**4. Physicochemical characterization results**

**Figure 2(a)** depicts the XRD spectra of the synthesized LNMO materials. In all cases a desired well-crystallized LiNi0.5Mn1.5O4 structure was obtained, with the characteristic peaks of the typical cubic structure at 19, 36, 44, 59, 64 *2θ* values; the higher resolution graph in **Figure 2(b)** referring to the pristine LNMO indicates two weaker peaks at ~37.5 and ~ 43.5 *2θ* values corresponding to the LixNi1-xO phase.

**Figure 2.**

*(a) XRD of the pristine and doped LiNi0.5Mn1.5O4 with Fe, Al and Mg materials (b) higher resolution XRD graph depicting the additional LixNi1-xO of the pristine sample.*

### **Figure 3.**

*Crystallite size (a) and specific surface area (b) of the doped LNMO materials.*

On the contrary, in the case of doped LNMO compositions these peaks are not present, assuming, therefore, the elimination of the undesired LixNi1-xΟ phase.

Crystallite size was calculated by the Scherrer's formula from the FWHM of the *(111)* LiNi0.5Mn1.5O4 peak; the calculated sizes in **Figure 3(a)** exhibit crystallites with an average size of ~53 nm for all the materials. Doping seems to affect the specific surface area in a different manner; in **Figure 3(b)** the pristine sample exhibits a 1.46 m2.gr−1 specific surface area which increases slightly to 1.68 m2.gr−1 for Mg and significantly to 2.32 m2.gr−1 for the Al sample, while in accordance to its crystallite size deviation the Fe sample exhibits lower surface area than the pristine at 1.24 m2.gr−1. The different surface areas can be related to the morphology exhibited by SEM in **Figure 4**, where spherical particles seem to exhibit a non-dense, macroporous structure. Particles synthesized by aerosol synthesis are expected to have a spherical morphology based on the aerosol process principle [19]. SEM images for the pristine and the doped particles depict multiple particulate aggregates forming the macroscopic spherical particles. The EDS mapping images show a homogeneous dispersion of the Ni, Mn and of the respective Mg, Al and Fe dopants per case,

*Aerosol Spray Pyrolysis Synthesis of Doped LiNi0.5Mn1.5O4 Cathode Materials… DOI: http://dx.doi.org/10.5772/intechopen.100406*

**Figure 4.**

*SEM images and EDS mapping analysis for the pristine and doped LNMO particles.*

**Figure 5.**

*TEM images depicting the crystallites of the LNMO of (a) pristine, (b) Mg-LNMO, (c) Al-LNMO and (d) Fe-LNMO.*

in consistency with the XRD patterns which also confirm the homogeneity of the synthesized structures.

The morphology of the polycrystalline material obtained from the TEM images in **Figure 5** shows the aggregated morphology in the nanoscale, revealing similar morphological characteristics for all three doped compositions.

### **Figure 6.**

*Particle volume probability density function distribution of the pristine and doped LNMO particles measured by an aerodynamic diameter measuring technique.*

Concerning the particle size distribution analysis, the mean particle diameter of pristine material was 2 μm; doping with Al and Mg led to smaller particle sizes while Fe doped had the higher particle size distribution at 2.2 μm, as observed in the normalized particle volume probability density function (PDF) plots of **Figure 6**.

Raman spectra was obtained in order to evaluate lattice differences of the pristine and doped LNMO materials. The spectra at **Figure 7** exhibits the 636 cm−1 peak, which is assigned to the Mn-O stretching vibration of the A1g mode shifted to slightly higher wavenumbers due to the insertion of the Ni2+ ions in the spinel lattice [59]. The decrease of Ni amount (doped compositions), shifts the corresponding peak to the nominal location at 625 cm−1 attributed to the symmetric stretching

**Figure 7.** *Raman spectrum of the doped LNMO materials.*

vibration of the Mn-O of the MnO6 groups. The broadening of the two peaks at 582 and 605 cm−1, which cannot be separated in the disordered structures, is attributed to the F(3)2g and the intensity of the shoulder located at 580 cm−1 is enhanced upon nickel substitution.
