Potassium Nickel Iron Hexacyanoferrate as Ultra-Long-Life Cathode Material for Potassium-Ion Batteries with High Energy Density

Abstract

The abundant reserve and low price of potassium resources promote K-ion batteries (KIBs) becoming a promising alternative to Li-ion batteries, while the large ionic radius of K-ions creates a formidable challenge for developing suitable electrodes. Here Ni-substituted Prussian blue analogues (PBAs) are investigated comprehensively as cathodes for KIBs. The synthesized K1.90Ni0.5Fe0.5­[Fe­(CN)6]0.89·0.42H2O (KNFHCF-1/2) takes advantage of the merits of high capacity from electrochemically active Fe-ions, outstanding electrochemical kinetics induced by decreased band gap and K-ion diffusion activation energy, and admirable structure stability from inert Ni-ions. Therefore, a high first capacity of 81.6 mAh·g–1 at 10 mA·g–1, an excellent rate property (53.4 mAh·g–1 at 500 mA·g–1), and a long-term lifespan over 1000 cycles with the lowest fading rate of 0.0177% per cycle at 100 mA·g–1 can be achieved for KNFHCF-1/2. The K-ion intercalation/deintercalation proceeds through a facile solid solution mechanism, allowing 1.5-electron transfer based on low- and high-spins FeII/FeIII couples, which is verified by ex situ XRD, XPS, and DFT calculations. The K-ion full battery is also demonstrated using a graphite anode with a high energy density of 282.7 Wh·kg–1. This work may promote more studies on PBA electrodes and accelerate the development of KIBs.

A Low‐Strain Potassium‐Rich Prussian Blue Analogue Cathode for High Power Potassium‐Ion Batteries

“…Thenon-stoichiometric proportion of Ni and Fe could be attributed to the formation of [Fe(CN) 6 ] 4À vacancies during the co-precipitation process. [26] Thec rystallographic information of KNiHCF was analyzed by Rietveld refinement (Figure 1a), and detailed refinement results are listed in the Supporting Information, Table S2. TheKNiHCF shows acubic phase with F " 43m(216) space group (a = b = c = 10.0443 ).…”

The Rise of Prussian Blue Analogs: Challenges and Opportunities for High‐Performance Cathode Materials in Potassium‐Ion Batteries

“…It should be noted that pushing the doping percentage higher to 8 wt% is harmful to the electrochemical performance of PBAs and leads to serious capacity degradation. Chong et al [ 103 ] also confirmed the electrochemical performance of PBAs can be significantly improved when half of Fe was replaced by Ni. As shown in Figure 7g,i, the Ni‐substituted KFHCF, K 1.9 Ni 0.5 Fe 0.5 [Fe(CN) 6 ] 0.89 ·0.42H 2 O, demonstrates improved rate capability (53.4 mA h g −1 at 0.5 A g −1 ) and enhanced cycling stability (82.3% after 1000 cycles), compared with the pristine KFHCF and other PBA cathode materials (Table 1).…”

Flexible Free‐Standing VO2/MXene Conductive Films as Cathodes for Quasi‐Solid‐State Zinc‐Ion Batteries

“…[9][10][11] Therefore, an increasing focus on sodium and potassium ion batteries has emerged rapidly. [12][13][14][15] Nevertheless, the large ionic radius is always a big challenge to find suitable host materials. Meanwhile, the use of organic electrolyte will bring about many safe and environmental issues.…”

“…However, future growth and prospect of LIBs would be hampered to some extent by reason of the maldistribution of lithium, high cost and safety concern [9–11] . Therefore, an increasing focus on sodium and potassium ion batteries has emerged rapidly [12–15] . Nevertheless, the large ionic radius is always a big challenge to find suitable host materials.…”