A method for refining a solid electrolyte based on hydrogen bond self-assembly composite aprotic solvent and its application

Abstract

The present invention discloses a method for refining a solid electrolyte based on a hydrogen-bond self-assembled composite aprotic solvent and its application. The composite aprotic solvent system is composed of acetonitrile and tetramethylurea, and the solvent molecules are self-assembled into ordered aggregates driven by the C-H···O type weak hydrogen bond interaction between the nitrile group (C≡N) and the carbonyl group (C=O). To further enhance the hydrogen bond network and improve the electrolyte stability, (2,4,6-tris(3,4,5-trifluorophenyl)cyclotriboroxane) is introduced into the system. This additive forms a synergistic hydrogen bond with the solvent molecules through the electron-deficient property of the B-O bond to construct a three-dimensional supramolecular network, and at the same time inhibits particle aggregation through the dynamic template effect. Experiments show that adding cyclic boroxane to the composite aprotic solvent can reduce the D50 of sulfide powder to 500 nm and increase the ionic conductivity by more than 300%, providing an innovative solution for the development of high-performance solid-state batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of solid-state batteries, and particularly to a method for refining a solid electrolyte based on a hydrogen-bond self-assembled composite aprotic solvent and its application, which is used for the sanding and refining treatment of sulfide solid electrolyte materials. Background Art

[0002] All-solid-state batteries have become a key direction for next-generation battery technologies due to their high safety and high energy density potential. Sulfide solid electrolytes are considered a solid electrolyte system with great application prospects due to their high ionic conductivity, good ductility, and cost advantages.

[0003] In order to improve the performance of sulfide solid electrolytes, refinement treatment is crucial. Refinement can increase the specific surface area, improve grain boundary contact, optimize the electrode / electrolyte interface, and ultimately improve ionic conductivity, battery performance, and the quality of the electrolyte film. The particle size distribution and dispersibility directly affect the rheology of the slurry, and thus affect processing and production.

[0004] As an efficient wet ultrafine grinding technology, sanding technology has the advantages of high-efficiency refinement, controllable particle size, continuous production, and wet operation. It shows great potential in the preparation of sulfide solid electrolyte powders and can meet the requirements of high-performance materials for particle size and uniformity.

[0005] Existing sanding and refining technologies for sulfide solid electrolytes still face challenges, and the core lies in solvent selection:

[0006] Insufficient dispersibility: The dispersion effect of traditional solvents is limited, and it is difficult to achieve efficient and uniform refinement.

[0007] Compatibility issues: The solvent needs to avoid adverse reactions with sulfide electrolytes.

[0008] Balance between efficiency and performance: Excessive grinding may damage the material structure and reduce performance.

[0009] Lack of a dedicated optimized solvent system: The existing solvent selection lacks systematicness and is difficult to fully meet the refinement requirements. There is an urgent need for a dedicated solvent system to break through the bottleneck.

[0010] The present invention innovatively proposes a composite aprotic solvent system based on hydrogen-bond self-assembly for sanding and refining sulfide electrolytes. The core innovation lies in using hydrogen-bond self-assembly to regulate the properties of the solvent, rather than simple mixing.

[0011] The present invention has the following potential advantages:

[0012] Stronger dispersing ability: The hydrogen-bond self-assembled structure enhances the solvation effect and improves dispersibility.

[0013] Higher refinement efficiency: Optimizing the properties of the solvent improves the energy transfer efficiency.

[0014] Better performance protection: The gentle refinement process reduces structural damage.

[0015] Strong designability of the solvent system: Solvents can be customized for different sulfide systems.

[0016] The present invention is expected to break through the bottleneck of the existing sanding and refinement technology for sulfide solid electrolytes, providing key technical support for high-performance all-solid-state batteries. Summary of the Invention

[0017] In view of this, the object of the present invention is to provide a method for refining solid electrolytes based on hydrogen-bond self-assembled composite aprotic solvents and its application. The solvent system used in this method forms self-assembled bodies with specific structures through hydrogen-bond interactions between solvent molecules, thereby being able to more effectively disperse and refine sulfide solid electrolytes, improving the efficiency and uniformity of sanding and refinement, and ultimately enhancing the performance of sulfide electrolyte materials.

[0018] Ion transport in sulfide solid electrolytes mainly occurs at grain boundaries and particle surfaces. After the particle size is reduced, the specific surface area of the particles increases significantly, and the number of grain boundaries also increases accordingly. This provides more transport channels for lithium ions, effectively reducing the grain boundary resistance and the contact resistance between particles, thereby enhancing the overall ionic conductivity of the electrolyte material. A higher ionic conductivity means a smaller internal resistance of the battery, allowing a larger current to pass through, thus enhancing the power density and rate performance of the battery. This is crucial for application scenarios that require fast charging and discharging, such as electric vehicles, high-power energy storage devices, etc. Therefore, for solid-state batteries prepared with small-particle-size sulfide electrolytes, under high-rate charge and discharge conditions, the capacity retention rate is significantly improved, and the energy density decay is smaller, meeting the requirements of fast charging and discharging and enabling high-power solid-state batteries.

[0019] In addition, reducing the particle size can also bring about an improvement in low-temperature performance. The ionic conductivity usually decreases significantly as the temperature drops, especially at grain boundaries. The increase in grain boundaries brought about by particle size reduction can partially compensate for the decrease in the grain boundary ion transport rate at low temperatures, improving the low-temperature performance of the battery. For example, in a low-temperature environment (such as -20°C, -30°C), for solid-state batteries using small-particle-size sulfide electrolytes, the capacity decay is smaller, the charge and discharge platform voltage is higher, and the low-temperature working performance is more excellent.

[0020] Although the reduction of particle size can bring about the improvement of electrolyte performance, and conventional refinement processes (such as sanding and ball milling) can also refine the electrolyte to a D50 particle size of about 500 nm, a relatively long sanding time (more than 10 h) is required. However, the long sanding time will damage the crystal structure of the electrolyte, resulting in a significant decrease in ionic conductivity, which will greatly offset the improvement effect brought about by the reduction of particle size. The composite aprotic solvent of the present invention not only has the function of protecting the crystal structure, but also has a good dispersion effect. It can make the D50 particle size of the obtained powder about 500 nm within a relatively short sanding time (within 2 h). At the same time, the damage to the crystal structure is reduced (due to the protection function and short sanding time), and the ionic conductivity decreases less. In the later application, the refined electrolyte has more advantages in overall performance.

[0021] The hydrogen-bond self-assembly structure of the present invention enhances the solvation effect and improves the dispersibility. The D50 particle size of the refined sulfide is reduced by 50% compared with the traditional refinement, and the ionic conductivity of the fine sulfide powder increases by about 300%.

[0022] The core of the present invention lies in constructing a composite aprotic solvent system based on hydrogen-bond self-assembly. This solvent system is composed of at least two aprotic solvent components, and the solvent components can self-assemble through hydrogen-bond interactions to form a composite solvent system with a hydrogen-bond self-assembly structure. This hydrogen-bond self-assembly structure endows the composite solvent system with unique properties, making it more suitable for the sanding and refinement of sulfide electrolytes.

[0023] Hydrogen-bond self-assembly mechanism: The acetonitrile molecule contains a nitrile group (-CN), which can act as a hydrogen-bond acceptor (HBA). The tetramethylurea molecule contains a carbonyl group (C=O) and four methyl-substituted nitrogen atoms. The carbonyl group can act as a hydrogen-bond donor (HBA). The methylation of the nitrogen atom in the amide group weakens its hydrogen-bond donor ability, but tetramethylurea can still form weak hydrogen-bond interactions of the O···H-C type (C-H···O hydrogen bond) with adjacent acetonitrile molecules through the carbonyl oxygen atom. In addition, the tetramethylurea molecule itself also has a certain dipole moment, which promotes self-assembly through dipole-dipole interactions. Importantly, this composite solvent system is not a simple mixture, but is driven by intermolecular hydrogen bonds (and possibly dipole interactions) to form dynamic, structured solvent aggregates. This aggregate structure may change the properties of the solvent, such as polarity, viscosity, surface tension, etc., making it more suitable for the dispersion and refinement of sulfide electrolytes, and at the same time can protect the crystal structure of the solid electrolyte from being damaged during the refinement process, and the integrity of the crystal structure can improve the conductivity.

[0024] Regulating the solvent polarity: The introduction of tetramethylurea may fine-tune the polarity of acetonitrile, making it more suitable for interacting with the surface of the sulfide electrolyte and enhancing the solvation ability.

[0025] Changing the solvent viscosity and surface tension: Hydrogen bond self-assembly may lead to a slight increase in the viscosity of the solvent system and a decrease in the surface tension, which may be beneficial for forming a more uniform liquid film during the sanding process and improving the dispersion efficiency.

[0026] Constructing a solvation layer: The solvent aggregates formed by self-assembly may form a more effective solvation layer on the surface of sulfide electrolyte particles, preventing particle agglomeration and improving dispersion stability.

[0027] Hydrogen bond self-assembly and additive synergistic mechanism:

[0028] Optimization of the composite solvent system: The molar ratio of acetonitrile to tetramethylurea (8:2) forms dynamic self-assembled aggregates through C-H···O hydrogen bonds, reducing the solvent surface tension and enhancing the dispersion efficiency.

[0029] Introduction of cyclic boroxane:

[0030] (1) Hydrogen bond synergy: The B-O bond of boroxane acts as a strong hydrogen bond acceptor, forming a B-O···H-C≡N bond with the C≡N of acetonitrile. At the same time, the rigid cyclic structure induces the directional arrangement of the carbonyl group of tetramethylurea, and the hydrogen bond density can be increased.

[0031] (2) Interface stabilization: Boroxane is adsorbed on the surface of sulfide particles through host-guest interactions. The hydrophobic group (trifluorophenyl) reduces the interaction between particles, and the polar B-O group guides the orderly arrangement of the solvent, further enhancing the refinement efficiency.

[0032] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0033] The present application provides a method for refining a solid electrolyte based on a hydrogen bond self-assembled composite aprotic solvent, comprising the following steps:

[0034] S1. Mix tetramethylurea and acetonitrile according to a molar ratio to obtain a composite aprotic solvent;

[0035] S2. Add 2,4,6-tris(3,4,5-trifluorophenyl)cyclotriboroxane (additive) and ultrasonically disperse to obtain a composite refining solvent;

[0036] S3. Add the sulfide solid electrolyte to the composite refining solvent, perform sanding treatment, and dry the obtained slurry to obtain the refined sulfide solid electrolyte powder.

[0037] As an embodiment of the present invention, in step S1, the preparation process of the composite aprotic solvent needs to be carried out in a dry atmosphere (argon) to avoid moisture absorption.

[0038] As an embodiment of the present invention, in step S1, the molar ratio of tetramethylurea to acetonitrile is 75-85:15-25, preferably 8:2.

[0039] As an embodiment of the present invention, in step S2, the addition amount of 2,4,6-tris(3,4,5-trifluorophenyl)cyclotriboroxane is 0.1-1.0 wt% of the composite aprotic solvent, preferably 0.5 wt%. Adding a small amount of 2,4,6-tris(3,4,5-trifluorophenyl)cyclotriboroxane has a synergistic effect with the composite aprotic solvent: (1) As a hydrogen bond crosslinking node, it forms a B-O···H-C≡N bond with the C≡N group of acetonitrile; (2) It induces the directional arrangement of the carbonyl group of tetramethylurea to form a three-dimensional hydrogen bond network with enhanced C-H···O bonds; (3) It reduces the van der Waals force between sulfide particles through hydrophobic groups to inhibit aggregation.

[0040] As an embodiment of the present invention, in step S2, the time of ultrasonic dispersion is 20-40 min, preferably 30 min. The ultrasonic dispersion is carried out under argon protection.

[0041] As an embodiment of the present invention, in step S3, the temperature of the sanding treatment is 8-12 °C, preferably 10 °C.

[0042] Set the cooling system of the sand mill at a constant low temperature of about 10 °C to ensure a stable temperature throughout the sanding process. The low temperature is conducive to the formation and stability of the hydrogen bond self-assembly structure of tetramethylurea and acetonitrile. At this temperature, the thermal motion of tetramethylurea and acetonitrile molecules weakens, which is conducive to the exertion of the intermolecular interaction force between the two, thereby enhancing the self-assembly effect and improving the dispersion ability of the composite solvent system.

[0043] As an embodiment of the present invention, in step S3, the sulfide solid electrolyte includes one or more of Li2S-P2S5-based, Li2S-GeS2-based, and Li2S-SiS2-based sulfide solid electrolytes.

[0044] As an embodiment of the present invention, in step S3, the solid-liquid ratio (sulfide solid electrolyte: composite refining solvent) of the sanding treatment is 1:8-12 (g / mL), preferably 1:10.

[0045] As an embodiment of the present invention, in step S3, the filling amount during the sanding treatment is 60%-80%. The grinding medium for the sanding treatment is selected as zirconia beads with a particle size of 0.1-1 mm.

[0046] As an embodiment of the present invention, in step S3, the rotation speed of the sanding treatment is 1000-2000 rpm, and the time is 30-120 min; the time is preferably 40-80 min.

[0047] As an embodiment of the present invention, in step S3, the drying temperature is 50 - 70 °C, preferably 60 °C, and the time is 10 - 14 h, preferably 12 h. The drying is vacuum drying.

[0048] As an embodiment of the present invention, in step S3, the D50 particle size of the refined sulfide solid electrolyte powder is 400 - 600 nm.

[0049] The present application also provides an application of the above refinement method in the preparation of solid-state batteries.

[0050] Compared with the all-solid-state lithium metal batteries in the prior art, the beneficial effects of the present invention are as follows:

[0051] (1) More efficient and uniform refinement effect of sulfide electrolyte: Compared with traditional solvents or simple mixed solvents, the composite solvent system of the present invention can achieve a smaller and more uniform particle size distribution. This is attributed to the optimized regulation of the solvent properties by the hydrogen bond self-assembly structure.

[0052] (2) Significantly improve the performance of sulfide electrolyte: The refined sulfide electrolyte exhibits higher ionic conductivity. This benefits from the more uniform particle size distribution and improved inter-particle contact, both of which are closely related to the effective dispersion of the hydrogen bond self-assembly solvent system.

[0053] (3) Mild refinement process, better protecting the structure of sulfide electrolyte: Based on the solvent system of hydrogen bond self-assembly, the acting force is mild and controllable, avoiding the side reactions or structure damage problems that may be introduced by traditional solvents. It is beneficial to maintain the chemical integrity and stability of the sulfide electrolyte material.

[0054] (4) The solvent system is easy to prepare, the operation is simple, and it has industrial application prospects. Description of the Drawings

[0055] By reading the detailed description of the non-restrictive embodiments with reference to the following drawings, other features, purposes and advantages of the present invention will become more obvious:

[0056] Figure 1 It is the particle size distribution diagram of the refined sulfide electrolyte for Example 1;

[0057] Figure 2 It is the particle size distribution diagram of the refined sulfide electrolyte for Comparative Example 1;

[0058] Figure 3 It is the comparison diagram of the bulk impedance diagrams of the refined sulfide electrolytes for Example 1 and Comparative Example 1. Detailed Embodiments

[0059] The present invention will be described in detail below in conjunction with embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several adjustments and improvements can still be made. These all belong to the protection scope of the present invention.

[0060] Conventional particulate powders, such as graphite, carbon, metals, alloys, are chemically stable, inert to water and common organic solvents, hardly soluble in common organic solvents, insensitive to structural defects, and have relatively stable conductivity. When refined, it is mainly a problem of size control, and the influence of the refining solvent is relatively small.

[0061] However, the sulfide solid electrolytes subjected to the refinement treatment of the present invention, such as Li6PS5Cl, have significant differences in chemical and physical properties from particles such as graphite, which results in completely different problems they face during the sanding and refinement process. Sulfide solid electrolyte particles have a high surface energy, are prone to agglomeration, and are difficult to disperse. Moreover, they may have a certain solubility in some organic solvents. In addition, their chemical stability is poor, they are sensitive to water and protic solvents, and are prone to hydrolysis and decomposition, and the solvent selection is limited. Since the ionic conductivity of sulfide solid electrolytes is sensitive to changes in crystal structure, mechanical force, and chemical environment, and these factors are affected by sanding conditions and solvents, the performance of sulfide electrolytes is more susceptible to sanding conditions and solvents.

[0062] For sulfide solid electrolytes, when selecting aprotic solvent components for constructing a hydrogen bond self-assembly composite solvent system, the following types of hydrogen bond interactions need to be considered:

[0063] Hydrogen Bond Donor (HBD): It refers to a group containing a hydrogen atom that can be provided in the molecular structure, such as an amide group (-NHCO-), etc. In the present invention, aprotic HBD solvents can be selected, such as certain urea derivatives, etc. Although they do not contain active protons, they can still act as hydrogen bond donors.

[0064] Hydrogen Bond Acceptor (HBA): It refers to a group containing a group that can accept a hydrogen atom in the molecular structure, such as a nitrile group (-CN), etc. Commonly used aprotic solvents such as acetonitrile can be used as HBA solvents.

[0065] Additive: 2,4,6-tris(3,4,5-trifluorophenyl)cyclotriboroxane) can promote the formation of hydrogen bonds, increase the density of hydrogen bonds in the solvent, and enhance the effect of the composite solvent.

[0066] For the dispersion solvent of sulfide electrolyte, the dispersion effect and performance protection need to be comprehensively considered. Tetramethylurea (TMU) and acetonitrile (ACN) of the present invention can form a stable hydrogen-bonded self-assembled structure under appropriate ratios and specific temperature conditions, which can improve the dispersion ability of the composite solvent system and have a certain protective effect on the crystal structure of the electrolyte, avoiding the destruction of the crystal structure during refinement. Further, boroxane is adsorbed on the surface of sulfide particles through host-guest interaction. The hydrophobic group (trifluorophenyl) reduces the interaction between particles, and the polar B-O group guides the ordered arrangement of the solvent, which can further improve the refinement efficiency.

[0067] Tetramethylurea (TMU) and acetonitrile (ACN) play roles mainly from the following aspects:

[0068] (1) Avoiding proton decomposition reaction

[0069] Tetramethylurea (TMU) and acetonitrile (ACN) of the present invention are both typical aprotic organic solvents. They do not contain active hydrogen atoms themselves and will not undergo proton decomposition reaction with sulfide electrolyte. At the same time, in the examples of the present invention, anhydrous TMU and acetonitrile are emphasized to be used, and drying measures are taken to minimize the water content in the solvent system, effectively avoiding the risk of hydrolysis of sulfide electrolyte due to the introduction of water by the solvent, and ensuring the chemical stability of sulfide electrolyte.

[0070] Tetramethylurea and acetonitrile of the present invention are superior to water or alcohol solvents. Obviously, protic solvents such as water or alcohol are completely unsuitable for the wet refinement of sulfide electrolyte. Even some weakly polar protic solvents may have a certain risk of hydrolysis. The present invention selects aprotic TMU and acetonitrile, fundamentally avoiding the hydrolysis problem brought by protic solvents.

[0071] (2) Not damaging the crystal structure and playing a protective role

[0072] The composite aprotic solvent of the present invention can solve the problem of sensitivity of ionic conductivity performance: gentle dispersion and structure protection. As aprotic solvents, TMU and ACN have relatively gentle solvation ability and moderate interaction force with sulfide electrolyte, and will not overly erode or damage the crystal structure of sulfide electrolyte. Compared with some strongly polar or corrosive solvents, the TMU and ACN system can provide a more gentle sanding and refinement environment, while achieving effective dispersion, better protecting the lattice structure integrity of sulfide electrolyte, minimizing the performance damage caused by mechanical force, and being beneficial to maintaining the high ionic conductivity performance of sulfide electrolyte.

[0073] The composite aprotic solvent of the present invention is superior to solvents that introduce structural damage: Some solvent systems that pursue dispersion effects may have strong solvation ability or corrosiveness. Although they can improve the dispersion efficiency, they may also cause irreversible damage to the structure of sulfide electrolytes, resulting in performance degradation. The TMU / ACN system of the present invention takes into account both the dispersion effect and performance protection, achieving a balance between refinement efficiency and performance retention.

[0074] (3) Good dispersion effect

[0075] The composite aprotic solvent of the present invention has moderate polarity and good dispersibility. Both TMU and ACN are aprotic solvents with medium polarity. Their polarity is moderate, which can provide a certain solvation effect on the surface of sulfide electrolyte particles, reduce the aggregation force between particles, achieve a good dispersion effect, and will not cause too high solubility of sulfide electrolytes due to excessive polarity. The mixed use of TMU and ACN can further fine-tune the polarity of the solvent system by adjusting the ratio of the two (8:2), optimize the dispersion performance, and make it more suitable for the dispersion requirements of sulfide electrolytes in different systems.

[0076] The composite aprotic solvent of the present invention is superior to non-polar solvents. Non-polar solvents (such as hexane) can reduce the solubility risk, but their dispersion ability is extremely poor, and they cannot effectively disperse sulfide electrolytes, resulting in low efficiency of sanding and refinement. The TMU / ACN system of the present invention selects medium-polarity solvents and achieves a good balance between solubility and dispersibility.

[0077] (4) Low solubility

[0078] The composite aprotic solvent of the present invention has a relatively low solubility, which can reduce the risk of material loss. Sulfide electrolytes such as Li6PS5Cl have relatively low solubility in TMU and ACN. During the sanding process, the dissolution loss of the material can be controlled at a relatively low level, ensuring the product yield.

[0079] The composite aprotic solvent is superior to solvents with high solubility. Some strongly polar aprotic solvents (such as DMSO, N,N-dimethylformamide (DMF)) may have a relatively high solubility in some sulfide electrolytes. Although the dispersion effect may be good, the risk of material dissolution loss is relatively high, and they are not suitable for long-term wet sanding and refinement. The TMU / ACN system of the present invention has moderate solubility and is more suitable as a sanding and dispersing medium.

[0080] (5) Introduction of cyclic boroxane additive:

[0081] A cyclic boroxane additive is introduced, which can not only form hydrogen bond synergistic action with acetonitrile through the B-O bond as a strong hydrogen bond acceptor and induce the directional arrangement of the carbonyl group of tetramethylurea to increase the hydrogen bond density, but also adsorb on the surface of sulfide particles through host-guest interaction, reduce the interaction between particles by using hydrophobic groups, and guide the orderly arrangement of the solvent with the help of polar B-O groups to stabilize the interface, and finally further improve the refinement efficiency.

[0082] Example 1

[0083] This example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this example is Li6PS5Cl (Yili Technology), the hydrogen bond donor solvent is tetramethylurea (99%, Acros), and the hydrogen bond acceptor solvent is acetonitrile (99%, Adamas).

[0084] The preparation method of the ion liquid electro-wetting modified electrolyte includes the following steps:

[0085] S1. Preparation of the composite solvent system:

[0086] Accurately measure analytical pure anhydrous acetonitrile and tetramethylurea, and mix them in a dry beaker according to a specific molar ratio (acetonitrile:tetramethylurea = 8:2). At room temperature, stir magnetically for 1 hour to ensure that the tetramethylurea is fully dissolved to form a homogeneous and transparent composite aprotic solvent system. The preparation process needs to be carried out in a dry atmosphere (argon) to avoid moisture absorption.

[0087] S2. Introduction of the additive:

[0088] Add 2,4,6-tris(3,4,5-trifluorophenyl)boroxane (Macklin, 99%) additive to the composite aprotic solvent prepared in S1, with a mass of 0.5 wt% of the composite aprotic solvent, and ultrasonically disperse for 30 minutes under argon protection to obtain a composite refining solvent.

[0089] S3. Sanding refinement experiment of the sulfide electrolyte:

[0090] Weigh 5 g of sulfide electrolyte powder (Li6PS5Cl) and add it to [50 mL] of the composite refining solvent, and control the solid-liquid ratio to be [1:10 (g / mL)]. Add the mixed material to an RTSM-AJ horizontal sand mill, and select zirconia beads with a particle size of 5 mm as the grinding medium, with a filling amount of 70%. Set the sand mill speed to 1500 rpm and the grinding time to 60 minutes. Control the temperature at 10°C during the sanding process. After sanding, separate the grinding medium and the slurry by centrifugation. The slurry is dried under vacuum at 60°C for 12 hours to obtain the refined sulfide electrolyte powder, and the particle size distribution is as Figure 1As shown, the body impedance is as Figure 3 shown.

[0091] Example 2

[0092] This example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The steps are basically the same as those in Example 1, except that in the composite solvent, the molar ratio of acetonitrile to tetramethylurea is 5:5.

[0093] Example 3

[0094] This example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The steps are basically the same as those in Example 1, except that the temperature is controlled at room temperature (25 °C) during the sanding process.

[0095] Comparative Example 1

[0096] This comparative example provides a composite solvent system not based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (the same as in Example 1, using high-purity Li6PS5Cl powder of the same batch and with a consistent particle size distribution. The operations are all carried out in a dry inert atmosphere), and the solvent is acetonitrile (99%, Adamas). The difference from the implementation example is that this comparative example only uses a single solvent, acetonitrile, does not add tetramethylurea, and does not require the preparation step of the composite solvent.

[0097] At the same time, this comparative example does not introduce additives, and its usage steps are the same as those in Example 1.

[0098] The particle size distribution of the refined sulfide electrolyte powder is as Figure 2 shown, and the body impedance is as Figure 3 shown. The particle size of the powder obtained by grinding for 60 min in this comparative example is about 900 nm, but the ionic conductivity decreases significantly. Although further sanding for 10 - 12 h can further reduce the particle size, the electrolyte crystal structure will be further degraded and the conductivity will be even worse.

[0099] Comparative Example 2

[0100] This comparative example provides a composite solvent system not based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (the same as in Example 1 and Comparative Example 1, using high-purity Li6PS5Cl powder of the same batch and with a consistent particle size distribution. The operations are all carried out in a dry inert atmosphere), and the solvent is a simple mixed solvent (acetonitrile + hexane) (99%, Adamas).

[0101] S1. Preparation of the mixed solvent:

[0102] In an inert atmosphere glove box, accurately measure dry acetonitrile and hexane, and mix them in a dry beaker according to the molar ratio (acetonitrile:hexane = 8:2). Stir magnetically for 1 hour at room temperature to form a homogeneous composite solvent system. The preparation process needs to be carried out in a dry atmosphere (argon) to avoid moisture absorption.

[0103] At the same time, no additive is introduced in this comparative example, and the remaining steps are the same as those in Example 1.

[0104] Comparative Example 3

[0105] This comparative example provides a composite solvent system that does not self-assemble based on hydrogen bonds and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (the same as in Example 1, using high-purity Li6PS5Cl powder of the same batch and with a consistent particle size distribution. The operations are all carried out in a dry inert atmosphere), and the solvent is tetramethylurea (99%, Acros). The difference from the implementation example is that this comparative example only uses a single solvent, tetramethylurea, without adding acetonitrile, and there is no need to carry out the preparation step of the composite solvent.

[0106] At the same time, no additive is introduced in this comparative example, and the remaining steps are the same as those in Example 1.

[0107] Comparative Example 4

[0108] This comparative example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (Yili Technology), and the hydrogen bond acceptor solvent is acetonitrile (99%, Adamas). The difference between this comparative example and Example 1 is that the hydrogen bond donor solvent is changed from tetramethylurea (99%, Acros) to acetamide (99%, Adamas).

[0109] The other preparation method step parameters are the same as those in Example 1.

[0110] Comparative Example 5

[0111] This comparative example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (Yili Technology), and the hydrogen bond acceptor solvent is acetonitrile (99%, Adamas). The difference between this comparative example and Example 1 is that the hydrogen bond donor solvent is changed from tetramethylurea (99%, Acros) to pyrrole (99%, Adamas).

[0112] The other preparation method step parameters are the same as those in Example 1.

[0113] Comparative Example 6

[0114] This comparative example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (Yili Technology), and the hydrogen bond donor solvent is tetramethylurea (99%, Acros). This comparative example is different from Example 1 in that the hydrogen bond acceptor solvent is changed from acetonitrile (99%, Adamas) to acetone (99%, Adamas). Other preparation method step parameters are the same as those in Example 1.

[0115] Comparative Example 7

[0116] This comparative example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (Yili Technology), and the hydrogen bond donor solvent is tetramethylurea (99%, Acros). This comparative example is different from Example 1 in that the hydrogen bond acceptor solvent is changed from acetonitrile (99%, Adamas) to DMF (99%, Adamas). Other preparation method step parameters are the same as those in Example 1.

[0117] Comparative Example 8

[0118] This comparative example provides a composite solvent system based on hydrogen bond self-assembly and its use in the sanding and refinement of sulfide solid electrolytes and its preparation method. The sulfide electrolyte used in this comparative example is Li6PS5Cl (Yili Technology), and the hydrogen bond donor solvent is tetramethylurea (99%, Acros). The hydrogen bond acceptor solvent is acetonitrile (99%, Adamas). This comparative example is different from Example 1 in that there is no S2 and no additive.

[0119] Other preparation method step parameters are the same as those in Example 1.

[0120] Performance Test Example

[0121] Use an electrochemical workstation to measure the AC impedance value of the refined sulfide electrolyte prepared in the above examples and comparative examples, and calculate the ionic conductivity. The calculation formula is σ = L / RS. Where, S is the area of the electrolyte sheet, L is the thickness of the electrolyte sheet, R is the impedance value, and σ is the ionic conductivity. In the examples and comparative examples, 120 mg of the electrolyte was weighed and pressed into tablets, and all were pressed into a sheet with an area of 0.785 cm 2, a thin sheet with a thickness of 1 mm. Then, the bulk impedance (R) of the electrolyte was measured. The bulk impedance of different electrolyte sheets was measured by electrochemical impedance spectroscopy (EIS) in Es-Lab. Two stainless steels (SS) were used as blocking electrodes, and the measurement was carried out at room temperature in the frequency range of 7000 kHz - 100 mHz and with an alternating current (AC) amplitude of 10 mV. An analytical pure, anhydrous, and dry dispersant (acetonitrile) was used to disperse the sulfide electrolyte, and the particle size was measured using a laser particle size analyzer. The results are shown in Table 1 below:

[0122] Table 1 Ionic conductivities of the electrolytes before and after refinement in the examples and comparative examples

[0123]

[0124] It can be clearly seen from the experimental data in Table 1 that simply relying on a simple solvent mixing strategy, such as the physical mixing of acetonitrile and hexane, although it can reduce the particle size of the sulfide electrolyte to a certain extent, its effect on performance improvement is rather weak. The increase in ionic conductivity is very limited, and the dispersion uniformity and long-term stability are still difficult to guarantee. Delving into the root cause, these simple solvent mixing systems essentially still remain at the macroscopic level stacking of solvent components, lacking effective design and fine regulation of the microstructure between solvent molecules, resulting in the optimization of solvent properties and performance improvement being unable to penetrate to the molecular level, and naturally it is difficult to fully exploit the full potential of the solvent in the dispersion and efficient refinement of sulfide electrolytes. More notably, when attempting to use other types of hydrogen bond acceptor solvents (such as highly polar acetone or DMF) or hydrogen bond donor solvents (such as acetamide or pyrrole), and replacing acetonitrile or tetramethylurea in the preferred composite solvent system of the present invention in equal amounts and containing additives, the experimental results show that the performance improvement effects of the refined sulfide electrolytes are all far inferior to the system of the present invention, and the advantages are not prominent. This phenomenon profoundly reveals a key issue: not all simple combinations of hydrogen bond donor and acceptor solvents can effectively improve the refinement effect of sulfide electrolytes. Merely relying crudely on the hydrogen bond donor or acceptor ability of the solvent cannot automatically achieve significant optimization of material properties. For example, highly polar hydrogen bond acceptor solvents such as acetone or DMF, although having a certain hydrogen bond acceptor ability, may due to their excessive polarity, instead have adverse and even destructive interactions with the sulfide electrolyte, ultimately offsetting the potential advantages that the hydrogen bond self-assembly strategy may bring, resulting in limited performance improvement. Similar problems may also occur in highly polar hydrogen bond donor solvents such as acetamide and pyrrole. Excessive polarity or mismatched solvation ability may all hinder the effective improvement of performance.

[0125] However, in sharp contrast to the above-mentioned technical status quo, the acetonitrile + tetramethylurea hydrogen-bonded self-assembled composite solvent system proposed by the present invention, especially after the innovative introduction of cyclic boroxane additives, has shown remarkable technological breakthroughs and performance leaps. Thanks to the introduction of cyclic boroxane additives, the original hydrogen-bonding synergy between acetonitrile and tetramethylurea is further strengthened and optimized. It not only induces the directional arrangement of the carbonyl groups of tetramethylurea, effectively improves the density of the hydrogen-bonding network, and constructs a unique and delicate hydrogen-bonded self-assembled structure, but also cleverly utilizes the host-guest interaction of the additives to enable them to be efficiently adsorbed on the surface of sulfide particles. It creatively uses the hydrophobic groups of the additives to reduce the interaction between particles, and at the same time, with the help of the polar B-O groups, cleverly guides the orderly arrangement of solvent molecules, achieving effective stabilization of the interface. It is this innovative mechanism of multiple synergies that enables the composite solvent system of the present invention to more significantly and efficiently improve the dispersion state of sulfide electrolytes, greatly improve the sanding and refining efficiency, and ultimately achieve a comprehensive and leapfrog improvement in various key performance indicators of sulfide solid electrolytes, including ionic conductivity and electrochemical performance, on the premise of ensuring the chemical stability of the material to the greatest extent.

[0126] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which does not affect the essence of the present invention.

Claims

1. A solid electrolyte refinement method based on hydrogen bond self-assembly composite aprotic solvent, characterized in that: The steps include: S1, mixing tetramethyl urea and acetonitrile according to a molar ratio to obtain a composite aprotic solvent; S2, adding 2,4,6-tris(3,4,5-trifluorophenyl)boroxine and dispersing by ultrasonic to obtain a composite refinement solvent; S3, adding the sulfide solid electrolyte to the composite refinement solvent, performing sand milling, and drying the obtained slurry to obtain the refined sulfide solid electrolyte powder; In step S1, the molar ratio of tetramethylurea to acetonitrile is 75-85:15-25; In step S2, the amount of 2,4,6-tris(3,4,5-trifluorophenyl)boroxine added is 0.1-1.0 wt % of the composite aprotic solvent.

2. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the temperature of the sanding treatment is 8-12°C.

3. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the sulfide solid electrolyte includes one or more of Li2S-P2S5-based, Li2S-GeS2-based, and Li2S-SiS2-based sulfide solid electrolytes.

4. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the solid-liquid ratio of the sand milling process is 1:8-12.

5. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the sand grinding process is performed at a rotation speed of 1000-2000 rpm and for a time of 30-120 min.

6. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the drying temperature is 50-70°C and the drying time is 10-14 hours.

7. The solid electrolyte refinement method according to claim 1, characterized in that: In step S3, the D50 particle size of the refined sulfide solid electrolyte powder is 400-600 nm.

8. Use of the solid electrolyte refinement method as claimed in claim 1 in the preparation of solid-state batteries.

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