Solid electrolyte modified by polymer ionic liquid composite interface layer and preparation method thereof

Abstract

The present invention belongs to the field of solid-state lithium-ion batteries, relates to solid electrolytes, and specifically relates to a solid electrolyte modified by a polymer ionic liquid composite interface layer and a preparation method thereof. It includes solid LAGP, the solid LAGP is a non-powdery solid, a polymer ionic liquid composite interface layer is provided on the surface of the solid LAGP, the material of the polymer ionic liquid composite interface layer is a mixture of a polymer ionic liquid and LLZTO powder filler, the polymer ionic liquid is PDDA-TFSI, and the PDDA-TFSI is obtained by an anion reaction of poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide. The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention has better interfacial compatibility with the lithium negative electrode, improves interfacial wettability, effectively inhibits the growth of lithium dendrites, and has a simple preparation method and has the prospect of industrial application.

Description

Technical Field

[0001] The present invention belongs to the field of solid-state lithium-ion batteries, relates to solid electrolytes, and particularly relates to a solid electrolyte modified by a polymer ionic liquid composite interface layer and a preparation method thereof. Background Art

[0002] Disclosing the information of this background art section is only intended to enhance the overall understanding of the present invention, and is not necessarily to be regarded as an admission or an implication in any form that this information constitutes the prior art already known to those of ordinary skill in the art.

[0003] Using a lithium-ion solid electrolyte to replace a liquid organic electrolyte to prepare a solid-state lithium battery is one of the effective ways to achieve high safety and high energy density of the battery. So far, the lithium-ion conductivity and electrochemical window of the inorganic solid electrolyte LAGP have reached a relatively high level, but the inorganic solid-state battery still cannot exhibit high electrochemical performance up to now. The poor interface contact and interface reaction at the inorganic solid electrolyte / metal lithium anode interface have become serious obstacles to the application of the metal lithium anode. On the one hand, the poor wetting between the metal lithium anode and the inorganic solid electrolyte results in a large interfacial resistance. On the other hand, the interface reaction at the inorganic solid electrolyte / metal lithium anode interface leads to the formation of an interfacial layer, which hinders the migration of Li + ions, causing the battery performance to decline. In addition, lithium dendrites grow and penetrate the solid electrolyte in the solid-state battery, causing an internal short circuit in the solid-state battery, leading to serious safety hazards in the solid-state battery. Adding an interface buffer layer between the inorganic solid electrolyte LAGP and metal lithium is an effective modification method.

[0004] According to the inventor's research and understanding, the material of the interface buffer layer can be a polymer or a gel electrolyte. For example, a polymer gel electrolyte 3DCPE has been proposed as an interface buffer layer between the inorganic solid electrolyte LAGP and metal lithium. It is prepared by adding a certain proportion of PEGDE and DPPO to a DMF solution of PVDF-HFP, stirring evenly, spreading the solution on a polytetrafluoroethylene plate, and heating at 80 °C for 48 hours to evaporate DMF to obtain the 3DCPE gel polymer electrolyte. The "sandwich" structure is used to place it between LAGP and metal lithium, thus playing a role in preventing LAGP from being reduced by metal lithium and improving the interface contact. However, the thickness of the gel electrolyte 3DCPE used in this scheme is as high as 100 microns, so it instead reduces the transmission rate of lithium ions inside the battery; and the mechanical properties of the gel electrolyte are poor, and it is often easily penetrated by dendritic lithium dendrites during charge and discharge, resulting in a short circuit. Summary of the Invention

[0005] To solve the deficiencies of the prior art, the object of the present invention is to provide a solid electrolyte modified with a polymer ionic liquid composite interface layer and a preparation method thereof. The solid electrolyte modified with the polymer ionic liquid composite interface layer provided by the present invention has better interfacial compatibility, improves interfacial wettability, and effectively inhibits the growth of lithium dendrites.

[0006] To achieve the above object, the technical solution of the present invention is as follows:

[0007] On the one hand, a solid electrolyte modified with a polymer ionic liquid composite interface layer, including solid LAGP, the solid LAGP is non-powdery solid, a polymer ionic liquid composite interface layer is provided on the surface of the solid LAGP, and the material of the polymer ionic liquid composite interface layer is a mixture of a polymer ionic liquid and LLZTO powder filler. The polymer ionic liquid is PDDA-TFSI, and the PDDA-TFSI is obtained by anionic reaction of poly(diallyldimethylammonium chloride) (PDDA-Cl) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0008] The material of the polymer ionic liquid composite interface layer of the present invention is a mixture of PDDA-TFSI and LLZTO powder filler. As a physical barrier, it can effectively prevent the LAGP electrolyte from being reduced by metallic lithium. At the same time, it has good flexibility to buffer the volume change of the lithium negative electrode during charge and discharge. Moreover, the LLZTO filler enhances the mechanical properties of the interface layer, thereby improving the ability to inhibit the growth of lithium dendrites.

[0009] On the other hand, a preparation method of a solid electrolyte modified with a polymer ionic liquid composite interface layer includes the following steps:

[0010] Perform anionic reaction on poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide to obtain a polymer ionic liquid, that is, PDDA-TFSI;

[0011] Dissolve PDDA-TFSI, add LLZTO powder filler and mix evenly to obtain a mixed solution, and drop the mixed solution onto the surface of solid LAGP and dry it to obtain.

[0012] The solid electrolyte modified with the polymer ionic liquid composite interface layer (PTL) prepared by the present invention can significantly improve the wettability with metallic lithium, improve the interfacial contact, and the preparation method is simple, having the prospect of industrial application.

[0013] In the third aspect, an application of the above solid electrolyte modified with a polymer ionic liquid composite interface layer in a solid-state lithium-ion battery.

[0014] The solid electrolyte modified by the polymer ionic liquid composite interface layer prepared by the present invention has better interfacial compatibility and exhibits a cycle life of more than 200 cycles when applied to solid-state lithium-ion batteries.

[0015] The beneficial effects of the present invention are as follows:

[0016] (1) The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention significantly improves the interfacial wettability with the lithium metal anode.

[0017] (2) The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention has a high ionic conductivity, which is conducive to the rapid transport of lithium ions at the interface.

[0018] (3) The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention has good comprehensive mechanical properties and effectively inhibits the growth of lithium dendrites.

[0019] (4) The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention has good flame retardancy;

[0020] (5) The solid electrolyte modified by the polymer ionic liquid composite interface layer provided by the present invention exhibits a cycle life of more than 200 cycles when applied to solid-state lithium-ion batteries;

[0021] (6) The preparation method provided by the present invention is simple and can be realized for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0023] Figure 1 It is the infrared spectra of poly(diallyldimethylammonium chloride) (PDDA-Cl) and PDDA-TFSI in the examples of the present invention;

[0024] Figure 2 It is the planar scanning electron micrographs of the solid electrolyte modified by the polymer ionic liquid composite interface layer (a) and the surface-unmodified LAGP electrolyte (b) in the examples of the present invention; (c) is the cross-sectional scanning micrograph of the solid electrolyte modified by the polymer ionic liquid composite interface layer;

[0025] Figure 3 It is the impedance diagrams of the solid electrolyte modified by the polymer ionic liquid composite interface layer and the surface-unmodified LAGP electrolyte in the examples of the present invention;

[0026] Figure 4Comparison of the lithiophilicity of the solid electrolyte modified by the composite interface layer of unmodified LAGP solid electrolyte and polymer ionic liquid in the embodiment of the present invention;

[0027] Figure 5 XPS spectra of the surface of the solid electrolyte modified by the polymer ionic liquid composite interface layer and the unmodified LAGP electrolyte in the embodiment of the present invention;

[0028] Figure 6 Thermal stability comparison diagram of the unmodified LAGP solid electrolyte (a) and the solid electrolyte modified by the polymer ionic liquid composite interface layer (b) in the embodiment of the present invention;

[0029] Figure 7 Cycling curve of the electrochemical performance of the solid-state lithium-ion battery using the solid electrolyte modified by the polymer ionic liquid composite interface layer in the embodiment of the present invention, with lithium iron phosphate (LFP) as the positive electrode material and metallic lithium as the negative electrode. Detailed implementation mode

[0030] It should be noted that the following detailed description is exemplary and is intended to provide further illustration of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0031] It should be noted that the terms used herein are only for describing specific implementation modes and are not intended to limit the exemplary implementation modes according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0032] In order to improve the interfacial compatibility and wettability of the solid electrolyte and inhibit the growth of lithium dendrites, the present invention proposes a solid electrolyte modified by a polymer ionic liquid composite interface layer and a preparation method thereof.

[0033] A typical implementation mode of the present invention provides a solid electrolyte modified by a polymer ionic liquid composite interface layer, including solid LAGP. The solid LAGP is a non-powdery solid, and a polymer ionic liquid composite interface layer is provided on the surface of the solid LAGP. The material of the polymer ionic liquid composite interface layer is a mixture of a polymer ionic liquid and LLZTO powder filler. The polymer ionic liquid is PDDA-TFSI, and the PDDA-TFSI is obtained by anionic reaction of poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide.

[0034] The non-powdery solid described in the present invention is, for example, sheet-like, block-like, columnar, etc.

[0035] In some embodiments, the LLZTO powder filler is 5-15% of the mass of PDDA-TFSI.

[0036] In some embodiments, the thickness of the polymer ionic liquid composite interface layer is 2-8 μm.

[0037] Another embodiment of the present invention provides a method for preparing a solid electrolyte modified with a polymer ionic liquid composite interface layer, comprising the following steps:

[0038] An anion reaction is carried out between poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide to obtain a polymer ionic liquid, namely PDDA-TFSI;

[0039] PDDA-TFSI is dissolved, LLZTO powder filler is added and mixed evenly to obtain a mixed solution, and the mixed solution is drop-coated onto the surface of solid LAGP and dried to obtain.

[0040] In some embodiments, the molar ratio of lithium bis(trifluoromethanesulfonyl)imide to the monomer unit of poly(diallyldimethylammonium chloride) is 1.0-1.5:1. The weight-average molecular weight of the poly(diallyldimethylammonium chloride) described in the present invention is 400,000-500,000.

[0041] The anion reaction described in the present invention belongs to a metathesis reaction, that is, a reaction in which the chloride ions in poly(diallyldimethylammonium chloride) are exchanged with bis(trifluoromethanesulfonyl)imide in lithium bis(trifluoromethanesulfonyl)imide. In some embodiments, the operation process of the anion reaction is: adding a lithium bis(trifluoromethanesulfonyl)imide solution to a poly(diallyldimethylammonium chloride) solution and stirring for reaction.

[0042] In some embodiments, N-methylpyrrolidone (NMP) is used to dissolve PDDA-TFSI. The concentration of PDDA-TFSI in the solution after dissolving PDDA-TFSI is 0.3-0.8 g / ml.

[0043] In some embodiments, the LLZTO powder filler is 5-15% of the mass of PDDA-TFSI.

[0044] In some embodiments, the solid LAGP is in sheet form, and the LAGP powder is pressed into a tablet and sintered to obtain sheet-like LAGP.

[0045] In one or more embodiments, the pressure (pressure) during tableting is 200-300 MPa.

[0046] In one or more embodiments, the sintering temperature is 800-900 °C. The sintering time is 10-15 h.

[0047] Specifically, the following steps are included:

[0048] (1) Weigh an appropriate amount of LAGP electrolyte powder and put it into a tablet pressing mold. Then, obtain a LAGP electrolyte tablet through tablet pressing, and obtain a dense LAGP electrolyte tablet after sintering. Polish the surface smooth with sandpaper;

[0049] (2) Weigh an appropriate amount of poly(diallyldimethylammonium chloride) (PDDA-Cl) at room temperature and dilute it with an appropriate amount of deionized water. At the same time, weigh lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and dissolve it in an appropriate amount of deionized water. Then, dropwise add the LiTFSI aqueous solution during magnetic stirring;

[0050] (3) Collect the precipitate PDDA-TFSI by suction filtration and washing with deionized water and absolute ethanol respectively. Then, dry it at 65 - 75 °C for 24 - 36 hours to obtain white PDDA-TFSI powder;

[0051] (4) Weigh an appropriate amount of PDDA-TFSI powder at room temperature and dissolve it in NMP. Stir magnetically at room temperature until dissolved;

[0052] (5) Add an appropriate amount of LLZTO powder to the above solution, continue magnetic stirring for 10 - 12 hours, and ultrasonicate for 20 - 40 minutes to obtain a homogeneous mixed solution;

[0053] (6) Use a pipette gun to extract an appropriate amount of the solution and evenly coat it on both sides of the surface of the LAGP electrolyte polished smooth. Then, dry it at 55 - 65 °C for 3 - 5 hours to obtain a surface-modified solid electrolyte.

[0054] The third embodiment of the present invention provides an application of the above polymer ionic liquid composite interfacial layer modified solid electrolyte in a solid-state lithium-ion battery.

[0055] Specifically, the solid-state lithium-ion battery is composed of a positive electrode, the polymer ionic liquid composite interfacial layer modified solid electrolyte, and a metallic lithium negative electrode.

[0056] More specifically, the positive electrode material of the positive electrode is lithium iron phosphate, lithium cobaltate, lithium manganate, or a ternary lithium positive electrode material.

[0057] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0058] Example 1

[0059] The preparation method of the polymer ionic liquid composite interfacial layer modified solid electrolyte is as follows:

[0060] Step 1: Weigh 0.5 g of LAGP electrolyte powder and put it into a tablet press mold with a diameter of 16 mm. Then, press it with a tablet press under a pressure of 300 MPa to obtain a LAGP electrolyte sheet.

[0061] Step 2: After sintering in a muffle furnace at 850 °C for 12 hours, a dense LAGP electrolyte sheet is obtained, and the surface is polished smoothly with 800-mesh and 1500-mesh sandpapers respectively.

[0062] Step 3: Weigh 5.11 g (18 mmol) of LiTFSI at room temperature and add it to 24 ml of deionized water, stir to dissolve. At the same time, weigh 12.17 g of PDDA-Cl (weight average molecular weight is 4500000, and the molar amount of PDDA-Cl units is 15.1 mmol), add it to 60 ml of deionized water and stir to dilute. Then, during magnetic stirring, all the above-obtained LiTFSI aqueous solution is added dropwise, and continue to stir for 2 hours.

[0063] Step 4: Filter and wash with deionized water and absolute ethanol respectively to collect the precipitate PDDA-TFSI, and then dry it at 70 °C for 30 hours to obtain white PDDA-TFSI powder.

[0064] Step 5: Weigh 0.6 g of PDDA-TFSI powder at room temperature, then add 2.0 ml of NMP, and stir magnetically at room temperature until dissolved.

[0065] Step 6: Weigh 0.06 g of LLZTO powder and add it to the solution obtained in step (3), continue magnetic stirring for 12 hours, and ultrasonic for 30 minutes to obtain a uniform mixed solution.

[0066] Step 7: Use a pipette to extract 20 μL of the above-obtained mixed solution, evenly coat it on both sides of the surface of the polished LAGP electrolyte, and then dry it at 60 °C for 4 hours to obtain a surface-modified solid electrolyte.

[0067] Comparative Example 1: Prepare a LAGP electrolyte sheet with an unmodified surface, which only includes steps 1 and 2 of the above Example 1.

[0068] Example 2: Assemble a coin cell with the above-obtained solid electrolyte and a positive electrode sheet in a glove box according to a conventional experiment, and conduct a rate discharge performance test.

[0069] Comparative Example 2: Just change the solid electrolyte modified with a polymer ionic liquid composite interface layer to a LAGP electrolyte sheet with an unmodified surface in Comparative Example 1, and the remaining steps are the same as those in Example 2.

[0070] Figure 1are the infrared spectra of poly(diallyldimethylammonium chloride) (PDDA-Cl) and PDDA-TFSI. As can be seen from the figure, infrared peaks corresponding to the initial polymer with chloride anions were observed at 3391 cm -1 . However, after the anion exchange reaction, this peak disappeared, and new peaks corresponding to TFSI anions appeared at 1354, 1194, 1136, and 1053 cm -1 . Figure 2 (a) and (b) are the comparison of the plane scanning electron micrographs of the solid electrolyte modified with the polymer ionic liquid composite interface layer and the surface-unmodified LAGP electrolyte. As can be seen from the figure, the surface of the modified electrolyte is flatter and smoother, and the LLZTO fillers are evenly distributed, which is beneficial to improving the wettability to metallic lithium; (c) is the cross-sectional scanning micrograph of the solid electrolyte modified with the polymer ionic liquid composite interface layer, indicating that the PTL interface layer is tightly attached to the surface of the electrolyte, with a thickness of about 5 μm. Figure 3 is the impedance diagram of the solid electrolyte modified with the polymer ionic liquid composite interface layer and the surface-unmodified LAGP electrolyte, indicating that the modified solid electrolyte has better interfacial compatibility with metallic lithium. Figure 4 Intuitively compares the lithiophilicity of the surface-unmodified LAGP electrolyte and the solid electrolyte modified with the polymer ionic liquid composite interface layer, indicating that the PTL layer improves the interfacial contact. Figure 5 is the XPS spectrum of the surface of the solid electrolyte modified with the polymer ionic liquid composite interface layer and the surface-unmodified LAGP electrolyte, indicating that the PTL interface layer effectively protects LAGP from being reduced by metallic lithium. Figure 6 Verifies the comparison of the thermal stability of the surface-unmodified LAGP electrolyte and the solid electrolyte modified with the polymer ionic liquid composite interface layer, proving that the PTL interface layer has good flame retardancy. As can be seen from Figure 7 , the full cell using the solid electrolyte modified with the polymer ionic liquid composite interface layer can be stably cycled 200 times.

[0071] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A solid electrolyte modified by a polymer ionic liquid composite interface layer, characterized in that, It includes a solid-state LAGP, the solid-state LAGP being non-powdery solid. A polymer ionic liquid composite interface layer is provided on the surface of the solid-state LAGP. The material of the polymer ionic liquid composite interface layer is a mixture of a polymer ionic liquid and LLZTO powder filler. The polymer ionic liquid is PDDA-TFSI, and the PDDA-TFSI is obtained by an anion reaction of poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide.

2. The solid electrolyte modified by the polymer ionic liquid composite interface layer as described in claim 1, wherein The LLZTO powder filler is 5 to 15% of the mass of the PDDA-TFSI.

3. The solid electrolyte modified by the polymer ionic liquid composite interface layer as described in claim 1, wherein, The thickness of the polymer ionic liquid composite interface layer is 2 to 8 μm.

4. A preparation method of a solid electrolyte modified by a polymer ionic liquid composite interface layer, characterized in that It includes the following steps: An anion reaction is carried out on poly(diallyldimethylammonium chloride) and lithium bis(trifluoromethanesulfonyl)imide to obtain a polymer ionic liquid, namely PDDA-TFSI. The PDDA-TFSI is dissolved, LLZTO powder filler is added and mixed evenly to obtain a mixed solution, and the mixed solution is drop-coated onto the surface of the solid-state LAGP and dried to obtain the product.

5. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer according to claim 4, characterized in that, The molar ratio of lithium bis(trifluoromethanesulfonyl)imide to the monomer unit of poly(diallyldimethylammonium chloride) is 1.0 to 1.5:

1.

6. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer as claimed in claim 4, characterized in that, The operation process of the anion reaction is: adding a lithium bis(trifluoromethanesulfonyl)imide solution to a poly(diallyldimethylammonium chloride) solution and stirring for reaction.

7. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer according to claim 4, characterized in that, N-methylpyrrolidone is used to dissolve the PDDA-TFSI. Or, the LLZTO powder filler is 5 to 15% of the mass of the PDDA-TFSI.

8. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer according to claim 7, characterized in that, The concentration of PDDA-TFSI in the solution after dissolving the PDDA-TFSI is 0.3 to 0.8 g / ml.

9. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer according to claim 4, characterized in that, The solid-state LAGP is in sheet form, and the LAGP powder is pressed and sintered to obtain the sheet-shaped LAGP.

10. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer according to claim 9, characterized in that, The pressure during pressing is 200 to 300 MPa.

11. The preparation method of the solid electrolyte modified by the polymer ionic liquid composite interface layer as described in claim 9, characterized in that, The sintering temperature is 800 to 900 °C.

12. Application of the solid electrolyte modified with the polymer ionic liquid composite interface layer according to any one of claims 1 to 3 or the solid electrolyte modified with the polymer ionic liquid composite interface layer obtained by the preparation method according to any one of claims 4 to 11 in a solid-state lithium-ion battery.

13. The application according to claim 12, characterized in that, The solid-state lithium-ion battery is composed of a positive electrode, the solid electrolyte modified with the polymer ionic liquid composite interface layer, and a metallic lithium negative electrode.

14. The application according to claim 13, characterized in that, The positive electrode material of the positive electrode is lithium iron phosphate, lithium cobaltate, lithium manganate, or a ternary lithium positive electrode material.

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