Electrolyte for lithium metal secondary battery, secondary battery, and electric device

Abstract

The invention provides an electrolyte for a lithium metal secondary battery, the secondary battery and an electric device. The electrolyte comprises a lithium salt, an organic solvent and a diluent. The organic solvent comprises at least one of a compound shown as a formula (I) or a compound shown as a formula (II). In the formula (I), R1 and R2 are independently selected from C1-C10 alkyl groups, and k is an integer selected from 1-3. In the formula (II), X, Y and Z are respectively and independently selected from O or S, in at least two of X, Y and Z, one is O, and the other is S; r3 and R4 are respectively and independently selected from alkyl groups of C1 to C10; and m and n are each independently an integer selected from 1 to 3. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to an electrolyte for a lithium metal secondary battery, a secondary battery, and an electrical device using the same. Background Art

[0002] In recent years, with the increasingly wide application range of secondary batteries, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind, and solar power stations, as well as in multiple fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the great development of secondary batteries, higher requirements are also put forward for their energy density, cycle performance, safety performance, etc.

[0003] Alkali metal batteries with metal lithium, sodium, potassium, and their alloys as the negative electrode are one of the most promising energy storage devices at present due to their low reduction potential and high theoretical energy density. However, the current electrolyte is prone to form a loose and unstable solid electrolyte interface (SEI) film with the negative electrode of the alkali metal battery, affecting the cycle performance of the battery. Therefore, how to improve the performance of the electrolyte has become an urgent problem to be solved in this field. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide an electrolyte for a lithium metal secondary battery, thereby promoting the formation of a stable SEI film, increasing the boiling point of the electrolyte, and further improving the cycle performance of the battery. The present application also provides a secondary battery and an electrical device using the same.

[0005] To achieve the above object, in a first aspect of the present application, there is provided an electrolyte for a lithium metal secondary battery, including a lithium salt, an organic solvent, and a diluent; wherein, the organic solvent includes at least one of a compound represented by formula (I) or a compound represented by formula (II);

[0006]

[0007] In formula (I), R 1 and R 2 are each independently selected from alkyl groups having 1 to 10 carbon atoms, and k is an integer selected from 1 to 3;

[0008]

[0009] In formula (II), X, Y, and Z are each independently selected from O or S, wherein, among at least two of X, Y, and Z, one is O and the other is S; R 3 and R 4 are each independently selected from alkyl groups having 1 to 10 carbon atoms, and m and n are each independently integers selected from 1 to 3.

[0010] The organic solvent in the embodiments of the present application is a thioether solvent containing at least one oxygen atom and at least one sulfur atom. Among them, the sulfur atom can contribute 3p lone pair electrons, exhibit nucleophilicity, and interact with lithium ions. At the same time, the electronegativity of the sulfur atom is lower than that of the oxygen atom. Therefore, the Li-S interaction will be weaker than the Li-O interaction, thereby reducing the solvation effect of the organic solvent on Li, increasing the anion coordination number in the Li solvation structure, and thus improving the stability of the SEI film.

[0011] In any embodiment, in formula (I), R 1 and R 2 are each independently selected from C1-C6 alkyl groups, optionally selected from C1-C4 alkyl groups; and

[0012] In formula (II), R 3 and R 4 are each independently selected from C1-C6 alkyl groups, optionally selected from C1-C4 alkyl groups. The selection of the above groups is conducive to forming a more stable SEI film, thereby improving the cycling performance of the battery.

[0013] In any embodiment, the organic solvent includes at least one of the compounds represented by formula (I), and in formula (I), k is 2, and R 1 and R 2 are each independently selected from C1-C4 alkyl groups.

[0014] In any embodiment, the organic solvent includes at least one of the following compounds:

[0015]

[0016] In this way, there are 2 carbon atoms between the sulfur atom and the oxygen atom, with a moderate distance, so that a relatively high ionic conductivity can be obtained after the organic solvent binds to lithium ions.

[0017] In any embodiment, the concentration of the lithium salt in the electrolyte is 0.1-4 mol / L, optionally 1-3 mol / L. By controlling the concentration of the lithium salt in the electrolyte within the above range, it is beneficial to the diffusion of lithium ions, making the provided electrolyte have a relatively high ionic conductivity.

[0018] In any embodiment, in the electrolyte, the volume ratio of the organic solvent to the diluent is σ, where 1:9 ≤ σ ≤ 9:1; optionally, 2:5 ≤ σ ≤ 5:2. By adjusting the addition ratio of the organic solvent and the diluent, it can help reduce the solvation effect, increase the anion coordination number, achieve the purpose of adjusting the solvation structure, thereby improving the stability of the SEI film, and further improving the cycling performance of the battery.

[0019] In any embodiment, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. The above lithium salts are convenient and easy to obtain, have high solubility in the electrolyte, make the electrolyte have high conductivity, and thus enable the battery to have good cycle performance.

[0020] In any embodiment, the diluent includes at least one of fluorinated alkanes, ethers, and silane compounds; optionally, the diluent includes at least one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, (trifluoromethyl)trimethylsilane, and (difluoromethyl)dimethylsilane. Selecting the above diluents helps to effectively adjust the solvation structure, improve the Coulomb efficiency, and reduce the viscosity of the electrolyte to improve the cycle performance of the battery.

[0021] In any embodiment, at standard atmospheric pressure, the boiling point range of the organic solvent is between 40 and 150 °C. When the organic solvent has a high boiling point, it helps the electrolyte containing the organic solvent to also have a high boiling point, making the electrolyte not easily volatilize and at the same time enabling better cycle performance to be obtained.

[0022] In any embodiment, at standard atmospheric pressure, the boiling point of the electrolyte is higher than 105 °C; optionally, higher than 115 °C; optionally, higher than 125 °C. In the embodiments of the present application, the electrolyte has a high boiling point and is not easily volatilized, so that the electrolyte has improved thermal stability and cycle performance, thereby broadening the use temperature range of the electrolyte.

[0023] The second aspect of the present application also provides a lithium metal secondary battery including the electrolyte of the first aspect of the present application. The electrolyte of the embodiments of the present application can reduce the solvation effect of Li, increase the anion coordination number in the Li solvation structure, and further increase the probability of anions participating in the film-forming reaction, thereby improving the stability of the SEI film. At the same time, compared with the electrolyte using an ether solvent without a sulfur atom, the electrolyte of the embodiments of the present application also has a high boiling point and thermal stability, broadening the use temperature range of the electrolyte. Furthermore, the electrolyte can improve the cycle performance of the lithium metal secondary battery.

[0024] In any embodiment, the lithium metal secondary battery further includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer includes lithium metal and / or lithium alloy. By including lithium metal and / or lithium alloy in the negative electrode film layer, the battery can have a lower reduction potential and / or a higher theoretical energy density.

[0025] The third aspect of the present application further provides an electrical device, including the lithium metal secondary battery of the second aspect of the present application.

[0026] The organic solvent in the electrolyte of the lithium metal secondary battery according to the embodiment of the present application can reduce the solvation of Li, increase the anion coordination number in the Li solvation structure, and thus increase the probability of anions participating in the film-forming reaction, thereby improving the stability of the SEI film. At the same time, compared with the electrolyte using an ether solvent without a sulfur atom, the electrolyte according to the embodiment of the present application also has a higher boiling point and thermal stability, broadening the operating temperature range of the electrolyte. Furthermore, the electrolyte can improve the cycling performance of the lithium metal secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a battery cell according to an embodiment of the present application.

[0028] Figure 2 is Figure 1 a exploded view of the battery cell shown in an embodiment of the present application.

[0029] Figure 3 is a schematic diagram of a battery module according to an embodiment of the present application.

[0030] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0031] Figure 5 is Figure 4 a exploded view of the battery pack shown in an embodiment of the present application.

[0032] Figure 6 is a schematic diagram of an electrical device using the secondary battery as a power source according to an embodiment of the present application.

[0033] Description of the Reference Numerals:

[0034] 1 battery pack; 2 upper box body; 3 lower box body; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; 53 top cover assembly DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] Hereinafter, embodiments of the electrolyte for a lithium metal secondary battery, the lithium metal secondary battery, and the electrical device to which the present application is specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the accompanying 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 recited in the claims. All documents cited in the present application, including published publications, patents, and patent applications, are hereby incorporated by reference in their entirety into this text.

[0036] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise specified, the numerical range "a - b" represents an abbreviated representation 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" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0038] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all steps of the present application can be carried out 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) carried out sequentially, or may include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can 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.

[0040] A lithium metal battery generally refers to a battery with a negative electrode of metallic lithium and its alloys. Due to its low reduction potential and high theoretical energy density, it is one of the most promising energy storage devices at present.

[0041] However, due to its high reactivity, poor safety and cycling performance, the application of lithium metal batteries is severely hindered.

[0042] In the first cycle of the battery, the electrolyte reacts with the electrode to form a passivation layer, namely the SEI film. A good SEI will block the subsequent reaction between the electrolyte and the electrode material, and at the same time, its morphology is relatively uniform and dense, and its electrochemical and other chemical properties are stable.

[0043] However, during the cycling process of lithium metal batteries, the organic solution often reacts with the negative electrode of the battery to form a loose and unstable SEI film rich in organic matter. This film is prone to rupture during the cycling process, resulting in irreversible loss of lithium metal and reducing the Coulomb efficiency.

[0044] In order to improve the stability of the SEI film, it is necessary to increase the content of inorganic elements such as F, S, N, P, etc. in the SEI film. One method is to increase the coordination number of anions in the lithium ion solvation structure, thereby increasing the probability of anions participating in the film-forming reaction. The currently widely used method is to combine an ether solvent with a diluent to form a local high-concentration solution. Although the use of an ether solvent in lithium metal batteries can improve the compatibility between the organic solvent and the electrode, the ether solvent generally has a strong interaction with Li, and it is impossible to further increase the coordination number of anions. At the same time, most ether solvents have relatively low boiling points, resulting in easy volatilization of the electrolyte and restricting the further application of the electrolyte.

[0045] Based on this, the present application proposes an electrolyte for a lithium metal secondary battery, a lithium metal secondary battery and an electrical device.

[0046] Electrolyte for a lithium metal secondary battery

[0047] The present application proposes an electrolyte for a lithium metal secondary battery, which includes a lithium salt, an organic solvent and a diluent.

[0048] The organic solvent includes at least one of the compounds represented by formula (I) or the compounds represented by formula (II).

[0049]

[0050] In formula (I), R 1 and R 2 are each independently selected from C1-C10 alkyl groups, and k is an integer selected from 1-3.

[0051]

[0052] In formula (II), X, Y, and Z are each independently selected from O or S, where among at least two of X, Y, and Z, one is O and the other is S; R 3 and R 4 are each independently selected from C1-C10 alkyl groups, and m and n are each independently integers selected from 1-3.

[0053] The organic solvent in the embodiments of the present application is a thioether solvent containing at least one oxygen atom and at least one sulfur atom. Among them, the sulfur atom can contribute 3p lone pair electrons, showing nucleophilicity and interacting with lithium ions. At the same time, the electronegativity of the sulfur atom is lower than that of the oxygen atom. Therefore, the Li-S interaction will be weaker than the Li-O interaction, thereby realizing the function of reducing the solvation effect and further increasing the coordination number of anions, thereby improving the stability of the SEI film.

[0054] Through quantum chemical calculations, the organic solvent in the embodiments of the present application has good reducibility resistance.

[0055] The boiling points of ordinary ether solvents (without any sulfur atoms) are generally low, seriously affecting the operating temperature range of the battery. The organic solvent in the embodiments of the present application contains at least one sulfur atom. This ether solvent substituted by at least one sulfur atom shows a significant increase in boiling point and enhanced volatility resistance. At the same time, the organic solvent molecule also contains at least one oxygen atom not substituted by a sulfur atom, so the stability of the organic solvent molecule is good. This is because if all the oxygen atoms in the ether solvent are substituted by sulfur atoms, the molecular stability will be weakened.

[0056] Although the mechanism is not yet clear, the applicant unexpectedly found that by including the above-mentioned organic solvents, the electrolyte of the embodiment of the present application can reduce the solvation of lithium ions, increase the coordination number of anions in the lithium ion solvation structure, and thus increase the probability of anions participating in the film-forming reaction, thereby improving the stability of the SEI film. At the same time, compared with the electrolyte using an ether solvent without a sulfur atom, the electrolyte of the embodiment of the present application has a higher boiling point and thermal stability, broadening the operating temperature range of the electrolyte. Furthermore, the electrolyte can improve the cycling performance of the lithium metal battery.

[0057] Herein, "C1-C10 alkyl" refers to a straight-chain or branched aliphatic hydrocarbon group having 1 to 10 carbon atoms. Optional C1-C10 alkyls include straight-chain or branched C1-C8 alkyls having 1 to 8 carbon atoms. Optional C1-C10 alkyls include straight-chain or branched C1-C6 alkyls having 1 to 6 carbon atoms. Optional C1-C10 alkyls include straight-chain or branched C1-C4 alkyls having 1 to 4 carbon atoms. Optional C1-C10 alkyls include C1-C2 alkyls having 1 to 2 carbon atoms. Examples of C1-C10 alkyls include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, sec-pentyl, hexyl, heptyl, octyl, isooctyl, nonyl, and decyl.

[0058] k is an integer selected from 1 to 3. For example, k can be 1, 2, or 3. m and n are each independently an integer selected from 1 to 3. For example, m can be 1, 2, or 3; n can be 1, 2, or 3.

[0059] In some embodiments, in formula (I), R 1 , R 2 are each independently selected from C1-C6 alkyls, optionally selected from C1-C4 alkyls. For example, R 1 , R 2 can each independently be selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, n-pentyl, sec-pentyl, or hexyl, etc. In formula (II), R 3 , R 4 are each independently selected from C1-C6 alkyls, optionally selected from C1-C4 alkyls. For example, R 3 , R 4 can each independently be selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, sec-butyl, n-pentyl, sec-pentyl, or hexyl, etc. The selection of the above groups is beneficial to forming a more stable SEI film, thereby improving the cycling performance of the battery.

[0060] In some embodiments, the organic solvent includes at least one of the following compounds:

[0061]

[0062]

[0063]

[0064] The above-mentioned organic solvents are beneficial to the formation of a more stable SEI film, increase the boiling point of the electrolyte, and thus improve the cycling performance of the battery.

[0065] In some embodiments, the organic solvent includes at least one of the compounds represented by formula (I), and in formula (I), k is 2, and R 1 and R 2 are each independently selected from C1-C4 alkyl groups, and optionally, selected from methyl or ethyl.

[0066] In some embodiments, the organic solvent includes at least one of the following compounds:

[0067]

[0068] In the above embodiments, there are two carbon atoms between the sulfur atom and the oxygen atom, with a moderate distance, so that a higher ionic conductivity can be obtained after the organic solvent combines with lithium ions. Therefore, during the battery cycling process, not only a SEI film with more inorganic components and more compact and stable structure is formed, but also a higher ionic conductivity is achieved, thereby improving the cycling performance of the battery.

[0069] In some embodiments, at one standard atmosphere, the boiling point range of the organic solvent is between 40 and 150 °C, for example, 45 °C - 150 °C, 50 °C - 150 °C, 55 °C - 150 °C, 60 °C - 150 °C, 65 °C - 150 °C, 70 °C - 150 °C, 75 °C - 150 °C, 80 °C - 150 °C, 85 °C - 150 °C, 90 °C - 150 °C, 95 °C - 150 °C, 100 °C - 150 °C, 110 °C - 150 °C, 120 °C - 150 °C, 130 °C - 150 °C, 140 °C - 150 °C, etc.

[0070] When the organic solvent has a higher boiling point, it helps the electrolyte containing the organic solvent to also have a higher boiling point, so that the electrolyte is not easily volatilized and good cycling performance can be obtained at the same time.

[0071] In some embodiments, the lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate. The above lithium salts are convenient and easy to obtain, have high solubility in the electrolyte, make the electrolyte have high conductivity, and thus enable the battery to have good cycling performance.

[0072] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.1 - 4 mol / L; optionally, the concentration range of the lithium salt is 1 - 3 mol / L. The lithium salt concentration calculation formula is (moles of lithium salt / total volume of electrolyte) × 100%. Optionally, the concentration range of the lithium salt is 1.5 - 3.5 mol / L, for example 2 mol / L.

[0073] Here, the value of the concentration of the lithium salt in the electrolyte can be the endpoint values or any value between the two endpoints. For example, it can be: 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.4 mol / L, 2.6 mol / L, 2.8 mol / L, 3 mol / L, 3.2 mol / L, 3.4 mol / L, 3.6 mol / L, 3.8 mol / L, etc.

[0074] By controlling the concentration of the lithium salt in the electrolyte within the above range, it is beneficial to the diffusion of lithium ions, making the provided electrolyte have high ionic conductivity.

[0075] In some embodiments, the anion coordination number of Li in the first solvation layer can be greater than or equal to 3. A higher anion coordination number is beneficial to the formation of a stable SEI film rich in inorganic substances, thereby improving the cycling performance of the battery.

[0076] In some embodiments, the diluent includes at least one of fluorinated alkanes, ethers, and silane compounds. Optionally, the diluent includes at least one of decafluoropentane, 1,1,2,2 - tetrafluoroethyl - 2,2,3,3 - tetrafluoropropyl ether, (trifluoromethyl)trimethylsilane, and (difluoromethyl)dimethylsilane. Selecting the above diluents can effectively adjust the solvation structure and reduce the viscosity of the electrolyte to improve the cycling performance of the battery.

[0077] In some embodiments, in the electrolyte of the embodiments of the present application, the volume ratio of the organic solvent to the diluent is σ, where 1:9 ≤ σ ≤ 9:1; optionally, 2:5 ≤ σ ≤ 5:2; optionally, 3:4 ≤ σ ≤ 4:3; optionally, σ = 2:5.

[0078] Here, the value of σ can be the endpoint values or any value between the endpoints. For example, it can be: 2:9, 3:9, 4:9, 5:9, 6:9, 7:9, 8:9, 2:5, 3:5, 4:5, 9:1, 9:2, 9:3, 9:4, 9:5, 9:6, 9:7, 9:8, 5:2, 5:3, 5:4, etc., but not limited thereto.

[0079] By adjusting the addition ratio of the organic solvent and the diluent, it can help reduce the solvation effect, increase the anion coordination number, achieve the purpose of adjusting the solvation structure, thereby improving the stability of the SEI film and further improving the cycle performance of the battery.

[0080] In some embodiments, at standard atmospheric pressure, the boiling point of the electrolyte is higher than 105 °C; optionally, higher than 115 °C; optionally, higher than 125 °C.

[0081] The boiling point of the electrolyte can be, for example, higher than 105 °C, higher than 110 °C, higher than 115 °C, higher than 120 °C, higher than 125 °C, higher than 130 °C, higher than 135 °C, higher than 140 °C, higher than 145 °C, higher than 150 °C, higher than 155 °C, higher than 160 °C, higher than 165 °C, higher than 170 °C, higher than 175 °C, etc., but not limited thereto.

[0082] Compared with the electrolyte using an ether solvent without sulfur atoms, the electrolyte in the embodiments of the present application has a higher boiling point and is not easily volatile, making the electrolyte have improved thermal stability and cycle performance, thereby broadening the operating temperature range of the electrolyte.

[0083] In some embodiments, the electrolyte may further include other organic solvents, such as at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0084] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature or low-temperature performance of the battery, etc.

[0085] The present application also provides a lithium metal secondary battery and an electrical device.

[0086] The lithium metal secondary battery and the electrical device of the present application will be described below with appropriate reference to the accompanying drawings.

[0087] In some embodiments of the present application, a lithium metal secondary battery is provided.

[0088] The term "secondary battery" mentioned herein refers to a battery cell, a battery module, or a battery pack. Explanation will be given separately below.

[0089] Generally, a secondary battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are inserted into and extracted from between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive and negative electrodes, and at the same time allowing ions to pass through.

[0090] Positive electrode sheet

[0091] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0092] As an example, the positive electrode current collector has two opposite sides in its own thickness direction, and the positive electrode film layer is provided on any one or both of the two opposite sides of the positive electrode current collector.

[0093] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one side of the polymer material base layer. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0094] In some embodiments, when the battery cell is a lithium-ion battery, the positive electrode active material can be the positive electrode active material for lithium-ion batteries well-known in the art. As an example, the positive electrode active material can include at least one of the following materials: lithium-containing phosphates with olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery can also be used. These positive electrode active materials can be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides can include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (which can also be abbreviated as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (which can also be abbreviated as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (which can also be abbreviated as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (which can also be abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (which can also be abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2 ) and their modified compounds, etc. Examples of lithium-containing phosphates with olivine structure can include, but are not limited to, lithium iron phosphate (such as LiFePO 4、 LiFeP 2 O 7 , Li 3 Fe 2 (PO 4 )3 , LiFe 4 (P 2 O 7 ) 3 ; It can also be abbreviated as LFP), the composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), the composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of the composite materials of lithium manganese iron phosphate and carbon.

[0095] During the charge and discharge process of the battery, the deintercalation and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0096] In the listing of the positive electrode active material in this application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0097] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0098] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0099] In some embodiments, the positive electrode plate can be prepared in the following manner: Disperse the components for preparing the positive electrode plate, such as the positive electrode active material, conductive agent, binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coat the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode plate can be obtained.

[0100] Negative electrode plate

[0101] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer provided on at least one side of the negative electrode current collector.

[0102] As an example, the negative electrode current collector has two opposite sides in its own thickness direction, and the negative electrode film layer is provided on any one or both of the two opposite sides of the negative electrode current collector.

[0103] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one side of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] In some embodiments, the negative electrode film layer includes lithium metal and / or lithium alloy. A lithium alloy refers to an alloy formed by metallic lithium and other metal or non-metal elements. The metal elements can include tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), platinum (Pt), etc., but are not limited thereto. The non-metal elements can include boron (B), carbon (C), silicon (Si), etc., but are not limited thereto. A battery including the above materials as the negative electrode active material can have a lower reduction potential and / or a higher theoretical energy density.

[0105] In some embodiments, the negative electrode plate can be prepared by the following method: laminating a lithium foil and / or a lithium alloy on the negative electrode current collector by a rolling method to obtain the negative electrode plate.

[0106] Electrolyte

[0107] The electrolyte plays a role in conducting ions between the positive electrode plate and the negative electrode plate. In the embodiments of the present application, the electrolyte uses the electrolyte for a lithium metal secondary battery described in the embodiments of the present application.

[0108] Separator

[0109] In some embodiments, the battery cell further includes a separator. The present application does not particularly limit the type of the separator, and any well-known porous structure separator with good chemical stability and mechanical stability can be selected.

[0110] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0111] In some embodiments, the positive electrode plate, the negative electrode plate, and the separator can be made into an electrode assembly by a winding process or a stacking process.

[0112] In some embodiments, a battery cell may include an outer package. The outer package may be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0113] In some embodiments, the outer package of the battery cell may be a hard case, such as a hard plastic case, an aluminum case, a steel case, etc. The outer package of the battery cell may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic. As plastics, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. may be listed.

[0114] This application does not particularly limit the shape of the battery cell, and it may be cylindrical, square, or any other arbitrary shape. For example, Figure 1 is a battery cell 5 with a square structure as an example.

[0115] In some embodiments, referring to Figure 2 , the outer package may include a housing 51 and a top cover assembly 53. Among them, the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode plate, the negative electrode plate, and the separator may form an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of electrode assemblies 52 included in the battery cell 5 may be one or more, and those skilled in the art can select according to specific actual needs.

[0116] In some embodiments, battery cells can be assembled into a battery module. The number of battery cells included in the battery module may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0117] Figure 3 is a battery module 4 as an example. Referring to Figure 3 , in the battery module 4, multiple battery cells 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other arbitrary manner. Further, the multiple battery cells 5 can be fixed by fasteners.

[0118] Optionally, the battery module 4 may further include a housing having a receiving space, and multiple battery cells 5 are received in the receiving space.

[0119] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack. The number of battery modules included in the battery pack may be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0120] Figure 4 and Figure 5is a battery pack 1 as an example. Refer to Figure 4 and Figure 5 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 can be covered on the lower box body 3 to form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0121] In addition, the present application also provides an electric device, and the electric device includes the secondary battery provided by the present application. The secondary battery can be used as the power supply of the electric device or as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, etc., but is not limited thereto.

[0122] As the electric device, a battery cell, a battery module or a battery pack can be selected according to its usage requirements.

[0123] Figure 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the electric device, a battery pack or a battery module can be adopted.

[0124] Another example of the device can be a mobile phone, a tablet computer, a laptop computer, etc. This device usually requires thin and light, and a battery cell can be used as the power supply.

[0125] Embodiment

[0126] Hereinafter, embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application and should not be construed as a limitation to the present application. For those not specified in the embodiments regarding specific technologies or conditions, they shall be carried out according to the technologies or conditions described in the literature in the field or according to the product specifications. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0127] Preparation Example: Compound of Formula I-10 Preparation of the compound

[0128] Referring to, for example, Bull.Chem.Soc.Jpn, 50, 1977, 650, the compound of Formula I-10 can be synthesized through the following route:

[0129]

[0130]

[0131] The obtained product can be purified by a distillation process at 135 °C.

[0132] The above-mentioned document is incorporated herein by reference in its entirety.

[0133] Here, taking the compound of formula I-10 as an example, the preparation method of the organic solvent in the embodiments of the present application is described. Regarding other exemplary organic solvents involved herein, those skilled in the art can obtain them by referring to the above preparation method or can obtain them through commercial purchase, and will not be elaborated herein.

[0134] Formula I-10 has a boiling point of 134-135 °C, which is higher than the boiling point of ethylene glycol dimethyl ether of 82-83 °C. By introducing at least one sulfur atom into a common ether solvent (without any sulfur atoms), the boiling point of the solvent can be increased. Therefore, using the organic solvent in the embodiments of the present application can increase the boiling point of the electrolyte.

[0135] Examples 1 to 13

[0136] Take 2 moles of lithium bis(fluorosulfonyl)imide and add it to a mixed solution of 286 ml of the organic solvent in the embodiments of the present application (specifically shown in Table 1) and 714 ml of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and mix evenly to form a colorless, transparent and homogeneous solution with a volume of 1 liter to obtain the electrolytes of Examples 1 to 13. Among them, the lithium salt concentration is 2 mol / L.

[0137] Examples 14 to 17

[0138] Take 2 moles of lithium bis(trifluoromethylsulfonyl)imide and add it to a mixed solution of 286 ml of the organic solvent in the embodiments of the present application (one of formula I-10, formula I-11, formula I-13 and formula I-16) and 714 ml of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and mix evenly to form a colorless, transparent and homogeneous solution with a volume of 1 liter to obtain the electrolytes of Examples 14 to 17.

[0139] Examples 18 to 21

[0140] Take 2 moles of lithium bis(fluorosulfonyl)imide and add it to a mixed solution of 286 ml of the organic solvent in the embodiments of the present application (one of formula I-10, formula I-11, formula I-13 and formula I-16) and 714 ml of decafluoropentane, and mix evenly to form a colorless, transparent and homogeneous solution with a volume of 1 liter to obtain the electrolytes of Examples 18 to 21.

[0141] Examples 22 to 25

[0142] Take 2 moles of lithium bis(fluorosulfonyl)imide and add it to a mixed solution of 714 ml of the organic solvent of the present application embodiment (one of Formula I-10, Formula I-11, Formula I-13, and Formula I-16) and 286 ml of (trifluoromethyl)trimethylsilane. Mix evenly to form a colorless, transparent, and homogeneous solution with a volume of 1 liter, obtaining the electrolytes of Examples 22 to 25.

[0143] Examples 26 to 27

[0144] Take 2 moles of lithium bis(fluorosulfonyl)imide and add it to a mixed solution of 100 ml of the organic solvent of Formula I-10 and 900 ml of (difluoromethyl)dimethylsilane. Mix evenly to form a colorless, transparent, and homogeneous solution with a volume of 1 liter, obtaining the electrolyte of Example 26.

[0145] Take 2 moles of lithium bis(fluorosulfonyl)imide and add it to a mixed solution of 900 ml of the organic solvent of Formula I-10 and 100 ml of (difluoromethyl)dimethylsilane. Mix evenly to form a colorless, transparent, and homogeneous solution with a volume of 1 liter, obtaining the electrolyte of Example 27.

[0146] Comparative Example 1

[0147] Take 3 ml of ethylene carbonate and 7 ml of dimethyl carbonate and mix them into a colorless, transparent solution. Take 3 g of lithium hexafluorophosphate and add it to the transparent solution. Stir well to form a colorless, transparent solution with a concentration of 2 M, obtaining the electrolyte of Comparative Example 1.

[0148] Comparative Example 2

[0149] Take 2 moles of lithium bis(fluorosulfonyl)imide salt and add it to 286 ml of ethylene glycol dimethyl ether (CH 3 OCH 2 CH 2 OCH 3 , DMET) and 714 ml of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether. Stir well to form a colorless, transparent solution with a volume of 1 liter, obtaining the electrolyte of Comparative Example 2.

[0150] Comparative Example 3

[0151] Take 2 moles of lithium bis(fluorosulfonyl)imide salt and add it to 286 ml of 1,2-dimethylthioethane (CH 3 SCH 2 CH 2 SCH 3, 1,2-bis(methylthio)ethane, BMTE) and 714 mL of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether were stirred well to form a colorless transparent solution with a volume of 1 L, and the electrolyte solution of Comparative Example 3 was obtained.

[0152] The electrolyte solutions obtained in the above Examples 1 to 27 and Comparative Examples 1 to 3 were made into secondary batteries, and the room temperature cycling performance of the secondary batteries was tested.

[0153] Preparation of the positive electrode sheet

[0154] The positive electrode active material lithium nickel cobalt manganese oxide (NMC 622 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 ), conductive agent acetylene black, and binder PVDF were mixed at a mass ratio of 98:1:1, and the solvent N-methylpyrrolidone (NMP) was added and stirred until the system became homogeneous to obtain a positive electrode paste. The positive electrode paste was evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature and then transferred to an oven for further drying, and then cut into a rectangle of 40 mm * 50 mm as the positive electrode sheet, and the positive electrode surface capacity was 3.5 mAh / cm 2 .

[0155] Preparation of the negative electrode sheet

[0156] A 50-μm lithium foil was laminated on a 13-μm copper foil by rolling, and then cut into a rectangle of 41 mm * 51 mm as a spare negative electrode sheet.

[0157] Preparation of the separator

[0158] A polyethylene porous membrane was selected as the separator.

[0159] Preparation of the secondary battery

[0160] One cut positive electrode sheet was matched with two cut negative electrode sheets. The positive and negative electrode sheets were insulated from each other with the above separator in the middle and wrapped in an aluminum-plastic film bag to form a stacked dry battery cell. 0.3 g of the previously prepared electrolyte solution was injected, and the aluminum-plastic film bag was vacuum heat-pressed and sealed. After standing at room temperature for at least 6 hours, the cycling test could be started. The rated capacity of the stacked battery prepared in this way was 140 mAh.

[0161] Room temperature cycling performance test

[0162] Normal-temperature cell cycling: The ambient temperature for cell cycling is set at 25°C, and charge-discharge cycling is carried out at a rate of 0.5C (i.e., 70 mA). The cut-off voltages for charging and discharging are set at 4.3V and 2.8V respectively. When the discharge capacity decays to 80% of the discharge capacity in the first cycle, the battery life is considered to end.

[0163] The test results are shown in Table 1 below:

[0164] Table 1: Composition of the electrolyte and cycling performance of the battery

[0165]

[0166]

[0167] In Examples 1 to 13, lithium bis(fluorosulfonyl)imide was used as the lithium salt, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether was used as the diluent, and the compounds of Formula I-1, Formula I-10 to I-18, Formula II-1, Formula II-79 and II-103 were used as organic solvents to prepare the electrolyte. In Comparative Example 1, a carbonate solution of lithium hexafluorophosphate commonly used in the related art was used as the electrolyte. According to the test results in Table 1, the batteries using the electrolytes of Examples 1 to 13 all showed significantly better cycling performance than the batteries using the electrolyte of Comparative Example 1.

[0168] In Examples 14 to 17, lithium bis(trifluoromethylsulfonyl)imide was used to replace lithium bis(fluorosulfonyl)imide as the lithium salt in Examples 2, 3, 5 and 8; in Examples 18 to 21, decafluoropentane was used to replace 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether as the diluent in Examples 2, 3, 5 and 8; in Examples 22 to 25, σ was changed to 5:2 instead of 2:5 in Examples 2, 3, 5 and 8, and (trifluoromethyl)trimethylsilane was used to replace 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in Examples 2, 3, 5 and 8; in Example 26, σ was changed to 1:9 instead of 2:5 in Example 2, and (difluoromethyl)dimethylsilane was used to replace 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in Example 2; in Example 27, σ was changed to 9:1 instead of 2:5 in Example 2, and (difluoromethyl)dimethylsilane was used to replace 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether in Example 2. Although the above examples changed one of the types of lithium salt, the types of diluent, and the σ ratio compared with Examples 2, 3, 5 and 8, these examples also showed significantly excellent cycling performance compared with Comparative Example 1.

[0169] The difference between Comparative Example 2 and Example 2 is only that ethylene glycol dimethyl ether DMET (CH 3 OCH 2 CH 2 OCH 3 ) is used to replace the organic solvent of Formula I-10 in Example 2. As can be seen from Table 1, the number of cycles of the battery prepared with the electrolyte of Example 2 is 798, while the number of cycles of the battery prepared with the electrolyte of Comparative Example 2 is 389. The test results show that although the electrolyte of Comparative Example 2 can be cycled at room temperature in the lithium metal secondary battery system, its cycling performance is worse than that of Example 2. On the other hand, the boiling point of the electrolyte of Comparative Example 2 is also significantly lower than that of Example 2 of the present application.

[0170] The difference between Comparative Example 3 and Example 2 is only that 1,2-dimethylthioethane (CH 3 SCH 2 CH 2 SCH 3 ) is used to replace the organic solvent of Formula I-10 in Example 2. The test results show that although the boiling point of the electrolyte of Comparative Example 3 is higher than that of the electrolyte of Example 2, its cycling performance is worse than that of Example 2. Different from the case where the organic solvent in Example 2 contains both oxygen atoms and sulfur atoms, in 1,2-dimethylthioethane of Comparative Example 3, there are two sulfur atoms and no oxygen atoms. Since the nucleophilicity of sulfur atoms is weaker than that of oxygen atoms, the lithium salt dissociates insufficiently in the electrolyte of Comparative Example 3, resulting in too low conductivity, which in turn affects the stability of the SEI film. At the same time, the electrolyte of Comparative Example 3 also has the problem of poor oxidation resistance.

[0171] These test results indirectly indicate that the electrolyte of the embodiment of the present application can form a stable SEI film on the negative electrode sheet, improving the cycling performance of the battery, while the carbonate solvents, ethylene glycol dimethyl ether or 1,2-dimethylthioethane in the comparative examples cannot form a stable SEI film on the surface of the negative electrode sheet.

[0172] It should be noted that the present application is not limited to the above embodiments. The above embodiments are only examples, and the embodiments having the same constitution and the same function and effect as the technical idea within the technical scope of the present application are all included in the technical scope of the present application. In addition, within the scope of not departing from the gist of the present application, various modifications that can be conceived by those skilled in the art are applied to the embodiments, and other embodiments constructed by combining some constituent elements of the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte for a lithium metal secondary battery, characterized in that: Comprising a lithium salt, an organic solvent and a diluent; wherein the organic solvent comprises at least one of a compound represented by formula (I) or a compound represented by formula (II); In formula (I), R1 and R2 are each independently selected from C1 to C10 alkyl groups, and k is an integer selected from 1 to 3; In formula (II), X, Y, and Z are each independently selected from O or S, wherein at least two of X, Y, and Z, one is O and the other is S; R3 and R4 are each independently selected from C1-C10 alkyl groups, and m and n are each independently selected from integers of 1-3.

2. The electrolyte according to claim 1, characterized in that In formula (I), R1 and R2 are each independently selected from C1-C6 alkyl groups, and optionally, selected from C1-C4 alkyl groups; and In formula (II), R3 and R4 are each independently selected from C1-C6 alkyl groups, and optionally, selected from C1-C4 alkyl groups.

3. The electrolyte according to claim 1 or 2, characterized in that The organic solvent comprises at least one of the compounds represented by formula (I), and in formula (I), k is 2, and R1 and R2 are each independently selected from C1-C4 alkyl groups.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The organic solvent comprises at least one of the following compounds:

5. The electrolyte according to any one of claims 1 to 4, characterized in that The concentration of the lithium salt in the electrolyte is 0.1 to 4 mol / L, and optionally 1 to 3 mol / L.

6. The electrolyte according to any one of claims 1 to 5, characterized in that In the electrolyte, the volume ratio of the organic solvent to the diluent is σ, wherein 1:9≤σ≤9:1; optionally, 2:5≤σ≤5:

2.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The lithium salt includes at least one of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate) and lithium tetrafluorooxalatophosphate.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The diluent includes at least one of fluorine-containing alkanes, ethers and silane compounds; optionally, the diluent includes at least one of decafluoropentane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, (trifluoromethyl)trimethylsilane and (difluoromethyl)dimethylsilane.

9. The electrolyte according to any one of claims 1 to 8, characterized in that At a standard atmospheric pressure, the boiling point of the organic solvent ranges from 40° C. to 150° C.

10. The electrolyte according to any one of claims 1 to 9, characterized in that At a standard atmospheric pressure, the boiling point of the electrolyte is higher than 105°C; optionally, higher than 115°C; optionally, higher than 125°C.

11. A lithium metal secondary battery, characterized in that: The lithium metal secondary battery includes the electrolyte according to any one of claims 1 to 10.

12. The lithium metal secondary battery according to claim 11, characterized in that: The lithium metal secondary battery further comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises lithium single substance and / or lithium alloy.

13. An electrical device, characterized in that: The electrical device comprises the lithium metal secondary battery according to claim 11 or 12.

Images