Solid-state electrolyte and preparation method and application thereof

Abstract

The present application relates to the field of solid-state batteries, and in particular, to a kind of solid-state electrolyte and its preparation method and application.The solid-state electrolyte has the following general chemical formula: Li 6+a P 1‑x‑y Ge x Sn y S 6‑δ Cl 1‑ω Br ω ;Wherein, 0.05≤x≤0.15, 0.01≤y≤0.10, x+y<0.20, 0.10≤ω≤0.50, -0.3≤a≤0.3, δ is the concentration of sulfur vacancy determined by charge balance.The solid-state electrolyte, by the synergistic co-doping of germanium, tin and bromine, significantly improves the comprehensive performance of the solid-state electrolyte. While maintaining structural stability, it achieves significant enhancement of ionic conductivity, and due to the introduction of bromine, a stable passivation layer is formed at the interface, thereby significantly improving the compatibility with lithium metal and long-term cycle stability.

Description

Technical Field

[0001] This invention relates to the field of solid-state batteries, and more specifically, to a solid electrolyte, its preparation method, and its application. Background Technology

[0002] Li6PS5Cl (LPSC), a silver sulfide-germanium ore-type electrolyte, is considered one of the most promising solid-state electrolyte candidates due to its high ionic conductivity and good processability. However, its commercial application still faces three major challenges: ionic conductivity needs further improvement: its intrinsic ionic conductivity is still lower than that of liquid electrolytes, limiting the fast-charging performance of batteries; poor interfacial stability: especially when in contact with lithium metal anodes, LPSC undergoes chemical / electrochemical reduction reactions, leading to increased interfacial impedance and battery failure; and limitations in fabrication processes: mainstream mechanical ball milling methods suffer from poor batch consistency, high energy consumption, and difficulty in preparing large-area dense films; while traditional solid-state sintering methods often require high temperatures, which easily lead to sulfide volatilization and performance degradation.

[0003] Existing technologies have made some attempts to improve them. For example, using Ge-doped Li6PS5Cl improves ionic conductivity by substituting P sites, but it does not solve the problem of interfacial side reactions with lithium metal, and may even exacerbate dendrite growth due to lattice shrinkage; using Br to completely replace Cl to synthesize Li6PS5Br improves interfacial stability, but significantly increases material cost, and ionic conductivity may even decrease under certain conditions; mechanical ball milling is used to prepare LPSC, but the resulting powder has a wide particle size distribution, and the pressed electrolyte sheet has insufficient density and a large amount of grain boundary resistance.

[0004] In summary, the existing technology lacks an LPSC electrolyte material and its preparation method that can synergistically optimize ionic conductivity, interface stability and preparation process.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The primary objective of this invention is to provide a solid electrolyte that achieves simultaneous improvement in ionic conductivity and interfacial stability through a specific element co-doping strategy.

[0007] The second objective of this invention is to provide a method for preparing the electrolyte, which is simple in process, low in cost, suitable for large-scale production, and can obtain a highly dense and high-performance electrolyte material.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: One aspect of the present invention relates to a solid electrolyte having the following general chemical formula: Li 6+a P 1-x-y Ge x Sny S 6-δ Cl 1-ω Br ω Where, 0.05≤x≤0.15, 0.01≤y≤0.10, x+y<0.20, 0.10≤ω≤0.50, -0.3≤a≤0.3, and δ is the sulfur vacancy concentration determined by charge balance.

[0009] The solid electrolyte described above significantly improves its overall performance through the synergistic co-doping of germanium, tin, and bromine. While maintaining structural stability, it achieves a significant enhancement in ionic conductivity, and the introduction of bromine forms a stable passivation layer at the interface, thereby greatly improving its compatibility with lithium metal and long-term cycle stability.

[0010] Another aspect of the present invention relates to a method for preparing the solid electrolyte, comprising the following steps: (a) subjecting a precursor suspension to vacuum distillation to obtain an intermediate; wherein the precursor suspension comprises: a lithium source, a phosphorus source, a germanium source, a tin source, a sulfur source, a chlorine source, and a bromine source; and (b) subjecting the intermediate to tableting, a first heat treatment, and a second heat treatment.

[0011] The method for preparing the solid electrolyte employs a "solvent-phase synthesis-two-step heat treatment" process, achieving uniform mixing and controllable crystallization of raw materials at the molecular level. This method avoids the contamination and uneven composition problems of traditional ball milling, is simple and efficient, and can repeatedly produce highly dense, high-performance electrolyte materials, making it suitable for large-scale production.

[0012] Another aspect of the present invention relates to a solid-state battery, comprising the solid electrolyte described above or a solid electrolyte prepared by the method for preparing the solid electrolyte described above.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The solid electrolyte provided by this invention achieves a breakthrough improvement in the comprehensive performance of materials through the synergistic design of three elements: Ge, Sn, and Br. At the product level, the electrolyte exhibits extremely high intrinsic ionic conductivity, excellent interfacial chemical and electrochemical stability, and good mechanical compactness. The co-doping of Ge and Sn effectively expands the lithium-ion migration channel and significantly reduces the migration energy barrier; while the partial introduction of Br forms a stable passivation layer in situ at the interface between the electrolyte and the lithium metal anode, fundamentally suppressing harmful side reactions and dendrite growth. This multi-element synergistic optimization strategy enables the material to maintain structural stability while simultaneously achieving excellent ion conductivity and long cycle life.

[0014] (2) At the preparation method level, the novel "solvent-phase synthesis-two-step heat treatment" process developed in this invention fundamentally solves the inherent limitations of traditional solid-state synthesis methods. This process ensures high uniformity and batch consistency of the final product composition by achieving uniform mixing of raw materials at the molecular level; combined with a precisely temperature-controlled two-step heat treatment process, it achieves controllable decomposition of the precursor and sufficient densification growth of the crystal, thereby preparing a target material with high purity and low porosity. This method avoids the problems of pollution, component segregation and high energy consumption that may be caused by mechanical ball milling. The process flow is simple and controllable, providing a reliable and efficient solution for the reproducible and large-scale preparation of high-performance solid electrolytes. Attached Figure Description

[0015] 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.

[0016] Figure 1 The X-ray diffraction patterns of the electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention are shown below. Figure 2 This is a scanning electron microscope image of the electrolyte prepared in Example 1 of the present invention; Figure 3 Electrochemical impedance spectroscopy of the electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 of this invention; Figure 4 and Figure 5 The circuit performance diagram shows the solid-state battery assembled using the electrolyte and NCM811 cathode of Example 1 of this invention. Detailed Implementation

[0017] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0018] One aspect of the present invention relates to a solid electrolyte having the following general chemical formula: Li 6+a P 1-x-y Ge x Sn y S 6-δ Cl 1-ω Br ω ; Where 0.05≤x≤0.15, the value of x reflects the amount of Ge doping; 0.01≤y≤0.10, where the value of y reflects the Sn doping amount; x+y<0.20, the value of x+y reflects the upper limit of the total doping amount; 0.10≤ω≤0.50, where the value of ω reflects the amount of substitution of Cl by Br; -0.3≤a≤0.3, where a represents a small fluctuation in the stoichiometric coefficient of Li; δ represents the sulfur vacancy concentration determined by charge balance.

[0019] The solid electrolyte described herein has a novel material system with synergistic co-doping of germanium, tin, and bromine, which achieves a simultaneous improvement in the ionic conductivity and interfacial stability of the sulfosilver germanium ore electrolyte.

[0020] This invention employs a co-doping scheme of Ge and Sn. 4+ and Sn 4+ The ionic radii are all greater than P. 5+ The synergistic doping of these two materials can more effectively expand the lithium-ion migration channels and reduce the migration energy barrier. At the same time, the different effects of the two on the lattice energy can produce a synergistic effect, improving conductivity while maintaining structural stability.

[0021] This invention employs a technique that partially substitutes Cl with Br. - The ionic radius is greater than that of Cl. - Its introduction can further expand the structural framework and promote lithium-ion migration. More importantly, Br - Having a higher concentration than Cl - A lower electrochemical reduction potential allows for the formation of a more stable, LiBr-rich interfacial passivation layer on the electrolyte surface, thereby significantly suppressing side reactions with lithium metal. Partial substitution, rather than complete substitution, aims to achieve the optimal balance between cost and performance.

[0022] Furthermore, the conductivity of the solid electrolyte is ≥13 mS / cm. This solid electrolyte exhibits high conductivity, overcoming the problem of low ionic conductivity in existing technologies.

[0023] Furthermore, the relative density of the solid electrolyte is 92%~96%. The high relative density of the solid electrolyte means that the material has fewer internal pores and a denser structure. When lithium ions migrate in the bulk phase, they encounter less resistance from grain boundaries and pores, resulting in a more continuous and efficient migration path.

[0024] Furthermore, the D of the solid electrolyte 50 The particle size distribution ranges from 1.5 to 5 μm, including but not limited to point values ​​or ranges between any two of 1.5 μm, 2 μm, 3 μm, 4 μm, or 5 μm. A smaller particle size distribution range is beneficial for improving the density of the pressed electrolyte sheet and reducing grain boundary resistance.

[0025] Another aspect of the present invention relates to a method for preparing the aforementioned solid electrolyte, comprising the following steps: (a) The precursor suspension was subjected to vacuum distillation to obtain the intermediate; The precursor suspension includes: lithium source, phosphorus source, germanium source, tin source, sulfur source, chlorine source and bromine source; (b) The intermediate is subjected to tableting, first heat treatment and second heat treatment.

[0026] The method for preparing the solid electrolyte is a novel "solvent-phase synthesis-two-step heat treatment" process. Through molecular-level mixing and controllable crystallization, a highly dense and uniformly composed electrolyte material is prepared, reducing the particle size distribution range of the solid electrolyte. The synergistic effect of the material and the process ultimately leads to a breakthrough in the overall performance of the electrolyte, exhibiting ultra-high conductivity, ultra-long cycle life, and excellent full-cell performance.

[0027] Further, the vacuum distillation temperature is 40~60℃ (e.g., any value or range between any two of 40℃, 45℃, 50℃, 55℃, or 60℃), the time is 2~6h (e.g., any value or range between any two of 2h, 3h, 4h, 5h, or 6h), and the pressure is -0.1~-0.05MPa (e.g., any value or range between any two of -0.1MPa, -0.08MPa, or -0.05MPa), equivalent to an absolute pressure of 0.05~0.1 MPa. Vacuum distillation removes most of the solvent, yielding a viscous gel-like intermediate.

[0028] Furthermore, the tableting process is performed at a pressure of 10-50 MPa (for example, it can be any value of 10 MPa, 20 MPa, 30 MPa, 40 MPa, or 50 MPa, or a range between any two), and for a time of 1-10 min (for example, it can be any value of 1 min, 3 min, 5 min, 7 min, 9 min, or 10 min, or a range between any two). This pressure range ensures that the precursor powder is sufficiently compacted to form a green body with a certain mechanical strength, while avoiding excessive pressure that could lead to over-hardening of the powder particles or damage to the mold. This lays a good physical foundation for uniform mass transfer and densification reactions in subsequent heat treatment.

[0029] Further, the temperature of the first heat treatment is 120~300℃ (for example, it can be any one of 120℃, 150℃, 170℃, 190℃, 210℃, 230℃, 250℃ or 300℃ or any range between two), the time is 1~4h (for example, it can be any one of 1h, 1.5h, 1.7h, 1.9h, 2.1h, 2.3h, 2.5h, 3h, 3.5h or 4h or any range between two), and the heating rate is 3~7℃ / min (for example, it can be any one of 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min or 7℃ / min or any range between two). This mild, low-temperature heat treatment process aims to completely remove residual organic solvents from the precursor and initiate a preliminary solid-phase reaction to form a uniform amorphous or microcrystalline mesophase. This creates a uniform and stable reaction precursor for the subsequent high-temperature crystallization steps, while effectively avoiding component segregation or premature and violent decomposition of sulfides caused by excessively rapid heating.

[0030] Further, the temperature of the second heat treatment is 400~600℃ (e.g., any one of 400℃, 430℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃, 550℃, 580℃, or 600℃, or a range between any two), the time is 3~12h (e.g., any one of 3h, 4h, 6h, 8h, 10h, or 12h, or a range between any two), and the heating rate is 1~5℃ / min (e.g., any one of 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min, or a range between any two). This step is crucial for achieving sufficient crystallization of the target silver-germanium sulfide phase and final densification of the material. Precise temperature control and sufficient time ensure the integrity of atomic rearrangement and grain growth, resulting in a final product with high crystallinity, low defect concentration, and clean grain boundaries. This is the core structural guarantee for achieving the material's ultra-high ionic conductivity and high mechanical strength. Crystallization is incomplete below 400℃, while temperatures above 600℃ may lead to sulfide decomposition or Li loss.

[0031] Furthermore, the first heat treatment and the second heat treatment are carried out in an argon atmosphere.

[0032] Furthermore, the lithium source includes, but is not limited to, at least one of lithium sulfide, lithium chloride, or lithium bromide.

[0033] Furthermore, the phosphorus source includes, but is not limited to, phosphorus pentasulfide.

[0034] Furthermore, the germanium source includes, but is not limited to, germanium disulfide (GeS2).

[0035] Furthermore, the tin source includes, but is not limited to, tin sulfide (SnS).

[0036] Furthermore, the sulfur source includes, but is not limited to, at least one of lithium sulfide, phosphorus pentasulfide, germanium disulfide, or tin sulfide.

[0037] Furthermore, the chlorine source includes, but is not limited to, lithium chloride and lithium bromide.

[0038] Furthermore, the bromine source includes, but is not limited to, lithium bromide.

[0039] In some specific embodiments, lithium sulfide (Li2S), phosphorus pentasulfide (P2S5), lithium chloride (LiCl), lithium bromide (LiBr), GeS2, and SnS are weighed according to the general stoichiometric ratio in an inert atmosphere glove box and added to a mixed solvent of anhydrous acetonitrile and 1,2-dimethoxyethane, with a volume ratio of anhydrous acetonitrile to 1,2-dimethoxyethane of 1~3:1. The mixture is magnetically stirred at room temperature for 12~48h to form a homogeneous, clear, or slightly turbid precursor suspension.

[0040] Another aspect of the present invention relates to a solid-state battery, comprising the solid electrolyte described above or a solid electrolyte prepared by the method for preparing the solid electrolyte described above.

[0041] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0042] Example 1 The general formula for the solid electrolyte provided in this embodiment is: Li 6.05 P 0.84 Ge 0.10 Sn 0.06 S 5.95 Cl 0.7 Br 0.3 ; The method for preparing solid electrolytes provided in this embodiment includes the following steps: 1. In an argon glove box (H2O<0.1ppm, O2<0.1ppm), accurately weigh the following: Li2S 0.388g, P2S5 0.446g, LiCl 0.084g, LiBr 0.078g, GeS2 0.035g, SnS 0.012g; 2. Add the above raw materials to a mixed solvent of 20 ml anhydrous acetonitrile and 30 ml 1,2-dimethoxyethane, and stir at room temperature for 24 hours to obtain a precursor suspension; 3. Vacuum-evaporation (vacuum distillation) is carried out under reduced pressure until a gel is formed. The vacuum distillation temperature is 50℃, the time is 3h, and the pressure is -0.09MPa. The gel is then pressed into a disc with a diameter of 10mm by holding it under pressure at 20MPa for 5min. 4. Place the green billet in a tube furnace and heat it to 200°C at 5°C / min under an argon flow. Hold it for 2 hours, then heat it to 500°C at 3°C / min and hold it for 6 hours. Cool it with the furnace to obtain a dense electrolyte sheet.

[0043] Example 2 The difference between this embodiment and Embodiment 1 lies in the general formula of the solid electrolyte, which is: Li 6.30 P 0.84 Ge 0.15 Sn 0.01 S5Cl 0.50 Br 0.50 .

[0044] Example 3 The difference between this embodiment and Embodiment 1 lies in the general formula of the solid electrolyte, which is: Li 5.70 P 0.85 Ge 0.05 Sn 0.10 S 4.78 Cl 0.90 Br 0.10 .

[0045] Example 4 The difference between this embodiment and Embodiment 1 is that the tableting pressure is 10 MPa; the temperature of the first heat treatment is 150°C and the time is 1.5 h; and the temperature of the second heat treatment is 450°C and the time is 4 h.

[0046] Example 5 The difference between this embodiment and Embodiment 1 is that the tableting pressure is 50 MPa; the temperature of the first heat treatment is 250°C and the time is 2.5 h; and the temperature of the second heat treatment is 550°C and the time is 10 h.

[0047] Comparative Example 1 Li6PS5Cl was prepared in stoichiometric proportions without doping; the steps were the same as in Example 1, but GeS2, SnS and LiBr were not added, and the amounts of Li2S, P2S5 and LiCl were adjusted accordingly.

[0048] Comparative Example 2 Prepare Li6P by single doping with Ge only 0.9 Ge 0.1 S 5.95 Cl 0.7 Br 0.3 The steps are the same as in Example 1, but without adding SnS.

[0049] Comparative Example 3 Using the exact same raw material ratio as in Example 1, high-energy ball milling was used instead of solvent phase synthesis. The ball milling speed was 500 rpm and the time was 20 h. The subsequent heat treatment process was the same.

[0050] Experimental Example Structural characterization: Figure 1The XRD patterns showed that all samples formed a standard silver-germanium sulfide structure. However, compared with Comparative Example 1, the main diffraction peak of Example 1 shifted significantly to the left, proving that Ge / Sn / Br co-doping successfully expanded the lattice parameters.

[0051] Microscopic morphology: Figure 2 SEM images show that the sample in Example 1 has uniform grain size (approximately 1-3 μm), is tightly packed, has very few pores, and has a relative density of 94% as determined by the Archimedes method.

[0052] Ionic conductivity: as measured by EIS ( Figure 3 And the calculation yielded: The ionic conductivity of Example 1 was 14.1 mS / cm; the ionic conductivity of Comparative Example 1 (undoped) was 4.1 mS / cm; the ionic conductivity of Comparative Example 2 (Ge monodoped) was 12.2 mS / cm; and the ionic conductivity of Comparative Example 3 (conventional ball milling method) was 9.8 mS / cm.

[0053] The results show that the co-doping strategy of the present invention has a significant synergistic enhancement effect on improving ionic conductivity.

[0054] A full cell was assembled using NCM811 as the positive electrode, the electrolyte from Example 1 as the separator, and lithium metal as the negative electrode. Tests were conducted within a voltage range of 2.0-4.2V at a rate of 0.5C. The results are as follows... Figure 4 and Figure 5 As shown, the battery has an initial discharge specific capacity of 185.2 mAh / g and a capacity retention rate of 88.5% after 200 cycles, demonstrating excellent electrochemical performance.

[0055] Comparative Example 3's lithium-lithium symmetric battery experienced a short circuit after only 600 hours of cycling. This demonstrates that the synthesis method of the present invention has significant advantages in terms of material uniformity and performance.

[0056] Table 1

[0057] In summary, the present invention achieves the following technical effects: Extremely high ionic conductivity: The lithium-ion transport pathway is significantly optimized through the synergistic diameter-expanding effect of Ge / Sn and the framework regulation of Br. Examples show that the room-temperature ionic conductivity reaches 14.1 mS / cm, far exceeding that of undoped and single-doped samples.

[0058] Excellent interfacial stability: The introduction of Br forms a stable LiBr passivation layer in situ on the material surface. Lithium-lithium symmetric cell tests show that at 0.2 mA / cm²... 2 At current densities, it can cycle stably for more than 1200 hours without short circuit.

[0059] Superior processability and density: The "solvent-phase synthesis-two-step sintering" method employed in this invention achieves initial mixing at the molecular / atomic level, avoiding the contamination and compositional inhomogeneity problems associated with traditional ball milling. The resulting electrolyte sheet has a relative density exceeding 92%, significantly reducing grain boundary resistance.

[0060] Excellent full-cell performance: Utilizing the electrolyte of this invention and LiNi 0.8 Co 0.1 Mn 0.1 A full cell assembled with an O2 (NCM811) cathode and a lithium metal anode retains a capacity of up to 88.5% after 200 cycles at a 0.5C rate.

[0061] Although the present invention has been illustrated and described with specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; those skilled in the art should understand that modifications can be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein, without departing from the spirit and scope of the present invention; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A solid electrolyte, characterized in that, The solid electrolyte has the following general chemical formula: Li 6+a P 1-x-y Ge x Sn y S 6-δ Cl 1-ω Br ω ; Where 0.05≤x≤0.15, 0.01≤y≤0.10, x+y<0.20, 0.10≤ω≤0.50, -0.3≤a≤0.3, and δ is the sulfur vacancy concentration determined by charge balance.

2. The solid electrolyte according to claim 1, characterized in that, The conductivity of the solid electrolyte is ≥13 mS / cm.

3. The solid electrolyte according to claim 1, characterized in that, The relative density of the solid electrolyte is 92%~96%.

4. The solid electrolyte according to claim 1, characterized in that, The solid electrolyte's D 50 It is 1.5~5μm.

5. A method for preparing a solid electrolyte as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (a) The precursor suspension was subjected to vacuum distillation to obtain the intermediate; The precursor suspension includes: lithium source, phosphorus source, germanium source, tin source, sulfur source, chlorine source and bromine source; (b) The intermediate is subjected to tableting, first heat treatment and second heat treatment.

6. The method for preparing a solid electrolyte according to claim 5, characterized in that, The vacuum distillation is carried out at a temperature of 40~60℃, for a time of 2~6h, and at a pressure of -0.1~-0.05MPa.

7. The method for preparing a solid electrolyte according to claim 5, characterized in that, The tablet compression process is performed at a pressure of 10-50 MPa for 1-10 minutes.

8. The method for preparing a solid electrolyte according to claim 5, characterized in that, The temperature of the first heat treatment is 120~300℃, and the time is 1~4 h.

9. The method for preparing a solid electrolyte according to claim 5, characterized in that, The second heat treatment is performed at a temperature of 400~600℃ for 3~12 hours.

10. A solid-state battery, characterized in that, Solid electrolytes include those prepared by the method of preparing solid electrolytes according to any one of claims 1 to 4 or any one of claims 5 to 9.

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