Battery electrodes are generally selected from materials which have crystalline structure, such as graphite. Ions intercalate into the voids of the crystal, for example between layers of graphite. Quantum mechanical analysis of a Li+ ion between two layers of graphene indicates that optimal interlayer spacing is about 0.43 nm which is 25% greater than the actual spacing of graphite (0.335 nm). Other ions under consideration for alternative batteries, such as Na+, require even greater room than Li+. The question is whether crystalline materials provide adequate empty space for battery ions.In this research molecular vesicles are investigated as alternatives to crystalline materials. Two types of vesicles are considered: (1) Ring shaped crown ethers (Crown 12, 15, and 18) as the cathode; (2) a new carbon ball constructed by joining four triphenyl benzene molecules at the corners, as the anode. This molecule, which resembles a partially open fullerene, has been synthesized by researchers at Kyoto University recently. Quantum mechanical calculations are used to determine the fitting of the ions into the vesicles. The method used is DFT with B3LYP hybrid functional and Pople type basis sets augmented with polarizations functions. Atomic models consist of a vesicle with an ion located at the center.Results of the calculations indicate that: (a) Crown 15 has an inner diameter (ID) of 0.43 nm which can accommodate Li+, Na+, or Mg++ without expanding; (b) Crown 18 (ID=0.54 nm) can also accommodate K+; (c) the carbon ball has an ID=0.8 nm, large enough for any of the ions; (d) surface of the ball has 0.6 nm openings, wide enough for the ions to enter and exit freely.A monolayer of such molecular vesicles coated onto copper and aluminum contacts of the battery would serve as light and thin electrodes.

Molecular vesicles as battery electrodes

248th National Meeting (2014)

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