A double-layer structure composite solid electrolyte and a preparation method and application thereof

Abstract

The application discloses a kind of double-layer structure composite solid electrolyte and its preparation method and application, the solid electrolyte includes laminated composite solid electrolyte main layer and composite solid electrolyte modification layer, composite solid electrolyte main layer is formed by polymer matrix, lithium salt and inorganic ceramic solid electrolyte mixed solidification;Composite solid electrolyte modification layer is formed by adding covalent organic compound material mixed solidification after polymer matrix, lithium salt, inorganic ceramic solid electrolyte are mixed.The application has high lithium ion conductivity and efficient polysulfide shuttle inhibition capacity, preparation process is simple, can realize the large-scale production of electrolyte membrane, is favorable for improving the actual specific capacity and cycle life of lithium-sulfur battery.

Description

Technical Field

[0001] This invention relates to a solid electrolyte, its preparation method and application, and more particularly to a bilayer composite solid electrolyte, its preparation method and application. Background Technology

[0002] Lithium-sulfur (Li-S) batteries are known for their high theoretical specific energy (~2600 Wh kg⁻¹). -1 Lithium-sulfur batteries are considered a promising next-generation energy storage system due to their advantages such as low cost and environmental friendliness. However, traditional liquid electrolyte systems suffer from the "shuttle effect" of polysulfides (LiPSs), leading to irreversible loss of active materials, rapid capacity decay, and low coulombic efficiency, which severely restricts their commercial application. Using solid-state electrolytes to replace liquid electrolytes in the construction of all-solid-state lithium-sulfur batteries is one of the effective strategies to improve the "shuttle effect" and enhance safety.

[0003] Among various solid-state electrolytes, composite solid-state electrolytes, by dispersing inorganic ceramic particles within an organic polymer matrix, improve the mechanical properties and electrode / electrolyte interface compatibility while maintaining high lithium-ion conductivity. Furthermore, covalent organic frameworks (COFs), with their regular porous structures and designable functionalized frameworks, can interact with polysulfides through physical adsorption or electrostatic interactions, thereby inhibiting polysulfide migration to some extent. Previous studies have attempted to introduce COFs into lithium-sulfur battery systems to construct polysulfide suppression layers on the cathode side, reducing the loss of active materials during cycling and improving battery cycle stability.

[0004] However, existing methods of simply combining COFs materials with inorganic ceramic particles or polymer electrolytes still have certain shortcomings. On the one hand, COFs materials themselves usually lack lithium-ion conductivity or have limited ion conduction channels. When introduced into the electrolyte system as an inert filler, excessive addition can easily create discontinuous ion transport regions within the electrolyte, thereby reducing the overall lithium-ion conductivity of the composite electrolyte. On the other hand, the interfacial bonding between COFs and inorganic ceramic particles or polymer electrolytes is limited, and interfacial defects are easily generated during repeated charge-discharge cycles, thus affecting the continuity and stability of ion transport. Furthermore, due to the regular porous structure and strong adsorption properties of COFs materials, when uniformly dispersed in the electrolyte, they easily and continuously adsorb polysulfides generated during the sulfur cathode reaction. This causes some polysulfides to remain in the electrolyte phase, making it difficult for them to re-participate in subsequent electrochemical reactions, leading to irreversible loss of the cathode active material and causing a gradual decline in battery capacity. Meanwhile, existing composite solid electrolytes mostly adopt a single uniform structure design, which makes it difficult to distinguish the polysulfide regulation function on the positive electrode side and the lithium metal interface stability requirement on the negative electrode side in terms of structure, thus limiting their further application in high-performance lithium-sulfur solid batteries.

[0005] Therefore, there is an urgent need to develop a composite solid electrolyte with a reasonable structural design and clear functional partitioning, so as to effectively suppress polysulfide shuttle and stabilize the lithium metal anode interface while ensuring high lithium-ion conductivity, thereby improving the overall electrochemical performance and application reliability of lithium-sulfur batteries. Summary of the Invention

[0006] Objectives of the invention: The first objective of this invention is to provide a bilayer composite solid electrolyte that can simultaneously suppress polysulfide shuttle in the sulfur cathode and stabilize the lithium metal anode; the second objective of this invention is to provide a method for preparing the above-mentioned bilayer composite solid electrolyte; the third objective of this invention is to provide applications of the above-mentioned bilayer composite solid electrolyte.

[0007] Technical solution: The dual-layer composite solid electrolyte of the present invention includes a composite solid electrolyte main layer and a composite solid electrolyte modification layer. The composite solid electrolyte main layer is formed by mixing and curing a polymer matrix, lithium salt and inorganic ceramic solid electrolyte. The composite solid electrolyte modification layer is formed by mixing a polymer matrix, lithium salt and inorganic ceramic solid electrolyte and then adding sulfonic acid-based COFs material and curing.

[0008] The thickness of the composite solid electrolyte main layer accounts for 50%-95% of the thickness of the double-layer composite solid electrolyte; the thickness of the composite solid electrolyte modification layer accounts for 5%-50% of the thickness of the double-layer composite solid electrolyte.

[0009] The sulfonic acid COFs are selected from TpBD-(SO3H)2 and TpBD-SO3H; the pore size of the sulfonic acid COFs is on the order of 1-2 nm.

[0010] The preparation method of the above-mentioned bilayer composite solid electrolyte includes the following steps:

[0011] (1) The polymer matrix, lithium salt and inorganic ceramic solid electrolyte are dissolved in an organic solvent to obtain a precursor solution for the main layer, which is placed in a mold and cured to obtain a composite solid electrolyte main layer.

[0012] (2) The polymer matrix, lithium salt, inorganic ceramic solid electrolyte and sulfonic acid COFs material are dissolved in an organic solvent to obtain a modified layer precursor solution;

[0013] (3) Place the modification layer precursor solution in the mold obtained in step (1) and let the modification layer precursor solution solidify on the surface of the composite solid electrolyte main layer to form a composite solid electrolyte modification layer, thereby obtaining a double-layer composite solid electrolyte membrane.

[0014] In step (1), the concentration of the polymer matrix in the precursor solution of the main layer is 0.1-0.2 g / mL.

[0015] In step (1), 5-15 mL of the precursor solution of the main layer is added to a mold with an area of ​​10 cm × 10 cm. After the solvent evaporates, a composite solid electrolyte main layer with a thickness of 50-120 μm is formed.

[0016] In step (1), the mass ratio of polymer matrix to inorganic ceramic solid electrolyte in the precursor solution of the main layer is 0.1-2:1.

[0017] In step (2), the sum of the concentrations of the polymer matrix and the sulfonic acid COFs material in the precursor solution of the modified layer is 0.15-0.2 g / mL.

[0018] In step (2), 0.5-2.0 mL of the modified layer precursor solution is poured onto the surface of the composite solid electrolyte main body layer located in the mold and spread evenly on the surface of the composite solid electrolyte main body layer. After the solvent evaporates, a modified layer with a thickness of 10-30 μm is formed.

[0019] The polymer matrix is ​​selected from at least one of PEO (polyethylene oxide), PEG (polyethylene glycol), PPO (polypropylene oxide), PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), and PAN (polyacrylonitrile); the lithium salt is selected from at least one of LiTFSI (lithium bis(trifluoromethanesulfonate)imide), LiFSI (lithium bis(fluorosulfonylimide)), LiBOB (lithium bis(oxalato)borate), LiClO4 (lithium perchlorate), and LiPF6 (lithium hexafluorophosphate).

[0020] In steps (1) and (2), the molecular weight (MW) of the polymer matrix is ​​40,000-600,000.

[0021] The inorganic ceramic solid electrolyte in steps (1) and (2) is selected from one or more of LLTO (lithium lanthanum titanium oxide), LLZO (lithium lanthanum zirconium oxide), LLZTO (lithium lanthanum zirconium tantalum oxide), and LATP (lithium aluminum titanium phosphorus).

[0022] The organic solvent in steps (1) and (2) is at least one of DMF (dimethylformamide), DMAc (dimethylacetamide), and AN (acetonitrile).

[0023] The curing process in steps (1) and (3) is as follows: the mold is placed at a temperature of 60-100℃ to dry, the solvent evaporates, and the curing is completed.

[0024] The above-mentioned bilayer composite solid electrolyte is used in lithium-sulfur batteries.

[0025] In the bilayer composite solid electrolyte, the bilayer solid electrolyte host layer contacts the negative electrode of the lithium-sulfur battery, and the bilayer solid electrolyte modification layer contacts the positive electrode of the lithium-sulfur battery.

[0026] Invention principle:

[0027] For pure PEO-based electrolytes, their room temperature ionic conductivity is typically below 10. -2 mS cm -1For composite electrolytes with only physical doping of inert fillers such as porous carbon, excessive inert fillers can hinder ion transport, resulting in limited or even decreased conductivity improvement. Based on these limitations, this invention introduces an inorganic ceramic solid electrolyte as an active filler into the main layer of a bilayer composite solid electrolyte. As a fast lithium-ion conductor, the inorganic ceramic solid electrolyte can construct continuous or semi-continuous lithium-ion transport pathways within organic polymers, providing additional channels for lithium-ion migration and improving overall ion conductivity without significantly sacrificing the mechanical properties of the electrolyte membrane. Simultaneously, a covalent organic framework (COF) material rich in sulfonic acid groups, specifically sulfonic acid-based COF materials, is introduced into the functional modification layer near the positive electrode. These functionalized COFs can interact with lithium salts (such as LiTFSI) through polar groups, promoting lithium salt dissociation and increasing the concentration of migratable lithium ions in the system. Testing shows that the bilayer composite solid electrolyte prepared in this invention achieves a lithium-ion conductivity of 0.74 mS·cm at 30 °C. -1 It is significantly higher than that of the monolayer homogeneous composite electrolyte prepared under the same conditions.

[0028] In traditional homogeneous composite electrolytes, if inorganic ceramic solid electrolytes and sulfonic acid-containing COFs are simultaneously doped into the same electrolyte layer, differences in ion transport mechanisms and interfacial behavior among the different functional components can easily lead to obstructed ion migration pathways or increased interfacial impedance, making synergistic effects difficult to achieve. Furthermore, COFs themselves possess a regular porous structure and strong adsorption capacity, which readily adsorbs polysulfides generated by the sulfur cathode during battery operation. This causes the polysulfides to gradually remain in the electrolyte phase, making it difficult for them to re-participate in subsequent electrochemical reactions. Consequently, this results in irreversible loss of the cathode active material and continuous capacity decay. This problem is particularly pronounced under high sulfur loading or long cycling conditions.

[0029] This invention confines sulfonic acid-rich COFs materials to a functional modification layer near the sulfur cathode, rather than dispersing them throughout the electrolyte matrix. This ensures that the adsorption and confinement of polysulfides by the COFs primarily occurs at the cathode interface. This effectively suppresses polysulfide migration to the anode while reducing polysulfide retention and loss within the electrolyte matrix, thus preventing irreversible capacity decay caused by the diffusion of active materials within the electrolyte. Based on this structural design, lithium-sulfur batteries assembled using the bilayer composite solid-state electrolyte of this invention maintain a capacity retention of 84.4% after 600 cycles at 0.5 C, with an average coulombic efficiency consistently above 99.3%, demonstrating the synergistic advantages of this bilayer structure in ion transport performance and polysulfide suppression.

[0030] Beneficial effects: Compared with the prior art, the present invention achieves the following significant effects:

[0031] (1) The composite solid electrolyte of the present invention, which consists of a composite polymer host layer and a composite solid electrolyte modification layer, has both high lithium-ion conductivity and efficient polysulfide shuttle suppression capability. It can ensure the overall high-efficiency ion transport of the battery through the optimized host layer, and can achieve efficient blocking and adsorption of polysulfides at the positive electrode interface through the special functional modification layer. (2) The present invention uses an inorganic ceramic solid electrolyte combined with a polymer substrate to form a composite polymer host layer. The inorganic ceramic solid electrolyte can reduce the crystallinity of the polymer substrate as an active filler, and also has the ability to transport lithium ions. Under the combined action of the two, it helps to improve the ion transport efficiency of the electrolyte. The other layer is a modification layer that introduces sulfonic acid COFs material into the composite electrolyte. The sulfonic acid COFs material has a rich pore structure that can adsorb polysulfides, and its surface has sulfonic acid functional groups that can interact with polysulfides, thereby inhibiting polysulfide shuttle and improving the cycle life of the battery. (2) The preparation process of this double-layer composite solid electrolyte is simple and can realize the large-scale production of electrolyte membrane, which is beneficial to improving the actual specific capacity and cycle life of lithium-sulfur batteries. Attached Figure Description

[0032] Figure 1 The preparation process of the bilayer composite solid electrolyte prepared in this invention;

[0033] Figure 2 A cross-sectional view of the bilayer composite solid electrolyte prepared in Example 12;

[0034] Figure 3 (a) is a scanning electron microscope image of one side of the main layer in the bilayer composite solid electrolyte prepared in Example 1, and (b) is a scanning electron microscope image of the bilayer composite solid electrolyte prepared in Example 1 facing the positive electrode surface.

[0035] Figure 4 The data on ionic conductivity and calculated activation energy of the bilayer composite solid electrolyte prepared in Example 1 and the monolayer control electrolyte prepared in Comparative Examples 1 and 2 at different temperatures;

[0036] Figure 5 The electrochemical stability window of the bilayer composite solid electrolyte prepared in Example 1 and the control electrolytes prepared in Comparative Examples 1 and 2;

[0037] Figure 6 The peak voltage difference between the bilayer composite solid electrolyte prepared in Example 1 and the control electrolyte prepared in Comparative Examples 1 and 2 was obtained by cyclic voltammetry testing.

[0038] Figure 7Limiting current density of lithium symmetric batteries assembled from the bilayer composite solid electrolyte prepared in Example 1 and the control electrolytes prepared in Comparative Examples 1 and 2.

[0039] Figure 8 The results show the cycle performance test results of lithium-sulfur batteries assembled from the bilayer composite solid electrolyte prepared in Example 1 and the control electrolytes prepared in Comparative Examples 1 and 2. Detailed Implementation

[0040] The present invention will now be described in further detail.

[0041] Example 1

[0042] S1. Polymer matrix PEO, lithium salt LiFSI and inorganic ceramic solid electrolyte LLZO are dissolved in AN at a mass ratio of 1:0.5:0.1. The solution is then magnetically stirred on a 50 ℃ hot plate for 8 h to obtain the precursor solution of the main layer; wherein the concentration of polymer matrix is ​​0.15 g / mL.

[0043] S2. Pour 8 mL of the precursor solution for the main layer into a 10 cm × 10 cm mold, so that the solution spreads evenly at the bottom of the mold to form a wet film, and vacuum dry at 60 ℃ for 10 h to remove the solvent, to obtain the composite solid electrolyte main layer.

[0044] S3. Polymer matrix PEO, lithium salt LiFSI, inorganic ceramic solid electrolyte LLZO, and sulfonic acid-based COFs material TpBD-(SO3H)2 were dissolved in AN at a mass ratio of 1:0.5:0.1:0.01 and fully dispersed to obtain a modified layer precursor solution. The total concentration of polymer matrix PEO and TpBD-(SO3H)2 in the modified layer precursor solution was 0.16 g / mL. TpBD-(SO3H)2 was synthesized according to the method reported in the literature Li Jilin, et al. Extremely stable sulfuricacid covalent organic framework for highly effective ammonia capture[J].Chinese Journal of Chemistry, 2022, 40(20): 2445-2450.

[0045] S4. Take 0.5 mL of the modified layer precursor solution and pour it into a mold with a dried composite solid electrolyte main layer. Then place the mold in a vacuum oven at 60 °C for 24 h to dry. After the modified layer precursor solution is cured, demold to obtain a double-layer composite solid electrolyte suitable for lithium-sulfur batteries.

[0046] Example 2

[0047] Based on Example 1, the difference from Example 1 is that in step (S1), the polymer matrix is ​​replaced with PAN.

[0048] Example 3

[0049] Based on Example 1, the difference is that in step (S3), the polymer matrix is ​​replaced with PAN.

[0050] Example 4

[0051] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the polymer matrix is ​​replaced with PAN.

[0052] Example 5

[0053] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the lithium salt is replaced with LiTFSI.

[0054] Example 6

[0055] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the inorganic ceramic solid electrolyte is replaced with LLZTO.

[0056] Example 7

[0057] Based on Example 1, the difference is that in step (S3), TpBD-(SO3H)2 is replaced with TpBD-SO3H, which is synthesized according to the method reported in the literature (Li Jilin, et al. Extremely stable sulfuric acid covalentorganic framework for highly effective ammonia capture[J]. Chinese Journal of Chemistry, 2022, 40(20): 2445-2450.).

[0058] Example 8

[0059] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), AN is replaced with DMF.

[0060] Example 9

[0061] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the mass ratio of polymer matrix PEO, lithium salt LiFSI and inorganic ceramic solid electrolyte LLZO is replaced with 1:0.5:0.2.

[0062] Example 10

[0063] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the mass ratio of polymer matrix PEO, lithium salt LiFSI and inorganic ceramic solid electrolyte LLZO is replaced with 1:0.2:0.1.

[0064] Example 11

[0065] Based on Example 1, the difference from Example 1 is that in steps (S1) and (S3), the mass ratio of polymer matrix PEO, lithium salt LiFSI and inorganic ceramic solid electrolyte LLZO is replaced with 1:0.2:0.2.

[0066] Example 12

[0067] Based on Example 1, the difference is that the precursor solution of the main layer poured in step (S2) is changed to 15 ml, and the precursor solution of the modification layer poured in step (S4) is changed to 2 ml.

[0068] Example 13

[0069] Based on Example 1, the difference from Example 1 is that the vacuum drying temperature in steps (S2) and (S4) is changed to 70°C.

[0070] Example 14

[0071] Based on Example 1, the difference from Example 1 is that the vacuum drying temperature in steps (S2) and (S4) is changed to 80°C.

[0072] Example 15

[0073] Based on Example 1, the difference from Example 1 is that the vacuum drying time in steps (S2) and (S4) is changed to 6 hours.

[0074] Example 16

[0075] Based on Example 1, the difference from Example 1 is that the vacuum drying time in steps (S2) and (S4) is changed to 12 hours.

[0076] Comparative Example 1

[0077] Based on Example 1, the steps (S3) and (S4) are omitted, and a single-layer composite solid electrolyte is obtained.

[0078] Comparative Example 2

[0079] Based on Example 1, the steps (S1) and (S2) are omitted, and a single-layer composite solid electrolyte is obtained.

[0080] The bilayer composite solid electrolytes prepared in Examples 1-16 and the monolayer composite solid electrolytes prepared in Comparative Examples 1-2 were cut into 17 mm diameter discs and transferred to an argon-filled glove box to assemble symmetrical cells with a steel sheet|electrolyte|steel sheet structure. Both sides of the electrolyte were used as electrodes with 15.6 mm diameter steel sheets. After successful assembly, ionic conductivity and intrinsic impedance were measured using an electrochemical workstation (AutoLab, PGSTAT302 N) in the frequency range of 1 kHz to 10 Hz. The half-cell cycle lifetime and interfacial impedance results for the different electrolytes are shown in Table 1 below.

[0081] Table 1. Ionic conductivity and intrinsic impedance results of different electrolytes in each embodiment and comparative example.

[0082]

[0083] The data in Table 1 shows that:

[0084] In Examples 2 and 3, the polymer matrix of the host layer and the modification layer were replaced with PAN, respectively. The results showed that the ionic conductivity of the electrolyte decreased, while the intrinsic impedance increased slightly. This indicates that when different types of polymer matrices are used for the host layer and the modification layer, the interfacial compatibility between the two layers decreases, and the continuity of lithium-ion migration channels at the interface is affected to some extent, thereby increasing the resistance to lithium-ion transport in the electrolyte.

[0085] In Example 4, the polymer matrix of both the host layer and the modification layer was replaced with PAN. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly. This indicates that when both layers use the same polymer matrix, a relatively continuous ion transport channel can still be formed inside the electrolyte, and the overall ion transport performance of the system remains stable.

[0086] In Example 5, the lithium salts in both the host layer and the modification layer were replaced with LiTFSI. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that the composite solid electrolyte system constructed in this invention has a certain adaptability to different types of lithium salts and can still maintain stable ion transport performance under different lithium salt systems.

[0087] In Example 6, the inorganic ceramic solid electrolytes in both the host layer and the modification layer were replaced with LLZTO. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that in the composite system constructed in this invention, different types of garnet-type inorganic ceramic fillers can effectively participate in the construction of the ion transport network with minimal impact on the overall electrochemical performance.

[0088] In Example 7, the sulfonic acid-based COFs material in the modified layer was replaced with TpBD-SO3H. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that the sulfonic acid-based COFs material can provide similar interfacial regulation in the electrolyte, which helps maintain the stability of the lithium-ion transport channel.

[0089] In Example 8, the solvent for both the host layer and the modification layer was replaced with DMF. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that solvents of different polarities have little impact on the final ion transport structure during electrolyte preparation, and that the system of this invention has certain process adaptability.

[0090] In Example 9, the content of LLZO was increased to control the electrolyte's conductivity. The results showed that the electrolyte's ionic conductivity and intrinsic impedance did not change significantly, indicating that increasing the content of inorganic ceramic filler within a certain range does not disrupt the ion transport network structure formed inside the electrolyte.

[0091] In Example 10, the lithium salt content was reduced to adjust the electrolyte's conductivity. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that within a certain range, variations in the lithium salt content have little impact on the overall ion transport performance of the system.

[0092] In Example 11, the LLZO content was increased and the lithium salt ratio was decreased. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, further demonstrating that the composite solid electrolyte system constructed in this invention has good sizing ability and a stable ion transport structure.

[0093] In Example 12, the thickness of the host layer and the modification layer was increased. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that the electrolyte membrane can still maintain stable ion transport performance within a certain thickness range.

[0094] In Examples 13 and 14, the vacuum drying temperature was increased to 70 °C and 80 °C, respectively. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that the drying conditions within this temperature range did not have a significant impact on the internal structure of the electrolyte.

[0095] In Examples 15 and 16, the vacuum drying time was adjusted to 6 h and 12 h, respectively. The results showed that the ionic conductivity and intrinsic impedance of the electrolyte did not change significantly, indicating that the drying time has little impact on the electrolyte performance within a certain time range, and the process has good stability and operability.

[0096] In Comparative Example 1, the electrolyte contains only PEO / LiFSI / LLZO, lacking the polar sites in the sulfonic acid COFs that affect Li. + The coordination effect of the lithium salt and its regulation of PEO crystallinity lead to insufficient lithium salt dissociation and restricted chain segment movement, resulting in low ionic conductivity and high intrinsic resistance. In Comparative Example 2, the electrolyte contains only PEO / LiFSI / LLZO / COF. Excess sulfonic acid COFs, as an inert filler, failed to effectively participate in the construction of the ion transport network and instead disrupted the continuous Li... + Migration channels increase interfacial impedance, thus exhibiting both lower ionic conductivity and higher intrinsic resistance.

[0097] In contrast, the bilayer composite solid electrolytes prepared in Examples 1-16 all exhibited higher lithium-ion conductivity and lower intrinsic impedance, indicating that the bilayer structure can effectively construct continuous ion transport channels and optimize interfacial compatibility, thereby significantly improving the Li-ion conductivity of the electrolyte. + Transportation capacity.

[0098] The synthesis process of composite solid electrolytes is as follows: Figure 1 As shown, the bilayer composite solid electrolyte (DLCSE) prepared using this invention was tested and characterized.

[0099] Figure 2 The image shows a cross-sectional view of the bilayer composite solid electrolyte prepared in Example 12 of this invention. It can be seen that the bilayer composite solid electrolyte mainly consists of two parts. The upper part, near the positive electrode, is a composite electrolyte layer modified with sulfonic acid COFs, i.e., a composite solid electrolyte modification layer, with a thickness of 26.9 μm. The lower part, near the negative electrode, is a composite electrolyte layer composed of PEO and LLZO, i.e., a composite solid electrolyte host layer, with a thickness of 126.7 μm. The thickness of the host layer and the modification layer can be controlled by adjusting the amount of electrolyte in the host layer and the modification layer.

[0100] from Figure 3 As can be seen in (a) of Example 1, the surface of the modified layer of the upper layer of the bilayer composite solid electrolyte has many micropores. These micropores can physically adsorb polysulfides, thereby inhibiting their shuttle movement. Figure 3 As can be seen in (b), the surface of the lower main layer also has many micropores. These micropore structures are conducive to accommodating a small amount of liquid electrolyte, thereby improving the ion transport efficiency of the composite solid electrolyte.

[0101] like Figure 4 As shown, the activation energies of the bilayer composite solid electrolyte (DLCSE) prepared in Example 1, the solid electrolytes obtained from Comparative Example 1 (COF / LLZO / PEO), and the solid electrolytes obtained from Comparative Example 2 (LLZO / PEO) are 1.66, 3.58, and 6.65 kJ / mol, respectively. -1 It can be seen that the activation energy of Example 1 is lower, indicating that the energy barrier for lithium ion migration inside the material is smaller, which facilitates lithium ion transport in the electrolyte.

[0102] like Figure 5 As shown, the electrochemical stability window of the solid electrolyte was tested using linear sweep voltammetry. The oxidation potential of the bilayer composite solid electrolyte (DLCSE) is 5.1 V, which meets the operating conditions of lithium batteries.

[0103] The bilayer composite solid electrolyte prepared in Example 1 was assembled into a lithium-symmetric battery: both sides of the electrolyte were used as electrodes with lithium sheets of 10 mm diameter, and the battery assembly was carried out in an argon-filled glove box. The limiting current density of the symmetric lithium-symmetric battery was characterized by the assembly of the solid electrolyte. Figure 6 As shown, the symmetric cell based on a dual-layer composite solid electrolyte (DLCSE) structure exhibits a surface current of 2 mA cm⁻¹. -2 1mAh cm -2 Under the test conditions, the overpotential was only 25.8mV.

[0104] The bilayer composite solid electrolyte prepared in Example 1 was assembled into a solid lithium-sulfur battery:

[0105] The bilayer composite solid electrolyte prepared in Example 1 was cut into discs with a diameter of 17 mm and transferred to a glove box filled with argon gas. The positive electrode was composed of S@C composite material, superconducting carbon black and polyvinylidene fluoride in a mass ratio of 80:10:10, and the negative electrode was a lithium metal sheet with a diameter of 14 mm.

[0106] Figure 7 Cyclic voltammetry tests were performed on the solid-state lithium-sulfur full cell assembled with the bilayer composite solid electrolyte (DLCSE) of Example 1, comparing the peak differences between the oxidation and reduction peaks. The results show that the DLCSE-based cell has a smaller peak voltage difference, indicating that its oxidation / reduction process is nearly reversible, with fast charge transfer kinetics and low polarization. In contrast, the larger voltage difference in the monolayer control group indicates significant kinetic constraints within the reaction system.

[0107] Figure 8 The cycling performance of this solid-state lithium-sulfur full cell at a 0.5C rate was demonstrated. Its initial discharge specific capacity reached 1543.1 mAh g⁻¹ at a current density of 0.5C. -1And after 280 cycles, the capacity can still be stabilized at 929.6 mAh g. -1 It exhibits high cycle stability while maintaining a high coulombic efficiency (>99%), indicating high cycle reversibility during battery charge and discharge.

Claims

1. A dual-layer composite solid electrolyte, characterized in that it comprises a stacked composite solid electrolyte host layer and a composite solid electrolyte modification layer, wherein the composite solid electrolyte host layer is formed by mixing and curing a polymer matrix, a lithium salt, and an inorganic ceramic solid electrolyte; and the composite solid electrolyte modification layer is formed by mixing a polymer matrix, a lithium salt, and an inorganic ceramic solid electrolyte, and then adding a sulfonic acid-based COFs material and curing the mixture.

2. The double-layer composite solid electrolyte according to claim 1, characterized in that, The sulfonic acid COFs are selected from one of TpBD-(SO3H)2 and TpBD-SO3H.

3. The double-layer composite solid electrolyte according to claim 1, characterized in that, The thickness of the composite solid electrolyte main layer accounts for 50%-95% of the thickness of the double-layer composite solid electrolyte; the thickness of the composite solid electrolyte modification layer accounts for 5%-50% of the thickness of the double-layer composite solid electrolyte.

4. The double-layer composite solid electrolyte according to claim 1, characterized in that, The polymer matrix is ​​selected from at least one of polyethylene oxide, polyethylene glycol, polypropylene oxide, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, and polyacrylonitrile; the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonate)imide, lithium bis(fluorosulfonyl)imide, lithium bis(oxalateborate), lithium perchlorate, and lithium hexafluorophosphate; the inorganic ceramic solid electrolyte is selected from one or more of lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, and lithium aluminum titanium phosphorus.

5. The double-layer composite solid electrolyte according to claim 1, characterized in that, The molecular weight (MW) of the polymer matrix is ​​40,000-600,000.

6. A method for preparing the bilayer composite solid electrolyte according to claim 1, comprising the following steps: (1) The polymer matrix, lithium salt and inorganic ceramic solid electrolyte are dissolved in an organic solvent to obtain a precursor solution for the main layer, which is placed in a mold and cured to obtain a composite solid electrolyte main layer. (2) The polymer matrix, lithium salt, inorganic ceramic solid electrolyte and sulfonic acid COFs material are dissolved in an organic solvent to obtain a modified layer precursor solution; (3) Place the modification layer precursor solution in the mold obtained in step (1) and let the modification layer precursor solution solidify on the surface of the composite solid electrolyte body layer to form a composite solid electrolyte modification layer, thereby obtaining a double-layer composite solid electrolyte membrane.

7. The method for preparing a bilayer composite solid electrolyte according to claim 6, characterized in that, In step (1), the concentration of the polymer matrix in the precursor solution of the main layer is 0.1-0.2 g / mL; the mass ratio of the polymer matrix to the inorganic ceramic solid electrolyte in the precursor solution of the main layer is 0.1-2:

1.

8. The method for preparing a bilayer composite solid electrolyte according to claim 6, characterized in that, In step (2), the sum of the concentrations of the polymer matrix and the sulfonic acid-based COFs material in the precursor solution of the modified layer is 0.15-0.2 g / mL.

9. The method for preparing a bilayer composite solid electrolyte according to claim 6, characterized in that, The curing process in steps (1) and (3) is as follows: the mold is placed at a temperature of 60-100℃ to dry, the solvent evaporates, and the curing is completed.

10. The application of the bilayer composite solid electrolyte of claim 1 in a lithium-sulfur battery.

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