Dynamic evolution of cathode electrolyte interphase (CEI) on high voltage LiCoO2 cathode and its interaction with Li anode

Realizing the charging of LiCoO2 to 4.6 V (vs. Li/Li+) reversibly has important value for achieving high volumetric and gravimetric energy density in rechargeable lithium batteries. However, the surface and interface instability of electrode at high voltage remains a primary problem. In this work, cathode electrolyte interphase (CEI) layer on LiCoO2 has been studied by X-ray photoelectron spectroscopy (XPS). In LiCoO2/Li battery, the dynamic evolution of CEI layer upon charging and discharging has been observed. Based on quantitative XPS analysis, a strong correlation on interface products between cathode and Li anode has been established. Such correlation mainly originates from the reversible formation and dissolution of the SEI layer on Li anode. The CEI layer evolution can be attributed to the sequential reactions through electrolyte and possibly physical migration of SEI fragments from Li anode. While in LiCoO2/graphite battery, the changes of the CEI on LiCoO2 becomes less significant due to the relative stable solid electrolyte interphase (SEI) layer forming on graphite anode, which further supports the strong correlation between CEI on cathode and solid electrolyte interphase (SEI) on Li anode. These results reveal the origin of the dynamical evolution of CEI on LiCoO2, and highlight that the impact of anode should be considered when interpreting the CEI on cathode, especially in rechargeable lithium batteries using lithium as anode.