Metal riveting structure for alumina fiber battery shell and preparation method

Abstract

The invention provides a metal riveting structure for an alumina fiber battery shell and a preparation method. The problem of debonding caused by thermal expansion difference and insufficient interface bonding force in traditional metal and ceramic riveting is solved. The structure comprises a metal riveting piece, a connecting layer and a transition layer, a connecting rod of the metal riveting piece penetrates through an inner threaded hole of the connecting layer and goes deep into a stepped groove of the transition layer, and double connection of threaded screwing and stepped groove mechanical embedding is formed; a metal ceramic gradient layer is arranged between the transition layer and the connecting layer and is matched with a thermal expansion coefficient; the thickness of the diffusion layer is 10-100 microns, and the shear strength of the diffusion layer is larger than or equal to 50 MPa. The structure obviously increases the contact area, relieves the thermal stress, improves the interface strength and the long-term reliability in a wide temperature range, and is suitable for high-temperature battery shell connection.

Description

Technical Field

[0001] The present invention relates to a metal riveting structure for an alumina fiber battery shell and a preparation method thereof, belonging to the technical field of new materials and new structures for lithium battery pack PACK shells. Background Art

[0002] With the development of new energy battery technology, alumina fiber has been widely used in the manufacture of high-temperature battery casings due to its high melting point, corrosion resistance, and low thermal expansion coefficient. However, the connection between alumina fiber ceramics and metal riveted parts has the following technical difficulties: The thermal expansion coefficients of ceramics and metals are greatly different, and traditional mechanical riveting is prone to interface cracking due to thermal stress; the chemical bonding between the ceramic surface and the metal is poor, and direct welding or gluing is difficult to meet the strength requirements for long-term use; the battery shell needs to take into account both lightweight and structural stability, and the traditional riveted structure is prone to local stress concentration due to insufficient contact area.

[0003] Therefore, the traditional battery housing with a ceramic-metal layer structure needs to be further improved and perfected. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a metal riveting structure and preparation method for an alumina fiber battery shell to enhance the bonding strength between the layer structures of the battery shell and effectively avoid problems such as cracking. According to an embodiment of the present invention, a first solution is provided: a metal riveted structure for an alumina fiber battery housing, comprising a polycrystalline alumina substrate, a transition layer, a connecting layer, and a metal riveted part; The polycrystalline alumina substrate is a pre-die-cast plate in the shape of a battery shell, and is formed by a nano-silicon oxide-doped high-temperature sintering process; The transition layer is formed on the surface mounting area of ​​the polycrystalline alumina substrate through a low-temperature sintering process after being impregnated with silica sol by an alumina fiber woven mesh or a silicon carbide fiber woven mesh; The outer surface of the transition layer is also provided with evenly distributed stepped grooves; The connecting layer covers the outer surface of the transition layer, and the connecting layer is provided with an internal threaded hole; The metal rivet comprises a connecting rod and a nut. The surface of the connecting rod is provided with an external thread adapted to the internal thread hole of the transition layer. The length of the connecting rod is ≥ the thickness of the connecting layer + the depth of the stepped groove. The connecting rod of the metal rivet is screwed into the internal thread hole through the external thread and then diffusely welded to form a diffusion layer with the connecting layer.

[0005] Furthermore, the fiber diameter of the alumina fiber mesh is 4-8 μm, and the weaving density is 80-100 fibers / square centimeter; the fiber diameter of the silicon carbide fiber mesh is 6-10 μm, and the weaving density is 100-120 fibers / square centimeter; the solid content of the impregnated silica sol is 25-45%; the high-temperature sintering process of the nano-silicon oxide doped polycrystalline alumina substrate is: doping 0.5-2.5wt% nano-silicon oxide, and the high-temperature sintering temperature range is 1700-1850°C; the low-temperature sintering temperature range of the alumina fiber woven mesh or the silicon carbide fiber woven mesh after impregnation with silica sol is 1500-1650°C, and during the low-temperature sintering process, the silica sol is converted into silica ceramics and tightly bonded to the polycrystalline alumina substrate.

[0006] Furthermore, the stepped grooves on the surface of the transition layer are formed by laser etching, the height of the stepped teeth is 50-200 μm, the tooth spacing is 200-800 μm, and the tooth shape of the stepped teeth includes sawtooth, trapezoid or wave.

[0007] Furthermore, the connection layer is a connection metal plate that is compatible with the material of the metal rivet, and the connection layer is fixed to the surface of the transition layer in a vertical direction through a hot pressing sintering process. At least one internal threaded hole is provided on the connection layer.

[0008] Furthermore, the hole position of the internal threaded hole corresponds to the stepped groove of the transition layer, and the hole depth of the internal threaded hole is ≥ the thickness of the connecting layer + 80% of the depth of the stepped groove.

[0009] Furthermore, the diameter of the nut of the metal rivet is ≥ 1.5 times the diameter of the internal threaded hole, and the length of the connecting rod is ≥ the thickness of the connecting layer + the depth of the stepped groove + 2 mm.

[0010] Furthermore, the diffusion layer is formed by mutual diffusion of metal atoms of the external thread of the connecting rod and the connecting layer under high-temperature diffusion welding conditions. The thickness of the diffusion layer is 10-100 μm, and the interface shear strength of the diffusion layer is ≥50 MPa.

[0011] Furthermore, a metal-ceramic gradient layer is provided on the surface of the connecting layer near the transition layer. The metal-ceramic gradient layer is composed of a metal matrix and silica ceramic particles of the same material as the connecting layer. The volume fraction of the ceramic particles decreases gradually along the thickness direction from 30-50% on the transition layer side to 5-10% on the connecting layer side. The particle size of the ceramic particles is 5-20 μm, and the number of gradient layers is 3-5 layers.

[0012] According to an embodiment of the present invention, using the metal riveting structure for the alumina fiber battery housing in the first embodiment provided by the present invention, a second embodiment is provided: A method for preparing a metal riveted structure of an alumina fiber battery shell, comprising the steps of: S1: Prepare a polycrystalline alumina substrate, dope 0.5-2.5wt% nano-silicon oxide into alumina powder, pre-die-cast it into a plate in the shape of a battery shell, and sinter it at a high temperature of 1700-1850℃ to form the main load-bearing substrate; S2: Prepare a transition layer by selecting an alumina fiber woven mesh or a silicon carbide fiber woven mesh, soaking it in a silica sol with a solid content of 25-45%, and then covering it on the surface mounting area of ​​the substrate. Sinter at a low temperature of 1500-1650°C to convert the silica sol into silica ceramics and tightly bond it to the polycrystalline alumina substrate; S3: Processing step grooves: using laser etching technology to process step grooves on the surface of the transition layer. The height of the step teeth is 50-200μm, the tooth spacing is 200-800μm, and the tooth shape of the step teeth includes sawtooth, trapezoidal or wavy; S4: Fix the connection layer, cover the connection metal plate that matches the material of the metal rivet on the surface of the transition layer, and fix it by hot pressing and sintering in the vertical direction; S5: Install and weld the riveted parts, screw the connecting rod of the metal riveted parts into the internal threaded hole of the connecting layer through the external thread, and perform diffusion welding under argon or nitrogen protection at 800-1000℃ and 0.5-2MPa pressure for 20-40 minutes to form a diffusion layer with a thickness of 10-100μm and an interface shear strength of ≥50MPa.

[0013] A lithium battery pack comprises any one of the above-mentioned metal riveting structures for an alumina fiber battery shell.

[0014] A lithium battery pack is prepared by any of the above-mentioned methods for preparing the metal riveting structure of an alumina fiber battery shell.

[0015] Compared with the existing technology, the technical solution provided by this application has the following unique beneficial effects: The basis of this metal riveted structure is a double-layer design of transition layer and connecting layer. The transition layer and the polycrystalline alumina substrate are infiltrated with silica sol to form silica ceramic to form a strong and tight structure. The stepped groove structure between the transition layer and the connecting layer increases the contact area between the ceramic and the metal and greatly improves the interface bonding strength. The length of the connecting rod of the metal rivet is ≥ the thickness of the connecting layer + the depth of the step groove, ensuring that the connecting rod passes through the connecting layer and penetrates into the step groove of the transition layer, thereby ensuring the redundancy of the mechanical connection of the rivet. In particular, the external thread structure of the connecting rod forms a dual connection structure with the battery shell, which is a threaded connection and a step groove mechanical interlocking. This significantly increases the riveting strength and anti-loosening ability between the metal rivet and the battery shell. At the same time, the diffusion welding forms a diffusion layer with a thickness of 10-100μm and a shear strength of ≥50MPa, which further enhances the interface bonding strength, connection sealing and fatigue resistance, effectively avoiding interface failure problems under thermal stress or cyclic loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0017] in: Figure 1 Schematic diagram of a metal riveting structure for an alumina fiber battery housing according to an embodiment; Figure 2 A schematic diagram of the specific structure between the connecting rod and the stepped groove in one embodiment; Figure 3 This is a flow chart of a method for preparing a metal riveted structure of an alumina fiber battery casing in one embodiment; Reference numerals: 10-polycrystalline alumina substrate; 20-transition layer; 21-step groove; 30-connecting layer; 31-inner thread hole; 40-metal rivet; 41-connecting rod; 42-external thread. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of this application.

[0019] Example 1 The technical issues addressed by this embodiment are the following: the connection between the alumina fiber ceramic and the metal rivet 40 presents the following problems: the significant difference in thermal expansion coefficients between the ceramic and metal makes traditional mechanical riveting susceptible to interfacial cracking due to thermal stress; the poor chemical bonding between the ceramic surface and the metal makes direct welding or gluing difficult to meet the strength requirements for long-term use; and the battery casing must balance lightweighting with structural stability, and traditional riveted structures are prone to localized stress concentration due to insufficient contact area. Therefore, traditional battery casings with ceramic-metal layer structures require further improvement and refinement.

[0020] In order to solve the above technical problems, this embodiment provides a metal riveting structure for an alumina fiber battery shell, such as Figure 1 As shown, it includes a polycrystalline alumina substrate 10, a transition layer 20, a connecting layer 30 and a metal rivet 40; The polycrystalline alumina substrate 10 is a pre-die-cast plate in the shape of a battery shell, and the polycrystalline alumina substrate 10 is formed by a nano-silicon oxide doped high-temperature sintering process; The transition layer 20 is formed on the surface mounting area of ​​the polycrystalline alumina substrate 10 by a low-temperature sintering process after the alumina fiber woven mesh or the silicon carbide fiber woven mesh is impregnated with silica sol; The outer surface of the transition layer 20 is also provided with evenly distributed stepped grooves 21; The connecting layer 30 covers the outer surface of the transition layer 20, and the connecting layer 30 is provided with an internal threaded hole 31; The metal rivet 40 includes a connecting rod 41 and a nut. The surface of the connecting rod 41 is provided with an external thread 42 adapted to the internal thread hole 31 of the transition layer 20. The length of the connecting rod 41 is greater than or equal to the thickness of the connecting layer 30 + the depth of the stepped groove 21. The connecting rod 41 of the metal rivet 40 is screwed into the internal thread hole 31 through the external thread 42 and then forms a diffusion layer with the connecting layer 30 through diffusion welding.

[0021] Specifically, the high-temperature sintering process of the polycrystalline alumina substrate 10 doped with nano-silicon oxide is as follows: doping with 0.5-2.5 wt% nano-silicon oxide, and the high-temperature sintering temperature range is 1700-1850° C.; The low-temperature sintering temperature range of the alumina fiber woven mesh or silicon carbide fiber woven mesh after being soaked in silica sol is 1500-1650° C. During the low-temperature sintering process, the silica sol is converted into silicon dioxide ceramics and is tightly bonded to the polycrystalline alumina substrate 10 .

[0022] The diameter of the alumina fiber mesh is 4-8 μm, and the weaving density is 80-100 fibers / cm2; the diameter of the silicon carbide fiber mesh is 6-10 μm, and the weaving density is 100-120 fibers / cm2; and the solid content of the impregnated silica sol is 25-45%.

[0023] Specifically, the stepped grooves 21 on the surface of the transition layer 20 are formed by laser etching, the height of the stepped teeth is 50-200 μm, the tooth spacing is 200-800 μm, and the tooth shape of the stepped teeth includes sawtooth, trapezoidal or wavy.

[0024] In another possible solution, the stepped groove 21 on the surface of the transition layer 20 is formed by pressing with a mold.

[0025] The connecting layer 30 is a connecting metal plate made of a material compatible with the metal rivet 40 . The connecting layer 30 is fixed to the surface of the transition layer 20 in a vertical direction through a hot pressing sintering process. At least one internal threaded hole 31 is provided on the connecting layer 30 .

[0026] The connecting layer 30 is a functional structural layer disposed outside the transition layer 20. Its core function is to achieve a mechanical connection with the metal rivet 40 through the internal threaded hole 31 and form an atomic-level bonding interface through diffusion welding, ultimately reliably fixing the metal rivet 40 to the polycrystalline alumina main layer and the battery housing. The material of the connecting layer 30 is preferably a metal or metal-based composite material that matches the material of the metal rivet 40, for example: If the metal rivet 40 is made of stainless steel, such as 304L or 316L, the connecting layer 30 may be made of a stainless steel sheet with a thickness of 0.5-2 mm. If the metal rivet 40 is made of a titanium alloy, such as Ti-6Al-4V, the connection layer 30 may be made of a titanium alloy foil with a thickness of 0.3-1.5 mm.

[0027] The forming of the connecting layer 30 needs to be closely matched with the structure of the stepped groove 21 of the transition layer 20 to ensure the interface bonding strength. The specific steps are as follows: Pretreatment of the transition layer 20: After the stepped groove 21 is machined on the surface of the transition layer 20 , the surface of the stepped groove 21 is roughened, such as by sandblasting, with a roughness Ra of 3.2-6.3 μm, to increase the contact area between the connection layer 30 and the transition layer 20 .

[0028] Material bonding of the connecting layer 30: Cut the metal sheet / foil into a structure that matches the outer contour of the transition layer 20, and align the connecting layer 30 with the stepped groove 21 of the transition layer 20.

[0029] Interface bonding and curing: A hot pressing sintering process is used to achieve the bonding of the connecting layer 30 and the transition layer 20: temperature: 800-1000°C, which is lower than the sintering temperature of the transition layer 20 1500-1650°C to avoid damaging the structure of the transition layer 20; pressure: 5-15MPa; holding time: 30-60 minutes; atmosphere: inert gas protection to prevent metal oxidation.

[0030] Subsequent processing: After the bonding is completed, the outer surface of the connection layer 30 is turned or polished, and then the internal threaded hole 31 is processed by hole positioning and ultrasonic vibration assisted tapping process to finally form a complete connection layer 30 structure.

[0031] Specifically, the position of the internal threaded hole 31 corresponds to the stepped groove 21 of the transition layer 20, and the depth of the internal threaded hole 31 is ≥ the thickness of the connecting layer 30 + 80% of the depth of the stepped groove 21. The diameter of the nut of the metal rivet 40 is ≥ 1.5 times the diameter of the internal threaded hole 31, and the length of the connecting rod 41 is ≥ the thickness of the connecting layer 30 + the depth of the stepped groove 21 + 2 mm.

[0032] The internal threaded hole 31 on the connecting layer 30 is positioned to ensure the precise assembly, interface bonding strength and long-term reliability of the metal riveted structure. The outer surface of the transition layer 20 is provided with a stepped groove 21, and the length of the connecting rod 41 of the metal rivet 40 must be ≥ the thickness of the connecting layer 30 + the depth of the stepped groove 21. If the hole position of the internal threaded hole 31 is not accurately positioned, the following problems may occur: the connecting rod 41 cannot be fully embedded in the stepped groove 21, resulting in "hanging" or partial contact, reducing the support stiffness of the rivet on the battery shell; the contact area between the stepped groove 21 and the connecting rod 41 is insufficient. Under battery charge and discharge cycles or vibration conditions, stress concentration can easily cause the edge of the stepped groove 21 to crack, destroying the structure of the transition layer 20. After the threaded connection part of the metal rivet 40 is screwed into the internal threaded hole 31, it needs to be diffused and welded to form a diffusion layer with the connecting layer 30. The key to diffusion welding is the sufficient diffusion of interface atoms, which requires the contact area and pressure uniformity between the threaded connection part and the internal threaded hole 31. If the hole position deviation is too large, the threaded connection and the internal threaded hole 31 may only partially contact each other, resulting in uneven diffusion layer thickness and substandard interface shear strength. Precise hole positioning ensures a tight fit around the entire perimeter of the threaded connection and internal threaded hole 31, providing uniform interface pressure for diffusion welding and improving the bonding quality of the diffusion layer. Lithium battery pack shells must withstand harsh conditions such as mechanical shock and temperature cycling, placing extremely high demands on the dimensional accuracy of the riveted structure. Excessive hole position deviation can lead to inconsistent installation positions of multiple riveted parts, uneven stress on the entire shell, and prone to local deformation or fracture during long-term use. Hole positioning ensures that the position and depth of all internal threaded holes 31 are consistent, achieving equal strength distribution in the riveted structure and improving the overall reliability of the shell.

[0033] Hole positioning is a key step in the processing of the threaded hole 31 in the connecting layer 30. By precisely controlling the hole position deviation, the tight fit between the stepped groove 21 and the connecting rod 41 and the uniform bonding of the diffusion welding interface can be achieved, ultimately ensuring the structural strength and long-term service performance of the lithium battery PACK shell.

[0034] Specifically, the diffusion layer is formed by the interdiffusion of metal atoms between the external thread 42 of the connecting rod 41 and the connecting layer 30 under high-temperature diffusion welding conditions. The diffusion layer has a thickness of 10-100 μm and an interfacial shear strength of ≥50 MPa. A metal-ceramic gradient layer is provided on the surface of the connecting layer 30 near the transition layer 20. This metal-ceramic gradient layer is composed of a metal matrix made of the same material as the connecting layer 30 and silica ceramic particles. The volume fraction of the ceramic particles decreases gradually along the thickness direction from 30-50% on the transition layer 20 side to 5-10% on the connecting layer 30 side. The particle size of the ceramic particles is 5-20 μm, and the number of gradient layers is 3-5.

[0035] In the riveted structure of traditional metal and alumina fiber ceramic, mechanical threaded connection alone is prone to interface debonding due to differences in thermal expansion coefficients, and simple physical contact cannot form a stable chemical bond, making it difficult to meet the long-term reliability requirements of high-temperature battery casings.

[0036] A titanium alloy connecting rod 41 with an external thread 42 on the surface is screwed into the internal threaded hole 31. The length of the connecting rod 41 = the thickness of the connecting layer 30 + the depth of the stepped groove 21 × 80% + 2 mm, so that the external thread 42 of the connecting rod 41 forms a point-surface contact with the serrated groove wall of the stepped groove 21, and each serration covers 3 thread teeth; under argon protection, diffusion welding is performed at 900°C and a pressure of 1.5 MPa for 30 minutes to allow the metal atoms of the external thread 42 of the titanium alloy connecting rod 41 and the aluminum alloy connecting layer 30 to diffuse into each other, forming a diffusion layer with a thickness of about 50 μm.

[0037] The length of the connecting rod 41 of the metal rivet 40 is ≥ the thickness of the connecting layer 30 + the depth of the stepped groove 21, ensuring that the connecting rod 41 passes through the connecting layer 30 and penetrates into the stepped groove 21 of the transition layer 20, thereby ensuring the redundancy of the mechanical connection of the rivet. In particular, the external thread 42 structure of the connecting rod 41 forms a dual connection structure with the battery shell, namely, threaded connection and mechanical engagement with the stepped groove 21, which significantly increases the riveting strength and anti-loosening ability between the metal rivet 40 and the battery shell. At the same time, diffusion welding forms a diffusion layer with a thickness of 10-100μm and a shear strength of ≥50MPa, which further enhances the interface bonding strength, connection sealing and fatigue resistance, and effectively avoids interface failure problems under thermal stress or cyclic loads.

[0038] Example 2 This embodiment specifically describes the connection method between the metal rivet 40, the connection layer 30, and the step groove 21 of the transition layer 20. Figure 2 shown.

[0039] The connection mechanism of the metal rivet 40 of this embodiment is one of the core innovations of the present invention, and the problem it solves is how to further improve the connection strength and stability between the metal rivet 40 and the battery housing.

[0040] Specifically, the metal rivet 40 penetrates the internal thread of the connection layer 30 and penetrates into the stepped groove 21 of the transition layer 20. The metal rivet 40 occupies 60%-90% of the depth of the stepped groove 21. During the rotation and advancement of the metal rivet 40, the groove wall of the stepped groove 21 is unscrewed to form a connecting thread. The connecting thread is adapted to the external thread 42. The number of thread teeth of the connecting thread is 1-5, forming a mechanical interlocking structure between the external thread 42 of the connecting rod 41 and the groove wall of the stepped groove 21. After combined with diffusion welding, a triple connection interface is formed: thread rotation fixation, mechanical interlocking of the stepped groove 21, and diffusion layer, thereby effectively solving the interface cracking problem caused by insufficient contact area in traditional riveting. This design requires the coordinated optimization of the machining accuracy of the stepped groove 21, thread parameters, and diffusion welding process to obtain an optimized implementation plan and produce the best connection interface.

[0041] Furthermore, the tooth profile of the stepped groove 21 of the transition layer 20 matches the tooth profile of the external thread 42 of the connecting rod 41 of the metal rivet 40 in geometrical parameters.

[0042] Specifically, the tooth top angle of the sawtooth stepped groove 21 is consistent with the tooth profile angle of the triangular thread; The difference between the tooth top width of the stepped groove and the tooth top width of the trapezoidal thread is less than 20μm; The difference between the crest radius of the wavy stepped groove 21 and the tooth bottom radius of the rectangular thread is less than 10 μm; At the same time, the ratio of the tooth spacing of the stepped groove 21 to the pitch of the external thread 42 is 1:1-1:3, so as to ensure that each stepped tooth covers 1-3 thread teeth.

[0043] In traditional riveted joints, the stepped groove 21 and the thread are typically designed independently, without considering the synergistic effect of their geometric parameters. This solution, by matching the tooth profile of the stepped groove 21 with the thread profile, evenly distributes interfacial stress along the stepped groove 21-thread interface, avoiding localized stress concentration. For example, when the tooth angles of the serrated stepped groove 21 match those of the triangular thread, the compressive stress distribution at the contact interface is more uniform; when the trapezoidal stepped groove 21 matches the top width of the trapezoidal thread, shear stress can be effectively dispersed.

[0044] After fatigue testing, the riveted structure with tooth-profile collaborative design showed no interface cracks under cyclic shear load, which is a 100% improvement over the traditional independently designed riveted structure; at the same time, the interface contact area was increased by 20-30% compared with the traditional design, and the shear strength stability of the diffusion layer was improved, which significantly improved the long-term reliability of the riveted structure.

[0045] Example 3 This embodiment provides a method for preparing a metal riveted structure of an alumina fiber battery shell. Figure 3 As shown, the steps include: S1: preparing a polycrystalline alumina substrate 10, doping 0.5-2.5 wt% of nano-silicon oxide into alumina powder, pre-die-casting it into a plate in the shape of a battery shell, and sintering it at a high temperature of 1700-1850° C. to form a main load-bearing substrate; S2: preparing a transition layer 20 by selecting an alumina fiber woven mesh or a silicon carbide fiber woven mesh, impregnating it with a silica sol having a solid content of 25-45%, and then covering the surface mounting area of ​​the substrate. The transition layer 20 is then sintered at a low temperature of 1500-1650°C to convert the silica sol into a silica ceramic that is tightly bonded to the polycrystalline alumina substrate 10; S3: Processing the stepped groove 21: using a laser etching process to process the stepped groove 21 on the surface of the transition layer 20. The height of the stepped teeth is 50-200 μm, the tooth spacing is 200-800 μm, and the tooth shape of the stepped teeth includes a sawtooth shape, a trapezoidal shape, or a wavy shape. S4: Fix the connection layer 30 by covering the connection metal plate that matches the material of the metal rivet 40 on the surface of the transition layer 20 and fixing it by hot pressing and sintering in a vertical direction; S5: Install and weld the rivet parts. Screw the connecting rod 41 of the metal rivet part 40 into the internal thread hole 31 of the connecting layer 30 through the external thread 42. Under the protection of argon or nitrogen, perform diffusion welding at 800-1000℃ and 0.5-2MPa pressure for 20-40 minutes to form a diffusion layer with a thickness of 10-100μm and an interface shear strength of ≥50MPa.

[0046] The preparation method of the metal riveted structure is based on a double-layer design of a transition layer 20 and a connecting layer 30. The transition layer 20 and the polycrystalline alumina substrate 10 are infiltrated with silica sol to form a silicon dioxide ceramic to form a strong and tight structure. The step groove 21 structure between the transition layer 20 and the connecting layer 30 increases the contact area between the ceramic and the metal and greatly improves the interface bonding strength. The length of the connecting rod 41 of the metal rivet 40 is ≥ the thickness of the connecting layer 30 + the depth of the step groove 21, ensuring that the connecting rod 41 passes through the connecting layer 30 and penetrates into the transition layer 20. Inside the stepped groove 21, the redundancy of the mechanical connection of the riveted parts is ensured. In particular, a dual connection structure of threaded connection and mechanical engagement of the stepped groove 21 is formed between the external thread 42 of the connecting rod 41 and the battery shell, which significantly increases the riveting strength and anti-loosening ability between the metal riveted part 40 and the battery shell. At the same time, diffusion welding forms a diffusion layer with a thickness of 10-100μm and a shear strength of ≥50MPa, which further enhances the interface bonding force, connection sealing and fatigue resistance, and effectively avoids interface failure problems under thermal stress or cyclic loads.

[0047] Example 3 The present embodiment provides a lithium battery pack, the battery shell of the lithium battery pack includes a metal riveted structure, including a polycrystalline alumina substrate 10, a transition layer 20, a connecting layer 30 and a metal riveted part 40; the polycrystalline alumina substrate 10 is a pre-cast plate having the shape of a battery shell, and the polycrystalline alumina substrate 10 is formed by a high-temperature sintering process doped with nano-silicon oxide; the transition layer 20 is formed on the surface mounting area of ​​the polycrystalline alumina substrate 10 by a low-temperature sintering process after being impregnated with silica sol by an alumina fiber woven mesh or a silicon carbide fiber woven mesh; the transition layer 20 is formed by a low-temperature sintering process; The outer surface is also provided with evenly distributed stepped grooves 21; the connecting layer 30 covers the outer surface of the transition layer 20, and the connecting layer 30 is provided with an internal threaded hole 31; the metal rivet 40 includes a connecting rod 41 and a nut, and the surface of the connecting rod 41 is provided with an external thread 42 that is compatible with the internal threaded hole 31 of the transition layer 20, and the length of the connecting rod 41 is ≥ the thickness of the connecting layer 30 + the depth of the stepped groove 21; the connecting rod 41 of the metal rivet 40 is screwed into the internal threaded hole 31 through the external thread 42, and a diffusion layer is formed between it and the connecting layer 30 through diffusion welding.

[0048] Example 4 This embodiment provides a lithium battery pack, which is prepared by the following steps: S1: preparing a polycrystalline alumina substrate 10, doping 0.5-2.5 wt% of nano-silicon oxide into alumina powder, pre-die-casting it into a plate in the shape of a battery shell, and sintering it at a high temperature of 1700-1850° C. to form a main load-bearing substrate; S2: preparing a transition layer 20 by selecting an alumina fiber woven mesh or a silicon carbide fiber woven mesh, impregnating it with a silica sol having a solid content of 25-45%, and then covering the surface mounting area of ​​the substrate. The transition layer 20 is then sintered at a low temperature of 1500-1650°C to convert the silica sol into a silica ceramic that is tightly bonded to the polycrystalline alumina substrate 10; S3: Processing the stepped groove 21: using a laser etching process to process the stepped groove 21 on the surface of the transition layer 20. The height of the stepped teeth is 50-200 μm, the tooth spacing is 200-800 μm, and the tooth shape of the stepped teeth includes a sawtooth shape, a trapezoidal shape, or a wavy shape. S4: Fix the connection layer 30 by covering the connection metal plate that matches the material of the metal rivet 40 on the surface of the transition layer 20 and fixing it by hot pressing and sintering in the vertical direction; S5: Install and weld the rivet parts. Screw the connecting rod 41 of the metal rivet part 40 into the internal thread hole 31 of the connecting layer 30 through the external thread 42. Under the protection of argon or nitrogen, perform diffusion welding at 800-1000℃ and 0.5-2MPa pressure for 20-40 minutes to form a diffusion layer with a thickness of 10-100μm and an interface shear strength of ≥50MPa.

[0049] The technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application. The description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of this application. It should be pointed out that for ordinary technicians in this field, without departing from the concept of this application, several variations and improvements can be made, which all fall within the scope of protection of this application.

[0050] It should be noted that when an element is referred to as being "fixed on" or "set on" another component, it may be directly on the other component or indirectly set on the other component; when a component is referred to as being "connected to" another component, it may be directly connected to the other component or indirectly connected to the other component. It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting this application.

[0051] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" or "several" means two or more, unless otherwise specifically defined.

[0052] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which this application can be implemented. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the efficacy and purpose that can be achieved by this application.

Claims

1. A metal riveting structure for an alumina fiber battery housing, characterized in that: It includes a polycrystalline alumina substrate, a transition layer, a connecting layer and metal riveted parts; The polycrystalline alumina substrate is a pre-die-cast plate in the shape of a battery shell, and is formed by a nano-silicon oxide-doped high-temperature sintering process; The transition layer is formed on the surface mounting area of ​​the polycrystalline alumina substrate through a low-temperature sintering process after being impregnated with silica sol by an alumina fiber woven mesh or a silicon carbide fiber woven mesh; The outer surface of the transition layer is also provided with evenly distributed stepped grooves; The connecting layer covers the outer surface of the transition layer, and the connecting layer is provided with an internal threaded hole; The metal rivet comprises a connecting rod and a nut. The surface of the connecting rod is provided with an external thread adapted to the internal thread hole of the transition layer. The length of the connecting rod is ≥ the thickness of the connecting layer + the depth of the stepped groove. The connecting rod of the metal rivet is screwed into the internal thread hole through the external thread and then diffusely welded to form a diffusion layer with the connecting layer.

2. The metal riveting structure for an alumina fiber battery housing according to claim 1, characterized in that: The diameter of the alumina fiber mesh is 4-8 μm, and the weaving density is 80-100 fibers / cm2; the diameter of the silicon carbide fiber mesh is 6-10 μm, and the weaving density is 100-120 fibers / cm2; The solid content of the infiltrated silica sol is 25-45%; The high-temperature sintering process of the polycrystalline alumina substrate doped with nano-silicon oxide is as follows: doping with 0.5-2.5 wt% nano-silicon oxide and sintering at a temperature range of 1700-1850° C. The temperature range of low-temperature sintering of the alumina fiber woven mesh or silicon carbide fiber woven mesh after being impregnated with silica sol is 1500-1650°C. During the low-temperature sintering process, the silica sol is converted into silicon dioxide ceramics and is tightly combined with the polycrystalline alumina substrate.

3. The metal riveting structure for an alumina fiber battery housing according to claim 1, characterized in that: The stepped grooves on the surface of the transition layer are formed by laser etching. The height of the stepped teeth is 50-200 μm, the tooth spacing is 200-800 μm, and the tooth shape of the stepped teeth includes sawtooth, trapezoid or wave.

4. The metal riveting structure for an alumina fiber battery housing according to claim 1, characterized in that: The connecting layer is a connecting metal plate that is compatible with the material of the metal rivet. The connecting layer is fixed to the surface of the transition layer in a vertical direction through a hot pressing and sintering process. At least one internal threaded hole is provided on the connecting layer.

5. The metal riveting structure for an alumina fiber battery housing according to claim 4, characterized in that: The hole position of the internal threaded hole corresponds to the stepped groove of the transition layer, and the hole depth of the internal threaded hole is ≥ the thickness of the connecting layer + 80% of the depth of the stepped groove.

6. The metal riveting structure for alumina fiber battery housing according to claim 1, characterized in that: The diameter of the nut of the metal rivet is ≥ 1.5 times the diameter of the internal threaded hole, and the length of the connecting rod is ≥ the thickness of the connecting layer + the depth of the stepped groove + 2 mm.

7. The metal riveting structure for alumina fiber battery housing according to claim 1, characterized in that: The diffusion layer is formed by mutual diffusion of the external thread of the connecting rod and the metal atoms of the connecting layer under high-temperature diffusion welding conditions. The thickness of the diffusion layer is 10-100 μm, and the interface shear strength of the diffusion layer is ≥50 MPa.

8. The metal riveting structure for alumina fiber battery housing according to claim 7, characterized in that: The connecting layer is provided with a metal ceramic gradient layer on the surface close to the transition layer. The metal ceramic gradient layer is composed of a metal matrix and silicon dioxide ceramic particles of the same material as the connecting layer. The volume fraction of the ceramic particles decreases gradually along the thickness direction from 30-50% on the transition layer side to 5-10% on the connecting layer side. The particle size of the ceramic particles is 5-20 μm, and the number of gradient layers is 3-5.

9. A method for preparing a metal riveted structure of an alumina fiber battery shell, characterized in that: Including steps: S1: Prepare a polycrystalline alumina substrate, dope 0.5-2.5wt% nano-silicon oxide into alumina powder, pre-die-cast it into a plate in the shape of a battery shell, and sinter it at a high temperature of 1700-1850℃ to form the main load-bearing substrate; S2: Prepare a transition layer by selecting an alumina fiber woven mesh or a silicon carbide fiber woven mesh, soaking it in a silica sol with a solid content of 25-45%, and then covering it on the surface mounting area of ​​the substrate. Sinter at a low temperature of 1500-1650°C to convert the silica sol into silica ceramics and tightly bond it to the polycrystalline alumina substrate; S3: Processing step grooves: using laser etching technology to process step grooves on the surface of the transition layer. The height of the step teeth is 50-200μm, the tooth spacing is 200-800μm, and the tooth shape of the step teeth includes sawtooth, trapezoidal or wavy; S4: Fix the connection layer, cover the connection metal plate that matches the material of the metal rivet on the surface of the transition layer, and fix it by hot pressing and sintering in the vertical direction; S5: Install and weld the riveted parts, screw the connecting rod of the metal riveted parts into the internal threaded hole of the connecting layer through the external thread, and perform diffusion welding under argon or nitrogen protection at 800-1000℃ and 0.5-2MPa pressure for 20-40 minutes to form a diffusion layer with a thickness of 10-100μm and an interface shear strength of ≥50MPa.

10. The method for preparing the metal riveted structure of the alumina fiber battery casing according to claim 9, characterized in that: The method for preparing the threaded hole in the connecting layer includes: S41: leaving an observation area on the surface of the transition layer, and retaining the observation area when the connecting layer covers the surface of the transition layer; S42: Scanning the connection layer and the observation area at the edge of the connection layer to obtain the step groove distribution, and marking hole positions on the surface of the connection layer using a laser marking machine according to the step groove distribution, wherein the hole positions correspond to the step grooves of the transition layer; S43: An internal threaded hole is formed along the hole position.

11. The method for preparing the metal riveted structure of the alumina fiber battery casing according to claim 10, characterized in that: The step of forming an internal threaded hole along the hole position includes: S431: During the drilling phase, longitudinal ultrasonic vibration is applied via a CNC precision machine tool equipped with a diamond drill bit. The machine spindle speed is 500-1500 rpm, the diamond drill bit diameter is 0.1-5 mm, the diamond drill bit apex angle is 118-135°, the longitudinal ultrasonic vibration frequency is 20-40 kHz, the amplitude is 5-15 μm, the feed rate is 0.05-0.2 mm / s, and 0.3-0.5 MPa compressed air is introduced simultaneously for cooling and chip removal. S432: During the tapping stage, a CNC tapping machine equipped with a hard alloy tap is used to apply transverse ultrasonic vibration. The pitch of the hard alloy tap is 0.5-1.5mm, the frequency of the transverse ultrasonic vibration is 15-30kHz, the amplitude is 3-10μm, the vibration direction is perpendicular to the thread rotation direction, the tapping speed is 50-150rpm, and the tapping depth is 0.5-1 times the diameter of the internal thread hole.

12. The method for preparing the metal riveted structure of the alumina fiber battery casing according to claim 9, characterized in that: The steps of preparing a metal-ceramic gradient layer between the transition layer and the connecting layer include: Obtain gradient design requirements; A mixed powder layer of metal powder and silicon dioxide ceramic particles is laid on the surface of the transition layer in sequence, with the volume fraction of silicon dioxide ceramic particles decreasing in each layer, and the thickness of each mixed powder layer is 10-30 μm; Apply a unidirectional pressing force of 100-300 MPa for each layer of mixed powder, maintain the pressure for 5-30 seconds, and after completing 3-5 layers of stacking, vacuum sinter at 1100-1300°C for 2-4 hours to form a gradient interface.

13. A lithium battery pack comprising the metal riveting structure for an alumina fiber battery casing according to any one of claims 1 to 8.

14. A lithium battery pack prepared by the method for preparing a metal riveted structure of an alumina fiber battery shell according to any one of claims 9 to 12.

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