A New Route Toward Improved Sodium Ion Batteries: A Multifunctional Fluffy Na0.67FePO4/CNT Nanocactus.

To improve the performance of energy storage systems, the rational design of new electrode configurations is a strategic initiative. Here, we present a novel monodisperse fluffy alluaudite Na0.67FePO4, prepared by a modified solvothermal method, as promising electrode for sodium ion battery. This porous Na0.67FePO4 with nanocactus-like morphology is composed by nanorods within an open three-dimensional structure. This unique nanocactus-based morphology offers three important advantages when used as electrode for sodium ion battery: (i) provides an open frame structure for a large Na+ ions transport; (ii) reduces the sodium ion and electron transport path by ≈20 nm; (iii) offers a large surface area for a more efficient interface between the electrode and the electrolyte. The electrochemical investigation revealed that this fluffy Na0.67FePO4 nanocactus exhibits the high discharge capacity of 138 mAh g(-1). Moreover, a battery with a Na0.67FePO4/CNT hybrid electrode delivered a discharge capacity as high as ≈143 mAh g(-1), coupled to an excellent stable cyclability (no obvious capacity fading over 50 cycles at a current rate of 5 mA g(-1)). This enhanced mechanism was studied by means of absorption measurements and ex situ XAFS characterizations. Results of the characterization of the Na0.67FePO4 suggests that the outstanding performance can be associated with the unique fluffy nanocactus morphology.