Electrolyte, secondary battery, and electric device

Abstract

The invention belongs to the technical field of batteries, and particularly relates to an electrolyte, a secondary battery and an electric device. The electrolyte provided by the invention comprises a compound with the following structural formula I: # imgabs0 #, wherein in the formula I, R1 and R2 respectively and independently comprise one of C1-C2 alkyl groups; r3 and R4 each independently comprise any one of hydrogen, methyl and fluorine-substituted methyl, and at least one of R3 and R4 comprises fluorine-substituted methyl; and n is any positive integer from 1 to 3. The compound meeting the structural formula can be used as an electrolyte solvent, is applied to a secondary battery, is beneficial to improving the solvation structure of metal ions and further influencing the deposition morphology of a negative electrode, and finally improves the first-circle coulombic efficiency and cycling stability of the secondary battery.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to an electrolyte, a secondary battery and an electrical device. Background Art

[0002] In recent years, with the development of secondary battery technology, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as electronic equipment power supplies, power tools, electric bicycles, electric motorcycles, electric vehicles and other fields.

[0003] With the development of science and technology and society, the performance of various products has been further improved, so higher requirements are also put forward for the cycle performance of secondary batteries. How to provide a secondary battery with better cycle performance is one of the key directions that technicians in this field focus on. Summary of the invention

[0004] In view of the above problems, the present application provides an electrolyte, a secondary battery and an electrical device, which can improve the cycle stability of the battery while also improving the first-cycle coulomb efficiency of the battery.

[0005] In a first aspect, the present application provides an electrolyte comprising a compound of the following structural formula I:

[0006]

[0007] And in Formula I, R1 and R2 each independently comprise one of C1-C2 alkyl groups;

[0008] R3 and R4 each independently include any one of hydrogen, methyl, and fluorine-substituted methyl, and at least one of R3 and R4 includes fluorine-substituted methyl;

[0009] n is any positive integer from 1 to 3.

[0010] In the present application, the compound satisfying the above structural formula contains an alkoxy group and a fluorine-substituted methyl group. These two groups have strong antioxidant capacity, and when used in the electrolyte, it is beneficial to improve the high oxidation resistance of the electrolyte; and the alkyl chain length of the compound is moderate, which can provide a suitable ability to bind metal ions while maintaining ionic conductivity. At the same time, the fluorine-substituted methyl group contained in the compound can play a certain role in regulating the electron cloud structure and steric hindrance due to the strong electron-withdrawing ability of fluorine. The application of the electrolyte in the secondary battery is beneficial to improve the solvation structure of the metal ions and further affect the deposition morphology of the negative electrode, and finally improve the first week coulomb efficiency and cycle stability of the secondary battery.

[0011] In some specific embodiments of the present application, in Formula I, one of R3 and R4 comprises a fluorine-substituted methyl group, and the other comprises any one of hydrogen and methyl group.

[0012] In some specific embodiments of the present application, the electrolyte comprises any one or a combination of two or more of the following compounds of structural formula I-1, I-2, I-3, I-4, I-5, I-6, and I-7:

[0013]

[0014] In formula I-1, Rf1 comprises a fluorine-substituted methyl group;

[0015] In formula I-2, Rf2 comprises a fluorine-substituted methyl group;

[0016] In formula I-3, Rf3 and Rf4 each independently include a methyl group or a fluorine-substituted methyl group;

[0017] In formula I-4, Rf5 comprises a fluoro-substituted methyl group;

[0018] In formula I-5, Rf6 and Rf7 each independently include a methyl group or a fluorine-substituted methyl group;

[0019] In formula I-6, Rf8 and Rf9 each independently include a methyl group or a fluorine-substituted methyl group;

[0020] In formula I-7, Rf 10 , Rf 11 , Rf 12 Each independently includes a methyl group and a fluorine-substituted methyl group.

[0021] In some specific embodiments of the present application, the compound of structural formula I is the first solvent of the electrolyte.

[0022] The electrolyte of the present application may only contain the first solvent as a solvent, and the first solvent can achieve the purpose of improving the solvation structure of the metal ions.

[0023] In some specific embodiments of the present application, the electrolyte further comprises a second solvent.

[0024] The second solvent of the present application is beneficial to improving the viscosity of the electrolyte, and a suitable electrolyte viscosity is beneficial to improving the solvation structure of metal ions.

[0025] In some specific embodiments of the present application, the volume ratio of the first solvent to the second solvent is (1-9): (9-1).

[0026] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (1-9):(9-1), the second solvent effectively improves the viscosity of the electrolyte and does not affect the solvation effect of the first solvent with the metal ions.

[0027] In some specific embodiments of the present application, the volume ratio of the first solvent to the second solvent is (2-8): (8-2).

[0028] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (2-8):(8-2), the second solvent has a relatively better effect on improving the viscosity of the electrolyte.

[0029] In some specific embodiments of the present application, the volume ratio of the first solvent to the second solvent is (3-7): (7-3).

[0030] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (3-7):(7-3), the improvement of the solvation structure of metal ions by the electrolyte and the deposition morphology of the negative electrode are relatively ideal.

[0031] In some specific embodiments of the present application, the second solvent comprises any one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, trifluoromethyltrimethylsilane, and difluoromethyldimethylsilane, or a combination of two or more thereof.

[0032] In some specific embodiments of the present application, the electrolyte further comprises an electrolyte salt.

[0033] In some specific embodiments of the present application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L.

[0034] In the present application, when the electrolyte salt meets this concentration range, a relatively good solvation structure can be formed between the solvent and the metal ions without affecting the ionic conductivity of the metal ions.

[0035] In some specific embodiments of the present application, the concentration of the electrolyte salt in the electrolyte is 1 mol / L to 4 mol / L.

[0036] In the present application, when the electrolyte salt concentration is 1 mol / L to 4 mol / L, the improvement of the solvation structure of metal ions by the electrolyte and the deposition morphology of the negative electrode are relatively ideal.

[0037] A second aspect of the present application is to provide a secondary battery, comprising:

[0038] Negative electrode;

[0039] Positive electrode;

[0040] Isolation film;

[0041] And the electrolyte described in the first aspect.

[0042] In some specific embodiments of the present application, the negative electrode plate comprises a negative electrode current collector, and the negative electrode current collector comprises a negative electrode current collector matrix and a modified layer disposed on at least one side of the surface of the negative electrode current collector matrix;

[0043] In some specific embodiments of the present application, the thickness of the modified layer is h2, the thickness of the negative electrode current collector matrix is ​​h1, and h2

[0044] In some specific embodiments of the present application, the thickness h1 of the negative electrode current collector matrix is ​​10 μm to 20 μm.

[0045] In some specific embodiments of the present application, the thickness h2 of the modification layer is 10 nm to 50 nm.

[0046] In some specific embodiments of the present application, the material of the modification layer includes any one of inorganic metal elements, inorganic oxides, and organic substances, or a combination of two or more thereof.

[0047] In some specific embodiments of the present application, the inorganic metal element comprises any one or a combination of two or more of platinum, aluminum, magnesium, zinc, gold, silver, and tin.

[0048] In some specific embodiments of the present application, the inorganic oxide comprises any one of aluminum oxide, silicon dioxide, and titanium dioxide, or a combination of two or more thereof.

[0049] In some specific embodiments of the present application, the organic matter comprises any one of polydimethylsiloxane, graphene oxide, silicon dioxide-polymethyl methacrylate, alkali metal fluoride-vinylidene fluoride-hexafluoropropane, or a combination of two or more thereof.

[0050] In some specific embodiments of the present application, the alkali metal fluoride-vinylidene fluoride-hexafluoropropane comprises any one of lithium fluoride-vinylidene fluoride-hexafluoropropane, sodium fluoride-vinylidene fluoride-hexafluoropropane, potassium fluoride-vinylidene fluoride-hexafluoropropane or a combination of two or more thereof.

[0051] In some specific embodiments of the present application, the positive electrode plate comprises a positive electrode active material and an additive, and the mass ratio of the positive electrode active material to the additive is 1:(0.01-0.1).

[0052] In some specific embodiments of the present application, the mass ratio of the positive electrode active material to the additive is 1:(0.04-0.1).

[0053] In some specific embodiments of the present application, the mass ratio of the positive electrode active material to the additive is 1:(0.06-0.1);

[0054] ​In some specific embodiments of the present application, the additive comprises RN3, R2C4O4, R2C2O4, R2C3O5, R2C4O6, [COCON(R)N(R)] n , any one of R2S / KB / PVP, R2S / Co, RF / Co, RNiO2, R2CuO2, RFeO4, and RReO4; and R contains any one of lithium ion, sodium ion, and potassium ion.

[0055] The third aspect of the present application is to provide an electrical device comprising the electrolyte described in the first aspect or the secondary battery described in the second aspect.

[0056] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0058] Figure 1 This is a schematic diagram of the structure of the negative electrode sheet of some embodiments of the present application;

[0059] The reference numerals in the specific implementation manner are as follows:

[0060] 100. negative electrode current collector;

[0061] 110, negative electrode current collector matrix; 120, modified layer;

[0062] Coordinate axis x direction: length direction of negative electrode current collector;

[0063] Coordinate axis z direction: thickness direction of negative electrode current collector. DETAILED DESCRIPTION

[0064] Hereinafter, the embodiments of the electrolyte, secondary battery and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0065] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a particular parameter, it is understood that a range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0066] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0067] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0068] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0069] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0070] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0071] The term "alkyl" is expected to be a straight chain saturated hydrocarbon structure with 1 to 20 carbon atoms. "Alkyl" is also expected to be a branched or cyclic hydrocarbon structure with 3 to 20 carbon atoms. When specifying an alkyl with a specific carbon number, it is expected to cover all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples include, but are not limited to methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0072] The term "substituted" includes the replacement of hydrogen atoms in the alkyl group by other groups, and the number of substitutions is determined by the number of hydrogen atoms.

[0073] Summary of the main line of invention:

[0074] The negative active material of metal ion batteries contains carbonaceous materials, such as graphite, but the mass specific capacity of graphite is limited, and there is very little room for improving the volume specific capacity, which seriously limits the further improvement of the weight energy density and volume energy density of metal ion batteries. With the current development of consumer electronics and electric vehicle technology, the development of battery systems with higher energy density has become a top priority.

[0075] Lithium metal and sodium metal have high mass energy density and volume energy density, so they are often used as negative electrodes in metal batteries. However, the ultra-high capacity is also accompanied by a huge volume effect, which challenges the interfacial stability between the electrode and the electrolyte and exacerbates the irreversible side reactions between the electrode and the electrolyte. Therefore, this battery system is often accompanied by a low first-cycle coulomb efficiency and poor cycle stability.

[0076] In order to solve the above technical problems, the prior art discloses the use of technologies such as optimizing the electrolyte, adding additives to the electrolyte, and surface modifying the negative electrode current collector. Through the analysis of the cycle process of metal batteries, it can be known that any irreversible loss of active metals during the cycle process is likely to cause the capacity of the battery to decay. For example, for a metal battery without a negative electrode, the metal cannot be deintercalated after being deposited on the negative electrode. For another example, the deposition of metal on the negative electrode side will spontaneously form a dendritic loose porous morphology. This high specific surface area morphology will further aggravate the irreversible reaction between the metal and the electrolyte and consume the content of active metals. If the adverse interface reaction can be improved, it will certainly be beneficial to improving the cycle performance of the battery.

[0077] Based on the above considerations, in order to solve the problem that metal negative electrode batteries cannot have good cycle performance while having high energy density, an electrolyte, a secondary battery and an electrical device are obtained according to the above design concept and related experimental research. Specifically, the electrolyte contains the following compound of structural formula I:

[0078]

[0079] In formula I, R1 and R2 each independently include one of C1-C2 alkyl groups; R3 and R4 each independently include any one of hydrogen, methyl, and fluorine-substituted methyl groups, and at least one of R3 and R4 includes a fluorine-substituted methyl group; n is any positive integer from 1 to 3.

[0080] The compound satisfying the above structural formula contains an alkoxy group and a fluorine-substituted methyl group. These two groups have strong antioxidant ability. When used in an electrolyte, they are beneficial to improving the high oxidation resistance of the electrolyte. The alkyl chain length of the compound is moderate, and it can provide a suitable ability to bind metal ions while maintaining ionic conductivity. At the same time, the fluorine-substituted methyl group contained in the compound can play a certain role in regulating the electron cloud structure and steric hindrance due to the strong electron-withdrawing ability of fluorine.

[0081] The electrolyte is applied to the secondary battery, which is beneficial to improve the solvation structure of metal ions and further affect the deposition morphology of the negative electrode, making the metal deposition more uniform and dense and reducing the probability of irreversible reaction between the metal and the electrolyte, and finally improving the first cycle coulomb efficiency and cycle stability of the secondary battery. The secondary battery can be a soft-pack battery, a square battery or a cylindrical battery, and this application focuses on the soft-pack battery.

[0082] The secondary battery can be used as a power source for an electrical device or as an energy storage unit for an electrical device, such as but not limited to laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, energy storage and capacitors, etc.

[0083] Electrolyte

[0084] According to some embodiments of the present application, the present application provides an electrolyte, which comprises a compound of the following structural formula I:

[0085]

[0086] In formula I, R1 and R2 each independently include one of C1-C2 alkyl groups; R3 and R4 each independently include any one of hydrogen, methyl, and fluorine-substituted methyl groups, and at least one of R3 and R4 includes a fluorine-substituted methyl group; n is any positive integer from 1 to 3.

[0087] In the structural formula I of the present application, the substituents R1 and R2 may be the same or different, and each independently comprises any one of methyl and ethyl. R3 and R4 each independently comprise any one of hydrogen, methyl, and fluorine-substituted methyl, and at least one of R3 and R4 comprises fluorine-substituted methyl. At the same time, fluorine-substituted methyl comprises that more than one hydrogen on the methyl is replaced, such as monofluoromethyl, difluoromethyl and trifluoromethyl.

[0088] In addition, n in the structural formula I of the present application represents the number of repetitions of the unit containing (R3)-C-(R4), which can be 1, 2, or 3 times.

[0089] The compound satisfying the above structural formula contains an alkoxy group and a fluorine-substituted methyl group. These two groups have strong antioxidant capacity. When used in an electrolyte, it is beneficial to improve the high oxidation resistance of the electrolyte; and the alkyl chain length of the compound is moderate, which can provide a suitable ability to bind metal ions while maintaining ionic conductivity to improve the solvation structure of metal ions. At the same time, the fluorine-substituted methyl group contained in the compound can play a certain role in regulating the electron cloud structure and steric hindrance due to the strong electron-withdrawing ability of fluorine. The electrolyte is applied to a secondary battery, which is beneficial to improve the solvation structure of metal ions and further affect the deposition morphology of the negative electrode, making the metal deposition more uniform and dense and reducing the probability of irreversible reaction between the metal and the electrolyte, and finally improving the first week coulomb efficiency and cycle stability of the secondary battery.

[0090] In the present application, the C1-C2 alkyl group includes any one of a methyl group and an ethyl group. When the substituents R1 and R2 are substituents higher than a propyl group, the polarity of the molecule decreases due to the increase in the carbon chain, and the increased steric hindrance is not conducive to improving the coordination binding ability between the electrolyte and the metal ions. In the present application, when the number of repetitions of the unit containing (R3)-C-(R4) is more than 4 times, the risk of increased steric hindrance being not conducive to improving the coordination binding ability between the electrolyte and the metal ions will also be brought about. Therefore, this application focuses on exploring compounds that can effectively improve the first-week coulomb efficiency and cycle stability of secondary batteries.

[0091] According to some embodiments of the present application, in Formula I, one of R3 and R4 comprises a fluorine-substituted methyl group, and the other comprises any one of hydrogen and a methyl group.

[0092] In the present application, R3 and R4 are not fluorine-substituted methyl groups at the same time. If R3 and R4 are fluorine-substituted methyl groups at the same time, it is easy to cause the steric hindrance of the molecule to be large, which is not conducive to improving the solvation structure of the metal ion. Among them, the solvation structure of the metal ion includes conventional concepts in the field, such as the combination of metal ions and solvents to form a certain structure, which can affect the construction of the molecular interface and the stability of the electrode, and thus affect the deposition morphology of the negative electrode. The solvation structure formed by the electrolyte and the metal ions in the present application is beneficial to the deposition morphology of the negative electrode.

[0093] According to some embodiments of the present application, the electrolyte comprises any one or a combination of two or more of the following compounds of structural formula I-1, I-2, I-3, I-4, I-5, I-6, and I-7:

[0094]

[0095]

[0096] Wherein, in Formula I-1 to Formula I-7, Rf1 contains a fluorine-substituted methyl group; Rf2 contains a fluorine-substituted methyl group; Rf3 and Rf4 each independently contain a methyl group or a fluorine-substituted methyl group; Rf5 contains a fluorine-substituted methyl group; Rf6 and Rf7 each independently contain a methyl group or a fluorine-substituted methyl group; Rf8 and Rf9 each independently contain a methyl group or a fluorine-substituted methyl group; Rf 10 , Rf 11 , Rf 12 Each independently includes a methyl group and a fluorine-substituted methyl group.

[0097] In the compound of formula I-1 of the present application, R1 and R2 include one of methyl and ethyl, Rf1 is a fluorine-substituted methyl group, and the types of compounds included in formula I-1 are shown in Table 1:

[0098] Table 1 List of compounds of formula I-1

[0099]

[0100] The compound of formula I-2 of the present application contains only one Rf2, wherein R1 and R2 contain one of methyl and ethyl, and Rf2 is a fluorine-substituted methyl. The types of compounds contained in formula I-2 are shown in Table 2:

[0101] Table 2 List of compounds of formula I-2

[0102]

[0103]

[0104] The compound of formula I-3 of the present application is based on formula I-2 and contains two substituents, namely Rf3 and Rf4, wherein R1 and R2 contain one of methyl and ethyl, and Rf3 and Rf4 each independently contain any one of methyl and fluorine-substituted methyl. The types of compounds contained in formula I-3 are shown in Table 3:

[0105] Table 3 List of compounds of formula I-3

[0106]

[0107]

[0108] The compound of formula I-4 of the present application contains only one Rf5, wherein R1 and R2 contain one of methyl and ethyl, and Rf5 is a fluorine-substituted methyl group. The types of compounds contained in formula I-4 are shown in Table 4:

[0109] Table 4 List of compounds of formula I-4

[0110]

[0111]

[0112] The compound of formula I-5 of the present application is based on formula I-4 and contains two substituents, namely Rf6 and Rf7, wherein R1 and R2 contain one of methyl and ethyl, and Rf6 and Rf7 each independently contain any one of methyl and fluorine-substituted methyl. The types of compounds contained in formula I-5 are shown in Table 5:

[0113] Table 5 List of compounds of formula I-5

[0114]

[0115]

[0116]

[0117] The compound of formula I-6 of the present application is based on formula I-4 and contains two substituents, namely Rf8 and Rf9, wherein R1 and R2 contain one of methyl and ethyl, and Rf8 and Rf9 each independently contain any one of methyl and fluorine-substituted methyl; the types of compounds contained in formula I-6 are shown in Table 6:

[0118] Table 6 List of compounds of formula I-6

[0119]

[0120]

[0121] The compound of formula I-7 of the present application is based on formula I-4 and contains three substituents, namely, Rf 10 , Rf 11 and Rf 12 , wherein R1 and R2 contain one of methyl and ethyl, and Rf 10 , Rf 11 , Rf 12 Each independently contains any one of methyl and fluorine-substituted methyl; the types of compounds contained in formula I-7 are shown in Table 7:

[0122] Table 7 List of compounds of formula I-7

[0123]

[0124]

[0125]

[0126]

[0127]

[0128] According to some embodiments of the present application, the compound of formula I is used as the first solvent of the electrolyte. The electrolyte may contain only the first solvent as a solvent. The compound of formula I can effectively solvate and combine with metal ions to form a solvation structure that is beneficial to the negative electrode deposition morphology, while not affecting the conductivity of the metal ions.

[0129] According to some embodiments of the present application, the electrolyte of the present application may further include a second solvent, wherein the second solvent disperses the first solvent and the electrolyte salt to improve the viscosity of the electrolyte, and a suitable electrolyte viscosity is beneficial to improving the solvation structure of metal ions.

[0130] According to some embodiments of the present application, the type of the second solvent includes but is not limited to any one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, trifluoromethyltrimethylsilane, and difluoromethyldimethylsilane, or a combination of two or more thereof.

[0131] According to some embodiments of the present application, if the electrolyte contains both the first solvent and the second solvent as solvents, the volume ratio of the first solvent to the second solvent is (1-9):(9-1).

[0132] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (1-9):(9-1), the second solvent effectively improves the viscosity of the electrolyte and does not affect the solvation effect of the first solvent with the metal ions.

[0133] According to some embodiments of the present application, the volume ratio of the first solvent to the second solvent is (2-8): (8-2).

[0134] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (2-8):(8-2), the second solvent has a relatively better effect on improving the viscosity of the electrolyte.

[0135] According to some embodiments of the present application, the volume ratio of the first solvent to the second solvent is (3-7): (7-3).

[0136] In the present application, when the volume ratio of the first solvent to the second solvent satisfies (3-7): (7-3), the viscosity of the electrolyte is relatively ideal, for example, the viscosity is relatively low, which is conducive to the solvation combination between the electrolyte and the metal ions without affecting the conductivity of the metal ions, and effectively improves the deposition morphology on the negative electrode surface, for example, making the negative electrode deposition more uniform, dense and effective.

[0137] According to some embodiments of the present application, the electrolyte further includes an electrolyte salt, and the type of the electrolyte salt includes any conventional type in the art, for example, including but not limited to inorganic metal salts, such as RClO4, RAsF6, RPF6, RBF4, RSbF6, RSO3F, RN(FSO2)2, etc.; fluorine-containing organic metal salts, such as RCF3SO3, RN(FSO2)(CF3SO2), RN(CF3SO2)2, RN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonyl imide lithium / sodium / potassium, cyclic 1,2-tetrafluoroethane disulfonyl imide lithium / sodium / potassium, RN(CF3SO2)( C4F9SO2), RC(CF3SO2)3, RPF4(CF3)2, RPF4(C2F5)2, RPF4(CF3SO2)2, RPF4(C2F5SO2)2, RBF2(CF3)2, RBF2(C2F5)2, RBF2(CF3SO2)2, RBF2(C2F5SO2)2, etc.; and metal salts containing dicarboxylic acid complexes, such as lithium / sodium / potassium bis(oxalato)borate, lithium / sodium / potassium difluorooxalato borate, lithium / sodium / potassium tri(oxalato)phosphate, lithium / sodium / potassium difluorobis(oxalato)phosphate, lithium / sodium / potassium tetrafluoro(oxalato)phosphate, etc. The metal and R here both contain one or a combination of two or more of lithium ions, sodium ions, and potassium ions.

[0138] According to some embodiments of the present application, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L.

[0139] In the present application, when the electrolyte salt meets this concentration range, a relatively good solvation structure can be formed between the solvent and the metal ions without affecting the ionic conductivity of the metal ions.

[0140] According to some embodiments of the present application, the concentration of the electrolyte salt in the electrolyte is 1 mol / L to 4 mol / L.

[0141] In the present application, when the electrolyte salt concentration is 1 mol / L to 4 mol / L, the improvement of the solvation structure of metal ions by the electrolyte and the deposition morphology of the negative electrode are relatively ideal.

[0142] Secondary battery

[0143] [Negative electrode]

[0144] According to some embodiments of the present application, the negative electrode sheet of the present application is a negative electrode current collector, combined with Figure 1 It can be seen that the negative electrode current collector 100 includes a negative electrode current collector substrate 110 and a modified layer 120 disposed on at least one side of the negative electrode current collector substrate 110. Figure 1Only one side of the surface is shown as having a modified layer, but the other surfaces of the negative electrode current collector substrate are also provided with a modified layer within the scope of protection of this application. At the same time, the formation method of the modified layer on the surface of the negative electrode current collector substrate includes any conventional form in the art, such as deposition, coating, etc.

[0145] In the present application, a modified layer is formed on the surface of the negative electrode current collector matrix, which is beneficial to reducing the deposition potential of the metal, can induce metal ions to deposit evenly and uniformly on the negative electrode surface, form a compact SEI film, inhibit the formation of metal dendrites, and has a direct effect on improving the cycle stability of the secondary battery.

[0146] According to some embodiments of the present application, the thickness of the modified layer is h2, the thickness of the negative electrode current collector matrix is ​​h1, and h2

[0147] In the present application, the thickness of the modified layer is consistent with the thickness of the negative electrode current collector matrix, and the specific thickness value can be directly measured by a measuring instrument or calculated by taking a photo. The thickness of the modified layer of the present application does not need to be too thick, and it can play a role in inducing uniform deposition of metal ions while not affecting the conductivity of the negative electrode current collector.

[0148] According to some embodiments of the present application, the thickness h1 of the negative electrode current collector matrix is ​​10 μm to 20 μm.

[0149] According to some embodiments of the present application, the thickness h2 of the modification layer is 10 nm to 50 nm.

[0150] In the present application, the thickness of the modified layer is reasonably and effectively designed according to the thickness of the negative electrode current collector matrix.

[0151] According to some embodiments of the present application, the material of the modification layer includes but is not limited to any one of inorganic metal elements, inorganic oxides, and organic substances, or a combination of two or more thereof.

[0152] According to some embodiments of the present application, the inorganic metal element includes any one or a combination of two or more of platinum, aluminum, magnesium, zinc, gold, silver, and tin.

[0153] According to some embodiments of the present application, the inorganic oxide includes any one of aluminum oxide, silicon dioxide, and titanium dioxide, or a combination of two or more thereof.

[0154] According to some embodiments of the present application, the organic matter includes any one of polydimethylsiloxane, graphene oxide, silicon dioxide-polymethyl methacrylate, alkali metal fluoride-vinylidene fluoride-hexafluoropropane, or a combination of two or more thereof.

[0155] ​According to some embodiments of the present application, the alkali metal fluoride-vinylidene fluoride-hexafluoropropane includes any one of lithium fluoride-vinylidene fluoride-hexafluoropropane, sodium fluoride-vinylidene fluoride-hexafluoropropane, and potassium fluoride-vinylidene fluoride-hexafluoropropane, or a combination of two or more thereof.

[0156] According to some embodiments of the present application, the negative electrode current collector substrate may be a metal foil or a composite current collector, the metal foil may be a copper foil, and the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0157] [Positive electrode]

[0158] According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector. The positive electrode film layer includes positive electrode active materials and additives, and the additives are used to supplement the metal ions consumed during the charge and discharge cycle, and improve the cycle life of the secondary battery by directly compensating for the consumed metal ions.

[0159] According to some embodiments of the present application, the mass ratio of the positive electrode active material to the additive is 1:(0.01-0.1).

[0160] According to some embodiments of the present application, the mass ratio of the positive electrode active material to the additive is 1:(0.04-0.1).

[0161] According to some embodiments of the present application, the mass ratio of the positive electrode active material to the additive is 1:(0.06-0.1).

[0162] In the present application, the appropriate additive content neither affects the energy density of the secondary battery nor helps to improve the cycle life of the secondary battery.

[0163] According to some embodiments of the present application, the types of additives include any conventional types in the art, such as but not limited to RN3, R2C4O4, R2C2O4, R2C3O5, R2C4O6, [COCON(R)N(R)] n , any one of R2S / KB / PVP, R2S / Co, RF / Co, RNiO2, R2CuO2, RFeO4, and RReO4; and R contains any one of lithium ion, sodium ion, and potassium ion.

[0164] According to some embodiments of the present application, when the positive electrode plate is applied to a lithium-ion battery, the positive electrode active material includes but is not limited to one or a combination of two or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphate containing an olivine structure; wherein the structural formula of the lithium phosphate containing an olivine structure is: LiFe 1-x-y Mn x M y PO4, 0≤x≤1, 0≤y<1, 0≤x+y≤1, M includes one or more combinations of transition metal elements or non-transition metal elements other than Fe and Mn, and M preferably includes one or more combinations of Cr, Mg, Ti, Al, Zn, W, Nb, and Zr. The present application specifically includes but is not limited to LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(NCM111), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 CO 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 CO 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 CO 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP) and LiMnPO4.

[0165] According to some embodiments of the present application, when the positive electrode plate is used in a sodium ion battery, the positive electrode active material includes but is not limited to at least one of a sodium transition metal oxide, a polyanionic compound, and a Prussian blue compound. Among them, in the sodium transition metal oxide, the transition metal can be one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0<x≤1. Polyanionic compounds include sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), sodium vanadium fluorophosphate (NaVPO4F), sodium vanadium phosphate (Na3V2(PO4)3), Na4Fe3(PO4)2P2O7, NaFePO4, etc. Prussian blue compounds are Na xM1M2(CN)6, wherein M1 and M2 are one or more of Fe, Mn, Co, Ni, Cu, Zn, Cr, Ti, V, Zr, and Ce, and 0<x≤2.

[0166] According to some embodiments of the present application, the positive electrode film layer also includes a conductive agent, a binder, etc. The conductive agent includes but is not limited to one or more combinations of graphite, superconducting carbon, carbon black (such as acetylene black, Ketjen black, Super P, etc.), carbon dots, carbon nanotubes, graphene and carbon nanofibers. The binder includes but is not limited to polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorine-containing acrylate resin, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, carboxymethyl chitosan, etc. One or more combinations. The positive electrode current collector in the present application can be a metal foil or a composite current collector, wherein the metal foil can be an aluminum foil, and 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 metal materials such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy on a polymer material substrate such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0167] [Isolation film]

[0168] In the present application, the separator between the positive electrode and the negative electrode can be any known porous structure separator with good chemical stability and mechanical stability. For example, the material of the separator may include but is not limited to a combination of one or more of the following: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film without special restrictions. When the separator is a multi-layer composite film, the materials of each layer can be the same or different without special restrictions.

[0169] In order to make the purpose, technical solution and advantages of this application clearer, the electrolyte and secondary battery protected by this application are described in detail below in combination with specific embodiments and when the electrolyte is applied to lithium-ion batteries. The chemical substances, reagents, etc. used in the following embodiments are all conventional models and manufacturers in the field.

[0170] Preparation of electrolyte

[0171] 1. Preparation of Compounds of Formula I

[0172] Taking compound I-1-3 as an example, the preparation method thereof is described in detail:

[0173] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of trifluoroacetaldehyde to the mixed solution, and continue stirring at 0°C-5°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-1-3.

[0174] Taking compound I-2-3 as an example, the preparation method thereof is described in detail:

[0175] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under an argon atmosphere. Slowly add 0.4 mol of 1,1,1-trifluoro-2,3-propanediol to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 1 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-2-3.

[0176] Taking compound I-3-9 as an example, the preparation method thereof is described in detail:

[0177] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of 1,1,1,4,4,4-hexafluoro-2,3-butanediol to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-3-9.

[0178] Taking compound I-4-3 as an example, the preparation method thereof is described in detail:

[0179] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of 2-(trifluoromethyl)propane-1,3-diol to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-4-3.

[0180] Taking compound I-5-3 as an example, the preparation method thereof is described in detail:

[0181] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of 1,3-butanediol-4,4,4-trifluoro-2-methyl to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-5-3.

[0182] Taking compound I-6-3 as an example, the preparation method thereof is described in detail:

[0183] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of 2,4-pentanediol-1,1,1-trifluoro to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-6-3.

[0184] Taking compound I-7-12 as an example, the preparation method thereof is described in detail:

[0185] Mix 400-600 ml of dehydrated tetrahydrofuran (THF) with 15-25 g of NaH, and stir at 0°C-5°C for 20 minutes under argon atmosphere. Slowly add 1 mol of 2,4-pentanediol-1,1,1-trifluoro-3-methyl to the mixed solution, and continue stirring at 0°C for 1 hour. Then, add 2.5-3 mol of iodomethane to the mixed solution. After overnight, filter the mixture, and take the liquid phase for subsequent purification to obtain compound I-7-12.

[0186] In addition, the compounds listed in Table 1 to Table 7 of the present application can be prepared by the same or similar methods as above.

[0187] 2. Prepare electrolyte

[0188] The solvent in the electrolyte solution is composed of the compound of structural formula I or the compound of structural formula I and a second solvent, wherein the volume ratio of the two is (1-9):(9-1). The type of the second solvent includes any one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, trifluoromethyltrimethylsilane, and difluoromethyldimethylsilane.

[0189] The electrolyte further contains lithium bis(fluorosulfonyl)imide at a concentration of 0.1 mol / L to 4 mol / L.

[0190] 3. Performance test of electrolyte

[0191] The present application uses a viscometer to directly measure the viscosity of the electrolyte at room temperature, as shown in Table 8. At the same time, the present application also uses a conductivity meter to measure the ionic conductivity of the electrolyte of the present application. The specific value is comparable to that of conventional electrolytes, so it is not listed in detail in Table 8 of the present application.

[0192] Table 8 Electrolyte performance parameters list

[0193]

[0194]

[0195]

[0196]

[0197]

[0198]

[0199]

[0200] Preparation of negative electrode

[0201] The negative electrode sheet of the present application is a negative electrode current collector, which is cut into a rectangle of 41 mm×51 mm and used as a negative electrode sheet for standby use.

[0202] The negative electrode current collector includes a negative electrode current collector matrix and a modified layer disposed on one side of the negative electrode current collector matrix, wherein the negative electrode current collector matrix is ​​made of copper foil with a thickness of h1, and the modified layer is made of any one or a combination of two or more of an inorganic metal element, an inorganic oxide, and an organic substance, and the thickness of the modified layer is h2, and h1 is 10 μm to 20 μm, and h2 is 10 nm to 50 nm. The parameters of the negative electrode sheet are shown in Table 9;

[0203] For example, in Example 1 of the present application, a 10 nm gold modification layer is deposited on the surface of the copper current collector by vacuum evaporation. The vacuum degree during the deposition process is <10 -6 Pa, deposition rate 0.2nm / s.

[0204] Preparation of positive electrode

[0205] The positive electrode active material is lithium nickel cobalt manganese oxide LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811) (NMC), conductive agent acetylene black, and binder PVDF were mixed in a mass ratio of 98:1:1, and solvent N-methylpyrrolidone (NMP) was added and stirred until the system was uniform to obtain a positive electrode slurry (solid content of 70%); the positive electrode slurry was heated to about 25 mg / cm 2 The loading amount is evenly coated on both sides of the positive electrode collector aluminum foil, dried at room temperature and transferred to an oven for further drying. The additive is taken to form a lithium supplement slurry and coated on the surface of the NCM positive electrode. The electrode is preheated for 2 hours, then kept at 120℃ for 10 hours, and then cut into 40mm×50mm rectangles as positive electrode sheets. The mass ratio of positive electrode active material to additive is 1: (0.01~0.1), and the additives include LiN3, Li2C4O4, Li2C2O4, Li2C3O5, Li2C4O6, [COCON(Li)N(Li)] n , Li2S / KB / PVP, Li2S / Co, LiF / Co, LiNiO2, Li2CuO2, LiFeO4, LiReO4. The selection of lithium supplement is shown in Table 10.

[0206] For example, in Example 1 of the present application, LiS / KB / PVP is formed into a lithium-replenishing slurry and coated on the surface of the NCM positive electrode.

[0207] Table 9 Parameters of positive and negative electrodes

[0208]

[0209]

[0210]

[0211]

[0212] Comparative Example 1

[0213] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 1, the negative electrode is an unmodified copper metal current collector. The electrolyte is 2M lithium bis(fluorosulfonyl)imide dissolved in a mixed solution of the compound of formula I-2-3 and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 7:3. The isolation membrane and the positive electrode material are the same as those in Example 1, and the test method is the same as that in Example 1.

[0214] Comparative Example 2

[0215] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 2, the negative electrode is a copper current collector modified with Au nanoparticles. The electrolyte is a 2M lithium bis(fluorosulfonyl)imide dissolved in a mixed solution of 1,3-dimethoxypropane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 7:3. The isolation membrane and the positive electrode material are the same as those in Example 1, and the test method is the same as that in Example 1.

[0216] Comparative Example 3

[0217] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 3, the negative electrode is a copper current collector modified with Au nanoparticles. The electrolyte is 2M lithium hexafluorophosphate dissolved in a mixed solution of 3mL ethylene carbonate and 7mL dimethyl carbonate. The isolation membrane and the positive electrode material are the same as those in Example 1, and the test method is the same as that in Example 1.

[0218] Comparative Example 4

[0219] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 4, the negative electrode is a copper current collector modified with Au nanoparticles. The electrolyte is a mixed solution of 2M lithium bis(fluorosulfonyl)imide dissolved in 2-trifluoromethyl-dimethoxypropane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 7:3. The positive electrode material is NCM811 positive electrode powder without adding a lithium supplement. The isolation membrane is the same as that in Example 1, and the test method is the same as that in Example 1.

[0220] Comparative Example 5

[0221] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 5, the negative electrode is a copper current collector modified with Au nanoparticles. The electrolyte is 2M lithium bis(fluorosulfonyl)imide dissolved in a mixed solution of the compound of the following formula II and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 7:3.

[0222]

[0223] Comparative Example 6

[0224] In the negative electrode-free lithium metal secondary battery provided in Comparative Example 6, the negative electrode is a copper current collector modified with Au nanoparticles. The electrolyte is 2M lithium bis(fluorosulfonyl)imide dissolved in a mixed solution of the following formula III compound and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a volume ratio of 7:3.

[0225]

[0226] Selection of isolation membrane

[0227] Use a polyethylene porous film and cut it into a 45mm×55mm rectangle for later use.

[0228] Secondary battery assembly

[0229] Take a cut positive electrode sheet and match it with two cut negative electrode sheets, use the above-mentioned isolation film to isolate the positive and negative electrodes in the middle, and wrap them in an aluminum-plastic film bag to form a laminated dry battery cell. Inject the above-prepared electrolyte, vacuum heat-press the aluminum-plastic film bag, and let it stand at room temperature for at least 6 hours before starting the cycle test. The rated capacity of the laminated battery prepared in this way is 120~160mAh.

[0230] Performance test of secondary batteries

[0231] (1) Capacity retention rate test after the first cycle of charge and discharge: Take the laminated battery cell prepared above, set the ambient temperature to 25°C, and perform the first charge and discharge. Use a constant current charge current of 0.2C (i.e., 28mA) to charge to 4.3V, and then charge at a constant voltage of 4.3V to a current of 0.05C. The test capacity is the first cycle charge specific capacity. Leave it for 5 minutes, and then discharge at 1C to 2.8V. The obtained capacity is recorded as the discharge specific capacity of the first cycle. The ratio of the two is the capacity retention rate after the first cycle of charge and discharge.

[0232] (2) Cycle stability test: Take the laminated battery cell prepared above, set the ambient temperature to 25°C, and use a charge and discharge rate of 0.2C (i.e. 28mA) for charging and 1C (i.e. 140mA) for discharge. The charge and discharge cut-off voltages are set to 4.3V and 2.8V, respectively, and the charging process adopts a constant current-constant voltage charging method. Specifically, when the 0.2C constant current charging reaches the cut-off voltage of 4.3V, continue to use a 4.3V constant voltage charging until the current decays to 0.1C (i.e. 14mA). When the discharge capacity decays to 80% of the first cycle discharge capacity, the battery life is considered to be over.

[0233] The performance of the above examples and comparative examples are shown in Table 10;

[0234] Table 10 Performance list of secondary batteries

[0235]

[0236]

[0237]

[0238]

[0239] It can be seen from Table 8, Table 9 and Table 10 that the compound of formula I designed in the present application can be used as an electrolyte, which can achieve effective dispersion of electrolyte salts and effective solvation binding with metal ions, further affecting the deposition morphology of the negative electrode, making the metal deposition more uniform and dense and reducing the probability of irreversible reaction between the metal and the electrolyte, and finally improving the first week coulomb efficiency and cycle stability of the secondary battery. At the same time, the compound of formula I protected in the present application can also be effectively matched with the second solvent listed to achieve the purpose of reducing the viscosity of the electrolyte, and the low-viscosity electrolyte not only promotes the solvation binding of metal ions, but also does not affect the ion conduction ability of metal ions, which further promotes the improvement of the first week coulomb efficiency and cycle stability of the secondary battery.

[0240] Table 10 shows Comparative Examples 2, 5 and 6, which, compared with the specific examples of the present application, again show the key role of the compound of formula I as an electrolyte in improving the first-week coulomb efficiency and cycle stability of the secondary battery. In addition, surface modification of the negative electrode current collector and addition of metal ion supplement components to the positive electrode active material can also effectively improve the first-week coulomb efficiency and cycle stability of the secondary battery. Technical purpose.

[0241] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. An electrolyte, characterized in that: A compound comprising the following structural formula I: Wherein, in Formula I, R1 and R2 each independently comprise one of C1-C2 alkyl groups; R3 and R4 each independently include any one of hydrogen, methyl, and fluorine-substituted methyl, and at least one of R3 and R4 includes fluorine-substituted methyl; n is any positive integer from 1 to 3.

2. The electrolyte according to claim 1, characterized in that In the formula I, one of R3 and R4 contains a fluorine-substituted methyl group, and the other contains any one of hydrogen and methyl group.

3. The electrolyte according to any one of claims 1 to 2, characterized in that The electrolyte comprises any one or a combination of two or more of the following compounds of structural formula I-1, I-2, I-3, I-4, I-5, I-6, and I-7: In formula I-1, Rf1 comprises a fluorine-substituted methyl group; In formula I-2, Rf2 comprises a fluorine-substituted methyl group; In formula I-3, Rf3 and Rf4 each independently include a methyl group or a fluorine-substituted methyl group; In formula I-4, Rf5 comprises a fluoro-substituted methyl group; In formula I-5, Rf6 and Rf7 each independently include a methyl group or a fluorine-substituted methyl group; In formula I-6, Rf8 and Rf9 each independently include a methyl group or a fluorine-substituted methyl group; In formula I-7, Rf 10 , Rf 11 , Rf 12 Each independently includes a methyl group and a fluorine-substituted methyl group.

4. The electrolyte according to any one of claims 1 to 2, characterized in that The compound of structural formula I is the first solvent of the electrolyte; the electrolyte also contains a second solvent; Preferably, the volume ratio of the first solvent to the second solvent is (1-9): (9-1), preferably (2-8): (8-2), and more preferably (3-7): (7-3); Preferably, the second solvent comprises any one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, trifluoromethyltrimethylsilane, and difluoromethyldimethylsilane, or a combination of two or more thereof.

5. The electrolyte according to any one of claims 1 to 2, characterized in that The electrolyte further comprises an electrolyte salt; Preferably, the concentration of the electrolyte salt in the electrolyte is 0.1 mol / L to 4 mol / L, preferably 1 mol / L to 4 mol / L.

6. A secondary battery, characterized in that: Include: Negative electrode; Positive electrode; Isolation film; And the electrolyte according to any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that: The negative electrode plate is a negative electrode current collector, and the negative electrode current collector comprises a negative electrode current collector matrix and a modified layer disposed on at least one side of the surface of the negative electrode current collector matrix; Preferably, the thickness of the modified layer is h2, the thickness of the negative electrode current collector matrix is ​​h1, and h2<h1 is satisfied.

8. The secondary battery according to claim 7, characterized in that: The thickness h1 of the negative electrode current collector matrix is ​​10 μm to 20 μm; Preferably, the thickness h2 of the modified layer is 10 nm to 50 nm.

9. The secondary battery according to claim 7 or 8, characterized in that: The material of the modification layer includes any one of inorganic metal elements, inorganic oxides, and organic substances, or a combination of two or more thereof; Preferably, the inorganic metal element comprises any one or a combination of two or more of platinum, aluminum, magnesium, zinc, gold, silver, and tin; Preferably, the inorganic oxide comprises any one of aluminum oxide, silicon dioxide, and titanium dioxide, or a combination of two or more thereof; Preferably, the organic matter comprises any one or a combination of two or more of polydimethylsiloxane, graphene oxide, silicon dioxide-polymethyl methacrylate, alkali metal fluoride-vinylidene fluoride-hexafluoropropane; Preferably, the alkali metal fluoride-vinylidene fluoride-hexafluoropropane comprises any one of lithium fluoride-vinylidene fluoride-hexafluoropropane, sodium fluoride-vinylidene fluoride-hexafluoropropane, potassium fluoride-vinylidene fluoride-hexafluoropropane or a combination of two or more thereof.

10. The secondary battery according to any one of claims 6 to 8, characterized in that The positive electrode sheet comprises a positive electrode active material and an additive, wherein the mass ratio of the positive electrode active material to the additive is 1:(0.01-0.1), preferably 1:(0.04-0.1), and more preferably 1:(0.06-0.1); Preferably, the additive comprises RN3, R2C4O4, R2C2O4, R2C3O5, R2C4O6, [COCON(R)N(R)] n , any one of R2S / KB / PVP, R2S / Co, RF / Co, RNiO2, R2CuO2, RFeO4, and RReO4; and R contains any one of lithium ion, sodium ion, and potassium ion.

11. An electrical device, characterized in that: A secondary battery comprising the electrolyte according to any one of claims 1 to 5 or any one of claims 6 to 10.

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