Research On The Key Materials For High Performance Lithium-Sulfur Battery

Lithium-sulfur battery has been considered to be one of the most promising candidates for next-generation energy storages due to its high theoretical capacity(1675 Ah kg^-1)and high energy density(2600 Wh kg^-1).However,despite intensive research there are certain limitations to be overcome to bring Lithium-sulfur battery to practical application.The low conductivity of sulfur,the volume expansion during charge and discharge,and the shuttle effect of polysulfide lead to rapid capacity decay of Lithium-sulfur batteries.To overcome the challenges mentioned above,this thesis started from designing the structure of the sulfur electrode,introducing functional interlayer and modifying separator,carried out extensive research work aiming at improving the performance of Lithium-sulfur battery.The details are as follows:1.A ternary confine-functional sulfur composite with a Host-Sulfur-Container(H-S-C)architecture was synthesized.In the prepared H-S-C composite,the host is a special porous carbon with interconnected tunnel macropores and micro/mesopores on macropore walls,and the container is the poly(3,4-ethylenedioxythiophene)layer.The carbon host with macroporous open structure containing meso/micro pores on its inside walls is beneficial for the permeation of electrolyte into the sulfur particles and ensuring high sulfur utilization.The interconnected tunnel macropores and the inside meso/micropores would facilitate the electron transfer and shorten Li-ion diffusion length.Meanwhile,the PEDOT coating layer would work as a physical barrier to block the dissolution of the polysulfide into the electrolyte,further trap polysulfide,and avert the irreversible loss of active materials.After 200 cycles at 0.5C,the Lithium-sulfur battery with H-S-C electrode delivers a specific discharge capacity of 831.9 m Ah g^-1.2.A self-supported Fe and N co-doped carbon nanofiber interlayer was prepared by electrospinning and a subsequent high-temperature carbonization method.The three-dimensional porous structure of the interlayer provides a physical place for trapping soluble polysulfides,and the doped Fe and N improve the chemical adsorption ability of the interlayer to polysulfide.Thus,the shuttle of polysulfides has been well suppressed.On the other hand,the three-dimensional conductive network could effectively shorten the diffusion path of lithium-ions,reducing the internal resistance of lithium sulfur battery.These characteristics of the Fe-N-C interlayer improve the reutilization of active material and thus prolong the cycle life of Li-S batteries.After 100 cycles at 0.5C,the Lithium-sulfur battery with Fe-N-C interlayer delivers a specific discharge capacity of 947.8 m Ah g^-1.3.An ultra-thin rGO/MoO₂ functional layer is introduced on the commercial PP separator by a simple hydrothermal method and a subsequent vacuum filtration method.The thickness of the functional layer is only 2?m,which would not affect the energy density of the lithium-sulfur battery.The rGO/MoO₂ functional layer has excellent electrical conductivity and could improve the utilization of elemental sulfur.Meanwhile,the chemisorption of polysulfide by Mo O₂ could effectively inhibit the shuttle of polysulfide.Lithium-sulfur batteries using this modified separator exhibit lower impedance,longer cycle life and lower self-discharge rate.