CN110649316A - Electrolyte additive, lithium ion battery electrolyte and lithium sulfur battery - Google Patents

Electrolyte additive, lithium ion battery electrolyte and lithium sulfur battery Download PDF

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CN110649316A
CN110649316A CN201910794287.2A CN201910794287A CN110649316A CN 110649316 A CN110649316 A CN 110649316A CN 201910794287 A CN201910794287 A CN 201910794287A CN 110649316 A CN110649316 A CN 110649316A
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compound
electrolyte
lithium
halogen
secondary carbon
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CN110649316B (en
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邓永红
肖映林
曾翼
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Southwest University of Science and Technology
Southern University of Science and Technology
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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
    • 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
    • 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
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive, a lithium ion battery electrolyte and a lithium sulfur battery. The electrolyte additive provided by the invention comprises at least one of a compound I, a compound II, a compound III and a compound IV; x1、X2、X3、X4、X5、X'1、X'2、X”1、X”2、X”3、X”4And X "5Each independently selected from H, halogen or haloalkyl, and X1、X2、X3、X4And X5Is not H, X at the same time'1And X'2Not simultaneously being H, X "1、X”2、X”3Not simultaneously being H, X "4And X "5Not H at the same time; m is a carbon or heteroatom containing group; m and n are respectively and independently selected from positive integers within 0 or 10And (4) counting. The complex can be added into electrolyte of a lithium-sulfur battery, so that the shuttle effect of polysulfide can be effectively inhibited, the utilization rate of active substances is improved, and the electrochemical performance and the safety performance of the lithium-sulfur battery are improved.

Description

Electrolyte additive, lithium ion battery electrolyte and lithium sulfur battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to an electrolyte additive, a lithium ion battery electrolyte and a lithium sulfur battery.
Background
Resources and energy are the source of development and survival for human beings, and are related to major and strategic problems of national security, social stability, economic development and the like. With the advent of the 21 st century, energy problems have become more severe and environmental pollution has continued to worsen, and the use and development of new and renewable energy sources has become a hot spot of research in countries around the world in order to realize sustainable development. Hydroenergy, wind energy, hydrogen energy, nuclear energy, tidal energy and solar energy are vigorously developed and utilized in various countries throughout the world. The improvement of the performance of the energy storage device can effectively promote the popularization of new energy application. Among a plurality of energy storage devices, electrochemical energy storage becomes one of the important research directions of all countries in the world due to the characteristics of high energy density, good energy conversion efficiency, small pollution, convenient combination and movement and the like.
The theoretical energy density of the lithium-sulfur battery prepared by adopting elemental sulfur or sulfur-based compound as a positive electrode material is as high as 2600Wh kg-1The actual energy density can reach 300Wh kg at present-1The weight of the rice can be increased to 600Wh kg in the coming years-1On the other hand, it is considered to be one of the secondary lithium battery systems with the most research value and application prospect at present. However, when elemental sulfur or a sulfur-based compound is used as a positive electrode material, lithium polysulfide (Li) which is an intermediate product generated during charge and discharge is used2SnAnd n is more than or equal to 3 and less than or equal to 8) is easy to dissolve in the electrolyte and diffuse to the negative electrode, so that the shuttle effect of irreversible loss of active substances and capacity is caused, and the electrochemical performance of the lithium-sulfur battery is greatly reduced.
Disclosure of Invention
The main object of the present invention is an electrolyte additive to effectively suppress the "shuttling effect" of polysulfides.
The invention also provides an electrolyte of the lithium ion battery and a lithium sulfur battery.
In order to achieve the above purpose, the invention provides the following specific technical scheme:
an electrolyte additive comprises at least one of a compound I, a compound II, a compound III and a compound IV;
wherein, X1、X2、X3、X4、X5、X'1、X'2、X”1、X”2、X”3、X”4And X "5Each independently selected from H, halogen or haloalkyl, and X1、X2、X3、X4And X5Is not H, X at the same time'1And X'2Not simultaneously being H, X "1、X”2、X”3Not simultaneously being H, X "4And X "5Not H at the same time;
m is a carbon or heteroatom containing group;
m and n are respectively and independently selected from positive integers within 0 or 10;
when no carbon-carbon double bond exists in the compound I, the compound I comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl substituent, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl;
when no carbon-carbon double bond exists in the compound II, the compound II comprises a plurality of secondary carbon atoms, each of the plurality of secondary carbon atoms is independently substituted by one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or haloalkyl;
when no carbon-carbon double bond is present in the compound iii, the compound iii comprises a number of secondary carbon atoms, each of which is independently substituted with one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom present in the number of secondary carbon atoms is substituted with halogen and/or haloalkyl;
when no carbon-carbon double bond exists in the compound IV, the compound IV comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl.
The electrolyte additive provided by the invention comprises at least one of the compound I, the compound II, the compound III and the compound IV with the chemical structures, and can be added into the electrolyte of a lithium-sulfur battery, so that the shuttle effect of polysulfide can be effectively inhibited, the utilization rate of active substances is improved, and the electrochemical performance and the safety performance of the lithium-sulfur battery are improved.
Correspondingly, a lithium ion battery electrolyte comprises: the electrolyte additive, the electrolyte and the organic solvent.
The lithium ion battery electrolyte provided by the invention contains the electrolyte additive, and when the electrolyte additive is applied to the preparation of a lithium sulfur battery, the shuttle effect of polysulfide can be effectively inhibited, and the electrochemical performance and the safety performance of the lithium sulfur battery are improved.
Accordingly, a lithium sulfur battery comprising: the anode, the cathode and the lithium ion battery electrolyte.
According to the lithium-sulfur battery provided by the invention, the electrolyte of the lithium-ion battery contains the electrolyte additive, so that the lithium-sulfur battery has excellent electrochemical performance and safety performance.
Drawings
Fig. 1 is an appearance of a separator after 50 cycles of a lithium sulfur battery of comparative example 1;
FIG. 2 is an appearance of the separator after 50 cycles of the lithium sulfur battery of example 1;
FIG. 3 is an SEM image of the anode of the lithium sulfur battery of comparative example 1 after 5 cycles;
FIG. 4 is an SEM image of the anode of the lithium sulfur cell of comparative example 1 after 50 cycles;
FIG. 5 is an SEM image of the anode of the lithium sulfur battery of example 1 after 5 cycles;
FIG. 6 is an SEM image of the anode of the lithium sulfur battery of example 1 after 50 cycles;
FIG. 7 is a graph of cycling performance of the lithium sulfur cells of example 1 and comparative example 1 cycled at a current density of 0.2C (1675 mAh/g);
FIG. 8 is a graph of rate performance of the lithium sulfur batteries of example 1 and comparative example 1, gradually increasing from a current density of 0.1C to 1.5C and then returning to 0.5C;
FIG. 9 is a result of testing in an ignition test of the electrolyte prepared in comparative example 1 of test example 5;
fig. 10 is a result of testing the ignition test of the electrolyte prepared in example 1 of test example 5.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, it is to be understood that the term "a number" means more than one unless specifically defined otherwise.
In order to effectively inhibit the shuttle effect of polysulfide, the embodiment of the invention provides an electrolyte additive which is applied to the preparation of a lithium-sulfur battery, and the specific technical scheme is as follows:
an electrolyte additive comprises at least one of a compound I, a compound II, a compound III and a compound IV;
Figure BDA0002180459470000051
wherein, X1、X2、X3、X4、X5、X'1、X'2、X”1、X”2、X”3、X”4And X "5Each independently selected from H, halogen or haloalkyl, and X1、X2、X3、X4And X5Is not H, X at the same time'1And X'2Not simultaneously being H, X "1、X”2、X”3Not simultaneously being H, X "4And X "5Not H at the same time;
m is a carbon or heteroatom containing group;
m and n are respectively and independently selected from positive integers within 0 or 10;
when no carbon-carbon double bond exists in the compound I, the compound I comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl substituent, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl;
when no carbon-carbon double bond exists in the compound II, the compound II comprises a plurality of secondary carbon atoms, each of the plurality of secondary carbon atoms is independently substituted by one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or haloalkyl;
when no carbon-carbon double bond is present in the compound iii, the compound iii comprises a number of secondary carbon atoms, each of which is independently substituted with one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom present in the number of secondary carbon atoms is substituted with halogen and/or haloalkyl;
when no carbon-carbon double bond exists in the compound IV, the compound IV comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl.
The electrolyte additive provided by the embodiment of the invention comprises at least one of the compound I, the compound II, the compound III and the compound IV with the chemical structures, and can effectively inhibit the shuttle effect of polysulfide, improve the utilization rate of active substances and improve the electrochemical performance and safety performance of a lithium-sulfur battery when being added into the electrolyte of the lithium-sulfur battery.
Specifically, in the embodiment of the present invention, the compound i as an electrolyte additive has the following general formula:
Figure BDA0002180459470000061
in the examples of the present invention, X1、X2、X3、X4、X5Each independently selected from H, halogen or haloalkyl, and not both H. When no carbon-carbon double bond is present in the compound I, the compound I comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are independently substituted by one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or haloalkyl. The secondary carbon atom refers to a carbon atom having two bonds substituted, for example, a methylene group when the secondary carbon atom is substituted with two hydrogen atoms.
It is understood that in compound I, at least one of its hydrogen atoms is replaced by a halogen including, but not limited to, F, Cl, Br, I. When X is present1、X2、X3、X4And X5When one of them is halogen or haloalkyl, X1、X2、X3、X4And X5The remainder of (a) may be H at the same time.
Preferably, the halogen is selected from F, Cl or Br, F has high electronegativity, can effectively improve the decomposition voltage, and is favorable for the electrolyte additive of the embodiment of the invention to decompose on the surface of the battery anode to form a CEI film; cl and Br have excellent flame retardant effect and high safety performance.
Preferably, the haloalkyl is selected from halogen-substituted alkyl or cycloalkyl; further, the number of carbon atoms of the haloalkyl group is preferably 10 or less; further, the haloalkyl group is a fluoroalkyl group.
In embodiments of the invention, M is a carbon or heteroatom containing group. Wherein the carbon-containing group includes, but is not limited to, methylene or methylene wherein at least one hydrogen atom is replaced by a halogen; the heteroatom is opposite to a carbon atom, preferably N, P, S or O, and further, the heteroatom-containing group includes, but is not limited to, O, S, a secondary amine group in which a hydrogen atom is substituted with a halogen, a secondary phosphine group in which a hydrogen atom is substituted with a halogen, and the like.
In the embodiment of the invention, m and n are respectively and independently selected from positive integers within 0 or 10, when m is 0, the compound I is a cyclic hydrocarbon compound containing double bonds or not containing double bonds; when m is not 0, the compound I is a saturated or unsaturated fused ring compound. It is understood that m and n may be 0 at the same time. Preferably, n is selected from 0, 1, 2 or 3; m is selected from 0, 1, 2, 3, 4, 5, 6 or 7.
As a preferred embodiment, said compound i comprises at least one of the following compounds:
in some embodiments, the electrolyte additive comprises compound i1To compound I23At least one of (1). In some test examples, any one of the compounds i listed above is added into an electrolyte of a lithium-sulfur battery, and after 50 cycles, sulfides shuttled on the surface of the separator are significantly reduced, so that the shuttle effect of polysulfides is effectively inhibited, the utilization rate of active substances is improved, and the cycle stability and the coulombic efficiency of the lithium-sulfur battery are effectively improved.
Specifically, in the embodiment of the present invention, the compound ii as an electrolyte additive has the following general formula:
Figure BDA0002180459470000082
in the inventive examples, the compound II contains double bonds or no double bonds, wherein X'1、X'2Each independently selected from H, halogen or haloalkyl, and not both H. When no carbon-carbon double bond is present in the compound II, the compound II comprisesA number of secondary carbon atoms, each of the number of secondary carbon atoms being independently substituted with one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom present in the number of secondary carbon atoms being substituted with halogen and/or haloalkyl. The secondary carbon atom refers to a carbon atom having two bonds substituted, for example, a methylene group when the secondary carbon atom is substituted with two hydrogen atoms.
It is understood that in compound ii, at least one of its hydrogen atoms is replaced by a halogen including, but not limited to, F, Cl, Br, I. When X'1Is halogen or haloalkyl, X'2May be H. Preferably, the halogen is selected from F, Cl or Br. Preferably, the haloalkyl is selected from halogen-substituted alkyl or cycloalkyl; further, the number of carbon atoms of the haloalkyl group is preferably 10 or less; further, the haloalkyl group is a fluoroalkyl group.
As a preferred embodiment, said compound ii comprises at least one of the following compounds:
in some embodiments, the electrolyte additive comprises compound ii1To compound II5At least one of; in other embodiments, the electrolyte additive comprises: compound II1To compound II5At least one of them, and a compound I1To compound I23At least one of (1).
Specifically, in the embodiment of the present invention, the compound iii as an electrolyte additive has the following general formula:
Figure BDA0002180459470000092
in the examples of the invention, the compounds III contain double bonds or no double bonds, where X "1、X”2、X”3Each independently selected from H, halogen or alkyl halideAnd not H at the same time. When no carbon-carbon double bond is present in the compound iii, the compound iii comprises a number of secondary carbon atoms, each of which is independently substituted with one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom present in the number of secondary carbon atoms is substituted with halogen and/or haloalkyl. The secondary carbon atom refers to a carbon atom having two bonds substituted, for example, a methylene group when the secondary carbon atom is substituted with two hydrogen atoms.
It is understood that in compound iii, at least one of its hydrogen atoms is replaced by a halogen including, but not limited to, F, Cl, Br, I. When X "1、X”2And X "3When one of them is halogen or haloalkyl, X "1、X”2And X "3The remainder of (a) may be H at the same time. Preferably, the halogen is selected from F, Cl or Br. Preferably, the haloalkyl is selected from halogen-substituted alkyl or cycloalkyl; further, the number of carbon atoms of the haloalkyl group is preferably 10 or less; further, the haloalkyl group is a fluoroalkyl group.
As a preferred embodiment, said compound iii comprises at least one of the following compounds:
Figure BDA0002180459470000101
in some embodiments, the electrolyte additive comprises compound iii1To compound III10At least one of; in other embodiments, the electrolyte additive comprises: III1To compound III10At least one of them, and a compound II1To compound II5At least one of; in yet another embodiment, the electrolyte additive comprises: III1To compound III10At least one of them, and a compound I1To compound I23At least one of; in yet another embodiment, the electrolyte additive comprises: III1To compound III10At least one ofSeed, compound II1To compound II5At least one of them, and a compound I1To compound I23At least one of (1).
Specifically, in the embodiment of the present invention, the compound iv as an electrolyte additive has the following general formula:
Figure BDA0002180459470000102
in the examples of the invention, the compounds IV contain double bonds or no double bonds, where X "4And X "5Each independently selected from H, halogen or haloalkyl, and not both H. When no carbon-carbon double bond exists in the compound IV, the compound IV comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl. The secondary carbon atom refers to a carbon atom having two bonds substituted, for example, a methylene group when the secondary carbon atom is substituted with two hydrogen atoms.
It is understood that in compound iv, at least one of its hydrogen atoms is replaced by a halogen including, but not limited to, F, Cl, Br, I. When X "4When it is halogen or haloalkyl, X "5May be H. Preferably, the halogen is selected from F, Cl or Br. Preferably, the haloalkyl is selected from halogen-substituted alkyl or cycloalkyl; further, the number of carbon atoms of the haloalkyl group is preferably 10 or less; further, the haloalkyl group is a fluoroalkyl group.
As a preferred embodiment, said compound iv comprises at least one of the following compounds:
in some embodiments, the electrolyte additive comprises compound iv1To chemical combinationSubstance IV5At least one of; in other embodiments, the electrolyte additive comprises: IV1To the compound IV5At least one of, and III1To compound III10At least one of (a) and/or (b) compound(s) II1To compound II5At least one of; in yet another embodiment, the electrolyte additive comprises: IV1To the compound IV5At least one of, and III1To compound III10At least one of (a) and/or (b) a compound I1To compound I23At least one of; in yet another embodiment, the electrolyte additive comprises: IV1To the compound IV5At least one member of (1), III1To compound III10At least one of (1), compound II1To compound II5At least one of them, and a compound I1To compound I23At least one of (1).
Correspondingly, a lithium ion battery electrolyte comprises: the electrolyte additive, the electrolyte and the organic solvent.
The lithium ion battery electrolyte provided by the embodiment of the invention contains the electrolyte additive, and when the electrolyte additive is applied to the preparation of a lithium sulfur battery, the shuttle effect of polysulfide can be effectively inhibited, and the electrochemical performance of the lithium sulfur battery is improved.
In an embodiment of the present invention, the electrolyte additive is used to inhibit the "shuttling effect" of polysulfides in a lithium sulfur battery, so as to improve the electrochemical performance and safety performance of the lithium sulfur battery. Preferably, the weight percentage of the lithium ion battery electrolyte additive is 0.1-50%, more preferably 1-10%, 0.5-4%, 1-3% or 2-4%, based on 100% of the total weight of the lithium ion battery electrolyte, and when the weight percentage of the lithium ion battery electrolyte additive is 0.1-1%, a thin CEI film can be formed on the surface of the battery anode, the battery capacity is high, but the battery cycle performance is poor; when the content of the electrolyte additive is 1% -10%, a stable thicker CEI film can be formed on the surface of the positive electrode, and the battery has higher capacity and excellent cycle performance; when the dosage of the electrolyte additive is 10-50%, the electrolyte has excellent flame retardant effect and good cycle performance, but the battery capacity is very low.
As a preferred embodiment, the lithium ion battery electrolyte further comprises a second additive; the second additive includes lithium nitrate, indium iodide, lithium nitride and LiAsF6To further adjust the viscosity, conductivity, passivation of oxide films, and suppression of hydrogen, etc. of the electrolyte. Further preferably, the second additive comprises lithium nitrate and/or LiAsF6Lithium nitrate can form a layer of Li-rich lithium on the surface of the lithium-sulfur battery lithium metal cathode3N, thereby improving the coulombic efficiency of the battery; LiAsF6Can form a stable CEI film on the surface of the battery anode and reduce Li2SnWhen lithium nitrate and/or LiAsF is added6The compound I, the compound II, the compound III and the compound IV are combined and added into the electrolyte to play a synergistic effect, so that the cycling stability and the coulombic efficiency of the battery can be improved.
In an embodiment of the present invention, the electrolyte functions to conduct charges, so that charged ions move in the direction of the electric field under the action of the electric field, for example, cations move to the cathode of the battery, so as to maintain the normal operation of the battery. Preferably, the electrolyte includes at least one of lithium bis (trifluoromethylsulfonyl) imide, sodium bis (trifluoromethylsulfonyl) imide, and potassium bis (trifluoromethylsulfonyl) imide, which is inexpensive and has high ionic conductivity.
In the embodiment of the present invention, the organic solvent is preferably at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene glycol dimethyl ether (DME), Ethyl Methyl Carbonate (EMC), Ethylene Carbonate (EC), methyl Propionate (PA), Propylene Sulfite (PS), 1, 3-Dioxolane (DOL), Propylene Carbonate (PC), fluoroethylene carbonate (FEC), and Vinylene Carbonate (VC). The DMC, the DEC, the DME and the EMC have lower viscosity, and the electrolyte wetting performance can be effectively improved; EC. FEC, PA, PC, PS and DOL have higher dielectric constants, and can effectively improve the ionic conductivity of the electrolyte; the FEC and the VC have good film forming characteristics and can effectively improve the cycling stability of the battery. In a preferred embodiment, the organic solvent is a mixed solvent of 1, 3-dioxolane and DME, DOL has a high dielectric constant, the ionic conductivity of the electrolyte can be effectively improved by using the electrolyte solvent, and DME has a low viscosity, and when the organic solvent is matched with DOL, the ionic conductivity of the electrolyte and the wettability of the electrolyte can be improved to a limited extent. In some embodiments, the 1, 3-dioxolane and the DME are mixed in equal volumes.
Accordingly, a lithium sulfur battery comprising: the anode, the cathode and the lithium ion battery electrolyte.
According to the lithium-sulfur battery provided by the embodiment of the invention, the electrolyte of the lithium-ion battery contains the electrolyte additive, so that the lithium-sulfur battery has excellent electrochemical performance and safety performance.
In the embodiment of the present invention, the lithium sulfur battery refers to a type of lithium ion battery in which a positive electrode material is elemental sulfur and/or a sulfur-based compound. As one embodiment, the material of the positive electrode of the lithium sulfur battery includes elemental sulfur; as another embodiment, the material of the positive electrode of the lithium sulfur battery includes a sulfur-based compound, such as a sulfur-carbon composite. In some embodiments, the positive electrode of the lithium sulfur battery is made of a mixture of elemental sulfur and ketjen black in a weight ratio of 1:3, which is effective in overcoming the disadvantage of low sulfur conductivity. In other embodiments, the negative electrode of the lithium sulfur battery is metallic lithium, metallic sodium, metallic potassium, or the like.
In order that the details of the above-described implementation and operation of the present invention will be clearly understood by those skilled in the art, and the improved performance of an electrolyte additive, an electrolyte for a lithium ion battery, and a lithium sulfur battery according to embodiments of the present invention will be apparent, the implementation of the present invention will be illustrated by the following examples.
Example 1
The lithium-sulfur battery is prepared by the embodiment, and the specific process flow is as follows:
1. preparation of the electrolyte
1, 3-Dioxolane (DOL), DME and bis (trifluoromethyl) were measured outSulfonyl) lithium imide, lithium nitrate and compound I4(ii) a Then, DOL and DME are mixed according to the equal volume, and then lithium bis (trifluoromethylsulfonyl) imide, lithium nitrate and compound I are added in sequence4And stirring uniformly.
In the electrolyte, the final concentration of lithium bis (trifluoromethylsulfonyl) imide was 1M, the final concentration of lithium nitrate was 1 wt%, and Compound I was4Is 4 wt%.
2. Preparation of lithium-sulfur Battery
Mixing sulfur and carbon black (ketjen black) in a ratio of 1:3, heating at 155 ℃ for 12 hours to obtain a C/S compound with the sulfur content of 66 wt%, mixing the compound with a 10 wt% NMP solution of PVDF, coating the mixed slurry on an aluminum foil, drying in vacuum at 60 ℃ for 12 hours, and cutting into a circular sheet with the diameter of 12mm as a button cell anode;
the diaphragm is selected as a celgard2325 type diaphragm, and the negative electrode is selected as a lithium sheet with the diameter of 16mm and the thickness of 0.4 mm; the dosage of the electrolyte is 20 mu L/mg; and assembling the positive electrode, the negative electrode, the diaphragm and the electrolyte to obtain the lithium-sulfur battery.
Comparative example 1
This comparative example provides a lithium sulfur battery that is comparable to that of example 1, except that: in the step of preparing the electrolyte, the addition of the additive compound I is omitted4；
The rest of the process is basically the same as that of embodiment 1, and the description thereof is omitted.
Test example 1
The lithium sulfur batteries prepared in example 1 and comparative example 1 were subjected to battery cycle 50 times, after which the batteries were disassembled, and surface morphology was observed from the battery separator and photographed.
Fig. 1 is an appearance of a separator of the lithium sulfur battery of comparative example 1 after 50 cycles, the separator having a yellow color derived from sulfide, and the shade of the yellow color being positively correlated with the sulfide content. In the drawing, the shade of yellow is expressed as a color transparency, and the darker the yellow, the smaller the transparency in the drawing.
FIG. 2 is a diagram of the separator after 50 cycles for the lithium sulfur battery of example 1Appearance morphology, pale yellow on the membrane, showing very little sulfide shuttling on the membrane surface of example 1 after 50 cycles, indicating addition of compound i to the electrolyte4The electrolyte additive can inhibit the shuttle effect of the lithium-sulfur battery on sulfide.
Test example 2
The lithium sulfur batteries prepared in example 1 and comparative example 1 were subjected to battery cycles of 5 times and 50 times, disassembled, and the battery anodes were taken out and observed for surface morphology using a Scanning Electron Microscope (SEM).
Fig. 3 is an SEM image of the anode after 5 cycles of the lithium sulfur battery of comparative example 1, which was found to have surface cracks and the electrode material completely exposed on the electrode surface after 5 cycles. Fig. 4 is an SEM image of the anode after 50 cycles of the lithium sulfur battery of comparative example 1, in which surface cracks are increased, compared with fig. 3.
FIG. 5 is an SEM image of the anode of the lithium sulfur battery of example 1 after 5 cycles, comparing with FIG. 3, and finding that the electrode surface has cracks, but the cracks are small, and the electrode material surface is covered with a gray-white organic electrolyte layer, the existence of which is beneficial to reduce Li2SnDissolving in the electrolyte, thereby improving the cycling stability of the battery. Fig. 6 is an SEM image of the anode of the lithium-sulfur battery of example 1 after 50 cycles, and after 50 cycles, the organic layer on the surface of the battery still exists.
In conclusion, it is shown that the addition of compound I to the electrolyte4As an electrolyte additive, the electrolyte is beneficial to keeping the battery performance stable and has better battery cycling stability.
Test example 3
The discharge capacity of the lithium sulfur batteries prepared in example 1 and comparative example 1 was measured by cycling 120 times at a current density of 0.2C (1675mAh/g), respectively, and fig. 7 is a graph showing the cycling performance of the lithium sulfur batteries of example 1 and comparative example 1 at a current density of 0.2C (1675 mAh/g).
As shown in fig. 7, the first discharge capacity of the lithium-sulfur battery of example 1 was 815mAh/g, and after 120 cycles, the battery capacity was still maintained at 680mAh/g, the capacity fade rate per cycle was 0.13%, and the battery efficiency after 120 cycles was maintained at 99%. The lithium sulfur battery of comparative example 1 had a first discharge capacity of 750mAh/g, a battery capacity of 410mAh/g after 100 cycles, a capacity fade rate of 0.45% per cycle, and a battery efficiency of 93% after 120 cycles.
In conclusion, it is shown that the addition of compound I to the electrolyte4As an electrolyte additive, the lithium-sulfur battery electrolyte can effectively improve the cycling stability and the coulombic efficiency of the lithium-sulfur battery.
Test example 4
The lithium sulfur batteries prepared in example 1 and comparative example 1 were taken and tested for their discharge performance from a gradual increase in current density from 0.1C to 1.5C and back to 0.5C.
Fig. 8 is a graph showing rate performance of the lithium-sulfur batteries of example 1 and comparative example 1, in which the specific discharge capacities of the lithium-sulfur batteries of comparative example 1 were about 794mAh/g, 549mAh/g, and 488mAh/g at current densities of 0.2C, 0.5C, and 1C, respectively, as shown in the graph. The lithium sulfur battery of example 1 had specific discharge capacities of about 898mAh/g, 738mAh/g, 663mAh/g, and 545mAh/g at current densities of 0.2C, 0.5C, 1C, and 1.5C, respectively, and the discharge capacity was restored to about 657mAh/g when the current density was returned to 1C; when the current density is recovered to 0.5C, the discharge specific capacity of the lithium ion battery is recovered to a value close to that before, and the lithium ion battery has good reversibility and stability.
Compared with the comparative example 1, the specific discharge capacity of the lithium-sulfur battery of the example 1 at the current densities of 0.2C, 0.5C and 1C is higher than that of the lithium-sulfur battery of 100-300mAh/g, which shows that the compound I is added into the electrolyte4As an electrolyte additive, the lithium-sulfur battery has better rate capacity and good reversibility and stability.
Test example 5 electrolyte ignition experiment
And taking a proper amount of the electrolyte prepared in the comparative example 1, putting the electrolyte in a stainless steel combustion vessel, carrying out an ignition experiment, and observing the combustion condition of the electrolyte. As shown in fig. 9, the electrolyte prepared in comparative example 1 exhibited a distinct flame after ignition.
An appropriate amount of the electrolyte prepared in example 1 was placed in a stainless steel burner for an ignition test, and the combustion of the electrolyte was observed. As shown in fig. 10, after ignition, the electrolyte prepared in example 1 did not burn, indicating that the electrolyte additive provided by the example of the present invention has significant flame retardant properties.
Examples 2 to 23 and comparative examples 2 to 10 provide lithium sulfur batteries having the same positive electrode material as in example 1, the remaining compositions as shown in table 1, and the corresponding cycle characteristics as shown in table 2.
TABLE 1
Figure BDA0002180459470000181
Figure BDA0002180459470000191
Figure BDA0002180459470000201
TABLE 2
Figure BDA0002180459470000202
Figure BDA0002180459470000211
Figure BDA0002180459470000221
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (10)

1. The electrolyte additive is characterized by comprising at least one of a compound I, a compound II, a compound III and a compound IV;
Figure FDA0002180459460000011
wherein, X1、X2、X3、X4、X5、X'1、X'2、X”1、X”2、X”3、X”4And X "5Each independently selected from H, halogen or haloalkyl, and X1、X2、X3、X4And X5Is not H, X at the same time'1And X'2Not simultaneously being H, X "1、X”2、X”3Not simultaneously being H, X "4And X "5Not H at the same time;
m is a carbon or heteroatom containing group;
m and n are respectively and independently selected from positive integers within 0 or 10;
when no carbon-carbon double bond exists in the compound I, the compound I comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl substituent, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl;
when no carbon-carbon double bond exists in the compound II, the compound II comprises a plurality of secondary carbon atoms, each of the plurality of secondary carbon atoms is independently substituted by one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or haloalkyl;
when no carbon-carbon double bond is present in the compound iii, the compound iii comprises a number of secondary carbon atoms, each of which is independently substituted with one or two of H, halogen and haloalkyl substitution, and at least one secondary carbon atom present in the number of secondary carbon atoms is substituted with halogen and/or haloalkyl;
when no carbon-carbon double bond exists in the compound IV, the compound IV comprises a plurality of secondary carbon atoms, the plurality of secondary carbon atoms are respectively and independently substituted by one or two of H, halogen and halogenated alkyl, and at least one secondary carbon atom in the plurality of secondary carbon atoms is substituted by halogen and/or halogenated alkyl.
2. The electrolyte additive of claim 1 wherein the heteroatom comprises N, P, S or O; and/or
The halogenated alkyl is selected from alkyl or cycloalkyl substituted by halogen; and/or
The halogen is selected from F, Cl or Br.
3. The electrolyte additive of claim 1 or 2, wherein the compound i comprises at least one of the following compounds:
Figure FDA0002180459460000021
Figure FDA0002180459460000031
4. the electrolyte additive of claim 1 or 2 wherein the compound ii comprises at least one of the following compounds:
and/or
The compound III comprises at least one of the following compounds:
Figure FDA0002180459460000033
Figure FDA0002180459460000034
and/or
The compound IV comprises at least one of the following compounds:
Figure FDA0002180459460000035
5. a lithium ion battery electrolyte, comprising: an electrolyte additive as claimed in any one of claims 1 to 4, an electrolyte, and an organic solvent.
6. The lithium ion battery electrolyte of claim 5, wherein the organic solvent comprises at least one of dimethyl carbonate, 1, 3-dioxolane, vinylene carbonate, propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene sulfite, and methyl propionate.
7. The lithium ion battery electrolyte of claim 6, wherein the organic solvent is a mixed solvent of 1, 3-dioxolane and ethylene glycol dimethyl ether.
8. The lithium ion battery electrolyte of claim 5, wherein the lithium ion battery electrolyte additive is present in an amount of 0.1% to 50% by weight, based on 100% by weight of the total lithium ion battery electrolyte; and/or
The electrolyte includes at least one of lithium bis (trifluoromethylsulfonyl) imide, sodium bis (trifluoromethylsulfonyl) imide, and potassium bis (trifluoromethylsulfonyl) imide.
9. The lithium ion battery electrolyte of claim 5, further comprising: a second additive comprising: lithium nitrateIndium iodide, lithium nitride and LiAsF6At least one of (1).
10. A lithium sulfur battery, comprising: a positive electrode, a negative electrode, and the lithium ion battery electrolyte of any of claims 5 to 9.
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