Energy and capacity projections for practical dual-graphite cells

Anion intercalation in graphite was investigated in the preceding paper. It was shown that about 140 mAh/g, corresponding to stage-two' (PF6)C-16 Of charge could be stored at potentials near 5 V vs. Li. Dual-graphite cells, where Li intercalates into the negative electrode and PF6 into the positive electrode, are therefore possible, as has been demonstrated before by others. Unlike a Li-ion cell, where the amount of electrolyte in the cell can be minimized to obtain high energy density, in a dual-graphite cell there must be enough electrolyte present to provide the ions needed during the charging of the cell. This leads to a strategy in cell design that differs from the Li-ion case, in that electrolytes with high salt concentration are crucial if high energy density is to be obtained. Here, the specific capacity, specific energy, volumetric capacity, and energy density of practical dual-graphite cells are predicted. The calculations focus on the effect of the maximum salt concentration difference in the electrolyte between the fully discharged and fully charged states. (C) 2000 The Electrochemical Society. S0013-4651(99)10-064-8. All rights reserved.