Electrochemical Compression and Structural Dynamics in Sodium-Intercalated Graphite Using Diamine Electrolytes

Graphite has potential as a negative electrode material for sodium-ion batteries with fast rate capabilities and long cycle lifetimes through solvent–Na+ cointercalation. Most studies use diglyme (G2) which coinserts with Na+ in a cointercalation mechanism that expands graphite by >200%. Recently, our group identified diamines, such as 1,3-diaminopentane (13DAP), with higher discharge capacities. Herein, we focus on the relationship between higher capacities and structural evolution of graphite during cointercalation with G2, 13DAP, and their mixtures. Using operando X-ray diffraction, we show that 13DAP and mixtures with G2 can undergo unique rearrangement of the graphite structure. Specifically, reversible expansion and compression events occur which are tied to a low voltage plateau. In contrast, mixtures with higher concentrations of G2 indicate minimal 13DAP coinsertion likely due to the stronger binding between Na+ and G2 in solution. This study opens up different concepts in cointercalation chemistry beyond staging to approach higher energy densities.