Recently, strong demand has arisen for batteries with large capacities to support various types of mobile equipment. Li-ion batteries (LIBs) have been widely used for this purpose. In Li ion battery, intercalation of Li is only used but anion in electrolyte is not used for storage of electric energy. However, there is high interest on PF₆^- intercalation into graphitic carbon and by using intercalation of Li⁺ and PF₆^- into graphitic carbon for anode and cathode, respectively, electric energy can be storage.  This battery is called dual carbon battery, however, electronic state of PF₆^- into graphitic carbon is not thoroughly understood up to now.  In this study, electrochemical intercalation reaction of PF₆^- into graphotic carbon was studied by using solid state NMR and also XPS. Quantum calculation is also applied for estimating the stable structure of PF₆^- sandwiched between graphitic sheets.

During electrochemical intercalation of PF₆^-, reduction of PF₆^- will be occurred and so XPS measurement was performed to estimate the change of oxidation state.  In spite of several oxidation number, there is no change in valence state of P⁵⁺, however, XPS spectra of F- shifter to high binding energy suggesting that reduction of F^- occurred during intercalation. NMR measurement of F and P also suggested that chemical shift was mainly observed on F peak but no change in P peak. In addition, coupling constant of F is significantly changed suggesting that the structure of PF₆ may be changed during intercalation of PF₆. From quantum calculation of stable structure of PF₆ in graphene sheet, tilting structure is the most stable structure which is well agreed with the results of NMR measurement.  Diffusivity of PF₆ in graphitic carbon is also estimated and the observed diffusion constant is almost the same with that of Li in carbon and this is well explained the superior rate property of dual carbon battery.