Electrochemical-Mechanical Parameterization and Modeling of Expansion, Pressure, and Porosity Evolution in NMC811∣SiOx-Graphite Lithium-Ion Cells

Abstract

Mechanical changes in active materials with large volume expansion such as silicon and nickel not only affect the electrochemical performance of modern batteries but also pose a great challenge to their mechanical design due to pressure increase during operation. We show that the large expansion and consequently changing mechanical properties of silicon and nickel strongly affect the electrochemical and mechanical performance. A multi-scale electrochemical model is developed, parameterized, and validated for a pouch cell with a SiOx-graphite anode (22 wt.-% SiOx) and an NMC|811 cathode. Mechanical parameters such as expansion and compressive properties are determined experimentally using an in-house-developed high-precision cell press and electrode dilatometer, thus parameterizing a semi-empirical mechanical model. We employ a new characterization technique to measure mechanical changes in the cell in-operando and propose a phenomenological parameterization where physical modeling is not yet sufficient. Through electrode porosity, we show that mechanical and electrochemical performance are interdependent, as the latter is reduced upon expansion and pressure development. On the one hand, the active material of the anode seems to expand into the pores at increased pressure, and on the other hand, the mechanical deformation of the cell components can no longer be neglected.

Investigation of the Influence of Silicon Oxide Content on Electrolyte Degradation, Gas Evolution, and Thickness Change in Silicon Oxide/Graphite Composite Anodes for Li-Ion Cells Using Operando Techniques

“…The total ion current (TIC) is plotted over the retention time. For this post mortem study of the gas atmosphere after three formation cycles, an electrode with a high Si content was used to have a better comparability with the other literature where electrodes with high Si contents were also investigated [29,30]. Furthermore, it was expected to ensure a better detectability of possible gaseous Si species with a Si-rich anode.…”

Modeling Rate Dependent Volume Change in Porous Electrodes in Lithium-Ion Batteries

“…Many methods have been used to quantify the volume change and deformation of lithium ion batteries during operation, 19,[35][36][37] both during a single cycle, as well as over the life of the battery. For much of the work focused on volume change, irreversible volume change has been a key focus, with the reversible volume change used as a validation or proof of concept.…”