Improving the cycle life of a high-rate, high-potential aqueous dual-ion battery using hyper-dendritic zinc and copper hexacyanoferrate

Prussian Blue Analogue (PBA)-Zn aqueous batteries are attractive because of the high potential of PBA against Zn (∼1.7 V), relative safety of the system, and high rate capability. But, despite the long cycle life of PBA half-cells, full PBA-Zn battery systems studied thus far have typically reported only up to 100 cycles and suffer significant capacity fade beyond that. In this work we demonstrate that the loss in capacity retention and cycle life is a combined effect of Zn²⁺ ion poisoning at the PBA cathode, as well as dendrite formation in the zinc anode. We address both these issues via the use of a dual ion (Na⁺ as the primary charge carrier) electrolyte and hyper-dendritic Zinc (HD Zn) as the anode. The copper hexacyanoferrate (CuHcf) vs. HD Zn system with Na⁺ ion electrolyte demonstrated herein exhibits 90% (83%) capacity retention after 300 (500) cycles at a 5C rate and a 3% reduction in usable capacity from 1C to 5C. Detailed characterization is done using in situ synchrotron energy-dispersive XRD (EDXRD), conventional XRD, XPS, SEM, TEM, and electrochemical techniques.