Prolonging the cycle life of zinc-ion battery by introduction of [Fe(CN)6]4- to PANI via a simple and scalable synthetic method

Coordinated cyanide ([Fe(CN)(6)](4-)) has been introduced into a PANI film by a facile and scalable two-step method: electrodeposition followed by solution-soaking. During solution-soaking, the [Fe(CN)(6)](3-) ions react with the PANI and are reduced to [Fe(CN)(6)](4-) on the PANI chains to form a carboncloth-polyaniline-[Fe(CN)(6)](4- )electrode (referred as CC-PANI-FeCN). Electrochemical tests show that the introduction of [Fe(CN)(6)](4-) can greatly improve the cycling stability of the PANI electrode while retaining its high initial specific capacity. After 1000 repeated charge/discharge cycles, the specific capacity retention rate of CC-PANI-FeCN is approximately 71%, while the retention rate of CC-PANI is only 17%. The enhancement of cycle performance after introduction of [Fe(CN)(6)](4-) could benefit from the strong interaction between [Fe(CN)(6)](4-) and -NH+ -/-NH+ = groups. In addition, a flexible zinc-ion battery assembled with CC-PANI-FeCN as the positive electrode, zinc foil as the negative electrode, and the aqueous quasi-solid PVA gel as electrolyte exhibits stable electrochemical performance in different bending states, demonstrating its application potential in flexible and portable electronic devices. By combining these effective electrochemical performances with the cost-effective synthetic method, this work may open an avenue for a broad range of flexible energy-storage devices that utilize traditional conducing polymers (PANI) as electrodes.