Meaning
Spectroscopic method that detects unpaired electrons in materials by absorbing microwave radiation in a magnetic field. Applying electron spin resonance to anode materials reveals the presence of localized defect sites and free radicals. The technique provides quantitative data about the structural changes occurring during cycling.
Defect Detection
Disordered carbon structures hold numerous active sites that can be identified by their magnetic response. Analyzing the materials with electron spin resonance yields a specific magnetic signature for each defect type. This analysis helps determine how processing temperatures affect the electronic structure.
Active Center
Free radicals and dangling bonds function as reaction centers during the formation of the solid electrolyte interphase. If the electron spin resonance signal indicates a high concentration of these centers, the material will exhibit higher initial capacity loss. This loss happens because more electrolyte is consumed to passivate the active surface, creating a thicker resistive layer that reduces power density in the finished cell.
Analytical Range
Measuring these transitions requires cryogenic temperatures to resolve the weak magnetic signals. Some applications of electron spin resonance are limited to ex-situ samples due to the high electrical conductivity of the current collectors, which can shield the microwave signals.
