Interfacial Engineering of Self-Activated MnCo <sub>2</sub> O <sub>4</sub> and 2D Layered Exfoliated Graphite: A Synergistic Approach to High-Energy-Density Asymmetric Supercapacitors with Exceptional Cycling Performance
Shivam Kumar Mittal, K. L. Yadav
Abstract
Advancements in materials research have resulted in the development of novel electrode materials for energy storage applications. However, challenges such as complex synthesis processes, low electrical conductivity, and poor cyclic stability hinder their practical implementation. To address these issues, we present a sustainable, calcination-free coprecipitation method for synthesizing MnCo 2 O 4 (MCO) and its nanocomposites with 2D layered exfoliated graphite (EG). Leveraging EG’s high conductivity, stability, and large surface area, this approach enhances charge transport and ion diffusion, leading to superior supercapacitor performance. The optimized MCO/EG composite (MCOG1) exhibits remarkable electrochemical properties, achieving a C s of 918 F/g at 0.5 A/g and maintaining 164% capacitance retention after 20,000 GCD cycles at 10 A/g. Its high surface area (107 m 2 /g), hierarchical porosity, enhanced conductivity, and abundant redox-active sites contribute to this performance. The asymmetric supercapacitor (ASC) constructed using MCOG1 as the cathode, activated carbon as the anode, and PVA–KOH gel electrolyte exhibits self-activation behavior during the initial 5000 charge–discharge cycles at 5 A/g, leading to an increase in specific capacitance to nearly 2.5 times its initial capacitance. After 60,000 cycles, the device maintains 93% capacitance retention with nearly 100% Coulombic efficiency, indicating exceptional long-term stability. Furthermore, the ASC achieves an energy density of 87.5 Wh/kg and power density of 18 kW/kg. Practical demonstrations using two ASC devices successfully powered different LED configurations, confirming real-world applicability. This work highlights a sustainable, calcination-free synthesis approach and the synergistic benefits of MCO/EG nanocomposites, paving the way for next-generation supercapacitors with improved sustainability and performance.