In-situ acoustic emission study of Si-based electrodes for Li-ion batteries

The mechanical degradation of a Si powder (∼2 μm) based electrode is investigated by acoustic emission (AE). AE signals are mainly detected during the first lithiation, suggesting that electrode cracking mainly occurs during this period. The formation of the solid electrolyte interface (SEI) is not very acoustically emissive, in contrast to the Si particle cracking which is initiated in the early stage of the lithiation in accordance with a core-shell lithiation mechanism. An increase of the AE activity is observed at the end of the discharge when the c-Li15Si4 phase is formed and during the charge when the potential reaches ∼0.45 V, corresponding to the delithiation of c-Li15Si4. From a clustering procedure, three types of signals are identified: type-1 signals consisting of a succession of very short waveforms with high peak frequency (∼700 kHz) are primarily detected when the Si lithiation is initiated and are ascribed to the nucleation of surface microcracks on the Si particles; type-2 signals (peak frequency ∼400 kHz), present all during the Si lithiation, are attributed to the propagation of cracks through the Si particles and into the composite film; type-3 signals (peak frequency ∼200 kHz), detected when the potential reaches 60 mV, are ascribed to the accentuation of the electrode cracking due to the c-Li15Si4 formation.