Non-uniform-thickness electrolyte solid oxide battery

Abstract

The invention discloses a non-uniform thickness electrolyte solid oxide battery. Comprising an anode, an electrolyte and a cathode, the thickness of the electrolyte is gradually reduced from an inlet to an outlet, and the thickness of the electrolyte at the outlet is 40-80% of the thickness at the inlet. The surface resistance of different positions of the single cell is changed by adjusting the thickness change of the electrolyte, the performance difference of different positions is reduced, the current density difference of different positions is reduced, the method has the characteristics of high distribution uniformity of the current density of the single cell, small thermal stress and the like, and high-performance, high-efficiency and long-life stable operation of the solid oxide cell can be realized.

Description

Technical Field

[0001] The present invention relates to a non-uniform thickness electrolyte solid oxide battery, belonging to the field of solid oxide batteries. Background Art

[0002] Solid oxide fuel cells and electrolyzers (SOFC / SOEC) are different from traditional Carnot heat engines, and they can directly achieve efficient direct conversion between chemical energy and electrical energy. Solid oxide fuel cells (SOFC) have the advantages of a wide range of fuel applicability, high energy conversion efficiency (power generation efficiency of 40% - 60%, comprehensive energy efficiency ≥ 80%), all-solid-state structure, modular assembly, and zero pollution. They are an important part of China's "clean, low-carbon, safe and efficient" modern energy system. As a fixed or distributed power generation, it can enhance the clean power supply capacity, safety, reliability and stability of the power grid. SOFC has a variety of different structures, and its power generation scale covers from dozens of watts to hundreds of megawatts. Different structures can be selected according to different application scenarios, and the application scenarios mainly include fields such as fixed power generation, distributed power supply, combined heat (cooling) and power supply, and auxiliary power sources for transportation vehicles.

[0003] The single cell is the most core component in the SOFC power generation system, generally a "sandwich" structure composed of an anode, an electrolyte, and a cathode. The flat plate type battery is the most main SOFC unit cell configuration for commercial applications at present. According to the different components that play a mechanical support role in the single cell, it can be divided into: electrolyte-supported type, anode-supported type, cathode-supported type, and support-supported type, etc. (as Figure 1 shown, the cathode and anode supports are collectively called electrode-supported types, and the support-supported type includes insulating ceramic supports and metal supports, etc.).

[0004] At present, the component design forms of widely used SOFC units are generally divided into two categories, namely tubular design and planar design. Most planar SOFC single cells are prepared by processes such as tape casting, screen printing, and spraying. The thicknesses of the thin films of each layer of the prepared cells are relatively uniform and flat. However, when large-sized (such as 10 cm * 10 cm up to 25 cm * 25 cm, etc.) single cells are actually operating, it is found that there are relatively large concentration polarization, low fuel utilization rate, and relatively large temperature differences at different positions of the single cell. The main reason is that on the anode side, during actual operation, when the fuel gas flows through the single cell, an electrochemical reaction will occur, the fuel gas is continuously consumed, its concentration will continuously decrease, while the concentrations of reaction products such as water and carbon dioxide will continuously increase, resulting in changes in the partial pressures of the components of the fuel gas participating in the electrochemical reaction. The performance of the subsequent part of the cell in contact with the fuel gas will change greatly, the concentration polarization effect of the cell increases, the polarization impedance increases accordingly, resulting in uneven current distribution and uneven temperature distribution, causing a relatively large stress difference inside the single cell, affecting the stability of the single cell, and thus affecting the output power and power generation efficiency of the cell. Similarly, on the cathode side, as the oxygen in the air is continuously consumed, the oxygen concentration near the outlet of the air flow is much lower than that at the inlet of the air flow, resulting in inconsistent performance at different positions of the single cell. Summary of the Invention

[0005] In order to reduce the problem of uneven output performance distribution inside a solid oxide cell stack, the present invention proposes to use a solid oxide cell with a non-uniform thickness electrolyte to make the output performance distribution inside the stack more uniform.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows: A solid oxide cell with a non-uniform thickness electrolyte includes an anode, an electrolyte, and a cathode. Among them, from the inlet to the outlet, the thickness of the electrolyte gradually decreases, and the thickness of the electrolyte at the outlet is 40% - 80% of the thickness at the inlet.

[0007] Preferably, the anode is composed of an anode functional layer and an anode support layer, and the electrolyte is connected to the anode functional layer.

[0008] Preferably, the cathode is composed of a cathode isolation layer, a cathode functional layer, and a cathode active layer, and the electrolyte is connected to the cathode isolation layer.

[0009] Preferably, from the inlet to the outlet, the thickness of the electrolyte decreases linearly or non-linearly continuously.

[0010] Preferably, the thickness of the electrolyte at the outlet is not less than 2 μm.

[0011] Preferably, the electrolyte is prepared by means of screen printing, spraying, physical and chemical deposition, tape casting.

[0012] Preferably, the solid oxide cell is flat or tubular.

[0013] Compared with the prior art, the present invention firstly proposes a novel and unique asymmetric SOFC single cell structure, which uses an electrolyte film with non-uniform thickness to replace the traditional flat and uniform electrolyte film layer, adjusts the cell performance by changing the ohmic resistance at different positions on the single cell, and enables large-size single cells to still maintain high-performance output at low fuel concentrations, thereby achieving the balance of the performance and temperature uniformity at various positions of the large-size single cell, and improving the power generation efficiency and fuel utilization rate of the cell. Description of the Drawings

[0014] Figure 1 Schematic diagrams of electrolyte cells with various structures.

[0015] Figure 2 Schematic diagram of preparing a non-uniform electrolyte by the tape casting method.

[0016] Figure 3 Schematic diagrams and scanning electron microscope images of a non-uniform electrolyte cell prepared by the tape casting method.

[0017] Figure 4 Electrochemical performance diagrams of a uniform-thickness electrolyte cell and a non-uniform electrolyte cell. Detailed Embodiments

[0018] To avoid the above problems, a new design scheme for the electrolyte of the solid oxide cell is proposed. The core of this scheme is "using an electrolyte with non-uniform thickness to replace the traditional flat and uniform electrolyte, adjusting the cell performance by regulating the surface resistance at different positions on the single cell, enabling large-size single cells to maintain high-consistency performance output within a wide range of fuel and oxidant concentrations, thereby balancing the apparent parameters such as current density and temperature at various positions of the large-size single cell, reducing thermal stress, and enhancing the lifespan and operation stability".

[0019] Combined with Figure 1 , the electrolyte in the traditional cell has a uniform thickness structure (a in Figure 1 ), while the electrolyte of the cell in the present invention has different thicknesses at the inlet and outlet positions. From the inlet to the outlet, the electrolyte thickness shows a linear gradient (b in Figure 1 ) or a non-linear gradient ( Figure 1In c) the decreasing change, the electrolyte of the battery is thicker at the fuel inlet position and the current density is slightly lower; the electrolyte of the battery is thinner at the fuel outlet position, and even under the condition of lower fuel concentration, the current density will be slightly higher. In this way, the performance of the entire area of the single cell is close, the current density distribution is relatively uniform, and the internal stress is small. According to the overall size of the existing battery and the limitation of the present invention that the thickness of the electrolyte at the outlet is 40-80% of the thickness at the inlet, the thickness difference of the electrolyte prepared by the present invention is generally less than 20 μm, so the thickness difference of the overall battery can be ignored.

[0020] The solid oxide battery has an all-solid structure. The anode includes an anode support layer and an anode functional layer. The anode support layer is generally composed of NiO and YSZ, with a thickness of 200-1000 μm. The anode functional layer is generally composed of small-particle-size Ni 2 O 3 and YSZ, with a thickness of 5-50 μm; the electrolyte is generally YSZ, and can also be other conventional materials such as GDC, with a thickness greater than 2 μm; the cathode includes an isolation layer, a cathode functional layer and a cathode active layer. The isolation layer is generally composed of a cerium oxide-based material with a thickness of 0.1-10 μm. The cathode active layer is generally composed of LSCF and GDC, with a thickness of 2-30 μm; the cathode active layer is generally composed of LSCF, with a thickness of 2-30 μm. In order to obtain a battery with a non-uniform electrolyte, methods such as screen printing, spraying, physical and chemical deposition, and tape casting can be used for preparation. Examples

[0021] A solid oxide battery with a non-uniform thickness electrolyte is prepared by the co-tape casting method. The steps are as follows, and the horizontal width of each layer is 20 cm: 1. Prepare the electrolyte slurry (the electrolyte slurry is obtained by ball milling 50 g of YSZ powder, 12 g of ethanol, 25 g of butanone, 3 g of polyvinyl butyral ester, and 3 g of dibutyl phthalate for 48 h), and then use the tape casting method to prepare the electrolyte. The tape casting process is shown in Figure 2. At this time, the slurry doctor blade in the existing tape casting technology process needs to be adjusted from horizontal to one end slightly higher, 100 μm high; the other end is lower, 60 μm high. Finally, due to the action of gravity and the volatilization of the solvent, the actually obtained electrolyte thickness gradually changes from 10.1 μm (inlet) to 4.4 μm (outlet). In this way, the thickness of the green body after forming gradually changes from one end to the other end on the cross-section; 2. Prepare the anode functional layer slurry (the anode functional layer slurry is composed of 50 g of YSZ powder, 50 g of Ni 2 O 3Powder (obtained by ball milling 75 g of YSZ powder, 75 g of NiO powder, 18 g of graphite powder, 36 g of ethanol, 50 g of butanone, 6 g of polyvinyl butyral ester, and 6 g of dibutyl phthalate for 48 h), cast the anode functional layer on the above electrolyte; after drying, continue to cast the anode support layer on it. The casting height of the anode functional layer is 200 μm, and due to gravity and solvent evaporation, the actual thickness of the functional layer is 15 μm; the casting height of the anode support layer is 1600 μm, and due to gravity and solvent evaporation, the actual thickness of the support layer is ~450 μm; 3. Prepare the anode support layer slurry (the anode functional layer slurry is obtained by ball milling 75 g of YSZ powder, 75 g of NiO powder, 18 g of graphite powder, 36 g of ethanol, 75 g of butanone, 9 g of polyvinyl butyral ester, and 9 g of dibutyl phthalate for 48 h), and use a forming method to obtain a flat half-cell, dry, cut, and calcine to obtain a battery with a non-uniform electrolyte layer. Since the electrolyte thickness difference prepared in this example is about 6 μm, and the thickness difference of the overall battery prepared is less than 10 μm, therefore, the battery thickness difference can be ignored; 4. After preparing the cathode LSCF-GDC and LSCF on the electrolyte surface, a single cell is obtained.

[0022] The casting length of each layer depends on the total amount of the prepared slurry until the slurry is used up.

[0023] We use the single-point method to estimate the change in the electrochemical performance of the entire battery. Small cells of 16 mm are cut at the inlet position, the middle position, and the outlet position respectively. The YSZ electrolyte thickness at the inlet position is 10.1 μm, the YSZ electrolyte thickness at the middle position is 6.6 μm, and the YSZ electrolyte thickness at the outlet position is 4.4 μm, as Figure 3 shown. The fuel utilization rate at the outlet position reaches 80%. Therefore, the fuel concentration at the inlet position is 100% hydrogen, the fuel concentration at the middle position is 50% hydrogen + 50% water, and the fuel concentration at the outlet position is 20% hydrogen + 80% water.

[0024] The small cell at the inlet position (10.1 μm) is tested in 100% hydrogen fuel concentration, the small cell at the middle position (6.6 μm) is tested in 50% hydrogen + 50% water fuel concentration, and the small cell at the outlet position (4.4 μm) is tested in 20% hydrogen + 80% water fuel concentration. For comparison, the small cell at the middle position (6.6 μm) is tested in 100% hydrogen, 50% hydrogen + 50% water, and 20% hydrogen + 80% water to represent the change in the battery performance of the electrolyte with the same thickness.

[0025] Test results Figure 4 as shown: When the electrolyte has a non-uniform thickness, the current density difference between the inlet and outlet of the battery is only 0.045 A / cm 2 ; while for a battery with the same thickness, the current density difference between the inlet and outlet of the battery is as high as 0.229 A / cm 2 . The results show that the battery with this non-uniform thickness electrolyte can better distribute the performance of each part of the battery, reducing the performance difference.

[0026] In summary, the present invention changes the surface resistance at different positions of the single cell by adjusting the thickness change of the electrolyte, reduces the performance difference at different positions, and reduces the current density difference at different positions. It has the characteristics of high uniformity of the current density distribution of the single cell and small thermal stress, and can achieve the stable operation of the solid oxide battery with high performance, high efficiency and long life.

Claims

1. A non-uniform thickness electrolyte solid oxide battery, comprising an anode, an electrolyte, and a cathode, Characterized in that, From the inlet to the outlet, the thickness of the electrolyte gradually decreases, and the thickness of the electrolyte at the outlet is 40 - 80% of the thickness at the inlet.

2. The solid oxide battery according to claim 1, Characterized in that, The anode is composed of an anode functional layer and an anode support layer, and the electrolyte is connected to the anode functional layer.

3. The solid oxide battery according to claim 1, Characterized in that, The cathode is composed of a cathode isolation layer, a cathode functional layer, and a cathode active layer, and the electrolyte is connected to the cathode isolation layer.

4. The solid oxide battery according to claim 1, Characterized in that, From the inlet to the outlet, the thickness of the electrolyte decreases continuously in a linear or non-linear manner.

5. The solid oxide battery according to claim 1, Characterized in that, The thickness of the electrolyte at the outlet is not less than 2 μm.

6. The solid oxide battery according to claim 1, Characterized in that, The electrolyte is prepared by means of screen printing, spraying, physical and chemical deposition, or tape casting.

7. The solid oxide battery according to claim 1, Characterized in that, The solid oxide battery is flat plate type or tubular type.

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