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

Abstract

The application specifically relates to a preparation method of a high-ionic-conductivity succinonitrile-based double-layer composite solid electrolyte film. The method comprises 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 film prepared in step 1); 3) preparing a lithiumated succinonitrile solution, soaking the electrolyte film prepared in step 2) into the solution, and drying to obtain a succinonitrile-based double-layer composite electrolyte. Through the synergistic impregnation process of the double-layer matrix structure design and the lithiumated succinonitrile, the method realizes the triple optimization of succinonitrile active site passivation, ion transmission strengthening and interface mechanical adaptation, and breaks through the technical barrier that high load and interface stability are difficult to be compatible.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion solid polymer electrolytes. Background Technology

[0002] The demand for high-capacity lithium-ion batteries is increasing year by year in fields such as electric vehicles and large-scale energy storage. As the capacity of lithium-ion batteries increases, safety issues will become increasingly serious. Most current lithium-ion batteries use flammable organic solvents as electrolytes. The flammable electrolyte, combined with thermal runaway caused by battery short circuits or other reasons, is the main cause of battery fires and explosions. Traditional lithium-ion batteries cannot meet the needs of current applications in terms of either energy density or safety. Therefore, exploring battery systems with superior performance is urgently needed.

[0003] Typically, succinic anionylene is preferred as an additive to improve the ionic conductivity of the electrolyte membrane. For example, research paper (10.1002 / smll.202405565) proposed a modification strategy based on a blend of succinic anionylene and polyvinylidene fluoride-hexafluoropropylene. However, the integration of succinic anionylene weakens the battery's mechanical properties and causes severe side reactions with lithium metal. Ultimately, its optimal blend loading is only 20 wt%, resulting in limited improvement in the ionic conductivity of the electrolyte system, with the room temperature conductivity only increasing to 3.2 × 10⁻⁶. -4 S cm -1 Furthermore, the research paper (10.1016 / j.ensm.2022.12.048) utilizes the La... 3+ The cationic assisted interaction between the cation and the N atom in succinate reduces the number of active -C≡N groups or converts them into less active -C=N- groups, preventing succinate from corroding the lithium anode. This increases the succinate blend loading to 60 wt%, while also improving the room temperature ionic conductivity to 6.74 × 10⁻⁶. -4 S cm -1 Although this method uses metal cations to limit the reaction between succinate and the lithium anode, the active -C≡N groups in the succinate are not completely passivated.

[0004] Recent studies have shown that using dual salts or appropriate functional additives can effectively improve the interfacial stability between succinic anion and lithium metal anode. Chinese patent CN118099513A uses lithium salt to lithiate succinic anion, with an electrolyte membrane as the framework, and simultaneously uses the lithiated succinic anion to fill the pores inside the electrolyte membrane, preparing a succinic anion-based composite solid electrolyte membrane. However, its rolling process makes it difficult to control the structure of the electrolyte matrix. Furthermore, research literature (10.1002 / adfm.202213211) proposes a succinic anion-controlled polyvinylidene fluoride-hexafluoropropylene porous support, using a method of impregnating with a lithiated succinic anion solution. The prepared matrix provides both a uniform porous network and robust mechanical support, facilitating the uniform containment of lithiated succinic anion and limiting dendrite growth. Chinese patent CN109638350B describes a method of drop-coating a succinic acid-based electrolyte onto the surface of a porous film. The film-forming additives undergo an electron reduction reaction with lithium ions at the negative electrode potential during battery charging and discharging, forming a uniform interfacial phase on the electrolyte surface and limiting dendrite growth. While the above research partially alleviates the problem through lithiation and porous supports, its single-layer structure design cannot achieve differentiated control of the anode and cathode interface characteristics.

[0005] In summary, existing methods mostly optimize succinate electrolytes through single means (such as cation modification and matrix filling), but they generally face two major contradictions: high loading increases conductivity while exacerbating interfacial side reactions, and the matrix structure design is difficult to coordinately meet the differentiated requirements of the anode and cathode. To address these issues, we propose a method of impregnating a bilayer electrolyte matrix with lithium-ionized succinate to further modify the inherent defects of succinate-based solid electrolytes. Summary of the Invention

[0006] To address the technical bottlenecks of existing succinate-based solid electrolytes, this invention aims to provide a composite modification method for impregnating a bilayer electrolyte matrix with lithium-modified succinate, specifically including the following objectives: 1. Synergistic passivation of active groups: Through the synergistic effect of a dual salt and fluoroethylene carbonate, the active -C≡N groups in succinate are converted into electrochemically inert -C=N- structures, completely eliminating unpassivated sites in succinate and suppressing lithium metal side reactions. 2. Differentiated interface regulation: While ensuring mechanical properties, the interface characteristics of the anode and cathode sides are optimized separately through a bilayer heterostructure design. Through the bilayer matrix structure design and the synergistic impregnation process of lithium-modified succinate, a triple optimization of succinate active site passivation, ion transport enhancement, and interface mechanical adaptation is achieved, overcoming the technical barrier of simultaneously achieving high loading and interface stability.

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

[0008] (1) Preparation of a bilayer composite solid electrolyte membrane:

[0009] S1. Preparation of polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte: Polyvinylidene fluoride-hexafluoropropylene, first lithium salt and lithium aluminum titanium phosphate are dissolved in a first solvent at a certain mass ratio. The solution is stirred at 50-80℃ for 8-14 hours until fully dissolved. The solution is then evenly spread with a scraper with a thickness of 200-400µm. The solution is then placed in a vacuum oven and vacuum dried at 50-80℃ for 10-16 hours to obtain the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte.

[0010] S2. Preparation of the bilayer composite solid electrolyte: Polyacrylonitrile, the first lithium salt and lithium aluminum titanium phosphate are dissolved in the second solvent at a certain mass ratio. The mixture is stirred at 50-80℃ for 8-14 hours until fully dissolved. The prepared solution is scraped onto the polyvinylidene fluoride-hexafluoropropylene composite solid electrolyte prepared in S1. The thickness of the scraper is set to 200-400µm. Then, it is placed in a vacuum oven and vacuum dried at 50-80℃ for 10-16 hours to obtain the bilayer composite solid electrolyte membrane.

[0011] (2) Preparation of succinic acid-based solution: Succinic acid, first lithium salt and second lithium salt are mixed at a certain mass ratio and stirred at 50-80℃ for 2-6 hours to dissolve evenly. Then, a certain mass ratio of fluoroethylene carbonate is added and the mixture is heated and stirred for 4-8 hours to completely dissolve and obtain succinic acid-based solution.

[0012] (3) Immerse the composite electrolyte obtained in step (1) in the succinic acid-based solution prepared in step (2) for 5-10 min, then take it out and place it in a vacuum oven. After vacuum drying at 50-80℃ for 10-16 h, a high ionic conductivity succinic acid-based bilayer composite electrolyte membrane is obtained.

[0013] Compared with existing technologies, the beneficial effects achieved by this invention are as follows:

[0014] Compared with existing technologies (such as reference 10.1016 / j.ensm.2022.12.048) using metal cations (La) 3+ Compared to the N atom interaction of succinate, which only partially passivates the active -C≡N groups and does not completely eliminate side reaction sites, this invention completely passivates the residual active -C≡N groups in succinate through a "chemical passivation (synergistic effect of dual salts and fluoroethylene carbonate)" strategy, thereby inhibiting lithium metal side reactions from the root and solving the problem of incomplete passivation in the prior art.

[0015] Existing technologies (such as patent CN118099513A and document 10.1002 / adfm.202213211) employ a single-layer structure design, which cannot be optimized for differentiated anode-cathode interface characteristics (such as mechanical strength and ion transport requirements). This invention, through a "double-layer heterogeneous structure design," uses polyvinylidene fluoride-hexafluoropropylene (PVDF-HFA) with strong reduction resistance on the anode side and polyacrylonitrile (PAB) with strong oxidation resistance on the cathode side. This achieves differentiated control of anode-cathode interface characteristics, overcoming the technical deficiency of single-layer electrolyte structures that cannot simultaneously meet reduction and oxidation resistance requirements. Attached Figure Description

[0016] The attached figure shows the performance curves obtained by using Example 2 of the present invention.

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

[0018] Figure 2 The AC impedance spectra of the bilayer composite electrolyte before and after modification with lithium succinic anhydride are shown in this invention.

[0019] Figure 3 The lithium-symmetric battery assembled with the prepared bilayer composite electrolyte membrane was tested at 30 °C and 0.1 mA cm⁻¹. -2 Cyclic curves at current density.

[0020] Figure 4 The cycling curves of the full cell assembled using the modified succinic acid-based bilayer composite electrolyte membrane according to the present invention are shown at 30°C and 1C rate. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects of this invention clearer and more understandable, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0022] Example 1:

[0023] (1) Preparation of a bilayer composite solid electrolyte membrane:

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

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

[0026] (2): Accurately weigh 10g of succinic acid, 3g of lithium bis(trifluoromethanesulfonylimide) and 2g of lithium difluorooxalate borate in a glove box, mix them evenly in a blue-mouth bottle, stir on a magnetic stirrer at 50°C for 6h, add 1.2g of fluoroethylene carbonate, and continue heating and stirring for 8h to completely dissolve to obtain a succinic acid-based solution.

[0027] (3) Immerse the bilayer composite solid electrolyte membrane prepared in step (1) into the succinic acid-based solution prepared in step (2) for 10 min, and then put it into a vacuum oven at 50°C for 16 h to dry it, and finally obtain a dry succinic acid-based bilayer composite electrolyte membrane with high ionic conductivity.

[0028] Example 2:

[0029] (1) Preparation of a bilayer composite solid electrolyte membrane:

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

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

[0032] (2): Accurately weigh 10g succinate, 2g lithium bis(trifluoromethanesulfonylimide) and 1.5g lithium difluorooxalate borate in a glove box, mix them evenly in a blue bottle, stir on a magnetic stirrer at 60°C for 4h, add 0.5g fluoroethylene carbonate, continue stirring and heating for 8h to completely dissolve and obtain succinate-based solution.

[0033] (3) Immerse the bilayer composite solid electrolyte membrane prepared in step (1) into the succinic acid-based solution prepared in step (2) for 8 min, and then put it into a vacuum oven at 60°C for 12 h to dry it, and finally obtain a dry succinic acid-based bilayer composite electrolyte membrane with high ionic conductivity.

[0034] Example 3:

[0035] (1) Preparation of a bilayer composite solid electrolyte membrane:

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

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

[0038] (2): Accurately weigh 10g succinate, 1g lithium bis(trifluoromethanesulfonylimide) and 0.6g lithium difluorooxalate borate in a glove box, mix them evenly in a blue-mouth bottle, stir on a magnetic stirrer at 80°C for 2h, add 0.4g fluoroethylene carbonate, continue stirring and heating for 4h to completely dissolve and obtain succinate-based solution.

[0039] (3) Immerse the bilayer composite solid electrolyte membrane prepared in step (1) into the succinic acid-based solution prepared in step (2) for 5 min, and then put it into a vacuum oven at 80°C for 10 h to finally obtain a dry succinic acid-based bilayer composite electrolyte membrane with high ionic conductivity.

[0040] Comparative Example 1:

[0041] This comparative example provides a solid electrolyte membrane, which is a double-layer composite electrolyte membrane without the addition of succinic acid matrix in step (1), the difference being that it is not soaked in succinic acid matrix solution.

[0042] Performance testing

[0043] Electrolyte membranes, both before and after succinate modification, were placed in a glove box to assemble blocked batteries. The assembled batteries were then tested on a Gamry electrochemical workstation in Germany at frequencies ranging from 0.1 Hz to 2 MHz at 30°C and 60°C for AC impedance measurement. Lithium-ion symmetric batteries and lithium-ion full cells were charged and discharged using a LANHE CT2001A battery tester (LAND). All electrochemical measurements were performed at 30°C.

[0044] Results Analysis

[0045] Figure 1 (a) and Figure 1 (b) shows the AC impedance of polyvinylidene fluoride-hexafluoropropylene (100µm) and polyacrylonitrile (100µm) at 30℃, respectively, reflecting the effective improvement of polymer electrolyte performance by lithium titanium aluminum phosphate. At 30℃, the impedance of the polyvinylidene fluoride-hexafluoropropylene-based composite solid electrolyte is 12Ω, and the impedance of the polyacrylonitrile-based composite solid electrolyte is 40Ω. Figure 2 This indicates that the ionic conductivity of the electrolyte membrane after the double-layer composite is 1.7 × 10⁻⁶. -4 S cm -1 After modification by soaking in a succinic acid solution, the electrolyte ionic conductivity was increased to 1.99 × 10⁻⁶. -3 S cm -1 The change in performance depends on the high ionic conductivity of succinate itself. Figure 3 The cycle performance of a lithium-ion symmetric battery assembled with a succinic acid-based bilayer composite electrolyte membrane at 30 °C was obtained. This demonstrates that, due to the effect of the composite electrolyte framework, the succinic acid-based bilayer composite electrolyte exhibits good performance at 0.1 mA cm⁻¹. -2 It can be stably cycled for 300 hours at a current density. Figure 4 The cycling performance of the full cell assembled with a succinic acid-based bilayer composite electrolyte was demonstrated. Under the action of the bilayer electrolyte membrane, the coulombic efficiency of the full cell stabilized at 100% after 500 cycles, and the specific capacity increased from 120.1 mAh g⁻¹. -1Decayed to 105.4 mAh g -1 The capacity retention rate was 87.76%.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and improvements made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a high ionic conductivity succinic acid-based bilayer composite solid electrolyte membrane, characterized in that, Includes the following steps: (1) Preparation of a bilayer composite solid electrolyte membrane: S1. Preparation of composite solid electrolyte: The first polymer, the first lithium salt and lithium aluminum titanium phosphate are dissolved in the first solvent in a certain mass ratio, heated and stirred until completely dissolved to obtain a casting solution, which is then dried to obtain a composite solid electrolyte membrane. S2. Preparation of bilayer composite solid electrolyte: The second polymer, the first lithium salt and lithium aluminum titanium phosphate are dissolved in the second solvent in a certain mass ratio, heated and stirred until completely dissolved, and the resulting solution is scraped onto the composite solid electrolyte prepared in S1 and dried to obtain a bilayer composite solid electrolyte membrane. (2) Preparation of succinic acid-based solution: Succinic acid, first lithium salt and second lithium salt are mixed in a certain mass ratio, heated and stirred until dissolved evenly, and then a certain mass ratio of fluoroethylene carbonate is added. The mixture is heated and stirred until completely dissolved to obtain succinic acid-based solution. (3) Immerse the bilayer composite solid electrolyte membrane obtained in step (1) in the succinic acid-based solution prepared in step (2), and then vacuum dry it at 50-80℃ to obtain a succinic acid-based bilayer composite electrolyte membrane with high ionic conductivity. In step (1), the first polymer is polyvinylidene fluoride, one of polyvinylidene fluoride-hexafluoropropylene, and the second polymer is polyacrylonitrile. 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. 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. In step (2), the mass ratio of succinate, the first lithium salt and the second lithium salt is 50:5-15:3-10, and the mass ratio of fluoroethylene carbonate to succinate is 1-3:

25.

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

3. 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.

4. 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.

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

6. The preparation method according to claim 1, characterized in that, In step (2), the second lithium salt is any one of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, and lithium difluorooxalate borate.

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