Application Of Graphene Based Composite In Lithium Sulfur Battery

Thanks to the features of impressive theoretical energy density(2600 Wh kg-1)and low cost,lithium-sulfur(Li-S)batteries become the most promising next-generation energy storage devices.However,due to the sluggish kinetics(caused by the multi-electron redox reaction)and poor electronic conductivity of elemental sulfur,the utilization of the sulfur in cathode is inefficient,As a result,the actual capacity and cycle life of Li-S batteries can't meet the industrial requirements.Among the discharge/charge process in Li-S batteries,the interaction between the conductive host and the intermediate lithium polysulfides(LiPSx,4?x?8)is essential to the electrochemical performance.Hence,designing and synthesizing candidate materials with excellent catalysis and adsorption capabilities to LiPSx are the key to achieve high-performance Li-S batteries.In order to solve the problems mentioned above,the research works in this paper are as follows:1.The sluggish kinetic and shuttle effect of LiPSx result in rapid capacity attenuation and low utilization of active material.Introducing adsorption-catalysis carriers to restrain the shuttle effect has become effective way high performance Li-S batteries.Based on the strong polar adsorption of TiN to LiPSx and catalytic effect of nitrogen-doped graphene to the conversion of LiPSx,a mesoporous titanium nitride/N-doped graphene(TiN@NG)composite is developed to host elemental sulfur.As a result,the cathode comosed of TiN@NG/S delivers a remarkable reversible capacity(1390 mAh g-1 at 0.1 C)and excellent cycling performance(730 mA h g'1 after 300 cycles).Symmetric cells and EIS tests show that TiN@NG can effectively inhibit the dissolution of LiPSx and accelerate the electrochemical reaction,thus alleviating the shuttle effect and improving the performance.2.In the redox reaction of Li-S batteries,the liquid-solid reaction of LiPSx to Li2S(final product)leads to slow reaction kinetics,resulting in low coulombic efficiency and poor cycle stability.Monatomic catalysts can achieve the highest atomic utilization and excellent selective catalytic ability on the atomic scale.Based on the above analysis,a series of M-NG(M=Fe,Co and Ni)monatomic catalysts with the similar coordination environment were designed,which shows distinguishing electrochemical performance in symmetrical cell and galvanostatic charge-discharge process(1 C),indicating that metal atoms played an important role in the the conversion of polysulfides.