Herein, ruthenium (Ru) nanoparticles were anchored on carbon nanotubes (Ru/CNTs) functionalized as catalyst cathodes for non-aqueous Li-CO₂ cells. For cycling tests through a low cut-off capacity (100 mA h g^-1), the origin of battery deterioration resulted from the accumulation of Li₂CO₃ discharging products on catalytic surfaces, identical to the observations in previous studies. However, the Li-CO₂ cells in this work showed a sudden death within several cycles of high cut-off capacity (500 mA h g^-1), and no Li₂CO₃ residues were investigated on the cathode. In contrast, Li dendrites and passivation materials (LiOH and Li₂CO₃) were generated on Li anodes upon cycling at a limited capacity of 500 mA h g^-1, which dominantly contributed to the battery degradation. A Li foil-replacement method was adopted to make the Ru/CNT cathode perform continuous 100 cycles under a cut-off capacity of 500 mA h g^-1. These results indicate that not only Li₂CO₃ residues blocked on the active sites of the cathode but also Li dendrites and passivation materials produced on the anode caused Li-CO₂ battery deterioration. Moreover, in the present work, a carbon thin film was deposited on Li metal (C/Li) by a sputtering system for suppressing the dendrite formation upon cycling and promoting the defense of the H₂O attack from the electrolyte disintegration. The Li-CO₂ cell with a Ru/CNT catalyst and a C/Li anode revealed an improved electrochemical stability of 115 cycles at a limited capacity of 500 mA h g^-1. This proto strategy provided a significant research direction focusing on Li anodes for elevating the Li-CO₂ battery durability.

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