Boosting Lithium Ion Storage of Copper Squarate Via Unsaturated Coordination Frameworks

Metal–organic frameworks (MOFs) have received extreme attention for their applications in lithium-ion batteries due to their large-specific surface area and adjustable composition. However, the limited active sites and low-ion diffusion of the MOF limit its practical applications. In this article, the coordination structure of SA–Cu–SQ is modulated by partially substituting acetic acid for squaric acid (SQ), thereby creating unsaturated coordination sites and exposing some of the metal's active sites. The electrochemical tests show that the introduction of the unsaturated coordination enables SA–Cu–SQ to possess a higher capacity (1012.5 mA h g–1 after 100 cycles at 0.1 A g–1) than that of Cu–SQ. Furthermore, kinetic tests and ex-situ characterization indicate that the unsaturated coordination not only facilitates Li+ diffusion but also generates additional active sites. Further introducing the unsaturated coordination strategy into rhodizonic acid (RA) gave SA–Cu–RA, which obtained a capacity of 1126.9 mA h g–1 at 0.1 A g–1. This work provides avenues to construct frameworks for high-performance electrochemical materials.