Fast and Long‐Lasting Potassium‐Ion Storage Enabled by Rationally Engineering Strain‐Relaxation Bi/Bi2O3 Nanodots Embedded in Carbon Sheets

Bismuth (Bi)‐based materials merit high theoretical volumetric specific capacity (3800 mAh mL⁻1) but suffer from huge volume variations and sluggish reaction kinetics during cycling. Herein, the optimal framework of Bi/Bi2O3 nanodots enriched in suitable outer amorphous carbon sheets (Bi/Bi2O3 NDs@CSs) is first proposed to alleviate volume variations and accelerate stable charge transport to boost K+ storage performance. The introduction of proper Bi2O3 not only provides an efficient K+ adsorption path, but also effectively buffers volume changes via conversion reaction. Accordingly, the as‐prepared anode exhibits a remarkable rate capability (149.3 mAh g−1 at 60 A g−1, 42% capacity retention with a 120‐fold current‐density increase) and extraordinary durability (1800 cycles at 5.0 A g−1, 95% capacity retention), among the best rate and cycling performance to date in potassium ion batteries (PIBs) anodes. Theoretical calculations reveal the feasible structures of Bi/Bi2O3 NDs@CSs with double protection of carbon sheets and Bi2O3 are conducive to enhance charge transfer and efficiency of electrochemical reaction. Substantial in situ/ex situ characterizations and finite element simulation further unveil high reversibility and robust mechanical behavior of Bi/Bi2O3 NDs@CSs, favorable for the reinforcement of structural stability. This study provides new insights into developing high‐performance and durable Bi‐based anodes for PIBs. The optimal framework of Bi/Bi2O3 nanodots enriched in suitable outer amorphous carbon sheets (Bi/Bi2O3 NDs@CSs) is elaborately prepared. Such a special structural design is favorable for superior potassium storage, delivering high rate capacity of 149.4 mAh g−1 at 60 A g−1, and robust cycling performance of 201.8 mAh g−1 is maintained over 1000 cycles at 10 A g−1.