Core-shell structure flame-retardant additive, preparation method thereof and sulfide solid-state battery

Abstract

The invention relates to the technical field of sulfide solid-state batteries, in particular to a core-shell structure flame-retardant additive, a preparation method thereof and a sulfide solid-state battery. The core-shell structure flame retardant additive provided by the invention comprises a core material as well as a shell material carrier layer and a shell material polymer layer which sequentially coat the surface of the core material, the core material comprises a phosphorus flame retardant; the shell material carrier layer is prepared from one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride, chitosan, polyacrylic acid, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, carboxymethyl chitosan and carboxymethyl cellulose; the shell material polymer layer comprises one or more of polyaniline, polyvinylidene fluoride, polyethylene, vinylene carbonate, polyvinyl alcohol, polyacrylonitrile, polyether, polythiophene, polyacetylene and polypyrrole. The flame-retardant additive with the core-shell structure has the advantages that both electrochemical performance and safety can be considered, thermal response can be quickly carried out, the interface stability is good, toxic gas is diluted and released, and the engineering implementation is simple.

Description

Technical Field

[0001] This invention relates to the field of sulfide solid-state battery technology, and in particular to a core-shell structure flame-retardant additive, its preparation method, and a sulfide solid-state battery. Background Technology

[0002] Sulfide solid-state batteries represent an important development direction for next-generation high-energy-density energy storage devices. They use sulfide solid electrolytes instead of traditional liquid electrolytes, offering advantages such as non-flammability and high ionic conductivity (up to 10⁻⁶ Ω·cm at room temperature). -2 Sulfide solid-state batteries offer advantages such as high energy density (theoretically exceeding 500 Wh / kg) and high efficiency (S / cm). However, they still face serious thermal safety issues in practical applications. Studies have shown that sulfide electrolytes may undergo violent exothermic reactions with highly active cathode materials (such as high-nickel NCM811) at high temperatures, leading to thermal runaway. This reaction typically occurs around 200°C, accompanied by the release of large amounts of toxic gases (such as SO and SO2), and may even trigger combustion or explosion. Currently, the main technical approaches to solving the thermal safety problems of sulfide solid-state batteries include: developing novel solid-state electrolyte materials, optimizing interface engineering, and introducing functional additives.

[0003] In terms of electrolyte materials, the industry mainly focuses on two major technical routes: oxides and sulfides. Among them, although the sulfide route has higher ionic conductivity and better interfacial contact characteristics, its thermal stability is poor and it is sensitive to air, which greatly increases the difficulty of industrialization.

[0004] In terms of interface engineering, applying appropriate pressure to the composite cathode of sulfide solid-state batteries can increase the contact area between the cathode material and the sulfide electrolyte, thereby generating in-situ inert P2S. X A protective layer is used to suppress the exothermic reaction between oxygen released from the positive electrode and the sulfide electrolyte, as well as the generation of toxic gases. However, this method can only delay, not completely prevent, thermal runaway. Furthermore, due to engineering implementation and application limitations, pressure-stabilized interface technology requires complex mechanical systems to maintain a stable high-pressure environment, increasing the complexity and cost of the battery system and reducing energy density. This technology is difficult to implement and maintain in actual cell manufacturing, especially in large battery modules. In addition, high-pressure conditions can cause mechanical damage to the sulfide electrolyte, leading to cracks and performance degradation.

[0005] Regarding additives, researchers have begun exploring various additives to improve the thermal safety of sulfide solid-state batteries. Existing additive technologies mainly include: 1. Flame-retardant additives: such as organophosphorus compounds, which can release free radical quenchers to interrupt chain reactions when thermal runaway occurs. 2. Thermally responsive electrolyte additives: These undergo physical or chemical transformations at specific temperatures to become insulating, thereby preventing thermal runaway. In August 2025, a research team from Southern University of Science and Technology reported a thermally responsive electrolyte additive called "fluorobenzoxazine" (mCF3-BA) in the journal *Joule*. This additive participates in the formation of a stable CEI / SEI interface during normal battery cycling, enhancing battery cycle stability. When thermal runaway occurs, it rapidly polymerizes into an insulating thermosetting polybenzoxazine resin gel, blocking electrochemical crosstalk between the positive and negative electrodes and suppressing electrolyte side reactions. 3. Conductive carbon-based additives: Shanghai Jiao Tong University and the University of Technology Sydney have jointly developed N-doped porous carbon (Mo-Ni@NPCs) embedded with Mo3Ni3N nanosheets, which are introduced as conductive carbon-based additives into the composite cathode of sulfide solid-state batteries. This additive inhibits the decomposition reaction of solid electrolytes initiated by hydroxide ions by forming a stable MoS2-Mo3Ni3N heterostructure, and at the same time builds an efficient electron / ion dual migration pathway at the cathode interface, thereby improving the electrochemical performance of the battery.

[0006] Although the aforementioned existing technologies have improved the thermal safety of sulfide solid-state batteries to some extent, they still have several technical defects and shortcomings: The balance between electrochemical performance and safety: Most existing additive technologies struggle to balance the requirements of electrochemical performance and safety. Additives introduced to improve safety often sacrifice the battery's energy density, power density, and cycle life. For example, flame retardant additives typically impair the battery's electrochemical performance, leading to a decrease in capacity and cycle life, which greatly limits their practical application value.

[0007] Thermal response delay issue: Thermally responsive electrolyte additives need to activate their polymerization function only after thermal runaway has already begun, resulting in a response delay issue; before the additives take effect, thermal runaway may have already developed to a certain extent, and irreversible damage may have occurred inside the battery; in addition, these additives are mainly designed for liquid electrolyte systems and are not entirely suitable for all-solid-state battery systems, and their diffusion and distribution in solid electrolytes are difficult.

[0008] Limitations of interface stability and thermal runaway prevention: Conductive carbon-based additives mainly improve the chemical stability and ion / electron transport efficiency of the cathode interface, but have limited effect on preventing thermal runaway; these additives cannot effectively solve the problem of violent exothermic reaction between sulfide electrolyte and high-nickel cathode material, especially under high-temperature abuse conditions; more importantly, these additives themselves may participate in interfacial side reactions, accelerating battery performance degradation during long-term cycling.

[0009] Toxic gas release and safety issues: Sulfide electrolytes may release flammable sulfur gas and highly toxic hydrogen sulfide at high temperatures, which can react violently with lithium metal at the negative electrode, triggering a thermal chain reaction and secondary combustion. Most existing technologies cannot effectively solve this safety problem, especially under extreme abuse conditions.

[0010] Sulfide solid-state batteries still lack additive technologies that can effectively prevent and promptly suppress the occurrence and development of battery thermal runaway without negatively impacting the electrochemical performance of sulfide solid-state batteries.

[0011] In view of this, the present invention is hereby proposed. Summary of the Invention

[0012] The primary objective of this invention is to provide a core-shell structured flame retardant additive that can balance excellent electrochemical performance and safety performance, rapid thermal response, good interfacial stability, dilute the release of toxic gases, and is simple to implement in engineering.

[0013] The second objective of this invention is to provide a method for preparing a core-shell structured flame retardant additive.

[0014] A third objective of this invention is to provide a sulfide solid-state battery.

[0015] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a core-shell structure flame retardant additive, comprising a core material and a shell material carrier layer and a shell material polymer layer sequentially coated on the surface of the core material; The nuclear material includes a phosphorus-based flame retardant; The shell carrier layer includes one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride, chitosan, polyacrylic acid, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, carboxymethyl chitosan, and carboxymethyl cellulose; The shell polymer layer includes one or more of polyaniline, polyvinylidene fluoride, polyethylene, polyvinyl carbonate, polyvinyl alcohol, polyacrylonitrile, polyether, polythiophene, polyacetylene, and polyarsenol.

[0016] Furthermore, the phosphorus-based flame retardant includes one or more of ammonium polyphosphate, hypophosphite, phosphate ester, and phosphonate.

[0017] Furthermore, the mass percentage of the core material in the core-shell structure flame retardant additive is 40% to 80%.

[0018] Furthermore, the average particle size of the core-shell structure flame retardant additive is 3~50μm.

[0019] Furthermore, the average thickness of the shell carrier layer is 50~100nm; And / or, the surface of the shell carrier layer has a pleated structure.

[0020] Furthermore, the average thickness of the polymer layer of the shell material is 50~300nm.

[0021] This invention also provides a method for preparing the core-shell structured flame retardant additive as described above, comprising the following steps: The material of the shell carrier layer is coated on the surface of the phosphorus-based flame retardant to form the shell carrier layer; The monomer is then polymerized in situ on the surface of the shell carrier layer to form a shell polymer layer, thus obtaining a core-shell structure flame retardant additive.

[0022] Furthermore, the mass ratio of the monomer to the phosphorus-based flame retardant is (0.2~1.5):1.

[0023] The present invention also provides a sulfide solid-state battery, comprising the core-shell structure flame-retardant additive described above.

[0024] Furthermore, the sulfide solid-state battery includes: a composite positive electrode; The composite cathode comprises a cathode active material, a sulfide solid electrolyte, a conductive agent, and the core-shell structure flame retardant additive.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: The core-shell structure flame retardant additive of this invention, through the design of material combinations and structural features, can achieve efficient suppression of thermal runaway while maintaining the excellent electrochemical performance of sulfide solid-state batteries, thus balancing electrochemical performance and safety. Specifically, this core-shell structure additive has good stability and does not react with the internal components of the battery, ensuring that the electrochemical performance of the battery is not affected. When the internal temperature of the battery rises abnormally to a critical value, it will intelligently respond and rapidly release a highly efficient flame retardant to suppress thermal runaway in its early stages, avoiding serious consequences. It can also dilute toxic gases generated at high temperatures in the battery. In addition, this additive has good compatibility and dispersibility, does not increase the complexity of sulfide solid-state battery manufacturing, and is suitable for large-scale industrial production. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. However, those skilled in the art will understand that the embodiments described below are some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of 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. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0027] In some embodiments of the present invention, a core-shell structure flame retardant additive is provided, comprising a core material and a shell material carrier layer and a shell material polymer layer sequentially coated on the surface of the core material. Nuclear materials include phosphorus-based flame retardants; The shell carrier layer includes one or more of the following: sodium carboxymethyl cellulose, polyvinylidene fluoride, chitosan, polyacrylic acid, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, carboxymethyl chitosan, and carboxymethyl cellulose; The shell polymer layer includes one or more of polyaniline, polyvinylidene fluoride, polyethylene, polyvinyl carbonate, polyvinyl alcohol, polyacrylonitrile, polyether, polythiophene, polyacetylene, and polypyrrole.

[0028] The core-shell structure flame retardant additive of this invention comprises a core material that is a highly efficient flame retardant; a shell material carrier layer that is a polymer compound with good water solubility and film-forming properties, and can serve as a good adhesion point for the outermost shell material, which is conducive to the formation of a dense and continuous shell material polymer layer; the shell material polymer layer is a polymer that forms chemical bonds with the shell material carrier layer, has a stable structure, and does not chemically react with phosphorus-based flame retardants, thereby solving problems such as compatibility, migration, and hydrolysis resistance; through the design of the above material combination and structural features, it is possible to effectively prevent and promptly suppress the occurrence and development of battery thermal runaway while maintaining the excellent electrochemical performance of sulfide solid-state batteries, thus achieving highly efficient suppression of thermal runaway.

[0029] The core-shell structure flame retardant additive of this invention features an outer polymer layer that remains stable under normal battery operating conditions and does not react with internal battery components, ensuring that the battery's electrochemical performance is unaffected. When the internal temperature of the battery abnormally rises to a critical value, the outer polymer layer intelligently responds and rapidly releases the inner high-efficiency flame retardant. These flame retardants effectively block electrochemical crosstalk between battery materials and inhibit electrolyte decomposition reactions, thereby suppressing thermal runaway in its early stages and preventing chain reactions. This additive solves the problem of exothermic side reactions between sulfide solid electrolytes and ternary cathode active materials under high-temperature conditions, and has good stability and ionic conductivity, without leading to a decrease in battery electrochemical performance. The inner phosphorus-based flame retardant decomposes under high-temperature conditions, producing non-flammable gases such as carbon dioxide, diluting the toxic gases generated by the battery at high temperatures. Furthermore, this additive can be directly mixed with sulfide electrolytes using dry or wet processes, exhibiting good compatibility and dispersibility, without increasing the complexity of sulfide solid battery manufacturing, and is suitable for large-scale industrial production.

[0030] The core-shell structure flame retardant additive of the present invention solves the problems of balancing safety and electrochemical performance, thermal response delay, interface stability and thermal runaway prevention, toxic gas release and safety, and engineering implementation in the prior art.

[0031] The core-shell structure flame retardant additive of the present invention has the following advantages: Balancing electrochemical performance and safety: It can suppress the exothermic reaction between the cathode material and the electrolyte without affecting the original electrochemical performance of the sulfide solid-state battery, thus achieving the goal of balancing electrochemical performance and safety. Rapid thermal response: It can release flame retardants when the battery heats up rapidly. At the same time, the flame retardants also decompose and release gases under heat, blocking the side reactions between electrode materials and solid electrolytes; it intervenes to suppress thermal runaway in the early stage, avoiding serious consequences. Good interface stability: Compared with batteries without core-shell flame retardant additives, batteries with added core-shell flame retardant additives show no significant degradation in electrochemical performance after long-term cycling. Diluting the release of toxic gases: Sulfide electrolytes may release flammable sulfur gas and highly toxic hydrogen sulfide at high temperatures, and react violently with lithium metal at the negative electrode, triggering a thermal chain reaction and secondary combustion; while phosphorus-based flame retardants decompose under high-temperature conditions, producing non-flammable gases such as carbon dioxide, which dilutes the toxic gases produced by the battery at high temperatures. The project is simple to implement: it does not require changes to the existing production line, and the core-shell structure flame retardant additive can be added during the preparation of the cathode material. It is also low in cost, simple to prepare, does not require a complex external system, is easy to implement and promote, and is conducive to achieving industrial mass production.

[0032] In some embodiments of the present invention, the phosphorus-based flame retardant includes one or more of ammonium polyphosphate (APP), hypophosphite, phosphate ester and phosphonate.

[0033] In some preferred embodiments of the present invention, the phosphorus-based flame retardant includes ammonium polyphosphate.

[0034] Ammonium polyphosphate is relatively stable. It begins to decompose and produce a flame-retardant effect at temperatures above 200-300℃. This temperature range is far beyond the normal battery temperature and falls within the temperature range where sulfide electrolytes and cathode materials produce side reactions. According to its flame-retardant mechanism, during the decomposition process, gases such as ammonia and carbon dioxide are generated to dilute flammable gases, and substances such as metaphosphoric acid and phosphoric acid block exothermic side reactions. Phosphoric acid and polyphosphoric acid, which are generated by the dehydration of ammonium polyphosphate upon heating, preferentially react with the decomposition products of the cathode. At the same time, the generated non-volatile phosphorus oxides, polyphosphoric acid, and phosphates cover the surface of the substrate, isolating it from air and thus achieving the purpose of flame retardancy.

[0035] In some embodiments of the present invention, the mass percentage of the core material in the core-shell structure flame retardant additive is 40% to 80%; typically, but not limitingly, for example, the mass percentage of the core material in the core-shell structure flame retardant additive can be 40%, 50%, 60%, 70%, 80%, and any value between any two.

[0036] In some embodiments of the present invention, the average particle size of the core-shell structured flame retardant additive is 3 to 50 μm; typically, but not limitingly, for example, the average particle size of the core-shell structured flame retardant additive can be 3 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, and any value between any two.

[0037] In some embodiments of the present invention, the average thickness of the shell carrier layer is 50-100 nm; typically, but not limitingly, for example, the average thickness of the shell carrier layer can be 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, and any value between any two of these.

[0038] In some embodiments of the present invention, the surface of the shell carrier layer has a pleated structure.

[0039] In some embodiments of the present invention, the average thickness of the shell polymer layer is 50 to 300 nm; typically, but not limitingly, for example, the average thickness of the shell polymer layer can be 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, and any value between any two of these.

[0040] In some embodiments of the present invention, a method for preparing the above-mentioned core-shell structure flame retardant additive is also provided, comprising the following steps: The material of the shell carrier layer is coated on the surface of the phosphorus-based flame retardant to form the shell carrier layer; Then, the monomer is polymerized in situ on the surface of the shell carrier layer to form a shell polymer layer, thus obtaining a core-shell structure flame retardant additive.

[0041] In some embodiments of the present invention, the preparation method of the core-shell structure flame retardant additive specifically includes the following steps: The material of the shell carrier layer is coated on the surface of the phosphorus-based flame retardant to form a shell carrier layer, thus obtaining a phosphorus-based flame retardant coated with a shell carrier layer. The dispersion, monomer, and initiator of the phosphorus-based flame retardant coated on the shell carrier layer are subjected to in-situ polymerization to form a shell polymer layer, thus obtaining a core-shell structured flame retardant additive.

[0042] In some embodiments of the present invention, the mass ratio of monomer to phosphorus-based flame retardant is (0.2~1.5):1; typically, but not limitingly, for example, the mass ratio of monomer to phosphorus-based flame retardant can be 0.2:1, 0.5:1, 0.7:1, 1:1, 1.2:1, 1.5:1, and any value between any two.

[0043] In some embodiments of the present invention, the initiator includes one or more of potassium persulfate (KPS), azobisisobutyronitrile (AIBN), and ammonium persulfate (APS).

[0044] In some embodiments of the present invention, the total mass ratio of monomer and initiator to phosphorus-based flame retardant is (0.5~1.5):1.

[0045] This invention does not impose strict limitations on the method of forming a shell carrier layer on the surface of a phosphorus-based flame retardant; existing methods can be used.

[0046] This invention does not strictly limit the conditions for in-situ polymerization; any conditions that enable the monomer to undergo in-situ polymerization can be used. For example, under the protection of an inert gas, the system is adjusted to the conditions that trigger the polymerization reaction of the monomer, and the reaction is carried out for 4 to 12 hours to enable the monomer to undergo in-situ polymerization and form a coating layer.

[0047] In some embodiments of the present invention, a sulfide solid-state battery is also provided, comprising the above-described core-shell structure flame-retardant additive.

[0048] The core-shell structured flame retardant of the present invention is a micron-sized powder particle with a core-shell structure. As a thermal runaway suppression additive for sulfide solid-state batteries, it can improve the thermal safety of sulfide solid-state batteries and maintain their electrochemical performance.

[0049] The use of the core-shell flame retardant of the present invention in sulfide solid-state batteries solves the problem of exothermic side reactions between sulfide solid electrolytes and ternary cathode active materials under high-temperature conditions. Furthermore, due to the good stability and ionic conductivity of the core-shell flame retardant, the electrochemical performance of sulfide solid-state batteries with the addition of the core-shell flame retardant is basically consistent with that of sulfide solid-state batteries without the addition of the core-shell flame retardant under a certain period of cycle testing.

[0050] In some embodiments of the present invention, the sulfide solid-state battery includes a lithium-ion battery or a lithium metal battery.

[0051] The core-shell structure flame retardant of the present invention is applied to all-solid-state lithium-ion battery or lithium metal battery system with sulfide solid electrolyte as the core. As a core safety material, it significantly improves the thermal safety threshold and wide temperature range performance of the battery system.

[0052] In some embodiments of the present invention, a sulfide solid-state battery includes: a composite positive electrode; Composite cathodes include cathode active materials, sulfide solid electrolytes, conductive agents, and core-shell flame-retardant additives.

[0053] The core-shell structure flame retardant of the present invention is mixed with sulfide solid electrolyte, positive electrode active material and conductive agent to construct a composite positive electrode. While ensuring the ion conduction pathway, it effectively improves the local thermal stability of the positive electrode and suppresses the occurrence of thermal runaway during charging and discharging. In particular, it suppresses the side reaction of the ternary positive electrode decomposing at about 220°C and reacting with the sulfide electrolyte.

[0054] In some embodiments of the present invention, the mass ratio of the positive electrode active material, the sulfide solid electrolyte, the conductive agent and the core-shell structure flame retardant additive in the composite positive electrode is (75~85):(10~20):(1~3):(2~5).

[0055] In some embodiments of the present invention, in the composite positive electrode, the concentration gradient of the core-shell structure flame retardant increases, decreases, or is distributed in layers along the current collector toward the electrolyte membrane interface.

[0056] The core-shell structure of the composite cathode has different flame retardant concentrations in different regions, which can achieve key protection for areas with high risk of thermal runaway.

[0057] In some embodiments of the present invention, the composite positive electrode includes a positive electrode active material, a sulfide solid electrolyte, a conductive agent, and a core-shell structure flame retardant additive, wherein the core-shell structure flame retardant additive is attached to the surface of the positive electrode active material.

[0058] Instead of simply mixing the positive electrode active material, sulfide solid electrolyte, conductive agent, and core-shell structure flame retardant additive, a specific process is used to selectively attach them to the surface of the positive electrode active material, enabling a "precision strike" against the origin of side reactions.

[0059] In some embodiments of the present invention, a sulfide solid-state battery includes: a solid electrolyte layer; The solid electrolyte layer includes a core-shell structured flame retardant and a sulfide solid electrolyte.

[0060] The core-shell structured flame retardant is directly dispersed in the solid electrolyte. It is mixed with the sulfide solid electrolyte as a functional filler to form a composite electrolyte system, which is used to enhance the mechanical strength and thermal safety of the electrolyte layer, prevent lithium dendrite piercing and isolate heat diffusion.

[0061] In some embodiments of the present invention, a sulfide solid-state battery includes: an interface buffer layer; The interface buffer layer is located between the positive electrode and the electrolyte, and the interface buffer layer is mainly made of core-shell structure flame retardant.

[0062] An independent interface buffer layer with flame-retardant function is set between the positive electrode and the electrolyte. This can not only physically isolate and suppress side reactions, but also exert flame-retardant effect under thermal abuse conditions, thus protecting the heat-sensitive sulfide electrolyte.

[0063] In some embodiments of the present invention, a battery system is also provided, comprising: a battery cell, a mechanical structure, a pressure sensor, and a control system; the battery cell includes a core-shell structure flame retardant.

[0064] This battery module architecture integrates battery assembly, packaging, and post-construction safety monitoring, providing comprehensive protection. It incorporates a pressure maintenance system and a thermal runaway monitoring and suppression system, and its core technology utilizes a core-shell structure flame retardant.

[0065] Example 1 The preparation method of the core-shell structure flame retardant additive provided in this embodiment includes the following steps: S1. Extract cellulose from wood fibers and alkalize the cellulose to obtain alkalized cellulose. S2. Weigh 2.2g of ammonium polyphosphate and dissolve it in a 3wt% sodium hydroxide aqueous solution to obtain an alkaline solution of ammonium polyphosphate. This provides the necessary alkaline environment for the next carboxymethylation reaction and disperses the ammonium polyphosphate to prevent agglomeration. In addition, the alkaline environment may make the surface of the ammonium polyphosphate particles negatively charged, which helps them to initially combine with the hydroxymethyl cellulose that is forming in the subsequent reaction through electrostatic interaction. S3. The alkalized cellulose and chloroacetic acid were reacted in an alkaline solution of ammonium polyphosphate. 1 mol of sodium chloroacetate was added to the solution and mixed thoroughly. The temperature was increased to 30°C at a rate of 5°C / min and held for 5 min. Then, the temperature was increased to 40°C at a rate of 2°C / min and held for 30 min. Finally, the temperature was increased to 80°C and held for 2 h to obtain carboxymethyl cellulose-coated ammonium polyphosphate, namely ammonium polyphosphate@carboxymethyl cellulose. The average thickness of the carboxymethyl cellulose layer was 75 nm, and the surface exhibited a wrinkled structure. By controlling the heating program, the generation and deposition rate of hydroxymethyl cellulose can be controlled, thereby forming a dense coating layer with uniform thickness and wrinkled surface. The wrinkled structure is usually caused by uneven shrinkage of the coating layer during the formation process, which actually increases the specific surface area and is beneficial for subsequent polyaniline coating. S4. React ammonium polyphosphate@carboxymethyl cellulose with sodium hydroxide to convert all the carboxymethyl groups into sodium salt form, and obtain water-soluble ammonium polyphosphate@carboxymethyl cellulose sodium; S5. Ammonium polyphosphate@sodium carboxymethyl cellulose is filtered, washed and dried sequentially to obtain a pure ammonium polyphosphate@sodium carboxymethyl cellulose product; S6. Disperse the pure ammonium polyphosphate@sodium carboxymethyl cellulose product in water to prepare a dispersion; add 2% (w / w) of purified aniline to the dispersion and adsorb the aniline by hydrogen bonding; stir for 0.5 h to ensure complete coating, and then place in an ice bath; S7. Slowly add an aqueous solution of 5 wt% ammonium persulfate (APS) to initiate aniline polymerization. The reaction is carried out at a low temperature of 4℃~10℃ for 6 hours using an ice bath to obtain polyaniline-coated ammonium polyphosphate@carboxymethyl cellulose sodium, wherein the average thickness of the polyaniline layer is 75 nm. Under the above reaction conditions, the aqueous solution of APS initiates the polymerization of aniline, which grows in an orderly manner on the surface of ammonium polyphosphate@sodium carboxymethyl cellulose, forming a complete, uniform, and dense coating layer. S8. The polyaniline-coated ammonium polyphosphate@sodium carboxymethyl cellulose is filtered, washed and dried sequentially to obtain a pure polyaniline-coated ammonium polyphosphate@sodium carboxymethyl cellulose product, namely a core-shell structure flame retardant additive, with an average particle size of 3μm.

[0066] The method for preparing the composite positive electrode provided in this embodiment includes the following steps: The positive electrode active material, sulfide electrolyte, conductive agent and flame retardant additive (core-shell structure flame retardant additive in this embodiment) are mixed evenly in a mass ratio of 80:15:2:3, dissolved in an ester solvent, and then evenly dispersed by a homogenizer to prepare a positive electrode slurry, which is then uniformly coated onto an aluminum foil current collector.

[0067] Example 2 The preparation method of the core-shell structure flame retardant additive provided in this embodiment includes the following steps: S1. Weigh 2.2g of ammonium polyphosphate and dissolve it in an aqueous solution of sodium hydroxide with a concentration of 3wt% to obtain an alkaline solution of ammonium polyphosphate. S2. Dissolve polyvinylidene fluoride in dimethylacetamide solution, stir, and obtain polyvinylidene fluoride solution; S2. The polyvinylidene fluoride solution is slowly and uniformly added to the alkaline solution of ammonium polyphosphate that is constantly being stirred. After the addition is complete, the solution is filtered, washed and dried in sequence to obtain polyvinylidene fluoride-coated ammonium polyphosphate, namely ammonium polyphosphate@polyvinylidene fluoride, wherein the average thickness of the polyvinylidene fluoride layer is 75nm. S3. Disperse ammonium polyphosphate@polyvinylidene fluoride in water to obtain a dispersion; add 2% (w / w) of purified aniline to the dispersion; stir for 0.5 h, and then place in an ice bath; S4. Slowly add an aqueous solution of 5wt% ammonium persulfate (APS) to initiate aniline polymerization. The reaction is carried out at a low temperature of 4℃~10℃ for 6 hours using an ice bath to obtain polyaniline-coated ammonium polyphosphate@polyvinylidene fluoride, wherein the average thickness of the polyaniline layer is 75nm. S5. The polyaniline-coated ammonium polyphosphate@polyvinylidene fluoride is filtered, washed and dried sequentially to obtain a pure polyaniline-coated ammonium polyphosphate@polyvinylidene fluoride product, namely a core-shell structure flame retardant additive, with an average particle size of 3μm.

[0068] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0069] Example 3 The preparation method of the core-shell structure flame retardant additive provided in this embodiment is the same as that in Example 1, except that the alkalized cellulose and chloroacetic acid are reacted in an alkaline solution of ammonium polyphosphate, and 1 mol of sodium chloroacetate is added to the solution and mixed evenly. The mixture is then heated directly to 80°C and kept at that temperature for 2 hours. The surface of the sodium carboxymethyl cellulose layer in the resulting ammonium polyphosphate@sodium carboxymethyl cellulose is smooth and wrinkle-free.

[0070] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0071] Example 4 The preparation method of the core-shell structure flame retardant additive provided in this embodiment is the same as that in Example 1, except that aniline is replaced with fluoroethylene, and the resulting core-shell structure flame retardant additive is polyvinylidene fluoride-coated ammonium polyphosphate@sodium carboxymethyl cellulose.

[0072] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0073] Example 5 The preparation method of the core-shell structure flame retardant additive provided in this embodiment is the same as that in Example 1, except that aniline is replaced with ethylene, and the resulting core-shell structure flame retardant additive is polyethylene-coated ammonium polyphosphate@sodium carboxymethyl cellulose.

[0074] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0075] Example 6 The preparation method of the core-shell structure flame retardant additive provided in this embodiment is the same as that in Example 1, except that aniline is replaced with vinylene carbonate, and the obtained core-shell structure flame retardant additive is poly(ethylene carbonate) coated with ammonium polyphosphate@sodium carboxymethyl cellulose.

[0076] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0077] Example 7 The preparation method of the core-shell structure flame retardant additive provided in this embodiment is the same as that in Example 1, except that ammonium polyphosphate is replaced with triphenyl phosphate (a non-gas-producing flame retardant).

[0078] The method for preparing the composite cathode provided in this embodiment is the same as in Embodiment 1.

[0079] Comparative Example 1 The flame retardant additive provided in this comparative example is the pure ammonium polyphosphate@sodium carboxymethyl cellulose product from Example 1.

[0080] The method for preparing the composite cathode provided in this comparative example is the same as that in Example 1.

[0081] Comparative Example 2 The flame retardant additive provided in this comparative example is ammonium polyphosphate.

[0082] The method for preparing the composite cathode provided in this comparative example is the same as that in Example 1.

[0083] Comparative Example 3 The method for preparing the composite positive electrode provided in this comparative example is the same as in Example 1, except that the core-shell structure flame retardant additive is replaced with the conductive agent acetylene black.

[0084] Comparative Example 4 The preparation method of the composite cathode provided in this comparative example is the same as that in Example 1, except that no core-shell structure flame retardant additive is added.

[0085] Test case The composite cathodes prepared in Examples 1-7 and Comparative Examples 1-4 were added to sulfide solid-state batteries for testing, and the test results are shown in Table 1.

[0086] In sulfide solid-state batteries, the positive electrode material is high-nickel ternary NCM811, the electrolyte is LPSC651, and the negative electrode is lithium-indium alloy.

[0087] The testing methods include: Thermal abuse test: The thermal abuse test was conducted in an explosion-proof chamber. First, the sulfide solid-state battery was placed in a heating device with an adjustable nut, and the battery was separated from the heating device by two mica sheets. A ceramic heating element was placed between one of the mica sheets and the battery. The ceramic element was initially heated rapidly to 300°C and then heating was stopped. A K-type thermocouple was fixed between the other side of the battery and another mica sheet, and the temperature changes during the battery abuse process were recorded.

[0088] Cyclic performance testing: Cyclic performance testing was conducted using the Blue Electric testing system; at room temperature, the sulfide solid-state battery with added microcapsules was charged to 4.2V and discharged to 2.75V at a constant current of 0.5C using the Blue Electric charge-discharge machine (CT3002A), and the test was repeated for 200 cycles.

[0089] Table 1

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A core-shell structured flame retardant additive, characterized in that, It includes a core material and a shell carrier layer and a shell polymer layer sequentially covering the surface of the core material; The nuclear material includes a phosphorus-based flame retardant; The shell carrier layer includes one or more of sodium carboxymethyl cellulose, polyvinylidene fluoride, chitosan, polyacrylic acid, polyvinyl alcohol, sodium alginate, polymethyl methacrylate, carboxymethyl chitosan, and carboxymethyl cellulose; The shell polymer layer includes one or more of polyaniline, polyvinylidene fluoride, polyethylene, polyvinyl carbonate, polyvinyl alcohol, polyacrylonitrile, polyether, polythiophene, polyacetylene, and polyarsenol.

2. The core-shell structure flame retardant additive according to claim 1, characterized in that, The phosphorus-based flame retardant includes one or more of ammonium polyphosphate, hypophosphite, phosphate ester, and phosphonate.

3. The core-shell structure flame retardant additive according to claim 1, characterized in that, The mass percentage of the core material in the core-shell structure flame retardant additive is 40% to 80%.

4. The core-shell structure flame retardant additive according to claim 1, characterized in that, The core-shell structure flame retardant additive has an average particle size of 3~50μm.

5. The core-shell structure flame retardant additive according to claim 1, characterized in that, The average thickness of the shell carrier layer is 50~100nm; And / or, the surface of the shell carrier layer has a pleated structure.

6. The core-shell structure flame retardant additive according to claim 1, characterized in that, The average thickness of the polymer layer of the shell material is 50~300nm.

7. The method for preparing the core-shell structured flame retardant additive according to any one of claims 1 to 6, characterized in that, Includes the following steps: The material of the shell carrier layer is coated on the surface of the phosphorus-based flame retardant to form the shell carrier layer; The monomer is then polymerized in situ on the surface of the shell carrier layer to form a shell polymer layer, thus obtaining a core-shell structure flame retardant additive.

8. The method for preparing the core-shell structure flame retardant additive according to claim 7, characterized in that, The mass ratio of the monomer to the phosphorus-based flame retardant is (0.2~1.5):

1.

9. A sulfide solid-state battery, characterized in that, Includes the core-shell structure flame retardant additive as described in any one of claims 1 to 6.

10. The sulfide solid-state battery according to claim 9, characterized in that, include: Composite cathode; The composite cathode comprises a cathode active material, a sulfide solid electrolyte, a conductive agent, and the core-shell structure flame retardant additive.

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