Distinguishing Li+ Charge Transfer Kinetics at 1. NCA/Electrolyte and Graphite/Electrolyte Interfaces and 2. NCA/Electrolyte and LFP/Electrolyte Interfaces in Li-ion Cells

In examining the Li+ charge transfer kinetics at the graphite anode and the lithium nickel cobalt aluminum oxide, LiNi0.80Co0.15Al0.05O2 (NCA), cathode in a complete cell, we found that the activation energy, Ea, for the charge transfer at the graphite/electrolyte interface is about 68 kJ/mol, which is consistent with the recently reported values. However, the Ea for the charge transfer at the NCA/electrolyte interface is about 50 kJ/mol, which is lower than that at the graphite anode. With desolvation as the predominate step for limiting the kinetics and both of the electrodes were subject to the same electrolyte, the difference in Ea suggests that the Ea is influenced greatly with respect to the nature of electrode materials and their associated SEIs. This is further confirmed by the examination of the LiFePO4 (LFP)/electrolyte and the graphite/electrolyte interfaces using a LFP/graphite complete cell.