Electrochemical Thermal-Mechanical Modelling of Stress Inhomogeneity in Lithium-Ion Pouch Cells

Abstract

Whilst extensive research has been conducted on the effects of temperature in lithium-ion batteries, mechanical effects have not received as much attention despite their importance. In this work, the stress response in electrode particles is investigated through a pseudo-2D model with mechanically coupled diffusion physics. This model can predict the voltage, temperature and thickness change for a lithium cobalt oxide-graphite pouch cell agreeing well with experimental results. Simulations show that the stress level is overestimated by up to 50% using the standard pseudo-2D model (without stress enhanced diffusion), and stresses can accelerate the diffusion in solid phases and increase the discharge cell capacity by 5.4%. The evolution of stresses inside electrode particles and the stress inhomogeneity through the battery electrode have been illustrated. The stress level is determined by the gradients of lithium concentration, and large stresses are generated at the electrode-separator interface when high Crates are applied, e.g. fast charging. The results can explain the experimental results of particle fragmentation close to the separator and provide novel insights to understand the local aging behaviors of battery cells and to inform improved battery control algorithms for longer lifetimes.

Analytical Solution for Coupled Diffusion Induced Stress Model for Lithium-Ion Battery

“…Moreover, a recent work [44] demonstrated how the assumptions of spherical geometry and isotropic and linear elastic material are accurate for LCO and graphite, since they found a good agreement between the macroscopic deformation predicted by their numerical model and the experimental measurements conducted on pouch cell. Finally, spherical assumption is widely accepted among several works [20][21][22]26,45].…”

An Initial Exploration of Coupled Transient Mechanical and Electrochemical Behaviors in Lithium Ion Batteries

“…The concentration gradient that develops in the electrolyte around the anode can be attributed to a mismatch between diffusion of lithium ions in the electrolyte and the intercalation/deintercalation of lithium ions in to and out of the surface of the anode particles. 8,[35][36][37] That is, upon the application of a charging current to the system, lithium ions in the electrolyte surrounding the anode particles are quickly intercalated into sites available at the electrode surface. This causes a precipitous drop in the average concentration of lithium ions in the electrolyte, a drop that is then arrested by diffusion of lithium ions towards the electrode particles.…”

An Insight into the Battery Degradation and a Proposal for a Battery Friendly Charging Technique

“…The governing equations are solved using Python Battery Mathematical Modelling (PyBaMM). The models of SEI formation, internal temperature variations and particle cracking were also incorporated [77][78][79][80] . These models are run for different types of charging and charging rates (0.3C to 5C) given in Table S.4 for 350 cycles.…”