All-iron sodium-ion full-cells assembled via stable porous goethite nanorods with low strain and fast kinetics

Iron-based hydroxyl oxides can be regarded as feasible electrodes for sodium-ion batteries due to the simple preparation and rich resources. Goethite nanorod clusters that are wrapped by multi-walled carbon nanotubes with an open tunnel structure exhibit a considerable capacity, a favourable durability and an excellent rate capability within loose working conditions. The structural and electrochemical stability of this anode can be maintained when exposed at ambient environment after 30 days. Moreover, this anode coupled with high-quality Prussian blue cathode delivers feasible energy density of 60 W h kg ⁻¹ calculated on the basis of the pouch cell. Abundant voids formed by Kirkendall effect in nanorods allow for the simultaneous promotion of electrolyte infiltration, ion transfer and the pseudocapacitive effect. According to a series of ex situ and in situ measurements, the intercalation and conversion reactions for sodium storage have been revealed and low-volume deformation was observed during the sodiated/desodiated process. In particular, the existence of Na _x FeOOH, Fe, NaOH and Na ₂ O species at fully discharged state indicates an incomplete conversion reaction, resulting in steerable volume expansion and high ionic/electrical conductivity. The advanced sodium storage kinetics can be attributed to the moderate diffusion barrier and remarkable pseudocapacitive effect.