A monomer and a method for preparing the same, a flame-retardant gel electrolyte precursor and a method for preparing the same, and a battery

Abstract

The application 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 application is shown in formula (2), and is used in the flame-retardant gel electrolyte precursor, so that a new structure of a phosphorus-containing flame-retardant polymer network is obtained through in-situ polymerization, the polymer skeleton does not contain oxygen atoms, the thermal stability is higher, and a better flame-retardant effect is achieved; and the monomer can be in-situ thermally initiated polymerization, so that a stable and compact interface is formed between the electrolyte gel and the positive and negative electrodes, and lower interface impedance is achieved. The flame-retardant gel electrolyte precursor provided by the application contains the monomer shown in formula (2), a lithium salt and an ionic liquid, the monomer shown in formula (2) is in-situ polymerized into a new structure of a phosphorus-containing flame-retardant polymer network in the battery, the new structure is matched with a certain ionic liquid gel and the lithium salt, the thermal stability of the battery is further improved, the ionic conductivity and the ion transference number are improved, and the cycle performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and particularly to a monomer and its preparation method, a flame-retardant gel electrolyte precursor and its preparation method, and a battery. Background Technology

[0002] Compared to traditional liquid electrolytes, gel electrolytes are less prone to leakage, which improves battery safety and stability, and thus they are gradually becoming a more popular electrolyte. 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, fires, or explosions, threatening their safety.

[0003] To address the aforementioned issues, flame-retardant gel electrolytes have been developed. Flame-retardant gel electrolytes are gel electrolytes with flame-retardant properties, which can help improve battery safety. CN116365019A discloses a flame-retardant gel electrolyte that uses acrylonitrile, a phosphorus-containing vinyl compound with a selected structure, and terminal vinyl silicone oil as reactive monomers. Under the action of an initiator and crosslinking agent, the desired flame-retardant gel electrolyte is prepared by in-situ thermal polymerization by directly adding it to a commercial liquid electrolyte and injecting it into the assembled battery. CN118231756A discloses a flame-retardant gel polymer electrolyte, wherein the lithium salt is lithium difluoro(oxalate)borate (LiDFOB); the solvent is one or a mixture of dimethyl carbonate (DMC), ethyl carbonate (EC), and diethyl carbonate (DEC); the monomer is vinylene carbonate (VC); and the initiator is azobisisobutyronitrile (AIBN); wherein the lithium salt concentration is 1 mol / L, the monomer to solvent ratio is 1:4 to 1:1, and the initiator ratio is 1 wt% to 3 wt% of the monomer. CN118412544A discloses an invention that uses a phosphate ester compound with flame-retardant properties as a gel skeleton, which is generated by free radical in-situ polymerization in the electrolyte solvent inside a lithium-ion battery by γ-rays or electron beams, thus avoiding the influence of the initiator.

[0004] However, the currently available flame-retardant gel electrolytes still have some problems: the current phosphate ester flame-retardant polymer skeleton has a high oxygen atom content and poor thermal stability; the organic liquid electrolyte is used, which is flammable; in addition, the electrode interface has not been well improved, resulting in high interfacial impedance; furthermore, some preparation processes are relatively complex and require the use of crosslinking agents. Summary of the Invention

[0005] In view of this, the present invention provides a monomer and its preparation method, a flame-retardant gel electrolyte precursor and its preparation method, and a battery. Using the monomer provided by the present invention to formulate the electrolyte precursor or using the flame-retardant gel electrolyte precursor of the present invention can effectively improve the thermal stability and electrochemical performance of the battery.

[0006] This invention provides a monomer having the 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 the compound shown in formula (1);

[0010] B) The compound shown in formula (1) reacts with 1,6-heptadien-4-ol to form the monomer shown in formula (2);

[0011]

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

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

[0014] Preferably, step A) specifically includes: cooling the phosphorus oxychloride solution to the target temperature, adding TEA solution, and then adding ethylene glycol solution dropwise, maintaining the reaction at the target temperature to obtain a reaction solution containing the compound shown in formula (1);

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

[0016] The ethylene glycol solution has a concentration of 1.67 mol / L and uses THF as the solvent.

[0017] Preferably, step B) specifically includes: adding a 1,6-heptadien-4-ol solution dropwise to the reaction solution obtained in step A), heating to room temperature to carry out the reaction, and obtaining a layered mixture; then, collecting the upper layer to obtain a reaction solution containing the monomer shown in formula (2);

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

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

[0020] The monomer was mixed with lithium salt and ionic liquid to obtain a flame-retardant gel electrolyte precursor.

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

[0022] Preferably, the mass ratio of the monomer, lithium salt and 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 in which the electrolyte precursor used during assembly is the flame-retardant gel electrolyte precursor described in the above technical solution.

[0025] The monomer provided by this invention is shown in formula (2). When used in a flame-retardant gel electrolyte precursor, it can be polymerized in situ after battery assembly to obtain a novel phosphorus-containing flame-retardant polymer network. The polymer backbone does not contain oxygen atoms, has higher thermal stability, and achieves better flame-retardant effect. Moreover, the monomer can be thermally initiated in situ without the need to introduce additional crosslinking agents, which can form a stable and tight interface between the electrolyte gel and the positive and negative electrodes, achieving lower interfacial impedance, which is beneficial to improving ionic conductivity and ion transference number, and improving the cycle performance of the battery.

[0026] The flame-retardant gel electrolyte precursor provided by this invention contains the monomer shown in formula (2), lithium salt, and ionic liquid. In the battery, the monomer of formula (2) is polymerized in situ to obtain a novel phosphorus-containing flame-retardant polymer network. The polymer skeleton does not contain oxygen atoms, has higher thermal stability, and achieves better flame-retardant effect. At the same time, the ionic liquid gel and lithium salt are used to match the monomer of formula (2). On the one hand, the composite of ionic liquid improves the solubility of lithium salt, and on the other hand, its thermal stability is much higher than that of organic liquid, which further improves the thermal stability of the battery and makes the flame-retardant performance better. Moreover, the monomer introduced in the precursor of this invention can be thermally initiated in situ without the need to introduce additional crosslinking agents. This can form a stable and tight interface between the electrolyte gel and the positive and negative electrodes, achieve lower interfacial impedance, improve ionic conductivity and ion transference number, and improve the cycle performance of the battery.

[0027] Experimental results show that the polymer gel of the precursor solution of this invention has a TGA decomposition temperature above 358℃, exhibiting excellent thermal stability and flame retardancy; simultaneously, the battery's cation transference number is above 0.6, and the ionic conductivity is 6.4 × 10⁻⁶. -4 With an S / cm or higher, an initial discharge specific capacity of over 185 mAh / g, an initial coulombic efficiency of over 90%, and a capacity retention rate of over 94% after 500 cycles, it maintains excellent ionic conductivity and ion transference number, achieving a high cycle capacity. Detailed Implementation

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0029] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0030] The term “and / or” as used herein includes any and all combinations of one or more of the related listed items.

[0031] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0032] In this article, when referring to units for data ranges, if the unit is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, -3 to 0℃ means that the units for the left endpoint "-3" and the right endpoint "0" are both in degrees Celsius.

[0033] This invention provides a monomer having the 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 the compound shown in formula (1);

[0037] B) The compound shown in formula (1) reacts with 1,6-heptadien-4-ol to form the monomer shown in formula (2);

[0038]

[0039] This invention prepares novel polymer monomer structures by introducing phosphorus-containing groups into the side groups of specific monomers, reducing the oxygen content in the polymer structure after polymerization and achieving higher thermal stability and flame retardant effects. Furthermore, the aforementioned monomers can undergo in-situ thermally initiated polymerization, enabling the formation of a stable and tight interface between the electrolyte gel and the positive and negative electrodes, resulting in lower interfacial impedance and improved electrochemical performance.

[0040] [Regarding step A]:

[0041] A) Phosphorus oxychloride reacts with ethylene glycol to form the compound shown in formula (1).

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

[0043]

[0044] In this 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 this invention, the reaction temperature is preferably -3 to 0°C, specifically -3°C, -2°C, -1°C, or 0°C.

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

[0047] in:

[0048] The phosphorus oxychloride solution is formed by dissolving phosphorus oxychloride in a solvent. The solvent is preferably THF (tetrahydrofuran). The preferred ratio of phosphorus oxychloride to solvent is 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℃, specifically -3℃, -2℃, -1℃, or 0℃. In this invention, after dissolving phosphorus oxychloride in a solvent to prepare a phosphorus oxychloride solution, it is first cooled to the reaction temperature before adding other materials.

[0050] The TEA solution concentration is 15.7 mol / L, and the solvent is THF. The main function of adding TEA in this invention is as an acid-base regulator to adjust the system to a suitable pH value, thereby facilitating the reaction. In this 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 this invention, after adding the TEA solution, it is preferable to wait a certain period of time before adding the next substance (i.e., ethylene glycol solution). The preferred interval is 10–30 min, specifically 10 min, 15 min, or 20 min, more preferably 20 min.

[0051] The ethylene glycol solution has a concentration of 1.67 mol / L, and the solvent is THF. In this invention, the ratio of 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 preferred time for adding the ethylene glycol solution is 1–3 hours, specifically 1 hour, 2 hours, or 3 hours.

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

[0053] In this invention, step A) is preferably performed under a protective atmosphere. In this invention, the protective atmosphere is preferably nitrogen.

[0054] In this invention, step A) is preferably performed under stirring conditions. The stirring rate is preferably 100–300 rpm, specifically 100 rpm, 150 rpm, 200 rpm, 250 rpm, or 300 rpm.

[0055] In this invention, more preferably, step A) specifically includes: 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; 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 adding ethylene glycol solution dropwise. After the addition is complete, stirring the reaction at the above temperature for 3 to 5 hours to obtain a reaction solution containing the compound shown in formula (1).

[0056] [Regarding step B]:

[0057] B) The compound shown in formula (1) reacts with 1,6-heptadien-4-ol to form the monomer shown in formula (2).

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

[0059]

[0060] In this invention, the molar ratio of 1,6-heptadien-4-ol to 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 this invention, the reaction temperature is not particularly limited and can be carried out at room temperature. The room temperature can be 20-30℃, specifically 20℃, 21℃, 22℃, 23℃, 24℃, 25℃, 26℃, 27℃, 28℃, 29℃, or 30℃.

[0062] In this invention, preferably, step B) specifically includes: adding a 1,6-heptadien-4-ol solution dropwise to the reaction solution obtained in step A), heating to room temperature to carry out the reaction, and obtaining a layered mixture; then, collecting the upper layer to obtain a reaction solution containing the monomer shown in formula (2).

[0063] in:

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

[0065] The room temperature is consistent with the previous description and will not be repeated here. The system is heated to room temperature and then the reaction is carried out. The reaction is preferably carried out under stirring conditions. After heating to room temperature, the reaction is stirred. The stirring time is preferably 3 to 5 hours, specifically 3 hours, 4 hours, or 5 hours. After the above reaction, a mixture is obtained, which is divided into two immiscible layers. The upper layer is the reaction liquid containing the reaction product, and the lower layer is the hydrochloric acid byproduct (i.e., hydrochloric acid solution is deposited in the lower layer). After obtaining the above-mentioned layered mixture, the upper and lower layers are separated, the lower hydrochloric acid solution is discharged and the upper reaction liquid is collected. There is no special limitation on the method of separating the upper and lower layers. Conventional liquid separation methods in the field are acceptable, such as filtering out the lower hydrochloric acid solution. After discharging the lower layer, the upper layer is obtained, which is the reaction liquid containing the monomer shown in formula (2). In this invention, after obtaining the upper layer, it is preferable to further evaporate and concentrate it 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, i.e., the monomer shown in formula (2).

[0067] This invention prepares a novel polymer monomer structure by introducing phosphorus-containing groups into the side groups of a specific monomer, thereby reducing the oxygen content in the polymer structure after polymerization and achieving higher thermal stability and flame retardant effect. When combined with a specific ionic liquid solvent, it not only has high thermal stability but also high lithium salt solubility, resulting in even higher thermal stability and flame retardant performance. At the same time, it maintains excellent ionic conductivity and ion transference number, achieving a high cycle capacity.

[0068] In this invention, the ionic liquid is preferably 1-ethyl-3-methylimidazolium tetrafluoroborate. This invention uses the aforementioned specific lithium salt and ionic liquid, which are well-matched and can be combined with the monomer of formula (2), thereby achieving the best performance.

[0069] In this invention, the preferred mass ratio of the monomer, lithium salt, and ionic liquid shown in formula (2) is 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, 1 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 this invention, there are no special restrictions on the method of mixing the monomer shown in formula (2) with the lithium salt and ionic liquid. The above materials can be mixed evenly according to the conventional mixing method in the art. After mixing, a flame-retardant gel electrolyte precursor solution is obtained.

[0071] In this invention, an initiator is preferably added during mixing. The initiator is preferably AIBN (azobisisobutyronitrile). The mass ratio of the initiator to the monomer shown in 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, or 0.1:100. Adding an initiator helps shorten 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, which allows the monomers in the flame-retardant gel electrolyte precursor solution to undergo a polymerization reaction to generate a polymer, that is, to form a polymer gel electrolyte in situ in the battery.

[0073] In this invention, after the above-mentioned flame-retardant gel electrolyte precursor is filled into the battery, the monomer of formula (2) undergoes in-situ polymerization under the action of an initiator to form a polymer, which combines with lithium salt and 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 novel phosphorus-containing polymer network with lower oxygen content, achieving better thermal stability and effectively retardant flames.

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

[0077] The present invention also provides a battery in which the electrolyte precursor used during assembly is the flame-retardant gel electrolyte precursor described in the above-mentioned technical solution. After the battery is assembled, a curing reaction is performed to form a flame-retardant gel electrolyte from the flame-retardant gel electrolyte precursor. Alternatively, the present invention provides a battery in which 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] This 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. Specifically, after the battery is assembled, a curing reaction is performed, causing the monomers in the flame-retardant gel electrolyte precursor solution to polymerize and form a polymer, thereby forming the flame-retardant gel electrolyte precursor into a flame-retardant gel electrolyte. In this invention, after battery assembly and before curing, it is preferable to allow the battery to stand and soak. The preferred temperature for this standing and soaking is 25°C, and the preferred time is 24 hours. In this invention, the preferred conditions for the curing reaction are: temperature 45–80°C, time 12–36 hours. Specifically, the temperature can be 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C. The specific time can be 12h, 14h, 16h, 18h, 20h, 22h, 24h, 26h, 28h, 30h, 32h, 34h, or 36h.

[0080] The flame-retardant gel electrolyte precursor provided by this invention contains the monomer shown in formula (2), lithium salt, and ionic liquid. In the battery, the monomer of formula (2) is polymerized in situ to obtain a novel phosphorus-containing flame-retardant polymer network. The polymer skeleton does not contain oxygen atoms, has higher thermal stability, and achieves better flame-retardant effect. At the same time, a certain amount of ionic liquid gel and a certain amount of lithium salt are used to match the monomer of formula (2). On the one hand, the composite of ionic liquid improves the solubility of lithium salt, and on the other hand, its thermal stability is much higher than that of organic liquid, which further improves the thermal stability of the battery and makes the flame-retardant performance better. Moreover, the monomer introduced in the precursor of this invention can be thermally initiated in situ without the need to introduce additional crosslinking agents. This can form a stable and tight interface between the electrolyte gel and the positive and negative electrodes, achieve lower interfacial impedance, improve ionic conductivity and ion transference number, and improve the cycle performance of the battery.

[0081] 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, and not for limiting the scope of the claims of the present invention.

[0082] Example 1

[0083] 1. Preparation of the monomer shown in formula (2)

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

[0085] B) Add 1,6-heptadien-4-ol solution (0.1 mol of 1,6-heptadien-4-ol, THF 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 complete, heat the solution to room temperature (25°C) and continue stirring for 4 hours at the same speed as in step A) to obtain a layered mixture. Then, filter off the lower layer of hydrochloric acid solution and concentrate the upper layer by rotary evaporation to obtain an amber liquid, which is the monomer shown in formula (2).

[0086] Characterization:

[0087] The obtained product was characterized by ¹H NMR, and the results are as follows: δ 5.76 (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 10g of the monomer shown in formula (2) obtained in step B), 0.5g of LiBF4 lithium salt, and 1g 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 shown in formula (2)

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

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

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

[0095] Example 3

[0096] 1. Preparation of the monomer shown in formula (2)

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

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

[0099] Take 10g of the monomer shown in formula (2) obtained in step B), 2.5g of LiBF4 lithium salt, and 3g 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 10g of 1,6-heptadien-4-ol, 0.5g of lithium salt LiBF4, and 1g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid, mix them evenly to obtain a precursor solution.

[0103] Comparative Example 2

[0104] The method was implemented according to Example 1, except that in the second step of preparing the flame-retardant gel electrolyte precursor solution, the lithium salt LiBF4 was replaced with another lithium salt, LiFSI.

[0105] Comparative Example 3

[0106] The procedure was carried out as in Example 1, except that in the second step of preparing the flame-retardant gel electrolyte precursor solution, the ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate was replaced with another ionic liquid, 1-ethyl-3-methylimidazolium hexafluoroborate.

[0107] Product Testing :

[0108] Battery assembly: Assemble the full cell in the order of negative electrode, separator, precursor solution, and positive electrode. Then, assemble the half cell according to the requirements of different testing systems, with a sealing pressure of 6 kg / cm². 2 After packaging, the battery is left to stand at 25°C for 24 hours, and then at 60°C for 12 hours to obtain the finished battery.

[0109] (1) TGA decomposition temperature test:

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

[0111] (2) Ionic conductivity test:

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

[0113] Then, the ionic conductivity of the electrolyte is calculated using 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 represents the impedance value obtained by fitting calculation (unit: Ω); and S represents the contact area between the solid electrolyte membrane and the electrode (unit: cm²). 2 ).

[0115] (3) Cation transport number test:

[0116] Measuring Li + The migration number requires chronoamperometry, which involves applying a polarization voltage (10mV) to the assembled Li|SSE|Li symmetric cell, recording the initial polarization current value, the steady-state current value over time, and the impedance before and after polarization. The calculation formula is shown below:

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

[0118] In the above formula, t Li + Rss is the lithium-ion transference number, Iss is the current value after polarization stabilization (A), Rss is the impedance after polarization stabilization (Ω), Io is the initial current value of polarization (A), Ro is the initial impedance 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 coin cells were assembled according to the positive electrode|electrolyte|Li system. Charge and discharge tests were conducted at a charge and discharge rate of 1C to test the cycle performance of the cells.

[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] As can be seen from the test results in Table 1, the TGA decomposition temperature of the precursor solutions obtained in Examples 1-3 of this invention is above 358℃, exhibiting excellent thermal stability and flame retardancy; simultaneously, the cation transference number of the battery is above 0.6, and the ionic conductivity is above 6.4×10⁻⁶. -4 With an S / cm or higher, an initial discharge specific capacity of over 185 mAh / g, an initial coulombic efficiency of over 90%, and a capacity retention rate of over 94% after 500 cycles, it maintains excellent ionic conductivity and ion transference number, achieving a high cycle capacity.

[0125] Compared with Examples 1-3, the performance of Comparative Example 1 is significantly worse, proving that the present invention uses a specific monomer of formula (2) to prepare the 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 performance of Comparative Examples 2-3 deteriorated significantly, proving that the present invention uses specific lithium salts and ionic liquids to match the monomer of Formula (2), which is beneficial to improving the electrochemical cycle performance of the battery.

[0127] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of these embodiments are merely to aid in understanding the method and core ideas of the present invention, including the best mode, and to enable any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be noted that those skilled in the art can make various improvements and modifications to the present invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims. The scope of protection of this patent is defined by the claims and may include other embodiments that can be conceived by those skilled in the art. If these other embodiments have structural elements similar to those expressed in the claims, or if they include equivalent structural elements that are not substantially different from those expressed in the claims, then these other embodiments should also be included within the scope of the claims.

Claims

1. A monomer characterized in that, having a structure represented by formula (2): Formula (2).

2. A process for the preparation of the monomer of claim 1, characterized in that, comprising the following steps: A) reacting chlorinated phosphine oxide with ethylene glycol to form a compound represented by formula (1); B) reacting the compound represented by formula (1) with 1,6-heptadiene-4-ol to form a monomer represented by formula (2); Formula (1); Formula (2).

3. The preparation method according to claim 2, characterized in that, In step A), the temperature of the reaction is -3~0℃.

4. The preparation method according to claim 2, characterized in that, In step B), the temperature of the reaction is room temperature.

5. The production method according to claim 2 or 3, characterized by, Step A) specifically comprises: cooling a chlorinated phosphine oxide solution to a target temperature, adding a TEA solution, then, dropwise adding an ethylene glycol solution, keeping the reaction at the target temperature to obtain a reaction liquid containing a compound represented by formula (1); The concentration of the TEA solution 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 production method according to claim 2 or 4, characterized by, Step B) specifically comprises: dropwise adding a 1,6-heptadiene-4-ol solution to the reaction liquid obtained in step A), heating to room temperature to react, obtaining a layered mixed liquid; then, collecting the upper liquid to obtain a reaction liquid containing a monomer represented by formula (2); The concentration of the 1,6-heptadiene-4-ol solution is 3.3 mol / L, and the solvent is THF.

7. A method of preparing a flame-retardant gel electrolyte precursor, characterized by, comprising the following steps: Mixing the monomer, a lithium salt and an ionic liquid to obtain a flame-retardant gel electrolyte precursor; The monomer is the monomer according to claim 1; The lithium salt is LiBF4; The ionic liquid is 1-ethyl-3-methyl imidazole tetrafluoroborate.

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 by, Prepared by the preparation method according to any one of claims 7~8.

10. A battery, characterized by The electrolyte precursor used when the battery is assembled is the flame-retardant gel electrolyte precursor according to claim 9.

Images