Sponge-Like Microfiber Electrodes for High-Performance Redox Flow Batteries.

Fabricating fiber-based electrodes with a large specific surface area while maintaining high flow permeability is a challenging issue in developing high-performance redox flow batteries. Here, a sponge-like microfiber carbon electrode is reported with a specific surface area of as large as 853.6 m2 g-1 while maintaining a fiber diameter in the range of 5-7 µm and a macropore size of ≈26.8 µm. The electrode is developed by electrospinning cross-linked poly(vinyl alcohol)-lignin-polytetrafluoroethylene precursors, followed by oxidation and pyrolysis. Applying the as-synthesized electrodes to a vanadium redox flow battery enables the battery to achieve an energy efficiency of 79.1% at the current density of 400 mA cm-2 and a capacity retention rate of 99.94% over 2000 cycles, representing one of the best battery performances in the open literature. The strategy to fabricate sponge-like porous carbon microfibers holds great promise for versatile applications in redox flow batteries and other energy storage systems.

A Highly Reversible Zinc Anode for Rechargeable Aqueous Batteries.

Zinc metal holds a great potential as an anode material for next-generation aqueous batteries due to its suitable redox potential, high specific capacity, and low cost. However, the uncontrollable dendrite growth and detrimental side reactions with electrolytes hinder the practical application of this type of electrodes. To tackle the issues, an ultrathin (∼1 µm) sulfonated poly(ether ether ketone) (SPEEK) solid-electrolyte interphase (SEI) is constructed onto the Zn anode surface by a facile spin-coating method. We demonstrate that the polymeric SEI simultaneously blocks the water molecules and anions, uniformizes the ion flux, and facilitates the desolvation process of Zn2+ ions, thus effectively suppressing the side reactions and Zn dendrite formation. As a result, the newly developed Zn@SPEEK anode enables a symmetric cell to stably operate over 1000 cycles at 5 mA cm-2 without degradation. Moreover, with the Zn anode paired with a MnO2 cathode, the full cell exhibits an improved Coulombic efficiency (over 99% at 0.1 A g-1), a superior rate capability (127 mA h g-1 at 2 A g-1), and excellent cycling stability (capacity retention of 70% over 1000 cycles at 1 A g-1). This work provides a facile yet effective strategy to address the critical challenges in Zn anodes, paving the way for the development of high-performance rechargeable aqueous batteries.