Investigating the effect of spark plasma sintering temperature and post-sintering annealing in LiNi0.5Mn1.5O4 for its ideal design towards practical battery applications

In this work, the effect of spark plasma sintering (SPS) and post-annealing in pure Ar and O₂ on structure, ac/dc-conductivity, impedance, and electronic properties of LiNi_0.5Mn_1.5O₄ (LNMO) are investigated, which establish a roadmap for the design of an ideal compound. Structural analysis using XRD reveals that the unit cell volume increases with SPS temperature and post-annealing in Ar and decreases in O₂ due to a reduction in oxygen vacancies. The dc-conductivity shows the dominance of SPH conduction up to 200 K, while Mott-VRH conduction prevails until 168 K. Frequency dispersion modeling of ac-conductivity (σ_ac) with modified JPL supports the NSPT model, and scaling of σ_ac follows the modified Summerfield model. In addition, DRT clearly distinguishes grain, grain boundary, interfacial, and electrode contributions and shows that post-annealing in Ar(O₂) can be effectively used to increase(decrease) the grain and grain boundary resistance, which can be utilized to design and property-tune LNMO for practical applications.