CN112805864B - Electrolyte, electrochemical device, and electronic device - Google Patents
Electrolyte, electrochemical device, and electronic device Download PDFInfo
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- CN112805864B CN112805864B CN202080004741.0A CN202080004741A CN112805864B CN 112805864 B CN112805864 B CN 112805864B CN 202080004741 A CN202080004741 A CN 202080004741A CN 112805864 B CN112805864 B CN 112805864B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0567—Liquid materials characterised by the additives
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
An electrolyte, an electrochemical device, and an electronic device, wherein the electrolyte comprises a compound of formula i:
wherein R1 and R2 are each independently selected from one of alkyl with carbon number between 1 and 11, substituted alkyl with carbon number between 1 and 11, alkenyl with carbon number between 2 and 11 and substituted alkenyl with carbon number between 2 and 11, and when substituted, the substituent is selected from at least one of fluorine, methyl and cyano; A. b is independently selected from one of imidazole, pyridine, piperidine and quaternary ammonium salt cations; x is selected from one of hexafluorophosphate, bistrifluoromethyl sulfonate, tetrafluoroborate, bisoxalaborate and tetrafluorooxalaborate. The electrolyte can reduce the internal resistance of the electrochemical device and improve the cycle performance and the rate performance of the electrochemical device.
Description
Technical Field
The present application relates to the field of electrochemistry, and in particular, to an electrolyte, an electrochemical device, and an electronic device.
Background
The electrolyte is an important component of an electrochemical device (e.g., a battery), and may be classified into an organic liquid electrolyte, an ionic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, an inorganic solid electrolyte, a mixed electrolyte, and the like. The electrolyte plays a role in transmitting charge between the positive electrode and the negative electrode of the battery, and plays a vital role in specific capacity, charge-discharge efficiency, cycle stability, rate capability, working temperature range, safety performance and the like of the battery.
Disclosure of Invention
In view of the above drawbacks of the prior art, an object of the present application is to reduce the internal resistance of an electrochemical device to improve the cycle performance and rate performance of the electrochemical device.
The application provides an electrolyte comprising a compound of formula i:
wherein R1 and R2 are each independently selected from one of alkyl with carbon number between 1 and 11, substituted alkyl with carbon number between 1 and 11, alkenyl with carbon number between 2 and 11 and substituted alkenyl with carbon number between 2 and 11, and when substituted, the substituent is selected from at least one of fluorine, methyl and cyano;
A. b is independently selected from one of imidazole cation, pyridine cation, piperidine cation and quaternary ammonium salt cation;
x is selected from one of hexafluorophosphate, bistrifluoromethyl sulfonate, tetrafluoroborate, bisoxalaborate and tetrafluorooxalaborate.
In the above electrolyte, the compound of formula i includes at least one of the following compounds:
in the electrolyte, the compound of the formula I accounts for 0.01-10% of the total mass of the electrolyte.
The electrolyte further comprises: at least one of lithium difluorophosphate, a polynitrile compound, or a cyclic ether compound.
In the above-described electrolytic solution, the electrolytic solution satisfies at least one of the following conditions (a) to (d):
(a) The lithium difluorophosphate accounts for less than 1% of the total mass of the electrolyte;
(b) The polynitrile compound accounts for 0.5-10% of the total mass of the electrolyte;
(c) The cyclic ether compound accounts for 0.01-2% of the total mass of the electrolyte;
(d) The compound of the formula I accounts for C, and the lithium difluorophosphate accounts for D, wherein C+D is less than 11%, and C/D is more than or equal to 0.5 and less than or equal to 10.
In the above electrolyte, the polynitrile compound includes at least one of the compounds shown below,
wherein R is 21 、R 22 、R 23 、R 24 Each independently selected from hydrogen, cyano, - (CH 2) a -CN、-(CH 2 ) b -O-(CH 2 ) c -CN、-(CH 2 ) d - (ch=ch) -CN, an alkyl group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 2 to 5 carbon atoms, and R 21 、R 22 、R 23 And R is 24 Wherein at least two of the groups are cyano groups, a, b and d are each independently selected from integers from 0 to 10, and c is selected from integers from 1 to 5.
In the above electrolyte, the polynitrile compound includes at least one of the compounds shown below;
in the above electrolyte, the cyclic ether compound includes at least one of 1, 3-dioxolane, 1, 3-dioxane, or 1, 4-dioxane.
The present application also provides an electrochemical device comprising:
a positive electrode, a negative electrode, a separator and any of the above electrolytes.
In the above electrochemical device, the electrolyte further contains cobalt ions, which account for 1ppm to 50ppm of the total mass of the electrolyte.
The application also proposes an electronic device comprising an electrochemical device as described in any one of the preceding claims.
According to the electrolyte provided by the embodiment of the application, the compound with the formula I containing the-R1-O-R2-group is introduced into the electrolyte, so that the mobility of lithium ions can be improved, more lithium salts can be dissolved, the conductivity can be improved, and the interface impedance can be reduced, so that the impedance of an electrochemical device (such as a lithium ion battery) can be reduced, the rate capability and the cycle performance of the electrochemical device can be improved, and the cycle problem and the large-rate charging problem of the electrochemical device can be solved.
Drawings
The above and other features, advantages, and aspects of embodiments of the present application will become more apparent by reference to the following detailed description when taken in conjunction with the accompanying drawings. The same or similar reference numbers will be used throughout the drawings to refer to the same or like elements. It should be understood that the figures are schematic and that elements and components are not necessarily drawn to scale.
FIG. 1 is a structural formula of a compound of formula 1 according to an embodiment of the present application.
Detailed Description
Embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While certain embodiments of the present application are shown in the drawings, it is to be understood that the present application may be embodied in various forms and should not be construed as limited to the embodiments set forth herein, but rather are provided to provide a more thorough and complete understanding of the present application. It should be understood that the drawings and examples of the present application are for illustrative purposes only and are not intended to limit the scope of the present application.
The following examples will allow those skilled in the art to more fully understand the present application, but are not intended to limit the present application in any way.
The following will describe in detail the schemes provided in the embodiments of the present application.
Ionic liquids are also known as room temperature ionic liquids or room temperature molten salts, also known as non-aqueous ionic liquids, liquid organic salts, and the like. It is generally considered to be a liquid composed of cations and anions, organic salts which appear liquid at or near room temperature. However, when the conventional ionic liquid is used in an electrolyte system, the rate charge and discharge performance of an electrochemical device such as a lithium ion battery is reduced, because the diffusion coefficient of cations of the ionic liquid is much larger than that of lithium ions, and when the battery is charged and discharged, cations having a faster diffusion rate than that of lithium ions migrate are adhered around a negative electrode and further intercalated into the negative electrode to form a blocking layer, thereby preventing intercalation and deintercalation of lithium ions.
From the above, the diffusion coefficient of cations in the ionic liquid is larger than that of lithium ions, so that a blocking layer is formed, and the internal resistance of the battery is increased due to the existence of the blocking layer, so that the rate performance and the cycle performance of the lithium ion battery are affected.
In order to reduce the internal resistance of the electrochemical device and improve the cycle performance and the rate performance of the electrochemical device, the electrochemical device is taken as a lithium ion battery as an example, please refer to fig. 1, and an electrolyte is provided in the embodiment of the present application, which includes a compound of formula i:
wherein R1 and R2 are each independently selected from one of alkyl with carbon number between 1 and 11, substituted alkyl with carbon number between 1 and 11, alkenyl with carbon number between 2 and 11 or substituted alkenyl with carbon number between 2 and 11, and when substituted, the substituent is selected from at least one of fluorine, methyl or cyano;
A. b is independently selected from one of imidazole cation, pyridine cation, piperidine cation or quaternary ammonium salt cation;
x is selected from one of hexafluorophosphate, bistrifluoromethyl sulfonate, tetrafluoroborate, bisoxalaborate or tetrafluorooxalaborate.
In this embodiment, the compound of formula i containing the-R1-O-R2-group is introduced into the electrolyte, and this group can improve mobility of lithium ions and dissolve more lithium salts, so, for the lithium ion battery using the electrolyte provided in this embodiment, the electrolyte can improve conductivity, reduce interface impedance, thereby reducing internal resistance of the lithium ion battery, improving rate performance and cycle performance of lithium ions, and solving cycle problems and high rate charging problems of the lithium ion battery.
In some embodiments of the present application, the compound of formula i comprises at least one of the following compounds:
in some embodiments of the present application, the compound of formula I comprises 0.01% to 10% by weight of the total electrolyte. The content of the compound shown in the formula I is in the range, so that the mobility of lithium ions can be obviously improved, and the deterioration of lithium ion transmission caused by the excessive content of the compound shown in the formula I can be avoided, so that the content of the compound shown in the formula I in the electrolyte needs to be controlled.
In some embodiments of the present application, the electrolyte further comprises: at least one of lithium difluorophosphate, a polynitrile compound, or a cyclic ether compound. The compound of the formula I and lithium difluorophosphate act together to preferentially perform oxidation-reduction reaction at the anode and the cathode of the battery to generate a LiF-rich protective film, so that the stability of the solid electrolyte interface film is enhanced, and the cycle performance of the lithium ion battery can be improved. The compound of formula I and the polynitrile compound act together to form an organic protective layer on the surface of the positive electrode, and organic molecules on the surface of the positive electrode can well separate easily-oxidized components in the electrolyte from the surface of the positive electrode, so that the oxidation of the surface of the positive electrode of the charged lithium ion battery to the electrolyte is greatly reduced, and the cycle performance and the high-temperature storage performance of the lithium ion battery are improved. The compound of formula I and the cyclic ether compound can improve the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery by coaction.
In some embodiments of the present application, the electrolyte satisfies at least one of the following conditions (a) - (d):
(a) The mass of the lithium difluorophosphate is less than 1 percent of the total mass of the electrolyte;
lithium difluorophosphate is advantageous for improving the cycle performance of a lithium ion battery, but has a deteriorated effect when the content thereof is too high, so that it is necessary to control the content thereof.
(b) The mass of the polynitrile compound accounts for 0.5-10% of the total mass of the electrolyte;
when the content of the polynitrile compound exceeds 10%, the high-temperature cycle performance improving effect is lowered because the high content of the polynitrile compound increases the viscosity of the electrolyte, deteriorating the dynamic performance of the battery, and thus it is necessary to control the percentage thereof in the electrolyte to 0.5% to 10%.
(c) The mass of the cyclic ether compound accounts for 0.01-2% of the total mass of the electrolyte;
when the mass percentage of the cyclic ether compound in the electrolyte exceeds 2%, the high-temperature cycle performance and the high-rate discharge performance of the lithium ion battery are reduced. This is because when the cyclic ether content is high, the impedance of the lithium ion battery increases, which accelerates the decay of the cycle capacity, deteriorating the cycle performance and the high-rate discharge performance of the lithium ion battery.
(d) The mass of the compound in the formula I is C, and the mass of the lithium difluorophosphate is D, wherein C+D is less than 11%, and C/D is more than or equal to 0.5 and less than or equal to 10.
When C+D is more than or equal to 11%, the transmission of lithium ions can be influenced due to excessive addition of the compound of the formula I and lithium difluorophosphate in the electrolyte, and the performance of the lithium ion battery can be deteriorated. The addition of the compound of formula I in a small amount does not have an effect of improving lithium ion properties when C/D < 0.5.
In some embodiments of the present application, the polynitrile compound includes at least one of the compounds shown below,
wherein R is 21 、R 22 、R 23 、R 24 Each independently selected from hydrogen, cyano, - (CH 2) a -CN、-(CH 2 ) b -O-(CH 2 ) c -CN、-(CH 2 ) d - (ch=ch) -CN, an alkyl group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 2 to 5 carbon atoms, and R 21 、R 22 、R 23 And R is 24 Wherein at least two of the groups are cyano groups, a, b and d are each independently selected from integers from 0 to 10, and c is selected from integers from 1 to 5.
In some embodiments of the present application, the polynitrile compound includes at least one of the compounds shown below;
in some embodiments of the present application, the cyclic ether compound includes at least one of 1, 3-dioxolane, 1, 4-dioxane, or 1, 3-dioxane.
In some embodiments of the present application, the electrolyte contains a lithium salt, which may be at least one of an organic lithium salt or an inorganic lithium salt, and in some embodiments of the present application, the lithium salt contains at least one of a fluorine element, a boron element, or a phosphorus element.
In some of the alternative embodiments of the present invention,the lithium salt comprises lithium hexafluorophosphate LiPF 6 Lithium bis (trifluoromethanesulfonyl) imide LiN (CF) 3 SO 2 ) 2 (abbreviated as LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO) 2 F) 2 ) (abbreviated as LiFSI), lithium bisoxalato borate LiB (C) 2 O 4 ) 2 (abbreviated as LiBOB), lithium tetrafluorophosphate oxalate (LiPF) 4 C 2 O 2 ) Lithium difluorooxalato borate LiBF 2 (C 2 O 4 ) (abbreviated as LiDFOB) or lithium hexafluorocesium (LissF) 6 ) At least one of (a) and (b). Alternatively, the lithium salt is lithium hexafluorophosphate LiPF 6 。
In some embodiments of the present application the concentration of lithium salt is 0.5mol/L to 1.5mol/L. The concentration of lithium salt is too low, and the conductivity of the electrolyte is low, so that the multiplying power and the cycle performance of the whole lithium ion battery system can be influenced; the concentration of lithium salt is too high, the viscosity of electrolyte is too high, and the multiplying power of the whole lithium ion battery system is also influenced. Alternatively, the concentration of the lithium salt is 0.8mol/L to 1.3mol/L.
In some embodiments of the present application the electrolyte comprises a nonaqueous organic solvent, wherein the nonaqueous organic solvent comprises one or a combination of two or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, gamma-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, or propyl butyrate in any proportion.
The present application also proposes an electrochemical device comprising: a positive electrode, a negative electrode, a separator, and an electrolyte of any of the above.
In some embodiments of the present application, the electrolyte in the electrochemical device further comprises cobalt ions, the cobalt ions comprising 1ppm to 50ppm of the total mass of the electrolyte.
The positive electrode of the above-described electrochemical device includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector. The specific type of the positive electrode active material is not particularly limited, and may be selected according to the need.
In some embodiments, the positive electrode active material includes a positive electrode material capable of absorbing and releasing lithium (Li). Examples of the positive electrode material capable of absorbing/releasing lithium (Li) may include lithium cobaltate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials.
Specifically, the chemical formula of lithium cobaltate may be as shown in chemical formula 1:
Li x Co a M1 b O 2-c chemical formula 1
Wherein M1 represents at least one selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr) and silicon (Si), and x, a, B and c values are respectively in the following ranges: x is more than or equal to 0.8 and less than or equal to 1.2, a is more than or equal to 0.8 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.2, and c is more than or equal to 0.1 and less than or equal to 0.2.
The chemical formula of the nickel cobalt lithium manganate or nickel cobalt lithium aluminate can be shown as chemical formula 2:
Li y Ni d M2 e O 2-f chemical formula 2
Wherein M2 represents at least one selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr) and silicon (Si), and y, d, e and f values are respectively in the following ranges: y is more than or equal to 0.8 and less than or equal to 1.2, d is more than or equal to 0.3 and less than or equal to 0.98, e is more than or equal to 0.02 and less than or equal to 0.7, and f is more than or equal to 0.1 and less than or equal to 0.2.
The chemical formula of lithium manganate can be as shown in chemical formula 3:
Li z Mn 2-g M3 g O 4-h chemical formula 3
Wherein M3 represents at least one selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr) and tungsten (W), and z, g and h values are respectively in the following ranges: z is more than or equal to 0.8 and less than or equal to 1.2, g is more than or equal to 0 and less than or equal to 1.0, and h is more than or equal to-0.2 and less than or equal to 0.2.
The positive electrode of the electrochemical device may be added with a conductive agent or binder, and in some embodiments of the present application, the positive electrode further includes a carbon material, and the carbon material may include at least one of conductive carbon black, graphite, graphene, carbon nanotubes, carbon fibers, or carbon black. The binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.
In some embodiments, the barrier film comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect.
In some embodiments, the release film surface may further include a porous layer disposed on at least one surface of the release film, the porous layer including inorganic particles selected from aluminum oxide (Al 2 O 3 ) Silicon oxide (SiO) 2 ) Magnesium oxide (MgO), titanium oxide (TiO) 2 ) Hafnium oxide (HfO) 2 ) Tin oxide (SnO) 2 ) Cerium oxide (CeO) 2 ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) 2 ) Yttria (Y) 2 O 3 ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is at least one selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolating membrane, and strengthen the isolating membrane and the pole pieceAdhesion between them.
The present application also proposes an electronic device comprising an electrochemical device according to any of the above. The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copier, a portable printer, a headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-compact disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable audio recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a power assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a household large-sized battery, a lithium ion capacitor, and the like. For example, electronic devices include cell phones that include lithium ion batteries.
In order to better illustrate the beneficial effects of the electrolytes presented in the examples of the present application, the following description will be made with reference to examples 1 to 53 and comparative examples 1 to 4, and examples 1 to 53 and comparative examples 1 to 4 differ only in the electrolytes used, and performance tests of lithium ion batteries using different electrolytes will be performed in examples 1 to 53 and comparative examples 1 to 4 to illustrate the effect of the electrolytes on the performance of lithium ion batteries.
Preparation of electrolyte
At the water content<In a 10ppm argon atmosphere glove box, ethylene carbonate (abbreviated as EC), diethyl carbonate (abbreviated as DEC) and propylene carbonate (abbreviated as PC) were uniformly mixed in a mass ratio of 3:4:3 to form a nonaqueous solvent, and then a sufficiently dried lithium salt LiPF was used 6 Dissolving in the above nonaqueous solvent, liPF 6 The concentration of (C) was 1mol/L, and the base electrolyte in examples was prepared. The electrolyte used in each of the examples and comparative examples was obtained by adding a compound of the formula I, a polynitrile compound, a cyclic ether compound, and LiPO as shown below to a base electrolyte 2 F 2 Or cobalt ions.
A compound of formula I:
polynitrile compound:
cyclic ether compounds:
battery preparation
1) Preparation of positive electrode: fully stirring and mixing lithium cobaltate, acetylene black and polyvinylidene fluoride (PVDF) in a weight ratio of 96:2:2 in a proper amount of N-methylpyrrolidone (NMP) solvent to form uniform anode slurry; and (3) coating the slurry on an Al foil of the positive electrode current collector, drying, cold pressing to obtain a positive electrode active material layer, and then cutting and welding the tab to obtain the positive electrode.
2) Preparation of the negative electrode: graphite, styrene Butadiene Rubber (SBR) and sodium carboxymethylcellulose (CMC) are fully stirred and mixed in a proper amount of deionized water solvent according to the weight ratio of 97:2:1, so that uniform negative electrode slurry is formed; and (3) coating the slurry on a Cu foil of a negative electrode current collector, drying, cold pressing to obtain a negative electrode active material layer, and then cutting and welding tabs to obtain the negative electrode.
3) Isolation film: PE porous polymer film is used as a isolating film.
4) Preparation of a lithium ion battery: and stacking the positive electrode isolating film and the negative electrode in sequence, enabling the isolating film to be positioned between the positive electrode and the negative electrode to play a role of isolating, winding, placing the isolating film in an outer packaging foil, injecting the prepared electrolyte into a dried battery, and performing the procedures of vacuum packaging, standing, formation, shaping and the like to prepare the lithium ion battery.
High temperature cycle test
Placing the lithium ion battery in a 45 ℃ incubator, and standing for 30 minutes to keep the lithium ion battery constant; constant current charging is carried out to 4.45V at 0.7C, and constant voltage charging is carried out to the current of 0.05C; then 0.7C is discharged to 3.0V, and the discharge capacity is recorded as the 1 st cycle discharge capacity based on the capacity of the step; this step was cycled for 300 cycles, the discharge capacity at cycle 300 was recorded, and the capacity retention rate was calculated.
Capacity retention after 300 cycles (%) =discharge capacity at 300 th cycle/discharge capacity at 1 st cycle×100%
High-temperature storage performance test for lithium ion battery
The lithium ion battery was discharged to 3.0V at 25C at 0.5C, charged to 4.45V at 0.7C, charged to 0.05C at constant voltage at 4.45V, and the thickness of the battery was measured and recorded as H using a micrometer 11 Placing in an oven at 85deg.C, maintaining at constant pressure for 16 hr at 4.45V, testing with micrometer after 16 hr, and recording thickness of lithium ion battery, denoted as H 12 Calculate the thickness expansion ratio, thickness expansion ratio= (H) 12 -H 11 )/H 11 ×100％
DC impedance (DCR) test of lithium ion battery at 0 DEG C
Standing the lithium ion battery in a high-low temperature box at 0 ℃ for 4 hours to keep the lithium ion battery constant temperature; charging to 4.45V at constant current of 0.1C, charging to current of 0.05C at constant voltage, and standing for 10 min; then discharging to 3.4V with constant current of 0.1C, and standing for 5 minutes to obtain the actual capacity. Charging the lithium ion battery to 4.45V at a constant current of 0.1 ℃ at a constant voltage of 0.05 ℃ and standing for 10 minutes; the voltage at this time was recorded as V by 0.1C constant current discharge for 8 hours (calculated from the actual capacity obtained in one step above the capacity) 1 The method comprises the steps of carrying out a first treatment on the surface of the Then discharging for 1s with 1C constant current (the capacity is calculated by the nominal capacity of the lithium ion battery), and recording the voltage at the moment as V 2 And calculating the direct current impedance of the lithium ion battery in a 20% SOC state.
20% soc dc impedance= (V 1 -V 2 )/1C
Multiplying power test
The lithium ion battery was charged to 4.45V at 25 ℃ with a constant current/constant voltage of 0.5C, left to stand for 10 minutes, discharged to a cut-off voltage of 3.0V with a constant current of 0.5C, and the discharge capacity Q1 was recorded. The discharge capacity Q2 was recorded by charging to 4.45V at a constant current/constant voltage of 0.5C at 25℃and discharging to 3.0V at a constant current of 2C after standing for 10 minutes. Dividing Q2 by Q1 yields 2C discharge efficiency.
Cyclic impedance testing
The lithium ion battery is charged to 4.45V at 45 ℃ at 0.7C, charged to 0.05C at constant voltage at 4.45V, and discharged to 3.0V at constant current at 1.0C, and the condition is circulated for 300 circles, and the resistance change condition of the lithium ion battery at 100% SOC in the circulation process is monitored by using a resistivity measuring instrument, and the circulation resistance of the circulation 300 circles is recorded.
Examples 1 to 16 and comparative examples 1 to 4
In examples 1 to 16 and comparative examples 1 to 4, the electrolytes used were obtained by adding one or more compounds as shown in Table 1 to the base electrolyte, and the results of performance tests on the lithium ion batteries in examples 1 to 16 and comparative examples 1 to 4 are shown in Table 2.
TABLE 1
TABLE 2
As can be seen from comparative examples 1 to 7 and comparative example 1, the 2C discharge efficiency of examples 1 to 7 is significantly higher than that of comparative example 1, the 20% SOC impedance of examples 1 to 7 is significantly lower than that of comparative example 1, and the capacity retention after 300 cycles of 45℃is also significantly higher than that of comparative example 1, i.e., by adding the compound of formula I to the electrolyte, the high rate discharge performance of the lithium ion battery can be improved, the impedance of the lithium ion battery can be reduced, and the cycle performance can be improved, becauseIs a compound of formula I having the formula-CH 2 -O-CH 2 -a group, the compound of formula i having the group contributes to an improvement in lithium ion mobility, and thus the electrolyte having the compound of formula i can dissolve more lithium salt, enhance a cation transport effect, and increase conductivity, thereby reducing the impedance of the lithium ion battery and improving cycle performance and rate performance.
From the results of the performance tests of comparative examples 1 and 2, it can be seen that the capacity retention rate after 300 cycles of 45 ℃ of comparative example 2 is significantly reduced relative to that of comparative example 1, because the addition of excessive compound of formula 1 in comparative example 2, when the amount of compound of formula I in the electrolyte is excessive, conversely results in a decrease in the cycle performance of the lithium ion battery, and from the results of the performance tests of comparative examples 1 and 3, it is seen that the performance improvement of the lithium ion battery is not significant when the amount of compound of formula I in the electrolyte is too small, and thus, the percentage of compound of formula I in the total mass of the electrolyte is limited to 0.01% to 10% in some examples of the present application.
As can be seen from the performance test results of comparative examples 1 and 4, the test results of comparative example 4, which are 20% SOC DC resistance and capacity retention after 300 cycles of 45℃are superior to those of comparative example 1, it can be seen that by adding LiPO to the electrolyte 2 F 2 Can improve the cycle performance of the lithium ion battery and reduce the impedance of the lithium ion battery because of LiPO 2 F 2 Has a lower oxidation potential and a higher reduction potential, so LiPO 2 F 2 The lithium ion battery can preferentially perform oxidation-reduction reaction at the interfaces of the positive electrode and the negative electrode to generate a protective film rich in LiF, so that the stability of the solid electrolyte interface film is enhanced, and the effect of improving the high-temperature cycle performance of the lithium ion battery is further realized.
As can be seen from the results of the performance tests of example 2 and example 8, liPO was added to the electrolyte solution while the compound represented by formula I was added 2 F 2 The direct current impedance of the lithium ion battery can be further reduced and the cycle performance of the lithium ion battery can be improved, and from the performance test results of examples 13 to 16 and comparative example 4, the same conclusion can be drawn, namely, the addition of the compound of formula I and LiPO 2 F 2 By using both of themThe synergistic effect of the components further improves circulation and reduces impedance.
As can be seen from the performance test results of examples 8-12, liPO was added to the electrolyte 2 F 2 The content is increased, the impedance of the lithium ion battery is firstly reduced and then increased, the capacity retention rate of the lithium ion battery after 300 circles of 45 ℃ circulation is firstly increased and then reduced, and LiPO in the electrolyte is visible 2 F 2 The higher the content is, the better, thus limiting LiPO in some embodiments of the present application 2 F 2 Less than 1% by weight of the total electrolyte to prevent excessive LiPO 2 F 2 Resulting in degradation of the performance of the lithium ion battery.
Examples 17 to 33
The electrolytes used in examples 17 to 33 were obtained by adding at least one compound to the base electrolyte as shown in Table 3, and the results of the performance test for examples 17 to 33 are shown in Table 4. For comparison, the parameters of the electrolytes and the results of the performance test for example 13 are shown in tables 3 and 4.
TABLE 3 Table 3
TABLE 4 Table 4
As can be seen from the performance test results of comparative examples 13 and 17 to 32, the thickness expansion rate of the lithium ion battery at 85 to 16 hours can be remarkably reduced by adding the polynitrile compound into the electrolyte, and the capacity retention rate after 300 cycles of 45 ℃ circulation is improved, namely, the high-temperature storage performance and the high-temperature circulation performance of the lithium ion battery can be improved by adding the polynitrile compound, because the nitrile compound can be complexed with the transition metal on the surface of the positive electrode, the dissolution of the transition metal is reduced, the contact between the electrolyte and the interface of the positive electrode is reduced, and the side reaction of the electrolyte at high temperature is further reduced, so that the high-temperature circulation and the high-temperature storage performance are improved.
From the performance test results of example 33, it can be seen that when the polynitrile compound content exceeds 10%, deterioration occurs in high-temperature cycle performance because the high content of the nitrile compound increases the viscosity of the electrolyte, deteriorating the dynamic performance of the lithium ion battery.
It can be seen from examples 20, 29 and 30 that the cyclic performance and the storage performance of lithium ion batteries are improved differently by different polynitrile compounds, because organic molecules containing nitrile functional groups of different structures will have different isolating effects on the electrolyte and the positive electrode surface. The more significant the isolation effect that results as the number of nitrile functions in the organic molecule increases. Meanwhile, the size of the organic molecule containing the nitrile functional group has an optimal value, the molecule is too small, the formed isolation space is limited, the easily-oxidized component in the electrolyte cannot be effectively isolated from the surface of the positive electrode, the molecule is too large, and the easily-oxidized component in the electrolyte can be contacted with the surface of the positive electrode through the gap of the organic molecule containing the nitrile functional group, so that a good isolation effect cannot be achieved.
Examples 34 to 47
The electrolytes used in examples 34 to 47 were obtained by adding one or more compounds as shown in Table 5 to the base electrolyte, and the results of the performance test for examples 34 to 47 are shown in Table 6. For comparison, the parameters of the electrolytes and the results of the performance test for example 22 are shown in tables 5 and 6.
TABLE 5
TABLE 6
From the performance test results of examples 22 and examples 37 to 45, it is understood that the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery are significantly improved when the cyclic ether compound is added at a mass fraction of 0.1% -2%. The method is characterized in that the oxidation potential of the cyclic ether is low, the cyclic ether is oxidized on the surface of the positive electrode to generate organic lithium salt, and the organic lithium salt is stable, so that the stability of a Solid Electrolyte Interface (SEI) film is enhanced, the oxidative decomposition of electrolyte of the lithium ion battery on the surface of the electrode in a high-temperature process is relieved, and the effects of improving the high-temperature storage performance and the high-temperature cycle performance of the lithium ion battery are further achieved.
Comparing the performance test results of examples 46, 47 and examples 37 to 45, it is understood that when the addition amount of the cyclic ether compound exceeds 2%, the high-temperature cycle performance and the high-rate discharge performance of the lithium ion battery are degraded. This is because when the content of the cyclic ether compound is too high, the impedance of the lithium ion battery increases, thereby causing the degradation of the cycle capacity of the lithium ion battery to be accelerated, deteriorating the cycle performance and the high rate discharge performance of the lithium ion battery.
As can be seen from comparison of the performance test results of examples 34 to 36, the compound of formula I-1 was used alone in combination with a cyclic ether or with lithium difluorophosphate (LiPO 2 F 2 ) The effect of improvement by the combination with the cyclic ether is not as remarkable as that of the additive nitrile.
Examples 48 to 53
Examples 48-53 are based on example 39, wherein the electrolyte further comprises cobalt ions, the electrolyte and the performance test results used in examples 48-53 are shown in Table 7, and the electrolyte parameters and the performance test results of example 39 are added in Table 7 for comparison.
TABLE 7
The results of the performance tests of comparative examples 39, 48-53 show that the cyclic resistance can be significantly improved by containing a small amount of cobalt ions in the electrolyte. This is mainly because a small amount of cobalt ions can enhance the conductivity of the electrolyte, thereby having the effect of improving the increase in the cycle resistance.
The electrolyte provided by the application can improve the rate performance and the cycle performance of a lithium ion battery using the electrolyte and reduce the internal resistance by adding the compound shown in the formula I.
The foregoing description is only of the preferred embodiments of the present application and is presented as a description of the principles of the technology being utilized. It will be appreciated by persons skilled in the art that the scope of the disclosure referred to in this application is not limited to the specific combinations of features described above, but it is intended to cover other embodiments in which any combination of features described above or equivalents thereof is possible without departing from the spirit of the disclosure. Such as the above-described features and technical features having similar functions (but not limited to) disclosed in the present application are replaced with each other.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are example forms of implementing the claims.
Claims (11)
1. An electrolyte comprising a compound of formula i:
wherein R1 and R2 are each independently selected from one of alkyl with carbon number between 1 and 11, substituted alkyl with carbon number between 1 and 11, alkenyl with carbon number between 2 and 11 and substituted alkenyl with carbon number between 2 and 11, and when substituted, the substituent is selected from at least one of fluorine, methyl and cyano;
A. b is independently selected from one of imidazole cation, pyridine cation, piperidine cation and quaternary ammonium salt cation;
x is selected from one of hexafluorophosphate, bistrifluoromethyl sulfonate, tetrafluoroborate, bisoxalaborate and tetrafluorooxalaborate;
the electrolyte further comprises: lithium difluorophosphate;
the lithium difluorophosphate accounts for less than 1% of the total mass of the electrolyte, the compound of the formula I accounts for C, and the lithium difluorophosphate accounts for D, wherein C+D is less than 11%, and C/D is more than or equal to 0.5 and less than or equal to 10.
2. The electrolyte of claim 1 wherein the compound of formula i comprises at least one of the following compounds:
3. the electrolyte of claim 1 wherein the compound of formula i comprises 0.01% to 10% by weight of the total electrolyte.
4. The electrolyte of claim 1, further comprising: at least one of a polynitrile compound or a cyclic ether compound.
5. The electrolyte of claim 4, wherein the electrolyte satisfies at least one of the following conditions (a) - (b):
(a) The polynitrile compound accounts for 0.5-10% of the total mass of the electrolyte;
(b) The cyclic ether compound accounts for 0.01-2% of the total mass of the electrolyte.
6. The electrolyte according to claim 4, wherein the polynitrile compound comprises at least one of the compounds shown below,
wherein R is 21 、R 22 、R 23 、R 24 Each independently selected from hydrogen, cyano, - (CH) 2 ) a -CN、-(CH 2 ) b -O-(CH 2 ) c -CN、-(CH 2 ) d - (ch=ch) -CN, an alkyl group having 1 to 5 carbon atoms, an alkoxycarbonyl group having 2 to 5 carbon atoms, and R 21 、R 22 、R 23 And R is 24 Wherein at least two of the groups are cyano groups, a, b and d are each independently selected from integers from 0 to 10, and c is selected from integers from 1 to 5.
7. The electrolyte according to claim 4, wherein the polynitrile compound comprises at least one of the compounds shown below;
8. the electrolyte of claim 4 wherein the cyclic ether compound comprises at least one of 1, 3-dioxolane, 1, 3-dioxane, or 1, 4-dioxane.
9. An electrochemical device, comprising:
a positive electrode, a negative electrode, a separator and the electrolyte as claimed in any one of claims 1 to 8.
10. The electrochemical device of claim 9, wherein the electrolyte further comprises cobalt ions, the cobalt ions comprising 1ppm to 50ppm of the total mass of the electrolyte.
11. An electronic device comprising the electrochemical device of any one of claims 9-10.
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