CN115458811B - Electrolyte based on sulfone-based eutectic solvent, preparation method thereof and lithium ion battery - Google Patents
Electrolyte based on sulfone-based eutectic solvent, preparation method thereof and lithium ion battery Download PDFInfo
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Abstract
The invention relates to the field of lithium ion batteries, in particular to an electrolyte based on a sulfone-based eutectic solvent, a preparation method of the electrolyte and a lithium ion battery. The electrolyte based on the sulfone eutectic solvent comprises: the eutectic solvent is obtained by blending lithium salt and a solid sulfone compound. The electrolyte has the advantages of incombustibility, high thermal stability, high lithium ion transference number, large electrochemical window and the like, is applied to a lithium ion battery, and can effectively improve the cycle performance and safety of the battery. And the preparation method of the electrolyte is simple, is suitable for large-scale industrial production, and has good application prospect.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to an electrolyte based on a sulfone-based eutectic solvent, a preparation method of the electrolyte and a lithium ion battery.
Background
The lithium ion battery has the advantages of high energy density, good cycle stability, environmental friendliness and the like, and is widely applied to the fields of portable electronic equipment, electric automobiles, energy storage and the like. With the continuous development of modern science and technology, higher requirements are put forward on the energy density and the safety performance of the lithium ion battery. The traditional organic electrolyte using a carbonate solvent has the characteristics of low flash point and easy volatilization, and is easy to cause safety problems such as combustion, explosion and the like. Meanwhile, in a battery system having a higher energy density, the safety problem of the battery is one of the important reasons that hinder the industrialization thereof.
At present, in order to solve the above-mentioned problems of high energy density and high safety, a flame retardant additive is usually added into a conventional electrolyte, and the flame retardant additive is usually added by more than 20wt%, although the flame retardant additive can achieve a certain flame retardant effect, the electrochemical performance of the lithium ion battery is always reduced, especially the cycle life and the rate capability, and the manufacturing cost of the battery is also increased, which is not beneficial to large-scale production.
Therefore, the development of non-flammable electrolyte while ensuring good cycle life is imminent, thereby promoting the development of next-generation high-safety and high-energy density lithium ion batteries.
Disclosure of Invention
In view of the defects of the prior art, the invention aims to provide an electrolyte based on a sulfone-based eutectic solvent, a preparation method thereof and a lithium ion battery, and aims to solve the problem that the cycle life of the battery is shortened although the existing non-combustible electrolyte can achieve a certain flame retardant effect.
The technical scheme of the invention is as follows:
an electrolyte based on a sulfone-based eutectic solvent, comprising: the eutectic solvent is obtained by blending lithium salt and a solid sulfone compound.
Optionally, the molar ratio of the lithium salt to the sulfone compound is 1-1.
Optionally, the sulfone compound is selected from one or more of dimethyl sulfone, diethyl sulfone, n-butyl sulfone, ethyl methyl sulfone, ethyl phenyl sulfone, diphenyl sulfone, methyl phenyl sulfone, 4-difluoro diphenyl sulfone and 3-sulfolene.
Optionally, the lithium salt is selected from one or more of lithium bistrifluoromethanesulfonylimide, lithium dioxalate borate, lithium hexafluorophosphate and lithium tetrafluoroborate.
Optionally, the additive is selected from at least one of cyclic carbonates, lithium nitrate, and lithium difluorooxalato borate.
Optionally, the cyclic carbonate is one or more of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate and vinylene carbonate.
The invention relates to a preparation method of an electrolyte based on a sulfone eutectic solvent, which comprises the following steps:
in an inert atmosphere environment, mixing lithium salt and a solid sulfone compound, heating and stirring to obtain a low co-solvent; and adding an additive into the low eutectic solvent, and stirring to prepare the electrolyte.
Optionally, mixing the lithium salt and the solid sulfone compound, heating and stirring to obtain a low co-solvent; adding an additive into the low eutectic solvent, and stirring, wherein the method specifically comprises the following steps: mixing lithium salt and solid sulfone compound, and stirring at 50-70 ℃ until the mixture is clear and transparent to obtain a low co-solvent; and (4) after cooling, adding an additive into the low eutectic solvent, and then uniformly stirring.
The lithium ion battery comprises the electrolyte based on the sulfone eutectic solvent.
Optionally, the lithium ion battery further comprises: a positive electrode, a negative electrode, a separator;
the material of the positive electrode is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, lithium nickel manganate, nickel cobalt manganese ternary material and nickel cobalt aluminum ternary material;
the negative electrode is one or more of a graphite negative electrode, a metal lithium negative electrode, a silicon-carbon negative electrode and a silicon-oxygen negative electrode;
the diaphragm is one or more of a polyethylene diaphragm, a polypropylene diaphragm, a PP/PE/PP three-layer composite film and a glass fiber diaphragm.
Has the advantages that: the invention provides a sulfone-based eutectic solvent electrolyte of a lithium ion battery, which has the advantages of incombustibility, high thermal stability, high lithium ion migration number, large electrochemical window and the like, still has excellent cycle life on the premise of ensuring high safety of the battery, and has good application prospect.
Drawings
FIG. 1 is a linear scanning voltammogram of the electrolyte prepared in example 1 of the present invention.
Fig. 2 is a thermogravimetric diagram of the electrolyte prepared in example 1 of the present invention and the conventional electrolyte of comparative example 1.
FIG. 3 is a graph showing long cycle performance of the electrolyte prepared in example 1 of the present invention.
Detailed Description
The invention provides an electrolyte based on a sulfone-based eutectic solvent, a preparation method thereof and a lithium ion battery, and further details of the invention are provided below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Eutectic solvents have many advantages, such as high thermal stability, low vapor pressure, non-flammability and good salt solubility. Particularly, the nonflammability of the eutectic solvent can effectively solve the problem of flammability of the current commercial carbonate electrolyte, and the electrolyte has good safety. Meanwhile, the electrolyte has the advantages of low cost, easy manufacture, no toxicity and biodegradability, and is an ideal choice for battery electrolytes.
Accordingly, the embodiment of the invention provides an electrolyte based on a sulfone-based eutectic solvent, which comprises the following components: the eutectic solvent is obtained by blending lithium salt and a solid sulfone compound.
The embodiment provides an electrolyte based on a sulfone-based eutectic solvent (DES), specifically, the DES is formed by lithium salts and solid sulfone compounds with different molar ratios, and a certain amount of additives are added to form the electrolyte. The electrolyte has the advantages of incombustibility, high thermal stability, high lithium ion transference number, large electrochemical window and the like, is applied to a lithium ion battery, and can effectively improve the cycle performance and safety of the battery. And the preparation method of the electrolyte is simple, is suitable for large-scale industrial production, and has good application prospect.
Eutectic solvents are eutectic mixtures consisting of two or more components in a stoichiometric ratio, resulting in a mixture having a melting point significantly lower than the melting point of each individual component due to intermolecular interactions, including hydrogen bonding, lewis acid-base interactions, and van der waals interactions. In the sulfone-based eutectic solvent provided in this embodiment, lithium ions in the lithium salt and the-S = O group in the sulfone compound have a strong coordination effect, and the lithium ions and anions (such as TFSI) are reduced – 、BOB – Etc.), and the intermolecular interaction of sulfone compounds, thereby lowering the melting point of the mixture and forming the sulfone-based eutectic solvent.
The existing electrolytic liquid is mainly carbonate and ether electrolyte, and carbonate and ether are volatile, inflammable and poor in thermal stability, and have serious potential safety hazard because fire or explosion is easy to occur when the battery is out of control due to heat. The compatibility of carbonates and lithium metal is poor, lithium dendrite is easily formed in the lithium ion deposition process, a diaphragm can be pierced, and the short circuit of the battery is caused; although ether electrolyte has better compatibility with lithium metal, the electrochemical window of the ether electrolyte is narrower, generally less than 4V, and the ether electrolyte cannot be applied to a high-voltage lithium ion battery system.
The inventor finds that after the lithium salt and the solid sulfone compound are heated and mixed in different stoichiometric ratios, the interaction force between the lithium salt and the solid sulfone compound can be utilized to reduce the melting point and form a liquid eutectic solvent, and the eutectic solvent electrolyte has high thermal stability and oxidation resistance (more than 5V), is nonflammable and has high lithium ion migration number. The lithium ion battery is suitable for various anode materials (high-nickel ternary, lithium iron phosphate, lithium manganese iron phosphate, lithium cobaltate, lithium manganate and the like) and various cathodes (graphite, lithium metal, silicon carbon and silicon oxygen cathodes), and has excellent cycle performance.
In addition, there are also a few electrolytic solutions using a low melting point liquid sulfone compound (dimethyl sulfoxide, sulfolane, etc.) as a solventThe electrolytes also have better thermal stability and oxidation resistance (more than 5V), but the electrolytes can not form a stable electrode/electrolyte interface film on a graphite cathode, so that the cycle decay of the battery is quicker; but also greatly limits the application of the sulfone compound with high melting point. The reason is that the existing electrolyte taking the sulfone compound as the solvent is more of SEI films derived from the solvent, and salt anions are less involved in the SEI film forming process, so that unstable SEI films rich in organic matters are formed. In the electrolyte based on the sulfone eutectic solvent, more salt anions are induced to participate in the formation process of the SEI film, and inorganic substances (LiF, li) are formed 3 N, B-O/F, etc.) more stable SEI films, ensuring long cycle stability of the battery.
In one embodiment, the molar ratio of the lithium salt to the sulfone compound is 1. The lithium salt and the sulfone compound can better form the eutectic solvent in the proportion range, and the content of the additive can form a more stable SEI interfacial film in the proportion range.
In one embodiment, the solid sulfone compound is selected from one or more of dimethyl sulfone, diethyl sulfone, n-butyl sulfone, ethyl methyl sulfone, ethyl phenyl sulfone, diphenyl sulfone, methyl benzene sulfone, 4-difluoro diphenyl sulfone, 3-sulfolene, etc.
In one embodiment, the lithium salt is selected from lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium bistrifluorosulfonylimide (LiFSI), lithium dioxalate borate (LiBOB), lithium hexafluorophosphate (LiPF) 6 ) And lithium tetrafluoroborate (LiBF) 4 ) And the like.
In one embodiment, the additive is selected from at least one of cyclic carbonates, lithium nitrate, lithium difluorooxalato borate, and the like. The use of these film-forming additives results in the formation of stable SEI interfacial films, including LiF, li formation 3 N, B-O/F compounds.
In one embodiment, the cyclic carbonate is one or more of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, and the like.
Compared with the prior art, the electrolyte based on the sulfone eutectic solvent has the following advantages and outstanding effects:
(1) compared with the traditional carbonate solvent electrolyte, the electrolyte is non-flammable, high in thermal stability and high in safety;
(2) the electrolyte is different from the traditional carbonate solvent electrolyte, and the electrochemical window of the electrolyte is wider and reaches about 5V; the material is suitable for various high-voltage cathode materials and has good electrochemical performance;
(3) compared with the traditional carbonate solvent electrolyte, the electrolyte has higher lithium ion migration number (more than 0.7), and the traditional carbonate solvent electrolyte is only between 0.2 and 0.4, so the electrolyte has more excellent rate performance;
(4) under the electrolyte system, a stable interface SEI film and a stable CEI film can be formed on the surfaces of the anode and cathode materials, so that the stability of the interface film in the long-cycle charge-discharge process is ensured, and the cycle life is effectively prolonged;
(5) the electrolyte has the advantages of simple and convenient synthesis method, easily obtained raw materials, low manufacturing cost and convenient large-scale application.
The embodiment of the invention provides a preparation method of the electrolyte based on the sulfone eutectic solvent, which comprises the following steps:
in an inert atmosphere environment, mixing lithium salt and a solid sulfone compound, heating and stirring to obtain a low cosolvent; and adding an additive into the low eutectic solvent, and stirring to prepare the electrolyte.
In one embodiment, the lithium salt and the solid sulfone compound are mixed, heated and stirred to obtain the low cosolvent; adding an additive into the low eutectic solvent, and stirring, wherein the method specifically comprises the following steps: mixing lithium salt and solid sulfone compound, and stirring at 50-70 deg.C (such as 60 deg.C) to obtain low cosolvent; and (4) after cooling, adding an additive into the low eutectic solvent, and then uniformly stirring.
In one embodiment, the inert atmosphere may be an argon atmosphere or a helium atmosphere. Furthermore, under the inert atmosphere environment, the water content and the oxygen content are both below 0.2 ppm.
The embodiment of the invention provides a lithium ion battery, which comprises the electrolyte based on the sulfone eutectic solvent.
The electrolyte described in this example is suitable for a lithium ion battery using metallic lithium as a negative electrode. Specifically, the lithium ion battery includes: electrolyte, positive pole, negative pole, diaphragm, wherein, electrolyte be this embodiment the electrolyte, anodal material is one or more in lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, nickel lithium manganate, nickel cobalt manganese ternary material and nickel cobalt aluminium ternary material, the negative pole is one or more in graphite negative pole, metal lithium negative pole, silicon carbon negative pole and the silica negative pole, the diaphragm is one of Polyethylene (PE) diaphragm, polypropylene (PP) diaphragm, PP/PE/PP three-layer composite diaphragm and glass fiber diaphragm.
The invention is further illustrated by the following specific examples.
Comparative example 1
The carbonate based solvent electrolyte of this comparative example was prepared from LiPF 6 Ethylene Carbonate (EC), dimethyl carbonate (DMC) and Ethyl Methyl Carbonate (EMC), wherein LiPF is contained in the electrolyte 6 1, wherein the volume ratio of the EC, DMC and EMC is 1. The electrolyte system is used for testing a full battery with metal lithium as a cathode and lithium iron phosphate as an anode, and tests show that the coulombic efficiency of the battery reaches 98.0 percent and the cycle life of the battery is 500 circles.
Comparative example 2
The carbonate based solvent electrolyte of this comparative example was prepared from LiPF 6 Ethylene Carbonate (EC) and diethyl carbonate (DEC), wherein LiPF is present in the electrolyte 6 1, the volume ratio of 1 to 1 for EC and DEC. The electrolyte system is used for a full battery test with graphite as a negative electrode and nickel-cobalt-manganese 811 as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.0% and the cycle life is 400 circles.
Example 1
Mixing lithium bistrifluoromethanesulfonimide and ethyl methyl sulfone according to a molar ratio of 1. The electrolyte system is used for a full battery test with metal lithium as a cathode and lithium iron phosphate as an anode, and tests show that the coulombic efficiency of the battery reaches 99.0 percent, and the cycle life can reach 2000 circles.
Fig. 1 is a linear scanning voltammogram of the electrolyte prepared in example 1 of the present invention, and it can be seen from the graph that the oxidation resistance potential of the electrolyte reaches 5.5V or more, and the electrolyte is suitable for all high voltage cathode materials.
Fig. 2 is a thermogravimetric diagram of the electrolyte prepared in example 1 of the present invention and the conventional electrolyte of comparative example 1, and it can be seen that the weight loss rate of the electrolyte of example 1 is less than 10% at 150 ℃, and the weight loss rate of the conventional carbonate electrolyte reaches more than 90%.
Fig. 3 is a graph showing long cycle performance of the electrolyte prepared in example 1 of the present invention, and it can be seen that the discharge capacity was 140mAh/g and the capacity retention rate was 92% after 2000 cycles at a 1C rate.
Example 2
Mixing lithium bis (fluorosulfonyl) imide and phenylmethanesulfone in a molar ratio of 1. The electrolyte system is used for a full battery test with metal lithium as a negative electrode and lithium cobaltate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.5 percent, and the cycle life can reach 1000 cycles.
Example 3
Mixing lithium bistrifluoromethanesulfonimide and 4, 4-difluorodiphenyl sulfone according to a molar ratio of 1. The electrolyte system is used for testing a full battery with graphite as a negative electrode and lithium iron phosphate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.2%, and the cycle life of the battery can reach 500 circles.
Example 4
Mixing the lithium bis (fluorosulfonyl) imide and dimethyl sulfone in a molar ratio of 1. The electrolyte system is used for a full battery test with metal lithium as a cathode and manganese iron phosphate lithium as an anode, and tests show that the coulombic efficiency of the battery reaches 99.5 percent, and the cycle life can reach 1000 circles.
Example 5
Mixing lithium bistrifluoromethanesulfonimide and ethyl methyl sulfone according to a molar ratio of 1. The electrolyte system is used for a full battery test with metal lithium as a negative electrode and nickel-cobalt-manganese 811 as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.5%, and the cycle life can reach 800 circles.
Example 6
Mixing lithium tetrafluoroborate and dimethyl sulfone according to a molar ratio of 1. The electrolyte system is used for testing a full battery with graphite as a negative electrode and lithium cobaltate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.0 percent, and the cycle life of the battery can reach 500 circles.
Example 7
Mixing the lithium bis (fluorosulfonyl) imide and diethyl sulfone according to a molar ratio of 1. The electrolyte system is used for testing a full battery with silicon as a cathode and lithium iron phosphate as an anode, and tests show that the coulombic efficiency of the battery reaches 99.0 percent, and the cycle life of the battery can reach 300 circles.
Example 8
Mixing lithium bistrifluoromethanesulfonimide and diphenyl sulfone according to a molar ratio of 1. The electrolyte system is used for a full battery test with silicon carbon as a negative electrode and lithium cobaltate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.5 percent, and the cycle life can reach 500 circles.
Example 9
Mixing lithium hexafluorophosphate and methyl phenyl sulfone according to a molar ratio of 1. The electrolyte system is used for a full battery test with graphite as a negative electrode and lithium iron phosphate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.1 percent, and the cycle life can reach 600 circles.
Example 10
Mixing the lithium bis (fluorosulfonyl) imide, the lithium bis (trifluoromethanesulfonyl) imide and the dimethyl sulfone according to a molar ratio of 0.6. The electrolyte system is used for testing a full battery with graphite as a negative electrode and lithium manganate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.0%, and the cycle life can reach 1000 cycles.
Example 11
Mixing the lithium bis (fluorosulfonyl) imide, the lithium hexafluorophosphate and the diethyl sulfone according to a molar ratio of 0.7 to 4, stirring at 60 ℃ until the mixture is clear and transparent, cooling, adding fluoroethylene carbonate accounting for 10% of the mass of the electrolyte, and stirring uniformly to prepare the electrolyte based on the sulfone eutectic solvent. The electrolyte system is used for a full battery test with metal lithium as a cathode and lithium iron phosphate as an anode, and tests show that the coulombic efficiency of the battery reaches 99.9 percent, and the cycle life can reach 2000 circles.
Example 12
Mixing lithium bistrifluorosulfonyl imide, lithium dioxalate borate and methyl phenyl sulfone according to a molar ratio of 0.8 to 0.2, stirring at 60 ℃ until the mixture is clear and transparent, cooling, adding fluoroethylene carbonate accounting for 10% of the mass of the electrolyte, and stirring uniformly to prepare the electrolyte based on the sulfonyl eutectic solvent. The electrolyte system is used for a full battery test with metal lithium as a negative electrode and lithium cobaltate as a positive electrode, and tests show that the coulombic efficiency of the battery reaches 99.3 percent, and the cycle life can reach 1000 circles.
In summary, the electrolyte based on the sulfone eutectic solvent, the preparation method thereof and the lithium ion battery provided by the invention are characterized in that lithium salts and sulfone compounds with different molar ratios are blended, and a certain proportion of additives are added to form the electrolyte. The electrolyte has the advantages of incombustibility, high thermal stability, high lithium ion transference number, large electrochemical window and the like, is applied to a lithium ion battery, and can effectively improve the cycle performance and safety of the battery. And the preparation method of the electrolyte is simple, is suitable for large-scale industrial production, and has good application prospect.
It will be understood that the invention is not limited to the examples described above, but that modifications and variations will occur to those skilled in the art in light of the above teachings, and that all such modifications and variations are considered to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. The electrolyte based on the sulfone-based eutectic solvent is characterized by comprising the following components in percentage by weight: the eutectic solvent is obtained by blending lithium salt and a solid sulfone compound.
2. The electrolyte based on the sulfone-based eutectic solvent as claimed in claim 1, wherein the molar ratio of the lithium salt to the sulfone compound is 1-1.
3. The electrolyte solution based on the sulfone-based eutectic solvent as claimed in claim 1, wherein the sulfone compound is selected from one or more of dimethyl sulfone, diethyl sulfone, n-butyl sulfone, ethyl methyl sulfone, ethyl phenyl sulfone, diphenyl sulfone, methyl phenyl sulfone, 4-difluoro diphenyl sulfone, and 3-sulfolene.
4. The electrolyte solution based on the sulfone-based eutectic solvent as claimed in claim 1, wherein the lithium salt is selected from one or more of lithium bistrifluoromethanesulfonylimide, lithium difluorosulfonylimide, lithium dioxalate borate, lithium hexafluorophosphate and lithium tetrafluoroborate.
5. The electrolyte solution based on the sulfone-based eutectic solvent according to claim 1, wherein the additive is at least one selected from the group consisting of cyclic carbonates, lithium nitrate, and lithium difluorooxalato borate.
6. The electrolyte based on the sulfone-based eutectic solvent as claimed in claim 5, wherein the cyclic carbonates are one or more of ethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate and vinylene carbonate.
7. The preparation method of the electrolyte based on the sulfone-based eutectic solvent as set forth in any one of claims 1 to 6, comprising the steps of:
in an inert atmosphere environment, mixing lithium salt and a solid sulfone compound, heating and stirring to obtain a low co-solvent; and adding an additive into the low eutectic solvent, and stirring to prepare the electrolyte.
8. The preparation method of the electrolyte based on the sulfone-based eutectic solvent as claimed in claim 7, wherein the lithium salt and the solid sulfone compound are mixed, heated and stirred to obtain the low-eutectic solvent; adding an additive into the low eutectic solvent, and stirring, wherein the method specifically comprises the following steps: mixing lithium salt and solid sulfone compound, and stirring at 50-70 ℃ until the mixture is clear and transparent to obtain a low co-solvent; and (4) after cooling, adding an additive into the low eutectic solvent, and then uniformly stirring.
9. A lithium ion battery comprising an electrolyte based on a sulfone-based eutectic solvent according to any one of claims 1 to 6.
10. The lithium ion battery of claim 9, further comprising: a positive electrode, a negative electrode, a separator;
the material of the positive electrode is one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium manganate, lithium cobaltate, lithium nickel manganate, nickel cobalt manganese ternary material and nickel cobalt aluminum ternary material;
the negative electrode is one or more of a graphite negative electrode, a metal lithium negative electrode, a silicon-carbon negative electrode and a silicon-oxygen negative electrode;
the diaphragm is one or more of a polyethylene diaphragm, a polypropylene diaphragm, a PP/PE/PP three-layer composite film and a glass fiber diaphragm.
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| CN117013066A (en) * | 2023-08-08 | 2023-11-07 | 常州千沐新能源有限公司 | Eutectic high-entropy electrolyte, preparation method and lithium ion battery |
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