Composite Modification Of Titanium Dioxide And Their Performance Study In Lithium Sulfur Batteries

Lithium-sulfur（Li-S）batteries have attracted unprecedented attentions due to their high energy density(2600 Wh kg^-1),low cost and low toxicity.However,the industrialization of Li-S batteries is still facing many challenges,such as the low electronic conductivity of the active substance,the“shuttle effect”of intermediate lithium polysulfides（Li PSs）and the slow conversion kinetics.In view of the above problems,based on the strong polarity and the chemical adsorption to Li PSs of titanium dioxide（Ti O₂）,this paper involved three kinds of composite host materials based on Ti O₂ by introducing conductive carbon,Ti₃C₂ MXene material and oxygen vacancy defect in several.Comprehensive physical and electrochemical characterizations were carried out,and the interaction mechanism of sulfur host material against sulfur cathode was further explored by theoretical simulation.Hollow TiO₂@C nanospheres with mesoporous structure were synthesized by hard-template and solvothermal methods.The mesoporous and hollow structure not only provides sufficient loading space for sulfur,but also alleviates the volume change of active substance.The polar Ti O₂ nanosheets can chemically interact with Li PSs,thus anchoring them to the host material,reducing the shuttle of Li PSs and the loss of active substances.Meanwhile,the carbon material in the composite can improve the overall electrical conductivity.Therefore,the composite sulfur electrode can obtain reversible specific capacity of 485.3 m Ah g^-1 after 500 cycles at 2 C.Due to the weak adsorption effect of carbon material to Li PSs,Ti₃C₂ MXene with stronger adsorption effect was used as conductive substrate.Ti O₂@MXene nanocomposites were constructed by solvothermal method.Their high specific surface area and abundant pores can facilitate the loading of sulfur and the infiltration of electrolyte.The“shuttle effect”of Li PSs can be inhibited by Ti₃C₂ MXene and Ti O₂cpmponents with polar adsorption ability in the composite.Meanwhile,Ti₃C₂ MXene nanosheets as conductive substrate can effectively improve the conductivity of the composites,while Ti O₂ nanosheet can effectively inhibit the stacking of Ti₃C₂ MXene nanosheets.Therefore,when Ti O₂@MXene nanocomposites were used as host material of sulfur,the reversible specific capacity of 611.8 m Ah g^-1 can be obtained by the composite sulfur electrode after 500 cycles at 2 C.Li-S batteries are not only faced with“shuttle effect”of Li PSs,but also slow conversion kinetics.Therefore,the conversion kinetics of Li PSs can be improved by introducing oxygen vacancy into Ti O₂.Hierarchical porous Ti O_2-x@C membranes with oxygen vacancies were prepared by phase transformation method combined with high temperature carbonization and thermal reduction.Through theoretical simulation study,the introduction of oxygen vacancy in Ti O₂ can reduce its band gap and improve its intrinsic conductivity.In addition,oxygen vacancy can strengthen the interactions between Ti O₂ and Li PSs and form a stronger Ti-S bond between Ti O₂ and Li PSs,which can weaken the S-S“bridge bond”in Li PSs and make it easier to fracture in the discharge process.Thus the catalytic conversion of Li PSs in the discharge process can be achieved.When Ti O_2-x@C membrane was used as host material of sulfur,a reversible specific capacity of 715.2 m Ah g^-1 could be obtained after 500 cycles at 2 C.Even when the sulfur loading was increased to 4.3 mg cm^-2,The Ti O_2-x@C/S membrane electrode remained a reversible specific capacity of 699.4 m Ah g^-1 after 100 cycles at 0.5 C.