The advantage of using Equation 2 rather than the coulombic efficiency shown in Figure is that it compares the lithiation capacity to the delitiation capacity in the previous cycle. Any lithiation in excess of the previous delithiation capacity can only be ascribed to electrolyte decomposition, especially when the delithiation capacity is itself degrading. There is a consistent downward trend in RICSEI with increasing cut-off voltage, coinciding with a downward trend in amount and persistence of the c-Li15Si4