Investigation of alkali-ion (Li, Na and K) intercalation in manganese hexacyanoferrate KxMnFe(CN)6 as cathode material

KxMnFe(CN)(6) are attractive cathode candidates for alkali-ion batteries due to the resource abundance and open three-dimensional framework. In this work, electrochemical characterizations combined with theoretical calculations are carried out to study the intercalation properties of Li+, Na+, K+ in MnFe(CN)(6) framework. It achieves reversible capacities of 120.9, 117.1 and 104.8 mAh g(-1) for Li, Na, and K storage, respectively, with average voltage of 3.7 V versus Li/Li+, 3.5 V versus Na/Na+ and 3.8 V versus K/K+. DFT calculations reveal the occupy sites, diffusion pathways and working potentials for the Li+, Na+ and K+-(de)intercalation in the MnFe (CN) 6 framework. It is demonstrated for the first time that the migration energy barriers of Na+ is lower than that of Li+ and K+, thus resulting in the best rate performances for Na+-storage. The higher potential for K+ intercalation could be attributed to the high binding energy of K+ and MnFe(CN) 6 framework. Electrochemical mechanisms suggest that the MnHCF undergoes reversible orthorhombic-cubic phase transition upon Li+/K+ insertion/extraction, while is irreversible during the repeated Na+ insertion/extraction. In addition, novel K-ion batteries based on all-PBA electrodes (KxMnFe(CN)(6) and Co-3[Co(CN)(6)](2)) are constructed, delivering reversible capacity of 84.9 mAh g(-1) with high average voltage of 2.8 V. This work provides theoretical guidance for the development of high performance and sustainable PBA materials for alkali-ion batteries.