CN113471536A - Lithium secondary battery electrolyte containing eutectic solvent and preparation method thereof - Google Patents
Lithium secondary battery electrolyte containing eutectic solvent and preparation method thereof Download PDFInfo
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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
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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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic 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
Abstract
The invention discloses a lithium secondary battery electrolyte containing an eutectic solvent and a preparation method thereof, wherein the lithium secondary battery electrolyte containing the eutectic solvent is composed of the eutectic solvent which is in a flowing liquid state at room temperature and the electrolyte of a lithium secondary battery, wherein the eutectic solvent accounts for 0.5-80% of the total weight percentage of the electrolyte; the eutectic solvent consists of a nitrogen-containing compound and a quaternary ammonium salt according to a molar ratio (2-4) to 1; the electrolyte of the lithium secondary battery is carbonate-based electrolyte or ether electrolyte. The invention adopts eutectic solvent as additive to prepare the electrolyte of the lithium secondary battery, which can enhance the solubility of insoluble or slightly soluble nitrogen-containing compound functional substance in organic electrolyte; the uniform deposition of the lithium metal is realized, so that the growth of lithium dendrites is inhibited, the cycling stability of the lithium metal secondary battery is improved, and the performance of the lithium secondary battery is obviously improved. The preparation method is simple, has good safety, is suitable for large-scale batch production, and has an industrial prospect.
Description
Technical Field
The invention belongs to the technical field of lithium secondary battery preparation, and particularly relates to a lithium secondary battery electrolyte containing an eutectic solvent and a preparation method thereof.
Background
With the development of science and technology, the demand of the current market for high energy density secondary batteries is increasingly urgent, and great interest in the development of the next generation of lithium metal secondary batteries (LMB) is aroused. However, due to the high reactivity of metallic lithium, persistent side reactions can occur when in contact with the electrolyte, resulting in low coulombic efficiency of the battery; meanwhile, LMB causes the cycle life to be shortened and even the battery to be exploded by the growth of lithium dendrites and the formation of dead lithium during charge and discharge cycles. In order to solve the problems faced by LMB, research personnel have conducted extensive research on various approaches such as developing a novel electrolyte lithium salt, adopting an all-solid electrolyte, constructing a metallic lithium negative electrode of a three-dimensional carrier framework, adding a functional additive and the like. Among them, development and optimization of functional additives based on commercial lithium secondary electrolytes are the simplest and most suitable for industrialization.
The types of the current functional additives are mainly as follows: the additives for constructing the stable SEI layer, the additives with the flame retardant effect, the additives for increasing the wettability of the electrolyte, the additives for improving the high/low temperature performance and the like are practically applied to commercial lithium ion battery systems, and the functional additives are proved to be capable of improving the battery performance. The eutectic solvent is a novel non-toxic, non-combustible and green ionic liquid, has the characteristics of high ionic strength, high polarity, a supermolecular structure, high dielectric constant, excellent stability in air, environmental friendliness and the like, and is widely applied to the fields of synthesis of cellulose derivatives, biodiesel purification, synthesis of polymers and organic matters, energy environment and the like. The eutectic solvent is reported as an ion conduction medium in a lithium ion battery as early as 2001, Huangshi Jie et al (J.Phys.chem.B,2001,105,9966-+/Li) and thus this work does not demonstrate its application in lithium metal secondary battery systems. Boisset et et al (Boisset et al, electrochemistry. acta,2013,15,120-126) further developed a novel eutectic solvent (DES) based on n-Methylacetamide (MAC) and LiTFSI, which will beThe eutectic solvent is used as electrolyte to assemble an LFP/Li battery, and a cycle test result at 80 ℃ shows that the eutectic solvent has good compatibility with an LFP electrode. However, the eutectic electrolyte developed by the above method has high viscosity, low electronic conductivity and other characteristics, and is not favorable for ion transfer and diffusion, so high temperature is required to exert performance, and the test cycle number is too short to evaluate the long-term cycling stability of the electrolyte. To this end, Dinh et al (Dinh et al, ACS Omega,2020,37,23843--1The capacity retention after 50 cycles was 84%. The faster capacity fade indicates that the eutectic solvent has poor compatibility with lithium metal and that the cathode transition metal ions dissolve in the electrolyte.
Based on the situation, the invention develops the electrolyte containing the eutectic solvent, improves the compatibility of the electrolyte and the lithium metal, and can be applied to the lithium metal secondary battery so as to meet the increasingly urgent requirements of the current market on the high-energy-density secondary battery.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides the lithium secondary battery electrolyte containing the eutectic solvent and having good compatibility with the metallic lithium and the preparation method thereof.
The purpose of the invention is realized by the following technical scheme:
a lithium secondary battery electrolyte containing a eutectic solvent is characterized in that: the electrolyte consists of an eutectic solvent in a flowing liquid state at room temperature and an electrolyte of a lithium secondary battery, wherein the eutectic solvent accounts for 0.5 to 80 percent of the total weight of the electrolyte of the lithium secondary battery; the eutectic solvent consists of a nitrogen-containing compound and a quaternary ammonium salt according to a molar ratio (2-4) to 1; the electrolyte of the lithium secondary battery is carbonate-based electrolyte or ether electrolyte.
A preparation method of a lithium secondary battery electrolyte containing an eutectic solvent is characterized by comprising the following steps: the steps and process conditions are as follows:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Respectively drying nitrogen-containing compound powder and quaternary ammonium salt powder, mixing the nitrogen compound and the quaternary ammonium salt according to the molar ratio of (2-4) to 1, magnetically stirring for at least 3 hours at 40-100 ℃, mixing to obtain an eutectic solvent in a flowing liquid state at room temperature, and placing the eutectic solvent in an inert atmosphere for later use;
step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Adding the eutectic solvent in the first step into the lithium secondary battery electrolyte according to 0.5-80% of the total weight of the electrolyte to obtain the lithium secondary battery electrolyte containing the eutectic solvent;
the lithium secondary electrolyte is a carbonate-based electrolyte or an ether-based electrolyte.
The nitrogen-containing compound refers to one or more of urea, thiourea or butanedinitrile.
The quaternary ammonium salt refers to one or more of lithium bis (trifluoromethyl sulfonyl imide) imide (LiTFSI) or sodium bis (trifluoromethyl sulfonyl imide) imide (NaTFSI).
According to the invention, a stable SEI layer is constructed on the surface of the lithium metal by utilizing the decomposition reaction of the eutectic solvent under low voltage, and the uniform deposition on the surface of the lithium metal is realized through the synergistic effect of different components in the eutectic solvent, so that the growth of lithium dendrite is inhibited and the cycling stability of the lithium metal secondary battery is improved.
Compared with the prior art, the invention has the following remarkable characteristics and positive effects:
1. the invention adopts the eutectic solvent as the additive, can enhance the solubility of the insoluble or slightly soluble nitrogen-containing compound functional substance in the organic electrolyte, and effectively improves the function of the functional electrolyte. The electrolyte can be used for electrochemically decomposing the surface of the lithium metal and forming a stable SEI layer through the synergistic effect of different components in the eutectic solvent, and the protective layer generates nitrogen-containing substances (such as Li)3N) has the function of rapidly conducting lithium ions, and further reduces the pole of the batteryChemical phenomena; in addition, the physical isolation of the metal lithium electrode and the liquid electrolyte (or the solid electrolyte) can be realized, and the problem of low coulombic efficiency caused by the side reaction of the continuity of the electrolyte is solved.
2. The invention realizes the uniform deposition of the lithium metal, thereby inhibiting the growth of lithium dendrite and improving the cycle stability of the lithium metal secondary battery, and obviously improving the performance of the lithium secondary battery.
3. The electrolyte containing the eutectic solvent component also has a good flame retardant effect, and can further improve the safety performance of the battery.
4. The preparation method is simple, is suitable for large-scale batch production, and has an industrial prospect.
Drawings
FIG. 1 is a graph comparing the change in voltage with respect to the number of cycles between the experimental group and the blank control group (test condition: 0.5mA cm)-2，0.5mAh cm-225 ℃); the experimental group is a lithium metal symmetrical battery assembled by the lithium secondary battery electrolyte containing the eutectic solvent prepared in the example 1, and the blank control group is 1M LiPF6DMC DEC EC electrolyte assembled lithium metal symmetrical cell.
FIG. 2 is a graph comparing the change of specific discharge capacity versus the change of cycle number in the experimental group and the blank group (test condition: 30mA g)-125 ℃); experimental group LiFePO assembled for the electrolyte of the lithium secondary battery containing the eutectic solvent prepared in example 24Li cell, blank control group 1M LiTFSI/FEC electrolyte assembled LiFePO4a/Li cell.
FIG. 3 is a graph showing the voltage-capacity curves of the lithium metal symmetrical batteries of the experimental group and the blank control group after 20 weeks of circulation (test condition: 0.5mA cm)-2，0.5mAh cm-225 ℃); the experimental group was a lithium metal symmetric battery assembled with the electrolyte of the eutectic solvent lithium secondary battery prepared in example 6, and the blank control group was 1M LiPF6DMC DEC EC assembled lithium metal symmetrical cell.
Detailed Description
The technical solutions claimed in the present invention have been fully described above, and the present invention will be described in further detail with reference to the following examples and drawings, but the embodiments of the present invention are not limited thereto.
Example 1
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Drying urea powder and LiTFSI powder at 100 ℃, then mixing according to a molar ratio of 3:1, placing the mixture in a 25mL glass bottle, magnetically stirring the mixture at 60 ℃ for 12 hours to obtain a eutectic solvent in a flowing liquid state at room temperature, and placing the eutectic solvent in a glove box under an inert atmosphere for later use.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.01g of the eutectic solvent prepared in the step one into a reagent bottle, adding 1g of carbonate lithium secondary battery electrolyte, and preparing the lithium secondary battery electrolyte containing 1 wt.% of the eutectic solvent. The carbonate lithium secondary battery electrolyte contains 1mol/L lithium hexafluorophosphate (LiPF)6) An electrolyte and a solvent composed of dimethyl carbonate (DMC), diethyl carbonate (DEC) and Ethylene Carbonate (EC) in a volume ratio of 1:1:1 (abbreviation: 1M LiPF6/DMC:DEC:EC)。
Comparative experiment:
the electrolyte of the lithium secondary battery prepared in the embodiment and containing 1 wt.% of eutectic solvent is used as an experimental group, and 1M LiPF containing no eutectic solvent component is adopted6DEC, EC carbonate lithium secondary battery electrolyte is used as a blank control group, a metal lithium symmetrical battery is respectively assembled, and the voltage of the battery is tested along with the change of cycle number, and the result is shown in figure 1. The comparison graph of the voltage-cycle frequency change of the experimental group and the blank control group shows that the battery of the experimental group can stably cycle for nearly 1200 hours, the cycle of the battery of the blank control group is only about 500 hours, and compared with the battery of the blank control group, the cycle stability of the battery of the blank control group is obviously improved, which shows that the addition of the eutectic solvent effectively improves the metal lithium/electrolyte interface, and the cycle stability of the lithium secondary battery is obviously improved.
Example 2
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Same as example 1 step one.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.5g of the eutectic solvent prepared in the step one into a reagent bottle, adding 1g of carbonate lithium secondary battery electrolyte, and preparing the lithium secondary battery electrolyte containing 50 wt.% of the eutectic solvent. The carbonate lithium secondary battery electrolyte comprises 1mol/L LiTFSI electrolyte and fluoroethylene carbonate (FEC) solvent (1M LiTFSI/FEC for short)
Comparative experiment:
LiFePO was assembled separately using the lithium secondary battery electrolyte containing 50 wt.% of eutectic solvent prepared in this example as an experimental group and the 1M LiTFSI/FEC carbonate lithium secondary battery electrolyte containing no eutectic solvent as a blank control group4The Li battery is tested, and the discharge specific capacity and the coulombic efficiency of the Li battery are tested along with the change of the cycle number. Two groups of LiFePO were used in this example4The discharge capacity and coulombic efficiency of the/Li battery are shown in the graph of FIG. 2. The result shows that the discharge specific capacity of the battery added with the electrolyte containing the eutectic solvent component has no obvious attenuation after 50 weeks, and the cycling stability of the battery is obviously superior to that of the battery of a blank control group; meanwhile, the coulombic efficiency of the experimental group is stabilized above 99% from the third week to the 50 th week, while the blank group gradually decreases from 89% of the first week to 58.7% of the 16 th week, and then the internal short-circuit charging failure of the battery occurs.
Example 3
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Same as example 1 step one.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.5g, 0.7g and 0.8g of the eutectic solvent prepared in the step one into a reagent bottle, respectively adding carbonic ester lithium secondary battery electrolyte to 1g, and preparing the lithium secondary battery electrolyte containing 50 wt.% of eutectic solvent, 70 wt.% of eutectic solvent and 80 wt.% of eutectic solvent. The carbonate lithium secondary battery electrolyte comprises 1mol/L LiTFSI electrolyte and fluoroethylene carbonate (FEC) solvent (1M LiTFSI/FEC for short)
Comparative experiment:
and calculating the mass contents of urea in the lithium secondary battery electrolyte containing 50 wt.% eutectic solvent, 70 wt.% eutectic solvent and 80 wt.% eutectic solvent in the second step to be 19.5 wt.%, 27.3 wt.% eutectic solvent and 31.2 wt.% eutectic solvent. Based on this, 19.5, 27.3 and 31.2 wt.% of urea powder is weighed in the FEC solvent by mass, and after the mixed solution is magnetically stirred for 12 hours, it is found that the urea in the mixed solution of the three proportions can not be completely dissolved, because the urea alone has low solubility in the carbonate electrolyte. And the lithium secondary battery electrolyte containing 50, 70 and 80 wt.% of eutectic solvent prepared in the second step is not precipitated, and the comparison result shows that the solubility of urea components in carbonate electrolyte can be greatly enhanced after the eutectic solvent is formed by urea and LiTFSI, so that the flame retardant property of the electrolyte is effectively improved.
Example 4
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Drying urea powder and LiTFSI powder at 100 ℃, then mixing according to the molar ratio of 2:1, placing the mixture into a 25mL glass bottle, magnetically stirring the mixture for 6 hours at 100 ℃ to obtain the eutectic solvent in a flowing liquid state at room temperature, and placing the eutectic solvent in a glove box under inert atmosphere for later use.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Respectively weighing the eutectic solvent prepared in the step one by 0.01g, 0.03g, 0.05g, 0.1g and 0.2g0.5g of the reagent solution was put in a reagent bottle, and 1M LiPF was added6DEC EC carbonate lithium secondary battery electrolytes are respectively prepared into lithium secondary battery electrolytes containing 1,3, 5, 10, 20 and 50 wt.% eutectic solvents.
Comparative experiment: the lithium secondary battery electrolyte containing 1,3, 5, 10, 20, 50 wt.% of eutectic solvent prepared in the second step of this example was used as an experimental group, and 1M LiPF containing no eutectic solvent component was used6and/DMC, DEC, EC carbonate lithium secondary battery electrolyte and the eutectic solvent prepared in the first step are used as a control group. And (3) immersing a glass fiber filter membrane with the porosity of 22 microns and the diameter of 25mm into the electrolyte, then respectively burning the electrolyte by using an ignition gun, and testing and comparing the flame self-extinguishing time of different components.
The eutectic solvent prepared in the embodiment still does not burn under the condition of flame ignition, and 1M LiPF6DEC EC carbonate lithium secondary battery electrolyte is ignited instantly and extinguished after the components are completely combusted. The electrolyte containing the eutectic solvent in a higher proportion is more difficult to ignite, and the flame self-extinguishing time is shorter, so that the lithium secondary battery electrolyte containing the eutectic solvent has a flame retardant effect, and particularly the electrolyte containing the eutectic solvent in a higher proportion has a better flame retardant effect.
Example 5
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Drying thiourea powder and NaTFSI powder at 100 ℃, then mixing according to the molar ratio of 3:1, placing the mixture into a 25mL glass bottle, magnetically stirring the mixture for 12 hours at the temperature of 60 ℃ to obtain the eutectic solvent which is in a flowing liquid state at room temperature, and placing the eutectic solvent in a glove box under an inert atmosphere for later use.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.01g of the eutectic solvent prepared in the step one into a reagent bottle, adding 1g of ether lithium secondary battery electrolyte, and preparing the lithium secondary battery electrolyte containing 1 wt.% of the eutectic solvent. The ether lithium secondary battery electrolyte is composed of 1mol/L LiTFSI electrolyte and a mixed solvent of 1, 2-Dimethoxyethane (DME) and 1, 3-Dioxolane (DOL) in a volume ratio of 1:1 (1M LiTFSI/DME: DOL for short).
Comparative experiment:
the lithium secondary battery electrolyte containing 1 wt.% of eutectic solvent prepared in the second step of the present embodiment is used as an experimental group, and the lithium metal symmetric battery is assembled with the lithium secondary battery electrolyte containing 1M LiTFSI/DME, DOL ether lithium secondary battery electrolyte without eutectic solvent components, as a blank control group, and then the ac impedance data before and after the two cycles are tested. The result shows that compared with the charge transfer impedance of a blank control group battery, the charge transfer resistance of the metal lithium/electrolyte is obviously lower when the eutectic solvent is used as an additive; after 100 cycles, the experimental group had significantly lower lithium metal/electrolyte charge transfer resistance than the blank.
Example 6
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Succinonitrile and NaTFSI powder are treated at 100 ℃, then mixed according to the molar ratio of 4:1, the mixture is placed in a 25mL glass bottle, magnetic stirring is carried out at the temperature of 40 ℃ for 3 hours, so as to obtain the eutectic solvent which is in a flowing liquid state at room temperature, and the eutectic solvent is placed in a glove box under an inert atmosphere for standby.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.01g of eutectic solvent prepared in the step one into a reagent bottle, and adding 1M LiPF6DEC EC 2g, and 0.5 wt.% eutectic solvent.
Comparative experiment:
the lithium metal symmetric battery assembled by using the electrolyte of the lithium secondary battery containing 0.5 wt.% of eutectic solvent prepared in the embodiment is an experimental group, and the lithium metal symmetric battery does not contain 1M LiPF (lithium ion power) of the eutectic solvent component6Lithium secondary battery of DMC DEC EC carbonateThe lithium metal symmetrical battery assembled by the electrolyte is a blank control group, after the lithium metal symmetrical battery of the experimental group and the blank control group circulates for 20 weeks, the voltage-capacity curve of the experimental group and the lithium metal symmetrical battery of the blank control group at the 20 th week is compared, and the result is shown in figure 3 (test condition: 0.5mA cm)-2，0.5mAh cm-225 ℃); the polarization of the battery assembled by the electrolyte containing the eutectic solvent component in fig. 3 is obviously lower than that of the blank control group, which shows that the addition of the eutectic solvent can obviously reduce the energy barrier of the dissolution and deposition of the metal lithium and improve the cycle stability of the metal lithium.
Example 7
The preparation method of the lithium secondary battery electrolyte containing the eutectic solvent comprises the following steps and process conditions:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Drying the urea powder, the thiourea powder, the LiTFSI powder and the NaTFSI powder at 100 ℃, then respectively mixing according to the proportion of the urea, LiTFSI ═ 3:1 and the thiourea, NaTFSI ═ 3:1, respectively placing the mixture into a 25mL glass bottle, and magnetically stirring the mixture at the temperature of 60 ℃ for 12 hours. Then mixing the two eutectic solvents according to the mass ratio of 1:1, continuously magnetically stirring for 5 hours at the temperature of 60 ℃ to obtain the eutectic solvent in a flowing liquid state, and placing the eutectic solvent in a glove box under inert atmosphere for later use.
Step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Weighing 0.01g of the eutectic solvent prepared in the step one in the same reagent bottle, and adding the carbonate lithium secondary battery electrolyte (1M LiPF)6DEC: EC) to 1g, to prepare a lithium secondary battery electrolyte containing 1 wt.% of eutectic solvent.
Comparative experiment: the electrolyte of the lithium secondary battery containing 1 wt.% of eutectic solvent prepared in the second step of this example was used as an experimental group, and 1M LiPF containing no eutectic solvent component was used6And DMC, DEC, EC carbonate lithium secondary battery electrolyte is used as a control group, metal lithium symmetrical batteries are assembled respectively, and then the electrode surface appearance after 20 cycles is analyzed and compared.
After two groups of batteries are cycled for 20 weeks, the scanning electron microscope chart shows that the battery containsThe surface of a metal lithium cathode of the lithium secondary battery electrolyte with the eutectic solvent component is smooth, no obvious metal lithium dendrite or damaged morphology appears, and a blank group obviously shows that a large amount of lithium dendrite is generated. XPS test on the surface of the electrode shows that the SEI layer on the surface of the metallic lithium cathode of the lithium secondary battery electrolyte containing the eutectic solvent component contains about 2.1 percent of nitrogen element, which indicates that Li is contained3N compounds were generated, while the blank group did not detect the presence of nitrogen.
The above description is made in detail for the preferred embodiments of the present invention, but the above description is only for the preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. All equivalent changes made within the scope of the application of the present invention should be considered to fall within the scope of the patent of the present invention.
Claims (4)
1. A lithium secondary battery electrolyte containing a eutectic solvent is characterized in that: the electrolyte consists of an eutectic solvent in a flowing liquid state at room temperature and an electrolyte of a lithium secondary battery, wherein the eutectic solvent accounts for 0.5 to 80 percent of the total weight of the electrolyte of the lithium secondary battery; the eutectic solvent consists of a nitrogen-containing compound and a quaternary ammonium salt according to a molar ratio (2-4) to 1; the electrolyte of the lithium secondary battery is carbonate-based electrolyte or ether electrolyte.
2. A preparation method of a lithium secondary battery electrolyte containing an eutectic solvent is characterized by comprising the following steps: the steps and process conditions are as follows:
the method comprises the following steps: preparation of eutectic solvent in the form of a flowing liquid at room temperature
Respectively drying nitrogen-containing compound powder and quaternary ammonium salt powder, mixing the nitrogen compound and the quaternary ammonium salt according to the molar ratio of (2-4) to 1, magnetically stirring for at least 3 hours at 40-100 ℃, mixing to obtain an eutectic solvent in a flowing liquid state at room temperature, and placing the eutectic solvent in an inert atmosphere for later use;
step two: preparation of lithium secondary battery electrolyte containing eutectic solvent
Adding the eutectic solvent in the first step into the lithium secondary battery electrolyte according to 0.5-80% of the total weight percentage of the lithium secondary battery electrolyte to obtain the lithium secondary battery electrolyte containing the eutectic solvent;
the lithium secondary electrolyte is a carbonate-based electrolyte or an ether-based electrolyte.
3. The method for preparing the eutectic solvent-containing electrolyte for a lithium secondary battery according to claim 2, wherein: the nitrogen-containing compound refers to one or more of urea, thiourea or butanedinitrile.
4. The method for preparing the eutectic solvent-containing electrolyte for a lithium secondary battery according to claim 2, wherein: the quaternary ammonium salt refers to one or more of lithium bis (trifluoromethyl sulfonyl imide) imide (LiTFSI) and sodium bis (trifluoromethyl sulfonyl imide) imide (NaTFSI).
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