Deposition and decomposition of electrolyte solutes caused by N-doped porous carbon: a kinetic study of ion migration

Abstract

Nitrogen-doped porous carbon has been widely used in electrochemical energy storage, particularly in electrochemical double-layer capacitors (EDLCs), where it demonstrates excellent capacitance performance. However, the impact of nitrogen doping on the migration of electrolyte ions and the rapid decay of electrochemical performance at high temperatures has been rarely reported. In this work, a series of advanced characterizations, such as electrochemical quartz crystal microbalance (EQCM), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and synchrotron radiation-based X-ray absorption near edge structure (XANES), were employed to analyze ion migration, deposition, and decomposition. Combining first-principles calculations, it was proved that the high-energy state lone pair electrons of amine and pyrrole-N trigger the continuous deposition/decomposition of anions BF₄^-, and prevent the deposition of cations SBP⁺. The deposited and decomposed cations further formed a passivation interface, which hindered ion migration. This interface led to dramatic fluctuations in electrode mass changes during charging and discharging, and reduced the total amount of ion migration. This work provides a novel kinetic study of ion migration within the electrochemical interface of nitrogen-doped porous carbon, which could contribute to enhancing the specific capacitance and cycle life of supercapacitors.