PEO-based solid electrolyte membrane as well as preparation method and application thereof

Abstract

The invention discloses a PEO-based solid electrolyte membrane and a preparation method thereof, and the preparation method comprises the following steps: (1) dissolving PEO in a polar aprotic solvent, and carrying out vortex stirring to obtain a uniform solution; (2) in a glove box in which the water content and the oxygen content are both less than 0.1 ppm, sequentially adding the cross-linking agent, the dilithium salt and the photoinitiator into the PEO solution, and carrying out vortex stirring until the mixture is completely dissolved to obtain a polymer mixed solution; and (3) coating the mixed solution in a polytetrafluoroethylene template, heating to remove the solvent, and performing ultraviolet radiation to obtain the solid electrolyte membrane. Compared with the prior art, the method has the advantages that simple preparation of the high-interface-stability solid electrolyte is realized through a plasticizer-free system, and the method is suitable for large-scale production of high-energy-density solid lithium batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer electrolytes, and specifically refers to a PEO-based solid electrolyte membrane, its preparation method and application. Background Art

[0002] With the increasing demand for high-energy density and high-safety energy storage, solid-state lithium metal batteries have become the core development direction in the new energy field. Polyethylene oxide (PEO)-based polymer electrolytes are regarded as one of the important candidate materials for solid-state battery electrolytes due to their excellent flexibility, good interfacial compatibility with lithium metal anodes, and simple processing technology.

[0003] However, PEO-based solid electrolytes have been troubled by problems such as low ionic conductivity and poor electrolyte / electrode interfacial compatibility, and it is difficult to meet the requirements of high-energy density batteries.

[0004] Existing modification technologies generally face the problem of performance balance: (1) Although adding inorganic fillers can improve mechanical strength, the interfacial impedance is high, resulting in rapid decay of cycle capacity; (2) Adding plasticizers (such as TEGDME, PEG, etc.) is prone to oxidative decomposition under high voltage, causing the SEI film to rupture, and traditional photocurable monomers (such as acrylate esters) have insufficient hydrophobicity and cannot inhibit lithium salt hydrolysis induced by moisture; (3) Existing interfacial stabilizers (such as LiAlO2 coatings) have complex processes and high costs, making it difficult to apply on a large scale.

[0005] Patent publication number CN119133589A uses a molecular coordination regulator DFBOP and a filler LLZTO to improve the lithium stability and poor high-voltage compatibility of PEO-based solid electrolytes, but there are still problems such as easy agglomeration of inorganic fillers and the need for precise matching of the molecular regulator with the dissociation ability of lithium salts.

[0006] Therefore, at present, through modification strategies such as filler design and development, polymer structure design, and introduction of plasticizers, the problem of positive and negative electrode interfacial compatibility cannot be solved well.

[0007] Therefore, there is an urgent need to develop a PEO-based electrolyte system with effective PEO-based interface regulation and a simple preparation process to promote the practical breakthrough of solid-state battery technology. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the above technical defects and provide a preparation method for a solid electrolyte membrane based on urethane dimethacrylate (UDMA).

[0009] To solve the above technical problem, the present invention first provides a PEO-based solid electrolyte membrane and its preparation method, including the following steps:

[0010] (1) Dissolve PEO in a polar aprotic solvent and vortex stir to obtain a homogeneous solution;

[0011] (2) In a glove box with water and oxygen content both less than 0.1 ppm, sequentially add the crosslinking agent, dilithium salt, and photoinitiator into the above PEO solution, and vortex stir until completely dissolved to obtain a polymer mixed solution.

[0012] (3) Coat the above mixed solution on a polytetrafluoroethylene template, remove the solvent by heating, and then irradiate with ultraviolet light to obtain a solid electrolyte membrane.

[0013] According to an embodiment of the present invention, the PEO and acetonitrile in step (1) need to be pre-dried. The molecular weight of PEO is 60 - 100w, and the polar aprotic solvent is acetonitrile.

[0014] According to an embodiment of the present invention, the lithium salt in step (2) is a mixture of LiTFSI and LiDFOB, where the molar ratio of LiTFSI to LiDFOB is 7:3, and the total lithium salt concentration is 15% of the molar concentration of EO units (i.e., EO:Li = 15:1), and it is dried before use.

[0015] According to an embodiment of the present invention, the photocrosslinking agent in step (2) is UDMA.

[0016] According to an embodiment of the present invention, the photoinitiator in step (2) is any one of benzophenone, 4-methylbenzophenone, and 2,2-dimethoxy-2-phenylacetophenone (DMPA).

[0017] According to an embodiment of the present invention, the mass ratio of PEO: the lithium salt: the crosslinking agent: the photoinitiator in step (2) is (0.3 - 0.5):(0.11 - 0.18):(0.15 - 0.25):(0.05 - 0.1).

[0018] According to an embodiment of the present invention, the initiator needs to be pre-powdered for more uniform dispersion.

[0019] According to an embodiment of the present invention, the photocrosslinking process in step (3) is as follows: coat the mixed solution on a polytetrafluoroethylene template at room temperature, then perform degassing treatment and keep it at 50 °C for 2 - 4 h to remove the solvent. While it is hot, irradiate with a 365 nm ultraviolet light source (intensity 1100 mV / cm 2 ) for 5 - 15 min, and then a solid electrolyte membrane is obtained.

[0020] According to an embodiment of the present invention, the solid electrolyte is prepared by the preparation method of any one of claims 1 - 8. The thickness of the solid electrolyte membrane is 50 - 150 μm, and the ionic conductivity reaches 0.1 -

[0021] 0.5×10 -4 S / cm, the lithium ion transference number reaches 0.58.

[0022] According to another aspect of the present invention, the present invention also provides a polymer electrolyte membrane prepared by the above method, and the electrochemical window of the polymer electrolyte membrane is greater than 5V.

[0023] According to another aspect of the present invention, the present invention also provides the application of the above polymer electrolyte membrane in a lithium ion battery.

[0024] UDMA is an acrylate monomer commonly used in dental materials. It not only has chemical corrosion resistance and high crosslinking properties, but also its hydrophobic groups can form a protective layer at the electrode interface. The present invention proposes the following technical solutions: Using UDMA as a crosslinking agent, blending with polyethylene oxide (PEO) and a lithium salt (such as LiTFSI), and then forming a three-dimensional crosslinked network structure through ultraviolet light curing. Specifically: (1) The urethane groups of UDMA can fix anions (such as TFSI-) and promote the dissociation of lithium ions through multiple coordination and hydrogen bonding, thereby improving the ion transference number; (2) The crosslinked structure effectively inhibits the crystallization of PEO chain segments, increases the proportion of amorphous regions, and avoids the use of plasticizers or reactive diluents, which reduces costs and simplifies the preparation process, improving the industrial feasibility; (3) The hydrophobicity of UDMA molecules can reduce the moisture absorption of the electrolyte, improving the chemical stability of the electrolyte, and making it suitable for high-energy density solid-state lithium batteries.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The three-dimensional crosslinked network constructed by the UDMA crosslinking agent destroys the crystalline region of PEO to increase the proportion of amorphous phase, which is beneficial to improving the room temperature ionic conductivity; at the same time, it overcomes the problem of strength loss caused by traditional plasticizers or inorganic fillers.

[0027] (2) Utilizing the synergistic effect of the amide groups of UDMA and the crosslinked structure, the electrolyte membrane has a flexible crosslinked network. The crosslinked network restricts the migration of anions through multiple coordination and hydrogen bonding, promoting the migration of lithium ions. At the same time, its hydrophobic long-chain alkyl groups can inhibit the corrosion of the lithium metal anode by moisture, forming a dense physical barrier and improving the chemical stability of the electrolyte.

[0028] (3) Through the one-step forming of the photocuring crosslinking process, it avoids the phase separation problem easily caused by the traditional blending method and is suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Optical photograph of the solid electrolyte prepared in Example 1.

[0030] Figure 2The lithium ion transference number of the solid electrolyte prepared in Example 2.

[0031] Figure 3 Electrochemical window analysis of the solid electrolyte prepared in Example 3. Detailed implementation manners

[0032] The present invention will be further described in detail below with reference to the accompanying drawings.

[0033] The present invention provides a PEO-based solid electrolyte membrane and a preparation method thereof, including the following steps:

[0034] (1) Dissolve PEO in a polar aprotic solvent, and vortex and stir to obtain a homogeneous solution;

[0035] (2) In a glove box with water and oxygen contents both less than 0.1 ppm, sequentially add the crosslinking agent, dilithium salt, and photoinitiator to the above PEO solution, and vortex and stir until completely dissolved to obtain a polymer mixed solution.

[0036] (3) Coat the above mixed solution on a polytetrafluoroethylene template, heat to remove the solvent, and then irradiate with ultraviolet light to obtain a solid electrolyte membrane.

[0037] In some embodiments, the PEO and acetonitrile in step (1) need to be pre-dried. The molecular weight of PEO is 60 - 100w, and the solvent is acetonitrile.

[0038] It should be noted that after PEO is dissolved in acetonitrile, it needs to be quickly stirred, and the vortex stirring speed is as high as 30,000 revolutions per minute, so as to effectively shorten the stirring time to within half an hour.

[0039] In some embodiments, the photo-crosslinking agent in step (2) is UDMA.

[0040] In some embodiments, the lithium salt in step (2) is a mixture of LiTFSI and LiDFOB, where the molar ratio of LiTFSI to LiDFOB is 7:3, and the total lithium salt concentration is 15% of the molar concentration of EO units (i.e., EO:Li = 15:1), and it is dried before use.

[0041] It should be noted that the role of the dilithium salt is to broaden the electrochemical window and inhibit side reactions at the positive electrode / electrolyte interface.

[0042] In some embodiments, the photoinitiator in step (2) is any one of benzophenone, 4-methylbenzophenone, and 2,2-dimethoxy-2-phenylacetophenone (DMPA).

[0043] In some embodiments, the mass ratio of PEO:lithium salt:crosslinking agent:photoinitiator in step (2) is (0.3 - 0.5):(0.11 - 0.18):(0.15 - 0.25):(0.05 - 0.1).

[0044] It should be noted that the initiator needs to be pre - pulverized.

[0045] In some embodiments, the photo - crosslinking process in step (3) is as follows: coat the mixed solution in a polytetrafluoroethylene template at room temperature, then perform degassing treatment and keep it at 50 °C for 2 - 4 h to remove the solvent. While it is still hot, irradiate it with a 365 nm ultraviolet light source (intensity 1100 mV / cm 2 ) for 5 - 15 min, and then a solid electrolyte membrane is obtained.

[0046] In some embodiments, the solid electrolyte membrane prepared by the preparation method according to any one of claims 1 - 8 has a membrane thickness of 50 - 150 μm, an ionic conductivity as high as 0.8×10 -4 S / cm, and an electrochemical window can be extended to 5 V.

[0047] The following are specific examples:

[0048] Example 1

[0049] A PEO - based solid electrolyte membrane and its preparation method are prepared by the following preparation steps:

[0050] (1) Dissolve 0.3 g of PEO (molecular weight 600,000) in 6 ml of acetonitrile, and stir vigorously for 30 min to obtain a PEO solution;

[0051] (2) In a glove box with water and oxygen content both less than 0.1 ppm, sequentially add 0.15 g of UDMA, 0.12 g of dilithium salt, and 0.06 g of benzophenone to the PEO solution, and stir vigorously until completely dissolved to obtain a mixed solution.

[0052] (3) Coat the above - mentioned mixed solution in a polytetrafluoroethylene template, perform degassing treatment and keep it at 50 °C for 2 h to remove the solvent. While it is still hot, irradiate it with ultraviolet light for 5 min, and then a solid electrolyte membrane is obtained. Its optical photograph is as Figure 1 shown, proving that a flexible solid electrolyte thin film is successfully prepared. The membrane thickness of this membrane is 102 μm.

[0053] Example 2

[0054] (1) Dissolve 0.5 g of PEO (molecular weight 1,000,000) in 6 ml of acetonitrile, and stir at high speed for 30 min to obtain a PEO solution;

[0055] (2) In a glove box with water and oxygen content both less than 0.1 ppm, 0.25 g of UDMA, 0.12 g of dilithium salt, and 0.1 g of benzophenone were successively added to the PEO solution, and the mixture was vigorously stirred until completely dissolved to obtain a mixed solution.

[0056] (3) The above mixed solution was coated on a polytetrafluoroethylene template, degassed, and kept at 50 °C for 2 h to remove the solvent. After hot ultraviolet irradiation for 10 min, a solid electrolyte membrane was obtained. It was proved that a solid electrolyte membrane with high ionic conductivity was successfully prepared. Its membrane thickness was 113 μm, and the room-temperature ionic conductivity was as high as 5.13×10 -5 S / cm.

[0057] Example 3

[0058] (1) 0.3 g of PEO (molecular weight 600,000) was dissolved in 6 ml of acetonitrile and stirred at high speed for 30 min to obtain a PEO solution;

[0059] (2) In a glove box with water and oxygen content both less than 0.1 ppm, 0.2 g of UDMA, 0.16 g of dilithium salt, and 0.06 g of benzophenone were successively added to the PEO solution, and the mixture was vigorously stirred until completely dissolved to obtain a mixed solution.

[0060] (3) The above mixed solution was coated on a polytetrafluoroethylene template, degassed, and kept at 50 °C for 2 h to remove the solvent. After hot ultraviolet irradiation for 15 min, a solid electrolyte membrane was obtained. The analysis of its lithium ion transference number and electrochemical window is as Figure 2 and 3 shown. The thickness of this solid electrolyte membrane was 125 μm, and the lithium ion transference number was greatly improved to 0.58. The oxidation potential reached 5.2 V. In a glove box filled with argon atmosphere (H2O ≤ 0.1 ppm, O2 ≤ 0.1 ppm), a PEO-based solid-state lithium battery was assembled using a CR2025 button battery case. The positive electrode material was a mixture of lithium nickel cobalt manganese oxide, polyvinylidene fluoride (PVDF) binder, and SuperP conductive agent, and the negative electrode material was lithium metal. The encapsulation pressure was 4 MPa. At 0.5C and a high cut-off voltage of 4.5 V, the capacity retention rate after 100 cycles was 78%, which was 23% higher than that of the single lithium salt system (Comparative Example 2).

[0061] The positive electrode material is composed of a positive electrode active material lithium nickel cobalt manganese oxide, polyvinylidene fluoride (PVDF) binder, and SuperP conductive agent, and the ratio is 8:1:1. The surface loading amount of the positive electrode active material is 2.5 mg / cm2.

[0062] Comparative Example 1 (without cross-linking agent)

[0063] (1) Dissolve 0.3 g of PEO (molecular weight 600,000) in 6 ml of acetonitrile, and stir at high speed for 30 min to obtain a PEO solution;

[0064] (2) In a glove box with water and oxygen content both less than 0.1 ppm, add 0.1 g of dilithium salt to the PEO solution, and stir vigorously until completely dissolved to obtain a mixed solution.

[0065] (3) Coat the above mixed solution on a polytetrafluoroethylene template, perform degassing treatment and keep it at 60 °C for 2 h to remove the solvent. After ultraviolet irradiation for 15 min while it is still hot, a solid electrolyte membrane is obtained. This membrane is extremely easy to break, resulting in difficult demolding. The membrane is colorless and transparent, and the membrane thickness is 51 μm.

[0066] Comparative Example 2 (single lithium salt)

[0067] (1) Dissolve 0.3 g of PEO (molecular weight 600,000) in 6 ml of acetonitrile, and stir rapidly and vigorously for 30 min to obtain a PEO solution;

[0068] (2) In a glove box with water and oxygen content both less than 0.1 ppm, sequentially add 0.2 g of UDMA, 0.11 g of LiTFSI, and 0.06 g of benzophenone to the PEO solution, and stir vigorously until completely dissolved to obtain a mixed solution. Among them, [EO]:Li = 15:1.

[0069] (3) Coat the above mixed solution on a polytetrafluoroethylene template, perform degassing treatment and keep it at 50 °C for 2 h to remove the solvent. After ultraviolet irradiation for 15 min while it is still hot, a solid electrolyte membrane is obtained. The cycling performance of this membrane is poor.

[0070] The present invention and its embodiments have been described above. Such description is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar structural forms and embodiments without creative work without departing from the purpose of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A preparation method of a PEO-based solid electrolyte membrane, characterized in that, It includes the following steps: (1) Dissolve PEO in a polar aprotic solvent and vortex stir to obtain a homogeneous solution; (2) In a glove box with water and oxygen content both less than 0.1 ppm, sequentially add a crosslinking agent, a dilithium salt, and a photoinitiator into the above-mentioned PEO solution, and vortex stir until completely dissolved to obtain a polymer mixed solution. (3) Coat the above-mentioned mixed solution on a polytetrafluoroethylene template, heat to remove the solvent and then irradiate with ultraviolet light to obtain a solid electrolyte membrane.

2. The preparation method of a PEO-based solid electrolyte membrane according to claim 1, wherein In step (1), PEO and acetonitrile need to be pre-dried. The molecular weight of PEO is 60-100w, and the polar aprotic solvent is acetonitrile.

3. The preparation method of a PEO-based solid electrolyte membrane according to claim 1, wherein, In step (2), the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluoro(oxalato)borate (LiDFOB), wherein: the molar ratio of LiTFSI to LiDFOB is 7:3, and the total lithium salt concentration is 15% of the molar concentration of the EO unit (i.e., EO:Li = 15:1), and it is dried before use.

4. The preparation method of a PEO-based solid electrolyte membrane according to claim 1, characterized in that, In step (2), the photo-crosslinking agent is urethane dimethacrylate (UDMA).

5. The preparation method of a PEO-based solid electrolyte membrane according to claim 1, characterized in that, In step (2), the photoinitiator is any one of benzophenone, 4-methylbenzophenone, and 2,2-dimethoxy-2-phenylacetophenone (DMPA).

6. The preparation method of a PEO-based solid electrolyte membrane according to claim 1, characterized in that, In step (2), the mass ratio of PEO:lithium salt:crosslinking agent:photoinitiator is (0.3-0.5):(0.11-0.18):(0.15-0.25):(0.05-0.1).

7. A method for preparing a PEO-based solid electrolyte membrane according to claim 5, characterized in that, The initiator needs to be pre-powdered.

8. A method for preparing a PEO-based solid electrolyte membrane according to claim 1, characterized in that, In the step (3), the photocrosslinking process is as follows: coat the mixed solution on a polytetrafluoroethylene template at room temperature, then perform degassing treatment and keep it at 50 °C for 2 - 4 h to remove the solvent. While it is still hot, irradiate it with a 365 nm ultraviolet light source (intensity 1100 mV / cm 2 ) for 5 - 15 min, and then a solid electrolyte membrane is obtained.

9. A solid electrolyte, characterized in that, The solid electrolyte is prepared by the preparation method of any one of claims 1-8. The thickness of the solid electrolyte membrane is 50-150 μm, and the lithium ion transference number is greater than 0.

58.

10. An application of the PEO-based solid electrolyte membrane as described in claim 9 in a lithium battery.

Images