The performance and longevity of lithium-ion batteries (LIBs) are significantly influenced by operating conditions such as C-rate and voltage range during cycling. This systematic study investigates the aging mechanisms of LIBs under high-stress conditions, with a specific focus on the differences between aging at high and low C-rates across varying voltage ranges. Using a combination of Arrhenius analysis of electrochemical data and advanced Post-Mortem characterization techniques: focused ion beam (FIB) milling, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FTIR). We examine the effects of these cycling conditions on the electrochemical performance and surface reactions of the anode materials. This multi-technique approach offers a comprehensive understanding of how different operational parameters impact the electrochemical and chemical stability of LIBs, and how aging alters the main aging mechanisms in cells with Si/graphite anodes. These findings are crucial for optimizing battery performance and extending cycle life through the effective management of temperature, C-rate, and voltage limits, as well as for battery material optimization.