Interaction between cathode and anode and its impact on the production of alkyl dicarbonates in lithium ion batteries

A new simple storage experiment is introduced to show direct evidence of a cathode-anode interaction. The delithiated positive electrodes and/or the lithiated negative electrodes from Li[Ni1/3Mn1/3Co1/3]O2/graphite and LiCoO2/graphite pouch cells are stored in Nalgene bottles (high-density polyethylene) filled with 1.0 M LiPF6 in an ethylene carbonate: diethyl carbonate (EC:DEC, 1:2 v/v ratio) electrolyte for 2 weeks in an Ar-filled glove box at room temperature. During the storage experiment, the color change of the electrolyte, the formation of alkyl dicarbonates, and the decomposition of LiPF6 are observed. The most important result of this storage experiment is that these reactions are significantly affected by the cathode-anode interaction. The electrolyte color change comes with slightly larger impedance growth during cycling and the alkyl dicarbonates improve coulombic efficiency. The decomposition of LiPF6 is suppressed by the negative electrode. The experiment and results shown here will be helpful to those who want to research the cathode-anode interaction and improve the performances of Li-ion batteries.