Abstract
Spinel metal oxides (general formula AB₂O₄) have received strong research attention as electrode materials for supercapacitors because of their rich redox activity, stable structure, and low cost [1]. Their unique crystal arrangement, where metal ions sit in tetrahedral and octahedral sites, allows easy tuning of electrical, magnetic, and electrochemical behavior. In recent years, many spinels such as NiCo₂O₄, MnCo₂O₄, ZnFe₂O₄, Co₃O₄, FeCo₂O₄, and high-entropy spinels have been studied for fast charge storage. Researchers have shown that controlling the synthesis method, morphology, porosity, and particle size can significantly improve their capacitance, cycling stability, and rate performance. Spinel-carbon composites, conducting polymer hybrids, and asymmetric devices further enhance practical device performance. However, challenges remain, including moderate conductivity, structural degradation during cycling, and difficulties in achieving high mass loading for real devices [2]. This review summarizes the