| With the rapid development of "3 C products" and the rise of electric vehicles,higher requirements are put forward for energy density and long-life energy storage systems.Lithium-sulfur battery(Li-S)is one of the most competitive secondary batteries in future owing to its extremely high energy density(2600 Wh kg-1),environmental friendliness,natural abundance,which make the Li-S batteries satisfy requirements for the development of renewable and clean energy.However,practical applications of Li-S batteries are still hindered due to the following issues:the elemental sulfur and discharged product have poor electronic and ion conductivity;the large volume expansion from S to Li2S;the highly soluble intermediate polysulfides could easily migrate to lithium anode causing the shuttle effects during the redox process.These issues can directly bring about the low coulombic efficiency,low utilization of sulfur and poor cycling stability.Therefore,high-performance cathode materials are designed,conductive carbon and polar materials are combined as the sulfur cathode carrier,and chemical adsorption strategies are applied to bind sulfur and polysulfides.Conductive carbon is used to improve the conductivity of elemental sulfur.In addition,the hollow structure can alleviat the electrode changes.The main research contents and results are as follows:(1)Cobalt-doped titanium nitride(TixCoi1-xN)was incorporated into carbon/sulfur cathodes,the nanosized TixCoi1-xN provides a high adsorption capability for polysulfides.Meanwhile,the high catalytic performance of TixCo1-xN facilitates the kinetics of LiPSs redox reaction during charging and discharging.By optimizing the doping ratio of Co element,It found that the rate performance of the material is the best,when the ratio of Ti:Co=8:2.Furthermore,the added amount of Ti0.8Co0.2N was investigated.We investigated that the optimum content of Tio.aCo0.2N to obtain the best cycling stability was 20 wt.%in the CNT/Ti0.sCo0.2N/S composite.Finally,our optimized materials to compare electrochemical performance with different additive matrix materials.As a result,the CNT/Ti0.8Co0.2N/S cathode delivers a high initial discharge capacity of 1492.8 mAh g-1 at 0.1 C current density.We also further demonstrated an ultralong cycle life up to 400 cycles at 2C with a decay rate of as low as 0.086%per cycle.(2)A composite material with NiO as the core and nitrogen doped hollow carbon spheres(NHCSs)as the shell was successfully prepared through simple hydrothermal method and calcination steps.We investigated the influence of addtion of urea raw materials on NiO nucleation and morphological changes during growth.And by adjusting the content of Ni(NO3)2·6H2O,the effects between the amount of NiO and the electrochemical performance of the product was explored,and the loading of different NiO was obtained,and its electrochemical performance was studied.When the NiO content is 30 wt.%and the cell with 30%-NiO@NHCSs/S cathode delivers the initial specific capacity of 1300.27 mAh g-1 at 0.1C.(3)Through hydrothermal reaction and high-temperature calcination,ultra-thin nickel cobalt layered double metal hydroxide(Ni-Co LDH)nanosheets were successfully grown on hollow carbon microspheres.The rules among urea content,hydrothermal temperature,nickelcobalt ratio and morphology,and electrochemical performance were explored.The results indicated that the Ni-Co LDH nanosheets have a uniform structure when reacted at 90℃.When the ratio of Ni(NO3)2·6H2O and Co(NO3)2·6H2O is 3:7,the performance of the material is the best.The cell with NHCSs@3Ni-7Co/S cathode delivers the initial specific capacity of 1279.42 mAh g-1 at 0.1C. |
