CN114122515A - Lithium secondary battery flame-retardant electrolyte based on two-dimensional structure design and application - Google Patents

Lithium secondary battery flame-retardant electrolyte based on two-dimensional structure design and application Download PDF

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CN114122515A
CN114122515A CN202111115177.2A CN202111115177A CN114122515A CN 114122515 A CN114122515 A CN 114122515A CN 202111115177 A CN202111115177 A CN 202111115177A CN 114122515 A CN114122515 A CN 114122515A
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electrolyte
flame
phase solvent
flame retardant
retardant additive
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谢佳
曾子琪
雷盛
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Huazhong University of Science and Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—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
    • H01M10/05—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
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention belongs to the technical field of lithium secondary batteries, and particularly relates to a lithium secondary battery flame-retardant electrolyte based on a two-dimensional structure design and application thereof. The electrolyte contains a first phase solvent of lithium salt and lithium-philic salt, a flame retardant additive and a second phase solvent of lithium-phobic salt and flame retardant additive, wherein the second phase solvent is used for introducing the flame retardant additive and inhibiting the reductive decomposition of the electrolyte in the lithium secondary battery on the surface of a negative electrode. According to the invention, through the two-dimensional electrolyte design method of the lithium salt-philic flame retardant and the lithium salt-phobic flame retardant, the flame retardant additive is introduced through the second-phase solvent, and meanwhile, the solvation structure of the lithium salt in the electrolyte is maintained, so that the safety, the fast lithium ion transmission capability and the stable electrode/electrolyte interface of the electrolyte are ensured, and the safe and stable operation of the lithium ion battery under the high coulombic efficiency can be maintained.

Description

Lithium secondary battery flame-retardant electrolyte based on two-dimensional structure design and application
Technical Field
The invention belongs to the technical field of lithium secondary batteries, and particularly relates to a lithium secondary battery flame-retardant electrolyte based on a two-dimensional structure design and application thereof.
Background
In recent years, safety accidents of lithium ion batteries frequently occur, which seriously threatens the safety of lives and properties of people, and the safety of the lithium ion batteries becomes a problem to be solved urgently.
Currently, commercial lithium ion battery electrolytes generally use organic carbonates and ethers, and these organic solvents have high vapor pressure and low flash point, are extremely flammable, and cause serious safety problems upon abuse (high temperature, overcharge, etc.). The electrolyte is one of the compositions for filling the whole battery and is one of the main reasons for battery combustion, so the development of the intrinsically safe flame-retardant electrolyte has important significance for improving the safety of the lithium ion battery.
The development of intrinsically safe electrolytes generally achieves flame retardant effects by improving the flame retardant capability of the electrolyte body or introducing flame retardant additives into the electrolyte body. The development of a highly safe electrolyte based on liquid electrolytes includes ionic liquids, fluoro-solvents, organic phosphate esters, phosphazene flame retardants and high concentration salt electrolytes, which are commonly used as electrolyte additives, co-solvents or directly as main solvents. When the electrolyte is used as an additive, the electrolyte is dissolved mutually, the additive affects the solvation structure of the bulk electrolyte, and the electrochemical performance of the electrolyte. There are documents and patents reporting that The common organic phosphate flame retardant has a problem of co-intercalation when used in graphite electrodes, and cannot be used as it is (Journal of The Electrochemical Society,2001,148(10): A1058, Journal of The Electrochemical Society,2002,149(5): A622, publication No. CN111668540A, publication No. CN 109860710A).
Therefore, a method of introducing the foreign phase additive without affecting the solubility and electrochemical properties becomes important. At present, no flame-retardant/non-combustible electrolyte completely considers electrochemical performance, cost and safety. Therefore, decoupling the electrochemical performance and safety of the high-safety electrolyte is a scientific problem to be solved urgently.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a lithium secondary battery flame-retardant electrolyte designed based on a two-dimensional structure, and the flame-retardant additive which is originally insoluble in the electrolyte is successfully introduced into the electrolyte by introducing a second-phase solvent which is hydrophobic in lithium salt and hydrophilic in flame-retardant additive into the electrolyte, and the second-phase solvent can dissolve the flame-retardant additive but not the lithium salt, so that the solvation structure of the lithium salt is not influenced, the electrochemical performance is not influenced, the decoupling with good flame-retardant performance and electrochemical performance is achieved, and the technical problem that the flame-retardant performance, the electrochemical performance and the like of an electrolyte body cannot be considered in the prior art is solved.
In order to achieve the above object, the present invention provides a lithium secondary battery flame retardant electrolyte based on a two-dimensional structure design, comprising:
a lithium salt;
a flame retardant additive;
a first phase solvent of a lithium philic salt hydrophobic flame retardant additive; and
a second phase solvent of a lithium salt-phobic flame retardant additive;
wherein the first phase solvent is used for dissolving lithium salt, and the first phase solvent and the flame retardant additive are not soluble with each other; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is immiscible with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt.
Preferably, the lithium salt used is at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis-fluorosulfonylimide, lithium bis-trifluorosulfonylimide, lithium tetrafluoroborate and lithium hexafluoroarsenate.
Preferably, the first phase solvent has a solvent donor number (DN value) greater than 10; the second phase solvent has a solvent donor number (DN value) and a dielectric constant both less than 10.
Preferably, the first phase solvent is an ester or ether solvent.
Preferably, the second phase solvent is an aromatic compound, a fluorine-containing ether compound or a fluorine-containing ester compound.
Preferably, the flame retardant additive is a flame retardant additive that is insoluble in a commercial electrolyte, which is a carbonate-based electrolyte or an ether-based electrolyte.
Preferably, the flame retardant additive is at least one of perfluorohexanone, ethyl perfluoro-n-pentanone, trifluoropropyl methyl cyclotrisiloxane, 2,4, 6-trimethyl-2, 4, 6-triphenyl cyclotrisiloxane, ethoxy pentafluoro cyclophosphazene and R-POSS, and R in the R-POSS is alkyl with the carbon number of 8-40, alkylene with the carbon number of 16-80 or phenyl with the carbon number of 8-16.
Preferably, the concentration of the lithium salt in the electrolyte is 0.5mol/L to 5mol/L, preferably 1mol/L to 2 mol/L.
Preferably, the ratio of the amount of the first phase solvent to the amount of the lithium salt is (1-20): 1, and more preferably (8-12): 1.
Preferably, the volume ratio of the second phase solvent to the first phase solvent is (0.01-1): 1, more preferably (0.02-0.5): 1, and the volume ratio of the flame retardant additive to the second phase solvent is (0.01-2): 1, more preferably 0.8-1.2: 1.
According to another aspect of the present invention, there is provided a lithium secondary battery whose electrolyte is the flame-retardant electrolyte.
According to another aspect of the present invention, there is provided a method for designing a two-dimensional structure of a flame-retardant electrolyte for a lithium secondary battery, comprising the steps of:
determining the type of lithium salt;
determining the type of the flame retardant additive;
determining a first phase solvent of the lithium-philic salt flame-retardant additive; and
determining the kind of the second-phase solvent of the lithium salt-phobic flame-retardant additive;
wherein the first phase solvent is capable of dissolving lithium salt and is immiscible with the flame retardant additive; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is immiscible with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
according to the invention, the second-phase solvent of the lyophobic lithium salt hydrophilic flame retardant additive is introduced into the electrolyte, the flame retardant additive which is originally insoluble in the electrolyte can be dissolved in an electrolyte system by utilizing the similar intermiscibility principle or the difference of solubility, and the second-phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is not mutually soluble with the lithium salt, so that the introduction of the flame-retardant additive does not influence the solvation structure of the lithium salt and further the performance of the battery, and the decoupling with good flame-retardant performance and electrochemical performance is achieved. The method greatly widens the application field of the flame retardant additive in the electrolyte, and the method for introducing the external phase is simple and efficient, thereby having great popularization significance.
Many flame retardants used in the field of polymer materials, when used as additives to be added to an electrolyte of a lithium secondary battery, are generally insoluble in the electrolyte, so that the flame retardant additives cannot improve the flame retardant property of the electrolyte bulk; while other flame retardants may be soluble in the electrolyte, they can affect the solvating structure of the lithium salt and, in turn, severely affect the electrochemical performance of the cell. The two-dimensional structure design method successfully applies some flame retardant additives which cannot be used in the electrolyte to the electrolyte, and the addition of the second-phase flame retardant solvent can enable the flame retardant additive to exist in the second-phase solvent or change the solvation structure of the flame retardant additive through the similarity and intermiscibility principle, so that the surrounding of the flame retardant additive is solvated by the second-phase solvent to improve the decomposition condition of part of the flame retardant in the electrolyte, and the electrochemical performance of the battery is improved.
The flame-retardant electrolyte provided by the invention can be regarded as a two-phase electrolyte or a two-dimensional structure electrolyte, the lithium salt and the first phase solvent are regarded as a first phase or a first-dimensional structure as a whole, the flame-retardant additive and the second phase solvent are jointly regarded as a second phase or a second-dimensional structure, the flame-retardant additive is dissolved in the electrolyte body between the first phase and the second phase or between the first-dimensional structure and the second-dimensional structure through the introduction of the second phase solvent, but the solvation structure of the lithium salt is not influenced, and the technical problem that the flame-retardant safety performance and the electrochemical performance of the electrolyte body in the prior art cannot be considered at the same time is solved skillfully.
The preparation method of the two-phase lithium secondary battery flame-retardant electrolyte provided by the invention is simple and low in cost, and various flame-retardant additives in the prior art can be introduced into the electrolyte by virtue of the second-phase solvent, so that the application field of the flame retardant is widened, and a new thought is provided for the research and development of safe electrolyte.
Drawings
Fig. 1 is an optical picture of an ignition test of comparative example 1.
Fig. 2 is an optical picture of the ignition test of comparative example 2.
Fig. 3 is an optical photograph of the ignition test of example 1.
Fig. 4 is an optical photograph of the ignition test of example 3.
Fig. 5 is an optical picture of the electrolyte of comparative example 2.
FIG. 6 is an optical picture of the electrolyte of example 3.
FIG. 7 is a graph comparing the self-extinguishing times of comparative example 1, comparative example 2, example 1 and example 2.
Fig. 8 is a graph of the cycle performance at 1C for a graphite half cell assembled with the electrolyte of comparative example 1.
Fig. 9 is a cycle performance graph of the electrolyte-assembled lithium iron phosphate half cell of example 3 at 1C.
Fig. 10 is a graph of rate performance at 0.2C, 0.5C, and 1C for the electrolyte-assembled graphite half-cell of example 4.
FIG. 11 is a photograph of the electrolyte before and after addition of the second phase solvent at the time of preparation of the electrolyte of example 4.
FIG. 12 is an optical photograph of the ignition test of the electrolyte of example 4.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention provides a lithium secondary battery flame-retardant electrolyte based on a two-dimensional structure design, which comprises:
a lithium salt;
a flame retardant additive;
a first phase solvent of a lithium philic salt hydrophobic flame retardant additive; and
a second phase solvent of a lithium salt-phobic flame retardant additive;
wherein the first phase solvent is used for dissolving lithium salt, and the first phase solvent and the flame retardant additive are not soluble with each other; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is immiscible with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt.
In some embodiments, the lithium salt used is at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis-fluorosulfonylimide, lithium bis-trifluorosulfonylimide, lithium tetrafluoroborate, and lithium hexafluoroarsenate.
In some embodiments, the first phase solvent has a solvent donor number greater than 10; the second phase solvent has a solvent donor number and a dielectric constant of less than 10. In general, the smaller the number of solvent donors (DN value), the poorer the solvent power for lithium salts. The first phase solvent is used for dissolving lithium salt, and generally a solvent with DN value more than 10 is selected; the second phase solvent is immiscible with lithium salt and is used for dissolving the flame retardant additive, and the solvent with DN value and dielectric constant less than 10 is generally selected.
In some embodiments, the first phase solvent is an ester or ether solvent. The first phase solvent of the present invention is a conventional solvent capable of dissolving lithium salt, and may be, for example, an ester or ether solvent. In some embodiments, the ester-based solvent is at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoro carbonate, and propylene carbonate; the ether solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether, tetrahydrofuran and 1, 3-dioxolane.
In some embodiments, the second phase solvent is an aromatic compound, a fluoroether compound, or a fluoroester compound.
In some embodiments, the aromatic compound is at least one of benzene, toluene, fluorobenzene, chlorobenzene, bromobenzene, methylfluorobenzene isomer, difluorobenzene isomer, trifluorobenzene isomer, tetrafluorobenzene isomer, pentafluorobenzene, and hexafluorobenzene. The fluorine-containing ether is at least one of desflurane, hydrofluoroether, isoflurane, sevoflurane, 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, 1,1,2, 2-tetrafluoro-1- (2,2,2-) trifluoroethoxy ethane, 1,1, 1-trifluoro-2- (2,2, 2-trifluoroethoxy) ethane, 1- (1,1,2, 2-tetrafluoroethoxy) propane, 2-methyl-1- (1,1,2, 2-tetrafluoroethoxy) propane and 2,2, 2-trifluoroethyl ether. The fluorine-containing ester compound is at least one of boric acid tri (2,2, 2-trifluoroethyl) ester, tri (2,2, 2-trifluoroethyl) phosphite ester and phosphoric acid tri (2,2, 2-trifluoroethyl) ester.
In some embodiments, the flame retardant additive is a flame retardant additive that is insoluble in a commercial electrolyte that is a carbonate electrolyte or an ether electrolyte.
In some embodiments, the flame retardant additive is at least one of perfluorohexanone, ethyl perfluoro-n-pentanone, trifluoropropyl methylcyclotrisiloxane, 2,4, 6-trimethyl-2, 4, 6-triphenylcyclotrisiloxane, ethoxy pentafluorocyclophosphazene, and R-POSS, and R in the R-POSS is an alkyl group having 8 to 40 carbon atoms, an alkylene group having 16 to 80 carbon atoms, or a phenyl group having 8 to 16 carbon atoms.
In some embodiments, the concentration of the lithium salt in the electrolyte is 0.5mol/L to 5mol/L, preferably 1mol/L to 2 mol/L.
In some embodiments, the ratio of the amount of the first phase solvent to the amount of the lithium salt is (1-20): 1, preferably (8-12): 1.
In some embodiments, the volume ratio of the second phase solvent to the first phase solvent is (0.01-1): 1, preferably (0.02-0.5): 1, and the volume ratio of the flame retardant additive to the second phase solvent is (0.01-2): 1, preferably 0.8-1.2:1, more preferably 1: 1.
The invention equivalently provides a two-dimensional structure design method of a lithium secondary battery flame-retardant electrolyte, which comprises the following steps:
determining the type of lithium salt;
determining the type of the flame retardant additive;
determining a first phase solvent of the lithium-philic salt flame-retardant additive; and
determining the kind of the second-phase solvent of the lithium salt-phobic flame-retardant additive;
wherein the first phase solvent is capable of dissolving lithium salt and is immiscible with the flame retardant additive; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is not mutually soluble with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt
Some flame retardant additives added in the prior art can form uniform electrolyte, improve the flame retardant capability of the electrolyte body, but affect the solvation structure of lithium salt and have negative influence on the electrochemical performance of the electrolyte; in other prior art, the addition of the flame retardant additive does not affect the solvation structure of the lithium salt, but the added flame retardant additive cannot form a uniform electrolyte, so that the flame retardant capability of the electrolyte body cannot be improved. The invention provides a flame-retardant electrolyte concept based on two-dimensional structure design, which is composed of a first phase solvent of a lithium salt-philic flame retardant and a second phase solvent of a lithium salt-phobic flame-retardant additive, and can solve the problems that some flame-retardant additives are incompatible with a bulk electrolyte, influence the solvation structure of the bulk electrolyte, influence the electrochemical performance and the like. The invention can lead some flame retardants which are insoluble in the common bulk electrolyte or flame retardant additives which influence the performance to be used in the electrolyte, and has important significance for the development of intrinsic safe electrolyte.
The electrolyte contains a first phase solvent of lithium salt and lithium-philic salt, a flame retardant additive and a second phase solvent of lithium-phobic salt and lithium-philic flame retardant additive, wherein the second phase solvent is fluorine-containing ether or aromatic compound; the second phase solvent is used for introducing a flame retardant additive, and the reductive decomposition of the electrolyte in the lithium secondary battery on the surface of the negative electrode is inhibited in a blocking or preferential decomposition mode. According to the invention, through the two-dimensional electrolyte design method of the lithium salt-philic flame retardant and the lithium salt-phobic flame retardant, the flame retardant additive is introduced through the fluorine-containing ether or aromatic compound, the solvation structure of the lithium salt in the electrolyte is maintained, the safety, the fast lithium ion transmission capability and the stable electrode/electrolyte interface of the electrolyte are ensured, and the safe and stable operation of the lithium ion battery under the high coulomb efficiency can be maintained.
The invention also provides a lithium secondary battery which mainly comprises a positive electrode, a negative electrode and electrolyte, wherein the electrolyte is the flame-retardant electrolyte designed based on the two-dimensional structure; the anode can be at least one of lithium iron phosphate, ternary lithium manganate, lithium cobaltate and Prussian blue; the negative electrode can be at least one of graphite, hard carbon, soft carbon, hard-soft composite carbon, silicon carbon, lithium titanate and metallic lithium. The above-mentioned various kinds of components include, but are not limited to, the above.
Comparative example 1
An electrolyte preparation step: mixing ethylene carbonate (DN value of 16.4) and dimethyl carbonate (DN value of 15.1) according to a volume ratio of 1:1 in a glove box filled with argon, then adding lithium hexafluorophosphate, stirring uniformly, and preparing the final concentration of the lithium hexafluorophosphate to be 1mol/L (marked as RCE), wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.
1 g of the prepared electrolyte is put into a 5 ml crucible and ignited to test the self-extinguishing time. And (4) rapidly igniting, and recording the time from the removal of the ignition device to the automatic extinguishment of the flame, namely the self-extinguishing time (SET). At least 3 tests per sample were averaged. And comparing the flame retardant performances of different electrolytes by taking the self-extinguishing time of the electrolyte in unit mass as a standard. The optical picture of the ignition test is shown in fig. 1, and it can be seen that when the fire source leaves, the diaphragm adsorbing the electrolyte burns violently, and has no flame retardant effect. The electrochemical performance of the electrolyte in a graphite half cell is tested, and as shown in figure 8, the electrolyte can exert 329mAhg at a current density of 1C-1And the capacity retention rate after 200 cycles is 93.6%.
Comparative example 2
An electrolyte preparation step: mixing ethylene carbonate and dimethyl carbonate solvent according to a volume ratio of 1:1 in an argon-filled glove box, then adding lithium hexafluorophosphate, uniformly stirring to prepare a final concentration of the lithium hexafluorophosphate of 1mol/L, then adding a flame retardant of 20% by volume of perfluorohexanone (FK), uniformly stirring to prepare a solution, wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1 ppm. The optical picture of the ignition test is shown in fig. 2, and it can be seen that when the fire source leaves, the diaphragm adsorbing the electrolyte is immediately self-extinguished, and has a good flame retardant effect. The optical picture of the electrolyte is shown in fig. 5, and it can be seen that the flame retardant additive is incompatible with the base electrolyte, resulting in delamination.
Comparative example 3
An electrolyte preparation step: mixing ethylene carbonate and dimethyl carbonate solvent according to a volume ratio of 1:1 in an argon-filled glove box, then adding lithium hexafluorophosphate, uniformly stirring to prepare a solution, wherein the final concentration of the lithium hexafluorophosphate is 1mol/L, then adding a flame retardant trifluoropropylmethyl cyclotrisiloxane (TTMC) with the mass fraction of 10%, uniformly stirring to prepare a solution, and the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.
Example 1
An electrolyte preparation step: mixing ethylene carbonate and dimethyl carbonate solvent according to a volume ratio of 1:1 in a glove box filled with argon, then adding lithium hexafluorophosphate, uniformly stirring to prepare a final concentration of the lithium hexafluorophosphate of 1mol/L, then adding a flame retardant additive of perfluorohexanone with a volume fraction of 10%, then adding a second phase solvent of fluorobenzene (FB, DN of 3 and dielectric constant of 5.4) with the same volume, uniformly stirring to prepare a solution, wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1 ppm. The optical picture of the ignition test is shown in fig. 3, and a trace amount of sputtering flame can be seen, but the flame retardant effect is general when the flame source is burnt for about 1-2 seconds after leaving. The optical picture of the electrolyte is shown in fig. 6, and it can be seen that the flame retardant additive is miscible with the base electrolyte and the delamination phenomenon disappears.
Comparing the self-extinguishing time of the electrolytes prepared in comparative example 1, comparative example 2, example 1 and example 2 with fig. 7, it can be seen that the self-extinguishing time of the electrolyte of example 1 is greatly reduced compared to that of comparative example 1, but the self-extinguishing time is slightly longer than that of comparative example 2 due to the flammability of the flame retardant solvent, but the flame retardant effect is not affected as a whole.
Example 2
The fluorobenzene quality was reduced to half of that of example 1, and the rest was the same as example 1. The reduction in the amount of fluorobenzene as the second solvent, which resulted in a slight decrease in the self-extinguishing time, remained almost the same as in comparative example 2, as shown in FIG. 7.
Example 3
The flame retardant solvent used, i.e., the second-phase solvent, was changed to 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE, DN value < 10, dielectric constant 6.2), and the remainder was the same as in example 1. The optical picture of the ignition test is shown in fig. 4, and it can be seen that when the fire source leaves, the diaphragm absorbing the electrolyte is immediately self-extinguished, and has good flame retardant effect.
The electrochemical performance of the electrolyte in the lithium iron phosphate half-cell is tested, and the lithium iron phosphate half-cell is assembled in the order of a positive electrode of a cell shell, a lithium iron phosphate pole piece, a diaphragm, metal lithium, foam nickel and a negative electrode of the cell shell. As shown in FIG. 9, 153mAhg can be exerted at a current density of 1C-1The specific capacity and the capacity retention rate can reach 98 percent after 67 cycles.
Example 4
An electrolyte preparation step: mixing ethylene carbonate and dimethyl carbonate solvent according to a volume ratio of 1:1 in an argon-filled glove box, then adding lithium hexafluorophosphate, uniformly stirring to prepare a final concentration of the lithium hexafluorophosphate of 1mol/L, then adding a flame retardant additive of trifluoropropylmethyl cyclotrisiloxane (TTMC) with a volume fraction of 10%, then adding a second phase solvent TTE with an equal mass, uniformly stirring to prepare a solution, wherein the water content in the glove box is less than 0.1ppm, and the oxygen content is less than 0.1 ppm.
The electrochemical performance of the electrolyte in a graphite half-cell is tested, and the graphite half-cell is assembled by a positive electrode of a cell shell, a graphite pole piece, a diaphragm, metal lithium, foamed nickel and a negative electrode of the cell shell. As shown in FIG. 10, 353mAhg was exhibited at 0.2C-1Specific capacity of (a); when the current density is increased to 1C, 336mAhg can still be exerted-1The specific capacity (higher than that exerted by comparative example 1) is obtained, and the capacity retention rate is up to 97.6 percent after 100 cycles under the current density of 1C. Fig. 11 is a picture of the electrolyte before and after the second-phase solvent is added during the preparation of the electrolyte in this example, and it can be seen that the electrolyte obtained before the second-phase solvent is added has a significant layering phenomenon, which illustrates that the flame retardant additive TTMC cannot be mixed with the lithium salt to form a uniform phase without adding the second-phase solvent TTE; however, when the second phase solvent TTE was added, the layers were not separated and a homogeneous phase was formed. Fig. 12 is an optical picture of the electrolyte ignition test of the present embodiment, which has a good flame retardant effect after the flame retardant additive and the second phase solvent are added.
Examples 5 to 9 the other conditions were the same as in examples 1 to 4 except that the flame retardant formulation was varied in the type of flame retardant additive or second phase solvent added and the amount or amount of the second phase solvent added, and the results of the comparative examples and the flame retardant formulation, flame retardant performance and electrochemical performance tests are summarized in Table 1.
TABLE 1 flame retardant effectiveness and electrochemical Properties of the flame retardant formulations
Figure BDA0003274999340000111
Figure BDA0003274999340000121
RCE in Table 1 shows that a solution of lithium hexafluorophosphate having a final concentration of 1mol/L was prepared by mixing ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1, adding lithium hexafluorophosphate, and stirring the mixture uniformly. FK represents a flame retardant additive, namely perfluoroketone, FB represents a second phase solvent, namely fluorobenzene, TTE represents a second phase solvent, namely 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether, and TTMC represents a flame retardant additive, namely trifluoropropylmethylcyclotrisiloxane; PFPN represents the flame retardant additive ethoxy pentafluorocyclophosphamide.
Shown in table 1 are the electrolyte formulations of each comparative example and the performance of the half cell assembled correspondingly, the flame retardant times represent the number of times of contact and separation of the fire source and contact (the flame retardant times are 2 times, which means that the half cell can be flame-retardant for 2 times, and the half cell can be ignited for the third time), the flame retardant performance of the electrolyte is shown, the coulomb efficiency of the first circle when testing the graphite (G) and lithium iron phosphate (LFP) half cell and the capacity under different multiplying power are also shown in the table, and the battery performance data of the comparative example 1 is the result of repeated tests of assembling the graphite half cell.
It can be seen from example 9 that the flame retardant effect of the second phase solvent alone is not obvious, while the flame retardant effect of the other examples with the flame retardant additive is obviously improved, and the flame retardant effect is brought by the flame retardant additive. Comparative example 2 no second phase solvent was introduced and the flame retardant additive delaminated from the base electrolyte and was not a homogeneous solution. In examples 1 to 8, the flame retardant additive is introduced into the electrolyte, and the second phase solvent is also introduced, so that the electrochemical performance and the flame retardant performance are excellent. In particular, the electrochemical performance of example 4 was comparable to that of comparative example 1, and 336mAhg of current density was exhibited even when the current density was increased to 1C-1Higher than the capacity exerted by comparative example 1. It can be seen from example 8 that the most flame retardant times the more flame retardant additives synergistically act to provide better flame retardant results.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (10)

1. A lithium secondary battery flame-retardant electrolyte designed based on a two-dimensional structure is characterized by comprising:
a lithium salt;
a flame retardant additive;
a first phase solvent of a lithium philic salt hydrophobic flame retardant additive; and
a second phase solvent of a lithium salt-phobic flame retardant additive;
wherein the first phase solvent is used for dissolving lithium salt, and the first phase solvent and the flame retardant additive are not soluble with each other; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is immiscible with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt.
2. The flame retarded electrolyte of claim 1 wherein the first phase solvent has a solvent donor number greater than 10; the second phase solvent has a solvent donor number and a dielectric constant of less than 10.
3. The flame-retardant electrolyte of claim 1, wherein the first phase solvent is an ester or ether solvent; the second phase solvent is an aromatic compound, a fluorine-containing ether compound or a fluorine-containing ester compound.
4. The flame-retardant electrolyte of claim 1, wherein the flame-retardant additive is a flame-retardant additive that is insoluble in a commercial electrolyte that is a carbonate-based electrolyte or an ether-based electrolyte.
5. The flame retardant electrolyte of claim 1, wherein the flame retardant additive is at least one of perfluorohexanone, ethyl perfluoron-pentanone, trifluoropropylmethylcyclotrisiloxane, 2,4, 6-trimethyl-2, 4, 6-triphenylcyclotrisiloxane, ethoxypentafluorocyclophosphazene, and R-POSS, and wherein R in the R-POSS is an alkyl group having 8 to 40 carbon atoms, an alkylene group having 16 to 80 carbon atoms, or a phenyl group having 8 to 16 carbon atoms.
6. The flame retardant electrolyte of claim 1 wherein the concentration of the lithium salt in the electrolyte is 0.5mol/L to 5 mol/L.
7. The flame-retardant electrolyte according to claim 1, wherein the ratio of the amount of the first phase solvent to the amount of the lithium salt is (1-20): 1.
8. The flame-retardant electrolyte according to claim 1, wherein the volume ratio of the second phase solvent to the first phase solvent is (0.01-1): 1, and the volume ratio of the flame-retardant additive to the second phase solvent is (0.01-2): 1.
9. A lithium secondary battery characterized in that the electrolyte is the flame-retardant electrolyte according to any one of claims 1 to 8.
10. A method for designing a two-dimensional structure of a flame-retardant electrolyte of a lithium secondary battery is characterized by comprising the following steps of:
determining the type of lithium salt;
determining the type of the flame retardant additive;
determining a first phase solvent of the lithium-philic salt flame-retardant additive; and
determining the kind of the second-phase solvent of the lithium salt-phobic flame-retardant additive;
wherein the first phase solvent is capable of dissolving lithium salt and is immiscible with the flame retardant additive; the second phase solvent and the first phase solvent can be mutually soluble, and the second phase solvent is used for dissolving the flame retardant additive, so that the flame retardant additive can be dissolved in the electrolyte and becomes a uniform phase with the electrolyte; meanwhile, the second-phase solvent is immiscible with the lithium salt, so that the introduction of the flame retardant additive does not influence the solvation structure of the lithium salt.
CN202111115177.2A 2021-09-23 2021-09-23 Lithium secondary battery flame-retardant electrolyte based on two-dimensional structure design and application Pending CN114122515A (en)

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CN115051032A (en) * 2022-08-17 2022-09-13 华中科技大学 Lithium ion battery electrolyte with negative electrode targeting passivation effect and preparation method thereof
CN117712487A (en) * 2024-02-02 2024-03-15 深圳海辰储能科技有限公司 Electrolyte, battery and power utilization system

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CN107293788A (en) * 2017-06-28 2017-10-24 常州市万昌化工有限公司 A kind of lithium ion battery flame-retardant electrolyte and preparation method thereof
CN112820941A (en) * 2019-11-15 2021-05-18 浙江中蓝新能源材料有限公司 Composition for electrolyte

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CN107293788A (en) * 2017-06-28 2017-10-24 常州市万昌化工有限公司 A kind of lithium ion battery flame-retardant electrolyte and preparation method thereof
CN112820941A (en) * 2019-11-15 2021-05-18 浙江中蓝新能源材料有限公司 Composition for electrolyte

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Publication number Priority date Publication date Assignee Title
CN115051032A (en) * 2022-08-17 2022-09-13 华中科技大学 Lithium ion battery electrolyte with negative electrode targeting passivation effect and preparation method thereof
CN115051032B (en) * 2022-08-17 2022-11-29 华中科技大学 Lithium ion battery electrolyte with negative electrode targeting passivation effect and preparation method thereof
CN117712487A (en) * 2024-02-02 2024-03-15 深圳海辰储能科技有限公司 Electrolyte, battery and power utilization system
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