Porous Na2Fe(SO4)2/C: high pseudocapacitive contribution for accelerated sodium storage kinetics†

To meet the urgent requirement for sustainable energy storage technologies, incorporating effective waste management into the design of energy storage materials can achieve a closed-loop supply chain from waste to energy. Herein, extrinsic pseudocapacitive (PDC) cathode materials with different carbon contents were synthesized using FeSO₄·7H₂O waste through a simple ball milling and annealing process, which enhances sodium storage kinetics and achieves waste recycling. The results indicate that NFSO particles and graphite flakes create a disordered porous structure, which enhances the PDC effect, thus overcoming the slow migration rate of sodium-ions. Specifically, the diffusion coefficient of NFSO/C-10 increased by around an order of magnitude compared to that of NFSO, increasing from 10⁻¹² to 10⁻¹¹. The discharge capacity reached 84 mA h g⁻¹ at 0.2C (1C = 91 mA g⁻¹). The present work realizes the high-value reuse of waste and highlights the crucial role of the PDC effect in enhancing diffusion dynamics, which opens up a new direction for the design and synthesis of high-rate iron-based sulfate cathode materials.