Boosting charge-transport kinetics in Na2Fe(HPO4)(C2O4) cathode via multi-dimensional carbon networks

As a promising polyanionic cathode for sodium-ion batteries, Na 2 Fe(HPO 4 )(C 2 O 4 ) (NFPC) exhibits a high operating voltage and excellent structural tunability. However, its practical application is largely restricted by sluggish Na + transport kinetics and poor intrinsic electronic conductivity, which severely limit reaction kinetics during cycling. To address these challenges, multidimensional conductive networks were constructed through an interfacial engineering strategy by incorporating Ketjen Black (KB) and carbon nanotubes (CNTs) into the NFPC matrix. The introduced carbon frameworks preserve the crystal structure of NFPC while establishing continuous electron-conduction pathways and intimate electrode/electrolyte interfaces. As a result, the apparent Na + diffusion kinetics are accelerated by one to two orders of magnitude, accompanied by enhanced pseudocapacitive sodium-storage behavior. Distribution of relaxation times (DRT) analysis further demonstrates that the homogeneous conductive network effectively suppresses charge-transfer resistance and alleviates interfacial degradation during repeated sodiation/desodiation processes. Among the investigated samples, NFPC@KB exhibits the best electrochemical performance, delivering a high initial discharge capacity of 95.70 mAh g −1 at 0.1C, close to its theoretical capacity, together with an outstanding capacity retention of 86.17% after 200 cycles at 0.5C. This work demonstrates an effective conductive-network engineering strategy for improving the electrochemical kinetics of NFPC and provides useful guidance for the rational design of high-performance polyanionic cathodes for large-scale sodium-ion energy storage.