CN114792806A - Lithium metal secondary electrolyte and lithium metal secondary battery - Google Patents
Lithium metal secondary electrolyte and lithium metal secondary battery Download PDFInfo
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- CN114792806A CN114792806A CN202210555228.1A CN202210555228A CN114792806A CN 114792806 A CN114792806 A CN 114792806A CN 202210555228 A CN202210555228 A CN 202210555228A CN 114792806 A CN114792806 A CN 114792806A
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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
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- H—ELECTRICITY
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- 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
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
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Abstract
The invention provides a lithium metal secondary electrolyte and a lithium metal secondary battery. The lithium metal secondary electrolyte comprises electrolyte salt, a non-aqueous solvent, a diluent and an ionic liquid; the cation of the ionic liquid is selected from any one or the combination of at least two of pyrrolidine cation, piperidine cation and imidazole cation. The invention provides an SEI film with high inorganic component content generated in situ through solvation regulation, lithium metal bulges are repaired by utilizing electrostatic shielding effect, and an electrolyte with lithium ions uniformly deposited is regulated and controlled through high lithium salt concentration, so that the uniform deposition of lithium and the growth of dendritic crystals are controlled, wherein the lithium metal secondary battery comprehensively improves the coulombic efficiency and the cycle life of the lithium metal secondary battery by adding a non-aqueous solvent and a diluent and exerting a synergistic effect with other components.
Description
Technical Field
The invention belongs to the technical field of electrolytes, and particularly relates to a lithium metal secondary electrolyte and a lithium metal secondary battery.
Background
The lithium metal has extremely high specific capacity (3860mAh g) -1 ) And lower oxygenThe energy density of the constructed battery system can reach more than ten times of that of the traditional lithium ion battery due to the reduction potential (-3.04Vvs. SHE). However, lithium metal negative electrodes tend to produce lithium dendrites during charging: on one hand, lithium dendrites have self-amplification action and can pierce through a diaphragm and extend to a positive electrode, so that the internal short circuit of the battery is caused, and even fire explosion and the like are induced; on the other hand, lithium dendrites have very high reactivity, and can continuously consume Electrolyte and active lithium, a Solid Electrolyte Interface (SEI) film which is continuously thickened is continuously generated, so that lower coulombic efficiency and shorter cycle life are caused, and the dendrites are wrapped or shed by the SEI film to form dead lithium through electrochemical loss, so that the coulombic efficiency is further reduced.
In order to solve the problems, researchers regulate and control the deposition behavior of lithium by optimizing electrolyte components, developing solid electrolytes, constructing artificial SEI films, designing three-dimensional lithium deposition frames and other strategies. The artificial SEI film is constructed to be beneficial to relieving the side reaction of the electrolyte and the lithium cathode, and the three-dimensional lithium host structure and the composite electrode can effectively inhibit the volume expansion of the lithium cathode to a certain extent, but the processes for constructing the artificial SEI film and designing the three-dimensional lithium host structure are complex and are not beneficial to large-scale production; the solid electrolyte has low ionic conductivity, although it can suppress the formation of dendrites well. In comparison, the development of a suitable electrolyte is suitable for the existing battery system, and has the characteristics of convenience and economy.
Therefore, in the art, it is desirable to develop a nonaqueous electrolyte capable of regulating lithium deposition behavior, which not only can inhibit the generation of lithium dendrites, but also has high ionic conductivity and the prepared battery has good electrochemical properties.
Disclosure of Invention
In view of the disadvantages of the prior art, an object of the present invention is to provide a lithium metal secondary electrolyte and a lithium metal secondary battery. In order to inhibit dendritic crystal growth of a lithium metal cathode and enable a lithium metal secondary battery to show good cycle performance, the invention provides an electrolyte interface (SEI) film with high inorganic component content through solvation regulation and in-situ generation, repair of lithium metal bulges through electrostatic shielding effect and regulation of uniform lithium ion deposition through high lithium salt concentration, which is beneficial to control of uniform lithium deposition and inhibition of dendritic crystal growth, wherein a non-aqueous solvent and a diluent are added and play a synergistic effect with other components, so that the coulombic efficiency and cycle life of the lithium metal secondary battery are comprehensively improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a lithium metal secondary electrolyte comprising an electrolyte salt, a non-aqueous solvent, a diluent and an ionic liquid;
the cation of the ionic liquid is selected from any one or combination of at least two of pyrrolidine cations, piperidine cations and imidazole cations.
The invention provides a lithium metal secondary electrolyte which has the function of inhibiting dendritic crystal growth of a lithium metal negative electrode, wherein a solvent for repairing lithium metal bulges under the electrostatic shielding function is ionic liquid. When the surface of the metal lithium has a deposition protrusion, the electric field at the protrusion position is stronger, ionic liquid cations are gathered at the protrusion position, and only the ionic liquid cations are adsorbed to form an electrostatic shielding layer due to the fact that the effective reduction potential is lower than that of the lithium ions, so that the lithium ions are not deposited at the protrusion position any more, and dendritic crystal growth is inhibited. The diluent does not dissolve lithium salt, is mutually soluble with the solvent, has good effects of reducing viscosity and improving wettability, is matched with electrolyte salt, an ionic liquid solvent and a non-aqueous solvent to form a local high-concentration electrolyte, and the high lithium ion concentration provides enough lithium ions to form a uniform ion flow balanced electric field, so that the lithium is uniformly deposited. The non-aqueous solvent plays a role in dissolving lithium salt and increasing the dissociation degree of the lithium salt, and because the binding energy of the non-aqueous solvent and lithium ions is lower than that of anions and lithium ions, the non-aqueous solvent is more distributed on the outer layer of a solvation sheath when participating in solvation, solvent molecules on the outer layer are removed when a solvation complex reaches the surface of metal lithium, anions on the inner layer participate in reduction to form an SEI film with high content of inorganic components, and the SEI film has high stability, mechanical strength, lithium ion conductivity and low lithium atom adhesion energy.
Preferably, the content of the ionic liquid in the lithium metal secondary electrolyte is 5% to 90% by mass, and for example, may be 5%, 8%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 90% by mass.
As a preferable embodiment of the present invention, the content of the ionic liquid in the lithium metal secondary electrolyte is 10% to 60% by mass, for example, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%.
In the invention, the electrolyte has the most excellent electrical property and safety property by adjusting the mass percentage of the ionic liquid in the lithium metal secondary electrolyte, if the mass percentage of the ionic liquid is too low, fewer cations playing an electrostatic shielding role can be caused, the deposition of lithium ions at the convex part can not be effectively inhibited, and fewer coulomb force actions of the ions in the electrolyte are caused, so that the flame retardant effect is poor, when the electrolyte is applied to a lithium metal secondary battery, the electrical property and the safety property are poor, otherwise, the prepared electrolyte has overlarge viscosity and poor wettability, and when the electrolyte is applied to the lithium metal secondary battery, the electrical property is poor;
preferably, the pyrrolidine cation has the structure shown in formula 1:
wherein R is 1 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 2 And is selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl.
Preferably, the piperidine type cation has a structure as shown in formula 2:
wherein R is 3 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 4 And is selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl.
Preferably, the imidazole based cation has a structure as shown in formula 3:
wherein R is 5 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 6 Is selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl.
Preferably, the anion of the ionic liquid is selected from any one of or a combination of at least two of bis-fluorosulfonylimide anion, bis-trifluoromethanesulfonimide anion, tetrafluoroborate ion, hexafluorophosphate ion, perchlorate ion, dioxaoxalato borate ion, or difluorooxalato borate ion, for example, bis-fluorosulfonylimide anion and hexafluorophosphate ion, bis-trifluoromethanesulfonimide anion, tetrafluoroborate ion, hexafluorophosphate ion, perchlorate ion, dioxaoxalato borate ion, or difluorooxalato borate ion, but is not limited to the listed species, and the non-listed species of the anion of the ionic liquid is equally applicable.
Preferably, the electrolyte salt is selected from LiPF 6 、LiBF 4 、LiBOB、LiODFB、LiClO 4 LiTFSI or LiFSI or a combination of at least two thereof, for example, LiPF 6 And LiFSI, LiBF 4 、LiBOB、LiODFB、LiClO 4 LiTFSI or LiFSI, but not limited to the listed species, said electrolyte salt not beingThe same applies to the species listed.
Preferably, the content of the electrolyte salt in the lithium metal secondary electrolyte solution is 5% to 60% by mass, and may be, for example, 5%, 8%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%.
In the invention, by adjusting the mass percentage of the lithium salt in the lithium metal secondary electrolyte, if the mass percentage of the lithium salt is too low, the lithium ion content of the electrolyte is too low, which is not favorable for lithium ion transmission, and the electrical property of the battery is influenced, otherwise, the viscosity of the electrolyte is high, the wettability is poor, which is not favorable for uniform deposition of lithium ions, and the electrical property and the safety property of the battery are deteriorated;
preferably, the non-aqueous solvent is selected from any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, acetonitrile, 1, 3-dioxolane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethoxymethane or diethylene glycol dimethyl ether, or a combination of at least two thereof, such as dimethyl carbonate and ethyl methyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, acetonitrile, 1, 3-dioxolane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethoxymethane or diethylene glycol dimethyl ether, but is not limited to the listed species, and the non-aqueous solvent is also applicable to the non-listed species.
Preferably, the content of the non-aqueous solvent in the lithium metal secondary electrolyte is 5% to 90% by mass, and may be, for example, 5%, 8%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 90%.
Preferably, the diluent is selected from any one or a combination of at least two of 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl-1, 2,3, 3-tetrafluoropropyl ether, bis (2,2, 2-trifluoroethyl) ether, dichloromethane, 1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether or 1,1,1,3,3, 3-hexafluoroisopropyl methyl ether, and may be, for example, 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether and 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, bis (2,2, 2-trifluoroethyl) ether, dichloromethane, methylene chloride, or the like, 1H,1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether or 1,1,1,3,3, 3-hexafluoroisopropyl methyl ether, but not limited to the species listed, and those not listed for the diluent are equally suitable.
Preferably, the mass percentage of the diluent in the lithium metal secondary electrolyte is 5% to 90%, and may be, for example, 5%, 8%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 42%, 45%, 47%, 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 90%.
In the invention, the electrolyte has the optimal electrical property and safety performance by adjusting the mass percentage of the diluent in the lithium metal secondary electrolyte, and if the mass percentage of the diluent is too low, the viscosity of the electrolyte is too high, the wettability is poor, the lithium ions are deposited unevenly, so that the electrical property and safety performance of the prepared lithium metal secondary battery are poor, otherwise, the prepared electrolyte has poor safety due to the inflammability.
In a second aspect, the present invention provides a lithium metal secondary battery comprising an electrode sheet, an electrolyte and a separator, the electrolyte being the lithium metal secondary electrolyte of the first aspect.
According to the invention, the aim of regulating and controlling lithium uniform deposition, inhibiting dendritic crystal growth, improving the coulombic efficiency of the lithium metal secondary battery and prolonging the cycle life of the lithium metal secondary battery is achieved by regulating and controlling solvation, generating an SEI film with high content of inorganic components in situ, repairing lithium metal protrusions through an electrostatic shielding effect and regulating and controlling the electrolyte of lithium ions uniformly deposited by using high lithium salt concentration.
Compared with the prior art, the invention has the following beneficial effects:
the present invention provides a lithium metal secondary electrolyte having an effect of inhibiting growth of lithium metal dendrites, wherein the lithium metal secondary electrolyte can effectively control uniform deposition of lithium and inhibit growth of lithium dendrites by adding a non-aqueous solvent and a diluent and exerting a synergistic effect with other components, thereby improving cycle life and safety of a lithium metal secondary battery, compared with conventional ester or ether electrolytes.
Compared with other electrolytes for inhibiting dendritic crystals, the electrolyte provided by the invention is suitable for the existing battery system, does not need a complex process, and has the characteristics of convenience and economy, and the ionic liquid in the non-aqueous electrolyte is based on a lossless electrostatic shielding mechanism, and a local high-concentration lithium salt system formed by compounding and using a diluent has the functions of effectively controlling uniform deposition of lithium and inhibiting self-amplification growth of the dendritic crystals; meanwhile, the high-concentration lithium salt enables flammable non-aqueous solvent molecules to completely participate in solvation of lithium ions and be difficult to volatilize, and in addition, the ionic liquid has the advantages of good thermal stability (the decomposition temperature is more than or equal to 300 ℃), non-flammability, difficult volatilization and the like, so that the flame retardance of the lithium metal secondary electrolyte provided by the invention is superior to that of the traditional ester or ether electrolyte, the safety of the battery is improved, and the lithium metal secondary electrolyte is further beneficial to maintaining the effect of inhibiting lithium dendrites in the long-term cycle of the battery.
Detailed Description
The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitation of the present invention.
Example 1
The embodiment provides a lithium metal secondary electrolyte, which comprises LiPF with the mass percentage of 20% respectively, based on the total mass of the lithium metal secondary electrolyte as 100% 6 15% of a non-aqueous solvent (wherein the mass ratio of 1, 3-dioxolane to glycol dimethyl ether is 1:1), 30% of 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent and 35% of an ionic liquid; the cation of the ionic liquid is selected from 1-methyl-1-propyl pyrrolidinium bis (fluorosulfonyl) imide cation, and the anion of the ionic liquidThe ions are selected from bis-fluorosulfonylimide anions.
The preparation method of the lithium metal secondary electrolyte comprises the following steps:
preparing electrolyte in a glove box, wherein the content of argon in the glove box is 99.999 percent, the actual oxygen content in the glove box is less than 0.1ppm, the moisture content is less than 0.1ppm, and mixing the LiPF 6 The lithium metal secondary electrolyte is prepared by mixing a non-aqueous solvent (1, 3-dioxolane and ethylene glycol dimethyl ether), a 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent and an ionic liquid.
Preparing a lithium ion battery: and (3) assembling the lithium cobaltate positive electrode material, the polypropylene diaphragm and the lithium metal negative electrode material, and adding the lithium metal secondary electrolyte to prepare the lithium metal secondary battery.
Example 2
The embodiment provides a lithium metal secondary electrolyte, which comprises LiPF with the mass percentage of 20% respectively, based on the total mass of the lithium metal secondary electrolyte as 100% 6 40% of a non-aqueous solvent (wherein the mass ratio of 1, 3-dioxolane to glycol dimethyl ether is 1:1), 30% of 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent and 10% of an ionic liquid; the cation of the ionic liquid is selected from N-butyl-N-methylpiperidine bis (trifluoromethanesulfonyl) imide cation, and the anion of the ionic liquid is selected from bis (trifluoromethanesulfonyl) imide anion.
The preparation method of the lithium metal secondary electrolyte comprises the following steps:
the preparation method of the lithium metal secondary electrolyte solution described in this example was the same as in example 1.
The preparation method of the lithium ion battery comprises the following steps:
the preparation method of the lithium ion battery described in this example is the same as that of example 1.
Example 3
The embodiment provides a lithium metal secondary electrolyte, which comprises LiPF with the mass percentage of 20% respectively, based on the total mass of the lithium metal secondary electrolyte as 100% 6 10% of non-aqueous solvent (1, 3-dioxygen in the solution)The mass ratio of the pentalane to the glycol dimethyl ether is 1:1), 10 percent of 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether diluent and 60 percent of ionic liquid; the cation of the ionic liquid is selected from 1-butyl-1-propyl imidazolium bis (fluorosulfonyl) imide cation, and the anion of the ionic liquid is selected from bis (fluorosulfonyl) imide anion.
The preparation method of the lithium metal secondary electrolyte comprises the following steps:
the preparation method of the lithium metal secondary electrolyte described in this example was the same as in example 1.
The preparation method of the lithium ion battery comprises the following steps:
the preparation method of the lithium ion battery in this example is the same as that in example 1.
Example 4
This example provides a lithium metal secondary electrolyte, which includes LiBF with a mass percentage of 10% respectively, based on 100% of the total mass of the lithium metal secondary electrolyte 4 10% of a non-aqueous solvent (wherein the mass ratio of the diethylene glycol dimethyl ether to the ethylene glycol dimethyl ether is 1:1), 75% of a bis (2,2, 2-trifluoroethyl) ether diluent and 5% of an ionic liquid; the cation of the ionic liquid is selected from 1-butyl-1-propyl imidazolium bis (fluorosulfonyl) imide cation, and the anion of the ionic liquid is selected from fluorosulfonyl imide anion.
The preparation method of the lithium metal secondary electrolyte comprises the following steps:
the preparation method of the lithium metal secondary electrolyte solution described in this example was the same as in example 1.
The preparation method of the lithium ion battery comprises the following steps:
the preparation method of the lithium ion battery described in this example is the same as that of example 1.
Example 5
This example provides a lithium metal secondary electrolyte, which includes, based on 100% of the total mass of the lithium metal secondary electrolyte, 5% of LiBF by mass 4 5 percent of glycol dimethyl ether non-aqueous solvent, 5 percent of 1,1,1,3,3, 3-hexafluoroisopropyl methyl ether diluent and 85 percent of dimethyl etherA sub-liquid; the cation of the ionic liquid is selected from 1-butyl-1-propyl imidazolium bis (fluorosulfonyl) imide cation, and the anion of the ionic liquid is selected from fluorosulfonyl imide anion.
The preparation method of the lithium metal secondary electrolyte comprises the following steps:
the preparation method of the lithium metal secondary electrolyte solution described in this example was the same as in example 1.
The preparation method of the lithium ion battery comprises the following steps:
the preparation method of the lithium ion battery in this example is the same as that in example 1.
Comparative example 1
The comparative example is different from example 1 in that no ionic liquid is added based on 100% of the total mass of the lithium metal secondary electrolyte, and the mass percentage of the 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent is 65%, and the rest is the same as example 1.
Comparative example 2
The comparative example is different from example 1 in that the ionic liquid was 65% by mass based on 100% by mass of the total lithium metal secondary electrolyte without adding 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent, and the rest was the same as example 1.
Comparative example 3
This comparative example is different from example 1 in that the ionic liquid is 1% by mass and the 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent is 64% by mass based on 100% by mass of the total mass of the lithium metal secondary electrolyte, and the rest is the same as example 1.
Comparative example 4
The comparative example is different from example 1 in that the lithium metal secondary electrolyte includes LiPF in an amount of 2% by mass, respectively, based on 100% by mass of the total mass of the lithium metal secondary electrolyte 6 The balance of the reaction solution was the same as in example 1, except that the reaction solution was changed to a solution containing 3% of a nonaqueous solvent (1, 3-dioxolane and ethylene glycol dimethyl ether in a mass ratio of 1:1) and 95% of an ionic liquid.
Comparative example 5
This comparative example is different from example 1 in that the ionic liquid is 64% by mass and the 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent is 1% by mass based on 100% by mass of the total mass of the lithium metal secondary electrolyte, and the rest is the same as example 1.
Comparative example 6
The comparative example is different from example 1 in that the lithium metal secondary electrolyte includes LiPF in an amount of 2% by mass, respectively, based on 100% by mass of the total mass of the lithium metal secondary electrolyte 6 3% of a nonaqueous solvent (wherein the mass ratio of 1, 3-dioxolane to ethylene glycol dimethyl ether is 1:1) and 95% of a 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent, the others being the same as in example 1.
Comparative example 7
The comparative example is different from example 1 in that a non-aqueous solvent is not added based on 100% of the total mass of the lithium metal secondary electrolyte, and the mass percentage of the 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether diluent is 45%, and the rest is the same as example 1.
Comparative example 8
The comparative example is different from example 1 in that the diluent of 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether was not added based on 100% by mass of the total mass of the lithium metal secondary electrolyte, and the content of the nonaqueous solvent was 45% by mass, and the rest was the same as example 1.
Test conditions
The lithium metal secondary electrolytes provided in examples 1 to 5 and comparative examples 1 to 8 were subjected to an ion conductivity performance test by the following method:
ionic conductivity: the prepared electrolytes of examples 1 to 5 and comparative examples 1 to 6 were subjected to conductivity test using a conductivity meter in a drying chamber at a dew point of-40 ℃ and a temperature of 25 ℃;
the lithium metal secondary electrolytes provided in examples 1 to 5 and comparative examples 1 to 8 were subjected to viscosity performance test by the following method:
viscosity: viscosity tests were conducted on the electrolytes of examples 1 to 5 and comparative examples 1 to 6 prepared above using a viscometer in a drying chamber at a dew point of < -40 ℃ in an environment of 25 ℃;
the lithium ion batteries prepared in examples 1 to 5 and comparative examples 1 to 8 were subjected to cycle performance tests by the following methods:
cycle performance: testing by using a charge-discharge test cabinet at 25 ℃, and recording the number of cycle turns of which the capacity retention rate reaches 80%;
the test results are shown in tables 1 and 2:
table 1:
table 2:
as can be seen from the data in tables 1 and 2, the ionic liquid proportion and the diluent proportion can affect the electrolyte performance, the ionic liquid proportion is controlled to be 5-90%, the diluent proportion is controlled to be 5-90%, the prepared battery has better cycle performance, the ionic liquid proportion is controlled to be 10-60%, the diluent proportion is controlled to be 5-90%, the electrolyte has optimal electrochemical performance and safety performance, the mass percentage of the ionic liquid is too low, it results in that cations that function as an electrostatic shield are small and lithium ion deposition at the projections cannot be effectively suppressed, the electrolyte has less coulomb force action and poor flame retardant effect due to less ions in the electrolyte, and has poor electrical property and safety performance when applied to a lithium metal secondary battery, and on the contrary, the prepared electrolyte has overlarge viscosity and poor wettability and has poor electrical property when applied to the lithium metal secondary battery; if the mass percentage of the diluent is too low, the viscosity of the electrolyte is too high, the wettability is poor, and the lithium ions are deposited unevenly, so that the electrical property and the safety property of the prepared lithium metal secondary battery are poor, otherwise, the prepared electrolyte is poor in safety due to the inflammability of the lithium metal secondary battery.
The applicant states that the present invention is illustrated by the above examples of the process of the present invention, but the present invention is not limited to the above process steps, i.e. it is not meant that the present invention must rely on the above process steps to be carried out. It will be apparent to those skilled in the art that any modification of the present invention, equivalent substitutions of selected materials and additions of auxiliary components, selection of specific modes and the like, which are within the scope and disclosure of the present invention, are contemplated by the present invention.
Claims (10)
1. A lithium metal secondary electrolyte, comprising an electrolyte salt, a non-aqueous solvent, a diluent, and an ionic liquid;
the cation of the ionic liquid is selected from any one or the combination of at least two of pyrrolidine cation, piperidine cation and imidazole cation.
2. The lithium metal secondary electrolyte as claimed in claim 1, wherein the mass percentage of the ionic liquid in the lithium metal secondary electrolyte is 5% to 90%;
preferably, the mass percentage of the ionic liquid in the lithium metal secondary electrolyte is 10-60%.
3. The lithium metal secondary electrolyte of claim 1 or 2, wherein the pyrrolidine cation has a structure according to formula 1:
wherein R is 1 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 2 Selected from methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butylOr a tert-butyl group.
4. The lithium metal secondary electrolyte of any one of claims 1-3, wherein the piperidine type cation has a structure according to formula 2:
wherein R is 3 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 4 Is selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl.
5. The lithium metal secondary electrolyte of any one of claims 1-4, wherein the imidazole-based cation has a structure according to formula 3:
wherein R is 5 Selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl, R 6 Is selected from any one of methyl, ethyl, n-propyl, isopropyl, primary butyl, sec-butyl or tert-butyl.
6. The lithium metal secondary electrolyte of any one of claims 1 to 5, wherein the anion of the ionic liquid is selected from any one of or a combination of at least two of bis-fluorosulfonylimide anion, bis-trifluoromethanesulfonimide anion, tetrafluoroborate ion, hexafluorophosphate ion, perchlorate ion, dioxalate borate ion, or difluorooxalato borate ion.
7. The lithium metal secondary electrolyte according to any one of claims 1 to 6,characterized in that the electrolyte salt is selected from LiPF 6 、LiBF 4 、LiBOB、LiODFB、LiClO 4 Any one or a combination of at least two of LiTFSI or LiFSI;
preferably, the mass percentage of the electrolyte salt in the lithium metal secondary electrolyte is 5-60%.
8. The lithium metal secondary electrolyte according to any one of claims 1 to 7, wherein the nonaqueous solvent is selected from any one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, ethylene carbonate, acetonitrile, 1, 3-dioxolane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxymethane, or diglyme, or a combination of at least two thereof;
preferably, the mass percentage of the non-aqueous solvent in the lithium metal secondary electrolyte is 5-90%.
9. The lithium metal secondary electrolyte of any one of claims 1 to 8, wherein the diluent is selected from any one of 2,2, 2-trifluoroethyl-1, 1,2, 2-tetrafluoroethyl ether, 1,1,2, 2-tetrafluoroethyl-2, 2,3,3, -tetrafluoropropyl ether, bis (2,2, 2-trifluoroethyl) ether, dichloromethane, 1H, 5H-octafluoropentyl-1, 1,2, 2-tetrafluoroethyl ether, or 1,1,1,3,3, 3-hexafluoroisopropylmethyl ether, or a combination of at least two thereof;
preferably, the mass percentage of the diluent in the lithium metal secondary electrolyte is 5-90%.
10. A lithium metal secondary battery comprising an electrode sheet, an electrolyte and a separator, the electrolyte being the lithium metal secondary electrolyte of any one of claims 1 to 9.
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