Study On Electrochemical Performance Of Metal Oxide Modified Lithium-Sulfur Battery Rich In Oxygen Vacancies

In recent years,secondary batteries have developed rapidly as energy storage devices.Among them,lithium-sulfur batteries have huge advantages in energy density and have become the focus of attention of many researchers.However,lithium-sulfur batteries are still a long way from commercialization due to the shuttle effect and lithium dendrites.The root cause of these problems is that the conversion reaction of lithium polysulfide is slow and the lithium ion kinetics is lagging.To solve these problems,researchers use the method of adding catalysts to lithium-sulfur batteries to improve battery performance.Studies have found that metal oxides have strong adsorption capacity and can catalyze the conversion of polysulfide,which is beneficial to improve the utilization of active material,but its ion and electronic conductivity cannot meet the needs of rapid charge and discharge.In response to the above problems,this topic synthesizes a composite material formed of a metal oxide with abundant oxygen vacancies and carbon nanotubes to be used as a lithium-sulfur battery catalyst,and uses the unique electronic structure of oxygen defect sites to further enhance its ion and electronic conductivity and capture polysulfide reduces its conversion energy barrier,improves the reaction kinetics and catalyzes the conversion of lithium polysulfide.On the other hand,the use of the lithium-philic characteristics of defects can capture lithium ions and promote the transmission of lithium ions,smooth the surface of the lithium negative electrode,inhibit the growth of lithium dendrites,and improve the cycle stability of the lithium negative electrode.Using the method of hydrothermal synthesis and hydrogen reduction,TiO_2-x@CNT composite with carbon nanotubes as the framework and in-situ supported titanium oxide nanoparticles with abundant oxygen vacancies was used as a catalyst to coat the lithium-sulfur battery separator.The first discharge specific capacity at a rate of 0.5C is 1183 mAh g-1,and the capacity retention rate is as high as 82%after 100 cycles.Compared with the TiO₂@CNT material before hydrogen reduction,the reversible specific capacity after 200 cycles at high rate of 2C is increased by 45%,and the capacity decay rate is only 0.193%per cycle.On the one hand,carbon nanotubes increase the electrical conductivity and enhance the binding force with lithium polysulfide;on the other hand,titanium oxide nanoparticles rich in oxygen vacancies enhance the catalytic activity of poly sulfide redox reactions,effectively inhibiting the shuttle effect.The cerium oxide with more free electrons is selected as the catalytic material,which is easier to form covalent bonds,which is beneficial to bond with lithium polysulfide,and has excellent chemical adsorption and catalysis.CeO_2-x@CNT composite with carbon nanotubes as the framework and in-situ supported titanium oxide nanoparticles with abundant oxygen vacancies was used as a catalyst to coat the lithium-sulfur battery separator.The first discharge specific capacity of the battery is 1293 mAh g-1 at a rate of 0.5C,the capacity retention rate is as high as 84%after 100 cycles.Compared with the CeO₂@CNT material before hydrogen reduction,the reversible specific capacity after 200 cycles at high rate of 2C is increased by 30%,and the capacity decay rate is only 0.121%per cycle.It is proved that cerium oxide has better catalytic performance than titanium oxide.Based on the above research,it is designed to disperse two metal oxides(TiO_2-x,CeO_2-x)with excellent catalytic performance on the carbon cloth to form an interlayer.The surface of the lithium metal modified by the interlayer is smooth after 200 cycles,and there is no tendency to form lithium dendrites.With the increase of current density and capacity,Li/CC/TiO_2-x and Li/CC/CeO_2-x electrodes can still maintain a relatively stable polarization voltage.This is because the oxygen vacancies in the metal oxide can efficiently capture lithium ions,combined with the porous carbon to promote the transmission of lithium ions in the horizontal direction,and improve the deposition kinetics of lithium ions,thereby inhibiting the growth of lithium dendrites.