A Comprehensive Review of Ammonium Ion Hybrid Supercapacitors: Exploring Recent Breakthroughs and Future Horizons

The demand for energy storage is exponentially increasing with the growth of the human population, which is highly energy intensive. This progress demands high-performing and reliable energy storage devices for storing and delivering charge efficiently. Hybrid ion supercapacitors are the most desirable electrochemical energy storage devices, owing to their versatile and tunable performance characteristics, as they are the optimized assembly of batteries (energy devices) and supercapacitors (power devices). In this regard, ammonium ion hybrid supercapacitors (AIHSs) have grabbed substantial research consideration in past years due to their notable advantages of affordability, safety, fast diffusion kinetics, ecofriendliness, high energy density, and unique tetrahedral structure with abundant charge carriers NH₄⁺ resources. Up to now, although there have been substantial research advancements in AIHSs over the past few years, including advancements in various electrode materials, device structures, and novel electrolytes, there remains a lack of comprehensive reviews that cover the recent developments and provide critical insights into this rapidly evolving field. Therefore, this review culminates with the fundamental principles, basic charge storage mechanisms, and approaches for enhancing the electrochemical performances of AIHSs, focusing on improving these parameters to improve energy density, specific capacitance, and longevity for the commercial success of hybrid ion capacitors, which are in the nascent stages of development. To the best of our knowledge, it is the first complete account of AIHSs from mechanism to recent developments.