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Spinel-NiMn 2 O 4 (NMO) nanofibers of high aspect ratio, high surface area (50 m 2 g −1 ) and homogeneous pore size distribution are fabricated by electrospinning process and characterized by XRD, FTIR, XPS, BET, FESEM, TEM techniques. Further, multifunctional properties (energy storage properties, magnetic and electrical properties) of NMO nanofibers are also examined. High specific capacitance (C s ) of 410 (±5) F g −1 at 1 A g −1 , good rate capability and high cycling stability (up to 5000 cycles) are demonstrated by NMO nanofibers. Furthermore, NMO-based solid-state symmetric supercapacitor (SSSC) shows a high C s of 170 (±5) F g −1 at 0.5 A g −1 in potential range of 0.0V–2.0 V and exhibits excellent energy density of ∼95 W h kg −1 and power density of 1030 W Kg −1 . The above storage properties i.e. high energy density and output voltage of 2.0 V are further supplemented by lighting up a red colored LED (1.8 V @ current 20 mA) at least for 5 min. The ionic diffusion coefficient of NMO based electrode is found to be ∼4.84 × 10 −11 cm 2 s −1 . Magnetic and dielectric properties of NMO nanofibers are also examined and results are discussed.

Porous nanofibric network of spinel CoMn2O4 (CMO) are fabricated by facile electrospinning process and characterized by XRD, BET, TGA, FTIR, FESEM, TEM, XPS techniques. CMO nanofibers are employed as supercapacitor electrode for first time which exhibits high specific capacitance (Cs) of 320(±5) F g−1 and 270(±5) F g−1 at 1 A g−1 and 5 A g−1, respectively in 1 M H2SO4. CMO nanofibers exhibit excellent cyclability (till 10,000 cycles @ 5 A g−1). To examine practical performance, solid-state symmetric supercapacitor (SSSC) is also fabricated using PVA-H2SO4 as gel electrolyte. The SSSC evinces high energy density of 75 W h kg−1 (comparable to Pb-acid and Ni-MH battery) along with high power density of 2 kW kg−1. Furthermore, a red colored LED (1.8 V @ current 20 mA) was lit for 5 min using single SSSC device supporting its output voltage of 2 V. This high performance of CMO in both aqueous and SSSC is attributed to one dimensional nanofibers consisting of voids/gaps with minimum inter-particle resistance that facilitates smoother transportation of electrons/ions. These voids/gaps in CMO (structural as well as morphological) act as intercalation/de-intercalation sites for extra storage performance, and also works as buffering space to accommodate stress/strain produced while long term cyclings.

The impact of both various binders and carbon additives on the electrochemical behavior of intermetallics-based (FeSn2, NiSb2, TiSnSb) negative electrodesvs.Li was evaluated and accurately studied for FeSn2. The formulation of the composite electrode allowed enhancement of both the capacity retention as well as the rate capability. CMC/VGCF (carboxymethyl cellulose/vapor grown carbon fiber) used as a binder/conductive additive allows retention of 100% of the specific capacity during 35 cycles at 2C rate (2Li h−1), whereas the fading is dramatic after only a few cycles at a low rate with classical powdered electrodes. Notably, an extra capacity is observed with CMC/VGCF. In the case of FeSn2, it is shown that the improvement of performance achieved with CMC/VGCF results from better efficiency of the conductive additive to form an electronic percolation web around the active material (AM) particles rather than from the buffering of the volume variations of the AM particles, contrary to the case of Si-based electrodes. The improved cycle life is also likely due to the better ability of CMC to cover the particles compared to PVDF (polyvinylidene fluoride), resulting not only in stronger interparticle bonding but also in a better SEI layer. It is suggested that the growing of an insulating SEI layer by the degradation of the liquid electrolyte is an important factor in the fading mechanism of FeSn2 composite electrodes. Finally, the aqueous processing of the FeSn2, NiSb2, and TiSnSb intermetallics-based composite electrodes is feasible.