“Porous and Yet Dense” Electrodes for High‐Volumetric‐Performance Electrochemical Capacitors: Principles, Advances, and Challenges

Abstract

With the ever-rapid miniaturization of portable, wearable electronics and Internet of Things, the volumetric performance is becoming a much more pertinent figure-of-merit than the conventionally used gravimetric parameters to evaluate the charge-storage capacity of electrochemical capacitors (ECs). Thus, it is essential to design the ECs that can store as much energy as possible within a limited space. As the most critical component in ECs, "porous and yet dense" electrodes with large ion-accessible surface area and optimal packing density are crucial to realize desired high volumetric performance, which have demonstrated to be rather challenging. In this review, the principles and fundamentals of ECs are first observed, focusing on the key understandings of the different charge storage mechanisms in porous electrodes. The recent and latest advances in high-volumetric-performance ECs, developed by the rational design and fabrication of "porous and yet dense" electrodes are then examined. Particular emphasis of discussions then concentrates on the key factors impacting the volumetric performance of porous carbon-based electrodes. Finally, the currently faced challenges, further perspectives and opportunities on those purposely engineered porous electrodes for high-volumetric-performance EC are presented, aiming at providing a set of guidelines for further design of the next-generation energy storage devices.

Advances in Carbon Xerogels: Structural Optimization for Enhanced EDLC Performance

“…The electrochemical performance of EDLCs is considerably affected by several key components, including the electrolyte, conducting additive, binder, and active material [ 95 , 96 , 97 , 98 , 99 , 100 , 101 ]. Electrolytes can be divided into aqueous and organic types, with the latter being preferred in the industry due to their higher electrical conductivity and stability at elevated voltages [ 102 , 103 ].…”

“…Binders, such as polytetrafluoroethylene and polyvinylidene fluoride (PVDF), bond the conductive additive and active material to the current collector [ 99 ]. The active material, which provides the necessary space for electrolyte ion adsorption, greatly influences the EDLC performance [ 100 , 101 ]. To enhance the performance of EDLCs, researchers have utilized carbon materials, such as activated carbons, carbon nanotubes, activated carbon fibers, and CXs, with extensive studies being conducted on active materials [ 101 , 104 , 105 ].…”

“…The electrochemical performance of EDLCs is considerably affected by several key components, including the electrolyte, conducting additive, binder, and active material [95][96][97][98][99][100][101].…”

Freestanding Carbon Nanofibers Derived from Biopolymer (Kraft Lignin) as Ultra-Microporous Electrodes for Supercapacitors

“…In addition, electrospinning is a relatively slow process, making it less appropriate for large-scale manufacturing. The later drawback can be resolved using solution blowing (SB) [8,20,21]. This method is, in a sense, similar to electrospinning, albeit relying on an aerodynamically driven, rather than electrically driven bending instability to form nanofibers [22].…”

O, N‐Codoped, Self‐Activated, Holey Carbon Sheets for Low‐Cost And High‐Loading Zinc‐Ion Supercapacitors

“…Developing cheap, porous yet dense electrodes is crucial for practical application. [24] Holey graphene with abundant micro-/mesopores enabled the making of dense, porous, and highloading electrodes up to 30 mg cm −2 . [25][26][27] Nonetheless, the high price, low surface area, and insufficient capacitive performance of holey graphene prevent it from being widely applied.…”