Study On The Lithium Storage Performance Of Lithium Ion Battery Anode Modified By Regulating Metal Sulfides

Both lithium metal and metal sulfide anodes have high specific capacity and become potential anode materials for lithium ion batteries(LIBs).However,poor cycling stability limits their applications.In order to solve this problem,the three-dimensional framework structures of metal sulfides(Ni₃S₂,Co9S8)with various morphologies are prepared in this paper,which can improve the Coulomb efficiency and cycle life during lithium metal plating/stripping;By regulating the sulfur defects of MoSx nanocrystals anode materials,the cycling stability is significantly increased.The details are as follows:(1)Three dimensional Ni₃S₂ nanosheets and nanorods are grown on the skeleton of foam nickel by controlling reaction time and temperature.The commercially available 3D foam nickel is modified to be a high-performance lithium deposition matrix.The integration of the grown Ni₃S₂ nanosheets/nanorods and the Ni current collector builds the fast electron transfer channel and guarantees good electron transfer.Especially,the porous structure composed of Ni₃S₂ nanosheets can promote the full penetration of electrolyte and effectively alleviate the volume change of lithium upon cycling.In addition,Ni₃S₂ nanosheets are connected with each other to form a conductive network,which ensures the uniform distribution of charge,thus inducing the uniform deposition of lithium and inhibiting the growth of lithium dendrites.A high Columbic effciency of 98.9%for 210 cycles at a current density of 1 mA/cm² can be achieved.At a current density of 1 mA/cm² with a capacity of 1 mAh/cm²,the assembled symmetrical cell can stably cycle for 2800 h without cells failure,and its overpotential is kept within 13 mV,showing a long cycle life.(2)The three-dimensional flower-like Co9S8 is grown on graphene film(3D Co9S8/GF),which is beneficial to reduce the local current density,increase the contact area with electrolyte and inhibit the growth of lithium dendrite.The lithiophilic Co9S8 can provide abundant nucleation sites and reduce the energy barrier of lithium nucleation.Meanwhile,Li2S and Li2S₂ formed by the reaction of Co9S8 with Li can be used as a protective layer to reduce the side reactions of electrolyte and lithium metal.Li2S/Li2S₂ with ionic conduction properties can further improve the uniformity of lithium ion flux distribution.At a current density of 1 mA/cm² with a capacity of 1 mAh/cm²,the Coulombic efficiency of 3D Co9S8/GF remains stable after 100 cycles,where it is as high as 98.3%.In the long cycle test,Li@Co9S8/GF symmetrical cell can maintain a low overpotential and cycle to 2000 h without cells failure.(3)MoS₂ nanocrystals with monolayer structure are prepared by ion intercalation,and the monolayered MoS1.5 nanocrystals with sulfur defect are prepared by removing part of sulfur from MoS₂ surface with cation exchange resin.The sulfur defects will lead to more surface active sites,which is conducive to the enhancement of conductivity.Meanwhile,the chemical bond(-C-O-Mo)can be formed between the sulfur-depleted MoS1.5 nanocrystals and reduced graphene oxide,which is helpful to stabilize the oxygen-containing groups on the surface of reduced graphene oxide,making the composite electrode show outstanding cycle capability and rate performance.The composites with the optimized loading of MoS1.5 nanocrystals shows excellent lithium storage performance,a high discharge capacity of 1409.5 mAh/g can be obtained at 0.1A/g upon 100 cycles.(4)A series of sulfur-depleted and monolayered MoSx nanocrystals/reduced graphene oxide composites are prepared.The more sulfur defects are beneficial to the improvement of the metallicity of MoSx nanocrystals,and MoSi.5 nanocrystals with higher sulfur defects exhibit the low lithium ion diffusion barrier,therefore,its composite electrode shows the specific capacity of 983.9 mAh/g at the high current density of 1 A/g in the 640th cycle.At the same time,the mechanism of its pseudocapacitive contribution to the building high-performance and long cycle LIBs is explored.The full charge of the capacity of 983.9 mAh/g with the current density of 1 A/g requires 3542 s,and the high capacity of?814.7 mAh/g has been obtained by the pseudocapacitive contribution.In addition,the increase of 1T phase structure of Mo-S nanocrystals is beneficial to reduce the charge transfer resistance of electrode materials and promote the improvement of cycle specific capacity.