Sandwich-structured polymer-based solid-state electrolyte, preparation method therefor and use thereof

Abstract

A sandwich-structured polymer-based solid-state electrolyte, a preparation method therefor and a use thereof. The sandwich-structured polymer-based solid-state electrolyte comprises a first solid-state electrolyte layer, a second solid-state electrolyte layer, and a third solid-state electrolyte layer located between the first solid-state electrolyte layer and the second solid-state electrolyte layer; the content of the inorganic filler in the third solid-state electrolyte layer is higher than that in the first solid-state electrolyte layer; the content of the inorganic filler in the third solid-state electrolyte layer is higher than that in the second solid-state electrolyte layer; the inorganic filler in the third solid-state electrolyte layer comprises a first inorganic filler and a second inorganic filler, and the particle size of the first inorganic filler is less than that of the second inorganic filler. The present invention helps to improve mechanical properties, effectively mitigates the problem of lithium dendrites, and contributes to improving cycle performance and addressing interfacial issues.

Description

A sandwich-structured polymer-based solid electrolyte, its preparation method and application Technical Field

[0001] This invention relates to a sandwich-structured polymer-based solid electrolyte, its preparation method, and its application, belonging to the field of solid electrolyte technology. Background Technology

[0002] Recent quality and safety issues in the new energy industry have become prominent. For example, multiple fires and explosions at energy storage power stations in South Korea have led to repeated shutdowns and restructuring of the industry. Fires at energy storage power stations in the United States have also had a significant impact on American society and industry. Liquid electrolytes contain 80% flammable organic solvents, posing serious safety hazards to batteries (such as lithium-ion batteries). Solid-state batteries, on the other hand, do not contain free electrolytes, exhibiting significant advantages and potential in safety performance, and represent an inevitable path for battery development.

[0003] The core of solid-state batteries is the solid electrolyte. Polymer solid electrolytes (SSEs) and oxide solid electrolytes (OSEs) possess advantages such as good flexibility, excellent interfacial contact, and high ionic conductivity, respectively, showing promising application prospects. However, the low conductivity of polymer SSEs and the fragility of oxide SSEs limit their applications. Combining polymer and oxide SSEs to prepare composite SSEs has become a new direction in solid-state electrolyte research. However, these composite SSEs still face challenges in thickness control, and the flexibility, mechanical properties, and conductivity of single-layer polymer / oxide composite SSEs cannot simultaneously meet requirements, further affecting the interfacial contact, cycle life, and other electrical properties of solid-state batteries.

[0004] Therefore, there is an urgent need to develop a solid electrolyte that can help improve performance such as interfacial contact and cycle life. Summary of the Invention

[0005] This invention provides a sandwich-structured polymer-based solid electrolyte, its preparation method, and its application. It has high mechanical properties, effectively improves the lithium dendrite problem, and helps to improve cycle performance and interface issues.

[0006] This invention provides a sandwich-structured polymer-based solid electrolyte, comprising a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer located between the first and second solid electrolyte layers; the content of inorganic filler in the third solid electrolyte layer is higher than the content of inorganic filler in the first solid electrolyte layer; the content of inorganic filler in the third solid electrolyte layer is higher than the content of inorganic filler in the second solid electrolyte layer; the inorganic filler in the third solid electrolyte layer includes a first inorganic filler and a second inorganic filler, wherein the particle size of the first inorganic filler is smaller than the particle size of the second inorganic filler.

[0007] Optionally, the ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler is 1:(1~1000), and the ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler is not 1.

[0008] Optionally, the particle size of the first inorganic filler is 10–500 nm, and the particle size of the second inorganic filler is 1–10 μm.

[0009] Optionally, the mass ratio of the first inorganic filler to the second inorganic filler is (1-2):(2-10).

[0010] Optionally, the first solid electrolyte layer comprises, by mass percentage, 40%–100% of a first polymer, 0%–60% of the inorganic filler, and 1%–10% of a first lithium salt; the second solid electrolyte layer comprises, by mass percentage, 40%–100% of a third polymer, 0%–60% of the inorganic filler, and 1%–10% of a third lithium salt; and the third solid electrolyte layer comprises, by mass percentage, 25%–100% of a second polymer, 0%–75% of the inorganic filler, and 1%–10% of a second lithium salt.

[0011] Optionally, the inorganic filler includes one or more of lithium aluminum titanium phosphorus oxide, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium titanium oxide, alumina, silicon oxide, hafnium oxide, and barium titanate; and / or, the first inorganic filler and the second inorganic filler each independently include one or more of alumina, silicon oxide, hafnium oxide, and barium titanate.

[0012] This invention also provides a method for preparing the sandwich-structured polymer-based solid electrolyte as described above, comprising: mixing a first polymer, an inorganic filler, a first lithium salt, and a first solvent, and then performing a first grinding to obtain a first solid electrolyte slurry; coating the first solid electrolyte slurry onto a substrate, and then performing a first drying to obtain a first solid electrolyte layer; mixing a second polymer, an inorganic filler, a second lithium salt, and a second solvent, and then performing a second grinding to obtain a second solid electrolyte slurry; coating the second solid electrolyte slurry onto a substrate, and then performing a second drying to obtain a second solid electrolyte layer; and mixing a third polymer, the first inorganic filler, the second inorganic filler, the third lithium salt, and a third solvent... The mixture is mixed to obtain a third solid electrolyte slurry; the third solid electrolyte slurry is coated onto a substrate and dried to obtain the third solid electrolyte layer; the sum of the amounts of the first inorganic filler and the second inorganic filler is higher than the amount of inorganic filler added in the first solid electrolyte layer, and the sum of the amounts of the first inorganic filler and the second inorganic filler is higher than the amount of inorganic filler added in the second solid electrolyte layer; the first solid electrolyte layer, the third solid electrolyte layer, and the second solid electrolyte layer are stacked sequentially and pressed at 80-120 MPa and 160-200 °C to obtain the sandwich structure polymer-based solid electrolyte.

[0013] Optionally, during the first grinding process, grinding is first performed at a speed of 80-120 rpm for 8-12 minutes, then at a speed of 480-520 rpm for 18-22 minutes, and finally at a speed of 780-820 rpm for 38-42 minutes; and / or, the process of coating the first solid electrolyte slurry onto the substrate and obtaining the first solid electrolyte layer after the first drying includes: after removing air bubbles from the first solid electrolyte slurry, coating 8-12 mL of the air-removed first solid electrolyte slurry onto a surface with a planar area of ​​380-420 cm². 2 On the substrate, after a first drying at 58–62°C, the first solid electrolyte layer is obtained; and / or, during the second grinding process, grinding is first performed at a speed of 80–120 rpm for 8–12 min, then at a speed of 480–520 rpm for 18–22 min, and finally at a speed of 780–820 rpm for 38–42 min; and / or, the process of coating the second solid electrolyte slurry onto the substrate and obtaining the second solid electrolyte layer after the second drying includes: after removing air bubbles from the second solid electrolyte slurry, coating 8–12 mL of the air-removed second solid electrolyte slurry onto a surface with a planar area of ​​380–420 cm². 2The process of obtaining the second solid electrolyte layer by performing a second drying at 58–62°C on the substrate; and / or, by coating the third solid electrolyte slurry onto the substrate and performing the third drying to obtain the third solid electrolyte layer, includes: removing air bubbles from the third solid electrolyte slurry, and then coating 8–12 mL of the air-removed third solid electrolyte slurry onto a surface with a planar area of ​​380–420 cm². 2 The third solid electrolyte layer is obtained by performing a second drying process on the substrate at 58–62°C.

[0014] Optionally, the first polymer, the second polymer, and the third polymer each independently include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer, and polyvinylidene fluoride-trifluoroethylene copolymer; and / or, the first lithium salt, the second lithium salt, and the third lithium salt each independently include one or more of lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate.

[0015] The present invention also provides a solid-state battery, comprising the sandwich-structured polymer-based solid electrolyte as described above or the sandwich-structured polymer-based solid electrolyte obtained by the preparation method described above.

[0016] The present invention provides a sandwich-structured polymer-based solid electrolyte, its preparation method and application, which has high mechanical properties, high density, effectively improves the lithium dendrite problem, controllable thickness, low thermal shrinkage, high ionic conductivity, effectively solves the interface problem and improves cycle performance. Attached Figure Description

[0017] Figure 1 shows the discharge energy retention rate curve of the solid-state battery in Example 1;

[0018] Figure 2 shows the discharge energy retention curve of the solid-state battery in Example 2;

[0019] Figure 3 shows the discharge energy retention rate curve of the solid-state battery in Example 3;

[0020] Figure 4 shows the discharge energy retention curve of the solid-state battery in Comparative Example 1.

[0021] Figure 5 shows the discharge energy retention curve of the solid-state battery in Comparative Example 2.

[0022] Figure 6 shows the discharge energy retention curve of the solid-state battery in Comparative Example 3.

[0023] Figure 7 is a schematic diagram of the sandwich-structured polymer-based solid electrolyte of some embodiments. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] This invention provides a sandwich-structured polymer-based solid electrolyte, comprising a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer located between the first and second solid electrolyte layers; the content of inorganic filler in the third solid electrolyte layer is higher than that in the first solid electrolyte layer; the content of inorganic filler in the third solid electrolyte layer is higher than that in the second solid electrolyte layer; the inorganic filler in the third solid electrolyte layer includes a first inorganic filler and a second inorganic filler, wherein the particle size of the first inorganic filler is smaller than that of the second inorganic filler.

[0026] According to the inventors' research and analysis: the third solid electrolyte layer of the sandwich-structured polymer-based solid electrolyte contains more inorganic fillers, that is, the middle solid electrolyte layer contains more inorganic fillers, which helps to enhance the mechanical properties of the sandwich-structured polymer-based solid electrolyte and inhibit lithium dendrites from piercing the electrolyte. The first and second solid electrolyte layers contain less inorganic fillers, that is, the two side solid electrolyte layers contain less inorganic fillers, which helps to improve the interface contact between the solid electrolyte and the positive and negative electrodes. In addition, the third solid electrolyte layer (middle layer) includes two kinds of inorganic fillers with different particle sizes (first filler and second filler). The smaller inorganic filler can fill the gaps of the larger inorganic filler, reducing the probability of lithium dendrites piercing through the gaps, and can further enhance the mechanical properties of the solid electrolyte, prevent lithium dendrites from penetrating the solid electrolyte, thereby preventing short circuits and improving cycle performance.

[0027] Therefore, the sandwich-structured polymer-based solid electrolyte provided in this embodiment of the invention has high mechanical properties, which effectively improves the lithium dendrite problem and helps to improve cycle performance and interface problems.

[0028] The ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler can be 1:(1~1000), and the ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler is not 1.

[0029] Furthermore, the particle size ratio of the first filler to the second filler can be (1-50):(100-1000), for example, 1:100, 10:200, 15:400, 20:500:40:700, 1:1000. Smaller inorganic fillers can better fill the gaps of larger inorganic fillers, reducing the probability of lithium dendrites penetrating through the gaps. They can also further enhance the mechanical properties of the solid electrolyte, prevent lithium dendrites from penetrating the solid electrolyte, thereby preventing short circuits and improving cycle performance.

[0030] In some embodiments, the particle size of the first inorganic filler is 10–500 nm, for example, 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm or any combination thereof, and the particle size of the second inorganic filler is 1–10 μm, for example, 1 μm, 5 μm, 8 μm, 10 μm or any combination thereof. The smaller particle size of the inorganic filler can better fill the gaps of the larger particle size of the inorganic filler, reduce the probability of lithium dendrites piercing through the gaps, and further enhance the mechanical properties of the solid electrolyte, prevent lithium dendrites from penetrating the solid electrolyte, thereby preventing short circuits and improving cycle performance.

[0031] The mass ratio of the first inorganic filler to the second inorganic filler can be (1-2):(2-10), for example, 1:1, 1:2, 1:5, 1:10 or any combination thereof. Smaller inorganic fillers can better fill the gaps between larger inorganic fillers, reducing the probability of lithium dendrites penetrating through the gaps. They can also further enhance the mechanical properties of the solid electrolyte, prevent lithium dendrites from penetrating the solid electrolyte, thereby preventing short circuits and improving cycle performance.

[0032] In some embodiments, the first solid electrolyte layer comprises, by mass percentage, 40% to 100% of a first polymer, 0% to 60% of an inorganic filler, and 1% to 10% of a first lithium salt.

[0033] The aforementioned first polymer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (P(VDF-TrFE-CTFE)), and polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)). In specific implementations, the same polymer as the binder in the electrode sheet (e.g., the positive electrode sheet) can be selected, which helps improve interfacial contact and increase ionic conductivity. Among them, P(VDF-TrFE-CTFE) has a high dielectric constant, providing lithium-ion percolation channels and improving ionic conductivity, while also possessing strong mechanical properties, suppressing lithium dendrite penetration, and contributing to improved cycle performance.

[0034] In the following text, the inorganic filler in the first solid electrolyte layer is referred to as the third inorganic filler. The third inorganic filler may include one or more of lithium aluminum titanium phosphorus oxide (LATP), lithium lanthanum zirconium oxide (LLZO), lithium lanthanum titanium oxide (LLTO), and lithium lanthanum zirconium titanium oxide (LLZTO).

[0035] The first lithium salt may include one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate.

[0036] Furthermore, in the first lithium salt described above, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to lithium hexafluorophosphate can be 10:(3-4), for example, 10:3, 10:3.2, 10:3.5, 10:4 or any combination thereof.

[0037] In some embodiments, the second solid electrolyte layer comprises, by mass percentage, 40% to 100% of a second polymer, 0% to 60% of an inorganic filler, and 1% to 10% of a second lithium salt.

[0038] The aforementioned second polymer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (P(VDF-TrFE-CTFE)), and polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)). In specific implementations, a polymer that bonds well with the electrode sheet (e.g., the negative electrode sheet) can be selected, which helps improve interfacial contact and increase ionic conductivity. Among them, P(VDF-TrFE-CTFE) has a high dielectric constant, providing lithium-ion percolation channels and improving ionic conductivity, while also possessing strong mechanical properties, suppressing lithium dendrite penetration, and contributing to improved cycle performance.

[0039] In the following text, the inorganic filler in the second solid electrolyte layer is referred to as the fourth inorganic filler, which may include one or more of alumina, silicon oxide, and hafnium oxide.

[0040] The second lithium salt may include one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate.

[0041] Furthermore, in the second lithium salt described above, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to lithium hexafluorophosphate can be 10:(3-4), for example, 10:3, 10:3.2, 10:3.5, 10:4 or any combination thereof.

[0042] In some embodiments, the third solid electrolyte layer comprises, by mass percentage, 25% to 100% of a third polymer, 0% to 75% of inorganic fillers (including a first inorganic filler and a second inorganic filler), and 1% to 10% of a third lithium salt.

[0043] The aforementioned third polymer may include one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (P(VDF-TrFE-CTFE)), and polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)). Among these, P(VDF-TrFE-CTFE) possesses a high dielectric constant, providing lithium-ion percolation channels and improving ionic conductivity. It also exhibits strong mechanical properties, inhibiting lithium dendrite penetration and contributing to improved cycle performance.

[0044] The first inorganic filler and the second inorganic filler each independently include one or more of alumina (Al2O3), silicon oxide, and hafnium oxide.

[0045] The third lithium salt may include one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium hexafluorophosphate.

[0046] Furthermore, in the second lithium salt described above, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to lithium hexafluorophosphate can be 10:(3-4), for example, 10:3, 10:3.2, 10:3.5, 10:4 or any combination thereof.

[0047] Figure 7 is a schematic diagram of the sandwich-structured polymer-based solid electrolyte of some embodiments.

[0048] This invention also provides a method for preparing the above-mentioned sandwich-structured polymer-based solid electrolyte, comprising: mixing a first polymer, an inorganic filler, a first lithium salt, and a first solvent, and then grinding the mixture to obtain a first solid electrolyte slurry; coating the first solid electrolyte slurry onto a substrate, and then drying it to obtain a first solid electrolyte layer; mixing a second polymer, an inorganic filler, a second lithium salt, and a second solvent, and then grinding the mixture to obtain a second solid electrolyte slurry; coating the second solid electrolyte slurry onto a substrate, and then drying it to obtain a second solid electrolyte layer; and then mixing a third polymer, a first inorganic filler, a second inorganic filler, and a second solvent to obtain a second solid electrolyte slurry. A third lithium salt and a third solvent are mixed to obtain a third solid electrolyte slurry. The third solid electrolyte slurry is coated onto a substrate and dried to obtain a third solid electrolyte layer. The sum of the amounts of the first and second inorganic fillers added is higher than the amount of inorganic filler added in the first solid electrolyte layer, and the sum of the amounts of the first and second inorganic fillers added is higher than the amount of inorganic filler added in the second solid electrolyte layer. The first solid electrolyte layer, the third solid electrolyte layer, and the second solid electrolyte layer are stacked sequentially and pressed at 80–120 MPa and 160–200 °C to obtain a sandwich-structured polymer-based solid electrolyte.

[0049] According to the inventors' research and analysis: adding more inorganic filler to the third solid electrolyte layer (middle layer) of the sandwich-structured polymer-based solid electrolyte helps enhance the mechanical properties of the sandwich-structured polymer-based solid electrolyte and inhibits lithium dendrites from piercing the electrolyte. Adding less inorganic filler to the first and second solid electrolyte layers (side layers), i.e., the side solid electrolyte layers contain less inorganic filler, helps improve the interfacial contact between the solid electrolyte and the positive and negative electrodes, and improves ionic conductivity. The third solid electrolyte layer (middle layer) includes two types of inorganic filler with different particle sizes (first filler and second filler). The smaller particle size inorganic filler can fill the gaps between the larger particle size inorganic filler, reducing the probability of lithium dendrites piercing through the gaps. Further enhancing the mechanical properties of solid electrolytes and preventing lithium dendrites from penetrating the solid electrolyte, thereby preventing short circuits and improving cycle performance (cycle life), the above preparation method obtains three electrolyte layers through coating (solution casting or casting), and then stacks and presses the three electrolyte layers (folding and hot pressing). By controlling the amount of coating and the content of polymer (organic polymer) and inorganic filler, a sandwich-structured polymer-based solid electrolyte (organic-inorganic hybrid polymer electrolyte or film) with a thickness of 5-50 μm can be obtained. This facilitates the control of the thickness of the sandwich-structured polymer-based solid electrolyte and makes it easier to further reduce the thickness of the sandwich-structured polymer-based solid electrolyte, thereby simultaneously solving the problems of difficult thickness control and interface issues of solid electrolytes.

[0050] In some embodiments, the first solvent mentioned above includes N-methylpyrrolidone and / or dimethylformamide (DMF) and dimethylacetamide (DMAc).

[0051] In some embodiments, during the first grinding process described above, grinding can first be performed at a speed of 80-120 rpm, for example, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, or any combination thereof, for 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, or any combination thereof. Then, grinding can be performed at a speed of 480-520 rpm, for example, 480 rpm, 490 rpm, 500 rpm, 510 rpm, 520 rpm, or any combination thereof, for 18-22 minutes, for example, 18 minutes, 19 minutes, 20 minutes, 21 minutes. The grinding process involves grinding at a speed of 780–820 rpm (e.g., 780 rpm, 790 rpm, 800 rpm, 810 rpm, 820 rpm, or any combination thereof) for 38–42 minutes (e.g., 38 minutes, 39 minutes, 40 minutes, 41 minutes, 42 minutes, or any combination thereof). Grinding at a lower speed first helps disperse the material, and then grinding at a higher speed further refines the material, resulting in a viscous first solid electrolyte slurry. This process helps improve the mechanical properties of the sandwich-structured polymer-based solid electrolyte, as well as improve interface problems and cycle performance.

[0052] In practice, the weighed first polymer, inorganic filler (referred to as the third inorganic filler), and first lithium salt can be added to the ball mill jar first, and then a certain volume of the first solvent can be added to the ball mill jar for the first grinding process to obtain the first solid electrolyte slurry.

[0053] The energy density of most solid-state electrolytes is lower than expected, mainly due to their excessive thickness and weight. Current methods for preparing polymer electrolytes primarily involve casting and coating. However, these methods struggle to precisely control the thickness of the polymer electrolyte (film). Some polymer electrolytes are too thin, resulting in poor mechanical properties, leading to lithium dendrite penetration and affecting battery cycle life. Conversely, excessively thick polymer electrolyte (films) increase the lithium-ion shuttle path, significantly reducing ionic conductivity and preventing battery cycling at room temperature, while also increasing battery weight and cost.

[0054] In some embodiments, the process of coating a first solid electrolyte slurry onto a substrate and obtaining a first solid electrolyte layer after a first drying includes: removing air bubbles from the first solid electrolyte slurry, and then coating 8-12 mL of the bubble-removed first solid electrolyte slurry onto a surface with a planar area of ​​380-420 cm². 2 On a substrate, after a first drying process at 58–62°C, a first solid electrolyte layer is obtained. Exemplarily, the volume of the first solid electrolyte slurry after degassing can be 8 mL, 9 mL, 10 mL, 11 mL, 12 mL, or any combination thereof, and the planar area of ​​the substrate can be 380 cm². 2 390cm 2 400cm 2 410cm 2 420cm 2 The initial drying temperature can be 58°C, 60°C, 62°C, or any combination thereof. Adjusting the amount of coating applied allows for flexible control of the thickness of the first solid electrolyte layer, thereby controlling the sandwich-structured polymer-based solid electrolyte.

[0055] In practice, a vacuum filter can be used to filter the first solid electrolyte slurry at least twice, with each filtration time being 20±5 minutes, to remove air bubbles from the first solid electrolyte slurry. Then, a certain volume of the first solid electrolyte slurry after removing air bubbles can be measured using a graduated cylinder (or drawn up using a dropper), poured onto the substrate, and after the first solid electrolyte slurry automatically spreads to the entire substrate, it can be placed in a vacuum oven for the first drying to obtain the first solid electrolyte layer.

[0056] In some embodiments, the second solvent includes N-methylpyrrolidone and / or dimethylformamide, dimethylacetamide (DMAc).

[0057] In some embodiments, during the second grinding process described above, grinding can first be performed at a speed of 80-120 rpm, for example, 80 rpm, 90 rpm, 100 rpm, 110 rpm, 120 rpm, or any combination thereof, for 8-12 minutes, for example, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, or any combination thereof. Then, grinding can be performed at a speed of 480-520 rpm, for example, 480 rpm, 490 rpm, 500 rpm, 510 rpm, 520 rpm, or any combination thereof, for 18-22 minutes, for example, 18 minutes, 19 minutes, 20 minutes, 21 minutes. The grinding process involves grinding at a speed of 780–820 rpm (e.g., 780 rpm, 790 rpm, 800 rpm, 810 rpm, 820 rpm, or any combination thereof) for 38–42 minutes (e.g., 38 minutes, 39 minutes, 40 minutes, 41 minutes, 42 minutes, or any combination thereof). Grinding at a lower speed first helps disperse the material, and then grinding at a higher speed further refines the material, resulting in a viscous second solid electrolyte slurry. This process helps improve the mechanical properties of the sandwich-structured polymer-based solid electrolyte, as well as improve interface problems and cycle performance.

[0058] In practice, the weighed second polymer, inorganic filler (fourth inorganic filler), and second lithium salt can be added to the ball mill jar first, and then a certain volume of the second solvent can be added to the ball mill jar for the second grinding process to obtain the second solid electrolyte slurry.

[0059] In some embodiments, the process of coating the second solid electrolyte slurry onto a substrate and obtaining the first solid electrolyte layer after a first drying includes: removing air bubbles from the second solid electrolyte slurry, and then coating 8-12 mL of the bubble-removed second solid electrolyte slurry onto a surface with a planar area of ​​380-420 cm². 2 On the substrate, after a second drying process at 58–62°C, a second solid electrolyte layer is obtained. Exemplarily, the volume of the second solid electrolyte slurry after degassing can be 8 mL, 9 mL, 10 mL, 11 mL, 12 mL, or any combination thereof, and the planar area of ​​the substrate can be 380 cm². 2 390cm 2 400cm 2 410cm 2 420cm 2 The second drying temperature can be 58°C, 60°C, 62°C, or any combination thereof. Adjusting the amount of coating allows for flexible control of the thickness of the second solid electrolyte layer, thereby controlling the sandwich-structured polymer-based solid electrolyte.

[0060] In practice, a vacuum filter can be used to filter the second solid electrolyte slurry at least twice, with each filtration time being 20±5 minutes, to remove air bubbles from the second solid electrolyte slurry. Then, a certain volume of the second solid electrolyte slurry after removing air bubbles can be measured using a graduated cylinder and poured onto the substrate. After the second solid electrolyte slurry automatically spreads to the entire substrate, it is placed in a vacuum oven for a second drying process to obtain the second solid electrolyte layer.

[0061] In some embodiments, the third solvent includes N-methylpyrrolidone and / or dimethylformamide, dimethylacetamide (DMAc).

[0062] In the process of mixing the third polymer, the first inorganic filler, the second inorganic filler, the third lithium salt, and the third solvent to obtain the third solid electrolyte slurry, the mixture can be stirred to make it uniform. For example, the mixture can be placed in a glass bottle and stirred with a constant temperature magnetic stirrer to obtain a viscous third solid electrolyte slurry. The stirring temperature can be 48 to 52°C, for example, 48°C, 50°C, 52°C, or any combination thereof.

[0063] In some embodiments, the process of coating the above-mentioned third solid electrolyte slurry onto a substrate and obtaining a third solid electrolyte layer after a third drying includes: removing air bubbles from the third solid electrolyte slurry, and then coating 8-12 mL of the bubble-removed third solid electrolyte slurry onto a surface with a planar area of ​​380-420 cm². 2 On the substrate, after a second drying at 58–62°C, a third solid electrolyte layer is obtained. Exemplarily, the volume of the third solid electrolyte slurry after degassing can be 8 mL, 9 mL, 10 mL, 11 mL, 12 mL, or any combination thereof, and the planar area of ​​the substrate can be 380 cm². 2 390cm 2 400cm 2 410cm 2 420cm 2 The third drying temperature can be 58℃, 60℃, 62℃, or any combination thereof. Adjusting the amount of coating allows for flexible control of the thickness of the third solid electrolyte layer, thereby controlling the sandwich-structured polymer-based solid electrolyte.

[0064] In practice, a vacuum filter can be used to filter the third solid electrolyte slurry at least twice, with each filtration time being 20±5 minutes, to remove air bubbles from the third solid electrolyte slurry. Then, a certain volume of the third solid electrolyte slurry after removing air bubbles can be measured using a graduated cylinder and poured onto the substrate. After the third solid electrolyte slurry automatically spreads to the entire substrate, it is placed in a vacuum oven for third drying to obtain the third solid electrolyte layer.

[0065] In some embodiments, the substrate includes a glass plate, such as an ultra-flat glass plate with a length and width of 20±1cm.

[0066] For example, the pressure of the pressing process can be within the range of 80 MPa, 90 MPa, 100 MPa, 110 MPa, 120 MPa, or any combination thereof, and the temperature of the pressing process can be within the range of 160°C, 170°C, 180°C, 190°C, 200°C, or any combination thereof. This facilitates flexible control of the thickness of the sandwich-structured polymer-based solid electrolyte.

[0067] In practice, the first solid electrolyte layer, the third solid electrolyte layer, and the second solid electrolyte layer can be stacked in a special mold in sequence and pressed at 80-120 MPa and 160-200°C for 40-50 minutes, such as 40 minutes, 45 minutes, 50 minutes, or any combination thereof. After cooling, a sandwich-structured polymer-based solid electrolyte is obtained.

[0068] The aforementioned special mold can be made of manganese steel, which has the characteristic of small deformation. The special mold can be divided into three parts: a square base, a square frame, and a square cover. The square cover has a groove, and the height of the groove can be 15 to 50 μm.

[0069] This invention also provides a solid-state battery, comprising the sandwich-structured polymer-based solid electrolyte described above or the sandwich-structured polymer-based solid electrolyte prepared according to the above preparation method.

[0070] In specific implementation, the aforementioned solid-state battery can be a semi-solid-state battery, a quasi-solid-state battery, or an all-solid-state battery, such as a semi-solid-state lithium-ion battery, a semi-solid-state sodium-ion battery, a quasi-solid-state lithium-ion battery, a quasi-solid-state sodium-ion battery, an all-solid-state lithium-ion battery, or an all-solid-state sodium-ion battery.

[0071] It is conceivable that, in addition to the aforementioned sandwich-structured polymer-based solid electrolyte, the solid-state battery of this invention also includes a negative electrode and a positive electrode.

[0072] The embodiments of the present invention are not strictly limited to the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, silver-carbon mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0073] The embodiments of this invention are not strictly limited to the negative electrode active material in the positive electrode sheet. It can be any positive electrode active material commonly used in lithium-ion batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium manganese oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium iron phosphate (LFP), lithium nickel manganese oxide, lithium-rich manganese-based materials, etc.

[0074] In the preparation of solid-state batteries, the positive electrode, the sandwich-structured polymer-based solid electrolyte, and the negative electrode are stacked, pressed, and packaged in an aluminum soft pack. Alternatively, a gel electrolyte can be added for in-situ curing to complete the preparation of the solid-state battery.

[0075] The present invention will now be described in more detail through specific embodiments.

[0076] The sources of some of the raw materials in the examples are as follows:

[0077] Polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (P(VDF-TrFE-CTFE)), polyvinylidene fluoride-trifluoroethylene copolymer (P(VDF-TrFE)): purchased from Aucma.

[0078] Example 1

[0079] This embodiment provides a method for preparing a sandwich-structured polymer-based solid electrolyte, including:

[0080] 2.5 g P (VDF-TrFE-CTFE), 2.5 g LATP, and 0.25 g LiTFSI were added to a ball mill jar. 50 mL of LDMF was added to the ball mill jar and mixed. The mixture was then ball milled at 100 rpm, 500 rpm, and 800 rpm for 10 min, 20 min, and 40 min, respectively, to obtain the first solid electrolyte slurry. The first solid electrolyte slurry was filtered twice using a vacuum filter for 20 min each time to remove air bubbles. 10 mL of the first solid electrolyte slurry after removing air bubbles was measured with a graduated cylinder and coated onto a 20 cm x 20 cm ultra-flat glass plate. The solution was allowed to spread automatically across the entire ultra-flat glass plate, and then the plate was placed in a vacuum oven and dried at 60 °C to obtain the first solid electrolyte layer.

[0081] 2.5 g P (VDF-TrFE-CTFE), 2.5 g Al2O3, and 0.25 g LiTFSI were added to a ball mill jar. 50 mL of LDM was added to the ball mill jar using a pipette and mixed. The mixture was then ball milled at 100 rpm, 500 rpm, and 800 rpm for 10 min, 20 min, and 40 min, respectively, to obtain a second solid electrolyte slurry. The second solid electrolyte slurry was filtered twice using a vacuum filter for 20 min each time to remove air bubbles. 10 mL of the second solid electrolyte slurry after removing air bubbles was measured with a graduated cylinder and coated onto a 20 cm x 20 cm ultra-flat glass plate. The solution was allowed to spread automatically across the entire ultra-flat glass plate before being placed in a vacuum oven and dried at 60 °C to obtain the second solid electrolyte layer.

[0082] 2.5g P(VDF-TrFE-CTFE), 2.5g Al2O3 with a particle size of 300nm, 2.5g Al2O3 with a particle size of 5000nm, and 0.25g LiTFSI were added to a glass bottle. 50mL of LDM was added to the glass bottle using a pipette and mixed. The mixture was then magnetically stirred at 50℃ to obtain a third solid electrolyte slurry. The third solid electrolyte slurry was filtered twice using a vacuum filter, with each filtration time being 20min, to remove air bubbles from the second solid electrolyte slurry. 10mL of the second solid electrolyte slurry after removing air bubbles was measured using a graduated cylinder and coated onto a 20cm x 20cm ultra-flat glass plate. The solution was allowed to spread automatically across the entire ultra-flat glass plate before being placed in a vacuum oven and dried at 60℃ to obtain the third solid electrolyte layer.

[0083] After stacking the first solid electrolyte layer, the third solid electrolyte layer, and the second solid electrolyte layer in sequence, the mixture was pressed at 100 MPa and 180 °C for 45 min to obtain a sandwich-structured polymer-based solid electrolyte (P(VDF-TrFE-CTFE) / LATP / LiTFSI composite solid electrolyte membrane).

[0084] Following the procedure in Example 1, the sandwich-structured polymer-based solid electrolytes of Examples 2-3 and Comparative Examples 1-3 were prepared. Comparative Example 4 used a commercially available separator purchased from Shenzhen Xingyuan Material Technology Co., Ltd.

[0085] Table 1 summarizes the parameters such as the types of components and the mass percentage (content) of each component in each layer of the solid electrolyte layer in each embodiment and comparative example.

[0086] Table 1

[0087] Experimental Example 1

[0088] 1. The following parameters of the above embodiments and comparative examples were tested:

[0089] 1) Thickness of sandwich-structured polymer-based solid electrolyte and the first solid electrolyte layer, the second solid electrolyte layer and the third solid electrolyte layer: The thickness was measured using a film thickness gauge. The film thickness gauge was used to clamp the sandwich-structured polymer-based solid electrolyte or the separated first solid electrolyte layer, the second solid electrolyte layer and the third solid electrolyte layer, and the thickness was measured. The specific results are shown in Table 2 and Table 3.

[0090] 2) Needle penetration strength of sandwich-structured polymer-based solid electrolyte and the first, second, and third solid electrolyte layers: First, cut a 100mm diameter sample (including the sandwich-structured polymer-based solid electrolyte, the separated first, second, or third solid electrolyte layers). The sample should have uniform thickness and be free of wrinkles, creases, stains, and other obvious defects. Then, select the 90° peel strength test item, with a value of (50±5) mm·min. -1 The puncture force value is obtained by piercing at a certain speed; each group of samples includes 5 test pieces, and the arithmetic mean of these 5 test pieces is used to obtain the final test result of the needle puncture strength. The specific results are shown in Table 2 and Table 3.

[0091] 3) Thermal shrinkage rate of sandwich-structured polymer-based solid electrolyte (solid electrolyte): A 10cm × 10cm square solid electrolyte sample was cut and sandwiched between two transparent and clean glass plates. The glass plates were then placed in a preheated drying oven at a set temperature and baked for 1 hour. After baking, the glass plates were allowed to cool to room temperature, and the morphological changes of the square solid electrolyte sample were observed and measured. The test temperature (the set temperature of the drying oven) was 120℃, and the baking time was 1 hour. The formula for calculating the thermal shrinkage rate S is: S / % = (S0 - S1) / S0 × 100%, where S is the thermal shrinkage rate; S0 is the area of ​​the square solid electrolyte sample cut before heat treatment (baking), and S1 is the area of ​​the square solid electrolyte sample after heat treatment (baking), in mm. 2 The specific results are shown in Table 3.

[0092] 4) Ionic conductivity of sandwich-structured polymer-based solid electrolyte and the first, second, and third solid electrolyte layers: Ionic conductivity is obtained by measuring the impedance using electrochemical impedance spectroscopy (EIS) and then calculating it using a formula. The specific testing method is as follows: Assemble the SS (circular stainless steel sheet) / polymer electrolyte / SS blocking battery in a glove box. The test temperature is 25℃, and it needs to be kept at a constant temperature for more than 2 hours before testing. The test frequency is 1MHz-0.1Hz, and the amplitude voltage is 3mV. Use Autolab... The test was conducted using the Shiwanhua electrochemical workstation. The measured graph was a semicircle and a straight line with a slope of approximately 45°. The real impedance at the intersection of the semicircle and the straight line is the bulk resistance Rb of the electrolyte membrane. The ionic conductivity can be calculated using the following formula: σ = L / (Rb*S), where: σ is the ionic conductivity of the test sample (e.g., a sandwich-structured polymer-based solid electrolyte membrane), in units of S / cm; L is the thickness of the test sample, in units of cm; Rb is the bulk resistance of the test sample, in units of Ω; and S is the area of ​​the test sample, in units of cm². 2 The specific results are shown in Tables 2 and 3.

[0093] 5) Porosity of sandwich-structured polymer-based solid electrolyte and the first, second, and third solid electrolyte layers: The porosity was tested using a surface area analyzer (UK, CANTA, Nova 1200e model) with nitrogen gas. The specific results are shown in Tables 2 and 3.

[0094] 2. Test Results

[0095] Table 2 Thickness, needle penetration strength, ionic conductivity, and porosity of the first, second, and third solid electrolyte layers.

[0096] Table 3 Thickness, ionic conductivity, density, and thermal shrinkage of sandwich-structured polymer-based solid electrolytes

[0097] Data Analysis:

[0098] Analysis of Tables 2 and 3 shows that the sandwich-structured polymer-based solid electrolyte of the present invention has high needle penetration strength and low thermal shrinkage rate.

[0099] Experimental Example 2

[0100] All sandwich-structured polymer-based solid electrolytes, positive and negative electrode sheets from the embodiments and comparative examples were stacked, pressed, and packaged in an aluminum pouch. After adding gel-state additives and solidifying in situ, a solid-state battery was formed. The gel-state additives were purchased from Sinopharm Group. The assembly of the battery cells included stacking, packaging, electrolyte injection, and formation steps, ultimately forming a complete pouch battery.

[0101] The preparation processes for the positive and negative electrodes are as follows:

[0102] Positive electrode preparation: Lithium iron phosphate positive electrode material is mixed evenly with conductive agent carbon black and binder polyvinylidene fluoride to form a slurry with good conductivity and adhesion; the prepared slurry is coated onto aluminum foil current collector, usually using a coating machine; the coated aluminum foil is dried to remove solvent and solidify the solid components in the slurry to obtain a dried positive electrode sheet; the dried positive electrode sheet is compacted by a rolling process to improve the volumetric energy density of the battery, thus obtaining the positive electrode sheet;

[0103] Negative electrode preparation: Graphite negative electrode material is mixed evenly with conductive agent carbon black and binder polyvinylidene fluoride to form a negative electrode slurry; the negative electrode slurry is coated on copper foil current collector, and after drying and rolling, a negative electrode sheet is obtained.

[0104] The cycle performance of the above solid-state batteries was tested:

[0105] The capacity retention of each solid-state battery was tested. The specific test method was as follows: the battery was placed at 45℃ for 5 hours, charged to 3.65V with a constant power of 1P, allowed to stand for 15 minutes, then discharged to 2.50V with a constant power of 1P, allowed to stand for 15 minutes, and this charge-discharge cycle was repeated 500 times. The discharge energy Q1 at the first cycle and the discharge energy Q at the 500th cycle were measured. 500 The discharge energy retention rate Q after 500 cycles is calculated using the following formula: Q = Q_0 500 / Q1*100%.

[0106] Cycle life: Battery cycle life is assessed using the capacity decay rate method. The number of charge-discharge cycles that occur when the battery's capacity drops to 80% or below its rated capacity under normal use conditions is the cycle life. In addition, the battery's degradation rate and remaining life are evaluated by calculating the capacity loss rate in each charge-discharge cycle and plotting the capacity decay curve.

[0107] Table 4. Battery cycle performance

[0108] As can be seen from Figures 1-6 and Table 4, the sandwich-structured polymer-based solid electrolyte provided in the embodiments of the present invention has good cycle stability.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A sandwich-structured polymer-based solid-state electrolyte, characterized by, It includes a first solid electrolyte layer, a second solid electrolyte layer, and a third solid electrolyte layer located between the first solid electrolyte layer and the second solid electrolyte layer; The content of inorganic filler in the third solid electrolyte layer is higher than the content of inorganic filler in the first solid electrolyte layer; The content of inorganic filler in the third solid electrolyte layer is higher than the content of inorganic filler in the second solid electrolyte layer; The inorganic filler in the third solid electrolyte layer includes a first inorganic filler and a second inorganic filler, wherein the particle size of the first inorganic filler is smaller than that of the second inorganic filler.

2. The sandwich-structured polymer-based solid-state electrolyte according to claim 1, wherein The ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler is 1:(1~1000), and the ratio of the particle size of the first inorganic filler to the particle size of the second inorganic filler is not 1.

3. The sandwich-structured polymer-based solid-state electrolyte according to claim 2, wherein The particle size of the first inorganic filler is 10–500 nm, and the particle size of the second inorganic filler is 1–10 μm.

4. The sandwich-structured polymer-based solid-state electrolyte according to claim 3, wherein The mass ratio of the first inorganic packing to the second inorganic packing is (1-2):(2-10).

5. The sandwich-structured polymer-based solid electrolyte according to claim 1, characterized in that, The first solid electrolyte layer comprises, by mass percentage, 40% to 100% of the first polymer, 0% to 60% of the inorganic filler, and 1% to 10% of the first lithium salt; The second solid electrolyte layer comprises, by mass percentage, 40%–100% of the third polymer, 0%–60% of the inorganic filler, and 1%–10% of the third lithium salt; The third solid electrolyte layer comprises, by mass percentage, 25-100% of the second polymer, 0%-75% of the inorganic filler, and 1%-10% of the second lithium salt.

6. The sandwich-structured polymer-based solid electrolyte according to claim 1, characterized in that, The inorganic filler includes one or more of the following: lithium aluminum titanium phosphorus oxide, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum zirconium titanium oxide, aluminum oxide, silicon oxide, hafnium oxide, and barium titanate; And / or, the first inorganic filler and the second inorganic filler each independently comprise one or more of alumina, silicon oxide, hafnium oxide, and barium titanate.

7. A method of producing the sandwich-structured polymer-based solid-state electrolyte according to any one of claims 1 to 6, characterized by, include: A first polymer, an inorganic filler, a first lithium salt, and a first solvent are mixed and then subjected to a first grinding process to obtain a first solid electrolyte slurry. The first solid electrolyte slurry is coated onto the substrate and dried first to obtain the first solid electrolyte layer. A second polymer, an inorganic filler, a second lithium salt, and a second solvent are mixed and then ground in a second process to obtain a second solid electrolyte slurry. The second solid electrolyte slurry is then coated onto a substrate and dried in a second process to obtain a second solid electrolyte layer. A third polymer, a first inorganic filler, a second inorganic filler, a third lithium salt, and a third solvent are mixed to obtain a third solid electrolyte slurry; the third solid electrolyte slurry is coated onto a substrate and dried to obtain a third solid electrolyte layer; the sum of the amounts of the first inorganic filler and the second inorganic filler added is higher than the amount of inorganic filler added in the first solid electrolyte layer, and the sum of the amounts of the first inorganic filler and the second inorganic filler added is higher than the amount of inorganic filler added in the second solid electrolyte layer; The first solid electrolyte layer, the third solid electrolyte layer, and the second solid electrolyte layer are stacked sequentially and then pressed at 80-120 MPa and 160-200°C to obtain the sandwich-structured polymer-based solid electrolyte.

8. The preparation method according to claim 7, characterized in that, During the first grinding process, the grinding is first carried out at a speed of 80-120 rpm for 8-12 minutes, then at a speed of 480-520 rpm for 18-22 minutes, and finally at a speed of 780-820 rpm for 38-42 minutes. And / or, the process of coating the first solid electrolyte slurry onto the substrate and obtaining the first solid electrolyte layer after the first drying includes: removing air bubbles from the first solid electrolyte slurry, and then coating 8-12 mL of the bubble-removed first solid electrolyte slurry onto a surface with a planar area of ​​380-420 cm². 2 On the substrate, after a first drying process at 58–62°C, the first solid electrolyte layer is obtained; And / or, during the second grinding process, first grind at a speed of 80-120 rpm for 8-12 minutes, then grind at a speed of 480-520 rpm for 18-22 minutes, and finally grind at a speed of 780-820 rpm for 38-42 minutes; and / or, the process of coating the second solid-state electrolyte slurry on the substrate, after the second drying, to obtain the second solid-state electrolyte layer comprises: coating 8-12 mL of the second solid-state electrolyte slurry after removing bubbles on the substrate with a planar area of 380-420 cm 2 after removing bubbles at 58-62°C for the second drying to obtain the second solid-state electrolyte layer; and / or, the process of coating the third solid-state electrolyte slurry on the substrate, after the third drying, to obtain the third solid-state electrolyte layer comprises: coating 8-12 mL of the third solid-state electrolyte slurry after removing bubbles on the substrate with a planar area of 380-420 cm 2 after the second drying at 58-62°C to obtain the third solid-state electrolyte layer.

9. The preparation method according to claim 7, characterized in that, The first polymer, the second polymer, and the third polymer each independently include one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer, and polyvinylidene fluoride-trifluoroethylene copolymer; And / or, the first lithium salt, the second lithium salt, and the third lithium salt each independently comprise one or more of lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate.

10. A solid state battery, characterized by, Includes the sandwich-structured polymer-based solid electrolyte according to any one of claims 1-6 or the sandwich-structured polymer-based solid electrolyte obtained according to the preparation method according to any one of claims 7-9.

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