Construction of Inorganic/Organic Hybrid Layer for Stable Na Metal Anode Operated under Wide Temperatures.

Sodium metal battery is supposed to be a propitious technology for high-energy storage application owing to the advantages of natural abundance and low cost. Unfortunately, the uncontrollable dendrite growth critically hampers its practical implementation. Herein, an inorganic/organic hybrid layer of NaF/CF/CC on the surface of Na foil (IOHL-Na) is designed and synthesized through the in situ reaction of polyvinylidene fluoride (PVDF) and metallic sodium. This protective layer possesses satisfactory Young's modulus, good kinetic property, and sodiophilicity, which can distinctly stabilize Na metal anode. As a result, the symmetric IOHL-Na cell achieves a lifespan of 770 h at 1 mAh cm-2 /1 mA cm-2 in carbonate electrolyte. The assembled full battery of IOHL-Na||Na3 V2 (PO4 )3 delivers a high discharge capacity of 85 mAh g-1 at 10 C after 600 cycles under ambient temperature. Furthermore, the IOHL-Na||Na3 V2 (PO4 )3 cell still can steadily operate at 10 C for 600 cycles at 55 °C. And when testing at an ultralow temperature of -40 °C, the full cell achieves 40 mAh g-1 at 0.5 C with a prolonged lifespan of 450 cycles. This work offers a new approach to protect the metal sodium anode without dendrite growth under wide temperatures.

Structure Engineering of Vanadium Tetrasulfides for High-Capacity and High-Rate Sodium Storage.

Structure engineering of electrode materials can significantly improve the life cycle and rate capability of the sodium-ion battery (SIB), yet remains a challenging task due to the lack of an effective synthetic strategy. Herein, the microstructure of VS4 hollow spheres is successfully engineered through a facile hydrothermal method. The hollow VS4 microspheres possess rich porosity and are covered with 2D ultrathin nanosheets on the surface. The finite element simulation (FES) reveals that such heterostructures can effectively relieve the stress induced by the sodiation and thereby enhance the structural integrity. The SIB with the hollow VS4 microspheres as anode displays impressively high specific capacity, excellent stability upon ultra-long cycling, and extraordinary rate capacity, e.g., a reversible capacity of ≈378 mA h g-1 at ultra-high 10 A g-1 , while retaining 73.2% capacity after 1000 cycles. The Na storage mechanism is also elucidated through in situ/ex situ characterizations. Moreover, the hollow VS4 microspheres demonstrate reliable rate performance at a low temperature of -40 °C (e.g., the capacity is ≈163 mA h g-1 at 2 A g-1 ). This work provides novel insights toward high-performance SIBs.

Direct Self-Assembly of MXene on Zn Anodes for Dendrite-Free Aqueous Zinc-Ion Batteries.

Metallic zinc is a promising anode candidate of aqueous zinc-ion batteries owing to its high theoretical capacity and low redox potential. However, Zn anodes usually suffer from dendrite and side reactions, which will degrade their cycle stability and reversibility. Herein, we developed an in situ spontaneously reducing/assembling strategy to assemble a ultrathin and uniform MXene layer on the surface of Zn anodes. The MXene layer endows the Zn anode with a lower Zn nucleation energy barrier and a more uniformly distributed electric field through the favorable charge redistribution effect in comparison with pure Zn. Therefore, MXene-integrated Zn anode exhibits obviously low voltage hysteresis and excellent cycling stability with dendrite-free behaviors, ensuring the high capacity retention and low polarization potential in zinc-ion batteries.

Non-Metal Ion Co-Insertion Chemistry in Aqueous Zn/MnO2 Batteries.

The co-insertion of dual ions can often offer enhanced electrochemical performance for the aqueous zinc batteries. Although the insertion of non-metallic ions has been achieved in aqueous zinc batteries, the co-insertion chemistry of non-metallic cations is still a challenge. Here, a reversible H+ /NH4 + co-insertion/extraction mechanism was developed in an aqueous Zn/MnO2 battery system. The synergistic effect between the dual cations endows the aqueous batteries with the fast kinetics of ion diffusion and the reversible structure evolution of MnO2 . As a result, the Zn/MnO2 battery displays excellent rate capability and cycling performance. This work will pave the way toward the design of aqueous rechargeable batteries with non-metallic ions.

Electrochemically Induced Metal-Organic-Framework-Derived Amorphous V2 O5 for Superior Rate Aqueous Zinc-Ion Batteries.

The electrochemical performance of vanadium-oxide-based cathodes in aqueous zinc-ion batteries (ZIBs) depends on their degree of crystallinity and composite state with carbon materials. An in situ electrochemical induction strategy was developed to fabricate a metal-organic-framework-derived composite of amorphous V2 O5 and carbon materials (a-V2 O5 @C) for the first time, where V2 O5 is in an amorphous state and uniformly distributed in the carbon framework. The amorphous structure endows V2 O5 with more isotropic Zn2+ diffusion routes and active sites, resulting in fast Zn2+ transport and high specific capacity. The porous carbon framework provides a continuous electron transport pathway and ion diffusion channels. As a result, the a-V2 O5 @C composites display extraordinary electrochemical performance. This work will pave the way toward design of ZIB cathodes with superior rate performance.

Scalable Assembly of Flexible Ultrathin All-in-One Zinc-Ion Batteries with Highly Stretchable, Editable, and Customizable Functions.

Aqueous zinc-ion batteries (ZIBs) are considered to be a promising candidate for flexible energy storage devices due to their high safety and low cost. However, the scalable assembly of flexible ZIBs is still a challenge. Here, a scalable assembly strategy is developed to fabricate flexible ZIBs with an ultrathin all-in-one structure by combining blade coating with a rolling assembly process. Such a unique all-in-one integrated structure can effectively avoid the relative displacement or detachment between neighboring components to ensure continuous and effective ion- and/or loading-transfer capacity under external deformation, resulting in excellent structural and electrochemical stability. Furthermore, the ultrathin all-in-one ZIBs can be tailored and edited controllably into desired shapes and structures, further extending their editable, stretchable, and shape-customized functions. In addition, the ultrathin all-in-one ZIBs display the ability to integrate with perovskite solar cells to achieve an energy harvesting and storage integrated system. These enlighten a broad area of flexible ZIBs to be compatible with highly flexible and wearable electronics. The scaling-up assembly strategy provides a route to design other ultrathin all-in-one energy storage devices with stretchable, editable, and customizable behaviors.