高性能热电发电器件的制备与服役稳定性研究

RESEARCH ON THE FABRICATION AND SERVICE STABILITY OF HIGH PERFORMANCE THERMOELECTRIC POWER GENERATION DEVICES

刘嬉嬉

11849273

硕士

材料工程领域工程

何佳清

2020-05-28

2020-07-20

哈尔滨工业大学

深圳

热电发电技术，是一种可直接将热能转换为电能的绿色环保技术。基于此技术的热电发电器件拥有结构简单、可靠性高、无运动组件、无噪音等独特优势，可广泛应用于工业废热和汽车尾气等废热利用场景，可有效地提高能源的综合利用率。然而当前热电技术的应用受到低效率、高成本以及服役稳定性差制约，因此开发高效率、低成本的热电发电器件，以及通过工艺优化提升热电发电器件的服役稳定性具有重要的意义。本课题针对适用于低温区发电的碲化铋基热电器件以及适用于中温区发电的铅基热电器件，对材料制备、阻挡层制备和器件组装进行研究，开发了高效率、高服役稳定性的热电发电器件，所取得的研究结果如下。本课题针对商用碲化铋基热电材料，分别通过电镀和化学镀的方法，成功在碲化铋材料上制备了致密化金属Ni层作为阻挡层材料，其中电镀Ni阻挡层的厚度为1-3 μm，化学镀Ni阻挡层的厚度为20 μm。然后采用BiSnAg合金作为焊接材料，采用回流焊技术将镀Ni的碲化铋材料焊接到覆铜陶瓷板上，从而组装制备碲化铋基热电发电器件。基于电流和热流分析，确定碲化铋基热电器件的尺寸，设计并制备了24对碲化铋基热电发电器件，所制备的热电发电器件在300-450 K温度区间内服役时，可以实现最大输出电压1.39 V，最大输出功率1.23 W，以及最大转换效率4.5%。本课题还制备了适用于中温区发电的铅基热电发电器件。通过掺杂优化载流子浓度，合金化调控电子迁移率和降低晶格热导率，优化热输运性能，成功制备了高性能p型PbTe基和n型PbS基热电材料，其中p型PbTe基热电材料的ZT值在800 K时达到1.8，n型PbS基热电材料的ZT值在900 K时达到1.7。然后采用Fe0.2Co0.8合金作为铅基材料的阻挡层材料，然后采用一步烧结法将银电极、Fe0.2Co0.8阻挡层和铅基材料烧结为接触良好、无开裂的一体材料，从而制备了2对铅基热电发电器件。对器件的输出参数进行评价，发现在565 K温差下，器件的输出电压为0.36 V，输出功率为0.37 W，转换效率达到8.0%。又针对铅基材料低温性能较差的缺点，将碲化铋基材料作为低温段使用，制备了（铅基材料、碲化铋材料）分段热电发电器件，器件的最大转换效率在585 K温差下达到了11.2%。采用长时间退火时效研究了碲化铋基材料和铅基材料与阻挡层材料的反应。发现Ni阻挡层能够有效阻止碲化铋与SnBiAg焊料之间的反应，从而避免材料性能的衰减；但是长时间的退火时效以后，发现Ni阻挡层与碲化铋之间仍然会发生缓慢的元素扩散，从而导致连接界面处孔洞和裂纹的出现，引起器件失效，因而还需要进一步研究碲化铋器件的阻挡层制备技术。针对铅基材料，长时间退火以后，n型PbS基材料界面由于Sb元素的迅速扩散，界面处出现孔洞和裂纹，导致界面的破坏，而p型PbTe材料则在长时间时效实验以后仍然保持很好界面连接和元素分布状态，表明Fe0.2Co0.8合金作为铅基材料阻挡层的较好作用。最后又采用器件长期服役情况下的输出参数变化进一步评价了器件的服役稳定性，对碲化铋基器件进行44次，总计1000 min的测试发现，器件的输出性能能够保持稳定；而对分段热电发电器件，通过涂覆铝硅酸盐防护涂层，在850 K的服役温度下，总计600 min的测试发现，器件的转换效率稳定为11%，波动较小（±0.2%）。

Thermoelectric generation technology is a environmental-friendly technology which can directly convert heat energy into electric energy. The thermoelectric generator (TEG) based on this technology has the unique advantages of simple structure, high reliability, no moving parts, no noise and so on. It can be widely used in industrial waste heat, automobile exhaust and other waste heat utilization scenarios; it can effectively improve the comprehensive utilization rate of energy. However, the current application of thermoelectric technology is restricted by low efficiency, high cost and poor service stability. Therefore, it is great significant to develop high efficiency, low cost TEG and improve the service stability of TEG through process optimization. For Bi2Te3 based TEG in low temperature region and lead-based TEG in medium temperature region, the research on material on syntheses and preparation, barrier layer preparation and device fabrication have been carried out in this project, and high efficiency and high stability thermoelectric generator have been developed, the main research results are as follows.For the commercial bismuth telluride based thermoelectric materials, Ni layer of densified metal was successfully prepared on bismuth telluride as barrier layer by electroplating and electroless plating respectively. The thickness of electroless plating Ni barrier is 1-3 μm, and the thickness of electroless plating Ni barrier is 20μm. Then, BiSnAg alloy was used as welding material, and the bismuth telluride material coated with Ni was welded to the copper-clad ceramic plate by reflow welding technology. So that the bismuth telluride based thermoelectric power generation device is assembled. Based on the analysis of current and heat flow, the size of the Bi2Te3 based TEG was determined. A 24-couple of Bi2Te3 based TEG was designed and fabricated. When the TEG are in service in the temperature range of 300-450 K, the maximum output voltage is 1.39 V, the maximum output power is 1.23 W, and the maximum conversion efficiency is 4.5%.The lead-based thermoelectric generator which is suitable for the power generation in the middle temperature region has been fabricated. High performance p-type PbTe-based and n-type PbS-based thermoelectric materials were successfully prepared by doping to optimize carrier concentration, alloying to adjust electron mobility, reduce lattice thermal conductivity and optimize thermal transport performance. The ZT value of p-type PbTe-based thermoelectric materials reached 1.8 at 800 K, and that of n-type PbS-based thermoelectric materials reached 1.7 at 900 K. Fe0.2Co0.8 alloy was used as the barrier material of lead-based material. Then silver electrode, Fe0.2Co0.8 barrier layer and lead-based material were sintered into a good contact and non-cracking integrated material by one-step sintering method, thus a 2 couple’s lead-based thermoelectric generator was fabricated. The output parameters of the device were evaluated. It is found that under the temperature difference of 565 K, the maximum output voltage reached 0.36 V, the maximum output power reached 0.37 W, and the conversion efficiency reached the maximum value of 8.0%. In view of the poor low-temperature performance of lead-based materials, the bismuth telluride based materials were used as the low-temperature section, and the 2 couples segmented thermoelectric power generation devices (lead-based materials, bismuth telluride materials) were fabricated. The maximum conversion efficiency of the devices reached 11.2% under the temperature difference of 585 K.The reaction of bismuth telluride based materials and lead based materials with barrier materials were studied by long time annealing aging. It is found that the Ni barrier layer can effectively prevent the reaction between bismuth telluride and SnBiAg solder to avoid the degradation of material properties. However, after a long time of annealing aging, it is found that slow diffusion of elements will still occur between Ni barrier and bismuth telluride, resulting in the occurrence of holes and cracks at the interface and causing device failure. Therefore, it is necessary to further study the barrier layer preparation technology of bismuth telluride devices. For lead-based materials, after long-time annealing aging, the interface of n-type PbS based materials is damaged due to the rapid diffusion of Sb element, and there are holes and cracks at the interface, while p-type PbTe materials still maintain a good interface connection and element distribution state after long-time aging experiment, which shows that Fe0.2Co0.8 alloy is a good barrier for lead-based materials. Finally, the stability of the device in service was further evaluated by the change of output parameters under the condition of long-term service. After 44 tests of bismuth telluride based TEG for a total of 1000 min, it is found that the output performance of the device can be kept stable; For segmented thermoelectric devices, the conversion efficiency of the device is stable at 11% and the fluctuation is small (± 0.2%) through the coating of aluminosilicate protective coating at the service temperature of 850 K for a total of 600 min.

碲化铋 硫化铅 热电发电器 界面 稳定性

bismuth telluride PbS thermoelectric generator interface stability

中文

联合培养

南方科技大学

刘嬉嬉. 高性能热电发电器件的制备与服役稳定性研究[D]. 深圳. 哈尔滨工业大学,2020.