High-safety temperature-responsive electrolyte, lithium ion battery and sodium ion battery

Abstract

The invention discloses a high-safety temperature-responsive electrolyte, a lithium ion battery and a sodium ion battery, the high-safety temperature-responsive electrolyte comprises a thermal response solvent, a cosolvent and an electrolyte salt, the thermal response solvent is a thermal response polymer monomer, the thermal response polymer monomer has at least one of the structures of vinyl ether, divinyl ether, dialkenyl amide and dialkenyl butanediimine, the thermal response polymer monomer can quickly form a polymer solid electrolyte under the catalysis of an initiator salt in electrolyte salt under a high-temperature condition, and the fixation of the solid electrolyte enables a diaphragm in a battery not to collapse, so that the battery diaphragm can be used as a lithium ion battery diaphragm. Therefore, short circuit caused by thermal shrinkage and fusion of the diaphragm is avoided, and thermal runaway is avoided. The electrolyte can be used for preparing the lithium-ion and sodium-ion battery, and the lithium-ion and sodium-ion battery can keep a relatively high capacity retention rate while giving consideration to the safety performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of high-safety batteries, in particular to a high-safety temperature-responsive electrolyte and a lithium ion battery and a sodium ion battery. BACKGROUND

[0002] As a key component of new energy vehicles, secondary batteries have made good progress in improving battery energy, but the safety problem of secondary batteries is also very prominent. For example, the safety problem related to thermal runaway (TR) has become one of the main challenges in pursuing higher energy batteries. Taking lithium batteries as an example, there are two key reasons for causing thermal runaway: internal short circuit between the positive and negative electrodes and strong chemical exothermic reaction, which can make the battery temperature rise to 400-1000℃ in a very short time. The internal short circuit between the positive and negative electrodes and the strong chemical exothermic reaction are mainly caused by the collapse of the separator of the lithium battery at high temperature. The lithium ion separator will inevitably shrink and melt at a high temperature of about 150℃, causing a short circuit, and thus leading to thermal runaway. Sodium ion batteries, as a representative of secondary batteries, also have similar thermal runaway problems. Therefore, the problem of thermal runaway prevents the development of high-energy-density secondary batteries on a large scale.

[0003] External abuse (such as needle puncture, extrusion), internal short circuit, overcharge and heat abuse, etc. can cause the battery to heat up, thereby triggering thermal runaway. The existing method to solve thermal runaway is still to use organic flame retardant, such as fluorinated organic or phosphate ester solvent, its mechanism of action is to capture the high-reactivity free radicals in the electrolyte by decomposing free radicals to block the chain reaction of battery thermal runaway. Flame retardant can improve the safety of electrolyte, but the use of a large amount of flame retardant will greatly increase the impedance of the battery, and also reduce the electrochemical performance such as cycle and rate performance. In addition, the improvement of the structure of the battery is also a way to improve the safety of the battery. Chinese patent CN104953083B discloses a battery cell structure for preventing battery fire and explosion, the outer part of the battery cell body is coated with a high-temperature self-cracking sealing device, and a damping device is arranged inside the battery cell shell. The damping device and the sealing device are provided with a cavity, and the cavity is filled with fire extinguishing material. Another Chinese patent CN110215642B discloses a thermal response core-shell structure fire extinguishing agent suitable for lithium ion batteries and a preparation method thereof, which includes an outer shell containing a thermal response polymer and an inner core containing a fire extinguishing agent or a flame retardant. The shell will change its conformation from collapse to stretch at a certain temperature, while releasing the internal fire extinguishing agent or flame retardant. Adjust the LCST (lower critical solution temperature) of the thermal response polymer to be approximately equal to the upper limit of the safety window temperature. When the temperature of the electrolyte is higher than the LCST, the thermal response copolymer will change from collapse to stretch state, releasing the inner core fire extinguishing material. However, it is difficult to match the polymer of the core-shell structure fire extinguishing agent, and the temperature regulation is relatively difficult. The improvement of the battery structure is also a complex process, which leads to poor practicability.

[0004] Therefore, it is necessary to further develop new methods to solve thermal runaway to improve the safety performance of secondary batteries. SUMMARY

[0005] Therefore, the purpose of the present application is to provide a high-safety temperature-responsive electrolyte and lithium ion battery, sodium ion battery. The electrolyte comprises a thermal response polymer monomer, an initiator salt, and the physical state of the polymer monomer changes from liquid to solid state when it reaches a certain temperature due to the presence of the initiator salt, thereby preventing the electrolyte from burning and avoiding the occurrence of thermal runaway.

[0006] To achieve or at least partially achieve the above-mentioned purposes, the present application provides the following technical solutions:

[0007] In a first aspect, the present application provides a high-safety temperature-responsive electrolyte, comprising: a thermal response solvent, a co-solvent and an electrolyte salt; wherein,

[0008] The heat-responsive solvent comprises or consists of a heat-responsive polymer monomer or a mixture of heat-responsive polymer monomers, wherein each heat-responsive polymer monomer has a structure as shown in

[0009] Further, the heat-responsive polymer monomer is any one of ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,6-hexanediol divinyl ether, terephthalic acid bis[4-(vinyleneoxy)-butyl] ester, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trihydroxymethylpropane triglycidyl ether, diallyl disulfide, N,N'-methylenebisacrylamide, tetramethyldivinyl disiloxane, diallyl tetramethyldisiloxane, and 2,4-divinyl-2,4,6,6,8,8-hexamethylcyclotetrasiloxane.

[0010] Further, the co-solvent comprises a first co-solvent and a second co-solvent, the first co-solvent is at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, fluoroethylene carbonate, fluoropropylene carbonate, methyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite; and the second co-solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, ethyl formate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate.

[0011] Further, the electrolyte salt comprises an initiator salt and a non-initiator salt; the initiator salt comprises an initiator lithium salt or an initiator sodium salt, wherein the initiator lithium salt comprises at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium nitrate, and the initiator sodium salt comprises at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bisfluorosulfonylimide, sodium nitrate; and the non-initiator salt comprises a non-initiator lithium salt or a non-initiator sodium salt, wherein the non-initiator lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, and the non-initiator sodium salt comprises at least one of sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate.

[0012] In a second aspect, the present application provides a lithium ion battery comprising the aforementioned high-safety temperature-responsive electrolyte.

[0013] In a third aspect, the present application provides a sodium ion battery comprising the aforementioned high-safety temperature-responsive electrolyte.

[0014] The technical solutions provided by the present application have at least the following advantages compared with the prior art:​

[0015] 1. The heat-responsive polymer monomer itself can exhibit similar physicochemical properties and electrochemical performance as the traditional commercial electrolyte at room temperature, and produce effective heat-responsive behavior within a certain temperature range, with the polymer monomer rapidly converting from liquid to solid under temperature stimulation. The high-safety temperature heat-responsive electrolyte provided by the present application can be intelligently temperature-controlled and take into account the flame-retardant effect, and before the separator of the secondary battery melts, the electrochemical behavior of the battery is cut off through the heat-responsive polymerization process of the electrolyte, and due to the presence of the flame-retardant cosolvent (first cosolvent), the polymer after polymerization can have a flame-retardant effect, timely cutting off the thermal runaway, and ensuring the safety of the battery.

[0016] 2. The high-safety temperature-responsive electrolyte provided by the present application is very suitable for manufacturing lithium ion batteries or sodium ion batteries. The heat-responsive polymer monomer can be adjusted to have a temperature range of 70-250℃ through changes in its own structure, and due to this certain controllability of the electrolyte, the electrolyte undergoes liquid-solid transition at a specific temperature, filling the pores of the separator while maintaining the extensibility of the separator. When the temperature reaches the melting point of the separator, the electrolyte changes from liquid to solid due to the heat-responsive polymerization process, and the fixation of the solid electrolyte does not cause the separator to collapse, so the separator will not cause thermal shrinkage and melting to cause short circuit, avoiding thermal runaway. The high-safety temperature heat-responsive electrolyte provided by the present application can adapt to separators of various melting temperatures, taking into account the electrochemical performance while ensuring the safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 Figure (a) is the experimental graph of the comparative example, and (b) is the experimental graph of example 8.

[0018] Figure 2 The results of the cone calorimeter experiment of comparative example 1, comparative example 2 and example 8 are shown in the following table. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0020] In the present application, the terms "first", "second", etc. are used to distinguish the same or similar items with basically the same function and effect, and are only used to clearly describe the technical scheme of the embodiments of the present application, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implying the number of the indicated technical features.

[0021] In the present application, the term "comprising" is intended to be inclusive and to mean that additional elements can be present in addition to the listed elements.

[0022] The present inventors found that certain heat-responsive polymer monomers (such as ethylene glycol divinyl ether, triethylene glycol divinyl ether) can rapidly polymerize under the catalysis of an initiator and change from a liquid state to a solid state as the temperature rises. The polymer monomers can be used as solvents in secondary battery electrolytes, which not only achieve the electrochemical performance of the battery, but also avoid the risk of thermal runaway caused by short circuit due to the collapse of the secondary battery separator, because the polymer monomers change from a liquid to a solid at high temperatures.

[0023] Before developing a high-safety secondary battery electrolyte, the present application systematically studies two parameters of the electrolyte. The first parameter is t (l→s) , the conversion time required for the electrolyte to change from a liquid to a solid; the second parameter is H (TR) , the total heat released when the electrolyte burns under a certain heat radiation value (25 kW / m 2 ). The t (l→s) value of the electrolyte reflects the delay of the electrolyte in responding to heat under relatively high temperature conditions, and represents the speed of the conversion of the electrolyte; the order of magnitude of the t (l→s) value can be seconds, minutes, or hours, and the response time of seconds and minutes is an ideal response level, which indicates that the lag of the heat response is small, and is very important for the safety of the battery. The conversion time at this level can effectively alleviate the safety problems caused by relaxation, such as internal short circuit and flammability of the electrolyte. The H (TR) of the electrolyte is evaluated by a cone calorimeter to assess the combustion process and fire hazard of the electrolyte, and is a parameter representing the total heat release of the electrolyte under constant radiation. The size of the H (TR) value of the electrolyte reflects the strength of the flame retardant ability of the electrolyte; the stronger the flammability of the electrolyte, the weaker the flame retardant ability of the electrolyte under high temperature, and the more likely the exothermic reaction of the electrolyte under high temperature, so the higher the H (TR) value; on the contrary, the lower the H (TR) value, the stronger the flame retardant ability of the electrolyte, and the more difficult the exothermic reaction under high temperature. Therefore, the heat-responsive electrolyte with low t (l→s) value and H (TR) value has the characteristics of high safety, which can enhance the safety of the battery, and is the development goal.

[0024] Based on this, the embodiment of the present application provides a high safety temperature responsive electrolyte, comprising: a thermal response solvent, a co-solvent and an electrolyte salt; wherein the thermal response solvent comprises a thermal response polymer monomer or a thermal response polymer monomer mixture composed of multiple thermal response polymer monomers, and the structure of each thermal response polymer monomer is as shown in The thermal response polymer monomer serves as an ion transmission medium, and when the electrolyte temperature rises to a certain range (such as above 150 DEG C), the thermal response polymer monomer rapidly polymerizes into a solid polymer to form a solid electrolyte, thereby preventing the battery diaphragm from shrinking at the melting point to cause short circuit, and the low reaction solid electrolyte coats the original battery diaphragm, thereby quickly and effectively preventing the occurrence of thermal runaway.

[0025] In some embodiments, the t (l→s) of the electrolyte is 5 s to 5 min. In some preferred embodiments, the t (l→s) of the electrolyte is 5 s to 5 min; and the t (l→s) of the electrolyte falls within the above preferred range, which is more conducive to improving the rate of conversion of the thermal response electrolyte from a liquid state to a solid state, and rapid conversion into a solid polymer electrolyte can reduce the probability of collapse of the diaphragm at its melting point, and further improve the safety of the battery.

[0026] In some embodiments, the H (TR) of the electrolyte is 0 to 5.2 kJ / g. In some preferred embodiments, the H (TR) of the electrolyte is 0 to 1.5 kJ / g; and the H (TR) of the electrolyte falls within the above preferred range, which is more conducive to reducing the generation of combustion free radicals at high temperatures, further reducing the short board effect of the electrolyte on the safety of the battery, and improving the flame retardancy of the electrolyte.

[0027] In some embodiments, the thermal response polymer monomer is any one of ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,6-hexanediol divinyl ether, terephthalic acid bis[4-(vinyleneoxy)-butyl] ester, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trihydroxymethylpropane triglycidyl ether, diallyl disulfide, N,N'-methylene bisacrylamide, tetramethyldivinyl disiloxane, diallyl tetramethyldisiloxane and 2,4-divinyl-2,4,6,6,8,8-hexamethylcyclotetrasiloxane; wherein the structure of the terephthalic acid bis[4-(vinyleneoxy)-butyl] ester is as shown in structural formula 1: The structure of the 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione is as shown in structural formula 2: The structure of the trihydroxymethylpropane triglycidyl ether is as shown in structural formula 3: 2,4-Diethenyl-2,4,6,6,8,8-hexamethylcyclotetrasiloxane has the structure shown in structural formula 4:

[0028]

[0029] In some embodiments, the thermal response solvent accounts for 25% to 70% of the volume of the high-safety temperature-responsive electrolyte. In some preferred embodiments, the thermal response solvent accounts for 35% to 65% of the volume of the high-safety temperature-responsive electrolyte. In some more preferred embodiments, the thermal response solvent accounts for 40% to 55% of the volume of the high-safety temperature-responsive electrolyte.

[0030] In some embodiments, the co-solvent includes a first co-solvent and a second co-solvent, the first co-solvent is at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, fluoroethylene carbonate, fluoropropylene carbonate, methyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphite; the first co-solvent is a flame-retardant co-solvent, which can effectively slow down the burning speed of the battery under high temperature conditions, and reduce the toxicity and corrosiveness of the combustion products.

[0031] In some embodiments, the first co-solvent accounts for 10% to 55% of the volume of the high-safety temperature-responsive electrolyte. In some preferred embodiments, the first co-solvent accounts for 20% to 40% of the volume of the high-safety temperature-responsive electrolyte.

[0032] In some embodiments, the second co-solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, ethyl formate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate.

[0033] In some embodiments, the second co-solvent accounts for 20% to 50% of the volume of the high-safety temperature-responsive electrolyte. In some preferred embodiments, the second co-solvent accounts for 20% to 35% of the volume of the high-safety temperature-responsive electrolyte.

[0034] In some embodiments, the electrolyte salt includes an initiator salt and a non-initiator salt, and the types of initiator salt and non-initiator salt in the electrolyte vary according to the type of secondary battery. For example, in a lithium ion battery, the electrolyte salt in the electrolyte is an electrolyte lithium salt, including an initiator lithium salt and a non-initiator lithium salt. Specifically, the initiator lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, and lithium nitrate, and the non-initiator lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate. In a sodium ion battery, the electrolyte salt in the electrolyte is an electrolyte sodium salt, including an initiator sodium salt and a non-initiator sodium salt. Specifically, the initiator sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bisfluorosulfonylimide, and sodium nitrate, and the non-initiator sodium salt includes at least one of sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalato)borate, and sodium difluoro(oxalato)borate.

[0035] In some preferred embodiments, the type of initiator lithium salt is lithium hexafluorophosphate or lithium nitrate. In some preferred embodiments, the non-initiator lithium salt is lithium trifluoromethanesulfonylimide. In some preferred embodiments, the type of initiator sodium salt is sodium hexafluorophosphate or sodium nitrate. In some preferred embodiments, the non-initiator sodium salt is sodium trifluoromethanesulfonylimide.

[0036] In some embodiments, the concentration of the electrolyte salt is 0.2-3 mmol / L in terms of metal ions (such as lithium ions or sodium ions). In some preferred embodiments, the concentration of the electrolyte salt is 0.5-1.2 mmol / L in terms of metal ions (such as lithium ions or sodium ions).

[0037] Based on the above, the embodiments of the present application also provide a secondary battery, which includes the aforementioned high-safety temperature-responsive electrolyte, a positive electrode sheet, and a negative electrode sheet.

[0038] In some embodiments, the secondary battery is a lithium ion battery, and different types of electrolyte solvents and lithium salts can be selected to adjust the response of the electrolyte of the lithium ion battery, considering the influence of the type and proportion of the electrolyte, the type and concentration of the salt, and the like on the thermal response temperature and time of the electrolyte of the battery. In some embodiments, the electrolyte salt is at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium difluoro(oxalato)borate, and lithium nitrate. In some preferred embodiments, the electrolyte salt is lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium bisfluorosulfonylimide, which can more reasonably adjust the thermal response polymer monomer polymerization temperature and time in the lithium ion battery.

[0039] In some embodiments, the secondary battery is a sodium ion battery. In some embodiments, the electrolyte salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bisfluorosulfonylimide, sodium difluoro(oxalato)borate, sodium nitrate. In some preferred embodiments, the electrolyte salt is sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bisfluorosulfonylimide, which can more reasonably adjust the polymer monomer polymerization temperature and time in the sodium ion battery.

[0040] Based on this, the application also provides a preparation method of the foregoing secondary battery. Taking a lithium battery as an example, the preparation method comprises the following steps: (1) preparation of a positive electrode sheet: mixing positive active material, acetylene black conductive additive and polyvinylidene fluoride (PVDF) binder in a mass ratio of 8:1:1, adding a solvent N-methyl pyrrolidone (NMP), stirring under the action of a stirrer until the system is uniform, to obtain a positive electrode slurry; uniformly coating the positive electrode slurry on a carbon-loaded aluminum current collector, drying in an oven at 80°C, to obtain a positive electrode sheet; taking metal lithium as a button-type negative electrode; (2) preparation of a soft package negative electrode sheet: mixing graphite active material, conductive agent acetylene black, thickening agent sodium carboxymethyl cellulose (CMC) and binder SBR in a mass ratio of 90:3:3:4, adding a solvent deionized water, magnetically stirring at room temperature until the system is uniform, to obtain a negative electrode slurry; uniformly coating the negative electrode slurry on a copper current collector, drying in an oven at 60°C for 3 hours, to obtain a graphite electrode sheet; taking a lithium strip as a soft package negative electrode; (3) preparation of an electrolyte: preparing the foregoing high-safety temperature-responsive electrolyte; (4) preparation of a separator: selecting a polyethylene film as a separator film; (5) assembling a lithium ion battery.

[0041] The technical solutions and technical effects of the application will be described in more detail through more specific embodiments.

[0042] Embodiment 1

[0043] A lithium ion battery is prepared according to the foregoing method, wherein the lithium ion electrolyte is a 0.3M LiFSI electrolyte solution of diallyl tetramethyl disiloxane and dimethyl carbonate (DMC); the positive electrode material is lithium cobaltate; and the upper limit cutoff voltage for testing is 4.2V.

[0044] Embodiment 2

[0045] A lithium ion battery is prepared according to the foregoing method, wherein the lithium ion electrolyte is a 0.25M LiPF6 electrolyte solution of bis[4-(ethylenoxy)-butyl] terephthalate, ethylene carbonate (EC), dimethyl carbonate (DEC) and fluoroethylene carbonate (FEC); the positive electrode material is lithium iron phosphate; and the upper limit cutoff voltage for testing is 3.7V.

[0046] Embodiment 3

[0047] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.05M LiPF6+0.3M LiFSI electrolyte solution of 2,4-divinyl-2,4,6,6,8,8-hexamethylcyclotetrasiloxane, dimethyl carbonate (DMC), fluoroethylene carbonate (FEC); the positive electrode material was high-nickel NCM811; and the upper limit cutoff voltage tested was 4.2V.

[0048] Example 4

[0049] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.05M LiPF6+0.3M LiFSI electrolyte solution of N,N'-methylenebisacrylamide, adiponitrile, fluoroethylene carbonate (FEC); the positive electrode material was high-nickel NCM811; and the upper limit cutoff voltage tested was 4.1V.

[0050] Example 5

[0051] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.01M LiPF6+0.5M LiTFSI electrolyte solution of ethylene glycol divinyl ether, diethylene glycol dimethyl ether (Diglyme); the positive electrode material was lithium iron phosphate; and the upper limit cutoff voltage tested was 3.7V.

[0052] Example 6

[0053] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.01M LiPF6+0.5M LiTFSI electrolyte solution of 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, diethyl carbonate (DEC); the positive electrode material was lithium cobaltate; and the upper limit cutoff voltage tested was 4.2V.

[0054] Example 7

[0055] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.1M LiFSI+0.5M LiTFSI electrolyte solution of triethylene glycol divinyl ether, ethylene glycol dimethyl ether (DME); the positive electrode material was lithium iron phosphate; and the upper limit cutoff voltage tested was 3.7V.

[0056] Example 8

[0057] A lithium-ion battery was prepared according to the foregoing method, wherein the lithium-ion electrolyte was a 0.1M LiFSI+0.5M LiTFSI electrolyte solution of triethylene glycol divinyl ether, triethylene glycol dimethyl ether (Triglyme), difluoroethylene carbonate (DFEC); the positive electrode material was lithium iron phosphate; and the upper limit cutoff voltage tested was 3.7V.

[0058] Comparative Example 1

[0059] Formulated lithium ion electrolyte: 1M LiPF6 electrolyte salt dissolved in solvent ethylene carbonate (EC) and solvent dimethyl carbonate (DMC) (V EC :V DMC =3:7) to form a commercial carbonate-based electrolyte.

[0060] Comparative Example 2

[0061] Formulated lithium ion electrolyte: 1M LiPF6 electrolyte salt dissolved in solvent diglyme to form a commercial ether-based electrolyte.

[0062] Comparative Example 3

[0063] Formulated lithium ion electrolyte: 0.268g LiI as catalyst, vinylene carbonate (VC) as thermal polymerization monomer, to formulate a thermal polymerization electrolyte solution.

[0064] The lithium ion batteries prepared in Examples 1-8 and the electrolytes formulated in Comparative Examples 1-3 were subjected to thermal chemical tests, and the lithium ion batteries prepared in Examples 1-8 were subjected to cycle performance tests, according to the following specific methods:

[0065] (1) Thermal chemical test: ① To verify the safety of the electrolyte by evaluating the flammability of the electrolyte in all examples, the self-extinguishing time method was selected to measure (as shown in Figure 1 ); the specific steps were to use glass fiber (GF / D) as raw material to make glass fiber sheets with a size of about 6cm*1.5cm, place them in a glass dish, take equal amounts of electrolytes with different formulations with a syringe, soak the glass fiber sheets with the electrolytes, hang and fix them with an iron stand and ignite them, control the ignition time to be 6s, record the time from the ignition device moving away to the flame automatically extinguishing, which is called self-extinguishing time; take the self-extinguishing time of unit mass electrolyte as the standard, compare the flame retardant performance of different electrolytes. ② Cone calorimeter experiment: place the sample on the sample holder of the loading table, and expose the outer surface to the heat radiation of the conical heater with a rated heat flow intensity of 25kW·m -2 . The combustible gas volatilized after heating of the sample is ignited by the igniter, and various parameters are obtained by the detector.

[0066] (2) Cycle performance test: at 25°C, the lithium ion batteries prepared in the examples and comparative examples were subjected to charge and discharge at a rate of 1C, and were subjected to cycle test after full charge and full discharge, and the cycle number and the corresponding capacity retention rate were recorded.

[0067] Table 1 below is the test results of each example and comparative example:

[0068] Table 1

[0069]

[0070]

[0071] Figure 1 For the self-extinguishing method test chart of Comparative Example 1 and Example 8, from Figure 1 It can be seen from the figure that the electrolyte of Comparative Example 1 can burn all the time, and has no self-extinguishing time; while the self-extinguishing time of Example 8 is only 7 s / g.

[0072] From the results in Table 1, it can be seen that in Comparative Examples 1-3, the electrolyte prepared by using commercially available carbonate-based, ether-based and other solvents does not have a thermal polymerization monomer and a flame-retardant cosolvent, and cannot perform thermal polymerization and has no flame-retardant characteristics at high temperature, which cannot guarantee the safety of lithium ions in the battery at high temperature; the thermal polymerization of VC initiated by LiI is too slow (t (l→s) >30 min) due to the mechanism of free radical polymerization, and thus cannot achieve rapid thermal polymerization, and therefore cannot guarantee the blocking of thermal runaway of lithium ions from the root.

[0073] The solvent activity in the battery electrolyte is too high, which is easy to decompose at high temperature and at the same time generate a large amount of heat, and the excessive accumulation of heat will trigger thermal runaway. In addition, under the damage of the outside world (short circuit, impact, overcharge, etc.), the temperature of the battery will also be positively fed back, and then the thermal runaway of the battery will be triggered. The commercial electrolyte without thermal response behavior has intrinsic flammable characteristics, which may greatly reduce the safety of the battery to a certain extent; on the other hand, the battery separator will collapse at a certain temperature at high temperature, causing a large-area short circuit of the lithium (sodium) ion battery, and then accelerating the thermal runaway behavior of the battery.

[0074] Figure 2 For the cone calorimeter test results of Comparative Example 1, Comparative Example 2 and Example 8, combined with the results in Table 1, it can be seen that the lithium ion battery and electrolyte prepared in Examples 1-8 have lower self-extinguishing time and H TR values due to the presence of the flame-retardant cosolvent during application, which improves the safety of the lithium ion battery. In addition, the thermal polymerization monomer of the electrolyte is selected as a thermal response solvent with polymerization characteristics, including but not limited to mono-olefin, di-olefin and poly-olefin compounds, five-membered / six-membered compounds prone to ring-opening, and preferably di-olefin and poly-olefin compounds. When in the above preferred range, the thermal response monomer has the characteristics of rapid thermal polymerization, and the monomer can be rapidly polymerized in 5 s≤t (l→s)The solid-liquid transition occurs rapidly in the range of ≤5 min, which is beneficial to improve the safety performance of the lithium ion battery under extreme conditions (Examples 5-8) in the case of inducing thermal runaway. When the thermal polymerization solvent meets the above-mentioned limitations but does not fall into the above-mentioned preferred range, such as Examples 1-4, the lithium ion battery can still have relatively high thermal reactivity, but the polymerization time will be longer, and when a more preferred thermal response polymer monomer solvent is selected, such as Examples 6-8, the thermal response time of the thermal response polymer monomer solvent meets 5s≤t (l→s) ≤5min, and the safety performance of the assembled lithium battery is more optimal.

[0075] Table 2 is the cycle test results of the batteries prepared in Examples 1-8:

[0076] Table 2

[0077]

[0078]

[0079] From the results in Table 2, the cut-off voltage of the lithium ion battery prepared in Examples 1-8 is 3.7-4.2V, and at 25℃, the lithium ion battery is charged and discharged at a rate of 1C, and the capacity retention rate after 200 cycles is maintained at more than 80%, among which the capacity retention rate of Example 8 is the highest, reaching 91%.

[0080] In summary, the secondary ion battery electrolyte prepared in the embodiments of the present application, when working in the battery, when the battery is affected by the environment or damaged, rapid thermal polymerization will occur in the process of rapid heating of the battery, and the polymerization temperature can be controlled before the collapse temperature of the battery separator, the polymerization reaction can quickly realize the liquid-solid transition of the battery electrolyte, prevent the collapse of the separator at its melting point, and avoid the thermal runaway caused by the collapse of the separator; At the same time, the high content of flame-retardant cosolvent components possessed by the electrolyte before and after polymerization ensures the flame-retardant properties of the battery, further improving the safety of the secondary battery.

[0081] The above has described the present application in detail, and the principles and implementation modes of the present application have been described by applying specific examples. The above description of the embodiments is only used to help understand the present application and the core idea. It should be pointed out that for ordinary skilled persons in the technical field, without departing from the principles of the present application, some improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A highly safe temperature-responsive electrolyte, characterized in that: Comprising: a heat-responsive solvent, a co-solvent, and an electrolyte salt; wherein, The heat-responsive solvent includes or consists of a heat-responsive polymer monomer or a heat-responsive monomer mixture of a plurality of heat-responsive polymer monomers, each heat-responsive polymer monomer having a structure as shown in as shown.

2. The high safety temperature-responsive electrolyte according to claim 1, characterized by the heat-responsive polymer monomer is any one of ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,6-hexanediol divinyl ether, terephthalic acid bis[4-(vinyleneoxy)-butyl] ester, 1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, trishydroxymethylpropane triglycidyl ether, diallyl disulfide, N,N'-methylenebisacrylamide, tetramethyldivinyl disiloxane, diallyltetramethyldisiloxane, and 2,4-divinyl-2,4,6,6,8,8-hexamethylcyclotetrasiloxane.

3. The high safety temperature-responsive electrolyte according to claim 1, characterized by The heat-responsive solvent accounts for 25% to 70% of the volume of the high-safety temperature-responsive electrolyte solution.

4. The high safety temperature-responsive electrolyte according to claim 3, characterized by The heat-responsive solvent accounts for 40% to 55% of the volume of the high-safety temperature-responsive electrolyte solution.

5. The high safety temperature responsive electrolyte of claim 1, wherein The co-solvent includes a first co-solvent and a second co-solvent, the first co-solvent is at least one of trimethyl phosphate, triethyl phosphate, tributyl phosphate, fluoroethylene carbonate, fluoropropylene carbonate, methyl nonafluorobutyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphite; the second co-solvent is at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, ethyl formate, ethyl propionate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate.

6. The high safety temperature-responsive electrolyte according to claim 5, wherein The first co-solvent accounts for 10% to 55% of the volume of the high-safety temperature-responsive electrolyte solution, and the second co-solvent accounts for 20% to 50% of the volume of the high-safety temperature-responsive electrolyte solution.

7. The high safety temperature-responsive electrolyte according to claim 1, characterized by The electrolyte salt is an electrolyte lithium salt or an electrolyte sodium salt; the electrolyte lithium salt includes an initiator lithium salt and a non-initiator lithium salt, wherein the initiator lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium nitrate, and the non-initiator lithium salt includes at least one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate; the electrolyte sodium salt includes an initiator sodium salt and a non-initiator sodium salt, wherein the initiator sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bisfluorosulfonylimide, sodium nitrate, and the non-initiator sodium salt includes at least one of sodium bis(trifluoromethylsulfonyl)imide, sodium bis(oxalato)borate, sodium difluoro(oxalato)borate.

8. The high safety temperature-responsive electrolyte according to claim 1, characterized by The concentration of the electrolyte salt in terms of metal ions is 0.2 to 3 mmol / L.

9. A lithium-ion battery, characterized by, The high-safety temperature-responsive electrolyte solution of any one of claims 1 to 8, wherein the electrolyte salt is an electrolyte lithium salt.

10. A sodium-ion battery, characterized in that, The high safety temperature-responsive electrolyte solution according to any one of claims 1 to 8, wherein the electrolyte salt is an electrolyte sodium salt.

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