No abstract

No abstract

Transition metal oxides have attracted lots of interest for lithium ion battery (LIB) due to the high theoretical capacity, however, the large specific volume change, low electrical conductivity and slow intrinsic lithiation/delithiation still limit the practical applications. In order to overcome the challenge, a novel type of high temperature annealing treatment for the synthesis of 3D porous FeOx nanocrystals embedded in a partially carbon matrix as an example for high-performance LIB is reported. The FeOx/carbon nanocomposites with coral-like architecture achieved at 700 °C (F700) exhibit good long term cyclability with a reversible capacity 1012 mAh g−1 remain after 500 cycles at 1.0 A g−1 and the high rate capacity with a reversible capacity of 233 mAh g−1 even at extremely high current density of 20 A g−1. These excellent electrochemical performances could be attributed to the 3D porous structure and carbon coating, which could not only provide excellent electronic conductivity and enough elastic buffer space to accommodate volume changes upon lithium insertion/extraction, but also effectively avoid agglomeration of the Fe3O4 nanocrystals and maintain the structural integrity of the electrode during the charge/discharge process.

Nickel compounds, especially Ni(HCO3)2 (here denoted as NiC), have been widely combined with other materials to obtain composites with a more favorable structure that exhibit excellent electrochemical performance as supercapacitors. Unfortunately, the complicated processes for preparing such composites directly restrict their further application. Herein, we prepared a NiC/nickel tetraphosphate (Ni(P4O11)) nanocomposite (NiC/NiP) by introducing H 2 PO 4 − ions into the NiC reaction system; this composite can be applied in high-performance supercapacitors. The micromorphology of NiC/NiP material displayed an appropriate combination of NiP nanowires and thin NiC nanosheets, which provide sufficient active sites, short ion diffusion paths and fast ion diffusion speeds. NiC/NiP material exhibited an excellent rate performance of 70.2% retained capacity, although the current was increased by 15 times (1196 F g−1 at 2.0 A g−1 and 840 F g−1 at 30 A g−1). The energy density of a NiC/NiP//active carbon (AC) asymmetric supercapacitor fabricated in 6 M KOH was as much as 39.02 W h kg−1 and 26.67 W h kg−1 under corresponding power densities of 160 W kg−1 and 8000 W kg−1, respectively. The asymmetric supercapacitor delivered a stable cyclic performance of 78% capacitive retention after 5000 continuous charge/discharge cycles. More importantly, a 2.5 V light-emitting diode was lit successfully by two NiC/NiP//AC asymmetric supercapacitors in series. These results confirm that NiC/NiP nanocomposite has great potential in practical applications of electrochemical energy storage devices.

No abstract