Preparation Of Three Dimensional Ultra-thin Carbons Wrapped Sb-Bi Nanomaterials And Study On The Properties Of Sodium/Potassium Ion Batteries

SbBi alloy can improve the cyclic stability and rate performance of sodium/potassium storage due to the interfacial synergistic effect,but researchers focus on the design of the composite structure of SbBi alloy and carbon substance,while ignoring in-depth study on the precise proportion of SbBi components,its catalytic ability,the difference in electrochemical behavior between sodium and potassium storage and so on.Herein,the volume expansion rates of SbBi alloy with different proportions of embedded Na+/K+ were calculated by first-principles,and three dimensional ultra-thin carbon wrapped Sb-Bi nanoparticles with various proportions were synthesize(SbBix@C).The electrochemical behaviors of sodium and potassium storage were discussed in detail.Further,the differences of the electrochemical mechanisms of sodium and potassium storage by SbBi0.5@C composite electrode were investigated from the perspectives of dynamic ion diffusion,composition of SEI film and microstructure of sodium and potassium storage by SbBi0.5@C composite electrode after circulation.The main research contents and results are as follows:(1)(SbBix@C,x=1,0.5,0.15)was prepared by facile salt template assisted pyrolysis method.The effects of calcining temperature(T)and alloy ratio on SbBix@C were systematically investigated.It is found that when T is 750℃ and Sb：Bi is 1:0.5,the diameter of SbBi0.5 nanoparticles can be ensured to be about 50 nm and uniformly embedded in the three-dimensional ultra-thin carbon skeleton.In addition,SbBi0.5@C electrode exhibits the best electrochemical performance for sodium storage.A capacity of 402 mAh g-1 is delivered at 0.1 A g-1 for sodium storage and maintained 300 mAh g-1 after 100 cycles with capacity retention of 75%.(2)The SbBi0.5@C electrode showed better electrochemical performance than sodium storage when used as the anode of potassium ion batteries.The results show that SbBi0.5@C can delivers 410 mAh g-1 at 0.1 A g-1 current density and still holds 390 mAh g-1 with a capacity retention rate of 90%after 100 cycles.(3)The reasons for the superior storage performance of SbBi0.5@C for potassium are as follows:the particles are obviously agglomerated after sodiation.However,the particles are dispersed uniformly on the carbon substrate after potassiation.Moreover,the size of nanoparticles are reduced to 10 nm;SEI film formed in the process of potassium storage is composed of chemical bonds with high chemical bond energy(C=O,S-O,etc)and the internal thick oxidized inorganic layer is closely connected with the metal layer and SEI film,which increases the structural stability of metal particles and alleviates the capacity attenuation caused by structural deterioration.Therefore,it shows excellent cyclicing and rate electrochemical performance when storing potassium.