Electrolyte of secondary battery, secondary battery and electronic device

Abstract

The invention provides an electrolyte of a secondary battery, the secondary battery and an electronic device. Wherein the electrolyte comprises a first component and a second component; the first component comprises a compound as shown in a formula I, and the second component comprises at least one of a compound as shown in a formula II or a compound as shown in a formula III. The electrolyte containing the first component and the second component at the same time is applied to the secondary battery, so that the cycle performance of the secondary battery is improved, and the electronic device has a relatively long service life. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to an electrolyte of a secondary battery, a secondary battery, and an electronic device. Background Art

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

[0003] The development of modern information technology and the expansion of electrochemical device applications have placed increasing demands on the cycle life of lithium-ion batteries. For example, lithium-ion batteries are required to have high energy density, a longer lifespan, and improved cycle performance. However, increasing the energy density of lithium-ion batteries often accelerates the decomposition of the electrolyte, thereby affecting the service life and cycle performance of lithium-ion batteries. Therefore, developing a suitable electrolyte has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] 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:

[0005] A first aspect of the present application provides an electrolyte for a secondary battery, comprising a first component and a second component;

[0006] The first component includes a compound represented by formula I;

[0007]

[0008] wherein R is selected from unsubstituted or replaced by R a Substituted C2-C6 alkyl, unsubstituted or replaced by R a Substituted C2-C6 alkenyl, unsubstituted or R a Substituted C2-C6 alkynyl, unsubstituted or R a Substituted C5-C 12 Nitrogen-containing heteroaryl, unsubstituted or replaced by R a Substituted C6-C 12 Aryl; substituent R of each group a Each is independently selected from fluorine or C1-C6 alkyl substituted by fluorine;

[0009] The second component comprises at least one of the compound represented by formula II or the compound represented by formula III;

[0010]

[0011] R1 and R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 Aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon;

[0012] R3 and R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon.

[0013] In one embodiment of the present application, the first component includes at least one of the following compounds;

[0014]

[0015] In one embodiment of the present application, the R1 and the R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl; the R3 and the R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl.

[0016] In one embodiment of the present application, the second component includes at least one of the following compounds:

[0017]

[0018]

[0019] In one embodiment of the present 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%.

[0020] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the second component is B, 5%≤B≤70%, preferably 10%≤B≤50%.

[0021] In one embodiment of the present application, the electrolyte further includes a first additive, which includes at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butane sultone, 2,4-butane sultone, 1,3-propane sultone or vinylene carbonate.

[0022] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the first additive is a, 0.1%≤a≤10%.

[0023] In one embodiment of the present application, the electrolyte further includes a second additive, which includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebacononitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, ethylene glycol bis(propionitrile) ether or butylene glycol cyanide.

[0024] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the second additive is b, and 0.5%≤b≤6%.

[0025] A second aspect of the present application provides a secondary battery comprising the electrolyte described in the first aspect of the present application.

[0026] A third aspect of the present application provides an electronic device, which includes the secondary battery described in the second aspect of the present application.

[0027] Beneficial effects of this application:

[0028] The present 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, wherein the second component is a better solvent for dissolving lithium salts, but has insufficient oxidative stability on the positive electrode side, and the ester functional group contained in it is easily decomposed to generate CO2 during the charging process, destroying the stability of the positive electrode interface and the adhesion of the battery interface, while the first component can decompose at the positive electrode interface to generate an inorganic positive electrode electrolyte interface (CEI) containing sulfide, preventing the decomposition of the second component at the positive electrode interface. When the second component is 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 oxidative decomposition of the second component at the positive electrode interface. The combination of the first component and the second component enables the secondary battery to have a higher cycle capacity retention rate, thereby improving the cycle performance of the secondary battery.

[0029] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0031] A first aspect of the present application provides an electrolyte for a secondary battery, comprising a first component and a second component;

[0032] The first component includes a compound represented by formula I;

[0033]

[0034] wherein R is selected from unsubstituted or replaced by R a Substituted C2-C6 alkyl, unsubstituted or replaced by R a Substituted C2-C6 alkenyl, unsubstituted or R a Substituted C2-C6 alkynyl, unsubstituted or R a Substituted C5-C 12 Nitrogen-containing heteroaryl, unsubstituted or replaced by R a Substituted C6-C 12 Aryl; substituent R of each group a Each is independently selected from fluorine or C1-C6 alkyl substituted by fluorine;

[0035] The second component comprises at least one of the compound represented by formula II or the compound represented by formula III;

[0036]

[0037] R1 and R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 Aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon;

[0038] R3 and R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon.

[0039] The present application adds a first component and a second component to the electrolyte at the same time, wherein the second component is a better solvent for dissolving lithium salts, but has insufficient oxidation stability on the positive electrode side, and the ester functional group contained in it is easily decomposed to generate CO2 during the charging process, destroying the stability of the positive electrode interface and the adhesion of the battery interface, while the first component can decompose at the positive electrode interface to generate an inorganic positive electrode electrolyte interface (CEI) containing sulfide, preventing the decomposition of the second component at the positive electrode interface. When the second component is 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 oxidative decomposition of the second component at the positive electrode interface. The combination of the first component and the second component enables the secondary battery to have a higher cycle capacity retention rate, thereby improving the cycle performance of the secondary battery.

[0040] In one embodiment of the present application, the first component includes at least one of the following compounds;

[0041]

[0042] Applying the electrolyte comprising the first component to a secondary battery can enable the secondary battery to have a higher cycle capacity retention rate without affecting other properties, thereby further improving the cycle performance of the secondary battery.

[0043] In one embodiment of the present application, the R1 and the R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl; the R3 and the R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl.

[0044] In one embodiment of the present application, the second component includes at least one of the following compounds:

[0045]

[0046]

[0047] Applying the electrolyte including the second component within the above range to the secondary battery can enable the secondary battery to have a higher cycle capacity retention rate without affecting other properties, thereby further improving the cycle performance of the secondary battery.

[0048] In one embodiment of the present 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%, and more preferably 10%≤A≤55%. For example, the mass percentage 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 consisting of any two values thereof. By regulating the mass percentage of the first component within the above range, it can better cooperate with the second component, so that the secondary battery has a higher cycle capacity retention rate, and further improve the cycle performance of the secondary battery.

[0049] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the second component is B, 5%≤B≤70%, preferably 10%≤B≤50%, and more preferably 15%≤A≤40%. For example, the mass percentage B of the second component is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70% or a range consisting of any two values thereof. By regulating the mass percentage of the second component within the above range, it can better cooperate with the first component, so that the secondary battery has a higher cycle capacity retention rate, and further improve the cycle performance of the secondary battery.

[0050] In one embodiment of the present application, the electrolyte further includes a first additive, the first additive including at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butane sultone, 2,4-butane sultone, 1,3-propane sultone, or vinylene carbonate. The electrolyte includes the first additive. During the first charge process, the first additive can form a solid electrolyte interface (SEI) at the negative electrode interface before the first component and the second component, effectively passivating the negative electrode interface and reducing side reactions at the negative electrode interface. At the same time, during the cycle process, the first additive can continuously decompose and repair 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.

[0051] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the first additive is a, 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. By controlling the mass percentage content of the first additive within the above range, the negative electrode interface can be better passivated, the side reactions at the negative electrode interface can be further reduced, the secondary battery has a higher cycle capacity retention rate, and the cycle performance of the secondary battery is further improved.

[0052] In one embodiment of the present application, the electrolyte further includes a second additive, wherein the second additive includes at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebacononitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, ethylene glycol bis(propionitrile) ether, or fumaronitrile. The electrolyte includes the second additive, which 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.

[0053] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of the second additive is b, 0.5% ≤ b ≤ 6%, for example, the mass percentage 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. By controlling the mass percentage of the second additive within the above range, the positive electrode interface can be better passivated, the side reaction at the positive electrode interface can be further reduced, the secondary battery has a higher cycle capacity retention rate, and the cycle performance of the secondary battery is further improved.

[0054] In one embodiment of the present application, the electrolyte further includes a lithium salt. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB), or lithium difluoroborate. The present application has no particular restrictions on the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%.

[0055] In one embodiment of the present application, the electrolyte further comprises other non-aqueous solvents. The present application has no particular limitation on the non-aqueous solvents, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include but is not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents.

[0056] The above-mentioned carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorocarbonate compound. The above-mentioned linear carbonate compound may include but is not limited to methyl propyl carbonate (MPC). The above-mentioned cyclic carbonate may include but is not limited to at least one of butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorocarbonate compound may include but is not limited to at least one of 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 or 1,1,2-trifluoro-2-methylethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application has no particular restrictions on the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent is 0% to 86%, preferably 0% to 81%, and more preferably 0% to 67%.

[0057] A second aspect of the present application provides a secondary battery comprising the electrolyte described in the first aspect of the present application.

[0058] It should be noted that in the specific embodiments of this application, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0059] The present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved. 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, metal materials or conductive polymers, and conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0060] The present application has no particular limitation on the binder, as long as the purpose of the present application can be achieved. For example, the binder 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.

[0061] In the present application, the secondary battery also includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the positive electrode current collector surface or a partial area of the positive electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0062] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0063] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0064] The positive electrode material layer may further include a conductive agent and a binder. This application does not particularly limit the types of the conductive agent and binder, as long as the purpose of this application can be achieved. For example, it can be at least one of the above-mentioned conductive agents and binders. This application does not particularly limit 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 can be achieved.

[0065] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0066] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.

[0067] In the present application, the secondary battery also includes a separator. The present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0068] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a film, or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0069] 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 a polymer and an inorganic layer.

[0070] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, 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. The application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0071] In some embodiments of the present application, a thickener and a wetting agent may also be included. The present application has no particular restrictions on the types of thickeners and wetting agents, as long as the purpose of the present application can be achieved. 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 lauryl sulfate, trialkyl phosphate, methyl decanoate, and lauryl acetate.

[0072] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 4 μm to 30 μm.

[0073] In the present application, the secondary battery also includes a negative electrode plate, 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 above-mentioned "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 own thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or it can be a partial area of the surface of the negative electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0074] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0075] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0076] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of the present application. For example, they can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit 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 they can achieve the purpose of the present application.

[0077] In some embodiments of the present application, a conductive agent, a binder, and a thickener may also be included. The present application does not particularly limit the types of the conductive agent and the thickener, as long as the purpose of the present application can be achieved. For example, the conductive agent and the binder can be at least one of the above-mentioned conductive agents and the above-mentioned binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickener in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0078] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm.

[0079] The present application has no particular limitation on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0080] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0081] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0082] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0083] The third aspect of the present application provides an electronic device, which includes the secondary battery described in the second aspect of the present application. The secondary battery provided in the second aspect of the present application has good cycle performance, so that the electronic device of the present application has a long service life.

[0084] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery or a lithium-ion capacitor, etc.

[0085] Example

[0086] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0087] Test methods and equipment:

[0088] Cyclic performance test:

[0089] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it rest for 30 minutes to allow the lithium-ion battery 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 rest for 5 minutes, and discharge it at a constant current of 0.5C to 3.0V. Record this as the initial discharge capacity C1. Repeat this step 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%.

[0090] Example 1-1

[0091] <Preparation of Electrolyte>

[0092] In an argon atmosphere glove box with a water content of less than 10 ppm, a non-aqueous organic solvent propyl propionate, a first component of formula I-1 and a second component of formula II-1 are added and mixed evenly, and then a lithium salt LiPF6 is added, dissolved and mixed evenly to obtain an electrolyte; wherein, based on the mass of the electrolyte, the mass percentage content of the lithium salt LiPF6 is 15%, the mass percentage content A of the first component of formula I-1 is 0.01%, the mass percentage content B of the second component of formula II-1 is 70%, and the remainder is the non-aqueous organic solvent propyl propionate.

[0093] <Preparation of positive electrode sheet>

[0094] The positive electrode active material LiCoO2, the binder polyvinylidene fluoride, and the conductive agent conductive carbon black are mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone is added as a solvent to prepare a slurry with a solid content of 70wt%. After vacuum stirring, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 14μm, and dried at 120°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. Then, the above steps are repeated on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a double-sided positive electrode material layer. After drying at 120°C under vacuum conditions, it is cold pressed, cut into pieces, and welded to the tabs to obtain a positive electrode sheet with a specification of 74mm×867mm for use. Among them, the compaction density of the positive electrode material layer is 4.15g / cm 3 The thickness of the single-sided positive electrode material layer is 45μm.

[0095] <Preparation of negative electrode sheet>

[0096] The negative electrode active material artificial graphite, thickener sodium carboxymethyl cellulose, and binder styrene-butadiene rubber are mixed in a mass ratio of 85:2:13, deionized water is added as a solvent, and a slurry with a solid content of 65wt% is prepared. After stirring evenly with a vacuum mixer, a negative electrode slurry is obtained. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12μm, and dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. Dry under vacuum conditions at 120°C, then cold press, cut into pieces, and weld the tabs to obtain a negative electrode sheet with a specification of 76mm×875mm. Among them, the compaction density of the negative electrode material layer is 1.6g / cm 3 The thickness of the single-sided negative electrode material layer is 60μm.

[0097] <Preparation of Separator>

[0098] The inorganic particles of aluminum oxide, the thickener sodium carboxymethyl cellulose and the wetting agent dimethylsiloxane 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 5wt%. After stirring evenly under the action of a vacuum mixer, a porous coating slurry with a viscosity of 40mPa·s was obtained. The porous coating slurry was evenly coated on one surface of a polyethylene porous substrate with a thickness of 10μm and dried at 85℃ to obtain a 2mg / 1540mm 2 Then repeat the above steps on the other surface of the polyethylene porous substrate to obtain a separator coated with a porous coating on both sides.

[0099] <Preparation of lithium-ion batteries>

[0100] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as an insulator. The electrodes are then wound, with the positive tabs connected to the positive and negative tabs connected to the negative tabs, to form an electrode assembly. The electrode assembly is placed in an aluminum foil bag, and the positive and negative tabs are led out of the interior of the bag to the exterior. The bag is dehydrated at 80°C, and the electrolyte prepared above is injected. The battery is vacuum packaged, allowed to stand, formed, degassed, and shaped to produce a lithium-ion battery. The upper limit of the formation voltage is 4.15V, the formation temperature is 70°C, and the formation standing time is 2 hours.

[0101] Example 1-2 to Example 1-20

[0102] Except that the types and mass percentages of the first component and the second component are adjusted according to Table 1 in <Preparation of Electrolyte>, 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 Example 1-1.

[0103] Example 2-1 to Example 2-9

[0104] In addition to adding the first additive as shown in Table 2 in <Preparation of Electrolyte>, and adjusting 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 Examples 1-7.

[0105] Example 3-1 to Example 3-10

[0106] In addition to adding a second additive as shown in Table 3 in <Preparation of Electrolyte>, and adjusting 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 Example 2-9.

[0107] Comparative Example 1

[0108] Except that the second component is not added in the preparation of the electrolyte, 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 Example 1-1.

[0109] Comparative Example 2

[0110] Except that the first component is not added in the preparation of the electrolyte, 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 Example 1-1.

[0111] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0112] Table 1

[0113]

[0114]

[0115] Note: “ / ” in Table 1 indicates no relevant parameters.

[0116] It can be seen from Examples 1-1 to 1-20 and Comparative Examples 1 to 2 that when the electrolyte to which only the first component or the second component is added is applied to a lithium-ion battery, the cycle capacity retention rate of the lithium-ion battery is poor; when the first component and the second component are added to the electrolyte at the same time, the second component is a better solvent for dissolving lithium salts, but has insufficient oxidative stability on the positive electrode side, and the ester functional group contained in it is easily decomposed to generate CO2 during the charging process, destroying the stability of the positive electrode interface and the adhesion of the battery interface, while the first component can decompose at the positive electrode interface to generate inorganic CEI containing sulfide, 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 properties of the second component, but also reduces the oxidative decomposition of the second component at the positive electrode interface. The combination of the first component and the second component enables the lithium-ion battery to have a higher cycle capacity retention rate and thus better cycle performance.

[0117] Table 2

[0118]

[0119] Note: “ / ” in Table 2 indicates no relevant parameters.

[0120] It can be seen from Examples 1-7 and 2-1 to 2-9 that when the electrolyte to which the first additive is added is applied to a lithium-ion battery, during the first charging process, the first additive can form SEI at the negative electrode interface before the first component and the second component, effectively passivating the negative electrode interface and reducing the side reactions at the negative electrode interface. At the same time, during the cycle process, the SEI can be continuously decomposed and repaired, thereby enabling the lithium-ion battery to have a higher cycle capacity retention rate and thus better cycle performance.

[0121] Table 3

[0122]

[0123] Note: “ / ” in Table 3 indicates no relevant parameters.

[0124] It can be seen from Examples 2-9, 3-1 and 3-10 that applying the electrolyte to which the second additive is added to the lithium-ion battery can better passivate the positive electrode interface through adsorption, reduce the side reactions at the positive electrode interface, and enable the lithium-ion battery to have a higher cycle capacity retention rate and thus have better cycle performance.

[0125] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0126] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte for a secondary battery, comprising a first component and a second component; The first component includes a compound represented by formula I; in, R is selected from unsubstituted or a Substituted C2-C6 alkyl, unsubstituted or replaced by R a Substituted C2-C6 alkenyl, unsubstituted or R a Substituted C2-C6 alkynyl, unsubstituted or R a Substituted C5-C 12 Nitrogen-containing heteroaryl, unsubstituted or replaced by R a Substituted C6-C 12 Aryl; substituent R of each group a Each is independently selected from fluorine or C1-C6 alkyl substituted by fluorine; The second component comprises at least one of the compound represented by formula II or the compound represented by formula III; R1 and R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 Aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon; R3 and R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl, unsubstituted or fluorine-substituted C2-C6 alkenyl, unsubstituted or fluorine-substituted C2-C6 alkynyl, unsubstituted or fluorine-substituted C6-C 12 aryl, unsubstituted or fluorine-substituted C1-C6 alkoxy, halogen, cyano, nitro, sulfonic acid, aldehyde, carboxyl or silicon.

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 The R1 and the R2 are each independently selected from hydrogen, unsubstituted or fluorine-substituted C1-C6 alkyl; the R3 and the R4 are each independently selected from unsubstituted or fluorine-substituted C1-C6 alkyl.

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, 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, 5%≤B≤70%.

7. The electrolyte according to claim 1, which 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, 10%≤B≤50%.

8. The electrolyte according to any one of claims 1 to 7, wherein The electrolyte further includes a first additive including at least one of vinyl sulfate, methyl vinyl sulfate, 1,4-butane sultone, 2,4-butane sultone, 1,3-propane sultone, or vinylene 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, and 0.1%≤a≤10%.

10. The electrolyte according to any one of claims 1 to 7, wherein The electrolyte further includes a second additive, the second additive including at least one of succinonitrile, glutaronitrile, methylglutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile, sebaconitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyano)propane, ethylene glycol bis(propionitrile) ether, or fumaronitrile.

11. The electrolyte according to claim 10, wherein Based on the mass of the electrolyte, the mass percentage of the second additive is b, and 0.5%≤b≤6%. 12 . A secondary battery comprising the electrolyte according to claim 1 . 13 . An electronic device comprising the secondary battery according to claim 12 .

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