Electrolyte for secondary battery, secondary battery, and electronic device

Abstract

The present application provides an electrolyte for a secondary battery, a secondary battery, and an electronic device. The electrolyte comprises a first component and a second component; the first component comprises a compound represented by formula I, and the second component comprises a compound represented by formula II. By applying the electrolyte comprising both the first component and the second component to the secondary battery, the cycle performance of the secondary battery is improved, thereby enabling the electronic device to have elongated service life.

Description

An electrolyte for a secondary battery, a secondary battery, and an electronic device. Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrolyte for a secondary battery, a secondary battery, and an electronic device thereof. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and power storage systems due to their advantages such as high energy density, miniaturization, and lightweight design.

[0003] The development of modern information technology and the expansion of electrochemical device applications have placed increasingly higher demands on the cycle life of lithium-ion batteries. For example, lithium-ion batteries are required to have high energy density while also possessing longer lifespan and better cycle performance. However, increasing the energy density of lithium-ion batteries often accelerates electrolyte decomposition, thereby affecting the battery's lifespan and cycle performance. Therefore, developing a suitable electrolyte has become a pressing technical problem for those skilled in the art.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide an electrolyte for a secondary battery, a secondary battery, and an electronic device to improve the cycle performance of the secondary battery. The specific technical solution is as follows:

[0006] The first aspect of this application provides an electrolyte for a secondary battery, which includes a first component and a second component;

[0007] The first component includes the compound represented by Formula I;

[0008] Wherein, R is selected from unsubstituted or R-substituted. a Substituted C2-C6 alkyl, unsubstituted or R a Substituted C2-C6 alkenyl groups, unsubstituted or R a Substituted C2-C6 ynyl groups, unsubstituted or R-substituted a Replacement C5-C 12 Nitrogen-containing heteroaryl groups, unsubstituted or R-containing a Replacement C6-C 12 Aryl group; substituents R of each group a Each is independently selected from fluorine or fluorine-substituted C1-C6 alkyl groups;

[0009] The second component includes the compound represented by Formula II;

[0010] R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl, unsubstituted or fluorinated C2-C6 alkenyl, unsubstituted or fluorinated C2-C6 alkynyl, and unsubstituted or fluorinated C6-C6 alkyl. 12 Aryl, unsubstituted or fluorinated C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silyl.

[0011] In one embodiment of this application, the first component includes at least one of the following compounds;

[0012] In one embodiment of this application, R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl groups.

[0013] In one embodiment of this application, the second component comprises at least one of the following compounds:

[0014] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage of the first component is A, 0.01% ≤ A ≤ 80%, preferably 0.5% ≤ A ≤ 60%.

[0015] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage of the second component is B, where 5% ≤ B ≤ 70%, preferably 10% ≤ B ≤ 50%.

[0016] In one embodiment of this application, the electrolyte further includes a first additive, which includes at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,3-propanesulfonate lactone, vinylene carbonate, or fluorovinyl carbonate.

[0017] In one embodiment of this application, the mass percentage of the first additive is a, based on the mass of the electrolyte, where 0.1% ≤ a ≤ 10%.

[0018] In one embodiment of this application, the electrolyte further includes a second additive, which includes at least one of butadionitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptacyanide, octadionitrile, nonadionitrile, sebacate, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, or trans-butenedionitrile.

[0019] In one embodiment of this application, the mass percentage of the second additive is b, based on the mass of the electrolyte, where 0.5% ≤ b ≤ 6%.

[0020] In one embodiment of this application, the electrolyte further includes a third additive, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

[0021] In one embodiment of this application, the mass percentage of the third additive is c, based on the mass of the electrolyte, where 0.01% ≤ c ≤ 3%.

[0022] A second aspect of this application provides a secondary battery comprising the electrolyte described in the first aspect of this application.

[0023] A third aspect of this application provides an electronic device comprising the secondary battery described in the second aspect of this application.

[0024] The beneficial effects of this application are:

[0025] This application provides an electrolyte for a secondary battery, a secondary battery, and an electronic device. The electrolyte includes a first component and a second component. The second component is a good solvent for dissolving lithium salts, but it lacks sufficient oxidative stability on the positive electrode side. Its ester functional groups easily decompose during charging to generate CO2, damaging the stability of the positive electrode interface and the adhesion of the battery interface. The first component can decompose at the positive electrode interface to generate a sulfide-containing inorganic positive electrode electrolyte interface (CEI), preventing the decomposition of the second component at the positive electrode interface. When the second component and the first component are used in combination, a passivation layer can be formed on the positive electrode surface, preserving the good lithium transport characteristics of the second component while reducing its oxidative decomposition at the positive electrode interface. The combined use of the first and second components results in a higher cycle capacity retention rate for the secondary battery, thereby improving its cycle performance.

[0026] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] The first aspect of this application provides an electrolyte for a secondary battery, which includes a first component and a second component;

[0029] The first component includes the compound represented by Formula I;

[0030] Wherein, R is selected from unsubstituted or R-substituted.a Substituted C2-C6 alkyl, unsubstituted or R a Substituted C2-C6 alkenyl groups, unsubstituted or R a Substituted C2-C6 ynyl groups, unsubstituted or R-substituted a Replacement C5-C 12 Nitrogen-containing heteroaryl groups, unsubstituted or R-containing a Replacement C6-C 12 Aryl group; substituents R of each group a Each is independently selected from fluorine or fluorine-substituted C1-C6 alkyl groups;

[0031] The second component includes the compound represented by Formula II;

[0032] R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl, unsubstituted or fluorinated C2-C6 alkenyl, unsubstituted or fluorinated C2-C6 alkynyl, and unsubstituted or fluorinated C6-C6 alkyl. 12 Aryl, unsubstituted or fluorinated C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silyl.

[0033] This application simultaneously adds a first component and a second component to the electrolyte. The second component is a good solvent for dissolving lithium salts, but its oxidation stability on the positive electrode side is insufficient. Its ester functional groups easily decompose during charging to generate CO2, damaging the stability of the positive electrode interface and the adhesion of the battery interface. The first component, on the other hand, can decompose at the positive electrode interface to generate an inorganic CEI containing sulfides, preventing the decomposition of the second component at the positive electrode interface. When the second and first components are used in combination, a passivation layer can be formed on the positive electrode surface, preserving the good lithium transport characteristics of the second component while reducing its oxidative decomposition at the positive electrode interface. The combined use of the first and second components results in a higher cycle capacity retention rate for the secondary battery, thereby improving its cycle performance.

[0034] In one embodiment of this application, the first component includes at least one of the following compounds;

[0035] Applying an electrolyte containing the first component mentioned above to a secondary battery can improve the cycle capacity retention rate of the secondary battery without affecting other performance characteristics, thereby further improving the cycle performance of the secondary battery.

[0036] In one embodiment of this application, R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl groups.

[0037] In one embodiment of this application, the second component comprises at least one of the following compounds:

[0038] Applying an electrolyte containing the second component within the aforementioned range to a secondary battery can improve the battery's cycle capacity retention rate and further enhance its cycle performance without affecting other properties.

[0039] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage content of the first component is A, preferably 0.01% ≤ A ≤ 80%, more preferably 0.5% ≤ A ≤ 60%, and even more preferably 10% ≤ A ≤ 55%. For example, the mass percentage content A of the first component can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range of any two of these values. Controlling the mass percentage content of the first component within the above range allows for better synergy with the second component, resulting in a higher cycle capacity retention rate for the secondary battery and further improving its cycle performance.

[0040] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage content of the second component is B, preferably 10% ≤ B ≤ 50%, and more preferably 15% ≤ A ≤ 40%. For example, the mass percentage content B of the second component is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or a range of any two of these values. Controlling the mass percentage content of the second component within the above range allows for better synergy with the first component, resulting in a higher cycle capacity retention rate for the secondary battery and further improving its cycle performance.

[0041] In one embodiment of this application, the electrolyte further includes a first additive, which comprises at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,3-propanesulfonate lactone, vinylene carbonate, or fluorovinyl carbonate. The electrolyte including the first additive allows it to form a solid electrolyte interface (SEI) at the negative electrode interface before the first and second components during the initial charging process. This effectively passivates the negative electrode interface and reduces side reactions at the negative electrode interface. Simultaneously, during cycling, it continuously decomposes and repairs the SEI, thereby enabling the secondary battery to have a higher cycle capacity retention rate and further improving the cycle performance of the secondary battery.

[0042] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage content of the first additive is 'a', where 0.1% ≤ a ≤ 10%. For example, the mass percentage content 'a' of the first additive is 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values. Controlling the mass percentage content of the first additive within the above range can better passivate the negative electrode interface, further reduce side reactions at the negative electrode interface, enable the secondary battery to have a higher cycle capacity retention rate, and further improve the cycle performance of the secondary battery.

[0043] In one embodiment of this application, the electrolyte further includes a second additive, which comprises at least one of butadionitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptacyanide, octadionitrile, anonadionitrile, sebaconitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, or trans-butenedionitrile. The inclusion of the second additive in the electrolyte can better passivate the positive electrode interface through adsorption, reduce side reactions at the positive electrode interface, and enable the secondary battery to have a higher cycle capacity retention rate, further improving the cycle performance of the secondary battery.

[0044] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage content of the second additive is b, where 0.5% ≤ b ≤ 6%. For example, the mass percentage content b of the second additive is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, or a range consisting of any two of these values. Controlling the mass percentage content of the second additive within the above range can better passivate the positive electrode interface, further reduce side reactions at the positive electrode interface, enable the secondary battery to have a higher cycle capacity retention rate, and further improve the cycle performance of the secondary battery.

[0045] In one embodiment of this application, the electrolyte further includes a third additive, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethanesulfonyl)imide. The inclusion of the third additive in the electrolyte can better passivate the positive electrode interface, reduce side reactions at the positive electrode interface, and enable the secondary battery to have a higher cycle capacity retention rate, further improving the cycle performance of the secondary battery.

[0046] In one embodiment of this application, based on the mass of the electrolyte, the mass percentage content of the third additive is c, where 0.01% ≤ c ≤ 3%. For example, the mass percentage content b of the third additive is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range consisting of any two of these values. Controlling the mass percentage content of the third additive within the above range can better passivate the positive electrode interface, further reduce side reactions at the positive electrode interface, enable the secondary battery to have a higher cycle capacity retention rate, and further improve the cycle performance of the secondary battery.

[0047] In one embodiment of this application, the electrolyte further includes a lithium salt. This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, or lithium difluoroborate. This application does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%.

[0048] In one embodiment of this application, the electrolyte also contains other non-aqueous solvents. This application does not have any particular limitation on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds or other organic solvents.

[0049] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of γ-butyrolactone, decanolactone, valproic acid, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of non-aqueous solvents is 0% to 86%, preferably 0% to 81%, and more preferably 0% to 67%.

[0050] A second aspect of this application provides a secondary battery comprising the electrolyte described in the first aspect of this application.

[0051] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0052] This application does not impose any particular limitation on the conductive agent, as long as it can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metallic materials, or conductive polymers. Conductive carbon black may include, but is not limited to, at least one of acetylene black or Ketjen black. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole.

[0053] This application does not impose any particular limitation on the adhesive, as long as it can achieve the purpose of this application. For example, the adhesive may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride.

[0054] In this application, the secondary battery further includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0055] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0056] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0057] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may include at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0058] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0059] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0060] In this application, the secondary battery also includes a separator. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. For example, the separator material may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The separator type may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0061] In some embodiments of this application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used.

[0062] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0063] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0064] In some embodiments of this application, thickeners and wetting agents may also be included. This application does not have any particular restrictions on the types of thickeners and wetting agents, as long as they can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; the wetting agent may include, but is not limited to, at least one of dimethylsiloxane, sodium dodecyl sulfate, trialkyl phosphate, methyl decanoate, and dodecyl acetate.

[0065] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 4 μm to 30 μm.

[0066] In this application, the secondary battery further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0067] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0068] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0069] In some embodiments of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0070] In some embodiments of this application, a conductive agent, a binder, and a thickener may also be included. This application does not particularly limit the types of conductive agents and thickeners, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0071] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm.

[0072] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0073] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0074] The secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0075] The fabrication process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the fabrication process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the secondary battery. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0076] A third aspect of this application provides an electronic device comprising the secondary battery described in the second aspect of this application. The secondary battery provided in the second aspect of this application has good cycle performance, thereby giving the electronic device of this application a long service life.

[0077] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries or lithium-ion capacitors, etc.

[0078] Example

[0079] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0080] Test methods and equipment:

[0081] Cyclic performance test:

[0082] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Charge it at a constant current of 0.5C to 4.45V, then charge it at a constant voltage to a current of 0.025C. Let it stand for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V. Record this as the initial discharge capacity C1. Repeat this process for 200 cycles and record the discharge capacity C2 after 200 cycles. Calculate the cycle capacity retention rate of the lithium-ion battery. Cycle capacity retention rate = C2 / C1 × 100%.

[0083] Example 1-1

[0084] <Preparation of Electrolyte>

[0085] In an argon atmosphere glove box with a water content of <10ppm, non-aqueous organic solvent propylene carbonate, first component I-1, and second component II-3 are added and mixed evenly. Then, lithium salt LiPF6 is added, dissolved, and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 is 15%, the mass percentage A of first component I-1 is 0.01%, the mass percentage B of second component II-3 is 70%, and the balance is non-aqueous organic solvent propylene carbonate.

[0086] <Preparation of the positive electrode>

[0087] LiCoO2 (positive electrode active material), polyvinylidene fluoride (PVDF) binder, and conductive carbon black (conductive agent) were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone was added as a solvent to prepare a slurry with a solid content of 70 wt%. After vacuum stirring, a positive electrode slurry was obtained. This slurry was uniformly coated onto one surface of a 14 μm thick aluminum foil used as a positive electrode current collector and dried at 120°C to obtain a single-sided coated positive electrode sheet. The above steps were repeated on the other surface of the aluminum foil to obtain a double-sided coated positive electrode sheet. After vacuum drying at 120°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a 74 mm × 867 mm positive electrode sheet for later use. The compaction density of the positive electrode material layer was 4.15 g / cm³. 3 The thickness of the single-sided positive electrode material layer is 45 μm.

[0088] <Preparation of Negative Electrode Sheets>

[0089] Artificial graphite (negative electrode active material), sodium carboxymethyl cellulose (thickener), and styrene-butadiene rubber (binder) were mixed in a mass ratio of 85:2:13. Deionized water was added as a solvent to prepare a slurry with a solid content of 65 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector and dried at 120°C to obtain a single-sided coated negative electrode sheet. The above steps were repeated on the other surface of the copper foil to obtain a double-sided coated negative electrode sheet. After drying under vacuum at 120°C, the sheet was cold-pressed, cut, and had tabs welded to obtain a negative electrode sheet with a size of 76 mm × 875 mm. The compaction density of the negative electrode material layer was 1.6 g / cm³. 3 The thickness of the single-sided negative electrode material layer is 60μm.

[0090] <Preparation of the separating membrane>

[0091] Inorganic alumina particles, sodium carboxymethyl cellulose thickener, and dimethylsiloxane wetting agent were mixed in a mass ratio of 95:0.5:4.5, and deionized water was added as a solvent to prepare a slurry with a solid content of 5 wt%. After uniform mixing under vacuum, a porous coating slurry with a viscosity of 40 mPa·s was obtained. This porous coating slurry was then uniformly coated onto one surface of a 10 μm thick porous polyethylene substrate and dried at 85 °C to obtain a 2 mg / 1540 mm² coating. 2 A diaphragm with a porous coating on one side is obtained. Then, the above steps are repeated on another surface of the polyethylene porous substrate to obtain a diaphragm with a porous coating on both sides.

[0092] <Preparation of Lithium-ion Batteries>

[0093] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, with the positive and negative tabs extended from the inside to the outside of the bag. Moisture is removed at 80°C, and the prepared electrolyte is injected. The battery undergoes vacuum sealing, settling, formation, degassing, and shaping processes to obtain a lithium-ion battery. The formation upper limit voltage is 4.15V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0094] Examples 1-2 to Examples 1-20

[0095] Except for adjusting the types and mass percentages of the first and second components according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the non-aqueous organic solvent accordingly, and keeping the mass percentage of the lithium salt unchanged, the rest is the same as in Example 1-1.

[0096] Examples 2-1 to 2-9

[0097] Except for the addition of the first additive as shown in Table 2 in the <Preparation of Electrolyte>, and the adjustment of the type and mass percentage of the first additive according to Table 2, the mass percentage of the non-aqueous organic solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 1-8.

[0098] Examples 3-1 to 3-10

[0099] Except for the addition of a second additive as shown in Table 3 in the <Preparation of Electrolyte>, and the adjustment of the type and mass percentage of the second additive according to Table 3, the mass percentage of the non-aqueous organic solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 2-9.

[0100] Examples 4-1 to 4-10

[0101] Except for the addition of a third additive as shown in Table 4 in the <Preparation of Electrolyte>, and the adjustment of the type and mass percentage of the third additive according to Table 4, the mass percentage of the non-aqueous organic solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Examples 3-5.

[0102] Comparative Example 1

[0103] Except that no second component is added in the <Preparation of Electrolyte>, the mass percentage of non-aqueous organic solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0104] Comparative Example 2

[0105] Except that the first component is not added in the <Preparation of Electrolyte>, the mass percentage of non-aqueous organic solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0106] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0107] Table 1

[0108] Note: In Table 1, " / " indicates that there are no relevant parameters.

[0109] As can be seen from Examples 1-1 to 1-20 and Comparative Examples 1 to 2, when electrolytes containing only the first or second component are applied to lithium-ion batteries, the cycle capacity retention rate of the lithium-ion batteries is poor. When both the first and second components are added to the electrolyte, the second component is a good solvent for dissolving lithium salts, but its oxidation stability on the positive electrode side is insufficient. The ester functional groups it contains are prone to decomposition to generate CO2 during charging, which damages the stability of the positive electrode interface and the adhesion of the battery interface. The first component can decompose at the positive electrode interface to generate inorganic CEI containing sulfides, preventing the decomposition of the second component at the positive electrode interface. When used in combination with the first component, a passivation layer can be formed on the positive electrode surface, which not only retains the good lithium transport characteristics of the second component, but also reduces the oxidation decomposition of the second component at the positive electrode interface. The combined use of the first and second components gives the lithium-ion battery a higher cycle capacity retention rate, and thus better cycle performance.

[0110] Table 2

[0111] Note: In Table 2, " / " indicates that there are no relevant parameters.

[0112] As can be seen from Examples 1-8 and Examples 2-1 to 2-9, when an electrolyte with the first additive is applied to a lithium-ion battery, the first additive can form an SEI at the negative electrode interface before the first and second components during the first charge, effectively passivating the negative electrode interface and reducing side reactions at the negative electrode interface. At the same time, during the cycle, it can continuously decompose and repair the SEI, thereby giving the lithium-ion battery a higher cycle capacity retention rate and thus better cycle performance.

[0113] Table 3

[0114] Note: In Table 3, " / " indicates that there are no relevant parameters.

[0115] As can be seen from Examples 2-9 and Examples 3-1 to 3-10, applying an electrolyte with a second additive to a lithium-ion battery can better passivate the positive electrode interface through adsorption, reduce side reactions at the positive electrode interface, and enable the lithium-ion battery to have a higher cycle capacity retention rate, thereby having better cycle performance.

[0116] Table 4

[0117] Note: In Table 4, " / " indicates that there are no relevant parameters.

[0118] As can be seen from Examples 3-5 and Examples 4-1 to 4-10, applying an electrolyte with a third additive to a lithium-ion battery can better passivate the positive electrode interface through adsorption, reduce side reactions at the positive electrode interface, and enable the lithium-ion battery to have a higher cycle capacity retention rate, thereby having better cycle performance.

[0119] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0120] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte for a secondary battery, comprising a first component and a second component; The first component includes the compound represented by Formula I; in, R is selected from unsubstituted or R-selected. a Substituted C2-C6 alkyl, unsubstituted or R a Substituted C2-C6 alkenyl groups, unsubstituted or R a Substituted C2-C6 ynyl groups, unsubstituted or R-substituted a Replacement C5-C 12 Nitrogen-containing heteroaryl groups, unsubstituted or R-containing a Replacement C6-C 12 Aryl group; substituents R of each group a Each is independently selected from fluorine or fluorine-substituted C1-C6 alkyl groups; The second component includes the compound represented by Formula II; R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl, unsubstituted or fluorinated C2-C6 alkenyl, unsubstituted or fluorinated C2-C6 alkynyl, and unsubstituted or fluorinated C6-C6 alkyl. 12 Aryl, unsubstituted or fluorinated C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silyl.

2. The electrolyte according to claim 1, wherein, The first component includes at least one of the following compounds; 3. The electrolyte according to claim 1, wherein, R1 and R2 are each independently selected from unsubstituted or fluorinated C1-C6 alkyl groups.

4. The electrolyte according to claim 1, wherein, The second component includes at least one of the following compounds:

5. The electrolyte according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage of the first component is A, where 0.01% ≤ A ≤ 80%.

6. The electrolyte according to claim 1, wherein, Based on the mass of the electrolyte, the mass percentage of the second component is B, where 5% ≤ B ≤ 70%.

7. The electrolyte according to claim 1, wherein it satisfies at least one of the following characteristics: (1) Based on the mass of the electrolyte, the mass percentage of the first component is A, 0.5% ≤ A ≤ 60%; (2) Based on the mass of the electrolyte, the mass percentage of the second component is B, where 10% ≤ B ≤ 50%.

8. The electrolyte according to any one of claims 1 to 7, wherein, The electrolyte further includes a first additive, which includes at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butanesulfonate lactone, 2,4-butanesulfonate lactone, 1,3-propanesulfonate lactone, vinylene carbonate, or fluorovinyl carbonate.

9. The electrolyte according to claim 8, wherein, Based on the mass of the electrolyte, the mass percentage of the first additive is a, where 0.1% ≤ a ≤ 10%.

10. The electrolyte according to any one of claims 1 to 7, wherein, The electrolyte further includes a second additive, which includes at least one of butadionitrile, glutaronitrile, methylglutaronitrile, adiponitrile, heptaonitrile, octadionitrile, nonadionitrile, sebaconitol, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, ethylene glycol bis(propionitrile) ether, or trans-butenedionitrile.

11. The electrolyte according to claim 10, wherein, Based on the mass of the electrolyte, the mass percentage of the second additive is b, where 0.5% ≤ b ≤ 6%.

12. The electrolyte according to any one of claims 1 to 7, wherein, The electrolyte further includes a third additive, which includes at least one of lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate borate), lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, or lithium bis(trifluoromethylsulfonyl)imide.

13. The electrolyte according to claim 12, wherein, Based on the mass of the electrolyte, the mass percentage of the third additive is c, where 0.01% ≤ c ≤ 3%.

14. A secondary battery comprising the electrolyte according to any one of claims 1 to 13.

15. An electronic device comprising the secondary battery of claim 14.

Images