Versatile Spinel Ferrites MFe₂O₄ (M = Co, Zn, Ni, Cu) Enhance Dischargeability and Efficiency in Li-CO_{2 Mars} Batteries with Mixed Solvent Electrolytes

Li-CO₂ batteries as next-generation electrochemical energy storage devices not only  potentially help reducing the greenhouse effect using CO₂ for energy storage, but also offer high-energy-density (1876 Wh kg^-1) secondary batteries. However, the primary challenges for this technology are the low applied current density and limited rechargeability. In this work, a rechargeable Li-CO_{2 Mars} battery is operated in a simulated Martian atmosphere using [EMIm]⁺[BF4]^- ionic liquid (IL) as an additive in the dimethyl sulfoxide (DMSO)-based electrolyte and a spinel MFe₂O₄ (M = Co, Ni, Cu, Zn) nanocomposite catalysts with conductive multiwalled carbon nanotubes  support prepared by a single-step chemical co-precipitation method. The combination of the catalysts and ionic liquids enables the battery to exhibit an ultra-high discharge capacity exceeding 31346.3 mAh g^-1, sustaining over 100 cycles with a cutoff capacity of 1000 mAh g^-1 at a current density of 500 mA g^-1. Furthermore, post-cycling studies and first-principles calculations reveal enhanced CO₂ adsorption, favorable reaction toward Li₂C₂O₄ formation, and high reversibility of the catalysts aiding toward significantly high dischargeability and long cycle life. Overall, this work contributes to the design of suitable, inexpensive, durable catalysts and novel electrolytes for Li-CO_{2 Mars} batteries for its practicalization on Earth and beyond for Mars exploration.