Positive pole piece and sulfide all-solid-state battery comprising same

Abstract

The invention relates to a positive pole piece which comprises a positive current collector and a positive active material layer arranged on at least one surface of the positive current collector, and the positive active material layer comprises a positive active material, sulfide solid electrolyte and a core-shell flame retardant, the core-shell type flame retardant comprises a core, a first shell layer coating the core, a second shell layer coating the first shell layer and a third shell layer coating the second shell layer, the core comprises an organic flame retardant, the first shell layer comprises a thermal response polymer, the melting point of the thermal response polymer is 125-275 DEG C, the second shell layer comprises an inorganic flame retardant, and the third shell layer comprises an inorganic flame retardant. And the third shell layer comprises a conductive polymer and a carbon nanomaterial. The positive pole piece provided by the invention has improved safety, and also has enhanced compression resistance and conductivity.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a positive electrode sheet and a sulfide all-solid-state battery comprising the positive electrode sheet. Background Art

[0002] All-solid-state batteries exhibit significant advantages over traditional liquid lithium-ion batteries. They have higher energy density and can use high-voltage cathode materials and metallic lithium anodes. The current energy density has reached 500Wh / kg, far exceeding the 20-300Wh / kg of traditional liquid lithium batteries. At the same time, all-solid-state batteries have also significantly improved safety. The solid-state electrolyte has good thermal stability, no risk of liquid leakage, and stable performance in low-temperature environments. In addition, all-solid-state batteries have a long cycle life, the solid-state electrolyte ages slowly, and the design is flexible, making them suitable for a variety of application scenarios.

[0003] Sulfide solid electrolytes are an important technical route for all-solid-state batteries due to their high ionic conductivity and good mechanical properties. Their ionic conductivity is comparable to that of liquid electrolytes, their electrochemical window exceeds 5V, and they can be in close contact with the positive electrode active material through simple cold pressing. However, sulfide solid electrolytes are reactive with both the positive electrode material and the lithium metal negative electrode, and the high-energy-density positive electrode material / sulfide electrolyte composite positive electrode has insufficient thermal stability, which becomes a safety performance shortcoming. In addition, although the thermal runaway temperature of sulfide all-solid-state batteries is higher than that of liquid batteries, the degree of harm after thermal runaway is higher, so it is crucial to improve the thermal safety performance of sulfide all-solid-state batteries. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a positive electrode plate, which has improved safety and enhanced compressive resistance and conductivity. The second purpose is to provide a sulfide all-solid-state battery including the positive electrode plate.

[0005] In order to achieve the above-mentioned objectives, one aspect of the present invention provides a positive electrode plate, which includes a positive electrode collector and a positive electrode active material layer arranged on at least one surface of the positive electrode collector, the positive electrode active material layer including a positive electrode active material, a sulfide solid electrolyte and a core-shell flame retardant, the core-shell flame retardant including a core, a first shell layer coated on the core, a second shell layer coated on the first shell layer and a third shell layer coated on the second shell layer, wherein the core includes an organic flame retardant, the first shell layer includes a thermoresponsive polymer, the melting point of the thermoresponsive polymer is 125°C to 275°C, the second shell layer includes an inorganic flame retardant, and the third shell layer includes a conductive polymer and a carbon nanomaterial.

[0006] In some embodiments, the conductive polymer is selected from one or more of polythiophene, polyaniline, poly(p-phenylene vinylene), polypyrrole, poly(p-phenylene vinylene), or polyacetylene.

[0007] In some embodiments, the carbon nanomaterial is selected from one or more of carbon nanotubes, nanographenes, or nanocarbon fibers.

[0008] In some embodiments, in the third shell layer, the weight ratio of the carbon nanomaterial to the conductive polymer is 1 to 5:6.

[0009] In some embodiments, the inorganic flame retardant is selected from one or more of aluminum hydroxide, magnesium hydroxide, or magnesium aluminum double hydroxide.

[0010] In some embodiments, the organic flame retardant is selected from one or more of decabromodiphenyl ethane, octabromoether, triphenyl phosphate, tricresyl phosphate, or decabromodiphenyl ether.

[0011] In some embodiments, the thermoresponsive polymer is selected from one or more of urea-formaldehyde resin, polylactic acid, polyethylene oxide, polystyrene, polyethylene glycol, or polyamide.

[0012] In some embodiments, relative to the total weight of the core-shell flame retardant, the weight percentage of the core is 20% to 45%, the weight percentage of the first shell layer is 5% to 25%, the weight percentage of the second shell layer is 5% to 30%, and the weight percentage of the third shell layer is 5% to 25%.

[0013] In some embodiments, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, or lithium nickel cobalt aluminum oxide.

[0014] In some embodiments, the sulfide solid electrolyte is selected from one or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0015] Another aspect of the present invention provides a sulfide all-solid-state battery, which includes the positive electrode sheet described above.

[0016] The positive electrode plate of the present invention includes a positive electrode active material layer, which includes a core-shell flame retardant. The core-shell flame retardant includes an organic flame retardant as a core, which can effectively capture active free radicals (such as OH·) and dilute combustible gases. The core-shell flame retardant includes a thermally responsive polymer as a first shell layer, and the melting point of the thermally responsive polymer is 125 to 275°C. When the battery reaches an abnormally high temperature and reaches the melting point of the thermally responsive polymer, the thermally responsive polymer melts, thereby exposing the organic flame retardant as the core and exerting its flame retardant effect. The core-shell flame retardant includes an inorganic flame retardant as a second shell layer, which decomposes and absorbs a large amount of heat when heated, while releasing water vapor, which plays a role in cooling and diluting combustible gases, thereby helping to enhance the flame retardant effect. The core-shell flame retardant includes a conductive polymer and a carbon nanomaterial as a third shell layer. The carbon nanomaterial and the conductive polymer form a composite network layer, which not only improves the compressive performance of the positive electrode sheet and helps maintain the structural integrity of the positive electrode sheet during the isostatic pressing process, but also helps enhance the conductivity of the positive electrode sheet. Even if some positive electrode active material particles move or deform during battery cycling, the conductive network can still remain relatively intact, which is conducive to the efficient transmission of electrons. Therefore, by including the above-mentioned core-shell flame retardant in the positive electrode active material layer, the thermal safety performance of the positive electrode sheet can be significantly improved, while enhancing its compressive performance and conductivity, thereby improving the thermal safety and electrical performance of the sulfide all-solid-state battery including it. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A schematic cross-sectional structure diagram of the core-shell flame retardant particles prepared in Preparation Example 1 is shown.

[0018] Description of reference numerals:

[0019] 1: core; 2: first shell; 3: second shell; 4: third shell. DETAILED DESCRIPTION

[0020] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0021] Sulfide solid electrolytes are an important technical route for all-solid-state batteries due to their high ionic conductivity and good mechanical properties. Their ionic conductivity is comparable to that of liquid electrolytes, their electrochemical window exceeds 5V, and they can be in close contact with the positive electrode active material through simple cold pressing. However, sulfide solid electrolytes are reactive with both the positive electrode material and the lithium metal negative electrode, and the high-energy-density positive electrode material / sulfide electrolyte composite positive electrode sheet has insufficient thermal stability, which becomes a safety performance shortcoming. In addition, although the thermal runaway temperature of sulfide all-solid-state batteries is higher than that of liquid batteries, the degree of harm after thermal runaway is higher, so it is crucial to improve the thermal safety performance of sulfide all-solid-state batteries.

[0022] Therefore, a technology is needed to improve the thermal safety performance of the positive electrode material / sulfide electrolyte composite positive electrode sheet, while enhancing its compressive resistance and conductivity, thereby improving the thermal safety and electrical performance of the sulfide all-solid-state battery containing it.

[0023] Based on this, one aspect of the present invention provides a positive electrode plate. The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a sulfide solid electrolyte and a core-shell flame retardant. The core-shell flame retardant includes a core, a first shell layer coated on the core, a second shell layer coated on the first shell layer and a third shell layer coated on the second shell layer. Among them, the core includes an organic flame retardant, the first shell layer includes a thermoresponsive polymer, the melting point of the thermoresponsive polymer is 125 to 275°C, the second shell layer includes an inorganic flame retardant, and the third shell layer includes a conductive polymer and a carbon nanomaterial.

[0024] The positive electrode active material layer of the positive electrode plate of the present invention includes a core-shell flame retardant. The core-shell flame retardant includes an organic flame retardant as a core, a thermally responsive polymer as a first shell layer, an inorganic flame retardant as a second shell layer, and a conductive polymer and a carbon nanomaterial as a third shell layer. The organic flame retardant as the core can effectively capture active free radicals (such as OH·) and dilute combustible gases. The melting point of the thermally responsive polymer as the first shell layer is 125 to 275°C. When the battery reaches an abnormally high temperature and reaches the melting point of the thermally responsive polymer, the thermally responsive polymer melts, thereby exposing the organic flame retardant as the core and exerting its flame retardant effect. The inorganic flame retardant as the second shell layer will decompose and absorb a large amount of heat when heated, while releasing water vapor, which plays a role in cooling and diluting the combustible gas, thereby helping to enhance the flame retardant effect. The carbon nanomaterial and conductive polymer used as the third shell form a composite network layer, which not only improves the compressive performance of the positive electrode sheet and helps maintain the structural integrity of the positive electrode sheet during the isostatic pressing process, but also helps enhance the conductivity of the positive electrode sheet. Even if some positive electrode active material particles move or deform during the battery cycle, the conductive network can still remain relatively intact, which is conducive to the efficient transmission of electrons. Therefore, by including the above-mentioned core-shell flame retardant in the positive electrode active material layer, the thermal safety performance of the positive electrode sheet can be significantly improved, while enhancing its compressive performance and conductivity, thereby improving the thermal safety and electrical performance of the sulfide all-solid-state battery including it.

[0025] In some embodiments, the organic flame retardant can be selected from one or more of decabromodiphenylethane, octabromoether, triphenyl phosphate, tricresyl phosphate, or decabromodiphenyl ether. Alternatively, the organic flame retardant can be selected from decabromodiphenylethane. These organic flame retardants are used to capture active free radicals (such as OH·) and dilute combustible gases, thereby exerting a flame retardant effect.

[0026] In some embodiments, the thermally responsive polymer can be selected from one or more of urea-formaldehyde resin, polylactic acid, polyethylene oxide, polystyrene, polyethylene glycol, and polyamide. Alternatively, the polyamide can be selected from polycaprolactam. These thermally responsive polymers are used to coat the organic flame retardant serving as the core. They can melt at an appropriate melting point to expose the organic flame retardant in the core, thereby allowing the core to exert its flame retardant effect.

[0027] In some embodiments, the inorganic flame retardant can be selected from one or more of aluminum hydroxide, magnesium hydroxide, and magnesium-aluminum double hydroxide. Alternatively, the inorganic flame retardant can be selected from aluminum hydroxide. These inorganic flame retardants are coated on the surface of the thermally responsive polymer serving as the first shell layer to absorb heat and reduce temperature, thereby helping to enhance the flame retardant effect.

[0028] In some embodiments, the conductive polymer may be selected from one or more of polythiophene, polyaniline, poly(p-phenylene vinylene), polypyrrole, poly(p-phenylene vinylene), or polyacetylene. Alternatively, the conductive polymer may be selected from polyaniline.

[0029] In some embodiments, the carbon nanomaterial can be selected from one or more of carbon nanotubes, nanographene, and nanocarbon fibers. Alternatively, the carbon nanomaterial can be selected from carbon nanotubes.

[0030] In the core-shell flame retardant of the present invention, the third shell layer includes carbon nanomaterials and conductive polymers. The carbon nanomaterials and the conductive polymers form a composite network layer, which is coated on the surface of the inorganic flame retardant as the second shell layer. Carbon nanomaterials have extremely high strength and modulus, and can significantly improve the compressive strength and impact resistance of the materials containing them. Therefore, it is beneficial to enhance the compressive performance of the positive electrode sheet. Conductive polymers and carbon nanomaterials have good electrical conductivity. They help to form a continuous conductive network in the positive electrode sheet, thereby effectively connecting the positive electrode active material particles, reducing the resistance to electron transfer, and thus improving the overall conductivity of the positive electrode sheet. Therefore, the third shell layer can not only improve the compressive performance of the positive electrode sheet, but also help to enhance the conductivity of the positive electrode sheet.

[0031] In some embodiments, in the third shell layer, the weight ratio of the carbon nanomaterial to the conductive polymer can be 1 to 5:6. For example, the weight ratio of the carbon nanomaterial to the conductive polymer can be 1:6, 2:6, 3:6, 4:6, 5:6, or a value between the ranges formed by any two of these values. Controlling the weight ratio of the carbon nanomaterial to the conductive polymer within this range is conducive to giving full play to the compressive enhancement effect of the carbon nanomaterial, while taking into account the conductivity increase effect produced by the conductive polymer and the carbon nanomaterial. Carbon nanomaterials with too low a content ratio cannot make the material exhibit a compressive enhancement effect, while carbon nanomaterials with too high a content ratio are prone to agglomeration, resulting in stress concentration, thereby reducing the compressive performance.

[0032] In some embodiments, relative to the total weight of the core-shell flame retardant, the weight percentage of the core can be 20% to 45%, the weight percentage of the first shell layer can be 5% to 25%, the weight percentage of the second shell layer can be 5% to 30%, and the weight percentage of the third shell layer can be 5% to 25%.

[0033] The weight percentage of the core can be 20% to 45% relative to the total weight of the core-shell flame retardant. For example, the weight percentage of the core can be 20%, 25%, 30%, 35%, 40%, 45%, or a range consisting of any two of these values ​​relative to the total weight of the core-shell flame retardant. The organic flame retardant content in the core must reach a certain proportion to exert an effective flame retardant effect. When its content is ≥20%, the core-shell flame retardant can have the required flame retardant properties. When its content is ≤45%, it helps balance the overall performance of the core-shell flame retardant. Excessive organic flame retardant may reduce the compatibility between the core and the shell layers, easily making the core-shell flame retardant brittle and reducing its mechanical properties.

[0034] The weight percentage of the first shell layer can be 5% to 25% relative to the total weight of the core-shell flame retardant. For example, the weight percentage of the first shell layer can be 5%, 10%, 15%, 20%, 25%, or a range between any two of these values ​​relative to the total weight of the core-shell flame retardant. Within the range of 5% to 25%, the first shell layer can effectively respond to thermal stimulation and form an effective thermal response layer. Below 5%, a complete and effective shell layer cannot be formed, and above 25% may make the first shell layer too brittle and hard, while also increasing costs.

[0035] The weight percentage of the second shell layer relative to the total weight of the core-shell flame retardant can be 5% to 30%. For example, the weight percentage of the second shell layer relative to the total weight of the core-shell flame retardant can be 5%, 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of these values. Within the 5% to 30% range, the second shell layer can effectively absorb heat and reduce temperatures without significantly increasing costs. A percentage below 5% can result in insufficient flame retardancy, while a percentage above 30% can result in an excessively thick shell layer, which can slow the release of the core organic flame retardant.

[0036] The weight percentage of the third shell layer can be 5% to 25% relative to the total weight of the core-shell flame retardant. For example, the weight percentage of the third shell layer can be 5%, 10%, 15%, 20%, 25%, or a range between any two of these values ​​relative to the total weight of the core-shell flame retardant. Within the range of 5% to 25%, the third shell layer can effectively improve electrical conductivity and compressive resistance. Below 5%, an effective conductive network cannot be formed, and above 25%, the material will become brittle due to interfacial stress concentration, while increasing costs.

[0037] By controlling the weight percentages of the core, the first, the second and the third shell layers within the above range, it is beneficial to achieve a comprehensive balance in terms of mechanical properties, processing properties, cost, etc. while achieving excellent flame retardancy, conductivity and compressive resistance of the core-shell flame retardant.

[0038] In some embodiments, the average thickness of the first shell layer can be 20nm to 120nm. For example, the average thickness of the first shell layer can be 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm or a value between the ranges consisting of any two of these values. By controlling the average thickness of the first shell layer within this range, the core can be effectively wrapped while maintaining the thermal response speed, and jointly exerting a flame retardant effect with the subsequent shell layers. When the average thickness of the first shell layer is greater than 120nm, the flame retardant effect is delayed and the cost increases. When the average thickness of the first shell layer is less than 20nm, there is a possibility that the core cannot be completely wrapped, thereby insufficient protection of the core and insufficient thermal response, thereby weakening the function of jointly exerting a flame retardant effect with the subsequent shell layers.

[0039] In some embodiments, the average thickness of the second shell layer can be 10 nm to 80 nm. For example, the average thickness of the second shell layer can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or a value between the ranges consisting of any two of these values. Controlling the average thickness of the second shell layer within this range is conducive to the inorganic flame retardant absorbing heat, releasing water vapor, cooling and diluting the combustible gas, thereby effectively exerting its flame retardant properties. When the average thickness of the second shell layer is greater than 80 nm, the flame retardant effect is limited, but the cost increases. When the average thickness of the second shell layer is less than 10 nm, the flame retardant effect is insufficient.

[0040] In some embodiments, the average thickness of the third shell layer may be 20 nm to 50 nm. For example, the average thickness of the third shell layer may be 20 nm, 30 nm, 40 nm, 50 nm, or a range consisting of any two of these values. Controlling the average thickness of the third shell layer within this range is conducive to the third shell layer fully exerting its electrical conductivity and compressive resistance. When the average thickness of the third shell layer is greater than 50 nm, the improvement in electrical conductivity and compressive resistance is limited, but the cost increases. When the average thickness of the third shell layer is less than 20 nm, the improvement in electrical conductivity and compressive resistance is not significant.

[0041] The average thickness of the first, second and third shell layers can be measured using instruments and methods known in the art, for example, using a transmission electron microscope.

[0042] In some embodiments, the positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, or lithium nickel cobalt aluminum oxide.

[0043] In some embodiments, the weight percentage of the core-shell flame retardant in the positive electrode active material layer can be 1% to 5% relative to the total weight of the positive electrode active material layer. For example, the weight percentage of the core-shell flame retardant can be 1%, 2%, 3%, 4%, 5%, or a range between any two of these values. Controlling the weight percentage of the core-shell flame retardant within this range helps provide an effective flame retardant effect while avoiding the negative impact of excessive flame retardant on energy density.

[0044] In some embodiments, the sulfide solid electrolyte can be selected from one or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I. The weight percentage of the sulfide solid electrolyte in the positive electrode active material layer can be 20% to 32% relative to the total weight of the positive electrode active material layer. For example, the weight percentage of the sulfide solid electrolyte can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, or a range consisting of any two of these values. Controlling the weight percentage of the sulfide solid electrolyte within this range can effectively increase the lithium ion diffusion rate and reduce interfacial impedance. When the weight percentage of the sulfide solid electrolyte exceeds 32%, the proportion of the positive electrode active material decreases, negatively impacting energy density. When the weight percentage of the sulfide solid electrolyte is less than 20%, the ion transport channels within the positive electrode plate become discontinuous or insufficient, increasing the ion transport resistance within the plate and leading to increased battery polarization.

[0045] Another aspect of the present invention provides a method for preparing a core-shell flame retardant. The method comprises the following steps:

[0046] S11: Provide organic flame retardant as core;

[0047] S12: Preparing a first shell layer on the surface of the core, comprising: preparing a solution of a monomer or prepolymer for forming the first shell layer; dispersing an organic flame retardant in the solution of the monomer or prepolymer to obtain a first mixed solution; adding an initiator or catalyst to the first mixed solution, and causing the monomer or prepolymer to undergo a polymerization reaction to obtain a first core-shell intermediate having the first shell layer on the surface of the core;

[0048] S13: preparing a second shell layer on the surface of the first shell layer, comprising: using a precursor of the second shell layer to prepare a sol for forming the second shell layer; immersing the first core-shell intermediate in the sol for a period of time; and then separating the first core-shell intermediate dipped in the sol from the sol to obtain a second core-shell intermediate having the second shell layer on the surface of the first shell layer;

[0049] S14: Preparing a third shell layer on the surface of the second shell layer, comprising: preparing a solution of a monomer or prepolymer for forming a conductive polymer; adding a carbon nanomaterial and a second core-shell intermediate to the solution of the monomer or prepolymer to obtain a second mixed solution; adding an initiator to the second mixed solution, and causing the monomer or prepolymer to undergo polymerization reaction to obtain a core-shell flame retardant having a third shell layer on the surface of the second shell layer.

[0050] In some embodiments, in step S11, the organic flame retardant can be selected from one or more of decabromodiphenylethane, octabromoether, triphenyl phosphate, tricresyl phosphate, or decabromodiphenyl ether. These organic flame retardants are used to capture active free radicals (such as OH·) and dilute combustible gases, thereby exerting a flame retardant effect.

[0051] In some embodiments, in step S12, the first shell layer includes a thermally responsive polymer. The thermally responsive polymer can be selected from one or more of urea-formaldehyde resin, polylactic acid, polyethylene oxide, polystyrene, polyethylene glycol or polyamide. These thermally responsive polymers are used to coat the organic flame retardant as the core, which can melt at an appropriate melting point to expose the core, thereby allowing the core to exert its flame retardant effect. Accordingly, the monomer or prepolymer used to form the first shell layer can include a monomer or prepolymer for forming the above-mentioned thermally responsive polymer. In step S12, the initiator or catalyst can be those conventionally used in the art, as long as the above-mentioned monomer or prepolymer can be polymerized. For example, the initiator or catalyst can be selected from one or more of p-toluenesulfonic acid, sodium hydroxide, ammonium chloride, and dibenzoyl peroxide. Alternatively, step S12 can also include the operation of separating the first core-shell intermediate from the reaction system. Exemplarily, the separation method includes centrifugation, filtration, etc., but is not limited thereto.

[0052] In some embodiments, in step S13, the second shell layer includes an inorganic flame retardant. The inorganic flame retardant can be selected from one or more of aluminum hydroxide, magnesium hydroxide, and magnesium-aluminum double hydroxide. These inorganic flame retardants are coated on the surface of the thermoresponsive polymer serving as the first shell layer to absorb heat and reduce temperature, thereby enhancing the flame retardant effect. Accordingly, the precursor of the second shell layer can be aluminum isopropoxide, magnesium isopropoxide, etc., but is not limited thereto.

[0053] In some embodiments, in step S14, the conductive polymer may be selected from one or more of polythiophene, polyaniline, poly(p-phenylene vinylene), polypyrrole, poly(p-phenylene vinylene) or polyacetylene. Accordingly, the monomer or prepolymer used to form the conductive polymer may include the monomer or prepolymer used to form the above-mentioned conductive polymer. In step S14, the initiator may be those initiators conventionally used in the art, as long as it can polymerize the above-mentioned monomer or prepolymer. For example, the initiator may be selected from one or more of ammonium persulfate, potassium persulfate, ferric chloride, and dibenzoyl peroxide. In step S14, the carbon nanomaterial may be selected from one or more of carbon nanotubes, nanographene, and nanocarbon fibers. In step S14, the carbon nanomaterial and the conductive polymer form a composite network layer, which can not only improve the compressive performance of the positive electrode sheet, but also help the positive electrode sheet maintain structural integrity during the isostatic pressing process, and can also enhance the conductivity of the positive electrode sheet.

[0054] Another aspect of the present invention provides a method for preparing a positive electrode sheet. The method comprises the following steps:

[0055] S21: preparing a dispersion of a core-shell flame retardant, comprising: dispersing the core-shell flame retardant of the present invention in a solvent to obtain a dispersion of the core-shell flame retardant;

[0056] S22: preparing a binder glue solution, including: dispersing a binder in a solvent to obtain a binder glue solution;

[0057] S23: preparing a conductive agent glue solution, comprising: adding a conductive agent to the binder glue solution obtained in step S22 to obtain a conductive agent glue solution;

[0058] S24: preparing a positive electrode slurry, comprising: adding the core-shell flame retardant dispersion obtained in step 21, the positive electrode active material, and the sulfide solid electrolyte to the conductive agent paste obtained in step S23 to obtain a positive electrode slurry;

[0059] S25: preparing a positive electrode sheet, including: coating the positive electrode slurry obtained in step S24 on at least one surface of the positive electrode collector; drying the positive electrode collector coated with the positive electrode slurry; and then compacting to obtain a positive electrode sheet.

[0060] In some embodiments, in step S21, the solvent used to disperse the core-shell flame retardant can be selected from one or more of xylene, tetrahydrofuran, and toluene. Alternatively, in step S21, dispersing the core-shell flame retardant of the present application in the solvent includes adding the core-shell flame retardant to the solvent to obtain a dispersion, and then ultrasonically treating the dispersion. This facilitates sufficient dispersion of the core-shell flame retardant in the solvent, forming a uniform and stable dispersion.

[0061] In some embodiments, in step S22, the binder can be selected from one or more of styrene-ethylene-butylene-styrene block copolymer (SEBS), polytetrafluoroethylene, polyvinylidene fluoride, and hydrogenated nitrile butadiene rubber. The solvent can be selected from one or more of xylene, tetrahydrofuran, and toluene. Alternatively, in step S22, dispersing the binder in the solvent includes slowly adding the binder to the solvent and stirring at an appropriate speed so that the binder is uniformly dispersed in the solvent. This helps to obtain a uniformly dispersed binder glue.

[0062] In some embodiments, in step S23, the conductive agent can be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon fibers. Alternatively, in step S23, after adding the conductive agent to the binder paste obtained in step S22, the resulting mixed paste is stirred to uniformly disperse the conductive agent in the mixed paste. This facilitates obtaining a conductive agent paste that is uniformly dispersed and has excellent conductivity.

[0063] In some embodiments, in step S24, the positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium iron manganese phosphate, lithium-rich manganese-based materials, or lithium nickel cobalt aluminum oxide. In some embodiments, in step S24, the sulfide solid electrolyte can be selected from one or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I.

[0064] In some embodiments, in step S25, the positive electrode current collector can be selected from one or more of aluminum foil and nickel foil. Optionally, the drying temperature can be 60°C to 120°C. For example, the drying temperature can be 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, or a range between any two of these values. Optionally, compaction includes roller pressing the dried positive electrode sheet. Compaction makes the positive electrode sheet more compact, thereby improving its mechanical strength and electrochemical performance.

[0065] Another aspect of the present invention provides a sulfide all-solid-state battery, which includes the positive electrode sheet described above or the positive electrode sheet prepared by the method described above.

[0066] The embodiments of the present invention are described in detail below with reference to the examples and drawings. It should be understood that the following examples are only for illustrative purposes only and should not be construed as limiting the present invention.

[0067] Preparation Example 1: Preparation of core-shell flame retardant FR1

[0068] The core-shell flame retardant FR1 was prepared by the following steps.

[0069] 1) Dissolve 10 g of caprolactam in 100 g of ethylene glycol to obtain a caprolactam solution.

[0070] 2) Weigh 40 g of decabromodiphenylethane and add it to the caprolactam solution, and then stir at a speed of 1000 r / min for 60 minutes to ensure that the decabromodiphenylethane particles as an organic flame retardant are fully mixed and dispersed in the caprolactam solution.

[0071] 3) The solution obtained in step 2) was heated to 70° C., and 0.5 g of sodium hydroxide catalyst was added thereto while stirring at a speed of 500 r / min. The polymerization reaction was carried out for 4 hours to polymerize the monomer caprolactam on the surface of the decabromodiphenylethane particles to form first core-shell intermediate particles having a first shell layer of polycaprolactam.

[0072] 4) Stop heating and cool naturally to room temperature to obtain a suspension of first core-shell intermediate particles. After separation and washing, obtain first core-shell intermediate particles.

[0073] 5) Weigh 78.6 g of aluminum isopropoxide, slowly add 100 g of deionized water, stir at 300 r / min, and hydrolyze for 1 hour. Slowly add 0.5 M dilute nitric acid to adjust the pH to 3-4, and let it stand for 12 hours to form a uniform gel sol.

[0074] 6) Immersing the first core-shell intermediate particles having a first shell layer into the above sol, stirring at a speed of 100 r / min for 15 minutes, and centrifugally drying to obtain second core-shell intermediate particles having a second shell layer of aluminum hydroxide.

[0075] 7) Dissolve 10.91 g of aniline in 50 g of ethanol to obtain an aniline ethanol solution. Add the second core-shell intermediate particles prepared in step 6) and 9.09 g of carbon nanotubes (CNTs) to the aniline solution and stir at 800 rpm for 30 minutes using a high-speed stirrer to fully disperse the particles. The weight ratio of the CNTs to the aniline is 5:6.

[0076] 8) Add ammonium persulfate to the system from step 7) in an amount of 1% by weight of the aniline monomer. The reaction system is kept at 0°C and stirred at 400 rpm for 6 hours to polymerize the aniline monomer on the surface of the core-shell structure, forming a conductive layer.

[0077] 9) Stop the reaction, separate and wash to obtain a core-shell flame retardant having a core and three shell layers. Figure 1 A schematic diagram of the cross-sectional structure of the core-shell flame retardant particles is shown.

[0078] Preparation Example 2: Preparation of core-shell flame retardant FR2

[0079] Core-shell flame retardant FR2 was prepared according to the method of Preparation Example 1, except that in step 7), the amounts of carbon nanotubes and aniline monomer added were 2.86 g and 17.14 g, respectively, with a weight ratio of carbon nanotubes to aniline of 1:6.

[0080] Preparation Example 3: Preparation of core-shell flame retardant C-FR1

[0081] The core-shell flame retardant C-FR1 was prepared according to the method of Preparation Example 1, except that in step 7), the amount of aniline monomer added was 20 g, and no carbon nanotubes were added.

[0082] Preparation Example 4: Preparation of core-shell flame retardant C-FR2

[0083] Core-shell flame retardant C-FR2 was prepared according to the method of Preparation Example 1, except that in step 7), the amounts of carbon nanotubes and aniline monomer added were 2.5 g and 17.5 g, respectively, and the weight ratio of carbon nanotubes to aniline was 0.85:6.

[0084] Preparation Example 5: Preparation of core-shell flame retardant C-FR3

[0085] Core-shell flame retardant C-FR3 was prepared according to the method of Preparation Example 1, except that in step 7), the amounts of carbon nanotubes and aniline monomer added were 10 g and 10 g, respectively, with a weight ratio of carbon nanotubes to aniline of 6:6.

[0086] Preparation Example 6: Preparation of core-shell flame retardant C-FR4

[0087] The core-shell flame retardant C-FR4 was prepared according to the method of Preparation Example 1, except that steps 5) and 6) were not performed. Accordingly, in step 7), the first core-shell intermediate particles having a first shell layer prepared in step 4) and carbon nanotubes were added to the aniline solution.

[0088] Preparation Example 7: Preparation of core-shell flame retardant C-FR5

[0089] The core-shell flame retardant C-FR5 was prepared according to the method of Preparation Example 1, except that, in step 2), 40 g of decabromodiphenylethane and 30 g of aluminum hydroxide were weighed and added to the caprolactam solution prepared in step 1), and steps 5) and 6) were not performed. Accordingly, in step 7), the first core-shell intermediate particles having a first shell layer and carbon nanotubes prepared in step 4) were added to the aniline solution.

[0090] Example 1: Preparation of positive electrode sheet P1

[0091] The positive electrode sheet P1 is prepared through the following steps.

[0092] 1) 3 parts by weight of the prepared core-shell flame retardant FR1 was added to 3 parts by weight of xylene, and the mixture was dispersed by ultrasonication for 30 minutes to prepare a core-shell flame retardant dispersion.

[0093] 2) 5 parts by weight of a binder styrene-ethylene-butylene-styrene block copolymer (SEBS) was added to 45 parts by weight of xylene, and the mixture was stirred and dispersed for 40 minutes while maintaining a viscosity of 5500±1800 mPa·s to prepare a glue solution.

[0094] 3) 3 parts by weight of the conductive vapor-grown carbon fiber VGCF was added to 16 parts by weight of the glue obtained in step 2) and stirred and dispersed for 60 minutes.

[0095] 4) 5 parts by weight of the core-shell flame retardant dispersion prepared in step 1) was added to the dispersion obtained in step 3) and stirred for dispersion.

[0096] 5) 50 parts by weight of ternary cathode material LiNi 0.8 Co 0.1 Mn 0.1 O2 and 15 parts by weight of xylene are added to the dispersion obtained in step 4), and the mixture is stirred and dispersed.

[0097] 6) 25 parts by weight of sulfide electrolyte Li6PS5Cl (LPSCl) was added to the slurry obtained in step 5), and the mixture was mixed and stirred at a revolution of 70 rpm and a rotation of 5000 rpm to disperse the mixture and maintain a viscosity of 6000±1000 mPa·s to obtain a positive electrode slurry.

[0098] 7) The positive electrode slurry obtained in step 6) is coated on both sides of a 12 μm thick aluminum foil positive electrode current collector and dried in a coating oven at 60° C. to 120° C. The dried positive electrode sheet is roll-pressed to obtain a positive electrode sheet P1.

[0099] Example 2: Preparation of positive electrode sheet P2

[0100] A positive electrode sheet P2 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant FR2 was used instead of the core-shell flame retardant FR1.

[0101] Comparative Example 1: Preparation of positive electrode sheet C-P1

[0102] A positive electrode plate C-P1 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant C-FR1 was used instead of the core-shell flame retardant FR1.

[0103] Comparative Example 2: Preparation of positive electrode sheet C-P2

[0104] A positive electrode plate C-P2 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant C-FR2 was used instead of the core-shell flame retardant FR1.

[0105] Comparative Example 3: Preparation of positive electrode sheet C-P3

[0106] A positive electrode plate C-P3 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant C-FR3 was used instead of the core-shell flame retardant FR1.

[0107] Comparative Example 4: Preparation of positive electrode sheet C-P4

[0108] A positive electrode plate C-P4 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant C-FR4 was used instead of the core-shell flame retardant FR1.

[0109] Comparative Example 5: Preparation of positive electrode sheet C-P5

[0110] A positive electrode sheet C-P5 was prepared in the same manner as in Example 1, except that in step 1), the core-shell flame retardant C-FR5 was used instead of the core-shell flame retardant FR1.

[0111] Comparative Example 6: Preparation of positive electrode sheet C-P6

[0112] The positive electrode sheet C-P6 was prepared in the same manner as in Example 1, except that step 1) was not performed, i.e., the core-shell flame retardant dispersion was not prepared, and accordingly, step 4) of adding the core-shell flame retardant dispersion was not performed.

[0113] The compositions of the core-shell flame retardants of Preparation Examples 1 to 7 are shown in Table 1 below.

[0114] Table 1: Composition of the core-shell flame retardants of Preparation Examples 1 to 7

[0115]

[0116] Test Method

[0117] 1. Thickness test of each shell layer of core-shell flame retardant

[0118] The average thickness of each shell layer of the core-shell flame retardants of Preparation Examples 1 to 7 was measured using a transmission electron microscope. The measurement results are shown in Table 2.

[0119] Table 2: Average thickness of each shell layer of the core-shell flame retardants of Preparation Examples 1 to 7

[0120] serial number Flame retardant type First shell Second shell The third shell Preparation Example 1 FR1 60nm 45nm 38nm Preparation Example 2 FR2 60nm 45nm 32nm Preparation Example 3 C-FR1 60nm 45nm 27nm Preparation Example 4 C-FR2 60nm 45nm 30nm Preparation Example 5 C-FR3 60nm 45nm 42nm Preparation Example 6 C-FR4 60nm / 38nm Preparation Example 7 C-FR5 60nm / 38nm

[0121] 2. Positive electrode conductive performance test

[0122] The conductivity of the positive electrode sheets cut from each embodiment and comparative example was tested under the same conditions using a four-probe method, and the test results are shown in Table 3. Comparing Examples 1 to 2 with Comparative Examples 1 to 5, the conductivity of Examples 1 to 2 is not much different from that of Comparative Examples 1 to 5. Comparing Examples 1 to 2 with Comparative Example 6, the conductivity of Examples 1 to 2 is higher. This is because the third shell layer of the core-shell flame retardant included in the positive electrode sheets of Examples 1 to 2 contains conductive polyaniline and conductive carbon nanotubes, thereby increasing its conductivity. Therefore, in the positive electrode sheet including the core-shell flame retardant prepared in the present invention, the third shell layer grown on the surface of the core-shell flame retardant can enhance the conductivity of the positive electrode sheet, which is beneficial to the efficient transmission of electrons.

[0123] 3. Positive electrode compression performance test

[0124] The compressive strength of the positive electrode sheets of each embodiment and comparative example was tested under the same conditions using a pressure testing machine, and the test results are shown in Table 3. Comparing Examples 1-2 with Comparative Examples 1-2, Examples 1-2 have improved compressive strength due to the presence of more carbon nanotubes. Comparing Examples 1-2 with Comparative Example 3, although Comparative Example 3 contains more carbon nanotubes, the excessively high content of carbon nanomaterials significantly reduces the dispersion in the matrix, making it prone to agglomeration and causing stress concentration, thereby reducing the compressive performance of Comparative Example 3. Comparing Example 1 with Comparative Examples 4-5, since all have the same content of carbon nanotubes, the three exhibit similar compressive performance. Comparing Examples 1-2 with Comparative Example 6, the positive electrode sheets of Examples 1-2 include a core-shell flame retardant, and the third shell layer of the core-shell flame retardant contains carbon nanotubes, thereby improving the compressive strength of the positive electrode sheets of Examples 1-2. Therefore, the results show that in the positive electrode sheet including the core-shell flame retardant prepared in the present invention, the third shell layer grown on the surface of the core-shell flame retardant can enhance the compressive performance of the positive electrode sheet.

[0125] 4. Electrode safety performance test

[0126] First, the positive pole pieces of each embodiment and comparative example are assembled into solid-state battery cells under the same conditions. The only difference is that the positive pole pieces used are the positive pole pieces of each embodiment 1 to 2 and comparative examples 1 to 6. Next, the battery cell is charged to full charge (100% SOC) and then placed in a constant temperature heating box. The temperature in the box is raised to 130°C at a rate of 5°C per minute and maintained for 30 minutes. After that, the temperature is raised at a rate of 5°C per minute, and the temperature is maintained for 30 minutes every time it is raised by 5°C. This process continues until the battery cell exhibits thermal runaway or the temperature reaches 250°C and is maintained for 30 minutes, after which heating is stopped.

[0127] The performance test results are shown in Table 3. Comparing Examples 1 to 2 with Comparative Examples 1 to 3, since the core, first shell and second shell designs of the core-shell flame retardant are the same, they exhibit the same thermal runaway temperature. Comparing Examples 1 to 2 with Comparative Example 4, the core-shell flame retardant included in the positive electrode sheet of Comparative Example 4 does not contain the second shell aluminum hydroxide, and the flame retardant effect is limited, resulting in the thermal runaway temperature of Comparative Example 4 being lower than that of Examples 1 to 2. Comparing Examples 1 to 2 with Comparative Example 5, although Examples 1 to 2 and Comparative Example 5 have the same content of decabromodiphenylethane and aluminum hydroxide, because the core-shell flame retardant included in the positive electrode sheet of Examples 1 to 2 is provided with a second shell aluminum hydroxide, the second shell aluminum hydroxide can absorb heat in advance, release water vapor, and slow down the overall heating rate of the material, thereby providing a guarantee for the thermal stability and action time of the core organic flame retardant, thereby enhancing the flame retardant effect. Comparing Examples 1 and 2 with Comparative Example 6, the thermal stability of the positive electrode plate including the core-shell flame retardant of the present invention is significantly improved, and the heating boundary under the same system is significantly increased by 15°C, which greatly improves the safety performance.

[0128] Table 3: Performance test results of the positive electrode sheets of Examples 1 to 2 and Comparative Examples 1 to 6

[0129]

[0130]

[0131] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that: The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, a sulfide solid electrolyte and a core-shell flame retardant, the core-shell flame retardant includes a core, a first shell layer coated on the core, a second shell layer coated on the first shell layer and a third shell layer coated on the second shell layer, wherein the core includes an organic flame retardant, the first shell layer includes a thermally responsive polymer, the melting point of the thermally responsive polymer is 125°C to 275°C, the second shell layer includes an inorganic flame retardant, and the third shell layer includes a conductive polymer and a carbon nanomaterial.

2. The positive electrode sheet according to claim 1, characterized in that: The conductive polymer is selected from one or more of polythiophene, polyaniline, poly(p-phenylene vinylene), polypyrrole, poly(p-phenylene vinylene) or polyacetylene.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The carbon nanomaterial is selected from one or more of carbon nanotubes, nanographenes or nanocarbon fibers.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: In the third shell layer, the weight ratio of the carbon nanomaterial to the conductive polymer is 1 to 5:

6.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The inorganic flame retardant is selected from one or more of aluminum hydroxide, magnesium hydroxide or magnesium aluminum double hydroxide.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The organic flame retardant is selected from one or more of decabromodiphenyl ethane, octabromoether, triphenyl phosphate, tricresyl phosphate or decabromodiphenyl ether.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The thermally responsive polymer is selected from one or more of urea-formaldehyde resin, polylactic acid, polyethylene oxide, polystyrene, polyethylene glycol or polyamide.

8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: Relative to the total weight of the core-shell flame retardant, the weight percentage of the core is 20% to 45%, the weight percentage of the first shell layer is 5% to 25%, the weight percentage of the second shell layer is 5% to 30%, and the weight percentage of the third shell layer is 5% to 25%.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The positive electrode active material is selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials or lithium nickel cobalt aluminum oxide.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The sulfide solid electrolyte is selected from one or more of Li6PS5Cl, Li6PS5Br, and Li6PS5I.

11. A sulfide all-solid-state battery, characterized in that: The sulfide all-solid-state battery comprises the positive electrode sheet according to any one of claims 1 to 10.

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