Typically, the constant consumption of conventional fossil fuels leads to over-emission of carbon dioxide (CO 2 ) and accelerates the trend of global warming. [2] Therefore, in recent years, researchers from both academia and industry have devoted tremendous efforts to developing new energy systems to reduce CO 2 emission as well as converting CO 2 into valuable chemicals. [3] Among all explored systems for CO 2 reduction, the idea of rechargeable metal-CO 2 batteries exhibits significant promise for effective CO 2 reduction, value-added CO 2 conversion, as well as high-performance energy storage. It is therefore considered a "kill two birds with one stone" strategy and becomes a new research hotspot in areas of both CO 2 reduction and electrochemical energy storage. [3j,4] The first article of a primary Li-CO 2 battery with a nonaqueous electrolyte was reported in 2013. [5] Since then, diverse rechargeable metal-CO 2 batteries using different alkali metal anodes (Li, Na, K) have been constructed and systematically analyzed in the past few years. [6] However, the alkali metals possess high reaction activities, [6g,7] and Li, Na, and K anodes all suffer from dendrite formation during cycling that leads to severe battery safety issues, reduces battery cycle life, and restricts their practical applications. It is urgent to explore new metal anodes for metal-CO 2 batteries with comparatively lower activities and meanwhile being dendrite-free. [8] With that in mind, magnesium metal could be a promising option. On the one hand, Mg possesses a high theoretical volumetric capacity of 3833 mAh cm −3 (vs 2062 mAh cm −3 for Li, 1128 mAh cm −3 for Na, and 591 mAh cm −3 for K), [9] enabling Mg to fix more CO 2 per unit volume. On the other hand, Mg storage in the Earth's crust is abundant (about 2.9%), which is about 1500 times compared to Li (0.002%), resulting in a theoretically significantly lower production cost of Mg batteries. Most importantly, Mg metal anode's dendrite-free nature is favorable for battery safety and long cycle stability. [10] As the rechargeable Mg-CO 2 battery processes the above advantages of high volumetric energy density, high safety, environmental friendliness, and low cost, it is envisaged as a promising strategy for excellent energy storage and effective CO 2 exploitations. [9c] In spite of the favorable factors, there are very few reports in the literature related to Mg-CO 2 batteries with nonaqueous
