Bi nanoparticles embedded in cyclic polyacrylonitrile enable binder free anode for high-performance potassium-ion batteries

Bismuth (Bi), a promising anode material for potassium-ion batteries (PIBs), suffers from the poor cycle stability and rate capability caused by the huge volume expansion during potassiation and intrinsic moderate conductivity. In this work, polyacrylonitrile (PAN) is used as both surface modification agent and binder to replace conventional carboxymethyl cellulose/styrene-butadiene rubber (CMC/SBR), and the cyclized PAN (cPAN)-coated Bi nanoparticles are fabricated within the electrode after calcining under argon protection. The ultrathin cPAN coating (2.3 nm) not only enhances potassium-ion and electronic conductivity but also effectively mitigates volume changes during cycling, ensuring rapid potassium-ion reaction kinetics and exceptional structural stability. Theoretical calculations further reveal that the Bi/cPAN interface exhibits high potassium adsorption capability and low potassium migration energy barriers. As a result, the Bi@cPAN electrode delivers outstanding cycling stability and remarkable rate capability in half cells. Furthermore, when paired with a potassium Prussian blue (KPB) cathode, the full cell demonstrates excellent cyclic stability with 82.0% capacity retention after 400 cycles at 15 C, exhibiting tremendous potential of Bi@cPAN composite as a high-performance anode material for PIBs.