Meaning
Mechanical force describes the pressure generated by the expansion of electrodes during battery charging and aging. Cells experience cell swelling stress as lithium ions insert into the anode, causing a physical volume change that exerts pressure against the pack enclosure. Sourcing engineers use this metric to design the structural constraints of the battery module.
Electrochemical Origin
Phase transitions in the active material drive the displacement of the cell casing. During the lithiation of the anode, the graphite sheets expand, which increases the internal volume. If the cell swelling stress is not constrained, the distance between electrodes increases, which degrades the ionic conductivity and increases internal resistance.
This loss of contact slows the transport of ions and degrades the high-power performance of the battery.
Structural Constraint
Module walls must resist the force exerted by the expanding cells. Engineers use compression pads to absorb some of the expansion while maintaining a baseline pressure. Sourcing contracts define the maximum allowable force to ensure the housing remains intact over the service life.
Cycle Degradation
Extended operation leads to irreversible expansion due to solid electrolyte interphase growth. This progressive increase in cell swelling stress accelerates the loss of active lithium. Monitoring the stress helps predict the remaining useful life of the system.
