Synthesis and electrochemical performance of hollow-structured NiO + Ni nanofibers wrapped by graphene as anodes for Li-ion batteries

Abstract

Hollow-structured NiO + Ni nanofibers wrapped by graphene were designed and successfully fabricated via a simple method. First, solid NiO + Ni nanofibers were prepared by electrospinning followed by calcination. Here, a portion of the metallic Ni was retained to improve the electrochemical performance of NiO by adjusting the calcination temperature. Next, the nanofibers were thoroughly mixed with different amounts of graphene and calcinated once more to form hollow-structured NiO + Ni nanofibers with an extremely high specific surface via the reaction between graphene and NiO on the nanofiber surface and subsequent migration of NiO into the nanofibers. Results showed that the obtained hollow-structured NiO + Ni electrode demonstrates optimal electrochemical performance when the graphene content is controlled to 3 wt%. The first cycle discharge/charge specific capacity of the electrode peaked (1596/1181 mAh · g−1 ) at 100 mA · g−1, with a coulombic efficiency of approximately 74% (60% for 0 wt% graphene, 65% for 1 wt% graphene, and 51% for 4 wt% graphene). It also presented excellent cycling stability after 100 cycles at 100 mA · g−1 on account of its high retained discharge specific capacity (251 mAh · g−1 for 0 wt% graphene, 385 mAh · g−1 for 1 wt% graphene, 741 mAh · g−1 for 3 wt% graphene, and 367 mAh · g−1 for 4 wt% graphene). Moreover, the synthesized electrode possessed outstanding rate capability owing to its large average discharge specific capacity of approximately 546 mAh · g−1 (45 mAh · g−1 for 0 wt% graphene, 256 mAh · g−1 for 1 wt% graphene, and 174 mAh · g−1 for 4 wt% graphene) from 100 mA · g−1 to 2000 mA · g−1. The observed improvement in electrochemical performance could be attributed to the increase in active sites and decrease in charge transport distance in the hollow-structured NiO + Ni nanofibers. Excessive introduction of graphene caused a sharp loss in electrochemical performance due to the agglomeration of graphene sheets on the nanofiber surfaces.

Study on the Controllable Preparation of Nd3+ Doped in Fe3O4 Nanoparticles for Magnetic Protective Fabrics

“…The stability of the functional fabrics at high temperatures was evaluated based on their magnetic susceptibility under a changing temperature M−T curve and magnetizing M−H curve. The samples exhibited fine magnetic properties and magnetic loss performances as the temperature increased from 300 K to 800 K ( Figure 7 f), and the magnetization ability decreased sharply from 3.3 emu.g −1 to close to 0 emu.g −1 , thus confirming the loss velocity of magnetic properties in hot environments [ 57 ]. Furthermore, the three as-prepared samples exhibited obvious differences in magnetic properties from Figure 7 g and the enlarged picture Figure 7 h. The fine magnetic value of the functional fabric with NdFe 2 O 4 NPs at 1:10 NaAC was 17.61 emu.g −1 , which was higher than 12.67 emu.g −1 for the sample with 1:8 NaAC and 4.89 emu.g −1 for the sample with 1:6 NaAC, which belonged to the reduction action of different mole ratios of NaAC in the synthesis process [ 58 , 59 ].…”

Advances on Nickel-Based Electrode Materials for Secondary Battery Systems: A Review

“…Owing to the high conductivity, considerable efforts have been focused on metal elements to improve the energy-storage capability of NiO, including nickel − and silicon (Si is a metalloid). , The Ni/NiO microwire hybrid network was prepared through partial oxidation reaction of Ni microwires, delivering 443 mA h g –1 at 0.5 A g –1 . Importantly, the samples oxidized at a lower temperature (400 °C) possessed fewer defects than those oxidized at a high temperature (450 °C).…”

“…As the content of nickel oxide was about 17.9%, the performance of Ni/NiO was further optimized, realizing 633.7 mA h g –1 after 100 cycles at 0.2 A g –147 . Using Ni/NiO as precursors, the enhancement of conductivity was obtained by the introduction of extra carbon materials, thus boosting the transportation of electrons. − For example, Ni/NiO embedded on waste graphite realized a specific capacity of 724 mA h g –1 at 0.1 A g –1 and outstanding cycle stability (500 cycles) . Compared to nickel, activities of Si in ESSs being explored were deemed to result from its high capacity.…”