A method for preparing a gel polymer electrolyte containing dynamic side chains and applications thereof

Abstract

The present application belongs to the field of gel polymer electrolyte, and particularly relates to a preparation method of a gel polymer electrolyte containing dynamic side chains and application thereof. + The strong polar groups (such as cyano, fluorine) in the dynamic side chains can adjust the ion-dipole interaction between the functional groups in the polymer and the nearby Li + , reorganize the solvation structure of Li + , improve the Li + desolvation process, and effectively promote the desolvation of Li + , accelerate the polysulfide conversion kinetics, and significantly improve the capacity and cycle stability of lithium-sulfur batteries in the environment of 0-25℃. The present application belongs to the field of gel polymer electrolyte, and particularly relates to a preparation method of a gel polymer electrolyte containing dynamic side chains and application thereof. + The strong polar groups (such as cyano, fluorine) in the dynamic side chains can adjust the ion-dipole interaction between the functional groups in the polymer and the nearby Li + , reorganize the solvation structure of Li + , improve the Li + desolvation process, and effectively promote the desolvation of Li + , accelerate the polysulfide conversion kinetics, and significantly improve the capacity and cycle stability of lithium-sulfur batteries in the environment of 0-25℃.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of gel polymer electrolyte, and particularly relates to a preparation method of a gel polymer electrolyte containing dynamic side chains and application thereof. BACKGROUND

[0002] At present, lithium-sulfur batteries generally use liquid electrolyte mixed with volatile and flammable ether-based organic solvents and lithium salt, which has safety hazards such as easy leakage, flammability and explosion. Lithium-sulfur batteries are considered as one of the most potential new secondary energy storage systems due to their high theoretical specific capacity (1675 mAh / g) and high theoretical energy density (2600 Wh / kg), and high-energy-density long-endurance lithium-sulfur batteries can meet the urgent needs of military and civilian use. However, the "shuttle effect" of soluble polysulfides in liquid electrolyte, slow polysulfide conversion kinetics and growth of negative lithium dendrites during the discharge process of lithium-sulfur batteries seriously affect the actual performance of lithium-sulfur batteries. The polymer full-solid-state electrolyte can fundamentally avoid the safety problems of electrolyte leakage, polysulfide shuttle and lithium dendrite growth. However, the poor interface contact between the full-solid-state electrolyte and the electrode leads to high interfacial impedance and slow reaction kinetics, which hinders the development of full-solid-state lithium-sulfur batteries. Gel polymer electrolyte has good compatibility with electrode interface due to the presence of more liquid electrolyte components, has better mechanical properties than liquid electrolyte, and also has better ionic conductivity than full-solid-state electrolyte, which can inhibit lithium dendrite growth to some extent and improve battery safety.

[0003] Gel polymer electrolyte is expected to solve the various challenges faced by lithium-sulfur batteries and has great application potential. However, due to the presence of liquid electrolyte, "shuttle effect" and lithium dendrite growth cannot be avoided, and the electrochemical reaction kinetics is slow, which seriously affects the performance of lithium-sulfur batteries.

[0004] Gel polymer electrolytes are generally obtained by physically and chemically swelling a polymer matrix in a lithium salt and a liquid plasticizer to obtain a gel polymer electrolyte (such as patent CN202110428183.7). The contact between the electrolyte and the electrode prepared by this method is not close, and the polymer skeleton is difficult to penetrate into the electrode pores. In situ polymerization gel polymer electrolytes solve this problem very well. The in situ generated polymer electrolyte not only has good stability and low interfacial impedance, but also has a high solution absorption rate, and can more uniformly fix the liquid electrolyte in the cross-linked network. In the prior art, the polymer skeleton in the gel polymer electrolyte is easy to modify, and modifying a variety of polar groups (such as ester groups, amino groups, sulfonic acid groups, etc.) on the polymer skeleton helps to increase the lithium salt dissociation rate and accelerate lithium ion transmission. However, the introduction of strong polar groups will increase the adsorption energy of lithium ions and polymers, making it difficult for lithium ions to escape from the strongly polar solvated structure to participate in the polysulfide conversion reaction, thereby resulting in slow reaction kinetics and reducing the utilization rate of active substances. Therefore, there is an urgent need to solve the problems of low active utilization rate, slow electrode reaction kinetics and poor cycle stability of lithium-sulfur batteries. Summary of the Invention

[0005] The purpose of the present invention is to solve the problems of polysulfide shuttling, slow electrochemical reaction kinetics and poor cycle performance in existing lithium-sulfur battery gel polymer electrolytes, and to provide a gel polymer electrolyte and its preparation method and application in low temperature environment.

[0006] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0007] A method for preparing a gel polymer electrolyte containing dynamic side chains comprises the following steps:

[0008] Step S1. Preparation of monomers containing dynamic covalent bonds.

[0009] Dissolve a monomer containing phenylboronic acid in an alcohol solvent and stir at 20-40°C for 1-2 hours to obtain solution A; dissolve 3-amino-1,2-propanediol in an alcohol solvent and stir at 20-40°C for 1-2 hours to obtain solution B; mix solution A and solution B in a volume ratio of 1:1, add anhydrous magnesium sulfate (MgSO4), stir at 20-40°C for 12-24 hours, take the upper suspension, and rotary evaporate at 60-80°C for 4-6 hours to obtain a concentrated solution; add ether to the concentrated solution to precipitate a light yellow solid, and vacuum dry the light yellow solid at 60-80°C for 12-24 hours to obtain a monomer containing a dynamic covalent bond.

[0010] Furthermore, in step S1, the alcohol solvent is one or a mixture of two or more of methanol, ethanol, and propanol.

[0011] Among them, the molar ratio of phenylboronic acid monomer to alcohol solvent is 1:(20-40); the molar ratio of 3-amino-1,2-propylene glycol to alcohol solvent is 1:(20-40); the molar ratio of anhydrous magnesium sulfate to phenylboronic acid monomer is (1-2):1; and the molar ratio of diethyl ether to phenylboronic acid monomer is (20-30):1.

[0012] Step S2. Adding the monomer containing a dynamic covalent bond, a difunctional or higher functional crosslinking agent, a monofunctional allyl linear monomer, and an initiator obtained in step S1 to the electrolyte of the lithium-sulfur battery, and stirring uniformly to obtain a gel polymer electrolyte precursor;

[0013] Step S3: The gel polymer precursor is thermally initiated to undergo in-situ polymerization to obtain a gel polymer electrolyte containing dynamic side chains.

[0014] Furthermore, in step S1, the phenylboronic acid-containing monomer is one or a mixture of two or more of 3-cyanophenylboric acid, 2-fluorophenylboric acid, 2,3,6-trifluorophenylboric acid, and 3,4,5,6-tetrafluorophenylboric acid.

[0015] Furthermore, in step S2, the monomer containing dynamic covalent bonds obtained in step S1 accounts for 1-5% of the total mass of the gel polymer precursor.

[0016] Furthermore, in step S2, the difunctional or higher cross-linking agent is one or a mixture of two or more of the following: polydipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, and polyethylene glycol dimethacrylate (molecular weight of 200-400 g / mol); the difunctional or higher cross-linking agent accounts for 1-5% of the total mass of the gel polymer precursor.

[0017] Furthermore, in step S2, the monofunctional allyl linear monomer is one or a mixture of two or more of 2-((allyloxy)methyl)ethylene oxide, 2-((2-(vinyloxy)ethoxy)methyl)ethylene oxide, and 2-(ethylene oxide)methacrylate; and the monofunctional allyl linear monomer accounts for 1-5% of the total mass of the gel polymer precursor.

[0018] Furthermore, in step S2, the initiator is one or a mixture of two or more of azobisisoheptanonitrile, azobisisobutyronitrile, dibenzoyl peroxide, and methyl ethyl ketone peroxide, and the initiator accounts for 1-5% of the total mass of the gel polymer precursor.

[0019] Further, in step S2, the electrolyte of the lithium-sulfur battery is prepared by dissolving lithium bistrifluoromethanesulfonimide (LiTFSI) and LiNO3 in 1,3-dioxolane (DOL) and 1,2-dimethoxyethane to obtain the electrolyte of the lithium-sulfur battery.

[0020] Further, in step S3, the thermal initiation temperature is 50-80 DEG C, and the polymerization time is 1-4 h.

[0021] The gel polymer electrolyte containing dynamic side chains prepared by the above method can be applied in lithium-sulfur batteries.

[0022] The beneficial effects of the present application are as follows:

[0023] The polar groups (such as carbonyl, ether oxygen) in the gel polymer electrolyte containing dynamic side chains of the present application can promote the dissociation of lithium salt as electron donors to form Li + fast migration channels. The strong polar groups (such as cyano, fluorine) in the dynamic side chains can adjust the ion-dipole interaction between the functional groups in the polymer and the nearby Li + , reorganize the Li + solvation structure, and improve the effective way of Li + desolvation process. At the same time, the movement of dynamic bonds on the polymer matrix can accelerate the Li + desolvation, accelerate the polysulfide conversion kinetics, and significantly improve the capacity and cycle stability of lithium-sulfur batteries in 0-25 DEG C environment. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The ion conductivity graph of Example 1, Comparative Example 1 and Comparative Example 2.

[0025] Figure 2 The electrochemical window graph of Example 1, Comparative Example 1 and Comparative Example 2.

[0026] Figure 3 The Li-Cu half-cell Coulomb efficiency graph of Example 1, Comparative Example 1 and Comparative Example 2.

[0027] Figure 4 The 0.1C charge-discharge curve graph of Example 2, Comparative Example 1 and Comparative Example 2.

[0028] Figure 5 The rate performance graph of Example 2, Comparative Example 1 and Comparative Example 2.

[0029] Figure 60.5C long cycle performance diagram of Example 3, Comparative Example 1 and Comparative Example 2.

[0030] Figure 7 This is a long cycle performance diagram of Example 1, Comparative Example 1 and Comparative Example 2 at 0°C and 0.5°C. DETAILED DESCRIPTION

[0031] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0032] Example 1

[0033] S1: Weigh 14.7 g of 3-cyanophenylboronic acid and dissolve it in 93 ml of methanol, stir at 20°C for 1 h to obtain solution A; weigh 9.1 g of 3-amino-1,2-propanediol and dissolve it in 65 ml of methanol, stir at 20°C for 1 h to obtain solution B; mix solution A and solution B, add 19 g of anhydrous magnesium sulfate (MgSO4), and stir at 20°C for 12 h; take the upper layer of suspension, rotary evaporate at 60°C for 4 h to obtain a concentrate; add 220 ml of ether to the concentrate to precipitate a light yellow solid, and dry the light yellow solid in vacuo at 60°C for 12 h to obtain the final product C.

[0034] S2: Weigh 0.01 g of polydipentaerythritol hexaacrylate, 0.05 g of 2-((allyloxy)methyl)ethylene oxide, 0.05 g of product C, and 0.025 g of azobisisobutyronitrile into 0.865 g of the electrolyte and mix well to obtain a gel polymer electrolyte precursor.

[0035] S3: The gel polymer precursor is thermally initiated to be in situ polymerized at 50° C. for 4 h to obtain a gel polymer electrolyte containing dynamic side chains.

[0036] Example 2

[0037] S1: Weigh 14.1 g of 2-fluorophenylboronic acid and dissolve it in 100 ml of ethanol, stir at 30°C for 1.5 h to obtain solution A; weigh 9.1 g of 3-amino-1,2-propanediol and dissolve it in 100 ml of ethanol, stir at 30°C for 1.5 h to obtain solution B; mix solution A and solution B, add 27 g of anhydrous magnesium sulfate (MgSO4), and stir at 30°C for 18 h; take the upper layer of suspension, rotary evaporate at 70°C for 5 h to obtain a concentrate; add 190 ml of ether to the concentrate to precipitate a light yellow solid, and dry the light yellow solid in vacuo at 70°C for 18 h to obtain the final product C.

[0038] S2: Weigh 0.05 g of pentaerythritol tetraacrylate, 0.025 g of 2-(epoxyethyl)methacrylate, 0.025 g of product C, and 0.01 g of dibenzoyl peroxide, add them to 0.89 g of electrolyte, and mix them evenly to obtain a gel polymer electrolyte precursor.

[0039] S3: The gel polymer precursor was heated to initiate in-situ polymerization at 80°C for 1 h to obtain the gel polymer electrolyte containing dynamic side chains.

[0040] Example 3

[0041] S1: 17.6 g of 2,3,6-trifluorobenzenboronic acid was dissolved in 150 ml of propanol, stirred at 40°C for 2 h to obtain solution A; 9.1 g of 3-amino-1,2-propanediol was dissolved in 130 ml of propanol, stirred at 40°C for 2 h to obtain solution B; solution A and solution B were mixed, 45 g of anhydrous magnesium sulfate (MgSO4) was added, and stirred at 40°C for 24 h; the upper suspension was taken, and rotary evaporation was performed at 80°C for 6 h to obtain a concentrated solution; 240 ml of ether was added to the concentrated solution to precipitate a light yellow solid, which was vacuum dried at 80°C for 24 h to obtain the final product C.

[0042] S2: 0.025 g of polyethylene glycol dimethacrylate (molecular weight of 200 g / mol), 0.05 g of 2-((2-(vinyl oxy)ethoxy)methyl)oxirane, 0.05 g of product C, and 0.05 g of methyl ethyl ketone peroxide were added to 0.825 g of electrolyte and mixed uniformly to obtain a gel polymer electrolyte precursor.

[0043] S3: The gel polymer precursor was heated to initiate in-situ polymerization at 65°C for 2.5 h to obtain the gel polymer electrolyte containing dynamic side chains.

[0044] Comparative Example 1

[0045] S1: 0.01 g of polydivalent pentaerythritol hexaacrylate, 0.05 g of 2-((allyloxy)methyl)oxirane, and 0.025 g of azobisisobutyronitrile were added to 0.915 g of electrolyte and mixed uniformly to obtain a gel polymer electrolyte precursor.

[0046] S3: The gel polymer precursor was heated to initiate in-situ polymerization at 50°C for 4 h to obtain the gel polymer electrolyte containing dynamic side chains.

[0047] Comparative Example 2

[0048] Comparative Example 2 is an electrolyte for lithium-sulfur batteries without any monomer. Lithium bistrifluoromethanesulfonimide (LiTFSI) and quantitative LiNO3 were dissolved in 1,3-dioxolane (DOL) and 1,2-ethyleneglycol dimethyl ether to obtain an electrolyte for lithium-sulfur batteries. The volume ratio of 1,3-dioxolane (DOL) and 1,2-ethyleneglycol dimethyl ether was 1:1, the concentration of lithium bistrifluoromethanesulfonimide (LiTFSI) was 1 M, and LiNO3 accounted for 2 wt% of the total mass of the electrolyte.

[0049] Application Example

[0050] The gel polymer electrolyte and lithium-sulfur battery electrolyte prepared in the Examples and Comparative Examples were used as test electrolytes. A simple melt-diffusion method was used to prepare the carbon / sulfur powder positive electrode material. The carbon / sulfur powder positive electrode material, the conductive agent Super P, and the binder PVDF-900 were mixed in a mass ratio of 7:2:1. A certain amount of N-methylpyrrolidone was added and mixed thoroughly to obtain a positive electrode slurry. The slurry was then coated onto carbon-coated aluminum foil, dried, roll-pressed, and slit to obtain positive electrode sheets. CR2032 button cells were assembled in an argon-filled glove box using a lithium sheet as the negative electrode. The following describes the material characterization and performance testing of selected specific examples.

[0051] Figure 1 Graphs showing the ionic conductivity at different temperatures for Example 1, Comparative Example 1, and Comparative Example 2. It can be seen that Example 1 and Comparative Example 2 have ionic conductivities of the same order of magnitude.

[0052] Figure 2 The electrochemical window diagrams of Example 1, Comparative Example 1, and Comparative Example 2 are shown. The decomposition voltages of Example 1, Comparative Example 1, and Comparative Example 2 are 4.45 V, 4.13 V, and 4.02 V, respectively, indicating that the gel polymer electrolyte containing dynamic side chains has improved electrochemical stability and anti-electrochemical oxidation ability.

[0053] Figure 3 Figure 2 shows the coulombic efficiency of the Li-Cu half-cells of Example 1, Comparative Example 1, and Comparative Example 2. It can be seen that the coulombic efficiency of Comparative Example 2 and Comparative Example 4 significantly decreases after 250 and 200 cycles, respectively. The average coulombic efficiency of Example 1 after 600 cycles is 98.2%.

[0054] Figure 4 The 0.1C charge-discharge curves for Example 2, Comparative Example 1, and Comparative Example 2 are shown. As can be seen, at a current density of 0.1C, the capacity of Example 2 is 1445 mAh / g, significantly higher than that of Comparative Examples 1 and 2. The polarization voltages for Example 2, Comparative Examples 1, and 2 are 138 mV, 145 mV, and 166 mV, respectively, demonstrating that the gel polymer electrolyte containing dynamic side chains accelerates electrochemical reaction kinetics, reduces battery polarization, and improves active material utilization.

[0055] Figure 5 The figure shows the rate performance of Example 2, Comparative Example 1, and Comparative Example 2. At current densities of 0.1C, 0.2C, 0.5C, 1C, and 2C, the capacity of Example 2 is higher than that of Comparative Example 1 and Comparative Example 2. At 2C, Example 2 can still provide a capacity of up to 840 mAh / g.

[0056] Figure 6The 0.5C long cycle performance graph at 25°C is shown for Example 3, Comparative Example 1, and Comparative Example 2. It can be seen that the initial discharge capacities of the lithium-sulfur batteries assembled in Example 3, Comparative Example 1, and Comparative Example 2 are 1088 mAh / g, 842 mAh / g, and 947 mAh / g, respectively. After 1000 cycles, the capacities of Example 3 and Comparative Example 1 are 583 mAh / g and 360 mAh / g, respectively, and after 400 cycles, the capacity of Comparative Example 2 is 285 mAh / g.

[0057] Figure 7 The 0.5C long cycle performance graphs at 0°C for Example 1, Comparative Example 1, and Comparative Example 2 show that the initial discharge capacities of the lithium-sulfur batteries assembled in Example 1, Comparative Example 1, and Comparative Example 2 are 940 mAh / g, 668 mAh / g, and 810 mAh / g, respectively. After 200 cycles, the capacities of Example 1, Comparative Example 1, and Comparative Example 2 are 810 mAh / g, 525 mAh / g, and 528 mAh / g, respectively.

[0058] The gel polymer electrolyte containing dynamic side chains prepared by the present invention promotes the dissociation of lithium salts through the polymer skeleton rich in polar groups, thus constructing a fast Li + The strong electronegative groups on the side chains mediate the Li transport channel through ion-dipole interactions. + The solvation structure and the movement of dynamic bonds on the polymer backbone accelerate the electrolyte / electrode interface treatment. + The desolvation of the electrolyte accelerates the electrochemical reaction kinetics, improves the utilization rate of active materials, and ultimately realizes high-capacity, long-cycle high-performance lithium-sulfur batteries.

Claims

1. A method for preparing a gel polymer electrolyte containing dynamic side chains, characterized in that: The following steps are involved: Step S1. Preparation of a monomer containing a dynamic covalent bond; Dissolve the phenylboronic acid-containing monomer in an alcohol solvent and stir at 20-40°C for 1-2 hours to obtain solution A; dissolve 3-amino-1,2-propylene glycol in an alcohol solvent and stir at 20-40°C for 1-2 hours to obtain solution B; mix solution A and solution B in a volume ratio of 1:1, add anhydrous magnesium sulfate, stir at 20-40°C for 12-24 hours, take the upper suspension, and rotary evaporate at 60-80°C for 4-6 hours to obtain a concentrate; add diethyl ether to the concentrate to precipitate a light yellow solid, and vacuum dry the light yellow solid at 60-80°C for 12-24 hours to obtain a monomer containing a dynamic covalent bond; The molar ratio of phenylboronic acid monomer to alcohol solvent is 1:(20-40); the molar ratio of 3-amino-1,2-propylene glycol to alcohol solvent is 1:(20-40); the molar ratio of anhydrous magnesium sulfate to phenylboronic acid monomer is (1-2):1; the molar ratio of ether to phenylboronic acid monomer is (20-30):1; The phenylboronic acid-containing monomer is one or a mixture of two or more of 3-cyanophenylboric acid, 2-fluorophenylboric acid, 2,3,6-trifluorophenylboric acid, and 3,4,5,6-tetrafluorophenylboric acid; The cross-linking agent with two or more functional groups is one or a mixture of two or more of polydipentaerythritol hexaacrylate, pentaerythritol tetraacrylate, pentaerythritol triacrylate, and polyethylene glycol dimethacrylate; Step S2. Adding the monomer containing a dynamic covalent bond, a difunctional or higher functional crosslinking agent, a monofunctional allyl linear monomer, and an initiator obtained in step S1 to the electrolyte of the lithium-sulfur battery, and stirring uniformly to obtain a gel polymer electrolyte precursor; The monomer containing dynamic covalent bonds obtained in step S1 accounts for 1-5% of the total mass of the gel polymer precursor; The cross-linking agent with two or more functional groups accounts for 1-5% of the total mass of the gel polymer precursor; The monofunctional allyl linear monomer accounts for 1-5% of the total mass of the gel polymer precursor; The initiator accounts for 1-5% of the total mass of the gel polymer precursor; Step S3. The gel polymer precursor is thermally initiated to polymerize in situ to obtain a gel polymer electrolyte containing dynamic side chains; the thermal initiation temperature is 50-80°C, and the polymerization time is 1-4h.

2. The method for preparing a gel polymer electrolyte containing dynamic side chains according to claim 1, characterized in that: In step S1, the alcohol solvent is one of methanol, ethanol, and propanol, or a mixture of two or more thereof.

3. The method for preparing a gel polymer electrolyte containing dynamic side chains according to claim 1 or 2, characterized in that: In step S2, the monofunctional allyl linear monomer is one or a mixture of two or more of 2-((allyloxy)methyl)ethylene oxide, 2-((2-(vinyloxy)ethoxy)methyl)ethylene oxide, and 2-(oxiranyl)methacrylate.

4. The method for preparing a gel polymer electrolyte containing dynamic side chains according to claim 1 or 2, characterized in that: In step S2, the initiator is one or a mixture of two or more of azobisisoheptanonitrile, azobisisobutyronitrile, dibenzoyl peroxide, and methyl ethyl ketone peroxide.

5. The method for preparing a gel polymer electrolyte containing dynamic side chains according to claim 1 or 2, characterized in that: In step S2, the electrolyte of the lithium-sulfur battery is specifically: lithium bis(trifluoromethanesulfonyl imide) and LiNO3 are dissolved in 1,3-dioxolane and 1,2-ethylene glycol dimethyl ether to obtain an electrolyte of the lithium-sulfur battery; wherein the volume ratio of 1,3-dioxolane and 1,2-ethylene glycol dimethyl ether is 1:1, the concentration of lithium bis(trifluoromethanesulfonyl imide is 1M, and LiNO3 accounts for 2wt% of the total mass of the electrolyte.

6. A gel polymer electrolyte containing dynamic side chains prepared by the method for preparing a gel polymer electrolyte containing dynamic side chains according to any one of claims 1 to 5, which is used in a lithium-sulfur battery.

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