Synthesis And Electrochemical Performance Of Core-shell Structured MoS₂@S And Spherical Nitrigon-doped Fe₃O₄/C

As electrode materials for lithium-sulfur and lithium-ion batteries,both sulfur and triiron tetraoxide have high theoretical specific capacities of 1675 and 926 mAh/g,respectively.In addition,they are abundant,cheap and environmentally affinity.However,both electrode materials have large volume variation during lithiation/delithiation process,which restrict there further application.In addition,sulfur cathodes have problems such as poor electrocial conductivity and polysulfide shuttle effects,which result in rapid capacity fading.To solve the above-mentioned problems,in this thesis,core-shell structured MoS₂@S cathode and spherical nitrigon-doped Fe₃O₄/C anode have been designed and synthesized.Their microstructure and electrochemical performance have been investigated.The conclusions are as follows:?1?MoS₂ shells composed of MoS₂ nanosheets have been obtained through a hydrothermal route using Na₂MoO₄·2H₂O,L-Cysteine and MnCO₃ templates as starting materials,and followed by acid corrosion.Then,the core-shell structured MoS₂@S composite cathodes have been synthesized through melting and diffusion of sulfur.?2?The core-shell structured MoS₂@S displays excellent rate capability,cyclic performance and structural stability.The discharge capacity can reach 538.5 mAh/g at4 C,which is 59%of the capacity at 0.2 C.The cyclic capacity reaches 632 mAh/g after 200 cycles at 1 C,and the capacity fading rate of each cycle is only 0.1%.?3?The spherial Fe₃O₄/C anode materials have been synthesized through a aerosol-pyrolysis process using PVP,citric acid and Fe?NO₃?₃·9H₂O as starting materials,where the nanosized Fe₃O₄ particles are embedded in the three-dimentional electrocial conductive carbon networks.The spherical nitrigon-doped Fe₃O₄/C anode materials have been obtained through adding of urea in the starting materials.?4?The spherical nitrigon-doped Fe₃O₄/C exhibits better rate capability and cyclic performance compared with those of the spherical Fe₃O₄/C.The delithiation capacity reaches 344.7 mAh/g at 2.5 C.The cyclilc capacity can maintain 562.5 mAh/g after200 cycles at 0.5 C.The capacity fading rate of each cycle is only 0.081%.