【作者】 吴波；

【导师】 李耀刚；

【作者基本信息】 东华大学 ， 材料学， 2023， 博士

【摘要】 近年来,可穿戴电子设备和物联网快速发展的同时,其持续性能源供应问题日益突出。目前常采用的化学电池在使用过程中需要频繁更换或充电,严重影响消费者的穿戴体验。人体通过新陈代谢持续向外界散发热量,将这部分人体热能转换成电能是解决未来智能服装能源问题的有效方案。柔性热电器件可将人体热能直接转换成电能且对运动状态和环境条件要求较低,是一种可靠的自供电能源装置。然而,目前的柔性热电器件仍存在穿戴舒适性差和输出功率低等问题,严重阻碍了其在可穿戴领域的应用,因此通过制备高性能热电材料和设计合理的器件结构来提高柔性热电器件的可穿戴性能已经成为亟待解决的问题。基于此,本论文围绕如何提高柔性热电材料的性能及器件可穿戴性展开,基于硫族纳米材料和碳纳米材料,从组分复合、界面调控和掺杂改性出发,设计制备了高性能全无机柔性热电材料以及面向可穿戴应用的高性能热电器件。具体的研究内容和主要结果如下:（1）冰模板法制备硫族纳米线气凝胶,并构筑热梯度型三维热电器件。为制备可在皮肤热梯度方向捕获人体余热的三维材料,通过定向冷冻的冰模板法,将p型Te纳米线和n型Ag₂Te纳米线分别组装成取向结构的热电气凝胶。利用乙二醇的弱还原性和聚乙烯吡络烷酮（PVP）的软模板作用控制溶剂热过程中Te纳米线的生长方向,所合成纳米线的长径比可达98。以Te纳米线作为模板原位生长Ag从而合成Ag₂Te纳米线,通过调控反应过程中Ag离子浓度和生长时间,获得最佳热电性能的Ag₂Te纳米线。得益于低维特性,Te和Ag₂Te纳米线气凝胶的最佳室温Seebeck系数分别为581.9μV K^-1和-115.2μV K^-1,对应的功率因子可以达到1.31μW m^-1 K^-2和4.08μW m^-1 K^-2。通过蛇形电极组装成的热梯度型热电器件可在25.8 K的温差下持续输出40.3 mV的开路电压,并在288 K的环境温度下将人体热能转换为16 mV的电能,表明了气凝胶在可穿戴热电领域的应用潜力。（2）热处理法制备硫族纳米片/碳纳米材料薄膜,并构筑平面型二维热电器件。三维气凝胶虽然具备低热导率的优势,但低电导率的劣势限制其在热电领域的应用。相比之下,无机复合薄膜不仅可以通过多孔结构降低热导率,还可通过引入的高导电碳纳米材料提高电导率。为此,在高度结晶的Bi₂Te₃和Sb₂Te₃纳米片中分别引入氧化石墨烯（GO）和单壁碳纳米管（SWCNTs）,经高温热处理后获得全无机的n型Bi₂Te₃/RGO和p型Sb₂Te₃/SWCNT复合薄膜,高导电碳纳米材料的载流子传输通道提高了材料热电性能。归因于复合薄膜中界面处的能量过滤效应和声子散射机制,p型和n型热电薄膜的室温功率因子分别达到55μW m^-1 K^-2和108μW m^-1 K^-2。构筑的平面结构热电器件可在70 K的温差下产生23.6μW的输出功率,对应的开路电压为130 mV。将由n型和p型薄膜组装的热电阵列与柔性光伏电池集成,构筑可穿戴的光伏热电一体化器件。一体化器件中的热电阵列在转移光伏电池余热的同时持续输出电能,并通过散热作用将光伏电池的转换效率提高了约2%,这为人体热能与太阳光能的转换研究提供了新思路。（3）溶剂浴法改性碳纳米管薄膜,并构筑折叠型二维热电器件。硫族纳米片/碳纳米材料薄膜主要通过真空过滤法制备,其产量较低。柔性热电材料的规模化制备是决定热电器件高密度集成的关键因素,为此分别采用聚乙烯亚胺（PEI）和FeCl₃溶剂浴对商业化碳纳米管（CNTs）薄膜进行改性,通过PEI和FeCl₃对碳纳米管的修饰改性从而实现大面积p型和n型CNTs薄膜的制备。改性后获得的p型和n型薄膜材料的室温功率因子分别达到617μW m^-1 K^-2和511μW m^-1 K^-2。设计了基于三明治结构的一级热电对,并以此为单元构筑可折叠的柔性热电器件,可折叠器件在44 K温差下可输出1.05 V的开路电压,对应的归一化功率密度为41μW g^-1 K^-2。得益于CNTs材料优异的光吸收能力,可折叠热电器件可将聚焦后的太阳光能直接转换为0.58 V的电能。在能源管理电路中,热电器件输出的0.35 V电压被直接转换至3.3～4.0 V,可用于驱动LED灯珠及电子体温计等电子设备。这项工作证明通过能源管理电路设计,柔性热电器件可将低温差热能转换为特定电压的电能并为便携式电子设备供能。（4）分段改性法制备p-n分段热电纱线,并构筑拉伸型一维热电器件。基于气凝胶和薄膜材料的柔性器件存在穿戴舒适性差等问题,而纱线是最为理想的可穿戴材料。为实现器件结构中热电纱线的电串联与热并联结构,需要设计基于p-n分段的热电纱线。为此,采用PEI和聚3,4-乙烯二氧噻吩/聚苯乙烯磺酸盐（PEDOT:PSS）对CNTs纱线进行分段改性,通过调控改性参数实现对热电性能的优化,纱线中p型段和n型段的最佳功率因子分别可以达到666.8μW m^-1 K^-2和443.7μW m^-1 K^-2。以弹性硅胶作为基体编织可拉伸热电腕带,并在腕带表层构筑基于Ag NW的红外反射层。在穿戴状态下,该腕带可以反射超过70%的人体红外辐射,实现在器件热端建立红外保温层的同时降低冷端辐射加热,通过增大器件温差的方式促进开路电压升高。通过防水层硅胶设计和封装,腕带可以在高湿度环境中稳定运行,在287 K的水环境中将人体热能转换成15 mV的电能。这项工作推动了热管理方案在可穿戴热电领域的应用。更多还原

【Abstract】 In recent years,wearable electronic devices and the Internet of Things（Io T）have been growing rapidly while their sustainable energy supply has become increasingly problematic.So far,the chemical batteries currently used need to be replaced or charged frequently during use,which seriously reduces the wearing experience of consumers.The human body continuously emits a large amount of heat to the outside world through metabolism,and converting human body heat into electrical energy is an effective solution to the energy problem of smart clothing in the future.Flexible thermoelectrical devices（TEGs）can directly convert human body heat into electricity without strict requirements on movement status and environmental conditions,which have been considered as a reliable self-powered energy device.However,the current flexible TEGs still have problems such as poor wearing comfort and low output performance,which seriously hinder the application in wearable field.Therefore,it has become an urgent problem to improve the wearability of flexible TEGs by preparing high-performance TE materials and designing reasonable device structures.Based on this,this thesis focuses on how to improve the performance of flexible TE materials and wearability of the devices.Based on inorganic chalcogenide nanomaterials and carbon nanomaterials,the preparation scheme of high-performance all-inorganic flexible TE materials and the design strategy of high-performance TEGs for wearable applications were investigated from the perspective of component recombination,interface regulation and doping modification.The specific research content and main results are as follows:（1）Preparing chalcogenide nanowire aerogels by ice template method,and constructing three-dimensional TEGs with thermal gradient structure.In order to prepare the three-dimensional materials that can harvest human heat in the thermal gradient direction of skin,the p-type Te nanowires and n-type Ag₂Te nanowires were assembled into oriented TE aerogels by the ice-template method of directional freezing.Ethylene glycol with weak reduction and the polyvinylpyrrolidone（PVP）with soft template effect were used to control the growth direction of Te nanowires during the solvothermal process,where the diameter ration is up to 98.The Ag₂Te nanowires were synthesized by in-situ growth of Ag using Te nanowires as a template,and then the maximum TE properties were obtained by adjusting the concentration of Ag ions and the growth time during the reaction.Owing to the low-dimensional properties,the optimal room temperature Seebeck coefficients of Te nanowire aerogel and Ag₂Te aerogel are 581.9μV K^-1 and-115.2μV K^-1,respectively,and the corresponding power factors can reach 1.31μW m^-1 K^-2 and 4.08μW m^-1 K^-2.A thermal gradient TEG assembled with serpentine electrodes can continuously output an open circuit voltage of 40.3 mV under a temperature difference of 25.8 K,and convert human body heat into electrical energy of 16 mV at an ambient temperature of 288 K,which indicates the outstanding application potential of aerogel in the field of wearable thermoelectrics.（2）Preparing chalcogenide nanosheets/carbon nanomaterial thin films by heat treatment,and constructing integrated two-dimensional TEGs with in-plane structure.Although three-dimensional aerogels have the advantage of low thermal conductivity,the disadvantage of low electrical conductivity limits its application in the field of thermoelectricity.In contrast,the inorganic composite film can not only reduce the thermal conductivity through the porous structure,but also improve the electrical conductivity through the introduction of highly conductive carbon nanomaterials.Therefore,the graphene oxide（GO）and single-walled carbon nanotubes（SWCNTs）were introduced into highly crystalline Bi₂Te₃ and Sb₂Te₃ nanosheets respectively,and then all-inorganic n-type Bi₂Te₃/RGO and p-type Sb₂Te₃/SWCNT composite films were obtained after high-temperature heat treatment,which the TE properties were improved by using highly conductive carbon nanomaterials as carrier transport channels.Due to the energy filtering effect and phonon scattering mechanism at the interface of the composite film,the power factors of the p-type and n-type TE films can reach 55μW m^-1 K^-2 and 108μW m^-1 K^-2 at room temperature,respectively.The constructed TEG with in-planar structure can generate 23.6μW output power at a temperature difference of 70 K,corresponding to an open circuit voltage of 130 mV.A TE array assembled from n-type and p-type thin films was further integrated with a flexible photovoltaic cell to design a wearable integrated photovoltaic-TEG.The TE array in the integrated device continuously outputs electric energy while transferring the thermal energy from the photovoltaic cell,while increases the conversion efficiency of the photovoltaic cell by 2%through heat dissipation,which provides a new idea for the conversion of human body heat energy and solar energy.（3）Modifying commercial carbon nanotube films by solvent bath,and constructing two-dimensional TEGs with foldable structure.Chalcogenide nanosheets/carbon nanomaterial thin films are mainly prepared by vacuum filtration method,and its yield is low.The large-scale preparation of flexible TE materials is key factor that determines the high-density integration of TEGs,therefore Polyethyleneimine（PEI）and FeCl₃ solvent baths were used to modify commercial carbon nanotubes（CNTs）films,where the large-area p-type and n-type CNTs films were achieved by modification of CNTs using modified solvent.The modified p-and n-type films reached 617μW m^-1 K^-2 and 511μW m^-1 K^-2,respectively.A sandwich-structured lst-level TE pair was designed as a unit to construct a foldable TEG,where the foldable device can output an open-circuit voltage of1.05 V under a temperature difference of 44 K,and the corresponding normalized power density is41μW g^-1 K^-2.Owing to the excellent light absorption capability of CNTs materials,the foldable TEG can directly convert the focused solar light energy into 0.58 V of electricity.In the energy management solution,the 0.35 V voltage output by the TEG was directly converted to 3.3～4.0 V,which can be used to drive electronic devices such as LED lamp beads and electronic thermometers.This work demonstrates that flexible TEGs can convert low-temperature differential heat into electrical energy with a specific voltage through the energy management solution,and realizing power supply for portable electronics.（4）Preparing p-n segmented TE yarns by segmented modification,and constructing one dimensional TEGs with stretchable structure.Flexible devices based on aerogel and film materials have problems such as poor wearing comfort,while yarn is the most ideal wearable material.In order to realize the electrical series and thermal parallel structures in the device,it is necessary to design high performance TE yarns based on p-n segmented structure.Therefore,the PEI and PEDOT:PSS were employed as the solvents to modify CNTs yarns,and the TE performance of p-n segmented yarns was optimized by using the transfer mechanism of the solution during the modification process.The maximum power factors of p-and n-type segments can reach 666.8μW m^-1 K^-2 and 443.7μW m^-1 K^-2,respectively.A stretchable TE wristband was woven with an elastic silicone matrix,where an infrared reflective layer based on Ag NW was constructed on the surface of the wristband.In the wearing state,the wristband can reflect more than 70%of the infrared radiation of the human body,while an infrared insulation layer was established at the hot end of the device and the radiation heating at the cold end was reduced,thus improving the open-circuit voltage by increasing the temperature difference.With the and encapsulation of waterproof silicone,the wristband can operate stably in high-humidity environments,which can convert human body heat energy into 15 mV of electricity in a 287 K water environment.This work promotes the application of thermal management solutions in the field of wearable thermoelectrics.更多还原