Electrolyte and preparation method and application thereof

Abstract

The invention provides an electrolyte and a preparation method and application thereof, the electrolyte comprises fluorine-containing lithium salt, a solvent and an additive, the solvent comprises a first solvent, the viscosity of the first solvent is 0.2-2.2 mPa.s, the melting point of the first solvent is (-90)-(-20) DEG C, and the boiling point of the first solvent is 79-280 DEG C; the additive comprises nitrate, and metal ions in the nitrate comprise at least one of transition metal cations and alkaline earth metal cations. The electrolyte provided by the invention contains the fluorine-containing lithium salt, the first solvent with the characteristics of low viscosity, low melting point and high boiling point and the nitrate containing transition metal cations or / and alkaline earth metal cations, so that high and low temperature performance of electrochemical devices such as lithium ion batteries and the like can be considered, and the service life of the electrochemical devices is prolonged while the usable range of the electrochemical devices is widened. And the long cycle performance of the electrochemical device is improved.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to an electrolyte and its preparation method and application. Background Art

[0002] Electrochemical devices are widely used. For example, in lithium-ion batteries, traditional lithium-ion batteries mainly consist of four major components: a positive electrode, a separator, a negative electrode, and an electrolyte. The electrolyte acts as an ion transport medium therein, allowing lithium ions to be transported between the positive and negative electrodes through the separator.

[0003] However, most of the lithium-ion battery electrolytes currently on the market use lithium hexafluorophosphate as the lithium salt, which is extremely easy to decompose into lithium fluoride at high temperatures. Lithium fluoride will generate hydrofluoric acid when encountering water, and hydrofluoric acid is extremely easy to react with each component in the battery, thus affecting the battery cycle performance. At the same time, for solvents, the currently used solvents are often organic carbonate solvents, among which diethyl carbonate is the most common component. However, most of these carbonate solvents have relatively high melting points. Therefore, the viscosity of the electrolyte will increase significantly at low temperatures, resulting in a decrease in the lithium ion concentration, and further a significant decrease in the lithium ion conductivity, affecting the low-temperature performance of the battery.

[0004] Therefore, how to improve the lithium ion concentration, conductivity, high-temperature stability and low-temperature performance of the electrolyte is an urgent problem to be solved. Summary of the Invention

[0005] The present application aims to solve at least one of the technical problems in the related technologies to some extent.

[0006] In view of this, one object of the present application is to provide an electrolyte, which contains a fluorinated lithium salt, a first solvent with the characteristics of low viscosity, low melting point and high boiling point, and a nitrate containing transition metal cations or / and alkaline earth metal cations, and can take into account the high and low temperature performance of electrochemical devices such as lithium-ion batteries. While broadening the applicable range of electrochemical devices, the long cycle performance of electrochemical devices is improved.

[0007] Another object of the present application is to provide a preparation method of the electrolyte.

[0008] Another object of the present application is to provide the application of the electrolyte.

[0009] Another object of the present application is to provide an electrochemical device.

[0010] Another object of the present application is to provide a vehicle.

[0011] To achieve the above object, an embodiment of the first aspect of the present application provides an electrolyte, comprising a fluorinated lithium salt, a solvent and an additive; the solvent includes a first solvent, the viscosity of the first solvent at 25 °C is 0.2-2.2 mPa·s, the melting point is (-90)-(-20) °C, and the boiling point is 79-280 °C; the additive includes a nitrate, and the metal ions in the nitrate include at least one of transition metal cations and alkaline earth metal cations.

[0012] In some embodiments, the volume content of γ-butyrolactone in the solvent is 30-50%.

[0013] In some embodiments, the first solvent includes at least one of γ-butyrolactone, methyl propionate and methyl butyrate.

[0014] In some embodiments, the solvent further includes a second solvent, and the second solvent includes at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0015] In some embodiments, the concentration of the nitrate in the electrolyte is 0.1-0.3 mol / L.

[0016] In some embodiments, the nitrate includes at least one of magnesium nitrate, calcium nitrate, barium nitrate, iron nitrate and copper nitrate.

[0017] In some embodiments, the concentration of the fluorinated lithium salt in the electrolyte is 1.8-2 mol / L;

[0018] In some embodiments, the fluorinated lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide and lithium tris(trifluoromethylsulfonyl)methyl.

[0019] To achieve the above object, an embodiment of the second aspect of the present application provides a method for preparing an electrolyte, comprising:

[0020] Dissolving the fluorinated lithium salt and the additive in the solvent to obtain the electrolyte.

[0021] To achieve the above object, an embodiment of the third aspect of the present application relates to the application of the electrolyte of the embodiment of the present application or the electrolyte prepared by the preparation method of the embodiment of the present application in the energy storage field and the vehicle field.

[0022] To achieve the above object, an embodiment of the fourth aspect of the present application provides an electrochemical device, comprising the electrolyte of the embodiment of the present application or the electrolyte prepared by the preparation method of the embodiment of the present application.

[0023] To achieve the above object, an embodiment of the fifth aspect of the present application provides a vehicle, including the electrolyte of the embodiment of the present application, or the electrolyte prepared by the preparation method of the embodiment of the present application, or the electrochemical device of the embodiment of the present application.

[0024] The electrolyte of the embodiment of the present application can at least bring the following beneficial effects:

[0025] 1. Since it contains a fluorinated lithium salt, a first solvent with the characteristics of low viscosity, low melting point and high boiling point, and a nitrate containing transition metal cations or / and alkaline earth metal cations, it can take into account the high and low temperature performance of electrochemical devices such as lithium-ion batteries. While broadening the applicable range of electrochemical devices, it improves the long cycle performance of electrochemical devices. Specifically:

[0026] The nitrate containing transition metal cations or / and alkaline earth metal cations and fluoride ions in the electrolyte can generate a fluorinated metal compound on the electrode surface. The SEI film formed by this compound has good mechanical properties and electrochemical stability, and can effectively prevent the problem that the metal cations of the positive electrode active material dissolve out during the reaction of electrochemical devices such as lithium-ion batteries at high temperature and affect the cycle, thereby improving the interface stability and high temperature performance of electrochemical devices such as lithium-ion batteries.

[0027] As the main component of the solvent, the first solvent has low viscosity, enabling electrochemical devices such as lithium-ion batteries to use a higher concentration of lithium salt. While increasing the concentration of free lithium ions in the electrolyte, it keeps the electrolyte at a lower viscosity, thereby improving the ionic conductivity of the electrolyte. At the same time, the first solvent has a low melting point and a high boiling point, decomposes less gas at high temperature, has a wide applicable temperature range, and can still maintain a high lithium ion transmission ability at low temperature.

[0028] The coexistence of the nitrate containing transition metal cations or / and alkaline earth metal cations and the first solvent can take into account the high and low temperature performance of the battery core and improve the cycle performance of electrochemical devices such as lithium-ion batteries under different temperature conditions.

[0029] 2. When used in portable mobile devices, electric vehicles, etc., it can improve the service life of electrochemical devices and the endurance at different temperatures.

[0030] Additional aspects and advantages of the present application will be given in part in the following description, become apparent in part from the following description, or be learned through the practice of the present application. Detailed Embodiments

[0031] The embodiments of the present application will be described in detail below. The embodiments are exemplary and are intended to explain the present application, and should not be construed as a limitation to the present application.

[0032] In an application, the disclosure of a numerical range includes the disclosure of all values within the entire range and further sub-ranges, including the endpoints and sub-ranges given for these ranges.

[0033] In an application, the raw materials, equipment, etc. involved, unless otherwise specified, are raw materials and equipment that can be obtained through commercial channels or made by well-known methods; the methods involved, unless otherwise specified, are conventional methods.

[0034] The electrolyte of the embodiment of the present application includes a fluorinated lithium salt, a solvent, and an additive; the solvent includes a first solvent, the viscosity of the first solvent at 25 °C is 0.2 - 2.2 mPa·s, the melting point is (-90) - (-20) °C, and the boiling point is 79 - 280 °C; the additive includes a nitrate, and the metal ions in the nitrate include at least one of transition metal cations and alkaline earth metal cations.

[0035] It can be understood that in the electrolyte of the embodiment of the present application, the nitrate may only include a nitrate containing transition metal cations or a nitrate containing alkaline earth metal cations, or may simultaneously include a nitrate containing transition metal cations and a nitrate containing alkaline earth metal cations.

[0036] The electrolyte of the embodiment of the present application, due to containing a fluorinated lithium salt, a first solvent with the characteristics of low viscosity, low melting point, and high boiling point, and a nitrate containing transition metal cations or / and alkaline earth metal cations, can take into account the high and low temperature performance of electrochemical devices such as lithium-ion batteries. While broadening the applicable range of electrochemical devices, it improves the long cycle performance of electrochemical devices. Specifically: The nitrate containing transition metal cations or / and alkaline earth metal cations and the fluoride ions in the electrolyte can generate a fluorinated metal compound on the electrode surface. The SEI film formed by this compound has good mechanical properties and electrochemical stability, and can effectively prevent the dissolution of metal cations of the positive electrode active material during the reaction of electrochemical devices such as lithium-ion batteries at high temperatures, affecting the cycle problem, and thus improving the interfacial stability and high temperature performance of electrochemical devices such as lithium-ion batteries. As the main component of the solvent, the first solvent has a low viscosity, enabling electrochemical devices such as lithium-ion batteries to use a higher concentration of lithium salt. While increasing the concentration of free lithium ions in the electrolyte, it keeps the electrolyte at a lower viscosity, thereby improving the ionic conductivity of the electrolyte. At the same time, the first solvent has a low melting point and a high boiling point, decomposes less gas at high temperatures, has a wide applicable temperature range, and can still maintain a high lithium ion transmission ability at low temperatures. The coexistence of the nitrate containing transition metal cations or / and alkaline earth metal cations and the first solvent can take into account the high and low temperature performance of the battery core and improve the cycle performance of electrochemical devices such as lithium-ion batteries under different temperature conditions.

[0037] It should be noted that it can be seen that in the embodiments of the present application, the first solvent has the characteristics of "low viscosity, low melting point and high boiling point", which is compared with conventional solvents, and these conventional solvents include but are not limited to dimethyl carbonate, ethylene carbonate, etc.

[0038] As a non-limiting example, the viscosity of the first solvent includes but is not limited to 0.25 mPa·s, 0.38 mPa·s, 0.5 mPa·s, 1 mPa·s, 1.6 mPa·s, 1.9 Pa·s or 2 mPa·s, etc.

[0039] As a non-limiting example, the melting point of the first solvent includes but is not limited to -90 °C, -80 °C, -70 °C, -60 °C, -43 °C, -42 °C, -36 °C, -56 °C or -20 °C, etc.

[0040] As a non-limiting example, the boiling point includes but is not limited to 79 °C, 150 °C, 180 °C, 210 °C, 280 °C, 248 °C, 127 °C, 90 °C, 108 °C or 130 °C, etc.

[0041] In some embodiments, the volume content of the first solvent in the solvent is 30-50%, including but not limited to 30%, 35%, 40%, 45% or 50%, etc. When the volume content of the first in the solvent is within the above range, due to the relatively lower viscosity of the first solvent, the concentration of the fluorinated lithium salt in the electrolyte composition can be increased from 1 mol / L to 1.8-2 mol / L. Increasing the lithium ion concentration is beneficial to increasing the ionic conductivity of the electrolyte; at the same time, the first solvent has the characteristics of low melting point and high boiling point, which can increase the operating temperature range of the electrolyte and produce less decomposed gas, which is beneficial to improving the safety of electrochemical devices such as lithium ion batteries. If the volume content of γ-butyrolactone in the solvent is less than 30%, the low-temperature performance of the battery cell will be poor; if it is higher than 50%, the cycle performance of the battery cell will decline.

[0042] In some embodiments, the first solvent includes but is not limited to at least one of γ-butyrolactone, methyl propionate, methyl butyrate, etc.

[0043] As an optional example, the first solvent is γ-butyrolactone. When the first solvent is γ-butyrolactone, its decomposition products are generally γ-alkoxy-β-ketoesters.

[0044] In some embodiments, the solvent further includes a second solvent, and the second solvent includes but is not limited to at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, etc.

[0045] In some embodiments, the concentration of nitrate in the electrolyte is 0.1 - 0.3 mol / L, including but not limited to 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, or 0.3 mol / L, etc. When the concentration of nitrate in the electrolyte is within the above range, transition metal cations or / and alkaline earth metal cations and fluoride ions in the electrolyte can form fluorides on the electrode surface, which can improve the battery interface stability and high-temperature performance; if it is lower than 0.1 mol / L, there is almost no improvement effect on the stability of the SEI film; if it is higher than 0.3 mol / L, the impedance of the formed SEI film is relatively large, and the internal resistance of the battery increases.

[0046] As an alternative example, the metal ions in the above nitrate are at least one of transition metal cations and alkaline earth metal cations. That is, the nitrate is at least one of nitrates containing transition metal cations and nitrates containing alkaline earth metal cations.

[0047] In some embodiments, the nitrate includes but is not limited to at least one of magnesium nitrate, calcium nitrate, barium nitrate, iron nitrate, copper nitrate, etc.

[0048] It should be noted that in this application, nitrates containing transition metal cations or / and alkaline earth metal cations are selected instead of metal salts containing other metal cations because nitrates containing transition metal cations or / and alkaline earth metal cations are beneficial to regulating the SEI film, and the SEI film formed by this compound has good mechanical properties and electrochemical stability, and can effectively prevent the dissolution of metal cations of the positive electrode active material in the battery reaction at high temperature from affecting the cycle problem.

[0049] In addition, it should also be noted that in the embodiments of this application, the additive can be only the above nitrate, or a composite additive that in addition to containing the above nitrate, also contains other materials that can improve the electrochemical performance.

[0050] When in addition to the above nitrate, the additive also contains other materials that can improve the electrochemical performance, these other materials that can improve the electrochemical performance include but are not limited to at least one of LiF, LiNO3, fluoroethylene carbonate (FEC), etc. for improving the cycle performance.

[0051] As a non-limiting example, the mass ratio of the total mass of the above other materials that can improve the electrochemical performance to the mass of the above nitrate is 7 - 9:1. For example, 7:1, 8:1, or 9:1, etc.

[0052] In some embodiments, the concentration of the fluorinated lithium salt in the electrolyte is 1.2 - 2.5 mol / L, including but not limited to 1.8 mol / L, 1.85 mol / L, 1.9 mol / L, 1.95 mol / L, or 2 mol / L, etc. When the concentration of the fluorinated lithium salt in the electrolyte is within the above range, it is beneficial to improve the conductivity of the electrolyte ions; if it is lower than 1.2 mol / L, the lithium ion conductivity is relatively low; if it is higher than 2 mol / L, the viscosity of the electrolyte increases, which is not conducive to lithium ion transport.

[0053] In some embodiments, the fluorinated lithium salt includes at least one of, but not limited to, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methyl, etc.

[0054] The preparation method of the electrolyte according to the embodiments of the present application includes the following steps: dissolving the above-mentioned fluorinated lithium salt and additives in a solvent to obtain the electrolyte.

[0055] The electrolyte according to the embodiments of the present application or the electrolyte prepared by the preparation method according to the embodiments of the present application can be widely applied to fields such as the energy storage field and the vehicle field.

[0056] As an optional example, the electrolyte according to the embodiments of the present application or the electrolyte prepared by the preparation method according to the embodiments of the present application is applied to an electrochemical device, and the electrochemical device includes the electrolyte according to the embodiments of the present application or the electrolyte prepared by the preparation method according to the embodiments of the present application.

[0057] In some embodiments, the above-mentioned electrochemical device includes, but not limited to, secondary batteries such as lithium ion batteries, and capacitors, etc. Among them, the secondary battery is not limited to one of a button battery, a soft package battery, etc.

[0058] In some embodiments, the above-mentioned electrochemical device further includes a positive electrode, a negative electrode, and a separator.

[0059] In some embodiments, the positive electrode includes a positive electrode material, and the positive electrode material includes at least one of a positive electrode active material, a positive electrode conductive agent, a positive electrode binder, etc. It should be noted that the present application does not have any particular limitations on the specific selection of the positive electrode active material, the positive electrode conductive agent, the positive electrode binder, etc. As a non-limiting example, the positive electrode active material includes, but not limited to, one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadate phosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate; the positive electrode conductive agent includes, but not limited to, one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes; the positive electrode binder includes, but not limited to, one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0060] In some embodiments, the positive electrode further includes a positive current collector, and the positive current collector can be selected from aluminum or any other suitable conductive metal foil known to those skilled in the art (such as solid or mesh or coated foil), metal grid or screen, or porous metal. In certain variants, the surface of the positive current collector may include a metal foil that has been surface-treated (such as carbon coating and / or etching).

[0061] In some embodiments, the negative electrode includes a negative electrode material, and the negative electrode material includes at least one of a negative active material, a negative conductive agent, a negative binder, a negative thickener, etc. It should be noted that the present application does not particularly limit the specific selection of the negative active material, the negative conductive agent, the negative binder, etc. As non-limiting examples, the negative active material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase carbon materials (such as mesophase carbon microspheres), soft carbon, hard carbon, elemental silicon, SiO, silicon-carbon composite materials (such as SiNPs - amorphous carbon, SiNPs - graphite, etc.) or metal oxide materials (such as TiO2 - B, MoO, CoO, etc.); the negative conductive agent includes, but is not limited to, at least one of carbon nanotubes, conductive carbon black, conductive graphite, vapor-grown carbon fibers, graphene, etc.; the negative binder includes, but is not limited to, at least one of styrene-butadiene rubber (SBR) or polyacrylic acid (PAA), etc.; the negative thickener includes, but is not limited to, at least one of carboxymethyl cellulose, etc.

[0062] In some embodiments, the negative electrode further includes a negative current collector, and the negative current collector can be selected from copper or any other suitable conductive metal foil known to those skilled in the art (such as solid or mesh or coated foil), metal grid or screen, or porous metal. In certain variants, the surface of the negative current collector may include a metal foil that has been surface-treated (such as carbon coating and / or etching).

[0063] In some embodiments, the separator includes, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polyolefin (PO) - based separators mainly composed of polytetrafluoroethylene, polyester films (such as polyethylene terephthalate (PET) films), cellulose films, polyimide films (PI), polyamide films (PA), spandex or aramid films, woven films, non-woven films (non-woven fabrics), microporous films, composite films, separator papers, rolled films or spun films, etc.

[0064] It should be noted that the present application does not limit the specific technical parameters such as the thickness of the above positive electrode, negative electrode, and separator, as long as the purpose of the present application can be achieved.

[0065] The preparation method of the electrochemical device of the embodiments of the present application is not limited and can be any method well-known to those skilled in the art.

[0066] As a possible example, the electrochemical device of the embodiment of the present application is a button cell, and its preparation method includes the following steps:

[0067] (1) Prepare the positive electrode sheet: Disperse the positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode solvent to obtain a positive electrode slurry. Subsequently, coat the positive electrode slurry on the positive electrode current collector, and then roll and dry to obtain the positive electrode sheet;

[0068] (2) Prepare the negative electrode sheet: Disperse the negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode thickening agent in the negative electrode solvent to obtain a negative electrode slurry. Subsequently, coat the negative electrode slurry on the negative electrode current collector, and then dry, roll, and dry to obtain the positive electrode sheet;

[0069] (3) Assembly: Assemble the positive electrode sheet, separator, electrolyte, and negative electrode sheet into a button cell in a glove box.

[0070] The vehicle of the embodiment of the present application can be any vehicle containing any one of the electrolyte of the embodiment of the present application, the electrolyte prepared by the preparation method of the electrolyte of the embodiment of the present application, and the electrochemical device of the embodiment of the present application, including but not limited to automobiles, motorcycles, motorized bicycles, bicycles, power tools, etc.

[0071] Optionally, the positive electrode solvent includes at least one of, but is not limited to, N-methyl-2-pyrrolidone, dimethyl carbonate, ethylene carbonate, etc.

[0072] Optionally, the negative electrode solvent includes but is not limited to water, etc.

[0073] The preparation method of the electrolyte of the embodiment of the present application, the application of the electrolyte, the electrochemical device, the vehicle, etc. all have at least the beneficial effects of the electrolyte of the embodiment of the present application.

[0074] In the following non-limiting examples, certain features of the present technology are further illustrated by way of example.

[0075] I. Examples and Comparative Examples

[0076] Example 1

[0077] (Electrolyte)

[0078] The electrolyte of this example is composed of a fluorinated lithium salt, a solvent, and an additive, wherein: the fluorinated lithium salt is lithium tetrafluoroborate with a concentration of 1.8 mol / L; the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone mixed in a volume ratio of 3:3:4; the additive is barium nitrate with a concentration of 0.2 mol / L.

[0079] (Preparation of Electrolyte)

[0080] Ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone were mixed in a volume ratio of 3:3:4 to obtain a solvent. Subsequently, lithium tetrafluoroborate and barium nitrate were dissolved in the solvent such that the concentrations of lithium tetrafluoroborate and barium nitrate were 1.8 mol / L and 0.2 mol / L, respectively, to obtain the electrolyte of this example.

[0081] (Electrochemical device)

[0082] The electrochemical device of this example is a CR2032 button cell, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. Among them: The positive electrode includes a positive current collector and a positive electrode material. The positive current collector is aluminum foil (thickness 12 μm). The positive electrode material includes the following components in parts by weight: 94 parts of the positive electrode active material lithium nickel cobalt manganese oxide (NCM622), 2 parts of the positive electrode conductive agent conductive carbon black, and 4 parts of the positive electrode binder polyvinylidene fluoride. The negative electrode includes a negative current collector and a negative electrode material. The negative current collector is copper foil (thickness 4.5 μm). The negative electrode active material includes the following components in parts by weight: 94 parts of the negative electrode active material graphite, 2 parts of the negative electrode conductive agent conductive carbon black, 2 parts of the negative electrode binder styrene-butadiene rubber, and 2 parts of the negative electrode thickener carboxymethyl cellulose. The separator is a 2320-type polymer separator from Celgard. The electrolyte is the electrolyte of this example, and the dosage is 150 mg.

[0083] (Preparation method of electrochemical device)

[0084] The preparation method of the electrochemical device of this example includes the following steps:

[0085] (1) Prepare the positive electrode plate: Disperse the above-mentioned positive electrode active material, positive electrode conductive agent, and positive electrode binder in the positive electrode solvent N-methyl-2-pyrrolidone in the formulated amounts to obtain a positive electrode slurry. Subsequently, coat the positive electrode slurry on the positive current collector, and then roll and dry to obtain the positive electrode plate.

[0086] (2) Prepare the negative electrode plate: Disperse the above-mentioned negative electrode active material, negative electrode conductive agent, negative electrode binder, and negative electrode thickener in the negative electrode solvent deionized water in the formulated amounts to obtain a negative electrode slurry. Subsequently, coat the negative electrode slurry on the negative current collector, and then dry, roll, and dry to obtain the positive electrode plate.

[0087] (3) Assembly: Assemble the positive electrode plate, separator, electrolyte, and negative electrode plate into a CR2032 button cell in a glove box.

[0088] Example 2

[0089] This example is basically the same as Example 1, except that:

[0090] In the electrolyte, the concentration of barium nitrate is 0.1 mol / L.

[0091] Example 3

[0092] This embodiment is basically the same as Embodiment 1, except that:

[0093] In the electrolyte, the concentration of barium nitrate is 0.3 mol / L.

[0094] Embodiment 4

[0095] This embodiment is basically the same as Embodiment 1, except that:

[0096] In the electrolyte, the additive is magnesium nitrate.

[0097] Embodiment 5

[0098] This embodiment is basically the same as Embodiment 1, except that:

[0099] In the electrolyte, the additive is a 1:1 mixture of barium nitrate and calcium nitrate.

[0100] Embodiment 6

[0101] This embodiment is basically the same as Embodiment 1, except that:

[0102] In the electrolyte, the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone in a volume ratio of 3.5:3.5:3.

[0103] Embodiment 7

[0104] This embodiment is basically the same as Embodiment 1, except that:

[0105] In the electrolyte, the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone in a volume ratio of 2.5:2.5:5.

[0106] Embodiment 8 (γ-butyrolactone is replaced by methyl butyrate)

[0107] This embodiment is basically the same as Embodiment 1, except that:

[0108] In the electrolyte, the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and methyl butyrate in a volume ratio of 3:3:4.

[0109] Embodiment 9

[0110] This embodiment is basically the same as Embodiment 1, except that:

[0111] In the electrolyte, the fluorinated lithium salt is lithium hexafluorophosphate, and its concentration is 2 mol / L.

[0112] Embodiment 10

[0113] This embodiment is basically the same as Embodiment 1, except that:

[0114] In the electrolyte, the fluorine-containing lithium salt is a mixture of lithium tetrafluoroborate and lithium bis(trifluoromethanesulfonyl)imide with a mass ratio of 1:1.

[0115] Comparative Example 1

[0116] This comparative example is basically the same as Example 1, except that:

[0117] In the electrolyte, the fluorine-containing lithium salt is lithium tetrafluoroborate with a concentration of 1 mol / L; the solvent does not contain γ-butyrolactone and is a mixed solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 1:1.

[0118] Comparative Example 2

[0119] This comparative example is basically the same as Example 1, except that:

[0120] The electrolyte does not contain additives.

[0121] Comparative Example 3

[0122] This comparative example is basically the same as Example 1, except that:

[0123] In the electrolyte, there are no additives and γ-butyrolactone; the fluorine-containing lithium salt is lithium tetrafluoroborate with a concentration of 1 mol / L; the solvent is a mixed solvent of ethylene carbonate and ethyl methyl carbonate mixed in a volume ratio of 1:1.

[0124] Comparative Example 4 (γ-butyrolactone is lower than the lower limit of this application, being 25%)

[0125] This comparative example is basically the same as Example 1, except that:

[0126] In the electrolyte, the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone mixed in a volume ratio of 3:3:2.

[0127] Comparative Example 5 (γ-butyrolactone is higher than the lower limit of this application, being 55%)

[0128] This comparative example is basically the same as Example 1, except that:

[0129] In the electrolyte, the solvent is a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and γ-butyrolactone mixed in a volume ratio of 4.5:4.5:11.

[0130] Comparative Example 6 (nitrate content is lower than this application)

[0131] This comparative example is basically the same as Example 1, except that:

[0132] In the electrolyte, the concentration of the additive barium nitrate is 0.08 mol / L.

[0133] Comparative Example 7 (nitrate content higher than that of the present application)

[0134] This comparative example is basically the same as Example 1, except that:

[0135] In the electrolyte, the concentration of barium nitrate as an additive is 0.32 mol / L.

[0136] II. Performance tests

[0137] 1. Test methods

[0138] (1) Actual concentration of lithium ions in the electrolyte

[0139] The test method for the concentration of the electrolyte is as follows: The electrolyte sample to be tested in the example or comparative example is hydrolyzed by heating with 75 wt% hydrochloric acid to 40 °C (the mass ratio of the electrolyte sample to be tested to hydrochloric acid is 1:1), and then diluted with 50 mL of distilled water. Using the standard curve method of an atomic absorption spectrometer, the mass concentration of lithium ions in the sample to be tested is calculated, and the mass fraction of the lithium salt is calculated based on the calculated mass concentration of lithium ions.

[0140] (2) Viscosity of the electrolyte

[0141] The test method for the viscosity of the electrolyte is as follows: The viscosity value is determined by measuring the torque generated when the electrolyte in the example or comparative example rotates 30 circles on a rotating cylinder at 25 °C using a rotational viscometer.

[0142] (3) Ionic conductivity of the electrolyte

[0143] The test method for the ionic conductivity of the electrolyte is as follows: At room temperature (25 °C), using a conductivity tester, insert the measuring electrode (platinum electrode) and the temperature sensor into the sample to be tested. The temperature sensor is suspended and left static, and the measuring electrode is suspended and slowly stirred clockwise in the liquid to be tested. Wait for the test data to stabilize and then record the experimental data.

[0144] (4) Electrochemical performance

[0145] The test method for high-temperature cycle performance is as follows: Place the electrochemical devices in the examples or comparative examples at 25 °C, 35 °C, and 45 °C respectively, charge at a constant current of 4C to 4.25V, then charge at a constant voltage of 4.25V until the current is 0.05C, and then discharge at a constant current of 1C to 2.5V. Repeat this cycle 500 times, and calculate the capacity retention rate after 500 cycles according to Equation (1).

[0146] Capacity retention rate after 500 cycles = (discharge capacity of the 500th cycle ÷ discharge capacity of the 1st cycle) × 100% Equation (1)

[0147] The low-temperature cycling performance test method is as follows: Place the electrochemical devices of the examples or comparative examples at -30°C, -20°C, and -10°C respectively, charge them at a constant current of 4C to 4.25V, then charge them at a constant voltage of 4.25V until the current reaches 0.05C, and then discharge them at a constant current of 1C to 2.5V. Cycle 500 times in this way, and calculate the capacity retention rate of 500 cycles according to formula (2).

[0148] Capacity retention rate of 500 cycles = (discharge capacity of the 500th cycle ÷ discharge capacity of the 1st cycle) × 100% Formula (2)

[0149] 2. Test results

[0150] Test the electrolytes of the examples and comparative examples and their corresponding electrochemical devices according to the above test method. The test results of the electrolytes are shown in Table 1, and the test results of the electrochemical devices are shown in Table 2.

[0151] Table 1 Test results of electrolytes of examples and comparative examples

[0152]

[0153]

[0154] It can be seen from Table 1 that for the electrolytes of the examples of the present application, since the first solvent with the characteristics of low viscosity, low melting point, and high boiling point is used as the main component, compared with the electrolytes of Comparative Example 1 and Comparative Example 3 without the first solvent, the lithium ion concentration has increased significantly, but the increase in viscosity is much smaller than the increase in lithium ion concentration, resulting in a significant increase in the ionic conductivity of the electrolyte.

[0155] By comparing Comparative Example 6, Example 2, Example 1, Example 3, and Comparative Example 7, it can be seen that as the concentration of the additive barium nitrate in the electrolyte increases, within the preferred additive content range of the electrolytes of the examples of the present application, the lithium ion concentration and viscosity change little, and the ionic conductivity gradually increases.

[0156] By comparing Comparative Example 4, Example 6, Example 1, Example 7, and Comparative Example 5, it can be seen that as the volume content of the first solvent γ-butyrolactone in the solvent of the electrolyte increases, below the lower limit of the preferred first solvent of the electrolytes of the examples of the present application and within the range defined by the present application, the lithium ion concentration remains unchanged, the viscosity gradually decreases, and the ionic conductivity first increases and then decreases, but within the range of the first solvent defined by the present application, the ionic conductivity is relatively high. In Comparative Example 5, the volume content of the first solvent γ-butyrolactone in the solvent exceeds the upper limit of the range defined by the first solvent of the present application, and the viscosity is basically the same as that of Example 7.

[0157] Table 2 Performance test results of the electrochemical devices corresponding to the electrolytes of examples and comparative examples

[0158]

[0159]

[0160] As can be seen from Table 2, compared with Comparative Examples 1-3, the electrolytes of the embodiments of the present application contain a fluorinated lithium salt, a first solvent with the characteristics of low viscosity, low melting point and high boiling point, and a nitrate containing alkaline earth metal cations, which can take into account the high and low temperature performance of the electrochemical device. While broadening the applicable range of the electrochemical device, the long cycle performance of the electrochemical device is improved.

[0161] By comparing Comparative Example 6, Example 2, Example 1, Example 3 and Comparative Example 7, it can be seen that with the increase in the concentration of barium nitrate additive in the electrolyte, at least within the preferred additive content range of the electrolytes of the embodiments of the present application, better high and low temperature cycle performance can be achieved. The amount of barium nitrate additive added in Comparative Example 6 is too small to form a film, and it basically has no effect on improving the high and low temperature cycle performance. In Comparative Example 7, an excessive amount of barium nitrate additive is added, and the metal cations (barium ions) have a competitive coordination effect with lithium ions, affecting the lithium ion transport effect and increasing the internal resistance.

[0162] By comparing Comparative Example 4, Example 6, Example 1, Example 7 and Comparative Example 5, it can be seen that with the increase in the volume content of the first solvent γ-butyrolactone in the solvent in the electrolyte, both the high temperature cycle performance and the low temperature cycle performance of the electrochemical device first increase and then decrease. However, within the volume ratio range of the first solvent in the electrolyte of the present application, better high temperature cycle performance and low temperature cycle performance can be obtained, where the capacity retention rate after 500 cycles at 45 °C is above 70%, and the capacity retention rate after 500 cycles at -30 °C is above 57%.

[0163] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0164] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features.

[0165] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present application. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present application.

Claims

1. An electrolyte, characterized in that, It includes a fluorinated lithium salt, a solvent and an additive; the solvent includes a first solvent, the viscosity of the first solvent at 25°C is 0.2 - 2.2 mPa·s, the melting point is (-90) - (-20)°C, and the boiling point is 79 - 280°C; the additive includes a nitrate, and the metal ions in the nitrate include at least one of transition metal cations and alkaline earth metal cations.

2. The electrolyte according to claim 1, wherein The volume content of the first solvent in the solvent is 30 - 50%.

3. The electrolyte according to claim 1, characterized in that, The first solvent includes at least one of γ-butyrolactone, methyl propionate, and methyl butyrate; And / or, the solvent further includes a second solvent, and the second solvent includes at least one of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

4. The electrolyte according to any one of claims 1 to 3, characterized in that, The concentration of the nitrate in the electrolyte is 0.1 - 0.3 mol / L.

5. The electrolyte according to any one of claims 1 to 3, characterized in that The nitrate includes at least one of magnesium nitrate, calcium nitrate, barium nitrate, copper nitrate, and iron nitrate.

6. The electrolyte according to any one of claims 1 to 3, characterized in that, The concentration of the fluorinated lithium salt in the electrolyte is 1.8 - 2 mol / L; And / or, the fluorinated lithium salt includes at least one of lithium tetrafluoroborate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, and lithium tris(trifluoromethylsulfonyl)methyl.

7. A method for preparing an electrolyte according to any one of claims 1 to 6, characterized in that, It includes: Dissolve the fluorinated lithium salt and the additive in the solvent to obtain the electrolyte.

8. The application of the electrolyte according to any one of claims 1 to 6 or the electrolyte prepared by the preparation method according to claim 7 in the energy storage field and the vehicle field.

9. An electrochemical device, characterized in that, It includes the electrolyte according to any one of claims 1 to 6 or the electrolyte prepared by the preparation method according to claim 7.

10. A vehicle, characterized in that, It includes the electrolyte according to any one of claims 1 to 6 or the electrolyte prepared by the preparation method according to claim 7 or the electrochemical device according to claim 9.

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