Environment-friendly polymer electrolyte membrane as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of electrolyte materials, and discloses an environment-friendly polymer electrolyte membrane as well as a preparation method and application thereof. The substrate material of the electrolyte membrane mainly takes a degradable bio-based polymer as a main material, an ionic conductive material is added, a nanofiber-based membrane is obtained through electrostatic spinning, and then the wettability of the membrane is improved through surface coating treatment. According to the invention, environment-friendly materials are adopted, and good mechanical properties, ionic conductivity and chemical stability are achieved. By improving the preparation process of the electrolyte membrane, the use of harmful solvents is reduced, and the recoverability of the material is improved. The electrolyte membrane is suitable for high-performance energy storage devices such as a lithium ion battery and a solid-state battery, can effectively improve the performance of the battery and reduce environmental pollution, and has relatively high green and environment-friendly characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolyte materials, and in particular to an environmentally friendly polymer electrolyte membrane and a preparation method and application thereof. Background Art

[0002] With the increasing attention paid to environmental protection around the world, the preparation process of traditional electrolyte membrane materials mostly uses toxic solvents and synthetic polymers that are not easy to recycle, which not only has a negative impact on the environment, but also limits the sustainable development of battery technology. Therefore, the development of environmentally friendly electrolyte membranes and their green preparation processes has become an important research direction in the field of battery materials. In the existing technology, the mechanical properties, ionic conductivity and long-term stability of environmentally friendly electrolyte membranes are often not comparable to those of traditional materials, which limits the widespread application of environmentally friendly electrolyte membranes and urgently needs to be improved on the basis of green environmentally friendly materials. Summary of the invention

[0003] The purpose of the present invention is to provide an environmentally friendly polymer electrolyte membrane and a preparation method and application thereof, so as to solve the problems of poor mechanical properties, ionic conductivity and long-term stability of existing environmentally friendly electrolyte membranes.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0006] A degradable bio-based polymer, a reinforced polymer and an environmentally friendly solvent are mixed to obtain a polymer solution; an ion conductive material is added to the polymer solution to obtain a spinning solution; the spinning solution is subjected to electrostatic spinning to obtain a nanofiber base membrane; a surface treatment solution is coated on the surface of the nanofiber base membrane, and after vacuum drying, an environmentally friendly polymer electrolyte membrane is obtained.

[0007] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the degradable bio-based polymer is polylactic acid and / or polyhydroxyalkanoate; and the reinforced polymer is polyvinyl alcohol and / or polyurethane.

[0008] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the mass ratio of the degradable bio-based polymer to the enhanced polymer is 6-9:1-4.

[0009] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the environmentally friendly solvent is water and / or ethanol.

[0010] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the ion conductive material is a lithium salt and / or an ionic liquid; the mass of the ion conductive material is 10 to 30% of the mass of the polymer solution.

[0011] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the conditions for the electrospinning are: voltage of 10 to 20 kV; working distance of 12 to 20 cm; injection rate of 0.3 to 1 mL / h.

[0012] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the solute of the surface treatment solution is polyurethane and / or polyvinyl alcohol; the solvent of the surface treatment solution is water and / or ethanol.

[0013] Preferably, in the above-mentioned method for preparing an environmentally friendly polymer electrolyte membrane, the coating amount is 0.5-1 mg / cm 2 .

[0014] The invention also provides an environmentally friendly polymer electrolyte membrane prepared by a method for preparing the environmentally friendly polymer electrolyte membrane.

[0015] The invention also provides an application of an environmentally friendly polymer electrolyte membrane in a battery.

[0016] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0017] The electrolyte membrane substrate material of the present invention is mainly composed of degradable bio-based polymers, and ion conductive materials are added. The nanofiber base membrane is obtained by electrostatic spinning, and then the surface is coated to improve the wettability of the membrane. The present invention not only uses environmentally friendly materials, but also has good mechanical properties, ionic conductivity and chemical stability. The present invention reduces the use of harmful solvents and improves the recyclability of materials by improving the electrolyte membrane preparation process. The electrolyte membrane is suitable for high-performance energy storage devices such as lithium-ion batteries and solid-state batteries. It can effectively improve battery performance while reducing environmental pollution and has strong green environmental protection characteristics. DETAILED DESCRIPTION

[0018] The present invention provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0019] A degradable bio-based polymer, a reinforced polymer and an environmentally friendly solvent are mixed to obtain a polymer solution; an ion conductive material is added to the polymer solution to obtain a spinning solution; the spinning solution is subjected to electrostatic spinning to obtain a nanofiber base membrane; a surface treatment solution is coated on the surface of the nanofiber base membrane, and after vacuum drying, an environmentally friendly polymer electrolyte membrane is obtained.

[0020] In the present invention, the degradable bio-based polymer is preferably polylactic acid (PLA) and / or polyhydroxyalkanoate (PHA), more preferably polylactic acid or polyhydroxyalkanoate, and more preferably polylactic acid.

[0021] In the present invention, the reinforcing polymer is preferably polyvinyl alcohol (PVA) and / or polyurethane (PU), more preferably polyvinyl alcohol or polyurethane, and more preferably polyvinyl alcohol.

[0022] In the present invention, the molecular weight of the polylactic acid is preferably 50,000 to 200,000 g / mol, more preferably 80,000 to 120,000 g / mol, and more preferably 90,000 to 110,000 g / mol.

[0023] In the present invention, the molecular weight of the polyhydroxyalkanoate is preferably 20,000 to 300,000 g / mol, more preferably 40,000 to 200,000 g / mol, and more preferably 50,000 to 100,000 g / mol.

[0024] In the present invention, the molecular weight of the polyvinyl alcohol is preferably 10,000 to 200,000 g / mol, more preferably 80,000 to 150,000 g / mol, and more preferably 100,000 to 120,000 g / mol.

[0025] In the present invention, the molecular weight of the polyurethane is preferably 50,000 to 150,000 g / mol, more preferably 70,000 to 120,000 g / mol, and more preferably 80,000 to 100,000 g / mol.

[0026] In the present invention, the mass ratio of the degradable bio-based polymer to the reinforced polymer is preferably 6-9:1-4, more preferably 7-9:2-3, and even more preferably 8:2.

[0027] In the present invention, the total mass fraction of the degradable bio-based polymer and the enhanced polymer in the polymer solution is preferably 10-20%, more preferably 12-18%, and more preferably 15%.

[0028] In the present invention, the environmentally friendly solvent is preferably water and / or ethanol, more preferably water or ethanol, and more preferably water.

[0029] In the present invention, the ion conductive material is preferably a lithium salt and / or an ionic liquid, more preferably a lithium salt or an ionic liquid, and more preferably a lithium salt.

[0030] In the present invention, the mass of the ion conductive material is preferably 10 to 30% of the mass of the polymer solution, more preferably 12 to 20%, and even more preferably 15%.

[0031] In the present invention, the lithium salt is preferably LiPF6 or LiTFSI, and more preferably LiPF6.

[0032] In the present invention, the ionic liquid is preferably one or more of an alkyl imidazole ionic liquid, an alkyl pyridine ionic liquid, a phosphate ionic liquid, an ionic liquid whose anion is thiocyanate, an ionic liquid based on a quaternary ammonium salt, a boron fluoride-based ionic liquid, and a fluoride sulfide-based ionic liquid, and is further preferably one or more of an alkyl imidazole ionic liquid, an alkyl pyridine ionic liquid, and a phosphate ionic liquid, and is more preferably an alkyl imidazole ionic liquid; the alkyl imidazole ionic liquid is preferably one or more of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]), and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]); the alkyl pyridine ionic liquid is preferably 1-butylpyridinium tetrafluoroborate ([BPY][BF4]) or 1-ethylpyridinium hexafluorophosphate ([EPY][PF6]); the phosphate ester ionic liquid is preferably trimethyl (trifluoromethylsulfonyl) phosphate (TMP[TFSI]) or triethylphosphonic acid hexafluorophosphate (TEP[PF6]); the ionic liquid whose anion is thiocyanate is preferably 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]) or 1-butylpyridinium thiocyanate ([BPY][SCN]); the quaternary ammonium salt-based ionic liquid is preferably tetrabutylammonium hexafluorophosphate ([TBA][PF6]) or tetraethylammonium tetrafluoroborate ([TEA][BF4]); the boron fluoride-based ionic liquid is preferably 1-ethyl-3-methylimidazolium fluoroborate ([EMIM][F3B]); the sulfide fluoride-based ionic liquid is preferably 1-butyl-3-methylimidazolium sulfide fluoride salt ([BMIM][SF5]). The ionic liquid used in the present invention has a wide electrochemical stability window (≥4.5V), can withstand high temperatures (>120°C), has a low viscosity (<100cP), can reduce the ion migration resistance of the electrolyte membrane, and has good compatibility with polymer (PLA, PVA, etc.) solutions, and can be dispersed and evenly distributed in the polymer solution.

[0033] In the present invention, the conditions for electrospinning are: the voltage is preferably 10-20 kV, more preferably 14-17 kV, and more preferably 15 kV; the working distance is preferably 12-20 cm, more preferably 14-17 cm, and more preferably 15 cm; the injection rate is preferably 0.3-1 mL / h, more preferably 0.4-0.7 mL / h, and more preferably 0.6 mL / h.

[0034] In the present invention, the porosity of the nanofiber-based membrane is preferably 40-50%, more preferably 42-48%, and more preferably 45%; the pore size is preferably 200-300 nm; the thickness is preferably 20-50 μm, more preferably 30-40 μm, and more preferably 30 μm.

[0035] In the present invention, after the electrospinning is completed, the nanofiber base membrane is further immersed in water or ethanol to remove the residual solvent and excess impurities on the surface.

[0036] In the present invention, the solute of the surface treatment solution is preferably polyurethane and / or polyvinyl alcohol, more preferably polyurethane or polyvinyl alcohol, more preferably polyurethane; the solvent of the surface treatment solution is preferably water and / or ethanol, more preferably water or ethanol, more preferably water.

[0037] In the present invention, the coating amount is preferably 0.5 to 1 mg / cm 2 , more preferably 0.6 to 0.9 mg / cm 2 , more preferably 0.8 mg / cm 2 .

[0038] The invention also provides an environmentally friendly polymer electrolyte membrane prepared by a method for preparing the environmentally friendly polymer electrolyte membrane.

[0039] The invention also provides an application of an environmentally friendly polymer electrolyte membrane in a battery.

[0040] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0043] (1) PLA (molecular weight 90000-110000 g / mol) and PVA (molecular weight 100000-120000 g / mol) were mixed in a mass ratio of 8:2, dissolved in water, and obtained a polymer solution with a concentration of 15 wt%; LiPF6 was added to the polymer solution, LiPF6 accounted for 15 wt% of the total mass of the polymer solution, and ultrasonic treatment was performed for 30 min to ensure uniform dispersion, thereby obtaining a spinning solution;

[0044] (2) electrospinning the spinning solution under the following conditions: voltage of 15 kV, working distance of 15 cm, injection rate of 0.6 mL / h, to obtain a nanofiber base membrane; the nanofiber base membrane has a thickness of 30 μm, a porosity of 45%, and a pore size distribution between 200 and 300 nm;

[0045] (3) Soaking the nanofiber base membrane in water to remove residual solvent and excess impurities on the surface, and then drying; using a 10 wt % polyurethane ethanol solution to coat the surface of the nanofiber base membrane, so that the coating amount of polyurethane is 0.8 mg / cm 2 , and then dried at 60 °C in vacuum to constant weight to obtain an environmentally friendly polymer electrolyte membrane.

[0046] The ionic conductivity of the electrolyte membrane at room temperature was found to be 1.5×10 -3 S / cm, at 50℃, the ionic conductivity increased to 2.2×10 -3 S / cm, suitable for use under different temperature conditions. The tensile test results show that the tensile strength of the electrolyte membrane is 40MPa, the elongation at break is 25%, and it has good mechanical strength and is suitable for long-term use. The lithium-ion battery prepared using the electrolyte membrane has an initial capacity of 150mAh / g. After 100 cycles, the capacity retention rate is 95%, proving that its application in the battery has good cycle stability.

[0047] Example 2

[0048] This embodiment provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0049] (1) PHA (molecular weight 50000-100000 g / mol) and PVA (molecular weight 100000-120000 g / mol) were mixed in a mass ratio of 7:3, dissolved in a mixed solution of water and ethanol in a volume ratio of 3:1, and obtained a polymer solution with a concentration of 12 wt%; LiTFSI was added to the polymer solution, LiTFSI accounted for 20 wt% of the total mass of the polymer solution, and ultrasonic treatment was performed for 40 min to ensure uniform dispersion, thereby obtaining a spinning solution;

[0050] (2) electrospinning the spinning solution under the following conditions: voltage of 14 kV, working distance of 14 cm, injection rate of 0.5 mL / h, to obtain a nanofiber base membrane; the nanofiber base membrane has a thickness of 32 μm, a porosity of 42%, and a pore size distribution between 200 and 300 nm;

[0051] (3) Soaking the nanofiber base membrane in water to remove the residual solvent and excess impurities on the surface, and then drying; using a 15wt% polyurethane ethanol solution to coat the surface of the nanofiber base membrane, so that the coating amount of polyurethane is 0.7mg / cm 2 , and then dried at 50 °C in vacuum to constant weight to obtain an environmentally friendly polymer electrolyte membrane.

[0052] The ionic conductivity of the electrolyte membrane at room temperature was found to be 1.6×10 -3 S / cm. The tensile test results show that the tensile strength of the electrolyte membrane is 38MPa and the elongation at break is 22%. It has good mechanical strength and is suitable for long-term use. The lithium-ion battery prepared using the electrolyte membrane has an initial capacity of 155mAh / g. After 100 cycles, the capacity retention rate is 96%, proving that its application in the battery has good cycle stability.

[0053] Example 3

[0054] This embodiment provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0055] (1) PLA (molecular weight 90000-110000 g / mol) and PVA (molecular weight 100000-120000 g / mol) were mixed in a mass ratio of 6:4, dissolved in a mixed solution of water and ethanol in a volume ratio of 1:1, and obtained a polymer solution with a concentration of 20 wt%; LiPF6 was added to the polymer solution, LiPF6 accounted for 25 wt% of the total mass of the polymer solution, and ultrasonic treatment was performed for 20 min to ensure uniform dispersion, thereby obtaining a spinning solution;

[0056] (2) electrospinning the spinning solution under the following conditions: voltage of 16 kV, working distance of 16 cm, injection rate of 0.7 mL / h, to obtain a nanofiber base membrane; the nanofiber base membrane has a thickness of 35 μm, a porosity of 47%, and a pore size distribution between 200 and 300 nm;

[0057] (3) Soaking the nanofiber base film in water to remove the residual solvent and excess impurities on the surface, and then drying; coating the surface of the nanofiber base film with a 12 wt % polyvinyl alcohol ethanol solution to make the coating amount of polyvinyl alcohol 0.9 mg / cm 2, and then dried at 70 °C in vacuum to constant weight to obtain an environmentally friendly polymer electrolyte membrane.

[0058] The ionic conductivity of the electrolyte membrane at room temperature was found to be 1.8×10 -3 S / cm. The tensile test results show that the tensile strength of the electrolyte membrane is 45MPa and the elongation at break is 28%. It has good mechanical strength and is suitable for long-term use. The lithium-ion battery prepared using the electrolyte membrane has an initial capacity of 148mAh / g. After 100 cycles, the capacity retention rate is 94%, proving that its application in the battery has good cycle stability.

[0059] Example 4

[0060] This embodiment provides a method for preparing an environmentally friendly polymer electrolyte membrane, comprising the following steps:

[0061] (1) PHA (molecular weight 50000-100000 g / mol) and PVA (molecular weight 100000-120000 g / mol) were mixed in a mass ratio of 9:1 and dissolved in water to obtain a polymer solution with a concentration of 10 wt%; LiPF6 and ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]) were added to the polymer solution in a mass ratio of 2:1, and the total mass of LiPF6 and the ionic liquid accounted for 30 wt% of the total mass of the polymer solution; ultrasonic treatment was performed for 30 min to ensure uniform dispersion to obtain a spinning solution;

[0062] (2) electrospinning the spinning solution under the following conditions: voltage of 17 kV, working distance of 15 cm, injection rate of 0.6 mL / h, to obtain a nanofiber base membrane; the nanofiber base membrane has a thickness of 35 μm, a porosity of 48%, and a pore size distribution between 200 and 300 nm;

[0063] (3) Soaking the nanofiber base membrane in water to remove the residual solvent and excess impurities on the surface, and then drying; using a 15wt% polyurethane ethanol solution to coat the surface of the nanofiber base membrane, so that the coating amount of polyurethane is 1mg / cm 2 , and then dried at 60 °C in vacuum to constant weight to obtain an environmentally friendly polymer electrolyte membrane.

[0064] The ionic conductivity of the electrolyte membrane at room temperature was found to be 2×10 -3S / cm. The tensile test results show that the tensile strength of the electrolyte membrane is 50MPa and the elongation at break is 30%. It has good mechanical strength and is suitable for long-term use. The lithium-ion battery prepared using the electrolyte membrane has an initial capacity of 160mAh / g. After 100 cycles, the capacity retention rate is 97%, proving that its application in the battery has good cycle stability.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing an environmentally friendly polymer electrolyte membrane, characterized in that: The following steps are involved: A degradable bio-based polymer, a reinforced polymer and an environmentally friendly solvent are mixed to obtain a polymer solution; an ion conductive material is added to the polymer solution to obtain a spinning solution; the spinning solution is subjected to electrostatic spinning to obtain a nanofiber-based membrane; a surface treatment solution is coated on the surface of the nanofiber-based membrane, and after vacuum drying, an environmentally friendly polymer electrolyte membrane is obtained.

2. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 1, characterized in that: The degradable bio-based polymer is polylactic acid and / or polyhydroxyalkanoate; the reinforced polymer is polyvinyl alcohol and / or polyurethane.

3. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 2, characterized in that: The mass ratio of the degradable bio-based polymer to the enhanced polymer is 6-9:1-4.

4. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 3, characterized in that: The environmentally friendly solvent is water and / or ethanol.

5. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 1 or 3, characterized in that: The ion conductive material is lithium salt and / or ionic liquid; the mass of the ion conductive material is 10-30% of the mass of the polymer solution.

6. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 5, characterized in that: The conditions for the electrospinning are: a voltage of 10 to 20 kV; a working distance of 12 to 20 cm; and an injection rate of 0.3 to 1 mL / h.

7. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 6, characterized in that: The solute of the surface treatment solution is polyurethane and / or polyvinyl alcohol; the solvent of the surface treatment solution is water and / or ethanol.

8. The method for preparing an environmentally friendly polymer electrolyte membrane according to claim 7, characterized in that: The coating amount is 0.5-1 mg / cm 2 .

9. An environmentally friendly polymer electrolyte membrane prepared by the method for preparing an environmentally friendly polymer electrolyte membrane according to any one of claims 1 to 8.

10. Use of the environmentally friendly polymer electrolyte membrane according to claim 9 in batteries.