Unravelling the safety improving and failure mechanisms of a 56.5 Ah high-energy–density Li-ion cell containing solid-state electrolyte

Safety issues of high-energy–density (HED) Li-ion cells have raised wide concerns and are impeding their application in electric vehicles (EVs). Developing the so-called quasi-solid or semi-solid Li-ion cells with solid-state electrolytes (SSEs) is a promising strategy but generally compromises the cell's electric performance. Moreover, the safety improving and failure mechanisms remain not fully understood. This study demonstrates a large-format (56.5 Ah) HED (260 Wh kg−1) Li-ion cell with significantly improved safety and good electric performances, which is realized by partial substitution of the liquid electrolyte with lithium aluminium titanium phosphate (LATP) SSE and rational cell material matching. The cell can pass various penetration tests with minimal temperature rises (≤20 °C), showing extraordinarily high tolerances for mechanical abuses, and exhibited a retarded thermal runaway (TR) evolution process during the accelerating rate calorimetry (ARC) test, providing valuable time for deploying predicting, alarming, and preventing tactics for the battery management systems (BMSs). X-ray computed tomography and a large depth-of-field digital microscope were used to uncover the detailed failure behaviors of cell materials, which were correlated to the variation of detectable external cell signals (impedance, voltage, and temperature) that could serve as the basis for upgrading the BMS. We expect that the insights achieved could guide the rational design and management of safe HED Li-ion cells.