CN113506914A - Ternary lithium ion battery electrolyte and lithium ion battery containing same - Google Patents

Ternary lithium ion battery electrolyte and lithium ion battery containing same Download PDF

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CN113506914A
CN113506914A CN202110794952.5A CN202110794952A CN113506914A CN 113506914 A CN113506914 A CN 113506914A CN 202110794952 A CN202110794952 A CN 202110794952A CN 113506914 A CN113506914 A CN 113506914A
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ion battery
lithium ion
carbonate
electrolyte
ternary
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周天易
江鹏
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National Center for Nanosccience and Technology China
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National Center for Nanosccience and Technology China
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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
    • 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
    • H01M10/42—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
    • 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 provides a ternary lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The ternary lithium ion electrolyte comprises the following components: lithium salt, additive and non-aqueous solvent; the additive is selected from 2-mercaptopyridine and/or ethylene thiourea. The ternary lithium ion battery comprises a positive pole piece, a negative pole piece, a diaphragm and the ternary battery electrolyte; the diaphragm is positioned between the positive pole piece and the negative pole piece. According to the invention, 2-mercaptopyridine and/or ethylene thiourea are/is used as the additive of the electrolyte, so that the prepared electrolyte can effectively avoid corrosion and cracking of positive active substance particles in the circulation process, the circulation performance of the ternary lithium ion battery is improved, and the electrolyte provided by the invention has low production cost and is suitable for industrial production and use.

Description

Ternary lithium ion battery electrolyte and lithium ion battery containing same
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a ternary lithium ion battery electrolyte and a lithium ion battery containing the same.
Background
In recent 20 years, with the gradual exhaustion of petrochemical energy and the increasing severity of greenhouse effect, people are continuously prompted to explore sustainable and clean energy. The lithium ion battery as a novel green high-energy battery has the advantages of high working voltage, high energy density, long service life, wide working temperature range, environmental friendliness and the like, is widely applied to the fields of digital products, electric tools, electric automobiles, aerospace and the like, and attracts wide attention. At present, lithium cobaltate, lithium manganate, lithium iron phosphate and ternary cathode materials are taken as the main cathode materials of the lithium battery, wherein the ternary cathode materials are the preferred materials for preparing the lithium battery due to low price and stable performance.
Commercial layered transition metal lithium salt LiNi with increasing energy densityxCoyMn1-x-yO2The (NCM) ternary material is updated from NCM333 to NCM523, even NCM622 and NCM811 are produced on a large scale by a plurality of manufacturers. Increasing the Ni content without changing the charge cut-off voltage is one of the methods for increasing the gram capacity of a layered lithium-nickel composite oxide (so-called ternary material) because Ni2+/Ni3+Oxidation to Ni3+/Ni4+Desired potential ratio Co3+Conversion to Co4+And lower. The ternary material (nickel cobalt lithium manganate) can greatly improve the specific capacity of the material by improving the content of nickel, so that the high-nickel ternary material is inevitably an ideal material for large-scale batteries in the future.
However, as the content of nickel is continuously increased, the ternary cathode material still has many problems in circulation, such as the electrolyte is decomposed on the surface of the material under high voltage, the electrolyte and active lithium are continuously consumed, and the transition metal is dissolved out to cause phase change of the crystal structure, and the service life of the material is shortened.
At present, measures for improving the performance of a lithium ion battery taking a ternary high nickel material as a positive electrode are mainly divided into two types: one is to coat the surface of the anode material and/or dope the counter body phase to improve the stability of the anode; the other is to use electrolyte additives to improve the stability and film-forming property of the electrolyte (as reported in Gulbinska M K et al, Lithium-ion Cell Materials in Practice [ J ]. Green Energy and Technology,2014,111: 1-29), wherein the electrolyte additives can be divided into film-forming additives, low-temperature additives, safety additives, etc. according to the functional division, wherein the film-forming additives will be decomposed on the electrode surface in preference to the electrolyte bulk solvent to form a layer of solid electrolyte film (SEI on the negative electrode and CEI on the positive electrode), thereby inhibiting the decomposition of the electrolyte and protecting the electrode from HF corrosion and the like generated by the electrolyte.
CN109818063A discloses a ternary lithium ion battery non-aqueous electrolyte and a ternary lithium ion battery. The nonaqueous electrolyte comprises electrolyte lithium salt, nonaqueous organic solvent and additive, wherein the additive contains conventional negative electrode film forming additive and also contains sulfonate additive shown in structural formula 1 or/and structural formula 2:
Figure BDA0003162336840000021
the sulfonate additive can form a layer of uniform and compact protective film on the surface of the ternary material, so that corrosion of HF generated by decomposition of a basic electrolyte to NCM particles is inhibited, and cracks in the NCM particles in the circulating process are avoided, so that the circulating performance and the rate capability of the nickel ternary lithium ion battery are effectively improved.
CN109873204A discloses a ternary lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. The electrolyte comprises a non-aqueous organic solvent, lithium salt and additives, wherein the additives comprise a first type of boron-containing lithium salt additive and a second type of sulfur-containing organic additive. The first type of lithium boron salt additive is of structural formula 3 and/or structural formula 4:
Figure BDA0003162336840000031
wherein R is1、R2、R3、R4、R5、R6Independently selected from hydrogen atom, fluorine atom, alkyl with 1-4 carbon atoms, attack, alkynyl, nitrile group, fluoroalkyl and aryl, and at least one of the first additive and the second additive contains unsaturated functional group. The first type of lithium borate salt additive may participate in the formation of the positive electrode CEI film; the second sulfur-containing organic additive and the first boron-containing lithium salt additive are matched for use to realize high-nickel ternaryAnd (4) stable circulation of the lithium ion battery.
However, the synthesis of complex additive molecules like these is difficult, the preparation process is complicated, the cost is high, and the application to practical production is difficult, so that the prepared electrolyte is high in price and not beneficial to industrial production and practical use. Therefore, how to provide an electrolyte with higher cycling stability and lower production cost has become a technical problem to be solved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a ternary lithium ion battery electrolyte and a lithium ion battery containing the electrolyte. According to the invention, 2-mercaptopyridine and/or ethylene thiourea are/is used as the additive of the electrolyte, so that the prepared electrolyte can effectively avoid corrosion and cracking of positive active substance particles in the circulation process, the circulation performance of the ternary lithium ion battery is improved, and the electrolyte provided by the invention has low production cost and is suitable for industrial production and use.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a ternary lithium ion battery electrolyte, comprising the following components: lithium salt, additive and non-aqueous solvent;
the additive is selected from 2-mercaptopyridine and/or ethylene thiourea.
In the invention, 2-mercaptopyridine and/or ethylene thiourea with a conjugated structure is/are selected as an additive, so that the prepared electrolyte can effectively avoid corrosion and cracking of positive active substance particles in a circulating process, the circulating performance of the ternary lithium ion battery is improved, and the electrolyte has lower production cost and is suitable for industrial production and use.
In the invention, the 2-mercaptopyridine and the ethylene thiourea with the conjugated structure can form a stable protective layer containing cobalt sulfide on the surface of the ternary material anode during initial circulation, thereby avoiding NCM (layered transition metal lithium salt LiNi)xCoyMn1-x-yO2) The agglomerate particles are recycledCracking occurs in the process, so that the high-nickel ternary lithium ion battery has higher cycle stability.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the object and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
In a preferred embodiment of the present invention, the lithium salt is selected from any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis fluorosulfonyl imide, lithium bis trifluoromethanesulfonyl imide, and lithium perchlorate.
In a preferred embodiment of the present invention, the concentration of the lithium salt in the electrolyte of the ternary lithium ion battery is 0.5 to 5mol/L (for example, 0.5mol/L, 1mol/L, 1.5mol/L, 2mol/L, 2.5mol/L, 3mol/L, 3.5mol/L, 4mol/L, 4.5mol/L, or 5 mol/L), and preferably 1 to 3 mol/L.
In the invention, the prepared electrolyte has better circulation stability and proper viscosity by controlling the concentration of the lithium salt in a specific range. If the concentration of the lithium salt is too low, the prepared electrolyte has lower conductivity and poorer circulation stability; if the concentration of the lithium salt is too high, the viscosity of the prepared electrolyte is high, so that the wettability and the cycling stability of the electrolyte to the anode and the cathode of the battery are poor.
In a preferred embodiment of the present invention, the concentration of the additive in the electrolyte solution for a ternary lithium ion battery is 0.1 to 5mg/mL (for example, 0.1mg/mL, 0.5mg/mL, 0.8mg/mL, 1mg/mL, 1.5mg/mL, 2mg/mL, 2.5mg/mL, 3mg/mL, 3.5mg/mL, 4mg/mL, 4.5mg/mL, or 5 mg/mL), and preferably 0.5 to 2 mg/mL.
In the invention, the prepared electrolyte has better circulation stability by controlling the concentration of the additive within a specific range. If the concentration of the additive is too low, an effective CEI protective layer containing CoS is difficult to form on the surface of the positive electrode, so that the prepared ternary lithium ion battery has poor cycle stability; if the concentration of the additive is too high, the CEI protective layer formed on the surface of the positive electrode by the additive is too thick, so that the ionic conductivity is low, the additive is wasted, and the production cost is increased.
In a preferred embodiment of the present invention, the nonaqueous solvent is selected from a cyclic carbonate and/or a chain carbonate.
Preferably, the cyclic carbonate is selected from ethylene carbonate and/or propylene carbonate.
Preferably, the chain carbonate is selected from any one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate or a combination of at least two thereof.
In a preferred embodiment of the present invention, the nonaqueous solvent is one or a combination of at least two selected from the group consisting of a combination of ethylene carbonate and diethyl carbonate, a combination of ethylene carbonate and dimethyl carbonate, and a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.
Preferably, the nonaqueous solvent is a combination of ethylene carbonate and diethyl carbonate, and the volume ratio of the ethylene carbonate to the diethyl carbonate is (0.5-2): 1, and may be, for example, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, or the like, and is preferably 1: 1.
Preferably, the nonaqueous solvent is a combination of ethylene carbonate and dimethyl carbonate, and the volume ratio of the ethylene carbonate to the dimethyl carbonate is (0.5-2): 1, and may be, for example, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, or the like, and is preferably 1: 1.
Preferably, the nonaqueous solvent is a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate is (0.5-2): 1, (0.5-2), and may be, for example, 0.5:1:0.5, 0.5:1:1, 0.5:1:2, 1:1:0.5, 1:1:1, 1:1:2, 2:1:0.5, 2:1:1 or 2:1:2, and preferably 1:1: 1.
In a second aspect, the present invention provides a ternary lithium ion battery, which is characterized in that the ternary lithium ion battery comprises a positive electrode plate, a negative electrode plate, a diaphragm and the ternary battery electrolyte according to the first aspect;
the diaphragm is positioned between the positive pole piece and the negative pole piece.
As a preferred technical scheme of the invention, the positive pole piece comprises a current collector and a positive pole diaphragm which are attached to each other.
Preferably, the raw materials for preparing the positive electrode membrane comprise a positive electrode active material, a conductive agent and a binder.
In a preferred embodiment of the present invention, the positive electrode active material has a chemical formula of LiNi1-x-yCoxMnyO2Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and x + y is more than or equal to 0 and less than or equal to 1.
In the present invention, x may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc., and y may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, etc.
As a preferred technical scheme of the invention, the negative electrode material in the negative electrode plate is lithium or graphite.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, 2-mercaptopyridine and/or ethylene thiourea are/is used as the additive of the electrolyte, and the concentration of lithium salt and the additive is controlled within a specific range, so that the prepared electrolyte can effectively avoid corrosion and cracking of positive active substance particles in the circulation process, the circulation performance of the ternary lithium ion battery is greatly improved, after 200-circle circulation test, the capacity retention rate of the battery is 62.19% -89.46%, the electrolyte provided by the invention has better protection on the positive material of the battery, after 200-circle circulation test, the positive active substance particles can still keep better integrity, and meanwhile, the electrolyte provided by the invention has lower production cost and is suitable for industrial production and use.
Drawings
FIG. 1 is an SEM image of the surface of a positive electrode active material of a lithium-NCM 811 half cell assembled from the ternary lithium ion battery electrolyte provided in example 1, after 200 cycles of cycle testing, with a scale of 10 μm;
FIG. 2 is an SEM image of the surface of the positive electrode active material of a lithium-NCM 811 half cell assembled from the ternary lithium ion battery electrolyte provided in example 1, after 200 cycles of cycle testing, with a scale of 2 μm;
fig. 3 is an SEM image of the surface of the positive active material without cycle test, with a scale of 10 μm;
fig. 4 is an SEM image of the surface of the positive active material without cycle test, with a scale of 2 μm;
FIG. 5 is an SEM image of the surface of the positive electrode active material of a lithium-NCM 811 half cell assembled from the ternary lithium ion battery electrolyte provided in comparative example 1, after 200 cycles of cycle testing, with a scale of 10 μm;
FIG. 6 is an SEM image of the surface of the active material of the positive electrode of the half-cell, which is assembled into a lithium-NCM 811 half-cell by the ternary lithium ion battery electrolyte provided in comparative example 1, after 200 cycles of cycle test, and the scale is 2 μm;
FIG. 7 is a graph of cycle performance of the ternary lithium ion battery electrolytes provided in example 1 and comparative example 1;
FIG. 8 is a graph showing the results of XPS testing of the surface of the positive active material of a lithium-NCM 811 half-cell assembled from the ternary lithium ion battery electrolyte provided in example 1, after 200 cycles of cycling;
fig. 9 is a graph showing the results of XPS testing on the surface of the positive electrode active material of a lithium-NCM 811 half-cell assembled from the ternary lithium ion battery electrolyte provided in example 1, after 200 cycles of cycling.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. 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 limitations of the present invention.
Example 1
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium hexafluorophosphate, ethylene thiourea, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate;
the concentration of lithium hexafluorophosphate in the electrolyte of the ternary lithium ion battery is 1mol/L, the concentration of ethylene thiourea is 0.5mg/mL, and the volume ratio of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate is 1:1: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing lithium hexafluorophosphate, ethylene thiourea, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Assembling the ternary lithium ion battery electrolyte into a lithium-NCM 811 half-battery, performing a cycle performance test under the charge-discharge rate of 1C, performing a cycle test for 200 circles, and then testing the surface of the positive active material of the half-battery by using a scanning electron microscope, wherein the test structure is shown in fig. 1 and 2; meanwhile, the NCM811 ternary material which is not subjected to the cycle performance test is tested by using a scanning electron microscope, and the test results are shown in FIGS. 3 and 4, and can be seen from comparison between FIGS. 1-2 and 3-4: after 200 cycles of the test, the positive active material particles still have better integrity, which indicates that the electrolyte provided in example 1 has better protection effect on the positive active material.
Example 2
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the difference from the embodiment 1 is only that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 0.1mg/mL, and other conditions are the same as the embodiment 1.
Example 3
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the difference from the embodiment 1 is only that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 0.2mg/mL, and other conditions are the same as the embodiment 1.
Example 4
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the difference from the embodiment 1 is only that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 1.0mg/mL, and other conditions are the same as the embodiment 1.
Example 5
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the difference from the embodiment 1 is only that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 2.0mg/mL, and other conditions are the same as the embodiment 1.
Example 6
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the ternary lithium ion battery electrolyte is only different from the embodiment 1 in that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 5.0mg/mL, and other conditions are the same as those in the embodiment 1.
Example 7
This example provides a ternary lithium ion battery electrolyte and a method for preparing the same, which is different from example 1 only in that lithium hexafluorophosphate is replaced by lithium tetrafluoroborate, and other conditions are the same as example 1.
Example 8
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium bis (fluorosulfonyl) imide, ethylene thiourea and ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate;
the concentration of the lithium bis (fluorosulfonyl) imide in the electrolyte of the ternary lithium ion battery is 1mol/L, the concentration of ethylene thiourea is 1mg/mL, and the volume ratio of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate is 1:1: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing the lithium bis (fluorosulfonyl) imide, ethylene thiourea, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 9
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium bistrifluoromethanesulfonimide, ethylene thiourea and ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate;
the concentration of lithium bistrifluoromethanesulfonylimide in the electrolyte of the ternary lithium ion battery is 1mol/L, the concentration of ethylene thiourea is 0.5mg/mL, and the volume ratio of ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate is 1:1: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing the lithium bistrifluoromethane sulfonyl imide, the ethylene thiourea, the ethylene carbonate, the dimethyl carbonate and the methyl ethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 10
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium perchlorate, 2-mercaptopyridine, ethylene carbonate and diethyl carbonate;
the concentration of lithium perchlorate in the electrolyte of the ternary lithium ion battery is 3 mol/L; the concentration of 2-mercaptopyridine was 0.5mg/mL, and the volume ratio of ethylene carbonate to diethyl carbonate was 1: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing the lithium perchlorate, the 2-mercaptopyridine, the ethylene carbonate and the diethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 11
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium hexafluorophosphate, 2-mercaptopyridine, ethylene carbonate and dimethyl carbonate;
the concentration of lithium hexafluorophosphate in the electrolyte of the ternary lithium ion battery is 5mol/L, the concentration of 2-mercaptopyridine is 0.2mg/mL, and the volume ratio of ethylene carbonate to dimethyl carbonate is 1: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing lithium hexafluorophosphate, 2-mercaptopyridine, ethylene carbonate and dimethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 12
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium tetrafluoroborate, 2-mercaptopyridine, ethylene carbonate, and dimethyl carbonate;
the concentration of lithium tetrafluoroborate in the electrolyte of the ternary lithium ion battery is 5mol/L, the concentration of 2-mercaptopyridine is 0.7mg/mL, and the volume ratio of ethylene carbonate to dimethyl carbonate is 0.5: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing lithium tetrafluoroborate, 2-mercaptopyridine, ethylene carbonate and dimethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 13
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium bis (fluorosulfonyl) imide, 2-mercaptopyridine, ethylenethiourea, ethylene carbonate and dimethyl carbonate;
the concentration of the lithium bis (fluorosulfonyl) imide in the electrolyte of the ternary lithium ion battery is 3mol/L, the concentration of 2-mercaptopyridine is 1mg/mL, the concentration of ethylene thiourea is 1mg/mL, and the volume ratio of ethylene carbonate to dimethyl carbonate is 2: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing the lithium bis (fluorosulfonyl) imide, 2-mercaptopyridine, ethylene carbonate and dimethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 14
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, wherein the ternary lithium ion battery electrolyte comprises the following components: lithium bistrifluoromethanesulfonimide, 2-mercaptopyridine, ethylene carbonate and diethyl carbonate;
the concentration of the lithium bis (fluorosulfonyl) imide in the electrolyte of the ternary lithium ion battery is 2mol/L, the concentration of 2-mercaptopyridine is 2mg/mL, and the volume ratio of ethylene carbonate to diethyl carbonate is 2: 1.
The preparation method of the ternary lithium ion battery electrolyte comprises the following steps:
and uniformly mixing the lithium bis (fluorosulfonyl) imide, 2-mercaptopyridine, ethylene carbonate and dimethyl carbonate to obtain the ternary lithium ion battery electrolyte.
Example 15
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the difference from the embodiment 1 is only that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 0.05mg/mL, and other conditions are the same as the embodiment 1.
Example 16
The embodiment provides a ternary lithium ion battery electrolyte and a preparation method thereof, and the ternary lithium ion battery electrolyte is only different from the embodiment 1 in that the concentration of ethylene thiourea in the ternary lithium ion battery electrolyte is 7mg/mL, and other conditions are the same as those in the embodiment 1.
Comparative example 1
The comparative example provides a ternary lithium ion battery electrolyte and a preparation method thereof, and only differs from example 1 in that the ternary lithium ion battery electrolyte does not contain ethylene thiourea, and other conditions are the same as those in example 1.
Assembling the ternary lithium ion battery electrolyte into a lithium-NCM 811 half-battery, performing a cycle performance test under a charge-discharge rate of 1C, performing a cycle test for 200 circles, and then testing the surface of the positive electrode material of the half-battery by using a scanning electron microscope, wherein the test structure is shown in fig. 5 and 6, and can be known from fig. 5 and 6: after 200 cycles of the cycle test, the positive active material particles are cracked, and the original appearance of the positive active material particles cannot be maintained.
The ternary lithium ion battery electrolytes provided in example 1 and the comparative example are respectively assembled into lithium-NCM 811 half batteries, and a cycle performance test is performed at a charge-discharge rate of 1C, wherein a cycle performance curve is shown in fig. 7, and as can be seen from fig. 7, the use of the additive can enable the batteries to have high specific capacity.
The ternary lithium ion battery electrolytes provided in example 1 and comparative example are respectively assembled into a lithium-NCM 811 half-battery, and after a first cycle test is performed at a charge-discharge rate of 1C, an XPS test is performed on the surface of a positive electrode plate of the lithium-NCM 811 half-battery, and the test results are shown in fig. 8 and 9, wherein fig. 8 is a test result diagram of the XPS test performed on the surface of the positive electrode plate after the first cycle test is performed on the lithium-NCM 811 half-battery assembled from the ternary lithium ion battery electrolyte of example 1, and fig. 9 is a test result diagram of the XPS test performed on the surface of the positive electrode plate after the first cycle test is performed on the lithium-NCM 811 half-battery assembled from the ternary lithium ion battery electrolyte of comparative example 1. As is clear from fig. 8, the positive electrode material of example 1 had a metal sulfide component on the surface, and was assumed to be a cobalt sulfide, and as is clear from fig. 9, the positive electrode material of comparative example 1 had no metal sulfide signal on the surface.
Comparative example 2
The comparative example provides a ternary lithium ion battery electrolyte and a preparation method thereof, and only differs from example 7 in that the ternary lithium ion battery electrolyte does not contain ethylene thiourea, and other conditions are the same as those in example 7.
Comparative example 3
The comparative example provides a ternary lithium ion battery electrolyte and a preparation method thereof, and only differs from example 9 in that the ternary lithium ion battery electrolyte does not contain ethylene thiourea, and other conditions are the same as those in example 9.
Comparative example 4
The present comparative example provides a ternary lithium ion battery electrolyte and a method for preparing the same, which is different from example 1 only in that thioethyleneurea is replaced with thiophenol, and other conditions are the same as example 1.
The performance of the ternary lithium ion battery electrolyte provided by the above examples and comparative examples was tested, the test method was as follows:
capacity retention ratio: the ternary lithium ion battery electrolytes provided in examples 1 to 16 and comparative examples 1 to 4 were assembled into a lithium-NCM 811 half-cell using lithium as a negative electrode and NCM811 aggregate as a positive electrode active material, and the cell was subjected to a charge and discharge test under the following test conditions: a blue battery test system is adopted to carry out 200-circle charge-discharge cycle test, the charge-discharge multiplying power is 1C, and the test temperature is controlled at 25 ℃;
integrity of positive electrode active material: the positive active material subjected to the 200-circle cycle test is tested by adopting a Hitachi S-4800 scanning electron microscope produced by Hitachi, and the surface morphology of the positive active material is observed and evaluated, wherein the evaluation standard is as follows: very good: the aggregate is complete and has no fragmentation; o: the aggregate is complete with tiny cracks; x: the agglomerates had significant cracking and chipping.
The results of the above tests are shown in table 1 below:
TABLE 1
Figure BDA0003162336840000141
As can be seen from table 1, the electrolyte prepared by using 2-mercaptopyridine and/or ethylenethiourea as an additive of the electrolyte and controlling the concentrations of the lithium salt and the additive within a specific range can effectively avoid corrosion and cracking of positive active material particles in a circulation process, and improve the cycle performance of the ternary lithium ion battery, and after a 200-cycle test, the battery capacity retention rate is 62.19% -89.46%, and the electrolyte provided by the invention has good protection on a battery positive material, and after the 200-cycle test, the positive active material particles can still maintain good integrity, and meanwhile, the electrolyte provided by the invention has low production cost and is suitable for industrial production and use.
Compared with example 1, if the concentration of the additive is too low (example 15), an effective CEI protective layer containing CoS is difficult to form on the surface of the positive electrode, and thus the prepared ternary lithium ion battery has poor cycle stability; if the concentration of the additive is too high (example 16), the CEI protective layer formed on the surface of the positive electrode by the additive is too thick, resulting in low ionic conductivity. Therefore, the electrolyte prepared by the method has better circulation stability by controlling the content of the additive in a specific range.
Compared with examples 1, 7 and 9, if no additive is added into the electrolyte (comparative examples 1-3), the prepared electrolyte has poor cycle performance, the capacity retention rate of the battery is 47.85-55.92% after 200 cycles of cycle test, and the positive active material particles have obvious cracks and are broken after 200 cycles of cycle test; compared with example 1, if other additives are used (comparative example 4), the prepared electrolyte has poor cycle performance, the battery capacity retention rate is only 58.20% after 200 cycles of test, and the positive electrode active material particles have obvious cracks and are broken after 200 cycles of test. Therefore, the electrolyte prepared by selecting 2-mercaptopyridine and/or ethylene thiourea as the additive of the electrolyte has good cycle performance and good protection on the cathode material.
In conclusion, the electrolyte prepared by adopting the 2-mercaptopyridine and/or the ethylene thiourea as the additive of the electrolyte and controlling the concentrations of the lithium salt and the additive within a specific range can effectively avoid the corrosion and cracking of positive active material particles in the circulation process and improve the circulation performance of the ternary lithium ion battery.
The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must be implemented depending on the above detailed structural features. It should be understood by those skilled in the art that any modifications of the present invention, equivalent substitutions of selected components of the present invention, additions of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (10)

1. The ternary lithium ion battery electrolyte is characterized by comprising the following components: lithium salt, additive and non-aqueous solvent;
the additive is selected from 2-mercaptopyridine and/or ethylene thiourea.
2. The ternary lithium ion battery electrolyte of claim 1, wherein the lithium salt is selected from any one or a combination of at least two of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis fluorosulfonylimide, lithium bis trifluoromethanesulfonylimide, or lithium perchlorate.
3. The ternary lithium ion battery electrolyte according to claim 1 or 2, wherein the concentration of the lithium salt in the ternary lithium ion battery electrolyte is 0.5-5 mol/L, preferably 1-3 mol/L.
4. The ternary lithium ion battery electrolyte according to any one of claims 1 to 3, wherein the concentration of the additive in the ternary lithium ion battery electrolyte is 0.1 to 5mg/mL, preferably 0.5 to 2 mg/mL.
5. The ternary lithium ion battery electrolyte of any one of claims 1 to 4 wherein the non-aqueous solvent is selected from cyclic carbonates and/or chain carbonates;
preferably, the cyclic carbonate is selected from ethylene carbonate and/or propylene carbonate;
preferably, the chain carbonate is selected from any one of dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate or a combination of at least two thereof.
6. The ternary lithium ion battery electrolyte of claim 5, wherein the nonaqueous solvent is selected from any one or a combination of at least two of a combination of ethylene carbonate and diethyl carbonate, a combination of ethylene carbonate and dimethyl carbonate, and ethyl methyl carbonate;
preferably, the non-aqueous solvent is a combination of ethylene carbonate and diethyl carbonate, and the volume ratio of the ethylene carbonate to the diethyl carbonate is (0.5-2): 1, preferably 1: 1;
preferably, the non-aqueous solvent is a combination of ethylene carbonate and dimethyl carbonate, and the volume ratio of the ethylene carbonate to the dimethyl carbonate is (0.5-2): 1, preferably 1: 1;
preferably, the non-aqueous solvent is a combination of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, and the volume ratio of the ethylene carbonate, the dimethyl carbonate and the ethyl methyl carbonate is (0.5-2): 1, (0.5-2), and preferably 1:1: 1.
7. A ternary lithium ion battery, characterized in that the ternary lithium ion battery comprises a positive electrode plate, a negative electrode plate, a diaphragm and the ternary battery electrolyte of any one of claims 1-6;
the diaphragm is positioned between the positive pole piece and the negative pole piece.
8. The ternary lithium ion battery of claim 7, wherein the positive electrode sheet comprises a current collector and a positive electrode membrane which are attached to each other;
preferably, the raw materials for preparing the positive electrode membrane comprise a positive electrode active material, a conductive agent and a binder.
9. The ternary lithium ion battery according to claim 8, wherein the chemical formula of the positive electrode active material is LiNi1-x-yCoxMnyO2Wherein x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, and x + y is more than or equal to 0 and less than or equal to 1.
10. The ternary lithium ion battery according to any one of claims 7 to 9, wherein the negative electrode material in the negative electrode sheet is lithium or graphite.
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