Operando Raman Spectroscopy-Guided 24-Hour Aging Assessment of Activated Carbon Positive Electrodes for Lithium-Ion Capacitors

Abstract While high-power lithium-ion capacitors (LICs) with high energy density emerge as promising pulse-/peak-power solutions for AI data centers, their long-term viability remains severely hindered by the degradation of the activated carbon (AC) positive electrode. To evaluate this aging behavior, we propose a 24-h high-voltage cycling (HVC) protocol integrated with operando Raman spectroscopy, demonstrating that the turning point in the D1 band can serve as a sensitive indicator of corrosion severity. During the early-stage HVC aging, cathode–electrolyte interphase (CEI) formation and gas evolution passivate defect-related Raman signals, narrowing the D1 band. As aging proceeds, carbon corrosion becomes dominant and broadens the D1 band. By validating this approach across various ACs, we establish a direct correlation between an earlier structural turning point and accelerated capacity decay, thereby uncovering carbon aging mechanisms and offering an unprecedented, rapid diagnostic technique for capacitor-type materials.