Electrolyte solution and secondary battery

Abstract

An electrolyte solution and a secondary battery. The electrolyte solution comprises a solvent, an electrolyte, and an additive, and the additive comprises a first component and a second component. The first component is selected from fluoroethylene carbonate, and the second component is selected from a compound represented by formula (I). Based on the mass of the electrolyte solution, the mass percentage content of the first component is a, wherein 5%≤a≤20%, and the mass percentage content of the second component is b, wherein 0.1%≤b≤2%.

Description

An electrolyte and a secondary battery

[0001] This application claims priority to Chinese Patent Application No. 202411512454.7, filed on October 28, 2024, entitled "An Electrolyte and a Secondary Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to an electrolyte and a secondary battery. Background Technology

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

[0004] Electrolytes, as the ion carriers between the positive and negative electrodes of secondary batteries, are crucial to battery performance. Therefore, there is an urgent need to develop more comprehensive electrolytes to improve the high-temperature cycling performance, high-temperature storage performance, low-temperature discharge performance, and reduce impedance of secondary batteries. Summary of the Invention

[0005] The purpose of this application is to provide an electrolyte and a secondary battery to improve the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and reduce impedance of the secondary battery. The specific technical solution is as follows:

[0006] 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; the first component is selected from fluoroethylene carbonate; and the second component is selected from compounds represented by Formula I.

[0007] Among them, R1 to R3 are each independently selected from unsubstituted or R-substituted individuals. a Replacement C1-C 10 Alkyl; Substituent R a Each is independently selected from fluorine, unsubstituted or fluorinated C6-C. 12 Aryl;

[0008] Based on the mass of the electrolyte, the mass percentage of the first component is a, 5% ≤ a ≤ 20%, and the mass percentage of the second component is b, 0.1% ≤ b ≤ 2%.

[0009] 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.

[0010] The beneficial effects of this application are:

[0011] This application provides an electrolyte and a secondary battery. The electrolyte of this application includes a solvent, an electrolyte, and an additive. The additive includes a first component and a second component. The first component is fluoroethylene carbonate, which, when used alone as an electrolyte additive, deteriorates rapidly under high-temperature conditions. It is prone to defluorination, generating HF that attacks the positive electrode material, causing transition metal ions in the positive electrode material to dissolve and catalyze the decomposition of the electrolyte, generating a large amount of gas. The solid electrolyte interface film formed by fluoroethylene carbonate has decreased stability under high-temperature conditions and decomposes in large quantities, leading to the continuous decomposition and polymerization of fluoroethylene carbonate at the interface. This results in an excessively thick solid electrolyte interface film, causing a sharp increase in battery impedance. During this process, the decomposition of fluoroethylene carbonate releases a large amount of carbon dioxide, further increasing the gas content. Adding the compound shown in Formula I to the electrolyte as an electrolyte additive can solve the problems mentioned above caused by using fluoroethylene carbonate alone as an electrolyte additive. Specifically, the compound shown in Formula I, as an electrolyte additive, can selectively oxidize on the positive electrode surface to form a stable low-resistance surface film, inhibiting electrolyte decomposition and the dissolution of transition metal ions from the positive electrode, thus reducing electrolyte decomposition. Simultaneously, the boron central atom of the compound shown in Formula I is an electron-deficient group; even if some transition metal ions are extracted from the positive electrode, they will be captured by boron atoms, reducing their catalytic effect on the electrolyte. Furthermore, BO is a low-resistance component that participates in the construction of the solid electrolyte interface film, reducing the impedance of the solid electrolyte interface film, making lithium ion insertion and extraction easier, and improving the ionic conductivity of the electrolyte. The electrolyte additive of this application includes both a first component and a second component, and the content of the first component and the second component is limited within the scope of this application, which can fully utilize the synergistic effect of the first component and the second component to improve the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance of the secondary battery, and reduce impedance.

[0012] 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

[0013] The technical solutions in the embodiments of this application are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0014] 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; the first component is selected from fluoroethylene carbonate; and the second component is selected from compounds represented by Formula I.

[0015] Among them, R1 to R3 are each independently selected from unsubstituted or R-substituted individuals. a Replacement C1-C 10 Alkyl; Substituent R a Each is independently selected from fluorine, unsubstituted or fluorinated C6-C. 12 Aryl;

[0016] Based on the mass of the electrolyte, the mass percentage of the first component is 'a', where 5% ≤ a ≤ 20%, and the mass percentage of the second component is 'b', where 0.1% ≤ b ≤ 2%. Preferably, 6% ≤ a ≤ 10% and 0.3% ≤ b ≤ 1%. For example, based on the mass of the electrolyte, the mass percentage 'a' of the first component can be 5%, 6%, 8%, 10%, 13%, 15%, 18%, 20%, or a range of any two of these values; the mass percentage 'b' of the second component can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, or a range of any two of these values. When the contents of the first and second components are within the above ranges, the synergistic effect of the first and second components can be achieved, improving the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance of the secondary battery, and reducing impedance.

[0017] The first component of this application is fluoroethylene carbonate. As an electrolyte additive, fluoroethylene carbonate can decompose and polymerize on the electrode surface to form an elastic polymer film, significantly improving the cycle life of the negative electrode material. However, when used alone as an electrolyte additive, the performance of fluoroethylene carbonate deteriorates rapidly under high-temperature conditions. It is prone to defluorination, generating HF that attacks the positive electrode material, causing transition metal ions in the positive electrode material to dissolve and catalyze the decomposition of the electrolyte, generating a large amount of gas. Simultaneously, the stability of the solid electrolyte interface film formed by fluoroethylene carbonate decreases under high-temperature conditions, leading to significant decomposition and polymerization of fluoroethylene carbonate at the interface. This results in an excessively thick solid electrolyte interface film, causing a sharp increase in battery impedance. During this process, the decomposition of fluoroethylene carbonate releases a large amount of carbon dioxide, further increasing the gas content. The inventors discovered in their research that simultaneously adding the compound shown in Formula I as an electrolyte additive to the electrolyte can solve the above problems caused by using fluoroethylene carbonate alone as an electrolyte additive. Specifically, the compound shown in Formula I can selectively oxidize on the positive electrode surface to form a stable, low-resistance surface film, inhibiting electrolyte decomposition and the dissolution of transition metal ions from the positive electrode, thus reducing electrolyte decomposition. Simultaneously, the boron central atom in the compound shown in Formula I is an electron-deficient group; even if some transition metal ions are extracted from the positive electrode, they will be captured by the boron atom, reducing their catalytic effect on the electrolyte. Furthermore, the BO component is a low-resistance component, participating in the construction of the solid electrolyte interfacial film, reducing the impedance of the solid electrolyte interfacial film, making lithium ion insertion and extraction easier, and improving the ionic conductivity of the electrolyte. Preferably, the compound shown in Formula I is a fluoroboronate compound, in which the introduction of fluorine increases electronegativity, thereby changing the local environment around the ionicly conductive salt, promoting the dissociation between cations and anions, and enhancing ion transport. In addition, the CF bond is one of the strongest single bonds, thus benefiting both the thermal and electrochemical stability of the battery. At low temperatures, the impedance of the SEI film (solid electrolyte interface film) on the negative electrode surface of a lithium-ion battery increases significantly, severely hindering the lithium-ion insertion / extraction process, leading to a sharp drop in discharge voltage and making it difficult to fully release the battery's internal capacity. The compound shown in Formula I can form a low-impedance interface film, effectively reducing the resistance of lithium-ion insertion / extraction during the process, thereby improving the battery's low-temperature discharge capability. In summary, the electrolyte additive of this application includes both the first component and the second component, and the content of the first component and the second component is limited within the scope of this application. This allows for full utilization of the synergistic effect of the first component and the second component, improving the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance of the secondary battery, and reducing impedance.

[0018] In one embodiment of this application, R1 to R3 are each independently selected from those that are not substituted or have been replaced by R. a Substituted C1-C6 alkyl groups; substituent R aEach is independently selected from fluorine, unsubstituted or fluorinated phenyl groups.

[0019] In one embodiment of this application, the second component is selected from at least one of the following compounds;

[0020] When an electrolyte comprising the first and second components is applied to a secondary battery, the synergistic effect of the first and second components can further improve the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and reduce impedance of the secondary battery.

[0021] In one embodiment of this application, the additive further includes a third component selected from at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and lithium difluorodioxane phosphate. Based on the mass of the electrolyte, the mass percentage of the third component is c, 0.5% ≤ c ≤ 5%, preferably 0.5% ≤ c ≤ 2%. For example, based on the mass of the electrolyte, the mass percentage c of the third component can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values. Within the scope of this application, the electrolyte includes the aforementioned third component, and the mass percentage of the third component is controlled. The synergistic effect of the first, second, and third components can further improve the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and reduce impedance of the secondary battery.

[0022] In one embodiment of this application, the electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), and lithium difluorooxalate-borate. Based on the mass of the electrolyte, the mass percentage of the electrolyte is d, 12% ≤ d ≤ 17%, preferably 12% ≤ d ≤ 15%. For example, based on the mass of the electrolyte, the mass percentage of the electrolyte d can be 12%, 13%, 14%, 15%, 16%, 17%, or a range of any two of these values. By including the above-mentioned electrolytes and controlling the mass percentage of the electrolyte within the scope of this application, the electrolyte can have high ionic conductivity and good electrochemical stability, further improving the high-temperature cycle performance, high-temperature storage performance, and low-temperature discharge performance of the secondary battery.

[0023] In one embodiment of this application, the solvent is selected from at least two of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl 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 is e based on the mass of the electrolyte, where 56% ≤ e ≤ 82%. For example, based on the mass of the electrolyte, the mass percentage e of the solvent can be 56%, 58%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, or a range of any two of these values. The electrolyte includes the above-mentioned solvents, and by adjusting the mass percentage of the solvents within the scope of this application, the electrolyte can have suitable viscosity, high ionic conductivity and good electrochemical stability, which can further improve the high-temperature cycle performance, high-temperature storage performance and low-temperature discharge performance of the secondary battery.

[0024] This application does not impose any particular restrictions on the preparation method of the electrolyte, as long as it can achieve the purpose of this application. For example, various solvents in the electrolyte can be mixed, and then electrolytes and additives can be added and mixed evenly.

[0025] 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.

[0026] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0027] 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 includes a negative electrode active material containing silicon. Based on the mass of the negative electrode active material, the mass percentage of silicon is f, preferably 5% ≤ f ≤ 30%, and preferably 5% ≤ f ≤ 20%. For example, based on the mass of the negative electrode active material, the mass percentage of silicon f can be 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of these values. Within the range of this application, the mass percentage of silicon in the negative electrode active material is beneficial for improving the energy density of the secondary battery, while also considering the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and reducing impedance of the secondary battery.

[0028] This application does not impose any particular limitation on the silicon-containing negative electrode active material, as long as it can achieve the purpose of this application. For example, the silicon-containing negative electrode active material can be selected from, but is not limited to, at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The negative electrode active material may also include at least one of soft carbon, hard carbon, and graphite. The silicon-containing negative electrode active material (hereinafter referred to as silicon-based material) has a high theoretical capacity, which is beneficial to improving the energy density of secondary batteries. However, during the charging and discharging process of secondary batteries, silicon-based materials undergo a volume expansion of 120% to 300% with the insertion and extraction of lithium ions. Using the electrolyte provided in this application is beneficial to forming a solid electrolyte interface film with high mechanical strength, good stability, high ionic conductivity, and toughness at the negative electrode interface. This can effectively suppress the rupture of the solid electrolyte interface film caused by the expansion of silicon-based materials, reduce the side reactions caused by direct contact between the negative electrode active material and the electrolyte, thereby improving the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance of secondary batteries, and reducing impedance.

[0029] In one embodiment of this application, the concentration of fluorine in the first component of the electrolyte is F. a The concentration of fluorine in the second component is F. b 0.4 mol / L <F a +F b <2.6 mol / L. F a +F b When the content of F is within the above range, F can participate in the construction of a stable interface film with suitable impedance, which is beneficial to further improve the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance, and reduce impedance of the secondary battery. Preferably, the secondary battery satisfies: 4mol / L ≤ (F a +F b Within the range of ) / f≤26mol / L, the interface film constructed by F element can better resist the expansion of silicon particles as a framework, allowing silicon components to better perform their functions, further improving the energy density of the secondary battery, while taking into account the high-temperature cycle performance, high-temperature storage performance, low-temperature discharge performance of the secondary battery and reducing impedance.

[0030] The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a part of the surface of the negative electrode current collector. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0031] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the negative electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, or foamed copper can be used. The composite current collector may include a polymer material substrate 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 (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.).

[0032] This application does not impose any particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 125 μm, and the thickness of the negative electrode current collector is 4 μm to 10 μm.

[0033] In one embodiment of this application, the negative electrode material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The 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). This application does not impose any particular limitation on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0034] In one embodiment of this application, the negative electrode material layer may further include a conductive agent, a binder, and a thickener. This application does not particularly limit the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent and binder may be at least one of the aforementioned conductive agents and binders. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0035] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0036] This application does not impose any particular limitation on the preparation method of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode active material, thickener, binder, and conductive agent can be mixed in a certain mass ratio, and deionized water can be added and stirred evenly to obtain a negative electrode slurry with a solid content of 45wt% to 55wt%. 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 negative electrode material layer is obtained. Then, the above coating steps are repeated on the other surface of the negative electrode current collector, and after drying, a negative electrode sheet with a double-sided negative electrode material layer is obtained. Then, it is rolled, slit, and electrode tabs are welded to obtain the negative electrode sheet.

[0037] In this application, the positive electrode includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface area of ​​the positive current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0038] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, aluminum foil, aluminum alloy foil, nickel foil, or nickel alloy can be used. The composite current collector can include a polymer material substrate 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 (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.).

[0039] This application does not impose any particular restrictions on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer is 20 μm to 90 μm, and the thickness of the positive electrode current collector is 9 μm to 20 μm.

[0040] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material can be selected from at least one of lithium manganese oxide, lithium nickel cobalt manganese oxide ternary materials, lithium nickel manganese oxide, and lithium-rich manganese-based materials.

[0041] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0042] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0043] This application does not impose any particular limitation on the preparation method of the positive electrode sheet, as long as it achieves the purpose of this application. For example, the positive electrode active material, conductive agent, and 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 50wt% to 75wt%. The positive electrode slurry is uniformly coated on one surface of the positive electrode current collector, and after drying, a positive electrode sheet with a single-sided coating of positive electrode material 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 sheet with a double-sided coating of positive electrode material is obtained. Then, it is rolled, slit, and electrode tabs are welded to obtain the positive electrode sheet.

[0044] This application does not impose any particular limitation on the diaphragm, as long as it can achieve the purpose of this application. For example, the diaphragm material 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 diaphragm can include at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, and spun membrane.

[0045] In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be 5 μm to 10 μm.

[0046] In this application, the secondary battery also includes a casing for housing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the casing; it can be a casing known in the art, as long as it achieves the purpose of this application. For example, the casing can be a rigid casing or a flexible casing. The material of the rigid casing can be metal; this application does not limit the type of metal and can use known metal rigid casings, as long as they achieve the purpose of this application. The flexible casing can be a metal plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0047] The secondary battery described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the secondary battery may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), etc.

[0048] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the secondary battery may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it; forming; capacity testing; and sorting to obtain the secondary battery. Furthermore, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0049] Example

[0050] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0051] Test methods and equipment:

[0052] ambient temperature cycling performance test

[0053] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C1. This process was repeated for 500 cycles, and the discharge capacity C2 after 500 cycles was recorded. The capacity retention rate at room temperature was calculated as C2 / C1 × 100%.

[0054] High-temperature cycling performance test

[0055] The lithium-ion battery was placed in a 45°C constant temperature test chamber and left to stand for 60 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C3. This process was repeated for 300 cycles, and the discharge capacity C4 after 300 cycles was recorded. The high-temperature cycle capacity retention rate of the lithium-ion battery was calculated as C4 / C3 × 100%.

[0056] High-temperature storage performance test

[0057] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C5. The battery was then charged again at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current was 0.05C. The thickness of the lithium-ion battery was measured and recorded as h1. The battery was then transferred to 60°C and left to stand for 28 days. The thickness of the battery was measured and recorded as h2. Finally, it was discharged at a constant current of 1.0C to 2.75V, and the discharge capacity was recorded as C6. High-temperature storage capacity retention rate = C6 / C5 × 100%, high-temperature storage thickness expansion rate = (h2 - h1) / h1 × 100%.

[0058] Low-temperature DC internal resistance (DCIR) test

[0059] Place the lithium-ion battery in a -20℃ constant temperature chamber and let it stand for 4.5 hours to allow it to reach a constant temperature. Charge it to 4.2V at a constant current of 1.0C, let it stand for 30 minutes, then discharge it at a constant current of 1.0C for 30 minutes, let it stand for 1 hour, and then discharge it at the current corresponding to a 2C rate (IC). 2C Discharge for 10 seconds, record the voltage values ​​V1 and V2 before and after 2C rate discharge, respectively, and calculate the DCIR of the lithium-ion battery at 50% state of charge (SOC). Low-temperature DCIR = (V1 - V2) / I 2C The unit is mΩ.

[0060] Low temperature discharge test

[0061] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C7. The lithium-ion battery was then charged at a constant current of 1.0C to 4.2V, followed by constant voltage charging at 4.2V until the cutoff current was 0.05C. After standing for 5 minutes, it was transferred to a -20°C constant temperature chamber and left to stand for 4.5 hours to allow it to reach a constant temperature. Finally, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C8. The low-temperature discharge capacity retention rate of the lithium-ion battery was calculated as C8 / C7 × 100%.

[0062] Example 1-1

[0063] <Preparation of Electrolyte>

[0064] In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), solvents ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed uniformly in a mass ratio of 1.5:1.5:5:2. Then, the first component (fluoroethylene carbonate) and the second component (the compound shown in Formula I-1) are added and mixed uniformly. Next, the electrolyte lithium hexafluorophosphate (LiPF6) is added, dissolved, and mixed uniformly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 is 12.5%, the mass percentage of the first component is 5%, the mass percentage of the second component is 0.5%, and the remainder is solvent.

[0065] <Preparation of the positive electrode>

[0066] Lithium nickel cobalt manganese oxide (NCM811), polyvinylidene fluoride (PVDF), and acetylene black were mixed at a mass ratio of 96.5:2:1.5. N-methylpyrrolidone (NMP) was added to prepare a slurry with a solid content of 69 wt%. The mixture was stirred under vacuum until a homogeneous and fluid positive electrode slurry was formed. The positive electrode slurry was then uniformly coated onto one surface of a 16 μm thick aluminum foil current collector and subjected to different temperature gradients (90℃, 2 ... After baking in an oven at 100℃ and 85℃ at a speed of 2200 mm / min, the sample is then dried at 120℃ to obtain a positive electrode sheet with a single-sided coating of positive electrode material. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After rolling, slitting, and welding of tabs, a positive electrode sheet with dimensions of 540 mm × 50 mm is obtained. The thickness of the single-sided positive electrode material layer is 59 μm, and the compaction density of the positive electrode sheet is 3.5 g / cm³. 3 .

[0067] <Preparation of Negative Electrode Sheets>

[0068] Artificial graphite (anode active material), CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), sodium carboxymethyl cellulose (CMC-Na) thickener, styrene-butadiene rubber (binder), acetylene black (conductive agent), and single-walled carbon nanotubes (SWCNTs) (conductive agent) were mixed in a mass ratio of 75.9:20:1:2:1:0.1. Deionized water was added as a solvent to prepare a slurry with a solid content of 49 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the anode slurry. The anode slurry was then homogenized. A negative electrode sheet with a single-sided coating of negative electrode material is obtained by coating one surface of a 6μm thick copper foil for the negative electrode current collector and drying it at 85℃. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After rolling, slitting, and welding of tabs, a negative electrode sheet with dimensions of 660mm × 59mm is obtained. The thickness of the single-sided negative electrode material layer is 46.5μm, and the compaction density of the negative electrode sheet is 1.65g / cm³. 3 Based on the mass of the negative electrode active material, the mass percentage of silicon is 10%.

[0069] <Preparation of the diaphragm>

[0070] The membrane is made of polyethylene with a thickness of 8μm (provided by Shenzhen Xingyuan Material Technology Co., Ltd.).

[0071] <Preparation of Lithium-ion Batteries>

[0072] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to act as a separator. They are then wound, with the positive tab connected to the positive electrode and the negative tab connected to the negative electrode, resulting in an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film, with the positive and negative tabs extended from the interior to the exterior of the film. Moisture is removed at 85°C, and the prepared electrolyte is injected. After vacuum sealing and standing for 24 hours, an application of 3 kg / cm² is performed at 45°C. 2 The pressure was adjusted, and the cells were formed by constant current charging at 0.1C for 6.5 hours. Then, the cells were sorted by capacity (charged at 0.1C constant current to 4.2V, then charged at 4.2V constant voltage to the cutoff current of 0.05C, allowed to stand for 5 minutes, and discharged at 0.5C constant current to 2.75V; then charged at 0.5C constant current to 4.2V, then charged at 4.2V constant voltage to the cutoff current of 0.05C, allowed to stand for 5 minutes, and discharged at 1.0C constant current to 2.75V; then charged at 1.0C constant current to 4.2V, then charged at 4.2V constant voltage to the cutoff current of 0.05C, allowed to stand for 5 minutes, and discharged at 1.0C constant current to 2.75V) to obtain lithium-ion batteries.

[0073] Examples 1-2 to Examples 1-7

[0074] Except for adjusting the mass percentage of the first component according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the solvent accordingly, and keeping the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0075] Examples 1-8 to Examples 1-12

[0076] Except for adjusting the mass percentage of the second component according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the solvent accordingly, and keeping the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0077] Examples 1-13

[0078] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 85.9:10:1:2:1:0.1, the rest is the same as in Examples 1-4. Based on the mass of the negative electrode active material, the silicon content is 5% by mass.

[0079] Examples 1-14

[0080] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 55.9:40:1:2:1:0.1, the rest is the same as in Examples 1-4. Based on the mass of the negative electrode active material, the silicon content is 20% by mass.

[0081] Examples 1-15

[0082] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 35.9:60:1:2:1:0.1, the rest is the same as in Examples 1-4. Based on the mass of the negative electrode active material, the silicon content is 30% by mass.

[0083] Examples 1-16 to Examples 1-18

[0084] Except for adjusting the type and mass percentage of the second component according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the solvent accordingly, and keeping the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0085] Examples 1-19

[0086] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 85.9:10:1:2:1:0.1, the rest is the same as in Examples 1-18. Based on the mass of the negative electrode active material, the silicon content is 5% by mass.

[0087] Examples 1-20

[0088] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 55.9:40:1:2:1:0.1, the rest is the same as in Examples 1-18. Based on the mass of the negative electrode active material, the silicon content is 20% by mass.

[0089] Examples 1-21

[0090] Except for the preparation of the negative electrode sheet, in which the negative electrode active material artificial graphite, CVD silicon@porous carbon (porous carbon to silicon mass ratio 1:1), thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, conductive agent acetylene black, and conductive agent single-walled carbon nanotubes (SWCNT) are mixed in a mass ratio of 35.9:60:1:2:1:0.1, the rest is the same as in Examples 1-18. Based on the mass of the negative electrode active material, the silicon content is 30% by mass.

[0091] Examples 1-22 to Examples 1-27

[0092] Except for adjusting the type and mass percentage of the second component according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the solvent accordingly, and keeping the mass percentage of lithium salt unchanged, the rest is the same as in Example 1-1.

[0093] Examples 2-1 to 2-14

[0094] Except for the addition of a third component as shown in Table 2 in the <Preparation of Electrolyte>, and the adjustment of the type and mass percentage of the third component according to Table 2, the mass percentage of the solvent is changed accordingly, and the percentage of other components in the electrolyte remains unchanged, the rest is the same as in Examples 1-4.

[0095] Examples 3-1 to 3-3

[0096] Except for adjusting the type and mass percentage of the electrolyte according to Table 3 in the <Preparation of Electrolyte> section, changing the mass percentage of the solvent accordingly, and keeping the percentages of other components in the electrolyte unchanged, everything else is the same as in Examples 1-4. Specifically, based on the mass of the electrolyte, the electrolyte in Examples 3-3 consists of 6.5% lithium hexafluorophosphate and 6.5% lithium difluorosulfonylimide.

[0097] Examples 4-1 to 4-3

[0098] Except for adjusting the type of positive electrode active material according to Table 4 in <Preparation of Positive Electrode Sheet>, the rest is the same as in Examples 1-4.

[0099] The charge / discharge range for ternary materials is 3-4.2V; for lithium iron phosphate, it is 2.5-3.65V; and for lithium cobalt oxide, it is 3-4.4V.

[0100] Comparative Examples 1 to 4

[0101] Except that the first component is not added in the <Preparation of Electrolyte>, and the type and mass percentage of the second component are adjusted according to Table 1, the mass percentage of the solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0102] Comparative Examples 5 to 6

[0103] Except that the second component is not added in the <Preparation of Electrolyte>, and the mass percentage of the first component is adjusted according to Table 1, the mass percentage of the solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as in Example 1-1.

[0104] Comparative Example 7

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

[0106] Comparative Examples 8 to 12

[0107] Except for adjusting the mass percentage of the first component and the type and mass percentage of the second component according to Table 1 in the <Preparation of Electrolyte>, changing the mass percentage of the solvent accordingly, and keeping the mass percentage of the lithium salt unchanged, the rest is the same as in Example 1-1.

[0108] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0109] As can be seen from Examples 1-1 to 1-27 and Comparative Examples 1 to 12, when electrolytes without the first or second component, or with only the first or second component added, are applied to lithium-ion batteries, or when the contents of the first and second components are not within the scope of this application, the lithium-ion batteries exhibit lower room temperature cycle capacity retention, high temperature cycle capacity retention, high temperature storage capacity retention, and low temperature discharge capacity retention, as well as higher high temperature storage thickness expansion rate and low temperature DCIR. When electrolytes with both the first and second components added are applied to lithium-ion batteries, and the contents of the first and second components are controlled within the scope of this application, the lithium-ion batteries exhibit higher room temperature cycle capacity retention, high temperature cycle capacity retention, high temperature storage capacity retention, and low temperature discharge capacity retention, as well as lower high temperature storage thickness expansion rate and low temperature DCIR. The above results demonstrate that the combined use of the first and second components, with the contents of the first and second components limited to the scope of this application, allows the two components to work synergistically, improving the high temperature cycle performance, high temperature storage performance, low temperature discharge performance, and reducing impedance of the lithium-ion battery.

[0110] Examples 2-1 to 2-14 demonstrate that when an electrolyte containing the first, second, and third components is applied to a lithium-ion battery, the battery exhibits higher capacity retention rates at room temperature, high temperature, high temperature storage, and low temperature discharge, as well as lower high temperature storage thickness expansion and low temperature DCIR. These results indicate that the combined use of the first, second, and third components, with their contents limited to the scope of this application, allows the three components to work synergistically, further improving the high-temperature cycling performance, high-temperature storage performance, low-temperature discharge performance, and reducing impedance of the lithium-ion battery.

[0111] As can be seen from Examples 3-1 to 3-3, by selecting the electrolyte of this application and limiting its content to the scope of this application, the lithium-ion battery has a high room temperature cycle capacity retention rate, high temperature cycle capacity retention rate, high temperature storage capacity retention rate and low temperature discharge capacity retention rate, as well as a low high temperature storage thickness expansion rate and low temperature DCIR.

[0112] As can be seen from Examples 1-4 and Examples 4-1 to 4-3, the first component and the second component are used in combination, and the contents of the first component and the second component are limited to the scope of this application. The two components can play a good synergistic role in ternary battery systems, lithium iron phosphate battery systems, lithium cobalt oxide battery systems and lithium nickel manganese oxide battery systems, which can improve the high temperature cycle performance, high temperature storage performance, low temperature discharge performance and reduce impedance of lithium-ion batteries.

[0113] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0114] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte comprising a solvent, an electrolyte, and an additive, said additive comprising a first component and a second component; the first component being selected from fluoroethylene carbonate; the second component being selected from compounds represented by Formula I; in, R1 to R3 are each independently selected from unsubstituted or R-substituted products. a Replacement C1-C 10 Alkyl; Substituent R a Each is independently selected from fluorine, unsubstituted or fluorinated C6-C. 12 Aryl; Based on the mass of the electrolyte, the mass percentage of the first component is a, 5% ≤ a ≤ 20%, and the mass percentage of the second component is b, 0.1% ≤ b ≤ 2%.

2. The electrolyte according to claim 1, wherein, 6% ≤ a ≤ 10%, 0.3% ≤ b ≤ 1%.

3. The electrolyte according to claim 1 or 2, wherein, R1 to R3 are each independently selected from unsubstituted or R-substituted products. a Substituted C1-C6 alkyl groups; substituent R a Each is independently selected from fluorine, unsubstituted or fluorinated phenyl groups.

4. The electrolyte according to claim 1 or 2, wherein, The second component is selected from at least one of the following compounds; 5. The electrolyte according to any one of claims 1 to 4, wherein, The additive further includes a third component selected from at least one of vinylene carbonate, ethylene ethylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfite, tris(trimethylsilane)borate, tris(trimethylsilane)phosphate, and lithium difluorodioxane phosphate; based on the mass of the electrolyte, the mass percentage of the third component is c, 0.5% ≤ c ≤ 5%, preferably 0.5% ≤ c ≤ 2%.

6. The electrolyte according to any one of claims 1-5, wherein, The electrolyte is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium di(fluorooxalateborate); based on the mass of the electrolyte, the mass percentage of the electrolyte is d, 12% ≤ d ≤ 17%, preferably 12% ≤ d ≤ 15%.

7. The electrolyte according to any one of claims 1-6, wherein, The solvent is selected from at least two of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl 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; based on the mass of the electrolyte, the mass percentage of the solvent is e, 56% ≤ e ≤ 82%.

8. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte according to any one of claims 1 to 7.

9. The secondary battery according to claim 8, wherein, 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 includes a negative electrode active material, which contains silicon. Based on the mass of the negative electrode active material, the mass percentage of silicon is f, 5% ≤ f ≤ 30%, preferably 5% ≤ f ≤ 20%.

10. The secondary battery according to claim 9, wherein, In the electrolyte, the concentration of fluorine in the first component is F. a The concentration of fluorine in the second component is F. b 0.4 mol / L <F a +F b <2.6 mol / L; preferably, the secondary battery satisfies: 4 mol / L ≤ (F a +F b ) / f≤26mol / L.

Images