A double-layer composite solid electrolyte membrane, a preparation method thereof, and a full solid-state battery

Abstract

The application provides a double-layer composite solid electrolyte film, a preparation method thereof and a full solid-state battery. The double-layer composite solid electrolyte film comprises a first composite solid electrolyte film and a second composite solid electrolyte film which are stacked in sequence; the mass ratio of inorganic fillers and polymers in the slurry of the first composite solid electrolyte film is (1-8):10; the mass ratio of inorganic fillers and polymers in the slurry of the second composite solid electrolyte film is (3-8):1; and the types of inorganic fillers and polymers in the first composite solid electrolyte film and the second composite solid electrolyte film are the same. The application aims to improve the electrochemical stability, high-temperature resistance and interface impedance between the composite electrolyte film and the electrode, and a double-layer composite solid electrolyte film with a specific structure is prepared.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte materials technology, specifically relating to a bilayer composite solid electrolyte membrane, its preparation method, and an all-solid-state battery. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, aerospace, and portable electronic devices due to their high energy density, wide operating voltage and temperature range, excellent cycle performance, and environmental friendliness. The electrolyte, as a key component of lithium-ion batteries, is closely related to the battery's electrochemical performance, including cycle life, safety, and capacity. Currently, the most widely used electrolytes on the market are organic liquid electrolytes, but these are prone to problems such as organic solvent leakage, combustion, and explosion, posing significant safety hazards. Replacing organic liquid electrolytes with non-flammable solid-state electrolytes is one of the main ways to improve the safety performance of lithium-ion batteries; therefore, all-solid-state batteries have become one of the important technological development directions for next-generation batteries.

[0003] In recent years, the types of solid electrolytes studied have mainly included three categories: inorganic solid electrolytes, polymer solid electrolytes, and organic / inorganic composite solid electrolytes. Inorganic solid electrolytes possess high mechanical strength, a wide electrochemical window, and high room-temperature ionic conductivity (10⁻⁶). -4 ~10 -3 While polymer solid electrolytes offer advantages such as high S / cm, they suffer from poor interfacial contact with the electrode and are expensive to prepare. Polymer solid electrolytes, on the other hand, exhibit good flexibility, excellent interfacial contact with the electrode, mature preparation processes, and low cost, but their ionic conductivity is relatively low (<10). -5 The current efficiency (S / cm) is insufficient for the commercial application of lithium-ion batteries. Organic / inorganic composite solid electrolytes, which combine the advantages of both organic and inorganic solid electrolytes, have become a promising composite solid electrolyte technology. However, composite solid electrolytes with high polymer content exhibit poor electrochemical stability and high-temperature resistance, making them prone to short circuits and thermal runaway at high temperatures. Furthermore, composite solid electrolytes with high inorganic filler content suffer from poor interfacial contact with the electrodes, hindering ion transport and impeding the full utilization of battery capacity.

[0004] In summary, in order to improve the electrochemical stability, high-temperature resistance and reduce the interfacial impedance between the composite solid electrolyte and the electrode, it is urgent to develop a composite solid electrolyte that meets the above requirements. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a bilayer composite solid electrolyte membrane, its preparation method, and an all-solid-state battery. This invention addresses the technical problems of improving the electrochemical stability, high-temperature resistance, and reducing the interfacial impedance between the composite electrolyte membrane and the electrode, and by preparing a bilayer composite solid electrolyte membrane with a specific structure.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a dual-layer composite solid electrolyte membrane, the dual-layer composite solid electrolyte membrane comprising a first composite solid electrolyte membrane and a second composite solid electrolyte membrane stacked sequentially.

[0008] The mass ratio of inorganic filler to polymer in the slurry of the first composite solid electrolyte membrane is (1-8):10;

[0009] The mass ratio of inorganic filler to polymer in the slurry of the second composite solid electrolyte membrane is (3-8):1;

[0010] The first composite solid electrolyte membrane and the second composite solid electrolyte membrane contain the same types of inorganic fillers and polymers.

[0011] In this invention, the mass ratio of inorganic filler to polymer in the slurry of the first composite solid electrolyte membrane is (1-8):10, for example, it can be 1:10, 2:10, 3:10, 4:10, 5:10, 6:10, 7:10, or 8:10.

[0012] In this invention, the mass ratio of inorganic filler to polymer in the slurry of the second composite solid electrolyte membrane is (3-8):1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1, or 8:1.

[0013] This invention designs the composition of inorganic fillers and polymers in a two-layer composite solid electrolyte membrane, resulting in a first-layer composite solid electrolyte membrane with a high polymer content and a second-layer composite solid electrolyte membrane with a high inorganic filler content. The high inorganic filler content of the second-layer composite solid electrolyte membrane enhances the high-temperature resistance and thermal shrinkage performance of the electrolyte membrane; the low inorganic filler content of the first-layer composite solid electrolyte membrane improves the flexibility of the electrolyte membrane and reduces the interfacial impedance with the electrode. Therefore, the dual-layer composite solid electrolyte membrane provided by this invention can effectively improve the electrochemical stability, high-temperature resistance, and reduce interfacial impedance of the solid electrolyte membrane, thereby further improving the safety performance of the battery.

[0014] Preferably, both the first composite solid electrolyte membrane and the second composite solid electrolyte membrane further include lithium salt.

[0015] Preferably, the mass ratio of lithium salt to polymer in the slurry of the first composite solid electrolyte membrane is (1-3.5):10, for example, it can be 1:10, 1.2:10, 1.5:10, 1.8:10, 2:10, 2.2:10, 2.5:10, 2.8:10, 3:10, 3.2:10, or 3.5:10.

[0016] Preferably, the mass ratio of lithium salt to polymer in the slurry of the second composite solid electrolyte membrane is (1-3.5):10, for example, it can be 1:10, 1.2:10, 1.5:10, 1.8:10, 2:10, 2.2:10, 2.5:10, 2.8:10, 3:10, 3.2:10, or 3.5:10.

[0017] In this invention, by controlling the mass ratio of lithium salt to polymer in the slurry of the composite solid electrolyte membrane, it is beneficial to Li + Rapid transport of electrolytes is crucial; a low mass ratio will reduce the ionic conductivity of the electrolyte membrane, while a high mass ratio will reduce its mechanical properties.

[0018] Preferably, the inorganic filler includes any one or a combination of at least two of lithium aluminum titanium phosphate and its derivatives, lithium lanthanum zirconium oxide and its derivatives, lithium aluminum germanium phosphate and its derivatives, lithium lanthanum titanate and its derivatives, silicon dioxide or aluminum oxide. For example, it can be lithium lanthanum zirconium oxide, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate or lithium lanthanum titanate. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0019] Preferably, the average particle size of the inorganic filler is 0.5 to 1 μm, for example, it can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or 1 μm.

[0020] In this invention, by controlling the average particle size of the inorganic filler, it is more conducive to improving the cycle stability of solid-state batteries. If the average particle size is too small, agglomeration is likely to occur. Conversely, if the average particle size is too large, the slurry will be unevenly dispersed and will be prone to rapid sedimentation.

[0021] Preferably, the polymer includes any one or a combination of at least two of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, or polyacrylonitrile. For example, it can be polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, or polyacrylonitrile. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0022] Preferably, the molecular weight of the polymer is 300,000 to 600,000, for example, 300,000, 350,000, 400,000, 450,000, 500,000, 550,000, or 600,000.

[0023] In this invention, by adjusting the molecular weight of the polymer, it is more beneficial to improve the thermal shrinkage performance and flexibility of the electrolyte membrane. If the molecular weight is too low, the thermal shrinkage performance of the electrolyte membrane will be poor, and vice versa, the flexibility of the electrolyte membrane will be poor.

[0024] Preferably, the lithium salt includes any one or a combination of at least two of the following: LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiB(C2O4)2, LiBF4, LiBF3(C2F5), LiDFOB, LIODFB, LiTFSI, LiN(SO2CF3)2, LiFSI, LiN(SO2F)2, LiCF3SO3, LiAsF6, LiSbF6, or LiClO4. For example, it can be LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, or LiB(C2O4)2. For the sake of brevity, the combinations within the above range will not be listed one by one.

[0025] Preferably, the thickness of the first composite solid electrolyte membrane is 9 to 10 μm, for example, it can be 9 μm, 9.1 μm, 9.2 μm, 9.3 μm, 9.4 μm, 9.5 μm, 9.6 μm, 9.7 μm, 9.8 μm, 9.9 μm, or 10 μm.

[0026] In this invention, by adjusting the thickness of the first composite solid electrolyte membrane, it is easier to integrate the electrolyte membrane into the battery cell. If the thickness is too thin, the mechanical properties of the electrolyte membrane will be reduced, and if the thickness is too thick, the energy density of the battery cell will be reduced when it is integrated into the battery cell later.

[0027] Preferably, the thickness of the second composite solid electrolyte membrane is 4 to 6 μm, for example, it can be 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, or 6 μm.

[0028] In this invention, by adjusting the thickness of the second composite solid electrolyte membrane, the thermal shrinkage performance of the electrolyte membrane can be improved. If the thickness is too small, the thermal shrinkage performance of the electrolyte membrane will be poor, and if the thickness is too large, the electrolyte membrane will crack.

[0029] In a second aspect, the present invention provides a method for preparing a bilayer composite solid electrolyte membrane according to the first aspect, the method comprising the following steps:

[0030] (1) The inorganic filler dispersion and polymer solution are mixed according to the formula amount, and then lithium salt is added to obtain the first composite solid electrolyte membrane slurry.

[0031] (2) The inorganic filler dispersion and polymer solution are mixed according to the formula amount, and then lithium salt is added to obtain the second composite solid electrolyte membrane slurry.

[0032] (3) The first composite solid electrolyte membrane slurry obtained in step (1) and the second composite solid electrolyte membrane slurry obtained in step (2) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (1) is coated on the substrate surface, and the slurry in step (2) is coated on the membrane surface in step (1) to obtain the double-layer composite solid electrolyte membrane.

[0033] In this invention, a dual-head coating machine is used for simultaneous coating to avoid wrinkling that would occur if the second layer of slurry is applied after the first layer has dried.

[0034] Preferably, the mixing in step (1) is carried out under stirring.

[0035] Preferably, the viscosity of the first composite solid electrolyte membrane slurry in step (1) is 3000-4000 mPa·s, for example, it can be 3000 mPa·s, 3100 mPa·s, 3200 mPa·s, 3300 mPa·s, 3400 mPa·s, 3500 mPa·s, 3600 mPa·s, 3700 mPa·s, 3800 mPa·s, 3900 mPa·s, or 4000 mPa·s.

[0036] In this invention, by adjusting the viscosity of the first composite solid electrolyte membrane slurry in step (1), it is beneficial to coat the slurry. If the viscosity is too low, the slurry will flow more strongly and will easily flow during the coating process. Conversely, if the viscosity is too high, the slurry will have poor fluidity and will easily clump during the coating process.

[0037] Preferably, the mixing in step (2) is carried out under stirring.

[0038] Preferably, the viscosity of the second composite solid electrolyte membrane slurry in step (2) is 5000-6000 mPa·s, for example, it can be 5000 mPa·s, 5100 mPa·s, 5200 mPa·s, 5300 mPa·s, 5400 mPa·s, 5500 mPa·s, 5600 mPa·s, 5700 mPa·s, 5800 mPa·s, 5900 mPa·s, or 6000 mPa·s.

[0039] In this invention, by adjusting the viscosity of the second composite solid electrolyte membrane slurry in step (2), it is beneficial to coat the slurry. If the viscosity is too low, the slurry will flow more strongly and will easily flow during the coating process. Conversely, if the viscosity is too high, the slurry will have poor fluidity and will easily clump during the coating process.

[0040] Thirdly, the present invention provides an all-solid-state battery, the all-solid-state battery comprising a positive electrode, a negative electrode and a solid electrolyte membrane, wherein the solid electrolyte membrane is a bilayer composite solid electrolyte membrane as described in the first aspect.

[0041] The lithium-ion battery prepared by the bilayer composite solid electrolyte provided by this invention has improved cycle performance at high temperatures.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] This invention designs the composition of inorganic fillers and polymers in a two-layer composite solid electrolyte membrane, resulting in a first-layer composite solid electrolyte membrane with a high polymer content and a second-layer composite solid electrolyte membrane with a high inorganic filler content. The bilayer composite solid electrolyte membrane provided by this invention can effectively improve the electrochemical stability, high-temperature resistance, and reduce interfacial impedance of solid electrolyte membranes, thereby further enhancing battery safety.

[0044] The production process of the double-layer composite solid electrolyte membrane provided by this invention is simple and low-cost, and the thickness of the resulting film is controllable, with the only impact being on environmental humidity, which is beneficial for industrial scale-up production. Detailed Implementation

[0045] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0046] Example 1

[0047] This embodiment provides a bilayer composite solid electrolyte membrane, which includes a first composite solid electrolyte membrane (10 μm thick) and a second composite solid electrolyte membrane (5 μm thick) stacked sequentially. The solid electrolyte membrane includes polyvinylidene fluoride (600,000 molecular weight), lithium aluminum titanium phosphate (0.6 μm average particle size) and lithium LiTFSI salt.

[0048] This embodiment also provides a method for preparing a bilayer composite solid electrolyte membrane, the preparation method is as follows:

[0049] (1) Mix lithium titanium aluminum phosphate and N-methylpyrrolidone, and disperse them by ultrasonication for 30 min to form a lithium titanium aluminum phosphate dispersion. At the same time, mix polyvinylidene fluoride and N-methylpyrrolidone, and stir at high speed of 1200 r / min using a planetary mixer until the polyvinylidene fluoride liquid is clear and transparent.

[0050] (2) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a first composite solid electrolyte membrane slurry with a solid content of 30.19%. The mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry was 57.80%, the mass percentage of lithium titanium aluminum phosphate was 23.12%, and the mass percentage of LiTFSI lithium salt was 19.08%.

[0051] (3) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a second composite solid electrolyte membrane slurry with a solid content of 34.53%. The mass percentage of polyvinylidene fluoride in the second composite solid electrolyte membrane slurry was 15.80%, the mass percentage of lithium titanium aluminum phosphate was 78.99%, and the mass percentage of LiTFSI lithium salt was 5.21%.

[0052] (4) The first composite solid electrolyte membrane slurry obtained in step (2) and the second composite solid electrolyte membrane slurry obtained in step (3) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (2) is coated on the substrate surface, and the slurry in step (3) is coated on the membrane surface in step (2) to obtain the double-layer composite solid electrolyte membrane.

[0053] Example 2

[0054] This embodiment provides a bilayer composite solid electrolyte membrane, which includes a first composite solid electrolyte membrane (10 μm thick) and a second composite solid electrolyte membrane (6 μm thick) stacked sequentially. The composite solid electrolyte membrane includes polyvinylidene fluoride (molecular weight of 500,000), lithium aluminum titanium phosphate (average particle size of 0.6 μm) and lithium LiTFSI salt.

[0055] This embodiment also provides a method for preparing a bilayer composite solid electrolyte membrane, the preparation method is as follows:

[0056] (1) Mix lithium titanium aluminum phosphate and N-methylpyrrolidone, and disperse them by ultrasonication for 30 min to form a lithium titanium aluminum phosphate dispersion. At the same time, mix polyvinylidene fluoride and N-methylpyrrolidone, and stir at high speed of 1200 r / min using a planetary mixer until the polyvinylidene fluoride liquid is clear and transparent.

[0057] (2) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a first composite solid electrolyte membrane slurry with a solid content of 28.95%. The mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry was 61.35%, the mass percentage of lithium titanium aluminum phosphate was 18.40%, and the mass percentage of LiTFSI lithium salt was 20.25%.

[0058] (3) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a second composite solid electrolyte membrane slurry with a solid content of 30.22%. The mass percentage of polyvinylidene fluoride in the second composite solid electrolyte membrane slurry was 23.09%, the mass percentage of lithium titanium aluminum phosphate was 69.28%, and the mass percentage of LiTFSI lithium salt was 7.63%.

[0059] (4) The first composite solid electrolyte membrane slurry obtained in step (2) and the second composite solid electrolyte membrane slurry obtained in step (3) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (2) is coated on the substrate surface, and the slurry in step (3) is coated on the membrane surface in step (2) to obtain the double-layer composite solid electrolyte membrane.

[0060] Example 3

[0061] This embodiment provides a bilayer composite solid electrolyte membrane, which includes a first composite solid electrolyte membrane (10 μm thick) and a second composite solid electrolyte membrane (5 μm thick) stacked sequentially. The composite solid electrolyte membrane includes polyvinylidene fluoride (600,000 molecular weight), lithium aluminum titanium phosphate (1 μm average particle size), and lithium LiTFSI salt.

[0062] This embodiment also provides a method for preparing a bilayer composite solid electrolyte membrane, the preparation method is as follows:

[0063] (1) Mix lithium titanium aluminum phosphate and N-methylpyrrolidone, and disperse them by ultrasonication for 30 min to form a lithium titanium aluminum phosphate dispersion. At the same time, mix polyvinylidene fluoride and N-methylpyrrolidone, and stir at high speed of 1200 r / min using a planetary mixer until the polyvinylidene fluoride liquid is clear and transparent.

[0064] (2) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a first composite solid electrolyte membrane slurry with a solid content of 26.34%. The mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry was 69.93%, the mass percentage of lithium titanium aluminum phosphate was 6.99%, and the mass percentage of LiTFSI lithium salt was 23.08%.

[0065] (3) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a second composite solid electrolyte membrane slurry with a solid content of 34.77%. The mass percentage of polyvinylidene fluoride in the second composite solid electrolyte membrane slurry was 18.76%, the mass percentage of lithium titanium aluminum phosphate was 75.05%, and the mass percentage of LiTFSI lithium salt was 6.19%.

[0066] (4) The first composite solid electrolyte membrane slurry obtained in step (2) and the second composite solid electrolyte membrane slurry obtained in step (3) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (2) is coated on the substrate surface, and the slurry in step (3) is coated on the membrane surface in step (2) to obtain the double-layer composite solid electrolyte membrane.

[0067] Example 4

[0068] The difference between this embodiment and Embodiment 1 is that the mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry is 57.80%, the mass percentage of lithium titanium aluminum phosphate is 36.42%, and the mass percentage of LiTFSI lithium salt is 5.78%. All other contents are the same as in Embodiment 1.

[0069] Example 5

[0070] The difference between this embodiment and Embodiment 1 is that the mass percentage of polyvinylidene fluoride in the second composite solid electrolyte membrane slurry is 10.75%, the mass percentage of lithium titanium aluminum phosphate is 86%, and the mass percentage of LiTFSI lithium salt is 3.25%. All other aspects are the same as in Embodiment 1.

[0071] Example 6

[0072] The difference between this embodiment and Embodiment 1 is that the mass ratio of lithium salt to polymer in the slurry of the first composite solid electrolyte membrane and the slurry of the second composite solid electrolyte membrane is 0.5:10, while all other aspects are the same as in Embodiment 1.

[0073] Example 7

[0074] The difference between this embodiment and Embodiment 1 is that the mass ratio of lithium salt to polymer in the slurry of the first composite solid electrolyte membrane and the slurry of the second composite solid electrolyte membrane is 7:10. All other aspects are the same as in Embodiment 1.

[0075] Example 8

[0076] The difference between this embodiment and Embodiment 1 is that the molecular weight of the polymer in the slurry of the first composite solid electrolyte membrane and the slurry of the second composite solid electrolyte membrane is 200,000, while all other aspects are the same as in Embodiment 1.

[0077] Example 9

[0078] The difference between this embodiment and Embodiment 1 is that the molecular weight of the polymer in the slurry of the first composite solid electrolyte membrane and the slurry of the second composite solid electrolyte membrane is 700,000, while all other aspects are the same as in Embodiment 1.

[0079] Example 10

[0080] The difference between this embodiment and Embodiment 1 is that the thickness of the first composite solid electrolyte membrane is 4 μm and the thickness of the second composite solid electrolyte membrane is 10 μm, while all other aspects are the same as in Embodiment 1.

[0081] Example 11

[0082] The difference between this embodiment and Embodiment 1 is that the thickness of the first composite solid electrolyte membrane is 15 μm and the thickness of the second composite solid electrolyte membrane is 10 μm, while all other aspects are the same as in Embodiment 1.

[0083] Example 12

[0084] The difference between this embodiment and Embodiment 1 is that the viscosity of the first composite solid electrolyte membrane slurry is 2500 mPa·s, and the viscosity of the second composite solid electrolyte membrane slurry is 4500 mPa·s. All other aspects are the same as in Embodiment 1.

[0085] Example 13

[0086] The difference between this embodiment and Embodiment 1 is that the viscosity of the first composite solid electrolyte membrane slurry is 4500 mPa·s, and the viscosity of the second composite solid electrolyte membrane slurry is 6500 mPa·s. All other aspects are the same as in Embodiment 1.

[0087] Comparative Example 1

[0088] The difference between this comparative example and Example 1 is that the mass ratio of inorganic filler to polymer in the slurry of the first composite solid electrolyte membrane is 0.5:10, and the mass ratio of inorganic filler to polymer in the slurry of the second composite solid electrolyte membrane is 1:1. All other aspects are the same as in Example 1.

[0089] Comparative Example 2

[0090] The difference between this comparative example and Example 1 is that the mass ratio of inorganic filler to polymer in the slurry of the first composite solid electrolyte membrane is 12:10, and the mass ratio of inorganic filler to polymer in the slurry of the second composite solid electrolyte membrane is 12:1. All other aspects are the same as in Example 1.

[0091] Comparative Example 3

[0092] This comparative example provides a bilayer composite solid electrolyte membrane, which includes a first composite solid electrolyte membrane (9 μm thick) and a second composite solid electrolyte membrane (4 μm thick) stacked sequentially. The composite solid electrolyte membrane includes polyvinylidene fluoride (molecular weight of 500,000), lithium aluminum titanium phosphate (average particle size of 0.5 μm) and lithium LiTFSI salt.

[0093] This comparative example also provides a method for preparing a bilayer composite solid electrolyte membrane, the preparation method is as follows:

[0094] (1) Mix lithium titanium aluminum phosphate and N-methylpyrrolidone, and disperse them by ultrasonication for 30 min to form a lithium titanium aluminum phosphate dispersion. At the same time, mix polyvinylidene fluoride and N-methylpyrrolidone, and stir at high speed of 1200 r / min using a planetary mixer until the polyvinylidene fluoride liquid is clear and transparent.

[0095] (2) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a first composite solid electrolyte membrane slurry with a solid content of 31.39%. The mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry was 54.64%, the mass percentage of lithium titanium aluminum phosphate was 27.32%, and the mass percentage of LiTFSI lithium salt was 18.04%.

[0096] (3) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a second composite solid electrolyte membrane slurry with a solid content of 18.90%. The mass percentage of polyvinylidene fluoride, lithium titanium aluminum phosphate, and LiTFSI lithium salt in the second composite solid electrolyte membrane slurry was 42.92% and 42.92% respectively.

[0097] (4) The first composite solid electrolyte membrane slurry obtained in step (2) and the second composite solid electrolyte membrane slurry obtained in step (3) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (2) is coated on the substrate surface, and the slurry in step (3) is coated on the membrane surface in step (2) to obtain the double-layer composite solid electrolyte membrane.

[0098] Comparative Example 4

[0099] This comparative example provides a bilayer composite solid electrolyte membrane, comprising a first composite solid electrolyte membrane (10 μm thick) and a second composite solid electrolyte membrane (6 μm thick) stacked sequentially. The solid electrolyte membrane comprises polyvinylidene fluoride (molecular weight 500,000), lithium aluminum titanium phosphate (average particle size 0.6 μm), and lithium LiTFSI salt.

[0100] This comparative example also provides a method for preparing a bilayer composite solid electrolyte membrane, the preparation method is as follows:

[0101] (1) Mix lithium titanium aluminum phosphate and N-methylpyrrolidone, and disperse them by ultrasonication for 30 min to form a lithium titanium aluminum phosphate dispersion. At the same time, mix polyvinylidene fluoride and N-methylpyrrolidone, and stir at high speed of 1200 r / min using a planetary mixer until the polyvinylidene fluoride liquid is clear and transparent.

[0102] (2) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a first composite solid electrolyte membrane slurry with a solid content of 27.67%. The mass percentage of polyvinylidene fluoride in the first composite solid electrolyte membrane slurry was 65.36%, the mass percentage of lithium titanium aluminum phosphate was 13.07%, and the mass percentage of LiTFSI lithium salt was 21.57%.

[0103] (3) The lithium titanium aluminum phosphate dispersion and polyvinylidene fluoride adhesive were mixed and stirred at high speed of 1200 r / min for 30 min using a planetary mixer. Then, LiTFSI lithium salt was added and stirred at high speed of 1200 r / min for 1.0 h using a planetary mixer to obtain a second composite solid electrolyte membrane slurry with a solid content of 24.98%. The mass percentage of polyvinylidene fluoride in the second composite solid electrolyte membrane slurry was 30.03%, the mass percentage of lithium titanium aluminum phosphate was 60.06%, and the mass percentage of LiTFSI lithium salt was 9.91%.

[0104] (4) The first composite solid electrolyte membrane slurry obtained in step (2) and the second composite solid electrolyte membrane slurry obtained in step (3) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (2) is coated on the substrate surface, and the slurry in step (3) is coated on the membrane surface in step (2) to obtain the double-layer composite solid electrolyte membrane.

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 1 is that only the first composite solid electrolyte membrane is retained, while everything else is the same as in Example 1.

[0107] Comparative Example 6

[0108] The difference between this comparative example and Example 1 is that only the second composite solid electrolyte membrane is retained, while everything else is the same as in Example 1.

[0109] Application Examples 1 to 13 and Comparative Application Examples 1 to 6

[0110] Lithium-ion batteries were prepared using the bilayer composite solid electrolyte membranes provided in Examples 1 to 13 and Comparative Examples 1 to 6, and the preparation methods are as follows:

[0111] Preparation of positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 The positive electrode slurry is obtained by mixing 95 wt.% O2 positive electrode material, 2 wt.% carbon black conductive agent, and 3 wt.% SEBS binder with a solvent and stirring evenly. The slurry is then uniformly coated onto an aluminum foil current collector, and the positive electrode sheet is obtained through baking, rolling, slitting, and die-cutting.

[0112] Preparation of negative electrode sheet: 96 wt% graphite negative electrode active material, 1.5 wt% carbon black conductive agent, and 2.5 wt% PAA binder are mixed with solvent and stirred evenly to obtain a negative electrode slurry. The slurry is then uniformly coated on both sides of the negative electrode current collector, and the negative electrode sheet is obtained through baking, rolling, slitting, and die-cutting.

[0113] Preparation of lithium-ion batteries: The positive electrode, the double-layer composite solid electrolyte membrane, and the negative electrode are stacked, and then encapsulated with an aluminum-plastic film. The process is vacuumed, heat-sealed at 190°C and 0.5MPa for 7s, hot-pressed at 90°C and 0.25MPa for 150s, and cold-pressed at 25°C and 0.25MPa for 150s to obtain the solid-state battery.

[0114] Test conditions

[0115] The lithium-ion batteries provided in Application Examples 1 to 13 and Comparative Application Examples 1 to 6 were subjected to performance tests, and the test methods are as follows:

[0116] (1) Heat shrinkage performance test: The electrolyte membrane is placed in a constant temperature oven at 150℃ and heated for 1 hour. The transverse (TD) and longitudinal (MD) lengths of the electrolyte membrane before and after heating are tested. The shrinkage rate S of the electrolyte membrane can be expressed as: S=(L1-L2) / L1×100%, where L1: length before heating (mm); L2: length after heating (mm).

[0117] (2) Tensile strength test: The tensile strength of the electrolyte membrane was tested using a universal tensile testing machine.

[0118] (3) Cyclic performance test: The solid-state battery 0.2C cycle performance was tested using a Blue Electric Tester in an environment of 25℃.

[0119] The test results are shown in Table 1:

[0120] Table 1

[0121]

[0122]

[0123] As shown in Table 1, the bilayer composite solid electrolyte membrane provided by the present invention can effectively improve the electrochemical stability, high temperature resistance and tensile strength of the solid electrolyte membrane, thereby further improving the safety performance of the battery.

[0124] Although the bilayer composite solid electrolyte membrane provided in Application Example 4 can be prepared, its tensile strength is less than 9 MPa, and it will break when stacked using a stacking machine. In Application Example 5, when the ratio of inorganic filler to electrolyte membrane in the second electrolyte membrane is 8:1, cracks appear on the surface of the second electrolyte membrane, while the first electrolyte membrane remains intact, and the composite electrolyte membrane is also very easy to break. Application Examples 6-7 illustrate cases where the mass ratio of lithium salt to polymer is out of range. A low mass ratio reduces the ionic conductivity of the electrolyte membrane, while a high mass ratio reduces its mechanical properties. Application Examples 8-9 illustrate cases where the molecular weight of the polymer is out of range. A low molecular weight results in poor thermal shrinkage of the electrolyte membrane, while a high molecular weight results in poor flexibility. Application Examples 10-11 illustrate cases where the membrane thickness is out of range. During the baking process, solvent evaporation further affects the distribution of inorganic filler particles. Due to the high proportion of inorganic filler in the second electrolyte membrane and the excessive coating thickness, stress concentration is aggravated, leading to cracking of the prepared electrolyte membrane. Application Examples 12-13 illustrate cases where the viscosity of the slurry is out of range. A low viscosity results in strong slurry flow, making it prone to flow during coating, while a high viscosity results in poor slurry flow, making it prone to clumping during coating.

[0125] Compared to Application Examples 1-4, where the mass ratio of inorganic filler to polymer was out of range, and Application Examples 5-6, which used a single-layer electrolyte membrane, the performance of the batteries prepared by these examples was not as good as that of the battery provided in Application Example 1.

[0126] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A double-layer composite solid electrolyte membrane, characterized in that, The dual-layer composite solid electrolyte membrane comprises a first composite solid electrolyte membrane and a second composite solid electrolyte membrane stacked sequentially. The mass ratio of inorganic filler to polymer in the slurry of the first composite solid electrolyte membrane is (1~8):10; The mass ratio of inorganic filler to polymer in the slurry of the second composite solid electrolyte membrane is (3~8):1; The inorganic filler and polymer are the same in the first composite solid electrolyte membrane and the second composite solid electrolyte membrane; The thickness of the first composite solid electrolyte membrane is 9~10μm; The thickness of the second composite solid electrolyte membrane is 4~6μm; The slurry of the first composite solid electrolyte membrane is coated on the surface of the substrate, and the slurry of the second composite solid electrolyte membrane is coated on the surface of the first composite solid electrolyte membrane. The inorganic filler includes any one or a combination of at least two of the following: lithium lanthanum zirconium oxide and its derivatives, lithium titanium aluminum phosphate and its derivatives, lithium germanium aluminum phosphate and its derivatives, lithium lanthanum titanate and its derivatives, silicon dioxide, or aluminum oxide.

2. The bilayer composite solid electrolyte membrane according to claim 1, characterized in that, Both the first composite solid electrolyte membrane and the second composite solid electrolyte membrane further include lithium salt.

3. The bilayer composite solid electrolyte membrane according to claim 2, characterized in that, The mass ratio of lithium salt to polymer in the slurry of the first composite solid electrolyte membrane is (1~3.5):

10.

4. The bilayer composite solid electrolyte membrane according to claim 2, characterized in that, The mass ratio of lithium salt to polymer in the slurry of the second composite solid electrolyte membrane is (1~3.5):

10.

5. The bilayer composite solid electrolyte membrane according to claim 1, characterized in that, The average particle size of the inorganic filler is 0.5~1μm.

6. The bilayer composite solid electrolyte membrane according to claim 1, characterized in that, The polymer includes any one or a combination of at least two of polyethylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl methacrylate, or polyacrylonitrile.

7. The bilayer composite solid electrolyte membrane according to claim 1, characterized in that, The polymer has a molecular weight of 300,000 to 600,000.

8. The bilayer composite solid electrolyte membrane according to claim 2, characterized in that, The lithium salt includes any one or a combination of at least two of the following: LiSCN, LiN(CN)2, Li(CF3SO2)3C, LiC4F9SO3, LiN(SO2CF2CF3)2, LiB(C2O4)2, LiBF4, LiBF3(C2F5), LiDFOB, LiTFSI, LiN(SO2CF3)2, LiFSI, LiN(SO2F)2, LiCF3SO3, LiAsF6, LiSbF6, or LiClO4.

9. A method for preparing a bilayer composite solid electrolyte membrane according to any one of claims 1-8, characterized in that, The method includes the following steps: (1) The inorganic filler dispersion and polymer solution are mixed according to the formula amount, and then lithium salt is added to obtain the first composite solid electrolyte membrane slurry; (2) The inorganic filler dispersion and polymer solution are mixed according to the formula amount, and then lithium salt is added to obtain the second composite solid electrolyte membrane slurry; (3) The first composite solid electrolyte membrane slurry obtained in step (1) and the second composite solid electrolyte membrane slurry obtained in step (2) are poured into the two barrels of the dual-die head coating machine for simultaneous coating. The slurry in step (1) is coated on the substrate surface, and the slurry in step (2) is coated on the membrane surface in step (1) to obtain the double-layer composite solid electrolyte membrane.

10. The method according to claim 9, characterized in that, The mixing described in step (1) is carried out under stirring.

11. The method according to claim 9, characterized in that, In step (1), the viscosity of the first composite solid electrolyte membrane slurry is 3000~4000 mPa·s.

12. The method according to claim 9, characterized in that, The mixing described in step (2) is carried out under stirring.

13. The method according to claim 9, characterized in that, In step (2), the viscosity of the second composite solid electrolyte membrane slurry is 5000~6000 mPa·s.

14. An all-solid-state battery, characterized in that, The all-solid-state battery includes a positive electrode, a negative electrode, and a solid electrolyte membrane, wherein the solid electrolyte membrane is a bilayer composite solid electrolyte membrane according to any one of claims 1-8.

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