An integrated strategy for upgrading Li-CO2 batteries: Redox mediator and separator modification

[Display omitted] •Ru(acac)3 as an efficient RM was introduced in Li-CO2 battery for the first time.•Shuttle effect caused by RM was remitted by Zn-MOF from both physical and chemical.•The deposition of Li+ on the anode was optimized by the ordered micropores in Zn-MOF. In Li-CO2 battery, redox mediators (RMs) are considered to have bright prospects due to their advantages of optimizing the mediated reaction pathway and reducing over-potential. However, some inherent defects caused by RMs, such as induced Li anode degradation and electron shuttle, limit its application in Li-CO2 battery. In this work, ruthenium acetylacetonate (Ru(acac)3) was innovatively applied as an efficient RM to boost the performance of Li-CO2 battery, and the “shuttle effect” of Ru(acac)3 to Li anode was also confirmed. To avoid the anode degradation caused by “shuttle effect” of RM, a novel Zn-MOF nanoplate modified glass fiber (M-GF) separator is skillfully prepared and used as a dual-function separator for Li-CO2 battery. Experiments coupled with density functional theory simulations verifies that M-GF can protect Li anode by preventing Ru(acac)3 from entering Li anode by physical and chemical interactions. Moreover, the highly ordered micropores in Zn-MOF also induce uniform deposition of Li+ on the Li anode to delay the degradation process of anode, and thus prolonged the cycle life of the battery. Thanks to the bidirectional support of Ru(acac)3 and M-GF strategy, the electrochemical performances of the Li-CO2 battery, especially the round-trip efficiency and cycle life, has been greatly improved.