Research On Preparation And Performance Of Carbon-based Cathode Materials For Lithium Sulfur Batteries

Lithium-sulfur batteries is sulfur composite for the cathode and lithium metal as anode.The high theoretical specific capacity of 1675 m Ah g^-1and high energy density of 2600 Wh kg^-1are several times higher than traditional lithium-ion batteries.Therefore,Li-S battery has received an extensive attention as one of the candidates for the next generation high-performance battery.During the discharge process,elemental sulfur(S₈)reduces to soluble high-order long-chain Li₂S_n(4?n?8)and insoluble low-order short-chain Li₂S₂/Li₂S.Thus,this paper focuses on the research of carbon-based cathode materials for Li-S batteries,aiming to solve the problems of poor sulfur conductivity,irreversible capacity attenuation caused by volume expansion of sulfur and diffusion of intermediate products between electrodes.The main research results are as follows:(1)The polyanilne(PANI)is firstly in-situ grown on the surface of N-doped carbon nanotube(NCNT).By a high-temperature carbonization process,the highly porous carbon covered CNT structure is obtained.After sulfur melting,the resultant NCNT@HPC/S composite is employed as the cahode of Li-S battery.The NCNT@HPC/S cathode demonstartes an excellent electrochemical performance under0.5 C with the initial capacity of 1210 m Ah g^-1,remaining at 621 m Ah g^-1after 250cycles.Furthermore,the Coulombic efficiency is close to 100%during the charge-discharge process.(2)The porous hollow carbon sphere HCS is firstly synthesized with the precursor of phenolic resin wrapped Si O₂nanosphere.After sulfur melting and diffusion,a 30nm thick Zn S film was evaporated on the surface to prepare the composite cathode of Zn S@HCS/S.The initial discharge capacity of the resultant Li-S battery is 1115.8 m Ah g^-1at 0.5 C,which maintains at 573.3 m Ah g^-1over 200 cycles with the Coulomb efficiency of?100%.Due to the chemically sulfur-fixing effect of Zn S nanolayer,the present cycling performance is superior to that of HCS/S cathode without Zn S coating.(3)HCS@Co-MXene800 powder is firstly prepared by a self-assembly process using HCS,MXene and Co O(OH)composite solution.Elemental sulfur is then fused into the composite powder and used as the cathode of Li-S battery.Results show that the HCS@Co-MXene800/S has a discharge capacity of 834.2 m Ah g^-1in the first cycle at a high current density of 1 C,and a capacity of 727.4 m Ah g^-1after 120 cycles.The composite structure exerts a strong chemical adsorption and catalytic conversion to polysulfides,which is account for the excellent cycling stability of battery under the high current density.