Self-Standing, Collector-Free Maricite NaFePO₄/Carbon Nanofiber Cathode Endowed with Increasing Electrochemical Activity

A new electrode design for sodium-ion batteries with a self-standing, collector-free, binder-free maricite NaFePO4/carbon nanofiber hybrid cathode is successfully realized via electrospinning. An increasing capacity is observed in the initial cycles, and finally, the electrode reached a capacity of 108 mAh g-1 at a 0.1 C rate after 200 cycles. In comparison, a slurry-based NaFePO4 electrode yields a capacity of only around 20 mAh g-1. An overall improved electrochemical performance was obtained in the hybrid cathode compared to pure slurry-based NaFePO4 electrode and pure carbon nanofibers. A comprehensive study of the morphology, structure, and electrochemical performance of the hybrid electrode is conducted. Mössbauer spectra show an increasing Fe3+ content from 43.2% in the first charged state to 63.0% in the charged state after 100 cycles, demonstrating an activating process of maricite NaFePO4 upon extensive charge-discharge cycling. This work has explored a direct electrospun self-standing maricite NaFePO4 electrode and its feasibility and mechanism as a cathode material in sodium-ion batteries.