Unveiling the In Situ Evolution of Li 2 O-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 Li ₂ O-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 Li ₂ O-rich SEIs until now. Herein, CoO _x embedded carbon nanofibers (CNF-CoO _x ) are successfully prepared as high-performance Li anode hosts. By employing ¹⁸ O isotope labeling, the role of CoO _x during SEI evolution is elucidated, revealing that CoO _x contributes significantly to Li ₂ O formation by delivering oxygen. Benefiting from the rich Li ₂ O 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.
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