Modeling and Simulation of Pore Morphology Modifications using Laser-Structured Graphite Anodes in Lithium-Ion Batteries

Abstract

The energy density of lithium-ion batteries can be enhanced by using thicker and denser electrodes, which leads to transport limitations in the electrolyte within the porous structures. A pore morphology modification of the electrodes can counteract this limitation mechanism and provide higher rate capabilities of the cells. In this work, graphite anodes are structured with a picosecond laser in order to create transport pathways for the lithium-ions and allow for enhanced penetration of the electrodes. Experimental data from graphite/NMC-111 coin cells with varying areal capacities are used for the development and parameterization of an electrochemical model. The modified pore morphology of the structured electrodes is represented in the model by an adapted tortuosity, which results in lower lithium-ion concentration gradients and reduced diffusion polarization in the electrolyte. The effect of electrode thickness and tortuosity on limiting mechanisms is analyzed via simulation studies in order to derive the impact of structured electrodes. As a result, improved discharge as well as charge rate capability appears beside enhanced safety features such as increased tolerance versus hazardous lithium-plating during fast charging scenarios.

Identifying the Association between Surface Heterogeneity and Electrochemical Properties in Graphite

“…and electrodes (tortuosity, loading level of active materials, etc.) need to be carefully optimized [ 23 , 24 , 42 , 43 , 44 ]. In addition, the overall rate performance of the electrode can be changed by adjusting the crystallographic orientation of the exposed planes, due to the Li + -diffusivity difference by a factor of ~10 4 between [100] and [001] directions in graphite [ 15 , 16 , 17 , 18 ].…”

Enhanced Fast Charging and Reduced Lithium-Plating by Laser-Structured Anodes for Lithium-Ion Batteries

“…However, previously published work in the field of electrochemical simulation suggests that a directional porosity intentionally created by laser structuring has further positive impact. 31,33 In addition, the rapid charging behavior of the two cell types was investigated. A special focus was placed on the detection of Li-plating at different ambient temperatures and charging rates.…”

“…29 Generally speaking, more particles are removed close to the surface of the electrode, resulting in conical structures which narrow toward deeper parts of the electrode. 31 The size and the distribution of the structures have a strong effect on the cell-internal resistance 32 and, thus, the electrochemical performance. When evaluating structure geometries that lead to a comparable total amount of removed electrode material, finer structures have proven to be more beneficial than coarser structures.…”

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.…”