Alloyed BiSb Nanoparticles Confined in Tremella‐Like Carbon Microspheres for Ultralong‐Life Potassium Ion Batteries

Bismuth–antimony alloy is considered as a promising potassium ion battery anode because of its combination of the high theoretical capacity of antimony and the excellent rate capacity of bismuth. However, the large volume change and sluggish reaction kinetic upon cycling have triggered severe capacity fading and poor rate performance. Herein, a nanoconfined BiSb in tremella‐like carbon microspheres (BiSb@TCS) are delicately designed to address these issues. As‐prepared BiSb@TCS renders an outstanding potassium‐storage performance with a reversible capacity of 181 mAh g−1 after ultralong 5700 cycles at a current density of 2 A g−1, and an excellent rate capacity of 119.3 mAh g−1 at 6 A g−1. Such a superior performance can be ascribed to the delicate microstructure. The self‐assembled carbon microspheres can strengthen integral structure and effectively accommodate the volume expansion of BiSb nanoparticles, and 2D carbon nanowalls in carbon microspheres can provide fast ion/electron diffusion dynamic. Theoretical calculation also suggests a thermodynamic feasibility of alloyed BiSb nanoparticles for storing potassium ion. Such a work shows that BiSb@TCS possesses a great potential to be a high‐performance anode of potassium ion batteries. The rational designing of multiscaled structure would be instructive to the exploitation of other energy‐storage materials. Nanoconfined BiSb in tremella‐like carbon microspheres are first synthesized by a facile method. It renders an extraordinary performance as anode of potassium ion batteries, due to the delicate microstructure with 2D carbon nanowalls and enhanced adsorption ability of BiSb alloy for K+. The rational designation is instructive to the exploitation of other energy‐storage materials.