Multilayer composite solid electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a multi-layer composite solid electrolyte and a preparation method and application thereof, and the multi-layer composite solid electrolyte comprises a first electrode contact layer, a second electrode contact layer, a third electrode contact layer, a fourth electrode contact layer and a fifth electrode contact layer, the ion conducting layer comprises an active filler, an ionic salt B and a polymer B; and a second electrode contact layer comprising a piezoelectric filler or plasticizer, an ionic salt C, and a polymer C. According to the multi-layer composite solid electrolyte disclosed by the invention, the filler of the ion conduction layer is active filler, so that ion conduction is effectively increased, the functional layer enhances interface contact between an electrode and the electrolyte, the interface contact internal resistance can be effectively reduced, and dendritic crystal growth is inhibited. The preparation method of the multi-layer composite solid electrolyte is universal, the preparation process is high in operability, raw materials are saved, the multi-layer composite solid electrolyte has disciplinary characteristics, and on-demand printing of the multi-layer composite solid electrolyte is expected to be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a multilayer composite solid electrolyte and a preparation method and application thereof. Background Art

[0002] All-solid-state batteries, due to their advantages such as high energy density and high safety, are considered an important development direction for next-generation battery technology. However, ideal solid-state batteries place extremely high demands on the solid electrolyte's ionic conductivity, chemical stability, and mechanical strength. Current material systems and preparation processes struggle to simultaneously meet these requirements. Therefore, accelerating the research and development of solid-state electrolytes and optimizing their preparation processes are crucial to achieving high-performance all-solid-state batteries.

[0003] By effectively combining the advantages of inorganic SEs and polymer SEs through interfacial modification strategies, multilayer composite solid electrolytes can be fabricated. These effectively optimize interfacial stability toward sodium metal and the cathode, potentially reducing interfacial resistance and inhibiting metal dendrite formation, which are crucial for the safe and stable operation of all-solid-state alkali metal batteries. However, current research focuses primarily on single-layer composite solid electrolytes, with relatively little research on multilayer composite solid electrolytes. Furthermore, some commonly used composite solid electrolyte preparation processes, such as solution casting, impregnation, and tape casting, struggle to precisely control the electrolyte structure and composition, particularly in the preparation of heterogeneous electrolytes. Solution casting, primarily used to prepare single-layer electrolyte membranes, struggles to precisely control the formation of specialized structures. The impregnation method, requiring multiple impregnation and drying steps, is complex and poses challenges in ensuring uniformity and consistency across the layers. The tape casting method, primarily used to prepare single-layer electrolyte membranes, requires multiple casting and stacking steps, resulting in complex and costly processes. The difficulty in preparing multilayer composite solid electrolytes lies in the need for precise control of electrolyte structure, composition, thickness, and interfacial contact. Consequently, these traditional processes struggle to meet these requirements. Summary of the Invention

[0004] The present invention aims to solve at least one of the above-mentioned technical problems in the prior art. To this end, the present invention aims to provide a multilayer composite solid electrolyte and its preparation method and application.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A first aspect of the present invention provides a multilayer composite solid electrolyte comprising:

[0007] A first electrode contact layer comprising a piezoelectric filler, an ionic salt A and a polymer A;

[0008] an ion conducting layer comprising an active filler, an ion salt B and a polymer B;

[0009] The second electrode contact layer includes a piezoelectric filler or a plasticizer, an ionic salt C, and a polymer C.

[0010] In the present invention, the active filler can effectively enhance the ion conduction of the ion conduction layer, and the piezoelectric filler or plasticizer can enhance the interface contact between the electrode and the electrolyte, effectively reduce the interface contact internal resistance, and inhibit dendrite growth, thereby improving the performance of the multilayer composite solid electrolyte.

[0011] In some embodiments of the present invention, the multilayer composite solid electrolyte includes at least one of a slurry direct writing type multilayer composite solid electrolyte and a blade coating type multilayer composite solid electrolyte.

[0012] In some embodiments of the present invention, the mass proportion of the piezoelectric filler in the first electrode contact layer is 0.1 to 90%.

[0013] In some embodiments of the present invention, the mass proportion of the ionic salt A in the first electrode contact layer is 0.1 to 50%.

[0014] In some embodiments of the present invention, the mass proportion of polymer A in the first electrode contact layer is 10 to 90%.

[0015] In some embodiments of the present invention, the mass proportion of the active filler in the ion conducting layer is 0.1 to 90%.

[0016] In some embodiments of the present invention, in the ion conducting layer, the mass proportion of the ionic salt B is 0.1 to 50%.

[0017] In some embodiments of the present invention, in the ion conducting layer, the mass proportion of polymer B is 10 to 90%.

[0018] In some embodiments of the present invention, the mass proportion of the piezoelectric filler or plasticizer in the second electrode contact layer is 0.1 to 90%.

[0019] In some embodiments of the present invention, the mass proportion of the ionic salt C in the second electrode contact layer is 0.1 to 50%.

[0020] In some embodiments of the present invention, the mass proportion of polymer C in the second electrode contact layer is 10 to 90%.

[0021] In some embodiments of the present invention, the first electrode contact layer is an anode contact layer, and the second electrode contact layer is a cathode contact layer. When the multilayer composite solid electrolyte is an electrolyte for a symmetrical battery, the first electrode contact layer and the second electrode contact layer are the same; otherwise, the two are different.

[0022] In some embodiments of the present invention, the piezoelectric filler includes at least one of zinc oxide (ZnO), aluminum oxide (Al2O3), zirconium oxide (ZrO2), bismuth ferrite (BiFeO3), lead zirconate titanate (Pb(Zr,Ti)O3), barium titanate (BaTiO3), and lithium niobate (LiNbO3).

[0023] In some embodiments of the present invention, the active filler includes at least one of NASICON-type sodium superion conductor, NaLaTiO4, NaAlSiO4, Na-β-Al2O3, and Na3PS4.

[0024] In some embodiments of the present invention, the plasticizer includes at least one of succinonitrile, dibutyl phthalate, tricresyl phosphate, and trioctyl phosphate.

[0025] In some embodiments of the present invention, the ionic salt A, ionic salt B, and ionic salt C each independently include any one of a lithium ion salt and a sodium ion salt.

[0026] In some embodiments of the present invention, the lithium ion salt includes at least one of LiPF6, LiTFSI, LiFSI, LiClO4, and LiBF4.

[0027] In some embodiments of the present invention, the sodium ion salt includes at least one of NaPF6, NaFSI, NaTFSI, NaClO4, and NaBF4.

[0028] In some embodiments of the present invention, the polymer A, polymer B, and polymer C each independently include at least one of polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), and polyvinyl alcohol (PVA).

[0029] In some embodiments of the present invention, the average thickness of the multilayer composite solid electrolyte is 50 μm to 500 μm.

[0030] In some embodiments of the present invention, in the multi-layer composite solid electrolyte, the average thickness of each layer is 10 μm to 400 μm.

[0031] In some embodiments of the present invention, the average thickness of the first contact layer is 10 μm to 200 μm.

[0032] In some embodiments of the present invention, the average thickness of the ion conducting layer is 40 μm to 300 μm.

[0033] In some embodiments of the present invention, the average thickness of the second contact layer is 10 μm to 200 μm.

[0034] In some embodiments of the present invention, the number of layers of the multi-layer composite solid electrolyte is 3 to 6, and each layer is independently provided individually or repeatedly.

[0035] The second aspect of the present invention provides a method for preparing the multilayer composite solid electrolyte, comprising the following steps:

[0036] The slurries of each layer are formed in sequence and dried to obtain the multi-layer composite solid electrolyte.

[0037] In some embodiments of the present invention, the forming includes at least one of direct writing printing and coating.

[0038] In some embodiments of the present invention, the method for preparing the multilayer composite solid electrolyte comprises the following steps: direct writing each layer of slurry in sequence, and drying to obtain the multilayer composite solid electrolyte.

[0039] In the present invention, direct write printing (DIW) can effectively control the structure and thickness of the solid electrolyte, and print out electrolytes with specific functional layers according to the required model, effectively optimizing the interfacial stability of the electrolyte to the alkali metal and the positive electrode, which is expected to reduce the interfacial resistance, which is crucial to the safe and stable operation of all-solid-state alkali metal batteries.

[0040] In some embodiments of the present invention, the method for preparing the multilayer composite solid electrolyte comprises the following steps: direct writing each layer of slurry in sequence according to the required model, and obtaining the multilayer composite solid electrolyte after drying.

[0041] In some embodiments of the present invention, the process parameters of the direct writing printing are: extrusion pressure of 0.2-1.0 MPa, extruded slurry diameter of 50-400 μm, and needle moving speed of 100-400 μm / s.

[0042] In some embodiments of the present invention, the drying includes freeze drying and / or vacuum drying; the drying time is 15 hours to 30 hours; the freeze drying temperature is -30°C to -60°C; the vacuum drying temperature is 40°C to 70°C.

[0043] In some embodiments of the present invention, the slurry is prepared by mixing the raw materials of each layer in a solvent; the solvent includes deionized water and / or an organic solvent, and the organic solvent is independently selected from at least one of N-methylpyrrolidone, anhydrous acetonitrile, ethanol, acetone, and N,N-dimethylformamide; the mixing is carried out under stirring; the stirring speed is 1200 rpm to 1800 rpm; the stirring time is 5 to 8 minutes; and the number of stirring times is 4 to 6 times. In the present invention, the type or ratio of each layer of filler, ionic salt, and polymer can be adjusted according to actual needs to achieve slurry composition adjustment, and the preparation of a multilayer composite electrolyte can be achieved by direct writing printing.

[0044] The third aspect of the present invention provides a secondary battery comprising the multi-layer composite solid electrolyte.

[0045] In some embodiments of the present invention, the secondary battery includes any one of a symmetrical battery, a half cell, and a full cell.

[0046] In some embodiments of the present invention, the secondary battery includes any one of a lithium ion secondary battery and a sodium ion secondary battery.

[0047] The beneficial effects of the present invention are:

[0048] The multi-layer composite solid electrolyte ion-conducting layer filler of this invention is an active filler, effectively enhancing ion conduction, while the functional layer strengthens the interfacial contact between the electrode and the electrolyte, effectively reducing interfacial contact resistance and inhibiting dendrite growth. The assembled symmetrical battery achieved long-term cycle stability of 1100 hours at 60°C, and the assembled asymmetric battery achieved a capacity retention rate of 93.1% after 400 charge-discharge cycles at a 1C rate.

[0049] The preparation method of the multilayer composite solid electrolyte of the present invention is universal and the preparation process is highly operable. In particular, the direct writing printing method saves raw materials and has interdisciplinary characteristics, and is expected to realize on-demand printing of multilayer functional solid electrolytes. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a flow chart of preparing a multilayer composite solid electrolyte from DIW in Example 1 of the present invention.

[0051] Figure 2 This is an optical picture of the process of preparing DIW multilayer composite solid electrolyte in Example 1 of the present invention.

[0052] Figure 3 Schematic diagram of the structure of a multilayer composite solid electrolyte in an embodiment of the present invention.

[0053] Figure 4This is an SEM image of the piezoelectric functional layer of the multi-layer composite solid-state electrolyte prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0055] Example 1

[0056] This example prepares a DIW multilayer composite solid electrolyte DIW-PBNZS, and the specific process is as follows:

[0057] (1) Take BiFeO3, NaClO4, and PEO and add them into deionized water, where EO:Na + The molar ratio is 15:1, and the mass percentage of BiFeO3 is 5wt%. At room temperature of 25°C, a planetary mixer is used to stir to obtain a mixed slurry A for preparing the metallic sodium contact layer, wherein the speed is 1000 rpm, the stirring time is 6 minutes, and the number of stirring times is 5 times. The mixed slurry B for the intermediate layer is Na3Zr2Si2PO 12 The mixed slurry C of the second electrode contact layer replaces BiFeO3 with succinonitrile at a mass percentage of 80wt%, and the other parts are the same as those of the metal sodium contact layer;

[0058] (2) The mixed slurry obtained in step (1) is transferred to the material cavity, and a 110 μm slurry discharge needle is selected for the mixed slurry of the functional layers on both sides, and a 210 μm slurry discharge needle is selected for the mixed slurry of the middle layer. The extrusion pressure is 0.6 MPa, and the needle movement speed is 150 μm / s to prepare the electrolyte DIW. The printing order of the electrolyte DIW-PBNZS-1 used for sodium symmetric batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry A; the printing order of the electrolyte DIW-PBNZS-2 used for Na3V2(PO4)3||Na batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry C.

[0059] (3) The 3D printed solid electrolyte obtained in step (2) was placed in a freeze dryer, freeze-dried at -30°C for 24 h, and then stored in an Ar glove box.

[0060] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid electrolyte was assembled into a Na||Na symmetric battery (DIW-PBNZS-1) and a Na3V2(PO4)3||Na battery (specifications: CR2032 button cells) (with a packaging pressure of 50 MPa) in an argon-filled glove box. The electrochemical properties of the solid-state electrolyte were then tested.

[0061] Figure 1 Flow chart of the DIW multilayer composite solid electrolyte DIW-PBZ prepared in this embodiment. Figure 1 It can be seen that the multilayer solid electrolyte prepared in Example 1 is printed by extruding the mixed slurry through a needle using DIW.

[0062] Figure 2 This is an optical picture of the DIW multilayer composite solid electrolyte DIW-PBZ process prepared in this embodiment. Figure 2 It can be seen that the solid electrolyte prepared in Example 1 is printed step by step and layer by layer by DIW.

[0063] Example 2

[0064] This example prepares a DIW multilayer composite solid electrolyte DIW-PZNZS, and the specific process is as follows:

[0065] (1) ZnO, TFSI, and PEO were added to deionized water, where EO:Na + The molar ratio is 15:1, and the mass percentage of ZnO is 5 wt%. At room temperature of 25°C, a planetary mixer is used to stir to obtain a mixed slurry A for preparing the metallic sodium contact layer, wherein the speed is 1000 rpm, the stirring time is 6 minutes, and the number of stirring times is 5 times. The mixed slurry B for the intermediate layer is Na3Zr2Si2PO 12 The mixed slurry C of the second electrode contact layer is the same as that of the metal sodium contact layer except that BiFeO3 is replaced by succinonitrile at a mass percentage of 80 wt % and BiFeO3 is replaced by succinonitrile at a mass percentage of 5 wt %.

[0066] (2) The mixed slurry obtained in step (1) is transferred to the material cavity, and a 110 μm slurry discharge needle is selected for the mixed slurry of the functional layers on both sides, and a 210 μm slurry discharge needle is selected for the mixed slurry of the middle layer. The extrusion pressure is 0.6 MPa, and the needle movement speed is 150 μm / s to prepare the electrolyte DIW. The printing order of the electrolyte DIW-PZNZS-1 used for sodium symmetric batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry A; the printing order of the electrolyte DIW-PZNZS-2 used for Na3V2(PO4)3||Na batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry C.

[0067] (3) The 3D printed solid electrolyte obtained in step (2) was placed in a freeze dryer, freeze-dried at -30°C for 24 h, and then stored in an Ar glove box.

[0068] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid electrolyte was assembled into a Na||Na symmetric battery (DIW-PZNZS-1) and a Na3V2(PO4)3||Na battery (specifications: CR2032 button battery) (DIW-PZNZS-2) in an argon-filled glove box with a packaging pressure of 50 MPa, and the electrochemical properties of the solid-state electrolyte were then tested.

[0069] Example 3

[0070] This example prepares a DIW multilayer composite solid electrolyte DIW-PBNLS, and the specific process is as follows:

[0071] (1) Take BiFeO3, NaClO4, and PEO and add them into deionized water, where EO:Na + The molar ratio was 15:1, and the mass percentage of BiFeO3 was 5 wt%. Mixed slurry A for preparing the sodium metal contact layer was prepared by stirring at room temperature (25°C) using a planetary mixer at a speed of 1000 rpm, a stirring time of 6 minutes, and a stirring cycle of 5 times. Mixed slurry B for the intermediate layer replaced BiFeO3 with NaLaTiO4 at a mass percentage of 80 wt%. Mixed slurry C for the second electrode contact layer replaced BiFeO3 with succinonitrile at a mass percentage of 5 wt%. All other conditions were the same as for the sodium metal contact layer.

[0072] (2) The mixed slurry obtained in step (1) is transferred to the material cavity, and a 110 μm slurry discharge needle is selected for the mixed slurry of the functional layers on both sides, and a 210 μm slurry discharge needle is selected for the mixed slurry of the middle layer. The extrusion pressure is 0.6 MPa, and the needle movement speed is 150 μm / s to prepare the electrolyte DIW. The printing order of the electrolyte DIW-PBNLS-1 used for sodium symmetric batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry A; the printing order of the electrolyte DIW-PBNLS-2 used for Na3V2(PO4)3||Na batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry C.

[0073] (3) The 3D printed solid electrolyte obtained in step (2) was placed in a freeze dryer, freeze-dried at -30°C for 24 h, and then stored in an Ar glove box.

[0074] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid electrolyte was assembled into a Na||Na symmetric battery (DIW-PBNLS-1) and a Na3V2(PO4)3||Na battery (specifications: CR2032 button cells) (with a packaging pressure of 50 MPa) in an argon-filled glove box. The electrochemical properties of the solid-state electrolyte were then tested.

[0075] Example 4

[0076] This example prepares a DIW multilayer composite solid electrolyte DIW-PZZ, and the specific process is as follows:

[0077] (1) ZnO, NaTFSI, and PEO were added to deionized water, where EO:Na + The molar ratio was 15:1, and the mass percentage of ZnO was 5 wt%. Mixed slurry A for preparing the sodium metal contact layer was prepared using a planetary mixer at room temperature (25°C) at a speed of 1000 rpm, a stirring time of 6 minutes, and a stirring cycle of 5 times. Mixed slurry B for the intermediate layer replaced BiFeO3 with NaLaTiO4 at a mass percentage of 80 wt%. Mixed slurry C for the second electrode contact layer replaced ZnO with succinonitrile at a mass percentage of 5 wt%. All other components were the same as for the sodium metal contact layer.

[0078] (2) The mixed slurry obtained in step (1) is transferred to the material cavity, and a 110 μm slurry discharge needle is selected for the mixed slurry of the functional layers on both sides, and a 210 μm slurry discharge needle is selected for the mixed slurry of the middle layer. The extrusion pressure is 0.6 MPa, and the needle movement speed is 150 μm / s to prepare the electrolyte DIW. The printing order of the electrolyte DIW-PBNLS-1 used for sodium symmetric batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry A; the printing order of the electrolyte DIW-PBNLS-2 used for Na3V2(PO4)3||Na batteries is: first print mixed slurry A, then print mixed slurry B, and finally print mixed slurry C.

[0079] (3) The 3D printed solid electrolyte obtained in step (2) was placed in a freeze dryer, freeze-dried at -30°C for 24 h, and then stored in an Ar glove box.

[0080] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid electrolyte was assembled into a Na||Na symmetric battery (DIW-PBNLS-1) and a Na3V2(PO4)3||Na battery (specifications: CR2032 button cells) (with a packaging pressure of 50 MPa) in an argon-filled glove box. The electrochemical properties of the solid-state electrolyte were then tested.

[0081] Example 5

[0082] This example prepares a BiFeO3 composite PEO-based solid electrolyte PNB, the specific process is as follows:

[0083] (1) BiFeO3, NaTFSI, and PEO were added to deionized water, where EO:Na + The molar ratio was 15:1, and the mass percentage of ZnO was 5 wt%. A mixed slurry for preparing the surface functional layer was obtained by stirring at room temperature (25°C) using a planetary mixer at a speed of 1200 rpm, a stirring time of 6 minutes, and a stirring cycle of 5 times. The mixed slurry for the intermediate layer was the same as that for the functional layer except that NaLaTiO4 replaced BiFeO3 at a mass percentage of 80 wt%.

[0084] (2) taking the surface functional layer mixed slurry of step (1) into a coating machine, adjusting the scraper height to 0.5 mm, and flattening the mixed slurry with the scraper to form a solid electrolyte membrane, and then placing it in a vacuum oven and drying it under vacuum at 60°C for 24 hours;

[0085] (3) The intermediate layer mixed slurry of step (1) is placed in a coating machine, and the scraper height is adjusted to 1.0 mm. The mixed slurry is flattened on the basis of the solid electrolyte membrane of step (2) with the scraper to form a solid electrolyte membrane, which is then placed in a vacuum oven and dried under vacuum at 60°C for 24 hours;

[0086] (4) taking the surface functional layer mixed slurry of step (1) into a coating machine, adjusting the scraper height to 0.5 mm, and using the scraper to flatten the mixed slurry on the basis of the solid electrolyte membrane of step (3) to form a solid electrolyte membrane, and then placing it in a vacuum oven and drying it under vacuum at 60°C for 24 hours;

[0087] (5) The solid electrolyte membrane obtained in step (4) was cut into 19 mm diameter discs and then stored in an Ar glove box.

[0088] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid-state electrolyte was assembled into Na||Na symmetric batteries and Na3V2(PO4)3||Na batteries (specifications: CR2032 button batteries) in a glove box filled with argon, with a packaging pressure of 50MPa, and then the electrochemical properties of the solid-state electrolyte were tested.

[0089] Comparative Example 1

[0090] This comparative example prepared a PEO-based solid electrolyte PN, and the specific process was as follows:

[0091] (1) Take NaTFSI and PEO and add them into deionized water, where EO:Na + The molar ratio is 15:1. A planetary mixer is used to stir the mixed slurry for preparing the surface functional layer at room temperature of 25°C at a speed of 1200 rpm, a stirring time of 6 minutes, and a stirring frequency of 5 times.

[0092] (2) The mixed slurry of step (1) was placed in a coating machine, and the scraper height was adjusted to 2 mm. The mixed slurry was flattened with the scraper to form a solid electrolyte membrane, and then placed in a vacuum oven and dried under vacuum at 60°C for 24 hours;

[0093] (3) The solid electrolyte membrane obtained in step (2) was cut into 19 mm diameter discs and then stored in an Ar glove box.

[0094] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid-state electrolyte was assembled into Na||Na symmetric batteries and Na3V2(PO4)3||Na batteries (specifications: CR2032 button batteries) in a glove box filled with argon, with a packaging pressure of 50MPa, and then the electrochemical properties of the solid-state electrolyte were tested.

[0095] Comparative Example 2

[0096] This comparative example prepared a PEO-based solid electrolyte PNZ, and the specific process was as follows:

[0097] (1) Take succinonitrile, NaTFSI and PEO and add them into deionized water respectively, where EO:Na + The molar ratio is 15:1, the mass percentage of succinonitrile is 5 wt %. A mixed slurry for preparing the surface functional layer was obtained by stirring with a planetary mixer at room temperature of 25°C at a speed of 1200 rpm, a stirring time of 6 minutes, and a stirring frequency of 5 times.

[0098] (2) The mixed slurry of step (1) was placed in a coating machine, and the scraper height was adjusted to 2 mm. The mixed slurry was flattened with the scraper to form a solid electrolyte membrane, and then placed in a vacuum oven and dried under vacuum at 60°C for 24 hours;

[0099] (3) The solid electrolyte membrane obtained in step (2) was cut into 19 mm diameter discs and then stored in an Ar glove box.

[0100] The above-mentioned composite solid-state electrolyte disc was applied to sodium-ion all-solid-state batteries: the solid-state electrolyte was assembled into Na||Na symmetric batteries and Na3V2(PO4)3||Na batteries (specifications: CR2032 button batteries) in a glove box filled with argon, with a packaging pressure of 50MPa, and then the electrochemical properties of the solid-state electrolyte were tested.

[0101] Test Example 1

[0102] The Na||Na symmetrical batteries prepared in Examples 1-4 and Comparative Examples 1-3 were tested for ion mobility, critical current density, and cycle stability at 60°C. The Na3V2(PO4)3||Na battery was tested for rate performance and cycle stability. Based on the test results, the ionic conductivity and stability were determined. Some of the results are shown in Table 1:

[0103] Table 1

[0104]

[0105]

[0106] As can be seen from Table 1, the DIW multilayer composite solid electrolytes of Examples 1 to 5 have outstanding ion migration numbers, which are much higher than the single-layer solid electrolyte prepared by the ordinary coating method of the comparative example. It can be seen from Example 1 and Comparative Example 1 that the electrochemical performance is very different when there is only a difference in whether it is a DIW multilayer electrolyte: in the Na||Na symmetric battery, the ion migration number of the DIW multilayer solid electrolyte is 0.49, and it can be cycled for 1100h; while the ion migration number of the single-layer solid electrolyte prepared in Comparative Example 1 is 0.18, and it short-circuit after 150h of circulation. This is because the piezoelectric effect of the BiFeO3 filler in the DIW multilayer electrolyte allows sodium ions to be uniformly deposited and effectively inhibits the growth of sodium dendrites, while Na3Zr2Si2PO 12 As an active filler, it effectively promotes the transmission of Na ions, thereby having a higher ion migration number and long-cycle stability. In the Na3V2(PO4)3||Na battery, the capacity retention rate of the DIW multilayer solid electrolyte after 400 cycles at 1C is 93.1%; while the capacity retention rate of the single-layer solid electrolyte prepared in Comparative Example 1 after 200 cycles at 1C is only 31.2%. This is because the succinonitrile plasticizer in the DIW multilayer electrolyte makes the cathode-electrolyte interface contact more closely, which is conducive to sodium ion conduction, while the single-layer solid electrolyte has a large number of voids at the cathode-electrolyte interface. In addition, the piezoelectric effect of the BiFeO3 filler can effectively inhibit the growth of sodium dendrites at the anode and allow sodium ions to be uniformly deposited. Therefore, the battery assembled with the multilayer solid electrolyte of the present invention exhibits excellent capacity reversibility and provides significant capacity.

[0107] Compared with Example 5, Examples 1 to 4 use direct writing printing to prepare multilayer composite solid electrolytes. The process is simpler and the slurry molding is better controlled, which can further improve the battery's ion migration number and cycle performance.

[0108] Figure 3 is a schematic diagram of a DIW multilayer composite solid electrolyte in an embodiment of the present invention, Figure 4 This is a SEM image of the piezoelectric functional layer of the DIW multilayer composite solid electrolyte prepared in Example 1 of the present invention. The effects of the other examples are similar and will not be described in detail.

[0109] from Figure 3 It can be seen that the composite solid electrolyte prepared in the embodiment has a multi-layer structure, which can be printed in a multi-layer structure according to the characteristics of the sodium anode and different cathode materials. The piezoelectric effect of the piezoelectric functional layer allows the sodium ions of the sodium metal anode to be uniformly deposited, effectively inhibiting the growth of sodium dendrites; and the active filler in the middle layer effectively promotes the transmission of Na ions, thereby having a higher ion migration number and long cycle stability; the plasticizer functional layer makes the cathode-electrolyte interface contact closer, which is beneficial to sodium ion conduction. Figure 4It can be seen that the surface of the DIW multilayer composite solid electrolyte prepared in Example 1 is relatively smooth and flat.

[0110] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A multilayer composite solid electrolyte, characterized in that: Including the following settings: A first electrode contact layer comprising a piezoelectric filler, an ionic salt A and a polymer A; an ion conducting layer comprising an active filler, an ion salt B and a polymer B; The second electrode contact layer includes a piezoelectric filler or a plasticizer, an ionic salt C, and a polymer C.

2. The multilayer composite solid electrolyte according to claim 1, characterized in that: The first electrode contact layer satisfies at least one of the following conditions: (I) The piezoelectric filler comprises at least one of zinc oxide, aluminum oxide, zirconium oxide, bismuth ferrite, lead zirconate titanate, barium titanate, and lithium niobate; (II) the mass proportion of the piezoelectric filler is 0.1 to 90%; (III) the mass proportion of the ionic salt A is 0.1 to 50%; (IV) the mass proportion of the polymer A is 10 to 90%; (V) The average thickness of the first contact layer is 10 μm to 200 μm.

3. The multilayer composite solid electrolyte according to claim 1, characterized in that: The ion conducting layer satisfies at least one of the following conditions: (I) The active filler comprises at least one of a NASICON-type sodium superion conductor, NaLaTiO4, NaAlSiO4, Na-β-Al2O3, and Na3PS4; (II) the mass proportion of the active filler is 0.1 to 90%; (III) the mass proportion of the ionic salt B is 0.1 to 50%; (IV) the mass proportion of the polymer B is 10 to 90%; (V) The average thickness of the ion conductive layer is 40 μm to 300 μm.

4. The multilayer composite solid electrolyte according to claim 1, characterized in that: The second electrode contact layer satisfies at least one of the following conditions: (I) The piezoelectric filler comprises at least one of zinc oxide, aluminum oxide, zirconium oxide, bismuth ferrite, lead zirconate titanate, barium titanate, and lithium niobate; (II) the plasticizer comprises at least one of succinonitrile, dibutyl phthalate, tricresyl phosphate, and trioctyl phosphate; (III) the mass proportion of the piezoelectric filler or plasticizer is 0.1 to 90%; (IV) the mass proportion of the ionic salt C is 0.1 to 50%; (V) the mass proportion of the polymer C is 10 to 90%; (VI) The average thickness of the second contact layer is 10 μm to 200 μm.

5. The multilayer composite solid electrolyte according to claim 1, characterized in that: The ionic salt A, ionic salt B, and ionic salt C each independently include any one of lithium ion salt and sodium ion salt.

6. The multilayer composite solid electrolyte according to claim 1, characterized in that: The polymer A, polymer B, and polymer C each independently include at least one of polyethylene oxide, polymethyl methacrylate, polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene, polyacrylonitrile, and polyvinyl alcohol.

7. The multilayer composite solid electrolyte according to claim 1, characterized in that: The average thickness of the multi-layer composite solid electrolyte is 50 μm to 500 μm.

8. A method for preparing the multilayer composite solid electrolyte according to any one of claims 1 to 7, characterized in that: The following steps are involved: The slurries of each layer are formed in sequence and dried to obtain the multi-layer composite solid electrolyte.

9. The method for preparing a multilayer composite solid electrolyte according to claim 8, characterized in that: The method for preparing the multi-layer composite solid electrolyte comprises the following steps: direct writing printing each layer of slurry in sequence, and preparing the multi-layer composite solid electrolyte after drying.

10. A secondary battery comprising the multilayer composite solid electrolyte according to any one of claims 1 to 7.

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