Cerium Hexacyanocobaltate: A Lanthanide-Compliant Prussian Blue Analogue for Li-Ion Storage

Electrode materials are the most significant components of lithium-ion batteries (LIBs) and play an important role in endowing them with high electrochemical performance. The exploration of new electrode materials and their comparative study with contemporary resources will help the design of advanced electrodes. Here, we have synthesized a new type of Prussian blue analogue (cerium(III) hexacyanocobaltate, CeHCCo) and systematically explored the effect of valence states of Fe²⁺ and Ce³⁺ on crystal structure and electrochemical properties of final products. We demonstrate that the unbalanced charge in iron(II) hexacyanocobaltate (FeHCCo), as opposed to that in CeHCCo, results in more residual K⁺ ions, thereby leading to the occupancy of cavities. As a result, the K⁺ ion-rich FeHCCo exhibits lower capacities of 55 ± 3 and 15 ± 3 mAh g^-1 at 0.1 and 1 A g^-1, respectively, compared with the K⁺ ion-deficient CeHCCo that exhibits capacities of 242 ± 3 and 111 ± 3 mAh g^-1 at the same current densities. This work provides a novel contribution for the exploration of new Prussian blue analogues and bestows a newer concept for electrode material design.