A method for preparing a composite polymer electrolyte membrane

Abstract

This invention provides a method for preparing a composite polymer electrolyte membrane, mainly comprising the following steps: mixing lignin derivatives, a polymer matrix, lithium salts, and an organic solvent in a certain proportion to obtain a uniform slurry with a certain viscosity; dripping the uniform slurry onto a glass plate, coating it to a certain thickness, and then placing it in a vacuum drying oven for drying at a specific temperature and vacuum level to obtain the composite polymer electrolyte membrane. Studies have found that the composite polymer electrolyte membrane obtained by this invention has excellent film-forming properties, stable structure, and exhibits high lithium-ion transference number and high room-temperature ionic conductivity.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials, specifically relating to a method for preparing a composite solid polymer electrolyte membrane. Background Technology

[0002] Currently, most commercial lithium-ion batteries use liquid electrolytes. However, liquid batteries have safety issues such as flammability and leakage, and their low energy density limits their large-scale application. Meanwhile, rapid societal development has placed higher demands on the energy density and safety of lithium-ion batteries. As a result, all-solid-state lithium-ion batteries, which use solid electrolytes instead of liquid electrolytes, have emerged. This eliminates the safety hazards of leakage and explosion associated with traditional liquid batteries and makes it possible to match high-voltage positive electrodes and high-specific-capacity negative electrodes to improve energy density.

[0003] Solid-state electrolytes are classified into polymer solid-state electrolytes and inorganic solid-state electrolytes. Polymer electrolytes are simple to prepare, have good film-forming properties and flexibility, and can achieve low internal resistance while improving the contact between electrolyte and electrode materials. This effectively improves electrochemical performance while meeting high safety requirements, showing broad development prospects. However, single polymer electrolyte membranes still have unresolved issues, such as a narrow electrochemical window, low mechanical strength, and low room-temperature ionic conductivity, making them unsuitable for all-solid-state lithium-ion battery applications. Our research team proposed an asymmetric composite polymer electrolyte membrane containing LATP electrolyte particles, which, combined with a low-voltage lithium iron phosphate cathode material, prepared an all-solid-state lithium-ion battery with good electrochemical performance (ACS SustainableChem. Eng. 2019, 7, 15896−15903). Yao et al. proposed an inorganic-organic composite electrolyte membrane composed of PVDF and magnesium aluminum oxide nanowires, which effectively improved the electrochemical window of the electrolyte membrane, but its conductivity was unsatisfactory (NanoLett. 2018, 18, 6113−6120).

[0004] In these methods, the filler material is mostly inorganic electrolyte particles, which have weak bonding with the polymer matrix and may separate during use, leading to the disruption of lithium-ion transport channels. Therefore, it is necessary to select suitable materials to modify the polymer electrolyte membrane to improve the chelating force between the filler and the polymer, thereby achieving excellent electrochemical performance of the composite electrolyte membrane. Summary of the Invention

[0005] To address the problems of low lithium-ion transference number and low room-temperature ionic conductivity in single polymer electrolyte membranes, this invention proposes a method for preparing a composite polymer electrolyte. Lignin derivatives are selected as inert fillers, and by leveraging their rich surface and interfacial structural characteristics, a high-performance composite polymer electrolyte membrane is obtained.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows.

[0007] Step S1: Disperse the lignin derivative in an organic solvent to obtain a first mixture.

[0008] Step S2: Add the polymer matrix to the first mixture to obtain the second mixture slurry.

[0009] Step S3: Add lithium salt to the second mixed slurry to obtain a composite polymer electrolyte slurry with a certain viscosity.

[0010] Step S4: Place the composite polymer electrolyte slurry on a glass plate and coat it to a certain thickness.

[0011] Step S5: After drying in a vacuum drying oven, a composite polymer electrolyte membrane is obtained.

[0012] In the composite polymer electrolyte slurry, the mass ratio of lignin derivative to polymer matrix is ​​0.02:1-0.2:1, the mass ratio of polymer matrix to lithium salt is 1:0.5-1:2, and the mass ratio of organic solvent to polymer matrix is ​​6:1-9:1.

[0013] Further, in step S1, the lignin derivative is one or a combination of lignin sulfonic acid and sodium lignin sulfonate.

[0014] Further, in step S1, the organic solvent is one or a combination of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetonitrile (ACN).

[0015] Furthermore, in step S1, the dispersion of the lignin derivative in the organic solvent requires ultrasonic vibration treatment.

[0016] Furthermore, the ultrasonic treatment conditions are: ultrasonic power 90W, treatment time 5-20min.

[0017] Further, in step S2, the polymer matrix is ​​one or a combination of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), and polyionic liquid.

[0018] Further, in step S3, the lithium salt is lithium bis(trifluoromethanesulfonylimide) (LiTFSI).

[0019] Further, in step S4, the coating is applied to a thickness of 40-100 μm.

[0020] Furthermore, in step S5, the drying temperature for obtaining the composite polymer electrolyte is 50-100℃, and the drying time is 4-12h.

[0021] The present invention also provides a composite polymer electrolyte membrane prepared by the above preparation method.

[0022] Implementing this invention has the following beneficial effects.

[0023] 1. The method for preparing the composite polymer electrolyte membrane provided by the present invention selects lignin derivatives as inert fillers and composites them with a polymer matrix. Due to the rich pore structure and functional groups at the filler surface and interface, the composite electrolyte membrane still exhibits good mechanical properties and excellent electrochemical performance.

[0024] 2. The lignin derivative selected in this invention has a smaller particle size. Compared with inorganic fillers, the lignin derivative has better compatibility with polymers, solving the problem of poor interfacial contact between composite phases. Secondly, the molecular structure contains groups that can bind lithium salt anions, restricting anion migration and thus promoting lithium ion transport, significantly increasing the lithium ion transference number of the composite electrolyte. At the same time, the addition of lignin derivatives breaks the crystalline structure of the polymer to a certain extent, increasing the amorphous regions of the polymer and making the polymer chain segments more active, greatly improving the ionic conductivity of the composite electrolyte and effectively improving the electrochemical performance of the polymer electrolyte.

[0025] 3. The preparation method used in this invention is simple. Furthermore, lignin derivatives are a type of biomass material with wide availability, facilitating the preparation of composite polymer electrolytes. Attached Figure Description

[0026] Figure 1 The graph shows the test results of lithium ion transference number and ionic conductivity of the composite polymer electrolyte membranes obtained in Examples 1-3 and Comparative Example 1 of this invention.

[0027] Figure 2 The graph shows the electrochemical window test results of the composite polymer electrolyte membranes obtained in Examples 1-3 of this invention.

[0028] Figure 3 The graphs show the 5C cycle performance of solid-state batteries assembled with composite polymer electrolyte membrane and lithium iron phosphate (LFP) cathode in comparative examples and Example 2 of this invention.

[0029] Figure 4 This is a surface morphology diagram of the composite polymer electrolyte membrane obtained in Example 2 of the present invention. Detailed Implementation

[0030] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0031] In step S1, the lignin derivative is dispersed in an organic solvent and subjected to ultrasonic vibration at 90W for 5-20 minutes to obtain a uniformly dispersed first mixture. Further, the lignin derivative is one or a combination of lignin sulfonic acid and sodium lignin sulfonate, and the organic solvent is one or a combination of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetonitrile (ACN). The organic solvent used in this invention is required to achieve both good dispersion of the lignin derivative and good dissolution of the polymer matrix. Preferably, the organic solvent is N-methylpyrrolidone (NMP).

[0032] In step S2, a polymer matrix is ​​added to the well-dispersed first mixture to obtain a second mixture. Further, the polymer matrix is ​​one or a combination of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), and polyionic liquid. Among these, polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) overcomes the high crystallinity defects of polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) and has better film-forming properties. Preferably, the polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

[0033] In step S3, lithium salt is added to the second mixture to obtain a uniformly mixed composite polymer electrolyte solution; further, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0034] In step S4, the composite polymer electrolyte solution is placed on a glass plate and coated to a certain thickness; further, the coating is coated to a thickness of 40-100 μm.

[0035] In step S5, the composite polymer electrolyte is obtained after being dried in a vacuum drying oven; further, the drying temperature for obtaining the composite polymer electrolyte is 50-100℃, and the drying time is 4-12h.

[0036] The present invention will be further described below with reference to specific embodiments and comparative examples.

[0037] Example 1.

[0038] 50 mg of lignin sulfonic acid was dispersed in 3.5 g of NMP and ultrasonically dispersed until uniform. 500 mg of PVDF-HFP was added, and the mixture was magnetically stirred for 6 hours. Then, 1 g of LiTFSI was added, and the mixture was stirred for 3 hours to obtain a uniform and stable composite polymer electrolyte solution. The electrolyte solution was dropped onto a glass plate and coated with a doctor blade to obtain a wet composite polymer electrolyte film. This film was then placed in a vacuum drying oven at 60°C for 8 hours to obtain the composite polymer electrolyte membrane with a thickness of 40-100 μm.

[0039] Example 2.

[0040] 75 mg of lignin sulfonic acid was dispersed in 3.5 g of NMP and ultrasonically dispersed until uniform. 500 mg of PVDF-HFP was added, and the mixture was magnetically stirred for 6 hours. Then, 1 g of LiTFSI was added, and the mixture was stirred for 3 hours to obtain a uniform and stable composite polymer electrolyte solution. The electrolyte solution was dropped onto a glass plate and coated with a doctor blade to obtain a wet composite polymer electrolyte film. This film was then dried in a vacuum drying oven at 60°C for 8 hours to obtain the composite polymer electrolyte membrane with a thickness of 40-100 μm.

[0041] Example 3.

[0042] 100 mg of lignin sulfonic acid was dispersed in 3.5 g of NMP and ultrasonically dispersed until uniform. 500 mg of PVDF-HFP was added, and the mixture was magnetically stirred for 6 hours. Then, 1 g of LiTFSI was added, and the mixture was stirred for 3 hours to obtain a uniform and stable composite polymer electrolyte solution. The electrolyte solution was dropped onto a glass plate and coated with a doctor blade to obtain a wet composite polymer electrolyte film. This film was then dried in a vacuum drying oven at 60°C for 8 hours to obtain the composite polymer electrolyte membrane with a thickness of 40-100 μm.

[0043] Comparative Example 1.

[0044] The main difference compared to the example is that lignin sulfonic acid was not added.

[0045] 500 mg of PVDF-HFP was dispersed in 3.5 g of NMP and magnetically stirred for 6 h. Then, 1 g of LiTFSI was added and stirred for 3 h to obtain a homogeneous and stable polymer electrolyte solution. The electrolyte solution was dropped onto a glass plate and coated with a doctor blade to obtain a polymer electrolyte wet film. The film was then placed in a vacuum drying oven at 60 °C for 8 h to obtain a polymer electrolyte membrane with a thickness of 40-100 μm.

[0046] The electrolytes prepared in Examples 1-3 and Comparative Example 1 were subjected to lithium-ion transference number tests.

[0047] Studies have shown that without the addition of lignin sulfonate or sodium lignin sulfonate, lithium ion migration in the single polymer electrolyte membrane is hindered, resulting in a low lithium ion transference number and poor electrochemical performance of the electrolyte. However, the addition of lignin sulfonate or sodium lignin sulfonate inhibits the migration of anions in the electrolyte, thereby providing a rapid transport channel for lithium ions and significantly increasing the lithium ion transference number.

[0048] The above description is merely a preferred embodiment of the present invention; however, the present invention is not limited thereto. Any technical combinations extended or modified based on the technical concept of the present invention should also be considered as part of the content disclosed in the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite polymer electrolyte membrane, mainly comprising the following steps: Step S1, dispersing lignosulfonic acid or sodium lignosulfonate in an organic solvent to obtain a first mixed solution; Step S2, adding a polymer matrix to the first mixed solution to obtain a second mixed slurry; Step S3, adding a lithium salt to the second mixed slurry to obtain a composite polymer electrolyte slurry with a certain viscosity; Step S4, placing the composite polymer electrolyte slurry on a glass plate and coating to a certain thickness; Step S5, obtaining a composite polymer electrolyte membrane after drying in a vacuum drying oven; wherein, in the composite polymer electrolyte slurry, the mass ratio of lignosulfonic acid or sodium lignosulfonate to the polymer matrix is 0.02:1-0.2:1, the mass ratio of the polymer matrix to the lithium salt is 1:0.5-1:2, and the mass ratio of the organic solvent to the polymer matrix is 6:1-9:

1. In Step S1, the organic solvent is one or a combination of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetonitrile (ACN). In Step S1, the dispersion of the lignin derivative in the organic solvent needs to be treated by ultrasonic oscillation. The ultrasonic treatment conditions are: ultrasonic power 90w, and treatment time 5-20min. In Step S2, the polymer matrix is one or a combination of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), and polyionic liquid. In Step S3, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In Step S4, the coating thickness is 40-100μm. In Step S5, the drying temperature for obtaining the composite polymer electrolyte is 50-100℃, and the drying time is 4-12h. 9.A composite polymer electrolyte prepared by the method of any one of claims 1-8. ​ ​ ​ ​ ​ 2. The production method according to claim 1, characterized by, ​ 3. The preparation method according to claim 1, characterized in that, ​ 4. The production method according to claim 3, characterized by, ​ 5. The method of claim 1, wherein, ​ 6. The method of claim 1, wherein, ​ 7. The preparation method according to claim 1, characterized in that, ​ 8. The method of claim 1, wherein, ​ ​

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