7. Conclusions

with the appropriate porosity and electrical conductivity for use in supercapacitors, should be focused on the upper right zone of the plot. To this end, carbon xerogel used as an active material offers a truly unique polymeric structure with a high electrical conductivity combined with a modulable micro- and mesoporosity and therefore optimizable supercapacitor energy and power supply. Figure 10 shows the location on the Ragone plot of a series of commercial carbons available for the supercapacitor market for use in EDLCs with aqueous electrolyte, in addition to the performances of different carbon xerogels. The advantage of the bespoke nanoporous carbon

Batteries are energy storage devices whose performance is based on the conversion of chemical energy into electrical energy via reversible reactions that take place between the anode and cathode electrodes. The working principle is based on the reversible migration of ions from the cathode during the charge stage, after which they migrate through the electrolyte to intercalate into the structure of a carbon-based anode material [73–77]. Figure 11 shows a schematic

However, during charging, secondary reactions also take place leading to the formation of a stable passivation layer, known as the solid-electrolyte interface that entraps the ions, reducing the energy storage over time. As a consequence, the service life of batteries is limited. The formation of this layer and the diffusion of the ions through the anode material are complex mechanisms that depend largely on the chemical composition and porous properties of the

Batteries provide high capacitances, i.e., they supply great energy densities, which is their most advantageous characteristic. However, the chemical process is relatively slow and so, unlike supercapacitors, the main challenge of batteries is to achieve high power densities. Different compounds can be used as electrodes: NaS, Ni-Cd, ion-Li, etc. Graphite is the most commonly used active material as anode material in lithium-ion batteries [1, 73, 78]. Nevertheless, its

xerogels discussed in this study is evident.

82 Porosity - Process, Technologies and Applications

Figure 10. Ragone plot of several active materials and carbon xerogels.

representation of a lithium-ion battery.

active material used as anode.

Nanoporous carbon xerogels have a great potential in numerous applications since their nanoporosity can be tailored quite accurately. Mesoporosity can be predetermined during the synthesis of the organic xerogel relatively easily by controlling the proportion of each component of the solution precursor. However, the numerous variables involved, i.e., pH and type of catalyst used, degree of dilution, proportion of methanol that comes with the formaldehyde and R/F ratio, require a better knowledge of how their interrelation influences the resulting mesoporosity. The mesoporosity formed in this stage is relatively well preserved during the subsequent carbonization and/or activation processes, during which the micropososity of the carbon xerogel is formed. Depending on the carbonization or activation method selected for obtaining the carbon xerogel, the microporosity can also be tailored. The versatility of these nanoporous carbons makes them suitable for use in numerous applications. Additionally, carbon xerogels possess a good balance between porosity and electrical conductivity, two opposite properties. Thus, high surface area carbon xerogels have an electrical conductivity that is superior to other high surface area carbons. This makes carbon xerogels the ideal materials for use as electrodes in storage devices like supercapacitors where a high surface area and high conductivity are required. The potential of carbon xerogels for serving as electrode in lithium-ion batteries is also currently under investigation with promising results.
