Research On Electrochemical Performance And Stress Sensitivity Of Bismuth Based Lithium-sulfur Batteries

In the press of energy crisis,the rapid development of electric vehicles and large-scale energy storage devices need to rely on lithium secondary batteries with higher energy density.Lithium-sulfur batteries have high energy density,which is considered as a potential candidate material for energy storage devices.In addition,elemental sulfur has the advantages of abundant reserves,low cost and non-toxicity,which could make lithium-sulfur batteries more competitive.However,the application of lithium-sulfur batteries is still restricted duo to the low conductivity,shuttle effect,volume expansion,lithium dendrite and so on.Among of them,the shuttle effect is the most serious.Therefore,how to limit the shuttle effect of lithium-sulfur battery is a research hotspot.Furthermore,the higher requirements will be put forward for the mechanical and electrochemical properties of lithium-sulfur batteries under mechanical load.In order to solve the above problems,bismuth based composite cathode materials were designed and prepared in this paper.The effects of Bi₂S₃and Bi₂O₃on the electrochemical performance of lithium-sulfur batteries were studied.On this basis,the sensitivity of the batteries to stress was studied,and the optimization strategy of lithium-sulfur batteries structure was put forward.（1）S@Co/N-CNTs@Bi₂S₃and S@Co/N-CNTs@Bi₂O₃composite cathodes were prepared by alcohol heating and melt diffusion method.Contrasting S@Co/N-CNTs and S@CNTs cathodes,we can find that when bismuth based compounds were compounded,the composite cathode had a high initial discharge specific capacity and an excellent rate capability.The as-prepared S@Co/N-CNTs@Bi₂S₃and S@Co/N-CNTs@Bi₂O₃cathodes delivered a capacity decay rate of 0.038%and 0.056%during 900 cycles at 1.0 C,respectively,which showed wonderful cycling stability,which can be attributed to the strong adsorption of bismuth oxide and bismuth sulfide on polysulfide,inhibiting their dissolution and diffusion.（2）The mechanical,thermal and electrochemical characteristics of bismuth based lithium sulfur batteries under multiple stresses were explored,and the flat plate compression experiment and the local compression experiment were carried out.The real-time temperature and voltage during the experiment were collected,the electrochemical performance of the batteries under different working conditions was tested,and the changes of batteries capacity,coulomb efficiency and cycle life under different stress were studied.Combined with the relationship between force deformation response,voltage and temperature,the electrochemical attenuation mechanism of the batteries under different stress was analyzed.The initial specific discharge capacities of the batteries after plane compression of 10%,30%and 50%were 928.6,816.8 and 777.6 m Ah/g respectively,while the initial specific discharge capacities of the batteries after partial compression of 10%,30%and 50%were 869.6,660.2and 467.2 m Ah/g respectively,which indicated that the battery capacity under the two kinds of compression decreases in varying degrees.The greater the compression,the greater the degree of reduction and the greater the damage to the internal structure of the batteries.Moreover,local compression had a more significant impact than plane compression.（3）The optimization strategy of battery structure is studied according to the conclusion data of（2）.The idea is to apply the stiffness adjustable negative Poisson’s ratio superstructure,metamaterial and intelligent bionic structure to lithium sulfur battery,which provides a reference for the development of high conductivity and impact resistant battery protective shell.