Study On Cobalt-Doped Molybdenum Disulfide Nanoflower Anode Modified By Carbon-Comples-Shell

Molybdenum disulfide has a graphite-like layered structure,and its theoretical specific capacity as an anode material for lithium-ion batteries（LIBs）reaches 670m Ah g^-1,higher than that of commercial graphite electrode(370 mAh g^-1).However,the poor conductivity of 2H phase MoS₂ and the structural pulverization during the cycle process lead to the rapid capacity decay and poor rate performance,which limits its application in LIBs.In this paper,the modification of MoS₂ was studied to improve its electrical conductivity and stability.First,MoS₂ nanoflower was synthesized with the assistance of cetyltrimethylammonium bromide（CTAB）.In order to improve the intrinsic conductivity of MoS₂,Co-doped MoS₂（CMS）was synthesized by solution method,the resistance was decreased,and the diffusion coefficient of lithium ion(7.07×10^-13cm² s^-1)was increased.The surface of CMS was further modified with polyaniline（PANI）to prepare CMSP.Based on the flexibility of PANI,the volume change of MoS₂ could be buffered and wrapped,which was conducive to the improvement of the stability of the material.Among them,the CMSP-2 sample containing 15 wt%PANI showed the highest specific capacity.The initial discharge capacity at 200 mA g^-1 was 1429.7 mAh g^-1,and the capacity was still 649.4 mAh g^-1 after 100 cycles.The improvement of the cycle performance was benefited from the improvement of conductivity,thus improving the electrochemical reaction speed of CMSP-2,showing excellent rate performance.In addition,CMSP-3（containing 20 wt%PANI）was partially carbonized to prepare a composite material（CMSP-3-500）with nitrogen-doped carbon and PANI double-coated.The formed outermost N-doped carbon shell had high electron conductivity,providing a complete and fast channel for electron conduction,so the cycle and rate performance of CMSP-3-500 could be significantly improved.The initial capacity at 200 mA g^-1 and the capacity at the 100th cycle were 1436.6 and 583 mAh g^-1,respectively,which were higher than the capacity values of CMSP-3(1071 and390.5 mAh g^-1).Furthermore,the CMSP-3-500 still had a capacity of 391.2 mAh g^-1after 250 cycles at a current density of 500 mA g^-1.The bimetallic organic framework（Bi-MOF）was successfully synthesized on the surface of MoS₂,and the carbon surface modification layer was formed after carbonization.The electrochemical reaction kinetics of the composite materials MS@C were accelerated,and the electrochemical performances were improved.MS@C-800calcined at 800℃had the highest cycle capacity and rate performance.At the current densities of 100,200,500,1000,2000 and 5000 mA g^-1,the specific capacities of MS@C-800 were 905.3,846.6,703.2,538.2,387.8 and 163.7 mA g^-1,respectively.When the current density was restored to 100 mA g^-1,MS@C-800 could still release699.7 mAh g^-1,which was 77.3%of the initial capacity.