Electrolyte and secondary battery

Abstract

The invention provides an electrolyte and a secondary battery. The electrolyte is used for the battery containing the lithium supplement agent and comprises a compound shown in the formula I. R is selected from hydrogen, fluorine, unsubstituted or fluorine substituted C1-C4 alkyl and C1-C4 alkoxy; r1 and R2 are respectively and independently selected from-C <->,-O-or-C-O-; n and m are each independently 0 or 1, and n + m > = 1. The electrolyte provided by the invention can solve the problems of gas expansion and lithium precipitation caused by the addition of the lithium supplement agent, so that the high-temperature cycle performance and the high-temperature storage performance of the secondary battery can be improved. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to an electrolyte and a secondary battery. Background Art

[0002] In recent years, with the rapid development and wide application of various portable electronic devices, new energy electric vehicles, and energy storage systems, the demand for secondary batteries with high energy density, long cycle life, large working temperature range, and good rate performance has become increasingly urgent.

[0003] The loss of lithium is the direct cause of battery cycle attenuation. For example, during the first charge and discharge process of the battery, the electrolyte will form a solid electrolyte interface film (SEI film) on the surface of the negative electrode. The formation of the SEI film will consume a large amount of active lithium ions, resulting in a low Coulomb efficiency in the first cycle of the battery. During the charge and discharge cycle of the battery, the cracking and pulverization of the positive active material particles, the thickening and repair of the SEI film, etc. will all consume active lithium ions, resulting in a significant decline in the cycle performance of the battery. The lithium-ion battery added with a lithium supplementing agent has the advantages of high irreversible capacity, good cycle improvement effect, low production cost, etc. However, the lithium supplementing agent itself has high chemical reactivity, activates and releases active lithium ions to achieve the effect of lithium supplementation, and at the same time, oxygen is generated. The oxygen will affect the embedding of the active lithium ions released by the lithium supplementing agent in the negative electrode, resulting in problems such as black spots and lithium deposition. And the lithium supplementing agent that is not completely reacted during the formation stage will still continuously react and release oxygen in the subsequent process (especially high-temperature storage), further causing gas evolution and expansion of the battery in the later stage of storage, and at the same time causing further lithium deposition on the negative electrode of the battery, resulting in the problem of high-temperature performance attenuation. Therefore, it is urgent to develop an electrolyte that can solve the problems of gas expansion and lithium deposition caused by the lithium supplementing agent, so as to improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery. Summary of the Invention

[0004] The purpose of the present application is to provide an electrolyte and a secondary battery to improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery. The specific technical solutions are as follows:

[0005] In the first aspect of the present application, an electrolyte is provided. The electrolyte is used for a battery containing a lithium supplementing agent, and the electrolyte includes a compound represented by Formula I;

[0006]

[0007] Wherein, R is selected from hydrogen, fluorine, unsubstituted or fluorine-substituted C 1 -C 4 alkyl, C 1 -C 4 alkoxy; R 1 and R 2each independently selected from -C-, -O- or -C-O-; n and m are each independently 0 or 1, and n + m ≥ 1.

[0008] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the compound represented by Formula I is A, 0.1% ≤ A ≤ 3%, preferably, 0.5% ≤ A ≤ 2.5%.

[0009] In one embodiment of the present application, the electrolyte further includes a film-forming additive, and the film-forming additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene carbonate ethyl ester, ethylene sulfate, 1,3-propane sultone, and 1,3-propylene sultone.

[0010] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the film-forming additive is B, 0.1% ≤ B ≤ 5%.

[0011] In one embodiment of the present application, the compound represented by Formula I is selected from at least one of the following compounds;

[0012]

[0013] In one embodiment of the present application, the electrolyte further includes an electrolyte, and the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate; based on the mass of the electrolyte, the mass percentage content of the electrolyte is C, 8% ≤ C ≤ 18%.

[0014] In one embodiment of the present application, the electrolyte further includes a solvent, and the solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, tetrahydrofuran, 1,3-dioxolane, diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; based on the mass of the electrolyte, the mass percentage content of the solvent is D, 74% ≤ D ≤ 91%.

[0015] The second aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte described in the first aspect of the present application.

[0016] In one embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material and a lithium supplementing agent; the lithium supplementing agent is selected from at least one of the lithium supplementing agents capable of releasing active oxygen. Preferably, the lithium supplementing agent capable of releasing active oxygen is selected from at least one of lithium ferrite, lithium nickelate, and lithium oxide.

[0017] In one embodiment of the present application, the positive electrode active material is selected from at least one of nickel-cobalt-manganese ternary materials, lithium iron phosphate manganese, and lithium iron phosphate.

[0018] In one embodiment of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based material and a silicon-based material.

[0019] Advantages of the present application:

[0020] The present application provides an electrolyte and a secondary battery. The electrolyte of the present application is used in a battery containing a lithium supplementing agent, and the electrolyte includes a compound shown in Formula I. The compound shown in Formula I is an aromatic ring-fused cyclic sulfate compound, which has a phenoxy unit and is easily oxidized by the oxygen generated by the lithium supplementing agent to form a quinoid structure, thereby absorbing oxygen. At the same time, the sulfuryl ring is broken, which can provide an inorganic part such as lithium sulfate or lithium sulfite for the SEI film formed by the film-forming additive, improve the hardness of the SEI film, make the SEI film take into account the toughness of the organic matter and the hardness of the inorganic matter, improve the lithium conduction performance, and thus inhibit lithium deposition. The compound shown in Formula I and the film-forming additive act synergistically, which is beneficial to improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0021] Of course, it is not necessary for any product or method implementing the present application to achieve all the above-mentioned advantages simultaneously. Detailed implementation manners

[0022] The technical solutions in the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0023] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium-ion battery.

[0024] The present application provides an electrolyte, the electrolyte is used in a battery containing a lithium supplementing agent, and the electrolyte includes a compound shown in Formula I;

[0025]

[0026] Wherein, R is selected from hydrogen, fluorine, unsubstituted or fluorine-substituted C 1 -C 4 alkyl, C 1 -C 4 alkoxy; R 1 and R 2 are each independently selected from -C-, -O- or -C-O-; n and m are each independently 0 or 1, and n + m ≥ 1.

[0027] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the compound shown in Formula I is A, 0.1% ≤ A ≤ 3%, preferably, 0.5% ≤ A ≤ 2.5%. For example, based on the mass of the electrolyte, the mass percentage content A of the compound shown in Formula I can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or a range composed of any two of these values. When the mass percentage content of the compound shown in Formula I is within the scope of the present application, the high-temperature cycle performance and high-temperature storage performance of the secondary battery can be improved.

[0028] In one embodiment of the present application, the electrolyte further includes a film-forming additive, and the film-forming additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, ethylene sulfite, ethylene sulfate, 1,3-propane sultone, and 1,3-propene sultone.

[0029] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of the film-forming additive is B, 0.1% ≤ B ≤ 5%. For example, based on the mass of the electrolyte, the mass percentage content B of the film-forming additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range composed of any two of these values. When the mass percentage content of the film-forming additive is within the scope of the present application, the high-temperature cycle performance and high-temperature storage performance of the secondary battery can be further improved.

[0030] The inventors found in the research that the compound shown in Formula I has a phenoxy unit and is easily oxidized by oxygen generated by the lithium supplementing agent to form a quinone structure, causing the rupture of the sulfuryl ring. It can provide inorganic components such as lithium sulfate and lithium sulfite for the organic film formed by the film-forming additive, improve the hardness of the SEI film, make the SEI film have both the toughness of the organic matter and the hardness of the inorganic matter, improve the lithium conduction performance, and thus inhibit lithium deposition. The compound shown in Formula I and the film-forming additive act synergistically to solve the problems of gas expansion and lithium deposition caused by the addition of the lithium supplementing agent, and further contribute to improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0031] In one embodiment of the present application, the compound represented by Formula I is selected from at least one of the following compounds;

[0032]

[0033] Among them, the CAS number of Compound I-1 is 4074-55-9, and the CAS number of Compound I-2 is 10284-44-3.

[0034] In one embodiment of the present application, the electrolyte solution further includes an electrolyte, and the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tetrafluoroborate; based on the mass of the electrolyte solution, the mass percentage content of the electrolyte is C, and 8% ≤ C ≤ 18%. For example, based on the mass of the electrolyte solution, the mass percentage content of the electrolyte can be 8%, 10%, 12%, 14%, 16%, 18%, or a range composed of any two of these values. The electrolyte solution includes the above electrolyte and regulates the mass percentage content of the electrolyte within the scope of the present application, which can make the electrolyte solution have high ionic conductivity and good electrochemical stability, and further improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0035] In one embodiment of the present application, the electrolyte solution further includes a solvent, and the solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, tetrahydrofuran, 1,3-dioxolane, diethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; based on the mass of the electrolyte solution, the mass percentage content of the solvent is D, and 74% ≤ D ≤ 91%. For example, based on the mass of the electrolyte solution, the mass percentage content of the solvent can be 74%, 80%, 85%, 88%, 91%, or a range composed of any two of these values. The electrolyte solution includes the above solvent and regulates the mass percentage content of the solvent within the scope of the present application, which can make the electrolyte solution have appropriate viscosity, high ionic conductivity, and good electrochemical stability, and can further improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0036] The present application has no particular limitation on the preparation method of the electrolyte solution, as long as the purpose of the present application can be achieved. For example, various solvents in the electrolyte solution can be mixed and then substances such as electrolytes and additives are added and mixed evenly.

[0037] The second aspect of the present application provides a secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte solution described in the first aspect of the present application.

[0038] In one embodiment of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector. The positive electrode material layer includes a positive electrode active material and a lithium supplementing agent; the lithium supplementing agent is selected from at least one of the lithium supplementing agents capable of releasing active oxygen. Preferably, the lithium supplementing agent capable of releasing active oxygen is selected from at least one of lithium ferrite, lithium nickelate, and lithium oxide. The lithium-ion battery added with the lithium supplementing agent has the advantages of high irreversible capacity (≥670 mAh), good cycle improvement effect (energy density increased by 6% - 8%), and low production cost. However, the lithium supplementing agent itself has high chemical reactivity, activates and releases active lithium ions to achieve the effect of lithium supplementation, and at the same time, oxygen is generated. The oxygen will affect the insertion of the active lithium ions released by the lithium supplementing agent into the negative electrode, resulting in problems such as black spots and lithium deposition; and the lithium supplementing agent that is not completely reacted during the formation stage will still continuously react and release oxygen in the subsequent process (especially high-temperature storage), further causing gas production and expansion of the battery in the later stage of storage, and at the same time causing further lithium deposition on the negative electrode of the battery, resulting in the problem of high-temperature performance decay. Using the electrolyte provided by the present application can absorb oxygen free radicals, reduce the formation of gas caused by oxygen free radicals, and at the same time can provide inorganic parts such as lithium sulfate or lithium sulfite for the SEI film, improve the lithium conduction performance, thereby inhibiting lithium deposition, and is beneficial to improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0039] In one embodiment of the present application, the positive electrode active material is selected from at least one of nickel-cobalt-manganese ternary materials, lithium iron manganese phosphate, and lithium iron phosphate. Selecting the above positive electrode active materials can further improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0040] The above-mentioned "positive electrode material layer provided on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be provided on one surface of the positive electrode current collector along its own thickness direction, or can be provided on both 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 surface of the positive electrode current collector, or can be a partial area of the surface of the positive electrode current collector. The present application has no special limitation, as long as the purpose of the present application can be achieved.

[0041] The present application has no special limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil, aluminum alloy foil, nickel foil, or nickel alloy can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0042] There is no particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector in this application, as long as the object of this application can be achieved. For example, the thickness of the positive electrode current collector is 10 μm to 20 μm.

[0043] In one embodiment of this application, the positive electrode material layer may further include a conductive agent and a binder. There is no particular limitation on the types of the conductive agent and the binder in this application, as long as the object of this application can be achieved. For example, the conductive agent may include, but is not limited to, at least one of Super P, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. There is no particular limitation on the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer, and those skilled in the art can select according to actual needs as long as the object of this application can be achieved.

[0044] Optionally, the positive electrode tab may further include a conductive layer, and the conductive layer is located 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 a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. There is no particular limitation on the conductive agent and the binder in the conductive layer in this application. For example, it may be at least one of the above conductive agents and the above binders.

[0045] There is no particular limitation on the preparation method of the positive electrode tab in this application, as long as the object of this application can be achieved. For example, the positive electrode active material, the lithium supplement agent, the conductive agent, and the binder are mixed in a certain proportion, and N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry with a solid content of 48 wt% to 65 wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode current collector, and after drying, a positive electrode tab with a single-sided coated positive electrode material layer is obtained. Then, the above coating steps are repeated on the other surface of the positive electrode current collector, and after drying, a positive electrode tab with a double-sided coated positive electrode material layer is obtained. After rolling, baking, slitting, and spot welding the tab, the positive electrode tab is obtained.

[0046] In one embodiment of this application, the negative electrode tab includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based material and a silicon-based material.

[0047] The present application has no particular limitation on the silicon-based material and the carbon-based material, as long as the purpose of the present application can be achieved. For example, the silicon-based material can be selected from at least one of, but not limited to, elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; the carbon-based material can include at least one of, but not limited to, artificial graphite, natural graphite, soft carbon, hard carbon, and mesophase microcarbon spheres.

[0048] The above-mentioned "negative electrode material layer provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector along its thickness direction, or can be provided 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 area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. The present application has no particular limitation, as long as the purpose of the present application can be achieved.

[0049] The present application has no particular limitation on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, or copper foam can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0050] The present application has no particular limitation on the thickness of the negative electrode material layer and 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 8 μm to 14 μm.

[0051] In an embodiment 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 the binder, 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 super P, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fiber. The above carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0052] The negative electrode material layer may further include a thickening agent, and the thickening agent may include, but is not limited to, at least one of sodium carboxymethyl cellulose and 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 thickening agent in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0053] Optionally, the negative electrode plate may further include a conductive layer, and the conductive layer is located 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 a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and the binder in the conductive layer. For example, it may be at least one of the above conductive agents and the above binders.

[0054] The present application does not particularly limit the preparation method of the negative electrode plate, as long as the purpose of the present application can be achieved. For example, the negative electrode active material, the conductive agent, the thickening agent, and the binder can be mixed in a certain proportion, deionized water is added and stirred evenly to obtain a negative electrode slurry with a solid content of 40 wt% to 60 wt%. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector, and after drying, a negative electrode plate with a single-sided coated negative electrode material layer is obtained. Then, the above coating step is repeated on the other surface of the negative electrode current collector, and after drying, a negative electrode plate with a double-sided coated negative electrode material layer is obtained. After rolling, baking, slitting, and spot welding the tab, the negative electrode plate is obtained.

[0055] There is no particular limitation on the separator in this application, as long as the object of this application can be achieved. For example, the material of the separator can be selected from, but not limited to, at least one of ceramics, polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of separator can include at least one of woven film, non-woven fabric, microporous film, composite film, rolled film, spun film, and ceramic separator.

[0056] In this application, there is no particular limitation on the thickness of the separator, as long as the object of this application can be achieved. For example, the thickness of the separator can be 10 μm to 20 μm.

[0057] In this application, the lithium-ion battery further includes a housing 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 lithium-ion batteries. This application does not limit the above-mentioned other components. There is no particular limitation on the housing in this application, and it can be a housing well-known in the art, as long as the object of this application can be achieved. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. This application does not limit the type of metal, and a metal hard shell housing known in the art can be used, as long as the object of this application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0058] The preparation process of the lithium-ion battery of this application is well-known to those skilled in the art, and there is no particular limitation in this application. For example, the preparation process of the lithium-ion battery can include, but not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into the housing, injecting the electrolyte into the housing and standing, performing formation and then vacuum sealing, and then performing secondary formation to obtain the lithium-ion battery.

[0059] Compound Preparation

[0060] Preparation of Compound I-1

[0061] Dissolve catechol (CAS: 120 - 80 - 9, 0.15 mol) in pyridine (23.70 g, 24.15 mL), and stir vigorously for 10 minutes in a dry argon atmosphere to obtain a cherry - colored solution. Subsequently, dilute the cherry - colored solution with hexane (150 mL) and cool it to 5 °C, then add dropwise a solution of sulfuryl chloride (20.4 g, 0.15 mol) in hexane (30 mL) over 4 hours, maintaining the temperature between 0 °C and 5 °C to obtain a reaction solution. Stir the reaction solution at 0 °C overnight and then stir at room temperature for another 6 h; collect the upper layer of the two - phase mixture, wash the lower semi - solid layer with ethyl acetate (350 mL) 3 times to obtain an ethyl acetate extract, and combine it with the upper layer. Wash the combined hexane and ethyl acetate extract with 5% aqueous copper(II) acetate until most of the catechol is removed (monitor the composition by TLC; hexane:ethyl acetate = 3:1 v / v). Then dry the solution with magnesium sulfate and filter, and evaporate the solvent by vacuum distillation to obtain a crude product. Purify the crude product: by column chromatography, elute with a hexane:ethyl acetate mixture in a volume ratio of 4:1 to obtain Compound I - 1.

[0062] Preparation of Compound I - 4

[0063] Except that catechol is replaced with 4 - methylcatechol (CAS: 452 - 86 - 8), the rest is the same as the preparation of Compound I - 1.

[0064] Preparation of Compound I - 7

[0065] Except that catechol is replaced with 3 - methoxycatechol (CAS: 934 - 00 - 9), the rest is the same as the preparation of Compound I - 1.

[0066] Preparation of Compound I - 2

[0067] A mixture of o-hydroxybenzyl alcohol (CAS: 90-01-7, 0.1 mol), sodium bisulfate (12.01 g, 0.1 mol) and distilled water (220 mL) was refluxed for 8 hours to obtain sodium (2-hydroxyaryl) methanesulfonate. Most of the water (190 mL) was evaporated to dryness using a rotary evaporator to obtain a milky white solid residue. The milky white solid residue was placed in a Soxhlet apparatus and extracted with ethanol (for 2 days). Then the precipitated white solid was filtered out, washed 3 times with ethanol, and the solid was dried under reduced pressure to obtain 18.28 g of sodium (2-hydroxyaryl) methanesulfonate. A mixture of sodium (2-hydroxyaryl) methanesulfonate (19.03 mmol) and phosphorus oxychloride (32.00 g, 208.70 mmol) was refluxed for 1.5 hours in a dry argon atmosphere, and then the excess phosphorus oxychloride was distilled off. The residue was cooled to 0 °C to 5 °C, and a mixture of crushed ice and water (60 mL) was added very slowly. After stirring for 4 hours, the precipitated white solid was filtered out, washed with cold water, and dried under vacuum. The crude product was purified by recrystallization from ethanol to obtain Compound I-2.

[0068] Preparation of Compound I-9

[0069] 2-Fluoro-6-hydroxybenzoic acid (CAS: 67531-86-6, 0.2 mol) was dissolved in 300 mL of anhydrous tetrahydrofuran solution, and active manganese dioxide (1.2 mol) was added at 0 °C for reduction. After filtration, the filtrate was obtained. It was concentrated under reduced pressure and eluted by column chromatography with a dichloromethane:methanol mixture with a volume ratio of 8:1 to obtain pure 2-fluoro-6-hydroxybenzyl alcohol.

[0070] Except that o-hydroxybenzyl alcohol was replaced with 2-fluoro-6-hydroxybenzyl alcohol, the rest was the same as the preparation of Compound I-2.

[0071] Preparation of Compound I-10

[0072] 4-Fluorosalicylic acid (CAS: 345-29-9, 0.2 mol) was dissolved in 300 mL of anhydrous tetrahydrofuran solution, and active manganese dioxide (1.2 mol) was added at 0 °C for reduction. After filtration, the filtrate was obtained. It was concentrated under reduced pressure and eluted by column chromatography with a dichloromethane:methanol mixture with a volume ratio of 8:1 to obtain pure 4-fluoro-2-hydroxybenzyl alcohol.

[0073] Except that o-hydroxybenzyl alcohol was replaced with 4-fluoro-2-hydroxybenzyl alcohol, the rest was the same as the preparation of Compound I-2.

[0074] Preparation of Compound I-11

[0075] Dissolve 3-fluorosalicylic acid (CAS: 341-27-5, 0.2 mol) in 300 mL of anhydrous tetrahydrofuran solution, add activated manganese dioxide (1.2 mol) at 0 °C for reduction, filter to obtain a filtrate; concentrate under reduced pressure, and elute by column chromatography with a dichloromethane:methanol mixture with a volume ratio of 8:1 to obtain the pure product 3-fluoro-2-hydroxybenzyl alcohol.

[0076] Except that o-hydroxybenzyl alcohol is replaced by 3-fluoro-2-hydroxybenzyl alcohol, the rest is the same as the preparation of compound I-2.

[0077] Preparation of compound I-12

[0078] Dissolve 4-trifluoromethylsalicylic acid (CAS: 328-90-5, 0.2 mol) in 300 mL of anhydrous tetrahydrofuran solution, add activated manganese dioxide (1.2 mol) at 0 °C for reduction, filter to obtain a filtrate; concentrate under reduced pressure, and elute by column chromatography with a dichloromethane:methanol mixture with a volume ratio of 8:1 to obtain the pure product 2-hydroxy-4-trifluoromethylbenzyl alcohol.

[0079] Except that o-hydroxybenzyl alcohol is replaced by 2-hydroxy-4-trifluoromethylbenzyl alcohol, the rest is the same as the preparation of compound I-2.

[0080] Preparation of compound I-3

[0081] Dissolve catechol (0.1 mol) in 300 mL of ethyl acetate solution, cool the reaction solution to 0 °C to 5 °C and maintain, add chloromethanesulfonyl chloride (0.11 mol) and triethylamine (0.2 mol), restore the obtained mixture to room temperature, and stir for 30 minutes. Then, add 200 mL of water to quench, extract with ethyl acetate 3 times, collect the upper organic phase, dry the organic phase over magnesium sulfate and concentrate in vacuo to obtain a crude product.

[0082] Add sodium hydride (60% dispersed in mineral oil) (100 mg, 2.5 mmol) in batches to a solution of the crude product (2.5 mmol) in anhydrous THF (10 mL), and cool to 0 °C to 5 °C. Stir the obtained mixture at 0 °C to 5 °C for 0.5 hour in an argon atmosphere, then stir at room temperature for 1 hour, and finally dilute the contents of the flask with anhydrous acetonitrile (50 mL) and reflux for 3 hours. Subsequently, filter out the precipitated sodium chloride and wash with acetonitrile (25 mL), evaporate the combined filtrate to dryness under reduced pressure to obtain a yellow crude product, and purify by column chromatography using n-hexane-ethyl acetate with a ratio of 4:1 (v / v) as the eluent to obtain the final pure product compound I-3.

[0083] Preparation of compound I-5

[0084] Except that catechol is replaced by 4-methylcatechol (CAS: 452-86-8), the preparation is the same as that of Compound I-3.

[0085] Preparation of Compound I-6 and Compound 1-8

[0086] Except that catechol is replaced by 3-methoxycatechol (CAS: 934-00-9), the preparation is the same as that of I-3, and Compound I-6 and Compound I-8 are obtained simultaneously.

[0087] Examples

[0088] Hereinafter, examples and comparative examples are given to illustrate the embodiments of the present application more specifically. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0089] Test method

[0090] 45°C High Temperature Cycling Performance Test

[0091] Place the lithium-ion battery in an incubator at 45°C and let it stand for 3 hours to reach a constant temperature. Then charge the lithium-ion battery at a constant current of 1C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 2V. Record the initial discharge capacity as C 1 , and take this as one charge-discharge cycle. Repeat the above charge-discharge cycle 500 times, and record the discharge capacity after the 500th cycle as C 2 .

[0092] 45°C Capacity Retention Rate (%) = C 2 / C 1 ×100%; evaluate the high temperature cycling performance of the lithium-ion battery by the 45°C capacity retention rate. The larger the capacity retention rate, the better the high temperature cycling performance of the lithium-ion battery.

[0093] Proportion of the Lithium Deposition Region at the Battery Negative Electrode Interface

[0094] Before the above high temperature cycling performance test, disassemble the battery and record the area of the entire negative electrode interface as S 0 , and the area of the lithium deposition region at the interface as S 1 ; after the high temperature cycling performance test, disassemble the battery and record the area of the entire negative electrode interface as S at this time, and the area of the lithium deposition region at the interface as S 2 .

[0095] Proportion of the Lithium Deposition Region at the Battery Negative Electrode Interface before High Temperature Cycling (%) = S 1 / S 0 ×100%;

[0096] Percentage of lithium deposition area at the negative electrode interface of the battery after high - temperature cycling (%) = S 2 / S×100%.

[0097] 60°C High - temperature storage performance test

[0098] Place the lithium - ion battery in an incubator at 25°C and let it stand for 30 minutes. Then charge the lithium - ion battery at a constant current of 1C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 2V. Record the initial discharge capacity as Q 1 Then charge the lithium - ion battery at a constant current of 1C until the voltage reaches 3.65V, then charge it at a constant voltage of 3.65V until the current reaches 0.05C. Suspend the lithium - ion battery with a thin wire and immerse it in a container filled with water. Record the reading of the balance at this time as m 1 After that, place the lithium - ion battery in an explosion - proof oven at 60°C. After storing for 30 days, place the lithium - ion battery in an environment at 25°C. Discharge the lithium - ion battery at a constant current of 1C until the voltage reaches 2V, and record the discharge capacity at this time as Q 2 Charge the lithium - ion battery at a constant current of 1C until the voltage reaches 3.65V again, then charge it at a constant voltage of 3.65V until the current reaches 0.05C, and then discharge the lithium - ion battery at a constant current of 1C until the voltage reaches 2V. Record the discharge capacity at this time as Q 3 Suspend the lithium - ion battery with a thin wire again and immerse it in a container filled with water. Record the reading of the balance as m 2 .

[0099] Storage capacity retention rate (%) = Q 2 / Q 1 ×100%;

[0100] Storage capacity recovery rate (%) = Q 3 / Q 1 ×100%;

[0101] Measure the gas production volume ΔV (mL) by the water - displacement method. ΔV=(m 2 - m 1 ) / ρ, where ρ is the density of liquid water.

[0102] Evaluate the high - temperature storage performance of the lithium - ion battery based on the storage capacity retention rate, storage capacity recovery rate, and gas production volume. The smaller the value of the gas production volume and the larger the values of the storage capacity retention rate and storage capacity recovery rate, the better the high - temperature storage performance of the lithium - ion battery.

[0103] DC Resistance (DCR) test

[0104] DCR of the lithium - ion battery before storage 1Test: Place the lithium-ion battery in an incubator at 25°C and let it stand for 30 minutes. Then charge the lithium-ion battery at a constant current of 1C until the voltage reaches 3.65V, and then charge it at a constant voltage of 3.65V until the current reaches 0.05C. Let it stand for 30 minutes, and then discharge it at a constant current of 1C for 30 minutes (adjusted to 50% SOC, where SOC refers to the state of charge of the battery), and record the end voltage as V 1 Let it stand for 1 hour, and then discharge it at a constant current of 2C for 10s, and record the end voltage as V 2 Calculate the DCR before storage 1 =(V 1 -V 2 ) / (2C - 1C);

[0105] DCR of the lithium-ion battery after storage 2 Test: Place the above lithium-ion battery in an explosion-proof oven at 60°C, take it out after 30 days of storage, and then take out the lithium-ion battery and cool it to room temperature. Charge it at a constant current of 1C until the voltage reaches 3.65V, and then charge it at a constant voltage of 3.65V until the current reaches 0.05C. Let it stand for 30 minutes, and then discharge it at a constant current of 1C for 30 minutes (adjusted to 50% SOC, where SOC refers to the state of charge of the battery), and record the end voltage as V 3 Let it stand for 1 hour, and then discharge it at a constant current of 2C for 10s, and record the end voltage as V 4 Calculate the DCR before storage 2 =(V 3 -V 4 ) / (2C - 1C);

[0106] Impedance growth rate (%)=(DCR 2 -DCR 1 ) / DCR 1 ×100%.

[0107] Example 1-1

[0108] <Preparation of electrolyte>

[0109] In an argon atmosphere glove box (water content < 0.1 ppm, oxygen content < 1 ppm), mix the non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) evenly according to a mass ratio of 3:1:6 to obtain a basic solvent. Then add the compound shown in Formula I (I-1) and the film-forming additive vinylene carbonate (VC), and then add lithium hexafluorophosphate (LiPF 6 ), dissolve and mix evenly to obtain an electrolyte; wherein, based on the mass of the electrolyte, the mass percentage content of LiPF 6 is 12.5%, the mass percentage content of the compound shown in Formula I is 0.1%, the mass percentage content of the film-forming additive is 2%, and the balance is the basic solvent.

[0110] <Preparation of the positive electrode plate>

[0111] Mix the positive active material lithium iron phosphate, the lithium supplement agent lithium ferrite, the binder polyvinylidene fluoride (PVDF), and the conductive agent Super P in a mass ratio of 93:3:2:2, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 55 wt%; evenly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 16 μm, and the coating amount is 4.2 mg / cm 2 , after drying at 85 °C, a positive electrode plate with a single-sided coated positive electrode material layer with a coating thickness of 168 μm is obtained; repeat the above steps on the other surface of the positive electrode current collector aluminum foil, that is, a positive electrode plate with a double-sided coated positive electrode material layer is obtained; after rolling, baking, slitting, and spot welding the electrode tabs, a positive electrode plate with a specification of 558 mm × 55 mm is obtained.

[0112] <Preparation of the negative electrode plate>

[0113] Mix the negative active material graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a mass ratio of 95:1.5:1.5:2, add deionized water, and stir evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 49 wt%; evenly coat the negative electrode slurry on one surface of a negative electrode current collector copper foil with a thickness of 9 μm, and the coating amount is 8.8 mg / cm 2 , after drying at 85 °C, a negative electrode plate with a single-sided coated negative electrode material layer with a coating thickness of 109 μm is obtained; repeat the above steps on the other surface of the negative electrode current collector copper foil, that is, a negative electrode plate with a double-sided coated negative electrode material layer is obtained; after rolling, baking, slitting, and spot welding the electrode tabs, a negative electrode plate with a specification of 708 mm × 59 mm is obtained.

[0114] <Preparation of the separator>

[0115] Use an Enjie wet-process biaxially stretched separator (PP / PE) with a thickness of 12 μm as the separator.

[0116] <Preparation of the lithium-ion battery>

[0117] Stack the prepared positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator in the middle of the positive electrode sheet and the negative electrode sheet to play an isolation role, and wind them to obtain an electrode assembly. Place the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 85 °C, inject the electrolyte prepared above, with a liquid injection coefficient of 3.3 g / Ah, let it stand for 24 hours, then perform pre-charging, formation, vacuum sealing, and then perform secondary formation to obtain a lithium-ion battery. Among them, the current for the two formations is 0.1C, the upper limit voltage for formation is 3.65V, and the formation temperature is 45 °C.

[0118] Examples 1-2 to Examples 1-10

[0119] Except that in <Preparation of Electrolyte>, the mass percentage contents of the compound shown in Formula I and the film-forming additive are adjusted according to Table 1, and the mass percentage content of the base solvent changes accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as Example 1-1.

[0120] Examples 1-11 to Examples 1-22

[0121] Except that in <Preparation of Electrolyte>, the type of the compound shown in Formula I is adjusted according to Table 1, the rest is the same as Example 1-3.

[0122] Example 1-23

[0123] Except that in <Preparation of Electrolyte>, the type of the film-forming additive is adjusted according to Table 1, the rest is the same as Example 1-21.

[0124] Example 1-24

[0125] <Preparation of Electrolyte>

[0126] In an argon atmosphere glove box (water content < 0.1 ppm, oxygen content < 1 ppm), mix ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as non-aqueous organic solvents evenly according to a mass ratio of 3:1:6 to obtain a base solvent, then add the compound shown in Formula I (I-12) and the film-forming additive vinylene carbonate (VC), and then add lithium hexafluorophosphate (LiPF 6 ) and dissolve and mix evenly to obtain an electrolyte; among them, based on the mass of the electrolyte, the mass percentage content of LiPF 6 is 12.5%, the mass percentage content of the compound shown in Formula I is 1%, the mass percentage content of the film-forming additive is 2%, and the balance is the base solvent.

[0127] <Preparation of Positive Electrode Sheet>

[0128] Mix the cathode active material lithium iron manganese phosphate (LMFP), the lithium supplement agent lithium ferrite, the binder polyvinylidene fluoride (PVDF), and the conductive agent Super P in a mass ratio of 93:3:2:2, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a cathode slurry with a solid content of 55 wt%. Uniformly coat the cathode slurry on one surface of a cathode current collector aluminum foil with a thickness of 16 μm, and the coating amount is 4.2 mg / cm 2 , after drying at 85 °C, a cathode electrode sheet with a single-sided coated cathode material layer with a coating thickness of 168 μm is obtained; repeat the above steps on the other surface of the cathode current collector aluminum foil, and a cathode electrode sheet with a double-sided coated cathode material layer is obtained; after rolling, baking, slitting, and spot welding the electrode tabs, a cathode electrode sheet with a specification of 558 mm × 55 mm is obtained.

[0129] <Preparation of the negative electrode sheet>, <Preparation of the separator>, and <Preparation of the lithium-ion battery> are the same as in Example 1-1.

[0130] Example 1-25

[0131] <Preparation of the electrolyte>

[0132] In an argon atmosphere glove box (water content < 0.1 ppm, oxygen content < 1 ppm), mix the non-aqueous organic solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) evenly in a mass ratio of 3:1:6 to obtain a basic solvent, then add the compound (I-3) shown in Formula I and a film-forming additive (fluoroethylene carbonate (FEC) + 1,3-propane sultone (PS)), and then add lithium hexafluorophosphate (LiPF 6 ), dissolve and mix evenly to obtain an electrolyte; wherein, based on the mass of the electrolyte, the mass percentage content of LiPF 6 is 12.5%, the mass percentage content of the compound shown in Formula I is 1%, the mass percentage content of the film-forming additive is 2% (the mass ratio of FEC and PS is 1:3), and the balance is the basic solvent.

[0133] <Preparation of the positive electrode sheet>

[0134] Mix the cathode active material nickel cobalt manganese 811 (NCM811), the lithium supplement agent lithium ferrite, the binder polyvinylidene fluoride (PVDF), and the conductive agent Super P in a mass ratio of 93:3:2:2, add N-methylpyrrolidone (NMP), and stir evenly under the action of a vacuum mixer to obtain a cathode slurry with a solid content of 55 wt%. Uniformly coat the cathode slurry on one surface of a cathode current collector aluminum foil with a thickness of 16 μm, and the coating amount is 4.2 mg / cm 2, after drying at 85 °C, a positive electrode sheet with a single-sided coated positive electrode material layer having a coating thickness of 168 μm is obtained; the above steps are repeated on the other surface of the positive current collector aluminum foil, and a positive electrode sheet with a double-sided coated positive electrode material layer is obtained; after rolling, baking, slitting, and spot welding the tab, a positive electrode sheet with a specification of 558 mm × 55 mm is obtained.

[0135] <Preparation of negative electrode sheet>, <Preparation of separator>, <Preparation of lithium-ion battery> are the same as in Example 1-1.

[0136] Comparative Example 1-1

[0137] Except that in <Preparation of electrolyte>, the compound shown in Formula I and the film-forming additive are not added, and the mass percentage of the base solvent is changed accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-1.

[0138] Comparative Example 1-2

[0139] Except that in <Preparation of electrolyte>, the film-forming additive is not added, and the mass percentage of the base solvent is changed accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-3.

[0140] Comparative Example 1-3

[0141] Except that in <Preparation of electrolyte>, the compound shown in Formula I is not added, and the mass percentage of the base solvent is changed accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-3.

[0142] Comparative Example 1-4

[0143] Except that in <Preparation of electrolyte>, the film-forming additive is not added, and the mass percentage of the compound shown in Formula I is adjusted according to Table 1, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-1.

[0144] Comparative Example 1-5

[0145] Except that in <Preparation of electrolyte>, the compound shown in Formula I is not added, and the mass percentage of the film-forming additive is adjusted according to Table 1, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-1.

[0146] Comparative Examples 1-6 to 1-9

[0147] Except that in <Preparation of electrolyte>, the mass percentages of the compound shown in Formula I and the film-forming additive are adjusted according to Table 1, and the mass percentage of the base solvent is changed accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Example 1-1.

[0148] Comparative Example 1-10

[0149] Except that the compound shown in Formula I is not added in the <Preparation of Electrolyte> and the mass percentage content of the base solvent changes accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Examples 1-24.

[0150] Comparative Examples 1-11

[0151] Except that the compound shown in Formula I is not added in the <Preparation of Electrolyte> and the mass percentage content of the base solvent changes accordingly, while the percentage contents of other components in the electrolyte remain unchanged, the rest is the same as in Examples 1-25.

[0152] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1.

[0153]

[0154]

[0155] It can be seen from Examples 1-1 to 1-25 and Comparative Examples 1-1 to 1-11 that without adding the compound shown in Formula I and the film-forming additive, or only adding the compound shown in Formula I or the film-forming additive, the secondary battery has relatively low capacity retention rate, storage capacity retention rate and storage capacity recovery rate at 45 °C, as well as relatively high impedance growth rate and gas generation amount, and the overall effect of the secondary battery is not good. Applying the electrolyte containing both the compound shown in Formula I and the film-forming additive to the secondary battery, and limiting the contents of the compound shown in Formula I and the film-forming additive within the scope of this application, the aromatic ring-containing cyclic sulfate compound in the compound shown in Formula I has a phenoxy unit and is easily oxidized by the oxygen generated by the lithium supplementing agent to form a quinone structure, thereby absorbing oxygen. At the same time, the sulfuryl ring is broken, which can provide inorganic parts such as lithium sulfate or lithium sulfite for the SEI film formed by the film-forming additive, improve the hardness of the SEI film, make the SEI film take into account the toughness of the organic matter and the hardness of the inorganic matter, improve the lithium conduction performance, and thus inhibit lithium deposition. Therefore, the secondary battery simultaneously has relatively high capacity retention rate, storage capacity retention rate and storage capacity recovery rate at 45 °C, and at the same time, the impedance growth rate and gas generation amount are also relatively low, and the overall effect of the secondary battery is the best. When the contents of the compound shown in Formula I and the film-forming additive are not within the scope of this application, the compound shown in Formula I and the film-forming additive cannot act synergistically, and the secondary battery has relatively low capacity retention rate, storage capacity retention rate and storage capacity recovery rate at 45 °C, as well as relatively high impedance growth rate and gas generation amount, and the overall effect of the secondary battery is not good. The above results illustrate that the compound shown in Formula I and the film-forming additive are used in combination, and the contents of the compound shown in Formula I and the film-forming additive are limited within the scope of this application, and the compound shown in Formula I and the film-forming additive act synergistically, which is beneficial to improving the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0156] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte is used for a battery containing a lithium supplement, and the electrolyte includes a compound shown in formula I; Wherein, R is selected from hydrogen, fluorine, unsubstituted or fluorine-substituted C1-C4 alkyl, C1-C4 alkoxy; R1 and R2 are each independently selected from -C-, -O- or -CO-; n and m are each independently 0 or 1, and n+m≥1.

2. The electrolyte according to claim 1, characterized in that Based on the mass of the electrolyte, the mass percentage of the compound represented by formula I is A, 0.1%≤A≤3%, preferably, 0.5%≤A≤2.5%.

3. The electrolyte according to claim 1, characterized in that The electrolyte further includes a film-forming additive, and the film-forming additive is selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, vinyl sulfate, 1,3-propane sultone and 1,3-propene sultone.

4. The electrolyte according to claim 3, characterized in that Based on the mass of the electrolyte, the mass percentage of the film-forming additive is B, and 0.1%≤B≤5%.

5. The electrolyte according to claim 1, characterized in that The compound represented by formula I is selected from at least one of the following compounds; 6. The electrolyte according to claim 1, characterized in that The electrolyte also includes an electrolyte, which is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide and lithium tetrafluoroborate; based on the mass of the electrolyte, the mass percentage of the electrolyte is C, 8%≤C≤18%.

7. The electrolyte according to claim 1, characterized in that The electrolyte also includes a solvent, and the solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, tetrahydrofuran, 1,3-dioxolane, ethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether; based on the mass of the electrolyte, the mass percentage of the solvent is D, 74%≤D≤91%.

8. A secondary battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, characterized in that: The positive electrode plate includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, the positive electrode material layer includes a positive electrode active material and a lithium supplement; the lithium supplement is selected from at least one of lithium supplements capable of releasing active oxygen, preferably, the lithium supplement capable of releasing active oxygen is selected from at least one of lithium ferrite, lithium nickelate and lithium oxide.

10. The secondary battery according to claim 8, characterized in that: The positive electrode active material is selected from at least one of nickel-cobalt-manganese ternary material, lithium manganese iron phosphate and lithium iron phosphate.

11. The secondary battery according to claim 8, characterized in that: The negative electrode plate 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 negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a carbon-based material and a silicon-based material.

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