No abstract

Rechargeable aqueous zinc-ion batteries (ZIBs) are an attractive alternative for flexible energy storage devices due to their excellent safety and low cost. One of the main challenges that plagues their practical applications is the restricted variety of cathode materials with fast reaction kinetics and good mechanical properties. Herein, we prepared rose-like VS2 nanosheets which have decent specific capacities, metallic conductivity, and open-enough channels and further incorporated them into a single-walled carbon nanotube (SWCNT) network, achieving a C–V chemical-bonded freestanding VS2@SWCNT (C-VS2) composite. Such chemical bonding in the composites builds a bridge for rapid electron transfer and ion diffusion in the longitudinal direction from one layer to another layer. As a result, the reversible Zn/C-VS2 system in core cells exhibits a high specific capacity (205.3 mA h g–1 at 0.1 A g–1), an excellent cyclic stability (115.4 mA h g–1 was obtained after 1500 cycles at 5 A g–1), and a remarkable rate capability (135.4 mA h g–1 at 10 A g–1). Furthermore, the freestanding C-VS2 films with good flexibility and conductivity can serve as a flexible cathode to assemble soft-packaged ZIBs. Meanwhile, the soft-packaged ZIB has good electrochemical stability even under different bending conditions (the discharge capacity dropped by only 2.1 mA h g–1 after bending). This work offers insights into the rational design of zinc-ion hosts throughout chemical bond engineering.

Although heteroatom doping and pore management separately influence the Li + adsorption and Li + diffusion properties, respectively, merging their functions into a single unit is intriguing and has not been fully investigated. Herein, we have successfully incorporated both heteroatom doping and pore management within the same functional unit of N 4 -vacancy motifs, which is realized via acid etching of formamide-derived Zn−N 4functionalized carbon materials (Zn 1 NC). The N 4 -vacancy-rich porous carbon (V-NC) renders multiple merits: (1) a high N content of 13.94 atom % for large Li-storage capacity, (2) edged unsaturated N sites favoring highly efficient Li + adsorption and desolvation, and (3) a shortening of the Li + diffusion length through N 4 vacancy, thereby enhancing the Li-storage kinetics and high-rate performance. This work serves as an inspiration for the creation of heteroatom-edged porous structures with controllable pore sizes for high-rate alkali-ion battery applications.

Lithium-ion capacitors (LICs) are considered ideal devices, which bridge the energy and power density gap between lithium-ion batteries (LIBs) and supercapacitors (SCs). However, the mismatched kinetics between the cathode and anode remains an obstacle to the development of LICs. Herein, an anode with excellent flexibility and fast electrochemical reaction kinetics is designed for advanced LICs by coupling highly conductive singlewalled carbon nanotubes (CNTs) with the bidirectionally designed Ti 3 C 2 T x MXene (KTi 3 C 2 -O). In such a composite (KTi 3 C 2 -O/ CNTs), the bidirectional design of Ti 3 C 2 T x MXene based on the interlayers of K + ions intercalation and interfaces of −O terminal groups modification will increase the interlayer distance, provide more active sites, and improve Li + ions storage capacity; the introduction of CNTs forming a three-dimensional (3D) interpenetrating structure with KTi 3 C 2 -O can alleviate Ti 3 C 2 T x MXene interlayer stacking and offer fast charge transfer kinetics. When evaluated as a self-supported anode of LIC, the LIC displays a high power density of 15.63 kW kg −1 , a high energy density of 138.89 Wh kg −1 , and an exceptional capacity retention of 77.75% over 10 000 cycles at 5 A g −1 . Such a bidirectional construction strategy based on interlayer and interfacial modification provides new ideas for the design of such two-dimensional (2D) materials that can be applied in advanced energy storage devices.