A high-volumetric-capacity bismuth nanosheet/graphene electrode for potassium ion batteries

Potassium ion batteries (PIBs) with high-volumetric energy densities are promising for next-generation low-cost energy storage devices. Metallic bismuth (Bi) with a structure similar to graphite, is a promising anode material for PIBs due to its high theoretical volumetric capacity (3763 mA h cm−3) and relatively low working potential (−2.93 V vs. standard hydrogen electrode). However, it experiences severe capacity decay caused by a huge volume expansion of Bi when alloying with potassium. This study reports a flexible and free-standing Bi nanosheet (BiNS)/reduced graphene oxide composite membrane with designed porosity close to the expansion ratio of BiNS after charging. The controlled pore structure improves the electron and ion transport during cycling, and strengthens the structural stability of the electrode during potassiation and depotassiation, leading to excellent electrochemical performance for potassium-ion storage. In particular, it delivers a high reversible volumetric capacity of 451 mA h cm−3 at the current density of 0.5 A g−1, which is much higher than the previously reported commercial graphite material.