Solid-state electrolyte and method for preparing the same, and solid-state battery including the same

Abstract

The application provides a solid-state electrolyte, a preparation method thereof and a solid-state battery comprising the solid-state electrolyte. The preparation method comprises the following steps: (1) adding a polymer matrix into an organic solvent, stirring and dissolving at 50-70 DEG C to obtain a polymer solution; (2) adding a lithium salt into the polymer solution, stirring at 60-80 DEG C for 2-4 hours to dissolve the lithium salt, and obtaining a polymer-lithium salt solution; (3) adding inorganic solid-state electrolyte powder, a flame retardant and an interface regulator into the polymer-lithium salt solution, stirring at 70-90 DEG C for 4-6 hours under nitrogen protection to obtain a mixed slurry; (4) coating the mixed slurry on a polytetrafluoroethylene substrate, and vacuum drying at 60-80 DEG C for 8-12 hours to obtain a thin film; and (5) performing light curing treatment on the thin film. The solid-state electrolyte has good comprehensive mechanical properties and electrical properties.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery materials technology, specifically relating to a solid electrolyte and its preparation method, as well as a solid battery including the solid electrolyte. Background Technology

[0002] With the rapid development of electric vehicles, large-scale energy storage, and other fields, higher demands are being placed on the energy density and safety of rechargeable batteries. Traditional lithium-ion batteries use flammable organic liquid electrolytes, posing a risk of thermal runaway, and their energy density is already close to its theoretical limit, making it difficult to meet the ever-increasing application demands. All-solid-state lithium batteries use non-flammable inorganic solid electrolytes, which not only fundamentally improves the intrinsic safety of the battery, but also holds the promise of achieving breakthroughs in energy density by being compatible with higher-capacity positive and negative electrode materials (such as high-nickel ternary cathodes and lithium metal anodes), and are considered the core direction of next-generation energy storage technology.

[0003] Currently, mainstream solid-state electrolytes mainly include oxide, sulfide, polymer, and halide systems. Among them, polymer solid-state electrolytes have become a research hotspot due to their good flexibility, processability, and interfacial contact with electrode materials. However, traditional solid polymer electrolytes have long been plagued by an irreconcilable contradiction: improving mechanical strength often means sacrificing ionic conductivity, and vice versa, which seriously hinders their practical application. For example, polyethylene oxide (PEO)-based polymer electrolytes have extremely low ionic conductivity at room temperature, typically below 10. -5 S•cm -1 This approach fails to meet practical application requirements; while increasing ionic conductivity through the introduction of plasticizers and other methods leads to a significant decrease in mechanical properties, making it difficult to suppress the growth of lithium dendrites.

[0004] Sulfide solid electrolytes are characterized by high room temperature ionic conductivity (>10) comparable to that of liquid electrolytes. -3 S•cm -1 With its relatively low grain boundary impedance and good mechanical ductility, sulfide electrolytes have become one of the most promising candidate materials for application. However, the practical application of sulfide electrolytes still faces many challenges, one of the most prominent being their narrow electrochemical stability window. The thermodynamic stability window of most sulfide electrolytes is only 1.7–2.3 V (vs. Li / Li). + The electrolyte is much lower than the working potential of the high-voltage positive electrode (>4 V) and also lower than the deposition potential of the lithium metal negative electrode. This causes the electrolyte to be easily oxidized on the positive electrode side and easily reduced on the negative electrode side, thus generating a high-resistivity interface layer, which leads to rapid capacity decay and failure of the battery.

[0005] Halide solid electrolytes have attracted widespread attention due to their excellent electrochemical stability and superior deformation capability. However, traditional halide solid electrolytes suffer from problems such as low ionic conductivity and insufficient high-voltage stability. For example, Na₂ZrCl₆ (NZC) has a trigonal crystal structure and is a typical sodium ion conductor, but it suffers from low ionic conductivity (approximately 6.46 × 10⁻⁶ at 25 °C). -6 S•cm -1 The limited electrochemical window (oxidative decomposition begins at >3.9 V) restricts its development in all-solid-state sodium-ion batteries. Fluoride-based sodium-ion conductors exhibit better performance at 4-5 V (vs. Na) and a narrower electrochemical window (oxidative decomposition begins at >3.9 V). + It exhibits excellent stability over a voltage range of / Na, but generally suffers from low ionic conductivity (approximately 10). -6 S•cm -1 The problem is mainly due to F - with Na + There are strong Coulomb interactions between them, which increases the activation energy barrier and limits the Na+. + transmission.

[0006] Furthermore, existing solid electrolytes generally suffer from problems such as high interfacial impedance and poor compatibility with positive and negative electrode materials. For example, although phase change solid electrolytes can produce good interfacial contact, they are prone to phase change at high temperatures, leading to structural instability and affecting battery life. PEO matrix composite solid electrolytes are prone to interfacial side reactions with positive and negative electrode materials during multiple charge-discharge cycles, resulting in increased interfacial impedance and rapid capacity decay.

[0007] Therefore, developing a solid electrolyte that combines high ionic conductivity, good mechanical properties, a wide electrochemical stability window, good interface compatibility, and simple preparation process is of great significance for promoting the practical application of all-solid-state lithium batteries. Summary of the Invention

[0008] Based on the technical problems described above, one objective of this invention is to provide a solid electrolyte, a method for preparing the same, and a solid-state battery comprising the solid electrolyte. The solid electrolyte prepared according to the technical solution of this invention possesses high ionic conductivity, good mechanical properties, a wide electrochemical stability window, good interface compatibility, and a simple preparation process.

[0009] Specifically, according to one aspect of the present invention, a method for preparing a solid electrolyte is provided, the method comprising the following steps:

[0010] (1) Add the polymer matrix to an organic solvent and stir to dissolve it at 50-70℃ to obtain a polymer solution;

[0011] (2) Add lithium salt to the polymer solution obtained in step (1) and stir at 60-80°C for 2-4 hours to dissolve the lithium salt and obtain a polymer-lithium salt solution.

[0012] (3) Add inorganic solid electrolyte powder, flame retardant and interface modifier to the polymer-lithium salt solution obtained in step (2), and stir at 70-90°C for 4-6 hours under nitrogen protection to obtain a mixed slurry;

[0013] (4) The mixed slurry obtained in step (3) is coated onto a polytetrafluoroethylene plate and vacuum dried at 60-80°C for 8-12 hours to remove the organic solvent, thereby obtaining a film;

[0014] (5) The film is subjected to photocuring treatment to obtain the solid electrolyte, wherein:

[0015] The polymer matrix is ​​a mixture of polyethylene glycol diacrylate (PEGDA) and polyethylene oxide (PEO);

[0016] The inorganic solid electrolyte powder is one or more of Li6PS5Cl and LiNbO3;

[0017] The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB);

[0018] The flame retardant is ethoxy(pentafluoro)cyclotriphosphazene;

[0019] The interface modifier is a mixture of γ-aminopropyltriethoxysilane (KH550) and tetrabutyl titanate; and

[0020] Based on the total weight of the polymer matrix, the inorganic solid electrolyte powder, the lithium salt, the flame retardant, and the interface modifier as 100%, the polymer matrix accounts for 40-60%, preferably 50-55%, the inorganic solid electrolyte powder accounts for 25-45%, preferably 30-40%, the lithium salt accounts for 8-15%, preferably 10-12%, the flame retardant accounts for 3-8%, preferably 5-8%, and the interface modifier accounts for 1-4%, preferably 1-2%.

[0021] According to certain preferred embodiments of the present invention, in the polymer matrix, the weight ratio of polyethylene glycol diacrylate to polyethylene oxide is 8:1-3:1, preferably 5:1-4:1.

[0022] According to certain preferred embodiments of the present invention, the number average molecular weight of the polyethylene glycol diacrylate is in the range of 200-1500, preferably 400-800.

[0023] According to certain preferred embodiments of the present invention, the weight-average molecular weight of the polyethylene oxide is 1 × 10⁻⁶. 2 -1×10 4 g / mol, preferably 5×10 2 -5×10 3 Within the range of g / mol.

[0024] According to certain preferred embodiments of the present invention, the inorganic solid electrolyte powder is a mixture of Li6PS5Cl and LiNbO3.

[0025] According to certain preferred embodiments of the present invention, in the inorganic solid electrolyte powder, the weight ratio of Li6PS5Cl to LiNbO3 is 1:2-1:7, preferably 1:3-1:5.

[0026] According to certain preferred embodiments of the present invention, the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB).

[0027] According to certain preferred embodiments of the present invention, the weight ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to lithium difluorooxalate borate (LiDFOB) is 1:2-1:6, preferably 1:3-1:5.

[0028] According to certain preferred embodiments of the present invention, in the interface modifier, the weight ratio of γ-aminopropyltriethoxysilane (KH550) to tetrabutyl titanate is 1:2-1:8, preferably 1:3-1:5.

[0029] According to certain preferred embodiments of the present invention, the organic solvent is one or more of acetonitrile, N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), preferably, the organic solvent is acetonitrile.

[0030] According to certain preferred embodiments of the present invention, in step (1), the weight ratio of the polymer matrix to the organic solvent is 1:5 to 1:10.

[0031] According to certain preferred embodiments of the present invention, in step (5), the photocuring wavelength used for the photocuring treatment is 365-405 nm, the photocuring time is 30-60 seconds, and the photocuring intensity is 50-100 mW / cm². 2 .

[0032] According to certain preferred embodiments of the present invention, the coating method in step (4) is scraper coating or spraying.

[0033] According to certain preferred embodiments of the present invention, the coating thickness in step (4) is 50-200 μm.

[0034] According to another aspect of the present invention, a solid electrolyte is provided, which is prepared by the method described above.

[0035] According to certain preferred embodiments of the present invention, the room temperature ionic conductivity of the solid electrolyte is 2.5-3.5 mS•cm. -1 .

[0036] According to certain preferred embodiments of the present invention, the solid electrolyte has a tensile strength of 8-12 MPa and a toughness of 6.5-8.5 MJ•m. -3 .

[0037] According to certain preferred embodiments of the present invention, the electrochemical stability window of the solid electrolyte is 0-4.8 V (vs. Li / Li). + ).

[0038] According to certain preferred embodiments of the present invention, the initial interfacial impedance between the solid electrolyte and the positive and negative electrode materials is 50-80 Ω•cm. 2 .

[0039] According to another aspect of the present invention, a solid-state battery is provided, the solid-state battery comprising the solid electrolyte, positive electrode, negative electrode and casing described above, wherein the solid electrolyte is located between the positive electrode and the negative electrode.

[0040] According to certain preferred embodiments of the present invention, the positive electrode is made by mixing a positive electrode active material, a conductive agent, a binder and the solid electrolyte in a weight ratio of 80-90 : 5-10 : 2-5 : 3-8, and the positive electrode active material is one or more of NCM811, NCM622 or LiCoO2.

[0041] According to certain preferred embodiments of the present invention, the negative electrode is one of lithium metal foil, silicon-based negative electrode, or graphite negative electrode. The silicon-based negative electrode is made by mixing silicon powder, conductive agent, binder, and solid electrolyte in a weight ratio of 60-70: 10-15: 5-10: 5-15, and the graphite negative electrode is made by mixing graphite, conductive agent, binder, and solid electrolyte in a weight ratio of 85-95: 2-5: 2-5: 1-5.

[0042] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0043] 1. By employing a PEGDA and PEO composite polymer matrix, combined with Li6PS5Cl and LiNbO3 composite inorganic powders, the contradiction between "high mechanical strength and high ionic conductivity" in traditional polymer electrolytes is resolved, achieving an ionic conductivity of 2.5-3.5 mS•cm at room temperature. -1 The tensile strength reaches 8-12 MPa, and the toughness reaches 6.5-8.5 MJ•m. -3 .

[0044] 2. Through the synergistic effect of LiTFSI and LiDFOB composite lithium salt and special flame retardant, the electrochemical stability window is widened to 0-4.8 V, which is suitable for high-voltage cathode materials, avoids electrolyte redox failure, and improves battery cycle stability.

[0045] 3. The KH550 and tetrabutyl titanate composite interface modifier reduced the solid-solid interface impedance, with an initial interface impedance of only 50-80 Ω•cm. 2 This reduces interfacial side reactions, thereby improving the contact stability between the electrolyte and the positive and negative electrodes.

[0046] 4. The process adopts a solution stirring-coating-photocuring process, which eliminates the need for high-temperature sintering, provides strong process controllability, and allows for flexible component ratios, making it suitable for large-scale production while ensuring both safety and practicality. Attached Figure Description

[0047] The accompanying drawings are provided in this specification to more clearly explain the technical solutions of the present invention; however, the art is not limited thereto.

[0048] Figure 1 A flowchart illustrating the preparation process of a solid electrolyte according to the present invention is shown.

[0049] Figure 2 A scanning electron microscope (SEM) image of the solid electrolyte prepared in Example 1 is shown. Detailed Implementation

[0050] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. It will be understood that other embodiments may be implemented without departing from the scope or spirit of the invention. Therefore, the following detailed description is non-limiting.

[0051] Unless otherwise specified, all figures used in this specification to represent characteristic dimensions, quantities, and physical properties should be understood to be modified by the term "about" in all cases. Therefore, unless otherwise stated, the numerical parameters listed in the foregoing specification are approximations, and those skilled in the art can appropriately modify these approximations to obtain the desired properties using the teachings disclosed herein.

[0052] As mentioned above, traditional polymer electrolytes present a trade-off between high mechanical strength and high ionic conductivity. Sulfide electrolytes have a narrow electrochemical stability window and are prone to electrode reactions, while halide electrolytes have low ionic conductivity and insufficient high-voltage stability. Meanwhile, existing solid-state electrolytes generally suffer from high interfacial impedance, poor compatibility with positive and negative electrodes, and susceptibility to interfacial side reactions. These defects lead to rapid battery capacity decay and short lifespan, making it difficult to meet the high energy density and high safety requirements of secondary batteries in electric vehicles, large-scale energy storage, and other fields. Therefore, it is necessary to develop solid-state electrolytes that combine high ionic conductivity, good mechanical properties, a wide electrochemical stability window, and excellent interfacial compatibility. This invention aims to solve the above problems.

[0053] Specifically, according to one aspect of the present invention, a method for preparing a solid electrolyte is provided, the method comprising the following steps:

[0054] (1) Add the polymer matrix to an organic solvent and stir to dissolve it at 50-70℃ to obtain a polymer solution;

[0055] (2) Add lithium salt to the polymer solution obtained in step (1) and stir at 60-80°C for 2-4 hours to dissolve the lithium salt and obtain a polymer-lithium salt solution.

[0056] (3) Add inorganic solid electrolyte powder, flame retardant and interface modifier to the polymer-lithium salt solution obtained in step (2), and stir at 70-90°C for 4-6 hours under nitrogen protection to obtain a mixed slurry;

[0057] (4) The mixed slurry obtained in step (3) is coated onto a polytetrafluoroethylene plate and vacuum dried at 60-80°C for 8-12 hours to remove the organic solvent, thereby obtaining a film;

[0058] (5) The film is subjected to photocuring treatment to obtain the solid electrolyte, wherein:

[0059] The polymer matrix is ​​a mixture of polyethylene glycol diacrylate (PEGDA) and polyethylene oxide (PEO);

[0060] The inorganic solid electrolyte powder is one or more of Li6PS5Cl and LiNbO3;

[0061] The lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB);

[0062] The flame retardant is ethoxy(pentafluoro)cyclotriphosphazene;

[0063] The interface modifier is a mixture of γ-aminopropyltriethoxysilane (KH550) and tetrabutyl titanate; and

[0064] Based on the total weight of the polymer matrix, the inorganic solid electrolyte powder, the lithium salt, the flame retardant, and the interface modifier as 100%, the polymer matrix accounts for 40-60%, preferably 50-55%, the inorganic solid electrolyte powder accounts for 25-45%, preferably 30-40%, the lithium salt accounts for 8-15%, preferably 10-12%, the flame retardant accounts for 3-8%, preferably 5-8%, and the interface modifier accounts for 1-4%, preferably 1-2%.

[0065] Figure 1 A flowchart illustrating the preparation of a solid electrolyte according to the present invention is shown. Specifically, the preparation method includes the following steps:

[0066] S1: Add the polymer matrix to an organic solvent to obtain a polymer solution;

[0067] S2: Add lithium salt to the polymer solution and stir to dissolve the lithium salt to obtain a polymer-lithium salt solution;

[0068] S3: Add inorganic solid electrolyte powder, flame retardant and interface modifier to polymer-lithium salt solution, stir under nitrogen protection to obtain mixed slurry;

[0069] S4: The mixed slurry is coated onto a polytetrafluoroethylene sheet and vacuum dried to obtain a film;

[0070] S5: Perform photocuring treatment on the thin film to obtain the solid electrolyte.

[0071] The polymer matrix, as the backbone structure of solid electrolytes, significantly influences the mechanical strength, flexibility, and ion transport channels of the solid electrolyte. According to the technical solution of this invention, a composite system of polyethylene glycol diacrylate (PEGDA) and polyethylene oxide (PEO) is used to balance mechanical properties and ion conduction efficiency through their synergistic effect. Specifically, PEGDA, as a cross-linking active polymer, contains acrylate groups in its molecular chain that can undergo free radical polymerization during photocuring to form a three-dimensional cross-linked network structure, which is beneficial for improving the mechanical strength of the solid electrolyte. Preferably, the number average molecular weight of PEGDA used in this invention is in the range of 200-1500, more preferably 400-800. When the number average molecular weight of PEGDA is 400-800, it ensures good compatibility with PEO and forms a uniform and dense network structure through cross-linking, further improving the tensile strength of the solid electrolyte. Furthermore, the ether oxygen bonds in the molecular chain of polyethylene oxide (PEO) can coordinate with lithium ions, providing channels for lithium ion transport. The weight-average molecular weight of the polyethylene oxide (PEO) that can be used in this invention is 1 × 10⁻⁶. 2 -1×10 4 g / mol, preferably 5×10 2 -5×10 3 Within the g / mol range. PEO with a preferred weight-average molecular weight range can not only form a complementary network structure with PEGDA, but its ether-oxygen bonds can also interact with the active sites on the surface of inorganic solid electrolyte powder, further optimizing the ion transport channels.

[0072] According to certain embodiments of the present invention, the weight ratio of PEGDA to PEO is 8:1-3:1, preferably 5:1-4:1.

[0073] In addition, the total mass percentage of the polymer matrix is ​​40-60%, preferably 50-55%. If the percentage is less than 40%, a complete skeleton structure cannot be formed, the electrolyte is prone to brittleness, and the mechanical properties will drop significantly; if the percentage is more than 60%, the content of inorganic solid electrolyte powder will be relatively reduced, and the ionic conductivity will be difficult to meet practical requirements.

[0074] The introduction of inorganic solid electrolyte powder is intended to improve the ionic conductivity of polymer-based electrolytes. According to the technical solution of the present invention, one or more of Li6PS5Cl and LiNbO3 are used as inorganic solid electrolyte powders, with a mixture of the two being particularly preferred, to simultaneously improve ionic conductivity and electrochemical stability through a synergistic effect.

[0075] Li6PS5Cl, as a typical sulfide solid electrolyte, exhibits high room-temperature ionic conductivity (the room-temperature ionic conductivity of pure-phase Li6PS5Cl can reach 10). -3 S•cm -1 Li6PS5Cl, with its abundant lithium-ion vacancies in its crystal structure, facilitates rapid lithium-ion migration. However, Li6PS5Cl alone suffers from a narrow electrochemical stability window and is easily oxidized and decomposed under high-voltage cathodes (>4V), generating a high-resistivity interface layer. On the other hand, LiNbO3, as an oxide electrolyte, while having low ionic conductivity, possesses excellent electrochemical stability and interfacial compatibility. Its surface oxygen atoms can form stable chemical bonds with the cathode material, suppressing interfacial side reactions. Combining the two allows for synergistic optimization of "high ionic conductivity" and "wide electrochemical stability window": Li6PS5Cl provides an efficient ion transport channel, while LiNbO3 modifies the interface and enhances electrochemical stability. Preferably, when using both Li6PS5Cl and LiNbO3, the weight ratio of Li6PS5Cl to LiNbO3 is 1:2-1:7, more preferably 1:3-1:5.

[0076] According to the technical solution of the present invention, the total mass percentage of the inorganic solid electrolyte powder is 25-45%, preferably 30-40%. If the percentage is less than 25%, the improvement effect on ionic conductivity is not significant, and it is difficult to exceed 2.5 mS•cm. -1 If the proportion is higher than 45%, the inorganic solid electrolyte powder is difficult to disperse uniformly in the polymer matrix, and agglomeration is likely to occur, resulting in defects inside the electrolyte, decreased mechanical properties (such as tensile strength dropping to below 7MPa), and increased interfacial impedance.

[0077] Lithium salts, as the source of lithium ions, significantly influence the electrical performance of solid electrolytes due to their degree of dissociation, ion mobility, and electrochemical stability. According to the technical solution of the present invention, one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB) are used as lithium salts, with a mixture of the two being particularly preferred. This synergistic effect enhances ion dissociation efficiency and electrochemical stability.

[0078] LiTFSI exhibits high dissociation degree and lithium-ion mobility, and its anion TFSI - LiTFSI has relatively large steric hindrance and weak interaction with lithium ions, which facilitates the free migration of lithium ions, making it a commonly used high-performance lithium salt in polymer electrolytes. However, LiTFSI suffers from insufficient stability under high voltage conditions, and its compatibility with metallic lithium needs improvement. LiDFOB, as a novel lithium salt, exhibits good electrochemical stability and interfacial compatibility. Its anion (DFOB... -It can form a stable SEI film on the surface of metallic lithium, inhibiting lithium dendrite growth, and is not easily decomposed under high voltage. Combining the two achieves a synergistic effect of "high ion mobility" and "high electrochemical stability". In a preferred embodiment of the present invention, when lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB) are used simultaneously, the weight ratio of LiTFSI to LiDFOB is 1:2-1:6, preferably 1:3-1:5.

[0079] According to the technical solution of the present invention, the total mass percentage of lithium salt is 8-15%, preferably 10-12%. If the percentage is less than 8%, the lithium ion concentration is insufficient and the ionic conductivity is low; if the percentage is greater than 15%, the excess lithium salt cannot be completely dissociated and is prone to crystallization inside the electrolyte, resulting in obstruction of ion transport channels and increasing the viscosity of the electrolyte, affecting the mixing uniformity of the components. The lithium salt percentage within the preferred range can ensure the lithium ion concentration while avoiding the negative effects of excess lithium salt, achieving a balance between ionic conductivity and interface stability.

[0080] According to the technical solution of the present invention, ethoxy(pentafluoro)cyclotriphosphazene is used as a flame retardant. This flame retardant has the following advantages: the phosphorus and nitrogen elements in the phosphazene structure of this flame retardant have a synergistic flame retardant effect. The phosphorus element can form a phosphate ester protective layer at high temperatures, isolating oxygen from combustibles, while the nitrogen element can release inert gases, diluting the concentration of combustible gases; the pentafluoroethoxy group in the molecular structure of this flame retardant not only improves the thermal stability of the flame retardant, but also improves its compatibility with polymer matrices and inorganic powders, avoiding phase separation; the flame retardant has good electrochemical stability, and no redox reaction occurs within the electrochemical stability window of 0-4.8V, thus not negatively affecting the electrical performance of the electrolyte. According to the technical solution of the present invention, the total mass percentage of the flame retardant is 3-8%, preferably 5-8%.

[0081] Furthermore, as mentioned above, high interfacial impedance and poor compatibility with positive and negative electrode materials are among the problems restricting the practical application of solid-state electrolytes. The technical solution of this invention uses a mixture of γ-aminopropyltriethoxysilane (KH550) and tetrabutyl titanate as an interfacial modifier. Through the synergistic effect of the two, interfacial impedance is reduced and interfacial compatibility is improved. The KH550 molecular structure contains amino and ethoxysilyl groups. The amino group can chemically react with active groups such as hydroxyl and carboxyl groups on the surface of the positive electrode material to form stable chemical bonds; the ethoxysilyl group can hydrolyze to generate silanol groups, which undergo condensation reactions with hydroxyl groups on the surface of the inorganic solid electrolyte powder, thereby forming a dense interfacial layer between the electrolyte and the electrode material, reducing the occurrence of interfacial side reactions. Tetrabutyl titanate, as a metal alkoxy compound, has a butoxy group in its molecular structure that can react with the silanol groups generated by the hydrolysis of KH550, further optimizing the structure of the interfacial layer. Simultaneously, the introduction of titanium can improve the ionic conductivity of the interfacial layer and reduce interfacial impedance. In addition, tetrabutyl titanate can coordinate with the ether oxygen bonds in the polymer matrix, enhancing the bonding force between the interface layer and the electrolyte bulk and preventing interface delamination.

[0082] Preferably, the weight ratio of KH550 to tetrabutyl titanate is 1:2-1:8, more preferably 1:3-1:5.

[0083] According to the technical solution of the present invention, the total mass percentage of the interface modifier is 1-4%, preferably 1-2%. If the percentage is less than 1%, the interface modulation effect is not obvious, and the interface impedance remains high; if the percentage is greater than 3%, the excessive interface modifier will form an impurity phase inside the electrolyte, affecting the ion transport channels, leading to a decrease in ionic conductivity, and may also reduce the mechanical properties of the electrolyte. The preferred range of interface modifier percentage can effectively improve interface compatibility without affecting the core performance of the electrolyte, achieving a balance between interface impedance, ionic conductivity, and mechanical properties.

[0084] According to the technical solution of the present invention, an organic solvent is used to dissolve the polymer matrix and disperse the components during the preparation process. Preferably, the organic solvent is one or more of acetonitrile, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), and more preferably, the organic solvent is acetonitrile.

[0085] Preferably, in step (1) of the present invention, the weight ratio of polymer matrix to organic solvent is 1:5-1:10.

[0086] Preferably, in step (5), the photocuring wavelength used for the photocuring treatment is 365-405 nm, the photocuring time is 30-60 seconds, and the photocuring intensity is 50-100 mW / cm². 2 .

[0087] Preferably, the coating method in step (4) is scraper coating or spraying.

[0088] Preferably, the coating thickness in step (4) is 50-200 μm.

[0089] According to another aspect of the present invention, a solid electrolyte is provided, which is prepared according to the method described above.

[0090] Preferably, the room temperature ionic conductivity of the solid electrolyte is 2.5-3.5 mS•cm. -1 The solid electrolyte of this invention exhibits a room-temperature ionic conductivity of 2.5-3.5 mS•cm. -1 It is far higher than that of traditional polymer electrolytes (typically below 10). -5 S•cm -1 It is close to or even better than some sulfide electrolytes.

[0091] Preferably, the solid electrolyte has a tensile strength of 8-12 MPa and a toughness of 6.5-8.5 MJ•m. -3 It has good mechanical strength and flexibility, and can effectively suppress lithium dendrite growth and avoid battery short circuits.

[0092] Preferably, the electrochemical stability window of the solid electrolyte is 0-4.8 V (vs. Li / Li). + It can be adapted to high-voltage cathode materials (such as NCM811, LiCoO2, etc., with a working voltage of 3.0-4.5 V), avoiding redox reactions in the electrolyte during charging and discharging, and improving the cycle stability of the battery.

[0093] Preferably, the initial interfacial impedance between the solid electrolyte and the positive and negative electrode materials is 50-80 Ω•cm. 2 It has low interfacial impedance and can remain stable during cycling, reducing the occurrence of interfacial side reactions.

[0094] According to another aspect of the present invention, a solid-state battery is provided, the solid-state battery comprising the above-described solid electrolyte, a positive electrode, a negative electrode and a casing, wherein the solid electrolyte is located between the positive electrode and the negative electrode.

[0095] Preferably, the positive electrode of the present invention is made by mixing positive electrode active material, conductive agent, binder and solid electrolyte in a weight ratio of 80-90 : 5-10 : 2-5 : 3-8. The positive electrode active material is selected from one or more of NCM811, NCM622 or LiCoO2. These materials have high specific capacity and energy density and are commonly used positive electrode materials in high-energy-density lithium batteries. The conductive agent is used to improve the electronic conductivity of the positive electrode, and can usually be selected from acetylene black, Ketjen black, conductive graphite, etc. The binder is used to bond the positive electrode active material, conductive agent and solid electrolyte together to form a stable positive electrode structure, and can usually be selected from polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The addition of solid electrolyte is to improve the interfacial contact between the positive electrode and solid electrolyte and reduce interfacial resistance.

[0096] Preferably, the negative electrode used in this invention can be one of lithium metal foil, silicon-based negative electrode, or graphite negative electrode. Different types of negative electrodes are suitable for different application scenarios: lithium metal foil has the highest theoretical specific capacity (3860 mAh / g), which can significantly improve the energy density of the battery and is an ideal negative electrode material for high energy density solid-state batteries; the theoretical specific capacity of silicon-based negative electrode (4200 mAh / g) is also much higher than that of traditional graphite negative electrode, and it is abundant in resources and environmentally friendly, making it an important development direction for next-generation negative electrode materials; graphite negative electrode has good cycle stability and low cost, making it suitable for scenarios with relatively low energy density requirements and high cycle performance requirements.

[0097] Preferably, the silicon-based anode used in this invention is prepared by mixing silicon powder, conductive agent, binder, and solid electrolyte in a weight ratio of 60-70 : 10-15 : 5-10 : 5-15. Silicon powder, as the active material, accounts for 60-70%, ensuring the high specific capacity of the anode; the conductive agent accounts for 10-15%, improving the electronic conductivity of the silicon-based material (silicon itself is a semiconductor with poor conductivity); the binder accounts for 5-10%, mitigating the volume expansion of silicon during charging and discharging (the volume expansion rate of silicon can reach over 300%), ensuring the stability of the anode structure; and the solid electrolyte accounts for 5-15%, improving the interfacial contact between the silicon-based anode and the solid electrolyte, reducing interfacial impedance.

[0098] Preferably, the graphite anode used in this invention is made by mixing graphite, conductive agent, binder, and solid electrolyte in a weight ratio of 85-95: 2-5: 2-5: 1-5. Graphite, as the active material, accounts for 85-95%, ensuring the specific capacity and cycle stability of the anode; the conductive agent accounts for 2-5%, improving the electronic conductivity of the anode; the binder accounts for 2-5%, ensuring the integrity of the anode structure; and the solid electrolyte accounts for 1-5%, improving interfacial contact and reducing interfacial impedance.

[0099] The present invention will now be described in more detail with reference to embodiments. It should be noted that these descriptions and embodiments are intended to facilitate understanding of the present invention and are not intended to limit the invention.

[0100] Example

[0101] In this invention, unless otherwise specified, all reagents used are commercially available products and are used directly without further purification. Furthermore, "%" refers to "weight %" and "parts" refers to "parts by weight".

[0102] Table 1 below lists specific information about the raw materials used in the embodiments and comparative examples of the present invention.

[0103]

[0104] Table 2 below lists specific information about the experimental equipment used in the embodiments and comparative examples of the present invention.

[0105] Table 2 List of Experimental Equipment

[0106]

[0107] Performance testing methods

[0108] (a) Room temperature ionic conductivity

[0109] The room temperature ionic conductivity of solid electrolyte samples prepared in the following examples and comparative examples was tested according to the methods described below.

[0110] Specifically, referring to the national standard GB / T 39864-2021 "Test Method for Ionic Conductivity of Solid Electrolytes", the AC impedance spectroscopy method was used for testing. The specific steps are as follows: The solid electrolyte sample was cut into a circular piece with a diameter of 14 mm. Surface residual impurities were removed in an argon glove box, and the film thickness (L) was accurately measured to 0.1 μm. Then, the sample was clamped between two polished stainless steel blocking electrodes to form a symmetrical battery with a stainless steel blocking electrode (SS) / solid electrolyte / stainless steel blocking electrode (SS) structure. Subsequently, using an electrochemical workstation, the test temperature was set to 25℃ (room temperature), the frequency range was 1Hz-1MHz, and the AC signal amplitude was 10mV. The temperature was kept constant during the test. Then, the Nyquist impedance spectrum was obtained, and the bulk resistance (R) corresponding to the intersection of the high-frequency region and the real axis was read. The ionic conductivity (σ) was calculated according to the formula σ = L / (R×A), where A is the effective contact area of ​​the electrode. Each group of samples was tested in parallel three times, and the average value was taken as the final result (unit: mS•cm). -1 ).

[0111] (2) Tensile Strength

[0112] According to the method described below, tensile strength tests were carried out on the solid electrolyte samples prepared in each of the following examples and comparative examples.

[0113] Specifically, referring to the national standard "GB / T 1040.3 - 2006 Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets", the specific steps are as follows: Cut the solid electrolyte sample into dumbbell - shaped standard specimens with a length of 50 mm and a width of 10 mm. Measure the thickness at 3 different positions and take the average value (accurate to 0.01 μm). Prepare 5 parallel specimens for each group. Then, place the specimens in an environment of 25°C and 50% relative humidity to equilibrate for 24 hours. During the test, start the tensile testing machine, set the tensile speed to 5 mm / min. Clamp both ends of the specimen on the machine fixture, ensure that the axis of the specimen is consistent with the direction of the tensile force, start the equipment for stretching, and record the maximum tensile force value at the moment of fracture. Calculate the tensile strength (σ) according to the formula σ = F / (b×d), where F is the maximum tensile force (N), b is the width of the sample (mm), and d is the thickness of the sample (mm). Take the average value of the test results of 5 parallel specimens as the final data (unit: MPa).

[0114] (3) Toughness

[0115] According to the method described below, toughness tests were carried out on the solid electrolyte samples prepared in each of the following examples and comparative examples.

[0116] Specifically, referring to the national standard "GB / T 1040.3 - 2006 Plastics - Determination of tensile properties - Part 3: Test conditions for films and sheets", combined with the energy method for determination, the specific steps are as follows: Similar to the tensile strength test mentioned above, cut dumbbell - shaped standard specimens with a length of 50 mm and a width of 10 mm, accurately measure the thickness at 3 different positions and take the average value (accurate to 0.01 μm). Prepare 5 parallel specimens for each group. Place the specimens in an environment of 25°C and 50% relative humidity to equilibrate for 24 hours. During the test, start the tensile testing machine, set the tensile speed to 5 mm / min. Clamp the specimen at the center of the fixture, ensure that the axis is consistent with the direction of the tensile force, start the equipment for stretching until the specimen fractures, and simultaneously record the force - displacement curve during the stretching process. Through the software supporting the tensile testing machine, integrally calculate the total area under the force - displacement curve (i.e., the fracture energy). Calculate the toughness (T) according to the formula T = W / (A×L0), where W is the fracture energy (J), A is the cross - sectional area of the specimen (m 2 ), L0 is the gauge length (m), and take the average value of 5 parallel specimens as the final result (unit: MJ•m -3 ).

[0117] (4) Electrochemical Stability Window

[0118] Electrochemical stability window tests were performed on solid electrolyte samples prepared in the following examples and comparative examples according to the methods described below.

[0119] Specifically, referring to the relevant electrochemical performance testing specifications in the national standard GB / T 39864-2021 "Test Method for Ionic Conductivity of Solid Electrolytes", the linear sweep voltammetry (LSV) method was adopted. The specific steps are as follows: the solid electrolyte sample was cut into 14mm diameter circular pieces, surface impurities were removed in an argon glove box, and the thickness was accurately measured. Lithium metal foil was used as the counter electrode and reference electrode (Li / Li + Stainless steel was used as the working electrode, and an SS / solid electrolyte / Li symmetric cell was assembled. Then, the electrochemical workstation was started, the test temperature was set to 25℃, and the scan range was 0-6V (vs. Li / Li). + The scan rate was 1 mV / s. A linear scan was initiated under argon protection, and the current-voltage (IV) curve was recorded to observe current abrupt changes. When the current density reached 10 μA / cm², the scan was completed. 2 The voltage value corresponding to the time is the upper limit of the electrochemical stability window (unit: V). The test results are expressed as 0 to the corresponding upper limit voltage. The average value is taken from 3 parallel tests.

[0120] (v) Interface impedance

[0121] Interfacial impedance tests were performed on solid electrolyte samples prepared in the following embodiments and comparative examples according to the methods described below.

[0122] Referring to the national standard GB / T 39864-2021 "Test Method for Ionic Conductivity of Solid Electrolytes", the electrochemical impedance spectroscopy (EIS) method was adopted. The specific steps are as follows: The solid electrolyte sample was cut into 14mm diameter discs, and surface impurities were removed in an argon glove box. The thickness was accurately measured. Using NCM811 positive electrode and lithium metal foil as positive and negative electrodes respectively, the solid electrolyte sample was sandwiched between them to assemble a Li / solid electrolyte / NCM811 coin cell. Then, the electrochemical impedance spectroscopy was started, the test temperature was set to 25℃, the frequency range was 1Hz-1MHz, and an AC voltage amplitude of 10mV was applied. Impedance testing was performed under argon protection, and the Nyquist impedance spectrum was recorded. The characteristic peaks of the interface impedance corresponding to the semicircles in the high-frequency region of the spectrum were identified. The Nyquist plot was fitted using impedance analysis software, and the interface impedance values ​​(unit: Ω•cm) were read. 2 The average value of three parallel tests is taken, and the result is the initial interfacial impedance between the solid electrolyte and the positive and negative electrodes.

[0123] Example 1 (E1)

[0124] As shown in the formulation of Example 1 in Table 3 below, polyethylene glycol diacrylate and polyethylene oxide were weighed at a weight ratio of 5:1 to form a polymer matrix accounting for 40% of the total mass. This was added to acetonitrile, with a weight ratio of polymer matrix to acetonitrile of 1:10. The mixture was stirred and dissolved at 50°C to obtain a polymer solution.

[0125] Add 8% by weight of lithium salt to the polymer solution. The lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalate borate (LiDFOB) in a weight ratio of 1:1. Heat the solution to 60°C and stir for 2 hours to dissolve the lithium salt, thus obtaining a polymer-lithium salt solution.

[0126] To a polymer-lithium salt solution, 45% by weight of inorganic solid electrolyte powder, 3% by weight of flame retardant ethoxy(pentafluoro)cyclotriphosphazene, and 4% by weight of interface modifier were added. The inorganic solid electrolyte powder was a mixture of Li6PS5Cl and LiNbO3 in a 1:1 weight ratio; the interface modifier was a mixture of γ-aminopropyltriethoxysilane (KH550) and tetrabutyl titanate in a 1:1 weight ratio. The mixture was stirred at 70°C for 4 hours under nitrogen protection to obtain a slurry.

[0127] The mixed slurry was coated onto a polytetrafluoroethylene substrate using a doctor blade coating method to a thickness of 100 μm. The substrate was then placed in a vacuum drying oven and vacuum dried at 60 °C for 8 hours to remove acetonitrile solvent, resulting in a solid film.

[0128] The above-mentioned film was photocured using a photocuring device with a photocuring wavelength of 365nm, a photocuring time of 30 seconds, and a photocuring intensity of 50mW / cm². 2 Solid electrolyte 1 was obtained.

[0129] The solid electrolyte 1 was tested for room temperature ionic conductivity, tensile strength, toughness, electrochemical stability window, and interfacial impedance according to the performance testing methods described above. The results are shown in Table 3 below. Specifically, the room temperature ionic conductivity of the solid electrolyte 1 prepared in Example 1 is 2.5 mS•cm. -1 The tensile strength is 8.0 MPa, and the toughness is 6.5 MJ•m. -3 The electrochemical stability window is 0-4.5V (vs. Li / Li). + The initial interfacial impedance between the electrode and the positive and negative electrode materials is 80 Ω•cm. 2 .

[0130] In addition, the morphology of the solid electrolyte 1 prepared in Example 1 was examined using scanning electron microscopy (SEM). Figure 2 A scanning electron microscope (SEM) image of the solid electrolyte 1 prepared in Example 1 is shown.

[0131] Examples 2-12 (E2-E12) and Comparative Examples 1-5 (CE1-CE5)

[0132] Examples 2-12 (E2-E12) and Comparative Examples 1-5 (CE1-CE5) were prepared in a manner similar to that of Example 1, with the only difference being the change in component types and ratios as shown in Tables 3 and 4 below.

[0133] Based on the performance testing methods described above, the room temperature ionic conductivity, tensile strength, toughness, electrochemical stability window, and interfacial impedance of solid electrolyte 2-12 and comparative solid electrolyte 1-5 were tested, and the results are shown in Tables 3 and 4 below, respectively.

[0134] Table 3. Formulation and performance test results of Examples 1-12 (E1-E12)

[0135]

[0136] Table 4. Formulation and performance test results of Comparative Examples 1-5 (CE1-CE5)

[0137]

[0138] Combining the performance test data of Examples 1-12 in Table 3 and Comparative Examples 1-5 in Table 4, it can be seen that the room temperature ionic conductivity of the solid electrolytes prepared in Examples 1-12 according to the technical solution of the present invention all reaches 2.4-3.5 mS•cm. -1 Tensile strength 8.0-12.0 MPa, toughness 6.4-8.5 MJ•m -3 The electrochemical stability window ranges from 0 to 4.3-4.8 V, with an initial interfacial impedance of 50-80 Ω•cm. 2 Its performance indicators are balanced and excellent.

[0139] Among them, Examples 10-12, which adopted the preferred formulation, showed particularly outstanding performance, with an ionic conductivity of 3.2-3.5 mS•cm at room temperature. -1 Tensile strength 11.2-12.0 MPa, toughness 8.0-8.5 MJ•m -3 The electrochemical stability window is extended to 0-4.8 V, and the interfacial impedance is as low as 50-60 Ω•cm. 2 This demonstrates the technical effect of the synergistic effect of each component.

[0140] On the other hand, Comparative Example 1, due to insufficient inorganic solid electrolyte powder content, had a room temperature ionic conductivity of only 1.4 mS•cm. -1The interfacial impedance is as high as 145Ω•cm 2 Comparative Example 2, using conventional LPS inorganic powder products (i.e., Li2S-P2S5 electrolyte), showed a tensile strength of only 5.8 MPa and a toughness of 3.9 MJ•m. -3 Comparative Example 3 uses conventional lithium salt LiPF6, with an electrochemical stability window narrowed to 3.8 V; Comparative Example 4 uses KH550 alone as an interface modifier, with a tensile strength of 5.5 MPa and an interfacial impedance of 1105 Ω•cm. 2 The polymer matrix content in Comparative Example 5 was too low, resulting in an ionic conductivity of 1.6 mS•cm. -1 Its toughness is only 5.2 MJ•m -3 .

[0141] The above results confirm that the present invention effectively solves the performance contradictions in the prior art by combining and optimizing the ratio of specific polymer matrix, inorganic powder, lithium salt and interface modifier, and achieves synergistic improvement of multiple properties of solid electrolyte.

[0142] Obviously, those skilled in the art can make various modifications and variations to this disclosure without departing from the spirit and scope of this disclosure. Therefore, if such modifications and variations fall within the scope of this invention, this disclosure is also intended to include such modifications and variations.

Claims

1. A method of preparing a solid-state electrolyte, characterized by, The preparation method of the solid-state electrolyte according to claim 1, wherein: (1) adding a polymer matrix into an organic solvent, stirring and dissolving at 50-70℃ to obtain a polymer solution; (2) adding a lithium salt into the polymer solution obtained in step (1), stirring at 60-80℃ for 2-4 hours to dissolve the lithium salt, to obtain a polymer-lithium salt solution; (3) adding an inorganic solid electrolyte powder, a flame retardant and an interface modifier into the polymer-lithium salt solution obtained in step (2), stirring at 70-90℃ for 4-6 hours under nitrogen protection to obtain a mixed slurry; (4) coating the mixed slurry obtained in step (3) on a polytetrafluoroethylene substrate, vacuum drying at 60-80℃ for 8-12 hours to remove the organic solvent, to obtain a thin film; (5) performing a photocuring treatment on the thin film to obtain a solid-state electrolyte, wherein: the polymer matrix is a mixture of polyethylene glycol diacrylate and polyethylene oxide; the inorganic solid electrolyte powder is a mixture of Li6PS5Cl and LiNbO3, and the weight ratio of Li6PS5Cl to LiNbO3 is 1:2-1:7; the lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate; the flame retardant is ethoxy(pentafluoro)cyclo-triphosphazene; the interface modifier is a mixture of γ-aminopropyl triethoxysilane and tetrabutyl titanate; and the polymer matrix accounts for 40-60%, the inorganic solid electrolyte powder accounts for 25-45%, the lithium salt accounts for 8-15%, the flame retardant accounts for 3-8%, and the interface modifier accounts for 1-4%, based on the total weight of the polymer matrix, the inorganic solid electrolyte powder, the lithium salt, the flame retardant and the interface modifier being 100%.

2. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: In the polymer matrix, the weight ratio of the polyethylene glycol diacrylate to the polyethylene oxide is 8:1-3:

1.

3. The preparation method of the solid-state electrolyte according to claim 1, wherein: the number average molecular weight of the polyethylene glycol diacrylate is in the range of 200-1500; and / or The weight average molecular weight of the polyethylene oxide is in the range of 1 x 10 2 -1 x 10 4 g / mol.

4. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: the lithium salt is a mixture of lithium bis(trifluoromethanesulfonyl)imide and lithium difluoro(oxalato)borate, and the weight ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium difluoro(oxalato)borate is 1:2-1:

6.

5. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: In the interface modifier, the weight ratio of γ-aminopropyl triethoxysilane to tetrabutyl titanate is 1:2-1:

8.

6. The method of claim 1, wherein the solid-state electrolyte is prepared by a method comprising: The organic solvent is one or more of acetonitrile, N,N-dimethylformamide and dimethyl sulfoxide.

7. The preparation method of the solid-state electrolyte according to claim 1, wherein: In step (5), the photo-curing wavelength for the photo-curing process is 365-405 nm, the photo-curing time is 30-60 seconds and the photo-curing intensity is 50-100 mW / cm 2 ; and / or the coating thickness of the coating in step (4) is 50-200 μm.

8. A solid state electrolyte, characterized by, The solid-state electrolyte is prepared according to the method of any one of claims 1-7.

9. A solid state battery, characterized by The solid-state battery comprises: a housing; a positive electrode; a negative electrode; the solid-state electrolyte according to claim 8, which is located between the positive electrode and the negative electrode.

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