Plug‐In Hybrid Vehicle and Second‐Life Applications of Lithium‐Ion Batteries at Elevated Temperature

Abstract

AbstractIn improving fuel economy and reducing carbon footprint, hybrid, plug‐in hybrid and all‐electric vehicles are considered as sustainable modes of transportation in the automotive industry. Here, commercial Li‐ion cells (26650 and 18650 with lithium iron phosphate (LFP) and nickel manganese cobalt (NMC) cathodes) were subjected to simulated plug‐in hybrid electric vehicle (PHEV) conditions, using the Federal Urban Driving Schedule (FUDS) under charge‐depleting mode at elevated temperature (50 °C and <10 % RH). The capacity degradation (16 % over 800 cycles) under the PHEV test protocol for Li‐ion batteries with 26650 NMC cathodes was twice of that using LFP cathodes (8 % over 800 cycles) under identical conditions. The Li‐ion batteries were also subjected to second‐life charge–discharge cycling at C/5 rate after evaluating them under the PHEV protocol (800 cycles for 26650 cells and 1200 cycles for 18650 cells). In addition, the high‐frequency resistance measured by electrochemical impedance spectroscopy was found to increase significantly with cycling for both the NMC‐ as well as LFP‐based batteries, leading to power fading. XRD analysis of the 18650 LFP‐based battery showed change of phase from LiFePO4 to FePO4, indicating Li+‐ion loss. However, the cathode active materials of the Li‐ion cells (26650 with LFP and NMC cathodes), examined using XRD, showed no significant phase change in the materials after 800 PHEV cycles and around 200 second‐life charge–discharge cycles.