Tridentate citrate chelation towards stable fiber zinc-polypyrrole battery with hybrid mechanism

The persistent challenge in Zn-ion batteries is the decomposition of coordinated water around Zn2+-induced side reactions and dendrite growth on Zn anode, leading to short lifespans. This situation is even worse in fiber-shaped Zn-ion batteries (FZIBs). Their curved and complex surface structure makes it even challenging to stabilize Zn anode via existing strategies. Herein, we address this dilemma via cost-effective citrate anion (Cit(3-)) additives which work as a tridentate chelating agent to regulate electrolytes on the molecular level. Synchrotron X-ray absorption fine structure analyses reveal that Cit(3-) manipulates the solvation shell of Zn2+ by forming [ZnCit(H2O)(3)](-) chelate complexes. Combining with density functional theory calculation, for the first time, we demonstrate that Cit(3-) facilitates dehydration in [ZnCit(H2O)(3)](-), passivates remaining coordinated water via mitigating H-O bond (H2O) elongation by 77.7%, suppresses Zn2+ transfer kinetics, homogenizes Zn2+ distribution at interfaces, enabling similar to 500% extended lifespan. Based on this, we developed high-performance FZIBs by coupling Zn/carbon fiber anodes with highly conductive polypyrrole/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate fiber (similar to 3700 S cm(-1)) cathodes. Further mechanism study suggests that polypyrrole provides extra charge storage capacity by accommodating dual ions, i.e., Zn2+ and SO42-. The obtained quasi-solid-state FZIB possesses excellent performance for practical applications.