Concentration-Gradient\nPrussian Blue Cathodes for\nNa-Ion Batteries

Abstract

A concentration-gradient composition is proposed as an\neffective\napproach to solve the mechanical degradation and improve the electrochemical\ncyclability for cathodes of sodium-ion batteries. Concentration-gradient\nNa_<i>x</i>Ni_<i>y</i>Mn_1–<i>y</i>Fe­(CN)₆·<i>n</i>H₂O particles, in which the Ni content gradually\nincreased from the interior to the particle surface, were synthesized\nby a facile co-precipitation process. Using these particles as the\nactive material in cathodes resulted in an improved electrochemical\nperformance compared to homogeneous Na_<i>x</i>MnFe­(CN)₆·<i>n</i>H₂O, delivering\na high reversible specific capacity of 110 mAh g^–1 at 0.2 C and outstanding cycling stability (93% retention after\n1000 cycles at 5 C). Electron microscopy illustrated that the promising\nelectrochemical properties obtained for the gradient composition can\nbe attributed to its robust microstructure, which alleviated the electrochemically\ninduced stresses and accumulated damage during sodiation/desodiation,\npreventing hence the fracture which was observed in the homogeneous\nsamples. . These findings render a prospective strategy to develop\nhigh-performance electrode materials for sodium-ion batteries.