Electrolyte and secondary battery

Abstract

Provided in the present application are an electrolyte and a secondary battery. The electrolyte of the present application comprises a solvent, an electrolyte, and an additive. The additive comprises a first component and a second component. The first component is selected from a compound represented by formula I. The second component is selected from a compound represented by formula II. The synergy of the first component and the second component can enhance the high-temperature storage performance and high-temperature cycle performance of the secondary battery, and reduce the impedance growth rate.

Description

Electrolyte and secondary battery

[0001] This application claims priority to the Chinese patent application No. 202411238595.4 filed on September 5, 2024, and entitled "Electrolyte and secondary battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the technical field of electrochemistry, in particular to an electrolyte and a secondary battery. BACKGROUND

[0003] In recent years, the rapid development and wide application of various portable electronic devices, new energy electric vehicles and energy storage systems have increasingly urgent demands for secondary batteries with high energy density, long cycle life, wide working temperature range and good rate characteristics.

[0004] As the ion conduction carrier between the positive and negative electrodes of a lithium ion battery, the electrolyte is very crucial to the performance of the lithium ion battery. Therefore, it is urgent to develop more comprehensive electrolytes to improve the high-temperature cycle performance, high-temperature storage performance and reduce the impedance growth rate of the lithium ion battery. SUMMARY

[0005] The purpose of the present application is to provide an electrolyte and a secondary battery to improve the high-temperature storage performance, high-temperature cycle performance and reduce the impedance growth rate of the secondary battery. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrolyte, which comprises a solvent, an electrolyte and an additive, the additive comprising a first component and a second component;

[0007] The first component is selected from a compound shown in Formula I;

[0008] wherein R1 is selected from C1-C6 alkylene unsubstituted or substituted with halogen, C3-C6 cycloalkylene unsubstituted or substituted with halogen, C3-C6 heterocycloalkylene unsubstituted or substituted with halogen, C6-C10 arylene unsubstituted or substituted with C1-C6 alkyl, C3-C6 heteroarylene unsubstituted or substituted with halogen; R2 or R3 is each independently selected from hydrogen, halogen, C1-C6 alkyl unsubstituted or substituted with halogen; the heteroatoms in the heterocycloalkylene and the heteroarylene are each independently selected from O, S or N; 12 C6 alkylene unsubstituted or substituted with halogen, C3-C6 cycloalkylene unsubstituted or substituted with halogen, C3-C6 heterocycloalkylene unsubstituted or substituted with halogen, C6-C10 arylene unsubstituted or substituted with C1-C6 alkyl, C3-C6 heteroarylene unsubstituted or substituted with halogen; R2 or R3 is each independently selected from hydrogen, halogen, C1-C6 alkyl unsubstituted or substituted with halogen; the heteroatoms in the heterocycloalkylene and the heteroarylene are each independently selected from O, S or N;

[0009] The second component is selected from a compound shown in Formula II;

[0010] A, 0.1%≤A≤3%, and a mass percentage of the second component is B, 0.1%≤B≤1%, based on the mass of the electrolyte solution.

[0011] In an embodiment of the present application, the mass ratio of the first component and the second component is 1~3:1.

[0012] In an embodiment of the present application, R1is selected from C1-C6alkylene unsubstituted or substituted with fluorine, C3-C6cycloalkylene unsubstituted or substituted with fluorine, C3-C6heterocycloalkylene unsubstituted or substituted with fluorine, C6-C10arylene unsubstituted or substituted with C1-C6alkyl, C3-C6heteroarylene unsubstituted or substituted with fluorine; R2or R3is each independently selected from fluorine or C1-C6alkyl substituted with fluorine. 12 In an embodiment of the present application, R1is selected from C1-C6alkylene unsubstituted or substituted with fluorine, C3-C6cycloalkylene unsubstituted or substituted with fluorine, C3-C6heterocycloalkylene unsubstituted or substituted with fluorine, C6-C10arylene unsubstituted or substituted with C1-C6alkyl, C3-C6heteroarylene unsubstituted or substituted with fluorine; R2or R3is each independently selected from fluorine or C1-C6alkyl substituted with fluorine.

[0013] In an embodiment of the present application, the first component is selected from at least one of the following compounds:

[0014] In an embodiment of the present application, the additive further comprises a third component selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, ethylene sulfate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate; a mass percentage of the third component is C, 0.5%≤C≤5%, based on the mass of the electrolyte solution; preferably, 0.5%≤C≤1.5%.

[0015] In an embodiment of the present application, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium bisoxalate borate, and lithium difluoro oxalate borate; a mass percentage of the electrolyte is D, 12%≤D≤18%, based on the mass of the electrolyte solution.

[0016] In an embodiment of the present application, the solvent is selected from at least two of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; a mass percentage of the solvent is E, 73%≤E≤87%, based on the mass of the electrolyte solution.

[0017] The second aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte described in the first aspect of this application.

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

[0019] The beneficial effects of this application are:

[0020] This application provides an electrolyte and a secondary battery. The electrolyte of this application includes a solvent, an electrolyte, and additives, wherein the additives include a first component and a second component. The mass ratio of the first component and the second component is limited within the range specified in this application. The synergistic effect of the first component and the second component is beneficial for forming a solid electrolyte interface (SEI) film with high mechanical strength, good stability, high ionic conductivity, and toughness at the negative electrode interface. This effectively reduces the risk of SEI damage caused by the volume change of the negative electrode sheet during the cycling process of the secondary battery, reduces side reactions caused by direct contact between the electrode material and the electrolyte, reduces the risk of lithium plating on the negative electrode surface, improves the high-temperature storage performance and high-temperature cycling performance of the secondary battery, and reduces the impedance growth rate.

[0021] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this application clearer, the following embodiments are provided to further illustrate this application in detail. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0023] A first aspect of this application provides an electrolyte comprising a solvent, an electrolyte, and an additive, wherein the additive comprises a first component and a second component;

[0024] The first component is selected from the compounds shown in Formula I;

[0025] Wherein, R1 is selected from unsubstituted or halogen-substituted C1-C6 alkylene groups, unsubstituted or halogen-substituted C3-C6 cycloalkylene groups, unsubstituted or halogen-substituted C3-C6 heterocycloalkylene groups, and unsubstituted or halogen-substituted C6-C6 alkylene groups. 12arylene, C3-C6heteroarylene unsubstituted or substituted with halogen; R2or R3are each independently selected from hydrogen, halogen, C1-C6alkyl unsubstituted or substituted with halogen; the heteroatom in the heterocycloalkylene and the heteroarylene is each independently selected from O, S or N;

[0026] the second component is selected from a compound shown in formula II;

[0027] The mass percentage content of the first component is A, 0.1%≤A≤3%, and the mass percentage content of the second component is B, 0.1%≤B≤1%, based on the mass of the electrolyte. For example, the mass percentage content A of the first component can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or a range between any two of them; the mass percentage content B of the second component can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, or a range between any two of them. The content of the first component and the second component within the above range can exert the synergistic effect of the first component and the second component, so that the secondary battery has higher high-temperature storage performance and cycle life.

[0028] In an embodiment of the present application, the mass ratio of the first component and the second component is 1-3:1. The mass ratio of the first component and the second component within the above range can better exert the synergistic effect of the first component and the second component, further making the secondary battery have higher high-temperature storage performance and cycle life.

[0029] The inventors found in the research that the compound shown in formula II is prone to hydrolysis or alcoholysis, and the residual alcohol group in the incomplete decomposition product formed after breaking one S-O bond on the ring can attack F - in LiPF6 - to make the octahedral PF6 +The space and the space charge layer formed between the interface defects can further improve the conductivity of the interface, and finally establish a SEI with excellent lithium ion conductivity. In addition, the organic layer formed by the breaking and polymerization of the double bond also has a certain toughness, which provides protection for the volume expansion during the cycle process of the negative electrode, and can improve the high-temperature storage performance, high-temperature cycle performance and reduce the impedance growth rate of the secondary battery. The synergistic effect of the first component and the second component is conducive to the formation of a SEI with high mechanical strength, good stability, high ion conductivity and toughness at the negative electrode interface, which can effectively reduce the risk of SEI damage caused by the volume change of the negative electrode sheet during the cycle process of the secondary battery, reduce the side reactions caused by the direct contact of the electrode material and the electrolyte, reduce the risk of lithium precipitation on the negative electrode surface, and improve the high-temperature storage performance, high-temperature cycle performance and reduce the impedance growth rate of the secondary battery.

[0030] In the present application, the term "halogen" means a fluorine, chlorine, bromine or iodine atom.

[0031] In one embodiment of the present application, R1 is selected from the group consisting of C1-C6 alkylene, which is unsubstituted or substituted by fluorine, C3-C6 cycloalkylene, which is unsubstituted or substituted by fluorine, C3-C6 heterocycloalkylene, which is unsubstituted or substituted by fluorine, C6-C10 arylene, which is unsubstituted or substituted by fluorine, C3-C6 heteroarylene, which is unsubstituted or substituted by fluorine; R2 or R3 is each independently selected from the group consisting of fluorine or C1-C6 alkyl, which is substituted by fluorine. 12 In one embodiment of the present application, R1 is selected from the group consisting of C1-C6 alkylene, which is unsubstituted or substituted by fluorine, C3-C6 cycloalkylene, which is unsubstituted or substituted by fluorine, C3-C6 heterocycloalkylene, which is unsubstituted or substituted by fluorine, C6-C10 arylene, which is unsubstituted or substituted by fluorine, C3-C6 heteroarylene, which is unsubstituted or substituted by fluorine; R2 or R3 is each independently selected from the group consisting of fluorine or C1-C6 alkyl, which is substituted by fluorine.

[0032] In one embodiment of the present application, the first component is selected from at least one of the following compounds:

[0033] Further preferably, the first component is compound I-1. When the first component is compound I-1, not only has the above-mentioned effect, but also because compound I-1 is affected by the large π bond of the benzene ring, the -OSO2F group will fall off one F when it is attacked by an electron, in addition, the S-F bond is relatively weak, and the F atom on compound I-1 can be removed before the lithium salt when it is attacked by the residual alcohol group formed by the compound shown in formula II, and the F ion removed from compound I-1 can inhibit the decomposition reaction of the lithium salt. Under this interaction, the synergistic effect of the first component and the second component can further improve the performance of the SEI, thereby further improving the high-temperature cycle performance, high-temperature storage performance and reducing the impedance growth rate of the secondary battery.

[0034] In an embodiment of the present application, the additive further comprises a third component selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, ethylene sulfate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilyl)borate and tris(trimethylsilyl)phosphate; the mass percentage of the third component is C, 0.5%≤C≤5%, based on the mass of the electrolyte; preferably, 0.5%≤C≤1.5%. For example, the mass percentage of the third component C can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range between any two of them, based on the mass of the electrolyte. The electrolyte includes the above-mentioned third component and regulates the mass percentage of the third component within the scope of the present application, and the third component can further enrich the SEI with inorganic components such as Li2SO4, which has a higher electrical conductivity and can improve the ion conduction capacity of the SEI; in addition, the introduction of the third component can further improve the performance of the SEI, for example, the introduction of vinylene carbonate, fluoroethylene carbonate, and ethylene sulfate can all be polymerized into a film to provide a strong elastic SEI cross-linked network structure to constrain the volume expansion of the negative electrode, while reducing the rupture of the SEI caused by volume expansion and continuous reaction with the electrolyte. In summary, the synergistic effect of the first component, the second component and the third component can further improve the performance of the SEI, thereby further improving the high-temperature cycle performance, high-temperature storage performance and reducing the impedance growth rate of the secondary battery.

[0035] In an embodiment of the present application, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium bisoxalate borate and lithium difluoro oxalate borate; the mass percentage of the electrolyte is D, 12%≤D≤18%, based on the mass of the electrolyte. For example, the mass percentage of the electrolyte D can be 12%, 13%, 14%, 15%, 16%, 17%, 18%, or a range between any two of them, based on the mass of the electrolyte. The electrolyte includes the above-mentioned electrolyte and regulates the mass percentage of the electrolyte within the scope of the present application, which can make the electrolyte have a higher ion conductivity and good electrochemical stability, and can further improve the high-temperature cycle performance and high-temperature storage performance of the secondary battery.

[0036] In an embodiment of the present application, the solvent is selected from at least two of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; the mass percentage of the solvent based on the mass of the electrolyte is E, 73%≤E≤87%. For example, the mass percentage E of the solvent based on the mass of the electrolyte can be 73%, 75%, 77%, 80%, 83%, 85%, 87%, or a range between any two of them. The electrolyte includes the above-mentioned solvent and regulates the mass percentage of the solvent within the range of the present application, so that the electrolyte has suitable viscosity, high ionic conductivity, and good electrochemical stability, and the high-temperature cycle performance and high-temperature storage performance of the secondary battery can be further improved.

[0037] The preparation method of the electrolyte of the present application is not particularly limited, as long as the purpose of the present application can be achieved. For example, various solvents in the electrolyte can be mixed, and then electrolyte lithium salt and additives and other substances are added and mixed uniformly.

[0038] 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 of the first aspect of the present application.

[0039] It should be noted that the specific embodiments of the present application explain the present application by taking lithium-ion batteries as examples of secondary batteries, but the secondary batteries of the present application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0040] In an embodiment of the present application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-based material.

[0041] The silicon-based material is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the silicon-based material can be selected from, but is not limited to, at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The negative electrode active material can also include a carbon-based material, which can include, but is not limited to, at least one of artificial graphite, natural graphite, soft carbon, hard carbon, and mesocarbon microbeads. The silicon-based material has a high theoretical capacity, which is beneficial to improve the energy density of the secondary battery. However, the silicon-based material will swell by 120% to 300% in volume during the charging and discharging process of the secondary battery due to the insertion and extraction of lithium ions. The use of the electrolyte provided by the present application is beneficial to form a solid-state electrolyte interface film at the negative electrode interface, which has high mechanical strength, good stability, high ionic conductivity and high toughness. The solid-state electrolyte interface film can effectively inhibit the rupture of the SEI film caused by the expansion of the silicon-based material, reduce the side reactions caused by the direct contact of the negative electrode active material with the electrolyte, and thus improve the high-temperature cycle performance, high-temperature storage performance and reduce the impedance growth rate of the secondary battery.

[0042] The "negative electrode material layer arranged on at least one surface of the negative electrode current collector" refers to that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector. The present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0043] The negative electrode current collector is not particularly limited in the present application, 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 a metal foil, a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam or a 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 base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base layer (such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0044] The thickness of the negative electrode material layer and the negative electrode current collector is not particularly limited in the present application, 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 50 μm to 180 μm, and the thickness of the negative electrode current collector is 3 μm to 10 μm.

[0045] In some embodiments of the present application, the negative material layer can further include a conductive agent and a binder, and the present application does not have a particular limitation on the kind of the conductive agent and the binder as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of Super P, acetylene black, Ketjen black, carbon nanotube, graphene, and carbon fiber. The above-mentioned carbon nanotube can include, but is not limited to, single-walled carbon nanotube and / or multi-walled carbon nanotube. The above-mentioned carbon fiber can include, but is not limited to, vapor grown carbon fiber (VGCF) and / or nano carbon fiber. The binder can 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 have a particular limitation on the mass ratio of the negative active material, the conductive agent, and the binder in the negative material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0046] In some embodiments of the present application, the negative material layer can further include a conductive agent, a binder, and a thickening agent, and the present application does not have a particular limitation on the kind of the conductive agent and the binder 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 agent and the above-mentioned binder. The thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose. The present application does not have a particular limitation on the mass ratio of the negative active material, the conductive agent, the binder, and the thickening agent in the negative material layer, and a person skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0047] Optionally, the negative electrode sheet can further include a conductive layer between the negative current collector and the negative material layer. The present application does not have a particular limitation on the composition of the conductive layer, which can 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 have a particular limitation on the conductive agent and the binder in the conductive layer, which can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0048] In some embodiments of the present application, the compaction density of the negative electrode sheet is 1 g / cm 3 ~ 4 g / cm 3 .

[0049] The preparation method of the negative electrode sheet is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the carbon-based material, silicon-based material, conductive agent, thickening agent and binder can be mixed in a certain proportion, deionized water is added and stirred uniformly to obtain a negative electrode slurry with a solid content of 45wt% to 70wt%. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector, and after drying, a negative electrode sheet 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 sheet with a double-sided coated negative electrode material layer is obtained. After the coating is completed, the negative electrode sheet is obtained by rolling and cutting.

[0050] In the present application, the positive electrode sheet 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 the thickness direction of the positive electrode current collector, or can be disposed on two surfaces of the positive electrode current collector along the thickness direction of the positive electrode current collector. 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 part of the area of the surface of the positive electrode current collector. The present application is not particularly limited, as long as the purpose of the present application can be achieved.

[0051] The present application does not have a particular 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 a metal foil, an aluminum foil, an aluminum alloy foil, a nickel foil or a 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 (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0052] The present application does not have a particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 50μm to 250μm, and the thickness of the positive electrode current collector is 7μm to 15μm.

[0053] The positive electrode material layer includes a positive electrode active material, and the present application does not have a 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 can be selected from, but 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 manganese iron phosphate and lithium titanate.

[0054] The positive electrode material layer can further include a conductive agent and a binder, and the type of the conductive agent and the binder is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of Super P, acetylene black, Ketjen black, carbon nanotube, graphene, and carbon fiber. The carbon nanotube can include, but is not limited to, single-walled carbon nanotube and / or multi-walled carbon nanotube. The carbon fiber can include, but is not limited to, vapor grown carbon fiber (VGCF) and / or nanocarbon fiber. The binder can 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 fluorine-containing acrylate resin. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode material layer is not particularly limited in the present application, and can be selected by a person skilled in the art as needed as long as the purpose of the present application can be achieved.

[0055] Optionally, the positive electrode tab can further include a conductive layer between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application and can be, for example, at least one of the above-mentioned conductive agents and the above-mentioned binders.

[0056] In an embodiment of the present application, the positive electrode tab has a compacted density of 2 g / cm 3 ~ 5 g / cm 3 .

[0057] The method for preparing the positive electrode tab is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the positive electrode active material, the conductive agent, and the binder are mixed in a certain ratio, N-methyl pyrrolidone (NMP) is added, and stirring is performed to obtain a positive electrode slurry having a solid content of 50 wt% to 85 wt%. The positive electrode slurry is uniformly coated on one surface of the positive electrode current collector, and after drying, a positive electrode tab having a single-coated positive electrode material layer is obtained. Then, the above coating step is repeated on the other surface of the positive electrode current collector, and after drying, a positive electrode tab having a double-coated positive electrode material layer is obtained. After the coating is completed, the positive electrode tab is obtained by rolling and cutting.

[0058] The separator is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the material of the separator can be selected from, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of the separator can include at least one of woven film, non-woven fabric, microporous film, composite film, calendered film, and spunlaid film.

[0059] In the present application, the thickness of the separator is not particularly limited as long as the object of the present application is achieved, for example, the thickness of the separator can be 4 to 20 pm.

[0060] In the present application, the secondary battery further includes a case for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte solution, and other components known in the art of secondary batteries, and the present application does not limit the above-mentioned other components. The case is not particularly limited in the present application, and can be a case known in the art as long as the object of the present application is achieved. For example, the case can be a hard case or a flexible case. The material of the hard case can be a metal, and the type of the metal is not limited in the present application, and a metal hard case known in the art can be used as long as the object of the present application is achieved. The flexible case can be a metal plastic film, for example, an aluminum plastic film, a steel plastic film, and the like.

[0061] The secondary battery of the present application is not particularly limited, and can include any device that undergoes an electrochemical reaction. In an embodiment of the present application, the secondary battery can include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a sodium ion secondary battery (sodium ion battery), and the like.

[0062] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in order, and winding, folding, and the like as needed to obtain an electrode assembly in a wound structure, placing the electrode assembly in the case, injecting the electrolyte solution into the case and sealing to obtain the secondary battery. Alternatively, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly in a stack structure, the electrode assembly is placed in the case, the electrolyte solution is injected into the case and sealed to obtain the secondary battery. In addition, a current overprotection element, a guide plate, and the like can also be placed in the case as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0063] Examples

[0064] Hereinafter, embodiments of the present application will be described more specifically by citing examples and comparative examples. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0065] Test methods and equipment:

[0066] High temperature cycle performance test

[0067] The lithium ion battery was placed in a 45°C constant temperature oven, and rested for 4 hours. Then the lithium ion battery was charged at 1C constant current to a voltage of 4.25V, and then charged at 4.25V constant voltage to a current of 0.05C. Then the lithium ion battery was discharged at 1C constant current to a voltage of 2.75V, and the initial discharge capacity was recorded as C1. This was one cycle of charging and discharging. The above charging and discharging cycle was repeated to 1000 times, and the discharge capacity after 1000 cycles was recorded as C2. The charging and discharging cycle tester was a new BTS.

[0068] 45°C capacity retention rate (%) = C2 / C1 x 100%; the high temperature cycle performance of the lithium ion battery was evaluated by the 45°C capacity retention rate, and the greater the capacity retention rate, the better the high temperature cycle performance of the lithium ion battery.

[0069] High temperature storage performance test

[0070] The lithium ion battery was placed in a 25°C constant temperature oven, and rested for 4 hours. Then the lithium ion battery was charged at 1C constant current to a voltage of 4.25V, and then charged at 4.25V constant voltage to a current of 0.05C. Then the lithium ion battery was discharged at 1C constant current to a voltage of 2.75V, and the initial discharge capacity was recorded as Q1. The initial thickness of the lithium ion battery was tested as D1. Then the lithium ion battery was charged at 1C constant current to a voltage of 4.25V, and then charged at 4.25V constant voltage to a current of 0.05C. Then the lithium ion battery was placed in a 45°C explosion-proof oven, and after 30 days of storage, the battery thickness was tested in the oven as D2. Then the lithium ion battery was taken out and cooled to room temperature. The lithium ion battery was discharged at 1C constant current to a voltage of 2.75V at 25°C, and the discharge capacity at this time was recorded as Q2. Then the lithium ion battery was charged at 1C constant current to a voltage of 4.25V, and then charged at 4.25V constant voltage to a current of 0.05C, and the charge capacity at this time was recorded as Q3. Storage thickness expansion rate (%) = (D2-D1) / D1 x 100%; storage capacity retention rate (%) = Q2 / Q1 x 100%; storage capacity recovery rate (%) = Q3 / Q1 x 100%;

[0071] The storage thickness expansion rate, the storage capacity retention rate and the storage capacity recovery rate were used to evaluate the high temperature storage performance of the lithium ion battery. The smaller the value of the storage thickness expansion rate, and the greater the values of the storage capacity retention rate and the storage capacity recovery rate, the better the high temperature storage performance of the lithium ion battery.

[0072] Direct current resistance (DCR) test

[0073] Test of DCR1 before storage of lithium ion battery: the lithium ion battery was placed in a 25℃ constant temperature box, and rested for 4 hours, then the lithium ion battery was charged at 1C constant current to 4.25V, and then charged at 4.25V constant voltage to 0.05C, rested for 30 minutes, and then discharged at 1C constant current for 30 minutes (adjusted to 50% SOC, SOC refers to the state of charge of the battery), and the end voltage was recorded as V1, rested for 1h, then discharged at 2C constant current for 10s, and the end voltage was recorded as V2, and the DCR1 before storage was calculated as (V1-V2) / (2C-1C);

[0074] Test of DCR2 after storage of lithium ion battery: the above lithium ion battery was placed in a 60℃ explosion-proof oven, and after 60 days of storage, it was taken out and cooled to room temperature, then charged at 1C constant current to 4.25V, and then charged at 4.25V constant voltage to 0.05C, rested for 30 minutes, and then discharged at 1C constant current for 30 minutes (adjusted to 50% SOC, SOC refers to the state of charge of the battery), and the end voltage was recorded as V3, rested for 1h, then discharged at 2C constant current for 10s, and the end voltage was recorded as V4, and the DCR2 before storage was calculated as (V3-V4) / (2C-1C); impedance growth rate (%) = (DCR2-DCR1) / DCR1x100%.

[0075] Example 1-1

[0076] Preparation of electrolyte

[0077] In an argon atmosphere glove box (water content <0.1 ppm, oxygen content <1 ppm), non-aqueous organic solvents ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of 3:5:2, then the first component (compound shown in formula 1-1) and the second component (compound shown in formula II) were added and mixed uniformly, and then electrolyte bisfluorosulfonylimide lithium (LiFSI) and lithium hexafluorophosphate (LiPF6) were added, dissolved and mixed uniformly to obtain the electrolyte; wherein, based on the mass of the electrolyte, the mass percentage of LiFSI is 1%, the mass percentage of LiPF6 is 12.5%, the mass percentage of the compound shown in formula 1-1 is 3%, the mass percentage of the compound shown in formula II is 0.1%, and the balance is non-aqueous organic solvent.

[0078] Preparation of positive electrode sheet

[0079] The positive active material LiNi 0.8 Co 0.1 Mn 0.1The positive electrode active material LiFePO4, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 55 wt% was prepared. After uniform stirring in a vacuum, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and was dried at 90°C to obtain a positive electrode sheet with a single-coated positive electrode material layer. Then, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-coated positive electrode material layer. After drying at 85°C, the positive electrode sheet was rolled, and then was cut and tabbed to obtain a positive electrode sheet with a size of 70 mm x 55 mm. The thickness of the single-coated positive electrode material layer was 158 μm, and the tap density of the positive electrode sheet was 3.3 g / cm3. 3 .

[0080] <Preparation of a negative electrode sheet>

[0081] The negative electrode active material artificial graphite (Jiangxi Zichen Technology Co., Ltd., SIC-1300L) and the silicon-based material (Si450), the conductive agent acetylene black, the thickening agent carboxymethyl cellulose sodium (CMC), and the binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 87.3:9.7:1:1:1, deionized water was added as a solvent, and a slurry with a solid content of 49 wt% was prepared. After uniform stirring in a vacuum, a negative electrode slurry was obtained. The negative electrode slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 9 μm, and was dried at 90°C to obtain a negative electrode sheet with a single-coated negative electrode material layer. Then, the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-coated negative electrode material layer. After drying at 85°C, the negative electrode sheet was rolled, and then was cut and tabbed to obtain a negative electrode sheet with a size of 74 mm x 59 mm. The thickness of the single-coated negative electrode material layer was 111 μm, and the tap density of the negative electrode sheet was 1.55 g / cm3. 3 .

[0082] <Preparation of a separator>

[0083] A polyethylene (PE) porous membrane (provided by Shenzhen Xingyuan Material Technology Co., Ltd.) with a thickness of 10 μm was used as a separator.

[0084] <Preparation of a lithium ion battery>

[0085] The positive electrode sheet, the separator, and the negative electrode sheet prepared above are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and are wound to obtain an electrode assembly. The electrode assembly is put into an aluminum plastic film packaging bag, and is dehydrated at 85°C, injected with the electrolyte prepared above, and injected with a coefficient of 1.6 g / Ah. After vacuum packaging, standing, formation, and shaping, a lithium ion battery is obtained. The standing time is 48 hours, the formation current is 0.1C, the upper limit voltage of formation is 4.25V, and the formation temperature is 45°C.

[0086] Examples 1-2 to 1-8

[0087] Except that the mass percentage content of the first component and the second component is adjusted according to Table 1 in the preparation of the electrolyte, the mass percentage content of the non-aqueous organic solvent changes accordingly, and the percentage content of other components in the electrolyte remains unchanged, the rest is the same as Example 1-1.

[0088] Examples 1-9 to 1-15

[0089] Except that the type of the first component is adjusted according to Table 1 in the preparation of the electrolyte, the rest is the same as Example 1-7.

[0090] Examples 2-1 to 2-7

[0091] Except that the third component is added according to Table 2 in the preparation of the electrolyte, and the type and mass percentage content of the third component is adjusted according to Table 2, the mass percentage content of the non-aqueous organic solvent changes accordingly, and the percentage content of other components in the electrolyte remains unchanged, the rest is the same as Example 1-7.

[0092] Examples 2-8 to 2-9

[0093] Except that the mass percentage content of the third component and the mass percentage content of the non-aqueous organic solvent changes accordingly in the preparation of the electrolyte, the percentage content of other components in the electrolyte remains unchanged, the rest is the same as Example 2-7.

[0094] Example 2-10

[0095] Except that the type of the electrolyte is adjusted according to Table 2 in the preparation of the electrolyte, the rest is the same as Example 2-7.

[0096] Examples 2-11 to 2-12

[0097] Except that the mass percentage content of the electrolyte and the mass percentage content of the non-aqueous organic solvent changes accordingly in the preparation of the electrolyte, the percentage content of other components in the electrolyte remains unchanged, the rest is the same as Example 2-7.

[0098] Comparative Example 1-1

[0099] Except that the mass percentage content of the first component, nonaqueous organic solvent, is changed in the <Preparation of electrolyte> without adding the second component, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-7.

[0100] Comparative Example 1-2

[0101] Except that the mass percentage content of the second component, nonaqueous organic solvent, is changed in the <Preparation of electrolyte> without adding the first component, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-7.

[0102] Comparative Example 1-3

[0103] Except that the mass percentage content of the second component is adjusted according to Table 1 in the <Preparation of electrolyte> without adding the first component, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-7.

[0104] Comparative Example 1-4

[0105] Except that the mass percentage content of the first component is adjusted according to Table 1 in the <Preparation of electrolyte> without adding the second component, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-7.

[0106] Comparative Example 1-5

[0107] Except that the mass percentage content of the nonaqueous organic solvent is changed in the <Preparation of electrolyte> without adding the first component and the second component, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-1.

[0108] Comparative Example 1-6 to Comparative Example 1-9

[0109] Except that the mass percentage content of the first component and the second component is adjusted according to Table 1 in the <Preparation of electrolyte>, the mass percentage content of the nonaqueous organic solvent is changed, the percentage content of other components in the electrolyte remains unchanged, and the rest is the same as Example 1-1.

[0110] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1 to Table 2.

[0111] As can be seen from Examples 1-1 to 1-15 and Comparative Examples 1-1 to 1-9, when the electrolyte with only the first component or the second component is applied to the lithium ion battery, or the content of the first component and the second component is not within the range of the present application, the lithium ion battery has a lower 45°C capacity retention rate, storage capacity retention rate and storage capacity recovery rate, and a higher storage thickness expansion rate and impedance growth rate. When the electrolyte with the first component and the second component is applied to the lithium ion battery, and the content of the first component and the second component is limited within the range of the present application, the lithium ion battery has a higher 45°C capacity retention rate, storage capacity retention rate and storage capacity recovery rate, and a lower storage thickness expansion rate and impedance growth rate. The above results show that the first component and the second component are used in combination, and the content of the first component and the second component is limited within the range of the present application, the two components synergistically act, which can improve the high-temperature storage performance, high-temperature cycle performance of the lithium ion battery and reduce the impedance growth rate.

[0112] As can be seen from Examples 2-1 to 2-12, when the electrolyte with the first component, the second component and the third component is applied to the lithium ion battery, the lithium ion battery has a higher 45°C capacity retention rate, storage capacity retention rate and storage capacity recovery rate, and a lower storage thickness expansion rate and impedance growth rate. This shows that the first component, the second component and the third component are used in combination, and the content of the first component, the second component and the third component is limited within the range of the present application, the three components synergistically act, which can further improve the high-temperature storage performance, high-temperature cycle performance of the lithium ion battery and reduce the impedance growth rate.

[0113] It should be noted that the relational terms herein such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any such actual relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0114] The above description is merely the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte comprising a solvent, an electrolyte, and an additive, the additive comprising a first component and a second component; said first component is selected from the group consisting of compounds of formula I; wherein R1is selected from the group consisting of C1-C6alkylene unsubstituted or substituted with halogen, C3-C6cycloalkylene unsubstituted or substituted with halogen, C3-C6heterocycloalkylene unsubstituted or substituted with halogen, C6-C10arylene unsubstituted or substituted with halogen, C3-C6heteroarylene unsubstituted or substituted with halogen; R2or R3are each independently selected from the group consisting of hydrogen, halogen, C1-C6alkyl unsubstituted or substituted with halogen; the heteroatoms in the heterocycloalkylene and the heteroarylene are each independently selected from O, S or N; 12 R1is selected from the group consisting of C1-C6alkylene unsubstituted or substituted with halogen, C3-C6cycloalkylene unsubstituted or substituted with halogen, C3-C6heterocycloalkylene unsubstituted or substituted with halogen, C6-C10arylene unsubstituted or substituted with halogen, C3-C6heteroarylene unsubstituted or substituted with halogen; R2or R3are each independently selected from the group consisting of hydrogen, halogen, C1-C6alkyl unsubstituted or substituted with halogen; the heteroatoms in the heterocycloalkylene and the heteroarylene are each independently selected from O, S or N; said second component is selected from the group consisting of compounds of formula II; a mass percentage of the first component is A, 0.1%≤A≤3%, and a mass percentage of the second component is B, 0.1%≤B≤1%, based on the mass of the electrolyte.

2. The electrolyte of claim 1, wherein, a mass ratio of the first component to the second component is 1~3:

1.

3. The electrolyte of claim 1, wherein, R1is selected from the group consisting of C1-C6alkylene unsubstituted or substituted with fluorine, C3-C6cycloalkylene unsubstituted or substituted with fluorine, C3-C6heterocycloalkylene unsubstituted or substituted with fluorine, C6-C10arylene unsubstituted or substituted with C1-C6alkyl, C3-C6heteroarylene unsubstituted or substituted with fluorine; R2or R3are each independently selected from the group consisting of fluorine or C1-C6alkyl substituted with fluorine. 12 R1is selected from the group consisting of C1-C6alkylene unsubstituted or substituted with fluorine, C3-C6cycloalkylene unsubstituted or substituted with fluorine, C3-C6heterocycloalkylene unsubstituted or substituted with fluorine, C6-C10arylene unsubstituted or substituted with C1-C6alkyl, C3-C6heteroarylene unsubstituted or substituted with fluorine; R2or R3are each independently selected from the group consisting of fluorine or C1-C6alkyl substituted with fluorine.

4. The electrolyte of claim 1, wherein, The first component is selected from at least one of the following compounds; 5. The electrolyte of claim 1, wherein, the additive further comprises a third component selected from at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, ethylene sulfate, 1,3-propane sultone, 1,3-propene sultone, vinyl sulfite, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate; a mass percentage of the third component is C, 0.5%≤C≤5%, based on the mass of the electrolyte.

6. The electrolyte of claim 5, wherein, 0.5％≤C≤1.5％。 7. The electrolyte of claim 1, wherein, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium bisoxalato borate, and lithium difluoro oxalato borate; a mass percentage of the electrolyte is D, 12%≤D≤18%, based on the mass of the electrolyte.

8. The electrolyte of claim 1, wherein, the solvent is selected from at least two of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate; a mass percentage of the solvent is E, 73%≤E≤87%, based on the mass of the electrolyte. 9.A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte according to any one of claims 1 to 8.

10. The secondary battery according to claim 9, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material.

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