Abstract：Lithium-ion batteries are widely used in electric vehicles due to their superiority of high energy density. However, the number of fire and explosion accidents of electric vehicles equipped with lithium-ion batteries has increased sharply in recent years because of the structural damages of the batteries in crashes. And repeated impact is a common scenario for lithium-ion batteries in service. Such cumulative damage may ultimately lead to short-circuit failure of the batteries or pose a potential long-term safety risk. To investigate the influence of repeated impact on the failure of lithium-ion batteries, dynamic tests with different energy levels were designed. By combining electrochemical characterization and inspection of the macro and micro damage to the internal structures of the impaired batteries, two failure modes (delayed failure and immediate failure) were discovered and the corresponding failure mechanisms were analyzed, which is revealed to be related to the impact energy. The relationship between battery failure and impact energy, as well as the number of impacts was discussed in detail. And the electrical performance degradation of non-failed batteries was evaluated. The results indicate that the failure of the battery is due to the cumulative damage of the separator, where the extent of separator damage is determined by the energy of single impact loads, corresponding to different failure modes of the battery. Repeated impacts with low energy led to delayed failure, while high energy impacts cause immediate failure. Additionally, the post-test performance decay of the batteries is also revealed to be related to the degree of electrode damage under different impact energy levels. The electrical performance of the battery can significantly deteriorate with the fracture of electrodes. By observing the disassembled battery, we also found that the positive and negative electrodes of the battery exhibit different behaviors after impact, where the negative electrode is more susceptible to the impact damage. These findings provide new perspectives for the reuse and safety assessment of impaired batteries and propose some new insights for the safety design of batteries.
2023, Vol. 44 
