Design Of Cathode Material And Functional Separator In Lithium-Sulfur Battery And Performance Study

The rechargeable battery has aroused more and more researcher’s attention as a fast and convenient energy storage device.At present,lithium-ion batteries have always occupied markets in various electrical storage applications such as portable electronic products,electric vehicles.However,traditional intercalated anode and cathode materials have reached the upper limit of energy density.Therefore,new battery systems and electrochemical techniques with higher energy density are urgently needed.Lithium-sulfur(Li-S)batteries are considered as one of the most promising next-generation battery systems due to the coupling of lithium metal and sulfur,which involves a multi-electron redox reaction process with an energy density of 2600 Wh kg-1.However,the practical application of Li-S batteries is still hindered by many aspects,such as low conductivity,polysulfides(LiPSs)shuttle,slow redox kinetics and corrosion of lithium metal anode.These will seriously lead to a low sulfur utilization rate of active materials,short battery cycle life,and quick attenuation of capacity and self-discharge effect.In view of the above problems of Li-S batteries,this work uses catalytic material as cathode and modified separator to accelerate the redox kinetics of LiPSs,suppress its shuttle effect and achieve high-performance Li-S batteries.The specific research contents are as follows:(1)The three-dimensional Ni(OH)2@Ti3C2Tx composite is synthesized by simple self-assembly strategy.Due to the strong interfaces interaction between Ni(OH)2 and Ti3C2Tx,the surface charge distribution of the composite structure has been changed greatly,which exposes more active sites to ensure the adsorption and excellent electrochemical reaction kinetics of LiPSs.The experimental results show that the Ni(OH)2@Ti3C2Tx/S cathodes have achieved excellent electrochemical properties with the discharge capacity of 1320 mAh g-1 at 0.1 C,and long cycle stability of 800 cycles at 1.0 C with a fading rate of 0.138%each cycle as well as 600 cycles at 2.0 C(fading rate 0.518%/cycle)with a reversibility of 508 mAh g-1.Our discovery provides a new idea of optimized electrocatalysts for energy storage and conversion fields.(2)Self-supporting materials with high area sulfur loading and long cycle performance were prepared by in-situ growth and heat treatment.The Co-NCNT@CF materials with integrity and flexibility can be obtained,when the precursor is CoZn-ZIF and heat treatment temperature is 900℃.It has been confirmed that Co-NCNT@CF has a high specific surface area and a large number of Co-Nx active using a series of methods such as XANES,which improves catalytic reaction kinetics of LiPSs and sulfur loading for Li-S batteries.The designed cathodes exhibit a high capacity(1259 mA h g-1)at 0.1 C and excellent cycling performance with an ultralow decay of 0.038%per cycle over 500 cycles at a high current density of 3 C.A high areal capacity of 7.35 mAh cm-2 is achieved with an area sulfur load of 7.0 mg cm-2(E/S=9μL mg-1).Density Function Theory(DFT)calculation explores the interaction between Co-Nx active sites and LiPSs.The result shows that the Co-Nx active sites have high adsorption energy for LiPSs,inhibiting the dissolution of LiPSs,which provides a new choice for high sulfur-containing electrodes.(3)In order to increase the cycle life of Li-S batteries,the cobalt metal single atomic catalyst on a nitrogen-doped graphene nanomesh(SA-Co/NGM)is synthesised using the zeolitic imidazolate frameworks(CoZn-ZIF)as a pyrolysis template.STEM and EXAFS characterization have confirmed that the coordination environment of Co is Co-N4 structure.The electrochemical performance of SA-Co/NGM functional separator in Li-S cell was systematacially studied using CNT as sulfur cathode.SA-Co/NGM@PP cells exhibit a high capacity of 1333 mAh g-1 at 0.2 C,high-rate performance of 649 mAh g-1 at 5 C,and superior cycle performance with a decay of 0.0232%per 1000 cycles at 2.0C.High-specific surface area and ultra-thin 2D texture can not only provide high-density single atomic active position,but also guarantee homogenize high-flux Li ion transport,alleviating the formation of lithium dendrites.DFT calculation,in situ Raman technology and electrochemical experiment show that the Co-N4 active center could use as an efficient regulator for anchoring LiPSs,reducing energy barrier of Li2S precipitation/decomposition and accelerating the redox conversion of LiPSs.