Research On Functionally Gradient Materials And Interface Connections In Thermoelectric Generator With Large Temperature Span

The shortage of resources, the waste of energy and environmental deteriorationhave become some of the most critical current issues. Thermoelectric powergeneration technology, which can realize the direct conversion of heat into electricityhas received renewed attention and now becomes a research hotspot. In this paper,relevant work were carried out based on the key problems of vehicle waste heatrecovery thermoelectric power generation devices. Functionally gradient materialsutilized between300K and800K were fabricated and optimized. Stable connectionbetween certain thermoelectric materials and copper electrode and thermoelectricmaterials to each other were realized by the low temperature sintering of nano-silverpaste. Aging tests on the interface of junctions were also carried out. Unicouplemodel of segmented thermoelectric generator applied between300K and680K weredeveloped and optimized based on the principle of maximum power output. Maininnovative conclusions in this paper were as follows:(1) P-type Bi0.5Sb1.5Te3utilized in low temperature zone were fabricated andoptimized based on mechanical alloying (MA) and spark plasma sintering (SPS). Amaximum figure of merit,1.8was obtained which was almost1.6times of thetraditional commercial one.(2) Proper doping of copper in Bi0.5Sb1.5Te3can promote the electricalconductivity substantially. Due to the increase of carrier and defect concentration, themaximum electrical conductivity can reach2×105S/m, almost5~10times of thenon-doped one. The corresponding temperature of the maximum figure of merit wasat the same time promoted to150℃which provides a big boost to the applicationpotential of Bi0.5Sb1.5Te3at100~200℃.(3) SEM, EDS, XRD and nanoindentation tests were combined to characterizethe process of mechanical alloying of Si-Ge represented brittle system. The resultsshowed that germanium cladding on the surface of silicon also existed except for theembedding of hard silicon particle to the soften germanium. The results ofnanoindentation tests showed a decrease of elastic modulus which suggestedcorresponding increase of plastic deformation of powders during the MA process. (4) Stable connections can be realized with the application of low temperaturesintering of nano-silver paste between p-type AgSbTe2and copper electrode, n-typeLAST and copper electrode, p-type AgSbTe2and Bi0.5Sb1.5Te3, n-type LAST andBi2Te2.7Se0.3. Both316stainless steel and nickel sputtered on the surface of the TEmaterials can prevent the diffusion of corresponding elements effectively during theaging process from200℃to400℃and keep fine heat stability of the junctions.(5) A unicouple model of segmented thermoelectric generator utilized between300K and680K was developed and optimized. The thermoelectric conversionefficiency and output power of the model within this temperature difference and withan external resistance of0.03Ω can reach10.21%and0.53W, respectively.