Freestanding MXene–MnO₂ Films for Li–CO₂ Cathodes with Low Overpotential and Long-Term Cycling

The Li−CO2 battery is a potential energy storage device that not only possesses a theoretical energy density as high as 1876 W h kg−1 but also alleviates the consumption of fossil resources by converting the greenhouse gas CO2 into electric energy. However, some technique bottlenecks, such as high overpotential, low recyclability, and low energy density, severely prohibit its application rhythm. Here, we prepare a binder-free MXene−MnO2 composite film using vacuum-assisted filtration and in situ reduction, which can be used as a freestanding cathode for Li−CO2 batteries. This MXene−MnO2 film electrode bestows good cycle stability (∼220 cycles), high specific capacity, and lower overpotential (∼0.89 V) in Li−CO2 batteries. Both experimental tests and first-principles calculations reveal that the enhanced electrochemical properties are associated with three aspects. First, the MXene−MnO2 film offers a high electrical conductivity and porous structure, which provide fast transport channels for electrons and ions. Then, the replacement of Mn by Ti increases the adsorption of Li ions, which facilitates the rapid decomposition of Li2CO3. Finally, the synergistic effect of MXene and MnO2 exposes a large number of active sites, which increases the capacity of Li−CO2 batteries. Therefore, this self-supporting strategy on the MXene composite paves a way to develop high-performance Li−CO2 batteries.