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 LixC6O6 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 first-principles analysis of LixC6O6 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 LixC6O6. 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.