Abstract
The electrochemical insertion of Rb into carbonaceous materials, including graphite, was achieved herein. Rubidium ions were reversibly inserted into and extracted from graphite via electrochemical processes using different non-aqueous electrolytes containing rubidium bis(trifluoromethanesulfonyl)amide (RbTFSA) salts in carbonate esters, glymes, and ionic liquids, similar to the process used for other lighter alkali metal ions such as Li(+) and K(+). The chemical compositions of the rubidiated graphite were determined to be RbC(8), RbC(24), and RbC(36) at each step of the electrochemical reduction process. Graphite underwent a phase transition to RbC(8) exhibiting a stage-1 structure, with stage-3 RbC(36) and stage-2 RbC(24) as intermediates, as confirmed by ex situ and in situ X-ray diffraction and ex situ Raman spectroscopy, similar to the electrochemical phase evolution of staged potassium graphite intercalation compounds (K-GICs). Furthermore, Rb was reversibly inserted into and extracted from graphitizable and non-graphitizable carbons such as pitch-derived soft carbon and commercial hard carbon, along with other alkali metals such as Li, Na, and K.