Lithium Storage Properties Of Nanoporous Silver-supported M-S(M=Co,Zn,Mn) Composites

The transition metal sulfide has attracted much attention due to its advantages of high theoretical capacity,low storage over-potential of lithium ions,low cost and pollution-free products.However,they have low conductivity and large volume expansion upon charging and discharging cycles.To solve these problems,Co_1-xS,Zn S and Mn S were supported by nanoporous Ag via hydrothermal method and chemical water bath deposition method in this dissertation.The phase composition and morphology were studied by XRD and SEM.The difference of lithium storage performance of different materials and the property improvement mechanism of nanoporous Ag on sulfide materials was analyzed based on electrochemical testing.Single Co_1-xS phase can be obtained by hydrothermal method and chemical water bath deposition method.Upon supporting,the nanoporous Ag skeleton reacts with Na₂S to generate Ag₂S after hydrothermal treatment.While part of nanoporous Ag skeleton still exists after chemical water bath deposition method.The phase composition of the composite prepared by hydrothermal method is Co_1-xS and Ag₂S.The electrochemical performance testing indicates that the addition of nanoporous Ag did not improve the lithium storage performance of the Co_1-xS material.In comparison,the phase composition of the sample prepared by chemical water bath deposition method is Co_1-xS,Ag and Ag₂S.The lithium storage performance of the electrode material prepared by this method is better than that of the pure Co_1-xS.When the current density is 100 m A/g,the initial discharge/charge capacities are 1182.3 and 1038.0 m Ah/g,respectively.After 50 cycles,the discharge capacity of the composite is 687.7 m Ah/g,exhibiting better cycling performance.The ZnS/NP-Ag composite prepared by chemical water bath deposition is composed of Zn S,Ag and trace Ag₂S.The effect of S/Zn ratio on the lithium storage performance of the composite was studied.At a current density of 100 m A/g,the discharge capacities of the electrode material with S:Zn=1:1 and 2:1 after 150 cycles are 370.5 and 403.5 m Ah/g,respectively.Those are improved to a certain extent as compared with the discharge capacities of the pure Zn S electrode material（257.6 and 306.1 m Ah/g）.For the high rate property,the electrode material with S:Zn=2:1 has a capacity of 91.3 m Ah/g at the current density of 2 A/g,which is two times higher than that of pristine Zn S.The improvement in performance is mainly attributed to the enhanced electrical conductivity of nano-porous Ag composites,in which the hollow porous structure provides a favorable channel for ion and electron transport and enhances the kinetics of ion diffusion.The MnS/NP-Ag composites with two different S/Mn ratios were prepared by chemical water bath deposition method.Both are composed of Mn S,Ag and Ag₂S phases.For the morphology,the particles for the case of S:Mn=2:1 is larger and more evenly deposited on the nanoporous Ag skeleton.It was found that the addition of nanoporous Ag improves the lithium storage performance of Mn S,especially for the material with S:Mn=2:1.At the current density of 100 m A/g,the discharge/charge capacity after 100 cycles are 908.9 and886.4 m Ah/g,respectively.For the high rate property,it has a capacity of 200.8 m Ah/g at the current density of 2 A/g,which is significantly improved in contrast with the capacity of4.6 m Ah/g for pure Mn S.This is due to the uniform deposition of Mn S on the nanoporous Ag skeleton without obvious agglomeration,which provides a convenient channel for ion and electron diffusion at high rate.