Understanding the degradation of silicon electrodes for lithium-ion batteries using acoustic emission

Silicon is a promising anode material for lithium-ion battery application due to its high specific capacity, low cost, and abundance. However, when silicon is lithiated at room temperature, it can undergo a volume expansion in excess of 280%, which leads to an extensive fracturing. This is thought to be a primary cause of the rapid decay in cell capacity routinely observed. Acoustic emission (AE) was employed to monitor activity in composite silicon electrodes while cycling in lithium-ion half-cells using a constant current-constant voltage procedure. The major source of AE was identified as the brittle fracture of silicon particles resulting from the alloying reaction that gives rise to Li_x Si phases. The largest number of emissions occurred on the first lithiation, corresponding to surface fracture of the silicon particles, followed by distinct emission bursts on subsequent charge and discharge steps. Furthermore, a difference in the average parameters describing the emission during charge and discharge steps was observed. The potential diagnostic and materials development applications of the presented AE techniques are discussed.