Preparation method of high-ionic-conductivity succinonitrile-based double-layer composite solid electrolyte membrane

Abstract

The invention particularly relates to a preparation method of a succinonitrile-based double-layer composite solid electrolyte membrane with high ionic conductivity. Comprising the following steps: 1) preparing a polyvinylidene fluoride-hexafluoropropylene-based composite solid electrolyte; 2) preparing a polyacrylonitrile-based composite solid electrolyte solution; scraping the solution on the polyvinylidene fluoride-hexafluoropropylene electrolyte membrane prepared in the step (1); and 3) preparing a lithiated butanedinitrile solution, soaking the electrolyte membrane prepared in the step 2) into the solution, and drying to obtain the butanedinitrile-based double-layer composite electrolyte. According to the method disclosed by the invention, triple optimization of butanedinitrile active site passivation, ion transmission enhancement and interface mechanical adaptation is realized through a double-layer matrix structure design and a synergistic impregnation process of lithiated butanedinitrile, and the technical barrier that high load and interface stability are difficult to achieve at the same time is broken through.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion solid polymer electrolytes. Background Art

[0002] The demand for large-capacity lithium-ion batteries in areas such as electric vehicles and large-scale energy storage is increasing year by year. As lithium-ion battery capacity increases, safety issues will become increasingly serious. Currently, most lithium-ion batteries use flammable organic solvents as their electrolyte. This flammable electrolyte, combined with thermal runaway caused by battery short circuits or other factors, is a major cause of battery fires and explosions. Conventional lithium-ion batteries cannot meet the demands of current applications in terms of both energy density and safety, making the exploration of battery systems with even higher performance a pressing need.

[0003] Generally, people prefer to use succinonitrile as an additive to improve the ionic conductivity of the electrolyte membrane. For example, a research paper (10.1002 / smll.202405565) proposed a modification strategy based on a blend system of succinonitrile and polyvinylidene fluoride-co-hexafluoropropylene. However, the integration of succinonitrile will lead to a weakening of the mechanical properties of the battery and will cause serious side reactions with lithium metal. Ultimately, its optimal blend loading is only 20wt%, resulting in limited improvement in the ionic conductivity of the electrolyte system, with the room temperature conductivity only increasing to 3.2×10 -4 S cm -1 Furthermore, the research paper (10.1016 / j.ensm.2022.12.048) uses La of lithium lanthanum zirconium tantalum oxide to 3+ The cationic auxiliary effect between the cations and the N atoms in succinonitrile reduces the number of active -C≡N groups or converts them into less active -C=N- groups, preventing succinonitrile from corroding the lithium anode. This increases the blend loading of succinonitrile to 60wt%, and the room temperature ionic conductivity is also increased to 6.74×10 -4 S cm -1 Although this method uses metal cations to limit the reaction of succinonitrile with the lithium anode, the active -C≡N groups in succinonitrile are not completely passivated.

[0004] Recent research has shown that the use of double salts or appropriate functional additives can effectively improve the interfacial stability between succinonitrile and the lithium metal anode. Chinese patent CN118099513A utilizes a lithium salt, lithiated succinonitrile, and an electrolyte membrane as a framework. The lithiated succinonitrile is then used to fill the pores within the electrolyte membrane to produce a succinonitrile-based composite solid electrolyte membrane. However, rolling the membrane makes the structure of the electrolyte matrix difficult to control. Furthermore, a research paper (10.1002 / adfm.202213211) proposes a succinonitrile-modulated polyvinylidene fluoride-co-hexafluoropropylene porous support, impregnated with a lithiated succinonitrile solution. The resulting matrix provides both a uniform porous network and strong mechanical support, facilitating uniform accommodation of the lithiated succinonitrile and limiting dendrite growth. Chinese patent CN109638350B applies a prepared succinonitrile-based electrolyte to the surface of a porous film. The film-forming additive undergoes an electron reduction reaction with lithium ions at the negative electrode potential during battery charge and discharge, forming a uniform interface phase on the electrolyte surface and limiting dendrite growth. Although the above research partially alleviates the problem through methods such as lithiation and porous supports, its single-layer structure design cannot differentiate the characteristics of the anode and cathode interfaces.

[0005] In summary, existing methods for optimizing succinonitrile electrolytes often rely on single approaches (such as cation modification and matrix filling), but these methods generally face two major contradictions: high loading improves conductivity while exacerbating interfacial side reactions, and matrix structural design struggles to synergistically meet the differentiated needs of the anode and cathode. To address these issues, we propose a method for impregnating lithiated succinonitrile into a double-layer electrolyte matrix to further modify the inherent defects of succinonitrile-based solid electrolytes. Summary of the Invention

[0006] In response to the technical bottlenecks of existing succinonitrile-based solid electrolytes, the present invention aims to provide a composite modification method for impregnating lithiated succinonitrile with a double-layer electrolyte matrix, which specifically includes the following objectives. 1. Synergistic passivation of active groups: Through the synergistic effect of double salts and fluoroethylene carbonate, the active -C≡N group in succinonitrile is converted into an electrochemically inert -C=N- structure, completely eliminating the unpassivated sites in succinonitrile and inhibiting lithium metal side reactions. 2. Differentiated interface regulation: Under the premise of ensuring mechanical properties, the interface characteristics of the anode side and the cathode side are optimized separately through the design of a double-layer heterogeneous structure. Through the synergistic impregnation process of the double-layer matrix structure design and the lithiated succinonitrile, the triple optimization of succinonitrile active site passivation, ion transport enhancement and interface mechanical adaptation is achieved, breaking through the technical barriers that are difficult to achieve both high load and interface stability.

[0007] The specific preparation method comprises the following steps:

[0008] (1) Preparation of double-layer composite solid electrolyte membrane:

[0009] S1. Preparation of polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte: dissolve polyvinylidene fluoride-hexafluoropropylene, a first lithium salt and lithium aluminum titanium phosphate in a first solvent in a certain mass ratio, stir at 50-80°C for 8-14 hours until fully dissolved, use a scraper to evenly scrape the solution with a scraper thickness of 200-400µm, then place in a vacuum oven, and vacuum dry at 50-80°C for 10-16 hours to obtain a polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte.

[0010] S2. Preparation of a double-layer composite solid electrolyte: dissolve polyacrylonitrile, a first lithium salt, and lithium aluminum titanium phosphate in a second solvent in a certain mass ratio, stir at 50-80°C for 8-14 hours until fully dissolved, scrape the prepared solution onto the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte prepared in S1, setting the scraper thickness to 200-400µm, and then place in a vacuum oven, and vacuum dry at 50-80°C for 10-16 hours to obtain a double-layer composite solid electrolyte membrane.

[0011] (2) Preparation of succinonitrile-based solution: succinonitrile, the first lithium salt and the second lithium salt are mixed in a certain mass ratio at 50-80°C and stirred for 2-6 hours to dissolve evenly, and then a certain mass ratio of fluoroethylene carbonate is added, and heating and stirring are continued for 4-8 hours to completely dissolve to obtain a succinonitrile-based solution.

[0012] (3) Soaking the composite electrolyte obtained in step (1) in the succinonitrile-based solution obtained in step (2) for 5-10 minutes, taking it out, and then placing it in a vacuum oven. After vacuum drying at 50-80°C for 10-16 hours, a high ionic conductivity succinonitrile-based double-layer composite electrolyte membrane is obtained.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] Compared with the existing technology (such as reference 10.1016 / j.ensm.2022.12.048), the metal cation (La 3+ ) Compared with the N atom of succinonitrile, which only partially passivates the active -C≡N group and does not completely eliminate the side reaction sites, the present invention uses the "chemical passivation (synergistic effect of double salt and fluoroethylene carbonate)" strategy to completely passivate the residual active -C≡N group in succinonitrile, inhibiting the lithium metal side reaction from the root, and solving the problem of incomplete passivation in the prior art.

[0015] Unlike existing technologies (such as patent CN118099513A and document 10.1002 / adfm.202213211), which use a single-layer structure design and are unable to differentiate and optimize the anode and cathode interface properties (such as mechanical strength and ion transport requirements), this present invention adopts a "double-layer heterogeneous structure design" by using polyvinylidene fluoride-hexafluoropropylene with strong reduction resistance on the anode side and polyacrylonitrile with strong oxidation resistance on the cathode side. This achieves differentiated control of the anode and cathode interface properties, thus overcoming the technical deficiency of a single-layer electrolyte structure that cannot meet both reduction and oxidation resistance requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawing is a performance curve obtained when using Example 2 of the present invention.

[0017] Figure 1 These are the AC impedance spectra of polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte and polyacrylonitrile composite solid electrolyte at 30°C.

[0018] Figure 2 The figure shows the AC impedance spectrum of the double-layer composite electrolyte before and after modification with lithiated succinonitrile in the present invention.

[0019] Figure 3 The lithium symmetric battery assembled with the prepared double-layer composite electrolyte membrane was tested at 30℃ and 0.1 mA cm -2 Cycling curves at different current densities.

[0020] Figure 4 The figure shows the cycle curve of a full battery assembled with the modified succinonitrile-based double-layer composite electrolyte membrane at 30° C. and 1C rate. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0022] Example 1:

[0023] (1) Preparation of double-layer composite solid electrolyte membrane:

[0024] S1: In a glove box, accurately weigh 3g of polyvinylidene fluoride-hexafluoropropylene, 1.8g of lithium bis(trifluoromethanesulfonyl)imide, and 1.8g of lithium aluminum titanium phosphate. Dissolve them in 20ml of N,N-dimethylformamide and stir on a magnetic stirrer at 50°C for 14 hours until fully dissolved. Then, use a 200µm spatula to evenly spread the solution onto a glass plate and dry it in a vacuum oven at 50°C for 16 hours to obtain a polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte.

[0025] S2: In a glove box, accurately weigh 2 g of polyacrylonitrile, 2 g of lithium bis(trifluoromethanesulfonyl)imide, and 0.4 g of lithium aluminum titanium phosphate, dissolve them in 20 ml of N,N-dimethylformamide, and stir on a magnetic stirrer at 50°C for 14 h until fully dissolved. Use a 200 µm scraper to evenly scrape the solution onto the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte dried in step (1), place the mixture in a vacuum oven, and dry it at 50°C for 16 h to obtain a double-layer composite solid electrolyte membrane.

[0026] (2): Accurately weigh 10 g of succinonitrile, 3 g of lithium bis(trifluoromethanesulfonyl)imide, and 2 g of lithium difluorooxalatoborate in a glove box, mix them evenly in a blue-mouthed bottle, stir them on a magnetic stirrer at 50 °C for 6 h, then add 1.2 g of fluoroethylene carbonate, continue heating and stirring for 8 h until they are completely dissolved to obtain a succinonitrile-based solution.

[0027] (3) The double-layer composite solid electrolyte membrane prepared in step (1) was immersed in the succinonitrile-based solution prepared in step (2) for 10 minutes, and then placed in a vacuum oven at 50°C for 16 hours to finally obtain a dry high ionic conductivity succinonitrile-based double-layer composite electrolyte membrane.

[0028] Example 2:

[0029] (1) Preparation of double-layer composite solid electrolyte membrane:

[0030] S1: In a glove box, accurately weigh 3g of polyvinylidene fluoride-hexafluoropropylene, 1.4g of lithium bis(trifluoromethanesulfonyl)imide, and 1.4g of lithium aluminum titanium phosphate. Dissolve them in 20ml of N,N-dimethylformamide and stir on a magnetic stirrer at 60°C for 12 hours until fully dissolved. Then, use a 250µm spatula to evenly spread the solution onto a glass plate and dry it in a vacuum oven at 60°C for 12 hours to obtain a polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte.

[0031] S2: In a glove box, accurately weigh 2 g of polyacrylonitrile, 1.5 g of lithium bis(trifluoromethanesulfonyl)imide, and 0.2 g of lithium aluminum titanium phosphate, dissolve them in 20 ml of N,N-dimethylformamide, and stir on a magnetic stirrer at 60°C for 12 h until fully dissolved. Use a 250 µm scraper to evenly scrape the solution onto the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte dried in step (1), place the mixture in a vacuum oven, and dry it at 60°C for 12 h to obtain a double-layer composite solid electrolyte membrane.

[0032] (2): Accurately weigh 10 g of succinonitrile, 2 g of lithium bis(trifluoromethanesulfonyl)imide, and 1.5 g of lithium difluorooxalatoborate in a glove box, mix them evenly in a blue-mouthed bottle, stir them on a magnetic stirrer at 60 °C for 4 h, then add 0.5 g of fluoroethylene carbonate, continue stirring and heating for 8 h until they are completely dissolved to obtain a succinonitrile-based solution.

[0033] (3) The double-layer composite solid electrolyte membrane prepared in step (1) was immersed in the succinonitrile-based solution prepared in step (2) for 8 minutes, and then placed in a vacuum oven at 60°C for 12 hours to finally obtain a dry high ionic conductivity succinonitrile-based double-layer composite electrolyte membrane.

[0034] Example 3:

[0035] (1) Preparation of double-layer composite solid electrolyte membrane:

[0036] S1: In a glove box, accurately weigh 3g of polyvinylidene fluoride-hexafluoropropylene, 0.9g of lithium bis(trifluoromethanesulfonyl)imide, and 0.9g of lithium aluminum titanium phosphate. Dissolve them in 20ml of N,N-dimethylformamide and stir on a magnetic stirrer at 80°C for 8 hours until fully dissolved. Then, use a 400µm spatula to evenly spread the solution onto a glass plate and dry it in a vacuum oven at 80°C for 10 hours to obtain a polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte.

[0037] S2: In a glove box, accurately weigh 2 g of polyacrylonitrile, 1 g of lithium bis(trifluoromethanesulfonyl)imide, and 0.1 g of lithium aluminum titanium phosphate, dissolve them in 20 ml of N,N-dimethylformamide, and stir on a magnetic stirrer at 80°C for 8 h until fully dissolved. Use a 400 µm scraper to evenly scrape the solution onto the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte dried in step (1), place the mixture in a vacuum oven, and dry it at 80°C for 10 h to obtain a double-layer composite solid electrolyte membrane.

[0038] (2): Accurately weigh 10 g of succinonitrile, 1 g of lithium bis(trifluoromethanesulfonyl)imide, and 0.6 g of lithium difluorooxalatoborate in a glove box, mix them evenly in a blue-mouthed bottle, stir them on a magnetic stirrer at 80 °C for 2 h, then add 0.4 g of fluoroethylene carbonate, continue stirring and heating for 4 h until they are completely dissolved to obtain a succinonitrile-based solution.

[0039] (3) The double-layer composite solid electrolyte membrane prepared in step (1) was immersed in the succinonitrile-based solution prepared in step (2) for 5 minutes, and then placed in a vacuum oven at 80°C for 10 hours to finally obtain a dry high ionic conductivity succinonitrile-based double-layer composite electrolyte membrane.

[0040] Comparative Example 1:

[0041] This comparative example provides a solid electrolyte membrane, which is a double-layer composite electrolyte membrane in step (1) without adding a succinonitrile matrix, except that it is not soaked in a succinonitrile-based solution.

[0042] Performance Testing

[0043] Electrolyte membranes, both pre- and post-modification, were assembled into blocked cells in a glove box. The assembled cells were then tested for electrochemical impedance spectroscopy (ECI) at 30°C and 60°C using a Gamry electrochemical workstation at frequencies ranging from 0.1 Hz to 2 MHz. Both symmetric and full lithium cells were charged and discharged using a LANHE CT2001A battery tester (LAND). All electrochemical measurements were performed at 30°C.

[0044] Result Analysis

[0045] Figure 1 (a) and Figure 1 Figure (b) shows the AC impedance of PVDF-HFP (100µm) and PAN (100µm) at 30°C, demonstrating the effective improvement of the polymer electrolyte performance achieved by lithium aluminum titanium phosphate. At 30°C, the impedance of the PVDF-HFP composite solid electrolyte is 12Ω, while that of the PAN composite solid electrolyte is 40Ω. Figure 2 It shows that the ionic conductivity of the electrolyte membrane after double-layer composite is 1.7×10 -4 S cm -1 After being soaked in a succinonitrile solution, the electrolyte ion conductivity was increased to 1.99×10 -3 S cm -1 The change in properties is due to the high ionic conductivity of succinonitrile itself. Figure 3 The cycling performance of the lithium symmetric battery assembled with the succinonitrile-based double-layer composite electrolyte membrane at 30 °C was obtained. It can be seen that due to the effect of the composite electrolyte skeleton, the succinonitrile-based double-layer composite electrolyte has a good cycling performance at 0.1 mA cm -2 It can be cycled stably for 300 h at a current density of 1. Figure 4 The cycling performance of the full battery assembled with the succinonitrile-based double-layer composite electrolyte was demonstrated. Under the action of the double-layer electrolyte membrane, after 500 cycles, the coulombic efficiency of the full battery was stabilized at 100%, and the specific capacity increased from 120.1 mAh g -1Decay to 105.4 mAh g -1 , the capacity retention rate is 87.76%.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other manner. Any person skilled in the art may utilize the above-disclosed technical content to modify or adapt the present invention into equivalent embodiments. However, any simple modifications, equivalent variations, and improvements to the above embodiments that do not depart from the technical content of the present invention and are based on the technical essence of the present invention shall remain within the scope of protection of the present invention.

Claims

1. A method for preparing a high ionic conductivity succinonitrile-based double-layer composite solid electrolyte membrane, characterized in that: The following steps are involved: (1) Preparation of double-layer composite solid electrolyte membrane: S1. Preparation of a composite solid electrolyte: dissolving a first polymer, a first lithium salt, and lithium aluminum titanium phosphate in a first solvent in a certain mass ratio, heating and stirring until completely dissolved to obtain a casting solution, and drying to obtain a composite solid electrolyte membrane; S2. Preparation of a double-layer composite solid electrolyte: dissolving the second polymer, the first lithium salt, and lithium aluminum titanium phosphate in a second solvent in a certain mass ratio, heating and stirring until completely dissolved, scraping the resulting solution onto the composite solid electrolyte prepared in S1, and drying to obtain a double-layer composite solid electrolyte membrane; (2) Preparation of succinonitrile-based solution: succinonitrile, the first lithium salt, and the second lithium salt are mixed in a certain mass ratio, heated and stirred until uniformly dissolved, and then a certain mass ratio of fluoroethylene carbonate is added, and heating and stirring are continued until completely dissolved to obtain a succinonitrile-based solution; (3) Soaking the double-layer composite solid electrolyte membrane obtained in step (1) in the succinonitrile-based solution obtained in step (2), and then vacuum drying at 50-80° C. to obtain a succinonitrile-based double-layer composite electrolyte membrane with high ionic conductivity.

2. The preparation method according to claim 1, characterized in that The first polymer is polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene, and the second polymer is polyacrylonitrile.

3. The preparation method according to claim 1, characterized in that The thickness of the solid electrolyte membrane is 50-100µm; the thickness of the double-layer composite solid electrolyte membrane is 100-200µm.

4. The preparation method according to claim 1, characterized in that In step S1, the mass ratio of the first polymer, the first lithium salt and lithium aluminum titanium phosphate is 1:0.3-0.6:0.3-0.

6.

5. The preparation method according to claim 1, characterized in that The first solvent in step S1 is any one of N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetone, and N-methylpyrrolidone.

6. The preparation method according to claim 1, characterized in that In step S2, the mass ratio of the second polymer, the first lithium salt and lithium aluminum titanium phosphate is 1:0.5-1:0.05-0.

2.

7. The preparation method according to claim 1, characterized in that The second solvent in step S2 is any one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

8. The preparation method according to claim 1, characterized in that In the step (1), the first lithium salt of S1 and S2 is any one of lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium oxalate, and lithium bis(fluorosulfonyl)imide.

9. The preparation method according to claim 1, characterized in that In the step (2), the mass ratio of succinonitrile, the first lithium salt and the second lithium salt is 50:5-15:3-10, and the mass ratio of fluoroethylene carbonate to succinonitrile is 1-3:

25.

10. The preparation method according to claim 1, characterized in that The second lithium salt in step (2) is any one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium difluorooxalatoborate.

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