In Situ Encapsulating Metal Oxides into Core-Shell Hierarchical Hybrid Fibers for Flexible Zinc-Ion Batteries toward High Durability and Ultrafast Capability for Wearable Applications

Recent advances in electrospinning nanofiber materials for aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) are regarded as one of the most promising large-scale energy storage systems because of their considerable energy density and intrinsic safety. Nonetheless, the severe dendrite growth of the Zn anode, the serious degradation of the cathode, and the boundedness of separators restrict the application of AZIBs. Fortunately, electrospinning nanofibers demonstrate huge potential and bright prospects in constructing AZIBs with excellent electrochemical performance due to their controllable nanostructure, high conductivity, and large specific surface area (SSA). In this review, we first briefly introduce the principles and processing of the electrospinning technique and the structure design of electrospun fibers in AZIBs. Then, we summarize the recent advances of electrospinning nanofibers in AZIBs, including the cathodes, anodes, and separators, highlighting the nanofibers' working mechanism and the correlations between electrode structure and performance. Finally, based on insightful understanding, the prospects of electrospun fibers for high-performance AZIBs are also presented.

Flexible and Antifreezing Fiber-Shaped Solid-State Zinc-Ion Batteries with an Integrated Bonding Structure

Fiber-shaped solid-state zinc-ion battery (FZIB) is a promising candidate for wearable electronic devices, but challenges remain in terms of mechanical stability and low temperature tolerance. Herein, we design and fabricate a FZIB with an integrated device structure through effective incorporation of the active electrode materials with a carbon fiber rope (CFR) and a gel polymer electrolyte. The gel polymer electrolyte incorporated with ethylene glycol (EG) and graphene oxide (GO) endows the FZIB with a high Zn stripping/plating efficiency under extreme low temperature conditions. A high power density of 1.25 mW cm^-1 and large energy density of 0.1752 mWh cm^-1 are obtained. In addition, a high capacity retention of 91% after 2000 continuous bending cycles is achieved. Furthermore, the discharge capacity is fairly retained at more than 22% even at the low temperature of -20 °C. Toward practical applications, the FZIB integrated into textiles to power electronic products is demonstrated.

Aqueous Rechargeable Zn-ion Batteries: Strategies for Improving the Energy Storage Performance

The growing demand for the renewable energy storage technologies stimulated the quest for efficient energy storage devices. In recent years, the rechargeable aqueous zinc-based battery technologies are emerging as a compelling alternative to the lithium-based batteries owing to safety, eco-friendliness, and cost-effectiveness. Among the zinc-based energy devices, rechargeable zinc-ion batteries (ZIBs) are drawing considerable attention. However, they are plagued with several issues, including cathode dissolution, dendrite formation, etc.. Despite several efforts in the recent past, ZIBs are still in their infant stages and have yet to reach the stage of large-scale production. Finding stable Zn²⁺ intercalation cathode material with high operating voltage and long cycling stability as well as dendrite-free Zn anode is the main challenge in the development of efficient zinc-ion storage devices. This Review discusses the various strategies, in terms of the engineering of cathode, anode and electrolyte, adopted for improving the charge storage performance of ZIBs and highlights the recent ZIB technological innovations. A brief account on the history of zinc-based devices and various cathode materials tested for ZIB fabrication in the last five years are also included. The main focus of this Review is to provide a detailed account on the rational engineering of the electrodes, electrolytes, and separators for improving the charge storage performance with a future perspective to achieving high energy density and long cycling stability and large-scale production for practical application.

High-Performance Anti-freezing Flexible Zn-MnO2 Battery Based on Polyacrylamide/Graphene Oxide/Ethylene Glycol Gel Electrolyte

It remains a great challenge for aqueous zinc-ion batteries to work at subzero temperatures, since the water in aqueous electrolytes would freeze and inhibit the transportation of electrolyte ions, inevitably leading to performance deterioration. In this work, we propose an anti-freezing gel electrolyte that contains polyacrylamide, graphene oxide, and ethylene glycol. The graphene oxide can not only enhance the mechanical properties of gel electrolyte but also help construct a three-dimensional macroporous network that facilitates ionic transport, while the ethylene glycol can improve freezing resistance. Due to the synergistic effect, the gel electrolyte exhibits high ionic conductivity (e.g., 14.9 mS cm-1 at -20 °C) and good mechanical properties in comparison with neat polyacrylamide gel electrolyte. Benefiting from that, the assembled flexible quasi-solid-state Zn-MnO2 battery exhibits good electrochemical durability and superior tolerance to extreme working conditions. This work provides new perspectives to develop flexible electrochemical energy storage devices with great environmental adaptability.

V6 O13-δ @C Nanoscrolls with Expanded Distances between Adjacent Shells as a High-Performance Cathode for a Knittable Zinc-Ion Battery

Herein, the defective vanadate oxide (V₆ O_13-δ )/C (denoted as DVOC) nanoscrolls with large distance between adjacent shells are constructed as a cathode material for ZIBs. By simultaneously enlarging the distance between adjacent shells and engineering the defective structure for oxide crystal, the DVOC nanoscrolls achieve fast kinetics, high reversibility and good energy storage capability. The formation process of DVOC nanoscrolls is investigated and a self-assembling-rolling sequential mechanism is disclosed. Moreover, the fiber-shaped flexible ZIBs are fabricated based on the DVOC cathode. Their admirable volumetric energy density, good high rate capability and excellent cycling stability demonstrate the superiority of the unique structure. Therefore, this work not only introduces a new strategy to improve the properties of vanadium oxides but also provide a new strategy for the design of knittable power sources for flexible electronics.

Unlocking the Door of Boosting Biodirected Structures for High-Performance VN x O y /C by Controlling the Reproduction Mode

Diverse reproduction modes of bio-organisms open new intriguing opportunities for biochemistry-enabled materials. Herein, a new strategy is developed to explore biodirected structures for functional materials via controlling the reproduction mode. Yeast with sexual or asexual reproduction mode are employed in this work. They result in two different biodirected structures, from bowl-like hollow hemisphere to "bubble-in-sphere" (BIS) structure, for the VN x O y /C composites. Benefitting from the hierarchical structure, nanoscale particles and conductive biomass-derived carbon base, both VN x O y /C biocomposites achieve high power/energy density, good reliability, and excellent long-term cycling stability in aqueous Zn-ion batteries. Deep investigations further reveal that different biodirected structures greatly influence the electrochemical properties of biocomposites. The bowl-like structures with thin shells and folded double layers achieve larger surface area and more active sites, which ensure their faster kinetics and better high rate capability. The BIS structures with a more compact assembly and higher stack capability are favorable to the better energy storage. Therefore, this work not only introduces a new clue to boost biodirected structures for functional materials, but also propels the development of Zn-ion batteries in diverse applications.