Garnet-type solid-state electrolyte and method for preparing the same

Abstract

This invention discloses a garnet-type solid electrolyte and its preparation method, belonging to the field of solid electrolyte technology. This invention achieves a comprehensive breakthrough in the performance bottlenecks of traditional garnet-type solid electrolytes from four dimensions: ion conduction, mechanical strength, interface stability, and dynamic repair, through a five-fold synergistic mechanism involving in-situ grain boundary repair of the glass phase, a space charge compensation layer, a thermodynamic dual-response self-healing network, grain boundary structure, and lattice oxygen vacancy pre-injection.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, specifically to a garnet-type solid electrolyte and its preparation method. Background Technology

[0002] Solid-state lithium batteries are considered the core development direction for next-generation energy storage batteries due to their combination of high energy density, high safety, and long cycle life. Among them, garnet-type Li7La3Zr2O 12 (LLZO)-based solid electrolytes have become the most promising oxide solid electrolyte system for industrialization due to their high room temperature ionic conductivity, wide electrochemical window, and good stability to lithium metal anodes. However, four core defects—high grain boundary impedance, mechanical brittleness, poor interface stability, and lack of self-healing ability—severely restrict the practical application of garnet-type solid electrolytes.

[0003] LLZO-based solid electrolytes are typical polycrystalline ceramic materials. Lithium-ion transport requires crossing grains and grain boundaries, and the high resistivity of these grain boundaries becomes a key bottleneck for ion conduction. During high-temperature sintering, LLZO ceramics readily generate highly resistive impurity phases such as Li₂CO₃ and La₂Zr₂O₇. Furthermore, the disordered atomic arrangement and uneven lithium-ion concentration distribution at grain boundaries create a significant space charge layer effect, generating a strong local electric field that hinders lithium-ion migration across grain boundaries. The grain boundary ionic conductivity of conventional LLZO solid electrolytes is 2-3 orders of magnitude lower than that of the bulk phase, significantly reducing the overall ion conduction efficiency and limiting the battery's rate performance and low-temperature discharge capability.

[0004] Meanwhile, the prominent mechanical brittleness of LLZO ceramic grain boundaries is a major cause of material failure. Grain boundaries are weak areas in the ceramic structure. Under the pressure of battery assembly and the stress of cyclic charging and discharging, microcracks easily initiate and rapidly propagate along grain boundaries, eventually leading to electrolyte penetration fracture. Furthermore, brittle fracture further exacerbates interfacial contact deterioration, inducing lithium dendrites to penetrate along grain boundary defects, resulting in battery short-circuit failure and severely reducing battery safety and cycle life.

[0005] Existing preparation and modification technologies are unable to fundamentally solve the above problems and have obvious limitations: although traditional high-temperature sintering (>1200℃) can improve density, it will aggravate lithium volatilization and impurity phase formation, and cannot eliminate the high-resistivity phase at grain boundaries. At the same time, it will lead to abnormal grain growth and further worsen the brittleness problem. Adding single sintering aids such as Al2O3 and Li3BO3 can lower the sintering temperature, but the low ionic conductivity of the second phase will increase the grain boundary resistance and has no toughening or repair function.

[0006] More importantly, current technologies lack the ability to self-repair grain boundary microcracks. Once irreversible damage occurs, defects will continue to accumulate until the material completely fails. Although self-healing materials have been studied in metal and polymer systems, grain boundary self-healing solutions adapted to the operating conditions of oxide ceramic solid electrolytes are still lacking. At the same time, the industry generally neglects space charge layer regulation, grain boundary structure design, and synergistic optimization of oxygen vacancies, making it impossible to achieve simultaneous improvement in ion conduction, mechanical properties, and interface stability.

[0007] In summary, current garnet-type solid electrolytes cannot simultaneously achieve low grain boundary impedance, high mechanical toughness, excellent interfacial compatibility, and dynamic self-healing, thus failing to meet the application requirements of high power, long life, and high safety in solid-state lithium batteries. There is an urgent need to develop novel multi-scale synergistic modification strategies and preparation technologies to break through existing technological bottlenecks. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a garnet-type solid electrolyte and its preparation method. Through a five-fold synergistic mechanism of in-situ repair of the glass phase at grain boundaries, space charge compensation layer, thermodynamic dual-response self-healing network, grain boundary structure, and lattice oxygen vacancy pre-injection, this invention comprehensively breaks through the performance bottleneck of traditional garnet-type solid electrolytes from four dimensions: ion conduction, mechanical strength, interface stability, and dynamic repair.

[0009] The technical solution of this invention is as follows: On one hand, the present invention provides a method for preparing a garnet-type solid electrolyte, comprising the following steps: Synthesis of S1 Ta / Nb co-doped LLZO powder: Under argon atmosphere, according to stoichiometric ratio Li 6.4 La3Zr 1.5 Ta 0.3 Nb 0.2 O 12 Weigh out lithium source, lanthanum source, zirconium source, tantalum source and niobium source and ball mill them together; then, remove the solvent by rotary evaporation, vacuum dry and sieve the resulting slurry, and then pre-calcine it at 900-950℃ for 4-5 hours to remove CO2; ball mill the pre-calcineed powder again and spray granulate it. Preparation of S2 glass phase precursor: Weigh H3BO3, Li2SO4, Li2CO3, and Li3N in a molar ratio of Li2O:B2O3:SO3:Li3N=3:0.8:0.8:0.4. Mix and melt them under argon protection to allow each component to react fully and form a homogeneous glass melt. Quench the melt to obtain glass fragments. After coarse crushing, ball mill the glass fragments to obtain glass powder. Preparation of S3 temperature-sensitive microcapsules: S3-1 core material preparation: Weigh each metal raw material according to the molar ratio of Bi:In:Sn=50:30:20, heat it to melt under argon atmosphere, cool it and grind it into nano powder; S3-2 Wall Material Preparation: Dissolve polymethyl methacrylate (PMMA) in dichloromethane, add emulsifier, and obtain wall material solution; S3-3 Microencapsulation: The core material nanopowder is added to the wall material solution, ultrasonically dispersed, and then dropped into a PVA aqueous solution. The mixture is stirred to evaporate the solvent and form microcapsules. S3-4 Separation and Drying: Centrifugation, washing with deionized water, and vacuum drying to obtain temperature-sensitive microcapsule powder; S4 pressure-responsive liquid metal droplet preparation: S4-1 Liquid Metal Preparation: Weigh each metal raw material according to the molar ratio of Ga:In:Sn=68:22:10, heat it to melt under an argon atmosphere to form a liquid alloy; S4-2 Emulsification: Liquid alloy is added to anhydrous ethanol, oleic acid is added as a surface modifier, and ultrasonic emulsification is performed in an ice-water bath to form nanodroplets and obtain an emulsion; S4-3 Freeze-drying: The emulsion is frozen and then freeze-dried under vacuum to obtain pressure-responsive liquid metal droplet powder; Preparation of S5 composite powder: First, the glass powder obtained in step S2 and the LLZTO powder obtained in step S1 are ball-milled and mixed to make the glass adhere evenly; then the temperature-sensitive microcapsule powder obtained in step S3 is added and ball milling continues; finally, the pressure-responsive liquid metal droplet powder obtained in step S4 is added and ball milling continues; the powder is then removed to obtain the composite powder. S6 Oxygen Vacancy Pre-Implantation: The composite powder is spread evenly in a quartz boat, placed in a plasma treatment chamber, and subjected to plasma treatment by introducing a mixture of Ar and H2 gas. + Bombardment selectively removes surface oxygen atoms, and H2 plasma modulates the oxygen vacancy concentration to form an oxygen-rich vacancy activation layer on the particle surface. S7 Electrolyte Sheet Sintering: The plasma-treated powder is pressed into discs, heated to 450-500℃ and held for 1-2 hours (glass phase softening and penetration), then heated to 600-650℃ and held for 1-2 hours (Li3N precipitation to form a nanocrystalline layer), then heated to 950-1000℃ and held for 4-5 hours (LLZTO grain densification), and finally cooled to 400-450℃ at a rate of 1-2℃ / min (promoting the orderly arrangement of grain boundary phases), and then naturally cooled to room temperature to obtain garnet-type solid electrolyte sheets.

[0010] Preferably, in step S1, the lithium source is Li2CO3, the lanthanum source is La2O3, the zirconium source is ZrO2, the tantalum source is Ta2O5, and the niobium source is Nb2O5.

[0011] Preferably, in step S3-2, the emulsifier is Span-80; in the wall material solution, the content of polymethyl methacrylate is 0.1-0.3 g / mL, and the content of emulsifier is 0.02-0.05 g / mL.

[0012] Preferably, in step S3-3, the mass ratio of the core nanopowder to polymethyl methacrylate is (0.5-0.8):1; the concentration of the PVA aqueous solution is 1-3 wt.%, and the volume ratio of PVA to dichloromethane is (5-8):1.

[0013] Preferably, in step S4-2, the content of liquid alloy in the emulsion is 0.05-0.1 g / mL, and the content of oleic acid is 0.01-0.05 g / mL.

[0014] Preferably, in step S5, the composite powder contains 5-7 wt.% glass powder, 1-2 wt.% thermosensitive microcapsule powder, and 1-2 wt.% pressure-responsive liquid metal droplet powder.

[0015] Preferably, in step S6, the volume ratio of Ar to H2 is 3:1, the total gas flow rate is 100-150 sccm, the working pressure is 30-50 Pa, the radio frequency power is 200-250 W, and the plasma treatment time is 20-60 min.

[0016] On the other hand, the present invention provides a garnet-type solid electrolyte by the above-described method for preparing the garnet-type solid electrolyte.

[0017] In this invention: (1) In-situ repair of glass phase at grain boundaries Main grains: Ta and Nb co-doped garnet-type LLZO grains, forming a bulk framework with high ionic conductivity.

[0018] Grain boundary repair phase: A layer of lithium-ion conductive glass phase is uniformly distributed between LLZO grains, with a chemical composition of a quaternary eutectic system of Li3BO3-Li2SO4-Li2O-Li3N. This glass phase is thermally reversible, becoming a low-viscosity liquid when heated above its melting point, and can flow to fill grain boundary microcracks.

[0019] (2) Space charge compensation layer Grain boundary space charge compensation layer: A Li3N-Li2O nanocrystalline layer is introduced at the interface between the glass phase and LLZO grains. This layer has the following functions: High polarization characteristics: Li3N has extremely high polarizability, which can generate a local electric field to counteract the space charge layer effect at grain boundaries; Interface dipoles: Forming oriented interface dipoles reduces the activation energy for lithium ions to cross grain boundaries; In-situ formation: Lithium nitride precursor is added to the glass phase and precipitated in situ during sintering.

[0020] (3) Thermal dual-response self-healing mechanism Dual-response repair network: a dual repair medium incorporating thermosensitive microcapsules and pressure-responsive liquid metal droplets into the glass phase. Thermosensitive microcapsules: encapsulated with a eutectic alloy (Bi-In-Sn). When the temperature rises above the melting point, the microcapsules rupture and release liquid metal to fill grain boundary cracks. Pressure-responsive droplets: These are gallium-based liquid metals (Ga-In-Sn). When stress concentrates at the crack tip, the liquid metal deforms and flows along the crack, achieving stress-triggered instant repair.

[0021] (4) Lattice oxygen vacancy pre-injection Lattice oxygen vacancy engineering: On the surface of LLZO grains, oxygen vacancies of controllable concentration are selectively injected through low-temperature plasma treatment, forming an oxygen vacancy gradient distribution layer. These oxygen vacancies: lower the energy barrier for lithium ions to cross the grain surface; provide preferential bonding sites for boron and sulfur in the glass phase; and enhance the chemical bonding strength between the grains and grain boundaries.

[0022] This invention achieves a comprehensive breakthrough in the performance bottlenecks of traditional garnet-type solid electrolytes through a five-fold synergistic mechanism: in-situ grain boundary repair of the glass phase, space charge compensation layer, thermodynamic dual-response self-healing network, grain boundary structure, and lattice oxygen vacancy pre-implantation. This breakthrough addresses the performance limitations of traditional garnet-type solid electrolytes across four dimensions: ion conduction, mechanical strength, interface stability, and dynamic repair. Specific beneficial effects are as follows: 1. By replacing the high-resistivity impurity phase at the grain boundaries with a quaternary low-resistivity glass phase of Li3BO3-Li2SO4-Li2O-Li3N, a continuous high-speed transport channel for lithium ions is provided; combined with an oxygen vacancy activation layer to reduce the interfacial transport energy barrier, the overall ionic conductivity at room temperature can reach 1.8 × 10⁻⁶. -3 With a strength of S / cm or higher, the grain boundary conductivity increases to 1.2 × 10⁻⁶. -3The S / cm level is above 1. The in-situ generated Li3N-Li2O nanocrystalline layer has high polarizability, reducing the lithium-ion cross-grain boundary activation energy to below 0.3 eV. A dual-repair system of temperature-sensitive microcapsules and pressure-responsive liquid metal is constructed: at 60-80℃, the glass phase melts and fills microcracks; with further heating, the capsules release alloys to repair wide cracks; under cyclic stress, the liquid metal can respond instantly and repair cracks as they appear, with a repair efficiency of ≥98% and a mechanical strength recovery rate of ≥95% at 60℃, solving the problem of irreversible damage to ceramic solid electrolytes. The grain boundary structure can deflect crack propagation paths and buffer cyclic stress. Combined with the plastic deformation of the glass phase and the stress release of the liquid metal, the electrolyte's three-point bending strength reaches 88-95 MPa; it is less prone to crack initiation under assembly pressure and long-term cyclic stress, effectively avoiding through-hole fracture of the electrolyte. The near-surface Li3N-rich layer can significantly reduce interface energy, achieving spontaneous lithium metal propagation and pressureless close contact; the critical current density of the lithium symmetric battery is increased to 3.2-3.8 mA / cm². 2 This technology fundamentally suppresses lithium dendrite formation and short circuits. Gradient segmented sintering effectively inhibits impurity phase formation; it boasts strong process compatibility and low equipment cost, and can be extended to other oxide solid electrolytes such as LATP and LLTO, demonstrating broad applicability. Pouch cells assembled with NCM811 cathodes and lithium metal anodes exhibit ≥92% capacity retention after 1200 cycles at 0.5C rate, with interface impedance increase controlled within 35%, demonstrating excellent long-term reliability.

[0023] 2. Traditional LLZO grain boundaries often contain low-conductivity impurity phases such as Li₂CO₃ and La₂Zr₂O₇. This invention introduces elements such as B, S, and N into the precursor, generating a Li₃BO₃-Li₂SO₄-Li₃O-Li₃N glass phase in situ during sintering. This glass phase preferentially occupies grain boundary sites, "squeezing out" or "dissolving" the high-resistivity impurity phases. It provides ion channels: the glass phase itself has high ionic conductivity, providing a "bridge" for lithium ions to cross grain boundaries, reducing grain boundary resistance by 2-3 orders of magnitude. At traditional grain boundaries, due to the lithium ion concentration gradient, a space charge layer forms, generating a local electric field that hinders lithium ion migration across grain boundaries. The Li₃N-Li₂O nanocrystalline layer introduced in this invention has a high dielectric constant and high polarizability. Under the influence of the grain boundary electric field, it polarizes, generating a reverse electric field that reduces the activation energy for lithium ions to cross grain boundaries to below 0.3 eV. Furthermore, the glass phase possesses certain plasticity and toughness, allowing it to absorb stress through plastic deformation when LLZO grains undergo minute relative displacement. Grain boundary design deflects crack propagation paths, consuming more energy. When stress concentrates at the crack tip, pressure-responsive liquid metal droplets immediately deform and flow along the crack, providing "instant filling" at the moment of crack propagation, achieving dynamic repair. When the battery operates at higher rates, Joule heating is generated internally, bringing the glass phase temperature close to its glass transition temperature, reducing viscosity, and allowing it to flow into microcracks under capillary force. As the temperature rises further, temperature-sensitive microcapsules rupture, releasing the alloy, which melts and fills wider cracks. These two repair mechanisms complement each other across different temperature ranges and crack scales, achieving hierarchical repair through "glass-filled microcracks and alloy-filled large cracks." Simultaneously, lattice oxygen vacancies, as positively charged defect sites, have an "attraction-acceleration" effect on lithium ions, lowering the surface transport energy barrier. Oxygen vacancies provide preferential bonding sites for B and S elements in the glassy phase, forming strong chemical bonds such as Zr-OB and La-OS, enhancing the bonding strength between grains and grain boundary phases. The oxygen vacancy concentration decreases from the grain surface to the interior, forming a "soft gradient" that alleviates lattice mismatch stress. The near-surface Li3N-LiF-rich layer has low interfacial energy, allowing lithium metal to spread spontaneously and achieve "pressureless contact." Good wettability makes lithium deposition more uniform, avoiding local current density concentration and significantly increasing the critical current density. Through polarization compensation of the Li3N-Li2O nanocrystalline layer, the lithium-ion cross-grain boundary activation energy is reduced to 0.28 eV. Detailed Implementation

[0024] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Example 1 The preparation method of the garnet-type solid electrolyte in this embodiment includes the following steps: Synthesis of S1 Ta / Nb co-doped LLZO powder In an argon glove box, according to the stoichiometric ratio of Li 6.4 La3Zr 1.5 Ta 0.3 Nb 0.2 O 12 Weigh out Li₂CO₃ (excess, to compensate for high-temperature volatilization), La₂O₃, ZrO₂, Ta₂O₅, and Nb₂O₅. Place the above raw materials and 200g of zirconia grinding beads (5mm diameter) into a 500mL zirconia ball mill jar. Add 100mL of isopropanol as a dispersant and ball mill at 450rpm for 8 hours, reversing the mill every 30 minutes. Remove the solvent by rotary evaporation at 80℃, vacuum dry at 100℃ for 12 hours, pass through a 200-mesh sieve, and pre-calcine at 900℃ for 4 hours to remove CO₂. Ball mill the pre-calcineed powder again for 6 hours to refine the particles. Add 5wt.% PVA binder and spray granulate.

[0026] S2 glass phase precursor preparation Weigh out H3BO3, Li2SO4, Li2CO3, and Li3N in a molar ratio of Li2O:B2O3:SO3:Li3N = 3:0.8:0.8:0.4 and mix them in an argon glove box. Place the mixture in a platinum crucible and melt it at 550℃ for 1.5 h to allow the components to react fully and form a homogeneous glass melt. Pour the melt into a copper plate and quench it to obtain glass fragments. Coarsely crush the glass fragments in an agate mortar and then ball-mill them at 500 rpm for 8 h to obtain glass powder.

[0027] Preparation of S3 temperature-sensitive microcapsules S3-1 core material preparation: Weigh each metal raw material according to the molar ratio of Bi:In:Sn=50:30:20, heat to 150℃ in an argon glove box to melt, cool and grind into nano powder.

[0028] S3-2 wall material preparation: Dissolve 1g of PMMA in 10mL of dichloromethane and add 0.2g of emulsifier Span-80.

[0029] S3-3 Microencapsulation: 0.5g of core nanoparticles were added to the wall material solution and ultrasonically dispersed for 10min. Then, the mixture was added dropwise to 50mL of 1wt.% PVA aqueous solution and stirred at 40℃ for 4h to allow the solvent to evaporate, thus forming microcapsules.

[0030] S3-4 Separation and Drying: Centrifuge, wash three times with deionized water, and vacuum dry at 40℃ to obtain temperature-sensitive microcapsule powder.

[0031] S4 Pressure Response Liquid Metal Droplet Preparation S4-1 Liquid Metal Preparation: Weigh each metal raw material according to the molar ratio of Ga:In:Sn=68:22:10, heat it to 50℃ in a glove box to melt it, and form a liquid alloy.

[0032] S4-2 Emulsification: Add 0.5g of liquid metal to 10mL of anhydrous ethanol, add 0.1g of oleic acid as a surface modifier, and ultrasonically emulsify in an ice-water bath (power 500W, ultrasonic for 3s, stop for 2s) for 30min to form nanodroplets.

[0033] S4-3 Freeze-drying: The emulsion is rapidly frozen and then freeze-dried under vacuum for 24 hours to obtain pressure-responsive liquid metal droplet powder.

[0034] S5 composite powder preparation Weigh out 9g of LLZTO powder, 0.6g of glass powder, 0.15g of thermosensitive microcapsule powder, and 0.15g of pressure-responsive liquid metal droplet powder. First, ball mill the glass powder and LLZTO powder at 300 rpm for 2 hours to ensure uniform adhesion of the glass. Then add the thermosensitive microcapsule powder and ball mill at 200 rpm for 1 hour (to prevent capsule rupture). Finally, add the pressure-responsive liquid metal droplet powder and ball mill at 150 rpm for 30 minutes. Remove the powder to obtain the composite powder.

[0035] S6 Oxygen Vacant Pre-Injection The composite powder was spread evenly in a quartz boat and placed in a plasma treatment chamber. A mixture of Ar and H2 (Ar:H2 volume ratio = 3:1) was introduced for plasma treatment, with a total gas flow rate of 100 sccm, an operating pressure of 30 Pa, a radio frequency power of 200 W, and a treatment time of 20 min. + Bombardment selectively removes surface oxygen atoms, and H2 plasma modulates the oxygen vacancy concentration, forming an oxygen-rich vacancy activation layer on the particle surface.

[0036] S7 electrolyte sheet sintering The treated powder was pressed into discs with a diameter of 20 mm and a thickness of about 1 mm under 300 MPa. The temperature was first increased to 450 °C at a rate of 3 °C / min and held for 1 h, then increased to 600 °C at a rate of 2 °C / min and held for 1 h, then increased to 950 °C at a rate of 4 °C / min and held for 4 h, and finally slowly decreased to 400 °C at a rate of 1 °C / min and allowed to cool naturally to room temperature to obtain the electrolyte sheet.

[0037] Example 2 The preparation method of the garnet-type solid electrolyte in this embodiment includes the following steps: Synthesis of S1 Ta / Nb co-doped LLZO powder In an argon-filled glove box, weigh out Li₂CO₃ (excess, to compensate for high-temperature volatilization), La₂O₃, ZrO₂, Ta₂O₅, and Nb₂O₅ according to stoichiometric ratio. Place the above raw materials and 200g of zirconia grinding beads (5mm diameter) into a 500mL zirconia ball mill jar, add 100mL of isopropanol as a dispersant, and ball mill at 450rpm for 8 hours, reversing the mill every 30 minutes. Remove the solvent by rotary evaporation at 80℃, vacuum dry at 100℃ for 12 hours, pass through a 200-mesh sieve, and pre-calcine at 925℃ for 4.5 hours to remove CO₂. Ball mill the pre-calcineed powder again for 6 hours to refine the particles. Add 5wt.% PVA binder and spray granulate.

[0038] S2 glass phase precursor preparation Weigh out H3BO3, Li2SO4, Li2CO3, and Li3N in a molar ratio of Li2O:B2O3:SO3:Li3N = 3:0.8:0.8:0.4 and mix them in an argon glove box. Place the mixture in a platinum crucible and melt it at 550℃ for 1.5 h to allow the components to react fully and form a homogeneous glass melt. Pour the melt into a copper plate and quench it to obtain glass fragments. Coarsely crush the glass fragments in an agate mortar and then ball-mill them at 500 rpm for 8 h to obtain glass powder.

[0039] Preparation of S3 temperature-sensitive microcapsules S3-1 core material preparation: Weigh each metal raw material according to the molar ratio of Bi:In:Sn=50:30:20, heat to 150℃ in an argon glove box to melt, cool and grind into nano powder.

[0040] S3-2 wall material preparation: Dissolve 2g of PMMA in 10mL of dichloromethane and add 0.3g of emulsifier Span-80.

[0041] S3-3 Microencapsulation: 1.2g of core nanoparticles were added to the wall material solution and ultrasonically dispersed for 10min. Then, the mixture was added dropwise to 60mL of 2wt.% PVA aqueous solution and stirred at 40℃ for 4h to allow the solvent to evaporate, thus forming microcapsules.

[0042] S3-4 Separation and Drying: Centrifuge, wash three times with deionized water, and vacuum dry at 40℃ to obtain temperature-sensitive microcapsule powder.

[0043] S4 Pressure Response Liquid Metal Droplet Preparation S4-1 Liquid Metal Preparation: Weigh each metal raw material according to the molar ratio of Ga:In:Sn=68:22:10, heat it to 50℃ in a glove box to melt it, and form a liquid alloy.

[0044] S4-2 Emulsification: Add 0.8g of liquid metal to 10mL of anhydrous ethanol, add 0.3g of oleic acid as a surface modifier, and ultrasonically emulsify in an ice-water bath (power 500W, ultrasonic for 3s, stop for 2s) for 30min to form nanodroplets.

[0045] S4-3 Freeze-drying: The emulsion is rapidly frozen and then freeze-dried under vacuum for 24 hours to obtain pressure-responsive liquid metal droplet powder.

[0046] S5 composite powder preparation Weigh out 9g of LLZTO powder, 0.6g of glass powder, 0.15g of thermosensitive microcapsule powder, and 0.15g of pressure-responsive liquid metal droplet powder. First, ball mill the glass powder and LLZTO powder at 300 rpm for 2 hours to ensure uniform adhesion of the glass. Then add the thermosensitive microcapsule powder and ball mill at 200 rpm for 1 hour (to prevent capsule rupture). Finally, add the pressure-responsive liquid metal droplet powder and ball mill at 150 rpm for 30 minutes. Remove the powder to obtain the composite powder.

[0047] S6 Oxygen Vacant Pre-Injection The composite powder was spread evenly in a quartz boat and placed in a plasma treatment chamber. A mixture of Ar and H2 (Ar:H2 volume ratio = 3:1) was introduced for plasma treatment, with a total gas flow rate of 120 sccm, a working pressure of 40 Pa, a radio frequency power of 225 W, and a treatment time of 40 min.

[0048] S7 electrolyte sheet sintering The treated powder was pressed into discs with a diameter of 20 mm and a thickness of about 1 mm under 300 MPa. The temperature was first increased to 475 °C at a rate of 3 °C / min and held for 1 h, then increased to 625 °C at a rate of 2 °C / min and held for 1 h, then increased to 975 °C at a rate of 4 °C / min and held for 4 h, and finally slowly decreased to 425 °C at a rate of 2 °C / min and allowed to cool naturally to room temperature to obtain the electrolyte sheet.

[0049] Example 3 The preparation method of the garnet-type solid electrolyte in this embodiment includes the following steps: Synthesis of S1 Ta / Nb co-doped LLZO powder In an argon-filled glove box, weigh out Li₂CO₃ (excess, to compensate for high-temperature volatilization), La₂O₃, ZrO₂, Ta₂O₅, and Nb₂O₅ according to stoichiometric ratio. Place the above raw materials and 200g of zirconia grinding beads (5mm diameter) into a 500mL zirconia ball mill jar, add 100mL of isopropanol as a dispersant, and ball mill at 450rpm for 8 hours, reversing the mill every 30 minutes. Remove the solvent by rotary evaporation at 80℃, vacuum dry at 100℃ for 12 hours, pass through a 200-mesh sieve, and pre-calcine at 950℃ for 5 hours to remove CO₂. Ball mill the pre-calcineed powder again for 6 hours to refine the particles. Add 5wt.% PVA binder and spray granulate.

[0050] S2 glass phase precursor preparation Weigh out H3BO3, Li2SO4, Li2CO3, and Li3N in a molar ratio of Li2O:B2O3:SO3:Li3N = 3:0.8:0.8:0.4 and mix them in an argon glove box. Place the mixture in a platinum crucible and melt it at 550℃ for 1.5 h to allow the components to react fully and form a homogeneous glass melt. Pour the melt into a copper plate and quench it to obtain glass fragments. Coarsely crush the glass fragments in an agate mortar and then ball-mill them at 500 rpm for 8 h to obtain glass powder.

[0051] Preparation of S3 temperature-sensitive microcapsules S3-1 core material preparation: Weigh each metal raw material according to the molar ratio of Bi:In:Sn=50:30:20, heat to 150℃ in an argon glove box to melt, cool and grind into nano powder.

[0052] S3-2 wall material preparation: Dissolve 3g of PMMA in 10mL of dichloromethane and add 0.5g of emulsifier Span-80.

[0053] S3-3 Microencapsulation: 2.4g of core nanoparticles were added to the wall material solution and ultrasonically dispersed for 10min. Then, the mixture was added dropwise to 80mL of 3wt.% PVA aqueous solution and stirred at 40℃ for 4h to allow the solvent to evaporate, thus forming microcapsules.

[0054] S3-4 Separation and Drying: Centrifuge, wash three times with deionized water, and vacuum dry at 40℃ to obtain temperature-sensitive microcapsule powder.

[0055] S4 Pressure Response Liquid Metal Droplet Preparation S4-1 Liquid Metal Preparation: Weigh each metal raw material according to the molar ratio of Ga:In:Sn=68:22:10, heat it to 50℃ in a glove box to melt it, and form a liquid alloy.

[0056] S4-2 Emulsification: Add 1g of liquid metal to 10mL of anhydrous ethanol, add 0.5g of oleic acid as a surface modifier, and ultrasonically emulsify in an ice-water bath (power 500W, ultrasonic for 3s, stop for 2s) for 30min to form nanodroplets.

[0057] S4-3 Freeze-drying: The emulsion is rapidly frozen and then freeze-dried under vacuum for 24 hours to obtain pressure-responsive liquid metal droplet powder.

[0058] S5 composite powder preparation Weigh out 9g of LLZTO powder, 0.6g of glass powder, 0.15g of thermosensitive microcapsule powder, and 0.15g of pressure-responsive liquid metal droplet powder. First, ball mill the glass powder and LLZTO powder at 300 rpm for 2 hours to ensure uniform adhesion of the glass. Then add the thermosensitive microcapsule powder and ball mill at 200 rpm for 1 hour (to prevent capsule rupture). Finally, add the pressure-responsive liquid metal droplet powder and ball mill at 150 rpm for 30 minutes. Remove the powder to obtain the composite powder.

[0059] S6 Oxygen Vacant Pre-Injection The composite powder was spread evenly in a quartz boat and placed in a plasma treatment chamber. A mixture of Ar and H2 (Ar:H2 volume ratio = 3:1) was introduced for plasma treatment, with a total gas flow rate of 150 sccm, a working pressure of 50 Pa, a radio frequency power of 250 W, and a treatment time of 60 min.

[0060] S7 electrolyte sheet sintering The treated powder was pressed into discs with a diameter of 20 mm and a thickness of about 1 mm under 300 MPa. The temperature was first increased to 500 °C at a rate of 3 °C / min and held for 2 h, then increased to 650 °C at a rate of 2 °C / min and held for 2 h, then increased to 1000 °C at a rate of 4 °C / min and held for 5 h, and finally slowly decreased to 450 °C at a rate of 1 °C / min and allowed to cool naturally to room temperature to obtain the electrolyte sheet.

[0061] Comparative Example 1 The difference from Example 1 is that the LLZTO powder synthesized in step S1 was directly pressed into tablets at 300 MPa and sintered at 1150 °C for 12 h to obtain dense LLZTO ceramic tablets, which served as blank control samples.

[0062] Comparative Example 2 The difference from Example 1 is that the LLZTO powder synthesized in step S1 and the glass powder (without Li3N added) in step S2 are mixed at a mass ratio of 94:6. The mixture is then pressed into tablets and sintered at 1000°C for 6 hours to obtain an electrolyte tablet modified only with the glass phase.

[0063] Comparative Example 3 The difference from Example 1 is that a 2 nm thick layer of Li3N was deposited on the surface of the LLZTO powder synthesized in step S1 by atomic layer deposition (ALD). The powder was then pressed into tablets and sintered at 800°C for 2 hours to obtain an electrolyte tablet with only space charge compensation.

[0064] Comparative Example 4 The difference from Example 1 is that 2 wt.% of the temperature-sensitive microcapsule powder prepared in step S3 was added to the LLZTO powder synthesized in step S1. The mixture was then compressed into tablets and sintered at 800°C for 2 hours to obtain a temperature-sensitive repair electrolyte tablet.

[0065] Comparative Example 5 The difference from Example 1 is that 2 wt.% of the pressure-responsive liquid metal droplet powder prepared in step S4 was added to the LLZTO powder synthesized in step S1. The mixture was then pressed into tablets and sintered at 800°C for 2 hours to obtain the electrolyte tablets repaired by the liquid metal.

[0066] Comparative Example 6 The difference from Example 1 is that step S6 is not performed.

[0067] Comparative Example 7 The difference from Example 1 is that in step S5, all components are added at once and ball-milled for mixing.

[0068] Comparative Example 8 Purchase commercial LLZO powder (purity 99.9%, D50=1μm) and press and sinter it according to the method of Comparative Example 1.

[0069] The electrolyte sheets from Examples 1-3 and Comparative Examples 1-8 were assembled into coin cells. The assembly process is as follows: (1) Preparation of positive electrode: NCM811 positive electrode material, conductive carbon black and PVDF are mixed in a mass ratio of 90:5:5, NMP is added to make slurry, coated on aluminum foil, vacuum dried at 80℃ for 12h, and cut into electrode sheets with a diameter of 12 mm.

[0070] (2) Electrolyte preparation: Polish the electrolyte sheets of Examples 1-3 and Comparative Examples 1-8 on both sides to a thickness of 500 μm.

[0071] (3) Battery assembly: In an argon glove box (H2O, O2 < 0.1 ppm), place the positive electrode shell, positive electrode plate, electrolyte plate, lithium plate (14 mm in diameter, 0.5 mm in thickness), gasket, spring, and negative electrode shell in sequence. Seal with a button cell sealing machine under a pressure of 50 MPa.

[0072] (4) Settling and Testing: After assembly, allow the battery to stand for 12 hours, then perform electrochemical performance testing on a battery testing system. Voltage range: 2.8-4.3V (vs. Li). + / Li).

[0073] Self-healing performance testing method: (1) Pre-cracks: Microcracks are pre-created on the surface of the electrolyte sheet using a nanoindenter (load 50-500g, crack width can be controlled 50nm-5μm).

[0074] (2) Heat treatment repair: Low-temperature repair: Heat at 60℃ for 30 minutes (simulating normal heat generation).

[0075] High-temperature repair: Heating at 100℃ for 30 minutes (simulating overload heat generation).

[0076] (3) Stress-triggered repair: During the four-point bending test, the liquid metal response at the crack tip is observed in real time.

[0077] (4) Characterization of repair effect: In-situ SEM observation: Observe the crack closure status.

[0078] EIS test: Tests the change in ionic conductivity before and after repair and calculates the repair efficiency.

[0079] Strength test: Test the bending strength at three points before and after repair, and calculate the strength recovery rate.

[0080] Cyclic repair test: Repeat the cracking and repair at the same location 10 times, and monitor the performance changes.

[0081] The performance test results of the electrolyte sheets and their assembled batteries in Examples 1-3 and Comparative Examples 1-7 are shown in Table 1-3: Table 1 Performance test results of electrolyte sheets in Examples 1-3 and Comparative Examples 1-7 Table 2. Test results of the self-healing performance of the electrolyte sheets in Examples 1-3 and Comparative Examples 1-8 Table 3 Performance test results of the assembled batteries in Examples 1-3 and Comparative Examples 1-8 As shown in Tables 1-3, Comparative Example 1, with its unmodified LLZO, exhibits extremely poor ion conductivity in its electrolyte sheet, with a room temperature conductivity of only 0.42 mS / cm, a grain boundary conductivity of 0.02 mS / cm, and an activation energy as high as 0.62 eV. This is because the grain boundaries are occupied by highly hindering phases such as Li₂CO₃ and La₂Zr₂O₇, resulting in complete uncompensated space charge layers and significant resistance to lithium ions crossing grain boundaries. Furthermore, it suffers from low mechanical strength, extremely poor wettability, a bending strength of 50 MPa, and a critical current density of only 0.4 mA / cm². 2This is because ceramics are inherently brittle, have non-wetting interfaces, and are extremely prone to lithium dendrite formation. They have no self-healing ability; the repair efficiency is 0% at both 60℃ and 100℃, and once a crack forms, it results in permanent failure. The battery experiences rapid cycle degradation; after 1200 cycles, the capacity retention is only 38%, the impedance increases by 380%, and the cycle life is only 150 hours before short-circuiting.

[0082] Comparative Example 2, using only a single glass phase modification, resulted in significantly limited conductivity and activation energy. This is because while the glass phase reduces grain boundary resistance, the space charge layer remains uncompensated, leading to a still high energy barrier for lithium ions crossing grain boundaries. Self-healing ability is weak, and there is no stress response, as the absence of microcapsules and liquid metal, relying solely on glass phase flow, cannot repair wide or dynamic cracks. Interface and stability are moderately poor due to the lack of a nitrogen-rich layer, absence of oxygen vacancy activation, weak interfacial bonding, and poor long-term stability.

[0083] Comparative Example 3 only had Li3N space charge compensation, without a glassy phase or repair, resulting in extremely high grain boundary resistivity, a grain boundary conductivity of only 0.12 mS / cm, and an overall conductivity of 0.65 mS / cm. This is because there was no highly conductive glassy phase, the highly resistive impurity phase at the grain boundaries was not replaced, and the ion channels were discontinuous. It also had low density and poor strength, with a relative density of 88%, a strength of 55 MPa, and a cycle life of only 600 h. This was because there were no sintering aids or grain boundary reinforcement, resulting in low ceramic density, numerous pores, and easy fracture. It had absolutely no repair capability; cracks were irreversible. The battery degraded rapidly, with a capacity retention of only 56% after 1200 cycles and an impedance increase of 210%.

[0084] Comparative Example 4 lacks treatments such as glass phase, space charge compensation, liquid metal, and oxygen vacancies, resulting in extremely poor basic conductivity (0.48 mS / cm, 0.03 mS / cm at grain boundaries, and 0.58 eV activation energy). This is because there are no grain boundary conductive channels, and the repair medium cannot improve intrinsic conductivity. Only high-temperature repair was performed, without immediate repair; microcrack repair at 60℃ was only 45%, with no stress response, and dynamic cracks could not be repaired. The interface and strength are poor, with a strength of 48 MPa, making it extremely prone to fracture and dendrite growth. The battery performance is close to pure LLZO, with a 45% retention rate after 1200 cycles and a 320% impedance increase, only slightly better than the blank sample.

[0085] Comparative Example 5 lacked treatments such as a glass phase, space charge compensation, thermosensitive repair, and oxygen vacancy removal, resulting in poor ion conductivity: 0.52 mS / cm, grain boundary conductivity 0.04 mS / cm, and activation energy 0.55 eV. This is because there are no continuous grain boundary ion channels, and the liquid metal does not provide a lithium-ion conduction path. Stress repair and low-temperature repair alone were ineffective; the repair efficiency at 60°C was only 35%, and it could not repair microcracks caused by static exposure. Interfacial wettability was poor, with a critical current density of only 0.9 mA / cm². 2 It has a short cycle life of only 400 hours, and a capacity retention rate of 49% after 1200 cycles.

[0086] Comparative Example 6, without oxygen vacancy pre-implantation, resulted in a significant decrease in conductivity and activation energy. This is because the absence of surface oxygen vacancies leads to a high lithium-ion surface energy barrier and weak grain-grain boundary bonding. This results in a reduction in interface and critical current density, with a CCD of 2.4 mA / cm². 2 Cycled for 3800 hours. Repair efficiency slightly decreased, cycle repair retention rate was 88%, and strength recovery was 88%. Battery performance decreased, with a retention rate of 83% after 1200 cycles and an impedance increase of 65%, which is far worse than in Example 1.

[0087] Comparative Example 7, with its grain boundary-free design, exhibits performance close to that of Example 1, but is comprehensively weaker, with a conductivity of 1.4 mS / cm, activation energy of 0.32 eV, and strength of 78 MPa. This is because the absence of grain boundaries prevents stress buffering and crack deflection, leading to decreased long-term stability. Significant differences are observed in interface and cycling performance, with a CCD strength of 2.6 mA / cm. 2 Cycle time: 4200 hours. Battery degradation is faster; retention rate is 86% after 1200 cycles; impedance increases by 55%.

[0088] Comparative Example 8 uses commercial LLZO, and its overall performance is slightly lower than that of Comparative Example 1. This represents a real bottleneck in current industrial products, proving that the present invention has a disruptive advantage over commercial products.

Claims

1. A method for preparing a garnet-type solid electrolyte, characterized in that, Includes the following steps: Synthesis of S1 Ta / Nb co-doped LLZO powder: Under argon atmosphere, according to stoichiometric ratio Li 6.4 La3Zr 1.5 Ta 0.3 Nb 0.2 O 12 Weigh out lithium source, lanthanum source, zirconium source, tantalum source and niobium source and ball mill them together; then, remove the solvent by rotary evaporation, vacuum dry and sieve the resulting slurry, and then pre-calcine it at 900-950℃ for 4-5 hours; ball mill the pre-calcineed powder again and spray granulate it. Preparation of S2 glass phase precursor: Weigh H3BO3, Li2SO4, Li2CO3, and Li3N in a molar ratio of Li2O:B2O3:SO3:Li3N=3:0.8:0.8:0.4, mix and melt them under argon protection to form a homogeneous glass melt; quench the melt to obtain glass fragments; coarsely crush the glass fragments and then ball mill them to obtain glass powder; Preparation of S3 temperature-sensitive microcapsules: S3-1 core material preparation: Weigh each metal raw material according to the molar ratio of Bi:In:Sn=50:30:20, heat it to melt under argon atmosphere, cool it and grind it into nano powder; S3-2 Wall Material Preparation: Dissolve polymethyl methacrylate in dichloromethane, add emulsifier to obtain wall material solution; S3-3 Microencapsulation: The core material nanopowder is added to the wall material solution, ultrasonically dispersed, and then dropped into a PVA aqueous solution. The mixture is stirred to evaporate the solvent and form microcapsules. S3-4 Separation and Drying: Centrifugation, washing with deionized water, and vacuum drying to obtain temperature-sensitive microcapsule powder; S4 pressure-responsive liquid metal droplet preparation: S4-1 Liquid Metal Preparation: Weigh each metal raw material according to the molar ratio of Ga:In:Sn=68:22:10, heat it to melt under an argon atmosphere to form a liquid alloy; S4-2 Emulsification: Liquid alloy is added to anhydrous ethanol, oleic acid is added as a surface modifier, and ultrasonic emulsification is performed in an ice-water bath to form nanodroplets and obtain an emulsion; S4-3 Freeze-drying: The emulsion is frozen and then freeze-dried under vacuum to obtain pressure-responsive liquid metal droplet powder; Preparation of S5 composite powder: First, the glass powder obtained in step S2 and the LLZTO powder obtained in step S1 are ball-milled and mixed; then the temperature-sensitive microcapsule powder obtained in step S3 is added and ball milling continues; finally, the pressure-responsive liquid metal droplet powder obtained in step S4 is added and ball milling continues; the powder is then removed to obtain the composite powder. S6 Oxygen Vacancy Pre-Injection: The composite powder is spread evenly in a quartz boat, placed in a plasma treatment chamber, and a mixture of Ar and H2 gas is introduced for plasma treatment; S7 Electrolyte Sheet Sintering: The plasma-treated powder is pressed into discs, heated to 450-500℃ and held for 1-2 hours, then heated to 600-650℃ and held for 1-2 hours, then heated to 950-1000℃ and held for 4-5 hours, and finally cooled to 400-450℃ at a rate of 1-2℃ / min, and then naturally cooled to room temperature to obtain garnet-type solid electrolyte sheets.

2. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S1, the lithium source is Li2CO3, the lanthanum source is La2O3, the zirconium source is ZrO2, the tantalum source is Ta2O5, and the niobium source is Nb2O5.

3. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S3-2, the emulsifier is Span-80; in the wall material solution, the content of polymethyl methacrylate is 0.1-0.3 g / mL, and the content of emulsifier is 0.02-0.05 g / mL.

4. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S3-3, the mass ratio of the core nanopowder to polymethyl methacrylate is (0.5-0.8):1; the concentration of the PVA aqueous solution is 1-3 wt.%, and the volume ratio of PVA to dichloromethane is (5-8):

1.

5. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S4-2, the liquid alloy content in the emulsion is 0.05-0.1 g / mL, and the oleic acid content is 0.01-0.05 g / mL.

6. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S5, the composite powder contains 5-7 wt.% glass powder, 1-2 wt.% thermosensitive microcapsule powder, and 1-2 wt.% pressure-responsive liquid metal droplet powder.

7. The method for preparing garnet-type solid electrolyte as described in claim 1, characterized in that, In step S6, the volume ratio of Ar to H2 is 3:1, the total gas flow rate is 100-150 sccm, the working pressure is 30-50 Pa, the radio frequency power is 200-250 W, and the plasma treatment time is 20-60 min.

8. A garnet-type solid electrolyte, characterized in that, The method for preparing garnet-type solid electrolytes as described in any one of claims 1-7.

Images