Strain Relaxation Characterization on Lithium-ion Batteries at Different States of Charge and Charging Rates

The strain on the cell casing can serve as an indicator of the internal state of the cell. Monitoring strain during the charging and discharging processes aids in determining optimal charging and discharging operations, thereby maximizing the lifespan and performance of the battery. Herein, strain dynamic curves are obtained for lithium-ion batteries at low, medium, and high charge and discharge rates by affixing strain gauges to individual cells. The investigation delves into parameters such as strain relaxation time, maximum strain, and residual strain at various charge rates and states of charge. The experimental findings reveal distinctive patterns, indicating that the strain curve during high-rate charging resembles a second-order function, exhibiting more pronounced fluctuations as the rate increases. This stands in stark contrast to the strain exponential decay observed during conventional medium and low-rate charging. Notably, the strain residual resulting from high-rate charging proves to be several times higher than that observed in low-rate charging, hinting at potential differences in the dynamic distribution of lithium ions within batteries during high-rate versus medium-low-rate charging modes. Experiments are conducted on the 18650 battery to investigate the correlation between battery volume overshoot and the insertion of lithium ions. The variation characteristics and differences in strain at different states of charge and rates are explored. Insights from a mechanical safety perspective are provided for the field of battery charging and discharging safety.image (c) 2024 WILEY-VCH GmbH