Towards Realizing Wearable Batteries: Dual Ion Prussian Blue Analog/Zinc Battery Architecture with Long Cycle Life and High Energy Efficiency

In recent years Prussian Blue Analogues (PBA) have attracted a lot of interest as a battery material due to their relative safety to skin contact and exceptionally high cyclability. Their open cage structure allow a variety of ions to shuttle in and out and thus store energy. This can be done very rapidly as there is no phase change associated with this process, which makes them stable for over thousands of cycles.(Pasta et al. 2012) Recent developments in this field show the use of zinc to act as the anode, which can exhibit a PBA vs. Zn cell potential as high as 1.7 V. But the performance of such a system reported thus far show less than 10% cycle life as that of  highly reversible PBA half cells. (Zhang et al. 2014)

In this work we demonstrate a high potential aqueous Sodium ion battery with high cycle life, to achieve as much as 500 cycles with over 80% cell capacity retention, which is five times of the maximum reported in literature. (Trócoli and La Mantia 2015)The high potential of Zn and high reversibility of Na+ ion cycling in Copper Hexacyanoferrate lattice is exploited in making a considerable improvement over previous Zn/ Zinc Hexacyanoferrate system. We validate the hypothesis that the slow kinetics of zinc intercalation compared to sodium in Hexacyanoferrates enables preferential intercalation of sodium ions and hence reduce zinc poisoning. We further show the use of Hyper Dendritic Zinc (HD Zn) to improve capacity retention and overall kinetics of the system. Prussian Blue has been used as a fabric dye for over 80 years. The relative safety of the dual ion PBA/HD Zn system that we demonstrate helps us step closer to realizing batteries on fibers woven integrated with wearable electronics.