Effect of Electrochemical Aging on the Mechanical–Electrical–Thermal Safety Response of Tabless 4695 Cylindrical Cells Under Quasi-Static Indentation

Electrochemical aging can alter the mechanical abuse tolerance of lithium-ion cells, but evidence for large-format tabless cylindrical cells remains limited. This study investigates commercial steel-cased 4695 cells under quasi-static hemispherical indentation at 100% State-of-Charge. Fresh cells were compared with two aged groups brought to 80% remaining capacity by either room-temperature cycling at 20 °C and 20 A or low-temperature/high-current cycling at −10 °C and 45 A. Aging shifted the onset of a major internal short circuit to lower displacement, force, and absorbed mechanical work. Relative to fresh cells, the mean displacement at internal short-circuit onset decreased by 15.9% after aging at 20 °C and 20 A and by 22.1% after aging at −10 °C and 45 A, while the corresponding force decreased by 10.8% and 19.4%. The absorbed mechanical work to short-circuit onset decreased by 24.0% and 37.3%, respectively. Peak surface temperatures did not clearly separate the groups, whereas integrating the surface-temperature rise over the first 30 s after short-circuit onset revealed an increase from 6894 Ks in fresh cells to 9872 Ks and 13,777 Ks in the two aged groups. The experiments also revealed a change in observed venting behavior, with top-terminal venting occurring more frequently in aged cells. These results indicate that, under the tested conditions, aging history can reduce mechanical abuse tolerance and modify post-failure severity in large-format cylindrical cells.