Electrolyte and electrochemical device including the same

Abstract

The invention provides an electrolyte and an electrochemical device comprising the electrolyte. The electrolyte comprises a compound as shown in a formula I and a polynitrile compound, in the formula, R1, R2, R3 and R4 are independently selected from any one of a fluorine atom, a difluorophosphoryloxy group, a methanesulfonic acid group and a trifluoromethanesulfonic acid group respectively, and R1, R2, R3 and R4 are independently selected from any one of a fluorine atom, a difluorophosphoryloxy group, a methanesulfonic acid group and a trifluoromethanesulfonic acid group; based on the total mass of the electrolyte, the mass percentage of the compound shown in the formula I is A, the mass percentage of the polynitrile compound is B, and A is larger than or equal to 0.01% and smaller than or equal to 10%; a / B satisfies 0.02 < = A / B < = 50. According to the invention, the compound shown in the formula I and the multi-nitrile compound are added into the electrolyte at the same time for synergistic matching, so that the cycle performance, the high-temperature storage performance and the impedance performance of the electrochemical device can be improved at the same time.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, particularly to the technical field of lithium-ion batteries, and specifically relates to an electrolyte and an electrochemical device comprising the electrolyte. Background Art

[0002] Electrochemical devices, especially lithium-ion batteries, are increasingly widely used in the field of portable electronic products because they have advantages such as high energy density, high working voltage, light weight, low self-discharge rate, long cycle life, no memory effect, and environmental friendliness. In addition to smart electronic products (including mobile phones, laptops, cameras, etc.) and energy storage products, there is an increasing demand in the fields of higher-power electronic products such as electric vehicles, power tools, drones, and electric ships. High-power electronic products require lower impedance, but also have higher requirements for the high-temperature storage and safety performance of electrochemical devices, especially lithium-ion batteries. Therefore, it is particularly important to develop electrochemical devices, especially lithium-ion batteries, with relatively low impedance and that can balance high-temperature storage and cycling performance. Summary of the Invention

[0003] The purpose of this application is to provide an electrolyte and an electrochemical device comprising the electrolyte to improve the high-temperature storage and cycling performance of the electrochemical device. The specific solutions are as follows:

[0004] According to the first aspect of this application, this application provides an electrolyte, which comprises: a compound of formula I and a polynitrile compound;

[0005]

[0006] Wherein, R 1 , R 2 , R 3 and R 4 are each independently selected from any one of a fluorine atom, a difluorophosphoryloxy group, a methylsulfonic acid group, and a trifluoromethylsulfonic acid group; based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A, and the mass percentage of the polynitrile compound is B, wherein, A satisfies: 0.01% ≤ A ≤ 10%; A / B satisfies: 0.02 ≤ A / B ≤ 50.

[0007] In the electrolyte, although polynitrile compounds can complex with transition metal ions at the cathode interface to reduce the dissolution of transition metals, the reduction products of polynitrile compounds at the anode interface are unstable. Therefore, the use of polynitrile compounds in the electrolyte will lead to deterioration of the cycling performance of the electrochemical device. However, through research, it is found in this application that by introducing a compound of Formula I into the electrolyte containing polynitrile compounds, while improving the cycling performance of the electrochemical device, the high-temperature storage and impedance performance can be enhanced. Introducing the compound of Formula I into the electrolyte, through the decomposition of the compound of Formula I at the anode interface, a boron-rich structure component is generated, improving the stability of the anode interface and suppressing the side effects of polynitrile compounds at the anode interface. Meanwhile, in the electrolyte, when the polynitrile compound and the compound of Formula I are used in combination, the nitrile structure has a strong dissociation ability, which can improve the dissociation of the compound of Formula I and, together with the anion of the compound of Formula I, form a solvent shell, improving the reduction decomposition of the structure of the compound of Formula I at the anode and enhancing the stability of the anode interface. In addition, the anion of this solvation shell migrates to the cathode interface through the action of the electric field and, through the complexation of the cyano group with the transition metal, improves the oxidative decomposition of the anion at the active sites of the cathode interface, promoting the formation of an interface film rich in P, N, and B and enhancing the stability of the interface. When the mass percentage ratio A of the compound of Formula I in the electrolyte and the ratio A / B of the mass percentage ratio A of the compound of Formula I in the electrolyte to the mass percentage ratio B of the polynitrile compound in the electrolyte are controlled within the above ranges, the cycling performance and storage performance of the electrochemical device can be further improved. When the range of A and / or the range of A / B are lower than the above ranges, the storage performance cannot be improved. When the range of A and / or the range of A / B are higher than the above ranges, a large amount of by-products will be generated at the interface, deteriorating the cycling performance.

[0008] In some embodiments of this application, the mass percentage ratio A of the compound of Formula I satisfies: 0.1% ≤ A ≤ 5%. When the mass percentage ratio A of the compound of Formula I is further controlled within the above range, better improvement of the high-temperature storage and cycling performance of the electrochemical device can be achieved.

[0009] In some embodiments of this application, the ratio A / B of the mass percentage ratio A of the compound of Formula I in the electrolyte to the mass percentage ratio B of the polynitrile compound in the electrolyte satisfies: 0.05 ≤ A / B ≤ 40. When the ratio A / B of the mass percentage ratio A of the compound of Formula I in the electrolyte to the mass percentage ratio B of the polynitrile compound in the electrolyte is further controlled within the above range, while further improving the storage performance, almost no impact on the cathode interface impedance is generated, achieving better improvement of the high-temperature storage and cycling performance of the electrochemical device.

[0010] In some embodiments of the present application, the mass percentage B of the polynitrile compound in the electrolyte satisfies: 0.1% ≤ B ≤ 5%; preferably, B satisfies: 0.1% ≤ B ≤ 3%. When the mass percentage B of the polynitrile compound in the electrolyte is further adjusted within the above range, the high-temperature storage and cycling performance of the electrochemical device can be further improved.

[0011] In some embodiments of the present application, the compound of Formula I includes at least one of the following compounds of Formula I-1 to Formula I-9:

[0012]

[0013] In the electrolyte system provided by the present application, when at least one of the above compounds is selected as the compound of Formula I, the synergistic effect with the polynitrile compound is more obvious, and the high-temperature storage and cycling performance can be further improved.

[0014] In some embodiments of the present application, the polynitrile compound includes at least one of the following compounds of Formula 1 to Formula 16:

[0015]

[0016]

[0017] In the electrolyte system provided by the present application, when at least one of the above compounds is selected as the polynitrile compound, the synergistic effect with the compound of Formula I is more obvious, and the high-temperature storage and cycling performance can be further improved.

[0018] In some embodiments of the present application, the electrolyte further includes a carbonate compound; preferably, the carbonate compound is selected from at least one of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate. In the electrolyte system provided by the present application, the polynitrile compound cannot form a stable interface film at the negative electrode interface, and the boron and phosphorus compounds formed by the compound of Formula I at the negative electrode interface cannot completely cover the negative electrode interface. The present application has found through research that by further introducing an appropriate amount of carbonate compound into the electrolyte, the formation of LiF at the negative electrode interface can be promoted, and at the same time, the decomposition products of the compound of Formula I are evenly distributed at the negative electrode interface, improving the stability of the negative electrode interface and achieving the effect of further improving the cycling performance of the electrochemical device.

[0019] In some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage of the carbonate compound is C, and 0.1% ≤ C ≤ 5%. By adjusting the mass percentage C of the carbonate compound within the above range, the stability of the negative electrode interface can be further improved, and the cycling performance of the electrochemical device can be improved.

[0020] In some embodiments of the present application, the mass percentage C of the carbonate compound, the mass percentage A of the compound of Formula I in the electrolyte, and the mass percentage B of the polynitrile compound in the electrolyte satisfy the following relationship: 0.02 ≤ C / (A + B) ≤ 20. By adjusting the ratio C / (A + B) of the mass percentage C of the carbonate compound, the mass percentage A of the compound of Formula I in the electrolyte, and the mass percentage B of the polynitrile compound in the electrolyte within the above range, the cycle performance of the electrochemical device can be improved without significantly increasing the impedance.

[0021] According to the second aspect of the present application, the present application also provides an electrochemical device, and the electrochemical device includes the electrolyte according to any one of the first aspects of the present application. The electrochemical device containing the above electrolyte has good storage and cycle performance.

[0022] According to the third aspect of the present application, the present application also provides an electronic device, and the electronic device includes the electrochemical device according to the second aspect of the present application. Detailed Embodiments

[0023] The technical solution of the present application is further described below through specific embodiments. The specific embodiments do not represent a limitation on the protection scope of the present application. Some non-essential modifications and adjustments made by others based on the concept of the present application still fall within the protection scope of the present application.

[0024] I. Electrolyte

[0025] According to the first aspect of the present application, the present application provides an electrolyte, and the electrolyte includes: a compound of Formula I and a polynitrile compound;

[0026]

[0027] wherein, R 1 、R 2 、R 3 and R 4 are each independently selected from any one of a fluorine atom, a difluorophosphoryloxy group, a methylsulfonic acid group, and a trifluoromethylsulfonic acid group; based on the total mass of the electrolyte, the mass percentage of the compound of Formula I in the electrolyte is A, and the mass percentage of the polynitrile compound in the electrolyte is B, wherein, A satisfies: 0.01% ≤ A ≤ 10%; A / B satisfies: 0.02 ≤ A / B ≤ 50.

[0028] Specifically, the structural formula of the difluorophosphoryloxy group may be When R 1 、R 2 、R 3 or R 4When selected from difluorophosphoryloxy, O in P-O of the difluorophosphoryloxy structural formula is connected to B to form a compound of Formula I. Specifically, the structural formula of the methylsulfonic acid group may be When R 1 , R 2 , R 3 or R 4 is selected from methylsulfonic acid group, O in S-O of the methylsulfonic acid group is connected to B to form a compound of Formula I. The structural formula of the trifluoromethylsulfonic acid group may be When R 1 , R 2 , R 3 or R 4 is selected from trifluoromethylsulfonic acid group, O in S-O of the trifluoromethylsulfonic acid group is connected to B to form a compound of Formula I.

[0029] Specifically, in the technical solution provided by the present application, the polynitrile compound refers to an organic compound containing two or more cyano groups (—CN), and the cyano group is a functional group formed by a carbon atom and a nitrogen atom connected by a triple bond. The polynitrile compound includes at least one of a dinitrile compound without ether, a trinitrile compound without ether, a polynitrile compound without ether, a dinitrile compound containing ether, a trinitrile compound containing ether, and a polynitrile compound containing ether.

[0030] Specifically, in some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage A of the compound of Formula I in the electrolyte may be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, 5.1%, 5.2%, 5.3%, 5.4%, 5.5%, 5.6%, 5.7%, 5.8%, 5.9%, 6.0%, 6.1%, 6.2%, 6.3%, 6.4%, 6.5%, 6.6%, 6.7%, 6.8%, 6.9%, 7.0%, 7.1%, 7.2%, 7.3%, 7.4%, 7.5%, 7.6%, 7.7%, 7.8%, 7.9%, 8.0%, 8.1%, 8.2%, 8.3%, 8.4%, 8.5%, 8.6%, 8.7%, 8.8%, 8.9%, 9.0%, 9.1%, 9.2%, 9.3%, 9.4%, 9.5%, 9.6%, 9.7%, 9.8%, 9.9%, 10% or a range composed of any two of the above values.Specifically, in some embodiments of the present application, the ratio A / B of the mass percentage A of the compound of Formula I in the electrolyte to the mass percentage B of the polynitrile compound in the electrolyte can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 4.0, 4.5, 5.0, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19.0, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or a range composed of any two of the above values.

[0031] In the electrolyte, although polynitrile compounds can complex with transition metal ions at the cathode interface to reduce the dissolution of transition metals, the reduction products of polynitrile compounds at the anode interface are unstable. Therefore, the use of polynitrile compounds in the electrolyte will lead to deterioration of the cycling performance of the electrochemical device. However, through research, it is found in this application that by introducing a compound of Formula I into the electrolyte containing polynitrile compounds, while improving the cycling performance of the electrochemical device, the high-temperature storage and impedance performance can be enhanced. Introducing the compound of Formula I into the electrolyte, through the decomposition of the compound of Formula I at the anode interface, a boron-rich structure component is generated, improving the stability of the anode interface and suppressing the side effects of polynitrile compounds at the anode interface. At the same time, in the electrolyte, when the polynitrile compound and the compound of Formula I are used in combination, the nitrile structure has a strong dissociation ability, which can improve the dissociation of the compound of Formula I while jointly forming a solvent shell with the anion of the compound of Formula I, enhancing the reductive decomposition of the structure of the compound of Formula I at the anode and improving the stability of the anode interface. In addition, the anion of this solvation shell migrates to the cathode interface through the action of the electric field and, through the complexation of the cyano group with the transition metal, improves the oxidative decomposition of the anion at the active sites of the cathode interface, promoting the formation of an interface film rich in P, N, and B and enhancing the stability of the interface. At the same time, when the mass percentage A of the compound of Formula I in the electrolyte and the ratio A / B of the mass percentage A of the compound of Formula I in the electrolyte to the mass percentage B of the polynitrile compound in the electrolyte are controlled within the above ranges, the cycling performance and storage performance of the electrochemical device can be further improved. When the range of A and / or the range of A / B are lower than the above ranges, the storage performance cannot be improved. When the range of A and / or the range of A / B are higher than the above ranges, a large amount of by-products will be generated at the interface, deteriorating the cycling performance.

[0032] In some embodiments of this application, the mass percentage A of the compound of Formula I in the electrolyte satisfies: 0.1% ≤ A ≤ 5%. When the mass percentage A of the compound of Formula I in the electrolyte is further controlled within the above range, the high-temperature storage and cycling performance of the electrochemical device can be further improved.

[0033] In some embodiments of this application, the ratio A / B of the mass percentage A of the compound of Formula I in the electrolyte to the mass percentage B of the polynitrile compound in the electrolyte satisfies: 0.05 ≤ A / B ≤ 40. When the ratio A / B of the mass percentage A of the compound of Formula I in the electrolyte to the mass percentage B of the polynitrile compound in the electrolyte is further controlled within the above range, while further achieving the effect of improving the storage performance, almost no influence is exerted on the cathode interface impedance, and better improvement of the high-temperature storage and cycling performance of the electrochemical device can be achieved.

[0034] In some embodiments of the present application, the mass percentage B of the polynitrile compound in the electrolyte satisfies: 0.1% ≤ B ≤ 5%. Specifically, in some embodiments of the present application, the mass percentage B of the polynitrile compound in the electrolyte can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% or a range composed of any two of the above values. Preferably, B satisfies: 0.1% ≤ B ≤ 3%. When the mass percentage B of the polynitrile compound in the electrolyte is further regulated within the above range, the high-temperature storage and cycling performance of the electrochemical device can be further improved.

[0035] In some embodiments of the present application, the compound of formula I includes at least one of the following compounds of formula I-1 to formula I-9:

[0036]

[0037] In the electrolyte system provided by the present application, when at least one of the above compounds is selected as the compound of formula I, the synergistic effect with the polynitrile compound is more obvious, and the effect of better improving the high-temperature storage and cycling performance can be achieved.

[0038] In some embodiments of the present application, the polynitrile compound includes at least one of the following compounds of formula 1 to formula 16:

[0039]

[0040]

[0041] In the electrolyte system provided by the present application, when at least one of the above compounds is selected as the polynitrile compound, the synergistic effect with the compound of formula I is more obvious, and the high-temperature storage and cycling performance can be further improved.

[0042] In some embodiments of the present application, the electrolyte further includes a carbonate compound. In some embodiments of the present application, the carbonate compound is selected from at least one of vinylene carbonate, ethylene vinylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate. In the electrolyte system provided by the present application, a stable interfacial film cannot be formed at the negative electrode interface by the polynitrile compound, and the boron and phosphorus compounds formed by the compound of formula I at the negative electrode interface cannot completely cover the negative electrode interface. The present application has found through research that by further introducing an appropriate amount of carbonate compound into the electrolyte, the formation of LiF at the negative electrode interface can be promoted, and at the same time, the decomposition products of the compound of formula I are evenly distributed at the negative electrode interface, improving the stability of the negative electrode interface and achieving the effect of further improving the cycle performance of the electrochemical device.

[0043] In some embodiments of the present application, based on the total mass of the electrolyte, the mass percentage of the carbonate compound is C, and 0.1% ≤ C ≤ 5%. Specifically, based on the total mass of the electrolyte, the mass percentage C of the carbonate compound can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4.0%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0% or a range composed of any two of the above values. By controlling the mass percentage C of the carbonate compound within the above range, the effect of further improving the stability of the negative electrode interface and improving the cycle performance of the electrochemical device can be achieved.

[0044] In some embodiments of the present application, the mass percentage C of the carbonate compound, the mass percentage A of the compound of Formula I in the electrolyte, and the mass percentage B of the polynitrile compound in the electrolyte satisfy the following relationship: 0.02 ≤ C / (A + B) ≤ 20. Specifically, in some embodiments of the present application, the ratio relationship C / (A + B) of the mass percentage C of the carbonate compound, the mass percentage A of the compound of Formula I in the electrolyte, and the mass percentage B of the polynitrile compound in the electrolyte can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 4.0, 4.5, 5.0, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19.0, 20 or a range composed of any two of the above values. By adjusting the ratio relationship C / (A + B) of the mass percentage C of the carbonate compound, the mass percentage A of the compound of Formula I in the electrolyte, and the mass percentage B of the polynitrile compound in the electrolyte within the above range, the cycle performance of the electrochemical device can be improved without significantly increasing the impedance.

[0045] In some embodiments of the present application, the electrolyte provided by the present application may further contain some other components. The other components may include but are not limited to: diethyl carbonate (DEC), ethyl methyl carbonate (EMC), or dimethyl carbonate (DMC). In some embodiments of the present application, the other components may include ether solvents. The ether solvents include but are not limited to at least one of 1,3 - dioxolane (DOL) and dimethoxyethane (DME).

[0046] In some embodiments of the present application, the electrolyte provided by the present application may further include a lithium salt as an electrolyte. The lithium salts in the electrolyte include, but are not limited to: lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimonate (LiSbF6), lithium fluorosulfonate (LiSO3F), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiN(FSO2)(CF3SO2)), lithium tris(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), LiN(C2F5SO2)2, lithium bis(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluoro bis(oxalato)phosphate, or lithium tetrafluoro(oxalato)phosphate. Additionally, the above lithium salts can be used alone, or two or more of them can be used simultaneously. In some embodiments, the lithium salt includes LiPF6. In some embodiments, based on the total mass of the electrolyte, the mass percentage of the lithium salt in the electrolyte is 10% to 20%. Specifically, based on the total mass of the electrolyte, the mass percentage of the lithium salt in the electrolyte is 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range composed of any two of the above values.

[0047] In some embodiments of the present application, the preparation method of the electrolyte provided by the present application is not limited and can be prepared in the conventional way of electrolytes. In some embodiments, the electrolyte of the present application can be prepared by mixing each component.

[0048] II. Electrochemical Device

[0049] According to the second aspect of the present application, the present application also provides an electrochemical device, and the electrochemical device includes the electrolyte according to any one of the first aspect of the present application. The electrochemical device containing the above electrolyte has good high-temperature storage and cycling performance of the electrochemical device.

[0050] In some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In some embodiments of the present application, the electrochemical device is a lithium secondary battery. In some embodiments of the present invention, the lithium secondary battery includes, but is not limited to: lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries. In some embodiments of the present application, the electrochemical device of the present application can also be a non-aqueous anode battery system.

[0051] 1. Anode

[0052] In some embodiments of the present application, the electrochemical device further includes a negative electrode, which includes a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, which is any material capable of electrochemically occluding and releasing metal ions such as lithium ions. In some embodiments of the present application, the negative electrode active material includes a carbonaceous material (graphite), a silicon material, a hard carbon material, or a lithium metal material. In some embodiments of the present application, the negative electrode active material includes one or more of the above.

[0053] In some embodiments of the present application, the negative electrode active material layer further includes a conductive agent to improve the electrode conductivity. Any conductive material can be used as the conductive material as long as it does not cause chemical changes. Examples of the conductive agent include, but are not limited to: carbon-based materials, such as carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials, such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof.

[0054] In some embodiments of the present application, the negative electrode active material layer further includes a thickening agent. The thickening agent can be selected from sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF).

[0055] In some embodiments of the present application, the negative electrode active material layer further includes a binder, which can include various adhesive polymers, such as polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0056] In some embodiments of the present application, the negative electrode current collector includes, but is not limited to: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and any combination thereof. In some embodiments, the negative electrode current collector is a copper foil.

[0057] In some embodiments of the present application, the structure of the negative electrode can be a negative electrode structure known to those skilled in the art and can be used in an electrochemical device.

[0058] In some embodiments of the present application, the method for preparing the negative electrode is a method known to those skilled in the art and can be used for preparing the negative electrode of an electrochemical device. Exemplarily, the negative electrode can be obtained by the following method: mixing a negative electrode active material, a conductive agent, and a binder in a solvent, and heating a thickener as needed to prepare a negative electrode active material slurry, and coating the negative electrode active material slurry on a negative electrode current collector, drying, and cold pressing to form a negative electrode active material layer. In some embodiments, the solvent may include, but is not limited to, water, N-methylpyrrolidone.

[0059] 2. Positive electrode

[0060] In some embodiments of the present application, the electrochemical device further includes a positive electrode, and the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector. The specific types of the positive electrode active materials in the positive electrode active material layer are not specifically limited and can be selected according to requirements. In some embodiments of the present application, the positive electrode active material includes a lithium transition metal composite oxide. In some embodiments, the positive electrode active material is selected from at least one of the following: lithium cobalt oxide, lithium nickel manganese cobalt ternary material, lithium manganese oxide, lithium nickel manganese oxide, or lithium iron phosphate.

[0061] In some embodiments of the present application, the positive electrode active material layer further includes a binder. The binder can improve the binding between the positive electrode active material particles and can also improve the binding between the positive electrode active material and the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon, etc.

[0062] In some embodiments of the present application, the positive electrode active material layer further includes a conductive agent to endow the electrode with conductivity. The conductive agent can include any conductive material as long as it does not cause chemical changes. Non-limiting examples of the conductive material include carbon-based materials (such as carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (such as metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (such as polyphenylene derivatives), and mixtures thereof.

[0063] In some embodiments of the present application, the positive electrode current collector is a metal, such as aluminum foil.

[0064] In some embodiments of the present application, the structure of the positive electrode is a positive electrode structure known to those skilled in the art and can be used for an electrochemical device.

[0065] In some embodiments of the present application, the method for preparing the positive electrode is a method well-known in the art and can be used for preparing the positive electrode of an electrochemical device. For example, the positive electrode can be obtained by the following method: mixing a positive electrode active material, a conductive agent, and a binder in a solvent to prepare a positive electrode active material slurry, and coating the positive electrode active material slurry on a positive electrode current collector, drying, and cold pressing to form a positive electrode active material layer. In some embodiments, the solvent may include water, N-methylpyrrolidone, etc., but is not limited thereto.

[0066] 3. Separator

[0067] In some embodiments of the present application, the electrochemical device further includes a separator, which is used to prevent short circuit. There are no particular limitations on the material and shape of the separator, and it can be any technology disclosed in the prior art. For example, in some embodiments, the separator includes a substrate layer, and the substrate layer is a non-woven fabric, a film, or a composite film with a porous structure. The material of the substrate layer can be selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, the material of the substrate layer can be selected from at least one of a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film. A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. Specifically, the inorganic layer includes inorganic particles and a binder. The inorganic particles can be selected from one or a combination of several of alumina, silica, magnesia, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder can be selected from one or a combination of several of polyvinylidene fluoride, a polymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinyl pyrrolidone, polyethylene ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0068] III. Electronic Device

[0069] According to the third aspect of the present application, the present application further provides an electronic device, and the electronic device includes the electrochemical device described in the second aspect of the present application. The electrolyte according to the present application can enable the electrochemical device to have good high-temperature storage and cycling performance, making the electrochemical device thus manufactured applicable to electronic devices in various fields. In some embodiments of the present application, the electronic devices of the present application include, but are not limited to: laptop computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc. In addition, the electrochemical device provided by the present application is applicable not only to the above-mentioned exemplified electronic devices, but also to energy storage power stations, marine vehicles, and air vehicles, and the air vehicles include air vehicles within the atmosphere and air vehicles outside the atmosphere.

[0070] Hereinafter, the present application will be described in more detail by means of specific examples and comparative examples.

[0071] I. Test methods used in examples and comparative examples:

[0072] (1) DCR test of lithium-ion battery direct current impedance

[0073] Place the lithium-ion battery in a constant temperature environment of 0°C and let it stand for 5 minutes to make the lithium-ion battery reach a constant temperature. Record the voltage of the lithium-ion battery at this time as U1. Discharge it at a constant current of 0.1C for 10 minutes, and record the voltage of the lithium-ion battery at this time as U2. The impedance DCR of the lithium-ion battery at 0°C = (U1 - U2) / 0.1C.

[0074] (2) High-temperature storage performance test of lithium-ion battery

[0075] Place the lithium-ion battery in a constant temperature environment of 25°C and let it stand for 30 minutes to make the lithium-ion battery reach a constant temperature state of 25°C. Charge it at a constant current of 0.5C to 4.5V, and then charge it at a constant voltage of 4.5V until the current is 0.025C. Record the thickness of the lithium-ion battery at this time as the initial thickness H0. Transfer the lithium-ion battery to a constant temperature oven at 60°C for storage for 30 days. During this period, test and record the thickness of the lithium-ion battery every 6 days. The test thickness recorded after 30 days is the storage thickness H1. The high-temperature storage thickness expansion rate = (H1 - H0) / H0 × 100%. The high-temperature storage performance of the lithium-ion battery is evaluated by the high-temperature storage thickness expansion rate.

[0076] (3) Cycle performance test of lithium-ion battery

[0077] Place the lithium-ion battery in a constant temperature environment of 25 °C and let it stand for 30 min to make the lithium-ion battery reach a constant temperature state of 25 °C. Charge it at a constant current of 0.5C to 4.5V, charge it at a constant voltage of 4.5V until the current is 0.025C, let it stand for 5 min, and discharge it at a constant current of 0.5C to 3.0V. Record the initial discharge capacity as C0. Cycle 150 times according to the above charge-discharge steps, and record the discharge capacity after 150 cycles as C1. The cycle capacity retention rate = C1 / C0 × 100%. Evaluate the cycle performance of the lithium-ion battery through the cycle capacity retention rate.

[0078] II. Specific examples and comparative examples

[0079] Example 1-1

[0080] (1) Preparation of the positive electrode

[0081] Mix the positive electrode active material LiCoO2, the conductive agent Super P, and the binder polyvinylidene fluoride in a weight ratio of 97:1.4:1.6, add them to the N-methylpyrrolidone (NMP) solvent, and stir evenly under the action of a vacuum mixer to obtain the positive electrode slurry. The solid content of the positive electrode slurry is 72 wt%. Coat the positive electrode slurry evenly on the positive electrode current collector aluminum foil. Dry the coated aluminum foil at 85 °C, and then after cold pressing, slicing, and slitting, dry it in a vacuum at 85 °C for 4 h to obtain the positive electrode.

[0082] (2) Preparation of the negative electrode

[0083] Mix the negative electrode active material artificial graphite, the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC), and the binder styrene-butadiene rubber (SBR) in a weight ratio of 96:2:0.8:1.2, add deionized water, and obtain the negative electrode slurry under the action of a vacuum mixer. The solid content of the negative electrode slurry is 54 wt%. Coat the negative electrode slurry evenly on the negative electrode current collector copper foil according to the area density of the negative electrode active material of 7.8 mg / cm 2 Dry the coated copper foil at 85 °C, and then after cold pressing, slicing, and slitting, dry it in a vacuum at 120 °C for 12 h to obtain the negative electrode.

[0084] (3) Preparation of the electrolyte

[0085] In a dry (water content < 10 ppm) argon atmosphere glove box, the solvents were mixed in a mass ratio of EC:DEC:EMC = 30:40:30. Then, fully dried lithium salt LiPF6 (1 mol / kg, abbreviated as 1M) was added. After dissolution and thorough stirring, Compound I (Formula I-1) and the polynitrile compound (Formula 1) were added. After mixing evenly, an electrolyte solution was obtained. Among them, based on the total mass of the electrolyte solution, the mass percentage of Compound I (Formula I-1) was 0.01%, the mass percentage of the polynitrile compound (Formula 1) was 0.02%, the mass percentage of LiPF6 was 12.5%, and the balance was the solvent composed of EC, DEC, and EMC.

[0086] (4) Preparation of the separator

[0087] A 9-μm-thick polyethylene (PE) separator was selected. After coating and drying with PVDF slurry and an inorganic particle (the mass ratio of flaky boehmite to Al2O3 was 70:30) slurry, the final separator was obtained. The coating thickness was 3 μm, and the porosity of the separator was 55%.

[0088] (5) Preparation of the lithium-ion battery

[0089] The positive electrode, separator, and negative electrode were stacked in sequence, with the separator placed between the positive and negative electrodes to play a role in isolation. Then, it was wound to obtain a bare battery cell. After welding the electrode tabs, the bare battery cell was placed in an outer packaging aluminum-plastic film, and the above-prepared electrolyte was injected. Then, through processes such as vacuum packaging, standing, formation (constant current charging at 0.02C to 3.3V, and then constant current charging at 0.1C to 3.8V), shaping, and capacity testing, a soft-pack lithium-ion battery was obtained.

[0090] Examples 1-2 to 1-32

[0091] Except for adjusting the specific types and mass percentage parameters of Compound I and the polynitrile compound according to Table 1, the remaining parameters of Examples 1-2 to 1-32 were the same as those of Example 1-1.

[0092] Comparative Examples 1-1 to 1-10

[0093] Except for adjusting the specific types and mass percentage parameters of Compound I and the polynitrile compound according to Table 1, the remaining parameters of Comparative Examples 1-1 to 1-10 were the same as those of Example 1-1.

[0094] According to the above test methods, the high-temperature cycle (cycle capacity retention rate, %), high-temperature storage performance (high-temperature storage thickness expansion rate, %), and impedance performance (impedance DCR, mΩ) of the lithium-ion batteries prepared through Examples 1-1 to 1-32 and Comparative Examples 1-1 to 1-10 were tested respectively. The results are shown in Table 1:

[0095] Table 1

[0096]

[0097]

[0098] According to the results presented in Table 1, referring to Comparative Examples 1-5 to Comparative Examples 1-10 and Examples 1-1 to Examples 1-32, adding the compound of Formula I and the polynitrile compound to the electrolyte simultaneously can significantly improve the high-temperature storage, cycling, and impedance performance of lithium-ion batteries. Further referring to Examples 1-1 to Examples 1-19, as the content of the compound of Formula I or the polynitrile compound increases, the improvement effects of the high-temperature storage, cycling, and impedance performance of lithium-ion batteries are gradually improved. However, when the content of the compound of Formula I or the polynitrile compound added is too high or too low, the improvement effects of the relevant performance of lithium-ion batteries gradually decline. It can be seen that although adding the compound of Formula I and the polynitrile compound to the electrolyte simultaneously can significantly improve the cycling and high-temperature storage performance of lithium-ion batteries, the dosage combination between the compound of Formula I and the polynitrile compound will also significantly affect the final improvement effect. Therefore, when adding the compound of Formula I and the polynitrile compound to the electrolyte simultaneously and regulating the dosage of the compound of Formula I in the electrolyte and the ratio between the dosage of the compound of Formula I in the electrolyte and the dosage of the polynitrile compound in the electrolyte within the scope of this application, the high-temperature storage, cycling, and impedance performance of lithium-ion batteries can be better improved.

[0099] Examples 2-1 to Examples 2-12

[0100] Based on the results in Table 1, this corresponding example further explores the effects of other components and dosages on improving the high-temperature cycling, storage, and impedance performance of lithium-ion batteries. Except for adjusting the specific category of the carbonate compound and the mass percentage C / %, the mass percentage A / % of the compound of Formula I, the mass percentage B / % of the polynitrile compound, and the ratio relationship C / (A + B) between the mass percentage C of the carbonate compound and the mass percentage A / % of the compound of Formula I and the mass percentage B / % of the polynitrile compound according to Table 2, the remaining parameters of Examples 2-1 to Examples 2-12 are the same as those of Example 1-12.

[0101] According to the above test methods, the performance of the lithium-ion batteries prepared by Examples 2-1 to Examples 2-12, such as (cycle capacity retention rate, %), high-temperature storage performance (high-temperature storage thickness expansion rate, %), and impedance performance (impedance DCR, mΩ), was tested respectively. The results are shown in Table 2:

[0102] Table 2

[0103]

[0105] The results presented in Table 2 show that, referring to Examples 1-12 and Examples 2-1 to 2-8, further adding carbonate compounds to the electrolyte can further improve the high-temperature cycling, storage, and impedance performance of lithium-ion batteries. Further referring to Examples 2-1 to 2-5 and Examples 2-9 to 2-12, as the amount of carbonate compounds in the electrolyte increases, the high-temperature cycling, storage, and impedance performance of lithium-ion batteries are gradually and better improved. However, when the amount of carbonate compounds added to the electrolyte is too much or too little, the improvement effect of related performance will be affected. Therefore, in the further solution provided in this application, carbonate compounds are further added to the electrolyte, and the amount of carbonate compounds is controlled within a reasonable range, so as to achieve a further better improvement effect on the high-temperature cycling, storage, and impedance performance of lithium-ion batteries.

[0106] It can be understood that this application is described through some embodiments. As is known to those skilled in the art, without departing from the scope of this application, various changes or equivalent substitutions can be made to these features and embodiments. Additionally, under the teaching of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the scope of this application. Therefore, this application is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by this application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises: a compound of formula I and a polynitrile compound; Among them, R 1 , R 2 , R 3 and R 4 Each is independently selected from any one of a fluorine atom, a difluorophosphoryloxy group, a methylsulfonate group, and a trifluoromethylsulfonate group; Based on the total mass of the electrolyte, the mass percentage of the compound of formula I is A, and the mass percentage of the polynitrile compound is B, wherein A satisfies: 0.01%≤A≤10%; and A / B satisfies: 0.02≤A / B≤50.

2. The electrolyte according to claim 1, characterized in that The electrolyte includes at least one of the following conditions: (1) The mass percentage A of the compound of formula I satisfies: 0.1%≤A≤5%; (2) The ratio A / B of the mass percentage A of the compound of formula I to the mass percentage B of the polynitrile compound satisfies: 0.05≤A / B≤40.

3. The electrolyte according to claim 1, characterized in that The mass percentage B of the polynitrile compound satisfies: 0.1%≤B≤5%.

4. The electrolyte according to claim 1, characterized in that 0.1％≤B≤3％。 5. The electrolyte according to claim 1, characterized in that The compound of formula I includes at least one of the following compounds of formula I-1 to formula I-9:

6. The electrolyte according to claim 1, characterized in that The polynitrile compound includes at least one of the following compounds of Formula 1 to Formula 16:

7. The electrolyte according to claim 1, characterized in that The electrolyte further includes a carbonate compound; based on the total mass of the electrolyte, the mass percentage of the carbonate compound is C, and C satisfies: 0.1%≤C≤5%.

8. The electrolyte according to claim 7, characterized in that The carbonate compound is selected from at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate or difluoroethylene carbonate.

9. The electrolyte according to claim 7, characterized in that The mass percentage C of the carbonate compound, the mass percentage A of the compound of formula I, and the mass percentage B of the polynitrile compound satisfy the following relationship: 0.02≤C / (A+B)≤20.

10. An electrochemical device, characterized in that: The electrochemical device comprises the electrolyte according to any one of claims 1 to 9.

11. An electronic device, characterized in that: The electronic device comprises the electrochemical device according to claim 10.

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