The reaction mechanism and capacity degradation model in lithium insertion organic cathodes, Li₂C₆O₆, using combined experimental and first principle studies

Herein, we explore the capacity degradation of dilithium rhodizonate salt (Li₂C₆O₆) in lithium rechargeable batteries based on detailed investigations of the lithium de/insertion mechanism in Li₂C₆O₆ using both electrochemical and structural ex situ analyses combined with first-principles calculations. The experimental observations indicate that the Li_xC₆O₆ electrode undergoes multiple two-phase reactions in the composition range of 2 ≤ x ≤ 6; however, the transformations in the range 2 ≤ x ≤ 4 involve a major morphological change that eventually leads to particle exfoliation and the isolation of active material. Through firstprinciples analysis of Li_xC₆O₆ during de/lithiation, it was revealed that particle exfoliation is closely related to the crystal structural changes with lithium deinsertion from C₆O₆ interlayers of the Li_xC₆O₆. Among the lithium ions found at various sites, the extraction of lithium from C₆O₆ interlayers at 2 ≤ x ≤ 4 decreases the binding force between the C₆O₆ layers, promoting the exfoliation of C₆O₆ layers and pulverization at the electrode, which degrades capacity retention.