A stable flame-retardant gel polymer for electrolyte

Abstract

The present invention relates to the field of polymer electrolytes for lithium batteries, and particularly to a stable flame-retardant gel polymer for electrolytes and a preparation method thereof. The stable flame-retardant gel polymer for electrolytes comprises, by weight: hyperbranched poly(ethylene oxide) PEO: 20-30 parts, lithium salt: 15-20 parts, and solvent: 60-70 parts. The hyperbranched poly(ethylene oxide) PEO is prepared by using trimethylolphosphine oxide and 2,2'-[methylenebis(sulfonyl)]diethanol as monomer initiators to initiate the ring-opening of ethylene oxide to prepare the main-chain A polymer and the branched-chain B polymer respectively, and then connecting the two polymers with a silane coupling agent. The stable flame-retardant gel polymer for electrolytes prepared by the present invention has excellent ionic conductivity at different temperatures and good flame-retardant properties, and has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer electrolytes for lithium batteries, and particularly to a stable flame-retardant gel polymer for electrolytes and a preparation method thereof. Background Art

[0002] Lithium batteries are widely used in electric vehicles, energy storage and other fields due to their high energy density and long cycle life. However, their safety issues (such as combustion and explosion caused by thermal runaway) limit further development. Traditional liquid electrolytes have high ionic conductivity, but are flammable and prone to leakage. Flame retardants need to be added to improve safety. However, the added flame retardants are prone to agglomeration and migration, resulting in a decline in the performance of the electrolyte. Traditional solid electrolytes have high safety, inhibit dendrite growth and good thermal stability, but have low ionic conductivity, high interfacial impedance and complex preparation processes at room temperature.

[0003] Polymer electrolytes (such as polyethylene oxide, PEO) have become a research hotspot due to their good film-forming properties and high safety. However, their high crystallinity leads to low ionic conductivity at room temperature and lack of intrinsic flame retardancy. Existing improvement methods include:

[0004] 1. Copolymerization modification: Introducing flexible chain segments (such as polyethylene glycol) to reduce crystallinity. However, the choice of comonomers is limited, and it is difficult to achieve high conductivity and flame retardancy simultaneously.

[0005] 2. Adding nano-fillers: Such as Al2O3, SiO2, etc. Although they can inhibit crystallization, the dispersion of the fillers is poor and it is easy to form an ion transport barrier.

[0006] 3. Gelation design: Blending linear PEO with a solvent / plasticizer to form a gel. Although the conductivity is increased to 10⁻ 6 ~10⁻ 4 S / cm, the stability is insufficient due to solvent volatilization or migration. Summary of the Invention

[0007] In view of this, the purpose of the present invention is to provide a stable flame-retardant gel polymer for electrolytes and a preparation method thereof, so as to solve the problem that the existing electrolyte materials cannot balance both conductivity and flame retardancy.

[0008] Based on the above purpose, the present invention provides a stable flame-retardant gel polymer for electrolytes, which comprises the following raw materials in parts by weight: hyperbranched polyethylene oxide PEO: 20-30 parts, lithium salt: 15-20 parts, and solvent: 60-70 parts;

[0009] The specific preparation process of the hyperbranched PEO is as follows:

[0010] (1) a. The preparation equation of the main chain A polymer is as follows:

[0011] Formula (1)

[0012] b. The preparation process of the main chain A polymer is as follows: Dissolve trimethylolphosphine oxide in anhydrous toluene. Apply a pressure of 3 - 5 MPa to ethylene oxide to ensure it is in a liquid state. Use a continuous flow microchannel reactor to pump the liquid ethylene oxide and trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 70 - 90 °C, the pressure at 1 - 3 MPa, the flow rate at 3 - 5 ml / min, and the residence time at 5 - 10 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the main chain A polymer. The product was characterized by ³¹P NMR and infrared spectroscopy. Peaks were observed in ³¹P NMR, indicating that the product contains P. In the infrared spectrum, two very strong peaks were observed at 1000 - 1500 cm -1 positions, and no peaks were observed at 900 - 950 cm - ⁻¹ and 820 - 830 cm - ⁻¹, indicating that the product contains both P=O and C - O - C functional groups, and the epoxy groups have all been ring - opened and disappeared, proving that the product is formed by the ring - opening of ethylene oxide and its polymerization with trimethylolphosphine oxide;

[0013] (2) i. The preparation equation of the branched chain B polymer is as follows:

[0014] Formula (2)

[0015] ii. The preparation process of the branched chain B polymer is as follows: Dissolve 2,2'-[methylenebis(sulfonyl)]diethanol in anhydrous tetrahydrofuran. Apply a pressure of 3 - 5 MPa to ethylene oxide to ensure it is in a liquid state. Use a continuous flow microchannel reactor to pump the liquid ethylene oxide and 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 70 - 80 °C, the pressure at 1 - 3 MPa, the flow rate at 3 - 5 ml / min, and the residence time at 5 - 10 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the branched chain B polymer. The product was characterized by ¹H NMR and infrared spectroscopy. Peaks were observed at 3.68 - 3.61 ppm in ¹H NMR, which is the obvious peak position of methylene on the polymer chain, indicating that a large amount of ethylene oxide has ring - opened and polymerized with 2,2'-[methylenebis(sulfonyl)]diethanol. In the infrared spectrum, peaks were observed at 1000 - 1500 cm -1There are three strong peaks, corresponding to the ether bond of the PEO main chain, the S=O of the sulfonyl group, and the C-S=O vibration respectively, which reflect the structural characteristics of the branched polymer B prepared by initiating ethylene oxide with 2,2'-[methylenebis(sulfonyl)]diethanol;

[0016] (3) Add methyltrimethoxysilane to the ethanol / water mixed solution, stir at room temperature for 30 - 60 min to obtain a silane solution. Add the main chain A polymer and the branched chain B polymer to tetrahydrofuran, stir at room temperature for 30 - 60 min, add the silane solution, raise the temperature to 60 - 80 °C, react for 4 - 8 h, cool to room temperature, precipitate the product in diethyl ether, wash with ethanol, and dry to obtain hyperbranched PEO. The schematic diagram of the reaction process is as follows:

[0017] Formula (3)

[0018] Preferably, in the step (1), the weight ratio of phosphine oxide, ethylene oxide, and toluene is 1:15 - 25:10 - 20.

[0019] Preferably, in the step (2), the weight ratio of 2,2'-[methylenebis(sulfonyl)]diethanol, ethylene oxide, and anhydrous tetrahydrofuran is 1:40 - 50:10 - 20.

[0020] Preferably, in the step (3), the weight ratio of methyltrimethoxysilane, the main chain A polymer, the branched chain B polymer, tetrahydrofuran, and the ethanol / water mixed solution is 1:2 - 4:6 - 12:100 - 120:10 - 20.

[0021] Preferably, the ethanol / water mixed solution in the step (3) is prepared by mixing ethanol and water in a weight ratio of 95:5.

[0022] Preferably, the lithium salt is one or more of lithium perchlorate, lithium trifluoromethanesulfonate, lithium hexafluorophosphate, or lithium tetrafluoroborate.

[0023] Preferably, the solvent is prepared by mixing triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05.

[0024] Furthermore, the present invention also provides a preparation method of the stable flame-retardant gel polymer for the above electrolyte, which specifically includes the following steps:

[0025] S1. Add the lithium salt to the solvent and stir to form a liquid electrolyte;

[0026] S2. Add the hyperbranched PEO to the liquid electrolyte to obtain the stable flame-retardant gel polymer for the electrolyte.

[0027] The beneficial effects of the present invention:

[0028] 1. The hyperbranched PEO prepared by the present invention forms a highly branched three-dimensional network structure through the reasonable combination of the rigid phosphorus groups in the main chain and the flexible sulfone groups in the branches. This structure effectively inhibits the crystallization behavior of PEO, increases the proportion of amorphous regions, thereby improving the segmental mobility and the density of lithium-ion migration channels. At the same time, the strong polarity of the sulfone groups forms a coordination interaction with lithium salts (such as lithium trifluoromethanesulfonate), promoting the dissociation of lithium salts and enhancing the ionic conductivity of the material, meeting the fast charging requirements of high-energy density batteries.

[0029] 2. Through molecular structure design, the present invention introduces phosphorus-containing groups (P=O) into the PEO main chain and sulfone-containing groups (O=S=O) into the branches simultaneously, forming a phosphorus-sulfur synergistic flame retardant system. Phosphorus generates phosphoric anhydride during combustion, promoting the formation of a carbon layer, while the sulfone group decomposes to produce SO2 gas to dilute oxygen. The synergistic effect of the two makes the flame retardant performance of the material far exceed that of general linear PEO materials. This intrinsic flame retardant property eliminates the need to add external flame retardants, avoiding problems such as uneven dispersion of traditional additive flame retardants and poor compatibility with electrolytes, while maintaining the homogeneity and stability of the material, significantly enhancing the thermal runaway safety of lithium batteries.

[0030] 3. The present invention synthesizes hyperbranched PEO using continuous flow microchannel reactor technology, which has significant environmental protection and high-efficiency advantages compared with traditional batch polymerization processes. The continuous flow process realizes efficient copolymerization by precisely controlling reaction parameters, shortening the reaction residence time and improving efficiency. At the same time, the high mass transfer and heat transfer characteristics of the microchannel reactor reduce the generation of by-products, lower the emissions of three wastes, and also reduce the usage of solvents such as toluene and tetrahydrofuran, conforming to the concept of green chemistry. In addition, the continuous flow process can achieve large-scale production through modular design, with small differences between product batches, suitable for industrial scale-up, providing technical support for the low-cost and sustainable preparation of high-performance electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the 31 P NMR spectrum of the main chain A polymer;

[0032] Figure 2 is the H NMR spectrum of the branched chain B polymer;

[0033] Figure 3 is the infrared spectrum of the main chain A polymer;

[0034] Figure 4 is the infrared spectrum of the branched chain B polymer. DETAILED DESCRIPTION OF THE INVENTION

[0035] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments.

[0036] The sources of the reagent raw materials used in the embodiments of the present invention are as follows:

[0037] Trimethylolphosphine oxide was purchased from Ningbo Chemical Raw Materials Co., Ltd., with a purity of 99%; ethylene oxide was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number E105779, with a purity of 99.5%; 2,2'-[methylenebis(sulfonyl)]diethanol was purchased from Shaanxi Didu Pharmaceutical Chemical Co., Ltd., with a purity of 98%; methyltrimethoxysilane was purchased from Shanghai Macklin Biochemical Co., Ltd., product number T819103, with a purity of 98%; triethyl phosphate was purchased from Shanghai Macklin Biochemical Co., Ltd., product number T818802, with a purity of 98%; ethylene carbonate was purchased from Shanghai Macklin Biochemical Co., Ltd., product number E808837, with a purity of 98%; lithium trifluoromethanesulfonate was purchased from Shanghai Macklin Biochemical Co., Ltd., product number L799204, with a purity of 99.5%.

[0038] Example 1: A specific preparation method of a stable flame-retardant gel polymer for electrolytes, including the following process:

[0039] (1) Dissolve 20 g of trimethylolphosphine oxide in 200 g of anhydrous toluene to make a trimethylolphosphine oxide solution. Apply a pressure of 3 MPa to ethylene oxide to ensure it is in a liquid state. Use a continuous flow microchannel reactor to pump 300 g of liquid ethylene oxide and the trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 70 °C, the pressure at 1 MPa, the flow rate at 3 ml / min, and the residence time at 5 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the main chain A polymer;

[0040] (2) Dissolve 10 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 100 g of anhydrous tetrahydrofuran to make a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 3 MPa to ethylene oxide to ensure it is in a liquid state. Use a continuous flow microchannel reactor to pump 400 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 70 °C, the pressure at 1 MPa, the flow rate at 3 ml / min, and the residence time at 5 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the branched chain B polymer;

[0041] (3) Add 30 g of methyltrimethoxysilane to 300 g of an ethanol / water mixed solution (ethanol and water are mixed at a weight ratio of 95:5), stir at room temperature for 30 min to obtain a silane solution. Add 60 g of the main chain A polymer and 180 g of the branched chain B polymer to 3 kg of tetrahydrofuran, stir at room temperature for 30 min, add the silane solution, heat up to 60 °C, react for 4 h, cool to room temperature, precipitate the product in diethyl ether, wash with ethanol, and dry to obtain hyperbranched PEO;

[0042] (4) Add 150 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 600 g of triethyl phosphate and ethylene carbonate at a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0043] (5) Add 200 g of hyperbranched PEO to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0044] Example 2: A specific preparation method of a stable flame-retardant gel polymer for electrolyte, including the following process:

[0045] (1) Dissolve 20 g of trimethylolphosphine oxide in 150 g of anhydrous toluene to prepare a trimethylolphosphine oxide solution. Apply a pressure of 4 MPa to ethylene oxide to ensure that ethylene oxide is in a liquid state. Use a continuous flow microchannel reactor to pump 400 g of liquid ethylene oxide and the trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 80 °C, the pressure at 2 MPa, the flow rate at 4 ml / min, and the residence time at 8 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet of the reactor. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the main chain A polymer;

[0046] (2) Dissolve 10 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 150 g of anhydrous tetrahydrofuran to prepare a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 4 MPa to ethylene oxide to ensure that ethylene oxide is in a liquid state. Use a continuous flow microchannel reactor to pump 450 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 75 °C, the pressure at 2 MPa, the flow rate at 4 ml / min, and the residence time at 8 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet of the reactor. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the branched chain B polymer;

[0047] (3) Add 30 g of methyltrimethoxysilane to 450 g of an ethanol / water mixed solution (ethanol and water are mixed at a weight ratio of 95:5), stir at room temperature for 45 min to obtain a silane solution. Add 90 g of the main chain A polymer and 270 g of the branched chain B polymer to 3.3 Kg of tetrahydrofuran, stir at room temperature for 45 min, add the silane solution, heat up to 70 °C, react for 6 h, cool to room temperature, precipitate the product in ether, wash with ethanol, and dry to obtain hyperbranched PEO;

[0048] (4) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate at a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0049] (5) Add 250 g of hyperbranched PEO to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0050] Example 3: A specific preparation method of a stable flame-retardant gel polymer for electrolyte, including the following process:

[0051] (1) Dissolve 20 g of trimethylolphosphine oxide in 700 g of anhydrous toluene to prepare a trimethylolphosphine oxide solution. Apply a pressure of 5 MPa to ethylene oxide to ensure that ethylene oxide is in a liquid state. Use a continuous flow microchannel reactor to pump 500 g of liquid ethylene oxide and the trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 90 °C, the pressure at 3 MPa, the flow rate at 5 ml / min, and the residence time at 10 min. Add methanol containing 0.1% hydrochloric acid to the outlet to quench the reaction, remove the solvent by vacuum distillation, and wash and dry the product with ethanol to obtain the main chain A polymer;

[0052] (2) Dissolve 10 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 200 g of anhydrous tetrahydrofuran to prepare a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 5 MPa to ethylene oxide to ensure that ethylene oxide is in a liquid state. Use a continuous flow microchannel reactor to pump 500 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 80 °C, the pressure at 3 MPa, the flow rate at 5 ml / min, and the residence time at 10 min. Add methanol containing 0.1% hydrochloric acid to the outlet to quench the reaction, remove the solvent by vacuum distillation, and wash and dry the product with ethanol to obtain the branched chain B polymer;

[0053] (3) Add 40 g of methyltrimethoxysilane to 800 g of an ethanol / water mixed solution (ethanol and water are mixed in a weight ratio of 95:5), stir at room temperature for 60 min to obtain a silane solution. Add 160 g of main chain A polymer and 480 g of branched chain B polymer to 4.8 Kg of tetrahydrofuran, stir at room temperature for 60 min, add the silane solution, heat up to 80 °C, react for 8 h, cool to room temperature, precipitate the product in diethyl ether, wash with ethanol, and dry to obtain hyperbranched PEO;

[0054] (4) Add 200 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 700 g of triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0055] (5) Add 300 g of hyperbranched PEO to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0056] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that the main chain A polymer is directly used and added to the liquid electrolyte. The specific process is as follows: A specific preparation method of a stable flame-retardant gel polymer for electrolyte includes the following steps:

[0057] (1) Dissolve 20 g of trimethylolphosphine oxide in 150 g of anhydrous toluene to prepare a trimethylolphosphine oxide solution. Apply a pressure of 4 MPa to ethylene oxide to ensure that ethylene oxide is in a liquid state. Using a continuous flow microchannel reactor, pump 400 g of liquid ethylene oxide and the trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain the temperature at 80 °C, the pressure at 2 MPa, the flow rate at 4 ml / min, and the residence time at 8 min. Add methanol containing 0.1% hydrochloric acid to quench the reaction at the outlet, distill off the solvent under reduced pressure, and wash the product with ethanol and dry to obtain the main chain A polymer;

[0058] (2) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0059] (3) Add 250 g of the main chain A polymer to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0060] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that the branched chain B polymer is directly used and added to the liquid electrolyte. The specific process is as follows: A specific preparation method of a stable flame-retardant gel polymer for electrolyte includes the following steps:

[0061] (1) Dissolve 10 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 150 g of anhydrous tetrahydrofuran to prepare a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 4 MPa to ethylene oxide to ensure it is in a liquid state. Using a continuous flow microchannel reactor, pump 450 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain a temperature of 75 °C, a pressure of 2 MPa, a flow rate of 4 ml / min, and a residence time of 8 min. Add methanol containing 0.1% hydrochloric acid at the outlet to quench the reaction. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the branched-chain B polymer;

[0062] (2) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0063] (3) Add 250 g of the branched-chain B polymer to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0064] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that polyethylene oxide is used and added to the liquid electrolyte. The specific process is as follows: A specific preparation method of a stable flame-retardant gel polymer for electrolyte includes the following steps:

[0065] (1) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0066] (2) Add 250 g of polyethylene oxide to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

[0067] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that when synthesizing hyperbranched PEO, the weight ratio of the main-chain A polymer to the branched-chain B polymer is 1:1. The specific process is as follows: A specific preparation method of a stable flame-retardant gel polymer for electrolyte includes the following steps:

[0068] (1) Dissolve 20 g of phosphite in 150 g of anhydrous toluene to prepare a phosphite solution. Apply a pressure of 4 MPa to ethylene oxide to ensure it is in a liquid state. Using a continuous flow microchannel reactor, pump 400 g of liquid ethylene oxide and the phosphite solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain a temperature of 80 °C, a pressure of 2 MPa, a flow rate of 4 ml / min, and a residence time of 8 min. Add methanol containing 0.1% hydrochloric acid at the outlet to quench the reaction. Remove the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the main-chain A polymer;

[0069] (2) Dissolve 10 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 150 g of anhydrous tetrahydrofuran to prepare a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 4 MPa to ethylene oxide to ensure it is in a liquid state. Using a continuous flow microchannel reactor, pump 450 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain a temperature of 75 °C, a pressure of 2 MPa, a flow rate of 4 ml / min, and a residence time of 8 min. Add methanol containing 0.1% hydrochloric acid to the outlet to quench the reaction. Remove the solvent by vacuum distillation. After the product is washed with ethanol and dried, branched polymer B is obtained;

[0070] (3) Add 90 g of methyltrimethoxysilane to 1.35 Kg of an ethanol / water mixed solution (ethanol and water are mixed at a weight ratio of 95:5), stir at room temperature for 45 min to obtain a silane solution. Add 270 g of main chain A polymer and 270 g of branched polymer B to 9.9 Kg of tetrahydrofuran, stir at room temperature for 45 min, add the silane solution, raise the temperature to 70 °C, react for 6 h, cool to room temperature. The product is precipitated in ether, washed with ethanol, and dried to obtain branched PEO;

[0071] (4) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate at a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0072] (5) Add 250 g of hyperbranched PEO to the liquid electrolyte to obtain a stable flame-retardant gel polymer for the electrolyte.

[0073] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that when synthesizing hyperbranched PEO, the weight ratio of the main chain A polymer to the branched chain B polymer is 1:6. The specific preparation method of a stable flame-retardant gel polymer for the electrolyte includes the following steps:

[0074] (1) Dissolve 20 g of trimethylolphosphine oxide in 150 g of anhydrous toluene to prepare a trimethylolphosphine oxide solution. Apply a pressure of 4 MPa to ethylene oxide to ensure it is in a liquid state. Using a continuous flow microchannel reactor, pump 400 g of liquid ethylene oxide and the trimethylolphosphine oxide solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain a temperature of 80 °C, a pressure of 2 MPa, a flow rate of 4 ml / min, and a residence time of 8 min. Add methanol containing 0.1% hydrochloric acid to the outlet to quench the reaction. Remove the solvent by vacuum distillation. After the product is washed with ethanol and dried, the main chain A polymer is obtained;

[0075] (2) Dissolve 20 g of 2,2'-[methylenebis(sulfonyl)]diethanol in 300 g of anhydrous tetrahydrofuran to prepare a 2,2'-[methylenebis(sulfonyl)]diethanol solution. Apply a pressure of 4 MPa to ethylene oxide to ensure it is in a liquid state. Using a continuous flow microchannel reactor, pump 900 g of liquid ethylene oxide and the 2,2'-[methylenebis(sulfonyl)]diethanol solution into a mixer through a metering pump. After mixing evenly, in the reactor, maintain a temperature of 75 °C, a pressure of 2 MPa, a flow rate of 4 ml / min, and a residence time of 8 min. Add methanol containing 0.1% hydrochloric acid to the outlet to quench the reaction. Remove the solvent by vacuum distillation. After the product is washed with ethanol and dried, branched polymer B is obtained;

[0076] (3) Add 30 g of methyltrimethoxysilane to a 450 g ethanol / water mixed solution (ethanol and water are mixed in a weight ratio of 95:5), and stir at room temperature for 45 min to obtain a silane solution. Add 90 g of main chain A polymer and 540 g of branched polymer B to 3.3 Kg of tetrahydrofuran, stir at room temperature for 45 min, add the silane solution, heat to 70 °C, react for 6 h, cool to room temperature, precipitate the product in diethyl ether, wash with ethanol, and dry to obtain branched PEO;

[0077] (4) Add 175 g of lithium trifluoromethanesulfonate to a solvent prepared by mixing 650 g of triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.05, and stir to form a liquid electrolyte;

[0078] (5) Add 250 g of hyperbranched PEO to the liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolytes.

[0079] Performance testing:

[0080] Ionic conductivity testing: Measure the ionic conductivities of the samples prepared in Examples 1-3 and Comparative Examples 1-5 at 25 °C, 50 °C, and 70 °C. The experimental results are shown in Table 1. Flame retardancy testing: Prepare films with a specification of 120 mm × 10 mm × 3 mm from the hyperbranched PEO in Examples 1-3, the main chain A polymer in Comparative Example 1, the branched polymer B in Comparative Example 2, the polyethylene oxide in Comparative Example 3, and the branched PEO in Comparative Examples 4-5, and conduct vertical burning tests and limiting oxygen index tests. The experimental results are shown in Table 2.

[0081] Table 1 Ionic conductivity

[0082]

[0083] Table 2 Flame retardancy

[0084]

[0085] Data analysis:

[0086] It can be seen from the experimental data in Table 1 and Table 2 that Examples 1-3 use a stable flame-retardant gel polymer prepared by the present invention, which has excellent ionic conductivity and good stable flame-retardant performance. Among them, the comprehensive performance of Example 2 is the best. While maintaining good flame-retardant performance, it has excellent ionic conductivity. This may be because the main-chain A polymer and the branched-chain B polymer form a hyperbranched structure under the action of the silane coupling agent, reducing the crystallinity of the material, improving the chain segment mobility, and promoting ion transport. The hyperbranched structure also provides a large number of terminal functional groups, enhancing the coordination with lithium salts and improving the ion dissociation efficiency; the P=O group and the O=S=O group form a dense carbon layer during combustion, inhibiting the release of heat and flammable gases, making the limiting oxygen index of Examples 1-3 ≥ 31.3%, all reaching the V0 level of flame retardancy.

[0087] It can be seen from the data of Comparative Example 1 and Example 2 that the ionic conductivity of Comparative Example 1 decreased significantly. This may be because the material prepared in Comparative Example 1 only contains the phosphorus-containing main-chain A polymer and lacks the flexible chain segments of the branched-chain B polymer, resulting in easy crystallization of the molecular chain, inhibiting the chain segment movement. At the same time, without the sulfur-containing group of the branched-chain B polymer, the phosphorus-sulfur synergistic flame-retardant effect is missing, and the fire protection grade of the material decreases, and the limiting oxygen index is also lower than that of Example 2.

[0088] It can be seen from the data of Comparative Example 2 and Example 2 that the ionic conductivity of Comparative Example 2 is far less than that of Example 2, and the flame-retardant performance also decreases. This may be because the flexible structure of the branched-chain B polymer reduces the crystallinity, but lacks the backbone structure provided by the main-chain A polymer, the degree of polymer branching is insufficient, and the ion transport channels are disordered, thus affecting the ionic conductivity of the material. At the same time, the material prepared in Comparative Example 2 only contains the sulfur-containing branched-chain B polymer and lacks the phosphorus element of the main-chain A. When the material burns, it cannot form a phosphorus-containing carbon layer, resulting in a decrease in the flame-retardant performance of the material.

[0089] It can be seen from the data of Comparative Example 3 and Example 2 that the performance of Comparative Example 3 is very different from that of Example 2. This may be because the linear molecular chain of polyethylene oxide used in Comparative Example 3 is highly crystalline, which will form an ion transport shield, and lacks polar groups (such as P=O, O=S=O) that coordinate with lithium salts, and the ion dissociation efficiency is low. It is very limited to improve the ionic conductivity only by solvent plasticization. At the same time, without phosphorus / sulfur flame-retardant groups, polyethylene oxide itself is very flammable. During the flame-retardant test, it burns violently and drips, and has no self-extinguishing property.

[0090] From the data of Comparative Examples 4 and 5 and Example 2, it can be seen that in Comparative Examples 4 and 5, when preparing hyperbranched PEO, too high a proportion of the main-chain A polymer or too high a proportion of the branched-chain B polymer has an adverse effect on both the ionic conductivity and the flame retardancy of the material. This may be because when the proportion of the main-chain A polymer is too high, the crosslinking density of the material is insufficient, the branched structure is loose, and the excessive rigid structure of the main chain increases the crystallinity, resulting in insufficient flexibility provided by the branched chains, restricted segmental motion, a decrease in the ionic conductivity of the material, and a smaller influence of the conductivity on temperature; when the proportion of the branched-chain B polymer is too high, the material undergoes excessive crosslinking to form a rigid network, restricting the segmental motion, thus causing a sharp drop in the ionic conductivity. At the same time, the lack of phosphorus content greatly reduces the flame retardancy of the material. Although the sulfur content of the material is too high, its flame retardant effect is not as significant as that of phosphorus. The too high sulfur content also destroys the phosphorus-sulfur synergistic flame retardant effect of the material, resulting in a decrease in the overall flame retardancy.

[0091] Those of ordinary skill in the art should understand that the discussion of any above embodiment is only exemplary and is not intended to imply that the scope of the present invention is limited to these examples; under the concept of the present invention, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A stable flame-retardant gel polymer for electrolyte, characterized in that: The method comprises the following raw materials in parts by weight: 20-30 parts of hyperbranched polyethylene oxide PEO, 15-20 parts of lithium salt and 60-70 parts of solvent; The specific preparation process of the hyperbranched PEO is as follows: (1) The preparation process of the main chain A polymer is as follows: dissolving trimethylolphosphine oxide in anhydrous toluene, applying a pressure of 3-5 MPa to ethylene oxide to ensure that ethylene oxide is in liquid state, using a continuous flow microchannel reactor to pump liquid ethylene oxide and trimethylolphosphine oxide solution into a mixer through a metering pump, and after uniform mixing, maintaining the temperature at 70-90°C, the pressure at 1-3 MPa, the flow rate at 3-5 ml / min, and the residence time at 5-10 min in the reactor, adding methanol containing 0.1% hydrochloric acid at the discharge port to quench the reaction, and removing the solvent by vacuum distillation. The product is washed with ethanol and dried to obtain the main chain A polymer; (2) The preparation process of the branched B polymer is as follows: 2,2'-[methylenebissulfonyl]diethanol is dissolved in anhydrous tetrahydrofuran, a pressure of 3-5 MPa is applied to ethylene oxide to ensure that ethylene oxide is in liquid state, and liquid ethylene oxide and 2,2'-[methylenebissulfonyl]diethanol solution are pumped into a mixer through a metering pump using a continuous flow microchannel reactor. After uniform mixing, the temperature in the reactor is maintained at 70-80°C, the pressure is 1-3 MPa, the flow rate is 3-5 ml / min, and the residence time is 5-10 min. Methanol containing 0.1% hydrochloric acid is added to the discharge port to quench the reaction, and the solvent is removed by distillation under reduced pressure. The product is washed with ethanol and dried to obtain the branched B polymer; (3) Add methyltrimethoxysilane to an ethanol / water mixed solution, stir at room temperature for 30-60 minutes to obtain a silane solution, add the main chain A polymer and the branched chain B polymer to tetrahydrofuran, stir at room temperature for 30-60 minutes, add the silane solution, heat to 60-80°C, react for 4-8 hours, cool to room temperature, precipitate the product in ether, wash with ethanol, and dry to obtain hyperbranched PEO; In the (3), the weight ratio of methyltrimethoxysilane, main chain A polymer, side chain B polymer, tetrahydrofuran and ethanol / water mixed solution is 1:2-4:6-12:100-120:10-20.

2. The stable flame-retardant gel polymer for electrolyte according to claim 1, characterized in that: In the (1), the weight ratio of trimethylolphosphine oxide, ethylene oxide and toluene is 1:15-25:10-20.

3. The stable flame-retardant gel polymer for electrolyte according to claim 1, characterized in that: In the (2), the weight ratio of 2,2'-[methylenebissulfonyl]diethanol, ethylene oxide and anhydrous tetrahydrofuran is 1:40-50:10-20.

4. The stable flame-retardant gel polymer for electrolyte according to claim 1, characterized in that: The ethanol / water mixed solution in (3) refers to a mixture of ethanol and water in a weight ratio of 95:

5.

5. The stable flame-retardant gel polymer for electrolyte according to claim 1, characterized in that: The lithium salt is one or more of lithium perchlorate, lithium trifluoromethanesulfonate, lithium hexafluorophosphate or lithium tetrafluoroborate.

6. The stable flame-retardant gel polymer for electrolyte according to claim 1, characterized in that: The solvent is prepared by mixing triethyl phosphate and ethylene carbonate in a weight ratio of 1:0.

05.

7. The method for preparing the stable flame-retardant gel polymer for electrolyte according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. Adding a lithium salt to a solvent and stirring to form a liquid electrolyte; S2. Hyperbranched PEO is added to a liquid electrolyte to obtain a stable flame-retardant gel polymer for electrolyte.

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