Impedance-based diagnosis of internal mechanical damage for large-format lithium-ion batteries

Recent technical advances of lithium-ion batteries (LIBs) are indispensable in prosperous development of electric vehicles (EVs). However, application of LIB still suffers some technical bottlenecks, among which an important issue is how to detect mechanical deformation inducing short circuit and subsequent fire or explosion. Here we propose an approach to diagnose early internal mechanical damage of large-format LIBs based on electrochemical impedance spectroscopy (EIS). Various stepwise indentation tests along side and bottom directions are performed with simultaneous EIS evolution recorded. An abrupt increase of impedance is observed in the both directions before ISC onset. Post-mortem inspection indicates that the intra-layer fracture of the active layer caused by micro-buckling of electrodes is the recipe for the impedance increase. The impedance change is substantially irreversible beyond the critical indentation depth and the level of the irreversibility is dependent on the local plastic deformation of electrodes. This work reveals the underlying risk in the scenarios of bottom and side indentations that a relatively small indentation could cause dramatic change in impedance, and sheds light on the early diagnosis of internal mechanical damage using EIS measurement. • Early internal mechanical damage for large-format LIB is diagnosed via EIS. • Impedance rises significantly under in-plane loading at a marginal indentation depth. • The loss of interfacial contact in active layer induces the impedance shifts. • Irreversible impedance shifts result from local plastic deformation of electrodes.