Analysing unbalanced ageing in EV battery Packs using the Low-Cost Lumped Single Particle Model (LSPM): the impact of temperature gradients among parallel-connected cells

Abstract

Lithium-ion battery cells are widely used in electric vehicles (EVs) due to their high energy density and long lifespan. However, these cells are sensitive to temperature and can age at different rates depending on the temperature they are subjected to. While EV battery packs are equipped with a battery thermal management system (BTMS) to regulate the temperature of the pack, it cannot completely eliminate temperature gradient within the pack due to the limited cooling capabilities. As a result, a maximum temperature gradient of 5°C is allowed in BTMS designs for EVs, which leads to uneven ageing speeds within the pack. Due to practical limitations of battery management system (BMS), it is difficult to directly measure the currents flowing through each parallel-connected cell, making it challenging to actively balance the cells. To investigate the pack-level current distribution and ageing trends caused by temperature gradient, this paper adopts the low computational cost Lumped Single Particle Model (LSPM) coupled with Arrhenius dependency to investigate the influence of temperature on current distribution as well as the resulting unbalanced ageing rates among parallel-connected cells in a 4s6p Panasonic NCR18650PF battery pack.