Lifetime Prediction of Lithium-Ion Batteries Based on the Correlation Between Internal Resistance Growth and State of Health (SoH)

This study analyzes the lifetime characteristics and degradation behavior of lithium-ion batteries under increasing charge–discharge cycles. The experiment focused on RE (Real Part), IM (Imaginary Part), and DCIR Degradation% (Direct Current Internal Resistance Degradation). The RE increased from 0.0023 Ω at the initial state to 0.00293 Ω after 1200 cycles, representing a 28% rise, with a sharp acceleration after 400 cycles due to interfacial resistance buildup and electrolyte decomposition. The IM shifted from negative to positive values, indicating delayed electrochemical reactions and enhanced inductive behavior. A pronounced transition occurred between 400 and 800 cycles, confirming this range as a critical phase of performance degradation. Correlation analysis between SoH (State of Health) and DCIR Degradation% showed that while SoH decreased slightly from 100% to 87.3%, DCIR Degradation% increased significantly to 137.8%, indicating that internal resistance growth is the dominant cause of aging. When SoH falls below 70%, the battery reaches its effective end-of-life, accompanied by severe heat generation and power loss. In conclusion, the combined analysis of RE, IM, and DCIR Degradation% demonstrates that accumulated internal resistance is the key factor determining battery lifetime. Stabilizing the SEI layer, reinforcing electrode structures, and improving electrolyte stability are essential strategies for extending battery durability.