Active formation of Li-ion batteries and its effect on cycle life

The formation of the solid electrolyte interphase during the formation and conditioning steps, is a very time consuming and expensive process. We present an active formation method in LiNi1/3Mn1/3Co1/3O2 (NMC-111) versus graphite lithium-ion batteries, which maintains the cycling performance of the cells. Ten different active formation protocols were evaluated, which consisted of cycling between an upper (Vu) and lower (Vl) voltages. The cells were evaluated using electrochemical impedance spectroscopy (EIS) and cycling. X-ray photoelectron spectroscopy was used to analyse the surface of the electrodes after cycling. Cycling performance and resistance measurements from the EIS results confirm the different effect of formation protocols in the lifetime and performance of the cells. We show that during the formation protocol the interface composition is optimised through the transport of lithium ions through the initial organic decomposition layer on the graphite at higher cell voltages (>3.65 V). These higher voltage cycling formation protocols giving an interface with greater stability and enhanced cycling are observed in the cells.