Electrolyte, preparation method thereof and lithium ion battery

Abstract

The invention relates to an electrolyte, a preparation method thereof and a lithium ion battery. The electrolyte comprises an ether solvent, an ionic liquid additive and a lithium salt, positive ions of the ionic liquid additive comprise pyrrolidine positive ions and / or piperidine positive ions; the cations and an ether solvent are subjected to solvation to form solvated cations; anions of the ionic liquid additive comprise any one or a combination of at least two of bis (trifluoromethanesulfonyl) imide radical, bis (fluorosulfonyl) imide radical, tetrafluoroborate radical, hexafluorophosphate radical and nitrate radical. According to the invention, the ionic liquid with solvation capability on the ether solvent is selected as an additive, the solvation structure of the electrolyte based on the ether solvent is regulated and controlled, and when the electrolyte is applied to the lithium metal battery, a high-stability solid electrolyte interface and a rapid desolvation process can be formed; and the development of high-energy-density and high-power-density lithium ion batteries is promoted.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to an electrolyte, and especially to an electrolyte, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries, as an important sustainable new energy, have been extended from electronic products to electric vehicles, large-scale energy storage and aerospace fields. The energy density of current commercial lithium ion batteries with graphite anode and carbonate electrolyte system has reached the theoretical limit (about 300 Wh / kg). The short endurance mileage and poor safety of commercial lithium ion batteries restrict the large-scale promotion of new energy electric vehicles and low-altitude economy fields, and high specific energy power batteries have become the most important research direction in the current energy storage field.

[0003] The lithium metal anode with low reduction potential (theoretical specific capacity 3860 mAh·g -1 ) is expected to break through the energy density bottleneck of traditional lithium ion batteries, but the contact of lithium metal with traditional ester electrolyte will cause severe side reactions to generate a solid-state electrolyte interface with poor chemical / mechanical stability, leading to lithium dendrite growth, dead lithium and other problems. The solvent-structured electrode-electrolyte interface (EEI) rich in anions tends to decompose to form inorganic components (such as LiF, Li2O and Li3N, etc.), which have higher chemical stability and mechanical strength, and are more conducive to Li + diffusion. How to balance the rapid desolvation process and optimize the EEI components by adjusting the solvation structure to improve the lithium ion transport kinetics is the key to the design of fast-charging electrolyte.

[0004] CN111276744A discloses a local high-concentration lithium metal battery electrolyte containing anion receptor additive, which contains lithium salt, solvent, diluent and anion receptor additive, and the anion receptor additive is selected from one or more of organic compounds centered on boron. In the local high-concentration lithium metal battery electrolyte, the anion receptor changes the decomposition mode of anions on the surface of lithium metal by interacting with anions, forming a solid-liquid interface film conducive to the uniform and rapid transport of lithium ions; in the local high-concentration lithium metal battery electrolyte, the proportion of non-flammable diluent is large, and at the same time the reduction of free solvent can greatly improve the safety of the electrolyte itself and the battery; the electrolyte has good wettability and low additive dosage. However, the ion conductivity and lithium ion migration speed of this type of electrolyte are low, and the high-rate performance of the battery is poor.

[0005] CN119361837A discloses an anion-regulated weakly solvated sulfone-based electrolyte and a preparation method thereof. The electrolyte comprises a common lithium salt, a lithium salt with a high donor number, and a sulfone-based solvent. The coordination between lithium ions and the sulfone-based solvent is effectively weakened by the anion of the lithium salt with a high donor number, and the interaction between lithium ions and the anion of the common lithium salt is enhanced. By constructing a weakly solvated structure in the above manner, the dissolution process of lithium ions and the decomposition of the common lithium salt are promoted, and the redox of the anion of the weakly solvated structure forms a solid-state electrolyte interface (SEI) layer rich in inorganic substances, thereby solving the problem of poor compatibility between the sulfone-based solvent and lithium metal and graphite negative electrodes, and achieving good electrochemical performance and wide temperature range adaptability. However, the weakly solvated electrolyte inhibits the complete dissociation of the lithium salt, resulting in relatively low lithium ion conductivity, which is difficult to meet the needs of fast-charging batteries.

[0006] CN120261699A discloses an ultra-fast charging liquid lithium metal battery electrolyte. The electrolyte is composed of a solvent and a lithium salt, and the total molar concentration is 0.5-2M. The solvent is one or a mixture of two of fluoroacetonitrile and N,N-dimethyl trifluoroacetamide, and the lithium salt is one or a mixture of two of lithium bisfluorosulfonylimide and lithium bis(trifluoromethanesulfonyl)imide. The ultra-fast charging liquid lithium metal battery electrolyte can match high-nickel positive electrodes and lithium metal negative electrodes, has high energy density and good rate performance, and can promote the application of liquid lithium metal batteries.

[0007] Therefore, it is of great significance to provide a new electrolyte system that can achieve rich anion solvation structure and rapid desolvation at low salt concentration for the development of high specific energy fast-charging batteries. SUMMARY

[0008] In view of the deficiencies of the prior art, the purpose of the present application is to provide an electrolyte, a preparation method thereof, and a lithium ion battery. The present application selects an ionic liquid with a weaker solvation ability for lithium salt than ether solvents as an additive to regulate the solvation structure of the electrolyte based on ether solvents. When applied in a lithium metal battery, it can form a high-stability solid-state electrolyte interface and a rapid desolvation process, ensuring high-voltage stable charge and discharge while also achieving fast charging of lithium metal batteries, thereby promoting the development of high-energy density and high-power density lithium ion batteries.

[0009] To achieve the purpose of the present application, the following technical solutions are adopted:

[0010] In a first aspect, the present application provides an electrolyte, the electrolyte comprising an ether solvent, an ionic liquid additive, and a lithium salt; a cation of the ionic liquid additive comprising a pyrrolidine cation and / or a piperidine cation; the cation being solvated with the ether solvent to form a solvated cation; an anion of the ionic liquid additive comprising any one or a combination of at least two of bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, tetrafluoroborate, hexafluorophosphate, or nitrate.

[0011] The present application selects an ionic liquid having solvation ability for ether solvents as an additive to regulate the solvation structure of the electrolyte based on the ether solvent, and based on the particularity of the anion and cation in the ionic liquid additive, an anion-rich solvation structure is formed in the electrolyte to form an inorganic EEI-rich layer; due to the positive charge characteristics of the cation in the ionic liquid selected by the present application, the ionic dipole has a certain attraction to the solvent in the solvation structure, can be solvated with the ether solvent to form a solvated cation, thereby competing with lithium ions to weaken the solvation ability of the ether solvent for lithium ions, and further facilitating the desolvation process of the lithium ion solvation structure at the interface, thereby achieving the effect of improving the fast charging performance of the battery. In addition, the ionic liquid additive has a coordination competition effect due to its large cation size and positive charge, has a certain coordination effect on the solvent, weakens the solvation of lithium ions, reduces the solvent in the lithium ion solvation structure, and increases the coordination of anions, has an electrostatic shielding effect on the cathode interface, and further realizes a uniform and high-stability solid-state electrolyte interface.

[0012] When the electrolyte provided by the present application is applied to a lithium metal battery, based on the formed high-stability solid-state electrolyte interface and the rapid desolvation process, high-voltage stable charging and discharging can be ensured while fast charging of the lithium metal battery is achieved, thereby promoting the development of high-energy density and high-power density lithium ion batteries.

[0013] Preferably, the ionic liquid additive comprises any one or a combination of at least two of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, N-butyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide, N-butyl-N-methylpyrrolidinium nitrate, 1-methylpiperidinium bis(trifluoromethanesulfonyl)imide, 1-methylpiperidinium bis(fluorosulfonyl)imide, 1-methylpiperidinium tetrafluoroborate, 1-ethylpiperidinium hexafluorophosphate, or 1-butylpiperidinium nitrate.

[0014] Preferably, the ether solvent comprises any one or a combination of at least two of dimethoxymethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, diethyl ether, or ethylene glycol dimethyl ether.

[0015] Preferably, the lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluoro(oxalato)borate or lithium tetrafluoroborate.

[0016] Preferably, the ether solvent comprises any one or a combination of at least two of 1,2-dimethoxyethane, 1,2-dimethoxypropane or dimethoxymethane.

[0017] Preferably, the lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium hexafluorophosphate or lithium difluoro(oxalato)borate.

[0018] Preferably, the concentration of the ionic liquid additive in the electrolyte is 0.01 mol / L to 1 mol / L.

[0019] Preferably, the concentration of the lithium salt in the electrolyte is 0.1 mol / L to 25 mol / L.

[0020] In the present application, the appropriate molar ratio of the lithium salt and the additive can ensure the poly-anion and desolvation ability in the solvation structure of the electrolyte, which helps the battery to ensure the formation of EEI with excellent electrochemical performance and achieve fast charging performance.

[0021] Preferably, the concentration of the ionic liquid additive in the electrolyte is 0.1 mol / L to 0.5 mol / L.

[0022] Preferably, the concentration of the lithium salt in the electrolyte is 1 mol / L to 5 mol / L.

[0023] In a second aspect, the present application provides a preparation method of the electrolyte according to the first aspect, the preparation method comprising:

[0024] Mixing the ether solvent and the lithium salt under a protective atmosphere, first stirring, then adding the ionic liquid additive, second stirring, to prepare the electrolyte.

[0025] Preferably, the second stirring time is more than 12 hours.

[0026] In a third aspect, the present application provides a lithium ion battery comprising the electrolyte according to the first aspect.

[0027] Preferably, in the lithium ion battery, the material of the negative electrode comprises any one of lithium metal or lithium alloy.

[0028] Preferably, in the lithium ion battery, the material of the positive electrode comprises any one or a combination of at least two of high-nickel ternary positive electrode material, lithium iron phosphate positive electrode material or lithium cobaltate positive electrode material.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The present application selects an ionic liquid having solvation ability for ether solvents as an additive to regulate the solvation structure of the electrolyte based on ether solvents, and based on the particularity of the anions and cations in the ionic liquid additive, forms an anion-rich solvation structure in the electrolyte, thereby forming a rich inorganic EEI layer.

[0031] (2) In the present application, the positive charge characteristics of the cations of the ionic liquid have a certain attractive effect on the solvents in the solvation structure through the ion dipole, can be solvated with ether solvents to form solvated cations, thereby competing with lithium ions, weakening the solvation ability of ether solvents for lithium ions, and further facilitating the desolvation process of the solvation structure at the interface, thereby realizing the fast charging effect of the battery.

[0032] (3) In the present application, the ionic liquid additive has a coordination competition effect due to its large cation size and positive charge, has a certain coordination effect on the solvent, weakens the solvation of lithium ions, reduces the solvent in the solvation structure of lithium ions, and increases the coordination of anions, and has an electrostatic shielding effect on the cathode interface, thereby realizing a uniform and highly stable solid electrolyte interface.

[0033] (4) When the electrolyte provided by the present application is applied to a lithium metal battery, it can form a highly stable solid electrolyte interface and a rapid desolvation process, which can ensure high-voltage stable cycle charging and discharging while also realizing fast charging of the lithium metal battery, thereby promoting the development of high-energy density and high-power density lithium ion batteries. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the Raman spectrum test result of the electrolyte in Example 1 and Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as a specific limitation on the present application.

[0036] "ranges" disclosed herein can be defined, for example, by the lower and upper values. Any lower limit can independently be combined with any upper limit to define a range of any value. For example, if a range of 60-120 and 80-110 is listed as exemplary, it is understood that a range of 60-110 and 80-120 is also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, the numerical values "a-b" for any numerical range indicate a shorthand way of describing any integer number combination between "a" and "b", where "a" and "b" are both integers. For example, the numerical range "0-5" indicates that all integers between "0" and "5" have been listed herein, and "0-5" is just a shorthand way of describing these numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to list the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is stated to be an integer selected from "2-10", it is equivalent to list the integer 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0037] In the present application, the phrase "combination of at least two" means, unless otherwise specified, more than two or equal to two. For example, "any one or a combination of at least two" means one or more than two. It is understood that the phrase "combination of at least two" means a combination of any suitable number of items, i.e., a combination of "at least two" items in a manner that does not conflict and enables the present application to be practiced.

[0038] If not specified otherwise, all embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0039] In the present application, the phrase "embodiments" means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment or embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor is it an independent or alternative embodiment to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in the present application can be combined with other embodiments.

[0040] Those skilled in the art can understand that the order of writing each step in the method of each embodiment does not mean a strict execution order, and the detailed execution order of each step should be determined by its function and possible inherent logic. If not specifically stated, all steps of the present application can be performed sequentially or randomly, and can be preferably performed sequentially. For example, the method comprises step (a) and step (b), which means that the method can comprise sequentially performed step (a) and step (b), or sequentially performed step (b) and step (a). For example, the method mentioned can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0041] In the present application, the open technical features or technical solutions described by the words such as "include" do not exclude additional members other than the listed members, and can be regarded as providing not only the closed features or technical solutions composed of the listed members, but also the open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members, or it can not include additional members, and it can be regarded as providing not only the technical features or technical solutions of "A composed of a1, a2 and a3" or "A selected from a1, a2 and a3", but also the technical features or technical solutions of "A including not only a1, a2 and a3, but also other members".

[0042] In the present application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more related listed items, and also include any and all combinations of related listed items, including any combination of two related listed items, any combination of more related listed items, or a combination of all related listed items. For example, "A and / or B" indicates a group consisting of A, B and a combination of A and B. Wherein "including A and / or B" can mean "including A, including B, and including A and B", and can also mean "including A, including B, or including A and B", which can be understood appropriately according to the sentence.

[0043] In the present application, in the terms "first aspect", "second aspect", "third aspect" and the like, the terms "first", "second", "third" and the like are only for description purposes, and cannot be understood as indicating or implying relative importance or quantity, nor can it be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first", "second", "third" and the like only serve the purpose of non-exhaustive enumeration description, and should be understood as not constituting a closed limitation on the quantity.

[0044] In the present application, “optional” means optional, that is, optional from “yes” or “no” two parallel schemes. If there are multiple “optional” in a technical solution, without special instructions, and without contradiction or mutual restriction, each “optional” is independent.

[0045] In the present application, unless otherwise specified, it is assumed to be carried out at room temperature or the temperature set in the art, wherein “room temperature” generally refers to 4℃-35℃, which can refer to 20℃±5℃. In some embodiments of the present application, room temperature refers to 20℃-30℃.

[0046] In some embodiments, the present application provides an electrolyte, the electrolyte comprising an ether-based solvent, an ionic liquid additive, and a lithium salt; the cation of the ionic liquid additive comprises a pyrrolidine cation and / or a piperidine cation; the cation is solvated with the ether-based solvent to form a solvated cation; the anion of the ionic liquid additive comprises any one of or a combination of at least two of bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, tetrafluoroborate, hexafluorophosphate, or nitrate.

[0047] The present application selects an ionic liquid with solvation ability for ether-based solvents as an additive to regulate the solvation structure of the electrolyte based on ether-based solvents. Based on the particularity of the anion and cation in the ionic liquid additive, an anion-rich solvation structure is formed in the electrolyte, thereby forming a rich inorganic EEI layer. In the ionic liquid selected by the present application, due to the positive charge characteristics of the cation, the ionic dipole has a certain attraction to the solvent in the solvation structure, which can be solvated with the ether-based solvent to form a solvated cation, thereby competing with lithium ions, weakening the solvation ability of the ether-based solvent for lithium ions, and further facilitating the desolvation process of the lithium ion solvation structure at the interface, thereby achieving the fast charging effect of the battery. In addition, the ionic liquid additive has a coordination competition effect due to its large cation size and positive charge, which has a certain coordination effect on the solvent, weakens the solvation of lithium ions, reduces the solvent in the lithium ion solvation structure, increases the coordination of anions, and has an electrostatic shielding effect on the cathode interface, thereby realizing a uniform and highly stable solid electrolyte interface.

[0048] When the electrolyte provided by the present application is applied in a lithium metal battery, based on the formed high-stability solid electrolyte interface and rapid desolvation process, high-voltage stable cycle charging and discharging can be ensured while achieving fast charging of the lithium metal battery, promoting the development of high-energy density and high-power density lithium ion batteries.

[0049] In some embodiments, the ionic liquid additive comprises any one or a combination of at least two of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidinium bisfluorosulfonylimide salt, N-butyl-N-methylpyrrolidinium nitrate salt, 1-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 1-methylpiperidinium bisfluorosulfonylimide salt, 1-methylpiperidinium tetrafluoroborate salt, 1-ethylpiperidinium hexafluorophosphate salt, or 1-butylpiperidinium nitrate salt, typically but not limitedly including a combination of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt and N-butyl-N-methylpyrrolidinium bisfluorosulfonylimide salt, a combination of N-butyl-N-methylpyrrolidinium nitrate salt and 1-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt, a combination of 1-methylpiperidinium bisfluorosulfonylimide salt and 1-methylpiperidinium tetrafluoroborate salt, or a combination of 1-ethylpiperidinium hexafluorophosphate salt and 1-butylpiperidinium nitrate salt.

[0050] In some embodiments, the ether-based solvent comprises any one or a combination of at least two of dimethoxymethane, 1,2-dimethoxyethane, 1,2-dimethoxypropane, diethyl ether, or ethylene glycol dimethyl ether, typically but not limitedly including a combination of dimethoxymethane and diethyl ether, a combination of 1,2-dimethoxypropane and diethyl ether, or a combination of ethylene glycol dimethyl ether and dimethoxymethane.

[0051] Ethylene glycol dimethyl ether is widely used as an electrolyte solvent for lithium metal batteries due to its inherent reduction stability, but its low oxidative stability poses a great challenge for the use of lithium metal batteries in high-voltage scenarios.

[0052] In some embodiments, the lithium salt comprises any one or a combination of at least two of lithium bisfluorosulfonylimide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluoro(oxalato)borate, or lithium tetrafluoroborate, typically but not limitedly including a combination of lithium bisfluorosulfonylimide and lithium bis(trifluoromethanesulfonyl)imide, a combination of lithium hexafluorophosphate and lithium hexafluoroarsenate, or a combination of lithium difluoro(oxalato)borate and lithium tetrafluoroborate.

[0053] The above-mentioned ether-based solvents have high oxidative stability, which is conducive to the application of lithium metal batteries in high-voltage scenarios. Moreover, the above-mentioned preferred ether-based solvents have low dielectric constants and weak solvation capabilities, thereby realizing the regulation of the ionic liquid additive on the solvation structure, promoting the interaction between the anion and Li + The interaction is conducive to the formation of an anion-driven stable interface and oxidative stability at the lithium metal negative electrode.

[0054] In some embodiments, the ether solvent includes any one or a combination of 1,2-dimethoxyethane, 1,2-dimethoxypropane or dimethoxymethane, typically but not limitedly, a combination of 1,2-dimethoxyethane and 1,2-dimethoxypropane, a combination of dimethoxymethane and 1,2-dimethoxyethane, or a combination of 1,2-dimethoxypropane and dimethoxymethane.

[0055] In some embodiments, the lithium salt includes any one or a combination of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium hexafluorophosphate or lithium difluoro(oxalato)borate, typically but not limitedly, a combination of lithium bisfluorosulfonylimide and lithium hexafluorophosphate, a combination of lithium bistrifluoromethanesulfonylimide and lithium difluoro(oxalato)borate, or a combination of lithium bisfluorosulfonylimide and lithium difluoro(oxalato)borate.

[0056] In some embodiments, the concentration of the ionic liquid additive in the electrolyte is 0.01 mol / L to 1 mol / L, for example, can be 0.01 mol / L, 0.05 mol / L, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0057] In some embodiments, the concentration of the lithium salt in the electrolyte is 0.1 mol / L to 25 mol / L, for example, can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, 7 mol / L, 9 mol / L, 10 mol / L, 15 mol / L, 20 mol / L or 25 mol / L.

[0058] In the present application, the appropriate molar ratio of the lithium salt and the additive can ensure the poly-anion and desolvation ability in the electrolyte solvation structure, which helps the battery to ensure the formation of EEI with excellent electrochemical performance and improve the fast charging performance.

[0059] In some embodiments, the concentration of the ionic liquid additive in the electrolyte is further preferably 0.1 mol / L to 0.5 mol / L.

[0060] In some embodiments, the concentration of the lithium salt in the electrolyte is further preferably 1 mol / L to 5 mol / L.

[0061] In another specific embodiment, the present application provides a preparation method of the electrolyte as described in the foregoing specific embodiment, the preparation method comprising:

[0062] The electrolyte is prepared by mixing an ether solvent with a lithium salt under a protective atmosphere, first stirring, then adding an ionic liquid additive, and second stirring.

[0063] In some embodiments, the second stirring is performed for 12 hours or more, such as 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 22 hours, or 24 hours.

[0064] In yet another specific embodiment, the present application provides a lithium ion battery comprising the electrolyte as described in the preceding specific embodiment.

[0065] In some embodiments, the lithium ion battery comprises a negative electrode material comprising any one of lithium metal or lithium alloy.

[0066] In some embodiments, the lithium ion battery comprises a positive electrode material comprising any one of high-nickel ternary positive electrode material, lithium iron phosphate positive electrode material, or lithium cobaltate positive electrode material, or a combination of at least two thereof.

[0067] The numerical ranges recited herein include all values from and including the lower and upper values. This is true even if the lower described and the higher described numeric limits are not actually achieved. The numerical ranges recited herein are approximations because some values that fall within the disclosed ranges are typical expected to be off in small increments. To the extent that any numerical limits recited herein are inclusive of the recited endpoint, the term "comprises" as used herein does not exclude the recited endpoint. To the extent that any numerical limits recited herein are not inclusive of the recited endpoint, the term "comprises" as used herein does not exclude the recited endpoint.

[0068] Example 1

[0069] The electrolyte is a 1,2-dimethoxypropane solution of lithium bisfluorosulfonylimide and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt, wherein the concentration of lithium bisfluorosulfonylimide is 1.8 mol / L, and the concentration of N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt is 0.2 mol / L.

[0070] The preparation method of the electrolyte comprises:

[0071] In an argon-filled glove box, 1.8 mol / L lithium bisfluorosulfonylimide is dissolved in 1,2-dimethoxypropane and stirred until uniform, then 0.2 mol / L N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt is added, and the electrolyte is obtained after stirring for 18 hours.

[0072] Example 2

[0073] The embodiment provides an electrolyte, which is a 1,2-dimethoxyethane solution of lithium bistrifluoromethanesulfonimide and N-butyl-N-methylpyrrolidinium nitrate, wherein the concentration of lithium bistrifluoromethanesulfonimide is 1.9 mol / L, and the concentration of N-butyl-N-methylpyrrolidinium nitrate is 0.1 mol / L.

[0074] The preparation method of the electrolyte comprises the following steps:

[0075] In an argon-filled glove box, 1.9 mol / L lithium bistrifluoromethanesulfonimide is stirred and dissolved in 1,2-dimethoxyethane, uniformly mixed, then 0.1 mol / L N-butyl-N-methylpyrrolidinium nitrate is added, and after stirring for 18 h, the electrolyte is obtained.

[0076] Embodiment 3

[0077] The embodiment provides an electrolyte, which is a dimethoxymethane solution of lithium hexafluorophosphate and N-butyl-N-methylpyrrolidinium bistrifluorosulfonimide, wherein the concentration of lithium hexafluorophosphate is 1.5 mol / L, and the concentration of N-butyl-N-methylpyrrolidinium bistrifluorosulfonimide is 0.5 mol / L.

[0078] The preparation method of the electrolyte comprises the following steps:

[0079] In an argon-filled glove box, 1.5 mol / L lithium hexafluorophosphate is stirred and dissolved in dimethoxymethane, uniformly mixed, then 0.5 mol / L N-butyl-N-methylpyrrolidinium bistrifluorosulfonimide is added, and after stirring for 18 h, the electrolyte is obtained.

[0080] Embodiment 4

[0081] The embodiment provides an electrolyte, which is a glycol dimethyl ether solution of lithium tetrafluoroborate and N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonimide, wherein the concentration of lithium tetrafluoroborate is 4 mol / L, and the concentration of N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonimide is 1 mol / L.

[0082] The preparation method of the electrolyte comprises the following steps:

[0083] In an argon-filled glove box, 5 mol / L lithium tetrafluoroborate is stirred and dissolved in glycol dimethyl ether, uniformly mixed, then 1 mol / L N-butyl-N-methylpyrrolidinium bistrifluoromethanesulfonimide is added, and after stirring for 18 h, the electrolyte is obtained.

[0084] Comparative Example 1

[0085] The comparative example provides an electrolyte, except that the electrolyte is a 1,2-dimethoxypropane solution of lithium bisfluorosulfonylimide, wherein the concentration of lithium bisfluorosulfonylimide is 2 mol / L, and in the preparation method, only 2 mol / L of lithium bisfluorosulfonylimide is stirred and dissolved in 1,2-dimethoxypropane, and the rest is the same as in Example 1.

[0086] Comparative Example 2

[0087] The comparative example provides an electrolyte, except that an equal amount of lithium bis(trifluoromethanesulfonyl)imide is used to replace N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide, and the rest is the same as in Example 1.

[0088] Application Example 1

[0089] The application example provides a lithium metal battery, which comprises an NCM811 positive electrode sheet, a lithium metal negative electrode sheet, a Celgard separator, and the electrolyte in Example 1.

[0090] The preparation method of the positive electrode sheet is as follows: NCM811 positive electrode powder, carbon black, and polyvinylidene fluoride are dispersed in N-methylpyrrolidone at a weight ratio of 96:3:1 to prepare a slurry, the slurry is coated on an aluminum foil, dried, and then rolled to obtain the positive electrode sheet.

[0091] Application Example 2

[0092] The application example provides a lithium metal battery, which comprises an NCM811 positive electrode sheet, a lithium metal negative electrode sheet, a Celgard separator, and the electrolyte in Example 2.

[0093] The preparation method of the positive electrode sheet is the same as in Application Example 1.

[0094] Application Example 3

[0095] The application example provides a lithium metal battery, which comprises an NCM811 positive electrode sheet, a lithium metal negative electrode sheet, a Celgard separator, and the electrolyte in Example 3.

[0096] The preparation method of the positive electrode sheet is the same as in Application Example 1.

[0097] Application Example 4

[0098] The application example provides a lithium metal battery, which comprises an NCM811 positive electrode sheet, a lithium metal negative electrode sheet, a Celgard separator, and the electrolyte in Example 4.

[0099] The preparation method of the positive electrode sheet is the same as in Application Example 1.

[0100] Comparative Application Example 1

[0101] This comparative application example provides a lithium metal battery, including an NCM811 positive electrode, a lithium metal negative electrode, a Celgard separator, and the electrolyte of Comparative Example 1.

[0102] The preparation method of the positive electrode sheet is the same as in application example 1.

[0103] Comparative Application Example 2

[0104] This comparative application example provides a lithium metal battery, including an NCM811 positive electrode, a lithium metal negative electrode, a Celgard separator, and the electrolyte of Comparative Example 2.

[0105] The preparation method of the positive electrode sheet is the same as in application example 1.

[0106] Performance testing:

[0107] The solvation structures of the electrolytes in Example 1, Comparative Examples 1 and 2 were characterized by Raman spectroscopy, and the results are as follows: Figure 1 As shown, compared to not adding N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt or only adding lithium bis(trifluoromethanesulfonyl)imide (i.e., without introducing a large cation structure of ionic liquid), the addition of the ionic liquid additive N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt to the electrolyte significantly increases the number of contact ion pairs (CIPs) and aggregates (AGGs) in the solvated structure of the electrolyte, while significantly reducing the number of solvated separated ion pairs (SSIPs). This indicates that the introduction of cations in specific ionic liquid additives effectively constructs an anion-enriched solvated structure of the electrolyte.

[0108] The lithium metal batteries provided in Application Examples 1 to 4, as well as Comparative Application Examples 1 and 2, were tested using the constant potential polarization method to characterize the lithium ion transference number of the electrolyte. The test results are shown in Table 1.

[0109] The coulombic efficiency of the lithium anode in the lithium metal batteries provided in Application Examples 1 to 4, as well as Comparative Application Examples 1 and 2, was tested using the modified Aurbach method. A Li-Cu half-cell was assembled, and the current density, energy density, and voltage range were 0.5 mA·cm⁻¹. -2 1mAh·cm -2 The tests were conducted under conditions ranging from 0.3V to 1V, and the results are shown in Table 1.

[0110] The lithium metal batteries provided in application examples 1 to 4 and comparative application examples 1 and 2 were placed in a 30℃ constant temperature box and connected with a charge-discharge tester, first charged to 4.3V at a constant current and constant voltage of 0.5C current, and then discharged to 2.8V at a constant current of 0.5C after 5min of standing, and the cycle charge-discharge test was carried out in this way until the discharge capacity retention rate was 80%, and the cycle number was shown in Table 1.

[0111] The lithium metal batteries provided in application examples 1 to 4 and comparative application examples 1 and 2 were placed in a 30℃ constant temperature box and connected with a charge-discharge tester, first charged to 4.3V at a constant current and constant voltage of 0.5C current, and then discharged to 2.8V at a constant current of 0.5C after 5min of standing, and the cycle charge-discharge test was carried out in this way until the discharge capacity retention rate was 80%, and the cycle number was shown in Table 1.

[0112] Table 1

[0113]

[0114] According to the test data in Table 1, the test results of comparative application examples 1 to 4 and comparative application examples 1 and 2, the addition of the ionic liquid selected by the application can obviously improve the lithium ion transference number of the electrolyte, the improvement of the lithium ion transference number indicates the improvement of the lithium ion transport capacity of the ionic liquid additive electrolyte, and the high ion transference number is beneficial to reducing the concentration polarization in the charge-discharge process and is beneficial to the rate performance of the battery. At the same time, the addition of the ionic liquid significantly improves the coulombic efficiency of the electrolyte, and the electrolyte provided by the application has more excellent cycle stability than the traditional ether-based electrolyte after adding the specific ionic liquid additive.

[0115] In the application, the electrolyte with the addition of the ionic liquid has good rate performance, and still maintains high discharge capacity and cycle stability at 4C rate, which proves that the addition of the specific ionic liquid additive in the electrolyte provided by the application can obviously improve the rate performance of the battery, and further verifies the promoting effect of the ionic liquid additive on the desolvation process of the electrolyte.

[0116] The applicant declares that the above is only a specific embodiment of the application, but the protection scope of the application is not limited thereto, and those skilled in the art should understand that any changes or replacements within the technical scope disclosed by the application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the application.

Claims

1. An electrolyte, characterized in that, The electrolyte comprises ether solvents, ionic liquid additives, and lithium salts; The cations in the ionic liquid additive include pyrrolidine cations and / or piperidine cations; The cation reacts with an ether solvent to form a solvated cation; The anion of the ionic liquid additive includes any one or a combination of at least two of the following: bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, tetrafluoroborate, hexafluorophosphate, or nitrate.

2. The electrolyte as described in claim 1, characterized in that, The ionic liquid additive includes any one or a combination of at least two of the following: N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bisfluorosulfonylimide salt, N-butyl-N-methylpyrrolidine nitrate, 1-methylpiperidinium bis(trifluoromethanesulfonyl)imide salt, 1-methylpiperidinium bisfluorosulfonylimide salt, 1-methylpiperidinium tetrafluoroborate, 1-ethylpiperidinium hexafluorophosphate, or 1-butylpiperidinium nitrate.

3. The electrolyte as described in claim 1, characterized in that, The ether solvents include any one or a combination of at least two of the following: dimethoxymethane, 1,2-dimethoxyethylene, 1,2-dimethoxypropane, diethyl ether, or ethylene glycol dimethyl ether. And / or, the lithium salt includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium difluorooxalateborate, or lithium tetrafluoroborate.

4. The electrolyte as described in claim 3, characterized in that, The ether solvent includes any one or a combination of at least two of 1,2-dimethoxyethylene, 1,2-dimethoxypropane, or dimethoxymethane. And / or, the lithium salt includes any one or a combination of at least two of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, or lithium difluorooxalateborate.

5. The electrolyte as described in claim 1, characterized in that, The concentration of the ionic liquid additive in the electrolyte is 0.01 mol / L to 1 mol / L; And / or, the concentration of lithium salt in the electrolyte is 0.1 mol / L to 25 mol / L.

6. The electrolyte as described in claim 5, characterized in that, The concentration of the ionic liquid additive in the electrolyte is 0.1 mol / L to 0.5 mol / L; And / or, the concentration of lithium salt in the electrolyte is 1 mol / L to 5 mol / L.

7. A method for preparing the electrolyte as described in any one of claims 1 to 6, characterized in that, The preparation method includes: Under a protective atmosphere, an ether solvent and a lithium salt are mixed, stirred for the first time, then an ionic liquid additive is added, and stirred for the second time to prepare the electrolyte.

8. The preparation method according to claim 7, characterized in that, The second stirring time is more than 12 hours.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrolyte as described in any one of claims 1 to 6.

10. The lithium-ion battery as described in claim 9, characterized in that, In the lithium-ion battery, the negative electrode material includes any one of lithium metal or lithium alloy. And / or, in the lithium-ion battery, the positive electrode material includes any one or a combination of at least two of the following: high-nickel ternary positive electrode material, lithium iron phosphate positive electrode material, or lithium cobalt oxide positive electrode material.

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