Low-temperature phase change electrolyte and preparation method thereof, secondary battery

Abstract

The application belongs to the technical field of batteries, and discloses a low-temperature phase change electrolyte, a preparation method thereof and a secondary battery. The low-temperature phase change electrolyte is an organic solvent system. A polymer containing a five-membered ring or a six-membered ring and an imidazole ionic liquid containing a five-membered heterocyclic cation have a pi-pi interaction. When the temperature is higher than the LCST temperature, the pi-pi interaction between the polymer and the imidazole ionic liquid is broken, and phase change occurs. Meanwhile, the benzene ring and the thiophene of the polymer both contain electron-withdrawing groups or C1-C3 alkyl groups, and the ethoxy / ether group segment based on the methyl acrylate structure can effectively reduce the phase change temperature of the polymer, and further reduce the phase change temperature of the electrolyte. The phase change electrolyte can change at a low temperature of 35-60 DEG C. When the battery temperature rises to 75 DEG C or above, the internal reaction of the battery completely stops, and the whole process of temperature rise prevents the battery from having thermal runaway.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a low-temperature phase change electrolyte and a preparation method thereof and a secondary battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high specific energy, light weight, long cycle life, etc., and dominate the application fields of consumer electronics, new energy vehicles, energy storage, etc. However, most of the current lithium ion batteries use organic solvents as electrolytes, which have a series of safety problems in high-temperature environments, such as electrolyte decomposition, gasification, etc. In addition, these electrolytes are flammable, which makes liquid lithium ion batteries face serious safety challenges in high-temperature environments.

[0003] Solid-state batteries use non-flammable solid electrolytes to replace flammable organic solvents, which can greatly reduce the safety hazards related to high-temperature thermal runaway and electrolyte combustion, and is a solution to improve battery safety. Moreover, solid-state batteries can also resist lithium dendrites, so they can match metal lithium with ultra-high theoretical specific capacity (3860 mAh / g) as the negative electrode material. However, solid-state batteries face the challenge of a significant decrease in ionic conductivity in low-temperature environments (below -15℃), which is one of the key bottlenecks restricting the application of solid-state batteries in low-temperature scenarios. For example, the ionic conductivity of sulfide solid-state electrolytes at -20℃ is only 0.1-0.2 mS / cm.

[0004] Temperature-sensitive polymers are a class of high molecular materials that can undergo reversible phase transition in response to temperature changes. They can be divided into lowest critical solution temperature (LCST) type and upper critical solution temperature (UCST) type according to the type of phase transition. When the temperature is higher than LCST, the polymer changes from hydrophilic dissolution to hydrophobic precipitation. When the temperature is lower than UCST, the polymer precipitates from the solution. Therefore, LCST type temperature-sensitive polymers provide a solution to the high-temperature thermal runaway problem of electrolytes.

[0005] Currently, temperature-sensitive polymers are mainly applied to aqueous electrolytes, and phase transition is achieved through the action of hydrogen bonds. For example, the invention patent with the publication number CN110938170A discloses a reversible overheat protection aqueous electrolyte based on methyl cellulose grafted isopropyl acrylamide. However, in order to adapt to lithium ion battery systems with higher voltage, the polymer needs to undergo phase transition in ionic liquids. However, the phase transition temperature of traditional temperature-sensitive polymers in ionic liquids is relatively high (about 80-120℃), and the ionic conductivity in low-temperature environments is also relatively low.

[0006] Therefore, it is urgent to develop a phase change electrolyte that has a lower phase transition temperature in an organic solvent system and can maintain a high ionic conductivity in a low-temperature environment. SUMMARY

[0007] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a low-temperature phase change electrolyte and a preparation method thereof, and a secondary battery, the electrolyte can undergo phase change at a low temperature of 35-60℃, and still maintain high ionic conductivity in a low temperature environment of-20℃.

[0008] The inventive concept of the present application is that the low-temperature phase change electrolyte of the present application is an organic solvent system, and a specific polymer and an imidazole-based ionic liquid are used as main raw materials. The polymer undergoes phase change in the ionic liquid through the LCST phenomenon, and the polymer contains a five-membered ring (thiophene) or a six-membered ring (benzene ring), which can form a large π bond. The cation of the imidazole-based ionic liquid contains a five-membered heterocyclic ring, which can also form a large π bond. Therefore, π-π interaction occurs between the polymer and the imidazole-based ionic liquid. When the temperature is lower than the LCST temperature, the polymer is dissolved in the ionic liquid in the form of a thread; when the temperature is higher than the LCST temperature, the π-π interaction between the polymer and the imidazole-based ionic liquid is broken, the polymer precipitates from the ionic liquid, and itself undergoes agglomeration to grow into larger particles, and the electrolyte changes from a liquid state to a solid state, thereby undergoing phase change.

[0009] Meanwhile, the benzene ring and the thiophene of the polymer of the present application both contain a substituent group, which can be an electron-withdrawing group such as a trifluoromethyl group, a trichloromethyl group, a cyano group or a nitro group. These electron-withdrawing groups can reduce the electron cloud density of the benzene ring and the thiophene, and weaken the π-π interaction between the polymer and the ionic liquid. The weaker the π-π interaction, the lower the phase change temperature of the polymer. The substituent group can also be a C1-C3 alkyl group, which increases the steric hindrance of the benzene ring and the thiophene, and also weakens the π-π interaction between the polymer and the ionic liquid, thereby reducing the phase change temperature of the polymer. In addition, by adding an ethoxy (EO) / ether group segment to the structure of methyl acrylate, the molecular flexibility can be improved, and the phase change temperature of the polymer can also be reduced.

[0010] In addition, a certain amount of lithium salt and specific additives (such as 2-thiouracil, 4-aminophenol, 3-sulfobenzoic acid, dimethyl sulfate, crown ether compounds, cryptand compounds) are added to the low-temperature phase change electrolyte of the present application. The additives are used to reduce the viscosity of the ionic liquid on the one hand, and to form a complex with lithium ions on the other hand, thereby promoting the dissociation of the lithium salt, and thus improving the ionic conductivity of the electrolyte in a low temperature environment.

[0011] Therefore, the phase change electrolyte of the present application can change phase from liquid to solid at low temperature of 35-60℃, and the phase change process is reversible, and the phase change temperature can be controlled by adjusting the types and contents of the polymer and the ionic liquid, and the content of the lithium salt. At the normal working temperature of the lithium ion battery (20-30℃), the electrolyte is in liquid state; when the battery temperature rises to 35-60℃, the electrolyte changes phase, and the decomposition temperature (about 80℃) of the SEI film has not been reached; after the phase change, the ionic conductivity of the electrolyte decreases, the capacity of the battery decreases, the electrochemical reaction in the battery is gradually blocked, and the continuous increase of the battery temperature is slowed down; when the battery temperature rises to above 75℃, the internal reaction of the battery is completely stopped, and the heat runaway of the battery during the whole temperature rising process is effectively prevented.

[0012] To solve the above technical problems, the first aspect of the present application provides a low-temperature phase change electrolyte, the raw material components of which include a polymer, an ionic liquid and an organic solvent, the ionic liquid is an imidazole ionic liquid, and the polymer is selected from one of the structures shown in formula (1) to formula (3):

[0013] Formula (1), Formula (2),

[0014] Formula (3);

[0015] wherein R1, R2 and R3 are independently selected from C1-C3 alkyl, trifluoromethyl, trichloromethyl, cyano or nitro, and n is an integer between 100 and 1500.

[0016] In some embodiments of the present application, R1, R2 and R3 are independently selected from methyl or trifluoromethyl.

[0017] In some embodiments of the present application, n is an integer between 200 and 1200; for example, an integer between 200 and 600, 500 and 800, 700 and 1000, 900 and 1100, 1000 and 1200, etc.

[0018] In some embodiments of the present application, the cation of the ionic liquid is selected from one of the structures shown in formula (4) to formula (6):

[0019] Formula (4), Formula (5),

[0020] Formula (6);

[0021] wherein m is an integer between 1 and 16;

[0022] the anion of the ionic liquid is selected from I- , Cl - , F - , [PF6] - , [TFSI] - , [FSI] - , [TFSM] - , [FTFSI] - , [CTFSI] - , [SbF6] - , [NTf2] - .

[0023] In some embodiments of the present application, the anion is selected from any one of F - , [FSI] - , [TFSM] - , [NTf2] - .

[0024] In some embodiments of the present application, the m is an integer between 1-10, for example, 1, 2, 5, 6, 8, 10, etc., including but not limited to the listed values.

[0025] In some embodiments of the present application, the organic solvent is selected from at least one of vinyl carbonate, propylene carbonate, ethanol, ethylene glycol, glycerol, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, trifluorinated propylene carbonate, fluorinated vinyl carbonate, nonafluoromethyl butyl ether, dimethyl sulfoxide, acetonitrile.

[0026] In some embodiments of the present application, the organic solvent is selected from at least one of vinyl carbonate, trifluorinated propylene carbonate, fluorinated vinyl carbonate.

[0027] In some embodiments of the present application, the raw material components include, by weight parts: polymer 2-13 parts, ionic liquid 30-70 parts, and organic solvent 10-30 parts.

[0028] In some embodiments of the present application, the raw material components include, by weight parts: polymer 3-10 parts, ionic liquid 40-70 parts, and organic solvent 15-30 parts.

[0029] In some embodiments of the present application, the raw material components include, by weight parts: polymer 4-7 parts, ionic liquid 45-65 parts, and organic solvent 20-27 parts.

[0030] In some embodiments of the present application, the raw material components further include 5-25 parts by weight of lithium salt and 0.1-5 parts by weight of additives.

[0031] In some embodiments of the present invention, the raw material components further include 7-22 parts by weight of lithium salt and 1-2 parts by weight of additives.

[0032] In some embodiments of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate-borate), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalate-borate), and lithium bis(fluorosulfonyl)imide.

[0033] In some embodiments of the present invention, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide.

[0034] In some embodiments of the present invention, the additive is selected from at least one of 2-thiouracil, 4-aminophenol, 3-sulfobenzoic acid, dimethyl sulfate, crown ether compounds, and cryptane compounds.

[0035] In some embodiments of the present invention, the crown ether compound is selected from at least one of 18-crown-6 ether and 15-crown-5 ether.

[0036] In some embodiments of the present invention, the cryptether compound is selected from at least one of cryptether 2,2,1 and cryptether 2,3,1.

[0037] In some embodiments of the present invention, the additive is selected from at least one of 2-thiouracil, 4-aminophenol, dimethyl sulfate, and 18-crown-6 ether.

[0038] A second aspect of the present invention provides a method for preparing the above-mentioned low-temperature phase change electrolyte, comprising the following steps:

[0039] The raw material components are mixed to obtain the low-temperature phase change electrolyte.

[0040] In some embodiments of the invention, the mixing is carried out under an inert atmosphere.

[0041] In some embodiments of the present invention, the inert atmosphere is an argon atmosphere.

[0042] In some embodiments of the present invention, the method for preparing the low-temperature phase change electrolyte includes the following steps:

[0043] Under an argon atmosphere, the polymer, ionic liquid, organic solvent, lithium salt, and additives are mixed and stirred until homogeneous to obtain the low-temperature phase change electrolyte.

[0044] A third aspect of the present invention provides a secondary battery comprising the aforementioned low-temperature phase change electrolyte.

[0045] In some embodiments of the present invention, the secondary battery is a lithium-ion battery.

[0046] In some embodiments of the present invention, the secondary battery further includes a positive electrode, a negative electrode, and a separator.

[0047] In some embodiments of the present invention, the active material of the positive electrode can be selected from conventional positive electrode active materials in the art, such as lithium iron phosphate (LiFePO4), lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium nickel oxide, ternary materials, etc.

[0048] In some embodiments of the present invention, the active material of the negative electrode can be selected from conventional negative electrode active materials in the art, such as graphite, silicon, and lithium metal.

[0049] In some embodiments of the present invention, the diaphragm material can be selected from conventional diaphragm materials in the art, such as polyethylene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, polytetrafluoroethylene, etc.

[0050] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages:

[0051] (1) The low-temperature phase change electrolyte of the present invention is an organic solvent system, using polymers with specific structures and imidazole ionic liquids as the main raw materials. It utilizes the π-π interaction between the polymer containing a five-membered ring (thiophene) or a six-membered ring (benzene ring) and the imidazole ionic liquid containing a five-membered heterocycle. When the temperature is higher than the LCST temperature, the π-π interaction between the polymer and the imidazole ionic liquid breaks, the polymer precipitates from the ionic liquid, agglomerates, and grows into larger particles, and the electrolyte changes from liquid to solid, undergoing a phase change. At the same time, the benzene ring and thiophene of the polymer contain electron-withdrawing groups or C1-C3 alkyl groups, as well as ethoxy (EO) / ether segments based on the methyl acrylate structure, which can effectively reduce the phase change temperature of the polymer, thereby reducing the phase change temperature of the electrolyte.

[0052] (2) The phase change electrolyte of the present invention can undergo phase change at a low temperature of 35-60℃. The phase change temperature can be controlled by adjusting the type and content of polymer and ionic liquid, as well as the content of lithium salt. After the phase change occurs, the ionic conductivity of the electrolyte decreases, the battery capacity decreases, and the electrochemical reaction inside the battery is gradually blocked, thus slowing down the continued rise in battery temperature. When the battery temperature rises to above 75℃, the reaction inside the battery completely stops, effectively preventing thermal runaway throughout the entire process of battery heating.

[0053] (3) The present invention adds a certain amount of lithium salt and specific additives to the phase change electrolyte. On the one hand, the additives help to reduce the viscosity of the ionic liquid, and on the other hand, they can form complexes with lithium ions to promote the dissociation of lithium salt, thereby improving the ionic conductivity of the electrolyte in the low temperature environment. This enables the lithium-ion battery to achieve an ionic conductivity of 1.35-1.84 mS / cm in the low temperature environment of -20℃. Attached Figure Description

[0054] Figure 1 The discharge capacity diagram shows the lithium-ion battery assembled using the low-temperature phase change electrolyte prepared in Example 1 of this invention.

[0055] Figure 2 The discharge capacity diagram shows the lithium-ion battery assembled using the low-temperature phase change electrolyte prepared in Example 2 of this invention.

[0056] Figure 3 The discharge capacity diagram shows the lithium-ion battery assembled using the low-temperature phase change electrolyte prepared in Example 3 of this invention.

[0057] Figure 4 The discharge capacity diagram shows the lithium-ion battery assembled using the low-temperature phase change electrolyte prepared in Example 4 of this invention.

[0058] Figure 5 The diagram shows the discharge capacity of a lithium-ion battery assembled using the low-temperature phase change electrolyte prepared in Example 5 of this invention. Detailed Implementation

[0059] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0060] Example 1

[0061] A low-temperature phase change electrolyte, the raw material components of which, by weight, include: 6 parts polymer, 54 parts ionic liquid, 12 parts lithium hexafluorophosphate, 5 parts lithium bis(trifluoromethanesulfonyl)imide, 21 parts ethylene carbonate and 2 parts 4-aminophenol.

[0062] Wherein: the chemical structure of the polymer is shown in formula (1):

[0063] Equation (1);

[0064] Where R1 is a methyl group and n is an integer between 1000 and 1200.

[0065] The anion of ionic liquids is F. - The chemical structure of the cation is shown in formula (6):

[0066] Equation (6);

[0067] Where m is 5.

[0068] The preparation method of the above-mentioned low-temperature phase change electrolyte includes the following steps:

[0069] In an argon-filled glove box, each raw material was weighed according to its composition, mixed, and stirred at 60 rpm for 30 minutes to obtain the low-temperature phase change electrolyte of this embodiment.

[0070] Example 2

[0071] A low-temperature phase change electrolyte comprises, by weight, the following raw material components: 4 parts polymer, 45 parts ionic liquid, 17 parts lithium bis(fluorosulfonyl)imide, 5 parts lithium bis(trifluoromethanesulfonyl)imide, 27 parts fluoroethylene carbonate, 0.5 parts dimethyl sulfate, and 1.5 parts 18-crown-6 ether.

[0072] Wherein: the chemical structure of the polymer is shown in formula (2):

[0073] Equation (2);

[0074] Where R2 is a methyl group and n is an integer between 900 and 1100.

[0075] The anion of the ionic liquid is [NTf2]. - The chemical structure of the cation is shown in formula (4):

[0076] Equation (4);

[0077] Where m is 2.

[0078] The preparation method of the low-temperature phase change electrolyte in Example 2 is the same as that in Example 1.

[0079] Example 3

[0080] A low-temperature phase change electrolyte, the raw material components of which, by weight, include: 7 parts polymer, 65 parts ionic liquid, 7 parts lithium difluorosulfonylimide, 20 parts propylene trifluorocarbonate, and 1 part 2-thiouracil.

[0081] Wherein: the chemical structure of the polymer is shown in formula (2):

[0082] Equation (2);

[0083] Where R2 is trifluoromethyl and n is an integer between 500 and 800.

[0084] The anion of ionic liquids is [FSI]. - The chemical structure of the cation is shown in formula (5):

[0085] Equation (5);

[0086] Where m is 2.

[0087] The preparation method of the low-temperature phase change electrolyte in Example 3 is the same as that in Example 1.

[0088] Example 4

[0089] A low-temperature phase change electrolyte, the raw material components of which, by weight, include: 5 parts polymer, 64 parts ionic liquid, 8 parts lithium bis(trifluoromethanesulfonyl)imide, 2 parts lithium hexafluorophosphate, 20 parts fluoroethylene carbonate, and 1 part dimethyl sulfate.

[0090] Wherein: the chemical structure of the polymer is shown in formula (1):

[0091] Equation (1);

[0092] Where R1 is trifluoromethyl and n is an integer between 200 and 600.

[0093] The anion of the ionic liquid is [TFSM]. - The chemical structure of the cation is shown in formula (5):

[0094] Equation (5);

[0095] Where m is 1.

[0096] The preparation method of the low-temperature phase change electrolyte in Example 4 is the same as that in Example 1.

[0097] Example 5

[0098] A low-temperature phase change electrolyte, the raw material components of which, by weight, include: 6 parts polymer, 55 parts ionic liquid, 14 parts lithium hexafluorophosphate, 2 parts lithium difluorosulfonylimide, 21 parts fluoroethylene carbonate and 2 parts 4-aminophenol.

[0099] Wherein: the chemical structure of the polymer is shown in formula (3):

[0100] Equation (3);

[0101] Where R3 is a methyl group and n is an integer between 100 and 300.

[0102] The anion of the ionic liquid is [CTFSI]. - The chemical structure of the cation is shown in formula (4):

[0103] Equation (4);

[0104] Where m is 1.

[0105] The preparation method of the low-temperature phase change electrolyte in Example 5 is the same as that in Example 1.

[0106] Comparative Example 1

[0107] The difference between Comparative Example 1 and Example 1 is that the raw material components of the low-temperature phase change electrolyte do not contain polymers. The raw material components of the low-temperature phase change electrolyte in Comparative Example 1, by weight, include: 54 parts of ionic liquid, 12 parts of lithium hexafluorophosphate, 5 parts of lithium bis(trifluoromethanesulfonyl)imide, 21 parts of ethylene carbonate, and 2 parts of 4-aminophenol.

[0108] Wherein: the anion of the ionic liquid is F - The chemical structure of the cation is shown in formula (6):

[0109] Equation (6);

[0110] Where m is 5.

[0111] Comparative Example 2

[0112] The only difference between Comparative Example 2 and Example 3 is the chemical structure of the polymer. The polymer in Comparative Example 2 does not contain substituents on its five-membered ring, and its chemical structure is shown in formula (7):

[0113] Equation (7);

[0114] Where n is an integer between 500 and 800.

[0115] Comparative Example 3

[0116] The difference between Comparative Example 3 and Example 1 is that the raw material components of the low-temperature phase change electrolyte do not contain the additive 4-aminophenol. The raw material components of the low-temperature phase change electrolyte in Comparative Example 3, by weight, include: 6 parts of polymer, 54 parts of ionic liquid, 12 parts of lithium hexafluorophosphate, 5 parts of lithium bis(trifluoromethanesulfonyl)imide, and 21 parts of ethylene carbonate.

[0117] Wherein: the chemical structure of the polymer is shown in formula (1):

[0118] Equation (1);

[0119] Where R1 is a methyl group and n is an integer between 1000 and 1200.

[0120] The anion of ionic liquids is F. - The chemical structure of the cation is shown in formula (6):

[0121] Equation (6);

[0122] Where m is 5.

[0123] Comparative Example 4

[0124] The only difference between Comparative Example 4 and Example 1 is the chemical structure of the polymer. The polymer in Comparative Example 4 is PMMA, which does not contain a benzene ring, and its chemical structure is shown in formula (8):

[0125] Equation (8);

[0126] Where n is an integer between 500 and 800.

[0127] Comparative Example 5

[0128] The only difference between Comparative Example 5 and Example 1 is the chemical structure of the polymer. The benzene ring of the polymer in Comparative Example 5 contains other substituents, and its chemical structure is shown in formula (9):

[0129] Equation (9);

[0130] Where n is an integer between 500 and 800.

[0131] Comparative Example 6

[0132] The only difference between Comparative Example 6 and Example 1 is the chemical structure of the ionic liquid. The cation of the ionic liquid in Comparative Example 6 does not contain a five-membered ring, and its chemical structure is shown in formula (10). The anion is F. - .

[0133] Equation (10).

[0134] Performance testing

[0135] The low-temperature phase change electrolytes prepared in Examples 1-5 and Comparative Examples 1-6 were respectively added to battery casings using lithium iron phosphate as the positive electrode material, lithium metal as the negative electrode, and polyethylene as the separator, to assemble lithium-ion batteries. Ionic conductivity, discharge capacity, and phase change temperature were tested, wherein the temperature at which the discharge capacity reached 0 was recorded as the turn-off temperature. Specific test conditions are as follows:

[0136] 1. Ionic conductivity

[0137] With an area of ​​2cm 2 Stainless steel gaskets were assembled into batteries with the low-temperature phase change electrolytes prepared in Examples 1-5 and Comparative Examples 1-6, respectively. The batteries were placed in a low-temperature test chamber at -20°C for 3 hours. An electrochemical workstation was connected, and a sinusoidal voltage signal with an amplitude of 20mV was applied. The frequency range of the test was between 4-100MHz. The resistance of the electrolyte was recorded and the ionic conductivity was calculated.

[0138] 2. Discharge capacity

[0139] Place the battery in a high and low temperature test chamber, set the temperature to 25℃, let the battery stand for 1 hour, connect the charge and discharge instrument, discharge at a rate of 0.2C, with a discharge cutoff voltage of 2V, and record the capacity of the first discharge at 25℃. Adjust the test chamber temperature to 75℃, let the battery stand for 1 hour, discharge at a rate of 0.2C, with a discharge cutoff voltage of 2V, and record the discharge capacity. Switch between the two temperatures.

[0140] 3. Phase transition temperature test

[0141] The phase transition temperature of an electrolyte is determined by measuring the transmittance of the electrolyte solution. A variable-temperature ultraviolet-visible spectrometer is used to measure the transmittance of the electrolyte solution. The solution is placed on the instrument's heating stage and heated at a rate of 1℃ / min. The transmittance curve is recorded, and the temperature at which the transmittance reaches 0 is defined as the phase transition temperature.

[0142] Test results are as follows Figures 1-5 As shown in Table 1.

[0143] Table 1:

[0144]

[0145] From Table 1 and Figures 1-5 It can be seen that the lithium-ion batteries assembled with the low-temperature phase change electrolytes of Examples 1-5 of the present invention can maintain a high ionic conductivity of 1.35-1.84 mS / cm in a low-temperature environment of -20℃; the discharge capacity at 25℃ is 154.7-160.1 mAh / g; the phase change temperature is as low as 35.5-58.5℃; and the turn-off temperature is 75℃.

[0146] Compared to Example 1, Comparative Example 1 does not contain polymers, so the electrolyte does not undergo a phase change and there is no thermal runaway prevention effect.

[0147] Compared to Example 3, Comparative Example 2 showed that the phase transition temperature of the electrolyte was 74.5°C higher than that of Example 3 because the polymer's five-membered ring did not contain substituents, indicating that substituents have a significant effect on reducing the phase transition temperature.

[0148] Compared to Example 1, Comparative Example 3 showed a 33.5% decrease in the ionic conductivity of the electrolyte due to the absence of the additive 4-aminophenol, indicating that the additive 4-aminophenol can effectively improve the ionic conductivity of the electrolyte at low temperatures.

[0149] Compared to Example 1, Comparative Example 4 uses the conventional polymer PMMA, so the electrolyte does not undergo a phase change and there is no thermal runaway prevention effect.

[0150] Compared to Example 1, Comparative Example 5, due to the presence of other substituents on the benzene ring of the polymer, cannot effectively regulate π-π interactions, the electrolyte does not undergo phase transition, and there is no thermal runaway prevention effect.

[0151] Compared to Example 1, Comparative Example 6, due to the absence of a five-membered ring in the ionic liquid, failed to form π-π interactions, and the electrolyte also did not undergo a phase transition, thus offering no thermal runaway prevention effect. The test results from Comparative Examples 4-6 show that only polymers with specific structures can undergo phase transitions and thus provide thermal runaway prevention.

[0152] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A low temperature phase change electrolyte characterized in that, The raw material components include, by weight: 2-13 parts of a polymer, 30-70 parts of an ionic liquid, 10-30 parts of an organic solvent, 5-25 parts of a lithium salt, and 0.1-5 parts of an additive; The additive is selected from at least one of 2-thiouracil, 4-aminophenol, 3-sulfobenzoic acid, dimethyl sulfate, crown ether compounds, and cryptand compounds; The ionic liquid is an imidazole ionic liquid, and the polymer is selected from one of the structures shown in formulas (1)-(3): Formula (1), Formula (2), Formula (3); wherein R1, R2, and R3 are independently selected from C1-C3 alkyl, trifluoromethyl, trichloromethyl, cyano, or nitro, and n is an integer between 100 and 1500.

2. The low temperature phase change electrolyte of claim 1, wherein, The cation of the ionic liquid is selected from one of the structures shown in formulas (4)-(6): Formula (4), Formula (5), Equation (6); wherein m is an integer between 1 and 16. The anion of the ionic liquid is selected from any one of I - , Cl - , F - , [PF6] - , [TFSI] - , [FSI] - , [TFSM] - , [FTFSI] - , [CTFSI] - , [SbF6] - , [NTf2] - .

3. The low temperature phase change electrolyte according to claim 1 or 2, characterized in that, The organic solvent is selected from at least one of vinyl carbonate, propylene carbonate, ethanol, ethylene glycol, glycerol, methyl formate, methyl acetate, methyl butyrate, ethyl propionate, trifluorinated propylene carbonate, fluorinated vinyl carbonate, nonafluoromethyl butyl ether, dimethyl sulfoxide, and acetonitrile.

4. The low temperature phase change electrolyte of claim 1, wherein, The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluoro)oxalato borate, and lithium bis(fluoro)sulfonimide.

5. A method of preparing a low temperature phase change electrolyte as claimed in any one of claims 1 to 4, characterised in that, The method comprises the following steps: Mixing the raw material components to obtain the low-temperature phase change electrolyte.

6. The method of claim 5, wherein the low temperature phase change electrolyte is prepared by the steps of: The mixing is performed under an inert atmosphere.

7. A secondary battery characterized by comprising: The low-temperature phase change electrolyte of any one of claims 1-4.

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