Improving cycling stability of Bi-encapsulated carbon fibers for lithium/sodium-ion batteries by Fe_2O_3 pinning

Bi draws increasing attention as anode materials for lithium-ion batteries and sodium-ion batteries due to its unique layered crystal structure,which is in favor of achieving fast ionic diffusion kinetics during cycling.However,the dramatic volume expansion upon lithiation/sodiation and an insufficient theoretical capacity of Bi greatly hinder its practical application.Herein,we report the Fe_2 O_3 nanoparticle-pinning Bi-encapsulated carbon fiber composites through the electrospinning technique.The introduction of Fe_2 O_3 nanoparticles can prevent the growth and aggregation of Bi nanoparticles during synthetic and cycling processes,re s pectively.Fe_2 O_3 with high specific capacity also contributes to the specific capacity of the composites.Consequently,the as-prepared Bi-Fe_2 O_3/carbon fiber composite exhibits outstanding long-term stability,which delivers reversible capacities 504 and 175 mAh/g after1000 cycles at 1 A/g for lithium-ion and sodium-ion batteries,respectively.