Electrolyte and its preparation method and application

Abstract

This application discloses an electrolyte, its preparation method, and its application, relating to the field of battery technology. The electrolyte comprises a lithium salt and a solvent. The lithium salt comprises a first lithium salt and a second lithium salt. The solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent. The solvent comprises a cyclic ether compound and a linear ether compound. The electrolyte provided in this application has clarity, transparency, and high conductivity.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to an electrolyte and a preparation method and application thereof. Background Art

[0002] With the development of contemporary society, people use lithium-ion batteries, a secondary battery, more and more frequently, and the demand has driven lithium-ion batteries to gradually develop in the direction of high energy density. From the perspective of positive and negative electrode materials, it is usually necessary to further increase the gram capacity of the positive electrode material by increasing the nickel content in the ternary material (NCM). Under the premise of ensuring that the capacity of the battery cell remains unchanged, the amount of positive electrode active material is reduced to a certain extent, thereby improving the overall energy density of the battery cell. On the negative electrode side, it has gradually evolved from graphite materials to silicon oxide and silicon carbon materials with higher gram capacity. Among them, since the theoretical capacity of metallic lithium is about ten times that of traditional graphite materials (lithium negative electrode 3860mAh / g vs graphite negative electrode 372mAh / g), directly using metallic lithium as the negative electrode has obvious advantages in improving energy density.

[0003] Lithium-ion batteries typically consist of a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, and separator are all immersed in the electrolyte. During the charge and discharge process, the electrolyte acts as a transport medium for lithium ions, providing some active lithium ions that function as conductive ions and providing ion channels for the free movement of lithium ions. The electrolyte plays a key role in the battery's energy density, power density, cycle life, safety, and wide temperature range.

[0004] Existing electrolytes generally include lithium salts and solvents, and additives are usually used to improve the performance of the electrolyte. However, lithium salts and additives are difficult to completely and evenly dissolve in the solvent, resulting in turbid electrolytes and difficulty in exerting their beneficial effects. Summary of the Invention

[0005] In view of this, the present application provides an electrolyte and a preparation method and application thereof.

[0006] An embodiment of the present application is implemented as follows: an electrolyte includes a lithium salt and a solvent, wherein the lithium salt includes a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent includes a cyclic ether compound and a linear ether compound.

[0007] Optionally, in some embodiments of the present application, in the electrolyte:

[0008] The molar concentration of the lithium salt is 1.5 mol / L to 2.5 mol / L; and / or

[0009] The mass fraction of the first lithium salt is 25wt% to 35wt%; and / or

[0010] The mass fraction of the second lithium salt is 0.5wt% to 8wt%; and / or

[0011] The mass fraction of the cyclic ether compound is 10 wt% to 60 wt%; and / or

[0012] The mass fraction of the linear ether compound is 10 wt% to 60 wt%.

[0013] Optionally, in some embodiments of the present application, the first lithium salt includes a fluorine-containing lithium salt, and the fluorine-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium hexafluoroarsenate; and / or

[0014] The second lithium salt includes one or more of a boron-containing lithium salt, a nitrogen-containing lithium salt, and a chlorine-containing lithium salt; the boron-containing lithium salt includes one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium tetrafluoroborate; the nitrogen-containing lithium salt includes lithium nitrate; the chlorine-containing lithium salt includes lithium perchlorate; and / or

[0015] The cyclic ether compound is a cyclic ether compound with 3 to 20 ring atoms, and the cyclic ether compound with 3 to 20 ring atoms includes one or more of a monooxy tricyclic compound, a dioxy pentacyclic compound, a dioxane compound, a furan compound, a pyran compound, and a crown ether compound; the monooxy tricyclic compound includes one or more of ethylene oxide, 1,2-propylene oxide, and 1,2-butylene oxide; the dioxy pentacyclic compound includes one or more of 1,3-dioxolane, 4-methyl- One or more of 1,3-dioxolane; the dioxane compound includes 1,4-dioxane; the furan compound includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran; the pyran compound includes one or more of tetrahydropyran and 3,6-dihydropyran; the crown ether compound includes one or more of 15-crown-5, 18-crown-6, and dicyclohexane-18-crown-6; and / or

[0016] The linear ether compound is a linear ether compound with 3 to 15 carbon atoms in the main chain, and the linear ether compound with 3 to 15 carbon atoms in the main chain includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, glycerol ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl propyl ether, methyl n-butyl ether, butyl ether, n-pentyl ether, isopentyl ether, n-hexyl ether, ethyl tert-butyl ether, methyl tert-butyl ether, ethyl vinyl ether, tert-butyl vinyl ether, butylphenyl ether, o-methoxytoluene, m-methoxytoluene, p-methylanisole, benzyl methyl ether, and o-dimethoxybenzene.

[0017] Optionally, in some embodiments of the present application, the electrolyte consists of the first lithium salt, the second lithium salt, the cyclic ether compound and the linear ether compound.

[0018] Accordingly, the present invention also provides a method for preparing an electrolyte, comprising the following steps:

[0019] Providing a lithium salt and a solvent, wherein the lithium salt includes a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent includes a cyclic ether compound and a linear ether compound;

[0020] The lithium salt and the solvent are mixed to obtain an electrolyte.

[0021] Optionally, in some embodiments of the present application, in the electrolyte:

[0022] The mass fraction of the first lithium salt is 25wt% to 35wt%; and / or

[0023] The mass fraction of the second lithium salt is 0.5wt% to 8wt%; and / or

[0024] The mass fraction of the cyclic ether compound is 10 wt% to 60 wt%; and / or

[0025] The mass fraction of the linear ether compound is 10 wt% to 60 wt%.

[0026] Optionally, in some embodiments of the present application, including:

[0027] The first lithium salt includes a fluorine-containing lithium salt, and the fluorine-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium hexafluoroarsenate; and / or

[0028] The second lithium salt includes one or more of a boron-containing lithium salt, a nitrogen-containing lithium salt, and a chlorine-containing lithium salt; the boron-containing lithium salt includes one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium tetrafluoroborate; the nitrogen-containing lithium salt includes lithium nitrate; the chlorine-containing lithium salt includes lithium perchlorate; and / or

[0029] The cyclic ether compound is a cyclic ether compound with 3 to 20 ring atoms, and the cyclic ether compound with 3 to 20 ring atoms includes one or more of a monooxy tricyclic compound, a dioxy pentacyclic compound, a dioxane compound, a furan compound, a pyran compound, and a crown ether compound; the monooxy tricyclic compound includes one or more of ethylene oxide, 1,2-propylene oxide, and 1,2-butylene oxide; the dioxy pentacyclic compound includes one or more of 1,3-dioxolane, 4-methyl- One or more of 1,3-dioxolane; the dioxane compound includes 1,4-dioxane; the furan compound includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran; the pyran compound includes one or more of tetrahydropyran and 3,6-dihydropyran; the crown ether compound includes one or more of 15-crown-5, 18-crown-6, and dicyclohexane-18-crown-6; and / or

[0030] The linear ether compound is a linear ether compound with 3 to 15 carbon atoms in the main chain, and the linear ether compound with 3 to 15 carbon atoms in the main chain includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, glycerol ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl propyl ether, methyl n-butyl ether, butyl ether, n-pentyl ether, isopentyl ether, n-hexyl ether, ethyl tert-butyl ether, methyl tert-butyl ether, ethyl vinyl ether, tert-butyl vinyl ether, butylphenyl ether, o-methoxytoluene, m-methoxytoluene, p-methylanisole, benzyl methyl ether, and o-dimethoxybenzene.

[0031] Optionally, in some embodiments of the present application, mixing the lithium salt and the solvent includes: mixing the first lithium salt, the second lithium salt, and the solvent simultaneously.

[0032] Optionally, in some embodiments of the present application, the lithium salt and the solvent are mixed and further stirred; the stirring temperature is 23° C. to 27° C.; and the stirring time is greater than or equal to 3 hours.

[0033] Correspondingly, an embodiment of the present application further provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the above-mentioned electrolyte, or the electrolyte prepared by the above-mentioned preparation method.

[0034] Correspondingly, an embodiment of the present application further provides an electrochemical device, comprising the above-mentioned electrolyte, or the electrolyte prepared by the above-mentioned preparation method.

[0035] The electrolyte provided by the present application has a first lithium salt that can ensure high ionic conductivity of the electrolyte, and a second lithium salt that can improve the conductivity of the electrolyte and the film-forming property of the SEI film; the combination of the cyclic ether compound and the linear ether compound with the solvent can weaken the shielding effect of the solvent molecules on the anions in the first lithium salt and the second lithium salt, so that the anions in the first lithium salt and the second lithium salt tend to pass through the Li + -Anions (ion-ion) interact with each other to enter the solvation sheath, promoting the formation of a stable solvation structure between the lithium salt and the solvent, so that the first lithium salt and the second lithium salt are fully and evenly dissolved in the solvent, thereby improving the clarity, transparency and conductivity of the electrolyte; in addition, the use of ether compounds as solvents can improve the stability and compatibility of the electrolyte with the battery negative electrode when applied to the battery, thereby avoiding the reaction between the lithium negative electrode and the electrolyte to reduce the performance of the battery; the electrolyte provided in this application has a high voltage window and can be used to prepare high-energy-density batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0037] Figure 1 This is a flow chart of a method for preparing an electrolyte provided in an embodiment of the present application;

[0038] Figure 2 is the LSV potential-current curve of the electrolyte provided in Example 1 of the present application;

[0039] Figure 3 is the voltage curve of the battery provided in Battery Example 1 of the present application;

[0040] Figure 4 This is the cycle curve of the battery provided in Battery Example 1 of the present application. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain the present application and are not used to limit the present application.

[0042] In this application, unless otherwise indicated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of a device in actual use or operation, specifically in the drawing directions of the accompanying drawings; whereas "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "including" means "including but not limited to." Terms such as first, second, and third are used merely as designations and do not impose numerical requirements or establish a sequential order.

[0043] In this application, "and / or" describes the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0044] In this application, "at least one" means one or more, and "plurality" means two or more. "One or several", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0045] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a hard limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0046] Currently, most commercial electrolytes are based on ester solvents such as organic carbonates, which have poor stability to metallic lithium negative electrodes. The continuous reaction between the metallic lithium negative electrode and the carbonate solvent will eventually lead to the depletion of the electrolyte and failure of the battery cell. Electrolytes based on ether solvents have good compatibility with metallic lithium negative electrodes, but most of them generally have a narrow electrochemical window and low antioxidant potential. They can only be used in low-voltage systems with an upper voltage limit below 4.0V, which to a certain extent limits the improvement of the overall energy density of the battery cell.

[0047] The electrolytes in the existing technology mainly have the following problems: 1. Traditional commercial electrolytes are mainly carbonates, which are incompatible with lithium negative electrodes. The two are easy to react and have poor stability; 2. Ionic liquid electrolytes are complex to synthesize, costly, and face great pressure to commercialize; 3. High-concentration electrolytes have a high lithium salt content, which greatly increases costs; 4. Conventional low-concentration ether electrolytes are not resistant to high voltages and are easily decomposed under high voltages (>4V), making them unsuitable for use with high-voltage positive electrode materials.

[0048] The technical solution of this application is as follows:

[0049] In a first aspect, an embodiment of the present application provides an electrolyte comprising a lithium salt and a solvent, wherein the lithium salt comprises a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent comprises a cyclic ether compound and a linear ether compound.

[0050] It should be noted that the first lithium salt, as the primary lithium salt, has a greater mass fraction than the second lithium salt. The first lithium salt has a lower degree of association and is easily soluble in ether solvents, ensuring high ionic conductivity in the electrolyte. The anion of the first lithium salt is resistant to oxidation and reduction, and its reduction product facilitates the formation of a stable, low-impedance SEI film. Furthermore, the first lithium salt has excellent chemical stability and does not react with electrode materials, separators, or other materials. Furthermore, the preparation process of the first lithium salt is simple, low-cost, and non-toxic. The second lithium salt, used as an additive, can promote SEI film formation or enhance conductivity.

[0051] The solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, which means that the first lithium salt is easily dissolved and dispersed in the solvent alone, while the second lithium salt is difficult to dissolve or even does not dissolve in the solvent alone, resulting in a turbid system.

[0052] The electrolyte provided by the present application has a first lithium salt that can ensure high ionic conductivity of the electrolyte, and a second lithium salt that can improve the conductivity of the electrolyte and the film-forming property of the SEI film; the combination of the cyclic ether compound and the linear ether compound with the solvent can weaken the shielding effect of the solvent molecules on the anions in the first lithium salt and the second lithium salt, so that the anions in the first lithium salt and the second lithium salt tend to pass through the Li + -Anions (ion-ion) interact with each other to enter the solvation sheath, promoting the formation of a stable solvation structure between the lithium salt and the solvent, so that the lithium salt is fully and evenly dissolved in the solvent, thereby improving the clarity, transparency and conductivity of the electrolyte; in addition, the use of ether compounds as solvents can improve the stability and compatibility of the electrolyte with the battery negative electrode when used in the battery, thereby avoiding the reaction between the lithium negative electrode and the electrolyte to reduce the performance of the battery; the electrolyte provided in this application has a high voltage window and can be used to prepare high-energy-density batteries.

[0053] In some embodiments, the molar concentration of the lithium salt in the electrolyte is 1.5 mol / L to 2.5 mol / L, for example, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, etc. Within this molar concentration range, the wide potential window, safety, and ionic conductivity of the electrolyte are improved.

[0054] In some embodiments, the mass fraction of the first lithium salt in the electrolyte is greater than the mass fraction of the second lithium salt in the electrolyte.

[0055] In some embodiments, the mass fraction of the first lithium salt is 25 wt% to 35 wt%, for example, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, 33 wt%, 34 wt%, 35 wt%, etc. Within the mass fraction range of the first lithium salt, the ionic conductivity of the electrolyte is improved.

[0056] In some embodiments, the mass fraction of the second lithium salt is 0.5 wt% to 8 wt%, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, etc. Within the mass fraction range of the second lithium salt, the film-forming performance and conductivity of the electrolyte are improved, and the second lithium salt can be uniformly dissolved and dispersed in the solvent together with the first lithium salt.

[0057] In some embodiments, the mass fraction of the cyclic ether compound is 10 wt % to 60 wt %, for example, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 45 wt %, 50 wt %, 55 wt %, etc. Within this mass fraction range, the cyclic ether compound is advantageously combined with the linear ether compound to dissolve the lithium salt.

[0058] In some embodiments, the mass fraction of the linear ether compound is 10 wt % to 60 wt %, for example, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 45 wt %, 50 wt %, 55 wt %, etc. Within this mass fraction range, the linear ether compound is advantageously combined with the cyclic ether compound to dissolve the lithium salt.

[0059] Under the synergistic effect of the components and their contents, the first lithium salt and the second lithium salt can be fully and evenly dissolved in the solvent, thereby improving the clarity and transparency of the electrolyte, effectively playing its role as a transmission medium, providing active lithium ions to be used as conductive ions to improve conductivity, and also providing ion channels to promote the free movement of lithium ions, thereby improving the energy density of the battery.

[0060] In some embodiments, the first lithium salt comprises a fluorine-containing lithium salt.

[0061] Furthermore, the fluorine-containing lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium difluorophosphate (LIPO2F2), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium hexafluoroarsenate (LIAsF6).

[0062] In some embodiments, the second lithium salt includes one or more of a boron-containing lithium salt, a nitrogen-containing lithium salt, and a chlorine-containing lithium salt.

[0063] Furthermore, the boron-containing lithium salt includes one or more of lithium difluorooxalatoborate (LiODFB), lithium dioxalatoborate (LiBOB), and lithium tetrafluoroborate (LiBF4).

[0064] The nitrogen-containing lithium salt includes lithium nitrate (LINO3). It is understood that lithium nitrate can participate in the solvation structure and decompose on the lithium metal surface at 1.7V (about 1.7V) to produce Li3N and Li x NO y . Li3N and Li x NO y Can participate in the construction of a stable SEI film, thereby reducing side reactions, while Li3N and Li x NO y Control of Li by adsorption + The deposition method results in spherical deposits on the surface of lithium metal.

[0065] The chlorine-containing lithium salt includes lithium perchlorate (LiClO4).

[0066] In some embodiments, the cyclic ether compound is a cyclic ether compound having 3 to 20 ring atoms, and the number of ring atoms can be, for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, etc.

[0067] In some embodiments, the cyclic ether compound having 3 to 20 ring atoms includes one or more of monooxytricyclic compounds, dioxypentacyclic compounds, dioxane compounds, furan compounds, pyran compounds, and crown ether compounds.

[0068] Furthermore, the monooxytricyclic compound includes one or more of ethylene oxide (CAS: 75-21-8), 1,2-propylene oxide (CAS: 75-56-9), and 1,2-butylene oxide (CAS: 106-88-7).

[0069] The dioxolane compounds include one or more of 1,3-dioxolane (DOL; CAS: 646-06-0) and 4-methyl-1,3-dioxolane (4-MeDOL; CAS: 1072-47-5).

[0070] The dioxane compounds include 1,4-dioxane (CAS: 123-91-1).

[0071] The furan compound includes one or more of tetrahydrofuran (THF; CAS: 109-99-9), 2-methyltetrahydrofuran (2-MeTHF; CAS: 96-47-9), 2-methylfuran (CAS: 534-22-5), 3-methylfuran (CAS: 930-27-8), and 2,5-dimethylfuran (CAS: 14920-89-9).

[0072] The pyran compound includes one or more of tetrahydropyran (THP; CAS: 142-68-7) and 3,6-dihydropyran (CAS: 3174-74-1).

[0073] The crown ether compound includes one or more of 15-crown-5 (CAS: 33100-27-5), 18-crown-6 (CAS: 17455-13-9), and dicyclohexaned-18-crown-6 (CAS: 16069-36-6).

[0074] In some embodiments, the linear ether compound is a linear ether compound with 3 to 15 main chain carbon atoms, and the main chain carbon atoms can be, for example, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, etc.

[0075] In some embodiments, the linear ether compound having a main chain carbon number of 3 to 15 includes ethylene glycol dimethyl ether (DME; CAS: 110-71-4), diethylene glycol dimethyl ether (G2; CAS: 111-96-6), triethylene glycol dimethyl ether (G3; CAS: 112-49-2), diethylene glycol diethyl ether (CAS: 112-36-7), ethylene glycol methyl ethyl ether (CAS: 5137-45-1), diethylene glycol dibutyl ether (CAS: 112 -73-2), tetraglyme (CAS: 143-24-8), glycerol ether (CAS: 627-82-7), ethylene glycol diethyl ether (DEE; CAS: 629-14-1), ethylene glycol dibutyl ether (CAS: 112-48-1), methyl ether (CAS: 115-10-6), ethyl ether (CAS: 60-29-7), propyl ether (CAS: 111-43-3), isopropyl ether (CAS: 108-20-3), methyl propyl ethyl ether (CAS: 557-17-5), methyl n-butyl ether (CAS: 628-28-4), butyl ether (CAS: 142-96-1), n-pentyl ether (CAS: 693-65-2), isopentyl ether (CAS: 544-01-4), n-hexyl ether (CAS: 112-58-3), ethyl tert-butyl ether (CAS: 637-92-3), methyl tert-butyl ether (CAS: 1634-04-4), ethyl vinyl ether (CAS: One or more of the following: tert-butyl vinyl ether (CAS: 926-02-3), butyl phenyl ether (CAS: 1126-79-0), o-methoxytoluene (CAS: 578-58-5), m-methoxytoluene (CAS: 100-84-5), p-methylanisole (CAS: 104-93-8), benzyl methyl ether (CAS: 538-86-3), and o-dimethoxybenzene (CAS: 91-16-7).

[0076] In some embodiments, the electrolyte consists of the first lithium salt, the second lithium salt, the cyclic ether compound, and the linear ether compound.

[0077] Second, see Figure 1 The present invention also provides a method for preparing an electrolyte, comprising the following steps:

[0078] S11, providing a lithium salt and a solvent, wherein the lithium salt includes a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent includes a cyclic ether compound and a linear ether compound;

[0079] S12, mixing the lithium salt and the solvent to obtain an electrolyte.

[0080] In some embodiments, mixing the lithium salt and the solvent comprises: mixing the first lithium salt, the second lithium salt, and the solvent simultaneously.

[0081] It should be noted that the solvent may be prepared by first mixing the cyclic ether compound and the linear ether compound and then mixing with the lithium salt; or the cyclic ether compound, the linear ether compound, the first lithium salt and the second lithium salt may be mixed simultaneously.

[0082] The first lithium salt is easily soluble in the solvent. If the first lithium salt is added first, it can be fully dissolved in the solvent and form a stable solvation structure with the solvent. If the second lithium salt is then added, it will have difficulty integrating into the stable solvation structure, resulting in turbidity in the electrolyte. If the second lithium salt is added first, it will be difficult to dissolve in the solvent, making it difficult to obtain a clear and transparent electrolyte. If the first lithium salt is then added, the system will still be turbid and will not be uniformly and fully dissolved.

[0083] This solution adopts a method of adding the first lithium salt and the second lithium salt to the solvent at the same time. The anions in the first lithium salt and the second lithium salt act synergistically with each other and can be fully dissolved in the mixed solvent of linear ether and cyclic ether, promoting the stabilization of the solvation structure between the lithium ions and the solvent, thereby improving the clarity, transparency and conductivity of the electrolyte.

[0084] In some embodiments, the lithium salt and the solvent are mixed and further stirred. The stirring may be magnetic stirring.

[0085] Furthermore, the stirring temperature is 23° C. to 27° C., for example, 24° C., 25° C., 26° C., etc.; and the stirring time is greater than or equal to 3 hours, for example, 3 hours, 4 hours, 5 hours, etc. Thus, under the aforementioned stirring conditions, the lithium salt is facilitated to be fully and evenly dissolved and dispersed in the solvent, thereby obtaining a clear and transparent electrolyte.

[0086] In a third aspect, an embodiment of the present application further provides a battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and the above-mentioned electrolyte, or the electrolyte prepared by the above-mentioned preparation method.

[0087] The battery provided in the present application includes the above-mentioned electrolyte, which is beneficial to improving the stability of the battery, thereby increasing the service life of the battery, and can improve the cycle performance of the battery and maintain a high capacity.

[0088] In some embodiments, the positive electrode active material in the positive electrode plate includes one or more of lithium nickel manganese oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, and lithium nickel cobalt manganese oxide.

[0089] In some embodiments, the negative electrode plate includes one or more of a metallic lithium negative electrode, a metallic lithium alloy negative electrode, a graphite negative electrode, a silicon-based negative electrode, a silicon-graphite composite negative electrode, and a copper foil lithium-free negative electrode.

[0090] In some embodiments, the diaphragm includes one or more of a woven membrane, a non-woven membrane (non-woven fabric), a microporous membrane, a composite membrane, a diaphragm paper, a laminated membrane, a single-layer polypropylene film (PP), a single-layer polyethylene film (PE), PP+ceramic coating, PE+ceramic coating, double-layer PP / PE, three-layer PP / PE / PP, polyester film (PET), cellulose film, polyimide film (PI), polyamide film (PA), spandex film, and aramid film.

[0091] In some embodiments, the battery comprises a button cell, and further, the button cell comprises a fully charged button cell or a symmetrical button cell.

[0092] In a fourth aspect, an embodiment of the present application further provides an electrochemical device, comprising the above-mentioned electrolyte, or the electrolyte prepared by the above-mentioned preparation method.

[0093] The electrochemical devices may be consumer electronics, new energy vehicles, power tools, energy storage devices, etc. For example, the consumer electronics include remote controls, flashlights, alarm clocks, digital cameras, portable audio and video devices, mobile phones, tablet computers, and laptop computers; the power tools include electric vehicles and robots; and the energy storage devices include photovoltaic power stations, wind power stations, AGC frequency modulation power stations, substation energy storage, and virtual power plants.

[0094] The present application will be described in detail below through specific examples. The following examples are only some examples of the present application and are not limitations of the present application.

[0095] Example 1

[0096] This embodiment provides an electrolyte solution, including a first lithium salt of lithium bis(fluorosulfonyl)imide, a second lithium salt of lithium nitrate, a cyclic ether compound of tetrahydropyran, and a linear ether compound of ethylene glycol dimethyl ether, and a preparation method thereof is as follows:

[0097] 29.34 g of lithium bis(fluorosulfonyl)imide, 2.16 g of lithium nitrate, 47.29 g of tetrahydropyran and 21.21 g of ethylene glycol dimethyl ether were directly mixed simultaneously, and magnetically stirred at 25° C. for 3 h to obtain an electrolyte.

[0098] Example 2

[0099] This embodiment is substantially the same as embodiment 1, except that the mass of tetrahydropyran in the electrolyte in this embodiment is 33.35 g, and the mass of ethylene glycol dimethyl ether is 35.15 g.

[0100] Example 3

[0101] This embodiment is substantially the same as embodiment 1, except that the mass of tetrahydropyran in the electrolyte in this embodiment is 20.98 g, and the mass of ethylene glycol dimethyl ether is 47.52 g.

[0102] Example 4

[0103] This embodiment is substantially the same as embodiment 1, except that the mass of lithium bis(fluorosulfonyl)imide in the electrolyte in this embodiment is 25 g, and the mass of lithium nitrate is 6.5 g.

[0104] Example 5

[0105] This embodiment is substantially the same as embodiment 1, except that the mass of lithium bis(fluorosulfonyl)imide in the electrolyte in this embodiment is 35 g, and the mass of lithium nitrate is 0.5 g.

[0106] Example 6

[0107] This embodiment is substantially the same as embodiment 1, except that, in the electrolyte of this embodiment, the mass of lithium bis(fluorosulfonyl)imide is 20 g, the mass of lithium nitrate is 5 g, the mass of tetrahydropyran is 40 g, and the mass of ethylene glycol dimethyl ether is 35 g.

[0108] Example 7

[0109] This embodiment is substantially the same as embodiment 1, except that the cyclic ether compound tetrahydropyran is replaced by 1,3-dioxolane in this embodiment.

[0110] Example 8

[0111] This embodiment is substantially the same as embodiment 1, with the only difference being that in this embodiment, the linear ether compound ethylene glycol dimethyl ether is replaced by diethylene glycol dimethyl ether.

[0112] Example 9

[0113] This embodiment is substantially the same as Embodiment 1, with the only difference being that in this embodiment, the first lithium salt, lithium bis(fluorosulfonyl)imide, is replaced by lithium hexafluorophosphate.

[0114] Example 10

[0115] This embodiment is substantially the same as embodiment 1, with the only difference being that, in this embodiment, the second lithium salt, lithium nitrate, is replaced by lithium difluorooxalatoborate.

[0116] Comparative Example 1

[0117] This comparative example provides an electrolyte, and its preparation method is as follows:

[0118] 2.16 g of lithium nitrate, 47.29 g of tetrahydropyran, and 21.21 g of ethylene glycol dimethyl ether were mixed, and then 29.34 g of lithium bis(fluorosulfonyl)imide was added and mixed to obtain an electrolyte solution.

[0119] Comparative Example 2

[0120] This comparative example provides an electrolyte, and its preparation method is as follows:

[0121] 29.34 g of lithium bis(fluorosulfonyl)imide, 47.29 g of tetrahydropyran, and 21.21 g of ethylene glycol dimethyl ether were mixed, and then 2.16 g of lithium nitrate was added and mixed to obtain an electrolyte solution.

[0122] Comparative Example 3

[0123] This comparative example is substantially the same as Example 1, except that in this comparative example, 47.29 g of tetrahydropyran and 21.21 g of ethylene glycol dimethyl ether are replaced by 68.5 g of carbonate.

[0124] Comparative Example 4

[0125] This comparative example is substantially the same as Example 1, except that this comparative example does not contain the cyclic ether compound tetrahydropyran, and the mass of the linear ether compound ethylene glycol dimethyl ether is 68.5 g.

[0126] Comparative Example 5

[0127] This comparative example is substantially the same as Example 1, except that this comparative example does not contain the linear ether compound ethylene glycol dimethyl ether, and the mass of the cyclic ether compound tetrahydropyran is 68.5 g.

[0128] Comparative Example 6

[0129] This comparative example is substantially the same as Example 1, except that this comparative example does not contain the first lithium salt, lithium bis(fluorosulfonyl)imide, and the mass of the second lithium salt, lithium nitrate, is 31.5 g.

[0130] Comparative Example 7

[0131] This comparative example is substantially the same as Example 1, except that this comparative example does not contain the second lithium salt, lithium nitrate, and the mass of the first lithium salt, lithium bis(fluorosulfonyl)imide, is 31.5 g.

[0132] The oxidation potential (electrochemical window) of the electrolytes of Examples 1 to 10 and Comparative Examples 1 to 7 was tested respectively, and the appearance of each electrolyte was observed to obtain the LSV potential-current curve of the electrolyte of Example 1. Figure 2 The oxidation potential and appearance of each electrolyte are shown in Table 1.

[0133] The oxidation potential can characterize the electrolyte's ability to withstand high voltages and is measured using linear sweep voltammetry. Specifically, under an argon atmosphere, the electrolyte, a stainless steel sheet, and a lithium sheet are combined to form a button cell (the stainless steel sheet serves as the working electrode, and the lithium sheet serves as the reference and counter electrodes). The electrochemical window is measured on an electrochemical workstation (CHI760) over an OCV (open circuit voltage) range of 5.5 V at a scan rate of 0.5 mV / s.

[0134] Table 1

[0135]

[0136]

[0137] Depend on Figure 2 From Table 1, we can see that:

[0138] From Example 1 and Comparative Examples 4 to 7, it can be seen that the oxidation potentials of the electrolytes of Example 1 and Comparative Example 5 are both greater than 5V, indicating that they have strong high-voltage resistance and a wide potential window, and the electrolytes are also clear and transparent; although the electrolyte of Comparative Example 7 is clear and transparent, its oxidation potential is less than 5V and it is not resistant to high voltage; Comparative Examples 4 and 6 do not contain a cyclic ether compound or the first lithium salt, and the electrolyte system cannot be effectively dissolved, resulting in a turbid state;

[0139] It can be seen from Examples 1 to 6 and Comparative Examples 1 to 2 that, within the range of the mass fractions of the first lithium salt, the second lithium salt, the cyclic ether compound, and the linear ether compound provided in the present application, dissolving them in one pot simultaneously is conducive to obtaining a clear and transparent electrolyte in which the lithium salt is uniformly dissolved and dispersed. In Example 6, the mass fraction of the first lithium salt is low and the solvent content is high. The prepared electrolyte is clear and transparent, but its oxidation potential is not significantly improved compared with other examples and is still less than 5 V. Comparative Examples 1 and 2, respectively, use the method of dissolving the first lithium salt first or dissolving the second lithium salt first to prepare the electrolyte. The resulting electrolyte is turbid and its oxidation potential cannot be measured.

[0140] It can be seen from Examples 1, 7 to 10 and Comparative Examples 1 to 3 that by replacing the materials of the first lithium salt, the second lithium salt, the cyclic ether compound, and the linear ether compound and using the preparation method provided in this application to prepare the electrolyte, a high potential window, high voltage resistance, and clear and transparent electrolyte can also be obtained.

[0141] Battery Example 1

[0142] This embodiment provides a battery, and the preparation method is as follows:

[0143] Lithium nickel cobalt manganese oxide, conductive agent Super P, and binder PVDF were mixed in a mass ratio of 8:1:1, dispersed in an organic solvent NMP (N-methylpyrrolidone), and stirred until stable and uniform to form a positive electrode slurry. The positive electrode slurry was then coated on a 10 μm thick aluminum foil, dried at 80°C, and then heated to 120°C for further vacuum drying. The positive electrode sheet was then produced by roller pressing and slicing.

[0144] Under the inert atmosphere of the glove box, the negative electrode shell, spring sheet, gasket, lithium sheet, electrolyte of Example 1, separator, positive electrode sheet, and positive electrode shell were assembled in sequence, and the assembly was completed by pressing at 800 kPa for 5 seconds to obtain a fully electric button cell.

[0145] Battery Examples 2 to 10

[0146] Battery Examples 2 to 10 are substantially the same as Battery Example 1, with the only difference being that the electrolyte of Example 1 is replaced by the electrolytes of Examples 2 to 10 in Battery Examples 2 to 10, respectively.

[0147] Based on the test results of the electrolyte comparative example, battery comparative example 5 and battery comparative example 7 were set.

[0148] Battery comparison examples 5 and 7

[0149] Comparative battery examples 5 and 7 are substantially the same as Example 1, with the only difference being that the electrolyte of Example 1 is replaced by the electrolytes of Comparative battery examples 5 and 7, respectively.

[0150] The service life, polarization potential and capacity retention rate of the batteries of battery examples 1 to 10 and battery comparative examples 5 and 7 were tested respectively, and the voltage curve results of the battery of battery example 1 were obtained as follows: Figure 3 As shown, the cycle curve of battery example 1 is as follows Figure 4 The data results of each battery are shown in Table 2.

[0151] The test method for service life and polarization potential (voltage curve) is as follows: the battery is placed at 25°C and 2 mA / cm 2 Current density, 2mAh / cm 2 The battery life is calculated as the time it takes for a hard short circuit or a polarization potential > 0.5 V. For comparison purposes, the polarization potential is the steady-state polarization value at the fourth cycle.

[0152] The test method for capacity retention (cycle curve) is as follows: the battery is charged to 4.2V at 0.33C constant current and constant voltage at 25°C, and then discharged to 3.0V at 0.5C constant current. This is one cycle. The remaining capacity is the capacity retention rate. The number of cycles or capacity retention rates of each battery are compared.

[0153] Table 2

[0154]

[0155]

[0156] Note: * indicates battery short circuit failure.

[0157] Depend on Figures 3-4 From Table 2, we can see that:

[0158] It can be seen from battery examples 1 to 6 and battery comparative examples 5 and 7 that the service life of batteries prepared using the electrolyte provided by the present application is greater than or equal to 100 hours, especially battery example 4, which is as high as 165 hours, while the service life of battery comparative example 5 and battery comparative example 7 is less than 100 hours; the polarization potential can characterize the internal impedance of the battery, reflect the rate of ion migration, and is related to the conductivity. The polarization potential of battery comparative example 5 is the lowest, indicating that its conductivity is poor, while battery comparative example 7 does not contain lithium salt additives, and its polarization potential is slightly higher than that of the battery examples; except for battery example 6, the capacity retention rate of other battery examples after 120 cycles is more than 89%, the capacity of battery example 6 still maintains 95% after 80 cycles, while battery comparative example 5 and battery comparative example 7 retain 82% of the capacity at 90 cycles and 92% of the capacity at 75 cycles, respectively. It can be seen that the present application can improve the service life of the battery and maintain a high capacity retention rate;

[0159] It can be seen from battery examples 1, 7 to 10 and battery comparative examples 5 and 7 that replacing the materials of each component does not affect the improvement of battery performance, and its service life is significantly improved. In particular, battery examples 7 to 8 have a polarization potential of 60 V, indicating that their conductivity is relatively high.

[0160] The above is a detailed introduction to the electrolyte provided in the embodiments of the present application, its preparation method, and application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea. At the same time, for those skilled in the art, based on the ideas of the present application, there may be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. An electrolyte, characterized in that: comprising a lithium salt and a solvent, wherein the lithium salt comprises a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent comprises a cyclic ether compound and a linear ether compound; The first lithium salt includes a fluorine-containing lithium salt; the second lithium salt includes one or more of a boron-containing lithium salt, a nitrogen-containing lithium salt, and a chlorine-containing lithium salt; in the electrolyte, the mass fraction of the first lithium salt is 25wt% to 35wt%; The mass fraction of the second lithium salt is 0.5wt% to 8wt%; The preparation method of the electrolyte comprises: The first lithium salt, the second lithium salt, and the solvent are mixed simultaneously.

2. The electrolyte according to claim 1, characterized in that In the electrolyte: The molar concentration of the lithium salt is 1.5 mol / L to 2.5 mol / L; and / or The mass fraction of the cyclic ether compound is 10 wt% to 60 wt%; and / or The mass fraction of the linear ether compound is 10 wt% to 60 wt%.

3. The electrolyte according to claim 1, characterized in that The fluorine-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium hexafluoroarsenate; and / or The boron-containing lithium salt includes one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium tetrafluoroborate; the nitrogen-containing lithium salt includes lithium nitrate; the chlorine-containing lithium salt includes lithium perchlorate; and / or The cyclic ether compound is a cyclic ether compound with 3 to 20 ring atoms, and the cyclic ether compound with 3 to 20 ring atoms includes one or more of a monooxy tricyclic compound, a dioxy pentacyclic compound, a dioxane compound, a furan compound, a pyran compound, and a crown ether compound; the monooxy tricyclic compound includes one or more of ethylene oxide, 1,2-propylene oxide, and 1,2-butylene oxide; the dioxy pentacyclic compound includes one or more of 1,3-dioxolane, 4-methyl- One or more of 1,3-dioxolane; the dioxane compound includes 1,4-dioxane; the furan compound includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran; the pyran compound includes one or more of tetrahydropyran and 3,6-dihydropyran; the crown ether compound includes one or more of 15-crown-5, 18-crown-6, and dicyclohexane-18-crown-6; and / or The linear ether compound is a linear ether compound with 3 to 15 carbon atoms in the main chain, and the linear ether compound with 3 to 15 carbon atoms in the main chain includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, glycerol ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl propyl ether, methyl n-butyl ether, butyl ether, n-pentyl ether, isopentyl ether, n-hexyl ether, ethyl tert-butyl ether, methyl tert-butyl ether, ethyl vinyl ether, tert-butyl vinyl ether, butylphenyl ether, o-methoxytoluene, m-methoxytoluene, p-methylanisole, benzyl methyl ether, and o-dimethoxybenzene.

4. The electrolyte according to claim 1, characterized in that The electrolyte consists of the first lithium salt, the second lithium salt, the cyclic ether compound and the linear ether compound.

5. A method for preparing an electrolyte, characterized in that: The method for preparing the electrolyte according to any one of claims 1 to 4 comprises the following steps: Providing a lithium salt and a solvent, wherein the lithium salt includes a first lithium salt and a second lithium salt, the solubility of the first lithium salt in the solvent is greater than the solubility of the second lithium salt in the solvent, and the solvent includes a cyclic ether compound and a linear ether compound; The first lithium salt, the second lithium salt and the solvent are mixed simultaneously to obtain an electrolyte.

6. The preparation method according to claim 5, characterized in that In the electrolyte: The mass fraction of the first lithium salt is 25wt% to 35wt%; and / or The mass fraction of the second lithium salt is 0.5wt% to 8wt%; and / or The mass fraction of the cyclic ether compound is 10 wt% to 60 wt%; and / or The mass fraction of the linear ether compound is 10 wt% to 60 wt%.

7. The preparation method according to claim 6, characterized in that include: The first lithium salt includes a fluorine-containing lithium salt, and the fluorine-containing lithium salt includes one or more of lithium hexafluorophosphate, lithium bistrifluoromethanesulfonyl imide, lithium bisfluorosulfonyl imide, lithium difluorophosphate, lithium trifluoromethanesulfonate, and lithium hexafluoroarsenate; and / or The second lithium salt includes one or more of a boron-containing lithium salt, a nitrogen-containing lithium salt, and a chlorine-containing lithium salt; the boron-containing lithium salt includes one or more of lithium difluorooxalatoborate, lithium dioxalatoborate, and lithium tetrafluoroborate; the nitrogen-containing lithium salt includes lithium nitrate; the chlorine-containing lithium salt includes lithium perchlorate; and / or The cyclic ether compound is a cyclic ether compound with 3 to 20 ring atoms, and the cyclic ether compound with 3 to 20 ring atoms includes one or more of a monooxy tricyclic compound, a dioxy pentacyclic compound, a dioxane compound, a furan compound, a pyran compound, and a crown ether compound; the monooxy tricyclic compound includes one or more of ethylene oxide, 1,2-propylene oxide, and 1,2-butylene oxide; the dioxy pentacyclic compound includes one or more of 1,3-dioxolane, 4-methyl- One or more of 1,3-dioxolane; the dioxane compound includes 1,4-dioxane; the furan compound includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 2-methylfuran, 3-methylfuran, 2,5-dimethylfuran; the pyran compound includes one or more of tetrahydropyran and 3,6-dihydropyran; the crown ether compound includes one or more of 15-crown-5, 18-crown-6, and dicyclohexane-18-crown-6; and / or The linear ether compound is a linear ether compound with 3 to 15 carbon atoms in the main chain, and the linear ether compound with 3 to 15 carbon atoms in the main chain includes one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, diethylene glycol dibutyl ether, tetraethylene glycol dimethyl ether, glycerol ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, methyl ether, ethyl ether, propyl ether, isopropyl ether, methyl propyl ether, methyl n-butyl ether, butyl ether, n-pentyl ether, isopentyl ether, n-hexyl ether, ethyl tert-butyl ether, methyl tert-butyl ether, ethyl vinyl ether, tert-butyl vinyl ether, butylphenyl ether, o-methoxytoluene, m-methoxytoluene, p-methylanisole, benzyl methyl ether, and o-dimethoxybenzene.

8. The preparation method according to claim 5, characterized in that The lithium salt and the solvent are mixed and then stirred; the stirring temperature is 23° C. to 27° C.; and the stirring time is greater than or equal to 3 hours.

9. A battery comprising a positive electrode sheet, a negative electrode sheet, and a separator, characterized in that: It also includes the electrolyte according to any one of claims 1 to 4, or the electrolyte prepared by the preparation method according to any one of claims 5 to 8.

10. An electrochemical device, characterized in that The invention comprises the electrolyte according to any one of claims 1 to 4, or the electrolyte prepared by the preparation method according to any one of claims 5 to 8.

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