Cation distribution between tetrahedral and octahedral sites within the ZnMn ₂ O ₄ spinel lattice, along with microstructural features, is affected greatly by the temperature of heat treatment. Inversion parameters can easily be tuned, from 5%–19%, depending on the annealing temperature. The upper limit of inversion is found for T = 400 °C as confirmed by x-ray powder diffraction and Raman spectroscopy. Excellent battery behavior is found for samples annealed at lower temperatures; after 500 cycles the specific capacity for as-prepared ZnMn ₂ O ₄ is 909 mAh g ⁻¹ , while ZnMn ₂ O ₄ heat-treated at 300 °C is 1179 mAh g ⁻¹ , which amounts to 101% of its initial capacity. Despite the excellent performance of a sample processed at 300 °C at lower charge/discharge rates (100 mAh g ⁻¹ ), a drop in the specific capacity is observed with rate increase. This issue is solved by graphene-oxide wrapping: the specific capacity obtained after the 400th cycle for graphene-oxide-wrapped ZnMn ₂ O ₄ heat-treated at 300 °C is 799 mAh g ⁻¹ at a charge/discharge rate 0.5 A g ⁻¹ , which is higher by a factor of 6 compared to samples without graphene -oxide wrapping.

In recent decades, the field of materials research has put significant emphasis on developing innovative platforms that have the potential to address the increasing global energy demand. Batteries have demonstrated their enormous effectiveness in the context of energy storage and consumption. However, safety issues associated with liquid electrolytes combined with a low abundance of lithium in the Earth’s crust gave rise to the development of solid-state electrolytes and cations other than lithium. The commercial production of solid-state batteries demands the scaling up of solid-state electrolyte syntheses as well as the mixing of electrode composites containing solid electrolytes. This review is motivated by the recent literature, and it gives a thorough overview of solid-state electrolytes and highlights the significance of the employed milling and dispersing procedures for the resulting ionic transport properties.