TW202002365A - Cathodes for solid-state lithium sulfur batteries and methods of manufacturing thereof - Google Patents

Abstract

A cathode for a lithium-sulfur battery includes a sulfur-based composite layer having a porosity in a range of 60% to 99%; and a conductive polymer disposed atop the composite layer and within pores of the composite layer. Moreover, a method of forming a cathode for a lithium- sulfur battery includes providing a substrate; disposing a sulfur-based slurry layer on the substrate; freeze-drying the slurry layer to form a sulfur-based composite layer having a porosity in a range of 60% to 99%; and disposing a conductive polymer atop the composite layer and within pores of the composite layer.

Description

Cathode for solid-state lithium-sulfur battery and its manufacturing method

Cross-reference of related applications: This application requests priority from US Patent Provisional Application No. 62/689,546 filed on June 25, 2018 and Chinese Patent Application No. 201811325286.5 filed on November 8, 2018, according to the Patent Law Rights, the entire content of the patent application is incorporated herein by reference.

This disclosure relates to cathodes for solid-state lithium-sulfur (Li-S) batteries and methods of manufacturing the same.

Because lithium-sulfur (Li-S) batteries are cheaper, lighter, and can store almost twice as much energy at the same quality, they are promising candidates for replacing traditional lithium-ion batteries. For example, lithium-sulfur (Li-S) battery chemistry has high energy density (for example, 2600W•h•kg ^-1 ) and theoretical specific capacity (for example, 1675 mA•h•g ^-1 ), is naturally rich and environmentally friendly .

One challenge of the conventional lithium-sulfur technology is the electronic and ionic insulating properties of elemental sulfur (used as a composition in the cathode). This property requires a large portion of conductive additives in the cathode, thus significantly reducing the actual capacity and applicability. Another disadvantage is the soluble nature of long-chain polysulfides produced during battery discharge in conventional organic electrolytes. As the polysulfide transitions from the cathode to the lithium (Li) anode, the shuttle of the polysulfide causes a reduction in Coulomb efficiency and continuous loss of active cathode materials, which can induce unwanted side reactions.

This application discloses an improved cathode for solid-state lithium-sulfur (Li-S) battery applications and a method of forming the same.

In some embodiments, a cathode for a lithium-sulfur (Li-S) battery includes: having a sulfur-based composite layer in the range of 60% to 99%; and disposed on top of the composite layer and within the pores of the composite layer Conductive polymer.

In one aspect, which can be combined with any other aspect or embodiment, the composite layer has a porosity in the range of 60% to 80%.

In one aspect, it can be combined with any other aspect or embodiment, and the pores of the composite layer have a size in the range of 1 μm to 50 μm.

In one aspect, it can be combined with any other aspect or embodiment, and the pore size is in the range of 2µm to 10µm.

In one aspect, it can be combined with any other aspect or embodiment, the composite layer includes nanoparticles, nanowires, nanofibers, nanorods, nanotubes, nanospheres, graphene, or Carbon materials that exist in at least one way in combination.

In one aspect, it can be combined with any other aspect or embodiment, and the content of the carbon material is in the range of 5 weight percent to 40 weight percent (wt.%).

In one aspect, which can be combined with any other aspect or embodiment, the composite layer includes metal carbide in a content ranging from 1 weight percent to 20 weight percent.

In one aspect, it can be combined with any other aspect or embodiment, the conductive polymer includes carbon polysulfide (CS), polyethylene oxide (PEO), polyaniline (PANI), polypyrrole (PPY), Poly(3,4-ethylenedioxythiophene) (PEDOT), polystyrene sulfonic acid (PSS), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), poly (Vinylidene fluoride-co-hexafluoropropylene) (P(VdF-co-HFP)), poly(methyl methacrylate) (PMMA), polyvinylidene fluoride (PVDF), poly(diallyl di Methyl)ammonium (bis(trifluoromethanesulfonyl)) amide imide (TFSI) (PDDATFSI) or at least one of its combination, and bis(trifluoromethane) sulfonimide lithium salt (LiTFSI), high chloride At least one of lithium oxide, lithium bis(oxalate) lithium borate (LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), or a combination thereof.

In some embodiments, a lithium sulfur (Li-S) battery includes: a lithium anode; a solid electrolyte; and a cathode disclosed herein.

In one aspect, which can be combined with any other aspect or embodiment, a lithium-sulfur (Li-S) battery is configured to have a discharge capacity retention rate of at least 90%.

In one aspect, it can be combined with any other aspect or embodiment. The solid electrolyte includes at least one of the following: Li6.4La3Zr1.4Ta0.6O12 (LLZTO), Li10GeP2S12, Li1.5Al0.5Ge1.5(PO4)3 , Li1.4Al0.4Ti1.6(PO4)3, Li0.55La0.35TiO3, interpenetrating polymer network of poly(ethyl acrylate) (ipn-PEA) electrolyte, three-dimensional ceramic/polymer network, in-situ plasticization polymerization Materials, composite polymers with well-arranged ceramic nanowires, solid polymers based on PEO, flexible polymers, polymeric ionic liquids, Li ₃ PS ₄ formed in situ, or a combination thereof.

In some embodiments, a method of forming a cathode for a lithium-sulfur (Li-S) battery includes: providing a substrate; providing a sulfur-based composite layer on the substrate; freeze-drying the composite layer to form a substrate having a range of 60% to 99% A sulfur-based composite layer with a porosity within the range; and a conductive polymer is provided on the top of the composite layer and in the pores of the composite layer.

In one aspect, it can be combined with any other aspect or embodiment, and the substrate is a current collector.

In one aspect, it can be combined with any other aspect or embodiment, the method further includes: mixing a metal carbide, a carbon material, and a sulfur material in a solvent to form a sulfur precursor; and drying and grinding the dried sulfur precursor To form sulfur complexes.

In one aspect, which can be combined with any other aspect or embodiment, the method further includes: stirring the sulfur composite with a binder to form a sulfur-based slurry.

In one aspect, it can be combined with any other aspect or embodiment, and the carbon material is at least one of the following: nanoparticles, nanowires, nanofibers, nanorods, nanotubes, nanospheres, graphite Olefin, or a combination thereof, and the binder includes at least one of styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid (PAA), sodium alginate, or a combination thereof.

In one aspect, which can be combined with any other aspect or embodiment, the composite layer has a porosity in the range of 60% to 80%.

In one aspect, it can be combined with any other aspect or embodiment, and the pores of the composite layer have a size in the range of 1 μm to 50 μm.

In one aspect, it can be combined with any other aspect or embodiment, and the pore size is in the range of 2µm to 10µm.

In one aspect, it can be combined with any other aspect or embodiment. The step of freeze drying includes: freezing the slurry layer at -50°C and 0°C for 1 hour to 12 hours; and in a freeze dryer The frozen slurry layer is dried for 1 hour to 24 hours.

In one aspect, it can be combined with any other aspect or embodiment by at least one of spin coating, dip coating, layer-by-layer deposition, sol-gel deposition, inkjet printing, or a combination thereof Conductive polymer steps.

In some embodiments, a method of forming a lithium-sulfur (Li-S) battery includes: providing a substrate; providing a cathode formed by arranging a sulfur-based composite layer on the substrate; freeze-drying the composite layer to form a battery having a temperature of 60% A sulfur-based composite layer with a porosity in the range of up to 99%; placing a conductive polymer on top of the composite layer and in the pores of the composite layer; providing a solid electrolyte; and providing a lithium anode.

In one aspect, it can be combined with any other aspect or embodiment. The solid electrolyte includes at least one of the following: Li6.4La3Zr1.4Ta0.6O12 (LLZTO), Li10GeP2S12, Li1.5Al0.5Ge1.5(PO4)3, Interpenetrating polymer network of Li1.4Al0.4Ti1.6(PO4)3, Li0.55La0.35TiO3, poly(ethyl acrylate) (ipn-PEA) electrolyte, three-dimensional ceramic/polymer network, in-situ plasticized polymer , Composite polymers with well-arranged ceramic nanowires, solid polymers based on PEO, flexible polymers, polymeric ionic liquids, Li ₃ PS ₄ formed in situ, or a combination thereof.

Reference will now be made in detail to example embodiments, which are illustrated in the accompanying drawings. Wherever possible, the same element symbols will be used in the drawings to indicate the same or similar parts. The components in the drawings are not necessarily drawn to scale, but focus on the principle of the illustrated example embodiments. It should be understood that the present application is not limited to the details or methods described in the specification or shown in the drawings. It should also be understood that the terminology is for descriptive purposes only and should not be regarded as limiting.

Additionally, any examples described in this specification are illustrative, not limiting, and only describe some of the many possible embodiments of the claimed invention. Other suitable improvements and adjustments to various conditions and parameters generally faced in the art, and which are obvious to those skilled in the art, are within the spirit and scope of the present disclosure.

This disclosure relates to solid-state lithium-sulfur (Li-S) batteries, and more specifically, to sulfur cathodes and methods of making the same, in which a lithium-ion conductive polymer layer (eg, polyethylene oxide (PEO)) is coated The porous sulfur cathode system is used for solid lithium-sulfur (Li-S) batteries.

FIG. 1 illustrates an example of a solid-state lithium-sulfur (Li-S) battery structure according to some embodiments. Those skilled in the art will understand that the method described herein can be applied to other configurations of solid-state lithium-sulfur (Li-S) battery structures.

In some embodiments, the battery 100 may include a substrate 102 (eg, current collector), a sulfur electrode (eg, cathode) 104 disposed on the substrate, a first intermediate layer 106 disposed above the cathode, and a first intermediate A solid electrolyte 108 above the layer, a second intermediate layer 110 disposed above the electrolyte, and a lithium electrode (eg, anode) 112 disposed above the second intermediate layer. They can be placed horizontally or vertically relative to each other.

In some examples, the substrate 102 may be a current collector including at least one of three-dimensional nickel (Ni) foam, carbon fiber, foil (eg, aluminum, stainless steel, copper, platinum, nickel, etc.), or a combination thereof. In some examples, the intermediate layers 106 and 110 may be independently selected from carbon-based (eg, interconnected independent, containing micro/mesoporous pores, functionalized, biomass-derived) intermediate layers, polymer-based (eg, PEO, At least one of a polypyrrole (PPY), polyvinylidene fluoride, etc.) intermediate layer, a metal-based intermediate layer (eg, Ni foam, etc.), or a combination thereof.

In some examples, the solid electrolyte 108 may be used to address safety concerns commonly found in leaks, poor chemical stability, and flammability, such as are commonly seen in lithium-sulfur (Li-S) batteries using liquid electrolytes. In addition, the solid electrolyte can also inhibit the polysulfide shuttle from the cathode to the anode, resulting in improved cathode utilization and high discharge capacity and energy density. In some examples, the solid electrolyte may include Li6.4La3Zr1.4Ta0.6O12 (LLZTO), Li10GeP2S12, Li1.5Al0.5Ge1.5 (PO4) 3, Li1.4Al0.4Ti1.6 (PO4) 3, Li0.55La0. 35TiO3, interpenetrating polymer network of poly(ethyl acrylate) (ipn-PEA) electrolyte, three-dimensional ceramic/polymer network, in-situ plasticized polymer, composite polymer with well-arranged ceramic nanowires, based on PEO At least one of a solid polymer, a flexible polymer, a polymeric ionic liquid, Li ₃ PS ₄ formed in situ, or a combination thereof.

In some examples, the anode 112 may include lithium (Li) metal. In some examples, the battery may include at least one anode protector such as an electrolyte additive (eg, LiNO ₃ , lanthanum nitrate, copper acetate, P ₂ S _5, etc.), an artificial interface layer (eg, Li ₃ N, (CH ₃ ) ₃ SiCl, Al ₂ O ₃ , LiAl, etc.), composite metals (for example, Li7B6, Li-rGO (reduced graphene oxide), layered Li-rGO, etc.) or a combination thereof.

The description of the sulfur cathode 104 and its forming method are described below.

2 illustrates a scheme 200 of (a) heating and drying; and (b) freeze-drying and drying a lithium-sulfur (Li-S) sulfur cathode. In the first step of the cathode formation scheme, the current collector substrate 206 is coated with a sulfur-based slurry layer including a binder 202 and a sulfur composite 204. The composite layer can be formed in the following manner. First, the metal carbide, carbon material, and sulfur material are mixed in a solvent to form a sulfur precursor. The metal carbide may include tungsten (W), iron (Fe), chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), titanium (Ti), zirconium (Zr), hafnium (Hf) , Vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), sodium (Na), calcium (Ca), or a combination of at least one carbide. The carbon material may be at least one of nanoparticles, nanowires, nanofibers, nanorods, nanotubes, nanospheres, graphene, or a combination thereof. The sulfur material is elemental sulfur. The solvent may be any known compatible solvent, such as at least one of water, hexane, octane, acetone, tetrahydrofuran, 2-butanone, toluene, xylene, ethanol, methanol, isopropanol, benzene, or a combination thereof By. In some examples, the mixing may be performed by at least one of ball milling processing, ultrasonic processing, magnetic mixing, vortex mixing, and the like.

Thereafter, the sulfur precursor may be ground (eg, dry milling treatment, etc.) to form a sulfur composite, and then the sulfur composite is mixed with a binder and stirred to form a sulfur-based slurry. In some examples, the binder includes at least one of styrene-diene rubber, carboxymethyl cellulose, polyacrylic acid (PAA), sodium alginate, or a combination thereof. In some examples, the binder includes styrene-butadiene rubber and carboxymethyl cellulose. In some examples, the binder contains water. The slurry having the sulfur composite 204 and the adhesive 202 is then positioned onto the substrate 206 by at least one of spin coating, dip coating, layer-by-layer deposition, sol-gel deposition, inkjet printing, or a combination thereof.

Conventionally, the composite layer is dried by heating, as shown in the route (a) of FIG. 2. Because the solvent is removed during the heating and drying process, this approach usually results in a dense packed structure 208. As demonstrated and explained in the following example, the densely packed structure 208 results in a lower amount of internal volume in the composite layer that can be used to incorporate the subsequently formed conductive polymer (ie, lower porosity, less irregularity) Porosity).

According to the disclosure in the route (b) of FIG. 2, after the sulfur-based slurry layer is provided on the substrate, the slurry layer is freeze-dried to form a sulfur group having a porosity in the range of 60% to 99% Composite layer 210. The structure of the sulfur cathode can be maintained by freezing the solvent in the slurry layer at a low temperature before drying. When the frozen solvent sublimates during the drying process, pores are formed in the composite layer (ie, the pores remain where the solvent originally was). In other words, during the freeze-drying process, the internal volume space of the composite layer occupied by the solvent can be retained, thereby avoiding shrinkage of the composite layer caused by volatilization of the solvent during the drying process. Compared with traditional heating and drying, freeze drying can increase the porosity of the composite layer by 3 to 5 times.

In some examples, the composite layer has a porosity in the range of 60% to 80% (compared to the porosity of the heat-dried slurry layer, the porosity of the heat-dried slurry layer is in the range of 30% to 50% Inside). In some examples, the pores of the composite layer may have a size in the range of 1µm to 50µm. In some examples, the pores may have a range of 2µm to 10µm. In some examples, freezing is performed at a temperature in the range of -50°C to 0°C, or a range of -35°C to -10°C, or a range of -25°C to -15°C. In some examples, freezing at a temperature of -20°C. In some examples, freezing is performed in the range of 1 hour to 12 hours, or in the range of 2 hours to 9 hours, or in the range of 4 hours to 7 hours. In some examples, freezing is performed for 6 hours. In some examples, freezing is performed at a temperature of -20°C for 6 hours. In some examples, drying is performed in the range of 1 hour to 24 hours, or 6 hours to 18 hours, or 9 hours to 15 hours in the freeze dryer. In some examples, 12 hours of drying is performed.

In some examples, the composite layer includes carbon material in the range of 5 to 40 weight percent, or carbon material in the range of 10 to 30 weight percent, or carbon in the range of 15 to 25 weight percent. material. In some examples, the composite layer includes metal carbide in the range of 1 to 20 weight percent, or metal carbide in the range of 3 to 17 weight percent, or in the range of 5 to 15 weight percent Metal carbide. Carbon materials and metal carbides are conductive parts that are evenly dispersed in the final sulfur cathode, helping to adsorb polysulfides (ie, minimizing polysulfide migration) to improve sulfur utilization (ie, loss of active cathode materials) minimize).

After the freeze-drying step, the conductive polymer 212 is disposed on top of the composite layer 210 and the composite layer by at least one of spin coating, dip coating, layer-by-layer deposition, sol-gel deposition, inkjet printing, or a combination thereof 210 within the pores to achieve the final cathode structure 214. In some examples, the conductive polymer includes carbon polysulfide (CS), polyethylene oxide (PEO), polyaniline (PANI), polypyrrole (PPY), poly(3,4-ethylenedioxythiophene ) (PEDOT), polystyrene sulfonic acid (PSS), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), poly(vinylidene fluoride-co-hexafluoropropylene) ( P (VdF-co-HFP)), poly (methyl methacrylate) (PMMA), polyvinylidene fluoride (PVDF), poly (diallyl dimethyl) ammonium (bis (trifluoromethanesulfonamide )) At least one of acetylenimine (TFSI) (PDDATFSI) or a combination thereof, and lithium bis(trifluoromethane)sulfonylimide (LiTFSI), lithium perchlorate, lithium bis(oxalate) lithium borate ( At least one of LiBOB), lithium bis(fluorosulfonyl)imide (LiFSI), or a combination thereof.

In some examples, the conductive polymer is polyethylene oxide. Because freeze-drying creates pores and channels inside the composite layer, the conductive polymer slurry (eg, PEO electrolyte) can be penetrated into the composite layer through its porous structure after being coated on the surface of the composite layer. This surface coating and internal penetration improve the interface compatibility and strengthen the ionic conductivity of the resulting sulfur electrode. example

Example 1

Sulfur, tungsten carbide (WC) and vapor-grown carbon fiber (VGCF) were ball-milled in ethanol at a weight ratio of 6:2:2. After 4 hours of ball milling treatment, the mixed powder was filtered and dried. After an additional dry milling (eg, dry milling treatment) for 24 hours, the mixture is sieved to form a sulfur complex. By ball milling treatment or stirring including pre-prepared sulfur compound with a weight ratio of 80:5:5:5:5, tungsten carbide (WC), vapor grown carbon fiber (VGCF), styrene-butadiene rubber (SBR) And carboxymethyl cellulose (CMC) to prepare a slurry. After that, the slurry was coated on aluminum foil with a thickness of 100µm.

The aluminum foil coated with the slurry was frozen at -20°C for about 6 hours, and then placed in a freeze dryer for about 12 hours to discharge the water content in the slurry. After freeze-drying, the electrode was cut into 12 mm diameter discs. The sulfur content of the cathode was measured to be about 1.78 mg/cm ² .

Dissolve polyethylene oxide (PEO) powder and bis(trifluoromethanesulfonylimide lithium salt (LiN(CF3SO2)2, or LiTFSI) at a molar ratio of PEO to Li ⁺ of about 18:1 in acetonitrile The solid content of the slurry is about 10%. The slurry is cast on the surface of the freeze-dried cathode, and then the cathode is vacuum dried at about 60° C., where the solvent is volatilized to form a sulfur cathode. In order to ensure sufficient in the cathode Ion and electron conduction network, the cathode is designed to have a thickness of less than 200µm. The final sulfur cathode is then assembled with other components (eg, intermediate layer, electrolyte, lithium anode) into a battery.

Comparative example 1

Except for the freeze-drying step, the samples prepared as Comparative Example 1 were prepared in such manners as provided in Example 1 above. However, after applying the slurry to the aluminum foil, the structure was heated and dried in a furnace at a temperature of about 60°C to discharge the water content in the slurry. Subsequently, the electrode was cut into 12 mm diameter discs.

Characterization of Example 1 and Comparative Example 1

3 illustrates a (a) surface (plan view) and (b) cross-sectional scanning electron microscope (SEM) image of the cathode electrode as shown in Comparative Example 1. FIG. The morphological analysis described herein was performed by a scanning electron microscope (SEM, Hitachi JSM 6700), and the element distribution image was characterized by an energy dispersive spectrometer (EDS) attached to a Hitachi SEM. As shown in Figures 3(a) and (b), furnace heating and drying causes considerable particles to agglomerate, and the agglomerated particles are separated from the conductive network. For example, set the initial coating thickness of the paste on the aluminum foil to 100µm. After heat treatment at 60°C, the thickness of the initial slurry film was significantly reduced by about 70% because the measured post-heat drying thickness was about 30 μm. More importantly, due to this shrinkage of the sulfur-based composite layer when the introduced water is evaporated, the composite layer maintains a low porosity, and the resulting cathode has an uneven thickness. In other words, the heat treatment corresponds to the lower internal volume space within the composite layer that can be used to incorporate conductive polymers.

FIG. 4 illustrates a cross-sectional SEM image of a cathode sample coated with a PEO conductive polymer (ie, PEO electrolyte) and the corresponding energy dispersion spectrum (EDS) mapping as shown in Comparative Example 1. FIG. As shown in the cross-sectional SEM image (upper left corner), when the coating is applied, although the surface of the sulfur electrode is completely covered by the PEO electrolyte, there is a gradient of oxygen distribution in the electrode (as shown in the lower right corner of the EDS mapping image ). In other words, oxygen is concentrated on the top surface of the electrode and cannot sufficiently penetrate the electrode body. This is observed as bright luminescence in the EDS image, where most of the oxygen is localized (ie, where PEO electrolyte is deposited on the top surface of the electrode), and the luminescence decreases sharply as the depth from the top surface to the electrode increases. Insufficient penetration of the PEO polymer layer indicates that it implies that less irregular pores are formed in the electrode by the heating and drying process. As seen in the upper right and lower left images, because high-luminescence scattering pockets were observed, the contents of sulfur and carbon were unevenly distributed throughout the electrode, which confirmed the aggregation of particles during the heating and drying process.

5 illustrates the (a) surface and (b) cross-sectional scanning electron microscope (SEM) images of the cathode as shown in Example 1; and the (c) surface and (c) surface of a cathode sample coated with a PEO-based electrolyte layer. (d) Cross-sectional scanning electron microscope (SEM) image. Compared with the results of the heating and drying process in Figure 3(a) and Figure 3(b), because the cathode obtained is relatively uniform, has a smooth, homogeneous surface, and a highly conductive mesh (ie, carbon nanofibers Connection), the aggregation of particles is alleviated (Figure 5 (a) and (b)). A comparison of the cross-sections between Figures 3(b) and 5(b) shows that the samples prepared by freeze-drying have a much smaller rough surface and a larger overall thickness (heat-drying is 30µm, freeze-drying is 80µm ), thereby suggesting a morphology with a lower degree of stacking and a larger amount of open space (ie, pore volume) in the cathode body. These results are consistent with the structures 208 (heat drying) and 210 (freeze drying) of FIG. 2. Because the lower cathode has a more consistent surface morphology and a larger internal pore volume, when covered with PEO electrolyte, a smooth PEO layer (about 20 µm) is formed on the top of the cathode, and the homogeneous PEO penetration into the electrode body (Figure 5( c) and (d)).

6 illustrates a cross-sectional scanning electron microscope (SEM) image and corresponding EDS mapping of a PEO electrolyte-coated cathode sample as shown in Example 1. FIG. As shown in the cross-sectional image (top left), the surface of the sulfur electrode is completely covered by the PEO electrolyte. Unlike the heat-drying process image of Fig. 4, the uniform distribution of sulfur (top right) and carbon (bottom left) in the electrode shows that the electrode prepared by freeze-drying does not exhibit particle aggregation. Furthermore, although there is a slightly larger amount of oxygen content towards the top surface of the electrode, oxygen penetrates more completely axially through the pores of the electrode and provides a relatively uniform lateral distribution of oxygen (lower right). In other words, the distribution of oxygen elements in the electrode indicates that the PEO slurry can penetrate more fully into the interior of the electrode prepared by freeze drying (defined by the extremely high pore structure) than the PEO slurry prepared by heat drying; thereby increasing the ion of the electrode Conductivity.

PEO penetrates into the electrolyte (for example, PEO intermediate layer, solid electrolyte, etc.) and the cathode active material to play an important role in the form of ion-conducting dielectric. In the conventional heat drying process, PEO is added by a simple casting process and subsequent heat drying. Therefore, the PEO slurry cannot sufficiently penetrate into the pores and other channels of the sulfur electrode (structure 20 of FIG. 2) to form an effective ion conductive path, resulting in poor utilization of effective materials. The cathode prepared by heating and drying without sufficient pore formation, at high temperature (ie, the shuttle effect), PEO penetration still suffers from the undue influence of polysulfide dissolution and migration through the PEO electrolyte.

7 and 8 show impedance graphs and cycle performance of lithium-sulfur (Li-S) batteries having cathodes prepared by freeze drying and heat drying, respectively. Electrochemical impedance spectrum analysis (EIS) was performed on an Autolab electrochemical workstation (ECO CHEMIE B.V, Netherlands) with a frequency response analyzer. Due to the pore volume generated in the cathode prepared by freeze-drying and incorporating conductive polymers (for example, PEO), PEO-based ionic conductors can better contact the effective materials, resulting in solid lithium-sulfur (Li-S) batteries. Lower overall impedance (60Ω, relative to 80Ω for heating and drying the cathode). The lower overall impedance due to the contact of PEO with the effective material of the cathode effectively reduces the charge transfer resistance. The lower porosity of the cathode prepared by heat drying is detrimental to PEO electrolyte penetration, which results in high charge transfer resistance.

FIG. 8 illustrates the cycle performance of a lithium-sulfur (Li-S) battery having a cathode prepared by freeze-drying and heat-drying methods. Compared with the cathode prepared by freeze drying, the cathode prepared by heating drying exhibits a higher initial discharge capacity and poorer cycle performance. The higher initial discharge capacity of the heat-dried cathode is due to the short charge transfer path, which causes PEO to penetrate into contact with the active material during rest. Due to the dissolution of the reaction products in the PEO layer, the capacity of the heated and dried cathode battery decreases with cycling. Due to the slow dissolution and diffusion of polysulfide from the thick electrode to the PEO layer, the freeze-dried cathode exhibits a relatively stable cycle capacity. Since a large amount of PEO electrolyte penetrates into the freeze-dried prepared cathode, the discharge product dissolves into the PEO still in contact with the conductive network of the electrode, so the discharge product can be reused.

9 illustrates a charge-discharge curve of a lithium sulfur (Li-S) battery having a sulfur cathode prepared by (a) heat drying; and (b) freeze drying. The electrochemical performance of solid-state lithium-sulfur (Li-S) batteries was measured at 60°C using a LAND CT2001A battery test system in the voltage range of 3V to 1.5V, at a current density of 0.1mA·cm ^-2 . Before testing, the sample was allowed to stand at 70°C for about 12 hours. Lithium-sulfur (Li-S) batteries including a heated and dry cathode initially exhibited a discharge capacity exceeding 1200 mAhg ^-1 S in the first cycle; however, this specific capacity decreased rapidly with additional cycles because it was in the tenth Reduced to about 800 mAhg ^-1 S during cycling. A lithium-sulfur (Li-S) battery including a freeze-dried cathode initially exhibits a discharge capacity exceeding 1000 mAhg ^-1 S in the first cycle, and can maintain the capacity even after ten cycles. In other words, batteries with lyophilized lithium-sulfur (Li-S) provide a reversible capacity of about 1000 mAhg ^-1 S in the first ten cycles, and because the curves of different cycles overlap with each other, this implies the benefit of the battery's enhanced cycle stability .

Example 2

The slurry was prepared as described in Example 1 and then coated on aluminum foil with a thickness of 150 µm.

Subsequently, the aluminum foil coated with the slurry was frozen at -20°C for about 6 hours, and then placed in a freeze dryer for about 12 hours to discharge the water content in the slurry. After freeze-drying, the electrode was divided into 2cm x 2cm segments. The sulfur content of the cathode was measured to be about 2.9 mg/cm ² .

PEO powder and LiTFSI were dissolved in acetonitrile at a PEO to Li ⁺ molar ratio of about 8:1. The solids content of the slurry is about 5%. The slurry was cast on the surface of the freeze-dried cathode, and then the cathode was vacuum dried at about 60°C, in which the solvent was volatilized to form a sulfur cathode. As in Example 1, the cathode is designed to have a thickness of less than 200µm.

Preparation of the intermediate layer

PEO powder and LiTFSI were dissolved in acetonitrile at a PEO to Li ⁺ molar ratio of about 18:1. Add ionic liquid and 10 weight percent silica particles (less than 1000 nm) and mix thoroughly. In some examples, the concentration of silica particles in PEO is 1 to 15 weight percent based on the silica particle size. Silicon dioxide particles help reduce the crystallinity of PEO and improve Li ⁺ conductivity. The intermediate layer electrolyte is obtained by pouring the obtained intermediate layer slurry mixture into a polytetrafluoroethylene (PTFE) mold and vacuum drying.

The intermediate layer between the cathode and the electrolyte reduces the interface resistance. In order not to significantly reduce the mass energy density and volume energy density of the solid state battery, the thickness of the intermediate layer is as thin as possible. In some examples, the thickness of the intermediate layer may be in the range of 5µm to 50µm.

Preparation of solid electrolyte

The cubic phase Li6.4La3Zr1.4Ta0.6O12 (LLZTO) starts from LiOH·H ₂ O (AR), La ₂ O ₃ (99.99% purity), ZrO ₂ (AR), Ta ₂ O ₅ (99.99% purity) The powder is synthesized in stoichiometric ratio. More than 2 weight percent lithium hydroxide aqueous solution was added to compensate for lithium loss during sintering. By heat treatment at 900°C for about 12 hours, a small amount of water and adsorbed carbon dioxide are removed from lanthanum oxide (La ₂ O ₃ ). The raw materials are mixed through a wet grinding process, in which yttrium stabilized zirconia (YSZ) balls and isopropyl alcohol (IPA) are used as grinding media. After the second mixing step, the mixture was dried and calcined in an alumina crucible at 950°C for about 6 hours, and then calcined again at 950°C for about 6 hours to obtain a pure cubic garnet phase powder. After the second calcination process, the powder was pressed into green particles with a diameter of about 16 mm and sintered at 1250° C. for about 10 hours, covered in a platinum crucible with LLZTO powder having more than 10 weight percent lithium. The sintered particles are polished to a thickness of approximately 0.8 mm.

In some examples (eg, Example 2), a thin layer of gold (Au) was ion-sputter coated on one side of the LLZTO ceramic for 10 minutes. The sample was then transferred to a glove box filled with argon. A part of the lithium foil is melted by heating to at least 250°C. The molten lithium was then cast on the surface of the LLZTO pellets including the gold layer coated with ion sputtering. The final sulfur cathode (as in Example 2) was then assembled with an intermediate layer and LLZTO-Au-Li solid electrolyte to form a battery.

Battery assembly

Composed of PEO-coated, freeze-dried sulfur cathode, PEO-based intermediate layer coated on it, LLZTO ceramic solid electrolyte, and lithium metal anode to obtain a lithium-sulfur (Li-S) battery obtained by the method described herein . The solid-state lithium-sulfur (Li-S) battery is assembled in a glove box filled with an inert gas (argon), and its structure is shown in FIG. 1 (sulfur cathode/intermediate layer 1/LLZTO/intermediate layer 2/lithium anode).

10 illustrates a lithium-sulfur (Li-S) battery having a cathode prepared by freeze-drying and a lithium-gold (Li-Au) anode with a current density of 0.1 mA·cm ^-2 at 60° C. (ie, Example 2) Cycle effectiveness. Solid lithium-sulfur (Li-S) batteries show an initial discharge capacity of 980 mAhg ^-1 and good cycle performance. After 30 cycles, the discharge capacity of the lithium-sulfur (Li-S) battery is maintained at 888mAhg ^-1 , which can provide a 90% capacity retention rate.

Therefore, as described herein, the present disclosure relates to a solid-state lithium-sulfur (Li-S) battery, and more specifically, to a sulfur cathode and a method of manufacturing the same, in which a porous sulfur cathode coated in a lithium ion conductive polymer layer is used Used in solid-state lithium-sulfur (Li-S) batteries. Compared with the traditional cathode prepared by heating and drying, the freeze-drying method disclosed herein produces more porous and uniform sulfur electrodes. In addition, this reinforced porous electrode structure helps PEO electrolyte penetrate into the cathode, thereby allowing good contact between the cathode effective material, conductive carbon, and ion conductive network, and improving the utilization of sulfur effective material. PEO electrolyte coating can also improve interface stress and reduce interface resistance. Therefore, the lithium-sulfur (Li-S) battery made by the sulfur cathode formed by the method proposed here has a higher reversibility than the lithium-sulfur (Li-S) battery formed by the cathode prepared by heating and drying Specific capacity, lower overall impedance and more stable cycling performance.

As used herein, the terms "approximately", "approximately", "substantially" and similar terms are intended to have a broad meaning, which is common and acceptable to those skilled in the art related to the subject matter of this disclosure Consistent. Those of ordinary skill in the art who read this disclosure should understand that these terms are not intended to limit the scope of these features to the precise numerical ranges provided before, allowing certain features to be described and claimed. Therefore, these terms should be construed to mean that the described and claimed subject matter is insubstantial or insignificant modifications or alterations, all of which are deemed to be within the scope of the invention described in the appended patent application.

As used herein, "optional", "optionally" or similar words are intended to mean that the subsequently described event or circumstance may or may not occur, and the description includes examples of the occurrence of the event or circumstance and does not occur. Examples of occurrences or situations. Unless otherwise stated, the indefinite article "a (an)" and its corresponding definite article "the" as used herein refer to at least one, or one or more.

References in this document to the location of elements (eg, "top", "bottom", "above", "below", etc.) are only used to describe the orientation of various elements in the drawings. It should be noted that according to other exemplary embodiments, the orientation of various elements may be different, and such changes are intended to be covered by the present disclosure.

With regard to the use of substantially any plural and/or singular terms herein, those skilled in the art may appropriately convert from plural to singular plural and/or from singular to plural according to the context and/or application. For clarity, various singular/plural arrangements can be clearly stated in this article.

It is obvious to those skilled in the art that various modifications and changes can be made without departing from the spirit or scope of the subject matter claimed in this case. Therefore, the subject matter requested is not limited except in accordance with the scope of the accompanying patent application and these equivalents.

100‧‧‧ battery 102‧‧‧ substrate 104‧‧‧sulfur electrode/cathode 106‧‧‧First middle floor 108‧‧‧Solid electrolyte 110‧‧‧Second middle layer 112‧‧‧Lithium electrode/anode 200‧‧‧ Plan 202‧‧‧adhesive 204‧‧‧Sulfur compound 206‧‧‧Current collector substrate 208‧‧‧filled structure 210‧‧‧Sulfur-based composite layer 212‧‧‧Conducting polymer 214‧‧‧ cathode structure

Through the following detailed description in conjunction with the accompanying drawings, this disclosure will be more fully understood, in which:

FIG. 1 illustrates the structure of a solid-state lithium-sulfur (Li-S) battery according to some embodiments.

FIG. 2 illustrates a scheme of a lithium sulfur (Li-S) sulfur cathode dried by (a) heat drying and (b) freeze drying.

FIG. 3 illustrates (a) the surface and (b) cross-sectional scanning electron microscope (SEM) images of the cathode electrode as in Comparative Example 1. FIG.

4 illustrates a cross-sectional scanning electron microscope (SEM) image and corresponding energy dispersive spectroscopy (EDS) mapping of a cathode sample (PEO-coated) as in Comparative Example 1. FIG.

5 illustrates the (a) surface and (b) cross-sectional scanning electron microscope (SEM) images of the cathode electrode as in Example 1; and the (c) surface and (c) of the cathode sample coated with the PEO-based electrolyte layer. d) Cross-sectional scanning electron microscope (SEM) image.

6 illustrates a cross-sectional scanning electron microscope (SEM) image and corresponding EDS mapping of a cathode sample (PEO-coated) as shown in Example 1. FIG.

FIG. 7 illustrates an impedance diagram of a lithium-sulfur (Li-S) battery having a cathode prepared by (I) freeze drying or (II) heat drying.

FIG. 8 illustrates the cycle performance of a lithium-sulfur (Li-S) battery having a cathode prepared by (I) freeze drying or (II) heat drying.

9 illustrates the charge and discharge of a lithium-sulfur (Li-S) battery having a sulfur cathode prepared by (a) heating and drying; and (b) freeze-drying at a current density of 0.1 mA·cm ^-2 at 60° C. curve.

FIG. 10 illustrates the cycle performance of a lithium-sulfur (Li-S) battery having a cathode prepared by freeze drying and a lithium-gold (Li-Au) anode as in Example 2. FIG.

Domestic storage information (please note in order of storage institution, date, number) no

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100‧‧‧ battery

102‧‧‧ substrate

104‧‧‧sulfur electrode/cathode

106‧‧‧First middle floor

108‧‧‧Solid electrolyte

110‧‧‧Second middle layer

112‧‧‧Lithium electrode/anode

Claims (19)

A cathode for lithium-sulfur (Li-S) batteries, including: A sulfur-based composite layer with a porosity in the range of 60% to 99%; and A conductive polymer is arranged on the top of the composite layer and is located in the pores of the composite layer. The cathode according to claim 1, wherein the composite layer has a porosity in the range of 60% to 80%. The cathode according to claim 1, wherein the pores of the composite layer have a size in the range of 1 µm to 50 µm. The cathode according to claim 3, wherein the pore size is in the range of 2µm to 10µm. The cathode according to claim 1, wherein the composite layer comprises a carbon material, the carbon material being nanoparticles, nanowires, nanofibers, nanorods, nanotubes, nanospheres, graphene, or At least one of its combinations exists. The cathode according to claim 5, wherein the content of the carbon material is in the range of 5 to 40% by weight (wt%). The cathode according to claim 1, wherein the composite layer includes a metal carbide in the range of 1 wt% to 20 wt%. The cathode according to claim 1, wherein the conductive polymer comprises carbon polysulfide (CS), polyethylene oxide (PEO), polyaniline (PANI), polypyrrole (PPY), poly(3,4- Ethylenedioxythiophene) (PEDOT), polystyrene sulfonic acid (PSS), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyallylamine hydrochloride (PAH), poly(vinylidene fluoride- Hexafluoropropylene) (P (VdF-co-HFP)), poly (methyl methacrylate) (PMMA), polyvinylidene fluoride (PVDF), poly (diallyl dimethyl) ammonium (bis ( At least one of trifluoromethanesulfonyl)imide (TFSI) (PDDATFSI), or a combination thereof. A lithium-sulfur (Li-S) battery, including: A lithium anode; A solid electrolyte; and The cathode as described in any one of claims 1 to 8. A method for forming a cathode of a lithium-sulfur (Li-S) battery includes the following steps: Provide a substrate; A sulfur-based slurry layer is provided on the substrate; Freeze drying the slurry layer to form a sulfur-based composite layer having a porosity in the range of 60%-99%; and A conductive polymer is placed on top of the composite layer and in the pores of the composite layer. The method according to claim 10, wherein the substrate is a current collector. The method according to claim 10, further comprising the following steps: Mixing a metal carbide, a carbon material and a sulfur material in a solvent to form a sulfur precursor; and Dry milling the sulfur precursor to form the monosulfide complex. The method according to claim 12, further comprising the following steps: The sulfur compound is stirred with a binder to form the sulfur-based slurry. The method according to claim 13, wherein: The carbon material is at least one of nanoparticles, nanowires, nanofibers, nanorods, nanotubes, nanospheres, graphene, or a combination thereof, and The binder includes at least one of styrene-butadiene rubber, carboxymethyl cellulose, water, or a combination thereof. The method of claim 10, wherein the composite layer has a porosity in the range of 60% to 80%. The method according to any one of claims 10 to 15, wherein the pores of the composite layer have a size in the range of 1 µm to 50 µm. The method according to claim 16, wherein the pore size is in the range of 2µm to 10µm. The method according to any one of claims 10 to 15, wherein the freeze-drying step includes the following steps: Freezing the slurry layer at a temperature of -50°C to 0°C for 1 hour to 12 hours; and The frozen slurry layer is dried in a freeze dryer for 1 hour to 24 hours. The method of claim 10, wherein the step of providing the conductive polymer is performed by at least one of spin coating, dip coating, layer-by-layer deposition, sol-gel deposition, inkjet printing, or a combination thereof get on.

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