Breaking the Stable Triangle of Carbonate via W–O Bonds for Li-CO2 Batteries with Low Polarization

Li-CO2 batteries are widely studied as a promising technology for greenhouse-gas CO2 fixation as well as for energy conversion and storage devices. Their further development, however, is hindered by the refractory discharge products, leading to large polarization voltage and low round-trip efficiency. Here, W2C nanoparticles embedded in the walls of carbon nanotubes (W2C-CNTs) are prepared successfully. An efficient Li-CO2 battery with a W2C-CNTs cathode displays ultralow charge voltage (3.2 V) and high round-trip efficiency (90.1%). The low polarization comes from electron-rich W atoms that break the stable triangle of CO32– via W–O bonds. The resulting amorphous discharge products could be readily and reversibly decomposed during charging. Raman and XAS spectra provide direct and solid evidence for the W–O bonds. Also, DFT calculations show there is electron transfer between the W2C surface and Li2CO3, resulting in a low decomposition barrier for Li2CO3 on the W2C substrate.