Oxide-coated modified sulfide composite solid electrolyte, its preparation method and application

Abstract

This invention discloses an oxide-coated modified sulfide composite solid electrolyte, its preparation method, and its applications, belonging to the field of solid electrolyte materials. The composite electrolyte uses sulfide particles as the matrix and selects oxides with low Young's modulus and lithium-ion conductivity from the Li3La(PO4)2 system as the coating material. A dense inorganic coating layer of 5-20 nm is constructed on the matrix surface through mechanical ball milling, sol-gel processes, etc. This invention breaks with traditional methods, utilizing the Young's modulus of the coating layer and the matrix to trigger synergistic deformation during cold pressing, constructing a seamless, continuous ion transport interface in situ, eliminating interface cracking and slippage. The modified composite electrolyte retains the high ionic conductivity of sulfides, with no decay in conductivity at room temperature and an electrochemical window of 4.5 V; simultaneously, it greatly improves air stability, with no hydrogen sulfide precipitation after 72 hours of exposure under normal conditions, overcoming the stringent low dew point storage limitations and exhibiting strong mass production compatibility.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery solid electrolyte material technology, specifically relating to an oxide-coated modified sulfide composite solid electrolyte, and more particularly to a composite electrolyte structure in which the coating layer and the sulfide matrix undergo synergistic deformation under molding pressure, and its preparation method. It is applicable to the field of preparation technology of various all-solid-state lithium battery electrolytes. Background Technology

[0002] Sulfide solid electrolytes (such as Li2S-P2S5 system, Li 10 GeP2S 12 The system (Li6PS5Cl, etc.) has high ionic conductivity at room temperature (up to 10). -3 Sulfide electrolytes, characterized by their low molecular weight (S / cm), low Young's modulus (15-25 GPa), and good mechanical plasticity, are readily cold-pressed to prepare dense electrolyte membranes, making them a highly sought-after material in the all-solid-state battery field. However, sulfide electrolytes suffer from a fatal air stability defect: they readily react with moisture in the air to generate highly toxic H2S gas, severely restricting their storage, transportation, and large-scale processing.

[0003] To improve the air stability of sulfides, existing modification methods mainly include: (1) Surface modification of small molecule organic matter relies on physical adsorption to form a temporary protective layer on the surface of sulfide, but the binding force is weak and it is easy to fall off when heated, so the protective effect is limited; (2) Element doping (such as oxygen, halogen, etc.) can slightly improve the intrinsic stability of sulfide by partially replacing sulfur in the sulfide lattice, but it cannot form a physical barrier, so the improvement effect is limited and it is easy to introduce impurities and reduce ionic conductivity. (3) A simple mechanical mixing of high Young's modulus rigid oxides (such as LLZO, LATP, Al2O3, etc., with Young's modulus > 90 GPa) with sulfides is attempted to use oxide particles to block water vapor. However, due to the low modulus of the sulfide matrix (15-25 GPa) and the extremely high modulus of the rigid oxide (usually > 90 GPa), a severe deformation mismatch occurs between the two under cold pressing pressure (50-500 MPa) - the sulfide particles deform and flow under pressure to fill the voids, while the rigid oxide particles remain basically undeformed, resulting in: (a) stress concentration at the coating layer or mixing interface, forming microcracks and pores, which cannot achieve dense protection; (b) the rigid oxide particles act as "hard points" inside the composite electrolyte, hindering the close contact between sulfide particles, increasing the interfacial ion transport impedance, and causing the ionic conductivity of the composite electrolyte to decrease by 1-2 orders of magnitude compared to pure sulfides.

[0004] Therefore, the fundamental reason why existing technologies have failed to effectively coat sulfides with oxides lies in neglecting the matching of interfacial mechanical properties. To date, no solution has been found that modulates the mechanical matching between oxides and sulfides to enable them to deform synergistically during cold pressing to form a dense, defect-free interface, while simultaneously maintaining air stability and ionic conductivity. Summary of the Invention

[0005] The present invention aims to solve the technical problem in the prior art that the severe mismatch in modulus between the sulfide solid electrolyte and the outer coating / modification material leads to interface deterioration, microcracks, and a sharp drop in ionic conductivity during subsequent processing (such as cold pressing), which in turn prevents the formation of an effective dense protective layer and results in poor air stability.

[0006] Therefore, this invention provides an oxide-coated modified sulfide composite solid electrolyte with stress-coated synergistic deformation characteristics and its preparation method. This invention breaks through the conventional approach in the field of "focusing only on the electrochemical performance of materials while neglecting mechanical compatibility," and for the first time proposes and realizes the modification principle of "mechanical matching-synergistic deformation." By selecting a specific oxide with a Young's modulus similar to that of the sulfide matrix and possessing lithium-ion conductivity as the coating layer, the coating layer and the sulfide matrix undergo synergistic deformation without peeling or cracking during low-pressure cold pressing, thereby spontaneously forming an integrated, seamless ion transport interface from the sulfide particle core to the oxide coating layer. Simultaneously, a dense, moisture-resistant inorganic protective layer is obtained, suitable for all-solid-state lithium batteries.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: An oxide-coated modified sulfide composite solid electrolyte with stress-coated deformation characteristics is disclosed, wherein sulfide electrolyte particles are used as the matrix and the surface of the sulfide electrolyte particles is coated with a dense oxide coating layer.

[0008] The dense oxide coating material is selected from at least one low Young's modulus oxide with lithium-ion conductivity in the Li3La(PO4)2 system. Maintaining the low modulus is mainly achieved by altering the crystal structure (e.g., monoclinic or orthorhombic) or slightly changing the lithium-lanthanum ratio. Examples include the lithium lanthanum orthophosphate matrix material Li3La(PO4)2, or Li3La(PO4)3 with a more open framework structure and a modulus of approximately 20 GPa. Alternatively, the metaphosphate-enriched phase LiLa(PO4)4 can be used, exhibiting higher glassy flexibility.

[0009] The sulfide electrolyte particles are unmodified by lattice doping and are selected from sulfides in the Li₂S-P₂S₅ system and Li₂S₅. 10 GeP2S 12The system contains at least one of the sulfides and Li6PS5Cl sulfides, with a median particle size D50 of 1–10 μm, which ensures a uniform and dense surface coating.

[0010] The difference in Young's modulus between the dense oxide coating layer and the sulfide electrolyte particle matrix is ​​≤10 GPa; the Young's modulus of the dense oxide coating layer material itself is 15-20 GPa, and the overall Young's modulus of the composite solid electrolyte is stably maintained at 15-25 GPa after coating. Multi-point micromodulus testing of the composite solid electrolyte using a nanoindenter shows that the maximum fluctuation range of Young's modulus between selected local areas is ≤5 GPa, meaning the maximum fluctuation range of Young's modulus between different points in the oxide coating layer is ≤5 GPa.

[0011] The thickness of the dense oxide coating layer is 5 nm to 20 nm, preferably 5 nm to 15 nm; its coating coverage on the surface of the sulfide electrolyte particles is ≥99%, and the mass percentage of the low Young's modulus oxide in the composite solid electrolyte is 0.8% to 3.5%. Under transmission electron microscopy (TEM), the contact interface between the dense oxide coating layer and the sulfide particle matrix exhibits a continuous phase contrast interface without microcracks or voids, and the oxide coating layer has conformal deformation characteristics that adapt to the geometric undulations of the matrix surface.

[0012] The composite solid electrolyte has a room temperature ionic conductivity of 2.7 × 10⁻⁶. -3 ~3.1×10 -3 The electrochemical stability window is ≥4.5 V. After exposure to normal air at 25℃ and 35% relative humidity for 72 hours, the ionic conductivity decay rate is ≤3.5%, the solid-solid interface contact impedance growth rate is ≤5%, and no hydrogen sulfide (H2S) gas is released.

[0013] A method for preparing an oxide-coated modified sulfide composite solid electrolyte with stress-coated deformation characteristics as described above includes the following steps: S1. Select sulfide electrolyte particles with a purity ≥ 99.9% as the matrix, and select at least one low Young's modulus oxide with a purity of 99.9% selected from the Li3La(PO4)2 system as the coating material.

[0014] S2. Using a surface modification process, the coating material is uniformly deposited on the surface of the sulfide electrolyte particles, and a dense, defect-free oxide coating layer with a thickness of 5 nm to 20 nm is constructed around the sulfide electrolyte particles to obtain composite electrolyte particles.

[0015] Preferably, the surface modification process can be a mechanical ball milling method, the specific steps of which include: first, placing the sulfide raw material in a ball mill for high-energy ball milling for 20 hours to obtain a pure sulfide electrolyte particle matrix; then, adding the low Young's modulus oxide coating material in proportion, and continuing mechanical ball milling coating, so that the coating material forms a conformal coating structure on the surface of the sulfide particles.

[0016] Preferably, the surface modification process can also be a sol-gel method, the specific steps of which include: preparing the low Young's modulus oxide coating material into a precursor sol, immersing pure sulfide electrolyte particles in the precursor sol, and forming the dense, defect-free oxide coating layer on the surface of the sulfide electrolyte particles through gelation and subsequent treatment.

[0017] Preferably, the surface modification process is atomic layer deposition or low-temperature calcination.

[0018] S3. Under normal air conditions, such as a temperature of 25°C, a relative humidity of 35%, and a normal pressure environment, the composite electrolyte particles obtained in step S2 are placed in a molding mold and subjected to cold pressing densification treatment under a molding pressure of 300 MPa. During this process, the outer low Young's modulus oxide coating layer and the core sulfide electrolyte matrix undergo synergistic deformation without peeling or cracking, constructing a continuous phase contrast interface in situ without microcracks or voids, and stably controlling the maximum fluctuation range of Young's modulus between various local selected areas of the composite solid electrolyte to ≤5 GPa, ultimately obtaining a dense composite solid electrolyte membrane.

[0019] This invention also provides an all-solid-state lithium battery comprising the aforementioned oxide-coated modified sulfide composite solid electrolyte, or comprising a composite solid electrolyte membrane prepared by cold pressing and densification using the aforementioned preparation method. This battery is compatible with high-voltage cathode materials and exhibits excellent cycle life and safety performance.

[0020] Compared to existing technologies that involve modification with traditional small-molecule organic compounds, elemental lattice doping, and blending with high Young's modulus hard ceramic oxides (such as LLZO), this invention relies on a unique modification mechanism of "mechanical matching-synergistic deformation" and has the following beneficial effects: 1. This invention, by strictly controlling the Young's modulus of the coating oxide to 15–20 GPa, achieves a high degree of matching with the sulfide matrix (modulus difference ≤10 GPa), completely eliminating the high-rigidity hard structure of traditional ceramic oxides (such as LLZO with a modulus as high as 120 GPa). Under a low forming pressure of 200 MPa, the outer shell and the core can undergo coordinated deformation, resulting in a microscopic local modulus fluctuation range of ≤5 GPa, effectively eliminating solid-solid interface collapse, slippage, and microcrack defects caused by cold pressing stress concentration.

[0021] 2. This invention modifies sulfides through dense coating with high oxide coverage (≥99%), eliminating the need for lattice doping that disrupts the intrinsic structure of the sulfide. While blocking moisture in the outer layer, the excellent lithium-ion conductivity of the Li3La(PO4)2 system itself ensures that the ion transport channels are not blocked. The room-temperature ionic conductivity of the modified sulfide is comparable to that of the pure sulfide, with virtually no conductivity decay.

[0022] 3. This invention utilizes an extremely dense and seamless 5-20nm anti-water vapor and oxide protective layer, resulting in a composite solid electrolyte exhibiting remarkable air stability. After 72 hours of storage in a typical exposure environment with 35% relative humidity, no toxic H2S gas is released, and the ionic conductivity decay rate is ≤3.5%, while the solid-solid interface contact resistance growth rate is ≤5%. This means that subsequent cold-pressing, testing, and even assembly of solid-state batteries can be performed without the extremely harsh low-dew-point glove box environment, significantly reducing industrial mass production costs.

[0023] 4. The modification scheme provided by this invention does not rely on complex extreme conditions, can be processed entirely at low temperatures, and exhibits extremely high compatibility with existing common coating processes such as mechanical ball milling, sol-gel, and ALD. The final composite electrolyte has an electrochemical stability window extended to above 4.5V, perfectly adaptable to high-voltage cathode materials, and possesses extremely high scientific research value and prospects for large-scale industrial application. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 These are the coated composite electrolyte particles in this invention. Detailed Implementation

[0026] The following description is intended to disclose the invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art.

[0027] Example 1: This example uses a sulfide electrolyte matrix Li 10 GeP2S 12 And the oxide coating layer Li3La(PO4)2.

[0028] S1. Raw material preparation: The sulfide electrolyte matrix is ​​selected from the superionic conductor Li. 10 GeP2S12 (LGPS), particle size D50 is 2 μm; the coating oxide is Li3La(PO4)2, with Young's modulus of 18 GPa and intrinsic ionic conductivity of 7.4 × 10⁻⁶. -4 S / cm; Li 10 GeP2S 12 The mass ratio of Li3La(PO4)2 is 100:3.

[0029] S2. Coating Preparation: The sulfide raw material was first placed in a ball mill and subjected to high-energy ball milling for 20 hours to obtain pure Li with uniform particle size distribution. 10 GeP2S 12 A particle matrix was prepared; then, Li3La(PO4)2 coating powder was added at a mass ratio of 2%, and the mixture was further added to a ball mill jar for low-energy mechanical coating modification. A dense coating layer with a thickness of approximately 20 nm and a coverage of 88.2% was constructed on the particle surface to obtain composite electrolyte particles.

[0030] S3. Under normal air conditions (humidity 35%), the above composite particles are loaded into a mold and subjected to a molding pressure of 200 MPa for room temperature cold pressing to obtain a composite solid electrolyte membrane.

[0031] Example 2: This example uses a sulfide electrolyte matrix Li6PS5Cl and an oxide coating layer Li3La(PO4)3.

[0032] S1. Raw material preparation: The sulfide electrolyte matrix is ​​made of Li6PS5Cl particles of the argillaceous germanite type with a particle size D50 of 5 μm; the coating oxide is Li3La(PO4)3 with a Young's modulus of 20 GPa and an intrinsic ionic conductivity of 6.8 × 10⁻⁶. -4 S / cm; The mass ratio of Li6PS5Cl to Li3La(PO4)3 is 100:1.7.

[0033] S2. Coating Preparation: A homogeneous precursor sol was prepared by dissolving lithium source, lanthanum source, and phosphate ester precursor in anhydrous ethanol. Pure Li6PS5Cl particles were immersed in this sol, and after temperature-controlled stirring, gelation, and subsequent anhydrous drying, a dense, defect-free oxide coating layer with a thickness of approximately 12 nm and a coverage of 99.5% was formed on the surface of the sulfide particles.

[0034] S3. Same as in Example 1, the composite particles are loaded into a mold and cold-pressed under a pressure of 200 MPa to obtain a composite solid electrolyte membrane.

[0035] Example 3: This example uses a sulfide electrolyte matrix Li2S-P2S5 and an oxide coating layer Li3La(PO4)2.

[0036] S1. Raw material preparation: The matrix is ​​a binary amorphous glass ceramic Li2S-P2S5; the coating material is the same as in Example 1, Li3La(PO4)2, with a modulus of 18 GPa.

[0037] S2. Coating preparation: The coating precursor is uniformly adsorbed onto the surface of Li2S-P2S5 particles using a liquid phase method. After drying, it is calcined at a low temperature for a short time under an inert atmosphere to solidify in situ on the particle surface and form a water vapor resistant inorganic layer with a thickness of 10 nm and a coverage of 99.0%.

[0038] S3. Preparation of cold-pressed film: Same as in Example 1, cold-pressed under 200 MPa pressure.

[0039] Comparative Example 1: High-modulus rigid LLZO oxide blending scheme.

[0040] Rigid garnet type Li7La3Zr2O was selected. 12 (LLZO), with a Young's modulus as high as 120 GPa and an ionic conductivity of 7 × 10⁻⁶. -4 S / cm. It was simply physically mixed with pure Li6PS5Cl sulfide electrolyte (mass ratio same as in Example 2). Without coating structure, it was cold-pressed into a film at 200 MPa.

[0041] Comparative Example 2: Surface modification scheme for small molecule organic compounds (oleylamine).

[0042] Pure Li6PS5Cl sulfide was selected, and the traditional route was adopted. The surface of the sulfide was modified by using the small molecule organic oleylamine to form an organic protective layer. The film was also formed by cold pressing at 200 MPa.

[0043] The composite solid electrolytes prepared in the above embodiments and comparative examples were subjected to performance tests, and the following data were obtained: Example 1 <![CDATA[Li3La(PO4)218 GPa]]> 18 / 2.4 <![CDATA[2.9×10 -3 ]]> No gas precipitation 2.0% Deformation-coherent, seamless and crack-free Example 2 <![CDATA[Li3La(PO4)320 GPa]]> 23 / 3.1 <![CDATA[3.1×10 -3 ]]> No gas precipitation 3.5% Continuous phase contrast, no gaps Example 3 <![CDATA[Li3La(PO4)218 GPa]]> 22 / 2.8 <![CDATA[2.7×10 -3 ]]> No gas precipitation 3.0% Closely integrated, in-situ conformal Comparative Example 1 LLZO120 GPa 75～115 / 40 <![CDATA[4.4×10 -6 ]]> Gas was produced 2 hours later 30% Numerous microcracks, collapse and slippage Comparative Example 2 Oleamine (small organic molecule) Untested <![CDATA[5.2×10 -5 ]]> Aging occurs after 12 hours, with continuous gas production. ＞25% Channel blockage, prone to aging The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. An oxide-coated modified sulfide composite solid electrolyte, characterized in that, It includes a sulfide electrolyte as the matrix and an oxide coating layer on the surface of the matrix; The oxide coating material is selected from at least one of the Li3La(PO4)2 system; the difference in Young's modulus between the oxide coating and the sulfide electrolyte matrix is ​​≤10 GPa, and the Young's modulus of the composite solid electrolyte is 15-25 GPa.

2. The oxide-coated modified sulfide composite solid electrolyte according to claim 1, characterized in that, The sulfide electrolyte matrix is ​​selected from Li2S-P2S5 system sulfides, Li 10 GeP2S 12 At least one of the system sulfides and Li6PS5Cl sulfides.

3. The oxide-coated modified sulfide composite solid electrolyte according to claim 1, characterized in that, The oxide coating has a thickness of 5 nm to 20 nm, and the oxide accounts for 0.8% to 3.5% of the total mass.

4. The oxide-coated modified sulfide composite solid electrolyte according to claim 1, characterized in that, The difference in Young's modulus between different points in the oxide coating layer is ≤5 GPa.

5. The oxide-coated modified sulfide composite solid electrolyte according to claim 1, characterized in that, The contact interface between the oxide coating layer and the sulfide electrolyte matrix is ​​a continuous phase interface without microcracks or voids.

6. A method for preparing an oxide-coated modified sulfide composite solid electrolyte as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Select sulfide electrolyte particles as the matrix and select at least one oxide from the Li3La(PO4)2 system as the coating material; S2. The coating material is uniformly deposited on the surface of the sulfide electrolyte particles using a surface modification process to construct an oxide coating layer with a thickness of 5 nm to 20 nm, thereby obtaining composite electrolyte particles. S3. The composite electrolyte particles are placed in a molding die and cold-pressed to form a continuous phase interface as described in claim 5 in situ, thereby obtaining a dense composite solid electrolyte membrane.

7. The preparation method according to claim 6, characterized in that, The surface modification process in step S2 is one of mechanical ball milling, sol-gel method, atomic layer deposition method, and low temperature calcination method.

8. The preparation method according to claim 6, characterized in that, In step S3, the material is cold-pressed under a pressure of 200 MPa.

9. An all-solid-state battery, characterized in that, The all-solid-state lithium battery comprises an oxide-coated modified sulfide composite solid electrolyte as described in any one of claims 1-5 or comprises a composite solid electrolyte membrane prepared by the method described in claim 6.

Images