on the battery capacity.

[0018] According to an embodiment of the present application, based on the total mass of the electrolyte solution, the mass ratio of the second additive is 0.1-2%. Thus, within the above mass ratio range, the second additive can form a sulfur-containing compound with good lithium conduction performance on the surface of the negative electrode, reduce the generation of benzene ring-containing carbonate compounds, optimize the components of the interfacial film, thereby effectively reducing the impedance of the SEI film, and reducing the irreversible capacity loss in the first cycle of the battery and improving the capacity retention rate.

[0019] According to an embodiment of the present application, the electrolyte solution further includes a lithium salt and a solvent. Thus, the transmission of lithium ions inside the battery can be achieved.

[0020] In the third aspect of the present application, the present invention proposes a lithium-ion battery. According to an embodiment of the present application, the battery includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the electrolyte solution described in the second aspect. Thus, the battery has excellent storage and cycling performance under high-temperature and high-pressure conditions.

[0021] According to an embodiment of the present application, the lithium-ion battery further includes at least one of the following additional technical features:

[0022] According to an embodiment of the present application, the positive electrode includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector; the positive electrode material layer includes a positive electrode active material, the positive electrode active material includes lithium nickel manganate, and the chemical formula of the lithium nickel manganate is LiNi x Mn 2-x O4, where 0 < x ≤ 0.5. Thus, the battery has excellent storage and cycling performance under high temperature and high pressure conditions.

[0023] According to an embodiment of the present application, the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector; the negative electrode material layer includes at least one of a silicon-based material and a carbon-based material. Thus, the battery has excellent storage and cycling performance under high temperature and high pressure conditions.

[0024] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Detailed Description of Specific Embodiments

[0025] The embodiments of the present application will be described in detail below, which are intended to explain the present application and should not be construed as a limitation to the present application.

[0026] Referring to "embodiment" herein means that a specific feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0027] For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or an upper limit and combined with any other point or single numerical value or combined with other lower limits or upper limits to form a range not explicitly recited.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs; the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit this application; the terms "comprising" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0029] As used herein, the term "comprising" or "including" is an open-ended expression, that is, it includes the content specified in this application, but does not exclude other aspects of the content.

[0030] It should be noted that the terms "first" and "second" are used only for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Further, in the description of this application, unless otherwise stated, the meaning of "plurality" is two or more.

[0031] Lithium-ion batteries have a series of advantages such as high energy density and long cycle life. Therefore, as high-quality power sources, they are widely used in consumer electronic products such as mobile phones and laptop computers. At the same time, with the booming development of electric vehicles, the demand for lithium-ion batteries as their power batteries has also increased greatly. With the development of technology, lithium-ion batteries with higher energy density are needed to better meet the growing demand for long endurance of the people.

[0032] A key way to improve the energy density of lithium-ion batteries is to increase the battery voltage. Voltages of 4.5 V and higher have become the focus and hotspot of the development of high-energy-density lithium-ion batteries. At present, high-temperature cycling and high-temperature storage of high-voltage lithium-ion batteries face great challenges. In order to further improve the performance of the battery at high voltages, whether a new type of high-efficiency functional electrolyte additive can be developed has become one of the keys.

[0033] In view of this, a first aspect of this application provides an electrolyte additive. According to an embodiment of this application, the electrolyte additive includes: a first additive, the first additive includes a compound represented by Formula I, and a second additive, the second additive includes a compound represented by Formula II,

[0034]

[0035] wherein, A1 and A2 are each independently selected from C x H 2x O y , x = 0 or 1, y = 0 or 1.

[0036] According to an embodiment of the present application, the combined action of the first additive and the second additive improves the cycling and storage performance of lithium-ion batteries under high temperature and high pressure conditions. Specifically, the first additive can effectively form an interfacial film of carbonate substances rich in benzene ring groups on the electrode surface. This type of interfacial film has good chemical stability, which not only enhances the stability at the electrode-electrolyte interface but also improves the compatibility between the electrolyte and the high-voltage cathode material, thereby improving the high temperature and high pressure performance of lithium-ion batteries. However, when the first additive is used alone, the boron-oxygen-containing compounds formed by the decomposition of the first additive under electron attack, due to its strong reducibility, are easily consumed and reduced in large amounts on the negative electrode surface to participate in the film-forming process. Therefore, when there is too much first additive, it is easy to make the solid electrolyte interface (SEI) film formed during the first charge and discharge process too thick, and the lithium-ion conductivity of the carbonate compounds containing benzene ring groups is poor, resulting in an increase in battery impedance and capacity loss. At this time, the second additive plays a key role. Due to its relatively high reduction potential, when the battery is first charged, a sulfur-containing compound with excellent lithium-ion conductivity will be preferentially formed on the negative electrode surface, reducing the generation of carbonate compounds containing benzene rings, optimizing the interfacial film composition, thereby effectively reducing the impedance of the SEI, reducing the irreversible capacity loss in the first cycle of the battery, improving the capacity retention rate of the battery, and reducing the consumption of the first additive at the negative electrode, enabling the first additive to participate more in the formation of the CEI film.

[0037] In some embodiments of the present application, the mass ratio of the first additive to the second additive is (1 - 30):1. For example, it can be 1:1, 2:1, 3:1, 4:1, 5:1, 10:1, 20:1, 30:1, etc., or it can be a range composed of any of the above values. Thus, by making the mass ratio of the first additive to the second additive within the above range, they can better play a combined role, enhance the high temperature and high pressure performance of lithium-ion batteries while reducing the generation of carbonate compounds containing benzene rings, optimizing the interfacial film composition, reducing the impedance of the SEI film, reducing the irreversible capacity loss in the first cycle, and improving the capacity retention rate of the battery. According to an embodiment of the present application, the mass ratio of the first additive to the second additive is (1 - 10):1.

[0038] In some embodiments of the present application, the second additive includes at least one of the following substances:

[0039]

[0040] Thus, the second additive of the above type can preferentially form a sulfur-containing compound with good lithium conduction performance on the surface of the negative electrode, optimize the components of the interfacial film, thereby effectively reducing the impedance of the SEI film, and can effectively reduce the consumption of the first additive at the negative electrode, and reduce the irreversible capacity loss in the first cycle of the battery and improve the capacity retention rate. Among them, the increase in the number of O atoms in the structure of Compound 2-1 can, on the one hand, effectively slow down the decomposition process of the second additive, making the generated SEI film more complete. On the other hand, it can make it more inclined to generate interfacial film components such as ROSO3Li, ROSO2Li, and Li2SO3, reduce the SEI film impedance, reduce the irreversible capacity loss in the first cycle, and improve the capacity retention rate of the battery.

[0041] In the second aspect of the present application, the present application proposes an electrolyte. According to an embodiment of the present application, the electrolyte includes the electrolyte additive described in the first aspect. Thus, adding this electrolyte to a secondary battery can form a sulfur-containing compound with good lithium conduction performance on the surface of the negative electrode, regulate the generation of benzene ring-containing carbonate compounds at the negative electrode, thereby forming a stable carbonate interfacial film on the electrode surface, enhancing the high-temperature and high-pressure performance of the battery, while reducing the SEI film impedance, reducing the irreversible capacity loss in the first cycle, and improving the capacity retention rate of the battery.

[0042] In some embodiments of the present application, based on the total mass of the electrolyte, the mass ratio of the first additive is 1-5%. For example, it can be 1%, 2%, 3%, 4%, 5%, etc., or it can be a range composed of any of the above values. Thus, within the above mass ratio range of the first additive, it can form a carbonate interfacial film on the electrode surface, while improving the storage and cycling performance of the battery under high-temperature and high-pressure conditions, avoiding the formation of an overly thick SEI film and an excessive increase in impedance during the first charge and discharge process, and reducing the negative impact on the battery capacity.

[0043] In some embodiments of the present application, based on the total mass of the electrolyte, the mass ratio of the second additive is 0.1-2%. For example, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, etc., or it can be a range composed of any of the above values. Thus, within the above mass ratio range of the second additive, it can form a sulfur-containing compound with good lithium conduction performance on the surface of the negative electrode, reduce the generation of benzene ring-containing carbonate compounds, optimize the components of the interfacial film, thereby effectively reducing the impedance of the SEI film, and reducing the irreversible capacity loss in the first cycle of the battery and improving the capacity retention rate.

[0044] In some embodiments of the present application, the electrolyte further includes a lithium salt and a solvent. Thus, the transmission of lithium ions inside the battery can be realized.

[0045] In some embodiments of the present application, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluoro(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and lithium bis(trifluoromethanesulfonyl)imide.

[0046] In some embodiments of the present application, the solvent includes, but is not limited to, at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone, phenyl acetate, 1,4-butanesultone, 3,3,3-trifluoropropylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, ethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, methyltrifluoroethyl carbonate, (2,2,2)-trifluoroethyl carbonate, 2,2-difluoroethyl acetate, 2,2-difluoroethyl propionate, and methyl 2,2-difluoroethyl carbonate.

[0047] In a third aspect of the present application, the present invention provides a lithium-ion battery. According to an embodiment of the present application, the battery includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte solution as described in the second aspect. Thus, the battery has excellent storage and cycling performance under high temperature and high pressure conditions.

[0048] [Positive Electrode]

[0049] In some embodiments of the present application, the positive electrode includes a positive electrode current collector, and the positive electrode current collector can be a metal foil, a foam metal, or a composite current collector. For example, as the metal foil, aluminum or stainless steel with a silver surface treatment, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, or titanium can be used. The composite current collector may include a polymer material substrate layer and a metal layer. The foam metal can be foam nickel, foam copper, foam aluminum, foam alloy, etc. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0050] In some embodiments of the present application, the positive electrode further includes a positive electrode material layer disposed on at least one surface of the positive electrode current collector, the positive electrode material layer includes a positive electrode active material, and the positive electrode active material includes lithium nickel manganate; the molecular formula of the lithium nickel manganate is LiNi x Mn 2-x O4, where 0 < x ≤ 0.5.

[0051] In some embodiments of the present application, the positive electrode material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0052] In some embodiments of the present application, the positive electrode material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0053] In some embodiments of the present application, the positive electrode can be prepared in the following manner: dispersing the components for preparing the positive electrode, such as the positive electrode active material, conductive agent, and binder, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode can be obtained.

[0054] [Negative electrode]

[0055] In some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.

[0056] In some embodiments of the present application, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0057] In some embodiments of the present application, the negative electrode active material can be a negative electrode active material known in the art for batteries. As an example, the negative electrode active material may include at least one of a silicon-based material and a carbon-based material. Specifically, it may be selected from at least one of the following materials: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, elemental silicon, silicon oxides, silicon-carbon composites, silicon alloys, tin-carbon composites.

[0058] In some embodiments of the present application, the negative electrode material layer may further optionally include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0059] In some embodiments of the present application, the negative electrode material layer may further optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0060] In some embodiments of the present application, the negative electrode material layer may further optionally include other additives, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), etc.

[0061] In some embodiments of the present application, the negative electrode can be prepared by the following method: dispersing the above-mentioned components for preparing the negative electrode, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode can be obtained.

[0062] The present application does not particularly limit the type of the separator, and any well-known porous separator with good chemical stability and mechanical stability can be selected.

[0063] In some embodiments of the present application, the material of the separator may include at least one of glass fiber, non-woven fabric, polyolefin film, aromatic polyamide film, polytetrafluoroethylene film, and polyethersulfone film.

[0064] The embodiments of the present application will be described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the art or according to the product specifications. For the reagents or instruments whose manufacturers are not indicated, they are all conventional products that can be obtained through commercial purchase.

[0065] Example 1

[0066] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then lithium hexafluorophosphate LiPF6 is added in small portions multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, the second additive is Compound 2-1, and the mass percentages of the first additive are 1%, 2%, 3%, 4%, and 5% respectively, and the mass percentage content of the second additive is 1%;

[0067]

[0068] The above components are mixed to obtain the electrolyte.

[0069] Example 2

[0070] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small portions multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, the second additive is Compound 2-1, and the mass percentages of the second additive are 0.1%, 0.5%, 1.5%, 2%, and the mass percentage content of the first additive is 3%.

[0071] The above components are mixed to obtain the electrolyte.

[0072] Example 3

[0073] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small portions multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, the second additive is Compound 2-2, and the mass percentage of the first additive is 3% respectively, and the mass percentage content of the second additive is 1%;

[0074]

[0075] The above components are mixed to obtain the electrolyte.

[0076] Example 4

[0077] This example provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is Compound 2-3. The mass ratio of the first additive is 3%, and the mass ratio of the second additive is 1%;

[0078]

[0079] The above components are mixed to obtain the electrolyte.

[0080] Example 5

[0081] This example provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is Compound 2-1. The mass ratio of the first additive is 1%, and the mass ratio of the second additive is 0.1%.

[0082] The above components are mixed to obtain the electrolyte.

[0083] Example 6

[0084] This example provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (moisture < 1 ppm, oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is Compound 2-1. The mass ratio of the first additive is 5%, and the mass ratio of the second additive is 2%.

[0085] The above components are mixed to obtain the electrolyte.

[0086] Example 7

[0087] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (with moisture < 1 ppm and oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is compound 2-1. The mass ratio of the first additive is 0.1%, and the mass ratio of the second additive is 0.1% and 1%.

[0088] Mix the above components to obtain the electrolyte.

[0089] Example 8

[0090] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (with moisture < 1 ppm and oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is compound 2-1. The mass ratio of the first additive is 6%, and the mass ratio of the second additive is 0.1% and 1%.

[0091] Mix the above components to obtain the electrolyte.

[0092] Example 9

[0093] This embodiment provides an electrolyte. Calculated by mass percentage, the composition of the electrolyte is as follows: In a glove box filled with high-purity argon (with moisture < 1 ppm and oxygen content < 1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:7, and then LiPF6 is added in small amounts and multiple times to make its concentration in the electrolyte 1 M. After LiPF6 is completely dissolved, a first additive and a second additive are added; the first additive is the compound shown in Formula I, and the second additive is compound 2-1. The mass ratio of the first additive is 3%, and the mass ratio of the second additive is 4% and 0.01%.

[0094] Mix the above components to obtain the electrolyte.

[0095] Example 10

[0096] This embodiment provides a lithium-ion battery, and the specific preparation method is as follows:

[0097] 1. Preparation of electrolyte: Use the electrolyte provided in the above embodiments.

[0098] 2. Preparation of the positive electrode sheet: Mix the LiNi 0.5 Mn 1.5 O4 positive electrode material (LNMO), conductive agent Super P (conductive carbon black), conductive agent CNT (carbon nanotube), and binder PVDF (polyvinylidene fluoride) evenly according to the mass ratio of 94:2.5:1.5:2, stir in vacuum until the fluidity is uniform, and then evenly coat the slurry on the aluminum foil current collector. After drying at 85 °C, rolling, trimming, slicing, slitting, and vacuum drying at 85 °C for 12 h in sequence, and welding the tab, a positive electrode sheet with a surface density of 30 mg / cm 2 is obtained.

[0099] 3. Preparation of the negative electrode sheet: Mix the graphite negative electrode material, conductive agent Super P (conductive carbon black), thickening agent CMC (sodium carboxymethyl cellulose), and binder SBR (styrene-butadiene rubber latex) evenly according to the mass ratio of 94.5:2:1.5:2 to form a uniform slurry. After coating on both sides of the copper foil and drying at 85 °C, then rolling, trimming, slicing, slitting, and finally drying at 85 °C under vacuum conditions for 12 h, and welding the tab to obtain a negative electrode sheet with a surface density of 11.7 mg / cm 2 is obtained.

[0100] 4. Preparation of the separator: Use a 9-μm-thick polyethylene porous polymer film as the substrate, and coat a 2-μm-thick adhesive coating on both sides of the substrate.

[0101] 5. Assembly of the lithium-ion battery:

[0102] Stack the above positive electrode sheet, separator, and negative electrode sheet in sequence, and then fabricate a bare battery cell with a theoretical capacity of 1600 mAh through the winding process. Place the bare battery cell in the outer packaging aluminum foil, vacuum bake it at 85 °C for 48 h, and then inject the above electrolyte. After vacuum packaging, standing, formation, aging, grading, and other processes, the production of the lithium-ion battery is completed.

[0103] Among them, the battery samples prepared with the electrolyte provided in Example 1 are named 1#, 2#, 3#, 4#, and 5# in sequence.

[0104] The battery samples prepared with the electrolyte provided in Example 2 are named 6#, 7#, 8#, and 9# in sequence.

[0105] The battery sample prepared with the electrolyte provided in Example 3 is named 10#.

[0106] The battery sample prepared with the electrolyte provided in Example 4 is named 11#.

[0107] The battery sample prepared with the electrolyte provided in Example 5 is named 12#.

[0108] The battery sample prepared with the electrolyte provided in Example 6 is named 13#.

[0109] The battery samples prepared with the electrolyte provided in Example 7 are named 14# and 15# in sequence.

[0110] The battery samples prepared with the electrolyte provided in Example 8 are named 16# and 17# in sequence.

[0111] The battery samples prepared with the electrolyte provided in Example 9 are named 18# and 19# in sequence.

[0112] Comparative Example 1

[0113] Battery 20# was prepared according to the method described in Example 1, except that the electrolyte additive used was 3% of the first additive.

[0114] Comparative Example 2

[0115] Battery 21# was prepared according to the method described in Example 1, except that the electrolyte additive used was 1% of the second additive (Formula 2-1).

[0116] Comparative Example 3

[0117] Battery 22# was prepared according to the method described in Example 1, except that the electrolyte additive used was 3% of PS (1,3-propane sultone).

[0118] The differences in the electrolyte additives in Batteries 1# - 22# are shown in Table 1.

[0119] Table 1

[0120]

[0121] Performance Test

[0122] I. Test Method.

[0123] 1. 45°C 0.5C / 0.5C Cycle Test

[0124] At 45°C, the battery was charged at a constant current of 0.5C to 4.85V, then charged at a constant voltage until the cut-off current of 0.05C, and then discharged at a constant current of 0.5C. The discharge capacity was denoted as C1. The charge-discharge steps were repeated for 250 cycles, and the discharge capacity was denoted as C 250 . The capacity retention rate of the battery after 250 cycles = C 250 / C1 * 100%.

[0125] 2. 45°C Storage for 15 Days Test

[0126] Charge the battery at a constant current of 0.5C to 4.85V at 25°C, then charge it at a constant voltage of 4.85V until the cut-off current is 0.05C, and then discharge the battery at a constant current of 0.5C. The discharge capacity is denoted as C2. Then charge the battery at a constant current of 0.5C to 4.85V again, and charge it at a constant voltage of 4.85V until the cut-off current is 0.05C. After reaching the fully charged state, transfer the battery to an environment of 45°C and let it stand for 15 days. After the storage is completed, take out the battery. After it cools down to room temperature, discharge the battery at a constant current of 0.5C. The discharge capacity is denoted as C3. Perform 3 cycles of constant current charge and discharge at 0.5C, and record the discharge capacity of the last cycle as C4. The capacity retention rate after storage at 45°C for 15 days = C3 / C2 * 100%. The capacity recovery rate = C4 / C2 * 100%.

[0127] II. Test results.

[0128] The performance test results are shown in Table 2.

[0129] Table 2

[0130]

[0131] It can be seen from the above results that when compared with batteries 20# and 21# (Comparative Examples 1 and 2), for batteries 1# - 13# (Examples 1 - 6), when the compounds shown in Formula I and Formula II are used alone as additives, they can effectively improve the high-temperature cycle and high-temperature storage performance of the battery to a certain extent under high-voltage conditions. However, in contrast, the high-temperature cycle and storage performance of the battery with the compounds shown in Formula I and Formula II added simultaneously are significantly better than those of the comparative examples, indicating that the substance with the structure of Formula II compound can synergistically interact with the Formula I compound to form a stable and high-voltage-resistant interfacial film on the electrode surface, inhibiting the side reactions of the electrolyte under high-temperature and high-voltage conditions, and ultimately achieving the purpose of improving the cycle and storage performance of the battery under high-temperature and high-voltage conditions. Among them, at the same addition amount, the compound 2-1 and the compound shown in Formula I have the best performance when used in combination. In addition, by comparing the test results of batteries 14# - 19#, it can be clearly seen that the addition amount of the compound shown in Formula I or Formula II in the electrolyte and the mass ratio of the compounds shown in Formula I and Formula II have a significant impact on the cycle and storage performance of the battery in a high-temperature and high-voltage environment. When the addition amount of these compounds is insufficient or excessive, or when the mass ratio of the two compounds is too small or too large, the performance of the battery will be adversely affected. Only by precisely controlling the addition amount of the compounds shown in Formula I and Formula II and the mass ratio of the two compounds in the electrolyte can the cycle performance and storage performance of the battery under high-temperature and high-voltage conditions be effectively improved.

[0132] Compared with the battery 22# (Comparative Example 3), the battery 1#-13# (Examples 1-6) has certain improvements in high-temperature cycling and high-temperature storage performance under high-voltage conditions. This is because the increase in the number of O atoms in the structure of Compound 2-1 can, on the one hand, effectively slow down the decomposition process of the second additive, making the generated SEI film more complete. On the other hand, it can make it more inclined to generate interfacial film components such as ROSO3Li, ROSO2Li, and Li2SO3, reduce the impedance of the SEI film, reduce the irreversible capacity loss in the first cycle, and improve the capacity retention rate of the battery.

[0133] In the description of this specification, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0134] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. An electrolyte additive, characterized in that, Comprising: A first additive, the first additive comprising a compound represented by Formula I, and A second additive, the second additive comprising a compound represented by Formula II, Among them, A1 and A2 are each independently selected from C x H 2x O y , x = 0 or 1, y = 0 or 1.

2. The electrolyte additive according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is (1 - 30):1, preferably, the mass ratio of the first additive to the second additive is (1 - 10):

1.

3. The electrolyte additive according to claim 2, wherein, The second additive comprises at least one of the following substances:

4. An electrolyte, characterized in that, Comprising the electrolyte additive according to any one of claims 1 to 3.

5. The electrolyte according to claim 4, characterized in that, Based on the total mass of the electrolyte, the mass proportion of the first additive is 1 - 5%.

6. The electrolyte according to claim 4, wherein Based on the total mass of the electrolyte, the mass proportion of the second additive is 0.1 - 2%.

7. The electrolyte according to any one of claims 4-6, characterized in that, The electrolyte further comprises a lithium salt and a solvent.

8. A lithium-ion battery, characterized in that, Comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and the electrolyte according to any one of claims 4 - 7.

9. The lithium-ion battery according to claim 8, characterized in that, The positive electrode comprises a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector; The positive electrode material layer includes a positive electrode active material, the positive electrode active material includes lithium nickel manganate, and the chemical formula of the lithium nickel manganate is LiNi x Mn 2-x O4, where 0 < x ≤ 0.

5.

10. The lithium ion battery according to claim 8 or 9, characterized in that, The negative electrode comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector; The negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises at least one of a silicon-based material and a carbon-based material.

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