Nickel cobaltite@Poly(3,4-ethylenedioxypyrrole) and carbon nanofiber interlayer based flexible supercapacitor

Binder free flexible symmetric supercapacitors are developed with nickel cobaltite micro-flowers coated poly(3,4-ethylenedioxypyrrole) (NiCo2O4@PEDOP) hybrid electrodes. Free standing films of carbon nano-fibers (CNF), synthesized by electrospinning, were sandwiched between the NiCo2O4@PEDOP hybrid and the electrolyte coated separators on both sides of the cells. The CNF film conducts both ions and electrons, and confines the charge at the respective electrodes, to result in an improved specific capacitance (SC) and energy density compared to the analogous cell without the CNF interlayers. High SC of 1,775 F g-1 at a low current density of 0.96 A g-1 and a SC of 634 F g-1 achieved at a high current density of 38 A g-1 coupled with a SC retention of ~95% after 5,000 charge-discharge cycles in the NCO@PEDOP/CNF based symmetric supercapacitor, are performance attributes superior to that achieved with NCO and NCO/CNF based symmetric cells. The PEDOP coating serves as a highly conductive matrix for the NCO micro-flowers and also undergoes doping/de-doping during charge-discharge, thus amplifying the overall supercapacitor response, compared to the individual components. The CNF interlayers show reasonably high ion-diffusion coefficients for K+ and OH- propagation implying facile pathways available for movement of ions across the cross-section of the cell, and they also serve as ion reservoirs. The electrode morphologies remain unaffected by cycling, in the presence of the CNF interlayer. LED illumination and a largely unaltered charge storage response was achieved in a mutli-cell configuration, proving the potential for this approach in practical applications

NiMoO4@NiMnCo2O4heterostructure: A poly(3,4-propylenedioxythiophene) composite-based supercapacitor powers an electrochromic device

The hierarchical heterostructure of NiMoO4@NiMnCo2O4 (NMO@NMCO) with furry structures of NMCO juxtaposed with NMO nanowires are endowed with multiple electrochemically active and accessible sites for ion storage, thus delivering an ultrahigh specific capacitance of 2706 F g-1, nearly two-fold times greater than that of sole NMCO. Electrodeposition of an overlayer of a highly robust and electrically conducting polymer, poly(3,4-propylenedioxythiophene) (PProDOT), not only improves the energy storage performance but also assists the binary oxide cathode in retaining its structural integrity during redox cycling. Coupling with an anode of porous flaky carbon (FC) derived from groundnut shells results in an asymmetric supercapacitor of FC//PProDOT@NiMoO4@NiMnCo2O4, which delivers an outstanding capacitance of 552 F g-1, energy and power density ranges of 172-40 Wh kg-1 and 0.75-10 kW kg-1, respectively, and a remarkable cycle life of 50 000 cycles, with ~97.8% capacitance retention, over an operational voltage window of 1.5 V. From an application perspective, the charged supercapacitor was connected to a complementary coloring reversible electrochromic device (ECD) of Prussian blue//PProDOT, and the ECD state transformed from a pale-blue to a deep blue hue, thus signaling the efficient utilization of energy stored in the supercapacitor. The energy-saving attribute of the ECD was realized in terms of an integrated visible-light modulation of 39% that accompanied the optical transition. Deployment of low-cost devices at homes and commercial spaces, capable of storing and saving energy, is the way forward, and this is one significant step in this direction. © XXXX American Chemical Society

Selenium/Graphite Platelet Nanofiber Composite for Durable Li–Se Batteries

Long-lasting Li-Se cells with a Se/graphite platelet nanofiber (GPNF) composite is prepared for the first time, and it shows a reversible capacity of 489 and 384.7 mAh g(Se)(-1) after 200 and 350 charge/discharge cycles, respectively. It shows superior rate capability and low Se polarization even with a high Se (75 wt %) proportion. It also shows higher capacity and better cycling stability compared to conventional Se/carbon material composites (with graphene oxide (GO), reduced GO, and carbon nanotubes). The effectiveness of GPNFs as a conductive support and for inhibiting the shuttle and dissolution of polyselenides in the electrolyte is also confirmed by conducting atomic force microscopy studies. Nanoscale current maps of Se/GPNFs reveal the presence of homogeneously distributed high -current domains, which are retained even after the first discharge. In contrast, the pristine Se electrode is characterized by predominant low -current regions after the first discharge. The ability of GPNFs to enable the preparation of durable and easily processable Li-Se cells is demonstrated

Carbon black free Selenium/CTAB decorated carbon nanotubes composite with high selenium content for Li-Se batteries

A cost effective, low temperature, scalable route is presented for the synthesis of Selenium nanoparticles-cetyltrimethylammonium bromide-decorated multiwalled carbon nanotubes (Se NPs@CTAB-MWCNTs) composite. The Se content in the carbon black (CB) free Li-Se NPs@CTAB-MWCNTs cell is ∼72 wt%, which is much higher than that reported in previous studies on Li-Se composite cells, where the Se loadings typically vary between 40 and 50 wt% in full cells. The high loading of Se imparts a high capacity to the composite cell due to a high electrical conductivity of Se NPs (∼0.1 S cm−1). The initial Li-ion storage capacity delivered by the same CB free cell is ∼709 mAh gSe−1 (at 0.5 current (C)-rate), and a reversible capacity of 157 mAh gSe−1 is retained after 500 cycles. In comparison, the reversible capacities offered by the Li-Se NPs-CB cell (at 80 wt% Se loading), and the Li-Se NPs@CTAB-MWCNTs-CB cell (at 64 wt% Se loading) are 13.8 and 172.5 mAh gSe−1 at the same C-rate, after 500 cycles. For the CB free cell, the capacity decay is 0.14% per cycle from 8th to 500th cycle. Though present in small quantities of 18 and 16 wt% in the two composite based cells without and with CB, CTAB-MWCNTs confer the following functional attributes to the cells. They (a) restrict polyselenide shuttle, (b) buffer the volume expansion during discharge and (c) allow Li-ion storage, without the use of any conducting CB additive (due to the composite's high inherent electrical conductivity). The electrochemical performance of the CB free Li-Se composite cell opens up opportunities to develop eco-friendly and robust Li-Se batteries