Ideal Three‐Dimensional Electrode Structures for Electrochemical Energy Storage

Abstract

Three-dimensional electrodes offer great advantages, such as enhanced ion and electron transport, increased material loading per unit substrate area, and improved mechanical stability upon repeated charge-discharge. The origin of these advantages is discussed and the criteria for ideal 3D electrode structure are outlined. One of the common features of ideal 3D electrodes is the use of a 3D carbon- or metal-based porous framework as the structural backbone and current collector. The synthesis methods of these 3D frameworks and their composites with redox-active materials are summarized, including transition metal oxides and conducting polymers. The structural characteristics and electrochemical performances are also reviewed. Synthesis of composite 3D electrodes is divided into two types - template-assisted and template-free methods - depending on whether a pre-made template is required. The advantages and drawbacks of both strategies are discussed.

Redox Electrolytes in Supercapacitors

“…3 As in all electrochemical devices, improved electron and ion transport in electrode materials, and reduced charge transfer resistance at electrode/electrolyte interfaces are also desirable. 31 Practically, such property improvements could be achieved from specially prepared (e.g. doping) carbon materials 6 or making the carbon into a monolithic binder-free coating on the electrode.…”

“…doping) carbon materials 6 or making the carbon into a monolithic binder-free coating on the electrode. 29,31 Thus, the mechanisms of charge storage accrued from redox electrolytes in SCs could be described based on the following three broad categories in relation with the retention of the redox species, particularly via electro-or chemisorption.…”

Recent Progress in Self‐Supported Metal Oxide Nanoarray Electrodes for Advanced Lithium‐Ion Batteries

“…In comparison to the 2D planar substrates, the 3D porous substrates have the following advantages ( Figure 9 ): First, the unique 3D structure provides more growth sites, thus a higher loading mass of active materials can be realized, leading to a higher specific areal capacity and a higher gravimetric capacity with respect to the whole electrode 126, 127. Second, the unique porous structure of 3D conductive substrates offers accessible pathways for the penetration of electrolyte, accelerating the Li + ion diffusion and interface reaction kinetics 128.…”

“…One reason lies in the difficulties in the fabrication of metal oxide nanoarray cathodes. Another reason could be related to the uneven electron transport lengths from different redox active sites to the bottom of current collector, which may give rise to unequal electrochemical reaction kinetics 126. Furthermore, the low loading mass of active materials for metal oxide nanoarrays on 2D planar substrate results in low specific areal capacity and energy density, limiting their practical utilization.…”

Transition metal oxides/hydroxides nanoarrays for aqueous electrochemical energy storage systems

“…In addition, these nanoarrays often exhibit fascinating properties, which are desirable for EES electrodes. It could provide large surface area and tunable free spaces for volume expansion, prevent agglomeration, facilitate the electron transfer rate and the penetration of the electrolytes into the whole electrode matrix, and strengthen the connection between active materials and substrates [2,[14][15][16][17]. A schematic representation of an idealized nanoarrays electrode is shown in Fig.…”