Facile Synthesis of Porous Hollow Cobalt‐Doped λ‐MnO 2 Nano Architectures as a High‐performance Anode Material for Li‐ion Batteries and Li‐ion Hybrid Supercapacitors

Hierarchical hollow porous structures of nickel-doped λ-MnO2 anodes for Li-ion energy storage systems

Metal oxides with hollow porous structures are attractive and promising anode candidates for Li-ion batteries due to their high surface area, high loading capacity, and low density. In this work, hierarchical hollow porous structures of nickel (Ni)-doped λ-MnO2 were prepared via a facile, and cost-effective approach, where different amounts of Ni were introduced into MnO2 structures to tailor their physical and chemical properties. When the prepared Ni-doped MnO2 hollow structures were studied as anode materials for Li-ion batteries, the electrode showed excellent electrochemical properties, such as stable cyclability and admirable rate capability. Moreover, Ni doping significantly enhances the diffusion properties of the active materials. The material was also investigated as an anode in another high power and energy Li-ion storage device, namely, a Li-ion hybrid capacitor, which exhibited excellent comprehensive electrochemical performance in terms of good specific cell capacity of 25 mA h g-1 at a high current density of 5 A g-1 and achieved a maximum power density of 29 W kg-1 (with energy density of 30 W h kg-1) with a long cycle life. These results indicate that the Ni-doped MnO2 is suitable for application as an anode material and give considerable insight into future Li-energy storage applications.

Hollow nanostructured NiO particles as an efficient electrode material for lithium-ion energy storage properties

This work has developed a straightforward approach to obtaining NiO hollow structures by using Li₂O₂ as an easily removable template. The easy availability and electrochemically active nature of NiO have attracted researchers' attention as an anode electrode for Li-ion storage applications, including Li-ion secondary batteries (LIBs) and for Li-ion hybrid supercapacitors (LiHSCs; which offer higher power densities than LIBs without compromising energy density). However, NiO usage has been limited to its low reaction reversibility, poor conductivity, and conversion reaction capability. Recently, hollow nanostructured materials have attracted attention as efficient battery materials due to their fascinating structural features. This study presents a modified Li₂O₂-assisted method to obtain porous open 3D architectures of NiO nanostructures. The resultant hollow structures are electrochemically studied as an anode for a LIB, exhibiting excellent stability over hundreds of cycles. The result is recognized as one of the finest among NiO anodes reported. Also, NiO hollow structures studied as anodes for LiHSC devices fabricated with activated carbon cathodes exhibit an outstanding comprehensive electrochemical performance which is better than the typical LIB and supercapacitors.

Co3ZnC@NC Material Derived from ZIF-8 for Lithium-Ion Capacitors

Metal-organic framework (MOF)-derived carbon materials were widely reported as the anodes of lithium-ion capacitors (LICs). However, tunning the structure and electrochemical performance of the MOF-derived carbon materials is still challenging. Herein, metal carbide materials of Co3ZnC@NC-8:2 were obtained by the pyrolysis of the MOF materials of Co0.2Zn0.8ZIF-8 (Zn/Co ratio of 8:2). A half-cell assembled with the Co3ZnC@NC-8:2 electrode exhibits a discharge capacity of the electrode material of 598 mAh g-1 at a current density of 0.1 A g-1. After 100 cycles, the retention rate of discharge specific capacity is about 90%. The high performance of Co3ZnC@NC-8:2 is ascribed to its high crystalline degree and well-defined structure, which facilitates the intercalation/deintercalation of lithium ions and buffers the volume change during the charge/discharge process. The high capacitance contribution ratio calculated by cyclic voltammetry (CV) curves at different scanning rates indicates the pseudocapacitance storage mechanism. LICs constructed from the Co3ZnC@NC-8:2 material have a rectangular CV curve, while the charge-discharge curve has a symmetrical triangular shape. This study indicates that MOF-derived carbon is one of the promising materials for high-performance LICs.