**2. LiNi0.5Mn1.5O4 spinel structure**

LNMO can be formed in two different space groups as it is also exhibited in **Figure 1(a)** the single cubic *P4*3*32* phase (ordered), where in the absence of Mn3+ the Mn4+ and Ni2+ ions are located at 12d and 4a sites of the lattice respectively, Li ions occupy the 8c sites and O ions the 8c and 24e sites and b) the face centered *Fd-3 m* phase (disordered) where Mn4+ and Ni2+ are randomly distributed at 16c sites of the lattice, while Li and O ions are located at 8a and 32e sites respectively [31]. *P4*3*32* demonstrates a stoichiometric amount of oxygen atoms, while *Fd-3 m* presents oxygen vacancies, represented by the non-stoichiometric parameter *δ*. Thus, a LiNi0.5Mn1.5O4-δ structure appears with certain Mn ions being reduced to Mn3+ due to charge balancing [32].

Despite the fact that LNMO exhibits promising electrochemical features, it may demonstrate significant capacity reduction during cycling due to Mn diffusion in the electrolyte mass, caused by various lattice modifications in conjunction with the Jahn-Teller effect [33]. Since the electrochemical performance of LNMO can be affected by the synthesis route and thus the stoichiometry, morphology, crystal structure and impurities [34], many synthesis methods have been employed in order to improve LNMO performance: hydrothermal route [35, 36], co-precipitation [37–40], sol–gel [41, 42], induction thermal plasma [43], molten salt [44–46], liquid phase self-propagating high-temperature synthesis (LPSHS) and aerosol spray pyrolysis [47].

The electrochemical performance of LNMO can be improved via cation doping [48–50] by Mg, Al and Fe. This approach contributes to LNMO lattice stabilization, increase of specific capacity, reduction of the LixNi1-xO phase which is formed in

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

**Figure 1.** *Crystal phases of LNMO: (a) ordered P4332, (b) disordered Fd-3 m.*

the case of the disordered *Fd-3 m* structure and increase of cycle life. Moreover, the doped compositions are less expensive, abundant and without scarcity or toxicity issues such as in the case of cobalt [51–58].
