Identifying cathode and anode polarizations during practical high-rate charging/discharging in different Li-ion pouch batteries

Abstract

Cell design is effective to improve the performances of lithium-ion batteries (LIBs). For identifying the bottleneck of a full battery used for high-rate charging/discharging, we developed a simple method, by a reference electrode in practical pouch cells, to quick obtain the polarizations of the cathode and the anode. For a Li(Ni0.6Co0.2Mn0.2)O2/graphite full cell, 63.9% and 97.0% of the polarizations originate from the anode at 50% state of charge (SOC) during 2.0 C charging and discharging rates, respectively. While for LiFePO4/graphite system, 62.5% and 55.8% of the polarizations originate from the anode at the same charging and discharging conditions. These indicate that the anode is the limitation during fast charging/discharging, which is consistent with the common understanding but in contrary to the results obtained by coin cells reported previously. While the rate limitation from anode in LiFePO4/graphite system during fast charging/discharging is significantly changed to both cathode and anode compared with Li(Ni0.6Co0.2Mn0.2)O2/graphite. Besides, graphite anodes in LiFePO4/graphite cells more readily dive to the Li-metal plating potential at high charging rate. This leads to safety concerns of LiFePO4/graphite cells during fast charging. This is a facile strategy for fast distinguishing polarizations from cathodes and anodes of high-rate LIBs.