Importance of nanostructure for reversible Li-insertion into octahedral sites of LiNi_0.5Mn_1.5O₄ and its application towards aqueous Li-ion chemistry

We demonstrate the significance of nanostructuring on the reversible Li-insertion into octahedral sites of the nickel substituted spinel Li[Ni_0.5Mn_1.5]O₄. One dimensional nanofibers (50-250 nm diameter) of the Li[Ni_0.5Mn_1.5]O₄ were prepared by a single spinneret electrospinning and their performance was compared with powders synthesized via a conventional solid state approach. Li-diffusion coefficient of electrospun fibers was an order of magnitude higher (5.8 × 10^-11 cm² s^-1) than that of conventional powders (1.22 × 10^-12 cm² s^-1). Galvanostatic studies revealed a much improved capacity and rate performance for electrospun fibers. The fibers delivered a reversible capacity of ∼87 mAh g^-1 after 150 cycles at 1C rate compared to negligible capacity for solid-state prepared material. Finally, the performance of this nanostructured spinel phase as an anode in aqueous rechargeable Li-ion system was demonstrated to require a strongly alkaline electrolyte.