A unified lifetime electrochemical-aging framework for lithium-ion batteries: Capturing degradation across expanded voltage boundaries

Understanding how upper/lower cutoff-voltage boundaries jointly govern lithium-ion battery degradation is essential for boundary-aware lifetime optimization and health estimation beyond standard windows. Here, commercial NCA/graphite 18,650 cells are cycled under a seven-protocol voltage matrix spanning 2.25–4.4 V and systematically diagnosed using capacity tracking, differential voltage analysis (DVA), electrochemical impedance spectroscopy (EIS)/ Direct Current Internal Resistance (DCIR), and post-mortem scanning electron microscopy (SEM)/ energy-dispersive X-ray spectroscopy (EDS) analyses. We reveal an asymmetric mechanism-shifting degradation governance: raising the upper cutoff accelerates cathode-driven degradation via high-voltage parasitic reactions and cathode structural/interfacial instability, whereas lowering the discharge cutoff aggravates anode mechanical/interfacial damage through repeated SEI rupture–reformation, increasing anode deactivation and lithium-inventory loss. Under high-voltage operation, enhanced acidic-species generation and crossover to the anode corrodes the anode Cu current collector and induces anode-side Cu deposition, amplifying impedance growth. Building on these insights, we develop a unified electrochemical–aging framework that couples boundary-activated pathways and achieves robust full-life reconstruction across all protocols within the 2.25–4.4 V range (SOH RMSE <1% and full-life voltage RMSE <55 mV). The validated model provides boundary-dependent internal-state trajectories, including electrode available capacities, cumulative proton inventory, and anode-side Cu deposition, linking operating boundaries to mechanistically interpretable degradation-state transitions.