Structural Regulation Of Ternary Chalcogenides And Its Application In Energy Conversion

The research and application of inorganic functional materials promote the development of science and technology.However,the intrinsic properties of most materials are not enough to meet the actual industrial application and demand.Therefore,the development of relatively effective inorganic functional materials requires manual and targeted adjustment and improve material properties to meet actual application needs.In the field of inorganic functional materials,structural regulation is one of the most commonly used means to improve material properties.In order to achieve more efficient combination of structural control,it is necessary to fully understand the mechanisms by which various structural control measures affect the electrical/thermal transport properties of materials.On the other hand,most of the current research work only emphasizes the effectiveness of a single structural control means and conducts related research on its mechanism.However,the combination of different structural control means in the same material system is relatively complicate due to its regulatory mechanism.In this dissertation,the author grasps the potential influencing factors of the material's physicochemical properties from the perspective of electrical/thermal properties of the material system,and uses structural regulation as a means of application to regulate the electrical/thermal properties of the material.In addition,under the premise of understanding the intrinsic properties of materials and the structural control methods(doping,filling,etc.)on the electrical/thermal effects mechanism of the material system,the various control methods are effectively combined to jointly change the electrical/thermal properties of the materials.Based on the theoretical research related to structural control mechanisms and methods,the author demonstrates the feasibility and effectiveness of the combination of structural control methods in the material system,and broadens the application space of material electrical/thermal transport characteristics control methods.The main content of this paper includes several aspects:1?In this chapter,a superlattice material PbNbS3 which is stacked by NbS2 and PbS layers and combined by van der Waals force is prepared and studied as a negative electrode material of lithium-ion battery and exhibits high application value.NbS2 is a layered structural material with high electrical conductivity and bulk modulus,but has a low lithium ion capacity as a negative electrode material for lithium batteries.The semiconductor PbS has a natural capacitive characteristic,however,as a negative electrode of a lithium battery,its conductivity is poor,and when combined with lithium,it causes a softening of the structure and finally causes electrode pulverization.The superlattice material PbNbS3 is formed by stacking PbS and NbS2 layers,and has high conductivity of NbS2,high bulk modulus and high capacity of PbS.PbNbS3 as a negative electrode material has a specific capacity of 710 mAh g-1 at current density of 100 mA g-1(1.6 and 3.9 times the specific capacity of NbS2 and PbS,respectively),and the capacity retention rate is about 96%.This work provides a material design structure model for lithium battery electrode materials,which can make full use of the performance advantages of different materials,combine them,synergistically reduce electrode expansion and increase capacity,and ensure high charge and discharge efficiency on this basis.This work provides an effective new idea for designing new anode materials for lithium-ion batteries.2?In this chapter,the author selects AgSbTe2 as the research object of thermoelectric materials.By replacing Mn by Mn doping,the carrier concentration in the material system is improved and the conductivity is improved.At the same time,Mn doping enhances the lattice structure of the material.The non-harmonicity reduces the thermal conductivity of the lattice.The experimental results show that the 7 mol%Mn doped sample has a ZT value of about 0.62 at 550 K,which is 29%higher than the original counterpart.In addition,due to the increase of the Mn doping ratio,the electrical conductivity is greatly improved.When the Mn doping ratio is more than 5%,the carrier thermal conductivity accounts for more than 50%of the total thermal conductivity,which greatly limits the further optimization of the performance of the thermoelectric material.By reverse doping,the authors use Mn doping instead of Ag to introduce electrons to compensate for the too high hole carrier concentration in the material system,and further enhance the crystal by introducing more Mn impurity atoms into the material system.The lattice scattering effect reduces the lattice thermal conductivity and finally optimizes the thermoelectric properties of the AgSbTe2 material system.The ZT value of the 5%mol MnAg-Mnsb co-doped AgSbTe2 sample reached a maximum of about 0.74 at 550 K,which was 54%higher than the original sample,and 35%higher than the 5%Mnsb single-doped sample.This work illustrates that bidirectional doping can remodulate conductivity(a)and Seebeck coefficient(S)to achieve higher power factor(PF)and further reduce total thermal conductivity(Ktotai)for better ZT performance.3?In the previous chapter,AgSbTe2 in the ?-?-(?)2 series with low intrinsic thermal conductivity was selected as the research object of thermoelectric materials,in which the carrier contribution thermal conductivity accounted for about 20%.As the doping regulation conductivity increases,the carrier thermal conductivity also increases significantly,limiting the further optimization of thermoelectric performance.For this reason,in order to maintain the relatively low intrinsic thermal conductivity while maximizing the space for conductivity regulation,the same series of samples CuSbS2 was selected as the research object,and the contribution of CuSbS2 carrier thermal conductivity to the total heat was between 300-650 K.One thousandth of the guide is almost negligible.Based on this condition,the introduction of impurity level by Ga doping instead of Sb improves the electrical conductivity of the whole material.At the same time,Ga substitution of Sb also enhances the non-harmonicity of the lattice structure of the material and reduces the thermal conductivity of the lattice.At 650 K,the 4%mol Gasb doped sample improved the conductivity by about 3 times and the thermal conductivity by about 24%while maintaining a relatively high Seebeck coefficient.In addition,based on the special layered structure of CuSbS2,the thermal conductivity is more effectively reduced by filling the material system with 4%mol Ga atoms.At 650 K,the thermal conductivity is reduced by about 46%compared with the pure sample.Ga doping instead of Sb can optimize the power factor(PF)more effectively,and Ga filling can reduce the thermal conductivity more effectively.Finally,the ZT value of the material is further optimized by the method of doping and filling sample GaSb0.98Ga0.04S2.The ZT value is about 4 times higher than that of the pure sample at 650K.This chapter is based on the previous chapter and avoids With the limitation of high carrier thermal conductivity,a new thermoelectric material system was selected and the thermoelectric performance was further optimized by combining the advantages of two different structural adjustments.