Research on the performance of membrane electrodes for fuel-powered lithium batteries made of domestic materials -Lithium - Ion Battery Equipment
Proton exchange membrane fuel-powered lithium battery (pEMFC) is a power generation device with the advantages of high specific power, high energy conversion efficiency, low-temperature start-up, and environmental friendliness. In recent years, it has still been a research hotspot in the field of fuel-powered lithium batteries. Its core component, the membrane electrode (MEA), is usually prepared by a hot pressing process from a gas diffusion layer, a catalytic layer and a proton exchange membrane. Key materials such as proton exchange membranes, catalysts and carbon paper play a decisive role in the electrical performance of pEM-FC. use. Currently, the key materials used in proton exchange membrane fuel-powered lithium batteries are almost all imported. There are the following typical sources of imported materials: Nafion series proton exchange membranes processed by DuPont in the United States, and TGp-H processed by Toray in Japan. Series carbon paper, platinum catalyst processed by Johnsonmatthey Company in the UK. The key materials for fuel-powered lithium batteries processed abroad are expensive, and there are disadvantages of monopoly control over my country. Therefore, it is of great strategic and practical significance to vigorously develop domestic fuel-powered lithium battery materials, use domestic materials to develop fuel-powered lithium battery components and stacks, and carry out localized development of fuel-powered lithium batteries.
This study selected domestic materials from Shandong Dongyue Shenzhou New Materials, Beijing Jinneng Fuel Power Lithium Battery, Shanghai Hesen Electric, Shanghai Panye Hydrogen Energy and other key materials to produce single cells among many key materials for domestic fuel power lithium batteries, and compared The impact of flattening layers and catalytic layers with different compositions and loadings on battery performance was explored, and the manufacturing process of fuel-powered lithium battery components suitable for domestic materials was explored, and a membrane electrode amplification test was conducted for the development of fuel-powered lithium battery stacks made of domestic materials.(Lithium - Ion Battery Equipment)
1. Test
1.1 Preparation of five-in-one membrane electrode
Mix nano activated carbon and polytetrafluoroethylene (pTFE) emulsion in a certain proportion, add a certain amount of dispersant, and mix evenly through ultrasonic waves to form a slurry. The slurry is evenly applied to domestic carbon paper that has been treated with hydrophobicity. The solved carbon paper is then sintered at a high temperature of 330 to 360°C for 60 minutes to remove the surfactant and dispersant contained in the pTFE emulsion. At the same time, the pTFE is plasticized and sintered, and evenly dispersed on the surface of the carbon paper fiber. Form an average hydrophobic network. Spray the ultrasonically mixed slurry containing pt/C catalyst, perfluorosulfonic acid resin solution, and isopropyl alcohol evenly on the surface of the pre-solved domestic proton exchange membrane. Finally, the prepared diffusion layer is placed on both sides of the proton exchange membrane sprayed with catalyst to form a five-in-one membrane electrode assembly.
1.2 Battery packaging and detection
In the test, a single cell was used to evaluate the performance of the fuel-powered lithium battery. The effective area of the electrode was 5 and 25cm2. The test used hydrogen and air as reactant gases, and the excess coefficients were 1.5 and 2.0 respectively. The operating temperature and humidification temperature were both 50°C; the battery The reaction system pressure is normal pressure. During the test, the current output was controlled by adjusting the electronic load, the voltage value was recorded, and the performance polarization curve was measured.
2. Results and discussion
2.1 Effect of the loading of pTFE and carbon powder in the flattening layer on single cell performance
In order to examine the effect of pTFE on the electrical properties of pEMFC, when making the carbon powder slurry of the flat layer, mixed slurries with pTFE mass fractions of 5%, 10%, 15%, 20%, 25%, and 30% were made. Slurries containing different pTFE contents were coated on hydrophobically treated domestic carbon paper, pEMFCs were prepared and assembled under the same process conditions, and the single cells were detected.
As the pTFE content increases, the performance of the battery increases. When the pTFE loading is 25% (mass fraction), the battery performance reaches the best. After that, when the pTFE loading is increased to 30%, The performance of the battery has decreased instead. This may be because at high temperatures, pTFE is sintered and plasticized, and the flat layer is evenly distributed on the base layer to form a hydrophobic network. With the increased pTFE content, the hydrophobicity of the flat layer is increased, which reduces the possibility of the electrode being flooded. At the same time, it can prevent the nanocatalyst from penetrating into the pores of the carbon paper. Therefore, the performance of the battery increases with the increased pTFE content. . However, when the pTFE content is too high, the overturned area of the hydrophobic network is too large, reducing the pores of the carbon paper, reducing the gas diffusion rate, and also increasing the internal resistance of the battery, which will lead to a decrease in battery performance.
The performance of the battery increases with the increase of toner loading. When the loading reaches 1.6mg/cm2, the battery performance is significantly improved. When the loading reaches 2.0mg/cm2, the battery performance is the best. When the loading capacity of toner is added again, when the loading capacity reaches 2.4mg/cm2, the performance of the battery decreases. This is because the toner loading directly determines the thickness of the diffusion layer. Although when the diffusion layer is thin, the gas transfer path is short, and sufficient gas can reach the catalytic layer to participate in the reaction when the battery is working. However, if the carbon powder loading is too low, the catalyst may leak into the gas diffusion layer, reducing the three-dimensional The opposite reaction zone affects the electrode performance. Similarly, the toner loading should not be too high, otherwise the diffusion layer will be thicker, which will reduce the gas channels and electron channels, and may cause "water flooding" of the battery cathode, reducing battery performance.
2.2 Effect of the loading of perfluorosulfonic acid resin and catalyst in the catalytic layer on single cell performance
In order to examine the impact of perfluorosulfonic acid resin loading on battery performance, perfluorosulfonic acid resin solutions of different qualities were mixed with catalysts and isopropanol ultrasonically into slurries, and the slurries were sprayed on domestic proton exchange membranes to make single Battery performance testing. The results are shown in Figure 3.
As the content of perfluorosulfonic acid resin increases, the electrical properties of the battery also increase. When the content of perfluorosulfonic acid resin is 20% (mass fraction), the electrical performance of the battery reaches the best. When the resin content is increased to 26%, the performance decreases, and when the perfluorosulfonic acid resin content is increased to 30%, the battery performance drops sharply. This is because the new content of perfluorosulfonic acid resin can increase the reaction area of the catalytic layer, add a new proton channel, and improve the three-dimensional effect of the reaction area, which is beneficial to improving battery performance. However, too much perfluorosulfonic acid resin makes the electrode more hydrophilic, reduces the gas transfer capacity, and shows obvious mass transfer polarization loss. When the content of perfluorosulfonic acid resin is increased to 30%, on the one hand, the electrode will be seriously "flooded", on the other hand, excessive perfluorosulfonic acid resin will reduce the porosity of the electrode, causing excessive mass transfer resistance and possibly Wrapping the catalyst in a large area reduces the utilization rate of the catalyst, causing rapid degradation of battery performance.
When the catalyst loading is small (such as 0.4mg/cm2), the battery power generation performance is poor. This may be because the catalytic layer is too thin and there are fewer catalyst active centers, resulting in insufficient reaction, resulting in poor battery performance; but when the catalyst loading is large Over time, the performance of the battery decreases instead. For example, the performance of a battery with a PT load of 2.0 mg/cm2 is lower than that of a battery with a power density of 0.8 mg/cm2, and the maximum specific power is lower than 360mW/cm2. This may be due to the fact that when the catalyst loading is large, the catalytic layer is too thick, causing difficulty in mass transfer in the reaction, resulting in reduced battery performance.
2.3 Effect of active area on battery performance
In order to examine the use of domestic material fuel-powered lithium batteries, domestic materials were prepared according to the above-mentioned improved process method with an active area of 25cm2 membrane electrode, and the performance of the membrane electrode with an active area of 5cm2 was compared. When the active area of the membrane electrode is enlarged 5 times, the battery performance decreases in the high-current discharge area, but the electrical performance of the battery in the actual operating voltage range from 0.5V to open circuit has almost no attenuation. This shows that domestically produced materials have good prospects for the development of large-area electric stacks.
3. Conclusion
Using key materials for fuel-powered lithium batteries such as domestic graphite carbon paper, domestic perfluorosulfonic acid proton exchange membrane, and domestic pt/C catalyst, domestic material pEMFC was produced through the CCM process. Through experimental research, it is stated that the carbon powder loading of the diffusion layer and the content of pTFE have a great impact on the performance of the battery. Under the experimental conditions, the optimal composition and loading of the flattening layer is that the content of pTFE is 30 %; toner loading is 2.0mg/cm2. Similarly, the composition and loading of the catalytic layer also directly affect the performance of the battery. Under the test conditions, the content of perfluorosulfonic acid resin is 20% and the catalyst loading is 1.2mg/cm2, which is a more suitable catalytic layer composition. and loading capacity. The domestic material fuel-powered lithium battery membrane electrode prepared in this research has excellent I-V performance and good stability, which lays a solid foundation for the development of domestic material proton exchange membrane fuel-powered lithium battery stack.
This study selected domestic materials from Shandong Dongyue Shenzhou New Materials, Beijing Jinneng Fuel Power Lithium Battery, Shanghai Hesen Electric, Shanghai Panye Hydrogen Energy and other key materials to produce single cells among many key materials for domestic fuel power lithium batteries, and compared The impact of flattening layers and catalytic layers with different compositions and loadings on battery performance was explored, and the manufacturing process of fuel-powered lithium battery components suitable for domestic materials was explored, and a membrane electrode amplification test was conducted for the development of fuel-powered lithium battery stacks made of domestic materials.(Lithium - Ion Battery Equipment)
1. Test
1.1 Preparation of five-in-one membrane electrode
Mix nano activated carbon and polytetrafluoroethylene (pTFE) emulsion in a certain proportion, add a certain amount of dispersant, and mix evenly through ultrasonic waves to form a slurry. The slurry is evenly applied to domestic carbon paper that has been treated with hydrophobicity. The solved carbon paper is then sintered at a high temperature of 330 to 360°C for 60 minutes to remove the surfactant and dispersant contained in the pTFE emulsion. At the same time, the pTFE is plasticized and sintered, and evenly dispersed on the surface of the carbon paper fiber. Form an average hydrophobic network. Spray the ultrasonically mixed slurry containing pt/C catalyst, perfluorosulfonic acid resin solution, and isopropyl alcohol evenly on the surface of the pre-solved domestic proton exchange membrane. Finally, the prepared diffusion layer is placed on both sides of the proton exchange membrane sprayed with catalyst to form a five-in-one membrane electrode assembly.
1.2 Battery packaging and detection
In the test, a single cell was used to evaluate the performance of the fuel-powered lithium battery. The effective area of the electrode was 5 and 25cm2. The test used hydrogen and air as reactant gases, and the excess coefficients were 1.5 and 2.0 respectively. The operating temperature and humidification temperature were both 50°C; the battery The reaction system pressure is normal pressure. During the test, the current output was controlled by adjusting the electronic load, the voltage value was recorded, and the performance polarization curve was measured.
2. Results and discussion
2.1 Effect of the loading of pTFE and carbon powder in the flattening layer on single cell performance
In order to examine the effect of pTFE on the electrical properties of pEMFC, when making the carbon powder slurry of the flat layer, mixed slurries with pTFE mass fractions of 5%, 10%, 15%, 20%, 25%, and 30% were made. Slurries containing different pTFE contents were coated on hydrophobically treated domestic carbon paper, pEMFCs were prepared and assembled under the same process conditions, and the single cells were detected.
As the pTFE content increases, the performance of the battery increases. When the pTFE loading is 25% (mass fraction), the battery performance reaches the best. After that, when the pTFE loading is increased to 30%, The performance of the battery has decreased instead. This may be because at high temperatures, pTFE is sintered and plasticized, and the flat layer is evenly distributed on the base layer to form a hydrophobic network. With the increased pTFE content, the hydrophobicity of the flat layer is increased, which reduces the possibility of the electrode being flooded. At the same time, it can prevent the nanocatalyst from penetrating into the pores of the carbon paper. Therefore, the performance of the battery increases with the increased pTFE content. . However, when the pTFE content is too high, the overturned area of the hydrophobic network is too large, reducing the pores of the carbon paper, reducing the gas diffusion rate, and also increasing the internal resistance of the battery, which will lead to a decrease in battery performance.
The performance of the battery increases with the increase of toner loading. When the loading reaches 1.6mg/cm2, the battery performance is significantly improved. When the loading reaches 2.0mg/cm2, the battery performance is the best. When the loading capacity of toner is added again, when the loading capacity reaches 2.4mg/cm2, the performance of the battery decreases. This is because the toner loading directly determines the thickness of the diffusion layer. Although when the diffusion layer is thin, the gas transfer path is short, and sufficient gas can reach the catalytic layer to participate in the reaction when the battery is working. However, if the carbon powder loading is too low, the catalyst may leak into the gas diffusion layer, reducing the three-dimensional The opposite reaction zone affects the electrode performance. Similarly, the toner loading should not be too high, otherwise the diffusion layer will be thicker, which will reduce the gas channels and electron channels, and may cause "water flooding" of the battery cathode, reducing battery performance.
2.2 Effect of the loading of perfluorosulfonic acid resin and catalyst in the catalytic layer on single cell performance
In order to examine the impact of perfluorosulfonic acid resin loading on battery performance, perfluorosulfonic acid resin solutions of different qualities were mixed with catalysts and isopropanol ultrasonically into slurries, and the slurries were sprayed on domestic proton exchange membranes to make single Battery performance testing. The results are shown in Figure 3.
As the content of perfluorosulfonic acid resin increases, the electrical properties of the battery also increase. When the content of perfluorosulfonic acid resin is 20% (mass fraction), the electrical performance of the battery reaches the best. When the resin content is increased to 26%, the performance decreases, and when the perfluorosulfonic acid resin content is increased to 30%, the battery performance drops sharply. This is because the new content of perfluorosulfonic acid resin can increase the reaction area of the catalytic layer, add a new proton channel, and improve the three-dimensional effect of the reaction area, which is beneficial to improving battery performance. However, too much perfluorosulfonic acid resin makes the electrode more hydrophilic, reduces the gas transfer capacity, and shows obvious mass transfer polarization loss. When the content of perfluorosulfonic acid resin is increased to 30%, on the one hand, the electrode will be seriously "flooded", on the other hand, excessive perfluorosulfonic acid resin will reduce the porosity of the electrode, causing excessive mass transfer resistance and possibly Wrapping the catalyst in a large area reduces the utilization rate of the catalyst, causing rapid degradation of battery performance.
When the catalyst loading is small (such as 0.4mg/cm2), the battery power generation performance is poor. This may be because the catalytic layer is too thin and there are fewer catalyst active centers, resulting in insufficient reaction, resulting in poor battery performance; but when the catalyst loading is large Over time, the performance of the battery decreases instead. For example, the performance of a battery with a PT load of 2.0 mg/cm2 is lower than that of a battery with a power density of 0.8 mg/cm2, and the maximum specific power is lower than 360mW/cm2. This may be due to the fact that when the catalyst loading is large, the catalytic layer is too thick, causing difficulty in mass transfer in the reaction, resulting in reduced battery performance.
2.3 Effect of active area on battery performance
In order to examine the use of domestic material fuel-powered lithium batteries, domestic materials were prepared according to the above-mentioned improved process method with an active area of 25cm2 membrane electrode, and the performance of the membrane electrode with an active area of 5cm2 was compared. When the active area of the membrane electrode is enlarged 5 times, the battery performance decreases in the high-current discharge area, but the electrical performance of the battery in the actual operating voltage range from 0.5V to open circuit has almost no attenuation. This shows that domestically produced materials have good prospects for the development of large-area electric stacks.
3. Conclusion
Using key materials for fuel-powered lithium batteries such as domestic graphite carbon paper, domestic perfluorosulfonic acid proton exchange membrane, and domestic pt/C catalyst, domestic material pEMFC was produced through the CCM process. Through experimental research, it is stated that the carbon powder loading of the diffusion layer and the content of pTFE have a great impact on the performance of the battery. Under the experimental conditions, the optimal composition and loading of the flattening layer is that the content of pTFE is 30 %; toner loading is 2.0mg/cm2. Similarly, the composition and loading of the catalytic layer also directly affect the performance of the battery. Under the test conditions, the content of perfluorosulfonic acid resin is 20% and the catalyst loading is 1.2mg/cm2, which is a more suitable catalytic layer composition. and loading capacity. The domestic material fuel-powered lithium battery membrane electrode prepared in this research has excellent I-V performance and good stability, which lays a solid foundation for the development of domestic material proton exchange membrane fuel-powered lithium battery stack.
