Investigating Thermal and Charge Rate Effects on Electric Vehicle Battery Degradation

Abstract

Electric vehicles (EVs) operate under diverse environmental conditions and charging scenarios, leading to significant variations in charging rates and ambient temperatures. This study explores the combined impact of charge rate and temperature on the degradation of lithium-ion batteries utilized in EVs, specifically focusing on lithium-ion phosphate (LFP), nickel cobalt aluminum oxide (NCA), and nickel manganese cobalt (NMC) chemistries. A novel XGBoost-Random Forest (XG-RF) model is employed for state of health (SOH) estimation, analyzing battery cycle life under varying charge rates (C/20, 1C, 2C, and 3C) and temperatures (5°C, 25°C, and 35°C) respectively. Results show that LFP batteries achieve the highest stability, with a cycle life of 5,293 cycles at 25°C and C/20, outperforming NCA and NMC. Furthermore, the proposed XG-RF model demonstrates high prediction accuracy, achieving a minimal mean squared error of 0.0006 for LFP at 25°C and C/20, but peaks at 0.4188 for NCA at 1C and 35°C, highlighting its sensitivity to extreme conditions. These findings highlight LFP’s superior thermal stability and emphasize the need for optimized charging and thermal management for NCA and NMC, with the hybrid model providing accurate SOH estimation to enhance EV battery reliability and lifespan.