Electrochemical Performance Of TiO₂ And Carbon Composites Based Lithium-sulfur Battery

The growing development for electronic equipment has stimulated the development of advanced energy storage equipment with stability and high energy density,and the most advanced lithium-ion batteries have almost reached their theoretical values,facing huge challenges for further development.As one of the next-generation energy storage technologies,lithium-sulfur batteries have great potential,such as high theoretical capacity(1675 m Ah g^-1)and energy density(2600 Wh kg^-1),as well as abundant earth resources,low cost,and Environmentally friendly.Despite its considerable advantages,the practical application of lithium-sulfur batteries is still plagued by the following problems:sulfur and discharge products Li₂S₂/Li₂S have poor electrical conductivity,large volume changes during charge and discharge,and shuttle effects caused by soluble lithium polysulfides,Resulting in low Coulomb efficiency,loss of active materials,high self-discharge rate and poor cycle stability.In view of the above problems,in the process of synthesizing titanium dioxide fibers by electrospinning in this thesis,carbon nanotube（CNT）and carbon fibers fiber（CNF）with high conductivity and large comparative area were introduced,and the titanium dioxide fiber matrix was used to prepare A-R-TiO₂/CNT and Co-TiO₂/CNF composites materials were obtained by high temperature heat treatment method and CVD method,respectively.The morphological structure and physical properties of the synthesized product were studied by the process parameters,and its electrochemical performance was explored,which provided an important reference for the application research of lithium-sulfur batteries.1.The precursors were prepared by electrostatic spinning and then subjected to high temperature heat treatment.A-R-TiO₂/CNT composites has a large specific surface area and has good mechanical properties and flexibility.A-R-TiO₂/CNT composites with mesoporous three-dimensional network has excellent electrochemical performance.The A-R-TiO₂/CNT composites has an initial specific capacity of 1457 m Ah g^-1at a current density of 0.1 C,and the capacity is retained after 100 cycles.1195 m Ah g^-1reversible discharge capacity,capacity retention rate is 82%;after testing its specific discharge capacity under different current densities,after charging and discharging at a rate of 4 C and returning to 0.2 C again for cycling,the discharge The specific capacity can still be restored to 1221 m Ah g^-1,which has excellent electrochemical reversibility.2.Co-TiO₂/CNF composites with novel structure were successfully synthesized by using CVD method based on the precursor of cobalt nitrate,and their morphology and electrochemical properties were characterized and analyzed.The electrochemical test of Co-TiO₂/CNF composites materials showed that the porous network-shaped Co-TiO₂/CNF composites materials have excellent electrochemical performance,and the first discharge specific capacity is 1420 m Ah g^-1at a current density of 0.1 C;after 100 cycles,the specific discharge capacity can still reach 1267 m Ah g^-1,and the capacity retention rate is 89.2%;when the current density is 1 C,the first specific discharge capacity is 864 m Ah g^-1,after500 times After cycling,the specific capacity is still maintained at 505 m Ah g^-1and the average Coulomb efficiency is as high as 99.2%.The capacity attenuation of 0.08%per cycle is extremely low.