A solvent-free LLZO-based composite solid electrolyte and its preparation method and application

Abstract

The present invention discloses a solvent-free LLZO-based composite solid electrolyte and its preparation method and application, comprising the following steps: reacting poly (diallyldimethylammonium) bis (fluorosulfonyl) imide (PDADMAFSI), lithium bis (fluorosulfonyl) imide (LiFSI) and N-butyl-N-methylpyrrolidine bis (trifluoromethylsulfonyl) imide (PyR 13 The method comprises the following steps: mixing lithium lanthanum zirconium oxide solid electrolyte powder and polytetrafluoroethylene (PTFE) in a molar ratio of 1:1 to 1.5:2 to 4, stirring at 70 to 90° C. to obtain a solid ion gel; mixing lithium lanthanum zirconium oxide solid electrolyte powder and polytetrafluoroethylene (PTFE) by ball milling for a set time, wherein the PTFE accounts for 2 to 5 wt.% of the total mass of the lithium lanthanum zirconium oxide solid electrolyte and the PTFE; then adding the ion gel in proportion, continuing ball milling until the mixture is uniform, and the mass ratio of the ion gel to the PTFE is 5 to 10:1, thereby obtaining a solid electrolyte.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolytes, and in particular relates to a solvent-free LLZO-based composite solid electrolyte and a preparation method and application thereof. Background Art

[0002] The statements herein merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Lithium-ion batteries have become an important source of power for electric vehicles and grid-scale energy storage. However, traditional lithium-ion batteries use flammable liquid electrolytes and flammable organic polymer separators, which pose safety risks during use, and their energy density is gradually approaching the theoretical limit. In this context, the development of all-solid-state batteries, replacing flammable liquid electrolytes and organic separators with inorganic solid electrolytes, is considered a strategic approach to spontaneously improve energy density and safety. Among them, garnet-type solid electrolytes LLZO have attracted great research interest due to their many advantages, including low cost, high lithium-ion conductivity, high Young's modulus, high electrochemical stability, wide electrochemical window, and good compatibility with lithium metal. However, due to the high hardness of LLZO-based solid electrolytes, large-scale production of solid electrolyte membranes still faces great challenges.

[0004] Polymer solid electrolytes (SPEs) have been widely studied due to their excellent flexibility, film-forming ability, and compatibility with positive and negative electrodes. However, polymer solid electrolytes have low lithium ion conductivity, low Young's modulus values, and poor thermal stability, which limit their use in large-scale applications. To address this problem, garnet solid electrolytes and polymer solid electrolytes have been used to fabricate composite electrolyte membranes. Composite electrolyte membranes have the excellent flexibility and processability of polymer solid electrolytes and the excellent mechanical strength, thermal stability, and excellent lithium ion conductivity of garnet electrolytes. However, the main method for preparing LLZO-SPE-based composite electrolyte membranes is the casting method. However, casting requires toxic and expensive organic solvents, which reduces the practical applicability of using this method to prepare electrolyte membranes. In addition, solvent evaporation requires an energy-consuming heating process, which is not conducive to achieving zero-emission manufacturing.

[0005] In recent years, the use of polytetrafluoroethylene (PTFE) fiberization technology to interweave inorganic solid electrolytes into independent solid electrolyte membranes has attracted much attention. Its preparation process does not require any solvents. For example, a study pre-mixed and ground garnet-type electrolyte powder and commercial PTFE powder, and then rolled at room temperature to produce a garnet solid electrolyte membrane. However, due to the high hardness of the garnet-type electrolyte, the self-supporting electrolyte membrane obtained using this method has obvious gaps between the particles, which seriously hinders the transmission of lithium ions and reduces the overall ionic conductivity of the electrolyte. In addition, there are side reactions between PTFE and metallic lithium, which increases the interfacial resistance and thus reduces the battery efficiency. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a solvent-free LLZO-based composite solid electrolyte, its preparation method, and its application. The solvent-free LLZO-based composite solid electrolyte provided by the present invention not only enhances interfacial conduction between electrolyte particles, improving ionic conductivity, but also hinders side reactions between the PTFE binder and metallic lithium, preventing the formation of a degraded interface, thereby improving the cycle life and structural stability of the full battery.

[0007] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a LLZO-based composite solid electrolyte by a solvent-free method, comprising the following steps:

[0009] Poly (diallyldimethylammonium) bis (fluorosulfonyl) imide (PDADMAFSI), lithium bis (fluorosulfonyl) imide (LiFSI) and N-butyl-N-methylpyrrolidinobis (trifluoromethylsulfonyl) imide (PyR 13 FSI) are mixed in a molar ratio of 1:1-1.5:2-4, and stirred at 70-90° C. to obtain a solid ion gel;

[0010] Lithium lanthanum zirconium-based solid electrolyte powder and polytetrafluoroethylene (PTFE) are mixed and ball-milled for a set time, with PTFE accounting for 2 to 5 wt.% of the total mass of the lithium lanthanum zirconium-based solid electrolyte and PTFE; then the ion gel is added thereto in proportion, and ball-milling is continued until the mixture is uniform, with a mass ratio of ion gel to PTFE of 5 to 10:1, thereby obtaining a solid electrolyte.

[0011] In some embodiments, PDADMAFSI, lithium bis(fluorosulfonyl)imide (LiFSI), and PyR 13 The FSI mixing and stirring time is 12 to 18 hours.

[0012] In some embodiments, the lithium lanthanum zirconium oxide solid electrolyte powder and PTFE are mixed and ball-milled for 0.5-2 hours at a rotation speed of 200-300 rpm.

[0013] Preferably, after the ion gel is added, the ball milling time is continued for 1-3 hours, and the ball milling speed is 500-800 rpm.

[0014] In some embodiments, the lithium lanthanum zirconium oxide solid electrolyte is selected from one of LLZO, LLZTO, LLZNO or LALZO.

[0015] In some embodiments, the process further includes hot rolling the prepared solid electrolyte and then rolling it to reduce the thickness to a set value to obtain an electrolyte membrane.

[0016] Preferably, the hot rolling temperature is 80-90°C.

[0017] Preferably, the electrolyte membrane is rolled and thinned using a double-roller machine, and the temperature of the rolling and thinning is 80-90°C.

[0018] Preferably, the thickness of the obtained electrolyte membrane is 80-100 μm.

[0019] In a second aspect, the present invention provides a solvent-free LLZO-based composite solid electrolyte prepared by the preparation method.

[0020] In a third aspect, the present invention provides the use of the solvent-free LLZO-based composite solid electrolyte in the preparation of solid-state lithium-ion batteries.

[0021] In some embodiments, the positive electrode material of the solid-state lithium-ion battery is lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide or a ternary lithium positive electrode material.

[0022] The beneficial effects achieved by one or more embodiments of the present invention are as follows:

[0023] (1) The solvent-free LLZO-based composite solid electrolyte particles provided by the present invention are filled with ion gel with a certain viscoelasticity, so the internal contact of the electrolyte is tight without gaps, which is beneficial to inhibiting the growth of lithium dendrites.

[0024] (2) The solvent-free LLZO-based composite solid electrolyte provided by the present invention forms a continuous ion transmission channel inside, thereby having high ionic conductivity, which is conducive to the rapid transmission of lithium ions inside the electrolyte and at the interface;

[0025] (3) The solvent-free LLZO-based composite solid electrolyte provided by the present invention has good flexibility and processability under the dual effects of PTFE binder and ion gel;

[0026] (4) The solvent-free LLZO-based composite solid electrolyte provided by the present invention hinders the side reaction between the PTFE binder and metallic lithium and has good interface stability;

[0027] (5) The solvent-free LLZO-based composite solid electrolyte LLZO-IPL provided by the present invention can be stably cycled for more than 500 cycles when applied to solid-state lithium metal batteries.

[0028] (6) The preparation method of the present invention is simple and can be mass-produced; the preparation process is environmentally friendly and does not require any toxic organic solvents. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0030] Figure 1 This is a planar scanning electron microscope image of the LLZTO-IPL composite solid electrolyte prepared by a solvent-free method in an embodiment of the present invention.

[0031] Figure 2 This is a planar scanning electron microscope image of the LLZTO solid electrolyte membrane prepared by the solvent-free method in an embodiment of the present invention.

[0032] Figure 3 These are the impedance spectra of the LLZTO-based composite solid electrolyte LLZTO-IPL prepared by a solvent-free method at different temperatures in an embodiment of the present invention.

[0033] Figure 4 The impedance spectra of the LLZTO solid electrolyte prepared by the solvent-free method at different temperatures in an embodiment of the present invention are shown.

[0034] Figure 5 This is the constant current and voltage cycling curve of a symmetrical battery assembled with the LLZTO-IPL composite solid electrolyte prepared by a solvent-free method in an embodiment of the present invention.

[0035] Figure 6 This is the constant current voltage cycling curve of a symmetrical battery assembled with the LLZTO solid electrolyte prepared by the solvent-free method in an embodiment of the present invention.

[0036] Figure 7 This is the full-cell electrochemical performance cycle curve of the LLZTO-IPL composite solid electrolyte prepared by the solvent-free method in the embodiment of the present invention.

[0037] Figure 8 Full-cell electrochemical performance cycling curves of LLZTO electrolyte prepared by solvent-free method.

[0038] Figure 9 This is a planar scanning electron microscope image of the solid electrolyte membrane of Comparative Example 2 of the present invention.

[0039] Figure 10 This is a scanning electron microscope image of a cross section of the solid electrolyte membrane of Example 1 of the present invention.

[0040] Figure 11 This is a bending optical photograph of Example 1 of the present invention. DETAILED DESCRIPTION

[0041] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0042] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are intended to explain rather than limit the present invention.

[0043] Example 1

[0044] The preparation method of the solvent-free LLZTO composite solid electrolyte comprises the following steps:

[0045] Step 1: Weigh 0.102 g of PDADMAFSI, 0.093 g of LiFSI, and 0.6 g of PyR 13 FSI was heated at 80 °C with magnetic stirring for 14 h to obtain yellow ion gel IPL.

[0046] Step 2: Weigh 3 g of LLZO nanopowder and 0.12 g of PTFE powder into a ball mill, then mechanically mix and ball mill at 200 rpm for 1 hour. Then, scrape the powder off the inner wall of the ball mill, add the ion gel IPL obtained in step 1, and then ball mill again at 500 rpm for 1 hour.

[0047] Step 3: The resulting flocculent mass was removed from the ball mill and placed on a hot plate within the glove box. It was then manually hot-rolled using a stainless steel cylindrical rod at 85°C to form the electrolyte membrane, LLZTO-IPL. To further reduce the thickness of the electrolyte and improve interparticle contact, the LLZTO-IPL was rolled to 80 μm using a double-roll mill at 85°C. Finally, it was cut into 16 mm diameter discs and placed in the glove box for later use.

[0048] Comparative Example 1

[0049] Compared with Example 1, the difference is that this comparative example does not include ion gel IPL, and the specific preparation process is as follows:

[0050] Step 1: Weigh 3 g of LLZO nanopowder and 0.12 g of PTFE powder into a ball mill, and then mechanically mix and ball mill at a speed of 200 rpm for 1 hour.

[0051] Step 2: The flocculent mass obtained in Step 1 was removed and placed on a hot plate in a glove box. The LLZTO electrolyte membrane was manually hot-rolled using a stainless steel cylindrical rod at 85°C. The LLZTO was then repeatedly rolled to 80 μm using a double-roll mill at 85°C. Finally, the LLZTO was cut into 16 mm diameter discs and placed in the glove box for later use.

[0052] Comparative Example 2

[0053] Compared with Example 1, the difference is that in step 2 of this comparative example, 0.1 g of ion gel IPL is added, and the rest is the same as Example 1.

[0054] Test example

[0055] Symmetrical battery assembly: Two lithium sheets with a diameter of 12 mm are placed symmetrically on both sides of a solid electrolyte with a diameter of 16 mm. They are then placed in a 2032-type battery shell in the order of gasket, lithium sheet, solid electrolyte, lithium sheet, gasket, and shrapnel. Finally, they are sealed using a battery packaging machine.

[0056] Assembly of button batteries: A lithium sheet with a diameter of 12 mm is used as the negative electrode, a solid electrolyte with a diameter of 16 mm is used as the electrolyte, and a lithium iron phosphate electrode with a diameter of 12 mm is used as the positive electrode. The 1 mm thick gasket, negative electrode, electrolyte, positive electrode, gasket, and spring are placed in order from bottom to top, and then packaged in a 2023 type battery shell through a battery packaging machine.

[0057] Figure 1 This is a planar scanning electron microscope image of the solvent-free LLZTO-based composite solid electrolyte LLZTO-IPL. It can be seen from the image that the electrolyte surface is flat and smooth, and there are no obvious gaps between the electrolyte particles, proving that lithium ions can form a continuous transmission channel inside the electrolyte.

[0058] Figure 2 This is a planar SEM image of a dry-process LLZTO electrolyte membrane without ion gel composite. The image shows that under the fibrillation of PTFE, the electrolyte particles can form an independent, self-supporting film. However, the contact between the particles is poor, with a large number of obvious gaps.

[0059] Figure 3 The impedance spectra of LLZTO-IPL electrolyte at different temperatures show that the ionic conductivity of LLZTO-IPL electrolyte at room temperature is 2.5x10 -4 S / cm, can be increased to 1.1x10 at 70℃ -3S / cm.

[0060] Figure 4 The impedance spectra of the LLZTO electrolyte membrane prepared by dry process at different temperatures show that the ionic conductivity of the LLZTO membrane electrolyte at room temperature is 8.48x10 -5 S / cm, and the ionic conductivity of the LLZTO-IPL electrolyte membrane is three times that of the LLZTO-IPL electrolyte membrane.

[0061] Figure 5 The electrochemical stability of the LLZTO-IPL electrolyte membrane is shown. As can be seen from the figure, at 0.2 mA cm -2 At a current density of 1.5 GHz, the symmetrical battery assembled with the LLZTO-IPL electrolyte membrane maintains a stable overpotential and a cycle life of up to 800 hours.

[0062] Figure 6 This is the symmetrical battery cycle voltage curve of the LLZTO electrolyte membrane. It can be seen from the figure that with the extension of the cycle time, the polarization voltage gradually increases. This is because the side reaction between PTFE and metallic lithium causes the contact to deteriorate and forms by-products with large impedance. With the continuous accumulation of by-products, the battery eventually fails after about 300 hours of circulation.

[0063] Figure 7 It can be seen that the button battery with LLZTO-IPL electrolyte membrane prepared by solvent-free method can stably cycle 1000 times at a current density of 0.5C (85mA / g) and then perform constant rate charge and discharge.

[0064] Figure 8 This is a full battery using LLZTO electrolyte membrane cycled at the same current density. It can be seen that the discharge capacity decays rapidly after 100 cycles, and the capacity drops to 75mAh / g after 300 cycles.

[0065] Figure 9 A planar scanning electron microscope image of the electrolyte membrane of Comparative Example 2 is shown. It can be seen from the image that when the amount of ion gel added is 5 wt.% of the mass of LLZTO and PTFE, some gaps still appear between the electrolyte particles, hindering the continuous transmission of lithium ions.

[0066] Figure 10 This is a cross-sectional scanning electron microscope image of the LLZTO-IPL electrolyte membrane prepared by the solvent-free method. From the image, it can be seen that the thickness of the electrolyte membrane is about 80 microns after manual rolling and rolling on a double-roller machine, and the electrolyte particles are densely distributed, which is conducive to resisting lithium dendrite penetration.

[0067] Figure 11 This is a bending optical photograph of Example 1. It can be seen from the figure that the electrolyte membrane has good flexibility.

[0068] Example 2

[0069] The preparation method of the solvent-free LLZTO composite solid electrolyte comprises the following steps:

[0070] Step 1: Weigh 0.06 g of PDADMAFSI, 0.07 g of LiFSI, and 0.4 g of PyR 13 FSI was magnetically stirred at 75 °C for 18 h to obtain yellow ion gel IPL.

[0071] Step 2: Weigh 2 g of LLZO nanopowder and 0.08 g of PTFE powder into a ball mill, then mechanically mix and ball mill at 220 rpm for 1.5 hours. Then, scrape the powder off the inner wall of the ball mill, add the ion gel IPL obtained in step 1, and then ball mill again at 600 rpm for 1 hour.

[0072] Step 3: The resulting flocculent mass was removed from the ball mill and placed on a hot plate in a glove box. It was then manually hot-rolled using a stainless steel cylindrical rod at 80°C to form the electrolyte membrane, LLZTO-IPL. To further reduce the thickness of the electrolyte and improve interparticle contact, the LLZTO-IPL was rolled to 85 μm using a double-roll mill at 80°C. Finally, it was cut into 13 mm diameter discs and placed in the glove box for later use.

[0073] Example 3

[0074] The preparation method of the solvent-free LLZTO composite solid electrolyte comprises the following steps:

[0075] Step 1: Weigh 0.25 g of PDADMAFSI, 0.2 g of LiFSI and 1.5 g of PyR 13 FSI was heated at 85 °C under magnetic stirring for 12 h to obtain yellow ion gel IPL.

[0076] Step 2: Weigh 5 g of LLZO nanopowder and 0.15 g of PTFE powder into a ball mill, then mechanically mix and ball mill at 300 rpm for 3 hours. Then, after scraping the powder off the inner wall of the ball mill, add the ion gel IPL obtained in step 1, and then ball mill again at 800 rpm for 1 hour.

[0077] Step 3: The resulting flocculent mass was removed from the ball mill and placed on a hot plate within the glove box. It was then manually hot-rolled using a stainless steel cylindrical rod at 90°C to form the electrolyte membrane, LLZTO-IPL. To further reduce the thickness of the electrolyte and improve interparticle contact, the LLZTO-IPL was rolled to 100 μm using a double-roll mill at 90°C. Finally, the membrane was cut into 14 mm diameter discs and placed in the glove box for later use.

[0078] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a solvent-free LLZO-based composite solid electrolyte, characterized in that: The steps include: Mixing poly(diallyldimethylammonium)bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, and N-butyl-N-methylpyrrolidine bis(trifluoromethylsulfonyl)imide in a molar ratio of 1:1-1.5:2-4, and stirring at 70-90° C. to obtain a solid ion gel; The lithium lanthanum zirconium-based solid electrolyte powder and polytetrafluoroethylene are mixed and ball-milled for a set time, and the PTFE accounts for 2-5 wt.% of the total mass of the lithium lanthanum zirconium-based solid electrolyte and PTFE; then the ion gel is added thereto in proportion, and the ball milling is continued until the mixture is uniform, and the mass ratio of the ion gel to the PTFE is 5-10:1, thereby obtaining a solid electrolyte.

2. The method for preparing a solvent-free LLZO-based composite solid electrolyte according to claim 1, characterized in that: PDADMAFSI, lithium bis(fluorosulfonyl)imide and PyR 13 The FSI mixing and stirring time is 12~18h.

3. The method for preparing a solvent-free LLZO-based composite solid electrolyte according to claim 1, characterized in that: The ball milling time of the lithium lanthanum zirconium oxide solid electrolyte powder and PTFE is 0.5-2 hours, and the ball milling speed is 200-300 rpm.

4. The method for preparing a solvent-free LLZO-based composite solid electrolyte according to claim 3, characterized in that: After adding the ion gel, the ball milling time is continued for 1-3 hours, and the ball milling speed is 500-800 rpm.

5. The method for preparing a solvent-free LLZO-based composite solid electrolyte according to claim 1, characterized in that: The lithium lanthanum zirconium oxide solid electrolyte is selected from one of LLZO, LLZTO, LLZNO or LALZO.

6. The method for preparing a LLZO-based composite solid electrolyte by a solvent-free method according to claim 1, characterized in that: The method also includes the steps of hot rolling the prepared solid electrolyte and then thinning it to a set thickness by rolling to obtain an electrolyte membrane.

7. The method for preparing a LLZO-based composite solid electrolyte by a solvent-free method according to claim 6, characterized in that: The temperature of hot rolling is 80-90℃.

8. The method for preparing a LLZO-based composite solid electrolyte by a solvent-free method according to claim 6, characterized in that: The electrolyte membrane is rolled and thinned by a double-roller machine, and the rolling and thinning temperature is 80-90°C.

9. The method for preparing a LLZO-based composite solid electrolyte by a solvent-free method according to claim 6, characterized in that: The thickness of the obtained electrolyte membrane was 80-100 μm.

10. A solvent-free LLZO-based composite solid electrolyte, characterized by: Prepared by the preparation method according to any one of claims 1 to 9.

11. Use of the solvent-free LLZO-based composite solid electrolyte according to claim 10 in the preparation of solid-state lithium-ion batteries.

12. The use according to claim 11, characterized in that: The positive electrode material of the solid-state lithium-ion battery is lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide or a ternary lithium positive electrode material.

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