| Flexible thermoelectric generators can harvest body heat and convert it directly into electricity,which has the advantages of small size,light weight,no working noise,no working fluid,and no moving parts.It is well-matched with the current flexible electronic devices and has broad development prospects as the power supply of wearable electronic products.The main purpose of this thesis is to increase the internal temperature difference and improve the output performance by theoretical analysis,simulation,and experimental verification to explore the three-dimensional inorganic flexible thermoelectric generators based on the analysis of previous research on wearable thermoelectric generators.The influences of module geometry design,matrix,and thermoelectric materials selection,boundary conditions of the operating environment on the output performance,and mechanical properties of the flexible thermoelectric generator are discussed,which ca n provide guidance for the optimization design and experimental preparation of three-dimensional inorganic flexible thermoelectric generator.The main research results are as follows:The effects of the thermoelectric leg height and the fill factor on outp ut performance for flexible thermoelectric generators were investigated by finite element simulation.As the height of the thermoelectric leg increases and the filling ratio decreases,the internal temperature difference of the flexible thermoelectric module increases,and the output voltage of the thermoelectric generator also increases.However,increasing the height of the thermoelectric leg and decreasing the filling ratio will also lead to an increase in internal resistance.Therefore,the output power of the flexible thermoelectric generator will increase first and then decrease with the increase of the height of the thermoelectric leg and the filling ratio,and there are optimal values for both the height of the thermoelectric leg and the filling ratio.The optimum parameters of thermoelectric leg height and filling ratio are determined by considering the effects of both aspects in designing devices.The bismuth telluride-based flexible thermoelectric generator filled with the porous polyurethane matrix was designed and fabricated.The ultra-low thermal conductivity(0.021 W m-1 K-1)and extremely low density(0.11 g cm-3)of the polyurethane matrix enable a larger internal temperature difference and a lighter equipment weight.Compared with the traditional flexible thermoelectric generator filled with polydimethylsiloxane（PDMS）matrix,the output voltage and power of the thermoelectric generator filled with polyurethane matrix are increased by 24%and 52%,respectively.In addition,the higher surface of the matrix can result in a stronger binding force with inorganic thermoelectric legs,which makes up for the lack of solid binding between the PDMS matrix and inorganic thermoelectric legs.In addition,the device adopts magnesium-based room-temperature thermoelectric materials and atomized pulverization technology to reduce manufacturing costs.Finally,a power density of 20.6μW cm-2 was obtained by the flexible thermoelectric generator filled with porous polyurethane matrix under natural convection at 289 K.When the temperature difference between hot and cold ends is maintained at 50 K,the peak power density of the device can reach 13.8 m W cm-2,and the resistance does not change significantly upon the bending of more than10000 times.The influence of different boundary conditions,such as ambient te mperature,wind speed,and surface heat radiation,on the output performance of flexible thermoelectric generators is investigated.An optimization strategy is proposed to improve the output performance of bismuth telluride-based thermoelectric generators by using enhanced thermal radiation.Through temperature distribution simulation and infrared thermography verification,increasing thermal radiation can increase the temperature difference inside the module by about one-third.As a result,the output performance of the flexible thermoelectric generator is significantly improved after enhanced thermal radiation.When the ambient temperature is 295 K,the open-circuit voltage and output power density reach～7 m V and～5.5μW cm-2,respectively.Considering that thermal radiation is sensitive to environmental conditions,the thermoelectric devices before and after the thermal radiation enhancement were tested at the same time.The comparison shows that the output voltage of the thermoelectric generator increased by～40%,and the power density increased by～96%in the closed space shielded by buildings after the increase of thermal radiation.In the open outdoor environment,the output voltage and power density are increased by～51%and～128%,respectively.A two-step impregnation method was developed to fabricate a three-dimensional Ag2Se thermoelectric network.The unique high porosity structure endows this material with ultra-low thermal conductivity,extremely small density,and enough elasticity（elongation>100%）,which makes up for the defects of traditional rigid inorganic thermoelectric materials and thermoelectric polymers that are difficult to combine flexibility and high thermoelectric properties.The output performance of the wearable thermoelectric generator based on the three-dimensional thermoelectric network is comparable to that of the wearable thermoelectric generator composed of rigid thermoelectric legs,producing open-circuit voltages of about 0.4 m V and 0.8 m V,and power densities of 1μW cm-2 and 4μW cm-2 at ambient temperatures of 297 K and 290 K,respectively.To practically evaluate the body heat harvesting performance,the thermoelectric network was incorporated into a commercial jacket to produce a"t hermoelectric jacket"that can generate milliwatts of electricity when normally worn,which can cover the energy consumption of most wearable electronics and components.In addition,the two-step impregnation method used in the thermoelectric network has the characteristics of a simple process,cheap production cost,and does not rely on complex vacuum equipment,which can meet the demand of future mass production of thermoelectric materials and thermoelectric devices.The method is also universal,allowing common fabrics such as cotton,linen,and silk to be processed into"personalized thermoelectric devices"for the power supply or temperature regulation.This efficient and diversified preparation technology opens a new way for the large-scale production and practical application of flexible thermoelectric generators. |
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