| Magnesium-ion batteries are considered to be one of the promising next-generation battery energy storage system due to their low cost,high energy density,high safety and almost no dendrites-formation.However,magnesium ion batteries are still in the early stages of development,and the development of electrode materials and new electrolytes is the current focus.In this paper,BixSn（1-x）/2Sb（1-x）/2,SnxSb（1-x）/2Bi（1-x）/2,SbxSn（1-x）/2Bi（1-x）/2（x=0.1,0.33,0.5,0.8）powders were prepared by high-energy ball milling.After that,the half cell was assembled using pure Mg counter electrode and Bi-Sn-Sb alloy anode and the electrochemical performance was tested in APC electrolyte.The galvanostatic measurement results at the current density of 0.01 m A/cm2 show that Bi-Sn-Sb ternary alloys possess very high specific capacities.The maximum specific capacities of Bi0.5Sn0.25Sb0.25,Sn0.1Sb0.45Bi0.45 and Sb0.1Sn0.45Bi0.45 are 575.8,568 and 587.1 m A h g-1,respectively.It is found that the interaction of Bi,Sn and Sb greatly improved the reactivity of Sn and made Sb have the ability of reversible reaction.Then the reaction mechanism of Bi0.5Sn0.25Sb0.25 by ex-situ XRD test was investigated,and it is found that the reversible reaction of Sb Sn is the key to"unlocking"the activity of Sb.Unfortunately,the rate capability and cycling performance of the Bi-Sn-Sb ternary alloy electrodes are not as good as expected.The discharge specific capacity of Sn0.1Sb0.45Bi0.45 electrode tested at 1 mA/cm2 is about 123 m A h g-1,and the capacity retention rate is 41.8%.Although the cycling performance of the alloy electrode is poor,the Bi0.5Sn0.25Sb0.25showed 112.4 m A h g-1 at 0.5m A/cm2 and the capacity retention is 30%after 60 cycles.the cycling stability of the alloy electrode is improved compared with that of the pure Bi electrode,which may be due to the increased phase interface through alloying and improved structural stability of the alloy electrode.The SEM images on the surface of Bi0.5Sn0.25Sb0.25 electrode after 25 cycles showed that the alloy particles could not bear the volume expansion during the cycling process,which resulted in serious cracking.The unstable structure and low specific surface area is the reasons for the poor electrochemical performance of Bi-Sn-Sb ternary alloy.Then,the coral-shaped Bi-Sn-Sb alloy powders with porous surface were prepared by high temperature melting.The results of nitrogen adsorption and desorption showed that the specific surface area and porosity of the powders with special morphology were much higher than those of the irregular bulk powders prepared by ball milling.the Mg2+transfer sites increase due to the increase of specific surface area,which leads to the improvement of the kinetics properties of Bi-Sn-Sb alloy negative electrode and the improvement of the rate performance.The discharge capacity of M-3 sample at 1 m A/cm2is about 283 m A h g-1,and the capacity retention is 75.7%.The porous surface structure reduces the damage of volume expansion to the negative electrode,and the capacity of M-4 is 262.2 m A h g-1 and the capacity retention rate is 82.7%after 60 cycles at the current density of 0.5 m A/cm2.However,the element distribution in Bi-Sn-Sb alloy is not uniform,and there is a part of Sb enrichment area,which leads to the capacity of the alloy electrode cannot be fully utilized.Future work is the improvement of the sythnesis method for the nano-structure alloy electrod. |
