Polyurethane with self-repairing capability, solid electrolyte, composite electrode and preparation method

Abstract

The invention belongs to the field of electrochemical energy, and relates to polyurethane with self-repairing capability, a solid electrolyte, a composite electrode and a preparation method, a soft segment part of the self-repairing polyurethane-based solid electrolyte has good segment motion capability, and compared with polyethylene glycol, the crystallinity is greatly reduced; and the ionic conductivity and the lithium ion transference number are greatly improved. The dynamic disulfide bond and the hydrogen bond of the hard segment part jointly form a dynamic reversible macromolecular network, so that the mechanical strength is considered, and the tensile property, the self-healing property and the repeatable processing property are good. The self-repairing polyurethane-based solid electrolyte has relatively high ionic conductivity and lithium ion transference number, and can be cured on an electrode in situ to eliminate the interface contact problem of the electrolyte and the electrode, and the positive electrode and the negative electrode of the battery are healed into a whole through the self-healing capability of polyurethane, so that the performance of the battery is greatly improved, and the service life of the battery is prolonged. And the material has a good application prospect in all-solid-state lithium batteries.

Description

Technical Field

[0001] The invention belongs to the field of electrochemical energy, and specifically relates to polyurethane with self-repairing ability, a solid electrolyte, a composite electrode and a preparation method. Background Art

[0002] Lithium metal secondary batteries, which are assembled with lithium metal negative electrodes, liquid electrolytes, and high-capacity positive electrodes, have become a new type of electrochemical energy storage device that has attracted much attention due to its high theoretical energy density. However, liquid lithium metal batteries have problems such as the electrolyte being flammable and easy to leak, the electrolyte being easily generated to corrode the electrodes when in contact with water, and the high amount of electrolyte used resulting in low actual energy density of the battery, which limits the practical application of liquid lithium metal batteries.

[0003] The use of solid electrolytes is an effective way to solve the above problems of liquid lithium metal batteries. Compared with inorganic solid electrolytes (such as oxide and sulfide solid electrolytes), although inorganic solid electrolytes have higher ionic conductivity and thermal stability, their severe mechanical brittleness and large electrode-electrolyte interface resistance limit their application. Solid polymer electrolytes, on the other hand, exhibit excellent mechanical flexibility and electrochemical stability. As a representative solid polymer electrolyte, polyethylene oxide-based electrolytes have been widely studied due to their excellent lithium salt solvation ability. However, their low lithium ion conductivity, poor mechanical strength and unsatisfactory electrochemical stability caused by their high crystallinity limit their further application. In addition, the interface between the electrolyte and the electrode in the solid-state battery cannot achieve the effect of the liquid electrolyte wetting the electrode in the liquid battery, so that the ion transfer rate between the electrolyte and the electrode is very fast. On the contrary, the solid electrolyte and the electrode are in rigid contact, with an interface transfer impedance much higher than that of the liquid battery, which greatly reduces the charge transfer rate at the electrode-electrolyte interface, making the real ionic conductivity of the solid electrolyte unable to be fully utilized. In-situ polymerization is an effective method to solve the interface problem of solid polymer electrolytes. However, in situ polymerization is limited to a few monomer types, the degree of polymerization is difficult to control, and the final product is often in the form of a gel or semi-solid. Summary of the invention

[0004] In order to solve the above problems, the present invention provides a polyurethane, solid electrolyte, composite electrode and preparation method with self-repairing ability. The soft phase polyether skeleton in the polyurethane-based solid polymer electrolyte can conduct lithium ions, and the combination of hydrogen bonds and disulfide bonds in the hard phase part helps to improve the self-healing ability and mechanical multifunctionality. While having high ionic conductivity and lithium ion migration number, a preparation method of the composite electrode is provided by means of the self-healing ability of polyurethane: the polyurethane solid electrolyte is in-situ cured on the electrode to eliminate the interface contact problem between the electrolyte and the electrode, and the positive and negative electrodes of the battery are healed into a whole through the self-healing ability of the polyurethane, thereby greatly improving the battery performance. The present invention can be used for lithium batteries, lithium-sulfur batteries, etc.

[0005] The present invention specifically provides a polyurethane with self-healing ability, and the structural general formula of the polyurethane is as follows:

[0006]

[0007] Among them, the value of the degree of polymerization n is 40 - 200, and the value of the molar coefficient m is 0.3 - 0.7;

[0008] The stress of the polyurethane elastomer can reach 17 - 30 Mpa, the strain can reach 1294 - 2080%, the thermal decomposition temperature can reach above 230 °C, and it has an amorphous structure at room temperature.

[0009] The present invention also provides a preparation method of a polyurethane with self-healing ability, which is carried out according to the following steps:

[0010] (1) Dissolve isophorone diisocyanate and polyethylene glycol in a solvent, add a catalyst and react to synthesize a prepolymer solution;

[0011] (2) Add bis(2-hydroxyethyl) disulfide and 2-urea-4-pyrimidinone to the prepolymer solution to obtain a mixed solution, and after reaction, pour it into a polytetrafluoroethylene plate and dry it to obtain a colorless and transparent polyurethane elastomer, that is, a polyurethane with self-healing ability.

[0012] As a preferred scheme, step (1) specifically includes: heat polyethylene glycol to remove moisture, then cool it to 60 - 70 °C, then add isophorone diisocyanate and a solvent thereto, and then add a catalyst and stir and react at 65 - 80 °C for 1.5 - 3 h to obtain a prepolymer solution.

[0013] As a preferred scheme, the average molecular weight of the polyethylene glycol is 1700 - 9000; the molar ratio of isophorone diisocyanate to polyethylene glycol is 2 - 3:1; the ratio of the addition amount of polyethylene glycol to the solvent is 1 g:5 ml; the solvent is selected from at least one of N-N dimethylformamide, tetrahydrofuran, N-N dimethylacetamide or dimethyl sulfoxide; the catalyst is dibutyltin dilaurate; the ratio of the addition amount of the catalyst to isophorone diisocyanate is 10 - 20 μL:1 - 2 mmol.

[0014] As a preferred scheme, the molar ratio of bis(2-hydroxyethyl) disulfide to 2-urea-4-pyrimidinone in step (2) is 3 - 7:7 - 3.

[0015] As a preferred scheme, in step (2), the mixed solution is stirred and reacted at 65 - 80 °C for 8 - 24 h.

[0016] The present invention also provides a polyurethane-based solid electrolyte with self-healing ability, which is characterized in that it is obtained by mechanically blending the polyurethane with self-healing ability described above and a lithium salt. The ionic conductivity of this polyurethane-based solid electrolyte at room temperature is ≥ 1.22×10 -4 S·cm -1 , the ion transference number is ≥ 0.53, the decomposition voltage is ≥ 4.4 V, and the activation energy is ≤ 0.37 eV.

[0017] The present invention also provides a preparation method of a polyurethane-based solid electrolyte with self-healing ability, which is carried out according to the following steps: dissolving the lithium salt in tetrahydrofuran to obtain a lithium salt solution, and then dissolving the polyurethane in the lithium salt solution.

[0018] As a preferred solution, the mass ratio of the lithium salt to the polyurethane is 0.3 - 0.6:1; the lithium salt is selected from at least one of lithium trifluoromethanesulfonimide, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium nitrate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide or lithium difluoro(oxalato)borate.

[0019] The present invention also provides a polyurethane-based solid electrolyte composite electrode. The above-mentioned polyurethane-based solid electrolyte is cast on the electrode sheet by the solution casting method and in-situ cured to obtain the polyurethane-based solid electrolyte composite electrode.

[0020] The present invention has the following advantages: Through reasonable ratio design, the soft segment part of the self-healing polyurethane-based solid electrolyte has good segmental movement ability. Compared with polyethylene glycol, the crystallinity is greatly reduced, and the ionic conductivity and lithium ion transference number are greatly improved. At the same time, the dynamic disulfide bonds and hydrogen bonds in the hard segment part jointly form a dynamically reversible macromolecular network, which has good tensile properties, self-healing properties and reprocessability while taking into account the mechanical strength. Through the self-healing ability of this electrolyte, two independent solid electrolyte composite electrodes can self-heal into a whole, greatly reducing the solid-solid interface contact between the electrolyte and the electrode. The self-healing polyurethane-based solid electrolyte in the present invention has good application performance and good application prospects in all-solid-state lithium batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0022] Figure 1X-ray diffraction patterns of the elastomers and PEG in Examples 1-3 and Comparative Example 1.

[0023] Figure 2 Thermogravimetric analysis curve of the elastomer in Example 2.

[0024] Figure 3 Stress-strain curves of the elastomers in Examples 1-3 and Comparative Example 1.

[0025] Figure 4 Ionic conductivity diagrams of the self-healing solid electrolyte and PEG solid electrolyte in Example 2.

[0026] Figure 5 Lithium ion transference number diagram of the self-healing solid electrolyte in Example 2.

[0027] Figure 6 Linear sweep voltammetry curves of the self-healing solid electrolyte and PEG solid electrolyte in Example 2.

[0028] Figure 7 Cycling performance diagram of the lithium battery assembled with the self-healing solid electrolyte in Example 2.

[0029] Figure 8 Self-healing performance diagram of the self-healing solid electrolyte in Example 2. Detailed implementation manners

[0030] The technical solutions of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only for illustrative and explanatory purposes of the present invention, and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0031] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods.

[0032] Example 1:

[0033] (1) Preparation of the prepolymer solution:

[0034] Polyethylene glycol with an average molecular weight of 2000 was added to a dry round-bottom flask, evacuated with a vacuum pump (<133 Pa), and then placed in an oil bath at 110 °C and stirred for 2 h to remove moisture. After cooling, it was transferred to a glove box filled with argon. 2 g (1 mmol) of dried and dehydrated polyethylene glycol was taken in a 50 ml bottle, 10 ml of tetrahydrofuran was added, 644 mg (2.9 mmol) of isophorone diisocyanate and 20 μL of dibutyltin dilaurate catalyst were slowly added, and after stirring evenly, the temperature was raised to 65 °C and stirred for 3 h to obtain the prepolymer solution.

[0035] (2) Preparation of polyurethane elastomer:

[0036] 108 mg (0.7 mmol) of bis(2-hydroxyethyl) disulfide and 50.7 mg (0.3 mmol) of 2-urea-4-pyrimidinone were added to the prepolymer solution, and the mixture was continuously stirred at 65 °C for 24 h to obtain a colorless transparent solution. The solution was poured onto a polytetrafluoroethylene plate and transferred to an oven at 60 °C for 2 h to remove part of the solvent, and then further dried under vacuum for 12 h to completely remove the residual solvent, obtaining a colorless transparent polyurethane elastomer PU-3.

[0037] Example 2:

[0038] (1) Preparation of prepolymer solution:

[0039] Polyethylene glycol with an average molecular weight of 2000 was added to a dry round-bottom flask, evacuated with a vacuum pump (<133 Pa), and then placed in an oil bath at 110 °C and stirred for 2 h to remove moisture. After cooling, it was transferred to a glove box filled with argon. 2 g (1 mmol) of dried and dehydrated polyethylene glycol was taken in a 50 ml bottle, 10 ml of tetrahydrofuran was added, 644 mg (2.9 mmol) of isophorone diisocyanate and 20 μL of dibutyltin dilaurate catalyst were slowly added, and after stirring evenly, the temperature was raised to 65 °C and stirred for 3 h to obtain a prepolymer solution.

[0040] (2) Preparation of polyurethane elastomer:

[0041] 77.1 mg (0.5 mmol) of bis(2-hydroxyethyl) disulfide and 84.5 mg (0.5 mmol) of 2-urea-4-pyrimidinone were added to the prepolymer solution, and the mixture was continuously stirred at 65 °C for 24 h to obtain a colorless transparent solution. The solution was poured onto a polytetrafluoroethylene plate and transferred to an oven at 60 °C for 2 h to remove part of the solvent, and then further dried under vacuum for 12 h to completely remove the residual solvent, obtaining a colorless transparent polyurethane elastomer PU-5.

[0042] (3) Preparation of solid electrolyte composite electrode:

[0043] 50 mg of lithium bis(trifluoromethanesulfonyl)imide was weighed and dissolved in 1 ml of tetrahydrofuran, stirred until the lithium salt was completely dissolved, and then 100 mg of polyurethane elastomer PU-5 was added and stirred for 3 h. 100 μL of the above solution was dropped onto a lithium sheet with a diameter of 14 mm to completely cover the surface of the lithium sheet. It was placed in a muffle furnace and heated at 60 °C for 2 h to cure the solid electrolyte membrane, and then the temperature was raised to 80 °C and heated for 12 h to completely volatilize the tetrahydrofuran, obtaining a transparent, homogeneous and bubble-free solid electrolyte composite electrode.

[0044] Assemble lithium symmetric cells with the electrolyte surfaces of solid electrolyte composite electrodes facing each other pairwise, with a current density of 0.1 mA / cm -2 , the charge and discharge times are 1 h respectively, and the test temperature is 70 °C.

[0045] Example 3:

[0046] (1) Preparation of prepolymer solution:

[0047] Add polyethylene glycol with an average molecular weight of 2000 into a dry round-bottom flask, evacuate it with a vacuum pump (<133 Pa), then place it in an oil bath at 110 °C and stir for 2 h to remove moisture. After cooling, transfer it to a glove box filled with argon. Take 2 g (1 mmol) of dried and dehydrated polyethylene glycol in a 50 ml bottle, add 10 ml of tetrahydrofuran, slowly add 644 mg (2.9 mmol) of isophorone diisocyanate and 20 μL of dibutyltin dilaurate catalyst, stir evenly, then raise the temperature to 65 °C and stir for 3 h to obtain a prepolymer solution.

[0048] (2) Preparation of polyurethane elastomer:

[0049] Add 46.2 mg (0.3 mmol) of bis(2-hydroxyethyl) disulfide and 118.3 mg (0.7 mmol) of 2-urea-4-pyrimidinone into the prepolymer solution, continue to stir at 65 °C for 24 h to obtain a colorless transparent solution. Pour this solution onto a polytetrafluoroethylene plate, transfer it to an oven at 60 °C and dry for 2 h to remove part of the solvent, and then further dry it under vacuum for 12 h to completely remove the residual solvent to obtain a colorless transparent polyurethane elastomer PU-7.

[0050] Comparative Example 1:

[0051] (1) Preparation of prepolymer solution:

[0052] Add polyethylene glycol with an average molecular weight of 2000 into a dry round-bottom flask, evacuate it with a vacuum pump (<133 Pa), then place it in an oil bath at 110 °C and stir for 2 h to remove moisture. After cooling, transfer it to a glove box filled with argon. Take 2 g (1 mmol) of dried and dehydrated polyethylene glycol in a 50 ml bottle, add 10 ml of tetrahydrofuran, slowly add 644 mg (2.9 mmol) of isophorone diisocyanate and 20 μL of dibutyltin dilaurate catalyst, stir evenly, then raise the temperature to 65 °C and stir for 3 h to obtain a prepolymer solution.

[0053] (2) Preparation of polyurethane elastomer:

[0054] 154.2 mg (1 mmol) of bis(2-hydroxyethyl) disulfide was added to the prepolymer solution, and the mixture was continuously stirred at 65 °C for 24 h to obtain a colorless transparent solution. The solution was poured onto a polytetrafluoroethylene plate and transferred to an oven at 60 °C for drying for 2 h to remove part of the solvent, and then further dried under vacuum for 12 h to completely remove the remaining solvent to obtain a colorless transparent polyurethane elastomer PU-0.

[0055] As Figure 1 shown, all the examples and comparative examples showed an amorphous structure, while obvious crystallization peaks appeared in the original PEG.

[0056] As Figure 2 shown, the thermal decomposition temperature of PU-5 was as high as 230 °C.

[0057] As Figure 3 shown, the maximum stress of Example 1 was 17 Mpa, and the maximum strain was 2080%; the maximum stress of Example 2 was 23 Mpa, and the maximum strain was 1729%; the maximum stress of Example 3 was 30 Mpa, and the maximum strain was 1294%. The mechanical properties and tensile properties of the elastomers prepared in Examples 1-3 were much higher than those of polyethylene glycol.

[0058] As Figure 4 shown, the ionic conductivity of the polyurethane-based all-solid polymer electrolyte at 30 °C was 1.2×10 -4 S·cm -1 , which was much higher than the ionic conductivity of polyethylene glycol.

[0059] As Figure 5 shown, the lithium ion transference number of the polyurethane-based all-solid polymer electrolyte was 0.53.

[0060] As Figure 6 shown, the electrochemical window of the polyurethane-based solid electrolyte was 4.4 V, which was higher than 3.8 V of the polyethylene glycol solid electrolyte.

[0061] As Figure 7 shown, at a current density of 0.1 mA / cm -2 , with the charge and discharge times being 1 h respectively and the test temperature being 70 °C, the lithium symmetric battery assembled with the polyurethane-based all-solid polymer electrolyte in Example 2 stably cycled for more than 300 h with an overpotential of ~48 mV.

[0062] As Figure 8 shown, at room temperature, after 12 minutes, Example 2 could cut the trace back to its original state, indicating that the composite solid electrolyte had good self-healing ability.

Claims

1. A polyurethane with self-healing ability, characterized in that, The general structural formula of the polyurethane is as follows: Among them, the value of the degree of polymerization n is 40 - 200, and the value of the molar coefficient m is 0.3 - 0.7; The stress of the polyurethane-based material can reach 17 - 30 Mpa, the strain can reach 1294 - 2080%, the thermal decomposition temperature can reach above 230 °C, and it has an amorphous structure at room temperature.

2. The preparation method of the polyurethane with self-healing ability according to claim 1, characterized in that, It is carried out according to the following steps: (1) Dissolve isophorone diisocyanate and polyethylene glycol in a solvent, add a catalyst and react to obtain a prepolymer solution; (2) Add bis(2-hydroxyethyl) disulfide and 2-urea-4-pyrimidinone to the prepolymer solution to obtain a mixed solution. After reaction, pour it into a polytetrafluoroethylene plate and dry it to obtain a colorless and transparent polyurethane elastomer, that is, a polyurethane with self-healing ability.

3. The preparation method of a polyurethane with self-healing ability according to claim 2, characterized in that, Step (1) specifically includes: After heating polyethylene glycol to remove moisture, cool it to 60 - 70 °C, then add isophorone diisocyanate and the solvent thereto, and then add a catalyst and stir and react at 65 - 80 °C for 1.5 - 3 h to obtain a prepolymer solution.

4. The preparation method of a polyurethane with self-healing ability according to claim 3, characterized in that, The average molecular weight of the polyethylene glycol is 1700 - 9000; the molar ratio of isophorone diisocyanate to polyethylene glycol is 2 - 3:1; the ratio of the addition amount of polyethylene glycol to the solvent is 1 g:5 ml; the solvent is selected from at least one of N-N dimethylformamide, tetrahydrofuran, N-N dimethylacetamide or dimethyl sulfoxide; the catalyst is dibutyltin dilaurate; the ratio of the addition amount of the catalyst to isophorone diisocyanate is 10 - 20 μL:1 - 2 mmol.

5. The preparation method of a polyurethane with self-healing ability according to claim 2, characterized in that, In step (2), the molar ratio of bis(2-hydroxyethyl) disulfide to 2-urea-4-pyrimidinone is 3 - 7:7 - 3.

6. The preparation method of a polyurethane with self-healing ability according to claim 2, characterized in that, In step (2), stir and react the mixed solution at 65 - 80 °C for 8 - 24 h.

7. A polyurethane-based solid electrolyte with self-healing ability, characterized in that: Obtained by mechanically blending the polyurethane described in claim 1 with a lithium salt, the polyurethane-based solid electrolyte has an ionic conductivity ≥ 1.22×10 -4 S·cm -1 , an ion transference number ≥ 0.53, a decomposition voltage ≥ 4.4 V, and an activation energy ≤ 0.37 eV.

8. A method for preparing the polyurethane-based solid electrolyte with self-healing ability according to claim 7, characterized in that, It is carried out according to the following steps: Dissolve the lithium salt in tetrahydrofuran to obtain a lithium salt solution, and then dissolve the polyurethane in the lithium salt solution.

9. The preparation method of a polyurethane-based solid electrolyte with self-healing ability according to claim 8, characterized in that, The mass ratio of the lithium salt to the polyurethane is 0.3 - 0.6:1; the lithium salt is selected from at least one of lithium trifluoromethanesulfonate, lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium nitrate, lithium difluorophosphate, lithium bis(oxalato)borate, lithium hexafluoroarsenate, lithium bis(trifluoromethanesulfonyl)imide or lithium difluoro(oxalato)borate.

10. A polyurethane-based solid electrolyte composite electrode with self-healing ability, characterized in that, Cast the polyurethane-based solid electrolyte described in claim 7 on the electrode sheet by solution casting method and in-situ cure to obtain a polyurethane-based solid electrolyte composite electrode.

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