"Grafting" NiSe onto Cu2-xSe with twinborn structure embedded in carbon-based nanofibers to weave freestanding sodium-ion storage electrode.

The fabrication of freestanding electrodes for Na+ storage is necessary to achieve high energy density. However, the large radius of Na+ results in a large volume fluctuation and sluggish reaction kinetics of active materials, particularly at a high active material content, thereby impeding electrochemical performance with undesirable cycling performance or rate capability. In this study, a freestanding electrode based on the "NiSe grafted on Cu2-xSe" heterostructure with double-carbon protective shells (NiSe/Cu2-xSe@C@NCNFs) was successfully constructed for Na+ storage. In this microstructure, N-doped carbon nanofibers (NCNFs) serve as the stem of the twinborn NiSe/Cu2-xSe heterostructure with a built-in electric field, where NiSe improves Na+ absorption and Cu2-xSe enhances Na+ diffusion. The "graft" design enabled the freestanding NiSe/Cu2-xSe@C@NCNFs electrode with a high active mass content of 76.1 wt% to exhibit superior electrochemical performance for Na+ storage (75 mAh g-1 at 2 A g-1) compared to those of Cu2-xSe@C@NCNFs (26 mAh g-1 at 2 A g-1) and NiSe@C@NCNFs (9 mAh g-1 at 2 A g-1).

Regulation of Outer Solvation Shell Toward Superior Low-Temperature Aqueous Zinc-Ion Batteries.

Aqueous Zn-ion batteries are well regarded among a next-generation energy-storage technology due to their low cost and high safety. However, the unstable stripping/plating process leading to severe dendrite growth under high current density and low temperature impede their practical application. Herein, it is demonstrated that the addition of 2-propanol can regulate the outer solvation shell structure of Zn2+ by replacing water molecules to establish a "eutectic solvation shell", which provides strong affinity with the Zn (101) crystalline plane and fast desolvation kinetics during the plating process, rendering homogeneous Zn deposition without dendrite formation. As a result, the Zn anode exhibits promising cycle stability over 500 h under an elevated current density of 15 mA cm-2 and high depth of discharge of 51.2%. Furthermore, remarkable electrochemical performance is achieved in a 150 mAh Zn|V2 O5 pouch cell over 1000 cycles at low temperature of -20 °C. This work not only offers a new strategy to achieve excellent performance of aqueous Zn-ion batteries under harsh conditions, but also reveals electrolyte structure designs that can be applied in related energy storage and conversion fields.