**3.1 Material synthesis**

The LNMO material was synthesized by the Aerosol Spray Pyrolysis method [19], which utilizes the principles of bottom up synthesis in droplet micro-reactors. A precursor solution is atomized into fine droplets which subsequently undergo evaporation of the solvent while transferred by a carrier gas, inside a heated tubular reactor. The advantages of the respective synthesis technique is the short production time of some seconds in the reactor zone and the scalability of the produced material quantities.

In the current synthesis campaigns, the precursor solution was a 1 M aqueous solution of LiNO3 (Merck, ≥98%), Ni(NO3)2·6H2O (Merck, ≥99%), Mn(NO3)3·4H2O (Alfa Aesar, 98%), Mg(NO3)2·6H2O (Sigma Aldrich, 98 + %, Al(NO3)3·9H2O (Sigma Aldrich, ≥98%) and Fe(NO3)3·9H2O (Merck, ≥99%), in molar ratios of Li:Ni:Mn:D: 1:0.5-x:1.5:x and the temperature of the heated reactor was 800°C. The collected powder was subsequently calcined at 850°C for 16 h (air atmosphere) in a muffle furnace in order to obtain the disordered phase of the LNMO material [11]. The temperature of the reactor controls the evaporation rate of the solvent and thus the chemical composition and morphology of the synthesized particles. The synthesis reactor is a pilot plant unit constructed and operated in CERTH's facilities. In this study, 4 different materials were produced; the pristine LNMO and 3 metal doped LNMO compositions using Mg, Al and Fe as additives, namely Mg-LNMO, Al-LNMO and Fe-LNMO, respectively.

### **3.2 Structural characterization**

The identification of the phase structure was performed by XRD analysis using a Siemens D500/501 X-ray diffractometer with Cu Kα radiation between 5° and 80° at a scan rate of 0.040°/s. SEM/EDS analysis as well as the mapping of the materials were performed with a JEOL JSM-6300 microscope, while the TEM analysis was performed using a JEOL JEM 2010 high-resolution microscope. The ordered/ disordered structure was identified with a Raman Renishaw microscope equipped with a 514 nm Argon laser of 50 mW. The specific surface area of the samples (BET method) was measured with the aid of a N2 adsorption porosimeter (Micromeritics ASAP 2000, at 77 K, after degassing the samples at 250°C). Finally, the particle size distribution of the materials synthesized (powder form) was performed using a TSI PSD 3603 Particle Size Distribution Analyzer.

### **3.3 Electrode assembly and electrochemical characterization**

The electrochemical performance of synthesized LNMO was evaluated at the laboratory scale by preparing electrodes and assembling half-coin cells (HCC). During the cathode formulation, an N-methyl-2-pyrrolidone (NMP) slurry was prepared, consisting in a first approach of 90 wt. % of active material with the rest 10 wt.% being carbon black (C-NERGY Super C65 from IMERYS Carbon & Graphite) and Poly-Vinylidene Fluoride (PVdF HSV900 from Arkema) as electronic conduction enhancer and binder, respectively, while different ratios followed (84/8/8, 80/10/10) when issues where observed on the slurry stability and electrical conductivity of the electrodes. After coating the slurry on an aluminum current collector foil (Showa Denko, 20 μm thickness) using the doctor blade technique to a targeted loading of 1.0–1.5 mA. cm−2, the resulted electrodes were dried at 120°C under vacuum overnight, and the coin cell assembly followed.

The electrochemical performance of the prepared electrodes has been analyzed by assembling and testing coin cells (CR2025, Hohsen), in HCC configuration using Li metal disk (50 μm thick, Albermale) as counter anode electrode. One layer of polyolefin Celgard 2325 separator was used in all coin cells with 50 μL of 1 M LiPF6 EC/EMC electrolyte from Arkema. The cells were tested in a potential window of 3.5-5 V at room temperature in a working C-rate range

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

between C/5 (5 h) and 5C (12 min). C-rate calculations were made based on a LNMO specific capacity of 135 mAh. g−1.
