Electrolyte, secondary battery and electric device

Abstract

An electrolyte, a secondary battery and an electric device. The electrolyte comprises a fluoroether solvent and a pyrrole ionic liquid. The electrolyte has flame retardance and can improve the safety performance of batteries.

Description

Electrolyte, secondary battery and electrical device Technical Field

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

[0002] Driven by the need for energy conservation and emission reduction, batteries are increasingly being used. They are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but are also widely used in electric vehicles like electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. As battery applications continue to expand, market demand is also growing.

[0003] However, secondary batteries in the prior art often have disadvantages such as poor safety, flammability, and explosion, which restrict their development.

[0004] Summary of the Invention

[0005] The present application is made in view of the above-mentioned shortcomings, and its purpose is to provide an electrolyte that is flame retardant and can improve the safety performance of secondary batteries.

[0006] A first aspect of the present application provides an electrolyte comprising a fluoroether solvent and a pyrrole-type ionic liquid.

[0007] Pyrrole-type ionic liquids have low vapor pressure and high thermal stability and are non-flammable; fluoroether solvents have excellent flame retardancy and can release fluorine at high temperatures to capture active groups and thus curb the combustion reaction. The synergistic effect of the two can effectively improve the flame retardancy of the electrolyte and improve the safety performance of secondary batteries.

[0008] In any embodiment, the cation of the pyrrole-type ionic liquid comprises a structure shown in Formula I,

[0009] Wherein, R1 and R2 each independently include one or more of C1-C6 alkyl and C1-C6 alkoxy.

[0010] In any embodiment, R1 and R2 each independently include one or more of methyl, ethyl, n-propyl, n-butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, methoxyethyl, ethoxyethyl, and propoxyethyl.

[0011] In any embodiment, the anions of the pyrrole-type ionic liquid include one or more of bisfluorosulfonyl imide anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, dinitrile amide anion, tetrafluoroborate anion, hexafluorophosphate anion, perchlorate anion, dioxalatoborate anion, and difluorooxalatoborate anion.

[0012] In any embodiment, the pyrrole-type ionic liquid includes one or more of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt, N-ethyl-N-methylpyrrolidine trifluoromethanesulfonate, N-butyl-N-ethylpyrrolidine perchlorate, N-methoxyethyl-N-ethoxyethylpyrrolidine tetrafluoroborate, and N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt.

[0013] In any embodiment, the fluoroether solvent includes one or more of 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octylfluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,3,3-tetrafluoropropyl) ether.

[0014] In any embodiment, the electrolyte further includes an ether solvent. Optionally, the ether solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethoxymethane, diethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane, and tetrahydrofuran.

[0015] In any embodiment, based on the total mass of the electrolyte, the mass proportion of the fluoroether solvent is 5% to 60%, and can be optionally 10% to 45%; based on the total mass of the electrolyte, the mass proportion of the pyrrole-type ionic liquid is 5% to 60%, and can be optionally 10% to 45%; based on the total mass of the electrolyte, the mass proportion of the ether solvent is 5% to 60%, and can be optionally 10% to 45%.

[0016] In any embodiment, the electrolyte further includes a lithium salt. Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium 2,2,2-(trifluoromethyl)sulfonyl-N-cyanamide.

[0017] In any embodiment, based on the total mass of the electrolyte, the mass proportion of the lithium salt is 2% to 40%, and can be optionally 10% to 30%.

[0018] In any embodiment, the viscosity of the electrolyte is 1.5 mPa·s to 15 mPa·s.

[0019] A second aspect of the present application provides a secondary battery, comprising the electrolyte of the first aspect.

[0020] In any embodiment, the secondary battery includes a negative electrode plate, and the negative electrode plate includes at least one of lithium metal and lithium alloy.

[0021] A third aspect of the present application provides an electrical device, which includes the secondary battery according to the second aspect. DETAILED DESCRIPTION

[0022] Hereinafter, only certain exemplary embodiments are briefly described. As will be appreciated by those skilled in the art, the described embodiments may be modified in various ways without departing from the spirit or scope of the present application. Therefore, the drawings and description are to be regarded as illustrative in nature and not restrictive.

[0023] Improving the energy density and cycle life of batteries has always been a research hotspot in the industry. Non-aqueous electrolytes containing organic solvents can effectively improve the energy density and cycle stability of batteries compared to aqueous electrolytes. However, non-aqueous electrolytes have a low melting point, are flammable, and have poor safety performance. Especially in lithium metal secondary batteries, the safety hazards are more serious. Lithium metal has the advantages of low electrochemical potential, ultra-high theoretical specific capacity, and low density, making it an ideal negative electrode for the next generation of high-energy density batteries. However, lithium metal negative electrodes are prone to uneven deposition during the cycle, forming dendrites and dead lithium. The continuously growing dendrites can easily pierce the diaphragm, causing a short circuit inside the secondary battery and releasing a large amount of heat, further exacerbating the combustion of the non-aqueous electrolyte and even explosion.

[0024] Based on this, the present application provides a flame retardant electrolyte that can improve the safety performance of secondary batteries.

[0025] The present application provides an electrolyte comprising a fluoroether solvent and a pyrrole-type ionic liquid.

[0026] Fluoroether solvents refer to ether solvents in which at least one hydrogen atom is replaced by a fluorine atom.

[0027] Ionic liquids are liquids composed entirely of ions.

[0028] Pyrrole-type ionic liquids refer to ionic liquids whose cations are derived from pyrrolidine and its derivatives.

[0029] Pyrrole-type ionic liquids have low vapor pressure and high thermal stability and are non-flammable; fluoroether solvents have excellent flame retardancy and can release fluorine at high temperatures to capture active groups to curb combustion reactions. The synergistic effect of the two can effectively improve the flame retardancy of the electrolyte and improve the safety performance of secondary batteries.

[0030] In some embodiments, the cation of the pyrrole-type ionic liquid comprises a structure shown in Formula I,

[0031] Wherein, R1 and R2 each independently include one or more of C1-C6 alkyl and C1-C6 alkoxy.

[0032] C1-C6 alkyl refers to a saturated hydrocarbon group containing 1 to 6 carbon atoms.

[0033] C1-C6 alkoxy refers to an alkoxy group containing 1 to 6 carbon atoms. Alkoxy consists of an alkyl group and an oxygen atom, and is usually represented by R'O-, where R' is an alkyl group.

[0034] In some embodiments, R1 or R2 includes a C1-C6 alkoxy group.

[0035] Alkoxy groups have better flexibility, and pyrrole-type ionic liquids containing alkoxy groups can further reduce the viscosity of the electrolyte, which is beneficial to improving the electrolyte conductivity and battery cycle stability.

[0036] In some embodiments, R1 and R2 each independently include one or more of methyl, ethyl, n-propyl, n-butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, methoxyethyl, ethoxyethyl, and propoxyethyl.

[0037] In some embodiments, R1 or R2 includes at least one of a methoxyethyl group and an ethoxyethyl group.

[0038] In some embodiments, the anions of the pyrrole-type ionic liquid include one or more of a bisfluorosulfonyl imide anion, a bistrifluoromethanesulfonyl imide anion, a trifluoromethanesulfonate anion, a dinitrile amide anion, a tetrafluoroborate anion, a hexafluorophosphate anion, a perchlorate anion, a dioxalatoborate anion, and a difluorooxalatoborate anion.

[0039] Due to the effect of charge, the anions of ionic liquids can participate in the solvation of active ions, such as lithium ions. Compared with solvent molecules, the anions of ionic liquids can be more distributed in the lithium ion solvation sheath. Because the highest occupied orbital (HOMO energy level) of the anions is lower than that of the solvent molecules, they are preferentially reduced in the solid electrolyte membrane (SEI membrane) to form a large number of inorganic components (such as lithium nitride, lithium fluoride, etc.). These inorganic components have the advantages of high stability, high mechanical modulus, and high lithium ion conductivity, which are conducive to the uniform deposition of lithium, can inhibit the growth of lithium dendrites, and improve the safety performance and cycle stability of the battery.

[0040] In some embodiments, the pyrrole-type ionic liquid includes one or more of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt (Py1EOEN(CN)2), N-ethyl-N-methylpyrrolidine trifluoromethanesulfonate (Py12Otf), N-butyl-N-ethylpyrrolidine perchlorate (Py24ClO4), N-methoxyethyl-N-ethoxyethylpyrrolidine tetrafluoroborate (Py(2o1)(2o2)BF4), and N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt (Py14TFSI).

[0041] In some embodiments, the fluoroether solvent comprises one or more compounds of Formula II:

[0042] Wherein, R3 and R4 are each independently selected from a fluorine-substituted or unsubstituted C1-C6 alkyl group, and at least one of R3 and R4 contains a fluorine atom.

[0043] In some embodiments, the fluoroether solvent includes one or more of 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octylfluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,3,3-tetrafluoropropyl) ether.

[0044] Fluoroether solvents are introduced into the electrolyte. Fluoroether solvents do not participate in the solvation of the electrolyte. While retaining the solvation structure and composition, the size of the lithium ion solvation structure can be regulated, effectively reducing the viscosity of the electrolyte, improving the wettability of the electrolyte, and improving the kinetic performance and cycle stability of the secondary battery.

[0045] In some embodiments, the electrolyte further includes an ether solvent.

[0046] In some embodiments, the ether solvent refers to an unsubstituted ether solvent.

[0047] In some embodiments, the ether solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethoxymethane, diethylene glycol dimethyl ether, tetrahydropyran, 1,4-dioxane, 1,3-dioxolane, and tetrahydrofuran.

[0048] When the electrolyte contains ether solvents, the ether solvents and the anions in the electrolyte (such as electrolyte salt anions, ionic liquid anions) play a competitive solvation role, which is beneficial to the solvation / desolvation process of lithium ions, increases the migration speed of lithium ions, reduces the lithium ion interface transfer impedance, and is beneficial to improving the conductivity of the electrolyte, achieving uniform deposition of lithium at the negative electrode, and improving the cycle stability of the battery.

[0049] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the fluoroether solvent is 5% to 60%, and optionally 10% to 45%.

[0050] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the fluoroether solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any numerical range therebetween.

[0051] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the ionic liquid is 5% to 60%, and optionally 10% to 45%.

[0052] In some embodiments, the mass proportion of the ionic liquid based on the total mass of the electrolyte is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any numerical range therebetween.

[0053] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the ether solvent is 5% to 60%, and optionally 10% to 45%.

[0054] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the ether solvent is 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any numerical range therebetween.

[0055] In some embodiments, the electrolyte further includes an electrolyte salt, and the electrolyte salt includes a lithium salt.

[0056] In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium 2,2,2-(trifluoromethyl)sulfonyl-N-cyanamide (LiTFSAM).

[0057] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the lithium salt is 2% to 40%, and can be optionally 10% to 30%.

[0058] In some embodiments, based on the total mass of the electrolyte, the mass proportion of the lithium salt can be selected as 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or any numerical range therebetween.

[0059] When the concentration of the electrolyte is within an appropriate range, it can not only improve the conductivity of the secondary battery through a high-concentration system, but also achieve the solvation of lithium ions, improve the kinetic performance of the secondary battery, and comprehensively improve the cycle stability of the battery.

[0060] The electrolyte anions, ionic liquids, and fluoroethers form a high-concentration system, which greatly reduces the free solvent content in the electrolyte, lowering the flammability of the electrolyte. The electrolyte has low viscosity and high conductivity, and the battery has good cycle performance.

[0061] In some embodiments, the viscosity of the electrolyte is 1.5 mPa.s to 15 mPa.s.

[0062] In some embodiments, the viscosity of the electrolyte is 1.5 mPa.s, 3 mPa.s, 4 mPa.s, 5 mPa.s, 6 mPa.s, 7 mPa.s, 8 mPa.s, 9 mPa.s, 10 mPa.s, 11 mPa.s, 12 mPa.s, 13 mPa.s, 14 mPa.s, 15 mPa.s or any range therebetween.

[0063] The electrolyte within the above viscosity range has good flame retardancy and electrical conductivity, which is beneficial for taking into account both the safety performance and cycle performance of the secondary battery.

[0064] A second aspect of the present application provides a secondary battery, comprising the electrolyte of the first aspect.

[0065] In some embodiments, the secondary battery includes a negative electrode plate, and the negative electrode plate includes at least one of lithium metal and lithium alloy.

[0066] Lithium alloy refers to an alloy material formed by lithium metal and other metals.

[0067] For secondary batteries with lithium metal as the negative electrode, since the cation reduction potential of pyrrole-type ionic liquids is lower than that of lithium ions, they compete with lithium ions for adsorption around dendrites when present in dendrites, and use their steric hindrance to repel lithium ions, thereby inhibiting dendrite growth. This can further play a role in regulating lithium deposition and improving the safety and cycle stability of secondary batteries.

[0068] In some embodiments, the secondary battery includes a positive electrode sheet, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0069] In some embodiments, the positive electrode active material includes a lithium-containing phosphate, a lithium transition metal oxide, and modified compounds thereof. The lithium transition metal oxide includes, but is not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide. The lithium-containing phosphate includes, but is not limited to, at least one of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0070] A third aspect of the present application provides an electric device, comprising the secondary battery according to the second aspect.

[0071] Example

[0072] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0073] 1. Preparation method

[0074] Example 1

[0075] 1) Preparation of electrolyte

[0076] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 10 parts by mass of lithium dioxalatoborate, 25 parts by mass of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt, and 25 parts by mass of ethylene glycol dimethyl ether were mixed at 35°C, and the prepared solution was mixed with 40 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at 35°C to obtain the electrolyte of Example 1.

[0077] 2) Preparation of positive electrode sheet

[0078] The positive electrode slurry is prepared by mixing lithium cobalt oxide (96 wt% of the positive electrode active material), 2 wt% of Ketjen Black (a conductive agent), and 2 wt% of polyvinylidene fluoride (PVDF) as a binder. N-methylpyrrolidone is then added and stirred to form a positive electrode slurry. The slurry is then coated onto aluminum foil. After the coating is completed, the positive electrode sheets are dried, cold-pressed, and cut into pieces.

[0079] 3) Preparation of negative electrode sheet

[0080] Lithium metal is used as the negative electrode.

[0081] 4) Isolation film

[0082] Polyethylene film is used as the isolation film.

[0083] 5) Battery preparation

[0084] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The bare cell is placed in an outer packaging, injected with the prepared electrolyte, and then packaged, injected, formed, and vented to produce a lithium-ion battery.

[0085] Example 2

[0086] The preparation method of the battery of Example 2 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Example 2 is as follows:

[0087] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 30 parts by mass of lithium hexafluorophosphate, 12 parts by mass of N-ethyl-N-methylpyrrolidine trifluoromethanesulfonate, and 43 parts by mass of tetrahydrofuran were mixed at 35°C, and the prepared solution was then mixed with 15 parts by mass of 1,1,2,2-tetrafluoroethyl ether at 35°C to obtain the electrolyte of Example 2.

[0088] Example 3

[0089] The preparation method of the battery of Example 3 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Example 3 is as follows:

[0090] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 12 parts by mass of lithium tetrafluoroborate, 45 parts by mass of N-butyl-N-ethylpyrrolidine perchlorate, and 25 parts by mass of 1,3-dioxolane were mixed at 35°C, and the prepared solution was then mixed with 18 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether at 35°C to obtain the electrolyte of Example 3.

[0091] Example 4

[0092] The preparation method of the battery of Example 4 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Example 4 is as follows:

[0093] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 2 parts by mass of lithium dioxalatoborate, 25 parts by mass of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt, and 25 parts by mass of ethylene glycol dimethyl ether were mixed at 35°C, and the above-prepared solution was mixed with 48 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at 35°C to obtain the electrolyte of Example 4.

[0094] Example 5

[0095] The preparation method of the battery of Example 5 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Example 5 is as follows:

[0096] In an argon atmosphere glove box (H2O <0.01ppm, O2 <0.01ppm), 10 parts by mass of lithium dioxalatoborate and 50 parts by mass of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt were mixed at 35°C, and then the above-prepared solution was mixed with 40 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at 35°C to obtain the electrolyte of Example 5.

[0097] Example 6

[0098] The preparation method of the battery of Example 6 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Example 6 is as follows:

[0099] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 10 parts by mass of lithium dioxalatoborate, 12 parts by mass of N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, and 25 parts by mass of ethylene glycol dimethyl ether were mixed at 35°C, and the above-prepared solution was mixed with 40 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at 35°C to obtain the electrolyte of Example 6.

[0100] Comparative Example 1

[0101] The preparation method of the battery of Comparative Example 1 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Comparative Example 1 is as follows:

[0102] In an argon atmosphere glove box (H2O <0.01ppm, O2 <0.01ppm), 10 parts by mass of lithium dioxalatoborate and 50 parts by mass of ethylene glycol dimethyl ether were mixed at 35°C, and then the above-prepared solution was mixed with 40 parts by mass of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether at 35°C to obtain an electrolyte solution of ratio 1.

[0103] Comparative Example 2

[0104] The preparation method of the battery of Comparative Example 2 is basically the same as that of Example 1, except for the preparation of the electrolyte. The preparation method of the electrolyte of Comparative Example 2 is as follows:

[0105] In an argon atmosphere glove box (H2O<0.01ppm, O2<0.01ppm), 10 parts by mass of lithium bis(oxalatoborate), 25 parts by mass of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt, and 65 parts by mass of ethylene glycol dimethyl ether were mixed at 35°C to obtain an electrolyte solution of ratio 2.

[0106] Table 1 shows the components of the electrolytes of various embodiments and comparative examples and their mass ratios.

[0107] Table 1

[0108] 2. Performance Testing

[0109] 1) Electrolyte viscosity test

[0110] The viscosity of the electrolyte was measured at 25°C using a Brookfield DV2TLV viscometer according to GB / T 10247-2008, with a spindle of LV-1.

[0111] 2) Electrolyte conductivity test

[0112] The conductivity of the electrolyte at 25°C was measured using an Orion Star A222 conductivity meter.

[0113] 3) Electrolyte flame retardancy test

[0114] Take 1mL of electrolyte and burn it with an open flame of a lighter for 5s in a non-sealed environment. If the electrolyte does not burn, it is judged to be flame retardant; if the electrolyte burns, it is judged to be flammable.

[0115] 4) Battery cycle stability test

[0116] The battery was left to stand at 25°C for 30 minutes, discharged at a constant current of 1C to 2.75V, and then charged at a constant current of 1C to 4.3V after standing for 5 minutes. Then, constant voltage charging was performed to a cut-off current of 0.05C, and the battery was left to stand for 5 minutes and discharged at a constant current of 1C to 2.75V. The capacity of the test cell was recorded as the initial capacity (C0). After standing for 5 minutes, the above steps were repeated for the same battery, and the discharge capacity of the battery after the nth cycle (C n ), then record the battery cycle capacity retention rate P n (P n =C n / C0×100%) is the number of cycles when the percentage is 80%.

[0117] 3. Analysis of test results of various embodiments and comparative examples

[0118] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in Table 2 below.

[0119] Table 2

[0120] Table 3

[0121] From the comparison between the embodiment and the comparative example, it can be seen that when the electrolyte includes a fluoroether solvent and a pyrrole-type ionic liquid, the electrolyte has flame retardancy.

[0122] From the comparison between Examples 1-3 and Example 4, it can be seen that when the mass proportion of lithium salt in the electrolyte is 10%-40%, the electrolyte has higher conductivity and the battery has better cycle stability.

[0123] From the comparison between Example 1 and Example 5, it can be seen that when the electrolyte contains an ether solvent, the conductivity of the electrolyte can be improved, the viscosity of the electrolyte can be reduced, the electrolyte has flame retardancy, and the battery has better cycle stability, taking into account both the cycle stability and safety of the secondary battery.

[0124] From the comparison between Example 1 and Example 6, it can be seen that when R1 or R2 of the pyrrole-type cation includes an alkoxy group, the viscosity of the electrolyte can be further reduced, and the conductivity of the electrolyte and the cycle stability of the battery are further improved.

[0125] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and within the scope of the technical solution of the present application, embodiments having substantially the same structure as the technical concept and exerting the same effects are all included in the technical scope of the present application. In addition, within the scope of the subject matter of the present application, various modifications that can be conceived by those skilled in the art to the embodiments, and other methods constructed by combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte includes a fluoroether solvent and a pyrrole-type ionic liquid.

2. The electrolyte according to claim 1, characterized in that The cation of the pyrrole-type ionic liquid includes a structure shown in Formula I, Wherein, R1 and R2 each independently include one or more of C1-C6 alkyl and C1-C6 alkoxy.

3. The electrolyte according to claim 2, characterized in that R1 and R2 each independently include one or more of methyl, ethyl, n-propyl, n-butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, methoxyethyl, ethoxyethyl, and propoxyethyl.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The anions of the pyrrole-type ionic liquid include one or more of bisfluorosulfonyl imide anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, dinitrile amide anion, tetrafluoroborate anion, hexafluorophosphate anion, perchlorate anion, dioxalatoborate anion, and difluorooxalatoborate anion.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The pyrrole-type ionic liquid includes one or more of N-methoxyethyl-N-methylpyrrolidine dinitrile amine salt, N-ethyl-N-methylpyrrolidine trifluoromethanesulfonate, N-butyl-N-ethylpyrrolidine perchlorate, N-methoxyethyl-N-ethoxyethylpyrrolidine tetrafluoroborate, and N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The fluoroether solvent includes one or more of 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl-2,2,2-trifluoroethyl ether, 1H,1H,5H-octylfluoropentyl-1,1,2,2-tetrafluoroethyl ether, and bis(2,2,3,3-tetrafluoropropyl) ether.

7. The electrolyte according to any one of claims 1 to 6, characterized in that The electrolyte further includes an ether solvent. Optionally, the ether solvent includes one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethoxymethane, diethylene glycol dimethyl ether, 1,4-dioxane, 1,3-dioxolane, and tetrahydrofuran.

8. The electrolyte according to claim 7, characterized in that Based on the total mass of the electrolyte, the mass proportion of the fluoroether solvent is 5% to 60%, and can be optionally 10% to 45%; Based on the total mass of the electrolyte, the mass proportion of the pyrrole-type ionic liquid is 5% to 60%, and can be optionally 10% to 45%; Based on the total mass of the electrolyte, the mass proportion of the ether solvent is 5% to 60%, and can be optionally 10% to 45%.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The electrolyte also includes a lithium salt. Optionally, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium 2,2,2-(trifluoromethyl)sulfonyl-N-cyanamide.

10. The electrolyte according to claim 9, characterized in that Based on the total mass of the electrolyte, the mass proportion of the lithium salt is 2% to 40%, and can be optionally 10% to 30%.

11. The electrolyte according to any one of claims 1 to 10, characterized in that The viscosity of the electrolyte is 1.5 mPa·s to 15 mPa·s.

12. A secondary battery, characterized in that: The electrolyte comprising the electrolyte according to any one of claims 1 to 11.

13. The secondary battery according to claim 12, characterized in that: The secondary battery includes a negative electrode plate, and the negative electrode plate includes at least one of lithium metal and lithium alloy.

14. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to claim 12 or 13.

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