Composite solid electrolyte film and preparation method thereof

Abstract

The invention belongs to the technical field of solid-state battery electrolyte materials, and particularly relates to a composite solid-state electrolyte film and a preparation method thereof. The method comprises the following steps: dissolving an epoxy fluoropropane homopolymer in chloroform, adding LiPF6 or LiBF4, mixing with sulfide solid electrolyte Li5.5 PS4.5 Cl0.75 Br0.75 powder to prepare slurry, and coating, drying and rolling to prepare the composite film. The composite film has a wide electrochemical window (at 60 DEG C, the electrochemical window is 3.1-3.5 V), can be matched with a high-voltage electrode, and improves the energy density of an all-solid-state battery.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery electrolyte materials technology, specifically relating to a composite solid-state electrolyte thin film and its preparation method. Background Technology

[0002] All-solid-state lithium batteries are considered an important development direction for next-generation energy storage devices due to their high safety and high energy density. Among various solid electrolytes, sulfide solid electrolytes stand out due to their extremely high room-temperature ionic conductivity (up to 10). －2 ~10 －3 With its good S / cm, excellent flexibility, and ease of processing, it has become a research hotspot in academia and industry.

[0003] However, sulfide solid electrolytes generally suffer from a critical drawback: their intrinsic electrochemical stability window is narrow, typically only 1.7–2.2 V (relative to Li / Li). ＋ This characteristic severely limits its compatibility with high-voltage cathode materials (such as LiCoO2, high-nickel ternary materials NCM, LiCrO2, etc., with operating voltages typically higher than 4.0 V). When the battery operates at high voltage, the electrolyte is prone to oxidative decomposition, leading to increased interfacial impedance, capacity decay, and shortened cycle life, thus restricting further improvements in the energy density of all-solid-state batteries.

[0004] In existing technologies, studies have attempted to improve the electrochemical stability of sulfides through methods such as interface modification, elemental doping, or composite polymers. For example, Lu et al. (Lu, TL; Meng, S.; Liu, M. Electrochemically and chemically stable electrolyte-electrode interfaces for lithium iron phosphate all-solid-state batteries with sulfide electrolytes. J. Mater. Chem. A 2024, 12 (3954) reported improving the compatibility of sulfide electrolytes with LiFePO4 cathodes through interface engineering. However, this method is complex and failed to significantly broaden the intrinsic electrochemical window of the electrolyte. Other methods, such as elemental doping, can improve stability to some extent, but often at the cost of sacrificing ionic conductivity or having limited effects, making it difficult to achieve both high ionic conductivity and a wide voltage window in practical applications.

[0005] Therefore, developing a composite solid electrolyte film that can maintain high ionic conductivity, significantly broaden the electrochemical window, and be stably compatible with high-voltage cathode materials has become a technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the shortcomings of existing sulfide solid electrolytes, such as narrow electrochemical windows and difficulty in matching with high-voltage cathode materials, the present invention aims to provide a composite solid electrolyte thin film and its preparation method. This method aims to significantly broaden the electrochemical stability window of the electrolyte while maintaining high ionic conductivity through unique component design and composite processes, thereby improving the energy density and electrochemical performance of all-solid-state batteries.

[0007] To solve the above-mentioned technical problems, the present invention is implemented as follows: This invention provides a method for preparing a composite solid electrolyte thin film, comprising the following steps: (1) Dissolve the epoxy fluoropropane homopolymer in chloroform solvent, add 0.06~0.12wt% of LiPF6 or LiBF4, stir at 50℃ until completely dissolved, and obtain a mixed solution with epoxy fluoropropane homopolymer concentration of 0.02~0.08g / mL. (2) In an inert atmosphere, the sulfide solid electrolyte powder is added to the mixed solution obtained in step (1), and the mixture is stirred at high speed to obtain a homogeneous slurry, wherein the sulfide solid electrolyte is Li 5.5 PS 4.5 Cl 0.75 Br 0.75 The mass fraction of the sulfide solid electrolyte in the homogeneous slurry is 90.8 wt% to 97.4 wt%. (3) In an inert atmosphere, the homogeneous slurry obtained in step (2) is coated onto the substrate, heated to 60°C and dried for 20 min, and then transferred to a vacuum oven and dried at 60°C for a long time to remove the solvent, thus obtaining a composite solid electrolyte membrane. (4) The composite solid electrolyte membrane obtained in step (3) is rolled and compacted, and the substrate is peeled off to obtain the composite solid electrolyte film.

[0008] Furthermore, in step (1), the molecular weight of the epoxy fluoropropane homopolymer is 60W.

[0009] Furthermore, in step (3), the substrate is a PTFE substrate.

[0010] Furthermore, in step (3), the drying time is not less than 720 minutes.

[0011] The present invention also provides a composite solid electrolyte film, which is prepared by the aforementioned preparation method.

[0012] Furthermore, the composite solid electrolyte film has an electrochemical window of 3.1V to 3.5V at 60°C.

[0013] Compared with the prior art, the advantages of this invention are as follows: (1) Significantly broadened electrochemical window: Thanks to the introduction of highly electronegative fluorine atoms in the epoxy fluoropropane homopolymer, and the synergistic effect with LiPF6 and LiBF4, the electrochemical stability window of the composite film prepared in this invention at 60℃ can be increased to 3.1V to 3.5V (relative to Li / Li ＋ ), which is much higher than that of conventional sulfide electrolytes (1.7~2.2V).

[0014] (2) Good compatibility: The wide electrochemical window enables the electrolyte to be stably compatible with conventional high-voltage cathode materials (such as LiCoO2, NCM, etc.), laying the foundation for building high-energy-density all-solid-state batteries.

[0015] (3) Simple process and easy to scale up: The solution coating process used in this invention is mature, has good compatibility with existing battery production processes, and has the potential for large-scale application. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 The flowchart illustrates the preparation method of the composite solid electrolyte thin film provided by this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments 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.

[0018] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0019] Please see Figure 1 As shown, the present invention also provides a method for preparing a composite solid electrolyte thin film, comprising the following steps: Step S1: Dissolve the epoxy fluoropropane homopolymer in chloroform solvent, add 0.06~0.12wt% of LiPF6 or LiBF4, and stir at 50℃ until completely dissolved to obtain a mixed solution with an epoxy fluoropropane homopolymer concentration of 0.02~0.08g / mL. Step S2: In an inert atmosphere, sulfide solid electrolyte powder is added to the mixed solution obtained in step S1, and the mixture is stirred at high speed to obtain a homogeneous slurry, wherein the sulfide solid electrolyte is Li. 5.5 PS 4.5 Cl 0.75 Br 0.75 The mass fraction of the sulfide solid electrolyte in the homogeneous slurry is 90.8 wt% to 97.4 wt%. Step S3: In an inert atmosphere, the homogeneous slurry obtained in step S2 is coated onto the substrate, heated to 60°C and dried for 20 minutes, and then transferred to a vacuum oven and dried at 60°C for a long time to remove the solvent, thus obtaining a composite solid electrolyte membrane. Step S4: The composite solid electrolyte membrane obtained in step S3 is rolled and compacted, and the substrate is peeled off to obtain the composite solid electrolyte film.

[0020] In step S1, the molecular weight of the epoxy fluoropropane homopolymer is between 300,000 and 600,000.

[0021] In step S2, the high-speed stirring refers to stirring at a speed of 1500-2500 rpm for 3 minutes.

[0022] In step S3, the substrate is a PTFE substrate. The drying time is not less than 720 minutes.

[0023] The present invention also provides a composite solid electrolyte film, which is prepared by the aforementioned preparation method.

[0024] The electrochemical window of the composite solid electrolyte film at 60°C is 3.1V to 3.5V.

[0025] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] Example 1 This embodiment 1 provides a method for preparing a composite solid electrolyte thin film, including the following steps: (1) Preparation of mixed solution: Weigh 0.06 g of epoxy fluoropropane homopolymer with a molecular weight of 300,000 Da and disperse it in 3 mL of chloroform solvent. Then add 0.0012 g of LiPF6 and stir at 1000 rpm in a constant temperature water bath at 50 °C until completely dissolved to obtain a clear mixed solution with an epoxy fluoropropane homopolymer concentration of about 0.02 g / mL.

[0027] (2) Slurry preparation: In a glove box filled with argon (H2O<0.1 ppm, O2<0.1 ppm), 2.94 g of sulfide solid electrolyte powder Li was weighed. 5.5 PS 4.5 Cl 0.75 Br 0.75 Add all of the mixed solution prepared in step (1), and stir at high speed of 2000 rpm for 30 minutes using a planetary homogenizer to obtain a uniform and viscous slurry. The mass fraction ratio of epoxy fluoropropane homopolymer to sulfide solid electrolyte in the slurry is 2:98%.

[0028] (3) Coating and drying: In a glove box, the above slurry was uniformly coated onto the PTFE substrate using a four-sided coater, with a wet film thickness of 200 μm. Subsequently, the coated film was immediately transferred to an infrared heating plate and pretreated at 60°C for 20 minutes. Afterward, the film, along with the substrate, was transferred into a vacuum oven and vacuum dried at 60°C for 12 hours to completely remove residual solvent.

[0029] (4) Roll forming: The dried self-supporting composite film is peeled off from the PTFE substrate and rolled using an electric roller press at a pressure of 10MPa to obtain a dense and flexible composite solid electrolyte film with a thickness of about 80μm.

[0030] Example 2 The difference between this embodiment and Embodiment 1 is that in step 1, the additive is changed to 0.0012g of LiBF4, while the remaining steps and parameters are exactly the same as in Embodiment 1.

[0031] Example 3 The difference between this embodiment and Embodiment 1 is that: In step (1), the amount of epoxy fluoropropylene homopolymer was increased to 0.24 g, the amount of LiPF6 was increased to 0.0192 g, and the final concentration of the mixed solution was approximately 0.08 g / mL.

[0032] In step (2), the sulfide solid electrolyte Li 5.5 PS 4.5 Cl 0.75 Br 0.75 The dosage was adjusted to 2.76g, and the mass fraction ratio of epoxy fluoropropylene homopolymer to sulfide solid electrolyte in the slurry was 8:92%.

[0033] The remaining steps and parameters are the same as in Example 1.

[0034] Example 4 The difference between this embodiment and embodiment 3 is that in step (1), the additive is changed to 0.0192g of LiBF4, and the remaining steps and parameters are exactly the same as in embodiment 3.

[0035] Comparative Example 1 A pure sulfide solid electrolyte film was prepared as a comparative example. 3.0 g of Li was weighed... 5.5 PS 4.5 Cl 0.75 Br 0.75 The powder was directly mixed with an appropriate amount of chloroform solvent to form a slurry without adding any polymer, and then a film was formed by coating, drying and rolling in the same manner as in Example 1.

[0036] Performance Tests and Results The electrolyte films obtained in Examples 1-4 and Comparative Example 1 were cut into 10mm diameter discs using a die-cutting machine. In an inert atmosphere, an 8mm diameter, 100μm thick lithium metal sheet was used as the counter electrode, and a 10mm diameter, 200μm thick stainless steel sheet was used as the working electrode. The electrolyte film was sandwiched between these two electrodes to assemble a CR2032 coin cell. After assembly, a pressure of 50MPa was applied and held for 3 minutes, followed by incubation at 60℃ for 2 hours to form a stable interface.

[0037] The electrochemical stability window of the battery was tested using a linear sweep voltammetry (LSV) method on an electrochemical workstation at a scan rate of 1 mV / s and a cutoff current of 1 mA. The test results are recorded in the table below: The test results in the table above show that: The composite solid electrolyte films prepared by this invention (Examples 1-4) all have significantly higher electrochemical windows than the pure sulfide electrolyte film of Comparative Example 1 (1.92V), which fully demonstrates the effectiveness of combining epoxy fluoropropane homopolymer with lithium salt additives in broadening the electrochemical window.

[0038] Comparing Example 1 with Example 3 (or Example 2 with Example 4), it can be seen that appropriately increasing the relative content of polymer and additives helps to further improve the electrochemical stability window.

[0039] Under the same formulation, the use of LiBF4 as an additive (Examples 2 and 4) showed a wider electrochemical window compared to the use of LiPF6 (Examples 1 and 3), demonstrating the performance differences between different lithium salt additives.

[0040] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0041] Furthermore, it should be noted that the scope of the methods and systems in the embodiments of the present invention is not limited to performing functions in the order shown or discussed, but may also include performing functions substantially simultaneously or in the reverse order, depending on the functions involved. For example, the described methods may be performed in a different order than described, and various steps may be added, omitted, or combined. In addition, features described with reference to certain examples may be combined in other examples.

[0042] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these forms are within the protection scope of the present invention.

Claims

1. A method for preparing a composite solid electrolyte thin film, characterized in that, Includes the following steps: (1) Dissolve the epoxy fluoropropane homopolymer in chloroform solvent, add 0.06~0.12wt% of LiPF6 or LiBF4, stir at 50℃ until completely dissolved, and obtain a mixed solution with epoxy fluoropropane homopolymer concentration of 0.02~0.08g / mL. (2) In an inert atmosphere, the sulfide solid electrolyte powder is added to the mixed solution obtained in step (1), and the mixture is stirred at high speed to obtain a homogeneous slurry, wherein the sulfide solid electrolyte is Li 5.5 PS 4.5 Cl 0.75 Br 0.75 The mass fraction of the sulfide solid electrolyte in the homogeneous slurry is 90.8 wt% to 97.4 wt%. (3) In an inert atmosphere, the homogeneous slurry obtained in step (2) is coated onto the substrate, heated to 60°C and dried for 20 min, and then transferred to a vacuum oven and dried at 60°C for a long time to remove the solvent, thus obtaining a composite solid electrolyte membrane. (4) The composite solid electrolyte membrane obtained in step (3) is rolled and compacted, and the substrate is peeled off to obtain the composite solid electrolyte film.

2. The preparation method according to claim 1, characterized in that, In step (1), the molecular weight of the epoxy fluoropropane homopolymer is 600,000.

3. The preparation method according to claim 1, characterized in that, In step (3), the substrate is a PTFE substrate.

4. The preparation method according to claim 1, characterized in that, In step (3), the drying time is not less than 720 minutes.

5. A composite solid electrolyte thin film, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 4.

6. The composite solid electrolyte film according to claim 5, characterized in that, The electrochemical window of the composite solid electrolyte film at 60°C is 3.1V to 3.5V.

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