Superfast Phase Transformation Driven by Dual Chemical Equilibrium Enabling Enhanced Electrochemical Energy Storage

Abstract Phase transformation engineering provides new synthetic opportunities and pathways toward functional materials with desirable phases and structures. However, current phase transformation processes are generally time‐consuming or low‐yielding due to the lack of favorable driving forces. Herein, a superfast and scalable phase transformation technique driven by dual chemical equilibrium is developed. Taking manganese hexacyanoferrate (MnHCF) as an example, precipitation–dissolution and oxidation‐reduction dual chemical equilibrium co‐drive the superfast phase transformation from cubic KMnFe(CN) 6 (C‐MnHCF) to monoclinic K 2 MnFe(CN) 6 (M‐MnHCF) and simultaneously oxidative polymerization of polypyrrole (PPy), enabling the formation of homogeneous M‐MnHCF/PPy hybrid materials. For electrochemical energy storage, the uniform hybridization of PPy improves the electrical conductivity, restrains the dissolution of Mn, and more importantly, promotes K + ‐intercalation kinetics of the K‐intercalated MnHCF‐based cathodes with a K + /Na + competing insertion/extraction mechanism. As a result, the M‐MnHCF/PPy hybrid cathode manifests enhanced structural integrity and charge‐transport capability and thus long‐term cyclic life (114.8 mAh g −1 after 200 cycles at 0.1 A g −1 ) and high rate performance (113.3 and 92.7 mAh g −1 at 0.5 and 1 A g −1 , respectively).