**2. Experimental procedure**

**1. Introduction**

40 Nanowires - Synthesis, Properties and Applications

LiMn<sup>2</sup> O4

ered Ni or Co oxide materials, the spinel LiMn<sup>2</sup>

To overcome this obstacle and permit the use of LiMn<sup>2</sup>

lithium ion batteries [4]. Spinel LiMn<sup>2</sup>

The energy storage field faces a critical challenge: namely, the development of rechargeable systems for load leveling applications (e.g. storing solar and wind energy). Among the available battery technologies to date, only Li-ion batteries may possess the power and energy densities necessary for high power applications. The Li ion battery interface materials can store a lot of Li ions but have large structure change and volume expansion, which can cause mechanical failure. In this work we exploited the use of nanowire (NW) cathode morphology to alleviate these issues. Nanowires offer advantages of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation [1]. In lithium-ion batteries, the cathode plays a critical role in determining energy density. Here the main requirements are a prolonged cycle life, components (i.e., relevant elements) abundant in high quantities in the earth's crust, and environmentally friendly systems [2, 3]. Among the commonly used lay-

O4

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rial with superior safety [5]. Conversely, its common drawback is a kinetic limitation, which is observed under fast scan rate or high current density, when the characteristic two peaks/plateaus associated with the charge and discharge mechanism of the spinel structure diminishes.

the use of nanostructured morphologies for the development of fast kinetic electrodes is an ideal approach [6]. Literature studies have shown that the one-dimensional nanosized materials have faster kinetics and higher rate capability than micrometer-sized materials due to the large surface-to-volume ratio that enhances the contact between active material grains and electrolyte. However, the high- temperature sintering process, which is necessary for high-

grain size and aggregation which alters the battery performance due to increased lithium ion diffusion length and decreased effective surface area contact with electrolyte. Here, the objective was to produce a highly crystalline nanostructured cathode electrode material. Single crystalline nanowire morphology has proven most appealing because the untwined material fabricated by the single crystalline nanowire reduces aggregation, electronic resistance and grain growth at elevated temperature [7]. Generally, the electrochemical performances of electrode materials are strongly influenced by the phase crystallinity, purity, particle size, and distribution. The internal channels in these nano-crystalline cathode material spheres serve

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performance cathodes based on high-quality crystallinity, such as LiMn<sup>2</sup>

two purposes. They admit liquid electrolyte to allow rapid entry of Li<sup>+</sup>

charging, and they provide space to accommodate expansion and contraction during Li<sup>+</sup>

performance. This research work produced highly crystalline LiMn<sup>2</sup>

nanowires followed by solid state reaction with LiOH. Concomitantly, LiMn<sup>2</sup>

calation and deintercalation, boosting battery power characteristics critical to improve the

synthesized using a facile, easy to scale up process, starting with the preparation of R-MnO<sup>2</sup>

were also prepared and studied as comparison [8]. The high rate capability as well as phase stability of the nanowires architecture and electrochemistry was demonstrated as probed by electrochemical and spectrochemical characterization techniques. Because determination of

appears to be a more favorable cathode in

in energy-demanding applications,

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leads to large

ions for quick battery

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O4

inter-

nanowires,

powders

is economical, nontoxic and a highly abundant mate-

#### **2.1. Modified LiMn<sup>2</sup> O4 nanowire syntheses**

In this work, the spinel LiMn<sup>2</sup> O4 powders were prepared following a procedure found in the literature with minor adjustments [9]. Typical synthesis includes the reaction of lithium hydroxide and manganese acetate (LiOH and Mn (CH<sup>3</sup> COO)<sup>2</sup> ) via a co-precipitation method. A stoichiometric amount of LiOH and Mn(CH<sup>3</sup> COO)<sup>2</sup> with the cationic ratio of Li/Mn = 1:2 were dissolved in deionized water and mixed by stirring. The solution is then evaporated at 100°C for 10 h to obtain the precursor powder [10]. Concomitantly we effectively produced ultrathin spinel LiMn<sup>2</sup> O4 nanowires using a facile, two-step process. First, single crystals were produced from a nonaqueous solution in an autoclave reaction to prepare R-MnO<sup>2</sup> nanowires, followed by solid state reaction with LiOH. In a typical process, a hydroalcoholic solution was formed in distilled water and adding first (NH<sup>4</sup> )2 SO<sup>4</sup> with (NH<sup>4</sup> ) 2 S2 O8 and then 1-octanol. The solvothermal reaction was then performed at 140°C for 12 h in an autoclave to obtain α-MnO<sup>2</sup> . This was followed by a solid state reaction between R-MnO<sup>2</sup> nanowires and LiOH at low pressure and oxygen atmosphere to achieve the pure LiMn<sup>2</sup> O4 nanowire phase. The chemistry of the nanostructures, the crystallinity and phase purity of LiMn<sup>2</sup> O4 powders, R-MnO<sup>2</sup> and LiMn<sup>2</sup> O4 nanowires were all characterized by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), electrochemical impedance spectroscopy and Nuclear magnetic resonance spectroscopy (7 Li NMR) technique to observe the local magnetic fields around atomic nuclei.
