Preparation And Performance Of Mid-temperature Cu₂Se Thermoelectric Device

As Cu2 Se prepared by SHS-PAS method has many advantages, such as high thermoelectric performance, simple preparation and large scale production, Cu2 Se is very suitable to be applied in thermoelectric generation. But from materials research to module fabrication to practical application, the road to the application of Cu2 Se has many difficulties and challenges, such as the choice of electrode materials and joint method, the choice of matched n-type thermoelectric materials and the design and measurement of thermoelectric device.In view of these difficulties and challenges during the research of Cu2 Se thermoelectric device, first we explore the suitable electrode materials for Cu2 Se and the joint process between Cu2 Se and electrode materials,and on the basis we study the stability of the interface between Cu2 Se and electrode materials; Then form many aspects such as thermoelectric performance, price, non-toxic, specific gravity and coefficient of thermal expansion, we choose n-type Mg-Si-Sn-based materials to match with p-type Cu2 Se, and by finite element analysis study the design of π-type p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 unicouple and thermoelectric module; Lastly, based on the design results of p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 thermoelectric couple device we study the measurement of p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 unicouple. The main research content and results are as follows:By studying chemical reactions and physical compatibility between common metals and Cu2 Se, only Al is a possible suitable electrode for Cu2 Se. By adding Ni-Al alloy which has smaller coefficient of thermal expansion to Al matrix and adding a gradient layer with 0.1-0.3 mm thickness between the Ni-Al+x wt%Al(x=30-40)electrode and Cu2 Se, the interfacial contact resistivity is very small and is about 25 μ??cm2. When Ni-Al+x wt%Al /Cu2 Se block with gradient layer anneales for 1 d in vacuum at different temperatures, its interfacial contact resistivity increases with the increase of temperature, and when the temperature is 500 ℃ the contact resistivity increases about 5 times.We study the design of π-type p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 unicouple and thermoelectric module By finite element analysis. Based on the principle of maximum conversion efficiency we study the design of p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 unicouple in which the original dimensions of p-type and n-type thermoelectric materials in Cu2Se/Mg2.16(Si0.3Sn0.7)0.98Sb0.02 thermoelectric couple device are 5?5?10 mm3. When the cross-sectional area of n-type leg is about 12.25 mm2 the conversion efficiency reaches to peak 9.02%; Based on the principle of maximum power ouput we study the design of p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 thermoelectric module in which the side length of the module is 30 mm and the the side length of the p-type and n-type leg is equal, When the side length of p-type(n-type) leg is 3-4 mm、the distance between p-type leg and n-type leg is 0.7 mm and the height of p-type(n-type) leg is 0.5 mm the power output reaches to peak 40 W.We study the measurement of p-Cu2Se/n-Mg2.16(Si0.3Sn0.7)0.98Sb0.02 unicouple and analyse the factors which cause measurement errors. The measured value of the resistance of device is high and so the measured power output is low; By regular calorimetric measurement the measured vaule of heat flow is high and the error between the measured vaule and theoretical vaule increases with the increase of measured temperature. The reason for the high measured resistance of device is that the measurement is based on two-probe method and the device itself has high interfacial contact resistivity; The reason for the high measured heat flow is that there is much radiative heat loss at the lateral surfaces. By taking effective measures, such as using four-probe method instead of two-probe method, the error of the resistance of the device between the measured vaule the theoretical value almostly is less than 10%. By using external radiation shield to reduce the heat loss at the lateral surfaces, the measured heat flow is low, but the error of heat flow between the measured vaule and theoretical value decreases with the increase of measured temperature. when the temperature difference is 477 ℃, the measured value of maximum conversion efficiency is 6.32%, which is 9.7% smaller than the theoretical value.