Research On The Fabrication And Service Stability Of High Performance Thermoelectric Power Generation Devices

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 ?m,and the thickness of electroless plating Ni barrier is 20?m.Then,Bi Sn Ag 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 Pb Te-based and n-type Pb S-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 Pb Te-based thermoelectric materials reached 1.8 at 800 K,and that of n-type Pb S-based thermoelectric materials reached 1.7 at 900 K.Fe_0.2Co_0.8 alloy was used as the barrier material of lead-based material.Then silver electrode,Fe_0.2Co_0.8 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 Sn Bi Ag solder to avoid the degradation of material properties.Howev er,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 n ecessary 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 Pb S based materials is damaged due to the rapid diffusion of Sb element,and there are holes and cracks at the interface,while p-type Pb Te materials still maintain a good interface connection and element distribution state after long-time aging experiment,which shows that Fe_0.2Co_0.8 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.