Applications of cathode additives, cathode active materials, cathode sheets, solid-state batteries and their preparation methods, and electrical devices.

Abstract

This invention discloses the application of a positive electrode additive, a positive electrode active material, a positive electrode sheet, a solid-state battery and its preparation method, and an electrical device, relating to the field of solid-state battery technology. The positive electrode additive comprises a conductive layered substrate and alkali metal ions. The conductive layered substrate has a multi-layered sheet structure, each sheet structure comprising a polymer chain. Every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent, and alkali metal ions are at least doped between adjacent sheet structures. Using this positive electrode additive to prepare the positive electrode active material improves the specific capacity of the positive electrode and the overall battery, solving the problems of difficulty in conducting electrons and ions in the positive electrode of solid-state batteries, as well as the high additive content. Furthermore, the positive electrode additive has a layered structure and easy slippage characteristics, reducing the contact resistance between the positive electrode active material and the additive, and enabling close adhesion between the positive electrode material and the electrolyte under relatively low external pressure.

Description

Technical Field

[0001] This invention relates to the field of solid-state battery technology, and in particular to the application of a positive electrode additive, a positive electrode active material, a positive electrode sheet, a solid-state battery and its preparation method, and an electrical device. Background Technology

[0002] Solid-state lithium batteries have advantages such as ultra-high theoretical specific capacity, lower cost, and higher safety, making them a potential replacement technology for traditional lithium-ion batteries and liquid lithium batteries. They are crucial for the development of power battery systems for future electric vehicles.

[0003] However, the positive electrode active materials in solid-state lithium batteries, such as sulfur, have the characteristics of being both electronically and ionicly insulated. Their reaction kinetics are slow, and they have extremely high internal resistance during operation, resulting in large overpotentials, low capacity, and poor cycle performance, which limits the application of solid-state lithium batteries. Summary of the Invention

[0004] The main objective of this invention is to propose an application of a positive electrode additive, a positive electrode active material, a positive electrode sheet, a solid-state battery and its preparation method, and an electrical device, aiming to solve the problems of high internal resistance and poor cycle performance of solid-state lithium batteries in the prior art.

[0005] To achieve the above objectives, the present invention proposes an application of a positive electrode additive in the preparation of positive electrode active materials. The positive electrode additive includes a conductive layered host and alkali metal ions. The conductive layered host has a multilayer sheet structure. Each sheet structure includes a polymer chain. Every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent. The alkali metal ions are at least doped between adjacent sheet structures.

[0006] In one embodiment, in the positive electrode additive, the mass ratio of the polymer chain, the polyoxometalate crosslinking agent, and the alkali metal ions is (3~10):(83~93):(0.5~6); and / or,

[0007] The alkali metal ions include lithium ions, sodium ions, or potassium ions; and / or,

[0008] The polyoxometallic acid crosslinking agent includes tungstic acid, molybdic acid, phosphotungstic acid, or silicotungstic acid; and / or,

[0009] The polymer in the polymer chain includes polyaniline, polypyrrole, or polythiophene; and / or,

[0010] The polyoxometallic acid crosslinking agent is connected to the polymer chains in every two adjacent lamellar structures via hydrogen bonds; and / or,

[0011] The positive electrode additive further includes a solvent, which is at least doped between adjacent sheet-like structures, and the solvent accounts for 5% to 7% of the mass of the positive electrode additive; and / or,

[0012] The positive electrode additive has an ionic conductivity of 0.3~1 mS / cm and an electronic conductivity of 5~7 S / cm.

[0013] The present invention also provides a positive electrode active material, which includes a positive electrode active substance and a positive electrode additive; the positive electrode additive includes a conductive layered host and alkali metal ions, the conductive layered host has a multilayer sheet structure, each sheet structure includes a polymer chain, every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent, and the alkali metal ions are at least doped between adjacent sheet structures.

[0014] In one embodiment, the positive electrode active material includes sulfur, selenium, or iodine; and / or,

[0015] In the positive electrode active material, the mass percentage of the positive electrode active substance is 50% to 80%; and / or,

[0016] The mass ratio of the positive electrode additive to the positive electrode active material is (2~10):9.

[0017] In one embodiment, the positive electrode additive is coated on the surface of the positive electrode active material.

[0018] In one embodiment, the positive electrode active material includes sulfur, and the positive electrode active material further includes a carbon-based conductive material having pores.

[0019] The sulfur fills the pores of the carbon-based conductive material to form a composite positive electrode active material, and the positive electrode additive coats the surface of the composite positive electrode active material.

[0020] In one embodiment, the positive electrode active material is obtained by grinding positive electrode additives and positive electrode active substances, or by synthesizing positive electrode additives in situ on the surface of positive electrode active substance nanoparticles.

[0021] The present invention also provides a positive electrode sheet, wherein the positive electrode sheet comprises the aforementioned positive electrode active material.

[0022] The present invention also provides a solid-state battery, the solid-state battery comprising the aforementioned positive electrode.

[0023] The present invention also provides a method for preparing the aforementioned solid-state battery, comprising the following steps:

[0024] A positive electrode is placed on one side of a solid electrolyte sheet, and external pressure is applied to make the positive electrode and the solid electrolyte sheet fit tightly together to obtain an intermediate body. The external pressure is 2~5MPa.

[0025] The negative electrode is placed on the other side of the solid electrolyte sheet of the intermediate, and external pressure is applied to make the negative electrode and the intermediate fit tightly together to obtain the solid battery.

[0026] The present invention also provides an electrical device comprising the aforementioned solid-state battery.

[0027] In the technical solution of this invention, the positive electrode additive comprises a conductive layered host and alkali metal ions. The conductive layered host has a multi-layered sheet structure, each sheet structure comprising a polymer chain. Every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent, and the alkali metal ions are at least doped between adjacent sheet structures. Because this positive electrode additive possesses both good electronic and ion conduction capabilities, it can replace traditional positive electrode additive materials and reduce the amount of positive electrode additive used, effectively increasing the mass ratio of positive electrode active material in the positive electrode active material. This improves the specific capacity of the positive electrode and the overall battery, solving the problems of difficulty in conducting electrons and ions in solid-state battery positive electrodes and the high additive ratio. Furthermore, this positive electrode additive has a layered structure and easy slippage characteristics, reducing the contact resistance between the positive electrode active material and the additive, and enabling the positive electrode material and electrolyte to adhere tightly under relatively low external pressure. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram illustrating the process of preparing the positive electrode active material by grinding in Example 1 of this invention, as well as the principle of mixed ion and electron conduction.

[0030] Figure 2 The following is a process diagram of the in-situ synthesis of cathode additives on the surface of nano-sulfur in Example 5 of this invention: Figure 2 (a) is a diagram of liquid-phase nano-sulfur; Figure 2 (b) shows the growth of polyaniline on the surface of nano-sulfur; Figure 2 (c) is a diagram showing lithium-ion doping after the surface of nano-sulfur is coated with a multi-metal oxo acid-polyaniline layered material;

[0031] Figure 3 This is the X-ray diffraction (XRD) pattern of the positive electrode active material in Example 5 of the present invention;

[0032] Figure 4 This is a scanning electron microscope (SEM) image of the positive electrode active material in Example 5 of the present invention;

[0033] Figure 5 EIS impedance diagram of the positive electrode active material assembled into a solid lithium-sulfur battery in Example 5 of the present invention;

[0034] Figure 6 This is a charge-discharge curve of the positive electrode active material assembled into a solid-state lithium-sulfur battery in Example 5 of the present invention;

[0035] Figure 7 This is a cycle performance diagram of the solid-state lithium-sulfur battery assembled from the positive electrode active material in Example 5 of the present invention;

[0036] Figure 8 The image shows the EIS impedance diagram of the positive electrode active material assembled into a solid-state lithium-sulfur battery in Comparative Example 1 of this invention.

[0037] Figure 9 This is a charge-discharge curve of the positive electrode active material assembled into a solid lithium-sulfur battery in Comparative Example 1 of the present invention.

[0038] Figure 10 This is a cycle performance diagram of the solid lithium-sulfur battery assembled from the positive electrode active material in Comparative Example 1 of the present invention.

[0039] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially. Furthermore, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Solid-state lithium batteries have advantages such as ultra-high theoretical specific capacity, lower cost, and higher safety, making them a potential replacement technology for traditional lithium-ion batteries and liquid lithium batteries. They are crucial for the development of power battery systems for future electric vehicles.

[0042] However, the positive electrode active materials in solid-state lithium batteries, such as sulfur, have the characteristics of being both electronically and ionicly insulated. Their reaction kinetics are slow, and they have extremely high internal resistance during operation, resulting in large overpotentials, low capacity, and poor cycle performance, which limits the application of solid-state lithium batteries.

[0043] Taking solid-state lithium-sulfur batteries as an example, two types of cathode additives are typically introduced into the cathode of solid-state lithium-sulfur batteries: (1) conductive materials such as carbon as electronic conductors; and (2) sulfide solid electrolytes as ionic conductors. However, the interfacial impedance of sulfide solid electrolytes is extremely high, requiring external high pressure (>20~30MPa) to achieve good contact between the cathode material and the solid electrolyte, which greatly limits the capacity of the sulfur cathode. In addition, the introduction of the two cathode additives greatly reduces the proportion of sulfur, the active material in the cathode, which is generally less than 50wt%, and cannot effectively improve the specific capacity of the cathode and the battery as a whole.

[0044] In view of this, the present invention proposes an application of a positive electrode additive in the preparation of positive electrode active materials. The positive electrode additive includes a conductive layered host and alkali metal ions. The conductive layered host has a multilayer sheet structure. Each sheet structure includes a polymer chain. Every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent. The alkali metal ions are at least doped between adjacent sheet structures.

[0045] In the technical solution of this invention, a positive electrode additive is used to prepare the positive electrode active material. Because this positive electrode additive possesses both good electronic and ion conduction capabilities, it can replace traditional positive electrode additive materials and reduce the amount of positive electrode additive used. This effectively increases the mass ratio of the positive electrode active material in the positive electrode active material, thereby improving the specific capacity of the positive electrode and the overall battery. This solves the problems of difficulty in conducting electrons and ions in solid-state batteries, as well as the high additive ratio. Furthermore, this positive electrode additive has a layered structure and easy slippage characteristics, reducing the contact resistance between the positive electrode active material and the additive, and enabling the positive electrode material and electrolyte to adhere tightly under relatively low external pressure.

[0046] It is understood that the positive electrode additive provided by the present invention is a layered additive, specifically an alkali metal ion-polymetallic hydrochloric acid-polymer layered material. This layered additive contains layered channels that can conduct ions. As long as the layered channels of the layered additive contain alkali metal ions, it has the ability to conduct alkali metal ions.

[0047] It is understandable that the conductivity principle of conductive layered structures is as follows: conductive layered structures have highly conductive, continuous conductive polymer chains, such as polyaniline.

[0048] It should be noted that the positive electrode additive can be prepared by the following steps: adding polymer monomer material, polyoxometalate crosslinking agent, oxidant, and lithium source to water, adjusting the pH to convert the polyoxometalate into polyoxoacid; under polymerization reaction conditions, the polymer monomer material undergoes polymerization reaction and crosslinks under the action of polyoxoacid to form a layered matrix, thereby obtaining the positive electrode additive.

[0049] It should be noted that the positive electrode additive can also be prepared through the following steps: adding polymer monomer material, polyoxometalate crosslinking agent, and oxidant to water, adjusting the pH to convert the polyoxometalate into a polyoxoacid; under polymerization reaction conditions, the polymer monomer material undergoes a polymerization reaction and crosslinks under the action of the polyoxoacid to form a layered matrix, obtaining a conductive layered matrix; replacing at least a portion of the cations in the conductive layered matrix with alkali metal ions to obtain the positive electrode additive. It is understood that polyoxometalates are a class of compounds composed of metals (generally transition metals), oxygen, etc.

[0050] The step of replacing at least a portion of the cations in the conductive layered substrate with alkali metal ions to obtain the positive electrode additive includes: mixing and impregnating the conductive layered substrate with an alkali metal ion solution to perform an ion exchange reaction to obtain the positive electrode additive. The concentration of alkali metal ions in the alkali metal ion solution is 0.1M to 3M; the number of mixing and impregnation cycles is 1 to 5.

[0051] In some embodiments, the mass ratio of the polymer chain, the polyoxometalate crosslinking agent, and the alkali metal ions in the positive electrode additive is (3~10):(83~93):(0.5~6). It is understood that the mass ratio of the polymer chain, the polyoxometalate crosslinking agent, and the alkali metal ions can be 3:93:6, 5:90:4, or 10:83:0.5, and a mass ratio within the above range can ensure that the positive electrode additive has good electronic and ionic conductivity.

[0052] In some embodiments, the alkali metal ions include lithium ions, sodium ions, or potassium ions. It is understood that the type of alkali metal ion varies depending on the battery type, and the type of alkali metal ion can be adjusted accordingly.

[0053] In some embodiments, the polyoxometalate crosslinking agent includes tungstic acid, molybdic acid, phosphotungstic acid, or silicotungstic acid. It is understood that tungstic acid, molybdic acid, phosphotungstic acid, or silicotungstic acid can act as proton donors or acceptors without affecting the structure. After forming hydrogen bonds with heteroatoms in the sheet-like structure, tungstic acid, molybdic acid, phosphotungstic acid, or silicotungstic acid can stably connect two adjacent sheet-like structures and maintain a certain interlayer spacing (1~1.4 nm), thereby providing a smoother path for the rapid conduction of alkali metal ions.

[0054] In some embodiments, the polymer in the polymer chain includes polyaniline, polypyrrole, or polythiophene. These polymers contain heteroatoms (N or S), enabling them to crosslink with polymetallic hydrochloric acid via hydrogen bonds to form a two-dimensional structure, providing a smoother path for the rapid conduction of alkali metal ions. Preferably, the polymer chains in each sheet-like structure of the conductive layered matrix are of the same polymer to ensure stable interlayer spacing, thereby stabilizing the alkali metal ion conduction rate.

[0055] In some embodiments, the polyoxometalate crosslinking agent is connected to the polymer chains in every two adjacent lamellar structures via hydrogen bonds. It is understood that when the polymer chains are connected to the polyoxometalate via hydrogen bonds, the conductive layered structure exhibits slip-prone properties, making the bonding between the polymer chains both strong enough to maintain structural integrity and flexible enough to allow for a certain degree of slippage. This helps the layered additive better adhere to the surface of cathode particles such as sulfur, reducing "voids" or "dead zones," thereby lowering interfacial resistance (i.e., contact impedance) and improving electrochemical reaction efficiency. Furthermore, it can significantly reduce dependence on external stacking pressure during solid-state battery assembly. Here, slip-prone refers to the relatively easy displacement or sliding phenomenon that occurs within the material or between layered structures due to hydrogen bonding.

[0056] In some embodiments, the positive electrode additive further includes a solvent, which is at least doped between adjacent sheet structures, and the mass percentage of the solvent in the positive electrode additive is 5% to 7%. It is understood that although the interlayer of the layered additive is doped with solvent, the amount of solvent is small, and the solvent will diffuse sufficiently between the layers, even causing the layers to expand without flowing out, thus maintaining or increasing the interlayer spacing. Simultaneously, the presence of the solvent can improve the conductivity of alkali metal ions.

[0057] It should be noted that, in some embodiments, the solvent includes one or more of water, acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, fluoroacetonitrile, ethylene carbonate, fluoroethylene carbonate, methyltrifluoroethyl carbonate, methyl methacrylate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, hydrofluoroether, dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxopentane, tetrahydrofuran, toluene, ethanol, ethyl acetate, propyl acetate, and ionic liquids. The ionic liquid includes one or more of imidazole ionic liquids, pyridine ionic liquids, and quaternary ammonium ionic liquids. In imidazole ionic liquids, the cation is 1,3-disubstituted imidazoleium; in pyridine ionic liquids, the cation is pyridinium or a derivative thereof; and in quaternary ammonium ionic liquids, the cation is an ammonium salt with four alkyl / aryl groups attached to a nitrogen atom.

[0058] In some embodiments, the ionic conductivity of the cathode additive is 0.3~1 mS / cm. It is understood that the alkali metal ionic conductivity of the cathode additive can be 0.3 mS / cm, 0.5 mS / cm, 0.7 mS / cm, or 1 mS / cm, all within the scope of this invention. The electronic conductivity of the cathode additive is 5~7 S / cm. It is understood that the alkali metal ionic conductivity of the cathode additive can be 5 S / cm, 6 S / cm, or 7 S / cm. Therefore, the addition of this layered additive can replace the sulfide electrolyte, polymer electrolyte, or oxide electrolyte doped in the cathode material. Compared with the sulfide solid electrolyte typically added to cathode materials to improve ionic conductivity, the cathode additive of this application can significantly improve the ionic and electronic conductivity of the cathode material.

[0059] The present invention also provides a positive electrode active material, which includes a positive electrode active substance and a positive electrode additive; the positive electrode additive includes a conductive layered host and alkali metal ions, the conductive layered host has a multilayer sheet structure, each sheet structure includes a polymer chain, every two adjacent sheet structures are connected by a polyoxometalate crosslinking agent, and the alkali metal ions are at least doped between adjacent sheet structures.

[0060] In the technical solution of this invention, the combined use of positive electrode active material and positive electrode additive results in a positive electrode active material possessing both good electronic and ion conduction capabilities. Simultaneously, it increases the mass proportion of the positive electrode active material in the positive electrode active material, and the contact resistance between the positive electrode active material and the positive electrode additive is low, facilitating battery fabrication. In some embodiments, the positive electrode active material includes sulfur, selenium, or iodine.

[0061] In some embodiments, the positive electrode active material comprises 50% to 80% by mass in the positive electrode active material. It is understood that the proportion of the positive electrode active material in the positive electrode active material can be 50%, 60%, 70%, or 80%, all within the scope of this application. Using the positive electrode additive of this application, a large mass proportion of the positive electrode active material can be maintained in the positive electrode active material, thereby increasing the specific capacity of the positive electrode material and improving the cycle stability of the battery.

[0062] In some embodiments, the mass ratio of the positive electrode additive to the positive electrode active material is (2~10):9. It is understood that the mass ratio can be 2:9, 3:9, 4:9, 5:9, 6:9, 7:9, 8:9, 9:9, or 10:9. Among these, the coulombic efficiency of the battery is lower when the mass ratio is in the range of (5~10):9, mainly because the positive electrode additive initiates an irreversible reaction. Reducing the content of layered additives, so that the mass ratio is within the range of (2~5):9, reduces the irreversible reaction caused by the layered additives, thereby improving the coulombic efficiency.

[0063] In some embodiments, the positive electrode additive is coated on the surface of the positive electrode active material. When the positive electrode additive is coated on the surface of the positive electrode active material, it can effectively suppress side reactions of the electrolyte at the electrode interface, improve the structural stability of the material, enhance electronic conductivity and ion transport performance, thereby improving the cycle performance, rate performance and thermal stability of the battery.

[0064] In some embodiments, the positive electrode active material includes sulfur, and the positive electrode active material further includes a carbon-based conductive material having pores: the sulfur fills the pores of the carbon-based conductive material to form a composite positive electrode active material, and the positive electrode additive is coated on the surface of the composite positive electrode active material.

[0065] It should be noted that the carbon-based conductive material includes porous materials such as carbon nanotubes, graphene, and porous carbon nanotubes, which provide space for sulfur to fill. Sulfur can enter the pores of the carbon-based conductive material in a molten state and fill them.

[0066] In some embodiments, the positive electrode active material is obtained by grinding positive electrode additives and positive electrode active substances, or by synthesizing positive electrode additives in situ on the surface of positive electrode active substance nanoparticles.

[0067] like Figure 1As shown, the preparation of positive electrode active material by grinding method may include the following steps: ball milling process, wherein 1g of sulfur powder and 0.2~0.8g of positive electrode additive are taken, and zirconia ball milling beads are used, with the ball-to-material ratio controlled at 2:1~10:1, that is, the mass of zirconia ball milling beads is controlled at 2.4g~18g. 5 mL of doping solution is added during ball milling; the total ball milling time is 2~4 hours at a speed of 100~300 r / min, wherein the ball milling is carried out alternately in the clockwise and counterclockwise directions, and each ball milling is 10~15min. After each ball milling, the mixture is allowed to stand for 15min before the next ball milling is carried out. The positive electrode active material (a complex of sulfur and positive electrode additive) is collected by vacuum filtration.

[0068] Sulfur can also be replaced with a composite powder composed of sulfur and other materials. Taking sulfur-carbon composite powder as an example, its preparation process is as follows: composite sulfur powder (sulfur powder size of 100nm~10μm) and carbon powder (nano-conductive carbon or carbon nanotubes) are ground in a ratio of 7:3~9.5:0.5, with a total mass of 0.2g~1g; the powder is then treated in a tube furnace at 150~160℃ under argon atmosphere for 12 hours, and the powder is collected and ground for later use.

[0069] The doped solution comprises a solvent and an alkali metal salt. Taking lithium salt as an example, the lithium salt comprises at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium chloride, lithium bromide, lithium hexafluorophosphate, lithium nitrate, lithium fluoroalkyl phosphate, lithium dioxalate borate, lithium difluorooxalate borate, and lithium tetrafluoroborate; the solvent comprises one or more of water, acetonitrile, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, fluoroacetonitrile, ethylene carbonate, fluoroethylene carbonate, methyltrifluoroethyl carbonate, methyl methacrylate, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, hydrofluoroether, dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxane, tetrahydrofuran, toluene, ethanol, ethyl acetate, propyl acetate, and ionic liquids.

[0070] like Figure 2 As shown, the method for in-situ synthesis of positive electrode additives on the surface of nano-sulfur may include the following steps: (1) Firstly, nano-sulfur is synthesized in the liquid phase: 50 mL of an aqueous solution containing 80 mM sodium thiosulfate and 50 mL of a polyvinylpyrrolidone containing 0.4 M with a molecular weight of 55000 Da are prepared; the two solutions are stirred and mixed at room temperature for 1 hour, and then 0.4 mL of concentrated hydrochloric acid is added dropwise to the solution under magnetic stirring. The reaction is carried out for 2 hours; the precipitate is obtained by centrifugation at 7000 r / min, and the precipitate is soaked and washed with 0.8 M polyvinylpyrrolidone aqueous solution for 1 hour, and then the precipitate is obtained by centrifugation at 6000 r / min, which is the nano-sulfur synthesized in the liquid phase. Figure 2(a)). (2) In-situ generation of layered additives on the surface of nano-sulfur: 50 mg of nano-sulfur synthesized in the liquid phase is dispersed in 15 mL of aqueous solution, and 10-150 μL of sulfuric acid or hydrochloric acid and 10-200 μL of polymer monomer material are added. Figure 2 (The product is aniline), stirred for 1 hour to form solution A; 20-1000 mg of crosslinking agent (ammonium metatungstate) and 30-1300 mg of initiator ammonium persulfate were added to 15 mL of deionized water to prepare solution B; solution B was added dropwise to solution A at -5 to 15℃, and the mixture was stirred evenly for 4-12 hours; the product was repeatedly filtered and washed to obtain a solid, which was then dried in a vacuum oven at 60-90℃ to obtain nano-sulfur (a product containing aniline) coated with a multi-metal oxyacid-polymer layered material. Figure 2 (b)). (3) Alkali metal doping (taking lithium doping as an example): 50 mg to 200 mg of nano-sulfur coated with polyoxometalate-polymer layered material is immersed in 10 to 20 mL of the above-mentioned doping solvent (lithium salt concentration of 0.1 M to 3 M) for more than 24 hours. The composition of the doping solvent is the same as above. After multiple immersions, filtration or direct drying with solvent, the positive electrode active material (a complex of sulfur and positive electrode additive) is obtained. Figure 2 (c)

[0071] It should be noted that the in-situ synthesis of nano-sulfur can also directly introduce lithium ions and carry out polymerization reaction in step (2), which can quickly obtain the complex of sulfur and positive electrode additive.

[0072] The present invention also provides a positive electrode sheet, which includes the aforementioned positive electrode active material. Therefore, it possesses all the beneficial effects of the aforementioned positive electrode active material, which will not be elaborated upon here.

[0073] The present invention also provides a solid-state battery, which includes the aforementioned positive electrode. Therefore, it possesses all the beneficial effects of the aforementioned positive electrode, which will not be elaborated further here.

[0074] This invention also provides a method for preparing the aforementioned solid-state battery, comprising the following steps: placing a positive electrode sheet on one side of a solid electrolyte sheet, and applying external pressure to tightly bond the positive electrode sheet and the solid electrolyte sheet to obtain an intermediate body, wherein the external pressure is 2-5 MPa; placing a negative electrode sheet on the other side of the solid electrolyte sheet of the intermediate body, and applying external pressure to tightly bond the negative electrode sheet and the intermediate body to obtain the solid-state battery. Typically, bonding the solid electrolyte and positive electrode material requires high external pressure (>20-30 MPa), which is far higher than the external pressure of this application.

[0075] The present invention also provides an electrical device comprising the aforementioned solid-state battery. Therefore, it possesses all the beneficial effects of the aforementioned solid-state battery, which will not be elaborated further here.

[0076] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0077] Example 1

[0078] A positive electrode active material is prepared by the following steps:

[0079] (1) Preparation of polyoxometalate-polymer layered material: 180 μL of aniline, a polymer monomer, was dissolved in an acidic aqueous solution prepared with 120 μL of sulfuric acid and 10 mL of deionized water to form solution A; 500 mg of ammonium metatungstate, a crosslinking agent, and 680 mg of ammonium persulfate, an initiator, were dissolved in 10 mL of deionized water to prepare solution B; solution B was added dropwise to solution A at below 0℃, and the mixture was stirred and mixed evenly for 12 hours. The solid was obtained by filtration and washing, and then dried in a vacuum oven at 80℃ to obtain polyoxometalate-polymer layered material.

[0080] (2) Preparation of lithium-ion-polyoxometalate-polymer layered additive: 100 mg of the polyoxometalate-polymer layered material obtained above was immersed in 20 mL of doping solution for 24 h. The solvent of the doping solution was N,N-dimethylacetamide, the solute was lithium bis(fluorosulfonyl)imide, and the lithium salt concentration was 2 M. The precipitate was obtained by vacuum filtration. Then the lithium salt solution immersion and vacuum filtration were repeated 3 times. The doping solution was kept consistent each time. Finally, the lithium-ion-polyoxometalate-polymer layered additive was obtained by vacuum filtration.

[0081] (3) Preparation of positive electrode active material: Sulfur powder and carbon nanotubes were ground at a mass ratio of 9:1, with a total mass of 1g. After grinding, the powder was treated in a tube furnace at 155℃ under argon atmosphere for 12 hours. The powder was collected and ground to obtain sulfur-carbon composite powder. Ball milling was used. The ball milling steps were as follows: 1g of sulfur-carbon composite powder and 0.2g of lithium ion-polyoxometalate-polymer layered additive were taken and zirconia ball milling beads were used. The ball-to-material ratio was controlled at 5:1, that is, the mass of the zirconia ball milling beads was controlled at 6g. 5 mL of the above doping solution was added during the ball milling process. The ball milling was carried out at a speed of 100 r / min for a total time of 3 hours. The ball milling was carried out alternately in the clockwise and counterclockwise directions. Each ball milling session lasted 15 minutes. After each ball milling session, the mixture was allowed to stand for 15 minutes before the next ball milling session. The positive electrode active material was collected by vacuum filtration.

[0082] Example 2

[0083] The difference between Example 2 and Example 1 is that:

[0084] In step (2), the solvent of the doping solution is acetonitrile, the solute is lithium bis(fluorosulfonyl)imide, and the lithium salt concentration is 2M.

[0085] Example 3

[0086] The difference between Example 3 and Example 1 is that:

[0087] In step (3), the ball milling step involves taking 1g of sulfur-carbon composite powder and 0.5g of lithium ion-polyoxometalate-polymer layered additive.

[0088] Example 4

[0089] The difference between Example 4 and Example 1 is that:

[0090] In step (3), the ball milling step involves taking 1g of sulfur-carbon composite powder and 0.3g of lithium ion-polyoxometalate-polymer layered additive.

[0091] Example 5

[0092] A positive electrode active material is prepared by the following steps:

[0093] (1) Preparation of wet nano-sulfur: Prepare 50 mL of an aqueous solution containing 80 mM sodium thiosulfate and 50 mL of polyvinylpyrrolidone containing 0.4 M with a molecular weight of 55000 Da. Stir the two solutions at room temperature for 1 hour, and then add 0.4 mL of concentrated hydrochloric acid dropwise to the solution under magnetic stirring. The reaction is carried out for 2 hours. The precipitate is obtained by centrifugation at 7000 r / min. The precipitate is soaked and washed with 0.8 M polyvinylpyrrolidone aqueous solution for 1 hour, and then centrifuged at 6000 r / min to obtain the precipitate, which is the nano-sulfur synthesized in the liquid phase.

[0094] (2) Preparation of nano-sulfur coated with polyoxometalate-polymer layered material: 400 mg of nano-sulfur synthesized in the liquid phase was dispersed in 15 mL of aqueous solution, 150 μL of sulfuric acid and 200 μL of aniline were added, and the mixture was stirred for 1 hour to form solution A; 500 mg of crosslinking agent ammonium metatungstate and 680 mg of initiator ammonium persulfate were added to deionized water to prepare solution B; solution B was added dropwise to solution A at -5℃ and stirred evenly for 4 hours; the solid was obtained by repeated filtration and washing, and dried in a vacuum oven at 90℃ to obtain nano-sulfur coated with polyoxometalate-polymer layered material;

[0095] (3) Preparation of positive electrode active material: 50 mg of nano sulfur coated with polyoxometalate-polymer layered material was immersed in 20 mL of doping solution for 24 h. The doping solution was composed of 1 M lithium bis(trifluoromethylsulfonyl)imide dissolved in dimethyl carbonate. The positive electrode active material was obtained by 5 immersion-filtration.

[0096] Example 6

[0097] The difference between Example 6 and Example 5 is as follows:

[0098] In step (2), 500 mg of crosslinking agent ammonium metatungstate is replaced with 200 mg of crosslinking agent ammonium molybdate.

[0099] Example 7

[0100] The difference between Example 7 and Example 5 is as follows:

[0101] In step (2), 200 μL of aniline is replaced with 200 μL of pyrrole.

[0102] Example 8

[0103] The difference between Example 8 and Example 5 is as follows:

[0104] In step (3), the doping solution is changed to an ethyl acetate solution containing 0.5M lithium bromide and 0.5M lithium hexafluorophosphate.

[0105] Example 9

[0106] The difference between Example 9 and Example 5 is as follows:

[0107] In step (2), the amount of aniline was changed to 300 μL, the amount of crosslinking agent ammonium metatungstate was changed to 750 mg, and the amount of ammonium persulfate was changed to 1020 mg.

[0108] Example 10

[0109] The difference between Example 10 and Example 1 is that:

[0110] In step (3), the ball milling step involves taking 1g of sulfur-carbon composite powder and 0.9g of lithium ion-polyoxometalate-polymer layered additive.

[0111] Example 11

[0112] The difference between Example 11 and Example 1 is that:

[0113] In step (3), the ball milling step involves taking 1g of sulfur-carbon composite powder and 0.1g of lithium ion-polyoxometalate-polymer layered additive.

[0114] Comparative Example 1

[0115] Comparative Example 1 provides a positive electrode active material, which is a sulfur-carbon composite powder (sulfur to carbon mass ratio of 9:1). The preparation method of the sulfur-carbon composite powder is the same as in Example 1 (3).

[0116] Comparative Example 2

[0117] Comparative Example 2 provides a positive electrode active material, which is nano-sulfur. The preparation method of the nano-sulfur is the same as that in Example 5 (1).

[0118] Comparative Example 3

[0119] Comparative Example 3 provides a positive electrode active material, which is sulfur powder.

[0120] Comparative Example 4

[0121] The difference between Comparative Example 4 and Example 1 is that:

[0122] Instead of steps (1) and (2), the lithium-ion-polyoxometalate-polymer layered additive in step (3) is replaced with an equal mass of lithium thiophosphate chloride.

[0123] Performance testing

[0124] The XRD and SEM analyses of the positive electrode active material in Example 5 were performed, and the results are as follows: Figure 3 and Figure 4 As shown. Figure 3 The composite of sulfur with lithium ions-polyoxometalates-polyaniline is shown. "Heteropolyacid-doped polyaniline" refers to the material formed in situ on the surface of elemental sulfur without lithium doping, while "sulfur / lithium-heteropolyacid co-doped polyaniline" refers to the material formed in situ on the surface of elemental sulfur with lithium doping. The peak shift of 6-8 degrees in the figure can show the interlayer spacing after lithium doping. It can be seen that the interlayer spacing increases to 1.35 nm after lithium doping. Figure 4 The morphology of lithium-ion-polyoxometalate-polyaniline-coated sulfur is shown. It can be seen that the sulfur is spherical after coating, with a particle size of 0.2~1μm.

[0125] The positive electrode active materials from Examples 1-11 and Comparative Examples 1-4 were prepared as positive electrode materials and then used to fabricate solid-state lithium-sulfur batteries for performance testing. The preparation methods are as follows:

[0126] (1) Preparation of positive electrode material: The positive electrode active material, conductive carbon black (Super-P) with conductive function, polyvinylidene fluoride (PVDF) with bonding function and N-methylpyrrolidone (NMP) are mixed in a mass ratio of 9:0.5:0.5:100. The mixed material is coated on the surface of carbon-coated aluminum foil and placed in an oven and vacuum dried at 60°C for 6 hours to obtain an electrode sheet. The obtained electrode sheet is made into a circular electrode sheet with a diameter of 12 mm.

[0127] (2) Solid-state lithium-sulfur battery preparation: The above circular electrode sheet is assembled with lithium metal and lithium lanthanum zirconium oxygen electrolyte to form a solid-state lithium-sulfur button cell. At the negative electrode, lithium metal is welded to the surface of lithium lanthanum zirconium oxygen electrolyte. 10~20 mg of succinate is added to the interface between the positive electrode and the solid electrolyte to lubricate the interface. An external pressure of 5 MPa is applied to make it fit tightly to obtain a solid-state lithium-sulfur battery.

[0128] The testing method is as follows:

[0129] (a) Electrochemical impedance spectroscopy (EIS): The assembled solid lithium-sulfur battery was tested using an electrochemical workstation. The test conditions were an AC signal frequency of 100 mHz to 1 MHz and a voltage amplitude of 10 mV. The EIS impedance diagram was obtained, and the sum of the diameters of the two semicircles of the EIS was obtained by fitting the EIS diagram.

[0130] (b) Test charge-discharge curve at 0.1C: The assembled solid lithium-sulfur battery was tested using a constant current charge-discharge tester with a charge-discharge current of 0.1C. The charge-discharge curve was obtained and the initial charging capacity was calculated. The initial coulombic efficiency was calculated: Initial coulombic efficiency (%) = initial discharge capacity / initial charge capacity.

[0131] (c) Battery Cycling: The assembled solid lithium-sulfur battery is cycled using a constant current charge-discharge tester. The constant current charge-discharge is 0.1C. The capacity retention rate is calculated as follows: Capacity retention rate (%) = Charged capacity after 20 cycles / Initial charged capacity.

[0132] The test results are shown in Table 1.

[0133] Table 1 Performance characterization of solid-state lithium-sulfur batteries corresponding to Examples 1-11 and Comparative Examples 1-4

[0134]

[0135] During the testing process, a control group battery was set up compared to the battery in Example 1. The control group battery differed from the battery in Example 1 in that the positive electrode active material, conductive carbon black (Super-P) with conductive function, polyvinylidene fluoride (PVDF) with binding function, and N-methylpyrrolidone (NMP) were mixed in a mass ratio of 8:1:1:100, while the remaining preparation steps were the same as those in Example 1. Testing revealed that at room temperature, the battery impedance obtained by EIS testing was 350Ω, and the first-cycle reversible charge-discharge capacity was 1360 mAh / g when the charge-discharge curve was tested at 0.1C. The post-cycle capacity was 940 mAh / g.

[0136] As shown in Table 1, due to the ion-conducting and electron-conducting effects of lithium ions-polyoxometalates-polyaniline, compared with the comparative example, the full cell with lithium ions-polyoxometalates-polyaniline as an additive in the positive electrode has a lower impedance, i.e., higher electronic conductivity, and a higher discharge capacity. A comparison of Examples 1 (additive to sulfur mass ratio of 2:9), 3 (additive to sulfur mass ratio of 5:9), 4 (additive to sulfur mass ratio of 3:9), and 10 (additive to sulfur mass ratio of 9:9) reveals that because of the irreversible reaction between lithium ions-polyoxometalates-polyaniline, when the mass ratio of its addition to sulfur is in the range of (2~3:9), the assembled battery exhibits a higher initial coulombic efficiency, which is beneficial for improving cycle stability. Comparing Examples 1, 3, and 4, it was found that when the mass ratio of additive to sulfur is greater than 2:9, the battery capacity retention rate decreases, but it can still maintain a good initial coulombic efficiency. Comparing Examples 4 and 5, the mass ratio of additive to sulfur in Example 5 is also 3:9, but its capacity retention rate is better than that of the polymer monomer in situ synthesized on the surface of nano-sulfur in Example 5. This is because the polyvinylpyrrolidone introduced during the synthesis of nano-sulfur may decompose during battery cycling, resulting in irreversible reactions and capacity loss.

[0137] The EIS impedance, charge-discharge curves, and cycle performance of the positive electrode active materials of Example 5 and Comparative Example 1 were tested, and the results are as follows: Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 , Figure 10 As shown in the figure, comparison revealed that the full cell with lithium-ion-polyoxometalate-polyaniline as an additive in the positive electrode exhibited lower impedance, higher discharge capacity, and higher cycle retention. In the figure, "additive" refers to the positive electrode additive provided by this invention.

[0138] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material comprises a positive electrode active substance and a positive electrode additive; the positive electrode additive comprises a conductive layered body and alkali metal ions, the conductive layered body has a multi-layer sheet structure, each sheet structure comprises a polymer chain, every two adjacent sheet structures are connected by a polyoxometallic crosslinking agent, and the alkali metal ions are at least doped between adjacent sheet structures; The positive electrode active material comprises a positive electrode active substance and a positive electrode additive, and the mass ratio of the positive electrode additive to the positive electrode active substance is (2-10):9; In the positive electrode additive, the mass ratio of the polymer chain, the polyoxometallic crosslinking agent, and the alkali metal ions is (3-10):(83-93):(0.5-6); The alkali metal ions comprise lithium ions, sodium ions, or potassium ions; The polyoxometallic crosslinking agent comprises tungstic acid, molybdic acid, phosphotungstic acid, or silicotungstic acid; The polymer in the polymer chain comprises polyaniline, polypyrrole, or polythiophene; The polyoxometallic crosslinking agent is connected to the polymer chain in every two adjacent sheet structures by a hydrogen bond; The positive electrode additive further comprises a solvent, the solvent is at least doped between adjacent sheet structures, and the mass fraction of the solvent in the positive electrode additive is 5%-7%.

2. The positive electrode active material according to claim 1, wherein The ionic conductivity of the positive electrode additive is 0.3-1 mS / cm, and the electronic conductivity of the positive electrode additive is 5-7 S / cm.

3. The positive electrode active material according to claim 1, wherein The positive electrode active substance comprises sulfur, selenium, or iodine.

4. The positive electrode active material according to claim 1, wherein In the positive electrode active material, the mass fraction of the positive electrode active substance is 50%-80%.

5. The positive electrode active material according to claim 1, wherein The positive electrode additive is coated on the surface of the positive electrode active substance.

6. The positive electrode active material according to claim 5, wherein The positive electrode active substance comprises sulfur, and the positive electrode active material further comprises a carbon-based conductive material, the carbon-based conductive material has pores: The sulfur is filled in the pores of the carbon-based conductive material to form a composite positive electrode active substance, and the positive electrode additive is coated on the surface of the composite positive electrode active substance.

7. The positive electrode active material according to claim 1, wherein The positive electrode active material is obtained by grinding a positive electrode additive and a positive electrode active substance, or by in-situ synthesizing a positive electrode additive on the surface of a positive electrode active substance nanoparticle.

8. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the positive electrode active material according to any one of claims 1-7.

9. A solid state battery, characterized by The solid-state battery comprises the positive electrode sheet according to claim 8.

10. A method of producing a solid-state battery as claimed in claim 9, characterized in that, The method comprises the following steps: placing a positive electrode sheet on one side of a solid-state electrolyte sheet, and tightly adhering the positive electrode sheet and the solid-state electrolyte sheet by applying an external pressure, to obtain an intermediate, wherein the external pressure is 2-5 MPa; placing a negative electrode sheet on the other side of the solid-state electrolyte sheet of the intermediate, and tightly adhering the negative electrode sheet and the intermediate by applying an external pressure, to obtain the solid-state battery.

11. An electrical device, characterized by The power utilization device comprises the solid-state battery according to claim 9.

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