Dense (non-hollow) carbon nanospheres: synthesis and electrochemical energy applications

Abstract Porous carbon materials have extraordinary importance as electrodes in many electrochemical devices used for energy storage and conversion. For this reason, there is a growing interest in the design of new carbon materials with improved chemical and structural properties that enhance their electrochemical performance providing high energy and power densities as well as long cyclability. To satisfy this demand, researchers are continuously looking for new types of carbon materials that fulfill the above requirements. In this respect, carbon nanospheres (CNSs) have attracted great attention because, besides the typical characteristics of carbon materials, they have short diffusional pathways that provide fast kinetics, which is an important feature for advanced electrochemical energy systems. This review summarizes the synthesis strategies used to produce non-hollow carbon nanospheres, including methodologies based on the use of hard (e.g. silica) or soft (e.g. surfactants) templates, as well as template-free procedures that involve the production of polymer nanospheres and their conversion to CNSs and porous carbon nanospheres (PCNSs). In addition, the use of CNSs and PCNSs as electrodes in energy storage devices such as supercapacitors, batteries (e.g. alkali-ion, lithium-sulfur, etc.), or Li-ion capacitors, as well as ORR electrocatalysts for energy conversion, is analyzed in detail.