Preparation and Electrochemical Performance of Three-Dimensional Vertically Aligned Graphene by Unidirectional Freezing Method

Three-dimensional vertically aligned graphene (3DVAG) was prepared by a unidirectional freezing method, and its electrochemical performances were evaluated as electrode materials for zinc−ion hybrid supercapacitors (ZHSCs). The prepared 3DVAG has a vertically ordered channel structure with a diameter of about 20−30 μm and a length stretching about hundreds of microns. Compared with the random structure of reduced graphene oxide (3DrGO), the vertical structure of 3DVAG in a three−electrode system showed higher specific capacitance, faster ion diffusion, and better rate performance. The specific capacitance of 3DVAG reached 66.6 F·g−1 and the rate performance reached 92.2%. The constructed 3DVAG zinc−ion hybrid supercapacitor also showed excellent electrochemical performance. It showed good capacitance retention up to 94.6% after 3000 cycles at the current density of 2 A·g−1.

Heterostructure Fe2O3 nanorods@imine-based covalent organic framework for long-cycling and high-rate lithium storage

Fe2O3 as anode for lithium-ion batteries has attracted intense attention because of its high theoretical capacity, natural abundance and good safety. However, the inferior cycling stability, low-rate performance and limited...

Porous Fe2O3 nanorod-decorated hollow carbon nanofibers for high-rate lithium storage

Transition metal oxides (TMOs) are considered as promising anode materials for lithium-ion batteries in comparison with conventional graphite anode. However, TMO anodes suffer severe volume expansion during charge/discharge process. In this respect, a porous Fe2O3 nanorod-decorated hollow carbon nanofiber (HNF) anode is designed via a combined electrospinning and hydrothermal method followed by proper annealing. FeOOH/PAN was prepared as precursors and sacrificial templates, and porous hollow Fe2O3@carbon nanofiber (HNF-450) composite is formed at 450 °C in air. As anode materials for lithium-ion batteries, HNF-450 exhibits outstanding rate performance and cycling stability with a reversible discharge capacity of 1398 mAh g−1 after 100 cycles at a current density of 100 mA g−1. Specific capacities 1682, 1515, 1293, 987, and 687 mAh g−1 of HNF-450 are achieved at multiple current densities of 200, 300, 500, 1000, and 2000 mA g−1, respectively. When coupled with commercial LiCoO2 cathode, the full cell delivered an outstanding initial charge/discharge capacity of 614/437 mAh g−1 and stability at different current densities. The improved electrochemical performance is mainly attributed to the free space provided by the unique porous hollow structure, which effectively alleviates the volume expansion and facilitates the exposure of more active sites during the lithiation/delithiation process. Graphical abstract Porous Fe2O3 nanorod-decorated hollow carbon nanofibers exhibit outstanding rate performance and cycling stability with a high reversible discharge capacity.

N/S co-doped CoSe/C nanocubes as anode materials for Li-ion batteries

The transition metal selenide can be used as a potential material for the negative electrode of lithium-ion batteries (LIBs) owing to its high density and conductivity. Unfortunately, a large volume change occurs in the transition metal selenide during the charging and discharging process, which eventually results in the poor rate performance and rapid capacity decay. In response to this, the N/S co-doped CoSe nanocubes (CoSe/C–NS) can be fabricated where the S-doped cobalt 2-methylimidazole (ZIF-67) as both sacrifice template and cobalt source to directly mix with selenium powder and followed by the annealing process. In the process, the carbon frameworks derived from ZIF-67 can establish a coating layer to protect the structure of materials, and simultaneously the N/S co-doping can enhance the conductivity and broaden the interlayer of frameworks. These can further accelerate the storage capacity and the Li+ insertion and deintercalation process. As a negative electrode material of LIBs, the CoSe/C–NS delivers the high capacity, high rate performance, and long-term cycle stability. This protocol opens up an approvable approach to fabricate efficient anode materials with persistent electrochemical stability in LIBs.