Exploration in materials, electrolytes and performance towards metal ion (Li, Na, K, Zn and Mg)-based hybrid capacitors: A review

Metal ion based hybrid capacitors (HCs) with a series of superiorities, such as exceptional electrochemical properties, cost-effective, safety and environmental benignity have come to the foreground in recent years. It is one of the indispensable energy storage systems that can not only hold high energy density and high power density simultaneously but also connect batteries and supercapacitors, thereby satisfying the energy storage needs of future multifunctional electronic devices. In this review, after a detailed introduction of the advanced electrode materials classified into battery-type and capacitive-type materials, the application of aqueous and non-aqueous electrolytes (organic electrolytes and ionic liquid electrolytes) were described sequentially as well. Furthermore, we addressed the recent advances on metal ion (Li, Na, K, Zn and Mg)-based HCs from the aspects of components, energy storage and conversion mechanism, selection and optimization of electrode materials and electrolytes as well as electrochemical performance evaluation and potential application. It can further comprehend the impact of key materials of metal ion based HCs on electrochemical performance, thus securing major advances in energy storage. Eventually, the principal challenges and future research prospects toward the metal ion based HCs were illustrated.