Tuning the solubility of polysulfides for constructing practical lithium-sulfur battery

Li-S batteries are regarded as one of the most promising candidates for next-generation battery systems with high energy density and low cost.However,the dissolution-precipitation reaction mechanism of the sulfur(S)cathode enhances the kinetics of the redox processes of the insulating sulfu r,which also arouses the notorious shuttle effect,leading to serious loss of S species and corrosion of Li anode.To get a balance between the shuttle restraining and the kinetic property,a combined strategy of electrolyte regulation and cathode modification is proposed via introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoroprpyl ether(HFE)instead of 1,2-dimethoxyethane(DME),and SeS_(7)instead of S_8.The introduction of HFE tunes the solvation structure of the LiTFSI and the dissolution of intermediate polysulfides with Se doping(LiPSSes),and optimize the interface stability of the Li anode simultaneously.The minor Se substitution compensates the decrease in kinetic due to the decreased solubility of LiPSs.In this way,the Li-SeS_(7)batteries deliver a reversible capacity of 1062 and 1037 mAh g^(-1)with 2.0 and 5.5 mg SeS_(7)cm^(-2)loading condition,respectively.Besides,an electrolyte-electrode loading model is established to explain the relationship between the optimal electrolyte and cathode loading.It makes more sense to guide the electrolyte design for practical Li-S batteries.

Thermal stability and thermoelectric properties of Cd-doped nano-layered Cu2Se prepared using NaCl flux method

Cu2Se is a promising"phonon liquid-electron crystal"thermoelectric material with excellent thermoelectric performance.In this work,Cd-doped Cu2-xSeCdx(x=0,0.0075,0.01,and 0.02)samples were prepared using NaCl flux method.The solubility of Cd in Cu2Se at room temperature was less than 6%,and a second phase of CdSe was found in the samples with large initial Cd content(x=0.01 and 0.02).Field-emission scanning electron microscopic image showed that the arranged lamellae formed a large-scale layered structure with an average thickness of approximately 100 nm.Transmission electron microscopy demonstrated that doping of Cd atoms did not destroy the crystal integrity of Cu2Se.A small amount of Cd in Cu2Se could reduce the electrical and thermal conductivities of the material,thus significantly enhancing its thermoelectric performance.With the increase in Cd content in the sample,the carrier concentration decreased and the mobility increased gradually.Thermogravimetric differential thermal analysis showed that no weight loss occurred below the melting point.Excessive Cd doping led to the emergence of the second phase of CdSe in the sample,thus significantly increasing the thermal conductivity of the material.A maximum ZT value of 1.67 at 700 K was obtained in the Cu1.9925SeCd0.0075 sample.

Thermoelectric Properties of Ag-doped In_4Se_(2.95) Polycrystalline Compounds

In_4Se_3-based materials are noticeable n-type thermoelectric materials because of lead-free and intrinsically low lattice thermal conductivity,but the In4Se_3-δ crystals（with Se-deficiency,δ） suffer strong anisotropy and cleavage habit. Thus the researches on polycrystalline In_4Se_3-based materials are of great importance. Herein,we experimentally and theoretically investigated the thermoelectric properties of In_（4-x）Se_（2.95）Ag_x polycrystalline compounds. Ag occupying the intercalation or In4 site is energetically most favorable in light of the density functional theory calculation. The maximum solubility of Ag（x_m） is very low（xm 〈 0.03） and the experimental result indicates that the electrical transport behavior of In_（4-x）Se_（2.95）Ag_x compounds is not significantly optimized by Ag-dopant. Consequently,a maximum ZT of 0.92 at 723 K is obtained by In_（3.98）Se_（2.95）Ag_（0.02） compound that represents 15% enhancement over that of the un-doped one which benefits from the slightly enhanced power factor and the reduced total thermal conductivity.

MOF-derived Se doped MnS/Ti_(3)C_(2)T_(x) as cathode and Zn-Ti_(3)C_(2)T_(x) membrane as anode for rocking-chair zinc-ion battery

Mn-based zinc ion battery has the advantages of low cost and high performance,which makes it the promising energy storage system.However,the poor conductivity and the agglomeration in the synthesis process of manganese-based materials restrict the performance of batteries.Herein,the Se-doped MnS/Ti_(3)C_(2)T_(x)(Se-MnS/Ti_(3)C_(2)T_(x))composite material derived from Mn-based metal-organic framework is reported.Electrochemical tests show that Se-doped could generate S defects and enhance the electrochemical activity of MnS.At the same time,the introduction of Ti_(3)C_(2)T_(x) substrate is conducive to exposing more sulfur defects and improving the utilization rate of defects.In the mechanism study,it is found that Se-MnS/Ti_(3)C_(2)T_(x) is transformed into S/Se co-doped Mn3O_(4) at the first charge,which innovatively elucidated the behavior of S/Se during activation.In the electrochemical performance test,the specific capacity can reach 74.7 mAh·g^(-1) at 5.0 A·g^(-1).In addition,the Zn-Ti_(3)C_(2)T_(x) membrane electrode is prepared by vacuum filtration as the zinc-poor anode,which is assembled into the rocking chair full battery to avoid dendrite growth and exhibit excellent rate performance.The addition of Zn2+weakens the electrostatic repulsion between the interlayers of MXene,and the formation of the folded morphology aids the penetration of the electrolyte.At 1.0 A·g^(-1),the capacity can reach 50.6 mAh·g^(-1).This work is helpful to promote the research and development of the reaction mechanism of manganese based rocking chair batteries.

Thermoelectric performance of p-type zone-melted Se-doped Bi_(0.5)Sb_(1.5)Te_3 alloys

For zone-melted （ZM） bismuth telluride-based alloys, which are widely commercially available for solidstate cooling and low-temperature power generation around room temperature, introducing point defects is the chief approach to improve their thermoelectric performance. Herein, we report the multiple effects of Se doping on thermoelectric performance of p-type Bi0.5Sb1,5Te3-xSex ＋ 3 wt% Te ZM ingots, which increases carrier concentration, reduces lattice thermal conductivity and deteriorates the carrier mobility. As a result, the peak figure of merit （ZT） is shifted to a higher temperature and a high ZT 1.2 at 350 K is obtained, due to the reduced thermal conductivity and suppressed intrinsic conduction. Further, decreasing Sb content is followed to optimize the room temperature performance and a ZT - 1.1 at 300 K is obtained. These results are significant for designing and optimizing the thermoelectric performance of commercial Bi0.5Sb1.5Te3＋ 3 wt% Te ZM alloys.

Thermoelectric properties of solution-synthesized n-type Bi2Te3 nanocomposites modulated by Se： An experimental and theoretical study

We report the investigation of the thermoelectric properties of large-scale solution-synthesized Bi2Te3 nanocomposites prepared from nanowires hot- pressed into bulk pellets. A third element, Se, is introduced to tune the carrier concentration of the nanocomposites. Due to the Se doping, the thermoelectric figure of merit （ZT） of the nanocomposites is significantly enhanced due to the increased power factor and reduced thermal conductivity. We also find that thermal transport in our hot-pressed pellets is anisotropic, which results in different thermal conductivities along the in-plane and cross-plane directions. Theoretical calculations for both electronic and thermal transport are carried out to establish fundamental understanding of the material system and provide directions for further ZT optimization with adjustments to carrier concentration and mobility.

Recent progress in Li-S and Li-Se batteries

Li–S and Li–Se batteries have attracted tremendous attention during the past several decades, as the energy density of Li–S and Li–Se batteries is high（several times higher than that of traditional Li-ion batteries）.Besides, Li–S and Li–Se batteries are low cost and environmental benign. However, the commercial applications of Li–S and Li–Se batteries are hindered by the dissolution and shuttle phenomena of polysulfide（polyselenium）, the low conductivity of S（Se）, etc. To overcome these drawbacks, scientists have come up with various methods, such as optimizing the electrolyte, synthesizing composite electrode of S/polymer, S/carbon, S/metal organic framework（MOF） and constructing novelty structure of battery.In this review, we present a systematic introduction about the recent progress of Li–S and Li–Se batteries, especially in the area of electrode materials, both of cathode material and anode material for Li–S and Li–Se batteries. In addition, other methods to lead a high-performance Li–S and Li–Se batteries are also briefly summarized, such as constructing novelty battery structure, adopting proper charge–discharge conditions, heteroatom doping into sulfur molecules, using different kinds of electrolytes and binders. In the end of the review, the developed directions of Li–S and Li–Se batteries are also pointed out. We believe that combining proper porous carbon matrix and heteroatom doping may further improve the electrochemical performance of Li–S and Li–Se batteries. We also believe that Li–S and Li–Se batteries will get more exciting results and have promising future by the effort of battery community.