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

Abstract

The 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 the pressure increase during operation. In this study, 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 SiO x -graphite anode (22 wt% SiO x ) 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.