Multiphase ceramic material connector for fuel cell
By designing a multiphase ceramic material connector, the problem of insufficient conductivity and mechanical properties of fuel cell connectors under medium and low temperature conditions is solved, and the high-temperature conductivity and safety redundancy are improved, with good processability and lightweight effect.
Patent Information
- Application Number
- CN202511675486.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-15
- Publication Date
- 2026-02-10
AI Technical Summary
Existing fuel cell connector materials have insufficient electrical conductivity and mechanical properties under low and medium temperature conditions, and pose a risk of chromium poisoning, affecting the stability and safety of fuel cells.
By employing a multiphase ceramic material connector and adjusting the volume ratio of the conductive and insulating phases, combined with a composite of lanthanum hexaboride, hexagonal boron nitride, and titanium diboride, a connector with high conductivity, good mechanical properties, and lightweight was prepared using a spark plasma sintering process.
It achieves full-temperature conductivity from room temperature to high temperature, improves the safety redundancy and mechanical properties of the connector, reduces the system weight, and has good processability and industrial feasibility.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of fuel cell technology, and specifically relates to a multiphase ceramic material connector. Background Technology
[0002] As the energy crisis intensifies, various new energy power devices are becoming increasingly common. Fuel cells can directly convert chemical energy into electrical energy under high-temperature conditions, exhibiting extremely high energy conversion efficiency. This surpasses the energy conversion efficiency limit of the traditional Carnot cycle in heat engines, making it a promising new energy power device for applications in numerous fields such as aviation, aerospace, and energy storage. The connector, located between the positive and negative electrodes of adjacent power units, plays a crucial role in transmitting current and ensuring the system's stable output of electrical energy.
[0003] SOFCo-EFS Holdings (now Rolls-Royce Fuel Cell Systems, Inc., USA) tested fuel cells produced on its production line and found that, initially, the resistance related to the connectors accounted for about 60% of the total resistance, and after 300 hours of operation, the resistance related to the connectors still accounted for one-third of the total resistance. Connector materials need to meet requirements such as high conductivity, high chemical and physical stability, high density, and compatibility with the thermal expansion coefficients of other components. Traditional connector materials are mainly ABO-type perovskite ceramics, whose conductivity relies on oxygen ion vacancy defects. These materials are mostly used at temperatures above 1000°C, and ceramic materials themselves have poor mechanical properties, are brittle, and have low machinability. As fuel cells are developing towards lower temperatures (below 800°C), metal connectors, represented by stainless steel, have begun to be used, offering better mechanical properties and machinability, as well as lower cost. However, stainless steel has a high density, and due to its high chromium content, oxidation reactions at high temperatures cause chromium volatilization, leading to chromium poisoning with other structural components, affecting the normal operation of the fuel cell and posing a safety hazard.
[0004] Therefore, it is necessary to improve existing technologies and develop novel multiphase ceramic material connectors. Summary of the Invention
[0005] In view of the problems existing in the prior art, the purpose of this invention is to provide a multiphase ceramic material connector with excellent comprehensive performance.
[0006] The theoretical basis of this invention is the conductive permeation model, which means that the conductivity of a material can be controlled by adjusting the volume ratio between the conductive phase and the insulating phase.
[0007] The conductive percolation model states that when the volume fraction of the conductive phase is below a threshold, the material as a whole is not conductive because it cannot form a network of conductive pathways within the material. When the volume fraction of the conductive phase is above the threshold, a network of conductive pathways forms, and the material exhibits conductivity. In other words, as the volume fraction of the conductive phase increases (while the volume fraction of the insulating phase decreases), the material's conductivity undergoes a step transition from an insulating state to a conductive state. Based on literature and experimental analysis, the percolation transition threshold is estimated to be 20–30% (conductive phase volume fraction).
[0008] Studies have found that when the volume fraction ratio of the conductive phase to the insulating phase is close to 1:1, the material exhibits good conductivity. Furthermore, introducing a large amount of low-density, processable insulating phase to achieve lightweight ceramic materials helps improve their mechanical properties and enables the construction of structurally and functionally integrated ceramics. In addition, further optimization of the conductive phase material can achieve high-temperature conductivity in the ceramic material.
[0009] This invention provides the following technical solutions: A multiphase ceramic material connector for fuel cells, wherein the multiphase ceramic material connector is divided into an upper surface layer, an intermediate matrix layer and a lower surface layer in the height direction, wherein the upper surface layer and the lower surface layer are both composed of lanthanum hexaboride (LaB6) and hexagonal boron nitride (hBN), and the intermediate matrix layer is composed of titanium diboride (TiB2) and hexagonal boron nitride.
[0010] In a preferred embodiment, the volume fraction of lanthanum hexaboride in the upper and lower surface layers is 30%-100%.
[0011] In a preferred embodiment, the volume fraction of titanium diboride in the intermediate matrix layer is 30%-80%.
[0012] In a preferred embodiment, the material composition and proportions of the upper and lower surface layers are the same.
[0013] In a preferred embodiment, the material composition of the upper and lower surface layers is 75% LaB6 and 25% hBN, and the material composition of the intermediate matrix layer is 50% TiB2 and 50% hBN.
[0014] In a preferred embodiment, the material composition of the upper and lower surface layers is 50% LaB6 and 50% hBN, and the material composition of the intermediate matrix layer is 50% TiB2 and 50% hBN.
[0015] In a preferred embodiment, the upper and lower surface layers are composed of 100% LaB6, and the intermediate matrix layer is composed of 50% TiB2 and 50% hBN.
[0016] In a preferred embodiment, the height ratio of the upper surface layer, the intermediate matrix layer, and the lower surface layer is 1:8:1.
[0017] In a preferred embodiment, the preparation method of the multiphase ceramic material connector includes the steps of batching, mixing and sintering, wherein the sintering step adopts a spark plasma process.
[0018] In a preferred embodiment, the temperature control program for the discharge plasma process is as follows: (a) From room temperature to 1850°C, heating rate 100°C / min; (b) Hold at 1850℃ for 5 minutes; (c) Cooling rate from 1850℃ to 850℃, 100℃ / min; (d) Allow to cool naturally to room temperature; An axial pressure of 35 MPa is applied simultaneously throughout the entire process.
[0019] This invention introduces metal borides with high-temperature oxidation resistance, and by controlling the powder ratio and addition order, achieves the following: Figure 2 The laminated composite material shown (the purple part in the figure represents the upper and lower surface layers, and the gray part represents the middle matrix) exhibits certain electrical conductivity at both room temperature and high temperature.
[0020] The beneficial effects of this invention are: 1. Excellent conductivity: By introducing LaB6 antioxidant conductive material, conductivity can be achieved across the entire temperature range from room temperature to high temperature. Under extreme conditions (such as failure of the silver / platinum protective coating on the contact layer between the electrode and the electrode), the connector can still be used for emergency purposes for a relatively long period of time (about 3 to 4 days), providing a large safety margin.
[0021] 2. Good mechanical properties and machinability: By introducing the hBN phase, the inherent brittleness of hard ceramic materials is reduced. Combined with the metal boride hard phase, the ceramic material as a whole has high compressive strength. Combined with the TiB2 and LaB6 conductive phases, it can be machined into any shape using electrical discharge machining methods, including wire cutting.
[0022] 3. Lightweight: By using low-density ceramic materials, the weight of fuel cell system components can be significantly reduced compared to metal connectors. In aerospace propulsion applications, this can reduce unnecessary energy waste caused by weight.
[0023] 4. Mature technology: The process flow of this invention is as follows: Figure 1 As shown, metal boride and hBN powder in a certain proportion are uniformly mixed by mechanical ball milling, and can be prepared by spark plasma sintering (SPS). The process is simple and industrially feasible. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the process flow for preparing the multiphase ceramic material connector according to the present invention.
[0025] Figure 2 This is a schematic diagram of the design structure of the multiphase ceramic material connector according to the present invention.
[0026] Figure 3 This is a physical image of the product prepared in Example 1.
[0027] Figure 4 The XRD patterns of the upper surface phase composition of Example 1 and Comparative Example 1 before and after oxidation at 600°C are shown.
[0028] Figure 5 The resistivity diagrams for Example 1 at room temperature before and after oxidation at 600°C are shown.
[0029] Figure 6 The image shows the microstructure and energy dispersive spectroscopy (EDS) analysis of the upper surface layer after oxidation at 600°C for 24 hours in Example 1.
[0030] Figure 7 The image shows the microstructure and energy dispersive spectroscopy (EDS) analysis of the intermediate matrix layer after oxidation at 600°C for 24 hours in Example 1.
[0031] Figure 8 The stress-strain curves of the compression test after different durations of oxidation at 600℃ in Example 1 are shown.
[0032] Figure 9 The stress-strain curves of the compression test after different oxidation times at 600℃ are shown for Comparative Example 1. Detailed Implementation
[0033] To fully describe the technical content, structural features, objectives, and effects of this invention, a detailed description will be provided below in conjunction with the accompanying drawings.
[0034] Example 1
[0035] This embodiment provides a multiphase ceramic material connector for fuel cells, the preparation method of which includes the following steps: (1) Prepare 75% LaB6 and 25% hBN powder (A1) and 50% TiB2 and 50% hBN powder (B1) by volume fraction. (2) Place the above raw material powders into a ball mill jar, add ZrO2 grinding balls, the ball-to-material mass ratio is 5:1; add deionized water, the solid-liquid mass ratio is 1:1, and mechanically ball mill at 400 r / min for 10 h; (3) Place the ball-milled slurry into a centrifuge tank and centrifuge it at 3500 r / min for 7 min in a low-speed centrifuge; (4) Remove the liquid after centrifugation, and place the remaining substance in a 70°C oven to dry for 24 hours; (5) Place the dried powder into a mortar and grind it to obtain the finished powder; (6) Place the above powders into the sintering mold in the order of A1-B1-A1, and control the loading according to the height ratio of the upper surface layer, the middle matrix layer and the lower surface layer as 1:8:1; (7) Start the spark plasma sintering. The temperature control program is as follows: (a) from room temperature to 1850℃, heating rate 100℃ / min; (b) hold at 1850℃ for 5 min; (c) from 1850℃ to 850℃, cooling rate 100℃ / min; (d) cool naturally to room temperature; 35MPa axial pressure is applied simultaneously throughout the above process. (8) After sintering, the sample is polished with sandpaper, washed with deionized water and dried thoroughly to obtain the finished product.
[0036] Example 2
[0037] The difference between this embodiment and Embodiment 1 lies in the steps: (1) Prepare 75% LaB6 and 25% hBN powder (A2) and 50% TiB2 and 50% hBN powder (B2) by volume fraction. (6) Place the above powders into the sintering mold in the order of A2-B2-A2, and control the loading according to the height ratio of the upper surface layer, the middle matrix layer and the lower surface layer as 1:8:1; All other steps are the same as in Example 1.
[0038] Example 3
[0039] The difference between this embodiment and Embodiment 1 lies in the steps: (1) Prepare 100% LaB6 powder (A3), 50% TiB2 and 50% hBN powder (B3) by volume fraction. (6) Place the above powders into the sintering mold in the order of A3-B3-A3, and control the loading according to the height ratio of the upper surface layer, the middle matrix layer and the lower surface layer as 1:8:1; All other steps are the same as in Example 1.
[0040] Comparative Example 1 The difference between this comparative example and Example 1 lies in the steps: (1) Prepare 50% TiB2 and 50% hBN powder by volume fraction (D1); (6) Place the above powders into the sintering mold in the order of D1-D1-D1, and control the loading according to the height ratio of the upper surface layer, the middle matrix layer and the lower surface layer as 1:8:1; All other steps are the same as in Example 1.
[0041] Performance testing section: The sample density was determined using the Archimedes water displacement method, and the results obtained in the above examples were all above 95%.
[0042] The phase composition of the sample before and after oxidation was determined using XRD technology.
[0043] The resistivity of the sample at room temperature before and after oxidation was determined using the four-probe method.
[0044] The sample was placed in a heating furnace and fully exposed to air atmosphere. Oxidation tests were performed at 600℃ for 24h, 48h, 72h and 100h. After completion, the temperature was raised to 600℃ to measure the in-situ resistivity at high temperature.
[0045] The microstructure before and after oxidation was characterized using SEM and EDS techniques.
[0046] The test results are as follows:
[0047] Table 1 shows the in-situ resistivity of the sample after oxidation at 600℃ for different durations in Example 1. Compared with Comparative Example 1, the sample oxidized under extreme conditions still has good conductivity at high temperature, that is, the resistivity is less than 1 Ω·cm (conductivity is greater than 1 S / cm).
[0048] Example 1: Actual product Figure 3 As shown, due to the large-scale introduction of hBN, the ceramic material has good machinability and can be processed into any shape, making it applicable.
[0049] The phase composition of the product after oxidation at 600°C for different durations in Example 1 is as follows: Figure 4 As shown, the pre-oxidation phases were mainly LaB6 and hBN, which did not react and form during sintering. After oxidation at 600℃ for different durations, there were no obvious signs of oxidation, and no La2O3 oxide was detected. Only a small amount of LaBO3 was formed, which is a preliminary stage for the formation of La2O3, indicating that the oxidation process was incomplete. In contrast, Comparative Example 1 clearly formed TiO2 oxide after oxidation at 600℃ for different durations.
[0050] Example 1: Resistivity at room temperature after oxidation at 600℃ for different durations is as follows Figure 5 As shown, compared to the unoxidized state (0h), the effect of oxidation on room temperature conductivity at this temperature is minimal. This is because the LaB6 on the upper and lower surfaces did not undergo significant oxidation, and corresponding oxides were not generated in large quantities on the particle surface, meaning the conductive pathway remained largely intact. Simultaneously, due to the protection of the upper and lower surfaces, the intermediate matrix only showed signs of oxidation within the micrometer-scale region near the outer periphery, while the sample core remained unoxidized. Therefore, the oxidized sample as a whole exhibited good room temperature conductivity. In contrast, Comparative Example 1, after oxidation at 600℃ for different durations, showed no conductivity at room temperature due to the significant formation of TiO2 oxide on the surface.
[0051] Furthermore, the inventors also studied the TiB2-LaB6-hBN three-phase homogeneous composite linker, with hBN volume fraction of 50%, TiB2 volume fractions of 40%, 42.5%, 45%, 47.5%, and 50%, and the balance being LaB6. The study found that with increasing LaB6 content, the high-temperature in-situ conductivity of the samples gradually improved after oxidation at 600℃ for different durations, which was positively correlated with the increase in the content of LaB6 antioxidant conductive material. However, due to the low LaB6 content, the area affected by the insulating oxide TiO2 on the sample surface was still relatively large, and all samples still lacked conductivity after cooling to room temperature.
[0052] The microstructure characterization results of Example 1 after complete air oxidation at 600℃ for different durations are as follows: Figure 6 , Figure 7 As shown, the upper and lower surfaces at 600℃ ( Figure 6 The oxidation characteristics are randomly distributed in a dotted pattern, which preliminarily explains the conductivity after oxidation. Furthermore, only after a relatively long oxidation period (e.g., more than 72 hours) can oxidation traces be observed in some metal boride particles near the surface, i.e., nanoscale protrusions form on the surface. Since the composition and ratio of the intermediate matrix are the same as in Comparative Example 1, Figure 7 This indirectly explains why the upper and lower surfaces of Comparative Example 1 have a greater degree of oxidation than those of Example 1 under the same conditions, indicating that LaB6 is more resistant to oxidation than TiB2 at this temperature.
[0053] The mechanical properties (compression test) of Example 1 after oxidation at 600℃ for different durations are as follows: Figure 8 As shown, oxidation in Example 1 significantly improves compressive strength, combined with... Figure 4 Analysis suggests that the brittle oxides (such as TiO2) and layered structure on the surface of the intermediate matrix may provide reinforcement, thus meeting the mechanical requirements for use under high-temperature conditions. Comparative Example 1 ( Figure 9 This indicates a trend of significantly reduced compressive strength with increasing oxidation time.
[0054] In summary, the present invention may have many other embodiments, and the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc., made within the spirit and substance of the present invention should be included within the scope of protection of the present invention.
Claims
1. A multiphase ceramic material connector for fuel cells, characterized in that, The multiphase ceramic material connector is divided into an upper surface layer, an intermediate matrix layer, and a lower surface layer in the height direction. The upper and lower surface layers are both composed of lanthanum hexaboride and hexagonal boron nitride, while the intermediate matrix layer is composed of titanium diboride and hexagonal boron nitride.
2. The multiphase ceramic material connector according to claim 1, characterized in that, The volume fraction of lanthanum hexaboride in the upper and lower layers is 30%-100%.
3. The multiphase ceramic material connector according to claim 1, characterized in that, In the intermediate matrix layer, the volume fraction of titanium diboride is 30%-80%.
4. The multiphase ceramic material connector according to claim 1, characterized in that, The material composition and ratio of the upper and lower surface layers are the same.
5. The multiphase ceramic material connector according to claim 4, characterized in that, The upper and lower surface layers are composed of 75% LaB6 and 25% hBN, while the intermediate matrix layer is composed of 50% TiB2 and 50% hBN.
6. The multiphase ceramic material connector according to claim 4, characterized in that, The upper and lower surface layers are composed of 50% LaB6 and 50% hBN, while the intermediate matrix layer is composed of 50% TiB2 and 50% hBN.
7. The multiphase ceramic material connector according to claim 4, characterized in that, The material composition of the upper and lower surface layers is 100% LaB6, and the material composition of the middle matrix layer is 50% TiB2 and 50% hBN.
8. The multiphase ceramic material connector according to claim 1, characterized in that, The height ratio of the upper surface layer, the middle matrix layer, and the lower surface layer is 1:8:
1.
9. The multiphase ceramic material connector according to claim 1, characterized in that, The preparation method of the multiphase ceramic material connector includes the steps of batching, mixing and sintering, wherein the sintering step adopts the spark plasma process.
10. The multiphase ceramic material connector according to claim 9, characterized in that, The temperature control procedure for the discharge plasma process is as follows: (a) From room temperature to 1850°C, heating rate 100°C / min; (b) Hold at 1850℃ for 5 minutes; (c) Cooling from 1850℃ to 850℃ at a rate of 100℃ / min; (d) Allow to cool naturally to room temperature; An axial pressure of 35 MPa is applied simultaneously throughout the entire process.