Unveiling the In Situ Evolution of Li₂O-Rich Solid Electrolyte Interface on CoO_x Embedded Carbon Fibers as Li Anode Host

Modification of three-dimensional (3D) carbon hosts with metal oxides has been considered as advantageous for the formation of Li₂O-rich solid electrolyte interface (SEI), which can show fast Li⁺ diffusion, and meanwhile alleviate dendrite problems caused by fragility and nonuniformity of native SEIs. However, the lack of convincing experimental evidence has made it difficult to unveil the true origin of oxygen in Li₂O-rich SEIs until now. Herein, CoO_x embedded carbon nanofibers (CNF-CoO_x) are successfully prepared as high-performance Li anode hosts. By employing ¹⁸O isotope labeling, the role of CoO_x during SEI evolution is elucidated, revealing that CoO_x contributes significantly to Li₂O formation by delivering oxygen. Benefiting from the rich Li₂O content, the as-formed SEIs greatly improve the Li⁺ migration kinetics, and therefore, the CNF-CoO_x@Li anode can exhibit excellent cycling stability in half, symmetrical, and full cells.