Structure Engineering on Prussian Blue Analog Anode Toward Rapid Na-Ion Storage

Abstract

Developing high-rate electrode materials is a critical enabler of fast-charging Na-ion battery (NIB). Prussian blue analog (PBA) with rapid charge transfer channels has shown significant potential as high-rate NIB cathodes; however, the fast-charging capability of reported PBA-based anodes remains limited. This challenge primarily stems from the complete transformation of their original PBA-based crystal structures during synthesis processes, resulting in loss of the inherent rapid charge transfer channels. Herein, a Ni-Fe based PBA (Ni₃[Fe(CN)₆]₂) with a representative PBA-based crystal structure is presented as a prototype to investigate its potential as a NIB anode, and structural modification strategies are implemented to unlock its rapid Na-ion storage. First, conversion reaction mechanism is demonstrated in the Ni₃[Fe(CN)₆]₂ during sodiation, with a theoretical specific capacity of 357.2 mAh g⁻¹. However, its reversible capacities after long-term cycling and at high rates are low. To address these issues, structural optimization strategies including S incorporation, configurational entropy modulation, and coordination environment regulation are utilized. Consequently, its fast-charging (≈40 s per charge with 245.0 mAh g⁻¹ input) and excellent cycling capabilities are realized. This study demonstrates the feasibility of PBA as high-rate NIB anodes, and promotes the further investigation into structural optimization strategies aimed at developing other fast-charging electrodes.