Formation of intercalation compounds providing enhanced energy density and excellent rechargeability is promising for secondary Li batteries. In this work we used DFT to determine the intercalation capacity of �-FePc. This system has shown significant capacity of intercalation up to 43 Li atoms, and excellent stability to charge/discharge cycles. This behavior is connected to the chemical processes occurring during the intercalation; however molecular detail has not been reported so far. Two functionals were used, RPBE and PBE-D2 where the D2 stands for the inclusion of a semiempirical treatment of vdW interactions. Using PBE-D2 functional an almost constant potential of 2 V during discharge was observed, in the other hand using standard DFT the intercalation voltage rapidly decreases as consequence of the tendency of Lithium atoms to attach to either the upper or lower FePc molecules, while using PBE-D2 functional the Li atoms remain in the middle of them. The Li atoms intercalated lost partial electronic density and became positively charged (+0.83 average charge) which indicates a charge transfer intercalation mechanism. The charge donated by the Li atoms is accepted by all the FePc constituents atoms, however is the Fe which suffers the most drastically charge change. In the free FePc the Fe atom charge is +1.2, from 1 to 6 Li atoms the charge changes gradually to +0.2, remaining in this value up to 14 atoms, and finally reaching negative values with 21 Li atoms intercalated. Other atoms receive electronic charge from Li; however the central Fe has the capacity to donate or withdraw atoms in order to keep the structural integrity of the system. Up to 29 intercalated Li atoms no bond rupture in the FePc or dramatic change in the unit cell size or shape was observed.

Li intercalation capacity of Fe-phthalocyanine

246th National Meeting (2013)

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