Stainless steel material for automobile battery case and method for manufacturing the same

Abstract

The present application relates to the field of new energy automobile power battery technology, and particularly relates to a stainless steel material for automobile battery shell and a preparation method thereof, comprising: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal framework, the pores of the three-dimensional porous metal framework are formed with a heat insulation reinforcing phase, the surface of the framework is attached with a catalytic active phase, and the surface and the pore inner wall of the layer are further loaded with an intumescent flame retardant phase. The present application integrates a high-performance thermoelectric composite material into a battery shell main body material, compounding an intumescent flame retardant system suitable for a metal / ceramic composite substrate, adopting a high-temperature co-sintering and low-temperature impregnation curing step-by-step process, realizing high-strength metallurgical / ceramic combination of the composite functional layer and the stainless steel substrate, and simultaneously optimizing a material system suitable for a harsh service environment, solving the technical problems of existing shell, such as fast heat conduction, single coating function, weak bonding force, high-temperature failure, and the like.

Description

Technical Field

[0001] This invention relates to the field of power battery technology for new energy vehicles, specifically to a stainless steel material for automobile battery casings and its preparation method. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the safety performance requirements for power batteries are becoming increasingly stringent. As an important component of the battery pack, the battery casing not only needs to possess good mechanical strength and corrosion resistance, but also needs to provide effective thermal management and flame-retardant protection in the event of battery thermal runaway.

[0003] Currently, automotive battery casings are primarily made of aluminum alloy or stainless steel. While aluminum alloy casings are lightweight, their high thermal conductivity can lead to rapid heat dissipation during battery thermal runaway, posing a safety hazard. Stainless steel casings, although possessing high mechanical strength and good corrosion resistance, also suffer from rapid heat conduction and lack active thermal management and flame-retardant properties.

[0004] Existing technologies include coating the battery casing with heat-insulating or flame-retardant coatings. However, these coatings typically have a single function and limited adhesion to the substrate, making them prone to peeling and failure during long-term use. Furthermore, traditional heat-insulating and flame-retardant materials are prone to decomposition and failure at high temperatures, failing to provide continuous and effective protection in the event of battery thermal runaway.

[0005] Therefore, developing a battery casing material that integrates multiple functions such as heat insulation, catalysis, and flame retardancy is of great significance for improving the safety performance of power batteries. Summary of the Invention

[0006] This invention provides a stainless steel material for automotive battery casings and its preparation method, in order to solve the technical problems in the prior art, such as rapid thermal conductivity, lack of long-term heat insulation and flame retardant function, single surface coating function, weak adhesion, and easy failure at high temperatures.

[0007] A first aspect of the present invention provides a stainless steel material for an automotive battery casing, comprising: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is loaded on the surface of the layer and the inner wall of the pores.

[0008] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0009] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0010] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 1:5 to 5:1.

[0011] The ceramic fiber is an alumina or mullite short fiber with a diameter of 1-10 μm and a length of 50-300 μm.

[0012] The catalytically active phase is a perovskite oxide or a spinel oxide.

[0013] The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is (2.5:1) to (3.5:1).

[0014] A second aspect of the present invention provides a method for preparing a stainless steel material for an automotive battery casing, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green compact is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1100-1300℃; during this sintering process, stainless steel powder forms the porous metal skeleton, metal oxide powder forms the catalytic active phase, and heat-insulating composite powder forms the heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200°C.

[0015] In step S1, by mass, the stainless steel metal powder is 60-80 parts, the metal oxide powder is 5-15 parts, and the heat-insulating composite powder is 15-30 parts.

[0016] In step S2, the solid content of the slurry is 60%-75%; the binder is polyvinyl butyral or acrylic resin, and the amount added is 3%-8% of the total mass of the mixed powder.

[0017] Therefore, the present invention has at least the following beneficial effects: (1) This invention is the first to successfully integrate high-performance thermoelectric composite materials as the core component with structural reinforcement, heat insulation, and thermoelectric sensing functions into the main material of the battery casing. Specifically, when local thermal runaway occurs inside the battery, heat is rapidly conducted to the composite functional layer through a three-dimensional porous metal framework. Since carbon nanotubes and antimony telluride thermoelectric nanoparticles are in close contact at the microscale and form a heterojunction network, directional diffusion of charge carriers occurs at the heterojunction interface under the drive of the temperature gradient, thereby directly converting thermal energy into Seebeck electromotive force. Antimony telluride is selected because it has higher charge carrier mobility and better power factor in its intrinsic excitation region, and its chemical stability is better in complex atmospheres containing trace amounts of electrolyte decomposition products such as fluorides and esters, thus ensuring long-term stable and reliable output of thermoelectric signals under actual battery failure conditions. Meanwhile, carbon nanotubes construct a three-dimensional conductive network in the composite phase, which not only integrates and amplifies the microvolt-level thermoelectric voltages generated on each antimony telluride nanoparticle into a millivolt-level macroscopic signal, solving the engineering problem of weak output signals and difficulty in direct detection of nano-thermoelectric materials, but also, as a highly conductive bridge, greatly reduces the contact resistance between antimony telluride particles, significantly improving the overall conductivity of the composite material. This results in a substantial increase in the final thermoelectric figure of merit, achieving stronger voltage output and higher detection sensitivity. Since this composite thermoelectric phase is uniformly distributed throughout the three-dimensional porous framework on the inner surface of the shell, the strength and spatial distribution of its thermoelectric signal directly reflect the gradient information of the internal temperature field, providing a physical basis for locating the origin of thermal runaway. (2) In view of the special metal / ceramic composite substrate environment of the battery shell, the present invention proposes an expansion flame retardant system, wherein a polyphosphate ammonium modified by melamine-cyanurate coating is combined with bio-based phytic acid. Specifically, the melamine-cyanurate coating layer significantly improves the interfacial compatibility between polyphosphate ammonium and inorganic substrate through the core-shell structure and effectively inhibits its hygroscopic hydrolysis, ensuring long-term stability. Under the high temperature trigger of thermal runaway, the polyphosphate produced by the decomposition of polyphosphate ammonium in this optimized ratio undergoes efficient esterification and phosphorylation cross-linking reaction with multiple phosphate groups released by phytic acid to form a three-dimensional network phosphate ester precursor. The gas released in synergy is captured in the network, driving the formation of a carbon layer with high expansion ratio, fine pores and excellent mechanical strength. At the same time, the abundant phosphate groups in phytic acid molecules can be further converted into pyrophosphate or metaphosphate glassy substances with extremely high thermal stability at high temperature, which encapsulate and strengthen the carbon layer skeleton, significantly improving its antioxidant and thermal erosion resistance, thereby ensuring that it can still maintain an effective physical barrier effect in the extreme high temperature environment of the battery. (3) In this invention, stainless steel metal powder, catalyst precursor powder, and a heat-insulating composite powder containing ceramic fibers, carbon nanotubes, and antimony telluride are uniformly mixed and co-sintered at a programmed temperature of 1100-1300℃ under a protective atmosphere to simultaneously form a catalytically active three-dimensional porous metal framework and a heat-insulating-thermoelectric composite phase solidified in the pores. Subsequently, the sintered body is immersed in a specific intumescent flame retardant solution and cured at a low temperature not exceeding 200℃. This process route completely avoids the destruction of the subsequently introduced organic flame retardant components by the high-temperature step, ensuring that the catalytic activity, thermoelectric properties, and flame retardant function can coexist in their optimal state, and realizing the efficient integration and synergy of the inorganic framework and the organic functional layer. (4) A high-strength and high-reliability metallurgical / ceramic bond between the composite functional layer and the stainless steel substrate was achieved through a co-sintering process. During the high-temperature sintering process, metallurgical bonds are formed between the stainless steel powders and between the powders and the substrate, while chemical bonds and three-dimensional mechanical interlocks are formed between the ceramic fibers and thermoelectric composite powders and the metal skeleton. This multi-layer bonding mechanism, from the atomic scale to the macroscopic scale, makes the bonding strength between the functional layer and the substrate far exceed that of traditional physical or adhesive coatings. It can withstand long-term vibration, damp heat aging and severe thermal shock cycles, fundamentally solving the long-term reliability problems such as functional layer peeling and cracking, and ensuring the long-term effectiveness of the active safety function of the battery throughout its entire life cycle. (5) The material system of this invention has undergone systematic optimization and adaptation for the harsh service environment of batteries, achieving comprehensive optimization of performance, lifespan and cost. Antimony telluride is selected as the thermoelectric material to accurately match the thermal runaway temperature range and improve its stability in complex atmospheres; the catalytic phase adopts non-precious metal perovskite or spinel oxide, which significantly reduces costs while ensuring high activity; the flame retardant system solves the compatibility problem with the substrate through the above-mentioned special compounding technology. The synergistic design of all components enables the final material to achieve an excellent balance in terms of early warning sensitivity, catalytic efficiency, flame retardant reliability, long-term durability and manufacturing cost control, and has a clear prospect for industrial application.

[0018] This solves the technical problems of existing technologies, such as rapid heat conduction, lack of long-term heat insulation and flame retardant function, single function of surface coating, weak adhesion, and easy failure at high temperatures.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein...

[0021] Figure 1This is a structural diagram of an automotive battery casing provided in an embodiment of the present invention. Detailed Implementation

[0022] The embodiments of this application are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0023] The following description, with reference to the accompanying drawings, illustrates an embodiment of a stainless steel material for automotive battery casings and its preparation method. Addressing the issue of rapid thermal conductivity mentioned in the background section, this application provides a stainless steel material for automotive battery casings. In this method, a heterojunction network constructed from carbon nanotubes and antimony telluride thermoelectric nanoparticles is integrated into a three-dimensional porous metal framework as the core thermoelectric composite component. Utilizing the high carrier mobility, excellent power factor, and chemical stability of antimony telluride in the thermal runaway temperature region, combined with the three-dimensional conductive network of carbon nanotubes, the integrated amplification and stable output of microvolt-level thermoelectric signals are achieved. This is achieved by leveraging the strength and spatial distribution of the thermoelectric signal. The system precisely locates the origin of thermal runaway; simultaneously, it designs an intumescent flame-retardant system adapted to metal / ceramic composite substrates, employing melamine-cyanurate-coated modified ammonium polyphosphate and bio-based phytic acid. Through high-temperature esterification and phosphorylation crosslinking reactions, a dense char layer with high expansion ratio and high mechanical strength is formed. This is further enhanced by pyrophosphate or metaphosphate glassy substances converted from phytic acid, improving the char layer's oxidation resistance and resistance to thermal erosion, achieving continuous physical barrier under extreme high temperatures. Furthermore, a step-by-step process of high-temperature co-sintering and low-temperature impregnation curing is used, first in a protective atmosphere... Stainless steel metal powder, catalyst precursor powder, and thermally insulating composite powder are co-sintered at 1100-1300℃ to form a catalytically active three-dimensional porous metal framework and a thermally insulating-thermoelectric composite phase solidified in the pores. Then, an intumescent flame retardant is impregnated and cured at a low temperature not exceeding 200℃ to avoid damage to the organic flame retardant components at high temperatures, ensuring optimal performance of catalytic, thermoelectric, and flame-retardant functions. This process also achieves a high-strength metallurgical / ceramic bond between the composite functional layer and the stainless steel substrate through metallurgical bonding between stainless steel powders and with the substrate, and ceramic fiber bonding. The chemical bonding and three-dimensional mechanical interlocking between the thermoelectric composite powder and the metal skeleton significantly improve the bonding strength between the functional layer and the matrix, solving the problems of peeling and cracking under long-term vibration, damp heat aging and thermal shock. Finally, through systematic optimization of the material system, non-precious metal perovskite or spinel oxide is selected as the catalytic phase, taking into account both high activity and low cost. Ultimately, the battery shell material achieves an excellent balance in terms of early warning sensitivity, catalytic efficiency, flame retardant reliability, long-term durability and manufacturing cost, effectively solving the defects of existing technologies and having prospects for industrial application.

[0024] All raw materials used in this invention can be purchased from domestic and international chemical product suppliers, and are all industrial-grade or chemically pure reagents. Specific specifications and potential supplier information are as follows: The stainless steel powder used is 316L stainless steel powder provided by Shandong Lingying Powder Metallurgy Co., Ltd., with a purity ≥99.5% and a particle size range typically of 50-150μm. It features high sphericity and low oxygen content, making it suitable for metal powder injection molding; the antimony telluride nanoparticles are purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of up to 99.9% and a particle size of 50-100nm; the melamine, cyanuric acid, phytic acid, and other chemicals all have a purity ≥98% and can be purchased from major chemical reagent suppliers as general-purpose chemical reagents.

[0025] Example 1 This invention provides a stainless steel material for automotive battery housings, such as... Figure 1 As shown, it includes: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

[0026] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0027] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0028] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 1:5.

[0029] The ceramic fiber is a short mullite fiber with a diameter of 1-10 μm and a length of 50-300 μm.

[0030] The catalytically active phase is a perovskite oxide.

[0031] The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is 2.5:1.

[0032] The present invention also provides a method for preparing a stainless steel material for automotive battery casings, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green compact is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1100℃; during this sintering process, stainless steel powder forms the porous metal skeleton, metal oxide powder forms the catalytically active phase, and heat-insulating composite powder forms the heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200℃.

[0033] In step S1, by mass, the stainless steel metal powder is 60 parts, the metal oxide powder is 5 parts, and the heat-insulating composite powder is 15 parts.

[0034] In step S2, the solid content of the slurry is 60%; the binder is polyvinyl butyral, and the amount added is 3% of the total mass of the mixed powder.

[0035] Example 2 This invention provides a stainless steel material for automotive battery housings, such as... Figure 1 As shown, it includes: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

[0036] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0037] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0038] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 1:3.

[0039] The ceramic fiber is made of alumina.

[0040] The catalytically active phase is a perovskite oxide.

[0041] The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is 2.7:1.

[0042] The present invention also provides a method for preparing a stainless steel material for automotive battery casings, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green body is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1150℃. During this sintering process, stainless steel powder forms a porous metal framework, metal oxide powder forms a catalytically active phase, and heat-insulating composite powder forms a heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200℃.

[0043] In step S1, by mass, the stainless steel metal powder is 65 parts, the metal oxide powder is 8 parts, and the heat-insulating composite powder is 18 parts.

[0044] In step S2, the solid content of the slurry is 63%; the binder is acrylic resin, and the amount added is 4% of the total mass of the mixed powder.

[0045] Example 3 This invention provides a stainless steel material for automotive battery housings, such as... Figure 1 As shown, it includes: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

[0046] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0047] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0048] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 1:1.

[0049] The ceramic fiber is a short mullite fiber with a diameter of 1-10 μm and a length of 50-300 μm.

[0050] The catalytically active phase is a spinel-type oxide.

[0051] The intumescent flame-retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is 3:1.

[0052] The present invention also provides a method for preparing a stainless steel material for automotive battery casings, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green body is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1100-1300℃; during this sintering process, stainless steel powder forms a porous metal skeleton, metal oxide powder forms a catalytically active phase, and heat-insulating composite powder forms a heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200℃.

[0053] In step S1, by mass, the stainless steel metal powder is 70 parts, the metal oxide powder is 10 parts, and the heat-insulating composite powder is 22 parts.

[0054] In step S2, the solid content of the slurry is 66%; the binder is acrylic resin, and the amount added is 5% of the total mass of the mixed powder.

[0055] Example 4 This invention provides a stainless steel material for automotive battery housings, such as... Figure 1 As shown, it includes: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

[0056] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0057] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0058] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 3:1.

[0059] The ceramic fiber is a short mullite fiber with a diameter of 1-10 μm and a length of 50-300 μm.

[0060] The catalytically active phase is a perovskite oxide.

[0061] The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is 3.2:1.

[0062] The present invention also provides a method for preparing a stainless steel material for automotive battery casings, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green body is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1250℃. During this sintering process, stainless steel powder forms a porous metal skeleton, metal oxide powder forms a catalytically active phase, and heat-insulating composite powder forms a heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200℃.

[0063] In step S1, by mass, stainless steel metal powder comprises 75 parts, metal oxide powder comprises 12 parts, and heat-insulating composite powder comprises 18 parts.

[0064] In step S2, the solid content of the slurry is 70%; the binder is polyvinyl butyral, and the amount added is 6% of the total mass of the mixed powder.

[0065] Example 5 This invention provides a stainless steel material for automotive battery housings, such as... Figure 1 As shown, it includes: a stainless steel substrate; and a composite functional layer integrally formed on one side of the substrate; wherein the composite functional layer has a three-dimensional porous metal skeleton, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal skeleton, a catalytically active phase is attached to the surface of the skeleton, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

[0066] The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

[0067] The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

[0068] The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 5:1.

[0069] The ceramic fiber is made of alumina.

[0070] The catalytically active phase is a spinel-type oxide.

[0071] The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of ammonium polyphosphate to phytic acid is 3.5:1.

[0072] The present invention also provides a method for preparing a stainless steel material for automotive battery casings, comprising the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green body is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1300℃. During this sintering process, stainless steel powder forms a porous metal skeleton, metal oxide powder forms a catalytically active phase, and heat-insulating composite powder forms a heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200℃.

[0073] In step S1, by mass, the stainless steel metal powder is 80 parts, the metal oxide powder is 15 parts, and the heat-insulating composite powder is 30 parts.

[0074] In step S2, the solid content of the slurry is 75%; the binder is acrylic resin, and the amount added is 8% of the total mass of the mixed powder.

[0075] Comparative Example 1 This comparative example provides a stainless steel material for automotive battery casings, comprising a stainless steel substrate and a composite functional layer integrally formed on one side of the substrate. The composite functional layer has a three-dimensional porous metal framework, with a heat-insulating reinforcing phase formed within the pores, and a catalytically active phase attached to the surface of the framework. The difference from Example 1 is that an intumescent flame-retardant phase is not provided.

[0076] Preparation method: Raw material compounding: By weight, 70 parts of 316L stainless steel metal powder, 10 parts of LaCoO3 metal oxide powder and 20 parts of heat insulation composite powder (containing 15 parts of alumina short fiber, 2 parts of carbon nanotubes and 3 parts of antimony telluride nanoparticles) are uniformly mixed. Green body forming: The mixed powder and binder are made into a slurry, which is coated on the surface of a 304 stainless steel substrate and dried at 80°C to form a green body; Co-sintering conversion: Sintering was carried out under an argon protective atmosphere with programmed temperature rise, and the final sintering temperature was 1200℃, held for 120 minutes.

[0077] Comparative Example 2 This comparative example provides a stainless steel material for automotive battery casings, comprising a stainless steel substrate and a composite functional layer integrally formed on one side of the substrate. The composite functional layer has a three-dimensional porous metal framework, with a heat-insulating reinforcing phase formed within the pores, and an intumescent flame-retardant phase loaded on the surface and inner walls of the pores. The difference from Example 1 is that no catalytically active phase is provided.

[0078] Preparation method: Raw material compounding: By weight, 70 parts of 316L stainless steel metal powder and 20 parts of heat insulation composite powder (containing 15 parts of alumina short fiber, 2 parts of carbon nanotubes, and 3 parts of antimony telluride nanoparticles) are uniformly mixed. Green body forming: The mixed powder and binder are made into a slurry, which is coated on the surface of a 304 stainless steel substrate and dried at 80°C to form a green body; Co-sintering conversion: Sintering was carried out under an argon protective atmosphere with programmed temperature rise, and the final sintering temperature was 1200℃, held for 120 minutes; Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant and dried and cured at 150°C.

[0079] Comparative Example 3 This comparative example provides a stainless steel material for automotive battery casings, comprising a stainless steel substrate and a composite functional layer integrally formed on one side of the substrate. The composite functional layer has a three-dimensional porous metal framework, with a heat-insulating reinforcing phase (containing only ceramic fibers) formed within the pores. A catalytically active phase is attached to the surface of the framework, and an intumescent flame-retardant phase is loaded on the surface of the layer and the inner walls of the pores. The difference from Example 1 is that only ceramic fibers are used in the heat-insulating reinforcing phase; carbon nanotubes and antimony telluride thermoelectric nanoparticles are not added, and a conventional external temperature sensor is used for thermal monitoring.

[0080] Preparation method: Raw material compounding: By weight, 70 parts of 316L stainless steel metal powder, 10 parts of LaCoO3 metal oxide powder and 20 parts of thermal insulation composite powder (containing only alumina short fibers) are uniformly mixed. Green body forming: The mixed powder and binder are made into a slurry, which is coated on the surface of a 304 stainless steel substrate and dried at 80°C to form a green body; Co-sintering conversion: Sintering was carried out under an argon protective atmosphere with programmed temperature rise, and the final sintering temperature was 1200℃, held for 120 minutes; Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant and dried and cured at 150°C; Sensor addition: A traditional thermocouple temperature sensor is added to the outside of the housing.

[0081] Performance testing The following performance tests were performed on the battery casing materials prepared in Examples 1-5 and Comparative Examples 1-3: Thermal conductivity testing: Laser flash emission method (LFA) was used, according to GB / T22588-2008 standard, with a test temperature range of 25-800℃; Flame retardancy testing: The flame retardancy rating of the material was evaluated according to the UL94 vertical burning test standard; Bond strength testing: Tensile test method was used, according to GB / T228.1-2010 standard, to test the bond strength between the functional layer and the substrate; Thermoelectric performance testing: Seebeck coefficient testing system was used to measure the thermoelectric voltage output of the material under a temperature gradient; Thermogravimetric analysis (TGA): Under a nitrogen atmosphere, the temperature was increased to 800℃ at 10℃ / min to analyze the thermal stability of the material, and the results are shown in Table 1 below.

[0082] Table 1. Battery casing material properties

[0083] As shown in Table 1, the battery casing materials of all embodiments meet the UL94V-0 flame retardant standard, have a thermal conductivity in the low thermal conductivity range of 0.25-0.48 W / (m・K), an interfacial bonding strength of up to 30 MPa, a thermoelectric figure of merit between 0.65 and 0.95, and a weight loss rate of only 6.5%-10.2% at 800℃ in a nitrogen atmosphere, demonstrating excellent heat insulation, flame retardancy, structural reliability, and thermoelectric sensing performance.

[0084] Comparing the data of the embodiments and comparative examples reveals that: although the thermal conductivity, interfacial bonding strength, and thermoelectric figure of merit of comparative example 1 are consistent with those of example 1, the flame retardant rating is only HB, which does not meet the high safety requirements for flame retardant standards; the flame retardant rating of comparative example 2 reaches V-0 and the interfacial bonding strength is good, but the weight loss rate at 800℃ is as high as 15.3%, and the thermal stability is far inferior to that of the embodiments; comparative example 3 has no thermoelectric figure of merit data, indicating that it does not have thermoelectric sensing function, and its thermal conductivity of 0.52W / (m・K) is higher than that of most embodiments, indicating that its thermal insulation performance is relatively insufficient.

[0085] The battery casing materials prepared in Examples 1-5 and Comparative Examples 1-3 were subjected to systematic mechanical property and durability tests, including tensile strength, flexural strength, impact toughness, fatigue life and surface hardness. Specific data are shown in Table 2 below.

[0086] Table 2 Results of Mechanical Properties and Durability Tests

[0087] As shown in Table 2, the battery casing materials prepared in Examples 1-5 of this invention exhibit significant advantages in both mechanical properties and durability. Regarding tensile strength, the values ​​of the sample samples ranged from 168 to 205 MPa, with Example 5 showing the highest tensile strength at 205 MPa; the flexural strength ranged from 230 to 280 MPa, with Example 5 again showing the best at 280 MPa; the impact strength was between 10 and 20 kJ / m. 2 Within the specified range, Example 5 exhibited the best impact toughness, reaching 20 kJ / m. 2 In terms of durability, the fatigue life of Examples 1, 2, and 5 all exceeded 1000,000 cycles, while the fatigue life of Examples 3 and 4 reached 850,000 cycles and 720,000 cycles, respectively. The Rockwell hardness (R scale) test results were 105-118, with Example 5 having the highest hardness, reaching 118.

[0088] As can be seen from the comparative data, Comparative Example 1 has the worst mechanical properties and durability indicators, with a tensile strength of only 150 MPa, a flexural strength of 205 MPa, and an impact strength of 10 kJ / m. 2 The fatigue life of Comparative Examples 1 was 300,000 cycles and the Rockwell hardness was 95, which was significantly different from the sample in the Example 1. Although the performance of Comparative Examples 2 and 3 was better than that of Comparative Example 1, they were still weaker than most of the Examples, especially in terms of fatigue life. Comparative Example 2 had only 600,000 cycles and Comparative Example 3 had 900,000 cycles, both of which were lower than the 1,000,000 cycles or more of Examples 1, 2 and 5.

[0089] In summary, the battery casing material prepared by this invention significantly improves the tensile, bending, impact strength and hardness of the material through component synergistic design and process optimization, while greatly extending the fatigue life and exhibiting excellent mechanical reliability and long-term service durability.

[0090] This application proposes a stainless steel material for automotive battery casings. In this method, a heterojunction network constructed from carbon nanotubes and antimony telluride thermoelectric nanoparticles is integrated into a three-dimensional porous metal framework as the core thermoelectric composite component. Utilizing the high carrier mobility, excellent power factor, and chemical stability of antimony telluride in the thermal runaway temperature region, combined with the three-dimensional conductive network of carbon nanotubes, the integrated amplification and stable output of microvolt-level thermoelectric signals are achieved. The strength and spatial distribution of the thermoelectric signal are used to precisely locate the thermal runaway origin point. Simultaneously… An intumescent flame-retardant system adapted to metal / ceramic composite substrates is designed, employing a melamine-cyanurate-coated modified ammonium polyphosphate compounded with bio-based phytic acid. Through high-temperature esterification and phosphorylation crosslinking reactions, a dense char layer with high expansion ratio and high mechanical strength is formed. This is further enhanced by pyrophosphate or metaphosphate glassy substances converted from phytic acid, improving the char layer's oxidation resistance and resistance to thermal erosion, achieving continuous physical barrier properties under extreme high temperatures. Furthermore, a step-by-step process of high-temperature co-sintering and low-temperature impregnation curing is used, first at 1100-1300°C under a protective atmosphere. Stainless steel powder, catalyst precursor powder, and thermal insulation composite powder are co-sintered at 00℃ to form a catalytically active three-dimensional porous metal framework and a thermal insulation-thermoelectric composite phase solidified in the pores. Then, an intumescent flame retardant is impregnated and cured at a low temperature not exceeding 200℃ to avoid damage to the organic flame retardant components at high temperatures, ensuring optimal performance of catalytic, thermoelectric, and flame-retardant functions. This process also achieves a high-strength metallurgical / ceramic bond between the composite functional layer and the stainless steel substrate. Through metallurgical bonding between stainless steel powders and with the substrate, and chemical bonding and three-dimensional mechanical interlocking between ceramic fibers and thermoelectric composite powders and the metal framework, the bonding strength between the functional layer and the substrate is significantly improved, solving the problems of peeling and cracking under long-term vibration, damp heat aging, and thermal shock. Finally, through systematic optimization of the material system, non-precious metal perovskite or spinel oxides are selected as the catalytic phase, balancing high activity and low cost. Ultimately, the battery casing material achieves an excellent balance in terms of early warning sensitivity, catalytic efficiency, flame retardant reliability, long-term durability, and manufacturing cost, effectively addressing the shortcomings of existing technologies and possessing promising prospects for industrial application.

[0091] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A stainless steel material for automotive battery casings, characterized in that, include: Stainless steel substrate; as well as A composite functional layer integrally formed on one side of the substrate; wherein, The composite functional layer has a three-dimensional porous metal framework, wherein a heat-insulating and reinforcing phase is formed in the pores of the three-dimensional porous metal framework, a catalytically active phase is attached to the surface of the framework, and an intumescent flame-retardant phase is also loaded on the surface of the layer and the inner wall of the pores.

2. The stainless steel material for automotive battery housing according to claim 1, characterized in that, The composite functional layer has a thickness of 0.1-2.0 mm, a porosity of 30%-70%, and an average pore size of 10-200 μm.

3. The stainless steel material for automotive battery housing according to claim 2, characterized in that, The heat-insulating reinforcing phase includes ceramic fibers, carbon nanotubes, and thermoelectric nanoparticles, wherein the thermoelectric nanoparticles are antimony telluride nanoparticles.

4. The stainless steel material for automotive battery housing according to claim 3, characterized in that, The mass ratio of carbon nanotubes to antimony telluride nanoparticles is 1:5 to 5:

1.

5. The stainless steel material for automotive battery housing according to claim 3, characterized in that, The ceramic fiber is alumina or mullite short fiber with a diameter of 1-10 μm and a length of 50-300 μm.

6. The stainless steel material for automotive battery housing according to claim 1, characterized in that, The catalytically active phase is a perovskite oxide or a spinel oxide.

7. The stainless steel material for automotive battery housing according to claim 1, characterized in that, The intumescent flame retardant phase comprises ammonium polyphosphate and phytic acid coated with melamine-cyanurate on the surface, wherein the mass ratio of the ammonium polyphosphate to phytic acid is (2.5:1) to (3.5:1).

8. A method for preparing a stainless steel material for an automotive battery casing as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Raw material composite: Stainless steel metal powder, metal oxide powder and thermal insulation composite powder containing ceramic fiber, carbon nanotube and thermoelectric nanoparticle are uniformly mixed. S2. Green body forming: The mixed powder and binder are made into a slurry, which is coated on a stainless steel substrate and dried to form a green body; S3. Co-sintering transformation: The green body is sintered under a protective atmosphere with a programmed temperature rise, and the final sintering temperature is 1100-1300℃; during this sintering process, stainless steel powder forms a porous metal skeleton, metal oxide powder forms a catalytically active phase, and heat-insulating composite powder forms a heat-insulating and reinforcing phase. S4. Flame retardant treatment: The sintered body is immersed in a solution containing an intumescent flame retardant, and after curing, an intumescent flame retardant phase is formed, wherein the curing temperature is not higher than 200°C.

9. The method for preparing stainless steel material for automotive battery casings according to claim 8, characterized in that, In step S1, by mass, the stainless steel metal powder is 60-80 parts, the metal oxide powder is 5-15 parts, and the heat-insulating composite powder is 15-30 parts.

10. The method for preparing stainless steel material for automotive battery casings according to claim 8, characterized in that, In step S2, the solid content of the slurry is 60%-75%; the binder is polyvinyl butyral or acrylic resin, and the amount added is 3%-8% of the total mass of the mixed powder.

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