Thermal Stabilization Kinetics of Pitch Precursors for Sodium Storage
Controlling pitch air-oxidation at 260°C yields oxygen uptake above 8 percent, preventing mesophase growth and maximizing sodium storage plateau capacity.
Mesophase Inhibition
Meaning
Prevention of the alignment of disc-like polycyclic aromatic molecules during the carbonization of pitch stops the formation of a liquid crystal state. In the production of carbon materials for battery electrodes, mesophase inhibition is used to control the degree of graphitization and the final porosity of the anode. This technique allows manufacturers to tailor the structure of the carbon to improve ion diffusion rates.
Molecular Interference
Chemical additives or rapid heating rates disrupt the natural tendency of the molecules to stack into ordered layers. When mesophase inhibition occurs, the resulting carbon possesses a disordered or hard structure rather than the highly crystalline structure of synthetic graphite. This lack of long-range order provides more sites for lithium insertion and reduces the physical expansion of the material during charging cycles.
Texture Development
Microscopic examination of the treated pitch reveals a fine-grained or isotropic morphology instead of the large coalesced spheres typical of uninhibited growth. The process of mesophase inhibition effectively locks the carbon atoms into a rigid framework that resists the high temperatures used in standard graphitization. This results in a material that is harder and more chemically stable in certain electrolyte environments.
Material Performance
Enhanced cycle life and higher power density are often achieved by using carbons that have undergone this structural modification.