Electrolyte and alkali metal secondary battery containing same

Abstract

Provided are an electrolyte, and an alkali metal secondary battery containing same. 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 being a cyclic ether solvent. The electrolyte has low viscosity and good flame retardance and wettability, and can perform in-situ repair when an artificial SEI film on a surface of an alkali metal negative electrode is damaged, thereby ensuring long-term cycle stability of the battery. A surface of the alkali metal negative electrode of the alkali metal secondary battery is coated in advance with a layer of polyionic liquid artificial SEI film, inhibiting side reaction between the electrolyte and the electrode, and also reducing consumption of the electrolyte in the process of forming an SEI film. Additionally, by means of an electrostatic shielding effect of ionic liquid cations on a polymer chain segment, ion distribution can be homogenized, promoting uniform deposition of ions, alleviating the growth of metal dendrites, further prolonging the cycle life of the battery, and improving coulombic efficiency.

Description

Electrolyte and alkali metal secondary battery containing same Technical Field

[0001] The present application relates to the technical field of alkali metal secondary batteries, for example, an electrolyte and an alkali metal secondary battery containing the electrolyte. Background Art

[0002] In recent years, with the rapid development of electric-driven new energy vehicles, people have put forward higher and higher requirements for the development of its power energy storage batteries. New energy storage batteries need to provide higher power within a limited volume and mass to solve the range anxiety problem caused by long-distance driving. Therefore, there is an urgent need to develop energy storage batteries with higher energy density to meet application needs. However, due to the limited theoretical specific capacity (372mA hg -1 ), making it difficult to achieve a breakthrough in the energy density of lithium-ion batteries at this stage. Using alkali metals as battery negative electrode materials, such as lithium metal, has a very high theoretical specific capacity (3860mA hg -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 the electrolyte, which can easily cause the loss of active substances and the consumption of electrolyte 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 to a certain extent, can improve the Coulombic efficiency and cycle performance of alkali metal secondary batteries. However, traditional artificial SEI membranes are mainly composed of organic or inorganic substances. Organic substances have poor ionic conductivity and stability, while inorganic substances have poor flexibility. At the same time, due to the severe volume expansion of the alkali metal electrode during the cycle, the artificial SEI membrane can easily rupture and fall off, making it difficult to ensure the stability of the battery for longer cycles. In addition, the electrolyte systems of the existing technology mostly use carbonate or ether solvents, which easily produce side reactions with the alkali metal surface, resulting in low battery Coulombic efficiency and poor cycle stability. At the same time, such electrolyte systems are highly flammable, increasing safety risks during battery use.

[0004] CN109888182A discloses an in-situ protected alkali metal electrode, preparation method, and application. 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. CN115863769A discloses a fluorinated carbonate electrolyte and a lithium metal battery. 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 the lithium fluoride are inorganic substances. As alkali metal protective coatings, such inorganic substances have poor flexibility and are prone to cracking and falling off during use, resulting in poor battery stability. In addition, the fluorinated carbonate electrolyte is prone to side reactions with the alkali metal surface and is flammable, posing a 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 takes into account flame retardancy and other properties, so as to improve the safety, coulombic efficiency and cycle life of alkali metal secondary batteries.

[0006] Summary of the Invention

[0007] The following is a summary of the subject matter described in detail herein. This summary is not intended to limit the scope of the claims.

[0008] The present application provides an electrolyte and an alkali metal secondary battery containing the same. The electrolyte can repair the artificial SEI film on the surface of the alkali metal negative electrode in situ 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 problems such as dendrite growth and interfacial side reactions of the alkali metal negative electrode, greatly improving the battery's coulombic efficiency, cycle life and safety.

[0009] In a first aspect, the present application provides an electrolyte, comprising a combination of an alkali metal salt and a solvent; the solvent comprising 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 having the following structures:

[0010] 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 、R19 、R 21 When it is a single bond, the oxygen atom is directly connected to the cycloalkane.

[0011] 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 linear or branched alkyl group, and a substituted or unsubstituted C3-C10 cycloalkyl group.

[0012] 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.

[0013] The electrolyte provided in the present application uses 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. It 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 an SEI film rich in inorganic and organic substances such as LiF, Li2O, and Li3N. If the artificial SEI film on the surface of the alkali metal negative electrode is damaged, it can be repaired in situ, 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.

[0014] In the present application, the C1-C10 can each independently be C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10.

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

[0016] The C2-C10 can each independently be C2, C3, C4, C5, C6, C7, C8, C9 or C10.

[0017] 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.

[0018] 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.

[0019] The C1-C10 (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10) straight or branched chain alkylene groups described in this application 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.

[0020] The C3-C10 (e.g., C3, C4, C5, C6, C7, C8, C9, or C10) cycloalkylene groups described in this application include, but are not limited to, cyclopropylene, cyclobutylene, cyclopentylene, cyclohexylene, or adamantylene.

[0021] The C1-C10 (e.g., C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10) straight or branched chain alkyl groups described in this application include, but are 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.

[0022] The C3-C10 (e.g., C3, C4, C5, C6, C7, C8, C9, or C10) cycloalkyl groups described herein include, but are not limited to, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, adamantyl, and the like.

[0023] In this application, the "substituted or unsubstituted" group may be substituted with one or more substituents. When there are multiple (at least two) substituents, the multiple (at least two) substituents may be the same or different groups. The substituents may be attached at any position in the group that can be attached. When the same expression is used below, it has the same meaning.

[0024] The halogens described in this application may be fluorine, chlorine, bromine or iodine.

[0025] The C2-C10 (e.g., C2, C3, C4, C5, C6, C7, C8, C9, or C10) alkenyl groups described in this application include, but are not limited to, ethenyl, propenyl, 1-butenyl, or 1-pentenyl.

[0026] 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 described in this application include, but are not limited to, phenyl, biphenyl, terphenyl, naphthyl, anthracenyl, phenanthrenyl, indenyl, fluorenyl, fluoranthenyl, triphenylene, pyrenyl, perylenyl, phenyl, tetraphenyl or triphenylene, etc.

[0027] 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 groups described in this application, wherein the heteroatoms include O, S, N, P or B, etc., illustratively include but are not limited to: furyl, thienyl, pyrrolyl, pyridyl, pyrazinyl, pyridazinyl, pyrimidinyl, triazine, quinolyl, isoquinolyl, quinazolinyl, 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, indolecarbazolyl, azacarbazolyl, etc.), phenothiazinyl, phenoxazinyl or hydroacridinyl, etc.

[0028] The following are optional technical solutions for this application, but are not intended to limit the technical solutions provided in this application. Through the following optional technical solutions, the objectives and beneficial effects of this application can be better achieved and realized.

[0029] As an optional technical solution, the weak 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.

[0030] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0031] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0032] In one embodiment, the alkali metal salt includes any one of lithium salt, sodium salt or potassium salt, or a combination of at least two thereof.

[0033] In one embodiment, 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-trifluoromethylimidazolium, or a combination of at least two thereof.

[0034] In one embodiment, 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.

[0035] In one embodiment, 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-trifluoromethylimidazolium, or a combination of at least two thereof.

[0036] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0037] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0038] In one embodiment, 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:

[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; 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 、R33 、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, and R' are each independently selected from at least one halogen.

[0041] A + The combination method 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 formed by 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 formed by removing one hydrogen atom, for example, A + Including but not limited to the following structures:

[0042] where R 31 and R' 31 Can be the same or different, R 32 and R' 32 Can be the same or different.

[0043] 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.

[0044] The C3-C12 (e.g., C3, C4, C5, C6, C7, C8, C9, C10, C11 or C12) heteroaryl groups illustratively include, but are not limited to, thienyl, benzothienyl, thienoimidazolyl, thienofuranyl or thiazinyl, and the like.

[0045] The C6-C12 can each independently be C6, C7, C8, C9, C10, C11 or C12.

[0046] The C1-C10 can each independently be C1, C2, C3, C4, C5, C6, C7, C8, C9 or C10.

[0047] The C3-C12 can each independently be C3, C4, C5, C6, C7, C8, C9, C10, C11, C12 or C13.

[0048] [B] - Selected from FSI - TFSI - 、BF4 - PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - or DFOB - Any one or a combination of at least two of .

[0049] In one embodiment, the A + Includes any one or a combination of at least two of the following cations:

[0050] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0051] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0052] In one embodiment, the inert diluent includes any one or a combination of at least two of halogenated ethers, halogenated benzenes or halogenated alkanes.

[0053] In one embodiment, 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.

[0054] In one embodiment, the halogenated benzene includes fluorobenzene and / or 1,2-difluorobenzene.

[0055] In one embodiment, the halogenated alkane includes any one or a combination of at least two of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, trichloroform, trichloropropane, monochlorodifluoromethane, dichloromonofluoromethane or difluoromethane.

[0056] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0057] In one embodiment, 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, this application no longer exhaustively lists the specific point values ​​included in the range.

[0058] In a second aspect, the present application provides an alkali metal secondary battery, comprising a negative electrode, a positive electrode, the electrolyte as described in the first aspect, and a separator.

[0059] In one embodiment, the negative electrode includes an alkali metal negative electrode and a negative electrode current collector.

[0060] In one embodiment, the alkali metal negative electrode includes any one of lithium, sodium or potassium.

[0061] In one embodiment, the negative electrode current collector includes any one of copper foil, nickel foil or nickel-plated steel strip.

[0062] In one embodiment, the outer surface of the alkali metal negative electrode is coated with a polyionic liquid artificial SEI film.

[0063] In one embodiment, the thickness of the polyionic liquid artificial SEI film is 2-2000 nm, for example, it can be 2 nm, 30 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1000 nm, 1200 nm, 1500 nm, 1800 nm or 2000 nm, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, this application no longer exhaustively lists the specific point values ​​included in the range.

[0064] In one embodiment, the material of the polyionic liquid artificial SEI membrane has a structure as shown in Formula I, Formula II or Formula III:

[0065] R1, 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.

[0066] The substituents substituted in R1, R2, R3, R4, R5, R6, R7, R8, R9, Z4 and Ar2 are each independently selected from at least one halogen.

[0067] X1 + Selected from any one or a combination of at least two of the following structures:

[0068] X1 + The combination method 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 formed by R 51 、R 53 、R 55 、R 58 、R63 、R 64 、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 linking sites is connected to form, for example X1 + Including but not limited to the following structures:

[0069] where R 54 , R' 54 Can be the same or different, R 53 , R' 53 Can be the same or different.

[0070] X2 + Select any one of the following structures:

[0071] X3 + Select any one of the following structures:

[0072] in, Represents the attachment site of the group.

[0073] 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 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; Ar3 is selected from any one of substituted or unsubstituted C6-C12 aryl, substituted or unsubstituted C3-C12 heteroaryl.

[0074] 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.

[0075] Z6 and Z7 are each independently selected from any one of substituted or unsubstituted C1-C10 linear or branched alkylene groups.

[0076] 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.

[0077] 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.

[0078] Y - Selected from FSI - TFSI - 、BF4- PF6 - PF2O2 - 、NO3 - CF3SO3 - 、BOB - DFOB - Any one or a combination of at least two of .

[0079] n and m are each independently selected from an integer of 1-100,000, for example, 1, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1,000, 10,000, 50,000, 80,000 or 100,000, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, this application no longer exhaustively lists the specific point values ​​included in the said range.

[0080] In one embodiment, the material of the polyionic liquid artificial SEI membrane includes any one or a combination of at least two of the following compounds:

[0081] wherein n1, n2, n3, n4, n5, n6, and n7 are each independently selected from an integer of 1-100,000.

[0082] The polycations in the polyionic liquid artificial SEI membrane material described in the present application, i.e., the portion minus the anions, can be purchased in the form of polycation salts. The polycation salts are subsequently used to experimentally prepare the polyionic liquid artificial SEI membrane material. The preparation method comprises: dripping 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 polyionic liquid artificial SEI membrane material; 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 5-10 hours; the drying temperature is 70-100° C.; the drying time is 24-72 hours; and the Y in the LiY is 0. - Y in the material of the polyionic liquid artificial SEI membrane provided by the present application - Same limitations.

[0083] This application uses a polyionic liquid containing cationic groups as an artificial SEI membrane on the surface of the alkali metal negative electrode. It 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.

[0084] In one embodiment, 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.

[0085] In one embodiment, 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.

[0086] In one embodiment, the nickel-manganese cathode material comprises LiNi 0.5 Mn 0.5 O2、LiNi 0.5 Mn 1.5 O4, LiNiMnCoO2.

[0087] In one embodiment, the sulfur-based cathode 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.

[0088] In one embodiment, the sulfur / polymer composite material includes sulfurized polyacrylonitrile, sulfurized polyvinyl nitrile, or sulfurized polyimide.

[0089] In one embodiment, the separator includes a glass cellulose membrane, a cellulose membrane, and a porous polyolefin compound membrane.

[0090] In one embodiment, the porous polyolefin compound membrane includes a polypropylene membrane, a polyethylene membrane, or a polytetrafluoroethylene membrane.

[0091] In one embodiment, the alkali metal secondary battery further includes a tab.

[0092] Compared with the prior art, this application has the following beneficial effects:

[0093] (1) The electrolyte provided by the present application has low viscosity and good flame retardancy and wettability. It 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;

[0094] (2) The alkali metal secondary battery provided in this application uses the above-mentioned electrolyte and polyionic liquid artificial SEI membrane, and has 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%.

[0095] Still other aspects will become apparent upon reading and understanding the accompanying drawings and detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] The accompanying drawings are used to provide a further understanding of the technical solution of this article and constitute a part of the specification. Together with the embodiments of this application, they are used to explain the technical solution of this article and do not constitute a limitation on the technical solution of this article.

[0097] FIG1 is a schematic diagram of the internal structure of an alkali metal secondary battery provided by the present application;

[0098] FIG2 is a hydrogen nuclear magnetic resonance spectrum of PDDATFSI-1. DETAILED DESCRIPTION

[0099] The technical solution of the present application will be further described below with reference to the accompanying drawings and through specific implementation methods. Those skilled in the art should understand that the embodiments are only for the purpose of helping to understand the present application and should not be regarded as specific limitations of the present application.

[0100] The materials described in this application, except for the materials of the polyionic liquid artificial SEI membrane, are all commercially available materials. The sources of some components in the following examples and comparative examples are as follows:

[0101] (1) Material of polyionic liquid artificial SEI membrane PDDATFSI-1: The structural formula is The preparation steps include:

[0102] 2g of LiTFSI salt was completely dissolved in 50mL of deionized water for later use. 5.63g of polydimethyldiallylammonium chloride (PDDACl) solution (20wt% aqueous solution, molecular weight 200,000, purchased from Adamas) was mixed and stirred with 200mL of deionized water. During the stirring process, the LiTFSI aqueous solution was added dropwise to react. At this time, a white flocculent solid gradually precipitated from the solution. The reaction time was 6h. After the stirring was stopped, the white solid quickly precipitated in the container. After standing for 10min, the liquid was poured out, leaving the white solid and washed with deionized water. This was repeated 5 to 6 times until no obvious precipitation was observed after the AgNO3 aqueous solution was added to the washed liquid. The cleaning was considered complete. Finally, the white solid was collected with a suction filter and dried in an 80°C oven for 48h to obtain a dry white solid. The powder was ground into PDDATFSI-1 using a mortar.

[0103] (2) Material of polyionic liquid artificial SEI membrane PDDAFSI: The structural formula is The preparation process differs from that of PDDATFSI-1 described above only in that an equal amount of LiTFSI aqueous solution is replaced with an equal amount of LiFSI aqueous solution. Other raw materials, process steps, and parameters are the same as those for PDDATFSI-1.

[0104] (3) Material of polyionic liquid artificial SEI membrane PDDATFSI-2: The structural formula is The preparation process differs from that of PDDATFSI-1 described above 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). Other raw materials, process steps, and parameters are the same as those for the preparation of PDDATFSI-1.

[0105] (4) Material of polyionic liquid artificial SEI membrane PDDATFSI-3: The structural formula is The preparation process differs from that of PDDATFSI-1 described above 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). Other raw materials, process steps, and parameters are the same as those for the preparation of PDDATFSI-1.

[0106] (5) N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0107] (6) N-Methyl-N-butylpiperidinium bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0108] (7) N-Methyl-N-butylpyrrole bis(fluorosulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0109] (8) N-methyl-N-propylpyrrole bis(trifluoromethanesulfonyl)imide salt: purchased from Chengjie Ionic Liquids;

[0110] (9) Polyethylene oxide: purchased from Adamas.

[0111] Example 1

[0112] An electrolyte, comprising a preparation method comprising: dissolving LiTFSI in 4 g of N-methyl-N-propylpyrrole bis(fluorosulfonyl)imide salt, 3 g of cyclopentyl methyl ether, and 3 g of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether in a glove box protected by an inert gas; and 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.

[0113] Preparation of a lithium metal negative electrode coated with a polyionic liquid artificial SEI film on the outside: Under dry conditions (H2O<1ppm), PDDATFSI-1 was dissolved in NMP (N-methylpyrrolidone) solvent, and then evenly coated on the surface of the lithium metal negative electrode. The NMP solvent was removed by vacuum drying at 80°C to obtain a lithium metal negative electrode coated with a polyionic liquid artificial SEI film on the outside. The thickness of the polyionic liquid artificial SEI film was 20nm.

[0114] 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% by mass 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.

[0115] A lithium metal secondary battery, the internal structure of which is shown in Figure 1, comprises positive and negative 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 comprises: using the lithium metal negative electrode and positive electrode sheets coated with the polyionic liquid artificial SEI film as prepared above, and assembling them with a polypropylene separator to form a lithium metal secondary battery cell; using aluminum and nickel as the positive and negative electrode tabs, respectively, encapsulating the exterior with aluminum-plastic film; and finally injecting the prepared electrolyte into the cells. After sealing, the lithium metal secondary battery is obtained.

[0116] Example 2

[0117] An electrolyte, which is the same as the electrolyte provided in Example 1.

[0118] A lithium metal secondary battery is provided, which differs 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.

[0119] Example 3

[0120] An electrolyte, which is the same as the electrolyte provided in Example 1.

[0121] A lithium metal secondary battery is provided, which differs 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.

[0122] Example 4

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

[0124] A lithium metal secondary battery is provided, which differs 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.

[0125] Example 5

[0126] An electrolyte, which differs from Example 1 in that the electrolyte is composed of: 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 Example 1.

[0127] A lithium metal secondary battery 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.

[0128] Example 6

[0129] An electrolyte, which differs from Example 1 in that the electrolyte is composed of 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.

[0130] A lithium metal secondary battery 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.

[0131] Example 7

[0132] An electrolyte, which differs from Example 1 in that the composition of the electrolyte is: LiTFSI, 6 g N-methyl-N-propylpyrrole bis(trifluoromethanesulfonyl)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.

[0133] A lithium metal secondary battery 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 8

[0135] An electrolyte, which is the same as the electrolyte provided in Example 1.

[0136] 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.

[0137] Comparative Example 1

[0138] An electrolyte, which differs from Example 1 in that the electrolyte comprises LiTFSI and 10 g of 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.

[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 comparative example, and the other components are the same as those in Example 1.

[0140] Comparative Example 2

[0141] 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.

[0142] 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.

[0143] Comparative Example 3

[0144] An electrolyte, which differs from Example 1 in that the electrolyte comprises: LiTFSI, 3 g ethylene carbonate and 7 g 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.

[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 4

[0147] An electrolyte solution is disclosed, which differs from Example 1 in that 3 g of cyclopentyl methyl ether is replaced by 3 g of ethylene glycol dimethyl ether, 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 5

[0150] An electrolyte, which is the same as the electrolyte provided in Example 1.

[0151] A lithium metal secondary battery is provided, which differs 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.

[0152] Performance testing:

[0153] (1) Nuclear Magnetic Resonance (NMR) Spectrum Test: PDDATFSI-1 was tested using a nuclear magnetic resonance spectrometer (Varian-400 MHz). The test results are shown in Figure 2, which shows the NMR spectrum of PDDATFSI-1. It can be seen from the figure that the four peaks a, b, c, and d correspond to the hydrogens at the relevant positions marked in the chemical structure. By comparing the peak sizes and positions, they can be well matched with the target structure, indicating that the substance is consistent with the target structure and has no other impurities.

[0154] (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 0.2 C. The test results are shown in Table 1:

[0155] Table 1

[0156] The test data of Examples 1 to 7 in Table 1 demonstrate that the lithium metal secondary batteries provided herein exhibit high coulombic efficiency and high capacity retention after 100 cycles. Comparison of Comparative Examples 1 and 2 with Example 1 reveals that the addition of a weakly polar solvent and an inert diluent to the ionic liquid effectively reduces the viscosity of the electrolyte, thereby further improving the battery's specific discharge capacity.

[0157] By comparing 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 use of the electrolyte provided in this application can effectively reduce the side reactions on the surface of the lithium metal negative electrode, thereby improving the battery performance.

[0158] By comparing Example 1 and Comparative Example 4, it can be found that compared with adding a strongly polar linear ether solvent to the electrolyte, the electrolyte prepared using a weakly 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 weakly polar ether solvent provided in this application can effectively reduce the side reactions at the electrode interface and improve the interface stability.

[0159] By comparing Example 1, Example 8 and Comparative Example 5, it can be found that the first-cycle Coulombic 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 both 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 Coulombic efficiency and excellent cycle stability of the battery.

[0160] The applicant declares that while the above-mentioned embodiments are used to illustrate the detailed process flow of the present application, the present application is not limited to the above-mentioned detailed process flow, which does not mean that the present application must rely on the above-mentioned detailed process flow in order to be implemented. Those skilled in the art should understand that any improvements to the present application, equivalent replacements for the raw materials of the present application's products, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present application.

Claims

1. 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 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, wherein 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.

3. The electrolyte according to claim 1 or 2, wherein The mass percentage of the weak polar solvent in the solvent is 10-85%, and can further be 20-60%.

4. The electrolyte according to any one of claims 1 to 3, wherein The alkali metal salt includes any one of lithium salt, sodium salt or potassium salt, or a combination of at least two of them.

5. The electrolyte according to claim 4, wherein 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; Optionally, 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; Optionally, 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; Optionally, the concentration of the alkali metal salt in the electrolyte is 0.1-6 mol / L, and further optionally 0.5-2 mol / L.

6. The electrolyte according to any one of claims 1 to 5, wherein 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: wherein, 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.

7. The electrolyte according to claim 6, wherein The A + Includes any one or a combination of at least two of the following cations: Optionally, the mass percentage of the ionic liquid in the solvent is 10-85%, further optionally 30-70%.

8. The electrolyte according to any one of claims 1 to 7, wherein The inert diluent includes any one of halogenated ethers, halogenated benzenes or halogenated alkanes, or a combination of at least two of them.

9. The electrolyte according to claim 8, wherein 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; Optionally, the halogenated benzene includes fluorobenzene and / or 1,2-difluorobenzene; Optionally, the halogenated alkane includes any one of dichloromethane, dichloroethane, dichloropropane, dichlorobutane, trichloromethane, trichloropropane, monochlorodifluoromethane, dichloromonofluoromethane or difluoromethane, or a combination of at least two thereof; Optionally, the mass percentage of the inert diluent in the solvent is 5-60%, further optionally 10-50%.

10. An alkali metal secondary battery, wherein: The alkali metal secondary battery comprises a negative electrode, a positive electrode, the electrolyte according to any one of claims 1 to 9, and a separator.

11. The alkali metal secondary battery according to claim 10, wherein The negative electrode comprises an alkali metal negative electrode and a negative electrode current collector; Optionally, the alkali metal negative electrode includes any one of lithium, sodium or potassium; Optionally, the negative electrode current collector includes any one of copper foil, nickel foil or nickel-plated steel strip.

12. The alkali metal secondary battery according to claim 11, wherein The outer surface of the alkali metal negative electrode is coated with a layer of polyionic liquid artificial SEI film; Optionally, the thickness of the polyionic liquid artificial SEI film is 2-2000 nm.

13. The alkali metal secondary battery according to claim 12, wherein 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 chain 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 independently selected from 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, a substituted or unsubstituted C6-C12 arylene group kind; 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.

14. The alkali metal secondary battery according to claim 12 or 13, wherein 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.

15. The alkali metal secondary battery according to any one of claims 10 to 14, wherein 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; Optionally, 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; Optionally, the separator includes a glass cellulose membrane, a cellulose membrane, and a porous polyolefin compound membrane; Optionally, the alkali metal secondary battery further includes a tab.

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