Preparation Of Metal Oxygen(Selenium) Compounds And Their Application In Lithium Sulfur Batteries

The high energy density(2600 Wh kg^-1),low cost and environment friendly make Li-S battery be one of the next-generation most promising high-energy-density energy storage technologies.Unfortunately,the severe shuttle behavior of polysulfides inevitably lead to low sulfur utilization.Besides,the sluggish reaction kinetics form polysulfides to Li2S in the discharge process and the high reaction energy barrier of transform Li2S to sulfur in the charge process,which would increase the difficulties for realizing high performance of Li-S battery.Herein,to solve above problems,in there,designed and constructed four different metal oxides(selenides)based on adsorption-conversion mechanism.The physical characterization and electrochemical properties of the prepared materials were comprehensively studied,while the working mechanism of the materials was further studied in combination with theoretical calculation.Herein,mesoporous SnO2 nanosheets on carbon nanofibers(CNFs)namely C@SnO2 was prepared with the novel topological method.The obtained unique structure of C@SnO2 composite has several advantages.Firstly,the polar SnO2 nanosheets not only show the strong chemisorption to trap polysul des but also can more effectively decrease the electrochemical polarization to enhance the polysul des redox.Furthermore,the mesoporous C@SnO2 can expose more active sites meanwhile increase electron transfer and electrolyte diffusion rates.Moreover,with these CNFs framework formed interconnected conductive network,the electrode materials can effectively increase electron transport rate during the cycle,even giving rise to high rate capabilities.As a polar mesoporous cathode material in Li-S batteries,the C@SnO2/S electrode delivered delivered outstanding capacity retention over more than 1000 cycles at 2 C and the decay is as low as 0.024%per cycle.Hence,hierarchical SnO2@1TMo S2 nanoarray on carbon cloth(C@SnO2/TMS)was designed and constructed as the sulfur cathode for Li S batteries based on adsorption-catalytic conversion mechanism.In this unique material architecture,each component synergistically serves a specific purpose:On the one hand,the porous SnO2 nanosheet could confine more sulfur within its nanoscale pores and provide more active sites to form strong chemisorption with the dissolvable polysulfides.Furthermore,the large pores between SnO2 nanosheets could effectively suppress the volume expansion of sulfur during the lithiation process and allow for the easy penetration of electrolyte and fast transportation of Li⁺.On the other hand,the high conductivity of 1T-Mo S2 nanosheet can expose abundant edge sites and enable fast electron transport,thus effectively accelerating the polysulfides redox kinetics.As a result,with the C@SnO2/TMS/S as the cathode materials,the batteries deliver high specific capacities,superb cycle stability,and excellent C-rate properties.Even undergoing an ultralong 4000 cycles at 5 C,it could retain a capacity decay as low as 0.009%per cycle.Hence,highly-conductive,porous NiSe2 nanosheets on carbon cloth(C@NiSe2)was designed and constructed as the sulfur host materials.In the meantime,the constructed flexible C@NiSe2 electrode has several advantages,such as the porous nanosheet shaped NiSe2 can form strong binding effect with Li2S and afford more active sites to catalyze Li2S decomposition process.In addition,the highly-conductive NiSe2 could shorten the nucleation path of Li2S and enhance electron conductivity to lower internal resistance of the battery.Furthermore,the 3D flexible conductive network can afford more sulfur,which is better for realizing high-sulfur-loading Li-S battery.As expected,the battery delivered a high specific capacity of 830 m Ah g^-1,corresponding to the area capacity of9.96 m Ah cm^-2.Herein,a new type of electrocatalyst was designed and constructed by manipulation of anion N doping in metallic Co Se2(N-Co Se2)to turn its intrinsic structure for realizing high performance Li-S battery.On one hand,introducing N element into Co Se2 could enhance the chemisorption with polysulfides benefiting for suppressing the dissolution and shuttle behaves of polysulfides.On the other hand,N-doped Co Se2 demonstrated glorious catalytic performance,which could not only significantly enhance polysulfides reduction kinetics in discharge process,but also obviously lower the decomposition barrier of Li2S during the charge process better for realize high energy density of Li-S battery.Benefiting from the intensive polysulfides adsorption and elevated catalytic ability,the N-Co Se2/S electrode demonstrated remarkably enhanced electrochemical performance.Notable,with N-Co Se2 as bifunctional catalyst,the battery exhibited ultrahigh areal capacity of 9.26 m Ah g^-1 under the low E/S(electrolyte/sulfur)ratio of 4.4?L mg^-1.