PEO-polyacrylonitrile (PAN)-PEO sandwich structure composite solid electrolyte membrane, preparation method thereof and all-solid-state battery

Abstract

The application belongs to the technical field of solid electrolyte preparation, and particularly relates to a PAN-PEO-PAN sandwich structure composite solid electrolyte film and a preparation method thereof and a solid-state battery; the sandwich structure composite electrolyte film is composed of upper and lower PEO layers and a PAN layer in the middle, and the preparation method comprises the following steps: uniformly mixing dopamine modified inorganic fillers and PEO powder in a mortar; adding lithium salt into acetonitrile solvent to form a uniform solution, then adding the obtained mixture into the uniform lithium salt solution to continue stirring until uniform to obtain a PEO suspension; pouring the PEO suspension on both sides of a PAN nanofiber framework, and drying completely to remove organic solvents to obtain a PEO-PAN-PEO sandwich structure composite solid electrolyte film; the technical scheme provided by the application reduces the interface resistance of the solid-state battery with a reduced lithium affinity of the PEO layer, accelerates solid-solid transport reaction kinetics, the PAN nanofiber layer endows the electrolyte film with higher mechanical strength, simultaneously provides a 3D lithium ion transport channel to accelerate ion transport, and the assembled full solid-state battery exhibits excellent electrochemical performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolyte preparation, and in particular relates to a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, a preparation method thereof, and a solid-state battery. Background Art

[0002] Lithium metal batteries have attracted widespread attention due to their high theoretical specific capacity (3860 mAh g-1) and energy density. However, conventional lithium metal batteries use flammable and volatile organic liquid electrolytes, which are severely hindered by uncontrolled dendrite growth, unstable electrolyte / Li interface, and poor cycling stability, thus severely hindering their practical application.

[0003] Solid-state electrolytes, as potential alternatives to liquid organic electrolytes, offer advantages in safety and dendrite suppression, and are expected to fully leverage the high specific energy of metallic lithium anodes. PEO / ceramic composite solid electrolytes have garnered widespread attention in solid-state lithium metal batteries due to PEO's high Li+ solubility, flexibility, processability, low cost, and synergistic performance with ceramic electrolytes. Polymer solid electrolytes offer flexibility, low cost, and ease of processing, but their room-temperature conductivity is typically low. Inorganic solid electrolytes offer high room-temperature conductivity, but their complex preparation processes and high cost, coupled with their high hardness, lead to poor interfacial compatibility with electrodes. The development of organic-inorganic composite solid electrolytes can effectively combine the advantages of both and is therefore considered one of the materials with the greatest potential for large-scale practical applications. Researchers have proposed a variety of effective strategies for the structural design of composite solid electrolytes, primarily including low-dimensional inorganic filler modification, three-dimensional inorganic filler modification, and multilayer electrolyte composites.

[0004] However, the further development of solid-state electrolytes is hindered by insufficient mechanical strength to resist the growth of dendrites during battery operation, which can cause the electrolyte membrane to pierce and lead to battery failure, and the narrow electrochemical window that cannot match high-voltage cathode materials.

[0005] Therefore, a PEO-PAN-PEO sandwich structure composite solid electrolyte was designed through electrospinning / casting strategy, which effectively enhanced the mechanical strength of the electrolyte membrane, broadened the electrochemical window, reduced the interfacial resistance, and thus enhanced the solid-solid transport reaction kinetics. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of existing PEO-based composite solid electrolytes, such as low mechanical strength, large interface resistance, and narrow electrochemical window, and to provide a PEO-based composite solid electrolyte membrane with high mechanical strength and wide electrochemical window.

[0007] Another object of the present invention is to provide a method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane.

[0008] Another object of the present invention is to provide a PEO-PAN-PEO sandwich structure composite solid electrolyte for use in an all-solid-state battery.

[0009] The above-mentioned purpose of the present invention, the first technical solution provided by the present invention is as follows:

[0010] 1) mixing the dopamine-modified inorganic filler and PEO powder in a mortar at a mass ratio of 0.007-0.07:0.2-1.0 to obtain a mixture;

[0011] 2) Adding lithium salt into an organic solvent and mixing to form a uniform lithium salt solution; the concentration of the solution is 0.02 mol / L-0.36 mol / L.

[0012] 3) adding the mixture obtained in step 1) to the lithium salt solution in step 2) and continuing to stir until uniform, to obtain a PEO suspension;

[0013] In step 3), the mass ratio of PEO to lithium salt is 0.2-1.0:0.1-0.5;

[0014] 4) dissolving the ceramic nanoparticles and PAN powder in DMF solvent at a mass ratio of 0.026-0.5:0.5-2.0, and stirring to obtain a spinning suspension;

[0015] 5) electrospinning the spinning suspension obtained in step 4) on a spinning machine to obtain PAN nanofibers;

[0016] 6) Casting the suspension obtained in step 3) on both sides of the PAN nanofibers obtained in step 5) and drying to obtain a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane.

[0017] Furthermore, in the above-mentioned method for preparing the PEO suspension, the organic solvent is acetonitrile.

[0018] Furthermore, in the above-mentioned method for preparing the PEO suspension, the concentration of the lithium salt solution is 0.3-1.8 mmol.

[0019] Furthermore, in the above-mentioned method for preparing the PEO suspension, the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorooxalate borate, and lithium bis(fluorosulfonyl)imide.

[0020] Furthermore, in the above-mentioned method for preparing the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, the drying is performed at 60° C. for 24 hours.

[0021] Furthermore, in the above-mentioned method for preparing the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, the dopamine-modified inorganic filler is prepared by the following method:

[0022] 1) dissolving dopamine hydrochloride in deionized water and stirring magnetically until completely dissolved to obtain a dopamine solution;

[0023] 2) dissolving tris(hydroxymethyl)aminomethane in deionized water, adding a filler-free solution after complete dissolution, and magnetically stirring to form a mixed solution;

[0024] 3) slowly adding the dopamine solution prepared in step 2) dropwise to the mixed solution in step 1), stirring at room temperature, then centrifuging and washing, and drying the washed solid to obtain a dopamine-modified inorganic filler.

[0025] The mass ratio of dopamine hydrochloride, tris(hydroxymethyl)aminomethane, and inorganic filler is: 0.1-0.5: 0.1-0.2: 0.1-0.8

[0026] Furthermore, in the above-mentioned method for preparing the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, the inorganic filler is one or more of Al2O3, TiO2, and CeO2.

[0027] Furthermore, in the above-mentioned method for preparing the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, the electrospinning voltage range of the spinning machine is 12-20 kV.

[0028] Furthermore, in the above-mentioned method for preparing the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, the ceramic nanoparticles are one or more of LATP, LLZTO, LLTO, and LLZO.

[0029] The second technical solution provided by the present invention is a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, which is prepared using the method described in the first technical solution; the sandwich structure composite electrolyte membrane consists of upper and lower PEO layers and a middle PAN layer.

[0030] The third technical solution provided by the present invention is an all-solid-state battery, comprising the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane described in the second technical solution.

[0031] The present invention has the following beneficial effects:

[0032] 1. The PEO-PAN-PEO sandwich structure composite solid electrolyte membrane provided by the present invention greatly improves the mechanical strength of the PEO-based composite solid electrolyte and broadens the electrochemical window, thereby improving the electrochemical performance of the all-solid-state battery.

[0033] 2. The technical solution provided by the present invention has a lithium affinity of the PEO layer, which reduces the interfacial resistance of the solid-state battery and accelerates the kinetics of the solid-solid transfer reaction. The PAN nanofiber layer gives the electrolyte membrane higher mechanical strength and provides a 3D lithium ion transmission channel to accelerate ion transmission. The assembled all-solid-state battery exhibits excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a structural diagram of a PEO-PAN-PEO sandwich composite solid electrolyte membrane according to an embodiment of the present invention.

[0035] Figure 2 Graph showing the tensile-stress test results for the embodiments of the present invention and the comparative example.

[0036] Figure 3 2 are LSV diagrams of the embodiments of the present invention and the comparative example.

[0037] Figure 4 This is a diagram of the electrochemical performance of the all-solid-state battery of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be further described below with reference to the accompanying drawings and specific examples, but the examples do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art.

[0039] Unless otherwise specified, the reagents and materials used in the following examples were commercially available.

[0040] Example 1

[0041] The preparation steps of the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane provided in this embodiment are as follows:

[0042] S1: Preparation of dopamine-modified inorganic filler:

[0043] Measure 12ml of deionized water into a beaker, weigh 0.5g of dopamine hydrochloride, and stir for 5 minutes to form a homogeneous solution A. Measure 100ml of deionized water into a beaker, weigh 0.1214g of tris(hydroxymethyl)aminomethane, add the mixture, and stir for 15 minutes. Then, add 0.5g of nano-alumina and continue stirring for 15 minutes until a homogeneous solution B is formed. Then, while stirring, slowly add solution A to solution B to form solution C. Seal solution C with plastic wrap and place it under magnetic stirring at room temperature for 24 hours. Solution C gradually turns black. After centrifugation and washing (5 times with ultrapure water, then twice with ethanol), the solid matter is dried (70°C for 72 hours) to obtain dopamine-modified alumina (Al2O3@PDA).

[0044] S2: Preparation of PEO suspension:

[0045] Accurately weigh 0.2g of LiTFSI (lithium bis(trifluoromethanesulfonyl imide)) powder into a glass bottle, add 8ml of acetonitrile, and stir magnetically to obtain a homogeneous solution A. Weigh 0.5g of PEO (polyethylene oxide, molecular weight 600,000) powder and 0.037g of Al2O3@PDA in an agate mortar and grind for 15 minutes to obtain a mixture B. Mixture B was added to the homogeneous solution A and magnetically stirred for 12 hours, followed by sonication for 2 hours and stabilization for 6 hours to obtain a PEO suspension.

[0046] S3: Preparation of PAN spinning solution:

[0047] 0.9 g of PAN powder and 0.1 g of LLTO (lithium lanthanum titanate) ceramic nanoparticles were accurately weighed into a glass bottle, and 10 ml of N,N-dimethylformamide (DMF) was added. The mixture was stirred magnetically to obtain a PAN spinning solution with a ceramic nanoparticle content of 10%.

[0048] S4: Preparation of PAN nanofibers:

[0049] The PAN spinning solution obtained in step S3 is electrospun in a spinning machine using a voltage of 12-20 kV to obtain PAN nanofibers.

[0050] S5: Preparation of PEO-PAN-PEO sandwich structure composite solid electrolyte membrane:

[0051] In a glove box, the PEO suspension obtained in S2 was first cast on one side of the PAN nanofiber and then allowed to stand in the glove box for 6 hours to allow the solvent to evaporate. The PEO suspension was then cast on the other side of the PAN nanofiber. After the solvent initially evaporated at room temperature, it was transferred to a vacuum oven and dried at 60°C for 24 hours to completely remove the solvent. A PEO-PAN-PEO sandwich structure composite solid electrolyte membrane was obtained. The structure diagram is shown in Figure 1 .

[0052] Example 2

[0053] The mass of PAN in step S3 of Example 1 was adjusted to 0.95 g, and the mass of LLTO was adjusted to 0.05 g. The other steps were the same as those in Example 1.

[0054] Example 3

[0055] The mass of PAN in step S3 of Example 1 was adjusted to 0.8 g, and the mass of LLTO was adjusted to 0.2 g. The other steps were the same as those in Example 1.

[0056] Example 4

[0057] The LLTO in step S3 of Example 1 was adjusted to LATP (lithium aluminum titanium phosphate), and the other steps were the same as in Example 1.

[0058] Example 5

[0059] The LLTO in step S3 of Example 1 was adjusted to LLZO (lithium lanthanum zirconium oxide), and the other steps were the same as in Example 1.

[0060] Comparative Example 1

[0061] By EO:Li + Accurately weigh 0.2g of LiTFSI powder in a 16:1 molar ratio into a glass bottle, add 8ml of acetonitrile, and stir magnetically to obtain a homogeneous solution A. Weigh 0.5g of PEO (molecular weight 600,000) powder and 0.037g of Al2O3@PDA in an agate mortar and grind them for 15 minutes to obtain a mixture B. Add mixture B to the homogeneous solution A, stir magnetically for 12 hours, then sonicate and let it stand for 6 hours to obtain a casting solution. Pour the casting solution obtained above into a silica gel mold with an inner diameter of 50mm×50mm×5mm. After the acetonitrile solvent evaporates naturally at room temperature for 12 hours to form a film, transfer it to a vacuum oven at 60°C and dry it for 24 hours to completely remove the acetonitrile, thereby obtaining a single-layer PEO composite solid electrolyte membrane.

[0062] Comparative Example 2

[0063] By EO:Li + Accurately weigh 0.2g of LiTFSI powder in a 16:1 molar ratio into a glass bottle, add 8ml of acetonitrile, and stir magnetically to obtain a homogeneous solution A. Weigh 0.5g of PEO (molecular weight 600,000) powder and 0.037g of Al2O3 in an agate mortar and grind for 15 minutes to obtain a mixture B. Add mixture B to the homogeneous solution A, stir magnetically for 12 hours, then sonicate and let it stand for 6 hours to obtain a casting solution. Pour the resulting casting solution into a silica gel mold with an inner diameter of 50mm×50mm×5mm. After the acetonitrile solvent evaporates naturally at room temperature for 12 hours to form a film, transfer it to a vacuum oven at 60°C and dry it for 24 hours to completely remove the acetonitrile, thereby obtaining a single-layer PEO composite solid electrolyte membrane.

[0064] Comparative Example 3

[0065] By EO:Li +0.2g of LiTFSI powder was accurately weighed into a glass bottle at a molar ratio of 16:1. 8ml of acetonitrile was added and magnetically stirred to obtain a homogeneous solution A. 0.5g of PEO (molecular weight 600,000) powder was weighed and added to the homogeneous solution A. The solution was magnetically stirred for 12 hours, then sonicated and allowed to stand for 6 hours to obtain a casting solution. The resulting casting solution was poured into a silicone mold with an inner diameter of 50mm x 50mm x 5mm. The acetonitrile solvent was allowed to evaporate naturally at room temperature for 12 hours to form a film. The film was then dried in a vacuum oven at 60°C for 24 hours to completely remove the acetonitrile, resulting in a single-layer PEO composite solid electrolyte membrane.

[0066] Experimental Example 1: Performance test of an all-solid-state battery prepared using the PEO composite solid electrolyte in the present invention.

[0067] The PEO composite solid electrolyte membrane obtained in Example 1 was assembled into a CR2032 button cell according to conventional operations in the art.

[0068] Positive electrode preparation: Lithium iron phosphate (LiFePO4) was mixed with superP conductive agent and PVDF in a mass ratio of 8:2:1. N-methylpyrrolidone (NMP) was added to create a slurry, which was then coated onto aluminum foil to form the positive electrode. After vacuum drying, the slurry was cut into 13mm diameter discs. The resulting electrode was then assembled into CR2023 button cells.

[0069] The charge and discharge performance of the above batteries were tested using a Xinwei charge and discharge tester in the voltage range of 2.8-4.0V. The long cycle performance test was performed on the all-solid-state lithium metal batteries prepared from the PEO composite solid electrolyte membranes obtained in Examples 1-5 and Comparative Examples 1-3 at a rate of 0.5C; the linear cyclic voltammetry (LSV) curve test was performed on the button batteries prepared from the PEO-based composite solid electrolyte membranes obtained in Examples and Comparative Examples. The results are as follows: Figures 3 and 4 shown.

[0070] from Figure 3 It can be seen that the electrochemical window of Example 1 reaches 5.1V, and the electrochemical windows of Examples 2 and 3 also reach 4.75V and 4.8V; while the electrochemical window of Comparative Example 1 is only 4.6V; this indicates that the designed PEO-PAN-PEO sandwich structure composite solid electrolyte effectively broadens the electrochemical window of the PEO composite solid electrolyte.

[0071] from Figure 4 It can be seen that the composite solid electrolyte prepared in Example 1 has a first cycle discharge capacity of 168.8 mAh g at 0.5C. -1 ; After 400 cycles, the discharge capacity is 131.2 mAh g -1; Capacity retention rate is 77.7%; The composite solid electrolyte prepared in Example 2 has a first cycle discharge capacity of 166.6 mAh g at 0.5C -1 After 337 cycles, the discharge capacity is 126.3 mAh g -1 ; Capacity retention rate is 75.8%; The composite solid electrolyte prepared in Example 3 has a first cycle discharge capacity of 157.13 mAh g at 0.5C -1 ; After 400 cycles, the discharge capacity is 110.1 mAh g -1 ; Capacity retention rate is 70.1%; The composite solid electrolyte prepared in Example 4 has a first cycle discharge capacity of 168.5 mAh g at 0.5C -1 After 294 cycles, the discharge capacity is 131.7 mAh g -1 ; Capacity retention rate is 78.1%; The composite solid electrolyte prepared in Example 5 has a first cycle discharge capacity of 152.2 mAh g at 0.5C -1 ; After 400 cycles, the discharge capacity is 110.8 mAh g -1 ; The capacity retention rate is 72.8%; the composite solid electrolyte prepared in Comparative Example 1 has a first cycle discharge capacity of 151.3 mAh g at 0.5C -1 After 328 cycles, the discharge capacity is 98.2 mAh g -1 ; The capacity retention rate is 64.9%; the composite solid electrolyte prepared in Comparative Example 2 has a first cycle discharge capacity of 142.9 mAh g at 0.5C -1 After 181 cycles, the discharge capacity is 123.9 mAh g -1 ; The capacity retention rate is 86.7%; the composite solid electrolyte prepared in Comparative Example 3 has a first cycle discharge capacity of 131.3 mAh g at 0.5C -1 After 303 cycles, the discharge capacity is 63.2 mAh g -1 ; The capacity retention rate is 48.1%; This shows that the prepared PEO composite solid electrolyte has a higher discharge specific capacity, a lower capacity attenuation rate and better long-cycle stability.

[0072] The tensile-stress test can reflect the mechanical strength of the electrolyte membrane. Figure 2 The stress-strain curves show that Example 1 has the highest mechanical toughness, with a tensile strength of 2.06 MPa. Examples 2 and 3 have tensile strengths of 1.64 MPa and 1.28 MPa, respectively. Comparative Examples 1-3, by contrast, have lower tensile strengths of 0.71 MPa, 0.173 MPa, and 0.123 MPa, respectively. This demonstrates that the designed PEO-PAN-PEO sandwich composite solid electrolyte membrane further enhances mechanical properties.

[0073] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, characterized in that: The following steps are included in sequence: 1) mixing the dopamine-modified inorganic filler and PEO powder in a mortar at a mass ratio of 0.007-0.07:0.2-1.0 to obtain a mixture; 2) adding lithium salt to an organic solvent and mixing to form a uniform lithium salt solution; 3) adding the mixture obtained in step 1) to the lithium salt solution in step 2) and continuing to stir until uniform, thereby obtaining a PEO suspension; In step 3), the mass ratio of PEO to lithium salt is 0.2-1.0:0.1-0.5; 4) Dissolving ceramic nanoparticles and PAN powder in a solvent at a mass ratio of 0.026-0.5:0.5-2.0 and stirring to obtain a spinning suspension; 5) electrospinning the spinning suspension obtained in step 4) in a spinning machine to obtain PAN nanofibers; 6) casting the suspension obtained in step 3) on both sides of the PAN nanofibers obtained in step 5), and drying to obtain a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane; The ceramic nanoparticles in step 4) are one or more of LATP, LLZTO, LLTO, and LLZO; The inorganic filler in step 1) is one or more of Al2O3, TiO2, and CeO2.

2. The method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 1, characterized in that: The organic solvent in step 2) is acetonitrile, and the solvent in step 4) is N,N-dimethylformamide.

3. The method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 1, characterized in that: The lithium salt in step 2) is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium difluorooxalatoborate, and lithium bis(fluorosulfonyl)imide.

4. The method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 1, characterized in that: The concentration of the lithium salt solution is 0.02 mol / L-0.36 mol / L.

5. The method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 1, characterized in that: The drying in step 6) is carried out at 60° C. for 24 hours; and the voltage of the spinning machine during the electrospinning in step 5) is 12-20 kV.

6. The method for preparing a PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 1, characterized in that: The dopamine-modified inorganic filler is prepared by the following method: S1) dissolving dopamine hydrochloride in deionized water with magnetic stirring until completely dissolved to obtain a dopamine solution; S2) dissolving tris(hydroxymethyl)aminomethane in deionized water, adding no filler after complete dissolution, and performing magnetic stirring to form a mixed solution; S3) slowly adding the dopamine solution prepared in S1) dropwise to the mixed solution described in S2), stirring at room temperature, then centrifuging and washing, and drying the washed solid to obtain a dopamine-modified inorganic filler; The mass ratio of dopamine hydrochloride, tris(hydroxymethyl)aminomethane and inorganic filler is: 0.1-0.5: 0.1-0.2: 0.1-0.8g.

7. A PEO-PAN-PEO sandwich structure composite solid electrolyte membrane, characterized in that: Prepared by the method described in any one of claims 1 to 6.

8. The PEO-PAN-PEO sandwich structure composite solid electrolyte membrane according to claim 7, characterized in that: The sandwich structure composite solid electrolyte membrane consists of upper and lower PEO layers and a middle PAN layer.

9. An all-solid-state battery, characterized in that: It includes the PEO-PAN-PEO sandwich structure composite solid electrolyte membrane as described in claim 8.

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