Aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte and preparation thereof

Abstract

The invention belongs to the technical field of solid electrolytes, and particularly relates to an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte and a preparation method thereof. Aiming at the problems of poor wettability of ceramic to lithium in the solid electrolyte and the like in the prior art, the invention adopts the following method for improvement: (1) mixing a lithium source, a lanthanum source, a zirconium source, an aluminum source and a tantalum source, then carrying out high-temperature roasting to obtain roasted mother powder, carrying out ball milling on the roasted mother powder again to obtain nanoscale aluminum-tantalum double-doped LLZATO particles, pressing the LLZATO particles into sheets, and carrying out vacuum drying to obtain a sheet material; the LLZATO ceramic wafer is obtained through two-step sintering under the coverage of the mother powder; (2) uniformly mixing polyethylene oxide, lithium bis (trifluoromethane sulfonimide), LLZATO particles and polytetrafluoroethylene to obtain composite dissolved slurry; and (3) coating one side of an LLZATO ceramic wafer with the composite dissolved slurry, and evaporating a solvent to obtain the rigid-flexible asymmetric double-layer solid electrolyte with the ceramic-composite membrane structure. The electrolyte is high in compatibility, high in thermal stability, extremely low in interface resistance, high in conductivity and excellent in cycling stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of solid electrolytes, and particularly relates to an aluminum tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte and its preparation. Background Art

[0002] As one of the new high-energy batteries successfully developed in the 20th century, lithium-ion batteries have been widely used in mobile devices, electric vehicles, energy storage systems and other fields due to their high energy density, high market maturity, long cycle life and other advantages. The energy density of current commercial liquid lithium-ion batteries has approached the theoretical limit of 300 Wh·kg -1 , and liquid lithium-ion batteries are prone to thermal runaway. A large number of side reactions will occur inside the battery during long-term operation and high-temperature conditions, generating heat energy, which will further cause the chemical reaction inside the battery to get out of control, and ultimately lead to serious consequences such as battery fire and explosion, and will also cause harm to the environment and human health.

[0003] At present, the energy density of liquid lithium batteries has approached the developed limit, while all-solid-state lithium batteries have the potential to exceed 500 Wh·kg -1 . Therefore, all-solid-state batteries have been comprehensively deployed, pointing out the way forward for the development of future lithium batteries, and are also an important field that enterprises are competing to research. Garnet electrolytes have been widely studied by scholars because of their high room-temperature ionic conductivity, wide electrochemical window and good chemical stability to cathode materials and lithium metal anodes.

[0004] However, there are still some problems to be solved in solid electrolytes. After multiple cycles, the anode surface will become uneven due to continuous petrification / depositing, exacerbating the poor wettability of the ceramic to lithium, thus increasing the interfacial resistance between the anode and the electrolyte. By introducing inorganic ceramic fillers into the polymer matrix, when the concentration of inorganic ceramic fillers in the matrix is insufficient, a continuous ion transport path cannot be formed in the electrolyte, and the ionic conductivity will deteriorate. As the concentration of ceramic fillers increases, an unwanted aggregation phenomenon will occur, thus hindering the ion transport path and damaging the overall conductivity. At the same time, ion transport in poly(ethylene oxide) (PEO) based on ion coupling only occurs in the amorphous region above the melting temperature (Tm), resulting in a higher battery operating temperature and an accelerated attenuation of the battery capacity at high temperatures, which is prone to cause short circuits. Summary of the Invention

[0005] In view of the above problems, the present invention proposes an Al, Ta dual-doped lithium lanthanum zirconium oxide (LLZO) ceramic-polyethylene oxide (PEO) based rigid-flexible asymmetric double-layer solid electrolyte and a preparation method thereof. The present invention in situ solidifies a composite layer on the surface of a ceramic with high ionic conductivity. During the solidification process of the solution, the composite electrolyte solution penetrates into the ceramic surface. The polymerization process can effectively promote the integration and compatibility of the rigid-flexible solid electrolyte interface, and prepare an asymmetric double-layer solid electrolyte with high density and a concentration gradient structure. The composite layer is modified and optimized, and polytetrafluoroethylene (PTFE) is used as a binder for cross-linking to alleviate the instability of the electrolyte layer caused by the high-temperature decomposition of the polyethylene oxide (PEO)-based composite, and enhance thermal stability. The present invention designs solid electrolytes with different structures and properties in view of the different electrochemical environments on the high-voltage positive electrode and the lithium metal negative electrode side and the different requirements for electrolyte performance. This double-layer electrolyte with a concentration gradient structure can accelerate the commercialization of high-performance next-generation all-solid-state batteries.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A method for preparing an Al and Ta dual-doped lithium lanthanum zirconium oxide (LLZO) ceramic-polyethylene oxide (PEO) based rigid-flexible asymmetric double-layer solid electrolyte comprises the following steps:

[0008] Preparation of S1 lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) electrolyte ceramic sheet:

[0009] Firstly, a lithium source, a lanthanum source, a zirconium source, an aluminum source, and a tantalum source are fully mixed with an organic solvent in a certain proportion, ball-milled and dried once, and calcined at high temperature to obtain a calcined mother powder, and then the calcined mother powder is fully ball-milled with an organic solvent, ball-milled and dried twice to obtain nano-scale Al and Ta double-doped lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles, and the nano-scale lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles obtained by the second ball milling are pressed into discs, and then respectively sintered in two steps under the coverage of the mother powder to obtain a ceramic sheet, and then the ceramic sheet is polished to obtain a lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic sheet;

[0010] Preparation of S2 polyethylene oxide (PEO)-polytetrafluoroethylene (PTFE) composite slurry:

[0011] A certain proportion of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were weighed and dissolved in an acetonitrile solution, and a certain mass fraction of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles prepared by S1 and a certain mass fraction of polytetrafluoroethylene (PTFE) were added after pre-stirring, and a milky white uniform composite slurry was obtained after stirring;

[0012] Preparation of S3 rigid-flexible asymmetric double-layer solid electrolyte:

[0013] The composite sol obtained in S2 was dropped onto one side of the polished LLZATO (lithium lanthanum zirconium aluminum tantalum oxide) ceramic sheet prepared in S1 until saturated, and then placed in an oven for baking to evaporate the solvent, obtaining a rigid-flexible asymmetric bilayer solid electrolyte (ASE) with a ceramic-composite film structure, that is, an aluminum tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte.

[0014] Preferably, the LLZATO ceramic sheet is a garnet-type solid electrolyte with the chemical formula Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12 , and when taking raw materials, the lithium source was weighed according to the ratio of 15 wt% excess lithium.

[0015] Preferably, the lithium source is at least one of lithium carbonate, lithium hydroxide monohydrate, lithium hydrogen phosphate, and lithium dihydrogen phosphate;

[0016] Preferably, the lanthanum source is at least one of lanthanum oxide, lanthanum carbonate, lanthanum nitrate, and lanthanum hydroxide;

[0017] Preferably, the zirconium source is at least one of zirconium oxide, zirconium carbonate, zirconium nitrate, and zirconium hydroxide;

[0018] Preferably, the aluminum source is at least one of aluminum oxide, aluminum carbonate, aluminum nitrate, and aluminum hydroxide;

[0019] Preferably, the tantalum source is tantalum oxide.

[0020] Preferably, in step S1, the organic solvent is isopropyl alcohol, and the mass ratio of the total mass of the lithium source, lanthanum source, zirconium source, aluminum source, and tantalum source to the mass of the organic solvent is about 1:(1 - 1.5).

[0021] Preferably, in step S1, the first ball milling time is 6 h, the second ball milling time is 12 h, and the rotational speed of the ball mill is 500 r / min - 600 r / min; the ball milling beads are zirconia beads, and 18 zirconia beads with diameters of 5 mm and 10 mm are placed in a ratio of 1:1 each; after ball milling, it is dried at 60 °C - 80 °C for 8 h - 12 h.

[0022] Preferably, in step S1, the calcination temperature is 950 °C and the heat preservation time is 6 h.

[0023] Preferably, in step S1, the nanoscale lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles after secondary ball milling are pressed into wafers, the pressure is 10 MPa, the duration is 3 min, the mass ratio of the mother powder to the mass of the wafer is 1:1, and the mass of the wafer is 0.55 g - 0.6 g.

[0024] Preferably, the temperatures and times of the two-step sintering in step S1 are 1200 °C × 2 h and 1100 °C × 10 h, respectively.

[0025] Preferably, the roughnesses of the sandpapers used for polishing in step S1 are 400 mesh, 800 mesh, 2000 mesh, and 4000 mesh in sequence.

[0026] Preferably, in step S2, the ratio of polyethylene oxide (PEO) to lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is in a molar amount of ethylene oxide (EO):Li = 18:1. The mass of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles is 15 wt% of the total mass of polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The required mass fraction of polytetrafluoroethylene (PTFE) is 15 wt% of the total mass of PEO and LiTFSI.

[0027] Preferably, in step S2, pre-stir for 6 h and mix and stir for 12 h.

[0028] Preferably, in step S3, the oven used for evaporating the solvent is a vacuum oven, the temperature is 80 °C, and the drying time is 8 h to 12 h.

[0029] The rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure obtained by the above method includes a rigid solid electrolyte and a flexible composite film electrolyte. The composite film electrolyte is attached to one side of the solid electrolyte;

[0030] The composite film electrolyte contains lithium lanthanum zirconium aluminum tantalum oxide particles and is obtained by compounding polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, and polytetrafluoroethylene; the solid electrolyte is a garnet-type lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet with the chemical formula Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12 , and is prepared from the lithium lanthanum zirconium aluminum tantalum oxide particles.

[0031] The present invention proposes an effective idea of an asymmetric integrated electrolyte layer strategy to improve the performance of the coupling between the solid electrolyte and the cathode and Li metal anode, and to avoid the physical and chemical incompatibility between the electrode and the electrolyte. By depositing a composite electrolyte on the surface of the ceramic-based electrolyte, that is, directly depositing a thin composite layer on the Al, Ta dual-doped LLZO ceramic (lithium lanthanum zirconium aluminum tantalum oxide LLZATO ceramic) as an ultrathin composite electrolyte layer with high ionic conductivity, effective penetration of the electrolyte solution during the curing stage of the composite layer solution is achieved to support charge transfer and optimize the electrochemical performance. The formed composite solid electrolyte layer is firmly riveted on the surface of the garnet-type solid electrolyte lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic, effectively alleviating the interfacial compatibility problem between the ceramic electrolyte and the polymer, strengthening the bond between the electrolyte and the ceramic, and building a bridge for rapid Li + ion migration, and promoting the formation of an asymmetric rigid-flexible solid electrolyte interface with a concentration gradient. In order to effectively alleviate the instability of the electrolyte layer caused by the decomposition of the poly(ethylene oxide) (PEO)-based composite at high temperature, polytetrafluoroethylene (PTFE) is used as a binder for cross-linking. The blend of polytetrafluoroethylene (PTFE) and poly(ethylene oxide) (PEO) has enhanced thermal stability. The lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic and the composite interface are in close contact. The anode side is tightly sealed by the lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic and molten Li metal, which can significantly reduce the interfacial resistance; the cathode side uses a soft poly(ethylene oxide) (PEO)-based composite solid electrolyte (LLZATO-poly(ethylene oxide) (PEO)-based composite solid electrolyte) to obtain better cycling performance and thermal stability. In addition, the present invention adapts the solid electrolyte to the different electrochemical requirements of the high-voltage cathode and the lithium metal anode, accelerating the commercialization process of the next-generation all-solid-state battery. Brief Description of the Drawings

[0032] Figure 1 is the XRD refined image of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles after secondary ball milling;

[0033] Figure 2 is the comparison chart of the total impedance of the lithium symmetric batteries of Example 1, Comparative Example 1 and Comparative Example 2 at room temperature;

[0034] Figure 3 is the comparison chart of the total impedance of the lithium symmetric batteries of Example 1, Comparative Example 1 and Comparative Example 2 at 60 °C;

[0035] Figure 4 is the interfacial SEM image of the lithium metal / ceramic / composite electrolyte layer of Comparative Example 2;

[0036] Figure 5 is the interfacial SEM image of the lithium metal / ceramic / composite electrolyte layer of Comparative Example 1;

[0037] Figure 6 It is the interfacial SEM image of the lithium metal / ceramic / composite electrolyte layer of Example 1;

[0038] Figure 7 It is the critical current density diagram of Example 1, Comparative Example 1 and Comparative Example 2;

[0039] Figure 8 It is the long cycle diagram of the lithium symmetric batteries of Example 1, Comparative Example 1 and Comparative Example 2 at a current density of 0.1 mA·cm -2 ;

[0040] Figure 9 It is the full cell cycling curve of Example 1 at different rates;

[0041] Figure 10 It is the full cell cycling curves of Example 1, Comparative Example 1 and Comparative Example 2 at a current density of 0.1 C. Detailed implementation manners

[0042] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments and the accompanying drawings. It should be noted that the embodiments described in the present invention are only used for further explanation and illustration, rather than limiting the scope of its application. Based on the present invention, all other embodiments obtained by those skilled in the art without making creative efforts belong to the protection scope of the present invention.

[0043] Example 1

[0044] (1) Preparation of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) electrolyte ceramic sheet:

[0045] Take 3.4477 g of lithium hydroxide monohydrate, 3.912 g of lanthanum oxide, 1.6928 g of zirconium oxide, 0.0408 g of aluminum oxide, 0.5330 g of tantalum oxide and an appropriate amount of isopropanol (just enough to cover the small ball mill beads) and add them into the ball mill tank. After fully ball milling and drying, place it in a muffle furnace and calcine it at 950 °C for 6 h to obtain Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12Calcined mother powder; the calcined mother powder is ball-milled uniformly with an appropriate amount of isopropanol, and after drying, lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles are obtained. The ball-milling beads used in the above ball-milling are zirconia beads, and 18 zirconia beads with diameters of 5 mm and 10 mm are placed in a ratio of 1:1 each. Take 0.55 g to 0.6 g of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles and press them into a disc with a diameter of 13 mm. Place the disc in a muffle furnace under the cover of the mother powder (the mass ratio of the mother powder to the disc is 1:1) and conduct two-step sintering at 1200 °C × 2 h and 1100 °C × 10 h. The sintered ceramic disc is about 10 mm, and a lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc is prepared. Subsequently, the ceramic disc is polished smoothly with sandpaper, and the roughness of the sandpaper used for polishing is 400 mesh, 800 mesh, 2000 mesh, and 4000 mesh in sequence. The thickness of the polished lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc is about 1 mm.

[0046] (2) Preparation of polyethylene oxide (PEO)-polytetrafluoroethylene (PTFE) composite slurry:

[0047] Polyethylene oxide (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are placed in a vacuum drying oven at 60 °C overnight to remove moisture during weighing. Take 0.5 g of polyethylene oxide (PEO) and place it in a beaker, add 10 ml of acetonitrile solvent and 0.181 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) (meeting EO:Li = 18:1), and stir the mixture at room temperature for 6 h to obtain a mixed solution. Add lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles and polytetrafluoroethylene (PTFE) with a mass fraction of 15 wt% of the total mass of PEO and LiTFSI to the mixed solution, and stir at room temperature for 12 h to obtain a composite slurry.

[0048] (3) Preparation of rigid-flexible asymmetric bilayer solid electrolyte:

[0049] Drop the composite slurry on one side of the polished lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc until it is saturated, and place it in an oven at 80 °C for 12 h after the solvent evaporates to obtain a rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure.

[0050] Assemble the rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure into a battery and conduct performance testing.

[0051] Positive electrode: The active material (LiFePO4), carbon black, and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 8:1:1. Take 0.4 g of LiFePO4, 0.05 g of carbon black, and 1 g of PVDF solution (the concentration of the PVDF solution is 5%). Use an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersant / solvent to prepare a slurry. After mixing evenly, it is coated on aluminum foil (the thickness of the aluminum foil is 10 μm). After drying at 80 °C, it is roll-pressed and stamped into a circular pole piece with a diameter of 10 mm. Subsequently, it is vacuum-dried at 120 °C overnight for battery assembly testing.

[0052] Negative electrode: Metal lithium is adsorbed on one side surface of the ceramic by the high-temperature molten lithium method. The melting temperature is 300 °C to 360 °C. After cooling to room temperature, the residual lithium is polished clean. All these operations are carried out in a glove box.

[0053] The electrochemical performance test is achieved by assembling a CR2032 battery model. The entire assembly process is completed in a glove box (the water and oxygen content are both less than 0.01 ppm). The full cell is assembled in the order of the negative electrode shell, nickel foam, one-side molten lithium, the ceramic sheet with in-situ polymerization on the other side, the positive electrode sheet, nickel foam, and the positive electrode shell. In order to improve the wettability of the positive electrode side with the electrolyte, 5 μL of ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ionic liquid, EMIM) is dropped on the solid electrolyte and the positive electrode side for wetting. After encapsulation and standing procedures, it is ready for the next electrochemical test; the symmetric cell is assembled in the order of the negative electrode shell, nickel foam, one-side molten lithium, the ceramic sheet with in-situ polymerization on the other side, the lithium sheet, nickel foam, and the positive electrode shell.

[0054] Phase characterization of the ceramic:

[0055] The XRD of the ceramic obtained after two-stage sintering is refined as Figure 1 shown. The space group is Ia-3d (230), indicating that LLZATO has a stable cubic garnet phase structure. And except for the pure cubic phase, no other impurities are found, proving that Al 3+ and Ta 5+ double doping plus two-step sintering can stabilize the cubic phase of LLZO at room temperature. The refinement confirms that the Rietveld refinement results are affected by the presence of Al 3+ and Ta 5+ ions. Ta 5+ substitutes the Zr site at 16a, while Al 3+ mainly occupies the Li site. The site preference of Al 3+ will be more randomized. Part of the Al 3+ occupies the tetrahedral 24d site, and part occupies the octahedral 96h. The interface of the lithium metal / ceramic / composite electrolyte layer is as Figure 6 shown.

[0056] Battery performance evaluation:

[0057] After the symmetrical battery was assembled and left standing for 10 h, it could stably cycle for more than 600 h at a current density of 0.1 mA·cm -2 as shown in Figure 8 , and its critical current density was 0.9 mA·cm -2 as Figure 7 , Figure 2 showing that its total interfacial impedance was 2,007.9 Ω·cm 2 , and the interfacial impedance was 494.53 Ω·cm 2 . The total impedance of the lithium symmetrical battery at 60 °C is as shown in Figure 3 .

[0058] After the full cell was cycled at 0.1 C at a voltage of 2.5 V to 3.9 V, the results were as shown in Figure 9 . The discharge specific capacity of its first cycle was 158.1 mAh·g -1 . After 200 cycles, the discharge specific capacity was 148 mAh·g -1 , the capacity retention rate was 93.6%, and the Coulomb efficiency was 99.8%. Its rate performance was that the discharge specific capacities at 0.1 C, 0.2 C, 0.5 C, and 1 C were 158.9 mAh·g -1 , 156 mAh·g -1 , 149.6 mAh·g -1 , and 141 mAh·g -1 respectively. After cycling at 0.1 C, the capacity increased to 153.7 mAh·g -1 .

[0059] Comparative Example 1

[0060] (1) Preparation of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) electrolyte ceramic sheet:

[0061] Take 3.4477 g of lithium hydroxide monohydrate, 3.912 g of lanthanum oxide, 1.6928 g of zirconium oxide, 0.0408 g of aluminum oxide, 0.5330 g of tantalum oxide, and an appropriate amount of isopropanol (just enough to cover the small ball mill beads) and add them to the ball mill jar. After fully ball milling and drying, place it in a muffle furnace and calcine it at 950 °C for 6 h to obtain Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12Calcined mother powder; the calcined mother powder is ball-milled evenly with an appropriate amount of isopropanol, and after drying, lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles are obtained. Take 0.55 g to 0.6 g of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles and press them into a disc with a diameter of 13 mm. Place the disc in a muffle furnace under the cover of the mother powder (the mass ratio of the mother powder to the disc is 1:1) and conduct two-step sintering at 1200 °C × 2 h and 1100 °C × 10 h to obtain a lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc. Subsequently, polish the ceramic disc smoothly with sandpaper, and the roughness of the sandpaper used for polishing is 400 mesh, 800 mesh, 2000 mesh, and 4000 mesh in sequence.

[0062] (2) Preparation of poly(ethylene oxide) (PEO) slurry:

[0063] Poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are placed in a vacuum drying oven at 60 °C overnight to remove moisture. Take 0.5 g of poly(ethylene oxide) (PEO) and place it in a beaker, add 10 ml of acetonitrile solvent and 0.181 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and stir the mixture at room temperature for 6 h to obtain a mixture. Add lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles with a mass fraction of 15% of the total mass of PEO and LiTFSI to the mixture, and stir at room temperature for 12 h to obtain a composite slurry.

[0064] (3) Preparation of rigid-flexible asymmetric bilayer solid electrolyte:

[0065] Drop the composite slurry on one side of the polished lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc until it reaches a saturated state. After the solvent evaporates, bake it at 80 °C for 12 h to obtain a rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure.

[0066] Assemble the rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure into a battery and conduct performance testing.

[0067] Positive electrode: Mix the active material (LiFePO4), carbon black, and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1. Take 0.4 g of LiFePO4, 0.05 g of carbon black, and 1 g of PVDF solution (the concentration of the PVDF solution is 5%), and use an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersant / solvent to prepare a slurry. After mixing evenly, coat it on an aluminum foil (the thickness of the aluminum foil is 10 μm). After drying at 80 °C, roll and punch it into a circular pole piece with a diameter of 10 mm. Subsequently, vacuum dry it overnight at 120 °C for battery assembly testing.

[0068] Negative electrode: Adsorb metallic lithium on the surface of one side of the ceramic by the high-temperature molten lithium method. The melting temperature is 300 °C to 360 °C. After cooling to room temperature, polish the residual lithium clean. All these operations are carried out in a glove box.

[0069] The electrochemical performance test was achieved by assembling a CR2032 battery model. The whole assembly process was completed in a glove box (with water and oxygen content both less than 0.01 ppm). The full cell was assembled in the order of negative electrode case, nickel foam, lithium melting on one side, ceramic sheet with in-situ polymerization on the other side, positive electrode sheet, nickel foam, and positive electrode case. To improve the wettability between the positive electrode side and the electrolyte, 5 μL of ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ionic liquid, EMIM) was dropped on the solid electrolyte and the positive electrode side for wetting. After encapsulation and standing procedures, it was ready for the next electrochemical test; the symmetric cell was assembled in the order of negative electrode case, nickel foam, lithium melting on one side, ceramic sheet with in-situ polymerization on the other side, lithium sheet, nickel foam, and positive electrode case.

[0070] Battery performance evaluation:

[0071] After the symmetric cell was assembled and stood for 10 h, it could stably cycle for more than 600 h at a current density of 0.1 mA·cm -2 as shown, but the overpotential was unstable. Figure 8 And Figure 7 and Figure 2 The results showed that its critical current density was 0.7 mA·cm -2 , the total interfacial impedance was 2880 Ω·cm 2 , and the interfacial impedance was 601.85 Ω·cm 2 . The total impedance of the lithium symmetric cell at 60 °C was as Figure 3 shown. The interface of the lithium metal / ceramic / composite electrolyte layer was as Figure 5 shown.

[0072] The cycling results of the full cell at a voltage of 2.5 V - 3.9 V at 0.1C were as Figure 10 shown. Its initial discharge specific capacity was 145.5 mAh·g -1 . After 200 cycles, the discharge specific capacity was 134.4 mAh·g -1 , the capacity retention rate was 92.4%, and the Coulomb efficiency was 99.71%.

[0073] Comparative Example 2

[0074] (1) Preparation of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) electrolyte ceramic powder:

[0075] Take 3.4477 g of lithium hydroxide monohydrate, 3.912 g of lanthanum oxide, 1.6928 g of zirconium oxide, 0.0408 g of aluminum oxide, 0.5330 g of tantalum oxide and an appropriate amount of isopropanol (just enough to cover the small ball mill beads) and add them to the ball mill jar. After fully ball milling and drying, place it in a muffle furnace and calcine at 950 °C for 6 h to obtain Li 6.4La3Zr 1.4 Al 0.1 Ta 0.3 O 12 Calcined mother powder; the calcined mother powder is fully ball-milled with an appropriate amount of isopropanol until uniform, and after drying, lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles are obtained. Take 0.55 g to 0.6 g of lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles and press them into a disc with a diameter of 13 mm. Place the disc in a muffle furnace under the cover of the mother powder (the mass ratio of the mother powder to the disc is 1:1) and conduct two-step sintering at 1200 °C for 2 h and 1100 °C for 10 h to obtain a lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) ceramic disc. Subsequently, polish the ceramic disc smoothly with sandpaper. The roughness of the sandpaper used for polishing is 400 mesh, 800 mesh, 2000 mesh, and 4000 mesh in sequence to obtain the LLZATO electrolyte ceramic disc. Subsequently, grind a certain amount of LLZATO ceramic powder in a mortar. Transfer these particles to an argon-filled glove box with O2 and H2O contents lower than 0.1 ppm.

[0076] (2) Preparation of poly(ethylene oxide) (PEO)-lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) composite film:

[0077] Poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) are dried overnight at 60 °C in a vacuum drying oven to remove moisture when weighing. Take 0.5 g of poly(ethylene oxide) (PEO) and place it in a beaker, add 10 ml of acetonitrile solvent and 0.181 g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and stir the mixture at room temperature for 6 h to obtain a mixed solution. Add lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) particles with a mass fraction of 15% of the total mass of PEO and LiTFSI to the mixed solution and stir for 12 h to obtain a milky white homogeneous slurry.

[0078] The cut glass fiber cloth (GFC) is ultrasonically cleaned with acetone, ethanol, and deionized water for 30 minutes in sequence, placed in an oven to dry, and laid flat on a polytetrafluoroethylene (PTFE) film. Subsequently, take half of the prepared slurry and pour it on the surface of the GFC. After it is completely wetted and dried, turn it over and pour the other side. After the organic solvent evaporates, place it in a vacuum oven at 80 °C overnight. Take it out, cut it into discs with a diameter of 14 mm, and peel it off from the PTFE film to obtain a poly(ethylene oxide) (PEO)-lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) composite film, and transfer it to the glove box for standby.

[0079] Assemble the electrolyte with a ceramic-composite film structure into a battery and conduct performance testing.

[0080] Positive electrode: The active material (LiFePO4), carbon black, and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 8:1:1. Take 0.4 g of LiFePO4, 0.05 g of carbon black, and 1 g of PVDF solution (the concentration of the PVDF solution is 5%), and use an appropriate amount of N-methyl-2-pyrrolidone (NMP) as a dispersant / solvent to prepare a slurry. After mixing evenly, it is coated on aluminum foil (the thickness of the aluminum foil is 10 μm). After drying at 80 °C, it is roll-pressed and stamped into a circular electrode sheet with a diameter of 10 mm. Subsequently, it is vacuum-dried at 120 °C overnight for battery assembly testing.

[0081] Negative electrode: The surface of the lithium sheet is polished clean, cut into small circular pieces with a φ10 mm punching knife, and stored in the glove box for standby. All these operations are carried out in the glove box.

[0082] The electrochemical performance test is achieved by assembling a CR2032 battery model. The entire assembly process is completed in the glove box (the water and oxygen content are both less than 0.01 ppm). The full battery is assembled in the order of the negative electrode shell, stainless steel sheet, lithium sheet, polyethylene oxide (PEO)-lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) composite electrolyte membrane, positive electrode sheet, stainless steel sheet, spring sheet, and positive electrode shell. In order to improve the wettability between the positive electrode side and the electrolyte, 5 μL of ionic liquid is dropped on the solid electrolyte and the positive electrode side for wetting (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ionic liquid, EMIM). After encapsulation and standing procedures, it is ready for the next electrochemical test; the symmetric battery is assembled in the order of the negative electrode shell, stainless steel sheet, lithium sheet, polyethylene oxide (PEO)-lithium lanthanum zirconium aluminum tantalum oxide (LLZATO) composite electrolyte membrane, lithium sheet, stainless steel sheet, spring sheet, and positive electrode shell.

[0083] Battery performance evaluation:

[0084] After the symmetric battery assembly is completed and left standing for 10 h, it can be stably cycled at a current density of 0.1 mA·cm -2 until it is penetrated by lithium dendrites after 280 h as Figure 8 shown, Figure 7 the results show that its critical current density is 0.5 mA·cm -2 , Figure 2 the results show that the total interfacial impedance is 2921 Ω·cm 2 , and the interfacial impedance is 642.9 Ω·cm 2 . The total impedance of the lithium symmetric battery at 60 °C is as Figure 3 shown. The interface of the lithium metal / ceramic / composite electrolyte layer is as Figure 4 shown.

[0085] After the full battery is cycled at 0.1 C under a voltage of 2.5 V - 3.9 V, the results are as Figure 10As shown, the discharge specific capacity of its first cycle is 134.6 mAh·g -1 . After 200 cycles, the discharge specific capacity is 140.4 mAh·g -1 , the capacity retention rate is 104.3%, and the Coulomb efficiency is 99.1%.

Claims

1. A preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte, characterized in that, It includes the following contents: Preparation of lithium lanthanum zirconium aluminum tantalum oxide electrolyte ceramic sheet: Mix a lithium source, a lanthanum source, a zirconium source, an aluminum source, a tantalum source with an organic solvent. After primary ball milling and then calcination, a calcined mother powder is obtained. Then, fully ball mill the calcined mother powder with the organic solvent. After secondary ball milling, nanoscale aluminum and tantalum co-doped lithium lanthanum zirconium aluminum tantalum oxide particles are obtained. Press the nanoscale lithium lanthanum zirconium aluminum tantalum oxide particles obtained by secondary ball milling into sheets, and through a two-step sintering process under the cover of the calcined mother powder, a lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet is obtained; Preparation of poly(ethylene oxide)-polytetrafluoroethylene composite slurry: Dissolve poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide in an acetonitrile solution, and add lithium lanthanum zirconium aluminum tantalum oxide particles and polytetrafluoroethylene to obtain a composite slurry; Preparation of rigid-flexible asymmetric bilayer solid electrolyte: Add the composite slurry to one side of the lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet until it reaches a saturated state. After removing acetonitrile, a rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite film structure is obtained, that is, aluminum and tantalum doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte.

2. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that The lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet is a garnet-type solid electrolyte with the chemical formula Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12 , and when taking raw materials, the lithium source is weighed according to the proportion of 15 wt% excess lithium.

3. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that, The lithium source is at least one of lithium carbonate, lithium hydroxide monohydrate, lithium hydrogen phosphate, and lithium dihydrogen phosphate; The lanthanum source is at least one of lanthanum oxide, lanthanum carbonate, lanthanum nitrate, and lanthanum hydroxide; The zirconium source is at least one of zirconium oxide, zirconium carbonate, zirconium nitrate, and zirconium hydroxide; The aluminum source is at least one of aluminum oxide, aluminum carbonate, aluminum nitrate, and aluminum hydroxide; The tantalum source is tantalum oxide.

4. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that In step S1, the organic solvent is isopropyl alcohol, and the mass ratio of the total mass of the lithium source, lanthanum source, zirconium source, aluminum source, and tantalum source to the mass of the organic solvent is 1:(1 - 1.5).

5. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that, In step S1: The primary ball milling time is 6 h, and the secondary ball milling time is 12 h; The rotational speed of the ball mill for primary ball milling and secondary ball milling is 500 r / min - 600 r / min, and the ball milling beads are zirconia beads with the same number of diameters of 5 mm and 10 mm; After ball milling, dry at 60 °C - 80 °C for 8 h - 12 h.

6. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that, In step S1: The calcination temperature is 950 °C, and the time is 6 h; The two-step sintering means sintering at 1200 °C for 2 h and then sintering at 1100 °C for 10 h.

7. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that, In step S1: The pressure for pressing into sheets is 10 MPa, the pressing time is 3 min, the mass ratio of the mother powder to the sheet is 1:1, and the mass of the sheet is 0.55 g - 0.6 g; The lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet is polished and reserved for use. The roughness of the sandpaper used for polishing is 400 mesh, 800 mesh, 2000 mesh, and 4000 mesh in sequence.

8. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, characterized in that, In step S2: The ratio of poly(ethylene oxide) to lithium bis(trifluoromethanesulfonyl)imide is in terms of the amount of substance as ethylene oxide:Li = 18:1; The mass of the lithium lanthanum zirconium aluminum tantalum oxide particles is 15 wt% of the total mass of poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide, and the mass of polytetrafluoroethylene is 15 wt% of the total mass of poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide.

9. The preparation method of an aluminum-tantalum-doped LLZO ceramic-PEO-based rigid-flexible asymmetric solid electrolyte according to claim 1, wherein, In step S2: After poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide are dissolved in the acetonitrile solution and stirred for 6 h, add lithium lanthanum zirconium aluminum tantalum oxide particles and polytetrafluoroethylene and mix and stir for 12 h to obtain the composite slurry; In step S3: the removal of acetonitrile means drying at 80 °C for 8 h to 12 h.

10. The rigid-flexible asymmetric bilayer solid electrolyte with a ceramic-composite membrane structure obtained by the method according to any one of claims 1 to 9, characterized in that, The rigid-flexible asymmetric bilayer solid electrolyte includes a rigid solid electrolyte and a flexible composite membrane electrolyte, and the composite membrane electrolyte is attached to one side of the solid electrolyte; The composite membrane electrolyte contains lithium lanthanum zirconium aluminum tantalum oxide particles and is obtained by compounding polyethylene oxide, lithium bis(trifluoromethanesulfonyl)imide, and polytetrafluoroethylene; the solid electrolyte is a garnet-type lithium lanthanum zirconium aluminum tantalum oxide ceramic sheet with the chemical formula Li 6.4 La3Zr 1.4 Al 0.1 Ta 0.3 O 12 , which is prepared from the lithium lanthanum zirconium aluminum tantalum oxide particles.

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