Ultra-stable calcium ion batteries with Prussian blue nanodisks

Abstract

Calcium ion batteries, though more sustainable than lithium-ion batteries, still face significant challenges, including the lack of highly rechargeable electrodes. Prepared Prussian blue nanodisk electrodes can significantly extend the longevity of Ca-based cells. The method involves precipitating 20-nm-thick nanodisks of Prussian green from Fe(NO3)(3) and K3Fe(CN)(6), followed by sodiation with NaI. The Prussian-blue-based cathode with polyacrylic acid/polyaniline binder delivers an initial discharging capacity of 77.6 mAh g(-1) at 0.1 A g(-1) and retains 91.0% capacity after 700 cycles. Polyvinyl fluoride is detrimental to the Ca-based cell, as its coulombic efficiency decreases from 94.8% (120th cycle) to 86.4% (400th cycle). With the same cathode, the Ca-based cell is much less sensitive to high current densities than the Na-based cell. This can be because only half the amount of cations is required to move in Ca-based systems compared to Na-based systems; thus, the charge-transfer resistance is noticeably reduced in Ca-based systems.