The electrochemical model coupled parameterized life cycle assessment for the optimized design of EV battery pack

Purpose With the increasing market share of electric vehicles (EVs), many studies have been devoted to the life cycle assess-ment (LCA) of lithium-ion batteries. However, current LCA results are diverse, leading to various material compositions, energy densities, and charging/discharging efficiencies. All of these performance indicators can have a significant influence on environmental impacts. This study establishes a parametric LCA model that can reflect the most current understanding of battery cell/pack design and greenhouse gas (GHG) emissions. Methods First, a practical parameterized life cycle inventory (LCI) of nickel-manganese-cobalt (NMC) battery cells and packs used in EVs is designed to integrate the simplified electrochemical method. By adjusting the cathode thickness and bilayer number, the changes in the composition of the battery cell and pack are studied. Next, a kinetic model of the battery cell and the pack is established to calculate their area-specific impedances (ASIs), internal resistance, sustainable power, and efficiency in the use phase. Finally, the GHG emissions of the battery pack in the entire life cycle are analyzed using Ecoinvent 3 - allocation, cut-off by classification - unit database in Simapro 9.1.1. Results and discussion The increase of cathode thickness (30-150 mu m) leads to significant expansions of mass proportion attributed to the positive active materials (from 26.2 to 38.5%) and negative active materials (from 17.0 to 24.9%). Thus, the energy density of the pack can be improved from 144 to 202 Wh/kg. On the other hand, a thicker cathode thickness triggers an increased internal resistance from 28.8 to 64.8 m Omega, which correspondingly degrades the charging/discharging efficiency from 96.5 to 90.2%. For the carbon emissions from the LCA, the CO2 equivalent per km exhibits a minimal point (70-90 mu m) under the cathode thickness range of 30-150 mu m. Moreover, CO2 eq/km is reduced by 9-16% for every additional 50,000 km mileage. Conclusions The model in this study reflects the change of parameters in practice according to the current and future requirements, increasing the transparency of LCA and benefitting future green design of the battery pack. The results indicate that cathode thickness should be 70 mu m for a 200,000-km total mileage. The optimized CO2 emissions are 16.0 CO2 eq/km, where the pack is configured to have a 400-km driving range per charge and 94.6-95.0% charging/discharging efficiency.

Automated summary

This study establishes a parameterized life cycle assessment (LCA) model to reflect the most current understanding of battery design and greenhouse gas (GHG) emissions. The results indicate that for a total mileage of 200,000 km, the cathode thickness should be 70 μm. The optimized CO2 emissions are 16.0 CO2 eq/km, with the battery pack configured to have a 400 km driving range per charge and 94.6-95.0% charging/discharging efficiency.