Magnetic Force Dilatometry of Silicon-NMC622 Lithium-Ion Coin Cells: The Effects of Binder, Capacity Ratio, and Electrolyte Selection

Abstract

Operando cell expansion measurements on Si-NMC622 coin cells using a magnetic dilatometer were performed to understand the effects of electrode binder content, electrode formulation, negative-to-positive electrode capacity ratio (N/P ratio), and electrolyte selection on reversible and irreversible cell expansions. Our experiments reveal a complex relationship between cell properties, imparted by the selected cell parameters, and cell expansion. Reversible cell expansions scaled with cell discharge capacity and electrode mechanical properties, while irreversible cell expansions were sensitive to capacity fade, silicon utilization, and electrolyte decomposition mechanisms. Additionally, volumetric cell energy densities were calculated using the measured capacities and irreversible expansions over the life of the cells. We show that judicious selection of cell parameters can improve volumetric energy density after 200 charge/discharge cycles by approximately two-fold. Our work provides valuable insight, at an early stage of cell development, towards minimizing the effects of cell expansion on battery cell, pack, and module designs.

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

“…Considering the design of modules and packs for electric vehicles, the intercalation induced expansion and aging induced expansion of the active material and electrodes must be taken into account. 31 In the module designs for the Chevrolet Volt 32 and Chevrolet Bolt, 33 the cell is a pouch 34 type format and the volume change is mitigated using foam inserts within a rigid structural module design. When considering a module with cylindrical cells, the volume change is generally assumed to be contained by the can and deformation of the can is ignored when considering the design of the module and pack, however, when considering prismatic cells and pouch cells, the volume change in these cells cannot be ignored and must be considered due to the expansion seen in the direction perpendicular to the orientation of the electrodes.…”