Distinguishing Li+ Charge Transfer Kinetics at NCA/Electrolyte and Graphite/Electrolyte Interfaces, and NCA/Electrolyte and LFP/Electrolyte Interfaces in Li-Ion Cells

Abstract

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 full 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 recently reported values. However, the Ea for the charge transfer at the NCA/electrolyte interface is about 50 kJ/mol, which is lower than at the graphite anode. With desolvation as the predominate step for limiting the kinetics and both electrodes subjected to the same electrolyte, the difference in Ea suggests that it is greatly influenced with respect to the nature of the electrode materials and their associated SEIs. This is further confirmed by the examination of Li+ charge transfer at the LiFePO4 (LFP)/electrolyte and the graphite/electrolyte interfaces using a LFP/graphite full cell.