**3. Characterization and analysis**

The morphology and particle size distribution of LiMn<sup>2</sup> O4 nanowire material was analyzed with a Transmission electron microscopy (TEM), taken with a JSM-6700F (JEOL). Raman spectra of all samples were recorded at wavelength of 514.5 nm using a laser-spectrometer (model Jobin-Yvon U1000) equipped with dual monochromators coupled with special filter and emission of an argon-ion laser (model Spectra-Physics 2020). To avoid sample photodecomposition or denaturation a power density as low as 10 W cm−2 was used. NMR was carried out at room temperature on Varian spectrometer (VNMRS WB 500 solids) with an 11.7 T magnet. Magic angle spinning (MAS) NMR experiments were performed using a 6 mm MAS probe. The <sup>7</sup> Li resonance frequency was 194.29 MHz with a sample spinning speed of 16 kHz. Single-pulse and echo-pulse sequences were used to acquire all spectra. The amount of lithium detectable in the materials was quantified using 1 M LiCl (116.571 MHz) as an external reference for chemical. XRD Measurements were carried out with a D8 ADVANCE diffractometer from BRUKER axs using an X-ray tube with copper K-alpha radiation operated at 40 kV and 40 mA and a position sensitive detector, Vantec\_1, which enables fast data acquisition. Measurement range: [12–90° in 2 theta], Step size: 0.027° in 2 theta, Measurement time: 1 s/step.

#### **3.1. Electrochemical tests**

The Electrochemistry of the LiMn<sup>2</sup> O4 nanowire cathode, were carried out with electrodes mounted on coin-cells operating at 30°C. Electrode mixtures were prepared by mixing the oxide powder (70 wt%) with acetylene black (current collector) (20 wt%) and polyvinylidene fluoride (PVdF) binder (10 wt%) in N-methylpyrrolidone (NMP) solvent to form a mixed slurry. The slurry was coated on an aluminum foil, followed by drying in a vacuum oven at 120°C for 48 h and a cathode electrode was formed.
