CN108539273B - Novel lithium secondary battery electrolyte and lithium secondary battery - Google Patents
Novel lithium secondary battery electrolyte and lithium secondary battery Download PDFInfo
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- CN108539273B CN108539273B CN201810344764.0A CN201810344764A CN108539273B CN 108539273 B CN108539273 B CN 108539273B CN 201810344764 A CN201810344764 A CN 201810344764A CN 108539273 B CN108539273 B CN 108539273B
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0568—Liquid materials characterised by the solutes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
- H01M10/0566—Liquid materials
- H01M10/0569—Liquid materials characterised by the solvents
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- 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 relates to the technical field of lithium secondary batteries, and discloses a novel lithium secondary battery electrolyte and a lithium secondary battery. The electrolyte consists of an additive A, an additive B, an organic solvent and a conductive lithium salt. The additive A is at least one of maleic anhydride and methylene methanedisulfonate; the additive B is at least one of tri (fluoromethyl) borate and tri (trisperfluoromethylsilane) borate. After the additive is used for the electrolyte of the lithium secondary battery, the stability of the lithium secondary battery can be improved, and the interface impedance is reduced, so that the cycle stability and the high and low temperature performance of the lithium secondary battery are improved; the gas generation caused by the decomposition of the organic solvent can be inhibited, and the expansion of the battery can be reduced. In addition, the invention also discloses a synthesis method of the tri (fluoromethyl) borate and the tri (trisperfluoromethylsilane) borate.
Description
Technical Field
The invention relates to the technical field of lithium secondary batteries, in particular to a novel lithium secondary battery electrolyte and a lithium secondary battery.
Background
The lithium secondary battery has been widely used in the fields of new energy electric vehicles, portable electronic products such as cameras, digital video cameras, mobile phones, notebook computers, and the like, due to its characteristics of large energy density, high operating voltage, long service life, environmental protection, and the like. The lithium secondary battery is mainly composed of a positive electrode, a negative electrode, an electrolyte and a diaphragm. The electrolyte is one of the key materials of the lithium secondary battery, plays a role in transferring lithium ions between the positive electrode and the negative electrode in the battery, and is a guarantee for the lithium secondary battery to obtain the advantages of high energy, long circulation, large multiplying power, safety and the like. At present, the electrolyte of the lithium secondary battery mainly consists of three parts, namely an organic solvent, lithium salt and an additive. The organic solvent is usually a mixture of cyclic esters (such as ethylene carbonate, propylene carbonate) and chain esters (such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate); lithium salt is generally prepared by adopting commercial lithium hexafluorophosphate as a conductive salt; the additive is widely varied and generally selected according to different use purposes, and the proportion of the additive in the electrolyte is small, but the additive is widely researched and developed due to obvious functions.
The film-forming additive is one of the important components of the electrolyte additive for lithium secondary batteries. The excellent film-forming additive can form a protective film on the surface of the electrode, the protective film is insoluble in an organic solvent, lithium ions are allowed to be freely inserted into and extracted from the electrode, solvent molecules are not allowed to pass through, and the damage of the further reaction of the organic electrolyte and the electrode to the electrode can be effectively prevented, so that the normal-temperature cycle performance and the high-temperature and low-temperature performance of the battery are improved.
A great deal of research has been conducted on film-forming additives. An electrolyte for lithium ion battery (CN201310624603) discloses application of film-forming additives of lithium bis (fluorosulfonyl) imide, fluoroethylene carbonate and triallyl phosphate to ternary LiNi0.5Co0.2Mn0.3O2On the natural graphite battery, the low-temperature discharge efficiency and the high-temperature cycle performance of the battery can be effectively improved. A non-aqueous electrolyte for lithium ion batteries and a corresponding lithium ion battery (CN201310038377) disclose that a film-forming additive containing an unsaturated phosphite compound can improve the high-temperature storage performance and the cycle performance of the battery. However, it can be seen from these two patents that the film-forming additive can only improve one or two of the normal temperature cycle performance, the high temperature performance and the low temperature performance of the battery, so it is of great significance to develop an electrolyte formula capable of simultaneously improving the normal temperature cycle performance, the high temperature performance and the low temperature performance by using the combined use method of the additives and utilizing the advantages of different additives.
The application mainly discloses a lithium secondary battery electrolyte formula capable of improving normal-temperature circulation and high-low temperature performance at the same time.
Disclosure of Invention
The invention provides a novel electrolyte of a lithium secondary battery, and further provides a lithium secondary battery comprising the electrolyte. In addition, the invention also provides a method for synthesizing the lithium secondary battery electrolyte additive tri (fluoromethyl) borate and tri (perfluoromethylsilane) borate.
The synthesis method of the tri (fluoromethyl) borate additive comprises the following steps: under the action of fluorine gas atmosphere and cobalt trioxide as a catalyst, trimethyl borate is added at the temperature of 200-220 ℃ to be completely converted into tri (fluoromethyl) borate. The remaining fluorine gas reacts with sulfur to produce sulfur hexafluoride (SF)6) And then discharged to remove the fluorine gas remaining in the reactor.
The synthesis method of the tris (trisperfluoromethylsilane) borate additive comprises the following steps: under the action of a fluorine gas atmosphere and cobalt trioxide as a catalyst, adding tris (trimethylsilane) borate at the temperature of 300-350 ℃ to convert all the tris (perfluoromethylsilane) borate into tris (perfluoromethylsilane). The remaining fluorine gas reacts with sulfur to produce sulfur hexafluoride (SF)6) And then discharged to remove the fluorine gas remaining in the reactor.
The specific scheme of the invention is as follows: the electrolyte of the lithium secondary battery consists of an additive A, an additive B, an organic solvent and a conductive lithium salt, wherein the additive A is at least one of maleic anhydride and methylene methanedisulfonate; the additive B is at least one of tri (fluoromethyl) borate and tri (trisperfluoromethylsilane) borate. (ii) a
The tris (fluoromethyl) borate ester has the following structural formula:
the tris (trisperfluoromethylsilane) borate has the following structural formula:
in the above-mentioned electrolyte solution for a lithium secondary battery, the additive B is used in an amount of 0.5 to 3.0% by mass based on the total mass of the electrolyte solution for a lithium secondary battery.
In the above-described electrolyte solution for a lithium secondary battery, the organic solvent includes at least one of a cyclic ester and a chain ester.
In the above electrolyte for a lithium secondary battery, the organic solvent is a cyclic ester: the mass ratio of the chain ester is 1: (1-3).
In the above electrolyte for a lithium secondary battery, the cyclic ester is at least one of ethylene carbonate, propylene carbonate, γ -butyrolactone and γ -valerolactone; the chain ester is at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate and methyl propyl carbonate.
In the above electrolyte for a lithium secondary battery, the conductive lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate, lithium difluorooxalate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium hexafluoroarsenate and lithium bistrifluoromethylsulfonyl imide; the concentration of the conductive lithium salt in the organic solvent is 15.0-20.0%.
The invention also discloses a lithium ion battery, which comprises a positive electrode, a negative electrode and the lithium ion electrolyte, wherein: the positive electrode material is selected from transition metal oxide of lithium, wherein the transition metal oxide of lithium is LiCoO2、LiMn2O4、LiMnO2、Li2MnO4、LiFePO4、Li1+aMn1-xMxO2、LiCo1-xMxO2、LiFe1-xMxPO4、 Li2Mn1-xO4Wherein M is one or more selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, and a is more than or equal to 0<0.2，0≤x<1; the negative electrode material is selected from at least one of graphite, silicon-carbon composite material and lithium titanate.
Compared with the prior art, the invention has the following advantages and effects:
the electrolyte of the invention can improve the electrode/electrolyte interface property of the lithium secondary battery, improve the stability of the electrolyte and reduce the interface impedance by adding at least one additive A and at least one additive B, thereby improving the cycle stability and high and low temperature performance of the lithium secondary battery.
In the electrolyte of the present invention, by adding at least one of the additives a and at least one of the additives B, gas generation due to decomposition of the organic solvent can be suppressed, and swelling of the battery can be reduced.
Detailed Description
The invention will now be further described with reference to the following examples, which are not to be construed as limiting the invention in any way, and any limited number of modifications which can be made within the scope of the claims of the invention are still within the scope of the claims of the invention.
Examples 1 to 1
(1) Mixing cyclic ester Ethylene Carbonate (EC), chain ester Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to the mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 15.0% of conductive lithium salt lithium hexafluorophosphate in mass fraction in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding maleic anhydride in the additive A and tri (fluoromethyl) borate in the additive B into the base electrolyte prepared in the step (2), wherein the use amounts of the maleic anhydride and the tri (fluoromethyl) borate in the additive A are respectively 0.5% and 0.5% of the mass of the electrolyte, and thus obtaining the electrolyte for the lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Graphite pouch cell, test LiNi0.5Co0.2Mn0.3O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 2
(1) Mixing cyclic ester Ethylene Carbonate (EC), chain ester Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to the mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 18.0% of conductive lithium salt lithium hexafluorophosphate in mass fraction in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding methylene methanedisulfonate in the additive A and tri (fluoromethyl) borate in the additive B into the base electrolyte prepared in the step (2), wherein the dosages of the methylene methanedisulfonate in the additive A and the tris (fluoromethyl) borate in the additive B are respectively 0.5% and 1.0% of the mass of the electrolyte, and thus obtaining the electrolyte for the lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Silicon-carbon soft-package battery, testing LiNi0.5Co0.2Mn0.3O2The silicon-carbon soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 3
(1) Mixing cyclic ester Ethylene Carbonate (EC), chain ester Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to the mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 20.0% of conductive lithium salt lithium hexafluorophosphate in mass fraction in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding maleic anhydride, methylene methanedisulfonate in the additive A and tri (fluoromethyl) borate in the additive B into the base electrolyte prepared in the step (2), wherein the use amounts of the maleic anhydride, the methylene methanedisulfonate and the tri (fluoromethyl) borate in the additive B are respectively 0.5%, 0.5% and 2.0% of the mass of the electrolyte, so as to obtain the electrolyte for the lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Lithium titanate pouch cell, test LiNi0.5Co0.2Mn0.3O2The lithium titanate soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 4
(1) Mixing cyclic ester Ethylene Carbonate (EC), chain ester Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to the mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 15.0% of conductive lithium salt lithium hexafluorophosphate in mass fraction in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding maleic anhydride and methylene methanedisulfonate in the additive A, and tris (perfluoromethylsilane) borate and tris (fluoromethyl) borate in the additive B into the base electrolyte prepared in the step (2), wherein the use amounts of the maleic anhydride, the methylene methanedisulfonate, the tris (perfluoromethylsilane) borate and the tris (fluoromethyl) borate in the additive B are respectively 0.5%, 1.0% and 2.0% of the mass of the electrolyte, so as to obtain an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Graphite pouch cell, test LiNi0.5Co0.2Mn0.3O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 5
(1) Mixing cyclic ester Ethylene Carbonate (EC) and chain ester dimethyl carbonate (DMC) according to a mass ratio of EC to DMC of 2 to 3 at room temperature;
(2) dissolving a conductive lithium salt lithium hexafluoroarsenate with the mass fraction of 15.0% in the solvent obtained in the step (1) at room temperature, and uniformly stirring to prepare a basic electrolyte;
(3) adding maleic anhydride in the additive A and tris (trisperfluoromethylsilane) borate in the additive B into the base electrolyte prepared in the step (2) respectively in an amount of 0.5% and 1.0% of the mass of the electrolyte to obtain an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Graphite pouch cell, test LiNi0.5Co0.2Mn0.3O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 6
(1) Mixing cyclic ester Ethylene Carbonate (EC) and chain ester dimethyl carbonate (DMC) according to a mass ratio of EC to DMC of 1 to 3 at room temperature;
(2) dissolving 15.0 mass percent of conductive lithium salt lithium bistrifluoromethylsulfonyl imide into the solvent obtained in the step (1) at room temperature, and uniformly stirring to prepare a basic electrolyte;
(3) adding methylene methanedisulfonate in the additive A and the tris (trisperfluoromethylsilane) borate in the additive B into the base electrolyte prepared in the step (2) respectively in an amount of 0.5% and 1.0% of the mass of the electrolyte to obtain an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Graphite pouch cell, test LiNi0.5Co0.2Mn0.3O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 7
(1) Mixing cyclic ester Ethylene Carbonate (EC) and chain carbonate dimethyl carbonate (DMC) according to the mass ratio of EC to DMC which is 1 to 1;
(2) under the condition of room temperature, dissolving conductive lithium salt lithium perchlorate with the mass fraction of 15.0 percent in the solvent obtained in the step (1), and uniformly stirring to prepare a basic electrolyte;
(3) adding maleic anhydride, methylene methanedisulfonate in the additive A and tris (trisperfluoromethylsilane) borate in the additive B into the base electrolyte prepared in the step (2), wherein the dosage of the maleic anhydride, the methylene methanedisulfonate and the tris (trisperfluoromethylsilane) borate in the additive B are respectively 0.5%, 0.5% and 1.0% of the mass of the electrolyte; obtaining an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.5Co0.2Mn0.3O2Graphite pouch cell, test LiNi0.5Co0.2Mn0.3O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 8
(1) Mixing a cyclic ester solvent of Ethylene Carbonate (EC), chain ester of Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to a mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 15% by mass of conductive lithium salt lithium hexafluorophosphate in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding maleic anhydride in the additive A, and tris (fluoromethyl) borate and tris (perfluoromethylsilane) borate in the additive B into the base electrolyte prepared in the step (2), wherein the amounts of the maleic anhydride, the tris (fluoromethyl) borate and the tris (perfluoromethylsilane) borate are respectively 0.5%, 0.5% and 1.0% of the mass of the electrolyte, to obtain an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.8Co0.1Mn0.1O2Graphite pouch cell, test LiNi0.8Co0.1Mn0.1O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Examples 1 to 9
(1) Mixing cyclic ester Ethylene Carbonate (EC) and chain carbonate solvent Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) according to the mass ratio of EC to EMC to DMC of 3 to 5 to 2 at room temperature;
(2) dissolving 15% conductive lithium salt LiPF6 in the solvent obtained in the step (1) at room temperature, and uniformly stirring to obtain a basic electrolyte;
(3) adding methylene methanedisulfonate in the additive A, tri (fluoromethyl) borate and tri (perfluoromethylsilane) borate in the additive B into the base electrolyte prepared in the step (2), wherein the use amounts of the methylene methanedisulfonate in the additive A, the tri (fluoromethyl) borate and the tri (perfluoromethylsilane) borate in the additive B are respectively 0.5%, 0.5% and 1.0% of the mass of the electrolyte, and thus obtaining an electrolyte for a lithium secondary battery;
(4) the electrolyte obtained in this example was used for LiNi0.8Co0.15Al0.05O2Graphite pouch cell, test LiNi0.8Co0.15Al0.05O2The graphite soft package battery has the charge-discharge cycle performance, high-temperature performance and low-temperature performance of 3.0-4.35V at the multiplying power of 1C in a normal temperature environment.
Comparative examples 1 to 1
The procedure of example 1-1 was repeated except that maleic anhydride was not added to the electrolyte.
Comparative examples 1 to 2
The electrolyte was the same as in example 1-2 except that methyl methanedisulfonate was not added.
Comparative examples 1 to 3
The electrolyte was the same as in examples 1 to 3 except that tris (fluoromethyl) borate was not added.
Comparative examples 1 to 4
The electrolyte was the same as in examples 1 to 4 except that maleic anhydride and methylene methanedisulfonate were not added.
Comparative examples 1 to 5
The electrolyte was the same as in examples 1 to 4 except that tris (fluoromethyl) borate and tris (trisperfluoromethylsilane) borate were not added.
Comparative examples 1 to 6
The electrolyte was the same as examples 1 to 5 except that maleic anhydride was not added.
Comparative examples 1 to 7
The electrolyte was the same as examples 1 to 6 except that methyl methanedisulfonate was not added.
Comparative examples 1 to 8
The electrolyte was the same as in examples 1 to 7 except that tris (trifluoromethylsilane) borate was not added.
Comparative examples 1 to 9
The electrolyte was the same as in examples 1 to 8 except that tris (fluoromethyl) borate and tris (trisperfluoromethylsilane) borate were not added.
Comparative examples 1 to 10
The electrolyte was the same as examples 1 to 9 except that tris (fluoromethyl) borate and tris (trisperfluoromethylsilane) borate were not added.
And (3) cycle experiment: the batteries obtained in examples 1-1 to 1-9 and comparative examples 1-1 to 1-10 were subjected to a charge-discharge cycle test at 25 ℃ and at a charge-discharge rate of 1C, and the 600 th cycle discharge capacity was divided by the first cycle discharge capacity to obtain a capacity retention rate, and the results are shown in tables 1 and 2.
High temperature experiment: the batteries obtained in examples 1-1 to 1-9 and comparative examples 1-1 to 1-10 were subjected to a charge-discharge cycle test at a charge-discharge rate of 1C at 45 ℃ and the capacity retention ratio was obtained by recording the 600 th cycle discharge capacity divided by the first cycle discharge capacity. The results are reported in tables 1 and 2.
The batteries obtained in examples 1-1 to 1-9 and comparative examples 1-1 to 1-10 were cycled 3 times at a charge/discharge rate of 1C, stored at 60 ℃ for 7 days in a fully charged state, and then subjected to a discharge test, and the obtained discharge capacity was divided by the discharge capacity of the first cycle to obtain the capacity retention rate after high-temperature storage, and the results are shown in tables 1 and 2.
The calculation method of the expansion rate of the battery after high-temperature storage is as follows:
wherein T is the thickness of the battery after high-temperature storage, T0Is the cell thickness before high temperature storage. The results of the lithium ion battery test section are shown in tables 1 and 2.
Low-temperature experiment: after cycling the batteries obtained in examples 1-1 to 1-9 and comparative examples 1-1 to 1-10 at a charge-discharge rate of 1C for 3 times, a low-temperature discharge test at-20 ℃ and 0.2C was performed in a full-charge state, and the obtained discharge capacity was divided by the discharge capacity of the first cycle to obtain the capacity retention rate of low-temperature discharge, and the results are shown in tables 1 and 2.
Table 1 test results of examples 1-1 to 1-9 and comparative examples 1-1 to 1-10:
it is apparent from the above data that additive a has a significant effect on the cycle performance, high-temperature performance and gassing inhibition of the lithium secondary battery, while additive B has a positive effect on its low-temperature performance. Therefore, the two are combined to combine the advantages of the two, so that the lithium secondary battery has better performance. Therefore, the formula of the lithium secondary battery electrolyte containing the lithium secondary battery electrolyte has extremely high market value and social benefit.
Claims (6)
1. The electrolyte of the lithium secondary battery is characterized by comprising an additive A, an additive B, an organic solvent and a conductive lithium salt, wherein the additive A is methylene methanedisulfonate or a combination of the methylene methanedisulfonate and maleic anhydride; the additive B is at least one of tri (fluoromethyl) borate and tri (trisperfluoromethylsilane) borate;
the tris (fluoromethyl) borate ester has the following structural formula:
the tris (trisperfluoromethylsilane) borate has the following structural formula:
the additive A is methylene methanedisulfonate accounting for 0.5% of the mass of the electrolyte, and the additive B is tri (fluoromethyl) borate accounting for 1% of the mass of the electrolyte;
or, the additive A is maleic anhydride equivalent to 0.5% of the electrolyte mass and methylene methanedisulfonate equivalent to 0.5% of the electrolyte mass, and the additive B is tris (fluoromethyl) borate equivalent to 2% of the electrolyte mass;
or, the additive A is maleic anhydride equivalent to 0.5 percent of the mass of the electrolyte and methylene methanedisulfonate equivalent to 0.5 percent of the mass of the electrolyte, and the additive B is tris (trisperfluoromethylsilane) borate equivalent to 1 percent of the mass of the electrolyte and tris (fluoromethyl) borate equivalent to 2 percent of the mass of the electrolyte;
or the additive A is methylene methane disulfonate which is 0.5 percent of the mass of the electrolyte, and the additive B is tris (trisperfluoromethylsilane) borate which is 1 percent of the mass of the electrolyte;
or the additive A is methylene methane disulfonate equivalent to 0.5% of the mass of the electrolyte, and the additive B is tris (fluoromethyl) borate equivalent to 0.5% of the mass of the electrolyte and tris (trisperfluoromethylsilane) borate equivalent to 1% of the mass of the electrolyte.
2. The lithium secondary battery electrolyte as claimed in claim 1 wherein the organic solvent comprises cyclic esters and chain esters.
3. The lithium secondary battery electrolyte as claimed in claim 2, wherein the organic solvent is a cyclic ester: the mass ratio of the chain ester is 1: (1-3) a mixed solvent.
4. The lithium secondary battery electrolyte as claimed in claim 2, characterized in that: the cyclic ester is at least one of ethylene carbonate, propylene carbonate, gamma-butyrolactone and gamma-valerolactone; the chain ester is at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, ethyl acetate and methyl propyl carbonate.
5. The electrolyte for a lithium secondary battery according to claim 1, wherein the conductive lithium salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium dioxalate borate, lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium perchlorate, lithium hexafluoroarsenate, lithium bistrifluoromethylsulfonylimide; the mass concentration of the conductive lithium salt in the electrolyte of the lithium secondary battery is 15.0-20.0%.
6. A lithium secondary battery characterized in that: the lithium secondary battery comprises a positive electrode, a negative electrode and the lithium secondary battery electrolyte according to any one of claims 1 to 5, wherein: the positive electrode material is selected from transition metal oxide of lithium, wherein the transition metal oxide of lithium is LiCoO2、LiMn2O4、LiMnO2、Li2MnO4、LiFePO4、Li1+aMn1-xMxO2、LiCo1-xMxO2、LiFe1-xMxPO4、Li2Mn1-xO4Wherein M is one or more selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, and a is more than or equal to 0<0.2，0≤x<1; the negative electrode material is selected from at least one of graphite, silicon-carbon composite material and lithium titanate.
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