Abstract
Tremendous efforts have been dedicated into the development of high‐performance energy storage devices with nanoscale design and hybrid approaches. The boundary between the electrochemical capacitors and batteries becomes less distinctive. The same material may display capacitive or battery‐like behavior depending on the electrode design and the charge storage guest ions. Therefore, the underlying mechanisms and the electrochemical processes occurring upon charge storage may be confusing for researchers who are new to the field as well as some of the chemists and material scientists already in the field. This review provides fundamentals of the similarities and differences between electrochemical capacitors and batteries from kinetic and material point of view. Basic techniques and analysis methods to distinguish the capacitive and battery‐like behavior are discussed. Furthermore, guidelines for material selection, the state‐of‐the‐art materials, and the electrode design rules to advanced electrode are proposed.
Highlights
The boundary between the electrochemical capacitors and batteries becomes less distinctive
His research interests include the green production of high-quality carbon allotropes (CNTs, GF, GF/ carbon nanotubes (CNTs) hybrid films), the sustainable development of high-performance electrochemical energy storage devices (Li/Na/K-ion batteries, alkaline rechargeable batteries, asymmetric supercapacitors) for renewable energy storage and delivery, and the in-depth understanding of fundamental device electrochemistry
Pseudocapacitance is a faradaic energy storage based on the fast redox reaction on the surface or near-surface region of the electrodes, where electrosorption/electrodesorption occurs with charge transfer but without any bulk phase transformation upon charging/discharging (Figure 2b).[26,52,53]
Summary
EC devices have attracted considerable interest over recent decades due to their fast charge–discharge rate and long life span.[18,19] Compared to other energy storage devices, for example, batteries, ECs have higher power densities and can charge and discharge in a few seconds (Figure 2a).[20] Since General Electric released the first patent related to ECs in 1957,[21] these devices have been applied in many fields, including power capture and supply, power quality applications, and backup power.[19]. The EDL capacitance is described as follows[9,10]. Where Cdl is the EDL capacitance of a single electrode, Q is the total charge transferred at potential V, εr is the dielectric constant of the electrolyte, εo is the dielectric constant of vacuum, d is the charge separation distance, and A is the electrode surface area. When Cdl is constant for EDLCs, the following equation describing the response current I can be derived from
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