▎ 摘　　要

The reaction mechanism of ceria as an anode in a lithium ion battery (LIB) is unknown. To solve this issue, a nano-LIB was constructed inside a transmission electron microscope (TEM) using an individual CeO2/graphene composite as the anode. The lithiation/delithiation cycles of the CeO2/graphene composite were conducted inside the TEM, and the electrochemical process was in situ monitored by simultaneous determination of the microstructure with high-resolution TEM, electron diffraction, and electron energy loss spectroscopy. The surfaces of the graphene nanosheets and ceria nanoparticles were covered by a nanocrystalline Li2O layer after lithiation, and the Li2O layer shrank and showed partially reversible changes after delithiation. The CeO2 nanoparticles showed imperceptible volumetric and morphological changes, while comprehensive analysis revealed a fully reversible phase transformation between fluorite CeO2 and cubic Ce2O3 during the electrochemical process. These results give direct evidence and profound insights into the lithiation/delithiation mechanism of CeO2/graphene anode in a LIB.