Monomer and preparation method thereof, flame-retardant gel electrolyte precursor and preparation method thereof, and battery

Abstract

The invention provides a monomer and a preparation method thereof, a flame-retardant gel electrolyte precursor and a preparation method thereof, and a battery. The monomer provided by the invention is shown as a formula (2), when the monomer is used in a flame-retardant gel electrolyte precursor, a phosphorus-containing flame-retardant polymer network with a new structure can be obtained through in-situ polymerization, and a polymer skeleton does not contain oxygen atoms, is higher in thermal stability and achieves a better flame-retardant effect; moreover, the monomers can be thermally initiated and polymerized in situ, so that a stable tight interface is formed between the electrolyte gel and the positive and negative electrodes, and lower interface impedance is realized. According to the flame-retardant gel electrolyte precursor provided by the invention, the monomer as shown in the formula (2), the lithium salt and the ionic liquid are subjected to in-situ polymerization in the battery to obtain a phosphorus-containing flame-retardant polymer network with a new structure, and the phosphorus-containing flame-retardant polymer network is matched with certain ionic liquid gel and the lithium salt, so that the thermal stability of the battery is further improved; and the ionic conductivity and the ionic transference number are improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] The invention relates to the field of electrochemistry, and in particular to a monomer and a preparation method thereof, a flame retardant gel electrolyte precursor and a preparation method thereof, and a battery. Background Art

[0002] Compared with traditional liquid electrolytes, gel electrolytes are less likely to leak and can improve battery safety and stability, so they are gradually becoming more popular electrolytes. However, with the development of high-energy batteries, for example, in order to achieve better energy density, some problems may arise in actual use, such as internal short circuits in the battery, easy fire or explosion, etc., threatening its safety.

[0003] In order to solve the above problems, flame retardant gel electrolytes are used. Flame retardant gel electrolytes are gel electrolytes with flame retardant effects, which can help improve the safety of battery use. The flame retardant gel electrolyte disclosed in CN116365019A uses acrylonitrile, a phosphorus-containing vinyl compound of a selected structure, and a vinyl-terminated silicone oil as reaction monomers. Under the action of an initiator and a cross-linking agent, the flame retardant gel electrolyte is directly added to a commercial liquid electrolyte and injected into the assembled battery to prepare the required flame retardant gel electrolyte by an on-site thermal polymerization method. CN118231756A invention discloses a flame retardant gel polymer electrolyte, wherein the lithium salt is lithium difluoro(oxalate)borate (LiDFOB); the solvent is one of dimethyl carbonate (DMC), ethyl carbonate (EC), diethyl carbonate (DEC) or a mixture thereof; the monomer is vinylene carbonate (VC); the initiator is azobisisobutyronitrile (AIBN); wherein the lithium salt concentration is 1 mol / L, the ratio of the monomer to the solvent is 1:4 to 1:1; the ratio of the initiator is 1wt% to 3wt% of the monomer; CN118412544A invention uses a flame retardant phosphate compound as a gel skeleton, and generates free radicals in the electrolyte solvent inside the lithium ion battery through gamma rays or electron beams for in-situ polymerization, thereby avoiding the influence of the initiator.

[0004] However, the flame-retardant gel electrolytes that have been disclosed so far still have some problems: the current phosphate flame-retardant polymer skeleton has a high oxygen atom content and poor thermal stability; an organic liquid electrolyte is used, which is flammable; in addition, the electrode interface is not well improved, resulting in a high interface impedance; in addition, some preparation processes are relatively complicated and require the use of a cross-linking agent. Summary of the invention

[0005] In view of this, the present invention provides a monomer and a preparation method thereof, a flame retardant gel electrolyte precursor and a preparation method thereof, and a battery. The use of the monomer provided by the present invention to prepare the electrolyte precursor or the flame retardant gel electrolyte precursor of the present invention can effectively improve the thermal stability and electrochemical performance of the battery.

[0006] The present invention provides a monomer having a structure shown in formula (2):

[0007]

[0008] The present invention also provides a method for preparing the monomer described in the above technical solution, comprising the following steps:

[0009] A) phosphorus oxychloride reacts with ethylene glycol to form a compound represented by formula (1);

[0010] B) reacting the compound represented by formula (1) with 1,6-heptadien-4-ol to form a monomer represented by formula (2);

[0011]

[0012] Preferably, in step A), the reaction temperature is -3 to 0°C.

[0013] Preferably, in step B), the reaction temperature is room temperature.

[0014] Preferably, step A) specifically comprises: cooling the phosphorus oxychloride solution to a target temperature, adding a TEA solution, and then dripping an ethylene glycol solution, maintaining the temperature to react, to obtain a reaction solution containing the compound represented by formula (1);

[0015] The TEA solution concentration is 15.7 mol / L, and the solvent is THF;

[0016] The concentration of the ethylene glycol solution is 1.67 mol / L, and the solvent is THF.

[0017] Preferably, step B) specifically comprises: adding 1,6-heptadien-4-ol solution to the reaction solution obtained in step A), heating to room temperature for reaction, and obtaining a layered mixed solution; then, collecting the upper layer to obtain a reaction solution containing the monomer represented by formula (2);

[0018] The concentration of the 1,6-heptadien-4-ol solution is 3.3 mol / L, and the solvent is THF.

[0019] The present invention also provides a method for preparing a flame retardant gel electrolyte precursor, comprising the following steps:

[0020] The monomer is mixed with a lithium salt and an ionic liquid to obtain a flame retardant gel electrolyte precursor;

[0021] Wherein, the monomer is the monomer described in the above technical solution.

[0022] Preferably, the mass ratio of the monomer, the lithium salt and the ionic liquid is 100:(5-25):(10-30).

[0023] The present invention also provides a flame retardant gel electrolyte precursor, which is prepared by the preparation method described in the above technical solution.

[0024] The present invention also provides a battery, wherein the electrolyte precursor used in assembling the battery is the flame-retardant gel electrolyte precursor described in the above technical solution.

[0025] The monomer provided by the present invention is as shown in formula (2). When used in a flame-retardant gel electrolyte precursor, it can be polymerized in situ after assembling a battery to obtain a phosphorus-containing flame-retardant polymer network with a new structure. The polymer skeleton does not contain oxygen atoms, has higher thermal stability, and achieves a better flame-retardant effect. Moreover, the monomer can be thermally initiated to polymerize in situ without the introduction of additional cross-linking agents, so that a stable and tight interface can be formed between the electrolyte gel and the positive and negative electrodes, achieving lower interface impedance, which is beneficial to improving ionic conductivity and ion migration number, and enhancing the cycle performance of the battery.

[0026] The flame-retardant gel electrolyte precursor provided by the present invention contains a monomer shown in formula (2), a lithium salt and an ionic liquid. In the battery, the monomer of formula (2) is polymerized in situ to obtain a phosphorus-containing flame-retardant polymer network with a new structure. The polymer skeleton does not contain oxygen atoms and has higher thermal stability, thereby achieving a better flame-retardant effect. At the same time, the ionic liquid gel and the lithium salt are used to match the monomer of formula (2). On the one hand, the composite of the ionic liquid improves the solubility of the lithium salt. On the other hand, its thermal stability is much higher than that of the organic liquid, further improving the thermal stability of the battery and making the flame-retardant performance better. Moreover, the monomer introduced into the precursor of the present invention can be thermally initiated to polymerize in situ without introducing an additional cross-linking agent, so that a stable and tight interface can be formed between the electrolyte gel and the positive and negative electrodes, thereby achieving a lower interface impedance, improving the ionic conductivity and the ion migration number, and improving the cycle performance of the battery.

[0027] The test results show that the TGA decomposition temperature of the polymer gel of the precursor solution of the present invention is above 358°C, showing excellent thermal stability and flame retardancy; at the same time, the cation migration number of the battery is above 0.6, and the ionic conductivity is above 6.4×10 -4 S / cm or above, the first discharge specific capacity is above 185mAh / g, the first coulombic efficiency is above 90%, and the capacity retention rate after 500 cycles is above 94%, maintaining excellent ionic conductivity and ion migration number, and achieving a higher cycle capacity. DETAILED DESCRIPTION

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0029] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0030] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0031] Herein, when it comes to numerical ranges, unless otherwise specified, the numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0032] In this article, when referring to the unit of a data range, if there is a unit only after the right endpoint, it means that the units of the left and right endpoints are the same. For example, -3~0℃ means that the units of the left endpoint "-3" and the right endpoint "0" are both ℃.

[0033] The present invention provides a monomer having a structure shown in formula (2):

[0034]

[0035] The present invention also provides a method for preparing the monomer described in the above technical solution, comprising the following steps:

[0036] A) phosphorus oxychloride reacts with ethylene glycol to form a compound represented by formula (1);

[0037] B) reacting the compound represented by formula (1) with 1,6-heptadien-4-ol to form a monomer represented by formula (2);

[0038]

[0039] The present invention introduces phosphorus-containing groups into the side groups of specific monomers to prepare a new polymer monomer structure, thereby reducing the oxygen content in the polymer structure after polymerization and achieving higher thermal stability and flame retardant effect. In addition, the above monomers can be thermally initiated to polymerize in situ, so that a stable and tight interface can be formed between the electrolyte gel and the positive and negative electrodes, achieving lower interface impedance, and helping to improve electrochemical performance.

[0040] [About Step A]:

[0041] A) Phosphorus oxychloride reacts with ethylene glycol to form a compound represented by formula (1).

[0042] The reaction route of step A) is as follows:

[0043]

[0044] In the present invention, the molar ratio of phosphorus oxychloride to ethylene glycol is preferably 0.1:(0.05-0.2), specifically 0.1:0.05, 0.1:0.1, 0.1:0.15, 0.1:0.2, and more preferably 0.1:0.1.

[0045] In the present invention, the reaction temperature is preferably -3 to 0°C, specifically -3°C, -2°C, -1°C, or 0°C.

[0046] In the present invention, preferably, step A) specifically comprises: cooling the phosphorus oxychloride solution to a target temperature, adding a TEA solution, and then dropwise adding an ethylene glycol solution, maintaining the reaction at the target temperature to obtain a reaction solution containing the compound represented by formula (1).

[0047] in:

[0048] The phosphorus oxychloride solution is a solution formed by dissolving phosphorus oxychloride in a solvent. The solvent is preferably THF (tetrahydrofuran). The ratio of phosphorus oxychloride to solvent is preferably 0.1 mol: (70-100) mL, specifically 0.1 mol: 70 mL, 0.1 mol: 80 mL, 0.1 mol: 90 mL, 0.1 mol: 100 mL, and more preferably 0.1 mol: 80 mL.

[0049] The target temperature is the reaction temperature mentioned above, i.e. -3 to 0° C., specifically -3° C., -2° C., -1° C., 0° C. In the present invention, after phosphorus oxychloride is dissolved in a solvent to prepare a phosphorus oxychloride solution, it is first cooled to the reaction temperature before adding other materials.

[0050] The concentration of the TEA solution is 15.7 mol / L, and the solvent is THF. The role of adding TEA in the present invention is mainly to act as an acid-base regulator to adjust the system to a suitable pH value, thereby facilitating the reaction. In the present invention, the molar ratio of TEA in the TEA solution to phosphorus oxychloride in the phosphorus oxychloride solution is preferably 0.315:0.1. In the present invention, after adding the TEA solution, it is preferred to wait for a period of time before continuing to add the next substance (i.e., ethylene glycol solution). The interval time is preferably 10 to 30 minutes, specifically 10 minutes, 15 minutes, 20 minutes, and more preferably 20 minutes.

[0051] The concentration of the ethylene glycol solution is 1.67 mol / L, and the solvent is THF. In the present invention, the usage ratio of the phosphorus oxychloride to ethylene glycol is as described above, and will not be repeated here. Taking 0.1 mol of ethylene glycol as an example, the time for dropping the ethylene glycol solution is preferably 1 to 3 hours, specifically 1 hour, 2 hours, or 3 hours.

[0052] After the ethylene glycol solution is added dropwise, the reaction is maintained at the target temperature. The reaction time at this temperature is preferably 3 to 5 hours, specifically 3 hours, 4 hours, or 5 hours. After the reaction, a reaction solution is obtained, which contains the reaction product shown in formula (1).

[0053] In the present invention, the implementation process of the above step A) is preferably carried out under a protective atmosphere. In the present invention, the protective atmosphere is preferably nitrogen.

[0054] In the present invention, the implementation process of the above step A) is preferably carried out under stirring conditions. In the present invention, the stirring rate is preferably 100-300 rpm, specifically 100 rpm, 150 rpm, 200 rpm, 250 rpm, 300 rpm.

[0055] In the present invention, more preferably, step A) specifically comprises: dissolving phosphorus oxychloride in a solvent to form a phosphorus oxychloride solution in a three-necked flask equipped with a stirring rod, a reflux condenser and a protective gas inlet, and then cooling the phosphorus oxychloride solution to -3 to 0°C under a protective atmosphere and stirring conditions; then adding TEA solution, stirring for 10 to 30 minutes, and then dropping ethylene glycol solution. After the dropwise addition is completed, the reaction is maintained at the above temperature and stirred for 3 to 5 hours to obtain a reaction solution containing the compound represented by formula (1).

[0056] [About step B]:

[0057] B) The compound represented by formula (1) reacts with 1,6-heptadien-4-ol to form a monomer represented by formula (2).

[0058] The reaction route of step B) is as follows:

[0059]

[0060] In the present invention, the molar ratio of the 1,6-heptadien-4-ol to the phosphorus oxychloride in step A) is preferably (0.05-0.2):0.1, specifically 0.05:0.1, 0.1:0.1, 0.15:0.1, 0.2:0.1, and more preferably 0.1:0.1.

[0061] In the present invention, the reaction temperature is not particularly limited and can be carried out at room temperature. The room temperature can be 20-30°C, specifically 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C.

[0062] In the present invention, preferably, step B) specifically comprises: adding 1,6-heptadien-4-ol solution to the reaction solution obtained in step A), heating to room temperature for reaction to obtain a layered mixed solution; then, collecting the upper layer to obtain a reaction solution containing the monomer represented by formula (2).

[0063] in:

[0064] The concentration of the 1,6-heptadien-4-ol solution is 3.3 mol / L, and the solvent is THF.

[0065] The room temperature is consistent with the above description and will not be described here. The system is heated to room temperature and then reacted. The reaction is preferably carried out under stirring conditions, and then heated to room temperature and stirred for reaction. The stirring time is preferably 3 to 5 hours, specifically 3 hours, 4 hours, or 5 hours. After the above reaction, a mixed solution is obtained, which is divided into two immiscible upper and lower layers, the upper layer liquid is the reaction solution containing the reaction product, and the lower layer liquid is the hydrochloric acid byproduct (i.e., the hydrochloric acid solution is deposited on the lower layer); after obtaining the above layered mixed solution, the upper and lower layers are separated, the lower layer hydrochloric acid solution is discharged, and the upper layer reaction solution is collected. Among them, there is no special limitation on the method for separating the upper and lower layers, and it can be a conventional liquid separation method in the art, such as filtering out the lower layer hydrochloric acid solution. After discharging the lower layer liquid, an upper layer liquid is obtained, which is a reaction solution containing the monomer shown in formula (2). In the present invention, after obtaining the upper layer liquid, it is preferably evaporated and concentrated to obtain an amber liquid, which is the monomer shown in formula (2).

[0066] The present invention provides a method for preparing a flame retardant gel electrolyte precursor, comprising: mixing a monomer with a lithium salt and an ionic liquid to obtain a flame retardant gel electrolyte precursor; wherein the monomer is the monomer described in the above technical solution, that is, the monomer shown in formula (2).

[0067] The present invention introduces phosphorus-containing groups into specific monomer side groups to prepare a new polymer monomer structure, thereby reducing the oxygen content in the polymer structure after polymerization, achieving higher thermal stability and flame retardant effect, and in combination with a specific ionic liquid solvent, it not only has high thermal stability but also has high lithium salt solubility, higher thermal stability and flame retardant properties, while maintaining excellent ionic conductivity and ion migration number, achieving a higher cycle capacity.

[0068] In the present invention, the ionic liquid is preferably 1-ethyl-3-methylimidazolium tetrafluoroborate. The present invention uses the above-mentioned specific lithium salt and ionic liquid, which can be well matched to be used with the monomer of formula (2), thereby bringing the best use effect.

[0069] In the present invention, the mass ratio of the monomer represented by formula (2), the lithium salt and the ionic liquid is preferably 100: (5-25): (10-30), specifically 100: 5: 10, 100: 5: 15, 100: 5: 20, 100: 5: 25, 100: 5: 30, 100: 10: 10, 100: 10: 15, 100: 10: 20, 100: 10: 25, 100: 10: 30, 100: 10: 10 00:15:10, 100:15:15, 100:15:20, 100:15:25, 100:15:30, 100:20:10, 100:20:15, 100:20:20, 100:20:25, 100:20:30, 100:25:10, 100:25:15, 100:25:20, 100:25:25, 100:25:30.

[0070] In the present invention, there is no particular limitation on the method of mixing the monomer represented by formula (2) with the lithium salt and the ionic liquid, and the above materials can be mixed uniformly according to the conventional mixing method in the art. After mixing, a flame retardant gel electrolyte precursor solution is obtained.

[0071] In the present invention, an initiator is preferably added during mixing. In the present invention, the initiator is preferably AIBN (i.e., azobisisobutyronitrile). In the present invention, the mass ratio of the initiator to the monomer represented by formula (2) is preferably (0.01-0.1):100, specifically 0.01:100, 0.02:100, 0.03:100, 0.04:100, 0.05:100, 0.06:100, 0.07:100, 0.08:100, 0.09:100, 0.1:100. Adding an initiator is beneficial to shortening the subsequent polymerization time.

[0072] In the battery production process, the flame retardant gel electrolyte precursor solution is filled into the battery. After the battery is assembled, there is a curing reaction time to make the monomers in the flame retardant gel electrolyte precursor solution undergo polymerization to form polymers, that is, a polymer gel electrolyte is formed in situ in the battery.

[0073] In the present invention, after the flame retardant gel electrolyte precursor is filled into the battery, the monomer of formula (2) is polymerized in situ under the action of the initiator to form a polymer, which is combined with the lithium salt and the ionic liquid to form a flame retardant gel electrolyte. The reaction route of the in situ polymerization is as follows:

[0074]

[0075] The polymer obtained on the right side of the above reaction route is a phosphorus-containing flame-retardant polymer, which is a new structure phosphorus-containing polymer network with lower oxygen content to achieve better thermal stability and can effectively retard flames.

[0076] The present invention also provides a flame retardant gel electrolyte precursor, which is prepared by the preparation method described in the above technical solution.

[0077] The present invention also provides a battery, wherein the electrolyte precursor used in the battery during assembly is the flame-retardant gel electrolyte precursor described in the above technical solution. After the battery is assembled, a curing reaction is performed to make the flame-retardant gel electrolyte precursor form a flame-retardant gel electrolyte. Alternatively, the present invention provides a battery, wherein the electrolyte is a flame-retardant gel electrolyte, and the polymer in the flame-retardant gel electrolyte is as shown in formula (3):

[0078]

[0079] The present invention also provides a method for preparing a battery, comprising: assembling a battery using the flame-retardant gel electrolyte precursor described above, and then performing an in-situ polymerization reaction to form a flame-retardant gel electrolyte from the flame-retardant gel electrolyte precursor, thereby obtaining a battery product. That is, after the battery is assembled, a curing reaction is performed to polymerize the monomers in the flame-retardant gel electrolyte precursor solution to generate polymers, thereby forming a flame-retardant gel electrolyte from the flame-retardant gel electrolyte precursor. In the present invention, after the battery is assembled and before curing, it is preferably allowed to stand and soak. The temperature of the standing soaking is preferably 25°C, and the time is preferably 24h. In the present invention, the conditions of the curing reaction are preferably: a temperature of 45 to 80°C and a time of 12 to 36h. Among them, the temperature can specifically be 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, and 80°C. The time may specifically be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, or 36h.

[0080] The flame-retardant gel electrolyte precursor provided by the present invention contains a monomer shown in formula (2), a lithium salt and an ionic liquid. In a battery, the monomer of formula (2) is polymerized in situ to obtain a phosphorus-containing flame-retardant polymer network with a new structure. The polymer skeleton does not contain oxygen atoms, has higher thermal stability, and achieves a better flame-retardant effect. At the same time, a certain ionic liquid gel and a certain lithium salt are used to match the monomer of formula (2). On the one hand, the composite of the ionic liquid improves the solubility of the lithium salt. On the other hand, its thermal stability is much higher than that of the organic liquid, which further improves the thermal stability of the battery and makes the flame-retardant performance better. Moreover, the monomer introduced into the precursor of the present invention can be thermally initiated and polymerized in situ without introducing an additional cross-linking agent, so that a stable and tight interface can be formed between the electrolyte gel and the positive and negative electrodes, thereby achieving a lower interface impedance, improving the ionic conductivity and the ion migration number, and improving the cycle performance of the battery.

[0081] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0082] Example 1

[0083] 1. Preparation of the monomer represented by formula (2)

[0084] A) In a three-necked flask equipped with a stirring rod, a reflux condenser and a nitrogen inlet, phosphorus oxychloride (0.1 mol) was dissolved in THF (80 mL) to form a phosphorus oxychloride solution, which was then vigorously stirred (speed 200 rpm) and cooled to -2°C under a dry nitrogen atmosphere; then a TEA solution (TEA is 0.315 mol, the solvent is THF, the amount of THF is 20 mL, and the solution concentration is 15.7 mol / L) was added, and after stirring at the above speed for 20 min, an ethylene glycol solution (ethylene glycol is 0.1 mol, the solvent is THF, the amount of THF is 60 mL, and the solution concentration is 1.67 mol / L) was added dropwise for 2 h. After the dropwise addition was completed, the reaction was stirred at the above temperature and speed for 4 h to obtain a reaction solution containing the compound represented by formula (1).

[0085] B) adding a 1,6-heptadien-4-ol solution (0.1 mol of 1,6-heptadien-4-ol, THF as solvent, 30 mL of THF, and a solution concentration of 3.3 mol / L) dropwise to the reaction solution obtained in step A); after the addition is completed, the temperature is raised to room temperature (25° C.), and stirring is continued for 4 h at the same speed as in step A) to obtain a layered mixed solution; then, the lower layer of hydrochloric acid solution is filtered off, and the upper layer is concentrated by rotary evaporation to obtain an amber liquid, which is the monomer represented by formula (2).

[0086] Characterization:

[0087] The obtained product was characterized by H NMR spectrum, and the results were as follows: 1H NMR: δ5.76 (2H), 5.02 (4H), 4.39 (1H), 3.48 (4H), 2.39 (4H). It can be seen that the compound has the structure shown in formula (2).

[0088] 2. Preparation of flame retardant gel electrolyte precursor solution

[0089] Take 10 g of the monomer represented by formula (2) obtained in step B), 0.5 g of LiBF4 lithium salt, and 1 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid, mix them evenly to obtain a precursor solution.

[0090] Example 2

[0091] 1. Preparation of the monomer represented by formula (2)

[0092] The monomer represented by formula (2) prepared in Example 1 was used.

[0093] 2. Preparation of flame retardant gel electrolyte precursor solution

[0094] Take 10 g of the monomer represented by formula (2) obtained in step B), 1.5 g of LiBF4 lithium salt, and 2 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid, mix them evenly, and obtain a precursor solution.

[0095] Example 3

[0096] 1. Preparation of the monomer represented by formula (2)

[0097] The monomer represented by formula (2) prepared in Example 1 was used.

[0098] 2. Preparation of flame retardant gel electrolyte precursor solution

[0099] Take 10 g of the monomer represented by formula (2) obtained in step B), 2.5 g of LiBF4 lithium salt, and 3 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid, mix them evenly to obtain a precursor solution.

[0100] Comparative Example 1

[0101] 1. Preparation of flame retardant gel electrolyte precursor solution

[0102] Take 10 g of 1,6-heptadien-4-ol, 0.5 g of LiBF4 lithium salt, and 1 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid, mix them evenly, and obtain a precursor solution.

[0103] Comparative Example 2

[0104] The method is implemented in accordance with Example 1, except that in the process of preparing the flame retardant gel electrolyte precursor solution in item 2, the lithium salt LiBF4 is replaced by another lithium salt LiFSI.

[0105] Comparative Example 3

[0106] The method is implemented in accordance with Example 1, except that in the process of preparing the flame-retardant gel electrolyte precursor solution in item 2, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate is replaced by another ionic liquid 1-ethyl-3-methylimidazolium hexafluoroborate.

[0107] Product Testing :

[0108] Assemble the battery: assemble the full battery in the order of negative electrode, separator, precursor solution, and positive electrode. Then, assemble the half-battery according to the requirements of different test systems, with a packaging pressure of 6kg / cm 2 After packaging, the battery was placed at 25°C for 24 hours and then at 60°C for 12 hours to obtain a finished battery.

[0109] (1) TGA decomposition temperature test:

[0110] The polymer gel after polymerization was used as the test object to conduct TGA decomposition temperature test. The higher the TGA decomposition temperature, the better the thermal stability and heat resistance of the material.

[0111] (2) Ionic conductivity test:

[0112] The button cell was assembled according to the SS|electrolyte|SS system (SS is stainless steel), and an AC impedance test was performed using an electrochemical workstation to obtain an impedance value. The AC impedance test frequency was 0.1 Hz to 5 MHz, and the voltage amplitude was 10 mV.

[0113] Then, the ionic conductivity of the electrolyte is calculated according to the formula σ=L / RS.

[0114] In the above formula, σ is the ionic conductivity to be solved (unit: S / cm); L is the thickness of the solid electrolyte (unit: cm); R is the impedance value obtained by fitting calculation (unit: Ω); S is the contact area between the solid electrolyte membrane and the electrode (unit: cm 2 ).

[0115] (3) Cation migration number test:

[0116] Measuring Li + The migration number needs to be calculated using chronoamperometry, which is to apply a polarization voltage (10mV) to the assembled Li|SSE|Li symmetric battery, record the initial current value of polarization and the stable current value after polarization time, as well as the impedance before and after polarization. The calculation formula is as follows:

[0117] t Li+ =IssRss(ΔV-IoRo)IoRo(ΔV-IssRss)

[0118] In the above formula, t Li + is the lithium ion migration number, Iss is the current value after polarization stabilization (A), Rss is the impedance after polarization stabilization (Ω), Io is the current value at the beginning of polarization (A), Ro is the impedance at the beginning of polarization (Ω), and ΔV is the polarization voltage value (V).

[0119] (4) Lithium metal battery cycle test:

[0120] Using NCM811 as the positive electrode, lithium metal button batteries were assembled according to the positive electrode|electrolyte|Li system. The charge and discharge test was carried out at a charge and discharge rate of 1C to test the battery's cycle performance.

[0121] The above tests were performed on each embodiment and comparative example, and the results are shown in Table 1.

[0122] Table 1: Test results

[0123]

[0124] It can be seen from the test results in Table 1 that the TGA decomposition temperature of the precursor solution obtained in Examples 1-3 of the present invention is above 358°C, showing excellent thermal stability and flame retardancy; at the same time, the cation migration number of the battery is above 0.6, and the ionic conductivity is above 6.4×10 -4 S / cm or above, the first discharge specific capacity is above 185mAh / g, the first coulombic efficiency is above 90%, and the capacity retention rate after 500 cycles is above 94%, maintaining excellent ionic conductivity and ion migration number, and achieving a higher cycle capacity.

[0125] Compared with Examples 1-3, the various properties of Comparative Example 1 are significantly deteriorated, proving that the present invention uses a specific monomer of formula (2) to prepare a precursor solution, which can effectively improve the thermal stability and flame retardancy of the material, as well as improve the electrochemical cycle performance of the battery.

[0126] Compared with Example 1, the various properties of Comparative Examples 2-3 are significantly deteriorated, which proves that the present invention uses specific lithium salts and ionic liquids to match the monomer of formula (2) to improve the electrochemical cycle performance of the battery.

[0127] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, the present invention can also be improved and modified, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. A monomer, characterized in that It has the structure shown in formula (2):

2. A method for preparing the monomer according to claim 1, characterized in that: The following steps are involved: A) phosphorus oxychloride reacts with ethylene glycol to form a compound represented by formula (1); B) reacting the compound represented by formula (1) with 1,6-heptadien-4-ol to form a monomer represented by formula (2); 3. The preparation method according to claim 1, characterized in that: In step A), the reaction temperature is -3 to 0°C.

4. The preparation method according to claim 1, characterized in that: In step B), the reaction temperature is room temperature.

5. The preparation method according to claim 1 or 3, characterized in that: Step A) specifically comprises: cooling the phosphorus oxychloride solution to a target temperature, adding a TEA solution, and then dropwise adding an ethylene glycol solution, maintaining the temperature to react, to obtain a reaction solution containing the compound represented by formula (1); The TEA solution concentration is 15.7 mol / L, and the solvent is THF; The concentration of the ethylene glycol solution is 1.67 mol / L, and the solvent is THF.

6. The preparation method according to claim 1 or 4, characterized in that: Step B) specifically comprises: adding 1,6-heptadien-4-ol solution to the reaction solution obtained in step A), heating to room temperature for reaction, and obtaining a layered mixed solution; then, collecting the upper layer to obtain a reaction solution containing the monomer represented by formula (2); The concentration of the 1,6-heptadien-4-ol solution is 3.3 mol / L, and the solvent is THF.

7. A method for preparing a flame retardant gel electrolyte precursor, characterized in that: The following steps are involved: The monomer is mixed with a lithium salt and an ionic liquid to obtain a flame retardant gel electrolyte precursor; Wherein, the monomer is the monomer according to claim 1.

8. The preparation method according to claim 7, characterized in that: The mass ratio of the monomer, the lithium salt and the ionic liquid is 100:(5-25):(10-30).

9. A flame retardant gel electrolyte precursor, characterized in that: The method is prepared according to any one of claims 7 to 8.

10. A battery, characterized in that: The electrolyte precursor used in assembling the battery is the flame-retardant gel electrolyte precursor according to claim 9.

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