Study On The Preparation And Performance Optimization Of Cu_1.8S-based Thermoelectric Materials

Thermoelectric material is a type of energy material that can realize the direct conversion between thermal energy and electric energy.It has wide application prospects in industrial waste heat recovery,waste heat power generation,thermoelectric refrigeration and other fields.The thermoelectric device with thermoelectric material as its core unit has many advantages such as stability,reliability,no moving parts,no noise,no pollution,and the like,and it has attracted extensive attention in current increasingly depleted energy sources.The Cu_1.8S thermoelectric material focused in this paper is a new thermoelectric material.Compared to traditional high-performance thermoelectric materials such as bismuth telluride and lead telluride,the copper sulfide thermoelectric material possesses the advantages of low cost,low toxicity,and environmental friendliness,but the thermoelectric performance for copper sulfide material is still low.This paper focuses on the p-type copper sulfide bulk thermoelectric materials,which mechanical?MA?alloying method is employed to synthesize compound powders and the spark plasma sintering?SPS?method is employed to densify the powder to the polycrystalline bulk.The thermoelectric properties of Cu_1.8S are improved by adjusting process parameters,doping,and preparing composite materials with the second phase nano particles.Results showed that the ball milling time in the MA process can significantly affect the activity of the synthetic powder,and thus affect the phase composition of the bulk after SPS.The maximum ZT value of 0.72 was obtained at 773K for Cu_1.8S bulk sample with 3 hours ball milling and being sintered at 723 K.On this basis,the second phase and the nano-pore were introduced by doping with Sn element,which effectively scattered the phonon and greatly reduced the thermal conductivity of the Cu_1.8S bulk.Nanostructuring is an effective method to optimize the thermoelectric properties of materials.In this paper,SiC and WSe₂ nanoparticles dispersed Cu_1.8S bulk materials were prepared by directly adding the second phase nanoparticles in the MA process.The carrier concentration and the thermoelectric properties of Cu_1.8S were optimized by energy filtering effect and energy band engineering effect.The ZT value of the Cu_1.8S+1 wt%SiC bulk material achieved 0.87 at 773K,and the ZT value of the Cu_1.8S+1wt%WSe₂ bulk material achieved 1.22 at 773K.In addition,we surprisingly found that the rare earth chlorides ReCl₃?RE=Y,La,Pr,Nd,Ce?doping can synergistically optimize both electrical transport properties and thermal conductivity of thermoelectric sulfides.The carrier concentration of Cu_1.8S samples are optimized due to the replacement of S by Cl.Meanwhile,the rare earth doping increases the complexity of the density of states,and the Seebeck coefficient of Cu_1.8S is significantly improved.At the same time,the thermal conductivity of Cu_1.8S sample with LaCl₃ doping was decreasd greatly benefiting form the strong phonon scattering of LaCu₆ nano precipitates.The ZT value of 1.2 at 773 K is obtained for Cu_1.8S+2 wt%LaCl₃sample which is 2.4 times higher than that of pristine Cu_1.8S.