Mechanism Of Performance Improvement Of Lithium-sulfur Batteries Based On MoTe₂

In recent decades,energy and environmental issues have gradually attracted people’s attention.Under the background of the country’s strategic goal of achieving carbon peaking and carbon neutrality,research on new energy materials and new energy storage devices has become a hot spot.Due to its high theoretical energy density(2600 Wh kg^-1),lithium-sulfur batteries are expected to become the next generation of high specific energy energy storage devices.However,the polysulfides generated during the charging and discharging process of the lithium-sulfur battery cathode have slow reaction kinetics and a shuttle effect,resulting in low battery coulombic efficiency and short cycle life,which has become a bottleneck hindering the development of lithium-sulfur batteries.At present,researchers have widely adopted different functional materials to solve the problems of polysulfide shuttling and slow redox kinetics through physical confinement,physical/chemical adsorption,and electrocatalysis.In this thesis,βphase molybdenum ditelluride（β-MoTe₂）was used as the cathode electrocatalyst of lithium sulfur battery to study its effect on the performance of lithium sulfur battery and its mechanism.The main findings of the study are listed below:1.Bulk single crystalβ-MoTe₂was synthesized by chemical vapor transport（CVT）method using TeBr₄as transport agent and then exfoliated into nanosheetsβ-MoTe₂.XRD and TEM test showed that single crystal bulkβ-MoTe₂was successfully synthesized.In order to exert the maximum effect ofβ-MoTe₂on improving the performance of lithium-sulfur batteries,carbon cloth was used as the counter electrode,β-MoTe₂was used as the working electrode,and hexadecyltrimethylammonium bromide（CTAB）was passed through the electrolytic cell.Electrochemical intercalation exfoliation ofβ-MoTe₂.The test results show that the CTAB electrochemical intercalation successfully exfoliates the bulkβ-MoTe₂into nanosheets without causing lattice distortion of theβ-MoTe₂.2.The exfoliatedβ-MoTe₂was used as an electrocatalyst and mixed with a sulfur-carbon composite（CNT@S）to prepare a lithium-sulfur battery cathode containingβ-MoTe₂electrocatalyst（β-MoTe₂/CNT@S）.Theoretical calculation and test show thatβ-MoTe₂can produce strong interactions with polysulfides（LiPSs）.Combined with the high conductivity and rich catalytic sites ofβ-MoTe₂,it can promote the redox kinetics of LiPSs and ensure the efficient utilization of sulfur.At the same time,β-MoTe₂has good wettability to electrolyte,which ensures the penetration of electrolyte and reduces the internal resistance to the battery.Therefore,β-MoTe₂/CNT@S exhibited strong adsorption and catalytic conversion of LiPSs during cycling,inhibiting the dissolution shuttling of LiPSs,lowering the activation energy during solid/liquid conversion,and increasing the diffusion coefficient of lithium ions.Benefiting from the adsorption and catalysis ofβ-MoTe₂,β-MoTe₂/CNT@S can provide a high specific capacity of 1213 mAh g^-1at 0.1 C,especially 598 mAh g^-1at 4 C rate,while the capacity retention rate was 64%after 300 cycles at 1 C rate.