Comprehensive investigation on the durability and safety performances of lithium-ion batteries under slight mechanical deformation

Mechanical abuse is a general abuse behavior in electric vehicles. To prevent the safety risk from mechanical deformation, it is necessary to understand its failure mechanism and its effects on battery performance. There is a knowledge gap in the influence of slight mechanical deformation on the durability and safety of lithium-ion batteries. This study comprehensively investigates the changes in electrochemical properties, morphology, and thermal stability in commercial ternary/graphite lithium-ion batteries by multiple techniques. Tested cells are indented from 4 mm to 6.8 mm and cycled for 620 cycles. The results of cycle aging exhibit that indentation can improve the cycle performance of tested cells, but the effect turns negative for the cells when the indentation depth exceeds 6.5 mm. The electrochemical impedance spectroscopy measurements exhibit that indentation retarded the increase of impedance of indented cells during the aging process. It could be due to the increase of compact density weakening the degradation in the anode electrode. But the degradation in the cathode electrode is aggravated by mechanical deformation. During the cycle aging of tested cells, the loss of lithium inventory dominates the degradation of indented cells in the first 500 cycles and then follows the loss of active material damage. The apparent morphology of electrodes in deformed and aged cells exhibits that active material particles are compacted in the dented area, and cracks are formed in the fold area. After cycle aging, the compressed area surrounding the dent is covered by a layer of reaction products of electrolyte with lithium at the anode electrode. The adiabatic tests show the thermal stability of indented cells reduces firstly and then increases with the increase of indentation depth, as well as the aged cells.