Electrolyte additive, electrolyte, secondary battery, and electronic apparatus

Abstract

An electrolyte additive, an electrolyte, a secondary battery, and an electronic apparatus. The electrolyte additive comprises a first component and a second component. The first component is selected from a compound represented by formula I, and the second component is selected from at least one of a compound represented by formula II, a compound represented by formula III, and a compound represented by formula IV. The synergistic effect of the first component and the second component can improve the high-temperature storage performance of the secondary battery and prolong the cycle life thereof.

Description

Electrolyte additive, electrolyte, secondary battery and electronic device

[0001] This application claims priority to the Chinese patent application No. 202411236441.1, filed on September 4, 2024, and entitled "Electrolyte additive, electrolyte, secondary battery and electronic device", 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 additive, an electrolyte, a secondary battery and an electronic device. BACKGROUND

[0003] Lithium ion batteries have high specific energy, large specific power and long cycle life, and have been widely used in consumer batteries and new energy vehicle power batteries. With the increasing requirements for endurance time, charging speed and application scenario adaptability, it is urgent to improve the fast charging cycle performance and stability of lithium ion batteries under high pressure and high temperature.

[0004] However, increasing the working voltage of lithium ion batteries usually has two major pain points: poor cycle performance and gas expansion. This is mainly due to the instability of the positive electrode material under high pressure, which easily causes structural phase transition, promoting the occurrence of oxygen evolution reaction and transition metal ion dissolution; leading to a decrease in electrolyte stability, accelerating the formation of carbon dioxide, ethylene and other gases, resulting in battery gas production. At the same time, the collapse of the positive electrode material structure hinders the diffusion of Li + , leading to increased impedance and capacity decay, and decreased battery cycle performance. The above processes will be even more serious under high temperature conditions, resulting in poor high temperature performance of the battery.

[0005] Therefore, it is of great significance to provide a solution that can improve the fast charging cycle and high temperature storage performance of lithium ion batteries. SUMMARY

[0006] The purpose of the present application is to provide an electrolyte additive, an electrolyte, a secondary battery and an electronic device to improve the high temperature storage performance and cycle life of the secondary battery. The specific technical solutions are as follows:

[0007] The first aspect of the present application provides an electrolyte additive comprising a first component and a second component;

[0008] The first component is selected from the compound shown in Formula I;

[0009] The second component is selected from at least one of the compound shown in Formula II, the compound shown in Formula III and the compound shown in Formula IV;

[0010] wherein R1and R2are each independently selected from fluorine or C1-C5alkyl substituted with fluorine;

[0011] R3is selected from hydrogen, C1-C6alkyl, C6-C 18 aryl, X is selected from n is selected from 0 or 1; each of the compound shown as formula II, the compound shown as formula III or the compound shown as formula IV independently contains at least one S atom;

[0012] The mass ratio of the first component and the second component is (0.01-60):1, preferably (0.05-20):1.

[0013] In an embodiment of the present application, the R3is selected from hydrogen, C1-C3alkyl, phenyl,

[0014] In an embodiment of the present application, the first component is selected from at least one of the following compounds:

[0015] In an embodiment of the present application, the second component is selected from at least one of the following compounds:

[0016] A second aspect of the present application provides an electrolyte solution, which comprises the electrolyte additive of the first aspect of the present application; the sum of the mass percentage content of the first component and the second component is (A+B)%, 0.1≤A+B≤6, based on the mass of the electrolyte solution.

[0017] In an embodiment of the present application, the mass percentage content of the first component is A%, 0.1≤A≤2, and the mass percentage content of the second component is B%, 0.1≤B≤2, based on the mass of the electrolyte solution.

[0018] In an embodiment of the present application, the electrolyte solution further comprises a lithium salt, which is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis-trifluoromethylsulfonylimide, lithium bis-fluorosulfonylimide, lithium monofluorosulfonate and lithium trifluoromethylsulfonate; the mass percentage content of the lithium salt is C%, 10≤C≤15, based on the mass of the electrolyte solution.

[0019] A third aspect of the present application provides a secondary battery, which comprises the electrolyte solution of the second aspect of the present application.

[0020] In an embodiment of the present application, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, the Dv50 of the negative electrode active material used by the negative electrode sheet is D μm, 10≤D≤20; X=D / (A+B), the X satisfies 1.66≤X≤100.

[0021] In an embodiment of the present application, 2.5≤X≤66.67.

[0022] A fourth aspect of the present application provides an electronic device comprising the secondary battery of the third aspect of the present application.

[0023] Advantages of the present application:

[0024] The present application provides an electrolyte additive, an electrolyte, a secondary battery, and an electronic device. The electrolyte additive comprises a first component and a second component, wherein the second component and the carbonate solvent, Li + form a four-coordination compound, can stabilize the carbonate solvent, and reduce the decomposition of the carbonate solvent to produce carbon dioxide, olefin, carbon monoxide, and other gases during high-temperature storage; at the same time, the decomposition products of the second component in the film formation process can undergo a free radical reaction with the decomposition products of the first component, blocking the negative effects of the decomposition products of the first component on the electrolyte and the positive electrode; at the same time, it can also jointly construct an electrode-electrolyte interface film rich in LiF, Li3N, Li2SO4, lithium alkyl sulfate, and other substances, improve the cycle life of the secondary battery under high-voltage conditions, and has good cycle life under large-rate charging and discharging. The electrolyte additive of the present application comprises the first component and the second component, and the mass ratio of the first component and the second component is limited within the scope of the present application. The synergistic effect of the first component and the second component can improve the high-temperature storage performance and cycle life of the secondary battery.

[0025] Of course, implementing any product or method of the present application does not necessarily require achieving all the advantages described above at the same time. DETAILED DESCRIPTION

[0026] To make the purpose, technical solutions, and advantages of the present application clearer and more apparent, the following examples are given to further illustrate the present application. Obviously, the described examples are only a part of the examples of the present application, not all examples. All other examples obtained by those skilled in the art based on the present application are within the scope of protection of the present application.

[0027] A first aspect of the present application provides an electrolyte additive comprising a first component and a second component;

[0028] The first component is selected from the compounds shown in Formula I;

[0029] The second component is selected from at least one of a compound shown in Formula II, a compound shown in Formula III and a compound shown in Formula IV;

[0030] wherein R1 and R2 are each independently selected from fluorine or C1-C5 alkyl substituted by fluorine;

[0031] R3 is selected from hydrogen, C1-C6 alkyl, C6-C 18 aryl, X is selected from n is selected from 0 or 1; each of the compound shown in Formula II, the compound shown in Formula III or the compound shown in Formula IV independently contains at least one S atom;

[0032] The mass ratio of the first component and the second component is (0.01-60):1, preferably (0.05-20):1. For example, the mass ratio of the first component and the second component can be 0.01:1, 0.03:1, 0.05:1, 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 60:1 or a range composed of any two of the above values. The inventors have found that when the mass ratio of the first component additive and the second component additive is higher than 60:1, the content of the compound of the second component is too low to inhibit the negative effects brought by the decomposition product B of the compound of Formula I, and ultimately the high-temperature storage stability of the lithium battery cannot be guaranteed; and when the mass ratio of the first component additive and the second component additive is lower than 0.01:1, the content of the compound of Formula I is too low, the content of the inorganic type film component formed is reduced, the electron insulation at the negative electrode interface is reduced, and the improvement of the fast charging cycle performance is insufficient.

[0033] The first component additive of the present application contains abundant F and S elements, which can construct a stable, high-ionic-conductivity SEI (Solid electrolyte Interface) / CEI (Chemical-electrochemical Interface) interface film on the surface of the negative electrode and the positive electrode, effectively reduce the decomposition of the electrolyte lithium salt during the cycle process, and thus improve the cycle performance and low-temperature discharge performance of the lithium secondary battery. However, the use of the first component additive alone in the electrolyte cannot solve the problems of battery swelling and low capacity retention rate of the secondary battery during high-temperature storage. The main reasons are as follows:

[0034] During the formation and cycle of the secondary battery, the reduction decomposition process of the first component after being attacked by electrons is as follows:

[0035] wherein R1and R2are each independently selected from fluorine or C1-C5 alkyl substituted by fluorine; wherein the decomposition product A has strong electron-donating ability, specifically the lone electron on the N atom, and the decomposition product A can be free in the electrolyte, attack the carbonate solvent in the electrolyte to cause the decomposition of the solvent to produce carbon dioxide, olefin, carbon monoxide and other gases, and when the ambient temperature rises, the process becomes violent, thereby causing the secondary battery to produce more gas. In addition, the decomposition product B is a relatively unstable "transition state" structure, which is prone to decomposition again under high temperature conditions to form F - hydrofluoric acid is formed in the electrolyte, which further corrodes the positive active material, causing ion leaching and structural damage of the positive active material, thereby causing the self-discharge of the electrode sheet to intensify, ultimately leading to the decline of the high-temperature storage performance of the secondary battery.

[0036] Further, the electrolyte additive of the present application also comprises a second component, which can react with the carbonate solvent, Li + to form a four-coordinated compound: the second component obtains electrons during formation, undergoes ring-opening reaction, and the S=O and C-O in the ring-opening reaction product can preferentially form a two / three-coordinated compound with Li + , and then weakly interact with the C=O bond in the carbonate solvent to form a four-coordinated compound. Therefore, the carbonate solvent can be stabilized, and the decomposition of the carbonate solvent to produce carbon dioxide, olefin, carbon monoxide and other gases during high-temperature storage can be reduced. At the same time, the decomposition product A of the first component during film formation can react with the ring-opening decomposition product of the second component to block the negative effects of the decomposition product A of the first component on the electrolyte; in addition, it can also jointly build an electrode-electrolyte interface film rich in LiF, Li3N, Li2SO4, lithium alkyl sulfate and other substances, which not only can inhibit the negative effects of the decomposition product B in the first component on the positive electrode, but also can improve the cycle life and storage performance of the secondary battery under high temperature conditions.

[0037] In summary, the electrolyte additive of the present application comprises a first component and a second component, and the mass ratio of the first component to the second component is limited within the scope of the present application, and the synergistic effect of the two components can improve the high-temperature storage performance and cycle life of the secondary battery.

[0038] In an embodiment of the present application, R3is selected from hydrogen, C1-C3 alkyl, phenyl,

[0039] The electrolyte comprising the above-mentioned second component can be applied to a secondary battery, which can have higher high-temperature storage performance and cycle life without affecting other performances.

[0040] In an embodiment of the present application, the first component is selected from at least one of the following compounds:

[0041] The electrolyte comprising the above-mentioned first component is applied to a secondary battery, which can have higher high-temperature storage performance and cycle life without affecting other performances.

[0042] In an embodiment of the present application, the second component is selected from at least one of the following compounds:

[0043] The electrolyte comprising the above-mentioned second component is applied to a secondary battery, which can further have higher high-temperature storage performance and cycle life without affecting other performances.

[0044] The method for preparing the additive of the present application is not particularly limited as long as the object of the present application is achieved. For example, the two components can be directly mixed. The method for preparing the compounds used in the present application is not particularly limited, and can be prepared by a method known in the art or directly purchased on the market.

[0045] A second aspect of the present application provides an electrolyte comprising the electrolyte additive of the first aspect of the present application; the sum of the mass percentage contents of the first component and the second component is (A+B)%, 0.1≤A+B≤6, based on the mass of the electrolyte. For example, A+B can be 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range between any two of them. The inventors have found that when A+B is less than 0.1, the electronic insulation of the interface cannot be sufficiently controlled, resulting in poor cycle performance; and when A+B exceeds 6, the inorganic interface film formed has too many components, resulting in blocked lithium ion transport, which in turn affects the cycle performance of the secondary battery. In summary, the amount of A+B in the above range can make the secondary battery have higher high-temperature storage performance and cycle life without affecting other performances.

[0046] In an embodiment of the present application, the mass percentage content of the first component is A%, 0.1≤A≤2, and the mass percentage content of the second component is B%, 0.1≤B≤2, based on the mass of the electrolyte. For example, A can be 0.1, 0.5, 1, 1.5, 2, or a range between any two of them; for example, B can be 0.1, 0.5, 1, 1.5, 2, or a range between any two of them. The contents of the first component and the second component in the above range can further make the secondary battery have higher high-temperature storage performance and cycle life without affecting other performances.

[0047] In an embodiment of the present application, the electrolyte further comprises a lithium salt, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis-trifluoromethylsulfonylimide, lithium bisfluorosulfonylimide, lithium monofluorosulfonate and lithium trifluoromethylsulfonate; the mass percentage of the lithium salt in the electrolyte is C%, 10≤C≤15, for example, C can be 10, 11, 12, 13, 14, 15 or a range between any two of them. Adding the above lithium salt and its content in the above range to the electrolyte can better form a four-coordinated compound with the second component, the carbonate-based solvent, stabilize the carbonate-based solvent, reduce the decomposition of the carbonate-based solvent to produce carbon dioxide, olefin, carbon monoxide and other gases during high-temperature storage, and jointly build an electrode-electrolyte interface film rich in LiF, Li3N, Li2SO4, lithium alkyl sulfate and other substances, thereby improving the cycle life of the secondary battery under high pressure conditions.

[0048] In an embodiment of the present application, the electrolyte further comprises a non-aqueous solvent, which is not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, the non-aqueous solvent can be selected from, but not limited to, at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, vinylene carbonate, methyl formate, ethyl formate, methyl acetate, ethyl acetate, ethyl propionate, ethyl butyrate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, cyclobutane sulfone and dimethyl sulfone.

[0049] The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the mass percentage of the non-aqueous solvent in the electrolyte is 79% to 89%, for example, the mass percentage of the non-aqueous solvent in the electrolyte can be 79%, 81%, 83%, 85%, 87%, 89% or a range between any two of them.

[0050] 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, the various solvents in the electrolyte can be mixed, and then the electrolyte lithium salt and additives and other substances are added and mixed uniformly.

[0051] The third aspect of the present application provides a secondary battery comprising the electrolyte of the second aspect of the present application.

[0052] In an embodiment of the present application, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, and a separator, the negative electrode sheet adopts a negative electrode active material with a Dv50 of D μm, 10≤D≤20; X=D / (A+B), A+B is the sum of the mass percentage of the first component and the second component in the electrolyte, X satisfies 1.66≤X≤100, preferably, 2.5≤X≤66.67. For example, X can be 1.66, 2.0, 2.5, 10, 20, 30, 45, 55, 60, 66.67 or a range between any two of them. The inventors have found that the additive of the first aspect of the present application can be preferentially reduced and decomposed to form an electrode-electrolyte interface film rich in inorganic components such as LiF, Li3N, Li2SO4 on the surface of the negative electrode, which can increase the electronic insulation of the negative electrode interface, thereby inhibiting the electron tunneling effect of the negative electrode, reducing the electrolyte side reaction caused by the electron tunneling effect in the early and middle stages of the cycle, reducing the consumption of electrolyte, and thereby enhancing the stability of the battery in the later stage of the cycle. At the same time, by adjusting the Dv50 of the negative electrode active material, the specific surface area of the negative electrode active material can be increased, and when the relationship 1.66≤X≤100 is satisfied, the electrolyte and the negative electrode active material can be more fully contacted during the formation stage of the battery, the additive of the first aspect of the present application can be more fully reduced and decomposed, and an inorganic interface film component that can inhibit the electron tunneling effect can be formed, thereby enhancing the cycle performance of the lithium battery.

[0053] In the detailed description of the present application, the lithium ion battery is taken as an example of the secondary battery to explain the present application. The specific technical solutions are as follows:

[0054] The conductive agent is not particularly limited in the present application as long as it can achieve the purpose of the present application, for example, the conductive agent can be selected from, but not limited to, at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0055] The binder is not particularly limited in the present application as long as it can achieve the purpose of the present application, for example, the binder can be selected from, but 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), carboxymethyl chitosan (CMCS), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0056] In the present application, the secondary battery further comprises a positive electrode tab, and the positive electrode tab comprises a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The "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" herein 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, and the present application does not have a particular limitation, as long as the purpose of the present application can be achieved.

[0057] 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 adopt a metal foil or a composite current collector. For example, as a metal foil, an aluminum foil or an aluminum alloy foil can be used. The composite current collector can comprise 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 (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0058] The positive electrode material layer comprises 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, NCM613, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate and lithium iron manganese phosphate.

[0059] Further, when the cut-off voltage of the secondary battery is 4.25 V or higher, the additive matching the present application can significantly reduce the initial DCR of the lithium ion battery, enhance the fast charging cycle performance at room temperature, and also have excellent high-temperature storage performance and excellent high-temperature stability, which can significantly reduce the battery expansion during high-temperature storage.

[0060] The positive electrode material layer can further comprise a conductive agent and a binder, and the present application does not have a particular limitation on the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved, for example, it can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The present application does not have a particular limitation on the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode material layer, and a person skilled in the art can select according to the actual needs, as long as the purpose of the present application can be achieved.

[0061] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 15 to 20 pm, and the thickness of the single-sided positive electrode material layer is 40 to 50 pm.

[0062] 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 conductive layer commonly used 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, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder.

[0063] The method for preparing the positive electrode tab is not particularly limited in the present application, as long as the object 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 proportion, N-methyl pyrrolidone (NMP) is added and stirred uniformly to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on one surface of the positive electrode current collector, and after drying, a positive electrode tab with a single-sided positive electrode material layer is obtained. Then repeat the above coating step on the other surface of the positive electrode current collector, and after drying, a positive electrode tab with a double-sided positive electrode material layer is obtained. After the coating is completed, the positive electrode tab is obtained by cold pressing and cutting.

[0064] In the present application, the secondary battery further includes a separator. The separator is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the material of the separator can be selected from, but not limited to, at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The number of layers of the separator is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the separator can be a single-layer film or a multi-layer composite film.

[0065] In some embodiments of the present application, the separator can include a substrate layer and a surface treatment layer. The substrate layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the substrate layer can be selected from, but not limited to, at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

[0066] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the surface treatment layer can be selected from, but not limited to, at least one of high-purity aluminum oxide and boehmite.

[0067] In the present application, the thickness of the separator is not particularly limited, as long as the object of the present application can be achieved, for example, the thickness of the separator can be 5 to 20 pm.

[0068] In the present application, the secondary battery further includes a negative electrode tab including 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 provided on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be provided on one surface of the negative electrode current collector in the thickness direction of the negative electrode current collector, or can be provided on both surfaces of the negative electrode current collector in 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 a partial area of the surface of the negative electrode current collector, and the present application does not have a particular limitation as long as the purpose of the present application can be achieved.

[0069] 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 the metal foil, a copper foil or an aluminum alloy foil 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.).

[0070] The negative electrode material layer includes a negative electrode active material, and the negative electrode active material 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 active material can be selected from, but not limited to, at least one of artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon-based material, tin-based material, and lithium titanate. The silicon-based material can be selected from at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can be selected from at least one of elemental tin, tin oxide compound, and tin alloy.

[0071] In some embodiments of the present application, the negative electrode material layer can further include a conductive agent and a binder, and the types of the conductive agent and the binder are not particularly limited in the present application as long as the purpose of the present application can be achieved, for example, can be at least one of the above-mentioned conductive agent and the above-mentioned binder. The mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer is not particularly limited in the present application, 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.

[0072] The thickness of the negative electrode material layer 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 40 μm to 60 μm.

[0073] The thickness of 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 negative electrode current collector is 5 μm to 15 μm.

[0074] In some embodiments of the present application, the negative material layer can further include a conductive agent, a binder, and a thickening agent. The present application does not have a particular limitation on the types of the conductive agent and the binder as long as the purpose of the present application can be achieved. For example, the conductive agent and the binder can be at least one of the above-mentioned conductive agents and the above-mentioned binders. 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.

[0075] 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 agents and the above-mentioned binders.

[0076] The present application does not have a particular limitation on the preparation method of the negative electrode sheet as long as the purpose of the present application can be achieved. For example, the negative active material, the conductive agent, the thickening agent, and the binder can be mixed in a certain proportion, deionized water is added and stirred uniformly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on one surface of the negative current collector, and after drying, a negative electrode sheet with a single-side coated negative material layer is obtained. Then the above coating step is repeated on the other surface of the negative current collector, and after drying, a negative electrode sheet with a double-side coated negative material layer is obtained. After the coating is completed, the negative electrode sheet is obtained by cold pressing and cutting.

[0077] The secondary battery further includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries. The present application does not limit the above-mentioned other components. The present application does not have a particular limitation on the shell, which can be a shell known in the art as long as the purpose of the present application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and the present application does not limit the type of metal, which can use a metal hard shell known in the art as long as the purpose of the present application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0078] 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, etc. as needed to obtain an electrode assembly of a wound structure, placing the electrode assembly into the case, injecting the electrolyte 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 of a stack structure, the electrode assembly is placed into the case, the electrolyte is injected into the case and sealed to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the case as needed, thereby preventing the pressure rise in the secondary battery.

[0079] The fourth aspect of the present application provides an electronic device comprising the secondary battery of the third aspect of the present application. The secondary battery provided by the third aspect of the present application has good high-temperature storage performance, so that the electronic device of the present application has a longer service life.

[0080] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery or a lithium ion capacitor, etc.

[0081] Embodiments

[0082] Hereinafter, embodiments and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations were carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are on a mass basis.

[0083] Example 1

[0084] <Preparation of electrolyte>

[0085] In an argon atmosphere glove box with water content <10 ppm, oxygen content <1 ppm, add non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate in a mass ratio of 3:5:2 to mix uniformly, then add the first component compound of formula I-1 and the second component compound of formula II-5 to mix uniformly, and then add lithium salt lithium hexafluorophosphate, dissolve and mix uniformly to obtain an electrolyte; wherein, based on the mass of the electrolyte, the mass percentage of lithium salt lithium hexafluorophosphate is 12.5%, the mass percentage of the first component compound of formula I-1 is A% 0.05%, the mass percentage of the second component compound of formula II-1 is B% 3%, and the balance is non-aqueous organic solvent 84.45%.

[0086] <Preparation of positive electrode sheet>

[0087] The positive electrode active material LiNi 0.6 Co 0.1 Mn 0.3 O2, a binder polyvinylidene fluoride (PVDF), and a conductive agent carbon black are mixed in a mass ratio of 97:1.2:1.8, N-methyl pyrrolidone (NMP) is added as a solvent, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity, and the solid content of the positive electrode slurry is 0.65 wt%; the positive electrode slurry is uniformly coated on one surface of a positive current collector aluminum foil with a thickness of 18 μm, and the coating amount is 2.5 g / m 2 , and dried at 85°C to obtain a positive electrode sheet with a single positive electrode material layer; then the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double positive electrode material layer; after drying at 85°C, cold pressing, edge cutting, sheet cutting, and striping are performed, the strips are dried at 85°C under vacuum for 4 hours, and the tabs are welded to obtain a positive electrode sheet with a size of 258 mm x 200 mm for use; wherein the thickness of the single positive electrode material layer is 45 μm.

[0088] <Preparation of negative electrode sheet>

[0089] The negative electrode active material artificial graphite (Dv50 is 12.1 μm) is mixed with a conductive agent carbon black, a thickening agent sodium carboxymethyl cellulose (CMC), and a binder styrene-butadiene rubber (SBR) in a mass ratio of 95.8:1.2:1.5:1.5, deionized water is added, and a negative electrode slurry with a solid content of 50 wt% is obtained under the action of a vacuum stirrer; the negative electrode slurry is uniformly coated on one surface of a negative current collector copper foil with a thickness of 8 μm, and the coating amount is 1.5 g / m 2The negative electrode material layer is dried at 85°C to obtain a single-side coated negative electrode sheet; then the above steps are repeated on the other surface of the copper foil to obtain a double-side coated negative electrode sheet; after drying at 85°C, cold pressing, edge cutting, sheet cutting, and strip dividing are performed, and after strip dividing, the sheet is dried at 85°C under vacuum for 4 hours, and the tab is welded to obtain a negative electrode sheet with a size of 260 mm x 198 mm for use; wherein the thickness of the single-side negative electrode material layer is 50 μm.

[0090] <Preparation of the separator>

[0091] A double-layer PP ceramic separator with a thickness of 16 μm is used.

[0092] <Preparation of the lithium ion battery>

[0093] The above-prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, then wound, the positive tab is connected to the positive electrode sheet, and the negative tab is connected to the negative electrode sheet to obtain an electrode assembly. The electrode assembly is placed in an aluminum foil packaging bag, and the positive tab and the negative tab are led out from the inside space of the aluminum foil packaging bag to the outside space of the aluminum foil packaging bag, water is removed at 80°C, the above-prepared electrolyte is injected, the injection coefficient is 3.0 g / Ah, and the lithium ion battery is obtained after vacuum packaging, formation, aging, and capacity distribution processes. The upper limit voltage of the formation is 4.4 V, the formation temperature is 45°C, the formation standing time is 24 h; the aging temperature is 45°C, the aging standing time is 24 h; the capacity distribution is 0.2 C charged to 4.4 V, left for 5 minutes, then discharged to 3.0 V at 0.2 C, and then the above steps are repeated at 0.5 C and 1 C.

[0094] Examples 2 to 42

[0095] The rest is the same as Example 1, except that in the preparation of the electrolyte, the types and mass percentages of the first component and the second component in Table 1 are adjusted, the mass percentage of the non-aqueous organic solvent changes accordingly, and the mass percentage of the lithium salt remains unchanged. In Example 35, the first component consists of a compound of formula I-1 and a compound of formula I-2 in a mass ratio of 1:1, and the second component consists of a compound of formula II-1 and a compound of formula III-1 in a mass ratio of 1:1; in Example 36, the first component consists of a compound of formula I-1 and a compound of formula I-3 in a mass ratio of 1:1, and the second component consists of a compound of formula II-2 and a compound of formula III-1 in a mass ratio of 1:1; in Example 37, the first component consists of a compound of formula I-2 and a compound of formula I-4 in a mass ratio of 1:1, and the second component consists of a compound of formula II-3 and a compound of formula IV-1 in a mass ratio of 1:1; in Example 38, the first component consists of a compound of formula I-1 and a compound of formula I-2 in a mass ratio of 1:1, and the second component consists of a compound of formula II-1 and a compound of formula II-5 in a mass ratio of 1:1; in Example 39, the first component consists of a compound of formula I-1 and a compound of formula I-2 in a mass ratio of 1:1, and the second component consists of a compound of formula II-5 and a compound of formula III-1 in a mass ratio of 1:1; in Example 40, the first component consists of a compound of formula I-1 and a compound of formula I-5 in a mass ratio of 1:1, and the second component consists of a compound of formula II-5 and a compound of formula IV-1 in a mass ratio of 1:1.

[0096] Example 43

[0097] Preparation of the electrolyte

[0098] In an argon glove box with water content <10 ppm and oxygen content <1 ppm, non-aqueous organic solvents ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate were mixed in a mass ratio of 3:5:2, then the first component compound of formula I-1 and the second component compound of formula II-5, and vinylene carbonate (VC) were mixed uniformly, and then lithium salt lithium hexafluorophosphate was added, dissolved and mixed uniformly to obtain the electrolyte; wherein the mass percentage of lithium salt lithium hexafluorophosphate was 12.5% based on the mass of the electrolyte, the mass percentage of the first component compound of formula I-1 was A 0.5%, the mass percentage of the second component compound of formula II-1 was B 1.5%, the mass percentage of vinylene carbonate (VC) was 2%, and the rest was non-aqueous organic solvent.

[0099] Preparation of the positive electrode sheet

[0100] In the preparation of the positive electrode sheet, the rest is the same as Example 1, except that the positive active material is lithium iron phosphate.

[0101] The <preparation of negative electrode sheet>, <preparation of separator>, and <preparation of lithium ion battery> are the same as in Example 1.

[0102] Examples 44 to 45

[0103] The rest is the same as in Example 43 except that the kind of the second component and the kind of the lithium salt are adjusted according to Table 1. The lithium salt of Example 45 consists of 10.0% of lithium hexafluorophosphate and 2.5% of lithium bisfluorosulfonylimide, based on the mass of the electrolyte.

[0104] Examples 46 to 49

[0105] The rest is the same as in Example 27 except that the kind and amount of the lithium salt are adjusted according to Table 1 in the <preparation of electrolyte>. Among them, the lithium salt of Example 48 consists of 12.5% of lithium hexafluorophosphate and 0.5% of lithium difluorophosphate, based on the mass of the electrolyte; and the lithium salt of Example 49 consists of 12.5% of lithium hexafluorophosphate and 0.5% of lithium trifluoromethylsulfonate.

[0106] Comparative Example 1

[0107] The rest is the same as in Example 1 except that the first component and the second component are not added in the <preparation of electrolyte>, the mass percentage content of the non-aqueous organic solvent is changed accordingly, and the mass percentage content of the lithium salt is unchanged.

[0108] Comparative Examples 2 to 3

[0109] The rest is the same as in Example 1 except that the second component is not added in the <preparation of electrolyte>, the kind and mass percentage content of the first component are adjusted according to Table 1, the mass percentage content of the non-aqueous organic solvent is changed accordingly, and the mass percentage content of the lithium salt is unchanged.

[0110] Comparative Examples 4 to 5

[0111] The rest is the same as in Example 1 except that the first component is not added in the <preparation of electrolyte>, the kind and mass percentage content of the second component are adjusted according to Table 1, the mass percentage content of the non-aqueous organic solvent is changed accordingly, and the mass percentage content of the lithium salt is unchanged.

[0112] Comparative Examples 6 to 7

[0113] The rest is the same as in Example 1 except that the kind and mass percentage content of the first component and the second component are adjusted according to Table 1 in the <preparation of electrolyte>, the mass percentage content of the non-aqueous organic solvent is changed accordingly, and the mass percentage content of the lithium salt is unchanged.

[0114] Examples 2-1 to 2-14

[0115] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1.

[0116] The preparation parameters and performance parameters of each example and comparative example are shown in Table 1.

[0117] Test methods and equipment:

[0118] Ternary battery system test:

[0119] Normal temperature cycle performance test

[0120] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes to reach a constant temperature. The lithium ion battery was charged at 3.0C constant current to 4.4V, then charged at constant voltage to the cutoff current of 0.05C, and allowed to stand for 30 minutes. The lithium ion battery was discharged at 1.0C constant current to 3.0V, and the discharge capacity C0was recorded. The above steps were repeated until the capacity decayed to 80% C0, and the cycle number was recorded, i.e. the normal temperature cycle number.

[0121] High temperature stability test

[0122] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes to reach a constant temperature. The lithium ion battery was charged at 3.0C constant current to 4.4V, then charged at constant voltage to the cutoff current of 0.05C, and allowed to stand for 30 minutes. The lithium ion battery was discharged at 1.0C constant current to 3.0V, and the discharge capacity C0was recorded. The above steps were repeated until the capacity decayed to 80% C0, and the cycle number was recorded, i.e. the normal temperature cycle number.

[0123] Initial direct current resistance (DCR) test

[0124] The lithium ion battery was placed in a 25°C constant temperature test box and allowed to stand for 30 minutes, then the lithium ion battery was charged at 1.0C constant current to a voltage of 4.4V, then discharged at 1.0C constant current for 30 minutes, then discharged at a current I1corresponding to a rate of 2.0C for 10s, and the corresponding voltage V1was recorded. The direct current resistance (DCR) of the lithium ion battery at 50% state of charge (SOC), i.e. the initial DCR = V1 / I1, is in mΩ.

[0125] Lithium iron phosphate battery system test:

[0126] Normal temperature cycle performance test

[0127] The lithium ion battery was placed in a 25°C constant temperature test box and rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to 3.65V at 3.0C constant current, then charged to 0.05C cutoff current at constant voltage, rested for 30 minutes, and discharged to 2.0V at 1.0C constant current. The discharge capacity C0was recorded. This step was repeated until the capacity decayed to 80% C0, and the cycle number was recorded, i.e., the normal temperature cycle number.

[0128] High temperature stability test

[0129] The lithium ion battery was placed in a 25°C constant temperature test box and rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to 3.65V at 1.0C constant current, then charged to 0.05C cutoff current at constant voltage, rested for 10 minutes, and discharged to 2.0V at 1.0C constant current. The discharge capacity C2was recorded. The lithium ion battery was removed and its initial thickness T1was tested using a thickness tester. The lithium ion battery was again placed in a 25°C constant temperature test box and rested for 30 minutes to allow the lithium ion battery to reach a constant temperature. It was charged to 4.4V at 1.0C constant current, then charged to 0.05C cutoff current at constant voltage, and then transferred to 60°C for 30 days. The thickness of the lithium ion battery after 15 days of storage was tested using a thickness tester, and was T2. It was then discharged to 3.0V at 1.0C constant current, and the discharge capacity C3was recorded. The high temperature storage capacity retention rate after 30 days at 60°C was C3 / C2x 100%, and the high temperature storage battery expansion rate was 100% x (T2-T1) / T1.

[0130] Initial direct current resistance (DCR) test

[0131] The lithium ion battery was placed in a 25°C constant temperature test box and rested for 30 minutes, then charged to a voltage of 3.65V at 1.0C constant current, then discharged at 1.0C constant current for 30 minutes and rested for 1h, then discharged at a current I1corresponding to a rate of 2.0C for 10s, and the corresponding voltage V1was recorded. The direct current resistance (DCR) of the lithium ion battery at 50% state of charge (SOC), i.e., the initial DCR, was V1 / I1, and the unit was mΩ.

[0132] As can be seen from Examples 1 to 42 and Comparative Examples 1 to 7, when the electrolyte without the first component and the second component, or only the first component or the second component, or the mass ratio of the first component to the second component is not within the range of the present application is applied to the lithium ion battery, the lithium ion battery has a high initial DCR and high-temperature storage battery swelling rate, and a low number of cycles at room temperature and a high-temperature storage capacity retention rate. When the electrolyte with the first component and the second component is applied to the lithium ion battery, and the mass ratio of the first component to the second component is limited within the range of the present application, the lithium ion battery has a low initial DCR and high-temperature storage battery swelling rate, and a high number of cycles at room temperature and a high-temperature storage capacity retention rate. The above results show that the combination of the first component and the second component, and the limitation of the mass ratio of the first component to the second component within the range of the present application can improve the high-temperature storage performance and cycle life of the lithium ion battery.

[0133] As can be seen from Examples 43 to 45, the electrolyte within the range of the present application applied to the lithium iron phosphate positive electrode battery system can play a good synergistic effect, which can further reduce the initial DCR and high-temperature storage battery swelling rate of the lithium ion battery, and greatly improve the number of cycles at room temperature and the high-temperature storage capacity retention rate.

[0134] As can be seen from Examples 46 to 49, when the type and mass percentage of lithium salt are within the range of the present application, the lithium ion battery has a low initial DCR and high-temperature storage battery swelling rate, and a high number of cycles at room temperature and a high-temperature storage capacity retention rate.

[0135] The cycle performance of the battery is jointly affected by the Dv50 of the additive and the negative electrode active material. When the Dv50 is small, the higher the content of the additive, the more fully the interface film rich in inorganic components can be formed during the formation stage, but it will cause the transmission of lithium ions on the interface film to be slow. As can be seen from Examples 2-1 to 2-14, when the sum of the mass percentages of the first component and the second component and the Dv50 of the negative electrode active material satisfy the formula within the range of the present application, the obtained lithium ion battery has a low initial DCR and high-temperature storage battery swelling rate, and a high number of cycles at room temperature and a high-temperature storage capacity retention rate.

[0136] It is to be noted that, as used in this specification and the appended claims, the singular forms "a," "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a component" can include a combination of two or more components, and the term "an element" can include comparable reference items. Similarly, the terms "comprise", "comprises", "comprising" or any variation 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 also include other elements not expressly listed or inherent to such process, method, article, or apparatus. The above description is merely that of the preferred embodiments of the application and is not intended to limit the application thereto. Therefore, modifications, equivalents, improvements, and the like, made in the application, are intended to be included in the scope of the application.

[0137] Any modification, equivalent replacement, improvement, etc. made in the application shall be included in the scope of protection of the application.

Claims

1. An electrolyte additive, comprising a first component and a second component; said first component is selected from the group consisting of compounds of formula I; The second component is selected from at least one of a compound of Formula II, a compound of Formula III, and a compound of Formula IV; wherein R1and R2are each independently selected from fluorine or C1-C5alkyl substituted by fluorine; R3is selected from hydrogen, Ci-C6alkyl, C6-Ci0aryl, 18 aryl, X is selected from n is selected from 0 or 1;each of the compound shown in formula II, the compound shown in formula III or the compound shown in formula IV independently contains at least one S atom; The mass ratio of the first component and the second component is (0.01-60) :

1.

2. The electrolyte additive according to claim 1, wherein, The mass ratio of the first component and the second component is (0.05-20) :

1.

3. The electrolyte additive according to claim 1, wherein, R3is selected from hydrogen, C1-C3alkyl, phenyl, 4. The electrolyte additive according to claim 1, wherein, The first component is selected from at least one of the following compounds; 5. The electrolyte additive according to claim 1, wherein, The second component is selected from at least one of the following compounds: 6.An electrolyte, comprising the electrolyte additive according to any one of claims 1 to 5;the mass percentage content of the first component and the second component is (A + B) %, 0.1 ≤ A + B ≤ 6, based on the mass of the electrolyte.

7. The electrolyte of claim 6, wherein, The mass percentage content of the first component is A %, 0.1 ≤ A ≤ 2, and the mass percentage content of the second component is B %, 0.1 ≤ B ≤ 2, based on the mass of the electrolyte.

8. The electrolyte of claim 6, wherein, The electrolyte further comprises a lithium salt, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium bis-trifluoromethylsulfonylimide, lithium bis-fluorosulfonylimide, lithium monofluorosulfonate and lithium trifluoromethylsulfonate;the mass percentage content of the lithium salt is C %, 10 ≤ C ≤ 15, based on the mass of the electrolyte. 9.A secondary battery, comprising the electrolyte according to any one of claims 6 to 8.

10. The secondary battery according to claim 9, wherein The secondary battery comprises a positive electrode sheet, a negative electrode sheet and a separator, the Dv50 of the negative electrode active material used by the negative electrode sheet is D μm, 10 ≤ D ≤ 20;X = D / (A + B), the X satisfies 1.66 ≤ X ≤ 100.

11. The secondary battery according to claim 10, wherein 2.5≤X≤66.67。 12.An electronic device, comprising the secondary battery according to any one of claims 9 to 11.

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