Experimental Study of Sidewall Rupture of Cylindrical Lithium-Ion Batteries under Radial Nail Penetration

To understand the relationship of the sidewall rupture at different states of charge (SOCs) of cylindrical cells with high specific energy, this work presents the results of radial nail penetration tests of 21700-format cylindrical cells at different SOCs. The thermal runaway and sidewall rupture behaviours were characterised by key performance indicators such as temperature, mass, fire behaviour, and voltage change. In addition, released gases from a subset of tests were measured using the Fourier transform infrared spectroscopy. The change in the internal structure of another subset of cells after the test was observed by X-ray computed tomography. The results show that the sidewall rupture still exists for tests at low SOC (< 30% SOC), but the outcome of thermal runaway and sidewall rupture is milder than those at high SOC (≥ 50% SOC). The average mass loss of cells increases with the increment of SOC. The cell casing thickness is reduced by 12.7% ± 0.3% of the fresh cell, which in combination with the reduction in the strength of the casing material at high temperatures could contribute to sidewall rupture.