A gel polymer electrolyte and preparation and application thereof

Abstract

The present application relates to a kind of gel polymer electrolyte and preparation thereof, belong to lithium battery field.The present application provides a kind of gel polymer electrolyte, the gel polymer electrolyte includes POSS-PMMA star polymer, ionic liquid and lithium salt, wherein, the dosage ratio of each raw material is as follows:POSS-PMMA star polymer 30~90 parts by weight, ionic liquid 10~70 parts by weight, lithium salt 10~35 parts by weight.The present application selects and introduces ionic liquid and lithium salt in POSS-PMMA star polymer, and a new type of gel polymer electrolyte is prepared;Wherein the introduction of POSS not only ensures mechanical strength but also greatly improves thermal performance, the introduction of ionic liquid can avoid a series of safety problems caused by the use of organic solvent, also increase the environmental friendliness of preparation process.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of gel polymer electrolyte and preparation thereof, belong to lithium battery field. BACKGROUND

[0002] Gel polymer electrolyte is introduced in high molecular matrix organic electrolyte, commonly used high molecular matrix has polymethyl methacrylate (PMMA), polyethylene oxide (PEO), polyacrylonitrile (PAN) etc., organic electrolyte is mainly propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC) etc..This kind of gel electrolyte due to the existence of a large number of organic solvents makes it lack enough mechanical integrity and easily appear short circuit between electrode, and increase polymer matrix / organic electrolyte ratio also ensures not ionic conductivity.

[0003] The main method to improve the electrochemical performance of gel polymer electrolyte is to inhibit the crystallization of polymer matrix and increase the ion concentration, currently commonly used blending, adding inorganic filler to inhibit the crystallization of polymer matrix chain and increasing the concentration of organic electrolyte to increase the ion concentration to realize high ionic conductivity.But this kind of method will reduce the mechanical strength of polymer, and a large number of organic solvents absorption may cause safety problems and environmental problems, which seriously hinders the development of gel polymer electrolyte.Therefore, how to ensure high ionic conductivity while also having certain mechanical properties has become a problem to be solved. SUMMARY

[0004] In view of the above problems that gel polymer electrolyte ionic conductivity and mechanical properties cannot be compatible, the present application selects to introduce ionic liquid and lithium salt in POSS-PMMA star polymer, and a new type of gel polymer electrolyte is prepared;The introduction of POSS not only ensures the mechanical strength but also greatly improves the thermal performance, the introduction of ionic liquid can avoid a series of safety problems caused by the use of organic solvent, and also increases the environmental protection of preparation process.

[0005] The technical scheme of the present application is as follows:

[0006] The first technical problem to be solved by the present application is to provide a kind of gel polymer electrolyte, the gel polymer electrolyte includes POSS-PMMA star polymer, ionic liquid and lithium salt, wherein the amount of each raw material is as follows: POSS-PMMA star polymer 30-90 parts by weight, ionic liquid 10-70 parts by weight, lithium salt 10-35 parts by weight.

[0007] Further, the ionic liquid is selected from: 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt ([EMIM][TFSI]), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt ([BMIM][TFSI]) or 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt ([HMIM][TFSI]).

[0008] Further, the lithium salt is selected from: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4) or lithium bis(difluorosulfonyl)imide (LiFSI).

[0009] Further, the POSS-PMMA star polymer is prepared by the following method:

[0010] 1) Methyl methacrylate (MMA), octachloropropyl oligomeric silsesquioxane (POSS-Cl8), catalyst, co-catalyst and solvent 1 are placed in an oxygen-free reaction vessel, and after at least three cycles of freezing-vacuumizing-thawing, they are reacted at 85-115°C for 12-48h (preferably 24h); wherein the molar ratio of methyl methacrylate (MMA), octachloropropyl oligomeric silsesquioxane (POSS-Cl8), catalyst and co-catalyst is 1200-2000:1:6-10:10-30;

[0011] 2) The reaction product obtained in step 1) is dissolved with solvent 2, then passed through a column, and then the catalyst is removed, and finally the white product POSS-PMMA is obtained by precipitation and filtration;

[0012] 3) The product obtained in step (2) is volatilized to remove the solvent, and then dried to obtain the purified POSS-PMMA.

[0013] Further, in step 1), the catalyst is cuprous chloride CuCl, Cu / CuCl2 or CuCl / CuCl2.

[0014] Further, in step 1), the co-catalyst is pentamethyldiethylenetriamine PMDETA or bipyridine bpy.

[0015] Further, in step 1), the solvent 1 is anhydrous toluene, xylene or dichloromethane; the solvent 1 is distilled with CaH2 when used; the amount of solvent 1 used is only enough to dissolve the reaction monomer MMA.

[0016] Further, in step 2), the solvent 2 is at least one of tetrahydrofuran, N,N-dimethylformamide or dichloromethane.

[0017] Further, in step 2), the amount of solvent 2 is 8-15 times the amount of solvent 1.

[0018] Further, in step 2), the precipitation is carried out by using anhydrous methanol, anhydrous ethanol or deionized water.

[0019] A second technical problem to be solved by the present application is to provide a preparation method of the gel polymer electrolyte, which comprises mixing, reacting POSS-PMMA star-shaped polymer, ionic liquid, lithium salt and solvent to obtain the gel polymer electrolyte.

[0020] Further, the preparation method comprises stirring POSS-PMMA star-shaped polymer, ionic liquid, lithium salt and solvent at room temperature for 12-24 h, then removing the solvent and drying to obtain the gel polymer electrolyte.

[0021] A third technical problem to be solved by the present application is to provide the use of the gel polymer electrolyte in lithium ion batteries or flexible supercapacitors.

[0022] A fourth technical problem to be solved by the present application is to provide a lithium ion battery comprising the obtained gel polymer electrolyte.

[0023] The present application has the following advantages:

[0024] The present application provides a star-shaped polymer gel electrolyte, which is formed by POSS-PMMA star-shaped polymer, ionic liquid and lithium salt in a certain mass ratio; the introduction of POSS improves the mechanical properties of pure PMMA matrix, greatly improves the thermal performance, and ensures high ionic conductivity; in addition, the use of ionic liquid instead of organic solvent as a plasticizer can not only improve the ionic conductivity, but also reduce the safety and environmental problems in the process. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 are TGA curves of POSS-PMMA, PMMA and POSS; from Figure 1 It can be seen that the thermal degradation temperature (Td) of pure PMMA is 259.6℃, and the Td of the synthesized POSS-PMMA star-shaped polymer is 307.6℃, which is nearly 50℃ higher than that of pure PMMA, close to the thermal degradation temperature of pure POSS; this indicates that the introduction of POSS can effectively improve the use temperature of the star-shaped polymer gel electrolyte.

[0026] Figure 2 a, Figure 2 b are DSC curves of PMMA and POSS-PMMA with different [EMIM][TFSI] contents; from Figure 2It can be seen that the glass transition temperature of pure POSS-PMMA is about 20℃ higher than that of pure PMMA, and the Tg of PMMA-based and POSS-PMMA-based gel electrolytes both decrease with the increase of the content of [EMIM][TFSI] ionic liquid, but the Tg of PMMA is higher than that of POSS-PMMA at the same ILs content, which also indicates that the ionic conductivity of the POSS-PMMA-based gel electrolyte is higher than that of the PMMA-based gel electrolyte, because the ionic conductivity is mainly contributed by the amorphous region in the polymer matrix.

[0027] Figure 3 is the stress-strain curve of the POSS-PMMA star-shaped polymer gel electrolyte obtained in Example 7; and Figure 3 It can be seen that the breaking strength (0.402 MPa) of the POSS-PMMA-based gel electrolyte is much higher than that (0.022 MPa) of the pure PMMA-based gel electrolyte at the same ILs content.

[0028] Figure 4 is the linear scan voltammetry curve of the star-shaped polymer gel electrolyte (POSS-PMMA:[EMIM][TFSI]:LiN(CF3SO2)2=4:6:1) prepared in Example 7; and Figure 4 It can be seen that the electrochemical stability window of the star-shaped polymer gel electrolyte can reach 4.6 V, which fully meets the use standard of lithium ion batteries.

[0029] Figure 5 is the AC impedance spectrogram of the POSS-PMMA gel polymer electrolyte with different ionic liquid contents obtained in Examples 8-9 and Comparative Example 8; and Figure 5 It can be seen that the increase of the ionic liquid can increase the ion carrying concentration in the system and thus improve the ionic conductivity when the content of lithium salt is unchanged; but too much addition of the ionic liquid as a small molecule plasticizer can greatly reduce the mechanical properties of the gel electrolyte, which has no any practical value.

[0030] Figure 6 is the AC impedance spectrogram of the POSS-PMMA gel polymer electrolyte with different lithium salt contents obtained in Examples 7, 10-12; and Figure 6 It can be seen that the increase of the lithium salt content can also increase the lithium ion concentration when the content of the ionic liquid is constant; but too much addition of the lithium salt as a small molecule plasticizer can greatly reduce the mechanical properties of the gel electrolyte, which has no any practical value. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application will be further described in combination with examples, and the present application is not limited in the scope of the described examples.

[0032] Examples 1-6

[0033] Preparation of POSS-PMMA star polymer:

[0034] A certain amount of substance mole ratio (1800:1:8:24) of methyl methacrylate (MMA), octachloropropyl oligomeric silsesquioxane (POSS-Cl8), cuprous chloride (CuCl), pentamethyldiethylenetriamine (PMDETA) and 20 ml of anhydrous toluene were placed in a reaction bottle, after three cycles of liquid nitrogen freezing-vacuumizing-thawing, the reaction was carried out in an oil bath pot at 110°C for 24h, the obtained product was dissolved with 200ml of tetrahydrofuran, and the catalyst was removed by passing through a neutral alumina column, then rotary evaporation was carried out, finally, anhydrous methanol was used for precipitation, and the product was extracted by suction, and dried in a vacuum oven at 60°C for 2-3 days to obtain the POSS-PMMA star polymer, the structural formula of which is shown as follows:

[0035]

[0036] The TGA curves of POSS-PMMA, POSS and PMMA were measured respectively, and the results are shown in Figure 1 It can be seen that the thermal degradation temperature (T d ) of pure PMMA is 259.6°C, while the T d of the POSS-PMMA star polymer synthesized by the present application is 307.6°C, which is nearly 50°C higher than the T d of pure PMMA, close to the thermal degradation temperature of pure POSS; this shows that the introduction of POSS can effectively improve the use temperature of the star polymer gel electrolyte.

[0037] POSS-PMMA: [EMIM][TFSI] (9:1, 8:2, 7:3, 6:4, 5:5) and a fixed mass fraction (5%) of lithium bis (trifluoromethanesulfonyl) imide and a proper volume (15ml) of tetrahydrofuran were mixed, stirred at room temperature for 24h, then poured into a four-fluorine plate, placed in a fume hood for volatilization, and dried in a vacuum oven at 60°C for 2-3 days to obtain a series of gel polymer electrolytes with ion liquid contents of 0 (Example 1), 10% (Example 2), 20% (Example 3), 30% (Example 4), 40% (Example 5), and 50% (Example 6); and secondary DSC temperature rise test was carried out, and the obtained DSC curves are shown in Figure 2 b.

[0038] Comparative Examples 1-6

[0039] A series of gel polymer electrolytes with ionic liquid content of 0 (Comparative Example 1), 10% (Comparative Example 2), 20% (Comparative Example 3), 30% (Comparative Example 4), 40% (Comparative Example 5), 50% (Comparative Example 6) were prepared by mixing different proportions of PMMA: [EMIM][TFSI] (9:1, 8:2, 7:3, 6:4, 5:5) and a fixed mass fraction (5%) of lithium bis(trifluoromethanesulfonyl)imide and an appropriate volume (15 ml) of tetrahydrofuran, stirring at room temperature for 24 h, then pouring into a fluorotetra plate, volatilizing in a fume hood, and drying in a vacuum oven at 60°C for 2-3 days. The DSC curves obtained by secondary DSC temperature rise testing are shown in Figure 1. Figure 2 The glass transition temperature results of the base gel polymer electrolytes obtained in Examples 1-6 are shown in Table 1.

[0040] As shown in Table 1, the glass transition temperature of pure POSS-PMMA is nearly 20°C higher than that of pure PMMA. With the increase of the content of [EMIM][TFSI] ionic liquid, the Tg of both PMMA-based and POSS-PMMA-based gel electrolytes decreases, but the Tg of PMMA is higher than that of POSS-PMMA at the same ILs concentration, which also indicates that the ionic conductivity of the POSS-PMMA-based gel electrolyte is higher than that of the PMMA-based gel electrolyte, because the ionic conductivity is mainly contributed by the amorphous region in the polymer matrix. Figure 2 Example 7

[0041] A gel electrolyte with 60% ionic liquid content was prepared by mixing 40 parts by mass of POSS-PMMA, 60 parts by mass of [EMIM][TFSI], and 10 parts by mass of lithium bis(trifluoromethanesulfonyl)imide, stirring at room temperature for 24 h, then pouring into a fluorotetra plate, volatilizing in a fume hood, and drying in a vacuum oven at 60°C for 2-3 days. The tensile property test results are shown in Figure 2. The POSS-PMMA star polymer gel electrolyte was assembled with lithium sheet, stainless steel sheet, gasket, positive and negative electrode covers in a glove box, then pressed into a lithium battery using a press plate machine, and the electrochemical stability was studied using linear sweep voltammetry (LSV).

[0042] Figure 3 Comparative Example 7

[0043] The preparation method is basically the same as that of Example 7, the only difference being that the polymer matrix used in Example 7 is a POSS-PMMA star polymer, and PMMA is used in this comparative example.

[0044] The preparation method is basically the same as that of Example 7, the only difference being that the polymer matrix used in Example 7 is a POSS-PMMA star polymer, and PMMA is used in this comparative example.

[0045] ​In addition, the ionic conductivities of the 60% ILs POSS-PMMA-based gel electrolyte and the 60% ILs PMMA-based gel electrolyte at different temperatures were respectively measured, and the activation energies of both were calculated. Table 2 is the ionic conductivities of the PMMA-based and the POSS-PMMA-based gel electrolyte at different temperatures, and Table 3 is the activation energies of both. Figure 3 are the stress-strain curves of the 60% ILs POSS-PMMA-based gel electrolyte and the 60% ILs PMMA-based gel electrolyte, Figure 4 is the linear sweep voltammetry curve of the 60% ILs POSS-PMMA-based gel electrolyte.

[0046] According to Figure 3 It can be seen that the breaking strength (0.402 MPa) of the POSS-PMMA-based gel electrolyte is much higher than that (0.022 MPa) of the pure PMMA-based gel electrolyte at the same ILs content; in combination with Tables 2 and 3, it can be seen that the ionic conductivity of the former is still higher than that of the latter, the activation energy of the former is less than that of the latter, and the dependence of the ionic conductivity of the POSS-PMMA-based gel electrolyte on temperature is more in line with the Arrhenius equation than that of the pure PMMA-based gel electrolyte . The ionic conductivity can be calculated according to the formula (L is the thickness of the gel electrolyte, R b and A s are the volume resistance and the electrode area, respectively) from the impedance spectrum. It can be seen from Figure 4 that the electrochemical stability window of the POSS-PMMA star polymer gel electrolyte can reach 4.6 V, fully meeting the use standard of lithium ion batteries

[0047] Examples 8-9

[0048] In this example, 30 (Example 9), 40 (Example 8) parts by mass of POSS-PMMA, 60 (Example 8), 70 (Example 9) parts by mass of [EMIM][TFSI] and 15 parts by mass of lithium bis-trifluoromethanesulfonimide were mixed, and after stirring at room temperature for 24 h, they were poured into a fluorotetra dish, volatilized in a fume hood, and dried in a vacuum oven at 60°C for 2-3 days to obtain a gel electrolyte with an ionic liquid content of 60% and 70%. The POSS-PMMA star polymer gel electrolyte was assembled with lithium sheet, stainless steel sheet, gasket, positive and negative electrode cover in a glove box, and then pressed into a lithium battery using a press machine. The impedance spectrum of the POSS-PMMA-based gel electrolyte with different ionic liquid contents was measured.

[0049] Comparative Example 8

[0050] In the comparative example, a PMMA-based gel electrolyte with 60% ILs was prepared. The operation of the comparative example was basically the same as that of Example 8, except that the polymer matrix used in Example 8 was a POSS-PMMA star polymer, and the PMMA was used in the comparative example, and because the pure PMMA-based gel electrolyte prepared with a higher IL content (70%) was difficult to be shaped, 60% was selected as the highest IL content; and the impedance spectrum of the PMMA-based gel electrolyte was measured.

[0051] In combination Figure 5 and Table 4, under the same conditions, the conductivity of the POSS-PMMA-based gel electrolyte was higher than that of the pure PMMA-based gel electrolyte, and the POSS-PMMA-based gel electrolyte could absorb more ILs due to its excellent mechanical properties, thereby achieving higher ionic conductivity. The increase of ILs was very helpful to the increase of ionic conductivity, and it could be seen that the ionic conductivity of the POSS-PMMA-based gel electrolyte with 70% ILs and 15% lithium salt could reach 1.14*10 ﹣3 S / cm.

[0052] Examples 10-12

[0053] The present application also prepared gel polymer electrolytes with different contents of lithium bis(trifluoromethanesulfonyl)imide, wherein 40 parts by mass of POSS-PMMA and 60 parts by mass of [EMIM][TFSI] were kept unchanged, and 10 (Example 7), 20 (Example 10), 30 (Example 11), and 35 (Example 12) parts by mass of lithium bis(trifluoromethanesulfonyl)imide were added. After mixing, the mixture was stirred at room temperature for 24 hours in a sealed container, then was placed in a four-fluorine disc and was volatilized in a fume hood, and after drying in a vacuum oven at 60°C for several days, gel electrolytes with lithium salt contents of 10%, 20%, 25%, and 35% were obtained. Then, the gel electrolytes with different lithium salt contents were assembled with stainless steel sheets, gaskets, positive and negative electrode covers, and were pressed into lithium batteries in a glove box.

[0054] Because the POSS-PMMA-based gel electrolyte prepared with a higher lithium salt content (40%) at an IL content of 60% was difficult to be shaped, 35% was selected as the highest lithium salt content.

[0055] The impedance spectrum of the POSS-PMMA-based gel electrolyte with different contents of lithium bis(trifluoromethanesulfonyl)imide was measured, and the corresponding ionic conductivity was calculated according to the formula.

[0056] Table 1 Glass transition temperature (℃) of the gel polymer electrolytes obtained in Examples 1-6

[0057]

[0058] Table 2 Ionic conductivity (10-4S / cm) of gel electrolytes of Comparative Example 7 and Example 7 at different temperatures -4 S / cm)

[0059] T(℃) 30 40 50 60 70 σ (PMMA) Comparative Example 7 1.79 3.13 5.00 6.74 12.5 σ (POSS-PMMA) Example 8 2.86 4.48 7.30 10.5 16.1

[0060] Table 3 Activation energy Ea (kJ / mol) of gel electrolytes of Comparative Example 7 and Example 7

[0061]

[0062] Table 4 Ionic conductivity (10-4S / cm) of gel electrolytes of Comparative Example 8, Examples 8-9 -4 S / cm)

[0063]

[0064] Table 5 Ionic conductivity (10-4S / cm) of POSS-PMMA based gel electrolytes of 60% ILs with different lithium salt content -4 S / cm)

[0065]

Claims

1. A gel polymer electrolyte, characterized by, The raw materials of the gel polymer electrolyte are composed of POSS-PMMA star-shaped polymer, ionic liquid and lithium salt, wherein the amount ratio of each raw material is as follows: POSS-PMMA star-shaped polymer 30-90 parts by weight, ionic liquid 10-70 parts by weight, and lithium salt 10-35 parts by weight; and the total amount of each raw material is 100 parts by weight. The POSS-PMMA star-shaped polymer is prepared by the following method: 1) Methyl methacrylate, octachloropropyl oligomeric silsesquioxane, catalyst, co-catalyst and solvent 1 are placed in an oxygen-free reaction vessel, and after at least three cycles of freezing-vacuumizing-thawing, they are reacted at 85-115℃ for 12-48h; wherein the molar ratio of methyl methacrylate, octachloropropyl oligomeric silsesquioxane, catalyst and co-catalyst is 1200-2000:1:6-10:10-30; and the solvent 1 is anhydrous toluene, xylene or dichloromethane; 2) The reaction product obtained in step 1) is dissolved with solvent 2, then passed through a column, and then the catalyst is removed, and finally the white product POSS-PMMA star-shaped polymer is obtained by precipitation and filtration; and the solvent 2 is at least one of tetrahydrofuran, N,N-dimethylformamide or dichloromethane; 3) The product obtained in step (2) is volatilized to remove the solvent, and then dried to obtain the purified POSS-PMMA star-shaped polymer.

2. The gel polymer electrolyte according to claim 1, characterized in that, The ionic liquid is selected from 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide or 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide.

3. The gel polymer electrolyte according to claim 1 or 2, characterized in that, The lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate or lithium bis(difluorosulfonyl)imide.

4. The gel polymer electrolyte of claim 1, wherein In step 1), the catalyst is cuprous chloride CuCl, Cu / CuCl2 or CuCl / CuCl2; and / or: In step 1), the co-catalyst is pentamethyldiethylenetriamine or bipyridine.

5. The gel polymer electrolyte of claim 1, wherein In step 2), the amount of solvent 2 is 8-15 times the amount of solvent 1.

6. The gel polymer electrolyte of claim 1, wherein In step 2), anhydrous methanol, anhydrous ethanol or deionized water is used for precipitation.

7. The method for producing a gel polymer electrolyte according to any one of claims 1 to 6, characterized by, The preparation method is as follows: mixing, reacting POSS-PMMA star-shaped polymer, ionic liquid, lithium salt and solvent, thereby obtaining the gel polymer electrolyte.

8. The method for preparing a gel polymer electrolyte according to claim 7, characterized by, The preparation method is as follows: first, stirring POSS-PMMA star-shaped polymer, ionic liquid, lithium salt and solvent at room temperature for 12-24h; then, removing the solvent and drying, thereby obtaining the gel polymer electrolyte.

9. Use of the gel polymer electrolyte in a lithium ion battery or a flexible supercapacitor, wherein the gel polymer electrolyte is the gel polymer electrolyte according to any one of claims 1-6; or is the gel polymer electrolyte prepared by the method of claim 7 or 8.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the gel polymer electrolyte according to any one of claims 1-6.

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