Thermal Stability Of Bi₂Te₃-based Bulks Anddevicesfor Thermoelectric Power Generation

In recent years,the environmental deterioration and energy crisis are increasingly more serious.More and more attentionshavebeen paid to the thermoelectric conversion materials.The Bi₂Te₃ alloys are currently the best TE materials with their practical application in the fields of solid-state cooling and power generation,and the solid-state cooling has been widely used in the market.In view of the thermal stability problem of Bi₂Te₃ alloys in practical applications,the domestic research on the Bi₂Te_3-based thermoelectric generator and the system started relatively late.Focused on the above problems,the main achievements in this study are summarized as follows:In this work,the thermal stabilities of the polycrystaland the zone-melted（ZMed）p-type Bi₂Te₃bulks were investigatedin relation to service temperature and time.For the corresponding powder metallurgy（SPS）samples,the results showedthere was no obvious influence of the service temperatureon the grain size,the crystal lattice constant,the density and the corresponding TE properties when the servicing below 473 K for 24h.Nevertheless,with annealing time was over 168 h,the thermal stabilities would obviously degrade.For the zone melting samples,the results showed the grain size,the density,dimension size and mass remained nearly unchanged when the service temperature was below 523 K.The evidences implied that the thermal stabilities of the ZMed p-type Bi₂Te₃ ingots in crystal structure,geometry size,power factor（PF）and Vickers hardness were better than that of the corresponding SPS samples.The service performance of the Bi₂Te₃-based TEGmodules with flexible Al electrodes was investigated.The obvious defects and the elements diffusion in the interface could result in the deterioration of the electrical output performance of the TEG device.The Ni barrier layer with a thickness of 8-10 um could not effectively block the inter-diffusion between the electrodes and TE legs for the TEG applications.The Al electrode easily absorbs Se in the n-type legs but could restrain the diffusion of the other elements such as Bi,Te,Sb,Cu,Ni,and I.In this paper,a kilowatt class TEG systembased on radiation heat transferwas designed and built.The performance of the TEG system wasanalyzed based on the finite element simulation and experiment,and the simulating results agree very well with the experimental data.The output power,the power density and the conversion efficiency of TEG systemwith 182 pieces of TEG modules could reach 684 W,845 W/m² and 3.5%at a（35）T of around 125 K,respectively.Not only that,when the（35）Tis 200 K in practical application,the output power and the power density could reach 1.23 KW and 1.51KW/m²,respectively.