Electrolyte and alkali metal secondary battery containing same

Abstract

The invention provides an electrolyte and an alkali metal secondary battery containing the same. The electrolyte comprises a combination of alkali metal salt and a solvent, the solvent comprises a combination of ionic liquid, a weak polar solvent and an inert diluent; the weak polar solvent is a cyclic ether solvent, the electrolyte is low in viscosity and has good flame retardance and wettability, and in-situ repair can be carried out under the condition that an artificial SEI film on the surface of an alkali metal negative electrode is damaged, so that the long-term cycle stability of the battery is ensured. The surface of the alkali metal negative electrode of the alkali metal secondary battery is coated with a layer of polyion liquid artificial SEI film in advance, so that the side reaction between the electrolyte and the electrode can be inhibited, and the consumption of the electrolyte in the SEI film forming process can be reduced; meanwhile, ion distribution can be homogenized through the electrostatic shielding effect of ionic liquid cations on polymer chain segments, uniform deposition of ions is promoted, growth of metal dendrites is relieved, the cycle life of the battery is further prolonged, and the coulombic efficiency of the battery is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of alkali metal secondary batteries, and in particular relates to an electrolyte and an alkali metal secondary battery containing the electrolyte. Background Art

[0002] In recent years, with the rapid development of electric-powered new energy vehicles, people have put forward higher and higher requirements for the development of power energy storage batteries. New energy storage batteries need to provide higher power within a limited volume and mass to solve the mileage anxiety problem caused by long-distance driving. Therefore, it is urgent to develop energy storage batteries with higher energy density to meet application needs. However, due to the limited theoretical specific capacity (372mAh g -1 ), making it difficult to achieve a breakthrough in the energy density of lithium-ion batteries at this stage. Using alkali metals as negative electrode materials for batteries, such as lithium metal, has a very high theoretical specific capacity (3860mAh g -1 ), lower electrochemical potential (-3.04 V vs. standard hydrogen electrode) and low density (0.534 g cm -3 ) and other advantages, which can greatly improve the energy density of energy storage batteries, and is expected to solve the mileage anxiety problem of new energy vehicles, and has broad application prospects. However, alkali metal negative electrodes also have many difficult to solve problems. First, the active chemical properties of alkali metals cause serious side reactions between them and electrolytes, which can easily cause the loss of active substances and the consumption of electrolytes during the cycle, resulting in low coulombic efficiency of the battery and short cycle life; secondly, alkali metals will undergo uncontrollable dendrite growth during repeated cycles, which can easily pierce the diaphragm and cause internal short circuits in the battery, thereby causing safety accidents such as battery combustion and explosion.

[0003] The use of an artificial solid electrolyte interface layer (SEI) can effectively inhibit the interface side reactions between the electrode and the electrolyte, while alleviating the problem of metal dendrite growth, and can improve the coulombic efficiency and cycle performance of alkali metal secondary batteries to a certain extent. However, the traditional artificial SEI membrane is mainly composed of organic or inorganic substances, among which the organic ion conductivity and stability are poor, and the inorganic substance has poor flexibility. At the same time, due to the serious volume expansion of the alkali metal electrode during the cycle, the artificial SEI membrane is easily broken and detached, making it difficult to ensure the stability of the battery for a longer cycle. In addition, the electrolyte system of the prior art mostly uses carbonate or ether solvents, which are easy to produce side reactions with the alkali metal surface, resulting in low battery coulombic efficiency and poor cycle stability. At the same time, this type of electrolyte system is highly flammable, which increases the safety risks during the use of the battery.

[0004] CN109888182A discloses an in-situ protected alkali metal electrode, a preparation method and application, wherein the alkali metal electrode comprises an alkali metal material and a protective coating, wherein the protective coating is an amalgam formed by coating mercury on the surface of the alkali metal, and CN115863769A discloses a fluorinated carbonate electrolyte and a lithium metal battery, wherein the fluorinated carbonate electrolyte forms a solid electrolyte interface film rich in lithium fluoride on the surface of the lithium metal battery electrode. Both the amalgam and lithium fluoride are inorganic substances, and such inorganic substances have poor flexibility as alkali metal protective coatings, and are easily broken and detached during use, resulting in poor battery stability, and the fluorinated carbonate electrolyte is easy to react with the alkali metal surface and is flammable, posing a potential safety hazard.

[0005] Therefore, there is an urgent need to develop an alkali metal secondary battery that uses a more stable artificial SEI film to inhibit interfacial side reactions and metal dendrite growth, while the electrolyte also has flame retardant properties, so as to improve the safety, coulombic efficiency and cycle life of alkali metal secondary batteries. Summary of the invention

[0006] In view of the deficiencies in the prior art, the object of the present invention is to provide an electrolyte and an alkali metal secondary battery containing the same, wherein the electrolyte can in-situ repair the artificial SEI film on the surface of the alkali metal negative electrode when it is damaged, which is beneficial to further improve the stability of the alkali metal negative electrode, and take into account certain flame retardancy to improve the safety of the battery; the alkali metal secondary battery can effectively improve the problems of alkali metal negative electrode dendrite growth and interface side reactions, and greatly improve the battery coulombic efficiency, cycle life and safety.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electrolyte, wherein the electrolyte comprises a combination of an alkali metal salt and a solvent; the solvent comprises a combination of an ionic liquid, a weak polar solvent and an inert diluent; the weak polar solvent is selected from any one or a combination of at least two of the compounds having the following structures:

[0009] Among them, R 11 , R 13 , R 15 , R 17 , R 19 , R 21 Each is independently selected from any one of a single bond, a substituted or unsubstituted C1-C10 straight or branched alkylene group, and a substituted or unsubstituted C3-C10 cycloalkylene group; when R 11 , R 13 , R 15 , R 17 , R 19 , R21 When it is a single bond, the oxygen atom is directly connected to the cycloalkane.

[0010] R 12 , R 14 , R 16 , R 18 , R 20 , R 22 Each is independently selected from any one of a substituted or unsubstituted C1-C10 straight or branched alkyl group, and a substituted or unsubstituted C3-C10 cycloalkyl group.

[0011] R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 , R 22 The substituents are each independently selected from at least one of a deuterium atom, a halogen, a nitro group, an amino group, a carboxyl group, a Z1-COO-, a C1-C10 straight or branched alkyl group, a C2-C10 alkenyl group, -O-Z2, a C6-C30 aryl group, and a C3-C30 heteroaryl group; wherein Z1 and Z2 are each independently selected from any one of a C1-C10 straight or branched alkyl group.

[0012] The electrolyte provided by the present invention adopts a flame-retardant ionic liquid, a low-viscosity weakly polar solvent and an inert diluent, so that the electrolyte has good flame retardancy, low viscosity and good wettability, and can effectively solve the problems of high cost, high viscosity, high melting point, low ionic conductivity and poor wettability of the current ionic liquid electrolyte. At the same time, it can also promote the preferential reduction of anions and ionic liquid cations on the surface of the alkali metal negative electrode to form a SEI film rich in inorganic substances and organic substances such as LiF, Li2O, Li3N, etc., and can in-situ repair the artificial SEI film on the surface of the alkali metal negative electrode when it is damaged, thereby improving the cycle life of the alkali metal secondary battery, ensuring the long-term cycle stability of the battery, and further improving the coulombic efficiency and safety of the alkali metal secondary battery.

[0013] In the present invention, the C1-C10 can each independently be C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10.

[0014] The C3-C10 can each independently be C3, C4, C5, C6, C7, C8, C9 or C10.

[0015] The C2-C10 can each independently be C2, C3, C4, C5, C6, C7, C8, C9 or C10.

[0016] The C6-C30 can each independently be C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C22, C24, C26, C28, C29 or C30, etc.

[0017] The C3-C30 can each independently be C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C22, C24, C26, C28, C29 or C30, etc.

[0018] The C1-C10 (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10) straight or branched alkylene groups described in the present invention include, but are not limited to, methylene, ethylene, n-propylene, isopropylene, n-butylene, isobutylene, tert-butylene, n-pentylene, isopentylene, neopentylene, tert-pentylene, n-hexylene, n-octylene, n-heptylene, n-nonylene or n-decylene, etc.

[0019] The C3-C10 (e.g., C3, C4, C5, C6, C7, C8, C9 or C10) cycloalkylene groups described in the present invention include, but are not limited to, cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene or adamantylene, etc.

[0020] The C1-C10 (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10) straight chain or branched chain alkyl group described in the present invention includes, but is not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-hexyl, n-octyl, n-heptyl, n-nonyl or n-decyl, etc.

[0021] The C3-C10 (e.g., C3, C4, C5, C6, C7, C8, C9 or C10) cycloalkyl group described in the present invention includes, but is not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl and the like.

[0022] In the present invention, the "substituted or unsubstituted" group may be substituted with one substituent or with multiple substituents. When there are multiple (at least 2) substituents, the multiple (at least 2) substituents may be the same or different groups; the substituents may be connected to any position in the group that can be connected. When the same expression is mentioned below, it has the same meaning.

[0023] The halogens described in the present invention may be fluorine, chlorine, bromine or iodine.

[0024] The C2-C10 (e.g., C2, C3, C4, C5, C6, C7, C8, C9 or C10) alkenyl groups in the present invention include, but are not limited to, ethenyl, propenyl, 1-butenyl or 1-pentenyl, etc.

[0025] The C6-C30 (e.g., C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C22, C24, C26, C28, C29 or C30, etc.) aryl groups in the present invention include, but are not limited to, phenyl, biphenyl, terphenyl, naphthyl, anthracenyl, phenanthrenyl, indenyl, fluorenyl, fluoranthenyl, triphenylene, pyrenyl, perylene, phenyl, tetraphenyl or triphenylene, etc.

[0026] The C3-C30 (e.g., C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19, C22, C24, C26, C28, C29 or C30, etc.) heteroaryl group described in the present invention, wherein the heteroatom includes O, S, N, P or B, etc., illustratively includes but is not limited to: furanyl, thienyl, pyrrolyl, pyridyl, pyrazinyl, pyridazinyl, pyrimidinyl, triazine, quinolyl, isoquinolyl, quinazoline, quinoxalinyl, cinnolinyl, o-phenanthroline, imidazolyl, thiazolyl, oxazolyl, benzimidazolyl, benzothiazolyl, benzoxazolyl, benzofuranyl, benzothiophenyl, indolyl, dibenzofuranyl, dibenzothiophenyl, carbazolyl and its derivatives (N-phenylcarbazolyl, N-naphthylcarbazolyl, benzocarbazolyl, dibenzocarbazolyl, indolcarbazolyl, azacarbazolyl, etc.), phenothiazinyl, phenoxazinyl or hydroacridinyl, etc.

[0027] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the objectives and beneficial effects of the present invention can be better achieved and realized.

[0028] As a preferred technical solution, the weakly polar solvent includes any one of cyclopropyl methyl ether, cyclobutyl ethyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclopentyl trifluoromethyl ether, cyclohexyl trifluoromethyl ether, cycloheptyl ethyl ether, cyclooctyl propyl ether or cyclooctyl butyl ether, or a combination of at least two thereof.

[0029] Preferably, the mass percentage of the weak polar solvent in the solvent is 10-85%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0030] Further preferably, the mass percentage of the weak polar solvent in the solvent is 20-60%, for example, it can be 20%, 24%, 29%, 34%, 39%, 44%, 49%, 54%, 59% or 60%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0031] Preferably, the alkali metal salt includes any one of lithium salt, sodium salt or potassium salt, or a combination of at least two of them.

[0032] Preferably, the lithium salt includes any one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium hexafluoroarsenate, lithium difluorooxalatoborate, lithium difluorophosphate or lithium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof.

[0033] Preferably, the sodium salt includes any one of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalatoborate), sodium hexafluoroarsenate, sodium difluorooxalatoborate, sodium difluorophosphate or sodium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof.

[0034] Preferably, the potassium salt includes any one of potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium bis(oxalatoborate), potassium hexafluoroarsenate, potassium difluorooxalatoborate, potassium difluorophosphate or potassium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof.

[0035] Preferably, the concentration of the alkali metal salt in the electrolyte is 0.1-6 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or 6 mol / L, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0036] Further preferably, the concentration of the alkali metal salt in the electrolyte is 0.5-2 mol / L, for example, it can be 0.5 mol / L, 0.7 mol / L, 0.9 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.7 mol / L, 1.9 mol / L or 2 mol / L, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0037] Preferably, the structure of the ionic liquid is A + [B] - ; Among them A + Selected from any one or a combination of at least two of the following structures:

[0038]

[0039] Among them, R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 , R 39 , R 40 , R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , R 49 , R 50 Each is independently selected from any one of substituted or unsubstituted C1-C20 straight or branched alkyl, -R'-O-Z3, -O-Ar1, amino, substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl, cyano, nitro or halogen; Z3 is selected from any one of substituted or unsubstituted C1-C10 straight or branched alkyl; R' is selected from any one of a single bond, a substituted or unsubstituted C1-C10 straight or branched alkylene, and when R' is a single bond, the oxygen atom is directly bonded to N, N + , S + or P + Directly connected by a single bond; Ar1 ​​is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl.

[0040] R 31 , R 32 , R 33, R 34 , R 35 , R 36 , R 37 , R 38 , R 39 , R 40 , R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , R 49 , R 50 The substituents in Z3, Ar1 and R' are each independently selected from at least one halogen.

[0041] A + The combination method described in is: multiple identical A + Structure or different A + The structure is connected by a carbon-carbon single bond, and the multiple refers to at least two, and the carbon-carbon single bond is composed of R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 , R 39 , R 40 , R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , R 49 or R 50 The hydrogen-containing carbon atoms on each of the above are each removed a hydrogen atom to form, for example A + Including but not limited to the following structures:

[0042]

[0043] Where R 31 and R' 31 Can be the same or different, R 32 and R' 32 Can be the same or different.

[0044] The C1-C20 can each independently be C1, C2, C3, C4, C5, C6, C7, C8, C9, C10, C11, C12, C13, C14, C15, C16, C17, C18, C19 or C20.

[0045] The C3-C12 (e.g., C3, C4, C5, C6, C7, C8, C9, C10, C11 or C12) heteroaryl group illustratively includes, but is not limited to, thienyl, benzothienyl, thienoimidazolyl, thienofuranyl or thiazinyl, and the like.

[0046] The C6-C12 can each independently be C6, C7, C8, C9, C10, C11 or C12.

[0047] The C1-C10 can each independently be C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10.

[0048] The C3-C12 can each independently be C3, C4, C5, C6, C7, C8, C9, C10, C11, C12 or C13.

[0049] [B] - Selected from FSI - TFSI - 、BF4 - PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - or DFOB - Any one or a combination of at least two of the following.

[0050] Preferably, the A + Includes any one or a combination of at least two of the following cations:

[0051]

[0052] Preferably, the mass percentage of the ionic liquid in the solvent is 10-85%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or 85%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0053] Further preferably, the mass percentage of the ionic liquid in the solvent is 30-70%, for example, it can be 30%, 34%, 39%, 44%, 49%, 54%, 59%, 64% or 70%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0054] Preferably, the inert diluent comprises any one of halogenated ethers, halogenated benzenes or halogenated alkanes, or a combination of at least two thereof.

[0055] Preferably, the halogenated ether includes any one of 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl nonafluorobutyl ether or ethyl nonafluorobutyl ether, or a combination of at least two thereof.

[0056] Preferably, the halogenated benzene includes fluorobenzene and / or 1,2-difluorobenzene.

[0057] Preferably, the halogenated alkane includes any one of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, trichloroform, trichloropropane, monochlorodifluoromethane, dichloromonofluoromethane or difluoromethane, or a combination of at least two thereof.

[0058] Preferably, the mass percentage of the inert diluent in the solvent is 5-60%, for example, it can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0059] Further preferably, the mass percentage of the inert diluent in the solvent is 10-50%, for example, it can be 10%, 14%, 19%, 24%, 29%, 34%, 39%, 44% or 50%, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0060] In a second aspect, the present invention provides an alkali metal secondary battery, comprising a negative electrode, a positive electrode, the electrolyte as described in the first aspect, and a separator.

[0061] Preferably, the negative electrode comprises an alkali metal negative electrode and a negative electrode current collector.

[0062] Preferably, the alkali metal negative electrode includes any one of lithium, sodium or potassium.

[0063] Preferably, the negative electrode current collector comprises any one of copper foil, nickel foil or nickel-plated steel strip.

[0064] Preferably, the outer surface of the alkali metal negative electrode is coated with a layer of polyionic liquid artificial SEI film.

[0065] Preferably, the thickness of the polyionic liquid artificial SEI film is 2-2000nm, for example, it can be 2nm, 30nm, 50nm, 80nm, 100nm, 200nm, 500nm, 800nm, 1000nm, 1200nm, 1500nm, 1800nm ​​or 2000nm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0066] Preferably, the material of the polyionic liquid artificial SEI membrane has a structure as shown in Formula I, Formula II or Formula III:

[0067]

[0068] R2, R3, R4, R5, R6, R7, R8, and R9 are each independently selected from a hydrogen atom, a substituted or unsubstituted C1-C10 straight or branched alkyl group, -O-Z4, -O-Ar2, an amino group, a substituted or unsubstituted C3-C12 heteroaryl group, a substituted or unsubstituted C6-C12 aryl group, a cyano group, a nitro group, or a halogen group; Z4 is selected from any one of a substituted or unsubstituted C1-C10 straight or branched alkyl group; Ar2 is selected from any one of a substituted or unsubstituted C6-C12 aryl group, or a substituted or unsubstituted C3-C12 heteroaryl group.

[0069] The substituents substituted in R1, R2, R3, R4, R5, R6, R7, R8, R9, Z4 and Ar2 are each independently selected from at least one of the halogens.

[0070] X1 + Selected from any one or a combination of at least two of the following structures:

[0071]

[0072] X1 + The combination method described in the above is: multiple identical X1 + Structure or different X1 + The structure is connected by a carbon-carbon single bond, and the multiple refers to at least two, and the carbon-carbon single bond is composed of R 51 , R 53 , R 55 , R 58 , R 63 , R64 , R 65 , R 67 , R 68 , R 69 , R 71 or R 72 Any hydrogen-containing carbon atom is removed and then reacts with R 52 , R 54 , R 56 , R 57 , R 59 , R 60 , R 61 , R 62 , R 66 or R 70 Any one of the connection sites is connected to form, exemplarily X1 + Including but not limited to the following structures:

[0073]

[0074] Where R 54 , R' 54 Can be the same or different, R 53 , R' 53 Can be the same or different.

[0075] X2 + Select any one of the following structures:

[0076]

[0077] X3 + Select any one of the following structures:

[0078]

[0079] in, Represents the attachment site of the group.

[0080] R 51 , R 53 , R 55 , R 58 , R 63 , R 64 , R 65 , R 67 , R 68 , R 69 , R 71 , R 72 , R 81 , R 82 , R 84 , R 85 , R 88Each is independently selected from any one of substituted or unsubstituted C1-C20 straight chain or branched alkyl, -O-Z5, -O-Ar3, amino, substituted or unsubstituted C3-C12 heteroaryl, substituted or unsubstituted C6-C12 aryl, cyano, nitro or halogen; Z5 is selected from any one of substituted or unsubstituted C1-C10 straight chain or branched alkyl; Ar3 is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl.

[0081] R 52 , R 54 , R 56 , R 57 , R 59 , R 60 , R 61 , R 62 , R 66 , R 70 , R 73 , R 74 , R 75 , R 76 , R 77 , R 78 , R 79 , R 80 , R 83 , R 86 , R 87 , R 89 , R 90 , R 91 , R 92 Each is independently selected from any one of a single bond, a substituted or unsubstituted C1-C20 straight or branched alkylene group, -O-Z6-, -O-Ar4-, -Z7-Ar5-, an imino group, a substituted or unsubstituted C3-C12 heteroarylene group, and a substituted or unsubstituted C6-C12 arylene group. 52 , R 54 , R 56 , R 57 , R 59 , R 60 , R 61 , R 62 , R 66 , R 70 , R 73 , R 74 , R 75 , R 76 , R 77 , R 78 , R 79 , R 80 , R 83 , R 86 , R 87 , R 89 , R90 , R 91 , R 92 When it is a single bond, the heteroatom or heterocation is directly connected to the main chain segment in the brackets.

[0082] Z6 and Z7 are each independently selected from any one of substituted or unsubstituted C1-C10 straight or branched alkylene groups.

[0083] Ar4 and Ar5 are each independently selected from any one of a substituted or unsubstituted C6-C12 arylene group and a substituted or unsubstituted C3-C12 heteroarylene group.

[0084] R 51 , R 52 , R 53 , R 54 , R 55 , R 56 , R 57 , R 58 , R 59 , R 60 , R 61 , R 62 , R 63 , R 64 , R 65 , R 66 , R 67 , R 68 , R 69 , R 70 , R 71 , R 72 , R 73 , R 74 , R 75 , R 76 , R 77 , R 78 , R 79 , R 80 , R 81 , R 82 , R 83 , R 84 , R 85 , R 86 , R 87 , R 88 , R 89 , R 90 , R 91 , R 92 The substituents substituted in Z5, Z6, Z7, Ar3, Ar4 or Ar5 are each independently selected from at least one halogen.

[0085] Y - Selected from FSI - TFSI - 、BF4- PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - DFOB - Any one or a combination of at least two of the following.

[0086] n and m are each independently selected from an integer of 1-100000, for example, 1, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 10000, 50000, 80000 or 100000, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0087] Preferably, the material of the polyionic liquid artificial SEI membrane includes any one or a combination of at least two of the following compounds:

[0088]

[0089] wherein n1, n2, n3, n4, n5, n6, and n7 are each independently selected from an integer of 1-100,000.

[0090] The polycations in the material of the polyionic liquid artificial SEI membrane of the present invention, i.e., the part without anions, can be purchased in the form of polycation salts. The polycation salts are subsequently used to prepare the material of the polyionic liquid artificial SEI membrane through experiments. The preparation method comprises: dropping a LiY aqueous solution into a polycation salt aqueous solution and reacting to obtain a solid, washing the solid with water and then drying to obtain the material of the polyionic liquid artificial SEI membrane; the mass fraction of LiY in the LiY aqueous solution is 1-10%; the mass fraction of the polycation salt in the polycation salt aqueous solution is 0.2-5%; the molar ratio of LiY to the polycation salt is n:1, where n is the degree of polymerization of the polycation salt; the reaction time is 5-10h; the drying temperature is 70-100°C; the drying time is 24-72h; the Y- in the LiY has the same molecular weight as the Y in the material of the polyionic liquid artificial SEI membrane provided by the present invention. - Same limitations.

[0091] The present invention adopts a polyionic liquid containing cationic groups as an artificial SEI membrane on the surface of the alkali metal negative electrode, which not only has excellent ionic conductivity and flexibility, but also can homogenize the ion distribution on the surface of the alkali metal negative electrode through the electrostatic shielding effect of the cationic groups on the polymer skeleton, thereby inducing uniform deposition behavior of ions and effectively inhibiting the growth of metal dendrites.

[0092] Preferably, the positive electrode active material of the positive electrode includes any one of lithium cobalt oxide, lithium manganese oxide, ternary positive electrode material, lithium-rich manganese-based positive electrode material, nickel-manganese positive electrode material, lithium iron phosphate, lithium manganese phosphate or sulfur-based positive electrode material.

[0093] Preferably, the ternary cathode material comprises LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2.

[0094] Preferably, the nickel-manganese positive electrode material comprises LiNi 0.5 Mn 0.5 O2、LiNi 0.5 Mn 1.5 O4, LiNiMnCoO2.

[0095] Preferably, the sulfur-based positive electrode material includes any one of elemental sulfur, lithium sulfide, lithium polysulfide, sulfur / carbon composite material, lithium sulfide / carbon composite material, sulfur / polymer composite material or lithium polysulfide / carbon composite material.

[0096] Preferably, the sulfur / polymer composite material includes sulfurized polyacrylonitrile, sulfurized polyvinyl nitrile, and sulfurized polyimide.

[0097] Preferably, the separator includes a glass cellulose membrane, a cellulose membrane and a porous polyolefin compound membrane.

[0098] Preferably, the porous polyolefin compound membrane includes a polypropylene membrane, a polyethylene membrane, or a polytetrafluoroethylene membrane.

[0099] Preferably, the alkali metal secondary battery further includes a tab.

[0100] Compared with the prior art, the present invention has the following beneficial effects:

[0101] (1) The electrolyte provided by the present invention has low viscosity and good flame retardancy and wettability, and can also perform in-situ repair when the artificial SEI film on the surface of the alkali metal negative electrode is damaged, thereby ensuring the long-term cycle stability of the battery;

[0102] (2) The alkali metal secondary battery provided by the present invention adopts the above-mentioned electrolyte and polyionic liquid artificial SEI membrane, and has a high cycle life, coulombic efficiency and safety. The average coulombic efficiency after 100 cycles can reach 99.7-99.9%, and the capacity retention rate is 98.1-99.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0103] Figure 1 It is a schematic diagram of the internal structure of the alkali metal secondary battery provided by the present invention;

[0104] Figure 2 This is the H NMR spectrum of PDDATFSI-1. DETAILED DESCRIPTION

[0105] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0106] The materials described in the present invention, except for the materials of the polyionic liquid artificial SEI membrane, are all commercially available materials. The sources of some components in the following embodiments and comparative examples are as follows:

[0107] (1) Material of polyionic liquid artificial SEI membrane PDDATFSI-1: The structural formula is The preparation steps include:

[0108] Dissolve 2g of LiTFSI salt completely in 50mL of deionized water for later use, then mix 5.63g of polydimethyldiallylammonium chloride (PDDACl) solution (20wt% aqueous solution, molecular weight 200000, purchased from Adamas) with 200mL of deionized water, and add LiTFSI aqueous solution dropwise during the stirring process to react. At this time, a white flocculent solid gradually precipitates out of the solution. The reaction time is 6h. After the stirring stops, the white solid quickly precipitates in the container. After standing for 10min, pour out the liquid, leave the white solid and wash it with deionized water, repeat 5 to 6 times, until there is no obvious precipitation after the AgNO3 aqueous solution is added to the washed liquid, it is judged to be completely cleaned. Finally, collect the white solid with a suction filter, place it in an oven at 80℃ and dry it for 48h, and finally obtain a dry white solid, which is ground into powder with a mortar to obtain PDDATFSI-1;

[0109] (2) Material of polyionic liquid artificial SEI membrane PDDAFSI: The structural formula is The preparation steps thereof differ from those of the above-mentioned PDDATFSI-1 only in that an equal amount of the LiTFSI aqueous solution is replaced by an LiFSI aqueous solution with the same proportion, and the other raw materials, process steps and parameters are the same as those for the preparation of PDDATFSI-1;

[0110] (3) Material of polyionic liquid artificial SEI membrane PDDATFSI-2: The structural formula is The preparation steps thereof differ from those of the above-mentioned PDDATFSI-1 only in that an equal amount of polydimethyldiallylammonium chloride (PDDACl) solution (20 wt% aqueous solution, molecular weight 200,000, purchased from Adamas) is replaced with a polydimethyldiallylammonium chloride (PDDACl) solution (20 wt% aqueous solution, molecular weight 500,000, purchased from Adamas), and the other raw materials, process steps and parameters are the same as those for the preparation of PDDATFSI-1;

[0111] (4) Material of polyionic liquid artificial SEI membrane PDDATFSI-3: The structural formula is The preparation steps thereof differ from those of the above-mentioned PDDATFSI-1 only in that an equal amount of polydimethyldiallylammonium chloride (PDDACl) solution (20 wt% aqueous solution, molecular weight 200,000, purchased from Adamas) is replaced with a polydimethyldiallylammonium chloride (PDDACl) solution (20 wt% aqueous solution, molecular weight 10,000, purchased from Adamas), and the other raw materials, process steps and parameters are the same as those for the preparation of PDDATFSI-1;

[0112] (5) N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0113] (6) N-methyl-N-butylpiperidinium bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0114] (7) N-methyl-N-butylpyrrole bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0115] (8) N-methyl-N-propylpyrrole bis(trifluoromethanesulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0116] (9) Polyethylene oxide: purchased from Adamas.

[0117] Example 1

[0118] An electrolyte, the preparation method of the electrolyte comprising: in a glove box protected by inert gas, dissolving LiTFSI in 4g of N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt, 3g of cyclopentyl methyl ether and 3g of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, stirring until the lithium salt is completely dissolved to obtain a clear and transparent electrolyte, wherein the concentration of LiTFSI in the electrolyte is 1 mol / L.

[0119] Preparation of a lithium metal negative electrode coated with a polyionic liquid artificial SEI film on the outer surface: Under dry conditions (H2O<1ppm), PDDATFSI-1 is dissolved in NMP (N-methylpyrrolidone) solvent, and then evenly coated on the surface of the lithium metal negative electrode, and vacuum dried at 80°C to remove the NMP solvent to obtain a lithium metal negative electrode coated with a polyionic liquid artificial SEI film on the outer surface, wherein the thickness of the polyionic liquid artificial SEI film is 20nm.

[0120] Preparation of positive electrode sheets: Under dry conditions, 5% by mass of polyvinylidene fluoride is fully dissolved in NMP, 5% by mass of conductive carbon black and 90% of lithium iron phosphate are added to the above solution and mixed evenly, the prepared slurry is evenly coated on aluminum foil, and the positive electrode sheets are obtained after drying, rolling and cutting.

[0121] A lithium metal secondary battery, the internal structure of the lithium metal secondary battery is as follows Figure 1 As shown, the internal structure of the alkali metal secondary battery includes positive and negative electrode current collectors, a positive electrode, a separator, a lithium metal negative electrode coated with a polyionic liquid artificial SEI film, and an electrolyte. The preparation of the lithium metal secondary battery includes: using the lithium metal negative electrode and positive electrode sheet coated with a polyionic liquid artificial SEI film prepared above, and assembling them into a lithium metal secondary battery cell with a polypropylene separator; using metal aluminum and metal nickel as positive and negative electrode tabs respectively, encapsulating the outside with an aluminum-plastic film, and finally injecting the electrolyte prepared above, and completing the sealing to obtain the lithium metal secondary battery.

[0122] Example 2

[0123] An electrolyte, wherein the electrolyte is the same as the electrolyte provided in Example 1.

[0124] A lithium metal secondary battery, which is different from Example 1 only in that the material of the polyionic liquid artificial SEI membrane is PDDAFSI, and the other components are the same as those of Example 1.

[0125] Example 3

[0126] An electrolyte, wherein the electrolyte is the same as the electrolyte provided in Example 1.

[0127] A lithium metal secondary battery, which is different from Example 1 only in that the material of the polyionic liquid artificial SEI membrane is PDDATFSI-2, and the other components are the same as those of Example 1.

[0128] Example 4

[0129] An electrolyte, wherein the electrolyte is the same as the electrolyte provided in Example 1.

[0130] A lithium metal secondary battery, which is different from Example 1 only in that the material of the polyionic liquid artificial SEI membrane is PDDATFSI-3, and the other components are the same as those of Example 1.

[0131] Example 5

[0132] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI, 3 g N-methyl-N-butylpiperidinium bisfluorosulfonyl imide salt, 2 g cyclohexyl methyl ether and 5 g 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, the concentration of LiTFSI in the electrolyte is 1 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0133] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this example, and the other components are the same as those in Example 1.

[0134] Example 6

[0135] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiDFOB, 7 g N-methyl-N-butylpyrrole bis(fluorosulfonyl)imide salt, 2 g cyclohexyl methyl ether and 1 g 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, the concentration of LiDFOB in the electrolyte is 0.5 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0136] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this example, and the other components are the same as those in Example 1.

[0137] Example 7

[0138] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI, 6 g N-methyl-N-propylpyrrole bistrifluoromethanesulfonyl imide salt, 2 g cyclobutyl methyl ether and 2 g 1,2-difluorobenzene, the concentration of LiTFSI in the electrolyte is 2 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0139] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this example, and the other components are the same as those in Example 1.

[0140] Example 8

[0141] An electrolyte, wherein the electrolyte is the same as the electrolyte provided in Example 1.

[0142] A lithium metal secondary battery, which differs from Example 1 only in that the outer surface of the lithium metal negative electrode is not coated with a polyionic liquid artificial SEI film.

[0143] Comparative Example 1

[0144] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI and 10 g N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt, the concentration of LiTFSI in the electrolyte is 1 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0145] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this comparative example, and the other components are the same as those in Example 1.

[0146] Comparative Example 2

[0147] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI, 7 g N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt and 3 g 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, the concentration of LiTFSI in the electrolyte is 1 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0148] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this comparative example, and the other components are the same as those in Example 1.

[0149] Comparative Example 3

[0150] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI, 3g ethylene carbonate and 7g dimethyl carbonate, the concentration of LiTFSI in the electrolyte is 1 mol / L, and the rest of the preparation process is the same as that of Example 1.

[0151] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this comparative example, and the other components are the same as those in Example 1.

[0152] Comparative Example 4

[0153] An electrolyte, which differs from Example 1 in that 3g of cyclopentyl methyl ether is replaced by 3g of ethylene glycol dimethyl ether, and the rest of the preparation process is the same as that of Example 1.

[0154] A lithium metal secondary battery, which differs from Example 1 only in that the electrolyte of the lithium metal secondary battery is the electrolyte provided in this comparative example, and the other components are the same as those in Example 1.

[0155] Comparative Example 5

[0156] An electrolyte, wherein the electrolyte is the same as the electrolyte provided in Example 1.

[0157] A lithium metal secondary battery, which is different from Example 1 only in that the material of the polyionic liquid artificial SEI membrane is polyethylene oxide (PEO), and the other components are the same as those of Example 1.

[0158] Performance Test:

[0159] (1) Nuclear magnetic resonance hydrogen spectrum test: PDDATFSI-1 was tested using a nuclear magnetic resonance spectrometer (Varian-400 MHz). The test results are as follows: Figure 2 The nuclear magnetic resonance hydrogen spectrum of PDDATFSI-1 is shown in the figure. It can be seen from the figure that the four peaks a, b, c, and d correspond to the hydrogen at the relevant positions marked in the chemical structure. By comparing the peak size and position, it can be well matched with the target structure, indicating that the substance is consistent with the target structure and has no other impurities;

[0160] (2) The electrochemical performance of the lithium metal secondary batteries provided in Examples 1-8 and Comparative Examples 1-5 was tested at a test voltage of 2.5 to 4.0 V and a cycle rate of 0.2C. The test results are shown in Table 1:

[0161] Table 1

[0162]

[0163]

[0164] From the test data of Examples 1 to 7 in Table 1, it can be seen that the lithium metal secondary battery provided by the present invention has high coulombic efficiency and high capacity retention rate after 100 cycles. By comparing Comparative Example 1 and Comparative Example 2 with Example 1, it can be found that adding a weak polar solvent and an inert diluent to the ionic liquid can effectively reduce the viscosity of the electrolyte, thereby better improving the discharge specific capacity of the battery.

[0165] By comparing Comparative Example 3 with Example 1, it can be found that due to the serious side reactions between the carbonate electrolyte and the lithium metal negative electrode, the average coulombic efficiency and capacity retention rate of the battery are low. This further illustrates that under the same battery structure, the electrolyte provided by the present invention can effectively reduce the side reactions on the surface of the lithium metal negative electrode, thereby improving the battery performance.

[0166] By comparing Example 1 and Comparative Example 4, it can be found that compared with adding a strong polar linear ether solvent to the electrolyte, the electrolyte prepared by using a weak polar ether solvent containing a large volume cyclic hydrocarbon can effectively improve the coulombic efficiency and capacity retention rate of the battery, indicating that the weak polar ether solvent provided by the present invention can effectively reduce the side reactions at the electrode interface and improve the interface stability.

[0167] By comparing Example 1, Example 8 and Comparative Example 5, it can be found that the first-cycle Coulomb efficiency and capacity retention rate of the battery using the lithium metal negative electrode without being coated with the polyionic liquid artificial SEI film and the PEO-coated lithium metal negative electrode are relatively low, indicating that the lithium metal negative electrode coated with the polyionic liquid artificial SEI film can effectively inhibit the interfacial reaction between the electrolyte and the electrode. At the same time, since the polyionic liquid artificial SEI film has high ionic conductivity, it can ensure the high capacity, high Coulomb efficiency and excellent cycle stability of the battery.

[0168] The applicant declares that the present invention illustrates the detailed process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a combination of an alkali metal salt and a solvent; The solvent comprises a combination of an ionic liquid, a weakly polar solvent and an inert diluent; The weakly polar solvent is selected from any one or a combination of at least two of the compounds of the following structures: Among them, R 11 , R 13 , R 15 , R 17 , R 19 , R 21 Each is independently selected from any one of a single bond, a substituted or unsubstituted C1-C10 straight or branched alkylene group, and a substituted or unsubstituted C3-C10 cycloalkylene group; R 12 , R 14 , R 16 , R 18 , R 20 , R 22 Each is independently selected from any one of a substituted or unsubstituted C1-C10 straight or branched alkyl group, and a substituted or unsubstituted C3-C10 cycloalkyl group; R 11 , R 12 , R 13 , R 14 , R 15 , R 16 , R 17 , R 18 , R 19 , R 20 , R 21 , R 22 The substituents are each independently selected from at least one of a deuterium atom, a halogen, a nitro group, an amino group, a carboxyl group, a Z1-COO-, a C1-C10 straight or branched alkyl group, a C2-C10 alkenyl group, -O-Z2, a C6-C30 aryl group, and a C3-C30 heteroaryl group; Wherein Z1 and Z2 are each independently selected from any one of C1-C10 straight chain or branched chain alkyl groups.

2. The electrolyte according to claim 1, characterized in that The weakly polar solvent includes any one of cyclopropyl methyl ether, cyclobutyl ethyl ether, cyclopentyl methyl ether, cyclopentyl ethyl ether, cyclopentyl propyl ether, cyclohexyl methyl ether, cyclohexyl ethyl ether, cyclopentyl trifluoromethyl ether, cyclohexyl trifluoromethyl ether, cycloheptyl ethyl ether, cyclooctyl propyl ether or cyclooctyl butyl ether, or a combination of at least two thereof; Preferably, the mass percentage of the weak polar solvent in the solvent is 10-85%, more preferably 20-60%.

3. The electrolyte according to claim 1 or 2, characterized in that The alkali metal salt includes any one of lithium salt, sodium salt or potassium salt or a combination of at least two thereof; Preferably, the lithium salt includes any one of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium hexafluoroarsenate, lithium difluorooxalatoborate, lithium difluorophosphate or lithium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof; Preferably, the sodium salt includes any one of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalatoborate), sodium hexafluoroarsenate, sodium difluorooxalatoborate, sodium difluorophosphate or sodium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof; Preferably, the potassium salt includes any one of potassium bis(fluorosulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, potassium hexafluorophosphate, potassium perchlorate, potassium tetrafluoroborate, potassium bis(oxalatoborate), potassium hexafluoroarsenate, potassium difluorooxalatoborate, potassium difluorophosphate or potassium 4,5-dicyano-2-trifluoromethylimidazole, or a combination of at least two thereof; Preferably, the concentration of the alkali metal salt in the electrolyte is 0.1-6 mol / L, more preferably 0.5-2 mol / L.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The structure of the ionic liquid is A + [B] - ; Among them A + Selected from any one or a combination of at least two of the following structures: Among them, R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 , R 39 , R 40 , R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , R 49 , R 50 Each is independently selected from any one of substituted or unsubstituted C1-C20 straight or branched alkyl, -R'-O-Z3, -O-Ar1, amino, substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl, cyano, nitro or halogen; Z3 is selected from any one of substituted or unsubstituted C1-C10 straight chain or branched alkyl groups; R' is selected from any one of a single bond, a substituted or unsubstituted C1-C10 straight chain or branched alkylene group; Ar1 is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl; R 31 , R 32 , R 33 , R 34 , R 35 , R 36 , R 37 , R 38 , R 39 , R 40 , R 41 , R 42 , R 43 , R 44 , R 45 , R 46 , R 47 , R 48 , R 49 , R 50 , Z3, Ar1, R', the substituents substituted are each independently selected from at least one of halogen; [B] - Selected from FSI - TFSI - 、BF4 - PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - or DFOB - Any one or a combination of at least two of the following: Preferably, the A + Includes any one or a combination of at least two of the following cations: Preferably, the mass percentage of the ionic liquid in the solvent is 10-85%, more preferably 30-70%.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The inert diluent includes any one or a combination of at least two of halogenated ethers, halogenated benzenes or halogenated alkanes; Preferably, the halogenated ether includes any one of 1,1,1,3,3,3-hexafluoroisopropyl methyl ether, 2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2,2-trifluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl nonafluorobutyl ether or ethyl nonafluorobutyl ether, or a combination of at least two thereof; Preferably, the halogenated benzene includes fluorobenzene and / or 1,2-difluorobenzene; Preferably, the halogenated alkane includes any one of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, trichloroform, trichloropropane, monochlorodifluoromethane, dichloromonofluoromethane or difluoromethane, or a combination of at least two thereof; Preferably, the mass percentage of the inert diluent in the solvent is 5-60%, more preferably 10-50%.

6. An alkali metal secondary battery, characterized in that: The alkali metal secondary battery comprises a negative electrode, a positive electrode, the electrolyte according to any one of claims 1 to 5, and a separator.

7. The alkali metal secondary battery according to claim 6, characterized in that The negative electrode comprises an alkali metal negative electrode and a negative electrode current collector; Preferably, the alkali metal negative electrode includes any one of lithium, sodium or potassium; Preferably, the negative electrode current collector comprises any one of copper foil, nickel foil or nickel-plated steel strip; Preferably, the outer surface of the alkali metal negative electrode is coated with a layer of polyionic liquid artificial SEI film; Preferably, the thickness of the polyionic liquid artificial SEI film is 2-2000 nm.

8. The alkali metal secondary battery according to claim 7, characterized in that The material of the polyionic liquid artificial SEI membrane has a structure as shown in Formula I, Formula II or Formula III: Wherein, R1, R2, R3, R4, R5, R6, R7, R8, and R9 are each independently selected from any one of a hydrogen atom, a substituted or unsubstituted C1-C10 straight or branched alkyl group, -O-Z4, -O-Ar2, an amino group, a substituted or unsubstituted C3-C12 heteroaryl group, a substituted or unsubstituted C6-C12 aryl group, a cyano group, a nitro group, or a halogen; Z4 is selected from any one of substituted or unsubstituted C1-C10 straight or branched alkyl groups; Ar2 is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl; The substituents substituted in R1, R2, R3, R4, R5, R6, R7, R8, R9, Z4, and Ar2 are each independently selected from at least one of halogens; X1 + Selected from any one or a combination of at least two of the following structures: X2 + Select any one of the following structures: X3 + Select any one of the following structures: in, The attachment site of the representative group; R 51 , R 53 , R 55 , R 58 , R 63 , R 64 , R 65 , R 67 , R 68 , R 69 , R 71 , R 72 , R 81 , R 82 , R 84 , R 85 , R 88 Each is independently selected from any one of substituted or unsubstituted C1-C20 straight or branched alkyl, -O-Z5, -O-Ar3, amino, substituted or unsubstituted C3-C12 heteroaryl, substituted or unsubstituted C6-C12 aryl, cyano, nitro or halogen; Z5 is selected from any one of substituted or unsubstituted C1-C10 straight or branched alkyl groups; Ar3 is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl; R 52 , R 54 , R 56 , R 57 , R 59 , R 60 , R 61 , R 62 , R 66 , R 70 , R 73 , R 74 , R 75 , R 76 , R 77 , R 78 , R 79 , R 80 , R 83 , R 86 , R 87 , R 89 , R 90 , R 91 , R 92 Each is independently selected from any one of a single bond, a substituted or unsubstituted C1-C20 straight or branched alkylene group, -O-Z6-, -O-Ar4-, -Z7-Ar5-, an imino group, a substituted or unsubstituted C3-C12 heteroarylene group, and a substituted or unsubstituted C6-C12 arylene group; Z6 and Z7 are each independently selected from any one of substituted or unsubstituted C1-C10 straight or branched alkylene groups; Ar4 and Ar5 are each independently selected from any one of a substituted or unsubstituted C6-C12 arylene group and a substituted or unsubstituted C3-C12 heteroarylene group; R 51 , R 52 , R 53 , R 54 , R 55 , R 56 , R 57 , R 58 , R 59 , R 60 , R 61 , R 62 , R 63 , R 64 , R 65 , R 66 , R 67 , R 68 , R 69 , R 70 , R 71 , R 72 , R 73 , R 74 , R 75 , R 76 , R 77 , R 78 , R 79 , R 80 , R 81 , R 82 , R 83 , R 84 , R 85 , R 86 , R 87 , R 88 , R 89 , R 90 , R 91 , R 92 , Z5, Z6, Z7, Ar3, Ar4 or Ar5, the substituents substituted are each independently selected from at least one of halogen; Y - Selected from FSI - TFSI - 、BF4 - PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - DFOB - Any one or a combination of at least two of the following: n and m are each independently selected from integers of 1-100,000.

9. The alkali metal secondary battery according to claim 7 or 8, characterized in that: The material of the polyionic liquid artificial SEI membrane includes any one or a combination of at least two of the following compounds: wherein n1, n2, n3, n4, n5, n6, and n7 are each independently selected from an integer of 1-100,000.

10. The alkali metal secondary battery according to any one of claims 6 to 9, characterized in that The positive electrode active material of the positive electrode includes any one of lithium cobalt oxide, lithium manganese oxide, ternary positive electrode material, lithium-rich manganese-based positive electrode material, nickel-manganese positive electrode material, lithium iron phosphate, lithium manganese phosphate or sulfur-based positive electrode material; Preferably, the sulfur-based positive electrode material includes any one of elemental sulfur, lithium sulfide, lithium polysulfide, sulfur / carbon composite material, lithium sulfide / carbon composite material, sulfur / polymer composite material or lithium polysulfide / carbon composite material; Preferably, the separator comprises a glass cellulose membrane, a cellulose membrane and a porous polyolefin compound membrane; Preferably, the alkali metal secondary battery further includes a tab.

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